Claude Universite

Bernard -Lyon

M Le Professeur

Frédéric Fleury

Hamda Ben

Hadid M Le Professeur Didier

Revel M Le Professeur

Philippe Chevalier

M Fabrice

Vallée Mme

Dominique Marchand

Composantes Sante

G Rode

La Mme

C Professeure

Burillon

D Bourgeois

Vinciguerra

M X Perrot

A-M Professeure

Schott

A José Manuel

A Celia

HC-SCR: Hydrocarbon-assisted Selective Catalytic Reduction

Keywords: Beta zeolite framework BET: Brunauer-Emmett-Teller theory Chabazite zeolite framework (SAPO-34, SSZ-16. SSZ-62, SAPO-47… Carbon, Hydrogen, Nitrogen and Sulphur analysis Cu-zeolite: Copper-based zeolite Nitrogen oxides emission control technologies DFT: Density Functional Theory Diesel Oxydation Catalyst DPF: Diesel Particulate Filter EDX: Energy-dispersive X-ray Spectroscopy Inductively Coupled Plasma Optical Emission Spectrometry Ammonia Storage Capacity NOx: Nitrogen Oxides Portable Emission Measurement Systems PM: Particulate Matter Raman Spectroscopy RDE: Real Driving Emissions SAPO: Silico-alumino-phosphate SCO-NH3: NH3 Selective Catalytic Oxidation SCR: Selective Catalytic Reduction SCRF: SCR on Diesel Particulate Filter SEM: Scanning Electron Microscopy TEM: Transmission Electron Microscopy Unburned Hydrocarbons UWS: Urea Water Solution XPS: X-Ray Photoelectron Spectroscopy XRD: X-Ray Diffraction

Parece mentira que ya hayan pasado tres años y esté a punto de cerrar esta etapa. Recuerdo perfectamente los nervios y las ganas que sentí al llegar a esta maravillosa ciudad, sin saber muy bien qué me esperaría. Como toda tesis ha habido momentos de lágrimas y maratones de trabajo a horarios de locura. Sin embargo, puedo decir que he sido muy feliz durante este periodo y me llevo un montón de experiencias fantásticas y enseñanzas vitales.

A día de hoy puedo decir que me siento orgullosa de haber sido capaz de cumplir mis objetivos y sacar adelante este proyecto. Por supuesto no habría sido posible sin el apoyo de familiares y amigos durante estos tres años, por eso: ABSTRACT Aftertreatment systems that combine various functionalities into the same catalytic device are considered to be an efficient solution to reach the target defined by the restrictive future emission standards that regulate the automotive industry emissions. They are able not only to reduce the intrinsic costs due to the packaging but also, in some cases, to promote catalytic reactions by thermal or synergistic effects. This concept is being particularly explored for Diesel engines whose exhaust line may comprise up to four separate elements. NOx abatement can be accomplished by ammonia selective catalytic reduction on filter (NH3-SCRF) using Cu or Fe-exchanged zeolite-based as catalysts. This catalysed soot filter assumes two functions, simultaneously: removal of particles and reduction of NOx species towards N2. Regarding the SCR catalysts, the active layer is conventionally deposited onto the walls of a high porosity substrate whose channels are blocked at alternative ends. An increased porosity of the filter (such as cordierite or SiC) substrate is required to allow the deposition of the amount of catalyst phase needed for the treatment of gaseous emissions while efficient filtration and without producing a backpressure effect. Furthermore, it is necessary to remark that new reactions will occur in this system as Diesel soot, NOx and the reductant agent are present in the same unit for the first time. Accordingly to the literature currently available, there are three main ways that NOx pollutants and soot may interact: 1) soot blocking the accessibility of gas flow to "classic" active sites of the catalyst; 2) possibility of NOx reduction takes place over the soot particles; and finally, 3) soot presence affects SCR reactions performance or, contrarily, SCR reactions affects PM oxidation process as far as competition for NO2 will be produced.

RESUME

Les systèmes de post-traitement qui combinent diverses fonctionnalités dans un même dispositif catalytique sont considérées comme une solution efficace pour réussir l'objectif définie par les restrictives futures normes qui régulent les émissions de l'industrie automobile. Ils permettent non seulement de réduire les coûts intrinsèques dus à l'encombrement mais aussi, dans certains cas, de favoriser les réactions catalytiques par des effets thermiques ou synergiques. Ce concept est particulièrement étudié pour les moteurs Diesel dont la ligne d'échappement peut comprendre jusqu'à quatre éléments. La réduction des NOx peut être réalisée par réduction catalytique sélective de l'ammoniac sur filtre (NH3-SCRF) en utilisant des catalyseurs à base de zéolite échangée par Cu ou Fe. Ce filtre à suie catalysé assume simultanément deux fonctions: l'élimination des particules et la réduction des espèces de NOx vers N2 et de l'eau. En ce qui concerne les catalyseurs SCR, la couche active est classiquement déposée sur les parois d'un substrat de grande porosité dont les canaux sont bloqués à des extrémités alternatives. Une porosité accrue du substrat du filtre (tel que la cordiérite ou SiC) est nécessaire pour permettre le dépôt de la quantité de phase de catalyseur nécessaire pour le traitement des émissions gazeuses en assurant une filtration efficace et sans produire un effet de contre-pression du system. En plus, il est nécessaire de remarquer que des nouvelles réactions se produiront dans ce système puisque la suie Diesel, le NOx et l'agent réducteur sont présents dans la même unité pour la première fois. Selon la littérature actuellement disponible, les polluants et la suie peuvent interagir de trois manières principales: 1) la suie bloque l'accessibilité du flux gazeux aux sites actifs «classiques» du catalyseur; 2) possibilité de réduction des NOx sur les particules de suie; et enfin, 3) la présence de suie affecte les performances des réactions SCR ou, au contraire, les réactions SCR affectent le processus d'oxydation des particules jusqu'à ce que la compétition pour le NO2 soit produite

TABLES AND FIGURES CAPTIONS

INTRODUCTION 1.CONTEXT

Particulate matter (PM) and nitrogen oxides (NOx), produced by Diesel vehicles [1], are considered to be primary pollutants of the atmosphere since they have a direct influence in several environmental issues such as acid rain or global warming [2][3][4][5]. In addition, NOx and PM are both associated with adverse health effects (breathing problems, headaches, reduced lung function, eye irritation…) [6].

Nitrogen oxide emissions

Nitrogen oxides are basically referred as nitrogen oxide (NO) and nitrogen dioxide (NO2), among others. NO constitutes 85-95% of NOx [3,4] and it is gradually converted to NO2 in atmospheric air.

Particulate matter emissions

PM is an extremely complex mixture of solid and condensates materials [7] whose composition will depend on fuel composition and engine operating conditions (combustion temperature, exhaust cooling…). It is basically composed of the following four main fractions [3,7,8]: (1) elemental carbon (EC, solid) such as soot, (2) soluble organic fraction (SOF, solid or liquid substances) from fuel and engine lubricant oil, (3) sulphates and ( 4) ash (inorganic materials). Particulate matter emissions in the exhaust gas are resulted from incomplete combustion process of the hydrocarbons in the fuel and lube oil [3]. The particles in diesel exhaust are of special concern because, due to their respirable size (approximately more than 90 % of PM is smaller than 1 μm in diameter) [3].

Normative standards and homologation cycles

Due to the growing environmental awareness in recent years, european authorities progressively restricted the permissible exhaust emission levels by developing the benamed Euro standards, which have continuously become more rigorous and stringent (Table 1.1). Nowadays, the Euro 6 is being applied since 2014 and it is especially focused on NOx emissions limitation (from 0.18 g/km allowed in 2009 with Euro 5 to 0.08 fixed by Euro 6). This Euro emission limits are based on the emissions measured in a serie of driving cycles, which defines a global harmonized standard for determining the levels of pollutants and CO2 emissions, fuel or energy consumption, and electric range from light-duty vehicles [11,12].

The WLTC cycles replace the current NEDC cycle (chassis dynamometer procedure) for the new norm Euro 6c/6d in September 2017 [13][14][15] as the NEDC cycle had been repeatedly criticized by experts for delivering economy figures which do not represent real life driving conditions. Indeed, accelerations are very soft, there are a lot of constant speed cruises and a lot of idle events [11]. This make impossible to obtain certified values when driving with the vehicle in real conditions. The WLTC is a more severe cycle which is expected to reproduce faithfully the real traffic conditions.

Also, the European Union will introduce testing in real-world conditions (using portable emission measurement systems, PEMS), in addition to laboratory emission tests. RDE testing requirements are being phased-in between 2017 and 2021 [13] for NOx (PM particle number being left for further study) in real operation (Table 1.2) [9]. These changes will create a larger temperature and mass flow range to be covered by the exhaust aftertreatment systems with high efficiencies under more transient conditions [16]. 1.3 presents United States emission standards (called "Tier" standards). Also the US test procedures have been adopted by other countries as Canada, Mexico, Brazil and some asian countries as China [15], among others. The continuous decrease of allowed emission values forced the vehicle manufacturers to reduce pollutant emission from vehicles in order to fulfill new government regulations, especially in relation to NOx and PM. Methods of NOx control can be categorized as pre-and post-combustion methods. However, the emission levels can be only achieved by post-combustion methods, also known as aftertreatment systems.

In diesel engines, oxygen is always in excess since only sufficient fuel is injected into compressed hot air producing fuel spontaneous combustion [17,18]. Due to this oxygen excess conditions, more fuel combustion occurs and fewer hydrocarbons and CO are emitted in comparison to gasoline systems. Accordingly, lower NOx concentrations are emitted due to the lower engine temperature. Since conventional three-way catalysts, traditionally used for gasoline vehicules, are not effective in reducing NOx under lean conditions [17,19,20] various alternative technologies have been developed. Automotive makers have been focusing significant research and development efforts on two main deNOx technologies: i) LNT [21][22][23], that can store NOx under lean conditions and reduce the stored NOx over a noble metal under rich conditions [8]; and ii) SCR by a reductant [24]. The aim of both technologies is to reduce NOx in the effluent gas to harmless N2 [25] meeting the European emission limits. However, the LNT application is more senstitive to ageing and fuel quality variations [26]; and it will be accompanied with significant fuel penality over NEDC, while SCR concepts would improve fuel economy. In addition, due to the very high cost of LNT system (because of the presence of noble metals onto the catalyst [27]) it seems that the SCR is the most promising solution [8,25].

SCR catalysts can selectively reduce NOx emissions in the exhaust gas in the presence of excess of O2 with a reducing agent (e.g., NH3, urea, hydrocarbons) yielding N2 and water [28]. Traditionally, SCR by ammonia has been applied to stationary sources with lean exhaust conditions [24]. In the case of mobile applications, the presence of different reductants in the exhaust stream has been studied, being the more studied ones NH3/urea and hydrocarbons [25]. Metal oxides (mainly Ag/Al2O3), Cu-ZSM-5 and Ptbased catalysts [29] have been found to be active and hydrothermally stable for HC-NOx Selective Reduction [25] in combination with hydrocarbon reductants as propane, octane and decane. However, due to the HC poor selectivity towards N2, inhibition by the high steam content and poor temperature match of the catalysts [25] it is considered that NH3-SCR is the most efficient technology in order to reduce NOx emissions from mobile applications.

Figure 1.1 presents a typical Diesel emission control system using SCR also includes an oxidation catalyst (DOC) and a Diesel particulate filter (DPF) in order to control the emissions of carbon monoxide, hydrocarbons (HC), and particulate matters (PM). They are placed in a specific order to achieve a desired level of emission reduction performance. Because soot is often removed from DPF at high temperatures (650 °C), high thermal stability and high-temperature NO reduction activity are both required for the SCR catalyst to remain effective for NOx emission control [START_REF] Masoudi | Validation of a Model and Development of a Simulator for Predicting the Pressure Drop of Diesel Particulate Filters[END_REF].

DOC (Diesel Oxidation Catalyst)

As aforementioned, the lean conditions of diesel engines produce very low exhaust temperatures, especially during driving at low speeds ("cold-start") [START_REF] Gil | Perovskites and Related Mixed Oxides[END_REF]. For this reason, diesel oxidation catalysts (DOC), a non-filter-based open monolith (flowthrough, Figure 1.2) catalytic system [22] normally containing platinum or paladium metals dispersed onto a high surface washcoat, are needed to facilitate the unburned HC and CO emission control [17], as well as the oxidation of SOF portion of PM emissions [7,[START_REF] Grossale | [END_REF]. In addition, DOC plays two more functions [7,[START_REF] Grossale | [END_REF]: firstly, to oxidize diesel fuel to create exothermic heat used for DPF active regeneration; and secondly, it promotes the oxidation of NO to NO2 which is used to continuously oxidize soot on a DPF (passive regeneration) [22,[START_REF] Grossale | [END_REF].

Diesel Particulate Filter (DPF)

As previously mentioned, the introduction of the DOC in the exhaust line systems allowed the abatement of soluble organic fractions of diesel exhaust PM. As a result, soot or particulate matter emissions have been reduced to low levels and consists on a large quantity of very small particles. Thus, the inclusion of PN abatement systems that traps the solid portion of the exhaust PM [32] became necessary to fulfil Euro 5 standard in 2009 (Table 1.1).

Ceramic wall-flow filters received the most attention as they are capable to retain in and on the filter wall over 95-97% [START_REF] Grossale | [END_REF] of particulate matter from diesel exhausts. DPFs are usually made of a porous materials such as cordierite (2MgO-2Al2O3-5SiO2), silicon carbide (SiC) or aluminium titanate (Al2TiO5). The thickness of the channel walls is typically 300-400 μm and typical channel size is 100-300 cpsi (specified by their cell density, channels per square inch). The honeycomb monolithic structure (Figure 1.3) made from a porous material has channels that are plugged alternately at the ends [32], so exhaust gas is forced through the channel walls. PM are retained by physical processes and diffused into the filter pore walls where they adhere.

a) Soot filtration mechanisms Filtration through diesel particulate filters takes place in two different stages: (i) Deep bed filtration is the initial filtration stage; here, the filter pore size is larger than the soot particles. Particle deposition is driven by various force fields resulting from flow inertia and concentration gradients. Particles penetrate through the filtration barrier via diffusion, inertial impaction or flow line interception [START_REF] Masoudi | Validation of a Model and Development of a Simulator for Predicting the Pressure Drop of Diesel Particulate Filters[END_REF]. An example of deep filtration mechanism is shown in Figure 1.4. Depending on the particulate filter, this initial stage could be relatively short or take longer to complete itself. (ii) Cake bed filtration takes place following the deep bed filtration. Here, the wall pore size becomes effectively smaller than the size of soot particles and deposition occurs on the surface of the filter. A 'cake' layer is therefore formed on the surface of the filtration wall which, itself, performs filtration. Cake bed filtration becomes predominant, especially, at high soot emission rates [START_REF] Masoudi | Validation of a Model and Development of a Simulator for Predicting the Pressure Drop of Diesel Particulate Filters[END_REF].

b) DPF regeneration

As the filter becomes increasingly saturated with soot, a layer of soot is formed on the channel walls surface. Consequently, pore-plugging phenomena [START_REF] Granger | [END_REF] builds up a backpressure effect that has many negative effects such as increased fuel consumption, engine failure, and stress in the filter [3]. To prevent them, the DPF has to be regenerated by continuously or periodically burning of trapped PM into CO2 and water.

There are subsequently two types of regeneration processes [7,22,25,32,[START_REF] Olowojebutu | [END_REF]: (i) active (introducing very high heat into the exhaust) and (ii) passive regeneration (from the engine's exhaust heat in normal operation or by adding a catalyst to the filter) as presented on Figure 1.5. On one hand, active regeneration can be periodically applied to DPF by removing the trapped soot through a controlled oxidation with O2 in excess already present on the exhaust gas. The oxidation of diesel soot, represented here as carbon (C) by O2, can be described by the following reactions [7]:

(1) C + O2 → CO2 (2) 2 C + O2 → 2 CO
Unfortunately, the soot combustion by this mean requires a minimum temperature (>550 °C [32,37] higher than is obtained in diesel exhaust [36]. Since these high temperatures generally do not occur during normal engine operation, a number of strategies [7,36,37] are used to actively increase the exhaust temperature: i) Engine management; ii) outside sources to directly heat the exhaust entering the DPF (such as an electric heater or a flame-based burner [7]); iii) the use of a DOC to oxidize an additional amount of diesel fuel over the oxidation catalyst as a mean for increasing the DPF temperature. This extra diesel fuel may be accomplished by a fuel injector placed upstream the DOC or by in-cylinder post-injection strategies [7,36,37]. Regardless of the specific strategy, active regenerations always require additional energy input (additional fuel or external electric sources) to heat the exhaust and the DPF until the temperature required to the soot combustion [37].The higher regeneration temperature, the diesel fuel overconsumption and the large amount of energy for heat supply are serious problems for active regeneration: while the temperatures as high as melting point of filter may generates DPF failure, the necessity of energy for heating increases the production cost of system.

On the other hand, passive regeneration occurs at operating exhaust gas temperatures being enough to oxidize trapped soot and PM without external heat sources or additional fuel injection [37]. Main approaches employed are: continuously regeneration trap (CRT) [5,36,37] or catalysed CRT (CCRT) presented on Figure 1.6; and fuel additives which decrease the soot combustion temperature. NOx-CRT [START_REF] Stanmore | [END_REF] is a two-stage and full-time passive regeneration system where an uncatalysed DPF is regenerated. The accumulated soot and PM oxidation is based on an ongoing catalytic reaction process which uses of the NO2 already present in the exhaust gas [7]. NO2 reacts with the trapped soot, substantially reducing the temperature required for regenerating the filter. Under a temperature range between 250 and 300 °C, reactions (3) and ( 4) are being produced [7, [39].

(

) C + NO2 → CO + NO (4) C+ 2 NO2 → CO2 + 2 NO 3
In this process generally, a wall-flow filter is used coupled with the DOC device; a sophisticated engine management system and sensors are necessary [START_REF] Johansen | [END_REF]. More aforementioned, DOC upstream of DPF increases the ratio of NO2 in the exhaust [22,[START_REF] Johansen | [END_REF] and lowers the burning temperature of PMs. The advantage of this system is that it requires no attention as it is continuously developed; however, NO2 consumed in the trapped soot and PM oxidation would not be able in the next step of the aftertreatment system. This will compromise the Fast SCR reaction development which is highly desirable to happen (this will be widely explained on 2.1.4.c section). To solve this and with the aim to improve the regeneration efficiency, some chemical species can be coated onto the filter surface (CCRT) [7,[START_REF] Maunula | Catalyzed Particulate Filters for Mobile Diesel Applications[END_REF]. Therefore, NO2 consumed by the soot might be regenerated by Pt catalyst in order to reoxidise NO to NO2 [START_REF] Punke | [END_REF].

Another passive solution consists in dosing very small quantities of fuel additive compounds (usually transitional and precious metals such as cerium, iron or platinum [START_REF] Rocher | New Generation Fuel Borne Catalyst for Reliable DPF Operation in Globally Diverse Fuels[END_REF]) into the fuel on-board. During the fuel burning at high temperature in the engine combustion chamber, the decomposition of these metallic complexes generates small oxide particles afterwards trapped by the DPF function, allowing to decrease the soot burning temperature [7,[START_REF] Granger | [END_REF].

As a conclusion it can be said that NO2 is a much stronger oxidizer than O2 [7], providing an optimum passive regeneration efficiency [32] at the lower regeneration temperatures while improving the fuel economy [START_REF] Maunula | Catalyzed Particulate Filters for Mobile Diesel Applications[END_REF] (active regeneration costs 2-3% of total fuel consumption while passive dropped about 80% this penalty). However, from the available experience and advanced research, it appears that a pure passive approach to regenerate DPFs may not be feasible for all operating conditions. The only DPF system in production at present appears to be a combination of both: the passive and active methods to regenerate DPF [7,36].

UREA AND NH3-SCR

NH3-SCR is the most widely used technology for the abatement of NOx emissions, due to its high efficiency and selectivity to nitrogen: NOx reduction is higher than 90% over a wide operating temperature window (200-450 °C) [25]. For mobile applications, the storage of NH3 inside a vehicle is not possible due to its toxicity, corrosive effect and possible burning of NH3 in the warm atmosphere before the reaction. Hence, the use of urea as ammonia source was selected [START_REF] Deka | [END_REF]. NH3 is provided in the form of an aqueous solution of urea (UWS), commercialized as AdBlue® in Europe (also known as DEF in US). This solution is obtained from mixing 32,5 % urea (NH2)2CO and 67,5 % pure water by mass. By spraying this solution on the exhaust gas, as a result of the pure water vaporization, solid urea begins to melt and thermolysis takes place as seen in reaction (5) [13,[START_REF] Johansen | [END_REF]44,45].

(5) (NH2)2CO NH3 + HNCO (thermolysis)

Later, the isocyanic acid is converted with water in a hydrolysis reaction (6) [44,46]:

(6) HNCO + H2O NH3 + CO2 (hydrolysis)
Higher temperature than 180°C would be required to complete urea decomposition and hence, NH3 generation by reaction ( 5) and ( 6), so this is the reason why urea SCR system has difficulty dealing with low temperature NOx performance [10] Ammonia is chemisorbed onto the active sites of the catalyst surface, where it reacts with adsorbed NOx from the gases; being the amount of NH3 stored onto the SCR catalyst one of the key factors for the NH3-SCR activity [47,48].

SCR catalysts

One of the most important characteristics needed for a NH3-SCR catalyst employed in automobile applications are the stability of the systems in hydrothermal conditions and the preservation of good selectivity towards nitrogen. Due to the location of the SCRsection after the diesel particulate filter, the catalyst needs to withstand temperatures over 650 °C during the soot oxidation processes (active DPF regeneration). Three types of commercial catalysts have been traditionally developed for NH3-SCR: noble metals, metal oxides and metal exchanged-zeolites [START_REF] Deka | [END_REF].

a) Noble metals (Pt, Pd, Ag…) Most used noble metals are active in NOx reduction with a very good selectivity in N2 at low temperatures (around 175 °C) [49]. However, they oxidize completely NH3 above 250 °C, being a discouraging choice especially for mobile applications where high exhaust temperatures are produced due to DPF regeneration. In addition, other drawbacks of these catalysts are of course their high cost and the possible formation of N2O [START_REF] Deka | [END_REF]49].

b) Metal oxides (V2O5-WO3/TiO2)

Metal oxides are less expensive but still very effective and are widely used for stationary SCR applications (Mn oxides). They are normally supported on SiO2, TiO2, carbon-based materials or zeolites [50]. Among the different support materials (alumina, silica, zirconia and titania) and metal oxides studied (iron, copper, chromium, manganese....), the most suitable catalyst is the one formed by the V2O5-WO3/TiO2 system [9,[51][52][53][54]. The commercial vanadia based catalyst consists of vanadium pentoxide (V2O5) and tungsten trioxide (WO3) supported on high-surface-area anataseform titania [9,22]. It has demonstrated high activity for NOx reduction at the medium temperature range (300-400°C) and superior resistance to sulfur poisoning [22]. Also, V2O5-WO3/TiO2 catalysts produced minor formation of N2O in comparison to other kind of SCR catalysts [START_REF] Johansen | [END_REF]. However, these systems often suffer from low activity and selectivity beyond 450 °C (example in Figure 1.7) and vanadium oxide begins to be sublimated beyond 650 °C, which leads to the formation of highly toxic species [14,55]. For these reasons, such materials are less effective for light duty mobile posttreatment [56]. However, they remain extensively used for stationary sources (power generation units) [57,[START_REF] Kröcher | Studies in Surface Science and Catalysis[END_REF] and high duty diesel engines (used in marine applications, offroad vehicles and trains); as high temperature exhausts enables good SCR performance with conventional vanadium-based catalysts. Due to the fuel invariably contains high sulfur levels, vanadium-based catalysts are preferred better than zeolite-based catalysts as they are not sensitive to sulphur presence. Contrarily, zeolites might be easily poisoned and do not work well at these high operating temperatures (sulfur dioxide, SO2, can be oxidised to sulfur trioxide,SO3) [START_REF] Tronconi | [END_REF].

c) Zeolites

Metal-exchanged zeolites started to catch attention due to their very good deNOx activity in a wide temperature window and their low price [START_REF] Grossale | [END_REF][61][62][63][64]. The selected metal-exchanged zeolites need to be able to resist the NH3-SCR hydrothermal conditions, which may cause zeolites framework degradation by loss of Al-atom (dealumination) [28]. From this overview, it becomes clear that the combination of high performance, (i.e. activity and selectivity) and hydrothermal stability [START_REF] Maunula | Intensification of Catalytic Aftertreatments Systems for Mobile Applications[END_REF], without the aforementioned problems, makes the metal-exchanged zeolites an excellent choice as SCR-catalyst. In addition to their high activity and selectivity towards N2, zeolites are relatively inexpensive to produce and non-toxic, which make them excellent candidates for mobile emission control applications [28].

Over the last few years research efforts have focused on the development of transition metal-exchanged SCR catalysts [61], as the presence of the metal had a beneficial effect on the activity. The presence of a TMI provides a redox catalytic centre [START_REF] Deka | [END_REF] over the (internal) surface of the zeolite structure. The special features of these materials are their adjustable acidic properties and their ability to stabilize transition metal redox couples such as Cu + /Cu 2+ , Fe 2+ /Fe 3+ [START_REF] Colombo | [END_REF][67][68][69].

Over the past two decades, multiple combinations of aluminosilicate and silicoaluminophosphate (SAPO) zeolite frameworks (MFI, MOR, BEA or FER) coupled with different transition metals (Cu, Fe, Cr, Ce, Co, Ni, etc) have been studied and showed good activity in the SCR process [28,[START_REF] Deka | [END_REF]. In the recent years, formulations containing copper and iron have been found to be the most appropriate TMIs for NH3-SCR due to their impressive deNOx activity at low temperature conditions and superior thermal durability for automotive applications [22], as well as good redox capacity [70]. Traditional iron-or copper-exchanged aluminosilicate zeolites (BEA or Y), displayed a beginning of deactivation after hydrothermal treatments carried out at 500°C [71] in wet atmosphere. For processing temperatures above 700 °C more than 90% of the acidity was destroyed due to the dealumination as well as the collapse of the structure [69]. For example, copper and iron zeolites with the BEA or MFI (ZSM-5 zeolites) framework (presented in Figure 1.8) have a limited low temperature activity and are therefore very dependent on available NO2, being their hydrothermal stability not sufficiently high. Furthermore, in comparison to CHA structures, the classic zeolitic structures (BEA, MFI…) have inferior SCR activity and N2 selectivity, producing higher amounts of the undesirable by-product N2O. [7,29,[START_REF] Johansen | [END_REF] a.

b. For this reason, more recently, the trend is hereby shifting to zeolites with smaller pore windows (mainly CHA structure, as observed in Figure 1.9) [28,[73][START_REF] Ishihara | Studies in Surface Science and Catalysis[END_REF][START_REF] Kang | [END_REF] resulting in an increased hydrothermal stability [76][77][78]. Small pores decelerate the dealumination rate, increasing the life span of the catalyst. CHA zeolite structure (Figure 1.10), Cu and Fe metals are gaining increasing attention due to their high deNOx performance over a wide range of operating conditions as well as significant hydrothermal aging durability [21,22].

Fe-zeolites:

Fe-zeolites showed great deNOx activity and selectivity towards N2, especially at high temperatures (> 400 ºC) [22,[START_REF] Deka | [END_REF]. Tronconi et al. [79] observed that Fe-zeolite just form small amounts of N2O when excess of NO2 conditions occurs [22]. However, Fezeolites present some drawbacks necessary to be remarked: some undesired Fe species (isolated cations or Fe-oxide particles) are produced during the introduction process depending on the zeolite structure, Si/Al ratio, iron content and aluminium distribution [START_REF] Johansen | [END_REF]. It is necessary to remark that the Fe-zeolite catalysts are especially sensitives to the method used for introducing the metal into the zeolite framework. In addition, at high temperatures under hydrothermal conditions, they suffer dealumination caused by the iron coordination to inactive oxide species.

Cu-zeolites:

They showed high deNOx activity and reactivity over a wide range of operating conditions (200-500 ºC), even at the low temperature region [20,[START_REF] Colombo | [END_REF]. Discussion of this catalyst family is going to be focused on the CHA framework type as more recent SCR studies used them as reference. The main raison was due to the Cu-CHA zeolites have a promising combination of high-temperature stability and high low temperature activity [START_REF] Maunula | Intensification of Catalytic Aftertreatments Systems for Mobile Applications[END_REF]. Cavataio et al. [80] carried out a broad range of time (1-256 h) and temperature (670-1100 °C) hydrothermal aging over a Cu-zeolites SCR catalyst. The results confirmed a remarkable high temperature hydrothermal stability even up to 950 °C while still maintaining high and stable NOx activity (200-500 °C) [80]. Two different formulations within the same structure have been evaluated as candidates: Cu-SAPO-34 [27] and Cu-SSZ-13 [15]. Cu is an easy specie to exchange with the zeolite, allowing a variety of Cu species present (Cu + , Cu 2+ , CuO particles…). However, the copper content needs to be optimized in order to achieve the best compromise between performance and stability. Despite the numerous advantages of Cu-zeolites systems, they present some noticeable limitations: in presence of CuO species, the high surface oxidation ability of Cu-zeolite catalysts can yield undesired ammonia oxidation above 350 °C [15,26,60], reducing the effective amount of NH3 available for the SCR reaction and thus limiting NOx reduction efficiency [15]; their higher non-negligible selectivity towards N2O [64] and; finally, they are specially sulfur-sensitive [18].

Fe vs Cu zeolites:

Both metal-exchanged zeolite systems show similar characteristics; however, Cu-zeolite demonstrated significantly higher low-temperature deNOx performance (<350 °C), whereas Fe-zeolites performed better at higher temperatures (>400 °C) [22,[START_REF] Deka | [END_REF]. Kamasamudram et al. [81] elucidated additional differences between them: Cu-zeolites are less sensitive on NO2/NOx ratio of the feed gas than Fe-zeolites at low temperature conditions (<250 °C) [79,82]. Some authors suggest that the Cu-zeolite SCR catalysts can better oxidize surface NO to NO2, without suffering from NH3 masking [START_REF] Deka | [END_REF]81]. However, Fe-based systems suffer from a NH3 inhibition effect [83] due to the NO2 presence, especially at temperatures lower than 300 °C [28,[START_REF] Deka | [END_REF]84]. This difference related to the NH3 inhibition also implies that Cu-zeolites showed higher ammonia storage capacity (NH3SC) at low temperatures [85]. Cavataio et al. [85] found that the low-temperature performance of both Cu-zeolites and Fe-zeolites was greatly improved when optimum NO2/NOx ratios were 0.5 (Fast SCR, Reaction 8) [28,[START_REF] Deka | [END_REF]71,86,87]. Nevertheless, at higher temperatures this advantage disappears as the thermodynamic NO/NO2 equilibrium switches to NO2 decomposition towards NO, what modifies again the NO2/NOx ratio [22]. Separately, formation of certain amount of nitrous oxide was detected over the copper catalyst even with negligible NO2 feed contents, whereas N2O formation occurred over the iron-based catalyst only when excess of NO2 [START_REF] Colombo | [END_REF]. Finally, it is necessary to remark that the impact of sulfur was more significant on Cu-zeolites than on Fe-based SCR catalysts (mainly <300 °C) [88,89]. However, the Cu-zeolite that Johnson Matthey has developed can be thermally re-activated from sulfur poisoning. Sumiya et al. verified that NOx conversion was almost fully recovered after exposure at 650°C. [10] In addition, Cheng et al. [90] investigated the difference by exposing Cu-zeolite SCR catalysts to SO2 and SO3. It was observed that SCR activity was significantly reduced for samples poisoned by SO3 compared to those poisoned by SO2 [90]. Reaction (7) is better known as Standard SCR, in which NO and NH3 react in presence of O2 yielding N2 and water as a result of NO reduction [91]. As far as NO2 is usually present on exhaust gas line, when equimolar NO and NO2 are present, reaction (8) (which is called "Fast SCR") takes place, being the fastest one [92][93][94][95]. On the other hand, if a high quantity of NO2 is formed and ratio NO2/NOx >0.5, a contribution of reactions ( 9) and (10) to the global process can be observed [96], considered to be the slowest SCR one. Metkar et al. [56] found that the NOx conversion was lower for the NO2/NOx fraction> 0.5 than the SCR with NO alone (Standard SCR, NO2/NOx=0) [95]. Hence, getting the optimum NO2 to NO ratio (NO2/NOx=0,5) is technically very demanding and a key issue in maximizing low temperature NOx reduction efficiency [10]. It can be said that the NO2/NOx ratio has an important effect over deNOx catalyst efficiency, especially over Fe-exchanged catalysts [88,[97][98][99]. In the case of Fe-zeolites an NH3 inhibition effect may happen under Standard SCR conditions at low temperatures, assuming that NH3 may block the red-ox sites for NO activation [100]. In addition, various authors found that the excess of NO2 yields of higher N2O formation (Reactions 13 and 14), which demonstrates a correlation between the amount of NO2 in the feed and the N2O production [96,101].

SCR Reactions

a) Active sites characterisation

One important parameter which must be considered for the zeolite catalysts family, is the acidity factor and the presence of two kind of acid active sites, depending on the character of its acidity (Brönsted or Lewis). The framework acidity of the catalyst material is considered to be decisive for NH3-SCR activity [102]. It is generally assumed that NH3 is adsorbed and activated on the Brønsted sites (showed on Figure 1.11) of the zeolite in the NH4 + form, and reacting later with the surface NOx species in NH3-SCR [63]. Also, NH3 can be adsorbed on the exchanged metals (Al, Cu…) that work as Lewis acid sites. Anyways, the NH3 storage capacity plays a crucial role in the NH3-SCR reaction, as NOx conversion is determined by the amount of stored NH3, especially at low temperatures (< 300°C) [103].

In the case of non-exchanged zeolites, the Brönsted acids sites are the OH groups near Al atoms (which plays the Lewis acid role) [104] (Figure 1.11). After the ionic metal exchange, same Brönsted acid sites are found but on a lower amount depending on the exchanged state of the zeolite, thus confirming an exchange between metallic species and protons [105]. Total acidity of a zeolite catalyst exchanged with Fe or Cu can be correlated with the Si/Al ratio (or Si+P/Al ratio in the case of SAPO structures) and hence, to the different population of Brønsted acid sites in the H-form [104]. Indeed, the cationic metals also act as Lewis acid sites, referring to the metal content in the zeolite and its exchange level [106].

b) Catalysis in the cage

In terms of the catalytically active centres and role of ion-exchanged in the SCR process, no consensus currently exists in the literature [START_REF] Deka | [END_REF]107]. This is normal because metal ions tend to migrate due to heat treatment and it is not clear which would be the active sites during the SCR reaction [108,109]. However, there is an agreement considering that the metal should be present in a cationic state (auto-reduction Cu + /Cu 2+ or Fe 2+ /Fe 3+ species) in order to be active, as the redox properties are a key factor along the SCR reaction [START_REF] Tronconi | [END_REF]. Major discrepancy is settled around the aggregation state of metal and their location within the zeolite active sites, which is directly related with the metal introduction method and the ionic exchanged level [110]. According to Brandenberger [28], the catalytic activity of the zeolite increases with metal content thus, binuclear species should be the active sites. However, a compromise between metal loading and SCR activity must be reached because excessive metal load leads to metal oxide (e.g., CuO, FexOy) species and clusters formation, which are inactive in the SCR process [111].

Regarding the CHA-type zeolite framework, extensive work have been done to identify active sites. Main conclusion was that the CHA is formed by two main secondary units: an hexagonal prism called d6r (double six-ring) and an another prim formed by eight members called 8MR (eight-member-ring) [72]. They are connected by double links and due to these connexion the called "cha cavity" is formed. 12.b) [112,113]. In addition, by H2-TPR they observed four types of copper species present on Cu/SAPO-34 samples: external surface CuO clusters, isolated Cu 2+ ions, and nanosize CuO and Cu + ions. They found that isolated Cu 2+ species located on Site I could be the responsible for the NH3-SCR activity in the temperature range between 100-200°C [114][115][116]. However, at T > 200 °C, the active sites for the NH3-SCR reaction are still unclear. Deka et al. [START_REF] Deka | [END_REF]114,115] also studied Cu migration within SAPO-34 zeolites and they confirmed isolated Cu 2+ species as active sites in these catalysts [114,115], being preferably located near the d6r subunits and slightly away ( 0.5 Å) from the d6r plane toward the cages of the structure (Site I). It should also be noted, however, that the presence of additional Cu species (as CuOx or a second site for Cu 2+ ) has been suggested within the SAPO-34 framework, even at low Cu loading [117]. In accordance to this, Zamadics et al. [116] suggested that Cu species could locate at either site (III) or site (I) in the CHA structure, the former being in the centre of the d6r, and the latter slightly off the plane and into the cages of the d6r. It is necessary to be remarked that after long-term hydrothermal aging, a small part of isolated Cu 2+ ions transferred to the 8MR (Site IV), where it may be easy for H2 to reduce the dehydrated Cu 2+ ions [111,118].

Furthermore, Deka et al. [114] developed a model based on DFT calculations referring to Cu/SSZ-13 zeolites. They maintain that the unique location for Cu 2+ cations in SSZ-13 structure is on the plane of the d6r subunits facing the cha cavity (Figures 1.10 and 1.12.b), being the active sites under SCR reaction conditions [START_REF] Deka | [END_REF]114]. Korhonen et al. [119] confirmed it. Cu-Cu interaction is not observed over the structure, which otherwise could result in the formation of dimeric species or Cu clusters. However, the large cha cage allow the diffusion of gas molecules, which could yield the mobile Cu 2+ cations to interact with guest molecules. However more recently, Beale et al. [102] maintain that Cu 2+ ions on a SSZ-13 are located in the 8MR cages and tend to migrate with temperature increase. At room temperature, Cu 2+ ions are located in the 8MR cages but on heating (> 220 °C) they move into the d6r corners (Figure 1.10) [120,121]. Cu species in the vicinity of the 8MR and d6r have different redox behaviour [122]: at low temperatures most of the Cu ions are present in the 8MR where they have a lower coordination with the framework and are therefore easier to reduce than those in the d6r (at higher temperatures) [121]. This contrast between Deka and Beale afirmations was explained by Lezcano-Gonzalez et al. [104] who observed that in Cu/SSZ-13 zeolites, two types of Cu sites exist depending on the Cu exchange level: at low Cu loadings, Cu 2+ ions are located in the d6r zeolite units, whereas at high loadings the ions are located inside the 8MR cages [118]. They also found by FTIR that despite complete Cu 2+ -exchange certain framework Bronsted sites remained, indicating a second type of Cu species on extra-framework position exists (clusters and CuO species are usually located in the large zeolite cages due to their size) [101,106,118,123].

However, it is necessary to take into account that some authors (as Paolucci et al. [186,187]) observed that Cu sites respond sensitively to exposure conditions. In particular that some Cu species (Cu I and Cu II ) were solvated by NH3 under SCR conditions. As a consequence, migration of the Cu between the cages of the zeolite occurred. In addition, high temperature Cu is expected to desolvate [186,187].

Regarding Fe-exchanged zeolites, Gao et al. [124,125] observed that in SSZ-13 structures the major Fe species are extraframework Fe 3+ species (hydrated monomeric [Fe(OH)2] + ; and dimeric [HO-Fe-O-Fe-OH] 2+ ) [START_REF] Bull | Copper CHA zeolite catalysts[END_REF][127][START_REF] Andersen | [END_REF][START_REF] Andersen | Small pore molecular sieve supported copper catalysts durable against lean/rich aging for the reduction of nitrogen oxides[END_REF][130]; and the larger oligomers with unknown nuclearity, poorly crystallized Fe oxide particles and isolated Fe 2+ ions, are minor Fe-containing moieties. Isolated Fe 3+ ions are the active sites for lowtemperature standard SCR based on the reaction rate and Fe loading correlations, and temperature and Fe loading effects on SCR selectivities. In contrast, dimeric sites provide the majority of reactivity at high temperatures [124]. In another study, Gao et al. [125] found that during harsh hydrothermal aging conditions (800 °C for 16h in the presence of H2O), a majority of cationic Fe species convert to FeAlOx and clustered FeOx species, accompanied by dealumination of the SSZ-13 framework. Upon dehydration (above 400 °C), much of the activity remains, suggesting that the FeAlOx and FeOx species become active at such elevated temperatures [28]. Alternatively, the high-temperature activity may be maintained by the remaining extraframework cationic species. The NH3-SCR reaction was proposed to be associated with a closed redox cycle between Cu 2+ and Cu + /H + formed at the d6r [131]. In the case of Cu/SAPO-34 zeolites, they found that the isolated Cu 2+ species are reduced to Cu + when the catalyst is exposed to NH3 feed above 250 °C. The following NOx purge leads to the consumption of the adsorbed NH3 and the recovery of isolated Cu 2+ species [111].

c) Mechanism and kinetics

A few years ago, it was believed that the NO oxidation to NO2 at the metal sites was the determining step of the SCR mechanism. However, more recently, Ruggeri et al. [132] proposed two different rate determining steps for the NO oxidation and the SCR reactions (Table 1.4), which require formation of oxidized intermediates (HONO, nitrites/nitrates species) in the presence of NO and O2 [133]. Surface nitrites can then decompose to gaseous NO2 (this can be identified as the slow step in the case of NO oxidation to NO2) [134]. Indeed, the HONO-Nitrites/nitrates equilibrium is strongly affected by water, which may explain the strong H2O inhibiting effect on NO oxidation remarked by various authors [135]. When ammonia is present, HONO/nitrites species quickly react instead with ammonia to form N2: in this case re-oxidation of the metal active sites by O2, then represents the standard SCR rate determining step. Moreover, different stabilities of nitrites/nitrates depending on their interaction with the metal sites, explain the differences noted between Cu and Fe zeolite activities in NO oxidation.

It is often discussed that the NH3-SCR reactions occur on the catalyst surface via two mechanisms [131]: (1) Eley-Rideal mechanism, NH3 is first adsorbed onto Lewis or Brønsted acid sites, then the adsorbed NH3 species react with gaseous or weakly adsorbed NOx to produce N2 and H2O; (2) Langmuir-Hinshelwood mechanism, the adsorbed NH3 species reacts with chemisorbed NOx species to accomplish the SCR reaction [136,137]. Wang et al. [8,48] proposed a reaction mechanism in which the SCR reaction mainly happens via the reaction as the first step between NH3 adsorbed on Lewis acid site and the directly formed NO2-. These adsorbed species react and form either ammonia nitrite (NH4NO2), or ammonia nitrate (NH4NO3) (Reactions 11 and 12) at low temperature region, which may be deposited in the zeolite pores producing partial deactivation [104,138]. Later, at the high temperature region, Yu et al. [139] observed the formation of N2O which is closely related with the the NH4NO3 decomposition, while NH4NO2 species decomposes easily to N2 and H2O.

In addition to SCR reactions, some non-selective to N2 reactions could take place, producing undesired by-products or overconsumption of the reductant agent. These undesired reactions depend on the catalyst formulation, the operational conditions and feed gas composition.

N2O is undesired by-product due to its contribution to the greenhouse effect and it can be formed in presence of NO2 excess by Reactions 13 and 14.

N2O decomposition is thermally favoured at temperatures higher than 350 °C, yielding N2 and water (Reactions 15 and 16).

However, Wang et al. [140] proposed that on a Cu/SAPO-34 at low temperatures involves the redution of NH4NO3 with NO by Reaction 17.

The different opinions on the roles of NH4NO3 in NH3-SCR reaction of Yu et al. [139] and Wang et al. [140] may arise from the different reaction temperatures examined by them (100 °C for Yu and 290 °C for Wang). These results indicate that the NH3-SCR reaction pathway over the Cu/SAPO-34 catalyst may change with the change of the reaction temperature. The decomposition of NH4NO2 is the main pathway for NH3-SCR reaction at high temperatures.

In addition to this, NH3 oxidation by O2 can be produced at high temperatures (>350 ºC), overconsuming reductant agent and producing a competition between the reduction (SCR reactions) and oxidation (SCO-NH3) reactions for the NH3 available in the reaction environment [22,141].

As Reaction 18 and 19 indicate, the SCO-NH3 reactions could lead either to NO or N2. Even if the reaction yields to N2 and water, it is undesired as they produce a NH3 default that will reduce the NOx conversion.

SCR ON DIESEL PARTICULATE FILTER (SCRF)

SCRF technology

Traditionally, separated SCR and DPF systems (Figure 1.13.a) have demonstrated to be effective solutions for controlling NOx and PM emissions separately [2]. However, as future diesel emission regulations are expected to be more stringent and in order to decrease the after treatment size, combining the catalytic treatment (SCR) and filtration (DPF) steps into the same catalytic unit (Figure 1.13.b) may be a viable solution to reach new standards [28,79,142]. This could be made by washcoating the SCR catalyst onto the highly porous walls of the DPF soot filter [79]. On this SCRF system, the catalysed soot filter assumes two functions: removal of the particles and conversion of the NOx species to N2. The SCRF system demonstrates the following potentials: (i) SCRF could be placed closer to the engine leading to high regeneration efficiency (benefit from high enthalpy) and light-off performance as well as less total thermal loss [10,79]; (ii) allows to reduction of packaging space and weight, so as to reduce the cost of the system (Figure 1.13) [79]; (iii) it allows an additional SCR catalyst coating loading without increasing system volume significantly [22,32]. Therefore, SCRF would be a combined, cost-efficient simultaneous NOx and soot reduction technology. In fact, an example of SCRF application commercialized in real life on 2016 are the new Mercedes-Benz OM 654. Daimler announced that the engine is designed to meet future emission legislation, including the RDE and WLTP testing. All emission system components are installed directly on the engine, in a close-coupled position. The exhaust gas from the turbocharger is sent first to a diesel oxidation catalyst. Then, it passes to a mixer-where urea (AdBlue®) is added using a water-cooled dosing module-and to a downstream SCRF unit. However, there are a few disadvantages of this SCRF units: i) as they combine SCR and DPF devices, shorter mixing lengths gases need to be considered, this could mainly affects to urea uniformity upstream the catalyst [16]. This can cause loss of NOx reduction efficiency as well as NH3 slip; and ii) the DPF regeneration frequency can be higher due to lower soot mass limit (in order to avoid uncontrolled soot burning and control passive soot oxidation) [16].

a) DPF substrate: description

Indifferently the kind of SCR catalyst formulation used, an additional aspect for consideration is the washcoat loading: in this system, the amount of SCR catalyst must be enough to achieve efficient NOx reduction. In order to achieve deNOx performance comparable to flow-through SCR units, the catalyst loading has to be up to three times more than for flow-through SCR units [START_REF] Johansen | [END_REF]. However, pressure drop increases along with the increase in catalyst amount and NOx conversion efficiency [79]. In order to overcome the trade-off between substrate pressure drop, washcoat loading and necessary filtration efficiency, the wall-flow substrate should have high porosity (such as cordierite and silicon carbide filter materials [32,[START_REF] Johansen | [END_REF] which have porosities in the range of 58%-75%) [START_REF] Johansen | [END_REF][START_REF] Patchett | Gas Catalysts Comprising Porous Wall Honeycombs[END_REF][START_REF] Johansen | SCR-DPF integrations for diesel exhaust. Performance and perspectives for high SCR loadings[END_REF].

In order to verify this, Hirose et al. [START_REF] Hirose | [END_REF] compared the deposition of the same amount of an SCR catalyst over a conventional substrate (porosity of approx. 35%) and a high porosity substrate (porosity of approx. 50%). In the high porosity substrate, they observed that SCR catalyst penetrated into the wall and catalyst amount accumulated on the wall surface was relatively small. In other words, high porosity substrates use pores in their walls as "added" catalyst storage (Figure 1.14), allowing to increase the washcoat loading without produce backpressure problems while maintaining the same NOx conversion efficiency level. Effectively, Cavataio et al. [88] settled that SCR washcoat should be ideally coated inside the filter wall pores rather than on the substrate channel wall surface (as represented in Figure 1.14), allowing space for SCR washcoat but also opening DPF channels for gas flow and PM storage. Referring to this, a heterogeneous distribution of SCR catalyst in the filter has an influence on the SCR performance and durability of the integrated solution [START_REF] Johansen | [END_REF]. A low SCR coating concentration on the channels is desirable in order to limit interaction between the SCR component and ash. All this requires special catalyst washcoating techniques that will allow reaching these SCR washcoat distribution requirements [START_REF] Johansen | [END_REF].

In addition to this, Iwasaki et al. [START_REF] Iwasaki | [END_REF] has recently shown that asymmetric hexagonaldesigned channel technology (called microgear) provides lower backpressure and higher ash-capacity for longer DPF lifetime usage, whilst maintaining essential filter properties such as robustness to thermal shock events. Microgear design provides the DPF of 1.3 higher surface area which could improve soot particles contact and combustion. In addition, HC and NO oxidation performance carried out on engine dynamometer showed improved catalytic activity.

b) Deposition methods

Referring to the washcoat loading, heterogeneous distribution of SCR catalyst in the filter has an influence on the SCR performance and durability of the integrated solution [START_REF] Johansen | [END_REF]. A small SCR coating on the channels is desirable in order to limit interaction between the SCR component and ash. All this requires special catalyst washcoating techniques that will allow reaching these SCR washcoat distribution requirements [START_REF] Johansen | [END_REF].

The literature describes some different patented methods of SCR catalyst washcoat deposition onto Diesel filters. i) One specific method is described in the reference [START_REF] Wan | Emissions Treatment System with Ammonia-Generating and SCR Catalysts[END_REF] in five steps. First, the wall flow monolith was immersed in aqueous slurry made of SCR catalyst composition from a first direction to deposit the catalyst in the inlet passages. Then the excess slurry is removed from the inlet passages by forcing a compressed gas steam through the outlet passages and applying a vacuum into the inlet passages. The second step consists on the immersion of the monolith in a second direction with the aim of depositing the catalyst on the outlet passages. The slurry excess was again removed by forcing a compressed gas stream through the inlet passages and applying a vacuum into the outlet passage this time. Finally, the coated wall flow was dried and calcinated. ii) One other alternative called "in-situ" hydrothermal synthesis consists on synthesize the zeolite directly inside the porous structure [START_REF] Deng | [END_REF][149][150][151][152][153][154]. The 'in-situ" method is thought to allow stronger contact between the support and the zeolite phase, to improve hydrothermal stability and to allow a more precise location of the zeolitic phases within subtract. The technological challenge is ambitious but original methods of catalyst phases deposit will certainly allow in the future locating more accurately the active phases, maintaining the filtration performances and catalyst efficiency of these SCRF.

In traditional DPF devices, the regeneration mechanism involved the separation of soot particles from the gas phase by mechanical filtration [26]. Until now, the soot regeneration on washcoated SCRF units has been achieved by combination of passive NO2-soot (275-450°C) regeneration (Reactions 3 and 4) and active O2-soot regeneration (600°C) by Reactions 1 and 2, due to the passive regeneration was still insufficient to completely clean soot of the DPF. For this reason, the different temperature ranges of both strategies impact the choice of the SCR catalyst formulations suitable for SCRF units: i) Vanadium-based SCR catalyst are sulfur-tolerant but cannot tolerate active O2soot regeneration temperatures, so they mainly rely on a fully passive NO2-soot regeneration; ii) Copper zeolite-based formulations are able to active O2-soot regeneration temperatures up to 800°C. However, a drawback is that the zeolite-based SCR catalysts are sulfur-sensitive, especially the Cu-zeolite formulations [155].

As a result, the choice of SCR catalyst for the DPF waschoat will depend on the feasibility of full passive NO2-soot regeneration, depending on the engine's NOx out/PM out ratio and the PM concentration in the exhaust; as well as the exhaust temperature range:

c) Zeolite-based SCR catalysts

In the case of passenger cars (with high PM out concentrations and a low exhaust temperatures), the periodically active O2-soot regeneration around 600°C is still needed to supplement the NO2-soot combustion. For this reason, the catalytic system used in this kind of vehicles must be durable and maintains its SCR catalytic activity even after the exposure to the high temperatures reached during the diesel filter regenerations (550-700 °C) [156,157]. Thus, some zeolite-based SCR formulations have been applied due to their high thermal stability [158,[START_REF] Dorenkamp | Schadstoffarme Antriebskonzepte Heute und Morgen FAD-Konferenz distributed presentations[END_REF]. This capacity is very desirable as other kind of catalysts suffer of thermal deactivation which causes support area loss due to the degradation of the catalyst framework or a sintering process in which catalytically active species agglomerate to form larger, inactive species [START_REF] Bartholomew | [END_REF]). Finally, the SCRF must also be able to handle uncontrolled NOx emissions during the active DPF regeneration events (450-700 °C) [7,161]. The state-of-the-art Cu-CHA catalysts have demonstrated good thermal durability and deNOx performance over a wide range of temperature [79,88] (as shown in Figure 1.15), suggesting them as an interesting possibility [START_REF] Dorenkamp | Schadstoffarme Antriebskonzepte Heute und Morgen FAD-Konferenz distributed presentations[END_REF]. Coated with such Cu-zeolite SCR formulation, SCRF can achieve a very good deNOx efficiency (almost 80%) under steady-state operating conditions across a wide temperature window [162].

d) Vanadium-based SCR catalysts

For off-road and heavy-duty applications, fully managed by passive NO2-soot regenerations, integration of V-based SCRF formulations represents an attractive solution due to high sulfur resistance accompanied by low-temperature NOx conversion and improved fuel economy [24,155,163,164]. V-SCRs are also active for HC and PM oxidation [165][166][167][168]. This dual functionality (oxidation and reduction reactions plus the filtration obtained on the filter substrate) can help to achieve the legislative emissions limits together with reduction of the aftertreatment packaging volume. Johnansen et al. [START_REF] Johansen | [END_REF] showed that vanadia based SCR formulations on cordierite filters achieved similar NOx conversion to that of conventional flow through SCR above 300 °C. Wolff et al. [169] described vanadia SCR coating and performance on a high porosity silicon carbide filter. They evaluated the performance of three different coatings. Higher performance was obtained for the parts that were coated with higher washcoat loading with a single layer of coating. Lopez de Jesus et al. [163] studied a V-based SCRF system under NRTC test conditions. As shown in Figure 1.16, a significant amount (70-80%) of NOx was reduced, demonstrating that passive soot regeneration was able to be produced. It is necessary to remark that very similar NOx conversions were obtained for the clean and soot loaded filters, which indicates that the soot accumulated on the filter before and during the tests does not affect the NOx conversion. In addition, Lopez de Jesus et al. [163] also simulated the V-SCRF system reactions by computational modeling tools and they concluded that their model was able to give a good NOx prediction for the V-based SCRF catalyst over steady-state and transient engine tests [163].

SCR-soot interaction phenomena into SCRF

Clearly, SCR reactions and soot oxidation take place in different temperature ranges [142]. However, SCRF configuration would lead to the parallel presence of NOx, reducing agent and diesel soot in the same unit, where they may react with each other. This combination comprises known and new reactions not considered until now (Table 1.6) [22]. There are three main challenges to overcome due to NOx pollutants and soot cross-interactions [79,84,142,170]: 1) soot blocking the accessibility of gas flow to "classic" active sites of the catalyst [84]; 2) soot presence affects deNOx SCR reactions performance (as passive soot oxidation consumes NO2 yielding NO formation altering the NO2/NOx ratio) [79,162,171]) or, contrarily, SCR reactions affects PM oxidation process (Reactions 3 and 4) as far as competition for NO2 will be produced [32,142,172,173]; and finally, 3) it is worthy to be studied the possible NOx selective catalytic reduction taking place over the soot particles thanks to NO2 adsorbed onto the soot surface.

a) PM loading effects on mass diffusion and NOx reduction.

Experimental observations:

Firstly, soot deposition impedes the mass transport process for species which correspondingly influences the SCR reaction rates [START_REF] Olowojebutu | [END_REF]. Marchitti et al. [82] observed an adverse effect of soot coverage of the zeolite active sites [82,171], for a crushed Cuzeolite coated on SiC substrate (powder catalyst). They observed that under Standard SCR conditions, the presence of soot inhibited the NO and NH3 consumptions at low temperature range (150-350°C). Mihai et al. [158] studied a Cu-CHA coated particulate filter and observed that in the presence of soot, the NOx conversion was slightly lower at 200-300 °C due to the blocking of the zeolite active sites. They performed four cycles of the Standard SCR reaction over the same sample. As a result, they observed that the NOx conversions for cycles 3 and 4 were slightly higher than for cycles 1 and 2. This is because most of the soot had been removed after cycle 2 (very low amounts of CO and CO2 were formed during cycles 3 and 4), and no soot was blocking part of the catalyst which could hinder the SCR reaction. This blocking effect is possible as soot particles were quite large (about 30-40 nm); thus, the soot particles were too big to enter into the small channels of the copper zeolite.

In a different study, Mihai et al. [94] analysed the effect of soot over a Cu-SCRF catalyst under NO2-SCR conditions. They found that the NO2-SCR reaction was significantly enhanced in the presence of soot. This could be explained due to the initial hydrothermal treatment at 850°C for 12h of the Cu-SCRF sample; thus, some CuxOy or other copper species were likely formed on the outside of the zeolite crystallites and that those had been blocked by the soot. They proposed that the soot interacts with the ammonium nitrate species on the CuxOy species, resulting in higher NO2-SCR activity and selectivity. Interestingly, less N2O is formed in the presence of soot, meaning that there are fewer ammonium nitrate species on the surface due to their interaction with the soot. As ammonium nitrate hinders the NOx reduction, it is advantageous to reduce these species, which explains the higher activity in the presence of soot. Accordingly, when the soot started to be removed from the catalyst at high temperatures, the N2O concentration slightly increased. Indeed, they observed CO2 production during this reaction conditions at 150-200 °C, confirming there is a reaction between the nitrates and the soot even at this very low temperature. Park et al. [171] made the assumption that soot deposits inside the filter wall work as a barrier for mass transfer and diffusion from gas flow to "classic" metal catalytic sites (Figure 1.17). This reduces the overall deNOx activity. Park et al. [171] suggest that during deep bed soot filtration, soot particles deposit on the inner surface of porous wall and the deposit layer grows to form pore bridging. Hence, contrarily to clean filters, on soot deposited filters the exhaust gas do not directly contact the active phase. This diffusion through the soot deposit is added to the mass transfer mechanism, significantly limiting the overall deNOx reaction rate. On the contrary, soot loading deposited in the form of deep bed contacts the catalytic material directly and it starts to oxidize first as temperature increases [START_REF] Johansen | [END_REF]171].

Model predictions :

The diagram illustrated in Figure 1.17 presents the phenomena of PM filtration in a SCRF, the passive soot oxidation taking place in the soot cake layer and the SCR reactions in the substrate wall. It can be affirmed that some passive regeneration is expected as NO2 firstly passes through the soot cake layer before reaching the catalyst on the substrate wall [172,173].

All the observations made from different authors and research groups referring to the blocking effect of PM loading are summarized on Table 1.6.

b) Trade-off between PM and NOx reduction efficiency.

The SCRF system performance is affected by competition for NO2 between SCR reactions and passive PM oxidation [32,142,172,173]. As aforementioned, the passive soot regeneration requires NO2 while SCR reactions reduce them, being competitive reactions. In literature, it has been found that the key parameters influencing the SCRF performance in presence of soot include: NH3 adsorption, NOx reduction efficiency and PM oxidation rate [32,88] which can be affected by SCR reactions and, especially, NO2 contribution.

Impact of NH3:

Tang et al. [172] found that PM oxidation in a Cu-zeolite on a SCRF started around 300 ºC in NH3 absence, being a lower temperature value than the thermal PM oxidation temperature on a regular DPF system (400 ºC) [32]. This seems to confirm that Cuzeolite catalyses the PM oxidation by NO2-passive regeneration [32,171]. The results also indicated that PM oxidation was significantly inhibited by NH3 presence because the required NO2 is being firstly converted by the reductant agent via SCR reactions [32,[START_REF] Johansen | [END_REF]82,172,174], suggesting that they are the preferred pathway for NO2 [175].

Tronconi et al. [79] studied the impact of ammonia on the soot combustion, both in presence and absence of NOx. They confirmed that the passive soot combustion was adversely affected by the NH3 presence in the low-medium temperature range, especially on NO2-SCR and Fast reactions (both in SCR powder catalysts and loaded SCRF system). However, in the case of Standard SCR reaction, soot combustion remained unaffected by the presence of either NO or NO+NH3 [82]. Referring to active O2-based oxidation of soot, a positive effect was observed in the absence of NOx as the CO and CO2 peaks where shifted to lower temperatures [79].

Impact of NO2:

In reference to NOx influence on soot combustion, Tang et al. [172] observed that passive regeneration of soot was inhibited due to SCR reactions competition, as sufficient NO2 concentration adsorbed in the soot cake is needed. Lower soot cake concentration of the adsorbed NO2 leads to slower C+NO2 reaction rates (reactions 3 and 4) and promotes the Fast SCR reaction (Reaction 8) as its kinetics is faster. Colombo et al. [84] studied this influence and they found that, in the case of the Standard reacting system, the presence of deNOx activity slightly promoted the soot oxidation due to the exothermicity of the reaction. However, in the NO2 reacting system, soot consumption resulted inhibited because NO2 was competitively consumed in both soot passive regeneration and SCR reactions, limiting the soot consumption rate. Watling et al. [142] used different NO2/NOx ratios between 250-550 ºC and they also found that, at temperatures above 400 ºC, the PM oxidation rate was limited due to the NO2 consumption. However, in the case of Fast SCR conditions, Colombo et al. [84] observed that the passive PM oxidation was enhanced as higher NO2/NOx ratios are smoothing the NO2 competition effect. Accordingly to them, Rappé [176] maintained that at NO2/NOx ≤0.5, NO2 consumption and diffusion are dominated by the fast SCR reaction, resulting in significantly reduced passive soot oxidation. In comparison, NO2/NOx >0.5 decreases this effect due to greater dependency on slower NO2-SCR reactions, which has the effect of decreasing the rate of depletion of NO2 in the inlet filter channel [176]. NO2 excess conditions seemed to satisfy both NO2 SCR and PM oxidation reactions.

But these tendencies are in contrast to results obtained from another research groups such as Johansen et al. [START_REF] Johansen | [END_REF][START_REF] Johansen | SCR-DPF integrations for diesel exhaust. Performance and perspectives for high SCR loadings[END_REF] who maintain that passive soot regeneration was not influenced by the SCR activity; or Tronconi et al. [79,82] who suggest that, the NO2 and Fast SCR reactions produce an positive effect over the passive soot regeneration process, whereas the NO alone (Standard SCR conditions) does not interact with soot [82].

Impact of soot:

As already discussed before, the NOx reduction efficiency is dependent of NH3 amount adsorbed on the catalyst [32,48,177]; and the soot loading on the filter may affects the NH3SC of the SCRF systems. Referring to NH3 adsorption capacity, how exactly it can be affected by soot loading presence is still under discussion: On one hand, Tang et al. [172] studied the NH3SC of a Cu-SCRF catalyst and found that this capacity decreased with temperature and PM loading increase, due to both reaction and diffusion phenomena. On the other hand, opposite conclusions were made by Schrade et al. [170] who found that NH3 adsorption increased with high PM loadings. This effect was not observed in absence of washcoat loading so, it seems that PM-washcoat interaction increases the NH3SC of SCRF systems compared to soot-free SCRF [82,88,170,176]. The acid sites [178], which could be produced by heating the soot in the presence of an oxidizing agent, might be responsible for such interaction between NH3 and soot. In Accordingly to Schrade results, Yang et al. [162] suggested that the high ammonia storage could be due to unconsumed ammonia which remains on surface.

In reference to soot impact on the NH3 oxidation reaction, Marchitti et al. [82] found that NH3 conversion was 10-20 % higher in presence of commercial soot than without it, suggesting that soot promotes ammonia oxidation (detrimental for NOx reduction on SCR reactions). They suggest that the oxygenated surface compounds and the absorbed O2 on the soot surface could be responsible since they work as "activated oxygen donors" [178][179][180].

Finally, the effect of soot over the SCR performances will be discussed. In the literature it is reported that it may be associated to various factors: including SCR catalyst formulation, soot loading level, and NH3/urea injection strategies, etc. Among others, Colombo et al. [84] studied the effects of PM loading in and on the filter walls on the NOx reduction performance of SCR catalyst. PM loadings up to 3g/L was not observed to negatively affect NOx reduction by various research groups on both steady-state and transient cycles. In agreement with this, some other authors [181] as Tang et al. [172] also reported that soot loading did not adversely affect NOx reduction, especially at low NO2/NOx ratios where no soot inhibition effect on deNOx activity has been found. In contrast, an increase in NOx reduction efficiency caused by PM loading presence was observed by other authors because the NO2-PM interaction (passive regeneration) helped to decreased NO2/NOx ratio to ideal value closer to 0.5 (Fast SCR) [82,142,171]. In addition, confirming this positive effect of soot on NO2-SCR conditions, the presence of soot also suppressed the N2O formation at 250-400 °C [32,79,82,172,174]. NO2 excess conditions imply to have enough NO2 available to produce the NO2-SCR and the soot combustion simultaneously. Finally, Rappé and Marchitti et al. observed inferior SCR performance in the Standard SCR conditions [82,176]. Also, for NO2/NOx=0.5 ratios (Fast SCR), the presence of soot reduced the deNOx activity, indicating the soot was being oxidized by NO2 [79], preventing achieve optimal 0.5 NO2/NOx ratios. Passive soot regeneration subtracts NO2 otherwise available for NOx reduction [82].

To sum up, it is clear that the impact of soot over the deNOx activity is strongly influenced by the NO2/NOx ratio [176]. It can be concluded that soot on the SCRF device could help the deNOx functionality if NO2 content was higher than optimal and hindered it if the NO2 was lower. [174]. This is because of the local reaction in the soot layer forms NO and, therefore, changes the SCR stoichiometry at the active sites. Johansen et al. [START_REF] Johansen | [END_REF][START_REF] Johansen | SCR-DPF integrations for diesel exhaust. Performance and perspectives for high SCR loadings[END_REF] suggests that the potential thermal decoupling of competitive SCR and soot oxidation reactions would be interesting as NO2 is primarily needed for the Fast SCR in the 180-300 °C range while NO2-passive soot regeneration happens between 300-450 °C. Therefore, during cold start step, NO2 will be fully available to NOx reduction.

All the observations made from different authors and research groups referring to the interactions between PM and NOx reduction (soot loading impact on SCR activity, NO2 and NH3 effect on PM oxidation...) are summarized on Table 1.7.a and Table 1.7.b. This ambiguity of the results obtained from different research groups may be explained by several factors: i) Ammonia storage capacity is improved by soot loading due to its high surface area gives more adsorption sites to NH3 [170], improving SCR reactions [170]; and ii) The competing consumption of NO2 for soot oxidation and SCR reactions alter the SCR reaction pathway leading to potentially ambiguous effect on deNOx efficiency values [142]. It is also important consider that research about these NOx-soot

SCRF catalyst

Tang et al. [ interactions have been made by authors using different operational conditions and different kinds of soot or catalyst configurations. This would lead to dissimilar conclusions about the effects observed. This only remarks the necessity of continuing the research about the SCRF catalysts.

c) Soot catalyses SCR activity

Mehring et al. [182] investigated SCR of NOx by ammonia on a Printex U bed (commercial soot) and various diesel soot samples between 200-350 °C, suggesting that soot particles are also active for deNOx activity. In this point some effects previously mentioned on 3.2.1 and 3.2.2 are also happening as they are closely linked to the SCR performance and soot reactivity. They found that in the presence of only NO, no NOx soot-reduction was observed. Colombo et al. [84] confirmed this affirmation.

However, in presence of only NO2, stoichiometry shifted to typical values of NO2-SCR reactions. Equally, the reaction on the soot surface was shifted from the NO2-SCR reaction to the fast SCR reaction just by the addition of NO. Due to the highlighting role of NO2 in passive regeneration [79], NO2/NOx ratio is continuously varying and this may affects SCR efficiency [22]. In fact, depending on the operating conditions, this can result either in a promoting or detrimental effect [START_REF] Maunula | Intensification of Catalytic Aftertreatments Systems for Mobile Applications[END_REF]79,82,84]. It can be considered that soot particles present catalytic activity as adsorption sites for NH3 and NOx, as Figure 1.18 illustrates. Related to this, they also found that carbon oxidation and SCR reactions occurred in parallel but they barely affected each other, suggesting that in the NOx reduction on soot most probably physisorbed species were involved [182]. Considering the effect of soot on the SCR reaction, soot has to be regarded as catalyst for this specific reaction. Since the Fast and the NO2-SCR reaction do not require a redox-active component, the catalytic function of soot is to provide adsorption sites for ammonia as well as NOx species. It is also remarkable that the concurrence of acidic surface functional groups was identified as an important property of an SCRactive carbon material [183,184] as they will enhance NH3 adsorption. In literature it was reported that presence of NO2 during soot oxidation promotes the formation of surface carboxylic acids and lactone. The SCR of NOx mechanism in these conditions, suggested by Mehring et al. [182], consisted on a first step which is the disproportionation of NO2 previously adsorbed on the soot surface, followed by the formation of ammonium nitrates and nitrites [185] due to the NH3 injection. The nitrites decompose directly into N2 and H2O, whereas the nitrates have to be reduced to nitrites either by NO or in its absence by NH3, which also leads to the formation of N2 and H2O.

CONCLUSIONS

Among the most harmful pollutants related with diesel engines, particulate matter and NOx are considered of major concern since they are released in quite huge amounts to the atmosphere and cause severe environmental and human health issues. Due to these adverse effects of main diesel emissions, authorities progressively restricted the permissible exhaust emission levels by developing the be-named Euro standards which have continuously become more and more stringent. Nowadays, the Euro 6 is being applied since 2014 and it is especially focused on NOx emissions limitation (from 0.18 g/km allowed in 2009 with Euro 5 to 0.08 fixed by Euro 6).

As a consequence, vehicule manufacturers are forced to develop new technologies in order to reduce pollutant emission from vehicles and fulfill new government regulations. The studies that have been carried out for decades allow to conclude that the desired emission levels can be only achieved by aftertreatment systems, being the preferred one the SCR technology to reduced NOx by means of ammonia as reductant agent. A typical diesel emission control system using SCR also includes an DOC and a DPF in order to control the emissions of carbon monoxide, hydrocarbons and PM, respectively. Nowadays, zeolite-based metal (specially, Cu and Fe) catalysts have been developed for mobile applications because of their high thermal stability and high NOx reduction activity over a wide range of conditions. Considerable advancement was recently achieved when the Cu was exchanged into small-pore zeolites and silicoalumina phosphates with a CHA structure, such as Cu-SSZ-13 and Cu-SAPO-34.

Compared to Cu-ZSM-5 (MFI) and Cu-BEA, they have been found to be more active and selective, and less sensitive to deactivation by hydrocarbon inhibition or thermal degradation.

This chapter summarized the main problematic of the current NH3-SCR aftertreatment technology on Diesel exhaust lines as a consequence of the constant evolution of the Euro standards. As a consequence of it, a new conception for the diesel after treatment systems has been presented as a possible alternative as it allows the integration in one single unit of the catalytic and the filtration step. On this SCRF (Selective Catalytic Reduction on Filter) system, the catalysed soot filter assumes two functions: removal of the particles (DPF) and conversion of the NOx species to N2 (SCR). However, high porosity filter substrates (such as cordierite and SiC) are needed in order to assure sufficient amount of SCR catalyst, which is coated onto the filter walls, without causing a backpressure issue on the system. Metal exchanged zeolite-based formulations offer an interesting potential due to their high thermal stability, necessary during the high temperature soot regeneration periods. Based on this review of the current literature available and the comprehension of the challenges to overcome with this new catalyst configuration, a first step on the objectives and the experimental approach of this thesis took shape: study of the NH3-SCR performance with a SCRF catalyst. Here, the deNOx activity of the SCRF system will be evaluated and compared to a flow-through SCR catalyst activity. Also, thermal stability of a Cu-based zeolite was evaluated until 600 ºC. Different NO/NOx ratios, NO and NH3 oxidation reactions were performed in order to completely characterize the catalytic behaviour of the SCRF system.

In the literature was also reported that this SCRF system comprises new reactions not considered until now as diesel soot, NOx and the reductant agent are present in the same unit. There are three main ways that NOx pollutants and soot may interact: 1) soot blocking the accessibility of gas flow to "classic" active sites of the catalyst; 2) possibility of NOx reduction taking place over the soot particles; and finally, 3) soot presence affects SCR reactions performance (as soot oxidation consumes NO2 in the soot cake layer) or, contrarily, SCR reactions affects PM oxidation process as far as competition for NO2 will be produced. Agreement about these cross-interactions results obtained by various authors in the literature have not been reached for now. Thus, a second step on this thesis objectives was focused on the study of the NH3-SCR catalysts behaviour in presence of soot and, especially, the NO2 availability to passive soot oxidation and its competition with the NOx reduction reactions. Again, different NO/NOx ratios were studied as soot presence influence might be related to the different gas conditions existing on a real Diesel exhaust. Information about the catalytic behaviour of the system will be completed with a set of characterizations of the soot and the catalyst. More details about the thesis objectives and the experimental approach followed to develop them will be further discussed on the next section.

OBJECTIVES AND EXPERIMENTAL APPROACH

As aforementioned, the analysis of the available literature presented on the previous section allowed determining two main challenges to overcome with the new SCRF systems: firstly, to study the reactive NH3-SCR behaviour of a SCRF catalyst under different gas mixtures (three SCR reactions). Secondly, the aim was to investigate the SCR-soot cross-interactions reported in the literature and, more specifically, the availability of NO2 for passive soot oxidation. It is necessary to remark that two kinds of soot were studied: a commercial Printex U and a real Diesel soot, in order to compare their physicochemical characteristics which will determine differences in their catalytic behaviour under SCR conditions.

STUDY OF THE NH3-SCR PERFORMANCE WITH SCRF CONFIGURATION

Mini-SCRF commercial catalyst

Based on the literature research of the state of the art of the NH3-SCRF technology realized during the first months of the thesis, it was decided to set as reference catalyst a commercial mini-SCRF sample. It consisted on an active phase made of a Cu-based zeolite and a cordierite filter as support. CHA framework type was selected as narrow pore zeolites are catching a great deal of attention in the last years due to their high hydrothermal stability and good N2 selectivity in a wide range of temperature. This commercial catalyst was supplied by an external company and it was studied under two different textures: the original mini-SCRF sample of 1"x 3" size and the powder (from crushing the mini-SCRF sample). The mini-SCRF sample was tested at IFPEN gas bench which was closer to real life conditions; whereas the powder was tested at IRCELYON system which allowed obtaining more detailed information about the kinetics of the SCR reactions. Proposed approach consisted on: first at IFPEN, studying separately each one of the simultaneous reactions that happen during the SCR reactions and increase the complexity step by step. This facilitated the comprehension of the really complex mechanism of SCR conditions which includes simultaneous competitive reactions.

Reorientation of the thesis approach

Unfortunately, an unexpected deactivation of the mini-SCRF catalyst activity was observed along the test serie at IFPEN. As a consequence, the strategy and the experimental approach were necessary to be changed. It was decided to synthesize a waschoat at IRCELYON laboratory consisting on a SAPO-34 zeolite (CHA framework) impregnated with Cu. Similar Cu loading and properties of the commercial reference catalyst were reproduced on this synthesized Cu-zeolite. The prepared Cu/SAPO-34 zeolite was mixed with commercial cordierite in similar proportions to the commercial sample in order to be evaluated under SCR conditions. Even though the initial approach of using a commercial mini-SCRF sample to simulate real life conditions as closest as possible had to be abandoned, the main objectives of the thesis remained the same: study the SCR-soot interactions and determine the availability of NO2 to passively oxidize soot. From now on, the following studies were only performed on this in-lab synthesized Cu/SAPO-34 powder.

PHYSICOCHEMICAL CHARACTERIZATIONS OF THE CATALYST AND BOTH KINDS OF SOOT.

Once the in-laboratory Cu/SAPO-34 zeolite was synthesized, calcined, impregnated and stabilized; a serie of basic physicochemical characterisations (XRD, ICP-OES, BET+isotherms, SEM+EDX, TEM, XPS…) was developed. The aim was verifying that the SAPO-34 structure was successfully achieved and the typical properties of SAPO-34 zeolites were obtained. Furthermore, chemical and textural characterization of both kinds of soot was also performed as it will explain certain differences in their catalytic behaviour during the test serie. It was based not only on the previous techniques (XRD, SEM+EDX…) but also in Raman technique which will provide information about the defects number and homogeneity of the samples. In this case, chemical composition will be studied by CHNS technique and TGA analysis will allow comparing the mass loss in function of the temperature, ashes amount and thermal stability of both kind of soots.

STUDY OF SCR REACTIONS AND SOOT CROSS-INTERACTIONS. INFLUENCE OF SOOT ON THE NH3-SCR ACTIVITY.

Once the in-laboratory synthesized catalyst was physicochemically characterized, it was necessary to study its deNOx activity under different NO/NOx ratios. First, a test serie without soot presence (similar strategy of increasing reactions complexity than the followed with the commercial mini-SCRF catalyst) was performed. The aim was to verify that our new SCRF system (mixed Cu-SAPO-34 + cordierite in powder form) produced a catalytic activity similar to the commercial sample when fresh and similar to results discussed by other authors in the literature.

Once the catalytic behaviour of the in-lab SCRF system was evaluated under a wide range of operational conditions, the second axe of the thesis started. The new SCRF system in the presence of a soot layer was evaluated with the aim of determine its influence over the NOx reduction activity. Based on some literature research [79], the catalyst-soot ratio used was of 10:1. The soot was deposited as a layer on top of the catalyst + cordierite mixture to simulate real soot deposition. The main effects which would be investigated in thesis were the following ones:

Soot interaction with the NOx would influence the SCR mechanism: i.e; affecting the NH3 storage capacity or modifying the NO/NOx ratio which affects the deNOx activity and selectivity.

Soot oxidation reaction could be affected by the NOx (NO/NOx ratio influence) or NH3 presence.

Competition for NO2 between SCR reactions and soot oxidation.

The diffusion phenomena and the competition for NO2 might be affected by the soot layer height as well as by the particulate matter composition of each soot sample. It step, it was decided to maintain constant the soot amount and to be better focused on the study of the effects of the aforementioned different kinds of soot.

MATERIALS AND EXPERIMENTAL METHODS

As literature chapter showed, the deNOx systems depends of numerous parameters such as catalyst nature and characteristics, as well as operational conditions.

LIST OF PRODUCTS

Chemical products

Main reactives used as listed below, indicating concentration, purity and supplier company:

Aluminium isopropoxide, Al[OCH(CH3)2]3, 98% purity (Sigma-Aldrich) Fumed silica, SiO2, 0.2-0.3 μm particle size (Sigma-Aldrich).

Ortho-phosphoric acid, H3PO4, 85 purity (Sigma-Aldrich).

Tetraethylammonium hydroxide (TEAOH), (C2H5)4N(OH), 40% wt. in H2O (Sigma-Aldrich). Cu (II) nitrate trihydrate, 99,999% of purity (Sigma Aldrich).

Distilled water produced in IRCELYON laboratories. Commerical Diesel soots (Printex U) Real Diesel soot obtained from an Euro 5 engine bench at IFPEN

Gases

NO/He, 8000 ppm of NO, in a B50 bottle at 300 bars (Linde). NO2/He/O2, 4000ppm of NO2 and 1% of O2, in a B50 bottle at 300 bars (Linde). NH3/He, 8000 ppm of NH3, in a B20 at 150 bars supplied (Air Liquide). He, 99,999% purity in a B500 at 200 bars (Linde). Oxygen, 99,999% purity in a B50 bottle at 200 bars (Linde). Nitrogen, 99,999% purity, in a B50 bottle at 200 bars (Linde).

CATALYST

Commercial mini-SCRF catalyst

The first 14 months of the thesis was focused on the catalytic characterisation of a commercial mini-SCRF catalyst, based on a Cu-exchanged zeolite as catalyst and cordierite as support. In this chapter will be presented and explained the experimental methods and materials used as experimental approach of the thesis.

Samples in particulate filter form were taken from a bigger monolith piece given and previously stabilized by calcination. This catalyst is found being high performing in activation, exothermicity and pollutant conversion terms. It consists on a non-highly charged Cu-exchanged zeolite type CHA as catalyst washcoated on a thin layer over a particulate filter (cordierite) that gives a high surface area. This catalyst was also tested at IRCELYON in powder form by crushing a piece of the commercial mini-SCRF sample. The aim of this is to compare not only the physicochemical and kinetic properties of each one (SCRF system is closer to real life conditions than powder one) but also, compare both with results obtained by another research groups available on literature.

Table 3.1 summarised main characteristics of samples aforementioned:

Synthesized powder catalyst

Due to the catalytic deactivation of the commercial catalyst, it was decided to synthesize in laboratory the SAPO-34 zeolite in powder form following hydrothermal method and later, to impregnate the zeolite structure with a Cu nitrate solution. The reaction precursors used as well as the hydrothermal synthesis procedure was adapted from the combination of some literature available [1][2][3][4]. Different parameters such precursors amount and time in the stainless steel autoclave were studied in order to find the optimal SAPO-34 crystallization. The hydrothermal synthesis and Cu impregnation processes are described as follows:

Precursors: Aluminium isopropoxide Fumed silica. Ortho-phosphoric acid. Tetraethylammonium hydroxide (TEAOH).

a) SAPO-34 zeolite synthesis:

First, 8,4g of aluminium isopropoxide was used as Al precursor and it was mixed with 16,9 mL of TEAOH used as template.

After mixing for 90 min, 0,37g of fumed silica (Si precursor) was added and stirred until a homogeneous mixture was obtained. Then, 4,37g of phosphoric acid (P precursor) were diluted in 6,8g of water and added to the main mixture.

Once, the main mixture is complete it was spilt into an autoclave and heated at 200 °C between 4-5 days.

Finally, the solution was cooled by means of liquid N2.

The obtained solution is acid so it was washed several times with water at 800 rpm in the centrifuge machine until neutral PH was reached.

Then, neutral solution is dried at 100 °C overnight.

b) Calcination:

Once SAPO-34 zeolite powder was completely dry, a calcination was performed in order to remove the template. Calcination was performed using 3 L/h of air on dry conditions. Then, a plateau of 2h at 200 °C was performed in order to assure that the zeolite structure is stable.

Later, a second step consisted on increasing again the temperature until 550 °C. This value was strategically chosen as maximum reacting temperature will be 500 °C. Calcination at 550 °C assures that zeolite will be already previously stabilized at reacting temperature and also, allows all samples tested to start from the same conditions.

A plateau of 6h was performed at 550 °C to the completely stabilization of the zeolite at this temperature value.

Finally, it was cooled until room temperature using 1°C/min as speed.

c) Cu impregnation method:

Once, the template was removed and the SAPO-34 zeolite was stabilized, Cu species were introduced on the zeolite active sites by impregnation method. A Cu (II) nitrate trihydrate salt was chosen as precursor and 2,5 % wt was the chosen load (to simulate commercial mini-SCRF loading of Cu). Impregnation technique consists on putting the catalytic support in contact with a solution which contains the active metal. To do that:

A round flask was filled with the synthesised zeolite (catalytic support) on a rotary evaporator with no heat and it rotated at vacuum during 2h in order to eliminate the humidity of the sample.

Later, the Cu (II) nitrate trihydrate solution (active phase) was carefully spilled onto the zeolite.

It was heated at 90 °C and it rotated at vacuum 2h again to remove the solvent.

After that, the impregnated zeolite was dried at 100 °C overnight.

Finally, the Cu/SAPO-34 zeolite was again calcined in order to stabilise the complete zeolite. Same calcination conditions and method was followed.

SOOT RECUPERATION METHOD at IFPEN

Diesel Particulate Filter it was extracted from a DPF filter from an engine bench DPF filter of an Euro 5 engine (Figure 3.3). Prior to start the procedure of soot recuperation, the DPF filter it was previously regenerated following a specific method, including both active and passive regeneration steps. Once charged of soot, the loaded DPF it was again weighted at hot conditions. The weight difference will be the soot quantity charged on the DPF. It was let to cool until room temperature. This difference was 10-11 mg of soot approximately.

Then a blowing and a suction tube were assembled up and down of the DPF, as showed on Figure 3.5, to blowing the soot particles through the filter soot. Blowing air in the contrary flow sense than engine gas exhaust pushed the soot particles and allowed to recover the soot captured over the round paper filter (Figure 3.6).

CATALYSTS PHYSICO-CHEMICAL CHARACTERISATION

Catalyst characterisation techniques a) Inductively coupled plasma optical emission spectrometry (ICP-OES)

By means of this spectrometry technique, the chemical composition of both commercial and synthesized catalysts were determined. Concretely, it was used to calculate the percentage in weight of the different elements which form the zeolite framework and the Cu metal content reached by the impregnation method. Main principle is to excite atoms of the sample by injection of an Argon plasma. This plasma has high electron density and temperature (10000K) and this energy is used in the excitation-emission of the sample atoms. When the excited energy stops, characteristic photons of each element are released when return to low energy position. Element type was determined based on the position of the spectrum and the content is determined based on the Palflex® filter Soot Soot spectrum intensity. Previously to the analysis itself, solid samples were diluted with nitric acid, sulfuric acid and hydrogen fluoride to dissolve metals. For Si it was necessary a fusion attack with Lithium thetraborate and heating until 1100°C.

Limitations: only the element with atomic number above Lithium are detectable by ICP-OES. To detect C, H and O, another technique such as C, H, N, S analysis might be necessary. b) X-Ray Diffraction (XRD) X-Ray diffraction were performed on a diffractometer model Bruker D8 Advance. 50 kV-35 mA and a LynxEye detector with 192 channel was used. XRD technique allows to qualitatively characterise a crystalline solid material. X-Ray wavelength is between 10 y 100 Å and is produced by high energy electrons or due to electron transitions between internal atomic levels. When X-Ray are dispersed in an ordered environment, the diffraction occurs due to the lengths between the dispersion centres of the same order that the incident radiation. Diffraction is produced by accumulation of the generated dispersion when X-Rays interacts with the crystalline layers at the same distance. To observe the diffraction, it is necessary that dispersion centres are distributed in organized planes with specific orientations. Planes with same orientation form a plane family with a characteristic diffraction signal same orientation that follow the Bragg law:

n•λ= 2• •sin θ (1)
Where n is the diffraction order, λ is the wavelength of the incident radiation, is the distance between plane families and θ is the diffraction angle.

Main parameters that give information are θ angles and intensity of rays emitted.

Method is based on the diffraction peaks width and the particle sizes by the Debye-Scherrer equation:

(2) Being d, the particle diameter in the diffraction plane direction, λ the wavelength of radiation, θ the diffraction angle of the peaks and K a constant whose value depends on the diffraction peaks width. Key information would be obtained from the diffractogram when analysing the peaks position (indicates the present phases), the peaks intensity and the crystal size and orientation.

c) Brunauer-Emmett-Teller (BET) theory

BET was performed on an ASAP2020 model. Adsorption preparation at vacuum was performed at the following conditions: vacuum of mmHg at 30 °C. Desorption conditions were 350 °C for 2 h and then, 3Flex. BET theory is based on the physical adsorption of gas molecules on a solid surface and allows the determination of the surface area of materials. Inert gases are used as adsorbates to quantify specific surface area, being Nitrogen the most commonly employed. For this reason, standard BET analysis is most often conducted at the boiling temperature of N2 (77 K). The technique combines external area and pore area to determine the total specific surface area in m 2 /g yielding important information about the surface porosity and pore size distribution. Hovarth-Kawazoe mathematical fitting can be employed to determine the pore area and specific pore volume of microporous materials based on the adsorption and desorption isotherms. This technique characterises pore size distribution independent of external area due to particle size of the sample. d) X-Ray Photoelectron Spectroscopy (XPS) XPS analysis were performed on a spectrometer model AXIS with a monochromatic characteristic X-ray source (1486.69 eV) and a passing energy of 0.05 eV. It is a surface-sensitive and semi-quantitative spectroscopy that measures the atomic composition, chemical state and electronic state of the elements that exist within the superficial layers of a material. XPS requires high vacuum (P ~ 10-8 milibar) conditions, although a current area of development is ambient-pressure, in which samples are analysed at pressures of a few tens of milibar.

This low resolution technique consists on irradiate the material surface with a beam of X-photons. When a photon of hυ energy interacts with a level electron, the photon energy is transferred to the electron emitting a photoelectron as result. Emitted photoelectrons give information about the energy level of each atomic layer and thus, about the nature of each emitting atom or element. h = EC + EL, being Ec the kinetic energy emitted and EL the binding energy between the electron and the energy layer. XPS completes the XRD analysis which only detects the crystalline structures but not yhe amorphous phases.

Limitations: only the external surface of the material is explored and not all the chemical species are distinguishable due to the frequent superposition of rays. The ambiguity in the identification could be particularly important in the low energy range. A previous knowledge of the mass composition (ICP-OES) could be useful.

e) Scanning Electron Microscope (SEM)

SEM microscopy allows the observation and characterisation of organic and inorganic materials, giving information about the sample's surface topography and composition. It is a type of electron microscope that produces images by scanning the sample surface with a focused beam of electrons. Electrons interact with atoms on the sample, emitting characteristic signals. By collecting the emitted secondary electrons using a special detector, an image displaying the topography of the surface is created. Specimens can be observed in high vacuum in conventional SEM in the case of conductive materials, or in low vacuum or wet conditions in variable pressure or environmental SEM for nonconductive materials. In our case it was completed with a quantitative analysis of the Xrays spectra of the elements on the surface (EDX). Limitations: it consists on a local analysis of μm resolution and it could be compromised by the non-homogeneity of the material.

f) Energy-Dispersive X-ray analyzer (EDX)

EDX technique was performed coupled to SEM microscopy with the aim of complete the chemical characterisation of the sample. It relies on an interaction of some source of X-ray excitation and the sample surface. This analytical technique is based on the main principle of the spectroscopy: each element has a unique atomic structure. So, once atoms become excited with an X-rays beam, a unique set of electromagnetic emission spectrums are obtained. The incident beam may excite an electron in an inner level, ejecting it while creating an electron hole. Then, an electron from an higher-energy level fills the hole and the energy difference between energy levels may be released in the form of an X-ray (characteristic the atomic structure of the emitting element).

g) Transmission Electron Microscopy (TEM)

It is a microscopy technique in which an image is formed from the interaction of a electrons beam with the sample. Transmission electron microscopes are capable of imaging at a significantly higher resolution than light microscopes. This enables the instrument to capture details a thousand of times smaller than a light microscope. TEM technique is useful to obtain information about the atomic structure, microtexture and the morphology of solid samples. This technique complements the XRD analysis, obtaining more precise information about the crystalline phases and their size.

Soot characterisation techniques a) Raman Spectroscopy

Raman spectroscopy is a local and non-destructive method that allow to study the vibrational modes of a material. In fact, the vibrational energies are not only characteristic of a specific material but also of a crystalline family. This technique will provide information about the soot reactivity. The method consists on focusing a monochromatic light beam on the sample and analysing the intensity of the diffused light. Only the inelastic diffused light is recovered. This energy exchange between the incident light and the diffused light is the be-named Raman effect. This characterisation technique is based on the light study that a material disperses when a monochromatic light beam is irradiated. A light portion is inelastically dispersed (energy gain or loss in reference to the incident light), suffering slight frequency changes that are characteristic of the analysed material and independent on the incident light. Infrarred radiation was produced by a laser wavelength of 532 nm and spectrum range of 0-800 cm -1 .

b) Elemental Analysis

Elemental analysis allow to determine the content of the main organic elements (C, H, N, O, S) in a sample. It is able to detect all the elements and determine their mass percentage. The element separation of the sample occurs by high temperature combustion (950 °C) by the injection of a high dosage of pure O2. Before being introduced on the analyser, the samples were dried to eliminate hydrogen and oxygen from the sample due to humidity. Elemental analyser splits the produced gases in a chromatography column and they are took by a TCD detector. Oxygen percentage is calculated as follows:

O= 100 -(C + H + N + S + ashes) (3)
being O, C, H, N, S and ashes the mass percentages of ashes, oxygen, carbon, nitrogen, sulphur and hydrogen in dry basis.

d) Thermogravimetric Analysis (TGA) Thermal stability of both commercial and real Diesel soot samples were studied on a ATG equipment under the following conditions: dry air, 700 °C, temperature ramp of 5 °C/min and 50 mL/min. TGA is a thermal analysis method in which the mass of a sample is continuously measured while the temperature is changed over time. It is based on the principle that reaction of the sample drives to a mass variation in function of the temperature. This difference will show if endothermic or exothermic reactions happened.

TGA analysis provides information not only about physical phenomena (absorptiondesorption of compounds) but also about chemical phenomena (chemisorption, thermal decomposition; even solid-gas reactions). Typically, the TGA analyser consists of a precision balance with a sample pan located inside a furnace with a programmable control of the temperature. Big variety of atmospheres could be used, including: air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases, etc. As well a variety of pressure conditions: high vacuum, high pressure, constant pressure or controlled pressure. TGA analysis can be interfaced with a mass spectrometer to identify and measure the vapours generated.

CATALYTIC EVALUATION

Two different catalytic systems were used to test each kind of sample (presented on Table 2.1), the mini-SCRF sample was tested on a synthetic gas bench at IFPEN and the powder catalyst samples were tested on a laboratory scale system at IRCELYON. Both catalytic equipment will be described in the following section as well as the operational conditions and method adapted to each one.

Synthetic gas bench available at IFPEN

Mini-SCRF catalyst were tested in the synthetic gas bench presented on Figure 3.7, which is composed by three main areas: feed, reaction and analysis systems. It is composed by three independent ramps used to feeding reactive gases (NO, NO2, NH3, N2, O2 and CO2) or inert N2 purge. This feed could go through the reactor or, contrarily, directly pass to the analysis area (Figure 3.7 presents both paths in blue and green colour, respectively). These ramps allow switching, for example, from inert gas (N2) to feed gas mixture and the path followed by them. This will be made by mean of a series of electrovalves and a data acquisition software called Morphée. Water was injected via liquid peristaltic pump, into a vaporizer and after vaporisation was embroiled by an amount of N2 flow.

b) Reaction system:

System presented on Figures 3.7 and 3.8 was composed by a quartz reactor with stainless steel flanges, linked to an electric oven where sample was placed. Impermeability between sample and reactor was assured by a refractory material (quartz moor). Temperature before and after reactor was measured in the flow gas centre, about 1 mm far of sample surface by mean of two thermocouples placed on the entry and exit of the oven. These thermocouples were connected to a temperature controller and a electric oven. After the reactor, exhaust gas were analysed by analysers: NO, NO2, NH3, N2O, CO2, O2. As aforementioned, three different ramps are used depending on the path and feed gas composition. Both ramp 1 or 2 can be used to feeding system with the pollutants mixture while Ramp 3, named "purge", was usually used for heating or cooling the catalyst. There are two different paths this feed gas could follow: At a first moment, pollutants were sent directly to analysers without passing through catalyst, just to determine the incertitude between the injected and measured amount for each pollutant. Meanwhile, catalyst was being heated using Ramp "purge" by N2 until desired temperature fixed on the oven set point.

On a second step, feed gas mixture was sent through catalyst to observe reactions and pollutant evolution after catalyst.

The third step of IFPEN tests was the NH3-TPD, which was performed using Ramp 2 by feeding just N2 total flow to increase temperature.

Finally, temperature decrease until room temperature was carried out by using Ramp "purge" to inject just N2 and cool the catalyst.

Operational conditions (IFPEN gas bench):

Samples are in mini-SCRF form of impregnated cordierite. Its dimensions are 2.5 cm for diameter and 7.5 cm length making a total cylinder volume of 37 cm 3 .

Total volume flow is 1288 L/h corresponding to a GHSV (Gas Hourly Space Velocity) of 35000 h -1 for the particulate filter described on Table 2.1.

Gas stream composition was fixed as: O2 (10%), NO (200 ppm or 500 ppm), NO2 (200 ppm or 500 ppm), CO2 (9%), H2O (10 %) and N2 as balance.

Data acquisition frequency used for each test was 1 Hz (1 acquisition/second).

Samples were previously stabilized by oxidation treatment.

Operational method (IFPEN gas bench):

There are two kinds of tests:

-Simple mixtures of NOx with NH3 or NOx with O2 -Complete gas mixtures (SCR reaction conditions)

The named "simple gas mixtures" will be studied at first and consist on NO, NO2 and NH3 oxidation reactions. Then, the complexity of the "simple mixtures" will be increased by studying NOx/NH3 mixtures (without any O2 and water present on feed gas) to better determine the pure reactivity between the reductant agent and the NOx pollutants. Here, two different NH3/NOx ratios will be used in order to investigate the potential effect of major NH3 concentration over the catalytic system reactivity. Later, continuing with the increasing complexity strategy, the Standard SCR reaction will be performed followed by NO2-SCR and, finally, by the Fast SCR. In both simple and complete reactions, conversion of main pollutants were evaluated (NOx and NH3) as well as selectivity towards N2 and N2O. Also, the evolution of concentration of each pollutant in function of time and temperature was followed. As Figure 3.9 shows, the initial temperature was settled as 80 ºC for SCR reaction tests (due to presence of water in the feed gas mixture) and as 200 ºC for simple mixture experiments (due to formation of NH4NO3). These temperature values were reached using N2 gas. Then, the feed gas mixture was injected at 200°C and after a stabilisation period of 5 minutes the temperature was increased by a heating ramp of 10 ºC/min until 500 ºC (oven set point). After that, temperature was kept constant during 10 minutes to allow reaction stabilisation. Then, feed gas flow was stopped and switched to N2 passage through catalyst with the aim of rising temperature until 600 ºC (NH3 -TPD), this increase of temperature under inert atmosphere will lead to a catalyst cleaning by desorption of pollutants traces already stocked. Temperature decrease until room temperature conditions was carried out under N2 inert conditions. c) Analysis system: Downstream the reactor, the gas flow was sent to a condenser to remove water from mixture and avoid its entrance to the analysis equipment. The liquid-free flow was separated to being analysed in different analysers. NOx, N2O and CO2 pollutants were measured by an LCD sensor model T32MD by Environnement S.A, NH3 was measure by an UV analyser model EXM40 by Tethys. Referring to N2O, it was measured by an NDIR sensor model NGA 2000 MLT4 by Emerson. CO2 was also measured by a NDIR sensor, model Ultramat by Siemens. Finally, O2 analyser was a paramagnetic equipment, model Oxymat by Siemens. There are two different paths this feed gas could follow: At a first moment, pollutants are sent to analysers without passing through catalyst, just to determine the incertitude between the injected and measured amount for each pollutant. Three or four measures are taken by analysers and verified on the calculations software before go through the next step.

Laboratory scale system available at IRCELYON

Second step is before reactor connexion, feed gas mixture is sent through the vaporisation trap to saturate all gases (avoiding liquid phases arrives to analysers), with exception of NO and NH3 which are following now a difference path that the rest of mixture for a while. Both paths are re-connected using a 3-way valve and once mixed, gas flow is sent to analysis area.

Third step consist on sending feed gas mixture through catalyst (reactor) to observe reactions and pollutant evolution after catalyst. Thus, path used is like this: feed gas starts from flowmeters and then, it pass through water saturator with exception of NO and NH3. As before, both gas stream are again mixed on the 3-way valve and the, sent to reactor and finally, gas flow is separated and each component arrives to it correspondent analyser.

Operational conditions (lab-scale system IRCELYON):

Two different samples are presented in powder form: a commercial obtained from a mini-SCRF section crushed (made of a Cu-exchanged zeolite impregnated on a cordierite support) and a Cu/SAPO-34 zeolite prepared on the laboratory.

Total load of the catalytic system was fixed in 65 mg in order to achieve a minimal height of the catalytic bed of h=3 mm. This 65 mg were distributed as follows: 55 mg cordierite and 10 mg of Cu/SAPO-34 catalyst (mixed). This catalyst/cordierite ratio was chosen to reproduce the commercial mini-SCRF sample characteristics. When soot was introduced on the catalytic system, it was placed as a layer on top of the Cu/SAPO-34 + cordierite mixture. This configuration was chosen as the real life soot is deposited onto the filter walls. In addition, the catalyst:soot ratio was chosen based on some literature and it consisted on a 10:1 ratio. When soot was introduced, the corresponding amount of cordierite was removed.

Total volume flow is 10 L/h corresponding GHSV of 135000 h -1 (in function of reactor dimensions and thickness catalytic bed).

Gas stream composition was fixed as: O2 (8%), NO (1000 ppm), NH3 (1000 ppm), H2O (3 %) and He as vector gas.

Data acquisition frequency used in tests is 1 acquisition/200 seconds.

Between tests, samples were changed on the reactor and substituted by a new powder amount of fresh catalyst. In the case of the commercial powder catalyst, the same test was reproduced with a new catalyst with the aim of compare catalytic behaviour and to determine analyser's measure incertitude between tests.

Operational method (lab-scale system IRCELYON):

Tests carried out at IRCELYON are the be-called complete gas mixture tests under SCR reaction conditions. Two tests were carried out with the commercial powder catalyst following the same method and having the same operational conditions from IFPEN but using each time a new amount of the same powder catalyst. In both of them, conversions of main pollutants were evaluated (NOx and NH3) as well as selectivity towards N2 and N2O. Also, concentration evolution of each pollutant in function of time and temperature were studied.

In this lab-scale catalytic system, the operational method used is described as follows (Figure 3.12): Initial temperature was settled as 200 ºC for Standard SCR reaction tests (due to formation of NH4NO3 caused by NH3 injection at lower temperatures). This temperature values were reached using N2 gas. Then, feed gas mixture was injected, stabilisation for 120 minutes was awaited and temperature increase was started by 2 ºC/min until 500 ºC (oven set point). After that, temperature was kept constant during 30 minutes to allow reaction stabilisation. Then, on the contrary as at IFPEN, feed gas was not stopped here, so feed gas mixture was kept during temperature decrease until 200 ºC (as initial temperature conditions) and analytical measurements continued during this temperature decrease. c) Analysis system: Downstream the reactor, the gas flow was sent to a peltier to remove water from mixture and avoid its entrance to the analysis equipment. The liquid-free flow was first sent to the μGC-NH3 (SRA Instruments, Series RV) in order to trap it in a first step and protect other equipment from corrosive NH3. Then, remaining flow was sent to the μGC (SRA Instruments, model R3000) and O2 and N2 were followed in order to assure that there is no air intro the system and also that N2 was being formed. Finally, flow gas passed through the FTIR analyser (Thermo Scientific, model Nicolet iS50) and NOx (NO, NO2 and N2O) were measured. Also, it is possible to accurately determine NH3 on FTIR equipment if needed.

EVALUATION OF THE COMMERCIAL CATALYST

SUMMARY

This chapter is focused on the catalytic characterization of the commercial mini-SCRF catalyst. Performed tests, feed gas composition and experimental strategy of each test were listed in the Annex A. In addition, the main reactions that may occur in NH3-SCR on a Cuexchanged zeolite and which might be mention during the results discussion were listed in the Annex B.

The aim of this section was to simulate the real Diesel exhaust conditions and to reproduce real SCRF filter technology. First step was to evaluate the catalytic behaviour under Diesel exhaust conditions of the mini-SCRF sample. Any soot was added to the system in this first serie, as it was necessary to evaluate the performance of the catalyst with this new configuration (a DPF cordierite filter coated with a Cu-zeolite). Typical Cu-based SCR catalysts are deposited onto a flow-through filter which is completely different to a Diesel Particulate filter. Also, washcoat amount loaded in the DPF support is not the same that could be reached with a flow-through filter as different loading techniques are used.

The strategy followed during this test serie was to start with the simplest reactions that takes place simultaneously during SCR reactions: the NO and NO2 oxidation reactions as lean conditions are typical of Diesel exhausts. Also, NH3 oxidation was studied as this reaction will be in competence with NOx reduction at high temperatures (> 350 °C, usually). Then, complexity was increased step by step. First, the interactions of NOx pollutants with the NH3 were also studied separately. Finally, complete the three different SCR reactions will be performed. Details about the mini-SCRF catalyst properties, about the IFPEN gas bench system or about the operational conditions used during the IFPEN tests serie are presented on Chapter 3 on the 3.5.1 section.

Finally, two Standard SCR reactions were tested at IRCELYON lab-scale system in order to complete the evaluation of the commercial sample. This tests complements the IFPEN results (more close to real life conditions) as Helium was the gas balance used. This allowed a more deep evaluation of the N2 selectivity and mass balance, kinetics and product selectivities calculations were only possible with the IRCELYON system.

SIMPLE REACTIONS AT IFPEN: NOx and O2, NH3 and O2 mixtures.

As aforementioned, this 4.2 part is dedicated to the study of the NO oxidation-to-NO2 and, the inverse disproportionation of NO2 into NO and O2. This equilibrium will be displaced to one reaction or the other depending on the temperature. This information will be of great value when complex feed gas mixture will be studied. Also, these simple mixtures are useful to study the catalyst redox properties in absence of the reductant agent. It is important to firstly understand this NO-NO2 equilibrium as far as it would be part of the Fast SCR reaction. So, it is necessary to well know this equilibrium without reductant agent presence (NH3) to, later, better identify and distinguish each reaction being produced simultaneously under SCR conditions. In Figure 4.1, feed gas was composed of 500 ppm of NO and (10%) O2. Initial temperature was fixed as room temperature because when NO and O2 are mixed, even if there is no heat, the catalyst activate the NO oxidation O2 yielding NO2 formation (Reaction 20) [1]. There was no evidence of significant NO storage onto the catalyst at room temperature [2]. Later, temperature was increased until 500 ºC. As a consequence, a small desorption peak was registered for all pollutants (around 1500 s). About 200 ºC, the NO oxidation to NO2 became specially important [2,3]. It was observed a 200 ppm decrease on the NO concentration and the formation of proportional amount of NO2. At 500 ºC, the thermodynamic equilibrium was reached and the concentrations became constant. It was also the results obtained by Colombo et al. [2] when a similar Cu-zeolite+cordierite catalyst was evaluated. Maximum NO conversion of 50% was obtained at 400°C (4500 s). Concentration of NO2 produced was consistent with the stoichiometry of Reaction 20. A catalytic test reactive gases were NO2 (500 ppm) and O2 (10 %) was performed in order to study the inverse Reaction 20. Figure 4.2 shows the evolution of NO2 and NO concentration in function of time and temperature. For this test, the initial temperature was also room temperature. It can be seen that at 100 s a 50 ppm NO peak was obtained. At 1000 s, temperature was increased until 500 ºC directly, being observed a NO2 desorption peak at low temperature and then, the concentration returned to the initial value after a while. NO2 concentration was constant until 375 ºC where it started to be decomposed and NO was formed in a proportional amount following Reaction 19 stoichiometry. This is caused by NO2 disproportionation into NO and O2 due to high temperatures, reaching a maximum disproportionation of 55% at 500 °C (4850 s). Colombo et al. [2] also studied the reverse NO-NO2 reaction. They observed that NO2 started to be decomposed around 400 ºC, reaching a maximum conversion of 45% at 550 ºC. Their results confirmed that typical catalytic activity of the Cu-zeolite catalyst was obtained using our mini-SCRF system. It can be concluded that this equilibrium is favoured towards NO oxidation at low temperatures (300 ºC) and towards NO2 disproportionation at higher temperatures (400ºC) [4]. Confirming that NO and NO2 equilibrium (Reaction 20) is strongly influenced by temperature.

NO oxidation. NO/O2 (10%) (Annex A. Test 6)

NO2 decomposition. NO2/O2 (10%) (Annex A. Test 8)

NH3 oxidation. NH3/O2 (10%) (Annex A. Test 11)

This has the aim of study the NH3 oxidation catalyst capacity at high temperatures. Reactions 18 and 19 (Annex B) might happen during this test. The information obtained in this test would be of great help when complete SCR reactions will be discussed, in the way that this kind of reaction will be more easily identified and not confused with a common SCR reaction as they happened simultaneously in a competitive way. This test was started at room temperature with a feed gas composed by NH3 (500 ppm) and O2 (10%) excess. It can be observed on Figure 4.3, during a small period of time (200 s) NH3 was being absorbed into the catalyst surface. Then, NH3 concentration started to be measured. Stability at room temperature was only reached after 1800 s. Then, temperature was increased until 500 ºC. Immediate desorption of NH3 from the catalyst surface was observed. At 325 ºC (4200 s), NH3 started to be converted until it was fully consumed at 500 ºC (5500 s).

Referring to NO, just 20-30 ppm were formed after 325 °C (5000-6800s). Anyways it is not an amount enough to consider Reaction 20 of main mechanism of the NH3 oxidation. No NO2 or N2O were formed so it is supposed that N2 is the main product obtained from the consumption of NH3 (Reaction 18). Similar results were obtained by Colombo et al. [2,4] who realized a NH3 oxidation test over a Cu-zeolite as catalyst and cordierite (400 cpsi) as support. They used a feed gas composed by 500 ppm of NH3, O2 (2%) and H2O (3%) and He as balance. They also found that NH3 was converted after 300 ºC mainly into N2 and water.

SIMPLE REACTIONS AT IFPEN: NOx and NH3

This part is dedicated to the study of NO and NO2 interactions with NH3 in function of temperature. Specific conditions of these tests are detailed on the Annex A (Tests 2 and 3).

No water, no O2 and no CO2 were introduced on the feed gas for these tests. This kind of tests were carried out with the aim of studying the behaviour of catalyst just in presence the reductant agent (NH3) and each NOx pollutant separately. Also, different NH3/NOx ratios were studied to evaluate the NH3 influence over the catalyst performance. Since insignificant NOx or NH3 consumption was observed in O2 absence, only tests with the NH3/NO mixture are going to be discussed in order to avoid repetitive information.

NH3/NO: ratio 1 and 1,2 (Annex A. Tests 2 and 3)

The feed gas composition in Tests 2 and 3 is detailed on Table 4.3: When stabilisation, the temperature was raised until 200 ºC and only when reached, the NH3 was injected. After the stabilization of both pollutants, the temperature was increased again at 500 ºC. Because of that, a NH3 desorption peak was registered until 400 ºC (5000-6000 s) on both tests. A slightly NO consumption was obtained at 500ºC but soon both pollutants became constant again. Then, only for Test 2, it was a small NH3 desorption peak at 600 ºC during NH3-TPD conditions (about 7000 s) as can be observed on Referring to NOx, conversions followed the same tendency but in the case of the NH3/NOx ratio=1.2, it started after 350 ºC whereas for the NH3/NOx ratio=1 test conversion started after 200 ºC. However, the NOx conversion value of Test 2 was twice than for Test 3 where only 10% conversion was achieved. In the case of ratio=1.2, NH3 conversion started only after 480 ºC. In comparison ratio=1 started to be converted around 400 °C. However, maximal NH3 conversion were similar around 10% in both cases. Both pollutants conversions were very low, being the highest one 20 % (for NO at 500 ºC).

On literature [5] it was found a possible mechanism that explains the low conversions observed in this experiment. It is based on redox active sites mechanism involving Cu + / Cu 2+ species: O2 extra-network in metallic complexes reacted with NO to form intermediate species type Cu 2+ -NxOy. Later, they reacted with NH3 forming N2 and water, as well as producing parallel exchanged metals reduction Cu 2+ → Cu + . After that metal should be reoxidized by the O2 present on the exhaust line to come back to the Cu 2+ form. However, in our test, it seemed that the last regeneration step was not achieved, as there was no O2 present in the feed stream. Because of that, such a poor catalytic activity was obtained. As a conclusion, it can be said that in O2 absence conditions, no SCR reaction could take place in an effective way.

COMPLEX MIXTURES. SCR REACTIONS AT IFPEN

As it is presented on Tables 4.4, 4.5 and 4.6, the three different SCR reactions were studied for two different concentrations: 200 ppm and 500 ppm, for both NOx and NH3. The aim was studying the influence of different amounts of pollutants over the catalytic behaviour of the commercial system. However, same reactions and tendencies were observed at same temperature values for both concentrations. Any secondary reactions were observed in variation of the pollutants concentration neither. Therefore, in the present report only tests performed at 200 ppm will be discussed in order to avoid repetitive information and make more dynamic the lecture. However, all tests performed (both at 200 and 500 ppm) are listed on Annex A. Initial temperature was fixed as 200 ºC due to NH3 presence on the feed gas which can form undesired N2O by reacting with NO by Reaction 14 (Annex B). In this test, complete feed gas was injected from the start, including 200 ppm of NO and NH3, O2 (10%), H2O (10%) and CO2 (9%). 200 °C temperature was kept constant about 10 min to assure the feed stabilisation.

Standard SCR reactions (Annex

It can be seen in Figure 4.7 that NOx after its injection started to drastically decrease until a constant value of 50 ppm was reached (2000 s). In addition, the aforementioned NH3 "dead time" was also observed in Standard SCR reaction. NH3 only started to be registered when catalyst surface was saturated. Also, it is remarkable that from 200 ppm of NH3 injected, only 30 ppm were measured. This behaviour apparently remarked that an important NOx and NH3 adsorption phenomenon was taking place onto the catalyst surface at the beginning of the test. This was confirmed as a high conversion was observed at this temperature region. When increasing temperature to 500 °C, the NOx concentration suffered a big drop during the temperature ramp and when 500 °C value was reached, NO concentration became stable at 110 ppm. Regarding NH3, it reacted with the absorbed NO since the moment it was injected. Later, when temperature was increased, a NH3 desorption pic took place (220-300 s). Due to it, the NO was reduced (Standard SCR reaction, Reaction 7) between 200-350 ºC, reaching a maximum value of 90% of conversion. Similar NOx conversion value at the same temperature region was obtained by Ballinger et al. [7] using a Cu-zeolite SCR catalyst coated on a high porosity cordierite (300 cpsi). Youngren et al. [8] obtained 90% of NOx conversion at 475 ºC with a Cu-zeolite SCRF catalyst on an engine bench.

NH3 oxidation started at 400 ºC [9][10][11] and at 450 °C the NH3 was fully consumed whereas NO concentration increased (90 ppm). This NO concentration increase was due to there was no NH3 available to reduce it anymore [12]. This effect was also reported by Mihai [13] and other authors [2,14,15] who tested Cu-zeolite SCRF catalysts. This might explain the NO increase as Reaction 19 might be taken place. But also, this NO might be formed due to the It can be seen on Figure 4.9 how Test 1 (stabilisation of the mini-SCRF sample under Standard conditions) presented a very good NOx conversion while in Test 13 (Standard at 200 ppm) barely reached the 50%. Standard SCR at 500 ppm was performed in the 7 th place of the serie and it already showed activity degradation on the low temperature region, however, it was not as strong as in the Test 13.

NO2-SCR reactions (Annex A: Tests 10 and 12)

This other kind of SCR reaction is considered the less active one in terms of NOx reduction and conversion and slower. Again, tests using 200 and 500 ppm of NO2 and NH3 were performed to confirm literature tendencies. However, only 200 ppm tests will be discussed to avoid repetitive information. Reactions ( 9) and ( 10) are waited to be observed under NO2, NH3 and O2 excess conditions. Table 4.5 summarises the feed gas mixtures used for simulate NO2 SCR reaction on Tests 10 and 12. This NO2-SCR test was carried out by using 200 ppm of NO2 and the same amount of NH3 in presence of O2 (10%), H2O (10%) and CO2 (9%). As usual for all SCR reactions, the initial temperature was fixed at 80 ºC (due to water presence) and NH3 was only injected at 200 ºC.

As it is showed on Figure 4.10, the NO2 remained at a constant value of 210 ppm until temperature was increased to 200 ºC. When this temperature was reached, the NH3 was injected (2800 s) and, as a consequence, the NO2 concentration dropped to 120 ppm. When both pollutant concentrations became stable, the temperature was again increased until 500 ºC. Due to this, desorption peaks of NH3 and NO2 were observed (500-6750 s) between 200-300 ºC as it can be seen on Figure 4.10. This might mean that different active sites were used to adsorb each pollutant over catalyst surface. Desorbed NO2 and NH3 reacted yielding an undesired and non-complete NO2-SCR reaction (between 300-425 ºC). Significant formation of N2O was observed between 200-400 ºC. A maximum of 50 ppm of N2O (by-product) was obtained at 275 ºC [9] (5100-7000 s). Its formation could be justified considering that the thermal decomposition of the ammonium nitrate (NH4NO3) gives N2O as a product, thus according to the Reaction 13 (Annex B) [2,9]. This non-complete NO2-SCR reaction would explain the low value of NO2 conversion obtained, being a maximum of 60% at 350 °C. As usual, the NH3 was fully consumed <400 ºC [9,10] and due to this, the NO2 concentration rised a little bit simultaneously. Full NH3 oxidation formed about 70 ppm of NO (6000-7000 s) between 250-500 ºC. This NO formation at high temperature might be explained by the NH3 oxidation (Reaction 19) or by the NO2 disproportion reaction at high temperatures (Reaction 20). As NO formation became constant at 500 °C where also NO2 it seem that main source of the NO is the NO2 decomposition [2,9]. It is necessary to remark that the non-discussed NH3/NO2 tests (Tests 4 and 5), presented the same partial NO2 reduction yielding N2O. Apparently, it can be concluded that the NO2 presence in our reacting system produced a non-selective behaviour of the catalyst. However, it must to be said that, for both NO2-SCR tests (12 and 13), the N2O peak was obtained at higher temperature and it was smaller.

Fast SCR (Annex A: Tests 14 and 15; Annex B: Reaction 8)

Fast SCR reactions (Reaction 8) are considered the most active of the three different SCR reactions. This is because of an optimised amount of NO and NO2 (NO/NOx ratio= 0,5) is present on the feed gas which increase the catalytic activity [6]. In this section, Fast SCR experiments were performed to confirm literature by using feed gas mixtures presented on Table 4.6.

(8) 2 NH3 + NO + NO2 → 2 N2 + 3 H2O Equimolecular amounts of NO and NO2 reacted with NH3 following the Fast SCR (Reaction 9) between 200-350 °C as it can be observed on Figure 4.11. Above 350 ºC, when the NH3 started to be consumed [9,10], a formation of NO it was observed [13][14][15]. Meanwhile, NO2 continued being consumed. As far as NO2 concentration dropped at the same time, a more feasible explanation for NO formation might be the NO2 disproportionation (Reaction 20). It is remarkable that under Fast SCR conditions any N2O formation was observed. This means that the commercial mini-SCRF catalyst only produced the non-complete SCR reaction when excess of NO2 was fed. However, even Fast SCR reaction was found to be successfully performed, the actual NOx and NH3 conversions achieved were quite low (<50%). Especially, if it is taken into account that Fast SCR is the faster and more active SCR reaction [1,2,16]. In addition was remarked that Test 15 which was the Fast SCR using 500 ppm of feed gas, conversion were even lower (30%). Here, the hypothesis of catalysts deactivation became stronger and more probable.

NOx and NH3 CONVERSIONS COMPARISON OF ALL SCR REACTION TESTS at IFPEN

Due to the previous remarks during the SCR reactions serie, on Figure 4.12 are presented the NOx conversion of all SCR tests. Test numbers were indicated with the aim of demonstrate that this deactivation was a progressive. In Figure 4.12, the NOx conversion values for all SCR reactions were presented and compared in function of temperature. As aforementioned, in the literature the Fast SCR reaction is considered to be the most active SCR reaction in terms of NOx conversion [1,2,16]. Various authors confirmed with their investigations with Cu-SCRF catalysts that the Fast SCR reaction obtained the highest NOx conversion value (> 90%) at temperatures around 400 ºC [2,8]. Also, that NO2-SCR reaction was the slowest one and the less active (70-80% of NOx conversion) [2,8]. Finally, authors also agreed that the detrimental effect of the NO/NOx ratio was less severe in the case of the Standard SCR reaction as NOx conversions near to 90% were reached [2,8,11]. However, in our case this main tendency could not be observed. In fact, the Standard SCR reactions performed with our commercial mini-SCRF sample were found to be the less performing ones, just obtaining a maximum of 30-45% of NOx conversion. This seemed to be caused by a deactivation phenomenon continuously produced along the test serie. As already discussed on Figure 4.9, a decrease on the catalyst activity was especially noticeable regarding the three different Standard SCR tests realized.

NOx conversion comparison

An evident decreasing tendency of the activity on Tests 1, 7 and 13 can be observed on Figure 4.12. Standard SCR reaction performed to stabilise the catalyst sample (Test 1) reached the highest NOx conversion value (90%) of all SCR reactions. However, the other Standard SCR reactions performed (Tests 7 and 13) showed already lower conversions in comparison. This degradation effect might explain why the Fast SCR reaction at 200 ppm not even reached 50% of NOx conversion and at 500 ppm barely 30%, as they were the last tests realized. As a consequence, the comparison of the NOx conversion values obtained for all SCR reactions is not accurate and impossible to be made. However, it can be said that maximum peaks for all SCR reactions were obtained between 300-350 ºC with exception of stabilisation test which was obtained between 275-300 ºC. These maximum NOx conversion values are linked to the different NOx reduction reactions taking place at that temperature window. For all of them, once reaction takes place and the NH3 was fully consumed, the NOx conversions dropped above 400 ºC [12,13,15]. Here, the NH3 oxidation at high temperatures played a role producing a competition between oxidation and reduction reactions for all reactions performed.

NH3 conversions and N2O selectivity comparison

Almost all SCR tests reached 100% of NH3 conversion at 400 ºC, with exception of both Fast SCR tests (Tests 14 and 15) and Standard SCR at 200 ppm (Test 13) which were the latest tests performed. In these three tests, the NH3 was continuously consumed until 500 ºC and the maximum values reached were much lower than 100%. That may indicates that, in these tests, there was no competition between the SCR reactions and the NH3 oxidation, allowing the NH3 being more continuously consumed. This might mean that the catalyst was very deactivated and any selective NOx reduction was taking place. This match with the NOx conversions presented on Figure 4.12 and also results summarized on Table 4.7 seems to confirm it. As aforementioned, this phenomenon was specially remarked on Standard SCR tests, even if the feed conditions were the same. This could be caused because stabilisation test (Test 1) was performed at the beginning of the series, the 500 ppm Standard SCR (Test 7) in the middle and 200 ppm Standard test at the end (Test 13). That verifies the aging effect produced over the catalyst which affects its performance and activity especially on the latest tests. On the NO2-SCR tests, similar NOx and NH3 conversions values were obtained at same temperature rates on both tests (Tests 10 and 12). However, activity degradation was already observed in comparison to Test 7. Finally, the Fast SCR reactions were the less performing in terms of NOx and NH3 conversion as they were the latest tests performed. This seems to confirm the catalyst deactivation hypothesis. Separately, as already mentioned on Figure 4.10 (NO2-SCR reaction), the be-named "NO2based reactions" (both simple NH3/NO2 and complex NO2-SCR) produced an incomplete NO2 reduction yielding N2O formation. It is important to precise that N2O was only obtained when significant amount of NO2 was injected on the feed gas. This is confirmed on the Table 4.7 where also the Fast and the Standard SCR reactions are present but only a negligible N2O selectivity (barely 3% in the Test 14) was produced [3]. For simple the NH3/NO2 tests, the N2O peaks were obtained around 275 ºC whereas for the complex NO2-SCR reaction it was obtained around 300 °C. This match literature data as Colombo et al. [4] obtained the N2O peaks around 300 °C. It is remarkable that the N2O peak obtained for the NO2-SCR was lower (10%) than in simple tests (Tests 4 and 5) where 20% was reached. This might mean that the presence of O2 on complex reactions helped to avoid the undesired formation of N2O. Also, the selectivity towards N2 was increased in O2 presence, thus it can be concluded that lean conditions typical of Diesel exhausts are more favourable to NOx selective reduction [2]. In reference to NOx and NH3 conversions, values obtained were identical for both simple NH3/NO2 reactions (Tests 3 and 4), confirming again that NH3/NO2 ratio (higher amount of reductant agent) did not improved the Cu catalyst behaviour.

CATALYST DEACTIVATION EVIDENCE AT IFPEN

Deactivated mini-SCRF sample evaluation

At this pointm the same stabilisation Standard SCR (200 ppm) test (Test 1) was performed with the deactivated mini-SCRF sample in order to confirm the catalyst deactivation detected on previous tests. Stabilisation test (Test 1) was chosen as the strategic one to reproduce for two reasons: it was the first to be carried out during IFPEN tests serie and also, it was a quick test as far as it started directly at 200 ºC with all pollutants injected from the beginning. This test was repeated two times on the deactivated sample to determine if deactivation was already complete or if degradation continued with tests. It can be clearly seen that Tests 21 and 22 barely produced 40% of NOx conversion whereas a 90% was obtained with the fresh sample. It can be concluded that, effectively, a deactivation phenomenon had happened after all test serie performed over the commercial mini-SCRF sample used as reference catalyst.

Hydrothermal aging evaluation

To try to clarify the origin of this catalyst deactivation, two new and fresh mini-SCRF samples with exact characteristics of the reference one (be-named sample 1-004) were artificially aged. These new samples are obtained from same original monolith that reference sample used on the test serie. Sample named 5-004 was hydrothermally aged in an oven for 4h at 600 ºC with 10% of humidity. Sample 6-004 was also hydrothermally aged in an oven for 4h and 10% of humidity but at 700 ºC. Once aged, these samples were tested under the same Stabilisation Standard SCR (200 ppm) test (Test 1 conditions) which was performed on the reference catalyst (1-004) at the beginning and at the end of the tests series. In As it can be observed on Figure 4.15, similar profiles were obtained for the fresh reference sample (1-004) and both aged samples (5-004 and 6-004). Similar NOx conversion values (a maximum around 90 % in all of them) and curves tendency were observed on the same temperature region. Even, aged sample 5-004 showed better NOx conversion at low temperatures (200-275 ºC) than the fresh 1-004 sample. Above 300 ºC, the fresh sample 1-004 presented slightly better conversion than the aged ones. However, this small difference might not related to the aged state of samples 5-004 and 6-004. These new samples were obtained from same monolith as the reference sample 1-004, however, it might be possible that different washcoat loadings were present in the samples depending of its location on the main monolith. Thus, slight differences on the catalyst behaviour are expected to be observed which might explain the observations made on Figure 4.15.

In any case, similar deNOx activity and tendency was obtained in these three different samples. Apparently, the hydrothermal aging treatment did not affect the catalytic activity of mini-SCRF samples, so this phenomenon seem not to be the responsible of the deactivation of the sample 1-004.

Because of this, it was decided to perform several cycles of the Stabilisation Standard SCR reaction on one of the aged samples (5-004). The aim was to determine if the Standard SCR conditions were enough to deactivate the sample and also, to verify the exact moment when the catalyst deactivation started. However, this kind of commercial catalysts based on metal-exchanged zeolites is supposed to have high hydrothermal stability and to be able of resist higher temperatures during the soot regeneration periods (700-800 ºC) [7]. In fact, Colombo et al. [2] realized additional experiments of the Standard SCR reaction varying the water content (3-10%). They found that only a negligible effect of the water on the SCR activity was produced. Also, seven tests are not a considered a prolonged period as these commercial catalysts will be applied on Diesel vehicles engines.

Unfortunately, the mechanism and causes of this deactivation could not be further investigated as these commercial samples were subject to a confidentiality agreement with the supplier company.

STANDARD SCR TESTS AT IRCELYON

A serie of Standard SCR tests over the commercial sample was realized at IRCELYON laboratory scale system. This test serie was complementary to IFPEN tests and allowed to complete the study of the commercial catalyst behaviour. In the case of the IFPEN, N2 was used as carrier gas allowing the test conditions to be closer to real life, higher gas flow and obtaining a macroscopic analysis of the SCR reactions. On the other hand, at the IRCELYON system, Helium was used as balance which is very expensive and limits the gas flow as a consequence. Using He as gas balance is interesting as it allows a more deep evaluation of the N2 selectivity of the commercial catalyst because it was not present on the feed gas. For the first time; mass balance, kinetics and product selectivities calculations would be possible with the IRCELYON system. However, to take advantage of the IRCELYON system, the mini-SCRF sample it was necessary to be adapted. It was crushed to obtain a powder catalyst composed of the Cuzeolite washcoat and the cordierite support. An important operational modification at IRCELYON was that the powder catalyst was replaced for a new one on each test while at IFPEN the same mini-SCRF sample was kept for the hole tests serie. Same Standard SCR test, feed gas composition and operational conditions (described on 3.5.2 section) were used for each new catalyst batch in order to determine the test reproducibility and the homogeneity of the samples used. Referring to operational conditions at IRCELYON, they were the most loyally adapted as possible to IFPEN conditions. Operational method was simplified in comparison to IFPEN methodology: initial temperature was fixed at 200 ºC and all reactive gases were injected at the same time. After 2 hours of stabilisation, temperature was raised to 500 ºC using a 5ºC/min ramp and then, a plateau of 30 min was performed. Then, temperature was decrease to the initial value. Also, feed gas composition gas adapted to IRCELYON gas bench requirements: 1000 ppm of NO and NH3 were injected, also O2 (8%) and H2O (3 %) making a total volume flow= 10 L/h. It is remarkable that 100 ppm of difference was produced during tests. As it can be observed on Figure 4.17, between 300-400 ºC, effective and selective NOx reduction happened as N2 started to being formed and almost 1000 ppm were produced at 500 ºC. Any undesired products were formed in significant amounts, so it can be concluded that effective Standard SCR reaction took place on both tests. In reference to NH3, after 250-300 ºC it started to be converted [2] and at 400 ºC it was completely consumed. Again, the NH3 oxidation was taking place consuming the reductant agent and impeding the correct development of the Standard reaction [13][14][15]. It can be seen on Figure 4.17, both possible NH3 oxidation reactions were happening simultaneously (Reactions 18 and 19) as both NO and N2 concentrations became constant at that temperature region. Then, temperature was decreased again until 200 ºC but using a slower ramp (1 ºC/min) and concentrations came back to stability. However, the reached concentration values were 100 ppm lower if compared to the initial 200 ºC plateau. It is remarkable that during the cooling ramp, a small peak of the NO, N2 and NH3 concentrations was observed between 350 and 250°C. Then, concentrations reached stability at 200 ºC. Figure 4.17 is revealing in the way that measure incertitude from analysers was evidenced. It can be seen that the measure incertitude was lower when the temperature was constant due to the pollutant concentrations and the reaction mechanism were stabilized. However, during temperature increase, it can be noticed that the distance between concentrations on both tests becomes bigger because the non-stable conditions. In addition, the N2 measure was even more influenced by the temperature increase because of its difficulty of measure when the SCR reactions are taking place where the concentrations were constantly changing. To sum up, reasons why both tests were not perfectly overlapped may be: 1) Different Cu-zeolite amounts, which means heterogeneous distribution of washcoat on each sample; 2) Effect of the analyser measure incertitude; and 3) N2 in small amount could be at the analyser detection limit. As aforementioned, the difference between both tests concentrations was more obvious when the reactions were taking place so, it can be concluded that this difference is linked to active phase amount. Again, the increase and decrease data followed same tendencies at temperatures higher than 300ºC. Measure incertitude between both IRCELYON tests can be remarked as well as in the previous one (Figure 4.18), giving about a 10% of incertitude.

First and second Standard SCR (1000 ppm) comparison (Annex A: Test 16 and 17)

Cyclic tests under Standard SCR (1000 ppm). (Annex A.Test 18, 19 and 20)

As a deactivation tendency was observed with the IFPEN catalyst, it was decided to verify the powder catalyst stability at the IRCELYON system under Standard SCR reactions. Followed strategy consisted on performing between 200-500 ºC three identical cycles (same as Test 16 and 17), that means, without changing the catalyst sample between tests. A temperature of 200 ºC was kept constant between cycles during 60 minutes to assure a stable starting point to the next cycle. It can be observed in Figure 4.20 that the powder catalyst showed good stability as the cycles showed good reproducibility. Similar NO and NH3 conversions were obtained for the three cycles in complete the temperature range. For all cycles, the NH3 conversion reached a 100% value at 450 ºC whereas the NO conversions barely 70% of conversion. This low conversion value might be due to the competition of the NH3 oxidation at that temperature window (Reactions 18 and 19). Powder sample did not suffer any deactivation after three cycles performed. These results showed that the deactivation phenomena observed on the commercial mini-SCRF sample (1-004) after a serie of 15 tests could not be explained by a simple mechanism.

CONCLUSIONS

This chapter presents the advancement of the thesis during its first 14 months which main objective was to evaluate the SCR performance of a commercial Cu-based mini-SCRF catalyst. Based on the literature knowledge of this reference catalyst, catalytic tests were performed on temperature window between 200-500 ºC. In order to well understand the SCR reactions, the be-named "simple reactions" were studied one by one and the, they were increasingly complicated. First, the simple NH3 and NOx oxidations were studied, the main conclusions obtained from them were:

NO/NO2 equilibrium (Reaction 20) is strongly influenced by the temperature. At temperature region below 250°C, the NO oxidation to NO2 is promoted; whereas, at temperatures above 350 °C, the inverse NO2 decomposition reaction happened.

NH3 oxidation reaction only took place after 350 ºC and lead the complete conversion of NH3 around 400 ºC.

Then, gas mixtures consisted on each NOx pollutant only mixed with the reductant agent (O2 absence). Main conclusions obtained were:

NH3/NOx tests demonstrated that in the absence of O2 excess, any NOx reduction happened, as the redox mechanism of the active sites was not completed. In these tests, barely a 20% of NOx conversion and 10% of NH3 conversion were obtained.

Different NH3/NOx ratios did not affected the catalyst reactivity as same reactions and tendencies were obtained for both ratios 1 and 1.2.

Finally, the three different SCR reactions, which are considered "complex mixtures", were studied. Here, O2 excess (10%), CO2 (9%) and H2O (10%), in addition to the NOx and NH3, were included on the feed gas composition in order to simulate real Diesel exhaust conditions. First, the Standard SCR was developed, then the NO2-SCR and, finally, the Fast SCR which is the most complex one. The most important conclusions obtained from the SCR reactions were:

All kinds of SCR reactions showed at high temperatures (> 350 °C) competition with the NH3 oxidation. NH3 was fully consumed around 400 ºC and was not available anymore to reduce NOx, as a consequence the NOx conversion decreased above 350 ºC.

NO2-based reactions performed a partial or non-complete reduction of NO2 yielding undesired N2O formation around 300 °C. General tendency indicated that no adsorbed compounds remained on the catalyst surface. This was confirmed by the N2-TPD (600 °C) step performed at the end of each test.

Nevertheless, the main conclusion that can be made is that from Test 1 to 15 a significant deactivation of the reference mini-SCRF catalyst (sample 1-004) happened. This could be noticed especially along the Standard SCR reactions where the NOx conversion decreased with each test developed. This was the reason why both Fast SCR reactions showed very low NOx conversion (barely 50%). Deactivation of the sample 1-004 was confirmed by repeating two "runs" of the Test 1 (used to stabilise the fresh sample at the beginning of the serie). Only about 30% of NOx conversion was obtained with these two "runs" that confirmed the sample deactivation if compared with the 95% of NOx conversion obtained with the fresh sample on Test 1.

To try to clarify the origin of this catalyst deactivation, two new fresh mini-SCRF samples were artificially aged. Sample named 5-004 was hydrothermally aged in an oven for 4h at 600 ºC with 10% of humidity. Sample 6-004 was also hydrothermally aged only varying the temperature at 700 ºC. Once aged, these samples were tested at Test 1 conditions to compare activity with fresh sample 1-004. Similar NOx conversion curves and tendencies were obtained. Apparently, the hydrothermal aging treatment did not affect the catalytic activity of the mini-SCRF samples; thus, this phenomenon might not be the responsible of the deactivation of the sample 1-004. Finally, it was decided to test one of this aged samples under Test 1 conditions in repetitive and continuous cycles. Results showed a certain degradation of the deNOx activity on the low temperature region (200-300 ºC) after the 6 th cycle. Apparently, the degradation of the catalytic activity was related with the resistance of the material to the strong and continuous oxidation/reductions conditions; or to the high hydrothermal conditions (10% of H2O) suffered during the tests. These conditions might have debilitated the zeolite framework, also evolution and migration of the Copper species might have occurred.

Apart from that, two Standard SCR tests were performed at IRCELYON using the commercial sample in powder form. The aim was to complete the study of the commercial sample as the IRCELYON lab-scale system uses He as balance. This allowed to calculate the N2 selectivity and to better understand the competitive reactions that happen simultaneously. The main conclusions obtained from IRCELYON powder tests were:

Certain incertitude was observed on the measure and due to this, both tests were not perfectly overlapped (possibly due to heterogeneous distribution of Cu-zeolite for each sample).

Catalyst behaviour during temperature increase and decrease was not the same at low temperature region (200-300°C). A possible explanation might be that the NOx reduction happened at that temperature window. However, at high temperatures (400-500 ºC) tendency is more favourable towards the NH3 oxidation and the NO-NO2 equilibrium.

Cyclic tests performed at IRCELYON did not showed any significant deactivation.

Once the commercial catalyst was evaluated on both catalytic systems the main conclusion was, on one hand, that the commercial mini-SCRF catalyst was confirmed to be deactivated.

Reasons and the origin of this deactivation stayed unclear as the commercial catalyst was requested to be returned at the supplier company. On the other hand, IRCELYON system allowed to realize Standard SCR reactions using the catalyst in powder form with good results. For this reason, a reorientation of the PhD subject was necessary to be made in order to be able of continuing the investigation. At this point, it was proposed to synthesize at the IRCELYON laboratory a home-made Cu-Chabazite zeolite with properties as similar as possible to the commercial catalyst (Cu loading (%), zeolite framework…) and then mix it with a commercial cordierite support to emulate real SCRF catalysts. The aim was take advantage that the IRCELYON system was adapted to powder catalysts and test this new synthesized catalyst in there. Appart from that, the main objectives of the thesis remained the same: the study of the interactions NOx, NH3 and soot, the competitions between reduction and oxidation reactions, availability of NO2 for passive soot oxidation… Thus, next chapter of the thesis will be focused on the synthesis, characterisation and catalytic evaluation of this new synthesized Cu-chabazite zeolite.

PHYSICOCHEMICAL CHARACTERIZATION OF THE SYNTHESIZED CATALYST

SUMMARY

This chapter is focused on the physicochemical characterization of the in-laboratory prepared Cu/SAPO-34 catalyst by hydrothermal method and Cu impregnation inspired and adapted from the literature [1,2]. Textural and physicochemical characterization techniques were realized: XRD analysis was used to determine that the SAPO-34 zeolite framework was effectively achieved and also to verify the crystallinity of the sample, ICP-OES technique was used to determine the chemical composition and to confirm that 2,5% wt of Cu was introduced by impregnation method on the SAPO-34 framework, BET and N2 isotherms allowed to determine the zeolite surface area and the pore size distribution. XPS analysis allowed identifying the nature of the Cu species present on the SAPO-34 surface. Finally, the morphology was observed by SEM and the chemical composition on the catalyst surface was studied by EDX.

More details about the synthesis method of the SAPO-34 zeolite and the Cu impregnation method, the analysis equipment and the measure conditions used for each characterisation technique were described on Chapter 3. On Figure 5.1, spectra of the calcined and stabilized non-impregnated SAPO-34 zeolite (red) and the spectra of the impregnated Cu/SAPO-34 zeolite (blue). It can be observed that any new peaks were observed on the Cu/SAPO-34 sample in comparison to the H-SAPO-34. This indicated that crystalline structure of the H-SAPO-34 after the copper introduction by impregnation was essentially unchanged [3,4]. In both cases, the obtained spectra were referenced to the databased typical peaks of the SAPO-34 zeolite (9.6, 13.0, 20.83 and 31.0°). This indicated that, effectively, the in-lab synthesized sample consisted on a pure phase of H-SAPO-34 zeolite [5,6].

X-RAY DIFFRACTION (XRD)

However, the intensity of the peaks of the Cu/SAPO-34 (red) was higher due to the effect of the Copper presence on the sample. The peaks of this material showed high intensities as the zeolites are known for being a very crystalline network. It was known that the crystallinity is related to the acidity of the zeolites, which was related to their NH3-SCR and NH3 oxidation activity.

On Figure 5.2, a more detailed X-Ray spectra of the impregnated Cu/SAPO-34 catalyst is presented. As it can be observed Figure 5.2, on the impregnated Cu/SAPO-34 catalyst, any peaks related to Cu metal were observed. This might be explained by the metal/zeolite ratio used in this synthesized zeolite. It was chosen to emulate the metal/zeolite ratio of the commercial mini-SCRF catalyst previously discussed and, obviously, the zeolite amount is higher than the impregnated metal (even if 2,5% wt of Cu is a quite big loading). The main reason is that too much metal loading would produce the formation of undesired and inactive Cu species (such as CuO) on the zeolite surface. Referring to this, no crystal phases related to the copper oxides (35,58 and 38,8°) were detected [7-10] on Figure 5.1 (blue spectra). This suggested that Cu species were successfully introduced and dispersed [5, 11-13], likely as isolated ions at the exchange sites in the SAPO-34 framework [8]. Another possibility was that the CuO phase was not in enough amounts or big to be detected on the XRD spectra [14]. Anyways, these CuO species are highly undesired as they are considered to catalyse the NH3 oxidation reaction and even generate NOx [8,10,15] This would affect the deNOx activity as there was not enough NH3 to oxidize the NOx.

On the Table 5.1 is summarized the main information about the location of the SAPO-34 peaks and the orientation of the crystals of both catalysts. Intensity values of each peak are presented on both on the Figure 5.1 and the Table 5.1.

INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION SPECTROSCOPY (ICP-OES)

The chemical compositions and the elements (Si, Al, P and Cu) distribution of the synthesized Cu/SAPO-34 catalyst were determined by ICP-OES. The element content results are summarized in Table 5.2. Element Synthesized H-SAPO-34 [10] H-SAPO-34 Synthesized Cu/SAPO-34 [7] were selected by taking into account the impregnation method to introduce the Cu in the SAPO-34 structure (in the case of the H-SAPO-34 a commercial zeolite was used). Gao et al. [11] impregnated the zeolite support with a Cu aqueous solution.

Referring to the H-SAPO-34 zeolite, it can be said that similar element contents and similar Si/Al and P/Al ratios were obtained between our synthesized H-SAPO-34 and the commercial one evaluated by Wang et al. [10]. Even a small difference was remarked regarding the Al and the Si contents, it was found to be negligible. In the case of the impregnated Cu/SAPO-34 comparison, also similar Si/Al and P/Al ratios were observed between our synthesized zeolite and the Cu/SAPO-34 zeolite studied by Cao et al [5]. However, in this case higher differences were obtained with reference to the Al content. As it can be seen on Table 5.3, the Al percentage on our synthesize zeolite was considerably higher than on the literature reference. P contents were also slightly different and it compensated the ratios values. These differences might be due to the reactive products and operational conditions used for the zeolites synthesis. But, in general, it can be concluded that our synthesized SAPO-34 zeolite achieved logical and good content of each element. This confirmed the XRD conclusion that SAPO-34 zeolite was successfully synthesized but also impregnated, as 2,5% wt of Cu was obtained on ICP-OES analysis (theoretical loading was 2,5% wt).

Talking about the content variations between the non-impregnated and the Cu/SAPO-34 zeolites, both in the experimental and the literature results, was remarked that the P content was higher (around 19%) in the H-SAPO-34 zeolites than one Cu was introduced (around 17-18%). This produced that P/Al ratios were also higher for the non-impregnated zeolites being 1 in comparison to the 0,80 of the Cu/SAPO-34.

To better understand the chemical composition of the in-laboratory synthesized catalyst, further discussion will be done with the EDX results.

SCANNING ELECTRON MICROSCOPY (SEM) + ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDX)

SEM technique will allow to observe the morphology and the distribution of the zeolite crystals as well as to determine the crystal size of the sample. From now on, only Cu/SAPO-34 results will be presented and discussed as the H-SAPO-34 did not provide additional information from the impregnated zeolite on the following analysis techniques. introduction did not affect the SAPO-34 crystals morphology as already mentioned on the XRD analysis. The crystal size observed on Figure 5.3 indicated that crystals between 2-3 μm were obtained. Similar average crystal size (2-5 μm) was reported by other author as Wang et al. [8], Gao et al. [11], Liu at al. [5] and Wang et al. [9]. On the Table 5.3, the chemical composition in the bulk and in the surface of the Cu/SAPO-34 zeolite were compared. First, the Cu content in EDX was found to be lower than the ICP-OES value. This confirmed the XRD hypothesis that the impregnated Cu phase was well introduced and dispersed into the zeolite framework and it was not as present on the surface of the zeolite as CuO species.

Si/Al and P/Al ratios obtained by these two methods can be considered to be almost [16]the same as it can be verified on Table 5.3. However, significant differences on the ICP-OES and EDX contents were observed for Al and P elements. This means that these elements are rather present on the external surface of the zeolite, the be-named "extra-framework" species. Further discussion about this will be done later in relation to the amorphous phase observed on the Figure 5.3.b.

In some areas of the sample, especially when using a bigger scale, some amorphous phase was observed connecting the cubic crystals of the SAPO-34 zeolite, as it can be observed on Figure 5.3.b. For this reason, precise EDX measures were performed on a cubic zeolite crystal and on the amorphous phase with the aim of comparing the chemical composition between them. Results of these EDX measures are represented on Table 5.4. In the literature [17] was found that, at lower Si/Al ratios than 0,3 a co-crystallization of an AlPO4-crystoballite dense phase may occur. This co-crystallization might be related to the amorphous phase observed on the SEM image (Figure 5.3.b). This hypothesis could be feasible as Si/Al= 0,15 were obtained at both EDX and ICP-OES analysis (as shows Table 5.3) and significant higher Al and P contents were obtained on the amorphous phase in relation to the cubic crystal (Table 5.4). This could be caused by an insufficient temperature value during the SAPO-34 synthesis that reached to a partial crystallization of the SAPO-34 in certain areas.

However, in the following analysis will be confirmed that the in-lab synthesized catalyst accomplished all the physicochemical and textural properties typical of a SAPO-34 zeolite. In addition in later chapter will be proved that also good thermal and catalytic activity were achieved.

TRANSMISSION ELECTRON MICROSCOPY (TEM)

TEM analysis was performed in order to try to observe the Cu atoms and their distribution on the zeolite structure. All this is related to the morphology and microtexture of the Cu/SAPO-34 sample. On TEM image displayed on Figure 5.4, particles related to Cu species could not being detected. This would be in agreement with previous observations made on XRD analysis and confirmed on the following XPS analysis which determined that impregnated Cu was well dispersed into the zeolite framework and it was not accumulated on the zeolite surface. Presumably, this might indicate that no Copper oxides species were present on the synthesized catalyst. This would be further discussed on the XPS analysis results.

In addition, TEM analysis was coupled with a EDX measure of the chemical composition on the catalyst surface. Almost identical compositions than the EDX performed coupled to the SEM analysis (Table 5.3) were obtained and, for fluidity reasons, they are not also presented.

BET SURFACE AREA AND N2 ISOTHERM

BET and N2 isotherms allowed determining the zeolite surface area and the pore size distribution of the in-laboratory synthesized Cu/SAPO-34 zeolite, presented on Table 5.5. Typical BET surface areas of SAPO-34 zeolites found in the literature are between 400-500 m 2 /g [18,19]. This is considered to be a high surface area and it is produced due to the micropores nature of the CHA zeolite family. As it can be observed the Table 5.5, the BET surface area measured on our synthesized Cu/SAPO-34 was 411 m 2 /g, being in the typical window reported in the literature [18]. Gao et al. [1] evaluated a Cu-SAPO-34 zeolite whose BET surface area of its zeolite was also 440 m 2 /g.

In reference to the pore size and distribution, data is summarized on Table 5.5 and represented on Figure 5.5. On Figure 5.5, it can be verified that the pore width values were concentrated around 0,85nm= 8,5 Å (green peak). This is in agreement with the literature results where average pore width of the CHA zeolites was reported to be around the 7,8-8 Å (3.8 x 3.8 Å) [1,17] and it is considered to be a small pore size that increases the hydrothermal stability of the zeolite and also decelerate its possible dealumination. Also, it can be observed that there was not presence of pores at higher size values which would mean that mesoporosity was not found on the sample. Only, micropores were formed during the hydrothermal synthesis of the SAPO-34 zeolite and homogeneous pore size distribution was achieved.

It is necessary to remark that the discussed pore size values were based on the Horvath-Kawazoe fitting which was reported to be the most accurate to microporous materials. Furthermore, the performed adsorption-desorption N2 isotherm on the synthesized Cu/SAPO-34 zeolite is presented on Figure 5.6. The accumulation of data at the beginning of the experiment as well as the almost horizontal tendency of the isothermal curve is usually observed on microporous materials such as CHA zeolites. In addition, it is necessary to remark that certain hysteresis was detected at the end of the curve at the highest pressure. At first, it was thought that it was related to certain microporosity maybe present on the sample but Horvath-Kawazoe fitting results confirmed that any mesoporosity was found. In addition, comparing the total pore volume with the microporous volume obtained by the N2 adsorptiondesorption and indicated on Table 5.5, it can be observed that almost the same value was obtained and only a negligible difference (0,01 cm 3 /g) was found. Moreover, the 0,15 cm 3 /g obtained as micropore volume of the studied Cu/SAPO-34 was compared with the literature values reported by various authors [7,16]and it was found to be quite similar. For example, Gao et al. [1] obtained 0,21 cm 3 /g as micropore volume for a SAPO-34 zeolite with a similar BET surface area (440 m 2 /g) and the same pore width (8 Å). Main conclusions obtained from BET and N2 isotherm analysis were that the typical high surface area of the CHA zeolites family was achieved. Also, it was confirmed that the synthesized catalyst was basically microporous with a pore width distribution and micropore volume values characteristics of the SAPO-34 zeolites.

X-RAY PHOTOELECTRON SPECTROSCOPY (XPS).

XPS analysis was realized with the aim of identifying the predominant Cu species present on the surface of the synthesized SAPO-34 zeolite.

As it can be observed on Figure 5.7, the main Cu 2p spectrum showed a set of two satellite peaks, corresponding to Cu 2p3/2. The Cu 2+ species displayed a satellite peak associated with the main peak of Cu 2p3/2 located at around 933.8 eV [16,20,21]. In addition, a small lump attached to the main peak was detected at 936,5 eV. Gaussian-Lorentzian fit to Cu 2p3/2 indicated that the main peak was composed of two peaks at 936.5 and 933.8 eV [21].This second peak was related to Cu(OH)2 species. However, the Cu 2+ /Cu(OH)2 ratio= 5,84, meaning that the cationic Cu specie was almost six times higher than the hydroxide one [7].

In the literature was reported that Cu(OH)2 and other CuO species are usually accumulated on the zeolite surface (especially when Cu was introduced by impregnation method) while Cu 2+ are normally found into the zeolite sites. These results were in agreement with the XRD and EDX analysis which suggested that the impregnated Cu was successfully introduced and dispersed into the SAPO-34 zeolite framework. XRD spectra did not showed the typical peaks of the CuO species and the Cu content on the zeolite surface (EDX) was significantly lower than in the bulk (ICP-OES).

CONCLUSIONS

This chapter presented the results obtained from the physicochemical characterization of the in-lab synthesized Cu/SAPO-34 catalyst. This new powder catalyst will be used from now on as reference catalyst on the SCR reactions with and without soot presence.

XRD diffractograms of the non-impregnated and the Cu/SAPO-34 zeolites were compared. Main conclusions from the XRD analysis were:

Typical peaks of the SAPO-34 zeolite were obtained, verifying that it was successfully synthesized.

Cu introduction did not affect the SAPO-34 zeolite framework.

Peaks related to CuO species (35,58 and 38,88°) were not observed, indicating that Cu metal was well dispersed within the zeolite framework.

Chemical composition was evaluated by ICP-OES technique. The main conclusions made were:

Desired 2,5% wt of Cu was well achieved by impregnation method.

Chemical composition of the non-impregnated zeolite in comparison to the Cu/SAPO-34 indicated that the Al content increased when Cu was introduced. Contrarily, the P content decreased.

Generally, element contents obtained were the typical of the SAPO-34 zeolites.

Morphology and crystal size of both samples were evaluated with SEM technique. SEM analysis was coupled with the EDX measure of the chemical distribution on the catalyst surface. Main conclusions were:

Synthesized zeolite showed the typical cubic-like crystals of the SAPO-34 zeolites as well as good homogeneity.

It was confirmed that the Cu introduction did not affect the SAPO-34 structure.

Crystal size was between 2-3 μm on both samples, which were in the average size reported on the literature.

Cu content on the surface was measured by EDX and it was observed to be lower than on the bulk (ICP-OES), confirming that the Cu was well introduced and dispersed into the zeolite framework. TEM analysis also were in agreement, as any particles related to Cu species were detected.

Certain amorphous phase was detected in some areas of the zeolite sample. It was decided to compare the EDX measured on the amorphous phase and on one of the cubic crystals. It was observed that higher Al and P contents were found on the amorphous area. A possible origin of this amorphous phase found on the literature was that, at lower Si/Al <0,3 ratios, co-crystallization of AlPO4 -might occur.

Surface area and pore size distribution was evaluated by BET and N2 isotherms techniques. Main conclusions obtained were:

Surface area obtained was 411 m 2 /g which was in the average value typical of the SAPO-34 zeolites (400-500 m 2 /g).

Average pore width obtained were 8,5 Å which is typical of the small pores CHA zeolite family.

Total pore volume and microporous volume were almost the same value (0,15 cm 3 /g), indicating that no mesoporosity was detected on the catalyst.

Main conclusion obtained by XPS analysis was:

It was observed that the main Cu specie present on the synthesized catalyst was the Cu 2+ which is normally present into the zeolite sites. This was in agreement with XRD and EDX results that suggested that Cu was mainly located inside the zeolite instead of its surface.

PHYSICOCHEMICAL CHARACTERIZATION OF SOOTS

SUMMARY

This chapter is focused on the physicochemical characterization of a commercial (Printex U) and a real Diesel soot (from an Euro V engine). Textural and physicochemical characterization techniques were realized on both kinds of soot with the aim of comparing the chemical composition and the morphology of the real Diesel soot with the Printex U. XRD analysis was used to determine the crystallinity of the samples, CHNS technique was used instead the ICP-OES to determine their chemical composition, with the TGA analysis the mass loss and ashes content were analysed and the morphology of both samples was observed by SEM+ EDX.

More details about the analysis equipment and measure conditions used for each characterisation technique were described on Chapter 3. On the Figure 6.1, two kinds of spectra were presented: X-ray diffractograms of the commercial and the real Diesel soot. As it can be observed, the main peaks at 24,22 and 42,08° were related with the Carbon oxide species and were detected for both soot samples. Castoldi et al. [1] also evaluated the Printex U soot and these two main carbon broad peaks were also observed.

X-RAY DIFFRACTION (XRD)

Furthermore, a very small peak (26,43º) attached to the bigger Carbon oxide peak was only observed on the real Diesel soot (blue spectra). This extra peak was related with the graphitic Carbon, indicating that a mixture of crystalline phases were present on the real Diesel soot. Sadezky et al. [2] evaluated various kind of commercial Printex 90 soot and also a synthetic graphite sample. Their commercial soot sample obtained peaks at 24, 9º and 43,6º which can be related with the two main peaks observed on our commercial Printex U sample. Slight deviation on the values was attributed to the different categories of the Printex soot compared. Furthermore, on the X-ray spectra of the commercial graphite sample a main peak was obtained at 26,8º [2]. This confirmed that the secondary peak observed on the real Diesel soot spectra (26,43º) was related to the graphite phase. Contrarily, only pure Carbon oxide phase formed the Printex U sample which was expectable due to its commercial character. Anyways, it can be concluded that both samples were found to be highly crystalline which is in agreement with the literature results [1,2].

On the Table 6.1, the main information about the peaks location and the crystal orientation obtained from both samples is summarized. Intensity values of each peak are indicated on both on the Figure 6.1 and the Table 6.1. The information about the small peak only obtained at 26,43° for the real Diesel soot is indicated on blue colour on the Table 6.1 to be clearly differenced. As it can be observed on Table 6.2, both kind of soot are mainly formed by Carbon (> 90% wt) and Hydrogen (< 1% wt). Ferraro et al. [3] who studied commercial carbon blacks and compared them with a real Diese soot, confirmed that major constituents were Carbon, Oxygen and Hydrogen. In the case of our real soot, also a very small percentage of Sulphur was detected (0,32% wt) [4] whereas, any sulphur trace was found on our Printex U sample. This same tendency was observed by Ferraro et al. [3] who maintained that carbon blacks generally contained just a small amount of Sulphur, which was instead more abundant in Diesel derived soot. This sulphur presence on the real soot might be explained by the remaining compounds of the fuel or the lubricant additives which reached the exhaust line units [3]. On the contrary, as Printex U is commercial soot, this Sulphur content is better controlled and easily avoided. It is remarkable that any Nitrogen species content was detected in any of the soots.

THERMOGRAVIMETRIC ANALYSIS (TGA)

TGA analysis was performed on both kinds of soot with two different objectives: to observe their thermal resistance and the consequent mass loss of both soots, and also to determine and compare the ashes content obtained from them. TGA analysis was complemented with a mass spectrometer which qualitatively measured the gases emitted during the thermal oxidation of soots. Operational conditions used during tests were: Air as carrier gas, 700 °C, ramp of temperature of 5 °C/min and gas flow of 50 ml/min. .c). Mass loss curves of both kinds of soot followed the same tendency at the low temperature region (400 °C) [7]. Later, it can be observed that both soot samples started to be oxidized at 400 °C. However, even if both onset temperatures were at higher temperatures than 500 °C, in the case of the real Diesel soot the onset temperature was observed at 503 °C whereas the onset temperature of the commercial Printex U was higher (550 °C). This might be explained due to the commercial character of the Printex U soot that provided higher thermal resistance [5]. A possible explanation of this different behaviour can be ascribed to the presence on the soot surface of strong adsorbed organics originating from the additives of the lubricant used in the engine [3].

In the literature, Boger et al. [6] compared the behaviour of a Printex U and a real Gasoline soot (collected during cold starts) under TGA analysis. They also observed that similar behaviour was produced between both soot samples at the low temperature window. However, at the high temperature region (> 500°C), less reactivity of the Printex U sample was registered as it was in the case of the Printex U sample evaluated in this thesis. The suggested that this difference might be potentially due to a lower elemental carbon (EC) content of the real soot that conferred higher reactivity. This theory is consistent with the Carbon values obtained at CHNS analysis on both soot samples (Table 6.2). Finally, in Figures 6.2.a and b it was observed at 600 °C that the mass loss of both soot samples was found to became constant. Piumetti et al. [7] evaluated the thermal oxidation of a Printex U as model soot until 800 °C (10 °C/min, air as carrier gas and 100 mL/min). They observed that uncatalysed soot combustion happened between 500 and 650 °C.

In reference to the remaining mass weight that was observed above 600 °C, it was related to the unburned ashes content on the soot samples. As expected the ashes percentage obtained for the real Diesel soot was higher (almost 20%) than for the Printex U sample (barely 5%). This is in agreement with XRD and CHNS analysis which showed that, contrarily to Printex U, the real Diesel soot presented certain impurities in its composition giving higher reactivity. Mahofa et al. [8] also evaluated Printex U soot by TGA analysis until 900°C under air balance (10 °C/min as temperature ramp and 100 mL/min flow). They also observed that 100% of Printex U mass was oxidized and no ashes remained on the sample.

Referring to the remaining ashes obtained from the real Diesel soot, they were analysed by ICP-OES. They were mainly composed by Fe (around 47%) and certain traces of Al and Cr (around 1%). Similar composition was observed by other authors in the literature: Liati et al. [9] analysed an ash PM obtained from a Diesel passenger car and it consisted of Fe by more than 50%. It was suggested that the high amount of Fe detected on the ashes was related to the Fe-based fuel-borne additive of Diesel fuel (be-named Eolys©) of passenger cars. Also, they indicated that the rest of traces (Cr, Al, Ni, Zn…) were originated from the engine wear [10]. This significant Fe content on the ashes of the real Diesel soot may affect the NH3-SCR activity of the catalyst in presence of this soot as Fe is also active to the selective reduction of NOx at high temperature range (> 400 ºC). Fe species also are known to promote the NH3 oxidation reaction which consumes the reductant agent necessary to reduce the NOx. This will be further discussed on Chapter 7 where the catalytic activity of the synthesized catalyst was evaluated. It is important to keep in mind that measures were qualitative and not quantitative, so values represented on Figure 6.3 are related with the intensity of the emitted gases. As it can be observed, same products were obtained from both soot samples and one of the more intense and import one was the CO (blue line). Also, C3H4 hydrocarbon was detected as well as O2. However, contrarily to the expected, CO2 intensity remained quite low on both cases. This might mean that the thermal oxidation of these soot samples was mainly produced following the Reaction 2 mechanism (Annex B).

(2) 2C + O2 → 2 CO

RAMAN

Raman analysis is a characterisation technique useful in the case of Carbon-based materials.

In this case it allowed to compare the defect number and the homogeneity of both kind of soots discussed in this chapter. As a consequence, information about the soot reactivity can be Jawhari et al. [15] and Sze et al. [16] suggested that the peak at 1585 cm -1 comprises not only the G band but also the D2 band. The curve fitting results obtained in the present study clearly supported the inclusion of the D2 band. In graphite samples, the G peak was associated to inplane nuclear displacements affecting the CC bond stretching coordinates However, even if these bands were found at the same positions on both soot samples, the width of the peaks, the intensity ratios and the distance between peaks was not the same on both samples. This allowed comparing the commercial Printex U and the real Diesel soot characteristics, which might affects or explain their different catalytic performances under SCR reaction conditions. Another difference between both soot samples worthy to remark was around 2900 cm -1 , where another band (assigned to G+D1) [2] was found only in the case of the commercial Printex U soot (might be related to the C-H links).

Information about the D/G bands ratio was collected on Table 6.3. This ratio values would give specific information about the defects number and homogeneity of the soot which complement the Raman spectres. D1 (Defects) band commonly represents the disordered graphite and the defect number of the soot which is directly related to the reactivity of that soot sample [1,17]. Whereas the G (Graphite) band corresponds to the ideal graphitic lattice vibration of the carbonaceous materials [18,19]. Relative intensity of the D band with respect to the G band (ID/IG) increases with the increasing degree of disorder in the graphitic structure [20][21][22]. The intensity of these D and G bands was measured on ten different analysis areas. These values as well as their average of each kind of soot were indicated on Table 6.3. The more obvious observation that can be extracted was that the intensity of the D band and, consequently, the higher D/G ratio was obtained in the case of the real Diesel soot. This higher ratio values was directly traduced on higher amount of defects and lower degree of graphitisation [16] on the real Diesel soot. This is logic due to the presence of combined crystalline phases on its structure (XRD) and it is consistent to the following SEM morphology investigations [2]. Also, is in agreement with previously discussed presence of impurities in its chemical composition (CHNS and TGA ashes). These impurities are considered as soot defects and usually provide the samples of higher (but not necessarily desired) reactivity.

An interesting to remark to do in reference to the D/G ratios obtained on ten different sample areas was that, in the case of the commercial Printex U sample, the values obtained were more heterogeneous that in the real Diesel soot. This was unexpected as the commercial soot was supposed to be more homogeneous and similar band intensities along the entire sample were expected to be found. Especially due to only pure phase was observed on the XRD spectra and minimal impurities were observed on CHNS and TGA analysis. On the other hand, the ten D/G ratios from the real Diesel soot were quite similar, meaning that band intensities was constant on the entire sample which was surprising due to the presence of impurities (defects).

SCANNING ELECTRON MICROSCOPE (SEM)

Finally, the soot characterisation was completed by studying the morphology of the samples with the SEM technique. Also, CHNS chemical analysis in the bulk was completed with EDX measures on the samples surface. For the practical application of these materials, the surface composition is even more important and relevant than the bulk composition [3].

a) ). This agglomeration of the spherical soot particles was also remarked by Yang et al. [23] and they suggested that it was caused by the action of Van der Waals, electrostatic and surface adhesive forces. Furthermore, the real Diesel soot image, apparently confirmed the theory made at XRD analysis of two different phases formed the sample (as the white colour was evident on Figure 6.5.b). Mihai et al. [24] analysed by SEM technique a real Diesel soot obtained from an engine bench at Volvo cars. In the obtained SEM images from Mihai it can be also observed the same uniform agglomerated spheres and also the aforementioned white phase. In the literature, Yang et al. [23] suggested that the white phase was related to a small amount of soluble organic matters as unburnt fuel was emitted into the exhaust system and was found to adsorb on the surface of the PM. This was consistent with observations made at CHNS and TGA analysis.

In reference to the crystal size, it was observed on both soot samples that the average size was around 50 nm. This average particle size was considered to be quite large. However, on the literature similar values were obtained by various authors such as Yang et al. [23] (20-60 nm) and Mihai et al. [24,25] (30-40 nm). Certain authors also suggested that the soot particles were too big to enter into the zeolite channels, blocking the accessibility of the gas flow to the active sites of the catalyst. Furthermore, as it can be observed on Figures 6.5.a and b, the crystal size distribution can be considered as homogeneous and uniform on both soot samples.

b

As aforementioned, the CHNS analysis on the bulk was complemented with the EDX measures on the soot surface. Table 6.4 compares the EDX and CHNS chemical composition of the commercial Printex U soot and the real Diesel soot. It can be observed, that similar values were obtained between the EDX and the CHNS analysis relating to C and S content. Again, chemical composition indicated that both soot are mainly composed by Carbon (> 90%) and the Sulphur content was only considered on the real Diesel soot due to the presence of impurities from the lubricant as already observed on CHNS analysis [3]. Also, on EDX a very small percentage of Si was measured for the real Diesel soot. In addition, the EDX analysis detected that the second main element was the Oxygen, with about 5% wt on both samples.

It is important to remark that the CHNS and EDX analysis seemed to verify the results obtained from Ferraro et al. [3]: higher percentages of Carbon were present in the commercial carbon blacks with respect to real soots, while Oxygen was more abundant in soot samples.

It can be concluded that both soot samples were mainly composed by carbonaceous compounds which is in agreement with the literature results.

It is necessary to remark that any significant difference on the element content distribution was observed between the white and darker areas of the real Diesel soot.

CONCLUSIONS

In this chapter two kinds of soot sample were physicochemically characterized: real Diesel soot and a commercial soot be-named Printex U. This evaluation was made with the aim of comparing the chemical and textural characteristics of both samples and, later, to connect these soot properties with their catalytic behaviour under SCR reactions. Differences observed between the physicochemical properties of both samples might be useful to explain different catalytic activity and reactivity.

The main conclusions obtained from the XRD analysis were:

The XRD diffractograms were compared with a theorical database. It allowed to determine that the main peaks observed on both samples (24,22 and 42,08°) were related with the Carbon oxides species.

An extra small peak (26,43°) attached to one of the Carbon oxide was only observed on the real Diesel soot sample. It was determined to correspond to graphitic carbon presence.

Chemical composition of both samples was evaluated by CHNS technique. The main conclusions made were:

Both soot samples were mainly composed by Carbon (> 90% wt) and Hydrogen ( 1% wt). Later on EDX analysis was determined that around 5% wt of Oxygen was also present.

Only on real Diesel soot sample a small percentage (0,3% wt) of Sulphur content was observed. This Sulphur might be originated by the unburnt fuel or certain fuel additives.

Thermal stability and ashes content of the soot sample were evaluated by TGA analysis. The main conclusions were: Both soot samples started to be thermally oxidized above 500 ºC. But, the onset temperature of the Printex U sample was 50 ºC higher than the real Diesel soot. This might mean that the commercial Printex U soot was more stable than the real soot.

The unburnt mass remaining was related to the ashes content of the soot samples. Significant ashes percentage was observed on the real Diesel soot (20% wt), whereas barely 5% wt of ashes was obtained for the Printex U soot.

TGA analysis was coupled to a mass spectrometer that allowed determining the gases compounds emitted during the thermal reaction. CO was the main product observed on both soot samples. Also O2 and C3H4 were obtained.

It was remarkable that any CO2 was observed on both soot samples oxidation. This might mean that the thermal oxidation of these soot followed the Reaction 2 (Annex B) mechanism.

Chemical composition of the ashes from Real Diesel soot was determined by ICP-OES. Important amount of Fe was found, originated from fuel-borne additive (Eolys©). Fe content on real Diesel soot may affect the NH3-SCR activity of the catalyst as Fe is also active to the selective reduction of NOx (> 400 ºC).

Main conclusions obtained from Raman analysis were:

Two main peaks at 1350 and 1585 cm -1 were obtained on both soot samples. These peaks were related to the D and G bands of the Lorentzian-Gaussian theory.

Another peak around 2900 cm -1 was only obtained for the Printex U sample. It was related with C-H links and it was also observed from other authors in the literature.

D band intensity was higher for the real Diesel soot that means that D/G ratio value was also higher than in the Printex U case. This ratio was related to the defect number and soot reactivity of the sample. This was logic due to the impurities presence on the real soot already remarked on the XRD, CHNS and TGA (ashes) analysis.

Ten different measures of the D and G band intensities were realized on different areas of each soot sample. Surprisingly, it was observed that the D/G ratios of the commercial Printex U were more heterogeneous than for the real Diesel soot.

Finally, the morphology and the crystal size of both soot samples were evaluated with SEM technique. SEM analysis was coupled with the EDX measure of the chemical distribution on the soot surface. Main conclusions were: Both samples showed similar homogeneous morphology and granulated texture.

Average crystal size observed on both soot samples was the same, around 50 nm which were in the average size reported on the literature by various authors.

EDX chemical analysis on the soot surface was similar to CHNS values: both soot samples were mainly formed by more than 90% of Carbon, about 5% of Oxygen and barely 1% of Hydrogen.

EDX confirmed that only a small percentage of Sulphur was obtained on the real Diesel soot sample as already observed on the CHNS analysis.

Barely a 0,1% of Silicon content was only detected by EDX for the real Diesel soot.

EVALUATION OF THE SYNTHESIZED Cu/SAPO-34 CATALYST

SUMMARY

Once the synthesized catalyst was well physicochemically characterized, it was necessary to study its deNOx activity. Thus, this chapter is focused on the catalytic evaluation of the synthesized Cu/SAPO-34 catalyst under different SCR conditions. Performed tests, feed gas compositions and experimental strategy of each test were listed in the Annex C. In addition, the main reactions that may occur in NH3-SCR zeolite and which might be mentioned during the results discussion were listed in the Annex B. Also, the operational method followed during this test serie was explained on Chapter 3, section 3.5.2.

It is remarkable that the IRCELYON lab-scale system show a smaller scale than the IFPEN gas bench. In addition, the catalysts configurations were completely different. They presented different hydrodynamic regimes due to their different scales which implied different GSHV and gas flows: the IFPEN gas bench allowed to use higher gas flow (1288 L/h) and a GSHV of 35.000 h -1 . In comparison, the IRCELYON lab-scale system allowed using a smaller gas flow due to its reduced volume: 10 L/h and a GHSV of 135000 h -1 . Furthermore, the higher scale and configuration of the IFPEN sample produced higher pressure drop issues in comparison to the powder sample. In reference to the catalytic beds: the commercial mini-SCRF consisted on a cordierite filter waschoated with the Cu/SAPO-34 catalyst while at IRCELYON both were mechanically mixed in powder form. Thus, the cordierite material and the catalyst were in closer contact at IRCELYON sample which will also react in a different way with the feed gas. Also, better gas diffusion was allowed with the powder sample. In addition, the gas balance used was also different due to economic reasons: He could be used at IRCELYON, allowing the study of the mass balance and selectivies. While at IFPEN, N2 was used instead as it was a cheaper option to use with high gas flows.

Separately, the aim of this section was to simulate the real Diesel exhaust reactions as close as possible by means of the synthesized catalyst. First step was to evaluate its catalytic behaviour under different Diesel exhaust conditions in soot absence. The strategy followed during the test series was similar to the strategy followed with the commercial mini-SCRF catalyst (Chapter 4). It started with the NH3 oxidation reaction that competes with the SCR reactions at high temperatures (> 350 °C). Then, the complexity was increased step by step. First, the interactions of NO pollutant with the NH3 were studied by Standard SCR reaction. Later, NO and NO2 pollutants were introduced in equimolecular amounts to reproduce the Fast SCR reaction. And, to complete the study of the influence of the NO/NOx ratio over the NH3-SCR activity of the catalyst, the NO2-SCR reaction was also reproduced. Finally, all the previous reactions were studied in the presence of two kinds of soot (a commercial Printex U and a real Diesel soot), being these two lasts the more complex systems as competition between the oxidation and reduction reactions will happen.

Effectively, once determined the catalytic behaviour under different conditions, the influence of the soot presence on the catalyst performance was studied and compared with the catalyst behaviour in soot absence. Also, the difference on the behaviours of the real Diesel soot and the commercial Printex U will be evidenced. Here, a thin layer of soot was introduced on top of the Cu/SAPO-34 + cordierite mixture. This configuration was chosen to better simulate the real soot deposition over the SCRF catalysts. A Cu-zeolite/soot ratio of 10:1 was chosen, similar to that selected by various authors such as Tronconi et al. [1], who studied it recently in their works.

EVALUATION OF THE CATALYTIC SYSTEM COMPONENTS

Prior to discuss the different reactions that may occur at the Diesel exhaust line, it was necessary to evaluate the catalytic activity of certain components of the catalytic system in an isolated way. First, the commercial cordierite support was evaluated under Standard SCR conditions to verify its inert nature and if it shows any deNOx activity was supposed to take place. Later, same reaction was reproduced in presence of each soot (in absence of the Cu/SAPO-34 catalyst). It is important to study separately the influence of the soot and its catalyst activity with the NOx and NH3 presence.

Cordierite evaluation under Standard SCR conditions (Annex C. Test 2)

Normally, only thermal NH3 oxidation would happen spontaneously at high temperatures even in the absence of catalyst. Starting temperature was fixed at 200 ºC using a feed gas composed by NO (1000 ppm), NH3 (1000 ppm), O2 (8%) and H2O (3%), using He as balance. As it can be observed on Figure 7.1, no NO conversion occurred over the cordierite sample during the complete Standard SCR test. As it was expected only NH3 conversion above 325 ºC was produced. This conversion was related to the thermal NH3 oxidation at high temperatures that happened even in the absence of a catalyst [2,3]. Maximum of NH3 conversion (40%) was obtained at 500ºC. This indicated that spontaneous NH3 reaction itself was not enough to completely consume the NH3. Information about the favoured NH3 oxidation mechanism will be obtained on the following Figure 7.2 where the NOx and N2 selectivities will be discussed. On Figure 7.2 it can be observed during the low temperature region (200-300 ºC) no byproduct was formed as NH3 oxidation did not started yet. On Figure 7.1 was remarked that it was not until 325 ºC where NH3 oxidation started and, consequently, considerable NO and certain N2O formation were registered. This N2O formation might be related to the NH3 oxidation following Reaction 21 mechanism [4,5].

This might confirm that NO formation was directly produced by the NH3 oxidation reaction as well (Reaction 19). Correspondingly, N2 selectivity dropped in proportional amount. Also, a small amount of NO2 was formed above 400 °C related to the NO/NO2 equilibrium (Reaction 20, Annex B) [2,7,8] which could oxidize some of the NO formed by the NH3 oxidation.

(20) 2 NO + O2 2 NO2

By-products tendencies were coincident with the NH3 oxidation increase after 400 ºC remarked on Figure 7.1. This indicated that the thermal NH3 oxidation following Reaction 18, 19 and 21 was simultaneously happening. However, it mainly occurred by means of the Reaction 19 (Annex B) [6], yielding NO as product. Consequently, cordierite support was considered to be inert to the deNOx activity.

Real Diesel soot + cordierite evaluation under Standard SCR conditions (Annex C. Test 12)

Reactivity of a layer of real Diesel soot on top of the commercial cordierite support (without catalyst presence) was evaluated under Standard SCR conditions. This information will be of great interest when the Cu/SAPO-34 would be also present in the system. This reaction will allow to study separately the catalytic interactions of the soot with NO and NH3 pollutants. Here, a fixed amount of cordierite was introduced and the system was completed with the real Diesel soot until the same catalytic bed height than with the 60 mg (cordierite + Cu/SAPO-34) system. In this way it was assured that the GHSV and the height of the catalytic bed were maintained constant.

It was decided to evaluate the cordierite + real Diesel soot system under Standard SCR conditions as they were the reference conditions used for the test with only cordierite.

Here, NOx reduction by NH3 is expected to occur due to the soot presence as it might allow the NH3 to be adsorbed on the surface and then react with NO. Also, NH3 oxidation at high temperature region is expected to happen.

Reaction 7 (Annex B) might happen during this test: NO conversion started at 250 ºC but significant conversion was only observed above 400 ºC. Maximum NO conversion barely reached 12% at 500 ºC. NH3 conversion started at 300 ºC (apparently in relation to the modest NO conversion) and it also became significant above 400 ºC. Then, slightly higher NH3 conversion was obtained in comparison to NO conversion which was caused by the thermal NH3 oxidation at high temperature. It is remarkable that, apparently, the soot presence inhibited the NH3 oxidation as maximum of only 20% conversion was achieved even at 500 °C. It might be possible that strong adsorption of NH3 and NO on different sites of the soot surface occurred and, only at high temperatures (>400 ºC), they were reactive. Above 400 ºC, N2O formation decreased and N2 selectivity increased consequently. This might be related to the the NH3 oxidation reaction competition which yielded N2 (Reaction 18) [6,12,13,29]. Also, certain contribution of the Standard SCR reaction (Reaction 7) was considered as NO conversion also ocurred (Figure 7.3).

(7) 4 NH3 + 4 NO+ O2 → 4 N2 + 6 H2O
Finally, CO and CO2 emitted from the real Diesel soot oxidation are discussed. Figure 7.5 presents the evolution of the concentrations in function of the temperature. This graphic would be interesting to speculate if the soot oxidation was maintly thermal (active soot regeneration) or due to the NO2 presence (passive soot regeneration). Figure 7.5 presents the concentration measures during the increasing and decreasing ramps of temperature. As it can be observed, any formation of CO was produced both at the increase (heating) and decrease (cooling) ramps. Contrarily, considerable amounts of CO2 were produced (especially during the heating ramp). Same observation was made by Tronconi et al. [1] who also studied a Cu-zeolite + cordierite + real soot under similar operational conditions. At the increasing (heating) ramp, the CO2 formation started around 400 ºC and produced a maximum value of 90 ppm at 500 ºC [1]. During the decreasing ramp, CO2 emission was still produced in smaller amount and it stopped at 450 ºC. This behaviour indicated that only thermal active oxidation of soot happened during the test [11] (400-500 ºC).

As no CO was formed, it can be concluded that thermal (active) soot oxidation followed the Reaction 1 mechanism (Annex B):

(1) C + O2 → CO2 Futhermore, any CO and CO2 formation was detected in the medium temperature range (300-400 ºC), indicating that passive soot oxidation by NO2 did not happened. This is in concordance with results discussed on Figure 7.4, as NO2 formation was not observed.

Printex U soot + cordierite evaluation under Standard SCR conditions (Annex C. Test 13)

It was decided to compare the reactivity of a real Diesel soot with the catalytic behaviour of a commercial Printex U soot under the same operational conditions. Consequently, Test 13 consisted on evaluating the Printex U activity on top of the cordierite under Standard SCR conditions. Again, a soot layer was placed on top of the cordierite support. Also, NOx reduction by NH3 is expected to occur due to the soot presence as well as NH3 oxidation at high temperature. NO conversion started at 300 ºC but slightly higher conversion was only observed above 400 ºC (maximum of 10%). NH3 conversion also started at 300 ºC and became especially significant (> 40%) above 400 ºC due to the thermal NH3 oxidation reaction. It was more important than with the real Diesel soot (Figure 7.3) but complete NH3 conversion was neither reached in this test. On Figure 7.7 it can be observed that between 300-400 ºC an important N2O peak was formed. Maximum formation of N2O (almost 80% of selectivity) was obtained around 325 ºC [3,9], as also observed with real Diesel soot results (Figure 7.4).

Correspondingly, a proportional drop on the N2 selectivity was also registered. Again, it seem that partial and non-selective NO reduction was promoted by the soot presence.

As aforementioned, Reaction 14 (Annex B) could be a possible mechanism of this N2O formation. In comparison to the N2O formation obtained with the real Diesel soot, here 20% higher N2O selectivity was produced. This was contrary to the expected behaviour as the commercial Printex U soot was supossed to be less reactive due to the absence of impurities in its composition detected on the CHNS and TGA analysis (Chapter 6). However, it might be explained by the phenomena observed on Raman analysis which stated that the D/G ratios (related to the homogeneity and deffects number) obtained with the Printex U soot were more heterogeneous than the real Diesel soot.

In addition, it is necessary to remark that above 400 ºC around a small production of NO2 (around 10% of selecivity) hapenned only with the Printex U soot. This production coincided with the N2O concentration decrease as well as higher NH3 conversion was observed on Figure 7.6. This might be related to the thermal NH3 oxidation (Reaction 19) yielding NO and its simultaneous oxidation to NO2 (Reaction 20) due to the high temperature and oxygen concentration in the gas feed.

Finally, Figure 7.8 displays the CO and CO2 formation as a consequence of the Printex U soot oxidation. Here were presented the concentration measures obtained both during the increasing (heating) and decreasing (cooling) ramps of temperature. As observed with the real Diesel soot, no formation of CO was produced. Contrarily, considerable amounts of CO2 were produced, especially during the increasing ramp [1].

The CO2 formation during the increasing ramp started around 340 ºC while it started above 400 ºC with the real Diesel soot (Figure 7.5). Also, here it can be observed that the maximum value obtained at 500 ºC [1] (Reaction 1) was significantly higher (200 ppm) comparing to the 90 ppm with the real Diesel soot. During the decreasing ramp, CO2 emission was still produced until 420 ºC. Printex U soot was oxidized between 350-500 ºC (Figure 7.8). Contrarily to the results obtained with the real Diesel soot, the Printex U sample produced CO2 formation on the medium temperature range (300-400 ºC), indicating that certain passive soot oxidation happened. This is in concordance with results discussed on Figure 7.7, as certain NO2 formation was observed above 400 °C. Probably, this NO2 formation occurred at lower temperatures but it was not registered as it might be simultaneosly consumed by the passive soot oxidation. Above 400 °C, bigger NO2 formation happened due to the NH3 conversion increase. This was also reflected on the higher concentration of CO2 obtained with Printex U soot: 200 ppm of CO2 were produced due to the cooperation of the passive and active soot oxidation. Again, due to the CO absence, it can be considered that the mechanism followed by the passive soot oxidation was related to Reaction 4 (Annex B):

(4) C+ 2 NO2 → CO2 + NO However, it might be affirmed that the passive soot contribution would not be enough to completely oxidize the soot itself without the active soot contribution [9].

INFLUENCE OF NO/NOx RATIO ON NH3-SCR ACTIVITY (without soot)

Isolated NH3 oxidation (Annex C. Test 3)

In this section, the NH3 oxidation reaction is going to be isolated and studied over the catalytic system in soot absence. This reaction will be found to be competitive with SCR reaction at high temperature range. For this reason, it was decided to study it separately with the aim of observing the influence of the Cu/SAPO-34 catalyst presence under these conditions (Table 7.3).

Due to the presence of catalyst in this test, the NH3 oxidation is expected to be accelerated and occur at lower temperature in comparison to Test 2 where only thermal NH3 oxidation happened above 350 ºC. Also, if the previous Standard SCR tests with real Diesel and Printex U soots (Tests 12 and 13) are considered, soot presence is expected to promote the undesired N2O formation.

Reactions 18, 19 or 21 from Annex B are expected to happen during this test.

Pollutants concentration Test 3 NH3 (ppm)

1000 H2O (%) 3 O2 (%) 8 As it can be observed on Figure 7.9, in presence of Cu/SAPO-34 catalyst the NH3 conversion onset at 250 ºC and complete NH3 consumption was reached at 400 ºC [6,12,13]. This temperature value for the NH3 oxidation was also reported in the literature by various authors who studied this kind of Cu-based zeolites and similar catalytic systems [9,10,14].

On Figure 7.10, it will be determined the different products formed due to the NH3 oxidation. took place between 250-325 ºC [8], possibly related to the NH3 oxidation Reaction 21 mechanism (Annex B) mechanism [4,5]. Anyway, the main product obtained in this experiment was N2, as the high value of its selectivity during the whole temperature range shows [9]. Consequently, it can be concluded that the NH3 oxidation reaction followed the Reaction 18 mechanism. However, even if N2 was the main product, the complete NH3 consumption presented on Figure 7.9 is not desirable as would not be available to reduce the NOx.

Standard SCR reactions (Annex C. Tests 4 and 5)

Once the different components of the catalytic system were evaluated individually and the competitive NH3 oxidation reaction was also isolated, it became necessary to study the complete catalyst system behaviour under Standard SCR conditions (Table 7.4).

In this section, Standard SCR conditions were finally evaluated over the Cu/SAPO-34 + cordierite catalyst in soot absence. Standard SCR reaction (Reaction 7, Annex B) is expected to take place. Figure 7.11. shows the NO and NH3 conversions of the catalyst system in soot absence under Standard SCR conditions. Even at 200 ºC a small conversion for NO and NH3 was observed and it progressively increased with temperature. Regarding NO conversion, maximum value barely reached 40% at 425 ºC. This value is very small in terms of NO reduction, however, as Standard SCR conditions are not the optimal and faster conditions for the NOx reduction, it could be expected. In reference to NH3 conversions it continued increasing until 500 ºC where it was completely consumed. At temperatures higher than 300 ºC there is an increasing difference between the NH3 and NO conversions, being this value always higher in the case of NH3 due to the previously commented oxidation of NH3 at the studied conditions. Information about the NH3 oxidation mechanism favoured will be obtained on the following Figure 7.12 where the NOx and N2 selectivities will be discussed.

Pollutants concentration

b) 3 cycles Standard SCR reactions (Test 5)

Once the single Standard SCR was performed, it was decided to study the reproducilibility of the test activity along 3 continous cycles of Standard SCR. The reactor was charged with 60 mg of Cu/SAPO-34 + cordierite and the sample was maintained during the 3 cycles. This will give information about the stabiblity of the synthesised catalyst. These 3 cycles will be also studied and compared under Fast and NO2-SCR conditions as well as in presence of both kinds of soot. It is expected to be of great interest in soot presence as soot oxidation will happen during each cycle and system behaviour might be affected. Operational conditions and feed gas compositions of these tests were summarized on Annex C. It was observed that the 3 different cycles were practically overlapped and same tendencies were obtained, both for NO and NH3 conversions. Catalytic activity of the catalytic system is considered to be reproducible and only a negligible uncertainty due to the measure analyser was produced. In addition, same tendencies at same temperature ranges than for the single Standard SCR reaction (Figure 7.11) were obtained. It can be observed that exact overlapping of cycles was obtained. Also it is remarkable that the major product obtained was the N2 on the three cycles [2], indicating that effective and selective NOx reduction reaction happened. Only a negliglible amount of N2O was formed above 400 ºC, as it was also the case on the single reaction (Figure 7.12).

Fast SCR reactions (Annex C. Tests 8 and 9)

In order to complete the study of the influence of the NO/NOx ratio over the synthesized Cu/SAPO-34 catalyst, Fast SCR reaction was the next SCR reaction to evaluate (Table 7.5). It is reported to be the "faster" and more selective SCR reaction [2,9,15] and it consists on introducing equimolecular amounts of NO and NO2 on the reactive system (in addition to the reductant agent). In this section, Fast SCR reaction will be reproduce in soot absence. Again, a single Fast SCR will be simulated and, later, 3 cycles Fast SCR will be done to analyse the reproduciblity of the catalyst activity under these conditions.

As a consequence, Reaction 8 (Annex B) is expected to take place:

+ NO + NO2 → 2 N2 + 3 H2O . On Figure 7.15, it can be observed that above 400 ºC, the NO conversion dropped as a result of the NH3 oxidation [6,12,13]. Contrarily, NO2 conversion was not affected as very high value (nearly to 100%) was obtained above 385 ºC. It can be said that no stechiometric Fast SCR was produced and NH3 reduces predominantly NO2.

Pollutants concentration

Finally, NH3 conversion increased continously until reaching maximum value of 100 % at 500 ºC. It is necessary to remark that equimolecular NO2 and NH3 conversions below 250 ºC indicated NH4NO3 formation [9], as confirmed Figure 7.16. Another possibility for the N2O formation were Reactions 13 or 14 mechanisms:

(13) 2 NH3 + 2 NO2 → N2O + N2 + 3 H2O
In comparison to the Standard SCR, the Fast SCR test produced slightly higher amount of N2O (10% of selectivity) which was not expected from the faster SCR reaction [9]. This effect would be caused by the non-proportional conversion of NO and NO2 pollutants, yielding undersired by-products (Reaction 14). Figure 7.17 presents the NOx and NH3 conversions of the 3 cycles Fast SCR reaction. It was observed that the 3 different cycles were practically overlapped and same tendencies were obtained, both for NOx and NH3 conversions. Catalytic activity is considered to be reproducible and only a negligible uncertainty due to the measure analyser was produced. Figure 7.18 presents the NOx and N2 selectivities in function of temperature of the 3 cycles of the Fast SCR reaction in soot absence. It can be observed that almost exact overlapping of cycles was obtained. Also it is remarkable that the major product obtained was the N2 on the three cycles [2], indicating that effective and selective NOx reduction reaction happened. Only a small amount of N2O was formed above 400 ºC, as it was also the case on the single reaction (Figure 7.16).

b) 3 cycles Fast SCR reaction (Test 9)

NO2-SCR reactions (Annex C. Tests 10 and 11)

In order to finish the study of the influence of the NO/NOx ratio over the synthesized Cu/SAPO-34 catalyst, NO2-SCR reaction were the last SCR reaction to evaluate (Table 7.6). It is reported to be the "slowest" SCR reaction [16,17] and it consists on introducing NO2 in excess on the reactive system. In this section, NO2-SCR reaction will be reproduce in soot absence. Again, a single NO2-SCR will be simulated and, later, 3 cycles NO2-SCR will be done to analyse the reproduciblity of the catalyst activity under these conditions.

As a consequence, Reaction 9 and 10 (Annex B) are expected to take place:

(9) 4 NH3 + 3 NO2 → 7/2 N2 + 6 H2O (10) 4 NH3
+ 2 NO2 + O2 → 3 N2 + 6 H2O Figure 7.19 presents the NH3 and NO2 conversions in function of temperature in soot absence. Again, certain NH3 and NO2 conversions were produced since the beginning of the NO2-SCR reaction and they remained almost constant until 300 ºC. Later, they continuously increased until 500 ºC. Maximum value of NO2 conversion was obtained at 500 ºC, being near to 80%. This value was 20% lower than in the Fast SCR reaction (Figure 7.16) which is in agreement with literature [16,17]. In reference to NH3 conversion, complete consumption was not reached even at 500 ºC. The maximum NH3 conversion value obtained was 85%, in comparison to the other SCR reactions which both reached 100%. As it can be observed on Figure 7.20, it is evident that the biggest undesired formation of N2O occurred in excess of NO2 [2,5,9] as partial and non-selective NO2 reduction (Reaction 13) took place [10]. Maximum N2O formation (30% of selectivity) was produced at 325 ºC.

Pollutants concentration

b) 3 cycles NO2-SCR reaction (Test 11)

Again, reproducibility of the catalyst activity was analysed under NO2-SCR conditions by repeating 3 cycles. Evolution of NO2 and NH3 conversions in function of temperature are displayed on Figure 7.21. Regarding the results obtained from the 3 cycles, it can be observed that overlapping of cycles was obtained. Also it is remarkable that an important production of N2O was obtained on the three cycles [2], indicating that non-effective and non-selective NO2 reduction reaction happened on the 3 different cycles (Reaction 13). Same mechanisms than in the single NO2-SCR test (Figure 7.20) are considered to take place here.

Conclusions of influence of NO/NOx ratio

The catalytic system composed by the synthesized Cu/SAPO-34 catalyst was mixed with a commercial cordierite support to simulate the real SCRF catalysts. It was tested under the three different SCR reactions that could take place on real Diesel exhaust in function of the NO/NOx ratio produced by the previous DOC catalyst. In this section, the influence over the catalyst activity in function of the NO/NOx ratio was studied and, to modify only one parameter each time, these reactions were realized in soot absence first.

In reference to the NOx conversions obtained under the three different SCR conditions, it is necessary to indicate that the Standard SCR reaction presented the lowest NO conversion (barely reaching 40%) at 425 ºC. Fast SCR reaction obtained higher NO conversion (70%) and it was reached at a lower temperature value (350 ºC). These results were in agreement with the literature which reports that Fast SCR is the more active and selective SCR [2,9,15]. However, it was observed that NO2 conversion was privileged in comparison to NO conversion achieved, indicating that non-proportional NO and NO2 conversions were produced. This might mean that no pure Fast SCR reaction was taking place and some undesired by-products originated from parasite reactions might happened. Regarding the NO2-SCR reaction, the maximum NO2 conversion value was only obtained at 500 ºC and reached 70%. If compared with the 99% of NO2 conversion obtained with the Fast SCR reaction, it is obvious that it was less perfoming. Comparing the NH3 conversions obtained from each SCR reaction, tendencies were quite similar and the only difference was produced with the NO2-SCR conditions where complete NH3 conversion did not occur (85% of maximum conversion).

All the SCR reactions mainly yielded to N2 and considerable N2O formation. However, the mechanism of N2O formation was different on each SCR reaction. In the case of the Standard SCR, negliglible N2O formation was produced above 400 ºC due to the NH3 oxidation by Reaction 21. In the case of the Fast SCR reaction, around 10% of N2O selectivity was obtained between 200-300 ºC due to the NH4NO3 decomposition. Finally, the most significant N2O formation (30% of selectivity) took place during the NO2-SCR reaction at 350 ºC. Various authors [5,9,10] observed that important N2O formation happens when excess of NO2 is present by means of Reactions 13 and 14.

Referring to the stability and reproducibility of the catalyst activity on 3 cycles, it can be concluded that all the SCR reactions showed overlapping NOx and NH3 conversions curves for the different cycles. Also, overlapped selectivities of products were registered. This indicated that in soot absence, the catalyst activity remained the same does not matter which NO/NOx ratio was used.

INFLUENCE OF SOOT PRESENCE ON THE NH3-SCR ACTIVITY

Here started the study of the soot presence influence under the three previously discussed SCR reactions. The NO/NOx ratio in presence of soot will also have an influence on the catalyst activity. Strategy followed was repeating the same test serie presented but in presence of a soot layer on top of the cordierite + Cu/SAPO-34 mixture. This system configuration pretended to simulate the soot accumulation over the SCRF filters on real life conditions. The catalyst/soot ratio stablished was chosen to be 10:1 as it was used by some authors the literature [1]. The corresponding amount of soot was eliminated of the cordierite amount in order to keep constant the total mg of the catalytic system. Two kinds of soot were studied: a commercial Printex U and a real soot obtained from an Diesel engine bench at IFPEN.

NH3 oxidation reaction: real Diesel soot vs Printex U (Annex C. Tests 14 and 15)

As in the previous section, the NH3 oxidation reaction was isolated and studied over the catalytic system in presence of both soots (Table 7.7).

Reactions 18, 19 and 21 from Annex B are expected to happen during this test.

Pollutants concentration Tests 14 and 15 NH3 (ppm)

1000 H2O (%) 3 O2 (%) 8 Figure 7.23 compared the NH3 conversions obtained from the real Diesel and commercial Printex U soots under NH3 oxidation conditions in function of the temperature. Square symbol was related to the real Diesel soot while triangle symbol represents the commercial Printex U results. As it can be observed, NH3 on real Diesel soot started at 310 ºC and complete NH3 consumption was reached at 375 ºC. In comparison, a maximum of only 85% of NH3 conversion at 500 ºC was obtained with the commercial Printex U. This last behaviour is preferable as the NH3 will be available until higher temperature to reduce the NOx. This difference on the NH3 conversions between soots might be explained by the Fe content in the real Diesel soot (found by the ICP-OES analysis in Chapter 6). Fe is reported on the literature to promote the NH3 oxidation reaction [2] as it was observed on Figure 7.23. Another influence was related with the higher soot reactivity of the real Diesel soot due to the presence of impurities detected on CHNS and TGA analysis.

If comparing with the NH3 conversion in soot absence (Figure 7.9), behaviour was found to be in between both soots. NH3 conversion in soot absence started at 250 ºC (as Printex U soot did); and complete oxidation was reached as in the case of the real Diesel soot. However, complete consumption of NH3 in presence of the real Diesel soot was reached at lower temperature, indicating that NH3 oxidation was promoted by the real Diesel soot. Contrarily, in presence of commercial Printex U soot, complete NH3 consumption was inhibited. Figure 7.24 present the obtained NOx and N2 selectivities from the real Diesel and Printex U soots under NH3 oxidation conditions. In both cases the major product obtained during the whole temperature range was N2 (Reaction 18). On one hand, with the commercial Printex U soot, a small amount of NO (<10% of selectivity) was formed after 250 ºC. NO formation was slightly higher above 400 ºC [12] as a result of the NH3 oxidation following Reaction 19 mechanism [9]. In addition, above 400 ºC a very small formation of N2O was also registered and related with the NH3 oxidation by Reaction 21 mechanism [4].

On the other hand, the real Diesel soot formed a considerable amount of N2O and small amount of NO2 above 300 ºC [12]. Maximum formation of N2O was obtained at 375 ºC by NH3 oxidation by Reaction 21 [4], with a 20% of selectivity. This important N2O formation might be promoted by the Fe content present on the real Diesel soot which enhanced the Reaction 21. NO2 formation was supposed to be directly converted from NO following the NO/NO2 equilibrium (Reaction 20).

In comparison to the NH3 oxidation reaction in soot absence (Figure 7.10), where only a negligible formation of N2O was registered between 250-300 ºC (Reaction 21), in soot presence significant formation of NOx and N2O was obtained [9]. For this reason, soot might be considered to promote the formation of undesired by-products when interacting with NH3. As expected, the commercial Printex U was less reactive and formed less undesired by-products as well as complete NH3 consumption was limited as previously remarked. However, the real Diesel soot enhanced the NH3 oxidation and formed more by-products due to the impurities detected on its physicochemical characterization (Chapter 6).

Standard SCR reactions

Here, the Standard SCR reaction was performed in presence of the real Diesel and the Printex U soots. Catalytic system consisted in a Cu/SAPO-34 washcoat mixed with the cordierite support and a layer of soot was included on top. Same feed gas composition (Table 7.8) and operational conditions from Test 4 and 5 were used (Annex C).

In this section, Standard SCR conditions were finally evaluated over the catalyst in soot absence. Standard SCR reaction (Reaction 7, Annex B) is expected to take place. Due to the presence of the soot in this test, the Standard SCR reaction is expected to be non-selective and considerable amount of N2O might be produced as it was already observed in previous tests. On Figure 7.25 the NO and NH3 conversions in presence of soot under Standard SCR conditions are presented in function of the temperature. It can be observed that similar values and tendencies were obtained on both kinds of soot. Both NH3 and NO conversions started at 200 ºC and continuously increased with temperature. It is remarkable that NO and NH3 showed equimolecular conversions until 300 ºC, as it was also observed by Marchitti et al. [9]. At higher temperatures the NH3 oxidation started to compete, as it can be observed on Figure 7.25.

Regarding NO conversion, maximum values obtained barely reached 40% at 425 ºC. This value is very small in terms of NO reduction, however, as Standard SCR conditions are not the optimal and faster to the NOx reduction, it could be logic. It is necessary to remark that NO conversion of the real Diesel soot was slightly higher due to its higher reactivity based on the physicochemical characterization results discussed on Chapter 5. In reference to the NH3 conversions, they started at 200 ºC and continued increasing until 500 ºC where conversions around 85% were obtained. Normally, the increase in NH3 conversion above 400 ºC would be produced by the NH3 oxidation reaction as NO conversion decreased consequently.

If compared with the NO conversion obtained in absence of soot, the same tendency and similar maximum value was obtained (Figure 7.11). Just in the case of the Printex U soot it was remarked a small limitation of the NO conversion compared with in absence of soot. Marchitti et al. [9] also studied the influence of Printex U soot on the NOx conversions of a Cu-zeolite catalyst mixed with cordierite (powdered form) under Standard SCR conditions and same drop on the NO conversion was reported. A possible explanation for the observed inhibition could derive from an adverse effect of soot coverage on the Cu-zeolite active sites [9,18]. However, in soot absence complete NH3 conversion was produced at 500 ºC whereas in presence of soot it was not completed. Apparently, the presence of soot inhibited the complete NH3 oxidation [12], as already observed with the Printex U soot on the NH3 oxidation test (Test 14, Figure 7.23). It can be concluded that soot presence did not increased the NO conversion but helped to restrict the full undesired NH3 oxidation. Figure 7.26 presents the NOx and N2 selectivities in function of temperature in presence of both soots. As it can be observed, in Standard SCR conditions in presence of the Cu/SAPO-34 catalyst, the NO was selectively reduced by the NH3 on N2 and water as major products [2]. However, significant formation of undesired N2O was obtained with both soots between 250-400 ºC [3,9,19], possibly by means of Reaction 14 mechanism. This N2O formation was especially important for the Printex U soot, reaching a maximum value near to 25% in comparison to the maximum 15% reached with the real Diesel soot. These results are in agreement with the N2O selectivities obtained on Tests 12 and 13 (cordierite + soot layer under Standard SCR conditions), where higher N2O formation was also produced for Printex U soot (Figure 7.7). Again a possible explanation might be found on the Fe content on the real Diesel soot which is reported to be also active for the NH3-SCR activity. This might produced higher deNOx activity and, thus, less N2O by-product was formed. Later, above 400 ºC, constant 5% of selectivity was maintained on both soots but main product of the NH3 oxidation was N2 (Reaction 18). Correspondingly, N2 selectivity values proportionally dropped at the same temperature window amount and it was almost restablished after 400 ºC (> 95% of selectivity).

In comparison to the catalyst behaviour on the Standard SCR reaction in absence in soots where only negligible amount of N2O was formed above 400 ºC, the presence of soot enhanced the formation of undesired N2O by-product instead of the selective reduction of NO into N2 (Reaction 14). presents the NO and NH3 conversions obtained with the presence of commercial Printex U soot during the 3 cycles Standard SCR reaction. In general the tendencies of both NO and NH3 conversions curves obtained with both kinds of soot, were maintained during the three cycles and were similar to tendencies obtained on the single Standard SCR reactions (Figure 7.25). However, contrarily to results obtained in soot absence where 3 cycles were completely overlapped (Figure 7.13), on presence of soots, the first cycle showed higher activity in comparison to the other two. Also, certain NO and NH3 conversion (< 10%) was produced from 200 °C with both soots.

b) 3 cycles Standard SCR reactions: real Diesel soot vs Printex U (Tests 18 and 19)

Referring to the real Diesel soot, on both NO and NH3 conversions, it was observed that the first cycle was quite different in comparison to cycles 2 and 3. Both NO and NH3 conversions, were about 10% higher on cycle 1. Maximum NO conversion were obtained at 425 °C on all the cycles; however, on the first cycle 40% was reached whereas 30% was obtained on cycles 2 and 3. Then, NO conversion dropped a little bit. Same effect was registered with NH3: maximum 80% of conversion at 500 °C was achieved on the first cycle whereas barely 70% was produced on cycles 2 and 3. Regarding conversions of NO and NH3 produced with the commercial Printex U (Figure 7.27.b), same effect was observed. It was related to the soot oxidation during the first cycle which produced that it was not present anymore during the other cycles. Thus, the catalytic system evolved (mass and height of the catalytic bed) as a result and the catalytic behaviour reflected. Accordingly, the NO and NH3 conversions with both soots were higher during the first cycle were the soot was still present on the system and they decreased along the cycles due to the soot combustion. performed. This effect was produced with both kinds of soots. Regarding the real Diesel soot selectivity presented on Figure 7.28.a, the maximum N2O formation about 12% was obtained at 300 °C during the first cycle and it decreased with cycles. The improvement observed on cycles 2 and 3 was presumably due to the thermal removal of soots during the first cycle [20]. Furthermore, N2O formation peaks shifted towards higher temperatures along cycles: at 325°C on cycle 2 and 340 °C on cycle 3. It is necessary to remark that N2O curves of cycles 2 and 3 showed the same tendency and shape whereas cycle 1 curve followed a different tendency. This phenomena seem to confirm that the origin of this catalyst activity evolution might be focused on the soot oxidation during the first cycle. At higher temperatures, above 400 °C, the N2O formation remained constant (8% of selectivity) during all the three cycles. Regarding Figure 7.28.b related with the Printex U soot, differences between the first and other cycles were more evident. Also, same N2O curves were obtained on cycles 2 and 3 producing similar maximum N2O values (≈ 15% of selectivity) at the same temperature (300 °C). In contrast, the N2O formation on cycle 1 showed a different shape and higher maximum value (25 % of selectivity) obtained at higher temperature 320 °C. This shifting effect on the N2O formation temperature along the Standard SCR cycles may also indicates that the soot presence promoted the unselective NO reduction by means of Reaction 14. Thus, after the first cycle where important soot oxidation have occurred, the N2O formation decreased it was produced at higher temperatures. If compared with the N2O selectivities obtained on the Standard SCR reaction in soot absence (Test 4, Figure 7.12), this seem to be confirmed as only negligible amount of N2O was produced.

Fast SCR reactions

As previously studied in absence of soots, the influence of the NO/NOx ratio over the catalyst activity was also evaluated in pesence of both kinds of soot. The influence of the soot presence could be affected by the NO2 and NO concentrations. It will also allow to reproduce all the possible situations that could happen in real Diesel exhaust lines. In this section, Fast SCR reactions were performed (Table 7.9) introducing equimolecular amounts of NO and NO2. Again, single Fast SCR reactions will be simulated and, later, 3 cycles Fast SCR will be done to analyse the reproduciblity of the catalyst activity under these conditions. Reaction 8 (Annex B) is expected to take place. As previously discussed on the Fast SCR reaction in absence of soots (Test 8, Figure 7.15), the NO2 conversion was higher in comparison to the NO conversion obtained. This indicates that non-equimolecular conversions were produced. This effect was also observed by some authors such as Marchitti et al. [9]. If comparing with the NO conversion achieved in absence of soot [1,9], it was much higher than in soot presence, where it barely reached 40% and then dropped until zero at high temperature. This might means that the soot enhanced the non-equimolecular reduction of NO2 rather than NO even more than in absence of soot.Probably due to the passive soot regeneration in the medium temperature range which consumes NO2 in competition to the Fast SCR reaction [9,19,21]. This passive soot oxidation subtracts the NO2 otherwise available for the Fast SCR reaction. NH3 conversions obtained from the real Diesel soot and the commercial Printex U soot under Fast SCR conditions are presented on Figure 7.30. As it can be remarked, 10% of NH3 conversion was produced from 200 °C and then increased until maximum conversion value was reached at 500 °C on both soots. Until 400 °C, the NH3 conversion curves of both kinds of soots were practically overlapped. Then, Printex U soot showed a quick increase on the NH3 conversion (85%) while real Diesel soot stayed more stable until 500 °C (70%). This different behaviour at high temperature window will be further understand when products selectivities will be discussed.

Pollutants concentration

Contrarily to the Fast SCR reaction in soot absence (Test 8, Figure 7.15), complete NH3 consumption was not reached in presence of soots. Same inhibition effect of soot on the NH3 oxidation was observed by Mihai et al. [12]. This was in agreement with NH3 oxidation and Standard SCR results obtained in presence of soots. This seem to indicate that, in presence of soots, the thermal NH3 oxidation was inhibited which was a positive effect as it remained available to reduce NOx. As it can be observed, only a small amount of N2O was produced as by-product under Fast SCR conditions with both kinds of soot. It started to be formed from the beggining as NO2 and NH3 were converted from the begining of tests. It sligthly increase above 300 °C and a maximum value of 10% of selectivity was obtained with both soots at 425 °C, as it can be seen on Figure 7.31. However, only with the Printex U soot some NO started to be formed at 440 °C and it reached a maximum value of 20% of selectivity at 500 °C. This NO formation would explain the NH3 conversion increase after 400 °C observed on Figure 7.30. This NO formation was related to the NH3 oxidation by means of Reaction 19. As a consequence, N2 selectivity dropped in proportional amount.

In comparison to the Fast SCR reaction in soot absence, slightly higher formation of N2O was produced, especially above 350 °C. This might be consequence of the much lower NO conversion produced due to the soot presence which indicated that not only Fast SCR raction took place. N2O formation was related to the NH3 and NO reaction by Reactions 13 or 14 mechanism which became more important in presence of soots. However, the main product obtained from the NOx conversion was the N2 as it can be observed on Figure 7.31.

Finally, comparing the Fast SCR with the Standard SCR reaction both in soot presence, it was observed that much lower formation of N2O was produced under the Fast SCR conditions in agreement with literature [9,15]. Then, similar maximum conversion values were obtained but in cycle 1 at 275 °C and in cycles 2 and 3 at 315 °C. Again, this shifting effect was related to the soot oxidation along the cycles and the consequent evolution of the catalytic system.

In reference to NO2 conversions, the previously discussed differences between cycles were also registered with both kinds of soot. This might mean that soot presence produced higher reactivity and, consequently, higher conversion values as well as maximum conversions at lower temperatures. This last effect of the shifting in conversion peaks was not obtained during the Standard SCR reaction (Test 18 and 19, Figure 7.27) as maximum peaks were obtained at the same temperature value in al the three cycles. This might be caused by the persence of NO2 on the Fast SCR conditions which probably was being reduced during the passive soot oxidation reaction. For this reason, on cycles 2 and 3 the conversion peaks were obtained at the same temperature value as main part of soot was previously consumed oon cycle 1. In addition, higher NO2 conversion was produced along the whole temperature window on cycle 1 in comparison to cycles 2 and 3. Again, it would be explained by the passive soot oxidation reaction. Here, the same difference between the cycle 1 and the other cycles remarked on Figure 7.32 was also detected. Also, the shifting effect of the conversion peaks but less pronunciated than for the NOx conversions. In addition, the starting conversion at 200 °C was also found to be higher on the first cycle in comparison to the others. However, the NH3 conversions followed the same tendency along all the three cycles on both kinds of soot (contrarily to the results observed on Figure 7.32). In comparison to the 3 cycles Fast SCR reaction in absence of soots, in soot presence the NH3 conversion was not complete as already remarked on the single Fast SCR reaction (Figure 7.30). equimolecular Fast SCR reaction or NO conversion by Reaction 14, yielding more N2O formation. Again, NO formation above 425 °C was observed with the Printex U soot. Drop on the N2 selectivity was consequently observed at the same temperature range as a result of the NH3 oxidation or by the NO/NO2 equilibrium from the injected NO2 (Reaction 20).

NO2-SCR reactions

Finally, the influence of the soot presence was completed under the NO2-SCR conditions (Table 7.10). It is reported to be the "slowest" SCR reaction [9,16] and it consists on introducing NO2 in excess on the reactive system. Again, a single NO2-SCR will be simulated and, later, 3 cycles NO2-SCR will be done to analyse the reproduciblity of the catalyst activity under these conditions. As a consequence, Reaction 9 and 10 (Annex B) are expected to take place. As it was already observed on NO2-SCR reaction without soot (Test 10, Figure 7.19), very similar conversion curves were obtained for the NO2 and NH3 with both soots. As it can be observed on Figure 7.35, the NO2 conversions of real Diesel soot and Printex U soot started around 15% at 200 °C. Later, they continuosly increased with temperature until 500 °C were maximum values of 85% were reached for both soots.

Compared with the NO2 conversions obtained in presence of soots under Fast SCR conditions, they were 10% smaller [22].

Referring to the NH3 conversions of real Diesel soot and Printex U soot, they started from 10% and 15%, respectively at 200 °C. Then, they increased until 500 °C where maximum conversion values were obtained, being 90% for the real Diesel soot and 95% for Printex U soot. It is necessary to remark that higher NH3 conversion was always obtained for the Printex U soot above 400 °C, indicating that it was especially sensible to NH3 oxidation reaction.

In comparison to the NO2-SCR reaction without soot (Figure 7.19), both NO and NH3 conversions obtained were smaller than in soot presence (75 and 85%, respectively) [4].

It might be concluded that the soot presence catalysed the NO2-SCR reaction [23]. Also, higher consumption of NO2 was expected in presence of soot due to the passive soot oxidation reaction. On following Figure 7.36 it will be discussed the NOx and N2 formation in soot presence under NO2-SCR conditions. This would help to better understand the mechanism that yields a higher NO2 and NH3 conversions in presence of soots. As it can be observed, very similar behaviours were produced and overlapped byproducts formation were obtained with both soots. On the low-medium temperature range, N2O formation was produced, reaching a maximum of 20% of selectivity at 300 °C on both cases. This N2O formation could be related to the non-selective NO2-SCR reaction by means of Reactions 13 or 14 mechanims. An important NO formation was observed from 250 until 500 °C where maximum formation was produced, reaching 20% of selectivity with both kinds of soot.This NO formation on the low temperature range (250-400 °C) might be related to the passive soot oxidation by NO2 following Reaction 4 mechanism (Annex B) [9]. Later, above 400 °C this NO formation became more important. If taking into account the small NO formation already obtained on Fast SCR conditions (Figures 7. 21 and 7.34), this seem to indicate that NO formation was related to the presence of NO2 on the feed gas composition. Thus, NO/NO2 equilibrium reaction (Reaction 20) might also contributed of this NO formation above 400 °C. This NO formation was not observed in absence of soots (Figure 7.20) and, contrarily to the other SCR conditions, here lower N2O formation was registered at the same temperature value [23]. This confirmed that the NO2 in presence of soots was being consumed to passively oxidize them while in soot absence it was only converted on the unselective NO2-SCR reaction, yielding N2O [9]. It can be concluded that the soot presence in excess of NO2 produced a positive effect on the NO2 and NH3 conversions as well as in the N2O selectivity [9,18,19,21,24]. Soot lowered the N2O formation between 250-400 °C [1] due to the passive soot oxidation that converted NO2 to NO [9]. This shifted the actual NO/NOx ratio to a more favourable value closer to the optimal 0.5 ratio [12,19,21,22] of the Fast SCR reaction. This was in agreement with various authors in the literature who also observed that NOx reduction improve due to the soot loading [2,9,19,21]. Around 20% of selectivity on the N2O formation was obtained durting the first cycle; however, it increased to 35% on cycles 2 and 3 (with both soots). This effect was already subtly remarked in NO2-SCR reaction on absence of soot discussed on Figure 7.22 but in soot presence was more significant. This might be related to the NO2 consumption due to the passive soot oxidation during the first cycle (in competition with the SCR reaction) [19,21] at the medium temperature range. Once the soot was oxidized, the contribution of the non-selective NO2-SCR reaction was higher and, thus, higher proportion of NO2 was converted to N2O [11,22]. It can be concluded that under NO2-SCR conditions with soot presence, the passive soot oxidation succesfully competed with NO2 selective reduction Looking into the NO formation between 250-400 °C it can be observed that, effectively, a decrease in the NO formation happened along cycles due to the lower soot presence on the system. However, above 400 °C the tendency was inverted and more NO was formed on cycles 2 and 3. This could be explained by the fact that the NO formed at high temperature was not dependant of the passive soot oxidation but of the NH3 oxidation (Reaction 19) and NO/NO2 equilibrium (Reaction 20). Higher NO formation above 400 °C was also produced on the 3 cycles Fast SCR (Figure 7.34).

Conclusions of soot influence

As previously did on the 7.3 section, first isolated NH3 oxidation reaction was studied and, then, the three different SCR reactions were realized in presence of both soots in order to complete the study of the influence of soot over the NH3-SCR activity. Main difference found under these conditions was that complete NH3 conversion was enhanced by real Diesel soot (due to the Fe content which enhanced NH3 oxidation [2]) while NH3 oxidation was inhibited by the commercial Printex U soot. This is considered as a positive effect as certain NH3 was still available to reduce NO. In agreement with the physicochemical characterization results (CHNS and TGA analysis) discussed on Chapter 5, real Diesel soot showed more reactivity than the commercial soot. In reference to the products formed in this test, only negiglible amount of N2O was formed before 300 °C without soot. In contrast, with the Printex U soot around 10% of NO was formed from 250 °C. With the real Diesel soot, significant N2O formation (20% of selectivity) and small NO2 formation occurred around 350 °C. Accordingly to conversion curves, the real Diesel soot was confirmed to be more reactive and to promote by-products formation when intereacting with NH3.

Regarding the Standard SCR conditions, NO conversion in presence of both soots was found to be 10% higher than in soot absence. Referring to the NH3 conversion it was completeted in soot absence and limited (≈ 80%) by the presence of both kinds of soot. Discusing about the selectivities, in soot absence only negliglible N2O formation was obtained above 400 °C due to the NH3 oxidation competition (Reaction 21). As previously observed, in presence of soot the by-products formation was promoted (Printex U soot produced higher N2O formation (25%).

Moving to the Fast SCR reaction, main influence of both kinds of soots was that the NO conversion was found to be quite limited (40%) in comparison with the soot absence results (75%) [12,22]. This might be caused by the competition for NO2 which was being consumed on the passive soot oxidation [19,21]. This produced partial Fast SCR reaction (Reactions 13 and 14). As already discussed with Standard SCR, without soot complete NH3 ocurred while it was limited with soots (only 75%). Talking about the products formation, again the presence of soot increased the by-products formation: without soot only negligible amount of N2O was obtained below 200 °C due to the NH4NO3 decomposition. In presence of soot a higher formation (10%) was produced above 350 ºC for both soots as well as certain NO formation (12%) above 450 ºC with the Printex U soot (as a result of the passive soot oxidation reaction).

If compared with the Standard SCR conditions, much lower N2O formation was produced on Fast conditions. Furthermore, Fast SCR conditions was the best performing SCR reaction in terms of NOx conversions [9]. Both effects indicated that it was the most selective and effective NOx reduction between the SCR reactions [2,9,15].

Finally, NO2-SCR reaction was also analysed in presence of both kinds of soot with the aim to complete the study of the soot influence on the NH3-SCR catalyst activity. Higher conversions were obtained in soot presence in comparison with the results obtained in their absence, indicating a positive effect on the deNOx activity due to the presence of soots. Contrarily, higher N2O formation was produced without soot (30% of selectivity). In addition, significant NO formation from 250 ºC was produced with both soots. This NO formation might explain the lower N2O formation in soot presence: the NO2 was not only being selectively reduced (Reactions 9 and 10) but also consumed on the passive oxidation of soots, yielding NO (Reaction 4). This produced less N2O formation as NO2 was being consumed in a competitive way [1,9,19,24].

To sum up, some authors as Guan et al. [4] observed same tendency: at low NO/NOx ratios, (Standard SCR) at any soot inhibition was produced on NOx reduction. Contrarily, at NO/NOx=0,5 the soot presence limited the Fast SCR reaction as the NO2 was being consumed on the passive oxidation of soots. Furthermore, at high NO/NOx ratios (NO2-SCR) an positive increase on the NO2 conversion was observed in presence of soots [9,18,22]. This was related to the passive oxidation activity in the soot layer, reducing the NO2/NOx ratio to optimal 0,5 value [12,19,21,22]. It is clear that the impact of soot over the deNOx activity is strongly influenced by the NO2/NOx ratio [13].

Finally, all the three 3 cycles SCR reactions without soots showed overlapped and reproducible conversions and product selectivities when soot was not present in the reaction environment. However, in reference to the 3 cycles SCR reactions in presence of both soots, same effect was obtained on the three different SCR reactions: first cycle showed different tendencies and values in the conversions and selectivities with respect to the other two cycles (which were more similar between them). This was related to the soot combustion during the first cycle which produced evolution of the catalyst activity on cycles 2 and 3. Under Standard SCR conditions, the by-products formation decreased with cycles as soot was oxidized and did not promoted unselective reactions. However, under Fast and NO2-SCR conditions, the contrary tendency was registered: by-products formation increased with cycles 2 and 3. This was explained by the passive soot oxidation competition during first cycle which consumed NO2 otherwise reduced on the SCR reaction [19,21]. Later, on cycles 2 and 3, soot was consumed and NO2-SCR mainly obtained a higher importance yielding higher amounts of N2O.

INFLUENCE OF NO/NOx RATIO ON PM OXIDATION

In this section, the CO and CO2 emissions during the soot passive and thermal oxidations are going to be discussed in function of the operational conditions. Evaluation of the impact of NOx as oxidizing species on the combustion of soot will be made and discussed. For that purpose, set of soot combustion experiments in the presence varying the NO/NOx ratio were performed.

NH3 oxidation: real Diesel and Printex U soots (Tests 14 and 15)

The first investigated conditions involved O2 as the only oxidant agent present in the catalytic system. NH3 oxidation conditions were reproduced in presence of the real Diesel soot and the commercial Printex U. As previously discussed on Figure 7.24 (selectivities of NH3 oxidation reactions with soots), certain NO and NO2 formation were measured on the medium temperature range. Consequently, on Figure 7.39, it can be observed that considerable amounts of CO2 were produced [1] between 300-425 ºC, probably due to the presence of volatile compounds in the soot [9]. Also under NH3 oxidation conditions, Tronconi et al. [1] observed that COx peaks recorded shifted to lower temperatures, suggesting that NH3 had some positive effect on the pure O2-based soot oxidation that needs be elucidated. Contrarily, any CO formation was produced in presence of any of the tested soots during the whole temperature window [1,20]. With both soots, the CO2 formation started at 300 ºC and produced a peak of about maximum 90 ppm around 375 ºC. Later, above 450 ºC an increase in CO2 emissions appeared, reaching a maximum of 160 ppm at 500 ºC [1] for the Printex U and barely 40 ppm for real Diesel soot. Tronconi et al.

[1] also evaluated the effect of NOx on soot oxidation in presence of a Cu-zeolite catalyst. They also used a catalyst-soot ratio of 10:1 as it was chosen in this thesis [9]. They also observed that higher temperatures enabled a rapid increase of the soot oxidation rate with an intense production of CO2 [9]. This might suggest that two soot oxidation mechanisms were produced in function of the temperature range: the step above 425 ºC was related to the thermal (active) soot oxidation by Reaction 1 (Annex B) [11]. And the peak at lower temperature seemed to coincide with the start of the NH3 oxidation and the products formation. As NO2 was formed during the procces, it might be possible to considered that also passive soot regeneration was happening by Reaction 4 [1,21,25]. Here were presented the concentration measures obtained both during the increasing and decreasing ramps of temperature with both soots. As it was previously noticed, only CO2 was formed [1] and any CO was registered [12]. Very similar increasing and decreasing CO2 emissions were obtained with both kinds of soot. Slightly higher concentration was produced with real Diesel soot due to its more reactive character remarked on Chapter 5. Ais it can be observed on Figure 7.40, during the increasing ramp the CO2 formation started above 450 ºC and reach maximum concentrations of 45-50 ppm at 500 ºC [9]. During the decreasing ramp CO2 was still emitted until 475 ºC but in lower amounts compared to the increase. It consisted on 25 ppm after the 30 min plateau at 500 ºC and then, dropped until zero. Here on Standard SCR conditions no NO2 formation was detected (Figure 7.26) and because of this it can be concluded that the only origin of the CO2 formation was the thermal soot oxidation by Reaction 1 (Annex B) mechanism. In the case of the real Diesel soot, the addition of NO did not affect the active soot oxidation [26] as CO2 formation was comparable with the observed in the absence of NO [1,9,25]. In contrast, the CO2 formation above 425 ºC from the Printex U soot was quite limited (40 ppm) in comparison to the obtained in absence of NO (160 ppm). It is necessary to remark that Standard SCR conditions allowed to determine that NO is unable to interact/react with soot [1].

Standard SCR: real Diesel and Printex U soots (Tests 16 and 17)

To simplify the discussion, the evolution of the CO and CO2 emissions during the 3 different cycles performed in soot presence under Standard SCR conditions was not presented on a Figure. This decission was made as CO2 was only obtained during the increasing and decreasing ramps of the first cycle (as already presented on Figure 7.40), then it was not measured anymore. This confirmed that, effectivley, soots were completely thermally oxidized on the first cycle [12,20]. This explained the different behaviour of the catalytic system on cycles 2 and 3 as previously discussed on Figures 7.28 As previously obtained for NH3 oxidation and Standard SCR reactions, any CO formation was produced. However, on Fast SCR conditions CO2 emissions were registered from the beginning of the test at 200 ºC. It can be observed that much higher soot oxidation activity in the low temperature region under Fast SCR conditions [9,27]. Due to the temperature range where CO2 started, it might be attributed to passive soot regeneration by the NO2 injected in the feed gas [1,21,25] following Reaction 4 mechanism (Annex B).

As it can be observed, higher CO2 emissions were detected with the real Diesel soot in comparison to the commercial soot but tendencies remained mostly the same until 400 ºC. In both cases, CO2 formation started at 200 ºC and increased until 400-425 ºC were maximum concentrations were obtained: 50 ppm for the Printex U soot and 60 ppm for the real Diesel soot. Contrary to other authors in the literature [1] (who still observed the COx peaks were at high temperatures), above 425 ºC, CO2 emissions started to decrease. This would mean that thermal soot oxidation was still active above 400 ºC [11] but it played a secondary role since most of the soot had been already oxidized by NO2 at lower temperatures. It is remarkable that any emissions were produced during the decreasing ramps of both kinds of soot, indicating that soot was already consumed during the increasing ramp and 500 ºC plateau [20]. This would also affect the 3 cycles Fast SCR soots as first cycle will be in presence of soots and cycles 2 and 3 not As NO2 in excess was present, CO2 formation was produced from the beginning of test and the decrease from 400 ºC was produced. Under NO2-SCR conditions, the lowtemperature passive soot oxidation was greater than in Fast conditions (Figure 7.41) [1,9,27]. Furthermore, the soot oxidation was already completed at 500 °C and CO2 peak related to the active thermal oxidation was not obtained. This indicated that passive soot oxidation under NO2-SCR conditions was able to fully oxidize the entire soot load before the O2-active oxidation became active [9,28].

In addition, similar curves and tendencies for real Diesel and Printex U soots, especially between 300-400 ºC. Maximum CO2 formations were obtained around 350 ºC, being 55 ppm for both soots. A previously mentioned for Fast conditions (Figure 7.41), any CO2 formation was obtained during the decreasing ramp. Also, on the 3 cycles NO2-SCR reactions, soot disappeared at cycle 1 [20] and it was not present on cycles 2 and 3 which also affected the increase of the by-products formation (Figures 7.37

Conclusions effect NO/NOx ratio on soot oxidation

Main conclusions obtained from the soots oxidation under different feed gas compositons indicated that in absence of NO2 on the feed gas, only thermal oxidation of soot ocurred above 400 ºC (Reaction 1) [11]. Standard SCR results indicated that the soot combustion was essentially unaffected by the presence of either NO or NO+NH3 [11,21], indicating that neither NO nor NH3 participate in soot thermal combustion [9]. In contrast, under Fast and NO2-SCR conditions, where NO2 was present, quite important passive soot oxidation happened on the low-medium temperature range while fewer emissions were produced above 400 ºC. This seemed to indicate that NO2 was able to fully oxidize the entire soot load by passive oxidation reaction (Reaction 4), so that the thermal soot combustion pathway was not necessary at high temperature range.

In addition, reffering to the mechanisms of the soot oxidation depending on the temperature range, it was concluded that the two kinds of soot oxidation (active and passive) were happening on the Cu/SAPO-34 + cordierite + soot layer systems at different temperature windows depending on the NO/NOx ratio used.

CONCLUSIONS

This chapter presents the catalytic evaluation of the in-lab synthesized Cu/SAPO-34 zeolite mixed with commercial cordierite and coated with a soot layer, when necessary. Based on the literature, catalytic tests were performed on temperature window between 200-500 ºC. The complete catalytic system was composed by various materials which could have a separated influence over the total system behaviour and, also, the SCR mechanism itself is quite complex (as various kinds of reactions take place in a competitive way). For this reason, the strategy followed consisted in firstly evaluate each different component of the catalytic system under Standard SCR conditions in an isolated way. Then, it was decided to determine the influence of the NO/NOx ratios on the NH3-SCR activity of the catalyst in absence of soots. Later, the influence of the presence of soot under the previously performed conditions was analysed. Two kinds of soot were used and compared: a real Diesel soot and a commercial Printex U soot. Differences on the behaviour between them was discussed and compared with the catalyst behaviour in soot absence.

First, only the commercial cordierite was studied under Standard SCR conditions. The aim was to verify its inert nature and any NOx reduction was expected to occur. Main conclusions obtained were:

Standard SCR reactions were performed using a feed gas composed by 1000 ppm NO, 1000 ppm NH3, 8% O2 and 3% H2O using He as balance. Again, Standard SCR reaction was performed in absence and presence of both soots. Main conclusions were:

In agreement with NH3 oxidation results, the soot presence decelerated the NH3 oxidation and produced slightly higher NO conversions (not necessarily selective).

Low Then, the reproducibility of the catalyst activity was evaluated by performing 3 continuous cycles of the Standard SCR reactions over the same catalyst (in soot presence and absence):

In Test without soot, overlapping conversions and selectivity curves were obtained on the three cycles; whereas, in presence of soots, the first cycle showed a different behaviour than the other two (more similar between them).

N2O formation decreased and shifted to slightly higher temperatures on cycles 2 and 3. This might be explained by the thermal soot oxidation produced on cycle 1 which produced a catalytic system evolution as well as different catalytic behaviour. As N2O formation was produced by the soot influence, on cycles 2 and 3 it decreased.

Regarding the CO2 emissions obtained along the three cycles, thermal soot oxidation was confirmed to completely burn the soots during the first cycle.

Later, Fast SCR reactions were realized using a feed gas composed by 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2 and 3% H2O using He as balance. Again, Fast SCR reaction was performed in absence and presence of both soots:

Without soot, the NO conversion was much higher than the obtained with Standard conditions, this was in agreement with literature that settled Fast as the most active and selective NOx reduction reaction. However, in presence of soot very poor NO conversion was produced. In all cases, very high NO2 conversion was produced, indicating that nonequimolecular amounts of NO and NO2 were converted as expected from Fast SCR. In the case of soot absence, this effect was less pronounced and almost pure Fast SCR occurred; whereas, in presence of soot much higher NO2 conversion was caused by its competitive consumption in the Fast SCR and the passive oxidation of soot.

This also would explain the lowest NH3 conversions obtained in presence of soot in the medium temperature range.

In agreement with NH3 oxidation and Standard SCR results, without soot only a very small amount of N2O was formed as selective Fast took place. But in presence of soot, higher by-products formation was promoted.

Here on Fast SCR conditions, CO2 formation started from the beginning at 200 ºC on both soots. Real Diesel soot formed higher amount of emissions comparing to the Printex U soot. Maximum CO2 concentrations were produced at 375 ºC, being 50 ppm and 60 ppm, respectively and they were related to the passive soot oxidation by NO2 (Reaction 4). Curiously, above 400 ºC, emissions started to decrease, meaning that small contribution of thermal soot oxidation happened.

Then, the reproducibility of the catalyst activity was evaluated by performing 3 continuous cycles of the Fast SCR reactions over the same catalyst (in soot presence and absence):

In the 3 cycles Fast SCR test, same effects than in Standard SCR conditions were observed: without soots all conversion selectivity curves were overlapped; while in presence of soots, first cycle showed different conversion values and tendency than the two other (almost overlapped between them). Especially, in the case of NO conversion.

Also, the shifting effect on conversion and by-products peaks was again detected on Fast conditions.

However, by-products formations in Fast SCR showed contrary tendency than in Standard SCR: it increased with cycles as NO2 was not being converted on passive oxidation of soot but on the SCR reaction.

Regarding the CO2 emissions obtained along the three cycles, passive soot oxidation was confirmed to completely burn the soot during the first cycle.

Finally, the NO2-SCR reactions were realized using a feed gas composed by 1000 ppm NO2, 1000 ppm NH3, 8% O2 and 3% H2O using He as balance. Again, NO2-SCR reaction was performed in absence and presence of both soots. Main conclusions were:

NO2 conversion obtained in all cases was smaller than in Fast SCR conditions as NO2-SCR is considered on the literature the slowest SCR reaction. As before, in presence of soot slightly higher conversions were produced. However, smaller N2O formation was obtained in presence of soot for the first time (contrarily to Standard and Fast conditions). This could be explained by the competitive NO2 consumption by passive oxidation and SCR reactions. This was confirmed due to significant NO formation occurred from 250 ºC only in presence of soot due to the passive soot oxidation (Reaction 4).

In agreement with Fast SCR tests, here on NO2 excess conditions, CO2 formation started from the beginning with both soots. Maximum CO2 concentrations were produced at 350 ºC, being 55 ppm on both soots and they were related to the passive soot oxidation by NO2 (Reaction 4). Curiously, above 400 ºC, emissions started to decrease, meaning that small contribution of thermal soot oxidation happened and the passive oxidation of soots was sufficiently efficient itself.

Reproducibility of the catalyst activity was also evaluated by 3 cycles of the NO2-SCR reactions in soot presence and absence:

Same effects than in the previously commented Fast SCR reaction were observed: the different catalytic behaviour during the first cycle and the shifting effect on the by-product peaks. As well as the increasing byproducts formation along cycles due to the competition by NO2 on cycle 1 which was not produced on cycles 2 and 3. Only NO2-SCR reaction occurred on cycles 2 and 3, yielding N2O. In the literature it is reported that N2O is promoted by excess of NO2. Consequently, in comparison to Fast SCR, the highest N2O formation was obtained under NO2-SCR conditions.

WORK CONCLUSIONS

This chapter summarizes the main problematic of the current NH3-SCR aftertreatment technology on Diesel exhaust lines as a consequence of the constant evolution of the Euro standards. Based on this review of the current literature available and the comprehension of the challenges to overcome, the objectives and the strategy of the thesis were established.

In addition, this chapter listed the main conclusions derived from the research performed in this PhD work.

Particulate matter (PM) and NOx are considered pollutants of major concern related with Diesel engines as they are released in quite big amounts to the atmosphere and they cause severe environmental and human health issues. Due to these adverse effects, since the 90's the european authorities progressively restricted the permissible exhaust emission levels by developing the be-named "Euro" standards which have continuously become more and more stringent.

As a consequence, vehicule manufacturers are forced to develop new technologies in order to reduce pollutant emission from vehicles and fulfill new government regulations. The studies that have been carried out for decades allow to conclude that the desired emission levels can be only achieved by aftertreatment means. A typical Diesel emission control system includes a Selective Catalytic Reduction (SCR) unit, which allows to reduce NOx by means of NH3 as reductant agent; and it also includes a Diesel Oxidation Catalyst (DOC) and a Diesel Particulate Filter (DPF) in order to oxidize the emissions of carbon monoxide, hydrocarbons and PM, respectively. Nowadays, metal-exchanged zeolite catalysts have been applied on mobile applications because of their high thermal stability and high NOx reduction activity over a wide range of conditions. Specially, considerable advancement was recently achieved when the Cu/Fe were exchanged into small-pore zeolites with a CHA structure, such as Cu-SSZ-13 and Cu-SAPO-34. Compared to Cu-ZSM-5 (MFI) and Cu-BEA, they have been found to be more active and selective, and less sensitive to deactivation and thermal degradation.

In order to be prepared to the upcoming Euro 6c and the new WLTP (Worldwide harmonized Light vehicles Test Procedure) procedure, the aftertreatment systems that combine various functionalities into the same catalytic unit have been proposed as alternative. They are able not only reduce the intrinsic costs and the packaging volume but also promote catalytic reactions by thermal and synergistic effects. This concept is particularly useful in the case of Diesel engines, whose exhaust line may comprise already up to four separate elements. One of the more studied combined configuration is the SCRF (Selective Catalytic Reduction on Filter) system, in which the catalysed soot filter assumes two functions: removal of the particles and reduction of the NOx species to N2 and water. Regarding the active phase, the SCR catalyst is conventionally deposited onto the walls of a honeycomb substrate whose channels are blocked at alternative ends. However, an increased porosity of the filter substrate (such as cordierite or SiC) is required to allow the deposition of sufficient amount of catalyst phase needed for the treatment of gaseous emissions without producing a backpressure effect. Again, the small pore zeolite-based formulations offer an interesting potential due to their high thermal stability and hydrothermal resistance.

However, it is necessary to remark that this new system comprises new reactions not happened until now as Diesel soot, NOx and the reductant agent are present in the same unit for the first time. Accordingly to literature currently available, there are three main ways that NOx pollutants and soot may interact: 1) soot blocking the accessibility of gas flow to "classic" active sites of the zeolite; 2) possibility of NOx reduction takes place over the soot particles; and finally, 3) soot presence affects SCR reactions performance or, contrarily, SCR reactions affects PM oxidation process as far as competition for NO2 will be produced. To sum up, this SCRF configurations would lead to competition between the reduction and oxidation reactions produced simultaneously on the same catalytic unit. Agreement in the results obtained by various authors about the influence of soot presence on the SCR reactions or the NOx and NH3 effect on PM oxidation have not been reached until now.

Hence, the goal of this thesis was decided to be focused on the evaluation of the reactive behaviour of the new SCRF configuration under different SCR conditions both in soot absence and presence. Information about the catalytic behaviour of the system was completed and linked to a set of textural and physicochemical characterizations of two kinds of soot (a real Diesel soot and a commercial Printex U) and of the reference catalyst. Thus, the approach followed in this thesis consisted of deeply understanding the very complex catalytic phenomena that happen while the SCR reactions were produced. This approach was based on two main issues: firstly, to study the reactive NH3-SCR behaviour of a SCRF catalyst under SCR gas mixtures. Secondly, once the catalytic system was already characterized and evaluated itself, the SCR-soot interactions were investigated. More specifically, the availability of NO2 for passive soot oxidation was especially considered.

In a first stage of the thesis a commercial mini-SCRF sample supplied by an industrial company was stablished as reference (Chapter 4 and Annex D). It consisted on a 1"x 3" inches cordierite filter washcoated with a Cu-zeolite. It allowed simulating at gas bench scale (IFPEN) the real life conditions of a Diesel exhaust line and a real SCRF system. By XRD with another analysis, it was determined that it consisted on a pure phase of Cu/SAPO-34 zeolite. This zeolite framework type was chosen due to their suitable acid properties, high hydrothermal stability and selectivity towards N2 on a wide operational range (200-500 °C).

In a first step it was decided to evaluate the NH3-SCR behaviour of this commercial mini-SCRF sample in absence of soot. The main reason was that this new configuration implies different washcoat introduction methods than the conventional SCR monoliths, among other operational differences. And it was necessary to verify that the mini-SCRF sample obtained comparable NH3-SCR activity and selectivity to the conventional SCR catalysts.

The experimental strategy followed at IFPEN for the test serie with the mini-SCRF system consisted of separately studying each one of the reactions that takes place simultaneously during SCR reactions in a Diesel exhaust. Simple NOx/NH3 tests (in O2 absence) stablished that any NOx reduction happened without Diesel lean conditions due to redox mechanism of the active sites was not completed. In this system, the SCR reactions showed competition with NH3 oxidation at T< 350 °C and after 400 ºC, the NH3 was fully consumed. Importance of the NH3 oxidation reaction might be related to the presence of Copper oxides species on the surface of the zeolite observed by EDX and XRD analysis. Moreover, it was observed that all NO2-based reactions performed incomplete NO2 reduction yielding N2O. Both effects were reported by various authors in the literature who also studied Cu/SAPO-34 + cordierite catalysts.

Nevertheless, the main conclusion obtained from Chapter 4 was that a remarkable deactivation of the reference mini-SCRF catalyst occurred after a few reactions. For that reason, the last performed reaction showed very low NOx conversion (barely reaching 50%).

Even when it was a Fast SCR reaction which was expected to be the most active one according to the literature. Activity degradation was confirmed by repeating two Standard SCR tests over the sample and the NOx conversion continued decreasing. At the end, the mini-SCRF sample barely reached a NOx conversion of about 30% in comparison to almost the 95% conversion reached when fresh. As industrial supplier asked to be returned the deactivated sample, physicochemical characterization of the deactivated sample could not being done. This characterization would have given strategic information about the origin of the deactivation: copper species migration from the zeolite sites to the cage, zeolite framework collapse, hydrothermal aging, fragility of the active sites, etc. Anyway, the mechanism of deactivation remained unclear but it was suspected that the very oxidant and highly hydrothermal conditions collapsed the commercial catalyst framework.

For that reason, it was decided to re-orientate the thesis approach was necessary to be made in order to being able to continue the investigation. At this point, it was decided to synthesize at the IRCELYON laboratory a SAPO-34 zeolite and impregnate it with a Cu nitrate aqueous solution. Then, the Cu/SAPO-34 catalyst was mixed with a commercial cordierite support to emulate the real SCRF catalyst and the commercial mini-SCRF sample previously used as reference. Apart from that the main objectives of the thesis as well as the experimental approach remained the same: the study of the physicochemical characterization of the new synthesized catalyst (Chapter 5) was coupled with its catalytic evaluation (Chapter 7). Again, the NH3-SCR activity and selectivity of the in-lab synthesized catalyst was firstly evaluated in absence of soot and later, in presence of a soot layer. Due to fluidity reasons, the conclusions of the set of tests performed over the synthesized Cu/SAPO-34 catalyst at IRCELYON labscale system will be discussed separated by reaction type and including both soot presence and absence.

Catalytic evaluation took place mixing the in-lab synthesized Cu/SAPO-34 with a commercial cordierite substrate in a 1:5 proportion. Then, (when necessary) a layer of soot was deposited on top of the previous mixture with the aim of simulate the real soot deposition on the SCRF filter on Diesel exhausts. Proportion Cu/SAPO-34/soot was fixed as 10:1 as it was used by some authors in the literature who studied similar catalyst systems under similar operation conditions. Strategy followed was similar that in the case of the commercial mini-SCRF sample: complexity of the catalytic system was increased step by step. First, the different components that formed the catalytic system were separately evaluated under Standard SCR conditions (as reference). Then, the NH3 oxidation was studied over the complete catalytic system (Cu/SAPO-34 + cordierite) and later, the three different NOx reduction reactions (benamed as SCR reactions) were realized. Finally, a layer of soot was added to the system and the NH3 oxidation as well as the three SCR reactions were repeated in soot presence. Two kinds of soot were evaluated: a real Diesel soot obtained from an engine bench at IFPEN and a commercial Printex U soot. Difference on the behaviour between them was discussed and compared with the catalyst behaviour in soot absence.

First of all, the commercial cordierite alone was analysed under Standard SCR conditions to verify its inert nature. In this study, only thermal NH3 oxidation was expected to be registered. Effectively, in soot absence, only NH3 conversion took place >350 °C, mainly yielding N2 (Reaction 18, Annex B) but also a considerable amount of NO (Reaction 19) and some N2O (Reaction 21). All these by-products were formed due to the thermal NH3 oxidation, consequently, cordierite support was considered to be inert. Later, this test was reproduced twice in presence of a layer of each soot (but still in absence of catalyst on the system) and it was observed that soot inhibited the NH3 oxidation. A small non-selective NO conversion was produced, yielding significant N2O formation (Reaction 14). Just with the Printex U soot, a small amount of NO2 above 400 °C (Reaction 20) was also registered. Contrarily to the physicochemical characterisation of soots (Chapter 6), the commercial Printex U was observed to be the more reactive and enhancing the by-products formation. Regarding the soot oxidations, only CO2 was produced with both soots above 375-400 ºC, indicating that only thermal (active) soot oxidation occurred (Reaction 4). It can be concluded that NO did not interacted with soot as reported in the literature. These soot oxidation results were in agreement with results obtained from the TGA analysis of both soots where 400 °C was the starting temperature of the soot combustion reaction. Contrarily, mass spectrometer coupled to TGA analysis showed that only CO formation was produced as a consequence. Apparently, the presence of NOx and NH3 on the feed gas privileged the Reaction 4 mechanism followed during the soot combustion. Later, the complete Cu/SAPO-34+cordierite system was evaluated under NH3 oxidation conditions, both in soot presence and absence. Without soots, complete NH3 consumption was produced at 420 ºC and the main product was N2 (Reaction 18). However, soot was found to inhibit the complete NH3 consumption as complete oxidation was not reached even at 500 ºC. The real Diesel soot was found to be especially reactive as significant N2O and NO2 formation was promoted. Due to the NO absence, the origin of these by-products seemed to be related with the interaction between NH3 and soot. Referring to the CO2 emissions, both passive (300-400 ºC) and thermal soot oxidation (>400 ºC) were produced.

Later, the NO/NOx ratio influence on the catalyst behaviour was evaluated. First, all the three different SCR reactions were evaluated without soots and, then, they were repeated in soot presence to complete the study of the soot influence on the deNOx activity of the catalyst.

First, a Standard SCR reaction was realized. In agreement with NH3 oxidation results, the soot presence decelerated the NH3 oxidation and produced slightly higher NO conversions. Again, considerable N2O formation (Reaction 14) was only obtained in presence of soots due to the non-selective NO conversion. CO2 formation only took place above 400 ºC due to the thermal soot oxidation (Reaction 4) with both soots. Then, the reproducibility of the catalyst activity was evaluated by performing 3 continuous cycles of the Standard SCR reactions over the same catalyst (in soot presence and absence). In test without soot, overlapping conversions and selectivity curves were obtained on the three cycles; whereas, in presence of soots, the first cycle showed a different behaviour than the other two (more similar between them). NOx and NH3 conversions as well as a N2O formation decrease was registered on cycles 2 and 3. This was explained by the thermal soot oxidation on cycle 1 which reduced the catalyst activity and the promotion of N2O formation.

Regarding the CO2 emissions obtained along the three cycles, thermal soot oxidation was confirmed to completely oxidize soots during the first cycle, as any CO2 emission was measured on cycles 2 and 3. Thermal soot oxidation was unaffected by the NO or NO+NH3 presence.

Later, Fast SCR reactions was performed in absence and presence of both soots. Without soot it was observed that the NO conversion was much higher than the obtained with Standard conditions. However, in presence of soots very poor NO conversion was produced as NO2 consumption on the passive soot oxidation was the preferred pathway instead of the NOx reduction. This was confirmed by the very high NO2 conversion obtained, indicating that non-equimolecular amounts of NO and NO2 were converted. In agreement with previous results, without soot only a very small amount of N2O was formed as selective Fast took place; whereas with soots by-products formation was promoted. On Fast conditions, CO2 formation started from 200 ºC on both soots. Maximum CO2 concentrations were produced at 375 ºC and they were related to the passive soot oxidation by NO2 (Reaction 4). Curiously, above 400 ºC, emissions started to decrease, meaning that only a small contribution of thermal soot oxidation took place.

Then, the reproducibility of 3 cycles of the Fast SCR reactions without soots showed overlapped curves; while in presence of soots, first cycle was different comparing to others. CO2 emissions indicated that passive soot oxidation completely oxidized the soots during the first cycle.

Finally, in the NO2-SCR reactions, the NO2 conversions in all cases were smaller than in Fast SCR. Again, in presence of soots higher conversions were produced. However, smaller N2O formation was obtained in presence of soots. This could be explained by the competitive NO2 consumption by passive oxidation and SCR reaction. This was confirmed due to significant NO formation formed above 250 ºC only in presence of soots due to the passive soot oxidation (Reaction 4). On NO2 excess conditions, CO2 formation started from the beginning on both soots. Maximum CO2 concentrations were produced at 350 ºC and they were related to the passive soot oxidation by NO2 (Reaction 4). It was concluded that the passive oxidation of soots was sufficiently efficient itself. Reproducibility of the 3 cycles showed an increase of the by-products formation along cycles due to the competition for NO2 was not produced on cycles 2 and 3 anymore. The, NO2 was available to being consumed on NO2-SCR reaction on cycles 2 and 3, yielding N2O (Reactions 13 and 14).

To sum up, the influence of the NO/NOx ratio on the deNOx activity of the catalyst without soots showed that the Standard SCR presented the lowest maximum NOx conversion and the Fast SCR reaction obtained the highest NO and NO2 conversions, accordingly to the literature. All the SCR reactions mainly yielded to N2 and N2O formation. However, the most significant N2O formation (30% of selectivity) took place during the NO2-SCR reaction. This high N2O formation was produced by the incomplete reduction of NO2 by means of Reactions 13 and 14.

Referring to the soot loading influence on the catalyst activity it was concluded that: in agreement with the physicochemical characterization results (CHNS and TGA analysis) discussed on Chapter 6, real Diesel soot showed more reactivity than the commercial soot. In presence of soots the by-products formation was promoted. Referring to the NH3 oxidation it was complete in soot absence and limited by the presence of both kinds of soot. At low NO/NOx ratios (Standard SCR) any inhibition was produced on NOx reduction due to the presence of soots. Contrarily, at NO/NOx=0,5 the soot presence limited the Fast SCR reaction as the NO2 was being consumed on the passive oxidation of soots. Furthermore, at high NO/NOx ratios (NO2-SCR) an positive increase on the NO2 conversion was observed in presence of soots. This was related to the passive oxidation activity in the soot layer which reduced the NO2/NOx ratio to optimal 0,5 value. It is clear that the impact of soot over the deNOx activity is strongly influenced by the NO2/NOx ratio. Finally, all the three 3 cycles SCR reactions without soots showed overlapped and reproducible conversions and product selectivities. However, in presence of soots the first cycle showed different tendencies in the conversions and selectivities curves to the other two cycles. Under Standard SCR conditions, the by-products formation decreased with cycles as soot was thermally oxidized and did not promoted unselective reactions. However, under Fast and NO2-SCR conditions, by-products formation increased with cycles. It was explaiened due to the disparition of the competiton for NO2 which privileged the NO2-SCR, yielding higher amounts of N2O on cycles 2 and 3.

Main conclusions obtained from the soots oxidation under different feed gas compositons indicated that in absence of NO2 on the feed gas, only thermal oxidation of soot ocurred above 400 °C (Reaction 1). In contrast, under Fast and NO2-SCR, quite important passive soot oxidation happened on the low-medium temperature range while fewer contribution of the thermal soot oxidation was produced.

In order to complete the study of the interactions and competition between the NOx reduction and the soot oxidation reactions, some suggestions will be done for further works: the influence of the absence of NH3 on the different SCR reactions in presence of soot would give crucial information about the NH3SC capacity of soot particles as well as about its reactivity, study of the influence of various soot loadings (implying different heights of the soot layer) over the deNOx activity of the catalyst, the study of the influence of different Cu loadings in presence of soot and the study of hydrothermal aging of the Cu-based catalyst in presence of soots. Also, the detrimental effect over the gas feed difussion or deNOx activity of remaining ashes on the catalytic bed surface after the soot oxidation may be an interesting parameter to study.

ANNEX A

A serie of catalytic tests have been done using a commercial mini-SCRF sample which consists on a DPF filter coated with a waschoat of Cu-zeolite. This serie is described below:

From test 1 to 15, GSHV= 35.000 h -1 was used and operational method described on 2.5.1 was followed.

The strategy followed during the test series was to start with the simplest reactions that takes place simultaneously during SCR reactions: the NO and NO2 oxidation reactions as lean conditions are typical of Diesel exhausts. Also, NH3 oxidation was studied as this reaction will be in competence with NOx reduction at high temperatures (> 350 °C, usually). Then, complexity was increased step by step. First, the interactions of NOx pollutants with the NH3 were also studied separately. Finally, complete three different SCR reactions will be performed Installation and feed gas were switched off during the night until next day.

Test 6. (500 ppm) NO/O2 (10%) test

-500 ppm NO and O2 (10%) under N2 atmosphere -Test initial temperature started at room temperature conditions.

-Then, temperature was decreased until 80 ºC by N2 flow passage during 2 hours and 30 minutes.

Test 7. Standard SCR test (500 ppm)

-500 ppm NO, 500 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off during the night until next day.

Test 8. (500 ppm) NO2/O2 (10%)

-500 ppm NO and 10% O2 under N2 atmosphere -Test initial temperature was fixed as room temperature. So, N2 passage through reactor was not needed to start test. -After test, temperature was decrease until 80 ºC by N2 flow passage during 2h and 10 min.

Test 10. NO2-SCR test (200 ppm)

-200 ppm NO2, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off during the night until next day.

Annex A

Test 11. (500 ppm) NH3/O2 test (10%)

-500 ppm NH3 and 10% O2 under N2 atmosphere -Test initial temperature was fixed as room temperature. So, N2 passage through reactor was not needed. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off during the night until next day.

Test 12. NO2-SCR test (500 ppm)

-500 ppm NO2, 500 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until 80 ºC by N2 flow passage during 1h and 20 min.

Test 13. Standard SCR test (200 ppm)

-200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off during weekend days.

Test 14. Fast SCR test (200 ppm)

-100 ppm NO, 100 ppm NO2, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition, so N2 flow passed through reactor to reach starting operational test conditions. -After test, temperature was decrease until 80 ºC by N2 flow passage during 1h and 30 min.

Test 15. Fast SCR test (500 ppm)

-250 ppm NO, 250 ppm NO2, 500 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off.

Another two catalytic tests have been done with same nº 1-004 as a powder at IRCELYON. GSHV= 60.000 h -1 was used and operational method described on 4.3. As far as, IFPEn catalyst deactivation tendency was observed as it was detailed on 5.4 part; it was decided to verify the powder catalyst stability under Standard SCR reactions by performing between 200-500 ºC three identical tests (18, 19 and 20) in a cyclic way, that means, without changing the catalyst between tests and keeping always the same sample 1-004. GSHV= 60.000 h -1 was used and operational method described on 4.3.2 was followed.

Test 18, Test 19 and Test 20. Standard SCR test (10000 ppm). Run 1, 2 and 3; respectively

-1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He atmosphere -Test initial temperature was fixed as 200 ºC.

-After test, temperature was decrease until room temperature by He flow passage and installation was kept like this until next test.

To verify mini-SCRF (IFPEn sample) catalytic deactivation, it was decided to perform a new test battery over an old sample (sample 1-004). GSHV= 35.000 h -1 was used and operational method described on 4.2.3 was followed.

Test 21 and Test 22. Stabilisation test Standard SCR conditions (200 ppm). Run 1 and 2.

-200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 200 ºC and all pollutants were injected from the beginning -Temperature decrease under N2 and once, room temperature was reached. Installation and feed gas were switched off during the night until next day.

Test 23. Standard SCR test (500 ppm)

-500 ppm NO, 500 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 80 ºC due to water presence into feed gas composition. -After test, temperature was decrease until room temperature by N2 flow passage.

Installation and feed gas were switched off during the night until next day.

As catalytic deactivation of sample 1-004 was confirmed, it was decided to carry out same stabilisation test under Standard SCR (200 ppm) conditions to two different artificially aged samples called: 5-004 and 6-004.

ANNEX C

A serie of catalytic tests have been done over the in-lab synthesized Cu/SAPO-34 catalyst. To emulate real life system as well as the commercial catalyst reference (Chapter 4 and 5), powdered catalyst was mixed with a commercial cordierite. Total amount of catalytic system that was introduced in the quartz reactor was 60 mg.

GSHV= 135.000 h -1 (corresponding to a gas flow of 10 L/h) was used and operational method described on Chapter 2 was followed.

The strategy followed during the test series was to start with the simplest reactions that takes place simultaneously during SCR reactions such as the NH3 oxidation. This reaction will be in competence with the NOx reduction at high temperatures (> 350 °C). Then, the complexity was increased step by step. First, the interactions of NO pollutant with the NH3 were studied under Standard SCR reaction. Later, NO and NO2 pollutants were introduced in equimolecular amounts to reproduced the Fast SCR reaction. Finally, all the previous reactions were studied in the presence of soot, being the more complex system as competition between the oxidation and reduction reactions will happen.

The performed test serie is described below. It is necessary to remark that catalytic system (cordierite+ Cu/SAPO-34) was substituted by a new one on each test:

Test 1. Empty reactor under Standard SCR reaction conditions (1000 ppm)

-Feed gas composition: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He as balance

Test 13. Cordierite + top layer of Printex U (60 mg) under Standard SCR conditions (1000 ppm)

-Feed gas composition: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was fixed as 200 ºC and all pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 14. NH3 oxidation reaction (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

-Feed gas composition: 1000 ppm NH3, 8% O2 and 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and reactives were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 15. NH3 oxidation reaction (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of Printex U)

-Feed gas composition: 1000 ppm NH3, 8% O2 and 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and reactives were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized.

Annex C -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day. -Feed gas composition: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 17. Standard SCR reaction (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of Printex U)

-Feed gas composition: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 18. 3 cycles of Standard SCR reaction (60 mg:mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

-Feed gas composition: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He as balance

Test 24. 3 cycles of Fast SCR reaction (60 mg:mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

-Feed gas composition: 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200 ºC again, this same cycle was restarted and repeated twice. The aim was to study the reproducibility of the Fast SCR reaction activity.

Test 25. 3 cycles of Fast SCR reaction (60 mg:mixed Cu/SAPO-34+ cordierite and top layer of Printex U)

-Feed gas composition: 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200 ºC again, this same cycle was restarted and repeated twice. The aim was to study the reproducibility of the Fast SCR reaction activity.

Test 26. NO2-SCR test (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

-Feed gas composition: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture.

Annex C -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 27. NO2-SCR test (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of Printex U)

-Feed gas composition: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200ºC, the feed gas and the analyser measure was stopped and the labscale system was set to room temperature until next day.

Test 28. 3 cycles of NO2-SCR reaction (60 mg:mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

-Feed gas composition: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200 ºC again, this same cycle was restarted and repeated twice. The aim was to study the reproducibility of the NO2-SCR reaction activity.

Test 29. 3 cycles of NO2-SCR reaction (60 mg:mixed Cu/SAPO-34+ cordierite and top layer of Printex U)

Annex C -Feed gas composition: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O under He as balance -Test initial temperature was also fixed as 200 ºC and pollutants were simultaneously injected from the beginning. Plateau of 2h was performed in order to stabilise the feed gas mixture. -Temperature was increased until 500 ºC (2ºC/min) where a plateau of 30 min was performed. Again, to assure gas mixture stabilisation at the higher temperature range. -Then, temperature was decreased to the initial 200 ºC (1ºC/min) and, again, stabilisation for 2h was realized. -Once at 200 ºC again, this same cycle was restarted and repeated twice. The aim was to study the reproducibility of the NO2-SCR reaction activity.

ANNEX D D.1.SUMMARY

This chapter is focused on the basic physicochemical characterization of the commercial mini-SCRF catalyst. In order to facilitate it, the sample was crushed to form a powder composed of a washcoat (Cu Chabazite zeolite) and a support (NGK cordierite). It is important to emphasise that, due to confidentiality reasons, only the most basic characterization analysis could be presented and discussed on this manuscript. For this reason, textural and physicochemical characterization of the deactivated commercial sample could not be done neither. As a result, this short chapter would present and discussed the results of the XRD, SEM+ EDX and ICP-OES techniques, which gave basic information.

More details about the analysis equipment and measure conditions used for each characterisation technique were described on Chapter 3.

It is necessary to remark that all the characterizations discussed in this chapter were performed over the commercial catalyst when it was fresh. It would have been interesting and clarifying to repeat these characterization analysis on the deactivated commercial sample.

Information obtained maybe would have done more clues about the origin of the deactivation phenomenon occurred. However, this was impossible as the supplier company of the commercial catalyst asked to be returned the deactivated mini-SCRF sample. the zeolites are known for being made of a very crystalline network. It was known that the crystallinity is related to the acidity of the zeolites, which was related to their NH3-SCR and NH3 oxidation activity. Reference red peaks given by the database program matched the real peaks obtained from the commercial washcoat. This indicated that, effectively, the commercial sample consisted on a pure phase of the H-SAPO-34 zeolite [1,2]. This indicated that the crystalline structure of the H-SAPO-34 after the copper introduction process was essentially unchanged [3,4]. As Ma et al. [5] also observed, the strong diffraction peak at approximately 10,4° could be ascribed to certain cordierite support remaining from the washcoat extraction process.

D.2. X-RAY DIFFRACTION (XRD)

On the Table D Referring to the other spectra obtained from the commercial washcoat, it was indicated in blue colour on Figure D.1 and it was linked to the Cu species introduced on the zeolite structure. Cu peaks showed a small intensity in comparison to the zeolite peaks (Table D.2). This might be explained by the metal/zeolite ratio normally used on this kind of catalysts. Obviously, the zeolite amount is higher than the introduced metal, the main reason is that too much metal loading would produce the formation of undesired and inactive Cu species (such as CuO) on the zeolite surface. Because of that, the Cu spectra obtained on Figure D.1 was eclipsed by the SAPO-34 signal. However, it was enough to confirm that typical peaks of the cationic species of the Cu metal were observed. Contrarily, the typical peaks of the undesired CuO phase (35,58 and 38,88°) [6][7][8] were not obtained. This suggest that Cu was successfully introduced and dispersed on the zeolite framework, as expected from a commercial sample [1,[9][10][11].

Annex D In reference to the crushed mini-SCRF sample (Cu/SAPO-34 washcoat and cordierite support), the XRD diffractogram was not presented and discussed as the cordierite signal intensity "eclipsed" the Cu/SAPO-34 signal due to its high crystallinity.

D.3. INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION SPECTROSCOPY (ICP-OES)

D.3.1. Chemical composition of the commercial washcoat

The chemical compositions and the elements (Si, Al, P and Cu) distribution of the commercial washcoat were determined by ICP-OES. The element content results are summarized in Table D.3. As the commercial sample under discussion, the Cu introduction method used and the specific products and quantities used for the synthesis of the SAPO-34 were unknown to us. Due to that, it was not possible to calculate the theorical content of each compound. However, the experimental chemical contents of the commercial washcoat obtained by ICP-OES analysis are compared with some literature results on Table D.3. Literature ICP-OES results were selected by taking into account different methods to introduce the Cu in the SAPO-34 structure. Liu et al. [1] synthesised directly the zeolite with the Cu content on a solid-gel synthesis. Wang et al. [12] used the ion-exchanged method to introduce the Cu on a commercial H-SAPO-34. And, finally, Cao et al. [6] used the impregnation method of the zeolite with a Cu aqueous solution. Based on the tendencies and results obtained by them, it might be concluded that the solid-gel synthesis gave the chemical composition closest to the commercial catalyst values. On the contrary, ion-exchange and impregnation methods gave lower silicon content and, consequently, higher Al and P percentages.

Annex D

D.3.2. Chemical composition of the crushed mini-SRCF catalyst

To complete the chemical characterization of the commercial catalyst, ICP-OES analysis was also measured with the crushed mini-SCRF catalyst. In this sample, in addition to the Cu/SAPO-34 washcoat there is an important amount of commercial NGK cordierite. For this reason, the element distribution in this sample is expected to be different compared with the washcoat. Si and Al content are expected to be higher as cordierite contribution will be added to the zeolite contribution. However, the Cu and P contents are expected to be reduced as cordierite would "diluted" the washcoat values. Comparison of the ICP-OES results obtained from the washcoat and from the crushed mini-SCRF catalyst is presented on Table D.4. As aforementioned, the Cu content was found to be reduced in comparison to the washcoat measure due to the cordierite dilution effect. However, the P content of the crushed mini-SCRF did not accomplish this hypothesis, as higher value was obtained. Due to this, the P/Al ratio of both samples were completely different. In reference to Si and Al content, there were not very much difference between results of both samples.

To better understand the chemical composition of the mini-SCRF catalyst, further will be discussed and compared the EDX results.

D.4. SCANNING ELECTRON MICROSCOPY (SEM) + ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDX)

D.4.1. Morphology of the commercial washcoat

SEM technique will allow to observe the morphology and the distribution of the crystals as well as to determine the crystal size of the sample. In almost the centre of the image it can be observed a big cluster that might be related to be a Si island which is a common phenomenon observed on the SAPO-34 crystallization. Other authors as Wang et al. [7] and Izadbakhsh et al. [13] also obtained these islands. Hypothesis of the Si islands seem possible if taking into account the EDX results presented on Table D.5 where it can be confirmed that Si content on the sample surface was found to be three times higher than in the bulk.

In some areas of the SEM image, especially, over the big cluster, certain fluffy scraps were observed on the external surface of the SAPO-34 zeolite. The EDX scan revealed that the Cu percentage was higher in comparison to the content in the zeolite crystals. These, scraps were ascribed to be CuO species in small amounts which were not enough to be detected on the XRD spectra [7].

Annex D D.5 the chemical composition in the bulk and in the surface of the commercial washcoat were compared. As aforementioned, the Cu content in EDX was found to be higher than the ICP-OES value. This was related to the formation of CuO scraps on the external surface of the zeolite. In addition, significant difference on the ICP-OES and EDX values were observed for Si and P contents. This means that these elements are rather present on the external surface of the zeolite, the be-named "extra-framework" species. In reference to the Si, it might be explained by the formation of Si islands. However, the origin of the P accumulation on the zeolite surface was unknown.

Element distribution values of the commercial washcoat sample presented on Table D Annex D

D.4.2. Morphology of the crushed mini-SCRF catalyst

Morphology of the crushed commercial mini-SCRF sample was decided to be also evaluated by SEM and EDX analysis. D.6 the chemical composition in the bulk and in the surface of the crushed sample were compared. As it was also obtained for the washcoat sample, the Cu content in EDX was higher than the ICP-OES value. The formation of CuO scraps on the sample surface might be Annex D the logic explanation. In reference to Al and P, the ICP-OES and EDX values were similar and it might be assumed that any surface species of this elements were formed. However, Si content of the EDX analysis was more than 6 times higher than ICP value. This might again explained by the Si islands formed on the external surface of the zeolite, as also was the case of the washcoat sample.

D.5. CONCLUSIONS

This chapter presented a very basic physicochemical characterization of the commercial mini-SCRF catalyst. Results obtained from the washcoat and the crushed mini-SCRF sample were compared and discussed.

In the case of the XRD analysis, only the washcoat spectra was discussed. The main reason was that the diffractogram obtained from the crushed mini-SCRF sample only showed the cordierite material as it is present in higher amount and its high crystalline signal covered the Cu metal signal. Main conclusions from the XRD analysis were:

The XRD diffractogram was compared with a theorical database peaks and it allowed to determine the SAPO-34 as the zeolite framework.

XRD spectra did not showed the presence of another zeolite type, only pure phase of SAPO-34 was present on the sample.

Peaks related to CuO species (35,58 and 38,88°) were not observed, indicating that Cu metal was well dispersed within the zeolite framework.

Annex D Chemical composition of both samples were evaluated by ICP-OES technique. The main conclusions made were:

Element contents of the commercial washcoat seemed to indicate that the Cu metal was introducted by means of the solid-gel synthesis method.

In comparison, the ICP-OES evaluation of the crushed mini-SCRF showed smaller Cu content maybe due to the cordierite "dilution" effect. And, significant higher P content was also observed.

Finally, morphology and crystal size of both samples were evaluated with SEM technique. SEM analysis was coupled with the EDX measure of the chemical distribution on the catalysts surface. Main conclusions were:

Both samples showed the typical cubic-like crystals of the SAPO-34 zeolites as well as good homogeneity.

Crystal size were between 2-3 μm on both samples, which were in the average size reported on the literature by various authors.

Even, some clusters and scraps were observed on both, it can be mainly concluded that pure SAPO-34 phase was present (as expected from commercial zeolites).

Effectively, by EDX it was confirmed that these clusters were related to Si islands formed on the zeolite surface. This would explain the important difference of the Si content between the ICP-OES (bulk) and EDX techniques (surface).

Also, a little amount of scraps were observed on both samples. Again, EDX analysis on the scraps gave the clue. They were related to CuO species located on the zeolite surface. However, their amount was not enough to be detected on the XRD spectra.

  Techniques des Activités Physiques et Sportives Observatoire des Sciences de l'Univers de Lyon Polytech Lyon Ecole Supérieure de Chimie Physique Electronique Institut Universitaire de Technologie de Lyon 1 Ecole Supérieure du Professorat et de l'Education Institut de Science Financière et d'Assurances Directeur : M. F. DE MARCHI Directeur : M. le Professeur F. THEVENARD Directeur : Mme C. FELIX Directeur : M. Hassan HAMMOURI Directeur : M. le Professeur S. AKKOUCHE Directeur : M. le Professeur G. TOMANOV Directeur : M. le Professeur H. BEN HADID Directeur : M. le Professeur J-C PLENET Directeur : M. Y.VANPOULLE Directeur : M. B. GUIDERDONI Directeur : M. le Professeur E.PERRIN Directeur : M. G. PIGNAULT Directeur : M. le Professeur C. VITON Directeur : M. le Professeur A. MOUGNIOTTE Directeur : M. N. LEBOISNE

CHAPTER 1 .

 1 INTRODUCTION ........................................................................................

1 . 4 .

 14 standards and engine cycles for Diesel passenger vehicles ................................................................................................................ Table 1.3. US emission standards evolution . ......................................................................... Table Summary of SCR reactions ...............................................................................

Figure 1 . 2 .Figure 1 . 3 .Figure 1 . 4 .Figure 1 . 5 .Figure 1 . 7 .Figure 1 . 9 .Figure 1 . 10 .Figure 1 . 11 .Figure 1 . 14 .Figure 1 . 15 .Figure 1 . 16 .Figure 1 . 17 .

 121314151719110111114115116117 ............................................................................................................................................ Table 1.7.b. Summary of research group results of soot-SCR interactions on SCRF catalysts ............................................................................................................................................ Figure 1.1. A diagram of a Diesel exhaust gas treatment system .......................................... Diesel oxidation flow through monolith catalysts ................................................ Diesel wall-flow particulate filter scheme ........................................................... Soot bed and cake filtration over DPF substrate .................................................. Classification of Filter Systems by Regeneration Method ................................... Figure 1.6. a) Regeneration by NOx added CRT; and b) CCRT system (b) ............................ NOx conversion efficiency for Vanadium and zeolite SCR catalysts in Standard SCR reaction ........................................................................................................................ Figure 1.8.a) BETA zeolite framework structure; b) MFI zeolite framework structure ......... Schematic overview of the CHA, MFI and BEA framework with indication of pore sizes and maximum cage dimensions .......................................................................... CHA zeolite framework structure ................................................................... Acid sites in a zeolite: Brönsted sites: a) Proton in exchange position and b) Silanols; and Lewis sites: c) Metal-ion in Exchange position and d) EFA ............................ Figure 1.12. a) double 6-ring (d6r units); b) cha cavity (formed by 8-member ring and d6r units connected) .................................................................................................................. Figure 1.13.a) Classic after treatment system in Diesel exhaust lines; b) Selective Catalytic Reduction on Filter (SCRF) ................................................................................................ Scheme of washcoated SCRF substrates and the catalyst loading deposition in fonction of the substrate porosity. Same catalyst loading on both systems ............................ NOx conversion of a Cu/SCRF (60 g/L) catalyst without soot in function of NO2/NOx ratio. Feed gas includes 300 ppm NOx ; ANR=0.8, 10% O2 and SV= 75K/h ...... NOx conversion as function of temperature over degreened and aged V/SCRF catalysts ............................................................................................................................. Schematic of physical and chemical processes in a single wall-flow substrate channel for the SCRF...........................................................................................................

Figure 1 . 18 .Table 3 . 1 .Figure 3 . 1 .Figure 3 . 2 .Figure 3 . 3 .Figure 3 . 4 .Figure 3 . 5 .Figure 3 . 6 .Figure 3 . 7 .Figure 3 . 8 .Figure 3 . 9 .Figure 3 . 10 .Figure 3 . 11 .Figure 3 . 12 .Table 4 . 1 . 4 . 2 . 4 . 3 . 4 . 4 . 4 . 5 . 4 . 5 . 4 . 6 . 4 . 7 .

 118313132333435363738393103113124142434445454647 Phenomena of PM filtration in a SCRF, the passive soot oxidation in the soot cake layer and the SCR reactions in the substrate wall. Black points represent acid carbonated species which adsorbs NH3 ................................................................................................. CHAPTER 3. MATERIALS AND EXPERIMENTAL METHODS ............................... Commercial sample characteristics ...................................................................... An example of the commercial mini-SCRF filter washcoated with a Cu-zeolite . SAPO-34 calcination procedure ........................................................................ Diesel engine exhaust line ................................................................................. Diesel Particulate Filter ..................................................................................... Aspiration of soot from DPF trough filter ......................................................... Recuperated soot from Palflex© filter .............................................................. IFPEN catalytic system scheme ........................................................................ Operational catalytic system (IFPEN) ................................................................ Operational method (IFPEN) ............................................................................. IRCELYON catalytic system scheme .............................................................. Operational catalytic system IRCELYON ....................................................... Operational method IRCELYON .................................................................... CHAPTER 4. EVALUATION OF THE COMMERCIAL CATALYST ........................ Tests matrix (500 ppm) NOx/ O2 (10%) ............................................................... Table Test matrix NH3/O2 (10%) ................................................................................... Table Tests matrix simple NH3/ NO ............................................................................. Table Test matrix for Standard SCR reactions .............................................................. Table Test matrix for NO2-SCR reactions ..................................................................... Table Test matrix for NO2-SCR reactions ..................................................................... Table Test matrix for Fast SCR reactions ...................................................................... Table Maximum NOx and NH3 conversions and N2O selectivity in function of temperature ..........................................................................................................................

Figure 4 . 1 .Figure 4 . 2 .

 4142 Simple (500 ppm) NO/O2 (10%). Concentrations in function of time and temperature ........................................................................................................................ Simple (500 ppm) NO2/O2 (10%). Concentrations in function of time and temperature..........................................................................................................................

Figure 4 . 3 .Figure 4 . 5 .Figure 4 . 6 .Figure 4 . 7 .

 43454647 Simple (500 ppm) NH3/O2 (10%). Concentrations evolution in function of time and temperature .................................................................................................................. Simple NH3/ NO ratio 1 and 1.2 tests (superposed). Concentrations evolution in function of time and temperature ........................................................................................ Simple NH3/ NO ratio 1 and 1.2 comparison. NOx and NH3 conversions evolution as a function of temperature ................................................................................................ Stabilisation test under Standard SCR conditions. Concentrations evolution in function of time and temperature .........................................................................................

Figure 4 . 8 .

 48 Standard SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature .........................................................................................

Figure 4 . 9 .

 49 Comparison of NOx conversions in function of temperature for all Standard SCR tests (Test 1, 7 and 13) ........................................................................................................ Figure 4.10. NO2-SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature ........................................................................................

Figure 4 . 11 .

 411 Fast SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature ........................................................................................

Figure 4 . 12 .Figure 4 . 13 .Figure 4 . 14 .Figure 4 . 16 .Figure 4 . 17 .Figure 4 . 18 .

 412413414416417418 Figure 4.12. NOx conversions of 200 ppm and 500 ppm SCR reactions ............................. Figure 4.13. Stabilisation Standard SCR (200 ppm) tests on deactivated sample. Concentrations evolution in function of time and temperature ............................................. Figure 4.14. NOx conversions as a function of temperature Tests 21 and 22 comparison with Test 1 ................................................................................................................................. Figure 4.15. . NOx conversions in function of temperature of aged samples (Tests 24 and 25) comparison with fresh reference sample (Test 1) ................................................................. Figure 4.16. NOx conversions in function of temperature of aged sample (Tests 26-31) ..... Figure 4.17. Standard SCR reaction (1000 ppm). Test 16 and 17 IRCELYON comparison. Test 16 is the named "Run 1" and test 17 corresponds to "Run 2" ....................................... Figure 4.18. NOx conversions in function of temperature. Tests 16 and 17 ..........................

Figure 4 . 19 .

 419 Figure 4.19. NH3 conversions in function of temperature comparison. Tests 16 and 17... ....................................................................................................................................

Figure 4 . 20 .Table 5 . 1 . 5 . 2 . 5 . 5 .Figure 5 . 1 .Figure 5 . 4 .Figure 5 . 5 .Figure 5 . 6 .Figure 5 . 7 .Table 6 . 1 . 100 Table 6 . 2 .

 42051525551545556576110062 Figure 4.20. NOx and NH3 conversions in function of temperature of each cycle Standard SCR (1000 ppm) .................................................................................................................

Figure 6 . 2 . 101 Figure 6 . 3 . 103 Figure 6 . 4 . 104 Figure 6 . 5 . 106 CHAPTER 7 .

 621016310364104651067 Figure 6.2. a) Mass loss (g) in function of the temperature, b) Mass loss (% ) in function of the temperature, c) Mass loss (%) in function of time; of the Printex U (black) and real Diesel soot (red) .......................................................................................................................... 101 Figure 6.3. a) Emitted gases in function of time of the Printex U; b) Emitted gases in function of time of the real Diesel soot ........................................................................................... 103 Figure 6.4. a) Raman spectra of the Printex U; and b) Raman spectra of the real Diesel soot .... 104 Figure 6.5. a) SEM image of the Printex U surface; and b) SEM image of the real Diesel soot surface .............................................................................................................................. 106

9 . 7 . 10 . 152 Figure 7 . 1 . 114 Figure 7 . 2 . 115 Figure 7 . 3 . 116 Figure 7 . 4 . 117 Figure 7 . 5 . 118 Figure 7 . 6 . 119 Figure 7 . 7 .Figure 7 . 8 .Figure 7 . 9 .

 9710152711147211573116741177511876119777879 Figure 7.7. NOx and N2 selectivities in function of the temperature of the Printex U soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + Printex U soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .............................. Figure 7.8. CO and CO2 concentrations in function of the temperature of the Printex U soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + Printex U soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 ................. Figure 7.9. NH3 conversion in absence of soot in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Black line: 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 ..........................................................................................................

Figure 7 . 10 .

 710 Figure 7.10. NOx and N2 selectivities in absence of soot in function of the temperature, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ...................................................

Figure 7 . 11 .Figure 7 . 12 .Figure 7 . 15 .

 711712715 Figure 7.11. NH3 and NO conversions in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 ............................................................................. Figure 7.12. NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ........................................... Figure 7.13. 3 cycles NO and NH3 conversions in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .......................................................................................................... Figure 7.14. 3 cycles NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ............... Figure 7.15. NH3 and NOx conversions in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h-1 ....................................................

Figure 7 . 16 .Figure 7 . 19 .Figure 7 . 20 .

 716719720 Figure 7.16. NOx and N2 selectivities in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ..................... Figure 7.17. 3 cycles NH3 and NOx conversions in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 ...................................... Figure 7.18. 3 cycles N2 and NOx selectivities in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 ...................................... Figure 7.19. NH3 and NO2 conversions in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 ............................................................................. Figure 7.20. NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ........................................... Figure 7.21. 3 cycles NO and NH3 conversions in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 ..........................................................................................................Figure 7.22. 3 cycles NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ............. Figure 7.23. Comparison of NH3 conversions of real Diesel (square symbol) and commercial Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 60 mg of Cu/SAPO-34 + cordierite+ soot layer, 10 L/h, GSHV= 135.000 h -1 .......................................................................................................................

Figure 7 . 22 .Figure 7 . 23 .

 722723 3 cycles NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ............. Comparison of NH3 conversions of real Diesel (square symbol) and commercial Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 60 mg of Cu/SAPO-34 + cordierite+ soot layer, 10 L/h, GSHV= 135.000 h -1 .......................................................................................................................

Figure 7 . 24 .Figure 7 . 25 .Figure 7 . 26 .Figure 7 . 30 .Figure 7 . 31 . 151 Figure 7 . 35 .

 724725726730731151735 Figure 7.24. NOx and N2 selectivities in presence of real Diesel (square symbol) and Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance .................................................................................................................... Figure 7.25. NH3 and NO conversions in presence of real Diesel (square symbol) and Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer, 10 L/h, GSHV= 135.000 h -1 ........................................................................................................... Figure 7.26. NOx and N2 selectivities in presence of real Diesel soot (square symbol) and Printex U soot (triangle) in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ......................................................................................... Figure 7.27. a) 3 cycles NO and NH3 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 ................................................... Figure 7.28. a) 3 cycles NOx and N2 selectivities in presence of real Diesel soot (square symbol); and b) in presence of commercial Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance ............... Figure 7.29. NO and NO2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 .................................................................................... Figure 7.30. NH3 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 ................................................................................................... Figure 7.31. NOx and N2 selectivities in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance .......................................................... Figure 7.32. a) 3 cycles NO and NO2 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .............................. Figure 7.33. a) 3 cycles NH3 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .............................................. Figure 7.34. a) 3 cycles NOx and N2 selectivities in presence of real Diesel soot (square symbol); and b) in presence of commercial Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance 151 Figure 7.35. NH3 and NO2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 ................................................................................................... Figure 7.36. NOx and N2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 . ..................................................................................................

Figure 7 .Figure 7 . 39 .Figure 7 . 40 .Figure 7 . 42 .

 7739740742 Figure 7.37. a) 3 cycles NO2 and NH3 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 ................................................... Figure 7.38. a) NOx and N2 conversions in presence of real Diesel soot (square symbol); b) and Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 ................................................................................................... Figure 7.39. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under NH3 oxidation conditions: 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 ....................................................................................... Figure 7.40. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 ............................................................... Figure 7.41. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Fast SCR conditions: 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 ............................................... Figure 7.42. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Fast SCR conditions: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 .................................................................

Figure 1 . 1 .

 11 Figure 1.1. A diagram of a Diesel exhaust gas treatment system. Source: Volvo.

Figure 1 . 2 .

 12 Figure 1.2. Diesel oxidation flow through monolith catalysts [30].

Figure 1 . 3 .

 13 Figure 1.3. Diesel wall-flow particulate filter scheme [12].

Figure 1 . 4 .

 14 Figure 1.4. Soot bed and cake filtration over DPFsubstrate [33].

Figure 1 . 5 .

 15 Figure 1.5. Classification of Filter Systems by Regeneration Method [36].

Figure 1 . 6 .

 16 Figure 1.6. Regeneration by NOx added CRT (a) and CCRT system (b) [30[38]].

Figure 1 . 7 .

 17 Figure 1.7. NOx conversion efficiency for Vanadium and zeolite SCR catalysts in Standard SCR reaction [60].

Figure 1 .

 1 Figure 1.8.a) BETA zeolite framework structure; b) MFI zeolite framework structure [72].

Figure 1 . 9 .

 19 Figure 1.9. Schematic overview of the CHA, MFI and BEA framework with indication of pore sizes and maximum cage dimensions.

Figure 1 . 10 .

 110 Figure 1.10. CHA zeolite framework structure [72].

Figure 1 . 11 .

 111 Figure 1.11. Acid sites in a zeolite: Brönsted sites: a) Proton in exchange position and b) Silanols; and Lewis sites: c) Metal-ion in Exchange position and d) EFAL.

Figure 1 .

 1 Figure 1.12. a) double 6-ring (d6r units); b) cha cavity (formed by 8-member ring and d6r units connected) .

Figure 1 .

 1 Figure 1.13.a) Classic after treatment system in Diesel exhaust lines; b) Selective Catalytic Reduction on Filter (SCRF).

Figure 1 . 14 .

 114 Figure 1.14. Scheme of washcoated SCRF substrates and the catalyst loading deposition in fonction of the substrate porosity. Same catalyst loading on both systems.

Figure 1 . 15 .

 115 Figure 1.15. NOx conversion of a Cu/SCRF (60 g/L) catalyst without soot in function of NO2/NOx ratio. Feed gas includes 300 ppm NOx ; ANR=0.8, 10% O2 and SV= 75K/h [162].

Figure 1 . 16 .

 116 Figure 1.16. NOx conversion as function of temperature over degreened and aged V/SCRF catalysts [163].

Figure 1 . 17 .

 117 Figure 1.17. Schematic of physical and chemical processes in a single wall-flow substrate channel for the SCRF [172].

Figure 1 . 18 .

 118 Figure 1.18. Phenomena of PM filtration in a SCRF, the passive soot oxidation in the soot cake layer and the SCR reactions in the substrate wall. Black points represent acid carbonated species which adsorbs NH3 [182].

Figure 3 . 1 .

 31 Figure 3.1. An example of the commercial mini-SCRF filter washcoated with a Cu-zeolite.

Figure 3 .

 3 Figure 3.1 shows an example of the mini-SCRF sample used at IFPEN. As Diesel particulate filters, their channels are plugged alternately at the ends, forcing the gas flow though the filter walls. They were obtained from a bigger monolith by cutting the rounded 1x3 inches shape.

Figure 3 . 2 .

 32 Figure 3.2. SAPO-34 calcination procedure.

Figure 3 . 3 .

 33 Figure 3.3. Diesel engine exhaust line.

Figure 3 . 4 .

 34 Figure 3.4. Diesel Particulate Filter.

Figure 3 . 5 .

 35 Figure 3.5. Aspiration of soot from DPF trough filter.

Figure 3 . 6 .

 36 Figure 3.6. Recuperated soot from Palflex© filter.

Figure 3 . 7 .

 37 Figure 3.7. IFPEN catalytic system scheme. Analyser N2O et CO2 : Nondispersive Infrarred sensor (NDIR) Analyser NH3: UV Analysers NOx: Liquid Crystal Display (LCD) Analyser O2: Paramagnetic

Figure 3 . 8 .

 38 Figure 3.8. Operational catalytic system (IFPEN).

Figure 3 . 9 .

 39 Figure 3.9. Operational method (IFPEN).

  Figures 3.10 and 3.11 present the lab-scale system available at IRCELYON to reduce NOx pollutants by NH3 on powder deNOx catalysts. a) Feed system: All gases of feed gas were introduced via flowmeters which should be previously fixed in the correct open position to let enter into the system just the desired amount of each gas of the mixture. Water was injected as a liquid via peristaltic pump into a saturator and evaporator there as it shows the Figure 3.10.

Figure 3 .

 3 Figure 3.10. IRCELYON catalytic system scheme.

Figure 3 . 11 .

 311 Figure 3.11. Operational catalytic system IRCELYON.

Figure 3 . 12 .

 312 Figure 3.12. Operational method IRCELYON.

  (20) 2 NO + O2 2 NO2

Figure 4 . 1 .

 41 Figure 4.1. Simple (500 ppm) NO/O2 (10%). Concentrations in function of time and temperature.

Figure 4 . 2 .

 42 Figure 4.2. Simple (500 ppm) NO2/O2 (10%). Concentrations in function of time and temperature.

  5 O2 → 4 NO + 6 H2O

Figure 4 . 3 .

 43 Figure 4.3. Simple (500 ppm) NH3/O2 (10%). Concentrations evolution in function of time and temperature.

Figure 4 . 5 .

 45 Figure 4.5. Simple NH3/ NO ratio 1 and 1.2 tests (superposed). Concentrations evolution in function of time and temperature.

Figure 4 .

 4 Figure 4.5 compares the NO and NH3 concentrations evolution on Tests 2 and 3. During first injection seconds, a ''dead time'' in the NH3 profile was observed in all tests. This transient was attributed to the NH3 adsorption onto the catalyst until its saturation[2]. Acid properties of zeolites play an important role on NOx reduction, as they are involved in the adsorption and activation of NH3 over the catalyst. Adsorbed NH3 onto the catalyst surface will react with NOx via Eley-Rideal mechanism[5]. This phenomena takes place especially with Cu-

  Figure 4.5. It can be concluded that the different NH3/NOx ratios used did not practically affected to catalyst activity, as both test NO concentrations are very similar along the whole temperature window. It can be assumed that more NH3 amount did not improved the catalytic activity. NO remained almost constant around 200 ppm during the test. This means that without O2 presence (lean conditions), any NOx reduction occur.

Figure 4 . 6 .

 46 Figure 4.6. Simple NH3/ NO ratio 1 and 1.2 comparison. NOx and NH3 conversions evolution as a function of temperature.

Figure 4 .

 4 Figure 4.6 presents NO and NH3 conversions in function of temperature for Tests 2 and 3.Referring to NOx, conversions followed the same tendency but in the case of the NH3/NOx ratio=1.2, it started after 350 ºC whereas for the NH3/NOx ratio=1 test conversion started after 200 ºC. However, the NOx conversion value of Test 2 was twice than for Test 3 where only 10% conversion was achieved. In the case of ratio=1.2, NH3 conversion started only after 480 ºC. In comparison ratio=1 started to be converted around 400 °C. However, maximal NH3 conversion were similar around 10% in both cases. Both pollutants conversions were very low, being the highest one 20 % (for NO at 500 ºC). On literature[5] it was found a possible mechanism that explains the low conversions observed in this experiment. It is based on redox active sites mechanism involving Cu + / Cu 2+ species: O2 extra-network in metallic complexes reacted with NO to form intermediate species type Cu 2+ -NxOy. Later, they reacted with NH3 forming N2 and water, as well as producing parallel exchanged metals reduction Cu 2+ → Cu + . After that metal should be reoxidized by the O2 present on the exhaust line to come back to the Cu 2+ form. However, in

  A: Tests 1 and 13)(7) 4 NH3 + 4 NO + O2 → 4 N2 + 6 H2O

Figure 4 . 7 .

 47 Figure 4.7. Stabilisation test under Standard SCR conditions. Concentrations evolution in function of time and temperature.

Figure 4 . 8 .

 48 Figure 4.8. Standard SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature.Same feed gas that in Test 1 (Figure4.7) was used. However, in this Test 13 an extra step was performed at the end. Here, after 500 °C plateau, feed gas injection was stopped and the temperature was increased until 600 ºC to develop a NH3-TPD step. Also, in this Test 13, 200 ppm of NO were initially injected with O2 (10%), H2O (10%) and CO2 (9%) at 80ºC. This temperature value was chosen for all SCR tests due to water presence in the feed. NH3 was only injected when 200 °C were reached to avoid the NH4NO3 formation at lower temperatures (Reactions 11 and 12).Here, contrarily to behaviour observed on Test 1 (Figure4.7), the NO concentration was constant until 200 °C when the NH3 was injected (2800 s). Then, when concentrations were stable again the temperature was increased to 500 °C. As a consequence, a NH3 desorption peak was registered (4600-5200 s) and the NO concentration slightly dropped due to the Standard SCR reaction (Reaction 7) between 200-475 °C. Later at 500°C plateau, NO concentration became stable again around 125 ppm due to the complete NH3 oxidation was reached (6500 s) at high temperatures (>400 ºC)[12][13][14][15]. Different catalytic behaviour obtained on Test 13 in comparison to Test 1 might be related to the different injection strategies followed. However, in Test 7 (Standard SCR at 500 ppm), the NH3 was only injected at 200 °C as in Test 13 but the concentration profiles observed were more similar to Test 1 (very low concentrations of NO and NH3). Here, a catalyst deactivation phenomena was remarked but confirmed along the test serie. In the case of Standard SCR tests this effect was especially remarkable as this concrete SCR reaction was performed at the beginning, in the middle and in the end of the serie. Three different Standard SCR tests performed over the same mini-SCRF sample are compared on Figure4.9.

Figure 4 . 9 .

 49 Figure 4.9. Comparison of NOx conversions in function of temperature for all Standard SCR tests (Test 1, 7 and 13).

Figure 4 .

 4 Figure 4.10. NO2-SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature.

Figure 4 . 11 .

 411 Figure 4.11. Fast SCR reaction (200 ppm), ratio NH3/NO=1. Concentrations evolution in function of time and temperature.Fast SCR reaction was performed injecting 100 ppm of NO and 100 ppm of NO2 and 200 ppm of NH3. Water, CO2 and O2 contents are maintained in the same proportion as usual (Table4.6). Feed gas was injected at 80°C with exception of NH3 which was only injected at 200 °C. Both, NO and NO2 concentrations, remained constant until NH3 injection at 200 ºC (2800 s). Then, both NO and NO2 concentrations dropped 50 ppm when reaction with NH3 took place. Later, all concentrations became stable and the temperature was increased until

Figure 4 . 12 .

 412 Figure 4.12.NOx conversions of 200 ppm and 500 ppm SCR reactions.

Figure 4 . 13 .

 413 Figure 4.13. Stabilisation Standard SCR (200 ppm) tests on deactivated sample. Concentrations evolution in function of time and temperature. In Figure 4.13 presents the evolution of the pollutant concentrations of two consecutive stabilisation tests (Tests 21 and 22) on the same deactivated sample. It can be observed that NO and NH3 concentrations followed the same tendency: practically all the injected NO and NH3 were measured along the test on both of them. Only when temperature was raised from 200 ºC to 500 ºC (2400 s), a weak NH3 desorption peak was produced and, as a consequence, a very small amount of NO was consumed until 450 ºC. It is noticeable that practically, no Standard SCR reaction took place on both tests, especially if compared to the first stabilisation test (Test 1) performed over this sample when fresh (presented on Figure 4.7). It can be seen that catalyst behaviour has nothing to do in comparison to Test 1 where big amounts of NO and NH3 reacted from the beginning.

Figure 4 . 14 .

 414 Figure 4.14. NOx conversions as a function of temperature Tests 21 and 22 comparison with Test 1.

Figure 4 .

 4 Figure 4.14 shows the NOx conversion during Tests 21 and 22 on the deactivated sample and both are compared with the NOx conversion of the fresh sample (Test 1 conditions). It can be clearly seen that Tests 21 and 22 barely produced 40% of NOx conversion whereas a 90% was obtained with the fresh sample. It can be concluded that, effectively, a deactivation phenomenon had happened after all test serie performed over the commercial mini-SCRF sample used as reference catalyst.

Figure 4 .

 4 15, the NOx conversion obtained from these aged samples is compared with NOx conversion obtained from the fresh sample 1-004. a) Stabilisation Standard SCR (200 ppm) on aged samples 5-004 and 6-004. (Annex A: Tests 24 and 25)

Figure 4 . 15 .

 415 Figure 4.15. NOx conversions in function of temperature of aged samples (Tests 24 and 25) comparison with fresh reference sample (Test 1).

Figure 4 . 16 .

 416 Figure 4.16. NOx conversions in function of temperature of aged sample (Tests 26-31).

Figure 4 .

 4 Figure 4.16 present the NOx conversion in function of temperature obtained from seven continuous cycles of the Standard SCR (200 ppm) reaction performed on the aged 5-004 sample.As it can be observed, from cycle 1 to 5, NOx conversion curve was reproducible and maximum value was maintained in 90-95% at 75 ºC. However, after the 6 th cycle certain degradation of the catalytic activity was observed on the low temperature region (200-300 ºC). If compared with reference sample 1-004, it was on Test 7 also when deactivation was remarked. So, it was not an isolated case of one of the samples and it seems a problem of the manufacturing conditions/treatment of the monolith. The degradation of the activity might be related with the resistance of the catalyst material to the strong and continuous oxidation/reduction conditions which could debilitated the zeolite framework or maybe produce the Copper species evolution or migration. In addition, an important possibility to cause the activity degradation were the hydrothermal conditions during the tests, especially if considered that 10% of H2O was used in all tests.

Figure 4 . 17 .

 417 Figure 4.17. Standard SCR reaction (1000 ppm). Test 16 and 17 IRCELYON comparison. Test 16 is the named "Run 1" and test 17 corresponds to "Run 2".

Figure 4 .

 4 Figure 4.17 shows the evolution of all compounds concentration in function of time and temperature for the First test performed at IRCELYON. Feed gas composition was settled as follows to simulate Standard SCR reaction: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O, using Helium as balance. During the initial 200 ºC plateau, both NO and NH3 concentrations were stable and constant around 800 ppm for Test 16 and 900 ppm for Test 17 (almost their injection value: 1000 ppm for both pollutants). However, when temperature was increased to 500 ºC, the Standard reaction started to take place. It is interesting to remark that between 300-350 ºC, the NO and NH3 concentrations showed a plateau (9000-11000 s). In the same temperature window, the N2 production also remained almost constant. Same tendency was observed by Colombo et al.[2] in the Standard SCR reaction on their powder Cu-zeolite+cordierite catalyst. However, the reasons of this phenomenon rested unclear. In reference to the NH3, it was consumed to selectively reduce the NO (Reaction 7) until 400 ºC, then the NO concentration became constant around 200 ppm for Test 16 and 300 ppm for Test 17. It is remarkable that 100 ppm of difference was produced during tests. As it can be observed on Figure4.17, between 300-400 ºC, effective and selective NOx reduction happened as N2 started to being formed and almost 1000 ppm were produced at 500 ºC. Any undesired products were formed in significant amounts, so it can be concluded that effective Standard SCR reaction took place on both tests. In reference to NH3, after 250-300 ºC it started to be converted[2] and at 400 ºC it was completely consumed. Again, the NH3 oxidation was taking place consuming the reductant agent and impeding the correct development of the Standard reaction[13][14][15]. It can be seen on Figure4.17, both possible NH3 oxidation reactions were happening simultaneously (Reactions 18 and 19) as both NO and N2 concentrations became constant at that temperature region. Then, temperature was decreased again until 200 ºC but using a slower ramp (1 ºC/min) and concentrations came back to stability. However, the reached concentration values were 100 ppm lower if compared to the initial 200 ºC plateau. It is remarkable that during the cooling ramp, a small peak of the

Figure 4 . 18 .

 418 Figure 4.18. NOx conversions in function of temperature. Tests 16 and 17.

Figure 4 .

 4 Figure 4.18 present the NO conversions obtained from both Standard SCR reactions (both increase and decrease are included). It can be noticed that, at low temperature region (200-300 ºC), the NOx conversion curves were not identical during the increase and decrease ramps. However, above 350 ºC tendencies were quite similar reaching a maximum NOx conversion of 70-80% at 450 ºC on both tests. This might be caused to the different temperature ramps used during the increase and decrease of temperature which could affect the catalyst stabilisation or an adsorption phenomena might occur. Figure4.17 (concentrations evolution) already showed these two "waves" at same region. Taking all this into account, different tendencies observed at high (400-500 ºC) and low (200-300 ºC) temperature windows were related to different reaction mechanisms in function of temperature. In the literature was reported than at the low-medium temperature reaction, the mechanism is determined by the SCR reaction that means the NOx reduction by NH3. However, at high temperatures (400-500

Figure 4 .

 4 Figure 4.18 present the NO conversions obtained from both Standard SCR reactions (both increase and decrease are included). It can be noticed that, at low temperature region (200-300 ºC), the NOx conversion curves were not identical during the increase and decrease ramps. However, above 350 ºC tendencies were quite similar reaching a maximum NOx conversion of 70-80% at 450 ºC on both tests. This might be caused to the different temperature ramps used during the increase and decrease of temperature which could affect the catalyst stabilisation or an adsorption phenomena might occur. Figure4.17 (concentrations evolution) already showed these two "waves" at same region. Taking all this into account, different tendencies observed at high (400-500 ºC) and low (200-300 ºC) temperature windows were related to different reaction mechanisms in function of temperature. In the literature was reported than at the low-medium temperature reaction, the mechanism is determined by the SCR reaction that means the NOx reduction by NH3. However, at high temperatures (400-500

Figure 4 . 19 .

 419 Figure 4.19. NH3 conversions in function of temperature comparison. Tests 16 and 17.

Figure 4 .

 4 Figure 4.19 can be observed that the same phenomena at low temperature was obtained for NH3 conversions. It is remarkable that both tests reached total NH3 consumption (100 % conversion) at 450 ºC. Again, the increase and decrease data followed same tendencies at temperatures higher than 300ºC. Measure incertitude between both IRCELYON tests can be remarked as well as in the previous one (Figure4.18), giving about a 10% of incertitude.

Figure 4 . 20 .

 420 Figure 4.20. NOx and NH3 conversions in function of temperature of each cycle Standard SCR (1000 ppm).

Figure 5 . 1 .

 51 Figure 5.1. X-Ray spectra of the non-impregnated H-SAPO-34 zeolite (red); and X-Ray spectra of the Cuimpregnated synthesized Cu/SAPO-34 zeolite (blue).

Figure 5 . 2 .

 52 Figure 5.2. X-Ray spectra of the Cu-impregnated synthesized Cu/SAPO-34 zeolite.

Figure 5 . 3 .

 53 Figure 5.3. a) SEM image of the in-laboratory synthesized Cu/SAPO-34 zeolite; and b) SEM image of the amorphous phase of the synthesized Cu/SAPO-34.

Figure 5 .

 5 Figure 5.3.a allows observing that the distribution and size of the SAPO-34 crystals was quite homogeneous. The SEM image clearly showed the typical cubic-like rhombohedra morphology of the SAPO-34 zeolites[4, 8, 11, 14]. Also, it can be concluded that the Cu

Figure 5 . 4 .

 54 Figure 5.4. TEM images of the synthesized Cu/SAPO-34 catalyst.

Figure 5 . 5 .

 55 Figure 5.5. Pore width distribution of the synthesized Cu/SAPO-34 catalyst (green peak).

Figure 5 . 6 .

 56 Figure 5.6. Adsorption and desorption isotherm curve of the synthesized Cu/SAPO-34 catalyst.

Figure 5 . 7 .

 57 Figure 5.7. Cu 2p XPS spectra of the synthesized Cu/SAPO-34 catalyst.

Figure 6 . 1 .

 61 Figure 6.1. X-Ray diffractograms of the commercial (Printex U) and real Diesel soot.

Figure 6 . 2 .

 62 Figure 6.2.a) Mass loss (g) in function of the temperature, b) Mass loss (% ) in function of the temperature, c) Mass loss (%) in function of time; of the Printex U (black) and real Diesel soot (red).

Figure 6 .

 6 Figure 6.2 shows the evolution of the mass of both soot samples in function of temperature (Figure 6.2.a and b) but also in function of time (Figure6.2.c). Mass loss curves of both kinds of soot followed the same tendency at the low temperature region (400 °C)[7]. Later, it can be observed that both soot samples started to be oxidized at 400 °C. However, even if both onset temperatures were at higher temperatures than 500 °C, in the case of the real Diesel soot the onset temperature was observed at 503 °C whereas the onset temperature of the commercial Printex U was higher (550 °C). This might be explained due to the commercial character of the Printex U soot that provided higher thermal resistance[5]. A possible explanation of this different behaviour can be ascribed to the presence on the soot surface of strong adsorbed organics originating from the additives of the lubricant used in the engine[3].

2

 2 Figure 6.2 shows the evolution of the mass of both soot samples in function of temperature (Figure 6.2.a and b) but also in function of time (Figure6.2.c). Mass loss curves of both kinds of soot followed the same tendency at the low temperature region (400 °C)[7]. Later, it can be observed that both soot samples started to be oxidized at 400 °C. However, even if both onset temperatures were at higher temperatures than 500 °C, in the case of the real Diesel soot the onset temperature was observed at 503 °C whereas the onset temperature of the commercial Printex U was higher (550 °C). This might be explained due to the commercial character of the Printex U soot that provided higher thermal resistance[5]. A possible explanation of this different behaviour can be ascribed to the presence on the soot surface of strong adsorbed organics originating from the additives of the lubricant used in the engine[3].

Figure 6 .

 6 Figure 6.3.a) Emitted gases in function of time of the Printex U; b) Emitted gases in function of time of the real Diesel soot.

Figure 6 . 3 .

 63 Figure 6.3.a and bshows the emitted gases from the thermal oxidation of the soot samples which were measured by a mass spectrometer. It is important to keep in mind that measures were qualitative and not quantitative, so values represented on Figure6.3 are related with the intensity of the emitted gases. As it can be observed, same products were obtained from both soot samples and one of the more intense and import one was the CO (blue line). Also, C3H4 hydrocarbon was detected as well as O2. However, contrarily to the expected, CO2 intensity remained quite low on both cases. This might mean that the thermal oxidation of these soot samples was mainly produced following the Reaction 2 mechanism (Annex B).

Figures 6 . 4 .

 64 Figures 6.4.a and 6.4.b show the Raman spectra obtained from the commercial Printex U and the real Diesel soot. These first-order spectra of soot generally exhibits two broad peaks with intensity maxima at 1350 cm -1 and at 1585 cm -1[2, 11]. These two broad signals are characteristic of carbon black and other related carbonaceous materials with similar structure, such as soot[1]. According to the literature[1, 12, 13], these peaks are linked to the first order D1 and G bands of the mathematical fitting, respectively. Some authors as Cuesta et al.[14],

Figure 6 . 5 .

 65 Figure 6.5.a) SEM image of the Printex U surface; and b) SEM image of the real Diesel soot surface.

Figures 6 .

 6 Figures 6.5.a and 6.5.b show the surface morphology of the Printex U and the real Diesel soot, respectively, at the same scale. Similar morphology and a granular texture were observed on both samples. The real Diesel soot image showed certain agglomeration of grains or spheres that was not observed on the Printex U image (Figure 6.5.a.). This agglomeration of the spherical soot particles was also remarked by Yang et al.[23] and they suggested that it was caused by the action of Van der Waals, electrostatic and surface adhesive forces. Furthermore, the real Diesel soot image, apparently confirmed the theory made at XRD analysis of two different phases formed the sample (as the white colour was evident on Figure6.5.b). Mihai et al.[24] analysed by SEM technique a real Diesel soot obtained from an engine bench at Volvo cars. In the obtained SEM images from Mihai it can be also observed the same uniform agglomerated spheres and also the aforementioned white phase. In the literature, Yang et al.[23] suggested that the white phase was related to a small amount of soluble organic matters as unburnt fuel was emitted into the exhaust system and was found to adsorb on the surface of the PM. This was consistent with observations made at CHNS and TGA analysis.

Figure 7 . 1 .

 71 Figure 7.1. NOx and NH3 conversion in function of the temperature of the commercial cordierite under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 2 .

 72 Figure 7.2. NOx and N2 selectivities in function of the temperature of the commercial cordierite under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 3 .

 73 Figure 7.3. NO and NH3 conversions in function of the temperature of the real Diesel soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + real Diesel soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 3 .

 73 Figure 7.3. shows the NO and NH3 conversions of the real Diesel soot under Standard SCR conditions.NO conversion started at 250 ºC but significant conversion was only observed above 400 ºC. Maximum NO conversion barely reached 12% at 500 ºC. NH3 conversion started at 300 ºC (apparently in relation to the modest NO conversion) and it also became significant above 400 ºC. Then, slightly higher NH3 conversion was obtained in comparison to NO conversion which was caused by the thermal NH3 oxidation at high temperature. It is remarkable that, apparently, the soot presence inhibited the NH3 oxidation as maximum of only 20% conversion was achieved even at

Figure 7 . 4 .

 74 Figure 7.4. NOx and N2 selectivities in function of the temperature of the real Diesel soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + real Diesel soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 5 .

 75 Figure 7.5. CO and CO2 concentrations in function of the temperature of the real Diesel soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + real Diesel soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 6 .

 76 Figure 7.6. NO and NH3 conversions in function of the temperature of the Printex U soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + Printex U soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 6 .

 76 Figure 7.6. shows the NO and NH3 conversions of the Printex U soot under Standard SCR conditions. NO conversion started at 300 ºC but slightly higher conversion was only observed above 400 ºC (maximum of 10%). NH3 conversion also started at 300 ºC and became especially significant (> 40%) above 400 ºC due to the thermal NH3 oxidation reaction. It was more important than with the real Diesel soot (Figure7.3) but complete NH3 conversion was neither reached in this test.

Figure 7 . 7 .

 77 Figure 7.7. NOx and N2 selectivities in function of the temperature of the Printex U soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + Printex U soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 8 .

 78 Figure 7.8. CO and CO2 concentrations in function of the temperature of the Printex U soot under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cordierite + Printex U soot mass: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 9 .

 79 Figure 7.9. NH3 conversion in absence of soot in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 10 .

 710 Figure 7.10. NOx and N2 selectivities in absence of soot in function of the temperature, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.10 presents the NOx and N2 selectivities of the catalytic system in soot absence in function of temperature. Only small N2O formation (lower than 10% of selectivity) took place between 250-325 ºC[8], possibly related to the NH3 oxidation Reaction 21 mechanism (Annex B) mechanism[4, 5]. Anyway, the main product obtained in this experiment was N2, as the high value of its selectivity during the whole temperature range shows[9]. Consequently, it can be concluded that the NH3 oxidation reaction followed the Reaction 18 mechanism. However, even if N2 was the main product, the complete NH3 consumption presented on Figure7.9 is not desirable as would not be available to reduce the NOx.

Figure 7 .

 7 Figure 7.11 NH3 and NO conversions in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 12 .

 712 Figure 7.12. NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.12 presents the NOx and N2 selectivities in function of temperature in soot absence. As it can be observed, the NOx were selective reduction was promoted by the Cu/SAPO-34 catalyst, yielding N2 and water as major products[2] (Reaction 7). Only a negligible amount of N2O was formed[9] above 400 ºC which might be related to the NH3 oxidation by Reaction 21 (Annex B)[4, 5]. Effectively, this N2O formation coincided with the NH3 conversion increase and the NO conversion decrease (Figure7.11).

First, 3

 3 cycles of Standard SCR reaction in soot absence were realized and results are presented on Figure7.13.

Figure 7 .

 7 Figure 7.13. 3 cycles NO and NH3 conversions in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.14. 3 cycles NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.14 presents the NOx and N2 selectivities of the 3 cycles Standard SCR in soot absence. It can be observed that exact overlapping of cycles was obtained. Also it is remarkable that the major product obtained was the N2 on the three cycles[2], indicating that effective and selective NOx reduction reaction happened. Only a negliglible amount of N2O was formed above 400 ºC, as it was also the case on the single reaction (Figure7.12).

Figure 7 .

 7 Figure 7.15 NH3 and NOx conversions in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.15 presents the NOx and NH3 conversion in function of temperature of the Cu/SAPO-34 + cordierite system. As it can be observed, certain conversion of NO2 and NH3 was obtained from the beginning (200 ºC). Referring to the NO conversion, a maximum value of 80% was obtained at 350 ºC. In comparison to the NO conversion obtained on Standard SCR (Figure 7.11) is much higher, which is in agreement with the literature of Fast SCR expectations [2, 9, 15]. On Figure7.15, it can be observed that above 400 ºC, the NO conversion dropped as a result of the NH3 oxidation[6, 12, 13]. Contrarily, NO2 conversion was not affected as very high value (nearly to 100%) was obtained above 385 ºC. It can be said that no stechiometric Fast SCR was produced and NH3 reduces predominantly NO2.

Figure 7 . 16 .

 716 Figure 7.16. NOx and N2 selectivities in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.16 presents the NOx and N2 selectivities in function of temperature in soot absence. As it can be observed, under Fast SCR conditions in presence of the Cu/SAPO-34 catalyst, from 300 ºC the NOx were successfully and selectively reduced by the NH3 yielding N2 and water as major products [2, 9]. These results indicated that the presence of the catalyst privileged the desired Fast SCR reaction (Reaction 8). Only a negligible amount of N2O was formed at the low temperature range (210-300 ºC) which might be related to the NH4NO3 decomposition (Reaction 11) [4, 5, 9]:

Figure 7 .

 7 Figure 7.17. 3 cycles NH3 and NOx conversions in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.18. 3 cycles N2 and NOx selectivities in absence of soot in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.19 NH3 and NO2 conversions in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 20 .

 720 Figure 7.20. NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.21. 3 cycles NO and NH3 conversions in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.21 presents the NO2 and NH3 conversions in function of temperature of the 3 cycles NO2-SCR reaction. As already observed with Standard and Fast SCR reactions, the 3 different cycles were practically overlapped and same tendencies were obtained.. Catalytic activity of the catalytic system is considered to be reproducible.

Figure 7 .

 7 Figure 7.22. 3 cycles NOx and N2 selectivities in absence of soot in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .

 7 Figure 7.22 presents the NOx and N2 selectivities in function of temperature of the 3 cycles of the NO2-SCR reaction in soot absence. Regarding the results obtained from the 3 cycles, it can be observed that overlapping of cycles was obtained. Also it is remarkable that an important production of N2O was obtained on the three cycles[2], indicating that non-effective and non-selective NO2 reduction reaction happened on the 3 different cycles (Reaction 13). Same mechanisms than in the single NO2-SCR test (Figure7.20) are considered to take place here.

Figure 7 . 23 .

 723 Figure 7.23. Comparison of NH3 conversions of real Diesel (square symbol) and commercial Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 60 mg of Cu/SAPO-34 + cordierite+ soot layer, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 24 .

 724 Figure 7.24. NOx and N2 selectivities in presence of real Diesel (square symbol) and Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

a)Figure 7 . 25 .

 725 Figure 7.25. NH3 and NO conversions in presence of real Diesel (square symbol) and Printex U (triangle symbol) soots in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg Cu/SAPO-34 + cordierite + soot layer, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 26 .

 726 Figure 7.26. NOx and N2 selectivities in presence of real Diesel soot (square symbol) and Printex U soot (triangle) in function of the temperature. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

Figure 7 .Figure 7 .

 77 Figure 7.27.a) 3 cycles NO and NH3 conversions in presence of real Diesel soot; and b) in presence of Printex U soot in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figures 7. 28

 28 Figures 7.28.a and b present the NOx and N2 selectivities of the 3 different cycles of the Standard SCR reactions in presence of a layer of the real Diesel and Printex U soots, respectively. As already discussed on single Standard SCR reaction with both soots (Figure7.26), important N2O formation was also obtained between 250-400 °C in presence of soots (Reaction 14). However, significant differences on the tendencies and the amounts of formed N2O were observed between the three different cycles

  Figures 7.28.a and b present the NOx and N2 selectivities of the 3 different cycles of the Standard SCR reactions in presence of a layer of the real Diesel and Printex U soots, respectively. As already discussed on single Standard SCR reaction with both soots (Figure7.26), important N2O formation was also obtained between 250-400 °C in presence of soots (Reaction 14). However, significant differences on the tendencies and the amounts of formed N2O were observed between the three different cycles

23 )Figure 7 . 29 .

 23729 Figure 7.29. NO and NO2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 30 .

 730 Figure 7.30. NH3 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 31 .

 731 Figure 7.31. NOx and N2 selectivities in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance.

b) 3 Figures 7 .Figures 7 .

 377 Figures 7.32. a) 3 cycles NO and NO2 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figures 7 . 1 .

 71 Figures 7.33. a) 3 cycles NH3 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figures 7 .Figures 7 .

 77 Figures 7.34.a and b display the NOx and N2 selectivities obtained along the 3 cycles Fast SCR in presence of real Diesel soot and Printex U soot, respectively.

  .a and b, selectivities obtained on the first cycle were slightly lower than on cycles 2 and 3. This might be caused by the soot combustion after first cycle which produced that the NO2 conversion on cycles 2 and 3 was caused by the non-

Figure 7 . 35 .

 735 Figure 7.35. NH3 and NO2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h - 1 .

Figure 7 .

 7 Figure 7.36. NOx and N2 conversions in presence of real Diesel soot (square symbol) and Printex U soot (triangle symbol) in function of the temperature. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance, 60 mg of Cu/SAPO-34 + cordierite + soot layer. 10 L/h, GSHV= 135.000 h - 1 .

b) 3 Figures 7 .

 37 Figures 7.37. a) 3 cycles NO2 and NH3 conversions in presence of real Diesel soot (square symbol); and b) in presence of Printex U soot (triangle symbol) in function of the temperature. 60 mg: Cu/SAPO-34 + cordierite+ soot layer on top. 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .Figures 7 . 1 .

 771 Figure 7.37.a presents the NH3 and NO2 conversions on the 3 cycles NO2-SCR reaction with real Diesel soot. As previously remarked on 3 cycles Standard and Fast SCR reactions, the first cycle showed different behaviour in comparison to cycles 2 and 3 due to the soot oxidation on cycle 1. Although the tendencies were the same for all the cycles. Cycles 2 and 3 appeared almost overlapped for both NH3 and NO2 conversions while higher conversions were obtained in the whole temperature range on cycle 1. Again, the reactivity and adsorption ability of soot seemed to promote higher NO2 and NH3 conversions during the first cycle. Same effects were observed with the Printex U soot on Figure 7.37.b.

Figure 7 . 39 .

 739 Figure 7.39. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under NH3 oxidation conditions: 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 . 40 .

 740 Figure 7.40. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Standard SCR conditions: 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.40 presents the concentrations of the CO and CO2 emitted in function of the temperature due to the soot oxidation under Standard SCR reaction on Tests 16 and 17.Here were presented the concentration measures obtained both during the increasing and decreasing ramps of temperature with both soots. As it was previously noticed, only CO2 was formed[1] and any CO was registered[12]. Very similar increasing and decreasing CO2 emissions were obtained with both kinds of soot. Slightly higher concentration was produced with real Diesel soot due to its more reactive character remarked on Chapter 5. Ais it can be observed on Figure7.40, during the increasing ramp the CO2 formation started above 450 ºC and reach maximum concentrations of 45-50 ppm at 500 ºC[9]. During the decreasing ramp CO2 was still emitted until 475 ºC but in lower amounts compared to the increase. It consisted on 25 ppm after the 30 min plateau at 500 ºC and then, dropped until zero. Here on Standard SCR conditions no NO2 formation was detected (Figure7.26) and because of this it can be concluded that the only origin of the CO2 formation was the thermal soot oxidation by Reaction 1

.a and b. 7 . 5 . 3 .Figure 7 . 41 .

 753741 Figure 7.41. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Fast SCR conditions: 500 ppm NO, 500 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

Figure 7 .

 7 Figure 7.41 presents the CO and CO2 concentrations in function of temperature emitted by the real Diesel and the Printex U soots under Fast SCR conditions. As previously obtained for NH3 oxidation and Standard SCR reactions, any CO formation was produced. However, on Fast SCR conditions CO2 emissions were registered from the beginning of the test at 200 ºC. It can be observed that much higher soot oxidation activity in the low temperature region under Fast SCR conditions[9, 27]. Due to the temperature range where CO2 started, it might be attributed to passive soot regeneration by the NO2 injected in the feed gas[1, 21, 25] following Reaction 4 mechanism (Annex B).

Figure 7 . 42 .

 742 Figure 7.42. CO and CO2 concentrations in function of the temperature of the real Diesel soot (square symbol) and the Printex u soot (triangle symbol) under Fast SCR conditions: 1000 ppm NO2, 1000 ppm NH3, 8% O2, 3% H2O and He as balance. Cu/SAPO-34 + cordierite + soot layer: 60 mg, 10 L/h, GSHV= 135.000 h -1 .

  .a and b) and the drop on the NO2 conversion along cycles, as a result (Figures 7.38.a and b). It is necessary to remark that between 250-400 ºC, NO formation (Figures 7.38.a and b) was produced by the passive soot oxidation (Reaction 4) on NO2-SCR reactions.

Test 24 .

 24 Stabilisation test Standard SCR conditions (200 ppm). Sample 5-004 -200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 200 ºC and all pollutants were injected from the beginning -Temperature decrease under N2 and once, room temperature was reached. Installation and feed gas were switched off during the night until next day Test 25. Stabilisation test Standard SCR conditions (200 ppm). Sample 6-004 -200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 200 ºC and all pollutants were injected from the beginning -Temperature decrease under N2 and once, room temperature was reached. Installation and feed gas were switched off during the night until next day Test 26-31. Stabilisation test Standard SCR conditions (200 ppm). Run 1 to 7. Sample 5-004 -200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere -Test initial temperature was fixed as 200 ºC and all pollutants were injected from the beginning -Temperature decrease under N2 and once, room temperature was reached. Installation and feed gas were switched off during the night until next day.

Test 16 .

 16 Standard SCR reaction (60 mg: mixed Cu/SAPO-34+ cordierite and top layer of real Diesel soot)

Figure D. 1 .

 1 Figure D.1. X-Ray diffractogram of the commercial washcoat.

  .1 is clearly summarized the main information about the location of the SAPO-34 peaks and the orientation of the crystals. Intensity values of each peak are indicated on both on the Figure D.1 and the Table D.1.

Figure D. 2 .

 2 Figure D.2. SEM image of the commercial washcoat.

Figure D. 2

 2 Figure D.2 allows to observe that the distribution and size of the SAPO-34 crystals was quite homogeneous, as it was expected from a commercial catalyst. High crystallinity and pure phase of the SAPO-34 zeolite were observed. The SEM image show clearly the typical cubiclike rhombohedra morphology of the SAPO-34 zeolites [4, 7, 9]. Also, it can be concluded that the Cu Introduction did not affect the SAPO-34 crystals morphology. The crystal size observed on Figure D.2 indicated that crystals between 2-3 μm were obtained. Similar average crystal size (2-5 μm) was reported by other author as Wang et al. [7], Gao et al. [9], Liu at al. [1] and Wang et al. [8].

  .5 was translated to Figure D.3.

Figure D. 3 .

 3 Figure D.3. EDX element distribution of the commercial washcoat.

On

  Figure D.4 it can be observed that two crystalline phases composed the analysed sample: bigger, darker and rectangular crystals are related to cordierite support and cubic, lighter and cubic crystals are linked to the SAPO-34 zeolite.Again, the typical cubic crystals of the SAPO-34 zeolites between 2-3 μm were observed. Si islands and surface CuO scraps were again observed in this sample.

Figure D. 4 .

 4 Figure D.4. SEM image of the crushed commercial mini-SCRF catalyst.

Figure D. 5 .

 5 Figure D.5. EDX element distribution of the crushed commercial mini-SCRF.

Table 1 . 1 .

 11 European Union emission standards for Diesel passenger vehicles in g/km ............

Table 1 . 2 .

 12 Evolution of European Union emission

Table 1 . 5 .

 15 . Summary of research groups results of catalysis in the cage ................................

Table 1 . 6 .

 16 Summary of research groups results about PM loading blocking effect ...............

Table 1 .

 1 7.a. Summary of research group results of soot-SCR interactions on powder catalysts

Table 7 . 1 .

 71 Feed gas composition for cordierite under Standard SCR ................................. 113

Table 7 . 2 .

 72 Test matrix of soot + cordierite under Standard SCR ........................................ 116

Table 7 . 3 .

 73 Test matrix of 60 mg of Cu/SAPO-34 + cordierite under NH3 oxidation ........... 122

Table 7 . 4 .

 74 Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Standard SCR conditions ..124

Table 7 . 5 .

 75 Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Fast SCR conditions 127

Table 7 . 6 .

 76 Test matrix of 60 mg of Cu/SAPO-34 + cordierite under NO2-SCR conditions. .....131

Table 7 . 7 .

 77 Test matrix of 60 mg of Cu/SAPO-34 + cordierite + soot under NH3 oxidation .136

Table 7 . 8 .

 78 Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Standard SCR conditions . 138

Table 7 .

 7

Table 1 .1. European Union emission standards for Diesel passenger vehicles in g/km [1, 9, 10].

 1

			Diesel engines
		CO	HC+ NOx	NOx	PM
	Euro 1 (1992)	2.72	0.97	-	0.14
	Euro 2 (1996)	1.00	0.90	-	0.10
	Euro 3 (2000)	0.64	0.56	0.50	0.05
	Euro 4 (2005)	0.50	0.30	0.25	0.025
	Euro 5 (2009)	0.50	0.23	0.18	0.005
	Euro 6 (2014)	0.50	0.17	0.08	0.005

Table 1 .2. Evolution of European Union emission standards and engine cycles for Diesel passenger vehicles

 1

	Euro 1 Euro 2 Euro 3 Euro 4	Euro 5a	Euro 5b	Euro 6b/c	Euro 6d
	Europe	Urban+ EUDC Cycle		Revised Urban+ EUDC Cycle	WLTC+RDE*
	1992	1996	2000	2005	2009	2011	2014	2017-2021

*Euro 6c test cycle WLTC: to be confirmed Not only european countries have emission standards, Table

Table 1 .3. US emission standards evolution.

 1

	US	Tier 0	Tier 1	Tier 2	Tier 3	Tier 4 Tier 4f
		1994	2000	2006	2011	2013	2015

Table 1 .4. Summary of SCR reactions.

 1

	(7) 4 NH3 + 4 NO + O2 → 4 N2 + 6 H2O
	(8) 2 NH3 + NO + NO2 → 2 N2 + 3 H2O
	(9) 4 NH3 + 3 NO2 → 7/2 N2 + 6 H2O
	(10) 4 NH3 + 2 NO2 + O2 → 3 N2 + 6 H2O
	(11) NH4 + + NO3 -→ NH4NO3 → N2O + 2 H2O
	(12) NH4 + + NO2 -→ NH4NO2 → N2 + 2 H2O
	(13) 2 NH3 + 2 NO2 → N2O + N2 + 3 H2O
	(14) 2 NH3 + 2 NO + 3 O2 → 4 N2O + 6 H2O
	(15) 2 N2O → 2 N2 + O2
	(16) 2 NH3 + 3 N2O → 4 N2 + 3 H2O
	(17) 7 NH4NO3 + NO →N2 + 2 H2O + NO2
	(18) 4 NH3 + 3 O2 → 2 N2 + 6 H2O
	(19) 4 NH3 + 5 O2 → 4 NO+ 6 H2O

SCR reactions appears in gas containing NOx when injecting reductant in a lean atmosphere. In function of the NO2/NOx content, different SCR reactions may occur (Reactions 7-10).

Table 1 .5. Summary of research groups results of catalysis in the cage. Author Zeolite type Active phase Characterisation technique T activity Active site and location Xue [111]

 1

		SAPO-34	Cu	Experimental EPR and TOF	100-200 °C	Isolated Cu 2+	d6r, 8MR
		SSZ-13	Cu	DFT/EXAFS [43]	200-500 °C	Cu 2+ ions	d6r
	Deka [43]	SAPO-34	Cu	TPR and FTIR [43]	-	Isolated Cu 2+ ions	d6r
				Experimental
		SSZ-13	Cu	SCR conditions [114]	-	Isolated Cu 2+ ions	d6r
	Beale [102]	SSZ-13	Cu	Standard SCR PXRD	200°C 500 °C	Isolated Cu ions	8MR
	Lezcano-
	Gonzalez	SSZ-13	Cu	Experimental (FTIR)	250 °C	Cu + /Cu 2+ redox pair	d6r
	[104]
							Tetra-coordinated
	Gao [125]	SSZ-13	Fe	Experimental FTIR	500 °C	Isolated Fe 3+	(extra-
							framework)

Table 1 .6. Summary of research groups results about PM loading blocking effect.

 1

Powder catalyst Ref. Catalyst Test type/ conditions Soot blocking effect Temperature affected (°C)

		Marchitti et al. [82]	Cu-zeolite+ SiC crushed	Standard SCR reaction	NO and NH3 inhibition consumption	150-350
		Mihai et al [158]	Cu-CHA+ Cordierite	Standard SCR reaction	NOx conversion inhibition	200-300
					a. Higher NO2-
	SCRF catalyst	Mihai et al. [94]	Cu-CHA+ Cordierite	NO2-SCR reaction	SCR activity and b. Less N2O selectivity	100-400
					formation
		Park et al. [171]	Cu-zeolite	Model simulation	Negative effect on conversions NH3 and NOx	200-600

Table 1 .7.a. Summary of research group results of soot-SCR interactions on powder catalysts.

 1

					Temperatu
	Ref.	Catalyst	Test type	NOx-soot interactions	re affected (°C)
				NH3 inhibition effect on soot
				oxidation
			a. Standard, NO2	a. Negative NH3 effect on PM
			and Fast SCR	oxidation
	Tronconi et al. [79]	Cu-zeolite + SiC	reactions (NOx absence) b. PM oxidation	b. Positive effect on O2-active soot regeneration	a. 200-450 b. 250-400
	catalyst Powder		e:Soot= 10:10:1) (Cu/SCRF:Cordierit Soot loading: 7 mg	activity and lower N2O c. Positive soot effect on SCR Soot effect on SCR activity	c. 200-500
				formation (NO2 excess
				conditions)
	Marchitti et al. [82]	Cu-zeolite + SiC/cordierit e substrates	a. Standard, NO2 and Fast SCR reactions b. PM oxidation (NOx absence) Soot loading: 5 mg (Cu/SCRF:Cordierit	NO2 content effect a. Positive NOx effect on PM oxidation Soot effect on SCR activity b. Negative soot effect over SCR activity (Standard and Fast SCR conditions)	a. 250-400 b. 200-500 c. 200-500
			e:Soot= 10:10:1)	c. Enhanced NH3 oxidation

Table 1 .7.a. Summary of research group results of soot-SCR interactions on SCRF catalysts.

 1

Table 3 .1 Commercial sample characteristics. IFPEN (mini-SCRF) IRCELYON (powder sample from crushed mini- SCRF) L*Ø (cm)

 3

		7.5	-
	Density (cpsi)	400	-
	Total mass (g)	15	0.025
	Volume (cm 3 )	37	-
	Support	cordierite	cordierite
	Mass of Cu-zeolite
	(60 g/L)	2.22*	0.0037*
	* Estimated values

Table 4 .1. Tests matrix (500 ppm) NOx/ O2 (10%)

 4

	NO/O2 (Test 6)	NO (ppm) O2 (10%)	500 10
	NO2/O2 (Test 8)	NO2 (ppm) O2 (10%)	500 10

Table 4 .2. Test matrix NH3/O2 (10%)

 4

		Pollutants	Test 11 (Annex A)
	NH3/O2	NH3 (ppm) O2 (10%)	500 10

Table 4 .3. Tests matrix simple NH3/ NO

 4

		Pollutants	Test 2 (Annex A)	Test 3 (Annex A)
		NO (ppm)	200	200
	NH3/NO	NH3 (ppm)	200	240
		NH3/NOx ratio	1	1,2

It can be observed on Table

4

.3 that, in Tests 2 and 3, the NH3/NO ratios were not the same. , being 1 for test 2 and 1,2 test 3. For Test 2, 200 ppm both of NH3 and NO were injected on the reactor. For test 3, 200 ppm of NO were added too but this time 240 ppm of NH3 were injected.

Table 4 .4. Test matrix for Standard SCR reactions

 4

	Pollutants concentration	Tests 1 and 13	Test 7
	NH3 (ppm)	200	500
	NO (ppm)	200	500
	NO2 (ppm)	0	0
	H2O (%)	10	10
	O2 (%)	10	10
	CO2 (%)	9	9

a) Catalyst stabilisation under Standard SCR conditions (200 ppm) (Annex A. Test 1)

Table 4 .5. Test matrix for NO2-SCR reactions

 4

	Pollutants	Test 10	Test 12
	NH3 (ppm)	200	500
	NO (ppm)	0	0
	NO2 (ppm)	200	500
	H2O (10%)	10	10
	O2 (10%)	10	10
	CO2 (10%)	9	9

a) NO2-SCR reaction (200 ppm) (Annex A.

Test 10)

Table 4 .6. Test matrix for Fast SCR reactions.

 4

	Pollutants	Test 14	Test 15
	NH3 (ppm)	200	500
	NO (ppm)	100	250
	NO2 (ppm)	100	250
	H2O (10%)	10	10
	O2 (10%)	10	10
	CO2 (10%)	9	9

a) Fast SCR reaction (200 ppm) (Annex A.

Test 14)

Table 4 .7. Maximum NOx and NH3 conversions and N2O selectivity in function of temperature.

 4

		NOx conversion	NH3 conversion	N2O selectivity
	Test	T (ºC)	NOx conversion (%)	T (ºC)	NH3 conversion (%)	T (ºC)	N2O selectivity (%)
	Test 1 Std. SCR (200 ppm)	300	93	400	100	0	0
	Test 4 NH3/NO2= 1	300	95	350	100	275	20
	Test 7 Std. SCR (200 ppm)	350	85	400	100	0	0
	Test 10 NO2-SCR (200 ppm)	350	65	400	100	300	13
	Test 14 Fast SCR (200 ppm)	325	45	500	75	300	3

Table 5 .1. Peak (ºTheta), counts and crystal orientation of the H-SAPO-34 and the Cu/SAPO-34.

 5

	Peak (ºTheta)	Counts	Crystal orientation h k l
	9,55	747,3	1	0	1
	12,99	511,9	1	1	0
	16,15	538,2	2	0	1
	17,81	480,9	0	0	3
	19,17	504,5	2	0	2
	20,78	440	2	1	1
	23,23	476,1	2	1	2
	25,01	421,0	1	0	4
	26,28	361,5	2	2	0
	27,99	431,2	3	1	1
	30,89	439,4	4	0	1
	31,23	422,1	2	1	4

Table 5 .2. Chemical composition of the commercial Cu/SAPO-34 catalyst.

 5

Cu/SAPO-34

  SAPO-34 zeolites were compared with the aim of evaluate if the Cu introduction affected the chemical composition of the zeolite. Literature ICP-OES results

	Si (% wt)	2,6	3,1	3,5	3,5
	Al (% wt)	19,2	18,4	22,8	19,9
	P (% wt)	19,3	19,0	18,3	17,1
	Cu (% wt)	-	-	2,5	3,1
	Ratio Si/Al	0,14	0,17	0,15	0,18
	Ratio P/Al	1,01	1,03	0,83	0,86

Experimental element contents of the in-laboratory synthesized catalyst obtained by ICP-OES analysis are compared with some literature results on Table

5

.2. Here, the H-SAPO-34 and the impregnated Cu/

Table 5 .3. EDX results in comparison to the ICP-OES values from the synthesized Cu/SAPO-34.

 5

		Cu (% wt) Si (% wt) Al (% wt) P (% wt)	Ratio Si/Al	Ratio P/Al
	EDX	1,4	2,8	18,3	12,6	0,15	0,7
	ICP-OES	2,5	3,5	22,8	18,3	0,15	0,8

Table 5 .4. EDX results on a cubic SAPO-34 crystal and on the amorphous phase. Cu (% wt) Si (% wt) Al (% wt) P (% wt) Si/Al ratio P/Al ratio

 5

	AR22 (amorphous phase)	1,8	1,9	20,3	12,4	0,10	0,61
	AR23 (cubic crystal)	1,8	3,3	16,2	9,6	0,20	0,60

Table 5 .5. Physical properties of the synthesized Cu/SAPO-34 catalyst.

 5

		BET surface area (m 2 /g)	Pore width (Å)	Total pore volume (cm 3 /g)	Micropores volume (cm 3 /g)
	Synthesized Cu/SAPO-34	411	8,5	0,16	0,15

Table 6 .1. Peak (ºTheta), counts and crystal orientation of the Printex U and real Diesel soot.

 6

	Peak (ºTheta)	Intensity (counts)	Crystal orientation h k	l
	24,22	2000	1	1	1
	26,43	1900	0	0	2
	42,08	900	1	0	0
	6.3. CHNS ANALYSIS

Table 6 .2. Chemical composition of the Printex U and real Diesel soot.

 6

		Content
	Element	(% wt)
		Printex U	Real Diesel soot
	Carbon	97,61	91,75
	Hydrogen	0,58	1,07
	Nitrogen	-	-
	Sulphur	-	0,32

* Dash symbol (-): not detected.

Table 6 .3. D/G band ratios of the Printex U and real Diesel soot.

 6

		Printex U	Real Diesel soot
		1,1794246	1,5783781
		1,1993346	1,4799488
		1,3411047	1,5822008
		1,340901	1,550617
	D/G ratio	1,4040836 1,3178123	1,6156924 1,6143243
		1,1759907	1,5502796
		1,1467196	1,5727514
		1,3187653	1,5395403
		1,3013042	1,56312
	Average	1,27254406	1,56344737

Table 6 .4. EDX results in comparison to the ICP-OES values of the Printex U and the real Diesel soot.

 6

	Sample	Technique C (% wt)	O (% wt) Si (% wt)	S (% wt)
		EDX	96,0	4,0	0	0,1
	Printex U
		ICP-OES	97,6	-	-	0
	Real Diesel	EDX	94,4	5,1	0,1	0,4
	soot	ICP-OES	91,8	-	-	0,3

Table 7 .1. Feed gas composition for cordierite under Standard SCR.

 7

	Pollutants concentration	Test 2
	NH3 (ppm)	1000
	NO (ppm)	1000
	H2O (%)	3
	O2 (%)

Table 7 .2. Test matrix of real Diesel soot + cordierite under Standard SCR.

 7

	Pollutants concentration	Test 12
	NH3 (ppm)	1000
	NO (ppm)	1000
	H2O (%)	3
	O2 (%)	8

Table 7 .3. Test matrix of 60 mg of Cu/SAPO-34 + cordierite under NH3 oxidation.

 7

Table 7 .4. Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Standard SCR conditions.

 7

Table 7 .5. Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Fast SCR conditions.

 7

Table 7 .6. Test matrix of 60 mg of Cu/SAPO-34 + cordierite under NO2-SCR conditions.

 7

Table 7 .7. Test matrix of 60 mg of Cu/SAPO-34 + cordierite + soot under NH3 oxidation.

 7

Table 7 .8. Test matrix of 60 mg of Cu/SAPO-34 + cordierite under Standard SCR conditions. Pollutants concentration Tests 16, 17, 18 and 19 NO (ppm)

 7

	1000

Table 7 .9. Test matrix of 60 mg of Cu/SAPO-34 + cordierite + soot layer under Fast SCR conditions.

 7

Table 7 .10. Mmatrix of 60 mg of Cu/SAPO-34 + cordierite + soot under NO2-SCR conditions.

 7

Test 1. Stabilisation test under Standard SCR conditions (200 ppm)

  Test initial temperature was fixed as 200 ºC and all pollutants were injected from the beginning -Temperature decrease under N2 and once, room temperature was reached. Installation and feed gas were switched off during the night until next day.

	-200 ppm NO, 200 ppm NH3, 10% O2, 10% H2O, 9% CO2 under N2 atmosphere
	-Test 2. NH3/NO (200 ppm) ratio 1 test
	-200 ppm NO, 200 ppm NH3 under N2 atmosphere
	-Test started at room temperature conditions, so no N2 passage had been previously done
	-Then, temperature increased until 200 ºC was done by N2 passage through reactor
	during an hour

Test 3. (240 ppm) NH3/NO (200 ppm) ratio 1.2 test -

  200 ppm NO, 240 ppm NH3 under N2 atmosphere -Test started at 200 ºC due to in Test 2 nothing special happened at lower temperatures.Then, temperature was decreased until room temperature and both, installation and feed gas were switched off during the weekend days. Test initial temperature started at room temperature. So N2 was not needed to make reactor reach test conditions -After test, temperature was decrease until room temperature by N2 flow passage.

	Annex A
	-Then, temperature was decreased until room temperature cooling the reactor by N2 flow
	passage for 2 hours.
	Test 5. (240 ppm) NH3/NO2 (200 ppm) ratio 1.2 test
	-200 ppm NO2, 240 ppm NH3 under N2 atmosphere
	-
	Test 4. (200 ppm) NH3/NO2 ratio 1 test
	-200 ppm NO2, 200 ppm NH3 under N2 atmosphere
	-Test initial temperature started at 200 ºC. To reach it, N2 was used to put reactor in
	testing conditions

Standard SCR test (1000 ppm). Run1 -

  2 was followed. 1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He atmosphere -Test initial temperature was fixed as 200 ºC for test developed at IRCELYON. -After test, temperature was decrease until room temperature by He flow passage and installation was kept like this until next test.-1000 ppm NO, 1000 ppm NH3, 8% O2, 3% H2O under He atmosphere -Test initial temperature was fixed as 200 ºC.-After test, temperature was decrease until room temperature by He flow passage. Installation and feed gas were switched off.

	Annex A
	Test 16. Test 17. Standard SCR test (10000 ppm). Run 2

Table D .1. Peak (ºTheta), counts and crystal orientation of the H-SAPO-34.

 D

	Peak (ºTheta)	Counts	h	Crystal orientation k	l
	10,968	8,541	1	0	1
	17,828	4,914	0	0	3
	19,152	4,684	2	0	2
	21,990	4,101	2	1	2
	26,107	3,386	2	2	0
	28,854	3,142	3	1	1
	29,837	3,029	4	0	1
	34,228	2,649	2	1	4
	36,873	2,455	1	1	0
	38,541	2,338	2	0	1
	41,323	2,174	2	1	1
	59,062	1,690	1	1	4

Table D .2. Peak (ºTheta), counts and crystal orientation of the Cu metal.

 D

	Peak (ºTheta)	Counts	h	Crystal orientation k	l
	9,543	9,303	1	0	0
	15,917	5,481	1	0	2
	20,862	4,267	1	1	4
	31 ,330	-	2	1	1

Table D .3. Chemical composition of the commercial Cu/SAPO-34 catalyst.

 D

		Si	Al	P	Cu	Ratio	Ratio
		(% wt)	(% wt)	(% wt)	(% wt)	Si/Al	P/Al
	Commercial Cu/SAPO-34	4,10	16,38	5,38	2,49	0,25	0,33
	[1] Cu-SAPO-34	13,1	13,5	5,3	3,4	0,40	0,39
	[12] H-SAPO-34	3,1	18,4	19,0	-	0,18	1,04
	[6] Cu/SAPO-34	3,5	19,9	17,1	3,1	0,18	0,86

Table D .4. Chemical composition of the crushed commercial mini-SCRF catalyst.

 D

		Cu	Si	Al	P	Ratio	Ratio
		(% wt)	(% wt)	(% wt)	(% wt)	Si/Al	P/Al
	Commercial Washcoat Cu/SAPO-34	2,49	4,10	16,38	5,38	0,25	0,33
	Commercial crushed mini-SCRF	1,76	3,01	17,56	15,95	0,16	0,91

Table D .5. EDX results in comparison to the ICP-OES values from commercial the washcoat.

 D

		Cu (% wt) Si (% wt) Al (% wt) P (% wt)	Ratio Si/Al	Ratio P/Al
	EDX	3,61	12,47	15,32	21,45	0,81	1,40
	ICP-OES	2,49	4,10	16,38	5,38	0,25	0,33
	On Table

Table D .6. EDX results in comparison to the ICP-OES values from the crushed mini-SCRF catalyst. Cu (% wt) Si (% wt) Al (% wt) P (% wt) Ratio Si/Al

 D

							Ratio
							P/Al
	EDX	2,26	20,08	20,66	12,25	0,97	0,59
	ICP-OES	1,76	3,01	17,56	15,95	0,16	0,91
	On Table

All authors afore-mentioned, and their investigated catalysts and operational conditions studied are summarized in Table 1.5.

Only thermal NH3 oxidation took place above 350 ºC, yielding NO as main product (Reaction 19). Also certain N2O formation happened at the same temperature range and negligible NO2 was produced above 400 ºC. However, 75% of selectivity yielded N2 (Reaction 18) which was considered to be the principal NH3 oxidation mechanism. Cordierite was confirmed to be inert to NOx reduction.

Then, real Diesel soot and the Printex U were separately mixed with the cordierite support to be studied under Standard SCR conditions. Main conclusions were: Very small conversions of NO and NH3 (15%) were obtained only at temperatures higher than 400 ºC. The non-selective NO reduction yielded 60% of N2O selectivity at 350 ºC by Reaction 14. This N2O formation is thought to be promoted by the soot, as it was registered with both soots. With Printex U soot, small formation of NO2 occurred above 400 ºC. In both cases, only CO2 was formed due the thermal oxidation of soots above 375 ºC. It is remarkable that higher CO2 formation was produced by the Printex U soot due to the cooperation of certain NO2 passive oxidation of soot.

Once, each component of the catalytic system was individually evaluated, the complexity was increased one step and the complete catalytic system was tested (Cu/SAPO-34 + cordierite and soot layer, when necessary). However, feed gas mixture was kept simple and NH3 oxidation reactions were performed on soot presence and absence as it will be in competition with the SCR reactions at high temperature region. Main conclusions were: Complete NH3 oxidation was not produced only with Printex U soot where a maximum of 90% was reached at 500 ºC. This was a positive effect as reductant agent will be still available to reduce NOx even at high temperatures. Without soot the main mechanism yielded N2 formation (Reaction 18) while in presence of soots, significant by-products formation occurred. Especially with the real Diesel soot, indicating that it was more reactive (accordingly to its physicochemical characterisation discussed on Chapter 5: CHNS and TGA analysis). Due to the absence of NO in this test, origin of these by-products might be related to the NH3 and soot interaction. Referring to the CO and CO2 produced due to the soots oxidation under NH3 oxidation conditions, it was registered that both passive (medium temperature range: 300-400 ºC) and thermal soot oxidation (high temperature range: 400 ºC) were produced. Only CO2 was obtained as product indicating that Reaction 1 and 4 were the followed mechanism, respectively. Later, complete catalytic system and complex feed gas composition was evaluated varying the NO/NOx ratio to observe its influence on the catalyst behaviour. First, all the three different SCR reactions were evaluated in absence of soot and, then, repeated in soot presence to complete the study of the soot influence.

LIST OF PUBLICATIONS AND CONFERENCES

PUBLICATIONS