Mouna Sayehi
email: sayahimouna@gmail.com

Gabriella Garbarino

Gerard Delahay

Guido Busca

Hassib Tounsi

Gérard Delahay

Synthesis of high value-added Na-P1 and Na-FAU zeolites using waste glass from fluorescent tubes and aluminum scraps

Keywords: Valorization, aluminum scraps, Fluorescent tube glass, faujasite, NaP1 zeolite

teaching and research institutions in France or abroad, or from public or private research centers.

Introduction

Zeolites are microporous solids, with 3-dimensional framework of [SiO 4 ] 4-and [AlO 4 ] 5-tetrahedra linked at their corners. This structure generated pores and channels with molecular dimensions which confer to zeolites sieving molecular properties and high thermal, mechanical and chemical stability. Due to their interesting properties, zeolites can be useful in many industrial fields such as catalysis [START_REF] Kumar | Nickel / zeolite and Copper-Nickel / zeolite catalysts[END_REF], water treatment [2], detergent builders adsorbents, agricultural application [START_REF] Gomes | Potassic zeolites from Brazilian coal ash for use as a fertilizer in agriculture[END_REF], biotechnology and medicine [START_REF] Bacakova | Biomaterials Science medicine -a review[END_REF]. Usually, zeolite preparation was effected by hydrothermal method using expensive starting materials like alumina, silica, mineralizer (alkali metal hydroxide), structure directing agents and water [START_REF] Breck | Zeolite molecular sieves, structure, chemistry, and use[END_REF].

The use of expensive starting materials may restrict the application of zeolites in some fields like environment and agriculture. Therefore, the recent studies are focused on an economical process for zeolite synthesis to satisfy the large demand of zeolitic materials. To achieve this goal, researches used natural raw materials and low-cost industrial by-products to prepare zeolites (Chaves Lima et al. 2019). Inexpensive materials are mainly clays [START_REF] Yang | [END_REF][START_REF] Abdullahi | A review on sustainable synthesis of zeolite from kaolinite resources via hydrothermal process A review on sustainable synthesis of zeolite from kaolinite resources via hydrothermal process[END_REF][START_REF] Abdullahi | A review on sustainable synthesis of zeolite from kaolinite resources via hydrothermal process[END_REF][START_REF] Yoldi | Microporous and Mesoporous Materials Zeolite synthesis from industrial wastes[END_REF] (Abdullahi et al., 2017;[START_REF] Liu | Microporous and Mesoporous Materials Rapid green synthesis of ZSM-5 zeolite from leached illite clay[END_REF][START_REF] Yoldi | Microporous and Mesoporous Materials Zeolite synthesis from industrial wastes[END_REF], volcanic glasses [11], Tunisian sand [START_REF] Tounsi | Hydrothermal Synthesis of Na-LTA , Na-X and HS Zeolites from Tunisian Sand and Aluminum Scraps[END_REF][START_REF] Tounsi | Preparation and characterization of Na-LTA zeolite from Tunisian sand and aluminum scrap[END_REF] or industrial waste products as coal fly, bagasse fly ash [START_REF] Dere | A Novel Synthesis Method of Zeolite X From Coal Fly Ash : Alkaline Fusion Followed by Ultrasonic-Assisted Synthesis Method[END_REF][START_REF] Yoldi | Microporous and Mesoporous Materials Zeolite synthesis from industrial wastes[END_REF][START_REF] Wahyu | Microporous and Mesoporous Materials Synthesis of pure Na -X and Na -A zeolite from bagasse fly ash[END_REF], waste sanitary porcelain [START_REF] Maatoug | Valorization of vitreous China waste to EMT/FAU, FAU and Na-P zeotype materials[END_REF], waste aluminum cans [START_REF] Abdelrahman | Synthesis of zeolite nanostructures from waste aluminum cans for efficient removal of malachite green dye from aqueous media[END_REF], aluminum scraps [START_REF] Tounsi | Hydrothermal Synthesis of Na-LTA , Na-X and HS Zeolites from Tunisian Sand and Aluminum Scraps[END_REF][START_REF] Tounsi | Preparation and characterization of Na-LTA zeolite from Tunisian sand and aluminum scrap[END_REF][START_REF] Abid | Preparation of LTA , HS and FAU / EMT intergrowth zeolites from aluminum scraps and industrial metasilicate[END_REF] and glass wastes [START_REF] Attari | A low-cost adsorbent from coal fly ash for mercury removal from industrial wastewater[END_REF][START_REF] Kim | Synthesis of uniform-sized zeolite from windshield waste[END_REF][START_REF] Yao | Recycling of typical difficult-to-treat e-waste: Synthesize zeolites from waste cathode-ray-tube funnel glass[END_REF][START_REF] Tsujiguchi | Synthesis and characterization of zeolite A from crushed particles of aluminoborosilicate glass used in LCD panels[END_REF][START_REF] Majdinasab | Microwave Synthesis of Zeolites from Waste Glass Cullet Using Landfill Leachate as a Novel Alternative Solvent[END_REF][START_REF] Majdinasab | Microwave synthesis of zeolites from waste glass cullet using indirect fusion and direct hydrothermal methods: A comparative study[END_REF][START_REF] Mamannajdinasab | Cost-e ff ective zeolite synthesis from waste glass cullet using energy e ffi cient microwave radiation[END_REF][START_REF] Terzano | Facile Zeolite Synthesis from Municipal Glass and Aluminum Solid Wastes[END_REF]. Due to the high silica content and its free composition of toxic and hazardous element, glass wastes are important starting materials for zeolite preparation. According to [28](Chaves Lima et al., 2019), the first study conducted to prepare porous materials (ANA and GIS zeolites) was completed using waste bottle glass. [START_REF] Takei | Preparation of porous material from waste bottle glass by hydrothermal treatment[END_REF]. Industrial raw powder glass was used in 2014 by [START_REF] Alves | Synthesis of high value-added zeolitic materials using glass powder residue as a silica source[END_REF] [START_REF] Alves | Synthesis of high value-added zeolitic materials using glass powder residue as a silica source[END_REF]) to prepare zeolite LTA, X and HS. [START_REF] Alves | Synthesis of high value-added zeolitic materials using glass powder residue as a silica source[END_REF]) used the alkaline fusion followed by a hydrothermal treatment technique since the glass powder residue is difficult to zeolitize by hydrothermal treatment in basic media. [START_REF] Kim | Synthesis of uniform-sized zeolite from windshield waste[END_REF] (Kim et al., 2015) successfully synthesized uniform-sized LTA zeolite from windshield waste via highenergy ball milling and a low-temperature hydrothermal process. [START_REF] Terzano | Facile Zeolite Synthesis from Municipal Glass and Aluminum Solid Wastes[END_REF] [START_REF] Terzano | Facile Zeolite Synthesis from Municipal Glass and Aluminum Solid Wastes[END_REF] showed the facile zeolite synthesis from municipal glass and aluminum solid wastes. They obtained by hydrothermal treatment at 60°C for 7 days a zeotype material containing 30% of zeolite LTA when NaOH is used as mineralizing agent. When KOH was employed, 25% of edingtonite has been produced in the final material after one week at 90°C. The e-wastes like LCD panel glass [START_REF] Tsujiguchi | Synthesis and characterization of zeolite A from crushed particles of aluminoborosilicate glass used in LCD panels[END_REF] and cathode-ray-tube funnel glass [START_REF] Yao | Recycling of typical difficult-to-treat e-waste: Synthesize zeolites from waste cathode-ray-tube funnel glass[END_REF] were also used in the preparation of LTA, FAU and NaP1 zeolites. Zeolite HS and NaP1 were prepared using microwave radiation from residue called waste glass cullet [START_REF] Majdinasab | Microwave Synthesis of Zeolites from Waste Glass Cullet Using Landfill Leachate as a Novel Alternative Solvent[END_REF][START_REF] Majdinasab | Microwave synthesis of zeolites from waste glass cullet using indirect fusion and direct hydrothermal methods: A comparative study[END_REF][START_REF] Mamannajdinasab | Cost-e ff ective zeolite synthesis from waste glass cullet using energy e ffi cient microwave radiation[END_REF]. On the other hand, [START_REF] Vinaches | Author ' s Accepted Manuscript study[END_REF][START_REF] Vinaches | Author ' s Accepted Manuscript[END_REF] used fluoride media for the zeolitization of raw powder glass to ZSM-5 and MEL zeolites.

Here we report for the first time, the co-valorization of waste glass (WG) derived from fluorescent tubes and aluminum scraps into Na-P1 and Na-FAU zeolites. It should be mentioned that the glass of the end-of-life of fluorescent tubes is an attractive material due to its high silica content. In Taiwan, the average number of end-of-life fluorescent lamps generated each year is about 3.8 tubes per person [START_REF] Peng | other developed countries[END_REF]. Unfortunately, the majority of fluorescent tubes contain hazardous elements (mercury) that present risks on the environment and on human health. We used the alkaline fusion method prior to hydrothermal treatment for the zeolitization of waste glass derived from fluorescent tubes. The influence of some parameters like alkalinity, reaction time and particle size on the nature of obtained zeolites has been also studied. The starting materials and the prepared zeolites were characterized by several techniques. The X-ray diffraction, Fourier-transform infrared spectroscopy and 27 Al, 29 Si magic angle spinning nuclear magnetic resonance were used for the structural characterization. The morphology, the particle size distribution and the textural properties were studied using scanning electron microscope, laser diffraction particle size analyzer and the adsorption-desorption of nitrogen gas at -196 °C, respectively.

Experimental procedure

Zeolite preparation

The aluminum source is scraps collected from aluminum workshop and the silica source was obtained by crushing the glass of the end-of-life fluorescent tubes collected from the special containers established by the administration of the National Engineering School of Sfax-Tunisia for the collection of hazardous waste. Various particle sizes of glass powder (63 µm, 125 µm and 315µm) as average particle diameter were used in this procedure. The chemical composition of the WG was as follows: SiO 2 -64.6%, Na 2 O-21.5%, CaO-6.9%, MgO-3.0%, Al 2 O 3 -2.5%, K 2 O-0.83%, Fe 2 O 3 -0.2%, SO 3 -0.12 % and TiO 2 -0.06%. The chemical composition of aluminum scraps (AS) is Al-99,77 % with very small quantities of iron Fe-0.207 % and copper Cu-0.08 %. Analytical grade NaOH pellets was purchased from Sigma Aldrich and 98%. The alkaline fusion technique followed by the treatment has been chosen for the zeolitization of the WG. This technique consists of heating various NaOH/WG mixtures with different mass ratios (R 1 =0.8; R 2 =1.0 and R 3 =1.2) at 550 °C for 1h in a nickel crucible. The fused products are named FP-R-y with R referred to the NaOH/WG mass ratio and y the particle size of the WG (63 µm; 125 µm; 315 µm). After fusion, the obtained product was cooled, ground again and mixed with 80 mL of sodium aluminate solution (SAS); L/S= 10. It is mentioned that the SAS was obtained by dissolving 0.5 g of aluminum scraps (AS) into 80 mL of 2.5 mol/L aqueous solution of NaOH. The mixture was vigorously stirred at room temperature (RT) for 2h and then let reacting in an oven for 6 days at 60°C. At the end of the process, the solid was separated by filtration and washed thoroughly several times with deionised water until pH 9. The precipitated solid was dried at 80°C for one night. The synthesized products are named ZFP-R-y with R referred to the NaOH/ WG mass ratio (0.8; 1.0; 1.2) and y the particle size of the WG (63 µm; 125 µm; 315 µm)(Figue 1 )

Characterization

The wastes, the fused products and the prepared zeolites were characterized by different techniques. X-ray fluorescence (XRF) was used to assess chemical composition of the WG using Philips X'UNIQUE II apparatus. The chemical composition of the aluminum scraps was analyzed by NITON XL3t GOLDD de THERMO. Structural phase analysis by Xray diffraction (XRD) was performed on a D8 AXS (DRX-Bruker D8) diffractometer, using

CuKα radiation (λ = 1.540598) in which the Bragg angle (2θ) was scanned from 5° and 60°.

FTIR spectra of the samples were recorded in air at RT using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The spectra were recorded using a Perkin Elmer Fourier transform infrared spectrometer in the wave-number range 4000-400 cm -1 . The examination of the morphology of both raw materials and solid products was investigated by scanning electron microscopy (SEM) with a JEOL JSM-5400 instrument.

Physisorption isotherms were measured at -196 °C on a Micromeritics ASAP 2020 instrument with nitrogen as probe molecule. Prior to measurement the samples were degassed for 12 hours at 200 °C before adsorption. 27 Al and 29

Results and discussion

Characterization of the fused waste

The X-ray diffraction patterns of the fused products using different NaOH/WG ratios are reported in figure 2. The fusion step at 550 °C for 1h facilitates the formation of soluble silicate and aluminate salts which are crystallized afterward into zeolites by the hydrothermal treatment. Indeed, the XRD profiles show the decrease of the amorphous content of the WG and the appearance of new peaks related to crystalline phases. The phase identification was carried out using X'Pert High Score Plus software. The FTIR spectra of the fused products displayed significant changes in relative intensities and width of vibration bands compared to WG spectrum (figure 3). There is a shift of the large band at 1050 cm -1 attributed to asymmetric stretching vibration of the Si-O groups in the WG to lower wavenumber at 925-1200 cm -1 [START_REF] Maatoug | Valorization of vitreous China waste to EMT/FAU, FAU and Na-P zeotype materials[END_REF][START_REF] Jiang | Reaction behaviour of Al 2 O 3 and SiO 2 in high alumina coal fly ash during alkali hydrothermal process[END_REF] .This result confirms the formation of silicate and aluminosilicate salts as showed by XRD technique. It should be mentioned that the fused products contains carbonate species confirmed by the presence of the peaks at 1450 cm -1 and 880 cm -1 .

Influence of NaOH/WG ratio on the nature of the obtained zeolites

To investigate the effect of NaOH/WG mass ratio on the resulting zeolite products, three mixtures (R 1 =0.8, R 2 =1.0 and R 3 =1.2) were tested using WG powder with a particle size Ø ). The analysis of the diffraction patterns showed that the nature of the prepared zeolite depends on the NaOH/WG ratio. The increase of the NaOH amount from R 1 =0.8 to R 2 =1.0 had no important effect on zeolite crystallization [START_REF] Rayalu | Highly crystalline faujasitic zeolites from flyash[END_REF]. For ZFP-1.2-125 sample, the increase of the mass ratio favors the formation of Na-P1 zeolite at the expense of FAU zeolite. This result can be explained by the influence of the residual amount of NaOH on the alkalinity of the solution. [START_REF] Volli | Selective Preparation of Zeolite X and A from Flyash and its use as Catalyst for Biodiesel Production Selective preparation of zeolite X and A from flyash and its use as catalyst for biodiesel production[END_REF] [START_REF] Volli | Selective Preparation of Zeolite X and A from Flyash and its use as Catalyst for Biodiesel Production Selective preparation of zeolite X and A from flyash and its use as catalyst for biodiesel production[END_REF] showed that with the increase in NaOH concentration; in the case of the zeolitization of fly ash; there is an increase in supersaturation which could change the type of zeolite. According to Ostwald's rule of successive transformation, the higher the supersaturation, better the condition to nucleate metastable phases, such as zeolite FAU, which later recrystallizes and is replaced by highly stable zeolite Na-P1. The 27 Al MAS-NMR spectra of the WG and of the zeotype materials are reported in figure 7. 27 Al MAS-NMR spectrum of WG displays a broad peak at 55.2 ppm with fullwidth-at-half-maximum (FWHM) of about 25 ppm. This peak is typical of aluminum atoms in a tetrahedral coordination, which is broadened to the more shielded side of the peak. After the zeolitization of the fused product, the samples ZFP-0.8-125, ZFP-1.0-125 and ZFP-1.2-125 exhibit strong peaks centered at 57-58 ppm ascribed to the aluminum atoms in a tetrahedral coordination [START_REF] Huo | Microporous and Mesoporous Materials Synthesis of zeolite NaP with controllable morphologies[END_REF]. For ZFP-1.2-125, an additional peak was observed at 10 ppm which may indicate the presence of another phase beside zeolite having the aluminum in octahedral environment. 27 Al MAS-NMR technique confirms the results of XRD and SEM in which the formed zeolite FAU tends to dissolve and re-crystallize during the experiment to zeolite Na-P1 [START_REF] Ruen-Ngam | Zeolite Formation from Coal Fly Ash and Its Adsorption Potential Zeolite Formation from Coal Fly Ash and Its Adsorption Potential[END_REF].

The 29 Si(4Al), Si(3Al), Si(2Al), Si(1Al) and Si(0Al) [START_REF] Miku | Microporous and Mesoporous Materials Synthesis of the zeolite granulate for potential sorption application[END_REF]. For the sample ZFP-1.2-125, despite the bad resolution one can distinguish three peaks at about ca. -85, -89, -92 ppm. On the other hand, it is possible to calculate the framework Si/A1 ratio according to the equation:

; where I Si(nAl) is the intensity of a 29 Si MAS NMR peak.

The Si/Al molar ratio determined by 29 Si-NMR of ZFP-0.8-125 is about 1.44, which is in good agreement with the Si/Al ratios of the FAU zeolites. Increasing the amount of sodium hydroxide (ZFP-1.0-125) increases the Si/Al ratio from 1.44 to 1.67. wavenumber at 925-1200 cm -1 and became sharper [START_REF] Jiang | Reaction behaviour of Al 2 O 3 and SiO 2 in high alumina coal fly ash during alkali hydrothermal process[END_REF]. The band at around 1005 cm -1 could be assigned to asymmetric stretching of T-O bonds (T = Si or Al) in zeolites, whereas the symmetrical stretching of T-O bonds is situated at 750 cm -1 . The bands near 668 cm -1 and 740 cm -1 are ascribed to a symmetric stretch of internal tetrahedra as well as of external linkages.

The band related to T-O bending mode in aluminosilicate zeolites is present near 445 cm -1 .

The bands at higher wavenumbers 3450 cm -1 can be assigned to stretching vibrations of O-H bonds whereas the bands at around 1652 cm -1 to bending vibrations of water molecules. In zeolite materials, the 800-500 cm -1 region is related to the bands originating from structural units, like S4R, S6R, D4R and D6R rings [START_REF] Nezamzadeh-Ejhieh | Hexadecylpyridinium surfactant modi fi ed zeolite A as an active component of a polymeric membrane sul fi te selective electrode[END_REF]. Thus, the bands at 600 cm -1 and 610 cm -1 for ZFP-0.8-125 and ZFP-1.0-125, respectively were assigned to the vibrations of tetrahedra from external linkages of the double six rings (D6R) in the framework of zeolite Na-FAU.

The presence of two bands at about 740 cm -1 and 668 cm -1 associated with four-membered ring vibrations occurring both in the structure of Na-FAU and Na-P1 zeolites. The absorption band at 569 cm -1 of ZFP-1.2-125 is due to the S4R T-O-T symmetric stretching of Na-P1

zeolite [START_REF] Azizi | Phase Transformation of Zeolite P to Y and Analcime Zeolites due to Changing the Time and Temperature[END_REF]. The band centered at about 1450 cm -1 may represent the vibration of carbonate species. Table 2: BET specific surface areas (S BET ), microporous surface (S mic ), external surface (S ext ), microporous volume (V mic ), total volume (V tot ) and BJH pore diameter (Ø pore ) of the prepared samples.

Influence of the reaction time

Figure 11 shows the XRD patterns of the synthesized samples obtained at different crystallization periods at 60 °C obtained from NaOH/WG ratio R 1 =0.8 using WG-125. The X-ray profile of the solid obtained after 2 days of hydrothermal treatment (ZPF-0.8-2d) shows a broad hump in the baseline between about 15 and 35° 2θ, which is related to the presence of

Samples

Figure 1 :

 1 Figure 1: Schematic diagram of Zeolite synthesis.

  Si MAS-NMR spectra were recorded on a Brucker 300 MHz (AMX 300) at 78.20 and 58.48 MHz, respectively. The chemical shift in ppm was obtained with respect to AlCl 3 .6H 2 O and TMS as external references for Al and Si, respectively. Particle size distribution (PSD) of the samples was determined by laser diffraction particle size analyzer type Malvern Instruments Ltd (Mastersizer). The standard volume percentiles at 10, 50, and 90, denoted as D10, D50 and D90, respectively, were recorded from the analysis and used to calculate the width of the distribution span.

Figure 2 :

 2 Figure 2: XRD patterns of the WG and the three fused products after the fusion step at 550

Figure 3 :

 3 Figure 3: Infrared spectra of the fused products.

<

  125 µm (WG-125). The XRD patterns of the recovered solids after hydrothermal treatment at 60 °C for 6 days were illustrated in figure 4. The phase identification was carried out using X'Pert High Score Plus software. The analysis of the diffraction patterns shows that ZFP-0.8-125 and ZFP-1.0-125 samples, contain a mixture of zeolite faujasite at 6.16°, 10.02°, 11.80°, 15.51°, 20.02° and 23.39° (|Na 4.43 (H 2 O) 8.882 |[Al 6 Si 6 O 24 ]; JCPDS N°01-072-2421) and the socalled zeolite Na-P1 (|Na 6 (H 2 O) 12 | [Al 6 Si 10 O 32 ]; JCPDS N°01-071-096). The sample ZFP-1.2-125 contains mainly the zeolite Na-P1 (2θ 12.53°; 21.76°; 28.12° and 33.48°

Figure 4 : 5 .Figure 5 : 6 .

 4556 Figure 4: Zeolites obtained by alkaline fusion followed by hydrothermal treatment.

Figure 6 :

 6 Figure 6: PSD of the samples ZFP-0.8-125, ZFP-1.0-125 and ZFP-1.2-125.

  Si MAS-NMR spectra of the WG and samples ZFP-0.8-125, ZFP-1.0-125 and ZFP-1.2-125 are reported in figure 8. The spectrum of the WG shows a broad peak (FWHM = 21 ppm) centered about -92 ppm with shoulder at about -103 ppm. According to the chemical shift ranges and the large amount of alkalis (Na 2 O + K 2 O = 22.33%) in the WG, one can assume that the majority of silicon species are of type Q 2 and Q 3 . After the zeolitization of the WG, one can see clear changes in the 29 Si MAS-NMR spectra of ZFP-0.8-125, ZFP-1.0-125 and ZFP-1.2-125 samples. ZFP-0.8-125 and ZFP-1.0-125 show five peaks centered at ca. -87, -91, -97, -102 and -107 related to the respective Q 4 Si coordination environments

Figure 7 :Figure 8 :ZFP- 1 . 2 -125 are summarized in Figure 9 .

 78129 Figure 7: 27 Al MAS NMR spectra of WG-125 and the recovered solids after hydrothermal

1 )Figure 9 :Figure 10 :

 1910 Figure 9: Infrared spectra of WG-125 and the recovered solids products ZFP-0.8-125, ZFP-

Figure 11 :

 11 Figure 11: XRD patterns of ZFP0.8 as function of time (2, 4, 6, 8 and 10 days).

Figure 12

 12 Figure 12 illustrated the XRD patterns of the obtained zeolites when the particle sizes

Figure 12 :

 12 Figure 12: XRD patterns of ZFP-0.8-63, ZFP-0.8-125 and ZFP-0.8-315.

Figure 13 :

 13 Figure 13: XRD patterns of ZFP-1.0-63, ZFP-1.0-125 and ZFP-1.0-315.

Figure 14 :

 14 Figure 14: XRD patterns of ZFP-1.2-63, ZFP-1.2-125 and ZFP-1.2-315.

ZFPFig. 16 :

 16 Fig. 16: SEM micrographs of zeolite obtained at NaOH/WG=1.2 from various particle size.

  In this study, it was shown that valorizing WG and AS into high added value zeolites at minimum energy consumption is possible. Alkaline fusion prior to hydrothermal treatment was employed as recycling process. The results indicated that alkalinity, reaction time and particle size of the powder of WG have a significant role in zeolite synthesis. Increasing the NaOH/WG ratio from 0.8 to 1.0 and 1.2, favors the transformation of zeolite Na-FAU to Na-P1. The same transformation was showed by prolonging crystallization time from 2 to 10 days and increasing particle size form 63 µm to 315 µm.

Table 1 summarized

 1 the different solids found in the fused products after the fusion step. The mainly compounds detected are the sodium silicates Na

3 HSiO 4 (H 2 O) 2 and Na 4 SiO 4 regardless

  the NaOH quantity. This result is expected since the SiO 2 /Al 2 O 3 molar ratio of the WG is about 43. Accordingly, the peaks detected at 2θ 16.92°, 17.57°, 18.96°, 29.46°, 32.26° and 34.23° are related to trisodium hydrogensilicate dihydrate Na

3 HSiO 4 (H 2 O) 2 and the peaks of sodium orthosilicate Na 4 SiO 4

	appeared at 18,29° , 34,85° , 38,80° and 39,58° . Besides, slight amount of NaAlSi 2 O 6
	(JCPDS No.01-071-1507) is also detected for FP-0.8-125 and FP-1.0-125 samples (30,40° ,
	31,42° , 35,86°and 36,96°). When the NaOH quantity is increased for samples

FP1.0-125 and FP-1.2-125, there is appearance of sodium calcium silicoaluminate Ca 0.86 Na 0.14 Al 1.84 Si 2.16 O 8 (21,97°, 27

  ,75°, 27,88° and 28,01° ). The residual NaOH with peaks at 15,56°, 31,42° and 38,23° can be related to the excess of NaOH used for the alkaline fusion[START_REF] Maatoug | Valorization of vitreous China waste to EMT/FAU, FAU and Na-P zeotype materials[END_REF][START_REF] Ma | Feasible conversion of solid waste bauxite tailings into highly crystalline 4A zeolite with valuable application[END_REF][START_REF] Majdinasab | Cost-effective zeolite synthesis from waste glass cullet using energy efficient microwave radiation[END_REF].

Table 1 :

 1 Quantitative analysis of the fused products.

	Compound

NaAlSi 2 O 6 (%) Na 3 HSiO 4 (H 2 O) 2 (%) Na 4 SiO 4 (%) Ca 0.86 Na 0.14 Al 1.84 Si 2.16 O 8

						NaOH
						(%)
					(%)
	JCPDS N°	01-071-1507	01-074-0667	01-078-1432	01-076-0832	01-078-0189
	FP-0.8-125	7	71	18	-	-
	FP-1.0-125	5	42	26	25	2
	FP-1.2-125	-	35	38	18	9

Table 2 :

 2 Granulometric

		ZFP-1.2-125
	Samples	ZFP-0.8-125	ZFP-1.0-125	ZFP-1.2-125
	D10 (µm)	0.71	3.21	1.70
	D50 (µm)	11.5	23.9	35.5
	D90 (µm)	59.4	60.4	96.2
	Span	5.1	2.4	2.7
	M1 (µm)	0.46	0.50	0.45
	M2 (µm)	2.13	3.61	2.00
	M3 (µm)	34.53	35.09	59.50

parameters of the obtained zeolites ZFP-0.8-125, ZFP-1.0-125 and

  After 4 days, one can see the development of the new peaks relative to crystalline phases and the decrease of the quantity of amorphous phase. Indeed, the peaks can be associated to zeolite Na-FAU (6.16°, 10.02°, 11.80°, 15.51°, 20.02° and 23.39°) The transformation of the metastable phase; zeolite Na-FAU to more thermodynamically stable phase zeolite Na-P1 at longer reaction time can be explained by Oswald's rule of successive transformations. It is well known that zeolite formation is a kinetically controlled process and the reaction is generally stopped when the desired zeolite has formed. Extended reaction time at high

	amorphous aluminosilicate gel. and Na-P1 (12.53°; 21.76°; 28.12° and 33.48°). After 6 days of crystallization, the amorphous
	S BET phase totally disappears in favor of the crystalline phases. The peak intensities of zeolite Na-S mic S ext V mic V tot Ø pore
	(m 2 /g) P1 increase after the prolonged crystallization period up to 6 days [40]. In table 3, is reported (m 2 /g) (m 2 /g) (cm 3 /g) (cm 3 /g) (nm)
	ZFP-0.8-63 the zeolite quantification as function of time from 6 to 10 days. The relative quantity of NaP1 40 12 29 0.005 0.115 12.7
	phase increased from 42% for ZPF-0.8-6d to 80% for ZPF-0.8-10d.
	ZFP-0.8-125	329	276	53	0.131	0.200	8.7
	ZFP-0.8-315	12	9	3	0.004	0.039	9.2
	ZFP-1.0-63	489	381	108	0.169	0.311	6.1
	ZFP-1.0-125	392	309	83	0.148	0.230	5.5
	ZFP-1.0-315	85	42	43	0.020	0.077	6.3
	ZFP-1.2-63	51	21	30	0.010	0.067	9.2
	ZFP-1.2-125	24	7	17	0.003	0.062	16.7
	ZFP-1.2-315	62	36	26	0.017	0.079	6.7

Table 4 : Quantification of ZFP0.8-6d, ZFP0.8-8d and ZFP0.8-10d samples. Compound JCPDS N° ZFP-0.8-6d ZFP-0.8-8d ZFP-0.8-10d

 4

	Na-FAU (%) 01-076-0843	58	24	20
	Na-P1 (%)	01-071-0962	42	76	80
	3.4.

Influence of the WG particle size


Magdalena Jabłońska
email: jablonska@itmc.rwth-aachen

Miren Agote Arán

Andrew M Beale

Gérard Delahay

Carolina Petitto

Marek Nocuń

Regina Palkovits
email: palkovits@itmc.rwth-aachen.de

Understanding the origins of N 2 O decomposition activity in Mn-Co-Al-O x hydrotalcite derived mixed metal oxides

Keywords: hydrotalcite-like compounds, mixed metal oxides, cobalt, N 2 O decomposition, XAFS

The catalytic decomposition of N 2 O was studied over a series of calcined (Mn,Fe)-Co-Al hydrotalcite-like compounds. The precursors were prepared by coprecipitation and characterized by XRD and TGA. While the mixed metal oxides derived after calcination at 600 °C were characterized by XRD, N 2 adsorption, H 2 -TPR and XPS. Moreover, in situ XAFS measurements over selected mixed metal oxides were performed. Such investigations under reaction conditions are rare, while a comprehensive understanding of the involved active species may facilitate a knowledge-based catalyst optimization. The activity of the Co-Al (Co/Al = 3/1, mol.%) catalyst varied depending on the loading of Mn or Fe (0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%). In the investigated series, Mn 0.1725 Co 3 A l mixed metal oxides reached the highest activity with T 50 of about 305 and 376 °C under N 2 O/N 2 and N 2 O,NO,O 2 /N 2 feed, respectively. In situ X-ray absorption experiments over Mn 0.1725 Co 3 A l O x suggested that Mn x Co y O 4 spinel undergo reduction to CoO and MnO upon heating up to 600 °C in He. Under N 2 O/He conditions initial reoxidation of cobalt species began at 350 °C. The lower activity obtained for Fe 0.1725 Co 3 A l O x is explained by the fact that the majority of Fe was not incorporated into the Co 3 O 4 structure but instead formed less reactive iron oxide clusters.

Introduction

The catalytic decomposition of N 2 O (deN 2 O) belongs to the best available technologies for N 2 O abatement from nitric acid production, which is one of the major industrial sources of N 2 O emission. The broad collection of catalysts were applied at temperatures below 450-500 °C [START_REF] Jablonska | Nitrogen oxide removal over hydrotalcite-derived mixed metal oxides[END_REF]. As implied by the published results, hydrotalcite derived mixed metal oxides present high activity for deN 2 O even in the presence of H 2 O, O 2 , SO 2 and/or NO x . The hydrotalcite-like compounds with a general formula of M 2+ 1-x M 3+ x (OH) 2 (A n-) x/n • mH 2 O, where M 2+ and M 3+ -bi-and trivalent metal cations, respectively, A n--an interlayer anion, and x -M 3+ /(M 3+ +M 2+ ) with a value between 0.17 -0.50 [START_REF] Cavani | Hydrotalcite-type anionic clays: Preparation, properties and applications[END_REF][START_REF] Vaccari | Preparation and catalytic properties of cationic and anionic clays[END_REF], serve as excellent precursors for the preparation of the catalysts of the desired chemical and phase composition for deN 2 O. Thermal decomposition of hydrotalcite-like compounds at middle temperatures (£600 °C) results in the formation of the relatively high surface mixed metal oxides, with a high dispersion of introduced transition oxide metal species [START_REF] Chmielarz | Selective Catalytic Oxidation (SCO) of Ammonia to Nitrogen over Hydrotalcite Originated Mg--Cu--Fe Mixed Metal Oxides[END_REF][START_REF] Jabłońska | Thermal transformations of Cu--Mg (Zn)--Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen[END_REF][START_REF] Jabłońska | Redox-performance correlations in Ag-Cu-Mg-Al, Ce-Cu-Mg-Al, and Ga-Cu-Mg-Al hydrotalcite derived mixed metal oxides[END_REF]. Recently, Jabłońska and Palkovits [START_REF] Jablonska | Nitrogen oxide removal over hydrotalcite-derived mixed metal oxides[END_REF][START_REF] Jablonska | It is no laughing matter: nitrous oxide formation in diesel engines and advances in its abatement over rhodium-based catalysts[END_REF] reviewed hydrotalcite derived mixed metal oxides in deN 2 O, and concluded that the activity of the mixed metal oxides varied depending on the type and loading of the catalytically active metal, its oxidation state as well as dispersion and aggregation state, etc. The research of hydrotalcite derived mixed metal oxides focusses mainly on cobalt-based materials: Co-Al-O x (e.g. [START_REF] Pérez-Ramı Ŕez | Structural promotion and stabilizing effect of Mg in the catalytic decomposition of nitrous oxide over calcined hydrotalcite-like compounds[END_REF][START_REF] Pérez-Ramírez | High activity and stability of the Rh-free Co-based ex-hydrotalcite containing Pd in the catalytic decomposition of N2O[END_REF]), Co-(Mg)-Mn-(Al)-O x (e.g. [START_REF] Obalová | Catalytic decomposition of nitrous oxide over catalysts prepared from Co/Mg-Mn/Al hydrotalcite-like compounds[END_REF][START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF][START_REF] Obalová | Alkali metals as promoters in Co-Mn-Al mixed oxide for {N2O} decomposition[END_REF]), Co-Mg-Al-O x or Co-Cu-Mg-Al-O x (e.g. [START_REF] Chmielarz | An influence of thermal treatment conditions of hydrotalcite-like materials on their catalytic activity in the process of N2O decomposition[END_REF]), etc. Kannan et al. [START_REF] Armor | Calcined hydrotalcites for the catalytic decomposition of N2O in simulated process streams[END_REF][START_REF] Kannan | Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds[END_REF][START_REF] Kannan | Catalytic decomposition of nitrous oxide over calcined cobalt aluminum hydrotalcites[END_REF] and furthermore Pérez-Ramírez et al. [START_REF] Pérez-Ramı Ŕez | Structural promotion and stabilizing effect of Mg in the catalytic decomposition of nitrous oxide over calcined hydrotalcite-like compounds[END_REF] found Co/Al with 3/1 molar ratio as optimal hydrotalcite derived catalyst dedicated to deN 2 O among catalysts varied between Co/Al = 3-1/1, mol.%. The Co 3 Al 1 mixed metal oxides reached 84-100% conversion at 450 °C.

Kannan et al. [START_REF] Kannan | Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds[END_REF][START_REF] Kannan | Catalytic decomposition of nitrous oxide over calcined cobalt aluminum hydrotalcites[END_REF] reported that the activity of Co-Al mixed metal oxides correlated with the Co/Al bulk composition, but, an even better correlation in the activity was obtained with the Co 2+ (generated by surface reduction and reconstruction) of mixed metal oxides, as determined by XPS. Obalová et al. [START_REF] Obalová | Catalytic decomposition of nitrous oxide over catalysts prepared from Co/Mg-Mn/Al hydrotalcite-like compounds[END_REF][START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF][START_REF] Kovanda | Mixed oxides obtained from Co and Mn containing layered double hydroxides: Preparation, characterization, and catalytic properties[END_REF] investigated numerous combinations of Co(Mg)-Mn(Al), and found Co 4 Mn 1 Al 1 O x as optimum catalyst for deN 2 O (82-97% conversion at 450 °C). The authors reported an optimum surface amount of Co 2+ /Co 3+ and Mn 2+ /Mn 3+ molar ratios at 1.13 and 2.27 by XPS. Moreover, as determined from H 2 -TPR, Co 4 Mn 1 Al 1 O x possessed an optimum amount of components reducible in the temperatures of the maximum conversion of N 2 O (between 350-450 °C) [START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF]. Since the detailed study of the involved active species of the hydrotalcite derived catalysts under reaction conditions was beyond of the previously published results. Thus, the above studies were the inspiration for Our present investigation focused on identifying in situ the exact nature of cobalt species in Mn(Fe)CoAl hydrotalcite-derived mixed metal oxides applied to deN 2 O. Moreover, precursors and/or mixed metal oxides were characterized by XRD, TG, N 2 adsorption and H 2 -TPR, in order to explore additional structure-activity correlations.

Experimental

Catalysts preparation

A series of Mn(Fe) x Co 3 Al 1 (x = 0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%) hydrotalcite-like compounds was prepared by the coprecipitation. An aqueous solution containing appropriate amounts of following metal

nitrates: Co(NO 3 ) 2 •6H 2 O (Roth), Al(NO 3 ) 3 •9H 2 O (Sigma), Mn(NO 3 ) 2 ×4H 2 O (Roth), Fe(NO 3 ) 3 ×9 H 2 O (Roth)
and 1 M NaOH (Chemsolute) was dropped simultaneously to a vigorously stirred at 60 °C aqueous solution containing a slight over-stoichiometric excess of Na 2 CO 3 (Sigma). The pH of the reaction mixture was maintained constant at 10.0 ± 0.2 throughout the whole synthesis by NaOH addition. The obtained suspension was aged at 60 °C for another 0.5 h after complete coprecipitation. The solid was filtered, washed carefully with distilled water and dried at room temperature. Finally, the prepared hydrotalcite-like compounds were crushed and calcined at 600 °C for 6 h with a heating ramp of 10 °C/min and in static air. The hydrotalcite derived mixed metal oxides were kept in a desiccator in order to avoid the reconstruction of the hydroxide-like structure. For catalytic experiments, a fraction of particle size in the range of 0.250-0.500 mm was used.

Catalysts characterization

The X-Ray diffraction (XRD) measurements of the all as-synthesized hydrotalcite-like compounds and mixed metal oxides formed by their thermal decomposition was performed applying a Siemens D5000 XRD diffractometer using Cu-Kα radiation (λ = 1.54056 Å, 45 kV, 40 mA). The difference thermogravimetric analysis (DTG) of the hydrotalcite-like compounds (~20 mg) was carried out using a Netzsch STA 409C/CD operated under a flow of air (10 cm 3 /min) in the temperature range of 30-1000 °C with a linear heating rate of 5 °C /min. The specific surface area (S BET ) of the mixed metal oxides was determined by low-temperature (-196 °C) N 2 sorption using a Quantachrome Quadrasorb SI. Prior to nitrogen adsorption the samples were outgassed at 250 °C for 12 h using a Quantachrome Flovac degasser. The specific surface area (S BET ) was calculated using the Brunauer-Emmett-Teller (BET) multiple point method in the p/p 0 range from 0.05 to 0.3. The chemical analysis of mixed metal oxides was determined by ICP-MS using an Agilent Technologies 8800 Triple Quad spectrometer. Prior to measurement, sample (50 mg) was dissolved in 6 cm 3 mixture of concentrated acids (HCl:HNO 3 , 1:1), and afterwards the resulted mixture was diluted with 64 cm 3 deionized water before warming up to 40 °C for 24 h. The redox properties of the selected mixed metal oxides were studied by the temperatureprogrammed reduction (H 2 -TPR) using Quantachrome ChemBET Pulsar TPR/TPD. H 2 -TPR runs for the samples (30 mg) were carried out starting from room temperature to 1000 °C, with a linear heating rate of 10 °C /min and in a flow (25 cm 3 /min) of 5.0 vol.% H 2 /Ar. Water vapour was removed from effluent gas by the means of a cold trap placed in an ice-water bath. The H 2 consumption was detected and recorded by TCD detector. The X-ray photoelectron spectra (XPS) of selected mixed metal oxides were measured on a VSW spectrometer equipped with a hemispherical analyzer. The photoelectron spectra were measured using a magnesium MgKa source (E = 1253.6 eV). The base pressure in the analysis chamber during the measurements was 3×10 -6 Pa and the spectra were calibrated on a main carbon C 1s peak at 284. The X-ray absorption spectra (XAS) of selected samples were collected in situ using the quartz capillary flow reactor cells, and gas delivery systems available on the beamline, on station B18 at the Diamond Light Source synchrotron facility. The measurements were carried out using a Si(111) monochromator at the Co K-edge, Mn K-edge or Fe K-edge with the respective Co, Mn or Fe monometallic foils (10 µm) used as an energy calibrant for the monochromator. The catalyst diluted with SiO 2 (1:5) was sieved into 0.200-0.250 mm and placed into the reactor. Prior to the reaction the catalyst was outgassed at 600 °C for 1 h in a flow of pure He (10 cm 3 /min), and subsequently cooled down to 100 °C. The reactant concentrations at the reactor inlet composed of [N 2 O] = 0.1 vol.% and [He] = 99.9 vol.% (10 cm 3 /min). The temperature was raised in steps of 50-100 °C up to 600 °C.

Each temperature was hold for 30 min. X-ray absorption spectra at appropriate K-edges was collected in fluorescence mode for 240 s for Co, Fe or Mn K-edges. At least three spectra for each sample were taken at room temperature, appropriate temperatures and after reaction at room temperature. CoO, Co 3 O 4 , FeO, Fe 2 O 3 , MnO 2 references were measured only at room temperature. The data were analysed using the Demeter software package [START_REF] Newville | IFEFFIT: interactive XAFS analysis and FEFF fitting[END_REF][START_REF] Ravel | HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT[END_REF]); the edge position was determined as the first maximum -after the pre-edge peak -of the derivative of the XANES spectra.

Catalytic tests

The catalytic performance of the mixed metal oxides was evaluated in the N

Results and discussion

Fig. 1 presents the XRD patterns of Mn(Fe) x Co 3 Al 1 (x = 0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%) hydrotalcite-like compounds, exhibiting rhombohedral symmetry (space group R3m, 3R 1 polytype) [START_REF] Newman | Synthesis of the 3R2 polytype of a hydrotalcitelike mineral[END_REF] with sharp and symmetrical reflections (0 0 3), (0 0 6), (1 1 0) and (1 1 3), and broad and asymmetrical reflections (0 1 2), (0 1 5) and (0 1 8). The intensity of the reflection corresponding to the hydrotalcite-like phase were very weak for samples with 0.0575 mol.% of Mn or Fe. However, the intensity of such phases increased with increasing loading of both transition metals. Table 1 summarizes the unit cell parameters of the hydrotalcitelike compounds and their derivatives. The cell parameters were calculated using a position of (1 0 1) reflection: (according to Allred-Rochow scale) [START_REF] Allred | A scale of electronegativity based on electrostatic force[END_REF]. The crystal sizes were calculated from the Scherrer equation D = 0.89×l/b×q, where D is the crystallite size, l is the X-ray wavelength, b is the line broadening and q is the Bragg angle. The Fe-containing materials revealed overall higher crystal size (with the exception of Fe 0.0575 Co 3 Al 1 )

a = 2(d 1 1
than corresponding MnCo 3 Al 1 compounds.

Fig. 2 presents the DTG profiles of Mn(Fe) x Co 3 Al 1 (x = 0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%) hydrotalcite-like compounds, while Table 2 gathers total mass loss of these materials. DTG profiles revealed the presence of two stages of weight loss, providing an additional proof of the achievement of the hydrotalcitelike structure. The thermal decomposition of Mn(Fe)-Co-Al precursors proceeded in two main stages with total mass losses of about 30-33%. The first DTG minimum centered at about 190-200 °C corresponded to the removal of interlayer and weakly adsorbed water without collapse of the structure. The second peak located at about 230-235 °C appeared due to the dehydroxylation of the brucite-like layers and thermal decomposition of interlayer carbonates and nitrates (e.g. [START_REF] Jabłońska | Thermal transformations of Cu--Mg (Zn)--Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen[END_REF][START_REF] Jabłońska | Redox-performance correlations in Ag-Cu-Mg-Al, Ce-Cu-Mg-Al, and Ga-Cu-Mg-Al hydrotalcite derived mixed metal oxides[END_REF][START_REF] Newman | Synthesis of the 3R2 polytype of a hydrotalcitelike mineral[END_REF]). The temperatures and peak intensities did not change significantly among studied precursors, possibly due to small differences in the Mn or Fe loading as well as similar size of Mn 2+ and Fe 3+ (as cations of metal precursors) in octahedral coordination of 0.058 and 0.055 0.070 nm, respectively [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF]. [START_REF] Ravel | HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT[END_REF][START_REF] Zhu | Highly Active and Stable Co3O4/ZSM-5 Catalyst for Propane Oxidation: Effect of the Preparation Method[END_REF][START_REF] Meena | Rietveld refinement and spectroscopic analysis of Co3-xMnxO4 (0.1≤ x≤ 1.0) ceramic compositions[END_REF][START_REF] Chang | Analysis of N2O decomposition over fixed bed mixed metal oxide catalysts made from hydrotalcite-type precursors[END_REF]45,56,59, 65, 77°) (e.g. [START_REF] Pérez-Ramı Ŕez | Structural promotion and stabilizing effect of Mg in the catalytic decomposition of nitrous oxide over calcined hydrotalcite-like compounds[END_REF][START_REF] Kannan | Catalytic decomposition of nitrous oxide over calcined cobalt aluminum hydrotalcites[END_REF]), exhibiting cubic symmetry (space group Fd3m) [START_REF] Klyushina | Effect of preparation method on catalytic properties of Co-Mn-Al mixed oxides for N2O decomposition[END_REF]. The lattice parameter a in the range of 0.8073-0.8099 nm was close to Co 3 O 4 (a = 0.8084 nm). Mn-or Fe-containing materials did not reveal any diffraction characteristic for transition metal oxides in the XRD patterns, which confirmed the absence of bigger crystallites. Crystal sizes of 26-33 nm were calculated from (3 1 1) brag reflection in the XRD patterns using the Scherrer equation. [START_REF] Genty | Co-Al mixed oxides prepared via LDH route using microwaves or ultrasound: Application for catalytic toluene total oxidation[END_REF]. Mn(Fe) x Co 3 Al (x = 0.1725, 0.2300, mol.%) revealed similar H 2 -TPR profiles to Co 3 Al 1 . However, the modification of Co 3 Al with Mn or Fe influenced its redox properties, i.e. the position of the first reduction peaks shifted to higher temperatures for Mn-or Fe-doped materials than for Co 3 Al 1 , while the position of the second peak shifted to lower temperatures, indicating depressed reducibility of Co 3 O 4 and improved of cobalt in Co 2 AlO 4 and CoAl 2 O 4 . Such effect was more visible for FeCoAlO x . Additionally, for the Fe-containing samples a broad shoulder appeared at about 700 °C possibly due to reduction of iron oxide species [START_REF] Chmielarz | Selective Catalytic Oxidation (SCO) of Ammonia to Nitrogen over Hydrotalcite Originated Mg--Cu--Fe Mixed Metal Oxides[END_REF][START_REF] Jabłońska | Thermal transformations of Cu--Mg (Zn)--Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen[END_REF]. Table 3 summarizes H 2 -TPR data of the studied materials. The H 2 uptake varied in the range of 5.22-6.64 mmol/g in the temperature range of 50-530 °C (where N 2 O decomposition proceeded). Furthermore, analysis of reduction peak areas (A b /A c , estimated from the integrated areas of the respective H 2 -TPR peaks) revealed comparable ratio (0.29 to 0.35) across the samples.

Due to different oxidation states of metal oxide species in spinel forms, the calculations of the H 2 uptake based on materials composition could be speculative. Fig. 5 shows the Co 2p, O 1s, Mn 2p and Fe 2p XPS spectra of Co 3 Al 1 O x and Mn(Fe) 0.1725 Co 3 Al 1 O x , while Table 3 summarizes the peaks positions, their binding energies, peak areas, full with at half maximum (FWHM) and O a /(O b +O g ) molar ratio. The Co 2p XPS spectra exhibited two main peaks characterized by binding energies in the ranges of 781.6-779.6 and 796.9-795.0 eV corresponding to the Co2p 3/2 and 2p 1/2 spin-orbit peaks, respectively [START_REF] Murthy | Catalytic decomposition of 2-propanol on Co1+xAl2-xO4 spinel system[END_REF]. Thus, since the spin-orbit values for the tested materials have varied in the range of 15.3-15.4 eV, we concluded that mainly Co 3 O 4 (spin-orbit value of 15.2 eV) together with CoAl 2 O 4 (as minor compound; spin-orbit value of 15.9 eV) existed on the catalysts surface [START_REF] Murthy | Catalytic decomposition of 2-propanol on Co1+xAl2-xO4 spinel system[END_REF][START_REF] Luo | Mesoporous Co3O4-CeO2 and Pd/Co3O4-CeO2 catalysts: Synthesis, characterization and mechanistic study of their catalytic properties for low-temperature CO oxidation[END_REF][START_REF] Zhu | Highly Active and Stable Co3O4/ZSM-5 Catalyst for Propane Oxidation: Effect of the Preparation Method[END_REF]. Considering that Mn or Fe are present only in small amounts in the materials, determination of manganese or iron chemical state in the measured Mn(Fe) 0.1725 Co 3 Al 1 O x based on the position of the binding energy could be speculative. Furthermore, Mn or Fe may be present in several chemical states with the overlapping spectra, which are close in energy [START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF][START_REF] Graat | Quantitative Analysis of Overlapping XPS Peaks by Spectrum Reconstruction: Determination of the Thickness and Composition of Thin Iron-oxide Films[END_REF]. The O 1s spectra were deconvoluted to lattice oxygen -O a , surface adsorbed oxygen, OH groups and oxygen vacancies -O b and adsorbed molecular water -O g [START_REF] Santos | The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds[END_REF].

Additional low peaks at about 527-528 eV appeared possibly due to the differential charging of the materials [START_REF] Konsolakis | Hydrogen Production by Ethanol Steam Reforming (ESR) over CeO2 Supported Transition Metal (Fe, Co, Ni, Cu) Catalysts: Insight into the Structure-Activity Relationship[END_REF]. The molar ratio of O a /(O b +O g ) varied in the range of 0.21-0.32. This suggested the presence of a CoAl 2 O 4 type spinel where the substitution of Co 3+ by Al 3+ in the octahedral position leads to a higher contribution of Co 2+ Td. Indeed it has previously been shown that CoAl 2 O 4 type spinel phase can form at temperatures as low as 390 °C [START_REF] Beale | Understanding the Crystallization of Nanosized Cobalt Aluminate Spinel from Ion-Exchanged Zeolites Using Combined in Situ QEXAFS/XRD[END_REF]. The Mn K-edge spectra acquired at room temperature (Fig. 6B) closely resembled that of a Mn 3 O 4 spinel reported previously [START_REF] Zhang | Respective Role of Fe and Mn Oxide Contents for Arsenic Sorption in Iron and Manganese Binary Oxide: An X-ray Absorption Spectroscopy Investigation[END_REF]. To date no XAFS data exists concerning mixed Mn and Co spinels although a detailed XRD/vibrational spectroscopic study of Co/Mn substitution suggests that such phases can readily be formed and therefore a mixed Mn x Co y O 4 and/or Mn x Co y Al z O 4 could be present in our Mn 0.1725 Co 3 Al 1 O x [START_REF] Meena | Rietveld refinement and spectroscopic analysis of Co3-xMnxO4 (0.1≤ x≤ 1.0) ceramic compositions[END_REF]. For Fe 0.1725 Co 3 Al 1 O x mixed metal oxides measured at room temperature, Co K-edge XANES revealed comparable Co speciation to the Mn-containing sample (Fig. 6E). Nevertheless, the Fe near-edge spectrum closely resembled that of a-Fe 2 O 3 (Fig. 6F), suggesting that unlike Mn, Fe did not incorporate so readily into the Co 3 O 4 structure. In agreement, our H 2 -TPR results showed separate reduction of iron oxide species in Fe 0.1725 Co 3 Al 1 O x ; however, the shift to higher temperatures of Co 3 O 4 reduction peak suggests that small amounts of iron must have incorporated into the spinel structure thereby affecting its redox properties.

Changes occurring in Mn 0.1725 Co 3 Al 1 O x mixed metal oxides, in the presence of He and N 2 O/He, were followed by studying the Co and Mn K-edge XANES spectra between room temperature and 600 °C. A shift in the Co absorption edge to lower energies as well as a decrease in the pre-edge intensity were observed upon He treatment at 600 °C, which is also consistent with a decrease in the nominal valence of Co in the material (Fig. 6A). The spectra resembled that of the CoO reference constituted by Co 2+ in an octahedral environment.

However, the sample's higher pre-edge intensity when compared to CoO/Co 3 O 4 suggested some Co 2+ was still present in a tetrahedral environment. Considering the H 2 -TPR results pertaining to the reducibility of both cobalt oxide species present in the catalyst, it seems that Mn x Co y O 4 is reduced to (Mn)CoO while CoAl 2 O 4 , with Co 2+ in a tetrahedral environment, remained unchanged. EXAFS k-plots for Co and Mn in Mn 0.1725 Co 3 Al 1 O x before and after reduction are shown in Fig. 1S. in the supplementary information. At room temperature the Mn and Co fine structure resembled closely the Co 3 O 4 reference while in the reduced sample the fine structure is similar to CoO. This further confirms the presence of the initial spinel environment for both Mn and Co and that in both cases this evolves into the rock salt M 2+ O phase. Similar to Co, Mn also undergoes reduction upon activation in He at 600 °C; the reduced spectra resembling features of MnO [START_REF] Zhang | Respective Role of Fe and Mn Oxide Contents for Arsenic Sorption in Iron and Manganese Binary Oxide: An X-ray Absorption Spectroscopy Investigation[END_REF]. Finally, in the presence of N 2 O/He, both Co and Mn oxide species reoxidized to their initial state. Fig 6C andD show the temperature dependence of this reoxidation process; the spectral changes were observed at 300-450 °C temperature range which coincided with the temperature needed to obtain full N 2 O conversion. The MnO appeared easier to reoxidize than CoO since the spectral changes in Mn K-edge XANES commenced at 300 °C while changes in Co K-edge occurred at 350 °C.

Furthermore, the changes in the oxidation state of Co at different reaction stages in Mn 0.1725 Co 3 Al 1 O x were studied by the investigation of the position of the absorption edge (defined as the first maximum of the derivative plot beyond the pre-edge peak). Table 4 presents Reproducibility of our results of catalytic tests was confirmed by repeated measurements. The activity differentiated among tested materials without clear trend neither related to the Mn or Fe nor Na (up to 2.3 wt.%) content in the materials. Obalová et al. [START_REF] Graat | Quantitative Analysis of Overlapping XPS Peaks by Spectrum Reconstruction: Determination of the Thickness and Composition of Thin Iron-oxide Films[END_REF] pointed out that 1.15 wt.% of Na introduced by impregnation already slightly enhanced activity of Co 4 MnAlO x . While materials with Na loaded by impregnation was reported to facilitate N 2 O decomposition than materials with Na present after preparation procedure [START_REF] Santos | The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds[END_REF][START_REF] Konsolakis | Hydrogen Production by Ethanol Steam Reforming (ESR) over CeO2 Supported Transition Metal (Fe, Co, Ni, Cu) Catalysts: Insight into the Structure-Activity Relationship[END_REF].

The optimum of deposited Na content varied also depending on the applied mixed metal oxides: 0.75 wt.% for Co 2.5 Rh 0.05 Al 1 O x [START_REF] Santos | The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds[END_REF], 1.5 wt.% for Co 3 Al 1 O x [START_REF] Beale | Understanding the Crystallization of Nanosized Cobalt Aluminate Spinel from Ion-Exchanged Zeolites Using Combined in Situ QEXAFS/XRD[END_REF] or 1.4 wt.% for Co 4 Mn 1 Al 1 O x [START_REF] Zhang | Respective Role of Fe and Mn Oxide Contents for Arsenic Sorption in Iron and Manganese Binary Oxide: An X-ray Absorption Spectroscopy Investigation[END_REF]. Farris et al. [START_REF] Meena | Rietveld refinement and spectroscopic analysis of Co3-xMnxO4 (0.1≤ x≤ 1.0) ceramic compositions[END_REF] found out an optimum Na residual content in the range of 3.0-6.0 wt.% in Co-Al-O x was supposed to promote the decomposition of N 2 O facilitating over 80% conversion at 475 °C. Doping with 1.0-2.0 wt.% of Na resulted in comparable results. Further research should be carried out in order to clarify these remarkable observations over investigated mixed metal oxides.

The highest activity among tested materials reached Mn 0.1725 Co 3 Al 1 . Such catalyst reached with T 50 at 305 °C with and full conversion at 400 °C. Furthermore, Mn 0.1725 Co 3 Al 1 possessed similar activity to the Ag-doped catalysts -(0.7 wt.%)AgCo 3 (Mg 1 )Al 1 , and only slightly lower to the (0.7 wt.%)RhCo 3 Mg 1 Al 1 , reported as one of the most active and stable hydrotalcite derived mixed metal oxides in the N 2 O decomposition with excellent activity and stability performance [START_REF] Jablonska | It is no laughing matter: nitrous oxide formation in diesel engines and advances in its abatement over rhodium-based catalysts[END_REF][START_REF] Konsolakis | Recent Advances on Nitrous Oxide (N2O) Decomposition over Non-Noble-Metal Oxide Catalysts: Catalytic Performance, Mechanistic Considerations, and Surface Chemistry Aspects[END_REF]. Catalytic tests were carried out under the same reaction conditions (Fig. 6C). Co 3 Al 1 and Mn(Fe) 0.1725 Co 3 Al 1 were also tested in the presence of NO and O 2 (350 mg of catalyst, 100 cm 3 /min total flow). Mn 0.1725 Co 3 Al 1 presented T 50 of 376 °C, thus temperature of about 70 °C higher than for tests without NO and O 2 . Slightly lower activity above 350 °C was obtained over Fe 0.1725 Co 3 Al 1 with T 50 at 380 °C. Furthermore, for practical applications, Co 3 Al 1 and Mn(Fe) 0.1725 Co 3 Al 1 were tested in the presence of H 2 O (70 mg of catalyst, 75 cm 3 /min), as displayed on Fig. 2SA. The highest resistance to water vapour showed Mn 0.1725 Co 3 Al 1 with T 50 of 549 °C. Other materials presented significantly lower resistance to water vapour. conversion for all materials significantly dropped, and reached stable level below 20%. However, switching from wet to dry reaction mixture resulted in an increase of the catalysts conversion to the former level. Thus, the introduction of H 2 O into the feed did not result in the permanent deactivation of the catalysts.

Obalová et al. [START_REF] Obalová | Catalytic decomposition of nitrous oxide over catalysts prepared from Co/Mg-Mn/Al hydrotalcite-like compounds[END_REF][START_REF] Kannan | Catalytic decomposition of nitrous oxide over calcined cobalt aluminum hydrotalcites[END_REF] reported that the high activity of Co 4 Mn 1 Al 1 hydrotalcite derived mixed metal oxides appeared due to an optimum content of components reducible in the temperatures of the maximum conversion of N 2 O (between 350-450 °C). Analysis of our reduction peak areas showed similar ratio (0.29 to 0.35) across the samples. Crystal sizes were calculated from (3 1 1) brag reflection in the XRD patterns using the Scherrer equation; the comparable results of 27, 26 and 30 nm for Co 3 Al 1 O x , Mn 0.1725 Co 3 Al 1 O x and Fe 0.1725 Co 3 Al 1 O x respectively discard size effects in the catalytic performance. Although, the strength of lattice oxygen-metal bonds was reported to determine the catalysts activity in deN 2 O [START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF], we did not observe clear correlation between O a /(O b +O g ) molar ratio and catalytic activity of mixed metal oxides. Thus it seems that the samples' different reactivity was related mainly to the Mn and Fe speciation observed by XAS. Mn in Mn 0.1725 Co 3 Al 1 O x appeared incorporated within spinel structure; MnO and CoO phases present after activation reoxidize under N 2 O/He feed. showing that both take part in redox processes for deN 2 O. Indeed it appears that MnO seemed to undergo faster reoxidation suggesting it may act as better electron donor in N 2 O activation step considered the rate determining stem of the mechanism [START_REF] Chang | Analysis of N2O decomposition over fixed bed mixed metal oxide catalysts made from hydrotalcite-type precursors[END_REF][START_REF] Obalová | Kinetic analysis of N2O decomposition over calcined hydrotalcites[END_REF]. Indeed this observation of Mn being easier to oxidise back to 3+ than Co, yet harder to reduce to 2+ is completely consistent with the respective redox potentials for the two elements [START_REF] Zhu | Highly Active and Stable Co3O4/ZSM-5 Catalyst for Propane Oxidation: Effect of the Preparation Method[END_REF]. Iron in Fe 0.1725 Co 3 Al 1 O x could have similar role as Mn due to its higher oxidability compared with cobalt oxides. Nevertheless, as most of the iron was not incorporated to the spinel but appeared as separate Fe 2 O 3 phase, its effect in catalytic activity was less pronounced than for Mn in the Mn 0.1725 Co 3 Al 1 O x sample.

Accordingly, decomposition of N 2 O over tested mixed metal oxides followed the cationic redox mechanism [START_REF] Obalová | Effect of Mn/Al ratio in Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors on catalytic decomposition of {N2O}[END_REF][START_REF] Klyushina | Effect of preparation method on catalytic properties of Co-Mn-Al mixed oxides for N2O decomposition[END_REF], consisting of N 2 O activation by electron transfer from metal sites, and diffusive recombination of the surface oxygen intermediates into oxygen, concerted with the back electron transfer that restores the oxidation state of the active sites. The regeneration of the active sites through oxygen desorption is considered as the ratedetermining step. In this context, Co oxidizes when N 2 O is adsorbed and then Co is again reduced when O 2 is released. Thus, during reaction under N 2 O/He conditions, Co is continuously oxidizing and reducing. The doping, in particular Mn, may generate new redox sites at the surface or may enhance the oxygen desorption from cobalt sites. Taking into account the very weak amount of manganese added and the fact that manganese appeared incorporated within structure, the latter assumption seems more likely.

  0 ) and positions of basal reflections: c = [3(d 0 0 3 ) + 6(d 0 0 6 )]/2. The lattice paramater a depends on the size of the cation in the brucite-like layers, while the parameter c refers to the interlayer thickness. The a values for Mn(Fe) x Co 3 Al 1 (x = 0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%) hydrotalcite-like compounds varied only slightly with increasing Mn or Fe content and were close to the one obtained for Co 3 Al 1 . The a values depends mainly on the ionic radii of the cations in octahedral coordination (0.070 nm Co 2+ , 0.070 nm Mn 2+ and 0.070 nm Fe 3+[START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF], as cations of metal precursors). The c values of about 2.3 nm stay characteristic for hydrotalcite-like compounds containing carbonates located in the interlayer space[START_REF] Cavani | Hydrotalcite-type anionic clays: Preparation, properties and applications[END_REF]. The interlayer distances increased upon decreasing electronegativity of the cations: Co (1.70) > Fe (1.64) > Mn (1.60) > Al(1.47)

Fig. 3

 3 Fig.3shows the XRD patterns of calcined Mn(Fe)CoAl hydrotalcite-like compounds. The hydrotalcite-like

Fig. 1 ,

 1 Fig. 1, Fig. 2, Fig. 3

Fig. 4

 4 Fig.4presents the H 2 -TPR profiles for the Co 3 Al 1 and selected Mn(Fe) x Co 3 Al 1

Fig. 4 ,

 4 Fig. 4, Fig. 5

  Calculated by equation: Y = 1E-08X + 1E-07, R 2 = 0.9996, and X, Y referred to the area of each reduction peak and the H 2 consumption, respectively. b In the region 50-530 °C. c In the region 530-1000 °C. d Estimated from the integrated areas of the respective XPS peaks.

Fig. 6

 6 Fig. 6 shows the XANES spectra of Mn(Fe) 0.1725 Co 3 Al 1 O x mixed metal oxides. In comparison to the Co 3 O 4

  the Co K-edge absorption positions relative to Co foil (ΔE = E sample -E foil ) of Mn 0.1725 Co 3 Al 1 O x mixed metal oxides at different stages of the experiment as well as the ΔE of Co 3 O 4 and CoO as references. Again, the ΔE of the sample after treatment with He at 600 °C was comparable to CoO. While the reoxidation, under N 2 O/He conditions, leads to the recovery of its initial oxidation state. Table 5 lists the results of the curve-fitting analysis for the first coordination shell. First shell quick fit analysis of the EXAFS was carried out to gain insight into the average Co-O distances and coordination numbers. Fitting revealed higher coordination numbers and Co-O bond distances of 0.208 nm for Mn 0.1725 Co 3 Al 1 O x mixed metal oxide pretreated with He at 600 °C, which is consistent with the appearance of CoO type structure. Otherwise, Mn 0.1725 Co 3 Al 1 O x at room temperature or in the presence of N 2 O/He at 600 °C showed a shorter Co-O of ~0.191 nm, corresponding to the presence of a majority spinel phase. As expected from XANES, the Co-O shell fitting results Mn 0.1725 Co 3 Al 1 O x and Fe 0.1725 Co 3 Al 1 O x at room temperature gave very similar results.

Fig. 6

 6 Fig.6

Fig. 7

 7 Fig. 7 presents the results of catalytic tests performed over Mn(Fe) x Co 3 Al 1 (x = 0.0575, 0.0821, 0.1150, 0.1725,

Fig

  Fig. 2SB presents the contribution of NO formation over Co 3 Al 1 and Mn(Fe) 0.1725 Co 3 Al 1 . The highest amount

  Fig. 7

Fig. 1 .

 1 Fig. 1. X-ray diffraction patterns of Mn(Fe)-Co-Al hydrotalcite-like compounds; H -hydrotalcite-like phase.

Fig. 2 .Fig. 3 .Fig. 4 .Fig. 5 .

 2345 Fig. 2. DTG profiles of Mn(Fe)-Co-Al hydrotalcite-like compounds; experimental conditions: mass of sample = 20 mg, flow of synthetic air = 10 cm 3 /min, liner heating rate of 5 K/min.

2 Fig. 6 .

 26 Fig. 6. In situ XANES spectra of A) Co K-edge for Mn 0.1725 Co 3 Al 1 O x at different reaction stages and Co

3 Fe 3 O 4 Fig. 7 .

 3347 Fig. 7. Results of catalytic tests performed over Co 3 Al 1 , (Mn,Fe) x Co 3 Al (x = 0, 0.0575, 0.0821, 0.1150, 0.1725,

  6 eV. The composition and chemical surrounding of the sample surface were investigated based on the areas and binding energies of Co 2p, Mn 2p, Fe 2p, Al 2p, O 1s and C 1s photoelectron peaks. Mathematical analyses of the XPS spectra were carried out using the XPSpeak 4.1 computer software (RWM. Kwok, The Chinese University of Hong Kong).

Table 1 .

 1 Lattice parameters of (Mn,Fe)-Co-Al hydrotalcite-like compounds and corresponding mixed metal oxides.Table2lists the specific surface areas (S BET ) of the (Mn,Fe)-Co-Al mixed metal oxides. S BET for Co-Al-O x of 82 m 2 /g, significantly decreased after introduction of Mn or Fe within its structure. A similar trend was observed for both series, i.e. decrease for materials with 0.0821 mol.% then increase up to 0.1725 mol.%, and finally drop in S BET for materials with the highest loading of transition metal (0.2300 mol.%). However, slightly higher values for S BET were reached over Mn-containing mixed metal oxides. Chemical analysis identified by ICP-MS evidenced sodium residual from preparation procedure up to 2.3 wt.%.

	Hydrotalcite-like compounds Cell parameter	Cell parameter	Crystallite size	Crystallite size	Mixed metal oxides Cell parameter	Crystallite size
		a [nm]	c [nm]	Da [nm]	Dc [nm]	a [nm]	Da [nm]
	Co 3 Al 1	0.3079	2.2956	29	20	Co 3 Al 1 O x	0.8093
	Mn 0.0575 Co 3 Al 1	0.3085	2.3065	33	22	Mn 0.0575 Co 3 Al 1 O x	0.8076
	Mn 0.0821 Co 3 Al 1	0.3086	2.3060	34	21	Mn 0.0821 Co 3 Al 1 O x	0.8083
	Mn 0.1150 Co 3 Al 1	0.3085	2.3006	25	24	Mn 0.1150 Co 3 Al 1 O x	0.8099
	Mn 0.1725 Co 3 Al 1	0.3080	2.2800	33	24	Mn 0.1725 Co 3 Al 1 O x	0.8079
	Mn 0.2300 Co 3 Al 1	0.3078	0.2790	27	24	Mn 0.2300 Co 3 Al 1 O x	0.8099
	Fe 0.0575 Co 3 Al 1	0.3085	2.3215	22	22	Fe 0.0575 Co 3 Al 1 O x	0.8073
	Fe 0.0821 Co 3 Al 1	0.3086	2.3100	39	26	Fe 0.0821 Co 3 Al 1 O x	0.8076
	Fe 0.1150 Co 3 Al 1	0.3085	2.3065	39	28	Fe 0.1150 Co 3 Al 1 O x	0.8093
	Fe 0.1725 Co 3 Al 1	0.3081	2.2839	34	28	Fe 0.1725 Co 3 Al 1 O x	0.8083
	Fe 0.2300 Co 3 Al 1	0.3081	2.2790	42	30	Fe 0.2300 Co 3 Al 1 O x	0.8096

Table 2 .

 2 Total mass losses of (Mn,Fe)-Co-Al hydrotalcite-like compounds, specific surface areas (S BET ), sodium residuals of mixed metal oxides, and T 50 of mixed metal oxides in N 2 O/N 2 , N 2 O,NO,O 2 /N 2 * and N 2 O,H 2 O/He** gas mixtures. of catalyst, 100 cm 3 /min total flow; b 70 mg of catalyst, 75 cm 3 /min total flow.

	Hydrotalcite-like compounds Total mass loss	Mixed metal oxides	S BET	Na	T 50
		[%]		[m²/g]	[wt.%]	[° C]
	Co 3 Al 1	32.62	Co 3 Al 1 O x	82	1.4	352 a *409 a
						**549 b
	Mn 0.0575 Co 3 Al 1 Mn 0.0821 Co 3 Al 1 Mn 0.1150 Co 3 Al 1 Mn 0.1725 Co 3 Al 1	31.90 31.54 30.53 30.89	Mn 0.0575 Co 3 Al 1 O x Mn 0.0821 Co 3 Al 1 O x Mn 0.1150 Co 3 Al 1 O x Mn 0.1725 Co 3 Al 1 O x	59 57 61 76	0.7 1.3 1.0 2.3	317 a 332 a 320 a 305 a *376 a
						**528 b
	Mn 0.2300 Co 3 Al 1	31.03	Mn 0.2300 Co 3 Al 1 O x	65	0.8	316 a
	Fe 0.0575 Co 3 Al 1 Fe 0.0821 Co 3 Al 1 Fe 0.1150 Co 3 Al 1 Fe 0.1725 Co 3 Al 1	31.43 31.34 31.10 30.27	Fe 0.0575 Co 3 Al 1 O x Fe 0.0821 Co 3 Al 1 O x Fe 0.1150 Co 3 Al 1 O x Fe 0.1725 Co 3 Al 1 O x	56 53 54 54	0.8 0.8 1.6 0.9	356 a 325 a 333 a 327 a *380 a
						**549 b
	Fe 0.2300 Co 3 Al 1	31.00	Fe 0.2300 Co 3 Al 1 O x	50	0.9	355 a
	a 350 mg

Table 3 .

 3 Amounts of H 2 consumed during H 2 -TPR measurements (H 2 uptake), the peaks positions, their binding energies, peak areas, full with at half maximum (FWHM) and O a /(O b +O g ) molar ratio of mixed metal oxides.

	Mixed metal	H 2 uptake a	A b /A c	Position	FWHM	Area	O a /(O b +O g ) d
	oxides	[mmol/g]	[a.u.]	Co 2p 3/2	[eV]	[a.u.]
				*O 1s
				¢ Mn 2p 3/2
				£ Fe 2p 3/2
	Co 3 Al 1 O x	26.48 6.64 b	0.33	780.35 786.26	4.09 7.90	11998 4073
		19.84 c		802.84	6.75	2239
				*527.07	1.72	462
				*528.77	1.92	2066	0.23
				*530.38	2.08	6369
				*531.91	2.10	2697
	Mn 0.1725 Co 3 Al 1 O x	22.84 5.90 b	0.35	781.63 785.80	3.79 8.90	8333 2826
		16.94 c		804.53	8.64	1134
				*528.51	1.43	239
				*530.07	2.09	2126	0.21
				*531.72	2.25	7926
				*533.41	1.95	2106
				¢ 643.03	4.00	1080
	Fe 0.1725 Co 3 Al 1 O x	23.46 5.22 b	0.29	779.63 784.18	3.94 8.19	7137 2085
		18.24 c		802.17	8.64	1244
				*526.58	1.63	324
				*528.37	2.20	2077	0.32
				*529.81	2.04	4523
				*531.28	2.06	1933

Table 4 .

 4 Co K-edge energy positions relative to Co foil (E 0 ) for Mn 0.1725 Co 3 Al 1 O x mixed metal oxides at room temperature, after reduction under He and after reoxidation under N 2 O/He at 600 °C as well as references at room temperature.

	Mixed metal oxides	ΔE	References	ΔE
		[eV]		[eV]
	Mn 0.1725 Co 3 Al 1 O x		room temperature
	room temperature	8.1	CoO	7.4
	600 °C He	7.4	Co 3 O 4	8.5
	600 °C N 2 O/He	8.1

Table 5 .

 5 Coordination numbers (CN), bond distances between adsorbed and backscatter atoms (R), inner potential corrections to account for the difference in the inner potential between the sample and the reference compound (E), Debye-Waller factors (2s 2 ), and residual factors (Rf) of Mn 0.1725 Co 3 Al 1 O x mixed metal oxides.

	Mixed metal oxides	Shell	CN	R	ΔE 0	10 2 *s 2	R f
		Co-O		[nm]	[eV]	[nm]	[%]
	Fe 0.1725 Co 3 Al 1 O x
	room temperature He		2.9	0.192	4.65	0.012	0.16
	Mn 0.1725 Co 3 Al 1 O x
	room temperature He		2.8	0.191	4.64	0.016	1.30
	after He 600 °C		4	0.208	2.29	0.16	3.2
	after N 2 O 600 °C		2.2	0.191	5.40	0.084	1.9

Acknowledgements

Funded by the Excellence Initiative of the German federal and state governments in the frame of the Center for Automotive Catalytic Systems Aachen (ACA) at RWTH Aachen University. The authors acknowledge the Diamond Light Source (project SP14834) for provision of beamtime on the beamlines B18, and Diego Gianolio for assistance in performing the XAFS measurements. The authors thank Andreas Holz for the assistance in preparation, characterization and catalytic tests.