Dr Wannaruedee Wannapakdee

Dr Duangkamon Suttipat

Saros Salakhum

Laurent Bouffier

Dr Sewnet Getnet

Kassahun

Keywords: Composés dérivés de la biomasse, Amélioration de l'alcool, Oxyde de cérium (CeO2), Zéolithes hiérarchiques, Électrochimie bipolaire, Particules Janus, Électrocatalyseur bifonctionnel Biomass-derived compounds, Alcohol upgrading, Cerium oxide (CeO2), Hierarchical zeolites, Bipolar electrochemistry, Janus particles, Bifunctional electrocatalyst X-ray Photoelectron Spectroscopy XRD X-ray diffraction

Amélioration de l'Utilisation de Composés Dérivés de la Biomasse en Chimie Fine Résumé : En raison de préoccupations énergétiques et environnementales, l'élaboration de nouveaux procédés de développement durable de produits chimiques, à partir de matières premières, est un thème de recherche en pleine expansion. Plus, particulièrement en ce qui concerne, l'utilisation de composés dérivés de la biomasse, qui peuvent être produits naturellement. Différents types de produits peuvent être dérivés de ces procédés, tels que les carburants, les cosmétiques, les parfums, les additifs alimentaires, les détergents et les plastiques. Par conséquent, la mise au point de catalyseurs pour ces processus constitue un défi majeur, tant du point de vue fondamental que du point de vue industriel. Dans cette thèse, nous allons nous concentrer sur le développement de nouveaux catalyseurs hétérogènes et aux électrocatalyseurs à base d'oxydes métalliques tels que l'oxyde de cérium (CeO2).

L'utilisation de ces matériaux ces dernières années est grandissante en raison de leurs propriétés uniques telles que leur capacité à stocker de l'oxygène ou encore leur propriété redox. De plus, les catalyseurs mis au point serviront à oxyder les bioalcools en produits chimiques, tels que la conversion de l'alcool benzylique en benzaldéhyde et les applications de valorisation de l'éthanol qui peuvent être utilisées pour produire d'autres produits chimiques et carburants à haute valeur ajoutée. En outre, l'électrochimie bipolaire est appliquée pour l'élaboration d'électrocatalyseurs. Sur la base de la distribution du potentiel, des fonctions de gradient et de sélection de site peut être réalisée. De plus, la structure et l'activité des catalyseurs seront étudiées par microscopie électrochimique à balayage (SECM) afin de comprendre la relation entre les structures et les performances électrocatalytiques. Cette thèse fournira de nouvelles connaissances pour l'élaboration de catalyseurs et d'électrocatalyseurs, dans le cadre du développement durable de produits chimiques à partir de ressources renouvelables.

List of Figures

1.4

Zeolite formation around carbon particles as hard templates.

Summary of desilication procedures used for different

Si/Al ratios.

1.6

The noble metals employed in catalysis can be rated by their bond-cracking capabilities. (E-H) 1Pt/20CeO2-Silicalite1-CON.

Conversion of biomass-derived compounds

Alcohols as bioproducts derived from biomass have several advantages. For example, bioethanol is one of the most important alcohols, because it can be used as a fuel additive and intermediate to produce versatile high-value products, such as olefins, higher alcohols, and aromatic compounds. [START_REF] Sousa | Ethanol conversion into olefins and aromatics over HZSM-5 zeolite: Influence of reaction conditions and surface reaction studies[END_REF][START_REF] Cimino | Catalysts for conversion of ethanol to butanol: Effect of acid-base and redox properties[END_REF] In addition, energy consumption has been continuously increasing every year, whereas typical energy resources (oil, natural gas, coal, shale oil) are decreasing. More than 75% of the energy demand is projected to come from fossil fuels in 2035 (Figure 1.1). Then, the global annual energy requirement of over 12 billion tons of oil equivalent (Btoe) generates a large CO2 emission, approximately 39.5 Gt. [START_REF] Védrine | Metal oxides in heterogeneous oxidation catalysis: State of the art and challenges for a more sustainable world[END_REF] Therefore, it is essential to provide in an efficient way energy for daily consumption and the chemical industry.

Many efforts have been focused on new catalytic processes and alternative energy resources. *Renewables: wind, solar, geothermal, biomass, and biofuels. Taken from ref. [START_REF] Védrine | Metal oxides in heterogeneous oxidation catalysis: State of the art and challenges for a more sustainable world[END_REF] emission against fossil fuels.[4] Therefore, not only fossil fuels have been replaced by renewable energy, but also the fine-chemicals industry tends to use alternative resources as feedstock.

Numerous studies have been devoted to the development of catalysts to achieve the transformation of biomass into higher value-added products. [START_REF] Inaba | Ethanol conversion to aromatic hydrocarbons over several zeolite catalysts[END_REF][START_REF] Nguyen | Conversion of ethanol in aqueous solution over ZSM-5 zeolites: study of the reaction network[END_REF][START_REF] Makshina | Catalytic study of the conversion of ethanol into 1, 3-butadiene[END_REF] Among these studies, alcohol upgrading is one of the most promising processes. For example, ethanol has been used as an initial reagent to produce many chemicals, such as paraffins, olefins, and aromatics. [START_REF] Takahara | Dehydration of Ethanol into Ethylene over Solid Acid Catalysts[END_REF][START_REF] Tan | Plasmon enhanced selective electronic pathways in TiO2 supported atomically ordered bimetallic au-cu alloys[END_REF][START_REF] Sushkevich | Ethanol conversion into butadiene over Zr-containing molecular sieves doped with silver[END_REF][START_REF] Jordison | Condensed-Phase Ethanol Conversion to Higher Alcohols[END_REF] To date, various solid acid catalysts have been developed for ethanol/bioethanol upgrading. [START_REF] Salem | Enhanced ethylene production by dehydration of ethanol over Al/SBA-15 mesoporous catalysts[END_REF][START_REF] Dewilde | Kinetics and Mechanism of Ethanol Dehydration on γ-Al2O3: The Critical Role of Dimer Inhibition[END_REF][START_REF] Clemente | Ethylene production via catalytic ethanol dehydration by 12-tungstophosphoric acid@ceria-zirconia[END_REF][START_REF] Ferreira Madeira | Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role[END_REF] Among them, HZSM-5 zeolite has emerged as one of the best catalysts in several studies. For example, K.B. Tayeb et al. [START_REF] Ferreira Madeira | Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role[END_REF] reported the catalytic performance of ethanol on HZSM-5 zeolites with various Si/Al ratios ranging from 16 to 500. The results exhibited an excellent activity in ethanol conversion with HZSM-5 (Si/Al = 40) due to optimal fine-tuned Brønsted acid density, which is beneficial to the chemical and refining industry. For further developments, integrating various types of metals into a zeolite framework could considerably improve ethanol transformation. For instance, M. Inaba et al.[5] prepared noble metals incorporated in a zeolite framework for ethanol transformation. They revealed that the addition of Au into zeolite could suppress further side reactions due to the reduction of the initial acidity of the zeolite and inhibit the deposition of coke on the catalyst surfaces during the reaction, resulting in a longer lifespan of the catalyst. However, these types of catalysts are less used because of the sintering effect due to the weak metal-support interaction. [START_REF] Wynblatt | Supported metal crystallites[END_REF] Therefore, other promoters or materials should be combined in order to improve the metal-support interaction. To illustrate this concept, X. Xie et al. [START_REF] Dai | A high-performance CeO2@ Pt-Beta yolk-shell catalyst used in low-temperature ethanol steam reforming for high-purity hydrogen production[END_REF] reported that the high catalytic performance could be attributed not only to the architecture of the catalyst, but also to the synergistic effect between CeO2 and Pt metal. Consequently, the addition of CeO2 is one of the most interesting approaches. [START_REF] Montini | Fundamentals and catalytic applications of CeO2-based materials[END_REF] The publication trend in the development of CeO2 based catalysts is increasing because CeO2 can be used as both catalyst itself and non-inert support catalysts [START_REF] Trovarelli | Catalytic properties of ceria and CeO2-containing materials[END_REF][START_REF] Kašpar | Use of CeO2-based oxides in the threeway catalysis[END_REF] due to its redox properties (Ce 3+ ↔Ce 4+ ) and oxygen-storage capacity, which are valuable for alcohol upgrading applications.

Furthermore, metal dispersion is also an important parameter that can be easily tuned when using zeolite as a support material to improve catalytic performance. [START_REF] Li | Tuning interactions between zeolite and supported metal by physical-sputtering to achieve higher catalytic performances[END_REF][START_REF] Lu | Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes[END_REF] To further develop, the modification of zeolite structures, such as the incorporation of additional meso-or macroporous structures, namely hierarchical zeolites, have been studied to overcome the diffusion limitation of originally microporous zeolite because of their higher surface area and tunable porosity. [START_REF] Liu | Recent progress in the direct synthesis of hierarchical zeolites: synthetic strategies and characterization methods[END_REF][START_REF] Sedighi | Enhanced electro-oxidation of ethanol using Pt-CeO2 electrocatalyst prepared by electrodeposition technique[END_REF][START_REF] Verboekend | Design of hierarchical zeolite catalysts by desilication[END_REF] Moreover, due to the aforementioned catalytic properties, the modified materials possessing designed properties were used for various alcohol upgrading (e.g., benzyl alcohol and ethanol)

to desired products. Therefore, in this work, we focused on the design materials having potential properties for upgrading applications. For instance, the oxidation reaction of benzyl alcohol can be used to produce benzaldehyde by using a modified hierarchical zeolite catalyst under an environmentally friendly condition. [START_REF] Dell'anna | Oxidation of benzyl alcohols to aldehydes and ketones under air in water using a polymer supported palladium catalyst[END_REF]

Design of heterogeneous catalysts

As stated above, metal-CeO2 modified zeolite is one of the most promising catalysts. The development of metals supported on hierarchical zeolite catalysts to demonstrate the improved properties such as nature of active species, the dispersion of active sites and metal-support interaction to enhance the catalytic activity of alcohol upgrading is illustrated in the following.

Hierarchical zeolites

Zeolites are aluminosilicate crystalline structures involving tetrahedral SiO4 and AlO4 as primary building units, associated with the division of one oxygen atom for two tetrahedra in order to form 3D frameworks with porous structures at molecular dimensions (typically 0.25-1 nm). [START_REF] Vu | Micro/Mesoporous Zeolitic Composites: Recent Developments in Synthesis and Catalytic Applications[END_REF] They have played an important role in many industrial processes due to their numerous distinctive properties, involving high specific surface area, strong acidity, good ion-exchange capability, and most significantly, high thermal/hydrothermal stability. [START_REF] Moshoeshoe | A Review of the Chemistry, Structure, Properties and Applications of Zeolites[END_REF][START_REF] Moliner | Multipore Zeolites: Synthesis and Catalytic Applications[END_REF][START_REF] Ivanova | Micro-mesoporous materials obtained by zeolite recrystallization: synthesis, characterization and catalytic applications[END_REF] However, the active sites of microporous zeolites turn out to be unreachable since bulky molecules cannot penetrate into active sites, which are normally located in a microporous framework due to the strong diffusion limitation of guest molecules inside a small microporous network. [START_REF] Zhang | Innovations in hierarchical zeolite synthesis[END_REF] Diffusion mechanisms are generally observed over solid materials containing mesopores (Knudsen regime) and macropores (molecular regime)). [START_REF] Feliczak-Guzik | Hierarchical zeolites: Synthesis and catalytic properties[END_REF] The low diffusivities in micropores decrease the transfer of several substances to and from active sites. The slow transportation of reagents facilitates the transformation of adsorbed molecules to undesired by-products, which can additionally produce coke precursors. This initiates a blocking of the micropores, eventually leading to catalyst deactivation and shortening of its lifespan. Consequently, only the outer part of the zeolite is involved in the catalytic reaction, whereas the interior remains catalytically inactive, as shown in Figure 1.2. ref. [START_REF] Hartmann | Catalytic test reactions for the evaluation of hierarchical zeolites[END_REF] Therefore, many efforts have been made to overcome these limitations of zeolites. One of the most promising strategies is to introduce an additional pore network with a diameter larger than 2 nm (meso-or macropores) to produce hierarchical zeolites. This approach intends to accelerate the accessibility of large molecules to the active centers of the materials, while the acidity and crystallinity of zeolites are maintained.

Hierarchical zeolites, with at least two levels of porous structures, have been continuously developed to improve the accessibility and molecular transport of guest molecules. [START_REF] Pérez-Ramírez | Hierarchical zeolites: enhanced utilisation of microporous crystals in catalysis by advances in materials design[END_REF] The benefits of hierarchical zeolites are shown in Figure 1.3, the yellow spheres are large molecules, which suffer from a low diffusion in a microporous network. Obviously, the secondary porosity improves the number of pore mouths that can increase the diffusion of molecules through the pores (indicated by the green spheres). For the modified zeolite, the increase of the exterior surface regularly conducts the improvement of reactivity and selectivity. The red dots stand for bulky molecules, which can only react on pore mouths, increasing the opportunity for big molecule transformation. Typically, there are two main approaches for producing hierarchical zeolites. The first one is primary synthesis, namely "Bottom-up", which typically employs templates. Another approach is post-synthetic adjustments, namely "Topdown", which comprises the treatment of completed zeolite.

Bottom-up approach

The bottom-up approach is based on using a template to modify the zeolite structure. In the procedure, the synthesis gel is typically composed of a molecular structure-directing agent (SDA), which is accountable for the micropore structure, and an additional template acting as a mesoporogen to create the desired mesoporous structures. The synthesis of hierarchical zeolites can be achieved by following one of the two approaches: (i) "hard" and (ii) "soft" templating methods. For the hard templating approach, rigid or solid materials containing various types of carbon materials, such as carbon nanoparticles, [START_REF] Sun | A facile route to synthesize endurable mesopore containing ZSM-5 catalyst for methanol to propylene reaction[END_REF][START_REF] Li | Realizing the Commercial Potential of Hierarchical Zeolites: New Opportunities in Catalytic Cracking[END_REF] carbon nanotube, [START_REF] Schmidt | Carbon Nanotube Templated Growth of Mesoporous Zeolite Single Crystals[END_REF] ordered mesoporous carbons, [START_REF] Chen | Hydrothermal Synthesis of Zeolites with Three-Dimensionally Ordered Mesoporous-Imprinted Structure[END_REF][START_REF] Ryoo | Ordered Mesoporous Carbons[END_REF] have been widely used. After removing the templates, mesopores are present in the porous zeolite network. For example, larger pores can be generated after the combustion of carbon particles, as shown in Figure 1.4. Apart from carbon materials, a polymer such as a polystyrene [START_REF] Holland | Dual Templating of Macroporous Silicates with Zeolitic Microporous Frameworks[END_REF] can also be used as a mesoporous template. The polymer can be simply eliminated by calcination under air atmosphere. However, the main drawback of this process is that the high temperature leads to polymer glassification. [START_REF] Feliczak-Guzik | Hierarchical zeolites: Synthesis and catalytic properties[END_REF] Additionally, soft templates such as surfactant, [START_REF] García-Martínez | Mesostructured zeolite Y-high hydrothermal stability and superior FCC catalytic performance[END_REF] block-copolymer, [START_REF] Zhou | Direct Synthetic Strategy of Mesoporous ZSM-5 Zeolites by Using Conventional Block Copolymer Templates and the Improved Catalytic Properties[END_REF] and organosilane [START_REF] Cho | Generation of Mesoporosity in LTA Zeolites by Organosilane Surfactant for Rapid Molecular Transport in Catalytic Application[END_REF][START_REF] Shanbhag | Mesoporous sodalite: A novel, stable solid catalyst for base-catalyzed organic transformations[END_REF] have also been widely used as template materials, which can induce the secondary porosity during the zeolite formation. For instance, R. Ryoo et al.[46] reported hierarchical zeolite synthesis using a surfactant. Compared to amorphous silica and bulk silica zeolite, the surfactantguided zeolite nanosheets displayed an extraordinarily long catalytic lifespan and high product selectivity for the cyclohexanone oxime conversion to ε-caprolactam, which can be used as a precursor of Nylon-6 synthesis.

Top-down approach

The top-down method starts with the original microporous zeolites, which are transformed to hierarchical zeolites via a post-synthetic procedure.

After synthesizing microporous zeolites, amorphous regions in the zeolite framework can be produced via special treatment, including dealumination or desilication. These amorphous regions can provide mesopores after their removal. For example, Figure 1.5, illustrates schematically the desilication procedure for zeolites with various Si to Al ratios starting from low to high ratios. Interestingly, Figure 1.5(a) demonstrates that the zeolite with a low ratio of Si/Al provides the displaced AlO4 --tetrahedra assemblies at the zeolite mesopore sides. A secondary acid wash can release mesopore blockage. However, in the case of Figure 1.5(b), a one-step standard desilication of the medium Si/Al zeolite is achievable (0.2 M NaOH, 30 min, and 65 °C). For a high ratio of Si/Al, with a lower stability (Figure 1.5(c)), the typical conditions cause an extreme dissolution. Therefore, alternative procedures such as using milder bases, recrystallization with surfactants, adding pore-directing agents (PDA), and partial detemplation were used for desilication. As mentioned above, because of the outstanding properties of hierarchical zeolites, they have been broadly employed as catalysts or support materials for various reactions. [START_REF] Michalkiewicz | Zeolite membranes for hydrogen production from natural gas: state of the art[END_REF] Especially, due to their high catalytic performance, noble metals supported on zeolites are widely employed for many reactions, such as selective oxidation of CO, hydro-addition reactions to alkynes and alkenes. [START_REF] Rosso | Development of A zeolites-supported noble-metal catalysts for CO preferential oxidation: H2 gas purification for fuel cell[END_REF][START_REF] Rubio-Marqués | Well-Defined Noble Metal Single Sites in Zeolites as an Alternative to Catalysis by Insoluble Metal Salts[END_REF]

Noble metals

Noble metals are materials that can resist corrosion and oxidation in moist air. One valuable aspect about the differences between noble metals is to categorize them regarding bond-breaking ability. [START_REF] Freyschlag | Precious metal magic: catalytic wizardry[END_REF] Noble metals have been widely used in various industries because of their high efficiency to catalyze reactions and their bond-breaking capabilities. [START_REF] Zhang | Synthesis of highly dispersed ruthenium nanoparticles supported on activated carbon via supercritical fluid deposition[END_REF] Because numerous transformations are required in catalysis, these processes need different selectivities and specificities of the catalyst to break bonds. Hence, the capability of each metal to interact specifically with certain chemical bonds is revealed.

Metal oxides

Metal oxides represent a class of inorganic materials that have been used for various applications ranging from biomedical features, [START_REF] Murthy | 11 -Metal oxide nanoparticles in biomedical applications[END_REF] sensors, [START_REF] Sun | Metal oxide nanostructures and their gas sensing properties: a review[END_REF][START_REF] Masikini | Metal oxides: Application in exhaled breath acetone chemiresistive sensors[END_REF] to catalysts, [START_REF] Védrine | Heterogeneous Catalysis on Metal Oxides[END_REF] and energy storage [START_REF] Wang | 5 -Structure and Basic Properties of Ternary Metal Oxides and Their Prospects for Application in Supercapacitors[END_REF]. Typically, oxide surfaces are terminated by oxide O 2-anions, as shown in Figure 1.7. Consequently, the M n+ cation symmetry is disturbed at the surface. Furthermore, several kinds of defects and environments (kinks, steps, terraces) can be obtained at the surface of an oxide, resulting in different catalytic properties. Metal oxides possess distinct properties, for instance, acidity and basicity (Lewis and Brønsted) and redox performance, leading to distinctive catalytic properties. In catalysis, the crucial considerations that influence the metal oxide properties are the surface area of materials involving the number of atoms within the metal oxides. The metal oxide performance is improved by reducing the particle size to the nanoscale, approximately 1 to 100 nm size range, leading to enhanced catalytic performances per unit weight compared to their bulk structure. An increase in surface area results in a higher amount of surface atoms, influencing the optical, electrical, and magnetic properties of metal oxide nanoparticles and eventually improving their reactivity and strength. [START_REF] Murthy | 11 -Metal oxide nanoparticles in biomedical applications[END_REF] Thus, the utilization of metal oxides at the nanoscale has been considered as a significant factor in the development of new properties and functions for catalysis.

In addition, metal oxides, such as alumina, silica, silica-alumina, porous oxides, and MOFs, can be employed as support materials for other active species like noble metals. Their combination can impact the catalytic features because of the complementary effect between active materials and metal oxide surface interactions.

Noble metal and metal oxide modified hierarchical zeolites

As stated above, noble metals have been used for various reactions because of their high efficiency. [START_REF] Zhang | Synthesis of highly dispersed ruthenium nanoparticles supported on activated carbon via supercritical fluid deposition[END_REF] However, their high cost limits their use.

Therefore, using noble metals as catalysts but still keeping the costs low has attracted increasing attention over the past decades. Several reports illustrate the development of various strategies to reach this goal. Among the most interesting solutions are, using supporting materials, improving the structure or morphology of the catalyst, and finding new synergies between materials. [START_REF] Liu | Catalytic removal of volatile organic compounds using ordered porous transition metal oxide and supported noble metal catalysts[END_REF][START_REF] Wang | Peptide-templated noble metal catalysts: syntheses and applications[END_REF] The strong interaction with support materials, such as ZrO2, [START_REF] Ilyas | Liquid-Phase Aerobic Oxidation of Benzyl Alcohol Catalyzed by Pt/ZrO2[END_REF] Al2O3, [START_REF] Mallat | Selective oxidation of cinnamyl alcohol to cinnamaldehyde with air over Bi-Pt/alumina catalysts[END_REF] TiO2 [START_REF] Bavykin | Deposition of Pt, Pd, Ru and Au on the surfaces of titanate nanotubes[END_REF], and CeO2 [START_REF] Peng | Size effect of Pt nanoparticles on the catalytic oxidation of toluene over Pt/CeO2 catalysts[END_REF][START_REF] Wang | Pt@ CeO2 multicore@ shell self-assembled nanospheres: clean synthesis, structure optimization[END_REF], can also enhance the catalytic activity. Especially, CeO2 (ceria) has been widely used in the catalysis field. The outstanding feature of ceria is enhanced when combining it with various precious metals such as Pt, Pd, Ru, and Rh. The combination is not only preventing the noble metal from sintering but also allows stabilizing the dispersed states. In 2004, A. Corma et al.[66] studied the synergistic effect between Au and CeO2 to increase the catalytic performance for CO oxidation. They found that the combination of Au and CeO2 promotes catalytic activity due to the presence of Ce 3+ ions on the nanocrystalline support surface that is able to adsorb and stimulate O2, enhancing the catalyst reactivity. In 2009, M. Inoue et al. [START_REF] Hosokawa | Effect of the preparation conditions of Ru/CeO 2 catalysts for the liquid phase oxidation of benzyl alcohol[END_REF] developed Ru combined with CeO2.

Interestingly, a 60% yield of benzaldehyde can be achieved over 2%Ru/CeO2. The surface Ce 4+ reduction was greatly enhanced by Ru species distributed on CeO2.

Recently, R. Bal et al. [START_REF] Singha | Pt-CeO 2 nanoporous spheres-an excellent catalyst for partial oxidation of methane: effect of the bimodal pore structure[END_REF] reported the partial oxidation of methane to synthesis gas (a mixture of CO and H2) over Pt/CeO2 catalyst. As stated above, the combination of noble metals and CeO2 can enhance the catalytic performance up to 80% of methane transformation at 600 o C. For this case, the high catalytic activity is related to the fact that smaller particles, easily reducible, can enhance the catalytic activity. R. Li and J. Fan et al.[69] reported the synthesis of three types of simple Pt-CeO2 hybrid nanostructures: nanoflowers, nanonecklaces, and nanosatellites. The modified morphology of CeO2 prolongs the catalytic lifetime compared to conventional Pt nanoparticles due to the inhibition of metal aggregation. In particular, Pt, which exhibits the highest efficiency among the noble metals (see and □ symbolizes an oxygen vacancy (Figure 1.9(a)). These sites can be defined as "asymmetric oxygen vacancies", which can play a key role as active sites in several redox reactions (Figure 1.9(b)). In these asymmetric sites, different surrounding cations influence different oxygen occupancy and redox properties. Figure 1.9(c) illustrates the generated asymmetric oxygen vacancy sites of M-□(-Ce)3 and their influence on the catalytic behavior of the oxides. [START_REF] Yu | Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts[END_REF] It can be seen that the modified CeO2 with other metals can have a great impact on its redox properties due to different oxygen storage-release capabilities. Compared to symmetric vacancy sites, asymmetric vacancies can be easily filled and released by adsorbed oxygen species, identified as the intrinsic active sites in a redox reaction, enhancing their catalytic performance. While symmetric vacancies prefer to be filled by adsorbed oxygen species but are difficult to release oxygen for Ce-□-(Ce)3, and the reverse results can be obtained in the case of M-□-M. The redox catalytic series on an asymmetric oxygen vacancy site for aerobic oxidation of CO as a model reaction. c) Schematic illustration of correlation of the oxygen vacancy microstructure and its redox property.

Taken from ref. [START_REF] Yu | Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts[END_REF] Owing to the outstanding properties of zeolites, they have been widely used as support materials. Materials, which can provide highly dispersed active sites, are required. Compared to the conventional γ-Al2O3 support material, zeolite has some distinct physical properties, such as an adjustable Si/Al ratio, special threedimensional channels, and a huge surface area. [START_REF] Liu | Effect of Preparation Processes on Catalytic Performance of PtSnNa/ZSM-5 for Propane Dehydrogenation[END_REF] As mentioned, Pt agglomeration should be avoided to retain high catalytic activity. Thus, the high surface area of zeolite as support plays a key role because of its exceptional ability to maintain the Pt nanoparticles dispersed, which is crucial to attaining the catalyst performance stability.

Furthermore, metal oxides, especially CeO2, are used to promote the performance of active sites. An optimized amount of CeO2 can be used to disperse Pt on the support and adjust the support acidity, eventually suppressing the formation of side reactions and coke deposition. [START_REF] Fuku | Highly Efficient Thermal Decomposition of Volatile Organic Compounds by Pt/CeO2/ZSM-5[END_REF][START_REF] Damyanova | Effect of CeO2 loading on the surface and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts[END_REF][START_REF] Santos | The effect of ceria content on the performance of Pt/CeO2/Al2O3 catalysts in the partial oxidation of methane[END_REF] For further understanding the catalysis process, apart from the heterogeneous catalyst, the metal-CeO2 modified materials are also interesting for electrocatalytic systems. P.K. Shen et al. [START_REF] Xu | Electrochemical oxidation of ethanol on Pt-CeO2/C catalysts[END_REF] have successfully fabricated a Pt-CeO2/C catalyst for ethanol electrochemical oxidation. They found that the addition of CeO2 to Pt catalyst could considerably enhance the performance of the electrode, especially in poisoning tolerance. Oxygen-containing molecules can be transformed from CO-like poisoning species on Pt to CO2 at low potential, providing the available active Pt sites for more electrochemical reactions. Similar results can be observed for methanol electro-oxidation. For example, X. Qiu et al.[78] discovered CeO2 as a cocatalyst together with Pt for electro-oxidation of methanol. Pt and CeO2 modified carbon nanotubes (CNTs) as Pt-CeO2/CNTs catalysts were synthesized. In contrast with Pt supported on CNTs, Pt-CeO2/CNTs demonstrated higher catalytic performance and lower potential for CO stripping, suggesting that CeO2 can facilitate the electro-oxidation of CO, which is useful for CO and methanol electro-oxidation.

Additionally, CeO2 can enhance not only poisoning resistance, but also active site dispersion of electrocatalyst. C-T Yeh et al. [START_REF] Huang | Promotion of platinum-ruthenium catalyst for electro-oxidation of methanol by ceria[END_REF] reported the synthesis of Pt-Ru/C catalyst combined with CeO2. The promotion of CeO2 was ascribed to an expanded alloy particle dispersion. The highest-exposed surface area of Pt-Ru nanoalloys displayed the best electroactivity for the oxidation of methanol. Recently, A.O. Neto et al. [START_REF] Cordeiro | Improved Pt/CeO2 Electrocatalysts for Ethanol Electro-oxidation[END_REF] developed CeO2 crystals as a support material for Pt nanoparticles as electrocatalysts for oxidation of ethanol. Compared to Pt/C, the nanocomposite demonstrated much higher mass activity and considerably enhanced anti-poisoning capability. The superior activity was assigned to improved metal-support interactions between CeO2 and metal coupled with a shrinkage of the CeO2 bandgap assisting the electron transport from the Pt-CeO2 boundary to the strongly adsorbed byproducts. In addition, H. Yu et al.[81] have successfully developed Ir/CeO2-C for the hydrogen oxidation reaction (HOR). The extremely dispersed Ir nanoparticles can be ascribed to the strong metal-support interaction of Ir and CeO2. The improved electrocatalytic performance is also due to the oxophilic effect owing to the sophisticated oxygen storage-release ability of CeO2.

As mentioned above, CeO2 has been widely used as electrocatalysts for various reactions due to its great properties when combined with other metals, eventually enhancing the catalytic performance. [START_REF] Sedighi | Enhanced electro-oxidation of ethanol using Pt-CeO2 electrocatalyst prepared by electrodeposition technique[END_REF][START_REF] He | Promoting effect of CeO2 in the electrocatalytic activity of rhodium for ethanol electro-oxidation[END_REF] To extend the scope of the designed catalyst apart from heterogeneous catalyst preparation, the elaboration of catalysts using electrochemical approaches is a low cost, easy process, combined with a controllable selectivity as shown in more detail below.

Design of electrocatalysts using bipolar electrochemistry

In electrochemistry, current can be used to perform organic synthesis reactions using electron transfer at the interface between the electrode surface and the species in solution. For this purpose, an external power supply connected with two electrodes, including cathode and anode, is employed to provide power to the system. In contrast to the classical electrochemical setup, a bipolar electrochemical system contains a pair of driving electrodes linked to an external power supply together with a bipolar electrode (BPE) located between the driving electrodes. [START_REF] Loget | True bulk synthesis of Janus objects by bipolar electrochemistry[END_REF][START_REF] Loget | Bulk synthesis of Janus objects and asymmetric patchy particles[END_REF] Such a wireless BPE can perform cathodic and anodic reactions simultaneously, as shown in Figure 1. 10(b). As there are no direct electrical connections, the key benefit of BPE over conventional electrochemistry is that objects can be modified in a true bulk process with almost no limitations with respect to shape, size, and the quantity of BPEs.

Therefore, these features offer interesting perspectives to design reaction systems. [START_REF] Shida | Bipolar electrochemistry: A powerful tool for electrifying functional material synthesis[END_REF] indicating the driving force variation along the bipolar electrode. Taken from ref. [START_REF] Fosdick | Bipolar electrochemistry[END_REF] Based on this polarization, reduction and oxidation reactions take place at the two opposite sides of the BPE. This offers site-selective functionalization, such as cathodic deposition. The feature gives access to various surface modifications such as electrografting, [START_REF] Kumsapaya | Wireless Electrografting of Molecular Layers for Janus Particle Synthesis[END_REF] electrodeposition, [START_REF] Fattah | Indirect bipolar electrodeposition of polymers for the controlled design of zinc microswimmers[END_REF] and sensing, [START_REF] Liu | Open bipolar electrode-electrochemiluminescence imaging sensing using paper-based microfluidics[END_REF] as shown in Figure 1.12.

Furthermore, the potential drop across the BPE provides means for gradient generation. For instance, Bouffier et al. [START_REF] Tisserant | Generation of metal composition gradients by means of bipolar electrodeposition[END_REF] studied the formation of a metal gradient with up to three different metals, including copper, nickel, and zinc on a flat gold electrode. It was found that bimetallic or trimetallic gradients can be successfully deposited in a single experiment. The variation of the chemical composition along the BPE surface can be predicted based on the different standard potentials. Thus, bipolar electrochemistry is a simple method to generate chemical gradients on a bipolar electrode. sensing, and modification of graphene. Taken from ref. [START_REF] Koefoed | Bipolar electrochemistry-A wireless approach for electrode reactions[END_REF] Especially gradients of electrocatalysts with varying properties can be generated in this way. Their local electrochemical properties be characterized among others by scanning electrochemical microscopy (SECM), an interesting technique for the local investigation of electroactivity.

Scanning Electrochemical Microscopy (SECM)

Scanning electrochemical microscopy (SECM) will be used to investigate the structure and functionality of the catalyst layers. SECM is quite unique among scanning probe techniques since it can image the electrochemical activity, i.e., the reaction rate at surfaces. [START_REF] Velmurugan | Fabrication of Scanning Electrochemical Microscopy-Atomic Force Microscopy Probes to Image Surface Topography and Reactivity at the Nanoscale[END_REF][START_REF] Kai | Scanning electrochemical microscopy at the nanometer level[END_REF] In general, the information of topology and discrete variations in conductivity and chemical reactivity is accessible at high resolution from SECM measurements. This technique of chemical imaging is based on a mobile ultramicroelectrode (UME). The tip is scanned at a close distance across the surface of the sample, and its current response is immediately monitored as a function of the

x-axis and y-axis tip position, [START_REF] Bard | Scanning electrochemical microscopy. Introduction and principles[END_REF] as shown in Figure 1. 14(a). SECM imaging relies strongly on the measurement of the electrochemical tip response as a function of the tip-to-sample distance and the sample's surface properties with respect to its electrochemical activity/conductivity. [START_REF] Katemann | Constant-Distance Mode Scanning Electrochemical Microscopy (SECM)-Part I: Adaptation of a Non-Optical Shear-Force-Based Positioning Mode for SECM Tips[END_REF][START_REF] Bard | Scanning electrochemical microscopy[END_REF] The current response leads to an electrochemical image of the topographical feature. [START_REF] Ummadi | Single-cell migration as studied by scanning electrochemical microscopy[END_REF][START_REF] Wain | High-aspect ratio needle probes for combined scanning electrochemical microscopy -Atomic force microscopy[END_REF]

SECM operation modes

According to various purposes of SECM experiments, different operation modes can be applied, as shown in Figure 1.13. [START_REF] Bard | Scanning electrochemical microscopy[END_REF][START_REF] Preet | A review: Scanning electrochemical microscopy (secm) for visualizing the real-time local catalytic activity[END_REF] The following equation shows the SECM study based on a reduced species "R" existing as a free redox mediator in the bulk solution, which gets oxidized to the oxidized species "O" by a polarized UME.

𝑅 → 𝑂 + 𝑛𝑒 -

In a bulk solution when the tip is placed at a large distance away from the substrate, a steady-state diffusion-limited current, iT,∞, is established, as shown in Figure 1. 13(a).

In feedback mode, the conductive nature of the substrate can be determined using the recorded current from the UME tip (iT). The insulator or non-active substrate demonstrates the negative feedback due to a consequence of the physical hindering of the diffusion of the redox mediator to the electrode surface by the substrate (Figure 1.13(b)), producing a decrease in the recorded current (iT < iT,∞). While the conductor or electrochemically active substrate shows positive feedback (Figure 1.13(c)) which means the substrate can immediately reduce the formed oxidized species leading to an increase of the tip current (iT > iT,∞). In generation/collection mode, the electrochemically active redox mediator is produced at either the probe electrode or the substrate electrode. If the production of the redox mediator is at the substrate surface and then reacts electrochemically on the tip, this is called substrate generation/tip collection (SG/TC) mode, Figure 1.13(d). Conversely, if the production of the redox mediator is at the UME probe surface and then reacts electrochemically on the substrate, this is called tip generation/sample collection (TG/SC) mode, Figure 1.13(e). These generation/collection modes offer higher sensitivity due to lesser background currents. Compared to feedback mode, this measurement can be achieved at larger distances between the tip and the substrate. Moreover, lesser background current can be achieved compared to TG/SC mode by using the redox competition mode (RC) based on the competition for the same analyte between the tip and the substrate, as shown in Figure 1.13(f). Therefore, to obtain a high resolution of SECM imaging, the selection of operation SECM mode plays an important role depending on many factors such as the source, concentration of analytes, background current, and the electrochemical reactions in the solution. In this thesis, we report the development of alternative design strategies for various catalyst materials, including noble metals, metal oxides, and hierarchical zeolites. The selected metal oxide, CeO2, supported on hierarchical zeolites was systematically studied and applied as promising catalyst for ethanol dehydration to ethylene in Chapter 3. Moreover, the combination of noble metal and metal oxide demonstrates the improvement of catalytic activity due to their synergy effect, which is beneficial for selective oxidation of alcohols. Chapter 4 illustrates the significantly enhanced catalytic performance of Pt-CeO2 modified hierarchical zeolites because of the synergistic effect. In addition, bipolar electrochemistry was applied to elaborate hybrid Pt-CeO2 catalyst gradients in Chapter 5 to find the best combination of these two materials for electrocatalysis. To investigate the electrocatalytic properties of the gradient film generated by bipolar electrodeposition, SECM was used as a local technique. Finally, Janus particles were designed as bifunctional catalysts in order to perform reduction and oxidation reactions simultaneously for the electrochemical conversion of furfural by using bipolar electrochemistry, as described in Chapter 6.

Hence, this thesis covers the development of both heterogeneous catalysts and electrocatalysts. It describes their catalytic properties in the frame of the upgrading of biomass-derived compounds, as well as the relationship between material structure and reaction mechanisms for both heterogeneous catalysts and electrocatalysts.

Chapter 2

Scope of Thesis

2.

The development of catalysts for alcohol upgrading processes has received particular attention due to the petroleum shortages and environmental concerns.

Therefore, alcohol upgrading can be considered as a clean process to meet human needs. This thesis presents the original design of various catalysts combining metal, metal oxides, and hierarchical structures of solids. They have been successfully elaborated via two different methods, ion exchange and impregnation. Moreover, they have been applied to numerous alcohol upgrading processes, including the dehydration of ethanol and the oxidation of benzyl alcohol, as shown in detail below.

Chapter 3 focuses on the development of catalysts for a sustainable process for the production of ethylene. A metal oxide (CeO2), supported on hierarchical zeolites via a simple hydrothermal synthesis approach, was investigated to improve the catalyst efficiency for alcohol upgrading. Ethanol is one of the most promising molecules which can offer many beneficial features, such as the lack of toxicity, easy handling, and availability from renewable resources. Various high value-added chemicals, especially ethylene, which is one of the most interesting compounds for plastic production industries, can be produced from ethanol conversion. Over the past decade, catalytic dehydration of ethanol to ethylene was considered as an environmentally friendly process that could be achieved at a lower reaction temperature than traditional ethylene production via thermal cracking of petroleum gas or naphtha. CeO2 nanoparticles supported on hierarchical zeolite catalysts have been successfully developed by two methods: wet impregnation and ion-exchange methods. Numerous factors, such as the type of support materials, CeO2 loading methods, CeO2 content, and Si to Al ratio of the zeolite support, influence the catalytic activity. This was confirmed by many techniques to gain detailed information on the synthesized catalysts that exhibit different properties allowing the optimization of catalytic performance. Interestingly, a higher ethylene yield (~99%) can be achieved over the modified CeO2 exchanged hierarchical zeolite prepared by the ion-exchange method. CeO2 contains mostly Ce +IV in the exchanged conventional zeolite. As a result, this zeolite exhibits an inferior catalytic activity for dehydration of ethanol.

However, by increasing the fraction of Ce +III in CeO2 exchanged hierarchical zeolite, the catalytic performance is enhanced. Moreover, the chemical state of Ce and acidity can be simply adjusted by employing a hierarchical zeolite and using an ion-exchange technique, improving the metal-support interaction, acidity, and Ce reducibility, eventually boosting the dehydration of ethanol to ethylene.

Besides that, CeO2-based hierarchical zeolite catalysts can be combined with other active sites such as noble metals for other important processes. In Chapter 4, the selective oxidation of alcohols to aldehydes, which is important for organic synthesis, from both, an academic and industrial point of view, was systematically studied. Among them, aromatic aldehydes are key intermediates for various fine chemicals; and therefore, their effective production has been widely investigated.

Benzaldehyde has various applications ranging from dye production, food and agrochemical issues to perfumery, cosmetics, and pharmaceutics. As a consequence, the oxidation of benzyl alcohol to benzaldehyde was chosen as a model reaction to study the catalytic performances of Pt supported on hierarchical zeolite catalysts.

Owing to cost effectiveness and environmental concerns, molecular oxygen and CeO2

were used as an oxidant and oxygen carrier in the reaction, respectively. The effect of CeO2, which could facilitate the lattice mobility of oxygen and play a key role in the catalytic performance of the material, has been systematically investigated.

Interestingly, the synergic effect between Pt and CeO2 can considerably improve the catalytic performances. The benzaldehyde yields reached almost 100 % for Pt supported on CeO2-hierarchical zeolite, whereas it was less than 40 % with the conventional catalyst. The hierarchical structure of zeolite can: (1) enhance the amount of available active sites due to its unique high surface area, ( 2) avoid the agglomeration of Pt and CeO2 nanoparticles, and (3) help to control the oxidation state of CeO2. The existence of a high fraction of trivalent Ce species (Ce +III ) on hierarchical zeolite nanosheets promotes the catalytic oxidation reaction. Furthermore, the tuneable Si to Al ratio of prepared zeolite catalysts can also significantly improve the catalytic performance because of its influence on metal-support interaction and thus Pt size leading to a better catalytic performance.

are also essential. In Chapter 5, Pt-CeO2 elaborated by using bipolar electrodeposition was used as an electrocatalyst for benzyl alcohol electro-oxidation. Therefore, this work builds on the previous chapter to explore in more detail the metal-modified electrocatalyst to complement the catalytic perspectives. Thanks to the potential distribution along the bipolar electrode, a Pt-CeO2 film gradient can be observed. The electrocatalytic properties of the gradient were characterized by scanning electrochemical microscopy (SECM). SECM is a powerful tool for studying the local electrochemical properties of substrates. This technique allows chemical imaging, by using a mobile ultramicroelectrode. SECM imaging is highly dependent on the distance between the tip and the substrate, but also on the local electrochemical properties of the substrate. Hence, SECM can help to elucidate in more detail the role of metal modified electrocatalysts in the catalysis process.

In addition, bipolar electrochemistry was further applied to synthesize a bifunctional electrocatalyst, as discussed in Chapter 6. Owing to the asymmetric behavior of conductive materials in a bipolar electrochemical set-up, gradual functionalization of surfaces can be achieved. We illustrate the proof-of-concept that bipolar electrochemistry can produce Janus particles as bifunctional electrocatalysts, which can be used to simultaneously reduce and oxidize a chemical species. Two active species covering the opposite sides of bipolar objects can play a crucial role in converting reactants into the corresponding reduction and oxidation products. Furfural was selected as a model system due to its capability to undergo both types of redox reactions. The investigation demonstrated that Au and Pt layers are suitable to play a crucial role in the catalytic reduction and oxidation reaction of furfural, respectively.

Therefore, furfuryl alcohol and furoic acid can be produced simultaneously via a reduction and oxidation of the furfural starting compound. This feature opens up interesting perspectives with respect to the use of Janus particles as bifunctional electrocatalysts.

Chapter 3

Fine-tuning catalytic structures of ceria incorporated in hierarchical zeolites for ethanol dehydration 3.

Introduction

Ethylene production is one of the most interesting industrial processes due to its utility for several applications, such as surfactant chemicals, plastics, and textiles.

[101-103] The thermal cracking of petroleum gas or naphtha is the typical primary process for ethylene production, commonly producing a lot of CO2 as a byproduct.[104, 105] However, the shortages of petroleum resources and serious environmental issues become the limitation for further development of this process.

Thus, bioethanol utilization as a renewable feedstock is considered as an alternative way to generate ethylene.

[106]

To date, various solid acid catalysts have been developed for ethanol/bioethanol dehydration into ethylene, ranging from mesoporous silica, [START_REF] Salem | Enhanced ethylene production by dehydration of ethanol over Al/SBA-15 mesoporous catalysts[END_REF] and alumina, [START_REF] Dewilde | Kinetics and Mechanism of Ethanol Dehydration on γ-Al2O3: The Critical Role of Dimer Inhibition[END_REF] to metal oxides [START_REF] Clemente | Ethylene production via catalytic ethanol dehydration by 12-tungstophosphoric acid@ceria-zirconia[END_REF] and zeolites. [START_REF] Ferreira Madeira | Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role[END_REF] However, their limitations for practical use are the harsh operating conditions and their high acidity. In addition, the fast deactivation of catalysts from coke formation is unavoidable.

[107] Among them, one of the most promising catalysts is ZSM-5, Zeolite Socony Mobil-5, an aluminosilicate zeolite belonging to the pentasil family of zeolites, even though its high acidity remains the main concern because it will result in fast catalyst deactivation.

[108] There are numerous attempts to overcome this drawback, such as fine-tuning the zeolite acidity depending on its Si/Al ratio and incorporating into hierarchical structures.

[109] For instance, the optimal Brønsted acid sites can be finely tuned by changing Si/Al ratios ranging from 16 to 500 to improve the catalytic performances of HZSM-5 assigned as proton exchanged ZSM-5. [START_REF] Ferreira Madeira | Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role[END_REF] To decrease the coke formation, a new class of zeolite with hierarchical structures is introduced. [110][111][112] In such a case, the addition of meso-or macroporous structures into initially microporous zeolite provides an exceptionally high surface area and tunable porous features. [109,112] Up to date, various post-processing concepts have been used to increase the catalytic activity for ethanol dehydration, such as desilication or dealumination, which allow to refine the acidity of the zeolites but also the modification of their hierarchical pore structure. [113] Recently, a high ethylene yield obtained from ethanol/bioethanol dehydration could be achieved with hierarchical HZSM-5 nanosheets having various Si/Al ratios. However, a high ethylene yield cannot be obtained by employing a silicarich HZSM-5.

[114]

Additionally, metal oxides, for instance, cerium oxide (CeO2), are among the most attractive materials with respect to their active catalytic sites. [START_REF] Montini | Fundamentals and catalytic applications of CeO2-based materials[END_REF]115,116] Currently, CeO2 catalysts have attracted considerable attention due to their superior properties, such as the redox states of Ce 3+ and Ce 4+ , that can be easily shifted from one to the other, an oxygen-storage capacity, high thermal stability, and acid-base

properties. [START_REF] Trovarelli | Catalytic properties of ceria and CeO2-containing materials[END_REF] The oxygen vacancy sites are also advantageous to be applied in ethanol dehydration. However, since the acidity of CeO2 is not sufficient to react with the hydroxyl group of ethanol, using pure CeO2 catalyst itself for ethanol dehydration is not efficient.

[117] It is therefore essential to adjust its acidic properties by combining it with additional acid catalysts or other promoters, such as Y/CeO2[117], Ce/NaY[118],

and H3PW12O40/Ce0.8Zr0.2O2. [START_REF] Clemente | Ethylene production via catalytic ethanol dehydration by 12-tungstophosphoric acid@ceria-zirconia[END_REF] The idea reported in this chapter is to modify the acidity and the chemical state of Ce species by incorporated them in hierarchical zeolites for ethanol dehydration.

The combination of Ce species and hierarchical zeolite would be a promising approach due to the above-mentioned distinct properties of Ce species and the capability of hierarchical zeolite to offer a high amount of exposed active sites.

[119] Herein, several types of zeolite were employed to investigate their effects on the acidity and chemical state of Ce species, to enhance the catalytic performance for ethanol dehydration.

Furthermore, different preparation techniques for Ce insertion, a wet impregnation, and an ion-exchange procedure, were also investigated to better understand the impact of the preparation process on the acidity and chemical state of Ce species.

Experimental section

Materials

All chemicals with analytical grade were employed as obtained without additional purification. The aluminium and silica sources were aluminium isopropoxide (Sigma-Aldrich, ≥98.0%) and tetraethyl orthosilicate (TEOS, Sigma-Aldrich, ≥99.0%), respectively. The mineralizing agent in the preparation process was sodium hydroxide (NaOH, Carlo Erba, ≥98.0%). Different structure-directing agents (SDAs) were used for conventional zeolites and hierarchical zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH, 1.0 M in H2O) was employed as an SDA for conventional zeolite, while tetrabutylphosphonium hydroxide (TBPOH, Sigma-Aldrich, 40% in H2O) was used for hierarchical zeolites. Moreover, cerium (III) acetate (TCI, >98.0%) was used as a cerium precursor. Besides, ethyl alcohol (Sigma-Aldrich, ≥99.0%) was used as a reactant to study the catalytic activity.

Catalyst preparation

Catalysts were prepared based on zeolite support materials including conventional zeolite and hierarchical zeolite. The distinctive features of structuredirecting agents (SDA) were used to construct different zeolite supports.

[120]

Synthesis of conventional ZSM-5 zeolite (ZSM5-CON)

The conventional ZSM-5 zeolite was typically synthesized according to the molar synthesis composition of 10SiO2: 0.05Al2O3: 1TPAOH:

1.03NaOH: 400H2O. After mixing 7 g of TEOS and 3.42 g of TPAOH to obtain a silica-SDA solution, 0.14 g of sodium hydroxide, dissolved in DI water, was added gently into the silica-SDA solution, and the mixture was stirred at room temperature for 2 hours. After that, the obtained gel was transferred to the hydrothermal synthesis reactor and heated to 180 °C for 3 days. Then, the prepared sample was washed with DI water, filtered, and dried at 110 °C. Finally, the calcination process was carried out at 650 °C for 6 hours to remove SDA and get the final product, namely ZSM5-CON, as illustrated in Figure 3.1. After zeolite preparation, CeO2 was loaded in the next step. Two methods were selected to load CeO2 nanoparticles on zeolite supports, including ionexchange and wet impregnation methods. The impregnation method consists of three basic steps: first, support with high surface area is impregnated with a solution containing the metal precursors, then the solvent is evaporated at an elevated temperature, and finally, the metal precursors are reduced under designated environment to produce the catalysts.

[121] The ion exchange method uses the ion exchange features of the support materials that can have binding preferences for certain ions, depending on the physical properties and chemical structure of both the ion exchanger and the ion. It depends on the size, charge, or structure of the ions.

Typically, impregnation leads to a rather weak metal-support interaction, leading to large metal particles, whereas ion exchange results in a higher initial dispersion.

[122]

Preparation of ceria supported on zeolites using ionexchange method (Exc)

The prepared zeolites were used as solid supports for the cerium species. The mixture of a zeolite and the desired amount of cerium (III) acetate was prepared using DI water as solvent at 80 °C for 2 hours. Subsequently, the mixture was filtered, washed with DI water, and finally dried at 100 °C overnight. Finally, the calcination process was carried out at 550 °C for 4 hours to get a catalyst corresponding to yCe(Exc)-ZSM5-HIE, and yCe(Exc)-ZSM5-CON for the hierarchical ZSM-5 and the conventional ZSM-5, respectively (y = 0, 1, 5, 10 and 20 wt% of CeO2).

Preparation of ceria supported on zeolites using impregnation method (Imp)

The prepared zeolites were combined with the desired cerium (III) acetate content and DI-water at room temperature for 24 hours using an impregnation method. Subsequently, the solvent was removed by a rotary evaporator, and the acquired materials were finally dried at 100 °C overnight. Then, the calcination process was carried out at 550 °C for 4 hours to obtain the catalysts, denoted as yCe(Imp)-Silicalite1-HIE, yCe(Imp)-ZSM5-HIE for the hierarchical silicalite-1, and the hierarchical ZSM-5, respectively (y = 5 wt% of CeO2).

It should be noted that all samples are denoted as yCe(M)-zeolite support, where y is the CeO2 content. M refers to the preparation method (Exc = ionexchange method; Imp = impregnation method).

Characterization

The powder X-ray diffraction (XRD) patterns of the synthesized catalysts were studied with a Bruker D8 ADVANCE device with CuKα radiation (40 kV, 40 mA) in the 2θ ranging from 5° to 60° with a step size of 0.02° and a scan rate of 1° min -1 .

Scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) images to study the morphology of the catalysts were recorded with a JEOL JSM-7610F microscope and JEOL JEM-ARM200F microscope at 200 kV, respectively. N2 adsorption-desorption measurement was used to determine the textural properties of all the prepared catalysts at -196 °C by using a MicrotracBEL, BELSORP-max model, and all samples were degassed at 350 °C for 24 hours prior to the investigation. The specific surface area (SBET), micropore surface area, and pore volume were evaluated by the Brunauer-Emmett-Teller (BET) and t-plot methods, respectively. Moreover, wavelength-dispersive X-ray fluorescence spectroscopy (WDXRF) recorded with a Bruker S8 TIGER ECO machine. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) acquired with a JEOL JSM-7610F microscope were used to analyze the elemental composition.

In addition, the surface properties were investigated, including acidity, performed by NH3 temperature-programmed desorption (NH3-TPD), basicity, performed by CO2 temperature-programmed desorption (CO2-TPD), and metal reducibility performed by H2 temperature-programmed reduction (H2-TPR). The measurements were conducted using a BELCAT II instrument equipped with thermal conductivity detectors (TCD).

Prior to the NH3-TPD and CO2-TPD measurements, 0.05 g of the sample was pretreated typically at 300 °C for 1 hour under He flow to entirely eliminate the adsorbed molecules on the sample surface, and then it was cooled down to 100 °C, together with supplying saturated NH3 gas (5 vol% in He) or CO2 gas for 30 min (50 mL min -1 ), followed by He flushing (50 mL min -1 ) for 30 min at 100 °C. The desorption steps of both NH3 and CO2 were recorded in the temperature range from 100 to 800 °C with a heating rate of 10 °C.min -1 . In the case of H2-TPR, the samples were pretreated typically at 300 °C for 1 hour with a heating rate of 10 °C min -1 under Ar flow and then cooled down to 50 °C. Subsequently, the measurement was performed from 50 °C to 900 °C with a heating rate of 5°C min -1 in a flow of 2 v/v% of H2 in Ar (50 mL min -1 ). Besides, the Ce oxidation state was carefully characterized using X-ray absorption near-edge structure (XANES). All samples were pretreated typically at 350 °C for 2 hours under a N2 flow to remove adsorbed molecules on the samples. Ce L3edge XANES spectra were obtained in transmission mode at the BL5.2 station at Siam Photon Laboratory (Synchrotron Light Research Institute (Public Organization), SLRI), Thailand.

Catalytic activity test

A fixed-bed reactor was used to study the catalytic performance for ethanol dehydration. Initially, 0.1 g of the catalyst was pretreated at 350 °C under a N2 flow of 5 mL min -1 for 2 hours. Then, the reaction was performed under N2 flow at 350 °C with a controlled weight of ethanol feed flowing per unit weight of catalyst per hour, called weight hourly space velocity (WHSVEtOH), equal to 5 h -1 . The quantification of products was investigated by a gas chromatograph (GC, Agilent 7890B) equipped with a flame ionization detector (FID) and a PoraBOND Q capillary column (25 m x 0.32 mm) at a time interval of 1 hour. Subsequently, the conversion of ethanol (XEtOH) and the product selectivity (Si) were estimated by the following equations:

𝑋 𝐸𝑡𝑂𝐻 = ( (𝑛 𝐸𝑡𝑂𝐻 ) 0 -(𝑛 𝐸𝑡𝑂𝐻 ) 𝑡 (𝑛 𝐸𝑡𝑂𝐻 ) 0 ) × 100%
Where (nEtOH)0, (nEtOH)t, ni, Σn are the initial mole content of ethanol, the ethanol mole content at a particular time, the mole content of the desired product i, and the total moles of all the products, respectively.

Results and discussion

The scheme of Figure 3.2 illustrates the preparation process of several zeolites involving hierarchical ZSM-5 (ZSM5-HIE), hierarchical silicalite-1 (Silicalite1-HIE), and conventional ZSM-5 (ZSM5-CON). The variation of Ce species (I, II, III, and IV) could be found due to the various solid supports and the different insertion procedures, including simple impregnation (Imp) and ion-exchange techniques (Exc).

() 3.1) demonstrate that CeO2 insertion does not destroy the MFI crystalline structure of ZSM-5, which belongs to the pentasil family of zeolites as compared to pristine ZSM5-HIE. Because the content of Ce species is quite high ( 5wt.% obtained from XRF measurement), the characteristic peaks of CeO2 at 2θ of 28, 33, 48, and 56 degrees[123] can be clearly seen, especially at 28 degrees (Figure 3.4A(d)). In contrast, the corresponding peaks are invisible in the XRD patterns of prepared hierarchical zeolites, even when using the same CeO2 content, suggesting that well-dispersed Ce species can be obtained on hierarchical zeolite surfaces. The X-ray absorption near edge structure (XANES) indicates the Ce oxidation states of the synthesized catalysts. Generally, CeO2 nanoparticles have a cubic fluorite structure with a mixed-valence state between Ce 4+ and Ce 3+ .[124] A major contribution of the Ce 3+ state can be observed for 5Ce(Imp)-Silicalite1-HIE, 5Ce(Imp)-ZSM5-HIE, and 5Ce(Exc)-ZSM5-HIE samples, while the Ce 4+ state is predominant in a conventional zeolite (5Ce(Exc)-ZSM5-CON) as can be seen in Figure 3.4B. These observations imply that the well-dispersed ultra-small Ce particles typically contain a high fraction of Ce 3+ .[125] Hence, it is reasonable to conclude that the hierarchical zeolite surfaces can provide highly dispersed Ce species. In addition, the hierarchical zeolites clearly demonstrate the higher surface roughness with respect to the conventional one (Figure 3.6). The average particle sizes are around 3.17 μm, 233 nm, 157 nm, and 154 nm for 5Ce(Exc)-ZSM5-CON, 5Ce(Imp)-Silicalite1-HIE, 5Ce(Imp)-ZSM5-HIE, and 5Ce(Exc)-ZSM5-HIE, respectively. This again confirms that the CeO2 loading doesn't influence the structure, morphology, and size of the zeolite supports. Moreover, further information of CeO2 dispersion at higher magnification was explored by transmission electron microscopy (TEM), as can be seen in Figure 3.8.

i i t n S n  =    
These observations again prove that the smallest Ce species can be obtained with 5Ce(Exc)-ZSM5-HIE. Energy-dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscopy (STEM) allows to perform the chemical mapping illustrated in Figure 3.9.

In the case of a conventional support, CeO2 nanoparticles can be clearly observed on the outer surface of ZSM5-CON, whereas a better CeO2 dispersion can be seen with hierarchical zeolites. The brighter spots compared to the zeolite background of the hierarchical structure can be assigned to Ce, which is a heavier element than the components of zeolites. The elemental analysis by SEM-EDS is illustrated in Figure 3.10 and detailed in Table 3. The textural properties of the prepared catalysts were studied using N2 physisorption measurements. Conventional zeolite normally reveals a type I isotherm, indicating that it possesses only a microporous structure, as can be seen in the case of 5Ce(Exc)-ZSM5-CON (Figure 3.11 and Table 3.3).

[128] In contrast, mixed isotherms between type I due to the micropore filling at the low relative pressure and type IV isotherm because of the high N2 uptake and mesopore capillary condensation at the relative pressure of 0.4 to 0.8 can be found for the hierarchical zeolites. [129] This confirms that hierarchical zeolites can provide a superior surface area, enhanced metal distribution, eventually improving the catalytic activity. b SBET: Specific surface area (m 2 g -1 ) determined by BET method.

c Sext: External surface area (m 2 g -1 ).

d Smicro: micropore surface area (m 2 g -1 ), determined by t-plot method.

e Vtotal: total pore volume (cm 3 g -1 ) obtained at P/P0=0.99.

f Vmicro: micropore volume (cm 3 g -1 ), determined by t-plot method.

g Vext: external pore volume (cm 3 g -1 ), Vext=Vtotal-Vmicro.

From the additional investigation of the surface properties of the prepared catalysts, as shown in Figure 3.12A, it can be seen that the type of support materials and modification methods to load CeO2 can impact the acid properties, including overall acidity and the acid strength compared to pristine ZSM5-HIE (Figure 3.13).

Two Besides, H2-TPR profiles of the prepared catalysts were recorded to evaluate the reducibility of the catalysts (Figure 3.14 and Table 3.6). Generally, two characteristic Ce peaks at 500 and 850°C are detected related to the reduction of Ce 4+

to Ce 3+ with surface oxygen and bulk oxygen, respectively,[132] as can also be seen in the profile of commercial CeO2.

[133] Interestingly, hierarchical catalysts offer a lower Ce reduction temperature, indicating the formation of ultra-small Ce particles, eventually leading to enhanced reducibility. These observations again verify that by using the hierarchical zeolite supports, higher surface/lattice oxygen mobility can be obtained.

[134] Normally, smaller particle sizes and higher surface areas of CeO2 materials are likely to have more crystal edges and corners, resulting in a greater density of surface oxygen species allowing using lower temperatures for reduction processes to occur.

[135] The most appropriate performance among these prepared catalysts is 5Ce(Exc)-ZSM5-HIE due to its active surface oxygen, which should be advantageous for the catalytic performance. Thus, the highest catalytic activity can be noted by employing 5 wt.% of Ce species. In addition to the highest metal dispersion and acidity of 5Ce(Exc)-ZSM5-HIE, another reason is the hierarchical ZSM-5 structure, offering higher stabilized Ce active sites (Figure 3.2, III). An ion-exchange process can also provide easily localized metal oxides in zeolite structures.

[137] It may then be easier to convert ethanol to ethoxy species using oxygen vacancies, and it is subsequently transformed to ethylene. [138] Moreover, the catalytic performance of pure hierarchical zeolites is neglectable, as shown in Figure 3.18. Although ZSM5-HIE can produce ethylene in the first period due to the surface properties, its active sites are too small, and then its performance dramatically drops after 5 hours. It can be implied that the enhanced catalytic performance of the prepared catalysts mainly comes from the active Ce species.

Conclusion

In

Introduction

It is well-known that the selective oxidation of alcohols to aldehydes counts as one of the most essential processes to provide several intermediate compounds for modern organic synthesis.

[139] In particular, the benzyl alcohol oxidation to benzaldehyde is an important challenge, because benzaldehyde is a vital compound, that can be converted to vanillin. It can be applied in various potential applications, such as for the synthesis of dyes, perfumes, food flavors, and industrial solvents. [140,141] Typically, the partial oxidation of toluene or the hydrolysis of benzylidene chloride has been used for benzaldehyde production.

[142] However, a low product yield and wastewater removal issues are the main drawbacks of these methods. [143] Therefore, the direct selective oxidation of benzyl alcohol, under moderate conditions at a mild reaction temperature, is an alternative approach for efficient benzaldehyde Theoretically, the metal dispersion might be improved by using hierarchical zeolites as promising solid supports for nano metal oxides, due to an extremely high surface area; however, the combination of nanoceria-modified platinum and hierarchical zeolite has not yet been illustrated, even though it would provide many advantages with respect to the activity of the redox-active species.

In this chapter, the improvement of nanoceria-platinum modified hierarchical zeolites for the selective alcohol oxidation to aldehyde will be presented. A systematic investigation was performed to study the corresponding catalytic activity when using hierarchical zeolite with various alumina contents. Moreover, to characterize catalyst properties, crystalline structures, morphologies, metal size and dispersion, the ability of metal reduction, and the oxidation state of metal species have been demonstrated

to obtain the structural detail of developed catalysts. It eventually resulted in understandings the mechanistic viewpoints of alcohol oxidation using different supports to stabilize redox species, which impacted the catalytic performance of selective alcohol oxidation.

Experimental section

Materials

The chemicals below with analytical grade were utilized without further purification. The main reagents to synthesize zeolites were aluminium isopropoxide (Sigma-Aldrich, ≥98.0%) and tetraethyl orthosilicate (TEOS, Sigma-Aldrich, ≥99.0%)

as alumina and silica sources, respectively. The mineralizing agent was sodium hydroxide (NaOH, Carlo Erba, ≥98.0%) . Different structure-directing agents (SDAs)

were used. To synthesize conventional zeolites, tetrapropylammonium hydroxide (TPAOH, 1.0 M in H2O) was employed. In contrast, tetrabutylphosphonium hydroxide ( TBPOH, Sigma-Aldrich, 40% in H2O) was utilized for hierarchical zeolite. Precursor materials include cerium acetate (TCI, >98.0%) for cerium oxide and tetraamineplatinum (II) nitrate (Sigma-Aldrich, ≥50.0% Pt basis) for active platinum sites. To test the catalytic performance, benzyl alcohol (Sigma-Aldrich, ≥99.0%) was used as a reactant together with toluene (Merck, ≥99.9%) and decane (Sigma-Aldrich, ≥99.0%) as a solvent, and an internal standard, respectively.

Catalyst preparation

Synthesis of conventional silicalite-1 zeolite (Silicalite1-CON)

In the typical synthesis procedure,[120] the conventional silicalite-1 zeolite was obtained with a molar synthesis composition of 10SiO2: 1TPAOH:

1.03NaOH: 400H2O. Initially, the mixture between 7 g of TEOS and 3.42 g of TPAOH was used as a silica-SDA solution. Then a solution of 0.14 g of sodium hydroxide in DI water was gently poured into the silica-SDA solution and stirred at room temperature for 2 h, to allow the aging process to occur. After that, the synthesis gel was heated at 180 °C for 3 days in a lined hydrothermal synthesis container. The synthesized sample was subsequently washed with DI water, filtered, and dried at 110 °C overnight. Finally, to remove SDA and obtain the product, namely Silicalite1-CON, calcination at 650 °C was carried out for 8 h.

Synthesis of hierarchical ZSM-5 zeolite

The different Si/Al ratios (100 and 400) of hierarchical ZSM-5 zeolite (ZSM5-HIE) were obtained using a molar synthesis composition of 60SiO2:

xAl2O3: 18TBPOH: 0. 75NaOH: 600H2O, where x was 0.075 and 0.3. The same procedure with the previous chapter to prepare hierarchical zeolite was taken. Briefly, the mixture of TEOS and aluminium isopropoxide was first used as a silica-alumina source. Another mixture, including 8.62 g of TBPOH, 0.02 g of sodium hydroxide, and DI water, were gradually poured into the silica-alumina source. Then the solution was blended at room temperature for 12 h, to allow aging. After that, the synthesis gel was heated at 130 °C for 2 days in a lined hydrothermal synthesis container. The synthesized sample was then washed with DI water, filtered, and dried at 110 °C overnight. Finally, to remove SDA and obtain the product, calcination at 650 °C was carried out for 8 h. Hierarchical Silicalite-1 possessing MFI structure with pure silica in the framework (Si/Al=∞) denoted as Silicalite1-HIE was also generated.

Preparation of Pt/CeO2 supported on zeolites

The desired amount of cerium acetate together with the prepared zeolites and DI water were mixed at room temperature for 24 h. Then the water was removed using a rotary evaporator and dried at 100 °C overnight. After that, calcination at 550 °C was performed for 6 h to obtain the product denoted as yCeO2-Silicalite1-HIE, yCeO2-ZSM5-HIE, and yCeO2-Silicalite1-CON for employing the hierarchical silicalite-1, the hierarchical ZSM-5, and the conventional silicalite-1 as a support material, respectively (where y = 0, 5, 10, 20 and 30 wt% of CeO2), as shown in Figure 4.1. Afterwards, the same sequence was followed for the platinum loading process.

The platinum precursor and ceria-modified zeolite involving yCeO2-Silicalite1-HIE, yCeO2-ZSM5-HIE, and yCeO2-Silicalite1-CON were mixed at room temperature for 24 h, and then evaporated with a rotary evaporator and dried at 100 °C overnight. Finally, calcination at 550 °C for 6 h allowed obtaining the final product denoted as zPt/yCeO2-Silicalite1-HIE, zPt/yCeO2-ZSM5-HIE, zPt/yCeO2-Silicalite1-CON, respectively

(where z = 0, 0.5, 1 and 2 wt% of Pt).

Characterization

The crystallographic structure of the materials was investigated from XRD patterns obtained using a Bruker D8 ADVANCE machine with CuKα radiation ( 40kV, 40 mA) in the 2θ ranging from 5° to 60° with 0.02° step size and 1° min -1 scan rate.

The SEM and TEM images were taken with a JEOL JSM-7610F microscope and JEOL JEM-ARM200F microscope at 200 kV, respectively, to investigate the morphology of the catalysts. To determine the textural properties, N2 adsorption-desorption measurements at -196 °C obtained with a MicrotracBEL, BELSORP-max model was used. Before the measurement, all the analyzed samples were first degassed at 350°C for 24 h. The specific surface area (SBET) was evaluated by the Brunauer-Emmett-Teller (BET) method, associated with quantifying the amount of physical adsorption of N2 probing gas by van der Waals forces.

[170] The micropore surface area and pore volume were determined by the t-plot method based on plotting the adsorbed volume at a given pressure against the average thickness of the adsorbate film obtained at the same pressure for the non-porous reference material. [171,172] Moreover, to analyze the elemental composition, wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) was used on a Bruker S8 TIGER ECO machine. The reducibility of the prepared catalysts was checked from the H2-TPR measurements using a BELCAT II machine equipped with thermal conductivity detectors (TCD).

Normally, 0.05 g of analyzed samples were pretreated under a flow of Ar at 300°C for 1 h with 10°C min -1 heating rate and then cooled down to 50°C. Afterwards, the samples were measured at temperatures ranging from 50°C to 900°C with 5°C min -1 heating rate under a 50 ml min -1 flow of 2 v/v% of H2 in Ar. The BELCAT II equipped with TCD was also used to investigate the metal dispersion by using the H2-pulse technique. First, the catalysts were treated under air flow at 350 °C for 30 min, followed by Ar purging for 15 min, and then pretreated under H2 flow at 350 °C for 20 min followed by Ar purging for 20 min to detach weakly adsorbed H2. Finally, the catalysts were cooled down to room temperature under Ar flow, and a series of H2 pulses was introduced until reaching a steady state. The metal dispersion (MD) and the average diameter of particles (Da presuming metal particles are spherical) were estimated from theoretical aspects [173] by applying the following equations:

where Vm is a monolayer volume (mol g -1 ), MW is metal atomic weight (g mol -1 ), W% is the metal percentage in the sample, SF is a stoichiometric factor (molecule of gas per metal atom), MS is the metal surface area (m 2 g -1 ) and ρ the metal density (g cm - 3 ), respectively. Furthermore, to study the Ce oxidation state, X-ray absorption nearedge structure (XANES) was used to carefully determine the Ce L3-edge XANES spectra by using the transmission mode at the BL5.2 station at Siam Photon Laboratory (Synchrotron Light Research Institute (Public Organization), SLRI), Thailand.

Catalytic activity test

The oxidation of benzyl alcohol was conducted in a batch reactor involving a two-neck round-bottom flask equipped with a condenser column. After pretreatment of the prepared catalysts at 350 °C under 5 ml min -1 of H2 flow for 2 h, 0.08 g of activated catalyst was moved to a batch reactor. After that, a mixture of 6 ml of toluene as a solvent and decane as an internal standard was added. The flask was closed and heated to 80 °C under vigorous stirring. Benzyl alcohol (50 μl) was inserted into the flask. A balloon of air was used to introduce air into the reactor under atmospheric pressure. The internal calibration analysis method was used to quantify the products. The samples were examined by a gas chromatograph (GC, Agilent 7890B) equipped with a flame ionization detector ( FID) and PoraBOND Q capillary column (25 m x 0.32 mm). Finally, the conversion of benzyl alcohol (XBenzyl alcohol), and the selectivity of benzaldehyde (SBenzaldehyde), were determined by the following calculations:

𝑋 𝐵𝑒𝑛𝑧𝑦𝑙 𝑎𝑙𝑐𝑜ℎ𝑜𝑙 (%) = 𝑛 0 -𝑛 𝑡 𝑛 0 × 100% 𝑆 𝐵𝑒𝑛𝑧𝑎𝑙𝑑𝑒ℎ𝑦𝑑𝑒 = 𝑛 𝐵𝑒𝑛𝑧𝑎𝑙𝑑𝑒ℎ𝑦𝑑𝑒 𝑛 0 -𝑛 𝑡 × 100%
Where n0 and ni are the amount of initial and remaining benzyl alcohol, respectively. This behavior could be related to the fact that the much smaller size coupled with hierarchical zeolite surface roughness can provide a higher surface area to accommodate CeO2 nanoparticles, leading to a higher dispersion. Moreover, the isotherm is completely different in the case of 1Pt/CeO2. Almost no adsorption ability at low relative pressure and a small hysteresis loop at high relative pressure can be described as non-porous structures with an interparticle void, as shown in Figure 4.8(d).

Results and discussion

[175] These explanations obviously indicate that a higher specific surface area can be obtained for hierarchical zeolites, which could offer superior metal dispersion, eventually resulting in better catalytic activity. Besides, even though the SEM image of the 1Pt/CeO2 (Figure 4.4D) illustrates a small particle size, it possesses a very low surface area due to the CeO2 aggregation. surface area (m 2 g -1 ); c Smicro: micropore surface area (m 2 g -1 ), determined by t-plot method; d Vtotal: total pore volume (cm 3 g -1 ) obtained at P/P0=0.90; e Vmicro: micropore volume (cm 3 g -1 ), determined by t-plot method; f Vext: external pore volume (cm 3 g -1 ), Vext=Vtotal-Vmicro.

Additionally, to further verify the metal dispersion ability, different supports modified by nanoceria-platinum were also characterized by H2 pulse chemisorption measurements. The number of exposed active Pt surfaces analyzed by chemisorption measurements is based on the amount of adsorbed H2 gas during the investigative [176] The metal dispersion, which represents the number of metal particles available on the support surface to participate in a reaction, corresponds to the calculation of the adsorbed H2 quantities. [173] As can be seen in Table 4.2, the metal dispersion of hierarchical samples is remarkably higher than that of the conventional sample. Therefore, these results again corroborate the dispersion improvement of Pt on CeO2 modified hierarchical zeolites, meaning that the prepared hierarchical catalysts can provide more exposed Pt sites for the reaction. However, it should be noted that the highest dispersion in the case of 1Pt/CeO2 can be attributed to the small size of CeO2 nanoparticles used to support Pt due to platinum-ceria interactions leading to well-spread Pt sites. It is noteworthy that an important factor for an oxidation reaction is the PtOx reducibility at the Pt-CeO2 interface. H2 consumption was detected at a lower temperature in the case of 1Pt/20CeO2-Silicalite1-HIE compared to 1Pt/20CeO2-Silicalite1-CON, meaning that the hierarchical support can well distribute Pt atoms. These behaviors are also in agreement with the results of XRD and TEM. Therefore, it can be assumed that extremely efficient active sites to stimulate the interfacial lattice oxygen could be favored by the hierarchical zeolite. This should boost the catalytic performance of the oxidation reaction. Furthermore, the reducibility of PtOx species of a 1Pt/20CeO2-ZSM5-HIE catalyst is comparable to the case of 1Pt/20CeO2-Silicalite1-HIE. In the meantime, the sample of 1Pt/CeO2 shows more distinctive peaks at 400 and 800 °C in Figure 4.9B, owing to the reduction of the ceria surface and bulk ceria, respectively.

[68] Apart from characterization experiments, the catalytic activity of the prepared catalysts was investigated using selective benzyl alcohol oxidation to benzaldehyde as a model reaction. As can be seen in Figure 4.10, the oxidation reaction requires some oxidants to carry out the process. This work was performed under the aerobic condition using a saturated air system offering a clean process to produce benzaldehyde from benzyl alcohol oxidation. The support materials also play an important role in the catalytic activity, as can be seen in Figure 4.12 and Figure 4.13. The catalytic performance of 1Pt/20CeO2-Silicalite1-HIE is clearly superior with respect to 1Pt/20CeO2-Silicalite1-CON.

Obviously, 1Pt/20CeO2-ZSM5-HIE provides the highest yield of benzaldehyde. In this case, the framework of ZSM5-HIE and Silicalite1-HIE is the same, but ZSM5-HIE contains the Al sites in the structure, while the Silicalite1-HIE is only a pure silica (Table 4.1). The higher catalytic performance of 1Pt/20CeO2-ZSM5-HIE compared to 1Pt/20CeO2-Silicalite1-HIE correlates to the fact that the metal-support interaction can be improved by the existence of alumina in the solid support.

[136] However, for 1Pt/CeO2, a considerably lower catalytic performance is observed compared to that of the hierarchical ones even though it has highly dispersed active sites (Table 4.2). To understand in more detail the active site structures, the Ce oxidation state of the prepared catalysts was examined by using X-ray absorption near-edge spectroscopy (XANES) measurement. Nevertheless, the highly dispersed active sites of 1Pt/CeO2 exhibit a lower catalytic performance, probably due to a higher Ce 4+ content compared with hierarchical supports. Besides, the reaction testing cannot change the Ce oxidation state (Table 4.3). Thus, it can be concluded that the prepared catalysts provide recyclable active sites for selective benzyl alcohol oxidation. %Ce 3+ = I I /(I I +I II +I III ), where I I , I II and I III are the intensities of the different peaks.

To understand the corresponding mechanistic aspects, the schematic illustration in Figure 4.17

Conclusion

In summary, the selective benzyl alcohol oxidation to benzaldehyde as a model reaction was developed over the Pt-CeO2 supported hierarchical zeolite catalysts. The catalytic performance can be greatly enhanced by the synergic effect of Pt, CeO2, and hierarchical zeolites not only due to an improvement of the dispersion of metal but also boosting the Ce 3+ portion with respect to inactive Ce 4+ species compared to when using a conventional zeolite as solid support. Additionally, a very high yield of benzaldehyde can be reached when using the combination of 1 wt% of Pt together with 20 wt% of CeO2 modified hierarchical ZSM-5 having a low Si/Al ratio. This indicates an advantageous catalyst with lowering the noble metal content, which satisfies cost-effective and environmentally friendly concerns, eventually improving potentially practical procedures for the sustainable production of fine chemicals

Chapter 5

Electrochemical activity mapping of Pt-CeO2 gradient films prepared by bipolar electrochemistry 5.

Introduction

Many organic chemistry syntheses involve electron transfer. In a classical redox reaction, the electron transfer takes place between two chemical species. When a dangerous and polluting reducing (or oxidizing) reagent is employed, it is possible to substitute it with an electric current coming directly from electrodes. This process is known as electrosynthesis. Due to its high versatility, simplicity, ease to scale up, and low-cost process, electroorganic synthesis has attracted much attention. Moreover, this method can deliver a cleaner process because it can avoid conventional chemical reagents that need to be well managed.

[186] Aromatic aldehydes are crucial intermediates for large industries of fine chemicals.

[139] Particularly, the oxidation of benzyl alcohol to benzaldehyde is a representative and attractive process because aromatic aldehydes can be used in various systems such as industrial solvents, plastic additives, and perfumes.

[140] The method usually used to synthesize benzaldehyde suffers from low yield and generates a problem in wastewater management. [143,144] Therefore, the direct selective oxidation of liquid benzyl alcohol is considered a credible option to generate benzaldehyde efficiently under mild conditions.

Recently, many catalysts have been used for selective oxidation, especially noble metals such as Pt, Pd, and Au. [148][149][150] Although they play a key role as useful metal catalysts, they still suffer from their lack of cost-effectiveness. Various studies have established new candidates to overcome this limitation by reducing the noble metal content via mixing with other materials. This promising approach, allowing to reduce the cost of catalyst and improve the catalytic performance in a sustainable way, uses metal oxide such as CeO2,TiO2,Fe3O4,and Al2O3.[154,[187][188][189] Among them, CeO2 is one of the most attractive materials for alcohol oxidation owing to its remarkable properties, such as the redox properties between Ce 3+ and Ce 4+ species, high oxygen vacancy capacity, and poisoning tolerance of hydrocarbons on metal surfaces. [190,191]. Its use combined with noble metals can considerably improve their catalytic activity. [119] Bipolar electrochemistry (BPE) is a powerful method to generate gradients on conductive substrates. In BPE, a conducting object is placed inside an electrolyte solution, between the anode and the cathode. There is no direct contact between the conducting object and these two electrodes. [START_REF] Fosdick | Bipolar electrochemistry[END_REF][START_REF] Tisserant | Generation of metal composition gradients by means of bipolar electrodeposition[END_REF] Thanks to the electric field applied between the two electrodes, a potential drop exists along the bipolar electrode generating an oxidation reaction at one side of the conducting object and a reduction reaction on the opposite side. This object is called a bipolar electrode because it has anodic and cathodic sides. [192] The key point is that the potential varies along the bipolar electrode generating different deposition rates. The electrochemical reaction rate depends on the local polarization, a gradient of composition, thickness, morphology, and other physicochemical parameters can be easily generated. Several compositional gradient films have been reported. For example, the synthesis of a CdS gradient was performed on a gold electrode. [193] An Ag-Au alloy gradient has been deposited on a stainless steel bipolar electrode, and also a Ni-Cu alloy gradient has been prepared in one step by BPE. A gradient in size and spatial distribution of gold and silver nanoparticles were reported. [194,195] Interestingly, up to three different materials were used to fabricate the gradient film containing Cu, Ni, and Zn in a single experiment using bipolar electrodeposition. [START_REF] Tisserant | Generation of metal composition gradients by means of bipolar electrodeposition[END_REF] Scanning electrochemical microscopy (SECM) utilized a microelectrode to investigate the local electrochemical performance of surfaces. The SECM is distinctive among scanning probe techniques because it can image the electrochemical activity to analyze inhomogeneous surfaces. [START_REF] Velmurugan | Fabrication of Scanning Electrochemical Microscopy-Atomic Force Microscopy Probes to Image Surface Topography and Reactivity at the Nanoscale[END_REF][START_REF] Kai | Scanning electrochemical microscopy at the nanometer level[END_REF] This technique introduces the concept of chemical imaging, which can be obtained by using a mobile ultramicroelectrode (UME). The tip is scanned at a very close distance (a few µm) above the sample surface, and its current response is simultaneously monitored as a function of the tip position. SECM imaging is highly dependent on the tip-sample distance and the nature of the sample surface with respect to its electrochemical activity/conductivity. [START_REF] Katemann | Constant-Distance Mode Scanning Electrochemical Microscopy (SECM)-Part I: Adaptation of a Non-Optical Shear-Force-Based Positioning Mode for SECM Tips[END_REF] Hence, SECM is a powerful tool to analyze the gradient of electrocatalyst materials generated by BPE. This type of study has been done by Beugré et al.[196], more precisely, they used scanning electrochemical cell microscopy (SECCM) to study the activity of nickel (oxy)hydroxide gradient.

In this chapter, Pt-CeO2 films were prepared by electrodeposition on a glassy carbon electrode. Its electrochemical activity of benzyl alcohol oxidation to benzaldehyde was characterized by cyclic voltammetry (CV). After this first study, a

Pt-C e O 2 gradient film was made by BPE. These surfaces were characterized by Scanning electron microscopy (SEM), energy dispersive X-ray (EDS) analysis, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy (RAMAN) to elucidate the nature and chemical state of the deposited catalyst films on a glassy carbon electrode. Finally, SECM was employed to investigate the local catalytic activity of the gradient in benzyl alcohol electrooxidation using the redox competition mode of SECM. [197] Therefore, this work builds on the previous chapter to further explore the different conditions for the preparation of cerium oxide combined with platinum particles in order to study the catalytic performance.

Experimental section

Materials

All chemicals were of analytical grade and used as received. Cerium(III) nitrate hexahydrate (Ce(NO3)3, >99%, Sigma-Aldrich) and potassium hexachloroplatinate(IV) (K2PtCl6, >99.9%, Sigma-Aldrich) were used as CeO2 and Pt precursor, respectively. Potassium nitrate (KNO3, >97%, Merck) was used as an electrolyte in the electrodeposition system. The glassy carbon plates (13x13x1 mm, TW Hochtemperatur-Werkstoffe GmbH) were used as substrate. To investigate the electrocatalytic performance, potassium hydroxide (KOH, >85%, Sigma-Aldrich) was used as an electrolyte. Benzyl alcohol (BnOH, 99%, Sigma-Aldrich) and ferrocenedimethanol (>97%, Sigma-Aldrich) were used to test the performance of the films. Milli-Q water (resistivity = 18.2 MΩ cm) was used for all experiments.

Film preparation

The homogeneous film and electrochemical properties of the sample electrode were measured on an electrochemical workstation (CHI900) with a conventional three-electrode system. The glassy carbon, Pt wire, and Ag/AgCl were alcohol. Cyclic voltammetry was measured to determine the global performance of homogeneous film for electrooxidation of benzyl alcohol at a scan rate of 50 mV s -1 .

In contrast, the local electrochemical performance of gradient film was investigated by SECM.

Results and discussion

The interest in the electrodeposition of catalysts over other deposition techniques lies in a variety of reasons, such as low cost of equipment, control of deposition thickness and uniformity, and the ability to form films on substrates with a complex shape. [198] The electrolytic deposition of CeO2 is based on the local increase of pH in the cathodic region. In this work, the homogeneous layers were fabricated using a constant potential of -0.6 V for 1 min, which is the optimized condition edited from the study by F. Kitamura et al.[199], in the presence of Ce(NO3)3 1 mM, K2PtCl6

1 mM, and KNO3 0.1 M. The mechanism of the cathodic electrodeposition of CeO2 film is quite complex. It can be divided into three parts. [200][201][202] Firstly, hydroxyl ions, OH -, are generated at the cathodic pole by the reduction of O2 and H2O, as shown in the following equations.

2H2O + 2e -→ H2 + 2OH -

O2 + 2H2O + 4e -→ 4OH -

O2 + 2H2O + 2e -→ H2O2 + 2OH -

Secondly, the Ce ions react with the hydroxyl ions.

2Ce 3+ + 2OH -+ H2O2 ⇄ 2Ce(OH)2 2+ (4) 4Ce 3+ + O2(g) + 4OH -+ 2H2O ⇄ 4Ce(OH)2 2+ (5) Ce 3+ + 3OH -⇄ Ce(OH)3 (6)
Finally, Ce(OH)3 and CeO2 precipitate at the surface of the electrode.

2Ce(OH)2 2+ + 4OH -→ 2CeO2 + 4H2O (7)
Ce(OH)3 → Ce(OH)3 (precipitate) [START_REF] Takahara | Dehydration of Ethanol into Ethylene over Solid Acid Catalysts[END_REF] Cyclic voltammograms (CVs) indicate the appropriate potential to fabricate the film using Ce(NO3)3 in KNO3 0.1 M as the precursor of CeO2 as shown in Figure 5.1.

From the mechanisms (Eq. 1-8), hydroxyl molecules, OH -, play an essential role in the formation of CeO2. Thus, the potential at which the formation of CeO2 films can take place is around -0.6 V using the OH -produced by the reduction of O2 as shown in the red line.

In the case of Pt deposition, the blue line in Figure 5.1 indicates the film generated from the reduction of Pt 4+ to Pt 2+ , then Pt 2+ to Pt metallic form assigned to the cathodic reduction at -0.35 and -0.6 V, respectively. Therefore, Pt film can be fabricated from cathodic electrodeposition as indicated in the following mechanisms (Eq. 9-10).

[199]

PtCl6 2-+ 2e -→ PtCl4 2-+ 2Cl - (9)
PtCl4

2-+ 2e -→ Pt + 4Cl - (10)
In addition, to further enhance the film performance, Pt combined CeO2 film (Pt-CeO2) was investigated. The pink line in Figure 5.1 demonstrates the two Pt reduction peaks coupled with another cathodic peak at -0.9 V and the anodic peak at -0.6 V.

These last two peaks were assigned to water splitting and reoxidation of Pt sites, respectively. It is in agreement with the film formation in phosphate solution.

[203] As discussed before, CeO2 film can be formed by using OH -, which can be generated from O2 reduction at -0.6 V, which is also suitable for Pt deposition. Then, the facile electrodeposition for Pt-CeO2 electrocatalyst was performed on a glassy carbon electrode (GC) at -0.6 V for 1 min. be observed in the case of Pt (90±23 nm) and Pt-CeO2 film (54±14 nm). Interestingly, the case of the Pt-CeO2 combination provides significantly smaller particles and higher density leading to a higher electroactive surface area. species. Four peaks of Ce 3+ , including 904.0, 900.4, 885.9, and 881.8, together with six peaks of Ce 4+ at 917.0, 907. 8, 901.3, 898.6, 889.4, and 882.8, respectively, [204] can be observed in Figure 5.3(a). It implies that Pt-CeO2 film is a mixture of Ce 3+ and Ce 4+ species with a major fraction of Ce 4+ (58%). It confirms the proposed mechanism that the film can be composed of both CeO2 and Ce(OH)3.

[205] The Pt 4f spectrum fitting indicates that the Pt NPs were composed of Pt 2+ and Pt 0 species, as illustrated by the peaks at 72.8 and 71.2 eV binding energies, respectively, [206,207] suggesting a significant portion of Pt 0 states (see For the calculation, the EAS can be obtained by the following equation[210]:

EAS = QH(Pt) x 0.21 (11)
where QH is the average charge for hydrogen adsorption/desorption (mC cm -2 ), (Pt) denotes the platinum loading (mg cm -2 ) at the surface of the electrode, and 0.21 corresponds to the charge required to oxidize a monolayer of H2 on Pt.

The BnOH oxidation (see Figure 5.5) was performed in KOH solution 0.1 M following the study of Y. Yang.[211] As illustrated in Figure 5.6, the CeO2 film on GC electrode does not exhibit any obvious peak corresponding to the benzyl alcohol oxidation. This indicates that benzyl alcohol oxidation is kinetically slow at the surface of CeO2. While on the Pt film, two oxidation peaks appear. These peaks correspond to benzyl alcohol and benzaldehyde oxidation at -0.1 V and 0.2 V, respectively.

Interestingly, the peak current density for BnOH oxidation is much higher on Pt combined with CeO2 film (Pt-CeO2). This can be explained by enhancing the electrocatalytic performance correlating to oxygen vacancies in CeO2 that can facilitate the oxidation reaction in accordance with previous work. [119] The synergistic effect between Pt and CeO2 can be described as a correlated feature of these two materials. CeO2 can facilitate the regenerated active Pt 0 from Pt-hydride, formed by adsorption of H atom of benzyl alcohol, eventually producing benzaldehyde and H2O. However, when the deposition was made in two steps, a lower performance was observed. The two-step Pt-CeO2 film was prepared by the electrodeposition at -0.6 V for 1 min at each step, as shown in Figure 5.7. A deposition of CeO2 first, then followed by the electrodeposition of Pt was denoted as Pt/CeO2 while an inverse sequence was assigned to CeO2/Pt. As presented in Figure 5.8, compared to the Pt-CeO2 film prepared in one step, the performance of the film prepared in two-step is considerably lower. This behaviour can emphasize the benefit of a single step deposition which is not only easier, faster but also achieves better performance due to the synergistic effect of metal-metal oxide interaction at the interface resulting in more charge transfer and better stability.[212] prepare the films. Because the potential is a key parameter for preparing the film, it is important to test different values. That is why we decided to use bipolar electrochemistry (BPE) to prepare Pt-CeO2 gradient film and to investigate the local electrochemical properties obtained thanks to the linear variation of the electrochemical driving force alongside the bipolar electrode. [START_REF] Tisserant | Generation of metal composition gradients by means of bipolar electrodeposition[END_REF] Thanks to BPE, the electrodeposition Pt-CeO2 was made at different potentials by using only one experiment. The bipolar electrodeposition experiment was set up as shown in Figure 5.9. The potential drop across the BPE, ΔE, can be approximated using the following equation [196]:

∆𝐸 = 𝐸 𝑡𝑜𝑡 (𝑙 𝐵𝑃𝐸 𝑑 ⁄ ) ( 12
)
where Etot is the potential difference between the feeder electrodes, lBPE is the length To verify the local electrochemical performance of Pt-CeO2 gradient film, scanning electrochemical microscopy (SECM) was used in redox competition mode.

In the redox competition mode, a constant potential of -0.4 V was applied to ultramicroelectrode (UME) to reduce the oxygen. Simultaneously a potential at -0.1 V was applied on the bipolar electrode to trigger the benzyl alcohol oxidation in order to consume the oxygen within the gap between UME and the substrate, as shown in Figure 5.12 SECM imaging in the redox competition mode was scanned from the electrode border (x=0) toward the middle of the electrode (x=4000) in the x-axis direction with a scan rate 50 µm s -1 in KOH 0.1 M solution containing BnOH 50 mM.

In this particular mode, the tip and the sample compete for the same analyte. As it can be seen in Figure 5.12(b), the lower current response corresponds to the higher density of Pt combined with CeO2 film. The active area width is around 3 mm, which is in accordance with SEM and SEM-EDS profiles. The most active area was obtained around 1-2 mm from the electrode border, implying that Pt-CeO2 density at that position is highest according to the XPS result.

Conclusion

The electrochemistry is a simple method to fabricate catalyst gradients and determine the optimal composition. Additionally, the SECM characterization offers an easy way to evaluate the local catalytic performance.

Chapter 6

Bifunctional Pt/Au Janus electrocatalyst for furfural electrochemical conversion 6. A

Introduction

The conversion of renewable biomass-derived compounds into high valueadded chemicals is one of the most interesting issues due to the increasing energy consumption, the gradual depletion of petroleum resources, and the severe environmental problems. [213,214] Therefore, using renewable starting compounds instead of fossil-based resources has become a potentially promising approach.

Among various biomass-based compounds, furfural is a promising biomass-derived species which can be converted into several chemical products. [215,216] In this regard, the synthesis of valuable chemicals using lignocellulose-derived furfural has In theory, electrocatalysis is a fascinating approach for transforming biomassderived intermediates because of its advantages, namely its ability to operate under ambient conditions, its versatility, and the ease of scaling up. In this context it is interesting to note that different surface coating technologies to generate bifunctional particles have been developed extensively. One of these techniques is called bipolar electrochemistry. [START_REF] Loget | True bulk synthesis of Janus objects by bipolar electrochemistry[END_REF] The asymmetric structure of the materials obtained by this technique is generated due to the polarization of the conductive materials induced by the applied electric field.

[228] The exposed materials act in this case as bipolar electrodes. The bipolar electrode has two distinct poles on its opposite sides.

Therefore, different electrochemical reactions can be carried out at the opposite extremities of the object. This means that the reduction and oxidation reactions can be performed simultaneously at the cathodic and anodic sites of the bipolar electrode, respectively. In addition, bipolar electrochemistry can be used to synthesize a bifunctional electrocatalyst by facilitating cathodic electrodeposition using the appropriate metal precursor together with a sufficiently high potential. Consequently, two-face materials, also known as Janus particles, can be obtained using this bipolar electrodeposition.

It is well-known that Janus particles, referring to the Roman god having two faces, exhibit different properties on opposite sides. Various types of micro-and nanosized particles with anisotropic properties have been reported.[229] Janus particles have unique features because they provide asymmetric chemical and physical properties on a single particle. [START_REF] Loget | Bulk synthesis of Janus objects and asymmetric patchy particles[END_REF][START_REF] Kumsapaya | Wireless Electrografting of Molecular Layers for Janus Particle Synthesis[END_REF] We present in this study the preparation of asymmetric particles (Janus particles) composed of two electrocatalytic materials by bipolar electrochemistry. In addition, to illustrate the valuable properties of the designed materials, they have been used as asymmetric electrocatalysts to achieve the reduction of furfural at the cathodic pole and its oxidation at the anodic pole simultaneously.

Materials

All chemicals were of analytical grade and used as received without further purification. Hexachloroplatinic (IV) acid hydrate (H2PtCl6.xH2O, Sigma-Aldrich, ≥99%), and Chloroauric acid trihydrate (HAuCl4.3H2O , Sigma-Aldrich, ≥99%) were used as metal precursors for Pt and Au deposition, respectively. To synthesize Janus particles, spherical glassy carbon beads (630 -1000 µm, type 2, Alfa Aesar) were used as a support material. The carbon graphite rods were used as driving electrodes for the bipolar electrochemical experiments. Potassium hydroxide (KOH, Sigma-Aldrich, ≥85%) was used as electrolyte. To carry out the electrochemical experiments, furfural (Sigma-Aldrich, ≥99%) was used as raw material. Milli-Q water (18.2 MΩ cm) was used for all experiments. with a scan rate of 20 mV/s at room temperature and ambient pressure.

Janus particle synthesis using bipolar electrodeposition

Bipolar electrodeposition was used to synthesize Janus particles composed of different metals on both sides employing an external power supply (KEITHLEY model 2450). Based on the results obtained from the CV measurements with the classic three-electrode system, Pt and Au were selected as the most appropriate materials to elaborate the Janus particles. In a first step glassy carbon beads were positioned at the center of the bipolar cell with a distance of 30 mm between the driving electrodes in a 1 mM solution of the metal precursor. Different potentials (20, 40, 60, and 80V) were applied to optimize the deposition conditions for a fixed deposition time of 10 min. Subsequently, the prepared objects were rinsed with water and dried under N2 flow, leading to the asymmetric particles modified with Pt or Au d on the cathodic side. In the case of Pt/Au Janus particles, Pt was deposited first on one side of the bipolar electrode, and then Au deposition was performed on the other side by switching the polarity of the driving electrodes in order to change electric field direction using the corresponding precursor solution again with a deposition time of 10 min. After that, the obtained materials were rinsed with water and dried under N2 flow.

Furfural electrochemical conversion using bipolar electrochemistry

To investigate the electrochemical activity of the Janus particles during the electrochemical conversion of furfural, the prepared Pt/Au Janus particles were positioned at the center part of the bipolar cell, which is separated from the driving electrodes by Nafion membranes. The bipolar reaction was performed by applying the selected potential for 30 min in 50 mM of KOH solution containing 15 mM of furfural. Then, quantitative analysis was performed by using a calibration method employing high-performance liquid chromatography (HPLC) with a Shimadzu LC-2030C3D equipped with a sugar HPLC column (SP0810, 300×8 mm inner diameter) and using Milli-Q water as a mobile phase at 80 °C with a flow rate of 1 ml/min and a photodiode array (PDA) detection at 211, 245, and 276 nm for furfuryl alcohol, furoic acid, and furfural, respectively. First, the absorption peak areas of the products were integrated using Lab Solution software. Then, calibration curves (see Figure 6.2) obtained from integrated peak areas were used to calculate the electrocatalytic performance. Subsequently, the conversion of furfural (XFAL) and the product selectivity (Si) were estimated by the following equations:

𝑋 𝐹𝐴𝐿 = (𝑛 𝐹𝐴𝐿 ) 0 -(𝑛 𝐹𝐴𝐿 ) 𝑡 (𝑛 𝐹𝐴𝐿 ) 0 × 100%
Where (nFAL)0, (nFAL)t, ni, Σn are the initial number of moles of furfural, the number of moles of furfural at a certain time, the number of moles of the desired product i, and the total number of moles of all the products, respectively. The conservation of mass in the system was analyzed for all experiments, and the mass balance is 94.22 ± 4.23%.

Additionally, scanning electron microscopy (SEM) images were obtained with a JEOL JSM-7610F microscope to study the morphology of the catalysts. The elemental analysis was carried out using SEM equipped with Energy Dispersive X-ray spectrometry (SEM-EDS).

Results and discussion

The electrocatalytic performance of different types of metals with respect to the reduction and oxidation of furfural was first investigated. Cyclic voltammetry (CV) was

() i i t n S n  =    
used to determine the oxidation and the reduction potential of furfural to obtain the electrochemical window, which can be used for bipolar electrocatalysis. For example, as shown in Figure 6.3(A, C), the Au electrode allows furfural reduction starting at -1.3 V, while the Pt electrode doesn't give a significant signal at the same potential. A lower current density was observed for the Pt electrode when adding furfural to the solution, which might be due to molecules adsorbing at the electrode surface. To further investigate the catalytic performance of several metals, other electrodes, including Ni and Cu, were also studied, as shown in Figure 6. 3(E,G). An electroactivity similar to Pt can be observed with the Ni electrode. However, for the Cu electrode, the furfural reduction starts at -1.4 V. Additionally, a characteristic peak of Cu oxidation coupled with two obvious peaks of the Cu oxide reduction at -0.8 and -1.2 V are observed. [230] From these observations, the most suitable candidate for furfural reduction is the Au electrode.

In parallel, furfural oxidation was also studied with different electrodes, as shown in Figure 6.3(B,D,F,H). Interestingly, all electrodes can promote to a certain extent furfural oxidation. Several anodic peaks are observed for the Au electrode assigned to the oxidation furfural in the potential domain between -0.2 and 0.4 V in agreement with previous studies of E.M. For the Pt electrode (Figure 6.3(D)), a characteristic broad peak related to furfural oxidation can be observed around 0.3 V. The other metals were also tested to examine their features (Figure 6.3(F,H)). For the Ni electrode, the current density of the classic nickel oxide peak is increasing in the presence of furfural accompanied by a slight shift of the peak position. [231] In the case of the Cu electrode, furfural oxidation can be performed from 0.2 V. Therefore, it can be concluded that the most suitable electrodes for furfural oxidation are in the following order: Pt > Cu > Au > Ni. As a global result it is therefore reasonable to use Pt for furfural oxidation and Au for its reduction. For further investigation, the Pt/Au Janus particles were generated using bipolar electrodeposition. In order to optimize the synthesis conditions, the impact of the potential difference between the driving electrodes was investigated. As can be seen in Figure 6.4, the most appropriate potential to deposit metal on one side of the carbon bead is 60 V with a deposition time of 10 min for both Pt and Au. It should be noted that potentials higher than 60 V are not suitable in both cases. For Pt deposition such high potentials can lead to bubble generation covering the cathodic extremity, and thus blocking Pt deposition. In contrast, for Au the deposit covers more than half of the bipolar electrode. The Pt/Au Janus particles were synthesized via bipolar electrochemistry. The procedure is illustrated in Figure 6.5. Initially, the optimized potential (60 V) was applied to the bipolar cell in order to polarize the carbon beads, which were used as a support material. To deposit a metal on the support material, the electrochemical reduction of the metal source proceeds at the cathodic pole. Pt was first deposited on one side of the support material. Subsequently, the electric field was switched to the opposite direction for the Au deposition on the other side, eventually producing the Pt/Au Janus particles. Additionally, the Pt and Au deposition sequence can be changed because both elements are known to be noble metals, implying a high stability when switching the electric field direction during the Janus particle synthesis. As mentioned above, the Pt/Au Janus particles were generated by Pt deposition at 60 V for 10 min on one side of the carbon beads followed by Au deposition on the other side using 60 V for 10 min after switching the electric field direction. Then, the successfully prepared Janus particles were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) together with the EDS line scan profiles, as shown in Figure 6.6. Each metal is deposited on one half sphere of the carbon beads without any overlap. It should be noted that the missing EDS signal at the bottom part of the SEM-EDS images originates from the angle of orientation of the EDS detector, which cannot collect the signal hidden by the carbon bead. Thus, the entire elemental map is obtained by superposing SEM-EDS images of the two individual measurements carried out at two different angles. Additionally, the successfully deposited metals were verified each part by rotating the bead towards the detector and obtaining the EDS images. In order for the electrocatalytic reactions to occur on the materials designed by using bipolar electrochemistry, the appropriate potential must be applied to polarize the bipolar object. The associated polarization voltage (E) is proportional to the potential window (∆V) between the electrochemical reduction and oxidation reactions of furfural as well as the distance between the driving electrodes (d) related to the length of the bipolar electrode (le). E is calculated by the following equation: [START_REF] Fosdick | Bipolar electrochemistry[END_REF] 𝑬 = ∆𝑽 𝒍 𝒆 × 𝒅

The calculated potential for the bipolar electrosynthesis was 48 V. This is due to the potential window between the electrochemical oxidation of furfural on the Pt side (0.3 V) and the electrochemical reduction on the Au side (-1.3 V) coupled with the configuration of the bipolar electrochemical cell with a distance of 30 mm between the driving electrodes and the size of the beads (le = ~1 mm). The control experiment was performed at 48 V for 30 min with furfural but without bipolar electrodes. This experiment is used as a reference in order to take into account the effect of furfural loss during the experiment (~6% loss). In contrast, the bipolar electrosynthesis reaction was carried out with a total of 24 Pt/Au Janus particles acting as bipolar electrodes at 48 V for 30 min. Interestingly, an equivalent amount of both furfuryl alcohol and furoic acid can be generated at the Pt/Au Janus particles. As can be seen in Figure 6.8(A), the selectivity for furfuryl alcohol and furoic acid is 47.8 and 52.2%, respectively, leading to a corresponding yield of 9.5 and 10.3%.

In order to analyze the total performance of the Janus Au/Pt particles in the frame of the electrosynthesis reactions, the electrocatalytic feature of each metal has been tested separately. The information on the catalytic activity is summarized in Figure 6.8(A). Furoic acid is, as expected, the main product when using Pt Janus particles, whereas the furfuryl alcohol is mostly formed with the Au Janus particle.

These results again confirm the preferential oxidation and reduction on Pt and Au, respectively. In strong contrast to this, the Pt/Au Janus particles can generate both furoic acid and furfuryl alcohol simultaneously due to the preferential reactions that occur on each metal. Although only a moderate overall conversion of furfural (19.8%) was observed, this value can be easily enhanced by various factors, in particular the number of catalyst beads (see Figure 6.8(B)). To further increase the yield of both products, the number of Janus particles was increased up to 96. It was found that the efficiency of furfural conversion increases linearly with the number of Pt/Au particles.

These results highlight that bipolar electrochemistry can be easily controlled and is a very valuable approach in the frame of electrocatalytic processes.

Conclusion

The simultaneous electrochemical conversion of furfural via both oxidation and reduction was studied as a model reaction using bipolar electrochemistry. Herein, Pt/Au Janus particles have been successfully generated using bipolar electrodeposition in order to provide the most suitable combination for furfural oxidation and reduction. Conversion of furfural into furfuryl alcohol and furoic acid can be achieved simultaneously by using Pt/Au Janus particle as bifunctional electrocatalysts. This work opens up very interesting perspectives for bipolar electrochemistry as a concept to perfectly control catalytic activity. Based on the reported proof-of-concept experiments and the obtained results, a further development for large-scale production can be envisioned, thus allowing real practical applications in the future.

Chapter 7

Conclusion and thesis perspectives

A

The studies performed in this thesis, were focusing on the following aspects: (i) ceria modified hierarchical zeolites for selective upgrading of ethanol dehydration to ethylene; (ii) the synergistic effect obtained by the combination of noble metal, metal oxide, and hierarchical zeolites for the selective oxidation of benzyl alcohol; (iii) the investigation of gradient films of ceria and platinum, obtained by bipolar electrochemistry, for benzyl alcohol electrooxidation using scanning electrochemical microscopy (SECM); and (iv) the design of bifunctional electrocatalysts using bipolar electrochemistry for biomass-derived compound upgrading.

In the first part, the development of a catalyst for a sustainable process to produce crucial compounds has been described. As an example, bioethanol was selectively converted to ethylene, a useful precursor for bioplastic industries. This production process derived from bio-based materials has the advantage of considering environmental and sustainable aspects. Among various catalysts, ceria (CeO2) is one of the most promising ones owing to its abundance and its potential properties to improve catalysis efficiency. However, the bulk ceria structure is inefficient due to a low surface area, and therefore to solve this problem, we decided to disperse ceria on a solid support. Herein, we demonstrated that the use of hierarchical zeolite as solid support overcomes the drawback of conventional zeolite with respect to diffusion limitations and the accessibility of active sites. Therefore, it can be concluded that the key factors to enhance the catalytic activity are related to the accessibility of active sites and the support material properties. This context revealed that the simple finetuning of different factors, such as the CeO2 insertion method, the CeO2 quantity, and type of support material improves the catalytic performance. The CeO2 modified hierarchical zeolite catalyst prepared by an ion-exchange method provides the best performance with a 99% yield for ethylene production. This performance is much lower for a conventional catalyst. These findings reveal the advantages of catalyst design to accelerate the desired reaction processes. Furthermore, due to the properties of CeO2, this CeO2 modified catalyst can facilitate the mobility of lattice oxygen, beneficial for oxygen-related reactions. Moreover, it should be noted that the hierarchical structure of zeolite can act as a support material due to its easily optimizable properties and a high surface area. Our findings open up perspectives of using these materials for other valuable reactions involving oxygen-dependent processes.

Regarding the second research axis, CeO2 based hierarchical zeolite catalysts have been developed for other oxygen-related reactions. As observed in the ethanol dehydration reaction, CeO2 modified hierarchical zeolite has demonstrated the benefits of its properties, such as redox property, and oxygen mobility. The performance was further improved by combining it with other active sites such as noble metals. Platinum (Pt) was selected to be incorporated into CeO2 and the modified hierarchical zeolite in order to enhance its catalytic performance based on a synergy effect. In this study, the selective oxidation of benzyl alcohol to benzaldehyde, which is significant for organic synthesis in academics and industry, was systematically analyzed as a model reaction for alcohol upgrading. The combination of the hydrogen adsorption capacity of Pt coupled with the oxygen mobility facilitated by CeO2 was tested for the alcohol oxidation reaction. The performance of Pt-CeO2 modified hierarchical zeolite with respect to the selective oxidation of benzyl alcohol with high benzaldehyde yield (~100%) again emphasizes the key role of rational catalyst design.

Compared to a conventional zeolite support, the hierarchical structure reveals important benefits for the catalytic performance, among others due to the high accessibility of the active sites. Furthermore, concerning cost-effectiveness, the welldispersed Pt on CeO2 modified hierarchical zeolite provides high catalytic efficiency with only a small amount of Pt. Moreover, CeO2-based materials can significantly enhance oxygen-related reactions due to their ability to facilitate oxygen mobility.

Therefore, they can be applied for a wide range of reactions involving oxygen species especially biomass-derived compound upgrading.

In addition to the design of heterogeneous catalysts, the research scope was extended to electrocatalytic aspects. As we illustrated that a significant improvement can be observed for the Pt-CeO2 modified hierarchical zeolite catalyst, we wanted to confirm the synergistic effect between Pt and CeO2 also by using electrochemistry. An It reveals that bipolar electrochemistry is a powerful approach to generate a gradient that helps to rapidly find the material composition with the best electrocatalytic performance.

Finally, bipolar electrochemistry was applied to the elaboration of a bifunctional electrocatalyst in the last part of the thesis. Due to the asymmetric properties of the bipolar electrode, the electrodeposition of different materials can be achieved on two opposite sides. We have shown that bipolar electrochemistry allows to synthesize Janus particles that can be used as a bifunctional electrocatalyst accelerating simultaneously reduction and oxidation reactions. In this case, electroconversion of furfural was selected as a model reaction for the upgrading of biomass-descended compounds. The transformation leads to furfuryl alcohol and furoic acid via reduction and oxidation reactions, respectively. According to the investigation, Au and Pt are suitable for the reduction and oxidation of furfural, respectively. Therefore, Pt/Au Janus particles, obtained by bipolar electrodeposition deliver, allow the simultaneous electrosynthesis of the two corresponding products, furfuryl alcohol and furoic acid, at opposite sides of the particles. This unique feature of bipolar electrochemistry paves the way for an efficient alternative procedure to generate bifunctional catalysts and perform two crucial reactions in parallel. For the moment, two noble metals have been chosen as catalyst layers, which might impact the cost-effectiveness. Moreover, in this bipolar system, only two-dimensional arrangement can be performed at the bottom part of the bipolar cell due to the cell configuration and particle size. Thus, non-noble metals and three-dimensional arrangement with improved Janus particle size should be further studied to enhance the activity of bipolar system for practical applications.

In summary, this thesis was devoted to the development of various strategies for heterogeneous catalysis and electrocatalysis for the conversion of biomassderived compounds. The designed materials emphasize the benefits of hierarchical zeolite structures and the synergic effects of combined materials that significantly improve the performance. Additionally, the advantages of bipolar electrochemistry allow a facile generation of gradient films and Janus electrocatalysts. Therefore, the overall results open promising perspectives for the development of environmentally friendly and sustainable processes for the valorization of biomass-derived compounds.

une activité électrochimique asymétrique. C'est l'une des techniques électrochimiques les plus puissantes pour la conception de catalyseurs asymétriques.

Afin de surmonter l'inconvénient principal de la structure microporeuse de la zéolithe conventionnelle, qui est la limitation de la diffusion, une structure poreuse bien algae. These compounds are considered as environmentally friendly substrates compared to natural gas and crude oil. Based on the abundance of biomass and its potential properties, many products could be synthesized. These products derived from biomass could be used in various fields, such as energy, cosmetics, perfumes, detergents, and plastics. Therefore, the advanced design of materials and processes for converting biomass-derived compounds to high value-added chemicals is a significant challenge from both an academic and industrial point of view.

In this dissertation, a novel design of heterogeneous catalysts and electrocatalysts is proposed, based on abundant metal oxides such as cerium oxide commonly called ceria (CeO2), which have been widely used in catalysis because of their unique properties such as the redox property and the oxygen-storage capacity.

Firstly, modified hierarchical heterogeneous zeolite catalysts have been successfully

prepared via two methods, the pre-synthesis, and post-synthesis modification. In addition, the benefits of the hierarchical structure of zeolites improve their catalytic performances for alcohol upgrading applications. In addition, an electrochemical study was also conducted to assist in the development of biomass valorization processes.

Especially, bipolar electrochemistry, which has been extensively studied due to its original features of being a wireless electrochemical technique to generate asymmetric reactivity, is a powerful concept for asymmetric catalyst design.

For the design of hierarchical zeolite catalysts, a well-organized porous structure of zeolites has been designed to overcome its original drawback, due to the microporous structure of conventional zeolite, inducing diffusion limitations. The advantages of hierarchical structures also offer a higher amount of exposed active sites, which can enhance the catalytic efficiency. In this instance, the synergic effect between hierarchical zeolite support and ceria (CeO2) plays an important role in ethanol dehydration to ethylene, a key material for plastic production. Indeed, the catalytic dehydration of ethanol to ethylene has been considered as an environmentally friendly process, which can be achieved at a lower reaction temperature with respect to the traditional ethylene production via thermal cracking of petroleum gas or naphtha. Using the ion-exchange technique, CeO2 modified hierarchical zeolite can provide better catalytic performance (~99% of ethylene yield) compared to the one prepared by the impregnation method. The reasons for this improved catalytic performance relate to the chemical state of Ce, the metal-support interaction, and Ce reducibility. Numerous parameters can be easily modified to enhance the catalytic activity, such as the type of support material, CeO2 loading methods, CeO2 content, and the Si to Al ratio of the zeolite support, eventually boosting dehydration of ethanol to ethylene.

To illustrate the beneficial aspect of the designed catalysts, the selective oxidation of other bio-alcohols such as benzyl alcohol to benzaldehyde was studied because it is one of the promising pathways to generate valuable chemicals. Owing to cost-effectiveness and environmental concerns, molecular oxygen and CeO2 were selected as an oxidant and an oxygen carrier for this reaction, respectively. Moreover, CeO2 has other advantageous properties, it can be used both as an active site and as a support material for other active species. Therefore, the concept of combining noble metals, CeO2, and hierarchical zeolite as an active site, promoter, and support material, respectively, was adapted in order to enhance the catalytic activity for selective benzyl alcohol oxidation. The effect of CeO2, which can assist the lattice mobility of oxygen and play an important role in the catalytic performance, was systematically investigated. The synergetic effect between Pt and CeO2 can considerably improve the catalytic performances. Consequently, the benzaldehyde yield reaches almost 100 % for Pt supported on CeO2-hierarchical zeolite, whereas it is less than 40 % when using the conventional catalyst. These observations clearly confirm that the hierarchical structure of zeolites as support material underlines the advantages of a higher amount of accessible active sites. Thus, these discoveries illustrate the benefits of rationally designed catalysts, including a structural design coupled with selective active materials to develop their efficiency for alcohol upgrading applications.

Apart from heterogeneous catalysis, and in order to extend the scope of catalyst design, the synthesis of electrocatalysts was also investigated. An interesting technique introduced in this part is bipolar electrochemistry, which can be briefly described as an electrochemical approach performed without a direct connection between the bipolar electrode and the feeder electrodes. It can offer various advantages, such as true bulk processes due to the simultaneous modification of many electrodes and the versatility in terms of shape, size, and materials composition.

Due to the wireless nature of bipolar electrochemistry, a potential gradient drops across the bipolar electrode which has been used to generate gradient films. In this contribution, a Pt-CeO2 gradient film was elaborated based on this approach. The obtained gradient film exhibits different local performances with respect to benzyl alcohol electrooxidation, evidenced by an advanced imaging procedure based on scanning electrochemical microscopy (SECM). SECM is an imaging technique using the measurement of an electrochemical current flowing between a mobile probe (an ultramicroelectrode) and the surface being analyzed. This method allows to rapidly identify the part of the Pt-CeO2 surface having the best electrocatalytic activity.

Bipolar electrochemistry was also employed to synthesize Janus particles in order to use them as bifunctional electrocatalysts for the simultaneous oxidation and reduction of one and the same molecule. The bipolar electrode can perform two distinct reactions at its opposite extremity and this feature allows designing a bifunctional electrocatalyst surface having two different components on each side, which can simultaneously accelerate the individual reduction and oxidation reactions.

To illustrate the beneficial aspect of the above-mentioned approach, electrochemical conversion of furfural was selected as a model reaction for biomass upgrading to study the performance of this bifunctional Janus particles. According to the obtained results, gold (Au) and platinum (Pt) demonstrate a preferable electrocatalytic activity for the reduction and the oxidation of furfural, respectively. These two elements were applications. Journal of the American Chemical Society.

1

 1

  illustration of the pore size effect on the diffusion of large (red) and small (black) molecules. b) Effects of pore diameter on molecular diffusivity (D) and of the energy of activation (Ea) on diffusion.

  Figure Page 1.11 a) Scheme of the principle of bipolar electrochemistry and b) Scheme indicating the driving force variation along the bipolar electrode.

17

 17

  Figure PageSilicalite1-HIE, and (B) conventional zeolite supports:(a) ZSM5-CON and (b) 5Ce(Exc)-ZSM5-CON. 3.4 (A) XRD results and (B) Normalized Ce L3 edge XANES spectra of (a) 5Ce(Exc)-ZSM5-HIE, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Imp)-Silicalite1-HIE and (d) 5Ce(Exc)-ZSM5-CON. 3.5 TEM images and nanosheet thickness distribution of (A-C) Silicalite1-HIE and (D-F) ZSM5-HIE. 3.6 SEM images and zeolite particle size distribution of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE. 3.7 SEM images of (A,B) 5Ce(Exc)-ZSM5-CON, (C,D) 5Ce(Exc)-ZSM5-HIE, (E,F) 5Ce(Imp)-ZSM5-HIE and (G,H) 5Ce(Imp)-Silicalite1-HIE employing a secondary electron detector (SE mode, left) and a low-angle backscattered electron detector (LABE mode, right), respectively. 3.8 TEM images and CeOx particle size distribution of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE. (C) 5Ce(Imp)-ZSM5-HIE, and (D) 5Ce(Imp)-Silicalite1-HIE. 3.9 STEM-EDS images of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE. 3.10 SEM-EDS elemental points analysis of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE. 3.11 N2 adsorption/desorption isotherms of (a) 5Ce(Exc)-ZSM5-CON, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Exc)-ZSM5-HIE, and (d) 5Ce(Imp)-Silicalite1-HIE.

  Figure Page 4.7 TEM-EDS images of (A-D) 1Pt/20CeO2-Silicalite1-HIE;

  H2-Temperature programmed reduction (H2-TPR) profiles of (a) 1Pt/20CeO2-Silicalite1-CON and (b) 1Pt/20CeO2-Silicalite1-HIE, and (B) H2-TPR profiles of (a) 1Pt/20CeO2-ZSM5-HIE and (b) 1Pt/different support catalysts: (a) 1Pt/20CeO2-ZSM5-HIE, (b) 1Pt/20CeO2-Silicalite1-HIE, (c) 1Pt/CeO2 and (d) 1Pt/20CeO2-Silicalite1-CON (100% selectivity towards benzaldehyde).

  Figure Page 5.5 Schematic illustration of benzyl alcohol electrooxidation to benzaldehyde.

  analysis from XPS of the Pt-CeO2 gradient film at different positions starting from the edge of the electrode and (b) Surface-enhanced Raman scattering (SERS) spectra of Pt-CeO2 gradient film at different positions.

  Figure Page 5.12 Schematic illustration of SECM measurement of Pt-CeO2 film fabricated by using Ce(NO3)3 1 mM, K2PtCl6 1 mM and KNO3 0.1 M at applied potential 1.93 V cm -2

  Figure Page 6.4 SEM-EDS images of (A-D) Pt bipolar electrodeposition at different potentials: (A) 20 V, (B) 40 V, (C) 60 V, (D) 70 V for 10 min, and (E-H) Au electrodeposition at different potentials: (E) 20 V, (F) 40 V, (G) 60 V and (H) 80 V for 10 min.

  the electrodeposition process to synthesize the Pt/Au Janus particles in two steps including: (i) Pt deposition on a carbon bead and (ii) Au deposition on the opposite side by switching electric field Electrocatalytic performance of different Janus particles in KOH 50 mM with 15 mM of furfural using the bipolar cell with an applied potential of 48 V for 30 min. Red and black bars represent furoic acid and furfuryl alcohol selectivity, respectively, while the circle refers 24 bifunctional Pt/Au Janus particles in KOH 50 mM with 15 mM of furfural in a bipolar cell at an applied potential of 48 V for 30 min for 3 cycles. Red and black bars represent furoic acid and furfuryl alcohol selectivity, respectively, while the circle symbol refers to furfural conversion.

Figure 1 . 1

 11 Figure 1.1 Primary energy utilization by fuels (toe = tonnes of oil equivalent).

Figure 1 .

 1 Figure 1.2 a) Schematic illustration of the pore size effect on the diffusion of large (red) and small (black) molecules. b) Effects of pore diameter on molecular diffusivity (D) and of the energy of activation (Ea) on diffusion. Taken from

Figure 1 . 3

 13 Figure 1.3 Schematic illustration of accessibility and transport/diffusion limitations in conventional and hierarchical zeolites. Taken from ref.[START_REF] Ennaert | Potential and challenges of zeolite chemistry in the catalytic conversion of biomass[END_REF]

Figure 1 . 4

 14 Figure 1.4 Zeolite formation around carbon particles as hard templates. Taken fromref.[START_REF] Li | Realizing the Commercial Potential of Hierarchical Zeolites: New Opportunities in Catalytic Cracking[END_REF]

Figure 1 . 5

 15 Figure 1.5 Summary of desilication procedures used for different Si/Al ratios. Taken from ref.[START_REF] Möller | Mesoporositya new dimension for zeolites[END_REF]

Figure 1 .

 1 6 displays examples of noble metals employed in catalysis with their bond-cracking capabilities.

Figure 1 . 6

 16 Figure1.[START_REF] Nguyen | Conversion of ethanol in aqueous solution over ZSM-5 zeolites: study of the reaction network[END_REF] The noble metals employed in catalysis can be rated by their bond-cracking capabilities. Taken from ref.[START_REF] Freyschlag | Precious metal magic: catalytic wizardry[END_REF]

Figure 1 . 7

 17 Figure 1.7 Optimized structures of a) ZnO and b) ZrO2 clusters. Taken from ref.[START_REF] Miyazawa | Fundamental roles of ZnO and ZrO 2 in the conversion of ethanol to 1, 3butadiene over ZnO-ZrO 2/SiO 2[END_REF]

Figure 1 . 8 )Figure 1 . 8

 1818 Figure 1.8 Relationship of reaction activity as a function of the heat of adsorption ofthe reactant and product on various noble metals. Taken from ref.[START_REF] Roduner | Understanding catalysis[END_REF]

Figure 1 .

 1 Figure 1.9 a) The asymmetric oxygen vacancy sites of M-□(-Ce)3 in doped ceria. b)

Figure 1 . 10

 110 Figure 1.10 Differences in terms of experimental set-up between a a) conventional and b) bipolar electrochemical cell. The red dotted line symbolizes an idealelectric field produced between the feeder electrodes. Taken from ref.[START_REF] Shida | Bipolar electrochemistry: A powerful tool for electrifying functional material synthesis[END_REF]

Figure 1 .

 1 Figure 1.11 a) Scheme of the principle of bipolar electrochemistry and b) Scheme

Figure 1 . 12

 112 Figure 1.12 Schematic illustration of a bipolar setup showing the different applications of bipolar electrochemistry such as electrografting, electrodeposition,

Figure 1 . 13

 113 Figure 1.13 Schematic illustration of SECM operation modes: (a) Steady-state diffusion in bulk solution, (b) Negative feedback mode, (c) Positive feedback mode, (d) Tip generation/substrate collection mode, (e)Substrate generation/tip collection mode and (f) Redox competition mode. Taken from ref.[START_REF] Preet | A review: Scanning electrochemical microscopy (secm) for visualizing the real-time local catalytic activity[END_REF]

Figure 1 .

 1 Figure 1.14 a) Scheme of the SECM measurement setup, b) Pt UME tip current densities obtained from the SECM scan attributed to the three products of CO2 reduction reaction: (a) HCOO -, (b) COad, (c) H2. Taken from ref.[100]

Figure 3 . 1

 31 Figure 3.1 Schematic illustration of conventional ZSM-5 preparation.

Figure 3 . 2

 32 Figure 3.2 Schematic illustration of fine-tuned CeO2 preparation using different support materials including conventional ZSM-5 (ZSM5-CON), hierarchical ZSM-5 (ZSM5-HIE), and hierarchical silicalite-1 (Silicalite1-HIE); I, II, III, and IV denoted as Ce(Imp)-Silicalite1, Ce(Imp)-ZSM5-HIE, Ce(Exc)-ZSM5-HIE, and Ce(Exc)-ZSM5-CON, respectively.

Figure 3 . 3

 33 Figure 3.3 XRD results of (A) hierarchical zeolite supports: (a) ZSM5-HIE, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Exc)-ZSM5-HIE, (d) Silicalite1-HIE, and (e) 5Ce(Imp)-Silicalite1-HIE, and (B) conventional zeolite supports: (a) ZSM5-CON and (b) 5Ce(Exc)-ZSM5-CON.

Figure 3 . 4 Figure 3 . 5

 3435 Figure 3.4 (A) XRD results and (B) Normalized Ce L3 edge XANES spectra of (a) 5Ce(Exc)-ZSM5-HIE, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Imp)-Silicalite1-HIE and (d) 5Ce(Exc)-ZSM5-CON.

Figure 3 . 6

 36 Figure 3.6 SEM images and zeolite particle size distribution of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE.

Figure 3 . 7

 37 Figure 3.7 SEM images of (A,B) 5Ce(Exc)-ZSM5-CON, (C,D) 5Ce(Exc)-ZSM5-HIE, (E,F) 5Ce(Imp)-ZSM5-HIE and (G,H) 5Ce(Imp)-Silicalite1-HIE employing a secondary electron detector (SE mode, left) and a low-angle backscattered electron detector (LABE mode, right), respectively.

Figure 3 . 8

 38 Figure 3.8 TEM images and CeOx particle size distribution of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE. (C) 5Ce(Imp)-ZSM5-HIE, and (D) 5Ce(Imp)-Silicalite1-HIE.

2 .

 2 The elemental mappings and the variation of the Ce to Si ratio again indicate a superior distribution of Ce modified hierarchical ZSM-5 obtained by the Ce-ion-exchange process.

Figure 3 . 9

 39 Figure 3.9 STEM-EDS images of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE.

Figure 3 .

 3 Figure 3.10 SEM-EDS elemental points analysis of (A) 5Ce(Exc)-ZSM5-CON, (B) 5Ce(Exc)-ZSM5-HIE, (C) 5Ce(Imp)-ZSM5-HIE and (D) 5Ce(Imp)-Silicalite1-HIE.

Figure 3 .

 3 Figure 3.11 N2 adsorption/desorption isotherms of (a) 5Ce(Exc)-ZSM5-CON, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Exc)-ZSM5-HIE, and (d) 5Ce(Imp)-Silicalite1-HIE.

Figure 3 . 12

 312 Figure 3.12 Chemisorption profiles of (A) NH3 TPD and (B) CO2 TPD for (a) 5Ce(Exc)-ZSM5-HIE, (b) 5Ce(Imp)-ZSM5-HIE, (c) 5Ce(Imp)-Silicalite1-HIE, (d) 5Ce(Exc)-ZSM5-CON, and (e) commercial CeO2 nanoparticles.

Figure 3 . 13

 313 Figure 3.13 Chemisorption profile of NH3 TPD for ZSM5-HIE.

Figure 3 . 14 Table 3 . 6

 31436 Figure 3.14 Chemisorption profiles of H2 TPR for (a) 5Ce(Exc)-ZSM5-HIE), (b) 5Ce(Imp)-ZSM5-HIE and (c) commercial CeO2 nanoparticles.

Figure 3 . 15 Figure 3 . 16

 315316 Figure 3.15 Catalytic activity in terms of ethylene yield for different CeO2 loadings on ZSM5-HIE prepared by ion-exchange process: Reaction condition at 350 o C after 12h of reaction time.

Figure 3 . 17

 317 Figure 3.17 Catalytic activity including ethanol conversion and product selectivity over various catalysts: (A) 5Ce(Exc)-ZSM5-HIE, (B) 5Ce(Imp)-ZSM5-HIE. (C) 5Ce(Imp)-Silicalite1-HIE and (D) 5Ce(Exc)-ZSM5-CON.

Figure 3 . 18

 318 Figure 3.18 Catalytic activity including ethanol conversion and product selectivity over hierarchical zeolites: (A) Catalytic activity of (a) Silicalite1-HIE and (b) ZSM5-HIE and (B) Product distribution over ZSM5-HIE.

Figure 3 . 19

 319 Figure 3.19 Catalytic activity including ethanol conversion and product selectivity of commercial CeO2 nanoparticles: (A) Catalytic activity, and (B) Product distribution.

Figure 3 . 20

 320 Figure 3.20 Catalytic activity including ethanol conversion and product selectivity: (A) Catalytic performance of (a) 5Ce(Imp)-ZSM5-CON, (b) 5Ce(Imp)-SiO2 and (c) 5Ce(Imp)-Al2O3 and product distribution of (B) 5Ce(Imp)-ZSM5-CON, (C) 5Ce(Imp)-SiO2 and (D) 5Ce(Imp)-Al2O3.

  summary, to develop the catalytic performance for dehydration of ethanol, the Ce properties, including acidity and chemical state, can be simply modified by employing hierarchical zeolite possessing the aluminum sites in the framework and fine-tuning the Ce insertion by means of an ion-exchange technique. All following parameters, including the acidity, Ce reducibility, and metal-support interaction, can strongly influence the dehydration of ethanol to ethylene. This study explores a new vision to develop ceria-modified hierarchical zeolite catalysts for practical applications of ethanol dehydration, which has not yet been stated before.

Figure 4 . 1

 41 Figure 4.1 Schematic illustration of impregnation method.

X

  -ray powder diffraction (XRD) was used to obtain the structures of the crystalline phase of nanoceria-platinum modified hierarchical silicalite-1 (Silicalite1-HIE) with different amounts of metal to confirm the effect of metal contents on the physicochemical features of the catalyst. For Silicalite1-HIE, XRD patterns of the controlled 1 %wt of Pt contents with varying amounts of CeO2 are shown in Figure 4.2A. In comparison, various quantities of Pt with a constant 20 %wt of CeO2 can be seen in Figure 4.2B. As expected, the characteristic peaks for CeO2 at 2θ of 28, 33, 48, and 56 degrees and Pt at 40 degrees [123] were observed as the number of loading increases for both cases. On the other hand, the silicalite-1 framework crystallinity related to the MFI network topology of zeolite support considerably diminishes as the CeO2 loading increases (see Figure 4.2A). All prepared catalysts are used later for further catalytic testing to fine-tune the optimized ratio between Pt and CeO2 contents.

Figure 4 . 2 1 (

 421 Figure 4.2 A) XRD patterns of Pt/CeO2 on hierarchical zeolites with different CeO2 contents: (a) Silicalite1-HIE; (b) 1Pt/5CeO2-Silicalite1-HIE; (c) 1Pt/10CeO2-Silicalite1-HIE; (d) 1Pt/20CeO2-Silicalite1-HIE; (e) 1Pt/30CeO2-Silicalite1-HIE and B) XRD patterns of Pt/CeO2 on hierarchical zeolites with different Pt contents: (a) 0.5Pt/20CeO2-Silicalite1-HIE; (b) 1Pt/20CeO2-Silicalite1-HIE; (c) 2Pt/20CeO2-Silicalite1-HIE.

Figure 4 . 3

 43 Figure 4.3 Structural information of prepared catalysts from XRD results of different nanoceria-platinum modified supports including (a) 1Pt/20CeO2-Silicalite1-CON, (b) 1Pt/20CeO2-Silicalite1-HIE, (c) 1Pt/20CeO2-ZSM5-HIE, and (d) 1Pt/CeO2.

Figure 4 . 4

 44 Figure 4.4 SEM images of (A) 1Pt/20CeO2-Silicalite1-HIE; (B) 1Pt/20CeO2-Silicalite1-CON; (C) 1Pt/20CeO2-ZSM5-HIE; (D) 1Pt/CeO2.

Figure 4 . 5

 45 Figure 4.5 Particle size distribution obtained from SEM images of (A) 1Pt/20CeO2-Silicalite1-HIE; (B) 1Pt/20CeO2-Silicalite1-CON; (C) 1Pt/20CeO2-ZSM5-HIE; (D) 1Pt/CeO2.

Figure 4 . 6

 46 Figure 4.6 TEM images and the particle size distribution of (A-C) 1Pt/20CeO2-Silicalite1-HIE; (D-F) 1Pt/20CeO2-Silicalite1-CON.

Figure 4 . 7

 47 Figure 4.7 TEM-EDS images of (A-D) 1Pt/20CeO2-Silicalite1-HIE; (E-H) 1Pt/20CeO2-Silicalite1-CON.

Figure 4 . 8

 48 Figure 4.8 N2 adsorption/desorption isotherms of (a) 1Pt/20CeO2-ZSM5-HIE; (b) 1Pt/20CeO2-Silicalite1-HIE; (c) 1Pt/20CeO2-Silicalite1-CON; (d) 1Pt/CeO2.

  has been suggested to perform H2 chemisorption at a lower temperature to prevent hydrogen spillover.

a

  Si/Al determined by wavelength dispersive x-ray fluorescence; b Pt dispersion and average particle size were determined by H2-pulse method.Temperature-programmed reduction with hydrogen (H2-TPR) profiles was used to consider the redox properties of active sites. It indicates that both 1Pt/20CeO2-Silicalite1-CON and 1Pt/20CeO2-Silicalite1-HIE in Figure4.9A have three main peaks at 200-350, 340-550, and 540-800 °C attributed to the reduction of PtOx, the surfaceactive oxygen adjacent to the Pt-CeO2 interface and the bulk ceria, respectively.[177]

Figure 4 . 9

 49 Figure 4.9 (A) H2-Temperature programmed reduction (H2-TPR) profiles of (a) 1Pt/20CeO2-Silicalite1-CON and (b) 1Pt/20CeO2-Silicalite1-HIE, and (B) H2-TPR profiles of (a) 1Pt/20CeO2-ZSM5-HIE and (b) 1Pt/CeO2.

Figure 4 . 10

 410 Figure 4.10 Schematic illustration of benzyl alcohol oxidation to benzaldehyde.

Figure 4 . 11

 411 Figure 4.11 Catalytic activity for the selective benzyl alcohol oxidation to benzaldehyde (selectivity=100%) at 24 h of reaction time using a batch reactor at 80 o C over (A) 1 wt% of Pt supported on Silicalite1-HIE combined with different CeO2 contents and (B) 20 wt% of CeO2 supported on Silicalite1-HIE combined with different Pt contents.

Figure 4 . 12 Figure 4 . 13

 412413 Figure 4.12 Catalytic performance of different support catalysts: (a) 1Pt/20CeO2-ZSM5-HIE, (b) 1Pt/20CeO2-Silicalite1-HIE, (c) 1Pt/CeO2 and (d) 1Pt/20CeO2-Silicalite1-CON (100% selectivity towards benzaldehyde).

Figure 4 .

 4 14 demonstrates the spectra of Ce L3 edge XANES measurements of Pt combined with CeO2 on different supports and two reference standards, which are Ce(NO3)3.6H2O and CeO2 representing Ce 3+ and Ce 4+references, respectively. The absorption into the 5d level with the 4f occupancy in the initial state is assigned to peak I, and it reasonably implies Ce 3+ existence in the sample. The occupancy of the 4f level in the final state, and the absorption into the 5d level with no occupancy in the 4f level in either the initial or final state are related to the double peaks (peak II and III, respectively). Therefore, these peaks are expected when Ce 4+ appears.[180]

Figure 4 .

 4 Figure 4.14 Normalized Ce L3 edge XANES spectra of different prepared catalysts: (a) 1Pt/20CeO2-ZSM5-HIE, (b) 1Pt/20CeO2-Silicalite1-HIE, (c) 1Pt/20CeO2-Silicalite1-CON, (d) 1Pt/CeO2 and Ce 3+ (yellow) and Ce 4+ (pink) standard references.

Figure 4 .

 4 Figure 4.16 by arranging an arctan function to imitate the edge jump and fit three Gaussian functions (I, II, III).[182] The quantitative summary of the Ce oxidation state from XANES was analyzed in Table 4.3.

Figure 4 . 15

 415 Figure 4.15 Schematic illustration of the proposed structures of the prepared catalysts.

Figure 4 . 16

 416 Figure 4.16 Fitting curves of XANES spectra of the Ce L3 edge for 1Pt/20CeO2-ZSM5-HIE.

  shows the proposed reaction mechanism of alcohol oxidation over Pt/CeO2 supported on hierarchical catalysts, including the subsequent three major steps: (i) a transfer of an electron from the reduced Ce 3+ to O2, then generating Ce 4+ and surface-active oxygen species (O 2-)[184]; (ii) the formation of a Pt-hydride by H atom adsorption from benzyl alcohol, which joins O 2-to create H2O and an O vacancy; (iii) an O vacancy comprising electron transfers to Ce 4+ , regaining fresh active sites of Pt 0 and Ce 3+ for the next catalytic cycle. [185] Hence, this behavior can be defined as an electron bridge to facilitate the relocation of electrons from reductants to oxidants in the catalytic oxidation system.

Figure 4 . 17

 417 Figure 4.17 Schematic illustration of catalytic reaction mechanism of alcohol oxidation on Pt/CeO2 supported on hierarchical zeolite surfaces.

Figure 5 . 1

 51 Figure 5.1 CV at a glassy carbon electrode in KNO3 0.1 M solution (black line) containing 1 mM of CeO2 precursor (red line), 1 mM of Pt precursor (blue line), and both of them (pink line) with the scan rate of 50 mV s -1 .

Figure 5 . 2 Figure 5 . 3 .

 5253 Figure 5.2 SEM images of the homogeneous (a) CeO2 film, (b) Pt film and (c) Pt-CeO2 film fabricated on GC electrode at -0.6 V for 1 min.

Figure 5 .

 5 3(b)). Moreover, the elemental analysis was determined as a function of the etching time. As shown inFigure 5.3(c), the amount of Pt and Ce elements decreases as the etching time increases. This allows to roughly estimate the thickness of Pt-CeO2 film. A thickness of about 78 nm was determined depended on the etching rates based on a silica substrate. Additionally, the existence of Pt and Ce can be proved by Raman spectra( Figure 5.3(d)). The characteristic peaks of CeO2 and PtOx are observed at 453 and 593 cm-1 , respectively.[208, 209] These results can again verify the existence of Pt and CeO2 over the successfully prepared Pt-CeO2 homogeneous film.

Figure 5 . 3 XFigure 5

 535 Figure 5.3 X-ray photoelectron spectra fitting of Pt-CeO2 homogeneous film for (a) Ce 3d and (b) Pt 4f binding energy regions at 0 s, (c) Elemental analysis along the different etching time and (d) Raman spectra of Pt-CeO2 homogeneous film.

Figure 5 . 4

 54 Figure 5.4 Cyclic voltammogram of the prepared electrode in H2SO4 0.5 M at scan rate 20 mV s -1 .

Figure 5 . 5

 55 Figure 5.5 Schematic illustration of benzyl alcohol electrooxidation to benzaldehyde.

Figure 5 . 6

 56 Figure 5.6 Benzyl alcohol electrooxidation at the homogeneous films: CeO2 (black line), Pt (red line) and Pt-CeO2 (blue line), in KOH 0.1 M solution containing benzyl alcohol 0.2 M under room temperature at v = 50 mV s -1 .

Figure 5 . 7

 57 Figure 5.7 Schematic illustration of a two-step deposition on a glassy carbon electrode at -0.6 V for 1 min in each step to prepare two layers of Pt and CeO2 film: (i) CeO2/Pt for Pt deposition first, then coated with CeO2 film and (ii) Pt/CeO2 for CeO2 deposition first, then coated with Pt film.

Figure 5 . 8

 58 Figure 5.8 Benzyl alcohol electrooxidation at the homogeneous films: Pt-CeO2 (blue line), Pt/CeO2 (green line) and CeO2/Pt (pink line), in KOH 0.1 M solution containing benzyl alcohol 0.2 M under room temperature with the potential scan rate = 50 mV s -1 .

  of the bipolar electrode, and d is the distance between the feeder electrodes. In this work, Etot = 10 V, lBPE = 13 mm, and d = 55 mm resulting in a potential drop of ca. 2.5 V across the BPE. The potential variation is high enough in this condition to allow the hydroxyl ion formation at the cathodic pole of the BPE (δ -). Due to the electric field across the electrolytic solution, different potential distributions generated different hydroxyl ion concentrations, which is the key factor for the CeO2 formation.

Figure 5 . 9

 59 Figure 5.9 Schematic illustration of bipolar electrodeposition experiment.

Figure 5 .

 5 10(b-d) shows the higher magnification of different areas of the Pt-CeO2 gradient film. It indicates that the aggregated nanoparticles, diameter around 200 nm, can be observed on the area (b) and (d) while tiny and uniform size (~50 nm) is obtained over the area (c), which is located at 1-2 mm from the electrode edge. Moreover, it can be seen that the deposited film width is around 3 mm from the edge of the electrode. SEM-EDS line scan profiles further verify that the Pt-CeO2 gradient film is successfully fabricated on a glassy carbon electrode using bipolar electrodeposition.

Figure 5 .

 5 Figure 5.10 (a) SEM image and SEM-EDS line scan profiles of the Pt-CeO2 film fabricated by using Ce(NO3)3 1 mM, K2PtCl6 1 mM and KNO3 0.1 M at applied potential 1.93 V cm -2 for 1 min and (b-d) a higher magnification of each area of film.

Figure 5 .

 5 Figure 5.11 (a) Elemental analysis from XPS of the Pt-CeO2 gradient film at different positions starting from the edge of the electrode and (b) Surface-enhanced Raman scattering (SERS) spectra of Pt-CeO2 gradient film at different positions.

Figure 5 . 12

 512 Figure 5.12 Schematic illustration of SECM measurement of Pt-CeO2 film fabricated by using Ce(NO3)3 1 mM, K2PtCl6 1 mM and KNO3 0.1 M at applied potential 1.93 V cm -2 for 1 min from the edge (x=0) toward the middle of the electrode (x=4000) using applied potential -0.4 V at the UME and -0.1 V at the substrate with scan rate 50 µm/s in a solution containing BnOH 50 mM and KOH 0.1 M

Figure 5 . 13

 513 Figure 5.13 Schematic illustration of SECM measurement of the Pt-CeO2 film fabricated by using Ce(NO3)3 1 mM, K2PtCl6 1 mM and KNO3 0.1 M at applied potential 1.93 V cm -2 for 1 min from the edge (x=0) toward the middle of the electrode (x=3000) using apply a potential of 0.5 V at the UME and 0 V at the substrate with scan rate 50 µm s -1 in solution containing ferrocenedimethanol 1 mM and KNO3 0.1 M, and (c) Surface profiles of Pt-CeO2 gradient film determined by optical profilometer.

  simultaneous cathodic electrodeposition of Pt and CeO2 in a homogeneous film on glassy carbon electrodes was successfully performed. The electrooxidation of benzyl alcohol was realized to evaluate the electrocatalytic performance of the Pt-CeO2 film. The homogeneous Pt-CeO2 film demonstrates a better performance for the electrooxidation of benzyl alcohol than the films containing either CeO2 or Pt. It also delivers better activity than the film prepared by successive electrodeposition of both compounds. This proved the existence of a synergy between two materials, indicating that the combination of the two materials can enhance the film activity in the one-step preparation of the Pt-CeO2 film. We also successfully prepared a gradient of Pt-CeO2 by bipolar electrochemistry. The different morphology and density due to the potential distribution along the bipolar electrode impact the film properties, leading to different local electrochemical performance. The SECM in redox competition mode allowed us to characterize the local electrochemical performance by mapping the benzyl alcohol electrooxidation of the Pt-CeO2 gradient film. Thus, this work demonstrates that bipolar

Figure 6 . 1

 61 Figure 6.1 Schematic illustration of furfural conversion to furfuryl alcohol and furoic acid via reduction and oxidation reaction, respectively.

  All experiments were performed with a potentiostat (AUTOLAB) and a conventional three-electrode system. A Pt wire and Ag/AgCl were used as the counter, and reference electrodes, respectively. Prior to all the experiments, the working electrodes were cleaned by ultrasonication in isopropanol and Milli-Q water for 15 min each time and then dried under N2 flow. Four commercial electrodes were tested, including Pt, Au, Ni, and Cu electrodes. All the electrochemical performance tests for furfural electrochemical conversion were carried out at room temperature (25 °C) using 50 mM KOH solution in the absence or presence of 15 mM furfural. Cyclic voltammetry was used to examine the electrocatalytic performance of each electrode

Figure 6 . 2

 62 Figure 6.2 Calibration curves based on the integrated peak area obtained from HPLC measurement for (A) Furfural, (B) Furfuryl alcohol, and (C) Furoic acid.

Figure 6 . 3

 63 Figure 6.3 Cyclic voltammograms of (A,C,E,G) furfural electroreduction and (B,D,F,H) furfural electrooxidation at a (A-B) Au electrode, (C-D) Pt electrode, (E-F) Ni electrode and (G-H) Cu electrode, respectively, in KOH 50 mM in the absence and the presence of 15 mM furfural using a scan rate of 20 mV/s.

Figure 6 . 4

 64 Figure 6.4 SEM-EDS images of (A-D) Pt bipolar electrodeposition at different potentials: (A) 20 V, (B) 40 V, (C) 60 V, (D) 70 V for 10 min, and (E-H) Au electrodeposition at different potentials: (E) 20 V, (F) 40 V, (G) 60 V and (H) 80 V for 10 min.

Figure 6 . 5

 65 Figure 6.5 Schematic illustration of the electrodeposition process to synthesize the Pt/Au Janus particles in two steps including: (i) Pt deposition on a carbon bead and (ii) Au deposition on the opposite side by switching electric field direction.

Figure 6 . 6

 66 Figure 6.6 (A) SEM-EDS images and (B) SEM-EDS line scan profiles of a Pt/Au Janus particle synthesized by bipolar electrodeposition at 60 V for 10 min each side.

Figure 6 . 7

 67 Figure 6.7 Schematic illustration of a bipolar cell coupling the two opposite furfural conversion mechanisms on a Pt/Au Janus particle.

Figure 6 . 8

 68 Figure 6.8 (A) Electrocatalytic performance of different Janus particles in KOH 50 mM with 15 mM of furfural using the bipolar cell with an applied potential of 48 V for 30 min. Red and black bars represent furoic acid and furfuryl alcohol selectivity, respectively, while the circle refers to the total furfural conversion.

  interesting technique, namely bipolar electrochemistry, was used in this context. The principle of bipolar electrochemistry is based on a wireless configuration. There is no direct electrical contact between the bipolar electrode and driving electrodes in the electrochemical system. This generates a potential distribution along the bipolar electrode, which leads to the formation of a gradient film. The Pt-CeO2 gradient film was directly formed using bipolar electrodeposition due to the potential drop across the bipolar electrode. Moreover, a fascinating imaging technique, SECM, was used to further identify the local electrocatalytic performance. This technique allows to study the local electrocatalytic performance of the electrocatalyst based on the interaction between a mobile ultramicroelectrode and the electrode surface at different positions.Therefore, the SECM technique was chosen to investigate the performance of the Pt-CeO2 gradient film in the frame of benzyl alcohol oxidation. The SECM imaging reveals that the local activity of the gradient film depends on the Pt-CeO2 composition on the surface. It offers the advantages of a facile and rapid characterization to study the electrochemical performance of non-homogeneous electrocatalysts such as multicomponent electrocatalyst and multi-array electrocatalysts. Additionally, the composition of the gradient film can be easily adjusted using bipolar electrochemistry.

  organisée des catalyseurs zéolithiques hiérarchiques a été conçue. Un des avantages des structures hiérarchiques est la présence de sites actifs plus exposés, ce qui peut améliorer leur efficacité catalytique. Dans ce cas, l'effet synergique entre le support en zéolite hiérarchique et l'oxyde de cérium (CeO2) joue un rôle important dans la déshydratation de l'éthanol en éthylène, un produit chimique à haute valeur ajoutée et un matériau clé pour les industries de production de plastique. En effet, la déshydratation catalytique de l'éthanol en éthylène, par cette méthode, est considérée comme un procédé respectueux de l'environnement, qui peut être réalisé à une température de réaction plus basse que la production traditionnelle d'éthylène par craquage thermique du gaz de pétrole ou du naphta. En utilisant la technique d'échange d'ions, la zéolithe hiérarchique modifiée par CeO2 peut fournir de meilleures performances catalytiques (~99% du rendement en éthylène) par rapport à celle préparée par la méthode d'imprégnation. Les raisons principales de cette amélioration des performances catalytiques sont liées à l'état chimique du Ce, à l'interaction métalsupport et à la réductibilité du Ce. De nombreux paramètres peuvent être facilement modifiés pour améliorer l'activité catalytique, tels que le type de matériaux de support, les méthodes de chargement en CeO2, la teneur en CeO2 et le rapport Si/Al du support zéolitique, ce qui permet de stimuler la déshydratation de l'éthanol en éthylène.Pour illustrer les bénéfices apportés par les catalyseurs préparés, l'oxydation sélective d'autres bioalcools en produits chimiques, tel que l'alcool benzylique en benzaldéhyde a été étudié. Il s'agit de l'une des voies prometteuses pour générer d'autres produits chimiques de haute valeur ajoutée. En raison de la rentabilité et des préoccupations environnementales, l'oxygène moléculaire et le CeO2 ont respectivement été choisis comme oxydant et transporteur d'oxygène pour cette réaction. De plus, le CeO2 possède d'autres propriétés avantageuses, il peut être utilisé à la fois comme site actif et comme matériau de support pour d'autres espèces actives. Par conséquent, la combinaison entre le métal noble, le CeO2 et la zéolite hiérarchique, respectivement comme site actif, promoteur et matériau de support, a été réalisée afin d'améliorer l'activité catalytique pour l'oxydation sélective de l'alcool benzylique. L'effet du CeO2, qui peut favoriser la mobilité de l'oxygène dans le réseau et jouer un rôle important dans la performance catalytique, a été systématiquement étudié. L'effet synergique entre le Pt et le CeO2 peut considérablement améliorer les performances catalytiques. Par conséquent, les rendements en benzaldéhyde ont atteint presque 100 % pour le Pt supporté sur la zéolite hiérarchique contenant du CeO2, alors qu'ils étaient inférieurs à 40 % en utilisant le catalyseur conventionnel. Ces observations confirment clairement que l'utilisation de la structure hiérarchique des zéolites comme matériau de support offre l'avantage d'une plus grande accessibilité du site actif. Ainsi, ces découvertes illustrent les avantages des catalyseurs synthétisés, y compris la conception structurelle couplée à des matériaux ayant une activité sélective pour améliorer leur efficacité dans les procédés de valorisation de l'alcool. Outre la catalyse hétérogène, la fabrication d'électrocatalyseurs a également été étudiée afin d'élargir les voies de synthèse des catalyseurs. Une technique intéressante présentée dans ce manuscrit est l'électrochimie bipolaire, qui peut être décrite brièvement comme une méthode électrochimique réalisée sans connexion directe entre les objets conducteurs placés dans la solution électrolytique et les électrodes d'alimentation reliées au générateur. Elle offre divers avantages, par exemple, la possibilité de modifier de nombreuses électrodes simultanément et une polyvalence en termes de formes, tailles et modifications de matériaux. En raison du champ électrique entre les deux électrodes sources un gradient de potentiel existe dans la solution et donc le long de l'électrode bipolaire. Cela permet de former des gradients de matériaux à la surface de l'électrode bipolaire. Ainsi un gradient de Pt-CeO2 a été synthétisé à l'aide de cette méthode. Ce film présente donc des performances, concernant l'électrooxydation de l'alcool benzylique, qui vont varier le long du gradient. Ces performances sont caractérisées par la microscopie électrochimique à balayage (SECM). La SECM est une technique d'imagerie basée sur la mesure d'un courant électrochimique circulant entre une sonde mobile (une ultramicroélectrode) et la surface qui est analysée. Cette méthode permet de repérer rapidement sur le gradient de Pt-CeO2 quelle partie présente la meilleure activité électrocatalytique. L'électrochimie bipolaire a également été utilisée pour elaborer des particules Janus afin de les utiliser comme électrocatalyseur bifonctionnel pour l'oxydation et la réduction simultanées d'une molécule. En effet, l'électrochimie bipolaire peut polariser un matériau conducteur afin d'y réaliser deux réactions distinctes à chacune de ses extrémités. Cette caractéristique permet de concevoir un électrocatalyseur bifonctionnel possédant deux matériaux de part et d'autre de l'électrode bipolaire. Ces composants, de nature différente peuvent contribuer simultanément à la réduction et à l'oxydation d'une espèce chimique. Pour illustrer l'approche susmentionnée, la conversion électrochimique du furfural a été choisie comme réaction modèle. Une première étude a montré que l'or (Au) et le platine (Pt) possèdent une activité électrocatalytique préférentielle par rapport à la réduction et l'oxydation du furfural. L'électrochimie bipolaire a permis dans un premier temps de les déposer à chaque extrémité de l'électrode bipolaire. Ensuite, ces particules Janus Pt/Au ont été utilisées comme électrocatalyseur bifonctionnel pour la conversion électrochimique du furfural afin de produire simultanément de l'alcool furfurylique et de l'acide furoïque. La réalisation de cet électrocatalyseur bifonctionnel Pt/Au permet également de mettre en avant les avantages de l'électrochimie bipolaire. C'est une méthode de préparation simple d'un électrocatalyseur bifonctionnel et c'est une approche qui permet de réaliser la conversion électrochimique de composé issu de la biomasse. Par conséquent, sur la base de tous ces résultats, nous espérons que cette thèse apportera de nouvelles connaissances pour le développement de catalyseurs et d'électrocatalyseurs ainsi que des procédures de synthèse dans le cadre du développement de la chimie verte afin de produire des produits chimiques à haute valeur ajoutée à partir de la biomasse renouvelable. Mots clés: Composés dérivés de la biomasse, Amélioration de l'alcool, Oxyde de cérium (CeO2), zéolithes hiérarchiques, Électrochimie bipolaire, Particules Janus, Électrocatalyseur bifonctionnel Direct Upgrading of Biomass-derived Compounds to Fine Chemicals Summary MARISA KETKAEW The development of sustainable chemical production processes using renewable feedstocks is one of the most crucial research fields in Chemical Engineering, Modern Chemistry, and Sustainable Science. Because of the petroleum shortage and environmental concerns, the direct upgrading of biomass-derived compounds has gradually attracted more attention. Basically, biomass-based compounds have been generally assigned as renewable organic materials derived from various sources ranging from plants, agricultural waste, and sewage sludge to

Table 3 . 2

 32 Elemental points analysis data

	Point		Ce/Si ratio
		5Ce(Exc)-	5Ce(Exc)-	5Ce(Imp)-	5Ce(Imp)-
		ZSM5-HIE	ZSM5-CON	Silicalite1-HIE	ZSM5-HIE
	1	1.24	7.18	8.59	6.57
	2	1.39	10.39	8.65	8.56
	3	1.05	22.70	8.16	5.99
	4	1.67	7.45	8.46	7.74
	5	1.11	13.58	4.77	5.90
	6	0.78	16.02	7.93	5.76
	7	0.89	14.69	9.76	6.48
	8	1.80	10.87	9.02	8.91
	9	0.78	15.20	7.12	8.86
	10	1.45	24.56	9.05	7.83
	Average	1.22 ±0.36	14.26 ±5.82	8.15 ±1.39	7.26 ±1.26

Table 3 . 3

 33 Textural properties of all the prepared catalysts

	Catalysts	Si/Al a SBET b	Sext c	Smicro d
		(m 2 g -1 )	(m 2 g -1 )	(m 2

g -1 ) Vtotal e (cm 3 g -1 ) Vmicro f (cm 3 g -1 ) Vext g (cm 3 g -1 )

	5Ce(Exc)-	60.7	464	206	258	0.956	0.147	0.809
	ZSM5-HIE
	5Ce(Exc)-	97.6	383	5	378	0.191	0.177	0.014
	ZSM5-CON
	5Ce(Imp)-	58.4	356	139	217	0.604	0.104	0.500
	ZSM5-HIE
	5Ce(Imp)-	∞	475	196	279	0.877	0.112	0.765
	Silicalite1-
	HIE

a Si/Al determined by wavelength dispersive x-ray fluorescence.

Table 3 . 4

 34 Acid density of all the prepared catalysts obtained from NH3-TPD

	measurement.
	Catalysts	Acidity amount (µmol g -1 )	Total acid density
		Weak	Strong	(µmol g -1 )
		(180-200 o C)	(350-400 o C)
	ZSM5-HIE	79	34	113
	5Ce(Imp)-ZSM5-HIE	73	39	112
	5Ce(Imp)-Silicalite1-HIE	24	4	28
	5Ce(Exc)-ZSM5-HIE	95	57	152
	5Ce(Exc)-ZSM5-CON	71	21	92
	CeO2	23	12	45

Table 3 . 5

 35 Basic density of all the prepared catalysts obtained from CO2-TPD

	measurement.
	Catalysts	Basicity amount (µmol g -1 )	Total basic
		Weak	Moderate	Strong	density
		(150-	(450-500 o C)	(600-700 o C)	(µmol g -1 )
		200 o C)
	5Ce(Imp)-ZSM5-HIE	37	101	247	385
	5Ce(Imp)-Silicalite1-HIE	8	95	171	273
	5Ce(Exc)-ZSM5-HIE	35	146	169	350
	5Ce(Exc)-ZSM5-CON	33	60	77	170
	CeO2	21	19	2	42

  still limited by the high costs. To overcome this drawback, many groups have developed catalysts by decreasing the number of noble metals and diluting them with other materials. For example, the bimetallic hybridization between Au and CuO as core-shell nanoparticles was proposed byEvangelisti et al. [151] to improve the catalytic performance for alcohol oxidation due to a synergistic effect between Au and CuO nanostructures. Additionally,Chen et al. [152] explored the cooperative behavior of a bimetallic Au-Pd catalyst. They discovered that the different TiO2[141, 153, 154] is another hopeful technique to cut the production cost and sustainably enhances the catalytic performance. Among them, one of the most attractive materials for the oxidation of alcohols is CeO2 with incorporated noble metals. Their notable features include the redox properties of the Ce species, high amount of oxygen vacancies, and hydrocarbon poisoning resistance on metal surfaces.[155, 156] These features can considerably boost the catalytic activity compared to pure metals. Additionally, it has been noted that CeO2 crystallites can be transformed by doping with silica or alumina, eventually resulting in shifting the oxidation state of ceria.[157] As strategies mentioned above to develop efficient catalysts, several other solid

	micropore structure in the zeolite framework causes intracrystalline-diffusion
	limitations, resulting in low active site utilization. To date, several studies on
	hierarchical zeolites containing at least two types of cavity systems, for example
	micropores combined with a meso-or/and macroporous network, [168, 169] have
	reported that this can enhance the accessibility and molecular transport of guest
	molecules into the porous structure. [34]

production.

[144]

Numerous materials have been developed for the highly selective oxidation of alcohol, especially Pt, Pd, Au, and Cu, as key metal catalysts. [145-150] However, practical utilization is nature of Au-Pd interactions supported on ceria-zirconia, which is strongly influencing the catalytic activity, can be fine-tuned by applying different synthesis methods.

Moreover, adding low-cost metal oxide materials, in particular, SiO2, CeO2, ZrO2, and supports, such as silica, [158] montmorillonite, [159] molecular sieves, [160], and medicinal stone

[161]

, have been employed to stabilize metals in order to boost their catalytic performance for numerous essential processes. A large variety of catalysts for selective benzyl alcohol oxidation have been reported so far. Besides the accessibility of the reactants to the active sites, surface features, for example, the acid/base properties of the support surface can impact the catalytic performance for alcohol oxidation.

[162][163][164]

The surface properties of the support have been reported to enhance the active site dispersion, eventually stimulating alcohol activation.

[165, 166]

Therefore, significant progress in catalyst development can be achieved by using the tunability of solid support properties. In this context, zeolites, which are aluminosilicate compounds, are well-known as solid support used for metal oxides due to their distinctive properties, for instance, a high metal ion-exchange capability, high surface area, and high thermal/hydrothermal stability. [167] Nevertheless, the

Table 4 . 1

 41 Textural properties.

	Catalyst	SBET a	Sext b	Smicro c	Vtotal d	Vmicro e	Vext f
		(m 2 g -1 )	(m 2 g -1 )	(m 2 g -1 )	(cm 3 g -1 )	(cm 3 g -1 )	(cm 3 g -1 )
	1Pt/20CeO2-	404.86 225.48 179.38	0.80	0.003	0.80
	ZSM5-HIE
	1Pt/20CeO2-	375.69 164.35 211.34	0.66	0.03	0.63
	Silicalite1-HIE
	1Pt/20CeO2-	331.45	13.98	317.47	0.19	0.15	0.04
	Silicalite1-CON
	1Pt/CeO2	38.58	6.03	32.55	0.17	0.16	0.02

a SBET: Specific surface area (m 2 g -1 ) determined by BET method; b Sext: External

Table 4 . 2

 42 Metal dispersion properties.

	Catalyst	Si/Al ratio a	Pt dispersion b	Particle size b
			(%)	(nm)
	1Pt/20CeO2-	110.2	37.89	2.99
	ZSM5-HIE
	1Pt/20CeO2-	∞	29.57	3.83
	Silicalite1-HIE
	1Pt/20CeO2-	∞	17.65	6.41
	Silicalite1-CON
	1Pt/CeO2	-	64.93	1.74

Table 4 . 3

 43 Quantitative analysis of Ce oxidation obtained from XANES for fresh and used catalysts[182, 183].

	Catalysts	I I	I II	I III	%Ce 3+
	1Pt/20CeO2-ZSM5-HIE-Fresh	5.79	5.353	3.044	65.5
	1Pt/20CeO2-ZSM5-HIE-Used	7.904	4.132	3.197	71.2
	1Pt/20CeO2-Silicalite1-HIE-	5.166	6.156	3.175	61.9
	Fresh
	1Pt/20CeO2-Silicalite1-HIE-	5.451	5.66	3.309	62.2
	Used
	1Pt/20CeO2-Silicalite1-CON-	0.69	5.853	7.714	8.2
	Fresh
	1Pt/20CeO2-Silicalite1-CON-	0.225	4.132	4.458	4.8
	Used
	1Pt/CeO2-Fresh	1.642	5.651	9.683	14.5
	1Pt/CeO2-Used	1.426	1.898	5.815	19.7

* Fittings of the Ce L3 edge XANES spectra of the synthesized samples and the estimation of Ce 3+ concentration in the sample is calculated as follows:

was supported by Campus France and the Embassy

precursors. The electrodeposition was performed by chronoamperometry at -0.6 V for 1 min. Finally, the obtained film was rinsed with Milli-Q water and then gently dried under air flow. Moreover, the gradient was fabricated by bipolar electrodeposition, and the electric field was applied with a high-power supply from Heinzinger (PNC 600-1000) in a homemade cell. The GC plate was used as a bipolar electrode. It was located between the feeder electrodes, which were separated by 55 mm, in a solution of Pt and CeO2 precursor (see Figure 5.9). Two glassy carbon plates were used as feeder electrodes. Teflon membranes were used to separate the anodic and the cathodic compartment from the bipolar electrode. A potential of 10.6 V was applied for 1 min in order to fabricate Pt-CeO2 gradient films. Then, it was followed by washing with Milli-Q water several times and gently drying under air flow.

Electrochemical System and Instrumentation

All the electrochemical performance tests for benzyl alcohol electrooxidation were carried out at room temperature conditions (25 °C) using KOH 0.1 M solution with the presence of 0.2 M benzyl alcohol. SECM experiments were performed with the CHI920C (CH Instruments Inc., the USA). Scanning electron microscopy (SEM) images were acquired with Hitachi Tabletop Microscope TM-1000.

High-resolution SEM images were recorded with a TESCAN VEGA3 SBH instrument.

Optical profilometry was performed with the KLA-Tencor Alpha-step profilometer. The glassy carbon electrode (d = 3 mm), Pt wire, and Ag/AgCl (NaCl 3 M) were used as working, counter, and reference electrodes, respectively. Prior to the electrodeposition, the glassy carbon electrodes were polished with alumina (0.05 µm) and subsequently cleaned by ultrasonication for 15 min in ethanol and Milli-Q water and then dried under air flow. For the SECM experiments, a homemade cell was used to analyze the GC plate. The tip was a homemade Pt disk UME with a diameter of 25 µm and an RG ≈ 7. RG is the ratio between the radius of the insulating sheath (rg) and the radius of the conductive disk (a) (i.e., RG = rg/a). Scanning electron microscopy (SEM) images were acquired with a Hitachi Tabletop Microscope TM-1000. Highresolution SEM images were recorded with a TESCAN VEGA3 SBH instrument.

Performance tests for the electrooxidation of benzyl alcohol were carried out at room temperature (25 °C) using a 0.1 M KOH solution with the presence of 0.2 M benzyl the furfural hydrogenation takes place over heterogeneous catalysts under heating and in the presence of H2. [220] On the other hand, electrocatalytic reduction can use the hydrogen adsorbed at the surface of the electrode (from H + or H2O) to reduce furfural. [221,222] Hence, the electrochemical reaction process has some advantages as it can be carried out under mild reaction conditions, at room temperature and under atmospheric pressure without requiring additional H2. [223] In addition, the oxidation of furfural to furoic acid and its derivatives, commonly utilized as pharmaceuticals, fungicides, and preservative precursors, has also been investigated. [213] Besides that, furoic acid is considered as one of the essential compounds to produce 2,5-furan-dicarboxylic acid (FDCA), a promising renewable monomer for plastic manufacturing. Indeed, electrocatalytic oxidation of furfural offers several advantages, such as low operating temperatures and pressures, easily controllable electric potential, and a low cost oxygen source because H2O can serve as the O-source instead of O2 gas or other oxidants. [214,224] In a conventional electrochemical process, at least two reactions occur in the system to ensure current flow. In other words, cathode and anode always provide reduction and oxidation reactions, respectively, when using a three-electrode system.

Regarding this point, an interesting idea is to simultaneously use the electrochemical reduction and oxidation of furfural to synthesize the molecules of interest.

Electrocatalysts have been widely used to achieve this goal. [225][226][227] Typically, the electrochemical conversion of furfural has been observed simultaneously with H2 or O2 evolution. For example, Y. Sun et al. reported the design of nickel-based electrocatalysts for furfural oxidation coupled with H2 evolution at the anode and the cathode, respectively.[225] Additionally, in the case of the electrochemical reduction of furfural, it can take advantage of O2 evolution at the other electrode as reported by S. Basu and co-workers.[226] Interestingly, the electrochemical conversion of furfural at both anode and cathode was recently developed by T. Noel et al.[227] They synthesized Cu3P and Ni2P on the surface of carbon fiber cloth (CFC) (Cu3P/CFC and Ni2P/CFC), using a vapor-phase hydrothermal method. The prepared Ni2P/CFC and Cu3P/CFC can be used as anode and cathode, respectively, for the simultaneous reduction and oxidation of furfural. However, to the best of our knowledge, the Additional experiments were performed to verify whether the Pt/Au Janus particles were reusable. The experiments were carried out using 24 Pt/Au Janus particles. After each catalytic cycle, the Pt/Au Janus particles were recovered from the reaction mixture without any regeneration process. As shown in Figure 6.9, the Pt/Au Janus particles can be used several times with a fairly constant furfural conversion.

Therefore, it is reasonable to believe that the designed Pt/Au Janus particles can be used as a bifunctional electrocatalyst for electrochemical conversion of furfural for several electrocatalytic cycles. Although a mixture of furfuryl alcohol and furoic acid was obtained after the electrocatalytic reaction, these two compounds can be easily separated due to their difference in boiling point. It is therefore not necessary to use other purification techniques. In addition, for practical applications, the process design can also be optimized. For example, the electrosynthesis might be integrated into a flow reactor in order to release each compound into separated chambers. Regarding this, the procedure should possess a liquid extraction or salting-out process, which selectively separates each product. Consequently, we will obtain the corresponding products from furfural electrochemical conversion in the separated container. De plus, une étude électrochimique a également été réalisée pour aider au développement de processus de valorisation de la biomasse. En particulier, l'électrochimie bipolaire, a été largement étudiée en raison de ses caractéristiques particulières, telles que la possibilité de faire de l'électrochimie sans fil et de générer combined on the particles by bipolar electrodeposition. Then, the successfully prepared Pt/Au Janus particles were used as a bifunctional electrocatalyst for electrochemical furfural conversion to produce simultaneously furfuryl alcohol and furoic acid. The performance of such bifunctional Pt/Au Janus electrocatalysts highlights the advantages of bipolar electrochemistry as a straightforward approach to efficiently perform two essential electrochemical reactions simultaneously in the context of biomass conversion.

Hence, based on all these findings, we expect that this dissertation will offer novel knowledge for the development of catalysts and electrocatalysts based on concepts which can help the sustainable production of chemicals from renewable