Over the past 15 years, ruthenium-catalyzed olefin metathesis has emerged as a cornerstone synthetic methodology in academia. Applications in fine-chemicals and pharmaceutical manufacturing, however, are just beginning to come on stream. Industrial uptake has been impeded by economic constraints associated with catalyst costs. These are due both to direct costs (exacerbated by intellectual property issues), and to further pressure exerted by the low turnover numbers attainable, and the need for extensive purification to remove ruthenium residues. From another perspective, however, these difficulties can be seen as arising from our rudimentary understanding of the fundamental organometallic chemistry of the Ru=CHR bond. In particular, we know little about the nature and reaction pathways of the Ru-methylidene unit present in the active species that propagates metathesis, and in the catalyst resting state. We know slightly more about the ruthenacyclobutane species, but still too little to guide us as to their non-metathetical reaction pathways, their contribution to deactivation relative to the methylidene species, and potential work-arounds. This thesis work was aimed at improving our understanding of the reactivity, speciation, and decomposition of key ruthenium intermediates in olefin metathesis. A major focus was the behaviour and deactivation of species formed from the second-generation Grubbs catalyst RuCl2(H2IMes)(PCy3)(=CHPh) (S-GII), which dominates ring-closing metathesis. Also studied were derivatives of the corresponding IMes catalyst A-GIIm, containing an unsaturated Nheterocyclic carbene (NHC) ligand. The methylidene complexes RuCl2(NHC)(PCy3)(=CH2) (GIIm) represent the resting state of the catalyst during ring-closing and cross-metathesis reactions: that is, the majority Ru species present during catalysis. Mechanistic studies of these key intermediates have been restricted, however, by the low yields and purity with which they could be accessed. Initial work therefore focused on designing a clean, high-yield route to the second-generation Grubbs methylidene complexes S-GIIm and A-GIIm. These routes were subsequently expanded to develop access to isotopically-labelled derivatives. Locating a 13C-label at the key alkylidene site, in particular, offers a powerful means of tracking the fate of the methylidene moiety during catalyst deactivation. Access to GIIm enabled detailed studies of the behaviour and decomposition of the Grubbs catalysts. First, the long-standing question of the impact of saturation of the NHC backbone (i.e. IMes vs. H2IMes) was examined. Dramatic differences in the behaviour of the two complexes were traced to profound differences in PCy3 lability arising from the diminished π-acidity of the IMes ligand. Secondly, the vulnerability of GIIm to nucleophiles was examined. This is an important issue from the perspective of decomposition by adventitious nucleophiles in the reaction medium during catalysis, but also reflects on substrate scope. For amine additives, the dominant deactivation pathway was shown to typically involve attack on the resting-state methylidene complex, not the metallacyclobutane, which has often been regarded as the most vulnerable intermediate. In addition, the sigma-alkyl intermediate formed by nucleophilic attack of displaced phosphine at the methylidene carbon was trapped by moving to the first-generation complex, and using a nitrogen donor (pyridine) that cannot promote decomposition via N–H activation pathways. Interception of this long-suspected species led to the proposal of “donorinduced” deactivation as a general decomposition pathway for Grubbs-class catalysts. Finally, the capacity of phosphine-free catalysts to overcome the shortcomings of the secondgeneration Grubbs catalysts was demonstrated, in a case study involving application of crossmetathesis (CM) to the synthesis of a high-value antioxidant. An efficient CM methodology was developed for the reaction of renewable essential-oil phenylpropenoids with vinyl acrylates. This work illustrates a new paradigm in sustainable metathesis. Rather than degrading unsaturated feedstocks via metathesis (a process that can be termed “metathe[LY]sis”), it demonstrates how metathesis with directly-functionalized olefins can be used to augment structure and function. From the perspective of organometallic chemistry and catalyst design, key comparisons built into this thesis are the effect of the NHC ligand (IMes vs. H2IMes) and its trans ancillary ligand on the efficient entry into catalysis; the susceptibility to nucleophilic attack of the alkylidene ligand (benzylidene vs. methylidene) vs. the metallacyclobutane; and the effect of replacing a phosphine ancillary ligand with a non-nucleophilic donor. From a practical standpoint, Chapter 2 brings new life to metathesis with the high-yield synthesis of the resting state species, Chapters 3 and 4 examine the deactivation, or death, of the methylidene complexes, and Chapter 5 establishes a new paradigm for olefin metathesis within the context of sustainable synthesis.

Stickoxide NOx werden von Menschenhand in verschiedenen Verbrennungsprozessen emittiert. Die selektive katalytische Reduktion mit Ammoniak (NH3-SCR) hat sich weltweit als wichtigste Methode zur Minderung von NOx-Emissionen etabliert. Derzeit erhältliche Katalysatoren für die NH3-SCR werden bei Temperaturen unterhalb von 473 K stark in Gegenwart von Wasser desaktiviert, welches unvermeidbar in Abgasen aus der Verbrennung von organischen Stoffen enthalten ist. In dieser Arbeit werden drei verschiedene Arten der Modifikation von SCR-Katalysatoren diskutiert, die eine gesteigerte H2O-Resistenz bewirken. Eine Methode ist die Verwendung von mischoxidischen Trägermaterialien, eine Andere ist eine mischoxidische aktive Komponente und schließlich eine postpräparative Oberflächenmodifikation mit Organosilylgruppen. Die Katalysatoren wurden sowohl auf ihre katalytische Aktivität als auch auf ihre adsorptiven, redox und andren Oberflächeneigenschaften untersucht. Die Wechselwirkungen zwischen H2O und der Katalysatoroberfläche wurden mittels temperaturprogrammierter Desorption (TPD), isothermaler Adsorption bei erhöhtem Druck und einer gravimetrischen Methode untersucht. Besonders die H2O-TPD hat sich als eine leistungsstarke Methode für diesen Zweck herausgestellt. Jede der drei Modifikationen bewirkte eine Verminderung der Wechselwirkungen zwischen H2O und der Katalysatoroberfläche. Neben einer allgemeinen Erhöhung der Aktivität eines SCR-Katalysators, wird die gezielte Verminderung dieser Wechselwirkungen als Schlüsselrolle in der Entwicklung von Katalysatoren mit verbesserter H2O-Resistenz angesehen. Jedoch gibt es zur Zeit kaum Publikationen, die diesen Zusammenhang behandeln. Daneben wurde auch die Bildung von N2O als ungewünschtes Nebenprodukt bei der SCR-Reaktion untersucht. Dessen Treibhauspotential entspricht ungefähr dem 300-fachen von CO2. Die Verwendung von einem mischoxidischem Trägermaterial kann die Freisetzung von N2O während der SCR verringern, was größtenteils auf die Unterdrückung der Bildung nach einem ER-Mechanismus zurückgeführt wurde. Auch die N2O-Bildung wird in vielen Publikationen über die Entwicklung von SCR-Katalysatoren nicht betrachtet.:0.1 Abbreviations 0.2 Symbols 1 Introduction and Objectives 2 Literature Overview 2.1 NH3-SCR 2.1.1 NH3-SCR Catalysts 2.1.2 Mechanisms of NH3-SCR Reaction 2.1.3 N2O-Formation under SCR-Conditions 2.2 Deactivation of NH3-SCR Catalysts 2.2.1 Deactivation by H2O 2.2.2 Deactivation by SO2 2.3 Low-Temperature NH3-SCR 2.3.1 Requirements and Challenges of LT-SCR 2.3.2 LT-SCR Catalysts 2.4 Silylation of Metal Oxide Surfaces 3 Experimental Section 3.1 Catalyst Preparation 3.1.1 Support Modification with Different Metal Oxides 3.1.2 Deposition of Active Component 3.1.3 Catalyst Modification with Organosilyl Groups 3.2 Catalyst Characterization 3.2.1 Texture Analysis 3.2.2 Phase Analysis 3.2.3 Elementary Analysis 3.2.4 Adsorption Properties 3.2.5 Surface Spectroscopy 3.2.6 Redox Properties 3.3 Catalytic Experiments 4 Results and Discussion 4.1 Impact of Mixed-Oxide Support on Catalyst Activity 4.1.1 Impact in Dry Gas-Flow: Reduced N2O-Emission 4.1.1.1 Catalytic Activity 4.1.1.2 Catalyst Characterization 4.1.1.3 Discussion 4.1.2 Impact in Wet Gas-Flow: Higher H2O-Resistance 4.1.2.1 Catalytic Activity 4.1.2.2 Catalyst Characterization 4.1.2.3 Discussion 4.1.3 Summary of SiO2-Impact 4.2 Mn-Ce Mixed-Oxide as Active Component 4.2.1 Catalytic Activity 4.2.2 Catalyst Characterization 4.2.3 Discussion and Summary 4.3 Catalyst Modification with Organosilyl Groups 4.3.1 Stability of Organosilyl Groups 4.3.2 Impact of Organosilyl Modification on H2O-Adsorption 4.3.3 Impact of Organosilyl Modification on Catalytic Activity in Pre- and Absence of H2O 4.3.3.1 Catalytic Activity 4.3.3.2 Catalyst Characterization 4.3.3.3 Discussion 4.3.4 Summary of Organosilyl Modification 4.4 Discussion on the Investigation of H2O-Adsorption 5 Conclusions and Outlook 5.1 Conclusions 5.2 Outlook 6 References 7 Appendix 7.1 Evaluation of H2O-Sorption Data through BET-Theory 7.2 Evaluation of Kinetic SCR Investigation 7.3 Calculation of the Average Oxidation State of Mnz+ from H2-TPR 7.4 Calculation of the Surface-Density of Mn 7.5 Supplementary Data 7.6 Scientific Contributions 7.7 Curriculum Vitae 8 Summary (german) 8.1 Einleitung 8.2 Experimentelles 8.3 Ergebnisse und Diskussion 8.3.1 Einfluss eines mischoxidischen Trägermaterials auf die katalytische Aktivität 8.3.2 Mn-Ce-Mischoxide als aktive Komponente 8.3.3 Modifikation von Katalysatoren mit Organosilyl-Gruppen 8.4 Schlussfolgerungen / Nitrogen oxides NOx were anthropogenically emitted by various combustion processes. The selective catalytic reduction with ammonia (NH3-SCR) has been established worldwide as the most important technique for the abatement of NOx . Currently available catalysts for NH3-SCR become strongly deactivated at temperatures below 473 K in presence of H2O which is unavoidable present in the exhaust gas arising from the combustion of organic matter. In this work three different kinds of a modification of an SCR-catalyst were discussed that cause a higher H2O-resistance. One is the application of a mixed-oxide support material, the other is a mixed-oxide active component and finally a post-preparative surface modification with organosilyl-groups. The catalysts were assessed for their catalytic activity as well as their adsorptive, redox and other surface properties. The interactions between H2O and the catalyst surface were investigated by means of temperature programmed desorption (TPD), isothermal adsorption at elevated pressure and a gravimetric method. Especially the H2O-TPD turned out to be a powerful method for this purpose. Each of the three modifications caused a reduction in the H2O-catalyst interactions. Beside a general increase of the activity of an SCR-catalyst, the purposeful reduction of these interactions is considered to play a key role in the development of catalysts with an enhanced H2O-resistance. However, there is a lack of publications that deal with this correlation. Also the formation of the unwanted by-product N2O was investigated. Its global warming potential is about 300-times that of CO2. The application of a mixed-oxide support can reduce the release of N2O during SCR which was attributed mainly to the suppression of the ER-type formation pathway. Also the N2O-formation is not considered in many publications dealing with the development of SCR-catalysts.:0.1 Abbreviations 0.2 Symbols 1 Introduction and Objectives 2 Literature Overview 2.1 NH3-SCR 2.1.1 NH3-SCR Catalysts 2.1.2 Mechanisms of NH3-SCR Reaction 2.1.3 N2O-Formation under SCR-Conditions 2.2 Deactivation of NH3-SCR Catalysts 2.2.1 Deactivation by H2O 2.2.2 Deactivation by SO2 2.3 Low-Temperature NH3-SCR 2.3.1 Requirements and Challenges of LT-SCR 2.3.2 LT-SCR Catalysts 2.4 Silylation of Metal Oxide Surfaces 3 Experimental Section 3.1 Catalyst Preparation 3.1.1 Support Modification with Different Metal Oxides 3.1.2 Deposition of Active Component 3.1.3 Catalyst Modification with Organosilyl Groups 3.2 Catalyst Characterization 3.2.1 Texture Analysis 3.2.2 Phase Analysis 3.2.3 Elementary Analysis 3.2.4 Adsorption Properties 3.2.5 Surface Spectroscopy 3.2.6 Redox Properties 3.3 Catalytic Experiments 4 Results and Discussion 4.1 Impact of Mixed-Oxide Support on Catalyst Activity 4.1.1 Impact in Dry Gas-Flow: Reduced N2O-Emission 4.1.1.1 Catalytic Activity 4.1.1.2 Catalyst Characterization 4.1.1.3 Discussion 4.1.2 Impact in Wet Gas-Flow: Higher H2O-Resistance 4.1.2.1 Catalytic Activity 4.1.2.2 Catalyst Characterization 4.1.2.3 Discussion 4.1.3 Summary of SiO2-Impact 4.2 Mn-Ce Mixed-Oxide as Active Component 4.2.1 Catalytic Activity 4.2.2 Catalyst Characterization 4.2.3 Discussion and Summary 4.3 Catalyst Modification with Organosilyl Groups 4.3.1 Stability of Organosilyl Groups 4.3.2 Impact of Organosilyl Modification on H2O-Adsorption 4.3.3 Impact of Organosilyl Modification on Catalytic Activity in Pre- and Absence of H2O 4.3.3.1 Catalytic Activity 4.3.3.2 Catalyst Characterization 4.3.3.3 Discussion 4.3.4 Summary of Organosilyl Modification 4.4 Discussion on the Investigation of H2O-Adsorption 5 Conclusions and Outlook 5.1 Conclusions 5.2 Outlook 6 References 7 Appendix 7.1 Evaluation of H2O-Sorption Data through BET-Theory 7.2 Evaluation of Kinetic SCR Investigation 7.3 Calculation of the Average Oxidation State of Mnz+ from H2-TPR 7.4 Calculation of the Surface-Density of Mn 7.5 Supplementary Data 7.6 Scientific Contributions 7.7 Curriculum Vitae 8 Summary (german) 8.1 Einleitung 8.2 Experimentelles 8.3 Ergebnisse und Diskussion 8.3.1 Einfluss eines mischoxidischen Trägermaterials auf die katalytische Aktivität 8.3.2 Mn-Ce-Mischoxide als aktive Komponente 8.3.3 Modifikation von Katalysatoren mit Organosilyl-Gruppen 8.4 Schlussfolgerungen

The inhibiting and deactivating effects of basic nitrogen species present in gas oils on catalyst active sites has been well recognized over the years; however, recent studies have shown comparable inhibiting and deactivating effects exhibited by non-basic nitrogen species. A novel pre-treatment technique employing the heterogeneously cross-linked macroporous polymer poly(glycidyl methacrylate) (PGMA) as the hydrophilic support coupled with organic compound tetranitrofluorenone has shown promising results for the selective elimination of non-basic nitrogen heterocyclic species from bitumen derived heavy gas oil (HGO). Characterization techniques such as Scanning electron microscopy (SEM), low temperature N2 adsorption–desorption (BET), CHNOS elemental analysis, fourier transform infrared spectroscopy (FT-IR), epoxy content titration, and thermo gravimetry/differential thermal analyzer (TG/DTA) were employed for determining the optimum parameters during each step of the polymer synthesis. Step 1 comprised of direct polymerization of the monomers under the determined optimum conditions, with specific surface area of 34.7 m2/g and epoxy content of 5.8 wt% for the PGMA polymer support. Step 2 comprised of substitution of the epoxy ring with the acetone oxime functionality; FT-IR results indicated characteristics peaks at 1650 cm-1 which ascertained the presence of acetone oxime on the polymer, with epoxy content titration indicating a decrease of up to 33% of the epoxy content due to the substitution. Coupling of the organic compound tetranitrofluorenone with the polymer was performed in the final step, with TGA and DTG results indicating highest weight loss of approximately 126.9 μg, which signified that sample T had the greatest amount of organic compound present in comparison to the other samples (sample N to Sample S). The optimized polymer (sample T) was capable of removing nitrogen up to 6.7%, while having little to no influence on the sulphur or aromatic species. These results were in agreement with step 4 TGA analysis that showed sample T had the highest presence of the organic compound. Reusability of the polymer multiple times with consistent removal is another known advantage of such a pre-treatment technique; hence reusability studies were performed, and showed that the polymer was indeed capable of multiple uses, with consistent removal of nitrogen compounds at approximately 6.5% from fresh heavy gas oil feedstocks. Kinetic studies were performed as the final phase in order to evaluate the performance of the treated HGO in comparison to non-treated HGO. The effect of parameters such as temperature and LHSV were determined, with higher temperatures resulting in higher conversion of HDS and HDN. Similarly, as the LHSV was decreased, the conversions were increased for both HDS and HDN due to longer contact time between the feed and the catalyst. The highest obtained conversions were at an LHSV of 0.5 hr-1 and temperature of 395°C with treated HGO having HDS of 97.5% and HDN of 90.3%; while non-treated HGO having HDS of 94.9% and HDN of 78.3%. Employing the power law model, the results indicated that for treated HGO the reaction order for both HDS and HDN was 1.50; while for non-treated HGO the reaction order for HDS was 2.25 and for HDN was 2.00. The activation energies were then calculated with 141.4 kJ/mol being obtained for HDS and 113.8 kJ/mol for HDN for treated HGO; while for non-treated HGO the activation energy for HDS was 150.4 kJ/mol and for HDN was 121.4 kJ/mol. It was observed that the conversion of both HDS and HDN were higher and the activation energies were lower for treated HGO, indicating that the removal of non-basic nitrogen species prior to hydrotreatment had a positive impact on catalyst performance and consequently the level of conversion.

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based on the fundamentals of the carbenium ion chemistry, the formation of over 100+ product species has been modeled in order to gain understanding of the underlying phenomena leading to rapid catalyst deactivation and product selectivity shifts observed in experimental runs. An experimental investigation of the solid acid alkylation process was carried out in a fixed bed catalytic reactor operating with an excess of isobutane under isothermal conditions at moderate temperatures (353-393 K) in liquid phase. Experimental data varying with run-time for a set of butene space-times and reaction temperatures were collected for parameter estimation purposes. A kinetic model was formulated in terms of rate expressions at the elementary step level including a rigorous modeling of deactivation through site coverage. The single event concept was applied to each rate coefficient at the elementary step level to achieve a significant reduction in the number of model parameters. Based on the identification of structural changes leading to the creation or destruction of symmetry axes and chiral centers in an elementary step, formulae have been developed for the calculation of the number of single events. The Evans-Polanyi relationship and the concept of stabilization energy were introduced to account for energy levels in surface-bonded carbenium ions. A novel functional dependency of the stabilization energy with the nature of the carbenium ion and the carbon number was proposed to account for energy effects from the acid sites on the catalyst. Further reductions in the number of parameters and simplification of the equations for the transient pseudohomogeneous one-dimensional plug-flow model of the reactor were achieved by means of thermodynamic constraints. Altogether, the single event concept, the Evans-Polanyi relationship, the stabilization energy approach and the thermodynamic constraints led to a set of 14 parameters necessary for a complete description of solid acid alkylation at the elementary step level.

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based on the fundamentals of the carbenium ion chemistry, the formation of over 100+ product species has been modeled in order to gain understanding of the underlying phenomena leading to rapid catalyst deactivation and product selectivity shifts observed in experimental runs. An experimental investigation of the solid acid alkylation process was carried out in a fixed bed catalytic reactor operating with an excess of isobutane under isothermal conditions at moderate temperatures (353-393 K) in liquid phase. Experimental data varying with run-time for a set of butene space-times and reaction temperatures were collected for parameter estimation purposes. A kinetic model was formulated in terms of rate expressions at the elementary step level including a rigorous modeling of deactivation through site coverage. The single event concept was applied to each rate coefficient at the elementary step level to achieve a significant reduction in the number of model parameters. Based on the identification of structural changes leading to the creation or destruction of symmetry axes and chiral centers in an elementary step, formulae have been developed for the calculation of the number of single events. The Evans-Polanyi relationship and the concept of stabilization energy were introduced to account for energy levels in surface-bonded carbenium ions. A novel functional dependency of the stabilization energy with the nature of the carbenium ion and the carbon number was proposed to account for energy effects from the acid sites on the catalyst. Further reductions in the number of parameters and simplification of the equations for the transient pseudohomogeneous one-dimensional plug-flow model of the reactor were achieved by means of thermodynamic constraints. Altogether, the single event concept, the Evans-Polanyi relationship, the stabilization energy approach and the thermodynamic constraints led to a set of 14 parameters necessary for a complete description of solid acid alkylation at the elementary step level.

The application of heterogeneous catalysts to industrial processes is a key factor in the synthesis of nearly all chemicals currently produced, however billions of pounds are lost every year due to unplanned reactor shutdowns and catalyst replacement as a result of catalytic deactivation processes. Poisoning of heterogeneous catalysts by sulfur compounds is a particularly prominent class of deactivation processes, affecting a wide range of catalytic materials and catalytic reactions, including the industrially-prominent Haber-Bosch process for the synthesis of ammonia and steam reforming of methane for the synthesis of hydrogen. However, while the effects of sulfur adsorption on catalytic behaviour are often unmistakably apparent, the fundamental interactions leading to these effects are not yet well understood. The work presented in this thesis uses a combination of models systems, novel and traditional characterization techniques, and methods of modifying catalyst geometric and electronic structure to approach the topic of sulfur poisoning from a fundamental perspective. Particular focus is placed on using selective decoration of active sites to develop a system of model hydrogenation reactions to relate changes in catalytic behaviour to changes in geometric and electronic structure. Application of these model reactions to investigate the sensitivities of palladium- and ruthenium-based catalytic systems to modification by sulfur shows contrasting effects for the two metals. While both systems exhibit similar geometric effects of modification, the palladium-based catalysts are far more sensitive than the ruthenium-based catalysts to modification of electronic structure. Additionally, controlled variation in particle size for the palladium-based catalysts demonstrates that catalytic behaviour is dominated by electronic structure for small nanoparticles and geometric structure for large nanoparticles. This leads small nanoparticles to show increased sensitivity to electronic modification effects resulting from sulfur adsorption. Ultimately, the research presented within this thesis provides a basis for the intelligent design of heterogeneous catalysts for improving tolerance for sulfur poisoning, and for utilizing the effects of sulfur modification to optimize catalytic activity and selectivity for the synthesis of fine chemicals.

No description available.

Cerium and zirconium oxides are important materials in industrial catalysis. Particularly, the great advances attained in the past 30 years in controlling levels of gaseous pollutants released from internal combustion engines can be attributed to the development of catalysts employing these materials. Unfortunately, oxides of sulfur are known threats to the longevity of many catalytic systems by irreversibly interacting with catalytic materials over some time period. In this work, polycrystalline cerium-zirconium mixed-metal-oxide (MMO) solid solutions of various molar ratios were synthesized. High resolution x-ray photoelectron spectroscopy (XPS) was used to characterize the model system. The spectral data was examined for revelation of the surface species that form on these metal oxides after insitu exposures to sulfur dioxide at various temperatures. The model catalysts were exposed to sulfur dioxide using a custom modified in-situ reaction cell. A reliable sample platen heater was designed and built to allow the exposure of the model system at temperatures up to 673 K. The results of this study demonstrate the formation of sulfate and sulfite adsorbed sulfur species. Temperature and compositional dependencies were displayed, with higher temperatures and ceria molar ratios displaying a larger propensity for forming surface sulfur species. In addition to analysis of sulfur photoemission, the photoemission regions of oxygen, zirconium, and cerium were examined for the materials used in this study before and after the aforementioned treatments with sulfur dioxide. The presence of surface hydroxyl groups was observed and metal oxidation state changes were probed to further enhance the understanding of sulfur dioxide adsorption on the synthesized materials. Palladium loaded mixed-metal oxides were synthesized using a unique solid-state methodology to probe the effect of palladium addition on sulfur dioxide adsorption. Microscopic characterization of the wafers made using palladium-loaded MMO materials provide justification for using this material preparation method in surface science studies. The addition of palladium to this model system is shown to have a strong effect on the magnitude of adsorption for sulfur dioxide on some material/exposure condition combinations. Ceria/zirconia sulfite and sulfate species are identified on the palladium-loaded MMO materials with adsorption sites located on the exposed oxide sites.

No description available.

The objective of the thesis was to analyze the ageing processes and the modifications of an Ir/CeO2catalyst for steam reforming of ethanol. Over a model Ir/CeO2 catalyst, the initial and fast deactivationwas ascribed to ceria surface restructuring and the build-up of intermediates monolayer (acetate,carbonate and hydroxyl groups). In parallel, a progressive and slow deactivation was found to come fromthe structural changes at the ceria/Ir interface linked to Ir sintering and ceria restructuring. Theencapsulating carbon, coming from C2 intermediates polymerization, did not seem too detrimental to theactivity in the investigated operating conditions. By doping ceria with PrOx, the oxygen storage capacityand thermal stability were greatly promoted, resulting in the enhanced activity and stability. The Ir/CeO2catalyst was then modified by changing the shape of ceria. It was found that the shape and therefore thestructure of ceria influenced the activity and stability significantly. A simplified modeling of theseprocesses has contributed to support the new proposals of this work.