La prise de conscience de l’enjeu environnemental est en train de transformer notre conception de la chimie, la faisant évoluer vers une chimie moderne portée par des concepts novateurs de chimie durable et plus respectueuse de l’environnement. Parmi ces concepts, la substitution à terme de la matière première pétrosourcée par la biomasse constitue actuellement avec le développement de procédés catalytiques, un des enjeux majeurs de la chimie verte. L’isosorbide est une molécule phare de cette nouvelle chimie, provenant de la filière sucre, ce diol est obtenu par anhydrisation du sorbitol lui-même obtenu par hydrogénation du glucose. Du fait de ses propriétés structurales et physico-chimiques, l’isosorbide est une molécule plateforme particulièrement intéressante en chimie de spécialité, son potentiel de développement est très vaste pour des applications diverses et variées, allant des solvants aux polymères en passant par la formulation et la pharmaco-chimie. A ce jour, la synthèse industrielle de cette molécule se heurte à différents problèmes de sélectivité qui entachent son bilan carbone, par la formation de produits peu valorisables, et compliquent ainsi les purifications. Au cours de ce projet, des méthodes d’accès alternatives faisant appel à différentes voies catalytiques seront étudiées afin de mieux comprendre les mécanismes mis en jeu, ainsi que les cinétiques de formations des différents intermédiaires réactionnels dans le but d’essayer d’en augmenter le rendement. / Awareness of the environmental issue is transforming our conception of chemistry, making it evolve towards a modern chemistry driven by innovative concepts of eco-friendly and sustainable chemistry. Among these concepts, the long-term substitution of petroleum raw materials by biomass based products is now establishing, with the development of new catalytic processes, one of the major stakes of green chemistry. Isosorbide is a key plateform molecule of this incipient chemistry, originating from the sugar chain, this diol is obtained by dehydration of the sorbitol itself obtained by hydrogenation of the glucose. Because of its structural and physicochemical properties, isosorbide is a particularly advantageous platform molecule in specialty chemistry. Its development potential is very broad for various applications ranging from solvents to polymers, to formulation and pharmacochemistry.To date, the industrial synthesis of this molecule encounters various problems of selectivity which stain its carbon balance, by the formation of colored and low valueable products, and which thus complicate purifications. In this project, alternative access roads using different catalytic pathways will be studied in order to better understand involved mechanisms and reaction intermediates formation kinetics. The main goal is to increase the overall synthesis yield in order to optimize and promote isosorbide production.

Les considérations environnementales actuelles encouragent la production d’intermédiaires chimiques bio-sourcés à travers des processus durables et plus respectueux de l'environnement nécessitent la conception de nouveaux systèmes catalytiques « sur mesure » recyclables. L’association de la catalyse biologique et de la catalyse chimique, appelée « catalyse hybride », fait partie de ces nouveaux concepts pouvant répondre aux défis émergents posés par la valorisation de la biomasse. C’est dans ce contexte d’émergence de la catalyse hybride que nous avons développé un procédé hybride innovant d’obtention de 5-hydroxyméthylfurfural (5-HMF), molécule plateforme clé pour l’obtention de monomères biosourcés, à partir du glucose. Les problèmes de compatibilités liées au couplage « one-pot » de l’enzyme d’isomérisation du glucose et du catalyseur chimique de déshydratation ont été résolus par la mise en œuvre d’une membrane liquide transportant le fructose. Les conditions réactionnelles optimales de chacune des 3 étapes du procédé (isomérisation du glucose, transport du fructose, déshydratation du fructose) ont été étudiées individuellement. Un premier procédé en « cascade » a alors été mis en place dans ces conditions, permettant de valider la faisabilité du procédé de production du 5-HMF. Un second procédé de catalyse hybride a ensuite été mis en place dans un réacteur innovant spécialement conçu. Ce procédé a permis de lever le verrou lié à la compatibilité des conditions des deux catalyseurs et de dépasser la limitation de rendement liée à l’équilibre thermodynamique de la réaction d’isomérisation. / Current environmental considerations encourage the production of bio-sourced chemical intermediates through sustainable and environmentally friendly processes that require the design of new, custom-made, recyclable catalytic systems. The combination of biological catalysis and chemical catalysis, called "hybrid catalysis", is part of these new concepts that can meet the emerging challenges posed by the biomass valorization. In this context of hybrid catalysis emergence, we have developed an innovative hybrid process for obtaining 5-hydroxymethylfurfural (5-HMF), a key platform molecule for biosourced monomers obtaining from glucose. Compatibility issues related to the "one-pot" coupling of the glucose isomerization enzyme and the chemical dehydration catalyst have been solved by the implementation of a liquid membrane carrying the fructose. Optimal reaction conditions of each of the 3 process steps (glucose isomerization, fructose transport, fructose dehydration) were studied individually. A first "cascade" process was then set up under these conditions, making it possible to validate the feasibility of the 5-HMF production process. A second hybrid catalysis process was then implemented in a specially designed innovative reactor. This process made it possible to remove the lock related to the compatibility of the operating conditions and to exceed the yield limitation related to the thermodynamic equilibrium of the isomerization reaction.

In this thesis I present my most relevant research work I performed as a main author from 2002 until these days in the field of Catalysis by Oxides by grouping it on a thematic basis. Consequently, each chapter in Section A presents a research direction which corresponds to several papers. I tried to avoid technical details in the text and illustrate the main ideas using results and their discussion. It is worth noting that the results presented here were mainly obtained in the Laboratory of Chemical Technology and Catalysis from the University of Bucharest but also in laboratories abroad where I worked or we are collaborating with. Chapter I presents the most relevant of my results on the subject of the oxidative dehydrogenation (ODH) of light alkanes following two main directions: i) enhancing the ODH selectivity of highly active catalysts and ii) developing new effective catalysts for ODH of light alkanes. Thus, we have shown that the ODH reaction of n-butane over highly active and selective TiP2O7 catalysts can be further improved by addition of CO2 in the feed and that phosphating ceria produces an increase in ODH selectivity mainly at the expense of total oxidation products. We studied new rare earth and transition metal-containing mixed-oxides obtained from layered double hydroxides (LDH) precursors as ODH catalysts. We have shown first that the use of the LDH-derived Mg-containing mixed oxides as catalysts in the ODH reaction favored the desorption of alkenes, and, consequently, improved the ODH selectivity. Among them the Co-containing system was the most active and selective for propane ODH. In this case we have shown that the well-dispersed cobalt species with tetrahedral coordination played a main role in the ODH reaction of propane into propene, the highest propene yields being obtained with the catalysts containing 7.5-9 at % Co with respect to cations. Chapter II is dedicated to the study of total oxidation of short-chain alkanes over different novel oxide-based catalysts with the aim of finding highly active catalysts for volatile organic compounds (VOCs) destruction, capable to replace the precious metal catalysts presently used. Thus, we have studied Pb and Ba titanates, LDH-derived transition metal-containing mixed oxides and Ni and Co ferrospinels. The most active and stable catalyst in the total oxidation of methane was the LDH-derived Cu-containing system. In this case we have shown that the active sites were the highly reducible copper species, their optimum dispersion being observed for the catalyst containing ~ 12 at % Cu with respect to cations. We have also shown for the first time that Co ferrite was highly active and stable in the total oxidation of propane as a VOC model. Chapter III is focussed on the study of oxidation catalysts by electrical conductivity measurements, a powerful technique for catalysts characterization that can provide information on the nature of surface oxidizing species, of structure defects and of the oxidic phase involved in the catalytic reaction which allows us to explain the catalytic behavior of the catalysts studied and to propose a reaction mechanism. Thus, we studied by electrical conductivity measurements ceria and phosphated ceria, catalysts for isobutane ODH, Pb and Ba titanates, catalysts for methane total oxidation, and vanadium antimonate and mixed vanadium and iron antimonate, catalysts for propane ammoxidation, the relationship existing between their redox and catalytic properties being evidenced and their catalytic behavior explained. Chapter IV is devoted to the study of catalytic processes involving the acid-base properties of the catalyst, such as conversion of ethanol into higher added value products over LDH-derived mixed oxides, cyanoethylation of methanol over transition-metal containing Mg-Al hydrotalcites and their corresponding mixed oxides and esterification of n-butanol with acetic acid over almina-supported molibdena and vanadia catalysts. Thus, we have shown that the Pd-containing LDH-derived mixed oxide was active for ethanol conversion into n-butanol while the Cu-based catalyst oriented the transformation towards n-butanol or 1,1-diethoxyethane depending on the reaction conditions and on the copper content. In the cyanoethylation reaction of methanol MgAlO system showed the best catalytic performances which diminished after introduction of the transition metal cations, the equilibrium between basic and acid sites being a key factor. Finally, we have shown that molybdena supported on γ-alumina acts as an efficient stable solid acid catalyst for the esterification of acetic acid with n-butanol, while vanadia supported on γ-alumina loose its activity because of the leaching of the active component. In Section B a plan for my research and academic career development is emphasized, different research topics in the field of Catalysis by Oxides that I intend to tackle in the future being described and justified based on a literature survey.