Catalytic ketonization of valeric acid

The 21st century is marked by a big challenge which is to mitigate fossil resources dependence and to manage the environmental issues (global warming, pollution, resource depletion etc.). On the other hand, the energy demand keeps increasing. Therefore, the biorefinery concept draws the attention as it can contribute to face these challenges. It aims to process biomass and upgrade it into valuable compounds usually obtained from the petrochemical industry. Starting from the biomass as raw material, valeric acid is a platform molecule that can be easily obtained in a cost-effective way and in high yields. Furthermore, the ketonization of this carboxylic acid is a promising way to obtain 5-nonanone. This molecule can be used for the fuel production or as platform chemical to produce valuable compounds. Driven by these motivations, this master thesis aims to develop active heterogeneous catalysts for the ketonization of valeric acid. Among the potentially active materials, amphoteric oxides – and in particular zirconia – have been highlighted as promising catalysts for the ketonization. In that scope, this master thesis has focussed on the preparation, catalytic evaluation, and physicochemical characterizations of different zirconia-based catalysts. First, pure zirconia catalysts prepared by sol-gel method with two different protocols have been studied and compared with a zirconia obtained by a simple thermal decomposition of a salt. Then, zirconia has been dispersed on different supports, either silica, alumina and titania, by wet impregnation to better exploit the active phase. Finally, zirconia based mixed oxides have been prepared by sol-gel method to obtain large specific surface area and high dispersity of the active phase. The effect of different loadings of zirconia in mixed oxides was also studied to investigate whether a synergy exists between either zirconia and titania or zirconia and alumina. The best results were obtained with the pure zirconia catalyst prepared by one of the sol-gel protocol. Our results indicate that the crystallinity has an impact on the activity, the tetragonal polymorph probably being more active compared to the monoclinic polymorph. On the other hand, the wet impregnation has proven to be relevant in the case of silica as a choice of support as it provides a large specific surface. Furthermore, it was shown that the sol-gel method was not more effective than the wet impregnation for preparing active bimetallic oxides catalysts, and finally, a negative effect of mixing zirconia with either alumina or titania was demonstrated regardless of the zirconia loading. All the bimetallic oxides were amorphous, so it is likely that a good catalytic activity is not linked to isolated (or highly dispersed) species. Instead, the results of this master thesis show that crystalline structures are active in the ketonization reaction.