Preparation of bifunctioal catalysts by aerosol-assisted sol-gel process for butadiene synthesis

For several years, butadiene production is experiencing a decrease and an urge to find a solution has risen. Ethanol conversion to butadiene is a sustainable alternative to petrol-based processes, which is in line with the current trend to find ecological solutions to produce polymers. Because of the mechanism, catalysts to enhance this reaction need to be bifunctional and to present features both acidic and redox. This master thesis has explored if peculiar textural properties, brought by an innovative synthesis process, such as aerosol-assisted sol-gel, would create catalysts with high performances. To position the results with more typical preparation method, benchmarks catalysts synthesized by dry impregnation on commercial or aerosol-made supports, have been studied too. In that scope, Ag-TaOx-SiO2 ternary catalysts have been synthesized. Mesoporous ternary catalyst or binary TaOx-SiO2 supports have been prepared by aerosol-assisted sol-gel process (AASG). On the other hand, silver was either incorporated in one-pot or by dry impregnation. Different effects on the catalysts have been investigated; two different calcination furnaces (under static air or flowing air), three calcination temperatures (500°C, 600°C and 700°C) and a screening on the loadings. The catalysts have been characterized by N2 physisorption, O2 chemisorption, NH3-TPD, XRD, XPS and infrared spectroscopy. The catalysts were then tested, after in-situ reduction, between 325°C and 415°C, to assess of their performances in the Lebedev one-step process. From the results, it appears that calcination temperature influences the migration of silver from the bulk towards the surface and 500°C brought the best silver dispersion at the surface of the materials. Higher temperatures favored more sintering. Calcination under air highlighted itself by the ability to improve the migration of silver nanoparticles towards the surface. AASG catalysts presented a high tantalum oxide dispersion, acid sites were taking over the redox sites. Best results were then obtained with rather low tantalum oxide loading. AASG catalysts displayed an equivalent dispersion to silver impregnated sample for the same silver loading but with less silver at the surface since all of it did not migrate from the bulk. Best results were obtained with 5 wt. % Ag. This work presents the advantages of the aerosol-assisted sol-gel process and the potential of the method.