Mixed metal oxides play an important role in many industrial applications, as adsorbents, sensors, electrolytes in batteries, heterogeneous catalysts, etc. Among them, metallosilicates are particularly useful in heterogeneous catalysis, since their acido-basic properties can be tuned by the amount, nature and dispersion of the metals incorporated in the silica matrix, by synthesis conditions, by post-treatments, etc. Metallosilicates are used as catalysts in epoxidation of alkenes, cracking, isomerization reactions, etc. Nowadays they are applied in the biomass and biofuel sector, where they catalyze the dehydration of bioalcohols, (trans)esterification and hydrolysis in oleochemistry, biopolymer hydrolysis, condensation reactions, etc. However for this modern purpose the performance of metallosilicates is not fully satisfactory, mainly due to their low stability in the presence of water. In this project, we proposed to explore and evaluate non-hydrolytic sol-gel processing of novel metallosilicate catalysts to tackle these challenges, thereby supporting the efficiency and competitiveness of biomass valorization. The main objective of our research project was to take advantage of the non-hydrolytic sol-gel chemistry to prepare, characterize and apply new homogeneous, hydrothermally stable, and porous mixed metal oxide catalysts with high performance in biomass conversion applications. In terms of catalyst synthesis, we (i) studied the dispersion of the metal in silica matrices, (ii) tried to improve the hydrothermal stability by using appropriate hybrid precursors and surface modifiers with hydrophobic moieties and (iii) controlled porosity by the use of various solvents, templates, and precursors. These catalysts were characterized by an array of advanced physico-chemical tools to evaluate the effects of preparation parameters on the desired properties – homogeneity, hydrothermal stability and texture. The materials were evaluated as heterogeneous catalysts in a topical reaction of biomass valorization: ethanol dehydration to ethylene. We followed the influence of the materials properties on catalyst activity, selectivity and lifetime. The main conclusions are as follows: (i) non-hydrolytic sol-gel chemistry allows to prepare metallosilicates with a high homogeneity of metal dispersion within silica matrices, this in turn leads to improved acido-basic properties and markedly better catalytic activity and selectivity to ethylene in comparison to commercial benchmarking catalysts, (ii) a broad variety of organic groups were introduced into the metallosilicate materials, direct bond between Si and aromatic groups is not stable under the reaction conditions, alkyl groups are stable and lead in some cases to an improvement of catalytic activity, and (iii) catalyst lifetime depends on the textural properties and strength of acid sites, some samples proved to be highly stable during our stability tests.
