AbstractThe quest for more sustainable processes in a future biomass-based industry,
guides the interest in the development of novel heterogeneous catalysts. In the panorama of bio-based feedstocks, glycerol, especially coming as a byproduct from the production of biodiesel, can be an attractive platform for the synthesis of valuable chemicals. Promising routes for its valorization are represented by the condensation of glycerol with acetone to produce solketal, or by the synthesis of ethyl lactate from dihydroxyacetone, which can itself be obtained by partial oxidation of glycerol. Both these added-value products present several applications in industrial areas related to chemicals, food, pharmaceuticals and cosmetic products. A sustainable way to perform these reactions envisages the use of heterogeneous silica-based catalysts presenting a metal inserted as single-site in the matrix, displaying Brønsted and/or Lewis acidity. A vivid interest is growing for the design of robust and active metalsubstituted silicates for these applications and, in this context, sol-gel chemistry demonstrated to be a powerful tool providing a wide range of tunable parameters to tailor the physico-chemical properties of these solids.
This thesis explores novel sol-gel routes proposing a valid improvement of knowledge in the field of metal-substituted silicates as versatile acid catalysts. The importance of the efficient insertion of metals in the silica matrix as well as the morphology is highlighted. Novel silica-based nanotubes and aerosol-made silicates presenting Sn and Ga inserted as single-site are prepared and properly characterized. The catalytic activity of each solid, presenting the desired balance of Brønsted and Lewis acid sites, is evaluated in the synthesis of solketal and ethyl lactate under specific reaction conditions. With the aim of improving both activity and selectivity, the efficient insertion of metals and the precise tuning of the morphology can be combined with the control of adsorption/ desorption thenomena on the surface. Since the affinity of reactants and products with the catalytic surface can be guided by hydrophilic/hydrophobic interactions, a systematic study is devoted in this work to the deep understanding of the impact of surface polarity on catalytic activity.
Exploiting the aerosol process, functionalized metal-silicates are prepared in one-pot using different organosilanes. The control of surface polarity, achieved with a proper surface functionalization, proved to be a powerful tool for the optimization of the global efficiency of the catalysts.
|Date of Award||14 May 2020|
|Sponsors||ARC (Actions de recherche concentrées)|
|Supervisor||Carmela Aprile (Supervisor), Damien P. Debecker (Co-Supervisor), Robert Sporken (President), Sonia Fiorilli (Jury), Eric Gaigneaux (Jury) & Michel Devillers (Jury)|