Soutenance publique de thèse de doctorat en Sciences chimiques - Martina Saitta

The development of efficient heterogeneous acid catalysts is essential for the sustainable valorization of biomass-derived platform molecules. This PhD thesis focuses on the design, synthesis, characterization, and catalytic evaluation of novel acidic materials for two representative biomass upgrading reactions: the ketalization of glycerol into solketal and the conversion of ethyl levulinate into γ-valerolactone. Several classes of catalysts were investigated, including Group IV metal-doped mesoporous silica nanotubes and hollow nanospheres, sulfonic acid-functionalized silica materials, and porous metal phosphonates. The aim was to establish relationships between the properties of the catalysts, in particular their acidity, and catalytic performance.

The results demonstrated that the nature of the metal cation in metal-doped nanostructured silica strongly influences catalyst acidity and reactivity. Furthermore, synthesis parameters such as the loading of the metal cation and preparation method were shown to control the Lewis/Brønsted ratio and strength of Lewis acid sites, allowing the tuning of catalytic performance. Materials rich in Lewis acidity preferentially promoted the conversion of ethyl levulinate, while catalysts with a higher Brønsted acidity were more effective in glycerol ketalization.

The introduction of sulfonic acid groups significantly enhanced Brønsted acidity and led to extremely active catalysts for solketal production. In parallel, studies on layered phosphonates highlighted the crucial role of the phosphoric spacer for ensuring material stability and enabling their reuse over multiple catalytic cycles. For amorphous porous metal phosphonates, key synthetic parameters, including acid concentration, solvent choice, and the use of templating agent, were found to significantly influence the acidity of the materials and, consequently, their catalytic activity.

Overall, this work provides valuable insights into structure-acidity-reactivity relationships and offers guidelines for the rational design of heterogeneous acid catalysts for biomass valorization.