Enhancing the Catalytic Performance of Zeolites for Aldose-Ketose Sugar Transformations

In the last ten years, Lewis acidic Sn-containing zeolites such as Sn-Beta zeolite have received considerable interest as efficient heterogeneous catalysts for aldose-ketose sugar transformations. Such transformations include in particular the isomerization of glucose to fructose, which is an essential reaction step in the valorization of lignocellulosic biomass and in the food industry. Despite significant progress in both materials syntheses, characterization and mechanistic insights, some important issues with respect to improvement of catalytic performance as well as large-scale applicability remains still uncharted. In this connection, investigation of structure-performance relationships is a useful approach and interesting research topic also to develop new catalysts.
In the current PhD thesis, Chapter 2 describes the modification of physicochemical properties and structures of two commercial Y zeolites by alkaline-treatment under different conditions. Tetrahedral extra-framework Lewis acidic Al sites and mesopores were identified to favor the isomerization of glucose to fructose. In Chapter 3, stannates with [Sn(OH)6]2- complex anions having similarity to partially hydrolyzed framework Sn-sites in Sn-Beta zeolite, Sn-(OH)x, were investigated as isomerization catalysts. Simple alkali-metal stannate salts were found to efficiently catalyze glucose-fructose isomerization in alcohols via a proton-transfer mechanism with low activation energy. In Chapter 4, active species of MoOx were supported on Beta zeolite as an alternative catalyst to Sn-Beta. The MoOx/Beta zeolite catalyst exhibited excellent catalytic performance for glucose epimerization to mannose in aqueous media.
Overall, the PhD work provides new insight on active sites in selected zeolite catalyst and attempts to develop new catalysts for aldose-ketose sugar transformations according to the active sites and species. Hopefully, the work can provide inspiration into rational catalyst design and applications.