Sugars from biomass are considered important renewable feedstocks in the chemical industry for future production of fuels and commodity chemicals. In this connection, aldose-ketose sugar transformations using Lewis acidic zeotype materials have received renewed interest, especially for the isomerization of glucose to fructose which is identified as a key reaction step in biomass valorization and the food industry. However, despite significant progress in both catalysts’ syntheses, characterization, and mechanistic insights within the last decade, some important issues with respect to improvement of catalytic performance as well as large-scale applicability remain still uncharted.
This thesis elucidates structure-activity relationships between zeolite structures and catalytic performance for aldose-ketose sugar transformations (glucose isomerization and epimerization) with attempts to develop new and improved catalyst systems. The physicochemical characteristics of two commercial Y zeolites were altered by alkaline-treatment to create tetrahedral extra-framework Lewis acidic aluminum and mesoporous structures favorable for isomerization of glucose to fructose. Moreover, cheap and commercially available alkali-metal stannates were demonstrated to facilitate higher fructose yield and higher fructose selectivity in alcohols within shorter reaction time at lower reaction temperature than state-of-the-art Sn-Beta zeolite catalyst. Lastly, MoOx supported on Beta zeolite catalyst was further demonstrated to efficiently epimerize glucose to mannose in aqueous media, reaching a near-equilibrium mannose yield within a short reaction time and with low activation energy. Interestingly, higher reaction temperatures lead to the formation of rare sugars such as allose and altrose.
Combined, the thesis provides new insight into catalytically active sites and species for aldose-ketose sugar transformations, which can inspire rational catalyst design and expand applications in biorefineries.