Unveiling the mechanism for selective cleavage of C-C bonds in sugar reactions on tungsten trioxide-based catalysts

Conversion of naturally occurring sugars, the most abundant biomass resources on Earth, to fuels and chemicals provides a sustainable and carbon-neutral alternative to the current fossil resource-based processes. Tungsten-based catalysts (e.g., WO3) are efficient for selectively cleaving C-C bonds of sugars to C-2,C-3 oxygenate intermediates (e.g., glycolaldehyde) that can serve as platform molecules with high viability and versatility in the synthesis of various chemicals. Such C-C bond cleavage follows a mechanism distinct from the classical retro-aldol condensation. Kinetic, isotope C-13-labeling, and spectroscopic studies and theoretical calculations, reveal that the reaction proceeds via a surface tridentate complex as the critical intermediate on WO3, formed by chelating both alpha- and beta-hydroxyls of sugars, together with the carbonyl group, with two adjacent tungsten atoms (W-O-W) contributing to the beta-C-C bond cleavage. This mechanism provides insights into sugar chemistry and enables the rational design of catalytic sites and reaction pathways toward the efficient utilization of sugar-based feedstocks.