Shape-selective Valorization of Biomass-derived Glycolaldehyde using Tin-containing Zeolites

A highly selective self-condensation of glycolaldehyde to different C-4 molecules has been achieved using Lewis acidic stannosilicate catalysts in water at moderate temperatures (40-100 degrees C). The medium-sized zeolite pores (10-membered ring framework) in Sn-MFI facilitate the formation of tetrose sugars while hindering consecutive aldol reactions leading to hexose sugars. High yields of tetrose sugars (74%) with minor amounts of vinyl glycolic acid (VGA), an a-hydroxyacid, are obtained using Sn-MFI with selectivities towards C-4 products reaching 97%. Tin catalysts having large pores or no pore structure (Sn-Beta, Sn-MCM-41, Sn-SBA-15, tin chloride) led to lower selectivities for C-4 sugars due to formation of hexose sugars. In the case of Sn-Beta, VGA is the main product (30 %), illustrating differences in selectivity of the Sn sites in the different frameworks. Under optimized conditions, GA can undergo further conversion, leading to yields of up to 44% of VGA using Sn-MFI in water. The use of Sn-MFI offers multiple possibilities for valorization of biomass-derived GA in water under mild conditions selectively producing C-4 molecules.