Mechanistic study of the catalytic conversion of 2,3-butanediol to butenes

Abstract

The reaction kinetics of 2,3-butanediol (2,3-BDO) and other key intermediates, including methyl ethyl ketone (MEK), 2-methylpropanal, acetoin, 2-butanol and 2-methyl-1-propanol, were investigated over acidic zeolites (ZSM-5, and Y-type zeolite), Cu/ZSM-5, Cu/Y and Cu/SiO2 to elucidate the roles of acid and metal sites in the process of hydrodeoxygenation of 2,3-BDO to butene. Hydrogenation and dehydrogenation reactions occur on Cu sites, while dehydration reactions take place on acid sites. At low space time, 2,3-BDO can readily be converted to acetoin by dehydrogenation over supported Cu catalysts, however, with increasing space time, the formed acetoin is hydrogenated back to 2,3-BDO. DFT (density functional theory) calculations suggest that the cage structure of Y zeolite allows the formation of larger Cu clusters, potentially blocking acid sites and preventing access of C4 alcohols (2-butanol, 2-methyl-1-propanol) to the acid sites for dehydration. This effect results in lower selectivity to butenes over Cu/Y than on Cu/ZSM-5.