Catalytic Dehydration of Glycerol to Acrolein over ZSM-5 Zeolites: Synergistic Effect of Pore Structure and Aluminum Distribution

Abstract

The catalytic dehydration of glycerol to acrolein offers a sustainable route for efficiently utilizing low-cost and renewable bioglycerol. This work deeply explores glycerol dehydration to acrolein over ZSM-5 zeolite catalysts with various pore structures and aluminum distributions. The results reveal that glycerol conversion is enhanced through the construction of a mesoporous structure and the increase in Brønsted acid sites of the catalysts, but acrolein selectivity is not directly related to these factors. Further characterizations, density functional theory calculation, kinetic study, and reaction mechanism analysis demonstrate that the richest Al_single sites in the zeolite framework and the least Al_pair sites in the straight and sinusoidal channels can prevent the generated acrolein from adsorbing on adjacent Al sites. This allows acrolein to immediately escape from the catalyst surface, reducing side reactions and enhancing its selectivity. Therefore, the synergistic between the mesoporous structure and more Al_single sites in the ZSM-5 zeolite framework promotes acrolein yield. Additionally, a descriptor φ, reflecting the amount of Al_single sites and the external specific surface area of the ZSM-5 zeolite, is first proposed to more clearly elucidate the structure–performance relationship. This study provides a new perspective for understanding the mechanism of catalytic dehydration of glycerol to acrolein, guiding the development of highly efficient catalysts. It is significant for the sustainable development of the biodiesel and acrolein production industry.