Active Site Identification for Glycerol Hydrodeoxygenation over the Oxygen Modified Molybdenum Carbide Surface

Abstract

Density functional theory and microkinetic reactor modeling were used to investigate the hydrodeoxygenation (HDO) mechanism of glycerol on the oxygenated Mo2C catalyst surface to understand the activity and product selectivity under practically relevant reaction conditions. Reactor simulations with multiple active site models predicted that a fully oxygenated surface with acid–base (OH,O) pairs is active for glycerol dehydration and it can selectively cleave one C–O bond to produce 3-hydroxypropanal (HPA). The acid sites are not directly involved in the C–O bond scission process; however, surface oxygen vacancy formation is promoted in the presence of acid sites. The rate-limiting C–O bond cleavage process occurs on the exposed Mo sites with a concerted β-hydrogen transfer to the nearest conjugate base (Mo–O) via an E2 elimination mechanism. Dehydration of HPA to acrolein was observed at longer residence times. Our analysis revealed that reaction conditions, such as temperature and partial pressure of H2, can be tuned to promote further deoxygenation of HPA and acrolein to produce propanal and propylene.