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

Density functional theory and microkinetic reactor modelingwereused to investigate the hydrodeoxygenation (HDO) mechanism of glycerolon the oxygenated Mo2C catalyst surface to understand theactivity and product selectivity under practically relevant reactionconditions. Reactor simulations with multiple active site models predictedthat a fully oxygenated surface with acid-base (OH,O) pairsis active for glycerol dehydration and it can selectively cleave oneC-O bond to produce 3-hydroxypropanal (HPA). The acid sitesare not directly involved in the C-O bond scission process;however, surface oxygen vacancy formation is promoted in the presenceof acid sites. The rate-limiting C-O bond cleavage processoccurs on the exposed Mo sites with a concerted beta-hydrogen transferto the nearest conjugate base (Mo-O) via an E-2 eliminationmechanism. Dehydration of HPA to acrolein was observed at longer residencetimes. Our analysis revealed that reaction conditions, such as temperatureand partial pressure of H-2, can be tuned to promote furtherdeoxygenation of HPA and acrolein to produce propanal and propylene.