Competition and Cooperation of Hydrogenation and Deoxygenation Reactions during Hydrodeoxygenation of Phenol on Pt(111)

Abstract

A combined experimental and density functional theory computational study was performed to understand the reaction mechanism of hydrodeoxygenation of phenol on the Pt(111) surface. Partial hydrogenation of phenyl ring reduces the barrier of deoxygenation. The intermediate formed by adding 5 H atoms to the phenyl ring and with α-C adsorption on Pt is identified as the key intermediate responsible for the formation of different products with mild barriers: deprotonating the hydroxyl to cyclohexanone at 0.38 eV, hydrogenation at α-C to cyclohexanol at 0.56 eV, and deoxygenation at 0.76 eV followed by dehydrogenation to benzene. Microkinetic parameter analysis indicates that the hydrogenation steps are fast and reversible while deoxygenation steps are slow and almost irreversible, which is consistent with the experimental observation that hydrogenation products are the major primary products at low conversions while deoxygenation product dominates at high conversions, at 523 K and ambient H2 pressure. H2 pressure plays an essential role on surface coverage of H and available adsorption sites, modulating the competition between hydrogenation and deoxygenation reactions and, thereby, the product distributions.