SEMINAR: Yaping Li [Georgia Southern University]
Effects of Hydrogen Coverage and Water on Hydrogenation of o-Cresol on Pt(111)
Feb 5, 2019 11:00 AM to Feb 5, 2019 12:00 PM at Building8-241
Biofuels derived from lignocellulosic biomass have received significant attention lately due to environmental concerns and energy needs. Hydrogenation of phenolics is a process to upgrade crude bio-oil. With first-principles density functional theory and ab initio molecular dynamics simulations, we investigated effects of hydrogen coverage and water on hydrogenation of o-cresol on Pt(111).
At a low hydrogen coverage (1/25 ML), dissociation of H in the OH group involves a low barrier, which results in the formation of the intermediate product 2-methyl-cyclohexanone after hydrogenation of the aromatic ring. Hydrogenations of o-cresol without dissociation of H in the OH group can generate the final product 2-methyl-cyclohexanol directly. At a high hydrogen coverage (1 ML), although the first step of hydrogenation is endothermic, the activation energy is reduced. All the following hydrogenation steps leading to the formation of intermediate and final products involve exothermic reactions and low barriers. These theoretical results agree well with the experimental observations.
In an aqueous phase, the hydrogen from the hydroxyl group dissociates into water and a hydronium is formed. Water plays a dual role of accelerating the rate of hydrogenation of these ketones by shuttling hydrogen from the surface while also decreasing the rate of desorption of the less polar ketone intermediate from the catalyst surface. These two effects, when combined, explain the lack of observation of these ketone intermediates from experimental work.