(464d) Mechanistic Studies of Direct Hydrodeoxygenation of M-Cresol over WOx-Decorated Pt Catalysts

Hydrodeoxygenation (HDO) is required for the upgrading of the aromatic oxygenates that are derived from the lignose fraction of biomass. This has motivated research on the development of catalysts that are active for the hydrogenolysis of the C-O bonds in these molecules. In this talk I will describe our recent work in this area on the development of WO_x-decorated Pt/C catalysts that exhibit unusually high selectivity for the HDO of m-cresol to produce toluene. In contrast to Pt/C which exhibits only modest activity for this reaction, produces a range of products in which the ring has been hydrogenated, and is prone to deactivation due to coking, Pt-WO_x/C was found to be highly active with a selectivity to toluene in excess of 94% while exhibiting little to no deactivation under a wide range of reaction conditions.Reactivity studies in combination with density functional theory (DFT) calculations indicate that the HDO reaction on Pt-WO_x/C proceeds via a direct hydrogenolysis of the C-O bond in m-cresol adsorbed on oxygen vacancy (or redox) sites on the supported WO_xspecies. Complimentary to the reactivity studies of high surface area catalysts, X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREEL), and temperature-programmed desorption (TPD) were used to study the structure and reactivity of model WO_x/Pt(111) catalysts as a function of the WO_x coverage. These studies showed that interactions of at the Pt-WO_x interface alters the redox properties of the tungsten oxide and help stabilize it in a partially reduced state thereby providing adsorption sites for the m-cresol via the hydroxyl oxygen, a result that is also predicted by DFT.