Vapor phase hydrodeoxygenation and hydrogenation of m-cresol on silica supported Ni, Pd and Pt catalysts

Abstract

Hydrodeoxygenation of m-cresol (a model compound of lignin derived phenolics in bio-oil) has been studied on silica supported Ni, Pd and Pt catalysts at 250°C and atmospheric pressure. Hydrogenation (to 3-methylcyclohexanone and 3-methylcyclohexanol) and hydrodeoxygenation (to toluene) are the primary reactions over all catalysts. The intrinsic hydrogenation activity follows the order of Ni<Pd<Pt, and the deoxygenation activity follows the order of Ni≪Pd≈Pt. The oxygen removal is mainly through a direct deoxygenation (DDO) route. The hydrogenation–deoxygenation (HYD) route is not important due to the lack of acidic sites to catalyze dehydration and a rather low hydrogenolysis activity of the C–OH bond of 3-methylcyclohexanol. At high conversions, the initial hydrogenation products are reversely dehydrogenated to m-cresol, making the deoxygenation to toluene and its subsequent hydrogenation to methylcyclohexane the major pathway. In general, increasing reaction temperature suppresses the hydrogenation reaction but promotes the hydrodeoxygenation as well as C–C bond hydrogenolysis. On Pd and Pt, increasing temperature improves deoxygenation to toluene over the C–C bond hydrogenolysis. In contrast, higher temperature favors the successive C–C hydrogenolysis to produce the low value methane on Ni.