Hydrodeoxygenation of cresols over Mo/Al2O3 and CoMo/Al2O3 and CoMo/Al2O3 sulfided catalysts

Abstract

The hydrodeoxygenation (HDO) of cresol isomers was investigated at 340 °C under 4 MPa over Mo/Al2O3 and CoMo/Al2O3 sulfided catalysts. Over both catalysts, the reactivity of cresols followed the order: m-cresol > p-cresol > o-cresol. These phenolic compounds were converted by two deoxygenation routes. The desired direct deoxygenation (DDO) route, leading to toluene, was strongly promoted by cobalt. On the contrary, the HYDrogenation route (yielding methylcyclohexenes and methylcyclohexane) was favored over Mo/Al2O3 and practically not affected by the presence of cobalt. To explain the formation of these deoxygenated products, the participation of different kinds of active sites such metal-decorated edge and brim-model was suggested. Thus, we proposed a reaction mechanism involving a schematic CoMoS active site which allowed to explain (i) the highest reactivity of m-cresol by the involvement of a stabilized cationic intermediate and (ii) the lowest reactivity of o-cresol, ascribed to a steric hindrance of methyl group during the initial tautomerization step.