Aromatic Alcohols as Model Molecules for Studying Hydrogenolysis Reactions Promoted by Palladium Catalysts

The hydrogenolysis reaction of aromatic alcohols (benzyl alcohol, 1-phenylethanol and diphenylmethanol), promoted by supported palladium catalysts, such as Pd/TiO2, Pd/SiO2 and Pd/Co3O4, has been investigated at 0.1 MPa H2 and 323 K. The catalysts have been characterized by BET, TPR, XRD, TEM and XPS. A different kinetic behaviour was observed: in presence of Pd/ TiO2 and Pd/SiO2 catalysts, prepared by impregnation, the hydrogenolysis activity follows the order benzyl alcohol > 1-phenylethanol ≥ diphenylmethanol, whereas it is totally reversed on Pd/Co3O4, prepared by co-precipitation. All results indicate that the reactivity of supported Pd catalysts, in the hydrogenolysis reaction, depends on the support nature, the preparation method of catalysts and the aromatic alcohols structure. Kinetic experiments carried out at different partial hydrogen pressure allow to elucidate the pathway of the C-OH bond scission, involving a radical substitution of the carbon bonded OH group by a hydrogen atom coming from the metal surface "via" associative and dissociative paths.