Investigation of the mechanism of the selective hydrogenolysis of C-O bonds over a Pt/WO3/Al2O3 catalyst

The hydrogenolysis of various polyols and ethers over a Pt/WO3/Al2O3 catalyst was investigated. The hydrogenolysis rate of a C-O bond at a secondary carbon was higher than that at a primary carbon, indicating that a hydroxyl (OH) group at a primary carbon played an important role in the dissociation of a C-O bond. Moreover, the dissociation position of the C-O bond in alcohols and ethers strongly depended on the stability of the carbocation intermediate, and hydrogenolysis via a secondary carbocation as an intermediate proceeded preferentially to that via a primary carbocation. The kinetics of the hydrogenolysis of C-3 polyols were also investigated. The reaction orders with respect to the concentrations of glycerol, 1,2- and 1,3-propanediol were almost the same. In contrast, different reaction orders with respect to the H-2 pressure were observed for the hydrogenolysis of C-3 polyols with or without vicinal OH groups, indicating that the dissociation of a C-O bond at primary and secondary carbons proceeded via completely different mechanisms. These investigations suggested that both the structure and position of a substrate on the catalyst surface must be controlled for highly selective hydrogenolysis.