Direct Oxidative Esterification of Propionaldehyde to Methyl Propionate Using Heavy-metal-free Palladium Catalysts under Pressurized Oxygen

Abstract

The use of pressurized oxygen greatly enhanced catalytic activity for oxidative esterification of propionaldehyde to methyl propionate with methanol using heavy-metal-free Pd/C and Pd/Al₂O₃. For example, the conversion of propionaldehyde, the selectivity to methyl propionate, and the yield of the propionate using 5 % Pd/Al₂O₃ were 99.9, 62.7, and 62.6 %, respectively, at 1.5 MPa of oxygen gas and 333 K. This result demonstrated that Pb doping of Pd catalysts was not needed to achieve comparable activity, which runs contrary to previous reports, in which it had been suggested that loading of Pd catalysts using a heavy metal such as Pb was needed for the great activity such as 93.2, 76.8, and 71.6 % of the conversion of propionaldehyde, the selectivity to methyl propionate, and the yield of the propionate, respectively, at 0.3 MPa of oxygen gas and 353 K using 5 % Pd/Al₂O₃ doped with 5 % Pb.