Heterogeneous palladium catalysts for the oxidation of propylene to propylene glycol acetates: effect of platinum and rhodium as promoters

摘要

Supported Pt catalysts show high activity and selectivity for liquid phase oxidation of propylene with dioxygen to propylene glycol (PG) and its acetates (PGA) in acetic acid solutions of nitric acid at 60 deg C and 0.1 MPa. The catalyst stability depends strongly on the promoter and support nature. The promoter effect of Pt and Rh has been studied. The promotion of Pd catalysts with Pt improves the efficiency of the reductive regeneration. The carbon supported Pd-Pt catalysts can be effectively reactivated many times, unlike Pd and Pd-Rh ones, and show higher activity and higher stability towards metal leaching and poisoning under the reaction conditions. Using X-ray photoelectron spectroscopy and X-ray phase analysis there have been studied the surface properties as well as the elemental and phase composition of the Pd-Pt and Pd-Rh catalysts during their use in the PG and PGA synthesis. It has been found that one of the main reasons for the beneficial effect of Pt on the catalyst properties is the ability of the surface Pt(0) species to activate molecular hydrogen and their stability under the reaction conditions.