Effect of Structure and Substituents in the Aqueous Phase Oxidation of Alcohols and Polyols Over Au, Pd, and Au–Pd Catalysts

Abstract

Reactivity trends for oxidation of various alcohols and polyols have been examined for carbon-supported Au, Pd, and Au–Pd catalysts. A Hammett σρ approach was used to study substituent effects, with Hammett factors (ρ) of 1.27, 1.31, and 0.40 obtained for Pd, Au, and Au–Pd catalysts, suggesting the formation of a net negative charge at the transition state of the rate limiting step. The lower ρ for the Au–Pd catalyst versus Au and Pd monometallic catalysts indicates the ability of the Au–Pd catalyst to stabilize the negative charge at the transition state, explaining the improved performance of Au–Pd bimetallic catalysts for alcohol oxidation. Hammett–Taft factors were used to explain the low selectivity of terminal diols and polyols to diacids.