The selective oxidation of ethylene glycol and 1,2-propanediol on Au, Pd, and Au–Pd bimetallic catalysts

The oxidation of ethylene glycol (HOCH2CH2OH) and 1,2-propanediol (HOCH(CH3)CH2OH) was investigated over Pd/C, Au/C, and a series of bimetallic catalysts prepared by electroless deposition of Au onto Pd/C. In order to explain the enhanced activity of the bimetallic catalysts, the oxidation kinetics of selectively deuterated reagents were investigated. On Au/C and 0.61Au–Pd/C, a primary kinetic isotope effect was observed for d4-ethylene glycol (HOCD2CD2OH), indicating that C–H bond scission is the rate-limiting step. Density functional theory and X-ray photoelectron spectroscopy experiments show a correlation between an increased electron density in Au core orbitals and more favorable thermodynamics for C–H scission as Au is added to Pd. Computational studies suggest that the rate enhancement on the bimetallic surfaces compared to Pd is likely due to a decrease in coverage of strongly bound adsorbates, while the enhancement over Au is likely due to a decrease in the barrier for C–H scission.