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

• Published in: Journal of catalysis 2013-11, Vol.307, p.111-120
• Main Authors: Griffin, Michael B., Rodriguez, Abraham A., Montemore, Matthew M., Monnier, John R., Williams, Christopher T., Medlin, J. Will
• Format: Article
• Language: English
• Subjects: 1,2-Propanediol; Antifreeze solutions; Bimetallic; Catalysis; Catalysts; Catalytic oxidation; chemical bonding; Chemistry; Electroless deposition; Ethylene glycol; Exact sciences and technology; General and physical chemistry; Glycerol; Glycolic acid; Gold; isotopes; Lactic acid; Metals; oxidation; Palladium; Rate-limiting step; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; thermodynamics; X-ray photoelectron spectroscopy
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2013.07.012

Bimetallic PdAu catalysts prepared by electroless deposition were found to exhibit superior activity for oxidation of ethylene glycol and 1,2-propanediol compared to either pure metal. The rate-determining step was C–H scission for both Au and PdAu catalysts. •Ethylene glycol and 1,2-propanediol were oxidized on Pd, Au, and Au–Pd catalysts.•Enhanced oxidation rates were observed on the bimetallic catalysts.•Rate enhancements result from decreased poisoning and lower activation barriers.•C–H bond scission is the rate-limiting step. 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.