The selective oxidation of ethanol on supported Pd is catalytically promoted by the presence of hydroxide species on the Pd surface as well as in solution. These hydroxide intermediates act as Brønsted bases which readily abstract protons from the hydroxyl groups of adsorbed or solution-phase alcohols. The C1H bond of the resulting alkoxide is subsequently activated on the metal surface via hydride elimination to form acetaldehyde. Surface and solution-phase hydroxide intermediates can also readily react with the acetaldehyde via nucleophilic addition to form a germinal diol intermediate, which subsequently undergoes a second C1H bond activation on Pd to form acetic acid. The role of O2 is to remove the electrons produced in the oxidation reaction via the oxygen reduction reaction over Pd. The reduction reaction also regenerates the hydroxide intermediates and removes adsorbed hydrogen that is produced during the oxidation.
Bibliographical noteFunding Information:
We are grateful to the National Science Foundation for the financial support of this work through the NSF PIRE program (OISE-0730277) and NSF Center for Biorenewable Chemicals (EEC-0813570) and to the Environmental Molecular Science Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory for supercomputing time. We would also like to thank Professor Robert J. Davis, Dr. Bhushan Zope and Ms. Sara Davis for helpful discussions.
- Alcohol oxidation
- Aqueous phase
- Ethanol oxidation
- Solvent effects