The critical role of water at the gold-titania interface in catalytic CO oxidation

• Published in: Science (American Association for the Advancement of Science) Vol. 345; no. 6204; pp. 1599 - 1602
• Main Authors: Saavedra, Johnny, Doan, Hieu A., Pursell, Christopher J., Grabow, Lars C., Chandler, Bert D.
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 26-09-2014; The American Association for the Advancement of Science
• Subjects: Activation; Carbon monoxide; Catalysts; Catalytic oxidation; Chemical reactions; Cobalt; Gold; Infrared spectroscopy; Kinetics; Oxidation; Reaction kinetics; Spectroscopy; Titanium dioxide; Water
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1256018

We provide direct evidence of a water-mediated reaction mechanism for room-temperature CO oxidation over Au/TiO₂ catalysts. A hydrogen/deuterium kinetic isotope effect of nearly 2 implicates O-H(D) bond breaking in the rate-determining step. Kinetics and in situ infrared spectroscopy experiments showed that the coverage of weakly adsorbed water on TiO₂ largely determines catalyst activity by changing the number of active sites. Density functional theory calculations indicated that proton transfer at the metal-support interface facilitates O₂ binding and activation; the resulting Au-OOH species readily reacts with adsorbed Au-CO, yielding Au-COOH. Au-COOH decomposition involves proton transfer to water and was suggested to be rate determining. These results provide a unified explanation to disparate literature results, clearly defining the mechanistic roles of water, support OH groups, and the metal-support interface.