Paper SS2-MoM3
The Oxidation of Benzyl Alcohol on Gold and its Implications Towards a Gold-Mediated Conversion of Hydrocarbons

Monday, October 31, 2011, 9:00 am, Room 110

In order to understand alcohol conversion on gold, we have explored the mechanism of the oxidation of benzyl alcohol (C₆H₅-CH₂OH) on a Au(111) surface - a test reaction commonly used to determine the efficiency and selectivity of novel gold-based catalysts. Using adsorbed atomic oxygen as the active oxidizing species, we find that a high selectivity towards the conversion to aldehyde (benzaldehyde, C₆H₅-CHO) is achieved at low oxygen coverages. However, in excess oxygen the selectivity decreases dramatically, and benzaldehyde is readily transformed to adsorbed benzoate, which is eliminated as benzoic acid (C₆H₅-COOH) and CO₂. In addition, we show that the production of the ester produced by self-coupling (benzyl benzoate) does not require the separate presence of acid, as might be expected from acid-alcohol condensation reactions. These surface transformations are extremely facile and exhibit small kinetic barriers of the rate-limiting steps. Lastly, by comparing the mechanism of benzyl alcohol oxidation to that of toluene oxidation, we extract information of a model hydrocarbon-to-alcohol reaction (toluene to benzyl alcohol, C₆H₅-CH₃ to C₆H₅-CH₂OH). Our results suggest that due to the relatively large kinetic requirements for toluene conversion, the alcohol cannot be selectively produced on a gold surface; indeed, preliminary TPRS data indicates that the gold-mediated conversion of toluene yields benzoic acid and combustion gases.