Credit: © 2009 Wiley

The research effort to understand the reactivity of gold has intensified since recent studies revealed that it can act as an efficient heterogeneous catalyst. The oxidation of alcohols has been suggested as one possible use of catalytic gold — providing an environmentally benign alternative to current methods that use heavy-metal salts as oxidizing agents — but its development requires a more detailed understanding at the molecular scale. Now, Cynthia Friend and colleagues at Harvard University have uncovered important mechanistic information about methanol oxidation over gold that leads to the formation of the ester product methyl formate1.

The reaction of methanol with adsorbed oxygen — derived from ozone — on a gold surface was investigated using temperature-programmed reaction spectroscopy and vibrational high-resolution electron energy-loss spectroscopy. These complementary studies show that the reactions are initiated by a Brønsted acid–base reaction between surface-adsorbed oxygen atoms and the hydrogen atom of the OH group, and that the ester is formed after cleavage of a methoxy C–H bond.

Because the reactive surface oxygen takes part in reaction initiation, product selectivity can be tuned by controlling the surface oxygen coverage. Higher oxygen coverage results in oxygen–gold bonding configurations that do not lead to production of methyl formate, thus low oxygen surface coverage increases the selectivity for methyl formate.