The promoting effect of adsorbed carbon monoxide on the oxidation of alcohols on a gold catalyst.

In heterogeneous catalysis and electrocatalysis, adsorbed carbon monoxide typically acts as a poison or poisoning intermediate in the oxidation of alcohols. However, gold as an (electro)catalyst often exhibits unexpected properties. Here we show that carbon monoxide irreversibly adsorbed on a Au(111) surface in aqueous alkaline media can act as a promoter for the electrocatalytic oxidation of certain alcohols, in particular methanol. In comparison with bare Au(111), the onset potential for methanol oxidation is significantly lower in the presence of adsorbed CO, and formation of the main methanol oxidation products--formaldehyde and formic acid--is enhanced. By studying the effect of adsorbed CO on the oxidation of other alcohols on gold, we conclude that the presence of adsorbed CO promotes beta-hydrogen elimination, that is, C-H bond breaking. Apart from its importance to gold catalysis, this is an unanticipated example of promotion effects by co-adsorbed small molecules in electrocatalysis.