We have used density functional theory to investigate the adsorption and oxidation of CO on the Mo doped Pt(111) surface to provide an insight into the interaction between CO and doped metal surface, an important issue in CO oxidation, and also in promotion and poisoning effects of catalysis. The NEB method was applied to find the minimum energy path for the oxidation process and the electronic structure was analyzed to give an explanation for why the alloy surface is a better catalyst for this reaction than the corresponding elemental surfaces. (c) 2006 Elsevier B.V. All rights reserved.