Methanol steam reforming(MSR), catalyzed by the PdZn alloy, produces hydrogen gas and carbon dioxide with high selectivity. However, the mechanism for MSR has not been completely elucidated. It has been proposed that formate and methyl formate are possible intermediates in MSR. In this study, plane-wave density functional theory was used to investigate the role of methyl formate in MSR on PdZn. It is shown that methyl formate can indeed be formed by a reaction between formaldehyde and methoxyl. In the presence of surface OH species, methyl formate can further react to form formic acid, which can finally dehydrogenate to produce CO2. However, our calculations show that this hydrolysis process might have difficulties competing with desorption of methyl formate, which is weakly adsorbed on the PdZn surface. Our calculated results thus suggest a minor role for the methyl formate pathway in MSR. Interestingly, the methyl formate reaction pathway shares many similarities with the same process on copper, which is the traditional catalyst for MSR. The insights gained by studying the reaction mechanism on these two surfaces shed valuable light on designing future catalysts for the MSR process. (C) 2012 Elsevier B.V. All rights reserved.