On the mechanism of the preferential oxidation of carbon monoxide over Cu n Pd (n = 3–12) catalysts

Preferential oxidation of CO (CO-PROX) is an important practical process for the purification of H2 for use in proton exchange membrane fuel cells. In order to clarify the mechanism of CO-PROX, the reaction promoted by Cu n Pd (n = 3–12) clusters has been studied by density functional theory calculations. The CO-PROX reaction via carboxylic and hydroxyl intermediates is found to be the most likely mechanism. The theoretical results show that CO oxidation is promoted by the attack of surface OH groups, which is different from the usual oxidation of CO with O2. The Cu6Pd cluster is predicted to have a lower activation barrier compared with other Cu n Pd clusters and is therefore proposed as the most effective nanocatalyst. To gain insights into the high catalytic activity of the Cu n Pd nanoparticles, the nature of the interaction between adsorbate and substrate has been analyzed by the detailed electronic local density of states. The results should be helpful in developing efficient catalysts for the CO-PROX reaction.