CO oxidation on bimetallic Re-Pt clusters: unraveling the role of oxygen coverage.

ReOx and PtOx clusters are able to catalyze CO oxidation under mild pressure and temperature conditions. One possible way of designing novel catalysts with enhanced activity is to form bimetallic alloys. Here, we present a systematic theoretical study of the oxidation of RexPty clusters (x + y = 5) and their performance as catalysts for CO oxidation. Re-rich clusters reach high oxygen saturation levels, with up to 16 adsorbed oxygen atoms under standard reaction conditions, with a tendency to form interconnected ReO3 and ReO4 units. In contrast, Pt-rich clusters maintain some Pt-Pt bonds, with the amount of oxygen adsorbed decreasing steadily with increasing Pt concentration. Comparing reaction mechanisms for oxidized and unoxidized clusters, a superior catalytic performance for CO oxidation is found for the oxidized clusters, due to both a weaker interaction with CO and to a less stable nature of the adsorbed CO2 reaction intermediate. Finally, strong changes in reactivity are found with varying Re:Pt stoichiometry. The most active cluster is Re4Pt1O12, which can catalyze the reaction even at low temperatures, while the Re3Pt2O12 and Re2Pt3O12 clusters require higher temperatures for similar performance. These results provide insight into the oxidation of metal clusters on a subnanometer scale and their potential use as catalysts for the CO oxidation reaction.