Identification of Active Sites in Pt-Co Bimetallic Catalysts for CO Oxidation

Identifying the active sites of catalysts under working conditions is crucial for precise understanding of reaction mechanisms and rational design of catalysts. However, the nature of active sites of bimetallic catalysts for CO oxidation is still a subject of debate. Herein, we employ in situ X-ray absorption and infrared spectroscopy to monitor the realistic structures of active centers in a bimetallic Pt-Co/Al2O3 catalyst during CO oxidation. This catalyst brings 100% CO conversion at room temperature and 30-fold higher turnover frequency than monometallic Pt/Al2O3 catalysts. The in situ studies reveal that under the CO oxidation condition, a fraction of Co atoms are segregated from the PtCo alloy into the surface CoO species that decorates the remaining PtCo nanoparticles through direct Pt-O-Co interfacial bonds. The bond-valence analysis unravels one dangling Co-O coordination per Co2+ in the surface CoO, which acts as the active sites for O-2 activation. The synergy between the CoO species and the PtCo alloy brings the superior catalytic activity. We also show that the directly connected Pt-O-Co interface is more beneficial to the catalytic performance than the unconnected Pt-CoO interface and provides a promising strategy toward the design of advanced catalysts for the redox reaction.