CO Oxidation Mechanisms on CoO_x-Pt Thin Films

The reaction of CO and O₂ with submonolayer and multilayer CoO_x films on Pt(111), to produce CO₂, was investigated at room temperature in the mTorr pressure regime. Using operando ambient pressure X-ray photoelectron spectroscopy and high pressure scanning tunneling microscopy, as well as density functional theory calculations, we found that the presence of oxygen vacancies in partially oxidized CoO_x films significantly enhances the CO oxidation activity to form CO₂ upon exposure to mTorr pressures of CO at room temperature. In contrast, CoO films without O-vacancies are much less active for CO₂ formation at RT, and CO only adsorbed in the form of carbonate species that are stable up to 260 °C. On submonolayer CoO_x islands, the carbonates form preferentially at island edges, deactivating the edge sites for CO₂ formation, even while the reaction proceeds inside the islands. These results provide a detailed understanding of CO oxidation pathways on systems where noble metals such as Pt interact with reducible oxides.