Structure of CoOₓ Thin Films on Pt(111) in Oxidation of CO

The combination of noble Pt group metals and reducible metal oxides has been extensively studied and demonstrated to display superior catalytic properties in low-temperature CO oxidation or preferential CO oxidation reactions. Here, we investigate CoOₓ films and nanoislands on Pt(111) as inverse model catalysts for CO oxidation, in order to shed light on the nature of the O species in CoOₓ that participate in CO oxidation. Through temperature-programmed desorption, scanning tunneling microscopy, and X-ray photoelectron spectroscopy of carefully prepared and atomically defined CoOₓ film structures on Pt(111), we study the changes in the oxide structure upon interaction with CO and reoxidation in O₂. The combined approach reveals structural motives representing both reversibly and irreversibly reduced forms of the oxide after CO oxidation. Overall, a remarkably facile release of lattice oxygen compared to the isostructural thin-film islands supported on Au(111) underlines the attractive properties as a CO oxidation catalyst system, ascribed to the synergy between the oxide film and Pt(111). We also conclude that bilayer Co–O structures, reflecting Co in a low oxidation state, facilitate the CO oxidation at lower temperatures compared with fully oxidized CoO₂ trilayers. This surprisingly points to a more facile O release from the bilayer structures.