Formation of superoxide and ozone-like species on Cu doped CeO2(111) and their CO oxidation reactivity: a DFT study

Abstract

The adsorption of O₂ on Cu/CeO₂(111) and the CO oxidation reactivity of the formed oxygen species were studied using the DFT method. The results showed that superoxide species (O₂^δ−), which directly interacted with Cu, formed when O₂ adsorbed on the surface oxygen vacancies, while O₂ adsorbed on the subsurface oxygen vacancies gave rise to ozone-like O₃^δ− species by combining with the nearest surface lattice oxygen (O1). PDOS showed that hybridization of the 2p orbitals between O₂ and O1 formed a delocalized π bond, confirming the formation of O₃^δ−. For O₂^δ−, electrons on Cu and O1 transferred to O₂ while the charge of Ce remained unchanged. However, for O₃^δ−, the transferred electrons were mainly from O1, and partially from O2, Ce1 and Ce2. It was very interesting that Cu also received a few electrons in the latter case. Compared with CO directly adsorbed on lattice oxygen, the two oxygen species were active for CO oxidation, forming CO₂ or carbonates, and higher absolute adsorption energy was obtained with the interaction between CO and O₃^δ−. The findings of this study provide new insight on the CO oxidation reaction mechanism, facilitating an in-depth understanding of Cu-doped CeO₂ catalysts.