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

The adsorption of O-2 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 (O-2(delta-)), which directly interacted with Cu, formed when O-2 adsorbed on the surface oxygen vacancies, while O-2 adsorbed on the subsurface oxygen vacancies gave rise to ozone-like O-3(delta-) species by combining with the nearest surface lattice oxygen (O1). PDOS showed that hybridization of the 2p orbitals between O-2 and O1 formed a delocalized pi bond, confirming the formation of O-3(delta-). For O-2(delta-), electrons on Cu and O1 transferred to O-2 while the charge of Ce remained unchanged. However, for O-3(delta-), 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 O-3(delta-). The findings of this study provide new insight on the CO oxidation reaction mechanism, facilitating an in-depth understanding of Cu-doped CeO2 catalysts.