Physisorbed, Chemisorbed, and Oxidized CO on Highly Active Cu−CeO₂(111)

Abstract

With the use of the DFT+U method, the properties of Cu adsorbed on the stoichiometric CeO 2 (111) surface, Cu-doped CeO 2 (111) (denoted as Cu 0.08 Ce 0.92 O 2 ) surface, and CO oxidation on the stoichiometric Cu 0.08 Ce 0.92 O 2 surface are studied systematically. It is found that (i) Cu is stable both as an adsorbed atom on the surface and as dopant in the surface region. Cu adsorbed at the surface is Cu(+I) while Cu as a dopant atom is Cu(+II). (ii) The Cu dopant facilitates O-vacancy formation considerably, while Cu adsorption on the stoichiometric CeO 2 (111) surface may suppress oxygen vacancy formation. (iii) Physisorbed CO, physisorbed CO 2, as well as chemisorbed CO (carbonate) species are observed on the Cu-doped CeO 2 (111) surface, in contrast, on the clean ceria(111) surface, only physisorbed CO was previously observed. C−O distances, adsorption energies, and surface-induced C−O vibrational frequency shifts were used to characterize these species.