Vanadium Oxide Oligomers and Ordered Monolayers Supported on CeO2(111): Structure and Stability Studied by Density Functional Theory

Structures and stabilities of vanadium oxide oligomers as well as two candidate structures for a monolayer on the CeO2(111) surface have been studied by density functional theory, employing a genetic algorithm to determine the global energy minimum structures. These ceria-supported structures have predominantly 4-fold coordinated V5+ ions with V═O groups in common. The agglomeration of VO2 clusters deposited on the surface is a strongly exothermic process, particularly when ring structures with three or six VO2 units are formed that are commensurate with the close-packed surface-terminating oxygen layer. The VO2 and V2O5 monolayers feature larger coordination numbers (5, 6) of V and contain V atoms without V═O groups. Relative to oligomers, VO2 and V2O5 monolayer structures with and without oxygen defects are thermodynamically more stable. This, together with the fact that flat “monolayer” clusters are preferred to taller “bilayer” clusters, indicates the preference for a complete two-dimensional wetting of the ceria support