Density Functional Theory Study of Active Oxygen at the Perimeter of Au/TiO2Catalysts

Abstract

In spite of numerous efforts, the nature of active oxygen generated at the perimeter of Au/TiO2 catalysts remains elusive; e.g., it is unclear whether the active species is atomic or molecular oxygen. Using plane-wave density functional theory (DFT) and rutile (110)-supported Au rod models, we have examined various oxygen species for their stability and reactivity to CO. Our calculation finds that O2 attached endon to a pentacoordinate Ti site (Ti5c) as well as to the Au perimeter (Ti-OO-Au) is a transient state, turning into states with both O attached to Ti5c. The latter are quite stable (< −1.5 eV) without O vacancies and bonding with the Au perimeter. The stability of O2 on Ti5c improves with increasing Au/oxide contact area per O2 because the contact is the origin of electrons used in adsorbing and activating O2. Even O–O bond dissociation between two Ti5c sites is probable at low O2 concentration. Both O and O2 on Ti5c readily react with CO, although the adatom is rather unreactive to CO(g). The act...