CO Oxidation at the Au/TiO2Boundary: The Role of the Au/Ti5cSite

Abstract

Density functional theory is used to determine the reaction mechanisms of CO oxidation and the active oxygen species on a Au/TiO2 model catalyst. The model consists of a Au rod supported along the TiO2 [11̅0] direction of the TiO2(110) surface. An interfacial Au/Ti5c site at the interface boundary is identified to be particularly active toward O2 adsorption and dissociation. At this site, O2 dissociation has an energy barrier of 0.5 eV, which is facile at room temperature. The resulting adsorbed Au/O/Ti5c oxygen species are shown to be stable and active for CO oxidation under relevant reaction conditions with an activation energy of 0.24 eV. Furthermore, the adsorbed Au/O/Ti5c oxygen species functions as an electron reservoir, and it lowers the oxygen vacancy formation energy of a surface lattice oxygen (Obri), as well as the Ti interstitial formation energy, due to electron transfer from high-energy defect states to low-energy p-states of the adsorbed Au/O/Ti5c oxygen species. Hence, the Obri species is activated at the oxidized Au/TiO2 interface boundary and the energy barrier of CO oxidation with Obri is calculated to be 0.55 eV. Thus, the CO oxidation reaction can proceed at room temperature either via a Langmuir–Hinshelwood mechanism with an adsorbed Au/O/Ti5c oxygen species or via a Au-assisted Mars–van Krevelen mechanism with Obri.