Over the past two decades, extensive studies have been conducted to investigate the origin of the high catalytic activity of the TiO2-supported gold nanoparticles (GNPs) to CO oxidation by using experimental or theoretical methods. However, mechanistic details are still incompletely understood. One main issue concerns the active oxygen species in CO oxidation process. In many studies, the adsorbed oxygen molecules are considered as active species rather than the surface lattice oxygen atoms due to the lack of the direct evidence of the oxygen exchange of the TiO2 and CO2. In this study,we present a Born-Oppenheimer molecular dynamics (BOMD) simulation evidence for the generation of oxygen vacancies in the course of CO oxidation. From the BOMD trajectory, the direct visualization of the CO molecule reacting with an adjacent lattice oxygen atom at the Au16-TiO2 interface demonstrates an active role of the surface lattice oxygen atoms, thus confirming the feasibility of the Mars-van Krevelen (M-vK) mechanism. The continued reaction-pathway searching suggests a promising role of M-vK mechanism over Langmuir-Hinshelwood (L-H) mechanism at the Au16-TiO2 interface. Furthermore, a comparative study of the CO oxidation at the golden cage Au18 and TiO2 interface suggests that the L-H mechanism is more favorable than the M-vK mechanism due to higher structural robustness of the Au18 cage. We conclude that the selection of either M-vK or L-H mechanism for the CO oxidation depends primarily on the structural fluxionality of the Au clusters on the TiO2 support. This study confirms an active role of the surface lattice oxygen atoms in CO oxidation over the Au/TiO2 systems as well as providing a better understanding on the selection of the M-vK or the L-H mechanism.

Direct simulation evidence of generation of oxygen vacancies at the golden cage Au16 and TiO2(110) interface for CO oxidation

249th National Meeting (2015)

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