CO oxidation over Au/TiO2 catalysts has attracted interest due to its high activity at low temperature. Au/TiO2 is also a prototypical system for studying the synergistic effects at the interface between metal nanoparticles and oxide supports. Here, we employ density function theory to gain insight into several important yet elusive issues on this catalytic system, including the active oxygen species, the mechanism of catalyst deactivation and regeneration, and the effects of moisture. We found that O2 can be easily activated at the interface boundary, which leads to an oxidized interface. CO interacts strongly with the oxidized interface to form an Au carbonyl (O-Au+-CO) species. Moreover, the oxidized interface also activates lattice oxygen in TiO2 as a result of electron transfer from Ti3+. Adsorbed CO molecules can subsequently react with lattice oxygen in the support following the Mars van-Krevelen mechanism, with a low barrier of 0.4 eV. The resulting surface oxygen vacancy could be filled with a dissociating O2 molecule, however this is a highly activated process with a barrier of 1.1 eV. In addition, a stable carbonate species (CO3) forms on the TiO2 support as a result of CO2 adsorption on active oxygen atoms adsorbed atop Ti atoms, which would lead to catalyst deactivation. Our calculations show that both difficulties can be overcome by introducing water in the reactant feed. For O2 activation, the barrier for O-O bond splitting is lowered by 0.4 eV as a result of OOH formation, and CO3 can be converted to bicarbonate species (CO3H) which significantly reduces the CO2 desorption barrier from 1.5 eV to 0.6 eV.

Theoretical insights on CO oxidation over Au/TiO2: A comprehensive picture of active sites, catalysts deactivation and moisture effects

254th National Meeting (2017)

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