A DFT + U study of CO oxidation at CeO2(110) and (111) surfaces with oxygen vacancies

Density functional theory calculations corrected by on-site Coulomb interaction have been conducted to illuminate the effect of O vacancies on the surface reactivities toward direct CO oxidation at CeO2(110) and (111). CO adsorption at and further reaction with various surface O at the vacancy were systematically calculated, and extensive geometric and electronic analyses were also performed to understand the calculation results. It has been shown that though the existence of O vacancy can reduce the activities of neighboring O as the barriers of elementary steps are generally higher than those at stoichiometric surfaces, the relative preference for CO2 desorption is also increased due to the missing of nearby O for carbonate formation. Moreover, our calculation results also showed that the characteristic localized 4f orbitals/electrons of Ce still play the key role in determining the surface reactivities as the vacancy induced localized electrons can hinder their further occurrence and the corresponding reactions.