Oxygen vacancies and alkaline metal boost CeO2 catalyst for enhanced soot combustion activity: A first-principles evidence

Abstract The molecular-level oxidation mechanism of graphene-type soot was systematically explored at the soot/CeO2(111) interface with and without oxygen vacancies (Ovac) by first-principles calculations. It was found to follow the Mars-van Krevelen mechanism on stoichiometric CeO2(111), but the low reactivity of lattice oxygen (Olat) results in a limited activity for oxidizing the most-inert edge-CH. By contrast, the molecular O2 species trapped by Ovac on reduced CeO2(111) exhibits a much superior reactivity to eliminate edge-CH, which can trigger subsequent inner-C oxidation to proceed easily. These results explicitly evidence the boosting role of Ovac and clarify the reduced CeO2, rather than the stoichiometric one, playing a more critical role for soot combustion in reality. Notably, increasing the initial surface Ovac concentration or decreasing Ovac formation energy to activate Olat are unambiguously proposed as effective optimization strategies for CeO2. Moreover, a long puzzle on the promotor effects of alkaline K+ on CeO2 was rationalized.