Insights into the full cycling of oxygen in VOCs oxidation on a-MnO2: A NAP-XPS study

a-MnO2-based catalysts are promising materials for VOC oxidation, and understanding how oxygen participates in the reaction is crucial for further improving its catalytic performance. Despite providing many insightful results, oxygen vacancy characterization cannot fully explain the oxygen cycling process, giving sometimes contradictory interpretations. In this paper, NAP-XPS was utilized to investigate the work function and element valence of catalyst surface under reaction conditions. Along with DFT calculation, EELS, and specially designed O2-TPD characterization, we further demonstrated that generating oxygen vacancies will lead to a decrease in the average valence state of Mn elements from Mn4+ to less active Mn3+. Activity data of various VOCs suggest that generating a large number of oxygen vacancies could not enhance the activity of all types of VOC; as for toluene oxidation, replenishing gas-phase oxygen into the bulk phase is also important. This work provides a novel way to explore the metal oxides' material exchange properties between its surface and gaseous oxygen and paves the way for the rational development of novel and versatile VOC oxidation catalysts.