Insights into the Reactive and Deactivation Mechanisms of Manganese Oxides for Ozone Elimination: The Roles of Surface Oxygen Species.

Manganese oxides with varied Mn valance states but identical morphologies were synthesized via a facile thermal treatment of γ-MnOOH. Also, their catalytic performance on ozone decomposition was investigated following the order of MnO < MnO < MnO < MnO-H-200. In combination with X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), H-temperature-programmed reduction (TPR), O-temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) characterization, it was deduced that the superior O decomposition capacity for MnO-H-200 was strongly associated with abundant oxygen vacancies on its surface. Among MnO, MnO, and MnO, the difference in O decomposition efficiency was dependent on the divergent nature of oxygen vacancy. Density functional theory (DFT) calculation revealed that MnO and MnO possessed lower formation energy of oxygen vacancy, while MnO had the minimum desorption energy of peroxide species (O*). It was deduced that the promotion of the O decomposition capability was attributed to the easier O* desorption. Insights into the deactivation mechanism for MnO-H-200 further validated the assumptions. As the reaction proceeded, adsorbed oxygen species accumulated on the catalyst surface, and a portion of them were transformed to lattice oxygen. The consumption of oxygen vacancy led to the deactivation of the catalyst.