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 Mn 3 O 4 < Mn 2 O 3 < MnO 2 < MnO 2 -H-200. In combination with X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), H 2 -temperature-programmed reduction (TPR), O 2 -temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) characterization, it was deduced that the superior O 3 decomposition capacity for MnO 2 -H-200 was strongly associated with abundant oxygen vacancies on its surface. Among Mn 3 O 4, Mn 2 O 3, and MnO 2, the difference in O 3 decomposition efficiency was dependent on the divergent nature of oxygen vacancy. Density functional theory (DFT) calculation revealed that Mn 3 O 4 and MnO 2 possessed lower formation energy of oxygen vacancy, while MnO 2 had the minimum desorption energy of peroxide species (O 2 *). It was deduced that the promotion of the O 3 decomposition capability was attributed to the easier O 2 * desorption. Insights into the deactivation mechanism for MnO 2 -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.