Exploring an efficient manganese oxide catalyst for ozone decomposition and its deactivation induced by water vapor

Abstract

A series of MnO_x catalysts supported by carbon spheres were prepared by calcining mixtures of manganese acetate and carbon spheres under a nitrogen atmosphere, and their performance for ozone decomposition under high humidity conditions (RH = 90%) was evaluated. The calcination temperature and the ratio of manganese acetate to carbon spheres have significant influences on the catalytic stability of Mn/C catalysts for ozone decomposition. Among all the Mn/C catalysts, the 1Mn/3C-900 catalyst showed the most robust catalytic stability (ozone conversion remaining 100% after 6 h) under high humidity conditions (RH = 90%). The size of MnO_x particles on the surface of the Mn/C-900 catalyst increased gradually from 18 nm to 74 nm with the increase of MnO_x loading, which would lead to the change of the oxygen vacancy density and Mn²⁺ content of MnO_x species. The 1Mn/3C-900 catalyst with a MnO_x particle size of 26 nm exhibited the highest surface oxygen vacancy density and Mn²⁺ content of MnO_x species on the surface, and thus the most stable activity was observed on the 1Mn/3C-900 catalyst. The high catalytic activity of the 1Mn/3C-900 catalyst remained for even 70 h under dry conditions. However, the significant deactivation of the 1Mn/3C-900 catalyst was observed in the presence of both gaseous ozone and water vapor (RH = 90%). Besides the competitive adsorption of water vapor on active sites, the obvious decrease of oxygen vacancy density and Mn²⁺ content on the catalyst surface induced by water vapor during the reaction should also be responsible for remarkable deactivation.