Role of Cryptomelane in Surface-Adsorbed Oxygen and Mn Chemical Valence in MnOx during the Catalytic Oxidation of Toluene

A series of manganese oxide catalysts were prepared via a coprecipitation method by adjusting the molar ratio of Mn(NO3)(2)/KMnO4 and used to catalyze the oxidation of toluene. The MnOx catalyst prepared by the Mn(NO3)(2)/KMnO4 ratio of 3:7 showed the best catalytic activity, and more than 90% conversion was obtained at 238 degrees C. The superior catalytic activity of MnOx could be attributed to its slightly higher specific surface area and better pore size distribution. Furthermore, more surface-adsorbed oxygen and Mn3+ species provided more oxygen vacancies, which could increase the ability of oxygen migration, resulting in the improvement of the redox performance and catalytic activity, which depended on the Mn(NO3)(2)/KMnO4 ratios. Importantly, the formation of cryptomelane (KMn8O16) contributed greatly to the toluene catalytic oxidation ability and CO2 selectivity.