Insights into the Sintering Resistance of Sphere-like Mn2O3 in Catalytic Toluene Oxidation: Effect of Manganese Salt Precursor and Crucial Role of Residual Trace Sulfur

Abstract

Manganese oxides, as a highly active oxidation catalyst, are expected to have great potential for replacing platinum group material (PGM) in volatile organic compound (VOC) degradation. Manganese sulfate and manganese chloride are usually adopted as raw materials for catalyst preparation, and Cl– and SO42– adsorbed on the catalyst might affect the catalytic activities. In this study, sphere-like Mn2O3 was prepared from different manganese sources with a simple carbonate precipitation method, which was further used to systematically study the potential poisoning effect of residual trace species on the catalytic activity of toluene oxidation. The fully washed samples all show excellent toluene oxidation activity at the beginning; however, both chloride- and sulfate-derived samples exhibited unexpected severe inactivation after the thermal aging treatment, and the light-off temperature (T90) of toluene oxidation increased by more than 116 and 252 °C, while this value is only 65 and 40 °C over nitrate- and acetate-derived Mn2O3, respectively. The characterization results of ICP-OES and XPS demonstrated that the incorporated traced sulfur and chloride species existing in fresh samples were difficult to wash away completely, which has little influence on the catalytic performance of fresh samples but will greatly affect their anti-sintering behavior. During the thermal aging process, doped sulfur gradually forms uniformly dispersed sulfate that will cover on the catalyst surface, where the transports of reactants and the supplementary lattice oxygen would be restrained significantly.