Catalytic oxidation of toluene over MnO2 catalysts with different Mn (II) precursors and the study of reaction pathway

MnO2-Ac, MnO2-N, MnO2-Cl and MnO2-S samples were prepared by the redox reaction between potassium permanganate and manganese acetate, manganese nitrate, manganese chloride and manganese sulfate and the effect of Mn (II) precursor on the toluene oxidation was studied. The physicochemical properties of these samples were characterized by XRD, TEM, N-2 asdorption-desorption isotherms, H-2-TPR and XPS. Results showed that the catalytic activity of the four samples decreased in the order of MnO2-Ac > MnO2-N > MnO2-Cl > MnO2-S, which was highly related to the specific surface areas, oxygen vacancy concentration and the content of adsorbed oxygen. MnO2-Ac owned potential for practical applications. It showed superior toluene oxidation activity with T90 of 200 degrees C, as well as excellent water-resistance and stability during 50 h at 300 degrees C. The good catalytic activities under high WHSV and high toluene concentration were also observed over MnO2-Ac. Moreover, the reaction pathway of toluene oxidation was presented with the aid of In-situ DRIFTS.