Catalytic oxidation of chlorobenzene on supported manganese oxide catalysts

Total oxidation of chlorinated aromatics on supported manganese oxide catalysts was investigated. The catalysts have been prepared by wet impregnation method and characterized by XRD and TPR. Among the catalysts with the supports of TiO2, Al2O3 and SiO2, titania-supported catalyst (MnOx/TiO2) gives the highest catalytic activity. MnOx/TiO2 (Mn loading, 1.9 wt.%) shows the total oxidation of chlorobenzene at about 400°C. The activity can be stable for over 82 h except for the first few hours. At lower Mn loadings for MnOx/TiO2, only one reduction peak appears at about 400°C due to the highly dispersed manganese oxide. With the increase of Mn loading, another reduction peak emerges at about 500°C, which is close to the reduction peak of bulk Mn2O3 at 520°C. TPR of the used catalyst is totally different from that of the fresh one indicating that the chemical state of the active species is changed during the chlorobenzene oxidation. The characterization studies of MnOx/TiO2 showed that the highly dispersed MnOx is the precursor of the active phase, which can be converted into the active phase, mainly oxychlorinated manganese (MnOyClz), under working conditions of chlorobenzene oxidation.