Catalytic Combustion Of Chlorobenzene On Modified LaMnO₃Catalysts

Modified LaMnO3catalysts with perovskite structure prepared by co-precipitation method were tested in the catalytic combustion of chlorobenzene (CB), which was taken as a model of chlorinated aromatics. Their physicochemical properties and redox ability were characterized by XRD、BET、XRF、Ramam、XPS、TG、H2-TPR、O2-TPD. The effect of reaction condition was evaluated and the probable mechanism was put forward. The main results as follow:(1) Well rhombohedral structure of LaMnO3.15can be prepared by co-precipitation method, and the best ratio of substitution is0.2. Different properties were generated from different modification and the best modification is Sr for A site or Al for B site.(2) Main products for CB combustion are COx, H2O, HCI and Cl2. At350(?), a stable activity could be achieved and the order is LSMO>LMAO>L0.8MO>LMO>LMFO. The plots of the stable TOFsa at350(?) vis surface active oxygen species, H2consumption used for the reduction of adsorbed oxygen species and the ratio of surface oxygen to total oxygen are almost proportional. This phenomenon indicates that the improvement of oxygen mobility promotes greatly removal of Cl species. La0.8Sr0.2MnO3catalyst with the largest oxygen mobility and redox ability presents the highest stable activity.(3) For all the samples, CB adsorption on the surface of the catalyst at200(?) would be the rate limiting below500ppm CB concentration. From500up to1000ppm of CB concentration, the reaction is probably limited by the desorption of Cl species. The oxidation of CB can occur on La0.8Sr0.2MnO3catalyst without oxygen and the effect of oxygen concentration is low after the oxygen concentration of2%.