The impact of CrOx loading on reaction behaviors of dichloromethane (DCM) catalytic combustion over Cr-O/HZSM-5 catalysts

A series of HZSM-5 supported CrO x catalysts at different loadings were prepared by wet impregnation method for catalytic combustion of dichloromethane (DCM) in this paper. The catalytic activity tests indicated that both DCM conversion and product selectivity varied greatly with Cr doping contents. The sample at 2   wt% loading showed the highest DCM conversion, while the selectivity toward CO/CO 2 increased at an elevated CrO x loading. The characterization results revealed that the surface acidity and the chemical states of Cr were strongly affected by the doping content. The surface acidity would decline at an elevated Cr loading owing to the interactions between surface OH groups and chromium ions. And higher surface Cr(VI)/Cr(III) ratios could be observed on the catalysts at lower CrO x doping, leading to the improvement of reducibility. The activity and selectivity of DCM catalytic degradation were found to be highly depended on the balance of surface acidity and redox property. The increased surface acidity could result in the enhancement of dissociated adsorption of DCM, which are beneficial to the catalytic activity. However, higher surface acidity meant lower Cr loading, which might lead the adsorbed intermediates incompletely oxidized and the decrease in CO x selectivity due to the limit redox ability.