Novel metal loaded KIT-6 catalysts and their applications in the catalytic combustion of chlorobenzene

A series of metal-loaded mesoporous silica catalysts, M/KIT-6 (M = Mn, Cu, Fe, Cr, Sn), were prepared by incipient-wetness impregnation method, and tested in the catalytic combustion of chlorobenzene (CB) as a model of chlorinated aromatics. The effects of metal oxide species and concentration on the textural structure and catalytic properties were studied in detail. It was found that the dispersion, specific surface area and reducibility are the main factors influencing the catalytic activity. On the basis of T50 (temperature at which 50% conversion is attained), the catalytic activity for the CB degradation decreases in the following order: Mn/KIT-6 > Cr/KIT-6 > Cu/KIT-6 > Fe/KIT-6 > Sn/KIT-6, correlating with the redox properties of the catalysts. Mn/KIT-6 catalysts having different molar ratios of Mn/Si were found to possess high catalytic activity for catalytic combustion of CB. Among these, Mn3/KIT-6 was the most active catalyst, for which the complete combustion temperature (T90) of chlorobenzene was 210.7 °C. By increasing the Mn/Si molar ratio to 1/2, T90 was raised to 238.5 °C. This is due to the decrease of pore volume and specific surface area caused by increase in the amount of Mn in the channels of KIT-6, increased agglomeration of Mn, and the lowering of Oads/(Olatt + Oads + Owat) concentration ratio. Conversion of CB over the Mn3/KIT-6 catalyst was maintained at 90% or more for 1000 min, indicating the excellent stability of this catalyst.