Mechanismic studies on the selective reduction of NO by CH4 over an In/HZSN-5 catalyst

CH4 oxidations in CH4 + O-2, NO + CH4 (+O-2) and NO2 + CH4 (+O-2) reaction systems over the catalyst of indium impregnated on HZSM-5 (In/HZSM-5) were studied. The efficacies of O-2, NO and NO2 for CH4 oxidation were evaluated. The dramatically different conversions of CH, in these different reaction systems suggested that NO2 played a key role in CH4 conversion. TPD studies of CH4, O-2, NO and NO2 on HZSM-5 and In/HZSM-5 were also investigated. It was found thar only NOx could absorb on the samples and the chemisorbed amount of NO2 was much larger than that of NO. This illustrated that the absorbed NO2 species were very important in the CH4-SCR process. Our TPD results and IR results from the literatures both indicated that not only the acid sites but also the In sites in the In/HZSM-5 catalyst facilitated the formation of NO2. Moreover, the reaction between NO2 and CH4 took place on the In sites.