A Mössbauer study of In–Fe2O3/HZSM-5 catalysts for the selective catalytic reduction of NO by methane

The selective catalytic reduction of NO by CH4 was compared over In–Fe2O3/HZSM-5 catalysts prepared by impregnation and co-impregnation methods. It was found that the catalyst preparation method greatly affected the catalyst activity. The impregnated catalyst was very active, but the co-impregnated one showed poor activity. The In–Fe2O3/HZSM-5 catalysts were investigated by Mössbauer spectroscopy. The results showed that indium cations entered into the iron oxide lattice in the co-impregnated catalyst, while the impregnated catalyst exhibited a more stable structure, when both of the catalysts were treated severely in the reaction atmosphere. Characterization by means of combined in situ temperature programmed reduction (TPR)-Mössbauer spectroscopy further revealed that the performances of the two catalysts were different in the TPR processes.