Influence of Framework n(Si)/n(Al) Ratio on the Nature of Cu Species in Cu-ZSM-5 for NH3-SCR-DeNO(x)

Nanosized Cu-containing ZSM-5 catalysts with different n(Si)/n(Al) ratio of 18.9-50.5 were prepared by ion-exchange. The physico-chemical characterization clearly shows that the molar ratio of framework T atoms influences the nature and distribution of copper species. According to DR UV-Vis, TPR-H-2, EPR, or FT-IR spectroscopy analyses, the amount of aggregated copper species increases with increasing the framework n(Si)/n(Al) ratio. Thus, the activity of the Cu-containing ZSM-5 with n(Si)/n(Al) ratio of 47.0-50.5 in the selective catalytic NO reduction with NH3 (NH3-SCR-DeNO(x)) significantly decreases compared to the other materials (n(Si)/n(Al) ratio of 18.9-19.6). The reaction mechanism has been discussed in light of the results of 2D COS (two-dimensional correlation spectroscopy) analysis of IR spectra and catalytic properties of the zeolites. The results make evident that enhanced activity of Cu-containing ZSM-5 in NH3-SCR-DeNO(x) is correlated with the formation of different NOx- under the experimental conditions.