Effect of Cu loading and addition of modifiers on the stability of Cu/ZSM-5 in lean NOx reduction catalysis

The stability of Cu/ZSM-5 catalysts of different Cu loadings or modified by addition of Na, La, or Ce was studied in lean NOx reduction. Samples were characterized by H-2-TPR, EPR and XRD before and after deactivation. Increasing the Cu loading above 68% of the exchange capacity improved the stability, as did La addition, presumably because these decreased the concentration of protons which were instrumental in the dealumination of the ZSM-5 framework. Addition of Ce had little effect, because CeO2 was formed and thus did not compete with protons for exchange sites. Addition of Na decreased the stability, because it promoted the formation of inactive CuO particles; in addition, migration of Cu2+ to a different coordination environment also seemed to contribute to the catalyst deactivation.