Effect of Cu loading and addition of modifiers on the stability of Cu/ZSM-5 in lean NO_x 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 NO_x reduction. Samples were characterized by H₂-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.