Enhanced resistance to calcium poisoning on Zr-modified Cu/ZSM-5 catalysts for the selective catalytic reduction of NO with NH3

Abstract

Ca/ZrCu/ZSM-5 catalysts containing different Zr contents were prepared by incipient wetness impregnation. The catalysts were tested for the selective catalytic reduction (SCR) of NO_x with ammonia and characterized by N₂-BET, N₂O titration, XRD, NH₃-TPD, H₂-TPR, and XPS techniques. In the temperature range of 100–170 °C, after calcium impregnation, NO_x conversion over the Cu/ZSM-5 catalyst decreased by 11.3–24.3%, while that over Zr_0.10/Cu/ZSM-5 only decreased by 3.8–12.2%. The improvement of the calcium poisoning resistance of the ZrCu/ZSM-5 catalyst is mainly attributed to an increase in the dispersion and the surface concentration of Cu. Moreover, the addition of zirconium promotes the reduction of CuO by decreasing the interaction between CuO and CaO, which also contributes to the improvement of resistance to CaO poisoning. The apparent activation energy and turnover frequency for the SCR reaction over the Ca/Zr_xCu/ZSM-5 catalysts were calculated and discussed.