Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH₃-SCR

The NH₃-SCR activities and hydrothermal stabilities of five xCu/MCM-22 zeolites with different Cu loadings (x = 2-10 wt%) prepared by incipient wetness impregnation method were systematically investigated. The physicochemical properties of xCu/MCM-22 zeolites were analyzed by XRD, nitrogen physisorption, ICP-AES, SEM, NH₃-TPD, UV-vis, H₂-TPR and XPS experiments. The Cu species existing in xCu/MCM-22 are mainly isolated Cu²⁺, CuO and unreducible copper species. The concentrations of both isolated Cu²⁺ and CuO species in xCu/MCM-22 increase with Cu contents, but the increment of CuO species is more distinct, especially in high Cu loadings (>4 wt%). NH₃-SCR experimental results demonstrated that the activity of xCu/MCM-22 is sensitive to Cu content at low Cu loadings (≤4 wt%). When the Cu loading exceeds 4 wt%, the NH₃-SCR activity of xCu/MCM-22 is irrelevant to Cu content due to the severe pore blockage effects caused by aggregated CuO species. Among the five xCu/MCM-22 zeolites, 4Cu/MCM-22 with moderate Cu content has the best NH₃-SCR performance, which displays higher than 80% NO conversions in a wide temperature window (160-430 °C). Furthermore, the hydrothermal aging experiments (xCu/MCM-22 was treated at 750 °C for 10 h under 10% water vapor atmosphere) illustrated that all the xCu/MCM-22 zeolites exhibit high hydrothermal stability in NH₃-SCR reactions.