Influence of co-cations on the performance and hydrothermal stability of Cu/SSZ-13 catalysts 2020-01-1317
NH3-SCR technology is a promising method to remove NOx in diesel emission control systems, and Cu/SSZ-13 has been widely used as NH3-SCR catalyst. However, regulatory requirements for higher performance and thermal durability lead to the limitation for further application of Cu/SSZ-13 catalyst. This study focuses on co-cations modified Cu-zeolite catalyst CuCe/SSZ-13. The SCR performance and hydrothermal stability of fresh and aged CuCe/SSZ-13 were evaluated to conclude the impact of Ce on the zeolite stability and mechanism of NH3-SCR reaction. For fresh samples, CuCe/SSZ-13 exhibited more than 80% efficiency at 210 ℃ to 600 ℃, and showed higher NOx conversion below 225 ℃ and above 450 ℃ than Cu/SSZ-13. For aged catalysts, CuCe/SSZ-13 exhibited higher efficiency at all test temperatures than Cu/SSZ-13, and showed more than 80% NOx conversion at 225 ℃ to 375 ℃, whereas, that was only 250 ℃ to 320 ℃ for Cu/SSZ-13.The effect of co-cation Ce on the physicochemical structure, acidity, oxidation capacity, Cu species migration, and framework stability of the fresh and aged samples were comprehensively characterized by NH3-TPO, H2-TPR, NH3-TPD, BET, and XRD. For the fresh samples, co-cation Ce promoted SCR performance of CuCe/SSZ-13 through increasing acid sites and inhibiting ammonia oxidation. After hydrothermal aging, CuCe/SSZ-13 had the less formation of CuO species, more active sites, more total pore volume, and remained the majority of surface adsorption and reaction sites than Cu/SSZ-13. Furthermore, in situ DRIFTS indicated that, with the addition of co-cation Ce, more active copper sites and adsorbed surface nitrate resulted in excellent SCR performance. Ce ions may replace H ions of Si-O(H)-Al bond to decrease the amount of dealumination sites, inhibiting acid sites hydrolysis reaction. In conclusion, modification by Ce could improve the SCR performance and hydrothermal stability over Cu/SSZ-13 catalyst.
Han Jiang, Bin Guan, Xuesong Peng, Yanfei Wei, Xinling Li, Lei Zhu, Lei Shi, Reggie Zhan, He Lin, Zhen Huang