Influence of Co-Cations on the Performance and Hydrothermal Stability of Cu/SSZ-13 Catalysts 2020-01-1317
This research focuses on co-cations modified Cu-zeolite catalyst CuCe/SSZ-13. The NOx conversion and hydrothermal stability of fresh and aged Cu/SSZ-13 and 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 225 °C to 600 °C, and showed higher NOx conversion below 225 °C and above 450 °C than Cu/SSZ-13. For aged catalysts, CuCe/SSZ-13 exhibited higher efficiency at all test temperatures than Cu/SSZ-13, and exhibited over 80% conversion at 225 °C to 350 °C, whereas, that was only 250 °C to 300 °C over fresh Cu/SSZ-13 sample. Furthermore, the effect of co-cation Ce on the phase structure changes, acid sites, redox capacity, transformation of various Cu species, and framework stability of the samples were evaluated by several techniques, such as TPD, TPO, TPR, BET, and XRD. For the fresh samples, co-cation Ce decreased the amount of CuxOy species, increased Cu2+ sites, and weakened interactions between CHA framework and Cu ions resulting in strong reducibility of active sites. After hydrothermal aging, CuCe/SSZ-13 remained the structural integrity of CHA framework, and had the less formation of CuO species, more active sites, and more total pore volume than sample without Ce addition. Furthermore, in situ DRIFTS indicated that, with addition of co-cation Ce, the formation of more monodentate nitrates adsorbed sites resulted in excellent SCR performance. Ce species also decreased the formation of N2O at low temperatures through decreasing excess nitrate adsorbed sites. In conclusion, modification by Ce could increase the NOx conversion and stability of Cu/SSZ-13 catalyst.