Effect of Si/Al ratio on the SCR active sites of Cu/SSZ-13
QIN Xuan1, YIN De-jia1, YU Li-ze1, ZHANG Tao1, CHANG Hua-zhen1, ZHU Yan1, LIU Guo-hua1, LI Jun-hua2
1. School of Environment&Natural Resource, Renmin University of China, Beijing 100872, China;
2. School of Environment, Tsinghua University, Beijing 100084, China
Cu/SSZ-13catalysts with different Si/Al ratio were prepared by a solid-state ion exchange method, which were used for selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction. Various characterization methods, including X-ray diffraction (XRD), temperature programmed reduction with H2 (H2-TPR), temperature programmed desorption (TPD) of NOx, temperature programmed desorption (TPD) of NH3, and in situ diffuse reflectance FTIR spectroscopy (in situ DRIFTS), were used to elucidate the different catalytic performance over these Cu/SSZ-13catalysts. Compared with Cu/SSZ-13(25) and Cu/SSZ-13(5), Cu/SSZ-13(10) showed relatively superior SCR activity, with more than 80% NO conversion between 200 and 450℃. The XRD and H2-TPR results suggested that Si/Al ratio could influence the dispersion of Cu species and redox property of Cu/SSZ-13 catalysts. The XRD and H2-TPR results indicated that there were the most isolated Cu2+ ions existed in Cu/SSZ-13(10). Cu2+ ions could provide NOx-adsorbed sites and Lewis acid sites over Cu/SSZ-13, which mainly account for its low-temperature SCR activity. However, the NO conversion of Cu/SSZ-13(25) decreased obviously in the whole temperature range, due to the significant loss of Lewis acid sites.
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