Promotional effect and mechanism of the modification of Ce on the enhanced NH3-SCR efficiency and the low temperature hydrothermal stability over Cu/SAPO-34 catalysts

Abstract

Abstract This study focuses on co-cations modified copper based molecular sieve catalyst CuCe/SAPO-34. The SCR performance and low temperature hydrothermal stability of Cu/SAPO-34 and CuCe/SAPO-34 before and after 70 ℃ hydrothermal aging were evaluated to conclude the impact of Ce on the structure stability and mechanism of NH3-SCR reaction. For fresh samples, CuCe/SAPO-34 showed higher catalytic activity at the whole temperature range, especially below 250 ℃ and above 400 ℃ in comparison to pure Cu/SAPO-34. For aged catalysts, CuCe/SAPO-34 exhibited higher efficiency at below 400 ℃ than Cu/SAPO-34, and showed more than 80 % NOx conversion at 175 ℃ to 450 ℃ , whereas, that was only 225 ℃ to 450 ℃ for Cu/SAPO-34. The effect of co-cation Ce on the physicochemical structure, acidity, redox capacity, Cu species migration, and framework stability of the fresh and aged samples were comprehensively characterized by NH3-TPO, NO-TPO, H2-TPR, NH3-TPD, BET, XRD and XPS. For the fresh samples, the addition of co-cation Ce decreased the amount of CuxOy species, increased Cu2+ sites, and improve the redox ability of active sites. After low temperature hydrothermal aging, CuCe/SAPO-34 remained the structural integrity of CHA framework. Ce species protected copper ions and prevented the dealumination in the process of aging. Furthermore, in situ DRIFTS indicated that, with the Ce doping, more active copper sites and monodentate nitrates adsorbed sites formed, resulting in excellent SCR performance and stability. In conclusion, modification by Ce could improve the SCR performance and low temperature hydrothermal stability of Cu/SAPO-34 catalyst.