A comparative study of the activity and hydrothermal stability of Al-rich Cu-SSZ-39 and Cu-SSZ-13

Abstract

Catalysts Al-rich Cu-SSZ-39 and Cu-SSZ-13 are applied in ammonia selective catalytic reduction (NH3-SCR) reaction for NOx removal. Al-rich Cu-SSZ-39 maintained its excellent NH3-SCR activity even after hydrothermal aging at 850 ℃ for 16 h, whereas Al-rich Cu-SSZ-13 lost its deNOx activities completely when subjected to the same conditions. The main reason is that the active Cu2+ species are more stable in the structure of Cu-SSZ-39, because SSZ-39 zeolite contained more paired framework Al, leading to that Cu-SSZ-39 catalysts have more hydrothermally stable Cu2+-2Z species as compared to Cu-SSZ-13, and this makes Cu-SSZ-39 accumulate less CuOx during hydrothermal aging. In addition, the framework Al in SSZ-39 is more stable than that in SSZ-13, and a great amount of Cu2+-2Z species coordinated with paired framework Al in Cu-SSZ-39, which leaves fewer residual uncoordinated Al sites. Moreover, SSZ-39 has a more tortuous channel structure than SSZ-13 does. This inhibits the detached Al(OH)3 from exiting the pores of the AEI zeolite framework, which would result in reincorporation of Al(OH)3 into the framework when cooling down. Therefore, the Al-rich Cu-SSZ-39 with large amounts of stable paired Al shows a competitive potential candidate as an NH3-SCR catalyst for NOx elimination in practical applications.