(14c) Excellent Hydrothermal Stability of Composite Catalyst Based on Two Cu-CHA Type Molecular Sieves

The hybrid catalysts consisting of Cu-SSZ-13 and Cu-SAPO-34 are designed to investigate the synergistic effect on the hydrothermal stability of Cu-SSZ-13. The Cu-SSZ-13 and Cu-SAPO-34 synthesized with one-pot method were physically mixed, and the weight ratio of the Cu-SSZ-13/Cu-SAPO-34 were 9:1, 7:3 and 1:1. Both the single catalyst and the composite were hydrothermal treated in 10 vol. % H₂O/air at 750 °C for 16 h. NH₃-SCR activity shows that the composite sample with the weight ratio of 1/1 exhibits a significantly enhanced hydrothermal stability compared with the single-component catalysts under the same test condition. Textural characterization results show that hydrothermal treatment leads to the collapse of Cu-SSZ-13 framework, while negligibly degenerate effect on framework of the composite is observed. The structure collapse of aged Cu-SSZ-13 is ascribed to the dealumination. However, Cu-SAPO-34 in the composite impedes the dealumination of Cu-SSZ-13 during hydrothermal aging treatment as proved by the ²⁷Al MAS NMR and NH₃-TPD results. EPR results reveal that a larger content of isolated Cu²⁺ remains in the composite after hydrothermal treatment compared with that in the aged Cu-SSZ-13, which are consistent with the H₂-TPR results. ²⁷Al NMR and ³¹P NMR results show that extra-framework P atoms in SAPO-34 transfer to certain sites and connect with the partially bonded framework Al of SSZ-13 during the hydrothermal process, maintaining the framework of Cu-SSZ-13. A large amount of Brønsted acid sites and Cu²⁺ species remained contribute to the excellent SCR performance of the aged composite. This work provides a new simple way to improve the hydrothermal stability of Cu-SSZ-13 and indicates that the SAPO-34 may provide the fragment to stabilize Cu-SSZ-13 during the aging process.