New insights into the NH3-SCR activity and SO2 resistance of Cu-SSZ-13 catalysts prepared by different methods†

Abstract

The Cu loading and Cu species in Cu-SSZ-13 catalysts, which are very important for the NH₃-SCR activity and hydrothermal stability, are usually affected by the method of introducing Cu. However, when the Cu loading was carefully controlled at the same level in this study, it was found that the preparation methods, including the novel impregnation method (NIM), solid-state ion exchange method (SSIE), and liquid ion exchange (IE), did not affect the hydrothermal stability of the prepared Cu-SSZ-13, since the [Cu(OH)]⁺–Z species converts to Cu²⁺–2Z during the hydrothermal aging process. Thus, all aged Cu-SSZ-13 catalysts possessed the same NH₃-SCR activity. The SO₂ resistance of a Cu-SSZ-13 catalyst is related to the Cu species present in the catalyst. Sulfated Cu-SSZ-13 850 catalysts (calcined at 850 °C) containing only Cu²⁺–2Z outperformed sulfated Cu-SSZ-13 550 catalysts (calcined at 550 °C) containing both [Cu(OH)]⁺–Z and Cu²⁺–2Z, since Cu²⁺–2Z species can maintain their SCR activity as Cu²⁺ ions while [Cu(OH)]⁺–Z do not. The NIM and SSIE methods proposed by our group can significantly reduce the time and capital needed to synthesize Cu-exchanged zeolite catalysts, compared with IE. Combining the NIM (or SSIE) method with high-temperature calcination, Cu-SSZ-13 catalysts possessing excellent hydrothermal stability and SO₂ resistance simultaneously can easily be synthesized.