Y-Doped Cu-SSZ-39 Zeolite with Only Cu²⁺-2Z Species: An NH₃-SCR Catalyst with Extremely High Hydrothermal Stability

Copper-exchanged SSZ-39 zeolite catalysts have been proven to be more hydrothermally stable than Cu-SSZ-13 catalysts. However, the synthesis of high-silica SSZ-39 zeolites is still a significant challenge. The excess framework Al in Cu-exchanged Al-rich SSZ-39 catalysts leads to not only severe dealumination during hydrothermal aging but also damage to the SCR-active Cu²⁺ ions by the detached Al. In this work, in-depth knowledge of the stabilization of Al by Y is provided. It was found that the energy needed to break the first Al-O bond is significantly enhanced due to the Y³⁺ located in the eight-membered rings. Additionally, Cu²⁺-2Z and Y have a synergistic effect on the stabilization of the framework Al. The introduction of Y into the Cu-SSZ-39 catalyst with hydrothermally stable Cu²⁺-2Z as the only Cu species remarkably enhanced both the low-temperature activity and the hydrothermal stability. The catalyst maintained excellent deNO_<i>x</i> activity even after hydrothermal aging at the extremely high temperature of 940 °C. Both stable Cu species and stable framework Al are essential for the design of hydrothermally stable Cu-exchanged zeolite catalysts.