Promotion of the performance of Cu-SSZ-13 for selective catalytic reduction of NO_x by ammonia in the presence of SO₂ during high temperature hydrothermal aging

The influence of SO₂ presence during high temperature hydrothermal aging (600, 700, and 800 °C) on the performance of Cu-SSZ-13 prepared by the conventional ion-exchange method for selective catalytic reduction of NO_x by NH₃ (NH₃-SCR) was studied. The high-temperature activity of Cu-SSZ-13 is obviously enhanced by the SO₂ presence for the 700 and 800 °C-aged samples and is not hampered for the 600 °C-aged sample. The presence of SO₂ during hydrothermal aging has no influence on the framework Al. The interaction of Cu²⁺ with SO₂ results in the formation of ZCuHSO₄, which helps suppress the aggregation of Cu²⁺ into CuO and maintain more isolated Cu²⁺, leading to higher activity at high temperatures. The low Cu content yields higher relative population of Cu²⁺ species at more stable sites. The low-temperature (≤350 °C) activity is slightly lowered for the 600 and 700 °C-aged samples.