Tuning the high-temperature hydrothermal stability of one-pot derived Cu-SSZ-13 in the presence of SO₂ for selective catalytic reduction of NO_x by ammonia

The high temperature hydrothermal stability in the presence of SO₂ of the one-pot synthesized Cu-SSZ-13 was investigated for selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). The uncalcined samples were treated with HNO₃ (pH = 1.0–1.1) with different duration (3, 6, and 9 h) and then calcined, finally subjected to 750 ^oC hydrothermal aging without/with the presence of SO₂. Various characterization results indicate that different duration of HNO₃ treatment results in dealumination but has almost no effect on the distribution of Al and Si species. In contrast, it leads to difference in the content of Cu species and finally in their distribution. The 6 and 9 h samples contain higher content of more stable Cu species, which contribute to the high hydrothermal stability in the presence of SO₂. H₂-temperature programmed reduction (H₂-TPR) is a powerful technique to reveal the properties of Cu-SSZ-13; the reduction behavior at lower temperatures (Cu²⁺ → Cu⁺) determines the NH₃-SCR activity whilst the case at higher temperatures (Cu⁺ → Cu⁰) determines the high-temperature hydrothermal stability in the presence of SO₂. This work demonstrates that the hydrothermal stability of Cu-SSZ-13 in the presence of SO₂ can be tuned by engineering the distribution of Cu species via post HNO₃ treatment.