Insight into SO₂ poisoning and regeneration of one-pot synthesized Cu-SSZ-13 catalyst for selective reduction of NO_x by NH₃

The effects of SO₂ on an one-pot synthesized Cu-SSZ-13 catalyst for selective reduction of NO_x by NH₃ were examined. The addition of SO₂ inhibited NO_x conversion significantly below 300 °C, while no effect on NO_x conversion was observed above 300 °C. TGA, TPD, and XPS results showed that the deactivation was caused by the formation of (NH₄)₂SO₄, SO₂ chemisorption on the isolated Cu²⁺ ion sites, as well as the formation of CuSO₄-like species. Among them, the site-blocking effect of (NH₄)₂SO₄ on Cu²⁺ was the primary reason for deactivation. Fortunately, 89% of deNO_x activity of the poisoned catalyst was recovered after thermal treatment at 500 °C in air, where (NH₄)₂SO₄ was completely decomposed. The activity was further recovered with regeneration temperature increasing to 600 °C, removing the adsorbed SO₂ on the Cu²⁺ sites. The regeneration at 600 °C could not recover the activity completely, because of the high stability of CuSO₄-like species.