Impact of hydrothermal aging on SO₂-deactivation of Cu-CHA catalysts for NH₃-SCR

SO₂ poisoning and hydrothermal aging are two major deactivation mechanisms limiting the long-term performance of Cu-CHA catalysts for NH₃-SCR of NO_x. SO₂ deactivates Cu sites and water exposure at high temperatures leads to loss of Brønsted acid sites and structural degradation. We study how the mechanism of SO₂-deactivation is affected by hydrothermal aging using activity measurements, NH₃-TPD, and NO-temperature-programmed reaction. NH₃-TPD measures the number of Brønsted acid sites, whereas the NO-temperature-programmed reaction probes the amount of [Cu₂(NH₃)₄O₂]²⁺ species, which is a key intermediate in the SCR-reaction. Exposure to SO₂ results in a 60-70% loss of activity for both fresh and hydrothermally aged catalysts, indicating that the mechanism of sulfur-induced deactivation is largely independent of prior hydrothermal aging. Furthermore, hydrothermal aging prior to SO₂ exposure reduces the possibility of catalyst regeneration, primarily due to irreversible hydrothermal deactivation.