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 NOx. 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.