Inert-Atmosphere Regeneration of Sulfur-Poisoned Cu/SSZ-13 Catalysts Unexpectedly Enhances Low-Temperature NH₃-SCR Activity Beyond the Fresh Catalyst

Nitrogen oxide (NOx) emissions pose a persistent environmental threat due to their adverse impacts on air quality, climate, and human health. Among current control strategies, Cu-exchanged SSZ-13 (Cu/SSZ-13) catalysts are widely recognized for their excellent low-temperature NH3-SCR activity and hydrothermal stability. However, their real-world performance is limited by sulfur poisoning, which deactivates active Cu sites through the formation of Cu-S species. Previous regeneration methods often result in incomplete recovery due to the formation of stable sulfates and/or insufficient redispersion of active Cu ions. In this study, we demonstrate that regeneration of sulfur-poisoned Cu/SSZ-13 in an inert atmosphere (Ar) at 800 °C can effectively prevent the oxidation of metastable Cu-S species into stable sulfate species while also promoting the decomposition of Cu-S species, thereby enabling a more complete recovery and redistribution of Cu ions into the zeolite framework. What is particularly noteworthy is that this regeneration method not only recovers the catalyst's functionality but also leads to a significant enhancement in low-temperature NH3-SCR efficiency, outperforming the fresh catalyst. Advanced microscopic and spectroscopic analyses reveal that this enhancement is associated with increased formation of [ZCu2+(OH)]+ species located in the 8-membered rings of SSZ-13, which are known to be the most active sites for low-temperature NH3-SCR.