SO2 Poisoning, Regeneration, and Impact on Dimer-Cu Intermediates in the NH3-SCR Reaction over Cu-Zeolites

This study demonstrates that Al-rich, high-Cu-loaded Cu-SSZ-13 exhibits superior resistance to SO2 poisoning under actual SCR conditions. The high Cu content mitigates the risk of SO2-induced structural degradation. A key finding is that lower regeneration temperatures can lead to more severe secondary poisoning, while high temperatures induce hydrothermal aging. Thus, controlling the regeneration temperature is critical for maintaining long-term catalyst stability. Additionally, experimental results and DFT calculations show that SO2 preferentially reacts with dimer-Cu species, especially hydrogenated dimer-Cu ([CuII2(NH3)4(OH)O]+), resulting in significant sulfate accumulation. This interaction inhibits the redox cycle of Cu+/Cu2+, thereby suppressing low-temperature activity. Overall, this work elucidates the mechanisms of SO2-induced deactivation in Cu-zeolite SCR catalysts and provides valuable insights into designing Cu-SSZ-13 catalysts with enhanced sulfur resistance through Cu-Al co-optimization.