The Effects of SO ₂ and SO ₃ Poisoning on Cu/Zeolite SCR Catalysts

Copper/zeolite catalysts are the leading urea SCR catalysts for NOx emission treatment in diesel applications. Sulfur poisoning directly impacts the overall SCR performance and is still a durability issue for Cu/zeolite SCR catalysts. Most studies on sulfur poisoning of Cu/zeolite SCR catalysts have been based on SO₂ as the poisoning agent. It is important to investigate the relative poisoning effects of SO₃, especially for systems with DOCs in front of Cu/zeolite SCR catalysts.

It was observed that SCR activity was significantly reduced for samples poisoned by SO₃ vs. those poisoned by SO₂. The sulfur was released mainly as SO₂ for both samples poisoned by SO₂ and SO₃. The temperatures and the magnitudes of released SO₂ peaks however, were very different between the samples poisoned by SO₂ vs. SO₃. The results indicate that sulfur poisoning by SO₂ and SO₃ are not equivalent, with different poisoning mechanisms and impacts. This study raises an important sulfur poisoning concern for the systems with DOCs in front of Cu/zeolite SCR catalysts in diesel engine applications.