The Effects of SO2 and SO3 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.