Effect of gas compositions on SO2 poisoning over Cu/SSZ-13 used for NH3-SCR

Abstract

This study focuses on the effect of gas composition during SO2 poisoning over Cu/SSZ-13 for NH3-SCR application and was performed by conducting SO2-TPD experiments in a variety of lean gas compositions. In addition, the poisoned monoliths were characterized in detail using ICP-SFMS, UV–vis and XPS. During SO2 poisoning under dry and lean conditions, two different sulfur species were found, which were assigned to weakly bound SO2 and copper sulfate like species. Moreover, a significantly larger amount of copper sulfates was present in humid environment. The presence of NH3 during the poisoning resulted in the formation of ammonium sulfate species which were decomposed at the same temperature independently if the poisoning with SO2 was conducted in ammonia oxidation conditions or under standard or fast SCR conditions. Moreover, if the temperature ramp was conducted with O2 and H2O compared to Ar alone, more stable sulfate species were formed. In addition, SO2 poisoning under standard SCR conditions resulted in mostly ammonium sulfate formation at 200°C, whereas copper sulfates were predominant after poisoning at 400°C. After hydrothermal aging at 800°C, more reducible copper species were noticeable and UV–vis showed that copper oxides had been formed. Sulfur poisoning of the hydrothermally aged sample resulted in the additional formation of copper sulfates during poisoning at 200°C, which was not the case for poisoning of the fresh catalyst. Thus, the copper oxide species enhanced the copper sulfate formation.