Experimental investigation on the coupling mechanism between sulfur poisoning and hydrothermal aging of the Cu-SSZ-13 SCR catalyst

Abstract

Cu-SSZ-13, a diesel vehicle selective catalytic reduction (SCR) catalyst, faces deactivation problems caused by sulfur poisoning and hydrothermal aging, which coexist in diesel vehicle after-treatment systems, complicating its actual deactivation. Activity evaluation and characterization tests were used to investigate the coupled deactivation properties as well as sulfur poisoning and hydrothermal aging mechanisms of the Cu-SSZ-13 SCR catalyst. The activity evaluation tests included the standard SCR reaction and NH₃ oxidation tests, and the characterization tests included the NH₃-TPD test, SO₂-TPD test, and NO + NH₃ TPR test. The sulfur-poisoned active sites of Cu-SSZ-13 inhibited the migration of ZCuOH to Z₂Cu in the subsequent hydrothermal aging, resulting in lower SCR activity at high temperatures than the samples hydrothermally aged only. The migration of ZCuOH to Z₂Cu caused by hydrothermal aging increased the sulfur resistance of the active sites, decreased the sulfur species production, and increased the SCR activity at low temperatures. For the samples that hydrothermally aged with SO₂ at 650 °C, some sulfur species were formed, which significantly affected the SCR activity in the whole temperature range. At 750 °C, the low-temperature SCR activity showed no reduction. At 850 °C, SO₂ promoted the formation of copper oxide. These research conditions closely resemble real-world aging conditions, refining the mechanism of coupled deactivation due to hydrothermal aging and sulfur poisoning in the Cu-SSZ-13 catalyst.