Laboratory sulfation of an ammonia slip catalyst with a real-world SO ₂ concentration

Upcoming, stricter diesel exhaust emissions standards will likely require aftertreatment architectures with multiple diesel exhaust fluid (DEF) introduction locations. Managing NH₃ slip with technologies such as an ammonia slip catalyst (ASC) will continue to be critical in these future aftertreatment systems. In this study, we evaluate the impact of SO₂ exposure on a state-of-the-art commercially available ASC. SO₂ is co-fed at 0.5 or 3 ppmv to either approximate or accelerate a real-world exhaust SO₂ impact. ASC performance during sulfur co-feeding is measured under a wide variety of simulated real-world conditions. Results indicate that the loss of NO conversion during SCR is dependent on the cumulative SO₂ exposure, regardless of the inlet SO₂ concentration. Meanwhile, N₂O formation under SCR conditions is nonlinearly affected by SO₂ exposure, with formation increasing during 0.5 ppmv SO₂ exposure but decreasing in the presence of 3 ppmv SO₂. TPO experiments reveal the formation of ammonium sulfate species, but only after prolonged SO₂ exposure at 0.5ppmv or accelerated SO₂ exposure at 3 ppmv. Reactivation at 550°C is sufficient to recover ASC reactivity following multiple SO₂ exposure tests in all cases. These findings are especially relevant for the development of diesel exhaust aftertreatment accelerated aging protocols.