Identification of sulfate species and their influence on SCR performance of Cu/CHA catalyst

Abstract

An investigation into sulfate formation on Cu/CHA zeolites was conducted to confirm the main sulfate species that deactivate the catalyst. SO₂-TPD and controlled regeneration of poisoned catalysts were carried out to study the physicochemical properties of the sulfates formed under different conditions. The results revealed that three sulfate species existed on the catalyst surface, namely H₂SO₄, CuSO₄ and Al₂(SO₄)₃. H₂O and NH₃-SCR feed could improve the formation of H₂SO₄via an increase in the reaction rate of SO_x with protons and decrease the thermal stability of all sulfates via the protons' strong polarization effect. The poisoning effect of ammonium sulfate was more emphasized during sulfation in the presence of simulated exhaust gas. Additionally, in contrast to Cu/SSZ-13, Cu/SAPO-34 favored the formation of stable Al₂(SO₄)₃ species, which resulted in unrecoverable SCR activity in an inert atmosphere below 650 °C.