Sulfur Poisoning, and Regeneration, of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

Abstract:

Cu ion-exchanged into SSZ-13 zeolites, Cu/SSZ-13, is widely used as a NOx reduction catalyst in diesel engine after-treatment systems. However, sulfur, a common component in diesel fuel and engine oil, can lead to catalyst deactivation. Literature has shown that the relative amounts of Cu sites identified as Z2Cu and ZCuOH, where Z represents an Al site of the zeolite, lead to different S poisoning extents. And those relative Cu site amounts can be influenced by different thermal treatments. We used density functional theory (DFT) and probe reaction experiments to characterize Cu amounts and types, with emphasis on ion-exchanged Cu and multinuclear Cu species. Our results, consistent with those in the literature, show that multinuclear Cu species are particularly prone to S poisoning, and that the extents of regeneration after exposure are also dependent on S exposure conditions. Furthermore, the catalyst with more ZCuOH and multinuclear species appears to be, in general, a better oxidation catalyst. “Mild” thermal treatments can induce the migration of the Cu from ZCuOH to Z2Cu, and with less ZCuOH, there is decreased CO, NO, NH3 and SO2 oxidation conversions. Our results describe a correlation between the extent of sulfur poisoning to the catalyst’s oxidation ability, specifically the extent of SO3 formation. Overall, the talk will focus on how Cu speciation influences the extent of S poisoning, and which species are more prone to forming stable S-bound species.