Effective Selective Catalytic Reduction of NO _x with NH ₃ over MnCeO _x /Cu‐SSZ‐39 Composite Catalyst: Improved Low Temperature Activity and Hydrothermal Stability

Abstract In this study, a composite catalyst, MnCeO x /Cu‐SSZ‐39, was synthesized by coupling MnCeO x with Cu‐SSZ‐39 zeolite and evaluated for NH 3 ‐SCR (selective catalytic reduction by NH 3 ) performance. The incorporation of MnCeO x significantly enhanced the low‐temperature SCR activity of Cu‐SSZ‐39 and broadened its operating temperature window. This improvement was attributed to the increased surface chemisorbed oxygen with high mobility, which facilitated NO oxidation to NO 2 , thereby promoting the fast SCR pathway and enhancing low‐temperature activity. Furthermore, the hybrid catalyst exhibited higher concentrations of isolated Cu 2 ⁺ and Ce 3+ /Mn 4+ species, improving redox capacity and surface acidity, both critical for low‐temperature SCR reactions. Notably, MnCeO x /Cu‐SSZ‐39 demonstrated superior hydrothermal stability compared to pure Cu‐SSZ‐39, maintaining higher SCR activity after aging. Mechanistic studies revealed a strong metal oxide‐zeolite interaction, where MnCeO x stabilized the zeolite framework, suppressed dealumination, and prevented Cu species aggregation during hydrothermal aging. These findings provide a promising strategy for designing Cu‐SSZ‐39 catalysts with excellent low‐temperature activity, broad‐temperature performance, and enhanced hydrothermal stability.