Effective Selective Catalytic Reduction of NOx with NH3 over MnCeOx/Cu-SSZ-39 Composite Catalyst: Improved Low Temperature Activity and Hydrothermal Stability

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 NH₃-SCR (selective catalytic reduction by NH₃) 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 NO₂, thereby promoting the fast SCR pathway and enhancing low-temperature activity. Furthermore, the hybrid catalyst exhibited higher concentrations of isolated Cu²⁺ and Ce³⁺/Mn⁴⁺ 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.