Cu-based zeolite catalysts for synergistic removal of NO and CO: Performance and mechanistic insights

The co-emission of NO _x and CO in industrial flue gas renders traditional single-pollutant control strategies insufficient to meet the practical operating requirements. The synergistic technology of NH₃ selective catalytic reduction (NH₃-SCR) and CO oxidation has been recognized as an effective approach for addressing these two complex co-pollutant emissions. This study aims to systematically evaluate the performance differences and reaction mechanisms of copper-based zeolite catalysts with different topological structures as dual-function catalysts for NH₃-SCR and CO oxidation. The results indicated that Cu-ZSM-5 achieved significantly higher NO and CO conversions over a broader temperature window than that of Cu-Beta and Cu-Y while maintained the highest N₂ selectivity. XRD, BET, and XPS analyses further confirmed that the superior performance of Cu-ZSM-5 originated from its MFI framework, which enabled higher dispersion of Cu species, higher efficient Cu⁺/Cu²⁺ redox cycle, and greater abundance of lattice oxygen (O_α). NH₃-TPD and H₂-TPR results indicated that Cu-ZSM-5 possessed higher acid-site density and stronger redox capability. In situ DRIFTS analysis revealed that the NH₃-SCR reactions over Cu-ZSM-5 and Cu-Beta mainly followed the Langmuir-Hinshelwood (L-H) mechanism, while Cu-Y primarily proceeded via the Eley-Rideal (E-R) pathway. In the CO oxidation reaction, Cu-ZSM-5 primarily followed the Mars-van Krevelen (MvK) mechanism, while Cu-Beta primarily operated via the L-H mechanism and Cu-Y mainly conformed to the E-R pathway . More importantly, transient co-feeding in situ DRIFTS analysis elucidated the dynamic competitive adsorption and transformation pathways of CO and NO _x species over Cu⁺ active sites on Cu-ZSM-5 during the reaction. This study provides an essential theoretical insight for the rational design of efficient catalysts for the synergistic removal of NO and CO.