Effect of citric acid complexation on the structure and NH3-SCR performance of CuCe/ZSM-5 catalysts

Abstract

Citric acid-assisted CuCe/ZSM-5 catalysts with different Ce loadings were prepared by an incipient wetness impregnation method and evaluated for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). Among the prepared catalysts, the sample containing 1.5 wt% Ce exhibited the highest NO conversion over a broad temperature window, while citric acid modification further enhanced the low-temperature catalytic activity. Characterization results revealed that Ce incorporation regulated the textural properties and the distribution of active species while preserving the ZSM-5 framework. XPS, UV–vis DRS, and H₂-TPR analyses indicate the coexistence of Cu²⁺/Cu⁺ and Ce⁴⁺/Ce³⁺ species and support a strong redox interaction between Cu and Ce, which contributes to the enhanced redox capability of the catalysts. Meanwhile, NH₃-TPD and NO-TPD results confirmed that Ce addition and citric acid modification enhanced NH₃ adsorption and NO activation, thereby promoting the NH₃-SCR reaction. Moreover, the optimized catalyst exhibited excellent resistance to H₂O and SO₂ poisoning and maintained stable catalytic performance during a 120 h continuous stability test. The superior catalytic performance is mainly attributed to the synergistic interaction between Cu and Ce species together with the dispersion regulation induced by citric acid, which contributes to enhanced redox properties, suitable surface acidity, and improved accessibility of active sites.