Developing low-temperature SCR catalysts is crucial for efficiently removing both NO and Hg⁰. Precisely adjusting the surface structure of Cu–Ce–BTC catalysts under the influence of halogen groups enhances their catalytic performance. In this study, we synthesized a series of halogen-modified Cu–Ce–BTC catalysts and investigated their structural characteristics and performance through a combination of calculations, characterization, and experiments. The characterization indicated that the original physicochemical properties remain unchanged after halogen modification, but the presence of C–X (Cl, Br, I) can be observed. During the NH₃-SCR reaction, we observed that halogen modification enhances the catalytic activity, with Cl having a notably higher effect than Br and I. Additionally, O₂ significantly promotes the removal of both NO and Hg⁰. Meanwhile NO has a minimal impact on NO and Hg⁰ removal. Furthermore, NH₃ promotes NO removal and inhibits Hg⁰ removal. However, both SO₂ and H₂O have an inhibitory effect on the removal of both NO and Hg⁰, with H₂O's effect being more pronounced. DFT verified that the NH₃-SCR reaction on Cl–Cu–Ce–BTC follows both E–R and L–H mechanisms, with NH₂NO identified as the primary reactant. The oxidation reaction of Hg⁰ mainly follows the Mars–Maessen mechanism.