Using the impregnation method, a series of Cu–Mn oxide catalysts were prepared and investigated for the selective catalytic reduction (SCR) of NO_x with NH₃ at temperatures ranging from 353 K to 453 K. The 0.05Cu–MnO_x/TiO₂ catalyst shows the highest activity and yields nearly 100% NO_x conversion at 453 K using GHSV = 40 000 h⁻¹, while the 0.20Cu–MnO_x/TiO₂ catalyst exhibits a certain level of potassium tolerance. In addition, the catalysts show favorable stability and water resistance. According to the XRD, EDS and SCR performance results, the existence of a new crystallized CuMn₂O₄ spinel phase is the dominant parameter for outstanding SCR activity between 413 K and 453 K. TPR, XPS and in situ DRIFT experiments indicate that CuMn₂O₄ is responsible for low reduction temperature, strong interaction between manganese oxides and copper oxides, high Mn³⁺ content and numerous acid sites on the surface. Compared with MnO_x/TiO₂ catalysts, Cu–Mn oxide catalysts could reduce the poisoning effect of potassium, illustrating that the CuMn₂O₄ phase may play a significant role in K-tolerance. Meanwhile, based on a certain level of potassium tolerance in CuMn₂O₄, an oxidation mechanism for NO is proposed due to the increase in Mn³⁺ and the special structure of a spinel oxide.