A series of CuMnOx catalysts were prepared through the coprecipitation method to explore the effect of CO participation on the NH3-SCR reaction. The results showed that the CM-3 sample reached 100 conversion of CO and NO at a temperature lower than 175 °C; this is mainly because the correct proportion of copper and manganese helps to form a solid solution and improve the coordination between metals. Moreover, the interaction principle of CO participating in the NH3-SCR reaction was thoroughly investigated through in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) and density functional theory (DFT). NH3 has different adsorption modes at different temperatures and competes with CO for the same active center, which significantly affects the catalytic reaction on the surface of the sample. It was confirmed that the deposition of CO32- is the main reason for the decline in activity. Finally, the improvement in N2 selectivity in the reaction with CO participation was due to the produced N2O not being directly released but being further reduced to N2 through species such as CO.
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