Developing new technologies for the simultaneous removal of NO x and dioxins from metallurgical facility and waste incinerator emissions remains challenging. Here, we present a new synergistic improvement effects of NO x and chlorobenzene (CB) on the MnO x-CeO2 catalyst. CB promoted both the NO x conversion and N2 selectivity below 300 °C during the NO x reduction process, in which the MnO x-CeO2 catalyst caused the undesired side reactions due to the over-oxidation of NH3. Meanwhile, NO x and NH3 promoted the CB oxidation activity above 100 °C in the presence of O2. On the basis of the diffuse reflectance infrared Fourier transforms and kinetic studies, the promotion was due to the separation of the MnO x-CeO2 catalyst into different temperature windows: NO x reduction at 100-200 °C and CB oxidation at 200-300 °C. The side reactions mainly occurred above 200 °C, which is suppressed by the coverage and activation of CB on catalyst surface.