A series of MnOx–CeO2 binary oxide catalysts were synthesized by polyvinylpyrrolidone -assisted supercritical antisolvent precipitation and the effects of the manganese (Mn)/cerium (Ce) molar ratio and calcination temperature on the structure and properties of MnOx–CeO2 were investigated. A solid solution was obtained at each experimental condition and the highest surface area of 107.6 m2/g was obtained at the Mn/Ce molar ratio of 3:5 and the calcination temperature of 400 °C. Low-temperature selective catalytic reduction of emissions of nitrogen oxides, namely NO, NO2, and N2O (deNOx) with ammonia (NH3) to convert them into nitrogen and water, was used as model reaction to evaluate MnOx–CeO2 catalytic performance. It is found that the activity first increased and then decreased with increasing Mn content and decreased with increasing calcination temperature. The highest catalytic activity (93.3% NO conversion and 100% N2 selectivity) was obtained at the Mn/Ce molar ratio of 1/1 and the calcination temperature of 400 °C, which was attributed to the combination of high surface area and high redox performance of the catalyst.