For low temperature selective catalytic reduction (SCR) of NOx with ammonia, the highly effective Sm-Mn mixed oxide (Sm-Mn-O, the molar ratio Sm/Mn is 0.1) catalysts was developed. The effect of the calcination temperature on the structure, physicochemical and catalytic properties of the Sm-Mn-O catalysts was investigated in detail. The results showed that the Sm-Mn-O catalyst calcined at 450 degrees C exhibited the highest activity, and after been calcined at >550 degrees C its catalytic activity markedly decreased. With an increase in the calcination temperature, its surface area firstly increased and then decreased, and the poorly crystallized MnO2 in Sm-Mn-O was transformed to highly crystalized Mn2O3 phase. These changes influenced the adsorption ability of the Sm-Mn-O catalyst for NH3 or NO + O-2. After calcination at >550 degrees C, the contents of Mn4+ and adsorbed oxygen (O-s) on the surface of Sm-Mn-O decreased obviously, resulting in the decrease in its catalytic properties for the NO oxidation and transformation of bridged nitrite to active intermediate of bidentate nitrate. Conversely, its catalytic activity for NH3 oxidation was enhanced after being calcined at high temperature. These adverse factors cause the decrease in the SCR activities of Sm-Mn-O calcined at >550 degrees C. (c) 2016 Elsevier B.V. All rights reserved.