A highly effective catalyst of Sm-Mn mixed oxide for the selective catalytic reduction of NO x with ammonia: Effect of the calcination temperature

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 °C exhibited the highest activity, and after been calcined at >550 °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 MnO 2 in Sm-Mn-O was transformed to highly crystalized Mn 2 O 3 phase. These changes influenced the adsorption ability of the Sm-Mn-O catalyst for NH 3 or NO + O 2 . After calcination at >550 °C, the contents of Mn 4+ 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 NH 3 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 °C.