Insights into the structure-activity relationships of highly efficient CoMn oxides for the low temperature NH3-SCR of NOx

A series of CoMn composite oxides with lamellar morphology was prepared by co-precipitation for low temperature selective catalytic reduction of NOx with NH3. CoMn oxide calcined at 250 °C (CoMn-LS-250) exhibited high activity, giving 91 % NOx conversion at 60 °C with good SO2 resistance (300 °C). The excellent activity of CoMn-LS-250 is related to its abundance of Lewis acid sites as well as its superior redox ability; consequently, the catalyst is able to trap NH3 and oxidize NH3(ad) to NH2(ad), this being the initial step for NH3-SCR of NOx. NH2(ad) subsequently combines with NO to form the key intermediate, NH2NO(ad), which decomposes at low temperature (ca. 85 °C) with release of N2. Residual OH(ad) reacts with gaseous O2 to complete the redox cycle.