Characterization and reactivity of natural manganese ore catalysts in the selective catalytic oxidation of ammonia to nitrogen

Natural manganese ore (NMO) catalysts were characterized and tested in the selective catalytic oxidation of ammonia to nitrogen oxides under dilute conditions. Also, the oxidation of ammonia (NH3) was carried out using pure MnO2, Mn2O3 for comparing with the activity. It is found that the activity of NMO was similar to that of MnO2 at low temperature below 150 °C but above this temperature, the activity of these catalysts showed the difference. In the course of NH3 oxidation, N2, NO, N2O and H2O were produced. But the quantity of NO2 produced in this experiment was negligible. At temperature below 250 °C, selectivity into N2 from NH3 oxidation was in the order, NMO > MnO2 > Mn2O3. This is the reverse of activity of these manganese oxides. Also the characterization of NH3 oxidation was proposed and supported by the effect of space velocity, inlet O2 and NH3 concentration. The increase of space velocity remarkably influenced not only the conversion but also selectivity into N2. The higher the reaction temperature was, the higher the effect of inlet O2 and NH3 concentration on the reaction rate was. By introducing NO during NH3 oxidation reaction, the possibility of NMO as selective catalytic reduction catalyst at low temperature was studied and showed positive results.