Effects of NO2 and SO2 on selective catalytic reduction of nitrogen oxides by ammonia

The selective catalytic reduction (SCR) characteristics of NO and NO2 over V2O5–WO3–MnO2/TiO2 catalyst using ammonia as a reducing agent have been determined in a fixed-bed reactor at 200–400 °C. The presence of NO2 enhances the SCR activity at lower temperatures and the optimum ratio of NO2/NOx is found to be 0.5. During the SCR reactions, there are some side reactions occurred such as ammonia oxidation and N2O formation. At higher temperatures, the selective catalytic oxidation of ammonia and the nitrous oxide formation compete with the SCR reactions. The denitrification (DeNOx) conversion decreases at lower temperatures but it increases at higher temperatures with increasing SO2 concentration. The presence of SO2 in the feeds inhibits N2O formation.