Effect of Mole Ratio of Inlet NO2/NO and Contribution of Oxygen in Catalytic Reduction of Nitrogen Oxides with Ammonia

For the purpose of obtaining catalysts with higher activity and stability for the reduction of nitrogen oxides with NH3, the mechanism of the reduction over V2O5-TiO2, V2O5-Al2O2, Fe2(SO4)3-TiO2, Fe2(SO4)3-Fe2O3, CuSO4-TiO2, CuSO4-Al2O2 and Cu (II) ion-exchanged Y type zeolite catalysts were studied. The experiments were carried out using a flow reactor (I. D.: 12.0 mm) at atmospheric pressure and 200∼450°C(mainly 350°C). The amount and composition of the inlet gas employed were mainly 500 ppm NO (NO, NO2, NO-NO2 mixture), 667 ppm NH3, 0∼5% O2, and 10% H20∼N2 and the space velocity of the gas was mainly kept at 1.2 × 105 hr-1. It was found that the rate of the equimolal mixture of NO and NO2 to N2 was much higher than that of NO or NO2 and the contribution of oxygen to the oxidation of NO to NO2 was very large for the reduction of NO with NH3. Also, for the reduction of NO to N2, the reduction of NO2 with NH3 to NO was important at the beginning of the reduction. These results suggest that the reduction of NO proceeds at the equimolal ratio of NO and NO2 and at the equimolal ratio of NOx and NH3 as well on the surface of the catalyst, regardless of the kinds of inlet NOx or catalysts employed. On the other hand, experimental results on the stoichiometry of the reaction showed that the reaction had the following overall reaction equations: