Effect of NO₂ on N₂O production and NO_x emission reduction in NH₃ Selective Catalytic Reduction

With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NOx) emissions and nitrous oxide (N2O) production from diesel engines have become the focus of research. At high temperature, the reaction of NO2 in the catalyst generates the intermediate product NH4NO3, which first crystallizes below 300 degrees C. These crystals tend to block the pores and inhibit the reaction. Subsequently, N2O is produced through the decomposition of NH4NO3, leading to additional pollution. Therefore, the concentration of NO2 has a direct impact on both the NOx conversion efficiency and the generation of N2O, requiring consideration of the optimal proportion of NO2 in SCR. Considering these two factors, it is concluded that the optimal amount of NO2 varies with temperature. To improve the NOx conversion rate of the Cu-SSZ-13 catalyst at low temperatures and reduce N2O generation, the optimal NO2 ratio of the Cu-SSZ-13 catalyst under various operating conditions is studied using numerical simulations. As the temperature rises, the optimal NO2/NOx ratio first increases and then decreases. Under the optimal NO2/NOx ratio, the NOx conversion rate significantly increases, while N2O generation decreases considerably. The optimal NO2/NOx ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.