Effect of NO₂ on N₂ O production and NO_x emission reduction in NH₃ Selective Catalytic Reduction

With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NO_x ) emissions and nitrous oxide (N₂ O) production from diesel engines have become the focus of research. At high temperature, the reaction of NO₂ in the catalyst generates the intermediate product NH₄ NO₃ , which first crystallizes below 300 °C. These crystals tend to block the pores and inhibit the reaction. Subsequently, N₂ O is produced through the decomposition of NH₄ NO₃ , leading to additional pollution. Therefore, the concentration of NO₂ has a direct impact on both the NO_x conversion efficiency and the generation of N₂ O, 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 NO_x conversion rate of the Cu-SSZ-13 catalyst at low temperatures and reduce N₂ O 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 /NO_x ratio first increases and then decreases. Under the optimal NO₂ /NO_x ratio, the NOx conversion rate significantly increases, while N₂ O generation decreases considerably. The optimal NO₂ /NO_x ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.