With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NO_x) 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 °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 NO_x 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 NO_x 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/NO_x ratio first increases and then decreases. Under the optimal NO₂/NO_x ratio, the NOx conversion rate significantly increases, while N₂O generation decreases considerably. The optimal NO₂/NO_x ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.

Abstract

With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NO_x) 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 °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 NO_x 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 NO_x 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/NO_x ratio first increases and then decreases. Under the optimal NO₂/NO_x ratio, the NOx conversion rate significantly increases, while N₂O generation decreases considerably. The optimal NO₂/NO_x ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.