Improvement in Selective Catalytic Reduction Model Accuracy for Predicting NO _x Conversion at High Temperature

As a result of WNTE regulations and the introduction of close-coupled aftertreatment systems, exhaust purification at high temperatures in commercial vehicles has become increasingly important in recent years. In this report, we improve the prediction accuracy for NO_x conversion at high temperatures in the kinetic model of conventional Cu-selective catalytic reduction (Cu-SCR). Reaction rate analysis indicated that the rate of NH₃ oxidation was extremely low compared to the rate of standard SCR. We found that NO_x concentration-dependent NH₃ oxidations (termed NO_x-assisted NH₃ oxidations) were key to the rate of NH₃ oxidation. The output of the improved Cu-SCR kinetic model was in agreed with experimental results obtained from the synthetic gas bench and engine dynamometer bench. We analyzed the contribution of each reaction to NH₃ consumption during Cu-SCR. Under NH₃ + NO + O₂, standard SCR was dominant at low temperature. At high temperatures, the rate of NO-assisted NH₃ oxidation increased, and this reaction competed with standard SCR. Under NH₃ + NO + NO₂ + O₂, fast SCR, NH₄NO₃ formation, and standard SCR were the dominant reactions at low temperature. With increasing temperature, NO₂-assisted NH₃ oxidation competed with the other reactions, resulting in a decreased NO_x conversion.