Assessment of the Single-Site Kinetic Model for NH3-SCR on Cu-Chabazite for the Prediction of NOx Emissions in Dynamometer Tests

Abstract

A transient single-site kinetic model consisting of NH3-SCR (selective catalytic reduction) related reactions (NH3 adsorption/desorption, NH3 oxidation, NO oxidation, standard SCR, fast SCR, NO2-SCR, NH4NO3, and N2O formation) on a commercial multi-site Cu-Chabazite washcoated monolith was developed using laboratory scale synthetic gas bench (SGB) data and its potential towards predicting the downstream NOx concentrations was assessed using SGB and dynamometer tests. Kinetic model described the transient and steady-state data obtained for the model development in the SGB well. Single-site nature of the model enabled the prediction of the reactivity of the lower temperature active Cu site much better than the activity associated with higher temperature Cu sites. Validation experiments in the SGB at 185 °C which consisted of varying NH3 and NO2/NOx ratios were very well predicted. The kinetic model was also successful in predicting the instantaneous NOx emissions and cumulative NOx and N2O amount released in real-size SCR reactors during World Harmonic Transient Cycle (WHTC) in the 220–290 °C range. Model was in slight disagreement with measured cumulative NO but was in good in agreement with NO2 for the World Harmonic Stationary Cycle (WHSC) tests in dynamometer and 235–339 °C range, respectively. The developed model was found sufficient for both design and calibration of aftertreatment systems (ATS).