Steady-state kinetic modeling of NH3-SCR by monolithic Cu-CHA catalysts

The kinetic modeling of NH3-SCR with a Cu-ion-exchanged chabazite (Cu-CHA) catalyst in steady-state reactions was investigated by a combination of flow reactor experiments and kinetic modeling with an in-house computational code. Here H-CHA and Cu-CHA monolith cylindrical catalyst specimens were used to identify the reactions at both Bronsted (H+) acid sites and Cu sites. Based on the proposals in the literature for NH3-SCR mechanism, a scheme for SCR and side reactions incorporating 17 reactions is proposed, and some of the reactions were verified by the experimental results here for the adsorption/desorption of NH3, unsteady-state reactions of the adsorbed NH3 with NO2 over the Cu-CHA and H-CHA, and NH3 oxidation over Cu-CHA. The Arrhenius parameters for Standard, Fast, and Slow SCR reactions, NH3 oxidation, NO oxidation to NO2, NO2 decomposition to NO, and NH3 desorption were obtained by kinetic experiments. This report develops a quantitative simulation model for SCR and side reactions, and the model was validated by experimental data for adsorption/desorption of NH3 and NO2, steady-state SCR reactions (Standard, Fast, and Slow SCR), and side reactions (NH3 and NO oxidation). The simulation model developed in this study can predict the steady-state SCR data and adsorption/desorption of NH3 and NO2 under unsteady-state.