Modeling Spatially Resolved Concentration and NH3 Storage Profiles During Selective Catalytic Reduction of NOx With NH3 Over Commercial Cu-Zeolite Catalyst

Zeolite based selective catalytic reduction (SCR) catalysts are widely used to convert NOx to N₂ in diesel engine applications. Accurate SCR catalyst performance models are essential to develop control strategies and to design aftertreatment systems to meet stringent tailpipe NOx emission limits. To address the above needs, a global SCR kinetic model is developed to predict all critical factors, such as axial species concentration and NH₃ storage profiles over a commercial Cu-zeolite catalyst.

Global SCR kinetic parameters are determined using measured axial concentration profiles of reactants and products under various reaction conditions.  From the above measurements, the intrinsic SCR kinetics are estimated using the data under differential reaction conditions. Bulk mass transfer coefficient (Sh_e) is estimated from the high temperature data where the conversions are well below 100 % and are not kinetically controlled. It is demonstrated that the developed SCR model captures all major SCR catalyst functions, including the concentration and NH₃ storage profiles under steady state and transient conditions over a wide operating window. Specifically, the effect of temperature on SCR zone is accurately predicted. Also, the model predicts complete NH₃ capacity utilization within the SCR zone.