NH₃-SCR by monolithic Cu-ZSM-5 and Cu-AFX catalysts: Kinetic modeling and engine bench tests

A simple kinetic model for the standard NH₃-SCR reaction by Cu-ZSM-5 catalysts has been developed by assuming three reaction steps: NH₃ adsorption (desorption), reactions of adsorbed NH₃ with O₂ (NH₃ oxidation) and NO (NH₃-SCR). The model is based on Arrhenius parameters for NH₃-SCR and NH₃ oxidation by a powder catalyst, combined with models for heat and mass transport and parameters of monolithic catalysts. The model is validated with the experimental results, not included in the estimation of the model, for NH₃-SCR by monolithic catalysts with different parameters (catalyst loading and cell density). NOx removal from diesel exhaust, generated by engine bench, was also carried out by using monolithic Cu-ZSM-5 and Cu-AFX catalysts. The results suggest the poisoning effect of hydrocarbons in the exhaust emissions on NOx conversion is more significant for Cu-ZSM-5 than Cu-AFX.