Detailed kinetic modeling of NH3 SCR over Cu-ZSM-5

A combination of flow reactor experiments and detailed kinetic modeling was used to study the selective catalytic reduction (SCR) of NOx with NH3 over Cu-ZSM-5. The model was developed in several steps and the SCR mechanism presented here is based on our earlier work on two subsystems: ammonia storage and ammonia oxidation with and without water, and NOx adsorption and NO oxidation. In this work, the subsystems were combined with reaction steps for the reduction of nitrogen oxides with ammonia. The SCR mechanism involves a reaction between adsorbed NO2 and NH3, formation of HNO2 and HNO3 and the final reduction to N2 or N2O. Seven experiments that describe the catalytic activity using various feed combinations of NO, NO2 and NH3 in both dry and wet feeds were used in the model development. These experiments investigate the SCR of NO over a wide temperature range, the influence of using various NO to NO2 ratios at 175 \ub0C, the influence of changing NO to NO2 ratio at 350 \ub0C, the NO oxidation in wet feed, and the ammonia inhibition at low temperature. The model was also validated using six new experiments. The predicted NOx conversions and formations of N2O correlated well with the experimental results and show that the detailed kinetic model developed in this study could be used successfully to describe several experimental observations over a wide range of temperatures