Development of a model based strategy for catalyst screening to control NOx and N2O emissions in NH3-SCR process towards Eu7 readiness

Abstract

Transient kinetic models were used to compare different commercial NH3-SCR catalytic monoliths under World Harmonized Transient Cycle (WHTC) conditions for NOx abatement performance, N2O formation and NH3 slip. Towards this goal, kinetic models for four Cu-zeolite, two Vanadia and one Fe-zeolite formulation were developed using experimental data of NH3 adsorption, desorption, NH3 oxidation, NO oxidation, Standard SCR and Fast SCR reactions. Models were in very good agreement with experimental data. Cu and Fe-zeolite formulations showed high deNOx activity with cycle efficiencies > 90% and > 95% respectively, for cold and warm WHTC runs, whereas Vanadia formulations outshined with negligible N2O formation. Simulations were performed to assess the variation of tailpipe NOx as a function of reactor volume. A plateau in deNOx performance was observed for all formulations as a function of the reactor volume which was around 30 and 50 L for cold and warm WTHC runs, respectively. This was found to be due to the decreasing temperature and fractional coverage of adsorbed NH3 along the axial distance of the reactors. Models were also used to develop hybrid reactor in series designs. Successive SCR reactors consisting of different formulations were simulated. The most successful design in terms of high deNOx performance and low N2O formation was with a reactor using a Vanadia catalyst followed by a reactor with Cu-zeolite catalyst. This resulted in a very similar deNOx performance but with a significantly lower N2O emissions as compared to a reactor with the same total volume consisting of Cu-zeolite.