Influence of hydrothermal ageing on NH3-SCR over Fe-BEA -Inhibition of NH3-SCR by ammonia

Paper in proceeding, 2013

The decay in ammonia adsorption capacity and the amount of active iron sites are important to consider in order to understand the deactivation processes of Fe-BEA as NH3-SCR catalyst. NH3 and NO storage capacity experiments together with kinetic modeling have been used to evaluate ammonia inhibition during NH3-SCR before and after hydrothermal treatment of H-BEA and Fe-BEA. The kinetic model shows that at least four types of acid sites for H-BEA and one additional site for Fe-BEA are required to predict the NH3 desorption well. NH3-TPD experiments together with simulations show that the strongest adsorption sites are the sites that are most affected by the hydrothermal treatment. For H-BEA a clear correlation between the ammonia storage capacity and the improved NOX conversion after NH3 cut-off during NH3-SCR is observed. However, Fe-BEA show an inhibiting effect of ammonia after NH3 cut-off but no significant difference (i.e. increased NOX conversion time) between fresh and aged samples can be observed, indicating that the inhibiting effect is unaffected by the hydrothermal treatment.