Influence of Hydrothermal Ageing on NH3-SCR Over Fe-BEA-Inhibition of NH3-SCR by Ammonia

摘要

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 for NH3-SCR catalyst applications. 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 NO_x conversion after NH3 cut-off during NH3-SCR is observed. However, for Fe-BEA an inhibiting effect of ammonia after NH3 cut-off is seen but no significant difference (i.e. increased NO_x conversion time) between fresh and aged samples can be observed, indicating that the inhibiting effect is unaffected by the hydrothermal treatment.