Improvement of low-temperature catalytic activity over hierarchical Fe-Beta catalysts for selective catalytic reduction of NOx with NH3

Hierarchical Fe-Beta obtained by hydrothermal synthesis exhibited higher low-temperature NH3-SCR activity than conventional Fe-Beta. In order to identify the main factors leading to the difference in catalytic activity, we investigated the pore structure, acidity and Fe sites of the hierarchical Fe-Beta and conventional Fe-Beta. The enhanced activity of hierarchical Fe-Beta was mainly due to the increase of the quantity of active Fe species. NH3-TPD and DRIFTS results of NH3adsorption clearly verified that hierarchical Fe-Beta had more Lewis acid sites, which is beneficial to the adsorption and activation of NH3. The H2-TPR, UV–vis DRS, and EPR results confirmed that the hierarchical Fe-Beta had more isolated active Fe species, which may be associated with that the hierarchical structure introduced more structural defects as ion-exchange sites. Based on the analysis of kinetics experiments and the abovementioned characterizations, it can be concluded that the improvement of NH3-SCR activity was not due to an intrinsic effect of the specific structural characteristics, but was related to more Fe active sites and better dispersion of Fe species in the hierarchical Fe-Beta.