Excellent Performance of One-pot Synthesized Fe-containing MCM-22 Zeolites for the Selective Catalytic Reduction of NOx with NH3

A superior Fe-containing MCM-22 zeolite prepared by one-pot synthesis method (OP-Fe/M22) showed excellent NH3 selective catalytic reduction (NH3-SCR) activity and almost 100% N2 selectivity in a wide temperature window (200–500 oC). To investigate the effects of preparation strategies on the NH3-SCR reaction, the other three Fe/MCM-22 zeolites with similar iron content (4.4–4.8 wt %) were prepared by solid-state ion exchange (SSIE-Fe/M22), incipient wetness impregnation (IM-Fe/M22) and mechanical mixture (MM-Fe/M22) methods, respectively. Catalytic results in NH3-SCR demonstrate that OP-Fe/M22 gives significantly higher activity in the whole temperature range (100–550 oC) than the other three post-synthesized catalysts. As revealed by XRD, UV-vis, H2-TPR, NH3-TPD, Py-IR experiments, OP-Fe/M22 has the highest concentrations of isolated Fe3+ species and acid sites, the least concentration of Fe2O3 nanoparticles among the four catalysts, which ensures its highest activity in NH3-SCR reaction. Besides, OP-Fe/M22 exhibits the higher activity both in NH3 oxidation and NO oxidation reactions than IM-Fe/M22, indicating the better NO oxidation ability and NH3 storage capacity of OP-Fe/M22 which also facilitates the NH3-SCR process. In contrast with Cu-based MCM-22 zeolite obtained from incipient wetness impregnation method at similar metal content (5%Cu/M22), OP-Fe/M22 shows comparable activity with 5%Cu/M22 in the low-temperature range (100–300 oC) while obviously higher activity at high temperatures (300–550 oC). Moreover, by removing part of undesired iron oxides in OP-Fe/M22 through mild acid post-treatments, the NH3-SCR activity of OP-Fe/M22 in the medium and high temperature range (200–550 oC) can be further improved, suggesting that OP-Fe/M22 is a potential catalyst with high-efficient NH3-SCR activity in a wide temperature window.