Excellent performance of one-pot synthesized Fe-containing MCM-22 zeolites for the selective catalytic reduction of NOxwith NH3

A superior Fe-containing MCM-22 zeolite prepared by a one-pot synthesis method (OP-Fe/M22) showed excellent NH(3)selective catalytic reduction (NH3-SCR) activity and almost 100% N(2)selectivity in a wide temperature window (200-500 degrees C). To investigate the effects of preparation strategies on the NH3-SCR reaction, 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 mixing (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 degrees C) than the other three post-synthesized catalysts. As revealed by XRD, UV-vis, H-2-TPR, NH3-TPD, and Py-IR experiments, OP-Fe/M22 has the highest concentrations of isolated Fe(3+)species and acid sites, and the lowest concentration of Fe(2)O(3)nanoparticles among the four catalysts, which ensures its highest activity in the NH3-SCR reaction. Besides, OP-Fe/M22 exhibits the higher activity both in NH(3)oxidation and NO oxidation reactions than IM-Fe/M22, indicating the better NO oxidation ability and NH(3)storage capacity of OP-Fe/M22 which also facilitates the NH3-SCR process. In contrast with Cu-based MCM-22 zeolite obtained from the 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 degrees C) while obviously higher activity at high temperatures (300-550 degrees C). 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 ranges (200-550 degrees C) can be further improved, suggesting that OP-Fe/M22 is a potential catalyst with highly-efficient NH3-SCR activity in a wide temperature window.