Iron-exchanged UZM-35: An active NH3-SCR catalyst at low temperatures

[Display omitted] •Fresh Fe-UZM-35 shows significantly higher low-temperature NH3-SCR activity than fresh Fe-beta.•When hydrothermally aged at 1173 K, however, the opposite result was observed.•Iron species in fresh Fe-UZM-35 are mostly present as isolated Fe3+ ions.•Zeolite framework topology is key to the hydrothermal stability of supported Fe catalysts. The catalytic properties of iron-exchanged UZM-35, beta, LTA, and SSZ-13 zeolites with similar Si/Al and Fe/Al ratios (8.9–12 and 0.35-0.37, respectively) and their hydrothermally aged forms at 1023−1173 K are compared in NH3-SCR. When fresh, the low-temperature (< 573 K) activity of Fe-UZM-35 is considerably better than the other three iron-exchanged zeolite catalysts. Unlike those in fresh Fe-beta, Fe-LTA, and Fe-SSZ-13, the iron species in fresh Fe-UZM-35 were found to be mainly present as isolated extraframework Fe3+ ions which may be responsible for the high low-temperature SCR activity. However, while hydrothermal aging at 1173 K led to a notable decrease in activity of all zeolite-supported iron catalysts, the extent of activity decrease differs according to the structure type of zeolite supports. The overall results of this study strongly suggest that zeolite framework topology is a key factor governing the activity and durability of zeolite-supported iron catalysts for NH3-SCR.