posted on 2022-10-05, 21:29authored byDominik Wierzbicki, Adam H. Clark, Oliver Kröcher, Davide Ferri, Maarten Nachtegaal
Monomeric
Fe species in zeolites are considered to be
the active
sites for the low temperature activity toward ammonia-assisted selective
catalytic reduction of nitrogen oxides (NH3-SCR) in exhaust
gases. Herein, we report on a preparation method to synthesize single-site
Fe/ZSM-5 by combination of dealumination with the use of a bulky iron
complex to introduce Fe. Transient in situ XAS experiments at the
Fe K-edge under dynamic NH3-SCR reaction conditions demonstrated
the involvement of all iron atoms in the redox cycle and, with that,
suggest that Fe species in the studied Fe/ZSM-5 catalyst are monomers.
Simulation of experimental X-ray absorption data revealed that the
Fe species in the sample obtained by this approach adopt a square
planar geometry, which changes into fivefold coordination at low temperature
by strongly binding either NO or NH3 as the ligand. The
presence of monomeric Fe species in this Fe/ZSM-5 conveys molecular
level insights into the temperature-dependent NH3-SCR activity
and might prove useful in the study of other reactions over monomeric
Fe species, such as methane partial oxidation or dehydroaromatization
reactions.