Characterization of Iron in Zeolites by X-band and Q-Band ESR, Pulsed ESR, and UV-Visible Spectroscopies

Goldfarb, Daniella; Bernardo, M.; Strohmaier, Karl G.; Vaughan, D. E. W.; Thomann, H.

doi:10.1021/ja00093a039

Cited by 250 publications

(191 citation statements)

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“…11a is assigned to the presence of isolated Fe 3? ions in high-spin state, likely corresponding to species absorbing at 270 nm in the DR-UV-Vis spectra. The relative intensity of the g eff = 4.3 line is slightly higher with Fe-0.025-IMO, the sample at lower Fe loading, in agreement with other authors (Goldfarb et al 1994). The g eff % 2.0 and 2.3 lines are usually associated to iron oxide clusters and/or particles where Fe 3?…”

Section: Resultssupporting

confidence: 91%

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Al/Fe isomorphic substitution versus Fe2O3 clusters formation in Fe-doped aluminosilicate nanotubes (imogolite)

et al. 2015

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Textural, magnetic and spectroscopic properties are reported of Fe-doped aluminosilicate nanotubes (NTs) of the imogolite type, IMO, with nominal composition (OH) 3 Al 2-x Fe x O 3 SiOH (x = 0, 0.025, 0.050). Samples were obtained by either direct synthesis (Fe-0.025-IMO, Fe-0.050-IMO) or postsynthesis loading (Fe-L-IMO). The Fe content was either 1.4 wt% (both Fe-0.050-IMO and Fe-L-IMO) or 0.7 wt% (Fe-0.025-IMO). Textural properties were characterized by High-Resolution Transmission Electron Microscopy, X-ray diffraction and N 2 adsorption/ desorption isotherms at 77 K. The presence of different iron species was studied by magnetic moment measurements and three spectroscopies: Mössbauer, UV-Vis and electron paramagnetic resonance, respectively. Fe 3? /Al 3? isomorphic substitution (IS) at octahedral sites at the external surface of NTs is the main process occurring by direct synthesis at low Fe loadings, giving rise to the formation of isolated high-spin Fe 3? sites. Higher loadings give rise, besides IS, to the formation of Fe 2 O 3 clusters. IS occurs up to a limit of Al/Fe atomic ratio of ca. 60 (corresponding to x = 0.032). A fraction of the magnetism related to NCs is pinned by the surface anisotropy; also, clusters are magnetically interacting with each other. Post-synthesis loading leads to a system rather close to that obtained by direct synthesis, involving both IS and cluster formations. Slightly larger clusters than with direct synthesis samples, however, are formed. The

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Section: Resultssupporting

confidence: 91%

“…The g eff % 2.0 and 2.3 lines are usually associated to iron oxide clusters and/or particles where Fe 3? ions strongly interact with each other (Goldfarb et al 1994;Bordiga et al 1996;Ferretti et al 2004). Any evaluation of the relative spin concentration of isolated and clustered Fe 3?…”

Section: Resultsmentioning

confidence: 99%

Al/Fe isomorphic substitution versus Fe2O3 clusters formation in Fe-doped aluminosilicate nanotubes (imogolite)

et al. 2015

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“…However, the proximity of other framework iron atoms in case of a higher Fe loading may induce similar spectral features [25]. Also for EPR caution is recommended regarding the exclusive assignment of certain g-values to the presence of one particular species [26]. Even though EXAFS can provide detailed information on the local structure of materials it will be difficult to distinguish similar sites.…”

Section: Mononuclear Fe Fementioning

confidence: 99%

New frontiers in X-ray spectroscopy in heterogeneous catalysis: Using Fe/ZSM-5 as test-system

et al. 2005

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We have applied a number of novel X-ray spectroscopic tools to Fe/ZSM-5 systems. Fe/ZSM-5 can be considered as an ideal test-system for the characterization techniques in heterogeneous catalysis. The existence of a large range of sites and structures creates a good testing ground to determine which experimental tools are able to resolve such complex system. In situ soft X-ray absorption provides important information on the valence and electronic structure of iron during treatments, with a time scale down to 30 s. Kb-detected XANES yields unprecedented resolution for pre-edge structures and using hard X-rays can be used under any condition and treatment, including high-pressures. It can be expected that both in situ soft X-ray absorption and Kb-detected XANES become 'standard' tools for catalysis research, similar to traditional XANES and EXAFS today. The X-MCD is also used in this paper but it will probably remain a rather specialized technique in the field of heterogeneous catalysis. Further new developments for catalysis characterization are for all to be expected from X-ray spectro-microscopy, where one will have the possibility to perform the in situ soft X-ray absorption and Kb-detected XANES experiments with nanometer size spatial resolution. #

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“…Nonetheless, the interpretation of the EPR spectra is not straightforward, and signal assignments are still controversial. 18 The X-band EPR spectrum of high-spin Fe(III) in zeolites usually exhibits two major signals, at g ³ 4.3 and g ³ 2. A third signal at g ³ 2.3, assigned to Fe(III) in an oxide phase, often appears as well.…”

Section: Introductionmentioning

confidence: 99%

“…None of these features can prove nor disprove framework substitution. 18,19 Better assignment can be achieved by combining conventional continuous wave (CW) EPR spectroscopy with methods such as electron spin echo envelope modulation (ESEEM) 20 -22 and electron nuclear double resonance (ENDOR), 23,24 which give more details about the close environment of the metal center. The ESEEM technique allows the measurement of weak superhyperfine interactions in solids.…”

Section: Introductionmentioning

confidence: 99%

Studies of Fe(III) incorporated into AlPO4-20 by X- and W-band EPR spectroscopies

et al. 1999

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Characterization of Iron in Zeolites by X-band and Q-Band ESR, Pulsed ESR, and UV-Visible Spectroscopies

Cited by 250 publications

References 0 publications

Al/Fe isomorphic substitution versus Fe2O3 clusters formation in Fe-doped aluminosilicate nanotubes (imogolite)

Al/Fe isomorphic substitution versus Fe2O3 clusters formation in Fe-doped aluminosilicate nanotubes (imogolite)

New frontiers in X-ray spectroscopy in heterogeneous catalysis: Using Fe/ZSM-5 as test-system

Studies of Fe(III) incorporated into AlPO4-20 by X- and W-band EPR spectroscopies

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