Identification of the iron oxidation state and coordination geometry in iron oxide- and zeolite-based catalysts using pre-edge XAS analysis

Boubnov, A.; Lichtenberg, H.; Mangold, S.; Grunwaldt, J.-D.

doi:10.1107/S1600577514025880

Figure 10
Analysis of the in situ pre-edge spectra of the 1% Fe/Al₂O₃ catalyst depicted in Fig. 9(b)

. (a) Variogram of the total integrated intensity and centroid position of the pre-edge peak at different temperatures of the TPR experiment, compared with data points of the reference compounds staurolite, FeO, FePO₄ and α-Fe₂O₃ from spectra measured with standard resolution (marked with circles and the grey fields for the four types of Fe species given in Fig. 8

). (b) Evolution of the peak width (FWHM) and Gaussian fraction (x_Gaussian) of pseudo-Voigt functions as a function of temperature. (c) Fraction of Fe³⁺ and Fe²⁺ species as a function of temperature as estimated from linear combination analysis [the first XANES spectrum is assumed to be Fe³⁺ and the last XANES spectrum is assumed to be Fe²⁺, carried out between 7105 eV and the isosbestic point at 7132 eV seen in Fig. 9(a)

]. (d) Linear relationship between the fraction of Fe³⁺ species calculated by LCA and the pre-edge centroid position. The grey lines in (b) and (c) indicate the temperatures where the transformation of Fe³⁺ to Fe²⁺ has advanced ca 10%, 50% and 90% to guide the eye.

JOURNAL OF
SYNCHROTRON
RADIATION

ISSN: 1600-5775

Volume 22| Part 2| February 2015| Pages 410-426

doi:10.1107/S1600577514025880

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