An Evaluation of Least-Squares Fitting Methods in XAFS Spectroscopy: Iron-Based SBA-15 Catalyst Formations
Journal Article
·
· Spectrochimica Acta, Part A
A detailed comparison has been made of determinations by {sup 57}Fe M{umlt o}ssbauer spectroscopy and four different XAFS spectroscopic methods of %Fe as hematite and ferrihydrite in 11 iron-based SBA-15 catalyst formulations. The four XAFS methods consisted of least-squares fitting of iron XANES, d(XANES)/dE, and EXAFS (k{sup 3}chi and k{sup 2}chi) spectra to the corresponding standard spectra of hematite and ferrihydrite. The comparison showed that, for this particular application, the EXAFS methods were superior to the XANES methods in reproducing the results of the benchmark M{umlt o}ssbauer method in large part because the EXAFS spectra of the two iron-oxide standards were much less correlated than the corresponding XANES spectra. Furthermore, the EXAFS and M{umlt o}ssbauer results could be made completely consistent by inclusion of a factor of 1.3 {+-} 0.05 for the ratio of the M{umlt o}ssbauer recoilless fraction of hematite relative to that of ferrihydrite at room temperature (293 K). This difference in recoilless fraction is attributed to the nanoparticle nature of the ferrihydrite compared to the bulk nature of the hematite. Also discussed are possible alternative non-least-squares XAFS methods for determining the iron speciation in this application as well as criteria for deciding whether or not least-squares XANES methods should be applied for the determination of element speciation in unknown materials.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 980008
- Report Number(s):
- BNL--92926-2010-JA
- Journal Information:
- Spectrochimica Acta, Part A, Journal Name: Spectrochimica Acta, Part A Journal Issue: 5 Vol. 72; ISSN SAMCAS; ISSN 0584-8539
- Country of Publication:
- United States
- Language:
- English
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