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Catalysts 2018, 8(2), 63; doi:10.3390/catal8020063

In Situ UV-Visible Assessment of Iron-Based High-Temperature Water-Gas Shift Catalysts Promoted with Lanthana: An Extent of Reduction Study

1
Department of Chemical Engineering, Ira A. Fulton School of Engineering and Technology, Brigham Young University, 350 CB, Provo, UT 84602, USA
2
Brookhaven National Laboratory, NSLS-II Building 743, Upton, NY 11973, USA
3
Department of Chemistry and Biochemistry, College of Physical and Mathematical Sciences, Brigham Young University, C209 BNSN, Provo, UT 84602, USA
Current address: Phillips 66, US Highway 60 & State Highway 123, Bartlesville, OK 74003, USA.
Current address: Micron Technology, 8000 S. Federal Way, P.O. Box 6, Boise, ID 83707, USA.
*
Author to whom correspondence should be addressed.
Received: 22 December 2017 / Revised: 26 January 2018 / Accepted: 29 January 2018 / Published: 4 February 2018
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Abstract

The extent of reduction of unsupported iron-based high-temperature water-gas shift catalysts with small (<5 wt %) lanthana contents was studied using UV-visible spectroscopy. Temperature- programmed reduction measurements showed that lanthana content higher than 0.5 wt % increased the extent of reduction to metallic Fe, while 0.5 wt % of lanthana facilitated the reduction to Fe3O4. In situ measurements on the iron oxide catalysts using mass and UV-visible spectroscopies permitted the quantification of the extent of reduction under temperature-programmed reduction and high-temperature water-gas shift conditions. The oxidation states were successfully calibrated against normalized absorbance spectra of visible light using the Kubelka-Munk theory. The normalized absorbance relative to the fully oxidized Fe2O3 increased as the extent of reduction increased. XANES suggested that the average bulk iron oxidation state during the water-gas shift reaction was Fe+2.57 for the catalyst with no lanthana and Fe+2.54 for the catalysts with 1 wt % lanthana. However, the UV-vis spectra suggest that the surface oxidation state of iron would be Fe+2.31 for the catalyst with 1 wt % lanthana if the oxidation state of iron in the catalyst with 0 wt % lanthana were Fe+2.57. The findings of this paper emphasize the importance of surface sensitive UV-visible spectroscopy for determining the extent of catalyst reduction during operation. The paper highlights the potential to use bench-scale UV-visible spectroscopy to study the surface chemistry of catalysts instead of less-available synchrotron X-ray radiation facilities. View Full-Text
Keywords: iron water gas shift catalysts; extent of reduction; UV-visible spectroscopy; XANES iron water gas shift catalysts; extent of reduction; UV-visible spectroscopy; XANES
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MDPI and ACS Style

Hallac, B.B.; Brown, J.C.; Stavitski, E.; Harrison, R.G.; Argyle, M.D. In Situ UV-Visible Assessment of Iron-Based High-Temperature Water-Gas Shift Catalysts Promoted with Lanthana: An Extent of Reduction Study. Catalysts 2018, 8, 63.

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