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Title: Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity

Abstract

A series of supported CrO 3/Fe 2O 3 catalysts were investigated for the high-temperature water-gas shift (WGS) and reverse-WGS reactions and extensively characterized using in situ and operando IR, Raman, and XAS spectroscopy during the high-temperature WGS/RWGS reactions. The in situ spectroscopy examinations reveal that the initial oxidized catalysts contain surface dioxo (O=) 2Cr 6+O 2 species and a bulk Fe 2O 3 phase containing some Cr 3+ substituted into the iron oxide bulk lattice. Operando spectroscopy studies during the high-temperature WGS/RWGS reactions show that the catalyst transforms during the reaction. The crystalline Fe 2O 3 bulk phase becomes Fe 3O 4 ,and surface dioxo (O=) 2Cr 6+O 2 species are reduced and mostly dissolve into the iron oxide bulk lattice. Consequently, the chromium–iron oxide catalyst surface is dominated by FeO x sites, but some minor reduced surface chromia sites are also retained. The Fe 3–-xCr xO 4 solid solution stabilizes the iron oxide phase from reducing to metallic Fe0 and imparts an enhanced surface area to the catalyst. Isotopic exchange studies with C 16O 2/H 2 → C 18O 2/H 2 isotopic switch directly show that the RWGS reaction proceeds via the redox mechanism and only O* sites frommore » the surface region of the chromium–iron oxide catalysts are involved in the RWGS reaction. The number of redox O* sites was quantitatively determined with the isotope exchange measurements under appropriate WGS conditions and demonstrated that previous methods have undercounted the number of sites by nearly 1 order of magnitude. The TOF values suggest that only the redox O* sites affiliated with iron oxide are catalytic active sites for WGS/RWGS, though a carbonate oxygen exchange mechanism was demonstrated to exist, and that chromia is only a textural promoter that increases the number of catalytic active sites without any chemical promotion effect.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1354339
Report Number(s):
BNL-112855-2016-JA
Journal ID: ISSN 2155-5435
DOE Contract Number:
SC00112704
Resource Type:
Journal Article
Resource Relation:
Journal Name: ACS Catalysis; Journal Volume: 6; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; in situ; isotope exchange; metal oxide; operando; spectroscopy; surface; water−gas shift

Citation Formats

Keturakis, Christopher J., Zhu, Minghui, Gibson, Emma K., Daturi, Marco, Tao, Franklin, Frenkel, Anatoly I., and Wachs, Israel E.. Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity. United States: N. p., 2016. Web. doi:10.1021/acscatal.6b01281.
Keturakis, Christopher J., Zhu, Minghui, Gibson, Emma K., Daturi, Marco, Tao, Franklin, Frenkel, Anatoly I., & Wachs, Israel E.. Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity. United States. doi:10.1021/acscatal.6b01281.
Keturakis, Christopher J., Zhu, Minghui, Gibson, Emma K., Daturi, Marco, Tao, Franklin, Frenkel, Anatoly I., and Wachs, Israel E.. Mon . "Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity". United States. doi:10.1021/acscatal.6b01281.
@article{osti_1354339,
title = {Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity},
author = {Keturakis, Christopher J. and Zhu, Minghui and Gibson, Emma K. and Daturi, Marco and Tao, Franklin and Frenkel, Anatoly I. and Wachs, Israel E.},
abstractNote = {A series of supported CrO3/Fe2O3 catalysts were investigated for the high-temperature water-gas shift (WGS) and reverse-WGS reactions and extensively characterized using in situ and operando IR, Raman, and XAS spectroscopy during the high-temperature WGS/RWGS reactions. The in situ spectroscopy examinations reveal that the initial oxidized catalysts contain surface dioxo (O=)2Cr6+O2 species and a bulk Fe2O3 phase containing some Cr3+ substituted into the iron oxide bulk lattice. Operando spectroscopy studies during the high-temperature WGS/RWGS reactions show that the catalyst transforms during the reaction. The crystalline Fe2O3 bulk phase becomes Fe3O4 ,and surface dioxo (O=)2Cr6+O2 species are reduced and mostly dissolve into the iron oxide bulk lattice. Consequently, the chromium–iron oxide catalyst surface is dominated by FeOx sites, but some minor reduced surface chromia sites are also retained. The Fe3–-xCrxO4 solid solution stabilizes the iron oxide phase from reducing to metallic Fe0 and imparts an enhanced surface area to the catalyst. Isotopic exchange studies with C16O2/H2 → C18O2/H2 isotopic switch directly show that the RWGS reaction proceeds via the redox mechanism and only O* sites from the surface region of the chromium–iron oxide catalysts are involved in the RWGS reaction. The number of redox O* sites was quantitatively determined with the isotope exchange measurements under appropriate WGS conditions and demonstrated that previous methods have undercounted the number of sites by nearly 1 order of magnitude. The TOF values suggest that only the redox O* sites affiliated with iron oxide are catalytic active sites for WGS/RWGS, though a carbonate oxygen exchange mechanism was demonstrated to exist, and that chromia is only a textural promoter that increases the number of catalytic active sites without any chemical promotion effect.},
doi = {10.1021/acscatal.6b01281},
journal = {ACS Catalysis},
number = 7,
volume = 6,
place = {United States},
year = {Mon Jun 13 00:00:00 EDT 2016},
month = {Mon Jun 13 00:00:00 EDT 2016}
}