UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Dynamics of CrO3-Fe2O3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity

Keturakis, CJ; Zhu, M; Gibson, EK; Daturi, M; Tao, F; Frenkel, AI; Wachs, IE; (2016) Dynamics of CrO3-Fe2O3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity. ACS Catalysis , 6 (7) pp. 4786-4798. 10.1021/acscatal.6b01281. Green open access

[thumbnail of Gibson_cjk WGS Cr-Fe Manuscript v3.pdf]
Preview
Text
Gibson_cjk WGS Cr-Fe Manuscript v3.pdf - Accepted Version

Download (2MB) | Preview

Abstract

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.

Type: Article
Title: Dynamics of CrO3-Fe2O3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acscatal.6b01281
Publisher version: http://dx.doi.org/10.1021/acscatal.6b01281
Language: English
Additional information: Copyright © 2016 American Chemical Society
Keywords: Science & Technology, Physical Sciences, Chemistry, Physical, Chemistry, Water-Gas Shift, Operando, In Situ, Spectroscopy, Metal Oxide, Isotope Exchange, Surface, Chromia-Promoted Magnetite, Iron-Based Catalysts, Ray Photoelectron-Spectroscopy, Fischer-Tropsch Synthesis, Supported Metal-Oxides, Oxygen Bond Strength, Raman-Spectroscopy, Infrared-Spectroscopy, Surface-Chemistry, Modified Ferrites
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1510114
Downloads since deposit
Loading...
727Downloads
Download activity - last month
Loading...
Download activity - last 12 months
Loading...
Downloads by country - last 12 months
Loading...

Archive Staff Only

View Item View Item