Abstract
The catalytic properties of unsupported iron oxides, specifically magnetite (Fe3O4), were investigated for the reverse water-gas shift (RWGS) reaction at temperatures between 723 K and 773 K and atmospheric pressure. This catalyst exhibited a fast catalytic CO formation rate (35.1 mmol h−1 gcat.−1), high turnover frequency (0.180 s−1), high CO selectivity (>99%), and high stability (753 K, 45000 cm3h−1gcat.−1) under a 1:1 H2 to CO2 ratio. Reaction rates over the Fe3O4 catalyst displayed a strong dependence on H2 partial pressure (reaction order of ~0.8) and a weaker dependence on CO2 partial pressure (reaction order of 0.33) under an equimolar flow of both reactants. X-ray powder diffraction patterns and XPS spectra reveal that the bulk composition and structure of the post-reaction catalyst was formed mostly of metallic Fe and Fe3C, while the surface contained Fe2+, Fe3+, metallic Fe and Fe3C. Catalyst tests on pure Fe3C (iron carbide) suggest that Fe3C is not an effective catalyst for this reaction at the conditions investigated. Gas-switching experiments (CO2 or H2) indicated that a redox mechanism is the predominant reaction pathway.
Highlights
X-ray powder diffraction patterns and X-ray photoelectron spectroscopy (XPS) spectra reveal that the bulk composition and structure of the post-reaction catalyst was formed mostly of metallic Fe and Fe3 C, while the surface contained
Today’s anthropogenic emissions of carbon dioxide to the atmosphere amount to about 35,000 Tg per year, and the greenhouse effect of these accumulated emissions has been recognized as an alarming hazard to the well-being of modern societies
A recent National Academies of Science and Engineering report [1] on CO2 waste gas utilization highlights the conversion of CO2 by hydrogenation into CO and water—the reverse water-gas shift (RWGS) reaction, Equation (1)— as critical, and points to the need for improved catalysts with high stability and durability
Summary
Today’s anthropogenic emissions of carbon dioxide to the atmosphere amount to about 35,000 Tg per year, and the greenhouse effect of these accumulated emissions has been recognized as an alarming hazard to the well-being of modern societies. A recent National Academies of Science and Engineering report [1] on CO2 waste gas utilization highlights the conversion of CO2 by hydrogenation into CO and water—the reverse water-gas shift (RWGS) reaction, Equation (1)— as critical, and points to the need for improved catalysts with high stability and durability. The RWGS reaction can be part of a two-step hydrogenation process for the conversion of CO2 to valuable products. CO2 is reduced to CO via the RWGS reaction, and second, CO can be converted to either hydrocarbons via the Fischer-Tropsch (FT) process or methanol via CAMERE (CArbon dioxide hydrogenation to form MEthanol via a Reverse WGS reaction) process [2]. The RWGS reaction is an endothermic reaction (∆H◦ 298 K = 41.2 kJ mol−1 ), and is thermodynamically favorable at higher temperatures
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