| Summary: | The catalytic properties of unsupported iron oxides, specifically magnetite (Fe<sub>3</sub>O<sub>4</sub>), 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<sup>−1</sup> g<sub>cat.</sub><sup>−1</sup>), high turnover frequency (0.180 s<sup>−1</sup>), high CO selectivity (>99%), and high stability (753 K, 45000 cm<sup>3</sup>h<sup>−1</sup>g<sub>cat.</sub><sup>−1</sup>) under a 1:1 H<sub>2</sub> to CO<sub>2</sub> ratio. Reaction rates over the Fe<sub>3</sub>O<sub>4</sub> catalyst displayed a strong dependence on H<sub>2</sub> partial pressure (reaction order of ~0.8) and a weaker dependence on CO<sub>2</sub> 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 Fe<sub>3</sub>C, while the surface contained Fe<sup>2+</sup>, Fe<sup>3+</sup>, metallic Fe and Fe<sub>3</sub>C. Catalyst tests on pure Fe<sub>3</sub>C (iron carbide) suggest that Fe<sub>3</sub>C is not an effective catalyst for this reaction at the conditions investigated. Gas-switching experiments (CO<sub>2</sub> or H<sub>2</sub>) indicated that a redox mechanism is the predominant reaction pathway.
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