Low-Temperature Hydrogen Reduction of Iron Oxide (Fe₂O₃) with SiO₂ (Lunar Regolith) Mixture: An Experimental Approach to Hydrogen Spillover

The low-temperature hydrogen reduction of iron oxide is essential for transforming the steel industry sustainably with zero carbon emissions. Previous studies have shown that physically mixed reducible supports (Na-MOR and Na-ZSM-5) with Fe₂O₃ can lower the reduction temperature. However, the effect of mixing Fe₂O₃ with non-reducible support of SiO₂ has not been explored. Therefore, this study aims to validate the effectiveness of SiO₂ in lowering the reduction temperature of Fe₂O₃, potentially simplifying the iron smelting process with high effectiveness. We conducted XRD, SEM/EDS, H2-TPR, and XPS analyses to investigate the reduction characteristics. H₂-TPR results revealed that the final reduction peak of Fe₂O₃, corresponding to the FeO → Fe step, decreased from 783.7 °C (pure Fe₂O₃) to 731.2 °C (Fe₂O₃/SiO₂) and 458.6 °C (Fe₂O₃ + SiO₂). After reduction at 500 °C, XRD and XPS analyses showed that the majority of Fe₂O₃ in the Fe₂O₃ + SiO₂ was reduced to metallic iron, while Fe2O3/SiO2 still contained iron oxides (Fe₂O₃, Fe₃O₄, and FeO) and fayalite (Fe₂SiO₄), indicating incomplete reduction and thermal agglomeration, respectively. These findings confirm that physically mixed SiO₂ enhances the reduction rate significantly. The formation of Si-OH bonds after reduction suggests that hydrogen was adsorbed on the SiO₂ surface, which has lower adsorption energy than the Fe₃O₄ → FeO and FeO → Fe reduction energy. Consequently, hydrogen was adsorbed on the SiO₂, diffused through the long-distance hydrogen spillover mechanism to Fe₂O₃, and reduced the Fe₂O₃ to metallic iron.