Mechanistic insights into H₂ and CO interactions with Fe₃O₄(111) surface: A computational study for hydrogen-based direct reduction process

The novel process of hydrogen-based shaft furnaces (HSFs) has attracted considerable attention because of their significant reduction of CO₂ emissions. In this study, the interaction of H₂ and CO with Fe_tet1- and Fe_oct2-terminated Fe₃O₄(111) surfaces under HSF conditions, including their adsorption and reduction behaviors, was investigated using the density functional theory method. The results indicated that the H₂ molecule adsorbed onto the Fe_tet1-terminated surface with an adsorption energy (AE) of −1.36 eV, whereas the CO molecule preferentially adsorbed on the Fe_oct2-terminated surface with an AE of −1.56 eV. Both H₂ and CO can readily undergo reduction on the Fe_tet1-terminated surface (corresponding to energy barriers of 0.83 eV and 2.23 eV, respectively), but kinetically the reaction of H₂ is more favorable than that of CO. With regard to the thermodynamics at 400–1400 K, the H₂ was easy to be adsorbed, while the CO would like to react on the Fe_tet1-terminated surface. These thermodynamically tendencies were reversed on the Fe_oct2-terminated surface. The thermodynamic disadvantage of the reaction of H₂ on the Fe_tet1-terminated surface was offset by an increase in the temperature. Furthermore, the adsorption of H₂ and CO on the Fe_tet1-terminated surface was competitive, whereas the adsorption of them on the Fe_oct2-terminated surface was synergistic. Therefore, iron ores with a higher proportion of Fe_tet1-terminated surface can be applied for the HSF process. In conjunction with the increase in reduction temperature, the increase in the ratio of H₂ in the reducing gas would promote efficient HSF smelting. These observations provide effective guidance for optimizing the practical operation parameters and advancing the development of the HSF process.