Mechanisms and interactions in the reduction of Fe₂O₃ by H₂/CO mixed gas: Atomic insights from ReaxFF molecular dynamics simulations and experiments

The experiment explored the Fe₂O₃ reduction process with H₂/CO mixed gas and confirmed a promoting effect from CO when its volume proportion in mixed gas is 20% at 850°C. The ReaxFF molecular dynamics (MD) simulation method was used to observe the reduction process and provide an atomic-level explanation. The accuracy of the parameters used in the simulation was verified by the density functional theory (DFT) calculation. The simulation shows that the initial reduction rate of H₂ is much faster than that of CO (from 800 to 950°C). As the reduction proceeds, cementite, obtained after CO participates in the reduction at 850°C, will appear on the iron surface. Due to the active properties of C atoms in cementite, they are easy to further react with the O atoms in Fe₂O₃. The generation of internal CO may destroy the dense structure of the surface layer, thereby affecting the overall reduction swelling of Fe₂O₃. However, excess CO is detrimental to the reaction rate, mainly because of the poor thermodynamic conditions of CO in the temperature range and the molecular diffusion capacity is not as good as that of H₂. Furthermore, the surface structures obtained after H₂ and CO reduction have been compared, and it is found that the structure obtained by CO reduction has a larger surface area, thus promoting the subsequent reaction of H₂.