Abstract: An atomic-level insight into the H₂ adsorption and oxidation on the Fe₂O₃ surface during chemical-looping combustion was provided on the basis of density functional theory calculations in this study. The results indicated that H₂ molecule most likely chemisorbs on the Fe₂O₃ surface in a dissociative mode. The decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the surface. In particular, the H₂ molecule adsorbed on an O top site could directly form H₂O precursor on the O₃-terminated surface. Further, the newly formed H-O bond was activated, and the H atom could migrate from one O site to another, consequently forming the H₂O precursor. In the H₂ oxidation process, the decomposition of H₂ molecule was the rate-determining step for the O₃-terminated surface with an activation energy of 1.53 eV. However, the formation of H₂O was the rate-determining step for the Fe-terminated surface with an activation energy of 1.64 eV. The Fe-terminated surface is less energetically favorable for H₂ oxidation than that the O₃-terminated surface owing to the steric hindrance of Fe atom. These results provide a fundamental understanding about the reaction mechanism of Fe₂O₃ with H₂, which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H₂.

Key words: Chemical-looping combustion, Fe₂O₃ oxygen carrier, H₂ adsorption, Density functional theory, Reaction mechanism

摘要： An atomic-level insight into the H₂ adsorption and oxidation on the Fe₂O₃ surface during chemical-looping combustion was provided on the basis of density functional theory calculations in this study. The results indicated that H₂ molecule most likely chemisorbs on the Fe₂O₃ surface in a dissociative mode. The decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the surface. In particular, the H₂ molecule adsorbed on an O top site could directly form H₂O precursor on the O₃-terminated surface. Further, the newly formed H-O bond was activated, and the H atom could migrate from one O site to another, consequently forming the H₂O precursor. In the H₂ oxidation process, the decomposition of H₂ molecule was the rate-determining step for the O₃-terminated surface with an activation energy of 1.53 eV. However, the formation of H₂O was the rate-determining step for the Fe-terminated surface with an activation energy of 1.64 eV. The Fe-terminated surface is less energetically favorable for H₂ oxidation than that the O₃-terminated surface owing to the steric hindrance of Fe atom. These results provide a fundamental understanding about the reaction mechanism of Fe₂O₃ with H₂, which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H₂.

关键词: Chemical-looping combustion, Fe₂O₃ oxygen carrier, H₂ adsorption, Density functional theory, Reaction mechanism