Theoretical study of reduction mechanism of Fe2O3 by H2 during chemical looping combustion

An atomic-level insight into the H-2 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 H-2 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 H-2 molecule adsorbed on an O top site could directly form H2O precursor on the O-3-terminated surface. Further, the newly formed HAO bond was activated, and the H atom could migrate from one O site to another, consequently forming the H2O precursor. In the H-2 oxidation process, the decomposition of H-2 molecule was the rate-determining step for the O-3-terminated surface with an activation energy of 1.53 eV. However, the formation of H2O was the ratedetermining step for the Fe-terminated surface with an activation energy of 1.64 eV. The Feterminated surface is less energetically favorable for H-2 oxidation than that the O-3-terminated surface owing to the steric hindrance of Fe atom. These results provide a fundamental understanding about the reaction mechanism of Fe2O3 with H-2, which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H-2. (C) 2021 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.