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

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 car-rier and the usage of green energy resource such as H2.