Theoretical study of oxidation-reduction reaction of Fe_2O_3 supported on MgO during chemical looping combustion

摘要

We applied density-functional theory (DFT) in periodic system to investigate the two reactions (CO + Fe_2O_3/MgO→CO_2 + Fe_2O_2/MgO, O_2 + Fe_2O_2/MgO→O + Fe_2O_3/MgO) in chemical looping combustion system. While Fe_2O_3 was supported on MgO(l00) surface Fe_2O_3 gathered together to form a cluster shape on MgO(l 00), denoted as Fe_2O_3/MgO, where the Fe_2O_3 was activated by MgO(l00). Then CO interacted with Fe_2O_3/MgO and carbonate generated during a stepwise reaction with the calculated maximum barrier energy of 0.95 eV, far less than that of the reaction between CO and the pure Fe_2O_3 cluster (2.59 eV). CO was oxidized by Fe_2O_3/MgO and then Fe_2O_3/MgO transformed into the reduced state Fe_2O_2/MgO, corresponding to the reaction in the fuel reactor in the CLC system. Then the breaking of the adsorbed O_2 molecule on Fe_2O_2/MgO made an 0 atom bind to a Fe site with the barrier energy of 0.20 eV, which played as the key step for the oxidizing of Fe_2O_2/MgO by O_2 into Fe_2O_3/MgO, corresponding to the reaction in the air reactor in the CLC system.