The synergetic effect of metal oxide support on Fe2O3 for chemical looping combustion: A theoretical study

This study deals with the synergetic effect of Al2O3 on Fe2O3 for chemical-looping combustion (CLC) of CO, in comparison with the synergetic effects of ZrO2 and MgO reported in our previous works. Property analysis of Fe2O3/Al2O3 shows that new bonds form cross the interface making Fe2O3 less prone to agglomerate on Al2O3, and 0.129 e transfers from Al2O3 to Fe2O3 to activate the electronic state of Fe2O3. Al2O3 [ZrO2 and MgO] favors the thermal stability of Fe2O3 by preventing the phase transformation, markedly regulates charge populations on the O-Fe bonds and their overlaps and hence tunes the redox properties of Fe2O3. The reaction mechanism analysis demonstrates that Al2O3 [ZrO2 and MgO] activates Fe2O3 for oxidizing CO into CO2 (accompanied by the reduction of Fe2O3) in the fuel reactor, which decrease the height of barrier energy (Ea), and the Ea follows clearly Fe2O3 > Fe2O3/Al2O3 > Fe2O3/MgO > Fe2O3/ZrO2. However, these supports usually increase the Ea for oxidizing Fe2O2 into Fe2O3 by O2 in the air reactor, and the Ea follows clearly Fe2O3/ZrO2 > Fe2O3/Al2O3 > Fe2O3/MgO > Fe2O3. It is argued that different supports could be applied to a given CLC system of different thermodynamic properties.