Role of metal oxide support in redox reactions of iron oxide for chemical looping applications: experiments and density functional theory calculations

Aided by an oxygen carrier such as iron oxide, the chemical looping process can convert carbonaceous fuels while effectively capturing CO2. Previous experimental studies indicate that adding TiO2 support to iron oxide can notably improve the reactivity of iron oxide over multiple redox cycles, making it more suitable for chemical looping applications. In this study, wustite (Fe1-xO) was used to represent pure iron(II) oxide and ilmenite (FeTiO3) was used to represent TiO2 supported iron(II) oxide. The underlying mechanisms for the improved iron oxide performance with TiO2 support are investigated through experiments and periodic Density Functional Theory (DFT) calculations. Both experimental and DFT studies indicate that TiO2 support is unlikely to reduce the activation energy for the reduction of iron(II) oxide. The support, however, can significantly lower the energy barrier for O2- migration within the dense solid phase, thereby enhancing the O2- diffusivity. The good agreements between experiments and DFT calculations confirm that the improved reactivity and recyclability of TiO2 supported iron oxide particles are likely to result from the significantly enhanced O2- diffusivity with the presence of support.