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

Abstract

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, wüstite (Fe_1−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.