Effects of supports on hydrogen production and carbon deposition of Fe-based oxygen carriers in chemical looping hydrogen generation

Abstract

Chemical looping hydrogen generation (CLHG) can produce high purity hydrogen from fuel gases with inherent separation of CO2. However, the performance of oxygen carrier in CLHG varies with the support materials. In this paper, the reactivity, carbon deposition, redox stability, hydrogen yield and purity, and sintering behavior of the Fe-based oxygen carriers were analyzed to investigate the effects of supports, i.e. Al2O3, SiO2, MgAl2O4, ZrO2 and YSZ (yttrium-stabilized zirconia). The results showed that the properties of the oxygen carriers, e.g. carbon deposition, reactivity and stability, mainly depended on the support and its interaction with iron oxides. The reactivity and hydrogen yield for the oxygen carriers investigated followed the order: Fe2O3/MgAl2O4 > Fe2O3/ZrO2 > Fe2O3/YSZ > Fe2O3/Al2O3 > Fe2O3/SiO2, and the order of hydrogen purity was identical with that of hydrogen yield as a result of carbon deposition. Furthermore, the hydrogen purity of the Fe-based oxygen carriers supported by MgAl2O4, ZrO2, or YSZ could reach above 99.5% and Fe2O3/YSZ showed the lowest carbon deposition. The oxygen carriers, Fe2O3/MgAl2O4 and Fe2O3/SiO2, were selected to be characterized by SEM images and XRD patterns before and after the redox cycles.