Effects of CeO2, ZrO2, and Al2O3 Supports on Iron Oxygen Carrier for Chemical Looping Hydrogen Generation

Fe2O3 is an excellent active metal oxide for chemical looping hydrogen generation (CLHG) with high conversion of CO to CO2 in the reduction stage, and high H2 mole fractions in the subsequent steam oxidation stage, especially for its low cost and abundance in nature. However, supports are generally used to improve its reactivity and stability and to eliminate its carbon deposition. In this paper, Fe-based oxygen carriers are prepared by a coprecipitation method with three supports, i.e., CeO2, ZrO2, and Al2O3. The reactivity, carbon deposition, redox stability, and sintering characteristics of the oxygen carriers are analyzed to investigate the effects of supports as well as the fundamental mechanism. The results show that the properties of the oxygen carriers highly rely on the support and its interaction with iron oxide. The oxygen carrier supported on Al2O3 exhibits poor reactivity and stability, and the oxygen carrier supported on ZrO2 leads to much carbon deposition, decreasing H2 purity, despite its high reactivity and stability. Nevertheless, the oxygen carrier supported on CeO2 demonstrates good reactivity and stability with no carbon deposition observed, and the reducible support CeO2 counteracts the negative effect originating from sintering and guarantees the reactivity and stability of Fe2O3/CeO2 due to its oxygen mobility property and the oxygen mobility enhancement originating from the formation of Fe–Ce solid solution and perovskite-type CeFeO3. Overall, the reducible CeO2 is a potential support to improve the redox characteristics of iron oxygen carrier in CLHG, and the Fe2O3/CeO2 exhibits the highest reactivity at 850 °C. In addition, all three oxygen carriers are characterized by scanning electron microscopy images, energy dispersive X-ray spectrometer analysis, and X-ray diffraction patterns before and after the redox cycles.