Evaluation of the Redox Performance and Characterization of Fe₂O₃/CeO₂/ZrO₂ Oxygen Carriers under High Temperature in Situ Gasification Chemical-Looping Combustion Conditions

Abstract

Iron-based oxygen carriers with a CeO2 support have interesting redox applications in chemical-looping combustion (CLC). CeO2 behaves as an active support for many oxygen carrier applications because of the reversible release of lattice oxygen. High temperature processes may lead to improved process efficiency; however, the poor thermal stability of CeO2 gives rise to a need for oxygen carriers that can resist sintering and agglomeration and maintain reactivity after multiple reduction and oxidation (redox) cycles during in situ gasification chemical-looping combustion (iG-CLC) at 1100 °C. In the present study, Fe-based oxygen carriers on CeO2, ZrO2, and Ce0.75Zr0.25O2 supports were prepared by a coprecipitation method. The redox stability, reactivity, and sintering of the oxygen carriers were evaluated to investigate the effect of the CeO2–ZrO2 solid solution support. The oxygen transport capability was evaluated in a drop tube fixed-bed reactor under iG-CLC conditions with coal char at 1100 °C for 10 redox cycles. The CeO2–ZrO2 solid solution improved the oxygen mobility of the support from the creation of more oxygen defects. The Fe–Ce oxygen carrier had the highest oxygen transport capability because of the formation of cerium orthoferrite (CeFeO3) during high temperature reduction. The Fe–Ce–Zr oxygen carrier showed improved reactivity over the Fe–Ce oxygen carrier as the number of redox cycles increased. The oxygen carriers, before and after multiple redox cycles, were characterized by X-ray diffraction, scanning electron microscopy, and surface/pore analysis.