Effects of Zr doping on Fe2O3/CeO2 oxygen carrier in chemical looping hydrogen generation

The CeO2-supported Fe2O3 is a satisfactory alternative oxygen carrier for chemical looping hydrogen generation (CLHG), which demonstrates good reactivity and stability with no carbon deposition observed due to the oxygen mobility property of CeO2. However, sintering always takes place because of the low thermal stability of CeO2. In the present work, the Fe2O3/CeO2 oxygen carriers doped by Zr cation, resulting in the CexZr1−xO2 mixed oxide supports, were prepared by co-precipitation method. To optimize the Fe2O3/CexZr1−xO2 oxygen carriers, the Ce/Zr ratio was systematically changed. The reactivity, redox stability, carbon deposition, and sintering characteristics of the oxygen carriers were analyzed to investigate the effects of Zr doping as well as the fundamental mechanism, and the results showed that Fe2O3/Ce0.75Zr0.25O2 was the best oxygen carrier considering the comprehensive characteristics with no CO or CO2 (detection limit 0.01% in volume) observed in the obtained hydrogen. The generated solid solution Ce0.75Zr0.25O2 could improve the oxygen mobility and thermal stability of the oxygen carrier. In addition, the Zr cation in Ce0.75Zr0.25O2 can inhibit the migration of the Fe element from the bulk to surface of the particles, enhancing its resistance to sintering, which can further promote the reactivity and redox stability. The Ce0.75Zr0.25O2 is a potential support to improve the redox characteristics of iron oxygen carrier in CLHG, although the phase segregation was observed after redox cycles, which can be inimical to the reactivity of the Fe2O3/Ce0.75Zr0.25O2 oxygen carrier. Furthermore, the oxygen carriers were characterized by X-ray diffraction patterns, hydrogen temperature-programmed reduction measurement, scanning electron microscopy images, energy dispersive X-ray spectrometer analysis, and Raman spectra before and after the redox cycles.