Evolution of Sm-Doped Fe2O3/CeO2 Oxygen Carriers in Chemical Looping Hydrogen Generation

The Sm-doped Fe2O3/CeO2 is desirable for chemical looping hydrogen generation (CLHG) owing to its satisfactory oxygen ion conductivity, and the reactivity of Fe2O3/Ce0.8Sm0.2O1.9 (FSDC20) is the highest among the Sm-doped Fe2O3/CeO2 oxygen carriers with different Sm-doping amounts. This work is focused on the performance evolution of FSDC20 in CLHG with Fe2O3/CeO2 (FSDC0) as comparison, and the related mechanisms are explored. The results show that the evolution of H-2 yield with redox cycles for both samples contain an activation and an attenuation process, and the fourth cycle acts as the demarcation point for FSDC20 before the H-2 yield stabilizes. Specifically, the activation mainly lie in the phase transition from Fe3O4 to FeO, and the activation and attenuation processes can be ascribed to the particle microstructure evolution. For the activation process in the first four cycles, the grains on the particle aggregate together, however, with porous structure, and the improved reactivity can be attributed to the enhanced interaction between Fe2O3 and CeO2 as well as the generation of CeFeO3. However, the grains continue to aggregate on a large scale after the fourth cycle, leading to serious sintering and thus the attenuation process.