Hydrogen production through methane–steam cyclic redox processes with iron-based metal oxides

The redox performance of pure iron oxide (Fe₂O₃) and iron oxide modified with ceria (CeO₂) and/or zirconia (ZrO₂) as an oxygen carrier was investigated for hydrogen (H₂) production through a methane-steam redox process. The addition of both CeO₂ and ZrO₂ were found to be a more effective modification of Fe₂O₃ than the addition CeO₂ or ZrO₂ alone. It was found that the reducibility of Fe₂O₃ was enhanced by CeO₂ and the thermal stability of Fe₂O₃ was improved by ZrO₂. These results, therefore, led to the conclusion of the synergistic effect in the Fe₂O₃-CeO₂-ZrO₂ mixed oxide. As a result, both the redox activity and the thermal stability were significantly improved, and increases in H₂ yield and purity could be maintained by the modification. The redox temperature was found to have a significant effect on redox performance. The production of H₂ was considerably improved when the redox temperature was increased from 650 to 750 °C. The ZrO₂ concentration in Fe₂O₃-CeO₂-ZrO₂ mixed oxide samples was also found to influence performance with the highest H₂ yield observed at a ZrO₂ concentration of 75 wt.%. Although all materials tested showed a reduction in surface area in the first redox cycle, the change in surface area in subsequent cycles was found to be smaller and the yield of H₂ could be maintained at a constant level over a longer period for the mixed oxide containing 75 wt.% ZrO₂.