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.

► The addition of both ceria (CeO2) and zirconia (ZrO2) effectively improved the stability of iron oxide for producing hydrogen from a methane–steam redox process.
► Synergistic effects were found in the mixed Fe2O3-CeO2-ZrO2 oxide. During methane–steam cycles, CeO2 provided a promoting effect for the redox reaction and ZrO2 provided added resistance against thermal sintering.
► The production of hydrogen from the Fe2O3-CeO2-ZrO2 oxide was maintained for up to 25 methane–steam cycles.