The steam iron process has been investigated for the production of pure hydrogen using iron oxide based materials. Hydrogen is produced in a cyclic process which is based upon reduction of a metal oxide via suitable reductants, followed by re-oxidation of the reduced material using steam.

Reduction:
Fe3O4 + 4H2 -> 3Fe + 4H2O
Fe3O4 + 4CO -> 3Fe + 4CO2
Fe3O4 + CO + 3H2 -> 3Fe + CO2 + 3H2O
Fe3O4 + 4CH4 -> 3Fe + 4CO + 8H2
Oxidation:
3Fe + 4H2O -> Fe3O4 + 4H2

Iron oxide reduction by carbon based reductants is prone to coking and possible formation of iron carbide species. Ceria has demonstrated high oxygen storage capacity and an ability to oxidize soot. Its use as a promoter should help overcome this problem, as well as facilitate better reducibility/reoxidation over a number of cycles. Addition of zirconia to ceria produces a marked increase in oxygen storage capacity, thereby improving the properties of ceria zirconia as a promoter. Sintering of reduced iron oxide can be mitigated by introduction of zirconia as a promoter.

The presence of promoters creates greater resistance to sintering over a number of cycles. Stabilisation of intermediate oxide phases promotes more rapid redox cycling, further decreasing sintering effects by reduced exposure time at high temperature. Higher retention of surface area results in a greater percentage of hydrogen being generated during the oxidation phase per gram of catalyst.