Comment by pfdietz

Reducing ferric oxide to magnetite, perhaps, but I think if you tried that with ferrous oxide you'd get iron vapor coming off along with the oxygen.

An issue with any high temperature process is things start evaporating. This is part of why carbothermal reduction of aluminum oxide doesn't work: at the required temperature aluminum oxide is volatile.

(There are thermochemical water splitting technologies that exploit partially reducing transition or rare earth oxides at high temperature, then reacting them with steam at a bit lower temperature to make hydrogen. I believe cerium oxides are the current best approach there, although still not competitive.)