In the case of Fe80-160, a decrease in the carbon dioxide and
hydrogen production was observed during the reduction and the
oxidation, respectively, with the number of cycles. Evidence for
phase changes could not be distinguished in terms of any kinetic
impact on the outlet gas phase mole fractions. When LSF731 was
used, hydrogen was formed only for a very short period of time.
A very narrow peak can be observed in Fig. 7. Nevertheless, the
shape of the curves was the same during the 1st and the 25th cycle,
indicating that the material behaviour was stable with time as
demonstrated by Murugan et al. [8] in a previous work. Carbon
dioxide and hydrogen production were much higher using the
composite material LSF-30Fe-Pec-P than with either the LSF731
or iron oxide alone. A larger peak was obtained with clear kinetic
evidence of what may be phase transitions between Fe–FeO and
FeO–Fe3O4. Mass balances showed that, within measurement
uncertainty, carbon formation did not take place with any of the
OCMs.