The kinetics of redox reactions of iron oxide in oxygen carrier 50Fe(2)O(3)/MgAl2O4 are examined using different time-resolved techniques. Reduction kinetics are studied by H-2 temperature-programmed reduction (H-2-TPR) monitored by time-resolved in situ XRD. In contrast to conventional TPR, in situ XRD distinguishes the three-stage reduction of Fe2O3 -> Fe3O4 -> FeO -> Fe. It also shows that the oxidation of Fe -> Fe3O4 by CO2 has no intermediate crystalline phases, explaining why its kinetics can easily be investigated by conventional CO2 temperature-programmed oxidation (CO2-TPO). A shrinking core model which takes into account solid state diffusion allows describing the experimental data.