We report a detailed reactor study of two sustainable Fe-based oxygen carriers (OC) prepared by spray drying. We compare Fe2O3 supported on Al2O3 and MgFeAlOx in isothermal Chemical Looping for Hydrogen Generation. In this process, CH4 is converted into syngas (H-2 + CO) and H2O is used as the oxidant that reduces to pure H-2. We noticed that the Al2O3 supported OC deactivates quickly while the MgFeAlOx supported OC withstands >60 cycles. We will show that the irreversible formation of an inactive FeAl2O4 phase is responsible for the deactivation of the alumina supported OC. We show detailed information on all the transient stages of the process and the different crystalline forms that are created, and combine this information into a full chemical looping cycle for both OC. Moreover, we evaluate the crushing strength of the oxygen carriers within a full chemical looping cycle and during long-term operation and we investigated the conversion of H2O and the selectivity to H-2-production during long-term oxygen carrier regeneration. The MgFeAlOx support with an extra Fe-based active phase is a promising material to replace the typical Ni-based oxygen carriers, as it forms a sustainable non-toxic, stable and green alternative for hydrogen generation by chemical looping. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.