A study of surface and structural changes of magnetite cycling material during chemical looping for hydrogen production from bio-ethanol

Magnetite samples were synthesized and studied as the cycling material of a chemical loop process for hydrogen production from ethanol and water used as reducing and oxidizing species, respectively. Surface and structural changes during the process were characterized by various techniques such as X-ray diffraction, X-ray photoelectron, and Mossbauer spectroscopy in order to evidence the real cycling process and understand the cause of the material deactivation so that it can be suppressed or minimized for an industrial application. We found that the complete recovery of the initial cycling material was possible, but that a slow accumulation of coke took place over time under cycling conditions. Indeed, this deposited coke corresponds to only a part of the coke formed, since water makes partial re-oxidation possible. A third step to burn the coke left over by the air will thus have to be periodically added for a sustainable industrial process, unless a cycling material and/or certain conditions capable of either totally preventing the formation of coke or leading to the formation of coke that is not oxidized by water are found.