Control of the mechanism of chemical-looping of ethanol in non-stoichiometric ferrites by Cu-Mn substitution

Copper-manganese spinel ferrites have been evaluated as solid oxygen carriers for the production of hydrogen from water by ethanol-steam redox cycles. The materials were characterized by X-ray diffraction, Mo center dot ssbauer spectroscopy, temperature-programmed reduction, oxygen isotope exchange and textural analysis. Surface re-actions were followed by DRIFT spectroscopy. The amount and purity of hydrogen, produced in redox cycles at constant temperature of 450 degrees C, were highly affected by the nature of the oxygen carrier phases in the reduction step of the cycle. Cu-rich ferrites were reduced by ethanol to metallic copper and iron carbides, whereas Mn-rich ferrites were less deeply reduced to manganowustite. Ethanol was mainly oxidized by Cu-ferrites to CO and CO2, while mainly oxydehydrogenation products were formed on Mn-ferrites. In the reoxidation of the oxygen carrier by steam, the production of CO and CO2 by oxidation of carbides negatively affected the purity of the hydrogen formed.