Kinetics of mixed copper–iron based oxygen carriers for hydrogen production by chemical looping water splitting

Water splitting for hydrogen production through chemical looping was investigated in a micro fluidized bed reactor. Iron, copper and mixed iron–copper based oxygen carriers were prepared by coprecipitation and incipient wetness impregnation and compared in terms of H2 production via decomposition of water. The powders were completely reduced in hydrogen (10%), and exposed to steam at temperature ranging from 500 to 800 °C producing about 0.2 mmol of H2 per gram of metal oxide in the case of a mixed Cu–Fe powder. Powders prepared by coprecipitation showed poor fluidization properties as well as poor reactivity compared to those synthesized through impregnation. Temperature Programmed Reductions (TPR) experiments carried out on a TGA showed that particles have different oxygen carrying capacities, ranging from 16% in the case of a copper oxide prepared by coprecipitation, to around 1% for other particles prepared impregnation. Kinetics were evaluated following gas–solid mechanisms for two mixed Fe–Cu carriers. Oxidation of the mixed Fe–Cu carrier prepared by impregnation is well represented by a shrinking core model (phase-boundary-controlled). The activation energy for oxidation of this carrier was 46 kJ/mol. Oxidation of the mixed Fe–Cu carrier prepared by coprecipitation is well represented by a nuclei growth model (Avrami) with random nucleation and an activation energy of 51 kJ/mol.