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 H-2 production via decomposition of water. The powders were completely reduced in hydrogen (10%), and exposed to steam at temperature ranging from 500 to 800 degrees C producing about 0.2 mmol of H-2 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. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.