Redox behavior and reduction mechanism of Fe2O3-CeZrO2 as oxygen storage material

Fe2O3-CeZrO2 is a suitable oxygen storage material for the production of pure hydrogen by a cyclic water gas shift (CWGS) process which is based on the reduction of the material by syngas followed by the re-oxidation of the reduced material with water vapor. For identification of the reduction kinetics H-2-temperature programmed reduction experiments were performed. Several kinetic models were tested and the activation energy of reduction was calculated by the Kissinger method, by model-based curve fitting and by the isoconversional analysis method. The reduction of Fe2O3-CeZrO(2)was found to occur in a four-step process including the reduction of Fe2O3,Fe3O4, and CeZrO2. The overall process can be interpreted as phase-boundary controlled reduction of Fe2O3 to Fe3O4, and two-dimensional nucleation controlled reduction of Fe3O4 to Fe and of CeO2 to Ce2O3. At higher oxygen conversion, the reduction of Fe3O4 and CeO2 are significantly influenced by volume-diffusion in the solid bulk.