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 reoxidation of the reduced material with water vapor. For identification of the reduction kinetics H2-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–CeZrO2was 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.