Redox behavior and reduction mechanism of Fe2O3–CeZrO2 as oxygen storage material
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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 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.
KeywordsFe2O3 CeO2 Mixed Oxide Proton Exchange Membrane Fuel Cell Isoconversional Method
Funding for this research work by the German federal state of Saxony-Anhalt within the joint project “Dezentrales Brennstoffzellen-basiertes Energieerzeugungssystem für den stationä ren Betrieb in der Leistungsklasse 20 kW” is gratefully acknowledged. The authors are also very thankful to Dr. Heike Lorenz, Max-Planck-Institute in Magdeburg, for her support in performing the XRD measurements, and to Dr. Veit, Institute for Experimental Physics of Magdeburg University, for preparing SEM images of our materials.
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