Nonflame combustion technology (NFCT) is a harmonious energy utilization technology. There are not environmental-unfriendly gases such as NOx, CO2 discharged in the whole combustion process. Combustion processes realizes zero emission through this technology. Fe2O3 is involved as oxygen carrier, is examined thermodynamically, and the thermodynamic data of the redox reactions are calculated. Using the criteria of minimizing the Gibbs free energy, the equilibrium composition was investigated. The equilibrium analysis shows that producing complete oxidized resultants must have high molar ratio of Fe2O3/CH4. If quantity of Fe2O3 is not sufficient, more partial oxidized products such as CO, H2, even C will be produced.
The cerium iron complex oxides oxygen carrier was prepared by the co-precipitation method. The reactions between methane and lattice oxygen from the complex oxides were investigated in a fixed micro-reactor system. The reduced oxygen carrier could be re-oxidized by air and its initial state could be restored. The characterizations of the oxygen carriers were studied using XRD, O2-TPD, and H2-TPR. The results showed that the bulk lattice oxygen of CeO2-Fe2O3 was found to be suitable for the partial oxidation of methane to synthesis gas. There were two kinds of oxygen species on the oxygen carrier: the stronger oxygen species that was responsible for the complete oxidation of methane, and the weaker oxygen species (bulk lattice oxygen) that was responsible for the selective oxidation of methane to CO and H2 at a higher temperature. Then, the lost bulk lattice oxygen could be selectively supplemented by air re-oxidation at an appropriate reaction con- dition. CeFeO3 appeared on the oxygen carrier after 10 successive redox cycles, however, it was not bad for the selectivity of CO and H2.
The Ce-Fe-O mixed oxide with a ratio of Ce/Fe=7:3, which was prepared by coprecipitation method and employed as oxygen carrier, for direct partial oxidation of methane to syngas in the absence of gaseous oxygen was explored. The mixed oxide was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the catalytic performances were studied in a fixed-bed quartz reactor and a thermogravimetric reactor, respectively. Approximately 99.4% H2 selectivity, 98.8% CO selectivity and 94.9% CH4 conversion were achieved at 900 oC in fixed-bed experiments, furthermore, the increase of reaction temperature was favourable for the production of syngas.The results of thermal gravity cycle experiments showed that the Ce-Fe-O mixed oxide catalyst could complete five cycles in 10949 s in methane and air alternately atmosphere, and the catalyst regenerated with air has the same substance phase structure as the fresh when characterized by XRD. The SEM micrograph characterizations revealed that catalyst did not exhibit obvious agglomeration when exposed to alternating oxidizing and reducing atmosphere at a higher reaction temperature. In conclusion, the Ce-Fe-O mixed oxide as the oxygen carrier showed good activity and cycle performance. It was suggested that using lattice oxygen of Ce-Fe-O mixed oxide instead of gaseous oxygen to react with methane for production syngas is viable.
