Transformation of methane into synthesis gas using the redox property of Ce–Fe mixed oxides: Effect of calcination temperature

Ce–Fe mixed oxides prepared by co-precipitation were used as oxygen carriers for converting methane into synthesis gas through gas–solid reactions. The structural evolution and reducibility of Ce–Fe oxygen carriers with calcination temperatures from 600 to 900 °C were investigated by XRD, BET, Raman, XPS and TPR techniques and correlated to their activity for methane selective oxidation. The Ce–Fe mixed oxides calcined at low temperatures (e.g., 600 °C) show abundant oxygen vacancies and high specific surface areas, which enhances the concentration of surface adsorbed oxygen and favors the complete oxidation of methane by means of gas–solid reactions. On the other hand, a calcination temperature of 900 °C results in serious sintering and militates against the formation of Ce–Fe solid solution, which brings about catalytic methane decomposition because of the low lattice oxygen mobility. A compromise calcination temperature at 800 °C favors the interaction between iron and cerium oxides, which could improve the lattice oxygen mobility of Ce–Fe oxygen carrier, leading to a high reactivity for methane selective oxidation. More importantly, the lattice oxygen mobility of the oxygen carrier is enhanced by the generation of oxygen vacancies after a repetitive redox treatment (methane reduction/air re-oxidation), which allows the Ce–Fe oxygen carrier to maintain a high activity and stability during the successive production of synthesis gas through a redox process.