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Temperature-programmed reaction of methane and temperature-programmed reduction were performed over gadolinia-doped ceria (GDC). It was found that CO2 formation can occur at very much lower temperature than CO formation. The surface lattice oxygen acts as the active site for CH4 adsorption. This active site has a dynamic characteristic due to the mobility of the lattice oxygen. The rates of CO and CO2 formations can be controlled by the supply rate of the lattice oxygen from the GDC bulk; this supply rate depends on the mobility and the concentration of the bulk lattice oxygen. CO2 formation is associated with the existing surface lattice oxygen while CO formation depends on the oxygen species coming from the bulk lattice during methane reaction. [ABSTRACT FROM AUTHOR]