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The improvement of methane combustion activity was observed in cyclic temperature-programed and isothermal reactions over Pd/ZrO₂ catalysts by simple reduction/reoxidation treatment. The catalytic activity increased during the initial stages of isothermal reaction, and the light-off temperature was lowered as the number of cycles increased in the cyclic temperature-programed reaction. To reveal the origin of activation, variations in the reduction properties after the activation period were carefully investigated through CH₄ temperature-programed reduction (TPR) measurements. From the CH₄-TPR results, it was confirmed that the reduction temperature decreased significantly after activation. The observation of the CH₄-TPR peak at relatively low temperatures is directly proportional to the catalytic activity of CH₄ combustion. It was therefore concluded that repeated reduction/reoxidation occurred in the reactant stream, and this phenomenon allowed the combustion reaction to proceed more easily at lower temperatures.