This study deals with the processes of converting trace CH4 in the oxidation reaction and adsorbing H2O. The conversion of CH4 was confirmed at various reaction temperatures and flow rates by injecting O2 above the equivalence ratio of CH4 in Ar. The conversion was higher at a higher reaction temperature and a lower flow rate. Also, the impurity effects of CO2, CO, and H2O coexisting in the feed gas with CH4 were investigated. When CO2 and H2O were included in the feed gas, CH4 conversion was decreased, and CO contained in the feed gas increased CH4 conversion by the heat of oxidation reaction. When CH4 is converted to CO2 and H2O through oxidation and H2O is adsorbed on the adsorbent, complete recovery of hydrogen isotopes can be obtained. Molecular sieve was used as the adsorbent, and the water adsorption capacity of the adsorbent was confirmed by generating water through the generator. Finally, it was confirmed that converted H2O from CH4 was adsorbed on the absorbent.