A Method of Decomposing Carbon Dioxide for Fixation of Carbon-14

To consecutively decompose 14CO2 into carbon (14C) through its reaction with Hz, an apparatus using microwave discharge and its conditioning were investigated. The reaction produces CO as an intermediate, and proceeds in the two steps of (1) “CO2+H2 → CO+H2O” and (2) “CO+H2+Cn → Cn+1+H2O”, where Cn denotes the carbon already deposited on the wall of the discharge tube. Preliminary dispersion of carbon to the wall of the discharge tube by sputtering of a graphite particle was effective to promote the reaction. Two silica discharge tubes (6 mm O.D., 4 mm I.D., and 150 mm length each) were connected in series to proceed the former reaction in the first discharge tube and the latter one in the second one. When a 1:3 mixture of CO2 and H2 (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60 h under microwave of 30–40 W supplied from two 2,450MHz power generators (200 W each), more than 90% of CO2 was converted into CO in the 1st ...