Decompositions of carbon dioxide, carbon monoxide and gaseous water by microwave discharge

Conditions for the effective decompositions of CO2, CO and H2O(g) in microwave discharge (20-100 W) were studied in a flow method, in connection with fixation of C-14 (in CO2). Carbon dioxide of 0.41 to 1.34 kPa was decomposed into CO in 73-92% yield in the linear gas velocity range of 0.01 to 0.56 m/s (the residence time in plasma, 4.50 to 0.08 s). For 0.83 kPa CO2, the maximum value of 92% was obtained at 0.04 to 0.06 m/s, and further increase in the linear gas velocity to 0.56 m/s decreased the yield to about 80%. Only 5% or less of CO (0.82 kPa) was converted to carbon under the same condition as above. Almost 100% of H2O(g) of 0.82 kPa was decomposed into H-2 and O-2 at 0.60 m/s (the residence time, 0.08 s) and 50 W. The effective decomposition of H2O(g) needs such a high linear gas velocity to suppress the reverse reaction. The use of the appropriate linear-gas-velocity is important for the effective decompositions of CO2 and H2O(g). The reaction of H-2 with O-2 to form H2O proceeds at temperature as low as 293 K on SUS and Cu metal surfaces; this phenomenon was applied to analysis of the decomposition of H2O(g).