Decompositions of Carbon Dioxide, Carbon Monoxide and Gaseous Water by Microwave Discharge

Abstract

Conditions for the effective decompositions of CO2, CO and H2 0(g) in microwave discharge (20–100 W) were studied in a flow method, in connection with fixation of 14C (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 H20(g) of 0.82 kPa was decomposed into H2 and O2 at 0.60 m/s (the residence time, 0.08 s) and 50 W. The effective decomposition of H2 0(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 H2 0(g). The reaction of H2 with O2 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).