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).

KEYWORDS:

• carbon 14 fixation
• microwave discharge
• flow rate
• flow method
• decomposition
• carbon dioxide
• carbon monoxide
• carbon
• gaseous water
• linear gas velocity dependence
• residence time
• forward reaction
• reverse reaction
• 0.2l(STP)-H₂/h