Conversion of Carbon Dioxide and Methane into More Valuable Compounds Using Electric Energy and Photoenergy

Abstract

The concentration of carbon dioxide in the atmosphere continues to increase with an increase of fossil fuel consumption. Methane is the dominant ingredient of natural gas, and is produced more widely throughout the world than crude oil. However, these gases are too inert to be used as raw materials for the chemical industry.
In the present study, an investigation has been made to convert CO₂ and CH₄ into more valuable compounds by using electric energy and photoenergy. CO₂ has been electrochemically reduced to methanol in the presence of homogeneous catalysts with a mediated electrode. The surface-confined compounds capable of functioning as a mediator were Everitt′s salt, metal porphyrins, and quinones. Methane has been converted into oxygen-containing compounds by photochemical reactions., Irradiation to gas mixtures of methane, water, and air with a low-pressure mercury lamp gave formaldehyde, methanol and acids as major products. The selectivity of this reaction was dependent on the molar ratio of methane to water vapor, the feeding rate of air and the rate of gas circulation. The methane conversion is initiated by the hydroxyl radical and hydrogen atom which are formed by photolysis of water vapor. The hydroxyl radical reacts with methane to produce methanol, and the hydrogen atom abstracts a hydrogen atom from methane to give a methyl radical. Further reactions of the methyl radical with methane and/or methanol yield species of higher order.