Fundamental Study on the Reduction of Carbon Dioxide to Methanol/Ethanol Using a Cyclic Fenton Reaction

Conversion of carbon dioxide to useful chemicals or fuels has become an active area of research. However, most methods used in these studies need expensive or precious reagents, such as hydrogen or rare metals. The objective of this study is the reduction of carbon dioxide to organic compounds using a cyclic Fenton reaction that uses only inexpensive reagents. We achieved carbon dioxide reduction to methanol and ethanol using this reaction at ambient temperatures and pressures. The Fenton reaction was promoted by the repetitive addition of H2O2 and Fe(II) salts, resulting in the synthesis of methanol/ethanol and formic/acetic acids from carbon dioxide saturated water. In addition, it was found that H2O2 and Fe(II) in a molar ratio of 1 or 2 is optimal for the reaction as this increase the generation of ·OH. The catalytic effects of magnetite, pyrite, sodium hypophosphite and copper sulfate were also investigated in the reduction of carbon dioxide to acetic acid. All reagents acted as a catalyst, and the concentration of TOC and acetic acid was increased. The highest concentration of acetic acid was achieved with the addition of copper sulfate. This enhanced the generation of H· or H− as Cu(II) forms more stable complexes with oxalic acid than Fe(II)/Fe(III), meaning more free Fe(II)/Fe(III) ions were present in the solution.