Chemistry in the greenhouse: CO2 conversion

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  • Published: Feb 15, 2011
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Chemistry in the greenhouse: CO2 conversion

Industrial carbon cycles

Technologies that can use carbon dioxide as a chemical feedstock are high on the agenda in the face of rising atmospheric levels of the greenhouse gas. A novel iron-based catalytic process studied using inductively coupled plasma (ICP) atomic emission spectrometry shows how carbon dioxide can be converted into the industrially useful formic acid at an 80% yield. Formic acid might also be used as a fuel cell fuel. The metal oxide by-product is readily reduced using glycerin derived from renewable sources releasing lactic acid, which could be used for biopolymer production.

Fangming Jin, Ying Gao, Yujia Jin, Yalei Zhang, Jianglin Cao and Zhen Wei of the State Key Laboratory of Pollution Control and Resources Reuse College of Environmental Science and Engineering, at Tongji University, in Shanghai, China and Richard L. Smith Jr of the Graduate School of Environmental Studies, at Tohoku University, in Sendai, Japan, discuss details in the journal Energy & Environmental Science.

Hydrothermal chemistry encompasses several important industrial reactions such as Fischer-Tropsch and Strecker-Sabatier for conversion of feed stocks into more useful starting materials. E.g. carbon monoxide and hydrogen into liquid hydrocarbons. On the geological scale, related hydrothermal chemistry underpins the global carbon cycle through geochemical reduction-oxidation (redox) couples in the mantle of the earth and in hot sea vents. Researchers have found evidence over the years that carbon dioxide can be reduced in the presence of aqueous hydrogen-bearing fluids when minerals such as magnetite, cobalt-containing magnetite, iron-chromium oxide. Indeed, there are many reaction pathways that can reduce carbon dioxide.

Pairing up redox couples

The team reasoned that coupling such redox reactions with hydrothermal chemistry might close the loop and allow carbon dioxide to be readily converted into useful, functional materials. They suggest that the large-scale conversion of carbon dioxide might be useful in reducing or maintaining atmospheric carbon dioxide levels, but perhaps more realistic is simply that we could "mine" the atmosphere as a novel carbon source.

The team defends the potential of their scheme in terms of it being an exothermic reaction cycle as well as having other advantages. "The proposed cycle has many advantages over water-splitting cycles that include: (i) no excess oxygen requirements since oxygen is recycled chemically, (ii) no hydrogen requirements including pumps or storage, because hydrogen is derived from water and is reacted with carbon dioxide in situ, (iii) no exotic catalysts or harsh reagents usage, because carbon dioxide promotes in situ hydrogen production and need not be pure, and (iv) no direct electrical requirements, since the cycle uses chemical energy in the oxidation and reduction steps and the cycle is exothermic," the report.

The team demonstrated, using X-ray diffraction, that the structure of the iron metal was essentially unchanged after five cycles. They used inductively coupled plasma (ICP) atomic emission spectrometry to analyse the dissolved amount of iron in the liquid samples and found losses were very low at 0.003%, essentially negligible.

Other researchers have investigated the potential to convert carbon dioxide into formic acid using iron, in 2010 a paper appeared in Organic Letters discussing how iron nanoparticles might be used, but did not discuss closing the carbon cycle in the same way as the current work does. (Org. Lett., 2010, 12, 649?651 DOI: 10.1021/ol9025414)

Photo by David Bradley. Technologies that can use carbon dioxide as a chemical feedstock are high on the agenda in the face of rising atmospheric levels of the greenhouse gas.
A cloud hangs over carbon dioxide emissions

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