Carbon dioxide iron hypothesis

The hypothesis of formation of oxygenated compounds as intermediate products was rejected by Eidus on the basis of experiments on the conversion over cobalt of methyl and ethyl alcohols and formic acid which were found to form carbon monoxide and hydrogen in an intermediate step of the hydrocarbon synthesis (76). Methylene radicals are thought to be formed on nickel and cobalt catalysts (76) by hydrogenation of the unstable group CHOH formed by interaction of adsorbed carbon monoxide and hydrogen, while on iron catalysts methylene radicals are probably formed by hydrogenation of the carbide (78,81). Carbon dioxide was found to interact with the alkaline promoters on the surface of iron catalysts as little as 1 % potassium carbonate was found to occupy 30 to 40% of the active surface area. The alkali also promotes carbide formation and the synthesis reaction on iron (78). 

Iron catalysts show a tendency to convert the oxygen of carbon monoxide to carbon dioxide, while under. similar conditions cobalt produces water. In all cases long contact times of the reacting products on the catalyst surface increase the carbon dioxide formation and short contact times increase the formation of water. These results (confirmed by experiments with many different catalysts) were the basis for the hypothesis that water is a primary reaction product while carbon dioxide is a secondary product produced by the water gas shift reaction according to equilibrium conditions. 

This preconditioning of the catalyst is necessary to separate the chemical reactions from the catalytic ones (7). In the first few minutes, the iron surface transforms to catalytically active pyrrhotite, as shown (7) by the gradual increase in carbon monoxide consumption and corresponding increase in carbon dioxide production. The initial gaseous sulfide by-products react with the iron in the catalyst to form iron sulfides. In a previous publication (8), it was shown that lattice sulfur is a more versatile and useful carbon monoxide-sufurizing agent than molecular sulfur. The hypothesis tested was that metal sulfides with relatively weak metal-to-sulfur bonds are more effective in forming the active intermediate (9) carbonyl sulfide. 

The question of iron limitation was brought into sharp scientific focus with a series of public lectures, reports by the US National Research Council, papers, special publications, and popular articles between 1988 and 1991. What was resolved was the need to perform an open ocean enrichment experiment in order to definitively test the hypothesis that iron limits phytoplankton growth and nutrient and carbon dioxide uptake in HNLC regions. Such an experiment posed severe logistical challenges and had never been conducted. 

Recently, studies have been conducted in which iron was added to surface waters of the southern ocean near Antarctica to study its effect on phytoplankton. Adding iron resulted in a substantial buildup in the amount of phytoplankton and at least a short-term drop in the amount of carbon dioxide in the air immediately above them. These results were consistent with similar experiments performed earlier in the equatorial Pacific Ocean, confirming the hypothesis that iron is the limiting nutrient of these microoiganisms in much of the ocean. However, there was no increase in the amount of microbes sinking out of the top layer of ocean water. Thus, this procedure may be of no use for the long-term reduction of atmospheric carbon dioxide. 

This idea can be taken too far. In 2012, a California businessman ran a large-scale experiment when he dumped 100 tons of iron dust into the Pacific Ocean northwest of Seattle. His hypothesis was that the iron would cause microbes to grow and pull carbon dioxide down from the atmosphere as their raw material for growth. (This is a little like the bacteria that pull electrons from the electrode.) Not much seems to have happened. The businessman wanted to save the world, but instead, the world swallowed up the iron and went on indifferently. 

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