Carbon dioxide to methane

Methanogens, which reduce carbon dioxide to methane... 

Apart from specific enzyme systems, the carbon dioxide reduction is mediated by a number of unusual coenzymes that can be categorized into two groups, namely Cj carriers and redox coenzymes [19]. The Cj carriers transport the Cl unit from the substrate carbon dioxide to the end-product methane, while the redox coenzymes provide the electrons that are required for the reduction of carbon dioxide to methane. Members of the first group include methanofuran (MF) (11), tetrahydromethanopterin (H4MPT) (12), and the coenzyme M (CoM-SH) (13), while coenzyme F420 (14) and coenzyme B (CoB-SH) (15) belong to the second group. 

Corphin is the F-430 cofactor found in methyl-coenzyme M reductase, a nickel-containing enzyme that participates in the conversion of carbon dioxide to methane in methanogenic bacteria. The nickel ion in F-430 is coordinated by the tetrahydrocorphin ligand, which contains structural elements of both porphyrins and corrins. 

A methanator converts the last traces of carbon dioxide to methane, a less interfering contaminant in hydrogen used for ammonia manufacture. 

A systematic attempt to correlate the catalytic effect of different surfaces with their adsorptive capacity was made by Taylor and his collaborators. Taylor and Burns, for example, investigated the adsorption of hydrogen, carbon dioxide, and ethylene by the six metals nickel, cobalt, palladium, platinum, iron, and copper. All these metals are able to catalyse the hydrogenation of ethylene to ethane, while nickel, cobalt, and palladium also catalyse the reduction of carbon monoxide and of carbon dioxide to methane. 

Figure 15-22 Tentative scheme for reduction of carbon dioxide to methane by methanogens. After Rouviere et al.352 and Thauer et al.435...

Ishitani O, Inoue C, Suzuki Y, Ibusuki T. Photocatalytic reduction of carbon dioxide to methane and acetic acid by an aqueous suspension of metal-deposited Ti02. J Photochem Photobiol A Chem 1993 72 269-71. 

It was found, that also Ru and Os colloids can act as catalysts for the photoreduction of carbon dioxide to methane [94, 95]. [Ru(bpy)3]2+ plays a role of a photosensitizer, triethanolamine (TEOA) works as an electron donor, while bipyridinium electron relays (R2+) mediate the electron transfer process. The production of hydrogen, methane, and small amounts of ethylene may be observed in such a system (Figure 21.1). Excited [Ru(bpy)3]2+ is oxidized by bipyridinium salts, whereas formed [Ru(bpy)3]3+ is reduced back to [Ru(bpy)3]2+ by TEOA. The reduced bipyridinium salt R + reduces hydrogen and C02 in the presence of metal colloids. Recombination of surface-bound H atoms competes with a multi-electron C02 reduction. More selective reduction of C02 to CH4, ethylene, and ethane was obtained using ruthenium(II)-trisbipyrazine, [Ru(bpz)3]2+/TEOA/Ru colloid system. The elimination of hydrogen evolution is thought to be caused by a kinetic barrier towards H2 evolution in the presence of [Ru(bpz)3]2+ and noble metal catalysts [96]. 

In microorganisms, vitamin B12 is involved in a variety of reactions, including methyl transfer the reduction of carbon dioxide to methane, a number... 

Romesser, J.A. (1978) The activation and reduction of carbon dioxide to methane in Melhanobacterium thermoautotrophicum, Ph.D. thesis. University of Illinois. 

Conrad R. and Klose M. (1999) Anaerobic conversion of carbon dioxide to methane acetate and propionate on washed rice roots. FEMS Microbiol. Ecol. 30, 147-155. 

When we started these investigations with Methanobacillus omeli-anskii, the culture was mass cultured in the ethanol—carbonate medium of Barker (J, 2), where ethanol was believed to be oxidized to acetate with the resulting electrons being transferred to reduce carbon dioxide to methane. About 1 gram of wet cells per liter of medium was obtained. 

S organism is inhibited by the hydrogen it produces Methanohacterium displaces the equilibrium by oxidizing hydrogen with reduction of carbon dioxide to methane. To survive in the ethanol-carbonate medium each organism requires the other. 

The oxidation of 2 mol butyric acid to 4 mol acetic acid is coupled with the reduction of 1 mol of carbon dioxide to methane. Tracer experiments showed that 98% of the methane is derived from carbon dioxide. In these examples of methane fermentation involving carbon dioxide reduction, no carbon dioxide is formed in the oxidation of the substrate. The fermentation of propionic acid by M. propionicum is more complicated because it involves both carbon dioxide formation and consumption (Stadtman and Barker, 1951) ... 

The nano-grained nickel catalysts supported on zdrconia or zirconia-rare earth element oxides are prepared by the oxidation-reduction pretreatment of amorphous Ni-Zr-rare earth element alloys. The conversion of carbon dioxide to methane on the catalyst prepared from amorphous Ni-40Zr alloy is improved by the addition of 5 at% or more rare earth elements (Y, Ce and Sm). 

However, Hori (1986) found the electrocatalytic reduction of carbon dioxide to methane on a molybdenum cathode to be electrocatalytic [11]. One hundred percent reduction of carbon dioxide to methanol at 0°C was reported. What remains open to research is the use of nonaqueous solvents, for example, acetonitrile, because there would be then no competition from hydrogen evolution. Carbon dioxide does undergo electrochemical reduction in acetonitrite to glycolic acid. Here is a research topic, which could have world consequences and cost very little (about 105 per year per researcher, even a dozen would make a great difference in five years). 

The hydrogenation of carbon monoxide and carbon dioxide to methane can be described by a series of elementary reaction steps [194, 196] that are given below ... 

Other energy-producing reactions of organisms involve the reduction of oxygen to water, the reduction of nitrate to ammonia and nitrogen gas, the reduction of sulfate to sulfide, and the reduction of carbon dioxide to methane. All of these reactions can exert a profound effect on water quality especially when it is realized that the affected chemical species also engage in many other chemical reactions. For example, the sulfide ion forms precipitates with many heavy metals. The microbial reduction of sulfate to sulfide could be accompanied by a reduction in the dissolved heavy metal content in a natural water. 

Wasmus, S., E. Cattaneo, and W. Vielstich (1990). Reduction of carbon dioxide to methane and ethane An on-line MS study with rotating electrodes. Electrochim. Acta 35(4), 771-775. 

Methanogenesis Methanosaeta, Methanosarcina (aceticlastic methanogens) convert acetate to methane and carbon dioxide Methanobacterium, Methanobreviacterium, Methanoplanus, Methanospirillum (hydrogenopbil methanogens) transform hydrogen and carbon dioxide to methane... 

The methods for the collection and introduction of gas samples in gas chromatography (GC) are described. Containers for samphng gases, sorption pipes, two- and three-position multiport valves and chambers capable of changing pressure with a mobile piston are presented. The methanizer in which the catalytic reduction of carbon monoxide and carbon dioxide to methane occurs is also presented. 

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