Catalysts meteoritic iron

The synthesis of fatty acids by a Fischer-Tropsch-type process as described in this chapter required the use of a catalyst (meteoritic iron) and a promoter. Potassium carbonate and rubidium carbonate were the only compounds evaluated which unambiguously facilitated the production of fatty acids. These catalytic combinations (meteoritic iron and potassium carbonate or rubidium carbonate) also produced substantial amounts of n-alkenes (in excess of n-alkanes) and aromatic hydrocarbons. A comprehensive study of the nonacidic oxygenated compounds produced in Fischer-Tropsch reactions (20,21) was not made. However, in the products analyzed (all promoted by potassium carbonate), long-chain alcohols and aldehydes were detected. 

We have studied the synthesis of fatty acids by the closed Fischer-Tropsch process, using various carbonates as promoters and meteoritic iron as catalyst. The conditions used were D2/CO mole ratio = 1 1, temperature == 400°C, and time = 24-48 hr. Sodium, calcium, magnesium, potassium, and rubidium carbonates were tested as promoters but only potassium carbonate and rubidium carbonate produced fatty acids. These compounds are normal saturated fatty adds ranging from C5 to Cis, showing a unimodal Gaussian distribution without predominance of odd over even carbon-numbered aliphatic chains. The yields in general exceed the yields of aliphatic hydrocarbons obtained under the same conditions. The fatty acids may be derived from aldehydes and alcohols produced under the influence of the promoter and subsequently oxidized to the acids. 

Nonoxidized and oxidized-reduced Canyon Diablo meteoritic iron produced fatty acids when potassium carbonate was admixed (runs 4-97 and 4-109). The level of potassium carbonate (0.1 g vs. 0.3 g) in the catalyst (0.5 g) had no eflFect on the production of fatty acids (runs 4-109 and 5-24). Oxidized Canyon Diablo iron and potassium carbonate did not produce fatty acids (run 4-94), thus showing that promoter effects are catalyst dependent. 

Fatty acids in relatively high yields (usually in excess of the yields of aliphatic hydrocarbons) can be produced in a closed-system Fischer-Tropsch process using meteoritic iron as a catalyst, provided potassium carbonate or rubidium carbonate is used as a promoter. Aldehydes and alcohols or oxygenated intermediate complexes attached to the catalyst may be the source of the fatty acids. 

Opportunities for such secondary reactions certainly existed in the history of meteorites. Temperatures in the nebula (360-400 K, Table 1) may alone have been high enough for secondary reactions in the time available, 10 -10 yr. Kinetic studies of a similar reaction (formation of benzene from alcohols, amines, or fatty acids on Fe Oj or iron-rich peat catalysts Galwey, 1972) indicate a benzene formation rate of 5 x 10 molecules g yr at 360 K. At this rate it would take only 5000 years to transform all the meteoritic carbon to benzene. Further opportunities were provided by brief thermal pulses during chondrule formation, impact, or transient shocks. Of couree, any high-temperature episodes must have happened early or on a local scale, to permit survival of other, more temperature-sensitive compounds. 

An answer to the first question was suggested by Lancet and Anders (1970). The principal meteoritic phases stable above 350-400 K (olivine, pyroxene, Fe, FeS) are not effective catalysts for the Fischer-Tropsch reaction, whereas the phases forming below this temperature (hydrated silicates, magnetite) are. P hough metallic iron is often regarded as a catalyst for this synthesis, the catalytically active phase actually is a thin coating of FCjO formed on the surface of the metal (Anderson, 1956)]. Thus CO may have survived metastably until catalysts became available by reactions such as ... 

Fig. 12. Fischer-Tropsch reaction at 1 atm is first-order in CO, with an activation energy of 27 kcal/ mole (Lancet, 1972). Rate in a flow system is 10 times faster than in the static system used here. Dashed line shows extrapolation to solar nebula, assuming that the rate is proportional to (PcoIIPhj) . Reaction proceeds at an undetectable rate when the Bruderheim L6 chondrite is used as a catalyst. Apparently the high-temperature minerals in this meteorite (olivine, orthopyroxene, troilite, and nickel-iron) do not catalyze the hydrogenation of CO. Thus CO can survive in the solar nebula down to 400 K, when catalytically active minerals first from (Fig. 1 and 10)...

The methods described in detail in Section 36.2, or only mentioned, have been used as follows for spectrophotometric determination of palladium the thio-Michler s ketone — in silver, copper, and anodic slime [32], in catalysts [31] with thiosemicarbazide derivatives — in water [44] and alloys [46] with palladium-carbon powder — with a-benzilmonoxime [48] with PAR — in catalysts and ores [58] with thiazolylazo derivatives — in Ni-Al catalysts [63] with 5-Br-PADAP — in titanium alloys with pyridylazo derivatives - in nickel alloys [68] with sulphonitrophenol - in silver alloys [70] with Arsenazo III — in iron and meteorites and with Palladiazo — in catalysts, minerals, silica gel, and calcium carbonate [78]. 

The Canyon Diablo (iron No. 34.6050, 10-20% nickel American Meteorite Laboratory see Figure 1) filings used as catalyst were extracted several times with benzene-methanol (3 1 v/v), and then carefully dried about 6 hr at 104°C (Canyon Diablo, nonoxidized). A portion of the Canyon Diablo filings was heated at red heat for several hours in air. After cooling, a small amount was retained for use as an oxidized catalyst (Canyon Diablo, oxidized). The remainder was then heated overnight... 

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