1031.    ---------------.  [FISCHER, F., BAHR, T., AND MEUSEL, A.] [Catalytic Reduction of Carbon Dioxide to Higher Hydrocarbons at Atmospheric Pressure.]  Ber. Dent. Chem. Gesell., vol. 69 B, 1936, pp. 183-186; Chem. Abs., vol. 30, 1936, p. 3401.

       Hitherto it was not possible to reduce CO₂ to higher hydrocarbons than CH₄, but it has now been found that this can be accomplished with a Ru catalyst to which have been added small amounts of alkali.  It had already been shown that in the active form in which it has recently been employed, Ru catalyzes the reduction of CO₂ even at 100°, but at these low temperatures, only CH₄ is formed.  Quite different is its behavior if alkali, for example, 2% K₂CO₃, is added to it.  The temperature of incipient CO₂ reduction is thereby raised to 150°, and beginning at 170°-180° there are formed not only CH₄ but also higher gaseous and liquid hydrocarbons.  There are deposited at the end of the reaction tube first a colorless, low-boiling oil, later a higher-boiling oil, and finally paraffin-like products.  The oil and water formed are at first neutral or faintly acid; later, increasing amounts of acid products with the odor of the lower fatty acids are produced.  The gaseous products formed at 180°-225° contain 1.32-1.45 C atoms. The most favorable temperature range for the production of an oil seems to be 200°-225°, although higher hydrocarbons can still be detected at 300°; above this temperature only CH₄ is formed.  The reactivity of the catalyst decreases quite rapidly, and the catalyst must be regenerated by passing air at 300°-400° over it.  Comparative experiments on the influence of the amount and nature of the alkali on the catalytic behavior of Ru showed that 0.5% K₂CO₃ was not enough to impart an oil-producing power; Li₂CO₃ up to 3% and Na₂CO₃ up to 1.5% were likewise ineffective.  Rb₂ CO₃ (3.4%) had the same effect as K₂CO₃.  Ru with 2.9% KalO₂ at 200° first gave only CH₄, but after about 20 hr. CH₄ homologs and liquid hydrocarbons began to be formed; at lower temperatures (180°) there were no detectable amounts of oil even after 66 hr. and only small amounts of acid products.  The formation of higher hydrocarbons by alkalized Ru is believed to proceed through CO, to which the catalyst first reduces the CO₂.  From analogy with the metals of the Fe group, it would seem probable that the catalyst is a carbide, although no Ru carbide is as yet known.