641.    ---------------.  [CRAXFORD, S. R.]  Fischer-Tropsch Synthesis With Cobalt Catalysts.  Jour. Soc. Chem. Ind., vol. 66, 1947, pp. 440-444; Chem. Abs., vol. 42, 1948, p. 3648.

      Summary of more academic aspects of the research and development work carried out in Germany and elsewhere in recent years.  The composition and method of preparation of the Co catalyst are described, and the influence of the activators ThO₂, MnO, and MgO on the working of the catalyst is discussed.  The importance of kieselguhr as a carrier is emphasized, and the 2 functions of maintaining the Co in a finely divided form after reduction and of preserving the porosity of the individual granules are examined.  The reduction of the catalyst is considered to be the most crucial step in the entire process, and the 3 factors of temperature, time, and H₂ rates must be carefully observed.  Deterioration of the catalyst during synthesis at both atmospheric and medium pressure appears to be mainly the result of wax formation on the catalyst granules, and the rate of deterioration can be closely correlated with the rate of deposition of such waxes on the catalyst.  It has been concluded that ordinary Co carbide plays no part in the synthesis reaction; the Co atoms appear to be isolated and do not form part of a Co lattice.  Reaction by way of chemisorbed C atoms, the so-called surface carbide, however, is thought to give an array of interacting CH₂ groups on the surface, and the composition of the products, which are obtained from this array, depends on the conditions surrounding the conversion.  Some recent work has even tended to emphasize the idea of a polymerization-depolymerization equilibrium.

      See abs. 1326, 1334, 1335, 1336.