2917.     RUBIO, F. B. L., AND PACHECO, J. R.  [Mechanism of the Catalytic Process for the Synthesis of Hydrocarbons by the Fischer-Tropsch Process.]  Ion, vol. 8, 1948, pp. 86-89; Chem. Abs., vol. 42, 1948, p. 5643.

        Most active catalysts for the Fischer-Tropsch synthesis are Fe, Co, and Ni.  Of these, Fe is probably the least active, but it has the advantage of being effective over a wide range of temperatures and is characterized by production of liquid hydrocarbons with CO2 as byproduct.  Co gives a product rich in olefins.  Ni tends to produce CH4 along with liquid and solid paraffins.  Previous theories have attributed the catalytic action of these metals either to formation of CH2 groups, with carbides of the metals acting as intermediates and polymerization of the CH2 groups, or of higher alcohols with subsequent dehydration to olefins.  According to a new theory, carbonyls of the metals are the primary active materials.  The existence of a compound [Fe(CO)5]4 including long chains of CO groups is assumed.  This is reduced to 2 mol. of C8H18 and a Fe carbonyl of much lower CO content.  After a number of reactions, with Fe3C, C3O2, FeO, and Fe2O3 among the intermediate products, the lower carbonyl is reconverted to Fe.  Overall reactions are:  18 CO+4 Fe→[Fe2(CO)9]2; [Fe2(CO)9]2+2 CO→[Fe(CO)5]4; [Fe(CO)5]4+34 H2→2 C8H18+15 H2O+CO2+3 CO+4 Fe+H2.  The volumes of CO and H2 to produce 1 mol. of C8H18 are 10 CO+17 H2 instead of the previously given 8 CO+17 H2, and the theoretical yield of octane is only 188.4 gm. per m.3 instead of 203.5.  The presence of Fe carbides and oxides in the catalyst is consistent with this theory, but these compounds only represent stages in the regeneration of the metallic Fe.  Hydrocarbon formation is by substitution of H for O in (COn) chains already formed.  Polymerization of CH2 groups is not inconsistent with this theory.  The action of alkalies added to Fe catalyst may be either (1) removal of O from CO groups to give percarbonate, H then combining with C and the percarbonate being subsequently reduced, or (2) polymerization of CO to chains, which combine with Fe to give carbonyls.

        RUCKES, W. L.  See abs. 625.