2137.    LÓPEZ-RUBIO, F. B., 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; Fuel Abs., 1949, No. 2916; Chem. Abs., vol. 42, 1948, p. 5643.

In the Fischer-Tropsch hydrocarbon synthesis the most active catalysts 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 to either (1) formation of methylene groups, with carbides of the metals acting as intermediates, and polymerization of the methylene groups; or (2) formation of higher alcohols by the oxide content of the catalyst, 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, lower carbonyl is reconverted to Fe.  Over-all reactions are:  18CO+4Fe→[Fe₂(CO)₉]₂; [Fe₂(CO)₉]₂+2CO→[Fe(CO)₅]₄; [Fe(CO)₅]₄+34H₂→C₈H₁₈ +15H₂O+CO₂+3CO+4Fe+H₂.  The volumes of CO and H₂ to produce 1 mol. of C₈H₁₈ are 10CO+17H₂ instead of the previously given 8CO+17H₂, 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 H₂ for O₂ in (CO)_n chains already formed.  Polymerization of methylene groups is not inconsistent with this theory.  The action of alkalies added to Fe catalysts 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.