3286.     ---------------.  [STORCH, H. H.]  Catalysts in Synthetic Liquid-Fuel Processes.  Ind. Eng. Chem., vol. 37, 1945, p. 340-351.

        Fischer-Tropsch catalysts that are active in the synthesis of normally liquid hydrocarbons from CO and H2 -- namely, Fe, Co, Ni, and Ru -- form relatively unstable carbides on exposure to CO in the temperature range of the synthesis (185-215 for Co and 240-320 for Fe catalysts).  Since the reaction 2 Co+2 CO→Co2C+CO2 is much too slow to account for the rate of hydrocarbon formation, it is conceivable that H2 acts as catalyst for metal carbide formation by way of an unstable metal hydride according to the equation 2 Co+CO+H2→Co2C+H2O.  The mechanism of carbide formation on the Co catalyst, where the main oxygenated product is H2O rather than CO2, is difficult to apply to Fe catalysts, and it is, probable therefore, that, although metal carbides are formed on both Co and Fe, the mechanism of the synthesis differs for the 2 substances.  The hydrocarbons produced on sintered Fe catalysts, reduced with H2 at 650-850, are largely branched-chain paraffins, whereas those formed on Fe catalysts reduced at 400 or less contain very little isoparaffins.  An essential condition for the production of isoparaffins, therefore, is apparently the absence of ferrous oxide in the Fe catalyst and a critical spacing of the Fe atoms in the Fe carbide lattice to permit cross linkages to form.  Previous investigations are reviewed on the effect of pressure, diluents, and contact time on the Fischer-Tropsch synthesis and the poisoning of catalysts by S compounds.