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.