2239a.     MERKEL, H. AND WEINROTTER, F. [Thermomagnetic Studies of Iron Catalysts for Hydrocarbon Synthesis.]  Brennstoff-Chem., vol. 32, 1951, pp. 289-297; Chem. Abs., vol. 46, 1952, p. 662.

           When precipitated Fe catalysts are reduced with technical H₂, the low partial pressure of CO, CO₂ and CH₄ is sufficient to cause appreciable carbide formation.  Catalysts treated in this way are fully active for synthesis in a few minutes, in contrast with those reduced with electrolytic H₂.  In addition to Fe₂C with a Curie point of 265°, Fe₃O₄ and Fe were also found.  The Fe content may be the cause of the CH₄ peak noted early in the synthesis.  Since precipitated Fe catalysts can be converted into Fe₃C at temperatures >400° by means of technical H₂, without the formation of free C, there is a possibility of preparing pure cementite by reduction of Fe preparations containing no additives.  This product was inactive as a catalyst.  Metallic Fe is generally formed in the pretreatment of fused Fe catalysts with technical H₂.  Carbides are only formed when additives favoring carbide formation (alkalies) are present; Fe₃C is formed due to the higher temperatures used.