2683.     PICHLER, H., AND MERKEL, H.  Chemical and Thermomagnetic Studies on Iron Catalysts for the Synthesis of Hydrocarbons.  Bureau of Mines Tech. Paper 718, 1949, 108 pp.; TOM Reel 259, frames 129-328; FIAT Reel CC-259.

        Literature review of the mechanism of the synthesis reaction by way of heterogeneous catalysis, on carbide formation in the treatment of Fe catalysts with CO, and on the thermomagnetic method of studying the carburization of Fe.  The composition of Fe catalysts at various stages of pretreatment and synthesis was determined by chemical and thermomagnetic analysis.  The latter method revealed the almost complete transformation of Cu-free Fe catalysts, carburized at 325°, to a ferromagnetic higher Fe carbide (Fe₂C) with a Curie point of 265°.  Carburization of Cu-promoted (20% Cu) Fe catalysts at 220°-230° yielded not only the Curie point 26° yielded not only the Curie point 265° carbide but also a second ferromagnetic Fe carbide whose Curie point was 380°.  Of these 2 carbides, the first is the more thermally stable; it reverts to Fe₃C above 400°, whereas the second carbide is unstable above 300°, being ultimately converted to cementite and free Fe above that temperature.  The higher Fe carbides formed during carburization were stable during the synthesis.  During carburization at 325° and during subsequent medium-pressure synthesis; the Curie point 265° carbide was virtually the only carbide present.  After carbide-oxide equilibrium was established, active catalysts maintained their carbide content unchanged.  A decrease in catalytic activity was marked by a drop in the carbide content and by an increase in the O content.  Fe catalysts with a high Cu content consisted of approximately equal amounts of Curie point 265° and Curie point 380° carbide during operation at atmospheric pressure.  These carbided catalysts gave almost quantitative conversion of the CO in water gas with liquid and solid hydrocarbons as the principal products.  When a catalyst thus carbided was operated at medium pressure, the maximum synthesis temperature dropped from 220° to 205° for the same conversion capacity.  This increase in activity probably was due to the presence of the Curie point 380° carbide, which characterizes atmospheric pressure synthesis.  When the synthesis proceeded at a lower temperature, no formation of free C appeared during carburization and synthesis.  At the end of the pretreatment process, carbide formation and conversion capacity had reached their maximum values and no further C appeared.  (See abs. 2239).