1448. HOFER, L. J. E., PEEBLES, W. C., AND DIETER, W. E. Magnetic and X-Ray-Diffraction Studies of Unreduced Ferric-Oxide Fischer-Tropsch Catalysts. Jour. Am. Chem. Soc., vol. 68, 1946, pp. 1953-1956; Chem. Abs., vol. 41, 1947, p. 644.

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Literature Abstracts

Catalysts prepared by precipitation with K₂CO₃ or KOH from a solution of a ferric salt are inactive in the Fischer-Tropsch synthesis if the original solution contains chloride anion and are active if the original solution contains nitrate ion only. This difference in activity is an extremely marked one. The catalysts precipitated in the presence of chloride ion in no case produced more than 2 or 3 gm. of liquid hydrocarbons per m.³ of synthesis gas, while catalysts precipitated in the presence of nitrate ion, in some cases, gave yields as high as 70 gm. per m.³ X-ray diffraction patterns showed that all the catalysts contained identifiable crystalline constituents. In the case of active catalysts, this was a-Fe₂O₃ (I), a-FeOOH (II), or both. In the case of the inactive catalysts, there was one exception, β-FeOOH (III). The magnetic susceptibility of the active catalysts was higher (100-300X10^-6) than that of either (I) (25 x 10^-6), (II) (42 x 10^‑6), (III) (40 x 10^-6). The magnetic susceptibilities of the inactive catalysts were quite close to the expected 40 x 10^-6. it should be remembered that both (II) and (III) decompose to (I) below 200°, so that the inactivity accompanying the presence of (III) in raw catalysts is not due to the (III) itself, but to some characteristic that it transmits to the ultimate catalyst. This hypothesis is supported by a subsequent investigation of the inactive, chloride-precipitated catalyst, which contained no (III). Repetition of the procedure leading to this catalyst showed that it was formed from (III) as an intermediate and, hence, had the undesirable poisoning characteristic owing to (III). That the chloride ion is not directly responsible for the poisoning action is shown by the fact that good active catalysts can be made starting with FeCl₂, in which case no (III) can be formed. Catalysts prepared by precipitation of Fe(NO₃)₃ solutions with K₂CO₃ or KOH contain a-Fe₂O₃ and in some cases a-Fe₂O₃·H₂O and are active in the Fischer-Tropsch synthesis. The magnetic susceptibility of active raw Fe₂O₃ or Fe₂O₃ hydrate, which would be identified in the diffraction pattern of the catalysts. The magnetic susceptibility of those catalysts containing β-Fe₂O₃·H₂O was very much lower than that of the active catalysts and did not greatly exceed that of β-Fe₂O₃·H₂O. Several suggestions are proposed to account for the deactivation of the catalyst.