1947. KÖLBEL, H., AND ENGELHARDT, F. [Reaction Mechanism of the Fischer-Tropsch Synthesis. I.] Erdöl u. Kohle, vol. 2, 1949, pp. 52-59; Chem. Abs., vol. 43, 1949, p. 4828.

Return to Abstracts of Literature 1750-1999

Literature Abstracts

Proposed mechanisms explaining the formation of CO₂ and H₂O by Fe and Co catalysts, respectively, are reviewed and the action of these catalysts in the water-gas reaction is studied. An Fe catalyst of composition 100, Fe; 0.5, Cu; 0.25, K₂CO₃ was used. Initial experiments were conducted with four different contact conditions: Carbidic, 24-hr. treatment with CO at 270° (I); metallic, 24-hr. treatment of (I) with electrolytic H₂ at 270° (II); oxidic, reduction of catalyst with H₂ at 270° (III); synthesis, treatment for 100 hr. at 1 atm. at 230°, CO:H₂O=1:2, space velocity 100 (IV). A graph of time, total 24 hr., versus conversion of CO at 240°, CO:H₂=1:1, space velocity=100, gives almost a straight line for (II) near equilibrium; (IV) runs parallel to (II) at a lower level; (III) is inactive at this temperature; and (I) is rapidly approaching (IV). Results at 240°, CO:H₂O=3:1 and space velocity=100, show that (I) and (II) have approached each other within the first 100 hr. and then run concurrently for more than 400 hr. Analysis of (I) for total C, elemental C, carbidic C, and unoxidized Fe, respectively, before test; 14.2, 7.35, 6.85, 62.7; after; 16.2, 12.0, 4.2, 57.3. Similar results for (II) are before; 7.0, 7.0, 0.0, 67.1; after; 19.0, 14.2, 4.8, 56.9. Results indicate that initially (II) is more active than (I), but that finally both attain the same activity and carbide concentration. Method for analysis is based on the fact that the velocity of ion exchange is a function of the carbide-C content in such a way that with increasing carbide-C the permutation velocity decreases; Hg** ions were used. Carbide-C was determined by difference of total C before and after treatment with H₂ at 270°. a highly reactive, commercial Co-Th-Mg catalyst with 100% kieselguhr was treated as follows: By reduction of a precipitated catalyst with H₂ at 450° (V); 24-hr. treatment of (V) with CO at 270° (VI); active use for 150 hr. (VII). (V) is by far the best, conversion close to equilibrium; (VI) is the poorest; (VII) midway between the two. For CO:H₂O=1:1 and space velocity=100, 180° was the lower limit of conversion for both Fe and Co catalysts. This is important in connection with the fact that the optimum synthesis for the Co catalyst is below 180° while that for Fe is considerably higher, which may explain that in the former O₂ from CO can escape in the form of H₂O. Experiments with a Co catalyst showed that lowering the space velocity from 100 to 10 at 180° and changing the H₂:CO ratio from 2:1 to 2:3.55, H₂O concentration decreased progressively and an almost parallel increase of CO₂ resulted. Division of the Fe catalyst into four portions separated by layers of caCl₂ (230°, space velocity 100) resulted in a progressive increase of H₂O formation and a parallel decrease of CO₂ concentration. These results are in disagreement with the opinion advanced by Craxford (see abs. 638). A working hypothesis for the mechanism is proposed.