X-ray Structural Analysis of Iron Catalysts for Synthesis Based on Carbon Monoxide
Abstract Generated abstract
This study examines phase changes in promoted iron catalysts used for carbon monoxide based synthesis during reduction, stabilization, and operation. Using X-ray structural analysis, the authors compare catalysts treated with carbon monoxide, hydrogen containing mixtures, and steam containing mixtures, tracking iron oxides, metallic iron, and carbide phases. The results indicate that stabilization with carbon monoxide characteristically forms an Fe3C type carbide structure, while subsequent reaction conditions alter the ratio of metallic iron to carbide. In synthesis from carbon monoxide and water vapor, unlike carbon monoxide and hydrogen synthesis, the catalyst retains FeO and Fe3O4 oxide phases.
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X-RAY STRUCTURAL ANALYSIS OF IRON CATALYSTS FOR CARBON MONOXIDE-BASED SYNTHESIS
S. I. Smolyaninov, A. V. Kravtsov, I. V. Goncharov, L. L. Ponomareva
(Presented by the scientific-methodological seminar of KhTF)
One of the cheapest and sufficiently active catalysts for carbon monoxide-based synthesis processes is iron contacts with various promoters [1, 2]. A distinctive feature of these catalysts is the change in their phase composition during their reduction, stabilization, and directly during synthesis. F. Fischer, Tropsch, and other authors [1] associated their catalytic activity with the formation of a metal carbide. A. N. Bashkirov and co-workers [3], on the basis of their investigations, proposed that under conditions in which oxidation of the catalyst can be neglected, the active surface formed represents a system of the type of a solid solution of iron in iron carbide.
In the work carried out by us, using X-ray structural analysis, the change in the phase composition of iron catalysts was studied during their activation and operation in the process of synthesis from carbon monoxide and hydrogen, and also from carbon monoxide and steam. The results are presented in Table 1.
Characteristic for all iron synthesis catalysts is the process of formation of a carbide structure of the \(\mathrm{Fe_3C}\) type during their stabilization with carbon monoxide. After the catalyst is acted upon by the reaction mixture \((\mathrm{CO}+\mathrm{H_2}\) or \(\mathrm{CO}+\mathrm{H_2O})\), the corres-
Table 1
Change in the phase composition of the catalyst during activation
| Phase | \(\mathrm{Fe_3O_4}\) | \(\mathrm{Fe_3O_4}\) | \(\alpha\)-Fe | \(\alpha\)-Fe | \(\gamma\)-Fe | \(\gamma\)-Fe | \(\mathrm{Fe_2O_3}\) | \(\mathrm{Fe_2O_3}\) | FeO | FeO | \(\mathrm{Fe_3C}\) | \(\mathrm{Fe_3C}\) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Unreduced iron catalyst | 43 | 212 | — | — | 10 | 50 | 41 | 205 | 7 | 42 | — | — |
| Reduced iron catalyst treated with steam | 106 | 894 | 72 | 504 | 56 | 357 | 10 | 80 | — | — | — | — |
| Reduced and stabilized iron catalyst | — | — | 131 | 1040 | — | — | 6 | 18 | 10 | 50 | 131 | 1040 |
| Catalyst after activation | 5 | 15 | 104 | 725 | — | — | 5 | 35 | 13 | 91 | 104 | 725 |
| Catalyst after activation | — | — | 63 | 754 | — | — | — | — | — | — | 63 | 754 |
…of the ratio of the amount of metallic iron to carbide. It should be noted that, in the process of synthesis from carbon monoxide and water vapor, the iron catalyst retains (in contrast to synthesis from carbon monoxide and hydrogen*) the iron oxide phases FeO and Fe₃O₄.
REFERENCES
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H. Storch, I. Golambik, K. Andersen. Synthesis of Hydrocarbons from Carbon Monoxide and Hydrogen. Foreign Literature Publishing House, Moscow, 1952.
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H. Kolbel und Hans Hammer. Zeitschrift für Electrohemie 64, No. 2, 435, 1960.
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A. N. Bashkirov, Yu. A. Kryukov, V. B. Shuikin. Neftekhimiya, vol. VIII, No. 5, 34–39, 1968.
* The catalysts for the synthesis of alcohols from carbon monoxide and hydrogen were kindly provided after the corresponding development by the Laboratory of Catalytic Synthesis, INKhSAN USSR.