Activation studies with a precipitated iron catalyst for Fischer-Tropsch synthesis. I. Characterization studies
- Texas A & M Univ., College Station, TX (United States); and others
A commercial promoted precipitated iron catalyst (100 Fe/5 Cu/4.2K/25 SiO{sub 2} by weight) was characterized after different pretreatment conditions and after Fischer-Tropsch (FT) synthesis in a fixed bed reactor. The BET-N{sub 2} surface area and pore volume of the catalyst decreased after pretreatments in hydrogen, carbon monoxide, or syngas. Isothermal and temperature-programmed reduction profiles indicate that iron reduction occurs in two steps: facile reduction of Fe{sub 2}O{sub 3} to Fe{sub 3}O{sub 4}, followed by slow reduction of Fe{sub 3}O{sub 4} to either metallic iron (H{sub 2} reduction) or an iron carbide (CO pretreatment). Calcined catalyst is in the form of poorly crystalline {alpha}-Fe{sub 2}O{sub 3}, which is partially converted to either magnetite (Fe{sub 3}O{sub 4}) or a mixture of {alpha}-Fe and Fe{sub 3}O{sub 4} after H{sub 2} reductions. During FT synthesis the {alpha}-Fe and a portion of iron oxides are carburized to a pseudohexagonal {epsilon}{prime}-Fe{sub 2.2}C. After CO or syngas pretreatments, the hematite is partly converted to a monoclinic {chi}-Fe{sub 5}C{sub 2} carbide. During FT synthesis this carbide is partially converted to magnetite. The degree of surface iron reduction, determined by X-ray photoelectron spectroscopy, was greater after the CO pretreatment at 300{degrees}C for 4 h than that obtained after the H{sub 2} reduction under the same conditions. However, in both cases a fraction of the surface iron remained in the form of unreduced Fe{sup 2+}/Fe{sup 3+} species. Also, the surface carbon deposits were formed during the CO pretreatment. 52 refs., 7 figs., 3 tabs.
- DOE Contract Number:
- AC22-85PC80011; AC22-89PC89868; AC22-90PC90039
- OSTI ID:
- 486295
- Journal Information:
- Journal of Catalysis, Vol. 155, Issue 2; Other Information: PBD: 1 Sep 1995
- Country of Publication:
- United States
- Language:
- English
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