Moessbauer spectroscopic studies of /sup 57/Fe-surface enriched /sup 56/Fe core Fischer-Tropsch synthesis catalysis

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6831386

Knoechel, D J

An /sup 57/Fe-surface-enriched /sup 56/Fe powder allows Moessbauer spectroscopy to selectively probe the surface of an unsupported iron Fischer-Tropsch synthesis (FTS) catalyst. The consistency in the characterization of the located sample by x-ray diffraction, x-ray photoelectron spectroscopy, secondary ion mass spectrometry and Moessbauer spectroscopy shows that the /sup 57/Fe is retained in the surface layer. A series of catalysts with the same metallic core but different surface compositions was made by varying the pretreatment of the as-coated sample. Catalysts with surfaces of iron oxide only, metallic iron only, an iron/iron oxide mixture and an iron/iron oxide/iron carbide mixture were tested in FTS using 3:1 H/sub 2/:CO at 523K. Regardless of initial surface composition, the post-reaction surface consisted exclusively of Chi Fe/sub 5/C/sub 2/. Room temperature titration of the post-reaction with N/sub 2/O perturbed the iron carbide Moessbauer spectrum as a whole inducing a collapse in the carbide magnetic structure. This indicates that the majority of the /sup 57/Fe giving the post-reaction Moessbauer spectrum still resides in the surface region of the catalyst. A catalyst with a starting surface of 68% magnetite, 13% metallic iron and 19% Chi-Fe/sub 5/C/sub 2/ was the most active by a factor of at least 2 and has a carbon poor iron carbide site which is completely oxidized by N/sub 2/O. The higher kinetic rates for this catalyst and a bulk magnetite catalyst demonstrate a synergistic role between magnetite and iron carbide which promotes the maintenance of free active sites even after the magnetite has been removed by reduction and carburization.

• Research Organization: Purdue Univ., Lafayette, IN (USA)
• OSTI ID: 6831386
• Country of Publication: United States
• Language: English

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