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Electron Energy Loss Spectroscopy (EELS) of Iron Fischer–Tropsch Catalysts

Published online by Cambridge University Press:  10 March 2006

Yaming Jin ,
Huifang Xu  and
Abhaya K. Datye
Yaming Jin
Affiliation:
Center for Microengineered Materials and Department of Chemical & Nuclear Engineering, University of New Mexico, MSC 01 1120, Albuquerque, NM 87131-0001, USA
Huifang Xu
Affiliation:
Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA
Abhaya K. Datye
Affiliation:
Center for Microengineered Materials and Department of Chemical & Nuclear Engineering, University of New Mexico, MSC 01 1120, Albuquerque, NM 87131-0001, USA
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Abstract

Electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy have been used to study iron catalysts for Fischer–Tropsch synthesis. When silica-containing iron oxide precursors are activated in flowing CO, the iron phase segregates into iron carbide crystallites, leaving behind some unreduced iron oxide in an amorphous state coexisting with the silica binder. The iron carbide crystallites are found covered by characteristic amorphous carbonaceous surface layers. These amorphous species are difficult to analyze by traditional catalyst characterization techniques, which lack spatial resolution. Even a surface-sensitive technique such as XPS shows only broad carbon or iron peaks in these catalysts. As we show in this work, EELS allows us to distinguish three different carbonaceous species: reactive amorphous carbon, graphitic carbon, and carbidic carbon in the bulk of the iron carbide particles. The carbidic carbon K edge shows an intense “π*” peak with an edge shift of about 1 eV to higher energy loss compared to that of the π* of amorphous carbon film or graphitic carbon. EELS analysis of the oxygen K edge allows us to distinguish the amorphous unreduced iron phase from the silica binder, indicating these are two separate phases. These results shed light onto the complex phase transformations that accompany the activation of iron catalysts for Fischer–Tropsch synthesis.

Keywords

Fischer-Tropsch CatalystElectron Energy Loss SpectroscopyIron CarbideSurface CarbonReactive CarbonIron Oxide
Type
MATERIALS APPLICATIONS
Information
Microscopy and Microanalysis , Volume 12 , Issue 2 , April 2006 , pp. 124 - 134
Copyright
© 2006 Microscopy Society of America

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References

REFERENCES

Ahn, C. & Krivanek, O. (1983). EELS Atlas. Warrendale, PA: Gatan, Inc.
Bukur, D.B., Lang, X.S., Rossin, J.A., Zimmerman, W.H., Rosynek, M.P., Yeh, E.B., & Li, C.P. (1989). Activation studies with a promoted precipitated iron Fischer–Tropsch catalyst. Ind Eng Chem Res 28, 1130–1140.Google Scholar
Butt, J.B. (1991). Carbide phases on iron-based Fischer–Tropsch synthesis catalysts 1. Characterization studies. Catal Lett 7, 61–81.Google Scholar
Chen, J.G. (1997). NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds. Surf Sci Rep 30, 5–152.Google Scholar
Colliex, C., Manoubi, T., & Ortiz, C. (1991). Electron energy loss spectroscopy near edge fine structures in the iron–oxygen system. Phys Rev B 44, 11402–11411.Google Scholar
Comelli, G., Stohr, J., Robinson, C.J., & Jark, W. (1988). Structural studies of argon-sputtered amorphous carbon films by extended X-ray absorption fine structure. Phys Rev B 38, 7511–7519.Google Scholar
Dry, M.E. & Hoogendoorn, J.C. (1981). Technology of the Fischer–Tropsch process. Catal Rev Sci Eng 23, 265–278.Google Scholar
Egerton, R. (1996). Electron Energy-Loss Spectroscopy in the Electron Microscope. New York: Plenum.
Hofer, F. (1995). Inner-shell ionization. In Energy-Filtering Transmission Electron Microscopy, Reimer, L. (Ed.), pp. 225–268. Berlin-Heidelberg: Springer Verlag.
Hofer, L.J.E., Cohn, E.M., & Peebles, W.C. (1949). The modifications of the carbide Fe2C; their properties and identification. J Am Chem Soc 71, 189–195.Google Scholar
Hwu, H.H., Fruhberger, B., & Chen, J.G.G. (2004). Different modification effects of carbidic and graphitic carbon on Ni surfaces. J Catal 221, 170–177.Google Scholar
Jackson, N.B., Datye, A.K., Mansker, L., O'Brien, R.J., & Davis, B.H. (1997). Deactivation and attrition of iron catalysts in synthesis gas. Stud Surf Sci Catal 111, 501–516.Google Scholar
Jin, Y. (1999). Phase transformation of iron-based catalysts for Fischer–Tropsch synthesis. Ph.D. Thesis, Albuquerque, NM: University of New Mexico.
Jin, Y. & Datye, A.K. (1998a). Phase transformations in iron Fischer–Tropsch catalysts. In Proceedings of the 14th International Congress on Electron Microscopy 1998, vol. 2, pp. 379–380. Durbam, South Africa.
Jin, Y. & Datye, A.K. (1998b). Characterization of bubble column slurry phase from Fischer–Tropsch catalysts. Stud Surf Sci Catal 119, 209–214.Google Scholar
Jin, Y. & Datye, A.K. (2000). Phase transformations in iron Fischer–Tropsch catalysts during temperature-programmed reduction. J Catal 196, 8–17.Google Scholar
Krishnan, K.M. (1990). Iron-L3,2 near edge fine structure studies. Ultramicroscopy 32, 309–311.Google Scholar
Kuivila, C.S., Stair, P.C., & Butt, J.B. (1989). Compositional aspects of iron Fischer–Tropsch catalysts—An XPS reaction study. J Catal 118, 299–311.Google Scholar
Leapman, R.D., Grunes, L.A., & Fejes, P.L. (1982). Study of the L2,3 edges in the 3d transition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory. Phys Rev B 26, 614–635.Google Scholar
Moulder, J.F., Stickle, W.F., Sobol, P.E., & Bomben, K.D. (1992). Handbook of X-ray Photoelectron Spectroscopy. Norwalk, CT: Perkin Elmer Corp.
Reymond, J.P., Meriaudeu, P., & Teichner, S.J. (1982). Changes in the surface-structure and composition of an iron catalyst of reduced or unreduced Fe2O3 during the reaction of carbon-monoxide and hydrogen. J Catal 75, 39–48.Google Scholar
Rightor, E.G. & Young, G.P. (1990). Probing the chemistry and spectroscopy of radiation-sensitive polymers by parallel-detection EELS. In XIIth International Congress for Electron Microscopy, Peachey, L.D. & Williams, D.B. (Eds.), pp. 34–35. San Francisco, CA: San Francisco Press.
Shroff, M.D. & Datye, A.K. (1996). The importance of passivation in the study of iron Fischer–Tropsch catalysts. Catal Lett 37, 1–2.Google Scholar
Shroff, M.D., Kalakkad, D.S., Coulter, K.E., Koehler, S.D., Harrington, M.S., Jackson, N.B., Sault, A.G., & Datye, A.K. (1995). Activation of precipitated iron Fischer–Tropsch synthesis catalysts. J Catal 156, 185–207.Google Scholar
Thole, B.T. & Vanderlaan, G. (1988). Branching ratio in X-ray absorption spectroscopy. Phys Rev B 38, 3158–3171.Google Scholar
Vosloo, A.C. (2001). Fischer-Tropsch: A futuristic view. Fuel Process Technol 71, 149–155.Google Scholar