In situ surface oxidation study of a planar Co/SiO2/Si(100) model catalyst with nanosized cobalt crystallites under model Fischer-Tropsch synthesis conditions.

The oxidation of nanosized metallic cobalt to cobalt oxide during Fischer-Tropsch synthesis (FTS) has long been postulated as a major deactivation mechanism. In this study a planar Co/SiO(2)/Si(100) model catalyst with well-defined cobalt crystallites, close to the threshold value reported for oxidation in the literature (4-10 nm), was prepared by the spin coating method. The planar Co/SiO(2)/Si(100) model catalyst was characterized with atomic force microscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering. The surface oxidation behavior of the nanosized metallic cobalt crystallites of 4-5 nm was studied using in situ near-edge X-ray absorption fine structure under model FTS conditions, i.e., H(2)/H(2)O = 1, P(Total) = 0.4 mbar, and 150-450 degrees C. No surface oxidation of metallic cobalt was observed under these model FTS conditions over a wide temperature range, i.e., 150-400 degrees C.