Low-temperature Fischer-Tropsch synthesis (CO + H2 to hydrocarbons) using cobalt catalysts is the key technology in modern gas-to-liquids processes. Cobalt Fischer-Tropsch catalysts deactivate mainly by sintering and deposition of inactive ('polymeric') carbon, but they can be regenerated by oxidative treatment. Surface science experiments using synchrotron X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy have given insight in the nature and reactivity of different carbon species on cobalt. While atomic carbon leaves room for coadsoption of CO and H2, albeit with weakened bonding to the surface, polymeric carbon resembles graphene-like structures, which precludes adsorption and blocks all chemistry. Transmission electron microscopy and XPS studies on model catalysts consisting of nanometer particles on a flat silica support provide a clear picture on the morphology changes and redispersion of the catalysts during regeneration. Platinum, present as a reduction promoter, segregates from the cobalt particles during oxidation, but mixes again in the reduction phase.

How cobalt Fischer-Tropsch catalysts deactivate and how they can be regenerated

244th National Meeting (2012)

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