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Fischer-Tropsch Synthesis on Cobalt Model Catalysts

In the industrial Fischer-Tropsch synthesis a mixture of hydrogen and carbon monoxide, so-called "syngas", reacts to give long chain hydrocarbons:

n CO + (2n+1)H2 → CnH2n+2 + n H2O

The process is expected to play a key role in the production of liquid fuels in the future and may also be used for energy storage. The catalyst in the modern Fischer-Tropsch synthesis consists of small metallic cobalt particles on oxide supports. The reaction mechanism has been studied for decades but, like with most other catalytic reactions, essential questions have remained open. In particular, the structure and chemical state of the active cobalt surface are unclear. To obtain an atomic view of the operating catalyst we use a high-pressure STM under pressure and temperature conditions close to those of the industrial process. For the cobalt catalyst we use Co(0001) single crystal models.

STM image of a Co(0001) surface covered by CO molecules. The image was taken in 0.25 mbar CO at 493 K, very harsh conditions for STM, but atomic resolution was still obtained. A unit cell with possible CO positions is marked. 60 Å x 30 Å. Reprinted from "In situ high-pressure high-temperature scanning tunneling microscopy of a Co(0001) Fischer-Tropsch model catalyst", M. Ehrensperger, J. Wintterlin, J. Catal. 319, 274 (2014). Copyright 2014, with permission from Elsevier.

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