In-situ probing of the Fischer-Tropsch reaction on Co single crystal surfaces up to 1 bar.

The surface chemistry of the Fischer-Tropsch catalytic reaction over Co has still several unknows. Here, we report an in-situ X-ray photoelectron spectroscopy study of Co and Co( ), and in-situ high energy surface X-ray diffraction of Co during the Fischer-Tropsch reaction at 0.15 bar - 1 bar and 406 K - 548 K in a H/CO gas mixture. We find that these Co surfaces remain metallic under all conditions and that the coverage of chemisorbed species ranges from 0.4-1.7 monolayers depending on pressure and temperature. The adsorbates include CO on-top, C/-CH and various longer hydrocarbon molecules, indicating a rate-limiting direct CO dissociation pathway and that only hydrocarbon species participate in the chain growth. The accumulation of hydrocarbon species points to the termination step being rate-limiting also. Furthermore, we demonstrate that the intermediate surface species are highly dynamic, appearing and disappearing with time delays after rapid changes in the reactants' composition.