To produce clean transportation fuels without emission of CO2, a possible route is the synthesis of hydrocarbons from CO and H2 via the Fischer-Tropsch process. In the industrial process, cobalt is the catalyst of choice. Although this process has been investigated intensively, open questions still remain. Examples are the oxidation state of cobalt during the actual chemical reaction, and the coverages of reactants, products, and possible impurities on the surface of the catalyst. Near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is an excellent method to try to answer these two questions. In this talk, I will present the results we obtained using NAP-XPS during the Fischer-Tropsch synthesis reaction on the Co(0001) model catalyst surface. I will show that the oxidation behavior of cobalt depends on the structure of the sample, the water partial pressure, and the H2-to-CO ratio. We found that CO is more effective than H2 to reduce cobalt. This behavior can be explained by the different adsorption and dissociation sites of H2, CO, and H2O on Co(0001). Furthermore, I will discuss a quantitative, theoretical model that we developed to convert the XPS intensities to absolute coverages on the cobalt surface. We found that at least 70% of carbon present on Co(0001) during Fischer-Tropsch synthesis is in carbidic form. We can also distinguish two different hydrocarbon peaks, one resulting from hydrocarbon impurities in the CO gas feed, and one being the product of the chemical reaction.

Spectroscopy of a model Co(0001) catalyst during Fischer-Tropsch synthesis

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.