In situ monitoring during the transition of cobalt carbide to metal state and its application as Fischer–Tropsch catalyst in slurry phase

Abstract

The low-temperature rapid transition of cobalt carbide to metal cobalt species in a H2 environment was studied using in situ analyses, including temperature-programmed decarburization, in situ diffuse reflectance infrared Fourier-transform spectroscopy, X-ray absorption spectroscopy, and time-resolved gas chromatography profiles, during hydrogenation of cobalt carbide. Cobalt carbide was readily prepared by treatment of cobalt metal species in pure CO. By monitoring the evolution of cobalt carbide during hydrogenation, the analysis results give direct evidence for the formation of the cobalt metal hexagonal close packed (hcp) phase and light hydrocarbons (methane, ethane, and propane) as the products of hydrogenation of carbonaceous species on/in the cobalt carbide and clearly demonstrate that hydrogenation was completed at 220°C in excess H2 within 2h. As a result of the low-temperature transition of cobalt carbide, before slurry-phase Fischer–Tropsch (FTS), an activated metal cobalt catalyst was easily obtained in situ by H2 bubbling at 220°C, in the slurry phase. Moreover, the cobalt metal hcp phase derived from cobalt carbide exhibited significantly improved catalytic performance in FTS compared with the cobalt metal face-centered cubic phase obtained by cobalt oxide catalyst reduction. These results not only broaden and deepen fundamental understanding of the hydrogenation of cobalt carbide but also provide a potential facile activation route for cobalt catalysts for the synthesis of clean hydrocarbon fuels from syngas.