Insitu magnetometer study on the formation and stability of cobalt carbide in Fischer–Tropsch synthesis

Abstract

While carbides are always present in iron-based Fischer–Tropsch synthesis, very little is known about the presence and the role of carbides in cobalt-based CO hydrogenation. Cobalt carbide, Co2C, has been reported in catalysts where operational upsets occurred and it is associated with low catalyst activity and increased methane selectivity. In this study, a novel insitu magnetometer was used to study the formation and the stability of cobalt carbide during the Fischer–Tropsch synthesis at fully relevant conditions. The formation of cobalt carbide was confirmed by means of insitu XRD and synchrotron XRD measurements. Cobalt carbide is relatively stable at typical reaction conditions, but a rapid decomposition into hcp cobalt occurs in hydrogen above 150°C. Cobalt carbide formation is inversely proportional to the H2/CO ratio and the reaction temperature. However, the amounts of cobalt carbide formed are small and the impact on deactivation at realistic Fischer–Tropsch conditions should generally be negligible.