Composition effects of carbon surface oxide ensembles on activity and stability of carbon supported Co Fischer-Tropsch catalysts

Abstract

Carbon catalyst supports offer an attractive alternative to traditional oxidic supports for Co-based Fischer-Tropsch synthesis (FTS) catalysts, however, weak metal/carbon interactions facilitate catalyst deactivation by cobalt nanoparticle sintering. In this study we investigated the introduction of carbon surface oxides to mitigate cobalt sintering, combining carbon model supports featuring various surface oxide profiles with size-defined, colloidal Co nanoparticles. Carbon surface oxidation was found to effectively suppress cobalt nanoparticle sintering. Employing in situ XRD and XAS, we could show that Co supported on carbon featuring surface carbonyls/quinones displays low reducibility and forms disordered, polycrystalline Co0 nanoparticles, which are associated with poor FTS performance. In contrast, Co on supports occupied by carboxylic acids were easily reducible and formed monocrystalline nanoparticles enabling comparatively high FTS activities. However, despite effectively suppressing Co nanoparticle sintering, carbon surface oxidation was proven detrimental for FTS performance, as Co supported on non-functionalized carbon outperformed all catalysts on oxidized supports.