Supported Cobalt Nanoparticles with a Single Active Phase for Fischer–Tropsch Synthesis

Cobalt (Co) with a hexagonal-close-packed structure (hcp-Co) has been documented as a preferred active phase for Co versus face-centered-cubic structure (fcc-Co) in a Fischer–Tropsch synthesis (FTS) reaction. Thus, hcp-Co with high dispersion and durability is highly attractive, and in this work, its controlled formation was targeted. This is challenging, however, because of the complexity of the phase transition during the materials synthesis and processing. With the use of carbon nanofiber (CNF) as the catalyst support, a two-step approach through the controlled formation of an oxide precursor CoO, followed by its reduction, has been demonstrated to synthesize single-phase Co. The obtained Co/CNF catalysts were thoroughly characterized by using in situ and ex situ techniques, and it is revealed that the formation of pure-phase CoO nanocrystals was responsible for the final pure-phase Co that was formed. Compared to the conventional reduction–carburization–reduction (RCR) process, this method allows for a higher dispersion of Co particles with higher activity by avoiding agglomeration of the nanoparticles before or after reduction. Equally important, under FTS conditions, no catalyst deactivation and phase transformation were observed for 400 h.