Synthesis of CNT-supported cobalt nanoparticle catalysts using a microemulsion technique: Role of nanoparticle size on reducibility, activity and selectivity in Fischer–Tropsch reactions

Abstract

The influence of cobalt particle size on catalyst performance in Fischer–Tropsch synthesis (FTS) has been investigated using inert carbon nanotube (CNT)-supported catalysts. The catalysts were produced by the core reverse micelle reactions with cobalt particles of various sizes (3–10 nm). It has been shown that particle size is proportional to the water-to-surfactant ratio (3–10) used for the catalyst preparation. Very narrow particle size distributions have been produced by the microemulsion technique and at relatively high loading (Co 10 wt%). Selectivity and activity were found to be dependant on cobalt particle size. The FTS rate increases from 0.36 to 0.44 g HC/g cat./h and the C 5+ selectivity increases from 89 to 92.5 wt% with increasing the average cobalt particle size from 2–3 to 9–10 nm, respectively. According to TEM analysis, small Co particles (2–6 nm) are mostly confined inside the CNTs where influence of its electron deficiency in the inside surface has changed the commonly expected catalyst's structure-sensitive results. Finally, the CNT-supported cobalt nanoparticles synthesized by the proposed microemulsion technique increased the CO conversion by 15% compared to those prepared by incipient wetness impregnation.