Correlating the preparation and performance of cobalt catalysts supported on carbon nanotubes and carbon spheres in the Fischer–Tropsch synthesis

A series of Co catalysts supported on carbon nanotubes (CNTs) and carbon spheres (CSs) with different cobalt particle sizes (3–45 nm) were prepared by different methods and using different cobalt precursors. The Co/CNTs and Co/CSs can be autoreduced by the supports in N2 at ca. 480 °C; they show better Fischer–Tropsch performance than those reduced in H2 when the reduction T > 400 °C. The turnover frequency (TOF) value for both Co/CNT and Co/CS was constant for cobalt particles above 10 nm and decreased sharply for the cobalt catalysts with smaller cobalt particles. Remarkably, the TOF for 11 catalysts prepared using different precursors and preparation methods on two different carbon supports depends only on particle size. Finally, a positive relationship was observed between cobalt particle size and C5+ selectivity for both Co/CNT and Co/CS catalysts.