Cobalt catalysts supported on a micro-coil carbon in Fischer–Tropsch synthesis: A comparison with CNTs and CNFs

Abstract

Shaped carbon materials with different nanostructures, i.e. carbon nanofibers (CNFs), carbon nanotubes (CNTs) and carbon micro-coils (CMCs) were prepared by catalytic chemical vapor deposition. Co catalysts supported on CNFs, CNTs and CMCs were prepared by incipient wetness impregnation. The structure and surface properties of these carbon materials were studied. The influence of the different supports on the appearance, size and dispersion of cobalt particles, as well as on their reducibility, was studied by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption desorption measurements, thermogravimetric analysis, temperature-programmed reduction, H2-chemisorption and O2 titration. The different shaped carbon supports were found to affect the Co reducibility and dispersion by modifying the functionalization on the support surface, i.e. by changing the metal–support interactions. The Fischer–Tropsch synthesis (FTS) performance of these cobalt catalysts was influenced by the reducibility and dispersion of the catalysts on the different carbon materials. Finally, cobalt catalysts with cobalt particles sited both inside and outside of the CNTs were prepared and revealed the effect of a pore confinement on the reducibility, dispersion and performance of cobalt catalysts in FTS.