Cobalt catalysts supported on silica nanotubes for Fischer-Tropsch synthesis

Abstract

Silica nanotubes (SNT) have been synthesized using carbon nanotubes (CNT) as a template. Silica-coated carbon nanotubes (SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis (FTS). The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption, X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR) and transmission electron microscopy (TEM). FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa. Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size, higher dispersion and stronger reducibility. The results also showed that structure of the support affects the product selectivity in FTS. The synergistic effects of cobalt particle size, catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT. On the other hand, the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT, due to its smaller average pore size and cobalt particle size.