Hydrothermal Carbon-Coated TiO₂ as Support for Co-Based Catalyst in Fischer–Tropsch Synthesis

A range of cobalt catalysts, prepared using TiO₂ enwrapped with a hydrothermal carbon (HTC) layer, was used as a support for the Fischer–Tropsch synthesis (FTS). The effects of the HTC coating thickness and annealing process of HTC–TiO₂ on the structure and performance of the cobalt catalysts were investigated. The HTC coating with enrichment functional groups (e.g., COOH and COH) generated a strong interaction with the Co species during catalyst preparation and finally enhanced cobalt oxide dispersion. Furthermore, the protection of the surface of TiO₂ by a HTC coating improved the reducibility of the cobalt catalysts. The Co particle size was correlated with the thickness of HTC coating and the HTC–TiO₂ support annealing process. It was found that the HTC–TiO₂ support with a coating thickness of 8 nm and without an annealing process gave catalysts with a cobalt particle size of 8.6 nm and optimal FTS performance. The corresponding Co/8C-TiO₂ catalyst exhibited an activity 2.4 times higher than that of a Co/TiO₂ catalyst and showed 85% selectivity to C₅₊ products under realistic FTS reaction conditions (210 °C, 1.0 MPa). The synergic effect of the HTC coating and the TiO₂ core had benefits on the catalytic properties of the Co/C-TiO₂ catalysts; the HTC coating improved dispersion and reducibility of cobalt species, while the existence of the TiO₂ core enhanced the stability of the catalyst structure in the reaction