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 degrees 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.