Fischer-Tropsch synthesis: Higher oxygenate selectivity of cobalt catalysts supported on hydrothermal carbons

The performance of carbon-supported cobalt catalysts was compared with that of Co/γ-Al₂O₃ reference catalysts for the Fischer-Tropsch synthesis (FTS) reaction. The carbon support (CS) was prepared using a hydrothermal method that formed mostly spherical ∼300-800 nm carbons that were first carbonized at 900 °C and then partially graphitized at 1900 °C. The FTS study was conducted using a continuously stirred tank reactor, and the cobalt catalysts were promoted with Pt (0.2% Pt-10% Co) to facilitate the reduction of cobalt oxides. Catalysts were prepared by an evaporative method (Co/CS-IWI) and by a chemical vapor deposition technique (Co/CS-CVD). The CVD technique led to a higher CO conversion (26.5%) relative to the conventional evaporative (IWI) method (7.4%) at the same temperature (220 °C) and space velocity (1.5 NL/g_cath). Remarkably, the Co/CS-CVD displayed a high oxygenate selectivity (∼10%) in comparison with cobalt alumina catalysts (i.e., including one having similar Pt and Co loadings, as well as a conventional cobalt alumina catalyst with a higher Co loading of 25% Co) at similar conversion levels. The difference in the CO conversion on a per gram catalyst basis observed between Co/CS-IWI and Co/CS-CVD catalysts was due to the smaller average Co particle size and more uniform distribution resulting from the CVD method.