Fischer Tropsch synthesis over Co/SiO2 and Co-M (M: Ru, Re)/SiO2 catalysts prepared by a high-temperature super-critical drying method Original Research Article

Co/SiO2-based catalysts for Fischer Tropsch synthesis (FTS) were prepared by a high-temperature super-critical drying (HT-SCD) method, and the effects of the drying method on the catalytic properties were investigated. X-ray diffraction analysis (XRD) of the calcined catalysts revealed that the cobalt species formed in the HT-SCD catalysts is mainly a less-reducible cobalt silicate (Co2SiO4-like species), whereas that formed in catalysts prepared by a conventional thermal drying (TD) is mainly the easily reducible Co3O4 species. Moreover temperature programmed reduction (TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H2 chemisorption measurements revealed that the addition of rhenium or ruthenium to the HT-SCD catalysts improves the reducibility of the cobalt species and the cobalt dispersion, and partially suppresses the covering cobalt particles with SiO2 layer. The type of cobalt precursors used for catalyst preparation also had an effect on the cobalt species formed in the calcined catalysts. The HT-SCD catalysts with cobalt silicate exhibited higher olefin selectivities for FTS than the Co3O4-based catalysts prepared by TD, whereas the C11+ selectivities of the TD catalysts were higher than those of the HT-SCD catalysts. On the other hand, turn over frequency (TOF) estimated from the amount of H2 chemisorbed was constant without depending on the drying method and the type of cobalt precursors.