Performance Of Ce- And La- Incorporated KIT-6 Supported Cobalt Catalysts For Fischer–Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) is a gas-to-liquid (GTL) technology, which catalytically converts carbon monoxide and hydrogen into transportation fuels and chemicals. Among typical FTS catalysts (Fe, Co, Ni and Ru), the cobalt catalyst is preferred due to its high selectivity for heavy hydrocarbons, lower activity for water-gas shift (WGS) reaction than iron catalysts and lower price than ruthenium.In the present work, A series of Ce- or La- incorporated into the structure of KIT-6 mesoporous molecular sieves with different Ce or La contents were synthesized by a direct hydrothermal process. Samples of Ce- or La- loaded KIT-6 material were synthesized by the incipient wetness impregnation technique. Catalysts with 15 wt% Co loading on the above supports were also prepared by the impregnation method. The supports and catalysts were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance UV-vis, X-ray photoelectron spectroscopy, solid-state ²⁹Si magic-angle spinning nuclear magnetic resonance, N2 physisorption, H2 temperature-programmed reduction, H2 temperature-programmed desorption and oxygen titration. The catalysts activity and selectivity were evaluated in a fixed-bed reactor under typical hydrocarbon synthesis conditions. The main results are as follows:1) The structure of the KIT-6 support was well retained after Ce incorporation. The samples of xCe-KIT-6 have both Ce3+ and Ce4+ sites in the framework. Catalysts with 15 wt % Co loading on the xCe-KIT-6 and 0.06Ce-KIT-6-I were prepared by the impregnation method. The percentage reduction of the 15Co/xCe-KIT-6 increased slightly for catalysts with low Ce content and decreased significantly with high Ce content. Small amounts of Ce were found to improve the activity of cobalt catalysts, and increase the selectivity to C5+ hydrocarbons of the Co catalysts for Fischer–Tropsch synthesis, while larger amounts of Ce had the reverse effect. Meanwhile, methane selectivity shows an opposite trend to C5+ selectivity. Ce-loaded KIT-6 supported Co catalyst presented lower activity than KIT-6 supported Co catalyst.2) The structure of the KIT-6 support was well retained after La incorporation. Small amounts of La incorporated into the framework of KIT-6 promoted the percentage reduction of catalysts, and the large amounts of La decreased it. The trend in the catalyst dispersion of the 15Co-yLa-KIT-6 increased and then decreased with increasing La content. Small amounts of La were found to improve the activity of cobalt catalysts, and increase the selectivity to C5+ hydrocarbons of the Co catalysts for Fischer–Tropsch synthesis.3) The same amounts of Ce or La as a promoter, Ce or La incorporated into the framework of KIT-6 had a higher activity more than Ce or La loaded at the surface of KIT-6.