Enhanced gasoline selectivity through Fischer-Tropsch synthesis on a bifunctional catalyst: Effects of active sites proximity and reaction temperature

The combination of Co-based catalysts and HZSM-5 has been reported to modify product distribution in Fischer-Tropsch synthesis (FTS) since the heavy hydrocarbons synthesized on Co0 could be hydrocracked to light hydrocarbons on HZSM-5. It has been accepted that the proximity between active Co0 sites and acidic sites as well as reaction temperature will significantly affect the product selectivity but no systematic report was found. In this paper, we designed two bifunctional catalysts to explore the effect of proximity and reaction temperature on FTS performance systematically. The tandem bifunctional catalyst Co/SZ-B possessed outstanding FTS activity and higher gasoline (C5-11) selectivity due to an appropriate proximity and metallic particle size. Reaction temperature was another sensitive impacting factor on FTS performance, especially on gasoline selectivity. With temperature increase, hydrocracking of heavy hydrocarbons on active Co0 sites and acidic sites all improved, which resulted in much increased formation of light hydrocarbons. The optimum reaction temperature for gasoline production was 270 °C due to the synergistic effect of active Co0 sites and acidic site. The finding about the effect of the active site proximity and reaction temperature on the FTS performance can provide a solid basis for rational design of bifunctional catalysts to modulate product distribution.