ZSM-5 Supported Cobalt Catalyst for the Direct Production of Gasoline Range Hydrocarbons by Fischer–Tropsch Synthesis

Abstract

Fischer–Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5–C9) from syngas was investigated on cobalt-based FTS catalyst supported on the ZSM-5 possessing a four different Si/Al ratio. The FTS catalysts were prepared by impregnation method using cobalt nitrate precursor in a slurry of ZSM-5, and they were characterized by surface area, XRD, H2-TPR and NH3-TPD. Cobalt supported catalyst on ZSM-5 having a low Si/Al ratio of 15 was found to be superior to the other catalysts in terms of better C5–C9 selectivity due to the formation of small cobalt particle and the presence of larger number of weak acidic sites. It also exhibited the highest catalytic activity because of the higher reducibility and the small cobalt particle size. Figure shows the variation of hydrocarbon selectivity and olefin selectivity in C2–C4 with increasing density of weak acid sites. As can be seen from the figure, the increase of the weak acidic site density is responsible for increasing C5–C9 selectivity and olefin selectivity in C2–C4 range hydrocarbons. Consequently, it could be stated that the enhancement of C5–C9 selectivity is preferable on the Co/ZSM-5 catalyst possessing a higher density of weak acid sites.