Active and Selective Bifunctional Catalyst for Gasoline Production through a Slurry-Phase Fischer−Tropsch Synthesis

Abstract

Catalytic performance of various bifunctional Co-based catalysts has been investigated in a slurry-phase Fischer−Tropsch synthesis at 1 MPa and 230 °C. The catalysts were prepared according to the conventional impregnation method using SiO2, Al2O3, montmorillonite (K10), and various zeolites (USY, ZSM-5, and MCM-22) as supports. Characterizations by XRD, N2 adsorption−desorption, H2-TPR, SEM, and TEM suggested the presence of at least two locally different Co species in the zeolite-supported catalysts: one with large particle sizes located on the external surface of the supports and the other one with small crystallites fixed inside the micropores. Co/MCM-22 catalysts exhibited high reducibility due to the small particle size of MCM-22 support that can accommodate more reducible active Co oxides with large crystal sizes on its external surface. It was found that the selectivity to long-chain hydrocarbon products was retarded obviously, and the carbon number distribution was shifted to gasoline range (C4−C12) when an acidic support was applied. The bifunctional catalysts also enhanced the selectivity to isoparaffins. Co/MCM-22 showed a superior CO conversion and selectivity to gasoline-range products and isoparaffins to other zeolite-supported Co catalysts. Its hydrogenation activity and hydrocarbons selectivity depended on the SiO2/Al2O3 ratio. Moreover, a mechanism of hydrocarbon formation over a zeolite-supported Co catalyst under the slurry-phase conditions was proposed.