Study on bimodal mesoporous Co/SiO₂ catalysts for the Fischer–Tropsch synthesis

Abstract

A series of SiO₂ supports were prepared with the sol–gel method. Bimodal mesoporous Co/SiO₂ catalysts with different pore size distributions were prepared. The samples were characterized by means of N₂ adsorption–desorption, powder X-ray diffraction, H₂-chemisorption, H₂ temperature programmed reduction and Raman spectroscopy. The catalysts were employed in Fischer–Tropsch synthesis under the reaction conditions of 240 °C, 2 MPa and 1,000 h⁻¹ to investigate their catalytic performance with different pore diameters. The experimental results revealed that the bimodal catalysts contain high specific surface area contributed from the formation of smaller mesopores during sol–gel process. Small Co particles of bimodal catalyst are able to be highly dispersed and behave moderate metal-support interaction without formation of hardly reducible species, which favors the production of sufficient active centers, contributing to the high catalytic activity. Moreover, increasing the pore size of the larger pores in bimodal mesoporous catalysts will facilitate the transportation of primary products and inhibit the hydrocracking to generate light hydrocarbons, promoting the production of heavy hydrocarbons with high C₅₊ selectivity.