Effect of hierarchical meso-macroporous silica supports on Fischer-Tropsch synthesis using cobalt catalyst

摘要

Hierarchical meso-macroporous (HS-X) silica with different mesopore diameters synthesized by using rice husk ash as a silica source and chitosan as a natural template were applied for the first time as the cobalt support for Fischer-Tropsch synthesis. Unimodal mesoporous silica (MS-X) supports with equivalent mesopore diameters to HS-X supports have also been prepared for comparison. Effects of diffusion in MS-X and HS-X supports of different particle sizes on the catalytic activity and hydrocarbon selectivity were investigated. The cobalt crystallite sizes were increased with increasing mesopore diameters, whereas the highest amount of H2 chemisorbed was found for the catalyst with the medium mesopore diameter. The HS-X supports revealed lower surface area and higher macroporosity which led to the formation of larger cobalt crystallite size and less chemisorbed H2. However, the catalytic activity was much higher for cobalt supported on HS-X silica of both small and large catalyst particle sizes. Moreover, with the large catalyst particle size, the C_(5+) selectivity of cobalt supported on HS-X silica was much higher than that on MS-X silica, indicating the influence of mass transfer of reactants and products in macropores of HS-X supports.