Direct synthesis of middle iso-paraffins from synthesis gas

This paper focuses on the synthesis of iso-paraffin-rich hydrocarbons by Fischer-Tropsch synthesis (FTS) over Co/SiO₂ catalyst. The basic concept was to secondarily isomerize and/or hydrocrack the primary FTS hydrocarbon products. A physical mixture of a small amount of added H-ZSM-5 in the Co/SiO₂ catalyst enhanced the formation of C₄-C ₁₀ iso-paraffins while suppressing the formation of longer hydrocarbons, probably because of the selective cracking of higher hydrocarbons on ZSM-5. The three-component catalyst (Co/SiO₂-Pd/SiO ₂-ZSM-5) promoted the formation of paraffins, whereas the yield of isomerized products was not high enough. For a two-step reaction, the first step catalyst was the Co/SiO₂+ZSM-5 catalyst and the second step catalyst was Pd/SiO₂+ZMS-5 catalyst where additional hydrogen was added. The selectivity of iso-paraffins was markedly promoted and the molecular weight of the product decreased while the syngas conversion was kept constant. The hydrocracking of n-octane (which is the model compound of FTS reaction) over hybrid catalyst composed of Pd/SiO₂-zeolite and showed high and stable activity giving iso-paraffin-rich hydrocarbons. The isomerization was favored for Pd rich catalyst. The role of Pd was thought to be the port hole of hydrogen spillover to zeolite.