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 C-4-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/SiO2-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. (C) 2003 Elsevier B.V. All rights reserved.