Direct Production of Iso-Paraffins from Syngas over Hierarchical Cobalt-ZSM-5 Nanocomposites Synthetized by using Carbon Nanotubes as Sacrificial Templates

摘要

This paper focuses on the effect of synthesis conditions on the structure of cobalt-ZSM-5 zeolites and the localization, dispersion, and reducibility of cobalt species and their catalytic performance in Fischer-Tropsch synthesis. The zeolite catalysts were prepared by using carbon nanotubes as sacrificial templates. Addition of pristine carbon nanotubes resulted only in a slight increase in the zeolite mesoporosity, whereas the presence of carbon nanotubes impregnated with cobalt drastically modified the zeolite morphology and texture. The zeolite mesoporous volume increased by 3-4 times. The catalysts prepared by using cobalt-impregnated carbon nanotubes as templates showed 5-8 times higher Fischer-Tropsch reaction rates normalized by reducible cobalt compared with the catalysts prepared by conventional impregnation. Higher selectivity to isomerized branched hydrocarbons on these zeolites was attributed to the enhanced diffusion favoring removal of isomerized products and avoiding their cracking.