HIGH YIELD CATALYSTS FOR GAS-PHASE SYNTHESIS OF SINGLE-WALLED CARBON NANOTUBES

摘要

Composite catalysts are employed for efficient gas-phase synthesis of single-walled carbon nanotubes (SWCNTs). Specifically, silicon is investigated as an additive to iron for synthesis of SWCNTs in inverse diffusion flames. Silicon is often used as a substrate in supported-catalyst processes to promote nanotube growth but this study demonstrates that it can also be beneficial for gas-phase nanotube synthesis in diffusion flames. An oxy-fuel ethylene inverse diffusion flame is employed to provide a soot-free, carbon-rich environment for nanotube growth. Iron and silicon precursors are added to the fuel stream for nucleation of iron/silicon/oxygen catalyst particles, with the amount of particle oxidation determined by the amount of oxygen enrichment and fuel dilution at a given temperature. Under optimum conditions, nearly 90% of the catalyst particles produce single-walled carbon nanotubes as compared to less than 10% if the catalyst consists of only iron and oxygen. The role of silicon for improving catalyst yield is investigated using Car-Parinello molecular dynamics simulations. The results of these simulations suggest that silicon prevents carbon encapsulation of the catalyst by preventing decomposition of the carbon source on part of the catalyst surface. Thus, a carbon cap can form on the iron-rich part of the catalyst for SWCNT nucleation.