Synthesis of carbon nanotubes and carbon nanofilaments over palladium supported catalysts

The synthesis of carbon nanotubes (CNTs) and carbon nanofilaments (CNFs) was investigated using the catalytic decomposition of acetylene over alumina-supported palladium catalysts prepared with the impregnation of palladium acetylacetonate (Pd/Al2O3) and deposition of dodecanethiol-protected palladium nanoparticles (DT-Pd/Al2O3). The synthesized carbon products consisted of multi-walled carbon nanotubes together with a significant number of CNFs. At 700 °C over Pd/Al2O3, the carbon products were mainly made up of CNFs in the range of 9-26 nm in diameter, while CNTs with well-defined layer structures were synthesized at 800 °C. When Pd loading was 0.5 wt.%, carbon tubules showed better crystallinity than those of 2.5 wt.% at 700 °C. DT-Pd/Al2O3, showing better dispersion of DT-Pd nanoparticles, showed narrower size-distribution of CNTs than that of Pd/Al2O3. Over several supports (Al2O3, SiO2-Al2O3, SiO2, and Y) with DT-Pd nanoparticles, we obtained amorphous carbon-free CNTs showing a narrower diameter range of 6-21 nm at 700 °C.