CoSO4/SiO2 catalyst for selective synthesis of (9, 8) single-walled carbon nanotubes: Effect of catalyst calcination

A sulfate-promoted CoSO4/SiO2 catalyst is developed for chirally selective synthesis of large-diameter single-walled carbon nanotubes needed for electronic applications. The catalyst shows tunable nanotube chiral selectivity by changing catalyst calcination temperature. After calcination in air at 400 °C, it has excellent single chiral selectivity toward large-diameter (9, 8) nanotubes at 1.17 nm. The selectivity shifts to small-diameter nanotubes, when it is calcined at 800 °C. Catalyst characterizations by hydrogen temperature-programed reduction, X-ray absorption spectroscopy at the cobalt K-edge and sulfur K-edge suggest that the presence of chelating bidentate image bonded with cobalt on the silica surface may limit the aggregation of cobalt and/or form cobalt–sulfur compounds during nanotube growth, leading to the selectivity toward the (9, 8) nanotubes. Furthermore, the removal of sulfur at higher calcination temperatures may form surface cobalt oxides and silicates that shift the chiral selectivity toward small-diameter nanotubes.