Decomposition of carbon-containing compounds on solid catalysts for single-walled nanotube production.
Different catalyst formulations and reaction conditions have been used to test the validity of a hypothesis that tries to elucidate the mechanism of single-walled nanotube (SWNT) formation by CO disproportionation over a highly selective cobalt-molybdenum catalyst. This model proposed an intrinsic dependence between the selectivity of the catalysts toward SWNT and the stabilization of Co species in a nonmetallic state, which in turn results from an interaction with Mo. The series of tests performed to examine this model include the doping of this highly selective catalyst with sodium, the substitution of molybdenum by tungsten in the original catalyst formulation, the variation on reaction temperature, and the introduction of hydrogen in the gas feedstock. All these modifications were carried out to modify the growth conditions in which the SWNTs are formed. The results are consistent with the hypothesis proposed by the authors.