Authors: F.C. Ramírez, B.L. López, L.F. Giraldo
Affilation: Universidad de Antioquia, Colombia
Pages: 207 - 210
Keywords: carbon nanotubes, catalyst, yield, silica precursors
In this work several silica precursors have been used for the MCM-41 mesoporous silica synthesis, i.e. Cab-O-sil, sodium silicate and TEOS with incorporation of cobalt in-situ during the synthesis of the molecular sieves. The materials have been characterized by TPR, nitrogen adsorption and XRD. The synthesized catalysts were employed in the chemical vapor deposition of methane in order to obtain single wall carbon nanotubes at 800 ºC for 30 minutes. The reaction products were characterized by RAMAN, TGA and TEM. The results show an important effect of the pH synthesis and silica precursors on the final selectivity and yield to SWCNTs. Although all the precursors gave way to uniform mesoporous silica type MCM-41, the selectivity to SWCNTs was higher for the catalysts prepared with Ca-b-O-sil, followed for the silica prepared with silicate and the catalyst prepared with TEOS shows the lowest activity to SWCNTs. This behavior is related with the TPR profile for each catalyst. It showed that cobalt ions are reduced at higher temperatures for the support prepared with Cab-O-Sil as precursor. The higher is the reduction temperature the inner is the cobalt species into the silica walls, then sinterization process is less feasible.