Nanotubes and nanofilaments from carbon monoxide disproportionation over Co/MgO catalysts: I. Growth versus catalyst state Original Research Article

A catalyst prepared from the pyrolysis of Co and Mg nitrates and citric acid after their co-dissolution in water was used for carbon deposition from CO. Good yields of nanotubes or nanofilaments were obtained over catalysts which had been reduced by H2 without preliminary treatment at high temperature. Nanotubes with 10 or more cylindrical carbon layers were obtained from pure CO or from CO+CO2 mixtures. Nanofilaments with truncated conical layers were obtained from CO+H2 mixtures in the 500–600 °C range. In both cases, high shape selectivity was obtained and almost all MgO could be eliminated by HCl treatment. The only significant impurities were embedded cobalt particles. This process is therefore suitable for preparing nanotubes or nanofilaments with good shape selectivity and 98 wt% purity. Lowering the Co content of the catalyst produces thinner nanotubes but reduces the yield.