Correlation between the characteristics of multi-wall carbon nanotubes and the structure of the metal oxides used as catalytic precursors for their production

Well defined La–Ni–O oxide structures are prepared by a sol–gel like method and treated at three different temperatures in order to modify their phases and degree of crystallinity, close to that of LaNiO3 perovskite. It is observed that depending on the temperature of the treatment, three crystalline structures (LaNiO3, La2Ni2O5 and La4Ni3O10) are obtained, some of them containing an additional NiO phase. All these structures, characterized by X-ray diffraction and scanning and transmission electron microscopy before reduction, are used for the synthesis of multi-wall carbon nanotubes (MWCNTs) by the catalytic decomposition of methane. The reducibility of each phase under hydrogen is studied by programmed thermo reduction. After reduction and chemical vapor decomposition, inner and outer diameters of the MWCNTs are analyzed. It is found that these characteristics are strongly correlated to the structure of the oxides formed as catalytic precursors.