New Ni–Cu–Mg–Al-based catalysts preparation procedures for the synthesis of carbon nanofibers and nanotubes

Catalytic decomposition of methane to produce carbon nanofilaments, CNFs (nanofibers and/or nanotubes), and hydrogen was carried out on Ni–Cu–Mg–Al catalysts. The catalysts used as mixed oxides were obtained from the calcination at 1073 K of the corresponding lamellar double hydroxides (LDHs). The subsequent reduction at 1023 K of the calcined LDHs gave rise to Ni0 and Cu0 (and possibly Ni–Cu alloy) associated to an inorganic substrate with a MgO–MgAl2O4–NiAl2O4 mixed composition that were able to produce quality CNFs at 923 K. The size of metal particles and the carbon filaments as well as the nanofilament texture depends on the copper content of the catalyst. At a Cu content of 7.6 wt%, the carbon nanofilaments are nanofibers with a platelet texture, and the particles and CNFs sizes are widely distributed (50–400 nm). On the other hand, for a Cu content of 3.8 wt%, the size distribution is narrower and the CNFs are thinner (20–50 nm), nanofibers and nanotubes showing a ‘herringbone’ texture with twice the angle between the graphene layers and fiber axis, exhibiting values mainly in the range of 40°–60°.