Development of Ni–Cu–Mg–Al catalysts for the synthesis of carbon nanofibers by catalytic decomposition of methane

This work presents the kinetics and characterization results of Ni–Cu–Mg–Al catalysts used for the synthesis of carbon nanofibers (CNFs) by catalytic methane decomposition (CCVD). Ni–Cu–Mg–Al-based lamellar double hydroxides (LDHs) were synthesized by the coprecipitation method using either a regular maturation stage or a colloid mill process. After calcination at 1073 K and reduction at 1023 K, the formation of alloyed Ni–Cu nanoparticles over a mixed MgO–MgAl2O4–NiAl2O4 support was observed. The kinetic study of CNF synthesis by CCVD of methane was carried out in a thermobalance operated as a differential reactor. Small proportions of Cu (⩽10 wt%⩽10 wt%) were found to improve the activity and mainly the stability over time of Ni–Mg–Al catalysts. On the other hand, large proportions of Cu dramatically decrease the activity of the catalysts in terms of CNF yield. The catalysts were able to produce high-quality CNFs with a graphitic or turbostratic structure. The size of metal particles and the diameter of carbon filaments obtained depend on the catalyst composition (i.e., Ni:Cu ratio). The application of a kinetic model based on the growing mechanism of CNFs allows us to determine the influence of the operating conditions on the kinetic parameters.