Development of Ni-Cu-Mg-Al catalysts for the synthesis of carbon nanofibers by catalytic decomposition of methane
Résumé
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%) 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. © 2007 Elsevier Inc. All rights reserved.