Catalytic Vapor Decomposition of Methane over Nickle Catalyst: Growth Rate and the Corresponding Microstructures of Carbon Nanofibers

Abstract

Time-resolved intrinsic reaction rate of catalytic vapor deposition of methane into carbon nanofibers (CNFs) and hydrogen on supported Ni catalysts was determined under different reaction temperatures (773-973 K) and feed compositions (P H 2 = 0 P H 2 = 0 P H 2 = 0-0.29 atm, P CH 4 = 0.28 P CH 4 = 0.28 P CH 4 = 0.28-0.71 atm) and the microstructure of the produced CNFs was characterized by Raman and TEM. The results showed that, increasing the reaction temperature, methane partial pressure and decreasing hydrogen partial pressure increased the initial reaction rate but generally led to fast catalyst deactivation. A high carbon yield per unit catalyst was obtained as a compromise between initial reaction rate and catalyst deactivation rate. The microstructures of the produced CNFs had a close relationship with the initial reaction rate. The CNFs produced with high initial rate tended to have a small angle between the graphene layers and the growth axis, thin diameter and a hollow core. This phenomenon can be used for monitoring and controlling the CNFs synthesis process.

Liquid-phase synthesis of vertically aligned carbon nanotubes and related nanomaterials on preheated alloy substrates

“…With respect to the distinctive diamond-shaped inclusions, catalyst particles (in this case, probably Ni-based particles) with low interaction with the substrate surface results in fibrous growth in both directions while remaining in the grown fibers, which generally form sterically bicone-shaped structures, as reported by some researchers. 41,42) Remarkably, the observed twisted structures and their inclusions have very similar morphologies to those of the products in the initial growth stage of carbon microcoils. 43,44) It is expected that optimization of the experimental conditions will make it possible to bring selective synthesis of characteristic helical carbon structures from the Monel ® 400 substrate for intended applications.…”