Optimization of Carbon Nanotubes Synthesis via Methane Decomposition over Alumina-Based Catalyst

Abstract

Carbon nanotubes (CNTs) were synthesized from alumina-based catalyst via decomposition of methane in a horizontal reactor system. By using statistical design of experiments (DoE), six process variables (reaction temperature, reaction duration, metal loading of catalyst, amount of catalyst, flow rate of methane and flow rate of nitrogen) were optimized for the synthesis of CNTs with satisfying quality. The response of the process towards the process variables was assessed using two quantitative signifiers, which are the yield of carbonaceous material and the I_D/I_G ratio from Raman spectrum. A total of 23 runs was required to achieve the optimum condition: 9 runs for the screening of decisive process variables by using Resolution III fractional factorial design (FFD), 13 runs for the response surface incurred from Box-Behnken design and 1 run for the validation of the final optimum condition. The optimum parameter set was found at a reaction temperature, reaction duration and metal loading of 762°C, 2.3h and 27%, respectively with the carbon yield and I_D/I_G of 350.0% and 0.595, respectively.

Keywords:

• Carbon nanotubes
• chemical vapor deposition
• process optimization
• raman spectroscopy
• transmission electron microscopy

Acknowledgment

The authors gratefully acknowledge the financial support provided by the Universiti Sains Malaysia under the Research University Grant Scheme (Project A/C No. 814004), USM-RU-PRGS (Project A/C No. 8032038) and the Malaysian Technology Development Corporation (MTDC) under the Commercialization of Research & Development Fund (CRDF) (MBF065- USM/05). The authors would also like to thank Prof. Seiji Takeda and Prof. Tadashi Itoh from Osaka University for allowing the authors to use their HRTEM.