Synthesis of carbon nanotubes and carbon nanofibers from CO/H2 Mixed Gases over Fe/Al2O3 Catalyst

Abstract

The production of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) by catalytic decomposition of carbon-containing compounds is the most potential technique for mass production. This technique processes many advantages such as low cost per unit, ability to grow on specified substrate, and capability to control the size by manipulating the catalyst formulation and operating condition. In this research, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are synthesized by using CO/H₂ mixed gases and Fe/AI₂O₃ catalyst. The effect of reaction temperature, Fe loading and CO/H₂ feed ratio are investigated in this study. Different forms of carbon are obtained at different temperature. No carbon nanofibers (CNTs) or carbon nanofibers (CNFs) are observed for the reaction at 400°C. Carbon nanofibers are synthesized at 500°C and 600°C and carbon nanotubes are synthesized at 700°C. The maximum carbon yield is obtained at 600°C. Furthermore, at 700°C, as the Fe loading increases, both CNTs’ diameter and carbon yield are also increased as well. Moreover, CNFs or CNTs cannot be observed when using only CO. The carbon yield is increased as the fraction of H₂ in the feed increases, however, the optimum is reached at CO:H₂ of 2:1. It is also observed the diameter of the CNTs increases with the increasing fraction of H₂ in feed gas.