Cerium Oxide Promoted Ni/MgO Catalyst for the Synthesis of Multi-walled Carbon Nanotubes

Abstract

Ni/MgO, Ni/CeO2-MgO, and Ni/CeO2 catalysts were prepared by the citric acid combustion method. Their catalytic properties for the synthesis of multi-walled carbon nanotubes (MWCNTs) by chemical vapor deposition using CH4 as carbon source were evaluated. The catalysts were characterized with N2 adsorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The quality and structure of the CNTs were characterized by thermogravimetry (TG) and transmission electron microscopy (TEM). H2-TPR showed that CeO2 helped decrease the reduction temperature and increase the content of an easily reducible Ni species. XPS showed an energy shift of the Ni catalyst that was modified by CeO2. XRD showed that the reduced nickel maintained their small particle sizes in the Ni/CeO2-MgO catalysts. These findings suggested that the addition of CeO2 changed the chemical environment of the nickel species, which resulted in a weaker interaction between the nickel and the support and increased the reducibility of the Ni species. Moreover, the reduced nickel was highly dispersed on the CeO2-MgO support. The change enhanced the catalytic activity for the growth of carbon nanotubes (CNTs). Characterization by TG and TEM showed that the quality of the CNTs grown on Ni/CeO2-MgO was better than those grown on Ni/MgO catalyst.