Fabrication of carbon nanotube with high purity and crystallinity by methane decomposition over ceria-supported catalysts

Abstract

Because of its unique properties, CeO2 is a widely used support material in steam reforming and dry reforming reactions conducted using CH4 as a reactant. However, it has been rarely used in the catalytic decomposition of methane (CDM). In a pre-test, a Co/CeO2 catalyst showed higher activity than Ni/Al2O3, Co/Al2O3, and Mo-Ni/MgO catalysts in the CDM conducted via catalytic chemical vapor deposition (CCVD). Therefore, in this study, the CDM for carbon nanotube (CNT) synthesis over CeO2-supported Co, Fe, and Ni catalysts was investigated, while focusing on the effects of CeO2 on the activities of the active metals in the CDM. Among the investigated catalysts, Ni/CeO2 showed a decent catalytic performance at 600 °C, which is a considerably lower temperature than those previously reported. X-ray diffraction, Brunauer–Emmett–Teller surface area, temperature-programmed reduction/desorption (TPR/TPD), and X-ray photoelectron spectroscopy (XPS) analyses were performed to characterize the catalysts. Through these experiments, it was found that Ni/CeO2 had many adsorption sites for CH4 molecules which could react with mobile oxygen existing in CeO2. Furthermore, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric (TG) analyses were performed to examine the morphologies and properties of the carbon material grown on the catalysts.