The effect of copper in the Ni/MgO catalysts for the production of carbon nanotubes via the decomposition of ethylene

Ni/MgO catalysts promoted by copper were prepared by the sol-gel method. X-ray diffraction (XRD) showed that only part of nickel could be reduced due to the strong interaction between NiO and MgO. Both XRD and TPR (Temperature-Programmed-Reduction) indicated that the addition of copper in the catalysts promoted the reduction of nickel. The adsorption of CO revealed that the number of surface Ni atoms increased with the increase of copper content, and thereby increased the activity and lifetime of the catalysts, leading to the substantial increase of the yield of the CNT from the decomposition of ethylene. However, extra copper might increase the size of the nickel particles on the surface, enhancing the production of carbon nanofibers (CNF) instead of CNT. It seems that the addition of 4%-6% Cu in the 60% Ni/MgO catalyst lead to the formation of CNT with high yield (36 g CNT per gram of catalyst) and high quality.