Catalytic synthesis of carbon nanotubes over Co, Fe and Ni containing conventional and sol-gel silica-aluminas

An attempt has been made to synthesise multiwalled carbon nanotubes using c obalt, iron and nickel supported on different types of silica-aluminas to i nvestigate the rules governing their nanotube producing activity. Acetylene was used as the source of carbon. Decomposition of acetylene has been carr ied out at atmospheric pressure. The effect of reaction temperature in the 770-970 K range and the flow rate of the hydrocarbon has been investigated. The catalysts were analysed by XRD, UV-VIS, surface area and porosity meas urements. Formation of carbon nanotubes was followed by electron microscopy . The amount of deposited carbon increased with increasing reaction tempera ture and the flow rate of acetylene, but decreased with increasing concentr ation of alumina in the catalyst support. Each catalyst showed high product ion of carbon nanotubes at 970 K; however, they were inactive at 770 K. The yield of tube formation was very low at 870 K. The high-resolution transmi ssion electron microscopic (HREM) analysis showed that the outer diameter o f the tubes generated varied from 8 to 40 nm, the tubes were multiwalled, a nd the number of the layers was between 8 and 30. Sol-gel derived samples w ere also found to be working catalysts, indicating the existence of an opti mal metal particle size.