Investigation of CoO_x/AC catalysts in methane chemical vapour decomposition process for carbon nanotube (CNT) synthesis

Nowadays, activated carbon (AC) is one of the most easily available and potentially significant materials for industrial applications because of its higher surface area and porosity as compared to other traditional supports. It has the advantage of decomposing hydrocarbon gases like methane (CH₄) at even lower temperature [1-3]. Previous studies by our group showed the significance of CoO/Al₂O₃catalyst over CoO/SiO ₂, CoO/CaO, CoO/CeO₂, CoO/H-ZSM-5, CoO/MgO, and CoO/TiO₂ in CNT formation [4-5]. The main purpose of this work is to investigate the CoO_x/AC catalyst in methane chemical vapour decomposition (m-CVD) for synthesizing CNTs. The effects of catalyst preparation conditions such as metal loading, calcination and reduction temperatures on the morphology and the quality of CNTs formed were investigated. CoO_x/AC catalyst samples were prepared with 5, 10, 15 and 20 wt% of cobalt oxide loadings by wetness impregnation method. The impregnated samples were dried at 105°C for 12 h and calcined in N₂ at 350/450°C for 3 h. The calcined samples were further subjected to a reduction under H₂ atmosphere in a tubular quartz reactor at two different temperatures of 450 and 550°C for 3 h. The schematic diagram of the experimental set-up was described elsewhere [6]. High purity CH₄ (99.99 %) was mixed with N₂ (99.99 %) with a flow rate ratio of 1: 2 (CH₄: N: ₂ = 120: 240 ml/min) before entering the reactor. For synthesizing nanotube materials, 0.2 g of CoO_x/AC catalyst was placed on a quartz boat in an electrical furnace and heated under N₂ flow to the desired temperatures for a period of 60 min to study the CoO_x/AC catalyst activity and its performance in m-CVD and CNT formation.