Factorial design optimization of monometallic (cobalt) catalyst on calcium carbonate support for carbon nanotubes synthesis

This study reports the preparation of monometallic (cobalt) catalyst supported on calcium carbonate for the synthesis of carbon nanotubes (CNTs). The catalyst was synthesized using wet impregnation method and optimized using factorial design of experiment to determine the effects of synthesis conditions (stirring speed, drying temperature, drying time and mass of the support) on the catalyst (Co/CaC0₃) yield. The catalyst best yield after calcination was 87.8% at stirring speed, drying temperature, drying time and mass of support of 700 rpm, 120°C, 7 hours and 5.5 g respectively. The selected best yield of the produced catalyst was characterized using, SEM/EDX, XRD and TGA to determine its morphology, crystallinity and thermal stability respectively. FTIR was also used to determine the functional groups present in the catalyst. The characterization result showed that the catalyst produced is thermally stable with about 0.034% weight loss at 808.3°C indicating that the catalyst will be suitable for the synthesis of CNT. The catalyst was utilized in a CVD reactor to synthesize carbon nanotubes by investigating the influence of carbon source (acetylene) flow rate on the yield of CNTs. The results obtained revealed that the highest yield of 27% of CNTs was obtained at acetylene flow rate of 90 ml/min. The raw CNTs were analyzed and the results obtained revealed that they were thermally stable with specific surface area of 389.4 m²/g. Meanwhile, the TEM result showed that the synthesized CNTs were multiwalled carbon nanotubes. It can be therefore inferred from the results of various analyses conducted that the prepared monometallic (Co) catalyst on CaCOj support is suitable for the synthesis of CNTs.