Kinetically controlled synthesis of carbon nanofibers with different morphologies by catalytic CO disproportionation over iron catalyst

• Published in: Chemical engineering science 2010, Vol.65 (1), p.193-200
• Main Authors: Lu, Wen-Xin, Sui, Zhi-Jun, Zhou, Jing-Hong, Li, Ping, Chen, De, Zhou, Xing-Gui
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbon nanofibers; Catalysis; Catalytic reactions; Chemical engineering; Chemistry; CO disproportionation; Exact sciences and technology; General and physical chemistry; Kinetics; Morphology; Nanostructure; Reactors; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2009.07.001

Carbon nanofibers (CNFs) were synthesized by CO disproportionation on iron catalyst at CO concentration between 58.3% and 75.0%, H 2 concentration between 8.3% and 25.0% and reaction temperature between 833 and 913 K. The time-depending rate of CNFs growth as a function of time was determined by an on-line mass spectrometer and the morphologies of all CNFs products were observed by electronic microscopy. Not only the CNFs growth rate but also the morphology of the grown CNFs were shown to vary with the three operating variables. SEM and TEM images showed that the three-dimensional morphologies of the CNFs were twist, helical or straight and an interesting relationship between the maximal growth rate and the morphology was observed. When the growth rate was between 0.8 and 0.9 mmol/(s gcat), the CNFs were twist. As the growth rate increased to 1.0 mmol/(s gcat), more helical nanofibers appeared. Straight nanofibers were produced when the growth rate reached the level of 1.2 mmol/(s gcat). Finally when the rate of CNFs growth was high at 1.8 mmol/(s gcat), the absolute majority of the solid products was amorphous carbon coexisting with some short and thick nanofibers. Under different operating conditions, the crystal faces of the catalysts had different anisotropy properties for carbon deposition, thus producing CNFs with different morphologies.