from first principles PP-I-1

PP-III-25Carbon Nanotube Synthesis by CCVD Process: Kinetic Studyon a Ni-Mo/MgO CatalystDouven S. 1 , Pirard S.L. 1 , Chan F.-Y. 2 , Heyen G. 3 , Pirard J.-P. 11 Laboratoire de Génie Chimique, B6a, Université de Liège, Liège, Belgium2 Nanocyl S.A., Sambreville, Belgium3 Laboratoire d’Analyse et de Synthèse des Systèmes Chimiques, B6a, Université de Liège,Liège, BelgiumS.Douven@ulg.ac.beA kinetic study was performed to determine the kinetic rate expression of methanedecomposition into carbon nanotubes by catalytic chemical vapor deposition over aNi-Mo/MgO catalyst using methane as the carbon source. A mass spectrometer was used todetermine experimental reaction rates for methane partial pressures ranging from 0.1 to0.9 atm balanced by hydrogen or hydrogen-helium and for three temperatures: 925°C, 975°Cand 1000°C. Three kinetic models based on different mechanisms were fitted ontoexperimental data. They differ by the presence of one or two types of active sites and by thenature of active sites involved in the rate-determining step. In this study, hydrogen seemed toinfluence the catalytic activity rather than the kinetics of carbon nanotube growth. A statisticalstudy is performed in order to discriminate between the different models and to validate thegood agreement between the chosen model and the experimental data. As the modelscorrespond to different mechanisms, the discrimination allows a better understanding of theelementary steps involved in carbon nanotube production. The best model involves thedissociative methane adsorption followed by the decomposition of the adsorbed methyl group,which is the rate-determining centre. The activation energy of methane adsorption was foundto be equal to 79×10 3 kJ kmol -1 , while the activation energy of adsorbed methyldehydrogenation was found to be equal to 221×10 3 kJ kmol -1 [1].References:[1] S. Douven, S.L. Pirard, F.-Y. Chan, R. Pirard, G. Heyen, J.-P. Pirard, Chem. Eng. J. 188 (2012)113.177