Kinetic study of carbon nanotube synthesis over Mo/Co/MgO catalysts

• Published in: Carbon (New York) Vol. 44; no. 11; pp. 2265 - 2272
• Main Authors: Ni, Lei, Kuroda, Keiji, Zhou, Ling-Ping, Kizuka, Tokushi, Ohta, Keishin, Matsuishi, Kiyoto, Nakamura, Junji
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2006; Elsevier Science
• Subjects: Carbon nanotube; Catalysis; Catalyst; Catalytic properties; Chemistry; Cross-disciplinary physics: materials science; rheology; Electron microscopy; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; Materials science; Physics; Specific materials; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Carbon nanotube; Catalytic properties; Electron microscopy; Catalyst; Methane; Catalytic reaction; Deactivation; Catalysts; Transition element compounds; Carbon nanotubes; Decomposition; Deposition rate; High temperature; Carbon; Chemical reduction; Synthesis; Magnesium oxides; Kinetics; Dissociation; Diameter; Deposition
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2006.02.031

The kinetics of carbon nanotube (CNT) synthesis by decomposition of CH 4 over Mo/Co/MgO and Co/MgO catalysts was studied to clarify the role of catalyst component. In the absence of the Mo component, Co/MgO catalysts are active in the synthesis of thick CNT (outer diameter of 7–27 nm) at lower reaction temperatures, 823–923 K, but no CNTs of thin outer diameter are produced. Co/MgO catalysts are significantly deactivated by carbon deposition at temperatures above 923 K. For Mo-including catalysts (Mo/Co/MgO), thin CNT (2–5 walls) formation starts at above 1000 K without deactivation. The significant effects of the addition of Mo are ascribed to the reduction in catalytic activity for dissociation of CH 4, as well as to the formation of Mo 2C during CNT synthesis at high temperatures. On both Co/MgO and Mo/Co/MgO catalysts, the rate of CNT synthesis is proportional to the CH 4 pressure, indicating that the dissociation of CH 4 is the rate-determining step for a catalyst working without deactivation. The deactivation of catalysts by carbon deposition takes place kinetically when the formation rate of the graphene network is smaller than the carbon deposition rate by decomposition of CH 4.