Role of catalyst and substrate in synthesis of single wall carbon nanotubes
Otto H. York Department of Chemical Engineering
Master of Science
Bozzelli, Joseph W.
Single wall carbon nanotubes
The synthesis of single wall carbon nanotubes (SWNTs) by the catalyticdisproportionation of carbon monoxide (CO) (i.e., Boudouard reaction) at I atm pressureand 700-800 C, has been systematically investigated in order to determine whether theprocess can be used for the large scale production. SWNT diameter distribution andmorphology were studied by Raman scattering, and scanning and transmission electronmicroscopy, respectively. X-ray diffraction was used to determine levels of the remnantcatalyst and support. Synthesis experiments were conducted using a three-stage processwith hydrogen to reduce the catalyst-precursor and argon to cool the system. Two typesof catalyst/support synthesis were studied: (1) Combustion synthesis to form catalyst onhigh surface area MgO support, and (2) Tetraethoxysilane synthesis to form catalyst onarrayed 200 nm silica opal support. Cobalt to molybdenum atomic weight ratios of 1:4and 5:1 respectively were found to be most effective for the selective production ofSVVNTs, and by contrast with previous observations in the literature, cobalt alone ascatalyst was also found to be very effective under these synthesis conditions.Molybdenum alone is not active, but having some Mo in combination with Co increasesSWNT yields. This suggests that Mo plays the role of a promoter by preventing thesegregation of the active Co particles. MgO support could be easily removed using 4 MHCl as confirmed by X-ray diffraction measurements, whereas silica support removalrequires more aggressive HF treatment, which is likely to chemically damage the SWNTs. The process using MgO support would therefore be scaleable for SWNT production. In this study this was preliminarily demonstrated by the production of gram quantities of highly pure SWNTs. Future work would need to focus on increasing SWNT yields and process continuity, by using a fluidized bed to facilitate point-to-point contact between gaseous precursor and catalyst particles, and admixing CO with small amounts of the more labile CH4 precursor to enhance the kinetics of CO disproportionation.
njit-etd2003-045 (60 pages ~ 2,974KB pdf)
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Created March 17, 2004