(570ar) Active Species in Single-Walled Carbon Nanotube (SWNT) Synthesis From Silica-Supported Cobalt Catalysts
In this paper, we report a simple catalyst preparation method to obtain a highly active Co/SiO2 catalyst for Single-Walled Carbon Nanotube (SWNT) synthesis. Although previous attempts have failed to produce Co/SiO2-impregnated catalysts that are highly active for SWNT growth, in the current research, we have found that by properly choosing the Co precursor, such as cobalt(II) acetate, cobalt(II) acetylacetonate, and cobalt(III) acetylacetonate, catalysts prepared by incipient wetness impregnation also show high yield (up to 75 wt %) for SWNT synthesis. The catalyst prepared from a simple inorganic cobalt salt, such as cobalt(II) nitrate, is not as effective. Detailed characterization indicates that the active sites for SWNT synthesis are small cobalt particles resulting from the reduction of a highly dispersed surface cobalt silicate species, which is formed during the calcination of the catalysts. XRD, XANES, and EXAFS results show that these surface cobalt silicate species are highly dispersed. When normalized by surface cobalt silicate, all four catalysts give similar adjusted carbon/SWNT yield per cobalt. Any formation of large cobalt oxide particles will adversely affect the effectiveness of the catalyst. This research provides direction for future design of SWNT-synthesis catalyst through a surface phase formation. The SWNTs produced by this catalyst are of high quality and easy to purify, and the process is simple and scalable.