Morphology and chemical state of Co–Mo catalysts for growth of single-walled carbon nanotubes vertically aligned on quartz substrates

Bimetallic catalysts (Co:Mo ≈2:1 in atomic ratio) were prepared on quartz substrates from metal acetate solutions using a procedure of dip coating, followed by calcination and reduction. High-purity single-walled carbon nanotubes (SWNTs) 1–2 nm in diameter were grown densely (∼1.0×1017 m−2) and vertically on these substrates during an alcohol catalytic chemical vapor deposition process. To clarify the mechanism of the high selectivity and activity of these catalysts, we studied the morphology and chemical state of the Co–Mo catalysts during their preparation using transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the stable existence of well-dispersed (∼1.3×1017 m−2) nano-sized (1–2 nm) catalyst particles composed of Co molybdates and metallic Co plays an important role in the SWNT growth. Based on these results, we propose a model to understand the good dispersion and high stability of these nano-sized catalyst particles against agglomeration during calcination and reduction.