Mass Spectroscopy of Chemical Reaction of 3d Metal Clusters Involved in Chemical Vapor Deposition Synthesis of Carbon Nanotubes

Abstract

The chemical reactions of transition metal clusters in the gas phase have aroused considerable scientific interest and are also of critical scientific importance. For example, these reactions are involved in the synthesis of single-walled carbon nanotubes, which are considered ideal materials because of their outstanding properties. Alcohol catalytic chemical vapor deposition (ACCVD) is one of the best synthetic processes for carbon nanotubes (CNTs); however, even the initial growth mechanism is still unclear, unlike those of other synthetic processes. In this study, we used a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to determine the initial reactions of transition metal cluster ions (iron, cobalt, and nickel) that are typically adopted in the alcohol CVD process. Metal clusters with approximately 10 -25 atoms each, generated by a pulsed laser ablation system in a supersonic-expansion cluster beam source, were directly carried into the FT-ICR cell. Subsequently, ethanol was introduced into the ICR cell. We observed two different results: one was simple chemisorption observed in the iron cluster and the other was dehydrogenated chemisorption observed in the nickel cluster; however, cobalt clusters exhibited both patterns, and a sequential reaction was observed. Furthermore, the dehydrogenation of ethanol on the cobalt cluster is fully described from isotope-labeled experiments.

Dissociation dynamics of ethylene molecules on a Ni cluster usingab initiomolecular dynamics simulations

“…In order to understand the effect of the carbon precursor molecules and additives described above, it is important to investigate the dissociation process of the carbon precursor molecules on the catalytic metals. Recent in-situ mass spectroscopic analysis [29][30][31] revealed some aspects of the dissociation of carbon precursor molecules during CNT growth by CCVD, in which ethylene molecules and acetylene molecules are key products of the dissociation of ethanol molecules [31]. However, it has not been easy to observe such reaction processes directly during the CCVD process, because it takes place at high temperatures.…”

Ab initio molecular dynamics simulation of ethanol decomposition on platinum cluster at initial stage of carbon nanotube growth

“…Moreover, the addition of a small amount of water during the CVD process enhances the activity and lifetime of the catalytic metal drastically, which enables the synthesis of nanotube forests with heights of up to 2.5 mm repeatedly [5]. In order to understand the dissociation of hydrocarbons and alcohols on the metal cluster, the mass spectroscopic analyses [6][7][8][9][10][11] have been widely employed. For example, an in situ mass spectroscopic analysis during the alcohol CCVD process revealed that ethylene molecules are formed by the ethanol dissociation, which suggests that the C O bond dissociation occurs at the initial stage of the CNT synthesis [11].…”

Generation and agglomeration behaviour of size-selected sub-nm iron clusters as catalysts for the growth of carbon nanotubes

“…To the best of our knowledge these are the first experimental studies on CNT growth employing size-selected, sub-nm iron clusters as catalyst or precatalyst precursors. (A study of 3-D metal clusters as catalysts in CNT growth was reported in [ 8 ], however, no CNT growth was studied therein; CNT growth derived from nm-sized, ligand-stabilized mixed metal clusters as precatalysts was reported in [ 9 ].) Non-agglomerated naked iron clusters of 0.6–0.9 nm size were generated, mass-selected and surface-implanted at room temperature under ultrahigh vacuum [ 10 ] at a surface coverage in the range of a few thousandths up to a few hundredths of a monolayer on standard substrate grids for transmission electron microscopy (TEM).…”