COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Microreactor utilizing a vertically-aligned carbon nanotube array
grown inside the channels
a
ab
ab
a
Naoki Ishigami, Hiroki Ago,* Yukihiro Motoyama, Mikihiro Takasaki, Masashi Shinagawa,
a
c
Kohji Takahashi, Tatsuya Ikuta and Masaharu Tsuji
c
ab
Received (in Cambridge, UK) 28th November 2006, Accepted 15th January 2007
First published as an Advance Article on the web 6th February 2007
DOI: 10.1039/b617356j
We have fabricated a microreactor incorporating vertically-
aligned carbon nanotubes supporting Pt nanoparticles and
found that the presence of aligned nanotubes significantly
enhances the catalytic reaction and extends the catalyst lifetime
as compared with conventional microreactors using a Pt metal
film or Pt nanoparticles directly deposited on the channel walls.
Fig. 1 Schematic illustration of (a) a conventional microreactor using Pt
film deposited on the walls of the flow channel and (b) a microreactor with
Pt-modified aligned nanotubes in the flow channel.
Carbon nanotubes, one-dimensional cylindrical graphene sheets
with a nanoscale diameter, have attracted a great deal of interest,
because they show excellent electron and thermal conduction as
nanotube-based microreactor. In the latter, the high contact area
formed by the aligned nanotubes is expected to realize high
catalytic conversion. Here, we have studied the hydrosilylation of
an olefin using the nanotube-incorporated microreactor and
observed a significant increase in the yield and extension of the
catalyst lifetime.
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well as high mechanical flexibility. Nanotubes are a promising
catalyst support material, because of their high surface area, ease
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of chemical modification and high mechanical stability. Several
studies on catalysis using metal-supporting carbon nanotubes have
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shown high catalytic activity in hydrogenation, dehydrogenation,
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hydroformylation and electrooxidation for fuel cells. However,
there are severe limitations in the use for catalyst supports due to
their poor solubility in organic solvents and high cost of nanotubes
which cannot be used in a large scale.
The nanotube-incorporated microreactor was fabricated by
growing multi-walled carbon nanotubes inside the channels made
on a Si substrate. The reaction zone (width: 2.5 mm, depth:
170 mm, length: 20 mm) was first covered with an evaporated Al
Recently, microreactors which consist of micro-scale flow
channels, reaction zones, mixers and so on, have been recognized
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as an efficient means for chemical synthesis. This is because
film (20 nm), followed by growing carbon nanotubes by thermal
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chemical vapour deposition (CVD) using ferrocene and xylene.
We found that the Al buffer layer is important to strengthen the
interface between the nanotubes and the Si substrate, as the
absence of the Al film resulted in peeling off of the nanotubes
when the reactant solution flows in. Fig. 2(a) shows a photograph
of the nanotube-incorporated microreactor before sealing; the
black part corresponds to the aligned nanotube array. Scanning
electron microscope (SEM) images of the cross-section of the
nanotube-based microreactor are shown in Fig. 2(b) and (c). The
nanotubes were aligned normal to the Si substrate, and their length
and diameter were around 100 mm and 30 nm, respectively.
The aligned nanotubes were modified with Pt nanoparticles for
the catalytic reaction by the following two methods; impregnation
of Pt salt and direct deposition of Pt nanoparticles. In the
microreactors have many advantages, such as high controllability
of the reaction conditions, laminar flow, uniformity of reaction
temperature and parallel-processibility. Catalytic reactions have
been widely studied in microreactors and, in most cases, metal
catalyst is deposited on the walls of the microchannel by
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evaporating thin metal films or by attaching metal nanoparticles.
Therefore, catalytic reactions occur only at the periphery of the
channel walls.
Here, we have fabricated a new type of microreactor which
possesses Pt-supported aligned carbon nanotubes in the reaction
zone and studied the efficiency of
Incorporating nanotubes in a microreactor has many advantages;
i) nanotubes are fixed inside the channel so that the difficulty in
a catalytic reaction.
(
impregnation method, an acetone solution of H
1.54 M) was dropped onto the nanotubes and reduced at 250 uC
for 2 h in hydrogen atmosphere. In the direct deposition method,
2 6 2
PtCl ?6H O
dispersing nanotubes in solvent is avoided, (ii) large contact area
between reactants and the catalyst is expected as the nanotubes
cover the whole channel and (iii) collection of nanotubes after a
chemical reaction, such as filtration, is not required. Fig. 1
illustrates the comparison of a conventional microreactor and the
(
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the micelle solution of Pt nanoparticles with 1.7 nm diameter was
dropped onto the nanotube array, followed by annealing in air at
350 uC for 2 h to remove the surfactant, dodecylamine. In both
a
methods, the Pt amount was fixed to be ca. 15 wt% against
nanotubes, which was estimated by thermogravimetry (TG)
measurements. Finally, the Si substrate was sealed with Pyrex
glass using a fluorine-based binder. For comparison, microreactors
without nanotubes, i.e. a Pt salt or Pt nanoparticles were deposited
directly on the channel wall, were prepared. A conventional
Interdisciplinary Graduate School of Engineering Sciences, Kyushu
University, Fukuoka, 816-8580, Japan. E-mail: ago@cm.kyushu-u.ac.jp;
Fax: +81-583-7817
Institute for Materials Chemistry and Engineering, Kyushu University
b
and CREST-JST, Fukuoka, 816-8580, Japan
Graduate School of Engineering, Kyushu University, Fukuoka,
c
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19-0395, Japan
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626 | Chem. Commun., 2007, 1626–1628
This journal is ß The Royal Society of Chemistry 2007
Ishigami, Naoki
