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Chemistry Letters Vol.35, No.8 (2006)
Preliminary Study on Cogeneration of Carbon Nanotubes and C2 Hydrocarbon
in CH4/H2 Corona Discharge
Kailu Yu,ꢀ1;2 Guoling Ruan,2 Yuheng Ben,3 and Jijun Zou3
1College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266003, P. R. China
2The Institute of Seawater Desalination and Multipurpose Utilization, Tianjin 300192, P. R. China
3School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
(Received April 5, 2006; CL-060400)
La-doped carbon nanotubes and valuable C2 hydrocarbon
(C2H2 and C2H4) are simultaneously generated in CH4/H2 coro-
na discharge. The analysis of off gas indicates that the addition
of anodic alumina membrane shows no influence on plasma
methane conversion reactions.
quartz tube reactor contained two axially centered electrodes,
an upper wire electrode and a plate electrode. The gap between
electrodes was fixed at 4 mm. A mixture of methane (2 mL/min)
and hydrogen (20 mL/min) was used as the reactants for the car-
bon nanotubes synthesis. A piece of as-prepared La-loaded
membrane was placed on the plate electrode. After the initiation
of the corona discharge between the two electrodes with 3600 V,
a white-color corona discharge was established. The feed and
effluent gases were analyzed by on-line mass spectrometry.
The microscopic features of the sample were observed with
The interest in carbon nanotube arrays by AAO membrane
and the breadth of research activities across the world on their
application potential have lasted tens of years. They have shown
unique properties in such fields as fuel cells, hydrogen adsorp-
tion, heterogeneous catalysis, field emission, and so on.1–5 Most
carbon nanotube arrays have at present produced by the plasma-
enhanced chemical vapor deposition (CVD) method.6 A variety
of plasma source and widely varying results have been reported
in the literature.6 Typical hydrocarbon sources used in plasma-
based growth of carbon nanotubes include methane, ethylene,
and acetylene. Since the plasma can dissociate them creating
a lot of reactive radicals, it is desirable to dilute the hydrocarbon
with hydrogen. For most of the carbon nanotube reactions, the
gaseous effluents are seldom studied and often considered as
by-product.
Methane (natural gas) is a potential cheap chemical materi-
al, and direct conversion of methane to more valuable hydrocar-
bons has been an attractive subject of investigation,7 but the high
thermal decomposition temperature of it is a big problem. Coro-
na discharge, as an unconventional technology, has been used for
methane conversion.8–10 Methane molecules can be decomposed
into some carbon-containing molecules in corona discharge,
such as CH, CH2, CH3, and atomic carbon. Therefore, valuable
hydrocarbons are synthesized by the combination between them.
But carbon deposition is inevitably formed in the corona dis-
charge reactor despite of addition of catalysts.
a
TECNAI-F20 transmission electron microscope (TEM,
200 kV) and a Philips XL 30 scanning electron microscope
(SEM).
Figure 1 presents a SEM image of La-doped carbon nano-
tubes produced in corona discharge. As indicated by the dashed
narrows, the hollow structure of carbon nanotubes is clearly ob-
served. When one part of these La-doped carbon nanotubes is
enlarged, several large particles are obviously found on the outer
surface, and their diameter is close to 100 nm. These particles are
more obviously observed in its TEM image (Figure 2). The den-
sity of them is very low, and the distance between them is longer
than 200 nm. The electron diffraction pattern (insert in Figure 2)
is composed of weak circles, which indicates that these large
particles are amorphous.
EDX spectrum of nanoparticles show some strong La peaks
and weak C, O, and Al peaks (Figure 3). Cu peaks are due to the
copper grid supporting the sample. The quantification analysis
indicates that the atomic contents of La, O, and Al are 18.55,
2.83, and 0.992%, respectively, so the nanoparticles are not
La2O3. Since La is dominant, they must be metallic La. Consid-
Considering the fact that the above two reactions are carried
out under the same conditions, it is meaningful to combine the
production of carbon nanotubes and the plasma methane conver-
sion. But the coverage of AAO membrane on electrode inevita-
bly affects the corona discharge system. Here, we reported the
cogeneration of La-doped carbon nanotubes and unsaturated
C2 hydrocarbons produced from methane using corona dis-
charge, and the influence of AAO membrane on the gaseous
products also is studied.
Nanoporous anodic alumina (Anodisc 47, 200 nm) was used
as a template to synthesize carbon nanotubes. The preparation of
La-loaded membrane is similar to that in the literature.11 A piece
of such membrane was immersed into an La(NO3)3 solution
(1 M) for 12 h, and then taken out for drying at 50 ꢁC, followed
by calcinations at 550 ꢁC. The corona discharge reactor used
here is the same as that used for methane conversion.12 The
Open tubes
La particles
Figure 1. SEM image of La-doped carbon nanotube arrays.
Copyright Ó 2006 The Chemical Society of Japan
Yu, Kailu
