Carbon nanotubes prepared from CO on pre-reduced La2NiO4 perovskite precursor

Article abstract of DOI:10.1016/S0025-5408(00)00480-3

A large amount multi-shelled carbon nanotubes with uniform diameter were obtained from catalytic disproportionation of CO using La₂NiO₄ oxides as catalyst precursor, which was prepared by citric acid complexing method. Nickel exists chiefly as Ni⁰ particles supported on La₂O₃ after reduction of perovskite-like mixed oxide La₂NiO₄. These nano-scale Ni⁰ particles play a key role for the growth of carbon nanotubes. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and oxidation weight loss analysis were employed to reveal the morphology and microscopic structure of carbon nanotubes.

Full text of DOI:10.1016/S0025-5408(00)00480-3

Materials Research Bulletin 36 (2001) 471–477
Pergamon
Carbon nanotubes prepared from CO on pre-reduced
La2NiO4 perovskite precursor
Qi Liang, Qing Li, Lizhen Gao, Zuolong Yu*
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041,
People’s Republic of China
(Refereed)
Received 27 March 2000; accepted 17 May 2000
Abstract
A large amount multi-shelled carbon nanotubes with uniform diameter were obtained from
catalytic disproportionation of CO using La2NiO4 oxides as catalyst precursor, which was prepared by
citric acid complexing method. Nickel exists chiefly as Ni0 particles supported on La2O3 after
reduction of perovskite-like mixed oxide La2NiO4. These nano-scale Ni0 particles play a key role for
the growth of carbon nanotubes. Transmission electron microscopy, scanning electron microscopy,
X-ray diffraction, Raman spectroscopy, and oxidation weight loss analysis were employed to reveal
the morphology and microscopic structure of carbon nanotubes. © 2001 Elsevier Science Ltd. All
rights reserved.
Keywords: A. Nanostructures; B. Chemistry synthesis; C. Raman spectroscopy; C. X-ray diffraction
1. Introduction
Recently, the synthesis of carbon nanotubes has become a hot point in the field of carbon
materials after the discover of fullerene [1–5]. As a new allotrope of carbon, carbon
nanotubes are provided with many extraordinary properties as a result of their special
quasi-one-dimensional structure. Some novel techniques are expected to develop for their
potential applications. Among of current methods, the catalytic production of carbon nano-
tubes is simple and reproducible. With this method, it is crucial to select and prepare an
* Corresponding author. Tel.: ϩ86-28-5229790; fax: ϩ86-28-5229790.
E-mail address: yzuolong@mail.sc.cninfo.net (Z.Yu).
0025-5408/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0025-5408(00)00480-3

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Fig. 1. (a) SEM image of carbon nanotubes and (b) Low-resolution TEM image and SAED pattern (inset) of
carbon nanotubes.
effective catalyst with appropriate size of active metal, usually Fe, Co, Ni. Dai et al. found
that the diameter of carbon nanotubes can be determined by the size of transition metal
particles [6]. Rodriguez et al. elucidated the impact of the nature of the metal surface during
the synthesis of carbon nanotubes [7].
In the past decade, perovskite and perovskite-like mixed metal oxides have been inves-
tigated extensively as the catalyst for some chemical reactions, for example, NH3 oxidation
[8]. Up to now, however, no report is seen in the literatures about using perovskite or
perovskite-like metal oxides as catalyst precursor for carbon nanotubes growth. In this

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Fig. 2. The Ni particle (about 10nm) encapsulated by nanotubes was shown by HRTEM image of carbon
nanotubes.
bulletin, we obtained bulk growth of carbon nanotubes by catalytic disproportionation of CO
over Ni nanoparticles prepared by reduction of La2NiO4 perovskite precursor.
2. Experimental
The La2NiO4 oxide was synthesized by decomposing the amorphous precursors [8]. In
brief, to a mixed aqueous solution of nickel and lanthanum nitrates with appropriate
stoichiometry, excess of citric solution was added. The resulting gel was evaporated to
dryness with stirring. The obtained residue was calcined in air at 773K for 4h and then
pelleted prior to calcination at 1073K for 6h. The pulverized samples (ca. 60–80 mesh) was
used as catalyst precursor to prepare carbon nanotubes.
The production of carbon nanotubes was carried out with a horizontal quartz glass reactor,
30mm in diameter and 1000mm in length. The constant temperature zone is 400mm in length
in the middle segment of the tube. Schlepping the catalyst precursor, the quartz boat was
placed in the reactor. The amount of catalyst in oxidation state used for all experiments was
100mg. In all experiments, the reaction pressure was maintained at ambient pressure. After
the La2NiO4 oxide were reduced in a flow of H2 at 1073K, the reactor was controlled to 873K
and CO was introduced into the reactor, passing over the catalyst with 30ml/min for 60
minutes. After cooled to the room temperature in a flow of Ar, the products were collected.

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Fig. 3. The walls of a typic carbon nanotube was shown by HRTEM image.
The product was sonicated and dispersed onto a copper grid for microscopic observation.
The microstructure of obtained carbon nanotubes were observed by means of scanning
electron microscopy (JOEL JXA-840), low-resolution transmission electron microscopy
(JOEL JEM-100CX) and high-resolution transmission electron microscopy (Hitachi 8100,

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Fig. 4. X-ray diffraction partten of synthesized carbon nanotubes.
operated at 200keV). Carbon nanotubes were also characterized by X-ray diffraction with Cu
K␣ radiation. Raman spectra (Dilor LABRAM-I instrument) of carbon nanotubes were
measured with the Arϩ wave length of 514.5 nm. The oxidation weight loss of carbon
nanotubes was analyzed by Perkin-Elmer (7th series system).
3. Results and discussion
The carbon nanotubes were prepared by disproportionation of CO at 873K on pre-reduced
La2NiO4, the Bouduard reaction 2CO ϭ CO2 ϩ C. A bulk growth of well-turbostratic carbon
nanotubes was obtained. Fig. 1a is a characteristic SEM image of carbon nanotubes. We can
observe innumerable carbon nanotubes with entangled and interlaced shapes. Most of them
are up to several 10 ␮m. In Fig. 1b, many rope-like carbon nanotubes were shown by a
typical TEM image. The diameter of them is mostly ca. 20nm, which is frequently close to
the size of Ni particles. Some Ni particles are found to be encapsulated by carbonaceous
tubes (Fig. 2). In our experiment, the metal particles play a key role in the formation of
carbon nanotubes. By XRD, we know that the catalyst precursor La2NiO4 is formed as sing
phase with a tetragonal structure. Ni2ϩ and La3ϩ ions were evenly distributed. After
reduction, La2O3 prevents Ni0 particles from agglomerating, and nickel exists chiefly as
nano-scale Ni0 particles. Well-dispersed Ni crystallites are very advantageous for carbon
nanotubes growth. Using this kind of catalyst precursor, other advantages of preparing
nanotubes are also shown obviously. The yield of product is higher and the reaction
temperature is milder comparing with arc discharge method. The purification and separation
of carbon nanotubes is convenient due to freely soluble catalyst.
A better degree of average graphitization of carbon nanotubes was exhibited by selected
area electron diffraction (SAED) pattern (inset to Fig. 1b). Details of the structure of carbon
nanotubes were opened out by HRTEM image (Fig. 3), which confirmed that multi-walled

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Fig. 5. Raman spectrum of obtained carbon nanotubes.
were obtained. Many cylindrical graphite layers were arranged regularly in the inner wall.
But some amorphous carbon layers can be observed to cover the outer periphery of carbon
nanotubes. Unlike our results, single-walled carbon nanotubes were produced with CVD
method utilizing CO and supported MoOx catalyst [6].
The X-ray diffraction was performed for carbon nanotubes (Fig. 4). A strongest peak at
26° corresponds approximately to that of graphite. The interlayer spacing (d002) within
multi-walled carbon nanotubes is 0.342nm, which is slightly wider than that of ideal
graphite. At ca. 44°, 54° Ni crystallite peaks can also be found. At room temperature with
frequence 700-3500 cm-1, Raman shift spectrum of carbon nanotubes was analyzed (Fig. 5).
Two sharp peaks present at about 1565 and 1323 cm-1, which are characteristic G-line and
Fig. 6. Weight loss curve of carbon nanotubes in the air.

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D-line. They are correspondingly characteristic peak of graphite. These features are close to
that of multi-walled carbon nanotubes.
The oxidation behavior of obtained carbon nanotubes was studied by thermogravimetric
instrument with increasing temperature rate 10°C/min (Fig. 6). In the air, the onset of
oxidation was at a temperature of 588°C, which is lower than results of Ajayan (over 700°C)
[9], but higher than that of Kukovitskii (ca. 420°C) [10]. The initial weight loss can be
ascribed to the exist of amorphous carbon on the outer wall of nanotubes and some surface
structure defects. In addition, the terminal of carbon tubes are usually active for oxidation
reaction.
Acknowledgments
The authors gratefully acknowledge the financial support from the Chinese Academy of
Sciences.
References
[1] S. Iijima, Nature 354 (1991) 56–58.
[2] T.W. Ebbesen, P. M. Ajayan, Nature 358 (1992) 220–222.
[3] P.M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Science, 265 (1994) 1212–1214.
[4] W.Z. Li, S.S. Xie, L.X. Qian, B.H. Chang, B.S. Zou, W.Y. Zhou, R.A. Zhao, G. Wang, Science 274 (1996)
1701–1704.
[5] J. Kong, A. M. Cassell, H.J. Dai, Chem. Phys. Lett. 292 (1998) 567–574.
[6] H.J. Dai, A.G. Rinzler, P. Nikolaev, A. Thess, D.T. Colben, R.E. Smalley, Chem. Phys. Lett. 260 (1996)
471–475.
[7] N.M. Rodriguez, A. Chambers, R.T.K. Baker, Langmiuir 11 (1995) 3862–3866.
[8] Z.L. Yu, L.Z. Gao, S.Y. Yuan, Y. Wu. J. Chem. Soc. Faraday Trans. 88 (1992) 3245–3249.
[9] P.M. Ajayan, T.W. Ebbesen, T.Ichihashi, S.Iijama, K.Tanigaki, H.Hiura, Nature 362 (1993) 522–525.
[10] E.F.Kukovitskii, L.A. Chernozatonskii, S.G. L’vov, N.N. Mel’nik, Chem. Phys. Lett. 266 (1997) 323–328.