Synthesis of ruthenium/reduced graphene oxide composites and application for the selective hydrogenation of halonitroaromatics

Article abstract of DOI:10.1016/j.cclet.2013.11.044

Reduced graphene oxide (RGO) supported ruthenium (Ru) catalyst was prepared by an impregnation method using RuCl₃ as a precursor and RGO as a support. The catalyst Ru/RGO was used for the selective hydrogenation of p-chloronitrobenzene (p-CNB)

Full text of DOI:10.1016/j.cclet.2013.11.044

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Chinese Chemical Letters xxx (2013) xxx–xxx
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Chinese Chemical Letters
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Original article
Synthesis of ruthenium/reduced graphene oxide composites and
application for the selective hydrogenation of halonitroaromatics
*
Guang-Yin Fan , Wen-Jun Huang
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering China West Normal University,
Nanchong 637009 , China
A R T I C L E I N F O
A B S T R A C T
Article history:
Reduced graphene oxide (RGO) supported ruthenium (Ru) catalyst was prepared by an impregnation
method using RuCl3 as a precursor and RGO as a support. The catalyst Ru/RGO was used for the selective
hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN), showing a selectivity of 96%
at complete conversion of p-CNB at 60 8C and 3.0 MPa H2. The Ru/RGO catalyst was extremely active for
the hydrogenation of a series of nitroarenes, which can be attributed to the small sized and the fine
dispersity of the Ru nanoparticles on the RGO sheets characterized by TEM. Moreover, the catalyst also
can be recycled five times without the loss of activity.
Received 11 July 2013
Received in revised form 28 October 2013
Accepted 5 November 2013
Available online xxx
Keywords:
p-Chloroaniline
Hydrogenation
Ruthenium
Graphene
ß 2013 Guang-Yin Fan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
1. Introduction
properties of supported ruthenium catalysts for the selective
hydrogenation of halonitroaromatics by using reduced graphene
Metal catalysts have been extensively investigated because of
their wide application in synthetic organic chemistry [1]. For the
selective hydrogenation of chloronitrobenzene (p-CNB), noble
metal catalysts such as Pd [2–5], Pt [6–11], and Ru [12–19] are
among the most widely investigated metal catalysts. With respect
to catalytic performance, ruthenium seems to be an attractive
option with its high selectivity and low cost, but its implementa-
tion is offset by low activity. Therefore, many efforts have been
exerted to develop effective ruthenium catalysts in order to
increase the activity while maintaining the selectivity. Many
supports, such as SnO2 [16], MgF2 [17–19], and carbon nanotubes
[12,13] have been used for dispersing ruthenium nanoparticles.
Despite these advances, it should be noted that the catalytic
properties of the reported ruthenium catalysts were still unsatis-
factory. It still remains a great challenge to develop simple,
environmentally friendly, and versatile methods to fabricate
ruthenium catalysts that achieve superior performance.
oxide (RGO) as a support. In this communication, we reported a
facile synthesis of ruthenium-reduced graphene oxide composites
(Ru/RGO) and investigated its catalytic properties for selective
hydrogenation of p-CNB. It was found that the small Ru
nanoparticles were uniformly embedded on the surface of RGO
sheets with a mean size of about 2.0 nm. The Ru/RGO composites
exhibited superior catalytic properties for the hydrogenation of p-
CNB to the desired product. In addition, the Ru/RGO composites
could be reused at least five times without loss of any activity.
From a practical point of view, this study may open the way to a
new approach for the synthesis of amines.
2. Experimental
2.1. Catalyst preparation
As a one atom-thick sheet of sp2-bonded carbon atoms,
graphene has been considered as a highly promising material
with special physical and chemical properties [6]. It is desirable to
explore such a material as a support for catalysis. As far as we are
aware, no attempt has yet been exerted to improve the catalytic
All aromatic compounds (A.R.), solvents (A.R.), and reagents
(A.R.) were used as received. GO was synthesized via the improved
synthesis method reported by Marcano et al. [20]. Then, 0.5 g
as-prepared GO was added into
a flask containing 200 mL
deionized water and ultrasonicated for 12 h to get a yellow-brown
solution. The solution was heated to 80 8C, and then 5.0 g NaBH4
was added into the flask. After 2 h, the black solid was washed with
ethanol and distilled water several times and vacuum dried at
60 8C for 12 h.
*
Corresponding author.
E-mail address: fanguangyin@cwnu.edu.cn (G.-Y. Fan).
1001-8417/$ – see front matter ß 2013 Guang-Yin Fan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.11.044
Please cite this article in press as: G.-Y. Fan, W.-J. Huang, Synthesis of ruthenium/reduced graphene oxide composites and application
for the selective hydrogenation of halonitroaromatics, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.11.044

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The Ru/RGO composite was synthesized as follows: The as-
prepared RGO (0.4 g) was filled with a solution of 5.08 mg/L RuCl3
(10 mL) ultrasonicated for 3 h. Then, an aqueous solution of NaBH4
stirring rate of 1200 rpm at 60 8C and 3.0 MPa hydrogen pressure
for 2 h.
(0.3 mol/L, 10 mL) was dropped into the solution to reduce Ru3+
.
3. Results and discussion
The black solid was rinsed with ethanol and distilled water several
times and vacuum dried at 60 8C for 12 h. For comparison, the
active carbon (AC) supported Ru catalyst (Ru/AC) was prepared
with the same procedures except that 0.4 g AC was employed as a
catalyst support.
3.1. Catalyst characterization
The content of Ru in catalyst Ru/RGO was 3.0 wt.%, as estimated
by ICP. Fig. 1 shows the typical TEM images of the product of Ru/
RGO. The results demonstrate that the graphene flakes are likely to
be in the form of single- or few-layer sheets, which indicates that
the graphite was exfoliated to graphene flakes upon oxidation and
ultrasonication [20]. Moreover, the images also show that the Ru
nanoparticles are well dispersed on the surface of the RGO with a
narrow particle size distribution of 1.0–2.0 nm. The average Ru
particle size was estimated to 1.5 nm. The small size and even
distribution of Ru nanoparticles on the surfaces of the RGO are
attributed to the surface functional groups of the RGO sheets that
can act as a capping material, inhibiting the aggregation of Ru
clusters during reduction.
2.2. Characterization of the catalyst
The content of metal was determined by ICP (IRIS Intrepid).
Transmission electron microscopy (TEM) measurements were
carried out on a JEOL model 2010 instrument operated at an
accelerating voltage of 200 kV. X-ray diffraction (XRD) patterns
were recorded on a Rigaku X-ray diffractometer D/max-2200/PC
equipped with Cu K
10–908. X-ray photoelectron spectroscopy (XPS, Kratos XSAM800)
spectra was obtained by using Al K radiation (12 kV and 15 mA)
as an excitation source (h = 1486.6 eV), Au (BE Au4f = 84.0 eV),
a radiation (40 kV, 20 mA) over the range of
a
n
The crystal structure of Ru-RGO was also characterized by XRD
in the range from 108 to 908. For comparison, the XRD patterns of
GO and RGO were also investigated and the results are shown in
Fig. 2. The major diffraction lines in the powder pattern of GO
and Ag (BE Ag3d = 386.3 eV) as reference. All hydrogenation
samples were analyzed by gas chromatography (Agilent 7890A)
with
a
FID detector and PEG-20M supelco column
(30 m  0.25 mm, 0.25
mm film).
comes at 2u = 10.08 (Fig. 2a), suggesting that graphite has been
successfully oxidized. When the GO was reduced by NaBH4, it can
be seen that the diffraction peaks at 10.08 disappeared and two
new peaks appeared at 25.4 and 43.18 (see inset of Fig. 2)
corresponding to (0 0 2) and (1 0 0) reflection of RGO [6],
respectively, indicating that GO was successfully reduced using
NaBH4 as a reducing agent. Moreover, no obvious changes were
observed after depositing Ru nanoparticles on the surface of the
RGO, and the corresponding diffraction peaks of Ru were not
2.3. Activity test
Typically, to study the catalytic activity, 5.0 mg of catalyst,
1.0 mmol of p-CNB, and a mixture of ethanol and water (5 mL,
volume ratio of 4:1) were introduced into a 60 mL stainless steel
autoclave, and the autoclave was purged with pure hydrogen five
times in order to remover air. The reaction was performed with a
Fig. 1. TEM images of the fresh Ru/RGO catalyst (a, b) and used five times (c, d); Ru particle size distribution of fresh Ru/RGO (e) and used five times (f).
Please cite this article in press as: G.-Y. Fan, W.-J. Huang, Synthesis of ruthenium/reduced graphene oxide composites and application
for the selective hydrogenation of halonitroaromatics, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.11.044

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3
reaction and the results are presented in Table 1. The conversion of
p-CNB was negligible without catalyst, which shows that the
presence of Ru is indispensable for high catalytic activity. The main
product was p-CAN; aniline (AN) and p-ClPhNHC2H5 were detected
as by-products in the hydrogenation process. It can be seen that the
Ru/RGO catalyst was extremely catalytically active for p-CNB
hydrogenation in ethanol-water mixture. The conversion of p-CNB
achieved 100% yield with a selectivity of 96% towards p-CAN at
60 8C and a hydrogen pressure of 3.0 MPa in 2 h, while the
conversion of Ru/AC was only 21.9% with a comparable selectivity
of Ru/RGO at the same reaction conditions.
(b)
(c)
10
20
30
40
50
60
70
80
90
2 theta (degree)
(a)
We also compared the hydrogenation of CNBs over the Ru based
catalysts reported recently. For example, Zuo et al. [16] developed
the synthesis of Ru/SnO2 nanoparticles, which exhibited a turnover
frequency number of 155 hÀ1 with a selectivity of 99.9% to o-CAN
at 60 8C and 4.0 MPa H2. Pietrowski et al. [17] reported that the Ru/
MgF2 catalyst exhibited high catalytic activity with a TOF of
1267 hÀ1 with a selectivity of 97% at 353 K and 4.0 MPa H2.
Oubenali et al. [13] prepared carbon nanofibers (CNFs) and carbon
nanotubes (CNTs) supported ruthenium catalysts for the selective
hydrogenation of p-CNB at 60 8C and 3.5 MPa H2. Although, a high
TOF value of 1898 hÀ1 was observed, they can only get a selectivity
of 92–94% towards p-CAN. The present work reports the use of RGO
as a support for the deposition of Ru for the selective hydrogena-
tion of p-CNB. A selectivity of 96% towards p-CAN coexisting with a
TOF value of 420 hÀ1 was obtained at relatively low temperature
and hydrogen pressure. The good catalytic performance of Ru/RGO
for the selective hydrogenation p-CNB is probably attributed to the
narrow mean particle size of Ru (1.5 nm) and the high dispersion of
Ru nanoparticles on the surface of the RGO sheets via reduction of
Ru3+ by aqueous NaBH4. The high dispersion of Ru on the surface of
RGO would offer more active sites for the hydrogenation, which
increase the adsorption probability of reactant molecules for
speeding up the reaction.
Furthermore, we also examined the catalytic properties of Ru/
RGO for other nitroarenes. As shown in Table 1, the catalyst
showed good catalytic performance in the investigated substrates
containing electron-donating groups or electron-withdrawing
groups. For example, chloronitrobenzenes can be quickly hydro-
genated to the desired product. Moreover, the aryl nitro containing
electron-donating substituents, such as –OH, –CH3, and –OCH3 also
can be easily reduced with extremely high yield (>99%). The
stability of the Ru/RGO catalyst was also studied using p-CNB as
substrate under the same conditions. The catalyst was separated
from the reaction system by centrifugation and the supernatant
liquid was removed. The black solid was thoroughly washed three
(b)
(c)
10
20
30
40
50
60
70
80
90
2 theta (degree)
Fig. 2. XRD patterns of (a) GO; (b) RGO; (c) Ru/RGO. Inset is the amplified pattern of
RGO and Ru/RGO.
observed in the as-synthesized composite, demonstrating that the
Ru nanoparticles are quite small and well-dispersed on the surface
of RGO, which agrees well with the TEM results.
The XPS elemental survey scans of the surface of the Ru-RGO
composites show that the peaks corresponding to oxygen, carbon,
and ruthenium are distinctly detected. In order to evaluate the
electronic state of Ru in the Ru-RGO catalyst, the binding energy of
Ru was also determined. Because of the partial overlap between
the C1s and Ru3d peaks, which prevents the accurate determination
of the Ru species, Ru3p spectrum was characterized to distinguish
the electronic state of Ru. As shown in Fig. 3a, the binding energy of
Ru3p level in Ru/RGO catalyst is 463.6 eV, which is higher than that
of standard zero-valent state Ru (462.9 eV), indicating that there is
a strong metal-support interaction [21,22]. In addition, The C1s
spectra of RGO (Fig. 3b) could be deconvoluted into four peaks at
284.6, 285.8, 287.7, and 289.6 eV, which are associated with C–C,
C–OH, C(epoxy/alkoxy), and C55O groups, respectively [23].
3.2. Catalytic hydrogenation of %p-CNB
The catalytic properties of the Ru/RGO catalyst were investi-
gated using the selective hydrogenation of p-CNB as a model
(a)
(b)
296 294 292 290 288 286 284 282 280 278 276
Binding energy (eV)
490 485 480 475 470 465 460 455 450
Binding energy (eV)
Fig. 3. XPS spectrum of catalyst Ru/RGO (a) Ru3p; (b) Ru3d+C1s.
Please cite this article in press as: G.-Y. Fan, W.-J. Huang, Synthesis of ruthenium/reduced graphene oxide composites and application
for the selective hydrogenation of halonitroaromatics, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.11.044

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Table 1
Hydrogenation of different substrates over Ru/RGO and Ru/ACa.
Entry
1
Nitro-aromatics
Product
Time (h)
2
Conv. (%)
100.0
Yield (%)
96.0
NO2
NH2
NH2
Cl
Cl
Cl
2b
2
2
21.9
21.6
99.0
NO2
Cl
3
NO2
100.0
NH2
NO2
4
5
3
2
100.0
100.0
96.8
97.3
NH2
Cl
Cl
NO2
Cl
NH2
Cl
6
7
8
2
3
3
100.0
100.0
100
99.4
99.2
99.9
NH2
NO2
H3C
H3C
HO
NO2
NH2
HO
NO2
NH2
H3C
H3C
O
O
a
Reaction conditions: catalyst amount: 5.0 mg; p-CNB: 1.0 mmol; temperature: 60 8C; hydrogen pressure: 3.0 MPa.
The catalyst used was Ru/AC.
b
times with ethanol, dried in vacuum, and reused for the next run.
nanoparticles happened after the recycling of catalyst Ru/RGO five
The results illustrated in Fig. 4 show that no loss of activity was
observed for p-CNB hydrogenation after the catalyst was reused
five times without leaching of Ru (assessed by ICP). However, the
selectivity of p-CAN has a little decrease from 96.0% to 92.0% during
the recycle process. Fig. 1c and d shows the TEM image of Ru/RGO
after the fifth recycling. It can be seen that the aggregation of Ru
times, which accounted for the decrease of selectivity of p-CAN.
4. Conclusion
In summary, a facile synthesis of Ru/RGO nano-catalyst has
been established. This catalyst shows extremely superior catalytic
properties for the selective hydrogenation of p-CNB to p-CAN and
can be reused at least five times. The excellent performance of the
Ru/RGO catalyst is attributed to the small size of Ru nanoparticles
and the even dispersion of the Ru nanoparticles on the surface of
the RGO sheet.
Conversion
Selectivity
100
Acknowledgments
90
80
70
60
This work was financially supported by the National Natural
Science Foundation of China (No. 21207109), Scientific Research
Fund of Sichuan Provincial Education Department (No. 11ZA034),
and the Opening Project of Key Laboratory of Green Catalysis of
Sichuan Institutes of High Education (No. LZJ1205).
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Please cite this article in press as: G.-Y. Fan, W.-J. Huang, Synthesis of ruthenium/reduced graphene oxide composites and application
for the selective hydrogenation of halonitroaromatics, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.11.044