Aqueous phase catalytic hydrodechlorination of 4-chlorophenol over palladium deposited on reduced graphene oxide

Article abstract of DOI:10.1016/j.catcom.2013.12.025

Palladium/reduced graphene oxide nanocomposites (Pd/RGO) are synthesized through the impregnation of polyvinyl-pyrrolidone-stabilized palladium nanoparticles on the surface of RGO sheets prepared from the reduction of graphene oxide in the presence of hydrogen gas. The Pd/RGO nanocomposites exhibited excellent catalytic property for the hydrodechlorination of 4-chlorophenol.

Full text of DOI:10.1016/j.catcom.2013.12.025

Catalysis Communications 46 (2014) 219–223
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Aqueous phase catalytic hydrodechlorination of 4-chlorophenol over
palladium deposited on reduced graphene oxide
b
c
Hongying Deng a, Guangyin Fan a,b, , Chenyu Wang , Lei Zhang
⁎
a
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of Chemistry and Chemical Industry, China West Normal University, Nanchong 637009, PR China
Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902, USA
Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 July 2013
Received in revised form 16 December 2013
Accepted 20 December 2013
Available online 29 December 2013
Palladium/reduced graphene oxide nanocomposites (Pd/RGO) are synthesized through the impregnation of
polyvinyl-pyrrolidone-stabilized palladium nanoparticles on the surface of RGO sheets prepared from the reduc-
tion of graphene oxide in the presence of hydrogen gas. The Pd/RGO nanocomposites exhibited excellent catalytic
property for the hydrodechlorination of 4-chlorophenol.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Palladium
Graphene
Hydrodechlorination
4-Chlorophenol
1. Introduction
years. In order to improve the catalytic stability and reusability, a meth-
od based on the addition of a large amount of base to neutralize the HCl
Chlorophenols are widely used as end products or intermediates
in the production of pesticides, disinfectants, wood preservatives,
and personal care formulations [1]. The residue of these compounds
causes a negative effect on the environment and human beings such
as the contamination of groundwater due to their acute toxicity and
poor biodegradability. Among the current approaches that have been
employed to deal with the wastewater containing chlorophenols, cata-
lytic hydrodechlorination (HDC) is considered to be an environmental-
friendly one by the breaking up of the C\Cl bond and thus transforming
toxic substances into safe compounds or even useful materials.
Generally, the catalytic HDC is conducted under a reduction atmo-
sphere of molecular hydrogen and by contacting with supported metal-
lic catalysts such as Pd [2–6], Pt [7,8], and Rh [9–12]. Pd has been proven
to be the most promising one due to its high activity in such degradation
of chlorophenols at ambient conditions. Nevertheless, severe catalyst
deactivation originated from the strong adsorption of chlorine on Pd
surface [13,14], aggregation of active Pd particles [15,16] and/or carbo-
naceous deposited on Pd surface [17–19] have been reported in recent
formed in the reaction process has been developed, however it calls for
extra work to segregate the additives from the reaction mixtures to
avoid the secondary pollution. So far, a more facile route to maintain
the activity of catalysts without introduction of additives still remains
as a challenging task to be fulfilled.
As one atom-thick sheet of sp2-bonded carbon atoms, graphene has
high surface area (theoretical value 2600 m2/g), good conductivity and
stability, and low cost. Therefore, graphene based materials obtained
from the chemical modification have attracted intensive research inter-
est recently. Especially, the use of RGO as a support to synthesize RGO/
nanoparticles (NPs) composites from the co-reduction of GO and metal
precursors was the promising one due to their versatile applications in
the area of hydrogenation, Suzuki–Miyaura and Heck coupling reac-
tions. By applying the RGO, the stability and dispersity of the NPs on
the surface of RGO can be improved through the interaction of the
oxygen containing groups. Meanwhile, the existence of metal/support
interaction between the NPs and RGO can lead to an increased perfor-
mance of the composites [20]. Thus, it is desirable to employ RGO as a
support for developing new catalysts with enhanced catalytic activity
and stability. As far as we are aware, no attempt has yet been exerted
to apply RGO as a support of catalyst in the HDC of chlorophenols. Here-
in, we reported the synthesis of RGO from the reduction of GO in a mix-
ture of ethanol and water and then used as support for depositing Pd
⁎
Corresponding author at: Chemical Synthesis and Pollution control Key Laboratory of
Sichuan Province, College of chemistry and Chemical Industry, China West Normal
University, Nanchong 637009, PR China. Tel./fax: +86 817 2568081.
E-mail address: fanguangyin@cwnu.edu.cn (G. Fan).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.12.025

220
H. Deng et al. / Catalysis Communications 46 (2014) 219–223
Scheme 1. Preparation of Pd NPs supported on RGO sheets.
Fig. 1. TEM images of fresh Pd/RGO (a and b) and used Pd/RGO(c and d).
NPs. The as-prepared catalyst was applied for the catalytic HDC of 4-
chlorophenol in aqueous phase. The Pd/RGO catalyst exhibited excellent
activity as well as stability at 40 °C under ordinary pressure (hydrogen
balloon) and can be reused four times.
2. Experimental
2.1. Catalyst preparation
GO was synthesized via improved synthetic method reported by
Marcano et al. [21]. RGO was synthesized as follows: a mixture of GO
(0.5 g), water (10 mL) and ethanol (20 mL) was transferred into an
autoclave. Then the autoclave was sealed and charged with H2 for five
times to expel the air. The reaction was carried out at 4.0 MPa H2 and
150 °C for 4 h. The generated black solid was washed with ethanol
and distilled water several times and dried under vacuum at 60 °C for
12 h.
Fig. 2. XRD patterns of GO, RGO and Pd/RGO.

H. Deng et al. / Catalysis Communications 46 (2014) 219–223
221
The Pd/RGO composite was synthesized as follows: 15.6 mg of PVP
and 5.0 mg of Pd were added into a 250 mL flask containing 20 mL
water and the mixtures were refluxed for 3 h to yield PVP-Pd NPs.
0.4 g of RGO was introduced into the flask and stirred for 12 h. The
black solid was rinsed with ethanol and distilled water several times
and dried under vacuum at 60 °C for 12 h. The percentage of Pd loading
estimated by ICP measurement was 0.91 wt.%.
with Cu Kα radiation (40 kV, 20 mA) over the range of 10–90°. X-ray
photoelectron spectroscopy (XPS, Kratos XSAM800) spectra were
obtained by using Al Ka radiation (12 kV and 15 mA) as an excitation
source (hv = 1486.6 eV) and Au (BE Au4f = 84.0 eV) and Ag (BE
Ag3d = 386.3 eV) as reference. All binding energy (BE) values were
referenced to C1s peak of contaminant carbon at 284.6 eV. A Fourier
transform infrared spectrum was recorded with a Nicolet 6700 infrared
spectrometer.
2.2. Characterization of the catalyst
2.3. Activity test
Transmission electron microscopy (TEM) measurements were
carried out on a JEOL model 2010 instrument operated at an acceler-
ating voltage of 200 kV. X-ray diffraction (XRD) patterns were re-
corded on a Rigaku X-ray diffractometerD/max2200/PC equipped
The HDC of 4-CP was performed in a 25 mL round-bottom-flask
equipped with a balloon. Typically, 5.0 mg of catalyst and 5 mL of aque-
ous solution containing 4-CP were transferred into the reactor. The
Fig. 3. XPS patterns of GO (a) and Pd/RGO (c); C1s XPS spectra of GO (b) and Pd/RGO (d), Pd3d XPS spectra of Pd/RGO (e).

222
H. Deng et al. / Catalysis Communications 46 (2014) 219–223
reactor was vacuumed and flushed with pure hydrogen and stirred at
1200 rpm. Reaction time was recorded when the designated reaction
temperature (40 °C) was achieved. The products were analyzed by gas
chromatography (Agilent 7890A) with a FID detector and PEG-20 M
supelco column (30 m × 0.25 mm, 0.25 μm film).
transferring between metal Pd and RGO sheets which makes Pd existing
as an electron-deficient state, indicating that there is a strong interac-
tion between Pd NPs and the support RGO. It has been reported that
the metals such as Pd have mobility on the surfaces of graphene sheets
and easily resulted in agglomeration, however, the interaction between
the defect sites of the graphene sheets and metals can anchor the parti-
cles on the graphene surfaces, reducing the mobility of metal particles
and maintaining the fine dispersion of particles on the surface of
graphene [24,25]. Our results further confirmed this argument.
Fig. 4 shows the FTIR spectra of GO, RGO and Pd/RGO. In the spec-
trum of GO, the broad characteristic band at 3428 cm−1 is ascribed to
the O\H stretching vibration arising from hydroxyl groups in GO and
water. The absorption bands associated with the C_O carbonyl
stretching were at 1720 cm−1 and the C\O stretching at 1050 cm−1
was detected as well as the C_C peak at 1630 cm−1 from unoxidized
sp2 C\C bonds. After the hydrothermal treatment, the peaks associated
with the functional groups became weak, indicative of the reduction of
GO to RGO. The absorption bands at 1570 cm−1 can be assigned to the
stretching vibration of C\C of RGO and another peak at 1202 cm−1 can
be assigned to the stretching vibration of C\O of RGO, which cannot be
reduced in the present reaction conditions. In the FTIR spectrum of PVP,
the bands at around 3441 cm−1, 2910–2960 cm−1, and 1658 cm−1are
attributed to the stretching mode of water, CH2 or CH, C_O. The bands
at 1460 cm−1, 1425 cm−1 and 1288 cm−1 are assigned to the CH2
bending, CH2 deformation and C\N stretching. A weak peak of C_O
groups can be observed in the Pd/RGO, showing the successful removal
of the residual PVP through washing because the excess PVP may slow
down the direct electron transfer of Pd and lead to reduced catalytic
activity.
3. Results and discussion
Scheme 1 gives a brief summary of the preparing process of Pd/RGO
composites. It is well-known that carboxyl, hydroxyl, and epoxy groups
are three major functional groups on the surface of GO. These oxygen-
containing groups can be reduced to form RGO at 150 °C and a hydro-
gen pressure of 4.0 MPa for 4 h in the mixture of ethanol and water.
Then the PVP-protected Pd nanoparticles can be absorbed on the
surface of RGO sheets, forming the Pd/RGO nanocomposites.
The morphology of PVP-Pd NPs on RGO sheets is shown in the TEM
images. All Pd nanoparticles with a mean size of approximate 3.9 nm
were well dispersed on the sheets of RGO (Fig. 1a and b). The XRD pat-
terns of GO, RGO and Pd/RGO are shown in Fig. 2. The XRD pattern of GO
exhibits a very strong peak at 10.0° (Fig. 2a), indicating that graphite has
been successfully oxidized by the improved oxidation method [22]. The
diffraction peaks at 10.0° disappeared and two new peaks appeared at
25.4 and 43.1° assigned to (002) and (100) reflections of RGO, respec-
tively, indicating that GO was successfully reduced through the hydro-
thermal process in the presence of H2. No obvious changes have been
observed after the impregnation of Pd NPs on the RGO sheets and the
corresponding diffraction peaks of Pd were not found in the Pd/RGO be-
cause of the low loading percentage and the small size of Pd NPs which
is consistent with the TEM results.
The catalyst Pd/RGO was used for the HDC of 4-CP and the results are
shown in Table 1. Blank test showed that no conversion of 4-CP was
detected in 60 min, indicating that Pd/RGO was the essential active
species. Moreover, the adsorption capability of the catalyst showed
that the adsorption of 4-CP was negligible. It can be seen that the com-
plete conversion of 4-CP with a selectivity to phenol of 100% was obtain-
ed when the reaction time was increased to 100 min while the
conversion of 4-CP was only 51% over Pd/C prepared by a similar meth-
od. It has been reported that the catalytic activity of the supported
catalysts can be gradually poisoned by HCl formed during the process.
During the HDC process, the chemistry of the support plays a key role
on the performance of the catalysts, especially in their deactivation
behavior through the metal/support interactions and reactant/support
The XPS elemental survey scans of the surface of the GO perform the
peaks corresponding to carbon and oxygen (Fig. 3a) with an atomic
weight ratio of 2.09. Fig. 3b shows the C1s spectra of GO sheets with
four deconvoluted peaks at 284.5, 285.5, 286.9 and 288.3 eV, which
are associated with C\C, C\OH, C(epoxy/alkoxy), and HO\C_O
groups, respectively [23]. The formation of Pd/RGO composites, which
can be seen from that Pd, oxygen and carbon is distinctly detected
during the elemental survey scans of the surface of Pd/RGO (Fig. 3c)
with the increasing atomic weight ratio of carbon and oxygen to 4.94.
At the same time, as illustrated in Fig. 3d, the intensities of the C1s
peaks associated with C (epoxy/alkoxy), and HO\C_O groups de-
creased gradually as a result of the removal of most of the oxygenous
functional groups. These results prove that the GO has been successfully
reduced during the solvothermal process. The Pd3d peaks in XPS
spectra(Fig. 3e) at 335.6 eV and 340.8 eV are attributed to the 3d5/2
and 3d3/2 peaks of metallic palladium, suggesting that the Pd2+ has
been successfully reduced by the mixture solvents at refluxing condi-
tions. However, the binding energy is higher than that of standard
zero-valent state of Pd (335.0 eV), possibly arising from the electron
Table 1
Catalytic HDC of different substrates over catalyst Pd/RGO.a
Entries
1
Substrates
Product
Time (min)
100
Conversion (%)
100
2
3
4
100
100
60
99b
51c
100
5
6
80
100
100
120
7
160
100
a
Reaction conditions: catalyst, 5.0 mg; substrates concentration, 1.5 g/L (5.0 mL);
temperature, 40 °C; hydrogen pressure: 1 atm.
b
The catalyst was reused four times
The catalyst was Pd/C prepared by similar method.
c
Fig. 4. FT-IR spectrum of GO, RGO, Pd/RGO, and PVP.

H. Deng et al. / Catalysis Communications 46 (2014) 219–223
223
metal–support interaction between Pd NPs and the RGO sheets.
Moreover, a large particle size of Pd also was ascribed to have a
positive effect on the deactivation of the catalyst. The as-prepared
catalyst provides a kind of advanced material with great promise
for HDC of 4-CP in practical application.
Acknowledgments
This work was financially supported by the National Natural Science
Foundation of China (21207109) and the Opening Project of Key Labo-
ratory of Green Catalysis of Sichuan Institutes of High Education (No.
LZJ1205).
References
Fig. 5. Initial reaction rates of the reused catalyst Pd/RGO.
[1] E. Díaz, J.A. Casas, Á.F. Mohedano, L. Calvo, M.A. Gilarranz, J.J. Rodríguez, Ind. Eng.
Chem. Res. 47 (2008) 3840–3846.
[2] H. Hildebrand, K. Mackenzie, F.-D. Kopinke, Energy Environ. Sci. 43 (2009)
3254–3259.
[3] T. Hara, T. Kaneta, K. Mori, T. Mitsudome, T. Mizugaki, K. Ebitani, K. Kaneda, Green
Chem. 9 (2007) 1246–1251.
[4] Z. Jin, C. Yu, X. Wang, Y. Wan, D. Li, G. Lu, J. Hazard. Mater. 186 (2011) 1726–1732.
[5] F.-D. Kopinke, D. Angeles-Wedler, D. Fritsch, K. Mackenzie, Appl. Catal. B Environ. 96
(2010) 323–328.
[6] H. Rong, S. Cai, Z. Niu, Y. Li, ACS Catal. 3 (2013) 1560–1563.
[7] Y. Hashimoto, A. Ayame, Appl. Catal. A Gen. 250 (2003) 247–254.
[8] T. Yoneda, T. Takido, K. Konuma, J. Mol. Catal. A Chem. 265 (2007) 80–89.
[9] C. Molina, A. Pizarro, M. Gilarranz, J. Casas, J. Rodriguez, Chem. Eng. J. 160 (2010)
578–585.
[10] Y. Mitoma, M. Kakeda, A.M. Simion, N. Egashira, C. Simion, Energy Environ. Sci. 43
(2009) 5952–5958.
[11] Y. Ukisu, S. Kameoka, T. Miyadera, Appl. Catal. B Environ. 18 (1998) 273–279.
[12] E. Diaz, A.F. Mohedano, J.A. Casas, L. Calvo, M.A. Gilarranz, J.J. Rodriguez, Appl. Catal.
B Environ. 106 (2011) 469–475.
[13] F. Urbano, J. Marinas, J. Mol. Catal. A Chem. 173 (2001) 329–345.
[14] Y. Shao, Z. Xu, H. Wan, H. Chen, F. Liu, L. Li, S. Zheng, J. Hazard. Mater. 179 (2010)
135–140.
[15] P. Albers, J. Pietsch, S.F. Parker, J. Mol. Catal. A Chem. 173 (2001) 275–286.
[16] D.Ju. Moon, M. Jo Chung, K. You Park, S. In Hong, Appl. Catal. A Gen. 168 (1998)
159–170.
[17] A. Wiersma, E. Van de Sandt, M. Makkee, C. Luteijn, H. Van Bekkum, J. Moulijn, Catal.
Today 27 (1996) 257–264.
[18] A. Wiersma, E.J. van de Sandt, M. Makkee, J.A. Moulijn, Appl. Catal. A Gen. 212
(2001) 223–238.
[19] M. Öcal, M. Maciejewski, A. Baiker, Appl. Catal. B Environ. 21 (1999) 279–289.
[20] Y. Gao, D. Ma, C. Wang, J. Guan, X. Bao, Chem. Commun. 47 (2011) 2432–2434.
[21] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany,
W. Lu, J.M. Tour, ACS Nano 4 (2010) 4806–4814.
[22] X. Du, M. Xiao, Y. Meng, Eur. Polym. J. 40 (2004) 1489–1493.
[23] H.P. Cong, X.C. Ren, S.H. Yu, ChemCatChem 4 (2012) 1555–1559.
[24] J.A. Rodríguez-Manzo, O. Cretu, F. Banhart, ACS Nano 4 (2010) 3422–3428.
[25] C. Nethravathi, E. Anumol, M. Rajamathi, N. Ravishankar, Nanoscale 3 (2011)
569–571.
interactions [26,27]. Coq et al. [28] and Juszczyk et al. [29] suggested
that the catalyst can be refreshed through the transformation of the
halide ions from the surface of the metal to the support to form haloge-
nated species, prohibiting the gradual deactivation of catalyst. More-
over, it was proposed that the larger particle size (ca.4 nm) of the
active site of the catalyst exhibited a stronger resistance for the passiv-
ation of the catalyst [27,30,31]. In this work, besides the possible reasons
mentioned above, the remained oxygen functional groups of RGO can
avoid the agglomeration and leaching the of Pd nanoparticles through
interaction between the nanoparticles and the functional groups of
graphene sheets, guaranteeing the high activity of the Pd/RGO. Conse-
quently, the high stability of the Pd/RGO was tentatively attributed to
the strong metal-support interaction with an electron-deficient state
and a larger Pd particle size (ca. 3.9 nm) of catalyst Pd/RGO with a
stronger resistance ability to the deactivation of the catalyst. We
also investigated the catalytic performance of Pd/RGO for the HDC
of other chlorophenols and the results are shown in Table 1. The
reaction time for complete conversion increased in the order of 3-
CP N 2-CP N 4-CP which was probably ascribed to the electronic
and steric hindrance of the substrates. Moreover, the catalyst also
showed excellent catalytic properties for the HDC of dichlorophenols
with increased reaction time of 120–160 min. The reusability of the Pd/
RGO nanocatalyst indicates that no obvious loss of activity as well as the
initial reaction rates (Fig.5) was detected for 4-CP HDC after the catalyst
was reused four times without leaching of Pd (assessed by ICP) and ob-
vious aggregation of Pd NPs (Fig. 1c and d).
[26] E. Díaz, S. Ordóñez, R.F. Bueres, E. Asedegbega-Nieto, H. Sastre, Appl. Catal. B Envi-
ron. 99 (2010) 181–190.
4. Conclusions
[27] S. Gómez-Quero, F. Cárdenas-Lizana, M.A. Keane, Ind. Eng. Chem. Res. 47 (2008)
6841–6853.
[28] B. Coq, J.M. Cognion, F. Figueras, D. Tournigant, J. Catal. 141 (1993) 21–33.
[29] W. Juszczyk, A. Malinowski, Z. Karpiński, Appl. Catal. A Gen. 166 (1998) 311–319.
[30] M. Aramendıa, V. Borau, I. Garcıa, C. Jimenez, F. Lafont, A. Marinas, J. Marinas, F.
Urbano, J. Catal. 187 (1999) 392–399.
In summary, Pd/RGO nanocomposites were synthesized through the
hydrothermal of GO and impregnation of PVP protected Pd NPs and
were used for the catalytic HDC of 4-CP at 40 °C and 1 atm H2. The Pd/
RGO catalyst was quite stable and could be reused four times without
significant deactivation which is probably attributed to the strong
[31] J.L. Benitez, G. Del Angel, React. Kinet. Catal. Lett. 70 (2000) 67–72.