Effective catalytic hydrodechlorination of 4-chlorophenol over a Rh immobilized on amine-functionalized magnetite nanoparticles in aqueous phase

Article abstract of DOI:10.1016/j.catcom.2014.04.006

Amine-functionalized magnetite nanoparticles synthesized from a facile one-pot template-free method were applied as carriers for depositing Rh nanoparticles using RhCl₃ as the precursor. The as-prepared nanocomposites were applied for the hydrodechlorination of 4-chlorophenol at room temperature and atmospheric pressure. A complete conversion of 4-CP was obtained with the generation of phenol, cyclohexanone as the main products. The excellent catalytic activity, stability and recyclability of the catalyst were probably contributed to the functionalities of amine groups for stabilizing the Rh nanoparticles and the magnetic effect of Fe₃O₄ support during consecutive recycling of the catalyst.

Full text of DOI:10.1016/j.catcom.2014.04.006

Catalysis Communications 52 (2014) 22–25
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Effective catalytic hydrodechlorination of 4-chlorophenol over a Rh
immobilized on amine-functionalized magnetite nanoparticles in
aqueous phase
a
b
c
b
b
Guangyin Fan a, , Yanlin Ren , Weidong Jiang , Chenyu Wang , Bin Xu , Fuan Liu
⁎
a
Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College Of Chemistry and Chemical Industry, China West Normal University, Nanchong 637002, China
Key Laboratory of Green Catalysis of Sichuan Institute of High Education, Zigong 643000, China
Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Amine-functionalized magnetite nanoparticles synthesized from a facile one-pot template-free method were
applied as carriers for depositing Rh nanoparticles using RhCl3 as the precursor. The as-prepared nanocomposites
were applied for the hydrodechlorination of 4-chlorophenol at room temperature and atmospheric pressure.
A complete conversion of 4-CP was obtained with the generation of phenol, cyclohexanone as the main products.
The excellent catalytic activity, stability and recyclability of the catalyst were probably contributed to the func-
tionalities of amine groups for stabilizing the Rh nanoparticles and the magnetic effect of Fe3O4 support during
consecutive recycling of the catalyst.
Received 28 February 2014
Received in revised form 3 April 2014
Accepted 5 April 2014
Available online 13 April 2014
Keywords:
Hydrodechlorination
4-Chlorophenol
Magnetite
© 2014 Elsevier B.V. All rights reserved.
Rhodium
1. Introduction
immobilize noble metal nanoparticles for HDC reaction, among which
Al2O3 and active carbon are commonly investigated. However, the cata-
Chlorophenols are of great concern not only because of their useful-
ness as end products or intermediates for the synthesis of herbicides,
dyes, and plant growth regulators but also due to their strong toxicity
and potential accumulation in the environment [1–3]. Among the tech-
niques that have been applied to deal with these compounds, catalytic
hydrodechlorination (HDC) without imposing any extra contamination
or producing hazardous byproducts is recognized as an effective ap-
proach of detoxifying wastewater containing chlorophenols [4]. As
such, a wide variety of heterogeneous catalysts have been developed
for HDC, among which noble metals such as Rh, Pt and Pd exhibit rela-
tively high activities and stabilities for this reaction. Particularly, Rh cat-
alysts with the advantages of high catalytic property, resistance to the
attack of acid and base, and relative stability under severe conditions
have been intensively investigated with the aim of producing high val-
ued products such as cyclohexanol and cyclohexanone. Therefore, the
HDC of chlorophenols catalyzed by Rh catalysts is considered as the
most promising pathway for detoxifying chlorophenols from the envi-
ronmental point of view [5].
lytic property of the catalysts reported in the literature was not satisfied
enough due to the possible deactivation of the catalysts and leaching of
the active sites during the recycling. Therefore, it still remains as a tre-
mendous challenge to seek stable and recyclable catalysts for the con-
version of chlorinated phenols under mild conditions. In recent years,
functionalized magnetic materials have emerged as applicable alterna-
tives to the conventional materials, which offer the advantage of being
magnetically separable without filtration [15]. Particularly, the func-
tional groups such as NH2 groups on the surface of the supports are
benefitted to inhibit the agglomeration of nanoparticles and further im-
prove the activity and stability of the catalysts through anchoring the
metal ion and improving the dispersing ability [16]. Therefore, the intro-
duction of functionalized magnetic nanocrystals as solid matrices have
been widely applied in a range of organic transformations such as oxida-
tion [17], hydrogenation [18–20] and C\C coupling reactions [21,22].
However, as far as we are concerned, rarely any literature about the
application of noble metal nanoparticles deposited on the amine func-
tionalized Fe3O4 supports as catalysts for the HDC reaction has been
reported.
Regarding the supports, a variety of solid materials such as active
carbon [6–9], Al2O3 [8–13], and ZrO2 [14] have been developed to
To this end, a facile approach to obtain Rh nanoparticles immobilized
on 1,6-hexanediamine-functionalized Fe3O4 support has been proposed
in this article. Subsequently, the as-prepared nanocomposites were ex-
amined in the catalytic HDC of 4-CP, exhibiting excellent activity, stabil-
ity and recyclability. We ascribe the extraordinary catalytic property to
⁎
Corresponding author. Tel./fax: +86 817 2568081.
E-mail address: fanguangyin@cwnu.edu.cn (G. Fan).
http://dx.doi.org/10.1016/j.catcom.2014.04.006
1566-7367/© 2014 Elsevier B.V. All rights reserved.

G. Fan et al. / Catalysis Communications 52 (2014) 22–25
23
the well-dispersed Rh particles, anchoring function of NH2 group and
magnetic property of Fe3O4 support.
b
a
2853
2930
2. Experiment
1055
1409
1623
1558
2.1. Synthesis of Rh/NH2–Fe3O4
The amine-functionalized Fe3O4 was prepared by the solvothermal
method reported by Li and co-workers [23]. In a typical procedure,
1,6-hexanediamine (6.5 g), anhydrous sodium acetate (2.0 g) and
FeCl3·6H2O (1.0 g) were added into a 30 mL ethylene glycol under vig-
orous stirring at 50 °C until a transparent solution was formed. Then the
as-prepared solution was transferred into a 100 mL Teflon-lined auto-
clave and the temperature was kept at 200 °C for 6 h. After cooling
down to room temperature, the black solid was separated from the su-
pernatant with a magnet and washed with deionized water and ethanol
in order to remove the solvent and unbound 1,6-hexanediamine. The
black solid was finally dried at 50 °C under vacuum for 12 h.
3432
Rh-NH2-Fe3O4
NH2-Fe3O4
579
1000
4000
3500
3000
2500
2000
1500
500
Wavenumbers(cm-1)
Fig. 1. FT-IR spectra of NH2–Fe3O4 (a) and Rh/NH2–Fe3O4 (b).
2.2. Synthesis of Rh/NH2–Fe3O4
The catalyst Rh/NH2–Fe3O4 was fabricated as follow: NH2–Fe3O4
(0.5 g) was added into a 100 mL round-bottom-flask containing ethanol
(50 mL) and was under ultrasonication for 30 min via an ultrasonic
cleaning bath. Then the aqueous solution of RhCl3 (1.6 mL, 32.1 mM)
was dropped into flask and maintained under ultrasonication for 2 h. Af-
terwards, an excessive NaBH4 solution was slowly added into above
mixture at 0 °C under vigorous stirring. The black solid was collected
with a magnet and washed with deionized water for three times, and fi-
nally dried under vacuum at 25 °C for 24 h. The weight percentage of Rh
in the catalyst was determined by ICP analysis (1.0 wt.% Rh/NH2–Fe3O4).
corresponding to the C\N stretching, N\H deformation and C\H
stretching models of the alkyl chain, and the peak at 1409 cm−1 was at-
tributed to the C\H symmetric blending vibration, which definitely
confirmed the functionalization of Fe3O4 with 1,6-hexanediamine [16].
Furthermore, it should be noted that the deposition of Rh NPs on the
NH2–Fe3O4 did not result in the change of the spectrum compared
with that of NH2–Fe3O4.
The morphology of the catalyst Rh/NH2–Fe3O4 was investigated and
the results are illustrated in Fig. 2. As shown in Fig. 2a, the support NH2–
Fe3O4 was a quadrilateral sheet with parallel sides (approximate 20 nm)
and truncation at the corners, which is different from the spherical
NH2–Fe3O4 as reported by Li et al. [23]. The corresponding high-
resolution TEM (HRTEM) image provided more structural details
about the Rh–NH2–Fe3O4 nanocomposites. The obvious lattice fringes
indicate a high crystallinity of the support Fe3O4. As illustrated in the
inset of Fig. 2b, the diffraction pattern shows that the Fe3O4 support is
projected along the [110] zone axis. Two spacings of 0.48 nm are
found on the basis of a measurement on more than 12 adjacent lattice
fringes, which are consistent with the (111) and (111) planes of Fe3O4
phase. As such, the growth direction of Fe3O4 was predicted to be [11
0], which is perpendicular to the (111) close-packed plane.
The XRD patterns of NH2–Fe3O4 and Rh/NH2–Fe3O4 are shown in
Fig. 3. The sharp and strong characteristic peaks of the support NH2–
Fe3O4 demonstrate that the as-prepared magnetite nanoparticles are
well crystallized. The peaks located at 18.9°, 31.2°, 36.8°, 44.7°, 55.6°,
59.3°, and 65.1° matched well with (111), (220), (311), (400), (422),
(511), and (440) Bragg diffractions of Fe3O4 (JCPDS no. 26-1136) re-
spectively, confirming the formation of Fe3O4 crystalline phase. Besides,
it can be seen that the XRD pattern has no apparent variations after the
Rh NPs were immobilized on the magnetite, indicative of that the crys-
talline structure and domain of the magnetic support were well main-
tained. Unexpectedly, no diffraction signals for metallic Rh were
observed in the pattern, which can be presumably attributed to the
small particle size of Rh NPs on the support.
To provide more evidence of the presence of elemental Rh crystal-
lites, XPS characterization of Rh/NH2–Fe3O4 was carried out. XPS survey
scan of the surface of the Rh/NH2–Fe3O4 particles was firstly performed.
As explicated in Fig. 4a, apart from the feature peaks of oxygen, carbon,
nitrogen, and iron, rhodium was clearly detected, confirming the suc-
cessfully immobilization of Rh on the surface Fe3O4. The further deter-
mination of electronic state of the Rh particles in the Rh/NH2–Fe3O4
catalyst was achieved via a high resolution narrow scan. As elaborated
in Fig. 4b, the binding energies of Rh3d5/2 and Rh3d3/2 level in Rh/
NH2–Fe3O4 composite are 308.6 and 313.3 eV, respectively, somewhat
higher than the standard zero-valent state values, indicating the
2.3. Catalyst characterization
Transmission electron microscopy (TEM) measurements were carried
out on a JEOL model 2010 instrument operated at an accelerating voltage
of 200 kV. The X-ray diffraction (XRD) patterns were obtained using a
modern multipurpose theta/theta powder X-ray diffraction system,
equipped with a fast linear detector. 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 references. A Fourier
transform infrared (FT-IR) spectrum was recorded with a Nicolet 6700
(resolution 0.4 cm−1) infrared spectrometer.
2.4. Activity tests
The catalytic HDC of 4-CP was performed at room temperature in a
25 mL round-bottom-flask equipped with a hydrogen balloon. The reac-
tor was immersed in a thermostatic water bath to keep the temperature
constant. Typically, catalyst (5.0 mg) and 4-CP aqueous solution (0.5 g/L,
5.0 mL) were transferred into the flask. Next, the flask was vacuumed
and flushed with pure hydrogen. The reaction time was accounted
when the designated reaction temperature was reached and the stirring
rate was adjusted to 1200 rpm. All liquid samples were analyzed by
gas chromatography (Agilent GC-7890) with a FID detector and HP-5
supelco column (30 m × 0.25 mm, 0.25 μm film) and nitrogen as a car-
rier gas.
3. Results and discussion
The characterization of FT-IR spectrum was firstly introduced to con-
firm the formation of amine-functionalized Fe3O4. As illustrated in Fig. 1,
the diffraction peak at 579 cm−1 was assigned to the Fe\O stretching
which confirmed the formation of Fe3O4. In addition, the peaks
at 1055, 1558, 1623, 3432 and around 2846–2923 cm−1 are

24
G. Fan et al. / Catalysis Communications 52 (2014) 22–25
Fig. 2. TEM image of Rh/NH2–Fe3O4 nanocomposites (a); HRTEM image showing the lattice fringes of Rh/NH2–Fe3O4 nanoparticles with the inset of corresponding Fourier transformation
pattern (b).
formation of the existence of electro-deficient Rh. This phenomenon
was probably attributed to the interaction between the metallic Rh
and the functionalized groups of support, in which the high electroneg-
ativity of nitrogen was supposed to decrease the electron density of Rh
atoms in the catalysts [24]. Interestingly, the existence of electro-
deficient Rh are benefitted to the catalytic performance of the catalysts
for HDC reaction, [25] which was approved by the excellent catalytic ac-
tivity of the Rh/NH2–Fe3O4 at room temperature and balloon hydrogen
pressure.
commonly used catalysts Rh/C, Rh/Al2O3 and the Rh/Fe3O4 without
functional groups were prepared by a similar method with the same
Rh loading of the Rh/NH2–Fe3O4. The catalytic properties of these cata-
lysts for the HDC of 4-CP under the same conditions were illustrated in
Table 1. It can be seen that the catalysts Rh/C and Rh/Al2O3 showed
moderate activity, while Rh/Fe3O4 exhibited the lowest activity toward
the HDC reaction. The excellent catalytic activity of the catalyst Rh/NH2–
Fe3O4 was probably attributed to the functionalities of amine groups for
The catalytic properties of the as-synthesized Rh/NH2–Fe3O4 nano-
composites were investigated using 4-CP as a model substrate. Phenol,
cyclohexanol and cyclohexanone were detected as products during
the HDC process. Simultaneously, HCl was also formed and dissolved
in the aqueous phase. Blank test in the absence of metallic catalyst
showed no occurrence of HDC reaction and thereby indicate that Rh
species was the indispensable active component for such reaction. Addi-
tionally, negligible adsorption of 4-CP on the surface of catalysts was ob-
served based on the adsorption experiments, showing that the removal
of 4-CP was under chemical transformation. As shown in Fig. 5, a com-
plete conversion of 4-CP was achieved within 90 min. Concerning the
product distribution, the selectivity to phenol decreased from 79.8%
with 15 min to 63.2% with 90 min, while an increase of the selectivity
to cyclohexanone from 20.2% to 33.7% was obtained. Furthermore a
trace amount of cyclohexanol (ca. 3.1%) was also detected in a reaction
time of 90 min. Our results suggest that the removal of chloride process
and reduction of the aromatic ring products (to generate cyclohexanol
and cyclohexanone) simultaneously occurred. For comparison, the
Rh/NH2-Fe3O4
NH2-Fe3O4
a
b
10
20
30
40
50
60
70
80
2 Theta(degrees)
Fig. 4. XPS spectrum of the elemental survey scan of Rh–NH2–Fe3O4 (a); XPS spectrum of
the Rh in Rh/NH2–Fe3O4 (b).
Fig. 3. XRD patterns of (a) NH2–Fe3O4 and (b) Rh/NH2–Fe3O4.

G. Fan et al. / Catalysis Communications 52 (2014) 22–25
25
Table 1
Catalytic properties of Rh/NH2–Fe3O4 for 4-chlorophenol.a
100
80
60
40
20
0
Catalysts
Conversion Time
Selectivity (%)
Phenol Cyclohexanol Cyclohexanone
(%)
(min)
Rh/C
Rh/Al2O3
Rh/Fe3O4
Rh/NH2–Fe3O4
Rh/NH2–Fe3O4
Rh/NH2–Fe3O4
78.6
50.3
15.6
100
89.8
89.7
90
90
90
90
60
60
87.4
74.0
99.0
63.2
66.0
68.3
0.2
1.1
0
3.1
2.4
2.0
18.4
24.9
1.0
33.7
31.5
29.7
Conv. of 4-CP
Sele. to phenol
Sele. to cyclohexanone
Sele. to cyclohexanol
b
a
Reaction conditions: Catalyst: 5.0 mg; solvent: 5.0 mL (4-CP concentration, 0.5 g/L);
reaction temperature: 25 °C; pressure: 1.0 atm.
b
The catalyst was recycled five times.
of Science and Technology Department of Sichuan Province (No.
2014JY0107), and the Opening Project of Key Laboratory of Green Catal-
ysis of Sichuan Institutes of High Education (No. LZJ1205).
20
40
60
80
100
Reaction time(min)
Fig. 5. HDC of 4-CP catalyzed by the catalyst Rh/NH2–Fe3O4.
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Acknowledgment
This work was financially supported by the National Natural Science
Foundation of China (21207109), the Applied Basic Research Programs