One-pot solvothermal synthesis of Pd/Fe3O4 nanocomposite and its magnetically recyclable and efficient catalysis for Suzuki reactions

Article abstract of DOI:10.1016/j.molcata.2012.03.025

A facile solvothermal synthetic route has been successfully developed to fabricate Pd/Fe₃O₄ nanocomposite with the assistance of polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) solution. The as-prepared Pd/Fe₃O₄ nanocomposite was composed of uniform 5 nm-sized Pd nanoparticles and Fe₃O₄ nanocrystals with dimension of 40 nm. In this fabrication, PVP played an important role as a capping agent. The as-prepared Pd/Fe₃O₄ nanocomposite exhibited superior catalytic performance and stability for various Suzuki coupling reactions, compared with single-component Pd nanoparticles under the same reaction conditions. More importantly, it displayed good magnetic property and could be easily separated from the reaction mixture by using a magnet and recycled for 10 times without losing its catalytic activity.

Full text of DOI:10.1016/j.molcata.2012.03.025

Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
One-pot solvothermal synthesis of Pd/Fe O nanocomposite and its magnetically
3
4
recyclable and efficient catalysis for Suzuki reactions
a
a
b
b
a
a,∗
Shaozhong Li , Wei Zhang , Man-Ho So , Chi-Ming Che , Runming Wang , Rong Chen
a
Key Laboratory for Green Chemical Process of Ministry of Education and School of Chemical Engineering & Pharmacy, Wuhan Institute of Technology, Wuhan 430073, PR China
Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile solvothermal synthetic route has been successfully developed to fabricate Pd/Fe O4 nanocom-
3
Received 20 January 2012
Received in revised form 6 March 2012
Accepted 25 March 2012
Available online 4 April 2012
posite with the assistance of polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) solution. The
as-prepared Pd/Fe3O4 nanocomposite was composed of uniform 5 nm-sized Pd nanoparticles and Fe3O4
nanocrystals with dimension of 40 nm. In this fabrication, PVP played an important role as a capping
agent. The as-prepared Pd/Fe3O4 nanocomposite exhibited superior catalytic performance and stability
for various Suzuki coupling reactions, compared with single-component Pd nanoparticles under the same
reaction conditions. More importantly, it displayed good magnetic property and could be easily separated
from the reaction mixture by using a magnet and recycled for 10 times without losing its catalytic activity.
Keywords:
Pd/Fe3O4
Nanocomposite
Catalysis
Recyclable
Suzuki reaction
© 2012 Elsevier B.V. All rights reserved.
1
. Introduction
Recently, nanostructured catalysts have been extensively inves-
Many works also demonstrated that Pd supported hybrid materi-
als displayed higher catalytic activity and stability [22–25]. Among
numerous supporting materials studied, Fe O4 is of scientific and
3
tigated due to their much higher activities than that of the
corresponding bulk materials [1–5]. Compared with frequently
used palladium (II) complexes catalysts, palladium nanoparticles
were found to exhibit remarkable catalytic activities for Suzuki,
Heck and Sonogashira cross-coupling reactions [6–11], which have
been extensively used in the synthesis of drugs and fine chem-
icals [12–17]. However, nanosized catalysts are usually hardly
separated and recovered from the reaction systems efficiently by
traditional filtration and centrifugation methods. For example, the
tiny palladium nanoparticles usually suffered from the problems
in catalyst separation and agglomeration, which resulted in the
decrease of catalytic activity and recyclable usage [18,19]. In order
to overcome these drawbacks, many efforts have been devoted
to synthesize nanoscaled magnetically recyclable catalysts (MRCs)
in recent years, which were composed of two or more differ-
ent materials. The hybrid nanocrystals realized the integration of
highly catalytic activity and easy separation in MRCs. For instance,
technological importance due to its intrinsic magnetic property
and preeminent applications in catalysis, biotechnology and envi-
ronmental remediation [26]. Up to now, different Pd/Fe O4 hybrid
3
nanocrystals were synthesized and exhibited good catalytic per-
formance on methanol oxidation, cross-coupling reaction, cis- and
trans-2-butene conversion [27–30]. Unfortunately, most reported
MRCs synthetic processes involved multi-step, complicated proce-
dures and harsh reaction conditions. Therefore, the development
of facile and rapid methods for the synthesis of efficient MRCs still
remains a great challenge.
Enlightened by the previous work, we reported a new simple
one-pot synthesis of Pd/Fe O4 nanocomposite with the assistance
3
of polyvinylpyrrolidone (PVP). In this study, a single FeCl2 precur-
sor was used to generate Fe O4 nanoparticles, which was seldom
3
reported in the synthesis of Fe O PVP played an important role as a
3
4.
capping agent in the formation of Pd/Fe O4 nanocomposite, which
3
resulted in the random distribution of Pd and Fe O4 nanocrystals.
3
Chen and co-workers synthesized Ag–Fe O4 nanocomposite as
Furthermore, it was found that the synthesized Pd/Fe O nanocom-
3
3 4
a magnetically recyclable and efficient catalyst for expoxidation
posites exhibited efficient catalytic activities for various Suzuki
of styrene [20]. Au–Fe O4 heterodimer nanocrystals were also
cross-coupling reactions. The Fe O4 nanocrystal was used as a
3
3
used for dual imaging probes for MRI and optical imaging [21].
support of Pd nanoparticles, as well as enhancing the dispersion
of catalysis active sites and improving its catalytic activity. More
importantly, the synthesized Pd/Fe O4 nanocomposite presented
3
good magnetic property, and could be easily separated from the
reaction mixture by using a magnet. By utilizing this property, it
∗ Corresponding author. Tel.: +86 13659815698; fax: +86 2787195671.
E-mail address: rchenhku@hotmail.com (R. Chen).
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.03.025

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2
S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
could be reused for 10 cycles without losing its catalytic activity,
indicative of a potential application in industry.
2
. Experimental
2.1. Chemicals
Polyvinylpyrrolidone (PVP, M.W. = 55,000), ferrous chlo-
ride tetrahydrate (FeCl ·4H O) and palladium chloride (PdCl )
2
2
2
were purchased from Sigma–Aldrich. Cetyltrimethylam-
monium bromide (CTAB) was purchased from Lancaster.
N,N-dimethylformamide (DMF), ethanol (EtOH), tetrabutyl
ammonium bromide (TBAB), sodium iodide (NaI) and all the
organic substrates were purchased from Aladdin (Shanghai,
China). Palladium (10%) on carbon catalyst (Pd/C) was purchased
from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All
the chemicals used in the experiment were analytical grade and
used without further purification.
2.2. Synthesis
In the typical synthesis, 0.0133 g PdCl (0.075 mmol), 0.16 g PVP
2
(
M.W. = 55,000) and 0.0149 g FeCl ·4H O (0.075 mmol) were added
2
2
into 12 mL mixed solution which contained 10 mL DMF and 2 mL
deionized water. The mixture was sonicated for 2 min to form
a turbid solution, and then transferred to a 30 mL Teflon-lined
stainless-steel autoclave to perform the solvothermal process at
◦
1
50 C for 8 h. After cooling down to room temperature, a black
product was collected by a magnet and washed with deionized
water for three times and ethanol for three times. The product
was finally dried in a desiccator at room temperature for further
characterization (S1). Other samples (S2–S8) were prepared under
identical reaction conditions by varying surfactants and solvents.
2.3. Characterization
Fig. 1. XRD pattern (a) and Raman spectrum (b) of Pd/Fe3O4 nanocomposite syn-
thesized by solvothermal method (S1).
Powder X-ray diffraction (XRD) was carried out on a Bruker AXS
◦
−1
D8 Discover (Cu K␣ = 1.5406 A˚ ). The scanning rate was 1 min in
◦
ethanol/H2O (v/v = 1:2) solution. The reaction mixture was then
refluxed under the temperature of 86 C for 30–180 min (see
Tables 2 and 3). After reaction, the reactor was cooled down to
the room temperature, and the product was extracted with diethyl
ether for three times. Then the organic phase was dried with anhy-
the 2ꢀ range from 20 to 80 . The transmission electron microscopy
TEM), high-resolution transmission electron microscopy (HRTEM)
◦
(
images and selected area electron diffraction (SAED) patterns were
recorded on a Philips Tecnai G2 20 electron microscope, using
an accelerating voltage of 200 kV. TEM samples were prepared
by dispersing some solid product into ethanol and then sonicat-
ing for approximately 30 s. A few drops of the suspension were
deposited on copper grids, which were then put into the desic-
cators for drying. The energy-dispersive X-ray (EDX) analysis was
performed on an Oxford Instruments INCA with a scanning range
from 0 to 20 keV. Raman spectrum was measured by a confocal laser
micro-Raman spectrometer (DXR, USA) equipped with a He–Ne
laser with excitation of 532 nm. Spectrum was obtained at a laser
power of 0.6 mW and a 60 s acquisition time in the wavenumber
drous Na SO4 and evaporated in vacuum. Finally, the product was
2
obtained and purified by column chromatography using diethyl
ether/petroleum ether (for yields see Tables 2 and 3). All the prod-
1
ucts were known in literatures and identified by comparing their H
NMR spectra with standard data. For recycle experiment, the sepa-
rated Pd/Fe O composite nanocatalyst was washed with deionized
3
4
water (4 mL × 3) and ethanol (4 mL × 3), and dried in vacuum for
2
4 h before the re-usage.
−1
range of 50–2000 cm . The concentration of Pd in the Pd/Fe O4
3. Result and discussion
3
nanocomposites was analyzed by inductively coupled plasma mass
spectrometry (ICP-MS, Agilent ICP-MS 7500ce). The magnetic mea-
surements were recorded on a SQUID magnetometer at 298 K,
Quantum Design MPMS (see Table 1).
3.1. Structure and morphology
The composition and crystallinity of the as-synthesized prod-
uct (S1) was characterized by the powder XRD analysis. Fig. 1a
shows the typical XRD pattern of the as-synthesized product pre-
pared by one-pot solvothermal method (S1). As shown in Fig. 1a,
all the diffraction peaks could be readily indexed to (1 1 1), (2 0 0),
(2 2 0) lattice planes of a face-centered cubic (fcc) Pd crystal struc-
ture (JCPDS 05-0681) and (2 2 0), (3 1 1), (2 2 2), (4 0 0), (5 1 1), (4 4 0)
2.4. Suzuki coupling reactions
Catalytic activity of the synthesized Pd/Fe O4 nanocompos-
3
ite was tested through the Suzuki reaction of aryl halides with
phenylboronic acid. In the typical experiment, a mixture of aryl
halide (1.0 mmol), phenylboronic acid (1.5 mmol), tetrabutylam-
lattice planes of fcc Fe O4 (JCPDS 75-0033). No other diffraction
3
monium bromide (1 mmol), K CO3 (2 mmol), and 5.6 mg Pd/Fe O4
peaks was detected, indicative of the high-purity of the Pd/Fe O4
2
3
3
nanocomposite (containing 0.2%, mmol Pd) were added into 9 mL
nanocomposites. As both magnetite (Fe O ) and maghemite
3
4

S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
83
Table 1
Experimental parameters for the preparation of Pd/Fe3O4 nanocomposites.
Sample
Fe source
Pd source
Capping agent
Salt
Solvent
S1
S2
S3
S4
S5
S6
S7
S8
FeCl2
–
PdCl2
PdCl2
–
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PVP
PVP
PVP
PVP
PVP
–
–
–
–
–
–
–
NaI
NaI
DMF + H2O
DMF + H2O
DMF + H2O
DMF
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
H2O
DMF + H2O
DMF + H2O
DMF + H2O
PVP
–
Note: The amount of NaI was 0.3 g.
Table 2
Products and yields for Suzuki coupling reactions of phenylboronic acid and various aryl halides catalyzed by Pd/Fe3O4 nanocomposite (S1) and Pd nanoparticles (∼5 nm)
.
Entry
1
Substrates
Products
Time (h)
1.5
Isolated yield (%)
S1
Pd Nps
85
94
2
3
4
5
1.5
3
96
98
98
97
40
30
94
92
0.5
0.5
Reaction condition: a catalyst containing 0.2%, mmol Pd, aryl halide (1.0 mmol), phenylboronic acid (1.5 mmol), K2CO3 (2 mmol), TBAB (1 mmol), 9 mL EtOH/H2O (v/v = 1/2)
◦
solution. T = 86 C.
(
␥-Fe O ) had good magnetism and similar XRD pattern [31],
average diameter of 5 nm and faceted Fe O4 nanocrystals with
2
3
3
Raman spectroscopy was used to distinguish the different struc-
tural phases of iron oxides. Fig. 1b illustrated the Raman
dimensions of about 40 nm (Fig. 2a). As shown in Fig. 2b and c,
well-dispersed Pd nanoparticles were homogeneously deposited
spectroscopy of as-synthesized Pd/Fe O4 nanocomposites (S1),
on the surface of Fe O4 nanocrystals. The selected area electron
diffraction (SAED) pattern of sample S1 revealed several diffraction
rings, which were the sum of diffraction patterns of different Pd
3
3
−
1
which showed the main features at 277, 632, 1348, and 1576 cm
The Raman peaks at 1348 and 1576 cm were assigned to char-
acteristic peak of palladium nanoparticles [32], and the peaks
.
−1
and Fe O4 nanocrystals, thus indicative of good crystallinity (inset
3
−
1
at 277 and 632 cm
were attributed to Fe O nanocrystals,
of Fig. 2b). The HRTEM image of the Pd/Fe O nanocomposites (S1)
3
4
3
4
−1
demonstrating a red-shift of 34 cm compared with the Raman
spectrum of commercial magnetite powder [33]. According to the
reported literature [34], the red-shift was ascribed to a compres-
sive strain induced by the substantial lattice mismatch between
Pd and Fe O , owing to the attachment of Pd nanoparticles on
was shown in Fig. 2d. It also clearly revealed that Pd nanoparti-
cles were directly attached on the Fe O4 nanocrystals. The lattice
3
fringes for both Pd and Fe O4 nanocrystals could be determined to
3
be (2 0 0) planes of Pd component with a d-spacing of 0.193 nm and
(1 1 1) planes of Fe O component with a d-spacing of 0.485 nm. The
3
4
3
4
Fe O surface. It further confirmed the presence of magnetite
elemental composition of the nanocomposite was also analyzed by
the energy-dispersive X-ray (EDX) spectrum (Fig. S1, Supplemen-
3
4
phase.
Fig. 2 showed the typical TEM images of as-synthesized
Pd/Fe O nanocomposites (S1). It was observed that the Pd/Fe O4
tary data). It further confirmed that the Pd/Fe O4 nanocomposite
3
(S1) was composed of palladium, iron and oxygen. The copper and
3
4
3
nanocomposites were composed of tiny Pd nanoparticles with an
carbon signals are from the carbon-coated copper grid.
Table 3
Products and yields for Suzuki coupling reactions of phenylboronic acid and various aryl halides catalyzed by Pd/Fe3O4 nanocomposite (S7).
Entry
1
Substrates
Products
Time (h)
Isolated yield (%)
88
6
2
3
4
5
6
83
94
96
94
6
0.5
0.5

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S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
Fig. 2. TEM (a–c) and HRTEM (d) images of Pd/Fe3O4 nanocomposites prepared by solvothermal method (S1). Inset of (b) is the corresponding SAED pattern of Pd/Fe3O4
nanocomposite (S1).
In order to understand the formation mechanism and opti-
mize the synthetic conditions, different control experiments were
nanocomposite coated with well-dispersed Pd nanoparticles. It was
found that little Pd nanoparticles were randomly deposited on the
Fe O nanocrystals in the absence of PVP (S6, Fig. S3, Supplemen-
performed. When PdCl was solely used as precursor, aggregated Pd
2
3
4
nanoparticles were obtained (S2), in so far that DMF could act both
tary data). It was proposed that the polyvinyl skeleton might be
as a solvent and a powerful reducing agent to generate Pd nanopar-
readily coated on Fe O4 nanocrystals through hydrophobic inter-
3
ticles in the presence of PVP [35–39]. However, no Fe O4 product
actions, while the group including nitrogen and oxygen atoms
absorbed on Pd plane surface due to the weak binding of PVP [41].
In this study, sodium iodide was also used in the synthesis of
3
was formed in the absence of palladium source under the identical
2+
condition (S3). It confirmed that Pd could be reduced by FeCl2 as
2
+
well and Fe ions were partly oxidized to from Fe O nanocrystals.
Pd/Fe O4 nanocomposites, which could depress the spontaneous
3
4
3
To further verify the speculation, a control experiment was carried
out under identical conditions in pure DMF solvent and deion-
nucleation [42]. Pd/Fe O4 nanocomposite was also obtained in
the presence of NaI salt (S7), as confirmed by its XRD pattern
3
ized water, respectively (S4 and S5). No Pd/Fe O4 nanocomposite
(Fig. S4, Supplementary data). All the diffraction peaks could be
3
was obtained in pure DMF or water solution (Fig. S2, Supplemen-
tary data). Hence, it indicated that the chemical reactions involved
readily matched with fcc phase of Fe O4 (JCPDS 75-0033) and
fcc phase of Pd (JCPDS 05-0681), indicative of the formation of
3
in the formation of Pd/Fe O4 nanocomposite were as following:
Pd/Fe O product. Fig. 3 shows the corresponding TEM and HRTEM
3
3 4
images of sample S7. TEM images of Fig. 3a–c revealed that uni-
form Pd nanoparticles with an average diameter of 25 nm were
Pd2 + 2Fe2+ → Pd + 2Fe3+
+
well-dispersed on the surface of Fe O4 nanocrystals. The particle
3
Pd2 + Me NCHO + H O → Pd + Me NCOOH + 2H
+
+
size of Pd/Fe3O4 nanocomposites was in the range of 200–300 nm.
HRTEM image of sample S7 (Fig. 3d) revealed clear lattice fringes
with a d-spacing of 0.217 and 0.485 nm corresponding to the (1 1 1)
2
2
2
2
Fe3 + Fe2+ + 4H O → Fe O + 8H
+
+
2
3
4
lattice plane of fcc Pd and Fe O4 respectively, indicative of good
3
crystallinity. The corresponding SAED pattern showed different
diffraction rings, which also confirmed the good crystallinity of
In this formation, PVP played an important role as a capping
agent which not only contained polyvinyl skeleton, but also pro-
vided nitrogen and oxygen atoms with polar groups [40]. We
Pd/Fe O4 naocomposite (Inset of Fig. 3a). These results demon-
3
strated that the particle sizes were larger than that of the sample
S1 synthesized in the absence of NaI. It indicated that the addition
also attempted to synthesize Pd/Fe O4 nanocomposites in the
3
absence of PVP. Unfortunately, it was difficult to obtain Pd/Fe O4
3

S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
85
Fig. 3. TEM (a–c) and HRTEM (d) images of Pd/Fe3O4 nanocomposites prepared by solvothermal method in the presence of NaI (S7).
of NaI could depress spontaneous nucleation of Pd nanoparticles.
evaluated through a series of Suzuki coupling reactions in aque-
Noticeably, Pd/Fe O4 nanocomposite was hardly formed in the
ous medium. Table 2 gives the reaction conditions and results for
3
absence of PVP, despite the addition of NaI salt (S8) (Fig. S5, Supple-
mentary data). It further verified the function of PVP as a capping
agent.
five coupling reactions. It was found that the Pd/Fe O4 nanocom-
posite (S1) exhibited excellent catalytic activity for Suzuki coupling
reactions of phenylboronic acid with various aryl bromides (entries
3
1
–3 in Table 2) and aryl iodides (entries 4–5 in Table 2). The
isolated yields could reach to 94–98% after 0.5–3 h refluxing at
3.2. ICP-MS measurement and magnetic property
The concentration of Pd in the Pd/Fe O4 nanocomposite (S1)
3
was determined by inductively coupled plasma mass spectrome-
try (ICP-MS) analysis. The ICP-MS data revealed that the relative Pd
concentration in the Pd/Fe O4 nanocomposite was 3.82 wt%. The
3
magnetic property of the Pd/Fe O4 nanocomposite (S1) was also
3
investigated. Fig. 4 shows the hysteresis loop of Pd/Fe O nanocom-
3
4
posite obtained in applied magnetic field at 298 K by using a SQUID
magnetometer. The magnetic saturation value of the composite
−1
was estimated to be 53.4 emu g . As shown in inset of Fig. 4, the
Pd/Fe O nanocomposite was easily separated from the solution,
3
4
indicating that it was suitable for magnetic separation applications.
3.3. Catalytic activity
Suzuki coupling reaction is an effective and versatile synthetic
route for the construction of biaryls, which involved the reaction
of arylboronic acids and aryl halides. In this study, the catalytic
activity of the as-prepared Pd/Fe O4 nanocomposite (S1) was
Fig. 4. Hysteresis loop of the as-prepared Pd/Fe3O4 nanocomposite (S1) at 298 K.
3

8
6
S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
Scheme 1. Magnetic separation and recycling of Pd/Fe3O4 catalyzed the reaction for the cycle.
◦
6 C. More importantly, the Pd/Fe O nanocomposite (S1) showed
3 4
8
enhanced catalytic activity for various Suzuki reactions, compared
with single-component Pd nanoparticles with the same particle
size (∼5 nm, Fig. S6, Supplementary data) under the identical exper-
imental conditions. It indicated that the choice of Fe O as catalyst
3
4
support played an important role on the overall performance of the
catalytic system. Fe O4 nanocrystals not only provided adequate
3
magnetic property for the separation of nanocomposites, but also
enhanced the dispersion of Pd active sites, leading to the improve-
ment of catalytic activity. In literatures, it was also reported that
supported catalyst could improve its activity, selectivity or stability
[
23,43–45].
It was also found that the Pd/Fe O nanocomposite (S1) afforded
3
4
better catalytic activity than the commercial Pd/C when the
same amount of Pd mol% was employed in the Suzuki reactions
(
Table S1, Supplementary data). Furthermore, the results implied
that it was possible to maximize the catalytic activity of Pd nanopar-
ticle through the supporting metal oxide nanocrystals, except for
the control of Pd nanoparticle size and shape.
It was worth noting that the catalytic activity of Pd/Fe O4
3
Fig. 5. Recycling results of Suzuki coupling reaction of phenylboronic acid with 4-
iodophenyl methyl ether over different Pd/Fe3O4 nanocomposite (S1 and S7) and
Pd/C catalysts.
nanocomposite prepared in the presence of NaI (S7) was obviously
lower than that of sample S1. Although it remained similar catalytic
activity for aryl iodides (entries 4–5 in Table 3), the Suzuki reactions
of phenylboronic acid with aryl bromides only afforded the cou-
pling product in 88%, 83%, and 94% isolated yield, respectively, even
after 6 h refluxing (entries 1–3 in Table 3). These results demon-
4
1% in the 7th recycling reaction. It indicated that the large parti-
strated that the Pd/Fe O4 nanocomposite (S7) showed a decrease
3
cle size of Pd/Fe O4 nanocomposite also easily resulted in the loss
3
in catalytic activity, compared with sample S1. It was proposed that
the increase of particle size resulted in the decrease of catalytic
activity [46,47].
of catalytic activity in the recycling use. Meanwhile, the commer-
cial Pd/C catalyst could only be reused for 5 times and lose its high
catalytic activity in the 6th recycling reaction.
Due to the good magnetic performance, Pd/Fe O nanocompos-
3
4
ite was very useful for overcoming the intrinsic difficulty associated
with the separation of homogeneous Pd (II) complex based and Pd
nanoparticles based catalysts in Suzuki coupling reactions. Hence,
4. Conclusions
the recycle of Pd/Fe O4 nanocomposite was investigated. We have
3
carried out recycling uses of the Pd/Fe O4 nanocomposite (S1) cat-
In summary, we developed a facile one-pot solvothermal route
to synthesize Pd/Fe3O4 nanocomposite from FeCl2 and PdCl2 in
the presence of PVP for the first time. Uniform Pd nanoparti-
cles were well-dispersed on the surfaces of Fe3O4 nanocrystals
to form Pd/Fe3O4 nanocomposite. In this fabrication, PVP played
3
alyst for the Suzuki reaction of 4-iodophenyl methyl ether with
phenylboronic acid, and the coupling product was obtained with a
yield of 98% in the first cycle. When the Suzuki coupling reaction
was completed, the Pd/Fe O4 nanocomposite (S1) catalyst could
3
be easily separated from the reaction mixture by using a mag-
net (Scheme 1), then washed and dried for re-usage. The recycled
Pd/Fe O catalyst was then used in model reaction under the same
an important role as a capping agent in the formation of
Pd/Fe3O4 nanocomposite. The as-prepared Pd/Fe3O4 nanocompos-
ite exhibited excellent catalytic activity for various Suzuki coupling
reactions. More importantly, the Pd/Fe3O4 nanocomposite dis-
played good magnetic property, which facilitated the collection by
magnetic method. It could be easily separated by a magnet when
the Suzuki coupling reactions completed, and then recycled for
10 times without losing its catalytic activity. This work provides
a new synthetic strategy for the fabrication of magnetically recy-
clable Pd/Fe3O4 nanocomposites, which could be applied to many
important industrial catalytic processes and extended to achieve
the synthesis of various noble-metal/Fe3O4 nanocomposites.
3
4
reaction conditions, and it could be recycled for many times with-
out losing its catalytic activity. As depicted in Fig. 5, the catalyst
(
S1) still remained excellent catalytic activity even after 10 times of
recycling. The recycling model reaction of phenylboronic acid with
-iodophenyl methyl ether was also carried out under identical
conditions by using the Pd/Fe O nanocomposite (S7) and commer-
4
3
4
cial Pd/C as a catalyst, respectively. Pd/Fe O4 nanocomposite (S7)
3
was recycled the Suzuki coupling reaction for 7 times, and afforded
good yield of 86% after six recycles. The isolated yield decreased to

S. Li et al. / Journal of Molecular Catalysis A: Chemical 359 (2012) 81–87
87
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