The controllable preparation of electrospun carbon fibers supported Pd nanoparticles catalyst and its application in Suzuki and Heck reactions

Article abstract of DOI:10.1016/j.cclet.2015.12.029

The palladium nanoparticles/carbon nanofibers (Pd NPs/CNFs) catalyst was prepared by the electrospinning method, the hydrazine hydrate solution reduction in an ice bath environment, the high temperature carbonization. The catalyst was characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). The nanofibers are not cross-linked and arranged in order. The surface of Pd NPs/CNFs is smooth, and it can be observed that a large number of particles were loaded and well-dispersed in carbon fiber matrix, and the particle distribution is uniform. The activity center of catalyst is Pd⁽⁰⁾. The Pd NPs/CNFs exhibited a high efficiency, good reusability and stability in the Suzuki and Heck reactions. It can be used for at least five consecutive runs without significant loss of its catalytic activity. The good recyclability of Pd NPs/CNFs provides a way to greatly reduce the cost of the catalyst.

Full text of DOI:10.1016/j.cclet.2015.12.029

G Model
CCLET 3522 1–5
Chinese Chemical Letters xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
1
2
Original article
3
4
The controllable preparation of electrospun carbon fibers supported Pd
nanoparticles catalyst and its application in Suzuki and Heck reactions
5
6
Q1 Shou-Jun Guo, Jie Bai *, Hai-Ou Liang, Chun-Ping Li
Chemical Engineering College, Inner Mongolia University of Technology, Hohhot 010051, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The palladium nanoparticles/carbon nanofibers (Pd NPs/CNFs) catalyst was prepared by the
electrospinning method, the hydrazine hydrate solution reduction in an ice bath environment, the
high temperature carbonization. The catalyst was characterized by X-ray diffraction (XRD), field-
emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). The
nanofibers are not cross-linked and arranged in order. The surface of Pd NPs/CNFs is smooth, and it can be
observed that a large number of particles were loaded and well-dispersed in carbon fiber matrix, and the
Received 14 September 2015
Received in revised form 9 December 2015
Accepted 24 December 2015
Available online xxx
Keywords:
(0)
particle distribution is uniform. The activity center of catalyst is Pd . The Pd NPs/CNFs exhibited a high
Pd NPs/CNFs
Electrospinning
Carbonization
Catalysts
efficiency, good reusability and stability in the Suzuki and Heck reactions. It can be used for at least five
consecutive runs without significant loss of its catalytic activity. The good recyclability of Pd NPs/CNFs
provides a way to greatly reduce the cost of the catalyst.
ß 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
7
8
1. Introduction
materials [16–18]. Carbon materials, including carbon black, 28
carbon nanofibers (CNFs), graphene and other derivatives, have 29
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
The Suzuki and Heck cross-coupling reactions are very
important in the synthesis of natural products and fine chemicals
[1–3]. They have been widely applied to diverse areas such as
pharmaceuticals, biologically active molecules, and material
science, where they provide a powerful and straightforward
method for C–C bond formation [4–6]. To date, many metallic
catalysts have been widely studied for Suzuki and Heck reactions.
Among the metallic catalysts, palladium-based catalysts have
become a hot topic because of their outstanding performance in
carbon–carbon cross-coupling [7–10]. The original Suzuki and
Heck reactions was catalyzed by a homogeneous palladium
catalyst, which made its separation and recovery tedious, if not
impossible, and might result in unacceptable palladium contami-
nation of the products. In order to avoid these disadvantages,
heterogeneous catalysts have received extensive attention [11]. As
a result, the load type catalyst was prepared, and there are a lot of
materials that can be used as the catalyst carrier.
all been used as catalyst carriers [19]. Among these carbon 30
materials, carbon nanofibers (CNFs) have recently attracted 31
considerable attention due to their unique structure, which has 32
a high surface area, a locally conjugated aromatic system, and high 33
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
chemical and thermal stability [20,21].
34
Recently, CNFs have been widely applied as solid supports for 35
catalysts [22,23]. The CNFs supported catalysts can be simply and 36
efficiently separated from the reaction system by simple filtration, 37
thus avoiding the cumbersome operating process [24]. Peng et al. 38
[25] prepared Pd nano-network structures supported on electro- 39
spun carbon nanofibers (Pd-NNSs-ECNFs) as a catalyst for Suzuki 40
coupling reactions, and satisfactory results were obtained in these 41
studies. The obtained Pd-NNSs-ECNFs catalyst showed good 42
activity, high efficiency, and reusability as heterogeneous catalysts 43
for Suzuki coupling under environmentally friendly solvents.
From this point of view, the aim of the present work is to prepare 45
a Pd NPs/CNFs catalyst, which is described in Scheme 1. The PdCl 46
44
2
/
Pd nanoparticles can be supported by a number of materials
such as carbon materials [12,13], polymers [14,15], and inorganic
PAN nanofibers were obtained by electrospinning. Then, they were 47
reduced by hydrazine hydrate solution in an ice bath, and the Pd/ 48
PAN nanofibers were obtained. Finally, the Pd NPs/CNFs were 49
obtained by the high temperature carbonization in a tube furnace. 50
Recently, we have efficiently used Pd supported on CNFs for Suzuki 51
(Scheme 2) and Heck (Scheme 3) reactions. Pd NPs/CNFs exhibited 52
*
Corresponding author.
E-mail address: baijie@imut.edu.cn (J. Bai).
http://dx.doi.org/10.1016/j.cclet.2015.12.029
1
001-8417/ß 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: S.-J. Guo, et al., The controllable preparation of electrospun carbon fibers supported Pd nanoparticles
catalyst and its application in Suzuki and Heck reactions, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2015.12.029

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S.-J. Guo et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
Scheme 1. Scheme of the preparation of Pd NPs/CNFs.
5
5
3
4
high efficiency, good reusability, and good stabilityin the Suzuki and
Heck reactions.
Pd/PAN nanofibers were heated in a tube furnace at 250 8C under
constant flow of atmosphere for 2 h, the subsequently heated to
87
88
350 8C under nitrogen and maintained at that temperature for 2 h.
89
Then, it was annealed at 600 8C under constant flow of nitrogen for
4 h and cooled to 250 8C in nitrogen atmosphere. Finally, it was
cooled to room temperature in air.
90
91
92
93
5
5
6
2. Experimental
5
2.1. Materials
Characterization of Pd NPs/CNFs catalyst: The UV–vis diffuse
reflectance spectrum (DRS) (UV-3600, Shimadzu Corporation) was
recorded at wavelengths of 200–700 nm. FT-IR spectra were
recorded on a Thermo Nicolet Corporation FT-IR-670. X-ray
diffraction (XRD) measurement was carried out using a D/MAX-
2500/PC XRD spectrometer. Field emission scanning electron
microscopy (FE-SEM, Quanta 650 FEG Scanning Electron Micro-
scope) was used to characterize the morphology of the catalyst.
TEM samples were prepared by drop-casting a dispersion of Pd
NPs/CNFs onto carbon-coated copper grids and natural drying.
Catalysis performance of Pd NPs/CNFs for Suzuki-Miyaura
cross-coupling reaction: In order to verify the activity of the
catalyst, the Suzuki-Miyaura cross-coupling reaction was carried
out in our experiments. 5 mL of deionized water, 5 mL of
anhydrous ethanol, 1.0 mmol of aryl halides, 1.1 mmol of
phenylboronic acid, 1.5 mmol of base, and 0.005 g of Pd NPs/CNFs
catalyst were stirred in a parallel reaction tube for 8 h at 80 8C.
After the reaction completed, the mixture was filtered at room
temperature. The filtrate was extracted with ethyl acetate three
times and the organic phase was added with anhydrous Na SO to
94
95
96
97
98
99
5
5
5
6
6
6
6
6
6
6
6
7
8
9
0
1
2
3
4
5
6
7
All reagents were used without further treatment. Polyacrylo-
nitrile (PAN, Mw = 80,000) was purchased from Kunshan Hong Yu
Plastic Co., Ltd. N,N-Dimethylformamide (DMF, C
and hydrazine hydrate (H O, 80%) were purchased from Tianjin
Fengchuan Chemical Reagent Technology Co. Ltd. Phenylboronic
acid (98%), anhydrous ethanol (C O, AR, 99.7%), palladium
chloride (PdCl , AR), methyl acrylate (C , CP, 98%), ethyl
acrylate (C CP, 98%), iodobenzene (C I, CP, 97%),
triethylamine (C 15N, AR, 99%), and n-butyl acrylate (C
3
H
7
NO, AR, 99.5%)
6
N
2
2
H
6
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
2
4 6 2
H O
5
H
8
O
2
,
6 5
H
6
H
7 12 2
H O ,
CP, 98%) were purchased from Sinopharm Chemical Reagent
(China). All other reagents were purchased from Alfa Aesar.
6
8
2.2. Preparation of catalyst
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
2 2
Preparation of PdCl /PAN/DMF solution: The PdCl /PAN/DMF
solution was prepared according to the previous report from our
group [26]. First, 8 wt% PAN/DMF solution was prepared, and then
the solution was added into the PdCl
the acrylonitrile monomer to the palladium chloride was 30. The
PdCl /PAN/DMF solution was obtained after 12 h of magnetic
2
powder; the molar ratio of
2
4
absorb residual water. Finally, the solution was filtered by an
organic membrane. The products were determined by GC analysis
2
stirring at room temperature.
with
the
area
normalization
method.
(Conversion
Preparation of Pd/PAN nanofibers: The PdCl
2
/PAN/DMF
rate = 100% Â (S /(S + S )), S is the area of all the products, S is
1
1
2
1
2
solution was electrospun to nanofibers by applying a 16 kV
voltage to a 15 cm gap between the spinneret and the collector.
the area of aryl halides after the reaction; selectivity = 100% Â (S /
1
(S + S )), S is the area of principal product, S is the area of all by-
1
2
1
2
Then, the PdCl
hydrate solution in an ice bath. First, hydrazine hydrate solution
at a concentration of 2 mol/L was prepared, and then the PdCl
2
/PAN nanofibers were reduced by hydrazine
products.) The filter cake (Pd NPs/CNFs) was washed with acetone,
ethanol, and distilled water three times.
2
/
Catalysis performance of Pd NPs/CNFs for Mizoroki-Heck cross-
coupling reaction: 10 g of DMF, 2.0 mmol of aryl halides, 2.7 mmol
of olefinic compounds, 6 mmol of base, and 0.001 g of Pd NPs/CNFs
catalyst were stirred in a parallel reaction tube for 6 h, at 120 8C.
After the reaction completed, the mixture was filtered at room
temperature. The filtrate was determined by GC analysis with the
PAN nanofibers were immersed in it and were reduced in an ice
bath environment. Deep brown Pd/PAN nanofibers were obtained
and washed several times with distilled water and then dried in air.
Preparation of Pd NPs/CNFs: The Pd NPs/CNFs was obtained by
the high temperature carbonization in a tube furnace. The obtained
area normalization method. (Conversion rate = 100% Â ((S
), S is the area of aryl halides before reaction, S is the area of aryl
halides after the reaction; selectivity = 100% Â (S /(S + S )), S is
the area of principal product, S is the area of all by-products.) The
1
À S
2
)/
Pd NPs/CNFs
S
1
1
2
X
+
BOH
2
1
1
2
1
R
R
2
Scheme 2. Suzuki-Miyaura coupling reaction of aryl halides with phenylboronic
filter cake (Pd NPs/CNFs) was washed with acetone, ethanol, and
distilled water three times.
acid catalyzed by Pd NPs/CNFs.
3
. Results and discussion
133
134
R2
3.1. Characterization of Pd NPs/CNFs catalyst
Pd NPs/CNFs
X
+
R2
R1
R1
The UV–vis spectra of PdCl
nanofibers were shown in Fig. 1. As shown in Fig. 1, the A curve
is PdCl /PAN, and the B curve is Pd/PAN. The absorption peak of A
2
/PAN nanofibers and Pd/PAN
135
136
137
Scheme 3. Mizoroki-Heck cross-coupling reaction of aryl halides with olefinic
compounds catalyzed by Pd NPs/CNFs.
2
Please cite this article in press as: S.-J. Guo, et al., The controllable preparation of electrospun carbon fibers supported Pd nanoparticles
catalyst and its application in Suzuki and Heck reactions, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2015.12.029

G Model
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S.-J. Guo et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
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3
1
3.0
2.5
2.0
1.5
1.0
0.5
0.0
A
2
44 nm
120
1
736
B
9
6
3
0
0
0
0
C
D
2939
3000
2
243
1
447
A
B
3425
1
588 1292
1500 1000
1
200
300
400
500
600
700
Wavelength (nm)
4000
3500
2500
2000
500
-
Wavenumber (cm )
Fig. 1. UV–vis spectra of (A) PdCl
2
/PAN and (B) Pd/PAN.
2
Fig. 2. FT-IR spectra of (A) PAN, (B) PdCl /PAN, (C) Pd/PAN and (D) Pd NPs/CNFs.
2
+
42À
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
curve in 244 nm is attributed to Pd or PdCl . The absorption
changed due to the swelling, as shown in Fig. 3C. After high 174
temperature carbonization, the surface of the Pd NPs/CNFs was 175
smooth, and it can be observed that a large number of particles were 176
loaded into the carbon fiber matrix, and the particle distribution is 177
uniform. The HRTEM and XRD results confirmed that these particles 178
peak at 244 nm disappeared after the PdCl
the hydrazine hydrate, as shown by the B curves. These changes
2
/PAN was reduced by
2+
(0)
clearly demonstrated that Pd can be reduced into Pd by the
hydrazine hydrate solution. At the same time, it also showed that
the activity of the catalyst group is divided into Pd . The HRTEM
and XRD results further proved that PdCl /PAN was reduced.
Fig. 2 shows the FT-IR spectra for the PAN fibers, the PdCl /PAN
nanofibers, the Pd/PAN nanofibers, and the Pd NPs/CNFs. For the
PAN nanofibers, the IR absorption peak at about 2243 cm was
attributed to the stretching vibrations of nitrile groups (–CN), and
the peaks at about 2939 cm and 1447 cm were attributed to
(0)
are palladium nanoparticles.
179
2
The TEM images in Fig. 4 provide a more direct view of the Pd 180
NPs/CNFs, it can be seen that the nanoparticles were loaded and 181
well-dispersed within the carbon fiber matrix. From Fig. 4A, the 182
size distribution of Pd nanoparticles were 11–15 nm. Some of these 183
particles have a small agglomeration phenomenon, which may be 184
formed during the reduction of hydrazine hydrate in an ice bath 185
environment. In addition, HRTEM in Fig. 4B revealed a direct view 186
of the palladium nanoparticles. The clear lattice fringes with an 187
interplanar lattice spacing of ꢀ0.2299 nm corresponded to the 188
(111) atomic planes of face centered cubic Pd. This is consistent 189
2
À1
À1
À1
the stretching vibrations and the bending vibration of methylene
À1
(–CH
2
–), respectively [27,28]. The peak at about 1736 cm might
originate from the vibration of C 55 O bonds formed in the
hydrolyzed PAN nanofibers and the stretching vibration of the
C 55 O bonds in the residual solvent DMF [29]. After the preoxidation
and carbonization process, the absorption peaks of the PAN
nanofibers all disappeared. For the carbon nanofibers, the IR
absorption peaks at 1588 cm and 1292 cm were attributed to
the stretching vibrations of C 55 C bonds, and the stretching
vibrations of C–O, respectively [30]. This is because the cyclization
reaction, the dehydrogenation reaction, the oxidation reaction
happened in the process of preoxidation, and the cyano
disconnected in the carbonization process, so the exhaust end
O, etc. [31]. Therefore, FT-IR indicated
that the catalyst carrier was the carbon fibers.
The structureandmorphologyofthePAN, PdCl
Pd NPs/CNFs were characterized by field emission scanning electron
microscopy (FE-SEM) and transmission electron microscopy (TEM).
The overall morphology of the nanofibers can be seen from the FE-
SEM images, and the fibers are not cross-linked and arranged in
order. Fig. 3A showed that PAN nanofibers had a large length to
diameter ratio and a smooth surface nanostructure. The diameters of
with the results of XRD diffraction angle of 40.18.
190
XRD patterns of the Pd NPs/CNFs were shown in Fig. 5. The first 191
characteristic diffraction peak at about 24.08 was originated from 192
the CNF carrier. The peaks at 2u values of 40.18, 46.68, 68.18, 82.18, 193
and 86.68 are due to the (111), (200), (220), (311), and (222) 194
diffraction peaks of face centered cubic Pd (JCPD-46-1043). So the 195
palladium nanoparticles formed the zerovalent palladium crystal 196
structure, which is in conformity with the UV–vis and HRTEM 197
results. In conclusion, the active center of catalyst is the zerovalent 198
À1
À1
discharged NH
3
, HCN, H
2
, H
2
palladium.
199
2
/PAN, Pd/PANand
3.2. Catalytic activity of Pd NPs/CNFs in Suzuki-Miyaura carbon
coupling reaction
200
201
The Pd NPs/CNFs is very stable and high-efficiency in the liquid- 202
phase reaction. To verify the practicability of the prepared catalyst 203
Pd NPs/CNFs, our study commenced with its application for the 204
Suzuki-Miyaura cross-coupling reaction. The reaction was per- 205
formed with different alkali salts to investigate their effects on the 206
reaction, and the results are shown in Table 1. By comparison, 207
2
PAN nanofibers ranged from 260 nm to 300 nm. After the PdCl /PAN
was reduced by hydrazine hydrate, the diameter of the fibers were
2
Fig. 3. FE-SEM images of (A) PAN, (B) PdCl /PAN, (C) Pd/PAN and (D) Pd NPs/CNFs.
Please cite this article in press as: S.-J. Guo, et al., The controllable preparation of electrospun carbon fibers supported Pd nanoparticles
catalyst and its application in Suzuki and Heck reactions, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2015.12.029

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S.-J. Guo et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
Fig. 4. TEM images and particle size distribution histogram of (A) Pd NPs/CNFs; HRTEM images of Pd NPs.
208
209
210
211
212
213
214
215
216
217
KOAc, Et
entries 4–6). It is observed that most inorganic bases are more
effective (Table 1, entries 1–4) than organic base Et N (Table 1,
entry 6). The results reveal that, in the presence of K CO , Cs CO
KOH, the conversion rate of iodobenzene is nearly 100% (Table 1,
entries 1–3). As Cs CO is radioactive, and when the KOH is
present, the Pd NPs/CNFs catalyst exhibited lower selectivity than
CO , so K CO was chosen for subsequent investigations.
The catalytic activity of Pd NPs/CNFs was tested for the Suzuki-
Miyaura reaction of phenylboronic acid and different aryl halides
3
N, and K
3
PO
4
were less effective for the reaction (Table 1,
under heterogeneous conditions with K
2
CO
3
as an acid binding
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
agent. The Pd NPs/CNFs showed good catalytic activity to different
aryl halides (Table 2, entries 1–3, 5–7). But the conversion rate was
low (Table 2, entries 4) when 1-iodo-4-nitrobenzene was used as
the substrate, which is due to the poor solubility of 1-iodo-4-
nitrobenzene in solvent.
3
2
3
2
3
,
2
3
To evaluate the reusability of Pd NPs/CNFs catalyst, the catalyst
after completion of the reaction was separated and was washed
with acetone, ethanol, and distilled water three times. The dried
and the recycled catalyst were reused directly for the next cycle
without further treatment. The reaction between phenylboronic
acid and iodobenzene was selected to explore the reusability of the
catalysts. Generally, the heterogeneous catalysts easily lose their
catalytic activity due to the extensive leaching of the active mental
species. To our surprise, the Pd NPs/CNFs catalyst can be recycled
five times with a negligible drop in activity (Table 3, entries 1–5).
Thus, the catalyst is stable during the Suzuki coupling reaction. The
good recyclability of Pd NPs/CNFs provides a way to greatly reduce
the cost of the catalyst.
K
2
3
2
3
1400
1200
1000
4
0.1
(
111)
800
600
400
200
0
46.6
200)
(
3.3. Catalytic activity of Pd NPs/CNFs in Heck carbon coupling reaction
237
24.0
6
8.1
8
2.1
311)
86.6
222)
To extend the scope of coupling reaction, we examined the Heck
reaction of different aryl iodides with olefinic compounds. As
shown in Table 4, the substituents at the phenyl ring of aryl iodides
and different olefinic compounds had no significant effect on the
238
239
240
241
(
220)
(
(
10
20
30
40
2
50
θ (degree)
60
70
80
90
Table 2
Suzuki-Miyaura coupling reaction of different aryl halides with phenylboronic acid
Fig. 5. XRD patterns of Pd NPs/CNFs.
a
catalyzed by Pd NPs/CNFs.
Table 1
Suzuki-Miyaura coupling reaction of iodobenzene with phenylboronic acid
.
a
catalyzed by Pd NPs/CNFs
b
b
Entry
R
Time (h)
Conversion rate (%)
Selectivity (%)
b
b
Entry
Base
Time (h)
Conversion rate (%)
Selectivity (%)
1
2
3
4
5
6
7
4-OCH
3-OCH
2-OCH
3
3
3
8
8
8
8
8
8
8
98
>99
>99
6
99
99
1
2
3
4
5
6
K
2
CO
CO
KOH
PO
KOAc
Et
3
8
8
8
8
8
8
>99
>99
>99
54
>99
97
Cs
2
3
99
92
4-NO
3-NO
2-NO
H
29
2
2
2
K
3
4
92
>99
>99
>99
95
9
90
96
3
N
30
96
>99
a
a
Reaction conditions: iodobenzene (1 mmol), phenylboronic acid (1.1 mmol),
base (1.5 mmol), deionized water (5 mL), ethanol (5 mL), and 0.005 g Pd NPs/CNFs,
Reaction conditions: aryl halides (1 mmol), phenylboronic acid (1.1 mmol),
(1.5 mmol), ethanol (5 mL), deionized water (5 mL), and 0.005 g Pd NPs/CNFs,
80 8C, under N
2 3
K CO
8
0 8C, under N
2
.
2
.
b
b
Determined by GC analysis with the area normalization method.
Determined by the GC-analysis with the area normalization method.
Please cite this article in press as: S.-J. Guo, et al., The controllable preparation of electrospun carbon fibers supported Pd nanoparticles
catalyst and its application in Suzuki and Heck reactions, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2015.12.029

G Model
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S.-J. Guo et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
5
Table 3
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a
Recyclability of Pd NPs/CNFs with iodobenzene catalyzed by Pd NPs/CNFs.
42579.
271
b
Run
Retrieval (g)
Time (h)
Conversion
Selectivity
(%)
[4] I. Favier, D. Madec, E. Teuma, M. Gomez, Palladium nanoparticles applied in 272
organic synthesis as catalytic precursors, Curr. Org. Chem. 15 (2011) 3127–3174. 273
b
rate (%)
[
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talysts for Suzuki cross-coupling reactions, Chem. Soc. Rev. 40 (2011) 5181–5203. 275
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one century after the discovery of the Ullmann reaction, Chem. Rev. 102 (2002) 277
1
2
3
4
5
0.0048
0.0047
0.0050
0.0043
0.0045
8
8
8
8
8
>99
88
87
78
95
81
93
[
95
96
1359–1470.
278
99
[7] X.M. Chen, G.H. Wu, J.M. Chen, et al., Synthesis of ‘‘Clean’’ and well-dispersive Pd 279
nanoparticles with excellent electrocatalytic property on graphene oxide, J. Am. 280
a
Reaction conditions: iodobenzene (1 mmol), phenylboronic acid (1.1 mmol),
(1.5 mmol), ethanol (5 mL), deionized water (5 mL), and 0.005 g Pd NPs/CNFs,
0 8C, under N
Chem. Soc. 133 (2011) 3693–3695.
281
2 3
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1
2
3
4
5
6
H
COOCH
3
6
6
6
6
6
6
98
99
94
92
96
81
86
93
H
COOC
COOC
2
H
H
5
9
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4-OCH
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3
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[
[
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2
2
2
42
43
44
reaction consequence. The catalytic activity of Pd NPs/CNFs was
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246
247
248
249
250
251
252
253
254
255
256
257
In summary, palladium nanoparticles supported on carbon
nanofibers (Pd NPs/CNFs) were successfully prepared by the
electrospinning method, hydrazine hydrate solution reduction in
an ice bath environment, and high temperature carbonization. The
results of FE-SEM and TEM conducted indicate that the arrange-
ment of nanofibers is regular and the palladium nanoparticles are
uniformly distributed in the matrix of carbon fibers. The Pd NPs/
CNFs catalyst was successful applied in Suzuki and Heck reaction
and exhibited high efficiency, good reusability and stability. It can
be used for at least five consecutive runs without a significant loss
of its catalytic activity. The good recyclability of Pd NPs/CNFs
provides a way to greatly reduce the cost of the catalyst.
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Acknowledgment
2
2
59 Q2
60
The authors gratefully acknowledge the support of the National
Natural Science Foundation of China (21266016).
2
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Please cite this article in press as: S.-J. Guo, et al., The controllable preparation of electrospun carbon fibers supported Pd nanoparticles
catalyst and its application in Suzuki and Heck reactions, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2015.12.029