Microwave-assisted fast fabrication of a nanosized Pt3Co alloy on reduced graphene oxides

Article abstract of DOI:10.1016/S1872-2067(14)60232-1

Ultrafine and homogenously dispersed Pt₃Co alloy nanoparticles were fabricated on reduced graphene oxide (RGO) in a few minutes under microwave irradiation. Characterization results confirmed that microwave irradiation was important for higher metal utilization, the easy control of alloy composition, improved dispersion of the Pt₃Co particles and minimizing the re-graphitization of the parent RGO by comparison with conventional solvent-thermal and impregnation methods. This Pt₃Co/RGO-MW catalyst was extremely active and selective during the hydrogenation of cinnamaldehyde to cinnamyl alcohol. The calculated specific activity of each Pt atom in the Pt₃Co/RGO-MW at 70 °C was 23.8 min^-1.

Full text of DOI:10.1016/S1872-2067(14)60232-1

Chinese Journal of Catalysis 35 (2014) 2029–2037
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e /c h n j c
Article
Microwave‐assisted fast fabrication of a nanosized Pt3Co alloy on
reduced graphene oxides
Juanjuan Shi, Renfeng Nie, Mengyuan Zhang, Mengsi Zhao, Zhaoyin Hou*
Institute of Catalysis, Department of Chemistry, Zhejiang University, Hangzhou 310028, Zhejiang, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Ultrafine and homogenously dispersed Pt3Co alloy nanoparticles were fabricated on reduced gra‐
phene oxide (RGO) in a few minutes under microwave irradiation. Characterization results con‐
firmed that microwave irradiation was important for higher metal utilization, the easy control of
alloy composition, improved dispersion of the Pt3Co particles and minimizing the re‐graphitization
of the parent RGO by comparison with conventional solvent‐thermal and impregnation methods.
This Pt3Co/RGO‐MW catalyst was extremely active and selective during the hydrogenation of cin‐
namaldehyde to cinnamyl alcohol. The calculated specific activity of each Pt atom in the
Pt3Co/RGO‐MW at 70 °C was 23.8 min–1.
Received 30 July 2014
Accepted 30 September 2014
Published 20 December 2014
Keywords:
graphene
Pt3Co
microwave irradiation
cinnamaldehyde
hydrogenation
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
rated aldehydes [15,16]. However, the controlled synthesis of
nanosized Pt‐alloys is a challenge in terms of controlling the
Nanosized metal particles have been extensively exploited
for potential application in catalysis, sensors and biosensors,
electro‐oxidation, energy conversion devices, and the produc‐
tion of hydrogen because of their unique physicochemical
properties. These nanostructures have allowed new insights
into traditional catalysis and many achievements have been
reported in recent years [1,2].
Nanosized Pt and Pt‐alloys have been extensively investigat‐
ed because of their excellent catalytic performance in fuel cells
[3,4], selective oxidation [5–7], and in the selective hydrogena‐
tion of unsaturated aldehydes [8–10]. Pt‐alloys can reduce the
amount of expensive Pt required and some have enhanced ac‐
tivity compared with monometallic Pt. The Pt3Co alloy shows
remarkable activity in electro‐catalytic oxygen reduction in fuel
cells [11–14], and the selective hydrogenation of α,β‐unsatu‐
particle size, size distribution and metal composition. Most
reported methods employ surfactants to control the Pt‐alloy
particle size [15–18]. However, for catalytic application, it is
more desirable to synthesize uncapped particles that exhibit
similar or higher stability compared with their capped coun‐
terparts [19]. Several methods such as co‐precipitation [20],
impregnation [6,7], and surface organometallic reactions [21]
have been reported. However, these processes are
time‐consuming and generate waste solvents while high tem‐
peratures and pressures are required to alloy different metal
components. Among the reported methods, impregnation is
simple and the loading efficiency of metal precursors is low. A
Pt‐Co alloy that was prepared by a precipitation method was
found to agglomerate easily and had a varied Pt‐Co alloy com‐
position [22].
* Corresponding author. Tel/Fax: +86‐571‐88273283; E–mail: zyhou@zju.edu.cn
This work was supported by the National Natural Science Foundation of China (21473155, 21273198, 21073159) and the Natural Science Founda‐
tion of Zhejiang Province (L12B03001).
DOI: 10.1016/S1872‐2067(14)60232‐1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 12, December 2014

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Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
Graphene possesses a high surface area that is useful for the
spectrometer).
dispersion of metal nanoparticles (NPs) and its micropore‐free
structure contains one or a few sheet layers, which is useful for
the transfer of reactants and products. Good electrical conduc‐
tivity is required for electron transfer in catalysis and graphene
is thought to have high chemical reactivity [23–28]. However,
graphene is prone to aggregation during drying and graphite
may form in these prepared catalysts because of van der Waals
interactions [29,30].
Microwave irradiation, as a rapid, uniform and effective
heating method, has received considerable attention as a new,
promising method to weaken the formation of “re‐graphitized”
carbon regions of graphene [25,31]. Microwave irradiation‐
assisted reduction has also been proposed for the controlled
synthesis of Pt‐based electro‐catalysts [32–34]. Knupp et al.
[32] reported that uniformly dispersed Pt NPs with a high
loading efficiency could be deposited on carbon nanotubes and
carbon nanofibers using microwave irradiation‐assisted heat‐
ing techniques. Yu et al. [34] found that polymer‐stabilized
platinum colloids with a near‐uniform spherical shape (narrow
size of 2–4 nm) could be prepared by microwave dielectric
heating.
In this work, we report a microwave irradiation‐assisted
and fast synthesis routine for the production of an ultrafine and
homogenously dispersed Pt3Co alloy on the surface of reduced
graphene oxide (Pt3Co/RGO‐MW). The synthesized Pt3Co/
RGO‐MW was compared with samples prepared by impregna‐
tion (Pt3Co/RGO‐IM) and conventional solvent‐thermal
(Pt‐Co/RGO‐ST) methods. The performance of these catalysts
in the chemoselective hydrogenation of α,β‐unsaturated alde‐
hydes (cinnamaldehyde, CAL) to their corresponding unsatu‐
rated alcohols (cinnamyl alcohol, COL) is discussed.
Synthesis of the Pt3Co/RGO‐IM catalyst. As a reference,
Pt‐Co alloyed NPs on RGO were also prepared by the impregna‐
tion method [22] and the product was designated
Pt3Co/RGO‐IM. Weighed amounts of H2PtCl6 and Co(CH3COO)2
with a Pt/Co molar ratio of 3:1 were added to an aqueous solu‐
tion of GO (100 mL). The solution of GO and metal ions was
magnetically stirred overnight. Finally, 50 mL of NaBH4 solu‐
tion (20 mmol/L) was added dropwise to the solution. After
continuously stirring for 24 h, the resulting solution was fil‐
tered and washed until it was free of Cl–. It was then dried in a
vacuum oven at 40 °C for 10 h.
Synthesis of the Pt‐Co/RGO‐ST catalyst. A conventional sol‐
vent‐thermal method was used, as previously reported [9]. The
produced catalyst was designated Pt‐Co/RGO‐ST. The prepared
GO (0.10 g C) was added to a solution containing EG (100 mL)
and this solution was sonicated for 30 min to obtain a liquid
suspension of GO. H2PtCl6 and Co(CH3COO)2 at a Pt/Co molar
ratio of 3:1 were then added. This mixture was further stirred
for 2 h to fully exfoliate the GO. Subsequently, the pH of the
above‐mentioned suspension was adjusted to 11–12 using a
NaOH/EG solution. The mixture was then transferred to a
stainless steel autoclave with a Teflon inner layer and put into
an oil bath at 145 °C for 24 h under constant stirring. The
formed catalyst was separated by filtration and washed with
ethanol until it was free of Cl–. It was then dried in a vacuum
oven at 40 °C for 10 h.
2.2. Characterization
X‐ray diffraction (XRD) patterns were recorded on a dif‐
fractometer (RIGAKUD/MAX 255/PC) at 40 kV and 100 mA
with Cu Kα radiation (λ = 0.15406 nm). The crystallite size of Pt
or the Pt‐Co alloy was calculated using the Scherrer equation.
Raman spectra were collected on a Rhenishaw 2000 Confocal
Raman Microprobe (Rhenishaw Instruments, UK) using a 514.5
nm argon laser. Tapping mode atomic force microscopy (AFM)
measurements were performed using a multimode scanning
probe microscope (SPM) from Digital Instruments with a Na‐
noscope IIIa controller. Scanning transmission electron mi‐
croscopy (STEM) and high‐angle annular dark field (HAADF)
imaging were used to observe individual particles at atomic
resolution with an aberration corrected JEOL 2200FS (S)TEM
operating at 200 kV. X‐ray energy dispersive spectrometer
(EDS) spectra of individual particles larger than 1–2 nm were
obtained. Pt, Co, and the Pt‐Co alloy were identified using fast
Fourier transform (FFT) high‐resolution TEM analysis. X‐ray
photoelectron spectra (XPS) were recorded on a Perkin‐Elmer
PHI ESCA System. The X‐ray source was a Mg standard anode
(1253.6 eV) operated at 12 kV and 300 W.
2. Experimental
2.1. Catalyst preparation
Synthesis of the Pt3Co/RGO‐MW catalyst. Graphene oxide
(GO) was prepared by a modified Hummers method [35]. Pt‐Co
alloyed NPs with a Pt/Co molar ratio of 3:1 on RGO sheets were
synthesized as follows: GO (0.10 g C) was added to a solution of
ethylene glycol (EG, 100 mL) and this solution was sonicated
for 30 min to obtain a homogenous liquid GO suspension.
Weighed amounts of H2PtCl6 and Co(CH3COO)2 at a Pt/Co mo‐
lar ratio of 3:1 were added to the suspension and it was stirred
for 2 h. The pH of the above mentioned suspension was ad‐
justed to 11–12 using a NaOH/EG solution. This solution was
subjected to microwave heating for 7.5 min in a microwave
oven (Sineo, MAS‐II, 600 W, 2.45 GHz) operated at 145 °C. After
microwave irradiation, the suspension was cooled to room
temperature and the solid product was isolated and washed
with distilled water until it was free of Cl–. It was then dried in a
vacuum oven at 40 °C for 10 h. This catalyst was designated
Pt3Co/RGO‐MW. Monometallic Pt/RGO‐MW and Co/RGO‐MW
were also prepared in a similar manner. The Pt and Co content
of the prepared catalysts were determined by inductively cou‐
pled plasma‐atomic emission spectroscopy (ICP, Plasma Spec II
2.3. Catalytic reactions
The selective hydrogenation of CAL was performed in a 100
mL stainless steel autoclave with a Teflon inner layer. In a typ‐
ical procedure, the catalyst was first dispersed in 20.0 mL eth‐
anol, and then 8.0 mmol CAL was added while stirring. After

Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
2031
sealing the reactor, the air content was quickly purged by
flushing three times with 2.0 MPa H2. The autoclave was then
heated to 70 °C and the reaction mixture was stirred (at 1000
rpm) with a magnetic stirrer (MAG‐NEO, RV‐06M, Japan). After
the reaction, the solid catalyst was separated by centrifugation
and the products were analyzed by gas chromatography (HP
5890, USA) using a 30 m capillary column (HP‐5) and a flame
ionization detector. All the products were confirmed by GC‐MS
(Agilent 6890‐5973N).
(4)
(3)
(2)
3. Results and discussion
(1)
3.1. Structural characterization
JCPDS 29-0499
JCPDS 04-0802
JCPDS 15-0806
Pt3Co
Pt
The Pt and Co content of the prepared Pt‐Co/RGO catalysts
were determined by ICP and are summarized in Table 1. We
found that the composition of the prepared Pt3Co/RGO‐MW fits
the controlled value well. The utilization efficiency of the Pt
precursor was as high as 98.1%, and the Pt/Co molar ratio was
3:1.02. This fits the control level (3:1) well. The utilization effi‐
ciency of the Pt precursor was low in the samples prepared by
the impregnation (77.8%, in Pt3Co/RGO‐IM) and conventional
solvent‐thermal (89.2%, in Pt‐Co/RGO‐ST) methods. The cal‐
culated Pt/Co molar ratio changed to 3:1.05 and 3:0.35, respec‐
tively. These data indicate that microwave irradiation is an
important method for the fabrication of bimetallic catalysts on
the surface of RGO. This method is characterized by short reac‐
tion time, high Pt and Co precursor utilization and the easy
control of sample molar ratio.
XRD patterns of the Pt‐Co/RGO catalysts prepared using the
different methods are shown in Fig. 1. The presence of metallic
Pt in Pt/RGO‐MW is indicated by the characteristic (111),
(200), and (220) plane diffraction peaks of Pt at 2θ = 39.8°,
46.3°, and 67.5°, respectively (JCPDS 04‐0802). Three distinct
peaks at 2θ = 40.5°, 47.1°, and 68.8° were found for
Pt3Co/RGO‐MW. These fit the (111), (200), and (220) planes of
the Pt3Co alloy well (JCPDS 29‐0499), respectively [36]. From
the broadening of the (220) plane, the calculated crystallite size
of these alloy particles is 2.1 nm (summarized in Table 1).
These diffraction peaks were sharp in the pattern of
Pt‐Co/RGO‐ST and Pt3Co/RGO‐IM. This behavior can be at‐
tributed to the uneven dispersion of the alloyed NPs. The cal‐
culated crystallite size of the alloyed NPs increased to 5.3 nm
and 10.6 nm, respectively. Since no separate Co or Co oxide
Co
10
20
30
40
50
60
70
80
2/(o )
Fig. 1. XRD patterns of Pt/RGO‐MW (1), Pt3Co/RGO‐MW (2),
Pt‐Co/RGO‐ST (3), and Pt3Co/RGO‐IM (4).
peaks are present in Fig. 1(2)–(4), the Pt‐Co alloy mainly
formed in the bimetallic catalysts.
A broad peak between 2θ = 17° and 30° is present in the
patterns of all the samples and this is assigned to the charac‐
teristic structure of RGO wherein the formation of
“re‐graphitized” carbon regions and disordered restacking
occurred because of van der Waals attractive interactions [23].
By comparison with Pt3Co/RGO‐IM and Pt‐Co/RGO‐ST, this
Pt3Co/RGO‐MW diffraction peak was broader, indicating the
relatively less dense and well‐exfoliated state of the graphene
sheets.
Raman spectra of the RGO‐supported Pt‐Co catalysts are
shown in Fig. 2. The D band of these catalysts is present at
~1350 cm–1 and it is associated with the defect‐related A1g
mode [37–39]. The G band at ~1580 cm–1 represents a
first‐order scattering of the E2g vibrational state with the gra‐
phitic hexagon‐pinch mode. The calculated R (ID/IG) intensity
D
G
Table 1
Metal loading and dispersion on RGO.
Metal content a
(%)
Particle size
(nm)
Utilization
of Pt b (%)
(1)
(2)
(3)
Catalyst
Pt
—
Co
1.6
—
XRD
—
TEM
—
Co/RGO‐MW
Pt/RGO‐MW
Pt3Co/RGO‐MW
Pt3Co/RGO‐IM
—
15.5
15.5
12.3
14.1
98.1
98.1
77.8
89.2
2.4
2.5
1.6
1.3
0.5
2.1
2.3
10.6
5.3
11.6
5.4
Pt‐Co/RGO‐ST
a
1000 1100 1200 1300 1400 1500 1600 1700 1800
Raman shift (cm1)
The controlled Pt and Co loading amounts were 15.8 and 1.6 mass
percent with respect to C, respectively.
b The utilization of Pt was calculated as: real loading amount of Pt in the
prepared catalysts/the amount of added Pt.
Fig. 2. Raman spectra of Pt3Co/RGO‐IM (1), Pt‐Co/RGO‐ST (2), and
Pt3Co/RGO‐MW (3).

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Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
ratios of Pt3Co/RGO‐IM (Fig. 2(1)), Pt‐Co/RGO‐ST (Fig. 2(2)),
and Pt3Co/RGO‐MW (Fig. 2(3)) were 1.37, 1.17, and 1.05, re‐
spectively. These results show that microwave irradiation is
effective in reducing GO and it subsequently results in the res‐
toration of the sp2 network with small and isolated aromatic
domains within the sheets by comparison with conventional
synthetic methods.
The thickness of the RGO support in these prepared cata‐
lysts was measured by AFM, and representative images are
shown in Fig. 3. The apparent height of the microwave‐treated
RGO‐MW sheets between the two red marks was 0.725 nm
(Fig. 3(a)), and this was expected to be thinner than that of GO
(typical thickness of about 0.8 nm) because of the removal of
covalently bound oxygen and the resumption of aromatic or
conjugated systems [38]. This thickness indicates that micro‐
wave‐treated RGO‐MW contains about two sheets because the
ideal thickness of a graphene plane is 0.335 nm [40]. However,
the distances between the closest RGO sheets prepared by the
conventional synthetic methods were 1.291 (in RGO‐IM, Fig.
3(b)) and 1.933 nm (in RGO‐ST, Fig. 3(c)) for four and six gra‐
phene layers, respectively. These data further confirm that
microwave irradiation can weaken the “re‐graphitization” of
exfoliated GO during the reduction of metal salts.
Typical TEM images and the corresponding particle size
distributions of the Pt3Co/RGO‐MW, Pt3Co/RGO‐IM and
Pt‐Co/RGO‐ST catalysts are given in Fig. 4. A large amount of
ultrafine, highly dispersed Pt3Co NPs of 1–5 nm in size (with an
average diameter of 2.3 nm) were present in the TEM and
STEM images of Pt3Co/RGO‐MW (Fig. 4(a)–(d)). The HRTEM
images and a FFT (Fig. 4(c), (d)) analysis of representative
Pt‐Co particles show the formation of a uniform Pt3Co alloy
with predominant (111) and (200) planes. HAADF (Fig. 4(e),
(f)) images of single Pt3Co NPs show that good spatial corre‐
spondence exists in the Co and Pt elemental maps which are
(c)
(a)
(b)
1.183x1.183 µm
0.787x0.787 µm
0.213x0.213 µm
nm
nm
nm
5.0
9.5
10.0
0
0.725 nm
1.291 nm
1.933 nm
0
0
-10.0
-9.5
-5.0
0
2.50
5.00 µm
0
1.0
2.0 µm
0
0.25 0.50 0.75 1.00 1.25 µm
Fig. 3. AFM images and section analysis of RGO‐MW (a), RGO‐IM (b), and RGO‐ST (c).
Fig. 4. (HR)TEM (a)–(d) images of Pt3Co/RGO‐MW, and its corresponding FFT (inset (c),(d)); (e),(f) HAADF‐STEM images and elemental maps for Pt
and Co metals of Pt3Co/RGO‐MW; (g) HRTEM images of Pt3Co/RGO‐IM and (h) Pt‐Co/RGO‐ST catalysts.

Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
2033
determined by the intensity of their K and L lines, respectively.
On the other hand, big Pt3Co clusters with an average diameter
of 11.6 nm formed in Pt3Co/RGO‐IM (Fig. 4(g)). The Pt‐Co alloy
NPs dispersed unevenly in Pt‐Co/RGO‐ST (Fig. 4(h)) and the
detected Pt‐Co particles were 1–11 nm in size (with an average
diameter of 5.4 nm). These results further confirm that micro‐
wave irradiation is an important method for the fabrication of
an ultrafine, homogenously dispersed Pt3Co alloy on the sur‐
face of RGO.
Fig. 5 shows C1s XPS spectra of GO, Pt3Co/RGO‐MW,
Pt3Co/RGO‐IM and Pt‐Co/RGO‐ST. Four kinds of carbon specie
carbon in the main frame (C–C, sp2) at 284.6 eV, carbon with
dangling OH groups or an epoxy linkage (C–OH/epoxy) at 286.6
eV, carbonyls (C=O) at 287.7 eV and carboxylates (O–C=O) at
289.0 eV [18,24] were detected in these samples. The ratios of
these carbon species in the GO and the prepared catalysts were
deconvoluted and are summarized in Table 2. The heterocar‐
bon group content (C–O, C=O, and O–C=O) decreased dramati‐
cally from 60.7% (in GO, Fig. 5(a)) to 17.1% (in
Pt3Co/RGO‐MW, Fig. 5(b)). This indicates that many oxygen
functional groups were partially removed during the reduction
process. The heterocarbon components of Pt3Co/RGO‐IM (Fig.
5(c)) and Pt‐Co/RGO‐ST (Fig. 5(d)) were also reduced to 21.1%
and 24.0%, respectively.
The Pt 4f XPS spectra of the Pt3Co/RGO‐MW, Pt3Co/RGO‐IM
and Pt‐Co/RGO‐ST catalysts are shown in Fig. 6. The most in‐
tense doublet with binding energy of 71.4 eV and 74.8 eV is
attributed to metallic Pt(0). The peaks at 72.4 eV and 75.8 eV
are attributed to Pt(II) in either PtO or Pt(OH)2 [24,41,42]. It is
interesting to note that the Pt(0) content of Pt3Co/RGO‐MW
and Pt3Co/RGO‐IM (80.3% and 79.8%, respectively) is higher
than that of Pt‐Co/RGO‐ST (75.8%). This might come from the
formation of the Pt3Co alloy that depresses the oxidation of Pt
by air or oxygen in the RGO (Fig. 6(a), (b), Table 2). The Co 2p
features consist of two main peaks of 2p3/2 and 2p1/2 at 780 eV
and 797 eV, respectively, and these are assigned to Co(II). Ad‐
ditional satellites centered at 786 eV and 804 eV also confirmed
the formation of Co(II) [43]. The shoulder peak at 778 eV indi‐
cated the presence of Co(0) and its intensity was weak because
Co is a more oxophilic metal compared with Pt and would show
an oxidation effect much more readily [44].
3.2. Catalytic activity during the hydrogenation of CAL
The selective hydrogenation of α,β‐unsaturated aldehydes
to their corresponding unsaturated alcohols is of great im‐
portance in the production of fine chemicals and pharmaceuti‐
cal intermediates. This reaction was also studied in detail to
(a)
(b)
C-C
C-O
C-C
C=O
C=O
C-O
O-C=O
O-C=O
280
282
284
286
288
290
292
294
280
282
284
286
288
290
292
294
Binding energy (eV)
Binding energy (eV)
(d)
C-C
(c)
C-C
C-O
C-O
C=O
C=O
288
O-C=O
O-C=O
290
280
282
284
286
292
294
280
282
284
286
288
290
292
294
Binding energy (eV)
Binding energy (eV)
Fig. 5. C1s XPS spectra of GO (a), Pt3Co/RGO‐MW (b), Pt3Co/RGO‐IM (c), and Pt‐Co/RGO‐ST (d).
Table 2
Distribution of functional groups from the XPS data.
Relative atomic content (%)
Heterocarbon
Component (%)
Relative atomic content (%)
Catalyst
C–C
39.3
82.9
78.9
76.0
C–O
40.7
14.1
12.8
12.6
C =O
15.2
2.7
6.3
6.8
O =C–O
4.8
0.3
2.0
4.6
Pt(0)
—
Pt(Ⅱ)
—
GO
60.7
17.1
21.1
24.0
Pt3Co/RGO‐MW
Pt3Co/RGO‐IM
Pt‐Co/RGO‐ST
80.3
79.8
75.8
19.7
20.2
24.2

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Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
(a)
(b)
Pt 4f7/2
Pt 4f7/2
Pt 4f5/2
Pt 4f5/2
68
70
72
74
76
78
80
82
84
68
70
72
74
76
78
80
82
84
Binding energy (eV)
Binding energy (eV)
(d)
(c)
Co 2P3/2
Pt 4f7/2
Pt 4f5/2
780
778
786
Co 2P1/2
793
804
797
770
780
790
Binding energy (eV)
800
810
68
70
72
74
76
78
80
82
84
Binding energy (eV)
Fig. 6. XPS spectra of Pt 4f in Pt3Co/RGO‐MW (a), Pt3Co/RGO‐IM (b), Pt‐Co/RGO‐ST (c) (Pt(0) in red, Pt(II) in blue), and Co 2p spectra for
Pt3Co/RGO‐MW (d).
probe the selective activation of C=C or C=O bonds
[8–10,15,16]. In this work, the selective hydrogenation of CAL
was carried out as a model reaction for the prepared
Pt‐Co/RGO, and the results are summarized in Table 3. Under
the reaction conditions used (CAL/Pt (substrate/catalyst, S/C)
molar ratio = 1127, 70 °C, 2.0 MPa), the main product was
found to be COL, and the byproducts were hydrocinnamalde‐
hyde (HCAL) and hydrocinnamyl alcohol (HCOL). Pure
RGO‐MW and Co/RGO‐MW were inactive during the reaction
(entries 1 and 2). A significant conversion of CAL was apparent
over Pt/RGO‐MW, Pt3Co/RGO‐MW, Pt3Co/RGO‐IM and
Pt‐Co/RGO‐ST (entries 3–6). The conversion of CAL over
Pt/RGO‐MW and Pt3Co/RGO‐MW at 90 min was 92.6% and
99.7%, respectively. However, the selectivity toward COL over
Pt3Co/RGO‐MW (95.3%) was obviously higher than that over
Pt/RGO‐MW (42.1%). The selectivity of COL toward
Pt3Co/RGO‐IM (92.2%, entry 5) and Pt‐Co/RGO‐ST (77.6%,
entry 6) was also higher than that over monometallic
Pt/RGO‐MW (42.1%, entry 3), which indicates that the addition
of Co to Pt can improve the selective activation of C=O and that
the Pt3Co alloy was extremely selective toward the formation of
COL. The calculated specific activity of each Pt atom in
Pt3Co/RGO‐MW reached 23.8 min–1, and this is 2.7 and 2.4
times that in Pt3Co/RGO‐IM and Pt‐Co/RGO‐ST (8.8 and 10.0
min–1), respectively. The activity of Pt3Co/RGO‐MW is better
than that of Pt‐Co/CNTs and Pt‐Co/graphite [45]. These results
suggest that the RGO sheets pretreated under microwave irra‐
diation contain less oxygen species and are relatively less dense
in terms of packing and that they are well exfoliated. This might
promote the accessibility of active sites and reactants. Addi‐
tionally, the proportion of Pt(0) in Pt3Co/RGO‐MW is higher
than that in Pt‐Co/RGO‐ST and Pt3Co/RGO‐IM, which is favora‐
ble for the hydrogenation reaction.
Table 3
Fig. 7(a) shows the time course of hydrogenation of CAL
over Pt3Co/RGO‐MW. The conversion of CAL increased quickly
to 90% in the first 60 min and further increased to 99.7% at 90
min. The selectivity toward COL remained higher than 90%
even upon the complete conversion of CAL (at 120 min). The
formation rate of HCOL was lower than that over Pt/RGO‐MW
(Fig. 7(b)). These results further confirm that the Pt3Co alloy
was selective toward the formation of COL during the complete
conversion of CAL. We also found excellent performance for the
selective formation of COL on the Pt3Co alloy over the time
course for Pt3Co/RGO‐IM (Fig. 7(c)). The selectivity toward
COL remained higher than 87.0%. However, the selectivity
Catalytic results for the hydrogenation of cinnamaldehyde.
Conversion
(%)
Selectivity (%)
HCAL HCOL COL
TOF a
(min–1)
—
Entry
Catalyst
1
2
3
4
5
6
RGO‐MW
Co/RGO‐MW
Pt/RGO‐MW
Pt3Co/RGO‐MW
Pt3Co/RGO‐IM
Pt‐Co/RGO‐ST
<1
<1
92.6
99.7
53.6
66.6
—
—
—
—
—
—
—
40.3 17.6 42.1 21.5
2.5
7.8
2.2 95.3 23.8
0.0 92.2 8.8
1.7 77.6 10.0
20.7
Reaction conditions: CAL 8.0 mmol, ethanol 20.0 mL, S/C = 1127, H2 2.0
MPa, 70 °C, 90 min.
a
TOF was defined as (the amount of converted CAL molecular at 20
min)/(total amount of Pt atom)/(reaction time, min).

Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
2035
(a)
(b)
100
100
80
60
40
20
0
80
Conversion of CAL
Selectivity for COL
Selectivity for HCAL
Selectivity for HCOL
Conversion of CAL
60
Selectivity for COL
Selectivity for HCAL
Selectivity for HCOL
40
20
0
0
20
40
60
80
100 120 140 160
0
20
40
60
Time (min)
80
100
120
Time (min)
100
80
60
40
20
0
(c)
(d)
100
80
60
40
20
0
Conversion of CAL
Conversion of CAL
Selectivity for COL
Selectivity for HCAL
Selectivity for COL
Selectivity for HCAL
Selectivity for HCOL
Selectivity for HCOL
0
50
100
150
200
250
300
0
50
100
150
200
250
Time (min)
Time (min)
Fig. 7. Time course of CAL hydrogenation over the Pt3Co/RGO‐MW (a), Pt/RGO‐MW (b), Pt3Co/RGO‐IM (c) and Pt‐Co/RGO‐ST (d).
toward COL over Pt‐Co/RGO‐ST decreased to 77.6% because of
the low Co content of the Pt‐Co alloy (Fig. 7(d)).
Pt3Co/RGO‐MW recycling experiments were also conducted
and the results are shown in Fig. 8. We found that the
Pt3Co/RGO‐MW catalyst still had good activity after five cycles.
As shown in Table 4 and Fig. 9, the decreased activity was
probably due to minor loss during the recycle. It is important to
highlight that the selectivity toward COL remained higher than
83% in these recycle experiments.
100
80
Conversion of CAL
60
Selectivity for COL
40
20
0
1
2
3
4
5
The recycle run
Fig. 8. Recycled Pt3Co/RGO‐MW catalyst during the hydrogenation of
CAL.
Table 4
Composition of Pt3Co/RGO‐MW before and after the hydrogenation of
CAL.
Metal content a (%)
Particle size b
Catalyst
(nm)
2.3
3.1
Pt
15.5
15.3
Co
1.6
1.6
Fresh
Recycled
Fig. 9. TEM images of fresh (a) and used (b) Pt3Co/RGO‐MW catalyst for
5 recycles.
a Analyzed by ICP–AES; b Measured by TEM.

2036
Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
2012, 51: 3440
4. Conclusions
[16] Kwon S G, Krylova G, Sumer A, Schwartz M M, Bunel E E, Marshall
C L, Chattopadhyay S, Lee B, Jellinek J, Shevchenko E V. Nano Lett,
2012, 12: 5382
[17] Shao Y Y, Zhang S, Wang C M, Nie Z M, Liu J, Wang Y, Lin Y H. J
Power Sources, 2010, 195: 4600
[18] Guo S J, Dong S J, Wang E K. ACS Nano, 2010, 4: 547
[19] Kundu P, Nethravathi C, Deshpande P A, Rajamathi M, Madras G,
Ravishankar N. Chem Mater, 2011, 23: 2772
[20] Bock C, Paquet C, Couillard M, Botton G A, MacDougall B R. J Am
Chem Soc, 2004,126: 8028
We investigated the convenient and efficient synthesis of
homogenously dispersed Pt3Co alloy NPs on RGO sheets. We
found that microwave irradiation heating is important for the
high utilization of Pt and Co precursors. The atomic ratio was
easily controlled compared with impregnation and sol‐
vent‐thermal methods. Additionally, microwave irradiation
heating prevented the re‐graphitization of graphene sheets. In
the hydrogenation of CAL, the Pt3Co/RGO‐MW was extremely
active and selective toward COL.
[21] Santori G F, Casella M L, Ferretti O A. J Mol Catal A, 2002, 186:
223
[22] Yue Q L, Zhang K, Chen X M, Wang L, Zhao J S, Liu J F, Jia J B. Chem
Commun, 2010, 46: 3369
References
[23] Scheuermann G M, Rumi L, Steurer P, Bannwarth W, Mülhaupt R. J
Am Chem Soc, 2009, 131: 8262
[24] Nie R F, Wang J H, Wang L N, Qin Y, Chen P, Hou Z Y. Carbon, 2012,
50: 586
[25] Siamaki A R, Khder A E R S, Abdelsayed V, El‐Shall M S, Gupton B F.
J Catal, 2011, 279: 1
[26] Zhao Y C, Zhan L, Tian J N, Nie S L, Ning Z. Electrochim Acta, 2011,
56: 1967
[1] Tian N, Zhou Z Y, Sun S G, Ding Y, Wang Z L. Science, 2007, 316:
732
[2] Stamenkovic V R, Mun B S, Arenz M, Mayrhofer K J J, Lucas C A,
Wang G F, Ross P N, Markovic N M. Nat Mater, 2007, 6: 241
[3] Ghosh T, Leonard B M, Zhou Q, DiSalvo F J. Chem Mater, 2010, 22:
2190
[4] Jusys Z, Behm R J. J Phys Chem B, 2001, 105: 10874
[5] Lee A F, Gee J J, Theyers H J. Green Chem, 2000, 2: 279
[6] Nie R F, Liang D, Shen L, Gao J, Chen P, Hou Z Y. Appl Catal B, 2012,
127: 212
[27] Verma S, Mungse H P, Kumar N, Choudhary S, Jain S L, Sain B,
Khatri O P. Chem Commun, 2011, 47: 12673
[28] Allen M J, Tung V C, Kaner R B. Chem Rev, 2010, 110: 132
[29] Si Y C, Samulski E T. Chem Mater, 2008, 20: 6792
[30] Chen S Q, Wang Y. J Mater Chem, 2010, 20: 9735
[31] Hu H, Zhao Z B, Zhou Q, Gogotsi Y, Qiu J S. Carbon, 2012, 50: 3267
[32] Knupp S L, Li W Z, Paschos O, Murray T M, Snyder J, Haldar P.
Carbon, 2008, 46: 1276
[7] Liang D, Gao J, Sun H, Chen P, Hou Z Y, Zheng X M. Appl Catal B,
2011, 106: 423
[8] Tsang S C, Cailuo N, Oduro W, Kong A T S, Clifton L, Yu K M K,
Thiebaut B, Cookson J, Bishop P. ACS Nano, 2008, 2: 2547
[9] Shi J J, Nie R F, Chen P, Hou Z Y. Catal Commun, 2013, 41: 101
[10] Vu H, Gonçalves F, Philippe R, Lamouroux E, Corrias M, Kihn Y,
Plee D, Kalck P, Serp P. J Catal, 2006, 240: 18
[33] Jiang S J, Ma Y W, Jian G Q, Tao H S, Wang X Z, Fan Y N, Lu Y N, Hu
Z, Chen Y. Adv Mater, 2009, 21: 4953
[11] Yang H Z, Zhang J, Sun K, Zou S Z, Fang J Y. Angew Chem Int Ed,
2010, 49: 6848
[34] Yu W Y, Tu W X, Liu H F. Langmuir, 1999, 15: 6
[35] Hummers W S Jr, Offemann R E. J Am Chem Soc, 1958, 80: 1339
[36] Fei L F, Sun T Y, Lu W, An X Q, Hu Z F, Yu J C, Zheng R K, Li X M,
Chan H L W, Wang Y. Chem Commun, 2014, 50: 826
[37] Li X L, Zhang G Y, Bai X D, Sun X M, Wang X R, Wang E G, Dai H J.
Nat Nanotechnol, 2008, 3: 538
[12] Choi S I, Choi R, Han S W, Park J T. Chem‐Eur J, 2011, 17: 12280
[13] Wang C, Wang G F, van der Vliet D, Chang K C, Markovic N M, Sta‐
menkovic V R. Phys Chem Chem Phys, 2010, 12: 6933
[14] Callejas‐Tovar R, Liao W T, de la Hoz J M M, Balbuena P B. J Phys
Chem C, 2011, 115: 4104
[38] Chen J L, Yan X P. J Mater Chem, 2010, 20: 4328
[15] Wu B H, Huang H Q, Yang J, Zheng N F, Fu G. Angew Chem Int Ed,
Graphical Abstract
Chin. J. Catal., 2014, 35: 2029–2037 doi: 10.1016/S1872‐2067(14)60232‐1
Microwave assisted fast fabrication of nanosized Pt3Co alloy on reduced graphene oxides
Juanjuan Shi, Renfeng Nie, Mengyuan Zhang, Mengsi Zhao, Zhaoyin Hou*
Zhejiang University
H
2
PtCl
6
CHO H
+
2
CH2OH
Co(CH
3
COO)
2
OH
OH
OH
OH
O
HO
OH
OH
O
O
O
O
O
O
OH
O
HO
OH
HO
HO
O
OH
O
O
O
OH
O
HO
OH
Pt3Co
HO
O
OH
OH
O
O
A microwave irradiation‐prepared nanosized Pt3Co alloy was supported on reduced graphene oxides and the synthesized
Pt3Co/RGO‐MW was used for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.

Juanjuan Shi et al. / Chinese Journal of Catalysis 35 (2014) 2029–2037
2037
[39] Pimenta M A, Dresselhaus G, Dresselhaus M S, Cançado L G, Jorio
J Catal, 2006, 238: 468
A, Saito R. Phys Chem Chem Phys, 2007, 9: 1276
[40] Paredes J I, Villar‐Rodil S, Solís‐Fernández P, Martínez‐Alonso A,
Tascón J M D. Langmuir, 2009, 25: 5957
[41] Vinayan B P, Ramaprabhu S. Nanoscale, 2013, 5: 5109
[42] Liang Y M, Zhang H M, Zhong H X, Zhu X B, Tian Z Q, Xu D Y, Yi B L.
[43] Gao C L, Liang Y Y, Han M, Xu Z, Zhu J M. J Phys Chem C, 2008, 112:
9272
[44] Duong H T, Rigsby M A, Zhou W P, Wieckowski A. J Phys Chem C,
2007, 111: 13460
[45] Li Y, Zhu P F, Zhou R X. Appl Surf Sci, 2008, 254: 2609