Gold nanoparticles supported on layered TiO2-RGO hybrid as an enhanced and recyclable catalyst for microwave-assisted hydration reaction

Article abstract of DOI:10.1039/c6ra08021a

In this study, we synthesized a novel composite material (Au-TiO₂-RGO) consisting of tiny gold nanoparticles (～4.5 nm) grown on a layered titania (TiO₂) and reduced graphene oxide (RGO) hybrid. After treatment with microwave and sulfuric acid, solid acid (SO₄^2-/TiO₂) was in situ formed on the surface of TiO₂, and the resulting Au-SO₄^2-/TiO₂-RGO was determined as an enhanced catalyst for hydration reaction. The strong metal-support interaction (SMSI) between Au and TiO₂ and the cooperative effect between Au and SO₄^2-/TiO₂ solid acid collectively account for the excellent performance. Moreover, due to the versatile RGO substrate, the catalyst could also be recycled and reused at least 5 times without obvious deactivation.

Full text of DOI:10.1039/c6ra08021a

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Gold Nanoparticles Supported on Layered TiO2–RGO Hybrid
as an Enhanced and Recyclable Catalyst for Microwave-assisted
Hydration Reaction
Received 00th January 20xx,
Accepted 00th January 20xx
Yunfeng Cheng,a Qingshan Zhao,a,b Yang Li, a Wenchao Peng,a Guoliang Zhang,a Fengbao
DOI: 10.1039/x0xx00000x
Zhang*a and Xiaobin Fan*a
www.rsc.org/
In this study, we synthesized a novel composite material (Au–TiO2–RGO) consisting of tiny gold nanoparticles (~4.5 nm)
grown on a layered titania (TiO2) and reduced graphene oxide (RGO) hybrid. After treatment with microwave and sulfuric
acid, solid acid (SO42–/TiO2) was in-situ formed on the surface of TiO2, and the resulting Au–SO42–/TiO2–RGO was
determined as an enhanced catalyst for hydration reaction. The strong metal–support interaction (SMSI) between Au and
TiO2 and the cooperative effect between Au and SO42–/TiO2 solid acid collectively account for the excellent performance.
Moreover, due to the versatile RGO substrate, the catalyst could also be recycled and reused for at least 5 times without
obvious deactivation.
employed support for Au NPs in heterogeneous catalysis.15ꢀ18
It has been reported that Au and TiO2 can form strong
support–metal interaction (SMSI) and promote the reactions in
1 Introduction
The hydration reaction is very important in organic synthesis,
which can produce valuable carbonyl derivatives from
accessible alkynyl substrates.1 In the last century, the most
extensively employed catalytic systems for this reaction are
mercury salts.2 Limited by their strong toxicity, green and
environment friendly catalysts are therefore needed. New
organometallic catalysts containing Ru,3 Rh,4 Pt,5 Au6ꢀ8 and
other metals have recently been developed and applied
successfully for this reaction. Although excellent catalytic
activities have been achieved, the homogeneous feature
limited their practical applications. These noble metal
containing catalysts are expensive and difficult to be separated
from the reaction system for recycle. Therefore, developing
efficient recyclable catalytic systems is an urgent task.
Heterogeneous catalysis using supported gold nanoparticles
(Au NPs) have been intensively explored in organic reactions
with great success.9ꢀ12 The catalytic performance of Au NPs
largely depends on the property of the support. In some cases,
the support can go further than being simple carriers.13, 14 They
can also form strong interactions with Au NPs and affect the
catalytic activity. On advantages of low cost, nontoxicity,
structural stability and safety, titania (TiO2) is the most widely
certain catalytic systems.19ꢀ21 Actually, to date, Au NPs
supported on TiO2 nanoparticles (Au–TiO2) have exhibited
high activity and selectivity in many important reactions, such
23
as photocatalytic degradation reactions,22,
hydrogen
production reactions,24, 25 hydrogenation reactions,26 oxidation
reactions27ꢀ29 and so on.30, 31
Considering its excellent catalytic performance, we
speculated Au–TiO2 might be an effective heterogeneous
catalyst for hydration reactions. However, despite of
heterogeneous feature, the separation and recycle process are
still difficult to be performed due to small particle size of the
Au–TiO2 composite. To facilitate the recycle process, a more
versatile support is needed for Au–TiO2. Considering the
advantages in facilitating the dispersion and mass transfer of
the supported catalysts in solvents,32 the twoꢀdimensional
reduced graphene oxide (RGO) possesses great potential as an
ideal substrate for Au–TiO2. Actually, many papers have
reported TiO2 supported on reduced graphene oxide (TiO2–
RGO), and the composite has been successfully employed as
catalysts for many reactions33ꢀ35. The strong interaction
between TiO2 and RGO36 confirms the excellent performance.
Hence, in this account, we designed a facile strategy to
synthesize a novel composite (Au–TiO2–RGO) as a catalyst
for hydration reactions. As seen in Scheme 1, TiO2
nanoparticles with anatase phase were firstly overlayed on the
twoꢀdimensional RGO nanosheets. Subsequently, tiny Au NPs
with uniform dispersion and size dimension (~4.5 nm) were
deposited on the sandwichꢀlike TiO2–RGO support. Finally,
with the assistance of microwave and the addition of sulfuric
acid, surface acid sites (SO42–/TiO2) with bridge bidentate
a.School of Chemical Engineering and Technology, State Key Laboratory of
Chemical Engineering, Collaborative Innovation Center of Chemical Science and
Engineering, Tianjin University, Tianjin 300072, China; Email:
xiaobinfan@tju.edu.cn (Xiaobin Fan); fbzhang@tju.edu.cn (Fengbao Zhang).
b.College of Chemical Engineering, State Key Laboratory of Heavy Oil Processing,
China University of Petroleum (East China), Qingdao 266580, China
† Electronic Supplementary Information (ESI) available: Preparation of Au–RGO,
Au–TiO2, Au–TiO2–RGOꢀ1 and Au–TiO2–RGOꢀ2, TEM image of Au–TiO2, C 1s
XPS spectra of GO and Au–TiO2–RGO, Full range XPS spectrum of Au–SO4
2–
/TiO2–RGO after 5 cycles. See DOI: 10.1039/x0xx00000x
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2–
structure was in-situ formed, and the obtained Au–SO4
/TiO2–RGO served as an enhanced catalyst for hydration
reaction. What’s more, owing to the versatile RGO substrate,
the catalyst could also be recovered and reused easily without
significant decrease of activity.
2.3 Catalytic hydration reaction
The catalytic reactions were conducted in a microwave reactor.
0.25 mmol of phenylacetylene, 25 mg of Au–SO42–/TiO2–
RGO (1 mol% equiv.), 0.5 mmol of deionized water and 1.0
mmol of sulfuric acid were added to 5 mL of dioxane. The
mixture was heated to 120 oC with the assistance of
microwave and stirred for 2 h. At the stated time, samples
were taken from the reaction mixture and analyzed by gas
chromatography (GC). For the recycling experiments, the
reactions were carried out under the same conditions. After
each run, the catalyst was recovered from the reaction mixture
by centrifugation, washed with ethanol and deionized water
three times, respectively, followed by freezeꢀdrying, and then
reused in next the run.
2.4 Characterization
The Xꢀray diffraction (XRD) was performed on a Brukerꢀ
Nonius D8 FOCUS diffractometer. Transmission electron
microscopic (TEM) and high resolution transmission electron
microscopic (HRTEM) images were recorded using a JEMꢀ
2100F transmission electron microscope operating at 200 kV.
Xꢀray photoelectron spectroscopy (XPS) measurements were
performed on a PHI 1600 spectrometer (PerkinꢀElmer).
Fourier transform infrared (FTIR) spectroscopy was carried
out on a Nicolet Nexus FTIR Spectrometer using KBr pellets
method. NH3 TemperatureꢀProgrammed Desorption (NH3ꢀ
TPD) was measured in a flowꢀtype fixedꢀbed reactor at
Scheme 1. Illustration of the preparation and structure of Au–SO42–/TiO2–RGO.
2 Experimental
2.1 Preparation of Au–TiO2–RGO
o
Graphite oxide (GO) was prepared by the Hummers method,37
and GO was obtained and purified as described in previous
studies.38 To prepare TiO2–RGO, 240 mg of GO and 3 mL of
tetrabutyl titanate were dispersed in 100 mL isopropanol by
sonication for 1 h. Subsequently, 3 mL of deionized water was
added dropwise, and the mixture was kept stirring for another
2 h. The solution was then transferred into a 150 mL Teflonꢀ
ambient pressure. 0.1 g sample was heated at 500 C for 2 h
o
o
and cooled to 120 C in flowing He. At 120 C, the sample
was treated by sufficient pulses of NH3 till adsorption
saturation, followed by a He purge for about 2 h. The
o
temperature was raised up from 120 to 500 C at a rate of 10
oC /min to desorb NH3 and maintained at 500 oC for 0.5 h. The
gold loading of the Au–TiO2–RGO composites was
spectrometer (ICPOES, VistaꢀMPX). The catalytic results
were measured by an Agilent 6890N GC using the standard
curve method.
o
lined stainless steel autoclave and heated at 180 C for 8 h.
GO could be reduced to RGO during the hydrothermal
process.36 The asꢀprepared TiO2–RGO was then purified by
centrifugation and washing with ethanol and deionized water
three times, respectively. To prepare Au–TiO2–RGO, TiO2–
RGO was firstly dispersed in 100 mL deionized water with
sonication for 0.5 h. 0.5 g of glucose and 0.5 g of sodium
citrate were then added into the suspension. After sonication
for another 5 min, 2.5 mL of chloroauric acid (HAuCl4) (0.02
M) was added to this mixture, and it was stirred for 4 h at
room temperature. The resulting mixture was centrifugated
and washed with deionized water three times, followed by
freezeꢀdrying.
3 Results and discussion
3.1 Characterization of Au–TiO2–RGO
The Xꢀray diffraction (XRD) pattern of the composite is
shown in Figure 1. The specific diffraction peaks of anatase
TiO2 and Au can be identified. They match well with the
standard patterns of anatase TiO2 (JCPDS card no. 21ꢀ1272)
and Au (JCPDS card no. 04ꢀ0784).
2.2 Preparation of Au–SO42–/TiO2–RGO
The Au–SO42–/TiO2–RGO was obtained during the hydration
reaction. 25 mg of Au–TiO2–RGO and 1.0 mmol of sulfuric
acid were added to 5 mL of dioxane. The mixture was heated
to 120 oC with the assistance of microwave and stirred for 2 h.
The asꢀprepared Au–SO42–/TiO2–RGO was then purified by
centrifugation and washing with ethanol and deionized water
three times, respectively.
2 |RSC Adv., 2016, 00, 1ꢀ3
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full range XPS spectrum of Au–TiO2–RGO, and an additional
signal of S appears in the spectrum of Au–SO42–/TiO2–RGO
(Figure 3a), indicating that Au–TiO2–RGO might be sulfated
during the reaction. Meanwhile, the content of S and Au are
estimated to be 4 atomic% and 0.2 atomic%, respectively. A
further study reveals the S band can be divided into two peaks
at binding energies of 168.5 and 169.6 eV, respectively,
corresponding to sulfur in a sixꢀoxidation state (S 6+) (Figure
3b).39 This result confirms the generation of SO42–/TiO2 solid
acid in the reaction process. The Ti and Au band of Au–TiO2–
RGO were also carefully analyzed. As seen in Figure 3c, Ti 2p
spectrum shows two peaks at 459.2 and 464.9 eV,
corresponding to the binding energies of Ti 2p 3/2 and Ti 2p
1/2.40 Au 4f spectrum exhibits two typical peaks at 83.7 and
87.4 eV, which correspond to the binding energy of Au (0)
(Figure 3d). Compared with the general binding energies of 4f
7/2 (84.0 eV) and 4f 5/2 (87.7 eV) for Au (0),41 the peaks shift
to lower value. Such phenomena reveals a charge transfer
from TiO2 to Au, and the SMSI between them can facilitate
the reaction rate.42 Moreover, compared with GO, C 1s XPS
spectrum of Au–TiO2–RGO shows a significant decrease in
the CꢀOꢀC and CꢀOH peaks at around 286.7 eV (Figure S2),
which indicates the GO precursor is partially reduced to RGO
in the hydrothermal process36. To study the stability of the
catalyst, the XPS spectrum of Au–SO42–/TiO2–RGO after 5
cycles is shown in Figure S3. The content of Au is estimated
as 0.2 atomic%, confirming the stability of Au–SO42–/TiO2–
RGO. Besides, S signal can also be seen, which further
confirms the generation of SO42–/TiO2 solid acid. However,
the content decreases to 1 atomic%, which might be caused by
loss of acid sites upon reuse.
- - - anatase TiO
- - - Au
2
20
30
40
50
60
70
80
2 Theta (Degree)
Figure 1. XꢀRay diffraction (XRD) pattern of Au–TiO2–RGO.
Figure 2a shows the transmission electron microscopic
(TEM) image of the Au–TiO2–RGO sample. As can be seen,
the RGO substrate is homogeneously and condensedly
decorated with TiO2 nanoparticles. Au NPs are dotted around
the TiO2 layer without any agglomeration. With narrow size
distribution, the average size of Au NPs and TiO2 are 4.5 nm
and 8.3 nm, respectively (Figure 2c, d) The high resolution
transmission electron microscopic (HRTEM) image in Figure
2b proves a very close contact between the three components,
and both of the characteristic finger lattices of TiO2 and Au
can be observed. The measured regular dꢀspacing of 0.352 nm
corresponds to the (101) face of the anatase TiO2, and the dꢀ
spacing of 0.235 nm is representative to the (111) face of the
Au nanocrystals. As a control, TEM image of Au–TiO2 was
also provided in the ESI† (Figure S1). As can be seen, TiO2
and Au would agglomerate seriously in the absence of RGO.
Therefore, the RGO substrate plays an important role on the
homogeneous dispersion of the catalytic sites.
(b)
989
1400
1214
3450
1049
1630
1136
(a)
1400
1220
3450
1630
4000 3500 3000 2500 2000 1500 1000
-1
Wavenumbers (cm )
Figure 4. FTIR spectra of (a) Au–TiO2–RGO and (b) Au–SO42–/TiO2–RGO.
The characteristic vibrational bands at 1214, 1136, 1049, and 989 cm−1
originated from the asymmetric and symmetric stretching vibration of the S=O
and S–O bonds.
Figure 2. (a) TEM and (b) HRTEM image of Au–TiO2–RGO; Size distribution
To further investigate the formation of surface SO42–/TiO2,
Fourier transform infrared (FTIR) spectra of Au–TiO2–RGO
and Au–SO42–/TiO2–RGO are provided in Figure 4. The
presence of peaks at around 3450 and 1400 cm−1 in both
spectra should be due to the absorbed water.
of (c) anatase TiO2 nanoparticles and (d) Au NPs.
The Xꢀray photoelectron spectroscopy (XPS) spectra of
Au–TiO2–RGO and Au–SO42–/TiO2–RGO are shown in
Figure 3. Au, Ti and C signals can be clearly observed in the
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(a)
(b)
Au-TiO2-RGO
Au-SO24-/TiO2-RGO
Raw
Sum
S 2p 3/2
S 2p 3/2
168.5 eV
169.6 eV
1200 1000 800 600
400
200
0
176
174
172
170
168
166
164
Binding EnAergy (eV)
Binding Energy (eV)
(d)
(c)
Raw
Raw
Sum
Ti 2p 1/2
Ti 2p 3/2
Sum
Au 4f 5/2
Au 4f 7/2
83.7 eV
459.2 eV
464.9 eV
87.4 eV
470 468 466 464 462 460 458 456 454
Binding Energy (eV)
92
90
88
86
84
82
80
Binding Energy (eV)
Figure 3. (a) Full range XPS spectra of Au–TiO2–RGO and Au–SO42–/TiO2–RGO; (b) S 2p XPS spectrum of Au–SO42–/TiO2–RGO; (c) Ti 2p and (d) Au 4f XPS
spectrum of Au–TiO2–RGO.
The band at about 1630 cmꢀ1 is attributed to inꢀplane vibration
mediumꢀstrong acid sites, the strong acid sites, and the super
strong acid sites, respectively.47 The ratio of four acidic peaks
is 0.61/0.65/1/0.16, indicating the Brønsted acid property of
Au–SO42–/TiO2–RGO.
of C=
C band, suggesting a partially reduction of GO.43 In the
spectrum of Au–TiO2–RGO, the peak at 1220 cm−1 should be
ascribed to the residual CꢀO groups of RGO. By contrast,
2–
characteristic frequencies of bidentate SO4 coꢀordinated to
3.2 Catalytic reaction
Ti4+ at 1214, 1136, 1049, and 989 cm−1 can be clearly
observed in Au–SO42–/TiO2–RGO. The result provides direct
evidence on the successful introducing of sulphate groups to
the TiO2 framework.44ꢀ46
The catalytic performance of the prepared catalyst was
systematically examined through the hydration of
phenylacetylene. As microwave is an efficient way to improve
catalytic performance, especially for solid acid involved
reactions,48 microwave was employed. Table 1 summarizes
the catalytic performance of different samples. In the absence
of H2SO4, all of the Au–RGO, Au–TiO2, Au–TiO2–RGO were
inactive (Entry 3, 5, 7). Pure H2SO4 without any catalyst
showed very low activity for the reaction (Entry 1). Therefore,
H2SO4 is an essential promoter for the reaction. With the
addition of H2SO4, RGO alone was hardly active (Entry 2).
When Au NPs was loaded (Au–RGO), the conversion and
yield reached up to 64% and 48%, respectively (Entry 4). The
result implied Au was a necessary active substance for
hydration process. Au–TiO2 showed a better performance,
resulting in 60% yield and 100% selectivity (Entry 6), which
should be attributed to the SMSI as probed above. Remarkably,
when Au–TiO2 was supported on RGO, namely Au–TiO2–
RGO, a yield of 100% could be achieved (Entry 9). It is worth
mentioning that TiO2–RGO exhibited a surprising conversion
of 63%, but a low selectivity (Entry 8). This should be mainly
ascribed to the significantly enhanced acidity of H2SO4 with
the assistance of the SO42–/TiO2 solid acid formed during the
reaction. 49 So the enhanced performance of Au–TiO2–RGO
should owe to not only the homogeneous dispersion and
promoted SMSI arising from the RGO substrate, but also the
in-situ formed SO42–/TiO2 acid
Medium-strong acid
(327 oC)
2.0
Strong acid
(396 oC)
Weak acid
(247 oC)
1.5
Super-strong acid
(486 oC)
1.0
0.5
0.0
200
300
400
500
Temperature (oC)
Figure 5. NH3ꢀTPD spectrum of Au–SO42–/TiO2–RGO.
The surface acidity of the Au–SO42–/TiO2–RGO is
measured by NH3ꢀTPD method. Four types of acid site can be
o
observed in Figure 5. The peak at 247 C should be generated
by weak adsorption in the low test temperature range. The
o
o
o
peaks at 327 C, 396 C and 486 C should correspond to the
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Table 1. Structural parameters and catalytic efficiencies in phenylacetylene hydration.a
Table 2. Alkyne hydrations over the Au–SO42–/TiO2–RGO catalyst.a
Conversion
(%)
Yield
(%)b
Entry
Substrate
Product
O
Au
H2SO4 Conversion Yield
Entry
Sample
(%)b
Br
1
2
100
96
99
94
Br
(mmol/g) (mmol)
(%)
1
2
Blank
RGO
/
1.0
1.0
0
14
15
0
11
11
0
O
/
3
Au–RGO
0.16
0.16
0.14
0.14
0.13
/
O
3
4
99
97
96
96
4
Au–RGO
1.0
0
64
0
48
0
O
5
Au–TiO2
6
Au–TiO2
1.0
0
60
0
60
0
aGeneral conditions: substrate (0.25 mmol), H2O (0.5mmol), dioxane (5 mL),
catalyst (1 mol% Au), H2SO4 (1.0 mmol), microwave heating at 120 oC, 2 h.
7
Au–TiO2–RGO
TiO2–RGO
bCalibrated yields determined by GC.
8
1.0
1.0
1.0
1.0
1.0
1.0
63
100
83
89
57
95
37
100
82
89
49
89
9
Au–TiO2–RGO
Au–TiO2–RGOꢀ1c
Au–TiO2–RGOꢀ2c
Au–TiO2–RGOd
Au–TiO2–RGOd
0.13
0.22
0.07
0.13
0.13
According to the catalytic results, a general mechanism has
been proposed to explain this catalytic process (Scheme 2).50
First of all, Au forms complex with the triple bond of
phenylacetylene. In this step, TiO2 bonds strong interactions
with the Au NPs to decrease surface energy of the
nanoparticles. So phenylacetylene can be more easily
adsorbed to the active sites and accelerate the catalytic cycle.51
Besides, charge transfer from RGO to Au–TiO2 further
regulates the strong interactions between Au and TiO2,
yielding electronꢀrich Au NPs, which are easier to form higher
valence gold species, thus rendering remarkable catalytic
performance. Subsequently, regioselective addition of water
happens, which is affected by the SMSI in Au–TiO2 and
generates desired acetophenone. Finally, acid catalyzed
reductive elimination of Au gives enol form, which rearranges
into keto form. With the assistance of microwave, the in-situ
formed solid acid SO42–/TiO2 may greatly facilitate this step.
Therefore, the enhanced catalytic performance should mainly
attributed to the SMSI between Au and TiO2, the versatile
RGO substrate, and the in-situ formed SO42–/TiO2 acid sites.
10
11
12
13
aGeneral conditions: phenylacetylene (0.25 mmol), H2O (0.5mmol), dioxane (5
mL), catalyst (1 mol% Au), microwave heating at 120 oC, 2 h.
bCalibrated yields determined by GC.
cAu–TiO2–RGO with different gold loading.
d Oil bath heating at 120 oC within 2h and 16 h.
sites. To optimize the loading weight of Au, Au–TiO2–RGO
with two more Au percentage were prepared (Entry 10, 11). It
was found that Au–TiO2–RGO with 0.13 mmol/g gold loading
showed the best catalytic activity. Controlling experiments
with oil bath heating were also conducted. Au–TiO2–RGO
gave a much lower conversion of 57% and yield of 49%
within the same time (Entry 12). When the reaction time was
extended to 16 h, the conversion and yield could just reach up
to 95% and 89%, respectively (Entry 13).
To demonstrate the universality of the Au–SO42–/TiO2–RGO,
different substrates with significant structural variation were
proceeded (Table 2). Au–SO42–/TiO2–RGO shows excellent
catalytic activity in the hydration of substrates with excellent
yields (94–99%). It can be noted that the presence of
substituent on the pꢀposition of benzene had very little
influence on the catalytic efficiencies, showing 100%
conversion and 99% yield for the corresponding product
(Entry 1). Importantly, when an unsymmetrical internal alkyne
engaged in the reaction, one exclusive regioisomer was
obtained in very high yield (94%, Entry 2). Aliphatic alkynes
also achieved excellent yield of 96% (Entry 3 and 4). The
catalytic results reveal that Au–SO42–/TiO2–RGO is a versatile
catalyst for hydration reaction.
Scheme 2. Plausible mechanism of the hydration of phenylacetylene.
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After the reaction, the solid catalyst can be easily recovered
from the reaction mixture by filtration or centrifugation. As
shown in Figure 6, the catalyst can be successively recycled
for 5 times without obviously decrease of the activity and
selectivity decreasing. According to the XPS results, we
speculate the drop in activity should be mainly ascribed to the
loss of acid sites. Metal leaching is also examined by ICP
analysis after each recycle, and no Au and Ti can be detected,
which is in accordance with the XPS analysis, revealing the
high stability of the catalyst.
2. S. Wang, C. Miao, W. Wang, Z. Lei and W. Sun, Chin. J.
Catal., 2014, 35, 1695ꢀ1700.
3. R. GarcíaꢀÁlvarez, A. E. DíazꢀÁlvarez, P. Crochet and V.
Cadierno, Rsc Adv., 2013, 3, 5889ꢀ5894.
4. L. Xu, L. Liu, Z. Wang and X. Fu, Chem. Commun., 2015,
51, 11896ꢀ11898.
5. H. Yuzawa, S. Yoneyama, A. Yamamoto, M. Aoki, K.
Otake, H. Itoh and H. Yoshida, Catal. Sci. Technol., 2013, 3,
1739ꢀ1749.
6. F. Li, N. Wang, L. Lu and G. Zhu, J. Org. Chem., 2015, 80
,
3538ꢀ3546.
7. A. Cavarzan, J. N. H. Reek, F. Trentin, A. Scarso and G.
Strukul, Catal. Sci. Technol., 2013, , 2898ꢀ2901.
8. T. Chen and C. Cai, Catal. Commun., 2015, 65, 102ꢀ104.
Conversion
3
Yield
100
9. B. Demir, F. B. Barlas, E. Guler, P. Z. Gumus, M. Can, M.
Yavuz, H. Coskunol and S. Timur, Rsc Adv., 2014,
34687ꢀ34695.
10. E. A. Artiukha, A. L. Nuzhdin, G. A. Bukhtiyarova, S. Y.
Zaytsev, P. E. Plyusnin, Y. V. Shubin and V. I.
4,
80
60
40
20
0
Bukhtiyarov, Catal. Sci. Technol., 2015,
11. Y. Ma, S. Qing, Z. Gao, X. Mamat, J. Zhang, H. Li, W. Eli
and T. Wang, Catal. Sci. Technol., 2015, , 3649ꢀ3657.
5, 4741ꢀ4745.
5
12. A. Corma and H. Garcia, Chem. Soc. Rev., 2008, 37, 2096ꢀ
2126.
13. A. Arcadi, Chem. Rev., 2008, 108, 3266ꢀ3325.
14. X. Wan, W. Deng, Q. Zhang and Y. Wang, Catal. Today
2014, 233, 147ꢀ154.
1
2
3
4
5
,
Recycle Runs
Figure 6. Catalyst recycling runs for alkyne hydration.
15. A. E. Lanterna, A. Elhage and J. C. Scaiano, Catal. Sci.
Technol., 2015, , 4336ꢀ4340.
16. K. Yang, C. Meng, L. Lin, X. Peng, X. Chen, X. Wang, W.
Dai and X. Fu, Catal. Sci. Technol., 2016, , 829ꢀ839.
17. Y. Choi, H. Kim, G. Moon, S. Jo and W. Choi, ACS Catal.
2016, , 821ꢀ828.
18. R. Daghrir, P. Drogui and D. Robert, Ind. Eng. Chem. Res.
2013, 52, 3581ꢀ3599.
19. D. W. Goodman, Catal. Lett., 2005, 99, 1ꢀ4.
20. A. Naldoni, F. Riboni, M. Marelli, F. Bossola, G. Ulisse,
A. D. Carlo, I. Pis, S. Nappini, M. Malvestuto and M. V.
5
4 Conclusions
6
,
,
In summary, we have prepared a novel Au–TiO2–RGO
composite with uniform and tiny Au NPs supported on layered
TiO2–RGO support. After treatment with microwave and
sulfuric acid, surface SO42–/TiO2 solid acid was in-situ formed.
The resulting Au–SO42–/TiO2–RGO was determined as an
enhanced and recyclable catalyst for the hydration. The SMSI
between Au and TiO2, versatile RGO substrate, and in-situ
formed SO42–/TiO2 account for the excellent performance.
The novel catalyst design strategy is readily extended to other
reaction systems with amazing catalytic performance.
6
Dozzi,
10.1039/C5CY01736J
21. C. T. Campbell, Nat. Chem., 2012,
22. D. Pang, L. Qiu, R. Zhu and F. Ouyang, Chem. Eng. J.
2015, 270, 590ꢀ596.
Catal.
Sci.
.
Technol.
,
2015,
DOI:
4, 597ꢀ598.
,
Acknowledgements
23. A. Bumajdad, M. Madkour, Y. AbdelꢀMoneam and M. Elꢀ
Kemary, J. Mater. Sci., 2013, 49, 1743ꢀ1754.
24. Z. Bian, T. Tachikawa, P. Zhang, M. Fujitsuka and T.
Majima, J. Am. Chem. Soc., 2013, 136, 458ꢀ465.
This study is supported by the National Natural Science Funds
for Excellent Young Scholars (No.21222608), Foundation for
the Author of National Excellent Doctoral Dissertation of
China (No.201251), Program for New Century Excellent
Talents in University (No. NCETꢀ12ꢀ0392) and the Program
of Introducing Talents of Discipline to Universities (No.
B06006).
25. J. Fang, L. Xu, Z. Zhang, Y. Yuan, S. Cao, Z. Wang, L.
Yin, Y. Liao and C. Xue, ACS Appl. Mater. Inter., 2013,
8088ꢀ8092.
5,
26. A. Corma and P. Serna, Science, 2006, 313, 332ꢀ334.
27. L. Liu, X. Gu, Y. Cao, X. Yao, L. Zhang, C. Tang, F. Gao
and L. Dong, ACS Catal., 2013, , 2768ꢀ2775.
3
28. A. Mahmood and S. I. Woo, Korean J. Chem. Eng., 2013,
30, 1876ꢀ1881.
29. D. I. Enache, J. K. Edwards, P. Landon, B. SolsonaꢀEspriu,
A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D.
Notes and references
1. F. X. Zhu, W. Wang and H. X. Li, J. Am. Chem. Soc., 2011,
133, 11632ꢀ11640.
6 |RSC Adv., 2016, 00, 1ꢀ3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 8
View Article Online
DOI: 10.1039/C6RA08021A
RSC Advances
ARTICLE
W. Knight and G. J. Hutchings, Science, 2006, 311, 362ꢀ
365.
30. M. M. Khan, S. A. Ansari, J. Lee and M. H. Cho, J. Ind.
Eng. Chem., 2013, 19, 1845ꢀ1850.
31. C. Lin, Y. Song, L. Cao and S. Chen, ACS Appl. Mater.
Inter., 2013, 5, 13305ꢀ13311.
32. Q. Zhao, C. Bai, W. Zhang, Y. Li, G. Zhang, F. Zhang and
X. Fan, Ind. Eng. Chem. Res., 2014, 53, 4232ꢀ4238.
33. W. Q. Fan, Q. H. Lai, Q. H. Zhang and Y. Wang, J. Phys.
Chem. C, 2011, 115, 10694ꢀ10701.
34. X. Liu, L. Pan, T. Lv and G. Zhu, RSC Adv., 2011, 47
,
11984ꢀ11986.
35. M. S. Shah, A. R. Park, K. Zhang, J. H. Park and P. J. Yoo,
ACS Appl. Mat. Inter., 2012, , 3893ꢀ3901.
4
36. X. Y. Zhang, H. P. Li, X. L. Cui and Y. Lin, J. Mater.
Chem., 2010, 20, 2801ꢀ2806.
37. W. S. Hummers, R. E. Offeman, W. S. Hummers and R. E.
Offeman, J. Am. Chem. Soc., 1958, 80, 1339ꢀ1339.
38. Y. Li, X. Fan, J. Qi, J. Ji, S. Wang, G. Zhang and F. Zhang,
Mater. Res. Bull., 2010, 45, 1413ꢀ1418.
39. G. X. Yu, D. L. Lin, Y. Hu, X. L. Zhou, C. L. Li, L. F.
Chen and J. A. Wang, Catal. Today, 2011, 166, 84ꢀ90.
40. B. Hao, Y. Yan, X. Wang and G. Chen, Nanoscale, 2013,
5
, 10472ꢀ10480.
41. Y. Wang, J. Yu, W. Xiao and Q. Li, J. mater. Chem. A
2014, , 3847ꢀ3855.
,
,
2
42. Z. Xu, J. Yu and G. Liu, Electrochem. Commun., 2011, 13
1260ꢀ1263.
43. Q. Zhao, Y. Li, R. Liu, A. Chen, G. Zhang, F. Zhang and
X. Fan, J. Mater. Chem. A, 2013, , 15039ꢀ15045.
1
44. J. L. RoperoꢀVega, A. AldanaꢀPérez, R. Gómez and M. E.
NiñoꢀGómez, Appl. Catal. A-Gen., 2010, 379, 24ꢀ29.
45. W. Li, F. Ma, F. Su, L. Ma, S. Zhang and Y. Guo,
ChemSusChem, 2011, 4, 744ꢀ756.
46. X. Wang, J. C. Yu, P. Liu, X. Wang, W. Su and X. Fu, J.
Photoch. Photobio. A, 2006, 179, 339ꢀ347.
47. P. Chen, M. Du, H. Lei, Y. Wang, G. Zhang, F. Zhang and
X. Fan, Catal. Commun., 2012, 18, 47ꢀ50.
48. B. Krishnakumar, R. Velmurugan and M. Swaminathan,
Catal. Commun., 2011, 12, 375ꢀ379.
49. S. Liang, G. B. Hammond and B. Xu, Chem. Commun.
2015, 51, 903ꢀ906.
,
50. M. Hassam and W. S. Li, Tetrahedron, 2015, 71, 2719ꢀ
2723.
51. J. A. Rodriguez, P. J. Ramírez, A. Gian Giacomo, V. E.
Francesc, E. Jaime, L. Ping, J. M. Ricart and I. Francesc,
Angew. Chem., 2014, 53, 11270–11274.
This journal is © The Royal Society of Chemistry 20xx
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A novel composite (Au–SO42–/TiO2–RGO) is synthesized and serves as an enhanced catalyst
for alkyne hydration.