Periodic mesoporous organogold(I)silica as an active and reusable catalyst for alkyne hydration

Article abstract of DOI:10.1016/j.molcata.2010.11.020

A periodic mesoporous organogold(I)silica catalyst was synthesized by surfactant-directed co-condensation of Au[PPh₂(CH₂) ₂Si(OCH₂CH₃)₃]₂Cl and (CH₃CH₂O)₃SiPhSi(OCH₂CH ₃)₃. The as-prepared Au-PPh₂-PMO(Ph) contained ordered mesopore channels with both phenyl (Ph) group and Au(I) organometal homogeneously embedded in silica walls. Such catalyst exhibited higher activity than free Au(PPh₃)Cl in hydration reactions of various terminal alkynes. This could be mainly attributed to the high surface area, the ordered mesoporous channels and the enhanced surface hydrophobility, which facilitated the diffusion and adsorption of reactants. Meanwhile, the unique coordination model between Au(I) and (PPh₂) was also favorable for the alkyne hydration. Besides the high activity, the catalyst could be easily recycled and used repetitively owing to the high hydrothermal stability and the stabilized Au(I) active sites against leaching.

Full text of DOI:10.1016/j.molcata.2010.11.020

Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Periodic mesoporous organogold(I)silica as an active and reusable catalyst for
alkyne hydration
Fengxia Zhu, Fang Zhang, Xushi Yang, Jianlin Huang, Hexing Li∗
The Education Ministry Key Lab. of Res. Chem., Shanghai Normal University, Shanghai 200234, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
periodic mesoporous organogold(I)silica catalyst was synthesized by surfactant-directed co-
Received 16 September 2010
Received in revised form
11 November 2010
Accepted 17 November 2010
Available online 24 November 2010
condensation of Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl and (CH3CH2O)3SiPhSi(OCH2CH3)3. The as-prepared
Au–PPh2–PMO(Ph) contained ordered mesopore channels with both phenyl (Ph) group and Au(I)
organometal homogeneously embedded in silica walls. Such catalyst exhibited higher activity than free
Au(PPh3)Cl in hydration reactions of various terminal alkynes. This could be mainly attributed to the high
surface area, the ordered mesoporous channels and the enhanced surface hydrophobility, which facil-
itated the diffusion and adsorption of reactants. Meanwhile, the unique coordination model between
Au(I) and (PPh2) was also favorable for the alkyne hydration. Besides the high activity, the catalyst could
be easily recycled and used repetitively owing to the high hydrothermal stability and the stabilized Au(I)
active sites against leaching.
Keywords:
Immobilization of homogeneous catalyst
Periodic mesoporous organogold(I)silica
[Au–PPh2–PMO(Ph)]
© 2010 Elsevier B.V. All rights reserved.
Phenyl (Ph)-functionalization [PMO(Ph)]
Hydration reaction of terminal alkyne
1. Introduction
Periodic mesoporous organosilicas (PMO) with organic groups
(e.g. methyl, ethyl, phenyl, biphenyl and amine) homogeneously
Organometallic catalysts have been widely used in organic syn-
thesis owing to the high activity and selectivity [1,2]. However,
it was limited in practical application because of the complicated
separation procedures from the reaction mixture as well as the dif-
ficulties in recycling, which will inevitably lead to high cost and
even environmental pollutions from heavy metallic ion [3,4]. Het-
erogeneous catalysts could overcome these limitations, but they
usually displayed poor catalytic activity and selectivity [5–8] due to
the low dispersion of active sites, the enhanced diffusion limit, and
the change of chemical microenvironment of active sites. Meso-
porous silica supports with high surface and ordered mesopore
channels allow to prepare immobilized organometallic catalysts
with high dispersion and low diffusion limit [9,10]. Meanwhile, the
functionalization with organic groups could enhance the surface
hydrophobicity which may facilitate the diffusion and adsorption
of organic reactant molecules, especially in aqueous medium [11].
However, the organometals and organic functionalities terminally
bonded to the pore surface might partially block the pore channels,
which might disfavor the catalytic efficiency. Moreover, they would
easily suffer from leaching during liquid phase reactions, leading to
the poor durability [12–14].
embedded in silica walls could diminish the pore blockage and also
inhibit the leaching of organic functionalities [15–19]. Previously,
we developed a general strategy to design periodic mesoporous
organometalsilica catalysts with organometals and organic groups
as the integral part of the pore walls [12,13]. Herein, as the con-
tinueous research studies of powerful immobilized catalysts, we
report the synthesis of a periodic mesoporous organogold(I)silica
catalyst with both Au(I) organometals and phenyl groups (Ph) inte-
graly incorporating into silica framework. Its catalytic performance
was evaluated in hydration reactions of various terminal alkynes,
which showed both high activity and strong durabilty comparing to
the similar catalyst with Au(I) organometals terminally bonded to
the Ph-bridged PMO support or even the Au(PPh3)Cl homogeneous
catalyst.
2. Experimental
2.1. Catalyst preparation
Firstly,
synthesized
Au(tht)Cl
the
by
(tht = tetrahydrothiophene)
Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl
was
0.064 g
0.15 mL
mixing
10 mL
CH2Cl2,
and
PPh2CH2CH2Si(OCH2CH3)3 under argon atmosphere, followed
by stirring at 25 ◦C for 2 h. The solid product was collected by
evaporating CH2Cl2, followed by washing with dried petroleum
ether and drying under vacuum at 25 ◦C for 24 h. Then, the periodic
∗
Corresponding author. Tel.: +86 21 64322272; fax: +86 21 64322272.
E-mail address: Hexing-Li@shnu.edu.cn (H. Li).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.11.020

2
F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
Scheme 1. Illustration of preparing Au–PPh2–PMO(Ph).
mesoporous organogold(I)silica, denoted as Au–PPh2–PMO(Ph),
was prepared according to the procedures illustrated in Scheme 1.
In a typical run of synthesis, 1.3 mL 37% HCl aqueous solution,
0.40 g poly(oxyethylene) (10) stearyl ether (Brij 76) and 0.76 g
(CH3CH2O)3SiPhSi(OCH2CH3)3 were mixed in 19 mL distilled H2O.
After being prehydrolyzed for 20 min at 50 ◦C, 1.0 mL tetrahydro-
furan (THF) containing 0.16 g Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl
was added into the solution, followed by stirring at 50 ◦C for
12 h and aging at 100 ◦C for another 24 h. The molar ratio of
Si:Brij76:HCl:H2O was 1.0:0.17:6.0:417, where Si referred to the
total silicon source. The solid product was filtrated and dried under
vacuum for 24 h. Finally, the surfactants and other organic sub-
stances were extracted and washed away by refluxing in ethanol
solution at 80 ◦C for 24 h. The Au(I) loading was determined as
0.22 wt% by ICP analysis.
isotherms were measured at 77 K on a Quantachrome NOVA 4000e
analyzer, from which the specific surface area (SBET) was cal-
culated by applying Brunauer–Emmett–Teller (BET) method and
Barrett–Joyner–Halenda (BJH) model on the adsorption branches,
respectively. Meanwhile, the average pore diameter (DP) and total
pore volume (VP) were calculated from the adsorption isotherms
using Barrett–Joyner–Halenda (BJH) model. Surface morpholo-
gies and porous structures were observed through a transmission
electron microscopy (TEM, JEOL JEM2011). The surface electronic
states were analyzed by X-ray photoelectron spectroscopy (XPS,
Perkin-Elmer PHI 5000C). All the binding energy (BE) values were
calibrated by using the standard BE value of contaminant carbon
(C1S = 284.6 eV) as a reference.
For comparison, the Au(I) organometal was also immo-
bilized onto Ph-bridged PMO support via grafting method
and denoted as Au–PPh2–PMO(Ph)–G. Briefly, 0.40 g Brij 76,
1.3 mL 37% HCl, 0.76 g (CH3CH2O)3SiPhSi(OCH2CH3)3 and 0.070 g
PPh2CH2CH2Si(OCH2CH3)3 were mixed in 19 mL distilled H2O.
After stirring for 12 h at 50 ◦C, the mixture was transferred into
an autoclave for 24 h hydrothermal treatment at 100 ◦C. The solid
product, denoted as PPh2–PMO(Ph), was collected and extracted
in ethanol solution at 80 ◦C for 24 h to remove Brij76 and other
organic residues. Then, 1.0 g PPh2–PMO(Ph) and 0.049 g Au(PPh3)Cl
were mixed in 10 mL toluene solution and stirred for 24 h at room
temperature. The solid product was dried at 80 ◦C under vacuum,
followed by Soxlet-extraction with CH2Cl2 for another 24 h to
remove physisorbed Au(I) species on the support. The Au(I) loading
was determined as 0.26 wt% by ICP analysis.
2.3. Activity test
The hydration reactions of terminal alkynes (see Scheme 2)
were carried out at 100 ◦C in a 10 mL round-bottomed flask by
adding a catalyst containing 0.010 mmol Au(I), 0.25 mmol alkyne,
0.25 mmol H2SO4, 4.0 mL distilled water and n-decane as an inter-
nal standard. After stirring for 7 h, the products were extracted
by acetic ether, followed by analysis on a gas chromatograph
(SHIMADZU, GC-17A) equipped with a JWDB-5, 95% dimethyl-1-
(5%)-diphenylpolysiloxane column and a FID detector. The column
temperature was programmed from 80 to 250 ◦C at a ramp speed
of 10 ◦C/min N2 was used as carrier gas. The reproducibility was
checked by repeating each result at least three times and was found
to be within 5%.
In order to determine the catalyst durability, the catalyst was
allowed to centrifuge after each run of reactions and the clear
supernatant liquid was decanted slowly. The catalyst was washed
thoroughly with distilled water and ethanol, followed by drying
at 80 ◦C for 8 h under vacuum condition. Then, the catalyst was
reused with fresh charge of reactants for subsequent recycle under
the identical reaction conditions.
2.2. Characterization
The compositions and Au(I) loadings were determined by ele-
mental analysis (Elementar Vario ELIII, Germany) and inductively
coupled plasma optical emission spectrometer (ICP-OES, Varian
VISTA-MPX). Fourier transform infrared (FTIR) spectra were col-
lected on a Nicolet Magna 550 spectrometer by using the KBr
method. Solid-state NMR spectra were recorded on a Bruker AV-
400 spectrometer. Thermogravimetric analysis and differential
thermal analysis (TG/DTA) were conducted on a DT-60. Low-angle
X-ray powder diffraction (XRD) patterns were obtained on a Rigaku
D/maxr B diffractometer with Cu Ka. N2 adsorption–desorption
O
H+, Catalyst
H2O
RC CH
R
C CH3
Scheme 2. Chemical equation of the hydration reactions with terminal alkynes.

F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
3
T2
29Si MAS
T3
T1
50
0
-50
-100
-150
Chemical Shift (ppm)
Cph
13C CP MAS
*
150
100
50
0
-50
-100
Chemical Shift (ppm)
*
C2
C1
Si-O -Et
Fig. 1. 31P NMR spectrum of Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl.
*
250
200
150
100
50
0
-50
3. Results and discussion
Chemical Shift (ppm)
3.1. Structural characteristics
31P CP MAS
The
composition
and
chemical
formula
of
the
Au(I) organometal-brideged silane were determined as
Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl based on ICP analysis (P/Au
molar ratio = 2.01), elemental analysis (calculated: C 49.45, H
5.45; experimental: C 49.25, H 5.55), melting point test (125 ◦C),
1H NMR (CDCl3): ı = 7.7–7.3 (m, 20 H, Ph); 3.6 (q, 12H), 2.50
(m, 4 H, CH2–P); 1.1 (t, 18H, Me); 0.60 (m, 4 H, SiCH2), and 31P
NMR spectrum (see Fig. 1). The FTIR spectra (Fig. 2) displayed no
significant signals indicative of Brij76, implying that the surfactant
in Au–PPh2–PMO(Ph) was mostly removed after extraction in
ethanol. The Au–PPh2–PMO(Ph) exhibited three absorbance bands
at 1064, 1152, and 1449 cm−1 characteristic of the vibrations
from Si–O, Si–C and P–C bonds [20,21], which were similar to
those observed in Au[PPh2CH2Ch2Si(OCH2CH3)3]2Cl, indicating the
successful incorporation of Au(I) organometal into the silica frame-
work. The other three peaks around 640, 1377 and 3050 cm−1 could
be assigned to ı(C–H), ␯(C–C) and ␯(C–H) vibrations from benzene
ring [22,23]. As shown in Fig. 3, the 29Si MAS NMR spectrum
revealed that the Au–PPh2–PMO(Ph) displayed three peaks down-
field corresponding to T1 (ı = −64 ppm), T2 (ı = −74 ppm) and T3
(ı = −79 ppm), where Tm = RSi(OSi)m–(OH)3-m, m = 1–3. No Qn peaks
*
*
*
*
150
100
50
0
-50
-100
Chemical Shift (ppm)
Fig. 3. Solid NMR spectra of Au–PPh2–PMO(Ph).
were observed, where Qn = Si(OSi)n–(OH)4-n, n = 2–4, indicating
that all the Si species were covalently bonded with carbon atoms
[24]. Meanwhile, two peaks around 18 and 38 ppm were observed
in the 13C CP MAS NMR spectrum, which could be assigned to two
C atoms in the –CH2–CH2– group connecting with the PPh2-group.
An intense peak around 135 ppm could be attributable to the C
atoms in the benzene ring (Ph). A weak peak around 59 ppm was
assigned to the C atoms in the C2H5O-group connecting with
silicon due to the incomplete hydrolysis [25]. Other peaks denoted
by asterisks were ttributed to spinning sidebands, as verified by
changing rotating speeds [26]. In addition, the 31P CP MAS NMR
spectrum revealed that the Au–PPh2–PMO(Ph) displayed only one
signal at 45 ppm indicative of P atom in the PPh2-group, similar to
that found in the Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl, indicating the
unique coordination model between PPh2 and Au(I). These results
clearly demonstrated the presence of both the Au(I) organometal
and the Ph group in the Au–PPh2–PMO(Ph).
Au[PPh CH CH Si(OEt) ] Cl
Au-PPh -PMO(Ph)
Fig. 4 shows TG/DTA curves of the Au–PPh2–PMO(Ph). A weak
endothermic peak around 65 ◦C with weight loss of about 7% could
be attributed to desorption of water, CH2Cl2, ethanol or other
organic residues. An exothermic peak around 283 ◦C with weight
loss less than 1% could be assigned to the oxidation removal of
residual C2H5O-groups connecting with silicon due to the incom-
plete hydrolysis (see the 13C CP MAS NMR spectrum in Fig. 3). A
broad exothermic peak ranging from 320 to 500 ◦C with weight
loss around 7% might be responsible for the oxidation removal of
–PPh2–CH2CH2– groups bridging Au(I) and Si. An intense exother-
640
1377
3050
1449
1152
1064
4000
3500
3000
2500
2000
1500
1000
500
Wavelength (cm-1)
Fig. 2. FTIR spectra of the Au[PPh2CH2CH2Si(OEt)3]2Cl and Au–PPh2–PMO(Ph).

4
F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
612 oC
100
80
283 oC
400
300
200
100
65 oC
60
200
400
600
800
1000
Temperature (ºC)
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Fig. 4. TG and DTA curves of Au–PPh2–PMO(Ph).
Fig. 6. N2 adsorption–desorption isotherm of Au–PPh2–PMO(Ph).
mic peak at 612 ◦C corresponding to weight loss around 28% was
resulted from the oxidation removal of phenyl groups embedded in
silica walls [24,27]. The weight losses were consistent with the the-
oretical values, which further confirmed the presence of both the
Au(I) organometals and the Ph groups in the Au–PPh2–PMO(Ph).
As shown in Fig. 5, the XPS spectra demonstrated that all the Au
species in the Au–PPh2–PMO(Ph) were present in +1 oxidation state
[28], corresponding to the binding energy around 85.2 eV in Au4f7/2
level. The single XPS peak in Au4f7/2 level further confirmed the sole
coordination model between the Au(I) ion and the PPh2–ligand.
In comparison with free Au(PPh3)Cl, the Au(I) binding energy in
the Au–PPh2–PMO(Ph) shifted negatively by 0.3 eV, possibly due
100
110 200
5
to the stronger electron-donating ability of P in the PPh2(CH2CH2)
ꢀ
than that in the PPh3, taking into account that
tem between P and three phenyl groups could dilute the electron
density on the P atom.
conjugated sys-
Fig. 6 revealed that the Au–PPh2–PMO(Ph) displayed a typical IV
type N2 adsorption–desorption isotherm with a H1 hysteresis loop
indicative of the mesoporous structure [29]. The low-angle XRD
pattern (Fig. 7) showed an intense peak around 2ꢀ = 1.5◦ indicative
of (1 0 0) diffraction and two additional weak peaks at higher 2ꢀ val-
ues corresponding to (1 1 0) and (2 0 0) diffractions. These results
demonstrated that the Au–PPh2–PMO(Ph) contained ordered 2-
dimensional P6mm hexagonal mesporous channels [30], which was
further confirmed by TEM images along [1 1 0] and [1 0 0] directions
(Fig. 8).
1
2
3
4
5
2 Theta (degree)
Fig. 7. Low-angle XRD patterns of Au–PPh2–PMO(Ph). The attached is the magnified
pattern with 2ꢀ ranging from 1.72◦ to 3.42◦.
Theco-condensation between Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl
and (CH3CH2O)3SiPhSi(OCH2CH3)3 resulted in two kinds of prod-
ucts. The first kind of product contained Au(I) organometals
incorporated into the pore walls of the PMO(Ph) support, as
described Scheme 1. The other contained Au(I) organometals
terminally bonded to the pore surface (see Scheme 3). Unfor-
tunately, we could not find a direct evidence for distinguishing
these two models. Dufaud pointed out that the organometals
incorporated in the pore walls had no significant influence on
the pore diameter while the organometals terminally bonded to
the pore surface might narrow the pore channels [14]. Based
on such a conclusion, we prepared the Au–PPh2–PMO(Ph)–Gꢀ by
grafting the Au[PPh2(CH2)2Si(OCH2CH3)3]2Cl onto the PMO(Ph)
support with all the Au(I) organometals stayed on the pore sur-
85.5 eV
Au4f7/2
Au(PPh3)Cl
Au-PPh2-PMO(Ph)
85.2 eV
Au
PPh2
Si
Ph2P
Si
O
O
O
O
O
85
90
95
-O-Si-Ph-Si-O-Si-Ph-Si-O-Si Wall
Binding Energy (eV)
Scheme 3. Structural model of the Au–PPh2–PMO(Ph)–Gꢀ with the Au(I)
organometals terminally bonded to the PMO(Ph) pore surface.
Fig. 5. XPS spectra of Au(PPh3)Cl and Au–PPh2–PMO(Ph) samples.

F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
5
Fig. 8. TEM images of Au–PPh2–PMO(Ph) viewing along [1 1 0] and [1 0 0] directions.
face. Then, we determined pore size distribution of PMO(Ph),
Au–PPh2–PMO(Ph) and Au–PPh2–PMO(Ph)–Gꢀ. As shown in Fig. 9,
the Au–PPh2–PMO(Ph) displayed similar pore diameter to the
PMO(Ph) (3.1 nm), while the Au–PPh2–PMO(Ph)–Gꢀ displayed
smaller pore diameter (2.8 nm) than the PMO(Ph). These results
implied that the Au(I) organometals in the Au–PPh2–PMO(Ph) were
possibly incorporated into the silica walls rather than grafted onto
the pore surface.
ings. A reasonable explanation was that the Au(I) organometal in
the Au–PPh2–PMO(Ph) were embedded into the silica walls. While,
the Au(I) organometal in Au–PPh2–PMO(Ph)–G were terminally
bonded to the pore surface, which might partially block the meso-
porous channels, leading to low SBET, DP and VP.
3.2. Catalytic performances
A key consideration of the Au–PPh2–PMO(Ph) catalyst is the
location of Au(I) species since they should contact with reactant
molecules. The bromination test was used to confirm that the
vinyl groups in the vinyl-bridged PMO were chemically accessi-
ble [16]. To make sure that the Au(I) organometals incorporated
into PMO(Ph) pore walls were chemically accessible to the reac-
tant molecules, the Au–PPh2–PMO(Ph) was allowed to react with
KMnO4 aqueous solution. Only the Au(I) organometals chemically
accessible could be oxidized by KMnO4 while those Au(I) embedded
in silica walls could not be oxidized. After complete reaction, the
unreacted KMnO4 was titrated by Na2C2O4, from which the amount
of Au(I) species was determined. The total Au(I) species were also
determined by ICP analysis. The molar ratio between Au(I) species
determined by KMnO4 oxidation and by ICP was 93%, suggesting
that most of Au(I) active sites in the Au(I)–PPh2–PMO(Ph) were
chemically accessible for catalytic reactions.
Table 1 summarized the performances of three kinds of Au(I)
organometallic catalysts in hydration of phenylacetylene. Besides
the unreacted phenylacetylene, only acetophenone was detected
by GC–MS analysis, indicating that all these catalysts were almost
absolutely selective. The Au–PPh2–PMO(Ph) exhibited much higher
activity than the Au–PPh2–PMO(Ph)–G, obviously owing to the
higher SBET and larger DP which facilitated the diffusion and adsorp-
tion of reactant molecules. The kinetic studies demonstrated that
hydration reaction was first order with respect to alkyne con-
centration but zero order to water concentration under present
conditions, implying the saturated water adsorption while the
unsaturated alkyne adsorption on the catalyst. Thus, the enhanced
alkyne adsorption could promote the alkyne hydration. To our
surprise, the Au–PPh2–PMO(Ph) was even more active than free
Au(PPh3)Cl catalyst. One possible reason was the change of coor-
dination model from PPh3–Au–Cl to PPh2–Au–PPh2, which might
be more efficiency as the chemical microenvironment of Au(I)
active sites for the alkyne hydrogenation. Meanwhile, the pres-
ence of phenyl groups in the silica walls might enhance the
surface hydrophobolity of the catalyst, which facilitated the alkyne
adsorption, especially in aqueous solution. Furthermore, accord-
ing to the FT-IR spectra of pyridine adsorption (Fig. 10), the
PPh2–PMO(Ph), PMO(Ph) and Au–PPh2–PMO(Ph) displayed Lewis
acidic sites around 1572, 1594 and 1446 cm−1 [31], which might
also promote the alkyne hydration [32–34]. Similarly, addition of
little amount of H2SO4 during alkyne hydration could also enhance
the catalytic activity of Au(PPh3)Cl (see Fig. 11). Although the
weaker acidity, the Au(I) organometallic catalyst still exhibited
higher activity in the presence of Lewis acid than that in the pres-
ence of H2SO4, which could be attributed to the stronger promoting
effect of Lewis acid [32–34]. Table 1 also demonstrated that both
the PMO(Ph) and the PPh2–PMO(Ph) displayed no significant activ-
ities for the phenylacetylene hydration in the presence of H2SO4.
Thus, the Au(I) organometals acted as the active center, while
the acidic sites acted as the co-catalyst. To make sure whether
the heterogeneous Au(I) anchored on the support or homoge-
neous Au(I) leached from the support was the real catalyst, the
following experiments were carried out according to the proce-
dure proposed by Sheldon et al. [35]. After reaction for 3 h with
the conversion exceeding 45%, the solid catalyst was filtered out
Some structural parameters including surface area (SBET), pore
diameter (DP) and pore volume (VP) were summarized in Table 1.
Obviously, the Au–PPh2–PMO(Ph) exhibited much higher SBET, DP
and VP than the Au–PPh2–PMO(Ph)–G with the similar Au load-
0.8
PMO(Ph)
Au-PPh2-PMO(Ph)
Au-PPh2-PMO(Ph)-G'
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
14
Pore size (nm)
Fig. 9. Pore size distribution curves of PMO(Ph), Au–PPh2–PMO(Ph) and
Au–PPh2–PMO(Ph)–Gꢀ samples.

6
F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
Table 1
Structural parameters and catalytic efficiencies of different catalysts in water-medium hydration of benzyl acetylene.a
Sample
Au loading (wt%)
SBET (m2/g)
DP (nm)
VP (cm3/g)
Yield (%)
b
PMO(Ph)
PPh2–PMO(Ph)
Au(PPh3)Cl
–
–
–
968
802
–
3.2
3.1
–
0.85
0.63
–
–
–
b
24
Au–PPh2–PMO(Ph)–G
Au–PPh2–PMO(Ph)
Used Au–PPh2–PMO(Ph)d
0.26
0.22
0.20
561
892
824
2.8
3.1
3.1
0.40
0.69
0.61
21 (24)c
91
90
a
Reaction conditions: a catalyst containing 0.010 mmol of Au, 0.25 mmol phenylacetylene, 0.25 mmol H2SO4, 4 mL H2O, n-decane as an internal standard, tempera-
ture = 100 ◦C, reaction time = 7 h.
b
Too low to be detected.
c
The value in the parenthesis was obtained on the Au–PPh2–PMO(Ph)–G catalyst prepared by using Au(tht)Cl instead of Au(PPh3)Cl as gold source.
After being used repetitively for three times.
d
100
80
60
40
(a)
(b)
(c)
20
0
1400
1500
1600
1700
1800
1900
2000
Wavelength (cm-1)
0.0
0.5
1.0
1.5
H2SO4 (mmol)
Fig. 10. FT-IR spectra of pyridine adsorption on (a) PPh2–PMO(Ph), (b) PMO(Ph),
and (c) Au–PPh2–PMO(Ph) at room temperature.
Fig. 11. Effect of the H2SO4 concentration on the yield of acetophenone duing
hydration of benzyl acetylene catalyzed by un-immobilized Au(PPh3)Cl. Reaction
conditions: Au(PPh3)Cl catalyst containing 0.010 mmol of Au, 0.25 mmol benzyl
acetylene, 4.0 mL H2O, reaction temperature = 100 ◦C, reaction time = 7 h.
and the liquid solution was allowed to react for another 7 h under
identical reaction conditions. No significant change in either the
alkyne conversion or the yield of product was observed, indicat-
ing that the active phase was not the Au(I) species leached from
the Au–PPh2–PMO(Ph). Therefore, it is reasonable to conclude that
the present catalysis was really heterogeneous in nature. Besides
the higher activity, the Au–PPh2–PMO(Ph) also showed superior-
ity over the free Au(PPh3)Cl catalyst since it could also be easily
recycled and used repetitively. On one hand, the Au(I) organomet-
als embedded in silica walls could effectively inhibit the leaching
of Au(I) active sites, which had been confirmed by ICP analysis
(see Table 1). On the other hand, the Au(I) organometals embed-
ded in silica walls might also enhance the hydrothermal stability
of Au–PPh2–PMO(Ph) [36]. As shown in Fig. 12, both the low-angle
XRD pattern and the TEM images demonstrated the preservation
of ordered mesoporous structure in the Au–PPh2–PMO(Ph) catalyst
after being used repetitively for 3 times, corresponding to the high
SBET, VP and DP values (see Table 1).
The catalytic behaviors of the Au–PPh2–PMO(Ph) were also
examined in hydration reactions with other terminal alkynes. As
shown in Table 2, the Au–PPh2–PMO(Ph) also exhibited higher
activity than the Au(PPh3)Cl. It was also found that hydration of ter-
minal aliphatic alkynes and phenylacetylene derivatives containing
electron-donating groups exhibited higher activity and yield to tar-
get products than those containing electron-withdrawing groups
since alkyne hydration was electrophilic in nature [37,38].
Fig. 12. The low-angle XRD pattern (a) and the TEM images viewing along [1 0 0] and [1 1 0] directions (b) of the Au–PPh2–PMO(Ph) after being used repetitively for 3 times.

F. Zhu et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 1–7
7
Table 2
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We are grateful to the National Natural Science Foundation of
China (20825724), Chinese Education Committee (20070270001)
and Shanghai Government (S30406).