Palladium supported on functionalized mesoporous silica as an efficient catalyst for Suzuki-Miyaura coupling reaction

Article abstract of DOI:10.1007/s10562-013-1054-y

Mesoporous SBA-15 was modified with organic functional groups by co-condensation method. The functionalized mesoporous silica can be loaded with palladium and the resulting material used as a catalyst for the Suzuki-Miyaura coupling reactions. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy. The Pd-SBA-15 nanocomposite with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Suzuki-Miyaura coupling reaction. The catalyst can also be reused at least six recycles in air with only a minor loss of activity. Graphical Abstract: Mesoporous SBA-15 was modified with organic functional groups by co-condensation method. The functionalized mesoporous silica can be loaded with palladium and the resulting material used as a catalyst for the Suzuki-Miyaura coupling reactions. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy. The Pd-SBA-15 nanocomposite with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Suzuki-Miyaura coupling reaction. The catalyst can also be reused at least six recycles in air with only a minor loss of activity.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-013-1054-y

Catal Lett (2013) 143:1188–1194
DOI 10.1007/s10562-013-1054-y
Palladium Supported on Functionalized Mesoporous Silica
as an Efficient Catalyst for Suzuki–Miyaura Coupling Reaction
•
Guoheng Zhang Peiyu Wang Xiufang Wei
•
Received: 23 April 2013 / Accepted: 23 June 2013 / Published online: 2 July 2013
Ó Springer Science+Business Media New York 2013
Abstract Mesoporous SBA-15 was modified with organic
functional groups by co-condensation method. The func-
tionalized mesoporous silica can be loaded with palladium
and the resulting material used as a catalyst for the Suzuki–
Miyaura coupling reactions. Highly dispersed and uniform
palladium nanoparticles could be detected using transmis-
sion electron microscopy. The Pd-SBA-15 nanocomposite
with controlled molar ratio of amino groups to palladium
exhibits an excellent catalytic activity and low Pd leaching
for the Suzuki–Miyaura coupling reaction. The catalyst can
also be reused at least six recycles in air with only a minor
loss of activity.
to handle. In addition, the removal of the catalysts from
reaction mixtures and products is difficult in most cases,
which is a drawback especially when these reactions are
applied in the pharmaceutical field.
Palladium supported on the hosts may offer solutions for
some of the above mentioned problems such as mesopor-
ous silicas [4], carbon nanotubes (CNT) [5–7], metal–
organic frameworks (MOF) [8], montmorillonites [9], and
zeolites [10]. Among these hosts, mesoporous silicas,
especially SBA-15, have been widely investigated thanks
to their controllable size, composition and morphology,
which are highly desirable for catalytic applications [11].
Although there have been several approaches for loading
palladium nanoparticles (Pd NPs) onto mesoporous silica
using solution infiltration and surface grafting methods,
development of a general and facile method to obtain Pd NPs
supported on mesoporous silica remains challenging due to
its easy agglomeration and leach without protecting groups
[12–16]. It is fairly accepted that amino groups can bind
strongly to noble metal nanoparticles [17, 18]. Palladium
supported on the amino group functionalized zeolite [19],
fumed silica [20], and mesoporous MCM-41 [21] are effi-
cient catalysts. Moreover, the diamine functionalized mes-
oporous materials are attracting much attention due to the
strong absorbing and chelating performance of ethylenedi-
amine groups [22]. More recently, controlled Au and Cu
nanoparticles were supported in ordered mesoporous mate-
rials functionalized by diamine groups on the pore surface
[17, 18, 23]. However, so far the Suzuki–Miyaura reactions
catalyzed by palladium anchored on diamine functionalized
SBA-15 catalyst have not been studied.
Keywords Mesoporous silica Á Suzuki–Miyaura coupling
reactions Á Catalytic activity
1 Introduction
Palladium-catalyzed cross coupling reactions, such as the
Suzuki–Miyaura reaction, have become the standard meth-
odologies for the synthetic organic chemists to construct
biaryl units [1–3]. Although homogeneous Pd catalysts have
gained enormous relevance, industrial applications of these
reactions remain challenging, because the homogeneous
catalysts require the use of ligands, which are often not easy
G. Zhang (&) Á P. Wang
Key Laboratory for Electronic Materials of the State National
Affairs Commission of PRC, Northwest University
for Nationality, Lanzhou 730030, Gansu, China
e-mail: dzclsys@163.com
In our present work, a novel approach to prepare Pd
supported on SBA-15 with high Pd loading and high Pd
dispersion was developed. Mesoporous SBA-15 was modi-
fied with organic functional groups by co-condensation
X. Wei
College of Bailie Engineering and Technology, Lanzhou City
University, Lanzhou 730070, China
123

Palladium Supported on Functionalized Mesoporous Silica
1189
method. Then, Pd2? ions were grafted and fixed compactly
onto the organo-functionalized SBA-15 via the coordination
bonds. The resulting sample thus was reduced by formalin to
obtain Pd supported on SBA-15 (Pd-SBA-15). The catalytic
activity of the Pd-SBA-15 was investigated by Suzuki–Mi-
yaura reactions.
2.2 Catalytic Testing
A typical experimental procedure was as follows: A mix-
ture of aryl bromide (10.0 mmol), phenylboronic acid
(13.0 mmol), potassium carbonate (18.0 mmol), the cata-
lyst (0.05 mol % with respect to palladium), and 4-tert-
butyltoluene (500 mg) as an internal standard for gas
chromatograph (GC) analysis were stirred in water (3 mL)
at 80 °C under N2 atmosphere. Every 15 min, an aliquot of
reaction mixture (*100 lL) was sucked out with degassed
syringe, filtered and washed with brine and diethyl ether.
After completion, the reaction mixture was diluted with
water (20 mL) and extracted with ether (3 9 20 mL). The
combined extract was washed with brine (2 9 20 mL) and
dried over Na2SO4. After evaporation of the solvent under
reduced pressure, the residue was chromatographed (silica
gel, ethyl acetate-hexane: 1:9) to obtain the desired prod-
ucts. The products were confirmed by comparing the H and
13C NMR and mass spectral data with authentic samples.
The Pd concentration was measured with inductively
coupled plasma atomic emission spectrometry (ICP-AES).
For the measurement of the Pd leaching from the Pd-SBA-
15 catalyst in the course of reaction, the solution was fil-
trated and the organic compounds were evaporated. The
residue obtained by calcination at 600 °C in air for 2 h was
dissolved in aqua regia. The recycling test was performed
with bromobenzene and phenylboronic acid under the same
reaction condition as described above. Each time, the cat-
alyst was isolated from the reaction mixture at the end of
the reaction, washed with water and diethyl ether, and then
dried at 100 °C under vacuum. The dried catalyst was then
reused in the next run.
2 Experimental Procedure
Triblock poly (ethylene oxide)-b-poly (propylene oxide)-b-
poly (ethylene oxide) copolymer (EO20PO70EO20, MW =
5,800, Pluronic P123) was from Aldrich. Hydrochloric acid
(HCl), tetraethoxysilane (TEOS), [3-(2-aminoethyl ami-
nopropyl)] trimethoxysilane (ATMS), 4-tert-butyltoluene,
phenylboronic acid, aryl bromide, potassium carbonate,
toluene and palladium chloride were all purchased from
Shanghai Reagent Factory Two Company. All the chemi-
cals used in the present investigation were in the as-
received forms without any further purification. The
deionized water was used in all experiments.
2.1 Synthesis
NH-SBA-15 prepared by co-condensation Method. In this
method, 1 g of (3-aminopropyl)trimethoxysilane (APTMS)
(6 mmol) was added 1 h after the addition of TEOS fol-
lowing the regular synthesis of SBA-15 [24]. The molar
ratio of APTMS to TEOS was 0.3. After being stirred at
room temperature for 1 day, the mixture was transferred
into an autoclave and heated at 100 °C for 24 h. The
product was collected by filtration and dried overnight at
100 °C. Then, the solvent extraction was performed by
stirring 0.5 g of the product in the mixture of 50 mL of
ethanol and 50 mL of diethyl ether for 24 h [25]. The
extraction products are denoted as NH-SBA-15. SBA-15
mesoporous silica powder was also prepared for
comparison.
2.3 Instrumentation
Pd elemental analysis of the nanocomposites was per-
formed on a Thermo IRTS advantage ICP-AES. N ele-
mental analyses of the nanocomposites were performed on
a VarioEL CHNS elemental analyzer. Fourier transform
infrared spectrometry (FTIR) was carried on a Nicolet
Nexus 670 Spectrometer. The X-ray powder diffraction
(XRD) experiments were carried out on a Rigaku D/Max-
2400 X-ray diffractometer using Cu Ka radiation. CO
chemisorption measurements were taken at 298 K using a
homemade pulse flow system. Prior to measurements,
samples were subjected to a pretreatment involving expo-
sure to hydrogen flow for 1 h at 300 °C, then the sample
was cooled down to room temperature in pure N2 stream.
The transmission electron microscopy (TEM) observations
of the Pd-SBA-15 nanocomposite were carried out on a
JEM 1010 operating at an acceleration voltage of 100 kV.
Nitrogen adsorption–desorption isotherms were measured
by a NOVA 2000e surface area and pore size analyzer. The
In a typical experiment, the NH-SBA-15 (0.5 g) was
added to a solution of PdCl2 (0.05 g) in water (5 mL) and
stirred for 24 h at room temperature. The mixture was
filtrated and washed 3 times with 5 mL water under
ultrasonic for 1 min, and then dried in vacuum. Afterward,
the dried sample was stirred with 5 mL of 1 M hydrazine
hydrate at 60 °C for 3 min. The mixture was then filtrated,
washed three times with 10 mL water, and dried at room
temperature. Finally, a dark gray powder (Pd-SBA-15) was
obtained. For comparison of the catalytic activity in Su-
zuki–Miyaura reaction, the other two samples (C1 and C3)
were also prepared in the similar way, but 0.1 g PdCl2 was
replaced by 0.05 g PdCl2 for C1 and 0.2 g PdCl2 for C2.
Also, the other one sample (C3) was prepared in the similar
way, but NH-SBA-15 was replaced by SBA-15 for C3.
123

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G. Zhang et al.
specific surface areas were evaluated using Brunauer-
Emmett-Teller (BET) method. Pore size distribution was
calculated using the Barrett-Joyner-Halenda (BJH) method
based on the desorption branch of the isotherms, and the
pore size was reported from the peak position of the dis-
tribution curve. The pore volume was taken from a single-
point adsorbed volume at a relative pressure P/P0 of 0.97.
presence of the band at 2,936 cm-1 in the spectrum of NH-
SBA-15 is associated with CH2 vibrations corresponding to
the CH stretching. These further confirm the incorporation
of organic species in the framework.
Figure 2 shows the small angle XRD patterns of SBA-15,
NH-SBA-15, and Pd-SBA-15. The samples all exhibit three
well-resolved peaks, one intense peak at about 0.85–0.908
and two weak peaks at about 1.50–1.558 and 1.70–1.758
which can be indexed as (100), (110), and (200) reflections
of two-dimensional hexagonal symmetry (P6mm) [21] (the
two-dimensional hexagonal structure of Pd-SBA-15 will be
verified by the TEM analysis). SBA-15 shows a diffraction
peak at 0.878 which corresponds to the (100) d-spacing of
10.2 nm (shown in Table 1). The repeat distance a0 between
two neighboring pore centers of the hexagonal structure is
11.8 nm (by the equation a0 = 2d100/H3 [27]). In compar-
ison to the diffraction pattern of SBA-15, no significant
change is observed in the diffraction pattern of NH-SBA-15
and Pd-SBA-15, indicating the retention of the hexagonal
pore array structure. The (100) d-spacing of NH-SBA-15
and Pd-SBA-15 are 10.1 and 10.0 nm; the corresponding
repeat distance a0 between two neighboring pore centers are
11.7 and 11.5 nm (listed in Table 1).
3 Results and Discussion
3.1 Structure and Morphology of Nanocomposites
FT-IR spectra of SBA-15 and NH-SBA-15 were shown in
Fig. 1. Bands at similar 458, 813 and 1,080 cm-1 in both
spectra of SBA-15 and NH-SBA-15 have been assigned to
characteristic vibrations of Si–O–Si bridges crosslinking
the silica network. The band at 1,630 cm-1 in the spectrum
of SBA-15 is attributed to the adsorbed water; and a broad
band at 3,432 cm-1 in the spectrum of SBA-15 can be
assigned to the hydrogen-bonding silanol groups and
adsorbed water. The weak band at 3,740 cm-1 in the
spectrum of SBA-15 is attributed to the fundamental
stretching vibrations of silanol groups on the surface,
which is invisible after the condensation of silanol groups
with organic silane. A weak peak at around 696 cm-1 in
the spectrum of NH-SBA-15 is attributed to N–H bending
vibration. In the spectrum of NH-SBA-15 the absorbance
peak of the C–N stretching vibration in the wave number
range of 1,000–1,200 cm-1 cannot generally be resolved
due to its overlap with the absorbance of Si–O–Si stretch in
the range 1,000–1,130 cm-1 and that of Si–CH2–R stretch
in the range 1,200–1,250 cm-1. The bands at 1,480 and
1,578 cm-1 in the spectrum of NH-SBA-15 are attributed
to the NH and NH2 bending vibrations, respectively. The
Figure 3 displays the wide angle XRD patterns of Pd-
SBA-15. The peaks at 2h = 40.18, 46.78, 68.18, and 82.08
are the (111), (200), (220), and (311) diffractions of the fcc
Pd, respectively. The average grain size of the Pd nano-
particles in the Pd-SBA-15 nanocomposite was estimated
from the full width at half maximum of the diffraction
peaks using Scherrer equation. The average grain size of
the Pd nanoparticles in the Pd-SBA-15 nanocomposite is
3.4 nm. The Pd content in the Pd-SBA-15 nanocomposite
was measured with ICP-AES and the N content was
measured with CHNS elemental analyzer. The palladium
Fig. 2 Small angle XRD patterns of SBA-15, NH-SBA-15, and Pd-
SBA-15
Fig. 1 FT-IR spectrum of SBA-15 and NH-SBA-15
123

Palladium Supported on Functionalized Mesoporous Silica
1191
Table 1 Physiochemical properties of SBA-15, NH-SBA-15, and Pd-SBA-15 nanocomposites obtained from small angle XRD and N2
adsorption–desorption
Sample
d100 (nm)
a0 (nm)a
BET surface
area (m2 g-1
BJH pore
size (nm)
Pore volume
(cm3 g-1
)
)
SBA-15
10.2
10.1
10.0
11.8
11.7
11.5
846
420
373
8.3
7.9
7.6
1.02
0.71
0.60
NH-SBA-15
Pd-SBA-15
a
a0 = 2d100/H3
PH-adjusting method on SBA-15 showed Pd dispersions
between 24 and 27 % [25]. The metal dispersion of the Pd-
SBA-15 is higher than this of Pd/SBA-15. This indicates
that Pd-SBA-15 prepared by our novel preparation process
exhibits a higher metal dispersion.
The TEM observations provide the direct observation of
the morphology and the distribution of the Pd nanoparticles
in Pd-SBA-15. The TEM micrograph in Fig. 4a clearly
shows that Pd-SBA-15 has a hexagonal pore array struc-
ture. The dark spots of the Fig. 4b are the Pd nanoparticles.
It can be clearly seen in Fig. 4 that highly dispersed Pd
nanoparticles with the size between 3–6 nm encapsulated
in the ordered pores of the mesoporous silica without any
agglomeration.
The nitrogen adsorption/desorption isotherms and the
pore size distribution for SBA-15, NH-SBA-15, and Pd-
SBA-15 are shown in Fig. 5. The isotherm for SBA-15
(circle in Fig. 5) presents the type IV with a H1-type
hysteresis loop defined by IUPAC [32]. This type of hys-
teresis loop is associated with capillary condensation and
desorption in open-ended cylindrical mesopores [26, 32].
Generally, the shape of the isotherm is preserved after a
modification step. Hysteresis loops with the similar shapes
reveal the absence of pore clogging [26]. The pore struc-
ture parameters of the samples are summarized in Table 1.
A specific surface area of 846 m2 g-1, a pore volume of
Fig. 3 Wide angle XRD pattern of Pd-SBA-15
and nitrogen contents of Pd-SBA-15 nanocomposite were
found to be 0.43 and 0.83 mmol g-1, respectively.
The metal dispersion and metal surface of the catalyst
were studied by the CO chemisorption. A stoichiometry of
CO/Pd = 1/1 [28–30] and a Pd surface density of
1.27 9 1019 atoms m-2 were used for calculations [31].
The Pd dispersion of Pd-SBA-15 is determined to be 33 %.
In comparison, the Pd/SBA-15 materials prepared using
Fig. 4 TEM micrograph of Pd-SBA-15: top view (a); side view (b)
123

1192
G. Zhang et al.
Fig. 5 Nitrogen adsorption–desorption isotherms (a) and pore size distributions (b) of SBA-15, NH-SBA-15, and Pd-SBA-15
1.02 cm3 g-1, and a pore size of 8.3 nm are obtained from
the isotherm of SBA-15. The BET surface areas of the NH-
SBA-15 and Pd-SBA-15 are 420 and 373 m2 g-1, respec-
tively. The pore volumes for NH-SBA-15 and Pd-SBA-15
are 0.68 and 0.60 cm3 g-1, respectively. The pore sizes for
NH-SBA-15 and Pd-SBA-15 are 7.9 and 7.6 nm, respec-
tively. Compared to the BET surface area, pore volume,
and BJH pore size of SBA-15, the decreased BET surface
area, pore volume, and BJH pore size for NH-SBA-15 can
be due to the occupation of large organic groups in the pore
channels. With the incorporation of Pd nanoparticles in the
channels of NH-SBA-15, the BET surface area, pore vol-
ume and BJH pore size of the Pd-SBA-15 nanocomposite
decrease slightly further.
the N:Pd molar ratio for the reaction of bromobenzene and
phenylboronic acid as the model reaction. The catalyst
activity of C3 was the lowest and the Pd leaching was the
highest among all the samples, these shown that the exis-
tence of amino groups could prevent the agglomeration of
Pd nanoparticles in the synthesis reaction and also could
prevent the leaching of Pd nanoparticles in the catalytic
reactions. As the N:Pd molar ratio increases, the Pd
leaching of the reaction decreases. An N:Pd molar ratio of
4:1 for the C1 sample, the Pd leaching is least but the
activity of the catalyst is lowest in these three samples
(Table 2, entry 1). At the standard N:Pd molar ratio of 2:1
for Pd-SBA-15, the Pd concentration in solution at the end
of the reaction is as little as 0.10 ppm (Table 2, entry 2). At
an N:Pd molar ratio of 1:1 for the C2 sample, the catalyst
shows an increased leaching (compared with entry 1 and 2).
An N:Pd molar ratio of 2:1 is the optimal N:Pd molar ratio
since it exhibits the highest activity and a moderate Pd
leaching.
3.2 Catalytic Characteristics of Pd-SBA-15
The catalytic performance of each prepared silica-immo-
bilized amino-palladium complex was probed in the Su-
zuki–Miyaura coupling reaction between aryl bromides
and phenylboronic acid to give the corresponding biphenyl
products. The activity of catalyst and Pd leaching in the
reaction are strongly affected by the molar ratio of func-
tional groups to Pd of the nanocomposite [12]. Table 2
shows the catalytic activity and Pd leaching as a function of
To investigate the reaction scope with Pd-SBA-15 as the
catalyst, various aryl bromides with different substituents
were employed. Fast conversion of aryl bromides were
achieved in all cases as indicated by gas chromatography
(GC) analysis. The results are summarized in Table 3. The
Suzuki reaction of bromobenzene with phenylboronic acid
Table 2 Catalytic activity and leaching as a function of N to Pd molar ratio with the bromobenzene and acrylic acid as the model reaction
Entry
Sample
N content
(mmol g-1
Pd content
(mmol g-1
)
N:Pd
Yielda
Pd leaching
(ppm)
)
1
2
3
4
C1
0.85
0.84
0.82
/
0.21
0.41
0.80
0.38
4:1
2:1
1:1
/
60
98
89
72
0.05
0.10
0.40
0.50
Pd-SBA-15
C2
C3
The reaction was carried out at 80 °C, 1 h with 0.05 mol% Pd-SBA-15 as catalyst
a
Determined by GC analysis using 4-tert-butyltoluene as an internal standard
123

Palladium Supported on Functionalized Mesoporous Silica
1193
Table 3 Suzuki–Miyaura coupling reactions of aryl halides over Pd-
SBA-15
Table 4 Recycling test for Suzuki–Miyaura coupling reaction
Recycle
Yield
1
2
3
4
5
6
7
98
98
96
97
92
90
80
0.05 mol % Pd-SBA-15 was used in this reaction
Entrya
Ar
Yieldb
1
Ph
98
96
97
98
99
96
98
90
92
98
95
21
78
2
4-CH3OC6H4
4-CHOC6H4
4-CH3C6H4
4-CH3OCOC6H4
4-O2NC6H4
4-CNC6H4
2-Pyridyl
2-Thienyl
Ph
3
4
5
6
7
8
9
10c
11d
12e
13e
a
4-CHOC6H4
Ph
Ph
Reaction conditions: aryl bromides (10.0 mmol), phenylboronic
acid (13.0 mmol), K2CO3 (18.0 mmol), catalyst (0.05 mol % Pd),
water (3 mL), 80 °C, 1 h
Fig. 6 Small angle XRD patterns of Pd-SBA-15 and the used Pd-
SBA-15 catalyst recovered from the sixth recycle
b
Determined by GC analysis using 4-tert-butyltoluene as an internal
standard
c
The reaction was catalyzed by 0.08 mol % Pd-SBA-15 related to
the amount of aryl halides at 80 °C for 1 h [13]
The reaction was catalyzed by 1 mol % NH-Pd-SH-SBA(SS)
related to the amount of aryl halides at 80 °C for 12 h with DMF/H2O
(20/1) as solution [33]
shows relatively higher catalytic activity in the Suzuki–
Miyaura reactions [33, 34]. We attributed this to the high
dispersion of the Pd nanoparticles throughout the meso-
porous silica structure and high surface area of catalysts.
As shown in Table 4, this Suzuki–Miyaura coupling
reaction of bromobenzene and phenylboronic acid exhibits
high yield at least up to 90 % until sixth recycling usage,
but the conversion drops to 80 % in the seventh recycling
usage. Therefore, the catalyst Pd-SBA-15 can be reused
and keeps its high catalytic activity in catalyst recycling for
Suzuki–Miyaura coupling reaction. Detailed studies were
carried out on Pd-SBA-15 that was recovered from the
sixth recycle in the reaction between bromobenzene and
phenylboronic acid. The palladium and the nitrogen con-
tents in the used catalyst recovered from the sixth recycle
are determined to be 4.1 and 0.79 mmol g-1 by the ele-
mental analysis, respectively. Compared to the fresh cata-
lyst, both the Pd and N content were slightly decreased,
indicating they both leached in the solution during reac-
tions. CO chemisorption of the used catalyst shows that
there is a little decrease in Pd dispersion (Pd dispersion
28 % compared to 33 % of fresh catalyst). These indicate
that there are a little Pd aggregation after six recycles. The
small angle XRD pattern of the used catalyst recovered
from the sixth recycle (Fig. 6) shows that the structure of
catalyst is maintained even when the catalyst is used for six
recycles. Based on the investigations above, a minor
decrease of the catalytic activity in recycle reaction can be
d
e
The reaction was catalyzed by Pd10 (entry 12) or Pd5Au5 (entry 13)
nanoparticles supported on SBA-15 at 100 °C for 0.5 h with micro-
wave-assisted [34]. Pd was 0.5 mol % related to the amount of aryl
halides [34]
also furnished an excellent yield of biphenyl in 1 h
(Table 3, entry 1). We also examined the reaction with
several substituted aryl bromides and phenylboronic acid
under the optimized reaction conditions. The reactions
were all carried out at 80 °C in 1 h, affording biphenyl
products with high yields (Table 3, entry 2–7). The cou-
pling reactions of heteroaryl bromides such as 2-bromo-
thiophene and 2-bromopyridine with phenylboronic acid
also gave the corresponding coupled products in 92 and
90 % yields, respectively (Table 3, entry 8 and 9). These
results show that the catalyst has high activity in the Su-
zuki–Miyaura reactions. Compared to the Pd nanoparticles
in carbon thin film-lined SBA-15 nanoreactors [13], the Pd-
SBA-15 shows relatively higher catalytic activity in the
Suzuki–Miyaura reactions (Table 3, entry 1 and 10). We
also compared the activity of our catalyst with these of NH-
Pd-SH-SBA (Table 3, entry 1 and 11) and Pd10 (Table 3,
entry 1 and 12) or Pd5Au5 (Table 3, entry 1 and 13)
nanoparticles supported on SBA-15, the Pd-SBA-15 also
123

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G. Zhang et al.
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method, grafting palladium ions on the functionalized
SBA-15, and reducing palladium ions in the functionalized
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composite has a Pd loading of the 0.43 mmol g-1. Highly
dispersed uniform Pd nanoparticles are distributed in the
hexagonal channels of SBA-15. The surface area, the pore
volume, and the pore size decrease slightly with the
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Acknowledgments This work was supported by the Fundamental
Research Funds for the Central Universities, China. (Grant No.
zyz2012057), Natural Science Foundation of Gan Su Province (Grant
No. 0803RJZA008), China.
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