3
66
P. Wang et al. / Materials Research Bulletin 59 (2014) 365–369
from Shanghai Reagent Factory Two Company. Pd(acetylaceto-
nate) (Pd(acac) ) was from Shanghai July Chemical Co., Ltd. All
2.3. Instruments
2
2
chemicals were used as received without any purification. The
deionized water was used in all experiments.
The Pd content of synthesized materials was estimated using a
Thermo IRIS advantage the inductively coupled plasma atomic
emission spectrometer (ICP-AES). The powder X-ray diffraction
patterns of the synthesized materials were collected on a Rigaku D/
2.1. Preparation of Pd/SBA-15 nanocomposite
Max-2400 X-ray diffractometer using Cu K
a
radiation. Surface area
ꢀ
A somewhat modified synthesis of Ha and co-workers was
was measured by nitrogen adsorption at À196 C using NOVA
2000e surface area and pore size analyzer. The transmission
electron microscopy (TEM) observations of the nanocomposite
were carried out on a JEM 2010 operating at an acceleration voltage
employed [20]. The triblock copolymer EO20PO70EO20 (2 g) was
ꢀ
dissolved in 64 g water and stirred separately for 5 h at 35 C.
Subsequently, 1 ml 3 wt/V%, 2 ml 3 wt/V%, 2 ml 3 wt/V% Pd(acac)
2
/
ꢀ
ꢀ
CHCl
3
solution were added and stirred for 1 h at 35 C in a sealed
of 200 kV. CO chemisorption measurements were taken at 25 C
container. 4.5 ml of TEOS was dispersed in 3.2 g of an HCl aqueous
solution (pH 2), and hydrolysis was performed under vigorous
stirring at 35 C for 1 h and a transparent solution was formed,
using a homemade pulse flow system. Prior to measurements,
samples were subjected to a pretreatment involving exposure to
ꢀ
ꢀ
hydrogen flow for 1 h at 300 C, then the sample was cooled down
which was dropped immediately into the template solution. The
combined mixture was stirred at 35 C for 2 h in a sealed container.
2
to room temperature in pure N stream. CO was pulsed at room
temperature over the reduced catalyst until the TCD signal from
ꢀ
The solid product was filtrated quickly and placed in an autoclave
at 100 C for 48 h. The resulting sample was then washed with
the pulse was constant. A stoichiometry of CO/Pd = 1/1 [21–23] and
ꢀ
19
2
a
Pd surface density of 1.27 Â10 atoms/m was used for
water three times and dried at room temperature. The dried
calculations [24].
ꢀ
sample was calcined at 400 C for 6 h and then reduced by H
3
2
gas at
ꢀ
00 C for 2 h, the resulting sample was denoted as S-1, Pd/SBA-15
3. Results and discussion
3.1. Structure of nanocomposite
and S-2. The SBA-15 was synthesized as above procedure without
the Pd(acac) /CHCl solution adding for comparison. For compari-
2
3
son of the catalytic activity in Suzuki–Miyaura reactions, the other
sample (WI) by the wetness impregnation method was also
The Pd loading of S-1, Pd/SBA-15, S-2 and WI were 0.83,1.46, 3.01
and 1.41 wt%. In this in-situ method, above 85% of the palladium is
incorporated into SBA-15 (Table 1), avoiding losses of this expensive
metal during the synthesis. Molecular assembly template was
employed as a hydrophobic carrier to provide the compatible
environment for the hydrophobic compounds. The hydrophobic
prepared. The SBA-15 (1.0 g) was added to a solution of PdCl
0.025 g) in water (5 ml) and stirred for 24 h at room temperature.
2
(
ꢀ
The mixture was dried 60 C for 24 h and reduced by H
3
2
gas at
ꢀ
00 C for 2 h.
2.2. Catalytic studies
solvent (CHCl
precursor (Pd(acetylacetonate)
3
) was used as a transport medium to inject the Pd
) directly into the inner core of the
2
A typical experimental procedure was as follows: a mixture of
surfactant micelles. One inherent advantage of using template
micellesasacarrierisitsstrictselectivityofmetalnanoparticlesonly
being charged into the channels [18,25,26]. Furthermore, the
orientations of pores have no effect on the distribution of the
nanoparticles in the channels of mesoporous silica.
aryl bromide (10.0 mmol), phenylboronic acid (13.0 mmol),
potassium carbonate (18.0 mmol), the catalyst (0.04 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. Every 15 min, an aliquot of reaction
Fig. 1 shows the low-angle XRD patterns of SBA-15, S-1, Pd/SBA-
15, S-2 and WI. The main diffraction peaks of SBA-15 with
mixture (ꢁ100
ml) 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 Â 20 ml). The combined extract was washed with
2
u
= 0.81 , 1.38 , and 1.61 are shown in Fig. 1. The d-spacing ratios
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
of three peaks are 1 : 1= 3 : 1=2; these three diffraction peaks can
be indexed as (10 0), (110), and (2 0 0) diffractions associated with
highly ordered mesoporous silica SBA-15 with a two-dimensional
hexagonal symmetry (space group p6 mm) [19]. In comparison to
SBA-15, S-1, and Pd/SBA-15 show low-angle XRD patterns similar
to that of SBA-15. Obviously, the hexagonal ordered structures are
retained well indicating that the introduction of Pd into SBA-15
does not collapse the mesoscopic order of a two-dimensional
hexagonal structure. In this method, higher loadings (3.01 wt%, S-2
sample) also cause a decrease in pore ordering. It is clearly visible
in small angle X-ray diffraction (Fig.1). For sample S-2 with 3.01 wt
% Pd, one broad (10 0) peak could be observed and the (110) and
(2 0 0) reflections almost invisible even magnified by five times.
However, the Pd loading also causes a slightly increase of the (10 0)
brine (2 Â 20 ml) and dried over Na
2 4
SO . After evaporation of the
solvent under reduced pressure, the residue was chromatographed
silica gel, ethyl acetate-hexane: 1:9) to obtain the desired
(
products. The products were confirmed by comparing the H
and13C NMR and mass spectral data with authentic samples. The
Pd concentration was measured with inductively coupled plasma
atomic emission spectrometry (ICP-AES). The recycling test was
performed with bromobenzene and phenylboronic acid under the
same reaction condition as described above. Each time, the catalyst
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.
Table 1
Synthesis condition and characterization of palladium containing SBA-15 materials.
Measureda Pd loading (wt%)
Surface area (m /g)
2
Pore volume (cm /g)
3
Sample
Concentration of solution (wt/V%)
Amount of solution (ml)
SBA-15
S-1
Pd/SBA-15
S-3
0
3
3
6
/
/
/
0.91
0.83
0.82
0.77
0.65
1
2
2
/
0.83
1.46
3.01
1.41
530
400
380
370
WI
a
Measured Pd loading determined by the ICP-AES.