G Model
CATTOD-9270; No. of Pages4
ARTICLE IN PRESS
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L. Zhong et al. / Catalysis Today xxx (2014) xxx–xxx
for the catalysts. However, to the best of our knowledge, the
“one-step” preparation of Pd supported on a carbon support for
Suzuki-Miyaura reaction is rarely reported [19,20]. In this paper,
we report a one-pot method to prepare new mesoporous carbon
embedded with Pd nanoparticles using SBA-15, furfuryl alcohol and
PdCl2 as template, carbon source and palladium source, respec-
tively. The Pd nanoparticles are attached in the skeleton of the
mesoporous carbon which show a high reactivity and selectivity
in the Suzuki-Miyaura reaction of aryl halides and phenylboronic
acid. The catalyst is found to be highly stable and can be reused up
to three times without loss of activity.
2. Experimental
2.1. Chemicals and materials
Reagents in the experiment were of analytical grade, used
directly without further treatment. Poly (ethylene glycol)-
block-poly (propylene glycol)-block-poly (ethylene glycol)
(EO20PO70EO20) with an average molecular weight of 5500,
PdCl2 (99%), Furfuryl alcohol, (≥98%). Phenyl boronic acid (95%),
2-bromo-toluene (99%), 4-bromoanisole (>99%), 4-bromo- phenol
(99%), 4-bromobenzaldehyde (99%), and 4ꢀ-bromoacetophenone
(98%) were purchased from Sigma Aldrich.
Scheme 1. Synthesis of Pd@MC. (a) adsorption of carbon and Pd sources, (b) poly-
merization and carbonization and (c) removal of the SBA-15 silica template.
2.4. Catalytic Suzuki-Miyaura reaction by Pd@MC
4 mg of Pd@MC catalyst (2 mol%), 0.5 mmol of aryl halides,
and 0.55 mmol of phenyl boronic acid were added into
a
2.2. Synthesis of mesoporous carbon embedded with Pd
nanoparticles (Pd@MC)
pressure-resistant reaction tube. Then, 1 mmol of Na2CO3 and 4 ml
water–ethanol (v/v = 1:1) were added into the tube. The tube was
sealed and the mixture was stirred at 80 ◦C for 1 h. The catalyst
was separated through a short column (silica gel). The pure prod-
uct was obtained after removal of solvents by rotary evaporation.
Finally, the product was purified by column chromatography (silica,
hexane/ethyl acetate) if it is necessary. The structures of the pure
products was confirmed by 1H NMR spectra. The conversion and
the yield were tested by gas chromatograph (Shimadzu GC-2010).
In a typical synthesis, 4 g poly (ethylene glycol)-block-poly
(propylene glycol)-block-poly (ethylene glycol) (EO20PO70EO20
)
was dispersed in deionized water (30 g) and dilute hydrochlo-
ric acid (120 ml, 2 M), and then the mixture was stirred at room
temperature for 5 h to produce a colloidal solution. Subsequently,
tetraethyl orthosilicate (TEOS, 9 g) was added to the solution under
stirring. The solution was aged for 24 h at 40 ◦C and then trans-
ferred into an autoclave for 48 h at 150 ◦C. Hydrothermal reaction
products were collected and milled into a fine powder, and then
the powder was calcined in a muffle furnace at 540 ◦C for 48 h to
give SBA-15 [21].
The Pd@MC was synthesized by a modified one-pot method [14].
SBA-15 (1 g) was degased at 250 ◦C under vacuum for 6 h to remove
the water adsorbed on the surface of SBA-15. Then furfuryl alcohol
(1.6 g, 16.3 mmol) and PdCl2 (50 mg, 0.28 mmol) in 2 ml of ethanol
were mixed thoroughly. The mixture was heated at 40 ◦C in a vac-
uum over (vacuum level ∼ −0.1 MPa) for 24 h. Then it was heated
to 80 ◦C and kept at the same temperature for 24 h under nitrogen.
The mixture was continued to be heated to 150 ◦C and retained for
another 8 h. The collected solid was heated to 900 ◦C with a heat-
ing rate of 5 ◦C/min in a tubular furnace in nitrogen atmosphere,
and maintained at this temperature for 5 h. Finally, the obtained
black powder was treated with a 2 M NaOH solution at 80 ◦C for 2 h
to remove the template. The solid was collected by filtration and
dried under vacuum to give Pd@MC.
2.5. The recycled experiment for Pd@MC
The catalyst Pd@MC (8 mg, 2 mol%), 4 - acetyl-bromobenzene
(1 mmol, 100 mg) and phenylboronic acid (1.1 mmol, 133 mg)
were added to a mixture of Na2CO3 (2 mmol, 212 mg) and 8 ml
water–ethanol (v/v = 1:1) in a pressure-resistant reaction tube and
then the tube was sealed. The mixture was stirred at 80 ◦C for 1 h.
The mixture was then transferred to a centrifugation tube and cen-
trifuged at a speed of 5000 rpm/min for 15 min. The supernatant
was carefully removed with a pipette and a small amount of ethanol
was added to the tube for washing the residue. The washing step
was repeated three times. Then, the separated catalyst was used in
the reaction for the next run.
3. Results and discussion
The preparation process of the catalyst is illustrated in Scheme 1.
The process consists of three steps. First, an ethanol solution of
palladium chloride and furfuryl alcohol was adsorbed into the
channels of the dehydrated SBA-15. In this step, the dehydrated
SBA-15 is a template, while palladium chloride and furfuryl alco-
hol is the source for palladium and carbon, respectively. The second
step for the catalyst preparation is very important for controlling
the morphology and its dispersion over the porous channels of the
support. During this step, furfuryl alcohol was polymerized first and
then gradually carbonated. The melting point of palladium chloride
is about 680 ◦C, thus below this temperature palladium chloride is
solid which was embedded into the formed polymer. When the
temperature exceeds the melting point of palladium chloride, Pd
2.3. Characterization
TEM images were obtained with a JEOL-3000F. X-ray photo-
electron spectra were collected on Kratos Axis Ultra Meter (AlK␣,
1253.6 eV). Pd content was measured by Varian Vista-Pro ICP-OE.
1H NMR spectra were recorded on a Bruker DPX 400 MHz spectrom-
eter in chloroform-d3. Conversion and product yield of the reaction
were obtained from Shimadzu GC-2010 with an autosampler. The
column is Agilent HP-Ultra 1 (25 m × 0.2 mm × 0.33 m). Split ratio
is 50:1, the temperature of vaporization chamber is 270 ◦C, and the
temperature of FID detector is 270 ◦C.
Please cite this article in press as: L. Zhong, et al., Pd nanoparticles embedded in mesoporous carbon: A highly efficient catalyst for