Synthesis of Gold Nanoparticles inside the Pores of MCM-48
FULL PAPERS
Synthesis of Gold Nanoparticles in scCO Medium
temperature of 508C. The reactor was sealed and flushed
2
with 2 MPa of CO for 3–4 times to remove the air and kept
2
for 90 min to attain a constant temperature. A prescribed
amount of hydrogen was first introduced into the reactor.
The synthesis of gold containing MCM-48 (referred to as
Au-MCM-48 in the text) in scCO medium was conducted
2
After that, liquid CO was charged using a high-pressure sy-
in a 50 mL stainless steel autoclave. In a typical experiment,
2
ringe pump, and then compressed to the desired pressure. A
back-pressure regulator was used to maintain the constant
pressure of the system. The reaction was conducted while
stirring the mixture with a magnetic stirrer for 2 h. The reac-
tor was then cooled to room temperature with an ice bath
and depressurized to atmospheric pressure. Finally, the
liquid product was separated from the catalyst by filtration
then identified by GC/MS and analyzed quantitatively by
GC (HP 6890) equipped with flame ionization detector.
Quantification of the products was obtained by a multipoint
calibration curve for each product.
5
g of calcined mesoporous support and 10 mL of HAuCl4
solution were loaded in the reactor before it was sealed. The
closed reactor was placed in a constant temperature circulat-
ing oven of 708C and allowed to equilibrate. After the ther-
mal equilibrium was reached, H was introduced in the reac-
tor and pressurized to 2.0 MPa. Then the reaction vessel was
2
charged with CO to the desired pressure using a high pres-
2
sure syringe pump (JASCO scf-bpg). The vessel contents
were mixed mechanically using a magnetic stirrer. The reac-
tion was allowed to proceed for 2–4 h. During the synthesis,
a back-pressure regulator maintained the constant reaction
pressure. After the reaction, the reactor was placed in ice-
cold water and depressurized very slowly and carefully. The
samples were recovered from the container, dried at room
temperature followed by the characterization.
The stability of the heterogeneous catalyst was evaluated
by recovering it from the hot reaction mixture (temperature
5
08C) by filtration and analysis by ICP-AES. On the other
hand, the filtrate has been used in a new reaction but no
catalytic activity was observed.
Characterization Methods
References
The powder X-ray diffraction pattern was recorded on a
Rigaku RAD-X system using monochromatized Cu Ka ra-
diation (l=1.542 ). In general, the diffraction data were
collected using the continuous scan mode with a scan speed
of 2 deg/min over the scan range 2q=1.5–158 and for wide-
angle (2q=30–708) measurements. Transmission electron
microscopy (TEM) of the material was performed on a Phi-
lips Technai operating at 200 kV. The powder was suspended
in ethanol by an ultrasonic method. A drop of this solution
was placed on the grid with a holey carbon/copper film and
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then allowed to dry, covered by a watch glass. N adsorp-
2
tion-desorption isotherms were obtained at À1968C with a
Micromeritics ASAP 2000 instrument. The sample was first
outgassed at 3008C for 24 h immediately prior to data col-
1
999, 41, 319.
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lection. The volume of the adsorbed N was normalized to
2
standard temperature and pressure. The surface area and
the pore size distribution were calculated by applying the
BET equation[
47]
and BJH formula from the adsorption
[48]
branch of the isotherm,
respectively, to avoid the pres-
ence of artificial maxima on the pore size and other undesir-
able effects.[ The UV-Vis spectra of the materials were re-
corded on a Shimadzu spectrophotometer operating in the
reflection mode at a resolution of 2 nm using aluminum
oxide as standard. The FT-IR spectrum in the framework
49]
À1
À1
region (1300 cm to 400 cm ) was recorded on a Horiba
FT-720 using a KBr pellet. About 1 mg of finely powdered
sample was mixed with 300 mg of dried KBr and then press-
ed to obtain the pellet.
[
[
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Catalytic Activity
The hydrogenation of crotonaldehyde was carried out in a
stainless steel batch reactor (50 mL) in scCO2 medium.[
50]
100 mg of the catalyst and 6.5 mmol of the reactant were
[17] B. Korgel, K. P. Johnston, P. S. Shah, Abstracts of
loaded into the reactor which was placed in an oven at a
Papers of ACS, 223, u663, 242, April 7, 2002.
Adv. Synth. Catal. 2006, 348, 1580 – 1590
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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