One-Pot Synthesis of Styrene Carbonate from Styrene and CO2 Over the Nanogold-Ionic Liquid…
PerkinElmer GC, Clarus 500 equipped with a capillary
column (SPB-5: 30 m 9 0.25 mm 9 0.25 lm film thick-
ness) and a FID detector. The detector temperature was
250 °C. The flow rate of He was 45 mL min-1 and air
450 mL min-1. The initial column temperature was 45 °C
and it increased to 150 °C (20 °C min-1). After a further
increase at 45 °C min-1 to 200 °C the temperature was
held for 2 min, and finally increased to 250 °C
(45 °C min-1) and held for 5 min. The crystal structure of
the Au nanoparticles supported on CNT was determined by
a powder XRD diffractometer (Panalytical X’Pert Pro, Co
Ka radiation, k = 0.1789 nm). The X-ray Photoelectron
Spectroscopy (XPS) measurements were performed on a
PHI 5700/660 spectrometer, while IR on FT-IR Nicolet
6700 (KBr pellet method).
77.1, 93.8 and 99.4 ° can be assigned to reflections from
the (111), (200), (220), (311) and (222) planes of the face-
centered-cubic Au. The average crystallite size of gold
nanoparticles calculated using the Debye–Scherrer formula
was approximately 10 nm. The IR spectrum (Fig. 2b) of
the catalyst (after use) shows no specific features that can
be attributed to the Au nanoparticles. Only oxygen-con-
taining functional groups O–H (3420 cm-1), C–O–C
(1185 cm-1), and the remains of [bmim]Br (2360;
2920 cm-1) can be identified. Figure 2C shows the XPS
spectrum of the Au/CNT catalyst, where C1s is the domi-
nant peak. The XPS signature of the Au 4f doublet (4f7/2
and 4f5/2) for the Au particles was shown in Fig. 2D. The
line shapes, and peak-to-peak distance of the Au 4f doublet
are consistent with the Au0 state, which confirms the earlier
reports, where it was shown that in this type of material Au
nanoparticles are non-covalently adsorbed onto CNT [28].
2.3 Synthesis and Characterization of the Au/CNT
Catalyst
2.4 Epoxidation of Styrene
0.1 gram of AuCl3 was dissolved in 50 mL of water and
then 1 mL of concentrated ammonia was added. This tur-
bid solution was then added to a 200 mL aqueous disper-
sion of 0.5 g of CNT placed in a large beaker under
continuous mechanical stirring. Next, NaBH4 (1 g) was
slowly added portionwise over a period of 1.5 h. After
addition, the suspension was stirred for further 2 h. The pH
was then adjusted to 5 using concentrated HCl. The Au/
CNT were separated by filtration through a 0.2 lm nylon
filter, washed with water, acetone and acetonitrile, and
dried in a vacuum desiccator. The content of Au in Au/
CNT was determined by ICP-AES after partial digestion of
approximately 0.01 g of Au/CNT in 1.6 mL of aqua regia.
After 48 h, the solution was diluted with water to 10 mL,
unreacted CNT were separated by centrifugation, and
finally filtered through a PTFE syringe filter. The deter-
Styrene (5 mmol) was placed in a round bottomed flask
(5 mL) equipped with a magnetic stirrer and a reflux
condenser. The appropriate quantity of the oxidant and then
the catalyst were added to the flask. The content of the flask
was heated with the agitation speed of 500 rpm. After
completion of the reaction, the mixture was cooled down to
room temperature.
2.5 Synthesis of SC from Styrene or Styrene Oxide
All the reactions using CO2 as the reagent were performed
in a stainless steel pressure reactor (Mettler Toledo) with a
mechanical stirrer (pitched-blade), immersed in a solid-
state thermostat (EasyMaxTM 102) with an automatic
temperature control system.
mined content of Au in the solution was 101 1 mg L-1
,
which corresponds to 8 % of Au in Au/CNT. The fraction
of gold incorporated into CNT was 62 % of the AuCl3
quantity, and the material yield was 0.5 g.
2.5.1 Synthesis of SC from Styrene Oxide
Styrene oxide (32 mmol) and the appropriate amount of the
catalyst were introduced into the autoclave reactor. The
reactor was purged twice using carbon dioxide and then
heated to the desired temperature. After the stabilization of
temperature, CO2 was charged into the reactor from a
reservoir tank to maintain a constant pressure. The con-
sumption of CO2 was controlled during the process using
iControlTM software (version 5.1.2.9). At the end of the
reaction the reactor was cooled down to 25 °C, and then
the excess of CO2 was released slowly.
Samples for the transmission electron microscopy were
prepared by dispersing the tested materials (black powder)
in ethanol, placing them in an ultrasonic bath, then putting
droplets onto 3 mm copper grids coated with an amorphous
carbon film, and air-dried at room temperature. The mor-
phology of Au/CNT was characterized by TEM, as shown
in Fig. 1. The material contained CNT which had similar
diameter of approximately 10–20 nm. Based on the TEM
images, we estimated the size distribution of Au nanopar-
ticles. The nanoparticles had a spherical shape with an
average diameter of 6 nm. The size distribution was narrow
between 1 and 13 nm.
2.5.2 Synthesis of SC from Styrene
The XRD pattern for the sample is shown in Fig. 2a.
The diffraction peaks in each XRD pattern at 45.0, 52.5,
The research on the direct synthesis of SC from styrene
was conducted in a similar way as in the case of the
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