Yang H, et al. Sci China Chem June (2014) Vol.57 No.6
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had excellent mesoporous structure [23]. Thus we thought
that if we could load Pd onto -AlOOH@Fe3O4 nanospheres,
this would combine their advantages of high activity, excel-
lent mesoporous structure, magnetic recyclability, and re-
usability.
In this paper, we illustrate the construction of magneti-
cally recyclable Pd/-AlOOH@Fe3O4 nanocomposites thou-
gh three simple steps. To evaluate the activity and the sta-
bility of the Pd/-AlOOH@Fe3O4 nanocomposites, Heck
coupling reactions were chosen as the model reaction for
testing. Results showed that this catalyst could be easily
separated from the reaction system by employing an exter-
nal magnetic field, because of the superparamagnetic be-
havior of Fe3O4, and that it can be reused for several cycles
with sustained selectivity and activity.
heated from room temperature to 200 °C (1°C/min) under
the H2 (5 mL/min) ambience, and kept at 200 °C for 3 h.
After cooling down to room temperature, Pd/-AlOOH@
Fe3O4 (0.141 mmol/g) was synthesized. By changing the
addition of PdCl2, we synthesized a series of Pd/-AlOOH@
Fe3O4 solutions with different Pd loadings.
2.2 Catalytic reaction
For Heck reactions, 10 mg of Pd/-AlOOH@Fe3O4 catalyst,
arylhalide (20 mmol), olefin (20 mmol), dodecane (10
mmol, as an internal standard substance), and base (24
mmol) were added to the solvent (40 mL). The reaction was
carried out under reflux condition. Different Pd content,
solvents, substrates, and time-dependences were investigat-
ed separately. The catalyst was collected by an external
permanent magnet, and the product was analyzed by gas
chromatography (GC). For recycling, the collected catalyst
was washed with tetrahydrofuran six times and dried under
vacuum at 60 °C for 12 h; then the catalysts were utilized
for another run of catalytic testing. Each time, catalyst loss
was measured by precision electronic balance.
2 Experimental
2.1 Synthesis of Pd/-AlOOH@Fe3O4
Fe3O4 was synthesized according to the literature, by a
slightly modified solvothermal method [24]. Briefly: 10.8 g
of FeCl3·6H2O, 28.8 g of NaAc and a certain amount of
CTAB (cetyltrimethyl ammonium bromide) were dissolved
in 400 mL of glycol under stirring. The obtained homoge-
neous yellow solution was transferred to a Teflon-lined
stainless-steel autoclave. The autoclave was sealed and
heated at 200 °C at 400 r/min speed. After heating for 12 h,
the autoclave was naturally cooled to room temperature.
The obtained black magnetite particles were separated with
a permanent magnet, washed with ethanol 6 times, and
dried in vacuum at 60 °C for 24 h.
The obtained Fe3O4 particles (0.1 g) were dispersed in an
AIP (aluminium isopropoxide) ethanol solution (60 mL,
0.016 mol/L) under ultrasonication. After 30 min, the solu-
tion was transferred to a three-neck flask (250 mL) and kept
at 45 °C. Then the solution was stirred for 12 h to obtain
saturated adsorption of AIP on the surface of the Fe3O4 par-
ticles. Subsequently, ethanol/water (5/1, v/v, 50 mL) was
added into the solution, with continued stirring for 1 h to
allow the hydrolysis of AIP. Then the solution mixture was
transferred to a Teflon-sealed autoclave and heated at 80 °C
for 20 h. The obtained particles were separated with a per-
manent magnet, washed several times with deionized water
and ethanol, and then dried in vacuum at 50 °C for 12 h to
obtain -AlOOH@Fe3O4.
2.3 Characterizations
The X-ray diffraction (XRD) pattern was collected on a
D/Max 2500 VB 2+/PC diffractometer (Rigaku, Japan) with
CuKα irradiation ( = 1.5418 Å, 200 kV, 50 mA) in the
range of 2 value between 10° and 80°. Transmission elec-
tron microscopy (TEM) was performed with a JEOL (JEM-
2100) transmission electron microscope (JEOL, Japan) op-
erated at 200 kV accelerating voltage. The N2 adsorption-
desorption analysis was tested with an ASAP 2020M auto-
matic specific surface area and aperture analyzer
(MICROMERITICS, USA). Magnetic properties of the
samples were measured using a vibration sample magne-
tometer (VSM; Lake Shore Model 7400, USA) under mag-
netic fields up to 18000 Oe. The Pd loading amount was
determined by inductively coupled plasma mass spectrome-
try (ICP-MS, SPECTRO ARCOS EOP; SPECTRO Analyt-
ical Instruments GmbH, Germany).
3 Results and discussion
3.1 Pd/-AlOOH@Fe3O4 structure
The crystallinity and phase composition of the Pd/-
AlOOH@Fe3O4 solutions were investigated by X-ray pow-
der diffraction (XRD). Figure 1 shows the wide-angle XRD
patterns of the samples. The peaks of all samples could be
indexed to face center cubic magnetite phase (Fe3O4;
JCPDS No. 19-0629). No other crystalline materials were
detected. Three additional peaks at 12.4°, 27.6°, and 49.4°
could be indexed to orthorhombic -AlOOH (JCPDS No.
Next, 0.1 g of the obtained -AlOOH@Fe3O4 particles
was dispersed in 2.5 mL PdCl2 aqueous solution (0.6
mg/mL) under ultrasonication. After 30 min, the solution
had diluted to 100 mL, and was transferred to a three-neck
flask, stirred for 12 h under 25 °C, separated by a permanent
magnet, and finally dried in vacuum at 100 °C for 12 h. The
obtained products were put into a tube furnace from which
the air was then emptied with H2. Then the tube furnace was