Bhattacharjee and Ahn
Palladium Nanoparticles Supported on MIL-101 as a Recyclable Catalyst
Table I. Summary of the characterization results for Pd0ꢅ9/MIL-101.
which are ecologically more acceptable for catalytic pro-
cesses in the chemicals industries.
Techniques
Parameters
Results
MIL-101 was synthesized following the recipe
reported by Férey and co-workers using chromium(III)
nitrate nonahydrate (99%, Sigma-Aldrich), hydrofluoric
acid (Duksan, 48%) and 1,4-benzenedicarboxylic acid
(99%, Sigma-Aldrich) through hydrothermal method.6 Pd
nanoparticles supported on MIL-101 was prepared using
acetone solution of Pd(OAc)2 (98%, Sigma-Aldrich) at
45 ꢁC for 24 h and subsequently treated with N ,N -
X-ray powder diffraction
N2 adsorption–desorption
isotherms
TEM
ICP analysis
2ꢆ (degree)
BET surface area
Total pore volume
Pd particles size
Pd (weight %)
5.2, 8.6, 9.1, −116.6
0.66 cm3 g−1
2–10 nm
0.91
2400 m2
g
Pd0ꢅ9/MIL-101. The results are shown in Table II. Ini-
tially, the Heck reaction using 4-methoxyiodobenzene
and butyl acrylate was carried out. At 98% conversion,
4-methoxyiodobenzene was converted to the Heck product
with excellent yield (97%) at 100 C after 6 h (Table II).
We then tested the catalytic activity of catalyst in the Heck
reaction using iodobenzene and butyl acrylate under the
identical reaction conditions. At 100 C, iodobenzene was
converted to Heck product with 96% yield within a shorter
reaction time (4 h) than 4-methoxyiodobenzene.
In order to investigate the influence of different sub-
stituent, the reaction was carried out using three different
types of aryl iodides such as iodobenzene, 1-iodo-4-
nitrobenzene and 4-methoxy-1-iodobenzene with styrene.
The catalytic activity was found to be influenced strongly
by the type of aryl iodides, and the reactivity order was
in the following order: p-NO2 > H ꢂ p-OCH3 (Table II).
Excellent product yields were achieved in the range
97–81%, however, reaction time varied in the following
order: p-NO2 < H ꢀ p-OCH3, indicating that iodoben-
zene having electron-withdrawing group reacts faster than
those electron-donating ones. Identical observations were
reported earlier for other catalysts.16 On the other hand,
butylacrylate exhibited higher activity than styrene under
identical conditions. A comparison of our work against
some earlier published data for the Heck reaction between
iodobenzene and styrene showed that the present cata-
lyst gave higher activity than those reported for Pd com-
plexed to dendrimer on silica24 or bifunctional PdCl2-Cs+
zeolite25 or Pd nanoparticles on polyoxometalate.26
ꢁ
dimethylformamide (5 cm3ꢀ at 100 C for 12 h.23
X-ray powder diffraction patterns were recorded on
a Rigaku diffractometer using CuKꢂ (ꢃ = 1.54 Å) at
0.5ꢁ min−1. N2 adsorption and desorption isotherms wꢁere
measured in a BELsorp-Max (BEL, JAPAN) at −196 C.
The specific surface areas and pore volume of sam-
ples were calculated by the BET (Brunauer–Emmett–
Teller) method. Prior to the measurement, the sample was
ꢁ
ꢁ
ꢁ
degassed at 150 C under vacuum for 12 h. TEM micro-
graphs were obtained on a JEOL JEM-2100F instrument
and the samples were dispersed in ethanol in an ultrasonic
bath, and a drop of supernatant suspension was placed onto
ꢁ
a holey carbon coated grid and dried at 60 C. Palladium
contents was measured using inductively coupled plasma
spectrometry (ICP-OES, Optima 7300DV).
Heck coupling reaction of aryl iodides and alkenes over
the Pd/MIL-101 (0.9 wt% Pd) catalyst was carried out in
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a round-bottom flask equipped with a condenser. In a typ-
Copyright: American Scientific Publishers
ical reaction, a mixture of aryl iodide (0.2 mmol), alkene
(0.24 mmol), sodium methoxide (NaOMe) (0.4 mmol),
tetrabutylammonium bromide (TBAB) (0.1 mmol), and
palladium catalyst (0.01 g) were stirred at the desired
reaction temperature. The organic phase was subsequently
extracted with diethyl ether, dried over MgSO4 and the
conversion was identified by GC analysis. Conversion and
product selectivity were measured using a GC (7890A GC
System, 7683B series injector, Agilent Technologies) fit-
ted with a high performance HP-5 capillary column (30 m,
0.32 mm, 0.25 ꢄm) and a FID.
The material, Pd0ꢅ9/MIL-101 was characterized by XRD,
N2 adsorption–desorption isotherms, TEM and ICP anal-
ysis. The Pd loading on the sample was 0.91 wt% based
on ICP analysis. The detailed characterization results are
summarized in Table I. XRD pattern showed that the struc-
ture of MIL-101 was unchanged during Pd deposition pro-
cess (Fig. 1). N2 sorption measurement of Pd0ꢅ9/MIL-101
shows a type I pattern identical to MIL-101.6ꢁ23 TEM
images of Pd0ꢅ9/MIL-101 showed that the Pd particles
are well dispersed through the MOF surface in nanome-
ter size between 2–10 nm. Pd particles trend to appear
along the edges of the MOF crystallites with near spherical
morphology.
The Heck C–C coupling reaction of aryl iodides and
alkenes was studied in water in the presence of tetra-
butylammonium bromide and sodium methoxide over
Figure 1. X-ray powder diffraction patterns of (a) MIL-101, (b)
Pd0ꢅ9/MIL-101 and (c) reused Pd0ꢅ9/MIL-101 catalyst after 3rd recycle.
J. Nanosci. Nanotechnol. 15, 6856–6859, 2015
6857