Immobilization of a molybdenum complex on the surface of magnetic nanoparticles for the catalytic epoxidation of olefins

Article abstract of DOI:10.1039/c5nj02218e

Novel organic-inorganic hybrid heterogeneous nanocatalysts were obtained by covalent anchoring of a molybdenum(vi) complex of salicylidene 2-picoloyl hydrazine, MoO₂(sal-phz)(CH₃OH), (1) on the surface of magnetic nanoparticles funct

Full text of DOI:10.1039/c5nj02218e

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DOI: 10.1039/C5NJ02218E
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ARTICLE
Immobilization of a Molybdenum Complex on the Surface
of Magnetic Nanoparticles for the Catalytic Epoxidation
of Olefins
Received 00th January 20xx,
Accepted 00th January 20xx
Maryam Zare,*a Zeinab Moradi–Shoeili,b Mojtaba Bagherzadeh,c Serdar Akbayrak,d and Saim
DOI: 10.1039/x0xx00000x
Özkar,d
www.rsc.org/
Abstract
Novel organic-inorganic hybrid heterogeneous nanocatalysts were obtained by covalent anchoring of molybdenum(VI)
complex of salicylidene 2-picoloyl hydrazine, MoO2(sal-phz)(CH3OH), (1) on the surface of magnetic nanoparticles
functionalized by one of two routes: In the first way, the surface of magnetic nanoparticles is directly modified with 3-
chloropropyltrimethoxysilane yielding 1A. In second way, magnetic nanoparticles were silica-coated by tetraethoxysilane
and then 3-chloropropyltrimethoxysilane yielding the intermediate 2B. Then the complex 1 was grafted on the surface of
1A or 2B through covalent interaction yielding 2A or 3B, respectively. The nanocatalysts 2A and 3B were characterized by
FT–IR, XRD, SEM, TGA, EDX and vibrating sample magnetometry techniques. Nanocomposite 2A shows a much higher
catalytic activity and stability in liquid phase epoxidation reactions, with t-BuOOH as oxidant, compared to that of 3B.
Additionally, the results of comparative study show that 2A is more active and reusable than the Mo complex immobilized
SBA-15.
activity loss during consecutive cycles.12 An attractive
approach to solve these problems involves immobilization of
Introduction
Epoxidation of alkenes and arenes is of importance in
manufacture of a wide variety of fine chemicals, e.g. epoxy
resins, paints and surfactants.1,2 The transition metal-catalyzed
catalysts on the surface of magnetic nanoparticles (MNPs).
Magnetic iron oxide nanoparticles have come into view as the
high specific surface area, distribution of the active sites on the
outer surface of the support which avoids diffusion through
pore and the very easy separation by using an external
magnetic field.13,14 The introduction of functional organic
epoxidation reaction provides a convenient route for preparing
3–5
epoxides.
Molybdenum complexes as homogeneous
catalysts are able to epoxidize alkenes with good to excellent
yield and selectivity.6,7 Additionally, Heterogeneous catalysts
are gaining much attention compared to homogeneous
catalysts since they can be easily separated and recycled from
a reaction mixture, which is of a significant industrial interest.
The use of mesoporous silica as support is a convenient
method for complex heterogenization due to high specific
surface areas, large and defined pore sizes, and excellent
mechanical stability.8–11 However, the rate of reaction
catalyzed using the mesoporous-supported catalysts are often
decreased, as the diffusion of substrates and products through
the pores of the support materials becomes a limiting factor.
Also these heterogeneous systems require filtration and
centrifugation steps to recover the catalysts leading to an
groups on magnetic nanoparticles surfaces causes they show
a
number of attractive properties for varied
applications, such as catalysis,15,16 MRI,17 bioseparation,18
drug delivery, 19 immobilization of biomolecules,20 etc.
Recently,
we
reported
the
application
of
dioxomolybdenum(VI) complex bearing salicylidene 2-picoloyl
hydrazone ligand, [MoO2(sal-phz)(CH3OH)] (1) grafted onto
mesoporous SBA-15 in the epoxidation of olefins, with tert-
buthylhydroperoxide (t-BuOOH) as the oxidizing agent.21
However, such system has provided slower rate for the
epoxidation reaction than the corresponding homogeneous
system because of diffusion limitations of some reactants
within the pores of SBA-15. Hence, it appears to be beneficial
to investigate the immobilization of such complex on the
surface of magnetic nanoparticles. Herein, we report the
binding of the molybdenum complex 1 to the surface of the
magnetite nanoparticles which was functionalized with
chloropropyl group by two routes. The resulting
nanocomposites were employed as catalyst in epoxidation of
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olefins with t-BuOOH under relatively mild reaction conditions The silica-coated Fe3O4 magnetite microspVhieewreArsticlewOnelirnee
of 84 ◦C and an approximate atmospheric pressure.
prepared following the previously publisDhOedI: 1p0r.1o0c3e9d/Cu5rNeJ.20322T1h8eE
prepared magnetic Fe3O4 (0.7 g) was dispersed in a mixture of
40 mL ethanol, 10 mL deionized water and 0.6 mL
concentrated ammonia solution and sonicated for 30 min.
Then 0.5 mL of tetraethylorthosilicate (TEOS) was added to the
solution and stirred for 24 h at room temperature. The
resulted solid was magnetically separated and washed three
times with deionized water and three times with ethanol and
dried at 70 °C for 5 h.
Experimental
Materials and methods
Starting reagents were purchased from Merck or Aldrich. All
solvents were reagent grade and dried and distilled before use
according to standard procedures. Powder X-ray diffraction
(PXRD) data were collected with a Philips X’Pert MPD
diffractometer (Co-Kα X-radiation, λ = 1.79 Å). The metal
loading of the host materials and leaching of molybdenum into
Chloro- functionalized Fe3O4/SiO2 (2B)
the solution were determined by inductively coupled plasma Functionalization of core-shell Fe3O4/SiO2 nonospheres was
atomic emission spectroscopy (ICP-AES) on Perkin-Elmer AA- performed by 3-chloropropyltrimethoxysilane (CPTES)
300 spectrophotometer. FT-IR spectra of samples in the form according to the procedure described previously.24 0.7 g of
of KBr pellets were recorded using an ABB Bomem MB-100 FT- prepared Fe3O4/SiO2 nanoparticles was sonicated in 100 mL
IR spectrophotometer. The scanning electron microscopy dry toluene for 30 min to achieve a uniform dispersion.
(SEM) images were taken on a KYKY-EM3200 scanning electron Subsequently, 1 mL of CPTES was added under vigorous
microscope. The TGA and DTA analysis were carried out by stirring and the mixture was heated at 110 °C for 24 h. The
using Thermo Gravimetric System Mettler Toledo TGA/DSC1 at product was separated with external magnet, washed by
◦
a heating rate of 5 C min−1 under air. A vibration sample toluene and ethanol several times and then dried in an oven at
magnetometer (VSM) was used to measure the magnetic 70 °C for 8 h.
properties of the samples at room temperature, whereby Ni Immobilization of MoO2(sal-phz)(CH3OH) onto 1A and 2B yielding
2A and 3B, respectively
was used as standard. The elemental analysis was recorded
with an energy dispersive X-ray (EDX) analyzer (KEVEX Delta
series) mounted on the Hitachi S-800. Gas chromatography
(GC) analyses were per-formed on an Agilent Technologies
6890N, equipped with a 19019J-413 HP-5, 5% phenyl methyl
siloxane, and a capillary column (60.0 m × 250 μm × 1.00 μm).
To a solution of MoO2(sal-phz)(CH3OH) in DMSO (100 mL), 1A
(1 g) or 2B was added and the mixture was vigorously stirred at
°
80 C for 48 h. At the end of the reaction, the mixture was
cooled down to room temperature; the solid material was
magnetically separated, washed with DMSO and methanol,
°
and then dried at 60 C for 48 h. The molybdenum content of
the material was determined by ICP-AES analysis.
Catalytic Reactions:
Preparation
Fe3O4 Magnetic Nanoparticles
The liquid-phase olefin epoxidation reactions were carried out
in air and autogenous pressure in a 5 mL batch microreactor
equipped with a stir bar and a sampling valve, and immersed in
a thermostated oil bath. Typically, a mixture of the substrate (1
mmol), 2A or 3B (0.0023 mmol Mo complex) and C2H4Cl2 (1
mL) was stirred in a 5 mL tube for 10 min at 84 °C. Then 182 μL
of 5.5 M solution of the oxidant t-BuOOH in decane (1 mmol)
was added and the system was stirred for 1-2 h under reflux.
The progress of reaction was monitored by GC. All the
reactions were performed at least two times and the products
were compared with standard samples.
Magnetic nanoparticles of Fe3O4 were synthesized by
improved chemical coprecipitation method as reported.22
Typically, 3.17 g (16 mmol) of FeCl2.4H2O and 7.57 g (28 mmol)
of FeCl3.6H2O were dissolved in 300 mL of degassed water,
such that the mole ratio between Fe2+ and Fe3+ ions was
1/1.75. The solution was stirred vigorously under N2
°
atmosphere at 80 C for 1h. Then, 40 mL of NH3.H2O were
rapidly added into the mixture. The reaction system turned
into black quickly, and then it was stirred under N2 for another
1 h. The product was separated using a 1.2 T magnet and
washed several times with hot water. The magnetic
nanoparticles were dried at 80 °C.
chloropropyltriethoxysilane coated magnetite nanoparticles (1A)
Results and discussion
2 g of Fe3O4 was added to 100 mL of ethanol, followed by the
addition of ammonium hydroxide 25% solution (2 mL). The
mixture was sonicated for 30 min to achieve a uniform
dispersion. Afterward, 5 mL of 3–chloropropyltriethoxysilane
was added dropwise over a period of 10 min, and the reaction
mixture was stirred at 50 °C for 48 h. The particles were
washed several times with ethanol and magnetically separated
to remove any excess of reagent and salts. The final product
dried at 70°C for 8 h.
Morphology and structural characterization
Magnetic nanoparticles containing molybdenum-salicylidene
2-picoloyl hydrazone complex could be prepared by using one
of two ways (Scheme 1). The first route involves the synthesis
of magnetic nanoparticles by coprecipitation method22 in the
first step. Then the covalently grafted molybdenum-Schiff base
complex (2A) is produced via the subsequent postsynthetic
treatment with 3-chloropropyltrimethoxysilane and MoO2(sal-
phz)(CH3OH) complex 1, respectively. In the second route, the
magnetic Fe3O4 nanoparticles were synthesized by co-
Fe3O4/SiO2 microspheres (1B)
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precipitation method. Then, tetraethylorthosilicate has been chloropropyltrimethoxysilane and then the MoO2(sal-
View Article Online
DOI: 10.1039/C5NJ02218E
used for production of core-shell nanoparticles Fe3O4/SiO2. The phz)(CH3OH) complex 1 was incorporated on the surface of
core-shell magnetic nanoparticles system Fe3O4/SiO2 magnetic nanoparticles through covalent interactions.
functionalization
was
performed
using
OH
OH
HO
Si
TEOS
Fe3O4
Fe3O4
1B
Cl
H2C
Cl
Cl
CH2
H2C
CH2
Cl
H2C
H2C
H2C
Cl
H2C CH2
Si
CH2
CH2
Cl
O
H2C CH2
H2C
O
Si
Si
H2C CH2
Si
O
O
H2C CH2
Si
O
O
O
O
Si
O
OH
Si
O
Fe3O4
Fe3O4
2B
1A
O
O
O
O
O
O
M
CH3OH
o
M
CH3OH
o
O
N
O
Cl
N
Cl
N
H2C
CH2
H2C
N
H2C
H2C
Cl
Cl
N
Cl-
CH2
CH2
H2C
N
Cl-
CH2
+
H2C
+
H2C CH2
Si
O
H2C CH2
Si
H2C CH2
Si
O
Si
O
O
O
H2C CH2
Si
O
O
Si
O
O
O
OH
Si
Fe3O4
Fe3O4
3B
2A
Scheme 1. Preparation of Fe3O4 containing molybdenium Schiff base complex following one of two routes A and B: TEOS:
Tetraethylorthosilicate, CPTES: 3-chloropropyltrimethoxysilane, MoO2(sal-phz)(CH3OH): dioxomolybdenum(VI) complex bearing
salicylidene 2-picoloyl hydrazone
complex on the surface of magnetic mesoporous
The crystalline structure of the nanocatalysts 2A and 3B was nanoparticles. The crystallite size was obtained using Scherrer
determined by powder X-ray diffraction (XRD) (Fig. 1). The formula with FWHM of 311 peak after correction for the
diffraction patterns and relative intensities of all the peaks instrumental broadening. The average crystallite size is 5
matched well with those of magnetite (JCPDS card no. 00-002- nm.27
1035).25,26 Broad XRD peaks clearly indicate the nanocrystalline
nature of the material. The XRD pattern of 2A and 3B catalysts
demonstrates that almost no change occurs after grafting Mo
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DOI: 10.1039/C5NJ02218E
Fig. 3 shows comparatively the Energy dispersive X-ray (EDX)
spectra of 2A and 3B. EDX analysis of two catalysts indicates
the presence of Fe, Si, N, O, C and Mo on both samples. This
result confirms the successful anchoring of the active sites on
the surface of magnetic nanoparticles. The EDX spectra also
give the molybdenum content of the samples 2A and 3B as
3.63 wt% (0.038 mol%) and 0.57 wt% (0.006 mol%) Mo,
respectively. These values are close to the molybdenum
contents of 0.04 mol % and 0.006 mol% for 2A and 3B,
respectively, determined by the inductively coupled plasma
optical emission spectroscopy (ICP/AES) analysis. The loading
value of molybdenum in 2A is much higher than that of 3B,
suggesting that elimination of silica coating step is highly
effective for grafting of Mo complex over MNPs.
Fig. 1. The XRD patterns of Fe3O4, 2A and 3B.
The morphology and structure of the synthesized materials
were examined by Scanning electron microscopy (SEM). SEM
analysis (Fig. 2) of the Fe3O4 nanoparticles, 2A and 3B shows
near monodispersed particles with spherical morphology.
Fig. 3. The EDX spectra of 2A and 3B.
FT-IR spectra taken from KBr pellet provide further evidence
for the presence of MoO2(sal-phz)(CH3OH) moiety on the
surface of magnetic nanoparticles. The FT-IR spectra of Fe3O4,
2A, 3B and MoO2(sal-phz)(CH3OH) in the range 400–4000 cm−1
are depicted in Fig. 4 altogether for comparison. In the IR
spectrum of magnetite nanoparticles, absorptions at 587, 1635
and 3474 cm-1 are observed, mainly resulting from the
stretching frequency of Fe-O, the O-H bending vibration of
absorbed H2O and the stretching vibration of O–H bonds,
respectively.28,29 The absorption band observed at 2923 cm-1 in
the spectra of 2A and 3B is due to the C–H stretching
vibration.28 The bands at the region 1030-1120 cm-1 in the
spectra of 2A and 3B are attributed to the Si−O−Si
stretching,28,29 thereby the intensity is lower in 2A than that in
3B because of absence of silica coating in 2A. In the spectra of
2A and 3B, additional bands are attributed to the presence of
the catalyst as compared to the homogeneous counterparts.
Two absorption bands at 943 and 955 cm–1 are due to ʋ
(Mo=O) of the cis-MoO2 moiety confirming the presence of
complex on the surface of magnetic nanoparticles.7 A band
with medium intensity at 1635 cm-1 is attributed to
Fig. 2. SEM images of Fe3O4 nanoparticles 2A and 3B.
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overlapping of C=N stretching (from ligand group) and O-H
bending of adsorbed water (atmospheric). The other bands at
1280–1635 cm-1 in the IR spectra are assigned to the
vibrational frequencies of the complex.7,21
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DOI: 10.1039/C5NJ02218E
Fig 5. Thermogravimetric curves of 2A and 3B.
Fig. 6 shows the plots of magnetization versus the applied
magnetic field (hysteresis loops) of Fe3O4 nanoparticles, 2A
and 3B measured by vibrating sample magnetometer (VSM) at
room temperature in an applied magnetic field sweeping from
−10 to 10 kOe. As shown in Fig. 6, no hysteresis was observed
in the hysteresis loops of three materials, and the remanence
and coercivity were nearly zero, exhibiting typical
superparamagnetic behavior at room temperature.31 The
saturation magnetizations for the Fe3O4 nanoparticles 2A and
3B are 60.98, 54.80 and 45.6 emu/g, respectively. Compared
with Fe3O4 nanoparticles, the decrease in the saturation
magnetization of 2A and 3B is due to the modification of
surface of the magnetic supports with non-magnetic shell
materials. It is worth mentioning that the saturation
magnetization of 3B is much less than that of 2A. The reason
behind this observation can be explained by the presence of
silica shell on the surface of magnetic nanoparticles in 3B.
Nevertheless, the final synthesized nanocatalysts can easily be
separated from solution with a magnet and redispersed rapidly
as soon as the magnet was taken away due to the
Fig. 4. . FT–IR spectra of (a) Fe3O4, (b) 2A, (c) 3B, (d) MoO2(sal-
phz)(CH3OH), taken from the KBr pellets.
The thermogravimetric analyses of the 2A and 3B
nanoparticles were carried out in the temperature range 25–
800 °C at a heating rate of 10 °C min–1 (Fig 5). As clearly shown,
both TGA curves exhibit a four step weight loss; all of the four
steps are completely quantitative because of nonoverlapping
nature of the steps in the curves. The first stage ranging from
°
°
25 C up to 120 C is ascribed to the removal of physically
adsorbed water and solvent in the nanomaterials. The next
one, ranging from 120 °C to 280 °C can be mainly attributed to
desorption of the chemisorbed water on the surface of
magnetic nanoparticles.30 The last two stages in the weight
°
°
superparamagnetic
magnetization.
property
with
large
saturation
loss, ranging from 300 C to 750 C can be attributed to the
complete removal of the fragments of the ligand and pendant
propyl chains on the surface.21 Comparison of two diagrams
shows that the sample 3B containing silica coating layer has
lower Mo complex loading on its surface than that of 2A which
is in good agreement with the results obtained by EDX and
ICP/AES analyses.
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products can easily be desorbed from the surface. Besides, the
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higher hydrophobicity is also believed toDbOeI: 1a0d.1v0a3n9t/aCg5eNoJ0u2s21f8oEr
the adsorption of the olefin substrate.32
120
100
80
60
1
40
20
0
2A
3B
Fig. 6 VSM magnetization curves of Fe3O4 nanoparticles 2A
and 3B.
0
50
100
Time (min)
150
200
Epoxidation of olefins catalyzed by 2A and 3B
In order to test the catalytic activity of the designed materials
in olefin epoxidation, we examined the oxidation of
cyclooctene, used as a model substrate, with t-BuOOH as the
oxygen donor under different conditions and solvents to form
epoxide as the main product (Table 1). 2A shows high activity
and selectivity (almost 100% for epoxycyclooctene), in
consistent with the homogeneous system we previously
reported.7 Under the reaction conditions in the present study,
2A provides faster reaction rate than that of 3B (Fig. 7). This
might be due to the higher hydrophobicity of 2A, which could
reduce the adsorption abilities for the reaction products, the
more polar epoxide and t-BuOH. Thus, the epoxidation
Fig. 7. Time-dependence of the conversion in the course of
catalytic cyclooctene oxidation catalyzed by 1, 2A and 3B
catalysts with t-BuOOH. Reaction conditions:
1 mmol
cyclooctene, 1 mmol T-BuOOH , 0.0023 mmol catalyst, 1 mL
dichloroethane, reflux.
Table 1. Screening of solvents and reaction conditions in the oxidation of cyclooctene.a
Entry
1
Catalyst
amount of catalyst (g)
Solvent Conversion%b
Time (h)
TOF(h-1)
-
-
-
C2H4Cl2
C2H4Cl2
CHCl3
26
28
72
53
30
16
98
98
91
88
46
92
92
1
1
1
1
1
1
1
1
1
1
3
3
3
2
Fe3O4 nanoparticles
-
-
3
4
5
6
7
8
9
10
11
12
13
2A
2A
2A
2A
2A
2A
2A
2A
3B
3B
3B
0.01
0.01
0.01
0.01
0.01
0.007
0.005
0.003
0.007
0.02
0.04
313
230
130
70
258
426
479
772
365
255
127
CH2Cl2
CH3OH
CH3CN
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
aReaction condition: 1 mmol cyclooctene: 1 mmol, TBHP. The reactions were run under reflux.
The reusability of the catalysts was also tested in cyclooctene cyclooctene, by magnetically separation and redispersing,
oxidation under reflux employing 1 mmol t-BuOOH for 1 mmol while the 3B catalyst shows a sharp decrease in activity even in
of substrate (Table 2). The catalysts were separated by using the second run. We may conclude that the first reaction cycle
an external magnet after each cycle, washed with C2H4Cl2 and is at least partly catalyzed in homogeneous phase, probably by
then redispersed into a fresh reaction mixture. The 2A catalyst weakly adsorbed molybdenum species that were not
can be reused nine times without significant loss in catalytic efficiently extracted after the final grafting step in the
activity and selectivity in the epoxidation reaction of synthesis of the material. To further assess the recyclability of
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both catalysts, the hot filtration test was performed for 2A and cyclooctene. These findings are consistent with the results
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3B catalysts by filtering off the reaction solution after 15 min obtained under homogeneous systemsDOwIh: 1i0ch.103w9e/C5rNeJp0o2r2t1e8dE
catalytic epoxidation at 84 °C, and leaving them to react for previously.7
180 min. No olefin conversion was observed after the filtration
step for 2A, but cyclooctene was observed to undergo further
epoxidation at relatively high rate in the filtered solution in the
case of 3B (Fig. 8).
50
40
30
Table 2. Reuses of the catalysts in the selective oxidation of
cyclooctene.a
20
Run
2A
3B
1
98
92
2
98
68
3
98
65
4
98
65
5
96
65
6
96
-
7
96
-
8
94
-
9
94
-
10
0
0
50
100
150
200
aReaction condition: 0.0023 mmol catalyst: 1 mmol t-BuOOH: 1
mmol cyclooctene. The reactions were run under reflux for 1 h
for 2A and 3B. bGC conversion based on starting alkene.
Time(min)
To demonstrate the scope of 2A as a catalyst for epoxidation Fig. 8. Kinetic profiles of cyclooctene epoxidation by continuing
reaction, it was employed in epoxidation of various alkenes the reaction after removing the catalysts 2A ( ) and 3B ( )
under the optimized reaction conditions (Table 3). 2A catalyzes
the conversion of all the olefins to the corresponding epoxides
in high to excellent yield similar to that obtained for
Table 3. Catalytic oxidation of various alkenes with t-BuOOH by 2A catalyst and MoO2(sal-phz)/SBA.a
Conversion%
Time(h)
Selectivity%
Entry
Substrate
MoO2(salphz)
MoO2(salphz)
MoO2(salphz)
2A
2A
2A
/SBA
97
98
94
80
65
81
58
93
/SBA
/SBA
>99
99
56
78
90
99
99
99
1
2
3
4
5
6
7
8
cyclohexene
cyclooctene
styrene
α-methylstyrene
4-methylstyrene
1-heptene
97
98
89
80
74
90
93
90
2
1
2
2
2
2
2
2
3
1
3
4
4
6
7
5
>99
99
56
72
83
>99
>99
>99
1-octene
limonene
aReaction condition: 0.0023mmol catalyst: 1 mmol alkene: 1mmol t-BuOOH. The reactions were run
under reflux in 1 mL dichloroethane.
arise from the presence of Lewis-acidic sites (here: Fe3+) on the
A comparison of the results obtained in the catalytic surface of support.32
epoxidation of olefins by using the MoO2(sal-phz)(CH3OH) For comparison, some of the most relevant systems reported
complex
grafted
on
chloropropyltrimethoxysilane to date have been included in table 4. These results clearly
functionalized surface of Fe3O4 nanoparticles or immobilized point out the efficiency of the proposed catalytic system (table
on the surface of SBA-15 clearly shows that activity and 4, first entriy) in activity and selectivity in epoxidation reaction
stability of 2A is much higher than that observed with the as compared to literature reports involving several
MoO2(sal-phz)(CH3OH) complex incorporated into SBA-15 heterogeneous systems under various conditions (table 4,
pores.21 The improved catalytic activity of 2A compared to the entries 2-5).
same complex on SBA-15 arises from the ideal exposition of
the active sites on the surface of the nanoparticles which is
almost similar to a quasi-homogeneous catalyst system. In
contrast, the diffusion limitation or pore constraints in SBA-15
decrease accessibility of the active sites for the substrate
molecules. Also, an additional increase in activity may possibly
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Table 4. Comparison of literature reports on the selective oxidation of cyclooctene under various conditions.
Molar ratio
Entary
catalyst
Temp (oC)
Time(h) Conversion%
Ref
cat:sub:ox
0.0023:1:1
0.01:1:1.2
0.01:1:1.2
0.059:3.5:22
1:100:154
1
2
3
4
5
2A
Reflux
Reflux
Reflux
60
1
6
98
96
This work
1Mo@SMNP
2Mo@SMNP
Mo-Fe3O4@SiO2@P4VP
PMO-ph/Mo(CO)6
12
12
33
34
6
58
12
0.5
85.6
100
55
3
4
S. N. Rao, N. Kathale, N. N. Rao and K. N. Munshi, Inorg.
Chim. Acta, 2007, 360, 4010.
P. Adao, J. C. Pessoa, R. T. Henriques, M. L. Kuznetsov,
F. Avecilla, M. R. Maurya, U. Kumar and I. Correia,
Inorg. Chem., 2009, 48, 3542.
S. Li, C. W. Kee, K. W. Huang, T. S. A. Hor and J. Zhao,
Organometallics, 2010, 29,1924.
M. Bagherzadeh, M. Amini, A. Ellern and L. K. Woo,
Inorg. Chem. Commun., 2012, 15, 52.
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Conclusions
Organic-inorganic hybrid heterogeneous nanocatalyst systems
were synthesized by covalent anchoring of Mo complex,
MoO2(sal-phz)(CH3OH) on magnetic nanoparticles by two
approaches, A and B routes, yielding the nanocatalysts 2A and
3B, respectively. In the first way, the surface of magnetic
5
6
7
8
9
nanoparticles
is
directly
modified
with
3-
chloropropyltrimethoxysilane. In second way, nanoparticles
were first coated with tetraethoxysilane, followed by a second
hydrolysis/condensation step using CPTES.The activity of the
organic/inorganic hybrid nanocatalysts 2A and 3B was tested
in the epoxidation of cis-cyclooctene. The 3B catalyst
possesses lower catalytic activity in cyclooctene epoxidation
than that of 2A. This might be due to the higher
hydrophobicity of 2A, which could reduce the adsorption
abilities for the reaction products, the more polar epoxide and
t-BuOH. The 2A nanocatalyst can be reused nine times, by
simple magnetic separation without any deterioration of
conversion and selectivity in the epoxidation reaction of
cyclooctene, while the catalytic activity of 3B decreases
drastically in the second run, but afterwards tends to remain
constant. Possibly, some metal species that were not desorbed
by the simple solvent extraction used in the catalyst
preparation procedure could be desorbed under the applied
reaction conditions. Moreover, a higher conversion is achieved
with 2A than that with SBA-15 supported Mo catalyst, which
may be due to the slower diffusion of the substrate molecules
inside the pores of SBA-15.
10 S.P. Shylesh, M. Jia, A. Seifert, S. Adappa, S. Ernsta and
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Akbayrak and S. Özkar, J. Mol. Catal. A: Chem., 2014,
395, 470.
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13 D. Astruc, F. Lu and J. R. Aranzaes, Angew. Chem. 2005,
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15 H. Keypour, M. Balali, M. M. Haghdoost and M.
Bagherzadeh, RSC Adv., 2015, 5, 53349.
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17 R. Qiao, C. Yang and M. Gao, J. Mater. Chem., 2009, 19,
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Acknowledgements
The authors are grateful to the Golpayegan University of
Technology, the University of Guilan and the Sharif University
of Technology for financial support. Partial support by Turkish
Academy of Sciences (TUBA) is gratefully acknowledged.
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Molybdenum complex was immobilized on the Fe3O4
nanoparticles modified with chloropropyl by two routes
and used as nanocatalysts for the oxidation of alkenes.