Co-Condensation Assisted Preparation of MoVI Schiff Base Modified Mesoporous Silica Catalyst for Enhanced Epoxidation of Olefins

Article abstract of DOI:10.1071/CH16030

An organic-inorganic catalyst was prepared by the reaction of p-salicylidine aminobenzoic acid with mesoporous silica modified with 3-chloropropyl groups. The hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and 3-chloropropyltrimethoxysilane (CPTES) took place during the preparation process. MoO₂(acac)₂ was then introduced into the mesoporous silica functionalized with a Schiff base ligand. The structural properties of the prepared catalysts were investigated by a series of techniques, such as elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption/desorption curves, and thermogravimetric analysis (TGA). The results demonstrated that the Mo^VI Schiff base complex was successfully tethered on the silica support, and the hexagonally ordered mesoporous structure of the SBA-15-type silica was well retained after the anchoring reaction. The heterogeneous catalyst showed good catalytic activities in the liquid-phase epoxidation of olefins with t-BuOOH as the oxygen source in 1,2-dichloroethane solvent at 80°C. Several important factors, including oxidant-to-substrate ratio, solvent, and catalyst reusability, were investigated. Under the optimum reaction conditions, using this heterogeneous catalyst for the cyclohexene epoxidation reaction, a high conversion of 97.20% and selectivity of >99% was achieved after 4h, while the catalytic activity nearly remained unchanged over four runs.

Full text of DOI:10.1071/CH16030

CSIRO PUBLISHING
Aust. J. Chem. 2016, 69, 817–825
Full Paper
http://dx.doi.org/10.1071/CH16030
VI
Co-Condensation Assisted Preparation of Mo Schiff Base
Modified Mesoporous Silica Catalyst for Enhanced
Epoxidation of Olefins
A
,
B
A
,
C
A
B
Jian Zhang,
Pingping Jiang,
Yirui Shen, Guohu Zhao,
A
A
Weijie Zhang, and Gang Bian
A
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education,
School ofChemical and MaterialEngineering, JiangnanUniversity, Wuxi214122, China.
Key Laboratory for City Environmental Pollution Control, School of Chemistry and
Environmental Science, Lanzhou City University, Lanzhou 730070, China.
B
C
Corresponding author. Email: ppjiang@jiangnan.edu.cn
An organic–inorganic catalyst was prepared by the reaction of p-salicylidine aminobenzoic acid with mesoporous silica
modified with 3-chloropropyl groups. The hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and
3
-chloropropyltrimethoxysilane (CPTES) took place during the preparation process. MoO (acac) was then introduced
2 2
into the mesoporous silica functionalized with a Schiff base ligand. The structural properties of the prepared catalysts were
investigated by a series of techniques, such as elemental analysis, X-ray diffraction (XRD), Fourier transform infrared
(
FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N adsorption/
2
VI
desorption curves, and thermogravimetric analysis (TGA). The results demonstrated that the Mo Schiff base complex
was successfully tethered on the silica support, and the hexagonally ordered mesoporous structure of the SBA-15-type
silica was well retained after the anchoring reaction. The heterogeneous catalyst showed good catalytic activities in the
liquid-phase epoxidation of olefins with t-BuOOH as the oxygen source in 1,2-dichloroethane solvent at 808C. Several
important factors, including oxidant-to-substrate ratio, solvent, and catalyst reusability, were investigated. Under the
optimum reaction conditions, using this heterogeneous catalyst for the cyclohexene epoxidation reaction, a high
conversion of 97.20 % and selectivity of .99 % was achieved after 4 h, while the catalytic activity nearly remained
unchanged over four runs.
Manuscript received: 23 October 2015.
Manuscript accepted: 4 February 2016.
Published online: 29 February 2016.
Introduction
Epoxides are important organic intermediates for the organic
dependent on the preparation procedures. In general, post-
synthetic grafting and co-condensation methods are used to
functionalize morphous silica materials, both of which involve
the co-condensation of siloxane and organosiloxane precursors
to produce hybrid organic–inorganic networks. The post-
synthetic grafting method typically results in serious non-
homogeneous surface coverage and an uneven distribution of
[
1]
synthesis of fine chemicals. Olefin epoxidation in the liquid
phase is one of the most important industrial reactions for
epoxide production. During these epoxidation reactions, the
catalyst plays a crucial role and dominates the whole reaction.
Finding an efficient catalyst for the epoxidation of olefins has
been a hot research field. To date, heterogeneous complexes
have been used as alternative structures to not only combine the
advantages (rich active sites and good compatibility with reaction
species) but also remedy the disadvantages (poor recyclability
and residues in products) of homogeneous complexes in catalytic
epoxidation. Several organic–inorganic heterogeneous catalytic
systems with transition metal (Mn, V, Mo, Ti, Co, etc.) Schiff
[
4]
organic species throughout the material. At the same time, the
low reactivity of the surface silanols in the post-synthetic
[5]
grafting process limits the extend of surface functionalization.
Alternately, the co-condensation method minimizes the number
of processing steps and produces mesoporous materials with a
relatively uniform distribution of the organic functionalities in
addition to high loadings of organic groups without blocking the
[2]
[6]
base complexes have been used to oxidize olefins to epoxides.
As a typical heterogeneous complex, a mesoporous silica
entranceof the pores. The welldispersed catalytic sitespartially
integrated on the wall of these materials offer reduced resistance
to the diffusion of molecules within the mesochannels and
are more resistant to leaching than if they were grafted onto the
VI
supported Mo Schiff base has been widely applied in olefin
[3]
epoxidation due to its high catalytic activity.
[7]
On the basis of these reported results, it is well acknowledged
that the surface properties of functionalized mesoporous silica
are crucial for their catalytic performances, which are largely
ordered mesoporous silica. This high loading of organic groups
imparts poor wettability during the epoxidation reaction leading
[8]
to favourable contact with reactive species. In addition to the
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8
18
J. Zhang et al.
OEt
OH
EtO Si OEt
OEt
HO Si OH
Hydrolysis
Co-condensation
Cl
Cl
OH
OH
OEt
P123, H O, HCl
2
EtO Si
OEt
Cl
HO Si
OH
Cl
Cl-SiO2
O
C
O
N
O
O
O
O
C
Mo
O
O
O
3
. MoO
C
O
N
(acac)
2
O
2
HO
N
O
HO
C
N
Mo-SB-Cl-SiO2
Scheme 1. Preparation of ordered Mo-SB-Cl-SiO
SB-Cl-SiO2
2
.
enhanced loading of functional groups, the particle size and shape
of the resulting mesoporous silicas could be controlled by the
Preparation of Cl-SiO2
The material was prepared by a co-condensation method. In a
typical synthesis, 1.0 g of Pluronic P123 was thoroughly dis-
solved in 35 mL of water and 5 mL of concentrated hydrochloric
acid. The solution was heated to 408C and 2.08 g (2.3 mL) of
TEOS was added. After 1 h of TEOS prehydrolysis, CPTES
[9]
co-condensation method. It can be thus deduced that this
co-condensation approach provides a new synthetic route for
functional mesoporous silica heterogeneous catalysts potentially
[10]
with enhanced catalytic activity in olefin epoxidation.
In this work the co-condensation assisted method was
employed for the synthesis of a novel mesoporous organosilica
(
0.5 mL) was added into the aqueous dispersion using a syringe
over 10 min. The resultant mixture was stirred at 408C for 24 h,
followed by hydrothermal treatment at 1008C for another 24 h
under static conditions. Finally, the solid was filtered off and
was then subjected to Soxhlet extraction with dry methanol for
72 h. The white solid (Cl-SiO ) was dried at 808C under vacuum
2
for 8 h.
VI
bearing a high density of Mo Schiff base complexes
(
Scheme 1). The obtained materials were characterised by using
elemental analysis, X-ray diffraction (XRD), FT-IR spectroscopy,
scanning electron microscopy (SEM), transmission electron
microscopy (TEM), N2 adsorption/desorption analysis, and
thermogravimetric analysis (TGA). The hybrid catalysts were
used for the epoxidation of olefins. The effects of different reaction
variables were investigated in the epoxidation reaction. Further-
more, the stabilityand reusabilityof the organic–inorganic catalyst
were evaluated.
Preparation of SB-Cl-SiO2
The preparation of SB-Cl-SiO was adapted from a similar
2
[
12]
procedure.
The previously synthesized Cl-SiO (1.0 g) and
2
DMF (10 mL) were placed in a flask equipped with a magnetic
stirrer and a reflux condenser. The mixture was stirred for
0 min, and afterwards a solution of 0.5 g H SB in 10 mL of
2
Experimental
1
Materials
DMF was added, followed by the addition of 10 mL of ethyla-
cetate with 2.25 g of triethylamine. The reaction mixture was
heated to 908C and kept for 10 h under stirring. After cooling to
room temperature, the pale yellow solid power was separated by
filtration, washed with hot DMF (3 ꢀ 50 mL), and ethanol
Analytical reagent grade olefins (Aladdin, China), Pluronic
P123 triblock copolymer (M ¼ 5800) (Sigma–Aldrich, China),
n
3-chloropropyltriethoxysilane (CPTES), and tetraethylorthosilicate
(TEOS) (Sinopharm Chemical Reagent Co., Ltd) were used as
obtained. MoO (acac) , SBA-15 (a mesoporous silica material),
several times. After drying at 808C, SB-Cl-SiO was obtained.
2
2
2
p-salicylidine aminobenzoic acid (abbreviated as H SB), and
2
Mo-SB (Mo complexed to p-salicylidine aminobenzoic acid)
Preparation of Mo-SB-Cl-SiO2
[
11]
were prepared according to the reported methods. Details of
synthetic procedures are given in the Supplementary Material.
Other chemicals and solvents of analytical reagent grade were
used without purification.
The preparation of Mo-SB-Cl-SiO was as follows: SB-Cl-
2
SiO (1 g) was added to 10 mL of methanol, and the mixture was
2
heated to 858C. A hot ethanolic solution (35 mL) of 0.75 g of
MoO (acac) was then added dropwise under stirring. The
2
2
colour of the solution gradually changed to deep blue. After
stirring for 24 h, the product was filtered, washed by Soxhlet
extraction with ethanol to remove the unreacted MoO (acac) ,
Synthesis of Mo-SB-Cl-SiO Material
2
(
Co-Condensation Method)
2
2
The sequence of events in the functionalization of Cl-SiO with
2
and dried at 808C. The acquired solid was labelled Mo-SB-Cl-
SiO2.
H SB and MoO (acac) is depicted in Scheme 1.
2
2
2

Organic–Inorganic Heterogeneous Catalyst
819
Synthesis of Mo-SB-Cl-SBA-15 Material
100
(
Post-Grafting Method)
9
5
0
For comparison, a counterpart material was prepared via the
same grafting method except Cl-SBA-15 was replaced by
Cl-SiO . The preparation of Cl-SBA-15 was in accordance with
our previous work.
Mo-SB-Cl-SBA-15.
9
a
85
2
[2a]
b
c
The grafted hybrid was denoted as
a Mo-SB-Cl-SBA-15
b SB-Cl-SiO2
8
0
5
c Cl-SiO2
d Mo-SB-Cl-SiO2
7
d
Epoxidation Procedures
70
100
200
300
400
500
600
700
800
The performance of the catalysts was investigated in the
epoxidation of a model cyclohexene substrate. In a typical
procedure, cyclohexene (2.5 mmol), oxidant (5.0 mmol),
tert-butyl hydroperoxide (TBHP, 65 wt.-% in water solution),
and catalyst (25 mg) were added to 1,2-dichloroethane (1,2-DCE,
Temperature [°C]
Fig. 1. TGA curves of (a) Mo-SB-Cl-SBA-15, (b) SB-Cl-SiO
2
,
(
c) Cl-SiO , and (d) Mo-SB-Cl-SiO
2
2
.
1
0 mL) in a 25 mL two-neck round bottom flask and the reaction
2927
a
b
was carried out under reflux for an appropriate duration at 808C.
After finishing the reaction, the reaction mixture was centrifuged
and analysed using a gas chromatograph (GC, SP-6890A)
equipped with an FID detector and a capillary column (SE-54
2983
1634
c
3
0 m ꢀ 0.32 mmꢀ 0.25 mm). The identity of the products
was confirmed using gas chromatography–mass spectrometry
GC-MS, Perkin-Elmer, Clarus 500).
d
(
d Mo-SB-Cl-SBA-15
a Cl-SiO2
Materials Characterization
TGA of the as-fabricated materials was performed using
Thermo Gravimetric System Mettler Toledo at a temperature
b SB-Cl-SiO2
c Mo-SB-Cl-SiO2
1080
1000
ꢁ1
ramping rate of 10 8C min under air. FT-IR spectra were
recorded on a NICOLET 6700 FT-IR Thermoscientific spec-
3500
3000
2500
2000
1500
500
ꢁ1
Wavenumber [cmꢀ1]
trometer using a KBr pellet technique in the 500–4000 cm
region. Adsorption and desorption isotherms for nitrogen were
obtained at ꢁ1968C using a Micromeritics ASAP 2010.
The materials were outgassed at 958C and 0.1 Pa for 6 h before
the measurement. XRD patterns were recorded by a Bruker
diffractometer (D8) using a curved detector from 0.8 to 10 (2y)
with a resolution of 0.02 at 40 kV, 40 mA, with Cu Ka radiation
Fig. 2. IR spectra of (a) Cl-SiO , (b) SB-Cl-SiO , (c) Mo-SB-Cl-SiO
2
2
2
, and
(
d) Mo-SB-Cl-SBA-15.
(Fig. 1b) had a lower weight loss below 3008C. When the
temperature increased to 7008C, SB-Cl-SiO2 underwent an
) certifying
the successful immobilization of the Schiff base ligand on the
˚
,17 wt-% weight loss (higher than that in Cl-SiO
2
(
l 1.54056 A). SEM and energy-dispersive X-ray spectroscopy
EDS) mapping were carried out using a Hitachi S-4800
(
equipped with a field-emission gun with an accelerating voltage
2
at 2 kV and an Oxford Instruments 80 mm silicon drifted
organic–inorganic silica matrix. As for Mo-SB-Cl-SiO (Fig. 1d),
2
its TGA curve also showed a weight loss between 25 to 3008C.
Furthermore, a ,20 wt-% loss for Mo-SB-Cl-SiO was observed
detector with an accelerating voltage of 15 kV and current of
1
2
from 300 to ,7008C, which indicated the decomposition of the
5 mA. TEM was performed on a JEOL JEM-2100F with an
VI
[15]
Mo Schiff base ligand complex. Comparing the weight losses
between SB-Cl-SiO and Mo-SB-Cl-SiO , it was found that the
acceleration voltage of 200 kV. All materials were prepared by
finely dispersing the materials in ethanol using sonication and
were deposited uniformly on a 400 mesh copper grid coated with
a perforated carbon film and dried in air. The content of
molybdenum in the host materials and leaching of molybdenum
into the solution were determined by inductively coupled
plasma–atomic emission spectroscopy (ICP-AES) on a Perkin-
Elmer AA-300 spectrophotometer.
2
2
difference was ,3.3 wt-%, which suggests the possible formation
VI
of MoO and grafting of the Mo Schiff base complex into the
3
[16]
organic–inorganic silica matrix. From Fig. 1a, it is clearly seen
that the mass loss of Mo-SB-Cl-SBA-15 is lower than that of
Mo-SB-Cl-SiO . The result indicates a lower amount of functional
2
groups bonded to the surface through the post-grafting method
compared with the co-condensation method. According to the
ICP-AES results, the Mo contents were determined to be 0.2366
Results and Discussion
Textural Characterisation
TGA and Element Analysis
ꢁ1
and 0.085 mmol g for Mo-SB-Cl-SiO and Mo-SB-Cl-SBA-15,
2
respectively. Mo-SB-Cl-SiO showed a higher amount of Mo than
2
Mo-SB-Cl-SBA-15, which is in good agreement with the TGA
results.
The TGA curve of Cl-SiO (Fig. 1c) exhibited a 3–4 wt-%
2
weight loss in the region of 25–1208C which was assigned to the
removal of physically adsorbed water and solvent inside the
FT-IR Spectroscopy
[13]
pores.
A further ,2 wt-% of weight loss in the region of
50–3008C was attributed to desorption of the chemisorbed water
on the silica surface. A major weight loss (,13 wt-%) between
FT-IR spectra provided further evidence for the successful
VI
immobilization of the Mo Schiff base on the mesoporous
material and the results are shown in Fig. 2. The characteristic
1
[14]
ꢁ1
300 and 7008C was attributed to the decomposition of the
absorption peaks at 3450 and 1634 cm for Cl-SiO , SB-Cl-
2
3
-chloropropyl groups. In comparison with Cl-SiO , SB-Cl-SiO
2
SiO , Mo-SB-Cl-SiO , and Mo-SB-Cl-SBA-15 are assigned to
2
2
2

8
20
J. Zhang et al.
(a)
(b)
110
200
i
100
110
200
ii
i Cl-SiO2
iii
iv
ii SB-Cl-SiO2
iii Mo-SB-Cl-SiO2
iv Mo-SB-Cl-SBA-15
1
2
3
4
5
1.5
2.0
2.5
2θ [deg.]
2θ [deg.]
Fig. 3. (a) X-Ray diffraction patterns of (i) Cl-SiO , (ii) SB-Cl-SiO , (iii) Mo-SB-Cl-SiO
2 2
2
, and (iv) Mo-SB-Cl-
SBA-15; (b) partly enlarged view.
an O–H stretching vibration and deformation vibration of
phyisorbed water and potential surface hydroxy groups. The bands
at 2983 and 2927 cm are attributed to the CH asymmetric and
2
comparison with Mo-SB-Cl-SBA-15, Mo-SB-Cl-SiO showed
2
diffraction peaks with lower intensity and higher position. This
might be due to loss of regularity and enlargement of the
pore in the 2D hexagonal structure of mesoporous silica by
a co-condensation assisted method.
ꢁ1
symmetric stretching vibrations of the propyl chain, respectively.
ꢁ
1
The broad peak between 1000 and 1250 cm corresponds to
ꢁ
1
Si–O–Si asymmetric vibrations, a slight peak at 800 cm to
ꢁ1
N Adsorption/Desorption
2
a Si–O–Si symmetric vibration, and the peak at 960 cm to the
Compared with Cl-SiO , SB-Cl-
[17]
Si–O stretching of Si-OH.
2
Nitrogen adsorption/desorption experiments were performed
on the Cl-SiO , SB-Cl-SiO , Mo-SB-Cl-SiO , and Mo-SB-Cl-
ꢁ1
SiO showed weaker absorption bands at 1634 and 960 cm due
2
2
2
2
to the introduction of the Schiff base ligand into the organic silica
matrix. For SB-Cl-SiO , the C=N stretching vibration peak
SBA-15 materials to compare their surface areas and pore size
distributions (Fig. 4a, b, Table 1). Cl-SiO , SB-Cl-SiO , and
Mo-SB-Cl-SiO revealed type IV isotherms with a H2-type
2
2
2
was not clearly apparent because it was overlapped with the
After treatment with
2
[18]
O–H deformation vibration peak.
hysteresis loop. The steep adsorption step around P/P ¼ 0.40–
0
ꢁ1
MoO (acac) , two new adjacent bands at 908 and 871 cm are
2
0.70 demonstrated the formation of well structured mesoporous
materials with narrow pore size distributions, as it was derived
from the Barrett-Joyner-Halenda (BJH) analysis shown in
Fig. 4a. The total pore volume decreased when loading of the
organic ligand increased. In addition, the mean pore size is
slightly shifted to lower values for the same reasons discussed
above. Cl-SiO , SB-Cl-SiO , and Mo-SB-Cl-SiO show a sharp
2
observed (Fig. 2c) and they are characteristic peaks of a cis-MoO
2
[19]
group. This is powerful evidence for the formation of Mo-SB-
Cl-SiO . The expected symmetric (Mo=O) band is not observed
2
due to the overlap with a broad band with medium intensity at
[20]
ꢁ
1
9
spectrum of Mo-SB-Cl-SBA-15 (Fig. 2d), due to the lower ligand
60 cm for Si–O vibrations in silanols.
For the FT-IR
2
2
2
ꢁ1
content, the characteristic C=N stretching vibration at 1643 cm
is weakened and the characteristic Mo=O stretching vibration is
not clearly apparent at 908 cm
peak (Fig. 4b) that indicates the uniform pore size distributions
of the materials. Their pore diameters were 3.82, 3.66, and
3.60 nm, respectively, as summarised in Table 1. The Brunauer–
Emmett–Teller (BET) surface area and pore volume of the
ꢁ1
.
XRD Analysis
Mo-SB-Cl-SiO catalyst were lower than those of SB-Cl-SiO2
2
confirming the successful immobilization of MoO (acac) in the
2
Fig. 3a displays the XRD patterns of Cl-SiO , SB-Cl-SiO ,
2
2
2
organosilane framework. Mo-SB-Cl-SBA-15 displayed a type
IV isotherm with H1-type hysteresis loop, which indicates a
typical mesoporous material with high regularity. Mo-SB-Cl-
SBA-15 had a larger pore diameter and pore volume and a lower
Mo-SB-Cl-SiO , and Mo-SB-Cl-SBA-15. Cl-SiO showed a
2
2
characteristic diffraction peak at 2y ¼ 0.8–1.2 corresponding
[
21]
to the (100) reflection of SBA-15-type materials.
firms the formation of a mesoporous structure. For SB-Cl-SiO2
This con-
BET surface area than Mo-SB-Cl-SiO . This is a result of the
2
and Mo-SB-Cl-SiO , the intense (100) reflections suggest that
2
greater number of organic ligands and metallic active sites in
Mo-SB-Cl-SiO prepared by the co-condensation assisted method,
which is consistent with TGA and ICP-AES analyses.
the mesoporous organosilica maintained its structural integrity
VI
after anchoring of the Mo Schiff base complex. Compared
2
with Cl-SiO , the XRD pattern of the SB-Cl-SiO and Mo-SB-
2
2
Cl-SiO (Fig. 3b, curve i) showed the (110) and (200) reflections
2
SEM, TEM, and EDS
with a lower intensity due to the decreased mesoscopic order of
the materials and the contrast matching between the silicate
framework and organic moieties located inside the Cl-SiO2
channels. It can also be seen from Fig. 3b, comparing Cl-SiO2,
SB-Cl-SiO , and Mo-SB-SiO , that the position of this reflec-
SEM images of Cl-SiO and Mo-SB-Cl-SiO were recorded
2
2
and the results are shown in Fig. 5a, d. The results show that both
Cl-SiO and Mo-SB-Cl-SiO had a wormlike structure with high
regularity. However, Mo-SB-Cl-SiO became slightly coarse.
2
2
2
2
2
VI
tion for Mo-SB-SiO is shifted to a lower angle (or higher
2
Loading Mo-SB-Cl-SiO with the Mo Schiff base affected the
2
d-value) which is caused by the incorporation of the Schiff base
ligands and the coordination with MoO (acac) in the pores of
surface morphology of the mesostructure. In addition, more
detailed structural information of the Cl-SiO and Mo-SB-Cl-
2
2
2
[5a]
Cl-SiO leading to expansion of the unit cell parameter.
2
In
SiO nanocomposite was determined by TEM. The TEM image
2

Organic–Inorganic Heterogeneous Catalyst
821
(a)
(b)
0.8
0.7
0.6
0.5
0.4
0.3
i Cl-SiO2
ii SB-SiO2
iii Mo-SB-Cl-SiO2
iv Mo-SB-Cl-SBA-15
i
i
ii
ii
iii
0.2
0.1
0
i Cl-SiO2
iii
iv
ii SB-Cl-SiO2
iii Mo-SB-Cl-SiO2
iv Mo-SB-Cl-SBA-15
iv
0
0.2
0.4
0.6
0.8
1.0
2
4
6
8
10
Relative pressure (P/P0)
Pore diameter [nm]
Fig. 4. (a) Nitrogen adsorption isotherms and (b) pore size distribution profiles of the initial material (i) Cl-SiO
iv) Mo-SB-Cl-SBA-15.
2
, (ii) SB-Cl-SiO
2
, (iii) Mo-SB-Cl-SiO
2
, and
(
Table 1. Characteristics of support and catalysts, specific surface area
BET: specific surface area; VBJH: pore volume; DBJH: pore diameter
effective heterogeneous epoxidation catalyst. In comparison with
Mo-SB-Cl-SBA-15, the Mo-SB-Cl-SiO2 showed a higher
conversion for the epoxidation under the same conditions. On
S
Sample
Mo content
S
BET
ꢁ1
V
BJH
ꢁ1
D
BJH
the one hand, the Mo-SB-Cl-SiO catalyst exhibited a higher
2
ꢁ1
2
[m g
3
[cm g
VI
density of Mo active sites leading to its higher catalytic
[
mmol g
]
]
]
[nm]
[7b,22]
epoxidation efficiency.
On the other, most of the –OH
Cl-SiO
2
–
–
681.58
523.09
486.59
476.88
0.62
0.50
0.44
0.62
3.82
3.66
3.60
5.24
groups on the surface of the silica mesoporous precursor were
replaced by 3-chloropropyl groups through the co-condensation
method, which could improve the hydrophobicity of Mo-SB-Cl-
SB-Cl-SiO
2
Mo-SB-Cl-SiO
Mo-SB-Cl-SBA-15
2
0.2366
0.0850
[23]
SiO and have a beneficial effect on the epoxidation reaction.
2
Effects of Different Oxidant/Olefin Molar Ratios
of the Mo-SB-Cl-SiO material shows a well ordered rodlike
2
structure of the channels (Fig. 5e) from the side view and a
typical honeycomb structure with SBA-15-type mesostructured
VI
materials from the profile view (Fig. 5f). Loading of the Mo
Schiff base did not destroy the mesoporous structure of the
support. This observation is in good agreement with the nitrogen
adsoption/desorption results. The mesoscopic order was further
confirmed by TEM images (Fig. 5b, c, e, f) as definitive
evidence of the structure ordering achieved. EDS mapping
was employed to probe the presence of Si, O, C, N, and Mo
elements and to corroborate the distribution throughout the
To study the effect of oxidant amount on epoxidation, four
different molar ratios of aqueous TBHP to cyclohexene (0.5 : 1,
1 : 1, 2 : 1 and 3 : 1) were investigated. As shown in Fig. 7, when
the TBHP-to-cyclohexene molar ratio increased to 2 : 1, the
highest conversion (97.20 %) was obtained during 4 h and the
selectivity was over 99 %. With a further increase of TBHP-to-
cyclohexene molar ratio to 3 : 1, the conversion slightly
decreased to 91.56 %. The excess TBHP probably led to the
generation of tert-butyl alcohol, which has been reported to act
as a competitive inhibitor for the attack of TBHP at a molyb-
[
24]
Mo-SB-Cl-SiO material (Fig. 5h–l). The existence of Si, O, C,
2
denum(VI) centre and restrain the epoxidation process.
In
N, and Mo elements and their uniform distribution was clearly
addition, the corresponding increase in water upon use of
excessive TBHP is adverse for the epoxidation of olefins.
VI
demonstrated, which further confirms that the Mo Schiff base
had been successfully chelated into the mesoporous silica.
Effects of Different Solvents
Catalytic Epoxidation Activity
To evaluate the influence of various solvents on the epoxidation,
The reaction conditions for the catalytic epoxidation were:
cyclohexene (2.5 mmol), n-octane (1.25 mmol, internal stan-
dard), 1,2-DCE (10 mL), TBHP (5 mmol), 808C, and catalyst
the epoxidation experiments for Mo-SB-Cl-SiO
formed in CHCl , CH Cl , 1,2-DCE, C OH, t-BuOOH,
EtOAc, and CH CN and the results are summarised in Table 2.
When using 1,2-DCE and CH Cl as solvents, the substrate and
oxidant could be easily transferred to the surface of Mo-SB-Cl-
SiO causing the good dispersion of the product and by-product.
Thus, 1,2-DCE and CH Cl mediated reactions showed the best
conversions and epoxide yields. It is worth mentioning that
CH Cl gave a low conversion largely due to the lower boiling
point of the solvent. In the case of C OH, EtOAc, and
CH CN, all of which contain donor atoms (O or N), these
2
were per-
H
2 5
3
2
2
3
(25 mg, homogeneous catalyst Mo-SB with the same amount of
Mo as heterogeneous catalyst Mo-SB-Cl-SiO ). As deter-
3
VI
2
mined by GC-MS, the product is cyclohexene epoxide, and the
by-products are 2-cyclohexene-1-ol, 1,2-cyclohexenediol, and
2
3
2
-cyclohexene-1-one.
The catalytic activity of Mo-SB, Mo-SB-Cl-SiO , and
Mo-SB-Cl-SBA-15 was investigated and the results are given
2
2
2
H
2 5
in Fig. 6. For Mo-SB-Cl-SiO , ,80.46 % cyclohexene conver-
3
2
VI
sion was obtained during the initial 0.5 h. When the reaction time
increased to 4 h, the conversion reached 97.20 % which is slightly
lower than that for the highly active homogeneous Mo-SB
solvents tended to coordinate strongly with the Mo centre.
Table 2 shows the turnover frequency (TOF) defined as the ratio
of produced epoxide to the number of Mo moieties in Mo-SB-
catalyst. These results indicate that the Mo-SB-Cl-SiO is an
2
Cl-SiO . The activity order of C H OH . EtOAc . CH CN
2 2 5 3

8
22
J. Zhang et al.
(TOF: 74.32 . 41.54 . 22.68) can be explained by the
increasing coordination ability of CH CN . C H OH . EtOAc
and their competition with the oxygen molecule to occupy the
coordination sites of the catalyst. The by-product t-BuOOH was
also employed as the solvent and a lower conversion and
selectivity were obtained in this case, which indicated that
t-BuOOH may inhibit the reaction by competing with the
oxidant for coordination to the metal centre. The results indicate
3
2 5
(a)
(b)
(c)
100 nm
100 nm
3.0 kV 8.0 mm ꢁ 20.0 k SE(M)
2.00 µm
(d)
(e)
(f)
200 nm
100 nm
2.0 kV 7.4 mm ꢁ 10.0 k SE(M)
5.00 µm
(g)
(h)
(i)
2
µm
2 µm
Si
2 µm
O
(j)
(k)
(l)
2
µm
C
2 µm
N
2 µm
Mo
Fig. 5. SEM and TEM images at different magnifications. (a, d) SEM of Cl-SiO
2
2
and Mo-SB-Cl-SiO ,
respectively; (b, c) TEM of Cl-SiO
2
; and (e, f) TEM of Mo-SB-Cl-SiO
2
. (h–l) EDS elemental mapping images
of Si, O, C, N, and Mo, respectively.
1
00
a
b
c
8
6
4
0
0
0
d
100
a
b
80
60
40
20
0
c 1 : 1
d 0.5 : 1
a 2 : 1
b 3 : 1
c
20
0
0
2
4
6
8
10
12
Time [h]
a Mo-SB
b Mo-SB-Cl-SiO2
c Mo-SB-Cl-SBA-15
Fig. 7. Epoxidation of cyclohexene with different molar ratios of oxidant/
olefin catalyzed by Mo-SB-Cl-SiO . Reaction conditions: cyclohexene
2
(2.5 mmol), oxidant (appropriate molar amount), 1,2-DCE (10 mL),
n-octane (1.25 mmol) as internal standard, catalyst (25 mg), and reaction
temperature (808C). Determined by GC-MS, the product is cyclohexene
epoxide, and the by-products are 2-cyclohexene-1-ol, 1,2-cyclohexenediol,
and 2-cyclohexene-1-one.
0
1
2
3
4
Time [h]
Fig. 6. Testing of different catalyst in the conversion of cyclohexene.

Organic–Inorganic Heterogeneous Catalyst
823
[
3a]
that the solvent, on the one hand, potentially influences
the adsorption of reagents and the diffusion of products during
the epoxidation. On the other, it possibly causes polarization and
inductive effects affecting the activity and stability of the metal
species. In addition, the solvent could transfer the energy of the
reaction from the system and avoid local overheating which can
cause low selectivity. According to the obtained results, the use of
TBHP oxidant and 1,2-DCE solvent resulted in a higher reactivity
of the catalyst and hence the epoxidation reaction for other sub-
strates was performed under this optimized reaction condition.
Table 2. Screening of solvents and reaction conditions in the oxidation
of cyclohexene
Effects of Different Olefin Substrates
Reaction conditions: cyclohexene (2.5 mmol), n-octane (1.25 mmol) as internal
standard, t-BuOOH (5 mmol), solvent (10 mL). Reactions were performed under
reflux at 808C in an oil bath. GC conversion based on starting olefin. Determined
by GC-MS, the product is cyclohexene epoxide, and the by-products are
In order to assess the general applicability of the method, various
olefins were subjected to the oxidation protocol over Mo-SB-Cl-
SiO under the optimized reaction condition and the results are
given in Table 3. As shown, the order of increasing reactivities
based on TOFs correspond to cyclooctene . cyclohexene .
cyclopentene . 1-pentene . 1-hexene . 1-octene. Branched
and cyclic olefins with double bonds attached to secondary
carbons were found to be better active substrates than linear
2
2-cyclohexene-1-ol, 1,2-cyclohexenediol, and 2-cyclohexene-1-one
A
Entry Solvent Time [h] Conversion [%] Selectivity [%] TOF [h
ꢁ1
]
1
2
3
4
5
6
7
CH
CHCl
1,2-DCE
CH CN
2
Cl
2
8
1
72.54
80.07
85.14
64.40
78.62
65.24
70.34
. 99
. 99
. 99
76.76
98.94
98.01
96.12
38.32
3
338.42
359.85
22.68
41.54
68.93
74.32
1
-olefins. To explain this trend, two determining factors
involving electronic effects and steric effects should be taken
1
12
8
[25]
3
into consideration.
The higher electronic density of the
EtOAc
double bond tended to exhibit more epoxidation reactivity.
Cyclooctene was more reactive than cyclohexene or cyclo-
pentene due to the existence of more electron donating (CH2)6
cyclic bridges connected to the double bond. In contrast, under
the same reaction conditions, the catalytic activities for the
t-BuOH
4
C
2
H
5
OH
4
A
Turnover frequency (TOF) was calculated by the expression, TOF ¼
VI
(mmol of epoxide)/(mmol of Mo ꢀ reaction time (h)).
A
2
Table 3. Epoxidation of various substrates with catalyst Mo-SB-Cl-SiO
B
TOF [h
ꢁ1
]
Entry
1
Substrate
Structure
Time [h]
1
Conversion [%]
63.54
Selectivity [%]
98.43
cyclopentene
268.55
2
3
4
5
cyclohexene
1
1
4
1
85.14
87.10
50.42
73.59
. 99
. 99
78.84
98.73
359.85
368.13
53.28
cyclooctene
1-phenyl-1-cyclohexene
4-methyl-1-cyclohexene
311.03
CH3
6
1-octene
8
61.53
. 99
32.51
7
8
9
1-hexene
8
4
4
74.50
82.08
64.73
98.41
. 99
61.74
39.36
86.73
68.40
1-pentene
2-vinylnaphthalene
10
trans-stilbene
12
45.34
56.45
15.97
A
Reactions were performed in 1,2-DCE (10 mL) with catalyst (25 mg), substrate (2.5 mmol), TBHP (5.0 mmol), n-octane (1.25 mmol) as internal standard.
The reactions were performed at 808C.
B
VI
TOF was calculated by the expression: TOF ¼ (mmol of epoxide)/(mmol of Mo ꢀ reaction time(h)).

8
24
J. Zhang et al.
epoxidation of the linear olefins increased with the decreasing
chain length of the olefins. The effect of epoxidation of 1-octene
was stronger than 1-hexene or 1-pentene, which could be attri-
buted to the larger hexyl group connected to the double bond
sterically hindering the approach to the catalyst metal centre with
respect to 1-hexene and 1-pentene with a smaller group. These
results clearly indicate that, in addition to the intrinsic reactivity of
the double bond, olefin length and accessibility to the active sites
of the catalyst were the major limiting factors of the catalytic
Recovery and Stability
The reusability of the catalyst is an important factor for
heterogeneous catalysts in the epoxidation of olefins. Recycling
experiments were carried out under the optimized reaction
conditions. For this purpose, after the first run of the epoxidation
reaction, the used catalyst was filtered, washed with ethanol, and
then employed for the next epoxidation reaction. In the
recycling study, the epoxidation conditions were the same as
that in the first run. It was observed that conversion with
cyclohexene decreased slightly after the second run (Fig. 8). The
above procedure was repeated for another two cycles. It was
determined that the cyclohexene conversions were 100, 99.35,
[25]
reaction.
Not only cyclohexene but also linear olefins were
catalytically oxygenated with high selectivity to epoxide products.
The selectivity for 1-epoxypentene, 1-epoxyhexane, and 1-
epoxyoctane were . 99, 98.41, and . 99 % in the reaction time
of 4, 8, and 8 h, respectively. The other cycloolefin compounds
bearing electron-donating groups, for example 4-methyl-1-
cyclohexene, gave excellent conversion of epoxidation products.
However, olefins bearing electron-withdrawing groups, such as
9
8.84, and 97.75 % over 8 h in the first, second, third, and fourth
cycle, respectively. We did not observe any substantial loss in
the catalytic activity of the immobilized catalyst. The results
VI
indicate that the Mo Schiff base complex is strongly bonded to
organic–inorganic silica matrix. In addition, in order to under-
stand the change of catalyst Mo-SB-Cl-SiO in the cycle test,
1-phenyl-1-cyclohexene, afforded lower conversion of the
2
corresponding coupling adducts. The conversion of 1-phenyl-1-
cyclohexene and 4-methyl-1-cyclohexene seemed to proceed in a
similar way. The lower catalytic activity of 1-phenyl-1-cyclo-
hexene compared with 4-methyl-1-cyclohexene was probably
FT-IR (Fig. S1, Supplementary Material), XRD (Fig. S2,
Supplementary Material), and CHN measurements were
performed during the recycling experiments. There were no
obvious changes in the FT-IR spectra and XRD patterns of the
fresh and recycled catalyst, indicating the unchanged structure
of Mo-SB-Cl-SiO in the epoxidation reaction. Accordingly,
2
the prepared Mo-SB-Cl-SiO2 hybrid could act as a stable
heterogeneous catalyst for epoxidation reaction.
In order to further confirm the stability of Mo-SB-Cl-SiO2,
we carried out comparative epoxidation reactions to evaluate the
effect of possible leaching of the metal complex from the
immobilized catalyst into the reaction medium and the results
are shown in Fig. 9. After 2 h of reaction, the organic phase and
the solid phase were separated. The epoxidation reaction was
afterwards performed at 808C in the organic phase for another
[26]
because of its increased steric hindrance. The electronic effects
and steric effects can also be used to explain the catalytic activity
of 1-phenyl-1-cyclohexene and 4-methyl-1-cyclohexene. Olefins
having double bonds with one or two electron-withdrawing groups
at the both ends were also investigated in this study. As a typical
olefin with an electron poor terminal, 2-vinylnaphthalene exhi-
bited medium conversion of 64.73 % and a selectivity of 61.74 %
over 8 h because its epoxide was prone to further unwanted ring-
opening reactions in the epoxidation reaction. The sterically
demanding substrate trans-stilbene lead to a 45.34 % conversion
and a 56.45 % selectivity for a longer reaction time of 12 h. The
formation of side products took place because of ring-opening
during the epoxidation of trans-stilbene. Furthermore, the epoxide
of trans-stilbene was unstable and apt to ring-opening at high
temperature.
8
h with the same amount of reagents. In this case, there was
nearly no generation of epoxide. Moreover, the ICP-AES
analysis result showed a negligible molybdenum loss of
0
.14 mol.-% for Mo-SB-Cl-SiO2.
100
100
a
b
90
80
70
60
50
b
9
0
0
a
d
c
8
a First
b Second
c Third
70
60
d Fourth
a Mo-SB-Cl-SiO2
b removed Mo-SB-Cl-SiO2
0
1
2
3
4
5
6
7
8
Time [h]
2
4
6
8
10
Time [h]
Fig. 8. Evaluation of the recyclability of Mo-SB-Cl-SiO
2
towards the
cyclohexene epoxidation reaction. Catalytic activity for the 1st, 2nd, 3rd,
and 4th run. Conditions: catalyst (25 mg), 1,2-DCE (10 mL), cyclohexene
Fig. 9. The plot of time against conversion for the epoxidation of
cyclohexene. Reaction conditions: cyclohexene (2.5 mmol), 1,2-DCE
(10 mL), n-octane (1.25 mmol), catalyst (25 mg), and temperature 808C.
Determined by GC-MS, the product is cyclohexene epoxide, and the by-
products are 2-cyclohexene-1-ol, 1,2-cyclohexenediol, and 2-cyclohexene-
1-one.
(2.5 mmol), TBHP (5 mmol), n-octane (1.25 mmol) as internal standard, and
temperature 808C. Determined by GC-MS, the product is cyclohexene
epoxide, and the by-products are 2-cyclohexene-1-ol, 1,2-cyclohexenediol,
and 2-cyclohexene-1-one.

Organic–Inorganic Heterogeneous Catalyst
825
Conclusion
[7] (a) M. Waki, N. Mizoshita, T. Tani, S. Inagaki, Angew. Chem. Int. Ed.
2
011, 50, 11667. doi:10.1002/ANIE.201104063
b) M. A. O. Louren c¸ o, L. Carneiro, A. Mayoral, I. Diaz, A. R. Silva,
In conclusion, the Mo-SB-Cl-SiO2 was prepared by a co-
condensation assisted method, and exhibited an enhanced
catalytic epoxidation activity that can compare with a
(
P. Ferreira, J. Catal. 2014, 320, 63. doi:10.1016/J.JCAT.2014.09.017
8] M. Bagherzadeh, M. Zare, M. Amini, T. Salemnoush, S. Akbayrak,
[
homogeneous counterpart. Mo-SB-Cl-SiO2 displayed a
D-hexagonal mesoporous framework. In comparison with
¨
S. Ozkar, J. Mol. Catal. Chem. 2014, 395, 470. doi:10.1016/J.MOL
2
Mo-SB-Cl-SBA-15 prepared by a post-grafting assisted method,
CATA.2014.09.004
[9] (a) C.-Y. Lai, B. G. Trewyn, D. M. Jeftinija, K. Jeftinija, S. Xu,
S. Jeftinija, V. S.-Y. Lin, J. Am. Chem. Soc. 2003, 125, 4451.
doi:10.1021/JA028650L
the Mo-SB-Cl-SiO showed a higher catalytic activity towards
2
VI
epoxidation reactions, mostly due to the higher density of Mo
active sites. Among the experiments on the effects of different
(
b) V. S. Y. Lin, D. R. Radu, M.-K. Han, W. Deng, S. Kuroki,
B. H. Shanks, M Pruski, J. Am. Chem. Soc. 2002, 124, 9040.
doi:10.1021/JA025925O
substrates, Mo-SB-Cl-SiO showed an increasing activity in the
2
order: cyclooctene . cyclohexene . cyclopentene . 1-pentene
. 1-hexene . 1-octene, which was determined by both electronic
effects and steric effects. The Mo-SB-Cl-SiO was a highly stable
(
c) V. S. Y. Lin, C.-Y. Lai, J. Huang, S.-A. Song, S. Xu, J. Am. Chem.
Soc. 2001, 123, 11510. doi:10.1021/JA016223M
[10] R. A. Garc ´ı a, V. Morales, T. Garc e´ s, J. Mater. Chem. 2012, 22, 2607.
doi:10.1039/C2JM15381E
[11] (a) P. Linton, H. Wennerstr o¨ m, V. Alfredsson, Phys. Chem. Chem.
Phys. 2010, 12, 3852. doi:10.1039/B923364D
2
catalyst in the epoxidation of olefins. This work potentially
provides an insight into a novel strategy for preparing organic–
inorganic epoxidation catalyst with enhanced activity.
(
b) M. M. Jones, J. Am. Chem. Soc. 1959, 81, 3188. doi:10.1021/
JA01522A005
c) S.-J. Xia, F.-X. Liu, Z.-M. Ni, W. Shi, J.-L. Xue, P.-P. Qian, Appl.
Catal. B 2014, 144, 570. doi:10.1016/J.APCATB.2013.07.060
d) S. L. Jain, B. Sain, Adv. Synth. Catal. 2008, 350, 1479. doi:10.1002/
Supplementary Material
(
The preparation process of SBA-15, MoO (acac) , p-salicylidine
2
2
aminobenzoic acid, and Mo-SB as well as the Fourier transform
infrared spectrum and small-angle XRD pattern of the catalyst
before and after reusing are available on the Journal’s website.
(
ADSC.200800264
(e) Y. Leng, J. Liu, C. Zhang, P. Jiang, Catal. Sci. Technol. 2014, 4,
9
97. doi:10.1039/C3CY01014G
12] M. R. Maurya, M. Kumar, A. Kumar, J. Costa Pessoa, Dalton Trans.
008, 48, 4220. doi:10.1039/B804823A
13] L. Saikia, D. Srinivas, P. Ratnasamy, Appl. Catal. A 2006, 309, 144.
doi:10.1016/J.APCATA.2006.05.011
14] D. Perez-Quintanilla, I. del Hierro, M. Fajardo, I. Sierra, J. Environ.
[
[
[
[
Acknowledgements
2
The support of this study by the National ‘Twelfth Five-Year’ Plan for Science
and Technology (2012BAD32B03), the Fundamental Research Funds for the
Central Universities (JUSRP51507), and the Innovation Foundation in Jiangsu
Province of China (BY2014023-08) is gratefully acknowledged.
Monit. 2006, 8, 214. doi:10.1039/B507983G
15] D. P e´ rez-Quintanilla, A. S a´ nchez, I. del Hierro, M. Fajardo, I. Sierra,
J. Hazard. Mater. 2009, 166, 1449. doi:10.1016/J.JHAZMAT.2008.
12.065
References
[1] (a) M. H. Valkenberg, W. F. H o¨ lderich, Catal. Rev. 2002, 44, 321.
doi:10.1081/CR-120003497
[16] M. R. Maurya, N. Kumar, J. Mol. Catal. Chem. 2015, 406, 204.
(
b) F. Hoffmann, M. Cornelius, J. Morell, M. Fr o¨ ba, Angew. Chem. Int.
Ed. 2006, 45, 3216. doi:10.1002/ANIE.200503075
c) A. Taguchi, F. Sch u¨ th, Microporous Mesoporous Mater. 2005, 77,
. doi:10.1016/J.MICROMESO.2004.06.030
doi:10.1016/J.MOLCATA.2015.06.002
[17] (a) A. C¸ ıtak, B. Erdem, S. Erdem, R. M. Oks u¨ zo g˘ lu, J. Colloid
¨
(
Interface Sci. 2012, 369, 160. doi:10.1016/J.JCIS.2011.11.070
(b) N. T. S. Phan, C. W. Jones, J. Mol. Catal. Chem. 2006, 253, 123.
doi:10.1016/J.MOLCATA.2006.03.019
1
[
2] (a) J. Zhang, P. Jiang, Y. Shen, W. Zhang, X. Li, Microporous
Mesoporous Mater. 2015, 206, 161. doi:10.1016/J.MICROMESO.
[18] (a) M. E. Judmaier, C. Holzer, M. Volpe, N. C. M o¨ sch-Zanetti, Inorg.
2
(
014.12.027
b) W. R. Thiel, T. Priermeier, Angew. Chem. Int. Ed. Engl. 1995, 34,
737. doi:10.1002/ANIE.199517371
Chem. 2012, 51, 9956. doi:10.1021/IC301464W
(b) S. Rayati, N. Rafiee, A. Wojtczak, Inorg. Chim. Acta 2012, 386, 27.
doi:10.1016/J.ICA.2012.02.005
1
¨
[
3] (a) M. Bagherzadeh, M. Zare, T. Salemnoush, S. Ozkar, S. Akbayrak,
[19] A. Syamal, M. R. Maurya, Coord. Chem. Rev. 1989, 95, 183.
doi:10.1016/0010-8545(89)80026-8
Appl. Catal. A 2014, 475, 55. doi:10.1016/J.APCATA.2014.01.020
(
b) M. R. Maurya, Curr. Org. Chem. 2012, 16, 73. doi:10.2174/
38527212798993130
c) A. C. Coelho, S. S. Balula, S. M. Bruno, J. C. Alonso, N. Bion,
[20] B. Monteiro, S. S. Balula, S. Gago, C. Grosso, S. Figueiredo,
A. D. Lopes, A. A. Valente, M Pillinger, J. P. Louren c¸ o, I. S. Gon c¸ alves,
J. Mol. Catal. A 2009, 297, 110. doi:10.1016/J.MOLCATA.2008.09.012
[21] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka, G. D. Stuckey, Science 1998, 279, 548. doi:10.1126/
SCIENCE.279.5350.548
1
(
P. Ferreira, M Pillinger, A.A. Valente, J Rocha, I.S. Gon c¸ alves,
Adv. Synth. Catal. 2010, 352, 1759. doi:10.1002/ADSC.201000042
(d) M. Amini, M. M. Haghdoost, M. Bagherzadeh, Coord. Chem. Rev.
2
013, 257, 1093. doi:10.1016/J.CCR.2012.11.018
[22] A. R. Silva, L. Carneiro, A. P. Carvalho, J. Pires, Catal. Sci. Technol.
2013, 3, 2415. doi:10.1039/C3CY00232B
[
[
4] P. Van Der Voort, D. Esquivel, E. De Canck, F. Goethals,
I. Van Driessche, F. J. Romero-Salguero, Chem. Soc. Rev. 2013, 42,
[23] M. Jia, A. Seifert, W. R. Thiel, Chem. Mater. 2003, 15, 2174.
doi:10.1021/CM021380L
[24] (a) A. Comas-Vives, A. Lled o´ s, R. Poli, Chem. – Eur. J. 2010, 16,
2147. doi:10.1002/CHEM.200902873
3913. doi:10.1039/C2CS35222B
5] (a) M. H. Lim, A. Stein, Chem. Mater. 1999, 11, 3285. doi:10.1021/
CM990369R
(
b) C. O. Kim, S. J. Cho, J. W. Park, J. Colloid Interface Sci. 2003, 260,
(b) A. Al-Ajlouni, A. A. Valente, C. D. Nunes, M. Pillinger,
A. M. Santos, J. Zhao, C. C. Rom a˜ o, I. S. Gon c¸ alves, F. E. K u¨ hn,
Eur. J. Inorg. Chem. 2005, 2005, 1716. doi:10.1002/EJIC.200400852
[25] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. Chem.
2006, 248, 53. doi:10.1016/J.MOLCATA.2005.12.008
3
74. doi:10.1016/S0021-9797(03)00039-0
[
6] (a) A. Mehdi, C. Reye, R. Corriu, Chem. Soc. Rev. 2011, 40, 563.
doi:10.1039/B920516K
(
b) A. Datt, I. El-Maazawi, S. C. Larsen, J. Phys. Chem. C 2012, 116,
8358. doi:10.1021/JP3063959
c) L.-B. Sun, X.-Q. Liu, H.-C. Zhou, Chem. Soc. Rev. 2015, 44, 5092.
doi:10.1039/C5CS00090D
1
[26] G. Grivani, S. Tangestaninejad, A. Halili, Inorg. Chem. Commun.
2007, 10, 914. doi:10.1016/J.INOCHE.2007.01.016
(