Molybdenum complex tethered to the surface of activated carbon as a new recoverable catalyst for the epoxidation of olefins

Article abstract of DOI:10.1016/j.apcata.2014.04.008

A new recoverable catalyst for the epoxidation of olefins was developed by covalent attachment of aminopropyl groups on the surface of oxidized activated carbon (AC) and next reaction with bis(acetylacetonato)dioxomolybdenum(VI). Characterization of the prepared catalyst was performed with different physicochemical methods such as Fourier transform infrared and atomic absorption spectroscopies, scanning electron microscopy, energy-dispersive X-ray and nitrogen sorption analyses. Nitrogen adsorption-desorption analysis revealed that the textural characteristics of the support were changed during the grafting experiments but the channels remained relatively accessible despite sequential reduction in surface area, pore volume and pore size. Elemental analysis showed the presence of 0.06 mmol g^-1 molybdenum in the catalyst. The prepared catalyst catalyzed the epoxidation of olefins and allyl alcohols with tert-butyl hydroperoxide (TBHP) and cumene hydroperoxide (CHP) quantitatively with excellent selectivity toward the corresponding epoxides under mild reaction conditions. The results indicated that the hydrophobicity of the AC support promoted the catalytic efficiency of the catalyst in the epoxidation of olefins.

Full text of DOI:10.1016/j.apcata.2014.04.008

Applied Catalysis A: General 478 (2014) 211–218
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Molybdenum complex tethered to the surface of activated carbon as a
new recoverable catalyst for the epoxidation of olefins
∗
M. Masteri-Farahani , S. Abednatanzi
Faculty of Chemistry, Kharazmi University, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A new recoverable catalyst for the epoxidation of olefins was developed by covalent attachment
of aminopropyl groups on the surface of oxidized activated carbon (AC) and next reaction with
bis(acetylacetonato)dioxomolybdenum(VI). Characterization of the prepared catalyst was performed
with different physicochemical methods such as Fourier transform infrared and atomic absorption
spectroscopies, scanning electron microscopy, energy-dispersive X-ray and nitrogen sorption analyses.
Nitrogen adsorption–desorption analysis revealed that the textural characteristics of the support were
changed during the grafting experiments but the channels remained relatively accessible despite sequen-
tial reduction in surface area, pore volume and pore size. Elemental analysis showed the presence of
Received 18 October 2013
Received in revised form 3 April 2014
Accepted 4 April 2014
Available online 13 April 2014
Keywords:
Molybdenum
Activated carbon
Tethering
−1
0
.06 mmol g molybdenum in the catalyst. The prepared catalyst catalyzed the epoxidation of olefins
Heterogeneous catalysis
Epoxidation
and allyl alcohols with tert-butyl hydroperoxide (TBHP) and cumene hydroperoxide (CHP) quantitatively
with excellent selectivity toward the corresponding epoxides under mild reaction conditions. The results
indicated that the hydrophobicity of the AC support promoted the catalytic efficiency of the catalyst in
the epoxidation of olefins.
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
made, including grafting of Mo compounds to functionalized poly-
mer supports [10,11], preparation of amorphous Mo silicates with
the sol-gel method [12], incorporation of Mo in the framework
of silicalite [13] and especially immobilization of homogeneous
molybdenum catalysts on the surface of silica coated magnetite
nanoparticles [14–16] and mesoporous materials (for example
MCM-41, MCM-48, etc) [17–23].
Due to its high surface area and porosity, activated carbon (AC)
is a good candidate as catalyst support in place of inorganic oxide
materials especially for liquid phase reactions, since it has the
advantages of higher stability in acid and base conditions and the
benefit of modification of its porous texture and surface properties
by appropriate methods. It possesses several types of oxygenated
surface groups which can be increased by thermal and chemical
processes and can be used for covalent tethering of homogeneous
catalysts. On the other hand, AC is a readily available and inex-
pensive material. Thus, immobilization of metal complexes on the
surface of AC has attracted much interest in recent years. Some
examples include chiral manganese(III) Schiff base complexes
anchored onto AC as enantioselective heterogeneous catalysts for
alkene epoxidation [24–29], amine-functionalized nickel(II) Schiff
base complexes immobilized onto AC treated with thionyl chloride
Recently, waste minimization by using supported reagents and
catalysts has increased trends to develop environmentally friendly
processes in industrial chemistry [1–9]. One of the most impor-
tant contributions to waste production in chemical processes is the
separation of products or catalysts from the reaction mixture. Thus,
preparation of supported catalysts through immobilization of sol-
uble transition metal complexes on solid supports has attracted
great interest due to combining the advantages of both homo-
geneous and heterogeneous catalysts especially easier work-up,
recyclability and stability of the heterogeneous systems. Among
the various approaches used for immobilizing metal complexes,
the covalent tethering has been the most efficient strategy as the
resulting heterogeneous catalysts have enough stability during the
course of catalytic reactions. The stable covalent bonds experience
no leaching from the support and thus provide an efficient method
to prepare truly heterogenized catalysts.
In this regard, heterogenization of molybdenum complexes has
been the subject of great interests and many attempts have been
[
30], rhodium complexes bound to AC [31–36], reusable cobalt(III)-
∗ Corresponding author. Tel.: +98 263 4551023; fax: +98 263 4551023.
E-mail address: mfarahany@yahoo.com (M. Masteri-Farahani).
salen complex supported on AC as an efficient heterogeneous
catalyst for synthesis of 2-arylbenzimidazole derivatives [37], and
http://dx.doi.org/10.1016/j.apcata.2014.04.008
0
926-860X/© 2014 Elsevier B.V. All rights reserved.

2
12
M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
Table 1
Elemental analysis and texture parameters of the samples taken from nitrogen sorption studies.
N content (mmol g 1
−
)
Mo content (mmol g
−1
)
SBET (m2
g
−1
)
Smicroa (m2
g
−1
)
VTb (ml g−1
)
Vmicroa (ml g−1
)
Vmesoc (ml g−1
)
Sample
AC
0.25
0.52
0.48
–
–
0.06
865
406
12
720
256
0
0.597
0.290
0.0264
0.353
0.120
0
0.244
0.170
0.0264
APTS-AC
Mo-APTS-AC
a
Calculated by the t-method.
Total pore volume at p/p0 = 0.98.
Obtained by subtracting the micropore volume from the total pore volume at p/p0 = 0.98.
b
c
copper(II) acetylacetonate anchored onto AC as a heterogeneous
catalyst for the aziridination of styrene [38].
The effect of hydrophobicity of the supports on the activity of
heterogeneous catalysts has been of less concern in the literature
2.1.1. Preparation of aminopropyl modified AC
First, the AC was washed with dichloromethane and toluene to
remove the organic species and then refluxed with a 5 M nitric acid
solution as oxidizing agent for 24 h to increase the surface oxygen
groups [35]. The oxidized AC was washed with deionized water
until pH 6–7 and then dried in vacuum oven at 383 K overnight.
The resulted material (1 g) was further treated with sodium boro-
hydride (5 g) in methanol (100 ml) at 277 K for 24 h to reduce the
carbonyl groups and increase the surface hydroxyl groups. After
washing with methanol and drying, the hydroxylated AC (1 g) was
refluxed with 3-aminopropyltrimethoxysilane (APTS) (2 mmol) in
dry toluene (100 ml) under nitrogen atmosphere for 24 h to give
aminopropyl modified AC (APTS-AC). The prepared material was
soxhlet extracted with dichloromethane to remove the unreacted
residue of silylating reagent, and dried in vacuum oven at 383 K
overnight.
[
39]. Hydrophobic properties affect the adsorption and desorption
of molecules on the surface of the catalysts. But, the study of the cor-
relation between the hydrophobicity of the supports and catalytic
activity is still lacking.
In continuation of our research program devoted to the devel-
opment of immobilized homogeneous molybdenum catalysts
[
13–15,19–23], our objective in this work is to functionalize AC with
aminoropropyl groups and then incorporate a molybdenum com-
plex with tethering method to obtain a heterogenized molybdenum
catalyst for the epoxidation of olefins. To the best of our knowledge,
there is no any report about the preparation and characterization
of such covalently attached molybdenum complex on the surface
of AC. The advantages of this system are the easy recovery of the
solid catalyst at the end of reaction as well as good activity, selec-
tivity and high stability in the epoxidation of olefins. Moreover, our
proposed method of preparation does not involve the requirement
of using thionyl chloride which is a toxic and hazardous reagent
and thus is environmentally friendly. Also, we aim to correlate the
hydrophobic effect of the AC support with the activity of the pre-
pared catalyst in the epoxidation of olefins. Our results indicate that
the more hydrophobicity of the AC support promotes the catalytic
efficiency of the catalyst in the epoxidation of olefins.
2.1.2. Preparation of supported molybdenum catalyst
A solution of MoO (acac)2 (2 mmol) in methanol (10 ml)
2
and APTS-AC (1 g) was refluxed under nitrogen atmosphere
for 24 h. The reaction mixture was filtered and the solid was
soxhlet extracted with dichloromethane for 24 h to remove
unreacted MoO (acac) . Finally, the resulting supported molybde-
2
2
num catalyst (Mo-APTS-AC) was dried in vacuum oven at 383 K
overnight.
2.2. Catalytic epoxidation of olefins in the presence of
Mo-APTS-AC catalyst
Epoxidation of olefins was carried out in a 25 ml round
bottom flask equipped with a condenser and a magnetic stir-
rer. Tert-butyl hydroperoxide (TBHP, 80% in di-tertiary butyl
peroxide) and cumene hydroperoxides (CHP, 80% in cumene)
2
. Experimental
2.1. Materials and instrumentation
were used as oxidants. In
ture of catalyst (100 mg) and olefin (8 mmol) in chloroform
10 ml) was added oxidant (14.4 mmol) under nitrogen atmo-
sphere and the mixture was refluxed for a given time. Samples
were withdrawn periodically and after cooling and dilution
with solvent were analyzed using a gas chromatograph (HP,
Agilent 6890N) equipped with a capillary column (HP-5) and
a flame ionization detector (FID). The products were quanti-
fied using isooctane (8.75 mmol) as internal standard. GC–MS
a typical procedure, to a mix-
Bis(acetylacetonato)dioxomolybdenum(VI), MoO (acac) , was
2
2
prepared according to the literature method [40]. All other chemi-
cals as well as AC (charcoal activated GR for analysis Art No. 102186)
were purchased from Merck chemical company. The details of the
surface area, pore volume and other surface properties of the AC
are given in Table 1.
(
Fourier transform infrared (FT-IR) spectra were recorded using
Perkin-Elmer Spectrum RXI FT-IR spectrometer, using pellets of the
materials diluted with KBr. Scanning electron microscopy (SEM)
images of the samples were taken with ZEISS-DSM 960A micro-
scope with attached camera. Elemental analyses were performed
by a scanning electron microscope with EDX (energy dispersive
X-ray) detector INCA Penta FETx3 and VARIAN VISTA-MPX ICP-
AES (inductively coupled plasma atomic emission spectroscopy)
atomic absorption spectrometer. Nitrogen content of the samples
was analyzed on Thermo Finnigan (Flash 1112 Series EA) CHN Ana-
lyzer. Nitrogen sorption studies were performed at liquid nitrogen
temperature (77 K) using Quantachrome Nova 2200e, Version 7.11
Analyzer. Before the adsorption experiments the samples were
outgassed under high vacuum at 393 K. All calculations were per-
formed using the program of Quantachrome Nova 2200e surface
area analyzer.
(
gas chromatography-mass spectrometry) of the products were
recorded using a Shimadzu-14A fitted with a capillary column
CBP5-M25).
(
3. Results and discussion
3.1. Preparation and characterization of the supported
molybdenum catalyst, Mo-APTS-AC
The tethering approach for functionalization of AC and proposed
structure of the Mo-APTS-AC catalyst is schematically shown in
Fig. 1. In the final step, according to literature [38], Schiff base con-
densation reaction of NH2 group of APTS-AC and carbonyl group of

M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
213
Fig. 1. The sequence of events in the preparation of Mo-APTS-AC.
acac ligand resulted in the formation of imine bond through which
the molybdenum complex was covalently attached to the surface
of AC.
spectrum of Mo-APTS-AC (Fig. 2c), the appearance of two adjacent
−
1
bands at 912 and 941 cm was characteristic of the presence of
cis-MoO2 groups [41] in this material and clearly confirmed the
formation of surface tethered molybdenum complex as depicted in
Fig. 1.
Further evidences for the presence of molybdenum complex and
surface chemical composition of the final product were provided by
CHN, EDX analysis (Fig. 3a) and ICP-AES.
In order to confirm the modification of the AC surface, the FT-
IR spectra of the AC, APTS-AC, and Mo-APTS-AC materials were
obtained and have been shown in Fig. 2. The aminopropyl silylation
of hydroxylated AC was confirmed by the observation of a rela-
−
1
tively broad band at about 1000–1100 cm in the FT-IR spectrum
of APTS-AC (Fig. 2b) which can be assigned to Si C stretching
O
The results of the CHN analysis showed that reaction of APTS
−
1
vibrations. Furthermore, the presence of anchored propyl groups
was confirmed by observation of C H stretching vibrations at 2852
with AC resulted in 0.27 mmol g
increase of nitrogen content
which indicated the extent of surface functionalization of the AC
with APTS molecules.
−1
and 2924 cm that was not present in the parent AC. In the FT-IR
Fig. 2. FT-IR spectra of (a) AC, (b) APTS-AC, and (c) Mo-APTS-AC.

2
14
M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
Fig. 3. (a) EDX spectrum, and (b) SEM image of Mo-APTS-AC.
ICP-AES analysis of the catalyst revealed the existence of
−
1
0
.06 mmol g molybdenum in the Mo-APTS-AC catalyst. It is worth
noticing that despite the excess of molybdenum precursor used
in the reaction, the amount anchored onto AC is lower than the
amount of APTS that was anchored onto the surface of AC. This
may be due to the poor accessibility of the amine groups of APTS-AC
material which located in the micro- or mesopores.
The surface morphology of the obtained catalyst was observed
by scanning electron microscopy (SEM). As can be seen in Fig. 3b,
the SEM image of the Mo-APTS-AC catalyst shows disordered three-
dimensional structure. The SEM image of the sample does not
reflect the effects of the treatments conducted on the AC. After
incorporation of molybdenum, there is no any significant difference
in the micrographs of the commercial AC and Mo-APTS-AC.
Textural properties of the AC, APTS-AC, and Mo-APTS-AC cata-
lyst were investigated with N2 adsorption–desorption isotherms.
Fig. 4a shows the adsorption isotherms of all materials at liquid
nitrogen temperature. In the adsorption isotherm of the parent AC
the uptake of N2 increases at high relative pressure and shows a
hysteresis loop which exhibits type IV isotherm according to the
Brunauer–Deming–Deming–Teller (BDDT) classification [42]. The
result suggests considerable amount of mesoporosity in parent
AC. In the adsorption isotherm of APTS-AC which exhibits type IV
isotherm with a hysteresis loop indicating the presence of some
mesopores the inflection point shifts to lower relative pressures
and the volume of nitrogen adsorbed decreases upon functional-
ization. As expected, this indicates the presence of aminopropyl
groups tethered to the pore walls of the micro- and mesopores.
The adsorption isotherm of Mo-APTS-AC is mainly type II, as
deduced from the shape of the isotherm at relative pressures below
Fig. 4. (a) Nitrogen sorption isotherms (inset image shows magnified view of Mo-
APTS-AC isotherm) and (b) BJH pore size distributions of AC, APTS, and Mo-APTS-AC
materials.
isotherm. The pore blocking is probably resulted from the reaction
of acac ligands of molybdenum precursor with aminopropyl groups
located near the pore entrances [43]. The isotherm also presents a
small hysteresis loop due to the presence of few mesopores in the
Mo-APTS-AC catalyst.
Pore size distributions of AC, APTS-AC, and Mo-APTS-AC were
obtained from the desorption branch of the isotherms using the
Barrett, Joyner and Halenda (BJH) method [42] and are shown in
Fig. 4b. AC shows a bimodal distribution with maxima located at
18 and 36 A˚ indicating the presence of micropores as well as meso-
pores. On the other hand, APTS-AC and Mo-APTS-AC present a
0
.2 and at higher relative pressures, which is characteristic of non-
broad monomodal distribution with the maximum radius centered
at 31 and 23 A˚ , respectively. This reveals the blocking of the micro-
pores during the immobilization of molybdenum complex and the
presence of mesopores in both materials.
porous materials. This is mainly due to a pore blocking effect,
especially micropores, which is also evident from the analysis of
the uptake at low relative pressures in the adsorption–desorption

M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
215
Fig. 5. Epoxidation of (a) olefins and (b) allyl alcohols with TBHP in the presence of
Mo-APTS-AC. Reaction conditions: catalyst (100 mg), olefin or allyl alcohol (8 mmol),
TBHP (14.4 mmol), refluxing chloroform (10 ml).
The textural parameters of AC, APTS-AC, and Mo-APTS-AC are
collected in Table 1. Determination of total surface area is com-
monly based on the theory of multilayer adsorption developed by
Fig. 6. Epoxidation of (a) olefins and (b) allyl alcohols with CHP in the presence of
Mo-APTS-AC. Reaction conditions: catalyst (100 mg), olefin or allyl alcohol (8 mmol),
CHP (14.4 mmol), refluxing chloroform (10 ml).
Brunauer, Emmett and Teller with the relative pressure (p/p ) in
0
range of 0.05–0.30. Micropore surface area and micropore volume
were obtained from the t-plot method. The total pore volume was
directly calculated from the volume of nitrogen held at the highest
order to clear up the catalytic effect of the prepared Mo-APTS-AC,
we have included the results of the epoxidation of cyclooctene in
the presence of parent AC and blank (no catalyst) as well as differ-
ent amounts of the catalyst in Table 2. As can be seen, no significant
reaction occurred in the absence of the catalyst. Furthermore, with
increasing the Mo-APTS-AC catalyst amount to 100 mg the con-
version increases, and then remains constant with increasing the
catalyst amount.
A clear point when comparing the results of Figs. 5 and 6
is the higher reactivity of TBHP in the epoxidation of olefins in
comparison with CHP. This observation can be explained with
more electrophilic character of the peroxidic oxygen in TBHP. On
the basis of earlier experimental and theoretical investigations, it
has been shown that the epoxidation of olefins in the presence
of cis-dioxomolybdenum(VI) complexes involves the coordina-
tion of TBHP to the Lewis acidic molybdenum center in the first
step [44]. The peroxidic oxygen would have electrophilic charac-
ter and the catalytic epoxidation proceeds through electrophilic
oxygen atom transfer from resulting molybdenum alkyl peroxide
to the olefin (Fig. 7). On the other hand, the reaction rates for
cyclic olefins with higher electron density are higher than that
−
3
relative pressure (p/p = 0.98), using 0.8081 g cm for the density
0
of N2 in its normal liquid state. The volume of mesopores (Vmeso)
was calculated by subtracting the micropore volume from the total
pore volume.
As can be seen in Table 1, surface functionalization of AC with
APTS resulted in approximately 53% decrease in the surface area.
This is due to the anchoring of the APTS molecules onto the AC
micropore and mesopore wall channels. Furthermore, upon tether-
ing the molybdenum complex on the surface of AC there is a more
significant decrease in the surface area and micropore volume
which confirm the above-mentioned pore blocking effect.
3.2. Catalytic epoxidation of olefins and allyl alcohols in the
presence of supported Mo-APTS-AC
Catalytic activity of the prepared catalyst was evaluated in the
epoxidation of some olefins and allyl alcohols with TBHP and CHP
as oxidants and the results are given in Figs. 5 and 6 and Table 2.
The selectivities of the reactions toward the production of epoxides
were found to be close to 100% in all of the entries of Figs. 5 and 6. In

2
16
M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
Table 2
Investigation of the catalytic effect of the prepared Mo-APTS-AC on the epoxidation of cyclooctene with TBHP.
Run no.
Catalyst
Catalyst amount (mg)
Time (h)
Conversion (%)
Selectivitya (%)
TOFb (h−1
)
1
2
3
4
5
6
AC
–
100
–
25
50
100
150
12
12
8
8
8
16
14
71
80
99
99
36
41
>99
>99
>99
>99
–
–
532
266
165
110
Mo-APTS-AC
Mo-APTS-AC
Mo-APTS-AC
Mo-APTS-AC
8
Reaction conditions: catalyst (100 mg), cyclooctene (8 mmol), TBHP (14.4 mmol), refluxing chloroform (10 ml).
a
Selectivity toward epoxycyclooctane.
Calculated as mmol of product formed per mmol of molybdenum in the catalyst per time.
b
Table 3
Investigation of the catalytic contribution of the possibly leached out molybdenum species.
Run no.
1
Time (h)
Conversion (%)
Selectivitya (%)
Before filtering the catalyst
After filtering the catalyst
2
24
70
73
>99
98
Reaction conditions: catalyst (100 mg), cyclooctene (8 mmol), TBHP (14.4 mmol), refluxing chloroform (10 ml).
a
Selectivity toward epoxycyclooctane.
Table 4
Results of the epoxidation of cyclooctene with TBHP in the presence of recycled catalysts.
Selectivitya (%)
Mo content of the catalyst (mmol g
−1
)
TOF
Run no.
Time (h)
Conversion (%)
1
2
3
4
5
6
st
3
3
3
3
3
3
89
87
84
82
79
78
100
100
100
100
100
100
0.06
0.06
0.05
0.05
0.05
0.05
395
387
448
437
421
416
nd
rd
th
th
th
Reaction conditions: catalyst (100 mg), cyclooctene (8 mmol), TBHP (14.4 mmol), refluxing chloroform (10 ml). A little fresh catalyst was added to the recovered catalysts to
keep the same amount of catalysts in the reaction system in each run.
a
Selectivity toward epoxycyclooctane.
of terminal olefins which further confirms the proposed mecha-
nism. Furthermore, allyl alcohols are more reactive than simple
olefins. This is probably due to the participation of hydroxyl
group in approaching the double bond to the electrophilic oxygen
center.
epoxides. It seems that the hydrophobic properties of the AC sup-
port compensate the loss of porosity of the Mo-APTS-AC catalyst
and as indicated in the catalytic results, the catalyst is active in
the epoxidation of olefins. The more catalytic activity of the AC
based catalyst in comparison with MCM-41 based catalyst indicates
the effect of hydrophobic nature of the support on the catalytic
activity of the catalyst. As a result of the presence of carbon atoms
and nonpolar structure, AC has more hydrophobic character than
MCM-41 which composed of hydrophilic silica material. It is evi-
dent that in comparison with more hydrophilic MCM-41 support,
the hydrophobic reagents i.e. olefins and nonpolar solvents have
more tendency to close to the catalytic active sites located on the
surface of more hydrophobic AC support, and so the latter catalyst
is more active than the former one.
Comparison of the obtained results with our earlier work on
the similar catalyst derived from mesoporous material (MCM-41),
MoO acacAmp@MCM-41 [22], is interesting and instructive. Com-
2
pared to MoO acacAmp@MCM-41 with higher surface area, the
2
Mo-APTS-AC shows comparable (e.g. in the case of cyclooctene
and cyclohexene) or even higher (e.g. in the case of 1-hexene) cat-
alytic activities which can be interpreted by considering the fact
that increasing the hydrophobic nature of the support increases
the activity and selectivity of the catalyst toward the formation of
Fig. 7. Mechanism of the epoxidation of cyclooctene with TBHP in the presence of Mo-APTS-AC.

M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
217
Fig. 8. FT-IR spectra of the (a) 1st, (b) 2nd, (c) 3rd, (d) 4th recycled Mo-APTS-AC catalysts.
In an attempt to assess the catalytic contribution of the solu-
[2] A.P. Wight, M.P. Davis, Chem. Rev. 102 (2002) 3589–3614.
[
[
[
3] A. Choplin, F. Quignard, Coord. Chem. Rev. 178–180 (1998) 1679–1702.
4] P. McMorn, G.J. Hutchings, Chem. Soc. Rev. 33 (2004) 108–122.
5] P.M. Price, J.H. Clark, D.J. Macquarrie, J. Chem. Soc., Dalton Trans. (2000)
101–110.
bilized molybdenum species, the solution was filtered off after 2 h
reaction and then left to react for a further 24 h. As can be observed
in Table 3, in this time interval the cyclooctene conversion rose only
% suggesting that there is no any significant molybdenum species
in the solution and the catalytic reaction is truly heterogeneous in
nature.
The recyclability of the catalyst was investigated after sepa-
ration of the catalyst from reaction mixture at the end of the
reaction and washing with methanol. The recovered catalyst was
reused at least six times for the epoxidation of cyclooctene and
the obtained results are given in Table 4. As can be seen, the
recovered Mo-APTS-AC maintains similar activity after 6 recy-
cles. The ICP-AES molybdenum analyses of the recycled catalysts
[
[
[
6] K.C. Gupta, A.K. Sutar, C.C. Lin, Coord. Chem. Rev. 253 (2009) 1926–1946.
7] C.A. McNamara, M.J. Dixon, M. Bradley, Chem. Rev. 102 (2002) 3275–3300.
8] L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85–93.
3
[9] M.H. Valkenberg, W.F. Holderich, Catal. Rev. 44 (2002) 321–374.
[10] R. Mbeleck, K. Ambroziak, B. Saha, D.C. Sherrington, React. Funct. Polym. 67
(
2007) 1448–1457.
[
11] St. V. Kotov, St. Boneva, Ts. Kolev, J. Mol. Catal. A: Chem. 154 (2000) 121–129.
[12] S. Teixeira, K. Dallmann, U. Schuchardt, R. Buffon, J. Mol. Catal. A: Chem.
182–183 (2002) 167–173.
[
13] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem. 192 (2003)
03–111.
14] M. Masteri-Farahani, N. Tayyebi, J. Mol. Catal. A: Chem. 348 (2011) 83–87.
1
[
[15] M. Masteri-Farahani, Z. Kashef, J. Magn. Magn. Mater. 324 (2012) 1431–1434.
16] S. Shylesh, J. Schweizer, S. Demeshko, V. Schunmann, S. Ernst, W.R. Thiel, Adv.
Synth. Catal. 351 (2009) 1789–1795.
[
(
Table 4) show no significant loss of the molybdenum content
after 6 successive catalytic cycles. On the other hand, similar to
[
17] M. Jia, A. Seifert, W.R. Thiel, Chem. Mater. 15 (2003) 2174–2180.
MoO acacAmp@MCM-41 catalyst, very low molybdenum species
[18] A. Fuerte, M. Iglesias, F. Sanchez, A. Corma, J. Mol. Catal. A: Chem. 211 (2004)
27–235.
2
2
was present in the filtrate as confirmed by ICP-AES analysis. More-
over, the FT-IR spectra of the recycled catalysts (Fig. 8) show no
considerable change in catalyst structure after at least 4 recycles.
Altogether, these results indicate the stability of the prepared cat-
alyst under the reaction conditions.
[
19] M. Masteri-Farahani, M. Sadeghi, Y. Abdollahi, M.M. Kashani Motlagh, F. Salimi,
J. Nanostruct. 2 (2012) 111–118.
[20] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem. 243 (2006)
70–175.
1
[
[
21] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, Catal. Commun. 8 (2007) 6–10.
22] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem. 248 (2006)
53–60.
[
[
23] M. Masteri-Farahani, J. Mol. Catal. A: Chem. 316 (2010) 45–51.
24] F. Maia, R. Silva, B. Jarrais, A.R. Silva, C. Freire, M.F.R. Pereira, J. Colloid Interface
Sci. 328 (2008) 314–323.
4
. Conclusion
[
[
25] A.R. Silva, J.L. Figueiredo, C. Freire, B. de Castro, Microporous Mesoporous Mater.
Surface functionalization of AC with aminopropyltriethoxysi-
68 (2004) 83–89.
lane and subsequent complexation with molybdenum complex
affords a heterogeneous catalyst for epoxidation of olefins. Physico-
chemical characterization of the product confirms the formation of
covalent bonds and successful tethering of molybdenum complex
to the surface of AC. The prepared catalyst was found to be very
efficient and stable heterogeneous catalyst in the selective epoxida-
tion of olefins with TBHP and CHP as oxidants. Due to its increased
hydrophobic nature, the activity and selectivity of the catalyst is
comparable or even higher than other inorganic supports which
besides its cheapness and availability makes it a good candidate for
use in large scale catalytic production of epoxides.
26] A.R. Silva, C. Freire, B. de Castro, Carbon 42 (2004) 3003–3042.
[27] A.R. Silva, V. Budarin, J.H. Clark, B. de Castro, C. Freire, Carbon 43 (2005)
096–2105.
28] A.R. Silva, K. Wilson, J.H. Clark, C. Freire, Microporous Mesoporous Mater. 91
2006) 128–138.
[29] A.R. Silva, V. Budarin, J.H. Clark, C. Freire, B. de Castro, Carbon 45 (2007)
951–1964.
2
[
(
1
[
30] A.R. Silva, M. Martins, M.M.A. Freitas, A. Valente, C. Freire, B. deCastro, Micro-
porous Mesoporous Mater. 55 (2002) 275–284.
[31] J.A. Diaz-Aunon, M.C. Roman-Martinez, C. Salinas-Martinez de Lecea, H. Alper,
Stud. Surf. Sci. Catal. 143 (2002) 295–304.
[
[
[
[
32] M. Carmen Roman-Martinez, J.A. Diaz-Aunon, C. Salinas-Martinez de Lecea, H.
Alper, J. Mol. Catal. A: Chem. 213 (2004) 177–182.
33] I. Such-Basanez, M.C. Roman-Martinez, C. Salinas-Martinez de Lecea, Carbon
42 (2004) 357–1361.
34] L. Lemus-Yegres, I. Such-Basanez, C. Salinas-Martinez de Lecea, P. Serp, M.C.
Roman-Martinez, Carbon 44 (2006) 587–610.
35] L.J. Lemus-Yegres, I. Such-Basanez, M.C. Roman-Martinez, C. Salinas-Martinez
de Lecea, Appl. Catal., A: Gen. 331 (2007) 26–33.
References
[
1] C. Li, Catal. Rev. 46 (2004) 419–492.

2
18
M. Masteri-Farahani, S. Abednatanzi / Applied Catalysis A: General 478 (2014) 211–218
[
[
[
[
36] M. Pérez-Cadenas, L.J. Lemus-Yegres, M.C. Roman-Martinez, C. Salinas-
Martinez de Lecea, Appl. Catal. A: Gen. 402 (2011) 132–138.
37] H. Sharghi, M. Aberi, M.M. Doroodmand, Adv. Synth. Catal. 350 (2008)
[40] G.J.J. Chen, J.W. McDonald, W.E. Newton, Inorg. Chem. 15 (1976)
2612–2615.
[41] J. Topich, Inorg. Chem. 20 (1981) 3704–3707.
[42] S.J. Gregg, K.S.W. Sing, Adsorption, Surface area and Porosity, Academic Press,
London, 1982.
[43] H. Ritter, M. Nieminen, M. Karppinen, D. Bruhwiler, Microporous Mesoporous
Mater. 121 (2009) 70–83.
[44] R.A. Sheldon, J.A. Vandoorn, J. Catal. 31 (1973) 427–437.
2
380–2390.
38] A.R. Silva, J.L. Figueiredo, C. Freire, B. de Castro, Catal. Today 102–103 (2005)
54–159.
39] Y. Xiang, L. Kong, P. Xie, T. Xu, J. Wang, X. Li, Ind. Eng. Chem. Res. 53 (2014)
197–2203.
1
2