Preparation, characterization and catalytic activity of a nano-Co(II)- Catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and benzyl alcohol

Article abstract of DOI:10.1016/j.crci.2013.01.002

This paper reports the preparation of a nano-Co(II)-catalyst (NCC) by anchoring of Co ions on immobilized bipyridylketone over the nano-sized SiO ₂/Al₂O₃ mixed oxides. The nano- Co(II)-catalyst has been characterized by elemental analysis, BET, FT-IR, DR UV-vis and SEM. The catalytic activity of the catalyst towards the oxidation of ethylbenzene, cyclohexene, and benzylalcohol to different chemically and pharmaceutically important products were evaluated with tert-butyl hydroperoxide (TBHP) in the absence of solvent. Under optimized conditions, the nano-catalyst proved highly selective towards the acetophenone, 2-cyclohexene-1-one and benzaldehyde as reaction products, with excellent conversion rates.

Full text of DOI:10.1016/j.crci.2013.01.002

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C. R. Chimie xxx (2013) xxx–xxx
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Full paper/Memoire
Preparation, characterization and catalytic activity of a nano-Co(II)-
catalyst as a high efficient heterogeneous catalyst for the selective
oxidation of ethylbenzene, cyclohexene, and benzyl alcohol
*
*
Davood Habibi , Ali Reza Faraji
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
This paper reports the preparation of a nano-Co(II)-catalyst (NCC) by anchoring of Co ions
on immobilized bipyridylketone over the nano-sized SiO2/Al2O3 mixed oxides. The nano-
Co(II)-catalyst has been characterized by elemental analysis, BET, FT-IR, DR UV–vis and
SEM. The catalytic activity of the catalyst towards the oxidation of ethylbenzene,
cyclohexene, and benzylalcohol to different chemically and pharmaceutically important
products were evaluated with tert-butyl hydroperoxide (TBHP) in the absence of solvent.
Under optimized conditions, the nano-catalyst proved highly selective towards the
acetophenone, 2-cyclohexene-1-one and benzaldehyde as reaction products, with
excellent conversion rates.
Received 14 November 2012
Accepted after revision 11 January 2013
Available online xxx
Keywords:
Co nano-catalyst
Oxidation
Ethylbenzene
Cyclohexene
ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Benzylalcohol
Aetophenone
2-cyclohexene-1-one
Benzaldehyde
1. Introduction
reagent mixture is corrosive, and the chemistry is seldom
selective [2]. In fact, as the traditional metal compounds
Designs of reaction systems for the oxidation of organic
compounds provide paths to synthesize a wide range of
functionalized molecules. Selective oxidation of hydro-
carbons to give oxygenic compounds is a fundamental
reaction in organic chemistry both for elemental research
and industrial manufacturing [1]. Investigation related to
the new solid oxidation catalysts is one of the most
significant current topics, connected with both industrial
and fundamental researches, because the traditional
techniques involve the use of large amounts of highly
toxic oxidation state of Co, Os, Mn, and Co reagents. Lower
oxidation state metals such as Co(II), Mn(II) and Cu(II) in
AcOH may be utilized with O2 as the eco-friendly oxidant.
However, the conditions in many cases are unpleasant, the
used in this process are in catalytic amounts, the reaction
conditions are harsh; the product selectivity is low and
often corrosive promoters like bromide anions are used
along with the traditional catalyst. However, the separa-
tion of the catalyst from the reaction mixture is very
difficult, the catalyst cannot be reused, and also a lot of
tarry waste is produced. Environmentally acceptable
catalytic oxidations that carried out under mild conditions
in the liquid phase with high selectivity are obviously
desirable. Transition metal complexes can be used as
excellent catalysts for oxidation reactions with a suitable
organic ligand [3,4]. The oxidation reactions catalyzed by
metal complexes are often prevented due to oxidative
degradation of the complex and/or the formation of
m-oxo
dimmers [5]. Several methods can be employed to
diminish the above-mentioned problems, such as separa-
tion of the catalyst from the reaction medium and increase
of the effectiveness of the catalysts by improving active
sites’ life. Always, transition metal catalysts have been
* Corresponding authors.
E-mail addresses: davood.habibi@gmail.com (D. Habibi),
alireza_ch57@yahoo.com (A.R. Faraji).
1631-0748/$ – see front matter ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.01.002
Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

G Model
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D. Habibi, A.R. Faraji / C. R. Chimie xxx (2013) xxx–xxx
immobilized on solid supports, such as organic polymers,
inorganic solids (SiO2, clay, zeolite. . .), colloids, molecular
sieves, ion-exchange resins and polymer membrance [6–
15]. The target of heterogenization of homogeneous
catalysts provides active heterogeneous catalysts, which
possess the same catalytic site as in their homogeneous
application offered by homogeneous catalysts and become
thermally more stable with the ease of separation and
recycling of heterogeneous catalysts [16–20,12]. The
special advantages of immobilized catalysts have
prompted several groups to introduce various types of
solid supports [6–20]. Among the various inorganic
supports, silica is the most common. A review article by
Jacobs et al. provides information about of such immobi-
lized complexes [21]. The most studies has focused on the
modified silica gel, as the supports in high performance
liquid chromatography (HPLC), inorganic compound
separations, ion-exchange, preconcentration of inorganic
compounds and pesticides preconcentration, as well as
being chemical sensors and finding use in catalysis [22–
27]. The present paper now reports a novel heterogeneous
catalyst for the liquid phase partial oxidation of alkyl
aromatic and alkene substrates based on a chemically
modified nano-sized SiO2/Al2O3 mixed oxides which
significantly enhanced catalytic activity and selectivity.
The synthesis of the catalyst is fully described together
with the results obtained in the catalytic oxidation of
ethylbenzene, cyclohexene and benzyl alcohol (used as a
model substrate) under solventless conditions and TBHP as
the consumable source of oxygen.
registered on a JASCO-550 UV-Vis spectrophotometer
that was equipped with a diffuse reflectance attachment
in which BaSO4 was as the reference. Type and quantity
of the resulting products from oxidation were deter-
mined by
a HP 6890/5973 GC/MS instrument and
analyzed by a Shimadzu GC-16A gas chromatograph
(GL-16A gas chromatograph with a 5 m ꢁ 3 mm OV-17
column, 60–220 8C (10 8C/min), Inj. 230 8C, Det. 240 8C).
For elemental analysis a CHN-Rapid Heraeus elemental
analyzer (Wellesley MA) was used. Before carrying out
the nitrogen (99.999%) adsorption experiments, the
sample was outgassed at 393 K for 14 h, then the
experiment has been carried out at 76 K using
a
volumetric apparatus (Quantachrome NOVA automated
gas sorption analyzer). The specific surface areas were
calculated using the BET (Stephen Brunauer, Paul Hugh
Emmett, and Edward Teller) method. The images of
scanning electron micrograph (SEM) and transmission
electron microscopy (TEM) were taken using a Philips
501 microscope and a Tecnai F30TEM operating at
300 kV, respectively. In addition, energy dispersive X-ray
analysis was conducted on each sample. Size distribution
in order to count nanoparticles in reverse microemulsion
was measured by a Zetasizer Nano-ZS-90 apparatus (ZEN
3600, MALVERN instruments).
2.2. Preparation of Organometallic-SiO2/Al2O3 nano-sized
Nano-sized SiO2/Al2O3 was used as the support
prepared by the sol–gel method [26]. The solid SiO2/
Al2O3which produced, was being used as the support in the
synthesis of the nano-catalyst. At first, 3.5 g of nano-sized
SiO2/Al2O3 was activated at 500 8C for 5 h under air and
then refluxed with 4.3 mL of trimethoxysilylpropylamine
(3-APTMS) in dry toluene (50 mL) for 24 h. The solid
achieved during this process was filtered and washed off
with dry methanol at 100 8C under vacuum for 5 h. Then
bipyridylketone (BPK) was added to a suspended solution
of SiO2/Al2O3-APTMS in dry methanol. To synthesize the
SiO2/Al2O3-APTMS-BPK-Co (Scheme 1), 2.0 g of SiO2/Al2O3-
APTMS-BPK was suspended in 50 ml of ethanol at a round
bottom flask followed by adding of 3.0 mmol Co(OA-
c)2.4H2O. The mixture was refluxed during 24 h under
magnetical stirring.
2. Experimental
2.1. Materials and instruments
All reagents were purchased from the Merck and Fluka
chemical companies. Reagents were used without extra
purification, but solvents were purified with standard
methods. Inductively coupled plasma (ICP) measurements
for Co content evaluation were performed using a Perkin-
Elmer ICP/6500. Infrared data were collected on KBr pallets
using a JASCO FT/IR (680 plus) spectrometer and the
position of an infrared band is given in reciprocal
centimeters (cmꢀ1). Diffuse reflectance spectra were
Scheme 1. Schematic representation of preparation process for Si/Al-APTMS-BPK-C.
Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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3
Table 1
Chemical composition and physicochemical properties of the immobilized Co-nano-catalyst on the SiO2/Al2O3 mixed oxide. Co(OAc)2.4H2O.
Sample
Elemental analysis Organic functional Immobilized
%Coordinated
Structural parameterse
(wt%)b
group
Co-Schiff base-complex Schiff base
(mmol/g mixed
odide)c
(mmol/g mixed
oxide)d
groups to Co ions
C
N
–
Co
Surface Pore volume Pore
area
(m2/g)
(cm3/g)
diameter
(A8)
SiO2/Al2O3 nanosizeda
Si/Al-APTMS
–
–
–
–
–
–
–
498
378
320
281
0.045
0.031
0.026
0.021
36
25
20
18
8.13 3.75
10.9 4.92
2.67
3.51
–
–
Si/Al-APTMS-BPK
Si/Al-APTMS-BPK-Co
–
–
7.45 1.38 1.14 0.98
0.193
58.7
a
Molar ratio of Si/Al was 60:40, determined from EDX analysis.
b
c
Nitrogen was estimated from the elemental analyses. Co content determined from EDX analysis.
Determined from the N-contents.
d
e
Determined from the Co-content, assume that cobalt ions coordinated with Schiff base ligands.
The pore size calculated using the BJH method.
2.3. General procedure for oxidation of ethylbenzene,
cyclohexene and benzyl alcohol
synthesized onto the SiO2/Al2O3 mixed oxides, as illustrat-
ed in Scheme 1. The formation of Co catalyst onto the SiO2/
Al2O3 was verified using CHN, FT-IR, UV–Vis, and SEM. The
surface area, pore size and volume of the modified support
were significantly reduced compared to the pristine SiO2/
Al2O3 (this decrease indicates the decline in interaction
between adsorbate, N2 molecules, and the nano-sized SiO2/
Al2O3 surface after modification with organic chains). The
loading of cobalt in the heterogeneous cobalt catalyst was
characterized by elemental analyses. The final metal
In this procedure, the heterogeneous catalyst (5.0 mg),
the substrate (9.0 mmol) and an oxidant (9.0 mmol, 80%
TBHP) were added in a three-necked round bottom flask
equipped with a refluxed condenser. The mixture was
stirred at the desired temperature. After filtering and
washing with solvent, the filtrate was monitored by GC.
The products were identified by GC–MS techniques. The
conversion and selectivity were calculated with GC area
normalization. Finally, comparative experiments were
performed under different conditions.
content was around 0.193 mmolgꢀ1
, indicating that
58.7% of the immobilized ligands were complexed with
cobalt ions (Table 1).
3. Results and discussion
3.1.1. The FT-IR spectra
In Fig. 1, the FT-IR spectra of SiO2/Al2O3-APTMS, SiO2/
Al2O3-APTMS-BPK, and SiO2/Al2O3-APTMS-BPK-Co are
shown. The strong absorption bands related to Si–O–Si
stretching vibrations were observed in the spectrum of
3.1. Characterization
Using BPK and Co(OAc)2.4H2O through the covalently
immobilization, caused heterogeneous Co catalyst being
100
1535
1466
1400
1509
1384
1561
1542
1449
1410
1467
1630
1627
80
60
40
20
1431
1509
1384
1320
633
566
603
877
791
466
C
B
694
624
1448
1493
872
678
796
796
1058
612
594
1383
1412
1563
1626
1088
457
1073
A
457
1074
0
1800
1500
1250
1000
400
750
Wavenumber (cm-1)
Fig. 1. FTIR spectra of: (A) SiO2/Al2O3-APTMS; (B) SiO2/Al2O3-APTMS-BPK; (C) SiO2/Al2O3-APTMS-BPKCo.
Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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Fig. 2. DR UV–vis spectra of: (A) SiO2/Al2O3; (B) SiO2/Al2O3-APTMS; (C)
SiO2/Al2O3-APTMS-BPK; (D) SiO2/Al2O3-APTMS-BPK-Co.
SiO2/Al2O3 at 1010–1290 and 798 cmꢀ1
. The FT-IR
spectrum of SiO2/Al2O3-APTMS shows several signals
originating from amino propyl groups, which are related
to C–H stretching modes of the propyl group, appeared in
the area of 1450–1560 cmꢀ1 and 2935–2860 cmꢀ1. The
results show that the SiO2/Al2O3 was successfully modified
by amine spacer groups. However, the N–H deformation
peak at 1540–1560 cmꢀ1 confirms the successful functio-
nalization of the SiO2/Al2O3 mixed oxide with 3-APTMS. In
Fig. 1B, the C5N imine vibration signal was observed at
1630 cmꢀ1 [21], which confirms the condensation reaction
between BPK and organo-functionalised SiO2/Al2O3. The
peaks in the ranges of 3066–3020 and 1437–1434 cmꢀ1 are
attributed to the C–H and C5C stretching vibrations of
pyridine groups, respectively [21,26]. After interacting of
cobalt ions with immobilized BPK over modified SiO2/
Al2O3, the weak absorption peak at 566 cmꢀ1 appeared; it
is attributed to the Co-N bands.
Fig. 3. SEM of SiO2/Al2O3-APTMS-BPK-Co nano-catalyst.
nanoparticles appearance and size of them were similar,
demonstrating that the nanoparticles of SiO2-Al2O3 have
good mechanical stability and they have not been
destroyed during the whole modifications. The particle
size distributions obtained for the reverse micro emulsion
solution was around 28 nm.
3.2. Oxidation of ethylbenzene
To optimize the effectiveness of reaction conditions on
the oxidation of ethylbenzene (EB) by TBHP in the presence
of the nano-cobalt catalyst, various parameters, such as the
amount of the substrate to oxidant, the temperature, and
the nature of the solvent, on the performance of the
heterogeneous catalyst were investigated. In this reaction,
major products are acetophenone (1) benzaldehyde (2)
and benzoic acid (3) (Scheme 2).
3.1.2. The UV-vis spectra
BycomparingtheUV–VisspectrumoftheSiO2/Al2O3 and
the Si/Al-APTMS-BPK (Fig. 2), it was observed that the
spectrum of the SiO2/Al2O3 showed an absorption band near
249 nm but, for the SiO2/Al2O3-APTMS-BPK transitions
p
!
p
* and n!
p
* of the ligands caused strong adsorption
at the 255–320 nm [28].
A
characteristic feature of
immobilized Co(II) species after the reaction of SiO2/
Al2O3-APTMS-BPK with Co(OAc)2ꢂ4H2O was observed
through a change of the color of powder from yellow to
deep brown. Consequently, UV-visible spectra indicated the
appearance of several new metal d–d transition bands at
around 570 nm upon cobalt immobilization.
The GC analysis did not show any oxidation products of
the aromatic ring in effluents. In order to study the effects
of solvents on the oxidation of EB, various solvents such as
acetonitrile, ethanol, water, benzene and dichloromethane
at 100 8C were experimented (Table 2). The reaction in the
presence of coordinating solvents such as ethanol had low
conversion, while using water as a solvent made no
reaction. It seems that the donor electrons of these solvents
had more ability to occupy the vacant space around the
existing metal in catalyst, so this prevents coordinating
3.1.3. Scanning electron microscope
Scanning electron microscope (SEM) images of the nano
Co catalyst is shown in Fig. 3. It could be seen that the
Scheme 2. Oxidation of ethylbenzene catalyzed by SiO2/Al2O3-APTMS-BPK-Co in the presence of tert-butyl hydroproxide.
Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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5
Table 2
Effect of solvents on ethylbenzene oxidation.
Solvent
Ethylbenzene conversion
Product selectivity (%)
Acetophenone
(wt%)
Benzaldehyde
Benzoic acid
Without
47.2
32.7
16.8
26.2
0.0
79.0
46.2
24.0
55.8
0.0
8.83
39.6
63.7
27.5
0.0
12.17
15.2
13.2
18.7
0.0
Acetonitrile
Ethanol
Benzene
Water
Dichloromethane
41.4
36.9
48.2
16.7
Reaction conditions: ethylbenzene, 2 mmol; Cat., 50 mg; TBHP, 2 mmol; 24 h; T, 100 8C.
from oxidant molecules [29]. The major product in the
oxidation of EB in all solvents except ethanol and dichlor-
omethane was acetophenone. The percent of EB conversion
decreased in the following order with different solvents;
41.0% (dichloromethane) > 32.0% (benzene) > 26.0% (acet-
onitrile) > 16.0% (ethanol) > 0.0% (water). The use of protic
solvents and chlorinated solvent favor the selectivity to
benzaldehyde and benzoic acid, while aprotic solvents lead to
acetophenone [30]. The acetophenone selectivity on different
solvents decreased in the following order; benzene
(55.0%) > acetonitrile (46.0%) > dichloromethane (36.0%)>
ethanol (24.0%)> water (0.0%) (Table 2). Thus, dipole
moments of the solvent probably play an essential role in
the oxidation of EB. More investigations showed that the
reaction under solventless conditions had higher selectivity
and more catalytic activity than in the presence of a solvent
(as protic and aprotic ones) (Table 2). This observation more
likely demonstrates that the EB and solvent molecules are
competitors for the active sites of metal center in catalyst.
In order to evaluate the effect of substrate to oxidant
molar ratio on the catalytic activity and selectivity in
solventless condition, the reactions were carried out at
different molar ratios of EB:TBHP (1:1, 1:3 and 1:5) at
100 8C after 24 h (Fig. 4). It was found that the different
molar ratio of EB:TBHP has strong effects on catalytic
activity and selectivity. In most of the experiments
acetophenone was the major product and catalytic activity
does rise with increasing concentration of TBHP to EB,
which is due to the presence of excess tert-butyl
hydroperoxide coordinated with active sites of the nano-
catalyst (heterogeneous Co catalyst) (Fig. 4). In all EB
oxidation reaction conditions, as the reaction time
increased, the conversion and selectivity to acetophenone
increased as well.
Increasing the temperature for accelerating the reac-
tion is apparently effective. Consequently, the tempera-
ture effect (50 8C, 80 8C and 100 8C) was also monitored on
the oxidation of EB at the EB:TBHP molar ratio of 1:1 after
24 h in the presence of NCC (Fig. 5). Generally, by
increasing reaction temperature and reaction time, the
conversions grow higher (74%) and also the reaction
selectivity to acetophenone increased (92%) while the
selectivity to benzaldehyde and benzoic acid decreased
when the reaction was carried out at 100 8C. Thus raising
temperature is effective for the oxidation reaction since
the energy was not sufficient for the activation of oxygen
molecules or the catalytic circulation at the low
temperature.
To estimate the reusability of NCC, after the first run,
the catalyst was filtrated and washed with ether and dried
at 80 8C under vacuum and then used for the next run
under the same conditions. For the third performance of
80
70
60
50
40
30
20
10
0
Conversion
Aldehyde
Ketone
1:1 (TBHP 80%)
Carboxylic
2
6
12
18
24
Time (h)
Conversion
Aldehyde
Ketone
100
90
80
70
60
50
40
30
20
10
0
1:3 (TBHP 80%)
Carboxylic
2
6
12
18
24
Time (h)
Conversion
Aldehyde
Ketone
100
90
80
70
60
50
40
30
20
10
0
1:5 (TBHP 80%)
Carboxylic
2
6
12
18
24
Time (h)
Fig. 4. The influence of different oxidant ratios on the ethylbenzene
oxidation by the SiO2/Al2O3-APTMS-BPKCo catalyst. Conditions:
ethylbenzene, 2 mmol; Cat., 50 mg; T, 100 8C; solventless.
Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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D. Habibi, A.R. Faraji / C. R. Chimie xxx (2013) xxx–xxx
80
100 ˚C
70
80 ˚C
60
50
40
30
20
10
0
50 ˚C
0
2
4
6
8
10
12
14
16
18
20
22
24
Time h
Fig. 5. The influence of reaction temperature on the ethylbenzene oxidation
and selectivity to acetophenone by the SiO2/Al2O3-APTMS-BPK-Co catalyst.
Conditions: ethylbenzene, 2 mL; Cat., 50 mg; TBHP, 10 mmol; solventless.
the catalyst, 89% selectivity with 69% conversion still can
be gained (Fig. 6). A few losses of activity and selectivity
was revealed, satisfying that NCC has high stability during
the catalytic process.
Finally, another experiment was carried out in order to
prove the important role of the catalyst in the oxidation of
EB. First, extra EB was added to the filtrate after the
removal of catalyst. Under these conditions, no more
products were produced. Then, to prove whether metal is
coordinated to the Schiff base ligand or with Si -OH and Al
-OH groups on the surface of SiO2/Al2O3, some Co acetate
was added to the blank SiO2/Al2O3, and the reaction took
place in the same conditions; then the conversion of
ethylbenzene was almost unnoticeable. In Table 3, our
catalyst is being compared with the literature catalysts.
The catalyst and applied method in this paper have the
advantages in terms of heterogeneous nature, high
reusability, high conversions and selectivity of the
catalyst.
Fig. 6. ReusabilityoftheCo-nano-catalystontheoxidationofethylbenzene
and selectivity to acetophenone. Conditions: ethylbenzene, 2 mmol; Cat.,
50 mg; TBHP, 10 mmol; T, 100 8C; solventless.
3.3. Oxidation of cyclohexene
To examine the catalytic activity of nano-cobalt
catalyst, oxidation of cylohexene was carried out under
solventless conditions at 100 8C by applying TBHP as
oxidant (Scheme 3). The products of this reaction were 2-
cyclohexene-1-one (1), cyclohexene oxide (2), and 1,2-
cyclohexandiol (3) which were identified by GC-MS and
quantified by GC analysis. Fig. 7 shows that at the same
temperature (100 8C), but with different molar ratios of
Table 3
Comparison of literature catalysts and our catalyst system for oxidation of ethylbenzene.
Entry
Catalytic system
Reaction conditionsa
EB conversion (%)
Selectivity
AP
85
BZ
9.1
–
Other
5.9
2
1
2
3
4
5
6
7
8
9
10
Bhoware and Singh [31]
Wang et al. [32]
0.05 g Co-MCM-41(100), TBHP, solvent-free, 80 8C, 24 h
0.09 g CoTPP-P(4VP-co-st)/SiO, O2, solvent -free, 95 8C, 0.2 h
2 mmol Co(III) complex, O2, solvent-free, 150 8C, 4 h
0.3 g Mn-MCM-41, TBHP, solvent-free, 80 8C, 24 h
0.05 g YCu, H2O2, benzene, 70 8C, 8 h
26
24
70
70
60
16
62
47
45
69
98
Qi et al. [33]
90
39
0.7
10
–
9.1
50
–
Veterivel and Pandurangam [34]
Xavirert et al. [44]
Radhika and Sugunam [45]
Jothiramalingam et al. [46]
Jana et al. [47]
100
75
0.1 g 6VC, H2O2, CH3CN, 60 8C, 6h
11
–
16
–
0.1 g Zr-k-OMS, TBHP, CH3CN, 65 8C, 10 h
98
2.45 g NiAl-hydrotalcite, O2, solvent-free, 135 8C, 9 h
0.1 g CNCr-2, TBHP, CH3CN, 70 8C, 8 h
99
–
0.7
30
2
Waters [48]
69
–
This work
5 mg Si/Al-ATMPS-BPK-Co, TBHP, solvent-free, 80 8C, 24 h
92
6
AP: acetophenone; BZ: benzaldehyde.
a
Co TPP-P (4VP-co-st)/SiO2: Co tetraphenylporphrins on P (4VP-co-st)/SiO2, YCu-fsal: Y zeolite encapsulated Cu(II) Complexe of 3-formylsalicylic acid,
6VC: Vanadia/Ceria catalysts (6 wt% of V2O5), Zr-K-OMS: Zireonium doped K-OMS-2 type manganese oxide material, CNCr-2: Cu1ꢀxNixCr2O4 (x = 0.5).
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Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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7
Scheme 3. Oxidation of cyclohexene catalyzed by Si/Al-APTMS-BPK-Co.
CH:TBHP (1:1, 1:3 and 1:5), cyclohexene conversion and
the selectivities of the products have been changed. As the
molar ratios of CH:TBHP and reaction time were raised to
(1:5) at 24 h, respectively, the cyclohexene conversion and
the selectivity to 2-cyclohexene-1-one increased from 36
to 55 and 67 to 88%, respectively, while the selectivities to
cyclohexene oxide and 2-cyclohexene-1-ol decreased
(Fig. 7). In general, the allylic oxidation of cyclohexene
requires 5:1 stoichiometric molar ratio of TBHP:substrate.
However, under the reaction condition used in this work,
all of the TBHP cannot be consumed for this reaction owing
to a possible partial decomposition and/or remaining
unreacted TBHP. Therefore, the reaction may consume
higher amount of TBHP for a complete conversion [48]. So,
it could be concluded from the results that under the
mentioned reaction conditions, the allylic hydrogen is
more reactive than the C5C double bond. However, the
abstraction of hydrogen from the allylic carbon leads to
allylic radical, which requires lower activation energy than
the reaction at the double bond.
In order to examine the reusability of the immobilized
cobalt catalyst onto the SiO2/Al2O3, several successive
experiments were carried out by application of the used
catalyst. According to Fig. 8, there is no significant loss of
activity and selectivity even after the fifth run. Therefore,
the results clearly proved that the NCC catalyst conversion
of cyclohexene (55%) with ca. 88.0% selectivity to 2-
cyclohexene-1-one under solventless condition. Further-
more, in Table 4, our catalyst is being compared with the
literate catalysts.
3.4. Oxidation of benzyl alcohol
The liquid-phase oxidation of benzyl alcohol was
performed by TBHP at 25, 40, 60, 80 and 100 8C on the
immobilized NMC under different conditions without the
use of any solvent (Scheme 4). Table 5 confirms the
highness of catalytic activity and excellent selectivity to
benzaldehyde (100%) in all experimental condition. GC
analysis showed that benzaldehyde was the sole product
100
80
60
40
20
0
Conversion
Selectivity
First cycle
Second cycle
Third cycle
Fourth cycle
Fifth cycle
Recycling number
Fig. 8. Reusability of the Co-nano-catalyst in the oxidation of cyclohexene
and selectivity to 2-cyclohexene-1-one. Conditions: cyclohexene, 2 mmol;
Cat., 50 mg; TBHP, 10 mmol; 24 h; T, 100 8C; solventless.
Fig. 7. The influence of different oxidant ratio on the cyclohexene
oxidation by the Si/Al-APTMS-BPK-Cocatalyst. Conditions: cyclohexene,
2 mmol; Cat., 50 mg; T, 100 8C; solventless.
Scheme 4. Oxidation of benzyl alcohol to benzyl aldehyde.
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Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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8
D. Habibi, A.R. Faraji / C. R. Chimie xxx (2013) xxx–xxx
Table 4
Comparison of literature catalysts and our catalyst system for oxidation of cyclohexene.
Entry
Catalytic system
Reaction condition
Conversion (%)
Selectivitya
Keton
Other
product
1
2
3
4
5
6
Luque et al. [37]
0.2 Co-salen-SBA 15, H2O2, MW300W, 90 8C, 0.33 h
5 mg (Ru/Co/Ce) (THNO), TBHP, CH2Cl2
> 99
73.6
43.6
43.2
92
89
11
Ghiaci et al. [35]
80.3
55.6
74
19.7
44.4
18
Salavati and Niasari [36]
Baricelli et al. [38]
Sehlotho and Nykong [39]
Li et al. [40]
1.02 ꢁ 10ꢀ5 mol [Co(H4C6N6S2)], TBHP, CH2Cl2, rt, 8 h
0.01 mol [Ir (CH3CN)4 NO2] (PF6)2, O2, CH3 CN 120 8C, 12 h
(1.7 mg/ml) CoPc, TBHP, DMF/dichloromethane, rt, 8 h
60.8
49.0
39.2
18.2
Trans–RuCl2 [k3–1R, 2R–P(NH)–(NH) P]Pph3/CNTS, O2,
80.7
solvent-free, 105 8C, 1 h
7
Dapurkar et al. [41]
20 mg CrMCM–41, O2, 70 8C, 24 h
41.5
50
74.2
100
56
25.8
–
8
Malumbazo and Mapolie [42]
Malumbazo and Mapolie [42]
Sujandi Han et al. [43]
This work
(0.01 mol) t-BuCo/MCM-41, H2O2, O2, CH3CN 60 8C, 5 h
(0.01 mol) tBu Co/Davisil 710, H2O2, O2, CH3CN 60 8C, 5 h
100 mg Co (III) SBA–15, H2O2, CH3CN 40 8C, 12 h
5 mg SiAl-ATMPS-BPK-Co, TBHP, solvent-free, 80 8C, 24 h
9
45
44
10
11
34.8
55
10.2
88
89.8
12
Co-Salen-SBA 15: Co-N,N0-ethylenebis (salicylidenaminato) on SBA 15; THNO: Trimetallic hybrid nanomixed oxide (Ru/Co/Ce), H6C6N6S2: 1,2,5,6,8,11-
hexazacylodoca-7, 12-dithione-2, 4,8,10-tetraene; ZnPc: zinc phthalocyanine.
a
Ketone: 2-cyclohexene-1-one.
Table 5
enous catalyst was investigated. The catalytic active
system designed by a nano-heterogeneous cobalt associ-
Oxidation of benzyl alcohol with heterogeneous cobalt nano-catalyst.
Selectivitye
(mol %)
ated with TBHP under solventless condition exhibited
Reaction temperature
Conversion
(mol %)
(T 8C)
efficient catalytic activity in the selective oxidation of
ethylbenenze, cyclohexene, and benzyl alcohol. The
catalyst appears to be of particular interest for the
industrial production of aromatic and alkyl ketones under
mild condition.
25
49.1
65.8
78.8
91.0
97.9
87.3
99.6
78.7
78.5
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
40
60
80
100
60a
60b
60c
60d
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Please cite this article in press as: Habibi D, Faraji AR. Preparation, characterization and catalytic activity of a nano-
Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002

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Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene, and
benzyl alcohol. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.002