Characterization and catalytic activity of a novel Fe nano-catalyst as efficient heterogeneous catalyst for selective oxidation of ethylbenzene, cyclohexene, and benzylalcohol

Article abstract of DOI:10.1016/j.molcata.2013.02.014

In the present study, heterogeneous Fe-nano-catalyst has been covalently anchored on a modified nanoscale SiO₂/Al₂O₃. The synthesized materials were characterized by FT-IR spectroscopy, DS UV-vis, CHN elemental analysis, BET, EDS, SEM, TEM, TGA and XPS. The catalytic activity of the Fe nano-catalyst (FNC) in the oxidation of ethylbenzene, cyclohexene, and benzylalcohol was studied using tert-butyl hydroperoxide as oxygen source, without the need of any solvent. Oxidation of ethylbenzene, cyclohexene, and benzylalcohol catalyzed by (FNC) gave acetophenone, 2-cyclohexene-1-one and benzaldehyde, respectively, as major products. A suitable reaction condition has been optimized for Fe-nano-catalyst by considering the effect of various parameters such as reaction time and the amount of oxidant, different solvents, concentration of substrate for the maximum conversion of substrates and high selectivity. This catalyst can be easily prepared from inexpensive, commercially available reagent and is stable and reusable for oxidation of ethylbenzene, cyclohexene, and benzylalcohol.

Full text of DOI:10.1016/j.molcata.2013.02.014

Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Characterization and catalytic activity of a novel Fe nano-catalyst as efficient
heterogeneous catalyst for selective oxidation of ethylbenzene, cyclohexene, and
benzylalcohol
D. Habibia,∗, A.R. Farajia,∗, M. Arshadib, J.L.G. Fierroc
a Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
b Department of Science, Fasa Branch, Islamic Azad University, PO Box 364, Fasa 7461713591, Fars, Iran
c Instituto de Catálisis y Petroleoquímica (CSIC), c/Marie Curie, 2 Cantoblanco, 28049 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, heterogeneous Fe-nano-catalyst has been covalently anchored on a modified
nanoscale SiO2/Al2O3. The synthesized materials were characterized by FT-IR spectroscopy, DS UV–vis,
CHN elemental analysis, BET, EDS, SEM, TEM, TGA and XPS. The catalytic activity of the Fe nano-catalyst
(FNC) in the oxidation of ethylbenzene, cyclohexene, and benzylalcohol was studied using tert-butyl
hydroperoxide as oxygen source, without the need of any solvent. Oxidation of ethylbenzene, cyclohex-
ene, and benzylalcohol catalyzed by (FNC) gave acetophenone, 2-cyclohexene-1-one and benzaldehyde,
respectively, as major products. A suitable reaction condition has been optimized for Fe-nano-catalyst
by considering the effect of various parameters such as reaction time and the amount of oxidant, differ-
ent solvents, concentration of substrate for the maximum conversion of substrates and high selectivity.
This catalyst can be easily prepared from inexpensive, commercially available reagent and is stable and
reusable for oxidation of ethylbenzene, cyclohexene, and benzylalcohol.
Received 27 November 2012
Received in revised form 13 February 2013
Accepted 15 February 2013
Available online xxx
Keywords:
Fe nano-catalyst
Oxidation
Ethylbenzene
Cyclohexene
Benzylalcohol
Aetophenone
2-Cyclohexene-1-one
Benzaldehyde
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
conditions and the catalyst can be used for many times. In past
decade, nanostructure has been developed that is claimed to allow
Catalytic technologies are of utmost importance for transfor-
mation crude and cheap raw material into products with high
economic value. Homogenous catalysts have many advantages
such as high reactivity and selectivity, because in homogenous cat-
alysts every single catalytic entity can act as a single active site.
Despite their advantages, some of homogenous catalytic processes
have not been commercialized because of difficulty encountered
when attempting to separate and recovery the catalyst from the
reaction mixture. Furthermore, some industrial problems such as
corrosion and deposition on reactor wall are associated with these
homogeneous catalysts. These disadvantages were minimized if
homogeneous complexes were immobilized onto the insoluble
solid supports. The majority of the heterogenized catalysts design
based on anchoring transition metal on inorganic compound with
excellent chemical and thermal stability and easily accessibil-
ity. Anchoring is robust enough to endure the harsh reaction
greater selectivity and control in heterogeneous catalysis. Needless
to say, transformation of organic compound to oxygenic com-
pound is one of the most important reactions in the chemistry with
fundamental research, general synthesis and industrial manufac-
turing. However, this transformation regularly leads to production
of a large amount of toxic material and hence environmental pol-
lution. Promote in the progression of new oxidation catalysts,
involving transition metal complexes with Schiff base ligand [1–6],
methodologies, synthesis and their applications could be one of the
considerable interest of current organometallic research [7,8]. Inor-
ganic compounds such as silica gel, clay, zeolite and mesoporous
material that have been used as the support for the heterogeniza-
tion of transition metal complexes with Schiff base ligands have
been widely applied in selective oxidation of alcohols, alkenes
and alkyl aromatics [9–13]. The development of new iron cata-
lysts as the commercial catalyst for oxidation of hydrocarbon is
attracting chemists intending to investigate new industrial access
[14,15]. In the past, many chemists have paid much attention to
produce benzilic and allylic ketones by oxidizing agent, such as
the oxidation of ethylbenzene (EB) to acetophenon (AP) by KMnO4
[16], H2O2 [17–25], TBHP [17,26–31], CrO3–SiO2 [32], SeO2 [33]
∗
Corresponding authors. Tel.: +98 811 8282807; fax: +98 811 8380709.
E-mail addresses: davood.habibi@gmail.com (D. Habibi),
alireza ch57@yahoo.com (A.R. Faraji).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.02.014

D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
91
and O2 [34–39]. Furthermore, the use of heterogynous catalyst
has afforded good to excellent conversion with good selective to
2-cyclohexene-1-one [40–48].
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 micro-
scope 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 Zetasizer Nano-ZS-90 (ZEN 3600,
MALVERN instruments).
In order to gain an insight into the catalytic activity of a simple
heterogeneous nano catalyst for the inert hydrocarbon bond oxi-
dation with tert-butyl hydroperoxide (TBHP) as the oxygen donor
under mild conditions and in absence of any additive, for the
first time a systematic and stepwise synthesis of a heterogeneous
environmental-friendly catalyst based on ferrocenecarboxalde-
hyde (FCA), as a commercially available molecule is reported.
Here, we have demonstrated the application of a stable covalently
immobilized ferrocene derivative on the surface of SiO2–Al2O3
mixed-oxide host by a linker approach and described the catalytic
activity of the heterogenized ferrocene group. The synthesized
materials were characterized by FT-IR spectroscopy, DS UV–vis,
CHN elemental analysis, BET, EDS, SEM, TEM, TGA and XPS. The
grafted complex (FCA) was employed in the oxidation of various
substrates (ethylbenzene, cyclohexene and benzyl alcohol) with
TBHP without additives under mild conditions. The results indicate
that Fe-nano-catalyst could activate TBHP to oxidize ethylbenzene
to acetophenone, cyclohexene to cyclohexene-1-one and benzyl
alcohol to benzaldehyde with high conversion and selectivity under
mild conditions.
2.2. Preparation of organometallic-SiO2/Al2O3 nanosized
SiO2/Al2O3 nanosized was used as the support prepared by the
sol–gel method [45]. At first, 3.5 g of nanosized SiO2/Al2O3 was acti-
vated at 500 ◦C 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 ◦C under vacuum for 5 h. Then fer-
rocenecarboxaldehyde (FCA) was added to a suspended solution
of SiO2/Al2O3 supported aminopropyl (SiO2/Al2O3 APTMS) in dry
methanol. The mixture was refluxed for 24 h to make a Fe nano-
catalyst on the surface of nanoscale SiO2/Al2O3 (Scheme 1).
2.3. General procedure for oxidation ethylbenzene, cyclohexene
and benzyl alcohol
2. Experimental
In this procedure the heterogeneous catalyst (5.0 mg), the sub-
strate (9.0 mmol) and an oxidant (9.0 mmol, 80% aqueous solution
TBHP) were added in three necked round bottom flask equipped
with a refluxed condenser. The mixture was stirred at desired tem-
perature. After filtering and washing the used catalyst with solvent,
the filtrate was monitored by GC analysis. The products were iden-
tified by GC–MS techniques. The conversion and selectivity were
calculated with GC area normalization. Finally, comparative exper-
iments were performed under different conditions.
2.1. Materials and instruments
All reagents were purchased from the Merck and Fluka chemi-
cal companies. Reagents were used without extra purification, but
solvents were purified with standard methods. Inductively coupled
plasma (ICP) measurement for Fe content evaluation was per-
formed using a Perkin-Elmer ICP/6500. Fourier transform infrared
was collected on KBr pellets using a JASCO FT/IR (680 plus) spec-
trometer and the position of an infrared band is given in reciprocal
centimeters (cm−1). Diffuse reflectance spectra were registered
on a JASCO-550 UV–vis spectrophotometer that was equipped
with a diffuse reflectance attachment in which BaSO4 was used
as the reference. Type and quantity of the resulting products from
oxidation were determined by a HP 6890/5973 GC/MS instru-
ment and analyzed by a Shimadzu GC-16A gas chromatograph
(GL-16A gas chromatograph with a 5 m × 3 mm OV-17 column,
60–220 ◦C (10 ◦C/min), Inj. 230 ◦C, Det. 240 ◦C). For elemental anal-
ysis a CHN-Rapid Heraeus elemental analyzer (Wellesley MA) was
used. Before carrying out the nitrogen (99.999%) adsorption exper-
iments, the sample was outgassed at 393 K for 14 h, then the
experiment have been carried out at 76 K using a volumetric appa-
ratus (Quantachrome NOVA automated gas sorption analyzer). The
specific surface areas were calculated, using the BET (Stephen
3. Results and discussion
3.1. Characterization
The heterogeneous Fe catalyst was synthesized on the nanoscale
SiO2/Al2O3 using ferrocenecarboxaldehyde through the covalently
immobilization, as illustrated in Scheme 1. The formation of Fe-
nano-catalyst onto the SiO2/Al2O3 mixed oxides was verified using
BET, CHN, FT-IR, UV–vis, BET, ICP, SEM, EDS, XPS, TGA and TEM.
The surface area, pore size and volume of the modified support
were significantly reduced compared to the parent SiO2/Al2O3 (this
decrease indicates the decrease in interaction between adsorbate,
N2 molecules, and the nano-sized SiO2/Al2O3 surface after mod-
ification with organic chains). The elemental analysis indicated
Scheme 1. Immobilization procedure of the immobilized Fe catalyst on the functionalized SiO2–Al2O3 mixed oxide.

92
D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
Table 1
Chemical composition and physicochemical properties of the immobilized ferrocene groups on the nanoscale SiO2/Al2O3 mixed oxides.
Catalyst
Elemental analyses
(wt%)b
Organic
functional
Immobilized the
ferrocenec
% coordinated
aliphatic
Structural parameterse
group (mmol/g
groups (mmol/g
groups to the
C
N
Fe
Surface area
(m2/g)
Pore volume
Pore
diameter (A)
mixed oxide)c
mixed oxide)d
ferrocened
(cm3/g)
˚
SiO2/Al2O3 nanosizeda
Si/Al APTMS
Si/Al APTMS ferrocene
–
3.75
3.03
–
–
7.68
–
2.67
2.16
–
–
1.37
–
–
498
378
264
0.045
0.031
0.023
36
25
19
8.13
12.35
63.42
a
Molar ratio of Si/Al was 60:40, determined from EDX analysis.
Nitrogen was estimated from the elemental analysis. Fe content determined from ICP analysis.
Determined from the N-contents.
Determined from the Fe-content, assume that Fe ions coordinated with aliphatic ligands.
The pore size calculated using the BJH method.
b
c
d
e
the fact that the CHN content increased with increase in organic
chain size, due to the immobilization of organometallic groups (fer-
rocenecarboxaldehyde) on the SiO2/Al2O3 matrix. The loading of Fe
in the heterogeneous FNC was characterized by elemental analyses.
The final metal content was 1.37 mmol g−1, indicated that 63.4% of
the aliphatic ligands were complexed with the ferrocene groups
(Table 1).
UV–vis spectrum of the SiO2/Al2O3 had the side-band adsorption
near 249 nm but, in the SiO2/Al2O3 APTMS ferrocene transitions
of ꢀ → ꢁ* and n → ꢁ* of the aromatic rings caused strong adsorp-
tion in the 260–360 nm .The color of the FNC changed from yellow
to red, a characteristic of immobilized Fe ion species, after the reac-
tion with Ferrocenecarboxaldehyde. Furthermore, UV–vis spectra
indicated the appearance of several new metal d–d migration bands
around ꢂ = 500–700 nm in FNC.
3.1.1. The FTIR spectra
In Fig. 1, the FT-IR spectra of SiO2/Al2O3 APTMS and
SiO2/Al2O3 APTMS ferrocene are shown. The strong absorption
3.1.3. SEM, TEM, and EDS
In Figs. 3 and 4 selected images showing scanning electron
microscope (SEM), TEM and also size distribution (Fig. 5) of
nanoscale SiO2/Al2O3 and SiO2/Al2O3 APTMS ferrocene are pre-
sented. The average particle size in reversed micro emulsion
solution was about 24 nm (Figs. 4 and 5). According to the small
nanoparticle size and ligand capping as an obstacle in agglomer-
ation, the Fe-nanocatalyst could be used as a suitable catalyst for
oxidation of different substrates such as ethylbenzene, cyclohex-
ene and benzyl alcohol. However, the presence of Fe ions in the
FNC resulted from the ferrocene groups that purposely coated to
increase the electrical conduction and hence to improve the quality
of SEM micrograph (Fig. 4).
bands related to Si
O Si stretching vibrations are observed in the
spectrum of SiO2/Al2O3 at 1010–1290 and 798 cm−1. The FT-IR
spectrum of SiO2/Al2O3 APTMS shows several signals originating
from amino propyl groups, which are related to C H stretch-
ing modes of the propyl, appeared in the area of 1450–1560 and
2935–2860 cm−1. It could be concluded from the above results
that the SiO2/Al2O3 was modified by amine spacer groups suc-
cessfully. The N H deformation peak at 1540–1560 cm−1 confirms
the successful functionalization of the Si/Al mixed oxide with 3-
APTMS. In Fig. 1A, the C N imine vibration signal was observed at
1637 cm−1, which shows the condensation reaction between fer-
rocene with organo-functionalised SiO2/Al2O3. The peaks at the
3025–3066 cm−1 ranges are attributed to the C H stretching vibra-
tions of ferrocene aromatic rings. The peaks at 1439–1435 cm−1 can
be assigned to C C stretching vibration of two organic ring systems
(cyclopentene groups).
3.1.4. XPS analysis
The XP spectroscopic analysis of the heterogeneous catalyst was
used to study the oxidation state of the active sites of immobi-
lized ferrocene molecules on the surface of nano-scale SiO2/Al2O
(Fig. 6). This technique has previously been shown to provide valu-
able information regarding the chemical state of the catalytically
active sites in different catalysts [49–52]. The XPS spectrum of FNC
produced a Fe 2p3/2 and a Fe 2p1/2 peak at 711.1 and 724.1 eV,
respectively, and are depicted in Fig. 6. However, there is a satellite
peak at 715.5 eV beside the main peak of Fe 2p3/2 and Fe 2p1/2 in
FNC. These results indicated that most of the Fe ions on the surface
3.1.2. The UV–vis spectra
By comparing the UV–vis spectrum of the SiO2/Al2O3 and
the SiO2/Al2O APTMS ferrocene (Fig. 2), was observed that the
100
B
604
1458
1438
2849
2927
80
3090
566
802
1637
3431
1389
60
40
20
A
460
%T
1447
1560
1465
1630
1089
2860
2935
798
3431
1073
457
0
4000
3000
2000
1000
400
Wavenumber [cm-1
]
Fig. 2. DR UV–vis spectra of: (A) SiO2/Al2O3; (B) SiO2/Al2O3 APTMS; and (C)
SiO2/Al2O3 APTMS ferrocene.
Fig. 1. FTIR spectra of: (A) SiO2/Al2O3 APTMS; and (B) SiO2/Al2O3
APTMS ferrocene.

D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
93
Fig. 3. SEM of SiO2/Al2O3 (left), SiO2/Al2O3 APTMS ferrocene (right).
state (In fact, oxidation of ferrocene gives a stable cation called
ferrocenium) [54].
3.1.5. Thermal stability
Thermal stability of the synthesize materials were studied with
TGA (thermo gravimetric analysis) in Ar atmospheres in the range
of 25–1200 ◦C with a ramping rate of 10 ◦C/min (Fig. 7). Thermal
analysis (TG) of nanoscale SiO2/Al2O3 showed two stages of weight
loss, Stage I (25–115 ◦C) corresponds to the desorption of physically
held water (2.6 wt.%), on the surface of nanoscale SiO2/Al2O3, and
Stage II (120–1200 ◦C) is due to the condensation of Al OH and
Si OH (13.4 wt.%), which present in the structure of support (for
example; 2Si OH → Si
O Si + H2O). However, NFC showed three
distinct steps: at 25–107, 110–625 and 625–1200 ◦C (Fig. 7). Stage
II (110–625 ◦C) is due to desorption of water molecules from the
pores of SiO2/Al2O3 and also decomposition of the immobilized
organic functional groups (–pr-NH2). The additional weight losses
in Stage III could be observed due to the several phenomena; the
Fig. 4. TEM image corresponding to SiO2/Al2O3 APTMS ferrocene sample.
of the heterogeneous catalyst were in +3 oxidation state (due to the
binding energy (BE) of 711.1 and 724.1 eV which are attributed to
Fe(III) state of iron) [53]. It is believed that during the immobiliza-
tion of ferrocene over the modified SiO2/Al2O3 under air condition
(in the presence of an atmospheric oxygen) iron oxidation state of
ferrocene (Fe(II)) was easily oxidized and began to prefer the Fe(III)
Fig. 5. Particle size distribution of the SiO2/Al2O3 APTMS ferrocene.
Fig. 6. XP spectroscopy of the SiO2/Al2O3 APTMS ferrocene.

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D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
Fig. 8. The influence of solvent on the ethylbenzene oxidation by the
SiO2/Al2O3 APTMS ferrocene catalyst. Conditions: ethylbenzene, 9 mmol; Cat.,
50 mg; TBHP, 9 mmol; 24 h; T, 50 ◦C.
acetophenone. It can be seen that acetophenone selectivity is high
with a dipolar aprotic solvent in the following order; acetonitrile
(74.0%) > dichloromethane (67.8%) > ethanol (29.0%) > water (0.0%).
Thus, dipole moment of the solvents probably is an essential fac-
tor in oxidation of EB. More investigations showed that the reaction
under the solventless condition in comparison with the presence of
solvent (like polar and nonpolar) had high selectivity and more cat-
alytic activity (Fig. 8). This shows that the EB and solvent molecules
are competitors for the active sites of metal center on the catalyst.
In order to evaluate the effect of substrate/oxidant molar ratio
on the catalytic activity and selectivity in solventless condition, the
reactions were experimented at different molar ratios of EB:TBHP
(1:1, 1:3 and 1:5) at 50 ◦C after 24 h (Fig. 9). It was indicated
that the different molar ratio of EB:TBHP has strong effects on
catalytic activity and selectivity. In most of the experiments ace-
tophenone was the major product, and the best condition was
1:3 molar ratio, due to the presence of excess TBHP coordi-
nated with active sites of the FNC (heterogeneous Fe catalyst)
(Fig. 9). In all EB oxidation system, as the reaction time increased,
the conversion and selectivity to acetophenone increased as
well.
Increasing the temperature for accelerating the reaction is
apparently effective. Therefore, the temperature effect (50 ◦C, 80 ◦C
and 100 ◦C) was also monitored on the oxidation of EB at the
EB:TBHP molar ratio of 1:1 after 24 h in the presence of FNC (Fig. 10).
Generally, by increasing reaction temperature and time, the con-
version grows higher (87%) and also the selectivity to acetophenone
increased (99%) while selectivity to benzaldehyde and benzoic acid
decreased. Thus, raising temperature is effective for the oxida-
tion reaction since the energy was not sufficient for the activation
of oxygen molecules or the catalytic circulation at low tempera-
ture.
Fig. 7. TG curve profiles of SiO2/Al2O3 and SiO2/Al2O3 APTMS ferrocene.
calcination of coke, the loss of the new generated Al OH and Si OH
groups and decomposition of the immobilized ferrocene group.
From thermogram analysis of samples, it could be concluded
that thermal stability of nanoscale SiO2/Al2O3 in NFC improved
rather than unmodified SiO2/Al2O3 and the weight losses of the
modified SiO2/Al2O3 with ferrocene group in the temperature
range of dehydration are less than that for unmodified SiO2/Al2O3.
3.2. Oxidation of ethylbenzene
To optimize the effectiveness of oxidation condition of ethyl-
benzene (EB) by TBHP in the presence of nano-Fe-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 Fe catalyst were investigated. In this reaction
major products are acetophenone (1), Benzaldehyde (2) and ben-
zoic acid (3) (Scheme 2). The GC analysis did not show any oxidation
products of the aromatic ring in effluents.
In order to study the effect of solvent on the oxidation of EB dif-
ferent solvents such as acetonitrile, ethanol, water, benzene and
dichloromethane at 50 ◦C were experimented (Fig. 8). The reac-
tion at the presence of coordinating solvents such as ethanol had
low conversion, while using water as a solvent made no reac-
tion. It seems that the donor electrons of these solvents had more
ability to occupy the vacant space around the existed metal in
catalyst, so this phenomena could prevents coordinating of Fe
active center by oxidant molecules [55]. The major product in
oxidation of EB in all solvents was acetophenone. The percent-
age of EB conversion obtained at different solvents decreased as
following; 35.5% (dichloromethane) > 27.0% (acetonitrile) > 18.0%
(ethanol) > 0.0% (water). In fact, the use of polar and protic solvents
favors selectivity to the production of benzaldehyde and benzoic
acid, while the aprotic and chlorinated solvents lead selectivity to
To estimate the reusability of FNC, after the first run, the cata-
lyst was filtrated and washed with ether and dried at 80 ◦C under
vacuum and then used for the next run under the same condi-
tions (Fig. 11). No apparent loss of activity and selectivity was
observed after 9th run, confirming that FNC has high stability
during the catalytic process. To further proof that the oxidation
reaction was catalyzed by the heterogeneous Fe-catalyst, we added
extra ethylbenzene to the filtrate after the removal of FNC and
found that no more products were produced under the same con-
ditions.
To explore the effect of active sites of FNC (Fe centers), oxida-
tion of ethylbenzene was performed by unmodified SiO2/Al2O3 as
the catalyst in the presence of TBHP. Consequently, a surprisingly
zero level of catalysis was observed under the detection limit of
Scheme 2. Reaction products of the catalytic oxidation of ethylbenzene with
SiO2/Al2O3 APTMS ferrocene.

D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
95
Fig. 10. The influence of reaction temperature on the ethylbenzene oxidation and
selectivity to acetophenone by the SiO2/Al2O3 APTMS ferrocene catalyst. Condi-
tions: ethylbenzene, 9 mmol; Cat., 50 mg; TBHP, 9 mmol; solventless.
be occurred through competing pathways (steps 4 and 5). In
the next steps (1-tert-butoxyethyl)benzene could be converted to
acetophenone via elimination of tert-butanol/water or turnover to
benzaldehyde with loosing methanol [26]. In step 8, the (1-tert-
butoxyethyl)benzene is reduced by Fe(II) ions and, that is, Fe(III)
active site will be generated again [59–61], and resulting of this
step is formation of products.
Fig. 9. The influence of different oxidant ratio on the ethylbenzene oxidation by
the SiO2/Al2O3 APTMS ferrocene catalyst. Conditions: ethylbenzene, 9 mmol; Cat.,
50 mg; T, 50 ◦C; solventless.
GC. However, the catalytic activity of TBHP toward the oxidation
of ethylbenzene in the absence of FNC was investigated and again
non product was detected in effluent.
Concerning the catalytic mechanism of FNC, Scheme 3 shows
a reasonable proposed mechanism based on the precedent litera-
ture for similar Fe(III) catalyst in hydrocarbon oxidation by TBHP
[56–58,28]. In first step, Fe(III) active site of the catalyst could coor-
dinate with distant oxygen of TBHP, and tert-butylperoxyl radical
(t-BuOO•) will be generated that could abstract a hydrogen atom
from ethylbenzene and the aryl radical is formed (steps 2 and 3).
This observation demonstrates that Fe(III) center is not engaged
with the solvent or any other substrate and is free to coordinate
with the distant oxygen of oxidant. In the next step, the activated
distant oxygen of co-coordinated TBHP reacted with ethylben-
zene to yield the products. After that the oxidation reaction might
Fig. 11. Reusability of the SiO2/Al2O3 APTMS ferrocene on through oxidation of
ethylbenzen. Conditions: ethylbenzene, 9 mmol; Cat., 50 mg; TBHP, 9 mmol; T, 50 ◦C;
solventless.

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D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
Scheme 3. Possible pathway for the oxidation of ethylbenzene to acetophenone by SiO2/Al2O3 APTMS ferrocene in the presence of tert-butyl hydroperoxide.
3.3. Oxidation of cyclohexene
which reaction needs a lower activation energy in comparison with
the reaction at double bond [63].
To examine the catalytic activity of synthesized catalyst (FNC),
oxidation of cyclohexene was carried out under solventless condi-
tions at 120 ◦C by applying TBHP as oxidant reagent (Scheme 4).
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. The formation of 1-
(tert-butylperoxy)-2-cyclohexene indicates the presence of radical
reactions (data not published) [43,62]. Fig. 12 shows that at same
temperature 120 ◦C, but with different molar ratios of CH:TBHP (1:1
and 1:3) cyclohexene conversion and the selectivity of the prod-
ucts have been changed. Changing the molar ratios of CH:TBHP to
(1:3) within 24 h increased the cyclohexene conversion and selec-
tivity to 2-cyclohexene-1-one from 27.7 to 39 and 96.0 to 99.0%,
respectively (Fig. 12). Thus, it is obvious to draw the conclusion that
under the mentioned reaction conditions, the C C double bond is
less reactive than allylic hydrogen. As we know, allylic radical is
the product of the hydrogen abstraction from the allylic carbon, in
In order to examine the reusability of the immobilized Fe-
catalyst onto the SiO2/Al2O3, several successive experiments were
carried out by application of the used catalyst (Fig. 13). The results
shown that there is no significant loss of activity and selectiv-
ity even after 8th run. Therefore, the results clearly proved that
under solventless condition FNC catalyze conversion of cyclohex-
ene (87.0%) with ca. 99.0% selectivity to 2-cyclohexene-1-one.
In fact metal ions which catalyze oxygen transfer reactions with
TBHP can be separated into two kinds based on the active inter-
mediate: peroxometal or an oxometal complex [64]. Proxometal
routes usually possess early transition elements with d0 configu-
ration, such as Mo(VI), W(VI), V(V) and Ti(IV). However, oxometal
routes possess late or first row transition elements, such as, Cr(VI),
V(V), Mn(V), Ru(VI), Ru(VIII) and Os(VIII). Some dependent ele-
ments on the substrate can involve oxometal or peroxometal routs.
Olefin epoxidation and heteroatom oxidations are the reactions
that especially involve peroxometal routes. On the other hand,
oxometal species display a broader range of activities including
allylic oxidations. Also, peroxometal routes do not possess any
changes in oxidations state of the metal. However, an oxometal
route involves redox reactions of the metal ions after the coor-
dination reaction between reactive oxygen of TBHP with iron,
consequently, oxidant activated and conversion of cyclohexene to
hydroperoxy-cyclohexene is carried out. Based on the above dis-
cussions, a plausible mechanism was proposed for the catalytic
oxidation of cyclohexene in the presence of FNC and TBHP as shown
Scheme 4. Possible products that can be obtained from the oxidation of cyclohex-
ene.

D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
97
Scheme 5. Proposed mechanism for the oxidation of cyclohexene catalyzed by SiO2/Al2O3 APTMS ferrocene in the presence of tert-butyl hydroperoxide.
in Scheme 5. At first the FNC needs to be converted to an active
form through the interaction with TBHP. Cyclohexene hydroper-
oxide were produced via the reaction of the FeIII-OO-tert-Butyl
intermediate with cyclohexene. Cyclohexene hydroperoxide has
four potential routes in the catalytic oxidation reaction: (1) elimi-
nation of water and generation of ketone; (2) redoxe conversion
of cyclohexene hydroperoxide into ketone and alcohol; In this
step, Fe(III) is reduced to Fe(II) via electron transfer procees; (3)
turnovering of cyclohexene to cylohexenepoxide by cyclohexene
hydroperoxide as the oxygen source, and (4) conversion of cyclo-
hexene hydroperoxide to alcohol, through transformation of Fe(II)
to Fe(III) [56,58,65].
Obviously, to demonstrate the efficiency and effectiveness of
catalytic system the obtained results should be compared with
other catalytic systems in order to evaluate the benefits and
disadvantages of the proposed system. The data are shown in
Table 2 show that the catalytic system presented in this paper
has the advantages in terms of simple process for the synthesis of
Table 2
Comparison of figure of merit of the present work with other studies in the literature for oxidation of ethylbenze and Cyclohexen.
Substrate
Catalysta (amount)
T
◦C/solvent
Oxidant
Reaction
time (h)
Product
Selectivity
(%)
[Refs.]
[Fe(tpa) (MeCN)2](ClO4)2 (5 ␮mol)
Au/SBA-15, B (15 mg)
Mn-SBA-15 (0.2 g)
TPFPPFeCl (2 mmol)
CNCr-2 (0.1 g)
Fe/MgO, NHPI (6 wt%, 20 mol%)
Fe (salen)-POM
This work
75 ◦C/2-butanone
70 ◦C/CH3CN
80 ◦C/–
O2
24 h
36 h
8 h
24 h
8 h
20 h
5 h
24 h
Acetophenon
Acetophenon
Acetophenon
Acetophenon
Acetophenon
Acetophenon
Acetophenon
Acetophenon
54
93
53.4
82.8
69
52
100
89
[66]
[67]
[68]
[69]
[73]
[69]
[70]
Ethylbenzene
TBHP
TBHP
O2
TBHP
O2
100 ◦C/–
70 ◦C/CH3CN
25 ◦C/–
80 ◦C/CH3CN
50 ◦C/–
H2O2
TBHP
[Fe (tpa) (MeCN)2] (ClO4)2 (5 ␮mol)
FePcS-SiO2 (0.5 mol%)Fe(III) (5,10,15,20-tetrakis)
(pentafluorophenyl) (prophirin) Cl (56 ␮g)
LFeIIICl (0.1 mol%)
25 ◦C/acetone
40 ◦C/CH3CN
50 ◦C/–
O2
TBHP
O2
H2O2
H2O2
24 h
3 h
2 h
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
2-Cyclohexen-1-one
64
43
64
30
44.7
60
64
66.34
74.62
96
[66]
[70]
[71]
[72]
[73]
[74]
[75]
[76]
[76]
Cyclohexene
80 ◦C/CH3CN
80 ◦C/CH3CN
80 ◦C/CH3CN
r.t-/H2O
4 h
LFeIIISiO 2(0.1 mol%)
24 h
12 h
8 h
5 h
5 h
MnTPPCl-Co(OAc)2 (6 × 10−5
)
O2
polymer anchored Cu(II) (0.03 g)
ZrP·Fe(Salen) (0.066 g) 80 ◦C/Benzene
ZrP·Fe(Salen) (0.066 g) 80 ◦C/Benzene
This work
TBHP
TBH P (70%)
TBHP (dry)
TBHP
80 ◦C/Benzen
80 ◦C/Benzen
‘120 ◦C/–
24 h
a
TPFPPFeCl:Fe (5,10,15,20-tetrakis (pentafluorophenyl)) porphyrin, CNCr-2:Nickel substituted copper chromite spinels, NHPI: N-Hydroxyphthalimide, POM: a kegging
type polyoxometalate (K8SiW11O39), FePcS-SiO2: Fe tetrasulfocyanine was immobilized on SiO2, L: (LFeIII·SiO2) [L = 3-{2-[2-(3-hydroxy-1,3-diphenylallylideneamino)-
ethylamino]-ethylimino}-1,3-diphenyl-propen-1-ol], ZrP·Fe(Salen): Iron(III)-Salen intercalated -zirconium phosphate.

98
D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
O
OH
Fe Nano Catalyst
H
t-Butyl hydroperoxide
Solventless
Scheme 6. oxidation of benzyl alcohol to benzyl aldehyde catalyzed by
SiO2/Al2O3 APTMS ferrocene in the presence of tert-butyl hydroproxid.
Table 3
Oxidation of benzyl alcohol with heterogeneous Fe nano-catalyst.
Catalyst
T
◦C
Conversion (mol%)
Selectivity
(mol%)
(benzaldehyde)
FNC
FNC
FNC
FNC
25
40
60
80
100
100
100
100
100
100
100
4.6
13.3
38.8
64.2
84.4
98.5
100
84.4
84.6
84.2
84.5
100
100
100
100
100
100
100
100
100
100
100
FNC
FNCa
FNCb
FNCc
FNCd
FNCe
FNCf
Reaction conditions: 1 mmol benzyl alcohol; 1 mmol TBHP; 0.03 g catalyst; 8 h; with-
out solvent.
a
Benzyl alcohol: TBHP (1:2).
Benzyl alcohol: TBHP (1:2) after 24 h.
Second run.
Third run.
Fourth run.
Fifth run.
b
c
d
e
f
Fig. 12. The influence of different oxidant ratio on the cyclohexene oxidation by
the SiO2/Al2O3 APTMS ferrocene catalyst. Conditions: cyclohexene, 9 mmol; Cat.,
50 mg; T, 120 ◦C; solventless.
3.4. Oxidation of benzyl alcohol
The liquid-phase oxidation of benzyl alcohol was performed by
TBHP at 25, 40, 60, 80 and 100 ◦C over immobilized FNC under
different conditions without the use of any solvent (Scheme 6).
Table 3 confirms the highness of catalytic activity and excellent
selectivity to benzaldehyde (100%) in all experimental condi-
tion. GC analysis showed that benzaldehyde was the sole product
(confirmed by performing three replicate experiments). With
increasing the temperature from 25 to 100 ◦C, the benzyl alcohol
conversion increased. However, by reusing the catalyst, the per-
centage of benzyl alcohol conversion and benzaldehyde selectivity
(and therefore, benzaldehyde yield) was constant after fifth times.
The nature of the recovered catalyst after reusing three times had
been followed by FTIR spectrum, and no significant changes could
be seen. Therefore, the heterogeneous nano-iron catalyst with high
catalytic activity and stability for the selective oxidation of benzyl
alcohol was developed by covalently anchored on the SiO2/Al2O3
nanoparticles.
nano-catalyst, heterogeneous nature of catalyst (easy separation
from the reaction mixture by simple filtration), use of the commer-
cially available molecule FCA as the one of the important starting
materials for the synthesis of Fe nano-catalyst, chemical and ther-
mal stability of catalyst, mild condition reaction in the absence of
additives and solvent, high conversion and selectively and widely
used in catalytic oxidation reactions (ethylbenzene, cyclohexene
and benzyl alcohol as substrates), therefore this protocol is very
suitable for practical organic synthesis.
4. Conclusion
In this study, a novel and simple catalysis system of SiO2/Al2O3
nanosized-anchored ferrocenecarboxaldehyde in the oxidation of
ethylbenzene, cyclohexene, and benzyl alcohol with TBHP have
been used. This catalytic system has some advantages included sup-
plying form cheap raw material, commercially available reagents
and is reusable for oxidation of ethylbenzen, cyclohexene and ben-
zylalcohol. Oxidation of alkyl aromatic, allylic site and double bond
were resulted with the oxidant of TBHP without the use of any sol-
vent. Under optimum reaction conditions such as substrate/TBHP
(1:1), absence of solvent, temperatures of 50–120 ◦C and reaction
time of 24 h, Fe-nano-catalyst showed higher ethylbenzene, cyclo-
hexene, and benzyl alcohol conversion (>84%) and more than 90%
Fig. 13. Reusability of the SiO2/Al2O3 APTMS ferrocene on the oxidation of cyclo-
hexene and selectivity to 2-cyclohexene-1-one. Conditions: cyclohexene, 9 mmol;
Cat., 50 mg; TBHP, 9 mmol; 24 h;T, 120 ◦C; solventless.

D. Habibi et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 90–99
99
selectivity to acetophenone, 2-cyclohexene-1-one and banzalde-
hyde, respectively. The cycle usage test indicated that the catalyst
prepared by this method was relatively stable after several run.
Finally, the felicitous combination of optimal conditions, catalyst
design, a highly available catalytic activity and selectivity toward
major products should lead to widespread applicability of catalysts
such heterogeneous ferrocene.
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