Selective oxidation of aromatic hydrocarbons by potassium and phosphorous-modified iron oxide-silica nanocomposite

Article abstract of DOI:10.1007/s11243-011-9554-3

Supported iron catalysts are active for hydrocarbon oxidation with H ₂O₂, but the hydrogen peroxide dismutation is a shortcoming that may constrain their applications. Herein, we attempted to address this problem using potassium and phosphate-doped iron oxide-silica nanocomposite (KPFeSi) synthesized via sol-gel methods. The promoted silica-iron oxide nanocomposite has been characterized by elemental analyses, FTIR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface-size determination. The synthesized KPFeSi was an active catalyst in the low-temperature liquid phase oxidation of various alkyl aromatics with hydrogen peroxide in conversions of 31-78%. Furthermore, the direct oxidation of benzene into phenol using hydrogen peroxide has been achieved in the absence of any acid with this KPFeSi compound. Springer Science+Business Media B.V. 2011.

Full text of DOI:10.1007/s11243-011-9554-3

Transition Met Chem (2012) 37:37–43
DOI 10.1007/s11243-011-9554-3
Selective oxidation of aromatic hydrocarbons by potassium
and phosphorous-modified iron oxide–silica nanocomposite
Shahla Masoudian Hassan Hosseini Monfared
•
Received: 9 October 2011 / Accepted: 17 October 2011 / Published online: 2 November 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Supported iron catalysts are active for hydro-
carbon oxidation with H O , but the hydrogen peroxide
the production of phenol. Benzaldehyde is used as an aroma
compound and as a starting material in a variety of aromatic
and flavoring product syntheses. Phenol is one of the most
important intermediates in the chemical industry that is
utilized in the fabrication of polycarbonates and epoxy
resins with more than 90% produced via the cumene process
[3]. This process displays several drawbacks, the main
being the overall yield of phenol that barely reaches 5%
relative to benzene. It also involves a potentially hazardous
cumyl hydroperoxide intermediate and furthermore gener-
ates acetone as a by-product. Because of this, the search for
a one-step process for the direct conversion of benzene into
phenol constitutes an area of permanent interest. Efforts
toward this end have usually been defeated by the fact that
oxidation of benzene is usually affected by a poor selec-
tivity; since phenol is more reactive toward oxidation than
the initial benzene, over-oxidation products are usually
formed, decreasing the selectivity.
2
2
dismutation is a shortcoming that may constrain their
applications. Herein, we attempted to address this problem
using potassium and phosphate-doped iron oxide–silica
nanocomposite (KPFeSi) synthesized via sol–gel methods.
The promoted silica–iron oxide nanocomposite has been
characterized by elemental analyses, FTIR, X-ray powder
diffraction (XRD), scanning electron microscopy (SEM)
and Brunauer-Emmett-Teller (BET) surface-size determi-
nation. The synthesized KPFeSi was an active catalyst in
the low-temperature liquid phase oxidation of various alkyl
aromatics with hydrogen peroxide in conversions of
3
1–78%. Furthermore, the direct oxidation of benzene into
phenol using hydrogen peroxide has been achieved in the
absence of any acid with this KPFeSi compound.
Introduction
Active catalysts for the selective side chain oxidation of
alkyl aromatic compounds have been used in the liquid
phase, gas phase [4] and supercritical media [5, 6]. The
selective liquid phase oxidation can be conducted both
homogeneously and heterogeneously involving mostly
metals with two or more stable oxidation states, typically
under acidic conditions. Most catalytic systems are based
on Co [7], Pt [6] and Cu [8]. Nevertheless, these catalytic
oxidation reactions still require harsh conditions in industry
[9]. Due to the relative inertness of the corresponding C–H
bonds, the reactions are often performed at high pressure.
Therefore, finding catalytic systems for these oxidation
reactions is of significant industrial importance. Catalytic
properties and, more generally, physicochemical properties
of both noble metal and oxide catalysts can be improved by
the introduction of additives [10]. The heterogeneous sys-
tems containing additions of different elements (promoters)
The selective side chain oxidation of alkyl aromatics is
one of the most important processes in the production of
industrial intermediates such as benzoic acid, acetophe-
none, benzophenone, toluic acid [1]. The oxyfunctionalized
aromatics are then further reacted to higher value products.
Products manufactured on a smaller scale include the
higher-priced aldehydes such as benzaldehyde and tereph-
thalaldehyde [2]. Benzoic acid finds use as an intermediate
in the dye and perfume industries and as a raw material for
S. Masoudian Á H. H. Monfared (&)
Department of Chemistry, University of Zanjan,
4
5195-313 Zanjan, Islamic Republic of Iran
e-mail: monfared@znu.ac.ir; monfared_2@yahoo.com
URL: http://www.znu.ac.ir/members/hosseini_hassan
123

3
8
Transition Met Chem (2012) 37:37–43
to silver- and vanadium-containing multimetal oxides are
extensively used as catalysts for the oxidation of aromatic
hydrocarbons [11].
Supported iron catalysts are active for hydrocarbon
oxidation with H O , but the hydrogen peroxide dismuta-
2
2
tion is a shortcoming that may constrain their applications.
Herein, we attempted to address this problem using
potassium and phosphate-doped iron oxide–silica nano-
composite (KPFeSi) synthesized via sol–gel synthesis. This
paper presents a study concerning the preparation of
potassium and phosphorus promoted Fe O –SiO catalyst.
2
3
2
The promoted and unpromoted Fe O –SiO systems
2
2
3
including Fe O –SiO (FeSi), K O–Fe O –SiO (KFeSi),
2
3
2
2
2
3
2
PO –Fe O –SiO (PFeSi) and K O–PO –Fe O –SiO
2
4
2
3
2
2
4
2
3
Fig. 1 SEM image of KPFeSi
(
KPFeSi) were prepared by sol–gel method. Various
techniques, such as FTIR, XRD and BET, were used to
study the structural properties of the catalyst. Finally,
reactivity of the catalysts was compared in aromatic
hydrocarbon oxidation.
promoter addition it dropped slightly and no correlation
of activity (see the next section) and surface area was
observed. In fact, FeSi and PFeSi with a larger surface area
2
533 and 511 m /g, respectively) were less active than
(
2
KPFeSi, which has a smaller surface area of 181 m /g. High
reduction in the pore volume (Vpore) was observed for PFeSi
and KPFeSi in comparison with FeSi, which was attributed
to the occupation of some internal and external surfaces by
the promoters (potassium and phosphorous). However, not
much change was observed in the average pore volume
(dpore) of KPFeSi as the promoters also created secondary
pores.
Results and discussion
Characterization of the catalyst
A nano-sized composite KPFeSi was prepared via sol–gel
methods. The homogeneous samples obtained under acidic
conditions did not show any apparent gelation. In this case,
the supercritical evaporation of the solvent is a fundamental
process for obtaining a transparent gel. It was subsequently
dried in an autoclave. Finally, the sample was calcined at
The catalyst KPFeSi has a black–brown color. The XRD
patterns of KPFeSi and the FeSi composite obtained under
calcination at 500 °C are shown in Fig. 2, and they show
the similar diffraction patterns. It can be seen that XRD
pattern of KPFeSi particles exhibits diffraction peaks at
2h = 20°–30°, corresponding to the characteristic peaks
of the silica, which is a typical amorphous structure. The
broadening near the peak baseline suggests the presence of
very small crystallites (a few nanometers) [12]. The XRD
diagrams of the FeSi and KPFeSi composites show the
5
00 °C for 10 min in an air flow. The iron, potassium and
phosphorous contents of the sample KPFeSi were 9.6, 5.4
and 5.61 wt%, respectively (Table 1). The SEM morphol-
ogy of the compound KPFeSi with particle size about
5
0–100 nm is shown in Fig. 1. While most of the compound
KPFeSi crystal particles are in spherical form, the BET
2
surface area was measured to be 181 m /g with mean pore
3
diameter 13.68 nm and total pore volume 0.62 cm /g.
presence of traces of haematite (a-Fe O ) in diffraction
2 3
These findings suggest the low porosity of KPFeSi. As
summarized in Table 1, surface analysis showed that FeSi
2
had a BET surface area (SBET) of 533 m /g and upon
patterns of the sample. XRD analysis also indicates that
they contain some amorphous structure, a feature that is
a reasonable indication that Fe O is well dispersed in the
2 3
silica matrix [13]. At temperatures about 400–500 °C, the
formed iron oxide phase is haematite. The peaks around
2h = 12.3°, 15.4°, 22.7°, 24.3°, 27.5°, 31.8°, 45.6°, 56.6°
and 75.4° were ascribed to iron oxide. The new phase of
Table 1 Characteristics of the catalysts
a
No. Sample
S
BET
V
(cc/g) (nm)
pore
d
pore
Additive (%)
2
m /g)
b
(
Fe (%) K (%) P (%)
K O can be observed at 2h = 25.8°, 29.5°, 30.7° and 39.3°,
2
1
2
3
a
FeSi
533
511
1.22
0.35
0.62
9.18 9.6
2.75
13.68 9.6
which are similar to reported ZrO /K system [14].
2
PFeSi
The FTIR spectra of FeSi and KPFeSi are shown in
Fig. 3. The IR spectrum of the dried silica (silica heated
at 500 °C) displays in the low-frequency bands at 1,200–
KPFeSi 181
5.4
5.6
Weight percent-based sample composition
-
1
b
1,000, 810 and 470 cm due to asymmetric stretching,
Measurements were taken for aerogels after being treated in air for
0 min at 500 °C
1
symmetric stretching and bending modes of Si–O–Si,
1
23

Transition Met Chem (2012) 37:37–43
39
a
b
c
d
Fig. 2 XRD pattern of a FeSi and b KPFeSi after heat treatment at
5
00 °C for 10 min
-
respectively [15]. The small sharp band at 982 cm is due
1
1600
1200
800
400
-1
to Si–OH stretching of surface silanol groups [16, 17]. The
-
high-frequency region shows a sharp band at 3,750 cm
Wavenumber / cm
1
Fig. 3 FTIR spectra of a silica gel, b FeSi, c PFeSi and d KPFeSi as
KBr pellet. The absorption bands at *800 and *1,100 cm are
characteristics of Si–O–Si bonding
due to the stretching vibrations of the isolated (noninter-
acting) surface silanols [18], preceded by a tail in the range
-1
-
,700–3,500 cm (not shown) due to hydrogen-bonded
1
3
silanols and adsorbed water molecules. That the hydrogen-
bonded groups resulted in no defined maxima has been
interpreted in terms of H bonds of different strengths [18].
The bending vibration band of O–Si–O bond [19] is found
intense band of SiO2 and their recognition becomes
uncertain.
Catalytic activity studies
-
1
around 470 cm in KPFeSi. Results suggest that the iron
did not form chemical bonds with silicon in the silica net-
The results of preliminary experiments showed that
hydrogen peroxide in the absence of catalyst does not
oxidize ethylbenzene (Table 2, run 1) and that with 30%
aqueous H O , the silica gel plays no catalytic role
-
1
work. The characteristics of Si–O–Fe (680 and 900 cm
20] were not observed. Therefore, iron oxide and silica in
the iron oxide–silica nanocomposite were segregated. The
)
[
2
2
3
-
internal vibrational modes of a free PO4 tetrahedron with
(Table 2, run 2). Homogeneous iron(III) ions and silica–
iron oxide nanocomposite decompose H O very fast to
T symmetry are decomposed as A ? E ? 2T . The mode
d
1
2
2 2
with the A symmetry type is the symmetric stretching
1
form oxygen, so that no oxidation product is observed
(Table 2, runs 3 and 4). We have found that the presence of
additives like potassium and phosphorous in iron oxide–
silica gel nanocomposite retards the nonproductive H O
2 2
mode (m ) of the P–O bonds. The modes with the E and T
1
2
symmetry types are bending O–P–O modes (m and m ,
2
4
respectively). The second mode with the T symmetry is the
2
3
-
asymmetric stretching mode (m ). For a free PO
tetra-
-1
decomposition and enhances its activation. High conver-
sion of ethylbenzene was obtained by the addition of
potassium and phosphorous promoters with 1:1 ratio rela-
tive to iron (Table 2, runs 5–10). Interestingly, the best
result, conversion of 47% after 3 h, was achieved when
3
4
-
1
-1
hedron, m = 938 cm , m = 420 cm , m = 1,017 cm
and m = 567 cm [21]. The intense bands of SiO mask
1
2
3
-
1
4
2
3
-
bands of PO
expected to appear at about 938, 1017,
3-
4
-
67 cm or PO4 bands being broad and adjacent to the
1
5
123

4
0
Transition Met Chem (2012) 37:37–43
Table 2 Catalytic oxidation of ethylbenzene with hydrogen peroxide
oxygen transfer. These results prove that catalytic activity
3
?
a
Conv. (%) Selectivity (%)
of KPFeSi is due to Fe and the presence of phosphate
and potassium promoters improves the catalytic activity of
KPFeSi to a great extent. The absence of hydroxyl radical
involvement in ethylbenzene oxidation by KPFeSi/H O
Run Catalyst
1
2
3
4
5
6
7
8
9
1
1
1
None
0
0
0
0
Silica gel
2
2
b
3
FeCl
FeSi
proved that when the reaction was performed in the pres-
ence of 10 equivalents of hydroquinone (a radical scav-
enger), the same conversion was obtained (Table 2, run
12).
PFeSi (P/Fe ratio, 0.5/1)
PFeSi (P/Fe ratio, 1/1)
PFeSi (P/Fe ratio, 2/1)
KFeSi (K/Fe ratio, 0.5/1)
KFeSi (K/Fe ratio, 1/1)
KFeSi (K/Fe ratio, 2/1)
18
27
22
9
[99
[99
[99
[99
[99
[99
[99
[99
The active centers for catalytic oxygen transfer are
formed by isolated iron species. Similarly, in oxidation of
aromatic hydrocarbons with hydrogen peroxide over Zn,
Cu, Al-layered double hydroxides, it has been proved that
catalytically active centers are formed by isolated copper
species [22]. The clustered copper ions are inactive in
oxidation reactions but accelerate the decomposition of
hydrogen peroxide. Although the exact mechanism of
the reaction is not clear at this stage, however, in analogy
to the reported studies [23], in the presence of H O , an
22
7
0
1
2
KPFeSi (K/P/Fe ratios, 1/1/1) 47
c
KPFeSi (K/P/Fe ratios, 1/1/1) 47
Reaction conditions: catalyst, 10 mg; ethylbenzene, mmol; CH
3
CN,
, 2 mmol; reaction temperature, 60 °C; reaction time, 3 h
Conversions are as percentage of initial ethylbenzene consumed
2
2 2
mL; H O
a
b
c
2
2
FeCl
3
, 0.062 mmol
adduct seems to be formed which may be an SiO –Fe(III)–
2
In the presence of 10 eq. hydroquinone
1
g -hydroperoxide species stabilized by hydrogen bonding
between the hydroperoxide ion and the oxygen atom of the
Table 3 Effect of various solvents on the oxidation of ethylbenzene
with hydrogen peroxide using KPFeSi as catalyst
phosphate. Thus, potassium and phosphate-doped Fe O –
2
3
SiO (KPFeSi) shows high activity for the oxidation of
2
Run Solvent
Conversion
a
Ethylbenzene selectivity
(%)
alkyl aromatics and benzene with hydrogen peroxide
without nonproductive decomposing H O . The involve-
(
%)
2
2
1
2
3
Acetonitrile
Methanol
78
51
100
100
100
ment of acid sites in the selective oxidation of aromatics is
?
seen in the fact that the incorporation of K gave raise to a
Dichloromethane 11
remarkable improvement in the carbonyl yield in the cat-
alyst studied. It is clear that neutralization of the acid sites
causes a depletion of the total oxidation of intermediates,
thereby favoring the oxidation products. Moreover, the
Reaction conditions: catalyst, 10 mg; ethylbenzene, 1 mmol, reaction
temperature, 60 °C; reaction time, 5 h
a
As percentage of initial ethylbenzene consumed
?
addition of K to neutralize the acid sites still exposed at
the surface of the catalyst resulted in a remarkable increase
in the yield of carbonyl compound.
Table 4 Hydrogen peroxide concentration effect on the oxidation of
ethylbenzene using KPFeSi as the catalyst
To evaluate the effect of solvent, we studied the oxi-
dation of ethylbenzene with H O in a molar ratio 1:2 in
Run mmol C
mmol H
8
H
10
/
% Ethylbenzene
a
conversion
% Selectivity to
acetophenone
2
2
2
O
2
the presence of KPFeSi as catalyst using different solvents
as reaction media under the described reaction conditions
1
2
3
4
1:2
1:4
1:6
1:8
78
83
90
94
[99
[99
[99
[99
(Table 3). Among various solvents such as acetonitrile,
methanol and dichloromethane, acetonitrile was found to
be most promising from conversion of ethylbenzene for
acetophenone point of view. The selectivity of 100% for
acetophenone was observed for these solvents as well. The
highest conversion in acetonitrile possibly is caused by its
Reaction conditions: catalyst, 10 mg; CH
0 °C; reaction time, 5 h
As percentage of initial ethylbenzene consumed. Values determined
1
by GC and H NMR spectroscopy
3
CN, 2 mL; temperature,
6
a
dielectric constant (e/e = 35.94) and dipole moment
0
(
l = 3.90 D), which are the highest of all solvents used.
Table 4 shows the hydrogen peroxide/ethylbenzene
both potassium and phosphorous promoters were added
to iron oxide–silica gel nanocomposite (catalyst KPFeSi,
Table 2, run 11). Further studies on oxidation of benzene
and alkyl aromatics with aqueous hydrogen peroxide were
carried out using this catalyst. Hydrogen peroxide dismu-
tation by KPFeSi is very slow, and it activates H O for
molar ratio effect screening, which indicates that ethyl-
benzene conversion increases with the molar ratio
increasing without changing the selectivity to acetophe-
none. It is interesting to note that blank experiments carried
out in the absence of ethylbenzene showed that the KPFeSi
2
2
1
23

Transition Met Chem (2012) 37:37–43
41
Table 5 Oxidation of various aromatic compounds with H
2
O
2
using KPFeSi as catalyst
Conversion (%)
a
a
b
Run
1
Substrate
Product
Selectivity (%)
TON
78
54
50
31
[99
44
31
29
18
O
2
3
4
[99
[99
[99
CHO
CHO
OH
OH
CHO
OH
CHO
OH
5
6
40
66
[99
[99
23
38
COOH
OH
Reaction conditions: catalyst KPFeSi, 10 mg; substrate, 1.0 mmol; acetonitrile, 2 mL; H
0 °C
2 2
O , 2 mmol; reaction time, 5 h; reaction temperature,
6
a
1
Substrate conversion and product identity were determined by GC and H NMR spectroscopy. Conversions are as percentage of initial
substrate consumed
b
TON: turnover number = number of moles of converted substrate per moles of Fe in the catalyst sample
nanocomposite also induced the slow decomposition of
hydrogen peroxide; therefore, ethylbenzene conversions
based on the oxidant could not be determined.
unsusceptible to oxidation by the KPFeSi/H O system.
2 2
The KPFeSi catalyst oxidized benzene into phenol using
hydrogen peroxide in the absence of any acid with 100%
selectivity and 66% conversion (Table 5, run 6). In this
respect, the activity and/or selectivity of the catalyst
KPFeSi is much better than the photocatalytic function of
the iron supported on porous graphitic carbon nitride (Fe–
g–C N /SBA-15) [24] or pyridine-modified molybdova-
The catalyst KPFeSi was found to exhibit excellent
selectivity for the oxidation of various alkyl aromatics
with H O in acetonitrile (Table 5). No over-oxidation of
2
2
products occurred, and selectivity for all studied aromatics
was about 100%. The catalytic reactions involve only
selective oxidation of the side chain. Ethylbenzene was
oxidized to acetophenone with highest conversion 78%
3
4
nadophosphates in acetic acid–acetonitrile mixed solvent,
which require an acid for the oxidation of benzene with
H O [25]. A majority of reported examples do not
(
Table 5, run 1). Toluene, o-cresol and p-cresol were oxi-
dized to the corresponding aldehydes with conversions
1–54% (Table 5, runs 2–4). The only product of benzal-
dehyde oxidation was benzoic acid with yield 40%
2
2
improve the results early reported in the Fenton chemistry
3
[26–28], the Fe(II)/H O system in water at pH = 2, that in
2
2
addition to the conversion of benzene into phenol provides
mixtures of other oxidation products, due to the involve-
ment of the hydroxyl radical. Bianchi and co-workers [29]
reported good results with a water-soluble iron catalyst that
afforded phenol through benzene oxidation with hydrogen
peroxide with a phenol selectivity of 97% at a benzene
(
Table 5, run 5).
Oxidations of phenol, nitrobenzene, naphthalene and
phenanthrene by this system were not successful. Strong
electron donating (like –OH) or electron-withdrawing (like
–
NO2 and aryl) substituents make the aromatic ring
123

4
2
Transition Met Chem (2012) 37:37–43
conversion of 8–10%. Importantly, this iron catalyst also
required trifluoroacetic acid as the co-catalyst. Recently, a
soluble copper complex has been reported for acid-free
oxidation of benzene to phenol [30] with low conversion
somewhat mild conditions. The KPFeSi/H O /CH CN
2
2
3
system is a simple, cheap and environmental friendly
oxidizing system that has potential for the use in prepara-
tion of fine chemicals and removal of hazardous aromatic
compounds from industrial sewage. The catalyst KPFeSi
showed some potassium leaching during the repeated use.
(
21%) but with good selectivity (81%).
The description of a plausible mechanism for hydro-
carbon oxidation by KPFeSi/H O , is not possible at this
2
2
stage but there are some reasons that show the absence
of hydroxyl radical involvement in the oxidation reactions
by KPFeSi/H O system: (1) the presence of a radical
Experimental
2
2
scavenger like hydroquinone does not decrease the activity
in the oxidation of ethylbenzene (Table 2, run 12), (2) the
KPFeSi/H O system does not oxidize phenol and (3) over-
Anhydrous FeCl from Merck, H PO 85% from Fischer
3
3
4
scientific, tetraethyl orthosilicate (TEOS) from Fluka,
Toluene from Sigma–Aldrich and potassium carbonate
from Merck were used. Other starting materials were as
follows: isopropanol (i-PrOH), nitric acid and acetylace-
tone (Fluka). The oxidant was 30% hydrogen peroxide
2
2
oxidation of benzene is not observed.
Catalyst recycling
(Merck). Substrates and solvents were purchased from
We checked the recyclability of the KPFeSi for the oxidation
of ethylbenzene with hydrogen peroxide in a molar ratio 1:2
under similar reaction conditions. After completion of the
reaction, the catalyst was separated by filtration and reused
as such for subsequent oxidation of ethylbenzene (for three
runs) after adding fresh substrate and oxidant. In these
experiments, conversion slightly decreased but selectivity
for acetophenone remained the same (Table 6). Iron and
potassium leaching experiments were performed to ascertain
whether the reaction is truly heterogeneous. Importantly, no
iron leaching was observed in this course as ascertained by
atomic absorption spectroscopy but potassium leaching
observed, indicating that the reaction is truly heterogeneous
in nature only in the early cycles of the reaction.
Merck. All chemicals were of highest grade and used
without further treatment. Fe O –SiO (FeSi) compound
2
3
2
was prepared according to the reported procedure [31].
Methods
X-ray powder diffraction analysis was performed using
an X’Pert diffractometer operating with Cu Ka Ni-filtered
radiation, a graphite monochromator and a proportional
counter with a pulse height discriminator. Specific surface
area was determined using a single point Brunauer–Emmett–
Teller (BET) method with N at 298 K on a Micromeritics
2
ASAP 2000 apparatus. IR spectra were recorded in KBr
1
disks using a Matson 1000 FTIR spectrophotometer. H
NMR spectra of oxidation products in CDCl solution were
3
recorded on a Bruker 250-MHz spectrometer. The reaction
products of oxidation were determined and analyzed by
HP Agilent 6890 gas chromatograph equipped with a HP-5
capillary column (phenyl methyl siloxane 30 m 9 320
lm 9 0.25 lm) and gas chromatograph–mass spectrometry
Conclusion
We have found that potassium and phosphate-doped iron
oxide–silica gel nanocomposite (KPFeSi) catalyzes the
selective oxidation of benzene and alkyl aromatics with
conversions that challenge other systems reported in the
literature. The promoted Fe O /SiO catalyst is much more
(Hewlett-Packard 5973 Series MS-HP gas chromatograph
with a mass-selective detector). Potassium content of the
catalysts was measured by Jenway FPF 7 flame photometer.
2
3
2
active than unpromoted iron-based catalyst in the oxidation
of aromatics. Particularly, this system does not require
the presence of an acidic medium and operates under
Synthesis of promoted Fe O –SiO nanocomposite
2
3
2
3
-
K O–Fe O –SiO (KFeSi), PO –Fe O –SiO (PFeSi) and
Table 6 Recycling studies with the catalyst KPFeSi in the oxidation
of ethylbenzene by hydrogen peroxide after 5 h of reaction time
2
2
3
2
4
2
3
2
K O–PO –Fe O –SiO (KPFeSi) were synthesized by the
2 4 2 3 2
same procedure. Here, the KPFeSi synthesis is given as a
general procedure.
Entry
No. recycle
Conversion (%)
Selectivity (%)
1
2
3
4
0
1
2
3
78
75
70
62
[99
[99
[99
[99
Synthesis of potassium and phosphorus promoted
Fe O –SiO nanocomposite (KPFeSi)
2
3
2
Sodium (0.25 g) was dissolved in 50 mL of anhydrous
Reaction conditions: catalyst, 0.01 g; ethylbenzene, 1 mmol; CH
mL; H
, 2 mmol; reaction temperature 60 °C
3
CN,
2
O
2 2
isopropanol under N atmosphere with vigorous stirring.
2
1
23

Transition Met Chem (2012) 37:37–43
43
When complete dissolution was attained, 1.458 g
of catalyst, under the same conditions as the catalytic runs.
No products were detected.
(
9.0 mmol) of FeCl was added to the solution and the
3
mixture was stirred for 120 min. A clear solution of
Acknowledgments The authors are grateful to the financial support
of this study by the Zanjan University.
Fe(OPr) in isopropanol was separated by centrifugation
3
and dried in vacuum, and the obtained solid was dissolved
in 20 mL of isopropanol. In a typical procedure, a solution
of acetylacetone (acacH, 18.0 mmol), i-PrOH (3 mL) and
Fe(OPr) (20.0 mL, acac/Fe(OPr) 2:1 molar ratio) was
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3
heated under reflux for 1 h under N with stirring. To this
2
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(
FID) and a HP-5 capillary column. The oxidation products
4
were identified by comparing their retention times with
1
those of authentic samples or alternatively by H NMR
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1
6:379–383
123