Study on Synthesis of Acid-Washed Illite Supported Fe3O4 Nanometer Catalyst and Baeyer–Villiger Oxidation Reaction of Cyclohexanone

Article abstract of DOI:10.1007/s10562-019-02673-2

Baeyer–Villiger oxidation allows for effective control of the stereochemical structure of the product, which is a significant feature for functional group conversion and ring expansion in organic synthesis. In this study, Fe₃O₄ nanoparticles were loaded on acid-washed porous illite silicon slag (I-SR) using an in situ hydrothermal method to obtain the magnetic composite Fe₃O₄@I-SR. This composite was characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, N₂ adsorption–desorption isotherm measurements, vibrating sample magnetometer analysis, etc. The results indicated that the Fe₃O₄ nanoparticles had a face-centered cubic lattice geometry with an average size of about 10?nm; the nanoparticles were uniformly dispersed on the surface of the carrier (I-SR) and exhibited strong paramagnetism. Fe₃O₄@I-SR composite was found to be a promising and efficient catalyst with high activity (> 99% cyclohexanone conversion and > 99% ε-caprolactone selectivity) for the Baeyer–Villiger of cyclohexanone to ε-caprolactone. The catalyst could be easily separated from the reaction mixture and reused many times. Thus, Fe₃O₄@I-SR is an attractive multiphase catalyst that is easy to handle and recycle under environmentally friendly reaction conditions. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02673-2

Catalysis Letters
https://doi.org/10.1007/s10562-019-02673-2
Study on Synthesis of Acid-Washed Illite Supported Fe O Nanometer
3
4
Catalyst and Baeyer–Villiger Oxidation Reaction of Cyclohexanone
Yong Yang · Dongdong Guan · Yu Liu · Shuang Chen · Wan Meng · Nanzhe Jiang1,2
1
1
1
1
1,2
Received: 13 October 2018 / Accepted: 13 January 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Baeyer–Villiger oxidation allows for effective control of the stereochemical structure of the product, which is a significant
feature for functional group conversion and ring expansion in organic synthesis. In this study, Fe O nanoparticles were
3
4
loaded on acid-washed porous illite silicon slag (I-SR) using an in situ hydrothermal method to obtain the magnetic composite
Fe O @I-SR. This composite was characterized by X-ray diffraction, transmission electron microscopy, scanning electron
3
4
microscopy, N adsorption–desorption isotherm measurements, vibrating sample magnetometer analysis, etc. The results
2
indicated that the Fe O nanoparticles had a face-centered cubic lattice geometry with an average size of about 10 nm; the
3
4
nanoparticles were uniformly dispersed on the surface of the carrier (I-SR) and exhibited strong paramagnetism. Fe O @I-SR
3
4
composite was found to be a promising and efficient catalyst with high activity (>99% cyclohexanone conversion and >99%
ε-caprolactone selectivity) for the Baeyer–Villiger of cyclohexanone to ε-caprolactone. The catalyst could be easily sepa-
rated from the reaction mixture and reused many times. Thus, Fe O @I-SR is an attractive multiphase catalyst that is easy
3
4
to handle and recycle under environmentally friendly reaction conditions.
Graphical Abstract
Keywords Illite · Fe O · Baeyer–Villiger oxidation
3
4
Abbreviations
SEM Scanning electron microscopy
XRF X-ray fluorescence
FT IR Fourier transform infrared
BET Barrett–Emmett–Teller
I-SR
Illite silicon slag
Fcc
Face-centered cubic
XRD X-ray diffraction
TEM Transmission electron microscopy
1
Introduction
*
Nanzhe Jiang
nzjiang@ybu.edu.cn
The green and effective Baeyer–Villiger oxidation of
cyclohexanone to ε-caprolactone is of particular importance
in the synthesis of new polymer materials. The conventional
Baeyer–Villiger reaction uses trifluoroperacetic acid or
peroxybenzoic acid as the oxidant. However, conventional
1
2
Department of Chemistry, College of Science, Yanbian
University, Yanji 133002, China
Department of Chemical Engineering and Technology,
College of Engineering, Yanbian University, Yanji 133002,
China
Vol.:(0
1
123456789)
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Y. Yang et al.
methods for the synthesis of ε-caprolactone often result
in serious environmental pollution, thus necessitating the
development of an alternative method that is highly efficient
and green. The modified Baeyer–Villiger reaction utilizes
H O as the oxidant, which is green, mild, and inexpensive.
an oxidant [6]. This layered montmorillonite silicate carrier
has a large specific surface area. The magnetic nanoparticles
with a dual functionality are highly dispersed in the load and
are not only easy to separate but also provide a large number
of active centers [7].
2
2
Lewis acid catalysts can react with the ketone carbonyl
group to activate it, so that H O can easily attack the ketone
Illite (KAl Si O (OH) ) is a low-grade potassium min-
3
3
10
2
eral that is used to extract potassic fertilizers and is of great
significance in areas that require potassium enrichment.
Potassium in the illite interlayers can be readily exchanged
through high-temperature roasting and acid leaching [8]. As
a result, K and other impurities can be thoroughly extracted,
yielding a large number of high-purity illite silica residues
(I-SR).
2
2
carbonyl group and promote the rearrangement. Corma et al.
[
1] reported that the Sn molecular sieve catalyst, doped
with Sn ions, can selectively activate the carbonyl group of
ketones, thereby improving the atomic economy of the rear-
rangement. The mild reaction conditions and small amount
of solvent required make the application of Sn-molecular
sieve catalysts highly desirable in industries. Sn-doped ani-
onic clay hydrotalcite with a special layered structure and
large pores shows high activity in the Baeyer–Villiger rear-
rangement. Kanda et al. [2] reported that the active center
in the Baeyer–Villiger rearrangement is the alkaline center
of hydrotalcite. high-valence metal ions can react with the
alkaline center of hydrotalcite, which promotes the trans-
fer of oxygen from the peracid to the ketone. This catalytic
system shows high activity and high selectivity in the oxida-
tion; however, it is difficult to separate the catalyst from the
reaction mixture, and conventional multiphase separation
methods such as filtration and centrifugation lead to catalyst
loss during recovery.
Here, we report a method to synthesize illite clay loaded
with Fe O magnetic nanoparticles (Fe O @I-SR) for use as
3
4
3
4
a catalyst in the Baeyer–Villiger oxidation of cyclohexanone
in the presence of H O as the oxidant. The Fe O nanopar-
2
2
3
4
ticles serve as an efficient, green, and heterogeneous catalyst
in the oxidation of cyclohexanone with excellent yields and
selectivity under mild, solvent-free conditions. This cata-
lytic system has many advantages: solvent-free conditions,
low cost of the metal, and easy magnetic separation of the
catalyst. Moreover, this catalyst can be reused several times
without significant loss of activity.
The novel magnetic catalyst prepared in the present study
not only has good activity but also shows unique magnetic
responsiveness. The catalyst can be easily separated and
recovered from the reaction mixture under an external mag-
netic field, thereby facilitating its reuse. In recent years, a
core–shell coating material has been developed using mag-
netic micro-nanoparticles as the core and carbon or other
inorganic oxides (such as SiO , TiO , and Al O ) as the
2 Experimental
2.1 Materials
Illite minerals were obtained from the Changbai Moun-
tain (Yanbian, China); iron(III) nitrate nonahydrate
(Fe(NO ) ·9H O) was a product of Alfa Aesar (China)
3
3
2
Chemical; ferric chloride (FeCl ·6H O) was obtained
2
2
2
3
3
2
shell. This type of catalyst can be recovered from the reac-
from Tianjin Guangfu Technology Development; urea
tion mixture by the application of an external magnetic field
(NH CONH ) was obtained from Shenyang Xinhua Reagent
2
2
[3]. The magnetic nanoparticles are supported on the surface
Factory; H O (mass fraction 30%) was obtained from Tian-
2 2
or in the pores of the carrier to obtain a composite mate-
rial with excellent magnetic responsiveness and adsorption
performance. For example, a certain amount of magnetic
nanoparticles has been supported on the surface of the
mesoporous silica, and the resulting composite was used
as a catalyst, which could be quickly separated from the
reaction mixture and efficiently recovered [4]. The loaded
Fe O @I-SR heterogeneous catalyst not only meets the
jin Komio Technology; cyclohexanone (C H O, 99.5%)
6 10
was obtained from Shanghai Aladdin Biochemical Tech-
nology; anhydrous ethanol (CH CH OH, analytical purity)
3
2
was obtained from Liaoning Quanrui Reagent Ltd.; acetone
(CH COCH , 99.5%) was obtained from Beijing Chemical
3
3
Plant; the distilled water was homemade. ε-caprolactone
(C H O ) was a product of Alfa Aesar (China) Chemical.
6
10
2
X-ray diffraction (XRD) patterns were recorded on a
Bruker D8 diffractometer,using Cu Kα radiation in the 2θ
range of 10°–80° with an angular step size of 0.02°. Trans-
mission electron microscopy (TEM) was performed on a
Tecnai G2F20 field-emission electron microscope (US FEI).
The morphology of the samples was determined by scanning
electron microscopy (SEM, SU8010, Hitachi). The chemi-
cal compositions of the samples were determined by X-ray
fluorescence (XRF) spectrometry (Epsilon3, Panalytical).
3
4
requirement that the product is in contact with the active
site of the catalyst and maintains high activity, but can also
be easily separated from the product [5]. Recently, Saikia
et al. reported the in situ generation of Fe O magnetic nano-
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4
particles (Fe O @AT-mont) into the nanopores of modified
3
4
montmorillonite (AT-mont) clay, which showed efficient
catalytic activity in the Baeyer–Villiger oxidation of vari-
ous cyclic and aromatic ketones in the presence of H O as
2
2
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Study on Synthesis of Acid-Washed Illite Supported Fe O Nanometer Catalyst and Baeyer–Vi…
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4
The hysteresis loop was measured by American Quantum
Design’s MPMS-XL-7. Infrared spectra of samples were
measured by a Fourier transform infrared (FT-IR) spec-
trometer from Shimadzu, Japan. The specific surface area
of the sample was calculated by the Barrett–Emmett–Teller
2.4 Catalytic Oxidation of Cyclohexanone
5 g (0.05 mol) of cyclohexanone, H O [2 mL, 18 mmol
2
2
(approx.)] and 0.04 g of Fe O @I-SR were added in a 25 mL
3
4
round-bottom flask. The reaction mixture was stirred at room
temperature for 45 min. In this study, the used catalyst was
simply separated from the reaction mixture by a magnet and
recovered. The separated catalyst was washed with acetone,
followed by washing with ethanol, and dried in an oven, and
the above mentioned procedure was repeated again.
(
BET) method. A Shen Yang Guang Zheng GC-2008B gas
chromatograph was used to detect and quantify the reaction
products (The GC measurement conditions: DB-5 chroma-
tographic column is 30 m×0.25 mm×0.25 µm. Gasification
chamber temperature is 280 °C. The column temperature is
increased from 100 to 280 °C at a rate of 10 °C/min).
3
Results and Discussion
2.2 Preparation of I‑SR
3
.1 Characterization of Fe O @I‑SR Sample
3 4
The illite powder was calcined in a muffle furnace at 550 °C
for 2 h. Then, 2 g of the calcined illite was mixed with
The XRD patterns of illite, activated illite, I-SR, and
Fe O @I-SR are illustrated in Fig. 1. The characteristic
1
5 mL of 4 mol/L HCl and placed in a 100 mL reaction
3
4
vessel. After the reaction was allowed to continue for 5 h
in the oven at 170 °C, the reaction vessel was taken out and
cooled naturally. The product in the vessel was filtered under
suction and dried to obtain active silicon slag. This high-
purity silicon slag obtained after pickling illite is referred
to as I-SR.
diffraction peaks of 2:1 silica tetrahedron-alumina octahe-
dron-silica tetrahedron layers (JCPDS card No. 26-0911)
were observed for the illite samples floated from raw min-
erals, along with the diffraction peaks of kaolinite, chlorite,
and muscovite. After thermal activation, the diffraction
peaks slightly broadened and became less intense, which
was attributed to the loosening of the layered structure
[9]. However, no obvious change in the layered structure
was observed. After acid leaching, the illite structure was
destroyed, which resulted in a broad and flat diffraction band
at 2θ=15°–38°, indicating the amorphous nature of I-SR.
The weak peaks at 2θ=20.8° and 26.6° indicated the pres-
ence of small amounts of quartz impurities in the I-SR. The
2
.3 Preparation of the Fe O @I‑SR Composite
3 4
1
.5 mmol (0.4 g) of ferric chloride hexahydrate, 1.5 mmol
(
0.6 g) of ferric nitrate nonahydrate, 2 g of urea, and 0.5 g
of I-SR were dissolved in 40 mL of distilled water, and this
mixture was stirred with a glass rod for 10 min to ensure
complete dissolution. The solution was transferred to a
XRF results (Table 1) indicated that the SiO content was
2
1
1
00 mL Teflon reactor, which was placed in an oven at
80 °C for 14 h. After cooling to room temperature, the
as high as 98% in the I-SR, whereas the K and Al contents
were very low. Thus, I-SR can be used as a silica source for
the synthesis of Fe O @I-SR.
product was magnetically separated, then washed several
times with deionized water and absolute ethanol, and placed
in an oven at 50 °C overnight to obtain a magnetic, func-
tional pickled illite material coated with Fe O nanoparticles
3
4
XRD analysis of Fe O @I-SR was also performed. Fig-
3
4
ure 1 illustrates six peaks at 2θ = 20.76°, 30.16°, 35.66°,
43.08°, 57.06°, and 62.6° corresponding to the (111), (220),
(311), (400), (511), and (440) indices, respectively, of a
3
4
(
Fe O @I-SR).
3 4
Fig. 1 XRD patterns of illite,
calcined illite, acid leached illite
and Fe O @I-SR samples
3
4
1
3

Y. Yang et al.
Table 1 Elemental composition of illite, acid leached illite and
Fe O @I-SR samples (wt%)
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4
Si (%)
Fe (%)
Impurity
Al (%)
Ti (%)
K (%)
Illite
I-SR
51.56
98.18
35.09
3.24
0.13
63.30
35.4
1.08
1.08
1.70
0.27
0.20
8.05
0.34
0.33
Fe O @ I-SR
3
4
face-centered cubic (fcc) lattice of the Fe O nanoparticles,
3
4
which are indexed to the spinel structure of pure stoichio-
metric Fe O (JCPDS Card No. 19-0629).
3
4
The SEM image of the illite raw material is illustrated in
Fig. 2-1, where the illite ore is clearly visible; clear stacking
and no obvious change in layered morphology of calcined
products are observed (Fig. 2-1, 2). After acid leaching,
the illite slag (Fig. 2-1, 3) disappeared. The SEM image of
Fe O @I-SR is illustrated in Figs. 2–4, which shows the
Fig. 3 The TEM image of Fe O @I-SR
3
4
adsorbate (nitrogen) and the metallic surface may affect
the measured values to some extent. However, the increase
in pore diameter may be due to rupture of some of the
pore walls to generate larger pores during the formation
of the Fe O nanoparticles. Another possibility is that the
3
4
formation of pores on the clay surface.
The Fe O nanoparticles were dispersed on I-SR (Fig. 3)
3
4
3
4
and had an average particle size of around 10 nm.
Fe oxide deposition was carried out in the presence of urea
at 180 °C, which should cause a partial dissolution of the
silica support and probably be responsible for changes in
the porous structure. This would be responsible for the
loss of the porous micro/mesostructure observed in the
graph Fig. 4.
The porosity and surface area of I-SR and Fe O @I-SR
3
4
were obtained from N adsorption–desorption measure-
2
ments at 77 K. N adsorption–desorption isotherms of
2
I-SR and Fe O @I-SR are illustrated in Fig. 4. The sur-
3
4
face area of I-SR and Fe O @I-SR was measured to be
3
4
2
2
7
2.8155 m /g and 97.3773 m /g, respectively, by the BET
A saturation magnetization (Ms) of 31.61 emu/g
with near-zero remanence (Mr) and coercivity (Hc) was
observed for the Fe O @I-SR sample, confirming its
method. Furthermore, the presence of Fe O nanoparti-
3
4
cles may cause complexities in porosity measurement with
3
4
nitrogen sorption, as the electrostatic forces between the
superparamagnetic nature (Fig. 5). Fe O @I-SR could be
3
4
Fig. 2 SEM images of 1 illite,
2
calcined illite, 3 acid leached
illite and 4 Fe O @I-SR
3
4
samples
1
3

Study on Synthesis of Acid-Washed Illite Supported Fe O Nanometer Catalyst and Baeyer–Vi…
3
4
manipulated by an external magnet, which is necessary for
magnetic separation.
3.2 Catalytic Activity
Usually, Bayer–Villiger oxidation requires solvents as cocat-
alysts (Table 2). Herein, we obtained a high yield of capro-
lactone without using solvents. The surface of illite silicon
slag (I-SR) is exposed with abundant hydrophilic Si–OH
groups and hydrophobic Si–O–Si groups. These intermedi-
ate channels are amphipathic (Fig. 6) [10, 11]. They can
accommodate both the hydrophobic ketone substrates and
the hydrophilic oxidant H O , which means that the inter-
2
2
mediate channel acts as a nanoreactor to enrich the substrate
and make the oxidation more efficient (Fig. 7). I-SR has
many channels. Fe O enters the mesoporous silicon slag
3
4
channel, we speculated that in the reaction mechanism, the
possible reactive sites are Fe(III) (Fig. 8) [12]. For exam-
ple, in the presence of H O , Fe(II) is easily oxidized to
Fig. 4 The BET of I-SR and Fe O @I-SR
3
4
2
2
Fe(III) [13]. Therefore, considering its high conversion rate
and environmental friendliness, Fe O @I-SR would be a
3
4
promising catalyst for such reactions.
Figure 9 shows the effect of the amount of H O added
2
2
on the oxidation of cyclohexanone Baeyer–Villiger. It can
be seen that with the increase of H O dosage, the conver-
2
2
sion of cyclohexanone increases. The optimal molar ratio
of cyclohexanone to H O is obtained. As the amount of
2
2
H O increases, the yield and selectivity of ε-caprolactone
2
2
decrease slightly, which may be due to a side reaction of
cyclohexanone and the hydrolysis of a small amount of
ε-caprolactone.
The effect of reaction time on the activity of the catalyst is
illustrated in Fig. 10. When the reaction was prolonged, the
conversion of cyclohexanone increased. When the reaction
time was increased to 45 min, the conversion of cyclohex-
anone increased to 99%. However, if the reaction time was
increased further, the conversion rate showed no significant
change. The extension of the reaction time also promoted the
side reaction. It is clear from the figure that the selectivity
of ε-caprolactone decreases with increasing reaction time.
The experimental results for the cycle of the Fe O @I-SR
Fig. 5 Room
temperature
magnetization
hysteresis
curve
Fe O @I-SR
3
4
3
4
catalyst are illustrated in Fig. 11. After each use, the catalyst
Table 2 Comparison of the
present catalyst with some
reported catalysts for the
Baeyer–Villiger oxidation of
ketones
o
Catalyst
Solvent
Temp. ( C)
Time (min)
Conversion/
yield (max.)
Sn exchanged hydrotalcites [14]
Sn-supported on clay [15]
Mg-Al mixed oxide [16]
Organoselenium [17]
Acetonitrile
70
240
120
720
1440
360
45
58
1,2-Dichloroethane
1,4-Dioxane
Acetonitrile
Solvent free
Solvent free
Refluxing
100
88.7
92
98
>99
70
25
25
25
Fe O @AT-mont [6]
3
4
Fe O @I-SR
3
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Y. Yang et al.
Fig. 9 Effect of H O content on Baeyer–Villiger oxidation of
2
2
Fe O @I-SR
3
4
Fig. 6 IR of Fe O @I-SR samples
3
4
4
Conclusions
was washed with acetone and ethanol, and then dried at
0 °C. The catalyst was stable after five runs, without nota-
5
Fe O nanoparticles were loaded on I-SR using an in situ
3 4
ble loss of activity, indicating Fe O @I-SR has good reus-
hydrothermal method, and a magnetically loaded material
(Fe O @I-SR) was obtained. The samples were character-
3
4
ability and is a potential new environmentally friendly cata-
3
4
lyst with industrial applications.
ized by XRD, TEM, SEM, BET, and VSM. The results indi-
cated that the Fe O nanoparticles have an fcc lattice and
3
4
an average size of around 10 nm. The Fe O nanoparticles
3
4
Fig. 7 Fe O @I-SR catalytic
3
4
reaction
Fig. 8 Formation and catalytic reaction mechanism of Fe O @I-SR
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4
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Study on Synthesis of Acid-Washed Illite Supported Fe O Nanometer Catalyst and Baeyer–Vi…
3
4
selectivity of Fe O @I-SR. The Fe O nanoparticles were
3
4
3
4
easily separated by an external magnet, recovered, and recy-
cled several times without significant loss of activity. Our
experiments showed that the reaction conditions for the use
of Fe O @I-SR do not pose a risk to the environment. More-
3
4
over, Fe O @I-SR is easy to use and recycle in addition to
3
4
being inexpensive, which make it an attractive heterogene-
ous catalyst.
Acknowledgements This work was supported by the National Natural
Science Foundation of China (Grant No. 21661031 and No. 21263026).
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Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
3
4
2
2
Baeyer–Villiger oxidation of cyclohexanone. After 45 min
of reaction, caprolactone was obtained, with a conversion
rate of 99%. This indicated the high catalytic activity and
1
3