Building MOF bottles (MIL-101 family as heterogeneous single-site catalysts) around Fe3O4 ships: A highly efficient and magnetically separable catalyst for oxidation of alcohols

Article abstract of DOI:10.1134/S1070427215080194

Fe₃O₄ supported on chromium-based metal-organic framework (MOF), MIL-101(Cr), has emerged as highly efficient and heterogeneous catalyst for selective oxidation of alcohols because of its high specific surface area, tuneable pore size, and unique structure. MIL-101 and its Fe₃O₄ composite (Fe₃O₄@MIL-101) was prepared via the impregnation of the Fe₃O₄ in MIL-101. The surface properties of the functionalized catalyst were analyzed by a series of characterization techniques like FTIR, XRD, N₂ adsorption-desorption, and TEM. XRD and adsorption-desorption analysis show that the mesostructure of MIL-101 remains intact after Fe₃O₄ modifications, while spectral technique show the successful immobilizing of the neat Fe₃O₄ inside the MIL-101 support. Fe₃O₄@MIL-101 can be reused several times although they get less active.

Full text of DOI:10.1134/S1070427215080194

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 8, pp. 1343−1350. © Pleiades Publishing, Ltd., 2015.
VARIOUS TECHNOLOGICAL
PROCESSES
Building MOF Bottles (MIL-101 Family as Heterogeneous
Single-Site Catalysts) Around Fe O Ships:
3
4
A Highly Efficient and Magnetically Separable
Catalyst for Oxidation of Alcohols1
Zahra Naghdi, Razieh Farzaeli, and Hamid Aliyan
Department of Chemistry, Shahreza Branch, Islamic Azad University, 86145-311, Iran
e-mail: fazaeli@iaush.ac.ir
Received October 3, 2015
Abstract—Fe O supported on chromium-based metal-organic framework (MOF), MIL-101(Cr), has emerged
3
4
as highly efficient and heterogeneous catalyst for selective oxidation of alcohols because of its high specific
surface area, tuneable pore size, and unique structure. MIL-101 and its Fe O composite (Fe O @MIL-101) was
3
4
3
4
prepared via the impregnation of the Fe O in MIL-101. The surface properties of the functionalized catalyst
3
4
were analyzed by a series of characterization techniques like FTIR, XRD, N adsorption–desorption, and TEM.
2
XRD and adsorption–desorption analysis show that the mesostructure of MIL-101 remains intact after Fe O
3
4
modifications, while spectral technique show the successful immobilizing of the neat Fe O inside the MIL-101
3
4
support. Fe O @MIL-101 can be reused several times although they get less active.
3
4
DOI: 10.1134/S1070427215080194
INTRODUCTION
to be considered as prospective materials for applications
in gas storage [4], separation [5], catalysis [6], and drug
The concept of single-site heterogeneous catalysts delivery [7]. MOFs are composed of isolated metal
SSHCs) has attracted a great deal of attention from atoms or clusters linked by polydentate organic ligands,
(
researchers working in the field of liquid phase catalysis. resulting in a rigid porous network. Hence, the structure
This is not surprising because SSHCs possess accessible, of MOFs meets the general requirements of single-site
spatially isolated and homogeneously distributed uniform catalysts.Although catalysis is one of the most important
active sites on the surface and, therefore, are expected to areas in these materials, their catalytic properties have
combine the merits of both homogeneous (activity and been largely unexplored as compared with recent
selectivity) and heterogeneous (simplicity of recovery and interest in porous hybrid solids with zeolitic guest-
recycling) catalysts [1, 2]. SSHCs are usually associated binding properties. The introduction or incorporation of
with transition-metal-containing molecular sieves or coordinatively unsaturated metal sites (CUS) into porous
supported catalysts prepared by grafting or anchoring hybrids is very beneficial since CUS can strongly interact
techniques [3].
with guest molecules such as gases [8] and organic
molecules [9] in adsorption and catalysis. MIL-101 is one
of the porous MOF materials, which have been studied
extensively [10]. MIL-101 is made from the linkage of
MOFs are functional porous coordination polymers
that possess a unique combination of properties, such as
extremely high surface areas, crystalline open structures,
tunable pore size and functionality. All these allow them
1
,4-benzene dicarboxylate (BDC) anions and inorganic
trimers that consist of three chromium atoms in an
octahedral environment with four oxygen atoms of the
1
The text was submitted by the authors in English.
1
343

1344
ZAHRA NAGHDI et al.
Scheme 1. Oxidation of alcohols with H O in the presence of Fe O @MIL-101.
2
2
3
4
Fe O @MIL-101
3
4
H O , CH CN, rt
2
2
3
bidentate dicarboxylate, one μ O atom, and one oxygen
atom from the terminal water or fluorine group [11].
distilled water in an erlenmeyer flask at room temperature
and under stirring for 12 h. The resulting pastes were dried
for 4 h at 100°C and calcined for 4 h at 400°C.
3
Encapsulating magnetic nanoparticles in silica is a
promising and important approach in the development of
magnetic nanoparticles for technological and biomedical
applications [12, 13]. Materials used this way can be
defined as magnetisable particles (i.e., ones that, when
under the influence of an external magnetic field, will
themselves become magnetic) and can enable the isolation
or extraction of a target molecule or substance. The non-
magnetic target binds to the surface of the magnetisable
solid-phase support (MSPS), either through a specific
affinity interaction, or another mechanism, for example,
ion exchange or hydrophobic interaction, so that it can
then be isolated or extracted by application of an external
magnetic field [14].
Oxidation of alcohols, general procedure. A 25-mL
round bottomed flask with 5 mL of CH CN equipped
3
with a mechanical stirrer and reflux condenser was
charged with Fe O @MIL-101 (0.015 g, 2 mmol) and
3
4
3 mmol aqueous hydrogen peroxide (30 %). The mixture
was stirred and then 1 mmol alcohol was added. The
o
biphasic mixture was stirred at 80 C for the required time.
Progress of the reaction was followed by the aliquots
withdrawn directly from the reaction mixture analysed
by GC using internal standard. After completion of the
reaction, Fe O @MIL-101 was removed by applying an
3
4
added magnetic field and the mixture was treated with a
0% sodium hydrogen sulfite solution to decompose the
unreacted hydrogen peroxide and then with 10% sodium
hydroxide. The product was extracted with n-butyl-ether.
The pure product was obtained by distillation or silica
gel column chromatography (hexane/ethyl acetate, 10/1).
1
Herein, we report on the catalytic behavior of Fe O @
3
4
MIL-101(Cr) catalysts (fabricated via the encapsulated
and impregnated methods) for the oxidation of alcohols
using H O (Scheme 1).
2
2
RESULTS AND DISCUSSION
Physico-Chemical Characterization
EXPERIMENTAL
All materials were commercial reagent grade. Infrared
–1
FT-IR spectra of MIL-101, Fe3O4 and Fe3O4@MIL-
spectra (400–4000 cm ) were recorded from KBr pellets
on a PerkinElmer Spectrum 65 spectrometer. The X-ray
powdered diffraction patterns were performed on a Bruker-
D8ADVANCE with automatic control. The patterns were
1
1
1
01 are shown in Fig. 1. In spectrum of MIL-101 (Fig.
a), sharp peaks with high intensity in the range of
−
1
400–1600 cm indicate the stretching vibrations of
C=C bound to aromatic ring. This notion is strength-
run with monochromatic CuK (1.5406 Å) radiation with
α
−
1
ened by C–H weak peak at 3070 cm . Strong bands in
–1
a scan rate of 2° min . Nitrogen adsorption measurements
were performed at −196°C by using an ASAP 2010M
surface analyzer, and the pretreatment temperature was
−
1
the region of 1800–1300 cm correspond to ν (COO),
as
νs(COO), and ν(C–C) vibrations, implying the presence
of dicarboxylate linker in the MIL framework. Rather
1
80°C. Transmission electron micrographs (TEM) were
−1
weak and narrow bands at 1017 and 748 cm can be
attributed to δ(C–H) and γ(C–H) vibrations of aromatic
rings, respectively. Weak bands in the spectral region
obtained on a Joel JEM 2010 scan-transmission electron
microscope. The sample for the TEM measurement was
suspended in ethanol and supported on a carbon coated
copper grid.
−1
of 700–400 cm are most likely due to in-plane and
out-of-plane bending modes of COO-groups [15]. The
−
1
Synthesis of Fe O @MIL. MIL-supported Fe O was
peak with medium strength in 577 cm is due to Cr–O
vibrations, which prove that the metal organic framework
3
4
3
4
prepared by method of incipient wetness: mixing 50 mg
of Fe O and 100 mg of the MIL sample with 10 mL of
−
1
indeed has been formed. The peak in 1560–1650 cm
3
4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

BUILDING MOF BOTTLES
1345
(c)
(b)
(a)
4
000 3500 3000 2500 2000 1500 1000 500
Wavenumber, cm–1
Fig. 1. FTIR spectra of (a) MIL-101, (b) Fe O , and (c) Fe O @MIL-101.
3
4
3
4
area relates to the vibration of C=O group. The broad peak
−
1
in 2400–3400 cm range can be because of crystalline
water or the acidic OH of carbonyl group. FT-IR analysis
reveals that Fe O @MIL-101 nanocomposites (Fig. 1c)
3
4
have characteristics peaks at around at 3435, 2342, 1630,
–
1
–1
1
405, 1093 cm for MIL-101. The peak at 561 cm could
(c)
be attributed to the Fe–O stretching of Fe O .
3
4
The XRD pattern (Fig. 2a) predicted the cubic
structure of MIL-101, which is in good agreement with
those reported by Ferey et al. [13]. The XRD patterns of
magnetic Fe O nanoparticles (Fig. 2b) reveal that the
3
4
(b)
crystal structure is indexed as face centered cubic (fcc)
JCPDS card no. 19-629). No other characteristic peaks
(
due to the impurities of hematite or hydroxides were
detected. It is found that the strong diffraction peaks
situated at 2θ of 18.90°, 30.220°, 35.530°, 43.240°,
5
3.970°, 57.440°, and 62.940°, corresponding to the
diffractions of [111], [220], [311], [400], [422], [511],
and [440] crystal faces of porous Fe O structures. Sharp
(a)
3
4
peaks in Fig. 2b suggest that the Fe O nanoparticles
3
4
have good crystalline abilities. The peak positions in the
XRD pattern of Fe O composite (Fig. 2c) materials are
3
4
5 10 20 30 40 50 60 70 80
not changed after Fe O incorporation and are in good
agreement with its parent MIL-101. The intensity of
3
4
2θ, deg
peak at 2θ = ~9° of Fe O @MIL-101 is lower than that
of parent MIL-101, attributed to the less ordered structure
3
4
Fig. 2. XRD of (a) MIL-101, (b) Fe O , and (c) Fe O @MIL-101.
3
4
3 4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

1346
ZAHRA NAGHDI et al.
Fig. 3. N -Adsorption-desorption isotherms of Fe O @MIL-101: (inset) pore size distributions calculated by the BJH method.
2
3
4
3
–1
after incorporating the optimum amount of Fe O . The
pore volume of 0.61 cm g . After Fe O modification,
3 4
3
4
average crystal sizes calculated from the XRD patterns
according to Scherrer formula are 38.3 and 38.6 nm for
the bare Fe O and for the Fe O of Fe O @MIL-101
the nitrogen adsorption isotherm became an even line and
the volume adsorbed decreased distinctly, suggesting the
occupation of the pore by Fe O . BET surface area and
3
4
3
4
3
4
3
4
samples, respectively.
pore volume of Fe O @MIL-101 decreased which con-
3 4
firms that Fe O have occupied the channels in MIL-101.
The maintenance of the MIL-101frameworks after
introduction of Fe O is further supported by the nitrogen
3
4
The TEM images of Fe O @MIL-101 sample is
3
4
3
4
sorption data. Figure 3 shows the N adsorption–
shown in Fig. 4. MIL-101 is extremely sensitive to the
electron beam, and in usual conditions, the structure
collapses under the electron beam exposure [16]. The
cubic symmetry of the MIL-101 was reflected in the shape
of the crystals [17]. The cubic symmetry of the MIL-101
2
desorption isotherms and pore size distributions of
Fe O @MIL-101. The samples exhibited typical IV type
3
4
isotherms and H1 type hysteresis loops at high relative
pressures. The pore size distribution of the sample is
shown in the inset of Fig. 3. Interestingly, the Fe O @
was not obtained for Fe O @MIL-101 sample.
3
4
3
4
MIL-101 showed very similar isotherm patterns and
pore size distributions (inset) compared to those of MIL-
It was found Fe O @MIL-101 surface morphology
3 4
was spherical-like. TEM analyses indicate that the
continuous 3D pore structure of the MIL-101 is robust
enough to survive the Fe O incorporation process and
1
01, indicating that the structure of MIL-101 was still
maintained even after the immobilizing step of Fe O .
3
4
3
4
so offers an excellent matrix to support highly dispersed
Fe O species. The places with darker contrast could be
Structural properties of MIL-101 are listed in Table 1.
MIL-101 showed BET surface area of 2191 m g and
2
–1
3
4
Table 1. The texture parameters of MIL-101 and Fe O modified MIL-101 in comparison with the bulk Fe O materials
3
4
3
4
Texture parameters (N adsorption)
2
b
Materials
Fe O , wt %
MIL-101
3
4
surface area,
pore volume,
cm g
pore diameter, nm
2
–1a
3
–1a
m g
MIL-101
Fe O
2191
4
0.61
0.01
0.34
2.1
–
100
–
11.7
1.53
100
32.1 ± 0.8
3
4
Fe O @MIL-101
501
67.9 ± 0.8
3
4
a
Total pore volume measured at p/p = 0.99.
0
b
The average results of atomic adsorption analysis, NAA and ICP.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

BUILDING MOF BOTTLES
1347
a
Table 2. Oxidation of alcohols by Fe O @MIL-101 in CH CN with H O
2
3
4
3
2
Entry
1
Substrate
Product
Time, h, : yield, %b
1 : 98
2
3
1.5 : 97
1.5 : 95
4
3.5 : 85
5
6
7
8
9
4 : 93
5 : 97
2 : 95
2 : 92
2.5 : 97
8 : 98
4 : 98
1
0
11
1
1
2
3
5 : 92
7.5 : 98
1
1
4
5
5 : 92
5.5 : 92
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

1348
ZAHRA NAGHDI et al.
Table 2. (Contd.)
Entry
Substrate
Product
Time, h, : yield, %b
10 : 45c
1
1
6
7
10 : 48
1
8
12 : 40
a
b
c
Reaction conditions: alcohol (1 mmol); H O (3 mmol); Fe O @MIL-101(0.015 g, 2 mmol); reflux in CH CN (3 mL).
GC yield based on an internal standard methods unless otherwise stated.
A trace amount of the corresponding esters (~9 %) and carboxylic acid (~14%) were formed.
2
2
3
4
3
assigned to the presence of Fe O particles with different
the fastest reaction rates. However, electronic effects do
not seem to have a significant effect on the isolated yields
for electron-rich and electron-poor benzylic alcohols.
3
4
dispersion. The small dark spots in the images could be
ascribed to Fe O particles, probably located into the
3
4
MIL-101 cavities. The larger dark areas over the cavities
most likely correspond to Fe O agglomerates on the
external surface.
The successful oxidation of benzoin and furfuryl
alcohol as model substrates shows a superior capabil-
ity of Fe O @MIL-101 in oxidizing similar substrates
3
4
3
4
(
Table 2, entries 7, 11). Catalyst Fe O @MIL-101 in
3 4
Catalytic Activity
particular showed excellent reactivity for the selective
oxidation of various types of allylic alcohols yielding
the corresponding α,β-unsaturated carbonyl compounds
in excellent yields (Table 2, entries 12–15). It is worth
mentioning that in the oxidation of allylic alcohols, C=C
Oxidation of alcohols. As summarized in Table 2,
benzylic and allylic alcohols are generally excellent sub-
strates for this catalyst with electron-rich alcohols having
3
00 nm
Fig. 4. TEM image for Fe O @MIL-101.
3
4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

BUILDING MOF BOTTLES
1349
9
7
5
0
0
0
Run no. 1
Run no. 2
Run no. 3
Run no. 4
Run no. 5
Fig. 5. Investigation of the feasibility of reusing Fe O @MIL-101 (3 mol %) in the oxidation of 4-methoy benzyl alcohol (1 mmol) to
3
4
the 4-methoy benzaldehyde with H O (3 mol %) in CH CN (5ml) after 1.5 h.
2
2
3
double bonds remained intact without an intramolecular
hydrogen transfer. Secondary benzylic alcohols were also
efficiently oxidized into the corresponding ketone (Table 2,
entries 8–11). Unfortunately, using Fe O @MIL-101, ali-
(Table 3). Comparison of Fe O @MIL-101 with these
3 4
catalysts for selective oxidation of alcohols shows that
activity of Fe O @MIL-101 seems to be higher than or
3
4
equal with other known catalysts (Table 3).
3
4
phatic alcohols such as 1-octanol and 2-octanol and 4-phe-
nyl cyclohexanol proved to be poor substrates, yielding the
corresponding carbonyl compound in 45%, 48%, and 40%
yields, respectively (Table 2, entries 16–18).
Recovery. Magnetic separation provides a very con-
venient approach for removing and recycling magnetic
composites by applying an added magnetic field. The
separation of Fe O @SBA-15 nanocatalyst from the
3
4
In order to show the merit of the present work in
comparison with recently reported protocols [18–24], we
compared the results with respect to the amounts of the
catalysts used, reaction times, and yields of the products
reaction mixture becomes very easy owing to the su-
perparamagnetic nature of Fe O nanoparticles at room
temperature. In the magnetic separation technique, the
catalyst became adsorbed onto the magnetic stirring bar
3
4
Table 3. Comparison of Fe O @MIL-101 with some other catalyst for oxidation of PhCH OH
3
4
2
Entry
1
Reagent
Conditions
Time, h Conversion, %
Yield, %a
98
Reference
19
Iron Chloride hexahydrate/
TEMPO (4 mol%)
O , toluene, 80°C
7
100
2
d
b
c
2
3
4
Au24 Clusters (Pd)/(CNT) (50 mg) O , 30°C
6
74
24 : 53 : 23
20
21
22
2
Immobilized Pd, KNO (4 mol %)
O , TFT, reflux
1.5
18
100
59
98
3
2
Polyesterbased Pd(II)
Toluene, 70°C
–
macrocomplexes (4 mol %)
5
6
Hemicryptophane-Ruthenium
complex (5 mol %)
CH CN : H O,
room temperature
1
–
91 : 9b
85
23
24
3
2
Liquid phase/Au NPpore
O , MeOH, 60°C
24
2
(
10 mol %)
Triple-site phosphotungstate
5 mol %)
Fe O @MIL-101 (2 mol %)
7
8
Toluene/H O ,
1
1
92
98
25
2
2
(
9
0°C
CH CN, H O ,
This work
3
4
3
2
2
reflux
a
b
c
d
Yield refers to the corresponding aldehyde.
Yield refers to the corresponding acid.
Yield refers to the benzoate.
CNT is carbon nanotube.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 8 2015

1350
ZAHRA NAGHDI et al.
when the stirring was stopped. In our experiments, the
reusability of the catalyst were examined by repetitive
use of the catalyst (Fig. 5). The wet catalyst was recycled
and no appreciable change in activity was noticed after
five cycles (Fig. 5).
Yoon, J.W., Jhung, S.H., Chang, J.-S., and Cheetham,A.K.,
J. Am. Chem. Soc., 2006, vol. 128, pp. 16846–16850.
9. Vimont, A., Goupil, J.-M., Lavalley, J.-C., Daturi, M.,
Surblé, S., Serre, C., Millange, F., Férey, G., and
Audebrand, N., J. Am. Chem. Soc., 2006, vol. 128,
pp. 3218–3227.
1
0. Férey, G., Mellot-Draznieks, C., Serre, C., Millange, F.,
Dutour, J., Surble, S., and Margiolaki, I., Science, 2005,
vol. 309, pp. 2040–2042.
CONCLUSIONS
Aseries of Fe O @MIL(101) catalysts were prepared
3
4
11. Latroche, M., Surble, S., Serre, C., Mellot-Draznieks, C.,
by the wet impregnation method. This catalyst is a safe
and magnetically recoverable heterogeneous system for
promoting the highly chemoselective and rapid oxidation
of alcohols to aldehydes with H O . The advantages of
Llewellyn, P.L., Lee, J.H., Chang, J.S., Jhung, S.H., and
Ferey, G., Angew. Chem. In. Ed., 2006, vol. 45, pp. 8227–
8231.
2
2
1
1
2. Levy, L., Sahoo, Y., Kim, K.S., Bergey, E.J., and
ths catalytic system is mild reaction conditions, short
reaction times, high product yields, easy preparation of
the catalysts, non-toxicity of the catalysts, simple and
clean work-up of the desired products.
Prasad, P.N., Chem. Mater., vol. 14, 2002, p. 3715.
3. Arundhathi, R., Damodara, D., Likhar, P.R., Kantam, M.L.,
Saravanan, P., Magdaleno, T., and Kwon, S.H., Adv. Synth.
Catal., 2011, vol. 353, pp. 1591 – 1600.
1
1
1
1
4. Robinson, P.J., Dunnill, P., and Lilly, M.D., Biotechnol.
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5. Brown, D.W., Floyd, A.J., and Sainsbury, M., Organic
Spectroscopy, Willey, New York, 1988.
We gratefully thank Shahreza Branch, Islamic Azad
University, for financial support.
6. Lebedev, O.I., Millange, F., Serre, C., Van Tendeloo, G.,
and Ferey, G., Chem. Mater., vol. 17, 2005, pp. 6525–6527.
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