Manganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous oxidation

Article abstract of DOI:10.1016/j.inoche.2015.08.019

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co₃O₄, Mn₃O₄ and Mn₂O₃ nanoparticles. The prepared metal oxide nanoparticles of Co₃O₄, Mn₃O₄ and Mn₂O₃ possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co₃O₄ and Mn₃O₄ exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co₃O₄ and Mn₃O₄ nanoparticles illustrated excellent catalytic stability and reusability for nine and four cycles, respectively, toward olefin oxidation.

Full text of DOI:10.1016/j.inoche.2015.08.019

Manganese and cobalt-terephthalate metal-organic frameworks as a precursor
for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts
for olefin heterogeneous oxidation
Fatemeh Ashouri, Maryam Zare, Mojtaba Bagherzade
PII:
DOI:
Reference:
S1387-7003(15)30061-7
doi: 10.1016/j.inoche.2015.08.019
INOCHE 6089
To appear in:
Inorganic Chemistry Communications
Received date:
Revised date:
Accepted date:
17 January 2015
15 August 2015
23 August 2015
Please cite this article as: Fatemeh Ashouri, Maryam Zare, Mojtaba Bagherzade, Man-
ganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis
of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous
oxidation, Inorganic Chemistry Communications (2015), doi: 10.1016/j.inoche.2015.08.019
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ACCEPTED MANUSCRIPT
Manganese and Cobalt-terephthalate Metal-Organic Frameworks as a Precursor for
Synthesis of Mn O , Mn O and Co O Nanoparticles: Active Catalysts for Olefin
2
3
3
4
3
4
Heterogeneous Oxidation
*,a
b
*,c
Fatemeh Ashouri , Maryam Zare , Mojtaba Bagherzade
a
Department of Applied Chemistry, Faculty of Pharmaceutical Chemistry, Pharmaceutical
Sciences Branch, Islamic Azad University, Tehran, Iran (IAUPS).
b
Department of Basic Science, Golpaygan University of Technology, P.O. Box 87717-65651,
Golpaygan, Iran.
c
Department of Chemistry, Sharif University of Technology, P.O. Box 11155-3516, Tehran, Iran
Corresponding author. Tel.: +98 21 66165354; fax: +98 21 66012983.
E-mail address: bagherzadeh@sharif.edu
f.ashouri@iaups.ac.ir
The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework
precursors was utilized as a synthetic route for fabrication of Co O , Mn O and Mn O
3
3
4
3
4
2
nanoparticles. The prepared metal oxide nanoparticles of Co O , Mn O and Mn O possess
3
4
3
4
2
3
average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel
structure nanoparticles of Co O and Mn O exhibit efficient catalytic activity toward
3
4
3
4
heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co O
3
4
and Mn O nanoparticles illustrated excellent catalytic stability and reusability for nine and four
3
4
cycles, respectively, towards olefin oxidation.
Keywords: metal-oxide nanoparticles, epoxidation reaction, heterogeneous catalyst, recyclable
catalyst.
Nanoscale materials, including nanoparticles (NPs), nanowires, nanorods, nanotubes and
nanoribbons, represent highly customizable and robust multifunctional platforms in many fields.
Nanoscale materials behaviors strongly depend on the shape and size of the particles [1].
Among wide variety of transition metal oxides, NPs, Co O and Mn O are important oxides
3
4
3
4
2
+
3+
with spinel structure comprising M and M ions. Chemical and thermodynamical stability of
1

ACCEPTED MANUSCRIPT
cobalt and manganese oxides make them promising materials that have received widespread
attention due to their appealing multi-functional properties of technological interest [2].
A wide range of synthetic techniques has been applied to grow cobalt and manganese oxide
nanosystems with controlled properties, for instance, hydrothermal route using hydrogen
peroxide [3], microwave-assisted synthesis via urea hydrolysis [4], hydrothermal process [5],
solvothermal method [6], CTAB-assisted solvothermal method [7], microwave-assisted
solvothermal method [8], micelle-assisted hydrothermal method [9] and microemulsion-based
method [10]. Among these synthetic routes, Metal-Organic Frameworks (MOFs) are favorable
for the formation of uniformly separated micrometric or nanometric particles [2, 11].
Manganese and cobalt oxides are useful, versatile and environmentally friendly catalysts which
were extensively used for the oxidation of a variety of molecules, especially water oxidation,
toluene oxidation, CO oxidation, carbon monoxide oxidation, the epoxidation of olefins and
oxidative cyclization [12]. Herein, we developed a novel MOF route to prepare Mn O , Mn O
4
2
3
3
and Co O NPs, which involves the processes of converting metal oxide subunits in MOF into
3
4
primary metal oxide NPs. The prepared metal oxide NPs were employed as heterogeneous
catalysts in olefins epoxidation.
The precursors of Manganese and cobalt-terephthalate MOFs, [Mn (BDC) (DMF) ] and
3
3
4 n
[
Co (BDC) (DMF) (H O) ] , were prepared previously [13, 14] and used for the production of
3 3 2 2 2 n
manganese and cobalt oxide NPs. The MOFs structures consist of M-O-C (M=Mn and Co) units
wherein the terephthalate links were coordinated with the metal centers to form a 2D-polymeric
chain. The organic linker in framework was removed at high temperature, through calcination
and M-O octahedral subunits convert to metal oxide NPs. The complete decomposition of
6
◦
◦
MOFs occurred at the temperature above 320 C for [Co (BDC) (DMF) (H O) ] and 520 C for
3
3
2
2
2 n
[
Mn (BDC) (DMF) ] based on TG curves (Fig. 1S). So, calcination temperature for synthesized
3 3 4 n
NPs was selected according to MOFs decomposition temperature. The Mn O NPs were
3
4
obtained as a fine brown powder using [Mn (BDC) (DMF) ] via a solid-state thermal
3
3
4 n
◦
◦
decomposition route at 500 C after 4h and Mn O NPs as black powder at 600 C after 6h. The
2
3
MOF of [Co (BDC) (DMF) (H O) ] was used as a precursor to produce Co O NPs at 400 and
3
3
2
2
2 n
3
4
◦
◦
−1
5
00 C for 4 h in air at a heating rate of 3 Cmin .
2

ACCEPTED MANUSCRIPT
Comparing the FT-IR spectra of the two MOFs with samples after heating confirms that the
templates have been completely destructed (Fig. 2S). Calcination of [Co (BDC) (DMF) (H O) ]
2 n
3
3
2
2
o
MOF at 400 or 500 C indicates only two characteristic strong absorption bands at about 663.47
−
1
and 572.82 cm which are assigned to the Co-O stretching providing clear evidence for the
presence of the crystalline spinel-type Co O4 structure [15]. After calcination of
3
o
[
Mn (BDC) (DMF) ] MOF at 500 C for 4h, three absorption peaks were observed at 400 to
3
3
4 n
-1
-1
6
50 cm . The vibration frequency at 639 cm is characteristic of Mn–O stretching modes in
-1
tetrahedral sites whereas vibration frequency at 533 cm corresponds to the distortion vibration
of Mn–O in an octahedral environment. The third vibration band, located at a weaker
-1
3+
wavenumber, 421 cm , can be attributed to the vibration of manganese species (Mn ) in an
o
octahedral site [16]. In calcinated [Mn (BDC) (DMF) ] MOF at 600 C for 6h, absorption peaks
3
3
4 n
-1
around 450-700 cm correspond to Mn–O bending vibrations [17]. Moreover, the broad band
-1
-1
about 3400 cm and the narrow one about 1650 cm correspond to the O-H vibrating mode of
-1
the adsorbed water in samples. The fingerprints of IR absorption at 400 to 700 cm for prepared
samples confirmed metal-oxides formation by thermal decomposition MOFs templates.
The crystalline phase purity of the NPs was confirmed by powder XRD analysis. The
◦
XRD patterns of manganese oxide NPs indicated that calcinated sample at temperature of 500 C
◦
has different crystallinity phase in comparison with calcinated sample at 600 C (Fig. 1 (a) and
◦
(
b)). The diffraction peaks of sample which was calcinated at 500 C can be indexed to pure
tetragonal phase of Hausmannite Mn O with the lattice parameters of a = 5.76, b= 5.76 and c=
3
4
9
.44 Å, Z = 4 and S.G= I41/amd which are in JCPDS card file No. 24-0734 (Fig. 3S). The
◦
diffraction peaks of sample which was calcinated at 600 C can be indexed to pure Cubic phase
of Bixbyite Mn O with the lattice parameters of a = 9.41 Å, Z = 16 and S.G= Ia3 which are in
2
3
JCPDS card file No. 10-0069 (Fig. 4S). The SEM images of prepared samples demonstrate that
NPs have spherical shapes (Fig. 2). The average size of the particles calculated by the Scherer
formula was 60 nm for Mn O (main (211) diffraction peak) and 80 nm for Mn O (main (222)
3
4
2
3
diffraction peak) which are in agreement with TEM images (Fig. 3, c-f). As it is clearly
noticeable in TEM images of Mn O , these NPs are agglomerated which can be achieved by the
2
3
MOF route as Xu et al. revealed [18].
3

ACCEPTED MANUSCRIPT
◦
The XRD patterns of cobalt oxide NPs indicated that calcinated sample at 500 C shows similar
◦
crystallinity with calcinated samples at 400 C. The sharp peaks and higher signal to noise ratio
indicate that the as-prepared Co O NPs are highly crystalline which can be further confirmed by
3
4
the SEM images (Fig. 2). All the diffraction peaks of samples can be indexed to pure cubic
spinel phase of Co O with the lattice parameters of a = 8.0837Å, Z = 8 and S.G= Fd3m with
3
4
3+
2+
octahedrally coordinated Co and tetrahedrally coordinated Co which are in JCPDS card file
No. 42-1467 (Fig. 5S). No impurity characteristic peaks related to CoO and Co O phases were
2
3
detected. The SEM images of prepared samples show that Co O NPs have uniform fine
3
4
spherical shapes. The particles size of the prepared sample were found to be about 40 nm which
was calculated through the major (222) diffraction peak using the Debye Scherrer approximation
which are in agreement with TEM images (Fig. 3, a, b).
The catalytic potential of NPs was examined in the olefins oxidation in the presence of tert-
buthylhydroperoxide (TBHP). In order to choose a suitable solvent, the oxidation of cyclooctene
(as a model substrate) was carried out in dichloromethane, chloroform, acetonitrile, acetone,
methanol and a mixture of CH OH/CH Cl (1:1). The results demonstrated that CH CN was a
3
2
2
3
more efficient solvent and Mn O NPs are not as efficient as Co O and Mn O NPs (Table 1S). It
2
3
3
4
3
4
seems that the oxidation state of Mn could play a key role in determining the catalytic behavior
of the manganese oxide species. This can well account for the superiority of Mn(II) in
comparison with other manganese oxidation states [19]. Aromatic and aliphatic alkenes react
with TBHP to produce the corresponding epoxides and/or oxides (Table 1) in the presence of
spinel type nanocatalysts. The catalytic oxidation reaction shows that nanocatalysts are superior
for oxidation of cyclic (entry 1, 2) and aromatic olefins (entries 3-5) with good yield and
moderate selectivity but are not efficient for oxidation of linear olefins (entry 6, 7).
The study on the catalytic activity of parent MOFs ([Mn (BDC) (DMF) ] and
3
3
4 n
[
Co (BDC) (DMF) (H O) ] ) and obtained Mn O and Co O NPs reveal that the extended
3 3 2 2 2 n 3 4 3 4
structure and steric effects of MOFs make them weak catalysts compared to NPs. The results of
olefin oxidations confirm that NPs are superior in conversion and catalytic reaction time [13, 14].
Since cyclohexene is a substrate that is particularly prone to allylic oxidation, its oxidation was
studied in the presence of Co O and Mn O NPs to pursue the catalytic mechanism. The
3
4
3
4
catalytic oxidation of cyclohexene, provided 2-cyclohexene-1-ol (80% for Co O and 88% for
3
4
4

ACCEPTED MANUSCRIPT
Mn O NPs) in 95% and 90% conversion, respectively (Table 2, entry 2). Also, oxidation of
3
4
styrene in the presence of Co O and Mn O nanocatalysts, involves C=C bond breaking,
3
4
3
4
yielding styrene oxide (65 and 61%) with benzaldehyde (35 and 39%) (Table 1, entry 3). These
oxidation products firmly imply a dominant radical pathway for this oxidation reaction, as was
expected on the basis of other Mn(II) or Co(II) heterogeneous catalysts [13, 14, 19, 20]. To probe
into the in situ formation of radical species in the oxidation reaction, ionol (2,6-di-tertbutyl-p-
cresol) was utilized as a radical scavenger in the oxidation of styrene and cyclohexene. Oxidation
was thoroughly inhibited in the presence of ionol which confirmed the formation of a radical
intermediate in the reaction pathway. Probably, the Mn(II) and Co(II) catalyze homolytic O–O
.
bond cleavage in t-BuOOH and alkoxy (t-BuO ) radicals which are produced start the oxidation
reaction. In the end, the olefin is oxidized to corresponding oxide/epoxide products.
The recyclability of the Mn O and Co O NPs catalysts was investigated in oxidation reaction of
3
4
3
4
o
cyclooctene in the presence of TBHP in CH CN at 75 C for 7 h. After the first catalytic reaction,
3
the solid catalyst was easily isolated by centrifuge and recovered by being washed with solvent
o
and dried at 70 C and used for the next run under the same reaction condition as the first run.
The Co O NPs could well be recycled for nine cycles with no significant loss in activity and
3
4
selectivity. During reusability studies, ninth run provided 88% conversion and 90% selectivity in
favor of cyclooctene epoxide. The Mn O NPs could be recycled four cycles with no significant
3
4
loss in activity and selectivity (Table 2). Therefore, Co O NPs are more efficient from
3
4
reusability point of view.
The XRD patterns and IR spectroscopy showed that the catalysts have nearly identical peaks
before and after catalytic reaction (Fig. 3, d, e and Fig. 2S, f, g), indicating that the basic lattice
structures of these NPs were well maintained after catalysis. The amount of solved Co and Mn
was found to be less than 1% by ICP analysis. This suggests that there is almost no Co and Mn
in the liquid phase from these catalysts and the nature of catalytic reactions is heterogeneous.
Co O , Mn O and Mn O NPs have been prepared by solid-state thermal decomposition from
3
4
3
4
2
3
manganese and cobalt-terephthalate Metal Organic Frameworks by heating at 400, 500 and 600
o
C. This synthetic route is a simple method for the preparation of uniform and high pure Co O ,
3
4
Mn O and Mn O NPs with average size of 40, 60 and 80 nm respectively. The results of
3
4
2
3
catalytic study exhibited that prepared NPs are active and selective heterogeneous catalysts for
5

ACCEPTED MANUSCRIPT
olefins oxidation with the TBHP oxidizing agent in acetonitrile solvent. Co O and Mn O NPs
3
4
3
4
can simultaneously provide high activity and selectivity to epoxide, easy separation of catalyst
and appropriate performance in the recycling reaction. It was found that Co O presented
3
4
superior performance to Mn O and Mn O in oxidation reaction in the case of reusability.
3
4
2
3
Acknowledgement
Authors acknowledge research council of Pharmaceutical Sciences Branch, Islamic Azad
University (F.A) and Sharif University of Technology (M.B) for the research funding of this
project.
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Fig. 1. XRD pattern of prepared Mn O (a), Mn O (b), Co O (c) fresh nanoparticles and Mn O
4
3
4
2
3
3
4
3
after fourth run (d) and Co O after ninth run (e) in catalytic cyclooctene oxidation.
3
4
9

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Fig. 2. SEM images of Co O (a, b), Mn O (c, d) and Mn O (e-h) prepared nanoparticles.
3
4
3
4
2
3
Fig. 3.TEM images of Co O (a, b), Mn O (c, d) and Mn O (e, f) nanoparticles.
3
4
3
4
2
3
1
0

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a
Table 1. Oxidation of olefins catalyzed by metal-oxide nanoparticles .
b
c
Entry
1
Substrate
Catalyst
Conversion
%)
Selectivity
(
(%)
95
95
86
cyclooctene
Co O4
98
95
3
Mn O4
3
d
[
3
Mn (BDC) (DMF) ]
66
67
3
3
4 n
e
[
Co (BDC) (DMF) (H O) ]
100
3
2
2
2 n
f
2
3
4
cyclohexene
styrene
Co O4
95
90
15 (80)f
10 (88)
3
Mn O4
3
Co O4
92
85
65
61
3
Mn O4
3
trans-
stylbene
Co O4
80
75
100
100
3
Mn O4
3
5
6
7
Indene
1-heptene
1-decene
Co O4
65
60
100
100
3
Mn O4
3
Co O4
17
12
100
100
3
Mn O4
3
Co O4
15
10
100
100
3
Mn O4
3
a
o
Reaction condition: The reactions were run in CH CN(2 mL) at 75 C for 7 h by amount of 0.01 mmol
3
catalyst, 1 mmol chlorobenzene, 1 mmol substrate and 1mmol TBHP. The molar ratio for catalyst:
substrate: TBHP is 1: 100: 100.
b
Conversion determined by GC based of chlorobenzene as internal standard.
c
Selectivity (%) to epoxide.
Reaction in 1,2-dichloroethane for 9 h [13].
Reaction in 1,2-dichloroethane for 7 h [14].
d
e
f
Selectivity (%) to cyclohexene-1-ol as a main product.
a
Table 2. Reusability investigation of nanoparticles catalyst in oxidation of cyclooctene by TBHP .
b
c
Entry
Run 1
Catalyst (NPs)
Mn O
Time (h) Conversion (%) Selectivity (%)
7
7
7
7
7
7
95
98
100
100
95
95
95
93
95
94
95
3
4
4
4
Co O
3
4
Run 2
Run 3
Mn O
3
Co O
3
4
Mn O
3
Co O
100
3
4
1
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Run 4
Mn O
7
6
6
6
7
6
6
85
98
92
100
99
92
92
93
94
95
94
92
90
3
4
Co O
3
4
Run 5
Run 6
Run 7
Run 8
Run 9
Co O
3
4
Co O
3
4
4
4
4
Co O
3
Co O
3
Co O
88
3
a
Reaction condition: same as Table 1.The molar ratio for catalyst: cyclooctene: TBHP is 1: 100: 100.
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Graphical abstract: Synopsis
Manganese and Cobalt-terephthalate Metal-Organic Frameworks as a Precursor for
Synthesis of Mn O , Mn O and Co O Nanoparticles: Active Catalysts for Olefin
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Heterogeneous Oxidation
Fatemeh Ashouri, Maryam Zare, Mojtaba Bagherzadeh,
Spinel structured Mn O and Co O and Mn O nanoparticles were prepared by thermal
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decomposition of manganese and cobalt-terephthalate Metal-Organic Framework (MOF)
o
precursor at 400, 500 and 600 C. Scanning electron microscopy, transmission electron
microscopy, Fourier transform infrared and X-ray diffraction spectrometry were used to
characterize the phase and the morphology of the metal oxide nanoparticles. Characterization of
prepared nanoparticles were indicate that these nanoparticles have average size diameter 60, 40
and 80 nm for Mn O , Co O and Mn O respectively. Catalytic efficacy of Mn O and Co O
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nanoparticles were evaluated in the epoxidation of a variety of alkenes using tert-butyl
hydroperoxide as an oxidant. In addition, metal oxide nanoparticles exhibited excellent catalytic
stability in several runs, demonstrating that these heterogeneous and recyclable catalysts are
promising for olefin epoxidation.
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Highlights
►
Co O , Mn O and Mn O nanoparticles (NPs) were prepared by hydrothermal decomposition
3 4 3 4 2 3
of [Co (BDC) (DMF) (H O) ] and [Mn (BDC) (DMF) ] MOFs.
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2 n
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4 n
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These NPs exhibit excellent catalytic activity and stability in olefins oxidation.
High activity and selectivity to epoxide, easy separation and appropriate performance in the
recycling reaction, make these NPs valuable.
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