Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted phosphomolybdic acid on SBA-15

Article abstract of DOI:10.1016/j.cattod.2015.04.042

A series of polyoxometalate-based heterogeneous catalysts were prepared by immobilized transition metal mono-substituted phosphomolybdic acids (PMo₁₁M, M = Fe, Co or Cu) or unsubstituted phosphomolybdic acid (PMo₁₂) on amino-functionalized SBA-15. A variety of characterization results demonstrated that the PMo₁₁M units are uniformly dispersed on the surface or in the channels of mesoporous SBA-15. The catalytic properties of these hybrid materials (denoted as PMo₁₁M/SBA or PMo₁₂/SBA) were investigated in the epoxidation of olefins with molecular oxygen as oxidant and isobutyraldehyde as co-reagent. It has been found that PMo₁₁Co/SBA and PMo₁₁Cu/SBA are catalytically active for the epoxidation of cyclooctene with acetonitrile as solvent, while PMo₁₁Fe/SBA and PMo₁₂/SBA are nearly inactive under the same reaction conditions. Moreover, the relatively active PMo₁₁Co/SBA catalyst could also efficiently convert cyclohexene and 1-octene to the corresponding epoxides, and its catalytic activity was solvent dependent. Using suitable solvent like acetonitrile could efficiently inhibit the deactivation of the catalyst, thus bringing excellent stability and recyclability for the PMo₁₁Co/SBA catalyst.

Full text of DOI:10.1016/j.cattod.2015.04.042

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Epoxidation of olefins with oxygen/isobutyraldehyde over
transition-metal-substituted phosphomolybdic acid on SBA-15
Xiaojing Songa, Wanchun Zhua, Kaige Lia, Jing Wanga, Huiling Niua, Hongcheng Gaoa,
Wenxiu Gaoa, Wenxiang Zhanga, Jihong Yub, Mingjun Jiaa,∗
a Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University, 130021 Changchun, China
b State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of polyoxometalate-based heterogeneous catalysts were prepared by immobilized transi-
tion metal mono-substituted phosphomolybdic acids (PMo11M, M = Fe, Co or Cu) or unsubstituted
phosphomolybdic acid (PMo12) on amino-functionalized SBA-15. A variety of characterization results
demonstrated that the PMo11M units are uniformly dispersed on the surface or in the channels of meso-
porous SBA-15. The catalytic properties of these hybrid materials (denoted as PMo11M/SBA or PMo12/SBA)
were investigated in the epoxidation of olefins with molecular oxygen as oxidant and isobutyraldehyde
as co-reagent. It has been found that PMo11Co/SBA and PMo11Cu/SBA are catalytically active for the epox-
idation of cyclooctene with acetonitrile as solvent, while PMo11Fe/SBA and PMo12/SBA are nearly inactive
under the same reaction conditions. Moreover, the relatively active PMo11Co/SBA catalyst could also effi-
ciently convert cyclohexene and 1-octene to the corresponding epoxides, and its catalytic activity was
solvent dependent. Using suitable solvent like acetonitrile could efficiently inhibit the deactivation of the
catalyst, thus bringing excellent stability and recyclability for the PMo11Co/SBA catalyst.
Received 28 February 2015
Received in revised form 27 April 2015
Accepted 28 April 2015
Available online xxx
Keywords:
Transition metal
Phosphomolybdic acid
Olefin
SBA-15
Epoxidation
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
separation and recycling problems of the homogeneous catalysts,
recent efforts were mainly focused on preparing efficient heteroge-
The epoxidation of olefins is an industrially important process
since epoxides are widely used as key intermediates in organic syn-
thesis [1–3]. Recently, considerable interests have been drawn on
studying the aerobic epoxidation of olefins for developing more
efficient and environmentally benign route [4–7]. It was reported
that aerobic epoxidation of olefins in solution can be efficiently
achieved under quite mild conditions over some transition metal
complexes by using molecular oxygen as oxidant and aliphatic
aldehyde as co-reactant, which is the so-called “Mukaiyama” pro-
cedure [8–13]. Although the usage of co-reactant aldehyde is
undesirable, the Mukaiyama method is still worthy of studying for
its great advantages, such as very mild operation conditions (low
temperatures, atmospheric pressure), high epoxide selectivity, low
cost and environmental-friendly nature of the oxidant [11–13].
In general, Mukaiyama epoxidation could be catalyzed by using
some homogeneous transition metal complexes like ␤-diketonate
complexes, Schiff’s base complexes, metal cyclam complexes
and metalloporphyrins complexes [8–13]. For overcoming the
neous catalysts [14–23]. Representative catalysts include various
transition metal complexes supported on porous materials, Co-
containing zeolitic imidazolate framework material, Cu/Ga-based
metal-organic framework (MOF) and so on [14–23]. However, in
most cases, either the catalytic activity or the selectivity to epoxide
of these heterogeneous catalysts is still not very satisfied. Moreover,
leaching of active species during the reaction course is commonly
occurred. Therefore, it is still an attractive subject to develop more
efficient heterogeneous catalysts for Mukaiyama epoxidation.
As an important catalyst system in selective oxidation, poly-
oxometalate (POM) including various transition metal-substituted
phosphomolybdate, has shown numerous advantageous proper-
ties, such as thermodynamic stability to oxidation, hydrostability,
tunability of redox and acid properties [24–30]. By immobi-
lizing various POMs on different supports like oxides, zeolites,
carbons etc., some highly efficient POM-based heterogeneous
catalysts have already been obtained for important catalytic oxi-
dation reactions [31–37]. Particularly, it was reported that a few
supported POM catalysts can also catalyze the aerobic epox-
idation of olefins in the presence of aldehydes. For instance,
Johnson and Stein [24] reported amine-modified silica supported
Co- and Zn-substituted phosphotungstates or silicotungstates are
∗
Corresponding author. Tel.: +86 431 85155390; fax: +86 431 85168420.
E-mail address: jiamj@jlu.edu.cn (M. Jia).
http://dx.doi.org/10.1016/j.cattod.2015.04.042
0920-5861/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: X. Song, et al., Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted
phosphomolybdic acid on SBA-15, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.042

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active catalysts for the aerobic epoxidation of cyclohexene in
the presence of isobutyraldehyde (IBA). Kholdeeva and coauthors
[25] found that amine-modified mesoporous silicate supported
[Bu4N]4H[PW11Co(H2O)O39] can efficiently catalyze the aerobic
oxidation of ␣-pinene to epoxide with IBA as co-reactant. Concern-
ing the diversity of POM in composition, structure and property,
one can expect that there will be very broad space for developing
more efficient heterogeneous POM-based catalysts for Mukaiyama
epoxidation reactions.
techniques [44]. About 1.0 g SBA-15 was treated at 150 ◦C for 2 h
under vacuum. About 30 ml dry toluene was added into the flask
quickly, then 2 mmol 3-aminopropyltriethoxysilane (APTES) was
added into the suspension under N2 protection and refluxed at
110 ◦C for 24 h. Afterwards, the solid was filtered and washed
with toluene and anhydrous ethanol for several times. Finally, the
solid was extracted using a Soxhlet 24 h with dichloroethane and
dried in vacuum overnight. The resulting material was denoted as
NH2-SBA-15.
Previously, our group has already carried out some works on
preparing various POM-based heterogeneous catalysts for olefin
epoxidation with tert-butyl hydroperoxide or H2O2 as oxidants
[38–41]. As a continuation of these works, we here tried to immobi-
lize a series of transition metal-substituted phosphomolybdic acids
on to NH2-modified SBA-15 (denoted as PMo11M/SBA, M = Co, Cu,
Fe) and to test their catalytic performance for the aerobic epoxida-
tion of olefins in the presence of IBA. It was found that supported
Co-substituted phosphomolybdate catalyst can efficiently catalyze
a variety of olefins to corresponding epoxides, and can also be easily
recycled for a few times without obvious loss in its catalytic activity.
2.1.3. Immobilization of PMo11M (M = Fe, Co, Cu) on NH2-SBA-15
A certain quality of NH2-SBA-15 was added into a 30 ml
methanol solution containing some amount of PMo11M (M = Fe, Co,
Cu), and refluxed for 6 h. It was then filtered and Soxhleted for 24 h
with methanol and dried in vacuum at 80 ◦C. The resulting product
is designated as PMo11M/SBA (M = Fe, Co, Cu). For comparison, a
reference catalyst of PMo12/SBA was also prepared by immobiliz-
ing commercial phosphomolybdic acids (PMo12) on NH2-SBA-15.
The loading of PMo11M (or PMo12) in the supported catalysts
was determined by inductively coupled plasma-optical emission
spectroscopy (ICP-AES), and the concreted values are given in
Table 1.
2. Experimental
2.1. Catalyst preparation
2.2. Catalysts characterization
2.1.1. Preparation of transition metal mon-substituted
phosphomolybdic acids
Powder X-ray diffraction (XRD) patterns were recorded on a Shi-
madzu XRD-6000 diffractometer (40 kV, 30 mA), using Ni-filtered
Cu K␣ radiation.
Transition metal (Fe, Co, Cu) mon-substituted phosphomolyb-
dic acids were prepared according to a literature procedure
for the preparation of molybdovanadophosphoric acids [42].
Na2HPO4·12H2O (0.01 mol) was dissolved in 20 ml of water and
mixed with nitrates of corresponding metal (0.01 mol) that had
been dissolved by boiling in 20 ml of water. The mixture was cooled
and acidified with 1.0 ml of concentrated sulfuric acid. To this mix-
ture a solution of 0.11 mol of Na2MoO4·2H2O dissolved in 40 ml of
water was added, large amount of flocculent precipitate appeared.
After that, some amount of concentrated sulfuric acid was added
slowly with vigorous stirring until it turned to a clear solution. The
heteropoly acid was then extracted with 400 ml of ethyl ether after
the water solution was cooled. In this extraction, the heteropoly
etherate was present as a bottom layer. After separation, a stream
of air was passed through the heteropoly etherate layer to free
it of ether. The green-yellow solid that remained was dissolved
in 50 ml of water, concentrated to the first appearance of crys-
tals in a vacuum desiccator over concentrated sulfuric acid, and
then allowed to crystallize further. Finally, H6PMo11FeO40·xH2O,
H7PMo11CoO40·xH2O and H7PMo11CuO40·xH2O were obtained, and
denoted as PMo11M (M = Fe, Co, Cu) hereafter. The calculated ana-
lytic values (at.%) presented below, all the relative errors were
within the scope permitted: PMo11Fe [P (7.19%) Mo (85.39%) Fe
(7.42%)]; PMo11Co [P (7.32%) Mo (81.45%) Co (6.98%)]; PMo11Cu [P
(8.26%) Mo (85.45%) Cu (7.95%)].
FT-IR spectra were recorded on a Nicolet AVATAR 370 DTGS
spectrometer in the range 4000–500 cm−1
.
N2 adsorption/desorption isotherms were measured at 77 K
using Micromeritics ASAP 2010 N analyzer. Samples were
a
degassed at 150 ◦C for 8 h before measurements. Specific surface
areas were calculated using BET model. Pore volumes are estimated
at a relative pressure of 0.94 (P/P0), assuming full surface saturation
with nitrogen. Pore size distributions are evaluated from desorp-
tion branches of the nitrogen isotherms using the BJH model.
Transmission electron microscopy (TEM) images were taken
with a H8100-IV electron microscope with an energy-dispersive
X-ray spectroscopy (EDX) operating at 200 kV. The samples were
suspended in ethanol by sonication and then picked up on a Cu grid
covered with a carbon film.
XPS measurements were made on a VGESCA LAB MK-II X-ray
electron spectrometer using Al K␣ radiation.
2.3. Catalyst test
The catalytic oxidation reaction was carried out in a 50 ml
three-necked bottle equipped with a stirring bar, reflux condenser,
and gas supply. Solvent, olefin, IBA and catalyst were added into
the flask respectively, and the whole device was placed in a
temperature-controlled oil bath. To commence the reaction, oxy-
gen was passed through the reactor at a flow rate of 10 ml/min−1
under atmosphere. The oxidation products of the reaction were
analyzed and quantified by Shimadzu GC-8A gas chromatograph
with HP-5 capillary column.
2.1.2. Preparation of amine-functionalized of SBA-15
SBA-15 was prepared according to the literature method
[43]. Functionalization of SBA-15 was conducted with schrank
Table 1
Texture parameters of SBA-15, PMo12/SBA and PMo11M/SBA materials.
Catalyst
PMo11M (mmol/g)
Surface Area (m2/g)
Pore volume (cm3/g)
Average pore diameter (nm)
SBA-15
–
794
265
244
231
316
1.48
0.53
0.46
0.41
0.64
7.2
5.7
5.2
5.8
4.9
PMo12/SBA
PMo11Fe/SBA
PMo11Co/SBA
PMo11Cu/SBA
0.093
0.105
0.101
0.066
Please cite this article in press as: X. Song, et al., Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted
phosphomolybdic acid on SBA-15, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.042

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3. Results and discussion
3.1. Catalyst characterization
The XRD patterns of PMo11M/SBA (M = Fe, Co, Cu) catalysts
and unsupported PMo11M are shown in Fig. 1. Unsupported
PMo11M samples exhibit characteristic XRD peaks at 2ꢀ = 15 and
30◦ (Fig. 1A). Compared with PMo12, the slight changes in 2ꢀ values
of PMo11M (M = Fe, Co, Cu) should be related to the partial substitu-
tion of Mo by M, which are consistent to the early literature results
[45]. The low-angle XRD patterns of PMo11M/SBA catalysts are
shown in Fig. 1B. SBA-15 exhibits an intense peak assigned to reflec-
tions at (1 0 0) and two low-intensity peaks at (1 1 0) and (2 0 0),
indicating a significant degree of long-range ordering in the struc-
ture and a well-formed hexagonal lattice. The NH2-SBA-15 shows
quite similar diffraction peaks to SBA-15, although slight decrease
in intensity can be observed. For PMo11M/SBA and PMo12/SBA,
significant decrease in diffraction peak intensity is detected, indi-
cating that POM anions have been introduced into the channels
of SBA-15. From wide-angle XRD patterns of supported catalysts
(inset of Fig. 1B), all hybrid materials exhibit only one very broad
peak, which is a characteristic of amorphous materials. The absence
Fig. 2. FT-IR spectra of unsupported PMo11M and PMo12, as well as the SBA-15
supported POM catalysts.
of diffraction peaks of crystalline POM in the wide-angle region,
suggests that the introduced POM units are highly dispersed on
the surface and/or in the channel of the SBA-15 supports support
[31,46].
The FT-IR spectra of unsupported PMo11M and PMo12, as well as
the SBA-15 supported POM catalysts are shown in Fig. 2. Character-
istic bands of PMo12 appeared at 1046 cm−1, 959 cm−1, 872 cm−1
and 794 cm−1 can be assigned to the vibrations of P O, Mo = O,
Mo Ob Mo and Mo Oc Mo bonds, respectively [45]. For the three
PMo11M samples, the corresponding vibration bands shift slightly,
which is an indication of the distortion induced by the partial
replacement of Mo by M (M = Fe, Co, Cu). As shown in Fig. 2B, SBA-15
and NH2-SBA-15 exhibit a few strong absorbed bands in the region
of 2000–400 cm−1, which can be mainly assigned to the character-
istic vibrations of Si
O Si bonds. The spectra of the PMo11M/SBA
catalysts are quite similar to that of SBA-15 support. No obvious
characteristic peaks of POM units can be distinguished in the spec-
tra, which should be due to the overlap with the absorbed peaks of
SBA-15 support.
The nitrogen adsorption-desorption isotherms of SBA-15 and
PMo11M/SBA (M = Fe, Co, Cu) are shown in Fig. 3. All the samples
displayed a type IV isotherm according to the IUPAC classification.
The appearance of H1 hysteresis loop is a characteristic of meso-
porous materials and the capillary condensation occurs at relative
pressure (P/P0) of 0.45–0.85. Compared with the support SBA-15,
there are pronounced decrease of the BET surface area, the pore
volume, and the pore size in the SBA-15 supported POM catalysts
Fig. 1. XRD patterns of (A) unsupported PMo11M and (B) supported PMo11M/SBA
(M = Mo, Fe, Co, Cu) catalysts.
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phosphomolybdic acid on SBA-15, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.042

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Fig. 3. N2 adsorption-desorption isotherms and pore size distribution of materials (A) SBA-15, (B) PMo11Fe/SBA, (C) PMo11Co/SBA, and (D) PMo11Cu/SBA.
(as shown in Table 1), which could be attributed to the introduction
of PMo11M.
(64% after 3 h) is achieved over the PMo11Co/SBA catalyst, indicat-
ing the solvent-dependent of this epoxidation reaction. Besides, all
catalysts exhibit very high selectivity to epoxide (>99%), and no
detectable side products are observed under the test conditions.
The recycling experiments of PMo11Co/SBA for the aerobic epox-
idation of cyclooctene were carried out with CH3CN as the solvent.
After each experiment, the filtrate catalyst was washed with CH3CN
and dried under vacuum, then reused without further treatment.
As shown in Fig. 6, PMo11Co/SBA shows very good recyclability, no
obvious loss in activity could be observed with the increase of recy-
cle numbers. In addition, a leaching test was conducted to verify the
heterogeneity of the catalytic process. It has been found that there
is no significant increase of conversion of cyclooctene after remov-
ing the PMo11Co/SBA catalyst by filtration at reaction temperature,
indicating the truly heterogeneous catalysis of the catalyst.
TEM images of the SBA-15, NH2-SBA-15, PMo11Fe/SBA and
PMo11Co/SBA are shown in Fig. 4. The results confirm the char-
acteristic pore dimensions and channel structures of the support
materials, and provide strong evidence that the mesoporous struc-
ture of SBA-15 supports remains intact after the introduction of
POM units.
XPS spectra of Mo 3d for PMo12/SBA and PMo11M/SBA (M = Fe,
Co, Cu) are shown in Fig. 5. PMo12/SBA displays characteristic 236.3
and 233.2 eV, which are attributed to Mo(VI) 3d3/2 and Mo(VI)
3d5/2, respectively [47]. For PMo11Fe/SBA and PMo11Co/SBA, there
are no obvious changes in the values of the binding energy (BE)
of Mo species in comparison with that of PMo12/SBA. As for
PMo11Cu/SBA, slightly lower binding energy of Mo species could
be detected. Apparently, the chemical states of Mo species in all
the PMo11M/SBA catalysts are quite similar. This might be due to
the fact that only a small portion of Mo species in the POM clusters
are substituted by transition metal ions.
Previously, mechanistic studies on the Mukaiyama epoxidation
of olefins have revealed that this reaction proceeds mainly through
a radical pathway [15,24]. The active epoxidizing species are acyl
peroxy radicals, which are produced from the decomposition of
acyl peroxy acid (formed from the autoxidation of aldehyde) over
3.2. Catalytic results
Table 2
Catalytic properties of PMo11M/SBA (M = Fe, Co, Cu) and PMo12/SBA in the aerobic
The catalytic properties of PMo11M/SBA (M = Fe, Co, Cu) and
PMo12/SBA catalysts were investigated for the aerobic epoxidation
of olefins with CH3CN or CHCl3 as solvent and isobutyraldehyde
as co-reagent (Table 2). When using acetonitrile (CH3CN) as sol-
vent, PMo11Co/SBA gives 98% of conversion of cyclooctene after 3 h
and performs the highest catalytic activity among the test catalysts.
Catalyst PMo11Cu/SBA shows a lower activity, 76.9% of conver-
sion is obtained after 3 h reaction. Notably, both PMo11Fe/SBA
and PMo12/SBA are nearly inactive for the aerobic epoxidation
of cyclooctene, and no obvious conversion of cyclooctene can be
detected under the test conditions. In the case of using chloro-
form (CHCl3) as solvent, relatively low conversion of cyclooctene
epoxidation of cyclooctene with IBA as co-reactant.a
Catalyst
Solvent
CH3CN
Time (h)
Conversion (%)
Selectivity (%)
>99
PMo11Co/SBA
1
3
1
3
1
3
3
3
43
98
15
64
6
76
<1
<1
CHCl3
>99
>99
PMo11Cu/SBA
CH3CN
PMo11Fe/SBA
PMo12/SBA
CH3CN
CH3CN
–
–
a
Reaction conditions: catalyst 10 mg, cyclooctene 1.0 mmol, CH3CN 10 ml, flow
of air 10 ml/min, IBA 2.0 mmol, reaction temperature 40 ◦C.
Please cite this article in press as: X. Song, et al., Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted
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Fig. 4. TEM for (A) SBA-15, (B) NH2-SBA-15, (C) PMo11Fe/SBA, and (D) PMo11Co/SBA.
catalyst. Therefore, the difference in catalytic activity of the differ-
ent PMo11M/SBA (M = Fe, Co, Cu) catalysts should originate from
the different activation ability of the transition metal cations to
form acyl peroxy radicals. Besides, their catalytic properties may
also reflect the ability of metal cations against complex reagents
(e.g., poisoned by acyl peroxy acid). The relatively high activity
of Co-based catalyst (PMo11Co/SBA) suggests that Co ions should
be the main active sites for decomposing acyl peroxy acids to
form acyl peroxy radicals. On other hand, the very poor activity of
PMo11Fe/SBA catalyst may be indicative that Fe species can strongly
coordinate with acyl peroxy acid to form the stable complexes that
inhibited the further oxidation of olefins [48].
Fig. 6. Recycling experiments of PMo11Co/SBA catalyst in the aerobic oxidation
of cyclooctene. Reaction conditions: catalyst 10 mg, cyclooctene 1.0 mmol, CH3CN
10 ml, flow of air 10 ml/min, IBA 2.0 mmol, reaction temperature 40 ◦C, and reaction
time 3 h.
Fig. 5. XPS spectra of Mo (3d3/2) and Mo (3d5/2) for PMo11M/SBA catalysts.
Please cite this article in press as: X. Song, et al., Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted
phosphomolybdic acid on SBA-15, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.042

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suggest that the IBAc/CHCl3 treated PMo11Co/SBA catalyst is nearly
inactive for the aerobic epoxidation of cyclooctene with CHCl3 as
solvent, while its activity can be recovered after the catalyst is
washed with CH3CN and dried in the vacuum. These results suggest
that IBAc could strongly interact with Co species in the presence of
CHCl3 solvent, which might be the main reason for decreasing the
catalytic activity of PMo11Co/SBA. When using CH3CN as solvent,
the negative effect of IBAc on catalytic activity can be overcome,
possibly due to the fact that CH3CN could act as a competitive ligand
to coordinate with Co ions during the reaction course, thus avoid-
ing the deactivation/poison caused by strong coordination role of
IBAc [49].
The catalytic properties of PMo11Co/SBA catalysts were also
investigated in the epoxidation of cyclohexene with O2/IBA, since
cyclohexene is a good substrate to study the issue of selectiv-
ity control for the POM-based catalysts [24,41]. As shown in
Table 3, the aerobic epoxidation of cyclohexene in the pres-
ence of IBA easily occurs even without addition of catalysts,
and 17% conversion of cyclohexene is obtained with nearly
100% selectivity of epoxide in the blank test. Among the three
supported POM catalysts, the reactivity follows the order of
PMo11Co/SBA > PMo11Cu/SBA > PMo11Fe/SBA, which is in agree-
ment with the active order for cyclooctene epoxidation. In fact, the
catalytic activity of PMo11Fe/SBA catalyst is neglectable, since it
gives almost the same conversion as the blank reaction. The activi-
ties of PMo11Co/SBA and PMo11Cu/SBA are comparable with other
heterogeneous catalysts reported in literatures (the representative
results are also given in Table 3). In addition, small amount of
2-cyclohexene-1-one can be detected over the two PMo11M/SBA
catalysts, whereas the epoxide product is still the main product
Fig. 7. DRS-UV spectra of PMo11Co/SBA catalyst (a) fresh one, (b) treated with 0.3 M
IBAc in CH3CN, and (c) treated with 0.3 M IBAc in CHCl3.
In addition, our results have shown that changing the sol-
vents could also significantly influence the catalytic activity of
PMo11Co/SBA catalyst. Much lower activity in CHCl3 is obtained as
compared to CH3CN. In order to explain this phenomenon, DRS-
UV–vis study was carried out to characterize the PMo11Co/SBA
catalysts treated either by isobutyric acid (IBAc)/CH3CN or by
IBAc/CHCl3, following a literature reported method [25]. As shown
in Fig. 7, the position of the d–d transition bands of Co species in
the IBAc/CH3CN treated catalyst is quite similar to the fresh cata-
lyst, whereas the bands position for the IBAc/CHCl3 treated catalyst
shifts toward higher wavelength. Additional experimental results
Table 3
Comparison of the catalytic properties of PMo11M/SBA catalysts with other literature reported catalysts for the aerobic epoxidation cyclohexene with IBA as co-reagent.a
Catalyst
Temp (◦C)
Time (h)
Con (%)
Selectivity (%)
Epoxide
Related work
oneb
ol or diolc
None (blank)
PMo11Co/SBA
PMo11Cu/SBA
PMo11Fe/SBA
Co/ZIFd
40
40
40
40
30
60
25
40
4
4
4
4
3
16
9
7
17
81
70
18
100
93
>99
90
90
>99
70
68
nd
10
10
nd
30
nd
13
4.3
nd
nd
nd
nd
nd
32
nd
6.5
This work
This work
This work
This work
[14]
[19]
[21]
[23]
CoPO4-MOFd
CoTE3PyP/MTd
Cu@COMOC-4d
76
49
87
89
a
Reaction conditions in this work: catalyst 10 mg, cyclohexene 1.0 mmol, IBA 2.0 mmol, 10 ml of CH3CN, O2 1 atm.
2-Cyclohexen-1-one.
2-Cyclohexen-1-ol or 1,2-cyclohexanediol.
b
c
d
See related reference to check the concreted information on the catalyst and reaction conditions.
Table 4
Catalytic epoxidation of different olefins over PMo11Co/SBA catalyst with O2/IBA.a
Substrate
Time (h)
Conversation (%)
Selectivity (%)
Epoxide
Others (%)
7
1
93
89
>99
7
nd
77 (Pha)b 15 (Bza)c
0.3
5
39
65
65
76
34 (Ketone)
23 (Bza)c
a
Reaction conditions: catalyst 10 mg, olefin 1.0 mmol, CH3CN 10 ml, flow of air 10 ml/min, IBA 2.0 mmol, reaction temperature 40 ◦C.
Phenylacetaldehyde.
Benzaldehyde.
b
c
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(90% of epoxide selectivity). Notably, the epoxidizing selectiv-
ity of these two catalysts are equivalent to the montmorillonite
supported cobalt porphyrin catalyst (CoTE3PyP/MT) and the Ga-
based metal-organic framework (MOF) supported copper catalyst
(Cu@COMOC-4) [21,23], and much higher than other Co-based cat-
alysts like Co/ZIF and cobalt phosphonate-based MOF [14,19].
Moreover, the catalyst PMo11Co/SBA was also used to catalyze
the epoxidation of other olefins with O2/IBA. As shown in Table 4,
the relatively inert terminal olefin of 1-octene can also be con-
verted to epoxide rapidly, and a 98% conversion of 1-octene with
nearly 100% selectivity of epoxide is achieved after 3 h. Besides,
PMo11Co/SBA is also active for the epoxidation of styrene, ␣-methyl
styrene and trans-stilbene. However, relatively low epoxidizing
selectivity can be detected for these reactions. In these cases, alde-
hyde or ketone turns to the main product, and very high selectivity
to phenylacetaldehyde (77%) can be obtained for the oxidation of
styrene.
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4. Conclusions
In summary, hybrid heterogeneous catalysts for aerobic epox-
idation of olefins can be obtained by immobilizing transition
metal-substituted phosphomolybdic acids (PMo11M, M = Fe, Co, Cu)
on amino-functionalized SBA-15. The SBA-15 supported PMo11Co
catalyst exhibits relatively high catalytic activity and selectivity
for the epoxidation of cyclooctene, cyclohexene and 1-octene with
O2 as oxidant and IBA as co-reagent. Selecting suitable solvent of
acetonitrile can inhibit the deactivation of the catalyst, which can
significantly improve the recyclability and stability of the SBA-15
supported PMo11Co catalyst.
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Financial support from the National Natural Science Foundation
of China (No. 21173100 and 21320102001) is gratefully acknowl-
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Please cite this article in press as: X. Song, et al., Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted
phosphomolybdic acid on SBA-15, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.042