Co2 +-exchanged SAPO-5 and SAPO-34 as efficient heterogeneous catalysts for aerobic epoxidation of alkenes

Article abstract of DOI:10.1016/j.catcom.2012.11.011

Co-SAPO-5 and Co-SAPO-34 were prepared by a simple ion-exchange route and firstly applied in the aerobic epoxidation of alkenes. Both catalysts exhibited high activities in the epoxidation of alkenes with air to achieve 92.0-91.9 mol% conversion with the epoxide selectivity of 89.5-90.5% for styrene, 71.6-80.0 mol% conversion with 94.8-95.0% selectivity for α-pinene, and 95.3-96.8 mol% conversion with 75.2-73.6% selectivity for α-methyl styrene. Recycling studies and control experiments showed the recyclability and stability of Co-SAPO-5 and Co-SAPO-34 as heterogeneous catalysts.

Full text of DOI:10.1016/j.catcom.2012.11.011

Catalysis Communications 31 (2013) 42–47
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Co2+-exchanged SAPO-5 and SAPO-34 as efficient heterogeneous catalysts for aerobic
epoxidation of alkenes
B. Tang a,b, X.-H. Lu a,b, D. Zhou a,b, P. Tian c, Z.-H. Niu a,b, J.-L. Zhang a,b, X. Chen a,b, Q.-H. Xia a,b,
⁎
a
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, PR China
School of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062, PR China
b
c
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 June 2012
Received in revised form 10 September 2012
Accepted 9 November 2012
Available online 16 November 2012
Co-SAPO-5 and Co-SAPO-34 were prepared by a simple ion-exchange route and firstly applied in the aerobic
epoxidation of alkenes. Both catalysts exhibited high activities in the epoxidation of alkenes with air to
achieve 92.0–91.9 mol% conversion with the epoxide selectivity of 89.5–90.5% for styrene, 71.6–80.0 mol%
conversion with 94.8–95.0% selectivity for α-pinene, and 95.3–96.8 mol% conversion with 75.2–73.6% selec-
tivity for α-methyl styrene. Recycling studies and control experiments showed the recyclability and stability
of Co-SAPO-5 and Co-SAPO-34 as heterogeneous catalysts.
Keywords:
© 2012 Elsevier B.V. All rights reserved.
Alkene epoxidation
Co-SAPO-5
Co-SAPO-34
Air
1. Introduction
Sulfated Y-ZrO2 is as well active for the epoxidation of styrene with
molecular oxygen [23].
The selective oxidation of alkenes is of significant importance in the
fine chemicals and pharmaceutical industries, since epoxides are key
building blocks in organic synthesis [1–3]. Traditionally, epoxides are
produced by the epoxidation of alkenes with stoichiometric amount of
peracid as oxidant, which is hazardous and environmentally undesirable.
In order to overcome this disadvantage, some studies have been dedicat-
ed to the epoxidation of alkenes with organic oxidants (m-CPBA, CHP or
TBHP) or inorganic oxidants (H2O2, NaClO or O2) [4–10]. Among these
oxygen donors, molecular oxygen is the most desired oxidant with re-
spect to the economic consideration. This requires a scrutiny of potential
catalysts that can efficiently catalyze the epoxidation reactions, for triplet
ground state of O2 disfavors reactions with singlet organic compounds
[11–17].
It is well known that transition metal complexes, such as Schiff's
base complexes, metalloporphyrin complexes and metal cyclam com-
plexes, exhibit high activity for the aerobic epoxidation of alkenes
[18–20]. However, theses homogeneous catalysts prepared by rela-
tively complicated procedures are difficult to be recycled. Due to the
inherent advantages of heterogeneous catalysts over homogeneous
ones, a number of solid catalysts have been developed [21]. Simple
transition metal oxides like NiO, CoOx, MoO3 and CuO show high ac-
tivities for the selective epoxidation of styrene to styrene oxide [22].
Recently, molecular sieve materials as heterogeneous catalysts,
compared to other solid catalysts, have been a subject of growing inter-
ests in the epoxidation of alkenes, which exhibit superior catalytic per-
formance because of their open structures giving rise to high surface
areas with molecular sieving properties. Typically, the selective oxida-
tion of alkenes with oxygen/air have achieved encouraging results
over Co2+-exchanged faujasite-type zeolites [11], Co-X [12,14], Co-Y
[15], Co-SBA-15 [16], Co-ZSM-5, and Co-Beta [17]. During the last de-
cade, silico-aluminophosphate molecular sieve SAPO, have attracted
much attention because of their excellent catalytic performance for a
series of reactions, e.g. isomerization [24], methanol-to-hydrocarbons
(MTH) [25], methanol-to-olefins (MTO) [26], and gas separation [27].
Furthermore, Jasra et al. [28] recently reported cobalt substituted
SSZ-51 to catalyze the epoxidation of styrene with O2. However, there
is no report, to date, focusing on the epoxidation of alkenes with air
over SAPO molecular sieves. Herein, our new progress firstly shows
highly catalytic activities of Co2+-exchanged SAPO-5 (AFI) and
SAPO-34 (CHA) in the epoxidation of styrene, α-methyl styrene and
α-pinene with air.
2. Experimental
2.1. Preparation of catalysts
SAPO-5 was hydrothermally synthesized with a gel composition of
Al2O3: P2O5: x SiO2: 2 Et3N: 50 H2O according to the procedure de-
scribed in the literature [29]. As-synthesized materials, designed as
⁎
Corresponding author at: School of Chemistry and Chemical Engineering, Hubei Uni-
versity, Wuhan 430062, PR China. Tel./fax: +86 27 5086 5370.
E-mail address: xiaqh518@yahoo.com.cn (Q.-H. Xia).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.11.011

B. Tang et al. / Catalysis Communications 31 (2013) 42–47
43
SAPO-5 (x), where x stands for the content of silica ranging from 0.3
to 0.6, were calcined at 873 K for 10 h in the flow of air to remove or-
ganic templates totally. SAPO-34 was provided by Dalian Institute of
Chemical Physics, CAS.
(f)
(e)
Co2+ cations or other metal ions were introduced into molecular
sieves by an ion-exchange route, as described in the literature [17],
where the used amount of molecular sieves, transition metal salts and
distilled water were 5.0 g, 2.6 mmol and 250 ml, respectively. The transi-
tion metal salts included Co(Ac)2·4H2O, Zn(Ac)2·2H2O, Mn(Ac)2·4H2O,
Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Cr(NO3)3·9H2O, and Fe(NO3)3·9H2O.
The solid powder was recovered by filtration, washed several times
with hot distilled water until no acidic residue was detected, and
followed by drying at 373 K for 10 h. Additionally, in order to test
the effect of Co loading on the epoxidation activity, Co-SAPO-34
with the Co loading of 0.5–6.0 wt.% was also prepared using the
same procedure.
(d)
(c)
(b)
(a)
5
15
25
35
45
55
65
2Theta (degree)
2.2. Characterization of catalysts
Fig. 1. XRD patterns of (a) Co-SAPO-5 (0.3), (b) Co-SAPO-5 (0.4), (c) Co-SAPO-5 (0.5),
(d) Co-SAPO-5 (0.5) recovered after 5 cycles, (e) Co-SAPO-34, and (f) Co-SAPO-34 re-
covered after 5 cycles.
X-ray diffraction (XRD) patterns of samples were recorded on a
Rigaku D/MAX-IIIC diffractometer with CuKα radiation (λ=1.54184 Å)
from 2θ=5 to 65° with a scanning speed of 2.0°/min. BET surface areas
were obtained by means of nitrogen adsorption measurements
performed at 77.35 K on a Quantachrome Autosorb-3B instrument.
X-ray fluorescence (XRF) analyses (Co, Si, Al and P) were conducted
on a Shimadzu XRF-1800 spectrometer. The morphology and size of
crystals were imaged on a JEOL JSM-6510A scanning electron mi-
croscope (SEM).
Co-SAPO-34. One can note that there was a slight decrease in the surface
area of catalysts after ion-exchange treatment.
3.2. Catalytic epoxidation of styrene
3.2.1. Effect of Co-SAPO-5 and Co-SAPO-34
2.3. Catalytic reactions
The catalytic activities of ion-exchanged Co-SAPO-5 and Co-SAPO-34
for the epoxidation of styrene with air were listed in Table 2. Obviously,
SAPO-5 (0.5) and SAPO-34 obtained extremely low conversion of
4.2–3.9 mol%. Once cobalt was introduced into the frameworks of mo-
lecular sieves, highly catalytic performance was immediately bestowed,
e.g. Co-SAPO-34 and Co-SAPO-5 (0.5) obtained 91.9 mol% conversion
(90.5% selectivity) and 92.0 mol% conversion (89.5% selectivity), appre-
ciably higher than 78.8–87.5 mol% conversion (84.6–86.3% selectivity)
over Co-SAPO-5 (0.3) and Co-SAPO-5 (0.4); however, a further increase
of Si content led to the decrease of epoxide selectivity to 85.4% over
Co-SAPO-5 (0.6). In contrast, the catalytic activities of other metal ion
(Zn2+, Mn2+, Ni2+, Cu2+, Cr3+, and Fe3+) exchanged SAPO-34 were
much low, with b15.9 mol% conversion and b79.9% selectivity, which
could be explained by the difference of the ability to activate molecular
oxygen. Our previous studies by means of UV spectrum and cyclic
Prior to use, all the solvents underwent redistillation treatment.
The aerobic epoxidation of alkenes was performed in a 50-ml two
necked round-bottom glass flask equipped with a cryogenic-liquid
condenser under atmospheric pressure. Typically, 3.0 mmol of al-
kene, 10.0 g of solvent and 0.1 g of catalyst were added to the reactor
and mixed vigorously by a magnetic stirrer, followed by addition of
0.3 mmol of initiator. Then, the mixture was heated to 363 K, while
air (40 ml/min) was bubbled to the bottom of reactor. After the com-
pletion of the reaction, the liquid products were separated by centri-
fugation and analyzed by a gas chromatograph equipped with a
capillary column (SE-30, 30 m×0.25 mm×0.25 μm) and an FID de-
tector, where chlorobenzene was used as an internal standard to
quantify all the components.
3. Results and discussion
3.1. Characterization of catalysts
The XRD patterns of different ion-exchanged SAPO-5 and SAPO-34
have been shown in Figs. 1 and 2, which indicate the maintenance of typ-
ical topologies after ion-exchange treatments as compared to those of
parent samples (Supplementary data Fig. S1). The diffraction patterns
of Co-SAPO-5 showed the characteristics of highly crystalline materials,
with the reflections at 2θ values 7.4, 12.9, 14.9, 19.7, 21.0, 22.4, and
25.9, in the range of 5–30°, typical of SAPO-5 molecular sieve. Typical dif-
fraction lines of transition metal ion exchanged SAPO-34 corresponding
to the CHA structure were also observed. The scanning electron micro-
graphs of catalysts were shown in Fig. 3, which indicated that the mor-
phology of catalysts was still similar to that of parent molecular sieves
after ion-exchange treatment, in agreement with the changes revealed
by X-ray diffractions. Co-SAPO-5 (0.5) contained irregular crystal parti-
cles with the size of 0.6–5.0 μm, while Co-SAPO-34 exhibited cubic crys-
tals with the size of 4.0–10.1 μm. As listed in Table 1, BET specific surface
areas and cobalt contents were determined to be 189–215 m2/g at
0.38–0.45 wt.% Co for Co-SAPO-5, and 546 m2/g at 2.16 wt.% Co for
(f)
(e)
(d)
(c)
(b)
(a)
5
15
25
35
45
55
65
2Theta (degree)
Fig. 2. XRD patterns of (a) Cr-SAPO-34, (b) Mn-SAPO-34, (c) Fe-SAPO-34, (d) Ni-SAPO-34,
(e) Cu-SAPO-34, and (f) Zn-SAPO-34.

44
B. Tang et al. / Catalysis Communications 31 (2013) 42–47
Fig. 3. SEM images of (a) SAPO-5, (b) Co-SAPO-5 (0.3), (c) Co-SAPO-5 (0.4), (d) Co-SAPO-5 (0.5), (e) SAPO-34, and (f) Co-SAPO-34.
Table 2
Epoxidation of styrene with air over various SAPO catalysts.
Catalyst
Conv. (mol%)
Selectivity (%)
Epoxide
Table 1
Ben.
Phen.
Physicochemical characterization of molecular sieves catalysts.
SAPO-5 (0.5)a
SAPO-34
4.2
3.9
71.6
75.7
84.6
86.3
89.5
85.4
90.5
77.0
76.9
79.9
75.3
75.6
78.0
28.4
11.1
4.0
5.8
7.5
0
13.2
11.4
7.9
3.0
6.0
5.9
0
0
1.4
0
0
0
Catalyst
Elemental analysisa (wt.%)
BETb
Pore
size
(Å)
Co
Si
Al
P
Surface area (m2/g)
Co-SAPO-5 (0.3)a
Co-SAPO-5 (0.4)a
Co-SAPO-5 (0.5)a
Co-SAPO-5 (0.6)a
Co-SAPO-34
78.8
87.5
92.0
91.9
91.9
8.3
7.3
15.9
8.5
SAPO-5 (0.3)
Co-SAPO-5 (0.3)
SAPO-5 (0.4)
Co-SAPO-5 (0.4)
SAPO-5 (0.5)
Co-SAPO-5 (0.5)
SAPO-5 (0.6)
Co-SAPO-5 (0.6)
SAPO-34
0
0.38
0
0.42
0
0.44
0
0.45
0
2.16
3.18
3.08
3.56
3.41
3.78
3.67
3.89
3.80
9.08
8.20
20.86
20.78
20.84
20.74
20.80
20.66
20.77
20.64
19.30
19.00
23.46
23.40
23.14
23.06
22.96
22.82
22.81
22.73
19.26
19.00
233
215
227
213
218
195
213
189
570
546
7.2
7.2
7.2
7.2
3.9
8.6
3.6
Cr-SAPO-34
Mn-SAPO-34
Fe-SAPO-34
Ni-SAPO-34
Cu-SAPO-34
23.0
23.1
18.7
24.7
24.4
22.0
13.4
9.7
Zn-SAPO-34
Co-SAPO-34
Styrene, 3 mmol; DMF, 10 g; catalyst, 0.1 g; initiator (CHP), 0.3 mmol; time, 6 h; tem-
a
Results obtained from XRF.
Values obtained from N2-adsorption results.
perature, 363 K; flow rate of air, 40 ml/min.
b
a
Time, 8 h.

B. Tang et al. / Catalysis Communications 31 (2013) 42–47
45
Table 4
voltammetry (CV) analyses, had revealed the coordination of DMF (sol-
Effect of different solvents on the epoxidation of styrene over Co-SAPO-34.
vent) to Co(II) [13,30]. Such a coordination could affect the binding abil-
ity of O2 to Co(II) as well as their redox potential, further leading to the
activation of O2 in the epoxidation, thus beneficial for the catalytic oxi-
dation of hydrocarbons involving molecular oxygen [31]. However, as
compared the ability of other transition metal ions to activate molecular
O2 was poor.
The effect of Co loading ranging from 0.5 to 6.0 wt.% on the epox-
idation of styrene over Co-SAPO-34 was shown in Table S1 (Supple-
mentary data). With increasing the Co loading from 0.5 to 3.0 wt.%,
the conversion of styrene and the selectivity of epoxide were in-
creased from 58.6 to 91.9 mol% and from 79.3 to 90.5%, respectively.
However, both the conversion and selectivity remained almost unaf-
fected with further increases in the Co loading.
Solvent
Conv. (mol%)
Selectivity (%)
Epoxide
Ben.
Phen.
Others
DMF
Toluene
Acetylacetone
Pyridine
91.9
15.3
10.3
–
90.5
10.5
40.4
–
3.6
5.9
13.5
1.8
–
0
63.7
49.5
–
12.3
8.3
–
MIBK
40.0
51.8
62.7
95.8
39.7
63.2
69.8
85.3
44.3
25.8
17.9
4.7
1.4
3.0
5.3
7.1
14.6
8.0
7.0
2.9
1,4-Dioxane
1,4-Dioxane+DMFa
1,4-Dioxane+IBAb
Styrene, 3 mmol; solvent, 10 g; catalyst, 0.1 g; initiator (CHP), 0.3 mmol; time, 6 h;
temperature, 363 K; flow rate of air, 40 ml/min.
a
1.0 g of 1,4-dioxane+9.0 g of DMF.
1.0 g of 1,4-dioxane+9.0 g of IBA.
b
3.2.2. Effect of different oxidants and initiators
The catalytic activity of Co-SAPO-34 in the epoxidation of styrene
with various oxidants was summarized in Table 3. No oxidation oc-
curred under inert N2 atmosphere without any oxidant or with
NaClO. The oxidants like H2O2 and NaIO4 showed very low oxidation
activities, in which H2O2 and NaIO4 oxidized only 20.2–15.0 mol% sty-
rene. When using either CHP or air as unique oxidant, no high conver-
sion or selectivity was achieved. However, air was used as oxidant
together with a small amount of CHP as initiator, 91.9 mol% of styrene
was converted to the epoxide with 90.5% selectivity, indicative of the
initiating effect of CHP on the titled reaction.
Meanwhile, TBHP, H2O2 and TEMPO have also been tested as initi-
ators (Table 3). As desired, TBHP showed excellently enhanced effect
for the epoxidation reaction similar to CHP. The rapid decomposition
of H2O2 over the Co-catalyst at 363 K could be responsible for its low
efficiency on the reaction. TEMPO used widely in the selective oxida-
tion of alcohols [32], did not display any effect under our experimen-
tal conditions.
the epoxidation of styrene with air in pyridine could not occur
completely.
DMF played a key role in the epoxidation of styrene with air due to
the strong coordination with cobalt and O2. However, whether DMF is
a reductant or not has been considered as a controversial topic
[17,30,33]. Actually, DMF could not be recognized as a real reductant
in our catalytic system, different from the case reported in the litera-
ture [33]. After the reaction was terminated, the amount of oxo-DMF
was detected to be ca. 0.15–0.30 mmol in the optimal experiments,
merely corresponding to 1/20-1/10 of quantity of alkene oxidized,
i.e. the molar ratios of oxo-DMF/epoxide were in the range of
0.05–0.11. In order to further confirm above-stated conclusion, two
experiments were carried out. For instance, adding a mixed solvent
of 9.0 g DMF and 1.0 g 1,4-dioxane instead of pure 1,4-dioxane merely
led to a small increase of the reactivity of styrene from 51.8 mol%
conversion (63.2% selectivity) to 62.7 mol% (69.8%); however, when
adding a mixture of 9.0 g isobutylaldehyde and 1.0 g 1,4-dioxane, the
conversion of styrene and the selectivity of epoxide were notably
increased up to 95.8 mol% and 85.3%, in which isobutylaldehyde took
effect as a real reductant.
3.2.3. Effect of various solvents
Table 4 lists the effect of various solvents on the epoxidation of sty-
rene with air over Co-SAPO-34. Obviously, the solvents did affect the
epoxidation reactions. The conversion of styrene decreased in the se-
quence of 91.9 mol% (DMF)>51.8 mol% (1,4-dioxane)>40.0 mol%
(MIBK)>15.3 mol% (toluene)>10.3 mol% (acetylacetone). However,
3.2.4. Recycling studies
In order to assess the stability and reusability of Co-SAPO-5 (0.5)
and Co-SAPO-34 catalysts, recycling studies have been conducted
for the epoxidation of styrene. As depicted in Fig. 4, the reuses of
Co-SAPO-5 (0.5) and Co-SAPO-34 (five times) did not appreciably de-
crease the conversion of styrene and the selectivity of epoxide. The
conversions of styrene showed an inconspicuous fluctuation in the
range of 91.0–92.0 mol% on Co-SAPO-5 (0.5) and 90.2–91.9 mol% on
Co-SAPO-34, while the selectivity of epoxide was kept a more or
less constant around 89.5% or 90.5%. XRD testified that the structures
of recovered catalysts were retained after 5 cycles (Fig. 1). Further-
more, control experiments were carried out according to the method
described in the literature [17]. As shown in Fig. S2 (Supplementary
data), after aerobic epoxidation reactions were initially conducted
for 1 h, then solid catalysts were filtered off and the reactions were
continued for another 5–7 h, the final conversions were analyzed by
GC. Only a small conversion increment of 3.9 mol% was achieved on
Co-SAPO-34, and that of 4.6 mol% on Co-SAPO-5 (0.5), attributed to
the contribution of a small amount of Co2+ ions leaching from
Co-SAPOs and the autoxidation of alkenes by air, which further con-
firmed the characteristics of heterogeneous catalysis.
Table 3
Effect of different oxidants and initiators on the epoxidation of styrene over
Co-SAPO-34.
Oxidant
Conv. (mol%)
Selectivity (%)
Epoxide
Ben.
Phen.
Others
Nonea
Airb
–
–
–
–
–
37.8
19.2
20.2
–
76.7
75.2
50.8
–
17.5
12.6
11.7
–
5.8
4.0
2.7
–
0
TBHPc
8.2
34.8
–
c
H2O2
NaClOc
c
NaIO4
15.0
57.6
13.5
21.8
–
81.2
53.4
90.0
85.6
–
18.8
3.4
5.4
7.9
–
0
0
41.7
0
0
–
CHPc
1.5
4.6
6.5
–
CHPd
TBHPd
Air+TEMPO
Air+H2O2
Air+CHP
Air+TBHP
31.2
91.9
90.5
76.7
90.5
90.2
14.7
3.6
3.7
6.8
5.9
6.1
1.8
0
0
Styrene, 3 mmol; DMF, 10 g; catalyst, 0.1 g; initiator, 0.3 mmol; time, 6 h; tempera-
3.3. Catalytic epoxidation of various alkenes
ture, 363 K; flow rate of air, 40 ml/min.
a
Reaction under N2 atmosphere.
Flow rate of air, 40 ml/min.
Oxidant, 3 mmol.
Initiator, 0.3 mmol.
Aside from the catalytic epoxidation of styrene with dry air as stat-
ed above, that of several other alkenes over Co-SAPO-5 (0.5) and Co-
SAPO-34 was as well described in Table 5. Comparatively, the
b
c
d

46
B. Tang et al. / Catalysis Communications 31 (2013) 42–47
100
90
80
70
60
50
40
30
20
10
4. Conclusions
95
Transition metal ion (Co2+, Zn2+, Mn2+, Ni2+, Cu2+, Cr3+, and
Fe3+) exchanged SAPO molecular sieves have been prepared by a simple
route. Co-SAPO-5 (0.5) and Co-SAPO-34 displayed high activities for the
epoxidation reaction to achieve 92.0–91.9 mol% conversion with the
selectivity of 89.5–90.5% for styrene, 95.3–96.8 mol% and 75.2–73.6%
for α-methyl styrene, 71.6–80.0 mol% and 94.8–95.0% for α-pinene.
For cyclooctene, the epoxide selectivity on both catalysts was 96.3–
98.1%, while the substrate conversions were relatively low with about
11.3–13.1 mol%. The epoxidation of linear 1-octene with air was negligi-
ble. Solvents, oxidants and initiators exerted notable impacts on the
epoxidation reaction. Recycling studies and control experiments showed
the recyclability and stability of Co-SAPO-5 and Co-SAPO-34 as heteroge-
neous catalysts.
85
75
65
55
45
35
25
conv.
sele.
conv.
sele.
Acknowledgments
This work was supported by National Natural Science Foundation
of China (no. 20901023, 21173073, 21273064), by the 2007 excellent
mid-youth innovative team project of the Education Department of
Hubei Province (no. T200701), and by Natural Science Foundation of
Hubei Province (no. 2011CBD065). Dr. D. Zhou thanks the financial
support by Chen Guang Scheme of Wuhan City (no. 201050231087).
0
1
2
3
4
5
Number of cycle
Fig. 4. Recycling studies of catalysts: Co-SAPO-5 (0.5) (▲ and △) and Co-SAPO-34
(♦ and ◊).
Appendix A. Supplementary data
reactivity of four olefins decreased in a sequence of α-methyl styrene
(95.3–96.8 mol% conversion)>styrene (92.0–91.9 mol%)>α-pinene
(71.6–80.0 mol%)>cyclooctene (13.1–11.3 mol%), totally different from
the descending order of the epoxide selectivity: cyclooctene (98.1–
96.3%)>α-pinene (94.8–95.0%)>styrene (89.5–90.5%)>α-methyl sty-
rene (75.2–73.6%). For cyclooctene, the epoxide selectivity on both cata-
lysts was 96.3–98.1%, while the substrate conversions were relatively
low with about 11.3–13.1 mol%, possibly assigned to the diffusion limita-
tion of larger cyclooctene molecules in small pores of both SAPO-5 and
SAPO-34 and to the difficult activation of these catalysts for cycloalkenes
with molecular oxygen [30]. The epoxidation of linear terminal 1-octene
with air was negligible because of low π-electron density weakening
the ability of electrophilic cycloaddition [34]. The comparison of our pres-
ent results with the earlier data reported for the epoxidation of alkenes
has been summarized in Table S2 (Supplementary data), which further
showed the excellent catalytic activity of our present system.
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.11.011.
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