100
X.-T. Ma et al. / Catalysis Communications 67 (2015) 98–102
filtered off. Then, the catalyst was washed with deionized water and
ethanol, dried at 80 °C for 3 h, and used for the next recycle. The liquid
filtrate was quantitatively analyzed by GC-9800.
shows the excellent activity of our aerobic epoxidation system using
CoOx/Y as the catalyst. According to the methods reported in the litera-
ture [32,33,35], we have prepared the corresponding catalysts. Under
identical reaction conditions, the conversion gradually decreases in
3
. Results and discussion
the order of CoOx/Y (61.2 mol%) N Co-ZSM-5(L
MCM-41 (36.8 mol%) N CoOx/SiO (36.1 mol%) N Co-MOF (35.6 mol%),
slightly different from the descending order of the epoxide selectivity:
1
) (43.0 mol%) N CoO-
2
3
.1. Structures of catalysts
1 2
CoO-MCM-41 = Co-ZSM-5(L ) (100%) N CoOx/Y (98.8%) N CoOx/SiO
Fig. S1 shows XRD patterns of CoOx/zeolite catalysts, which indicate
(94.6%) N Co-MOF (93.5%).
that the framework structures of zeolites remain intact after the im-
pregnation treatment. The absence of diffraction peaks of CoOx oxides
indicates that the samples do not contain detectable amount of aggre-
gated crystalline phase of cobalt oxides, which have been highly dis-
persed on the surface of porous supports. UV–vis spectra are shown in
Fig. S2, where it exhibits several resolved absorbances at ca. 260–
3.3. Effect of various factors on the epoxidation of cis-cyclooctene over
CoOx/Y
The effect of the cobalt content on the activity of CoOx/Y is shown in
Fig. 2, where the Co content is 1.0, 2.4, 3.2, 4.0 and 5.6 wt.%, respectively.
With the increase of the Co content, the conversion of cis-cyclooctene is
first increased from 35.6 mol% for 1.0 wt.% Co to 61.2 mol% for 2.4 wt.%
Co, and to 61.6 mol% for 3.2 wt.% Co. Then, the conversion remains al-
most unaffected with a further increases of the Co loading from 4.0 to
5.6 wt.%. And, the selectivity of epoxide slightly reduces from 98.8%
(2.4 wt.% Co) to 94.3% (5.6 wt.% Co). Thus, 2.4% CoOx/Y catalyst has
the best catalytic activity for the titled epoxidation (61.2 mol% conver-
sion of cis-cyclooctene and 98.8% selectivity of epoxide) under our ex-
perimental conditions. This shows that the excess cobalt loading does
not favor the epoxidation of cis-cyclooctene by air over CoOx/Y further,
possibly associated with the low dispersion of CoOx species on Y zeolite.
As revealed by IR spectra (Fig. S4), with increasing the Co loading
amount from 1.0 to 5.6 wt.% onto NaY, the IR peaks of Co–O bonds
4
00 nm, resulting from the O2− → Co2+ charge transfer transition
and the interaction of CoOx with the support [27,28].
Fig. S3 shows SEM images of catalyst particles. Obviously, the mor-
phologies and particle sizes of catalysts that have undergone the im-
pregnation treatment are still similar to those of the parent zeolites or
molecular sieves. The average crystal size observed by SEM is 0.5–
1
1
.5 μm for CoOx/ZSM-5 and CoOx/SBA-15, 0.5–2.0 μm for CoOx/Y, 0.5–
.0 μm for CoOx/β, 1.0–5.0 μm for CoOx/MCM-22, 0.5–3.0 μm for
CoOx/3A and CoOx/4A, and 0.2–1.0 μm for CoOx/MCM-41. TEM images
of various CoOx/zeolite catalysts have been added in Fig. 1, where it
shows high dispersions of Co onto zeolite Y. The BET surface areas and
pore sizes of various samples determined by BET analysis are given in
Table 1. The surface areas of supported CoOx/zeolite catalysts are slight-
ly less than those of the parent porous materials.
−
1
−1
(
471 cm , 513 cm ) of CoOx phase are visible and gradually intensi-
3
.2. Epoxidation of cis-cyclooctene over various catalysts
fied, indicating that the increase of CoOx species will enhance the aggre-
gation of oxide particles, further affecting the catalytic activity.
Table S1 compares the effect of various oxidants on the epoxidation
of cis-cyclooctene under identical conditions. When only TBHP is used
as the oxidant, the conversion of cis-cyclooctene is only 7.5 mol% in
The catalytic activity of different CoOx/zeolite catalysts for the epox-
idation of cis-cyclooctene with air is summarized in Table 2. When no
catalyst is added (blank test), only 11.8 mol% of cis-cyclooctene is con-
verted with 100% selectivity of epoxide. The use of CoOx/Y as the cata-
lyst increases the conversion of cis-cyclooctene to 61.2 mol%,
accompanied with 98.8% selectivity of epoxide; whereas CoOx/MCM-
2 2
5 h. Other oxidants like H O and NaClO are less efficient for the epoxi-
dation of cis-cyclooctene. Without the addition of TBHP, dry air oxidizes
17.6 mol% of cis-cyclooctene at 120 °C. However, if air is used as oxidant
together with a small amount of TBHP added as the initiator, the conver-
sion of cis-cyclooctene is largely elevated to 61.2 mol%, indicating the
enhanced effect of a small amount of TBHP as the initiator on the titled
reaction.
2
2 converts 52.2 mol% of cis-cyclooctene to 98.9% of epoxide. In con-
trast, the catalytic activities of CoOx/ZSM-5, CoOx/β, CoOx/SBA-15,
CoOx/MCM-41, CoOx/4A and CoOx/3A are appreciably lower than
those of CoOx/Y and CoOx/MCM-22. Meanwhile, those parent porous
zeolites or molecular sieves have displayed relatively poor performance
with conversions lower than 14 mol% for the epoxidation of cis-
cyclooctene with air, which further emphasizes the significance of the
introduction of Co for aerobic epoxidation reaction. Cobalt is an effective
1
00
100
90
80
70
60
50
40
30
20
10
0
90
component for catalyzing the epoxidation of alkenes with O
9–34].
A comparison of our results with the earlier data reported for the ep-
2
/air [21,
8
7
6
5
4
0
0
0
0
0
2
oxidation of cis-cyclooctene is summarized in Table 3, which further
Table 2
Epoxidation of cis-cyclooctene with dry air over various CoOx/zeolites.
Entry Catalyst
Conversion Selectivity (%)
mol%)
Carbon balance
(%)
(
30
20
10
0
Epoxide 2-ene-1-one
1
2
3
4
5
6
7
8
9
No (blank)
CoOx/ZSM5
CoOx/Y
CoOx/β
CoOx/SBA-15
CoOx/MCM-22 52.2
CoOx/MCM-41 44.7
CoOx/3A
CoOx/4A
12.3
37.2
61.2
35.2
47.7
100
96.9
0
100
3.1
1.2
2.6
1.5
1.1
3.2
1.8
1.1
99.7
99.9
99.8
99.2
99.7
99.3
100.1
99.9
98.8
97.4
98.5
98.9
96.8
98.2
98.9
Conversion
Epoxide Selectivity
0
1
2
3
4
5
6
Co contents (%)
42.9
43.4
Fig. 2. Effect of Co contents on the epoxidation of cis-cyclooctene over CoOx/Y catalyst. Re-
action conditions: 3 mmol cis-cyclooctene, 10 g DMF, 100 mg catalyst, 0.3 mmol TBHP;
120 °C, 5 h; 30 ml/min air.
Reaction conditions: 3 mmol cis-cyclooctene, 10 g DMF, 100 mg catalyst, 0.3 mmol TBHP;
20 °C, 5 h; 30 ml/min air.
1