An environmentally friendly route for grafting of molybdenum carbonyl onto a diaminosilane-modified SBA-15 molecular sieve and its catalytic behaviour in olefin epoxidation

Article abstract of DOI:10.1039/c4nj02402h

A simple route has been established for grafting molybdenum carbonyl onto the surface of a diaminosilane-modified SBA-15 molecular sieve. The successful grafting of the molybdenum carbonyl species onto diamine-functionalized SBA-15 was evident from FT-IR studies. The resultant molybdenum-carbonyl-complex-grafted SBA-15 (SBA-DA-Mo) materials show promising activity for the epoxidation of various olefins with good conversion (90-95%) and the formation of epoxide as the major product. The catalytic activity remains constant over several runs.

Full text of DOI:10.1039/c4nj02402h

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An environmentally friendly route for grafting of
molybdenum carbonyl onto a diaminosilane-
modified SBA-15 molecular sieve and its catalytic
behaviour in olefin epoxidation†
Cite this:DOI: 10.1039/c4nj02402h
Thangaraj Baskaran,a Raju Kumaravel,a Jayaraj Christopher,b
Thalasseril G. Ajithkumarc and Ayyamperumal Sakthivel*a
A simple route has been established for grafting molybdenum carbonyl onto the surface of a diaminosilane-
modified SBA-15 molecular sieve. The successful grafting of the molybdenum carbonyl species onto diamine-
functionalized SBA-15 was evident from FT-IR studies. The resultant molybdenum-carbonyl-complex-grafted
SBA-15 (SBA-DA-Mo) materials show promising activity for the epoxidation of various olefins with good
conversion (90–95%) and the formation of epoxide as the major product. The catalytic activity remains constant
over several runs.
Received (in Victoria, Australia)
25th December 2014,
Accepted 23rd February 2015
DOI: 10.1039/c4nj02402h
www.rsc.org/njc
Introduction
The epoxidation of olefin is an important organic transformation,
which is of great interest in academic and industrial research.1
In general, epoxidation is carried out using transition metal com-
plexes.1 In particular, molybdenum-based compounds are exten-
sively studied for various olefin oxidations.1–8 The development of
the Arco-Lyondell process for the epoxidation of propene using the
molybdenum carbonyl Mo(CO)6 precursor in the presence of tert-
butylhydroperoxide (TBHP) as the oxidant led to increased interest
in the oxidative synthesis of dioxo molybdenum(VI) complexes of the
type CpMoO2L, MoO2X2L, etc. from their carbonyl precursors.2–8 For
example, molybdenum complexes with a cyclopentadienyl(Cp)-
based precursor are considered to be very promising catalysts.2–4,6
Heterogenization of such homogeneous catalysts on various sup-
ports showed promising recyclable catalysts.8 It is important to
mention here that supports based on mesoporous molecular sieves
have greater advantages over the homogeneous catalysts, such as
the uniformity of channels, large surface area, ease of handling,
and recyclability.7–10 Although a few reports show the importance of
Cp–Mo-complexes on mesoporous supports, the synthesis of the
homogeneous counterpart involves multiple steps and results in the
formation of air sensitive and carcinogenic products.3,4 Thus, it is
vital to develop molybdenum-based heterogenized catalysts from
stable homogeneous counterparts that can be synthesized using
simple methods and can be handled easily.
Scheme 1 Schematic representation of the grafting of molybdenum
carbonyl onto SBA-15 molecular sieve.
In this regard, we report herein a simple environmentally friendly
method (Scheme 1) for grafting of molybdenum carbonyl onto SBA-15
molecular sieves via a diaminosilane moiety (SBA-DA-Mo). The
resultant molybdenum-carbonyl-grafted SBA-15 materials were
studied for their catalytic activity in the epoxidation of various
olefins. For comparison, the homogeneous complex 1 was
prepared as per the modified procedure described earlier and
studied for the oxidation of olefin.11
Experimental section
a Department of Chemistry, Inorganic Materials and Catalysis Laboratory,
University of Delhi, New Delhi-110007, India. E-mail: asakthivel@chemistry.du.ac.in
b Indian Oil Corporation Ltd, R&D Centre, Faridabad-12100, India
All the catalyst preparation and grafting procedures were carried out
using standard Schlenk techniques under a nitrogen atmosphere.
c Central NMR Facility, CSIR-National Chemical Laboratory, Pune-411008, India
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nj02402h Solvents were dried via standard procedures (THF, toluene with
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Na/benzophenone ketyl; CH2Cl2 with CaH2), distilled under nitrogen vacuum. The resultant material was denoted as SBA-DA. In a
and kept over 4 Å molecular sieves.
second step, about 3 mmol of Mo(CO)6 was introduced into the
SBA-DA material in the presence of toluene and refluxed for 24 h
in a N2 atmosphere. After the completion of the reaction, the
Synthesis of the mesoporous SBA-15 molecular sieve
A mesoporous SBA-15 molecular sieve was synthesized as per the final product was filtered and washed with dichloromethane
procedure described elsewhere.9a Mesoporous silica were synthe- several times and dried under vacuum to get SBA-DA-Mo.
sized using Pluronic 123 triblock copolymers (poly(ethylene oxide)-
poly(propylene oxide)-poly(ethylene oxide); (Aldrich)) EOnPO70EOn as
templates. In a typical synthesis, 4.0 g of the EO20PO70EO20 copolymer
Characterization of materials
was dissolved in 150 g of 1.6 M HCl. To this solution 8.50 g of TEOS
Pure SBA-15 and molybdenum carbonyl complex grafted SBA-15
(tetraethyl orthosilicate), was added and the resulting mixture was
were systematically characterized using various analytical and
stirred until TEOS was dissolved. The final molar gel composition of
spectroscopic techniques. Powder XRD was performed to deter-
mine the bulk crystalline phases of the materials using an
18 KW XRD Rigaku (2500 V), Japan with Cu-Ka radiation
(l = 1.54184 Å). The diffraction patterns were recorded in the 2y
the synthesis mixture was 6.89 Â 10À4 P123 triblock copolymers:
0.24 HCl:0.041 TEOS:7.88 H2O. The mixture was placed in an oven
for 24 h at 308 K and then additionally for 24 h at 373 under static
conditions. The products were filtered, dried, and calcined at 823 K.
The calcined SBA-15 was used as the support material.
range 0.5–101, with a scan speed and step size of 11/min and 0.021,
respectively. FT-IR spectra were obtained in the range 400–4000
cmÀ1 using KBr pellets (Perkin-Elmer 2000, FT-IR spectrometer).
Preparation of tetracarbonylmolybdenum N-[3-(trimethoxysilyl)
propyl]ethylenediamine: complex (1)
The textural properties (BET surface area, BJH pore volume) of the
synthesized materials were derived from N2 sorption measure-
Tetracarbonylmolybdenum N-[3-(trimethoxysilyl)propyl]ethylene-
ments carried out at À196 1C using an automatic micropore
diamine was prepared (Scheme 1) using the modified procedure4
physisorption analyser (Micromeritics ASAP 2020, USA) after the
via reaction of 1.1 g (4.16 mmol) of Mo(CO)6 in 40 ml dry
samples were degassed at 250 1C for at least 8 h under 10À3
toluene with the addition of 1.08 g (4.16 mmol) N-[3-(trimethoxysilyl)-
Torr pressure prior to each run. The 29Si MAS and 13C CPMAS
experiments were carried out on a JEOL ECX 400 MHz spectro-
propyl]ethylenediamine. The resultant solution was refluxed at
80 1C for 20 minutes. The solvent was removed under reduced
meter using a 4 mm MAS probe, which was tuned to 79.4 MHz for
pressure to get a brown oily liquid. IR of complex 1 (CH2Cl2):
29Si and 100.5 MHz for 13C at a spinning speed of 10 KHz. The
1825 (m), 1865 (s, sh), 1885 (vs), 2005 (w) cmÀ1 corresponds
29SiMAS experiments were recorded using a one pulse sequence
to 4(CO), ligand L11H NMR (d, 400 MHz, CDCl3) 0.62–0.66
with high power 1H decoupling with a 1H power of 70 KHz, and a
(q, 2H, CH2–Si), 1.23 (s, –NH & H2N–), 1.6 (m, 2H, –CH2–),
29Si a 901 pulse of 2.6 ms. 11 000 scans were recorded with a recycle
2.59–2.65 (m, 4H, –CH2–NH–CH2), 2.75–2.77 (t, 2H, CH2–NH2),
delay of 3 s between the scans. The 13C NMR experiments were
3.55(s, 9H, O–CH3) and complex 1, 1H NMR (d, 400 MHz,
acquired using a ramped amplitude cross-polarization contact time
CDCl3) 0.62–0.66 (q, 2H, CH2–Si), 1.45 (s, –NH & H2N–),
of 3.5 ms with high power TPPM 1H decoupling during the
1.5–1.6 (m, 2H, –CH2–), 2.59–2.65 (m, 4H, –CH2–NH–CH2),
acquisition time. 7900 scans were collected with a recycle delay
2.75–2.77 (t, 2H, CH2–NH2), 3.55(s, 9H, O–CH3). The shift in
of 5 seconds between them.
the broad peak corresponding to the amine proton signal from
Thermogravimetry analysis (TGA) was carried out in a Thermal
Analyzer (Model-2950, TA Instruments, and USA). About 5–10 mg
1.23 to 1.45 supports the formation of complex 1. Ligand L1 13C
NMR (d, 400 MHz, CDCl3); 6–7 (CH2–Si), 23 (–CH2–CH2–Si), 42
of the sample was taken in the platinum pan and heated in air at
(–CH2–NH2), 50 (O–CH3), 52 (–CH2–NH–CH2), 80 (CDCl3);
the heating rate of 10 1C minÀ1 up to 800 1C. Proton NMR spectra
complex 1,13C NMR (d, 400 MHz, CDCl3); 6–7 (CH2–Si),
were recorded on a JEOL AL-400 FT NMR instrument using CDCl3
as the solvent. The molybdenum content in the sample (SBA-DA-
Mo) was determined by inductively coupled plasma–atomic emis-
23 (–CH2–CH2–Si), 40 (–CH2–NH2), 50 (O–CH3), 52 (–CH2–NH–CH2),
200 (–CO), 80 (CDCl3), 130 (toluene-peak);
sion spectroscopy (ICP–AES; Model: Optima 8300, Make: Perkin
Grafting of Mo(CO)6
Elmer). The sample was first digested with a mixture containing
The molybdenum carbonyl grafting was carried out using a
equal volume (6 ml) of H2O2, ammonium hydroxide and ethanol.
two-step process. First, the SBA-15 support (1 g) was pre-activated
The resultant mixture was filtered and the filtrate solution was
at 200 1C overnight in an air oven followed by dried under vacuum
in a Schlenk round bottom flask for 1 hour to remove physisorbed
molecules. A calculated amount (3 mmol) of N-[3-(trimethoxysilyl)-
propyl]ethylenediamine was introduced into the activated SBA-15
aspirated into ICP–AES equipment. The concentration of Mo in
the samples was obtained with respect to a standard solution of
Mo (Emerck, Germany) for (ICP–AES) analysis.
support material after it was cooled down to room temperature.
The mixture was refluxed with dry toluene (30 ml gÀ1 support) for Epoxidation of olefin using grafted
24 h in a N2 atmosphere. After completion, the reaction mixture
was cooled to room temperature, and toluene and excess diamine
materials
were removed by vacuum filtration. Subsequently, it was washed The catalytic activity of SBA-DA-Mo was studied for epoxidation
with dichloromethane several times and dried at 40 1C under of olefins using t-butyl hydroperoxide (5.5 M TBHP in decane;
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used without further purification) as the oxidant. The reaction
was carried out with a constant molar ratio of the substrate: the
oxidant, at 70 1C temperature in the presence of mesitylene as
the internal standard. The products were analyzed using gas
chromatography equipped with an FID (Agilent 7890A Series)
connected to a HP-5 capillary column (30 m; HP-5). For comparison
the parent SBA-15 sample and complex (1) were studied under
identical conditions.
Results and discussion
Powder XRD patterns of pure SBA-15 SBA-15-DA and SBA-DA-Mo
are shown in Fig. 1. All the samples exhibit very well-resolved
reflections corresponding to the (100), (110), and (200) planes in
the 2y range 0.5–2.01, characteristic of the mesoporous hexagonal
structure.9,12 Compared to the parent SBA-15 sample, SBA-DA and
SBA-DA-Mo showed a clear shift in 2y values towards higher angles,
and there is a slight decrease in the relative intensities of the XRD
reflections. The above results support the grafting of molybdenum
carbonyl onto N-[3-(trimethoxysilyl)propyl]ethylenediamine-modified
SBA-15 surface.8,9
Fig. 2 FT-IR spectra of (a) SBA-15, (b) SBA-DA, (c) SBA-DA-Mo, and
(d) SBA-DA-Mo after the reaction.
Mo–O–Mo bridging bond, which is formed upon TBHP treatment.5c–e
However, the observed low intensity of these vibrational bands
corresponding to the SBA-DA-Mo catalyst indicates the presence
of the molybdenum-oxo species and it is present as a monomeric
species.
Fig. 2 shows the FT-IR spectra of the parent mesoporous SBA-15,
SBA-DA, SBA-DA-Mo, and used SBA-DA-Mo samples. All the sam-
The parent SBA-15, SBA-DA, and SBA-DA-Mo samples were
ples exhibit bands at 1082, 953, and 807 cmÀ1, are attributed to the analysed using solid-state 29Si MAS NMR spectroscopy. The
stretching vibrations of the mesoporous framework (Si–O–Si).8–10,14 parent SBA-15 sample exhibits (Fig. 3) three broad resonances
The band around 960 cmÀ1 is assigned to a vibration mode of
the silanol (Si–OH) groups8 present in the mesoporous channels.
Two additional vibrational bands were present around 2927 and
2854 cmÀ1 for the SBA-DA sample; these result from the C–H
stretching of the alky diamine group present on the ligand. SBA-
in the 29Si MAS NMR spectrum at the chemical shift (d) values
of À110, À101, and À97 ppm, which can be assigned to the
Q4, Q3, and Q2 species of the silica framework, respectively
[Qn = Si(OSi)n(OH)4Àn].8,13
The 29Si MAS NMR spectrum of the molybdenum-carbonyl-
grafted sample shows a major peak centred around À110.0 ppm,
DA-Mo showed a new broad band around 2005 and 1891 cmÀ1
,
which could be assigned to the terminal carbonyl group vibrations8b attributed to the Q4 species, and also exhibits additional
of the in situ grafted complex 1; the observed signal was due to the broad signals between À55 and À70 ppm, which can be
loading of the molybdenum carbonyl species on the surface of
SBA-DA. When SBA-DA-Mo is treated with TBHP, two new bands
are observed around 900 and 955 cmÀ1 (Fig. 2d), indicating the
oxidative conversion of the molybdenum carbonyl species into the
active Mo(VI) oxo-species (MoQO).3–5,8,15 An additional vibration
assigned to the T2 and T3 organosilica species, respectively
[Tm = RSi(OSi)m(OR)3Àm],8,13 supporting the anchoring of
the N-[3-(trimethoxysilyl)propyl]ethylenediamine functionality
and molybdenum carbonyl on the surface of the SBA-15
molecular sieve. The 29Si MAS NMR of SBA-DA displays an
bands are appeared between 700 to 850 cmÀ1 is characteristic of identical spectrum (Fig. 3b) of SBA-DA-Mo since the chemical
Fig. 3 29Si CP-MAS NMR spectra of (a) SBA-15 and (b) SBA-DA (c) SBA-DA-Mo.
Fig. 1 Powder XRD pattern of (a) SBA-15, (b) SBA-DA and (c) SBA-DA-Mo.
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Fig. 4 13CCP-MAS NMR spectra of (a) SBA-DA and (b) SBA-DA-Mo.
Fig. 5 N2 sorption isotherms of (a) SBA-15, (b) SBA-DA and (c) SBA-DA-Mo.
Table 1 Textural properties of various SBA-15 molecular sieves
environment of the Si atoms is not changed during the grafting
process.
Surface area (m2
Sample code BET
g )
À1) Pore volume (cm3 gÀ1
Further, the 13C NMR spectra (Fig. 4) of SBA-DA and SBA-DA-Mo
showed peaks around 10, 25, 45, and 52 ppm, which correspond to
different aliphatic functionalities arising from the siloxane func-
tional group.14a,b The additional unexpected peak seen around
165 ppm for SBA-DA corresponds to the carbamic acid type carbonyl
functionality.14c The observed carbamic acid type carbonyl may be
due to interaction of atmospheric CO2 with diamine functionality
present on the surface of SBA-15.14c The weak signal appearing
around 186 ppm may be due to the presence of the terminal
carbonyl group which is associated with the molybdenum species.18
The N2 adsorption isotherm studies of SBA-15 and grafted
SBA-15 samples and the corresponding pore size distribution
(inset) are depicted in Fig. 5. All the samples show typical type
IV isotherms, as per the IUPAC classification,14 characteristic
of mesoporous materials. A well-defined sharp inflection is
observed between relative pressures (p/p0) of 0.6 and 0.8 due
to capillary condensation of nitrogen inside the primary meso-
porous sample.8,12,16 Compared to the parent mesoporous
sample, the samples modified with ligand and molybdenum
carbonyl display a drastic decrease in the nitrogen uptake and a
shift in the isotherm towards low relative pressures owing to
the presence of an organometallic Mo-complex grafted onto the
surface of mesoporous channels.8,9
Total
Micropore
Moa (wt%)
SBA-15
SBA-DA
SBA-DA-Mo 276.6
769.0
347.6
1.10
0.56
0.44
0.018
0.000
0.000
—
—
28
a
Calculated based (ICP–AES) analysis.
the methyl and methylene group from the complex and amino
silane moiety, respectively.
Further, in order to confirm the formation of the molybdenum
carbonyl diammine complex, an unsupported homogenous complex
1 (DA-Mo) was prepared by the treatment of N-[3-(trimethoxysilyl)-
propyl]ethylenediamine with Mo(CO)6 using dry toluene as the
solvent under a nitrogen atmosphere. The 1H NMR spectra of
complex 1 showed a shift in the chemical shift values (see Fig. S1,
ESI†) of the amine proton, clearly supporting the formation of the
adduct complex 1. The 13C NMR (d, 400 MHz, CDCl3) spectra of
complex 1 are shown in Fig. S2 (ESI†) and they are compared with
those of the diaminosilane ligand. 13C NMR spectra (a) and (b) show
peaks around 10–65 ppm which corresponds to aliphatic region of
Table 1 summarizes the textural properties of the SBA-15, SBA-DA,
and SBA-DA-Mo samples. The parent SBA-15 shows a surface area
and total pore volume of around 769 m2 gÀ1 and 1.10 cm3 gÀ1
respectively, which reduces drastically in diamine-functionalized
materials owing to the grafting of diamine silane in the mesoporous
channel. SBA-DA-Mo samples exhibit a further decrease in
the surface area and total pore volume to 276 m2 gÀ1 and
0.44 cm3 gÀ1, respectively. The observed decrease in the surface
area and total pore volume support the grafting of the organo-
metallic complex 1 onto the surface of mesoporous SBA-15; this
is also in agreement with the FT-IR data.8,9
The thermal stability of the SBA-DA-Mo sample was studied
using TGA (Fig. 6). A weight loss of around 17% was observed in
the grafted materials due to the loss of the carbonyl group and
Fig. 6 TGA profile of SBA-DA-Mo.
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Table 2 Effect of catalyst loading on epoxidation using the SBA-DA-Mo
catalysta
S. no.
Catalyst amount (mg)
Conversion (%)
Selectivity (%)
1
2
3
4
12.5
25
50
39
72
89
97
97
96
97
96
100
a
Reaction details; catalyst: oxidant : substrate: 2 : 1, temperature: 70 1C,
time: 24 h; solvent: mesitylene (4 ml).
present studies, similar conversion has been observed. The
effect of the catalyst amount on epoxidation of olefin was further
studied by varying the catalyst amount ranging from 12.5 to 100 mg
per 50 mmol of octene and the results are summarized in Table 2.
From the table it is evident that upon increase in the catalyst
amount, increase in olefin conversion was observed. Maximum
olefin conversion was obtained for the reaction which was
carried out using 100 mg of the catalyst. Based on the above
kinetic studies, the optimum reaction conditions viz., temperature
of 70 1C, catalyst loading of 100 mg and mesitylene as the solvent
were chosen for further studies.
The reaction was also studied using different catalysts and
results are reported in Table 3. The pure complex showed only
about 10% conversion at 4 h, which increases to 50% after 24 h
of reaction. The slow decomposition of complex 1 in solution
results in the lower activity observed.
Further, no significant conversion was observed in the absence
of the catalyst and parent SBA-15 materials. The molybdenum
carbonyl grafted onto diamine-functionalized SBA-15 (SBA-DA-Mo)
shows about 93% conversion at 4 h, reaching almost 97% after 24 h
of reaction. The conversion of the molybdenum carbonyl species
into the active Mo(VI) species was responsible for the observed higher
catalytic activity.3–5,8,9 Importantly, the FT-IR spectrum of SBA-DA-Mo
after the reaction (Fig. 2) retains the vibrational band around 910
and 955 cmÀ1, indicating the stability of the Mo complex on the
support. After the reaction, the SBA-DA-Mo samples were filtered and
washed with dichloromethane and reused; the results are shown in
Table 3. It is clear that molybdenum is retained as a dioxo complex
on the diamine-functionalized SBA-15 surface and remains active for
several recycle runs.
Fig. 7 Effect of temperature on epoxidation using the SBA-DA-Mo catalyst.
amine-functional group and they are in good agreement with those
in the literature.17 Further, an additional peak observed around
200 ppm indicates the presence of the carbonyl group (CO) in
complex 1.18 The estimated molybdenum percentage in the
SBA-DA-Mo sample is shown in Table 1. The sample shows
about 28 wt% Mo content which is similar to the theoretically
calculated value. The above fact indicates that all the molybdenum
species are effectively anchored on the surface of the diamine.
A thorough characterization of SBA-DA-Mo was carried out for
epoxidation of cyclooctene at different temperatures, catalyst loadings,
solvents etc., in the presence of 5.5 M TBHP in decane as the oxidant.
Fig. 7 shows the effect of reaction temperature on epoxidation
of cyclooctene. It can be seen from the figure that as the reaction
temperature increases, the olefin conversion increases linearly. The
maximum conversion of about 90–95% was observed at 60–70 1C
with the exclusive formation of epoxide as the major product.
Subsequently, by keeping the reaction temperature at 70 1C, the
reaction was studied to understand the role of various solvents, such
as methanol, acetonitrile, hexane and mesitylene. The results are
displayed in Fig. 8. It is evident from the figure that, irrespective
of the solvent, the olefin conversion was found to be more than
90% in all cases. Since the solvent is not coordinating with active
molybdenum species, irrespective of the solvent chosen for the
Table 3 Oxygenation of olefin using various materialsa
S. no.
1
Catalyst
Time (h)
Con. (%)
Epoxide sel. (%)
Without catalyst
4
24
4
24
4
24
4
24
4
18
23
22
30
10
50
93
97
96
97
94
15
12
17
14
43
94
86
96
87
92
90
2
3
4
SBA-15
Complex 1
SBA-DA-Mo
5b
6c
7d
1st recycled
2nd recycled
3rd recycled
4
4
a
Reaction details; catalyst: oxidant: substrate: 0.0063: 2 : 1, temperature:
b
70 1C, solvent: mesitylene. 1st-recycled SBA-DA-Mo catalyst respectively.
c
d
2nd-recycled SBA-DA-Mo catalyst respectively. 3rd-recycled SBA-DA-Mo
catalyst respectively.
Fig. 8 Effect of solvent on epoxidation using the SBA-DA-Mo catalyst.
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Table 4 Oxygenation of various olefins over the SBA-DA-Mo catalysta
(b) C. L. Hill, in Advances in Oxygenated Processes, ed.
A. L. Baumstark, JAI, London, 1988, vol. 1, p. 1; (c) N. Mizuno,
K. Yamaguchi and K. Kamata, Coord. Chem. Rev., 2005,
249, 1944; (d) S. A. Hauser, M. Cokoja and F. E. Kuhn, Catal.
Sci. Technol., 2013, 3, 552.
2 (a) A. Sakthivel and M. Sathiyendiran, in Molybdenum and its
compounds, ed. V. S. Saji and S. I Lopatin, Nova Science
Publishers, 2014, ISBN: 978-1-63321-210-7 at press and the
reference therein; (b) N. Grover and F. E. Kuhn, Curr. Org.
Chem., 2012, 16, 16; (c) K. R Jain, W. A. Hermann and
F. E. Kuhn, Coord. Chem. Rev., 2008, 252, 556;
(d) F. E. Kuhn, A. M. Santos and M. Abrantes, Chem. Rev.,
2006, 106, 2455.
Epoxide
Time (h) Con. (%) sel. (%)
S. no. Reactant
1
Product
4
93
97
86
96
24
4
24
91
98
78
34
2
3
4
4
24
24
42
96
59
95
16
70
4
24
4
24
4
16
89
39
77
19
60
82
91
19
86
76
86
5
6
3 (a) J. Zhao, K. R. Jain, E. Herdtweck and F. E. Kuhn, Dalton
Trans., 2007, 5567; (b) J. Zhao, A. M. Santos, E. Herdtweck
and F. E. Kuhn, J. Mol. Catal. A: Chem., 2004, 222, 265;
(c) F. E. Kuhn, A. D. Lopes, A. M. Santos, E. Herdtweck,
7
24
˜
J. J. Haider, C. C. Romao and A. Gil Santos, J. Mol. Catal. A:
a
Reaction details; catalyst: oxidant: substrate: 0.0063: 2 : 1, temperature:
Chem., 2000, 151, 147; (d) F. E. Ku¨hn, A. M. Santos, A. D. Lopes,
70 1C, solvent: mesitylene.
˜
I. S. Gonçalves, E. Herdtweck and C. C. Romao, J. Mol. Catal. A:
Chem., 2000, 164, 25.
Further, SBA-DA-Mo was studied for a series of olefins and the
results are summarized in Table 4. The catalyst showed excellent
conversion for both cyclic and acyclic olefins, forming epoxide as
the major product. In the case of cyclohexene, a considerable
amount of the ring-opening product was formed after 24 h, as
evident from GC-MS. The catalyst also showed about 59% conversion
after 24 h for stilbene. However, in the case of styrene, the polymer-
ization of styrene occurred under these reaction conditions. For
acyclic olefins, the double bond at the terminal position (1-octene)
showed better conversion compared to olefins containing a double
bond at the 2- or 4-(2-octene and 4-octene) position owing to the
orientation effect of olefins on active sites. Overall, the catalyst is
found to be stable and active for the epoxidation of several olefins
under moderate reaction conditions.
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Conclusion
In summary, the current work established a simple method to
graft molybdenum carbonyl onto the surface of mesoporous
molecular sieves. The presence of active molybdenum oxo-species
on SBA-DA-Mo, which was formed upon TBHP treatment, resulted
in promising catalytic activity for olefin epoxidation. Importantly,
the active species are found to remain intact on the surface and the
catalyst is recyclable.
¨
E. Manoury, J.-C. Daran, P. Sozen-Aktas, F. Demirhan and
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Acknowledgements
The authors extend their sincere and grateful thanks to CSIR
(Project No. 01(2516)/11/EMR-II), New Delhi, for financial support.
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