Novel economic and green approach to the synthesis of highly active W-MCM41 catalyst in oxidative cleavage of cyclopentene

Article abstract of DOI:10.1039/b211666a

A highly active and perfectly structured W-MCM41 catalyst for the oxidative cleavage of cyclopentene to glutaraldehyde was synthesized through a novel economic and green synthetic method by using Na₂SiO₃ as the Si source and CH₃COOC₂H₅ as the hydrolyzer.

Full text of DOI:10.1039/b211666a

Novel economic and green approach to the synthesis of highly active
W-MCM41 catalyst in oxidative cleavage of cyclopentene
Wei-Lin Dai,*a Hao Chen,a Yong Cao,a Hexing Li,b Songhai Xiea and Kangnian Fana
a Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry,
Fudan University, Shanghai 200433, P. R. China. E-mail: wldai@fudan.edu.cn; Fax: 86-21-65641740;
Tel: 86-21-65643792-6
b Department of Chemistry, Shanghai Normal University, Shanghai 200234, P. R. China.
E-mail: Hexing-Li@shtu.edu.cn
Received (in Cambridge, UK) 26th November 2002, Accepted 21st February 2003
First published as an Advance Article on the web 5th March 2003
A highly active and perfectly structured W-MCM41 catalyst
for the oxidative cleavage of cyclopentene to glutaraldehyde
was synthesized through a novel economic and green
synthetic method by using Na2SiO3 as the Si source and
CH3COOC2H5 as the hydrolyzer.
solution (Na2WO4·2H2O, 0.2 mmol g21) is mixed with the
above solution. Under vigorous stirring, 7.5 ml of ethyl acetate
is rapidly added into the solution one time. After vigorous
stirring for 6 min, the obtained mixture is stirred moderately for
24 h at 358 K and then centrifuged to obtain the solid. After
washing with de-ionized water 3 times, the solid is air-dried and
then calcined in air at 873 K for 2 h to remove the template,
CTMAB. It should be also noted that this kind of W-MCM41
material is very stable after the removal of the template.
Changing the amount of the sodium silicate or sodium tungstate
initially added can obtain a series of samples with different
molar ratios of Si to W. In this procedure, ethyl acetate is
employed as the acid-producing precursor instead of the
conventional strong acid, such as HCl, employed by other
authors in their work. When the ethyl acetate is mixed with
water at a certain temperature, ethyl acetate will hydrolyze to
produce acetic acid, a mild acid. So this synthesis occurs under
mild acidic conditions and is environmentally friendly. No
noxious substances are needed and no toxic waste is generated.
Hence, it can be called a green process.
As confirmed by the ICP-AES (Jarrell-As Atom Scan 2000),
the as-synthesized W-MCM41 sample consists of only three
elements: Si, O and W. The residue Na is too low to be detected
( < 0.01 mass%). The XRD (Bruker Advance D8) pattern of the
W-MCM41 shows three well-defined sharp Bragg peaks
indexed as (100), (110) and (200), respectively, characteristic of
MCM41 materials. In all the XRD patterns of the sample with
Si/W ratios larger than 30, no peaks corresponding to the
crystalline WO3 are observed, meaning that tungsten oxide is
highly dispersed in the silica matrix.
The typical structure of the W-MCM41 was further attested
through TEM (Jeol JEM2010) as shown in Figure 1, a very clear
and perfectly ordered hexagonal structure of the pores of the W-
MCM41 is observed. To the best of our knowledge, the
extremely long range ordered mesoporous structure of W-
MCM41 is reported for the first time.
The FT-IR (Nicolet Model 205) spectrum of the W-MCM41
showed the typical band peak at 963 cm21, indicating that the
tungsten species was incorporated into the inner framework of
MCM41. Similar assignments had been made for Ti- and V-
containing molecular sieves.7,8 When the Si/W ratio was as high
as 27, the collapsed mesoporous structure of W-MCM41
framework resulted in the WOx species being present only on
the matrix surface, as evidenced by the absence of the FT-IR
band peak at 963 cm21 of the sample. In the mild acidic
synthesis situation, the tungsten exists with low polymerization,
which may make the tungsten oxide easy to be dispersed and
incorporated into the matrix composed of tetragonal SiO4.
Raman (JY Super LabRam) and DR UV-VIS (Jasco V-550)
spectra also support this suggestion since no absorption band
corresponding to crystalline WO3 appeared.
MCM41, first reported by Mobil in 1992,1,2which shows not
only very large specific area of up to 1500 m2 g21, but also
uniform dimensional and hexagonally shaped pores indexed in
the space group p6m, is widely studied in many fields. Metal
ion-containing MCM41, possessing regular nano-ordered me-
sopores and high density of isolated active sites, has attracted
much attention as a new host of oxidation catalysts, especially
for liquid-phase oxidation reactions because convenient diffu-
sion of relatively bulky molecules can be expected. Many
researchers reported the synthesis and characterizations of
metal ion-containing MCM41, and some of these materials,
e.g., Ti-, Fe- and V-MCM41, presented peculiar catalytic
characters for the reaction of larger molecules.3–9Only one
study has been reported on the synthesis and characterization of
W-MCM41 using a different method,10,11but the details about
the location and the leaching behavior of active tungsten
components are still not clear. On the other hand, the promising
catalytic character of W-MCM41 is limited by a shortage of
suitable synthesis methods reported in the literature; in all cases,
the source of the silica for the synthesis is the costly organic
silica precursor, ethyl silicate (TEOS). The use of expensive
ethyl silicate limits synthesis of W-MCM41 on a large scale in
industry. Using a convenient and cheap inorganic silica
precursor in place of an organic one may be a very important
improvement to the synthesis of the W-MCM41. Furthermore,
almost every process for the synthesis of MCM41 needs strong
acid—HCl as hydrolyzer, which will bring about considerable
pollution to the circumstance and inevitable corrosion to the
equipment when applied to large scale production. Herein we
report for the first time the synthesis of W-MCM41 using
inorganic silicate as the silica precursor and ethyl acetate as the
hydrolyzer. The as-synthesized W-MCM41 is found to show
perfect uniform dimensional and hexagonal structure which has
not been reported yet and extremely high catalytic activity
towards the oxidative cleavage of cyclopentene (CPE) to
prepare glutaraldehyde (GA), a very important chemical used as
disinfectant and germicide widely. It is well known that the
commercial process for GA production is an acrolein route, in
which the high price of the raw materials restricts its wide
application. The new route using CPE as the raw material,
aqueous H2O2 as the oxidant and supported WO3 as the catalyst
developed by our group is not yet ready for industry owing to
the leaching of active components and the expensive raw
materials needed in the synthesis of the catalyst.12–15In the
present work, the as-prepared W-MCM41 exhibits excellent
anti-leaching properties towards the targeted reaction.
It is very interesting to find that the as-synthesized W-
MCM41 sample shows extremely high activity and selectivity
toward the cleavage reaction of CPE by using aqueous H2O2 as
the oxidant, different from that reported previously,9,10 which
only showed a hydroxylation effect towards the oxidation
A typical synthesis is as follows: to the stirred water at 358 K
are added 5.825 g of sodium silicate, denoted as Na2SiO3·9H2O,
and 2.45 g of cetyltrimethyl-ammonium bromide (CTMAB), to
obtain an aqueous solution, then 2 ml of sodium tungstate
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CHEM. COMMUN., 2003, 892–893
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Fig. 1 HRTEM images of W-MCM41 samples (a), taken with the electronic beam parallel to the pore direction; (b) taken with the electronic beam
perpendicular to the pore direction.
Table 1 Catalytic behaviour of various W-containing catalysts
Sample
SBET/m2 g21
Pore diameter/nm
CPE conv./%
H2O2 conv./%
GA Yield/%
TOFe/h21
Leached W/ppm
Si-MCM41
aWO3
bWO3/SiO2*
cWO3/SiO2**
dW-MCM41
1152
–
200
230
1100
2.5
–
1.0
3.0
2.6
0
1.5
51
83
100
0
0.1
72
90
100
0
0
15
48
71
0
0
0
4
70
0.8
0.04
1.4
2.2
3.2
Reaction time: 24 h, reaction temperature: 35 °C, the mole ratio of H2O2+CPE+WO3 = 2+1+0.016, the volume ratio of t-BuOH/CPE = 10.a crystalline WO3
b prepared through incipient wetness impregnation with ammonium tungstate solution (* and** are commercial products of silica). c prepared through
incipient wetness impregnation with ammonium tungstate solution (* and** are commercial products of silica). d Si/W = 32. e TOF: moles of CPE converted
per mole of WO3 in the catalyst per hour.
reaction of cyclohexene in a H2O2–HAc medium. As shown in
Table 1, the W-MCM41 gives 100% conversion of CPE and
71% selectivity towards GA, much higher than that over WO3
and WO3/SiO2 catalysts, showing attractive potential for
practical applications. As also shown in Table 1, unsupported
WO3 shows little activity towards the title reaction, suggesting
that the WOx species incorporated into the uniform framework
of mesoporous materials, such as MCM41, shows essential
activity and selectivity towards the cleavage reaction. The TOF
values shown in Table1 unambiguously verified the conclusion.
The high specific surface area ( ~ 1100 m2 g21) and ordered
large pore diameter ( ~ 2.6 nm) of the W-MCM41 were affirmed
to be important factors for its high catalytic activity as compared
to the supports from commercial silica. Another outstanding
property of this novel catalyst is its good stability and
reproducibility. It can be reused after washing with acetone at
35 °C and dried at 120 °C. No loss of activity and selectivity or
the collapse of its mesporous structure were observed after 7
runs. We verified that the reaction did not occur in the absence
of catalyst and it was not the result of homogeneous catalysis by
leached active sites. The leached WOx species after 7 runs was
lower than 1 ppm, which could also be confirmed by the
elemental analysis of W in the used catalyst after 7 runs.
The present results confirm that WOx species incorporated
into framework of MCM41 materials are efficient catalytic sites
for cleavage reaction of alkenes. Preliminary characterization
results suggest that the novel synthesis method leads to a
uniform distribution of the WOx active sites throughout the
mesoporous structure of MCM41 without any conglomeration.
This novel W-MCM41 catalyst is an efficient, selective and
recyclable catalyst for the production of GA by the selective
oxidation of CPE using H2O2 as the oxidant. Thus, efficient
WOx sites can be created by a simplified hydrothermal method
and the highly selective and recyclable catalyst does not need
any expensive organic precursors or toxic materials.
This work was financially supported by NSFC (Project
20073009), the Natural Science Foundation of Shanghai
Science & Technology Committee (02DJ14021), and the
Committee of the Shanghai Education (02SG04).
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