Highly active delaminated Ti-MWW for epoxidation of bulky cycloalkenes with hydrogen peroxide

Article abstract of DOI:10.1246/cl.2003.326

A novel titanosilicate, prepared by the partial delamination of acid-treated Ti-MWW, possesses an extremely high specific surface area and proves to be a selective and active liquid-phase oxidation catalyst for bulky alkenes.

Full text of DOI:10.1246/cl.2003.326

326
Chemistry Letters Vol.32, No.4 (2003)
Highly Active Delaminated Ti-MWW for Epoxidation of Bulky Cycloalkenes with
Hydrogen Peroxide
Duangamol Nuntasri, Peng Wu, and Takashi TatsumiÃ
Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University,
79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501
(Received November 26, 2002; CL-021011)
A novel titanosilicate, prepared by the partial delamination of
resulting mixture was placed in an ultrasonic bath (300 W,
35 kHz) for 1 h, and its pH was then adjusted below 2 by using 2 M
HNO3 aqueous solution. The solid product was collected by
centrifugation or filtration. The organic species were removed by
the calcination at 823 K to yield the modified samples, Ti-MWW-
m (No. 2-5 in Table 1). ICP analyses indicated that the
modification dissolved a part of Ti out of the framework with
increasing TPAOH amount. Nevertheless, the tetrahedral site of
Ti species survived the above treatment since UV-vis spectro-
scopy showed that all the samples exhibited only the 220 nm band
in their spectra.
The structural change during the treatment was traced by X-
ray diffraction (XRD) patterns. After the acid treatment of as-
synthesized Ti-MWW partially the 001 and 002 diffraction peaks
due to the layered structure disappeared as a result of the removal
of the organic structure-directing agent intercalated within the
layers (Figures 1a and b). Subsequent calcination caused a
complete dehydroxylation condensation to lead to the 3D MWW
structure (Figure 1c). The treatment of acid-washed Ti-MWW
with the surfactant solution expanded its layers to give diffraction
with a d spacing of 3.8 nm (Figure 1d). After the expanded sample
was subjected to the ultrasonic treatment followed by acidifica-
tion and calcination, the expanded layers almost disappeared
(Figure 1e). Although the modified samples maintained the
MWW structure, their specific surface area turned out to be 742-
873 m2gÀ1, extremely larger than common Ti-MWW samples,
which is in agreement with the case of ITQ-2, indicating that Ti-
MWW has been delaminated partially to exhibit more accessible
space.5
acid-treated Ti-MWW, possesses an extremely high specific
surface area and proves to be a selective and active liquid-phase
oxidation catalyst for bulky alkenes.
It is a main current in the research field of titanosilicate
catalysts to look for new ones with open reaction space suitable
for the liquid-phase oxidation of bulky organic chemicals with an
environmentally friendly oxidant of hydrogen peroxide. Recent-
ly, a novel titanosilicate with the MWW topology (typically
known as MCM-22), Ti-MWW, has been successfully hydro-
thermally synthesized using boric acid as a crystallization-
supporting agent1 or postsynthesized from highly deboronated
MWW through a reversible structural conversion.2 Ti-MWW,
having a unique crystalline structure of supercages, 12-membered
ring (MR) side pockets and sinusoidal 10 MR channels, exhibits
superiority to conventional TS-1 and Ti-Beta in the epoxidation
of both linear and cyclic alkenes.3 Since the three-dimensional
crystalline structure of MWW originates from a lamellar
precursor, pillaring and delamination techniques have been
adopted to convert its aluminosilicate, i.e. MCM-22 into a
micro-mesoporous hybrid and a highly accessible material,
respectively.4;5 In this study, the delamination method has been
applied to Ti-MWW for the first time to prepare a highly active
epoxidation catalyst for bulky alkenes.
B-free Ti-MWW was prepared by following the procedures
reported previously.2 As-synthesized Ti-MWW (Si/Ti=30) was
refluxed with 2 M HNO3 for 18 h to remove the extraframework
Ti species. The acid-washed Ti-MWW (1 g) was then treated at
353 K for 16 h in a mixture of hexadodecyl trimethylammonium
bromide (5.6 g), 22.5 wt% tetrapropylammonium hydroxide
(TPAOH) aqueous solution (3.8-5.6 g) and water (12 g). The
Table 1 compares the results of cyclopentene epoxidation
with H2O2 over various titanosilicates. The products were mainly
cyclopentene oxide together with diol resulting from the acidic
hydrolysis of epoxide, and 2-cyclopentene-1-one and 2-cyclo-
Table 1. Physicochemical and catalytic properties of various titanosilicatesa
Si/Ti ALANG Cyclopentene epoxidation
mole ratio /m2gÀ1 Alkene conv. TON
Epoxide selec. H2O2 conv. H2O2 selec.
No. Catalyst
/mol%
/mol (mol Ti)À1
/mol%
/mol%
/mol%
1
2
3
4
5
6
7
Ti-MWWb
46
48
56
61
68
36
35
559
783
742
873
839
525
621
15.7
32.6
29.4
27.1
25.6
17.3
9.9
95
95
98
97
96
96
94
61
15.9
33.4
30.2
27.4
27.0
20.5
11.1
99
98
98
96
93
83
89
Ti-MWW-m (3.8)c
Ti-MWW-m (4.9)c
Ti-MWW-m (5.1)c
Ti-MWW-m (5.6)c
TS-1d
193
202
203
213
77
Ti-Betae
43
b
aReaction conditions: cat., 25 mg; cyclopentene, 5 mmol; H2O2, 5 mmol; CH3CN, 5 mL; temp., 313 K; time, 2 h. As-synthesized
material was refluxed with 2 M HNO3 and calcined subsequently. cThe number in parentheses indicates the amount of TPAOH used for
1 g of acid-treated Ti-MWW. dSynthesized according to Ref. 8. eSynthesized according to Ref. 9.
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.4 (2003)
2θ = 2.3, d = 3.8 nm.
327
e
d
001 002
c
b
a
0
5
10
15
20
25
30
2 Theta / deg
Figure 1. XRD patterns of as-synthesized Ti-MWW (a), sample a treated with 2 M HNO3 and dried Ti-MWW
(b), sample b calcined (c), sample b treated with surfactant and TPAOH solution (d), sample d subjected to
ultrasound treatment and calcination (e).
pentene-1-ol produced from allylic oxidation. Ti-MWW showed
higher specific activity than TS-1 and Ti-Beta, and also good
selectivity to cyclopentene oxide and H2O2 efficiency. The
inferior performance of larger pore Ti-Beta should be ascribed to
its high hydrophilicity related to the hydroxyl groups on defect
sites within the framework. The delamination, on the other hand,
doubled the TON for cyclopentene conversion irrespective of the
amount of TPAOH used (Table 1, No. 2-5). As the epoxidation of
cylopentene favors the Ti active sites located in more accessible
reaction space, the above results suggested that the delamination
treatment has resulted in such sites. The delamination generally
cleaves a part of Si-O-Si linkage to form a large amount of acidic
silanol groups.5{7 Interestingly, such silanol groups did not
contribute to the hydrolysis of oxide product since the epoxide
selectivity was maintained at a high level (>96 mol%).
Furthermore, the epoxidation of cyclooctene and cyclodo-
decene were carried out to investigate the possibility of
delaminated Ti-MWW catalyst for more bulky substrates
(Table 2). Compared with cyclopentene epoxidation, the TON
decreased sharply with increasing carbon number of cycloalkenes
to 12 for both Ti-MWW and Ti-Beta, which is simply due to a
more serious restriction of their pores on the diffusion of bulky
molecules. Especially, Ti-Beta, without such open pores as the
side pockets of Ti-MWW, was less active for cyclododecene
oxidation. The activity of Ti-MWW-m was nearly two times as
high as that of Ti-MWW for cyclooctene and cyclododecene. The
higher activity of Ti-MWW-m proves that the delamination
presents a benefit to produce more open and accessible reaction
space to large molecules. A partial opening of the parts where the
supercages are formed upon a normal calcination process is
presumed to correspond to such space.
In conclusion, delamination modification on acid-treated Ti-
MWW has provided a selective oxidation catalyst with extremely
high specific surface area and improved catalytic activity for
cycloalkenes with various molecular sizes.
References
1
P. Wu, T. Tatsumi, T. Komatsu, and T. Yashima, Chem. Lett.,
2000, 774; P. Wu, T. Tatsumi, T. Komatsu, and T. Yashima, J.
Phys. Chem. B, 105, 2897 (2001).
2
3
P. Wu and T. Tatsumi, Chem. Commun., 2002, 1026.
P. Wu, T. Tatsumi, T. Komatsu, and T. Yashima, J. Catal.,
202, 245 (2001).
4
W. J. Roth, C. Kresge, J. C. Vartuli, M. E. Leonowicz, A. S.
Fung, and S. B. McCullen, Stud. Surf. Sci. Catal., 94, 301
(1995).
5
6
7
A. Corma, V. Fornes, S. B. Pergher, Th. L. M. Maesen, and J.
G. Buglass, Nature, 396, 353 (1998).
´
A. Corma, U. Diaz, M. E. Domine, and V. Fornes, J. Am.
Table 2. Cycloalkene
titanosilicatesa
epoxidation
with
H2O2
over
Chem. Soc., 122, 2804 (2000).
A. Corma, U. Diaz, M. E. Domine, and V. Fornes, Angew.
Catalyst
TON/mol (mol Ti)À1
cyclooctene cyclododecene
´
Chem., Int. Ed., 39, 1499 (2000); A. Corma, U. Diaz, M. E.
´
Domine, and V. Fornes, Chem. Commun., 2000, 137.
Ti-MWW
Ti-MWW-m (5.0)
Ti-Beta
aReaction conditions: cat., 25 mg; cyclooctene, 5 mmol;
cyclododecene, 2.5 mmol; H2O2, equal to alkene amount;
CH3CN, 10 mL; temp., 333 K; time, 2 h.
24
37
23
9
18
5
8
9
M. Taramasso, G. Perego, and B. Notari, U. K. Patent
2071071 (1981); Chem. Abstr., 95, 206272k.
T. Blasco, M. A. Camblor, A. Corma, P. Esteve, J. M. Guil, A.
´
Martꢁnez, J. A. Perdigon-Melon, and S. Valencia, J. Phys.
Chem. B, 102, 75 (1998).
´
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