carbonyl vibration of the keto group at 1719 cm21, a second
Table 2 Activity over Zr- and Sn-beta in the presence of water
2
1
signal appeared at 1675 cm . Upon desorption at 200 °C, the
former signal disappeared completely, whereas the latter still
had substantial intensity, indicating a strong dative bond from
the carbonyl oxygen to the Zr-centers in the zeolite. The shift of
Zr100
TOFa
Sn125
Conv. (%) TOFa
Water added
wt.%)
b
b
(
Conv. (%)
2
1
45 cm
is comparable to that reported for Sn-substituted
0
0
2.9
9.1
632
447
410
304
99
97
95
84
425
251
86
81
60
29
7
11
zeolite beta and larger than that observed for Ti-substituted
zeolite.
.6
Some structural data and catalytic activities of the various
zeolite beta catalysts for the MPV reduction of 4-tert-
butylcyclohexanone are given in Table 1. Zr-beta catalysts were
much more active than the Al- and Ti-zeolite beta catalysts.
They performed even better than a Sn-zeolite beta. 4-tert-
butylcyclohexanol was the only reaction product. The thermo-
dynamically less favored cis-isomer was formed with 99%
selectivity. This high regioselectivity of the reduction proves
that the reaction proceeds in the channels of the zeolite
structure, where steric constraints force the reaction to proceed
via the less bulky transition state.6 Si-beta impregnated with
zirconium oxychloride was inactive indicating that isolated Zr
atoms in the framework of zeolite beta are important for
activity. The appropriate acidity and ligand exchangeability of
Zr-beta may be the cause of the high activity. IR spectra of
adsorbed pyridine showed that Lewis acid sites are predominant
in Zr-beta, Ti-beta, and Sn-beta, with essentially no Brønsted
acid sites.
Of particular interest is the high tolerance of the new material
towards moisture. Table 2 compares the turnover numbers
measured over the Zr-zeolite beta catalyst and a Sn-zeolite beta
synthesized following Corma’s procedure.11 The turnover
frequency has been calculated from the integral reaction rate
over the first 5 minutes of reaction. Zr-beta retained almost 50%
of its activity in the presence of 9.1% water. In contrast, Sn125
was drastically affected by the presence of water. This
observation agrees with the result of Corma et al. who found
that the TON dropped from 109 to 3.8 upon exposure to about
21
Reaction conditions: 1.3 mmol of 4-tert-butylcyclohexanone in 83 mmol
2-propanol, 100 mg catalyst under reflux and stirring 82 °C. Turn-over
frequency after initial 5 min reaction: mol per mol·h b Conversion after 30
a
min.
by hydrophobizing the surface in a post-synthesis silylation step
with hexamethyldisilazane. The activity of the modified
material at 10% water content was 48 mol per mol·h, or about
,15
5
0% of the activity under dry conditions. The Zr-beta
synthesized for this study retained this level of activity in the
presence of water, without requiring additional surface mod-
ification. The catalyst can be easily recovered by filtration and
could be re-used after washing with 2-propanol. Even after the
eighth cycle, the activity of the catalyst was essentially
unchanged.
In conclusion, we have shown that framework substitution
with Zr in the zeolite beta structure is possible to a level of 1.3%
(
Si/Zr = 75). Well crystallized Al-free Zr-zeolite beta can be
obtained in a seeded synthesis in fluoride medium. The material
is an excellent catalyst for the MPV reduction, and is
particularly valuable because of its tolerance to moisture.
Notes and references
1
C. F. de Graauw, J. A. Peters, H. van Bekkum and J. Huskens, Synthesis,
994, 10, 1007.
1
1
0% water content. The authors reported that the water
2
T. Ooi, H. Ichikawa and K. Maruoka, Angew. Chem. Int. Ed., 2001,
40(19), 3610.
resistance of their Sn catalyst could be considerably improved
3
4
E. J. Campbell, H. Zhou and S. T. Nguyen, Org. Lett., 2001, 3, 2391.
Lebrun, J. L. Namy and H. B. Kagan, Tetrahedron Lett., 1991, 32,
2355.
Table 1 MPV reduction of 4-tert-butylcyclohexanone over various
substituted zeolite beta catalysts
5 P. Leyrit, C. McGill, F. Quignard and A. Choplin, J. Mol. Catal. A,
996, 112, 395.
1
Surf. Area
6 E. J. Creyghton, S. D. Aneshie, R. S. Downing and H. van Bekkum,
Chem. Commun., 1995, 1859.
2
21
Conv. (%)a
cis : transb
Catalyst
Si-beta
Zr-beta
Zr75
Zr100
Zr200
Sn125
Ti100
Al100
Si/M
(m g
)
7
R. Anwander, C. Palm, G. Gerstberger, O. Groeger and G. Engelhardt,
Chem. Commun., 1998, 1811.
—
95
84
107
194
125
100
100
487
308
499
490
474
500
468
451
0
0
97.3
95.2
72.8
70.6
—
—
c
8 P. S. Kumbhar, J. Sanchez-Valente, J. Lopez and F. Figueras, Chem.
Commun., 1998, 535.
> 99 : 1
> 99 : 1
> 99 : 1
98 : 2
100 : 0
—
9 Y. Zhu, S. Jaenicke and G. K. Chuah, J. Catal., 2003, 218, 396.
10 S. H. Liu, S. Jaenicke and G. K. Chuah, J. Catal., 2002, 206, 321.
11 A. Corma, M. E. Domine and S. Valencia, J. Catal., 2003, 215, 294.
12 K. Tanabe and W. F. Hölderich, Appl. Catal. A, 1999, 181, 399.
13 B. Rakshe, V. Ramaswamy, S. G. Hegde, R. Vetrivel and A. V.
Ratnasamy, Catal. Lett., 1997, 45, 41.
14 T. Blasco, M. A. Camblor, A. Corma, P. Esteve, J. M. Guil, A. Martinez,
J. A. Perdigon-Melon and S. Valencia, J. Phys. Chem. B, 1998, 102,
75.
d
2.9
< 0.25
d
Reaction conditions: 5.2 mmol 4-tert-butylcyclohexanone, 83 mmol
a
2-propanol, 100 mg catalyst, under reflux and stirring at 82 °C. Conversion
b
c
after 60 min. 4-tert-butylcyclohexanol only product formed. ZrOCl
impregnated on Si-beta. 1.3 mmol substrate.
2
d
1
5 R. A. Sheldon, Pure Appl. Chem., 2000, 72, 1233.
CHEM. COMMUN., 2003, 2734–2735
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