a higher benzoylation activity compared to that of the
commercial zeolite regarding the difference in the Si/Al ratio,
i.e. Si/Al ratio of 50 for the supported zeolite instead of 12.5 for
the commercial zeolite. The dispersion of the zeolite on the
support surface which leads to a higher contact surface with the
reactants was advanced to explain the observed results.
Larger zeolite particles are more sensitive to deactivation due
to the formation of heavier coke inside the micropore. From the
results obtained, one should thus expect that the deactivation of
the commercial zeolite originated from another factor. The
difference in activity observed between the supported and
unsupported HBEA catalysts can be attributed to the bigger
apparent size of the bulk zeolite due to the easy aggregation
between the different zeolite particles on the commercial
catalyst. The apparent particle size of the active supported
zeolite was expected to be smaller than that of the unsupported
one due to its dispersion on the support surface. The bigger
apparent size of the commercial zeolite probably decreased the
rate of the reactant and product diffusion in and out of the
zeolite pores leading to irreversible deactivation by heavier
compounds formed later within the pores. It is though that the
partition between the reactants and products inside the zeolite
pores and the bulk solvent plays an important role in the
maintenance of the catalytic activity and prevents deactivation
by the formation of coke or heavier products.12
Temperature-Programmed Oxidation (ESI†) carried out on
the catalysts after reaction clearly indicates that a higher amount
of coke was formed inside the commercial zeolite compared to
the supported one. Such results are in line with the low Si/Al
ratio of the commercial zeolite which is more sensitive to coke
formation. The range of combustion temperature on the
commercial unsupported zeolite was also broader and sig-
nificantly shifted towards high temperatures, i.e. 100 °C,
indicating the presence of coke with heavier molecular
weight.
Scheme 1
pure SiC) to more than 100 m2
microporous contribution (ca. 60 m g ) according to the N
adsorption isotherm. Taking into account the unmodified
surface area of the starting SiC support the real surface area of
the zeolitic deposit amounted to about 500 m g with a
microporosity surface area contribution of about 350 m g
which was in good agreement with the surfaces generally
obtained with zeolitic materials.
Catalytic tests were carried out under the following reaction
conditions: catalyst weight, 0.2 g of zeolite (for the supported
zeolite the total catalyst weight was 2 g with about 8 ± 2 wt.%
zeolite loading), reaction temperature, 120°C, anisole (0.03
mmol), benzoyl chloride (0.02 mmol). The benzoylation (see
Scheme 1) catalytic results obtained on the supported beta
zeolite catalyst are reported in Fig. 2A and compared with those
obtained on an unsupported HBEA zeolite (Fig. 2B). On the SiC
supported catalyst the benzoylation activity was relatively high
with a total conversion of 71% after 24 h on stream. The
selectivity towards aromatic ketone I, para-methoxybenzophe-
none, reached about 95% (Fig. 2A) while isomer II, ortho-
methoxybenzophenone, only amounted to less than 5%. It is
significant to note that no trace of ester has been observed. The
catalyst was then washed several times with dichloromethane in
order to remove the trapped products inside its pores and then
re-tested for benzoylation under the same reaction conditions.
The conversion and ketone selectivity remained almost un-
changed for the second and third tests on the supported zeolite
catalyst as show in Fig. 2A.
g
21
21
along with a large
2
2
2
21
2
21
The benzoylation activity and selectivity obtained under the
same reaction conditions on the commercial bulk beta zeolite
catalyst with higher acidity strength (Zeolysts International,
with a Si/Al ratio given by the supplier of 12.5 and an average
particle size of ca. 10 nm) are reported in Fig. 2B. The post-
reaction treatment (washing) was identical to that used for the
supported catalyst. During the first cycle, similar activity and
ketone selectivity were observed. However, significant deacti-
vation was observed during the second cycle on the unsupported
In summary, beta zeolite activity and stability in the
benzoylation reaction can be greatly improved by supporting it
on a silicon carbide carrier using classical hydrothermal
synthesis. In addition, the macroscopic shaping of the zeolite
renders recovery and cleaning easier as compared to the
unsupported material. Work is ongoing in the laboratory to
investigate the physico-chemical properties of the supported
zeolite, before and after reaction, using more sensitive tech-
27
29
niques such as NMR ( Al and Si) and to evaluate its activity
directly in a fixed-bed configuration which is commercially
more attractive.
catalyst. Similar results have been reported earlier by different
authors9
,10
during the benzoylation of anisole by acetic
anhydride in a batch reactor over HBEA. The loss of catalytic
performance was due to several factors: coke formation during
the test by acidic condensation of the products inside the zeolite
pores9 and/or de-alumination of the catalyst by the product,
i.e. acetic acid, based on Al MAS NMR spectroscopy. The
similar rates of benzoylation as a function of time on stream
shown in Fig. 1A and B indicate that supported zeolite displays
Notes and references
1 H. L. Hoffman and L. Riddle, Hydrocarbon Process., Int. Ed., 1988, 67,
,10
27
11
41.
2
3
4
R. M. Barrer, in Hydrothermal Chemistry of Zeolites, Academic Press,
London, 1987.
V. Valtchev, J. Hedlund, B. J. Schoeman, J. Sterte and S. Mintova,
Microporous Mater., 1997, 8, 93.
J. C. Jansen, J. H. Koegler, H. van Bekkum, H. P. A. Calis, C. M. van
den Bleek, F. Kapteijn, J. A. Moulijn, E. R. Geus and N. van der Puil,
Microporous Mesoporous Mater., 1998, 21, 213.
5
6
M. Xu, M. Cheng and X. Bao, Chem. Commun., 2000, 1873.
J. Garcia-Martinez, D. Cazorla-Amoros, A. Linares-Solano and Y. S.
Lin, Microporous Mesoporous Mater., 2001, 42, 255.
S. Basso, J. P. Tessonnier, C. Pham-Huu and M. J. Ledoux, Fr. Pat.
Appl. No. 02-00541, 2002.
7
8
9
M. J. Ledoux and C. Pham-Huu, CaTTech, 2001, 5, 226.
U. Freese, F. Heinrich and F. Roessner, Catal. Today, 1999, 49, 237.
1
0 E. G. Derouane, C. J. Dillon, D. Bethel and S. B. Derouane-Abd Hamid,
Fig. 2 Alkylation results, conversion and ortho-methoxybenzophenone
J. Catal., 1999, 187, 209.
(
labelled I) and para-methoxybenzophenone (labelled II) selectivity,
11 T. Jaimol, A. K. Pandey and A. P. Singh, J. Mol. Catal. A: Chem., 2001,
170, 117.
12 E. G. Derouane, CaTTech, 2001, 5, 214.
obtained after 24 h of reaction as a function of the catalytic cycling over the
SiC supported beta zeolite (A) and the unsupported one (B).
CHEM. COMMUN., 2002, 2418–2419
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