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E. Yoda / Applied Catalysis A: General 390 (2010) 45–50
Fig. 5. Time on stream of the yield of methyl butyrate for the transesterification of
ethyl butyrate with methanol over [bmim]M20(10) at 343 K. The concentrations of
NaCl in the reaction solution are (a) 0.0 and (b) 10 mmol L−1. The molar ratio of ethyl
butyrate to methanol is 1:4, and 0.1 g of the catalyst is used.
Fig. 4. Time course of the integrated intensities of the isolated acidic OD groups
for (a) ethyl butyrate adsorption on DM20, (b) deuterated [bmim]M20(1), and (c)
deuterated [bmim]M20(5) at 353 K.
ual penetration of ethyl butyrate into the micropores by diffusion
is observed on DM20 [Fig. 4(a)] but 47% of the isolated acidic OD
groups still remain even after 30 min. Therefore, it is shown that it
is difficult for ethyl butyrate to enter the micropores of DM20. Sim-
ilarly, on [bmim]M20 samples, penetration of ethyl butyrate into
the micropores by diffusion is observed, but about 70% of the acidic
OD groups did not interact after 30 min for [bmim]M20(5). Thus,
it is also difficult for ethyl butyrate to enter into the micropores of
generated by water dissociation, they became absent after water
desorbed from the acidic OH groups.
3.1.3. Ethyl butyrate adsorption on [bmim]M20
Because it has been reported that it is difficult for 2-propanol
to enter the micropores of [bmim]M20 where bulky [bmim] exists,
ethyl butyrate may also be inaccessible to the inside of the microp-
ores [2]. Therefore, the adsorption of ethyl butyrate on [bmim]M20
the acidic OH groups on zeolite, a decrease in the band of the
isolated acidic OH groups and a lower frequency band of hydrogen-
bonded OH groups should be observed. Since it is believed that
most of the acidic OH groups on zeolite are in the micropores
[14], a decrease of the isolated acidic OH groups is expected to be
of acidic OH groups in the micropores are required. Thus, two par-
tially ion-exchanged samples, [bmim]M20(1) and [bmim]M20(5),
were prepared. The IR spectra of these samples are shown in
Figs. 1 and 2.
Fig. 4 shows the time course of the ratio of the isolated acidic
OD groups when ethyl butyrate was adsorbed on deuterated mor-
denite (DM20) and deuterated [bmim]M20(1) and [bmim]M20(5)
at 353 K. The amount of the acidic OD groups on [bmim]M20(1)
and [bmim]M20(5) is less than on DM20 because some of them
are ion-exchanged with [bmim]. Therefore, the ratio of the isolated
acidic OD groups is calculated by defining the amount of the iso-
lated acidic OD groups on the ion-exchanged samples as 100%. The
ratio of the isolated OD groups sharply decreases immediately after
ethyl butyrate introduction (within 3 min) for each catalyst. It has
been reported that even though the molecules cannot entirely enter
the micropores, if the molecules have functional groups that can
enter the micropores such as straight alkyl chains, these can form
hydrogen bonds with acidic OH groups near the entrance of the
micropores [15]. Therefore, the sharp decrease of the isolated acidic
OD groups within 3 min is attributable to the interaction of the alkyl
chains of ethyl butyrate with the acidic OD groups, but most of the
molecules have not entirely entered the micropores. This indicates
that isolated acidic OD groups near the entrance of the micropores
on partially ion-exchanged [bmim]M20 still remain. It is supposed
that ion exchange of the acidic OD groups in the micropores is
comparatively homogeneous, and priority to ion exchange is not
given to the acidic OD groups near the entrance. After 3 min, grad-
3.2. Transesterification of ethyl butyrate with methanol
Fig. 5(a) shows time on stream of the yield of methyl butyrate
for the transesterification of ethyl butyrate with methanol over
[bmim]M20(10) at 343 K. Although the yield at 6 h is very low,
described above, since it is difficult for ethyl butyrate to enter
the micropores of [bmim]M20, only the methoxide ions near the
entrance of the micropores may react. In order to improve the
yield, methoxide ions in the micropores have to diffuse outside
of the micropores. From the results shown in Fig. 3, it is found
that the methoxide ions interacting with [bmim] are stable when
methanol adsorbs on the acidic OH groups generated by disso-
ciative methanol adsorption. Simultaneously, it is indicated that
desorption of methanol from the acidic OH groups makes methox-
ide ions return to methanol by recombination with H+. The very
low yield for the transesterification over [bmim]M20(10) can be
explained in two ways. The first possibility is that the methox-
ide ions are not released from [bmim]. The second possibility is
recombination of the methoxide ions with acidic OH groups during
diffusion in the micropores. These two possibilities are considered
to interrupt the exit of methoxide ions from the micropores. In
the former case, when Cl− ions which could become counter ions
of [bmim] are added to the reaction solution, the methoxide ions
are expected to diffuse outside the micropores due to methoxide
ion exchange with Cl−. In the latter case, when Na+ ions which
could become counter ions of methoxide are added, the methox-
ide ions may diffuse outside the micropores due to suppression of
Therefore, transesterification of ethyl butyrate with methanol over
[bmim]M20(10) was carried out by adding NaCl to the reaction
solution.
Fig. 5(b) shows time on stream of the yield of methyl butyrate
for the transesterification in 10 mmol L−1 of NaCl-containing reac-