Acylation of 2-methoxynaphthalene in the presence of modified zeolite HBEA

Article abstract of DOI:10.1006/jcat.1999.2526

The influence of postsynthesis treatment such as calcination and acid treatment of zeolite HBEA has been studied in the acylation of 2-methoxynaphthalene with acetic anhydride. The contribution of the inner and outer surface of zeolite HBEA is examined by conversion and product selectivity to a bulky product, which can be formed only on the outer surface of HBEA, and to a linear product, which can be formed on the inner and outer surfaces. Calcination under high heating rate enhances the catalytic activity of the inner surface due to the formation of extraframework alumina species in the micropores. FTIR-adsorption experiments of the bulky probe molecule 2,4,6-tri-tert-butylpyridine, which does not fit into the micropores, revealed that these alumina species are located preferentially in the micropores of HBEA. Acid treatment increases the catalytic activity of the outer surface due to the extraction of catalytically active extraframework alumina species out of the micropores and due to the formation of silanol groups, respectively.

Full text of DOI:10.1006/jcat.1999.2526

Journal of Catalysis 185, 408–414 (1999)
Article ID jcat.1999.2526, available online at http://www.idealibrary.com on
Acylation of 2-Methoxynaphthalene in the Presence
of Modified Zeolite HBEA
H. K. Heinichen and W. F. Ho¨lderich1
Department of Chemical Technology and Heterogeneous Catalysis, University of Technology RWTH Aachen,
Worringerweg 1, 52074 Aachen, Germany
Received December 2, 1998; revised April 6, 1999; accepted April 6, 1999
(Fig. 1a) and on FTIR adsorption experiments of the bulky
probe molecule 2,4,6-tri-tert-butylpyridine (4) (Fig. 1b).
During the acylation of 2-methoxynaphthalene with
acetic anhydride the linear 6-acetyl-2-methoxynaphthalene
(2) and the bulky 1-acetyl-2-methoxynaphthalene (3) can
be formed. Compound 2 can be created at the inner and
outer surfaces of zeolite HBEA. Compound 3 is too bulky
and cannot enter the micropores (4). Harvey et al. (5) re-
ported that 1-acetyl-2-methoxynaphthalene can be formed
only on the outer surface of HBEA. The electrophilic at-
tack in the 1- and 6-position of the aromatic ring system
is most likely to occur (4). Furthermore, deacylation of
1-acetyl-2-methoxynaphthalene (3) was observed in the
presence of HBEA (4) (Fig. 1a). Hence, conversion of 2-
methoxynaphthalene and product selectivity can be taken
as a measure for the contribution of the inner and outer sur-
face to the catalytic activity (5). It is known that the outer
surface of zeolite HBEA can contribute significantly to acy-
lation reactions since it can be up to one-third of the total
surface area (5, 6).
The influence of postsynthesis treatment such as calcination and
acid treatment of zeolite HBEA has been studied in the acylation
of 2-methoxynaphthalene with acetic anhydride. The contribution
of the inner and outer surface of zeolite HBEA is examined by
conversion and product selectivity to a bulky product, which can be
formed only on the outer surface of HBEA, and to a linear product,
which can be formed on the inner and outer surfaces. Calcination
under high heating rate enhances the catalytic activity of the
inner surface due to the formation of extraframework alumina
species in the micropores. FTIR-adsorption experiments of the
bulky probe molecule 2,4,6-tri-tert-butylpyridine, which does not
fit into the micropores, revealed that these alumina species are
located preferentially in the micropores of HBEA. Acid treatment
increases the catalytic activity of the outer surface due to the
extraction of catalytically active extraframework alumina species
out of the micropores and due to the formation of silanol groups,
c
respectively.
1999 Academic Press
Key Words: acylation; HBEA; 2-methoxynaphthalene; FTIR;
adsorption; 2,4,6-tri-tert-butylpyridine.
Additionally, the use of tert-butyl-substituted pyridines
as probe molecules is a known technique for the FTIR ad-
sorption (7) on acidic hydroxyl groups of a catalyst sur-
face. At least, the aromatic ring system should interact with
the hydroxyl groups and a typical shift of the O–H stretch-
ing vibration should be observed (8, 9). Even though other
authors report about protonation of these sterically hin-
dered pyridines (10). A coordination onto Lewis acid sites
is impossible (8). 2,4,6-Tri-tert-butylpyridine (4) is chosen
as probe molecule because it is too large to enter the micro-
pores of HBEA. Hence, after adsorption of this pyridine (4)
it should be possible to find out which hydroxyl groups are
located on the inner and outer surfaces, respectively. In ad-
dition, it is interesting to know whether the EFAL species
are located on the outer surface of HBEA.
INTRODUCTION
The Friedel–Crafts acylation of aromatic compounds is
a method of choice for the synthesis of aromatic ketones.
They are used as intermediates for the production of fine
and pharmaceutical chemicals (1). The conventional homo-
geneously catalyzed synthesis has known disadvantages (3).
Therefore, an environmentally benign process is desired. In
this context zeolite HBEA showed good catalytic activity
in the acylation of anisole (2) and m-xylene (3).
We could show(3) that extra framework alumina (EFAL)
species formed by calcination under high heating rate are
beneficial for the catalytic activity of HBEA in the acyla-
tion of m-xylene and anisole, respectively. This effect might
be due to the migration of catalytically active EFAL species
onto the outer surface of HBEA, thereby enhancing the ac-
cessibility for the reactants. In order to clarify the location
of the EFAL species, now we report on a study of the acy-
lation of 2-methoxynaphthalene (1) with acetic anhydride
METHODS
Preparation of Catalysts
The acid form of the -zeolite (HBEA) was obtained
from a commercial catalyst kindly provided by Zeolyst
1 To whom correspondence should be addressed.
408
0021-9517/99 $30.00
c
Copyright
1999 by Academic Press
All rights of reproduction in any form reserved.

ACYLATION OF 2-METHOXYNAPHTHALENE
409
FIG. 1. (a) The acylation of 2-methoxynaphthalene (1) to 6-acetyl-2-methoxynaphthalene (2) and 1-acetyl-2-methoxynaphthalene (3). (b) 2,4,6-
Tri-tert-butylpyridine (4) and 2,6-di-tert-butylpyridine (5).
(Valfor CP-806-B25). The zeolite was calcined with 1 K/min into a vacuum cell. First the wafer was pretreated at 423 K
up to 823K for 8h. Subsequent ion exchange wasdone twice for 30 min and then held at 673 K for 16 h under vacuum
with 2 M aqueous NH4Cl solution (10 ml/gBEA) at 353 K for (2.5 Pa). After that, the wafer was cooled down to 313 K
24 h. The zeolite was washed with deionized water, dried at under vacuum and the first spectra was recorded. Then
393 K, and calcined with 1 K/min up to 823 K for 8 h. This 2,4,6-tri-tert-butylpyridine was allowed to adsorb at 313 K
sample HBEA1 was the starting material for all the other for up to 19 h. The adsorption process lasted such a long
catalysts.
time since 2,4,6-tri-tert-butylpyridine is solid under these
Subsequent modifications (Table 1) were done by acid conditions. FTIR spectra were recorded during the course
treatment (HBEA1-a0.01, HBEA1-a0.1, HBEA1-a1), by of adsorption. The hydroxyl band associated with ex-
calcination under high heating rate (HBEA1-c), and by traframework alumina species (3781 cm 1) and the bands
such a calcination in combination with subsequent acid associated with the amount of 2,4,6-tri-tert-butylpyridine
treatment (HBEA1-c-a0.1). The samples were character- adsorbed were evaluated in relation to the area of the
ized by ICP-AES, XRD, and nitrogen sorption.
overtone vibration of the T–O–T stretching vibration of
the framework (1981 and 1870 cm 1). This area is taken as
a kind of internal standard, since it is assumed that this area
is a measure for the sample mass reached by the IR-beam.
Adsorption experiments with 2,6-di-tert-butylpyridine
were done correspondingly at an adsorption temperature
of 373 K. FTIR measurements of pure 2,4,6-tri-tert-
butylpyridine and of 2,4,6-tri-tert-butylpyridine contacted
with HCl, respectively, were performed using a mixture of
KBr and the corresponding substance.
FTIR Adsorption Experiments
FTIR spectroscopy was done with a nicolet 460 Protege´.
FTIR spectra of self-supported wafers were recorded
1
between 4000 and 1380 cm
(hydroxyl and pyridine
region). In a typical experiment 10 mg of the zeolite were
pressed into a self-supported wafer (13 mm diameter). The
wafer was fixed by stainless steel holders and introduced
TABLE 1
Physicochemical Properties of the HBEA Samples Used in the Acylation of 2-Methoxynaphthalene
HBEA
sample
Bulk
Si/Al
XRD crist.a
(% )
BET surf. area
(m2/g)
Ext. surf. area
(m2/g)
Micropore vol.
(cm3/g)
Mesopore vol.b
(cm3/g)
Treatment
1
—
15
15
21
80
15
20
100
91
93
88
80
70
579
566
597
591
522
517
200
187
208
208
188
187
0.181
0.181
0.190
0.187
0.164
0.161
0.252
0.227
0.254
0.263
0.247
0.234
1-a0.01
1-a0.1
1-a1
1-c
1-c-a0.1
a.t.c 0.01 m/L HCl 298 K 24 h
a.t.c 0.1 m/L HCl 298 K 24 h
a.t.c 1 m/L HCl 298 K 24 h
Calc. 12 K/min 1023 K 8 h
Calc. 12 K/min 1023 K
8 h, a.t.c 0.1 m/L HCl 298 K 20 h
a XRD signal 22 = 22.4.
b 2–20 nm BJH.
c Acid treated.

¨
HEINICHEN AND HOLDERICH
410
Acylation Reaction
lytic activity of the inner and outer surface, respectively,
took place. Generally, there are two possible explanations
for these findings. Either the catalytic activity on the outer
surface was reduced and less bulky product (3) could be
formed or the activity of the inner surface was increased
and more linear product (2) was created. N2-sorption data
show (Table 1) that the external surface area as well as the
mesopore volume decrease for HBEA1-c. In addition, BET
surface and micropore volume decrease due to the loss of
crystallinity. However, this change can hardly account for
the selectivity change of the two products. The yield of the
bulky product (3) achieved over HBEA1-c is about 18%
and has not changed drastically compared to the yield of
24% obtained over HBEA1. In contrast, the yield for the
linear 6-acetyl-2-methoxynaphthalene wasincreased signif-
icantly in the presence of HBEA1-c. Therefore, it can be
concluded that the increase in the conversion is due to an
increase of the catalytic activity of the inner surface in the
micropores of HBEA1-c and that the catalytic activity of
the outer surface remained unchanged.
The acylation reaction of 2-methoxynaphthalene with
acetic anhydride was carried out in the liquid phase in a
batch reactor. Sulfolane was used as solvent (25 ml/g cata-
lyst). All chemicals were purchased from Aldrich or Fluka
in synthetic quality, dried over a molecular sieve, and used
without further purification. Reaction conditions are 373 K,
molar ratio of 2-methoxynaphthalene to acetic anhydride
of 2, and weight ratio of acetic anhydride to catalyst of 2.5.
Liquid sampleswere taken out ofthe reactor after 3and 24h
and analyzed by GC equipped with a RTX 170-1 (30 m) and
a FID detector. Conversion is based on the maximal possi-
ble conversion of 2-methoxynaphthalene. The selectivity is
based on the aromatic compound.
RESULTS AND DISCUSSION
Acylation of 2-Methoxynaphthalene in the Presence
of HBEA1, HBEA1-c, and HBEA1-c-a0.1
The conversion and the selectivity in the acylation of
2-methoxynaphthalene are presented in Table 2.
After the acid treatment of HBEA1-c (HBEA1-c-a0.1)
a slight decrease of conversion can be observed. However,
the product selectivities change again drastically. Now, the
formation of the bulky product is again preferred and the
selectivity is more or less similar to the selectivity obtained
over HBEA1. Once more simple acid treatment has led to a
change in the catalytic activity of the inner and outer surface
of the sample HBEA1-c-a0.1 compared to HBEA1-c.
The difference in product selectivity observed for
HBEA1 and HBEA1-c-a0.1 compared to HBEA1-c can be
explained by the extraframework alumina species formed
during the calcination process with high heating rate. These
EFAL species were already found to be responsible for an
activity increase in the acylation of anisole and m-xylene
with acetic anhydride (3). Hence, the observed increase in
conversion for the acylation of 2-methoxynaphthalene can
be explained by the amount of extraframework alumina
In the presence of HBEA1, 2-methoxynaphthalene is
32% converted after 24 h reaction time. The selectivity
to the bulky product 1-acetyl-2-methoxynaphthalene (3) is
74% and to the linear product 6-acetyl-2-methoxynaphtha-
lene (2) 26% . In this and in all other cases no evidence
was found that other products have been formed. The con-
version is significantly lower compared to the results of
Harvey et al. (4), although the selectivity to both products
is similar. The high selectivity to 3 indicates that it is formed
preferentially on the outer surface. In contrast, the catalytic
results obtained over the calcined HBEA1-c are related to
two remarkable effects. First, after 24 h the conversion was
increased up to 47% and, second, the selectivity to the lin-
ear product (2) was enhanced up to 61% , whereas the bulky
product (3) decreased to 39% . Hence, a change in the cata-
TABLE 2
Conversion of 2-Methoxynaphthalene (1) and Selectivity to 6-Acetyl-2-methoxynaphthalene (2) and
1-Acetyl-2-methoxynaphthalene (3) in the Acylation of 2-Methoxynaphthalene with Acetic Anhydride
in a Batch Reactor after 3 and 24 h
3 h
24 h
Conversion
Selectivity
Selectivity
Conversion
Selectivity
Selectivity
HBEA sample
of 1 (% )
to 2 (% )
to 3 (% )
of 1 (% )
to 2 (% )
to 3 (% )
1
1-c
1-c-a0.1
1-a0.01
1-a0.1
1-a1
30
39
29
28
53
54
19
53
23
13
10
10
81
47
77
87
90
90
32
47
43
40
46
49
26
61
31
15
10
14
74
39
69
85
90
86
Note. Reaction conditions: 373 K, n-2-methoxynaphthalene/n-acetic anhydride = 2, m-acetic anhydride/
m-catalyst = 2.5; solvent: 25 ml sulfolane/g catalyst.

ACYLATION OF 2-METHOXYNAPHTHALENE
411
species formed. Furthermore, those species could migrate
onto the outer surface of the zeolite as the calcination pro-
cess becomes more accessible for the reactants. If so, a
greater catalytic activity of the outer surface is expected
and in consequence, a higher yield of the bulky product
should be achieved.
In contrast to the linear 6-acetyl-2-methoxynaphthalene
(2) the deacylation of the bulky 1-acetyl-2-methoxynapht-
halene (3) can occur over HBEA (4). Therefore, it might
be that the outer surface is catalytically so active that the
formed bulky product is very rapidly deacylated. In conse-
quence, the stable linear product is enriched in the reaction
mixture and a high selectivity of the linear product could
be observed although the extraframework alumina species
are located on the outer surface.
On the other hand, if the newly formed extraframework
alumina species are preferentially located in the zeolitic mi-
cropores of HBEA1-c, this sample would have enhanced
catalytic activity in the micropores. This would lead to the
observed increase in the selectivity to the linear product
(2). In addition it would explain the unchanged yield of
the bulky product for HBEA1 and HBEA1-c. In summary,
the preferential location of the newly formed extraframe-
work alumina species is of interest in order to explain the
observed change in product selectivity.
FIG. 2. FTIR spectra in the hydroxyl and framework region of the
sample HBEA1 before and after adsorption of 2,4,6-tri-tert-butylpyridine
at 313 K (0.5, 1, and 12.5 h adsorption time).
well as a broad band between 3300 and 3700 cm 1 (Fig. 2a).
The different hydroxyl groups can be attributed as follows
(3). The hydroxyl groups at 3611 cm 1 are bridging hydrox-
yls (13), which are directly linked to the aluminum content
in the framework. The band at 3673 cm 1 is caused by par-
tially attached aluminum to the framework (14). The bands
at 3735 cm 1 and 3743 cm 1 represent internal and external
silanol groups (13). Furthermore, the band at 3782 cm 1 is
caused by hydroxyl groups associated with extraframework
FTIR Adsorption Experiments
of 2,4,6-Tri-tert-butylpyridine
In order to evaluate the location of the extraframework
alumina species in these catalysts the following consider-
ation was made. Extraframework alumina species show a
typical FTIR band at 3781 cm 1 in the hydroxyl region (11).
This band should disappear when a probe molecule is ad-
sorbed on the hydroxyl groups of the EFAL species. In con-
trast, EFAL species located in the pores of HBEA should
not be affected by such an adsorption if the probe molecule
1
is larger than the pore opening. Then the band at 3781 cm
should still be visible after the adsorption of the probe
molecule. HBEA has a pore opening of 0.76 0.64 nm (12).
Hence, 2,4,6-tri-tert-butylpyridine (4) (Fig. 1b) exceeds this
pore size because of its bulky tert-butyl groups.
Unfortunately, the basic center of 2,4,6-tri-tert-butyl-
pyridine at the nitrogen atom is strongly shielded by the
two neighbored tert-butyl groups. In consequence, the ba-
sic center might not be protonated by the Brønsted acid
hydroxyl groups. Nevertheless, the interaction of the aro-
matic ring system of 4 with the Brønsted acidic hydroxyl
groups should give a typical shift of about 100 cm 1 of the
concerning hydroxyl band (9).
Figures 2 and 3 show the spectra in the hydroxyl and pyri-
dine region of the samples HBEA1 and HBEA1-c before
and after the adsorption of 2,4,6-tri-tert-butylpyridine at
313 K. The spectrum of HBEA1 shows six different types of
FIG. 3. FTIR spectra in the hydroxyl and framework region of
the sample HBEA1-c before and after adsorption of 2,4,6-tri-tert-
hydroxyl groups at 3611, 3673, 3735, 3743, and 3782 cm 1 as butylpyridine at 313 K (0.5, 1, and 19 h adsorption time).

¨
HEINICHEN AND HOLDERICH
412
alumina species (11, 14). Finally, the broad band between
3300 and 3700 cm 1 can be associated to very weak or not pyridine on zeolite HBEA1 typical bands appear for
acidic hydrogen bonded silanol groups (14). 2,4,6-tri-tert-butylpyridine and for protonated 2,4,6-tri-
In summary, after the adsorption of 2,4,6-tri-tert-butyl-
During adsorption of 2,4,6-tri-tert-butylpyridine the band tert-butylpyridine. This indicates that some 2,4,6-tri-tert-
1
at 3743 cm 1 disappeared, the bands at 3782 and 3735 cm
were reduced and new bands arose at 3705, 3647, 3370 cm
butylpyridine molecules are protonated, whereas some in-
teract only with their aromatic ring system with hydroxyl
1
,
and in the range of 2900 cm 1. The disappearance of the groups. Furthermore, bands appear that are associated with
1
3743 cm band for external silanol groups indicates that 2,6-di-tert-butylpyridine or pyridine. These moleculesmight
these hydroxyl groups are strongly affected by the ad- be brought into the vacuum cell together with the probe
sorption of the bulky probe molecule. The arising band at molecule or may have been formed on the zeolite. Indeed,
1
1
3647 cm shifted nearly 100 cm in comparison to the a dealkylation of tert-butylbenzene has already been ob-
3745 cm 1. It shows that at least some of the external silanol served during IR adsorption experiments on zeolite HBEA
groups interact with the aromatic ring system of 2,4,6-tri- in the literature (16). Therefore, dealkylation of the tert-
tert-butylpyridine. A band in the range of 3350 cm 1 is typ- butyl groups on an acidic catalyst might occur.
ical for a protonated nitrogen atom, indicating that also
some nitrogen atoms are protonated. The reason for the adsorb onto hydroxyl groups in the micropores. Thereby,
appearance of a band at 3705 cm 1 is not clear.
the results of the adsorption of 2,4,6-tri-tert-butylpyrdine
Unfortunately, pyridine and 2,6-di-tert-butylpyridine can
In the range of 1700 to 1400 cm 1 several new bands ap- can be distorted. That is why it is assumed that the dealky-
pear in the spectrum (Fig. 2d0) at 1612, 1600, 1561, 1533, lation of 2,4,6-tri-tert-butylpyridine had taken place only
1480, 1465, and 1407 cm 1 as well as typical bands for pyri- after a considerable amount of 2,4,6-tri-tert-butylpyridine
dine adsorbed on Brønsted and Lewis acid sites at 1548, was adsorbed onto the zeolite. However, such a dealky-
1490, and 1454 cm 1. For a better band identification a spec- lation reaction can be neglected at the beginning of the
trum of pure 2,4,6-tri-tert-butylpyridine had been recorded adsorption time, i.e., after 0.5 and 1 h.
1
with the KBr technique (Figs. 4a and 4a0). Comparing this
The band at 3782 cm representing the amount of ex-
spectrum with the spectrum of HBEA1 (Figs. 2d and 2d0), traframework alumina species not affected by adsorption
the bands in the range of 2900 cm 1 and the bands at 1600, and the bands around 2900 cm 1 representing the amount
1561, and 1407 cm 1 can be attributed to the pure 2,4,6-tri- of 2,4,6-tri-tert-butylpyridine adsorbed will be discussed in
tert-butylpyridine. Furthermore, 2,4,6-tri-tert-butylpyridine more detail (Table 3). For the moment we will assume that
was contacted with gaseous HCl to get protonation of the the EFAL species are equally distributed over the inner
nitrogen atom and a spectrum was recorded (Figs. 4b and and outer surface of the sample HBEA1. A decrease of
1
1
4b0). This spectrum shows that bands at 1480 and 1465 cm
the band area at 3782 cm of about one-third can be ex-
can be attributed to protonated 2,4,6-tri-tert-butylpyridine. pected after adsorption of 2,4,6-tri-tert-butylpyridine since
In addition, the spectrum of the protonated 2,4,6-tri-tert- the outer surface is considered to be up to 35% of the to-
butylpyridine showed a similar band for N–H vibration tal surface area of HBEA (5). Furthermore, the hydroxyl
1
at 3351 cm like in the hydroxyl spectrum of HBEA1 groups of the EFAL species are more acidic than the termi-
(Fig. 2d). In addition the band at 1533 cm 1 is typical for 2,6 nalsilanolgroups. Therefore, the 2,4,6-tri-tert-butylpyridine
di-tert-butylpyridine (5) (Fig. 1b) contacted with HCl (15). should first adsorb onto the hydroxyl groups of the EFAL
species on the outer surface and afterward on the terminal
silanol groups.
In contrast to these considerations, a preferential adsorp-
tion onto acidic sites other than the hydroxyl groups of
the extraframework alumina species can be observed dur-
ing the first hour (Table 3) in the case of HBEA1. The
1
area of the 3782 cm band reduced only around 8% af-
ter 0.5 h adsorption time in relation to the reduction after
1 h. On the other hand, at the same time the amount of
2,4,6-tri-tert-butylpyridine adsorbed after 0.5 h is already
40% of the amount adsorbed after 1 h. Hence, the first
probe molecules adsorbed preferentially not on such hy-
droxyl groups but on other sites, presumably for the most
part terminal silanol groups. One explanation is the pref-
erential location of the extra framework alumina species
in the micropores of zeolite HBEA. In that case the ad-
sorption of 2,4,6-tri-tert-butylpyridine is not possible and
FIG. 4. FTIR spectra in the hydroxyl and pyridine region of pure
2,4,6-tri-tert-butylpyridine (a and a0) and of 2,4,6-tri-tert-butylpyridine con-
tacted with gaseous HCl (b and b0).

ACYLATION OF 2-METHOXYNAPHTHALENE
413
TABLE 3
Evaluation of the Band Areas of the Hydroxyl Group Associated with Extra Framework
1
Alumina at 3781 cm and of the Bands Associated with 2,4,6-Tri-tert-butylpyridine (4) at
2900 cm 1 after the Adsorption of 4 at the Samples HBEA1 and HBEA-c
Band area in relation to the overtone
vibration of the framework vibration
Reduction of the
total area (% ),
HBEA
sample
Adsorption
time (h)
Hydroxyl groups at
Amount of 4
2900 cm
hydroxyl groups at
1
1
1
3781 cm
3781 cm
1
0.0
0.5
1.0
0.0204
0.0203
0.0192
0.0149
0.0000
0.1283
0.3255
1.1177
0
0.5
5.9
27.0
12.5
1-c
0.0
0.5
1.0
0.0176
0.0175
0.0169
0.0117
0.0000
0.1292
0.3359
1.0656
0
0.6
4.0
33.5
19.0
the probe molecules adsorb preferentially onto the termi- that the micropore volume of HBEA1-c is reduced in
nal silanol groups. The sample HBEA1-c showed the same comparison to HBEA1 (Table 1). This is caused by the
preferential adsorption of 2,4,6-tri-tert-butylpyridine onto partial framework damage and the larger amount of ex-
the terminal silanol groups. A second reason can be that traframework alumina species which partially block the
the adsorption of 2,4,6-tri-tert-butylpyridine on the EFAL pores. So even 2,6-di-tert-butylpyridine has no access to
species is hindered.
all EFAL species. Furthermore, adsorption experiments
with pyridine (3) showed the complete disappearance of
the 3782 cm band for HBEA1-c, indicating that all ex-
1
FTIR Adsorption Experiments of 2,6-Di-tert-butylpyridine
traframework alumina species should be accessible for all
molecules having similar size like pyridine. In summary, it
can be concluded that the extraframework alumina species
are located preferentially in the micropores for both sam-
ples HBEA1 and HBEA1-c.
In a second experiment 2,6-di-tert-butylpyridine (5,
Fig. 1b) was adsorbed onto the sample HBEA1 and
HBEA1-c since that probe molecule fits into the microp-
ores of HBEA. This investigation should disclose whether
1
the band at 3782 cm does really disappear when EFAL
species are accessible for the probe molecule.
Figure 5 illustrates that only a small shoulder of the
3781 cm band remained visible after the adsorption of
2,6-di-tert-butylpyridine overnight for HBEA1. It can be
Acylation of 2-Methoxynaphthalene in the Presence
of HBEA1-a0.01, HBEA1-a0.1, and HBEA1-a1
1
concluded that the hydroxyl groups of the EFAL species
The acid treated samples HBEA1-a0.01, HBEA1-a0.1,
disappear if a similar, but smaller probe molecule than and HBEA1-a1 show the same behavior as the sample
2,4,6-tri-tert-butylpyridine has access to the micropores. HBEA1-c-a0.1 (Table 2). There is an increase in conver-
1
The disappearance of the 3782 cm band is not so pro- sion and in the selectivity of the bulky product 1-acetyl-
nounced in case of HBEA1-c. Nitrogen sorption data shows 2-methoxynaphthalene with the increase of the concentra-
tion of the acid treatment. The N2-sorption data (Table 1)
show only a slight increase in BET and external surface
area as well as in micro- and mesopore volume so that
the changes in conversion and selectivity cannot be ex-
plained by the changes in zeolite texture. Instead, the ef-
fect can be explained by the extraction of EFAL species
out of the micropores—indicated by the increase in the
bulk Si/Al ratio—leading to a decrease of the activity in
the micropores. Furthermore, the acid treatment causes the
creation of silanol groups as defect sites (3) which might
lead to enhanced activity onto the outer surface. After
24 h a drop in conversion can be observed for the samples
HBEA1-a0.1 and HBEA1-a1 in comparison to 3 h. For
FIG. 5. FTIR spectra in the hydroxyl region of the samples HBEA1
and HBEA1-c before (a and a0) and after (b and b0) the adsorption of
2,6-di-tert-butylpyridine at 423 K overnight.

¨
HEINICHEN AND HOLDERICH
414
all other treatments of HBEA1 there was always an in-
Acid treatment lead to the preferential formation of the
crease in 2-methoxynaphthalene acylation after 24 h. This bulky product (3) due to the extraction of catalytically ac-
behavior can be explained by significant deacylation of the tive extraframework alumina species out of the micropores
bulky product 1-acetyl-2-methoxynaphthalene. It indicates and maybe also due to the formation of terminal silanol
again the enhanced catalytic activity on the outer surface groups.
since deacylation can take place only outside of the micro-
pores. Additionally, an increase in conversion compared to
HBEA1 could be observed after 24 h. This should be due to
the more hydrophobic character of the zeolite with increas-
ingSi/Alratio facilitatingthe adsorption ofthe hydrophobic
aromatic compound (Table 1).
ACKNOWLEDGMENTS
Financial support of Hoechst Research and Technologies GmbH and
Co KG is gratefully acknowledged. The authors express their sincere
thanks to Prof. Dr. Klaus Ku¨hlein and Dr. U. Dingerdissen for stimulating
discussions.
CONCLUSION
REFERENCES
In summary, the adsorption of 2,4,6-tri-tert-butylpyridine
showed that the main part of the extraframework alu-
mina species are located in the micropores of the samples
HBEA1 and HBEA1-c. Hence the increase in the selec-
tivity of the linear product 6-acetyl-2-methoxynaphthalene
(2) in the presence of HBEA1-c can be explained by the
formed EFAL species located in the micropores. In conse-
quence the formation of the bulky product (3) is sterically
hindered. The bulky product (3) is formed on the outer
surface of HBEA. In contrary the formation of the linear
product 6-acetyl-2-methoxynaphthalene occurs on the in-
ner and outer surfaces. Furthermore, the change in product
selectivity after the treatment with acid can be explained
by the partial removal of EFAL species out of the micro-
pores of the zeolite. Then, the zeolite loses catalytic activity
in the micropores and the formation of the bulky product
is preferred.
This results are in line with the observations of Jansen
et al. (17). These authors discussed that Lewis acid sites
are preferentially located in the micropores of HBEA and
are due to aluminum atoms partially bonded to the frame-
work. These authors assumed that the band at 3782 cm 1 is
caused by hydroxyl groups associated with these partially
bonded aluminum atoms and not by hydroxyl groups of
extraframework alumina species. Nevertheless, whatever
is responsible for the band at 3782 cm 1, the correspond-
ing hydroxyl groups are preferentially located in the micro-
pores of zeolite HBEA.
1. Kouwenhoven, H. W., and van Bekkum, H., in “Handbook of Het-
erogeneous Catalysis” (G. Ertl, H. Kno¨zinger, and J. Weitkamp, Eds.),
p. 2358. VCH, Weinheim, 1997.
2. Smith, K., Zhenhua, Z., Delaude, L., and Hodgson, P. K. G., “Pro-
ceedings, 4th International Symposium on Heterog. Catalysis Fine
Chemisty.” Basel (1996).
3. Heinichen, H. K., Thesis, RWTH-Aachen, 1999.
4. Harvey, G., and Ma¨der, G., Collect. Czech. Chem. Commun. 57, 862
(1992).
5. Harvey, G., Binder, G., and Prins, R., Stud. Surf. Sci. Catal. 94, 397
(1995).
6. Gaare, K., Akporiaye, D., Holm, K., and Skattebol, L., Acta Chem.
Scand. 51, 1229 (1997).
7. Kno¨zinger, H., in “Handbook of Heterogeneous Catalysis ” (G. Ertl,
H. Kno¨zinger, and J. Weitkamp, Eds.), p. 707. VCH, Weinheim, 1997.
8. Kno¨zinger, H., Krietenbrink, H., and Ratnasamy, P., J. Catal. 48, 436
(1977).
9. Su, B. L., and Norberg, V., Zeolites 19, 65 (1997).
10. Dewing, J., Monks, G. T., and Youll, B., J. Catal. 44, 226 (1976).
11. Loeffler, E., Lohse, U., Peuker, Ch., Oehlmann, G., Kustov, L. M.,
Zholobenko, V. L., and Kazansky, V. B., Zeolites 10, 266 (1990).
12. Meier, W. M., Olson, D. H., and Baerlocher, C., “Atlas of Zeolite
Structure Types.” Elsevier, London, 1996.
13. Kiricsi, I., Flego, C., Pazzuconi, G., Parker, W. O., Jr., Millini, R.,
Perego, C., and Bellussi, G., J. Phys. Chem. 98, 4627 (1994).
14. Jia, C., Massiani, P., and Barthomeuf, D., J. Chem. Soc. Farady Trans.
89, 3659 (1993).
15. Matulewicz, E. R. A., Kerkhof, F. P. J., Moulijn, J. A., and Reitsma,
H. J., J. Colloid Interface Sci. 77, 110 (1980).
16. Flego, C., Kiricsi, I., Perego, C., and Bellussi, G., Stud. Surf. Sci. Catal.
94, 405 (1995).
17. Jansen, J. C., Creyghton, E. J., Lan Njo, S., van Koningsveld, H., and
van Bekkum, H., Catal. Today 38, 205 (1998).