Shape-selective organic-inorganic zeolitic catalysts prepared via interlayer expansion

Article abstract of DOI:10.1016/j.cattod.2014.02.035

Interlayer expansion of layered zeolite precursors is achieved via the insertion of an additional T-atom in between the layers, typically by means of a silylating agent as source of the T-atom. (3-Mercaptopropyl) methyldimethoxysilane was used as Si-source in the interlayer expansion of the layered zeolite precursors RUB-36 and RUB-39. The structure expansion was confirmed with PXRD. The incorporation of the silylating agent was followed with ²⁹Si MAS NMR, ¹³C CP MAS NMR and thermogravimetric analysis. The incorporated thiol groups were oxidized with H₂O ₂ to obtain sulfonic acid groups in between the layers. ¹³C CP MAS NMR was used to characterize the organic species and monitor the conversion of thiol to propylsulfonic groups. The shape-selective properties of the obtained materials were investigated in acid-catalyzed tetrahydropyranylation reactions.

Full text of DOI:10.1016/j.cattod.2014.02.035

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Contents lists available at ScienceDirect
Catalysis Today
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Shape-selective organic–inorganic zeolitic catalysts prepared via
interlayer expansion
Trees De Baerdemaekera, Wannes Vandebroecka, Hermann Giesb, Bilge Yilmazc,
Ulrich Müllerd, Mathias Feyend, Dirk De Vosa,∗
a Centre for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium
b Institute of Geology, Mineralogy and Geophysics, Ruhr-University Bochum, 44780 Bochum, Germany
c BASF Corporation, Chemicals Research and Engineering, Iselin, NJ 08830, USA
d BASF SE, Chemicals Research and Engineering, 67056 Ludwigshafen, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Interlayer expansion of layered zeolite precursors is achieved via the insertion of an additional
T-atom in between the layers, typically by means of a silylating agent as source of the T-atom. (3-
Mercaptopropyl)methyldimethoxysilane was used as Si-source in the interlayer expansion of the layered
zeolite precursors RUB-36 and RUB-39. The structure expansion was confirmed with PXRD. The incorpo-
ration of the silylating agent was followed with 29Si MAS NMR, 13C CP MAS NMR and thermogravimetric
analysis. The incorporated thiol groups were oxidized with H2O2 to obtain sulfonic acid groups in between
the layers. 13C CP MAS NMR was used to characterize the organic species and monitor the conversion of
thiol to propylsulfonic groups. The shape-selective properties of the obtained materials were investigated
in acid-catalyzed tetrahydropyranylation reactions.
Received 15 November 2013
Received in revised form 8 February 2014
Accepted 17 February 2014
Available online xxx
Keywords:
Interlayer expansion reaction
Functionalized micropores
Sulfonic acid
© 2014 Published by Elsevier B.V.
Tetrahydropyranylation
Shape selectivity
Organic–inorganic hybrid
1. Introduction
condensed to the three-dimensionally connected zeolite RUB-37
(CDO topology) or interlayer expanded with dichlorodimethylsi-
Layered zeolite precursors are versatile building blocks for
the synthesis of zeolitic catalysts. Besides their transformation
into fully three-dimensionally connected zeolite frameworks by
topotactic condensation of the silicate sheets, the layers can be
rearranged in a variety of ways. Examples are interlayer expan-
sion by placing an additional T-atom in between the layers, or
swelling followed by pillaring, delamination or recombination of
the sheets [1–8]. The resulting materials differ from their corre-
sponding zeolite condensation products in pore size and shape,
accessibility of active sites in the layers, sorption characteristics
and other physicochemical and catalytic properties. In the case of
interlayer expansion, typically a silylating agent containing two
methyl- and two leaving groups (chloro-, ethoxy-) is used to link
the opposite layers of the precursor instead of directly connecting
those layers. This is illustrated in Fig. 1 for RUB-36, the layered zeo-
lite precursor consisting of the ferrierite-type layer,which can be
lane (DCDMS) to the methyl group-containing, hydrophobic COE-3
[9]. As another example, the layered silicate RUB-39, which con-
sists of heulandite-type layers, can be condensed to RUB-41 (RRO
topology) or interlayer expanded to COE-1 [10,11].
One way of introducing catalytic activity into the materials
derived from layered, siliceous zeolite precursors is the isomor-
phous substitution of Al or other heteroatoms in the silicate layer
[4,5,12–15]. Alternatively, the layers themselves can also serve as a
support for catalytic sites through e.g. grafting of a metal precursor,
or by creating hybrid organic–inorganic materials using organosi-
lanes [16–18]. One interesting possibility is selectively placing the
active sites in between the layers. Corma and co-workers used
for instance 1,4-bis(triethoxysilyl)benzene as organic linking group
between the layers of Al-containing MCM-22. Subsequent ami-
nation of the organic linkers introduced basic functionalities in
close proximity of the layer-associated acid sites, resulting in a
bifunctional catalyst [19].
In previous reports on the interlayer expansion of RUB-36
and RUB-39, the possibility of introducing reactive functional
groups via interlayer expansion has been suggested [9,11]. In
this contribution, we demonstrate one of these possibilities by
altering the interlayer expansion protocol to introduce sulfonic
∗
Corresponding author at: Kasteelpark Arenberg 23, Post Box 2461, 3001 Hever-
lee, Belgium. Tel.: +32 16321639.
E-mail address: Dirk.DeVos@biw.kuleuven.be (D. De Vos).
http://dx.doi.org/10.1016/j.cattod.2014.02.035
0920-5861/© 2014 Published by Elsevier B.V.
Please cite this article in press as: T. De Baerdemaeker, et al., Shape-selective organic–inorganic zeolitic catalysts prepared via interlayer
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Fig. 1. Materials derived from layered zeolite precursors RUB-36 (A) and RUB-39 (B). Displayed are the layered precursors (1) and the products of topotactic condensation
(2) and interlayer expansion with DCDMS (3) or with 3-MPS (4) followed by oxidation with H2O2. Framework O-atoms and the organic SDAs in the layered precursors are
omitted for clarity. In the case of RUB-39, two linking sites eclipsing each other are shown.
acid sites in between the layers, consequently obtaining a hybrid
catalyst with acid sites placed selectively inside the interlayer
gallery of the inorganic zeolite. Similar types of organic–inorganic
hybrid catalysts containing propylsulfonic groups have been used
in e.g. tetrahydropyranylations for the protection of alcohols, in
bisphenol A synthesis, acetalizations, condensation of acetone
and 2-methylfuran and esterifications [20–25]. We have modi-
fied the interlayer expansion by using a silylating agent containing
besides two leaving groups also one methyl group and an alkylth-
iol group, which can be oxidized to a sulfonic acid group. The
appropriate conditions for this oxidative transformation have been
investigated. Finally, the acid and shape-selective properties of the
functionalized catalysts in the protection of alcohols via tetrahy-
dropyranylation were explored.
2. Experimental
2.1. Catalyst synthesis
2.1.1. Synthesis of the layered precursors
Purely siliceous RUB-36 and RUB-39 were synthesized accord-
ing to Refs. [9,10] using the respective organic structure
directing agents (SDA) diethyldimethyl ammonium hydroxide
and dimethyldipropyl ammonium hydroxide. After drying the
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2.2. Characterization
3
Table 1
Overview of the applied oxidation conditions.
Powder X-ray diffraction patterns were collected on a STOE Stadi
MP diffractometer in Debye–geometry with Cu-K␣1 radiation and
equipped with a linear position-sensitive detector (PSD) (6◦2ꢀ win-
dow). The samples were measured in a capillary sample holder. The
morphology of the crystals was investigated with scanning elec-
tron microscopy (SEM) on a Philips XL30 FEG. N2-physisorption
isotherms were recorded on a Micromeritics 3Flex surface ana-
lyzer at 77 K. Prior to measurement, the samples were evacuated
under vacuum at 393 K for 16 h. The amount of incorporated 3-MPS
was determined using thermogravimetric analysis on a TGA Q500
(TA Instruments). Samples were heated at 10 ◦C/min from room
temperature to 800 ◦C under O2-flow (O2:N2 = 9). The amount of
water desorbing below 120 ◦C was taken into account in determin-
ing the amount of incorporated 3-MPS. The acid capacities were
determined using titration based on Zeidan et al. [26]. 50 mg of
catalyst was stirred at room temperature in 15 ml of 2 M NaCl for
48 h. The suspension was filtered, rinsed with water and the filtrate
was titrated with 0.01 N NaOH using phenol red as indicator. Titra-
tions were repeated three times per catalyst and the average was
reported.
Treatment
H2O2 amount
a/conc.b
T (◦C)
Solvent
Number of
oxidation steps
A c
B
C
D
E
F
2.04/35
20.4/35
20.4/35
20.4/35
20.4/50
20.4/50
r.t.d
50
50
70
70
70
Methanol
Methanol
Methanol
Ethanol
Ethanol
Ethanol
1
1
4
1
1
4
a
g H2O2 solution/g material.
wt.%.
Optimized conditions of Bossaert et al. [23]. In this case, a ratio of one part H2O2
b
c
solution to three parts of methanol was used.
d
Room temperature.
synthesis products overnight at 120 ◦C, they were stored under
ambient conditions and used as such in the interlayer expansion
treatment. TG analysis under O2 (vide infra) indicates that under
these conditions, both of these materials realize a weight loss of ca.
20 wt.% in the temperature range from room temperature to 800 ◦C
due to the loss of water (less than 2 wt.% weight loss below 120 ◦C),
decomposition and removal of the SDA and condensation of the
neighboring silicate layers [10].
29Si MAS NMR spectra were recorded on a 7.0 T Bruker AMX300
spectrometer (29Si resonance frequency 59.6 MHz). 4000 scans
were accumulated with a recycle delay of 60 s. The pulse length
was 5.0 ␮s. The samples were packed in 4 mm zirconia rotors and
a 5000 Hz spinning frequency was used. 13C CP MAS NMR spectra
were recorded on a Bruker Avance400 spectrometer (9.4 T), with a
13C resonance frequency of 100.6 MHz. 22,000 scans were accumu-
lated with a recycle delay of 10 s. The contact time was 4.0 ms. The
samples were packed in 4 mm zirconia rotors (spinning frequency
6000 Hz). Tetramethylsilane was used as chemical shift reference
in both 29Si MAS NMR and 13C CP MAS NMR.
2.1.2. Interlayer expansion and incorporation of thiol groups
RUB-36 and RUB-39 were interlayer expanded with (3-
mercaptopropyl)methyldimethoxysilane (3-MPS, Fluka 95%) as
silylating agent. 200 mg of the layered precursor was added to 12 ml
of an aqueous 0.3 M HCl solution. The suspension was stirred for
5 min at room temperature in a Teflon cup. The 3-MPS was slowly
added under stirring. 2 mmol 3-MPS was used per g layered precur-
sor. After stirring for another 15 min, the Teflon cup was inserted
in a stainless steel autoclave, sealed and treated hydrothermally
at 150 ◦C for 24 h. The suspension was recovered and the solid
product was washed repeatedly with water via centrifugation until
the pH of the supernatant was neutral. The obtained material was
dried overnight at 60 ◦C. For comparison, the expansions were also
performed with DCDMS instead of 3-MPS.
Interlayer expansion of RUB-36 and RUB-39 with DCDMS results
in materials referred to as COE-3 and COE-1, respectively [9,11]. The
materials obtained with 3-MPS as silylating agent are correspond-
ingly labeled HS-COE-3 and HS-COE-1. A schematic overview of the
different treatments and names for RUB-36 related materials can
be found in Fig. 1.
2.3. Catalytic testing
Tetrahydropyranylation reactions of different alcohols were
performed in presence of excess 3,4-dihydro-2H-pyran (DHP,
molar ratio DHP:alcohol 2). For the tetrahydropyranylation of
ethanol, 30 mg of catalyst was weighed into a 10 mL crimp cap
vial with a magnetic stirring bar. 1.2 mmol ethanol, 2.4 mmol
DHP and 7 mL heptane as solvent were added. The vial was
closed, placed into a heated copper block at 70 ◦C and stirred
at 500 rpm. A hot filtration test was performed by removing the
catalyst at reaction temperature from the reaction mixture by
filtration and transferring the filtrate quickly into a fresh, hot
reactor. Tetrahydropyranylation of 2-butanol was performed using
0.6 mmol 2-butanol and 1.2 mmol DHP in 7 mL heptane. Compet-
itive tetrahydropyranylation reactions of ethanol and cholesterol
were performed using 0.3 mmol cholesterol, 0.3 mmol ethanol,
1.2 mmol DHP and 7 mL heptane. The reaction was also performed
with Amberlyst-15 as a non-shape selective catalyst containing sul-
fonic acid groups. The amount of Amberlyst-15 was adjusted to
obtain the same molar amount of sulfonic groups as for the other
materials. Samples (0.1 ml) were taken periodically and analyzed
on a Shimadzu 2014 GC equipped with an FID and 60 m CP Sil8 col-
umn. Peaks were identified by injecting authentic samples and by
GC–MS.
2.1.3. Oxidation of the thiol groups
For the oxidation of the incorporated thiol groups to the cor-
responding sulfonic acid groups, an aqueous hydrogen peroxide
solution was used as oxidant with methanol or ethanol as solvent.
Starting from the procedure optimized by Bossaert et al. [23] for the
oxidation of thiol groups incorporated in ordered mesoporous sil-
ica, a screening – guided by the detection of thiol and propylsulfonic
groups in 13C CP MAS NMR – was performed to find the optimal
oxidation conditions for the case of HS-COE-3 and HS-COE-1. In a
typical oxidation treatment, the powder was treated with 20.4 g
H2O2 solution (35–50 wt.%) per g material for 24 h. A ratio of two
parts H2O2 solution to three parts solvent was used. The amount
of H2O2, the H2O2 concentration, the solvent, the number of oxi-
dation steps and the treatment temperature were varied. After the
H2O2 treatment, the powder was washed three times with water
and suspended for 4 h in 0.1 M H2SO4 (60 ml of acid solution per g
of solid). The powder was washed with water until neutral wash-
ings were obtained and dried at 60 ◦C. The oxidized materials were
labeled HO3S-COE-3-x and HO3S-COE-1-x with x referring to the
applied oxidation treatment (Table 1).
3. Results and discussion
3.1. Incorporation of (3-mercaptopropyl)methyldimethoxysilane
Powder X-ray diffraction patterns for HS-COE-3 and HS-COE-
1 are shown in Figs. 2 and 3. For both materials, the shift of the
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-112
-104
d
c
b
-116
-14
a
5
15
25
35
45
55
60 40 20
0
-20 -40 -60 -80 -100 -120 -140 -160 -180
(ppm)
(°)
Fig. 2. Powder XRD patterns of RUB-36 (a), RUB-37 (b), HS-COE-3 (c) and HO3S-
COE-3-E (d).
Fig. 4. 29Si MAS NMR spectrum of HS-COE-3.
-114
d
c
b
a
-108
-102
-13
5
15
25
35
45
55
60 40 20
0
-20 -40 -60 -80 -100 -120 -140 -160 -180
(ppm)
(°)
Fig. 5. 29Si MAS NMR spectrum of HS-COE-1.
Fig. 3. Powder XRD patterns of RUB-39 (a), RUB-41 (b), HS-COE-1 (c) and HO3S-
COE-1-E (d).
and experimentally observed Q3/Q4 ratio amounts to 0.29 [27].
This indicates that Q3 species have been consumed in the linking
reaction of 3-MPS with the layers. The amount of incorporated 3-
MPS was estimated from both the 29Si MAS NMR and TG analysis
of the expanded materials (Table 3). Full occupation of all pos-
sible linker sites in COE-3 and COE-1 would result in a unit cell
composition of [Si20O38(CH3)2(CH2CH2CH2SH)2] with a ratio of
layer-related Si to linker Si of 9 to 1 (1: 0.11) for both types of
layers [9]. Integration of the 3-MPS related signal and the layer
related signals results in a ratio of 1:0.12 and 1:0.09 for HS-COE-3
and HS-COE-1, respectively. These values are in close agreement
with the maximum incorporation of 3-MPS. It should be noted that
the presence of a significant amount of Q3 species, especially in
the case of HS-COE-1, indicates that not all linking sites are occu-
pied. Part of the 3-MPS may have condensed with another 3-MPS
molecule and/or may be present at the outer surface of the crys-
tals. This could explain the weak signal at −20 ppm in the 29Si MAS
first and most intense diffraction line towards lower 2ꢀ values indi-
cates an increase in the interlayer distance compared to the layered
precursor and the corresponding product of topotactic condensa-
tion. For comparison, d-spacings and reflection angles are shown
in Table 2. The interlayer distances for the materials expanded
with 3-MPS are very similar to the values obtained for DCDMS
expanded materials. The 29Si MAS NMR spectrum of HS-COE-3
(Fig. 4) shows the presence of Q4 (−112 ppm, −116 ppm) and some
residual Q3 (−104 ppm) species [9]. At −14 ppm, the Si signal of
the bridging group derived from 3-MPS can be observed. Also for
HS-COE-1 (Fig. 5), the Si bridging atom (at −13 ppm) is clearly
present in addition to the layer related Q4 (−108 ppm, −114 ppm)
and Q3 (−102 ppm) species. The Q3/Q4 ratios for HS-COE-1 and HS-
COE-3, obtained by integrating the corresponding areas, are 0.09
and 0.02, respectively. They clearly show a significant reduction in
the relative amount of Q3 species compared to the layered pre-
cursors, as for both types of layered precursors, the theoretical
Table 3
Physicochemical properties of the thiol and sulfonic acid functionalized materials.
Table 2
Overview of the d-spacings corresponding to the first and most intense reflection in
the XRD patterns of the layered materials.
Organic
SO3H
BET area
(m2/g)
Vmicro
(cm3/g)c
content
(mmol/g)b
(wt.% loss)a
Material
2ꢀ (◦)
d-spacing (Å)
HS-COE-3
HS-COE-1
HO3S-COE-3-E
HO3S-COE-1-E
14.3
12.0
14.8
13.7
–
–
0.31
0.50
10.2
4.4
26.5
24.8
<0.001
<0.001
0.002
RUB-36
RUB-37
COE-3
HS-COE-3
RUB-39
RUB-41
COE-1
7.9
9.6
7.5
7.5
8.2
10.1
7.9
7.8
11.1
9.2
11.7
11.8
10.8
8.7
0.004
a
wt.% lost in the range 120–550 ◦C after taking into account the desorption of
water below 120 ◦C.
11.2
11.4
b
Determined via titration.
From t-plot analysis of the N2 physisorption isotherms.
HS-COE-1
c
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Table 4
5
Chemical shift of different C-atoms in the interlayer expanded and oxidized mate-
rials in 13C CP MAS NMR (peak assignment based on Ref. [29]).
C-atom
Chemical shift (ppm)
Si-CH3
Si-CH2CH2CH2SH
Si-CH2CH2CH2SH
Si-CH2CH2CH2SH
Si-CH2CH2CH2S-SCH2CH2CH2-Si
Si-CH2CH2CH2S-SCH2CH2CH2-S
Si-CH2CH2CH2SO3H
Si-CH2CH2CH2SO3H
Si-CH2CH2CH2SO3H
0
13
27
27
23
41
11
18
54
detected. Although the 13C CP MAS NMR measurement is not fully
quantitative, the oxidation of the incorporated thiol groups to sul-
fonic acid groups can be observed from the disappearance of the
peak at 27 ppm and the appearance of a (broad) signal at 54 ppm.
Under the conditions used by Bossaert et al. [23] for the oxida-
tion of incorporated thiol groups in ordered mesoporous silica,
hardly any oxidation occurred, indicating that the thiol groups
must be in a less accessible environment. Fig. 6 clearly shows that
increasing the oxidation temperature and the H2O2 concentration
results in an increased conversion of the thiol groups. Increasing
the number of oxidation steps results in a higher number of sul-
fonic acid groups as well (Fig. 6c and d). For HO3S-COE-3-E the
signal corresponding to the thiol groups is no longer detected.
Also for HO3S-COE-1-E the thiol oxidation is essentially complete
(Fig. 7).
Fig. 6. 13C CP MAS NMR of HS-COE-3 (a), HO3S-COE-3-A (b), HO3S-COE-3-B (c),
HO3S-COE-3-C (d), HO3S-COE-3-D (e), HO3S-COE-3-E (f) and HO3S-COE-3-F (g).
Weak signals at 58, 52 and 8 ppm in (a) are attributed to residual SDA [3,30].
After the more harsh oxidation treatments, the XRD-patterns
(Figs. 2 and 3), especially of HO3S-COE-1-E, show some peak broad-
ening indicating a partial loss of crystallinity. This is in agreement
with the SEM images (Fig. 8f) that show the formation of some
debris after oxidation treatment, though the plate-like morphol-
ogy is generally very well preserved. BET surface areas before and
after oxidation treatment E (Table 3) show very low N2 uptakes.
These can be explained by the limited micropore area available due
to the additional mass of the mercaptopropyl and propylsulfonic
groups. The limited accessibility of the pores to N2 in physisorption
experiments, however, does not exclude the access of reactants in
liquid phase processes, as will be demonstrated by the catalytic
properties.
In the TG analysis of the materials after the oxidation treat-
ment (Table 3), an increased weight loss is expected because of
the higher molecular weight of the propylsulfonic group compared
to the mercaptopropyl group. However, for HO3S-COE-3-E, this
increase is very small. The rather harsh oxidation conditions may
have hydrolyzed part of the linkers resulting in a lower weight loss.
Furthermore some residual SDA is removed during the several steps
of the oxidation treatment, as the SDA is no longer detected in the
13C CP MAS NMR. On the other hand, the increase in weight loss
after oxidation is more clear in the case of HO3S-COE-1-E.
Fig. 7. 13C CP MAS NMR of HS-COE-1 (a), HO3S-COE-1-B (b) and HO3S-COE-1-E (c).
Weak signals at 67, 51 and 9 ppm in (a) are attributed to residual SDA [11].
NMR spectra of both HS-COE-3 and HS-COE-1 [28]. The expected
weight loss upon calcination in air for HS-COE-3 and HS-COE-1 is
8.3 wt.% if all linker sites are occupied by 3-MPS. TG analysis shows
a slightly higher weight loss for both materials (Table 3). This can
be ascribed to the loss of residual SDA, the presence of which is also
confirmed in 13C CP MAS NMR (Figs. 6 and 7).
3.3. Catalytic properties
3.2. Oxidation of the incorporated thiol groups
Tetrahydropyranylation reactions can be catalyzed by a number
of different catalysts, like zeolites [31–33], aluminum phosphates
[34], sulfonated charcoal [35], polystyrene supported Lewis acids
[36], etc. An alternative method is using sulfonic acid functionalized
materials such as sulfonic acid functionalized MCM-41 [20]. The
HO3S-COE-1 and HO3S-COE-3 type materials are analogous to the
latter type of materials but their active sites are located in a spatially
more restricted environment.
Several oxidation procedures were screened to find the opti-
mal oxidation conditions regarding conversion of the thiol groups
and number of oxidation steps. Table 1 lists the applied oxida-
tion conditions. The degree of oxidation was monitored using 13C
CP MAS NMR (Figs. 6 and 7). The peak assignments are listed in
Table 4. Remarkably, even if the silylating treatment was con-
ducted in drastic conditions (150 ◦C), without any precautions to
exclude air, the thiol groups were the major sulfur species observed
and only trace amounts of disulfide bridges from oxidation were
Tetrahydropyranylation reactions of ethanol and 2-butanol
show the presence of accessible acid sites in both HO3S-COE-3-E
and HO3S-COE-1-E (Figs. 9 and 10). On mass basis, HO3S-COE-3-E
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Fig. 8. SEM images of RUB-36 (a), HS-COE-3 (b), HO3S-COE-3-E (c), RUB-39 (d), HS-COE-1 (e) and HO3S-COE-1-E (f) (scale bar = 10 ␮m).
Fig. 9. Ethanol conversion in the tetrahydropyranylation with HO3S-COE-3-E (a) and HO3S-COE-1-E (b). Dashed lines show the hot filtration test.
Table 5
TOF in the tetrahydropyranylation of ethanol and 2-butanol.
a
a
TOF (h−1
)
ethanol
TOF (h−1
) 2-butanol
HO3S-COE-3-E
HO3S-COE-1-E
87
34
52
8
a
mol alcohol converted per mol acid sites per h, based on the acid site density
determined via titration.
To demonstrate the shape-selective properties of the interlayer
expanded materials with functionalized linker groups, competi-
tivetetrahydropyranylationreactionswereperformed. Ethanoland
cholesterol were used as small resp. bulky alcohols. Although their
reactivity is not the same, differences in relative reaction rates
can be used to demonstrate shape selectivity. Fig. 11 shows the
alcohol conversion as a function of time for different catalysts.
Even with the macroporous Amberlyst resin, ethanol is converted
more rapidly than cholesterol. However, the bulky cholesterol is
converted significantly more slowly than ethanol on the inter-
layer expanded zeolites. This clearly shows that the active sites
are located in a restricted environment in between the layers.
As cholesterol is too large to fit into the pores of the zeolite
materials, its conversion should be attributed to the presence of
sulfonic acid sites at the outer surface of the crystals or at the pore
entrance.
Fig. 10. 2-Butanol conversion in the tetrahydropyranylation with HO3S-COE-3-E(x)
and HO3S-COE-1-E (+).
shows a higher activity in both reactions, even though it has a lower
acid site loading (Table 3). However, the TOF numbers of HO3S-
COE-3-E are higher for both ethanol and 2-butanol (Table 5). The
hot filtration tests in the ethanol tetrahydropyranylation show no
increase in conversion after catalyst removal, indicating that the
reaction is fully heterogeneous.
Please cite this article in press as: T. De Baerdemaeker, et al., Shape-selective organic–inorganic zeolitic catalysts prepared via interlayer
expansion, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.035

G Model
CATTOD-8927; No. of Pages7
ARTICLE IN PRESS
T. De Baerdemaeker et al. / Catalysis Today xxx (2014) xxx–xxx
7
Fig. 11. Conversion of ethanol (x) and cholesterol (+) in the competitive tetrahydropyranylation with HO3S-COE-3-E (a), HO3S-COE-1-E (b) and Amberlyst-15 (c).
4. Conclusions
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The layered zeolite precursors RUB-36 and RUB-39 were suc-
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Complete oxidation of the incorporated thiol groups to sulfonic
acid groups was obtained, while preserving the layer structure.
The competitive tetrahydropyranylation of ethanol and cholesterol
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Please cite this article in press as: T. De Baerdemaeker, et al., Shape-selective organic–inorganic zeolitic catalysts prepared via interlayer
expansion, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.035