UTL titanosilicate: An extra-large pore epoxidation catalyst with tunable textural properties

Article abstract of DOI:10.1016/j.cattod.2015.09.036

The UTL titanosilicate was prepared together with related lamellar Ti-IPC-1PISi material and zeolites Ti-IPC-2 (OKO) and Ti-IPC-4 (PCR) via top-down synthesis. The titanium can be incorporated to the UTL framework by conventional hydrothermal synthesis and it does not affect the so-called ADOR chemistry of the UTL material. Silica-titania pillaring concept was successfully applied providing very active Ti-IPC-1PITi catalyst for bulky molecules epoxidation with hydrogen peroxide. The textural properties of catalysts prepared can be tuned widely keeping the same crystalline titanosilicate active phase. All the materials were characterised by XRD, nitrogen sorption measurement, SEM, and DR-UV/vis spectroscopy. Ti-IPC-1PITi was the most active catalyst in cyclooctene, norbornene, and linalool epoxidation due to the lowest diffusion constraints and sufficient titanium content. Ti-UTL showed activity similar to Ti-BEA in epoxidation of cyclooctene and it provided different products than other titanosilicates in oxidation of linalool with hydrogen peroxide.

Full text of DOI:10.1016/j.cattod.2015.09.036

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UTL titanosilicate: An extra-large pore epoxidation catalyst
with tunable textural properties
∗
ˇ
Jan P rˇ ech , Ji rˇ í Cejka
J. Heyrovsk y´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolej sˇ kova 3, CZ-182 23 Prague 8, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2015
Received in revised form 8 September 2015
Accepted 10 September 2015
Available online xxx
The UTL titanosilicate was prepared together with related lamellar Ti-IPC-1PISi material and zeolites
Ti-IPC-2 (OKO) and Ti-IPC-4 (PCR) via top-down synthesis. The titanium can be incorporated to the UTL
framework by conventional hydrothermal synthesis and it does not affect the so-called ADOR chemistry
of the UTL material. Silica-titania pillaring concept was successfully applied providing very active Ti-
IPC-1PITi catalyst for bulky molecules epoxidation with hydrogen peroxide. The textural properties of
catalysts prepared can be tuned widely keeping the same crystalline titanosilicate active phase. All the
materials were characterised by XRD, nitrogen sorption measurement, SEM, and DR-UV/vis spectroscopy.
Ti-IPC-1PITi was the most active catalyst in cyclooctene, norbornene, and linalool epoxidation due to the
lowest diffusion constraints and sufficient titanium content. Ti-UTL showed activity similar to Ti-BEA in
epoxidation of cyclooctene and it provided different products than other titanosilicates in oxidation of
linalool with hydrogen peroxide.
Keywords:
Titanosilicate UTL
Top-down synthesis
Epoxidation
Catalysis
Cyclooctene
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
Ti-YNU-1 1100 vs. Ti-MWW 50). These results demonstrated the
potential of lamellar titanosilicates for oxidation of bulky molecules
[5]. Kim et al. described a preparation of Ti-MCM-36 (MWW lay-
ers) catalyst by swelling of the Ti-MCM-22P layers with a surfactant
and supporting of the layers (pillaring) with amorphous silica. The
pillaring preserves the layer separation after removing of the sur-
factant by calcination. This pillared material exhibited more than 3
times higher TON than conventional TS-1 (Ti-MCM-36: 257, TS-1:
Titanosilicate zeolites (e.g. TS-1 (MFI topology), Ti-BEA, Ti-
MWW) represent valuable catalysts for epoxidation of C C double
bonds in organic molecules with both organic hydroperoxides and
hydrogen peroxide as oxidation agents. The discovery of the TS-
1
by Taramasso et al. [1] was a considerable breakthrough in the
field of oxidation catalysis. Since that, a number of titanosilicates
with 10-ring and 12-ring channels has been developed [2]; how-
ever, these suffer from diffusion limitations for bulky substrates.
Therefore, titanosilicates with enhanced accessibility of the active
sites, namely extra-large pore titanosilicates (possessing 14-ring
channels) and lamellar titanosilicates, are subject of interest.
Lamellar titanosilicates possess the active Ti sites on the external
surface of the crystalline layers and these are accessible with-
out diffusion restrictions of the channel system [3]. Corma et al.
incorporated titanium into lamellar ITQ-6 (FER structure) and
demonstrated its activity in epoxidation of 1-hexene and nor-
bornene [4]. Fan et al. prepared Ti-YNU-1 (possessing a structure
similar to MWW-lammelar precursor) and this material exhibited
◦
81) in 1-hexene epoxidation at 45 C [6]. Ryoo et al. synthesised
nanosheet TS-1 using a specially designed surfactant template
+
+
−
(C18H37-N (CH ) -C H -N (CH ) -C H OH2 ) instead of con-
3
2
6
12
3
2
6
13
ventional tetrapropylammonium hydroxide [7]. Nanosheet TS-1
exhibits an order of magnitude higher activity in epoxidation of
cyclohexene and cyclooctene in comparison with conventional TS-
1 (cyclooctene conversion: nanosheet TS-1 15.3% vs. TS-1 0.6% at
◦
60 C after 2 h) [7]. Xiao et al. prepared Ti-COE-4 material by inter-
layer silylation of lamellar Ti-RUB-36 with dimethyldichlorosilane.
Ti-COE-4 possesses free hydroxyl groups on the silane bridges
between the layers and it is an active catalyst of 1-hexene (con-
◦
version 14.2% at 60 C after 4 h vs. TS-1: conversion 21.2%) and
◦
enhanced activity in epoxidation of C5–C cycloalkenes in compari-
cyclohexene oxidation (conversion 14% at 60 C after 4 h vs. TS-1:
8
son with 3-dimensional Ti-MWW (Si/Ti = 45) and Ti-BEA (Si/Ti = 35)
although it had a Si/Ti ratio as high as 240 (e.g. cycloheptene TON:
conversion 2.3%). The main products of the oxidation over Ti-COE-
4 were 1-hexene-3-one and 2-cyclohexen-1-ol respectively [8].
Recently, our group reported pillaring of the TS-1 nanosheets with
tetratethyl orthosilicate (TEOS) or its mixture with titanium (IV)
butoxide (Ti(OBu)4). The addition of Ti(OBu)4 (0.05 eq based on
TEOS) into the pillaring mixture led to a strong increase in the yield
∗ Corresponding author. Tel.: +420 266 053 856.
E-mail address: jan.prech@jh-inst.cas.cz (J. P rˇ ech).
http://dx.doi.org/10.1016/j.cattod.2015.09.036
0
920-5861/© 2015 Elsevier B.V. All rights reserved.
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of cyclooctene oxide over silica-titania pillared lamellar TS-1 (TS-
-PITi, titanosilicate-1 silica-Titania Pillared) catalyst being 16.9%
after 4 h in contrast to silica pillared lamellar TS-1 (TS-1-PI, yield
The synthesis of B-UTL, which was used as a parent material in
the preparation of IPC-1TiPI catalyst, is described in Ref. [15].
1
3
.5%) [9].
2.2. Post-synthesis modifications
From extra-large pore zeolites, only Ti-DON [10] and Ti-CFI [11]
extra-large pore titanosilicates, both having 1-dimensional chan-
nels, has been reported until now. Ti-DON proved to be active
catalyst in cyclohexane oxidation with both hydrogen peroxide and
tert-butyl hydroperoxide [12] at room temperature. The Ti-CFI pro-
All the post-synthesis modifications of the Ti-UTL were per-
formed according to procedures reported earlier [15,16]. The Ti-UTL
was converted into lamellar Ti-IPC-1P by hydrolysis of the germa-
nium D4R units with 0.01 M HCl. 250 ml of the HCl solution were
used per 1 g of the calcined Ti-UTL and the material was hydrolysed
vided conversion of cyclooctene 21% and cyclooctene oxide yield
◦
5
.3% after 3 h at 60 C.
◦
at 75 C for 16 h under agitation. The resulting lamellar precursor
We turned our attention towards an extra-large pore ger-
Ti-IPC-1P was collected by filtration, washed with water and dried
manosilicate UTL containing 14-ring channels intersecting 12-ring
channels. This material can be prepared with a number of triva-
lent heteroelements (B, Al, Ga, Fe, In) incorporated into the crystal
framework [13]. This is a promising feature, because isomorphous
incorporation of titanium into a zeolitic framework is a complex
problem with many variables affecting the final outcome. Further-
more, the UTL zeolite can be converted into a number of related
materials [14]. The structure can be disassembled into lamellar
precursor IPC-1P (Institute of Physical Chemistry -1 precursor) by
hydrolysis of germanium rich D4R units connecting germanium
poor dense crystalline layers. The IPC-1P material may be turned
into sub-zeolite IPC-1 or swollen and pillared, forming material
IPC-1PISi (Institute of Physical Chemistry -1 Silica Pillared) [15].
Furthermore, it can be reassembled into OKO and PCR zeolites with
smaller channels (12 × 10 resp. 10 × 8-ring 2-dimensional channel
systems) [16] and a proper intercalation of the IPC-1P provides a
◦
at 65 C.
The Ti-IPC-1PISi and Ti-IPC-1PITi (Institute of Physical Chem-
istry -1 silica-Titania Pillared) samples were prepared in a following
way. The Ti-IPC-1P was swollen with a solution of cetyltrimethy-
lammonium hydroxide (CTMA OH, 30 g/g of theTi-IPC-1P). The
swelling occurred at room temperature for 24 h under stirring. The
swollen product was centrifuged, washed with water and dried at
◦
6
5 C. The pillaring was done using tetraethyl orthosilicate (TEOS)
or its mixture with Ti(OBu)4 to form pillared lamellar Ti-IPC-1PISi
resp. Ti-IPC-1-PITi catalyst. 10 ml of the pillaring medium were
used per 1 g of the swollen material and the mixture was stirred
◦
at 85 C for 24 h. Then the mixture was centrifuged and the solid
material was dried for 48 h at room temperature. Subsequently, the
product was hydrolysed in water with 5% of ethanol (100 ml/1 g) at
ambient temperature for 24 h under vigorous stirring. Finally, the
◦
solid material was centrifuged again, dried at 65 C and calcined in
‘
shift’ of the layers forming two new zeolites IPC-9 and IPC-10 with
◦
◦
an air flow at 550 C for 8 h using a temperature ramp of 2 C/min.
The Ti-IPC-2 catalyst was prepared by stabilisation of the Ti-
IPC-1P with diethoxydimethylsilane in 1 M HNO3 in a 25-ml
unique channel systems (two-dimensional with 10 × 7 resp. 12 × 9
rings) [17]. This, so-called, ADOR chemistry of the UTL zeolite has
been reviewed in detail recently in Ref. [18].
In this contribution, we report on the preparation of UTL
titanosilicate (Ti-UTL) and its transformations to lamellar Ti-IPC-
◦
Teflon-lined autoclave at 175 C for 16 h without agitation. 10 ml
of the HNO3 solution and 0.5 g of the diethoxydimethylsilane were
used per 1 g of the Ti-IPC-1P. The strongly hydrophobic product was
1
PISi material and titanosilicates Ti-IPC-2 (OKO structure) and
◦
obtained. Final calcination was performed at 550 C for 8 h using a
temperature ramp of 2 C/min.
Ti-IPC-4 (PCR structure). Silica-titania pillaring of the Ti-IPC-1P, in
the same way as the preparation of TS-1-PITi (vide supra), is also
presented. The activity of the catalysts is demonstrated in epoxi-
dation of a group of linear and cyclic olefins (linalool, cyclooctene
and norbornene) with hydrogen peroxide as the oxidant.
◦
The Ti-IPC-4 was formed via intercalation of the Ti-IPC-1P with
1
-aminooctane. 1 g of the Ti-IPC-1P was mixed with 30 ml of 1-
◦
aminooctane (Aldrich, 99%) and stirred at 90 C for 16 h. The solid
material was centrifuged and dried at room temperature for 24 h.
◦
Finally the material was calcined at 750 C for 8 h with a tempera-
ture ramp of 2 C/min.
◦
2
. Experimental
2.3. Synthesis of TS-1 and Ti-BEA
2.1. Synthesis of Ti-UTL
Conventional titanosilicate TS-1 (3D TS-1) was prepared from a
The Ti-UTL was prepared using a procedure reported earlier
13]. The titanium was introduced into the framework directly
during the hydrothermal synthesis. The initial gel with Si/Ti
molar ratio (Si/Ti) 50 was prepared from Cab-O-Sil M5 sil-
icon oxide (Havel Composites, Czech Republic), titanium (IV)
gel with initial Si/Ti ratio 40 according to the procedure described
in Ref. [20] using tetraethyl orthotitanate (Aldrich, technical grade)
and tetraethyl orthosilicate with tetrapropylammonium hydroxide
Aldrich, 20% in water) as a structure directing agent.
Ti-BEA was prepared from a gel with initial Si/Ti ratio 80,
according to the procedure described in Ref. [21], using tetraethyl
orthosilicate and tetraethyl orthotitanate (Aldrich, technical grade)
in the presence of hydrogen peroxide (Aldrich, 35% in water) with
tetraethylammonium hydroxide (Aldrich, 40% in water) as a struc-
ture directing agent.
[
(
butoxide (Ti(OBu) , Aldrich, 97%), germanium oxide (Alfa Aesar,
4
Germany, 99.999%), distilled water, and (6R,10S)-6,10-dimethyl-
-azoniaspiro[4.5]decane hydroxide as a structure directing agent
SDA). The preparation of the SDA is described in Ref. [19]. The
aqueous solution of the SDA was diluted with water and Cab-O-
Sil M-5 and GeO2 were added under stirring. After 30 minutes of
5
(
homogenisation, Ti(OBu) , dilluted 1:3 with 1-butanol, was added
4
dropwise and the gel was stirred for another 30 minutes. The ini-
2.4. Characterisation techniques
tial molar composition of the synthesis gel was 2 Ti(OBu) :50
4
GeO :50 SDA:100 SiO :3750 H O. The zeolite crystallised in a 90-
X-ray powder diffraction (XRD) patterns were collected using a
Bruker AXS D8 Advance diffractometer equipped with a graphite
monochromator and a position sensitive detector Våntec-1 using
CuK␣ radiation in Bragg–Brentano geometry. Data were collected
2
2
2
◦
ml Teflon-lined autoclave at 175 C under agitation for 7 days. The
◦
final product was filtered off, washed with water, dried at 85 C and
finally calcined with a stepwise increase of the temperature. At first
◦
◦
◦
◦
at 200 C for 2 h, then at 350 C for 4 h and finally at 550 C for 8 h,
in continuous mode over the 2Â range of 1–40 with a step size of
◦
◦
using a temperature ramp of 2 C/min.
0.00853 and time per step 0.25 s.
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The size and shape of zeolite crystals were examined by scan-
ning electron microscopy (SEM) on a JEOL, JSM-5500LV microscope.
The images were collected with acceleration voltage of 20 kV.
Nitrogen sorption isotherms were measured at liquid nitro-
◦
gen temperature (−196 C) with Micromeritics Gemini volumetric
instrument. Prior to the sorption measurements, individual zeolites
◦
were outgassed in a stream of helium at 300 C for 3 h.
BET area was evaluated using adsorption data in the range of a
relative pressure from p/p = 0.05 to p/p = 0.20. The t-plot method
0
0
[
22] was applied to determine the volume of micropores (Vmicro).
The adsorbed amount of nitrogen at p/p = 0.95 reflects the total
0
adsorption capacity (Vtotal) of the material.
DR-UV/vis absorption spectra were collected using Perkin-
Elmer Lambda 950 Spectrometer with 2 mm quartz tube and large
8
mm × 16 mm slit. The data were collected in the wavelength
range of 190–500 nm. All the samples were analysed after calci-
nation.
Fig. 1. Powder XRD patterns of parent Ti-UTL, lamellar precursor Ti-IPC-1P, lamellar
precursor after swelling Ti-IPC-1-sw and pillared calcined Ti-IPC-1PISi material.
Chemical composition of the materials (expressed hereafter as a
Si/Ti ratio) was determined by ICP-OES ThermoScientific iCAP 7000
instrument.
the pillaring. A scheme describing the post-synthesis treatment is
presented in the Supporting information (Fig. S1).
The Ti-IPC-1P lamellar precursor can be directly calcined form-
ing a sub-zeolite Ti-IPC-1. The crystalline layers of Ti-IPC-1 are
oriented randomly one on another with a d-spacing of 1.9 nm (cal-
2.5. Catalytic tests
The epoxidations of cis-cyclooctene (Aldrich, 95%), norbornene
(
Aldrich, 99%), and linalool (Aldrich, 97%) were carried out in a
culated from (2 0 0) reflection, Fig. 2). Stabilisation of the Ti-IPC-1P
2
5 ml magnetically stirred glass three-necked round bottom flask
◦
with diethoxydimethylsilane in 1 M HNO at 175 C and subsequent
3
◦
equipped with a Dimroth condenser at 60 C. The alkene/catalyst
calcination resulted in the formation of Ti-IPC-2 material [16] with
the OKO topology and Si/Ti ratio 210. The XRD pattern is presented
in Fig. 2. The increase in the Si/Ti ratio with respect to the parent
Ti-UTL results from the introduction of purely siliceous S4R units
during the stabilisation.
Intercalation of the Ti-IPC-1P with 1-aminooctane enables to
organise the layers leading to the formation of titanosilicate Ti-IPC-
4 (PCR topology). The XRD pattern is presented in Fig. 2. The Ti-IPC-
mass ratio was 10 (S/C = 10) and alkene/H O2 molar ratio was 2.
2
Acetonitrile (Fisher chemical, HPLC grade) and methanol (Fisher
chemical, HPLC grade) were used as a solvents and mesitylene
(
99%, Acros-Organics) served as an internal standard. In a standard
experiment, 500 mg of norbonene or cyclooctene were mixed with
50 mg of the internal standard, 50 mg of the catalyst and 6.65 ml of
acetonitrile. The reaction was started by addition of H O aqueous
2
2
2
solution (35 wt.%, Aldrich) into the mixture. Epoxidation of linalool
6 mmol, 0.925 g) was performed in methanol (9 ml) using 60 mg
of the catalyst (S/C = 15) and 250 mg of the internal standard. The
reaction was started by addition of H O aqueous solution (1 molar
4
material possesses narrow 10-ring intersecting 8-ring pores. In
(
general, the introduction of Ti into the UTL structure did not affect
the possibility of its top-down transformations as described in Ref.
[15,16].
2
2
eq of linalool) keeping the C C double bond/H O2 ratio 2. Samples
2
Having in mind the low titanium content in the Ti-IPC-1PISi
material as the most promising catalyst in the term if active sites
accessibility, we used the same approach as in the case of silica-
titania pillared lamellar TS-1 [9]. Therefore, a set of materials
denoted Ti-IPC-1PITi has been prepared, where different amounts
of Ti(OBu)4 were added into the TEOS used for the pillaring treat-
ment (typically in the range Si/Ti 30–100). One sample of IPC-1P
without titanium present form the hydrothermal synthesis was
were taken in regular intervals, centrifuged, cooled and analysed
using an Agilent 6850 GC system with 50 m long DB-5 column, an
autosampler and a FID or a MS detector. Helium was used as a car-
rier gas. The results were compared with standard Ti-BEA and TS-1
catalysts.
3
. Results and discussion
3.1. Catalyst structure
Well crystalline Ti-UTL zeolite has been prepared with the Si/Ti
ratio 139. The XRD pattern of the material is presented in Fig. 1 and
it is well consistent with standard UTL pattern [23]. The hydrolysis
of the Ti-UTL led to a lamellar precursor denoted Ti-IPC-1P. Most
of the diffraction lines disappeared with the structure disassem-
bly. A shift of the most intensive (2 0 0) reflection towards higher
angles can be observed between the Ti-UTL and Ti-IPC-1P. It charac-
terises the d-spacing of 2.9 nm and 2.1 nm, respectively. When the
Ti-IPC-1P was swollen with a solution of cetyltrimethylammonium
hydroxide, intensive reflections (1 0 0), (2 0 0) and (3 0 0) appeared
in the diffraction pattern, indicating the extension of the d-spacing
to 3.7 nm. The interlayer distance of the swollen material is pre-
served also in the pillared Ti-IPC-1PISi material (Fig. 1). The Si/Ti
ratio increased to 480 in Ti-IPC-1PI. This is a result of the removal of
part of the crystalline material during D4R hydrolysis together with
dilution of the titanosilicate phase by the amorphous silica used for
Fig. 2. Powder XRD patterns of calcined Ti-IPC-1, Ti-IPC-2 and Ti-IPC-4 materials.
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Table 1
4
Textural properties and Ti content of the Ti-UTL and derived catalysts.
2
Titanosilicate
BET (m /g)
Vmic (ml/g)
Vtot (ml/g)
Si/Ti
Ti-UTL
Ti-IPC-1-PI
Ti-IPC-1
Ti-IPC-2
Ti-IPC-4
IPC-1-PITi (40)
Ti-IPC1-PITi (30)
Ti-IPC1-PITi (50)
Ti-IPC1-PITi (100)
Ti-BEA
TS-1
539
1001
192
383
237
664
910
662
763
339
450
0.239
0
0.29
0.67
0.13
0.22
0.15
0.34
0.46
0.35
0.43
0.19
0.16
139
480
n.d.a
210
n.d.a
43
16
18
69
116
44
0.07
0.15
0.10
0.11
0
0.14
0.10
0.14
0.13
b
b
b
b
a
Ti content was not determined because the material was not intended to be used
in catalytic tests.
b
Si/Ti molar ratio of the pillaring medium is given in brackets.
Fig. 3. Powder XRD patterns of Ti-IPC-1-PITi samples with different composition of
the pillaring medium.
different titanosilicate samples demonstrate the possibilities of the
texture tuning. All the presented materials were prepared from
one parent Ti-UTL zeolite. The Ti-UTL, Ti-IPC-2, and Ti-IPC-4 mate-
rials exhibit type I isotherms, typical for microporous materials.
The isotherm of Ti-IPC-1 is also type I, although its pores are dis-
ordered [18]. The BET areas, micropore volumes, (Vmic) and total
adsorption capacities (Vtot) decrease with decreasing size of the
pores in the order Ti-UTL > Ti-IPC-2 > Ti-IPC-4 > Ti-IPC-1 (e.g. BET
prepared in this way (denoted IPC-1PITi) from B-UTL with initial
Si/B ratio 27 as well. A comparison of their XRD patterns with silica-
pillared Ti-IPC-1PISi is shown in Fig. 3. Two weak diffraction lines
◦
◦
at 2Â = 12.8 and 25.7 are the main features of the pattern and their
intensities are similar for all the samples.
2
2
2
Scanning electron micrographs (SEM), showed in Fig. 4, reveal
characteristic thin plate shape of the Ti-UTL crystals (a). This mor-
phology is preserved also during the post-synthesis modifications.
In the case of the pillared samples (b, c), the crystals are partially
covered with amorphous silica resp. silica-titania phase resulting
from the excess of the pillaring medium. The thin plate morphology
is characteristic also for the Ti-IPC-2 (d).
The textural properties and Ti content of all discussed sam-
ples are listed in Table 1. Selected nitrogen sorption isotherms are
presented in Fig. 5. The positions of the isotherms belonging to
area: Ti-UTL = 539 m /g, Ti-IPC-2 = 383 m /g, Ti-IPC-4 = 237 m /g,
2
Ti-IPC-1 = 192 m /g). The swelling and pillaring treatment of Ti-IPC-
2
1P lead to a material with BET area up to 1001 m /g (Ti-IPC-1PI).
This material possesses no micropores because it consists only of
dense layers supported by amorphous silica pillars. The addition
of titanium during the pillaring resulted in a decrease in the BET
area and adsorption capacity and in some cases in formation of
some micropores. The Si/Ti molar ratio of the pillaring medium for
different samples is given in brackets. We ascribe this observation
to higher reactivity of Ti(OBu)4 in comparison with the TEOS [24]
Fig. 4. SEM micrographs of catalysts Ti-UTL (a), Ti-IPC-1PISi (b), Ti-IPC-1PITi (c) and Ti-IPC-2 (d).
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Fig. 5. Nitrogen sorption isotherms of the Ti-UTL and derived materials. Empty
points denote desorption. Number in brackets indicate Si/Ti ratio of the pillaring
medium.
and it is consistent with our experience with lamellar TS-1 pillar-
ing [9]. The titanium containing pillars are thicker. The shape of
the isotherms, which belong to the pillared samples, is typical for
these materials. The increase in the amount of adsorbed nitrogen in
the range of p/p0 0.05–0.4 is typical for the filling of the interlayer
space, which belongs to the region of small mesopores [25]. Once
this space is filled, the nitrogen uptake is strongly diminished.
The coordination of titanium in the discussed catalysts was
investigated by DR-UV/vis spectroscopy. It is generally assumed
that isolated framework tetrahedrally coordinated titanium species
are the active sites in the epoxidation reactions [26]. The DR-UV/vis
spectra of the Ti-UTL derived catalysts are presented in Fig. 6. All
the spectra were collected in air after calcination.
The most intensive absorption band in the spectra of Ti-UTL
(
a), Ti-IPC-2 (b), Ti-IPC-1PISi (c), Ti-BEA (i) and TS-1 (j) is cen-
tred between 205 and 210 nm. Zecchina et al. ascribed this band
to tetrahedrally coordinated framework Ti(OSi)4 species [27]. That
means the titanium is incorporated into the framework during the
hydrothermal synthesis. It is known that there exists a limit for the
titanium amount which can be incorporated into the framework
of TS-1 [28]. Similarly, we expect there exists a limit in the case
of Ti-UTL. A weak absorption above 300 nm in the spectrum of Ti-
UTL (Fig. 6a) may indicate that the Ti content in the sample is close
to the UTL limit of titanium incorporation. The spectra of silica-
titania pillared samples (Fig. 6d, e, f, h) exhibit another intensive
absorption band between 240 and 290 nm. This absorption results
from presence of penta- or hexa-coordinated extra-framework
Ti(OH)(OSi) (H O) and Ti(OH) (OSi) (H O) species [29]. The cat-
3
2
2
2
2
2
alytic activity of these species is a subject of debate and it is believed
that extra-framework species with coordination number 5 and
6
are inactive [2]. However, there exists some indicia that non-
tetrahedral titanium species might be active in oxidation catalysis
as-well [30–32]. A shoulder above 300 nm can be observed addi-
tionally to the bands mentioned in the above discussion. It points
to a presence of a certain amount of an anatase-like TiO2 phase
containing Ti–O–Ti species (absorbing at typically at 330 nm). The
anatase-like species are known to be inactive or to cause unpro-
ductive H O decomposition during the epoxidation reaction [2].
Fig. 6. DR-UV/vis spectra of the discussed titanosilicates. (a) Ti-UTL, (b) Ti-IPC-2,
(
c) Ti-IPC-1PI, (d) Ti-IPC-1PITi (30), (e) Ti-IPC-1PITi (50), (f) Ti-IPC-1PITi (100), (g)
Ti-IPC-1-Ti-stab, (h) IPC-1PITi (40), (i) Ti-BEA, (j) TS-1.
3.2. Catalytic tests
2
2
The observed catalytic performance is discussed below.
An attempt to prepare Ti-IPC-2 material by stabilisation with
Ti(OBu)4 instead of diethoxydimethylsilane was performed, but
only a disordered Ti-IPC-1 was obtained (denoted Ti-IPC-1-Ti-stab),
containing high amount of anatase phase. Its DR-UV/vis spectrum
is shown in Fig. 6g.
The Ti-UTL derived catalysts were tested in epoxidation of
cyclooctene, norbornene, and linalool at 60 C with hydrogen per-
oxide as the oxidant. The results are compared with Ti-BEA and
TS-1 catalysts as benchmarks (Table 2). The Ti-UTL provided a yield
of cyclooctene oxide 4.7% after 4 h what is similar to the large-pore
Ti-BEA catalyst with similar Ti content (Si/Ti 139 resp. 116). The
◦
ˇ
Please cite this article in press as: J. P rˇ ech, J. Cejka, UTL titanosilicate: An extra-large pore epoxidation catalyst with tunable textural
properties, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.09.036

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CATTOD-9835; No. of Pages7
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6
J. P rˇ ech, J. Cˇ ejka / Catalysis Today xxx (2015) xxx–xxx
Table 2
◦
Epoxidation of cyclooctene, norbornene and linalool at 60 C for 4 h.
Entry
Catalyst
Substrate
Solvent
X(Substrate) (%)a
y(Epoxide) (%)b
S (X) (%)c
1
2
3
Ti-UTL
Ti-IPC-1PI
Ti-IPC-2
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Norbornene
Norbornene
Norbornene
Norbornene
Linalool
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Methanol
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Methanol
14.3
21.3
11.2
4.7
8.0
0.4
30 (20%)
38 (20%)
n.d.e
d
d
4
a
Ti-IPC-1PITi (30)
Ti-IPC-1PITi (30)
Ti-IPC-1PITi (50)
Ti-IPC-1PITi (100)
IPC-1PITi (40)
Ti-IPC-1PITi (30)
Ti-BEA
TS-1
Ti-IPC-1PITi (30)
Ti-UTL
Ti-IPC1-1PI
Ti-BEA
Ti-UTL
Ti-IPC1-1PI
Ti-IPC-1PITi (30)
Ti-IPC1-PITi (100)
TS-1
26.0
19.5
–
4
b
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
35.8
29.0
34.7
28.3
34.8
14.0
5.9
57.2
60.5
49.2
54.3
31.7
6.4
23.3
16.1
24.7
15.5
19.1
4.7
2.9
12.6
0.9
80 (20%)
65 (20%)
80 (20%)
67 (20%)
78 (20%)
32 (20%)
55 (10%)
30 (20%)
n.d.e
19 (20%)
8.0 (10%)
9 (10%)
64 (10%)
50 (10%)
58 (10%)
n.d.e
1
1
1
1
1
1
1
1
1
1
6.5
3.8
f
3.3
f
Linalool
Linalool
Linalool
Linalool
Methanol
Methanol
Methanol
Methanol
3.8
f
46.6
43.5
3.0
23.5
f
22.2
f
3.0
a
b
c
d
e
f
Conversion of the substrate after 4 h.
Yield of the epoxide after 4 h.
Selectivity of the reaction at the conversion in brackets; defined as [produced epoxide]/[consumed substrate].
Conversion and yield given after 1 h of the reaction.
Selectivity was not determined due to low conversion or yield.
Yield is calculated for 2-(5-methyl-5-vinyltetrahydro-1-furyl)-2-propanol, the main product of in-situ rearrangement of the 6,7-epoxylinalool.
selectivity of the reaction was 30–32% at 20% conversion (reached
after 8.3 h) for both catalysts. The transformation of the Ti-UTL into
a pillared material Ti-IPC-1PISi resulted in an increase in the yield
incorporated into vacancies after boron atoms similarly to the Ref.
[30].
Furthermore, we expect that some impregnation of the
crystalline layers with titanium species occurred during the silica-
titania pillaring and at least a part of those new Ti centres is
catalytically active. On the other hand, the activity of the titanium in
the pillars is questionable, because the sites which are not located
on the surface might be inaccessible.
In the epoxidation over Ti-IPC-1PITi (30) as a representative
catalyst, methanol was used as a solvent instead of acetonitrile;
however, the change of the solvent did not influence the con-
version significantly (see Table 2 entry 4b (acetonitrile) vs. entry
8 (methanol): cyclooctene conversion 35.8% vs. 34.7%). Only the
yield of the epoxide decreased (23.3% vs. 19.1% after 4 h). This
is in accordance with previous observations because the epoxide
undergoes a ring-opening reaction with methanol [33]. Following
the development of cyclooctene conversion and cyclooctene oxide
yield in time over the Ti-IPC-1-PITi (30) as a representative cat-
alyst, conversion of 26% and yield 19.5% were observed after 1 h
(Table 2, entry 4a). Then the rate of the reaction decreased rapidly
and after 4 h it stopped. The cyclooctene conversion at this time
was 35.8% but a theoretical maximum conversion is 50% (0.5 eq
(
8% after 4 h with Ti-IPC-1PI) as well as the selectivity (38% at 20%
conversion), although the active phase was diluted by the pillaring
treatment. We ascribe this to lower diffusion restrictions of the Ti-
IPC-1PISi material. The yield of cyclooctene oxide over Ti-IPC-2 was
only 0.4% after 4 h (less than the yield over TS-1: 2.9%). We expect
that this is a result of both diffusion restrictions in 12 × 10-ring
channel system and low titanium content. When silica-titania pil-
lared catalysts were tested, both yield of the cyclooctene oxide and
the selectivity of the reaction increased dramatically. The highest
yields of the epoxide after 4 h were obtained using Ti-IPC-1PITi (30)
and Ti-IPC-1PITi (100) catalysts (23.3% resp. 24.7) with 80% selec-
tivity at 20% conversion. It should be noted that these catalysts are
2
those possessing the highest BET area (910 resp. 763 m /g) and
total adsorption capacities (0.46 resp. 0.43 ml/g) among the silica-
titania pillared catalysts (Table 1). In other words, the catalysts with
most open structures and therefore the lowest diffusion limitations
exhibited the highest yields. The conversion and yield are inde-
pendent on the titanium content among the silica-titania pillared
catalysts, but there exists a linear dependence of the cyclooctene
conversion on the total adsorption capacity. Lower conversion (29%
after 4 h) and yield (16.1% after 4 h) obtained using the Ti-IPC-1PITi
of H O2 is used). Iodometric titration of the sample revealed total
2
conversion of the hydrogen peroxide, which means, that approx-
imately 28% of hydrogen peroxide was ineffectively decomposed
(due to the presence of anatase-like phase) or consumed in some
side reactions (e.g. further oxidation of the ring opening prod-
2
2
(
50) (BET = 662 m /g, Vtot = 0.35 m /g) well confirms this hypothe-
sis. We conclude that the open structure of the catalyst allows the
reactants to access the active sites rapidly (resulting in high conver-
sion in comparison with the others) and on the other hand allow the
products to leave rapidly preventing their further conversion on the
titanium sites [29] reaching therefore high selectivity. The IPC-1PITi
ucts observed by Pirovano et al. [34]). When a dose of fresh H O2
2
(0.5 eq base on initial substrate amount) was added after 3 h, the
reaction was restored reaching cyclooctene conversion 53,7% and
epoxide yield 30.7% after 5 h since the beginning of the experi-
ment and cyclooctene conversion 86% and epoxide yield 40% after
24 h. Development of the conversion and yield in time during the
reaction is presented in the supplementary information (Fig. S2).
The leaching test was performed with the Ti-IPC-1PITi (30)
as a representative catalyst. The reaction mixture containing
cyclooctene, mesitylene and hydrogen peroxide in acetonitrile
(
40) catalyst (possessing no titanium from the hydrothermal syn-
thesis) fits to the group of Ti-pillared catalysts providing conversion
and yield of 28.3% resp. 15.5% after 4 h. Its UV/vis spectrum is also
similar to the other Ti-pillared catalysts (Fig. 6). This is very close
to the results obtained over Ti-IPC-1PITi (50) (possessing also simi-
2
2
2
lar textural properties: BET = 662 m /g vs. 664 m /g, Vtot = 0.35 m /g
2
vs. 0.34 m /g). We expect boron atoms were washed out during
◦
the hydrolysis of the starting B-UTL and titanium atoms have been
reacted at 60 C for 30 min reaching conversion of 12.9% and yield of
ˇ
Please cite this article in press as: J. P rˇ ech, J. Cejka, UTL titanosilicate: An extra-large pore epoxidation catalyst with tunable textural
properties, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.09.036

G Model
CATTOD-9835; No. of Pages7
ARTICLE IN PRESS
J. P rˇ ech, J. Cˇ ejka / Catalysis Today xxx (2015) xxx–xxx
7
1
0%. Then the catalyst was separated from the reaction mixture by
Acknowledgements
◦
centrifugation (the temperature decreased to 45 C during centrifu-
gation) and the mixture was stirred further at 60 C and samples
were taken in 1 h intervals. No further formation of cyclooctene
oxide was observed for 4 h confirming that the epoxidation do not
occur in homogenous phase.
◦
The authors acknowledge support of the Czech Science Founda-
tion P106/12/G015. In addition, the authors thank to G. Sádovská
for DR-UV/vis measurement and Valeryia Kasneryk for the SEM.
When norbornene was used as the substrate, the order of
epoxide yields over different catalysts was similar to cyclooctene
epoxidation: Ti-IPC-1PITi (30) y = 12.6% > Ti-IPC-1PISi y = 6.5% > Ti-
BEA y = 3.8% > Ti-UTL y = 0.9% after 4 h. Norbornene is more rigid
molecule in comparison with cyclooctene and therefore the advan-
tage of 3-dimensional 12-ring channel system of the Ti-BEA over
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cattod.2015.09.
036.
2
-dimensional system of Ti-UTL manifests itself.
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Please cite this article in press as: J. P rˇ ech, J. Cejka, UTL titanosilicate: An extra-large pore epoxidation catalyst with tunable textural
properties, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.09.036