Synthesis of TS-1 zeolites from a polymer containing titanium and silicon

Article abstract of DOI:10.1039/d0ta11876a

The synthesis of TS-1 zeolites is regarded as a milestone in zeolite history, and it has led to the revolution of the green oxidation system of using H₂O₂as an oxidant, leaving only water as the byproduct. However, because of the highly hydrolyzable titanium source, the preparation of TS-1 requires complex synthesis conditions. Moreover, the difference in the hydrolysis rate between the silicon source and titanium source tends to increase the difficulty of titanium insertion into the framework, and it is easy to generate extra-framework Ti species during the synthesis. Here, a high-quality TS-1 zeolite with a large external surface area and free of extra-framework Ti species has been successfully synthesized by using a kind of novel polymer containing titanium and silicon. Due to the high hydrolysis resistance of the polymer reagent, a good matching of the hydrolysis rate between the silicon source and the titanium source is realized during crystallization, which facilitates the incorporation of titanium into the framework. Furthermore, the TS-1 zeolite exhibited excellent catalytic performance inn-hexane oxidation with hydrogen peroxide as the oxidant. This method of synthesizing zeolites from polymers is expected to be widely applied for the synthesis of other titanium-containing zeotype materials.

Full text of DOI:10.1039/d0ta11876a

Journal of
Materials Chemistry A
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PAPER
Synthesis of TS-1 zeolites from a polymer
containing titanium and silicon†
Cite this: J. Mater. Chem. A, 2021, 9,
205
6
Jiacheng Xing,‡ Danhua Yuan,‡ Hanbang Liu, Yansi Tong, Yunpeng Xu *a
ab
a
ab
ab
ab
and Zhongmin Liu
*
The synthesis of TS-1 zeolites is regarded as a milestone in zeolite history, and it has led to the revolution of
the green oxidation system of using H as an oxidant, leaving only water as the byproduct. However,
2 2
O
because of the highly hydrolyzable titanium source, the preparation of TS-1 requires complex synthesis
conditions. Moreover, the difference in the hydrolysis rate between the silicon source and titanium
source tends to increase the difficulty of titanium insertion into the framework, and it is easy to generate
extra-framework Ti species during the synthesis. Here, a high-quality TS-1 zeolite with a large external
surface area and free of extra-framework Ti species has been successfully synthesized by using a kind of
novel polymer containing titanium and silicon. Due to the high hydrolysis resistance of the polymer
reagent, a good matching of the hydrolysis rate between the silicon source and the titanium source is
realized during crystallization, which facilitates the incorporation of titanium into the framework.
Furthermore, the TS-1 zeolite exhibited excellent catalytic performance in n-hexane oxidation with
hydrogen peroxide as the oxidant. This method of synthesizing zeolites from polymers is expected to be
widely applied for the synthesis of other titanium-containing zeotype materials.
Received 7th December 2020
Accepted 3rd February 2021
DOI: 10.1039/d0ta11876a
rsc.li/materials-a
The tetrahedrally coordinated titanium can activate H
2 2
O and
Introduction
lead to the formation of an intermediate peroxo or hydroperoxo
11
Titanium silicalite-1 (TS-1) is a very useful and special zeolite species. More recently, Gordon et al. presented fresh evidence
1
4
with an MFI-type framework composed of tetrahedral titanium to suggest that the active sites in TS-1 are dinuclear. These
1–3
and silicon atoms. In 1983, Taramasso et al. of Snamprogetti ndings might further the optimization of these titanium
SPA led the rst patent for TS-1 zeolites. The discovery of TS-1 containing industrial catalysts. However, the synthesis of high-
4
is regarded as a milestone in the history of zeolite and hetero- performance TS-1 zeolites with tetrahedrally coordinated tita-
geneous catalysis, and it has led to the revolution of the green nium in the framework is still a challenging task. Previous
5
–11
oxidation system with H
2
O
2
as an oxidant.
TS-1 zeolites studies showed that the easy hydrolysis of a titanium source
catalyse several oxidation reactions, most notably the epoxida- such as tetraethyl titanate (TEOT) used in the zeolite synthesis
tion of propylene. Through this reaction, the oxygen atom in made it difficult for titanium to be incorporated into the TS-1
1
5–17
hydrogen peroxide (H O ) is added to the propylene's carbon– framework.
Thus, extra-framework Ti will be formed,
carbon double bond. Propylene oxide, a widely used compound, including octahedrally coordinated Ti and anatase TiO . The
is produced. Propylene oxide is always used as a raw material to anatase TiO may cover the active sites in TS-1 and lead to the
2
2
2
2
12
18
manufacture the building blocks of polyurethane plastics. Due inefficient decomposition of H
O
.
Therefore, the early TS-1
2
2
to its great importance, the synthesis of TS-1 has been one of the synthesis method using TEOT as a titanium source was
most popular topics in zeolite synthesis research over the past complicated and needed to be performed in an ice water bath
13
5
few decades.
2
under a CO atmosphere. Later, for an easier operation, tetra-
The tetracoordinated titanium part of the TS-1 zeolite is also butyl titanate (TBOT) was selected instead of TEOT as the tita-
called framework titanium. The framework titanium in TS-1 nium source in TS-1 synthesis because TBOT is more stable
5
19,20
zeolites has been thought to be the mononuclear active site.
than TEOT.
However, the subsequent steps of alcohol
evaporation and aging processes would readily lead to the
formation of extra-framework Ti species, which are unfavorable
a
National Engineering Laboratory for Methanol to Olens, Dalian National Laboratory
for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian 116023, P. R. China. E-mail: xuyp@dicp.ac.cn; liuzm@dicp.ac.cn
21–24
for the catalytic activity of TS-1.
Therefore, numerous kinds
of crystallization-mediating agents, such as hydrogen peroxide,
ammonium carbonate, isopropyl alcohol or starch, were added
b
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
†
Electronic supplementary information (ESI) available: Experimental and into the system to inhibit the formation of extra-framework Ti
characterization details. See DOI: 10.1039/d0ta11876a
15,19,25–27
species.
Fan et al. reported the synthesis of titanium-rich
‡
These authors contributed equally to this work.
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TS-1 zeolites free of extra-framework titanium species based on Si polymer. During the transesterication reactions, the alkyl
21
the addition of (NH ) CO . Zhang et al. proposed a strategy to titanate served as both the reactant and the transesterication
4
2
3
synthesize anatase-free TS-1 zeolites by using Triton X-100 and catalyst. The Ti–diol–Si polymer is similar to polyethylene
28
rotational crystallization conditions. However, most of the as- terephthalate (PET), a widely used polymer, with the exception
synthesized TS-1 samples still need to be treated with an acid to that the terephthalate in the PET polymer structure is
30
eliminate the extra-framework octahedral Ti species and substituted by a silicate or titanate. The polymer sample (Ti–
21,29
anatase TiO
2
.
PEG–Si polymer) shown in Fig. 1b was synthesized with TEOT,
In this work, a polymer containing titanium and silicon was tetraethyl orthosilicate (TEOS), and polyethylene glycol
used to synthesize the TS-1 zeolite, which overcame the prob- (PEG200). The photos show that the liquid raw materials are
lems faced in the conventional synthesis of the zeolite and successfully transformed into a transparent solid product
made the synthesis conditions less difficult and easier to through transesterication polymerization, as shown in Fig. 1d.
perform, as well as avoiding the formation of extra-framework In this study, a series of polymers were prepared by varying the
Ti species. This method of synthesizing zeolites from poly- diols in the studies (Fig. 1c). The resulting polymers generally
mers is expected to have widespread applications.
have polymerization degrees of 10–13 with a maximum of 15
Table S1†). The degree of polymerization is determined by
(
several parameters: the type of diol, reaction time, temperature,
etc. The type of diol also affects the water solubility of the
synthesized polymers. The polymers (Fig. 1e) synthesized with
ethylene glycol (EG), 1,3-propanediol (PDO), 1,4-butanediol
Results and discussion
Ti–diol–Si polymer preparation and characterization
The polymer containing titanium and silicon was synthesized
by using alkyl titanates, alkyl silicates and alkyl diols as the
reactants through transesterication reactions. In these reac-
tions, the alkoxy groups of the alkyl titanate and alkyl silicate
were transesteried with alkyl diols to form a network-like
polymer compound (Fig. 1a). The product was named Ti–diol–
(BDO), 1,6-hexanediol (HDO) and polyethylene glycol 200 (PEG)
have good water solubility, whereas those synthesized with 1,4-
cyclohexanediol (CHD), 1,4-cyclohexanedimethanol (CHDM),
and p-phenylenedimethanol (PXG) are insoluble in water.
Regardless of which diol is used, the common feature of the
Fig. 1 (a) Synthesis of the TS-1 zeolite from Ti–diol–Si polymers. (b) Photos of the liquid raw materials and solid polymer products. (c) Types of
alkyl titanates, alkyl silicates and alkyl diols used. (d) Transesterification reaction. (e) Photos of the Ti–diol–Si polymers.
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polymer is that it is stable in water and difficult to hydrolyze. For analysis (TGA) result for the Ti–CHDM–Si polymer. It can be seen
example, TEOT, a quite easily hydrolyzed ester, was used as that the sample decomposes signicantly at approximately
ꢀ
a raw material to synthesize the Ti–PEG–Si polymer with PEG as 500 C, which means that the polymer has quite high thermal
the diol reactant. The obtained polymer was observed to be stability and provides clear evidence of the successful polymeri-
1
3
stable and to dissolve in water and did not hydrolyze aer more zation of titanium and silicon esters with the diol species. The
C
than 12 months at room temperature, as shown in Fig. S1.† It is MAS NMR analysis shows that the peaks of the methylene and
known that the synthesis of the TS-1 zeolite requires strict methyl groups on the silicon ester and the titanium ester at 58.2
avoidance of the rapid hydrolysis of the titanium source, so the and 18.2 ppm, respectively, are signicantly weakened and low-
13
synthesis conditions are complicated and harsh. From this ered, which proves that the ethyl groups of the original TEOS and
point of view, the hydrolysis-resistant Ti–diol–Si polymers TEOT are removed in the transesterication reactions (Fig. 2f II).
1
3
should be an ideal raw material for the synthesis of TS-1 From the C MAS NMR spectra of the other polymers, it can also
zeolites. In the following experiments, the TS-1 zeolite was be seen that the peaks at 58.2 and 18.2 ppm are signicantly
successfully synthesized from the polymers, and the synthesis weakened. Other Ti–diol–Si polymers have similar properties,
process was a very simple, mild and easy operation.
such as a transparent solid appearance, high decomposition
As a representative sample among the synthesized polymers, temperature, and hydrolysis resistance.
the Ti–CHDM–Si polymer (polymer synthesized by using TEOT,
TEOS and CHDM) is thoroughly investigated and presented here.
Fig. 1e shows that the Ti–CHDM–Si polymer is a transparent solid
with a certain toughness. Fig. 2f shows the thermogravimetric
TS-1 zeolite preparation and characterization
The synthesis procedures of TS-1 zeolites from the Ti–diol–Si
polymers are illustrated as follows: the water-soluble polymers
13
Fig. 2 (I) Thermogravimetric analysis (TGA) and (II) C MAS NMR spectrum of the Ti–diol–Si polymer. Different diols in Ti-diol-Si polymers (a) EG
b) HDO (c) PDO (d) CHD (e) BDO (f) CHDM (g) PEG (h) PXG.
(
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In order to study the coordination environment of Ti species
more clearly, the samples were also characterized by X-ray
photoelectron spectroscopy (XPS), as shown in Fig. S20.† In
the Ti 2p region, signals at binding energies of 458.4 and
464.1 eV appeared for all samples, while signals at binding
energies of 459.8 and 465.2 eV appeared mainly in the samples
synthesized by conventional methods. Generally, the binding
energy values of 458.4 and 464.1 eV are assigned to the 2P3/2 and
2
P
1/2 photoelectrons of tetrahedrally coordinated framework
Fig. 3 (a) XRD patterns and (b) UV-Vis spectra of conventional TS-1
and TS-1 synthesized from different polymers. Inset: enlarged UV-Vis
spectra in the region between 250 nm and 350 nm.
Ti(IV) species. On the other hand, the binding energy values of
4
59.8 and 465.2 eV were mainly attributed to the 2P3/2 and 2P1/2
photoelectrons of octahedrally coordinated Ti(VI) species in
35,36
extra-framework positions.
The tetrahedrally coordinated
are dissolved in an aqueous solution of tetrapropylammonium
hydroxide (TPAOH) with a certain ratio at room temperature
and then are crystallized with or without rotation at a certain
temperature. For the insoluble polymers, they are put into an
aqueous solution of TPAOH and then directly crystallized under
similar conditions to the water-soluble polymers. TPAOH with
different ratios is provided in the ESI.† The molar ratio of tita-
nium to silicon in the polymers is controlled at 1 : 24. The above
methods did not require conventional alcohol evaporation and
aging steps. Fig. 3a shows the X-ray diffraction (XRD) patterns of
zeolites synthesized with eight different polymers, named EG–
TS-1, PDO–TS-1, BDO–TS-1, HDO–TS-1, CHD–TS-1, CHDM–TS-
framework Ti species are the dominating species in the TS-1
zeolites synthesized from different polymers. However,
a signicant increase of the octahedrally coordinated Ti(VI)
species (extra-framework Ti) were observed in TS-1 synthesized
by conventional methods. This also proved that TS-1 zeolites
synthesized from the Ti–diol–Si polymer could effectively match
the hydrolysis rate of the silicon source and titanium source and
avoid the formation of extra-framework titanium species.
FTIR was used to evaluate the titanium species in the TS-1
zeolite samples. As shown in Fig. S22,† all the samples
ꢁ1
showed a band at 960 cm , which was ascribed to the
stretching vibration of the Si–O–Ti bond or the Si–O bond per-
1, PXG–TS-1, and PEG–TS-1. These patterns are in good agree-
37
turbed by the presence of Ti atoms in the framework. Besides,
ment with the XRD patterns typical of the MFI topology. All the
samples have ve characteristic diffraction peaks of the MFI
framework, which proves that the synthesized TS-1 zeolites have
ꢁ1
38
the band at 800 cm is characteristic of the MFI topology.
Therefore, the presence of titanium in the framework could be
inferred from the FTIR analysis as shown in Fig. S22.†
Previous studies have found that the different hydrolysis
rates of Si and Ti alkoxides lead to the formation of extra-
31
a pure phase and high crystallinity.
UV-Vis spectroscopy was used to detect the coordination
state of titanium in TS-1 (Fig. 3b). All the TS-1 zeolites synthe-
sized from different polymers have a strong absorption band at
a wavelength of 210 nm. The absorption peak here represents
the tetrahedrally coordinated titanium in the framework. This
tetracoordinated titanium part of the zeolite, which is also
called framework Ti, is widely recognized as the active center of
21
framework titanium species during TS-1 crystallization.
Therefore, many strategies, such as careful operation of the
alcohol evaporation and aging steps and the addition of
crystallization-mediating agents, have been used to control the
hydrolysis rate, mainly that of the titanium source, to suppress
17,21,27
extra-framework titanium formation.
However, in the
32,33
a catalytic oxidation reaction.
Peaks in the wide band
method described herein, an extra-framework titanium-free TS-
zeolite could be synthesized easily and conveniently without
between 240 and 280 nm as well as at 330 nm are generally
1
18,34
considered to indicate extra-framework titanium species.
All
complicated steps or additional crystallization-mediating
agents. The mechanism might be interpreted as follows.
When the Ti–diol–Si polymers were used for the synthesis of TS-
the TS-1 samples synthesized using different polymers have no
absorption band here, which proves that the extra-framework
titanium species is not signicantly formed in TS-1 during
crystallization.
UV-Raman spectroscopy with excitation lines at 244 nm was
employed to characteristic the Ti species in TS-1 zeolites
synthesized from different polymers, as shown in Fig. S19.† The
Raman spectra of the TS-1 zeolites synthesized from different
polymers showed strong Raman bands at 490, 530, and
ꢁ
1
1
125 cm , which had been assigned to the symmetric
stretching and asymmetric stretching vibrations of framework
22
Ti–O–Si species due to the resonance Raman effect. Besides,
ꢁ1
the Raman bands at 960 cm also came from the asymmetric
stretching of the framework TiO units. It can be seen from the
4
UV-Raman spectrum that titanium was incorporated in the
framework of the TS-1 zeolites synthesized from different
polymers.
Fig. 4 Titanium sources and silicon sources were detached uniformly
from the Ti–diol–Si polymers during crystallization.
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Table 1 Brunauer–Emmett–Teller (BET) surface area and pore volume of TS-1 synthesized from different polymers
a
2
ꢁ1
b
2
ꢁ1
b
2
ꢁ1
b
3
ꢁ1
c
3
ꢁ1
Samples
S
BET m g
S
micro m g
S
ext m g
V
micro cm g
Vmeso cm g
EG–TS-1
406
409
407
406
410
408
405
398
402
395
304
303
303
300
286
308
311
317
334
351
102
106
104
106
124
100
94
81
68
44
0.15
0.15
0.14
0.15
0.13
0.15
0.15
0.14
0.14
0.15
0.04
0.05
0.06
0.05
0.06
0.04
0.05
0.05
0.10
0.02
PDO–TS-1
BDO–TS-1
HDO–TS-1
PEG–TS-1
HDO–TS-1-R
CHD–TS-1
CHDM–TS-1
PXG–TS-1
d
TS-1–C
a
b
S
BET (total surface area) calculated using the BET method.
Smicro (micropore area), Sext (external surface area) and Vmicro (micropore volume)
d
c
calculated using the t-plot method.
Vmeso (mesopore volume) calculated using the BJH method (from adsorption). TS-1 synthesized by
conventional processes.
Fig. 5 (a)–(j) SEM and (k) and (l) TEM images of TS-1 synthesized from Ti–diol–Si polymers.
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a
Table 2 Catalytic results of the prepared TS-1 for the oxidation of n-hexane
Sel. [%]
2 2
H O
Conv. [%]
based on n-hexane
Conv.
[%]
b
Sample
Si/Ti ratio in the catalyst
2- and 3-ol
2- and 3-one
Sel. [%]
EG–TS-1
48.6
52.8
55.0
48.8
52.1
55.0
52.0
35.8
53.3
43.3
78.0
78.5
74.9
77.5
69.0
56.4
52.2
74.4
78.8
34.4
41.3
45.4
52.1
41.3
49.8
52.2
39.3
51.1
46.3
39.3
58.7
54.6
47.9
58.7
50.2
47.8
60.7
48.9
53.7
60.7
59.9
53.1
45.89
61.4
46.7
37.1
26.4
56.1
48.9
26.4
76.0
87.5
86.4
80.7
77.8
73.0
47.14
74.9
97.6
47.1
PDO–TS-1
BDO–TS-1
HDO–TS-1
CHD–TS-1
CHDM–TS-1
PXG–TS-1
PEG–TS-1
HDO–TS-1-R
c
TS–1-C
a
ꢀ
Reaction conditions: 0.1 g of catalyst, 60 C, 4 h, 10 ml of CH
3
OH as solvent, 10 mmol of n-hexane, and 20 mmol of H
2
O
2
(30% in aqueous
b
c
solution). The elemental compositions of TS-1 are determined by ICP. TS-1 synthesized by conventional processes.
1, the titanium source and the silicon source in the polymers are products had a large particle size, and the size distribution of
uniformly connected by diols, so the opportunities for the the zeolite crystal was broad, as shown in Fig. 5g to i. Crystal-
titanium source and the silicon source to be detached from the lization under rotating conditions was also investigated, and
polymers are equal. Therefore, a good matching of the hydro- the sample was named HDO-R. The results show that the
lysis rate between the silicon source and titanium source is particle size of the samples obtained using rotating crystalli-
realized during crystallization. As a result, the method of zeolite zation is uniform and small and that the crystal size is
synthesis from Ti–diol–Si polymers can effectively promote the approximately 500 nm (Fig. 5f).
incorporation of titanium into the lattice and avoid the gener-
ation of extra-framework Ti species (Fig. 4).
On the basis of the above characterization results, TS-1
zeolites synthesized from polymers has high crystallinity,
In addition, it is noteworthy that the conventional alcohol a large external surface area, small particle size, and no extra-
evaporation process is transferred to the synthesis process of framework titanium species. All these properties indicate that
the polymers. Therefore, the alcohol evaporation and aging the TS-1 samples should have good catalytic activities. The
processes are omitted in zeolite synthesis, which will reduce the catalytic performances of the synthesized TS-1 samples were
probability of extra-framework Ti species formation. Further- tested in the oxidation of n-hexane with hydrogen peroxide as
more, in contrast to the conventional alcohol evaporation the oxidant (Table 2). The results show that the TS-1 zeolite
process, the polymer synthesis process produces anhydrous synthesized from polymers has excellent oxidation perfor-
alcohol, which will facilitate recycling of the subsequent alcohol mance. Among the zeolites tested, the zeolite sample synthe-
byproducts and reduce the cost of synthesis. The characteriza- sized from HDO-based polymers under rotating conditions
tion of the low-temperature N
2
physical adsorption (Fig. S10,† (HDO–TS-R) has the highest conversion rate of n-hexane
Table 1) revealed that TS-1 synthesized from Ti–diol–Si poly- (78.8%), and the utilization rate of hydrogen peroxide can reach
2
ꢁ1
mers has a higher external surface area (124 m g ) than the 97.6%. Besides, there are no obvious changes of the n-hexane
2
ꢁ1 28
samples synthesized by conventional methods (44 m
g
).
conversion with several reaction–regeneration cycles on TS-1
These results suggest that the diols in the polymers may play an zeolites synthesized from polymers, as shown in Fig. S23.†
39
important role in the formation of the external surface area.
The TS-1 zeolites synthesized from polymers also show higher
SEM and TEM images of the TS-1 zeolites synthesized from activities in the oxidation of 1-hexene (Table S2†) and large
the polymers are displayed in Fig. 5. All samples have a typical molecules such as cyclohexene (Table S4†).
MFI hexagonal morphology with a size distribution ranging
from 0.3 mm to 1.8 mm. Besides, the TS-1 zeolites exhibit
a knobbed surface spherical morphology with the assembly of
Conclusions
nano-size particles, and this imparts a high external surface
area character. The TEM images (Fig. 5k and l) of the TS-1
zeolites synthesized from Ti–PEG–Si polymers also demon-
strated that the TS-1 zeolites had a vertical arrangement of all
these nanoparticles. It was also found that the solubility of the
Ti–diol–Si polymers has important effects on the morphology
and crystal sizes of the TS-1 products. For soluble polymers such
as Ti–EG–Si, Ti–HDO–Si, and Ti–PEG–Si, the crystals of the TS-1
products are uniform, as shown in Fig. 5a to e. For insoluble
polymers (Ti–CHD–Si and Ti–CHDM–Si), the resultant TS-1
In summary, the method of synthesizing TS-1 from a polymer
containing titanium and silicon (Ti–diol–Si polymers) is proven
to be effective, simple, mild and easy to operate. Due to the
hydrolysis resistance of the Ti–diol–Si polymers, a good
matching of the hydrolysis rate between the silicon source and
the titanium source is realized during crystallization, which
facilitates the production of high-quality TS-1 zeolites free of
extra-framework titanium species. Different crystallization
procedures are selected according to the water solubilities of the
polymers. The diol species in the polymers can also increase the
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external surface area of TS-1. Most importantly, TS-1 synthe- SACHEM Americas) at room temperature to obtain a clear
sized from polymers showed excellent catalytic performance in solution, without heating to evaporate alcohol as well as aging
n-hexane oxidation with hydrogen peroxide as the oxidant. It is to hydrolyze titanium and silicon sources under a water bath.
worth mentioning that the synthesis method of zeolites from The clear solution was directly transferred to a stainless steel
ꢀ
the Ti–diol–Si polymers could be successfully applied to the autoclave with a Teon liner and crystallization at 170 C for
preparation of other titanium-containing materials, such as 24 h under static conditions by using a conventional oven. The
mesoporous titanium materials (Ti†MCM-41, Ti†MCM-48, etc.) water insoluble polymers were Ti–CHD–Si, Ti–CHDM–Si, and
and Ti†MOF materials (Ti†MIL125); the related work will be Ti–PXG–Si; a certain amount of polymers was added to an
presented in subsequent reports. In addition, the titanium in aqueous solution of tetrapropylammonium hydroxide (TPAOH)
the Ti†diol†Si polymers can be replaced by other heteroatoms, at room temperature, transferred to a stainless steel autoclave
ꢀ
such as zirconium, tin, aluminum, phosphorus, and boron, and with a Teon liner directly, and crystallized at 170 C for 24
the resulting polymers can be used for the synthesis of under static conditions by using a conventional oven. The
heteroatom-doped materials, thereby reducing the difficulty in optimized molar composition of the synthetic TS-1 is as follows:
synthesizing or obtaining relevant materials with enhanced 0.96 SiO
2
2 2
: 0.04 TiO : 0.5 TPAOH : 40 H O. The solid product
properties.
was centrifuged, washed several times with deionized water,
ꢀ
ꢀ
dried overnight in an oven at 100 C, and then calcined at 550 C
for 6 h. The samples were named according to the polymer
used: EG–TS-1, PDO–TS-1, BDO–TS-1, HDO–TS-1, PEG–TS-1,
CHD–TS-1, CHDM–TS-1, and PXG–TS-1. If not specially speci-
Experimental
Synthesis of polymers containing titanium and silicon

ed, the polymers with a titanium content of 4% were used for
Polymers were synthesized basically according to the following
molar composition: 0.96 SiO : 0.04 TiO : 2 diol. Polymers with
2 2
the synthesis of TS-1 zeolites.
TPAOH with different ratios is also investigated and the Ti–
PEG–Si polymer is used as the precursor; the molar composition
a titanium content of 2% and 3% were also synthesized by the
same method, and if not particularly emphasized, polymers
with a titanium content of 4% were used as raw materials. A
certain amount of diols was added to a round bottom ask. The
diols used here were chosen among ethylene glycol (EG,
2 2 2
is 0.96 SiO : 0.04 TiO : 0.2 TPAOH : 40 H O. When the
concentration of TPAOH in the system decreases, TS-1 zeolites
can also be synthesized. The size of the TS-1 zeolites is
increased, up to 1.5 mm (Fig. S16 and S21†).
For the TS-1–HDO-Rotation sample, the same synthetic
procedure as described above was used, except for using a rotary
9
1
9
8.0 wt%, Aladdin), 1,3-propanediol (PDO, 98.5 wt%, Aladdin),
,4-butanediol (BDO, 99.0 wt%, Aladdin), 1,6-hexanediol (HDO,
9.0 wt%, Aladdin), 1,4-cyclohexanediol (CHD, 98.0 wt%,
ꢀ
oven and crystallization at 170 C for 1 day with a rotation rate
of 35 rpm.
Aladdin), 1,4-cyclohexanedimethanol (CHDM, 99.0 wt%,
Aladdin), p-phenylenedimethanol (PXG, 99.0 wt%, Aladdin),
and polyethylene glycol 200 (PEG, M ¼ 200, Macklin). Then,
n
tetraethyl orthosilicate (TEOS, 99.0 wt%, Aladdin) was added to Synthesis of conventional TS-1 zeolites
ꢀ
the round bottom ask and stirred at 110 C in an oil bath,
Titanium tetra-butoxide (TBOT, 99.0 wt%, Aladdin) and tetra-
propylammonium hydroxide (TPAOH, 25.0 wt% aqueous solu-
tion, SACHEM Americas) were mixed under stirring. Aer 30
minutes, tetraethyl orthosilicate (TEOS, 99.0 wt%, Aladdin) as
the silicon source was added to the solution. Then, the solution
was heated to 353 K to remove alcohol produced by hydrolysis.
Aer cooling down, the clear solution was directly transferred to
2
followed by addition of tetraethyl titanate (TEOT, 35 wt% TiO ,
Aladdin). In the process of product polymerization, the by-
produced ethanol was collected by using a condensation tube,
and the temperature of the oil bath was controlled according to
the rate of ethanol distillation and gradually increased to 170 C
and maintained at 170 C for 1 h. In order to promote the
ꢀ
ꢀ
polymerization of the product and accelerate the reaction, the
system was vacuumed at 170 C, and vacuum treated for 1 h.
a stainless steel autoclave with a Teon liner and crystallized at
ꢀ
ꢀ
1
70 C for 3 days under static conditions by using a conven-
Aer the reaction is completed, the polymerized solid product
can be collected. Through the amount of ethanol collected in
the reaction process, the number of ethoxy groups in TEOS and
TEOT participating in the reaction can be calculated, and the
degree of polymerization can be estimated.
tional oven. The optimized molar composition of the synthetic
conventional TS-1 is as follows: 0.96 SiO : 0.04 TiO : 0.5
TPAOH : 40 H O. The solid product was centrifuged, washed
several times with deionized water, dried overnight in an oven
2
2
2
ꢀ
ꢀ
at 100 C, and then calcined at 550 C for 6 h.
Synthesis of TS-1 zeolites from polymers
Catalyst reaction
TS-1 zeolites were synthesized from the above polymers. The The oxidation of n-hexane was carried out by using hydrogen
synthesized eight different polymers had different water solu- peroxide as an oxidizing agent (30 wt% aqueous solution,
bility. The water soluble polymers were Ti–EG–Si, Ti–PDO–Si, Aladdin) in a closed stainless steel reactor with a Teon liner
Ti–BDO–Si, Ti–HDO–Si, and Ti–PEG–Si polymers. The method under vigorous stirring. The reaction temperature was
ꢀ
for synthesizing TS-1 is as follows: a certain amount of polymers controlled at 60 C with a water bath, and the reaction time was
was directly dissolved in an aqueous solution of tetrapropy- 4 h. In a typical run, 0.1 g of catalyst, 10 ml of methanol,
lammonium hydroxide (TPAOH, 25.0 wt% aqueous solution, 10 mmol of n-hexane, and 20 mmol of hydrogen peroxide
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Paper
(
30 wt%) were mixed in the reactor. Aer the completion of the with a Hitachi SU8020 scanning electron microscope. Trans-
reaction, the product was analyzed with a gas chromatograph mission Electron Microscope (TEM) images were collected with
Agilent 7890A), equipped with a 50 m capillary column (HP- a JEOL2100 transmission electron microscope. N adsorption–
(
2
PONA), and an FID detector was used. All products were desorption isotherms of the samples were obtained at 77 K on
conrmed by GC-MS (Agilent 7890B-5977A). The amount of the a Micromeritics Gemini VII system aer the zeolites were
unconverted H
tion of Ce(SO
n-hexane conversion with several reaction–regeneration cycles Emmett–Teller (BET) equation. Micropore surface areas (Smicro
2
O
2
was determined with a 0.1 M aqueous solu- degassed at 623 K for 4 h. The specic surface areas (SBET) and
4
)
2
by using a titration method. The changes of the total pore volume (V ) were obtained using the Brunauer–
t
)
2
9
on TS-1 zeolites synthesized from polymers (TS-1–HDO-R) were were calculated based on the t-plot method. The solid state Si-
1
3
carried out as follows: aer the rst catalytic reaction, the NMR and C-NMR experiments were conducted on a Bruker
catalyst was recovered by ltration and washed with ethanol Avance III spectrometer equipped with a 14.1 T wide-bore
ꢀ
and acetone several times. The catalyst was dried at 120 C and magnet. The UV-Vis DRS (diffuse reectance spectroscopy)
ꢀ
further calcined at 550 C for 3 h under air before checking the spectra of the catalyst were recorded over the range of 200 nm to
catalytic recyclability.
600 nm against the support as the reference, on a VARIAN CARY
The oxidation of 1-hexene was carried out by using hydrogen 5000. Thermogravimetric analysis (TGA) measurement was
peroxide as an oxidizing agent (30 wt% aqueous solution, conducted on a TA Q-600 analyzer with a heating rate of
ꢀ
ꢁ1
ꢀ
Aladdin) in a closed stainless steel reactor with a Teon liner 10 C min from ambient temperature to 700 C in a 100
ꢁ1
under vigorous stirring. The reaction temperature was ml min N ow. Inductively coupled plasma optical emission
2
ꢀ
controlled at 60 C with a water bath, and the reaction time was spectrometry (ICP-OES) analysis was performed with a Perki-
2
1
h. In a typical run, 0.05 g of catalyst, 10 ml of methanol, nElmer 7300DV. X-ray photoelectron spectroscopy (XPS) was
0 mmol of n-hexane, and 10 mmol of hydrogen peroxide performed on a Thermo Fisher ESCALAB 250Xi spectrometer
(
30 wt%) were mixed in the reactor. Aer the completion of the (monochromated AlKa, hn ¼ 1486.6 eV, 15 kV, and 10.8 mA)
reaction, the product was analyzed with a gas chromatograph with a resolution of pass energy of 50 eV. The XPS peaks were
Agilent 7890A), equipped with a 50 m capillary column (HP- calibrated with the binding energy of C 1s peaks at 284.8 eV. UV-
PONA), and an FID detector was used. All products were Raman spectra were recorded using a home-made single stage
(
ꢁ1
conrmed by GC-MS (Agilent 7890B-5977A). The amount of the UV-Raman spectrograph with a spectral resolution of 2 cm
.
unconverted H O was determined with a 0.1 M aqueous solu- The single-frequency UV laser line at 244 nm was from an effi-
2
2
tion of Ce(SO ) by using a titration method. The oxidation of cient external cavity frequency doubler (WaveTrain, Spectra-
4
2
cyclohexene was carried out by the same process with the Physics) of a 488 nm single-frequency laser (Genesis, CX 488,
ꢀ
following reaction conditions: 0.1 g of catalyst, 60 C, 4 h, 5 ml Coherent). The exciting source had an output of 10 mW and the
of acetonitrile as the solvent, 4.5 mmol of cyclohexene, and power of the laser at the sample was about 2.0 mW. Fourier
2 2
4.5 mmol of H O (30% in aqueous solution). The results of the transform infrared spectroscopy (FTIR) was performed on
oxidation of the substrates were calculated as follows:
a Bruker Vextex70 spectroscope equipped with an MCT detector.
ðinitial moles ꢁ final molesÞ
Substrate conversion ðmol%Þ ¼
initial moles
Author contributions
ꢂ 100%
The manuscript was written through the contributions of all
authors. All authors have given approval to the nal version of
the manuscript. Yunpeng Xu and Zhongmin Liu conceived and
guided the research project. Jiacheng Xing and Danhua Yuan
designed and carried out the experiments and characterization.
The manuscript was draed by Jiacheng Xing and Danhua
Yuan. Hanbang Liu and Yansi Tong took part in the discussion
of experimental data and gave some suggestions.
moles of a defined product
moles of products produced
Product selectivity ð%Þ ¼
ꢂ 100%
ꢂ 100%
ꢂ 100%
moles of H
conversion ðmol%Þ ¼ moles of H
2
O
2
consumed
H
2
O
2
2
2
O in the feed
Conflicts of interest
moles of products produced
H
2
O
2
selectivity ð%Þ ¼
moles of H
2
O
2
consumed
There are no conicts to declare.
Acknowledgements
Material characterization
The work was supported by the National Natural Science
The X-ray diffraction (XRD) patterns were acquired using Foundation of China (Grant No. 21802136) and the Talent
a PANalytical X'Pert PRO X-ray diffractometer using Cu-Ka Program
for
Revitalization
of
Liaoning
Province
ꢀ
radiation with l ¼ 1.54059 A, operating at 40 kV and 40 mA. The (XLYC1905017). We thank Shu Zeng and Shutao Xu (Dalian
ꢀ
ꢁ1
ꢀ
samples were scanned at 12 min between 2q angles of 5–65 . Institute of Chemical Physics) for their assistance in the NMR
Scanning Electron Microscopy (SEM) images were collected characterization of the Ti–diol–Si polymers.
6212 | J. Mater. Chem. A, 2021, 9, 6205–6213
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Paper
Journal of Materials Chemistry A
1
7 A. Thangaraj and S. Sivasanker, J. Chem. Soc., Chem.
Commun., 1992, 123–124.
Notes and references
1
2
3
D. R. C. Huybrechts, L. Debruycker and P. A. Jacobs, Nature, 18 Z. F. Liu and R. J. Davis, J. Phys. Chem., 1994, 98, 1253–1261.
1
990, 345, 240–242.
19 A. Thangaraj, R. Kumar and P. Ratnasamy, J. Catal., 1991,
131, 294–297.
20 A. Tuel and Y. Bentaarit, Appl. Catal., A, 1994, 110, 137–151.
T. Tatsumi, M. Nakamura, S. Negishi and H. Tominaga, J.
Chem. Soc., Chem. Commun., 1990, 476–477.
C. Li, G. Xiong, Q. Xin, J. K. Liu, P. L. Ying, Z. C. Feng, J. Li, 21 W. B. Fan, R. G. Duan, T. Yokoi, P. Wu, Y. Kubota and
W. B. Yang, Y. Z. Wang, G. R. Wang, X. Y. Liu, M. Lin,
T. Tatsumi, J. Am. Chem. Soc., 2008, 130, 10150–10164.
X. Q. Wang and E. Z. Min, Angew. Chem., Int. Ed., 1999, 38, 22 Q. Guo, K. J. Sun, Z. C. Feng, G. N. Li, M. L. Guo, F. T. Fan and
220–2222.
C. Li, Chem.–Eur. J., 2012, 18, 13854–13860.
M. Taramasso, G. Perego and B. Notari, US Pat., 4410501, 23 J. Su, G. Xiong, J. C. Zhou, W. H. Liu, D. H. Zhou, G. R. Wang,
983.
X. S. Wang and H. C. Guo, J. Catal., 2012, 288, 1–7.
X. B. Wang, X. F. Zhang, Y. Wang, H. O. Liu, J. S. Qiu, 24 J. Q. Zhuang, G. Yang, D. Ma, X. J. Lan, X. M. Liu, X. W. Han,
2
4
5
1
J. Q. Wang, W. Han and K. L. Yeung, ACS Catal., 2011, 1,
37–445.
X. H. Bao and U. Mueller, Angew. Chem., Int. Ed., 2004, 43,
6377–6381.
4
6
Y. Kuwahara, K. Nishizawa, T. Nakajima, T. Kamegawa, 25 E. Jorda, A. Tuel, R. Teissier and J. Kervennal, Zeolites, 1997,
K. Mori and H. Yamashita, J. Am. Chem. Soc., 2011, 133,
2462–12465.
G. J. Hutchings, D. F. Lee and A. R. Minihan, Catal. Lett.,
995, 33, 369–385.
J. E. Gallot, M. P. Kapoor and S. Kaliaguine, AIChE J., 1998,
4, 1438–1454.
C. Shen, Y. J. Wang, J. H. Xu and G. S. Luo, Chem. Eng. J.,
015, 259, 552–561.
0 Z. C. Shan, Z. D. Lu, L. Wang, C. Zhou, L. M. Ren, L. Zhang,
19, 238–245.
1
26 J. G. Wang, Y. B. Wang, T. Tatsumi and Y. L. Zhao, J. Catal.,
2016, 338, 321–328.
27 T. Zhang, Y. Zuo, M. Liu, C. Song and X. Guo, ACS Omega,
2016, 1, 1034–1040.
28 T. Zhang, X. Chen, G. Chen, M. Chen, R. Bai, M. Jia and J. Yu,
J. Mater. Chem. A, 2018, 6, 9473–9479.
29 T. Tatsumi, K. A. Koyano and Y. Shimizu, Appl. Catal., A,
2000, 200, 125–134.
7
8
9
1
4
2
1
X. J. Meng, S. J. Ma and F. S. Xiao, ChemCatChem, 2010, 2, 30 R. D. Daubeny and C. W. Bunn, Proc. R. Soc. London, Ser. A,
07–412.
1954, 226, 531–542.
1 O. J. Kerton, P. McMorn, D. Bethell, F. King, F. Hancock, 31 M. M. J. Treacy, J. B. Higgins and R. vonBallmoos, Zeolites,
4
1
A. Burrows, C. J. Kiely, S. Ellwood and G. Hutchings, Phys.
Chem. Chem. Phys., 2005, 7, 2671–2678.
2 V. Russo, R. Tesser, E. Santacesaria and M. Di Serio, Ind. Eng.
Chem. Res., 2014, 53, 6274–6287.
1996, 16, 327–328.
32 F. Geobaldo, S. Bordiga, A. Zecchina, E. Giamello,
G. Leofanti and G. Petrini, Catal. Lett., 1992, 16, 109–115.
33 G. N. Vayssilov, Catal. Rev.: Sci. Eng., 1997, 39, 209–251.
1
1
3 L. Nemeth and S. R. Bare, in Advances in Catalysis, Vol. 57, ed. 34 G. Xiong, Y. Y. Cao, Z. D. Guo, Q. Y. Jia, F. P. Tian and
F. C. Jento, Elsevier Academic Press Inc, San Diego, 2014,
vol. 57, pp. 1–97.
4 C. P. Gordon, H. Engler, A. S. Tragl, M. Plodinec,
L. P. Liu, Phys. Chem. Chem. Phys., 2016, 18, 190–196.
35 J.-P. Nogier, Y. Millot, P. P. Man, C. Methivier, M. Che and
S. Dzwigaj, Catal. Lett., 2009, 130, 588–592.
1
T. Lunkenbein, A. Berkessel, J. H. Teles, A.-N. Parvulescu 36 B. Tang, W. Dai, X. Sun, N. Guan, L. Li and M. Hunger, Green
and C. Coperet, Nature, 2020, 586, 708–713.
Chem., 2014, 16, 2281–2291.
5 A. Keshavaraja, V. Ramaswamy, H. S. Soni, A. V. Ramaswamy 37 Z. F. Liu and R. J. Davis, J. Phys. Chem., 1994, 98, 1253–1261.
and P. Ratnasamy, J. Catal., 1995, 157, 501–511.
38 S. L. Burkett and M. E. Davis, Chem. Mater., 1995, 7, 920–928.
6 A. Thangaraj, M. J. Eapen, S. Sivasanker and P. Ratnasamy, 39 S. T. Du, F. Li, Q. M. Sun, N. Wang, M. J. Jia and J. H. Yu,
Zeolites, 1992, 12, 943–950.
Chem. Commun., 2016, 52, 3368–3371.
1
1
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J. Mater. Chem. A, 2021, 9, 6205–6213 | 6213