The synthesis, characterization and catalytic activity of the hierarchical TS-1 with the intracrystalline voids and grooves

Article abstract of DOI:10.1016/j.catcom.2015.12.007

Hierarchical TS-1 with grooves and intracrystalline voids was prepared by TPAOH/NaOH treatment. With increasing NaOH concentration, the dissolution-recrystallization process was intensified, the relative crystallinity and microporous properties decreased, the secondary pore volume increased. Although the dissolved species could be recrystallized, Na⁺ prevented the titanium incorporation, which increased the extra-framework titanium content. In phenol hydroxylation, improved activity and H₂O₂ efficiency were achieved when NaOH was no more than 0.1 mol/L, which may be a result of the positive influences of the secondary pores. At higher NaOH concentration (> 0.1 mol/L), the activity and H₂O₂ efficiency decreased due to the negative influences of the non-framework titanium.

Full text of DOI:10.1016/j.catcom.2015.12.007

The synthesis, characterization and catalytic activity of the hierarchical TS-1
with the intracrystalline voids and grooves
Baorong Wang, Min Lin, Bin Zhu, Xinxin Peng, Guangtong Xu, Xing-
tian Shu
PII:
DOI:
Reference:
S1566-7367(15)30160-6
doi: 10.1016/j.catcom.2015.12.007
CATCOM 4524
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
28 July 2015
31 October 2015
9 December 2015
Please cite this article as: Baorong Wang, Min Lin, Bin Zhu, Xinxin Peng, Guangtong
Xu, Xingtian Shu, The synthesis, characterization and catalytic activity of the hierar-
chical TS-1 with the intracrystalline voids and grooves, Catalysis Communications (2015),
doi: 10.1016/j.catcom.2015.12.007
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The synthesis, characterization and catalytic activity of the
hierarchical TS-1 with the intracrystalline voids and grooves
Baorong Wang, Min Lin*, Bin Zhu, Xinxin Peng, Guangtong Xu, Xingtian Shu
State Key Laboratory of Catalytic Material and Reaction Engineering, Research Institute of Petroleum Processing, SINOPEC, Beijing
100083, China
Abstract: Hierarchical TS-1 with grooves and intracrystalline voids was prepared by
TPAOH/NaOH treatment. With increasing NaOH concentration, the
dissolution-recrystallization process was intensified, the relative crystallinity and
microporous properties decreased, the secondary pore volume increased. Although the
dissolved species could be recrystallized, Na+ prevented the titanium incorporation,
which increased the extra-framework titanium content. In phenol hydroxylation,
improved activity and H2O2 efficiency were achieved when NaOH was no more than
0.1mol/L, which may be a result of the positive influences of the secondary pores. At
higher NaOH concentration(>0.1mol/L), the activity and H2O2 efficiency decreased
due to the negative influences of the non-framework titanium.
Keywords: hierarchical TS-1; intracrystalline voids; grooves; TPAOH; NaOH
1. Introduction
Titanium silicalite-1(TS-1) with MFI topology is well-known for the excellent
selective oxidation performance under mild condition[1]. With aqueous H2O2 as the
* Corresponding author. Tel. : +86 010 82368801 Email Address: linmin.ripp@sinopec.com

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oxidant, TS-1 has been widely used in phenol hydroxylation[2,3], epoxidation of
alkenes[4,5], oxidation of alkanes[6], cyclohexanone ammoximation[7] and oxidative
desulfurization[8]. Nowadays, TS-1 has been successfully industrialized in phenol
hydroxylation, cyclohexanone ammoximation and propylene epoxidation[9,10].
Although TS-1 exhibits good activity in the oxidation of many organic
compounds, but the micropore size is about 0.55nm. Thus, substrates with larger
molecular size cannot enter the channels, and they could only interact with the active
sites on the external surface. In order to enhance the accessibility of active centers,
hierarchical TS-1 with well-developed secondary porosity was synthesized by
desilication[11], silanization[12,13], dissolution-recrystallization[14,15], dry gel
conversion[16], soft templating[17,18] and hard templating[19]. When TS-1 was
treated with aqueous NaOH, the silica framework was dissolved, and mass loss was
inevitable[11]. When TS-1 was modified with tetrapropyl ammonium
hydroxide(TPAOH), the erosion was mainly in the inner part of zeolite particles, and
the dissolved species could be recrystallized[14,20]. Then, hierarchical TS-1 with
intracrystalline voids, better catalytic activity and stability could be obtained.
When inorganic base or organic alkali was used only in the post-synthesis of
hierarchical TS-1, the influences on physiochemical properties and catalytic activity
were reported in many literatures. But when inorganic base and organic alkali were
simultaneously used, the influences are still unknown. Herein, we report the
preparation of hierarchical TS-1 by treatment with TPAOH and NaOH, and influences
of NaOH concentration on the physiochemical properties and catalytic activity were

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studied.
2. Experimental
2.1 Synthesis of TS-1
TS-1 was synthesized following the procedure reported by Thangaraj[21].
Tetraethosilicate(TEOS) was the silica source, tetrabutyl titanate(TBOT) was the
titanium source, and TPAOH(25wt%) was both the structure directing agent and alkali
source. TEOS was firstly hydrolyzed with TPAOH for 3 hours, then TBOT dissolved
in anhydrous isopropyl alcohol was dropped into the hydrolyzed solution. Finally,
water was added and the mixture was stirred at 80℃ for 3 hours to remove alcohol.
The chemical composition of the final gel was SiO2:TiO2:TPAOH:H2O=1:0.04:0.4:40,
and it was transferred to a Teflon-lined stainless-steel autoclave. The crystallization
was carried out under autogenous pressure at 175℃ for 5 days. The mixture obtained
was filtered, washed with distilled water, dried at 110℃ for 6h, and calcined at 550℃
for 5h.
2.2 Post-synthesis
Firstly, 1g of the previous prepared TS-1 was mixed with 15mL mixed solution
of TPAOH(0.2mol/L) and NaOH(0.05, 0.10, 0.15 and 0.20mol/L), the mixture
obtained was transferred to a Teflon-lined stainless-steel autoclave. The treatment was
carried out under autogenous pressure at 145℃ for 4h. Secondary, the mixture was
filtered, washed with distilled water, dried at 110℃ for 6h, and calcined at 550℃ for
5h. Finally, the samples were magnetically stirred in aqueous HNO3(80℃, 0.5mol/L)
for 6h. Then, the samples were filtered, washed with distilled water, dried and

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calcined. The samples obtained were denoted as TS-1-P-xNaOH, in which x
represents the NaOH concentration.
2.3 Characterization
X-ray diffraction (XRD) patterns were obtained on a Philips Panalytical X'pert
diffractometer with nickel-filtered Cu Kα radiation. Scanning electron microscopy
(SEM) images were taken from a Hitachi 4800 microscope, transition electron
microscopy (TEM) images were recorded on a JEOL JEM-2100 microscope. N2
adsorption-desorption isotherms were collected at 77K on a Micromeritics ASAP
2405 apparatus. The samples were previously dried under vacuum (0.1Pa) at 573K for
6h, and surface parameters were derived from the isotherms using BET and t-plot
methods. UV-visible (UV-Vis) spectra were recorded on a JASCO UV-visible 550
spectrometer. The X-ray photoelectron spectroscopy (XPS) spectra were recorded on
a Thermo-Fischer-VG ESCALAB250 with Mg Kα radiation, and the framework
titanium content and non-framework titanium content were integrated results of the Ti
2p3/2 peaks at 460.3 and 458.7eV.
2.4 Phenol hydroxylation
The phenol hydroxylation was carried out in a round-bottomed flask equipped
with a condenser and a magnetic stirrer. Typically, 0.2 mol phenol was dissolved in
17.2mL acetone, then 0.9g catalyst and 6.8g aqueous hydroperoxide (30wt%) were
added, the molar ratio of H2O2 and phenol was 0.3. Under stirring, the reaction system
was kept at a constant temperature of 80℃ for 0.5h. The reaction products were
analyzed by an Agilent 6890N equipped with a FFAP capillary column. The H2O2

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concentration was analyzed by iodometric titration.
3. Results and discussion
3.1 Physichemical properties
Fig.1 shows the XRD patterns of TS-1 and hierarchical TS-1, in which the
crystallinity of parent TS-1 was denoted as 100%, while the relative crystallinity(RC)
of hierarchical TS-1 was calculated by comparing the integrated area of the
characteristic peaks between 22~26° with that of TS-1. It was clearly illustrated that
the MFI topology was preserved after the TPAOH/NaOH treatment. However, the
relative crystallinity decreased by about 12% when NaOH was 0.05mol/L, and the
decrease was more significant with higher NaOH concentration(≥0.10mol/L). It has
been reported that the silica species in MFI topology could be selectively dissolved in
basic media[22]. When TS-1 was treated with aqueous NaOH, the crystals could be
eroded[11]. However the dissolved species could be recrystallized to protect the MFI
topology in presence of TPAOH[15]. In TPAOH and NaOH solution, there were
dissolution and recrystallization. However the erosion effect should be more
significant than the recrystallization effect, especially when the NaOH concentration
was high, which was proved by the decrease of the relative crystallinity.
The N2 adsorption desorption isotherms are collected at 77K. Large hysteresis
loops in hierarchical TS-1 were observed, indicating that mesopores with pore size
larger than 4nm were created by TPAOH/NaOH[23,24]. As the hysteresis loops
suddenly closed at about P/P0=0.45, the adsorption branch was preferred for pore size
calculation with BJH method, and the results were shown in Fig. 2. The mesopores in

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TS-1-P-0.05NaOH were widely distributed in the range of 16-32nm, and a wider
distribution of the mesopores could be observed in TS-1-P-0.15NaOH and
TS-1-P-0.2NaOH. Moreover, the surface parameters are illustrated in Table 1. For
TS-1-P-0.05NaOH, the specific surface area(SBET), microporous area(SMI) and
microporous volume(VMI) decreased separately by 4.8%, 21.1% and 25.6%, while the
external surface(SMA) and secondary pore volume(VSP) increased respectively by
154.8% and 127.0%. At higher NaOH concentration, the changes of the surface
parameters were more significant. When NaOH was 0.20M, the SBET, SMI and VMI
decreased respectively by 8.5%, 27.6% and 30.9%, while the SMA and VSP increased
by 183.3% and 205.6%. Combined with the results of pore size distribution, the
secondary pores were introduced at the expense of the micropores, and larger
secondary pore volume could be obtained at high NaOH concentration.
Fig. 3 shows the SEM imagines. The parent TS-1 crystal was an aggregate of
small particles, but the surface of the particles was smooth. However the surface was
etched by TPAOH/NaOH, and grooves on the surface could be observed, which was
different from the relative smooth surface obtained by TPAOH modification. It gave
direct information of the severe erosion in TPAOH/NaOH solution. Although the
TPA+ cations were supposed to deposit on the external surface of the zeolite particles,
and protect the surface from the OH- attack[25]. The faster dissolution of the
framework in NaOH than in TPAOH may result in the severe etching on the
surface[26], even when NaOH was 0.05mol/L.
The TEM imagines are shown in Fig. 4. Accumulated pores were observed in

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parent TS-1, and hierarchical TS-1 with intracrystalline voids, part of which linked
directly to the surface, was prepared by TPAOH/NaOH treatment. Crystals with
smaller size and no intracrystalline voids could also be observed in the treated
samples, which should be the recrystallization products, and the amount of which
increased with increasing NaOH concentration, indicating that the
dissolution-recrystallization process was intensified at high NaOH concentration.
Fig.5 shows the UV-Vis spectra. The absorption bands at 330nm and 210nm are
respectively assigned to anatase and four-coordinated isolated titanium ions, while the
broad band in the region of 270~290nm is generated by five- or six-coordinated
extra-framework titanium species[1,27,28]. The titanium species in parent TS-1 were
mainly four-coordinated Ti ions and anatase. For hierarchical TS-1, the band intensity
at 210nm was as strong as usual, but the intensity of the bands at 270-290nm and
330nm increased significantly, which give direct information that part of the titanium
was still in framework position, while the extra-framework titanium content increased.
It has been postulated that alkali metal ions in the gel may prevent the incorporation
of titanium ions into the framework position[29]. Thus, the dissolved silicon species
may preferentially interact with TPAOH and be recrystallized, while extra-framework
titanium species were generated from the dissolved titanium ions, leading to an
increase of the extra-framework titanium content.
The XPS results in Table 2 further illustrated the oxidation state and content of
titanium on the surface. In the Ti 2p3/2 spectra of TS-1, the characteristic peaks at
460.3eV and 458.8eV are respectively attributed to framework and extra-framework

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Ti4+[30,31], and the molar ratio of which could be obtained from the integrated areas.
On the surface of parent TS-1, the framework titanium content was 57.3%. In
hierarchical TS-1, the framework titanium content decreased significantly to less than
37.1%, which should be the result of the negative influence of sodium on the
incorporation of titanium into the framework position. Moreover, the Na+
concentration exerted little influence on the oxidation state and content of titanium on
the surface.
3.2 Catalytic activity
The catalytic activity were evaluated by phenol hydroxylation, and the results are
illustrated in Table 3. When TS-1 was used as the catalyst in phenol hydroxylation,
the main products are catechol(CAT) and hydroquinone(HDQ), and a small part of the
hydroquinone could be deeper oxidized to p-benzoquinone(BZQ), which may
preferentially occur in the zeolite channels[32]. Besides, diffusional constraints for
phenol and geometric constraints for catechol were observed, but catechol could also
be formed inside the channels[3,33]. When grooves and intracrystalline voids were
introduced, the constraints for phenol and catechol released, which would lead to an
increase of the phenol conversion, H2O2 efficiency and catechol selectivity. On the
other hand, the extra-framework titanium increased after the TPAOH/NaOH treatment,
which would decompose hydrogen peroxide and start a homolytic hydroxylation
pathway, leading to a decrease of the activity and dihydroxybenzenes(DHB)
selectivity[34,35]. For parent TS-1, the phenol conversion and H2O2 efficiency was
about 22.8% and 76.1%, while the molar ratio(northo:npara) of ortho-product(CAT)

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and para-product(HDQ and BZQ) was 1.09, and the BZQ selectivity was only 0.1%.
When the NaOH concentration was no more than 0.1mol/L, the positive influences of
the TPAOH/NaOH treatment should be more significant, and the phenol conversion,
H2O2 efficiency and northo:npara increased respectively to about 26.5%, 88.4% and 1.25,
while the selectivity of BZQ increased slightly. At higher NaOH
concentration(>0.1mol/L), the negative effects of extra-framework titanium became
stronger, the phenol conversion, H2O2 efficiency and DHB selectivity decreased, the
BZQ selectivity increased, while the northo:npara remained almost the same. When
NaOH was 0.2 mol/L, the phenol conversion was only 20.2%, while the BZQ
selectivity increased to 8.6%.
4. Conclusion
Hierarchical TS-1 with grooves and intracrystalline voids was prepared by
treatment with TPAOH and NaOH. During the combined treatment, the OH- diffused
into the micropores could etch the framework topology, and mesopores inside the
zeolite particle were created. Besides, the erosion may be so severe that part of the
mesopores could link directly to the surface. With increasing NaOH concentration, the
erosion was more severe, the relative crystallinity and microporous properties
decreased, while the secondary pore volume increased. Moreover, the
extra-framework titanium content increased due to the Na+ in the solution. When
NaOH was no more than 0.1mol/L, the positive influences of pore structure may be
more significant, the catalytic activity and H2O2 efficiency improved for better
accessibility of the active centers. However the negative effect of non-framework Ti

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became stronger at higher NaOH concentration(>0.1mol/L), leading to the decrease of
catalytic activity and H2O2 efficiency.
TS-1-P-0.20NaOH
TS-1-P-0.15NaOH
TS-1-P-0.10NaOH
RC=80.5%
RC=84.6%
RC=85.2%
RC=88.0%
RC=100%
TS-1-P-0.05NaOH
TS-1
5
10
15
20
25
30
35
2θ/°
Fig. 1 XRD patterns of TS-1 and hierarchical TS-1
TS-1
0.24
0.20
0.16
0.12
0.08
0.04
TS-1-P-0.05NaOH
TS-1-P-0.10NaOH
TS-1-P-0.15NaOH
TS-1-P-0.20NaOH
2
4
8
16
32
64
Diameter/nm
Fig. 2 Pore size distribution of TS-1 and the hierarchical TS-1

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(1)
(2)
(3)
(4)
Fig. 3 SEM imagines of TS-1 and the hierarchical TS-1
(1) TS-1 (2)TS-1-TPAOH-0.2NaOH (3)TS-1-TPAOH-0.1NaOH
(4)TS-1-TPAOH-0.05NaOH
(1)
(1)

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(2)
(2)
(3)
(3)
(4)
(4)
(5)
(5)
Fig. 4 SEM imagines of TS-1 and hierarchical TS-1
(1) TS-1 (2)TS-1-TPAOH-0.2NaOH (3)TS-1-TPAOH-0.15NaOH (4)TS-1-TPAOH-0.1NaOH
(5)TS-1-TPAOH-0.05NaOH

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0.7
0.6
TS-1-P-0.20NaOH
TS-1-P-0.15NaOH
TS-1-P-0.10NaOH
TS-1-P-0.05NaOH
TS-1
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
200
250
300
350
400
450
500
550
Wavelength/nm
Fig. 5 UV-Vis spectra of TS-1 and hierarchical TS-1
Table 1 The surface parameters of TS-1 and hierarchical TS-1
S MA
/
SMI/
( m2·g-1)
VMI/
(cm3·g-1)
VSP/
(cm3·g-1)
Sample
SBET/( m2·g-1)
( m2·g-1)
TS-1
455
433
428
418
417
42
413
326
315
303
299
0.191
0.142
0.139
0.134
0.132
0.089
0.202
0.219
0.264
0.272
TS-1-P-0.05NaOH
TS-1-P-0.10NaOH
TS-1-P-0.15NaOH
TS-1-P-0.20NaOH
107
108
116
119
SBET: the specific surface area, calculated by BET method
SMA: external surface area, calculated by t-method
SMI: microporous surface area, calculated by t-method
VMI: microporous volume, calculated by t-method
VSP: secondary pore volume, subtraction of total pore volume and microporous volume

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Table 2 XPS results of TS-1 and hierarchical TS-1
Sample
Framework Ti/%
Extra-framework Ti/%
TS-1
57.3
37.1
32.8
34.0
31.7
42.7
62.9
67.2
66.0
69.3
TS-1-P-0.05NaOH
TS-1-P-0.10NaOH
TS-1-P-0.15NaOH
TS-1-P-0.20NaOH
Table 3 The catalytic activity in phenol hydroxylation
BDQ
H2O2
DHB
selectivity/%
Sample
Conv./%
22.8
nOrtho:nPara
1.09
selectivity/%
efficiency/%
TS-1
0.1
0.4
0.2
2.3
8.6
99.7
99.6
99.8
97.7
91.4
76.1
88.4
88.5
77.4
73.1
TS-1-P-0.05NaOH
TS-1-P-0.10NaOH
TS-1-P-0.15NaOH
TS-1-P-0.20NaOH
26.4
1.25
26.5
1.26
22.7
1.26
20.2
1.23
BDQ: p-benzoquinone、DHB: dihydroxybenzene
northo:npara: molar ratio of ortho-product(catechol) and para-product(hydroquinone and
p-benzoquinone)

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TPA+
TPA+
TPA+ TPA+
TPA+
TPA+
TPA+
TPA+
TPA+
Graphical abstract

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Highlights
1 Hierarchical TS-1 with grooves and intracrytalline voids was prepared by
combined-treatment with TPAOH and NaOH
2 The secondary pore volume increased with increasing NaOH concentration
3 When NaOH was no more than 0.1M, the accessibility of the active sites,
catalytic activity and H2O2 efficiency was improved