Synthesis of micro/mesoporous silica material by duallate method as a heterogeneous catalyst support for alkylation

Article abstract of DOI:10.1039/c5ra01250c

A series of micro/mesoporous composites were synthesized using non-ionic block copolymer Pluronic P123 and protic ionic liquid (triethylamine acetate) as the colates. The structures of all the composites were characterized by using small angle X-ray scattering, N₂ gas sorption, dynamic laser light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reflected that the structure of the final silica materials changes along with the content of protic ionic liquid (PIL) and hydrothermal temperature. It was found that the sample whose mass ratio of PIL to (P123 + PIL) was 40% had a t-plot micropore area of 404 m² g^-1 at the hydrothermal temperature of 373 K, without destroying the ordered mesoporous structure. The formation mechanism of the micro/mesoporous silica which is based on the interaction between PIL and P123 is tentatively elucidated. 12-Tungstophosphoric acid (HPW) catalysts supported on these micro/mesoporous materials were prepared by impregnation, and their catalytic performances were investigated in the alkylation of o-xylene with styrene. Alkylation results showed that all the catalysts showed high catalytic performance in terms of propane conversion and selectivity to propene.

Full text of DOI:10.1039/c5ra01250c

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PAPER
Synthesis of micro/mesoporous silica material by
dual-template method as a heterogeneous catalyst
support for alkylation
Cite this: RSC Adv., 2015, 5, 28124
*
*
Shuo Zhao, Man He, Yuming Zhou, Xiaoli Sheng, Xiaoqin Fu and Yiwei Zhang
A series of micro/mesoporous composites were synthesized using non-ionic block copolymer Pluronic
P123 and protic ionic liquid (triethylamine acetate) as the co-templates. The structures of all the
composites were characterized by using small angle X-ray scattering, N2 gas sorption, dynamic laser
light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
The results reflected that the structure of the final silica materials changes along with the content of
protic ionic liquid (PIL) and hydrothermal temperature. It was found that the sample whose mass ratio of
PIL to (P123 + PIL) was 40% had a t-plot micropore area of 404 m2 gꢀ1 at the hydrothermal temperature
of 373 K, without destroying the ordered mesoporous structure. The formation mechanism of the micro/
mesoporous silica which is based on the interaction between PIL and P123 is tentatively elucidated. 12-
Tungstophosphoric acid (HPW) catalysts supported on these micro/mesoporous materials were prepared
by impregnation, and their catalytic performances were investigated in the alkylation of o-xylene with
styrene. Alkylation results showed that all the catalysts showed high catalytic performance in terms of
propane conversion and selectivity to propene.
Received 29th January 2015
Accepted 13th March 2015
DOI: 10.1039/c5ra01250c
www.rsc.org/advances
Nowadays, ionic liquids (ILs), which are molten salts at room
temperature, have attracted much interest due to their unique
1. Introduction
Since mesoporous silica materials were discovered,1 hierar-
chical porous silica materials have received signicant atten-
tion due to their important role in the systematic study of
structure property relationship and their technological promise
in applications.2,3 On one hand, hierarchical porous silica
materials possess high surface area, large pore volumes and
various frameworks like mesoporous materials, on the other
hand, these materials have high thermal, hydrothermal and
mechanical stability like microporous materials.4–7 During the
past decades, signicant efforts have been devoted to design
micro/mesoporous materials by using different approaches,8,9
such as postsynthetic demetalation process and template
synthesis. And the approach using templates has been regarded
as one of the most promising ways to obtain such this type of
hierarchical porous silica materials.10 These templates include
the solid templates which contain carbon nanoparticles, ion-
exchange resins and the so materials which contain surfac-
tants and colloids.8,9 The interaction between templates and
siliceous precursors is very important to obtain the expected
structures. Thus, it is crucial to nd a series of appropriate
templates.
properties such as low vapor pressure, mild reaction condition,
solvating ability, easy recycle ability and so on.5,11–13 Hence, the
ionic liquids were actively studied by many research groups
working in all kinds of elds, such as chemistry, organome-
tallic, biocatalyzed reactions.14,15 ILs can act as multiple roles of
cosolvent, cosurfactant as well as salt in the system.16 So, ILs
may greatly affect the aggregation behavior of aqueous surfac-
tant solution. Long-chain amphiphilic ILs can self-assemble
into ordered structures like surfactants.17 Hence, ILs can
induce micro or mesoporous materials.18–20
In the previous work, these inorganic materials were mostly
prepared by imidazolium based ILs. Hu et al.21 synthesized a
high-quality cubic gyroid mesoporous silica (MCM-41) with the
ionic liquid 1-hexadecyl-3-methylimidazolium bromide as the
template under basic condition. Gao et al.22 obtained a series of
micro/mesoporous silica composites with P123 and imidazo-
lium ILs ([Cnmim]X) as the cotemplates. They found that the
structure of the materials changed along with the change of the
alkyl chain length and anion. Hu et al.23 synthesized the micro/
mesoporous silicate materials using CTAB and imidazolium
ILs ([Cnmim]X). They found the cations [C4mim]+ can embed
into CTA+ micelles and aggregated into mixed micelles which
acted as co-templates for synthesis of mesoporous materials at
the room temperature, while at 373 K, the mixed micelles
divided into CTA+ micelles and [C4mim]+ aggregates which were
acted as mesoporous templates and microporous templates,
School of Chemistry and Chemical Engineering, Southeast University, Jiangsu
Optoelectronic Functional Materials and Engineering Laboratory, Nanjing 211189,
P. R. China. E-mail: ymzhou@seu.edu.cn; Fax: +86 25 52090617; Tel: +86 25
52090617
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respectively. So, imidazolium based ILs are appropriate to NMR. 1H-NMR (CDCl3) d: 7.979 (s, 1H, –NH), 2.762 (s, 3H,
synthesize the micro/mesoporous silica materials.
CH3COO–), 1.277–1.86 (t, 2H, –CH2ꢀ), 0.86 (s, 3H, –CH3), which
The synthesis of highly ordered mesoporous silicate mate- is consistent with literature reports.
rials by a hydrothermal method has rarely been reported using
protic ionic liquids (PILs) which are formed via the proton
transfer from a Bronsted acid to a Bronsted base. Many PILs are
miscible with water to form mixtures at any composition, and
both the component ions favorably form hydrogen bonds with
water.24–26 Chen et al.27 reported that the hierarchically nano-
structured silica materials were obtained by using protic ionic
liquid (ethylammonium nitrate) and non-ionic block copolymer
Pluronic P123 as templates through the sol–gel method. These
materials contained a disordered population of micropores and
an ordered population of mesopores. And the micropores
caused by ethylammonium nitrate. The micro/mesoporous
materials, combining the advantages of mesoporous materials
and microporous materials, are expected to be more suitable
for catalytic reactions as catalysts support material. It is said
that the product of Friedel–Cras alkylation of o-xylene and
styrene, 1-phenyl-1-xylyl ethane (PXE) is an appropriate
solvent for many materials. In general, 12-tungstophosphoric
acid (HPW) and ordered mesoporous SBA-15 are used as acid
catalysts and support, respectively to obtain PXE.28,29 Sheng
et al.30 successfully loaded HPW onto sulfonate-functionalized
ionic liquid-modied mesoporous silica SBA-15 by total
anion-exchange. And the nal catalyst showed a high efficiency
in alkylation. Thus, the micro/mesoporous materials can
instead of the traditional supports to synthesize PXE to inves-
tigate if micro/mesoporous materials are suitable for this
reaction.
2.3 Synthesis of micro/mesoporous materials
In a typical synthesis, 4 g P123 and an appropriate amount of
PIL were completely dissolved in water; its pH was controlled by
HCl (2 M). Under strong stirring, 9 g tetraethyl orthosilicate
(TEOS) was dripped slowly. Aer stirring at 313 K for 24 h, the
whole slurry was transferred into an autoclave for aging at an
appropriate temperature for 48 h. The PIL and organic
components were extracted by ethanol and then water in an
oven overnight. The white as-synthesized solid powders were
then calcined at 823 K for 6 h in ambient air, with a heating rate
of 3 K minꢀ1
.
Similarly, a series of micro/mesoporous materials were
synthesized by changing the ratio of PILs and temperature
during synthesis. The nal products were denoted as PIL-X-Y,
in which X represents the mass ratio of PIL to (P123 + PIL); Y
represents the aging temperature, respectively. As
a
comparison, samples either without P123 (denoted as PIL) or
using water to replace PIL (denoted as P123) were also
prepared.
2.4 Catalysts preparation
1 g of micro/mesoporous materials were added into the mixture
of 20 mL ethyl alcohol and 0.4 g of 12-tungstophosphoric acid at
333 K. The mixture continuously stirred until ethyl alcohol
steamed. The obtained white solid was dried at 393 K overnight
and calcined in air at 573 K for 4 h.
In this work, a new approach to prepare micro/mesoporous
silica materials possessing both micropores and mesopores
has been suggested. The porous silica materials were synthe-
sized with P123 and PIL (triethylamine acetate) as the co-
templates by the hydrothermal method. A number of samples
were synthesised by changing the PIL to P123 weight ratio and
temperature during synthesis. Moreover, HPW supported on
micro/mesoporous materials were prepared by impregnation
method. The catalytic properties of the catalysts were assessed
in the alkylation of o-xylene with styrene.
2.5 Catalytic tests
The alkylation reactions were carried out in a continuously
stirred oil batch reactor under 393 K. Styrene (6 g), o-xylene (45
g) (quality ratio of o-xylene to styrene, 7.5 : 1) and 1.02 g of
catalyst were introduced in a three-neck 100 mL round-bottom
ask equipped with a condenser for 3 h. Firstly, the mixture of
the small amount of o-xylene and the desired amount of catalyst
were added to the round-bottom ask at 393 K, the mixture of a
certain amount of styrene and the remaining o-xylene then
dropwise into the ask for 2 h. The nal reaction mixture
remained for another 1 h. Aer the reaction, unreacted o-xylene
was distilled out under atmospheric pressure, and then the
obtained liquid was denoted by crude product which was
analyzed with GC-9890A gas chromatograph equipped with OV-
1 capillary column and a ame ionization detector (FID). The
yield of PXE was dened as follows:
2. Experimental section
2.1 Chemicals
P123 (PEO20PPO70PEO20) was purchased from Sigma-Aldrich,
the inorganic silica precursor was silicon(IV) tetraacetate
(TEOS 97%, Fluka) and HCl (37% in water, Aldrich) was used as
reaction catalyst, triethylamine (Merck) and acetic acid (Merck)
were used to synthesise PIL.
actual product weight
Yield of PXEð%Þ¼
ꢁ 100%
theoretical product weight
2.2 Preparation of PIL
Triethylamine acetate was obtained according to the litera-
ture.31 A typical polymerization procedure is described as
follows. Acetic acid (30.025 g) was added dropwise into
triethylamine (50.595 g) at 353 K. Aer stirring for 5 h, PIL
which was yellow was obtained. PIL was characterized by 1H
Actual product weight ¼ crude product weight ꢁ PXE
(chromatography) %.
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2.6 Characterization
The structure of the calcined samples was characterized by an X-
ray powder diffractometor (Rigaku, RINT-Ultima III) using Cu
Ka radiation with 40 kV and 200 mA. All scans were continuous
and run between 2q values of 0–5ꢂ. The N2 physical adsorption
and desorption isotherms were adopted at 77 K to obtain
surface areas with ASAP 2020 apparatus (Micromertics USA) by
means of the Brunauer–Emmett–Teller (BET) method. The pore
size distribution in mesopore range was analyzed by the BJH
(Barrett–Joyner–Halenda) method using the Halsey equation for
multilayer thickness. Micropore volume was calculated by the t-
plot method. Transmission Electron Microscopy (TEM) was
performed on FEI Tecnai G20 instrument. Infrared spectra were
recorded on a Bruker Tensor 27 (German) using DRIFT tech-
niques, scanned from 4000 to 400 cmꢀ1. The sample was
ground with KBr and pressed into a thin wafer. The samples
were evacuated at 573 K for 4 h before the measurement.
Scanning electron microscopy (SEM) images were recorded on a
JEOL JSM-5600L SEM Instrument with a working distance of 3–4
mm and an electron voltage of 3.0 kV. The size distributions of
micelles were determined by dynamic laser light scattering
(DLS) on a Malvern Nano-ZS, with a detecting angle of 90ꢂ.
Fig. 1 XRD patterns of the samples induced by PIL/P123 co-templates
at 393 K.
the existence of PIL micro scale micelles and P123 mesoscale
micelles. From the data above, it can be concluded that PIL and
P123 are miscible and can form mixed micelles at lower PIL
concentration, while, PIL micelles can separated from the
mixed micelles with the increase of PIL concentration. And two
different scale micelles which induce the micro/mesoporous
material are formed. And the sample PIL-70 only has one
peak at 3.8 nm, indicating the structure of ordered channel has
been destroyed. That certies the function of ionic liquid for the
material structure.
The characteristic data on the samples are summarized in
Table 1. From Table 1, it can be seen that with increasing PIL,
the average pore size of each sample is 7.14, 5.14, 4.35, 3.32 nm,
respectively. Among them, PIL-40 and PIL-30 possess extremely
large pore volume of 1.23, 1.31 cm3 gꢀ1, which are larger than
that of the pure SBA-15 of 1.10 cm3 gꢀ1. This phenomenon
indicates the positive contributions of PIL to the volume.
The TEM images of the calcined sample prepared at 393 K
show the structure of the samples obtained with different PIL
content, meaning P123/PIL templates can induce micro/
mesoporous composites. The images for PIL-30 and PIL-40
show very ordered mesoporous structure, these mesopores are
arranged in a hexagonally ordered array. The order–degree of
samples decreases with increasing the content of PIL. If making
a local enlargement, the wall lled with the cycle-like micro-
pores is found. The Fig. 3C of the sample PIL-50 lacks orderli-
ness because of the existence of PIL, which is consistent with
the XRD result. And the hexagonally ordered array structure of
PIL-70 totally disappear, only disordered worm-like mesopores
can be found in the Fig. 3E, illustrating the excess of PIL affect
the conformation of samples. The morphology of the PIL-40
particles prepared at 373 K is shown in the SEM Fig. 3F,
which exhibits worm-like shapes.
3. Results and discussion
3.1 Effect of the PIL content
The XRD patterns of the samples induced by PIL/P123 co-
templates are shown in Fig. 1. When the mass ratio of PIL to
(P123 + PIL) is 30% and 40% (PIL-30, PIL-40), three well-resolved
diffraction peaks which include a strong reection at 2q ¼ 0.86ꢂ
for d100 and two other weaker reections at 2q ¼ 1.55ꢂ and 2q ¼
1.71ꢂ respectively for d110 and d200 are observed in the curve,
which is
a typical pattern characterizing the hexagonal
arrangement of SBA-15. Only one broad diffraction peak with a
much lower intensity is preserved for PIL-50, indicating its less
ordered structure. No other obvious diffraction peak is observed
with increasing the content of PIL, stating a poor periodicity for
PIL-60 and PIL-70.
N2 adsorption isotherms of the calcined samples in Fig. 2A
exhibit the typical IV adsorption. The presence of a pronounced
hysteresis loop in the isothermals indicates the intersection
network of porous structures. At very low relative pressure P/P0,
an increase at the adsorption isothermal of all materials proves
the presence of micropores. With the increase of PIL content,
the pressure onset of the hysteresis gradually shis to lower
values from 0.6 (PIL-40) to 0.4 (PIL-70), which illustrates pore
size shrinkage. Distortion of the characteristic hysteresis loop of
PIL-70 demonstrates the loss of ordered pore structure, which
agrees with the XRD result. There is a clear hysteresis loop in the
isothermals of PIL, indicating protic ionic liquid can self-
assemble to micelles which act as the mesoporous templates
at higher PIL concentration.
Fig. 2B shows the pore size distribution calculated by BJH
model based on desorption curves. Two peaks are observed
from the pore size distributions of the sample PIL-60, whereas
the others have only one peak. The difference may be caused by
Fig. 4 shows the size distribution of P123/PIL micelles in
aqueous solutions with different PIL concentration at room
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Fig. 2 (A) N2 adsorption–desorption isotherms, (B) pore size distributions calculated by BJH model based on desorption curves of the calcined
samples induced by P123/PIL co-templates at 393 K.
Table 1 Physicochemical properties of the calcined samples induced
by P123/PIL co-templates at 393 K
with increasing the PIL concentration, representing the PIL may
self-assembly form a new micelles, which is consistent with
pore size distribution of PIL-60.
BET surface area
Pore volume
Average pore
size (nm)
Sample name
(m2 gꢀ1
)
(cm3 gꢀ1
)
3.2 Effect of the hydrothermal temperature
PIL-70
PIL-60
PIL-50
PIL-40
PIL-30
PIL
838
796
844
691
681
720
881
0.70
0.86
1.08
1.23
1.32
0.65
1.10
3.32
4.35
5.14
7.14
7.73
3.59
5.01
The low-angle XRD patterns of the samples induced by PIL/P123
co-templates at different temperature are shown in Fig. 5. When
the temperature is 393 K and 373 K, three well-resolved
diffraction peaks are observed in the curve, which correspond-
ing to the (100), (110) and (200) reections. While, the intensity
of PIL-40-373 is much lower than PIL-40-393. It means that the
ordered mesoporous structure is affected by temperature. Three
peaks are disappeared when the temperature is 353 K, which
shows a poor periodicity of the sample's structure.
The N2 adsorption isotherms of the calcined samples at
different temperature are shown in Fig. 6A. Pronounced
hysteresis loop characterizing the cylindrical mesopores can be
observed at 393 K or 373 K, representing that the samples have a
P123
temperature. Only one peak could be found in the sample P123
and PIL-40 at 18 and 20 nm, respectively. While, the average
diameter of PIL-40 has a higher value than that of P123,
demonstrating the PIL maybe around the P123 micelles owing
to the hydrogen bonding. Another new peak at 7 nm appears
Fig. 3 The images of the calcined samples induced by P123/PIL at 393 K. The TEM image of (A) PIL-30, (B) PIL-40, (C) PIL-50, (D) PIL-60, (E) PIL-
70, (F) the SEM image of PIL-40. The insets are the local enlargements with the same enlargement scale.
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ordered porous structure. While, the adsorption of PIL-40-393 is
higher than that of PIL-40-373. The distortion of hysteresis loop
indicates the loss of the ordered pore structure at 353 K, which
according to the XRD results. Fig. 6B shows the pore size
distribution calculated by BJH model based on desorption
curves. The mesopore size distribution of PIL-40-373 is similar
with that of PIL-40-393 whose mesopore size is about 6.3 nm.
While, from the Table 2, it is can be seen that PIL-40-373 has a t-
plot micropore area of 404 m2 gꢀ1, which is larger than other
samples. When the temperature increase to 393 K, there is still a
t-plot micropore area of 21 m2 gꢀ1, certifying the effect of PIL
microporous template. Through the analysis, it is known that
the ordered mesoporous channels with small amounts of
micropores can be obtained at 393 K, and materials which not
only possess more micropores but also remain the hexagonally
ordered array structure are induced at a low temperature of 373
K. When the temperature decreases to 353 K, the material with
disordered structure is obtained. Thus, the hydrothermal
temperature is a signicant factor to obtain the micro/
mesoporous material.
Fig. 4 Size distribution of P123/PIL aqueous solutions determined by
DLS.
Fig. 7 shows the TEM images of PIL-40 synthesized at
different temperature. A little disordered structure can be seen
when the temperature is 353 K. The two-dimensional hexagonal
structure has been destroyed. When the temperature increases
to 373 K or 393 K, the mesopores are arranged in an ordered
array as observed in Fig. 7B and C. And both of the samples
show uniformly distributed pores with the pore size estimated
to be 6.3 nm from the image, which is consistent with the result
of N2 gas sorption. A part of the walls of mesoporous channels
are destroyed a little in the enlarged insert, which may during to
the existence of worm-like micropores. Compared with PIL-40-
393, PIL-40-373 has a higher t-plot micropore area of 404 m2
gꢀ1. Thus, the favorable temperature to synthesis the micro/
mesoporous SBA-15 materials is 373 K.
Formation mechanism of hierarchical micro/mesoporous
silica: in aqueous systems, mesopores were produced in an
analogous liquid templating approach. Micropores and meso-
pores were obtained with the elimination of PIL and P123,
respectively. P123 micelles have a hydrophobic core and a
Fig. 5 XRD patterns of the PIL-40 at different temperature.
Fig. 6 (A) N2 adsorption–desorption isotherms, (B) pore size distributions calculated by BJH model based on desorption curves of the calcined
samples induced by PIL-40 co-templates at different temperature.
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Table 2 Physicochemical properties of the calcined samples induced by PIL-40 co-templates at different temperature
Temperature
(K)
BET surface area
Micropore surface
Pore volume
Average pore
size (nm)
Sample name
(m2 gꢀ1
)
area (m2 gꢀ1
)
(cm3 gꢀ1
)
PIL-40-353
PIL-40-373
PIL-40-393
353
373
393
676
722
691
133
404
21
0.48
0.91
1.23
2.84
5.05
7.14
Fig. 7 TEM images of the PIL-40 at different temperature (A) 353 K, (B) 373 K, (C) 393 K. The insets are the local enlargements with the same
enlargement scale.
hydrophilic head group. There is a strong interaction between
PIL and P123 mainly due to the hydrogen bond. And the inor-
ganic network also has a strong interaction with the polar
domain of the PIL molecules, thus creating micropores. The
ammonium-based ionic liquid (triethylamine acetate) can act as
multiple roles of cosolvent, cosurfactant as well as salt in the
system. When the content of PIL is low, the co-solvent and co-
surfactant functions are dominant. PIL and P123 are miscible
and can form mixed micelles in aqueous solution. The short
chains of PIL probably incline to swell the P123 micelles. Thus,
the average diameter of P123/PIL mixed aggregates may shi to
a higher value. Which is analogous to the function of the
diameter expander, reagent 1,3,5-trimethylbenzene (TMB). In
the case of P123/TMB mixed micelles, TMB molecules are totally
solubilized in the core of P123 micelles, which obviously forms
the swollen P123 micelles, consequently the size of mixed
micelles can be higher than P123 micelles. Protic ionic liquids
can separated from the mixed micelles at higher concentration
of protic ionic liquid. And the large micelles induced by
numbers of ionic liquid micro scale micelles act as the meso-
porous template. This phenomenon is certied by pore size
distribution of PIL-60 which has two peaks (3.9 nm, 7.7 nm).
And the structure of the nal sample is inuenced by PIL as
well. The mesoporous structure becomes disordered with
increasing the content of protic ionic liquid, which is conrmed
by the XRD pattens and TEM results. PIL micelles are dominant
in the solution under the high PIL concentration, and the P123
micelles almost disappear, which is conrmed by the size
distribution curve of PIL-70. The presence of disordered
micropores may contribute to the disappearance of the (110)
and (200) peaks in the XRD patterns of the nal samples. The
formation mechanism of the micro/mesoporous silica material
which is based on the interaction between PIL and P123 is
schematically presented in Fig. 8.
3.3 Catalytic activity of micro/mesoporous materials
supported HPW
The IR spectra of the pure HPW, PIL-X and HPW/PIL-X-Y are
shown in Fig. 9A.
IR peaks of pure HPW show approximately at 1080 (P–O in
the central tetrahedron), 980 (terminal W]O) and 890 and 800
(W–O–W) cmꢀ1 corresponding to asymmetric vibration associ-
ated with Keggin ion. IR peak of SBA-15 at 3440 cmꢀ1 is
stretching frequency for hydroxyl and silicon hydroxyl, 1630
cmꢀ1 peak is bending vibration peak for O–H of adsorbed water,
1080 cmꢀ1, 808 cmꢀ1 and 461 cmꢀ1 peaks are vibration
absorption peaks for Si–O–Si, including 1080 cmꢀ1 peak is the
strong asymmetric stretching vibration absorption peak of
Si–O–Si, 968 cmꢀ1 peak is bending vibration peak for silicon
hydroxyl. Fig. 9B presents the IR spectra of all different HPW/
PIL-X-Y samples. It can be seen that the IR bands at approxi-
mately 980 cmꢀ1, 890 cmꢀ1 and 800 cmꢀ1 are clearly observed.
This indicates the primary structure of 12-tungstophosphoric
acid is preserved even aer immobilization at the surface of PIL-
X-Y.
The catalytic performance of different carriers with HPW
were investigated owing to the carriers contain high surface
area and narrow size distribution which are favorable condi-
tions for the reaction. Sheng et al.32 found that pure HPW
showed high catalytic performance for the reaction, while, it
was difficult for recovery. HPW/SBA-15 showed the low product
yield (68.3%) in their work. From Table 3, it is found that the
support itself has no catalyst performance and other samples
exhibit the much higher catalytic properties than those of HPW/
SBA-15 in their work. Among the catalysts investigated, HPW/
PIL-30-393 with large pore size of the support exhibited the
best catalytic performance. Thus, the catalytic activity may
change along with the pore size of supports because large pore
size material is conducive to the macromolecular reaction. So,
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Fig. 8 The template mechanism of IL cationic [N(CH2CH3)3]+ and P123 (A) synergism for mesoporous material at lower PIL content, and (B) for
the micro/mesoporous materials at higher PIL content.
suitable pore size may contribution to the high catalytic the activity is observed aer 4 runs on the HPW/PIL-30-393
performance.
catalyst. In contrast, the deactivation of HPW/SBA-15 cata-
Stability and reusability of the catalyst are signicant for lyst is much faster and PXE yield drops to 40% aer
any catalytic system. The reusability of the HPW/PIL-30-393 the fourth reaction cycle. The poor catalytic stability of
and HPW/SBA-15 catalysts has been evaluated by carrying HPW/SBA-15 may be due to the possibility that HPW leaching
out the reaction with used catalyst under the optimized from the catalyst support into the liquid reaction system
conditions. Aer each run, the catalyst was recovered by may result in the low conversion. Furthermore, micropores
ltration, then washed with ethanol, dried and calcined at of HPW/PIL-30-393 may be another reason for better
573 K for 4 h, and used again. The data obtained are stability.
summarized in Fig. 10. It can be seen only 15% reduction in
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Fig. 9 (A) FT-IR spectra of pure HPW, PIL-X and HPW/PIL-X and (B) FT-IR spectra of different HPW/PIL-X-Y samples.
Table 3 Activity of various supported HPW catalystsa in alkylation of
4. Conclusion
o-xylene with styrene
In summary, a series of micro/mesoporous silica materials are
obtained using P123 and PIL (triethylamine acetate) as co-
templates. The structure of the nal materials was investi-
gated by two important factors: the PIL content and hydro-
thermal temperature. The formation mechanism of the micro/
mesoporous silica which is based on the interaction between
PIL and P123 is tentatively elucidated. At low concentration of
PIL, PIL and P123 can form mixed micelles in aqueous solution
because of the hydrogen bond. PIL may separate from P123
micelles and form mesoscale micelles with the increase of PIL
Catalyst
Yieldb (%)
Selectivityc (%)
PIL-40
—
—
HPW/PIL-70-393
HPW/PIL-60-393
HPW/PIL-50-393
HPW/PIL-40-393
HPW/PIL-30-393
HPW/PIL-40-373
HPW/PIL-40-353
85.46
86.28
89.42
90.29
93.80
86.52
80.38
85.66
86.47
89.57
90.55
94.57
86.72
80.56
a
Reaction conditions: o-xylene : styrene ¼ 7.5 : 1, reaction temperature
¼ 393 K, reaction time ¼ 3.0 h, catalyst loading ¼ 20% (w/w of styrene). content. The results showed that the sample PIL-40-373 not only
b
c
possessed a t-plot micropore area of 404 m2 gꢀ1 but also
remained the hexagonally ordered array structure. A serious of
micro/mesoporous materials supported HPW catalysts were
obtained, and their catalytic performances were investigated in
the alkylation of o-xylene with styrene. Alkylation results
showed that catalysts had much higher product yield and longer
catalytic life, which might be due to the large pore size of the
support and the strong interaction between the HPW and the
supports.
Isolated yield based on the amount of styrene. Target product: all
products.
Acknowledgements
The authors are grateful to the nancial supports of National
Natural Science Foundation of China (Grant no. 21306023,
21376051, 21106017 and 51077013), Fund Project for Trans-
formation of Scientic and Technological Achievements of
Jiangsu Province of China (Grant no. BA2011086), Key Program
for the Scientic Research Guiding Found of Basic Scientic
Research Operation Expenditure of Southeast University (Grant
no. 3207043101) and Instrumental Analysis Fund of Southeast
University.
Fig. 10 Catalytic stability of the HPW/PIL-30-393 and HPW/SBA-15
catalysts in the alkylation of o-xylene with styrene (reaction condi-
tions: o-xylene : styrene ¼ 7.5 : 1, reaction temperature ¼ 393 K,
reaction time ¼ 3.0 h, catalyst loading ¼ 20% (w/w of styrene)).
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