Alkylation of O-xylene and styrene catalyzed by cross-linked poly acidic ionic liquids catalyst with novel mesoporous-macroporous structure

Article abstract of DOI:10.1016/j.apcata.2017.12.027

Cross-linked poly acidic ionic liquids (MPM-C₆V-SO₃CF₃-IL) with mesoporous and macroporous network structure have been synthesized in different solvents. The novel solid acid catalyst with special network structure has a large surface area (103.83 m²/g), large pore volume (0.72 cm³/g) and abundant mesopores and macropores, which help to improve the contact between active site and reactants. Catalytic performance of catalyst was investigated through alkylation of o-xylene and styrene. Different reaction parameters specifically solvent on obtained catalyst and production of PXE were systematically investigated. Under optimal reaction conditions (reaction time was 3 h, reaction temperature was 120 °C, catalyst amount was 0.17 g (0.5 wt%), and o-xylene/styrene mass ratio was 7.5:1), a high conversion of styrene (100%) and 1,2-diphenylethane (PXE) yield of 99.67% was obtained, which is superior to commercial acid in liquid and even previous acids synthesized by our own group. Moreover, catalyst could keep relatively high thermostability under reaction and are easy to be separated and recycled from the solution, which are critical for heterogeneous solid catalysts. Thus, this novel catalyst can be potentially applied in other acidic reactions.

Full text of DOI:10.1016/j.apcata.2017.12.027

Accepted Manuscript
Title: Alkylation of O-xylene and Styrene Catalyzed by
Cross-linked Poly Acidic Ionic Liquids Catalyst with Novel
Mesoporous-macroporous Structure
Authors: Huaying Gao, Yuming Zhou, Xiaoli Sheng, Shuo
Zhao, Chao Zhang, Jiasheng Fang, Beibei Wang
PII:
S0926-860X(17)30582-3
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2017.12.027
APCATA 16507
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
25-9-2017
24-12-2017
30-12-2017
Please cite this article as: Gao H, Zhou Y, Sheng X, Zhao S, Zhang C, Fang J, Wang
B, Alkylation of O-xylene and Styrene Catalyzed by Cross-linked Poly Acidic Ionic
Liquids Catalyst with Novel Mesoporous-macroporous Structure, Applied Catalysis A,
General (2010), https://doi.org/10.1016/j.apcata.2017.12.027
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Alkylation of O-xylene and Styrene Catalyzed by Cross-linked
Poly Acidic Ionic Liquids Catalyst with Novel
Mesoporous-macroporous Structure
Huaying Gao*, Yuming Zhou, Xiaoli Sheng, Shuo Zhao,
Chao Zhang, Jiasheng Fang, Beibei Wang
School of Chemistry and Chemical Engineering, Southeast University, Jiangsu Optoel
ectronic Functional Materials and Engineering Laboratory, Nanjing 211189, P. R. Chi
na.
*Corresponding authors: Huaying Gao (E-mail: m15261898298@163.com; Fax: +86
2552090617; Tel: +86 25 52090617;)
GRAPHICAL ABSTRACT

HIGHLIGHTS



Cross-linked poly acidic ionic liquids have been synthesized in different solvents.
Utilization in the alkylation of o-xylene and styrene for the first time.
Obtained catalyst with mesoporous and macroporous network structure.
Abstract
Cross-linked poly acidic ionic liquids (MPM-C6V-SO3CF3-IL) with mesoporous and
macroporous network structure have been synthesized in different solvents. The novel
solid acid catalyst with special network structure has a large surface area (103.83 m2/g),
large pore volume (0.72 cm3/g) and abundant mesopores and macropores, which help
to improve the contact between active site and reactants. Catalytic performance of
catalyst was investigated through alkylation of o-xylene and styrene. Different reaction
parameters specifically solvent on obtained catalyst and production of PXE were
systematically investigated. Under optimal reaction conditions (reaction time was 3 h,
reaction temperature was 120 °C, catalyst amount was 0.17 g (0.5 wt%), and o-
xylene/styrene mass ratio was 7.5:1), a high conversion of styrene (100 %) and 1,2-
diphenylethane (PXE) yield of 99.67 % was obtained, which is superior to commercial
acid in liquid and even previous acids synthesized by our own group. Moreover, catalyst
could keep relatively high thermostability under reaction and are easy to be separated
and recycled from the solution, which are critical for heterogeneous solid catalysts.
Thus, this novel catalyst can be potentially applied in other acidic reactions.
Keywords: Poly acidic ionic liquids; catalyst; mesoporous–macroporous structure;
alkylation; cross-linked polymer
1. Introduction

As an industrially important Friedel–Crafts (FC) reaction, the alkylation of o-xylene
with styrene has been extensively studied and reviewed for many years. Nowadays,
Phenylxylylethane (PXE) has been widely used in various areas, e.g., the pressure-
sensitive record materials, a heating medium, an electric-insulating oil and so on. PXE
is generally produced through homogeneous Brønsted, Lewis or compound acid
catalysts, such as H2SO4, HF, AlCl3 and FeCl3 [1, 2]. However, the aforementioned
traditional acids are generally high cost and corrosion, low active performance,
selectivity and recyclability. Therefore, the environmental friendly heterogeneous solid
catalysts are highly desirable to optimize catalytic technology. Sun et. al. demonstrated
that binary mixtures [BMIM]Br-AlCl3 can be used as catalyst for the alkylation of o-
xylene and styrene，with good separation and regeneration, but it generated a large
portion of byproduct BPXE during the reaction [3]. Zhao et. al. investigated alkylations
of 2-methylnaphthalene with long-chain alkenes catalyzed by ethyl-containing amine
chloroaluminate ionic liquids modified with HCl [4]. Cao et. al. explored the alkylation
mechanism of o-xylene with styrene, using DFT method in AlCl3-ionic liquid catalytic
system. The reactive energy catalyzed by superelectrophilic AlCl2+ (12.6 kcal/mol) was
distinctly lower than AlCl3 (43.0 kcal/mol), which was considered as the
ratedetermining step in long-chain styrene with o-xylene [5]. These explorations
concentrated on the catalysis of AlCl3-ionic liquid, which AlCl3 molar ratio was a key
factor for deciding catalysis activity in above.
Up to date, solid acid materials has been widely utilized in various reactions such
[8]
like esterification [6], Beckmann rearrangements [7], Friedel-Crafts reaction
,

transesterification [9]. Numerous solid acids can be prepared facilely, including, zeolites,
heteropolyacids (HPAs), metal oxides, sulfonated carbon materials and ion-exchanged
resins [10]. Among which, HPAs, exemplified with Keggin structured phosphotungstic
acid (H3PW), have exhibited excellent performance in different kinds of acid-catalyzed
reactions due to their superior acidity, versatile composition and structure [11]. Moreover,
the strategy of combing zeolite and H3PW has been demonstrated as an efficient method
to synthesize high active catalyst [12]. The replacement of homogeneous liquid catalysts
by heterogeneous solid catalysts has received wide attention in the synthesis of green
or sustainable chemistry [13-15]. In particular, ionic liquids (ILs) supported on porous
materials and polystyrene-based polymers are efficient catalysts with excellent
recyclability for the production of fine chemicals [9, 16]. Specifically, these kinds of
catalysts with exposed active sites, synthesized by the introduction of cross-linking
agent, show a relatively higher catalytic activity than normal heterogeneous IL catalysts.
As an immerging group of smart ionic liquids, poly (ionic liquids) (PILs) or ionic
liquid (IL) polymers not only present attractive mechanical characteristics of polymers,
but also retain the superior physicochemical properties of ionic liquids [17]. Such as, the
unique physicochemical properties of negligible vapor pressure, fine physical and
chemical stability, specifically, low volatility, non-flammability, high thermal stability,
high ionic conductivity and wide electrochemical potential window [18-20]. Li and co-
workers had synthesized sulfonic group tethered mesoporous poly (ionic liquid)
Poly(DVB-VMPS) for catalyzing deoximation reactions with improved activity and
enhanced stability [21]. Yan et. al. had prepared a lot of excellent functional materials

based poly(ionic liquid)s, which shown superior performances in electronic devices [22,
23]. Poly (Ionic Liquid) as an brilliant new class of polymers exhibited applications in
numerous areas such as: fuel desulfurization [24], biodiesel production [25], deoximation
catalyst [21], gas separation membranes [26], flexible electrolytes [27], and dye sensitized
solar cells [28]. Moreover，the polymerized acidic ionic liquid is a relatively unexplored
sub-group in the polymeric ionic liquids arena and these acidic polymers can combine
ionic liquid, acidic and polymer characteristics into a single material [29]. Lots of
research groups have made great efforts to synthesize polymerized acidic ionic liquid
during past three to four years, polymeric compounds with acidic ionic liquid pendant
groups had been successfully synthesized. Additionally, the acidic IL functionalized
polymeric materials with imidazolium-SO3H, and pyridinium-SO3H as pendant groups
have been used as catalysts for the biodiesel synthesis from waste oil [30]. Ananda et. al.
had firstly reported the novel strategy to synthesize a polymeric acidic ionic liquid with
imidazolium ionic liquid moieties and p-phenylene-sulfonic acid units in the main
polymer chain named poly (bis-imidazolium-p-phenylenesulfonic acid), catalyzed in
the preparation of 1-amidoalkyl-2-naphthols [31]
.
Therefore, mesoporous and macroporous poly (ionic liquid)s are promising
multifunctional materials with the features of multiporous materials, polymers and
ionic liquids (ILs) [32]. In this work, cross-linked poly acidic ionic liquids with
mesoporous and macroporous structure were successfully synthesized, via
hydrothermal polymerization and anion exchange, sequentially. The catalyst could be
separated and recycled easily and exhibited enhanced catalytic activities in alkylation

of o-xylene and styrene. Furthermore, a series of contrasting experiments were carried
out to investigate the effect of solvents, addition of catalysts, reaction temperature.
Among the obtained samples, compared with traditional solid acid, MPM-C6V-
SO3CF3-IL (DMF) occupies a large surface area (103.83 m2/g), high pore volume
(0.72cm3/g) and abundant mesopores and macropores. Thus, the results achieved in this
study may provide important insight into the field of alkylation, which has never been
reported yet.
2. Experimental
2.1. Materials
All chemicals and solvents were commercially available and used as received. 1-
Vinylimidazole (99 wt%) (V), N,N’-Methylenebis (acrylamide) (M), 2,2’-Azobis (2-
methylpropionitrile) (AIBN) were purchased from Aladdin Industrial Corporation,
N,N-Dimethylformamide (AR) (DMF), acetone (AR), anhydrous ether (AR),
isopropanol (AR) (IPA) and Ethanol absolute (AR) were purchased from Sinopharm
Chemical Reagent Co., Ltd. 1-Bromohexane(99 wt%), o-xylene, methylbenzene and
styrene were supplied by Shanghai Lingfeng Chemical Reagent Co., Ltd., Tr
fluoromethanesulfonic acid was acquired from Sun chemical Technology (Shanghai)
Co., Ltd.
2.2. Preparation of mesoporous and macroporous polymer (MPM-V)
The mesoporous and macroporous polymer (MPM-V) was hydrothermally synthesized
from copolymerization of M with V, according to the previous literature [33] with a slight

modification. In a typical procedure, the mixture composed of M (1.68 g) and V (0.68
g) was dissolved into 30 mL DMF (acetone or IPA) in a 100ml flask, followed by
addition of AIBN (0.08 g). After vigorous stirring at room temperature for 3 h, the
mixture was transferred into a 100 mL Teflon-lined stainless-steel autoclave and sealed
to hydrothermally treat at 100 °C in an oven for 24 h. After evaporating DMF (acetone
or IPA) at 40 °C in vacuum drying oven for 12 h, the monolithic solid was grounded
into the powder, and finally, mesoporous and macroporous polymer (MPM-V) sample
in yellowish powder morphology was obtained.
2.3. Preparation of cross-linked poly acidic ionic liquids (MPM-C6V-SO3CF3-IL)
The ionic liquids functionalized on mesoporous and macroporous polymers were
prepared by quaternary ammoniation CH3CH2CH2CH2CH2CH2Br (C6H13Br), followed
by anion-exchange treatments (HSO3CF3). As a typical synthesis of MPM-C6V-
SO3CF3-IL. 1.0 g of MPM-V was added to 25 mL of ethanol under stirring, followed
by addition of 2.5 mL of C6H13Br in the dark. After stirring for 12 h, the sample was
filtered and washed with a large amount of ethanol to remove C6H13Br. After drying at
60 °C for 12 h, the MPM-C6V sample was obtained, where C6 stands for the C6H13Br
alkylation reagent. Furthermore, MPM-C6V was treated with a solution containing 25
mL of toluene and 3mL HSO3CF3 for 24 h at room temperature, followed by filtering,
washing with anhydrous ether, drying at 50 °C for 6 h. After repeating this procedure
once again, followed by filtration, washed with anhydrous ether, and dried at 50 °C for

6 h, the MPM-C6V-SO3CF3-IL sample was obtained, where SO3CF3 stands for the
treatment of acid.
2.4. Catalyst characterizations
Transmission electron microscopy (TEM) experiments were conducted on a JEM-1230
with an acceleration voltage of 100 kV. Scanning electron microscopy (SEM) images
were recorded on a JEOL JSM-5600L SEM instrument. Fourier transform infrared (FT-
IR) spectra were recorded on a BRUKERALPHA FT-IR spectrometer.Thermo
Gravimetric Analysis (TGA) was performed using a Rigaku ThermoPlus TG8120
system at a rate of 10 °C min−1 under air. The nitrogen adsorption-desorption isotherms
were measured on an ASAP 2020 (Micromeritics, USA). Specific surface area was
calculated by Brunauer-Emmett-Teller (BET) algorithm, and the pore size and pore
volumes distributions were calculated using the Barrett-Joyner-Halenda (BJH) method.
The X-ray photoelectron spectroscopy (XPS) spectra were performed on a Thermo
ESCALAB 250 with Al Kα radiation, and the binding energies were calibrated using
the C1s peak at 284.8 eV.
2.5. The alkylation of o-xylene with styrene
The catalytic activities of the as-prepared samples were evaluated through alkylation of
o-xylene with styrene to produce 1,2-diphenylethane (PXE). In a general procedure, o-
xylene (30 g), styrene (4 g), and 0.17 g catalyst (0.5 wt%, relative to the weight of o-
xylene and styrene) were mixed in a 250 ml flask. The reactant mixture was heated to

120 °C in an oil bath with magnetic stirring for 3 h under autogenous pressure. After
this reaction, catalyst was recycled by vacuum filter. Cross-linked poly acidic ionic
liquids catalyst was synthesized in three steps as shown in Fig. 1.
Fig. 1. Synthesis of cross-linked poly acidic ionic liquids catalyst
3. Results and discussion
3.1. Catalysts characterization
FT-IR was used to evaluate the special functional group of samples and the results were
exhibited in Fig. 2. For Fig.2a-c, peaks at 1668 cm−1 and 1533 cm−1 were attributed to
C=O, N-H and C-N stretching vibration of amide group, suggesting amide group
structure had been embedded in the mesoporous and macroporous polymers. The FT-
IR spectrum of MPM-C6V-SO3CF3-IL clearly showed the new bands at 641 cm−1, 1031
cm−1, and 1175 cm−1 (Fig. 2c-e), which was attributed to the presence of S−O and C−F.
It was noteworthy that different solvent exhibited different peak intensity. Especially,
the peak intensity of Fig. 2c was stronger than Fig. 2 (a, b), which indicates that there
existed many SO3CF3.

Fig. 2. FT-IR spectra of (a) MPM-V, (b) MPM-C6V, and (c) MPM-C6V-SO3CF3-
IL (DMF), (d) MPM-C6V-SO3CF3-IL (IPA), (e) MPM-C6V-SO3CF3-IL (acetone).
X-ray photoelectron spectroscopy measurement was carried out to study the
valence state of different elements of MPM-C6V-SO3CF3-IL (DMF). Fig. 3a displayed
three peaks at binding energies of 292.2, 288.5 and 284.8 eV, which were assigned to
C−F, C−N, and C−C bonds, respectively. It confirmed the ionic liquid functionalized
on the mesoporous and macroporous polymers. As shown in Fig. 3b, F1s peak was
located at 688.1 eV, besides, N1s peaks at 401.4 and 400.1 eV were associated with
N−C bonds (Fig. 3c). The O1s exhibited a single peak at around 531.7 eV (Fig. 3d),
which corresponds to O atoms in SO3CF3. As shown in Fig. 3e, S2p peaks at 168.4 eV
were assigned to S–O bonds. These data were in good agreement with the presence of
C6V-SO3CF3 in the sample [3134]
.

Fig. 3. XPS spectra of (a) C1s, (b) F1s, (c) N1s, (d) O1s, (e) S2p, (f) wide-scan
survey in MPM-C6V-SO3CF3-IL (DMF)
According to above analysis, the purity of the product was ascertained by various
compositional techniques (FT-IR and XPS)，and results indicated that alkyl and ionic
liquid groups have been incorporated on the copolymer of N,N’-Methylenebis
(acrylamide) and vinylimidazole.

Fig. 4 showed transmission electron microscopy (TEM) images of specific
synthesize step of MPM-C6V-SO3CF3-IL and cross-linked poly acidic ionic liquids
synthesized from different solvent. Abundant net-like hierarchical mesopores and
macropores can be found in the sample. It is obviously that following acidification had
little destruction on the multiporous structure of original sample. In addition,
multiporous network could be clearly found by introducing cross-linking agent M.
Notably, the solvent of MPM-V played an important role in controlling the structure of
final catalyst. In other words, heterogeneous catalysts cross-linked poly acidic ionic
liquids showed different morphology in different solvents. Specifically, MPM-C6V-
SO3CF3-IL (acetone) occupied blocky-shaped particles and heaped up together to form
interspaces. MPM-C6V-SO3CF3-IL (DMF) showed stable and multilayer network,
while, cross-linked poly acidic ionic liquids synthesized from IPA displays irregularly
network. Morphology of different cross-linked poly acidic ionic liquids had enormous
effects on catalyst performance. In contrast with blocky-shaped particles structure, the
net-like mesoporous and macroporous structure not only facilitated the diffusion of
reactants and heat, but also provided high exposition degree of active sites. Moreover,
network with uniform pore distribution, promoting the dispersion of reactant molecules.
It could be seen that MPM-C6V-SO3CF3-IL (DMF) with stable network, meanwhile,
possessing abundant mesopores and macropores (Fig. 4e).

Fig.4. transmission electron microscopy (TEM) images of specific synthesize
step of MPM-C6V-SO3CF3-IL and cross-linked poly acidic ionic liquids synthesized
from different solvent: (a) MPM-V (DMF), (b) MPM-C6V (DMF), (c) MPM-C6V-
SO3CF3-IL (DMF), (d) MPM-C6V-SO3CF3-IL (IPA), (e) MPM-C6V-SO3CF3-IL
(DMF), (f) MPM-C6V-SO3CF3-IL (acetone)
Fig. 5 shows scanning electron microscope (SEM) images of specific synthesize
step of MPM-C6V-SO3CF3-IL and cross-linked poly acidic ionic liquids synthesized
from different solvents, which were in good agreement with TEM results. From a level
of relatively macroscopical micron order, it can be clearly found the differences among
the cross-linked poly acidic ionic liquids synthesized in different synthesize solvents.
The network of cross-linked poly acidic ionic liquids kept stable during the whole
synthesis process. Multilayer and pores were related to the introduction of cross-linking
agent M, and can be demonstrated by Fig.5 (a-c). Fig.5 (d-f) give differences on
morphology of final sample synthesized in various solvent, certifying the solvent had

inevitable influence on the synthesis of cross-linked poly acidic ionic liquids. Only
MPM-C6V-SO3CF3-IL (DMF) shows special network among all the samples. And a
net-like structure with rough and loose surfaces of MPM-C6V-SO3CF3-IL (DMF) may
be ascribed to the presence of abundant mesopores and macropores in the catalyst,
which benefited the exposure of active sites and finally enhanced the catalytic activity.
In contrast, most active sites of the blocky-shaped of cross-linked poly acidic ionic
liquids, focus on the interspace between particles, which provided passage for reactant
molecules at the same time. Thus, synthesis solvents of cross-linked poly acidic ionic
liquids influenced the morphology of catalysts and catalytic activity.
Fig.5 scanning electron microscope (SEM) images of specific synthesize step of
MPM-C6V-SO3CF3-IL and cross-linked poly acidic ionic liquids synthesized from
different solvent: (a) MPM-V (DMF), (b) MPM-C6V (DMF), (c) MPM-C6V-SO3CF3-
IL (DMF), (d) MPM-C6V-SO3CF3-IL (IPA), (e) MPM-C6V-SO3CF3-IL (DMF), (f)
MPM-C6V-SO3CF3-IL (acetone)

From the image of TG curves of different cross-linked poly acidic ionic liquids,
which was showed in Fig. 6, we can have a clear recognition that thermal
decomposition of catalyst was generally divided into three parts. Every part of down
trend represents the decomposition of a kind of monomer. At the original part,
decomposition probably referred to solvent, and then monomer of polymer began to
decompose at about 150 °C. From then on, major bond between cross-linking M and V
started to decompose at 300 °C. Finally, the whole cross-linked poly acidic ionic liquids
were decomposed thoroughly over 600 °C. Overall, the synthesized catalyst occupied
heat stability to some extent, specifically, keep stable under relatively lower
temperature (below 300 °C), which definitely fits to the alkylation of o-xylene and
styrene.
Fig.6. TG curves of (a) MPM-C6V-SO3CF3-IL (DMF), (b)MPM-C6V-SO3CF3-IL
(acetone), (c) MPM-C6V-SO3CF3-IL (IPA)

To measure the specific pores distribution of final cross-linking poly acidic ionic
liquid, BET analysis was carried out and the results were exhibited in Fig. 7. As
demonstrated in Fig. 7b, the sample MPM-C6V-SO3CF3-IL (DMF) shows a type-IV
curve with a sharp capillary condensation step at p/p0 of 0.5-1.0, indicating the
existence of mesopores and macroporous in the sample. Correspondingly, its pore size
was mainly distributed at 40 nm and 5 nm (Fig. 7a), besides, parts of pore size
distributed at over 80 nm. To a great extent, the smaller pores were formed due to cross-
linking. Compared with cross-linking poly acidic ionic liquids synthesized from
different solvents, the sample synthesized in DMF exhibited a relatively higher surface
area (103.83 m2/g) and larger pore volume (0.72 cm3/g) than that of samples
synthesized in acetone and IPA (surface area 13.19 m2/g and 80.96 m2/g, pore volume
0.16 cm3/g and 0.65 cm3/g, respectively), which was favorable for good catalytic
activity.
Fig.7. N2 adsorption-desorption isotherm (a) and Pore size distribution (b) of
MPM-C6V-SO3CF3-IL

3.2. Catalytic performace evaluation
3.2.1 Effect of the reaction temperature
A serious of factors optimization have been made in following for evaluating
catalyst performance, moreover, specific procedure of alkylation of o-xylene and
styrene was show on Fig. 8. Temperature of reaction was confirmed as principal factor.
In a specific routes of optimization, the addition of catalysts were indentical controlled
in a certain amount of 0.05 g, and then change the temperature of reaction，40 °C，
60 °C, 80 °C, 100 °C, 120 °C，respectively. Styrene conversion rate (%) was confirmed
as one of standard of catalyst performance, which was detected by gas chromatograph,
GC 9890A. The results showed that styrene conversion rate (%) gradually increased as
the temperature went up. Even at the temperature of 120 °C，styrene conversion rate
(%) reached 100 %. On the one hand, it can be concluded that the alkylation of o-xylene
and styrene suit a relatively higher temperature condition, and styrene can achieve
almost conversion under this temperature. On the other hand, the yield of PXE
advanced by the addition of catalyst, but still is not good enough under a relatively
lower addition of catalyst cross-linked poly acidic ionic liquids, with the best PXE yield
just 72.17 %. Naturally, it is needed to make deeper discussion on other factors which
have a connection with PXE yield (%).

Fig. 8. Reaction scheme of alkylation of o-xylene with styrene over a
heterogeneous catalyst.
3.2.2 Effect of the MPM-C6V-SO3CF3-IL amount
After confirm the adequate reactant temperature 120 °C，a deeper discussion on
the PXE yield (%) from the aspect of addition of catalyst MPM-C6V-SO3CF3-IL have
been made. It is noteworthy that addition of catalyst made a great effect on the whole
alkylation of o-xylene and styrene. PXE yield (%) increased with the increasing of
catalyst amount. There is no doubt that active sites increased by the addition of catalysts.
Under same react temperature, more catalysts provide more active sites for the
transformation of both reactants and products. In comparison with different addition of
cross-linked poly acidic ionic liquids MPM-C6V-SO3CF3-IL, it can be found that PXE
yield almost achieve 100 % with 0.17 g catalyst.

3.2.3 Effect of the solvent system
Solvents of precursor mesoporous polymer make enormous effects on the whole
structure of final sample, which can be proved by TEM and SEM of MPM-C6V-
SO3CF3-IL (Fig. 4 & Fig. 5). DMF as an excellent solvent can dissolve kinds of organics,
similarly, M and V can be dissolved completely in DMF, and then cross-linking
polymerization can be carried definitely through hydrothermal method. The radical of
cross-linking reaction decided the stability of network of cross-linked poly acidic ionic
liquids. In other words, more radically of the cross-linking reaction have been carried,
more stable and pyknotic network was formed. Compared with other different solvents,
the solubleness of M and V in IPA and acetone were far from DMF, which results in
abnormal structure, partly network and blocky-shaped, respectively. These two kinds
of structure possess intuitively less active sites compared with network, leading not
good enough catalytic performance during the alkylation of o-xylene and styrene.
Styrene was transformed during the reaction with catalyst MPM-C6V-SO3CF3-IL
(DMF), with yields of PXE up to 99.67 % (Table 1). In contrast, the yields of PXE
catalyzed by MPM-C6V-SO3CF3-IL (IPA) and MPM-C6V-SO3CF3-IL (acetone) were
relatively lower, with the yield of PXE at 91.68 % and 90.43 %, respectively. Finally,
the results was collected as following (Table1), and the optimum conditions (reaction
time was 3h, reaction temperature was 120 °C, catalyst amount was 0.17 g (0.5 wt %),
and o-xylene/styrene mass ratio was 7.5:1) was obtained.

Table1 yield of 1,2-diphenylethylane and conversion of styrene in the alkylation of o-
xylene and styrene catalyzed by various cross-linked poly acidic ionic liquids
Styrene
1,2-
addition( Temperatu conversio Diphenylet
Catalyst
re（°C）
g)
n rate
(%)a
36.78
57.5
82.73
93.46
100
hylane
yield (%)a
29.31
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(DMF)
MPM-C6V-SO3CF3-IL(IPA)
MPM-C6V-SO3CF3-
0.05
0.05
0.05
0.05
0.05
0.003
0.02
0.08
0.17
0.17
0.17
40
60
80
33.49
43.78
58.84
72.86
100
120
120
120
120
120
120
120
100
25.55
100
32.15
100
90.05
100
99.67
100
91.68
100
90.43
IL(acetone)
a Measured by gas chromatograph, detection condition: initial temperature 150°C, hold
time was 2 min, heating rate was 5 °C /min, final temperature was 250 °C, hold time
was 2 min, the whole detection time was 0.5 h. Styrene conversion rate (%) and 1,2-
diphenylethylane yield (%) was calculated by area normalization method.
According to our previous work and as listed in Table 2, Sheng et al. [35] found that pure
HPW showed high catalytic performance for the reaction, however, it was difficult for
separation and recovery. Furthermore, HPW/SBA-15 catalyst exhibited high
conversion, while, showed the low product yield (68.3%) in their work. Besides, Zhao
[36]
et. al
found that HPW/PIL-30-393 with large pore size of the support exhibited
excellent catalytic performance, but styrene conversion and PXE yield still not high
enough. From Table 2, it is found that MPM-C6V-SO3CF3-IL(DMF) shows much
higher conversion (100%) and higher yield (99.7%) than those of other catalysts. It is

noteworthy that the addition of catalyst is only 0.5wt% much fewer than other catalysts
with 2wt%
Table 2 Activity of HPW catalystsa and MPM-C6V-SO3CF3-IL(DMF) in alkylation of
o-xylene with styrene
Catalyst
HPWc
Styrene Conversion(%) PXE Yieldb (mol/g cat)
100
91
1.86
1.30
1.74
1.73
7.59
HPW/SBA-15-PS
HPW/SBA-15-DS
HPW/PIL-30
100
95.9
100
MPM-C6V-SO3CF3-IL(DMF)
a Reaction conditions: o-xylene : styrene = 7.5 : 1, reaction temperature=393 K, reaction
time = 3.0 h, catalyst loading = 20% (w/w of styrene).
b Isolated yield based on the amount of styrene.
c Homogeneous catalyst, 0.30 g.
3.2.4 Recyclability of MPM-C6V-SO3CF3-IL (DMF) catalyst
Recycling utilization of catalyst could be another effective way to judge the
performance of catalysts, besides the heat stability showed by TGA. Although the
activity of catalyst showed great performance during the alkylation of o-xylene and
styrene, which can be proved by both the styrene conversion rate (%) and 1,2-
diphenylethylane yield (%), stability still need to be considered. It is noteworthy that
the recycling of the catalyst that we made was not stable as we expected. Take the
MPM-C6V-SO3CF3-IL (DMF) as an example, it has a rapid decline since the first

catalyst reaction, with the yield of PXE from 99.67 % down to 46.11 % after 4 times
recycling. After reaction of alkylation of o-xylene and styrene, structure of catalyst was
destroyed, for the reason that amido bond in poly acidic ionic liquid can be destroyed
under higher temperature. In addition, part of acidic group SO3CF3 may stay in the
solvent of reactants, which can be proved by the directly orange color of reaction
product and weaker transmittance reflect on the FT-IR compared with sample which
before catalyst reaction (Fig. 9). This may be the reason for the lower recycling
utilization.
Fig. 9. Recycling of catalyst (MPM-C6V-SO3CF3-IL(DMF)) (a); FT-IR spectrum
of before reaction and after reaction(b)；TEM of MPM-C6V-SO3CF3-IL(DMF) after
alkylation of o-xylene and styrene (c); SEM of MPM-C6V-SO3CF3-IL(DMF) after

alkylation of o-xylene and styrene (d)
3.3. Plausible catalyst synthesis mechanism
Fig.10. plausible synthesis mechanism for MPM-C6V-SO3CF3-IL catalyst
According to above specific analysis of catalyst from different kinds of aspects, a
plausible catalyst synthesis mechanism can be come up with (Fig.10). Cross-linked
poly acidic ionic liquids shows excellent catalytic activity in alkylation of o-xylene and
styrene, due to the special mesoporous and macroporous structure. Acidic functional
group SO3CF3 was introduced to the acidic condition of alkylation, which provide great
possibility for the activity performance of catalyst. With the help of cross-linking regent
M, an initial network can be architected through the first strict hydrothermal
polymerization, which can be clearly seen from the image (Fig. 4 and Fig. 5). It is
noteworthy that the introduction of cross-linking regent M enhanced the stability and
compactness of whole network structure to some extent. Moreover, the cross-linking

degree of first step controlled the pore diameter and distribution. Besides energy
between covalent bond, the interaction between cation and anion also enhanced whole
stability of network structure. Anion exchange keeps original network stable after
functionalization of the cross-linking poly ionic liquids, realized the synthesis of acid-
functional catalyst. Mesopores and macropores of MPM-C6V-SO3CF3-IL (DMF) have
little change during the process of synthesis. Moreover, the obtained sample was in
solid and the catalyst after reaction can be easily separated from the solution. Except
for the recycling was not fit to our expectation, catalysts were completely up to the
standard of green chemistry. After reaction of alkylation of o-xylene and styrene, part
of acidic group SO3CF3 may stay in the solvent of reactants, which can be proved by
the directly orange color of reaction product and weaker transmittance reflect on the
FT-IR compared with sample which before catalyst reaction. This may be the reason
for the lower recycling utilization.
4. Conclusion
In summary, a novel cross-linked poly acidic ionic liquids catalyst for efficient
alkylation of o-xylene and styrene was synthesized through free radical polymerization
and ionic change. The polymer composite was characterized by different techniques,
and results demonstrated that nanoporous polymeric network was multi-layered and
exhibited repeating units of SO3CF3. The combination of mesopores and macropores
would significantly reduce the limitation of mass transfer in alkylation of o-xylene and
styrene and finally promote the catalytic performance compared with other porous solid

acidic catalysts. Besides, cross-linked poly acidic ionic liquids as a heterogeneous
acidic catalyst can be easily separated from the solvent. The catalytic performance of
the cross-linked poly acidic ionic liquids was discussed from three aspects, temperature,
addition of catalyst, solvent, respectively. Under the optimum conditions (reaction time
was 3h, reaction temperature was 120°C, catalyst amount was 0.17g (0.5 wt%), and o-
xylene/styrene mass ratio was 7.5:1), a high conversion of styrene (100 %) and 1,2-
diphenylethane (PXE) yield of 99.67 % was obtained. This study may help develop
green routes for reactions under acid condition such as transesterification, esterification,
Friedel-Crafts reaction and so on.
Acknowledge
The authors are grateful to the financial supports of the National Natural Science
Foundation of China (Grant No. 21676056, 21376051, 51673040 and 21306023), ‘‘Six
Talents Pinnacle Program’’of Jiangsu Province of China (JNHB-006), Qing Lan Project
of Jiangsu Province (1107040167), Graduate student scientific research innovation
program of Jiangsu Province (KYCX17_0134 and KYCX17_0136), Scientific
Research Foundation of Graduate School of Southeast University (YBJJ1732,
YBJJ1733, YBJJ1731), Fund Project for Transformation of Scientific and
Technological Achievements of Jiangsu Province of China (Grant No. BA2014100),
Fundamental Research Funds for the Central Universities (2242015k30001,
3207047402, 3207046409) and A Project Funded by the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD) (1107047002).

Reference
[1] Sheng X, Zhou Y, Zhang Y, Duan Y, Zhang Z, Yang Y. Immobilization of 12-
Tungstophosphoric acid in alumina-grafted mesoporous LaSBA-15 and its
catalytic activity for alkylation of o-xylene with styrene. Micropor. Mesopor. Mat.
2012; 161: 25-32.
[2] Malshe VC, Sujatha ES. Phenol based resin as alkylation catalyst. React Funct
Polym. 2000; 43(1-2): 183-194.
[3] Sun XJ, Zhou XM, Cao BB, Cao ZP, Fu H, Green synthesis of 1-phenyl-1-ortho-
xylene ethane in IL and reaction mechanism. RSC Adv. 2017; 7, 14998.
[4] Zhao ZK, Li ZS, Wang GR, Qiao WH, Cheng LB, Friedel–Crafts alkylation of 2-
methylnaphthalene in room temperature ionic liquids. Applied Catalysis A:
General. 2004; 262, 69.
[5] Cao BB, D JY, C ZP, S HT, S XJ, F H. Theoretical study on the alkylation of o-
xylene with styrene in AlCl3-ionic liquid catalytic system. Journal of molecular
graphics & modelling. 2017; 74, 8.
[6] Ho WK, Zhang ZZ, Xu MK, Zhang XW, Wang XX, Huang Y. Enhanced visible-
light-driven photocatalytic removal of NO: Effect on layer distortion on g-C3N4
by H-2 heating. Appl Catal B-Environ. 2015; 179: 106-112.
[7] Li DF, Mao D, Li J, Zhou Y, Wang J. In situ functionalized sulfonic copolymer
toward recyclable heterogeneous catalyst for efficient Beckmann rearrangement
of cyclohexanone oxime. Appl Catal a-Gen. 2016; 510: 125-133.
[8] Wei YC, Jiao JQ, Zhao Z, Liu J, Li JM, Jiang GY, Wang YJ, Duan AJ. Fabrication

of inverse opal TiO2-supported Au@CdS core-shell nanoparticles for efficient
photocatalytic CO2 conversion. Appl Catal B-Environ. 2015; 179: 422-432.
[9] Liu F, Wang L, Sun, Q, Zhu L, Meng X, Xiao FS. Transesterification catalyzed by
ionic liquids on superhydrophobic mesoporous polymers: heterogeneous catalysts
that are faster than homogeneous catalysts. J Am Chem Soc. 2012; 134(41): 16948-
16950.
[10] Shi HF, Li JH, Jin YM, Yin YP, Zhang XX. Preparation and properties of
poly(vinyl alcohol)-g-octadecanol copolymers based solid-solid phase change
materials," Mater. Chem. Phys. 2011; 131(1-2): 108-112.
[11] Shen LQ, Yin HB, Wang AL, Feng YH, Shen YT, Wu ZA, Jiang TS. Liquid phase
dehydration of glycerol to acrolein catalyzed by silicotungstic, phosphotungstic,
and phosphomolybdic acids. Chem. Eng. J. 2012; 180: 277-283.
[12] Zhao S, He M, Zhou YM, Sheng XL, Fu XQ, Zhang YW. Synthesis of
micro/mesoporous silica material by dual-template method as a heterogeneous
catalyst support for alkylation. RSC Adv. 2015; 5(36): 28124-28132.
[13] Busca G. Acid catalysts in industrial hydrocarbon chemistry. Chem. Rev. 2007;
107(11): 5366-5410.
[14] Deng WP, Liu M, Zhang QH, Tan XS, Wang Y. Acid-catalysed direct
transformation of cellulose into methyl glucosides in methanol at moderate
temperatures. Chem. Commun. 2010; 46(15): 2668-2670.
[15] Corma A, Garcia H. Lewis acids: From conventional homogeneous to green
homogeneous and heterogeneous catalysis. Chem. Rev. 2003; 103(11): 4307-4365.

[16] Liu F, Kamat RK, Noshadi I, Peck D, Parnas RS, Zheng A, Qi C, Lin Y.
Depolymerization of crystalline cellulose catalyzed by acidic ionic liquids grafted
onto sponge-like nanoporous polymers. Chem. Commun. 2013; 49(76): 8456-8458.
[17] Yuan JY, Mecerreyes D, Antonietti M. Poly(ionic liquid)s: An update. Prog. Polym.
Sci. 2013; 38(7): 1009-1036.
[18] Blanchard LA, Hancu D, Beckman EJ, Brennecke JF. Green processing using ionic
liquids and CO2. Nature. 1999; 399(6731): 28-29.
[19] Dupont J, de Souza RF, Suarez PAZ. Ionic liquid (molten salt) phase
organometallic catalysis. Chem. Rev. 2002; 102(10): 3667-3691.
[20] Armand M, Endres F, MacFarlane DR, Ohno H, Scrosati B. Ionic-liquid materials
for the electrochemical challenges of the future. Nat. Mater. 2009; 8(8): 621-629.
[21] Li DF, Li J, Mao D, Wen HM, Zhou Y, Wang J. Direct synthesis of sulfonic group
tethered mesoporous poly(ionic liquid) for catalyzing deoximation reactions.
Mater. Chem. Phys. 2017; 189: 118-126.
[22] Lin BC, Qiu LH, Lu JM, Yan F. Cross-Linked Alkaline Ionic Liquid-Based
Polymer Electrolytes for Alkaline Fuel Cell Applications. Chem. Mat. 2010;
22(24): 6718-6725.
[23] Yuan C, Guo JN, Si ZH, Yan F. Polymerization in ionic liquid-based
microemulsions. Polym. Chem. 2015; 6(22): 4059-4066.
[24] G Y, Wu J, Zhang W, Tan Y, Tang A, Men Y, Tang B. Deep oxidation
desulfurization with a new imidazole-type acidic ionic liquid polymer. RSC Adv.
2014; 102(4): 5.

[25] Wu ZW, Chen C, Guo QR, Li BX, Que YG, Wang L, Wan H, Guan GF. Novel
approach for preparation of poly (ionic liquid) catalyst with macroporous structure
for biodiesel production. Fuel. 2016; 184: 128-135.
[26] Bara JE, Gabriel CJ, Lessmann S, Carlisle TK, Finotello A, Gin DL, Noble RD.
Enhanced CO2 separation selectivity in oligo(ethylene glycol) functionalized
room-temperature ionic liquids. Ind. Eng. Chem. Res. 2007; 46(16): 5380-5386.
[27] Zhou T, Gao XP, Dong B, Sun N, Zheng LQ. Poly(ionic liquid) hydrogels
exhibiting superior mechanical and electrochemical properties as flexible
electrolytes. J. Mater. Chem. A 2016; (4): 7.
[28] Freitas FS, de Freitas JN, Ito BI, De Paoli, MA, Nogueira AF. Electrochemical and
Structural Characterization of Polymer Gel Electrolytes Based on a PEO
Copolymer and an Imidazolium-Based Ionic Liquid for Dye-Sensitized Solar
Cells. ACS Appl. Mater. Inter. 2009; 1(12): 2870-2877.
[29] Amarasekara AS. Acidic Ionic Liquids. Chem. Rev. 2016; 116(10): 6133-6183.
[30] Liang XZ, Xiao HQ, Qi CZ. Efficient procedure for biodiesel synthesis from waste
oils using novel solid acidic ionic liquid polymer as catalysts. Fuel Process.
Technol. 2013; 110: 109-113.
[31] Amarasekara AS, Nguyen J, Razzaq A. Acidic ionic liquid polymers: poly(bis-
imidazolium-p-phenylenesulfonic acid) and applications as catalysts in the
preparation of 1-amidoalkyl-2-naphthols. J. Polym. Res. 2017;24(3).
[32] Soll S, Zhao Q, Weber J, Yuan JY. Activated CO2 Sorption in Mesoporous
Imidazolium-Type Poly(ionic liquid)-Based Polyampholytes. Chem. Mat. 2013;