Supported phosphotungstic acid catalyst on mesoporous carbon with bimodal pores: A superior catalyst for Friedel-Crafts alkenylation of aromatics with phenylacetylene

Article abstract of DOI:10.1016/j.apcata.2016.08.028

Supported phosphotungstic acid (PTA) catalysts on diverse carriers containing the modified commercially available activated carbon (AC), classical mesoporous carbon via SBA-15 hard template method (CMK-3), and the mesoporous carbon with high surface area and bimodal pores through evaporation-induced tri-constituent co-assembly approach (MC) by using a facile wet impregnation method were employed as solid acid catalysts for Friedel-Crafts alkenylation of p-xylene with phenylacetylene. N₂ adsorption–desorption, X-ray diffraction (XRD), and NH₃ temperature-programmed desorption (NH₃-TPD) characterization techniques were employed to reveal the structure-performance relationship. PTA/MC exhibits much superior catalytic performance to the previously reported PTA/AC, and even to PTA/CMK-3. The PTA/MC catalysts were optimized by varying the PTA loading, and the optimum PTA loading is 35%. The close to 100% of conversion towards phenylacetylene can be achieved in the presence of 2.67% of the 35% PTA/MC solid acid catalyst. It is also found that catalytic properties of the solid acids are strongly depended on acidic properties that affected by the textural properties of supports and PTA loading, as well as the accessibility of active sites affected by specific surface area and pore structure of catalyst. Moreover, the 35?wt.% PTA/MC catalyst has demonstrated outstanding catalytic performance for the Friedel-Crafts alkenylation of diverse aromatics to their corresponding α-arylstyrenes.

Full text of DOI:10.1016/j.apcata.2016.08.028

Applied Catalysis A: General 526 (2016) 139–146
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Applied Catalysis A: General
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Supported phosphotungstic acid catalyst on mesoporous carbon with
bimodal pores: A superior catalyst for Friedel-Crafts alkenylation of
aromatics with phenylacetylene
Zhongkui Zhao∗, Xianhui Wang
State Key Laboratory of Fine Chemicals, Department of Catalysis Chemistry and Engineering, School of Chemical Engineering, Dalian University of
Technology, 2 Linggong Road, Dalian, 116024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 June 2016
Received in revised form 26 August 2016
Accepted 27 August 2016
Available online 28 August 2016
Supported phosphotungstic acid (PTA) catalysts on diverse carriers containing the modified commer-
cially available activated carbon (AC), classical mesoporous carbon via SBA-15 hard template method
(CMK-3), and the mesoporous carbon with high surface area and bimodal pores through evaporation-
induced tri-constituent co-assembly approach (MC) by using a facile wet impregnation method were
employed as solid acid catalysts for Friedel-Crafts alkenylation of p-xylene with phenylacetylene. N2
adsorption–desorption, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (NH3-
TPD) characterization techniques were employed to reveal the structure-performance relationship.
PTA/MC exhibits much superior catalytic performance to the previously reported PTA/AC, and even to
PTA/CMK-3. The PTA/MC catalysts were optimized by varying the PTA loading, and the optimum PTA
loading is 35%. The close to 100% of conversion towards phenylacetylene can be achieved in the presence
of 2.67% of the 35% PTA/MC solid acid catalyst. It is also found that catalytic properties of the solid acids
are strongly depended on acidic properties that affected by the textural properties of supports and PTA
loading, as well as the accessibility of active sites affected by specific surface area and pore structure of
catalyst. Moreover, the 35 wt.% PTA/MC catalyst has demonstrated outstanding catalytic performance for
the Friedel-Crafts alkenylation of diverse aromatics to their corresponding ␣-arylstyrenes.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Mesoporous carbon
Phosphotungstic acid
Support effect
Alkenylation
Clean synthesis
1. Introduction
the broad use of zeolites as solid acid catalysts in alkenylation
[6–8]. Nowadays, the rare report on zeolite mediated alkenyla-
Alkenylation of aromatic compounds by alkynes has become
a direct and efficient strategy for synthesizing alkenylaromatics,
which serve as industrially important intermediates for producing
pharmaceuticals, agrochemicals, natural products, flavors and dyes
[1–5].
Heterogeneous catalysis presents a promising approach for
organic transformations with respect to its clean, easy-separation,
catalyst reusability, and its applicability toward continuous pro-
duction in a large scale. Owing to their regular pore channels,
a large amount of acidic sites, corrosion-resistance, and environ-
mentally benign feature, zeolites have attracted great attention in
Friedel-Crafts alkylation in academic and industrial fields [9–12].
However, the serious coke deposition due to the narrow pore chan-
nels of zeolites and the stability of vinyl cation species depresses
tion can be found. Sartori did a pioneering work on alkenylation
of aromatics over HSZ-360 zeolite [13]. Unfortunately the results
are not very satisfactory, and there is an irreconcilable contra-
diction between the selectivity and catalytic activity. The zeolites
calcined at lower temperature exhibited high catalytic activity, but
the considerable amount of acetophenone (5–20%) was detected;
the higher calcination temperature could efficiently compress the
formation of acetophenone, but led to remarkable decrease in the
catalytic activity. Moreover, HY demonstrated low catalytic effi-
ciency for the alkenylation, ascribed to the reaction only taking
place on the external surface of the catalyst because of its narrow
pore channels within. Besides the relatively low catalytic effi-
ciency, the enlargement in scope of substrates for alkenylation over
zeolites is also desirable. Recently, it was demonstrated that the Fe-
containing mesoporous alluminosilicate exhibited vey high activity
for the Friedel–Crafts alkenylation of phenols with aryl-substituted
alkynes under mild conditions [14]. However, the further increase
in selectivity is indispensable. Therefore, the development of novel
∗
Corresponding author.
E-mail address: zkzhao@dlut.edu.cn (Z. Zhao).
http://dx.doi.org/10.1016/j.apcata.2016.08.028
0926-860X/© 2016 Elsevier B.V. All rights reserved.

140
Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
Table 1
and robust solid acid catalysts for Friedel–Crafts alkenylation is
highly desirable, but it still remains a challenge.
Textural properties of the as-prepared supported PTA catalysts on diverse carriers
and the bare supports.
The heteropolyacid (HPA) has been demonstrated to act as an
efficient solid acid catalyst for alkylation, owing to its strong acid-
ity and Brønsted type. Among them, PTA is usually employed as a
good catalyst for its high acidic strength and relatively high thermal
stability [15]. But its lower surface area (about 5–8 m2/g) is a seri-
ous drawback while it serves as a heterogeneous catalyst. To load
HPA on a support with large specific surface area demonstrated
to be an efficient approach to address this issue. The supported
PTA catalysts on diverse supports have demonstrated outstanding
catalytic properties for various organic transformations [16–20].
It was previously demonstrated that the supported PTA catalyst
on MCM-41 under optimized conditions exhibited good catalytic
performance in alkenylation [6]. However, further improvement in
catalytic activity, selectivity and the expansion in reactants scope
are required. Moreover, the high cost of ordered mesoporous sil-
ica due to its complex and high cost preparation process limits its
use in a large scale. The AC production from agricultural waste,
lignocellulosics and plant origin could be considered as a simple
protocol to obtain high-added value products from low cost raw
materials and even wastes, as well as to resolve environmentally
pollution problems in some degree. The pristine and modified AC
with high surface area has been considered as a promising sup-
port for preparing supported metal catalysts. Moreover, the ability
for facile recovery of the active metals and high stability in acidic
and basic media are its visible advantages in comparison with the
oxide supports. From literature [21], the modified AC by oxida-
tion pretreatment can serve as a promising carrier for supported
PTA catalysts for Friedel-Crafts alkenylation. However, the narrow
microporous channels of AC may confine the diffusion of substrate
which leads to the formation of more oligmer and the poor stability,
besides lead to unsatisfactory catalytic activity.
The ordered mesoporous structure and large specific sur-
face area of mesoporous carbon endow it with many merits for
being used as supports towards preparing supported type cata-
lysts in comparison with AC [22–26]. Herein, the two kinds of
mesoporous carbon materials containing CMK-3 and MC were
prepared and used to serve as support for synthesizing sup-
ported PTA solid acid catalysts. The catalytic performance of the
PTA/CMK-3, PTA/MC, as well as the previously developed PTA/AC
[21] for Friedel-Crafts alkenylation of p-xylene with phenylacety-
lene was measured. N2 adsorption–desorption, X-ray diffraction
(XRD), and NH3 temperature-programmed desorption (NH3-TPD)
characterization techniques were employed to reveal the structure-
performance relationship. PTA/MC exhibits much superior catalytic
Samples
SBETa(m2 g−1
)
VBJHb(m3 g−1
)
Smicc(m2 g−1
)
Vmicd(m3 g−1
)
AC
799
547
797
0.19
0.12
1.1
0.6
1.7
741
505
–
–
–
0.37
0.25
–
–
–
30% PTA/AC
CMK-3
30% PTA/CMK-3 497
MC
30% PTA/MC
1539
1010
1.0
–
–
a
Denoted as the BET specific surface area.
b
c
Denoted as the BJH pore volume from the adsorption branch.
Denoted as micropore surface area by t-plot method.
Denoted as micropore volume by t-plot method.
d
performance to the previously reported PTA/AC, and even to
PTA/CMK-3. The PTA loading of PTA/MC solid acid catalysts and the
dosage of PTA/MC catalyst were optimized. The close to 100% of
conversion towards phenylacetylene can be achieved in the pres-
ence of 2.67% of the 35% PTA/MC solid acid catalyst. It is also found
that catalytic properties of the solid acids are strongly depended on
acidic properties that affected by the textural properties of supports
and PTA loading, as well as the accessibility of active sites affected
by specific surface area and pore structure of catalyst. Moreover, the
as-prepared 35 wt.% PTA/MC catalyst has demonstrated outstand-
ing catalytic performance for the clean synthesis of ␣-arylstyrenes
through Friedel-Crafts alkenylation of diverse aromatics.
2. Experimental
2.1. Catalyst preparation
A commercially available AC (Aladdin, China) was ground into
final particles (less than 125 ␮m) for use. The AC surface modi-
fication process via H2O2 oxidation pretreatment was performed
as follows: 10 g AC was immersed into a 35 wt.% H2O2 aqueous
solution (5 ml g−1 AC) in a water–ice bath with continuously stir-
ring for 6 h. The sample was filtered, washed with deionized water,
and followed by drying at 105 ◦C overnight. The classical CMK-
3 was synthesized with SBA-15 as structure-directing agent and
sucrose as carbon source according to the typical procedure in the
previous reports [27,28]. Briefly, a solution obtained by dissolving
1.25 g of sucrose and 0.14 g of H2SO4 in 5 g of H2O was injected
with another 1 g of SBA-15 to form a milky homogeneous sus-
pension. The mixture was placed in a drying oven at 100 ◦C for
6 h and then at 160 ◦C for another 6 h. The sample turned dark
brown or black during the treatment in the oven. The sample was
treated with the same temperature and time after the addition of
0.8 g of sucrose, 0.09 g of H2SO4 and 5 g of H2O. The carbonization
was completed by pyrolysis with heating to typically 900 ◦C under
vacuum. The as-obtained carbon-silica composite after pyrolysis
was washed with 5 wt% hydrofluoric acid at room temperature,
to remove the silica template. The template-free carbon product
thus obtained was filtered to neutral, washed with ethanol, and
dried at 393 K overnight. The mesoporous carbon MC was fab-
ricated with a commercially avlaible surfactant block copolymer
F127 (EO106PO70EO106, Sigma-Aldrich) and something strong
was needed to support the MC, thus extra Tetraethyl orthosili-
cate (TEOS) was added into the mixture [29,30]. Carbon source
resol ethanolic solution was prepared as follows: 10 g phenol was
melt, and then 2.3 g 20 wt% NaOH solution was dropwise added
into melting phenol, after stirring for 10 min, 17.7 g 37 wt.% HCHO
solution was dropwise added into the above solution, and then
the reaction mixture was heated up to 70 ◦C and maintained at
this temperature for 1 h. After that, the mixture is cooled to room
temperature, and pH value was adjusted to 6 by adding 2 M HCl
Fig. 1. Reaction results for the alkenylation of p-xylene with phenylacetylene
over supported PTA catalysts on diverse carriers. Reaction conditions: Wcat = 1.33%;
nAr/Phen = 10; Tr = 150C; Pr = 1.0 MPa; t = 4 h.

Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
141
Fig. 2. N2 adsorption–desorption isotherms (a,b) and Barrett–Joyner–Halenda (BJH) pore diameter distribution from adsorption branch (c,d) of the AC, CMK-3 and MC
supports (a,c) and their corresponding supported PTA catalysts (b,d).
solution. The resol was obtained after rotary evaporation, and
then Carbon source resol ethanolic solution was obtained by dis-
solving the resol solid into ethanol. The mesoporous carbon (MC)
was synthesized by previously reported evaporation-induced tri-
constituent co-assembly approach. Briefly, 5.2 g of Pluronic F127
was dissolved in a solution of 26.0 g of ethanol with 3.25 g of HCl and
stirred at 40 ◦C for 1 h. Then, TEOS and resol ethanolic solution were
added into forementioned mixture. After additional stirring for 2 h,
ethanol evaporation was carried out, and then the resulting solid
was thermo-polymerized at 100 ◦C for 24 h. The resultant products
were scraped from the dish and carbonized under N2 atmosphere at
350 ◦C for 3 h and 800 ◦C for 2 h in a tube furnace. Finally, the meso-
porous carbon was recovered after removing silica by HF solution.
The supported PTA catalysts were prepared by wet impregnation
method. Typically, the desired amount of PTA (analytical reagent,
AR, bought from China National Medicines Corp. Ltd.) was dissolved
into 10 ml deionized water to obtain PTA impregnant. 0.5 g of MC
was dispersed into the forementioned PTA solution. The mixture
was stirred and then stood for 24 h. The PTA impregnated catalysts
were obtained after rotary evaporation and drying at 105 ◦C in air
Fig. 3. NH3-TPD profiles of 30%PTA/AC, 30%PTA/CMK-3 and 30%PTA/MC catalysts.
overnight followed by calcinations in air at 300 ◦C for 3 h. Then the
series of PTA/MC catalysts with desired PTA loading were obtained.
iments at −196 ◦C were carried out on a Beishide 3H-2000PS1
The size of all supports is less than 125 ␮m to eliminate diffusion
instrument to measure the surface area and pore volume, and the
samples were degassed at 130 ◦C for 10 h prior to the N2 adsorp-
tion experiment. NH3-TPD measurements were performed on an
in-house constructed system equipped with a thermal conductiv-
ity detector (TCD) to measure the desorbed NH3. 50 mg sample was
loaded in quartz reactor between two quartz wool plugs, and then
was pretreated in Ar at 300 ◦C (a ramp rate of 10 ◦C min−1) for 0.5 h,
followed by cooling to room temperature. The pretreated sample
was saturated with ammonia at 100 ◦C via the pulse injection of
resistance.
2.2. Catalyst characterization
XRD patterns of the samples were recorded using a Rigaku
D/max-2400 apparatus using Cu K␣ radiation. The diffractograms
were recorded in the 2Â range 10–80◦ with a 2Â step size of 0.02◦
and a step time of 0.12 s at each point. Nitrogen adsorption exper-

142
Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
Fig. 4. Reaction results for the alkenylation of p-xylene with phenylacetylene over
PTA/MC catalysts with diverse PTA loadings. Reaction conditions: Wcat = 1.33%;
nAr/Phen = 10; Tr = 150C; Pr = 1.0 MPa; t = 4 h.
Fig. 6. N2 adsorption–desorption isotherms (a) and Barrett–Joyner–Halenda (BJH)
pore diameter distribution from adsorption branch (b) of the as-synthesized PTA/MC
catalysts with diverse PTA loadings.
Fig. 5. NH3-TPD profiles of PTA/MC catalysts with diverse PTA loadings.
of byproducts including acetophenone, ␤-(2,5-dimethylphenyl)
ethylbenzene, and oligomers were detected. As the evaluation
index, the phenylacetylene conversion was calculated by weight
percentage of the consumed phenylacetylene in the total amount
of added phenylacetylene in the reaction mixture; the selectivity
to ␣-arylstyrene was calculated by weight percentage of desired
␣-arylstyrene in total products included main and side products.
The yield corresponding ␣-arylstyrene was the GC yield, which
was calculated based on the conversion of phenylacetylene and the
selectivity of the desired products.
ammonia. The desorption process was carried out from 100 ◦C to
600 ◦C at a heating rate of 10 ◦C min−1 then kept at 600 ◦C for 30 min
with an Ar flow of 30 ml min−1
.
2.3. Catalytic performance measurement
A stainless steel autoclave reactor was employed for measuring
the catalytic performance of the as-synthesized solid acid catalysts
towards the direct alkenylation of aromatics with phenylacety-
lene. In addition to the desired amount of catalyst, 15 g reactant
mixture containing aromatics and phenylacetylene was added into
autoclave reactor. After that the autoclave was purged with N2 for
three times, and pre-filled with N2 to 0.7–0.75 MPa to maintain the
1.0 MPa of reaction pressure at reaction temperatures. The reaction
mixture got a homogeneous state after stirring 30 min at room tem-
perature, then heated up to the desired reaction temperature, and
start to count reaction time. After the reaction, the mixture was
quickly cooled down to room temperature and then filtered for
catalyst separation. Quantitative analysis of the collected products
was performed on a FULI 9790 II GC equipped with HP-5 column,
30 m × 0.32 mm × 0.25 ␮m, and FID detector. The GC/MS and 1H
NMR were performed for the structure identification of samples
(qualitative analysis, see supporting information). From our previ-
ous report [6,7,21], the acid mediated alkenylation is a complex
competition process. Based on the GC–MS data (Fig. S1–6) and
the literatures, besides the main product (␣-arylstyrene), a series
3. Results and discussion
3.1. Effect of carrier
From our previous report [21], owing to the low cost and sustain-
ability of AC and the outstanding catalytic performance of PTA/AC,
the PTA/AC can be considered as a promising catalyst for clean
␣-arylstyrene production through Friedel-Crafts alkenylation of
aromatics with phenylacetylene. However, the improvement in
both catalytic activity and efficiency of PTA/AC are required. It was
previously demonstrated that the PTA dispersion of supported PTA
catalysts is significantly affected by the nature of support with
different surface area and pore size distribution [33,34], which sub-
sequently affects their acidic properties. Besides the accessibility of
acidic sites to substrates dependent on the specific surface area and

Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
143
Table 2
by improved accessibility of acidic sites. Although the PTA/CMK-3
catalyst shows a lower specific surface area and total pore vol-
ume than those of PTA/AC, the mesoporous structure endows it
with higher catalytic performance. Furthermore, from Fig. 2, the
MC prepared by evaporation-induced tri-constituent co-assembly
approach demonstrates much different textural properties from
the CMK-3 prepared by SBA-15 template method. Besides the dra-
matically increased specific surface area and pore volume of MC
in comparison with CMK-3, it shows bimodal porous structures
composed of around 4.3 nm wide mesopores caused by the F127
assembly and around 2.4 nm small mesopores generated from the
removal of silica [30]. The nature of MC endows the PTA/MC with
unique porous structures, which is one reason for its higher cat-
alytic activity than the other two owing to the intensification of
mass transfer.
Effect of PTA loading on the textural properties of the as-prepared PTA/MC catalysts.
a
b
WPTA (%)
SBET (m2 g−1
)
VBJH (m3 g−1
)
0
1539
1388
1174
1010
937
1.7
1.5
1.2
1.0
0.9
0.8
10
20
30
35
40
947
a
Denoted as the BET specific surface area.
Denoted as the BJH pore volume from the adsorption branch.
b
The catalytic performance of solid acid catalysts is strongly
dependent on the acidic properties. The NH3-TPD technique was
used to reveal the relationship between the acidic nature and the
catalytic properties of supported PTA catalysts on different carriers.
NH3-TPD profiles are shown in Fig. 3. From Fig. 3, the three solid
acids show different profiles, suggesting the support effect on the
acidic properties of supported PTA catalysts. The profiles can be
roughly divided into three zones: lower than 300 ◦C, 300–470 ◦C,
and higher than 470 ◦C, which can be assigned to weak, medium,
and strong acidic sites [6,21]. PTA/MC catalyst possesses visibly
higher total amount of acidic sites, especially it has more medium
acidic sites than the others, which favor alkenylation reaction. From
the XRD patterns of the supported PTA catalysts on diverse carri-
ers shown in Fig. S7, the visible XRD peaks corresponding to PTA
on the PTA/AC can be well resolved, while no XRD peaks towards
PTA can be observed on the other two, which suggests the high PTA
dispersion on the two mesoporous carbon carriers. The weak acidic
sites on the PTA/AC become stronger in comparison with those for
the other two, ascribed to the poor PTA dispersion. From Fig. 3,
it can also be seen that the peak on PTA/MC towards strong acidic
sites is much wider than that on PTA/CMK-3, which can be ascribed
to the unique PTA-support interaction and PTA dispersion led by
the different textural properties. In a word, the textural properties
of carriers strongly affect acidic properties of supported PTA cata-
lysts, besides have significant influence on the mass transfer. The
as-preparedsupported PTA solid acid catalyst on the special MC car-
rier with large specific surface area, pore volume, and pore diameter
as well as bimodal pore systems endow it with more acidic sites and
higher accessibility of acidic sites. As a consequence, PTA/MC cat-
alyst exhibits much higher catalytic performance in Friedel–Crafts
alkenylation of aromatics with alkynes than the other two.
Fig. 7. Reaction results for the alkenylation of p-xylene with phenylacetylene over
the as-prepared 35% PTA/MC catalyst with diverse catalyst dosages. Reaction con-
ditions: nAr/Phen = 10; Tr = 150C; Pr = 1.0 MPa; t = 4 h.
pore structure affected by the nature of carrier, the feature of acidic
sites significantly affects the catalytic performance in alkenylation
of supported PTA catalyst. Therefore, we investigated the effect of
carrier on the supported PTA catalysts for Friedel-Crafts alkenyla-
tion of p-xylene with phenylacetylene. Fig. 1 and Table S1 represent
the catalytic reaction results. From Fig. 1 and Table S1, the order of
catalytic activity is: PTA/MC > PTA/CMK–3 > PTA/AC, and the three
supported PTA solid acid catalysts show similar selectivity (about
95%) towards to ␣-(2,5-dimethylphenyl) ethylbenzene. The main
sideproducts are acetophenone, isomer (␤-(2,5-dimethylphenyl)
ethylbenzene), and oligomers. The mesoporous carbon prepared by
evaporation-induced tri-constituent co-assembly approach (MC)
can be considered as a much superior support for the supported
PTA catalyst for Friedel-Crafts alkenylation of p-xylene.
From the above, the catalytic performance of PTA supported cat-
alysts is significantly dependent on the properties of carrier. The
PTA/MC catalyst sample can be chosen as a promising solid acid
catalyst for ␣-arylstyrene production via the Friedel–Crafts alkeny-
lation of aromatics with alkynes. The N2 adsorption-desorption
and NH3-TPD experiments were performed to reveal the sup-
port effect. The textural feature of the bare supports and the
as-synthesized supported PTA catalysts were characterized by
3.2. Effect of PTA loading
It has been demonstrated that the PTA loading has a signifi-
cant influence on the type and amount of the acidic sites on the
supported PTA catalyst, and subsequently affects the catalytic per-
formance of solid acid catalysts [6,16,21]. The optimum PTA loading
can be dependent on the feature of support. Therefore, the effect
of PTA loading on the catalytic performance of PTA/MC catalysts in
Friedel–Crafts alkenylaion of p-xylene with phenylacetylene was
investigated, although the effect of PTA loading of PTA/AC was
investigated in our previous report. Fig. 5 and Table S2 present the
reaction results. In order to obtain the inherent catalytic perfor-
mance of the investigated catalysts, the reaction was performed
at the conditions for a low conversion. From Fig. 4 and Table S2,
bare MC-3 is almost inert for alkenylation, it only shows 4.3% of
conversion with 72.7% of selectivity towards ␣-arylstyrene due to
the lack of acid sites, which is similar to the non-catalytic process
(3.4% conversion with 55.9% selectivity). the conversion rises as the
PTA loading is increased, and the it reaches maximum conversion
N2 adsorption–desorption experiments. Fig.
2 shows the N2
adsorption–desorption isotherms and the BJH pore size distribu-
tion. Table 1 presents the specific surface area and pore volume.
From Fig. 2 and Table 1, The bare MC shows much higher spe-
cific surface area and pore volume than the other two supports,
which may favor the PTA dispersion. The AC features no visible
mesopores but abundant micropores, which may be unfavorable
for PTA dispersion. Moreover, an obvious decrease in surface area
and pore volume can be observed while the supports are suffered
from the PTA loading process. However, no visible change in pore
size distribution can be observed. From Table 1, PTA/MC-3 shows
much higher specific surface area and mesoporous volume than the
other two supported PTA catalysts, which favors the alkenylation

144
Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
Table 3
Reaction results for the alkenylation of diverse aromatics with phenylacetylene over the 35 wt.% PTA/MC catalyst.
Entry
1
Aromatics
Products
Conversion (%)
Selectivity (%)
79.3
Yield (%)
57.4
72.4
2
3
100
100
91.7
89.3
91.7
89.3
4
99.8
94.6
94.4
5
6
100
94.5
94.2
94.5
90.8
96.4
7
95.4
86.3
82.3
8
9
98.7
97.6
90.2
83.4
89.0
81.4
10
95.5
82.7
79.0
11
12
95.9
99.0
92.6
91.3
88.8
90.4
13
94.4
92.3
93.5
91.3
88.3
84.3
14
Reaction conditions: Wcat = 2.67 wt%; nAr/Phen = 10; T = 150 ◦C; P = 1.0 MPa; t = 4 h.
(67.3%) with 95.2% of selectivity while a 35% of PTA loading is used.
The further increase in PTA loading leads to a decrease in catalytic
activity. 35% is the optimum PTA loading for best catalytic perfor-
mance From Table S2, the lower selectivity over bare MC and the
supported PTA catalyst with 10% of PTA loading mainly comes from
the formation of oligomers from thermal oligomerization of pheny-
lacetylene. The much higher percentage of oligomers over the bare
MC support and 10%PTA/MC in comparison with the others can
be resulted from the lower conversion [21]. Herein, the structure-
performance relationship of the as-synthesized PTA/MC catalysts
with diverse PTA loadings in alkenylation of p-xylene was investi-
gated by correlating the reaction results to the nature of catalysts.
The catalytic performance of solid acid catalysts is strongly
affected by their acidic properties. The NH3-TPD technique was
used to reveal the relationship between the acidic nature and the
catalytic properties of supported PTA catalysts with different PTA
loadings. The NH3-TPD profiles are shown in Fig. 5. From Fig. 5,
a monotonic increase in the numbers of strong acid sites can be
observed as the PTA loading rises, which is in agreement with
the reported results [16,21]. However, interestingly, the amount

Z. Zhao, X. Wang / Applied Catalysis A: General 526 (2016) 139–146
145
towards weak and medium acidic sites decreases along with the
4. Conclusions
increased PTA loading, which can be ascribed to the weaker and
weaker PTA-support interaction led by worse PTA dispersion owing
to the increased PTA loading confirmed by XRD patterns shown as
Fig. S8. Correlated to reaction results, the increased strong acidic
sites favor the alkenylation as the PTA loading is not higher than
35%. However, as the PTA loading increases from 35% to 40%,
the amount of weak and medium acidic sites notably decreases
although the amount of strong acidic sites increases. Therefore,
the total amount of acidic sites may decides the catalytic activity.
From Fig. 6 and Table 2, the specific surface and mesopore volume
decrease as the PTA loading rises, ascribed to partial jam of pores
by the loaded PTA. The decrease in surface area and pore volume
also depresses the accessibility of active sites. As a comprehensive
result, the 35% of optimum PTA loading is required to obtain high
catalytic activity. Moreover, from Fig. 5, along with the increasing
PTA loading, weak acidic sites become stronger and stronger. This
phenomenon is suitable to the strong acidic sites as the PTA loading
rising from 30 to 40%. The increased acidic strength can be ascribed
to weaker and weaker PTA-support interaction due to worse and
worse PTA dispersion. As a result, an increase in the amount of
oligomers can be observed as the PTA loading rises from 30% to 50%.
From the forementioned analysis, more acidic sites and their higher
accessibility are essential to obtain outstanding catalytic perfor-
mance of PTA/MC catalysts in alkenylation, which requires 35% of
optimum PTA loading.
In this work, the supported PTA solid acids on diverse supports
including AC, CMK-3, and MC as well as the PTA/MC solid acids
with diverse PTA loadings were prepared and used as catalysts for
Friedel- Crafts alkenylation of p-xylene with phenylacetylene. It
can be found that the catalytic performance of supported PTA cat-
alysts for alkenylation is strongly dependent on the properties of
acidic sites and their accessibility that significantly affected by tex-
tural feature of support and PTA loading. 35%PTA/MC demonstrates
outstanding catalytic performance in Friedel-Crafts alkenylation,
ascribed to more acidic sites and the larger specific surface area
and unique bimodal pore systems with larger pore size. From the
viewpoint of low cost, clean, sustainable feature and outstanding
catalytic performance, 35%PTA/MC can be considered as promis-
ing catalyst for production of ␣-arylstyrenes through Friedel-Crafts
alkenylation of diverse aromatics.
Acknowledgments
This work is financially supported by the National Natural Sci-
ence Foundation of China (grant no. 21276041) and the Chinese
Ministry of Education via the Program for New Century Excellent
Talents in University (Grant NCET-12-0079).
Appendix A. Supplementary data
3.3. Effect of catalyst dosage
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.apcata.2016.08.
028.
Effect of dosage of 35 wt.% PTA/MC catalyst (Wcat) on the
Friedel–Crafts alkenylation of p-xylene with phenylacetylene was
investigated. Fig. 7 and Table S3 represent the reaction results. From
Fig. 7 and Table S3, the Wcat has significant effect on the conversion
and selectivity. The reaction can hardly take place in the absence of
catalyst, and there is a monotonic increase in conversion of pheny-
lacetylene along the increase of Wcat from 1.33% to 2.67%. The 99.7%
of conversion with 94.3% of selectivity can be achieved as 2.67% of
Wcat is used.
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