Supported phosphotungstic acid catalyst on modified activated carbon for Friedel-Crafts alkenylation of diverse aromatics to their corresponding α-arylstyrenes

Article abstract of DOI:10.1016/j.apcata.2015.07.007

Abstract The supported phosphotungstic acid catalysts on modified activated carbon (PTA/AC) prepared by a facile wet impregnation method were employed for Friedel-Crafts alkenylation of diverse aromatics with phenylacetylene to synthesize their corresponding α-arylstyrenes. Reaction results demonstrate that the fabricated PTA/AC catalyst with 30 wt.% PTA loading exhibits outstanding catalytic performance. The 100% conversion of phenylacetylene with 95.7% selectivity towards α-(2,5-dimethylphenyl) styrene can be achieved over the developed 30 wt.% PTA/AC catalyst under optimized reaction conditions, and no visible loss in catalytic performance can be observed after it suffers from several times recycling. The various characterization techniques including X-ray diffraction, N₂ adsorption-desorption, Fourier transform infrared spectroscopy, and NH₃ temperature-programmed desorption were employed to reveal the relationship between the catalysts nature and catalytic properties. Moreover, the results on the scope of aromatics for the Friedel-Crafts alkenylation illustrate that the developed PTA/AC alkenylation catalyst can be efficiently catalyze the diverse aromatics and even for the electron deficient chlorobenzene. The developed PTA/AC catalyst, using the modified low-cost and sustainable AC as support, may be a robust and promising candidate for highly-efficient and clean α-arylstyrenes production through Friedel-Crafts alkenylation of diverse aromatics including electron-donating and electron-withdrawing groups substituted benzene derivatives as well as heterocyclic and polypolycyclic arenes with phenylacetylene.

Full text of DOI:10.1016/j.apcata.2015.07.007

Applied Catalysis A: General 503 (2015) 103–110
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Supported phosphotungstic acid catalyst on modified activated
carbon for Friedel–Crafts alkenylation of diverse aromatics to their
corresponding ␣-arylstyrenes
∗
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 18 May 2015
Received in revised form 24 June 2015
Accepted 5 July 2015
Available online 15 July 2015
The supported phosphotungstic acid catalysts on modified activated carbon (PTA/AC) prepared by a
facile wet impregnation method were employed for Friedel–Crafts alkenylation of diverse aromatics
with phenylacetylene to synthesize their corresponding ␣-arylstyrenes. Reaction results demonstrate
that the fabricated PTA/AC catalyst with 30 wt.% PTA loading exhibits outstanding catalytic performance.
The 100% conversion of phenylacetylene with 95.7% selectivity towards ␣-(2,5-dimethylphenyl) styrene
can be achieved over the developed 30 wt.% PTA/AC catalyst under optimized reaction conditions, and
no visible loss in catalytic performance can be observed after it suffers from several times recycling. The
various characterization techniques including X-ray diffraction, N2 adsorption–desorption, Fourier trans-
form infrared spectroscopy, and NH3 temperature-programmed desorption were employed to reveal the
relationship between the catalysts nature and catalytic properties. Moreover, the results on the scope of
aromatics for the Friedel–Crafts alkenylation illustrate that the developed PTA/AC alkenylation catalyst
can be efficiently catalyze the diverse aromatics and even for the electron deficient chlorobenzene. The
developed PTA/AC catalyst, using the modified low-cost and sustainable AC as support, may be a robust
and promising candidate for highly-efficient and clean ␣-arylstyrenes production through Friedel–Crafts
alkenylation of diverse aromatics including electron-donating and electron-withdrawing groups substi-
tuted benzene derivatives as well as heterocyclic and polypolycyclic arenes with phenylacetylene.
Keywords:
Activated carbon
Phosphotungstic acid
Alkenylation
Clean synthesis
Heterogeneous catalysis
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
[5–7]. Not like the well-established Friedel–Crafts alkylation, the
Friedel–Crafts alkenylation still remains a rigorous challenge to be
resolved. The biggest issue is to efficiently eliminate the oligomer-
ization of alkynes owing to the poor stability of alkenyl cation
species [8–11]. However, the rare reports on alkenylation over
solid acid catalysts can be found. Sartori had made some pio-
neering work on alkenylation of aromatics over HSZ-360 zeolite
[12], unfortunately the results are not very satisfactory, and there
exists an irreconcilable contradiction between the selectivity and
the 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 tem-
perature could efficiently compress the formation of acetophenone,
but led to remarkable decrease in the catalytic activity. More-
over, the low catalytic efficiency could be observed while the HY
was used as catalyst for the alkenylation, ascribed to the reac-
tion only taking place on the external surface of the catalyst
because of its narrow pore channels within the HY zeolite, as
well as the improvement in the catalytic efficieny and enlarge-
Alkenylaromatics, serve as industrially important intermediates
for producing pharmaceuticals, agrochemicals, natural products,
flavors and dyes, can be synthesized by the alkenylation of aro-
matics with alkynes, also known as hydroarylation of alkynes.
Alkenylation has attracted considerable attention owing to the
continuously growing demand for alkenylaromatics in chemical
industry [1–4].
The heterogeneous catalysis provides an efficient approach
for organic transformations in terms of clean, easy separation,
reusability, and high selectivity. Recently, zeolite is being more and
more regarded as an environmentally benign solid acid catalyst
for Friedel–Crafts alkylation, and the acidity and pore size deci-
sively affect the catalytic activation, selectivity and coke-resistance
∗ Corresponding author. Fax: +86 411 84986354.
E-mail address: zkzhao@dlut.edu.cn (Z. Zhao).
http://dx.doi.org/10.1016/j.apcata.2015.07.007
0
926-860X/© 2015 Elsevier B.V. All rights reserved.

1
04
Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
ment in scope of substrates are deirable [11,13]. Recently, it was
demonstrated that the Fe-containing mesoporous alluminosili-
cate exhibited vey high activity for the Friedel–Crafts alkenylation
of phenols with aryl-substituted alkynes under mild conditions
2. Experimental
2.1. Catalysts preparation
[
14]. However, the further increase in selectivity is indispens-
A commercially available AC derived from coconut shells
(Aladdin, China) was used as support. The as-received AC was
ground and sieved into final particles (less than 125 ␮m) for use.
able. Till now, the Friedel–Crafts alkenylations over solid acid
catalysts are still scarcely reported, although this strategy could
be a promising approach with easy separation, green and atom-
economic features for the synthesis of 1,1-diarylalkenes. Therefore,
the development of novel and robust solid acid catalysts for
Friedel–Crafts alkenylation is highly desirable, but it still remains a
challenge.
It was demonstrated that heteropolyacid (HPA) can act as an
efficient catalyst for the alkylation, due to its strong acidity and
the Brønsted type fundamentally, which are comparable to those
of HF and H SO . Among them, the phosphotungstic acid (PTA) is
The AC surface modification process via H O2 oxidation pretreat-
2
ment was performed as follows: a certain amount of AC was
−
1
immersed into a 35 wt.% H O2 aqueous solution (5 ml g AC) in
2
a water–ice bath with continuously stirring for 6 h. The sample
was filtered, washed with deionized water, and followed by dry-
◦
ing at 105 C overnight, and then the modified AC supports were
obtained. The PTA/AC catalysts with diverse PTA loadings (10, 20,
30, and 40 wt.%) were prepared by wet impregnation method. The
typical wet impregnation process is as follows: 0.23 g PTA (analyt-
ical reagent, AR, bought from China National Medicines Corp. Ltd.)
was dissolved into 10 ml deionized water to obtain PTA impregant.
0.5 g treated AC was dispersed into the above PTA solution. The
mixture was stirred and then stood for 24 h. The PTA impregnated
2
4
usually employed as the good catalyst for its high acidic strength
and relatively high thermal stability [15]. But its lower surface area
(
2
about 5–8 m g) is a serious drawback as the heterogeneous cata-
lyst. The immobilization of HPA was considered as a sophisticated
approach to increase PTA surface area. The supported PTA cata-
lysts on diverse supports have demonstrated outstanding catalytic
properties for various organic transformations [16–20], however,
rare report on supported PTA catalyst promoted alkenylation can
be found. We previously demonstrated that the supported PTA
catalyst on MCM-41 under optimized conditions exhibited good
catalytic performance in alkenylation. It was found that supported
PTA catalyst could be a promising catalyst for the clean pro-
duction of ␣-arylstyrenes [10]. However, further improvement
in catalytic activity, selectivity and the expansion in reactants
scope are required. Moreover, the complex and high cost prepa-
ration process of mesoporous silica leads to the high cost for
production of ␣-arylstyrenes via solid acid catalyzed alkenylation.
Therefore, searching a low cost and efficient support for PTA is
desirable.
Activated carbon (AC) has been widely used as support for many
kinds of catalysts [21–26]. 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 environmen-
tally pollution problems in some degree. Moreover, AC supports
show the visible advantages compared to oxide supports such as
high surface area, high stability in acidic and basic media and at
the same time the ability for facile recovery of the active metals
by burning off the support [22,23]. With oxidation treatment, AC
can gain more surface oxygen-containing groups, which can act as
nucleation centers for the generation of well dispersed active com-
ponents [26–28], which benefits the improvement in the catalytic
performance of supported-type catalysts on AC.
◦
catalysts were dried at 105 C in air overnight, followed by calci-
◦
nations in air at 300 C for 3 h. Then the series of PTA/AC catalysts
were obtained.
2.2. Catalysts 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. The FT-IR spectra of the
samples were collected on a Nexus Euro infrared spectrometer
using the KBr pallet method, and the same collection conditions for
◦
all samples are used. Nitrogen adsorption experiments at −196 C
were carried out on a Beishide 3H-2000PS1instrument to measure
the surface area and pore volume, and the samples were degassed
◦
at 200 C for 6 h prior to the N2 adsorption experiment. NH -TPD
3
measurements were performed on an in-house constructed system
equipped with a thermal conductivity detector (TCD) to measure
the desorbed NH . 50 mg sample was loaded in quartz reactor
3
between two quartz wool plugs, and then was pretreated in Ar at
◦
◦
−1
300 C (a ramp rate of 10 C min ) 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 ammonia. The desorp-
tion process was carried out from 100 C to 700 C at a heating rate
of 10 C min with an Ar flow of 30 ml min .
◦
◦
◦
−1
−1
2.3. Catalytic performance measurement
The experiments of the alkenylation of aromatics with pheny-
lacetylene were performed in the stainless steel autoclave reactor.
Firstly, 15 g reactant mixture containing aromatics and pheny-
lacetylene with desired molar ratio of aromatics to phenylacetylene
was added into autoclave reactor, and then the desired amount
of catalyst was added. After that, the autoclave was purged three
In this work, the modified AC by oxidation pretreatment was
employed as a carrier for preparing the supported PTA catalysts.
It was found that the supported PTA catalyst on modified AC
(
PTA/AC) with appropriate PTA loading exhibited excellent catalytic
performance in Friedel–Crafts alkenylation reactions of diverse aro-
matics, and even for the electron withdrawing groups substituted
aromatics like nitrobenzene and chlorobenzene. Correlated cat-
alytic performance with catalyst characteristics, it was illustrated
that the catalytic performanceof PTA/AC catalysts for Friedel–Crafts
alkenylation was strongly dependent on the acidic properties, PTA
dispersion, surface area and pore volume significantly affected
by PTA loadings. Owing to the high activity and selectivity, good
recyclability, the wide scope of aromatics, as well as the inherent
sustainable and low cost feature of AC, the developed PTA/AC may
be a robust and promising solid acid catalyst for the production
of ␣-arylstyrenes via Friedel–Crafts alkenylation of aromatics with
alkynes.
times with N , and then the reactor was pre-filled with N2 to
2
0.7–0.75 MPa (it reaches 1.0 MPa at reaction temperatures). After
stirring 30 min at room temperature to make the reaction mixture
homogeneous, the mixture was heated up to the desired reaction
temperature, and then start to count the reaction time. After the
reaction, the mixture was quickly cooled down to room temper-
ature and then was filtered for catalyst separation. The 96–98%
of carbon balance was obtained by external standard method.
The carbon loss can be resulted from the possible adsorption
and/or coke on catalyst. Quantitative analysis of the collected prod-
ucts 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

Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
105
Fig. 1. Reaction results of the alkenylation of p-xylene with phenylacetylene over
PTA/AC catalysts with diverse PTA loadings. Reaction conditions: Wcat 2.67 wt.%;
nAr/Phen 10; T 150 C; P 1.0 MPa; t 5 h.
Fig. 2. FT-IR spectra of PTA/AC samples with diverse PTA loadings and bulk PTA is
included for comparison.
◦
on AC and 10 wt.% PTA/AC). The much higher oligomers percentage
in comparison with the other three samples is caused by the lower
conversion. For blank experiment (entry 1 in Table S2), 0.955% of
oligomers can be produced by thermal oligomerization. That is to
say, the oligomers in the reaction mixtures over pure AC and 10 wt.%
PTA/AC samples are mainly resulted from the thermal oligomer-
ization under the reaction conditions. The amount of oligomers
increases as the PTA loading rises (Table S1). The 82.3% of maximum
yield for desired product with highest conversion and selectivity
as well as medium oligomerization can be obtained on the 30 wt.%
PTA/AC catalyst. Then the structure-performance relationship of
the as-synthesized PTA/AC catalysts with diverse PTA loadings in
alkenylation of p-xylene was investigated by correlating the reac-
tion results to the nature of catalysts.
and 1HNMR were performed for the structure identification of
samples (qualitative analysis, see supporting information). From
our previous report, the alkenylation is a complex competition
process. Based on the GC–MS data (Fig. S1–6) and the related ref-
erences [22–24,29], it can be seen that, besides the main product
(
␣-arylstyrene), a series of byproducts like acetophenone, ␣-(2,5-
dimethylphenyl) ethylbenzene, ␤-(2,5-dimethylphenyl) styrene
and oligomers can be detected. As the evaluation index of the
alkenylation reaction, the phenylacetylene conversion was cal-
culated by weight percent of the consumed phenylacetylene in
the total phenylacetylene amount in the reaction mixture; the
selectivity to ␣-arylstyrene was calculated by weight percent of
desired ␣-arylstyrene in total products. The yield corresponding
␣
-arylstyrene was the GC yield, which was calculated based on the
FT-IR is a good tool to investigate the structural characterization
of supported PTA on AC. The FT-IR spectra of the PTA/AC samples
with diverse PTA loadings are presented in Fig. 2, and the bulk PTA
was also included for comparison. From Fig. 2, four characteristic
conversion of phenylacetylene and the selectivity of the desired
products.
−
1
3
. Results and discussion
peaks corresponding to P–O (␣-peak, at around 1080 cm ), W
O
−
1
(
␤-peak, at around 982 cm ), and W
O
W (␥- and ␦-peaks, at
−
2
3.1. Effect of PTA loading
around 893–798 cm ) appear on all of the samples, suggesting that
the typical Keggin structure can be remained after being supported
on AC [10,20]. The continuously intensified adsorption peaks with
the increased PTA loadings are not surprised. By carefully compar-
ing the peak positions on the diverse samples, the shift to lower
wave number can be observed as the PTA loading decreases from
40 wt.% to 10 wt.%, might be ascribed to the possible interaction
between PTA and AC. It looks like the high PTA dispersion at low
loading may strengthen this kind of interaction. All in all, the Keggin
structure of PTA still can be maintained although PTA suffers from
impregnating and calcining for preparation of PTA/AC catalysts.
The acidic properties decisively affect the catalytic performance
It was previously demonstrated that the PTA loading has a sig-
nificant influence on the type and amount of the acidic sites on
the supported PTA catalysts [30], and subsequently affects the cat-
alytic performance of solid acid catalysts. Therefore, the effect of
PTA loading on the catalytic performance of PTA/AC catalysts with
diverse PTA loadings (10, 20, 30, 40 wt.%) in Firedel–Crafts alkenyla-
tion of p-xylene with phenylacetylene has been investigated firstly.
The reaction results are presented in Fig. 1 and Table S1, and the
pure AC was also included for comparison.
From Fig. 1, pure AC is almost inert for the alkenylation, owing to
its lack of acid sites, only 4.1% of conversion with 75.4% of selectiv-
ity towards ␣-arylstyrene can be obtained, which is similar to the
noncatalytic process (3.4% conversion with 55.9% selectivity). As for
the supported PTA catalysts, the conversion increases with the rise
of PTA loadings, and reaches the maximum (85.1%) while the PTA
loading increases up to 30%. The further increased PTA loading leads
to a decrease in conversion. The 30 wt.% PTA loading is appropri-
ate for obtaining higher conversion of phenylacetylene and higher
selectivity, and the 82.4% of maximum yield can be obtained over
the 30 wt.% PTA/AC catalyst. The polymerization of phenylacety-
lene is a bottle-neck problem for solid acid catalyzed alkenylation.
From Table S1, for the pure AC and the PTA/AC catalyst with 10 wt.%
of low PTA loading, 23.9% and 9.1% of oligomers in product distribu-
tion can be observed (0.98 and 1.29% of oligomers were produced
of solid acid catalysts. The NH -TPD technique was employed to
3
reveal the acidic sites nature and catalytic performance of PTA/AC
catalysts with diverse PTA loadings for Friedel–Crafts Alkenyla-
tion of p-xylene. Fig. 3 gives the NH -TPD profiles. From Fig. 3,
3
both the amount and the strength of acidic sites for the PTA/AC
catalysts monotonically increase as the PTA rises from 10 wt.% to
40 wt.%. Moreover, we cannot see any medium acid sites on the as-
synthesized PTA/AC catalysts. However, the medium acidic sites on
PTA/MCM-41 were definitely observed even if the 10 wt.% of low
PTA loading [10]. Then why do the acid site strengths increase with
larger PTA crystallite sizes? In fact, similar conclusion was drawn in
many papers. But the reason can hardly be mentioned. The nature
of acid sites is significantly dependent on PTA structure and support
type [16–20]. From the XRD results, the dispersion becomes poor

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Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
Fig. 3. NH3-TPD profiles of PTA/AC samples with different PTA loadings. (a) 10 wt.%;
b) 20 wt.%; (c) 30 wt.%; (d) 40 wt.%.
(
as the PTA loading increases, and the low loading results in good
PTA dispersion. The good dispersion may strengthen the interac-
tion of PTA and support, which can be identified by the shift of IR
peaks towards PTA on support in comparison of the bulk PTA. The
smaller the PTA loading is, the more the shift is. The strong interac-
tion leads to different acid species in comparison with the bulk PTA.
From the reference [31], the supported PTA exhibits much weaker
acid strength than the bulk PTA, which supports our above proposal.
Also only a few weak acidic sites on the samples can be observed.
Correlated to reaction results, the higher concentration of acidic
sites benefits the alkenylation, however the strong acidic sites also
promotes oligomerization to produce oligomers and also leads to
the deep polymerization for coke formation. The former can lead to
the decrease in selectivity, and the latter can lead to deactivation of
catalysts owing to the covering of acidic sites by coke. Therefore, the
appropriate acidic properties are required for alkenylation, which
is consistent with the previously reported results.
The PTA dispersion of the supported PTA catalysts can notably
affect the acidic properties. Herein, the XRD technique was
employed to investigate the PTA dispersity for the PTA/AC cata-
lysts diverse PTA loadings, and the XRD patterns are presented in
Fig S7. From Fig. S7, the characteristic peaks towards PTA crystalline
phases become sharper and stronger as the PTA loading is increased
from 20 wt.% to 40 wt.%, suggesting that the increased PTA loading
can lead to larger PTA crystalline size owing to the agglomerization
of PTA, which is consistent with the reported result [10]. This may
cause the formation of much stronger acid sites, and also lead to
the decrease in specific surface areas and pore volume those iden-
tified by the NH -TPD and N2 adsorption–desorption experiments,
3
which is consistent with the reported results. As a result, the too
high PTA loading leads to the decrease in conversion and leads to
the increase in formed oligomers.
The texture feature of the as-synthesized PTA/AC catalysts with
diverse PTA loadings (10 wt.%, 20 wt.%, 30 wt.% and 40 wt.%) and the
pure AC support were characterized by N2 adsorption–desorption
experiments. Fig. 4 presents the N2 adsorption–desorption as well
as the specific surface area and total pore volume for microp-
ores of the samples by t-plot method. From Fig. 4, the sharp
increase in adsorbed N2 at initial period for increasing P/P0 can
be clearly observed, but no hysteresis can be seen. This shows
that the presence of micropores but absence of mesopores on
the samples [32–34]. Furthermore, the continuous decreased sur-
face area and pore volume for micropores can be seen as the PTA
loading rises. High loading can produces acidic sites, but it also
leads to the decreased microporous surface area and pore vol-
ume, which may contribute the decrease in conversion and the
Fig. 4. N2 adsorption–desorption isotherms (a), specific surface area for microproes
by t-plot method (b), and pore volume for micropores by t-plot method (c) of the
as-synthesized PTA/AC catalysts with diverse PTA loadings and the pure AC support.
increase in oligomers, besides the increased strong acid sites and
their strength. Therefore, too high PTA loading is inappropriate for
alkenylation over PTA/AC catalyst.
From the above, the catalytic performance of PTA/AC catalysts
is significantly dependent on their acidic properties, PTA disper-
sion, surface area, and pore volume, which is strongly affected by
the PTA loading. The 30 wt.% PTA/AC sample can be chosen as a
promising solid acid catalyst for ␣-arylstyrenes production via the

Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
107
Fig. 5. Reaction results of the alkenylation of p-xylene with phenylacetylene over
Fig. 7. Reaction results of the alkenylation of p-xylene with phenylacetylene over
30 wt.% PTA/AC catalysts at different reaction temperature. Reaction conditions:
Wcat 3.33 wt.%; nAr/Phen 12; P 1.0 MPa; t 5 h.
3
0 wt.% PTA/AC catalyst with diverse catalyst dosages. Reaction conditions: nAr/Phen
◦
1
0; T 150 C; P 1.0 MPa; t 5 h.
coke formation, as well as can produce more oligomers. Thus, the
optimum Wcat is 3.33%.
Friedel–Crafts alkenylation of aromatics with alkynes. In order to
further improve the reaction properties, the effect of reaction con-
ditions including the dosage of catalyst, molar ratio of p-xylene to
phenylacetylene, reaction temperature, and reaction time on cat-
alytic performance in Friedel–Crafts alkenylation of p-xylene with
phenylacetylene over the 30 wt.% PTA/AC has been investigated.
3.2.2. Effect of molar ratio of p-xylene to phenylacetylene
Fig. 5 provides the effect of molar ratio of p-xylene to pheny-
lacetylene (np-xylene/Phen) on the alkenylation in the presence of
.33% Wcat of the developed 30 wt.% PTA/AC catalyst. From Fig. 5,
3
the uninterrupted increase in conversion can be obtained as the
np-xylene/Phen rises from 6:1 to 12:1, ascribed to enhanced collision
probability of alkenyl cations with aromatic rings. The 100% of con-
version with 95.1% of maximum selectivity can be obtained while
the 12:1 of np-xylene/Phen is used. The solvent effect of p-xylene can
efficiently inhibit the self-polymerization of the alkyne. As a result,
the increase in np-xylene/Phen leads to the increase in percentage of
the desired product, as well as compress the formation of oligomers
3
.2. Effect of reaction conditions
3.2.1. Effect of catalyst dosage
Effect of dosage of 30 wt.% PTA/AC catalyst on the Friedel–Crafts
alkenylation of p-xylene with phenylacetylene was investigated by
changing the catalyst dosage from 2.33% to 3.67%. The dosage of
catalyst (Wcat) is defined as the mass concentration of PTA/AC cat-
alyst in the reaction mixture. The reaction results are presented in
Fig. 5 and Table S2. From Fig. 5, the Wcat has significant effect on the
conversion and selectivity. The continuous increase in conversion
of phenylacetylene can be observed as the Wcat increase from 2.33%
to 3.67%, and the reaction can hardly take place in the absence of
catalyst. More than 90% (90.8%) of high yield with 94.2% selectivity
can be obtained while the 3.33% of Wcat is used, and the further
increase in Wcat up to 3.67% can lead to the decrease in selectiv-
ity. Moreover, the higher Wcat can lead to obvious polymerization
(Table S3). The 12:1 of np-xylene/Phen is essential for obtaining excel-
lent reaction results.
3.2.3. Effect of reaction temperature
Fig. 6 illustrates the alkenylation results with different reac-
tion temperatures, and the product distribution is presented in
Table S4. From Fig. 6, the increase in reaction temperature results
in a continuous increase in conversion, and the 100% conversion
◦
of phenylacetylene with 95.1% selectivity are obtained at 150 C.
(
Table S2), which may in turn lead to deactivation of catalyst by
Moreover, from Table S4, the increased reaction temperature can
Fig. 6. Reaction results of the alkenylation of p-xylene with phenylacetylene over
Fig. 8. Reaction results of the alkenylation of p-xylene with phenylacetylene over
3
0 wt.% PTA/AC catalysts at different np-xy./Phen reaction conditions: Wcat 3.33 wt.%;
30 wt.% PTA/AC catalysts for different reaction times. Reaction conditions: Wcat
◦
3.33 wt.%; nAr/Phen 12; T 150 ◦C; P 1.0 MPa.
T 150 C; P 1.0 MPa; t 5 h.

1
08
Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
Table 1
Reaction results of the alkenylation of different aromatics with phenylacetylene over 30 wt.% PTA/AC catalyst.
Entry
Aromatics
Products
Conversion (%)
Selectivity (%)
81.6
Yield (%)
57.6
1
70.6
2
3
100
100
90.2
91.3
90.2
91.3
4
100
95.1
95.1
5
6
100
96.1
90.6
96.1
85.7
94.6
7
96.8
98.2
83.1
93.4
80.4
91.7
8
9
95.3
98.3
93.9
82.1
89.5
80.7
1
0
1
1
100
83.6
83.6
1
2
3
99.0
98.3
91.2
90.3
90.3
88.8
1

Z. Zhao, X. Wang / Applied Catalysis A: General 503 (2015) 103–110
109
Table 1 (Continued)
Entry
Aromatics
Products
Conversion (%)
99.0
Selectivity (%)
93.5
Yield (%)
1
4
5
92.6
86.2
1
92.6
93.1
◦
Reaction conditions: Wcat 3.33 wt.%; nAr/Phen 12; T 150 C; P 1.0 MPa; t 4 h.
reduce the formation of acetophenone. Among the investigated
temperature range, the higher reaction temperature doesn’t lead to
a decrease in oligomers. From above, the 150 C is an appropriate
sustainable AC as support, the developed PTA/AC catalyst can be
considered as a promising catalyst for clean and atomic economic
synthesis of ␣-arylstyrenes via solid acid catalyzed Friedel–Crafts
type of alkenylation reaction.
◦
reaction temperature.
3
.2.4. Effect of reaction time
From Fig. 7 and Table S5, the increase in reaction time can lead to
4. Conclusions
an increased conversion and selectivity but does not lead to the by-
products formation. The 4 h is enough, and 100% conversion with
In this work, the supported PTA catalysts on low-cost and sus-
tainable oxidation-modified AC carrier with diverse PTA loadings
have been prepared. The catalytic performance of PTA/AC catalysts
for Friedel–Crafts alkenylation is significantly dependent on their
acidic properties, PTA dispersion, surface area, and pore volume,
which strongly affected by the PTA loading. The 30 wt.% PTA/AC
sample can be chosen as a promising solid acid catalyst for ␣-
arylstyrenes production via the Friedel–Crafts alkenylation. The
developed approach can be applied to various aromatics includ-
ing electron-donating groups substituted benzenes, polycyclic
arenes, heterocyclic aromatics, and even the electron-withdrawing
group substituted chlorobenzene for the production of their cor-
responding ␣-arylstyrenes. On the basis of the excellent catalytic
performance, wide scope of substrates, good recyclability of used
catalyst, as well as the use of low cost and sustainable AC as sup-
port, the developed 30 wt./% PTA/AC catalyst can be considered as
a promising candidate for the synthesis of diverse ␣-arylstyrenes
through the acid catalyzed Friedel–Crafts alkenylation reaction.
9
5.1% selectivity can be obtained. Moreover, from, Fig. 8, the 80%
conversion has been achieved in 2 h, but further carrying out the
reaction to get 20% more conversion to achieve 100% at the end of
4
h indicates that the reaction is slowed down. The decrease in rates
with the extension of reaction time from 2 h to 4 h can be due to the
continuously decreased concentration of the active intermediate
alkenyl cation with the consumption of alkyne along with increased
reaction times. The possible product inhibition cannot be excluded.
Since the catalyst can be reused without visible loss in activity, the
catalyst deactivation can be excluded.
3.3. Recyclability of the as-synthesized catalyst
In an industrialized production process, the recyclability of
catalyst is definitely significant in heterogeneous catalysis. There-
fore, the recyclability of the developed 30 wt.% PTA/AC catalyst for
alkenylation was preliminarily investigated (a few fresh catalyst
was recruited to reach the required 3.33% of Wcat). Results show
that the developed catalyst can be reused 4 times without visible
loss in catalytic performance, suggesting the large potential for the
application in ␣-arylstyrenes via solid acid catalyzed Friedel–Crafts
type of alkenylation reaction.
Acknowledgments
This work is financially supported by the National Natural
Science Foundation of China (grant no. 21276041), the Chinese
Ministry of Education via the Program for New Century Excellent
Talents in University (Grant NCET-12-0079), and by the Funda-
mental Research Funds for the Central Universities (grant no.
DUT15LK41).
3.4. Scope of aromatics
From the above, the PTA/AC solid acid catalyst has a good perfor-
mance on the direct alkenyaltion of p-xylene with phenylacetylene.
00% conversion and 95.1% selectivity can be obtained. Herein, the
1
Appendix A. Supplementary data
scope of the developed 30 wt.% PTA/AC catalyst was investigated by
employing diverse aromatics as substrates, and the reaction results
are listed in Table 1. The products molecular structures are identi-
fied by HNMR (Fig. S8–22). From Table 1, the developed supported
PTA catalyst on AC exhibits outstanding catalytic performance
in alkenylation of diverse aromatics including electron-donating
groups substituted benzenes, polycyclic arenes, and heterocyclic
aromatics. More interestingly, even if the electron-withdrawing
group substituted chlorobenzene is used as substrate, the 92.6% of
conversion with 93.1% of selectivity has still been obtained. Comb-
ing the higher catalytic efficiency (only 3.33% of catalyst dosage
is used) with the excellent catalytic performance in the alkenyla-
tion of extensive substrates and the use of inherent low-cost and
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.apcata.2015.07.
0
07
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