Spherical hollow mesoporous silica supported phosphotungstic acid as a promising catalyst for α-arylstyrenes synthesis via Friedel-Crafts alkenylation

Article abstract of DOI:10.1016/j.cclet.2018.08.014

In this work, a spherical hollow mesoporous silica (SHMS) with high surface area (902 m²/g) and large mesopore volume (1.31 cm³/g) was prepared via a facile and scalable two-step soft-hard dual template-assisted sol-gel approach (OSD

Full text of DOI:10.1016/j.cclet.2018.08.014

Accepted Manuscript
Title: Spherical hollow mesoporous silica supported
phosphotungstic acid as a promising catalyst for
α-arylstyrenes synthesis via Friedel-Crafts alkenylation
Authors: Xianhui Wang, Zhongkui Zhao
PII:
DOI:
Reference:
S1001-8417(18)30340-1
https://doi.org/10.1016/j.cclet.2018.08.014
CCLET 4635
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
7-7-2018
9-8-2018
27-8-2018
Please cite this article as: Wang X, Zhao Z, Spherical hollow mesoporous
silica supported phosphotungstic acid as a promising catalyst for α-arylstyrenes
synthesis via Friedel-Crafts alkenylation, Chinese Chemical Letters (2018),
https://doi.org/10.1016/j.cclet.2018.08.014
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Communication
Spherical hollow mesoporous silica supported phosphotungstic acid as a promising
catalyst for α-arylstyrenes synthesis via Friedel-Crafts alkenylation
Xianhui Wang, Zhongkui Zhao*
State Key Laboratory of Fine Chemicals, Department of Catalysis Chemistry and Engineering, School of Chemical Engineering, Dalian University of
Technology, Dalian 116024, China

Corresponding author.
E-mail address: zkzhao@dlut.edu.cn
Graphical Abstract
This work presents a scalable approach for preparing spherical hollow mesoporous silica with high surface area/pore volume,
serving as outstanding support for supported phosphotungstic acid catalyst with much superior catalytic performance to the one
on previously reported spherical mesoporous silica toward diverse transformations, ascribed to the strengthened mass transfer
and the enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and mesoporous morphology.
.
ARTICLE INFO
ABSTRACT
2
Article history:
In this work, a spherical hollow mesoporous silica (SHMS) with high surface area (902 m /g)
3
Received 10 July 2018
Received in revised form 9 August 2018
Accepted 17 August 2018
Available online
and large mesopore volume (1.31 cm /g) was prepared via a facile and scalable two-step soft-
hard dual template-assisted sol-gel approach (OSDSG) by using glucose-derived carbon
nano/micro particles (NMCP) as a hard template and cetyltrimethylammonium bromide
(CTAB) as a soft template, respectively, in which the size-preselected carbon submicro-

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particle was used to replace ploymer sphere, and no extra precious additives like n-
octadecyltrimethoxysilane (C18TMS). Supported phosphotungstic acid (PTA) catalysts on
SHMS (PTA/SHMS) and on previously reported spherical mesoporous silica (PTA/SMS) with
2
5 wt% of PTA loading were prepared and employed as solid acid catalysts for diverse
reactions. Transmission electron microscopy (TEM), adsorption-desorption, X-ray
diffraction (XRD), and NH temperature-programmed desorption (NH -TPD) techniques were
N
2
Keywords:
Spherical hollow mesoporous silica
Solid acid
Mass transfer
Alkenylation
Heterogeneous catalysis
3
3
employed to characterize the nature of carriers and supported PTA catalysts for revealing the
structure-performance relationship. The developed PTA/SHMS catalyst demonstrates much
higher catalytic activity than PTA/SMS for diverse reactions including alkenylation,
esterification, alkylation, and benzylation, ascribed to the strengthened mass transfer and
enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and
mesoporous morphology. Moreover, PTA/SHMS catalyst also exhibits outstanding catalytic
performance for the diverse α-arylstyrenes via solid acid-mediated alkenylation. PTA/SHMS
could be considered as a practical solid acid catalyst for diverse transformations.
Alkenylation of aromatics with alkynes has been considered as a direct and efficient method for synthesizing alkenylaromatics,
which serve as many industrially important intermediates for producing pharmaceuticals, agrochemicals, natural products, flavors and
dyes [1-3]. Owing to its low-cost and high activity, the acid catalyzed process shows great potential for the synthesis of
alkenylaromatics [4-8]. Catalysis by solid acid presents a promising strategy for diverse transformations in terms of its feature of clean,
easy-separation, catalyst reusability, and its applicability toward continuous production in an industrial scale.
In contrast to well-established alkylation, the acid-catalyzed alkenylation still remains a great challenge. The biggest issue is to
efficiently overcome the heavy oligomerization of alkynes, owing to the poor stability of vinyl cation intermediate species [9]. The
regular pore channels, a large amount of acidic sites, corrosion-resistance, and environmentally benign feature of zeolites endow them
with great attention in alkylation in academic and industrial fields [10-13]. However, the serious coke deposition due to the narrow
pore channels of zeolites and the stability of vinyl cation species depresses the broad use of zeolites as solid acid catalysts in
alkenylation [14,15]. Therefore, rare report on alkenylation over zeolite can be found.
From reference, Sartori did a pioneering work on alkenylation of aromatics over HSZ-360 zeolite [16]. Unfortunately, the
irreconcilable contradiction between the selectivity and catalytic activity led to an unsatisfactory reaction. The zeolite 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 resulted in remarkable decrease in catalytic
activity. Moreover, the enlargement in scope of substrates for alkenylation over zeolite is also required. Recently, it was demonstrated
that the Fe-containing mesoporous alluminosilicate exhibited vey high activity for alkenylation of phenols with aryl-substituted alkynes
under mild conditions [17]. However, the further increase in selectivity is indispensable. Therefore, the development of novel and
robust solid acid catalysts for alkenylation is highly desirable, but it still remains a great challenge.
Owing to its strong acidity, the heteropolyacid (HPA) acted as a very efficient solid acid catalyst for alkylation. Among them, PTA
is usually employed as a good catalyst for its high acidic strength and relatively high thermal stability [18,19]. However, the lower
2
surface area (about 5–8 m /g) limits its application as a heterogeneous catalyst. Loading HPA on an appropriate carrier with high
specific surface area and pore volume can be an efficient approach to address this issue [20-24]. It was previously demonstrated that
the supported PTA catalyst on MCM-41 under optimized conditions exhibited good catalytic performance in alkenylation [14].
However, further improvement in catalytic activity, selectivity and the expansion in reactants scope are required.
From the previous report in our Advanced Catalytic Materials (ACM) research group, owing to high PTA dispersity and facilitated
mass transfer by the short mesoporous channels of the spherical morphology, the supported PTA catalyst on monodisperse mesoporous
silica nanosphere (MSN) demonstrated much higher catalytic activity and stability for alkenylation and the other diverse
transformations in comparison with traditional mesoporous silica carriers like MCM-41. PTA/MSN has been considered as a promising
practical solid acid catalyst for diverse reactions [25]. However, the further increase in catalytic performance is required.
Owing to the influence of unique morphology on the diffusion length of the reactants and products, exposure degree of active sites,
dispersity, crystalline phase, and so on, the supported-type catalyst on spherical hollow mesoporous silica demonstrated much superior
catalytic performance in many transformation processes [26-33]. In this work, the hollow mesoporous silica submicrosphere with high
2
3
surface area (902 m /g) and large mesopore pore volume (1.31 cm /g) was prepared through a facile and scalable soft-hard dual-
template assisted sol-gel approach. In comparison with the previously reported papers [34-39], in this process, the size-preselected
glucose-derived carbon submicro-particle was used to replace ploymer sphere, and no extra precious additives like n-
octadecyltrimethoxysilane (C18TMS), as well as the hollow mesoporous silica submicrosphere with both higher surface area and larger
mesopore volume were achieved. The supported PTA on SHMS demonstrates much higher catalytic activity than PTA/SMS for
diverse reactions including alkenylation, esterification, alkylation, and benzylation, and also exhibits outstanding catalytic performance
for the diverse α-arylstyrenes via solid acid-mediated alkenylation. Various characterization techiniques including TEM, N
adsorption–desorption, XRD, and NH -TPD were used to characterize the nature of SHMS and SMS carriers and their corresponding
2
3
supported PTA catalysts, and also to reveal the structure-performance relationship. PTA/SHMS could be considered as a practical solid
acid catalyst for diverse transformations.
In a typical experiment, the carbon submicrospheres with pre-selected particle size were prepared by a modified hydrothermal
process of glucose followed by step-by-step centrifugation process [34]. Typically, 5 g of glucose were dissolved in 80 mL deioned
water under stirring at room temperature to form a clear solution, and then the resulting aqueous solution was transferred into a Teflon-

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o
lined autoclave (100 mL) for the hydrothermal carbonization process at 170 C for 10 h to form carbon nano/micro-particles under
autogeneous pressure. After that, the larger particles were removed by centrifugalizing the upper black liquid of the above resulting
mixture by hydrothermal process at 3000 rpm. Subsequently, the size preselected samples from further centrifugation at 10000 rpm
o
were purified by repeatedly washing them in water and ethanol for three times, followed by drying at 60 C for 6 h. The spherical
hollow mesoporous silica was prepared by a facile and scalable two-step soft-hard dual-template assisted sol-gel approach by using the
as-synthesized size-preselected NMCP as a hard template and CTAB as a soft template, respectively. The as-synthesized NMCP (0.2 g)
.
were re-dispersed in a mixed solution of ethanol and water by stirring and ultrasonic treatment, and then 570 μL NH
3
H
2
O and 0.28 g
CTAB were added into the above solution. After vigorously stirring for 1 h, 400 μL TEOS was dropwisely added into the dispersion
liquid with continuous stirring for 6 h. The products were collected by filtration and washed with water and ethanol, followed by
o
o
drying at 80 C for 5 h. Finally, the SHMS was prepared by calcining the sample at 550 C for 6 h to remove both soft and hard
templates. SMS was synthesized by the previously reported method [25]. Typically, the synthesis was performed under mild conditions
with a typical composition of 1.0 TEOS:0.064 CTAB:2.5 urea:300 H
2
O at a molar basis. 0.816 g CTAB and the required amount of
urea were dissolved in 200 g H O and stirred for 1 hour, and then 7.3 g of TEOS was added dropwisely into the above solution. The
2
o
resulting mixture was stirred at 80 C for 2 h. After that, the milky liquid was transferred into Teflon-lined autoclave and heated at 100
o
o
C for 20-60 h. The obtained solid product was recovered, washed, and then dried at 105 C for 20 h. The final SMS was obtained by
o
calcining the above samples at 550 C for 6 h. The supported PTA catalysts containing PTA/SHMS and PTA/SMS with 25 wt% of
PTA loading were prepared by our previously reported vacuum assisted wet impregnation with heating method (IMPVH) [14].
Typically, SHMS (1.0 g) was merged into an aqueous solution of PTA (according to previous reports [25], Keggin structure of PTA,
the concentrations is 0.36 g/mL) in a vacuum environment with heating at 128 C. After that, the impregnated samples were dried at
1
o
o
o
05 C in air overnight, followed by calcinations in air at 300 C for 3 h, and the PTA/SHMS catalyst with a loading of 25 wt% were
obtained. By using same process, the PTA/SMS catalyst was prepared for comparison [25].
The morphology and textural properties of the as-formed supports and the supported PTA catalysts were characterized by
Transmission electron microscopy (TEM) and nitrogen adsorption-desorption experiments. TEM images were obtained by using a
o
Tecnai F30 HRTEM instrument (FEI Corp.) at an acceleration voltage of 300 kV. Nitrogen adsorption experiments at −196 C were
carried out on a Beishide 3H-2000PS1 instrument to measure the surface area and pore volume, and the samples were degassed at 130
o
C for 10 h prior to the N
The crystalline structure and acidic properties of the supported PTA catalysts on the as-formed SHMS and SMS silica spheres were
measured by X-ray diffraction (XRD) and NH temperature programmed desorption (NH -TPD) techniques. XRD profiles were
collected from 10° to 80° at a step width of 0.02° using Rigaku Automatic X-ray Diffractometer (D/Max 2400) equipped with a CuKα
source (λ = 1.5406 Å). NH -TPD measurements were performed on a Builder Chemisorption (PCA-1200) instrument with a thermal
conductivity detector (TCD) to measure the desorbed NH
2
adsorption experiment.
3
3
3
o
3
. After pre-treatment of 50 mg samples in Ar (up to 300 C with a ramp rate
-90% Ar) at 10
C via the pulse injection of ammonia in an Ar stream. The desorption step was carried out from 100 C to 700 C at a ramp rate of 10
C/min with an Ar flow rate of 30 mL/min. The NH -TPD profiles were obtained via monitoring the desorbed ammonia with a thermal
o
of 10 C/min, and then kept for 0.5 h under 30 mL/min Ar flow), the samples were saturated with ammonia (10% NH
3
o
o
o
o
3
conductivity detector (TCD).
The catalytic performance of the as-synthesized containing PTA/SHMS and PTA/SMS for direct alkenylation of aromatics with
phenylacetylene was on a stainless steel autoclave reactor. 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 N
2
for three times,
and pre-filled with N upto 0.7-0.75 MPa to maintain 1.0 MPa of reaction pressure at reaction temperature. The reaction mixture got a
2
homogeneous state after stirring 30 min at room temperature, then was heated up to the desired reaction temperature, and start to a
required reaction time. After the reaction process, the mixture was quickly cooled down to room temperature and then filtered for
catalyst separation. Quantitative analysis of the collected product was performed on a FULI 9790 II GC equipped with HP-5 column,
1
3
0 m × 0.32 mm × 0.25 μm, and FID detector. HNMR experiments were performed for the structure identification of samples (see
supporting information). The phenylacetylene conversion was calculated by weight percent of the consumed phenylacetylene in the
total phenylacetylene amount added; the selectivity to α-arylstyrene was calculated by weight percent of desired α-arylstyrene in total
products. The similar process was performed for synthesizing diverse α-arylstyrenes via solid acid-mediated alkenylation of diverse
aromatics as substrates. The other solid acid catalyzed transformations were performed in a three-neck flask, and the detailed reaction
conditions are as follows: a) For esterification reaction, acetic acid 100 mmol, ethanol 1 mol, catalyst dosage 50 mg, reaction
o
temperature 70 C, reaction time 5 h. b) For alkylation reaction, styrene 100 mmol, benzene 500 mmol, catalyst dosage 50 mg, reaction
o
temperature 70 C, reaction time 5 h. c) For benzylation, benzyl alcohol 50 mmol, benzene 125 mmol, catalyst dosage 200 mg, reaction
o
temperature 110 C, reaction time 5 h. The reaction rate was calculated on the basis of molar amount of transformed reactants per gram
catalyst per hour.
TEM experiments were performed to obtain the morphology and size of the as-formed SHMS and SMS silica spheres. Fig. 1
presents the typical TEM images of the as-synthesized, and their particle size is depicted in Table S1 (Supporting information). Figs. 1a
and b clearly demonstrate that the spherical hollow mesoporous silica with 80-100 nm of cavity size and about 30 nm shell thickness
was successfully synthesized by the a facile and scalable two-step soft-hard dual-template assisted sol-gel approach by using the as-
synthesized size-preselected NMCP as a hard template and CTAB as a soft template. The SHMS submicrospheres feature the rough
outer surface. For comparison, the spherical solid mesoporous silica (SMS) with about 114 nm (113 ± 4 nm) particle size was also
prepared (Figs. 1c and d). From Fig. 1 and Table S1, SHMS definitely exhibits a larger particle size than SMS.

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Fig. 1e illustrates the preparation process of SHMS. The size-preselected carbon nano/micro-spheres were prepared by
hydrothermal carbonization of glucose with the subsequently controlled centrifugation process. The carbon spheres were used as the
hard template to prepare SHMS without further modification. From references [40,41], the large amount of silicates are quickly formed
under a high alkali concentration, which can wrap several surfactant micelles. Then the worm-like silicated micelles are formed. The
worm-like-silicated-micelles-containing aggregates are produced on the carbon sphere surface. After removing both soft and hard
template through subsequent calcination process, SHMS submicrospheres with cavities were successfully synthesized.
Fig. 1. (a-d) TEM images of the as-synthesized SHMS (a,b) and SMS (c,d) mesoporous silica submicrospheres. (e) Schematic illustration for the formation of
SHMS with high surface area and large mesopore volume via a facile and scalable OSDSG method.
Nitrogen adsorption-desorption isotherms of the as-synthesized SHMS and SMS are presented in Fig. 2a, and the BJH pore size
distribution from adsorption is shown as inset in Fig. 2a. The textural properties of both of the two silica nanospheres are listed in
Table S1. From Fig. 2a, all of the isotherms feature a typical type IV characteristic according to IUPAC classification and exhibit H1
hysteresis with a featured capillary condensation in mesopores, indicating the existence of mesopore [42,43]. From Fig. 3, the quick
rising adsorption at a quite low P/P
micropores, which is a result of removing CTAB tails trapped into the silica structure [35]. It is interesting that the isotherms present
two clear capillary condensation steps: one is at 0.15-0.60 of a lower relative pressure (p/p ) and the other is at 0.7-1.0 of a higher
0
on the isotherms of the as-synthesized hollow mesoporous silica spheres suggests the existence of
0
relative pressure region, implying the feature of bimodal pores [44-47]. The former features the formation of mesopores in both of the
two samples, and the latter shows the existence of cavities. From the inset in Fig. 2, the SHMS and SMS exhibit two types of pores
containing both mesopores (the centre of pore distribution from the adsorption branch is 2.1 nm and 2.9 nm towards SHMS and SMS,
respectively) and macropores (50-200 nm, based on IUPAC classification). The mesopores are generated by removing the templating
surfactant, whereas the macropores can be originated from the removal of carbon hard template for SHMS and the accumulation of
silica sphere for SMS. SHMS shows a smaller pore size of mesopores than SMS (2.1 vs. 2.9 nm). From Table S1, SHMS exhibits
higher specific surface area towards total and larger pore volume for both of micropores and mesopores than SMS.

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c)
a) 840
0
.15
SHMS
PTA/SHMS
SMS
b)
7
6
4
3
2
1
20
00
80
60
40
20
0
0.12
PTA/SHMS
PTA/SMS
0
0
0
0
.09
.06
.03
.00
PTA/SMS
2
4
6
8
10
5
0
100 150 200 250 300
Pore size (nm)
PTA/SHMS
PTA/SMS
0
.0
0.2
0.4
0.6
0.8
1.0
20
30
40
2 ( )
50
60
70
100
200
300
400
500
600
700
o
o
Relative pressure (P/Po)
Temperature ( C)
2
Fig. 2. (a) N adsorption-desorption isotherms of the as-synthesized SHMS and SMS carriers and the supported PTA solid acid catalysts. Inset is the Barrett-
Joyner-Halenda (BJH) pore size distribution from adsorption branch. (b,c) XRD patterns (b) and NH
PTA/SMS catalysts with 25 wt% of PTA loading.
3
-TPD profiles (c) of the as-prepared PTA/SHMS and
The supported PTA solid acid catalysts on mesoporous silica supports have attracted great attention in diverse transformations
owing their excellent catalytic performance [48-52]. By employing the as-synthesized SHMS and SMS as carriers, the supported PTA
solid acid catalysts with 25 wt% of PTA loading (PTA/SMSN and PTA/WMSN) were prepared via the previously reported
impregnation method [14]. The N
2 3
adsorption desorption isotherms, XRD patterns, and NH -TPD profiles are presented in Figs. 2a and
4
, respectively. From Fig. 2a and Table S1, both PTA/SHMS and PTA/SMS catalysts exhibit a lowering specific area and a decreasing
pore volume in contrast to their corresponding carriers, which is consistent with those in previous reports [53-55]. More interestingly,
the decreasing degree of specific surface area and pore volume of PTA/SMS after supporting PTA is much larger than that of
PTA/SHMS (almost no change in volume and pore diameter for the as-synthesized PTA/SHMS can be observed). Thus would be
ascribed to the higher dispersity of PTA on SHMS than that on SMS, depending on their different morphologies. The higher PTA
dispersity of PTA/SHMS than that of PTA/SMS can be affirmed by the XRD patterns (Fig. 2b). From Fig. 2b, the XRD characteristic
peaks corresponding to PTA on PTA/SHMS can be hardly seen, implying the high PTA dispersity by the high surface and large pore
volume of SHMS [14,56-58]. Furthermore, the acidic properties of the two supported PTA catalysts were investigated, and Fig. 2c
presents the NH -TPD profiles. From Fig. 2c and quantitative result, PTA/SHMS shows much higher amount of acidic sites (0.56
3
mmol/g) in contrast to PTA/SMS (0.26 mmol/g), ascribed to its larger exposure degree of acidic sites, higher surface area, larger pore
volume, and the resulting higher PTA dispersity in comparison with PTA/SMS, those are strongly dependent on its unique hollow
mesoporous morphology.
Table 1
Reaction rate for diverse model reactions over the different solid acid catalysts.
-
1
-1
Reaction rate (mmol h g cat)
Catalyst
[a]
[b]
[c]
[d]
Alkenylation
PTA/SHMS 14.2
Esterification
Alkylation
25.7
Benzylation
23.1
16.7
0.9
3.0
2.0
0.2
PTA/SMS
10.5
-
18.2
[
e]
Blank
0.3
o
[
1
a] Reaction condition: reactant 15 g, catalyst dosage 100 mg, molar ratio of p-xylene to phenylacetylene 10:1, reaction temperature 160 C, reaction pressure
o
.0 MPa, reaction time 7 h; [b] Reaction condition: acetic acid 100 mmol, ethanol 1 mol, catalyst dosage 50 mg, reaction temperature 70 C, reaction time 5 h. [c]
Reaction condition: styrene 100 mmol, benzene 500 mmol, catalyst dosage 50 mg, reaction temperature 70 C, reaction time 5 h. [d] Reaction condition: benzyl
alcohol 50 mmol, benzene 125 mmol, catalyst dosage 200 mg, reaction temperature 110 C, reaction time 5 h. [e] without catalyst, the rate was defined as the
o
o
transformed mmol per hour.
Employing alkenylation, esterification, alkylation, and benzylation as acidic mediated model reactions, the catalytic performance of
PTA/SHMS and PTA/SMS catalysts were investigated, and the reaction rate results are presented in Table 1. From Table 1, in
comparison with the blank experiments, both PTA/SHMS and PTA/SMS catalysts demonstrate significant catalysis in the diverse solid
acid catalyzed transformations. Although SHMS shows much higher particle diameter (outer diameter, larger than 150 nm) than SMS
(about 113 nm), the PTA/SHMS catalyst shows much higher reaction rate for the diverse reactions than PTA/SMS, ascribed to the
unique hollow mesoporous sphere morphology and their resulting high surface area and pore volume lead to high PTA dispersity,
which leads to high amount of acidic sites, besides the strengthened mass transfer by hollow structure [26-33]. However, it can be
found that the increasing degree in activity is less than the one in the amount of acidic sites (0.56 vs. 0.26 mmol/g), which might be the
smaller mesopore size of PTA/SHMS in contrast to PTA/SMS.
Fig. 3 illustrates the enhancing effect of hollow mesoporous morphology of PTA/SHMS. Owing to the hollow morphology of
PTA/SHMS, the diffusion of reactants, intermediates, and products can be efficiently enhanced by the shortening diffusion length [26-
3
3]. As a result, the PTA/SHMS solid acid catalyst demonstrates much superior catalytic activity in comparison with PTA/SMS. From
the reaction results listed in Table 1, the lower degree in the increasing activity than that in the increasing acidic sites can be the
weakened mass transfer from the smaller mesopore size of PTA/SHMS, although the shortened diffusion distance by hollow structure
strengthens mass transfer. Therefore, in order to further improve the catalytic performance of supported PTA catalyst, the modulation
of mesopore size of hollow mesoporous silica spheres would be addressed in the future work. This approach by shorting length of

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mesopore of the mesoporous solid acid catalysts can be considered as a sapiential strategy for improving reaction rate of solid acid
catalysts for diverse transformations, besides the increasing acidic sites resulting from the enlarged surface area and pore volume by
the unique hollow mesoporous morphology. The catalytic performance of PTA/SHMS catalyst can be further modulated and optimized
through adjusting the size of cavity, shell thickness, and also the size and structure of mesopores within the mesoporous shells of
SHMS.
Fig. 3. Schematic illustration for improved catalytic performance over PTA/SHMS solid acid catalyst in contrast to PTA/SMS.
Moreover, the catalytic cycle performance of PTA/SHMS catalyst was investigated, and the results are preented in Table S2
(Supporting information). The results shows that no visible loss in catalytic performance on the devloped PTA/SHMS catalyst can be
observed, suggesting the outstanding catalytic stability. Furthermore, the developed PTA/MSN-0.025 in this work could be a
promising solid acid catalyst for the production of alpha-arylstyrenes through direct alkenylation of diverse aromatics with
phenylacetylene. Herein, the scope of substrates for the alkenylation over the developed PTA/SHMS catalyst was investigated, and the
1
reaction results are listed in Table 2. The molecular structures of alkenylated products are identified by HNMR (Supporting
information). From Table 2, the developed solid acid catalyst demonstrates excellent catalytic performance with more 95% conversion
with high selectivity for the alkenylation of diverse aromatics, suggesting the broad scope of aromatics for the alkenylation for
production of diverse α-arylstyrenes over the developed solid acid catalyst.
In summary, the supported PTA solid acids on the two spherical mesoporous silica carriers including SHMS and SMS were
prepared and evaluated for diverse solid acid-mediated transformations. PTA/SHMS catalyst demonstrates much superior catalytic
performance for the investigated diverse transformations than PTA/SMS, ascribed to the more acidic sites and intensified mass transfer
by the unique hollow mesoporous morphology. This work also shows that the modulation of diffusion distance through morphology
adjustment of mesoporous silica carriers can be considered as a sapiential strategy for preparing the outstanding solid acid catalysts.
The PTA/SHMS also shows promising catalytic properties for alkenylation of diverse aromatics. Moreover, the size-preselected
glucose-derived carbon nano/micro-spheres were used as hard template, which presents a facile method for controlling the size of
cavities of diverse spherical hollow materials.
Table 2
Summary of the alkenylation of diverse aromatics with phenylacetylene to their corresponding α-arylstyrenes over the developed supported PTA solid acid
[a]
catalyst on SHMS.
Entry Aromatics
Products
Conversion
%)
Selectivity
(%)
(
1
100
100
90
96
2
3
95
98
91
82
4
5
6
99
98
91
90
o
[
a] Reaction conditions: reactant mixture 15 g, catalyst dosage 100 mg, molar ratio of aromatics to phenylacetylene 15:1, reaction temperature 160 C, reaction
pressure 1.0 MPa, reaction time 8 h.
Acknowledgment

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This work is financially supported by the National Natural Science Foundation of China (Nos. 21276041 and U1610104) and by
the Chinese Ministry of Education via the Program for New Century Excellent Talents in University (No. NCET-12-0079).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cclet.2018.xx.xxx.

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