Efficient synthesis of styrene from toluene with MeOH: Via a ternary composite catalyst

Article abstract of DOI:10.1016/j.apcata.2020.117807

To achieve high selectivity of styrene from toluene and methanol, a new strategy, the coupling of methanol dehydrogenation and side-chain alkylation of toluene by ternary composite catalyst combining methanol dehydrogenation, B/SiO₂ and CsX com

Full text of DOI:10.1016/j.apcata.2020.117807

AppliedCatalysisA,General605(2020)117807
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Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Efficient synthesis of styrene from toluene with MeOH: Via a ternary
composite catalyst
Qiao Hana,b,c,1, Peidong Lib,1, Yangyang Yuanb, Xiaomin Zhangb, Hongchen Guoa,*, Lei Xub,*
a State Key Laboratory of Fine Chemicals & School of Chemical Engineering, Dalian University of Technology, Dalian 116024, People’s Republic of China
b National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People’s Republic of China
c University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
A R T I C L E I N F O
A B S T R A C T
Keywords:
To achieve high selectivity of styrene from toluene and methanol, a new strategy, the coupling of methanol
dehydrogenation and side-chain alkylation of toluene by ternary composite catalyst combining methanol de-
hydrogenation, B/SiO2 and CsX components, is proposed. The methanol dehydrogenation component could
promote the in-situ formation of formaldehyde (HCHO) intermediate, transferring to B/SiO2 and CsX compo-
nents. The formation of HCHO over dehydrogenation component is driven by the side-chain alkylation reaction
over CsX-B/SiO2 during the coupling reaction. In addition, B/SiO2 is beneficial to stabilize HCHO. When CuO/
SiO2 is applied as the dehydrogenation component, the styrene and ethylbenzene yield reaches 31.0 % at a
methanol conversion of 60.1 % with the styrene/ethylbenzene molar ratio in products of 3.1 over CsX-CuO/
SiO2-B/SiO2. The effective method to prepare a ternary composite catalyst provide helpful guideline for de-
veloping a more efficient CsX-based catalyst for conversion of toluene with methanol into styrene in the further.
Toluene
Methanol
Dehydrogenation
Side-chain alkylation
Composite catalyst
1. Introduction
charge (Oδ−) in CsX framework acting as base sites polarize methyl
side-chain of toluene and dehydrogenate methanol to formaldehyde
Being in extremely large volume demand, styrene is an important
industrial product to synthesize and manufacture various polymers,
such as polystyrene (PS), styrene-butadiene rubber (SBR) and other
industrial resins [1,2]. The commercial synthesis strategy of styrene
mainly relies on two-step route—Friedel-Crafts alkylation of ethylene
with benzene, followed by energy-intensive (generally 550–700 °C)
dehydrogenation of ethylbenzene [3–5]. As a sustainable one-step al-
ternative, the side-chain alkylation of toluene with methanol is con-
sidered as an attractive process because of economic advantages such as
large availability and low cost of feedstock, as well as energy con-
servation [6]. Despite extensive research efforts in this area for few
decades, the commercialization of the process still remains challenging
due to lack of an efficient catalyst with high yield of side-chain alky-
lation products (styrene and ethylbenzene, YST+EB) as well as high
styrene/ethylbenzene ratio (ST/EB) in the products.
(HCHO) [26]. Itoh et al. pointed out that specific configurations with
spatially limited acid and base sites were essential for the efficient side-
chain alkylation [27]. It is generally believed that HCHO is regarded as
the real alkylating reagent and undergoes aldol-like condensation with
toluene to produce styrene [27–29]. However, many side reactions can
happen simultaneously over CsX (Scheme 1). On one hand, ethylben-
zene is produced together with styrene during the reaction
[7,8,13,14,30,31]. On the other hand, HCHO can self-decompose into
CO and H2 before side-chain alkylation reaction [8,30,31].
To further enhance the activity and selectivity of CsX, many at-
tempts have been undertaken by the modification with metal compo-
nents (Cu, Ag, Zn, etc.), and promoting addition (B and P) through
different ways such as impregnation, physical mixing, and ion-ex-
change [10,32–36]. Among those process, the modifications by in-
troducing alkali oxides and boron containing compounds have been
extensively received attention as they showed high catalytic activity or
selectivity for styrene [3,10,24,31,37,38]. Previous works illustrated
that the modification of CsX with alkali oxides, especially cesium oxide,
could greatly improve the side-chain alkylation products yield for
conversion of toluene with methanol [20–22]. Our team demonstrated
The cesium ion-exchanged zeolite X (CsX) has been widely accepted
to be the more suitable catalyst for side-chain alkylation of toluene with
methanol owing to its appropriate acidity and basicity [6–25]. Typi-
cally, the cesium cations acting as Lewis acid sites adsorb and stabilize
the ring of toluene, on the other hand, the oxygen atoms with a negative
⁎ Corresponding authors.
E-mail addresses: hongchenguo@dlut.edu.cn (H. Guo), leixu@dicp.ac.cn (L. Xu).
1 These authors contributed equally to this work and are considered as co-first authors.
https://doi.org/10.1016/j.apcata.2020.117807
Received 10 July 2020; Received in revised form 22 August 2020; Accepted 24 August 2020
Availableonline26August2020
0926-860X/©2020ElsevierB.V.Allrightsreserved.

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
Scheme 1. A flow chart of the various interlinked reaction pathways involved in conversion of toluene with methanol.
that the promoting effect for cesium oxide modified CsX catalyst was
attributed to the increased base strength of the oxygen atoms with
negative charge (Oδ−) in the zeolite framework by electron donating
function of cesium oxides in the supercage of CsX, which enhanced
methanol dehydrogenation to HCHO in side-chain alkylation [22].
However, the styrene selectivity in products was relatively low. The
reason was that the stronger basicity of CsX modified with cesium oxide
could enhance the formation of active hydrogen atoms and further gave
rise to the conversion of styrene to ethylbenzene in products [22].
Besides, it has been reported that modification of CsX with impreg-
nating boric acid or metal borates could greatly facilitate styrene se-
lectivity in products, which was generally attributed to the neu-
tralization of strongly basic sites in CsX, resulting in restraining transfer
hydrogenation of styrene with methanol and HCHO to form ethylben-
zene [3,39]. Recently, a CsX-based modified with B/SiO2 catalyst was
prepared using a mortar-mixing method by us, which could greatly
improve styrene selectivity. Results indicated that the boron played a
crucial role in adsorbing, stabilizing and activating HCHO during side-
chain alkylation [40]. Based on the promotion effect and mechanism of
cesium oxides and boron modified CsX, our group has designed a high-
efficient catalyst prepared by grinding CsX, CsX modified with cesium
oxide and B/SiO2 for side-chain alkylation of toluene with methanol
[40]. It showed an outstanding YST+EB of 39.5 %. But, ST/EB of around
1.8 was low. Therefore, it still remains challenging to obtain a catalyst
with high ST/EB as well as maintaining relatively high YST+EB. It might
be the presence of cesium oxide led to increasing the basicity of CsX,
which intensified the conversion of styrene to ethylbenzene in products.
Instead of the modification of CsX with cesium oxide, we found the
introduction of dehydrogenation component into CsX (Scheme 2) could
not only improve methanol dehydrogenation to HCHO, but also main-
tained the basicity of CsX [25]. Combination with the role of boron in
side-chain alkylation might be expected to solve the issue of low ST/EB
on composite catalysts. Recently, many efforts were devoted into the
study of methanol dehydrogenation [41–63]. Among them, the main
catalysts used for direct methanol dehydrogenation to HCHO were so-
dium salts, metal-containing catalysts and ZSM-5-based zeolites
[54–63].
Here, we explore the development of a highly active ternary com-
posite catalyst combining methanol dehydrogenation component, B/
SiO2 and CsX for the conversion of toluene with methanol into styrene.
Our results indicate the design of a composite catalyst composed of the
granules of CsX, CuO/SiO2 and B/SiO2 (CsX-CuO/SiO2-B/SiO2) showed
the highest catalytic activities. The promotion effects of different
components are comprehensively investigated. The effects of compo-
sition of composite catalyst, basicity of CsX component, proximity of
different components and reaction conditions on the catalytic beha-
viours are also discussed in detail.
2. Experimental
2.1. Catalysts preparation
2.1.1. Preparation of CsX catalyst
CsX catalyst was obtained by conventional ion-exchange of NaX (Si/
Al = 1.13, Catalyst Plant of Nankai University). The detailed procedure
was reported by our previous work [25]. The preparation parameters of
CsX with different cesium ion exchanging degree (CsED) denoted as X1-
X6 were displayed in Table S1.
2.1.2. Preparation of dehydrogenation catalysts
Typically, the sodium salts, such as sodium carbonate, sodium bo-
rate, sodium molybdate and sodium aluminate, were prepared from the
corresponding analytical grade compounds or hydrated compounds.
The preparation of catalysts containing both sodium salt and nickel or
indium oxide was carried out by mortar-mixing of finely ground sodium
carbonate and nickel or indium oxide [54,55]. The CuO/SiO2, ZnO/
SiO2, ZrO2/SiO2 and P-CuO/SiO2 catalysts were prepared by a con-
ventional wetness impregnation method with an aqueous solution of
the corresponding metallic nitrate or phosphoric acid as the precursor
and SiO2 (Qingdao Ocean Chemical Co. Ltd.) as the support [57,58,63].
Therein, the loading amount of Cu was 1.9 wt%. The Ag-SiO2-MgO-
Al2O3 catalyst prepared by sol-gel methods [59]. The Na-ZSM-5 mate-
rial was prepared from ZSM-5 zeolite according to sodium nitrate so-
lution exchange procedures [58,62]. Similarly, the Cu(II)-ZSM-5, Cs-
ZSM-5 and Mg-ZSM-5 catalysts were derived from Na-ZSM-5 by the
Scheme 2. Illustration of two process of conversion of toluene with methanol
into styrene and ethylbenzene: (A) over CsX, (B) over composite catalyst
(containing CsX and dehydrogenation components).
2

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
styreneoutlet + ethylbenzeneoutlet
conventional ion-exchange procedure with aqueous solution of corre-
sponding metallic nitrate [58]. The specific preparation methods of
dehydrogenation catalysts mentioned above were described in our
previous work [25].
Y
ST+EB(%)=
×100%
methanolinlet
(5)
(6)
(7)
styreneoutlet
ST/EB=
ethylbenzeneoutlet
2.1.3. Preparation of boron-containing catalyst
styreneoutlet
methanolinlet
Y
ST(%)=
×100%
SiO2 was loaded with the aqueous solutions of boric acid (Tianjin
Kemiou Chemical Reagent Co. Ltd., 99.5 %) by conventional incipient
wetness impregnation, in which the loading amount of boric acid was
16 wt%. After impregnation, the solid was dried at 120 °C overnight and
subsequently calcined in air stepwise up to 600 °C for 6.0 h. The ob-
tained material was denoted as B/SiO2.
Similarly, the reaction of HCHO with toluene was also manipulated
by pumping a mixture liquid into fixed-bed flow reactor. The mixture
liquid was comprised of toluene and triformol (molar ratio of 18/1,
corresponding to toluene/HCHO molar ratio of 6/1), and the triformol
was used as a precursor for in situ producing HCHO [8,13]. The
pumped triformol was first decomposed into HCHO over H3PO4/SiO2
catalyst at about 295 °C.
2.1.4. Preparation of composite catalyst
The composite catalysts were prepared by a simple granule-stacking
method. Specifically, CsX, dehydrogenation catalyst and B/SiO2 were
pelleted into 20–40 mesh respectively, and then the separate samples
were mixed with a varied mass ratio while keeping the amount of CsX
constant of 1.0 g. The obtained catalysts were denoted as CsX-DE-a-B/
SiO2-b, therein DE referred to the kind of dehydrogenation catalyst, and
a and b referred to the mass content of dehydrogenation catalyst and B/
SiO2 to CsX respectively. If not specified, the mass content of dehy-
drogenation catalyst and B/SiO2 to CsX was 0.15 and 0.20, respectively,
and the composite catalyst was denoted as CsX-DE-B/SiO2.
2.3. Catalyst characterization
Powder X-ray diffraction (XRD) was performed on a PANAlytical
X’Pert Pro X-ray diffractometer using Cu Kα radiation (λ = 1.54059 Å)
at 40 kV and 40 mA. The morphological information and element dis-
tribution were examined with scanning electron microscopy (SEM) and
energy dispersive X-Ray spectroscopy (EDX) analysis obtaining on a
JSM-7800 F microscope. The composition of a catalyst was quantified
using X-ray fluorescence (XRF) spectroscopy on a PANAlytical Zetium
X-ray fluorescence spectrometer. In-situ FTIR spectroscopy of adsorbed
methanol was operated on Bruker Tensor 27. A thin wafer (about
10 mg) sample was placed in an in-situ cell with KBr windows. Prior to
measurement, the sample was pretreated at 500 °C for 1.0 h in a va-
cuum. All of samples were exposed to 220 Pa methanol at 350 °C for
30 min, and the spectrum were recorded at room temperature. The
acidity and basicity of catalyst were characterized by Temperature-
Programmed-Desorption of NH3 and CO2 measurement (NH3-TPD and
CO2-TPD) on a Micromeritics Autochem 2920, respectively. At first,
each catalyst sample loaded in a quartz U tube was pretreated under Ar
flow for 1.5 h at 550 °C, and then cooled to the desired temperature.
The sample was saturated with 8 % NH3/He (vol./vol.) at 100 °C or CO2
at 80 °C for 30 min. Subsequently, the recording was started at a heating
rate of 10 °C/min to 600 °C. Desorbed NH3 or CO2 was detected con-
tinuously as a function of temperature by TCD. For CO2-TPD experi-
ment, a cold trap filling with a mixture of m-xylene and liquid nitrogen
(−47 °C) was installed upstream to avoid the possible errors caused by
water.
The mortar mixing samples of CsX, dehydrogenation catalyst and B/
SiO2, which were separately ground for 15 min preliminarily, were
manually mixed in an agate mortar for 15 min. Here, the mortar mixing
catalysts were denoted as CsX∼DE∼B/SiO2, where DE referred to the
dehydrogenation catalyst and the mass content of dehydrogenation
catalyst and B/SiO2 to CsX were 0.15 and 0.20, respectively.
2.2. Activity measurements
The conversion of toluene and methanol was performed in a fixed-
bed flow reactor. Typically, a certain amount of the composite catalyst
with grain sizes of 20–40 mesh was loaded in a quartz tube and pre-
treated at 550 °C under a flow of air (40 mL/min) for 1.0 h before re-
action. The liquid mixture with a toluene and methanol molar ratio of 6
was fed into the reactor at a weight hourly space velocity (WHSV) of 2
h−1 with a constant helium flow rate of 10 mL/min at a reaction
temperature of 430 °C unless otherwise stated.
Products were analyzed by on-line gas chromatographs (Angilent
GC7890A), which were equipped with a thermal conductivity detector
(TCD) and a flame ionization detector (FID). A Porapark Q (4 m × 1/
8″) packed column was connected to TCD, while an Agilent CP-WAX
(25 m × 32 μm × 1.2 μm) capillary column was connected to FID. The
light gas (H2, CH4, CO, CO2) and HCHO were analyzed by TCD, while
other products were analyzed by FID. The catalytic performance after
50 min of reaction was typically used for discussion.
3. Result and discussion
CsX with CsED of 46.3 % was used as the main component for side-
chain alkylation of toluene in combination with methanol dehy-
drogenation catalyst and B/SiO2 by a granule-stacking way to finally
generate composite catalysts. The catalytic behavious of composite
catalysts for conversion of toluene with methanol was displayed in
Table 1.
Methanol conversion (XCH3OH), toluene conversion (Xtoluene), side-
chain alkylation in alkylation products selectivity (Sside-chain), CO and
CO2 yield (YCO+CO2), styrene and ethylbenzene yield (YST+EB), styrene/
Compared with catalytic performance of CsX, Xtoluene, YST+EB, ST/
EB and YST increased over all composite catalysts, demonstrating that
introducing methanol dehydrogenation components and B/SiO2 to-
gether could improve the catalytic activity for side-chain alkylation of
toluene. Meanwhile, the ternary composite catalysts showed high side-
chain alkylation in alkylation products selectivity except CsX-ZrO2/
SiO2-B/SiO2, which could be attributed to the existence of Brønsted
acid sites on ZrO2/SiO2 [13,64]. The results indicated that our strategy
to improve the side-chain alkylation products and ST/EB in conversion
of toluene with methanol into styrene by designed the ternary com-
posite catalysts is practical and worth in-depth studies.
ethylbenzene molar ratio in products (ST/EB) and styrene yield (YST
)
were calculated according to the equations shown below:
methanolinlet methanol and DMEoutlet
XCH3OH(%)=
Xtoluene (%)=
Sside-chain (%)=
YCO+CO2 (%)=
×100%
methanolinlet
(1)
(2)
tolueneinlet tolueneoutlet
×100%
tolueneinlet
styreneoutlet + ethylbenzeneoutlet
×100%
styreneoutlet + ethylbenzeneoutlet + xyleneoutlet
(3)
(4)
Compared with the binary composite catalysts comprised of dehy-
drogenation catalysts and CsX (Table S2), introduction of B/SiO2 could
significantly improve ST/EB and YST (Table 1), as well as decease YCO
COoutlet + CO2
outlet
×100%
methanolinlet
3

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
Table 1
Conversion of toluene with methanol over CsX and composite catalysts composed of CsX, dehydrogenation catalysts and B/SiO2.a.
Catalysts
XCH3OH (%)
Xtoluene (%)
SSide-chain (%)
YST+EB (%)
ST/EB
YST (%)
CsX
41.9
34.1
43.4
39.2
25.0
44.7
40.3
34.5
54.6
60.1
49.3
56.1
41.5
38.8
59.7
40.0
2.3
3.2
3.3
3.4
2.8
3.6
3.1
3.2
5.0
5.4
4.5
5.1
3.6
3.4
5.4
3.4
98.1
99.2
99.7
99.9
98.0
99.7
99.7
90.6
99.4
99.7
99.5
99.6
99.8
99.6
98.5
99.3
12.2
17.2
19.7
19.6
14.6
20.5
18.0
16.7
28.2
31.0
25.2
28.8
20.5
19.4
29.3
18.9
1.2
3.0
1.9
2.2
4.4
1.5
1.8
1.8
2.8
3.1
2.4
3.1
2.3
2.1
2.3
2.0
6.5
CsX-Na2CO3-0.15-B/SiO2-0.2
CsX-(Na2CO3-Ni)-0.1-B/SiO2-0.2
CsX-(Na2CO3-In2O3)-0.1-B/SiO2-0.2
CsX-Na2B4O7-0.15-B/SiO2-0.2
CsX-Na2MoO4-0.1-B/SiO2-0.2
CsX-NaAlO2-0.1-B/SiO2-0.2
12.9
12.4
13.4
11.9
12.3
11.6
10.6
20.8
23.5
17.7
21.7
14.2
13.1
20.3
12.5
CsX-ZrO2/SiO2-0.15-B/SiO2-0.2
CsX-ZnO/SiO2-0.15-B/SiO2-0.2
CsX-CuO/SiO2-0.15-B/SiO2-0.2
CsX-(P-CuO/SiO2)-0.1-B/SiO2-0.2
CsX-(Ag-SiO2-MgO-Al2O3)-0.1-B/SiO2-0.2
CsX-(Na-ZSM-5)-0.1-B/SiO2-0.2
CsX-(Cs-ZSM-5)-0.1-B/SiO2-0.2
CsX-(Cu(II)-ZSM-5)-0.1-B/SiO2-0.2
CsX-(Mg-ZSM-5)-0.1-B/SiO2-0.2
a
The composite catalysts were prepared with 1.0 g of CsX, 0.1 or 0.15 g of dehydrogenation catalysts and 0.2 g of B/SiO2 by granule-stacking way. The catalytic
performance was obtained at 430 °C under WHSV of 2 h−1 and reactant with a toluene/methanol ratio of 6/1.
(Table S3). It was due to the fact that the promotion effect of
with increase of temperature, ascribing to the lower catalytic activity
for side-chain alkylation reaction over CsX at high temperature [29].
Although a large amount of HCHO was produced over CuO/SiO2 at
500 °C, the catalytic activity of CsX-CuO/SiO2 and CsX-CuO/SiO2-B/
SiO2 composite catalyst was still relatively low. This result implied that
the smooth proceeding of side-chain alkylation of toluene was critical
for effective conversion of toluene with methanol into styrene over the
composite catalyst. Besides, when the reaction temperature increased,
the aromatics selectivity for ethylbenzene increased along with C9+
elevated, on the contrary, the styrene selectivity decreased (Fig. 1B).
This was due to the fact that the secondary transfer hydrogenation of
styrene became significant at higher temperatures [8].
+CO2
boron was favorable for styrene selectivity and restrained the decom-
position of HCHO [40]. However, XCH3OH declined over the ternary
composite catalysts. This was ascribed to the synergistic catalysis effect
between the boron sites and CsX restraining the methanol conversion
[40].
A CuO/SiO2 catalyst showed high selectivity of HCHO from me-
thanol in a wide-temperature range (Fig. S1). When CsX was combined
with CuO/SiO2 by the granule-stacking way to form CsX-CuO/SiO2-
0.15 (CsX-CuO/SiO2), it showed higher side-chain alkylation products
yield than that of CsX (Table S2) [25]. Moreover, the introduction of B/
SiO2 into CsX-CuO/SiO2 (CsX-CuO/SiO2-0.15-B/SiO2-0.2, CsX-CuO/
SiO2-B/SiO2) could generate styrene as the major product (styrene se-
lectivity of about 40 % in products), which was shown on Fig. 1A, in
contrast to CsX and CsX-CuO/SiO2 with high selectivity for methanol
decomposition products of CO and CO2.
3.1. Effect of the composition on catalytic activity of composite catalysts
The effect of the composition, such as mass ratio of CsX, CuO/SiO2
and B/SiO2 as well as loading amount of Cu and boric acid, on catalytic
activity of CsX-CuO/SiO2-B/SiO2 composite catalysts for conversion of
toluene with methanol were discussed, which was shown on Fig. 2.
It was found that CsX-B/SiO2 catalyst without CuO/SiO2 showed a
65.0 % of selectivity for styrene in aromatic products, but XCH3OH was
low (Fig. 2A). The introduction of CuO/SiO2 could enhance the me-
The optimized temperature for CsX-catalyzed styrene synthesis was
430 °C (Fig. S2). On the other hand, the CuO/SiO2 catalyst alone ex-
hibited high production of HCHO at 500 °C (Fig. S1). As the tempera-
ture rose from 430 °C to 500 °C, the CO and CO2 selectivity significantly
increased (Fig. S3), and YST+EB decreased (Fig. 1B) over CsX, CsX-CuO/
SiO2 and CsX-CuO/SiO2-B/SiO2. Particularly, the major products over
CsX-CuO/SiO2-B/SiO2 shifted from styrene to CO and CO2 (Fig. S3)
thanol conversion without
a significant change in aromatics
Fig. 1. Catalytic activity and selectivity corre-
lation of CsX, CsX-CuO/SiO2-0.15 and CsX-
CuO/SiO2-0.15-B/SiO2-0.2. (A) Product dis-
tribution over CsX-CuO/SiO2-0.15-B/SiO2-0.2
in comparison to that over CsX and CsX-CuO/
SiO2-0.15 at 430 °C. (B) The catalytic perfor-
mance of CsX, CsX-CuO/SiO2-0.15 and CsX-
CuO/SiO2-0.15-B/SiO2-0.2 at 430 °C and
500 °C, respectively. The composite catalysts
were prepared with 1.0 g of CsX, 0.15 g of
CuO/SiO2 and 0.2 g of B/SiO2 by granule-
stacking way. The catalytic performance was
obtained at 430 °C under WHSV of 2 h−1 and
reactant with a toluene/methanol ratio of 6/1.
4

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
Fig. 2. Effect of composition on catalytic behaviours of composite catalysts by granule of CsX, CuO/SiO2 and B/SiO2. (A) and (B) Effect of mass ratio of CsX, CuO/
SiO2 and B/SiO2. (C) and (D) Effect of loading amount of Cu and boric acid. The composite catalysts were prepared with 1.0 g of CsX, 0.15 g of CuO/SiO2 and 0.2 g of
B/SiO2 by granule-stacking way. The catalytic performance was obtained at 430 °C under WHSV of 2 h−1 and reactant with a toluene/methanol ratio of 6/1.
distribution. With the mass ratio of CuO/SiO2 to CsX-B/SiO2 increasing
from 0 to 0.20 (Fig. 2A) or the corresponding loading amount of Cu
increasing from 0.5 wt% to 3.0 wt% (Fig. 2C), YST+EB and YST over the
composite catalysts first increased and subsequently decreased, which
was consistent with the variation tendency of methanol conversion. It
demonstrated that XCH3OH, YST+EB and YST could be tuned by varying
the relative mass ratio of CuO/SiO2 to CsX-B/SiO2, which lent support
to the fact that the composite catalysts were multifunctional and the
reaction involved intermediate transport in gas phase. Fig. 2A and C
also showed that when the mass ratio of CuO/SiO2 to CsX-B/SiO2 in-
creased from 0.05 to 0.15 or loading amount of Cu changed from 0.5 wt
% to 1.9 wt%, the variation tendency of YST+EB and YST was similar to
the corresponding changing of the amount of HCHO by increasing mass
ratio of CuO/SiO2 (Fig. S4) and the Cu loading amount (Fig. S5). It
suggested that the CuO/SiO2 component in the composite catalyst
played a key role in increasing the content of HCHO and corroborated
that the intermediate over CsX-CuO/SiO2-B/SiO2 composite catalyst
was HCHO. Besides, C9+ selectivity declined with increase of the mass
ratio of CuO/SiO2 to CsX-B/SiO2 from 0.05 to 0.15 and loading amount
of Cu from 0.5 wt% to 1.9 wt%, respectively. However, further in-
creasing the mass ratio of CuO/SiO2 to CsX-B/SiO2 from 0.15 to 0.25
and loading amount of Cu from 1.9 wt% to 3.0 wt%, respectively, de-
creased YST+EB and YST, but increased the C9+ selectivity. This might
attribute to the high content of HCHO around CsX favorable for
producing further side-chain alkylation of ethylbenzene, resulting in
decline of styrene and ethylbenzene yield and selectivity [25]. As
HCHO yield decreased by changing the loading amount of Cu from
3.0 wt% to 4.0 wt% over CuO/SiO2 (Fig. S5), YST+EB and YST increased
again. It indicated that the amount of HCHO formed over dehy-
drogenation component dominated the conversion of toluene with
methanol into styrene over the composite catalyst. The different de-
hydrogenation components exhibited the different dehydrogenation
ability [56]. Thus, introduction of the different dehydrogenation com-
ponents into CsX and B/SiO2 would remarkably influence the catalytic
performance (Table 1). Meanwhile, our previous work pointed out that
many factors, such as formation, decomposition and diffusion of HCHO,
as well as the possible competitive reactions over the different com-
ponents, also might affect the catalytic activity of the composite cata-
lysts in conversion of toluene with methanol [25].
Except decomposition products of methanol or HCHO and ring al-
kylation products of toluene, no side-chain alkylation products was
detected over B/SiO2 in conversion of methanol or HCHO with toluene
(Table S4), indicating that the role of B/SiO2 was not involved in the
formation of active intermediate species of side-chain alkylation. This
result was similar with the previous report by us [40]. Hence, according
to the researching intermediate of CsX-CuO/SiO2 catalyst [25], it was
further believed that the active intermediate over CsX-CuO/SiO2-B/
SiO2 composite catalyst was HCHO. With the mass ratio of B/SiO2 to
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AppliedCatalysisA,General605(2020)117807
3.2. Effect of basicity of CsX component on catalytic activity of composite
catalysts
It was generally deemed that the side-chain alkylation was a base
catalyzed reaction, and relatively strong base sites were required for the
formation of styrene [6]. To understand the effect of basicity of CsX on
catalytic behaviours of the composite catalysts for XCH3OH, YST and
aromatic products distribution, we have systematically tuned the ba-
sicity by tuning the CsED of CsX. The basicity of NaX and CsX with
different CsED could be determined by CO2-TPD curves, which was
shown on Fig. S6. Both NaX and CsX with different CsED showed a
desorption peak in a CO2-TPD profile. The CO2 desorption peak of NaX
centered at 135 °C. With the increase of CsED, the desorption tem-
perature and peak area of CsX gradually increased, demonstrating that
both the strength and the amount of base sites increased. The observed
trend in basicity of CsX with different CsED was consistent with that
reported by the earlier reports [8,13,20,21]. The composition and XRD
patterns of NaX and CsX with different CsED was shown on Table S5
and Fig. S7, respectively. The SiO2/Al2O3 ratios of CsX with different
CsED exhibited no obvious changes after the ion-exchanging processes
and all catalysts showed typical faujasite structure XRD peaks of zeo-
lites X. The results indicated that CsX preserved the molecular sieve
structure of zeolites X after ion-exchanging process.
Fig. 3. IR spectra of adsorbed methanol on the indicated catalysts. The samples
were exposed to methanol at 350 °C for 30 min, and all the spectrum were re-
corded at room temperature.
CsX-CuO/SiO2 increasing from 0 to 0.40 or the boric acid loading
amount of B/SiO2 increasing from 8 to 24 %, YST+EB and YST first in-
creased and then decreased over composite catalysts, as well as ST/EB
increased considerably (Fig. 2B and D). Besides, the incorporation of B/
SiO2 into CsX-CuO/SiO2 declined XCH3OH. According to our previous
work, B/SiO2 could adsorb and stabilize HCHO from methanol dehy-
drogenation [40].
The ternary composite catalysts containing CsX with different CsED,
CuO/SiO2 with a 1.9 wt% of Cu loading amount and B/SiO2 with a
16 wt% of boric acid loading amount were investigated for the XCH3OH
,
Y
ST+EB, YST and aromatic products distribution and the results were
depicted on Fig. 4C and D. The XCH3OH increased significantly from 30
% to 80 % with the increasing CsED of CsX in composite catalysts
(Fig. 4C). This could be mainly explained by the fact that the increase of
CsED enhanced the basicity of CsX, which improved the ability of de-
hydrogenation methanol to HCHO [20]. However, the composite cat-
alyst composed of granules of NaX, CuO/SiO2 and B/SiO2 showed high
XCH3OH because of mainly ring alkylation of toluene with methanol to
xylene (Fig. 4D). The XCH3OH over composite catalysts (Fig. 4A) was far
higher than that over the corresponding CsX (Fig. 4C), resulting from
the significant increase of XCH3OH derived from the thermodynamic
driving force for dehydrogenation catalysts [25].
Based on above, the CuO/SiO2 dehydrogenation component could
increase the conversion of methanol to HCHO, and B/SiO2 component
could adsorb and stabilize HCHO, which improved styrene selectivity.
Meanwhile, the control of composition of composite catalyst is crucial
toward both catalytic activity and product selectivity.
In order to better understand the promoting effect of CuO/SiO2 and
B/SiO2 components, the formation of surface species after being ex-
posed to methanol over indicated catalysts were detected by an FT-IR
and the results were shown in Fig. 3. The two bands over CsX, CsX-
CuO/SiO2 and CsX-CuO/SiO2-B/SiO2 were detected at about
1664 cm−1 and 1608 cm−1, which were assigned to unidentate formate
and bidentate formate, respectively [25,65], indicating that there were
similar products from methanol over the three catalysts. It has been
deemed that the unidentate formate might be related to side-chain al-
kylation of HCHO with toluene, while bidentate formate was associated
with decomposition of HCHO to CO [45]. Besides, Hattori et al. con-
sidered that the unidentate formate, activated HCHO over CsX and
HCHO in gas phase were in equilibrium. Thus, it could deduce that the
sum of unidentate formate and bidentate formate was connected with
the amount of HCHO. In this work, the sum of unidentate and bidentate
formate over CsX-CuO/SiO2 was higher than that over CsX. It indicated
that the introduction of CuO/SiO2 into CsX could increase the content
of HCHO intermediate. Moreover, the content of unidentate formate
over CsX, CsX-CuO/SiO2 and CsX-CuO/SiO2-B/SiO2 was consistent with
the catalytic performance (Fig. 1). This was because that the content of
unidentate formate was proportional to that of activated HCHO, which
improved production of styrene [14]. Furthermore, compared with that
over CsX-CuO/SiO2, the bidentate formate over CsX-CuO/SiO2-B/SiO2
decreased, which was similar with the FT-IR results of introduction of
B/SiO2 into CsX [40]. It was determined that the introduction of boron
was favorable for stabilization of HCHO instead of decomposition.
Therefore, CuO/SiO2 was favorable for formation of HCHO inter-
mediate, and B/SiO2 played role in stabilizing HCHO over CsX-CuO/
SiO2-B/SiO2 in side-chain alkylation.
When the CsED of CsX was lower than about 20 %, the YST+EB, YST
and styrene selectivity were relatively low and xylene was a main
product (Fig. 4C and D), due to weak strength of basicity with low CsED
insufficient active methyl group of toluene, resulting in the weak ability
of side-chain alkylation over the corresponding CsX [13]. A further
increase of the basicity of CsX in composite catalysts facilitated YST+EB
and side-chain alkylation products selectivity because sufficient basicity
of CsX with increasing CsED could activate methyl group of toluene and
dehydrogenate methanol to HCHO. When CsED of CsX was over about
43 %, the ST/EB decreased, which could explained by the too strong
basicity of CsX leading to accelerate transfer hydrogenation from
styrene to ethylbenzene in high CsED of CsX [13].
As the CsED of CsX increased, similar trends with XCH3OH, YST+EB
,
Y
ST and aromatic products distribution were observed, comparing with
CsX and the composite catalyst (Fig. 4). Combined with no side-chain
alkylation products detected over CuO/SiO2 and B/SiO2 components
[25,40], it indicated that the main component for side-chain alkylation
reaction was CsX over CsX-CuO/SiO2-B/SiO2 catalyst. Based on above,
the results clearly demonstrated that the basicity of CsX was a key
factor in determining the catalytic activities and product selectivity.
Meanwhile, there was an optimum basicity of the composite catalyst for
the selective formation of styrene.
3.3. Effect of proximity of different components on catalytic activity of
composite catalysts
The proximity of different active sites in composite catalysts has
been reported to make significant effect on the catalytic activity and
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Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
Fig. 4. Effect of exchange degree of CsX on catalytic behaviours of the NaX/CsX (A and B) and composite NaX/CsX-CuO/SiO2-B/SiO2 (C and D) catalysts. (A) and (C)
Methanol conversion, yield of styrene and ethylbenzene and yield of styrene. (B) and (D) Aromatic products selectivity. The composite catalysts were prepared with
1.0 g of NaX/CsX, 0.15 g of CuO/SiO2 and 0.2 g of B/SiO2 by granule-stacking way. The catalytic performance was obtained at 430 °C under WHSV of 2 h−1 and
reactant with a toluene/methanol ratio of 6/1. X-CB represents CsX-CuO/SiO2-B/SiO2.
products selectivity [66–72]. Thus, we investigated the effect of the
spatial arrangement of CsX, CuO/SiO2 and B/SiO2 in composite cata-
lysts on catalytic behaviours, which was shown on Fig. 5.
alkylation [25]. XCH3OH first increased because of aggravated methanol
decomposition (Table S7), and then decreased.
Using a dual-bed configuration with B/SiO2 loaded above CsX-CuO/
SiO2 and separated by quartz wool (B/SiO2+CsX-CuO/SiO2, Fig. 5I),
YST+EB, YST and styrene selectivity were lower than that over catalysts
by mixing components of B/SiO2 and CsX-CuO/SiO2, but the catalytic
performance of B/SiO2+CsX-CuO/SiO2 was similar with that of CsX-
CuO/SiO2 catalyst (Table S2), due to the role of boron being neither
generating the active species, nor providing activity zones for side-
chain alkylation [40]. Compared with the result of the dual-bed model
catalyst, XCH3OH was low over CsX-CuO/SiO2-B/SiO2 (Fig. 5H), but
The separation of CuO/SiO2 from CsX-B/SiO2 by quartz wool in one
reactor (CuO/SiO2+CsX-B/SiO2, Fig. 5A), the dual-bed configuration,
led to low XCH3OH, YST+EB and YST. This was due to lack of the ther-
modynamic driving force when the zeolite CsX was far from CuO/SiO2
[25]. It also found that XCH3OH and YST+EB over CuO/SiO2+CsX-B/SiO2
were higher than that over CsX-B/SiO2 (Table S6), which implied that
formation of HCHO from methanol over the dehydrogenation compo-
nent could efficiently diffuse in the gas phase toward the active sites of
CsX to improve the side-chain alkylation of toluene. The spatial ar-
rangement of the three components increased as the integration manner
changed from granule-stacking (CsX-CuO/SiO2-B/SiO2, Fig. 5B and H)
to mortar-mixing (CsX∼CuO/SiO2∼B/SiO2, Fig. 5E), as demonstrated
by the SEM and EDX characterization, which was illustrated on Fig. S8
and Fig. S9, respectively. The CsX-CuO/SiO2-B/SiO2, which was typi-
cally used in our work, and CsX∼CuO/SiO2∼B/SiO2 sample preserved
the crystal structure and acid-base properties of CsX according to the
characterization of XRD (Fig. S10), NH3-TPD and CO2-TPD (Fig. S11).
This result suggested that composite catalysts by granule-stacking and
mortar-mixing showed the same ability for side-chain alkylation. As the
proximity of components between CuO/SiO2 and CsX increased from
granule-stacking (CsX-CuO/SiO2-B/SiO2, Fig. 5B) to impregnation
(CuO/CsX-B/SiO2, Fig. 5D), the YST+EB, YST and styrene selectivity
declined with C9+ selectivity elevated. This was attributed that the
proximity of CuO/SiO2 and CsX increased resulted in the relatively high
HCHO content around CsX to reduce thermodynamic driving force for
methanol dehydrogenation and further restrained the side-chain
YST+EB, YST and styrene selectivity over CsX-CuO/SiO2-B/SiO2 was
higher than that over B/SiO2+CsX-CuO/SiO2. However, when the
proximity of B/SiO2 and CsX further increased by the grinding of the
two components together combining with granules of CuO/SiO2
(CsX∼B/SiO2-CuO/SiO2, Fig. 4G), XCH3OH, YST+EB and YST declined. It
suggested that the spatial arrangement of B/SiO2 and CsX was too
closer to restrain the conversion of methanol, resulting in decreasing
the catalytic activities of side-chain alkylation. Surprisingly, the ST/EB
over CsX∼B/SiO2-CuO/SiO2 was higher than that over other catalyst
and it might be because inhibition of “active hydrogen” generated from
methanol decomposition reduced the transfer hydrogenation from
styrene to ethylbenzene (Table S7). A further increase in the proximity
of B/SiO2 and CsX by impregnation increased XCH3OH, YST+EB and YST
,
but decreased ST/EB.
Moreover, the grinding catalyst of CsX, CuO/SiO2 and B/SiO2
(CsX∼CuO/SiO2∼B/SiO2) maintained the high XCH3OH, YST+EB, YST
,
ST/EB and selectivity for styrene with low C9+ selectivity. Although
this proximity mode of three components showed excellent catalytic
7

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
keeping ST/EB of 3.1 were obtained at 430 °C under WHSV of 2 h−1
and reactant with a toluene/methanol ratio of 6/1 over the ternary
composite catalyst containing the granules of CsX, CuO/SiO2 and B/
SiO2. Compared with the composite catalyst prepared by grinding CsX,
CsX modified with cesium oxide and B/SiO2 [40], CsX-CuO/SiO2-B/
SiO2 catalyst reported in this work showed not only relatively high
Y
ST+EB, but also provided relatively high ST/EB. This might be because
that the introduction of CuO/SiO2 increased the content of HCHO in-
termediate, which was favorable for YST+EB [25], and the introduction
of B/SiO2 improved styrene selectivity. Moreover, in contrast to cesium
oxide modified CsX component, the introduction of CuO/SiO2 dehy-
drogenation component into CsX by granule-stacking way would not
affect the basicity of CsX, which meant that the ability of transfer hy-
drogenation of “active hydrogen” with styrene over CsX component was
not improved. Thus, introduction of CuO/SiO2 and B/SiO2 into CsX
exerted highly conversion of toluene with methanol into styrene.
To be insight into the working mechanism in the composite catalyst,
conversion of toluene with methanol over CsX-CuO/SiO2-B/SiO2, CsX-
B/SiO2 and SiO2-CuO/SiO2 samples were compared at reaction tem-
perature, which was displayed on Fig. 6D. In this work, we had an
assumption that all formation of HCHO over CuO/SiO2 reacted with
toluene for side-chain alkylation reaction. Y[ST+EB] referred to theore-
tical side-chain alkylation products yield, which derived from the sum
of side-chain alkylation products yield over CsX-B/SiO2 sample and
HCHO yield over SiO2-CuO/SiO2 sample. Surprisingly, it was found that
XCH3OH over CsX-CuO/SiO2-B/SiO2 catalyst significantly enhanced at
range from 410 °C to 430 °C compared with the sum of that over CsX-B/
SiO2 and SiO2-CuO/SiO2 (CsX-B + C). More interestingly, YST+EB over
CsX-CuO/SiO2-B/SiO2 composite catalyst was higher than Y[ST+EB]
over CsX-B + C. This result indicated that for the overall reaction,
conversion of toluene with methanol into styrene over the composite
catalyst was not a simple sum of the two individual reactions (forma-
tion of HCHO from methanol and conversion of HCHO with toluene
into styrene). Instead, it was a coupling reaction. Therefore, it was
unambiguous to deduce that the HCHO synthesis on CuO/SiO2 was
driven by the side-chain alkylation reaction on CsX-B/SiO2 during the
conversion of toluene with methanol into styrene over the composite
catalysts. Meanwhile, the coupling reaction could only be well per-
formed within a certain temperature range.
Fig. 5. Effect of proximity of CuO/SiO2, B/SiO2 and CsX on catalytic behaviours
of composite catalysts. (A) and (I) Dual bed (A: CuO/SiO2+CsX-B/SiO2, I: B/
SiO2+CsX-CuO/SiO2); (B) and (H) Mixing of granules of three components
(CsX-CuO/SiO2-B/SiO2); (C) and (G) Mortar-mixing of two components com-
bining with granules of another component (C: mortar-mixing of CsX and CuO/
SiO2 combining with granules of B/SiO2, CsX∼CuO/SiO2-B/SiO2; G: mortar-
mixing of CsX and B/SiO2 combining with granules of CuO/SiO2, CsX∼B/SiO2-
CuO/SiO2); (D) and (F) Impregnation of one component into CsX combining
with granules of another component (D: Impregnation of Cu(NO3)2 into CsX
combining with granules of B/SiO2, CuO/CsX-B/SiO2; Impregnation of boric
acid into CsX combining with granules of CuO/SiO2, B/CsX-CuO/SiO2); (E)
Mortar-mixing of three components (CsX∼CuO/SiO2∼B/SiO2). The composite
catalysts were prepared with 1.0 g of CsX, 0.15 g of CuO/SiO2 and 0.2 g of B/
SiO2 by granule-stacking way. The catalytic performance was obtained at
430 °C under WHSV of 2 h−1 and reactant with a toluene/methanol ratio of 6/
1.
performance, it was more easily deactivated leading to the catalytic
activity of YST+EB from 34.4 % decreasing to 13.8 % during 210 min.
Interestingly, it was found that YST+EB and YST was mainly similar as
the proximity of CuO/SiO2 and B/SiO2 increasing from the granules to
the impregnation (Fig. S12), implying that the proximity of CuO/SiO2
and B/SiO2 in composite catalysts made slight effect on the catalytic
activities of side-chain alkylation.
The reaction results of toluene with methanol over some reported
CsX-based catalysts with a relatively high activity, as well as CsX-CuO/
SiO2-B/SiO2 composite catalyst used in this work were listed in Table 2.
It can be found that an outstanding ST/EB (3.1) with a satisfactory
YST+EB (30.1 %) was obtained over the CsX-CuO/SiO2-B/SiO2 compo-
site catalyst in this work. For the reported catalysts, the ST/EB was
relatively low when the YST+EB could reach about 30 %. On the other
hand, when the ST/EB over the reported catalyst could reach about 3,
such as ZnO/Cs-X catalyst, the YST+EB would not high enough. The
contradiction between obtaining a high ST/EB and a high YST+EB was
well solved over the CsX-CuO/SiO2-B/SiO2 composite catalyst in pre-
sent work. This was attributed to the promotion effect among CuO/
SiO2, B/SiO2 and CsX components. Besides, the formation of HCHO
over CuO/SiO2 was driven by the side-chain alkylation over CsX-B/
SiO2. More importantly, preparation method of the ternary composite
catalyst could give a new idea for design a more efficient catalyst for
conversion of toluene with methanol into styrene. And it might be
helpful in realizing commercial application of this technology in the
future. Besides, a higher conversion of toluene could be realized by
cyclic utilization of toluene and multiple reactors in series with mul-
tiply methanol feed. Developing the effective methanol dehydrogena-
tion component would further improve the conversion of toluene into
styrene in the future.
3.4. Effects of reaction conditions on catalytic activity of composite
catalysts
The effects of different reaction conditions, such as temperature,
WHSV and ratio of reactant, were further investigated over CsX-CuO/
SiO2-B/SiO2 composite catalyst for conversion of toluene with me-
thanol, which was shown on Fig. 6.
As to the effects of reaction temperature (Fig. 6A), XCH3OH increased
with temperature. With increasing reaction temperature from 390 °C to
470 °C, YST+EB increased. However, YST increased from 390 °C to
430 °C, and then decreased. This was attributed that an increase in
temperature was favorable for methanol decomposition to form “active
hydrogen” (Table S8), giving rise to intensifying transfer hydrogenation
reaction of styrene to ethylbenzene over CsX and decreasing styrene
selectivity [22]. As reasonably expected, the increase of WHSV resulted
in the decrease of XCH3OH (Fig. 6B). The ST/EB and styrene selectivity
gradually increased with the increasing WHSV, because styrene was the
primary product in side-chain alkylation of toluene with HCHO [8].
X
CH3OH, YST+EB and YST increased with increase of the reactant ratio
(toluene/methanol) from 1/2–10/1 (Fig. 6C). Meanwhile, the forma-
tion of CO and CO2 was suppressed (Table S9). This could be explained
by fact that the higher partial pressure of toluene increased the toluene
content within the micropores of CsX, and HCHO could have a greater
chance to react with toluene before its self-decomposition into CO and
H2 [8].
4. Conclusion
A XCH3OH of 60.1 %, a Xtoluene of 5.4 % and a YST+EB of 31.0 %
An efficient ternary composite catalyst consisted of methanol
8

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
Fig. 6. Catalytic performances of CsX-CuO/SiO2-B/SiO2 under different reaction conditions. (A) and (D) Reaction temperature was varied at constant reactant ratio
(toluene/methanol = 6/1) and space velocity (WHSV = 2 h−1). CsX-C-B represents the catalytic performance of CsX-CuO/SiO2-B/SiO2 sample and CsX-B + C (CsX-
B/SiO2+SiO2-CuO/SiO2) stands for the sum of the catalytic performance of CsX-B/SiO2 sample and SiO2-CuO/SiO2 sample. (B) Space velocity was varied at constant
temperature (430 °C) and reactant ratio (toluene/methanol = 6/1). (C) Reactant ratio was varied at constant temperature (430 °C) and space velocity
(WHSV = 2 h−1).
dehydrogenation component, B/SiO2 and CsX was developed for highly
conversion of toluene with methanol into styrene. Our work revealed
that the ternary composite catalyst could efficiently bridge the coupling
reaction of methanol dehydrogenation and side-chain alkylation of to-
luene into styrene. HCHO was the key reaction intermediate, and the
synthesis of HCHO over methanol dehydrogenation component was
driven by the side-chain alkylation over CsX-B/SiO2. Furthermore, it
found that an optimum composition, a suitable basicity of CsX and a
reasonable spatial arrangement of components in the composite cata-
lyst facilitated formation of styrene. When CuO/SiO2 is selected as the
methanol dehydrogenation component, the composite catalyst not only
showed relatively high YST+EB of 31.0 % at a XCH3OH of 60.1 % for
conversion of toluene with methanol into styrene, but also provided
relatively high ST/EB of 3.1 at 430 °C under WHSV of 2 h−1 and re-
actant with a toluene/methanol ratio of 6/1. This might be attribute
that the introduction of CuO/SiO2 increased the content of HCHO,
which was favorable for YST+EB, and the introduction of B/SiO2 worked
for adsorbing and stabilizing HCHO functions, improved the selectivity
for styrene. Besides, the introduction of CuO/SiO2 dehydrogenation
component into CsX would not affect the ability of transfer hydro-
genation of “active hydrogen” with styrene over CsX component. All in
all, this studies not only give an effective method to prepare a ternary
composite catalyst with high YST+EB as well as high ST/EB, but also
provide helpful guideline for developing a more efficient CsX-based
catalyst for conversion of toluene with methanol into styrene in the
further. Based on the above, further developing effective methanol
dehydrogenation component and researching kinetics in this system
would be worth in-depth studies.
CRediT authorship contribution statement
Qiao Han: Investigation, Writing - original draft. Peidong Li:
Investigation, Writing - original draft. Yangyang Yuan: Writing - ori-
ginal draft, Funding acquisition. Xiaomin Zhang: Writing - original
Table 2
The CsX-CuO/SiO2-B/SiO2 composite catalyst and some reported catalysts with high activity for conversion of toluene with methanol into styrene.
Catalysts
Toluene/methanol (mol/mol)
XCH3OH (%)
Xtoluene (%)
YST+EB (%)
ST/EB
CsX-CuO/SiO2-B/SiO2
ZrB2O5/Cs2O/CsX [24]
1.5BPO4/CsX [35]
ZnO/Cs-X [15]
6/1
6/1
3/1
1/1
6/1
5/1
6/1
60.1
–
5.4
5.4
9.6
4.6
4.1
8.5*
6.9
30.1
31.2*
30.3*
4.6
3.1
0.6
–
0.6*
3.2*
1.9
42.4
49.1
94.6
63.3
CsX-Na2B4O7-0.15 [25]
B/CsX+2%Cu [33]
X1(8C)B-G [40]
25.4
40.5
39.5
0.6
1.8
–Not given in the references; * Not given in the references and estimated from the relevant given data.
9

Q. Han, et al.
AppliedCatalysisA,General605(2020)117807
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The authors declare that they have no known competing financial
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