Side-chain alkylation of toluene with methanol to styrene over cesium ion-exchanged zeolite X modified with metal borates

Article abstract of DOI:10.1016/j.apcata.2012.08.003

Cesium ion-exchanged zeolite X (Cs-X) was modified with metal borates to prepare efficient catalysts for side-chain alkylation of toluene with methanol to styrene. The catalytic behavior of Cs-X was improved by the modification with metal borates such as

Full text of DOI:10.1016/j.apcata.2012.08.003

Applied Catalysis A: General 443–444 (2012) 214–220
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Side-chain alkylation of toluene with methanol to styrene over cesium
ion-exchanged zeolite X modified with metal borates
∗
Balkrishna B. Tope, Wahab O. Alabi, Abdullah M. Aitani, Hideshi Hattori , Sulaiman S. Al-Khattaf
Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2012
Received in revised form 1 August 2012
Accepted 2 August 2012
Available online 10 August 2012
Cesium ion-exchanged zeolite X (Cs-X) was modified with metal borates to prepare efficient catalysts for
side-chain alkylation of toluene with methanol to styrene. The catalytic behavior of Cs-X was improved by
the modification with metal borates such as zirconium borate, zinc borate, copper borate and lanthanum
borate. Modification was performed by mechanical mixing of Cs-X and a metal borate in dry state fol-
lowed by calcination. Significant enhancement of activity was observed for modification with zirconium
borate and zinc borate. The selectivity to styrene was increased by modification with all metal borates.
Modification with metal component or boron alone was not so effective as that with metal borate. The
highest activity was obtained with the Cs-X modified with 10 wt% zirconium borate and calcined at 773 K.
The high activity of metal borate-modified Cs-X is due to the ability to selectively form formaldehyde
from methanol, which is suggested by appearance of clear IR peak at 1690 cm assigned to unidentate
formate species on adsorption of methanol. The basic sites and acidic sites of Cs-X were slightly weakened
by modification with metal borates. It was revealed that mechanical mixing of Cs-X and metal borates
followed by calcination is a good method to prepare Cs-X modified with both metal components and
boron.
Keywords:
Styrene
Toluene
Methanol
Side-chain alkylation
Metal borate-modified cesium
ion-exchanged zeolite
−1
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
formaldehyde is the actual alkylating agent of toluene is widely
accepted [3–9]. Ethylbenzene is simultaneously produced with
styrene in all the cases reported. Ethylbenzene is suggested to
result from hydrogenation of styrene [2,8,10]. For the industrial
purpose, a high selectivity of styrene relative to ethylbenzene is
desirable.
Two functions are required for the catalyst active for the side-
chain alkylation: dehydrogenation of methanol to formaldehyde
and activation of the methyl group of toluene. Both functions are
related to the basic sites of the catalyst. It was suggested that the
dehydrogenation of methanol might proceed on less basic sites and
the activation of toluene might proceed on more strongly basic sites
[8].
Styrene is currently produced by two steps: alkylation of ben-
zene with ethylene to ethylbenzene, and dehydrogenation of
ethylbenzene to styrene. Since the dehydrogenation step is energy
intensive, alternate process to produce styrene is desired to be
developed.
One of the possible alternate routes to styrene is the side-
chain alkylation of toluene with methanol to styrene in one step.
The reaction has been known since Sidorenko et al. reported that
K and Rb ion-exchanged zeolite X (K-X and Rb-X, respectively)
catalyzed the reaction to produced styrene and ethylbenzene
[
1]. Soon after the report of Sidorenko et al., Yashima et al.
studied the reaction in detail and reported that Rb-X and
Cs-X were efficient catalysts as compared to other alkali ion-
exchanged zeolites X and Y [2]. They also supported the reaction
pathway proposed by Sidorenko et al. that methanol is first
dehydrogenated to formaldehyde which undergoes aldol-type
condensation with toluene to produce styrene. The idea that
Enhancements of catalytic activity and selectivity for styrene
were attempted by modification of Cs-X with various compounds.
Positive effects of modification with B component have been
reported in literature [9,11] as well as in patents [12–14]. In
addition to B, several metal components were proposed to have
promoting effect on the alkylation. The metal components pro-
posed to be effective so far include Ca, Mn, Ni, Cu, Zn, Ag, Ce, Cr,
and Fe. The oxide forms of these metal components are either
methanol decomposition catalysts or basic in character. Referring
to the development of solid base catalysts, there will be such metal
components other than those described above that have possibility
to be effective in enhancing the catalytic activity of Cs-X by addition
together with B. It is worthy to examine metal components which
have not been examined so far.
∗ Corresponding author. Permanent address: Catalysis Research Center, Hokkaido
University, Kita-ku, Kita 21, Nishi 10, Sapporo 001-0021, Japan.
Tel.: +81 11 706 9120; fax: +81 11 667 3734.
E-mail addresses: balatope@yahoo.co.in (B.B. Tope), gistawo33@yahoo.com
(
(
W.O. Alabi), maitani@kfupm.edu.sa (A.M. Aitani), hattori@cat.hokudai.ac.jp
H. Hattori), skhattaf@kfupm.edu.sa (S.S. Al-Khattaf).
0
926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.08.003

B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
215
Since many metal borates are insoluble in water, B compo-
nent and metal components are normally added by successive
one is Cs-X containing only Zr component prepared by impregna-
tion with zirconium nitrate (Zr/Cs-X) in which Zr was supposed to
impregnation; impregnation with aqueous H BO3 followed by
be in the form of ZrO . These three catalysts were calcined with a
3
2
impregnation with aqueous metal salts soluble in water. Unique
method for addition of B component and metal component was
disclosed in a patent in which Cs-X and a metal borate were
mechanically mixed in a dry state [15]. The catalysts prepared from
Cs-X and borates of Mg, Ca, Al, Mn, Fe, Co, Ni, and Cu by the mechan-
ical mixing showed a high selectivity for styrene as compared to
non-modified Cs-X.
In the present study, we have prepared Cs-X based catalysts
from novel metal borates, Zr and La as metal components, by
mechanical mixing and examined for their catalytic activities
for side-chain alkylation of toluene with methanol. The cata-
lyst containing Zr and B showed the highest activity, its activity
being twice as high as that of Cs-X. The selectivity for styrene
slow ramp rate of 2 K/min at 773 K for 3 h. The total of the added
compounds were all 10 wt% unless otherwise stated.
2.2. Reaction procedures
The catalytic runs were carried out in a fully integrated,
discrete, micro-processor controlled fixed bed continuous flow
reactor system (Model # 401C-0286, Autoclave Engineers). The
system consists of one tubular stainless steel reactor (8 mm
I.D. × 14 mm O.D. × 40 cm) attached with stainless steel one-zone
furnace assembly through reactor furnace wall thermowell. The
catalysts sample (400 mg) was pretreated with flowing N2 at 723 K
for 2 h, and then cooled to a reaction temperature of 698 K. The
flow rates of the reactant (toluene/methanol = 6/1) and N2 were
maintained at 0.12 ml/min and 40 ml/min (STP) with high pressure
feeding pump (Series III Digital HPLC Pump, Autoclave Engineers),
and mass flow controller (Model # 5850S/BC, Brooks), respectively.
The products were analyzed with online gas chromatograph (Agi-
lent technologies, Model # 6890N) equipped with a WCOT fused
silica capillary column coated with squalane (Varian, Cat. # CP7520,
length: 100 m, ID: 0.25 mm) with FID detector. The products were
identified by comparison with authentic samples. Because of FID
detector, H2, CO2 and H2O could not be analyzed by gas chromatog-
raphy.
(
styrene/(styrene + ethylbenzene)) exceeded 90%.
2
. Experimental methods
2.1. Catalyst preparation
The base catalyst of Cs-X was prepared from NaX (Junsei Chem-
+
icals, Japan) by ion-exchanged with Cs . Cesium hydroxide (Alfa
+
Aesar) was used as a source of Cs according to Engelhardt et al.
2
[
16]. The NaX has Si/Al ratio of 1.24 and surface area of 527 m /g.
In an aqueous solution of cesium hydroxide (75 ml, 0.5 M), NaX
15 g) was immersed, stirred for 5 min and stand for ca. 8 h. The
(
2.3. Characterization
slurry was filtered with Buchner funnel. The filtered cake was again
immersed in an aqueous solution of the cesium hydroxide (75 ml,
IR spectra of adsorbed CO2, pyridine and methanol were mea-
sured with in situ IR cell with CaF2 windows. Samples were pressed
into a thin wafer (∼50 mg/20 mm dia) and placed in the cell which
was attached to a vacuum system. The samples were pretreated at
723 K for 2 h in a vacuum prior to exposure to the adsorbate. All
spectra were measured at room temperature.
Powder XRD patterns were measured with RigakuMiniflix II
XRD powder diffraction system, Cu K␣ being used as a radiation
source at 30 kV and 15 mA.
SEM images were measured with a JEOL JSM-5800 scanning
microscope. Magnification was 7000×. Before taking SEM pho-
tographs, the samples were loaded on sample holder, held with
conductive aluminum tape and coated with a film of gold in vacuo
with cressington sputter ion-coater for 20 s with 15 mA current.
Surface areas were measured by N2 adsorption at 77 K, BET
equation being adopted to calculate the surface areas.
TG/DTA curves were measured with Rigaku Thermo plus TG
8120 for the uncalcined samples (9.0 mg), ␣-Al2O3 being used as
a reference sample. The sample was heated at a rate of 10 K/min in
a static air.
0.5 M), stirred and stand for ca. 8 h. The immersion and filtra-
tion procedures were repeated two more time (total 4 times). The
resulting slurry was filtered. To minimize the reverse ion-exchange
of Cs+ with H+ during washing with water, the resulting cake was
immersed in 100 ml water and filtered. The filtered cake was dried
in an oven at 353 K and calcined at 753 K for 3 h in air.
The Cs-X’s modified with metal borates were prepared by grind-
ing a mixture containing the Cs-X and a metal borate with mortar
for 30 min in a dry state. A ground mixture was calcined with a
slow ramp rate of 2 K/min at 773 K unless otherwise stated for
3
h. The weight % of the metal borate was 10 wt% for all the cat-
alysts unless otherwise stated. Zinc borate (2ZnO·3B O ·3.5H O)
2
3
2
was supplied from Wako Pure Chemicals, Ind., Japan. Zirconium
borate (ZrB O5), lanthanum borate (LaBO ), and copper borate
2
3
(
Cu(BO ) ) were prepared according to the reported procedures.
2 2
Zirconium borate was prepared according to Knyrim et al. from
aqueous solutions of disodiumtetraborate and zirconium nitrate
[
6
17]. The precipitate was washed with water, dried and calcined at
23 K in air. Lanthanum borate was prepared according to Lin et al.
from a mixture containing boron trioxide and lanthanum oxide by
heating at 1373 K in argon atmosphere [18]. Copper borate was
prepared from aqueous solutions of disodiumtetraborate and cop-
per nitrate [19]. The precipitate was washed with water, dried and
calcined at 723 K. Cs-X catalysts modified with zirconium borate,
zinc borate, lanthanum borate, and copper borate are denoted by
ZrB/Cs-X, ZnB/Cs-X, LaB/Cs-X, and CuB/Cs-X, respectively.
3. Results
3.1. Catalytic activity
The products consisted mostly of styrene and ethylbenzene
in addition to the reactants, toluene and methanol. Small hydro-
carbons were detected, but their quantities were less than 5% of
styrene produced. These were excluded from the product quantifi-
cation.
Figs. 1 and 2 show the variations in toluene conversion and
styrene selectivity, respectively, as a function of time on stream
under the reaction conditions: toluene/methanol = 6/1, feed rate
0.12 ml/min, N2 flow rate 40 ml/min, catalyst 400 mg and the
reaction temperature 683 K. Since the molar ratio of toluene to
methanol was 6, the attainable conversion of toluene was 16.7%.
In addition to these Cs-X containing metal borates, three more
catalysts were prepared. The first one is the Cs-X containing B with-
out metal component which was prepared by grinding Cs-X with
boric acid (B/Cs-X) in which boron was supposed to be in the form
of B O . The second one is the B and Zr loaded on Cs-X by impreg-
2
3
nation with a mixed aqueous solution of boric acid and zirconium
nitrate (B-Zr/Cs-X). The slurry was aged at room temperature for 1 h
under stirring conditions, and then the excess solvent was removed
by heating at 363 K under vacuum in a rotary evaporator. The third

2
16
B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
Fig. 1. Toluene conversion as a function of time on stream in side chain alkylation of
toluene with methanol at 683 K over Cs-X and Cs-X’s modified with metal borates.
Fig. 3. Variation in toluene conversion as a function of zirconium borate loading of
ZrB/Cs-X in side chain alkylation of toluene with methanol at 683 K.
Fig. 2. Selectivity to styrene as a function of time on stream in side chain alkylation
of toluene with methanol at 683 K over Cs-X and Cs-X’s modified with metal borates.
Fig. 4. Variation in toluene conversion as a function of calcination temperature of
ZrB/Cs-X in side chain alkylation of toluene with methanol at 683 K.
Modification of Cs-X with metal borates brought about sig-
nificant changes in the conversion of toluene depending on the
type of borate as shown in Fig. 1. The toluene conversion for
ZnB/Cs-X was high at a time on stream of 10 min, but decreased
considerably with time on stream. ZrB/Cs-X showed a high con-
version and did not decay with time on stream. LaB/Cs-X showed
almost the same toluene conversion as non-modified Cs-X, their
conversions decreased slightly with time on stream. The toluene
conversion for CuB/Cs-X, on the other hand, slightly increased
with time on stream and significantly exceeded that of Cs-X in
enhanced the toluene conversion, but the selectivity of styrene was
low, ethylbenzene being produced much more than styrene (entry
7
). Addition of 10 wt% BO3 alone resulted in a marked decrease in
toluene conversion (entry 8), but addition of 0.8 wt% BO increased
3
the toluene conversion but decreased the styrene selectivity (entry
9
).
The effect of zirconium borate loading on the toluene conversion
9
0 min.
Modification of Cs-X with metal borates resulted in distinct
was examined, and the results are shown in Fig. 3. The maximum
toluene conversion was obtained with 10 wt% zirconium borate
loaded Cs-X, that is ZrB/Cs-X.
The effect of calcination temperature of ZrB/Cs-X on the toluene
conversion was examined, and the results are shown in Fig. 4.
The maximum toluene conversion was observed when calcined at
improvement in the selectivity for styrene as shown in Fig. 2.
In particular, ZrB/Cs-X showed the selectivity higher than 92%
throughout the time on stream, which was higher than the selec-
tivity below 86% for non-modified Cs-X.
In addition to the reaction results for the catalysts shown in
Fig. 1, the results for other catalysts are summarized in Table 1.
Data were taken at a time on stream of 50 min. Modification with
B and Zr by impregnation with a mixed aqueous solution contain-
ing boric acid and zirconium nitrate did not improve the catalytic
activity of Cs-X (entry 6). The activity and selectivity were even
worse than those of non-modified Cs-X. Addition of ZrO2 alone
7
73 K.
3.2. Characterization
3.2.1. Surface area
Surface areas are summarized in Table 2. Since the weight of the
zeolite unit cell increased by ion-exchange of Na with Cs and addi-
tion of other components, the normalized surface areas as defined
below were calculated and included in Table 2.
measured surface area × unit cell weight of zeolite X containing Cs and borate
Normalized surface area =
unit cell weight of Na-X

B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
217
Table 1
Catalytic activities for alkylation of toluene with methanol at 683 K.
Entry
Catalyst
Methanol conv. (%)f
Toluene conv. (%)g
EB select. (%)h
ST select. (%)i
ST yield (%)j
1
2
3
4
5
6
7
8
9
Cs-X
36.8
45.2
27.9
37.6
44.9
37.3
31.3
7.9
1.5
3.1
1.5
3.0
1.6
1.1
1.8
0.3
1.8
13.8
6.8
9.9
6.6
6.1
33.8
87.0
0
86.2
93.2
90.1
93.4
93.9
66.2
13.0
100
1.3
2.9
1.4
2.8
1.5
0.7
0.2
0.3
1.3
ZrB/Cs-Xa
a
LaB/Cs-X
ZnB/Cs-Xa
CuB/Cs-Xa
b
B-Zr/Cs-X
Zr/Cs-X
c
d
B/Cs-X
B(0.8)/Cs-Xe
34.0
30.4
69.6
a
Prepared by mechanical mixing with metal borates.
b
c
d
e
f
Prepared by co-impregnation method with H3BO3 aq. and Zr(NO3)4 aq.
Prepared by impregnation with Zr(NO3)4 aq.
Prepared by mechanical mixing with H3BO3.
Containing 0.8 wt% H3BO3 prepared by impregnation.
Methanol conv. = {1 − (methanol recovered)/(methanol fed)} × 100%.
Toluene conv. = {1 − (toluene in products)/(toluene fed)} × 100%.
EB select. = ethylbenzene/(ethylbenzene + styrene) × 100%.
ST select. = styrene/(ethylbenzene + styrene) × 100%.
g
h
i
j
ST yield = (toluene conv.) × styrene/(total hydrocarbon products) × 100%.
Table 2
Surface areas of catalysts.
The normalized surface area of Cs-X was close to that of Na-
X indicating crystalline structure was retained after ion-exchange
with Cs. For LaB/Cs-X, ZrB/Cs-X and CuB/Cs-X, addition of the
borates followed by calcination at 773 K resulted in a decrease
in surface area by about 14–20%. For ZnB/Cs-X, however, distinct
decrease in surface area was observed, the normalized surface area
of ZnB/Cs-X was less than a half of the original one. Although addi-
2
2
Catalyst
BET surface area (m /g)
Normalized surface area (m /g)
Na-X
Cs-X
527
373
317
286
234
260
137
299
196
195
27
527
513
459
438
378
398
209
457
300
299
41
ZrB(5%)/Cs-X
ZrB/Cs-X
ZrB(15%)/Cs-X
LaB/Cs-X
ZnB/Cs-X
CuB/Cs-X
B-Zr/Cs-X
Zr/Cs-X
tion of 0.8% H BO3 did not decrease much, addition of 10% H BO3
3
3
decreased the surface area to 8% of the original one.
3
.2.2. XRD
Fig. 5 shows XRD patterns of Cs-X, LaB/Cs-X, ZrB/Cs-X and
B/Cs-X
ZnB/Cs-X. All samples retain crystalline structure of FAU, but the
intensity of diffraction peaks decreased in the order of Cs-X, ZrB/Cs-
X, LaB/Cs-X and ZnB/Cs-X. This order is the same order of decrease
in the surface area.
B(0.8%)/Cs-X
319
444
3.2.4. TG/DTA
TG/DTA curves for ZrB/Cs-X are shown in Fig. 8. Weight loss
observed in the range ∼500 K accompanied by endothermic heat is
ascribed to desorption of physically adsorbed water. Above 500 K,
gradual changes in weight and heat were observed, which could be
ascribed to desorption of chemisorbed water and carbon dioxide.
3
.2.3. SEM
SEM images for Cs-X and ZrB/Cs-X are shown in Figs. 6 and 7,
respectively. Cs-X is composed mostly of crystallites in the range
1
1
–3 ␮m, while ZrB/Cs-X is composed of crystallites in the range
–3 ␮m and small particles of 0.1–1 ␮m attached to the larger crys-
tallites.
Fig. 5. XRD patterns of Cs-X and Cs-X’s modified with metal borates. (A) Cs-X, (B)
ZrB/Cs-X, (C) CuB/Cs-X, (D) LaB/Cs-X and (E) ZnB/Cs-X.
Fig. 6. SEM image of Cs-X.

2
18
B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
Fig. 9. IR spectra of CO2 adsorbed on Cs-X and ZrB/Cs-X. (A and B) CO2 adsorbed
on Cs-X and evacuated at 373 K and 523 K, respectively; (C and D) CO2 adsorbed on
ZrB/Cs-X and evacuated at 373 K and 523 K, respectively.
Fig. 7. SEM image of ZrB/Cs-X.
The band position, however, was the same for the two samples.
The number of Lewis acid sites is slightly reduced by modification
with zirconium borate. It should be noted that Lewis acid sites on
which pyridine can be retained after evacuation at 523 K exist on
the surfaces of Cs-X and ZrB/Cs-X.
3
.2.5. IR study
Fig. 9 shows IR spectra of CO2 adsorbed on Cs-X and ZrB/Cs-X
followed by evacuation at 373 K and 523 K. Two bands at 1480 and
−1
1
650 cm appeared on Cs-X after evacuation at 373 K are assigned
Distinct difference in IR spectrum between Cs-X and ZrB/Cs-X
was observed when the catalysts were exposed to 133 Pa methanol
at 623 K and cooled down to room temperature. Fig. 11 shows the
to bidentate carbonate. No bands assigned to other carbonates such
as unidentate carbonate and bicarbonate were observed. By evac-
uation at 523 K, these bands were eliminated. Because of strong
−1
spectra observed. Two bands were observable at 1610 cm and
−1
band below 1500 cm
due to the presence of B, only one band
−1
1
670 cm which were assigned to bidentate formate and uniden-
−
1
at 1650 cm was observable for ZrB/Cs-X. The band was assigned
tate formate, respectively [4]. On Cs-X, a strong band assigned to
bidentate formate was observed, while the band to unidentate for-
mate was very weak. On ZrB/Cs-X, in contrast, strong band assigned
to unidentate formate appeared as well as the band to bidentate
formate.
−
1
to bidentate carbonate. The intensity of the band at 1650 cm is
slightly weaker for ZrB/Cs-X than for Cs-X. The basic sites on Cs-
X were slightly weakened by modification with zirconium borate.
A small difference in O H stretching region between Cs-X and
ZrB/Cs-X was noted. The intensity of the band at 3740 cm was
weaker for ZrB/Cs-X than for Cs-X. Zirconium borate may interact
with OH groups of Cs-X.
−
1
4. Discussion
Fig. 10 shows IR spectra of pyridine adsorbed on Cs-X and
ZrB/Cs-X followed by evacuation at 473 and 523 K. No bands
4
.1. Catalytic activity
−
1
assigned to pyridinium ion were observed at 1540 cm for both
Cs-X and ZrB/Cs-X. No protonic acid sites exist on both catalysts. As
Addition of metal components together with B to Cs-X has been
reported in literature and patents. Lacroix et al. observed improved
−1
compared the band intensity at 1580 cm which is due to Lewis
acid sites, the intensity was weaker for ZrB/Cs-X than for Cs-X.
Fig. 10. IR spectra of pyridine adsorbed on Cs-X and ZrB/Cs-X. (A and B) Pyridine
adsorbed on Cs-X and evacuated at 473 K and 523 K, respectively; (C and D) pyridine
adsorbed on ZrB/Cs-X and evacuated at 473 K and 523 K, respectively.
Fig. 8. TG/DTA of ZrB/Cs-X. Dotted line, TG; solid line, DTA.

B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
219
Cs-X. The decrease in the surface area by 17% seems to be consistent
with the dispersed model. Some of the zirconium borate particles
located on the external surface of Cs-X to decrease the surface area.
From TG and DTA results of ZrB/Cs-X, an occurrence of the chem-
ical reaction of zirconium borate with Cs-X was not detected. It is
plausible that fine particles of zirconium borate are dispersed on
Cs-X and interact with Cs-X at the interface. Since the IR band due
to OH groups was weaker for ZrB/Cs-X than for Cs-X, it is suggested
that the zirconium borate particles interact with Cs-X crystallites
through OH groups on the external surface of Cs-X.
4.3. Acidity and basicity
Although it was reported that balanced acidity and basicity
is important for an efficient catalyst for side-chain alkylation of
toluene, IR studies of adsorbed pyridine and CO2 could not detect
clear differences in acidity and basicity between Cs-X and ZrB/Cs-
X. For pyridine adsorption study, only a small decrease in the band
intensity was observed without change in the band position for
Fig. 11. IR spectra of surface species remaining on (A) Cs-X, (B) ZrB/Cs-X and (C)
ZnB/Cs-X after exposure to 133 Pa methanol at 623 K followed by cooling down to
room temperature.
−
1
8
a vibration mode (∼1580 cm ). The band position reflects the
strength of the interaction between pyridine and Lewis acid sites
20]. No change in the band position for Cs-X and ZrB/Cs-X indicates
activity for Cs-X loaded with Cu and Ag and B doped Cs-X [10].
Addition of Cu and Ag was done separately from addition of B to
Cs-X. They used aqueous solutions of metal components and boric
acid. Addition of the two components was done by two steps in
most cases: addition of B in the first step and addition of metal
component in the second step. One exception can be found in a
patent [15]. The patent used metal borates to add two components
in one step. A mixture containing metal borate and Cs-X was mixed
with kneader in dry state and calcined. The patent reported high
activities of Cs-X’s mixed with several metal borates. As metallic
components, Mn, Zn, Ca, Ni, Cu were used. Although all the catalysts
showed higher activities than Cs-X, the reaction conditions were
not described in detail.
[
that the strength of Lewis acid sites is similar for both catalysts.
Decrease in the band intensity is suggested to be due to a decrease in
the number of Lewis acid sites by the addition of zirconium borate.
This idea is consistent with a small decrease in the surface area for
ZrB/Cs-X. The same thing can be said about basic sites. CO2 was
adsorbed as bidentate carbonate and the band position was the
same for both samples. Only difference between two samples was
the band intensity; the intensity was slightly weaker for ZrB/Cs-X
than for Cs-X. It is suggested that the strength of basic sites is the
same for both catalysts, and the number of basic sites was smaller
for ZrB/Cs-X than for Cs-X.
The present study confirmed that addition of metal components
and B by mechanical mixing of metal borates in a dry state is a good
way to prepare the Cs-X containing both metal components and B.
Among the catalysts prepared based on the Cs-X, the best catalyst
was the Cs-X modified with 10 wt% zirconium borate by means of
mechanical mixing of Cs-X and zirconium borate followed by cal-
cination at 773 K. Addition of Zr and B separately from zirconium
nitrate and from boric acid aqueous solutions did not result in the
formation of efficient catalyst as compared to addition of zirconium
borate in a dry state. Addition of Zr has never examined before.
Addition of B to Cs-X has been widely adopted in patents, but has
rarely been studied in literature. One of the studies was reported
by Wieland et al. [7]. Addition of B to Cs-X promoted the side-chain
alkylation. Role of B was proposed to suppress the decomposition
It should be noted that the discussion about acidity and basicity
described above is applicable only to relatively strong adsorption
sites. Because the spectra were measured after evacuation at a
high temperature, the species retained on the surface should be
adsorbed on strong adsorption sites. Spectra measured after evac-
uation at such a low temperature as weakly adsorbed species are
retained on the surface may contain information about weak acid
and base sites. However, distinct information about weak acid and
base sites may be difficult to obtain because the band observed
after evacuation at the low temperature contains information of
all the sites. Isolation of the band due only to weak sites could not
be successful. The possibility cannot be excluded that addition of
zirconium borate caused some changes in weak acidic and basic
sites.
of methanol into CO and H . The optimum loading was reported to
2
be 0.8 wt% H BO .
3
3
4.4. Interaction with methanol
Our results indicated that loading of 10 wt% H BO3 strongly
3
reduced the toluene conversion, but loading of 0.8 wt% increased
the toluene conversion a little as reported by Wieland et al. [7]. The
selectivity to styrene, however, reduced to 69.6%. Drastic decrease
In contrast to the results of IR studies of adsorbed pyridine and
CO , a distinct difference was observed for IR study of methanol.
2
In addition to a band ascribed to bidentate formate which was
observed both for ZrB/Cs-X and Cs-X, a distinct band ascribed
observed for 10 wt% loading of H BO3 is suggested to be caused by
3
a marked decrease in surface area; the surface area decreased to
−1
to unidentate formate was observed for ZrB/Cs-X at 1670 cm
2
less than 10% of the original Cs-X. Since the melting point of B O3
when exposed to methanol near the reaction temperature. It was
reported that the bidentate formate undergoes decomposition to
is 733 K, it is suggested that B O3 melted during calcination and
2
covered the external surface of the Cs-X crystallites, resulting in a
decreased surface area as well as a low activity.
CO and H , and the unidentate formate could be an intermedi-
2
ate for aldol-type condensation with toluene [3,4]. At least, the
presence of unidentate formate indicates that formaldehyde is
present in a high concentration in the gas phase. Accordingly, it is
suggested that selective dehydrogenation of methanol to formalde-
hyde proceeds much smoother over ZrB/Cs-X than over Cs-X. The
same phenomenon was observed for ZnB/Cs-X; a distinct band
of the unidentate formate was observed for ZnB/Cs-X. The strong
band of the unidentate formate strongly suggests the formation of
4.2. States of metallic component and boron
The states of Zr and B in ZrB/Cs-X are suggested to be mostly
in the fine particles of zirconium borate dispersed on the exter-
nal surface of Cs-X crystallites as shown in the SEM image (Fig. 7).
2
The normalized surface area was 427 m /g which was 83% of that of

2
20
B.B. Tope et al. / Applied Catalysis A: General 443–444 (2012) 214–220
formaldehyde is facilitated on ZrB/Cs-X and ZnB/Cs-X. Accordingly,
a high ability of the formation of formaldehyde is suggested to be
the cause of a high activity of these catalysts for the formation of
styrene.
Petrochemicals at KFUPM. H.H. wishes to thank the Japan Coop-
eration Center, Petroleum (JCCP) for financial support under the
High-level Researcher Dispatching Program, JCCP.
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