Effect of mesoporosity on selective benzylation of aromatics with benzyl alcohol over mesoporous ZSM-5

Article abstract of DOI:10.1016/j.jcat.2012.04.006

The effect of mesoporosity on product distribution in benzylation of aromatics such as benzene, toluene, anisole and mesitylene with benzyl alcohol was investigated over various ZSM-5 catalysts with different degree of mesoporosity, which were prepared by microwave-induced assembly via ionic interaction between sulfonic acid-functionalized or non-functionalized ZSM-5 nanozeolites and counter cationic surfactant, and hydrothermal synthesis with or without sulfonic acid functionalization and surfactant. The product distribution of the aromatic benzylation was found to vary with the different mesoporosity. The selectivity of desired monobenzylated aromatic was increased from 19.8% to 75.5% with increasing mesopore volume from 0.11 to 0.75 cm ³/g. Meso ZSM-5 (SO₃H-CTAB)-MW with the highest external acid sites and mesopore volume showed better conversion as well as much higher selectivity of desired bulky monobenzylated aromatics than those of other catalysts, whereas microporous ZSM-5 mainly showed dibenzyl ether as major product due to diffusion limitation of bulky product.

Full text of DOI:10.1016/j.jcat.2012.04.006

Journal of Catalysis 291 (2012) 55–62
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Effect of mesoporosity on selective benzylation of aromatics with benzyl alcohol
over mesoporous ZSM-5
⇑
Hailian Jin, Mohd Bismillah Ansari, Eun-Young Jeong, Sang-Eon Park
Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, Incheon 402-751, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The effect of mesoporosity on product distribution in benzylation of aromatics such as benzene, toluene,
anisole and mesitylene with benzyl alcohol was investigated over various ZSM-5 catalysts with different
degree of mesoporosity, which were prepared by microwave-induced assembly via ionic interaction
between sulfonic acid–functionalized or non-functionalized ZSM-5 nanozeolites and counter cationic
surfactant, and hydrothermal synthesis with or without sulfonic acid functionalization and surfactant.
The product distribution of the aromatic benzylation was found to vary with the different mesoporosity.
Received 6 February 2012
Revised 30 March 2012
Accepted 7 April 2012
Available online 7 May 2012
Keywords:
Selective benzylation
Aromatic
The selectivity of desired monobenzylated aromatic was increased from 19.8% to 75.5% with increasing
3
mesopore volume from 0.11 to 0.75 cm /g. Meso ZSM-5 (SO
3
H-CTAB)-MW with the highest external acid
sites and mesopore volume showed better conversion as well as much higher selectivity of desired bulky
monobenzylated aromatics than those of other catalysts, whereas microporous ZSM-5 mainly showed
dibenzyl ether as major product due to diffusion limitation of bulky product.
Ó 2012 Elsevier Inc. All rights reserved.
Mesoporous ZSM-5
Mesoporosity
Product distribution
1
. Introduction
Catalytic benzylation of aromatics with benzyl alcohol or benzyl
zeolites show the remarkable change in product selectivity com-
pared with microporous zeolites due to improved diffusion to
and/or from active sites in micropores through the mesopores
[18,19]. Recently, Sun and Prins [20] have reported the enhanced
catalytic activity of hierarchical mesoporous ZSM-5 in the alkyl-
ation of benzene with benzyl alcohol, which is 23 times larger than
that for microporous ZSM-5. The similar phenomenon is observed
in case of mesoporous mordenite obtained by acid–base leaching
[21]. Groen et al. have found the superior performance of alka-
line-mediated mesoporous mordenite in the alkylation of benzene
with ethylene compared with mordenite [22]. The enhanced
catalytic performance indicates that the existence of mesopore
remarkably overcomes the diffusion limitation from micropore,
and suggests the mesoporous zeolites have potential application
in alkylation reactions of bulky molecules.
Recently, microwave irradiation has been considered as a useful
method for synthesis of nanoporous materials such as zeolites,
mesoporous materials and mesoporous zeolites [23]. According
to our previous works, microwave synthesis could provide distinct
advantages [9,24,25] over the conventional hydrothermal
synthesis such as fast crystallization, homogeneous heating and
nucleation, morphology control and enhanced hydrophobicity,
moreover it is efficient for mesopore generation by desilication
[26], carbon templating method [27,28] and supramolecular self-
assembly [29]. In this regard, we have developed a new synthetic
strategy for synthesis of mesoporous ZSM-5 with enhanced
mesoporosity by microwave-induced assembly via ionic interac-
tion between sulfonic acid–functionalized ZSM-5 nanoparticles
chloride is one of the commercial significance reaction processes to
produce benzylated aromatics (diphenylmethane and substituted
diphenylmethane), which are key intermediates in fine chemicals
and pharmaceuticals such as analgesic or anti-inflammatory agent,
reagent for inhibiting agglomeration of blood, backbone, and skel-
eton [1–4]. To control the selective formation of desired monoben-
zylated aromatics is quite challenging in this reaction process.
Zeolites such as ZSM-5 [5], Zeolite X, Y [6,7] and Zeolite BETA [8]
are used as heterogeneous acid catalysts in the benzylation process
3
instead of mineral acid (e.g., AlCl ) due to less corrosiveness, strong
acidity, shape-selectivity and high hydrothermal stability [9–13].
However, zeolites with small pore size (<1 nm) cause diffusion lim-
itation for bulky substrates [14]. This diffusion limitation in micro-
porous zeolites is also responsible for poor selectivity and loss in
lifetime of the catalysts. Hence, mesoporous zeolites having peri-
odic mesoporosity, strong acidity and stability like microporous
zeolites and shape-selectivity in catalysis are desirable without
sacrificing acidity [15,16].
Mesoporous zeolites containing both structured microporosity
and secondary mesoporosity inside of zeolite single crystals exhibit
high catalytic activity of bulky reactants in various organic reac-
tions due to diffusion alleviation [17]. Moreover, these mesoporous
⇑
Corresponding author.
E-mail address: separk@inha.ac.kr (S.-E. Park).
0
021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2012.04.006

5
6
H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
and counter cationic alkyltrimetyl ammonium surfactant. Sulfonic
acid group plays an important role as negative charge enhancer on
the surface of zeolite nanoparticles that interact with cationic sur-
factants to create the mesoporosity inside of the zeolite single crys-
tals [30].
In the present study, we report a novel investigation on the
effect of mesoporosity on the catalytic activity and selectivity of
desired monobenzylated aromatics in the aromatic benzylation.
For this analysis, mesoporous ZSM-5 were synthesized by assem-
bly via ionic interaction between sulfonic acid–functionalized or
non-functionalized ZSM-5 nanozeolites and counter cationic
CTAB with 15 g H
165 °C for 2 h) as [Meso ZSM-5(SO
2
O) and stirred 3 h, then moved to MW (600 W,
H-CTAB)-MW].
3
2
.1.2. Meso ZSM-5(CTAB)-MW
A similar procedure to that of [Meso ZSM-5(SO
with omission of steps for functionalization with MPTES and oxida-
tion with H has been adopted for the synthesis of [Meso ZSM-
(CTAB)-MW].
3
H-CTAB)-MW]
2 2
O
5
2
.1.3. ZSM-5(SO
The synthesis procedure was same with that of [Meso ZSM-
(SO H-CTAB)-MW] except the final step, whereby the resulted
3
H-CTAB)-HT
3
surfactant under microwave [Meso ZSM-5 (SO H-CTAB)-MW and
Meso ZSM-5 (CTAB)-MW], and hydrothermal synthesis with or
without sulfonic acid functionalization and surfactant [ZSM-5
5
3
solution in the vessel is subjected to hydrothermal treatment
HT) at 165 °C for 3 days instead of microwave irradiation.
(
(
3
SO H-CTAB)-HT] and ZSM-5 (HT)] (Scheme 1). The catalytic
performances of these ZSM-5 catalysts with different degree of
mesoporosity were studied in benzylation of aromatics such as
benzene, toluene, anisole and mesitylene with benzyl alcohol as
benzylating agent. Furthermore, the effects of mole ratio of
aromatic to benzyl alcohol, reaction time and recyclability have
also been investigated.
2
.1.4. ZSM-5 (HT)
The conventional microporous ZSM-5 [ZSM-5 (HT)] was synthe-
sized from a clear solution with the following molar composition:
Al : 60SiO : 11.5TPAOH: 1500H O under hydrothermal treat-
ment at165 °C for 3 days.
1
2
O
3
2
2
2.2. Characterization methods
2
. Experiment
Crystallinity of obtained materials was determined by powder
X-ray diffraction (XRD) using a Rigaku X-ray diffractometer with
CuK radiation (40 kv and 20 mA). N adsorption and desorption
isotherms were conducted on a micromeritics ASAP 2020 at
À196 °C. The Brunauer–Emmett–Teller (BET) surface areas were
calculated from the liner part of the BET plot according to IUPAC
recommendations. Pore size distribution was calculated by the
Barrett–Joyner–Halenda (BJH) method from adsorption branch
of the isotherm.
2
.1. Catalysts preparation
a
2
The chemicals used for the preparation of materials were tetra-
ethyl orthosilicate (TEOS, 98%; Aldrich) as silica source, aluminum
isopropoxide (AIP; Aldrich) as alumina source, tetrapropylammo-
nium hydroxide (TPAOH, 20–25%; TCI) as a template for micropore,
3
-mercaptopropyltriethoxysliane (MPTES; TCI) as anionic func-
tional group, hydrogen peroxide (H , 30% in the water; Duksan)
2 2
O
as oxidizing agent, cetyltrimethylammonium bromide (CTAB; TCI)
as supramolecular template and distilled water.
The ZSM-5 catalysts were prepared according to following
procedure.
3
Temperature-programmed desorption (TPD) of NH was carried
out with a Micromeritics TPD/TPR/TPO 2900 apparatus with ther-
mal conductivity detector (TCD). The samples were first outgassed
in a He flow (20 ml/min) under 500 °C for 1 h with heating rate of
2
0 °C/min before the measurement. After cooling to 100 °C, the
samples were saturated in an NH stream (5% in He) for 1 h with
30 ml/min flow and consequently treated in He (50 cm /min) for
120 min for removing physisorbed NH . Finally, the TPD profile
was determined by increasing temperature from 100 to 500 °C
2
.1.1. Meso ZSM-5(SO
As an initial stride, ZSM-5 nanozeolites were pre-crystallized
from a clear solution with the following molar composition:
3
H-CTAB)-MW
3
3
3
1
2
Al O
3 2 2
: 60SiO : 11.5TPAOH: 1000H O (20.8 g TEOS, 19.1 g TPAOH,
0
.33 g AIP, 15 g H
2
O) under microwave irradiation (600 W, 120 °C
3
with a heating rate of 5 °C/min while recording NH desorption
and 30 min) followed by functionalization with MPTES (5 mol% of
with a thermal conductivity detector.
silica) under MW (600 W, 120 °C and 60 min). The precursor solu-
tion was continuously treated by 5 g H O in order to oxidize thiol
2 2
group for obtaining sulfonic acid–functionalized zeolite nanoparti-
cles. The resultant solution was added to CTAB solution (1.78 g
The number of external acid sites (i.e., acid sites at the
mesopore walls) in ZSM-5 catalysts was measured by the chemi-
sorption of 2,6-di-tert-butylpyridine (DTBPy) in a thermoanalyzer
(Bruker axs 2000SA) equipped with high resolution balance
Scheme 1. Schematic representation of the synthesized ZSM-5 catalysts.

H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
57
(
Sensitivity = 0.1
l
g). Prior to the adsorption of DTBPy, the samples
nanoparticles and counter cationic surfactants. As shown in
Fig. 2A, the Meso ZSM-5 (SO H-CTAB)-MW showed type IV N
adsorption–desorption isotherm with H4 hysteresis capillary
condensation at 0.2 < (P/P ) < 0.5 due to the presence of mesopores
(2–3 nm size) with narrow distribution (Fig. 2B). However, the
ZSM-5 (SO H-CTAB)-HT showed type I isotherm, which was similar
to microporous ZSM-5. The surface area and mesopore volume of
were pretreated at 350 °C overnight under vacuum. Followed by
exposure to 2,6-DTBPy at room temperature for 1 h, desorption
of DTBPy was carried out at 150 °C for 4 h under vacuum to remove
physisorbed DTBPy. The amount of adsorbed DTBPy was obtained
from weight loss before and after adsorption. The external acid
sites were calculated with assumption of one DTBPy molecule
per acid site [31].
3
2
0
3
2
3
3
Meso ZSM-5 (SO H-CTAB)-MW were 529 m /g and 0.75 cm /g,
respectively, which were much larger than those of other ZSM-5
catalysts (Table 1).
2.3. Catalytic benzylation
Acidic properties of the ZSM-5 catalysts were investigated by
NH
3
TPD. The TPD profiles of ZSM-5 catalysts given in Fig. 3
Prior to the catalytic experiments, all the catalysts were acti-
showed two desorption peaks of NH
These desorption peaks were corresponding to two different type
of acid sites of varying strengths. The low temperature desorption
3
in the range below 500 °C.
vated at 450 °C for 90 min and then cooled down in a desiccator.
The benzylation reactions were carried out with aromatics such
as benzene, toluene, anisole and mesitylene (16 mmol) and benzyl
alcohol (4 mmol) in the presence of catalysts (0.05 g) in a 25-ml
single-necked flask at 100 °C for 1 h. The mole ratio of the aromat-
ics with benzyl alcohol was varied as 1:2, 1:1, 2:1, 3:1 and 4:1. The
reaction time was varied from 15 to 120 min. The catalyst was fil-
tered after the reaction and washed with acetone followed by dry-
ing and calcining in air at 450 °C for 6 h prior to reuse. The course
of the reaction was followed by analyzing the reaction mixture
periodically using a gas chromatograph (HP 6890) equipped with
a flame ionization detector (FID) and a capillary column (HP 5% sil-
icone gum). The products were also identified by GC/MS.
peak (100–300 °C) was due to NH
the high temperature desorption peak in the range of 300–500 °C
was caused by NH desorption from strong acid sites (Brønsted
and Lewis acid sites). The number of acid sites of the catalysts
was calculated by peak area with the assumption of one NH mol-
ecule per acid sites as depicted in Table 2. The strong acid sites of
Meso ZSM-5 (SO H-CTAB)-MW were 8% less than the ZSM-5 (HT).
The acid strengths were found to be approximately similar. This re-
sult indicated that mesoporous ZSM-5 catalysts could be prepared
without significantly sacrificing acidity during microwave-induced
assembly through ionic interaction, which was in good agreement
with earlier report regarding the acidity of hierarchical porous
zeolites by Suzuki et al. [32].
3
bound to weak acid sites, and
3
3
3
3
. Results and discussion
3.1. Catalysts characterization: porosity and acidity
3.2. Benzylation of aromatics with benzyl alcohol (BA)
The wide-angle XRD patterns of all ZSM-5 catalysts displayed
well-resolved peaks that were characteristic reflections for typical
crystalline MFI structure as shown in Fig. 1. The Meso ZSM-5
Benzylation of aromatics with benzyl alcohol is presented sche-
matically in Scheme 2, where R is –H, –CH , –OCH , –(CH ) group
3 3 3 3
(
3
SO H-CTAB)-MW prepared with sulfonic acid–functionalized
corresponding to benzene, toluene, anisole and mesitylene, respec-
tively. This reaction mainly produces dibenzyl ether and monoben-
zylated aromatic in different competitive reaction pathways. The
dibenzyl ether was formed by self-condensation of benzyl alcohols.
On the other hand, benzylation reaction was occurred between
aromatics and benzyl alcohol to produce desired monobenzylated
aromatic. The monobenzylated aromatic further reacted with
benzyl alcohol to produce bulky dibenzylated aromatics at high
reaction temperature or strong acidity.
ZSM-5 nanoparticles and CTAB by microwave showed much higher
intensity of the diffraction peak in low-angle XRD patterns com-
pared with mesoporous ZSM-5 synthesized by using non-function-
alized ZSM-5 nanoparticles, which were used to reflecting the
mesopore arrays, whereas the low-angle XRD pattern of ZSM-5
(
3
SO H-CTAB)-HT exhibited no distinct peak. This inferred that
mesoporous ZSM-5 with improved mesoporosity could be prefera-
bly synthesized by the microwave-induced rapid assembly
through the ionic interaction between anionic enhanced zeolite
Fig. 2. (A) N
ZSM- 5 catalysts (a) Meso ZSM-5 (SO
(c) ZSM-5 (SO H-CTAB)-HT and (d) ZSM-5 (HT).
2
adsorption–desorption isotherms and (B) pore size distribution of
Fig. 1. XRD patterns of ZSM-5 catalysts (a) Meso ZSM-5 (SO
3
H-CTAB)-MW, (b)
3
H-CTAB)-MW, (b) Meso ZSM-5 (CTAB)-MW,
Meso ZSM-5 (CTAB)-MW, (c) ZSM-5 (SO H-CTAB)-HT and (d) ZSM-5 (HT).
3
3

5
8
H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
Table 1
and mesitylene (0.87 nm) [35] is close to or much larger than the
Textural properties of various ZSM-5 catalysts.
size of micropore. It indicated that benzene and toluene reacted
in both micropores and mesopores; however, in case of anisole
and mesitylene, the reaction mainly occurred in mesopore wall
and pore mouth of micropores. This significant difference in cata-
lytic activity indicated that the presence of mesopore remarkably
enhanced the accessibility of reactants and products to overcome
the diffusion limitation from micropore.
Catalysts
S
BET
2
S
Ext
V
total
3
V
Meso
3
2
(
m /g)
(m /g)
(cm /g)
(cm /g)
Meso ZSM-5 (SO
3
H-CTAB)-MW
529
500
388
348
400
390
226
145
0.81
0.40
0.30
0.23
0.75
0.35
0.21
0.11
Meso ZSM-5 (CTAB)-MW
ZSM-5 (SO H-CTAB)-HT
ZSM-5 (HT)
3
Fig. 5A and B showed the selectivity of benzylation product
(
monobenzylated aromatic) and self-condensation product (diben-
zyl ether), respectively. Meso ZSM-5 (SO H-CTAB)-MW showed
3
Table 2
much higher selectivity of monobenzylated aromatic compared
with the ZSM-5 (HT), which showed dibenzyl ether as major prod-
uct. However, the selectivity of dibenzyl ether in benzylation of
Acidic properties of ZSM-5 catalysts.
Catalysts
NH
3
Strong acidity External
a
chemisorbed (300–500 °C) acid
3
benzene over Meso ZSM-5 (SO H-CTAB)-MW is rather higher than
c
(
mmol/g)
NH
desorbed
mmol/g)
3
sites
that of monobenzylated aromatic (diphenylmethane). It indicated
that the self-condensation of benzyl alcohol is more favorable than
benzylation of aromatic in case of benzene benzylation due to less
reactivity of benzene. According to early report by Prins and co-
workers [21], the alkylation reaction mainly occurred in the meso-
porous parts of zeolite due to diffusion limitation of bulky mole-
cules; hence, the mesitylene was chosen for the detail study of
benzylation, which can prove the effect of mesoporosity on the cat-
alytic activity and selectivity.
b
(mmol/g)
(
Meso ZSM-5 (SO
Meso ZSM-5 (CTAB)-MW
ZSM-5 (SO H-CTAB)-HT
3
H-CTAB)-MW
0.73
1.03
0.64
0.90
0.32 (44%)
0.50 (49%)
0.42 (65%)
0.46 (52%)
0.08
0.07
0.04
0.03
3
ZSM-5 (HT)
a
b
c
Determined by NH
Determined by NH
Determined by the chemisorption of 2,6-di-tert-butylpyridine (DTBPy).
3
3
desorption (chemisorbed at 100 °C).
desorption (chemisorbed at 100 °C).
3.2.2. Effect of mole ratio of mesitylene to benzyl alcohol (BA)
Benzylation of mesitylene with benzyl alcohol was carried out
by varying the mole ratio of mesitylene to benzyl alcohol from
:2 to 4:1 over Meso ZSM-5 (SO H-CTAB)-MW to assess its effect
1
3
on the catalytic activity and selectivity. The conversion of both
mesitylene and BA was found to increase with an increase in reac-
tant mole ratio from 1:2 to 2:1 as can be seen in Fig. 6A. Further
increase in mole ratio has no significant effect on conversion of
both reactants. The conversion of BA was significant in the mole ra-
tio of 1:2 and 1:1. However, the rate of benzylation of mesitylene
with benzyl alcohol was quite slow, and dibenzyl ether was formed
mainly due to self-condensation of benzyl alcohol. With increase in
the mole ratio of mesitylene to benzyl alcohol, the selectivity of
monobenzylated mesitylene (2-benzyl-1,3,5-trimethylbenzene,
9
1
.6 Â 6.8 Å) was found to increase from 15.5% at mole ratio of
:2 to 75.5% at mole ratio of 4:1. 2-Benzyl-1,3,5-trimethylbenzene
was shown as predominant product over Meso ZSM-5 (SO
CTAB)-MW at higher mole ratio of mesitylene to benzyl alcohol
Fig. 6B). Thus, all the reactions were performed with a mole ratio
of 4:1.
3
H-
(
Fig. 3. NH
Meso ZSM-5 (CTAB)-MW, (c) ZSM-5 (SO
3
TPD profiles of ZSM- 5 catalysts (a) Meso ZSM-5 (SO
3
H-CTAB)-MW, (b)
3.2.3. Effect of catalyst porosity
3
H-CTAB)-HT and (d) ZSM-5 (HT).
The catalytic performance of four different ZSM-5 catalysts for
the benzylation of mesitylene with benzyl alcohol was investigated
to examine the role of mesoporosity on selective production of
monobenzylated aromatics (Table 3). The conversion of mesitylene
3
.2.1. Effect of substituent on aromatic
Benzylation of substituted aromatics such as benzene, toluene,
anisole and mesitylene with benzyl alcohol over Meso ZSM-5
SO H-CTAB)-MW and ZSM-5 (HT) was performed in order to dem-
over Meso ZSM-5 (SO
was 30.7% and 27.8%, respectively, which was nearly 5 times high-
er than ZSM-5 (SO H-CTAB)-HT and ZSM-5 (HT). The most active
catalyst for the reaction was Meso ZSM-5 (SO H-CTAB)-MW with
3
H-CTAB)-MW and Meso ZSM-5 (CTAB)-MW
(
3
onstrate the role of mesoporosity and electronic or molecular size
effect of substrates on catalyst performance. The conversion of all
3
3
substrates and benzyl alcohol over Meso ZSM-5 (SO
MW was much higher than those of ZSM-5 (HT) as shown in
Fig. 4A and B. Meso ZSM-5 (SO H-CTAB)-MW without diffusion
restriction exhibited the increasing aromatic conversion from ben-
zene to mesitylene, which was mainly due to ring activation by
3
H-CTAB)-
the highest external surface area and mesopore volume. These
observations were in line of report by Candu et al. [36,37] that zeo-
lite behavior was dictated not only by their acidity but also by their
porosity in benzylation of benzene with benzyl alcohol. The differ-
ent porosities caused certain surface chemical composition
changes (acidity) again the product distribution. A similar phe-
nomenon was observed by de Jong and co-workers [38] in the
alkylation of benzene with propylene to produce cumene over
mesoporous mordenite. The catalytic activity was increased due
to enhanced accessibility and the selectivity of cumene/DIPB and
was mainly affected by the acid site on the external surface of
3
3 3 3 3
electron donating effects (–(CH ) > –OCH > –CH > –H). In case
of the ZSM-5 (HT), the conversion of anisole and mesitylene was
less than those of benzene and toluene due to diffusion limitation
of large molecular size. The molecular size of benzene (0.49 nm)
and toluene (0.54 nm) is smaller than the pore size of ZSM-5
(
5.4 Â 5.6 A) [33]. However, the molecular size of anisole [34]

H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
59
Scheme 2. Benzylation reaction mechanism of aromatics with benzyl alcohol.
Fig. 4. Conversion of (A) aromatics and (B) benzyl alcohol in benzylation of benzene, toluene, anisole and mesitylene with benzyl alcohol over Meso ZSM-5 (SO
3
H-CTAB)-MW
and ZSM-5 (HT).
crystallites. Pérez-Ramírez and co-workers [39] also stated that in
alkylation of toluene with benzyl alcohol, the selectivity to (meth-
ylbenzyl)benzene was mainly affected by the acidity and the alkyl-
ation activity was dominated by the mesoporous surface area.
Based upon these reports, we measured the external acid sites
3
affected the external acid sites. The Meso ZSM-5 (SO H-CTAB)-
MW gave around 4 times higher selectivity of benzylated mesity-
lene (2-benzyl-1,3,5-trimethylbenzene) than the microporous
ZSM-5. In case of ZSM-5 (HT), the dibenzyl ether was mainly
formed due to self-condensation of benzyl alcohol. This significant
difference in catalytic selectivity resulted from the existence of
mesopores, which definitely allowed the mesitylene benzylation
by acid sites in mesopores. The selectivity of benzylated mesity-
lene was increased with increasing mesopore volume which
(
i.e., acid sites at mesopore walls) by chemisorption of 2,6-di-
tert-butylpyridine as shown in Table 2. The external acid sites were
increased with increasing external surface area and mesopore
volume. These observations indicated the improved mesoporosity

6
0
H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
Fig. 5. Selectivity of (A) monobenzylated aromatic and (B) dibenzyl ether in benzylation of benzene, toluene, anisole and mesitylene with benzyl alcohol over Meso ZSM-5
SO H-CTAB)-MW and ZSM-5 (HT).
(
3
Fig. 6. (A) Conversion and (B) product distribution plotted as a function of various mole ratio of mesitylene to benzyl alcohol from 1:2 to 4:1 for benzylation of mesitylene
with benzyl alcohol over Meso ZSM-5 (SO H-CTAB)-MW.
3
inferred that it was mainly due to the improved external acid sites
which were affected by mesopore generation. This investigation
revealed that the mesoporosity played a significant role on control-
ling the selectivity of desired monobenzylated product.
time, whereas that of dibenzyl ether was decreased. This result
indicates that the benzylation of mesitylene with benzyl alcohol
is predominant reaction, whereas the formation of dibenzyl ether
through the self-condensation of benzyl alcohol is side reaction
and dibenzyl ether generated can act as benzylating agent to par-
ticipate in the benzylation reaction (Fig. 7B).
3.2.4. Effect of reaction time and recyclability
To further investigate the catalytic performance of Meso ZSM-5
3
The reusability of Meso ZSM-5 (SO H-CTAB)-MW as heteroge-
(
SO
3
H-CTAB)-MW, the effect of reaction time and reusability of
neous catalysts in the benzylation of mesitylene with benzyl alco-
hol was investigated for three cycles. Table 4 shows the catalytic
activities of fresh and reused Meso ZSM-5 (SO H-CTAB)-MW. The
3
fresh catalysts gave 100% of BA conversion and 75.2% of 2-ben-
zyl-1,3,5-trimethylbenzene selectivity, respectively, which was
maintained even after reusing catalysts two times. These results
catalyst was tested through the benzylation of mesitylene with
benzyl alcohol. The conversion of both reactants was increased
with increasing reaction time from 15 min to 30 min and stabilized
after 30 min as presented in Fig. 7A. The selectivity of 2-benzyl-
1
,3,5-trimethylbenzene was increased with increasing reaction

H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
61
Fig. 7. (A) Conversion and (B) product distribution plotted as a function of reaction time for benzylation of mesitylene with benzyl alcohol over Meso ZSM-5 (SO
3
H-CTAB)-
MW.
Table 3
Benzylation of mesitylene (MES) with benzyl alcohol (BA) over various ZSM-5 catalysts.
3
Catalysts
Aromatics conv. (%)
BA conv. (%)
Product distribution (%)
V
meso (cm /g)
A
B
C
Meso ZSM-5 (SO
3
H-CTAB)-MW
30.7
27.8
5.5
100
75.5
56.8
36.6
19.8
–
8
39.9
49.7
24.5
35.2
23.5
30.5
0.75
0.35
0.21
0.11
Meso ZSM-5 (CTAB)-MW
ZSM-5 (SO H-CTAB)-HT
ZSM-5 (HT)
99.6
77.2
23.0
3
6.3
Reaction conditions: MES:BA = 4:1; Catalyst = 50 mg; 100 °C, 1 h. (A) 2-Benzyl-1,3,5-trimethylbenzene; (B) dibenzyl ether; (C) others: (2,4,6-trimethyl-1,3-phenylene)-
bis(methylene)-dibenzene; (2-benzylphenyl)methanol; 9,10-dihydroanthracene.
Table 4
with microporous ZSM-5 due to enhanced intracrystalline
mesoporosity. Moreover, this Meso ZSM-5 (SO H-CTAB)-MW with
Reusability of Meso ZSM-5 (SO
with benzyl alcohol (BA).
3
H-CTAB)-MW in the benzylation of mesitylene (MES)
3
the highest external acid sites and mesoporosity showed much
higher selectivity of desired monobenzylated aromatic than those
of other ZSM-5 catalysts. The microporous ZSM-5 produced
dibenzyl ether as major product due to diffusion limitation of
bulky reactant or product. Controllable mesoporosity play an
important role on controlling the selectivity of desired monoben-
Catalysts
Fresh
BA conv. (%)
2-Benzyl-1,3,5-TMB Select. (%)
100
100
100
75.2
77.6
75.0
1
2
st reuse
nd reuse
Reaction conditions: MES: BA = 4:1; catalyst = 50 mg; 100 °C, 1 h.
zylated aromatic. The Meso ZSM-5 (SO
reused for three cycles without loss of acidity. This Meso ZSM-5
SO H-CTAB)-MW can be regarded as promising heterogeneous
3
H-CTAB)-MW can be
(
3
3
indicated that the Meso ZSM-5 (SO H-CTAB)-MW can be reused
acid catalyst to improve the selectivity of desired monobenzylated
product in aromatic benzylation and has potential application for
pharmaceutical industry.
without a significant change in the activity and selectivity and
has potential for industrial application.
4
. Conclusions
Acknowledgments
In this investigation, the selectivity of desired monobenzylated
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korea Government (MEST) (No.
aromatic was mainly controlled by the external acid sites that were
affected by degree of mesoporosity of various ZSM-5 catalysts. The
selectivity of desired monobenzylated aromatic increased with the
increase of mesoporosity was confirmed.
2
011-0020436) and Inha University.
References
3
The Meso ZSM-5 (SO H-CTAB)-MW showed nearly 5-fold
increase in catalytic activity in aromatic benzylation compared
[1] B. Viswanathan, B. Jacob, Catal. Rev. 47 (2005) 1.

6
2
H. Jin et al. / Journal of Catalysis 291 (2012) 55–62
[
[
2] C. Perego, P. Ingallina, Catal. Today 73 (2002) 3.
3] E. Aleksandrova, G. Nosova, N. Solovskaya, K. Romashkova, V. Luk’yashina, E.
Konozobko, V. Kudryavtsev, Semiconductors 38 (2004) 652.
[22] J.C. Groen, T. Sano, J.A. Moulijn, J. Pérez-Ramírez, J. Catal. 251 (2007) 21.
[23] S.-E. Park, J.-S. Chang, Y.K. Hwang, D.S. Kim, S.H. Jhung, J.S. Hwang, Catal. Sur.
Asia 8 (2004) 91.
[
4] S. Van der Beken, E. Dejaegere, K.A. Tehrani, J.S. Paul, P.A. Jacobs, G.V. Baron,
J.F.M. Denayer, J. Catal. 235 (2005) 128.
5] G. Mirth, J. Cejka, J. Krtil, J.A. Lercher, Stud. Surf. Sci. Catal. (1994) 241.
6] U. Sridevi, B.K. Bhaskar Rao, N.C. Pradhan, Chem. Eng. J. 83 (2001) 185.
7] H.-j. Dong, L. Shi, Ind. Eng. Chem. Res. 49 (2010) 2091.
[24] H. Jin, N. Jiang, S.-E. Park, J. Phys. Chem. Solids 69 (2008) 1136.
[25] H. Jin, N. Jiang, S.-M. Oh, S.-E. Park, Top. Catal. 52 (2009) 169.
[26] S. Abello, J. Pérez-Ramírez, PCCP 11 (2009) 2959.
[27] N. Jiang, D.-S. Han, S.-E. Park, Catal. Today 141 (2009) 344.
[28] J.-B. Koo, N. Jiang, S. Saravanamurugan, M. Bejblová, Z. Musilová, J. Cejka, S.-E.
Park, J. Catal. 276 (2010) 327.
[
[
[
[
8] G. Girotti, F. Rivetti, S. Ramello, L. Carnelli, J. Mol. Catal. A: Chem. 204–205
(
2003) 571.
[29] Sujandi, S.-E. Park, D.-S. Han, S.-C. Han, M.-J. Jin, T. Ohsuna, Chem. Commun.
(2006) 4131.
[30] H. Jin, M. Bismillah Ansari, S.-E. Park, Chem. Commun. 47 (2011) 7482.
[31] J. Kim, M. Choi, R. Ryoo, J. Catal. 269 (2010) 219.
[32] K. Suzuki, Y. Aoyagi, N. Katada, M. Choi, R. Ryoo, M. Niwa, Catal. Today 132
(2008) 38.
[33] J.J. Vijaya, L.J. Kennedy, G. Sekaran, K.S. Nagaraja, Mater. Lett. 61 (2007)
5213.
[34] M. Álvaro, D. Das, M. Cano, H. Garcia, J. Catal. 219 (2003) 464.
[
9] Y.K. Hwang, J.-S. Chang, S.-E. Park, D.S. Kim, Y.-U. Kwon, S.H. Jhung, J.-S. Hwang,
M.S. Park, Angew. Chem. Int. Ed. 44 (2005) 556.
10] C.H. Christensen, K. Johannsen, E. Törnqvist, I. Schmidt, H. Topsøe, C.H.
Christensen, Catal. Today 128 (2007) 117.
11] A. Corma, Chem. Rev. 95 (1995) 559.
12] J. Cˇ ejka, B. Wichterlová, Catal. Rev. 44 (2002) 375.
[
[
[
[
[
[
13] S. Barman, N.C. Pradhan, J.K. Basu, Ind. Eng. Chem. Res. 44 (2005) 7313.
14] A. Corma, Chem. Rev. 97 (1997) 2373.
15] J. Pérez-Ramírez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen,
Chem. Soc. Rev. 37 (2008) 2530.
[35] S. Nakashima, Y. Takahashi, M. Kiguchi, Beilstein J. Nanotech.
755.
2 (2011)
[
16] X. Gu, T. Jiang, H. Tao, S. Zhou, X. Liu, J. Ren, Y. Wang, G. Lu, W. Schmidt, J.
Mater. Chem. 21 (2011) 880.
[36] N. Candu, M. Florea, S.M. Coman, V.I. Parvulescu, Appl. Catal. A: Gen. 393
(2011) 206.
[
[
17] V.N. Shetti, J. Kim, R. Srivastava, M. Choi, R. Ryoo, J. Catal. 254 (2008) 296.
18] C.H. Christensen, K. Johannsen, I. Schmidt, C.H. Christensen, J. Am. Chem. Soc.
[37] N. Candu, S. Wuttke, E. Kemnitz, S.M. Coman, V.I. Parvulescu, Appl. Catal. A:
Gen. 391 (2011) 169.
[38] A.N.C. van Laak, S.L. Sagala, J. Ze cˇ evi c´ , H. Friedrich, P.E. de Jongh, K.P. de Jong, J.
Catal. 276 (2010) 170.
[39] M. Milina, S. Mitchell, Z.D. Trinidad, D. Verboekend, J. Pérez-Ramírez, Catal. Sci.
Technol. (2012).
1
25 (2003) 13370.
[
[
[
19] J.S. Jung, J.W. Park, G. Seo, Appl. Catal. A: Gen. 288 (2005) 149.
20] Y. Sun, R. Prins, Appl. Catal. A: Gen. 336 (2008) 11.
21] X. Li, R. Prins, J.A. van Bokhoven, J. Catal. 262 (2009) 257.