Chemoselective O-Versus C-Alkylation of substituted phenols with cyclohexene over mesoporous ZSM-5

Article abstract of DOI:10.1016/j.apcata.2013.12.025

Chemoselective O- versus C-alkylation of substituted phenols such as phenol, p-cresol, and guaiacol with cyclohexene were investigated over various ZSM-5 catalysts with different degree of mesoporosity and external acidity such as mesoporous ZSM-5 synthesized by microwave induced assembly via electrostatic interaction between sulfonic acid, functionalized or non-functionalized ZSM-5 nanozeolites and counter cationic surfactant, and hydrothermal synthesized microporous ZSM-5 with or without sulfonic acid functionalization and surfactant. The selectivity of O- and C-alkylated products varied with different degree of mesoporosity. The selectivity of C-alkylated products increased with increasing mesopore volume and external acid sites, whereas that of O-alkylated product decreased. The mesoporous ZSM-5 synthesized under microwave via sulfonic acid functionalization showed not only the highest mesoporosity and external acid sites but also the best catalytic activity and selectivity of C-alkylated products, whereas the other ZSM-5 catalysts mainly produced O-alkylated products due to diffusion limitation of bulky product.

Full text of DOI:10.1016/j.apcata.2013.12.025

Applied Catalysis A: General 472 (2014) 184–190
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Chemoselective O- versus C-alkylation of substituted phenols
with cyclohexene over mesoporous ZSM-5
Hailian Jin, Mohd Bismillah Ansari, Sang-Eon Park∗
Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemicals Fusion Technology, Department of Chemistry and Chemical Engineering, 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:
Chemoselective O- versus C-alkylation of substituted phenols such as phenol, p-cresol, and guaiacol with
cyclohexene were investigated over various ZSM-5 catalysts with different degree of mesoporosity and
external acidity such as mesoporous ZSM-5 synthesized by microwave induced assembly via electro-
static interaction between sulfonic acid, functionalized or non-functionalized ZSM-5 nanozeolites and
counter cationic surfactant, and hydrothermal synthesized microporous ZSM-5 with or without sulfonic
acid functionalization and surfactant. The selectivity of O- and C-alkylated products varied with differ-
ent degree of mesoporosity. The selectivity of C-alkylated products increased with increasing mesopore
volume and external acid sites, whereas that of O-alkylated product decreased. The mesoporous ZSM-5
synthesized under microwave via sulfonic acid functionalization showed not only the highest meso-
porosity and external acid sites but also the best catalytic activity and selectivity of C-alkylated products,
whereas the other ZSM-5 catalysts mainly produced O-alkylated products due to diffusion limitation of
bulky product.
Received 5 September 2013
Received in revised form 4 December 2013
Accepted 20 December 2013
Available online 28 December 2013
Keywords:
Chemoselective
Alkylation
Mesoporous ZSM-5
Mesoporosity
Substituted phenols
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
ment of these mineral acids with environmental-friendly solid acid
catalysts is one of major demand for industrial green process. Sev-
The catalytic alkylation of substituted phenols with cyclohex-
ene [1] or various alcohols such as cyclohexanol [2], methanol
[3–8], ethanol [9], n-propanol [10], n-butanol [10], and tert-butanol
[11] are one of the most important industrial organic reactions.
These reactions yield both O- and C-alkylated products having com-
mercial utility. The O-alkylated products are promising perfumery
compound [1], whereas the C-alkylated products are used as impor-
tant intermediates in the preparation of dyestuffs, drugs, printing
inks, wire enamels, rubber chemicals, petroleum additives, poly-
mer additives, resins and so on [12]. Hence, the selective production
of each alkylated products is quite challenging in these reaction
processes.
These chemoselective alkylation processes have been normally
catalyzed by mineral acids such as AlCl3, H2SO4, HF, and BF3 which
give rise to many technological and environmental problems such
as equipment corrosion, industrial hazard, difficult separation, and
catalyst recovery [13,14]. Moreover these homogenous catalysts
show poor selectivity in such organic reactions. Hence, the replace-
eral alternative heterogeneous acid catalysts such as cationic ion
exchange resins [1], silica-supported BF3 [13], styrene divinylben-
zene sulfonic resins (Amberlyst 15TM and Amberlyst 36TM) [14,15],
various Starbon supported acids [16], dodecatungstophosphoric
acid supported K-10 clay [17], sulphonic acid treated hexagonal
mesoporous silica [17], and zeolites (H-Y, ZSM-5, H-FER and H-
mordernite) [2,18] have been used in selective alkylation reactions
of phenol with cyclohexene or cyclohexanol. p-Toluenesulfonic
acid (p-TSA) treated clays and cation-exchange resins have been
also used as acid catalysts in alkylation of guaiacol [12] and p-cresol
[19], respectively. From the prior works, it can be stated that the
selective formation of O- and C-alkylated products is affected by
several parameters such as temperature, alkylating agent, solvent,
pore size, and nature of active sites in catalyst [20]. Recent studies
by Yadav et al. on chemoselective alkylation of guaiacol [20] and p-
cresol [21] with cyclohexene over sulphated zirconia revealed that
existence of Lewis acid sites inside the mesopores were required to
selectively yield desired bulky O-alkylated product. As per reports,
large pore size of catalysts is contributing to ring alkylation whereas
narrow pore size favors O-alkylation [17,18]. Earlier report by Prins
et al. [22] mentioned that the alkylation mainly occurred in the
mesoporous parts of zeolites due to diffusion limitation of bulky
molecules. Moreover, the selectivity was mainly affected by the
acidity [23]. Based on these reports we can deduce that both meso-
porosity and external acid sites of catalysts play an important role
∗
Corresponding author at: Laboratory of Nano-Green Catalysis and Nano Center
for Fine Chemicals Fusion Technology, Department of Chemistry and Chemical Engi-
neering, Inha University, 253 Yonghyun-dong, Incheon 402-751, Republic of Korea.
Tel.: +82328607675.
E-mail address: separk@inha.ac.kr (S.-E. Park).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.12.025

H. Jin et al. / Applied Catalysis A: General 472 (2014) 184–190
185
Vosko–Wilk–Nusair (VWN) functional implemented in the DMOL3
software package Material Studio 6.0 from Accelrys.
on activity and selectivity in such chemoselective alkylation reac-
tions.
Mesoporous zeolites containing both crystalline micropores
and developed intracrystalline mesopores have attracted much
attention in various alkylation reactions [24–31], which exhib-
ited enhanced catalytic activity and remarkable change of product
selectivity due to improved accessibility to and/or from active
sites in micropores through the mesopores [32–36]. Recently, we
reported the novel method for synthesis of mesoporous ZSM-
5 by microwave induced assembly via electrostatic interaction
between anionic sulfonic acid functionalized ZSM-5 nanoparti-
cles and counter cationic surfactant (Cetyltrimethylammonium
bromide: CTAB) [37]. This mesoporous ZSM-5 showed not only
remarkably improved catalytic activity in aromatic benzylation
but also much higher selectivity of desired monobenzylated
aromatic compared with microporous ZSM-5, which was due
to enhanced intracrystalline mesoporosity and external acid
sites. Moreover, the selectivity of desired monobenzylated aro-
matic increased with increase in mesoporosity was observed
[38].
2.3. Catalytic tests
All the experiments were carried out in a 25 ml single-necked
flask equipped with reflux condenser. The mole ratio of phenol,
p-cresol, and guaiacol with cyclohexene was 5:1. In a typical reac-
tion, 1 ml solution containing 9.41 mmol of phenol and 1.88 mmol
of cyclohexene were placed into the reactor. The 0.05 g/ml of cata-
lyst was loaded with respect to total volume of the reaction mixture.
The reaction was carried out at 80 ◦C for 4 h. Small amounts of clear
liquid reaction mixture was analyzed by using a gas chromatograph
(Agilent Technologies, GC 6890 N) equipped with a flame ionization
detector (FID) and a capillary column (HP 5% silicone gum, 0.25
micron i.d. with 30 m long). The products were also confirmed by
GC–MS (Agilent Technologies GC 6890 N, and MS5975).
3. Results and discussion
In continuation to our earlier studies on aforementioned zeolitic
catalyst, in the current study, we investigated the effect of meso-
porosity and external acid sites on the catalytic activity and
selectivity of O- and C-alkylated products in the chemoselective
alkylation of phenol with cyclohexene as an alkylating agent over
ZSM-5 catalysts with different degree of mesoporosity such as Meso
ZSM-5 (SO3H-CTAB)-MW, Meso ZSM-5 (CTAB)-MW (mesoporous
ZSM-5 were synthesized by assembly via electrostatic interac-
tion between sulfonic functionalized or non-functionalized ZSM-5
nanozeolites and counter cationic surfactant under microwave),
ZSM-5 (SO3H-CTAB)-HT, and ZSM-5 (HT) (hydrothermal synthe-
sis with or without sulfonic acid functionalization and surfactant).
Moreover, the effects of mole ratio of phenol to cyclohexene, reac-
tion temperature and time, catalyst loading, substituent on phenol,
and recyclability have also been investigated.
3.1. Porosity and acidity of catalyst
All the obtained ZSM-5 catalysts such as Meso ZSM-5 (SO3H-
CTAB)-MW, Meso ZSM-5 (CTAB)-MW, ZSM-5 (SO3H-CTAB)-HT, and
ZSM-5 (HT) showed typical crystalline structure of MFI in wide-
angle XRD patterns. In low-angle XRD patterns, The meso ZSM-5
(SO3H-CTAB)-MW exhibited remarkably higher intensity of the
diffraction peak at 2Â = 1–3◦ which was an evidence for the pres-
ence of mesopore arrays compared with meso ZSM-5 (CTAB)-MW.
Whereas there was no distinct peak observed in case of ZSM-5
(SO3H-CTAB)-HT which was similar to microporous ZSM-5 (HT)
[38]. These results coincided with the N2 adsorption–desorption
isotherms and physical properties which are summarized in Table
S1. The three types of pores such as micropores (<2 nm), uni-
form mesopores (2.7 nm), and intercrystalline mesopores (∼12 nm)
were observed from the N2 adsorption–desorption isotherm and
pore size distribution of meso ZSM-5 (SO3H-CTAB)-MW [37,38].
The forced closure at relative pressure of 0.45 was due to ten-
sile strength effect which was in consonance with earlier reports
[39–41]. The BET surface area, external surface area, and mesopore
volume of meso ZSM-5 (SO3H-CTAB)-MW were 529, 400 m2/g and
0.75 cm3/g, respectively, which were much higher than those of
other catalysts due to enhanced mesoporosity.
The number of strong acid sites and external acid sites
were measured by NH3 TPD and chemisorptions of 2,6-di-tert-
butylpyridine, respectively as shown in Table S1. The strong acid
sites of meso ZSM-5 (SO3H-CTAB)-MW (0.32 mmol/g) were only 8%
less than the ZSM-5 (HT) (0.46 mmol/g). This was approximately
similar which indicated that the meso ZSM-5 (SO3H-CTAB)-MW
was prepared without significantly sacrificing acidity [42]. More-
over, the external acid sites increased with the increasing of
mesoporosity were confirmed.
2. Experiment
2.1. Chemicals and catalysts
Phenol, p-cresol, guaiacol, cyclohexene, tetraethyl orthosilicate
(TEOS, 98%), and aluminum isopropoxide (AIP) were purchased
from Sigma–Aldrich Co. Ltd. Tetrapropylammonium hydroxide
(TPAOH, 20 ∼ 25%), 3-mercaptopropyltriethoxysliane (MPTES) and
cetyltrimethylammonium bromide (CTAB) were obtained from
Tokyo Chemical Industry CO. Ltd. (TCI). Hydrogen peroxide (H2O2,
30% in the water) was procured from Duksan Company (Korea).
The ZSM-5 catalysts with different degree of mesoporosity such
as Meso ZSM-5 (SO3H-CTAB)-MW, Meso ZSM-5 (CTAB)-MW, ZSM-
5 (SO3H-CTAB)-HT, and ZSM-5 (HT) were prepared according to
established procedures reported in Ref. [37]. Prior to reaction all
the catalysts were pretreated at 450 ◦C for 2 h.
2.2. Catalysts characterization
3.2. Chemoselective alkylation of substituted phenols with
cyclohexene
All the catalysts were characterized by powder X-ray diffrac-
tion (XRD), N2 adsorption and desorption isotherms (BET surface
area and external surface area were calculated from the linear part
of the BET plot and t-plot, respectively. The amount adsorbed at
the relative pressure (P/Po) of 0.99 was used to evaluate the total
pore volume), temperature-programmed desorption (TPD) of NH3,
chemisorption of 2,6-di-tert-butylpyridine, and the details were
published recently by our group [38]. Molecular size of products in
Scheme 2A was estimated by geometry optimizations which were
calculated using the local density approximation (LDA) with the
Chemoselective alkylation of phenol, p-cresol, and gua-
iacol with cyclohexene are presented in Scheme 1. These
reactions mainly produce both O- and C-alkylated products. The
O-alkylated products are cyclohexylphenyl ether, 1-cyclohexyloxy-
4-methylbenzene,
and
1-cyclohexyloxy-2-methylbenzene;
the C-alkylated products are O- and p-cyclohexylphenol, 2-
cyclohexyl-p-cresol and o- and m- and p-cyclohexyl guaiacol,
respectively [14,19,20]. Moreover, several parallel reactions can be
occurred such as cyclohexene oligomerization (to form cyclohexyl

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H. Jin et al. / Applied Catalysis A: General 472 (2014) 184–190
Scheme 1. Reaction paths for chemoselective O- versus C-alkylation of substituted phenols with cyclohexene.
cyclohexene and/or cyclohexenylbicyclohexane), rearrangement
and/or isomerisation of O- and C-alkylated products (to form
di-alkylated products) [14]. The effects of several parameters on
selective production of O- and C-alkylated products are described
in detail as below:
cyclohexene were found to increase remarkably with an increase
in temperature from 60 to 80 ◦C, further increase in tempera-
ture to 100 ◦C had no significant effect on the conversion of both
reactants. The selectivity of C-alkylated products increased with
3.2.1. Effect of mole ratio of phenol to cyclohexene
The mole ratio of phenol to cyclohexene was varied from 1:3 to
5:1 in chemoselective alkylation of phenol with cyclohexene over
meso ZSM-5 (SO3H-CTAB)-MW in order to access its effect on the
catalytic activity and selectivity. As summarized in Table 1, the con-
version of phenol decreased with increasing mole ratio of phenol
to cyclohexene, whereas the selectivity of monoalkylated prod-
ucts (O- and C-alkylated products) increased from 41.8 to 100%.
The low selectivity at lower mole ratio (1:3 and 1:1) was due to a
fast formation of cyclohexene oligomerization products like cyclo-
hexyl cyclohexene and cyclohexenylbicyclohexane. The selectivity
of O-alkylated products was 44.0% in a mole ratio of 5:1 which was
slightly lower than that of 3:1 (45.6%), it was because that the O-
alkylated products (cyclohexylphenylether) further isomerised to
C-alkylated products [14]. The selectivity of C-alkylated products
reached a maximum of 56.0% at mole ratio of 5:1. Thus, all the
subsequent reactions were investigated with a mole ratio of 5:1.
3.2.2. Effect of reaction temperature and time
The chemoselective alkylation of phenol with cyclohexene over
meso ZSM-5 (SO3H-CTAB)-MW was investigated in the temper-
ature range of 60–100 ◦C (Fig. 1). The conversion of phenol and
Fig. 1. Catalytic performance of meso ZSM-5 (SO3H-CTAB)-MW in chemoselec-
tive O- versus C-alkylation of phenol with cyclohexene as a function of reaction
temperature (60, 80, and 100 ◦C).

H. Jin et al. / Applied Catalysis A: General 472 (2014) 184–190
187
Table 1
Catalytic performance of meso ZSM-5 (SO3H-CTAB)-MW in chemoselective O- versus C-alkylation of phenol with cyclohexene as a function of various mole ratio of phenol
to cyclohexene.
Mole ratio of phenol to cyclohexene
Conversion (%)
Cyclohexene
Selectivity (%)a
Phenol
O-alkylation
C-alkylation
1:3
1:1
3:1
5:1
95.6
94.4
92.6
92.5
96.9
81.4
30.1
18.3
15.8
32.3
45.6
44.0
26.0
50.0
52.2
56.0
a
Reaction condition: total reactor volume = 1 ml; catalyst = 0.05 g/ml; reaction temperature = 80 ◦C; stirring speed = 800 rpm; reaction time = 4 h.
increasing reaction temperature, whereas that of O-alkylated prod-
ucts decreased. This result indicated that the alkylation reaction
was of higher activation energy than the etherification [1] and the
O-alkylated products as an intermediate further isomerised to C-
alkylated products at high temperature [18].
The effect of reaction time from 15 to 240 min was carried out
through the same reaction over meso ZSM-5 (SO3H-CTAB)-MW at
80 ◦C as shown in Fig. 2. The conversion of both reactants remark-
ably increased from 30 to 60 min, and then increased gradually
with increasing reaction time. Selectivity of O- and C-alkylated
products depicted similar trend with the effect of reaction temper-
ature. Moreover, the selectivity of C-alkylated products was higher
than that of O-alkylated products after certain longer reaction time
(240 min). Hence further investigations were carried for reaction
time of 4 h.
3.2.4. Effect of substituent on phenol
Chemoselective alkylation of phenol, p-cresol, and guaiacol with
cyclohexene over meso ZSM-5 (SO3H-CTAB)-MW were investi-
gated in order to demonstrate the effect of substituent on phenol
(Fig. 4A and B). As illustrated in Fig. 4A, the conversion of p-cresol
was higher than that of phenol which was mainly due to ring acti-
vation by electron donating effects ( CH3 > H) [38]. Whereas the
conversion of guaiacol was little lower than those of phenol and
p-cresol due to its larger molecular size which caused less acces-
sibility to active sites compared with the others. The selectivity of
C-alkylated products was higher than that of O-alkylated products
in case of all substituted phenols as shown in Fig. 4B. The selectivity
for C-alkylated products among the three substrates was the high-
est in case of guaiacol whereas the least in case of phenol, which was
attributed to ring activation effect by electron donating substituent
(
OCH3 > CH3 > H).
3.2.3. Effect of catalyst loading
3.2.5. Effect of catalyst mesoporosity and acidity
Fig. 3 showed the effect of catalyst loading on the catalytic con-
version and selectivity over meso ZSM-5 (SO3H-CTAB)-MW at 80 ◦C
for 4 h. The catalyst amount was varied over a range of 0.01–0.1 g/ml
on the basis of total volume of reaction mixture. The conversion of
both phenol and cyclohexene increased with increase in catalyst
loading, which was due to the proportional increase in the num-
ber of active sites [43]. The same trend of selectivity with effect
of reaction temperature and time was observed. The selectivity of
C-alkylated products was higher than that of O-alkylated products
with catalyst loading more than 0.05 g/ml; it indicated the more
active sites favor to form more C-alkylated products. Hence, all the
further experiments were performed by using 0.05 g/ml loading of
catalyst.
Various ZSM-5 catalysts with different mesoporosity such as
Meso ZSM-5 (SO3H-CTAB)-MW, Meso ZSM-5 (CTAB)-MW, ZSM-
5 (SO3H-CTAB)-HT, and ZSM-5 (HT) were used as catalysts in
phenol alkylation with cyclohexene to examine the effect of meso-
porosity and external acid sites on catalytic activity and selectivity
(Table 2). The conversion of both phenol and cyclohexene were in
the following order: meso ZSM-5 (SO3H-CTAB)-MW > meso ZSM-
5 (CTAB)-MW > ZSM-5 (SO3H-CTAB)-HT > ZSM-5 (HT). The meso
ZSM-5 (SO3H-CTAB)-MW with the highest external surface area
and mesopore volume (Table S1) showed the best catalytic activ-
ity which was much higher than that of ZSM-5 (HT). Moreover, the
meso ZSM-5 (SO3H-CTAB)-MW mainly produced bulky C-alkylated
Fig. 2. Catalytic performance of meso ZSM-5 (SO3H-CTAB)-MW in chemoselective
O- versus C-alkylation of phenol with cyclohexene as a function of reaction time (15,
30, 60, 120, and 240 min).
Fig. 3. Catalytic performance of meso ZSM-5 (SO3H-CTAB)-MW in chemoselective
O- versus C-alkylation of phenol with cyclohexene as a function of catalyst loading
(0.01, 0.03, 0.05, and 0.1 g/ml).

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H. Jin et al. / Applied Catalysis A: General 472 (2014) 184–190
Table 2
Chemoselective O- versus C-alkylation of phenol with cyclohexene over various ZSM-5 catalysts.
Catalysts
Conversion (%)
Cyclohexene
Selectivity (%)a
Phenol
O-alkylation
C-alkylation
Meso ZSM-5 (SO3H-CTAB)-MW
Meso ZSM-5 (CTAB)-MW
ZSM-5 (SO3H-CTAB)-HT
ZSM-5 (HT)
92.5
63.0
32.1
26.0
18.3
12.5
6.3
44.0
66.1
85.9
100
56.0
33.9
14.1
–
5.0
a
Reaction condition: phenol: cyclohexene = 5:1; total reactor volume = 1 ml; catalyst = 0.05 g/ml; reaction temperature = 80 ◦C; stirring speed = 800 rpm; reaction time = 4 h.
Fig. 4. (A) Conversion and (B) selectivity in chemoselective O- versus C-alkylation of phenol with cyclohexene, p-cresol and guaiacol with cyclohexene over meso ZSM-5
(SO3H-CTAB)-MW.
Scheme 2. Correlation between catalytic activity and selectivity and (A) mesoporosity and external acidity, (B) diffusion of reactants and products.

H. Jin et al. / Applied Catalysis A: General 472 (2014) 184–190
189
Table 3
of mesopore remarkably enhanced the accessibility of bulky C-
alkylated products to/from active sites. Controllable mesoporosity
play an important role on product distribution in chemoselec-
tive alkylation reaction. The selectivity of C-alkylated products
increased with increase in reaction temperature, time, catalyst
loading and mole ratio of phenol to cyclohexene. The meso ZSM-5
(SO3H-CTAB)-MW is promising heterogeneous catalysts which
can be reused for three cycles without significant loss of activity.
Reusability of meso ZSM-5 (SO3H-CTAB)-MW in chemoselective O- versus C-
alkylation of phenol with cyclohexene.
Catalysts
Conversion (%)
Cyclohexene
Selectivity (%)a
Phenol
O-alkylation
C-alkylation
Fresh
1st reuse
2nd reuse
92.5
92.9
91.4
18.3
18.5
18.1
44.0
46.3
47.1
56.0
53.7
52.9
a
Reaction condition: phenol: cyclohexene = 5:1; total reactor volume = 1 ml; cat-
alyst = 0.05 g/ml; reaction temperature = 80 ◦C; stirring speed = 800 rpm; reaction
time = 4 h.
Acknowledgements
This work was supported by the National Research Foundation
of Korea [NRF] grant funded by the Korea government [MSIP] [No.
20090083525] and Inha University.
products whereas O-alkylated products were mainly formed in
case of the other ZSM-5 catalysts. It indicated that the presence
of enhanced mesoporosity significantly improved the accessibil-
ity of both reactants and products to and/or from active sites. As
shown in Scheme 2A, both the reactants phenol (kinetic diam-
eter: ca. 0.66 nm [44]) and cyclohexene (kinetic diameter: ca.
0.58 nm [45]) have less diffusivity in the ZSM-5 micropore channels
(0.51 × 0.55 and 0.53 × 0.56 nm) thereby limiting the accessibil-
ity due to larger molecular size. Hence the alkylation was mainly
occurred inside of the mesopores and micropore mouths. Fur-
thermore, the C-alkylated products (0.97 × 0.58 nm) were difficult
to pass through the micropore channels due to diffusion lim-
itation whereas the O-alkylated products (1.00 × 0.53 nm) were
able to go through the micropores. According to previous reports
[30,38,46], the selectivity of alkylated products was found to be
mainly affected by the external acid sites due to diffusion lim-
itation of bulky molecule. The external acid sites were affected
by mesopore generation which increased with increase in exter-
nal surface area and mesopore volume as shown in Table S1 and
Scheme 2B. The selectivity of C-alkylated products increased with
increasing external acid sites whereas that of O-alkylated prod-
ucts decreased, which inferred that the improved mesoporosity
and external acid sites enhanced the accessibility and preferentially
form bulky C-alkylated products. These observations revealed that
the mesoporosity and external acid sites play a significant role on
product distribution.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2013.12.025.
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catalysts were filtered, washed with methanol, dried at 120 ◦C and
calcined at 550 ◦C for 5 h after each reaction. The conversion of
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