Synthesis, characterization and catalytic activity studies on cordierite honeycomb coated with ZrO2 based solid super acids

Article abstract of DOI:10.1016/j.crci.2012.05.020

Cordierite honeycomb coated with solid acids such as ZrO₂, Mo/ZrO₂ and W/ZrO₂ were synthesized. These solid acid catalysts were also synthesized in their powder forms. The catalytic materials were characterized for their physicochemical properties such as surface area, surface acidity, crystallinity and morphology by using techniques such as BET, NH₃-TPD/n-butylamine back titration, powder XRD and SEM respectively. The catalytic activity of these catalytic materials was determined in an acid catalyzed transesterification reaction of methyl salicylate with phenol to synthesize phenyl salicylate (salol). The effect of concentration of Mo or W ions on ZrO₂, nature of the catalyst (whether honeycomb coated or powder form), reaction temperature, reaction time and reusability of the catalytic material in transesterification was studied. Formation of diphenyl ether as a by-product was observed on increasing the concentration of Mo or W ions on ZrO₂ and also at higher reaction temperature. The catalytic activity of catalytic materials was correlated with surface acidity and the crystalline phases of catalytic material. Transesterification reactions were also carried out with methyl salicylate and benzyl alcohol or cyclohexanol to synthesize their respective salicylate esters. A probable mechanism of transesterification of methyl salicylate with an alcohol is also proposed. The honeycomb catalysts were found to be efficient, ecofriendly, economical and reusable catalysts compared to their powder forms.

Full text of DOI:10.1016/j.crci.2012.05.020

C. R. Chimie 15 (2012) 799–807
Contents lists available at SciVerse ScienceDirect
Comptes Rendus Chimie
www.sciencedirect.com
Full paper/M e´ moire
Synthesis, characterization and catalytic activity studies on cordierite
honeycomb coated with ZrO based solid super acids
2
a,
a
a
a
S.Z. Mohamed Shamshuddin *, M. Shyam Sundar , N. Thimmaraju , Venkatesh ,
a
b
G. Vatsalya , M. Senthilkumar
a
Chemistry Research Laboratory, HMS Institute of Technology, NH4, Kyathsandra, Tumkur 572 104, Karnataka, India
Department of Chemistry, SKP Engineering College, Tiruvannamalai, Tamil Nadu, India
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Cordierite honeycomb coated with solid acids such as ZrO , Mo/ZrO and W/ZrO2 were
2
2
Received 11 April 2012
synthesized. These solid acid catalysts were also synthesized in their powder forms. The
catalytic materials were characterized for their physicochemical properties such as surface
Accepted after revision 23 May 2012
Available online 27 June 2012
3
area, surface acidity, crystallinity and morphology by using techniques such as BET, NH -
TPD/n-butylamine back titration, powder XRD and SEM respectively. The catalytic activity
of these catalytic materials was determined in an acid catalyzed transesterification
reaction of methyl salicylate with phenol to synthesize phenyl salicylate (salol). The effect
Keywords:
Cordierite honeycomb
Mo(VI)/ZrO
W(VI)/ZrO
2
2
of concentration of Mo or W ions on ZrO , nature of the catalyst (whether honeycomb
2
coated or powder form), reaction temperature, reaction time and reusability of the
catalytic material in transesterification was studied. Formation of diphenyl ether as a by-
Transesterification
Salicylate esters
Solid acids
2
product was observed on increasing the concentration of Mo or W ions on ZrO and also at
higher reaction temperature. The catalytic activity of catalytic materials was correlated
with surface acidity and the crystalline phases of catalytic material. Transesterification
reactions were also carried out with methyl salicylate and benzyl alcohol or cyclohexanol
to synthesize their respective salicylate esters. A probable mechanism of transesterifica-
tion of methyl salicylate with an alcohol is also proposed. The honeycomb catalysts were
found to be efficient, ecofriendly, economical and reusable catalysts compared to their
powder forms.
ß 2012 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
1
. Introduction
loaded on the monolith is highly effective, easy separation
and complete recovery of the catalyst from the reaction
Cordierite (Mg
2
Al
4
Si
5
O
18) honeycomb monoliths play a
mixture [10]. Though cordierite honeycomb monoliths
have been used mostly for automotive applications, their
use in liquid phase/vapor phase organic synthesis is less
explored.
vital role as catalyst carriers in heterogeneous catalysis [1].
Catalyst coated honeycomb monoliths are widely used in
automotive catalytic convertors (TWCs), combustion of
VOCs, selective reduction of NO
x
, etc., which involve
Solid acids as heterogeneous catalysts are extremely
useful in many large-volume applications, especially in the
production of fine and specialty chemicals [11,12]. Among
various solid acid materials, metal oxides and their
modified forms, which exhibit exceptional acidic proper-
ties, are more interesting with a wide range of applications
as catalysts and catalyst supports. Especially among metal
mainly gas phase reactions [2–9]. The catalyst coated
honeycomb monoliths have advantages over powder
catalysts, such as formation of a thin layer of catalyst
with high active surface area, less amount of catalyst
2
oxides, zirconia (ZrO ) a versatile oxide used as a catalyst
*
Corresponding author.
E-mail address: em_es@rediffmail.com (S.Z. Mohamed Shamshuddin).
as well as a catalyst support, is employed in many
1
631-0748/$ – see front matter ß 2012 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
http://dx.doi.org/10.1016/j.crci.2012.05.020

8
00
S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
industrially important organic transformations. Much
work has been done on sulfated zirconia as a solid acid in
the field of fine chemical synthesis [13,14]. Due to a
major disadvantage associated with sulfated zirconia,
many efforts have been made to synthesize sulfate free-
zirconia based solid acids. Sulfate free-zirconia based
by impregnation method. The honeycomb was wash coated
with zirconia before coating the active catalysts. Wash
coating is done to increase the surface area and to have a
support material which has a better interaction with the
active catalyst [21]. For wash coating, a dilute solution of
zirconyl nitrate in presence of a binder (cellulose) was
prepared which was then coated on a bare honeycomb
monolith by dipping and drying in a furnace maintained at
400 8C.
x 2 x 2
solid acids such as MoO /ZrO and WO /ZrO have been
synthesized and used as solid acid catalysts in a few
liquid and vapor phase reactions [15–17]. It is reported
that modification of ZrO
2
with Mo or W ions can
Typically, for coating 5%Mo/ZrO
dilute solution containing 0.96 g of zirconyl nitrate
[ZrO(NO . 8H O] and 0.25 g of ammonium molybdate
[(NH Mo 24. 4H O] with 50 mL of deionised water, was
prepared. The resulting solution was coated on a wash-
coated monolith by dipping and drying in a furnace pre-
heated at 400 8C. The dipping and drying steps were
repeated for 12 to 15 times until ꢀ0.2 g of the catalyst is
coated on the monolith. The honeycomb coated with
2
on a honeycomb,
generate strong acid sites including super acid sites [18].
Though these sulfate free-zirconias are superior solid
acid catalysts and free form deactivation, unlike sulfated
zirconia, they are less explored for organic synthesis
3
)
3
2
4
)
6
7
O
2
[
19].
Salicylates are an important group of esters used in the
synthesis of drugs, food preservatives, plasticizers,
pharmaceuticals, polyesters, solvents, perfumes and
cosmetics [20]. Especially, phenyl salicylate (salol) is an
ester, which has a pleasant taste and odor, is more useful
in sun-tan lotions, as an antiseptic, anodyne and pain-
relieving agent. It can be prepared by simple esterification
of salicylic acid with phenol in presence of a liquid/solid
acid catalyst. But an anhydrous condition prevalent in
transesterification is advantageous in increasing the yield
of the desired ester and also in increasing the lifetime of
the catalyst system.
5%Mo/ZrO
furnace before its use as a catalyst. Similarly, 10% and
15%Mo/ZrO were synthesized by using the above-
2
was calcined at 550 8C for 5 h in a muffle
2
described procedure.
2
Five percent, 10% and 15%W/ZrO were coated on a
honeycomb by adopting the procedure described in the
above paragraph using known amounts of zirconyl nitrate
and ammonium tungstate salts.
In this article, the work done on the synthesis of
2.1.2. Synthesis of catalytic material in powder form
cordierite honeycomb coated with solid acids such as ZrO
2
,
2 2 2
ZrO , Mo/ZrO and W/ZrO were also prepared in
Mo/ZrO and W/ZrO , determination of their physico-
2
2
powder forms by impregnation method using salts such as
zirconyl nitrate with/without ammonium molybdate or
ammonium tungstate. Known amounts of the required
salts were taken in a china dish and a paste is made by
using small amount of water. The paste was then dried in
an air oven at 120 8C for 12 h and calcined at 550 8C for 5 h
in a muffle furnace.
chemical properties and catalytic properties in liquid
phase synthesis of phenyl salicylate and other salicylate
esters via transesterification is reported. The effect of
2
concentration of Mo or W ions on ZrO , nature of the
catalyst (whether honeycomb coated or powder form),
reaction temperature, reaction time and reusability of the
catalytic material in transesterification is studied to obtain
highest possible yield of salol with good selectivity. The
use of honeycomb monoliths as catalyst carriers especially
2.2. Physicochemical characterization of catalytic materials
for solid acids such as ZrO
2
and its modified forms would
The catalytic material (both honeycomb coated and
be a very cost effective and ecofriendly process and also
will be very interesting initiative step in the field of organic
synthesis.
powder forms of ZrO
characterized by BET, NH
tion, powder XRD and SEM techniques for their specific
surface area, surface acidity, crystallinity and morphology,
respectively.
2
, Mo/ZrO
2 2
and W/ZrO ) were
3
-TPD/n-butylamine back titra-
2
. Experimental
The specific surface area of the catalytic material was
evaluated by a NOVA 1000 Quanta chrome high-speed gas
sorption analyzer instrument. In this analysis, the catalytic
material was degassed at 523 K for 5 h before measure-
ments. Specific surface area was calculated using the BET
2.1. Preparation of the catalytic material
Cordierite honeycomb monoliths (height = 1.20 cm,
diameter = 2.50 cm and hole size = 0.2 cm) were used for
the present work and they were supplied by Shrey
Ceramics, Baroda, India.
Zirconyl nitrate, ammonium molybdate and ammoni-
um tungstate were supplied by M/S LOBA Chemie India
Ltd., India.
3
equation. The total surface acidity was measured by NH -
TPD method by using Puls Chemi-sorb 2705 from
Micromeritics. Here, the catalytic material was degassed
under a helium stream for 1 h, ammonia (99.99%) gas was
injected into the stream until saturation was reached,
cooled to 323 K. The system was maintained at 323 K for
3
0 min. After purging, the system with flowing helium for
ꢁ
1
2
.1.1. Synthesis of catalytic material in honeycomb coated
form
Solid acids such as ZrO
W/ZrO (%W = 5, 10, 15) were coated on different monoliths
2 h at 323 K, the sample was heated at the rate of 5 K min
in helium to 973 K. The change in concentration of the
desorbed NH was monitored using an online thermal
conductivity detector. The total surface acidity was also
2
, Mo/ZrO
2
(%Mo = 5, 10, 15) and
3
2

S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
801
measured by n-butyl amine back titration method using
dry benzene as the solvent and bromothymol blue
indicator [22]. The X-ray powder diffraction (PXRD)
patterns of the catalytic material were collected on an
2
ZrO are compared, the latter has higher surface area than
the former ones. This indicates that wash coating helps in
increasing the surface area of the bare honeycomb.
2
However, surface area of pure ZrO (both honeycomb
X-pert Pro Philips diffractometer equipped with Ni filtered
˚
coated and powder forms) was found to be the least among
the other catalytic materials. It is observed that when pure
Cu-Ka radiation
l = 1.5418 A using a graphite crystal
mono-chromator. The Scanning Electron Micrographs
SEM) were obtained using a JEOL JED-2300 analysis
station microscope.
2
ZrO was incorporated with either 5%Mo(VI) or 5%W(VI)
(
ions the surface area increased to nearly two fold. But
when the concentration of Mo or W ions was increased
beyond 5%, not much increase in the surface area of ZrO
was observed which can be attributed to stabilization
effect of ZrO . A similar trend was observed with the BET
surface area of powder form of the catalytic materials.
2
2
.3. Catalytic activity studies
2
Typically, a liquid phase transesterification of methyl
salicylate (MS) with phenol (P) was carried out by taking
MS: P in 2: 1 ratio. The reactants along with the catalytic
material (either honeycomb coated or powder forms of
3.1.2. Surface acidity measurements by NH
butylamine back titration methods
3
-TPD/n-
ZrO
2
, Mo/ZrO
2
and W/ZrO
2
) were placed in the reactor and
Among the catalytic materials used in the present work,
total surface acidity of pure ZrO was found to be the
lowest and incorporation of Mo or W ions on ZrO
increased the total surface acidity of pure ZrO drastically
which may due to electron deficient states formed by the
incorporation of Mo or W cations in to ZrO lattice (Table
1). Total surface acidity values obtained by NH -TPD
method and n-butylamine back titration method were
found to be almost similar and therefore surface acidity
values obtained by the latter method are not shown in
Table 1.
refluxed for a definite period of time. The total volume of
the reaction mixture was always kept constant at 20 mL.
After a definite period of time, the reaction mixture was
cooled to room temperature, the catalytic material was
separated from the reaction mixture, and the products
obtained by the transesterification reaction were analyzed
quantitatively by gas chromatograph (Mayura) fitted with
2
2
2
2
3
0
0
a (10% SE-30 chromosorb w-AW, 3 m ꢂ 1/8 ) column
coupled with FID detector and qualitatively by GC–MS
(Varian).
Similarly, transesterification reactions of methyl salic-
ylate with benzyl alcohol or cyclohexanol were carried out
under a definite set of reaction conditions over both
However, surface acidic properties of the catalytic
material were found to be independent of their forms
whether they are in honeycomb coated form or powder
form.
honeycomb coated and powder forms of ZrO
and W/ZrO
2 2
, Mo/ZrO
2
.
3.1.3. Powder XRD studies
3
. Results and discussion
The solid acids, ZrO or Mo/ZrO
Powder XRD (PXRD) patterns of the catalytic materials
(
honeycomb coated forms only) are shown in Fig. 1. It can
be seen in the figure that pure ZrO consists of peaks
arising from both monoclinic (M) and tetragonal (T) phases
(Fig. 1a). But when pure ZrO was incorporated with Mo or
2
2
or W/ZrO
2
were coated
2
on different honeycomb monoliths by using impregnation
method because it is easy and fast compared to other
2
known techniques. In this article, pure ZrO
and W(VI)/ZrO
respectively.
2
, Mo(VI)/ZrO
2
are abbreviated as Z, MZ and WZ
2
W ions the intensity of tetragonal phase increased with a
decrease in the intensity of the peak corresponding to
monoclinic phase. When the concentration of Mo or W ions
was increased in the order 5%, 10%, 15%, a gradual increase
in the intensity of peaks corresponding to tetragonal phase
with decrease in the intensity of the peaks related to
3.1. Catalyst characterization
3.1.1. BET surface area measurement
2
monoclinic phase of ZrO was observed. This shows that
BET surface areas of catalytic materials used in the
present study are given in Table 1. When the surface areas
of bare honeycomb (HC) and honeycomb wash coated with
the phase transition of both crystal phases (monoclinic and
tetragonal) is dependent on the Mo or W ion concentration.
For 10%MZ or 10%WZ, it is interesting to note that PXRD
Table 1
Surface properties of catalytic material used in the present study.
2
Sl. No.
Catalytic material
BET surface area (m /g)
Total surface acidity (mmols/g)
1
2
3
4
5
6
7
8
Z
42(48)
99(125)
97(122)
96(115)
92(119)
89(115)
85(112)
19
0.42(0.40)
1.14(1.13)
1.21(1.20)
1.28(1.24)
1.12(1.11)
1.15(1.16)
1.20(1.19)
–
5%MZ
10%MZ
15%MZ
5%WZ
10%WZ
15%WZ
Bare HC
Numbers in the parenthesis correspond to the values obtained for powder form of the catalysts.

8
02
S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
Fig. 1. Powder X-ray diffraction (PXRD) patterns of (a) Z and MZ; (b) HC and WZ.
peaks corresponding to monoclinic phase have been
totally eliminated, and only peaks from tetragonal phase
are seen. However, neither diffraction peaks correspond-
3.1.4. SEM studies
SEM images of honeycomb catalysts are shown in Fig. 2.
2
SEM image of the monolith wash coated with ZrO (Fig. 2a)
ing to crystalline MoO
3
nor peaks corresponding to any
shows flakes which appear more strongly sticking to the
surface of the monolith. In Fig. 2b–c, the SEM image of the
honeycomb coated with 5%MZ and 5%WZ shows that the
coating of the catalyst is considerably uniform. This
information obtained from SEM also indicates that the
method used for coating the catalytic material was suitable
enough to obtain adherent and homogenous coating of the
catalytic material.
new crystalline phases are observed. Further, no
diffraction lines corresponding to cordierite honeycomb
were detected after the monolith was coated with the
catalyst. This shows that the surface of bare honeycomb
was fully and effectively covered with the active
catalyst. PXRD pattern of bare honeycomb (HC) is also
shown in Fig. 1b.
Fig. 2. Scanning Electron Micrograph images of (a) honeycomb wash coated with zirconia; (b) honeycomb coated with 5%MZ; (c) honeycomb coated with
%WZ.
5

S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
803
3
.2. Catalytic activity
by-product. The catalytic activity of a solid acid catalyst in
the formation of a definite product in an organic reaction
depends on the acid strength and concentration of active
sites present on the solid acid. Formation of diphenyl ether
indicates that the catalytic materials 10%MZ, 15%MZ and
15%WZ consisted of very strong (super acidic) sites which
are responsible for the dehydration of phenol resulting in
the formation of ether. Further, when the selectivity of MZ
and WZ towards the formation of diphenyl ether was
observed, MZ was found to be more active than WZ
The activity of the catalytic materials such as Z, MZ and
WZ (both honeycomb coated and powder forms) was
examined in the transesterification reaction of methyl
salicylate with phenol.
acid catalyst
C
6
H
4
ðOHÞCOOMe þ C
6
H
5
OH
Ð
C
6
H
4
ðOHÞCOOC
6
H
5
ðmethyl salicylateÞ
ðphenolÞ
ðsalolÞ
þ MeOH
ðmethanolÞ
indicating the stronger interaction of Mo with ZrO
compared to W ions. This strong interaction between Mo
and ZrO may have resulted in the formation of more
2
when
First of all, when the reaction was carried out without
any catalyst, no conversion of phenol into salol was
observed. This suggests that transesterification reaction is
a catalyzed reaction and a suitable catalyst must be used.
The transesterification reaction was carried out by
taking methyl salicylate in excess to make the reaction
proceed in forward direction so that a maximum yield of
the desired ester is obtained. It has been reported [23] that
adsorbed phenol does not react, only poisons the catalytic
sites. Therefore, excess of phenol was avoided.
2
number of super acid sites which facilitate dehydration of
phenol. The difference in the activity of Z, MZ and WZ in
honeycomb coated and powder forms are explained in the
next section.
3.2.1. Effect of nature of the catalyst
Catalytic activity of Z, MZ and WZ in their honeycomb
coated forms and powder forms were compared in
transesterification of methyl salicylate with phenol. Even
though same amount of the catalyst (0.2 g) was used in
both the forms, a ꢀ2-fold increase in the conversion (%) of
phenol was observed over honeycomb form of the catalyst
(Fig. 3a–d). This may be attributed to the availability of
more number of active sites on the surface of the
honeycomb catalyst due to homogenous dispersion of
solid acids which is not possible when used in their powder
All the catalytic materials used in the present study
(both honeycomb coated and powder forms) were found to
be active in the transesterification reaction (Fig. 3a–d). The
GC and GC–MS analyses showed the presence of only four
components, i.e., methyl salicylate, phenol, salol and
methanol over Z, 5%MZ, 5%WZ and 10%WZ. But in presence
of 10%MZ, 15%MZ as well as 15%WZ, in addition to salol
and methanol, diphenyl ether was also formed as the
1
20
00
120
(a)
(b)
Conversion of phenol
Selectivity of salol
Selectivity of diphenyl ether
Conversion of phenol
Selectivity of salol
1
100
Selectivity of diphenyl ether
80
60
40
20
0
80
60
40
20
0
Z
5%MZ
10%MZ
15%MZ
Z
5%MZ
10%MZ
15%MZ
Honeycomb catalyst
Powder catalyst
1
20
00
Conversion of phenol
Selectivity of salol
Selectivity of diphenyl ether
120
100
80
60
40
20
0
Conversion of phenol
(d)
(c)
Selectivity of salol
Selectivity of diphenyl ether
1
8
6
4
2
0
0
0
0
0
Z
5%WZ
10%WZ
15%WZ
Z
5%WZ
10%WZ
15%WZ
Honeycomb catalyst
Powder catalyst
Fig. 3. Catalytic activity of the materials used in the present study for transesterification of methyl salicylate with phenol (molar ratio of methyl salicylate:
phenol = 2:1; reaction temperature = 130 8C; catalyst weight = ꢀ0.2 g of Z or MZ or WZ; reaction time = 4 h).

8
04
S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
form. The drastic difference in the activity of the catalytic
materials in their honeycomb coated and powder forms
can be explained as follows.
increased rapidly in the beginning (up to 4 h) and gradually
leveled off after 4 h. For example, over 5%MZ (honeycomb
coated), the conversion increased from 17% in the first 0.5 h
to 66% in the next 4 h and the conversion increased only to
an extent of 89% in 8 h. However, over 5%MZ (powder), the
conversion increased from 6 to 32% in the first 4 h and only
37% in 8 h (Fig. 5a). Selectivity (%) of salol remained 100%
up to 6 h over 5%MZ (both honeycomb coated and powder
forms) but after 6 h a greasy compound started forming on
the surface of the catalyst which could not be separated/
detected by GC or G-MS. A similar trend of conversion (%)
of phenol and selectivity (%) of salol was observed over
5%WZ catalyst with respect to reaction time (Fig. 5b).
Hence, reaction also played a vital role in obtaining high
yield of the desired product.
The number of channels, their diameter and wall
thickness determine the cell density, expressed as cells per
square inch (cpsi), which in turn allows the calculation of
the geometric surface area; the sum of the areas of all the
channel walls upon which the catalyst is deposited. This
leads to one of the most important advantages of the
honeycomb in that it has a large open frontal area. The
lower catalyst loading in case of honeycomb catalyst is
compensated by the higher efficiency due to the good
mass-transfer characteristics [1]. However, selectivity (%)
towards either salol or diphenyl ether remained the same
over both the forms of the catalytic material. This also
indicates that dispersion of a catalyst over a honeycomb
increases the number of active sites (acid sites) should be
available for the reaction. But acid site distribution
remained almost the same in both the forms.
3.2.4. Effect of nature of alcohol
The transesterification of methyl salicylate was carried
out with benzyl alcohol (BA) or cyclohexanol (CH) and the
results of which are presented in Fig. 6 (a–d). The reactions
were carried out over all the honeycomb catalysts except
over 10%MZ and 10%WZ. At the first instance, Z, 5%MZ,
5%WZ as well as 15%WZ were found to be 100% selective
towards the formation of either benzyl salicylate or
cyclohexyl salicylate. However, Z showed no conversion
of cyclohexanol to either its ester or ether. The nature of
alcohol affects the formation of either salicylate ester or
ether. Since cyclohexanol is a secondary alcohol it showed
less conversion may be due to more steric hindrance when
compared to benzyl alcohol which is a primary alcohol. A
maximum conversion (8%) was observed over 15%MZ with
98% selectivity towards cyclohexyl salicylate and 2%
selectivity towards cyclohexyl ether. Formation of ether
suggests that the super acidic sites are also capable of
dehydrating a secondary alcohol to produce its corre-
sponding ether to a certain extent.
3.2.2. Effect of reaction temperature
The transesterification of methyl salicylate with phenol
was carried out at three different temperatures i.e., 120 8C,
30 8C and 140 8C over honeycomb catalysts such as 5%MZ
1
and 5%WZ to study the effect of reaction temperature on
the conversion (%) of phenol and selectivity (%) towards the
products i.e., either ester or ether.
The results pertaining to the effect of reaction
temperature are presented in the form of bar diagram
(Fig. 4). As can be seen, at 140 8C of reaction temperature,
diphenyl ether was formed over both 5%MZ and 5%WZ
suggesting that, higher reaction temperature also may
favor the dehydration of phenol. However, at 120 8C and
1
(
5
30 8C, conversion of phenol increased but the selectivity
%) towards the ester remained 100% over both 5%MZ and
%WZ.
A considerable conversion of benzyl alcohol into benzyl
salicylate was observed over 5%MZ and 15%WZ catalytic
materials.
3
.2.3. Effect of reaction time
The effect of reaction time on the conversion (%) of
phenol and selectivity of the products over 5%MZ and
%WZ was also taken up by varying reaction time from 0.5
to 8 h and the results are presented in the form of a graph
as shown in Fig. 5a, b. The conversion (%) of phenol
On the other hand, Z and 5%WZ showed no conversion
of cyclohexanol into either its ester or ether. But over
15%WZ, ꢀ8% conversion was observed with 100% selec-
tivity towards the ester. Even though 15%WZ consisted of
5
1
20
00
Conversion of phenol
Selectivity of salol
Selectivity of ether
120
[
5%MZ]
[5%WZ]
Selectivity of salol
Conversion of phenol
1
100
80
60
40
20
0
Selectivity of ether
8
6
4
2
0
0
0
0
0
120
130
Reaction Temperature ( C)
140
120
130
Reaction Temperature ( C)
140
Fig. 4. Effect of reaction temperature on the transesterification of methyl salicylate with phenol over honeycomb catalysts (molar ratio of methyl salicylate:
alcohol = 2:1; catalyst weight = ꢀ0.2 g of 5%MZ or 5%WZ coated on the honeycomb; reaction time = 4 h).

S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
805
(
a) 100
(b) 100
[5%WZ]
[5%MZ]
80
60
40
20
0
80
60
40
20
honeycomb coated
honeycomb coated
powder
powder
0
0
2
4
6
8
0
2
4
6
8
Time (h)
Time (h)
Fig. 5. a, b: effect of reaction time on the transesterification of methyl salicylate with phenol (molar ratio of methyl salicylate: alcohol = 2:1; catalyst
weight = ꢀ0.2 g of 5%MZ or 5%WZ; reaction temperature = 130 8C).
1
20
00
Conversion of BA
Selectivity of ester
Selectivity of ether
120
100
80
60
40
20
0
Conversion of BA
Selectivity of ester
Selectivity of ether
(a)
(c)
1
8
6
4
2
0
0
0
0
0
Z
5%MZ
15%MZ
Z
5%WZ
15%WZ
Catalyst
Catalyst
Conversion of CH
1
20
00
Selectivity of ester
Selectivity of ether
120
(b)
Conversion of CH
Selectivity of ester
Selectivity of ether
(d)
1
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
Z
5%WZ
15%WZ
Z
5%MZ
15%MZ
Catalyst
Catalyst
Fig. 6. Effect of alcohol in the transesterification of methyl salicylate over honeycomb catalysts (molar ratio of methyl salicylate: alcohol = 2:1; reaction
temperature = 130 8C; catalyst weight = ꢀ0.2 g of Z or MZ or WZ coated on the honeycomb; reaction time = 4 h).
small number of super acidic sites, trace amounts of ether
would have formed which was not detectable by the GC.
and used in transesterification to study the performance of
reactivated catalyst. After reactivation of used honeycomb
catalyst, when weight of fresh honeycomb catalyst and
reactivated catalyst were compared, no change in weight
was observed. This indicates that there is no loss of catalyst
from the surface of honeycomb. However, 100% recovery of
the catalyst is not possible when used in powder form.
3.2.5. Effect of reactivation
The honeycomb catalysts used (Z or 5%MZ or 5%WZ)
recovered from the reaction mixture were washed with
acetone, dried at 120 8C for 2 h, calcined at 550 8C for 1 h,

8
06
S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
100
4
. Mechanism of transesterification over a solid acid
Z
catalyst
5
Z
5Z
80
60
40
20
0
A possible mechanism for the transesterification of
adsorbed methyl salicylate and an alcohol (R’’OH) over
protonic acid sites of a solid acid catalyst is given in
Scheme 1.
In the first step, methyl salicylate accepts a proton from
the acid site of a solid acid. The second step is the
nucleophilic attack of an alcohol molecule to the carbonyl-
carbon of methyl salicylate to give an intermediate. In the
final step, a proton is lost at one oxygen atom and gained at
another to form another intermediate, which further loses
a molecule of methanol that gives a salicylate ester. This
mechanism is similar to the acid catalyzed Fischer
esterification [24].
1
2
3
4
Reaction cycle
5. Conclusion
Fig. 7. Effect of reusability of honeycomb catalyst in the
transesterification of methyl salicylate with phenol (molar ratio of
MS:P = 2:1; reaction temperature = 130 8C; catalyst weight = ꢀ0.2 g of Z or
In summary, the honeycomb catalysts are very efficient
compared to their powder forms for organic synthesis.
These monolithic catalysts are easy to prepare, easy to use,
easily recoverable, easily regenerable, reusable and there-
fore honeycomb catalysts are more advantageous than
their powder form. In addition, they are ecofriendly.
5
%MZ or 5%WZ coated on the honeycomb; reaction time = 4 h).
The results are shown in Fig. 7. As can be seen in the
figure, no considerable decrease in the conversion (%) of
phenol is observed when reused up to four reaction cycles.
The reused catalysts were 100% selective towards the
formation of only salol. After every reaction cycle, the used
honeycomb catalyst was reactivated by using the proce-
dure described above.
2 2
Further, both Mo(VI)/ZrO and W(VI)/ZrO coated on
honeycomb monoliths were found to be efficient catalytic
materials for liquid phase transesterification reactions.
Further studies are in progress to use honeycomb coated
with solid acids as catalytic materials in vapor phase
transesterification. The selectivity towards the desired
Scheme 1. Transesterification of methyl salicylate and an alcohol over solid acids (protonic acid sites).

S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
807
[
6] A.A. Klinghoffer, R.L. Cerro, M.A. Abraham, Catal. Today 40 (1998)
9–71.
7] D.L. Trimm, Catal. Today 26 (1995) 231.
salicylate ester can be controlled by incorporating suitable
amount of Mo or ions on ZrO Increasing the
5
W
2
.
[
concentration of Mo or W ions may result in the increase
in concentration of super acid sites which are responsible
for the formation of ether due to dehydration of alcohol
used in transesterification reaction.
[8] S.H. Knickerbocker, A.H. Kumar, L.W. Herson, Am. Ceram. Soc. Bull. 72
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9] (a) M.A. Subramanian, D.R. Corbin, U. Chowdhry, Bull. Mater. Sci. 16 (6)
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(
[
(
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[10] Sudhanshu Sharma, PhD Thesis, Gas phase and electro catalytic reac-
Acknowledgement
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interaction between noble metal ions and the reducible oxide, 2009.
2
[
[
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3
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