Investigation of the catalytic efficiency of a new mesoporous catalyst SnO2/WO3 towards oleic acid esterification

Article abstract of DOI:10.1016/j.molcata.2010.05.015

The synthesis of a new, effective and reusable heterogeneous catalyst, mesoporous SnO₂/WO₃ (SW) to promote the esterification involving oleic acid and ethanol for the production of ethyl oleate is presented here. The developed mesoporous SnO₂/WO₃ with surface area of 130 m²/g and pore size of 3.9 nm exhibits up to 90% conversion of oleic acid (for 2 h reaction, at 80 °C) with high yield (～92%) to the ethyl oleate, a product of the esterification reaction of oleic acid. The catalyst exhibits a comparable activity of H₂SO₄, which is a known catalyst for esterification of organic acids. Kinetic investigation reveals that the experimental data follows a first order dependency on the concentration of the oleic acid and the catalyst. The conversion of oleic acid also has noticeable dependency on the reaction temperatures and different alcohols. Regeneration through heating of the used mesoporous SnO ₂/WO₃ catalyst at 400 °C for 3 h allows it for reuse without losing of its catalytic activity.

Full text of DOI:10.1016/j.molcata.2010.05.015

Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Investigation of the catalytic efficiency of a new mesoporous
catalyst SnO2/WO3 towards oleic acid esterification
Arpita Sarkara, Sudip K. Ghoshb, Panchanan Pramanika,∗
a Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
b Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of a new, effective and reusable heterogeneous catalyst, mesoporous SnO2/WO3 (SW) to
promote the esterification involving oleic acid and ethanol for the production of ethyl oleate is pre-
sented here. The developed mesoporous SnO2/WO3 with surface area of 130 m2/g and pore size of 3.9 nm
exhibits up to 90% conversion of oleic acid (for 2 h reaction, at 80 ◦C) with high yield (∼92%) to the ethyl
oleate, a product of the esterification reaction of oleic acid. The catalyst exhibits a comparable activity
of H2SO4, which is a known catalyst for esterification of organic acids. Kinetic investigation reveals that
the experimental data follows a first order dependency on the concentration of the oleic acid and the
catalyst. The conversion of oleic acid also has noticeable dependency on the reaction temperatures and
different alcohols. Regeneration through heating of the used mesoporous SnO2/WO3 catalyst at 400 ◦C
for 3 h allows it for reuse without losing of its catalytic activity.
Received 2 February 2010
Received in revised form 4 May 2010
Accepted 23 May 2010
Available online 31 May 2010
Keywords:
Mesoporous
SnO2/WO3
Solid acid catalyst
Esterification
Oleic acid
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
compounds are also used as homogeneous catalyst in fatty acid
esterifications [11]. In spite of several advantages, homogeneous
In recent years, biodiesel consisting of methyl or ethyl esters
of fatty acids are gaining increasing demands as a substitute for
conventional petroleum derived diesel because of the increasing
price of the later. The methyl or ethyl esters of fatty acids can
be produced by the esterification of fatty acids. For the produc-
tion of fatty acid esters, biocatalysts [1–4] should be the useful
examples in terms of exceptional selectivity but their low reaction
rates, short cell life spans, inhibitor tolerance, difficulties in product
separation and expensive sterile equipments increase the produc-
tion cost and thus limit them for commercial application [5]. The
homogeneous and heterogeneous catalysts are also employed for
esterification reactions of fatty acid for the production of fatty acid
ester. Among the homogeneous catalysts sulfuric acid, methane
sulfonic acid, p-toluene sulfonic acid are the most common acid
catalysts. Basic catalysts are on the other hand not favorable for
the production of fatty acid esters owing to the disadvantages
such as high sensitivity of the catalysts to water and free fatty
acids [6,7] and formation of the soap [8]. Formation of soap low-
ers the yield of esters and makes the separation of esters difficult.
Besides, the base catalyzed reaction requires the use of expensive
refined oils that should have low free fatty acids content (infe-
rior to 0.5 wt%) [9,10]. Apart from these catalysts, many organo tin
catalysts have some limitations which include problem in recover-
ing the catalysts, disposal of toxic wastes formed during reactions,
separation of the products, and loss of catalysts. So, an effective,
environmentally benign, low cost production of biodiesel exten-
sively demands solid heterogeneous catalysts. The recent works on
the esterifications of free fatty acids to produce biodiesels involve
the use of different heterogeneous inorganic catalysts such as, zeo-
lite [12–14], heteropolyacids [15,16], ion exchange resin [14,17,18],
carbon based material [14,15], sulfated ZrO2 [14,19], sulfated TiO2
[19], sulfated SnO2 [19], and Nb2O5.5H2O [19], WO3/ZrO2 [20,21],
tungstophosphoric acid [22], tungstosilicic acid [22] and molyb-
dophosphoric acid immobilized on SiO2 [22], propylsulfonic acid
functionalized mesoporous SiO2 [23,24], SnO [25], etc. However,
to our knowledge the mesoporous SnO2/WO3 has not yet been
explored as a catalyst. Although in the last decade SnWO4 and
SnO2/WO3 were insinuated as gas sensors the synthesis of meso-
porous SnO2/WO3 and its catalytic behavior have not been reported
so far.
Aiming this inadequacy, in the present manuscript, we report
the synthesis of mesoporous SnO2/WO3 (SW) using stannous chlo-
ride and sodium tungstate as precursor compounds in presence of
an anionic surfactant, sodiumdodecyl sulfate. The catalytic behav-
ior of mesoporous SW has been examined in the esterification of
oleic acid with ethanol to produce ethyl oleate for the first time.
In this study, the optimization of the reaction has been done and
reusuability of the catalyst has also been checked. We have found
∗
Corresponding author. Tel.: +91 3222 283322; fax: +91 3222 255303.
E-mail address: panchanan 123@yahoo.com (P. Pramanik).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.05.015

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A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
Fig. 1. High angle XRD patterns of mesoporous SW calcined at 500 ◦C for 4 h.
Fig. 3. X-ray photoelectron spectra of (a) Sn 3d core level and (b) W 4f core level of
mesoporous SW calcined at 500 ◦C for 4 h.
that the mesoporous SW shows high conversion of oleic acid fol-
lowing pseudo first order kinetics.
2. Experimental
2.1. Reagents
Stannous chloride (SnCl2), hydrochloric acid (HCl), hydrogen
peroxide (H2O2) and sodium tungstate (Na2WO4) were procured
from E. Merck (India). Sodiumdodecyl sulphate (SDS) was obtained
from Sisco research laboratory.
2.2. Synthesis of mesoporous SnO2/WO3
In a typical synthesis 4.5 g of SnCl2 was dissolved in 20 ml dis-
tilled water after addition of 10 ml concentrated HCl to it. To this
solution, 6.2 ml H2O2 was added and stirred. Under stirring con-
dition, this solution was mixed well with the aqueous solution of
SDS which was prepared before by dissolving 1.72 g of SDS in 12 ml
distilled water. An aqueous solution of Na2WO4 prepared by dis-
solving 11.8 g of Na2WO4 in 30 ml distilled water was then added
Fig. 2. (a) Combined FTIR spectra of the surfactant, as-synthesized SW and calcined
mesoporous SW and (b) selected portion of the FTIR spectrum of calcined SW.

A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
75
Fig. 4. N2 adsorption–desorption isotherms of mesoporous SW calcined at 500 ◦
for 4 h and (inset) the corresponding BJH pore size distribution.
C
Fig. 6. NH3 temperature-programmed desorption curve of mesoporous SW calcined
at 500 ◦C for 4 h.
slowly by a small portion at a time to the well-mixed solution mix-
ture under constant stirring condition. After complete addition of
Na2WO4, the solution mixture was stirred for an additional 30 min.
After that, the resultant solution was set aside for 24 h for complete
precipitation. Pale yellow gel type precipitate was formed which
was aged in Teflon lined autoclave at 120 ◦C for 24 h. The autoclave
was cooled and the precipitate was filtered, washed thoroughly
with distilled water to make free from Cl− and then dried at 100 ◦C.
The as-synthesized sample was finally calcined at 500 ◦C for 4 h to
remove the surfactant.
area analyzer. The pore size distribution curve was obtained from
the analysis of the adsorption branch of the isotherm by the BJH
(Barrett–Joyner–Halenda) method. The surface morphology was
studied using a JEOL-JSM6500 scanning electron microscope (SEM).
The high resolution transmission electron microscopy (HRTEM)
study was carried out using JEOL 2010 (ultrahigh-resolution model,
equipped with a Gatan multi-scan CCD camera). For the HRTEM
experiment, the sample was prepared by suspending the cal-
cined powder in ethyl alcohol by sonication and taking a drop
of the suspension on 200-mesh carbon coated copper grid. X-
ray photoelectron spectra (XPS) analyses were carried out using
a VG Scientific (ESCALAB 250) X-ray photoelectron spectrome-
ter with an Al K␣ X-ray source (1486.6 eV) at a base pressure of
2 × 10−9 Torr and all the spectra were curve fitted using bands with
a Gaussian–Lorentzian line shape and a Shirley baseline. To deter-
mine the surface acidity by temperature-programmed desorption
(TPD) of ammonia a Quantachrome CHEMBET-3000 instrument
interfaced to a computer was used. The computer was employed to
perform the programmed heating and cooling cycles, data record-
ing, data valve switching, data storage and analysis. Before the
TPD study, the sample was treated at 200 ◦C for 1 h in helium
flow (50 cm3/min) and then the sample was cooled to ambient
temperature and saturated with high purity anhydrous ammo-
nia (80 cm3/min) for 1 h. The sample was then heated to 105 ◦C
2.3. Characterization techniques
Fourier transform infrared (FTIR) spectra were obtained on a
Thermo Nicolet NEXUS 870 FTIR spectrometer. The calcined SW
powder at 500 ◦C for 4 h was analyzed by X-ray powder diffrac-
tion using an X’Pert-pro Diffractometer operated at 40 kV and
25 mA and Cu K␣ radiation and Ni filter. Analysis was performed
at room temperature under vacuum to minimize air scatter. The
data were collected over the 2ꢀ angle range of 10◦ ≤ 2ꢀ ≤ 80◦.
The BET (Brunauer–Emmett–Teller) surface area of the calcined
SW powder (after out-gassing the powders at 200 ◦C for 4 h) was
determined through N2 adsorption–desorption study performed
at liquid N2 temperature using Beckman Coulter SA3100 surface
Fig. 5. (a) SEM micrograph and (b) bright field TEM micrograph of mesoporous SW calcined at 500 ◦C for 4 h.

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A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
Fig. 7. Esterification of oleic acid in presence of 0.1 g mesoporous calcined SW and
in absence of catalyst. Reaction conditions: reaction temperature = 80 ◦C, molar ratio
of oleic acid:ethanol = 1:120, reaction time = 12 h.
and flushed with helium (50 cm3/min) at the same temperature to
remove the physisorbed ammonia. TPD analysis was carried out
from ambient temperature to 900 ◦C.
2.4. General procedure of catalytic test
The esterification reaction of oleic acid was carried out in a
three-necked round bottom flask, equipped with a reflux con-
denser, a thermometer and a sampling system. The whole system
was kept in an oil bath which was placed upon a magnetic stir-
rer. In a typical catalytic reaction, 120 mmol ethanol and 1 mmol
oleic acid were reacted in presence of 0.1 g (1.7 wt% calculated fol-
lowing the expression of (amount of catalyst in g × 100/amount of
(oleic acid + ethanol) in g)) of mesoporous SW in a round bottom
flask at different temperatures under continuous stirring. All the
catalytic tests were performed in triplicate to examine the repro-
ducibility of the result. In this study, the esterification of oleic acid
with ethanol was also carried out in absence of mesoporous SW,
Fig. 9. (a) Esterification of oleic acid executed at different temperatures (40, 60
and 80 ◦C) in presence of 0.1 g mesoporous calcined SW. Reaction conditions: molar
ratio of oleic acid:ethanol = 1:120, reaction time = 12 h. (b) Plot of ln k vs. 1/T for the
esterification of oleic acid and ethanol using mesoporous SW (from initial reaction
rate data).
in presence of different amounts of mesoporous SW, and also in
presence of 0.1 mol H2SO4, which is a known catalyst for esterifi-
cation of organic acids. The influence of the reaction temperature
and the effect of different alcohols have also been investigated in
the esterification of oleic acid, catalyzed by the mesoporous SW.
The conversion of the oleic acid to the ethyl oleate was deter-
mined by titration of the aliquots, taken out from the reaction
mixture at different time intervals with a standard (0.01 M) alco-
holic solution of KOH and the reaction was also monitored by
gas chromatography (GC) analysis of the aliquots taken at regular
interval. Prior to titration as well as GC analysis, the catalyst was
separated from the aliquot of reaction mixture through centrifuga-
tion to inhibit further reaction. The yield of ethyl oleate formed
in the catalytic reaction was calculated from the GC peak area
of the ethyl ester in comparison to the corresponding analytical
curve. The GC analysis was done using Shimadzu GC-17A instru-
ment (with FID detector), equipped with a 30 m × 0.25 mm DB-1
column at a temperature range of 80–180 ◦C with a heating rate of
10 ◦C/min.
Fig. 8. Esterification of oleic acid in presence of H2SO4 and 0.1 g mesoporous cal-
cined SW. Reaction conditions: reaction temperature = 80 ◦C, molar ratio of oleic
acid:ethanol = 1:120, reaction time = 12 h.

A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
77
3. Results and discussions
depicts the uniform porous network in the mesoporous range with
open-pore structure of 3–4 nm diameter pores in an unordered
array. The pores appear to be worm-like as evident from the HRTEM
micrograph. The ammonia temperature-programmed desorption
method which is a conventional method for characterizing the
surface acidity in mesoporous materials, has been used for deter-
mining the acid strength distribution of the mesoporous SW. The
acid strength distribution is indicated by the temperature range at
which most of the ammonia desorbed [30,31]. Fig. 6 indicates the
temperature-programmed desorption curve of mesoporous SW.
This curve shows that one well-resolved desorption peak of NH3
appears at 158 ◦C which is attributed to NH3 adsorbed on weak
acid sites. A broad desorption signal (at the range of 250–650 ◦C)
likely centered at around 350 ◦C appears corresponding to the NH3
adsorbed on medium-strong acid sites.
3.1. Characterization
XRD and FTIR studies have been carried out to elucidate the
structural properties of the synthesized mesoporous SW. Fig. 1 dis-
plays the XRD of the mesoporous SW calcined at 500 ◦C for 4 h.
The XRD profile shows that the mesoporous material possesses
mixture of tetragonal SnO2 (JCPDS PDF #41-1445 cassiterite, syn)
and monoclinic WO3 (JCPDS PDF #43-1035). Thus the XRD study
reveals the coexistence of SnO2 and WO3 resulting a composite
oxide. FTIR spectra of the surfactant (SDS), as-synthesized SW and
calcined SW are shown in Fig. 2a. As we observe no band corre-
sponding to surfactant present in the FTIR of calcined SW, we can
conclude from FTIR study that after calcination at 500 ◦C for 4 h
SW lacks any surfactant. Absence of any surfactant is also sup-
ported by elemental analysis. In all FTIR spectra, the bands near
3432 and 1631 cm−1 (Fig. 2a) appear due to the presence of O–H and
H–O–H species, respectively. Selected portion of the FTIR spectrum
of calcined SW in Fig. 2a has been enlarged in Fig. 2b to show one
absorption band centered at approximately 818 cm−1 along with an
additional band at 763 cm−1, which can be identified as the stretch-
ing frequency of O–W–O groups [26]. A less intense band appeared
3.2. Catalytic activity
3.2.1. Esterification reaction of oleic acid
In the present study catalytic performance of the synthesized
mesoporous SW and the dependency of its catalytic efficiency on
different reaction parameters for the esterification of oleic acid with
ethanol has been investigated.
The esterification of oleic acid with ethanol generally proceeds
via formation of ethyl oleate and water as given below.
In a typical esterification reaction, molar ratio of ethanol to oleic
acid has been maintained at 120:1. The esterification reaction is
an equilibrium reaction. To achieve a high conversion of oleic acid
a high ethanol-to-oleic acid molar ratio has been employed [32].
The esterification reaction executed at 80 ◦C for 2 h in presence of
0.1 g mesoporous SW gives rise to ∼90% conversion (Fig. 7) of oleic
acid into ethyl oleate and the corresponding yield of ethyl oleate
has been found to be ∼92%. While the same reaction performed at
80 ◦C for 2 h in absence of any catalyst produces only ∼10% con-
version (even after 12 h reaction, Fig. 7). The same experiment has
been repeated using a well-known catalyst H2SO4 to compare the
catalytic efficiency of our catalyst. In this study, we have found as
shown in Fig. 8 that the mesoporous SW achieves the similar effi-
ciency of H2SO4 in conversion (∼90%) of oleic acid into ethyl oleate.
As is observed from the experiment that in presence of the catalyst,
the conversion of oleic acid in esterification reaction significantly
speed up within the initial 2 h and after 2 h, the conversion reaches
saturation where it remains almost invariable. The catalytic tests
have been carried out in triplicate to examine the reproducibility
of the results and presented the average results which accord the
experimental results obtained by GC analysis.
at 968 cm−1 can be attributed to the W O group [26] whereas
the band at 592 cm−1 can be assigned to the Sn–O–Sn of the tin
oxide framework [27]. XPS analyses (Fig. 3) of the mesoporous SW
calcined at 500 ◦C for 4 h gives information on the chemical com-
position as well as the chemical bonding states of Sn and W in the
powder material. The Sn 3d core-level spectra (Fig. 3a) exhibits that
two peaks correspond to Sn 3d5/2 and Sn 3d3/2 appear at 486.5
and 494.9 eV, respectively. These values of the peaks for the syn-
thesized mesoporous SW are identical to the Sn(IV) oxide [28]. In
addition, the photoelectron peaks (Fig. 3b) of W 4f7/2 and W 4f5/2
,
appeared at 35.3 and 37.4 eV respectively are identical to that of
W(VI) oxide [28]. The surface compositions for our synthesized
mesoporous SW obtained from XPS analysis shows the presence
of 7.89% Sn and 14.17% W. The textural properties such as BET sur-
face area and the pore diameter of the SW calcined at 500 ◦C for 4 h
have been evaluated using the N2 adsorption-desorption measure-
ments at liquid N2 temperature in a relative pressure range from
0.05 to 1.0. Fig. 4 exhibits the N2 adsorption–desorption isotherm
and the corresponding pore size distribution curve (Fig. 4, inset)
of the synthesized SW calcined at 500 ◦C for 4 h. The shape of
N2 adsorption–desorption isotherm corresponds to type IV [29]
indicating typical mesoporous nature of the sample. The BET sur-
face area and the pore volume of the calcined SW are found to
be 130 m2/g and 0.198 cm3/g, respectively. The porous texture of
the calcined SW was analyzed and the pore size distribution was
measured through BJH method from the adsorption branch of the
isotherm. The pore size distribution, centered at 3.9 nm, is uni-
form but a small fraction of pores are present in the range of >3.92
and10 nm, probably due to thermal collapse of the pore struc-
ture of the calcined samples. The morphology of the mesoporous
SW calcined at 500 ◦C for 4 h, investigated by scanning electron
microscopy is shown in Fig. 5a. SEM image shows the powder
material being composed of largely spherical particles. The HRTEM
micrograph of mesoporous SW calcined at 500 ◦C for 4 h (Fig. 5b)
3.2.2. Effect of different reaction conditions on the reaction
3.2.2.1. The effect of the reaction temperature. Three reaction tem-
peratures such as 40 ◦C, 60 ◦C and 80 ◦C have been selected to
investigate the influence of reaction temperatures on the meso-
porous SW catalyzed esterification of oleic acid with ethanol. The
conversion of oleic acid into ethyl oleate via esterification has
noticeable dependency on the reaction temperatures as seen in the
Fig. 9a. Fig. 9a shows that the oleic acid conversion increases from
40 to 67 to 90% as the temperature increases from 40 to 60 to 80 ◦C.
The increased conversion might be not only due to the effect of
increase of the reaction rate by increasing temperatures but also
some improvement of the mass transfer limitation between reac-
tant and catalyst [22].

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A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
Fig. 11. Plot of ln(1 − x/a) vs. time. Reaction conditions: reaction temperature = 80 ◦C,
molar ratio of oleic acid:ethanol = 1:120, amount of catalyst = 0.1 g, reaction
time = 2 h.
Fig. 10. Esterification of oleic acid in presence of different amount of mesoporous
calcined SW (0.01, 0.05, 0.1 g). Other reaction conditions: reaction tempera-
ture = 80 ◦C, molar ratio of oleic acid:ethanol = 1:120, reaction time = 2 h.
where k = rate constant of the pseudo first order reaction,
a = concentration of oleic acid, b = concentration of ethanol,
x/a = conversion, t = time. So, the plot of ln(1 − x/a) versus t should
produce a straight line and the pseudo first order rate constant (k)
can be calculated from the slope of this plot. Fig. 11 presents the
plot of ln(1 − x/a) versus time for the esterification reaction of oleic
acid at 80 ◦C catalyzed by 0.1 g mesoporous SW and it indicates that
the data are well fitted to this model exhibiting a straight line, con-
firming the esterification of oleic acid in this study, follows pseudo
first order kinetics. The rate constant evaluated from the slope of
The activation energy (Ea) has been calculated from the plot of
ln k versus 1/T (Fig. 9b), constructed from the data obtained at each
temperature of the reaction following the Arrhenius equation as
given below:
ꢀ
ꢁ
−Ea
k = A exp
RT
or
Ea
ln k = ln A −
RT
the above plot for the esterification is found to be 0.0131 min−1
.
where k is the rate constant and the T denote the reaction temper-
ature in Kelvin. The value of activation energy has been found to be
39.5 kJ/mol.
3.2.3. The esterification of oleic acid with different alcohols
Finally, the esterification of oleic acid has been carried out with
propanol and butanol at 80 ◦C for 2 h in presence of 0.1 g meso-
porous SW and the molar ratio of oleic acid:alcohol has been
maintained at 1:120. The conversion of oleic acid with different
alcohols is depicted in Fig. 12. It can be seen from Fig. 12 that the
conversion of oleic acid decreases from ethanol to the higher alco-
3.2.2.2. The effect of the amount of mesoporous SW. The effect of cat-
alyst loading on the esterification reactions has also been studied
using different amount of mesoporous SW (0.01, 0.05 and 0.1 g). The
results displayed in Fig. 10 show that the maximum oleic acid con-
version (∼90%) has been achieved in presence of 0.1 g mesoporous
SW whereas in presence of 0.01 and 0.05 g catalyst the conversions
are up to 47 and 62%, respectively. The increase in the conversion of
oleic acid with the increasing catalyst amount is expected because
total surface area of the catalyst is increased and also more cat-
alytic active sites are available [33]. The convergence behavior to
the same final conversion using different amount of catalyst has not
been observed within the time duration of the experiment, which
is 2 h for the present study.
3.2.2.3. The effect of oleic acid concentration. In the present study of
the esterification of oleic acid with ethanol, the ethanol is used in
excess amount compared to the oleic acid. Therefore, the concen-
tration of ethanol can be considered to be constant throughout the
reaction duration and thus the reaction should follow the pseudo
first order kinetic model [34]. Therefore, the rate constant can be
expressed by the following equation:
ꢀ
ꢁ
1
tb
a − x
1
tb
x
a
kR = −
ln
= −
ln 1 −
a
or
ꢀ
ꢁ
Fig. 12. Esterification of oleic acid executed with different alcohols. Reaction condi-
tions: reaction temperature = 80 ◦C, molar ratio of oleic acid:alcohol = 1:120, amount
of catalyst = 0.1 g, reaction time = 12 h.
x
ln 1 −
= −kRbt = −kt
a

A. Sarkar et al. / Journal of Molecular Catalysis A: Chemical 327 (2010) 73–79
79
130 m2/g and average pore size of 3.9 nm has been synthesized and
employed successfully in esterification of oleic acid with ethanol to
produce ethyl oleate. The ethyl oleate is an important constituent of
biodiesels. The synthesized mesoporous SnO2/WO3 exhibits ∼90%
conversion of oleic acid and the corresponding yield of ethyl oleate
has been achieved to ∼92%. The catalyst has been recovered after
the catalytic test and regenerated by heating at 400 ◦C for 3 h and
successfully reused in the same esterification reaction. The meso-
porous SnO2/WO3 can be used for the production of different fatty
acid esters through the acid catalyzed conversion of biorenewable
lipid feedstocks, i.e., the free fatty acids.
Acknowledgement
AS greatly acknowledge CSIR, New Delhi, for providing the
grants to support the completion of this work.
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4. Conclusion
In the present study, a new heterogeneous solid acid cata-
lyst mesoporous SnO2/WO3 composite with BET surface area of