New mesoporous perovskite ZnTiO3 and its excellent catalytic activity in liquid phase organic transformations

Article abstract of DOI:10.1016/j.apcata.2010.11.037

A new mesoporous perovskite ZnTiO₃ material has been synthesized by the evaporation-induced self-assembly (EISA) method using non-ionic surfactant Pluronic P123 as template. After calcination of the dried gel of equimolar concentrations of Zn(II) and Ti(IV) at 673 K, a new perovskite mesophase of ZnTiO₃ (MZT-11) formed, having highly crystalline cubic ZnTiO₃ pore wall. Interestingly, in the absence of P123 but otherwise identical synthesis conditions showed no cubic structure and a mixed phase consisting of ZnO and TiO₂ phases (ZT-11). The BET surface area of the mesoporous perovskite materials (MZT-11) was 136 m² g ^-1 and the average dimension of the pores was ca. 5.1 nm. The material was thoroughly characterized by different analytical methods including small and wide angle powder XRD, FE SEM, TEM, FT IR, UV-visible, photoluminescence (PL) and X-ray fluorescence (XRF) analysis. This new mesoporous perovskite material showed excellent catalytic activity in the Friedel-Crafts (FC) benzylation of aromatics and in the Fischer esterification of different long chain carboxylic acids in the presence of methanol under solvent-free conditions.

Full text of DOI:10.1016/j.apcata.2010.11.037

Applied Catalysis A: General 393 (2011) 153–160
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
New mesoporous perovskite ZnTiO3 and its excellent catalytic activity in liquid
phase organic transformations
Nabanita Pal, Manidipa Paul, Asim Bhaumik∗
Department of Materials Science, Indian Association for the Cultivation of Science, 2A & B Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new mesoporous perovskite ZnTiO3 material has been synthesized by the evaporation-induced self-
assembly (EISA) method using non-ionic surfactant Pluronic P123 as template. After calcination of the
dried gel of equimolar concentrations of Zn(II) and Ti(IV) at 673 K, a new perovskite mesophase of ZnTiO3
(MZT-11) formed, having highly crystalline cubic ZnTiO3 pore wall. Interestingly, in the absence of P123
but otherwise identical synthesis conditions showed no cubic structure and a mixed phase consisting
of ZnO and TiO2 phases (ZT-11). The BET surface area of the mesoporous perovskite materials (MZT-11)
was 136 m2 g−1 and the average dimension of the pores was ca. 5.1 nm. The material was thoroughly
characterized by different analytical methods including small and wide angle powder XRD, FE SEM, TEM,
FT IR, UV–visible, photoluminescence (PL) and X-ray fluorescence (XRF) analysis. This new mesoporous
perovskite material showed excellent catalytic activity in the Friedel-Crafts (FC) benzylation of aromatics
and in the Fischer esterification of different long chain carboxylic acids in the presence of methanol under
solvent-free conditions.
Received 8 September 2010
Received in revised form
19 November 2010
Accepted 22 November 2010
Available online 27 November 2010
Keywords:
Liquid phase catalysis
Mesoporous materials
Perovskite
ZnTiO3
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
organic–inorganic hybrid materials [17–22], non-siliceous meso-
porous metal oxides [23], phosphates [24] and organic polymers
Crystalline ceramics mainly perovskite-type mixed metal
oxides of chemical formula ABO3 have attracted keen interest over
the years owing to their unique physical and chemical proper-
ties [1]. Their physical properties (dielectric, ferroelectric etc.) are
exploited in electrical and optical applications along with their
chemical properties, including their potential in the generation of
thermoelectric power [2]. ABO3-type perovskites are mixed oxides
having BO6 octahedra with A2+ cations inserted in the framework.
Titanium-based perovskite oxides of AIITiIVO3 type, where A is Pb,
Sr, Ba, Zn or Fe, have attracted wide-spread attention in differ-
ent frontier areas of research due to their outstanding potential in
electronics [3], semiconductor [4], solid oxide fuel cell (SOFC) [5],
gas sensors [6], memory devices [7], magnetic materials [8], pho-
tocatalysis [9] and heterogeneous catalysis [10]. However, there
are only very few reports on the liquid phase heterogeneous acid
catalyzed reactions over these perovskite oxides.
[25] have been studied intensively due to their versatile applica-
tions. However, in this context very little attention has been paid to
the synthesis of mesoporous mixed metal oxides and their appli-
cation potentials [26–28]. This may be due to the lack of phase
purity [29] and the low thermal stability during synthesis of those
materials. The removal of template from the as-synthesized meso-
porous mixed metal oxide composites through solvent extraction
in many instances causes collapse of the mesophases. From these
circumstances a pure phase can only be generated at very high
temperature calcination. But this may result in reduction of the sur-
face area and often in loss of mesoporosity. Thus the synthesis of
pure mesoporous perovskite type mixed oxide is a great challenge.
Titanium containing mixed perovskite oxide is generally synthe-
sized via sol–gel method [30] or solid state reactions [31]. But the
evaporation-induced self-assembly (EISA) method [32] has been
rarely employed in the synthesis of mixed oxides as there is a pos-
sibility of heterogeneity in the reaction medium due to the rapid
hydrolysis and coagulation at the time of solvent evaporation.
Nonporous perovskite ZnTiO3 has been employed as cata-
lyst in various organic reactions like dehydrogenation reactions
[33] as well as in the detoxification of chemicals [34,35].
Although mesoporous zinc oxide-layered titanate nanocomposites,
a closely related material, have been synthesized by an exfoliation-
restacking route [36] and possess good surface areas, but to the best
of our knowledge the pure mesoporous perovskite ZnTiO3 has not
been reported so far. Further, nonporous ZnTiO3 perovskite oxide
In addition, when a perovskite type multimetal oxide attains
mesoporosity with appreciably good surface area, it can play a key
role in gas storage [11], ion-exchange [12], adsorption [13], ion-
conduction [14] or catalysis [15] based on the nature of the hetero
atoms. Since the discovery of MCM-41/48 by Mobil researchers
[16], a large variety of mesoporous materials, including silica based
∗
Corresponding author. Tel.: +91 33 2473 4971.
E-mail address: msab@iacs.res.in (A. Bhaumik).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.11.037

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N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
is usually synthesized through a high temperature mixed-oxide
method. Herein, we wanted to explore the possibility of the synthe-
sis of mesoporous ZnTiO3 through solution phase low temperature
evaporation-induced self-assembly (EISA) method via a surfactant
templating pathway. Our synthesis strategy for the preparation of
this material is energy saving and this method introduces meso-
porosity, which can enhance the surface properties of the material.
Herein, we first synthesized mesoporous ZnTiO3 material having
cubic perovskite structure through EISA method. Moreover, the
material exhibits good efficiency as heterogeneous catalyst in liquid
phase acid catalyzed Friedel-Crafts benzylation and Fischer esteri-
fication reactions. Both these reactions are commercially practiced
organic reactions [37,38]. Alkylation of benzene and substituted
benzenes by benzyl chloride produces a variety of important fine
chemicals, which have many useful applications in designing drug
molecules. On the other hand, carboxylic acid esters are widely used
in numerous cases like biodiesel fuel, detergents, and emulsifica-
tion. FC benzylation or esterification reactions in the presence of
homogeneous catalysts like AlCl3 or H2SO4 although giving bet-
ter yields in industrial scale [39]; these catalysts, however, have
severe drawbacks such as difficulty of separation and handling, cor-
rosiveness, toxicity, etc. Thus, we need a non-corrosive, non-toxic,
reusable heterogeneous solid catalyst, which can be synthesized in
a convenient, cost-effective and environment friendly route [40].
In this context, successful synthesis and utilization of mesoporous
perovskite ZnTiO3 material is very much important.
silicon sample, using Ni-filtered Cu K␣ (ꢀ = 0.15406 nm) radiation.
Nitrogen adsorption/desorption isotherms were obtained using
a Beckmann Coulter SA 3100 surface area analyzer at 77 K. Prior
to the measurement, all the samples were degassed at 453 K for
3 h. TEM images were recorded by a JEOL JEM 2010 transmission
electron microscope. A JEOL JEM 6700F field emission scanning
electron microscope with an energy dispersive X-ray spectroscopic
(EDS) attachment was used to record SEM images of the sample and
its surface chemical composition. Fourier transform infrared (FT IR)
spectra of these samples on KBr pellets were recorded by using a
Shimadzu FT IR 8300 spectrophotometer. Thermogravimetry (TG)
study and differential thermal analysis (DTA) were carried out on
a TA instrument Q600 DSC/TGA thermal analyzer. For optical mea-
surement, each powder sample was pressed into the sample holder
carefully. UV–visible diffuse reflectance spectra were obtained by
using a Shimadzu UV 2401PC spectrophotometer with an integrat-
ing sphere attachment; a BaSO4 pellet was used as background
standard. A high-resolution Perkin Elmer LS 55 luminescence
spectrometer was used to detect the photoluminescence (PL) from
the sample. Energy dispersive X-ray fluorescence spectroscopic
(EDXRF) analysis was done using an in-house developed set-up
consisting of a 109Cd source (AEA technologies, 4 mm dia and
115 MBq effective activity) and a Si(Li) detector (Canberra, 8 ␮m Be
window, 30 mm2 active area, 5 mm effective thickness, and 145 eV
resolution or FWHM at 5.9 keV). The detection medium was air
with an X-ray detection range of 3–20 keV. The spectrum analysis
and quantification was done using the AXIL-QXAS code (IAEA).
2. Experimental
2.4. Catalytic methods
2.1. Materials
Liquid phase Friedel-Crafts (FC) benzylation reactions were car-
ried out with benzene or substituted aromatics as substrates in a
two-necked round bottom flask fitted with a water condenser and
placed in an oil bath at 343–348 K temperature under stirring. We
have preheated the as-prepared powder samples at 423 K for 2 h
before conducting the liquid phase catalytic reactions. Benzylating
agent benzyl chloride had been added at the start of the reaction,
keeping the ratio of substrate:reagent = 10:1. This is followed by
the addition of our solid mesoporous catalyst in required amount.
At different time intervals the products were collected from the
reaction mixture and analyzed by capillary gas chromatography
(Agilent 7890D, FID). The products were identified by using known
standards.
Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly
(ethylene glycol), Pluronic P123 (Mav = 5800, EO20PO70EO20
,
template) and titanium(IV) isopropoxide (Ti-precursor) were pur-
chased from Sigma–Aldrich. Zn(NO3)2·6H2O, concentrated HCl
(35%), benzene, toluene, p-xylene, benzyl chloride, methanol, and
oleic acid were purchased from Merck, India. Palmitic and lau-
ric acid were purchased from Loba Chemie, India. Ethyl alcohol
(absolute ethanol) AR.99.9% was received from Changshu Yangyuan
Chemical, China. Water used was distilled water manufacturer
company Broadway chemicals (India). PE film was purchased from
Parafilm “M” of American National Can. All the chemicals were used
as received.
The Fischer esterification reactions of different carboxylic acids
(CA) were carried out in the same equipment at 333 K taking dry
methanol in CA:methanol = 1:120 molar ratio. The required amount
of each catalyst was added to it under continuous stirring in the
presence of 0.3 g of molecular sieves. After the reaction was com-
pleted, solid catalyst was filtered and the methanol was removed
through a rotary evaporator. The products were identified by FT
NMR and the percentage of conversion was measured by acid–base
titration method using 0.001 N NaOH solution. 1H and 13C NMR
experiments were carried out on a Bruker DPX-300 NMR spectrom-
eter.
2.2. Synthetic procedure
In a typical synthesis (for MZT-11), 1.0 g of Pluronic P123 was
dissolved in a mixture of 20 ml of ethanol and 1.2 g of concentrated
HCl at room temperature with 1 h continuous stirring. Then 3.0 g of
zinc nitrate was added to this solution. After half an hour stirring,
2.85 g of titanium isopropoxide was mixed with the clear sol solu-
tion. The mixture was kept under stirring at RT for another 5–6 h
covering with small pieces (70 mm × 80 mm) of PE (polyethylene)
film. Gradually a white gel was formed, which was aged at RT for
3 days in a slow evaporation process followed by slow heating at
333 K for 4 days. The white solid formed was calcined at 673 K for
4 h in air to remove the Pluronic P123 template. Similarly, a refer-
ence non porous Zn–Ti mixed oxide sample was synthesized under
identical conditions in the absence of Pluronic P123 template. The
white solid obtained has been designated ZT-11.
3. Results and discussions
3.1. Chemical composition
The surface composition of the as-synthesized and calcined
MZT-11 is estimated by XRF analysis (Table 1). It reveals that the
ratio of Zn:Ti is 1:1.02 in MZT-11, which is almost the same as the
composition of the reaction mixture gel. Thus the stoichiometry of
this novel mesoporous material resembles well a unimolar ratio of
Zn and Ti in ZnTiO3.
2.3. Characterization methods
Powder X-ray diffraction (XRD) patterns of the materials were
recorded on a Bruker AXS D-8 Advance diffractometer operated
at 40 kV voltage and 40 mA current and calibrated with a standard

N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
155
Table 1
Chemical composition of mesoporous perovskite ZnTiO3.
Sample
name
Element Atomic % (from Ratio of
wt% (from
XRF data)
Ratio of
Zn:Ti
EDS data)
Zn:Ti
Ti
Zn
18.31
17.99
34.4 0.1
32.0 0.3
MZT-11
1:1.02
1:1.075
Fig. 1. Small angle powder XRD patterns of calcined MZT-11.
3.2. Nanostructure
Fig. 3. HRTEM image of mesoporous MZT-11 (upper) and corresponding selected
area electron diffraction (SAED) pattern (lower).
The small angle powder XRD pattern of the calcined MZT-11 is
shown in Fig. 1. The material exhibit a broad peak near 2ꢁ = 0.61◦.
The 2ꢁ values correspond to the inter-pore separation of 14.5 nm.
This result suggested that our mesoporous perovskite ZnTiO3 mate-
rial has nanostructure consisting of disordered mesophases with no
short or long range ordering. In Fig. 2A the wide angle XRD pattern
of MZT-11 is shown. The material showed good crystallinity having
a good correspondence with the XRD pattern of cubic perovskite
ZnTiO3 structure (JCPDS file no. 39-0190) [41]. Major diffraction
peaks agree very well with the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1)
and (4 4 0) planes and can be indexed to a cubic phase of ZnTiO3. The
lattice parameter of the cubic unit cell is a = b = c = 0.841 nm (as per
the JCPDS data) [41]. The mean size of the crystalline domain (calcu-
lated using the Scherrer equation) from the high angle XRD pattern
suggests ca. 5.05 nm grain size. Very broad and moderate intensity
peaks with preferential growth of (3 1 1) cubic phase of perovskite
ZnTiO3 has been clearly observed here [41]. No peak correspond-
ing to the ZnO, TiO2 or zinc titanates of other stoichiometries
(␣-Zn2TiO4 or Zn2Ti3O8) [42] is observed. Further, there is hardly
any resemblance of this wide angle powder XRD pattern to that of
hexagonal form of ilmenite ZnTiO3 [43]. Thus it is clear that a 1:1
molar ratio in the synthetic gel is properly maintained in the sto-
ichiometric ratio of MZT-11 and that the pore walls of this novel
mesoporous material consist of crystalline ZnTiO3 domains. Fig. 2B
exhibits the XRD pattern of nonporous mixed oxide sample ZT-11,
which is a mixed phase of individual ZnO and TiO2 synthesized in
the absence of Pluronic P123. Crystalline domain size calculated is
13.3 nm, i.e. the grain size is much larger than that of MZT-11. Thus
it is evident from high angle powder XRD that cubic perovskite
ZnTiO3 phase does not form in the absence of a Pluronic template
and such low calcination temperature. In Fig. 3 HR TEM images of
our mesoporous perovskite ZnTiO3 material are shown. As seen
from these images, these mesopores are disordered wormhole-
Fig. 2. Wide angle powder XRD of calcined MZT-11 (A) and ZT-11 (B) samples.

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N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
Fig. 5. FE SEM image of calcined MZT-11 material. (A) EDS pattern of mesoporous
MZT-11.
3.4. Morphology
The FE SEM image (Fig. 5) of our mesoporous perovskite
ZnTiO3 material shows a uniform distribution of tiny spherical
particles. In some parts of the specimen these nanoparticles are
self-assembled to form large aggregates. The EDS chemical analysis
plot of mesoporous perovskite ZnTiO3 is shown in Fig. 5A. Chemi-
cal composition obtained from EDS agrees very well with the XRF
result (Table 1).
Fig. 4. (A) N2 adsorption (ꢀ)–desorption (ꢁ) isotherms of MZT-11 measured at 77 K.
(B) Corresponding pore size distribution using NLDFT method.
3.5. Framework and bonding
like in nature [44,45]. The dimension of the pores varies around
5.0–5.5 nm. Hence the porosity is generated due to interparticle
spacing of ZnTiO3 nanoparticles. A close look to the image exhibits
uniform distribution of particles with ca. 5.0 nm size. The SAED pat-
ternshownin theinsetof this figurealsoresembles closelythe cubic
perovskite ZnTiO3 structure.
Infrared spectra of the as-synthesized and calcined MZT-11
samples are shown in Fig. 6. The absence of any peak for a C–H bond
near 3000 cm−1 in the calcined mesoporous perovskite ZnTiO3
material suggests complete removal of organic Pluronic template
after calcination. A broad band observed near 3425 cm−1 and
1618 cm−1 could be attributed to O–H stretching and H–O–H bend-
ing vibrations of the adsorbed water molecules. The absorption
peak of –O–R bond around 1090 cm−1 in the as-synthesized sam-
ple disappears in the calcined one, which signifies the complete
hydrolysis of titanium precursor during the EISA method. Peaks at
598 cm−1 and 438 cm−1 could be attributed to the stretching vibra-
tions for the Ti–O and Zn–O bonds [47]. Thus the FT IR spectroscopic
results suggested the presence of different framework vibrations in
the mesoporous ZnTiO3 material.
3.3. Mesoporosity
In Fig.
4 we have plotted the N2 adsorption–desorption
isotherms of the calcined MZT-11 material at liquid nitrogen tem-
perature (77 K). Typical type IV isotherms with H1 type hysteresis
loops at high P/P0 value are observed, characteristic of large meso-
pores [45]. More specifically the mesoporosity coming up due to
the interparticle voids of large numbers of very small particles
distributed throughout the specimen is responsible for the verti-
cal slope at high P/P0 region. The BET surface area of MZT-11 was
136 m2 g−1 together with a pore volume of 0.23 cm3 g−1; whereas
the surface area of ZT-11 was only 56 m2 g−1 (isotherm not shown).
From the isotherms in Fig. 4B we have plotted the pore size distri-
bution employing NLDFT (Non-Local Density Functional Theory)
method [46]. The material MZT-11 showed a very narrow pore size
distribution with peak maxima centered at ca. 5.1 nm.
3.6. Optical measurements
The UV–visible absorption spectrum of mesoporous perovskite
ZnTiO3 sample is shown in Fig. 7. The figure indicates that the mate-
rial shows absorption maxima ca. 265 nm and a shoulder at ca.
363 nm. These absorption bands are considerably different from
those of anatase TiO2 [48] and wurzite ZnO [49] and agree well
with the nonporous perovskite ZnTiO3 [50]. On the other hand the

N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
157
Fig. 6. FTIR spectrum of as-synthesized (a) and calcined (b) MZT-11.
absorption spectrum of ZT-11 showed a quite different pattern. The
features of both oxides ZnO and TiO2 in sample ZT-11 are reflected
in high intensity peaks at ca. 365 nm and 315 nm, respectively. The
direct optical band gaps estimated from the absorption spectra for
the sample MZT-11 and ZT-11 are shown in Fig. 8A and B. An opti-
cal band gap is obtained by plotting (˛hꢂ)2 vs hꢂ where ˛ is the
absorption co-efficient and hꢂ is photon energy. Extrapolation of
the linear portion at (˛hꢂ)2 = 0 gives the band gaps of 3.59 eV for
our mesoporous perovskite ZnTiO3 material and 3.07 eV for the
ZnO–TiO2 mixed oxide sample. The optical band gap of MZT-11
is smaller than those of the nonporous ZnTiO3 (band gap 3.70 eV)
thin films obtained by radio frequency cosputtering of ZnO and
TiO2 [51]. Thus, for our mesoporous ZnTiO3 mixed oxide, the mini-
mum energy required for the excitation of an electron from valence
to conduction band is considerably higher than that required for
the pure anatase TiO2 and ZnO (ca. 3.2 eV). The room temperature
photoluminescence (PL) spectrum of our mesoporous perovskite
Fig. 8. Estimated band gap of MZT-11 (A) and ZT-11 (B) materials.
ZnTiO3 sample is shown in Fig. 9. The material shows a very broad
and strong photoluminescence band centered at 390 nm and one
weak emission peak at 419 nm upon excitation at 270 nm. These
emission bands are not band to band transitions because the peak
positions (390 nm, 3.18 eV) and (419 nm, 2.96 eV) are much smaller
than the optical band gap of the mesoporous ZnTiO3 material
(3.59 eV). The existence of intrinsic defect states in our mesoporous
ZnTiO3 material (synthesized in the presence of non-ionic template
and calcined in air at 673 K) such as O2− vacancy, Zn2+ interstitial
and/or Zn2+ vacancy could be responsible for these UV and blue
emissions [51].
3.7. Catalytic properties
The FC benzylation (Scheme 1) of different aromatic molecules
over mesoporous perovskite ZnTiO3 sample is shown in Table 2.
Fig. 7. UV–visible diffuse reflectance spectra of mesoporous perovskite MZT-11 and
ZT-11.

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N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
Scheme 1.
Table 2
Benzylation of different aromatics over MZT-11.a
Substrate
Product
Time (h)
Conversion (%)
Selectivity (%)
CH3
CH3
Ph
24
92.3
100
CH3
CH3
CH3
CH3
and
CH3
24
90.2
34.6 (o-product)
65.4 (p-product)
Ph
Ph
14
93.6
100
a
Reaction conditions: temperature 348 K (for benzene 343 K), substrate:benzyl chloride = 10:1, catalyst 1 wt% of the total reactants.
Scheme 2.
Table 3
Esterification of carboxylic acids (CAs) with methanol over MZT-11.a
Substrate (CA)
Product
Time (h)
16
Conversion (%)
O
O
92.3
OH
OH
O
9
9
O
O
15
18
78.1
73.2
O
13
13
OH
O
7
7
7
7
O
O
a
Reaction conditions: CA:methanol = 1:120, temperature 333 K, catalyst 2 wt% with respect to the total reactants.

N. Pal et al. / Applied Catalysis A: General 393 (2011) 153–160
159
molecule to the carbonyl carbon of (II). The active cationic species
formed (III) immediately rearranges to eliminate the correspond-
ing methyl-ester. The intermediate catalyst species (IV) regenerates
the solid catalyst via elimination of one H2O molecule. Molecu-
lar sieves added in the reaction medium removes these byproduct
water molecules and accelerate the forward reaction. Thus it is clear
that the presence of strong Lewis acid sites as well as a high sur-
face area of the catalyst accelerates the reaction pathway. In the
cases of higher molecular weight aliphatic compounds the –R group
provide a steric hindrance to the incoming MeOH molecule, which
could result in low conversion for the corresponding methyl-ester
(Table 1).
4. Conclusion
Mesoporous perovskite ZnTiO3 having cubic pore wall struc-
ture has been synthesized using a non-ionic template Pluronic
P123 through an evaporation-induced self-assembly method. The
material exhibits high crystalline feature together with a moder-
ately good surface area and narrow pore size distribution after
the removal of the template molecules. With a similar synthetic
strategy, applied without using Pluronic P123 as template, a mixed
ZnO–TiO2 phase material is formed having very poor surface area
and no mesoporosity. This result suggested that Pluronic P123 plays
a crucial role in the formation of cubic perovskite ZnTiO3 struc-
ture with mesoporosity at a low calcinations temperature of 673 K.
The novel mesoporous ZnTiO3 material showed excellent catalytic
efficiency in acid-catalyzed Friedel-Crafts benzylation and in Fis-
cher esterification of many organic substrates under solvent-free
condition. The high conversion rate observed in the esterification
reactions can open up new potential applications of this meso-
porous perovskite ZnTiO3 material in the production of biodiesels
with catalytic reactions of vegetable oils or animal fats having long
chain aliphatic alcohols.
Fig. 9. Room temperature photoluminescence spectrum of mesoporous MZT-11
upon using 270 nm light excitation.
High conversion of benzene, toluene or p-xylene into their
respective benzylated derivatives is observed together with high
selectivity for monobenzylated product. For toluene the observed
ratio of p-/o- benzylated isomers was ca. 2.0, suggesting consid-
erable steric hindrance at the ortho position to the methyl group
that could be attributed to low ortho-benzylation. The presence
of strong Lewis acid sites at the surface could be responsible for
this acid catalyzed reaction. On the other hand the esterification
reaction (Scheme 2) is an important reaction for the production of
biodiesels from the catalytic reaction of long chain fatty acids with
aliphatic alcohols. In Table 3 we have summarized our results on the
esterification of lauric, palmitic and oleic acids with methanol in the
presence of mesoporous ZnTiO3 material. Here we observed rather
high yields of the corresponding methyl-esters (Table 3) [52]. As the
aliphatic chain length of the monobasic acids increases from lau-
ric < palmitic < oleic acid, the respective molecular mass increases
and this is reflected in a consequent decrease in the esterification
rate. In Scheme 3 we have shown a possible mechanism for the
acid catalyzed esterification reaction. Initially, the carboxylic acid
coordinates to the Lewis acidic site present at the catalyst surface
(I). This is followed by an attack of an oxygen atom of the methanol
Acknowledgements
AB wishes to thank the Department of Science and Technology
(DST), New Delhi for financial support. NP and MP are grateful to
the Council of Scientific and Industrial Research (CSIR), New Delhi
for their senior research fellowships. The authors also express their
sincere thanks to Saha Institute of Nuclear Physics (SINP), Kolkata
for providing the ED-XRF facility.
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(0.794–0.822 (t, 3H), 1.158–1.235 (m, 24H), 1.545–1.560 (m, 2H), 2.252–2.267
(t, 2H), 3.662 (s, 3H). 13C NMR (500 MHz, CDCl3): (14.25, 18.57, 22.84, 24.91,
29.4–29.83 (9C), 32.08, 33.77, 58.63, 171.49. Oleic acid methyl ester: 1H NMR
(300 MHz, CDCl3): (0.82–0.85(t, 3H), 1.20–1.30 (m, 19H), 1.56–1.59 (m, 2H),
1.95–1.98(m, 4H), 2.24–2.26 (t, 2H), 3.61(s, 3H), 5.28–5.30 (m, 2H). 13C NMR
(500 MHz, CDCl3): (14.2, 22.6, 24.9, 25.7, 29.1–29.8 (8C), 31.6, 31.9, 34.1, 51.3,
130.1-128.1 (2C), 174.2. Lauric acid methyl ester: 1H NMR (300 MHz, CDCl3):
(0.82–0.85(t, 3H), 1.22–1.25 (m, 16H), 1.55–1.61 (m, 2H), 2.25–2.30 (m, 2H),
3.43, 3.63 (s, 3H). 13C NMR (500 MHz, CDCl3): (14.1, 22.7, 25.0, 29.2-29.7 (6C),
31.9, 34.1, 50.6, 179.1. %Conversion was estimated from 1H NMR: [Peak area of
one proton near 3.6 (for –CH3 gr.) divided by that of one proton at 2.25 (–CH2
gr.)] × 100.
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