Preparation of highly superacidic sulfated zirconia via combustion synthesis and its application in Pechmann condensation of resorcinol with ethyl acetoacetate

Article abstract of DOI:10.1016/j.jcat.2012.05.004

A novel zirconia-based catalyst, with high sulfur content (15% w/w) and preservation of the tetragonal phase of zirconia, was synthesized for the first time via a solution combustion synthesis approach. Such high sulfur content with preservation of the tetragonal phase has not been reported so far. The catalyst synthesis parameters were optimized using a probe reaction of Friedel-Crafts alkylation. The optimized catalysts, fuel-lean sulfated zirconia (FLSZ) and fuel-rich sulfated zirconia (FRSZ), were characterized by XRD, FTIR, TPD, EDAX, SEM, and BET surface area and pore size analysis. Further, the activity and stability of FLSZ was tested using a Pechmann condensation reaction between resorcinol and ethyl acetoacetate to produce 7-hydroxy 4-methyl coumarin selectively. A complete theoretical and experimental analysis is presented, and a kinetic model is developed for this reaction. The model explains the experimental data well. The characterization and reaction studies show that combustion-synthesized sulfated zirconia exhibits higher superacidity than the conventional sulfated zirconia catalyst.

Full text of DOI:10.1016/j.jcat.2012.05.004

Journal of Catalysis 292 (2012) 99–110
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Preparation of highly superacidic sulfated zirconia via combustion synthesis
and its application in Pechmann condensation of resorcinol with ethyl acetoacetate
Ganapati D. Yadav , Naishadh P. Ajgaonkar , Arvind Varma b
a,
⇑
a
a
Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400 019, India
School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 January 2012
Revised 1 May 2012
Accepted 2 May 2012
Available online 21 June 2012
A novel zirconia-based catalyst, with high sulfur content (15% w/w) and preservation of the tetragonal
phase of zirconia, was synthesized for the first time via a solution combustion synthesis approach. Such
high sulfur content with preservation of the tetragonal phase has not been reported so far. The catalyst
synthesis parameters were optimized using a probe reaction of Friedel–Crafts alkylation. The optimized
catalysts, fuel-lean sulfated zirconia (FLSZ) and fuel-rich sulfated zirconia (FRSZ), were characterized by
XRD, FTIR, TPD, EDAX, SEM, and BET surface area and pore size analysis. Further, the activity and stability
of FLSZ was tested using a Pechmann condensation reaction between resorcinol and ethyl acetoacetate to
produce 7-hydroxy 4-methyl coumarin selectively. A complete theoretical and experimental analysis is
presented, and a kinetic model is developed for this reaction. The model explains the experimental data
well. The characterization and reaction studies show that combustion-synthesized sulfated zirconia
exhibits higher superacidity than the conventional sulfated zirconia catalyst.
Keywords:
Sulfated zirconia
Superacidity
Combustion synthesis
7
-Hydroxy 4-methyl coumarin
Pechmann condensation
Kinetics
Ó 2012 Elsevier Inc. All rights reserved.
1
. Introduction
Environmentally friendly processes and technologies have gath-
Parera [9] studied the optimum amount of sulfuric acid to be used
for sulfation and its effect on percentage sulfate loading. He found
that percolation with sulfuric acid at concentrations varying from
0.05 to 2 M led to about the same amount of sulfur in sulfated zir-
conia after calcination. Nascimento et al. [4] and Morterra et al.
[10] found an increase in Brønsted acidity with an increase in sul-
fate concentration up to a certain maximum, after which the
amount of Brønsted acidity remained constant. Thus, sulfur in
the form of sulfate present above 4% w/w is lost during thermal
activation and represents a thermally more labile fraction when
prepared with conventional methods. Fârcasiu and co-workers
[11] reported that the sulfur content could be controlled and zirco-
nia with high sulfur loading could be achieved. Their report sug-
gests that zirconia exhibits a pure tetragonal phase at low values
of sulfur content but at higher values (S > 4 wt%), its crystallinity
is strongly affected and a monoclinic phase of zirconia is formed
in addition to the tetragonal phase. In another study, sulfated zir-
conia was prepared by different procedures using a colloidal sol–
gel technique and impregnation [12]. The colloidal sol–gel tech-
nique leads to the formation of sulfated zirconia with a high sulfur
content along with mono- and polynucleate sulfate species, as well
as supported sulfuric acid. Yadav and Murkute [6,7] obtained the
highest sulfate loading when zirconium hydroxide was treated
with chlorosulfonic acid. This catalyst designated as UDCaT-5
showed 9 wt% sulfur retention without the presence of a polynu-
clear sulfate group.
ered considerable attention worldwide, and continuous efforts are
made to achieve these goals. Heterogeneous catalysts and espe-
cially solid acid catalysts play an important role in this pursuit.
Among all the solid acid catalysts, special attention has been given
to the preparation, characterization, and catalytic investigation of
sulfated zirconia [1–4]. Holm and Bailey were the first to disclose
in the early 1960s that Pt containing sulfate-modified zirconia
was an acid catalyst suitable for alkylation of hydrocarbons [2].
Ever since Hino et al. [3] reported in the late 1970s that sulfated
zirconia (SZ) was a superacid, it has been the subject of many
investigations due to its ability to activate light alkanes at lower
temperatures. These authors also claimed that this catalyst is able
to catalyze the isomerization of n-butane at temperatures as low as
room temperature.
The amount of sulfur retained and the pore structure play
important roles in determining the activity and selectivity of sul-
fated zirconia catalyst, respectively [1,5–7]. Some control on sul-
fate loading can be achieved by changing the calcination
temperature, but the tetragonal phase and crystallinity are affected
[
4,8]. Wender [8] has reported that sulfated zirconia derived from
impregnation with 0.25 M sulfuric acid and calcined at 600 °C for
h possessed 2.5% w/w sulfur content (in the form of sulfate ions).
3
The other important parameter that decides the selectivity of
the catalyst is the pore structure of S-ZrO , which is largely
2
⇑
Corresponding author. Fax: +91 22 410 2121.
E-mail address: gd.yadav@ictmumbai.edu.in (G.D. Yadav).
0
021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2012.05.004

1
00
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
Nomenclature
A
AS
B
reactant species A, resorcinol
chemisorbed cyclohexene
d
E
G/N
K
P
diameter of catalyst particle, cm
7-Hydroxy-4-methyl coumarin
glycine-to-nitrate ratio
surface reaction equilibrium constant, k1=k
surface reaction rate constant
reactant species B, ethyl acetoacetate
chemisorbed ethyl acetoacetate
0
BS
1
1
C
A
concentration of A in mol/cm3
k
2
3
CA0
initial concentration of A at catalyst (solid) surface (mol/
cm )
A B i
K ,K ,K ,. . . adsorption equilibrium constant for A, B, i cm /mol
3
6
ꢀ1
ꢀ1 ꢀ1
kR2
surface reaction rate constant, cm mol g-cat
s
C
B
concentration of B in mol/cm3
initial concentration of B in bulk liquid phase, mol/cm
M
molar ratio of initial concentrations ðCB =ðCA Þ
0
0
3
CB0
r
A
rate of reaction of A based on liquid phase volume,
3
ꢀ3 ꢀ1
C
C
C
C
C
BS
concentration of B at solid (catalyst) surface, mol/cm
mol cm
s
concentration of E in mol/cm3
S
t
vacant site
time, s
E
3
ES
S
concentration of E at solid (catalyst) surface, mol/cm
concentration of vacant sites, mol/cm3
w
W
catalyst loading, g/cm of the liquid phase
ethanol
3
3
t
total concentration of the sites, mol/cm
diffusion coefficient of A in B, cm /s
diffusion coefficient of B in A, cm /s
2
D
D
AB
X
A
fractional conversion of A
2
BA
DI
deionized
controlled by the method of preparation and calcination tempera-
ture. Use of higher calcination temperatures result in collapse of
pores or sintering of material, which creates a wider pore size dis-
method produces fine nanoscale metal oxides with high surface
area and mesoporosity, which makes it a vital tool for synthesizing
a tailor-made catalyst [25,26]. A combustion synthesis approach
combined with catalysis techniques can be used to impose better
activity and probable shape selectivity. The combustion synthesis
method explores an exothermic, generally very fast, and self-sus-
tained chemical reaction between the desired metal salts and a
suitable organic fuel, which is ignited at a temperature much lower
than the actual phase formation temperature. Its key feature is that
the heat required to drive the chemical reaction and accomplish
the compound synthesis is supplied by the reaction itself and not
by an external source. We report, for the first time, a preparation
of sulfated zirconia with high sulfur content (15 wt%) possessing
better activity, including preservation of its tetragonal phase via
combustion synthesis route and using chlorosulfonic acid as a
new source for sulfate ions. This catalyst was also used in an indus-
trially important reaction.
Coumarins are benzo-2-pyrone derivatives mainly found in
plants of the families Rutaceae and Umbelliferae. Coumarin and its
derivatives have been attracting great interest because of their
importance in synthetic organic chemistry. Among the various
coumarin derivatives, 7-substituted coumarins are an important
group showing various bioactivities. 7-Hydroxy-4-methylcouma-
rin is used as fluorescent brightener, an efficient laser dye, a stan-
dard for fluorometric determination of enzymatic activity, and a
starting material for the preparation of insecticides and furano
coumarins [27].
2
tribution. The conventional preparation method for S-ZrO results
in microporous material, which is more suitable for reactions of
small molecules in the vapor phase and in liquid phase, particu-
larly for reactions not involving water [1]. To form a catalyst that
has shape selectivity for larger molecules, mesoporous material
with a narrow pore size distribution needs to be created. Many at-
tempts have been made to synthesize mesoporous sulfated zirco-
nia, most commonly using a charged template, but removal of
the template by calcination or extraction often causes the material
to collapse [7,13–15]. Hudson and Knowles [16] were able to syn-
thesize mesoporous zirconia using cationic surfactants. However,
the materials formed had broad pore size distributions [width at
half height (WHH) > 2.0 nm] that would not be suitable for
shape-selective catalytic reactions. A neutral templating method
was successfully used and mesoporous sulfated zirconia that did
not collapse upon removal of the template was formed [17]. An-
other approach to overcoming the lacunae of conventional S-ZrO
is to make use of highly ordered mesoporous material such as
HMS, MCM-41, or SBA-15 as a support for S-ZrO . In this context,
the novel synthesis of S-ZrO supported on hexagonal mesoporous
2
2
2
silica (HMS) was first reported by Yadav and Murkute [18] and des-
ignated as UDCaT-6. A series of new superacid catalysts, MCM-41-
2
supported S-ZrO were prepared by an impregnation–calcination
method by Lei et al. [19]. Shape selectivity has also been achieved
by using a combination of S-ZrO
UDCaT-2 catalysts [6].
All previous literature suggests that S-ZrO
so far with a maximum 9 wt% of sulfur with preservation of the
tetragonal phase of zirconia, and above this value, the tetragonal
2
and carbon molecular sieves in
has been prepared
Chemically, coumarins can be synthesized by various methods,
such as the Pechmann reaction [28–33], Knoevenagel condensation
[34–37], Claisen rearrangement [38], and Perkin [39–41], Wittig
[42–45], Reformatsky [46], and catalytic cyclization reactions
[47]. However, the acid-catalyzed Pechmann reaction is a simple
and commonly used method for synthesizing coumarins from acti-
vated phenols, mostly m-substituted phenols containing electron-
donating substituents at the m-position and b-keto-esters or an
unsaturated carboxylic acid [28,29,48]. Conventionally, the Pech-
mann reaction is carried out in the presence of concentrated sulfu-
ric acid catalyst [30,49], phosphorus pentoxide [50], trifluoroacetic
acid [51], and aluminum chloride [52]. These acids are corrosive
and required in excess. Taking environmental and economic fac-
tors into consideration, there has been renewed interest in the
preparation of coumarins using heterogeneous catalysts and under
benign reaction conditions.
2
phase is strongly affected. Retention of mesoporosity in S-ZrO
2
without using any support has also been a challenge. Thus, it will
be most advantageous to synthesize sulfated zirconia with high
sulfur content, particularly above 9%, with a pure tetragonal phase
to exhibit high superacidity and generation of mesopores with nar-
row pore size distribution that would not collapse on calcination.
To achieve these goals, a novel route of combustion synthesis
2
was developed to prepare sulfated zirconia (S-ZrO ). In recent
years, combustion synthesis has emerged as a powerful alternative
to material synthesis [21–26]. This method is reproducible and less
time-consuming and does not involve multistep synthesis. The

G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
101
The current work deals with synthesis and characterization of a
novel material, combustion-synthesized sulfated zirconia [53], and
its application in the synthesis of 7-hydroxy-4-methylcoumarin by
Pechmann condensation. Both the method of preparing the stron-
gest superacid and its application in Pechmann condensation are
novel.
2.3.2. Synthesis of fuel-lean sulfated zirconia
In synthesis of FLSZ, the glycine and zirconium oxynitrate hexa-
hydrate were taken in a 1:2 mol ratio. The above-mentioned proce-
dure of combustion synthesis was followed to obtain fuel-lean
zirconium dioxide powder. This material was immersed in
3
15 cm /g of 1 M chlorosulfonic acid in ethylene dichloride. With-
out moisture absorption being allowed, the material was trans-
ferred to an oven, and the heating was started to evaporate the
solvent. It was kept in an oven at 120 °C for 24 h and calcined at
2
. Experimental
6
50 °C for 3 h to obtain the active catalyst FLSZ.
2.1. Chemicals
2.3.3. Synthesis of fuel-rich sulfated zirconia
A.R. grade glycine, toluene, ethyl acetoacetate (EAA), resorcinol,
In synthesis of FRSZ, glycine and zirconium oxynitrate hexahy-
diphenylmethane, benzyl chloride, n-undecane, 98 wt% sulfuric
acid, and ammonium sulfate were obtained from S.D. Fine Chem.
Pvt. Ltd., Mumbai. Chlorosulfonic acid was obtained from Spectro-
chem Pvt. Ltd., Mumbai. Zirconium oxynitrate hexahydrate was
purchased from Sigma Aldrich, Germany.
drate were taken in a 2:1 mol ratio. The same procedure of com-
bustion synthesis was followed to obtain fuel-rich zirconium
dioxide powder. The fuel-rich oxide contained a considerable
amount of residual carbon. To remove this unwanted carbon, the
zirconium dioxide powder was calcined at 550 °C for 4 h prior to
3
acid treatment. The material was then immersed in 15 cm /g of
1
M chlorosulfonic acid in ethylene dichloride. Without moisture
2
.2. Optimization of synthesis parameters
absorption being allowed, the material was transferred to an oven
and the heating started to evaporate the solvent. This material was
kept in the oven at 120 °C for 24 h and calcined at 650 °C for 3 h to
get the active catalyst FRSZ.
Synthesis of any sulfated metal oxide via combustion synthesis
has not been reported so far, and thus, the current work is the first
attempt of its kind to synthesize sulfated zirconia. To obtain a cat-
alyst with high activity and required textural properties, a number
of parameters need to be optimized. The important parameters are
glycine-to-nitrate ratio, acid to be used for sulfation and its nor-
mality, and calcination temperature prior to acid treatment. All
these parameters were varied systematically, and the activity of
the catalyst was optimized using a probe reaction of Friedel–Crafts
alkylation of toluene with benzyl chloride [5].
UDCaT-5 was prepared by immersing dried zirconium hydrox-
3
ide in 15 cm /g of a 0.5 M solution of chlorosulfonic acid in ethyl-
ene dichloride, followed by drying at 120 °C for 24 h and
2
calcination at 650 °C for 3 h [10]. Sulfated zirconia (S-ZrO ) was
3
prepared by immersing zirconium hydroxide in 15 cm /g of
0.5 M of sulfuric acid, followed by drying at 120 °C for 24 h and cal-
cination at 650 °C for 3 h [49].
Three different G/N ratios were selected (G/N = 0.5, 1.1, 2).
Using these ratios, zirconium dioxide was synthesized using the
method of solution combustion synthesis, and the three oxides
were used for further experiments. Sulfuric acid, ammonium sul-
fate, and chlorosulfonic acid were used as sources of sulfate ion.
2.4. Catalyst characterization
Crystallinity and textural patterns of the catalysts were pre-
dicted from XRD data, which were recorded using a Philips PW
1729 powder diffractometer with Cu K
was used to confirm the presence of bidentate sulfated ligands in
S-ZrO solid acid catalyst. Infrared spectra of samples pressed in
KBr pellets were obtained at a resolution of 2 cm
a (1.54-Å) radiation. FTIR
3
The amount of acid used was 15 cm /g with molarity 0.5 and
1
M. Calcination prior to acid treatment is necessary when the
2
ꢀ1
oxide contains considerable amounts of residual carbon. This phe-
nomenon is observed at a G/N ratio of 2. Trials were conducted to
determine the calcination temperature on the basis of the color of
the calcined oxide. It was observed that most of the residual carbon
is burnt off at 550 °C. The effect of calcination time was studied for
between
ꢀ1
4000 and 350 cm . Spectra were collected with a Perkin–Elmer
(Spectrum BX instrument), and in each case, the sample was refer-
enced against a blank KBr pellet. The wafers were subjected to 32
scans, after which the spectra were recorded.
2
and 4 h.
Ammonia TPD experiments were performed in an Autochem II
(
Micromeritics Model 2920) instrument equipped with a TCD
detector. Approximately 0.1 g of catalyst was loaded in the sample
holder, heated to 573 K in argon, and subsequently cooled to 298 K.
After being dosed with 5 vol.% of ammonia in argon mixture at a
flow rate of 30 ml min for 30 min, the system was purged with
argon for 1 h at the same temperature. The physisorbed ammonia
was removed by passing argon gas at RT for 30 min. After cooling
to 298 K, the temperature was raised to 923 K at 10 K/min, and
the outlet gases were analyzed by a thermal conductivity detector.
Nitrogen adsorption–desorption for BET surface area, pore vol-
ume, and pore size distribution were carried out by BJH and mul-
2
.3. Catalyst preparation
ꢀ1
On the basis of optimization results, two catalysts were
screened: fuel-lean sulfated zirconia (FLSZ) and fuel-rich sulfated
zirconia (FRSZ).
2.3.1. Synthesis of zirconium dioxide by combustion synthesis
In a typical application of combustion synthesis to produce zir-
conium dioxide, predetermined amounts of glycine and zirconium
oxynitrate hexahydrate were taken in minimum amounts of DI
water (ꢁ2 cm /g of precursors). The solution was stirred on a mag-
tipoint BET methods using
a
Micromeritics ASAP-2010
instrument. The analysis was carried out at 77 K, maintained by li-
quid nitrogen, after the sample was preheated to 300 °C for 4 h.
SEM micrographs and electron-dispersive scanning (EDS) data for
the catalysts were obtained on a JEOL JSM 7400 microscope oper-
ated at 10 kV with a working distance of 2.6–8 mm and resolution
up to 1 nm. The dried samples were mounted on specimen studs
and sputter-coated with a thin film of gold to prevent charging.
The gold-coated surface was then scanned at various magnifica-
tions using a scanning electron microscope.
3
netic stirrer at 80 °C for 2 h to transform the aqueous solution into
a highly viscous gel. The temperature and time of stirring de-
pended on the amount of precursors used. The viscous gel was then
transferred to a silica crucible and kept in a muffle furnace main-
tained at 350 °C. The gel underwent self-ignition and transformed
into a fluffy mass, which upon mild crushing resulted in a fine crys-
talline zirconium dioxide powder.

1
02
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
2.5. Experimental setup
stationary phase of 10% OV-17 supported on Chromosorb-WHP.
Typically ethyl acetoacetate was taken in excess and conversions
were based on the limiting reactant, resorcinol. The product was
confirmed by GC–MS (Perkin–Elmer Clarus 500 with software Tur-
bomass version 5.0.0) and melting point.
The Friedel–Crafts benzylation reaction was conducted in a
glass reactor of i.d. 5 cm and height 10 cm with four glass baffles
and a four-bladed disk turbine impeller located 0.5 cm from the
bottom of the vessel and mechanically agitated with a motor. In
a typical reaction, 0.5 mol of toluene was reacted with 0.05 mol
2.7. Reaction scheme
3
of benzyl chloride at 90 °C with 0.018 g/cm catalyst loading, and
1
000 rpm speed of agitation.
Scheme 1 shows the described reaction.
All experiments for Pechmann condensation of resorcinol with
ethyl acetoacetate were carried out in a high-pressure autoclave
Amar Equipments, Mumbai) of capacity 100 ml. The autoclave
3
. Results and discussion
(
was equipped with a 45°-inclined four-bladed pitched turbine
impeller, temperature controller (±1 °C), pressure indicator (kg/
cm ), and speed regulator (±5 rpm). Predetermined quantities of
3
.1. Optimization of synthesis parameters
2
Table 1 shows various experiments carried out in order to opti-
reactants and the catalysts were charged into the autoclave. The
reaction mixture was heated to the required temperature, and
the samples were withdrawn at specific intervals of time starting
from zero time. A standard (control) experiment consisted of
mize the synthesis parameters to attain maximum activity for the
benzylation of toluene to give benzyltoluene. First, sulfuric acid
was used for sulfation of zirconia with three G/N ratios. The con-
version obtained was not significant as compared to reported val-
ues under otherwise similar conditions [10]. Then ammonium
sulfate was used for sulfation. The catalyst showed even less activ-
ity compared to sulfuric acid-treated zirconia. Finally, chlorosul-
fonic acid was used for sulfation. The strength of chlorosulfonic
acid and calcination temperature were varied systematically to
get maximum conversion in the probe reaction. Two catalysts were
screened on the basis of catalytic performance (Sr. No. 10 and Sr.
No. 13). The catalyst with fuel-lean composition (G/N ratio of
0
.03 mol resorcinol and 0.09 mol ethyl acetoacetate. The total reac-
tion volume was maintained at 50 ml with makeup of toluene. The
temperature was maintained at 150 °C and the speed of agitation
3
at 1200 rpm with a catalyst loading of 0.03 g/cm .
After the completion of the reaction, the reaction mixture was
cooled to room temperature, and the contents were poured into
ice-cold water. The products were collected by filtration, washed
with ice-cold water, and then recrystallized from hot ethanol to
provide the coumarin derivative. All the coumarin derivatives
could be identified by comparison with reported physical and
spectral data.
0
.5) was named FLSZ, and the one with fuel-rich composition (G/
N ratio of 2) was named FRSZ. Detailed characterization of these
catalysts was conducted in order to study their properties.
2.6. Analysis
3.2. Catalyst characterization
Analysis of the reaction mixture was performed by GC (Chemi-
3.2.1. X-ray diffraction studies
to, Model 8610) using a flame ionization detector and a stainless
steel column (diameter 3.25 mm and length 4 m) packed with a
The crystal structure of sulfated zirconia is strongly affected by
the sulfur content. When the sulfur content is low or medium
HO
OH
HO
O
O
O
O
+
+ C2H5OH + H2O
H3C
OC2H5
Ethyl acetoacetate
Resorcinol
CH3
7
-Hydroxy-4-methyl-coumarin
Scheme 1. Pechmann condensation of resorcinol with ethyl acetoacetate.
Table 1
Experiments for optimization of parameters.
No.
G/N ratio
Calcination temperature prior to acid treatment
Acid
Strength and amount
Conversion after 1 h in probe reaction (%)
3
1
2
3
4
5
6
7
8
9
0.
1.
2.
3.
.
.
.
.
.
.
.
.
.
1.1
0.5
2
1.1
0.5
2
1.1
1.1
0.5
0.5
2
550 °C for 2 h
–
550 °C for 2 h
550 °C for 2 h
–
550 °C for 2 h
550 °C for 2 h
550 °C for 4 h
–
SA
SA
SA
AS
AS
AS
CSA
CSA
CSA
CSA
CSA
CSA
CSA
15 cm /g, 0.5 M
10.5
13.5
12.0
0.58
1.48
1.10
0.0
15.0
45.0
85.0
25.0
55.0
84.0
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
15 cm /g, 0.5 M
3
1
1
1
1
–
15 cm /g, 1 M
3
550 °C for 2 h
550 °C for 4 h
550 °C for 4 h
15 cm /g, 0.5 M
3
2
2
15 cm /g, 0.5 M
3
15 cm /g, 1 M
Note. G: glycine, N: nitrate, SA: sulfuric acid, AS: ammonium sulfate, CSA: chlorosulfonic acid.

G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
103
ble for increased crystallinity and tetragonal phase. The fuel-rich
oxide shows the highest crystallinity and minimum monoclinic
phase. The crystallinity decreases as the oxides are sulfated.
3.2.2. Fourier transform infrared spectroscopy
FTIR spectroscopy was used to study the nature of sulfur re-
tained on the surface and the nature of the acidic sites generated.
The spectra of acid-treated zirconia exhibit peaks in the range of
ꢀ1
1
000–1250 cm , whereas pure zirconia does not show any bands
in this range. The IR spectra of FLSZ (Fig. 3) show a broad peak hav-
ing shoulder peaks at 1321.2, 1289, 1119.45, 1009.87, and
ꢀ
1
9
(
72 cm , which are typical of a chelating bidentate sulfate ion
ꢀ
2
SO ) coordinated to a metal cation. The absence of a band at
4
ꢀ
1
Fig. 1. XRD of (1) ZrO
2
, (2) FLSZ, and (3) FRSZ. T—tetragonal phase; M—monoclinic
1400 cm indicates that there is no formation of polynuclear sul-
ꢀ
2
ꢀ1
phase.
fates S
2
O
on the surface. The band at 1637 cm is attributed to
7
the dO–H bending frequency of water molecules associated with
ꢀ
1
2
sulfate groups [50]. The feature at 752 cm is due to Zr–O –Zr
(
S < 4 wt%), the sulfated zirconia crystallizes in the tetragonal form.
asymmetric and Zr–O stretching modes, which confirms formation
phases. The IR bands between 450 and 800 cm are char-
acteristic of crystalline zirconia. An additional broad band at
When the sulfur content is high (S > 4 wt%), it exists in monoclinic
form in addition to the major tetragonal form [7,11]. In this case,
the sulfur content in both the sulfated catalysts is very high
ꢀ1
of ZrO
2
ꢀ1
3
402 cm corresponds to the stretching vibration of
v
OH of the hy-
(
ꢁ15 wt%), which is the reason behind the presence of monoclinic
droxyl group.
phases in the XRD of FLSZ and FRSZ (Fig. 1).
The IR spectra of FRSZ (Fig. 4) show a similar pattern. A broad
peak with shoulder peaks in the range from 1000 to 1300 cm
confirms the presence of bidentate SO4 ions coordinated to metal
It is generally observed that pure zirconia transforms into the
monoclinic phase from the tetragonal phase above the calcination
temperature of 600 °C [1]. The XRD patterns of combustion-syn-
thesized zirconia prior to acid treatment with different G/N ratios
are shown in Fig. 2. The splitting of 013 and 121 peaks is the char-
acteristic feature of tetragonal zirconia. Also, the XRD result shows
the presence of a monoclinic zirconia phase along with major
tetragonal zirconia, in the oxides produced with G/N = 0.5 (fuel-
lean). The hump at 2h = 28° in the fuel-lean sample is characteristic
of the monoclinic phase. In all three compositions, the percentage
of the monoclinic phase is less than 5%. Thus, FLSZ has more tetrag-
onal phase.
ꢀ1
ꢀ2
ꢀ1
cations. The absence of bands at 1400 cm indicates that there is
ꢀ2
no formation of polynuclear sulfates S
2
O
on the surface. The
7
ꢀ1
band at 1633 cm is attributed to the dO–H bending frequency of
water molecules associated with sulfate groups [50]. The IR bands
between 450 and 800 cm are characteristic of crystalline zirco-
nia. A sharp band at 754.62 cm is due to Zr–O
and Zr–O stretching modes, which confirms the formation of
phases. An additional broad band at 3398 cm corresponds
to the stretching vibration of vOH of the hydroxyl group.
ꢀ1
ꢀ1
2
–Zr asymmetric
ꢀ1
ZrO
2
Table 2 shows percentage crystallinity of pure zirconia and cor-
responding sulfated samples. The crystallinity increases with in-
creased G/N ratio in all combustion-synthesized zirconia
powders. As the G/N increases, the amount of fuel taking part in
combustion increases. This results in higher temperatures in the
combustion flame. Formation at higher temperatures is responsi-
3
.2.3. Ammonia temperature-programmed desorption
Temperature-programmed desorption using NH was used to
3
measure the total acidity and the nature of acidic sites generated
on the catalyst surface. Fig. 5 shows a typical desorption curve
for FLSZ. Well-defined peaks were obtained at 150 and 400 °C, indi-
cating the presence of intermediate and strong acid sites. The
desorption curve of FRSZ is shown in Fig. 6. The peak at 400 °C is
wider than that for FLSZ, indicating that strong acidic sites are
more dominant in the case of FRSZ.
FRSZ has considerable amounts of residual carbon present be-
fore acid treatment as compared to FLSZ. When the oxide is cal-
cined at 650 °C after acid treatment, this carbon escapes from the
2
inner crust of the oxide in the form of CO . This evolution of gases
results in violent changes in the morphology of the oxide, generat-
ing large numbers of pores and surface defects. This phenomenon
is practically absent in fuel-lean oxide with relatively small
amounts of residual carbon. This is likely the reason behind gener-
ation of stronger acidic sites in FRSZ than in FLSZ.
Table 3 shows a comparison between the acidity of combus-
tion-synthesized and conventional sulfated zirconia catalysts. FLSZ
shows remarkably higher acidity than other catalysts. It must be
noted, however, that higher concentrations of acid were used in
2
Fig. 2. XRD results of combustion-synthesized ZrO . T—tetragonal phase; M—
monoclinic phase.
3
3
preparation of FLSZ (1 M, 15 cm /g) and FRSZ (1 M, 15 cm /g) than
Table 2
3
3
2
of UDCaT-5 (0.5 M, 15 cm /g) and S-ZrO (0.5 M, 15 cm /g). More
Crystallinity of zirconia before and after acid treatment.
acid is required in the case of combustion-synthesized catalysts
because of the presence of excess residual carbon in oxides prior
to acid treatment.
Sample
Glycine-to-nitrate ratio
Crystallinity (%)
Fuel-lean ZrO
2
0.5
1.1
2
0.5
2
35
37.5
41
24.4
31.4
Stoichiometric ZrO
Fuel-rich ZrO
Fuel-lean sulfated ZrO
Fuel-rich sulfated ZrO
2
These results can now be compared with UDCaT-5 and UDCaT-
2
5
2
b vis-à-vis S-ZrO , as reported in our previous work [7]. The most
2
striking feature of the spectra of the UDCaT-5 and UDCaT-5b is the
generation of an additional peak at 550 °C in both. Corma et al. [54]
2

1
04
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
3
5.0
3
2
2
1
1
0
5
0
5
0
2359.83
1637.04
752.15
%
T
5
02.51
3402.13
611.87
1
119.45
1
321.20
1
5
289.35
9
72.09
1
009.87
0
.0
4
000.0
3000
2000
1500
1000
400.0
cm-1
Fig. 3. FTIR spectra of FLSZ.
3
5.0
3
2
2
1
1
0
5
0
5
0
5
462.45
7
54.62
1633.48
2
343.82
%
T
6
49.39
12.57
587.63
5
01.80
3
398.36
6
1
116.04
1332.26
0
.0
000.0
4
3000
2000
1500
1000
400.0
cm-1
Fig. 4. FTIR spectra of FRSZ.
Fig. 5. Ammonia TPD of FLSZ.

G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
105
Fig. 6. Ammonia TPD of FRSZ.
Table 3
Acidity measurement of various superacids by ammonia TPD in mmol/g.
oxides. Fuel-lean ZrO
and fuel-rich ZrO
show narrow pore size
2
2
distributions prior to acid treatment. In the case of their sulfated
counterparts, a narrow pore size distribution can be seen only in
FLSZ (width at half height <2 nm), while FRSZ shows a compara-
tively wider pore size distribution (Fig. 8). The additional step of
calcination for FRSZ may be responsible for this feature.
FLSZ
.628
FRSZ
UDCaT-5
0.584
S-ZrO
0.433
2
0
0.502
2
assign this peak to superacidic centers of S-ZrO calcined at 550 °C.
It is thus inferred here that there is a generation of superacidic cen-
ters in UDCaT-5, even though it was calcined at 650 °C for 3 h and
3
.2.5. Scanning electron microscopy
The SEM images of FLSZ and FRSZ are shown in Figs. 9 and 10,
respectively. Formation of lumps and agglomerates can be seen
in SEM images of FLSZ. The SEM image of FRSZ shows no such
agglomerate formation. Images of FRSZ indicate formation of flakes
of uniform size and shape.
Agglomeration in FLSZ may be due to the comparatively small
amount of fuel used in combustion. Use of less fuel results in rela-
tively less gas formation. On the other hand, in FRSZ, excessive gas
formation avoids agglomerate formation.
2
the same peak is not observed in S-ZrO calcined at 650 °C. The to-
ꢀ1
tal acid sites of each of UDCaT-5 (0.584 mmol g ) and FLSZ
ꢀ
ꢀ
1
1
(
(
0.628 mmol g
)
are
much
higher
than
for
S-ZrO
2
0.433 mmol g ) and UDCaT-5. The acidity of both UDCaT-5 and
FLSZ is dependent on the molar strength of chlorosulfonic acid,
and they are more superacidic than S-ZrO
2
.
3.2.4. BET surface area and pore size analysis
The surface area of S-ZrO gradually increases at low sulfate
2
3.2.6. Energy-dispersive X-ray spectroscopy
2
content up to 4% w/w (119 m /g), but it decreases abruptly at
EDXS was conducted to confirm complete decomposition of
chlorosulfonic acid in synthesized catalyst and to check any resid-
ual carbon after combustion. Chlorosulfonic acid may decompose
to sulfuryl chloride, pyrosulfuryl dichloride, sulfuric acid, sulfur
dioxide, chlorine, and water. Elemental analysis (Table 5) showed
complete absence of Cl species, and absence of C confirmed com-
plete removal of carbon after combustion and calcination.
Table 6 shows sulfur retention of various catalysts compared
with combustion-synthesized sulfated zirconia. FLSZ and FRSZ
show high retention of sulfur compared with conventionally syn-
2
the maximum sulfate content of 5.64% w/w (71 m /g), due to
migration of sulfate ions in the bulk phase of zirconia [7,11].
A similar reason could be suggested in the current case. The
XRD results also indicate that migration of sulfate ions into the
bulk phase of zirconia has resulted in generation of monoclinic
phases. The higher sulfur loading may have resulted in reduction
of the surface area (Table 4). The combustion-synthesized catalysts
have comparatively larger pore size and ordered mesoporosity.
Fig. 7 shows the pore size distribution of combustion-synthesized
2
thesized S-ZrO [1,5,18].
Table 4
Surface area characteristics.
3.3. Efficacies of various catalysts
2
3
The efficacy of various solid acid catalysts in this reaction was
assessed. The catalysts used were FLSZ, FRSZ, UDCaT-5, 20 wt%
Catalyst
Surface area (m /g) Pore size (nm) Pore volume (cm /g)
FLSZ
FRSZ
UDCaT-5
53.3
21.6
84
9.85
9.14
4.0
0.131
0.051
0.21
Cs-DTP/K-10, and conventional S-ZrO
as follows: FLSZ (highest) > 20 wt% Cs-DTP-K10 >FRSZ > UDCaT-
> S-ZrO (lowest).
Cs-DTP/K-10 is cesium dodecatungstophoshoric acid supported
on K-10 clay (Cs2.5 40/K-10). Combustion-synthesized
2
. The order of activity was
S-ZrO
Fuel-lean ZrO
Fuel-rich ZrO
2
103
17
10
4.1
8.5
6.1
0.11
0.142
0.076
5
2
2
2
H0.5PW12O

1
06
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
Fig. 7. Pore size distribution of (a) fuel-lean ZrO
2
(FLSZ) and (b) fuel-rich ZrO
2
(FRSZ).
Fig. 8. Pore size distribution of (a) FLSZ and (b) FRSZ.
Fig. 9. SEM image of FLSZ.

G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
107
Fig. 10. SEM image of FRSZ.
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
Table 5
Elemental analysis of FLSZ and FRSZ.
Element
FLSZ (%)
FRSZ (%)
O
S
Zr
38.8
15.14
46.06
38.6
15.1
46.3
Table 6
Sulfur content of different superacids by elemental analysis (w/w %).
a
FLSZ
5.14
FRSZ
15.1
UDCaT-5
9
S-ZrO
4
2
1
a
Reference material.
0
30
60
90
120
150
180
Time (mins)
40
35
30
25
20
15
10
5
0
Fig. 12. Effect of speed of agitation.
200 rpm,
600 rpm,
800 rpm,
1000 rpm,
1
1400 rpm. Reaction conditions: temperature 150 °C, catalyst loading
0.03 g/cm , mole ratio (EAA:resorcinol) 3:1, ethyl acetoacetate 90 mmol, resorcinol
0 mmol, reaction volume – 50 ml. (For interpretation of the references to color in
3
3
this figure legend, the reader is referred to the web version of this article.)
70
6
0
FLSZ
Cs/DTP/K 10
FRSZ
UDCaT -5
S-ZrO2
Fig. 11. Efficacies of different catalysts for Pechmann condensation reaction.
Reaction conditions: temperature 150 °C, catalyst loading 0.01 g/cm , mMole ratio
50
3
(
EAA:resorcinol) 3:1, ethyl acetoacetate 90 mmol, resorcinol 30 mmol, reaction
4
0
volume 50 ml.
fuel-lean sulfated zirconia showed the highest activity in compar-
ison with other catalysts (Fig. 11). The selectivity was almost sim-
ilar. The catalyst showed nearly 95% selectivity with FLSZ. The
obvious reason is the high sulfur content and retention of tetrago-
nal phase in this catalyst. Although the surface area is smaller than
that of Cs-DTP/K10, the pore sizes are in the meso region, and thus,
there is no intraparticle diffusion limitation for formation of a
bulky product. Further experiments were carried out using FLSZ
due to its better activity toward this reaction.
30
0.005 g/cm3
2
1
0
0
0
0
30
60
90
120
150
180
210
Time (min)
Fig. 13. Effect of catalyst loading.
0.005 g/cm3,
0.01 g/cm3,
0.02 g/cm3,
3.4. Effect of speed of agitation
3
3
0.03 g/cm ,
0.04 g/cm . Reaction conditions: temperature 150 °C, speed of
agitation 1200 rpm, mole ratio (EAA:resorcinol) 3:1, ethyl acetoacetate 90 mmol,
resorcinol 30 mmol, reaction volume 50 ml. (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
The effect of speed of agitation on the rate of reaction was stud-
ied in order to eliminate the external mass transfer resistance. The

1
08
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
speed of agitation was varied in the range 600–1400 rpm under
otherwise similar conditions (Fig. 12), maintaining temperature
at 150 °C.
80
70
The initial rate of reaction increased as the speed of agitation
was increased from 600 to 1200 rpm. It remained practically un-
changed above 1200 rpm. The reaction is mass transfer controlled
below 1200 rpm. All further experiments were carried out at
6
5
4
0
0
0
1
200 rpm, which ensured the absence of mass transfer resistance.
3
.5. Effect of catalyst loading
30
20
The initial rate of a reaction is proportional to the number of ac-
tive sites, when external mass transfer resistance and intraparticle
diffusion resistance are absent. Reactions can be carried out at
widely varying concentrations of active sites to ensure the elimina-
tion of mass transfer limitations. So the catalyst loading based on
the total volume of the reaction mixture was varied from 0.005
1
0
0
0
30
60
90
120
150
180
210
Time (mins)
3
to 0.04 g/cm at 1200 rpm. There was an increase in conversion
3
when the loading was increased from 0.005 to 0.04 g/cm
Fig. 15. Effect of temperature.
conditions: speed of agitation 1200 rpm, catalyst loading 0.03 g/cm , mole ratio
EAA:resorcinol) 3:1, ethyl acetoacetate 90 mmol, resorcinol 30 mmol, reaction
volume – 50 ml. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article.)
130 °C, 140 °C,
150 °C,
160 °C. Reaction
3
(Fig. 13). This trend is due to the increase in active sites with in-
(
creased catalyst loading.
The relative increase in conversion is comparatively less when
the reaction is carried out at catalyst loadings of 0.03 and 0.04 g/
3
cm , which indicates that there is an onset of intraparticle resis-
tance. This would suggest that the number of sites available is
more than that required. This is also confirmed by the Wiesz–Pra-
ter criterion (modulus).
3.7. Effect of temperature
The reaction was carried out over a wide range of temperatures
ranging from 130 to 160 °C. Self-condensation of ethyl acetoace-
tate takes place above 160 °C, resulting in undesirable side prod-
ucts. The conversion increased with temperature, indicating a
kinetically controlled reaction (Fig. 15). This suggests a kinetically
controlled mechanism, which is discussed later.
Hence, further experiments were carried out at 0.03 g/cm3.
3.6. Effect of mole ratio
The mole ratio of ethyl acetoacetate to resorcinol was varied
from 1:2 to 1:4, keeping the total volume of reactants and volume
of solvent constant. It was found that the rate of reaction increased
with increased mole ratio from 1:2 to 1:3 (Fig. 14). At lower mole
ratios, the number of moles of ethyl acetoacetate in the vicinity of
resorcinol is comparatively less, resulting in a decreased rate of
reaction. At higher molar ratios, this effect is less dominating.
Hence, the molar ratio of 1:3 was used for further reactions.
3
.8. Catalyst reusability
Reusability of FLSZ was tested by conducting two runs. After the
completion of the experiment, the catalyst was filtered, washed
with 100 ml of methanol, and dried for 3 h at 110 °C. In each run,
completely used catalyst was employed without addition of fresh
catalyst. It was observed that the there was only a marginal de-
crease in conversion. Experiments were also done with used cata-
lyst with makeup quantities of fresh catalyst. The conversions were
similar, with experimental error of ±2%. Thus, the catalyst was
found to be reusable.
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
3.9. Development of kinetic model
In the absence of both external mass transfer and intraparticle
diffusion resistances, it is possible to develop a kinetic model. Sev-
eral models were tried, and the following was observed to fit the
data well. Chemisorption of A (resorcinol) and B (ethyl acetoace-
tate) takes place on two adjacent vacant surfaces (S) according to
the Langmuir–Hinshelwood–Hougen–Watson (LWHW) mecha-
nism to produce E (7-hydroxy-4-methyl coumarin) and W (etha-
nol). A standard derivation can be done.
If the surface reaction controls the rate of reaction, then the rate
of reaction of A is given by
dC
dt
A
ꢀ
r
A
¼ ꢀ
¼ k
2
C
AS
C
BS ꢀ k2
0
C
ES
C
WS
;
ð1Þ
ð2Þ
0
30
60
90
120
150
180
210
Time (min)
n
o
K
E
K
W
C
E
C
W
2
k
2
K
A
K
B
C
A
C
B
ꢀ
þ K
Ct
dC
dt
A
K
2
Fig. 14. Effect of mole ratio. 1:2, 1:3, 1:4. Reaction conditions: temperature
ꢀ
¼
:
2
3
1
50 °C, speed of agitation 1200 rpm, catalyst loading 0.03 g/cm , reaction volume
ð1 þ þK
A
C
A
þ K
B
C
B
S
C
E
þ K
W
C
W
Þ
5
0 ml. (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of this article.)
When the reaction is far away from equilibrium,

G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
109
of the rate constants at different temperatures were calculated, and
an Arrhenius plot was used to estimate the activation energy of the
reaction (Fig. 17). The apparent activation energy was found to be
y = 0.006x
R² = 0.994
3
6.0 kJ/mol. This activation energy also supported the conclusion
y = 0.004x
R² = 0.995
that the overall rate of reaction is not influenced by either external
mass transfer or intraparticle diffusion resistance, and it is an
intrinsically kinetically controlled reaction on active sites.
y = 0.004x
R² = 0.994
4
. Conclusions
y = 0.002x
R² = 0.992
We report, for the first time, that sulfated zirconia prepared via
a combustion synthesis route, which is treated with chlorosulfonic
acid, has superior acidity compared to sulfuric acid-treated S-ZrO
2
.
The catalyst shows mesoporosity with a narrow pore size distribu-
tion, making it a shape-selective catalyst. The combustion-synthe-
sized sulfated zirconia catalyst is more stable and also is more
active than S-ZrO2. Fuel-lean sulfated zirconia (FLSZ) is more active
than fuel-rich sulfated zirconia (FRSZ). Characterization and reac-
tion tests support the above results. The activity and stability of
FLSZ was studied by using Pechmann condensation reaction
between resorcinol and ethyl acetoacetate to produce selectively
Time (min)
Fig. 16. Plots of ln{(M ꢀ X
A
)/M(1 ꢀ X
A
)} vs time. 130 °C,
60 °C. (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of this article.)
140 °C,
150 °C,
1
7
-hydroxy 4-methyl coumarin. A kinetic model is also developed.
Acknowledgments
N.P.A. acknowledges support from the UGC as JRF. G.D.Y.
acknowledges support from the R.T. Mody Distinguished Professor
Endowment and Department of Science and Technology (DST), GoI,
as J.C. Bose National Fellow. A.V. and G.D.Y. thank DST for support
under the CP-PIO program of the DST.
References
[
[
[
[
1] G.D. Yadav, J.J. Nair, Micropor. Mesopor. Mater. 33 (1999) 1–48.
2] V.C.F. Holm, G.C. Bailey, U.S. Patent 3032599 (1962).
3] M. Hino, S. Kobayashi, K. Arata, J. Am. Chem. Soc. 101 (21) (1979) 6439–6441.
4] P. Nascimento, C. Akratopoulou, M. Oszagyan, G. Coudurier, C. Travers, J.F. Joly,
J.C. Vedrine, Stud. Surf. Sci. Catal. 75 (1993) 1185.
[
5] P.S. Kumbhar, V.M. Yadav, G.D. Yadav, in: D.E. Layden (Ed.), Chemically
Modified Oxide Surfaces, Gordon and Breach, New York, 1989.
6] G.D. Yadav, A.D. Murkute, Langmuir 20 (2004) 11607–11619.
7] G.D. Yadav, A.D. Murkute, J. Catal. 224 (2004) 218–223.
[
[
Fig. 17. Arrhenius plot for Pechmann reaction.
[8] I. Wender, Stud. Surf. Sci. Catal. 75 (1993) 1194.
9] J.M. Parera, Catal. Today 15 (1992) 481.
[
[
[
10] C. Morterra, G. Cerrato, C. Emanuel, Mater. Chem. Phys. 29 (1991) 447.
11] D. Fârcasiu, J.Q. Li, S. Cameron, Appl. Catal. A 154 (1997) 173.
2
t
[12] V. Pârvulescu, S. Coman, P. Grange, V.I. Pârvulescu, Appl. Catal. A 176 (1999)
27.
[13] U. Ciesla, S. Schacht, G.D. Stucky, K.K. Unger, F. Schuth, Angew. Chem. Int. Ed.
Engl. 35 (1996) 541.
[14] G.D. Yadav, A.D. Murkute, Adv. Synth. Catal. 346 (2004) 389.
[15] Y. Huang, W.H.M. Sachtler, J. Chem. Soc., Chem. Commun. (1997) 1181.
dC
dt
A
k
2
C K
A
K
B
C
A
C
B
2
ꢀ
ꢀ
¼
¼
P
;
ð3Þ
ð4Þ
ð1 þ
K
i
C
i
Þ
B
dC
dt
A
k
R
wK
B
C
A
C
2
P
;
2
ð1 þ
K
i
C
i
Þ
[
16] M.J. Hudson, J.A. Knowles, J. Mater. Chem. 6 (1996) 89.
2
[17] Y. Huang, T.J. McCarthy, W.H.M. Sachtler, Appl. Catal. A Gen. 148 (1996) 35.
[18] G.D. Yadav, A.D. Murkute, J. Phys. Chem. A 108 (2004) 9557.
[19] T. Lei, W. Hua, Y. Tang, Y.H. Yue, Z. Gao, Chem. J. Chin. Univ. 21 (2000) 1240.
where kR2 w ¼ k
2
C K
A
K
B
, where w is catalyst loading. If the adsorp-
t
tion constants are small, then the above equation reduces to
[
20] C.N.R. Rao, Chemical Approaches to the Synthesis of Inorganic Materials, Wiley
Eastern Limited, New Delhi, 1994.
dC
A
ꢀ
R
¼ k 2
wK
B
C
A
C
B
:
ð5Þ
[21] A.G. Merzhanov, J. Mater. Chem. 14 (2004) 1779.
dt
[
[
[
22] K.C. Patil, S.T. Aruna, T. Mimani, Curr. Opin. Solid State Mater. Sci. 6 (2002) 507.
23] K. Deshpande, A. Mukasyan, A. Varma, Chem. Mater 16 (2004) 4896–4904.
24] G. Ranga Rao, H.R. Sahu, B.G. Mishra, Colloids Surf. A Physicochem. Eng.
Aspects 220 (2003) 261.
Let CB0 =CA0 ¼ M be the molar ratio of ethyl acetoacetate to res-
orcinol at time t = 0. Then Eq. (5) can be written in terms of frac-
tional conversion as
[25] P. Erri, P. Dinka, A. Varma, Chem. Eng. Sci. 61 (2006) 5328–5333.
[
26] K.C. Patil, Chemistry of Nanocrystalline Oxide Materials, World Scientific
Publishing Co. Pvt. Ltd., 2008.
dX
A
¼
k
R2 wCA0 ð1 ꢀ X
A
ÞðM ꢀ X
A
Þ ¼ k
1
C
A0 ð1 ꢀ X
A
ÞðM ꢀ X
A
Þ:
ð6Þ
ð7Þ
[27] G. Smitha, C.S. Reddy, Synth. Commun. 34 (2004) 3997–4003.
28] V. Pechmann, C. Duisberg, Chem. Ber. 16 (1883) 2119.
[29] H.V. Pechmann, Chem. Ber. 17 (1884) 929.
dt
[
This upon integration leads to
[
[
[
30] E.C. Horning, Org. Synth. 3 (1955) 281.
31] E.V.O. John, S.S. Israelstam, J. Org. Chem. 26 (1961) 240.
32] A.K. Bose, S. Pednekar, S.N. Ganguly, G. Chakraborthy, Tetrahedron Lett. 45
ln fðM ꢀ X
A
Þ=Mð1 ꢀ X
A
Þg ¼ k
1
C
A0 ðM ꢀ 1Þt:
(
2004) 8351.
Thus, a plot of ln{(M ꢀ X
A
)/M(1 ꢀ X
A
)} versus t was made at dif-
[
[
33] P.R. Singh, D.U. Singh, S.D. Samant, Synlett 11 (2004) 1909.
34] E. Knoevenagel, Chem. Ber. 29 (1896) 172.
ferent temperatures to get an excellent fit, thereby supporting the
model (Fig. 16). This is an overall second-order reaction. The values
[35] E. Knoevenagel, Ber. Deutsch. Chem. Ges. 37 (1904) 446.

1
10
G.D. Yadav et al. / Journal of Catalysis 292 (2012) 99–110
[
36] A. Shockravi, H. Sharghi, H. Valizadeh, M.M. Heravi, Relat. Elem. 177 (2002)
555.
[46] R.L. Shriner, Org. React. 1 (1942) 1.
[47] M.R. Saidi, K. Bigdeli, J. Chem. Res. (1998) 800.
2
[
[
[
[
[
[
[
[
[
37] A. Song, X. Wang, K.S. Lam, Terahedron Lett. 44 (2003) 1755.
38] N. Cairns, L.M. Harwood, D.P. Astles, J. Chem. Soc. Perkin Trans. 1 (1994) 3101.
39] W.H. Perkin, W. Henry Sr., J. Chem. Soc. 28 (1875) 10.
40] W.H. Perkin, J. Chem. Soc. 31 (1887) 388.
41] J.R. Johnson, Org. React. 1 (1942) 210.
42] A. Maercker, Org. Synth. 14 (1934) 270.
43] G. Wittig, W. Hagg, Chem. Ber. 88 (1955) 1654.
44] I. Yavari, R. Hekmat-shoar, A. Zonouzi, Tetrahedron Lett. 39 (1998) 2391.
45] A. Shockravi, H. Valizadeh, M.M. Heravi, H.A. Ghadim, J. Chem. Res. (2003) 718.
[48] V. Singh, J. Singh, K.P. Kaur, G.L. Kad, J. Chem. Res. (1997) 58.
[49] Russell, J.R. Frye, Org. Synth. 21 (1941) 22.
[50] F.W. Canter, F.H. Curd, A. Robertson, J. Chem. Soc. (1931) 1255.
[51] L.L. Woods, J. Sapp, J. Org. Chem. 27 (1962) 3703.
[52] A.K. Das Gupta, R.M. Chatterje, K.R. Das, B. Green, J. Chem. Soc. C (1969) 29.
[53] G.D. Yadav, N.S. Ajgaonkar, Indian Patent Appl. 16/MUM/2011, 2011.
[54] A. Corma, V. Fornès, M.I. Juan-Rajadell, J.M. López Nieto, Appl. Catal. 116
(1994) 151–163.