Selective synthesis of natural benzaldehyde by hydrolysis of cinnamaldehyde using novel hydrotalcite catalyst

Article abstract of DOI:10.1016/j.cattod.2012.04.052

A novel Al-Mg hydrotalcite catalyst was synthesized by using combustion synthesis with glycerol as fuel. It was fully characterized. It was used in the hydrolysis of cinnamaldehyde to produce natural benzaldehyde. This is the first report of using a heter

Full text of DOI:10.1016/j.cattod.2012.04.052

Catalysis Today 207 (2013) 162–169
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Catalysis Today
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Selective synthesis of natural benzaldehyde by hydrolysis of cinnamaldehyde
using novel hydrotalcite catalyst
∗
Ganapati D. Yadav , Godfree P. Fernandes
Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel Al–Mg hydrotalcite catalyst was synthesized by using combustion synthesis with glycerol as
fuel. It was fully characterized. It was used in the hydrolysis of cinnamaldehyde to produce natural
benzaldehyde. This is the first report of using a heterogeneous hydrotalcite for making natural benzalde-
hyde. The effects of different parameters on rate of hydrolysis were studied systematically to establish
the kinetics of reaction. The reaction follows pseudo first order kinetics at a fixed catalyst loading with
apparent activation energy of 10.00 kcal/mol. The reaction is intrinsically kinetically controlled. The max-
imum conversion obtained at optimum conditions was 70% in 4 h with 100% selectivity towards natural
benzaldehyde. The catalyst can be reused several times without loss of activity.
Received 14 January 2012
Received in revised form 24 April 2012
Accepted 25 April 2012
Available online 2 June 2012
Keywords:
Retro-aldol condensation
Natural benzaldehyde
Cinnamaldehyde
Kinetics
Both the catalyst synthesis and application in retro-aldol reaction are novel aspects of the current work.
Combustion synthesis
Hydrotalcite
© 2012 Elsevier B.V. All rights reserved.
1
. Introduction
Heterogeneous catalysis is one of the fundamental pillars of
essence. Benzaldehyde is an important precursor in perfumery
industry with numerous applications in pharmaceuticals industries
[13].
Alkaline hydrolysis of cinnamaldehyde using ␤-cyclodextrin
green chemistry. The design and applications of new catalysts and
catalytic systems are simultaneously achieving the dual goal of
environmental and economic benefit. Catalysis by solid acids is very
common and several solid acids have been extensively studied as
prospective catalysts for industrial processes [1–5]. However, in
contrast with solid acids, comparatively a few efforts have gone into
studying solid bases as industrial catalysts [1,6–9]. Base catalyzed
reactions include alkylation, isomerization, Michael addition, aldol,
Knoevenagel and Claisen-Schmidt condensations, which are used
for the production of bulk chemicals, fine chemicals, pharmaceu-
ticals, perfumes and flavors. More than 1.5 million tonnes of bulk
chemicals are produced annually via processes catalyzed by alka-
gives retro-aldol condensation as well as aldol condensation prod-
uct; hence selectivity to benzaldehyde decreases [14]. The only
reported method for selective hydrolysis is the use of near-critical
water as the solvent to facilitate the hydrolysis because the near-
critical water can dissolve both organic and inorganic materials.
◦
Nevertheless, the method requires high temperature (280 C) and
high pressure (15 MPa), which are unfavorable to preserve the
natural essence of benzaldehyde [15,16]. Benzaldehyde has been
prepared by oxidation reaction using different techniques among
others by us [17–20]. However, there are no such studies using
water as a reagent. The hydrolysis of cinnamaldehyde with water
followed by retro-aldol condensation is very attractive to generate
natural benzaldehyde. The current work is an effort in that direction
using heterogeneous catalysis.
There are several methods for preparing basic heterogeneous
hydrotalcite catalysts including co-precipitation [21], sol–gel [22],
decomposition of nitrates, template assisted synthesis, etc. These
methods involve a number of processes to get the final cat-
alyst and are time consuming and require high amounts of
water. So several different methods have been suggested for the
metal or metal mixed oxide synthesis such the ceramic method
lies such as NaOH, KOH and Ca(OH) . After the reaction, the alkaline
2
medium is neutralized with acids, which contributes to ∼30% of the
product cost, resulting from product separation, purification and
waste-water treatment [6–12].
The use of heterogeneous base catalyst is very common in
aldol condensation but retro-aldol condensation reactions are very
uncommon. One of the examples is the retro-aldol condensation
reaction of cinnamaldehyde to produce benzaldehyde of natural
[
23,24], mechano-chemical synthesis [25,26], thermal decompo-
∗ Corresponding author. Tel.: +91 22 3361 1001; fax: +91 22 3361 1002/1020.
E-mail addresses: gd.yadav@ictmumbai.edu.in, gdyadav@yahoo.com
G.D. Yadav).
sition of complex combinations [27] and co-precipitation [28]. In
recent years, combustion synthesis has emerged as a powerful
(
0
920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2012.04.052

G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
163
reagent (A.R.) grade. These were used as received without any
further purification.
Nomenclature
A
B
CA
CA0
reactant species A, cinnamaldehyde
reactant species B, water
2
.2. Catalyst preparation
3
concentration of A, cinnamaldehyde (mol/cm )
initial concentration of A in bulk liquid phase
In a typical combustion synthesis method, Mg–Al–O mixed
oxide catalyst was prepared by dissolving Mg(NO ) ·6H O
3
2
2
(
mol/cm3)
(
0.048 mol) and Al (NO ) ·9H O (0.016 mol), with glycerol
3
3
2
C
AS1
adsorption concentration of A on active site S1
(0.051 mol) as fuel in minimum amount of water. The ratio of Al
3
CB
CB0
concentration of B (mol/cm )
◦
and Mg nitrate was 1:3. The resulting mixture was heated at 80 C
in crucible to remove excess water. The thick paste so obtained was
then introduced into a preheated muffle furnace at 500 C which
led to spontaneous combustion. The voluminous solid material was
initial concentration of B in bulk liquid phase
3
(
mol/cm )
◦
C
BS1
concentration of B on active sites (mol/g)
3
CE
CES1
concentration of E, benzaldehyde (mol/cm )
concentration of E on active sites of type S1 (mol/g)
concentration of vacant sites of type S1 (mol/g)
concentration of vacant sites of type S2 (mol/g)
◦
calcined at 650 C for 3 h.
C
S1
2.3. Catalyst characterization
CS2
CT1
CT2
CW
total concentration of vacant sites of type S (mol/g)
1
Mg–Al–O mixed oxide was characterized by Scanning Elec-
tron Micrography (SEM) and Energy Dispersive X-ray Spectroscopy
total concentration of vacant sites of type S (mol/g)
2
3
concentration of W, acetaldehyde (mol/cm )
(
EDXS) (JEOL JSM 6380LA Analytical scanning Microscope) using
a 10 kV voltage at a counting rate 519 cps and energy range of
–20 keV. The surface area, pore volume and pore size distribu-
tion were measured by nitrogen BET by using Micromeritics ASAP
020 instrument. Basic and acidic site densities were measured
C
WS2
concentration of W on active sites of type S (mol/g)
2
E
KA
KB
KE
KW
M
product species E benzaldehyde
adsorption equilibrium constant for A (cm mol
adsorption equilibrium constant for B (cm mol
adsorption equilibrium constant for E (cm mol
0
3
−1
−1
−1
−1
)
)
)
3
2
3
by temperature programmed desorption of CO2 and NH , respec-
3
3
adsorption equilibrium constant for W (cm mol
)
tively. Powder X-ray diffraction (XRD) patterns were obtained using
molar ratio of CB /C
rate of reaction(mol cm min )
0
A0
Bruker AXS diffractometer D8 Cu-K␣ radiation (ꢀ = 1.540562). Sam-
−3
−1
−
W
w
XA
t
rA
◦
ples were step scanned from 10.0 to 99.9 in a stepping time of
product species W acetaldehyde
1
7.7 s.
3
catalyst loading (g/cm )
fractional conversion of A
time (min)
2.4. Reaction procedure of retro-aldol condensation
The retro-aldol condensation reaction was carried out in an
autoclave of 100 cm3 capacity (Amar equipments Pvt. Ltd., Mum-
◦
alternative for material synthesis [29–35]. This method is repro-
ducible, less time consuming and does not involve multi-step
synthesis. It produces fine nanoscale metal oxides with high sur-
face area and mesoporosity which makes it a vital tool to synthesize
a tailor made catalyst [36]. Combustion synthesis approach com-
bined with generation of catalytic sites can be used to impose better
activity and shape selectivity. The combustion synthesis method
explores an exothermic, generally very fast and self-sustained
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. Combustion synthesis can be used to prepare cata-
lysts in less number of steps and the particle size and pore diameter
can be tailored according to application for which it is to be used
bai). It was equipped with a 45 four blade-pitched turbine
impeller, temperature controller, pressure indicator and speed reg-
ulator. Predetermined quantities of reactants and the catalyst were
charged into the autoclave. The reaction mass was heated to 130 C
and agitation started after withdrawing an initial sample. In a typ-
ical experiment 0.006 mol cinnamaldehyde and 0.555 mol water
◦
3
(10 cm ) were charged in the autoclave. The total volume of reac-
3
tion mixture was made up to 50 cm with methanol as solvent. The
3
catalyst loading was taken as 0.005 g/cm of liquid volume. The
temperature was maintained at 130 C and the speed of agitation
at 1000 rpm. The conversion was calculated based on the limiting
reactant cinnamaldehyde.
Samples were withdrawn periodically and the progress of reac-
tion monitored by HPLC (Knauer) using Reversed Phase C-18
column (SS) with Plurospher 100-5 Packing having dimension,
5 ␮m, 250 mm × 4 mm and UV detector (K-2501). A mobile phase
of acetonitrile:water (1:1, v/v with 0.1% orthrophosphoric acid)
◦
[
37].
The current work is concerned with a novel synthetic method
3
was used at a flow rate of 1.0 cm /min. The detection was done
of preparing basic hydrotalcite catalyst by combustion synthe-
sis, its characterization and application for the preparation of
natural benzaldehyde from cinnamaldehyde. Both the catalyst
synthesis and its applications are novel. A kinetic model is also
presented.
at 253 nm wavelength. The product was confirmed by standard
benzaldehyde compound.
3. Results and discussion
3
3
.1. Catalyst characterization
2
. Experimental
.1.1. Scanning Electron Microscopy (SEM) and Energy Dispersive
2.1. Chemicals
X-ray Spectroscopy (EDXS)
Two SEM images of the Al–Mg oxide at different magnifications
are shown in Fig. 1(a) and (b). The average particle size is in the
range of 50–100 ␮m. As is generally observed in the case of mate-
rials synthesized by combustion method, these catalytic samples
show particles of irregular morphology, which are fairly uniform in
Cinnamaldehyde, methanol, magnesium nitrate hex-
ahydrate (Mg(NO ) ·6H O), aluminum nitrate nonahydrate
3
2
2
(
Al(NO ) ·9H O) and glycerol were obtained from M/s s.d. Fine
3
3
2
Chemicals Pvt. Ltd., Mumbai, India. All chemicals were of analytical

1
64
G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
Fig. 1. SEM images of Al–Mg oxide. Magnification (a) 200× and (b) 500×.
Fig. 2. (a) N2 adsorption/desorption isotherm at 77 K. (b) Pore diameter of Mg–Al
oxide.
size. EDXS was done to confirm complete composition of aluminum
and magnesium which was maintained constant (Mg/Al ratio of 3)
in synthesized catalyst. The sample composition is given in Table 1.
indicates the presence of strong basic sites (Fig. 3(a)). Single broad
◦
3
.1.2. BET surface area and pore size analysis
The nitrogen adsorption–desorption isotherm was of type IV or
peaks obtained at 154 C indicate the presence of intermediate and
strong acidic site which may be due to H+ ions associated with
V with small plateau at high relative pressure, characteristic of a
surface hydroxyl groups (Fig. 3(b)).
mesoporous material. Characteristic nitrogen BET surface area is
2
1
27 m /g. As observed from BJH adsorption pore size distribution,
3
.1.4. X-ray powder diffraction
Fig. 4 shows XRD pattern for Mg–Al oxide ratio of 3:1. The
a major part of the surface area is contributed by pores with a diam-
eter characteristic of pores ranging from 5 to 20 nm which signify
mesoporous character (Fig. 2(a) and (b)). The catalyst is essentially
mesoporous.
◦
◦
characteristic reflections observed at 2ꢁ ≈ 43 and 62 correspond
to mixed Mg–Al oxide and especially MgO (PC-PDF card number
0
2-1207). Mg–Al oxide shows reflection (0 0 3), (0 0 6) and (0 1 2)
for 2ꢁ values of 11.441, 23.168 and 34.138, respectively (PC-PDF
card number 35-0965), indicating layered crystalline structure. The
broadness of peaks indicates the nano-crystalline nature of Al–Mg
oxide. The particle size of the nano-Al–Mg oxide powder was
estimated using Scherrer’s formula (Table 2) [38]. The crystalline
size was obtained as 8.9 nm.
3
.1.3. Temperature programmed desorption (TPD)
Temperature programmed desorption using CO2 and NH3 was
used to measure total basic and acidic nature of sites generated
on the surface of the catalyst. Well defined peaks obtained at
1
◦
52 C show the presence of weak and medium basic sites due
◦
to physisorbed surface basic oxygen atoms and the peak at 505 C
Table 1
Table 2
X-ray analytical data.
Composition of element in Al–Mg oxide by EDXS.
Element (w/w)
Composition (%)
Sample
Method of preparation
Combustion
2ꢁ
FWHM
0.994
Crystal size
8.49 nm
Magnesium
Aluminum
76.44
23.56
◦
Mg–Al–O
43.146

G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
165
3.2. Catalyst activity
Scheme 1 shows the hydrolysis of cinnamaldehyde to produce
benzaldehyde and acetaldehyde.
In this reaction, 1 mol of water reacts with cinnamaldehyde
to produce benzaldehyde and acetaldehyde. Since the reaction
was conducted in an autoclave, there was autogenous pressure.
A possible mechanism based on the synergistic cooperation of
the weak acid sites with the basic sites, adjacent to one another
on hydrotalcite catalyst, is proposed (Scheme 2). Initially, cin-
namaldehyde is exclusively adsorbed on the basic site adjacent to
hydrated acidic sites on the surface of the catalyst and the carbo-
cation of cinnamaldehyde is formed by abstraction of proton from
water molecule on acidic site. Nucleophilic hydroxyl group which
is highly activated by the presence of Lewis acidic site attacks the
␤-carbon atom of ␣–␤ unsaturated carbocation to give hydrated
molecule. Finally deprotonation of hydrated molecule leads to
carbon carbon bond cleavage and desorption of benzaldehyde and
abstraction of proton to give acetaldehyde.
3
.2.1. Effect of speed of agitation
The effect of speed of agitation was studied at 130 C for a cat-
◦
alyst loading of 0.005 g/cm3 loading (Fig. 5). It was found that in
the range of stirrer speeds 800–1200 rpm, there was no effect of
the speed of agitation on the rates of reaction. Both conversion and
selectivity remained constant after 1000 rpm. Selectivity to ben-
zaldehyde was 100%. In the range of stirrer speeds employed, the
reaction was free from external mass transfer resistance. Hence,
H
O
C
H
O
C
Fig. 3. (a) TPD of CO2 thermogram for Mg–Al oxide. (b) TPD of NH3 thermogram for
Mg–Al oxide.
H
O
+
H O Hydrotalcite
2
o
1
30 C
H 3C
+
C
Cinnamaldehyde Water
Benzaldehyde
Acetaldehyde
Scheme 1. Overall reaction scheme to produce natural benzaldehyde.
1
00
8
6
4
2
0
0
0
0
0
0
1
2
3
4
5
Time (h)
Fig. 5. Effect of speed of agitation on conversion. Al–Mg-oxide catalyst, cata-
Fig. 4. XRD of Mg–Al oxide.
3
◦
lyst loading: 0.005 g/cm , temperature: 130 C, cinnamaldehyde: 0.006 mol, water:
.555 mol, 800 rpm ( ), 1000 rpm ( ), 1200 rpm ( ).
0

1
66
G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
Scheme 2. Catalytic cycle for the retro-aldol condensation over hydrotalcite (S1 – acid sites, S2 – base sites).
all further experiments were carried out at 1000 rpm. A theoretical
analysis of the assessment of external mass transfer of this the-
ory for general slurry reactions was also done as given elsewhere
moles of water (Fig. 8). Thus, all the subsequent reactions were car-
ried out with a 1:92 mole ratio. This clearly indicated an increase
in overall rate of hydrolysis of cinnamaldehyde with an increase in
water concentration.
[
39–42].
3.2.2. Effect of catalyst loading
In the absence of external mass transfer resistance, the rate of
reaction is directly proportional to catalyst loading. The catalyst
loading was varied over a range of 0.003–0.009 g/cm3 on the basis
of total volume of reaction mixture (Fig. 6). The conversion of cin-
namaldehyde increases with increasing catalyst loading, which is
obviously due to the proportional increase in the number of active
100
80
60
40
20
0
3
sites. However, beyond a catalyst loading of 0.005 g/cm , there was
no significant increase in the conversion and also there was no
effect on selectivity of benzaldehyde. Hence all further experiments
3
were carried out at this catalyst 0.005 g/cm .
The rate of reaction (−r = C (dX /dt)) is linear in catalyst load-
A
A
A
0
ing (w). For a fixed C , the rate can be plotted as dX /dt against w
A
A
0
(
Fig. 7). Thus the reaction rate is directly proportional to the number
of catalytic sites available.
3.2.3. Effect of mole ratio
The mole ratio of cinnamaldehyde to water was varied with
methanol as a solvent where the liquid-phase volume was kept
3
0
1
2
3
4
5
constant at 50 cm . The amount of water in methanol solvent was
Time (h)
changed from 1:46 to 1:138 in order to assess its effect on the rate
and selectivity. In this range the liquid phase was homogeneous. A
decrease in the solubility of cinnamaldehyde was found when mole
ratio of cinnamaldehyde to water was kept beyond 1:138. The over-
all rate of reaction of benzaldehyde increased with an increase in
Fig. 6. Effect of catalyst loading on conversion. Al–Mg-oxide catalyst, catalyst
3
◦
loading: 0.005 g/cm , temperature: 130 C, cinnamaldehyde: 0.006 mol, water:
3
), 0.007 g/cm3
0
(
.555 mol, speed of agitation: 1000 rpm, total volume: 50 cm (
3
3
), 0.003 g/cm
(
), 0.009 g/cm
(
).

G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
167
0
0
0
0
0
0
0
.30
.25
.20
.15
.10
.05
.00
100
80
60
40
20
0
0
1
2
3
4
5
0
0.002
0.004
0.006
0.008
Time (h)
w (g/cm3)
Fig. 9. Effect of temperature on conversion of cinnamaldehyde. Al–Mg-oxide cat-
alyst, catalyst loading: 0.005 g/cm , cinnamaldehyde: 0.006 mol, water: 0.555 mol,
◦
3
Fig. 7. Plot of initial rate versus catalyst loading. Temperature: 130 C;
Al–Mg-oxide catalyst: cinnamaldehyde: 0.006 mol, water: 0.555 mol, speed of agi-
tation:1000 rpm.
3
◦
◦
◦
speed of agitation: 1000 rpm, total volume: 50 cm , 120 C ( ), 130 C ( ), 140
C
◦
(
), 150 C ( ).
3
.2.4. Effect of temperature
The effect of temperature was studied from 120 to 150 C. It
was stable and retained its activity. In subsequent experiments, the
same procedure was followed. The catalyst was stable and reusable
four times without any loss of activity. There was no change in the
selectivity.
◦
was found that with an increase in temperature the rate of reac-
tion is increased (Fig. 9). This also suggested that the reaction was
intrinsically kinetically controlled.
3
.2.6. Development of kinetic model
In the absence of both external mass transfer and intra-particle
3
.2.5. Reusability of catalyst
After the reaction, the catalyst was filtered and then refluxed
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 (cinnamaldehyde) and B (water)
takes place on two adjacent vacant surfaces (S , S ) according to the
Langmuir–Hinshelwood–Hougen–Watson (LWHW) mechanism to
produce E (Benzaldehyde) and W (acetaldehyde)
with 10 cm methanol and washed with 15 cm3 with methanol in
order to remove any adsorbed material from catalyst surface and
pores and then dried at 120 C. It was also calcined at 650 C for 3 h
and then cooled to room temperature and weighed. On an average,
there was attrition of particles during intense agitation and some
loss of catalyst during filtration. This loss varied between 10% and
3
◦
◦
1
2
Adsorption:
2
0% on an average. The lost catalyst was made up with fresh catalyst
Adsorption of cinnamaldehyde (A) on a vacant site S1 is given
by:
and the activity was tested. Table 3 demonstrates that the catalyst
K
A
1
00
A + S1←→ AS1
(1)
Adsorption of water (B) on a vacant site S2 is given by:
80
60
40
20
0
KB
B + S ←→ BS
(2)
2
2
Surface reaction:
Surface reaction of AS1 and BS2 in the vicinity of an active site,
leading to the formation of ES and WS on the active:
K
2
AS1 + BS2←→ ES1 + WS2
(3)
Table 3
3
Reusability of catalyst. Catalyst loading: 0.005 g/cm ; Al–Mg-oxide catalyst: tem-
perature 140 C; cinnamaldehyde (0.006 mol), 20% Aq. methanol, 1000 rpm, total
volume 50 cm and time 4 h.
◦
3
Run no.
Conversion of cinnamaldehyde
in percentage
Selectivity of benzaldehyde
in percentage
0
.0
1.0
2.0
3.0
4.0
5.0
Time (h)
Fresh
70.78
70.33
71.43
70.21
96.57
96.17
95.23
95.00
First use
Second use
Third use
Fig. 8. Effect of mole ratio of water in methanol. Speed of agitation: 1000 rpm, tem-
perature: 130 C, cinnamaldehyde: 0.006 mol, catalyst loading: 0.005 g/cm , total
volume: 50 cm , 1:138 ( ), 1:92 ( ), 1:46 ( ).
◦
3
3

1
68
G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
Desorption:
Desorption of benzaldehyde (ES ) and acetaldehyde (WS ) is
1.6
1
2
y = 0.353x
R² = 0.946
given by:
1.4
1.2
1
1
/KE
ES ←→ E + S
(4)
(5)
1
1
1
/KW
WS ←→ W + S
2
2
y = 0.239x
R² = 0.996
The total concentration of the sites, Ct expressed as:
0
.8
CT1 = CS1 + CAS1 + CES1
(6a)
(6b)
(6c)
(7a)
(7b)
CT2 = CS2 + CBS2 + CWS2
0.6
CT = CT1 + CT2
y = 0.174x
R² = 0.946
0
0
.4
.2
0
CT1 = CS1 + K C C + KECECS1
A
A
S1
CT2 = CS1 + KBCBCS2 + KWCWCS2
When the adsorption and desorption steps are assumed to be in
equilibrium, the concentration of vacant sites can be written as:
0
1
2
3
4
5
CT1
Time (h)
CS1 = (
CS2 = (
(8a)
(8b)
1 + K CA + KECE)
A
Fig. 10. Kinetic plots for various temperatures. Al–Mg oxide catalyst, catalyst load-
3
ing: 0.005 g/cm , cinnamaldehyde: 0.006 mol, water: 0.555 mol, speed of agitation:
CT2
◦
◦
◦
1000 rpm, 120 C ( ), 130 C ( ), 140 C ( ).
1 + KBCB + KWCW)
If the surface reaction controls the rate of reaction, then the rate
of reaction of A is given by
8
8
.4
.2
8
dCA
−
rA = − dt = k CASCBS − k2
ꢀ
CESCWS
(9)
2
dCA
dt
k2(KAKBCACB − (KEKWCECW/K2))CT CT
1
2
−
=
(10)
(1 + K C + KECE)(1 + KBCB + KWCW)
A
A
When the reaction is far away from equilibrium:
dCA
k2CT CT KAKBCACB
1
2
−
−
=
=
ꢀ
ꢀ
(11)
(12)
7.8
dt
(1 +
K C )(1 +
K C )
j j
i
i
dCA
dt
kR wKBCACB
2
ꢀ
ꢀ
7
.6
(1 +
K C )(1 +
K C )
j j
i
i
where kR w = k CT CT K KB where, w is catalyst loading. If the
2
2
1
2
A
adsorption constants are small, then the above equation reduces
to:
7.4
7.2
dCA
−
= kR wKBC CB
(13)
2
A
dt
0
.00235
0.00240
0.00245
0.00250
0.00255
0.00260
Let CB /C = M be the molar ratio of water to cinnamaldehyde
0
A0
/T K-1
1
at time t = 0. Then Eq. (13) can be written in terms of fractional
conversion as:
Fig. 11. Arrhenius plot.
dXA
=
kR wC (1 − X )(M − X ) = k C (1 − X )(M − X )
(14)
2
A0
A
A
1
A0
A
A
dt
at different temperatures were used to make the Arrhenius plot
(Fig. 11).
This upon integration leads to:
The apparent activation energy was found to be 10.00 kcal/mol
which conformed that the reaction rate was controlled by intrinsic
kinetics at surface of catalyst.
(
M − X )
A
ln
= k CA0 (M − 1)t
(15)
1
M(1 − X )
A
When M ꢁ 1, then the above Eq. (13) as a pseudo-first order equa-
tion:
4. Conclusion
−
ln(1 − X ) = k t
(16)
(17)
A
1
A novel Al–Mg hydrotalcite catalyst was synthesized by using
where
combustion synthesis with glycerol as fuel. It was fully char-
acterized. It was used in the hydrolysis of cinnamaldehyde to
produce natural benzaldehyde. This is the first report of using a
heterogeneous hydrotalcite for making natural benzaldehyde. The
effects of various parameters on rate of hydrolysis were studied sys-
tematically to establish the kinetics of reaction. The reaction rate is
intrinsically kinetically controlled. The reaction follows pseudo first
order kinetics at a fixed catalyst loading with apparent activation
k1 = kR wKBCB0
2
A plot of − ln(1 − X ) versus time was made for at various tem-
A
peratures (Fig. 10). These are straight lines passing through origin,
which confirms the pseudo-first order behavior of the reaction.
From the R values it can be seen that the pseudo-first order model
2
describes the experimental data very well. The slopes of these lines

G.D. Yadav, G.P. Fernandes / Catalysis Today 207 (2013) 162–169
169
energy of 10.00 kcal/mol. The maximum conversion obtained at
optimum conditions was 70% in 4 h with 100% selectivity towards
natural benzaldehyde. The catalyst can be reused several times.
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