Synthesis of nano-sized protonic acid catalyst and initial kinetic study of esterification reaction of methanol with acetic acid

Article abstract of DOI:10.14233/ajchem.2014.16290

Nano-sized protonic acid catalysts were synthesized and their catalytic properties in the esterification reaction over methanol whith acetic acid were evaluated. The surface chemistry of the synthesized catalysts was investigated using solid-state magic-angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscope and elemental analysis techniques (CHNS-O). The results showed that the appropriate increment of sulfonation temperature can facilitate the attachment of -SO₃H groups and also benefit for the enhancement of acetic acid conversion. The initial kinetic study of esterification reaction of methanol and acetic acid, which was catalyzed by synthesized nano-sized protonic acid catalysts, indicates that only one active site was involved in the surface reaction and thus the initial reaction mechanistic paths under our reaction conditions were proposed.

Full text of DOI:10.14233/ajchem.2014.16290

Asian Journal of Chemistry; Vol. 26, No. 16 (2014), 4988-4994
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16290
Synthesis of Nano-Sized Protonic Acid Catalyst and Initial Kinetic
Study of Esterification Reaction of Methanol with Acetic Acid
1
1
1
2
1
1
1,*
JIANJUN ZHU , QIUQING CUI , JIANGPING PENG , LI LI ZHANG , ZHONGQING JIANG , LIJUAN LUO and XIAONING TIAN
1
2
Department of Chemistry Engineering, Ningbo University of Technology, Ningbo 315016, P.R. China
Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117576, Singapore
Corresponding author: Tel/Fax: +86 574 87081204; E-mail: boxertxn@hotmail.com
Received: 5 September 2013; Accepted: 30 January 2014; Published online: 28 July 2014;
*
AJC-15617
Nano-sized protonic acid catalysts were synthesized and their catalytic properties in the esterification reaction over methanol whith acetic
acid were evaluated. The surface chemistry of the synthesized catalysts was investigated using solid-state magic-angle spinning nuclear
magnetic resonance, X-ray photoelectron spectroscope and elemental analysis techniques (CHNS-O). The results showed that the appropriate
3
increment of sulfonation temperature can facilitate the attachment of -SO H groups and also benefit for the enhancement of acetic acid
conversion. The initial kinetic study of esterification reaction of methanol and acetic acid, which was catalyzed by synthesized nano-sized
protonic acid catalysts, indicates that only one active site was involved in the surface reaction and thus the initial reaction mechanistic
paths under our reaction conditions were proposed.
Keywords: Nano-sized protonic acid catalyst, Polystyrene nanospheres, Esterification reaction, Initial kinetic study.
15
in our previous research work . Moreover the relationship
between material structure and attached acid groups was
investigated. Through the design of material structure, resultant
acid catalyst can show different catalytic properties.
INTRODUCTION
Organic esters are important fine chemicals widely used
in the manufacturing of pharmaceuticals, flavors and
plasticizers, etc. They are also used as emulsifiers in the food
and cosmetic industries. The most-used way for ester synthesis
is direct esterification of carboxylic acids with alcohols in the
presence of strong mineral acid, such as sulfuric acid. However,
the use of liquid sulfuric acid leads to inevitable problems,
such as safety and difficulty of separation from the reaction
In this work, continuing with our previous research work,
nano-sized protonic acid catalysts were synthesized. It was
observed that synthesized nano-sized protonic acid catalysts
show better acid conversion capability than commerical solid
acid catalyst. Moreover, the catalysts prepared with a sulfona-
tion temperature of 80 ºC exhibited the highest acid conversion
and best recycleability. The initial kinetic study of the esteri-
fication reaction over methanol with acetic acid catalyzed by
prepared strong nano-sized protonic acid catalyst was investi-
gated and the result showed that only one active site was
involved in the surface reaction.
1
-5
medium. Therefore, solid acid catalysts based on silicas ,
11,12
6
-10
organic/inorganic solid hybrids and carbons have been
widely explored over the past decade.
3
Introducing sulfonic acid group (-SO H) on organic-based
materials is more desirable because the organic-based materials
in general exhibit hydrophobic features, thus favorable for
13
hydrocarbon conversion reactions . Esterification involved
carboxylic acids with alcohols was carried out by using sulfo-
nated alkylated polystyrene as solid acid catalyst. And the
highly hydrophobic nature of the resultant polymer based
sulfonic acid catalyst played a very important role for activity
EXPERIMENTAL
Sulfuric acid (98 %, Merck), styrene (99 %, Alfa Aesar),
divinylbenzene (DVB) (80 % mixture of isomers, Aldrich),
potassium presulfate (KPS) (Aldrich). In this work, nano-sized
crosslinking polystyrene spheres (NCPSs) were synthesized
using the emulsifier-free emulsion polymerization method.
The nano-sized protonic acid catalyst was prepared through
sulfonation reaction of nano-sized crosslinking polystyrene
spheres.
1
4
in the esterification reaction . However, the stability and
recycleability of sulfonated polystyrene should be further
evaluated for practical application and the related research
work was limited. Sulfonated polystyrene nanospheres, which
show excellent stability and recycleability, have been reported

Vol. 26, No. 16 (2014)
Synthesis of Nano-Sized Protonic Acid Catalyst 4989
Synthesis of nano-sized crosslinking polystyrene
spheres: The synthesis of nano-sized cross linking polystyrene
spheres was conducted following the method described
16
previously . Styrene monomer (21.4 mL) and 0.8 mL divinyl-
benzene were combined with 200 mL of dionized water. The
mixture was stirred at 60 ºC under the protection of nitrogen
for 1 h. Then, 0.14 g potassium presulfate was dissolved in
50 mL of dionized water and then was added to the mixture
under stirring at 60 ºC for 30 h. The final solids were collected
by centrifuge and dried at 60 ºC in an oven. The diameter of
prepared nano-sized crosslinking polystyrene spheres is shown
in Table-1.
TABLE 1
PREPARATION PARAMETERS AND
DIAMETERS OF RESULTANT NANO-SIZED SPHERES
Styrene Divinyl- Potassium Sulfonation
Diameter
Sample
Amount benzene persulfate temperature
(
nm)
(
g)
(mL)
0.8
(g)
(ºC)
NCPSs (0.8)
SNCPSs (40)
SNCPSs (80)
19.6
19.6
19.6
0.14
0.14
0.14
0.14
–
446
441
465
494
0.8
40
0.8
80
2
50
200
150
100
50
0
SNCPSs (100) 19.6
0.8
100
ppm
NCPSs: nano-sized crosslinking polystyrene spheres; SNCPSs:
sulfonated nano-sized scrosslinking polystyrene sphere
13
C MAS NMR spectra for (a) nano-sized crosslinking polystyrene
spheres, (b) sulfonated nano-sized crosslinking polystyrene spheres
Fig. 1.
(80) (*spinning side bands)
Synthesis of nano-sized protonic acid catalyst: About
g of nano-sized crosslinking polystyrene spheres were combined
3
spheres and nano-sized protonic acid catalyst (80). The reso-
nances at 41 and 46 ppm for nano-sized crosslinking poly-
2 4
with 60 mL of concentrated H SO at a given temperature.
After 24 h, the sample was cooled down to room temperature.
The solids were washed with deionized water repeatedly to
ensure no sulfate ions were detectable in the filtrate. The resul-
tant nano-sized protonic acid catalysts were donated as nano-
sized protonic acid catalyst (x), where x stands for sulfonation
temperature. The diameters of prepared nano-sized protonic
acid catalyst were exhibited in Table-1.
2
styrene spheres were assigned to methylene (-CH -) and
17,18
methane (-CH-) carbon, respectively . At the same time,
the resonances at 146 and 128 ppm were ascribed to non-proto-
1
nated and protonated aromatic carbons . After sulfonation
7,18
13
reaction an additional C NMR signal was found out with
chemical shift at about 138 ppm, which was attributed to the
1
7,18
sulfonated aromatic carbon , indicating the attachment of
SO H groups.
The chemical shifts assigned to -CH
Detection method: Solid-state magic-angle spinning
nuclear magnetic resonance (MAS-NMR) spectra were collec-
ted on a Bruker DRX400 MHz FT-NMR spectrometer. X-ray
photoelectron spectroscopy (XPS) spectra were recorded on
an AXIS HIS 165 spectrometer (Kratos Analytical) with a
monochromatizedAlKα X-ray source. The elemental compo-
sitions of the samples were detected using a CHNS-O analyzer
-
3
2
- and -CH- carbon
for nano-sized protonic acid catalyst (80) were similar com-
pared to that of nano-sized crosslinking polystyrene spheres,
which indicated that the local structure of prepared nano-sized
crosslinking polystyrene spheres was only slightly influenced
by the presence of the sulfonic acid group, indicating the well
maintenance of the polymer backbone after sulfonation process
for the nano-sized protonic acid catalyst.
(FLASH EA 1112 series, Thermo electron corporation). The
catalytic performance of prepared nano-sized protonic acid
catalyst was evaluated using the esterification reaction between
methanol and acetic acid. The reaction was carried out in a
round bottom flask immersed in a silicon oil bath at 55 ºC. 1
mol of methanol, 0.1 mol of acetic acid and 0.2 g of catalyst
were added into the flask. Quantitative analysis was carried
out after 5 h of reaction using a gas chromatograph (HP 6890
series GC) mass spectrometer (HP 5973 Mass selective detector)
with a capillary column ( HP 5MS, L = 30 m, I.D. = 0.25 mm,
film thickness = 0.25 mm). The used catalyst was collected,
washed using dionized water and dried at 60 ºC for the next
reaction run.
3
The attachment of -SO H groups onto the aromatic carbon
atoms can also be testified by XPS technique. The XPS spectra
for nano-sized protonic acid catalyst (40) and nano-sized
protonic acid catalyst (80) are shown in Fig. 2. All samples
exhibited a single S2p peak at about 168.6 ev, which is assigned
3
to the aromatic carbon atoms in connection with -SO H
11,19
groups . The S2p spectra can be deconvoluted into two peaks
with binding energies of 168.5 and 169.7 ev, which are
3
assigned to S2p3/2 and S2p1/2 of the sulfur in -SO H, respec-
18,20,21
tively
.
Sulfur content investigated by elemental analysis:
As shown in Fig. 3, the S content for the resultant samples
increased initially with the increase of sulfonation temperature
and then decreased with the continuous increment of sulfonation
RESULTS AND DISCUSSION
13
MAS NMR and XPS spectra: Fig. 1 shows the C NMR
spectra of prepared nano-sized crosslinking polystyrene-

4
990 Zhu et al.
Asian J. Chem.
temperature. Since sulfur exits only in the form of -SO
3
H, high
sulfur content indicates large amount of attached -SO H groups
3
SNCPSs(40)
and high acidity for nano-sized protonic acid catalyst. It can
be assumed that the appropriate increment of sulfonation
3
temperature can facilitate the attachment of -SO H groups onto
the nano-sized crosslinking polystyrene spheres.
Catalytic performance: It can be seen from Fig. 4 that
all nano-sized protonic acid catalyst show high acetic acid
th
conversion efficiency even after the 4 reaction run. Moreover,
the same mass of commercial strong acid catalyst Amberlyst-
1
5 was also evaluated at the same reaction conditions.
However, the conversion of acetic acid forAmberlyst-15 is 58
, which is lower than that of nano-sized protonic acid catalyst.
%
Therefore, we can conclude that the prepared nano-sized
catalysts are strong protonic acid catalysts.
174
172
170
168
166
164
Binding energy (ev)
100
SNCPSs(80)
80
60
40
20
0
SNCPSs(40) SNCPSs(60) SNCPSs(80) SNCPSs(100)
174
172
170
168
166
164
Fig. 4. Catalytic conversion of acetic acid for four reaction runs over
SNCPSs (40), SNCPSs (60), SNCPSs (80) and SNCPSs (100).
Binding energy (ev)
st
(Four columns indicate the 1 to 4 reaction run)
th
Fig. 2. S2p XPS spectra for SNCPSs (40) and SNCPSs (80)
Initial kinetic study: The initial kinetic study of the
esterification reaction over methanol with acetic acid in this
work was also investigated. Sample nano-sized protonic acid
catalyst (80) shows the best conversion efficiency and
recyclability among all the resultant catalysts. Therefore, the
esterification reaction catalysed by nano-sized protonic acid
catalyst (80) was chosen for the initial kinetic study target.
Effect of polymer swelling and stirring speed: In the
initial kinetic study process, reagents were heated to the desired
temperature before the reaction. Once the desired temperature
was reached, the esterification reaction was started upon
addition of the catalyst.
1
5
1
0
5
0
Nano-sized protonic acid catalyst (80) is a polymer based
catalyst, therefore, swelling of the polymer in polar solvent is
21
known to occur . Even slight swelling of the catalyst could
affect the catalytic activity because additional acid sites can be
exposed during swelling process, which will lead to inaccurate
kinetic measurement. In order to determine whether swelling
played a role in conversion, two sets of experiments were
carried out. First, nano-sized protonic acid catalyst (80) was
presoaked in methanol overnight before the reaction. Methanol
was used as the soaking solvent because acetic acid has much
SNCPSs
22
less capability to swell the polymeric resin than methanol .
Fig. 3. S content obtained from elemental analysis for SNCPSs

Vol. 26, No. 16 (2014)
Synthesis of Nano-Sized Protonic Acid Catalyst 4991
The esterification reaction was then initiated by charging the
acetic acid. On the other hand, another experiment was carried
out by direct addition of the catalyst without the presoaking
condition. The initial reaction rates (a particular instantaneous
rate, the rate of reaction just after the reactants are mixed is
called the initial reaction rate) obtained from the above two
experiments were listed in Table-2. It can be seen that nearly
identical reaction rates were obtained, which confirmed that
the swelling of the catalyst due to methanol had a negligible
effect on the initial reaction rate.
reactant while keeping the other in excess and measuring initial
kinetics at 55 ºC. The results are given in Table-3. The concen-
trations of both acetic acid and methanol had positive effects
on the reaction rate with increasing reactant concentration.
Using a power law approximation (1.1), the apparent reaction
orders were determined to be 0.8 for methanol and 1.0 for
acetic acid.
α
β
A0 M0
r = k C C
(1)
0
0
TABLE-3
INITIAL REACTION RATE FOR THE DETERMINATION
OF APPARENT REACTION ORDERS OF ACETIC ACID AND
METHANOL IN SNCPSs (80) CATALYZED ESTERIFICATION
AT 55 ºC WITH STIRRING RATE OF 1250 RPM
TABLE-2
INITIAL REACTION RATE BY USING CATALYST
WITH/WITHOUT SWELLING IN METHANOL
a
C (mol/L) C (mol/L) r0(mol/L*min)*100
b
c
SNCPSs (80)
a
b
c
A0
M0
C (mol/L)
A0
C (mol/L)
M0
r0(mol/L*min)*100
With swelling in
methanol overnight
Without swelling
in methanol
1
0
10
9.8800
7.8385
5.0935
3.2127
7.5152
5.2373
9.6875
1
0
0
10
10
1.0
1.1
3
.85
2.17
.36
19.23
21.74
22.73
3.03
1
1
a
b
CA0 the initial concentration of acetic acid; C the initial concent-
M0
1
1
1
5.15
5.82
4.20
c
ration of methanol; The initial reaction rate; SNCPSs: sulfonated nano-
sized crosslinking polystyrene spheres
1.90
4.26
a
b
CA0 the initial concentration of acetic acid; C the initial concen-
M0
Since the kinetic study required the reaction to be operated
at the kinetically controlled regime, the diffusion limitations
were ruled out by varying the stirring speed between 0-1250
rpm. Since the particle size of the catalyst sample nano-sized
protonic acid catalyst (80) is small (about 465 nm), it can be
dispersed in the reactant mixtures homogeneously. In addition,
it is non-porous material. Hence, the effect of particle size
and the pore diffusion was not involved. The initial reaction
rates under different stirring speed were shown in Fig. 5. It
can be seen that no obvious change was found in initial reaction
rate under different reaction stirring speed. Therefore, a stirring
speed of 1250 rpm was used in the initial rate studies to rule
out the diffusion limitation. In our experiment the catalyst was
not prepared in pellets, therefore, the investigation of the effect
of particle size on initial reaction rate was not involved.
The catalytic reaction runs were carried out under the
kinetically controlled regime with the exclusion of polymer
swelling, stirring speed and particle size effect.
c
tration of methanol; The initial reaction rate
Proposed reaction mechanism: In order to determine
whether the adsorption/desorption of acetic acid was compa-
rable to or slower than the surface reaction, experiments using
nano-sized protonic acid catalyst (80) pre-saturated with acetic
acid before initiating the reaction by charging preheated
methanol were carried out (Table-4). The results for esterifi-
cation at 55 ºC showed no improvement in the initial reaction
rate compared with the experiments using the catalyst without
pre-adsorbed acetic acid.
TABLE 4
INITIAL REACTION RATES WITH/WITHOUT
PRE-ADSORPTION IN ACETIC ACID
a
b
c
SNCPSs (80)
CA0(mol/L) CM0(mol/L) r (mol/L*min)*100
0
Pre-adsorption in acetic
acid overnight
1
0
0
10
10
7.3
8.0
Without pre-adsorption
in acetic acid
1
1
0
5
0
a
b
CA0 = Initial concentration of acetic acid; C = Initial concentration of
M0
c
methanol; Initial reaction rate.
Moreover, the adsorption of methanol is considered. It is
based on the consideration that methanol is a strong nuclephile
21
and also competes for the acid site .As mentioned in the polymer
swelling part pre-adsorbed methanol also had a negligible
effect on the initial reaction rate. Therefore, the surface reaction
should be the rate-limiting step due to the rapid reactant
adsorption/desorption equilibrium.
Two reactants were involved in the esterification reaction,
namely methanol and acetic acid. Therefore pyridine adsorbing
experiments were conducted to determine whether single active
site or dual active sites involved in the esterification reaction.
Before each run, nano-sized protonic acid catalyst (80) was
first immersed in the solvent containing methanol and a known
amount of pyridine overnight to allow a complete equilibrated
adsorption of the organic base on the acid sites of the catalyst.
0
400
800
Stirring rate (rpm)
1200
Fig. 5. Initial reaction rates versus different reaction stirring rate
Effect of reactant concentration: Apparent reaction
orders were determined by varying the concentration of one

4
992 Zhu et al.
Asian J. Chem.
OH
The reactor was heated to 55 ºC and then preheated acetic
acid was charged into the reactor to initiate the reaction. As
shown in Fig. 6, the initial reaction rates decreased linearly
with increasing amounts of pyridine, suggesting that single
active site involves in the heterogeneous reaction. Otherwise,
a non-linear figure should be obtained if dual active sites
participated in the esterification reaction.
O
OH
+
H+
1
R -OH
+
R
R
R
C
OH
OH
OH
OH+
+
O
HO
R
-H
2
O
-H
HO
+
2
OH
OH
OH+
R
R
O
R
O
O
R1
R
1
R1
R
1
Fig. 7. Mechanistic route of sulfuric acid catalyzed esterification reaction
of methanol with acetic acid
1.0
0.8
0.6
0.4
30
2
0
0
0
H SO
2
2
1
SNCPSs(80)
0.0
0.5
1.0
1.5
2.0
2.5
Cpyridine (M × 1000)
Fig. 6. Pyridine adsorbed SNCPSs (80) catalyzed esterification of methanol
with acetic acid
0
100
200
300
400
Reaction time (min)
Fig. 8. Acetic acid conversion vs. time for esterification reaction catalyzed
by H SO and SNCPSs (80) at 55 ºC
The mechanism of the esterification reaction catalyzed
by sulfuric acid (Fig. 7) shows that the oxygen on the carbo-
xylic acid is protonated, thereby activating nucleophilic attach
2
4
As we known water is a byproduct of esterification reaction
for methanol with acetic acid, which can inhibit the reaction
rate. For sulfuric acid catalyzed esterification reaction for
methanol with acetic acid the deactivating effect of water was
due to the water solvation of the protons. The loss in acid
strength of catalytic protons due to water solvation leads to a
decrease in the concentration of protonated carboxylic acid,
2
2-24
by alcohol . In our heterogeneous esterification reaction
system, it can be assumed that acetic acid is protonated first,
which is attacked by methanol. From the result of pyridine
adsorbing experiment, it can be concluded that only single
active site was involved in our heterogeneous esterification
reaction. Hence, the surface reaction should be the nucleophilic
attack of protonated acetic acid by methanol forming ester
and water. Hence, rapid reactant adsorption/desorption
equilibrium with surface reaction as the rate-limiting step is
likely the initial reaction mechanistic paths under our reaction
22
thus inhibiting the formation of esters . The sulfuric acid and
nano-sized protonic acid catalyst (80) had the similar water
deactivation profile (Fig. 9).
Based on the experimental observed kinetic data, it is
proposed that the esterification catalyzed by prepared nano-
size protonic acid catalyst proceeds via a mechanism analogous
to the homogeneous catalyzed one. By considering the initial
reaction period when reverse hydrolysis is not important, the
conditions, which were shown in eqns. 2-4.
k1
A
+
S
A
S
(2)
k-1
k2
initial set of mechanistic paths are as mentioned in eqns. 5-7:
k1
M +S
M
S
(3)
(4)
k-2
k3
A
+
S
A
S
(5)
k-1
k2
A S
+
M
Product
where A represents acetic acid, M represents methanol, S is a
vacant acid site on the solid catalyst surface A·S and M·S are
molecules adsorbed on the catalytic acid site, respectively.
Modeling kinetics: Fig. 8 shows the conversion of acetic
acid catalyzed by sulfuric acid and nano-sized protonic acid
catalyst (80) at 55 ºC, respectively. The amount of active sites
for both sulfuric acid and nano-sized protonic acid catalyst-
M +S
M S
(6)
k-2
k3
+
M
Product
(
7)
A S
Using the pseudo-steady-state approximation for the
adsorption steps (A·S and M·S) with surface reaction as the
rate limiting step, the initial reaction rate can be expressed as:
(
80) were kept to be the same. It can be seen that the homo-
k K C CM0C
S0
3
A
A0
r0 =
geneous acid catalyst shows similar acetic acid conversion as
the heterogeneous catalyst within 10 min reaction time. How-
(8)
K C + K C + 1
A
A0
M
M0
where k
the concentrations of acetic acid, methanol and the total acid
sites, respectively. KA (KA = k /k ) and KM (K = k
3
is the surface reaction constant, CA0, CM0 and CS0 are
2 4
ever, after 6 h the acetic acid conversion for H SO is higher
than that of nano-sized protonic acid catalyst (80). Both catalysts
exhibit the same trend for the whole reaction run process.
/k−2 )
2
1
−1
M

Vol. 26, No. 16 (2014)
Synthesis of Nano-Sized Protonic Acid Catalyst 4993
SNCPSs(80)
H SO
Fitting data
Experimental data
1.0
0.8
0.6
0.4
0.2
40
30
20
10
2
4
0.0
0.2
0.4
0.6
0.8
0
1
Water concentration (mol/L)
2
3
4
1/CA0
Fig. 11. Comparison of experimental data with predicted data derived from
the mathematical model by plot of 1/r vs. 1/C
Fig. 9. Water sensitivity of esterification reaction for methanol with acetic
acid at 55 ºC on ( ) nano-sized protonic acid catalyst (80) and on
0
A0
(
) H
2
SO
4
k2
M+ S
M
S
(10)
(11)
k-2
k3
are the adsorption equilibrium constants of acetic acid and
methanol, respectively.
A S+ M
W+S
Product
W S
kW
Using eqn. 8 and the initial kinetic data measured at
various initial reactant compositions, a mathematical model
was developed by curve fitting method using Matlab.
Employing least squares fitting algorithm, the kinetic
(
12)
k-W
where W represents water and W·S is the adsorbed water.
Defining as KW = k / k the adsorption equilibrium constant
for water, the rate expression for the presence of initial water is:
k K C C C
w
−w
parameters K
L/mol), respectively. Figs. 10 and 11 showed the fitting results
by plotting 1/r vs. 1/CM0 and 1/r vs. 1/CA0, respectively. As
A M
and K are estimated to be 0.2 (L/mol) and 0.5
(
3
A
A0 M0 S0
0
0
r0 =
(13)
K C + K C + K C +1
can be seen, the mathematical model derived can successfully
predict the initial rate data.
A
A0
M
M0
W
W0
Since K and K are determined previously, hence, the only
A M
parameter in eqn. 13 is the adsorption equilibrium constant
M
for water K . Rearrange the above eqn. 13, we get:
Fitting data
Experimental data
K C + K C +1
KW
A
A0
M
M0
40
30
20
10
1/r =
+
CW0
0
(14)
k K C C C
k K C CM0C
S0
3
A
A0 M0 S0
3
A
A0
K
W
can be easily obtained from the plot of 1/r
0
vs. Cw0 as 4.1
(
L/mol).As can be seen from Fig. 12, the model can accurately
assess the dependency of reaction rate with the presence of
initial water, supporting the estimated water inhibition effect
on solid acid catalyst.
55
50
45
40
35
30
0.0
0.2
0.4
0.6
1/CM0
Fig. 10. Comparison of experimental data with predicted data derived from
the mathematical model by plot of 1/r vs. 1/CM0
0
25
2
0
5
As discussed earlier, the presence of water can seriously
inhibit the catalysis reaction. Hence, the effect of water must
be included in the kinetic expression. The initial reaction
mechanistic paths with the presence of water are:
1
10
5
0
1
2
3
4
5
6
7
8
9
10
k1
Fig. 12. Dependency of initial reaction rate on the initial water concentration
for nano-sized protonic acid catalyst (80)
A+S
A S
(9)
k-1

4
994 Zhu et al.
Asian J. Chem.
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6
.
.
J.A. Melero, R.V. Grieken, G. Morales and V. Nuño, Catal. Commun.,
5, 131 (2004).
T. Okuhara, Chem. Rev., 102, 3641 (2002).
Conclusion
The prepared strong nano-sized protonic acid catalysts
show excellent catlaytic performance. The appropriate elevated
sulfonation temperature is beneficial for the attachment of
7. S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416, 304 (2002).
8
9
.
.
E. Cano-Serrano, J.M. Campos-Martin and J.L.G. Fierro, Chem.
Commun., 246 (2003).
-
3
SO H groups onto nano-sized crosslinking polystyrene
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spheres, which in turn improve the conversion efficiency. The
initial rate study showed that the surface reaction should be
the rate-limitting step and only single active site was involved
in the surface reaction.
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(
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1. M. Hara, T. Yoshida, A. Takagaki, T.I. Takata, J.N. Kondo, S. Hayashi
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ACKNOWLEDGEMENTS
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This work was financially supported by the Science and
Technology Innovation Project (Emerging Artists Talents
Scheme) of Zhejiang Province (No. 2012R422020 and
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Ann. Magn. Reson., 6, 46 (2007).
2
011R422007), the Chinese National Natural Science Foun-
dation (No.11105078 and 21306091), the MoE AcRF Tier 1
grant (R279000224112), the Scientific Research Fund of
Zhejiang Education Department (Y201224425), Ningbo
Natural Science Foundation (2012A610130), the Zhejiang
Province Natural Science Foundation (LQ13E020002).
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