Esterification of itaconic acid using Ln～SO4 2-/TiO2-SiO2 (Ln = La3+, Ce 4+, Sm3+) as catalysts

Article abstract of DOI:10.1016/j.molcata.2012.11.008

A series of itaconate esters, e.g. dimethyl itaconate, dibutyl itaconate and diisooctyl itaconate, were synthesized using solid acid SO₄ ^2-/MxOy (M = Ti⁴⁺, Fe³⁺, Zr⁴⁺, Al³⁺) and SO₄^2-/TiO₂-SiO₂ modified with lanthanide ion (Ln = La³⁺, Ce⁴⁺, Sm ³⁺) as catalysts. It was found that SO₄ ^2-/TiO₂-SiO₂ modified with lanthanide ion were of the same excellent catalytic activity as sulfuric acid (H₂SO ₄). Moreover, Ln～SO₄^2-/TiO ₂-SiO₂ is of excellent stability. Take La ³⁺～SO₄^2-/TiO₂-SiO₂ for example, the influence of the preparation conditions on catalytic performance was in detail examined by Py-FTIR, NH₃-FTIR, XRD and NH₃-TPD, and the optimum preparation conditions were obtained. Furthermore, the effective separation of product combined with the recyclable catalyst is expected to contribute to the development of clean and environmental friendly strategy for the synthesis of itaconate esters.

Full text of DOI:10.1016/j.molcata.2012.11.008

Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Esterification of itaconic acid using Ln∼SO42−/TiO2–SiO2 (Ln = La3+, Ce4+, Sm3+) as
catalysts
Lu Lia, Shiwei Liua, Junming Xub, Shitao Yua,∗, Fusheng Liua, Congxia Xiec, Xiaoping Gea, Jianyun Rena
a College of Chemical Engineering, Qingdao University of Science and Technology, 53 Zhengzhou Road, Qingdao 266042, PR China
b Institute of Chemical Industry of Forestry Products, CAF, Nanjing 210042, PR China
c Key Laboratory of Eco-Chemical Engineering, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, 53 Zhengzhou
Road, Qingdao 266042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 August 2012
Received in revised form 5 November 2012
Accepted 12 November 2012
Available online 22 November 2012
A series of itaconate esters, e.g. dimethyl itaconate, dibutyl itaconate and diisooctyl itaconate, were
synthesized using solid acid SO42−/MxOy (M = Ti4+, Fe3+, Zr4+, Al3+) and SO42−/TiO2–SiO2 modified
with lanthanide ion (Ln = La3+, Ce4+, Sm3+) as catalysts. It was found that SO42−/TiO2–SiO2 modified
with lanthanide ion were of the same excellent catalytic activity as sulfuric acid (H2SO4). Moreover,
Ln∼SO42−/TiO2–SiO2 is of excellent stability. Take La3+∼SO42−/TiO2–SiO2 for example, the influence of
the preparation conditions on catalytic performance was in detail examined by Py-FTIR, NH3-FTIR, XRD
and NH3-TPD, and the optimum preparation conditions were obtained. Furthermore, the effective sepa-
ration of product combined with the recyclable catalyst is expected to contribute to the development of
clean and environmental friendly strategy for the synthesis of itaconate esters.
Keywords:
Solid acid
Itaconic acid
Esterification
Lanthanide
© 2012 Elsevier B.V. All rights reserved.
was of the same catalytic activity as H2SO4. However, SO42−/TiO2
catalyst exhibits no satisfactory stability due to the surface sul-
1. Introduction
phate leached [7]. Next, how to improve the stability of SO42−/TiO2
is the main core to promote its application. To overcome the
limitation, the modification is usually considered as an effective
method. Considerable literature reported that mixed oxides often
showed better acidity and thermal stability than their constituent
single oxide [3,8]. Huang et al. reported SO42−/MoO3–ZrO2 was
of higher catalytic activity than SO42−/ZrO2 in the esterification
of 1-butanol with acetic acid [9]. The addition of Mo retarded
the transformation of ZrO2 from metastable tetragonal phase,
which exhibited higher activity in the esterification, into more
stable monoclinic phase with low activity. The solid acid catalyst
SO42−/ZrO2–TiO2/La3+ modified by a rare earth was also much bet-
ter than SO42−/ZrO2–TiO2 in terms of activity and stability in the
esterification of free fatty acids [10]. SO42−/ZrO2–Nd2O3 prepared
by precipitation-co-impregnation method displayed an excellent
activity in esterification [11]. Yu et al. reported that doping both
Yb2O3 and Al2O3 on SO42−/ZrO2 not only boosted the activity for
esterification but also alleviated deactivation of catalyst resulted
from the surface sulphate leached [12]. For SO42−/TiO2-based solid
acids, the addition of rare earth was also a good method to improve
its stability and activity. SO42−/TiO2/Ln3+ was successfully prepared
from SO42−/TiO2 by modifying with the rare earth ion. It showed
a good behavior in initiating ring-opening polymerization of chol-
romethyl thiirane [13]. Cui et al. reported that rare earth ions, such
as La, Sm, Nd and Y, were used to modify SO42−/TiO2, and the mod-
ified SO42−/TiO2 is of excellent catalytic activity and stability in
Recently, much attention has been paid to the development
of environmental benign, sustainable chemical processes. Itaconic
acid, or methylene succinic acid, is an unsaturated acid with conju-
gated double bonds and two carboxyl groups. Because of its unique
structure and characteristics, itaconic acid and its esters are useful
materials in industry [1], such as the synthesis of fiber, resin, plastic,
rubber, paints, surfactant, ion-exchange resins and lubricant [2]. For
a long time, sulfuric acid (H2SO4), as the conventional catalyst for
the esterification of itaconic acid, has many disadvantages, such as
too large amount of catalyst usage, serious corrosion of equipments,
complicated separation procedures, environmental problems, and
by-products. In view of these reasons, it is a long-felt need and
demand to develop a noncorrosive and environment friendly mate-
rials to replace the traditional catalyst in the esterification. In other
words, an environmental benign process is desired.
Traditional SO42−/MxOy solid acid catalysts, which are of high
activity and selectivity for target product, easy separation from
the products, reduction of corrosion and environmental problems,
recycling and regeneration, are widely used in esterification [3–6].
We carried out experiment with solid acid, such as SO42−/TiO2,
SO42−/ZrO2, SO42−/Al2O3 and SO42−/Fe2O3, as catalysts for the
esterification of itaconic acid. The results showed that SO42−/TiO2
∗
Corresponding author.
E-mail address: zhanglilu@126.com (S. Yu).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.11.008

L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
25
esterification [14]. From the literature mentioned above, it could be
seen that the addition of rare earth element and other subgroup ele-
ment could enhance the activity and stability of SO42−/MxOy-based
solid acid. However, the dependence of the acidity and activity of
the catalyst on its texture property needs more research.
In the present work, we reported the preparation and char-
acterization of SO42−/TiO2-based solid acids promoted by Si and
lanthanide ion (Ln = La3+, Ce4+, Sm3+), and their application in the
esterification of itaconic acid. The effect of co-addition of Si and La3+
on the activity, structure and acidity of the catalysts was investi-
gated as well.
at 80 ◦C until being dried to powder. Then the materials were pow-
dered below 100 mesh, calcined in air at 400, 450, 500, 550 and
600 ◦C for 6 h to prepare SO42−/TiO2, respectively.
2.2.2. Ln∼SO42−/TiO2–SiO2
10 g mixture of Ti(SO4)2 and Na2SiO3 are dissolved in 90 g dis-
tilled water under vigorous stirring, and the molar ratio of Ti and Si
is 15:1, 20:1, 25:1, 30:1, 35:1, respectively. Through drop wise add
aqueous ammonia (28 wt.%) to adjust the pH value of the above
solution to the range of 9–10, then the solid is formed slowly.
After separated and washed with deionized water, the obtained
TiO2–SiO2 solid was dried at 100 ◦C for 24 h. An appropriate amount
of La2O3 (CeO2 or Sa2O3) was dissolved in 2 mol/L H2SO4 to prepare
2. Experimental
a mixture solution, and the concentration of La3+ ion (Ce4+ or Sa3+
)
was 0.05, 0.06, 0.07, 0.08, 0.09 mol/L, respectively. The TiO2–SiO2
was impregnated into the mixture solution for 2 h and the ratio was
15 g TiO2–SiO2 per 100 mL solution. After that the precipitate was
evaporated and calcined by the same way in SO42−/TiO2 prepa-
ration to obtain La3+∼SO42−/TiO2–SiO2, Ce4+∼SO42−/TiO2–SiO2,
Sa3+∼SO42−/TiO2–SiO2, respectively.
2.1. Regent and equipment
All materials, such as itaconic acid, methanol, 1-butanol, 2-
isooctanol, lanthanum oxide, cerium oxide, samarium oxide,
sulfuric acid, ammonia, aluminum chloride (AlCl3), zirconium
oxychloride (ZrOCl2), ferric chloride (FeCl3), titanium sulfate
(Ti(SO4)2), silver nitrate (AgNO3), sodium silicate (Na2SiO3),
sodium carbonate (Na2CO3) and sodium hydroxide (NaOH), were
all purchased from Aldrich, and all materials were directly used
after drying without further purification.
2.3. Esterification of itaconic acid
2.3.1. Esterification of itaconic acid with methanol
A mixture of itaconic acid, methanol and catalyst was put into
100 mL autoclave and stirred at 120 ◦C. Various parameters, such
as the molar ratio of methanol to itaconic acid, amount of catalyst,
and reaction time, were varied to optimize the reaction conditions.
After the reaction, catalyst was separated by filtering.
Fourier transform infrared spectroscopy of adsorbed NH3 (NH3-
FTIR) or pyridine (Py-FTIR) on the catalysts were recorded on a
NEXUS 670 FTIR spectrometer. Before measurement, the catalyst
sheets were evacuated at 200 ◦C for 2 h under vacuum of 10−2 Pa
and then cooled to ambient temperature. After NH3 or pyridine
adsorption for 30 min and evacuation at 100 ◦C for 1 h, IR spectra
were recorded. The X-ray powder diffraction (XRD) of the cata-
lyst was carried out on a Bruker D8 Advance X-ray diffractometer
using nickel filtered Cu K␣ radiation at 40 kV and 20 mA. The ther-
mal gravimetric analysis (DTA) data were obtained by a Setaram
Labsys TG (STA) in temperature range of 25–1000 ◦C and heat-
ing rate of 10 ◦C min−1 in N2 atmosphere. Total acidity of the
samples is determined by temperature-programmed desorption of
ammonia (NH3-TPD). Measurements are carried out by a DLUT-
1 automatic temperature programmed desorption apparatus. The
sample is treated at 500 ◦C in nitrogen flow for 120 min. Then the
temperature is reduced to 120 ◦C and keeps the sample in a flow of
NH3 for 60 min. The amount of desorbed NH3 is determined after
heating the sample up to 600 ◦C (heating rate of 10 ◦C min−1).
The aim products were analyzed by GC–MS (TRACE-GC-MS
chromatographer with an FID and a DB-17MS phenyl methyl
siloxanes capillary column (30 m × 0.25 mm)). The temperature of
injector and transference line were maintained constant at 280 ◦C.
The temperature of the furnace was maintained at 180 ◦C for
30 min. The carrier gas was helium. The injection volume was
0.1 ␮L. FT-IR (NEXUS470 FTIR spectrometer) was also used to ana-
lyze products in the range of 2000–800 cm−1, using KBr powder
containing ca. 1 wt.% of sample.
2.3.2. Esterification of itaconic acid with 1-butanol(2-isooctanol)
A mixture of itaconic acid, 1-butanol(2-isooctanol) and catalyst
were put into a 100 mL three-neck flask equipped with a reflex
condenser under continuous stirring. Various parameters, such as
the molar ratio of 1-butanol(2-isooctanol) to itaconic acid, amount
of catalyst and reaction time were varied to optimize the reaction
conditions. After the reaction, catalyst was separated by filtering.
Reaction equation was shown in Scheme 1.
2.4. Stability measurement
The reusability of catalyst was studied using the used catalyst in
the next consecutive reaction cycles. After being used eight times,
the catalyst was washed with water and calcined in a muffle furnace
at 500 ◦C for 3 h.
3. Results and discussion
3.1. Choice of catlaysts
The catalytic activity of different catalysts in the esterification of
itaconic acid were examined and shown in Table 1. From Table 1, it
can be seen that SO42−/TiO2 and modified SO42−/TiO2 were of the
same catalytic activity as H2SO4, conversion of itaconic acid and the
yield of ester were both more than 90%. The La3+∼SO42−/TiO2–SiO2,
Ce4+∼SO42−/TiO2–SiO2 and Sa3+∼SO42−/TiO2–SiO2 exhibited the
similar excellent catalytic activity, so take La3+∼SO42−/TiO2–SiO2
as an example to research its catalytic stability in the synthe-
sis of dimethyl itaconate. The fresh SO42−/TiO2, La3+∼SO42−/TiO2
and La3+∼SO42−/TiO2–SiO2 exhibited similar catalytic activity
(Fig. 1). With the increasing repeated times of catalysts, the cat-
alytic activity of SO42−/TiO2 obviously diminished, and when
reuse in the fifth time, the conversion of itaconic acid was
below 60%. Compared with SO42−/TiO2, La3+∼SO42−/TiO2–SiO2
and La3+∼SO42−/TiO2 still maintained high catalytic activity, espe-
cially La3+∼SO42−/TiO2–SiO2. The Py-FTIR studies of the above
2.2. Catalysts preparation
2.2.1. SO42−/MxOy
The typical synthesis of SO42−/MxOy solid acid catalyst is
according to the paper by Hino et al. [15]. Take the synthesis
of SO42−/TiO2 as an example: 10 g Ti (SO4)2 is dissolved in 90 g
distilled water under vigorous stirring. Through drop wise add
aqueous ammonia (28 wt.%) to adjust the pH value of the above
solution to the range of 9–10, then the solid is formed slowly. After
separated and washed with deionized water, the obtained TiO2
solid was dried at 100 ◦C for 24 h. Take 2 g TiO2 and impregnate it
with 30 mL of 1 N H2SO4 for 2 h. The treated solid was evaporated

26
L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
O
O
C
CH2 C O CH3
CH2
O CH3
H2C
C
H2C
C
or
C
O
O CH3
COOH
H
O
H 3
C
O
C
O
C
CH2 COOH
COOH
CH2
O CH2CH2CH2CH3
CH2
O CH2CH2CH2CH3
CH3CH2CH2CH2OH
H2C
C
H2C
C
H2C
C
or
C
O
O CH2CH2CH2CH3
COOH
C
H
3 C
H
2 C
H
2 C
C2H5
C2H5
H
O
C
O
C
2 C
H
C
H
CH2
O CH2CHCH2CH2CH2CH3
CH2
O CH2CHCH2CH2CH2CH3
2 O
H
C2H5
H2C
C
or H2C C
C O CH2CHCH2CH2CH2CH3
COOH
O
C2H5
Scheme 1. Esterification of itaconic acid.
Table 1
The effect of catalysts on the esterification.a
Catalystsc
Dimethyl
Dibutyl
Diisooctyl
Conversion/%
Yield/%b
Conversion/%
Yield/%b
Conversion/%
Yield/%b
None
H2SO4
41.57
87.05
52.58
63.22
56.62
94.07
94.21
94.31
93.43
93.19
35.91
84.92
47.49
59.37
51.06
91.43
91.78
92.27
91.58
91.25
53.97
98.01
82.79
86.15
83.65
96.31
96.45
96.76
95.34
95.25
47.39
88.53
78.61
81.25
80.36
93.82
93.93
94.64
93.65
93.82
61.70
99.63
75.39
80.29
76.17
99.07
99.10
99.15
98.89
98.95
55.39
94.25
71.68
75.45
72.36
97.43
97.56
97.61
97.63
97.39
SO42−/Al2O3
SO42−/ZrO2
SO42−/Fe2O3
SO42−/TiO2
SO42−/TiO2–SiO2
d
La3+∼SO42−/TiO2–SiO2
Ce4+∼SO42−/TiO2–SiO2
d,e
d,e
Sm3+∼SO42−/TiO2–SiO2
d,e
a
Reaction conditions: 4 wt.% of catalyst based on all reactants, itaconic acid 0.1 mol, molar ratio of methanol/itaconate acid = 10/1, and reaction for 6 h at 120 ◦C in 100 mL
autoclave.
b
Yield: dimethyl itaconate, dibutyl itaconate or diisooctyl itaconate.
c
All solid catalysts were calcined at 500 ◦C.
d
e
The molar ratio of Ti/Si = 25:1.
The concentration of Ln(La3+, Ce4+, Sm3+) = 0.07 mol/L.
mentioned three catalysts after used for eight times were shown
in Fig. 2. The presence of the band at 1450–1470 cm−1 was
associated with Lewis acid sites, and that at 1540–1550 cm−1
was characteristic Brönsted acid sites [16]. It was shown that
Brönsted acid and Lewis acid sites co-exists on the surface of
La3+∼SO42−/TiO2–SiO2 and La3+∼SO42−/TiO2 after used for eight
times, while the Brönsted acid sites and Lewis acid sites almost
disappeared for SO42−/TiO2. Compared with relative intensity of
100
90
80
70
60
50
40
100
90
80
70
60
50
40
a
b
c
d
e
f
0
1
2
3
4
5
6
7
8
9
reused time
Fig. 1. The results of three catalysts reused on the preparation of dimethyl
itaconate. Conversion of itaconic acid using different solid acid as catalyst (a:
La3+∼SO42−/TiO2–SiO2; c: La3+∼SO42−/TiO2; e: SO42−/TiO2); yield of dimethyl
itaconate using different solid acid as catalyst (b: La3+∼SO42−/TiO2–SiO2; d:
La3+∼SO42−/TiO2; f: SO42−/TiO2); molar ratio of Ti/Si = 25:1, concentration of
La3+ = 0.07 mol/L, all solid catalysts were calcined at 500 ◦C.
Fig. 2. IR spectra of the eighth reused catalysts adsorption with pyridine. Molar
ratio of Ti/Si = 25:1, concentration of La3+ = 0.07 mol/L, the catalysts were calcined at
500 ◦C.

L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
27
Brönsted acid and Lewis acid sites of La3+∼SO42−/TiO2–SiO2 and
La3+∼SO42−/TiO2, La3+∼SO42−/TiO2–SiO2 was of more acidic site
than La3+∼SO42−/TiO2. Based on the above results, it suggests
that co-addition of La and Si into SO42−/TiO2-based solid acid
is favorable to obtaining high activity and keeping the stabil-
ity [3,13,17]. La3+∼SO42−/TiO2–SiO2 was calcinated in a muffle
furnace at 500 ◦C for 3 h after the eighth reuse and the color
of catalyst changed from yellow to white. When the activated
La3+∼SO42−/TiO2–SiO2 was reused as catalyst in the esterification
of itaconic acid with methanol, the conversion of itaconic acid
and the yield of ester still could reach 92.52% and 91.03%, respec-
tively. The results showed that the activated catalyst was of the
same catalytic activity as the fresh catalysts, and the carbona-
ceous deposit was the main reason which decreased the activity
of catalyst in the process of the reuse [18]. At the same time,
La3+∼SO42−/TiO2–SiO2 also exhibit the good catalytic activity and
stability in the preparation of dibutyl itaconate and diisooctyl ita-
conate. This illuminates that La3+∼SO42−/TiO2–SiO2 is an excellent
catalyst in the esterification of itaconic acid. Next, the catalytic
performance of La3+∼SO42−/TiO2–SiO2 was examined in detail.
600ºC
550ºC
500ºC
450ºC
400ºC
10
20
30
40
50
60
70
80
2θ
Fig. 4. XRD spectra of La3+∼SO42−/TiO2–SiO2 prepared at various calcinations
temperature. Molar ratio of Ti/Si = 25:1, concentration of La3+ = 0.07 mol/L in the
synthesis of catalyst.
3.2. Catalytic performance of La3+∼SO42−/TiO2–SiO2
samples. This indicated that Si and La were highly dispersed on
the catalysts [21]. The anatase structure increased with the calcina-
tion temperature according to the intensified diffraction peaks for
TiO2. When La3+∼SO42−/TiO2–SiO2 was calcined at 500 ◦C, anatase
structure was obvious, for the diffraction peak near 25.3◦ was
of strong intensity in XRD patterns. When La3+∼SO42−/TiO2–SiO2
was calcined at 550 ◦C or higher temperature, the reduction on
the conversion of itaconic acid was possibly attributed to the
decomposition of surface sulfur species [22]. It could be con-
firmed from the NH3-FTIR (Fig. 5) and NH3-TPD (Fig. 6) of
La3+∼SO42−/TiO2–SiO2. Infrared spectroscopic studies of ammonia
adsorbed (NH3-FTIR) on solid surfaces have made it possible to dis-
tinguish between Brönsted acid and Lewis acid sites [3]. NH3-FTIR
studies of La3+∼SO42−/TiO2–SiO2 calcined at different temperature
were shown in Fig. 5. As seen from Fig. 5, for La3+∼SO42−/TiO2–SiO2,
Using synthesis of dimethyl itaconate as model, the influences
on catalytic performance of La3+∼SO42−/TiO2–SiO2, such as calcina-
tion temperature, concentration of lanthanide ion, and molar ratio
of Ti/Si were studied.
3.2.1. Calcination temperature
The calcination temperature had great influence on the cat-
alytic activity of solid acid [19]. The conversion of itaconic acid
increased with the increasing of the calcination temperature, and
reached a maximum value of 94.31% when the catalyst was cal-
cined at 500 ◦C (Fig. 3). Then, the conversion descended sharply
when La3+∼SO42−/TiO2–SiO2 was calcined at 550 ◦C or higher tem-
perature. The XRD patterns of the calcined La3+∼SO42−/TiO2–SiO2
were present in Fig. 4. All the samples showed the anatase struc-
ture, there were three obvious diffraction peaks near 25.3◦, 37.8◦
and 48.0◦ [20]. It could be seen that no independent peak was
observed due to SiO2 or any compound formed between SiO2 and
TiO2, and no diffraction patterns of La compound existed in all
2−
the ꢀS or ꢀS of inorganic bidentate SO4 ions coordinated to
O
O
TiO2 was detectable at 800–1630 cm−1 [23,24]. The presence of
the band at 1400–1401 cm−1 was associated with NH3 adsorbed
on Brönsted acid sites, and that at 1631–1632 cm−1 was char-
acteristic NH3 adsorbed on Lewis acid sites [25]. It was shown
96
94
92
90
88
86
84
82
80
78
76
96
94
92
90
88
86
84
82
80
78
76
600
550
500
450
conversion
yield
400
400
450
500
550
600
2000
1500
1000
500
calcinations temperature ºC
Wavenumber(cm-1)
Fig. 3. The effect of calcinations temperature on activity of La3+∼SO42−/TiO2–SiO2.
Molar ratio of Ti/Si = 25:1, concentration of La3+ = 0.07 mol/L in the synthesis of cat-
alyst. Reaction conditions: 4 wt.% of catalyst based on all reactants, itaconic acid
Fig. 5. NH3-FTIR spectra of La3+∼SO42−/TiO2–SiO2 at different calcinations temper-
ature. Molar ratio of Ti/Si = 25:1, concentration of La3+ = 0.07 mol/L in the synthesis
of catalyst.
0.1 mol, molar ratio of methanol/itaconate acid = 10/1, and reaction for 6 h at 120 ◦
in 100 mL autoclave. Yield: dimethyl itaconate.
C

28
L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
conversion
yield
0.05
0.06
0.07
0.08
0.09
concent ration of La3+mol/L
Fig. 6. NH3-TPD of the catalysts prepared by different calcinations temperature.
Molar ratio of Ti/Si = 25:1, concentration of La3+ = 0.07 mol/L in the synthesis of cat-
alyst.
Fig. 7. The effect of concentration of La3+ on activity of La3+∼SO42−/TiO2–SiO2.
Molar ratio of Ti/Si = 25:1, all solid catalysts were calcined at 500 ◦C. Reaction con-
ditions: 4 wt.% of catalyst based on all reactants, itaconic acid 0.1 mol, molar ratio of
methanol/itaconate acid = 10/1, and reaction for 6 h at 120 ◦C in 100 mL autoclave.
Yield: dimethyl itaconate.
that Brönsted acid and Lewis acid sites co-exists on the surface
of La3+∼SO42−/TiO2–SiO2 when the calcination temperature was
below 550 ◦C or at 550 ◦C, and when the calcination tempera-
ture was above 550 ◦C, the Brönsted acid sites almost disappeared,
which means the high calcination temperature could promote the
surface SO42− ions to decompose. The relative intensity of Brönsted
acid/Lewis acid sites (B/L) over La3+∼SO42−/TiO2–SiO2 (calcined
at 500 ◦C) was 5.25, B/L over La3+∼SO42−/TiO2–SiO2 (calcined at
450 ◦C) was 3.17, and over La3+∼SO42−/TiO2–SiO2 (calcined at
400 ◦C) was 3.85. Brönsted acid sites play a prior effect on catalytic
activity. It was also reported that the catalytic activity of sulfated
zirconia-based solid acid correlated with the amount of Brönsted
acid sites [26]. The amount of acid sites and acid strength distri-
bution obtained from the NH3-TPD spectra was shown in Fig. 6.
The La3+∼SO42−/TiO2–SiO2 from different calcination temperature
exhibited weak acid strength. Among the La3+∼SO42−/TiO2–SiO2,
the amounts of acid sites on La3+∼SO42−/TiO2–SiO2 (calcined at
500 ◦C) were highest. This result was consistent well with the
high activity of La3+∼SO42−/TiO2–SiO2 (calcined at 500 ◦C) [27].
These results indicate that calcination temperature plays a key role
in the crystallite formation and the interaction of the active sul-
fur species with TiO2, which would affect the catalytic activity of
La3+∼SO42−/TiO2–SiO2.
The results were shown in Fig. 10. The conversion of itaconic
acid increased greatly with the increasing of the molar ratio
of Ti/Si, and was up to the maximum value of 94.31% at the
molar ratio of Ti/Si = 25/1. However, the activity decreased with
further increase of the molar ratio of Ti/Si. The spectrum of NH3-
FTIR of La3+∼SO42−/TiO2–SiO2 with different molar ratio of Ti/Si
were shown in Fig. 11. From these pattern, La3+∼SO42−/TiO2–SiO2
(molar ratio of Ti/Si = 25/1) was of strongest concentration of Brön-
sted acid site among all samples. This result was consistent well
with the high activity of La3+∼SO42−/TiO2–SiO2 (molar ratio of
Ti/Si = 25/1).
Based on the above results, the optimal conditions on prepa-
ration of La3+∼SO42−/TiO2–SiO2 were obtained. The conditions
were as follows: molar ratio of Ti/Si was 25/1, concentra-
tion of La3+ was 0.07 mol/L, and calcination temperature was
500 ◦C.
0.09mol/L
0.08mol/L
3.2.2. Concentration of lanthanide ion
The concentration of La3+ had great influence on the catalytic
activity of solid acid. The conversion of itaconic acid increased
with the increasing of the concentration of La3+, and reached a
maximum value of 94.31% when the concentration of La3+ was
0.07 mol/L (Fig. 7). Then, the conversion descended sharply when
the concentration of La3+ further increasing. The spectrum of
NH3-FTIR and NH3-TPD of La3+∼SO42−/TiO2–SiO2 with different
concentration of La3+ were shown in Figs. 8 and 9, respectively.
From these pattern, the concentration of Brönsted acid sites of
La3+∼SO42−/TiO2–SiO2 (concentration of La3+ = 0.07 mol/L) was
maximum among all samples. This result was consistent well
with the high activity of La3+∼SO42−/TiO2–SiO2 (concentration of
La3+ = 0.07 mol/L).
0.07mol/L
0.06mol/L
0.05mol/L
3.2.3. Molar ratio of Ti and Si
2000
1500
1000
Wavenumber(cm )
500
0
The content of Si was of great effect on the catalytic activity
of solid acid [28]. In order to study the catalytic performance of
La3+∼SO42−/TiO2–SiO2 in detail, the effect of molar ratio of Ti/Si
on the activity of La3+∼SO42−/TiO2–SiO2 catalyst was examined.
-1
Fig. 8. NH3-FTIR spectra of La3+∼SO42−/TiO2–SiO2 prepared by different concentra-
tion of La3+. Molar ratio of Ti/Si = 25:1, all solid catalysts were calcined at 500 ◦C.

L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
29
Fig. 9. NH3-TPD of the catalyst prepared by different concentrations of La3+. Molar ratio of Ti/Si = 25:1, all solid catalysts were calcined at 500 ◦C.
3.3. Esterification of itaconic acid using La3+∼SO42−/TiO2–SiO2 as
dibutyl itaconate and diisooctyl itaconate, was also tested in
the present work, as shown in Table 2. The conversions of
itaconic acid were similar in different esterifications. The tech-
nological conditions of synthesis of dimethyl itaconate were as
follows: itaconic acid 0.1 mol, n(itaconic acid):n(methanol) = 1:10,
catalyst
The catalytic activity of La3+∼SO42−/TiO2–SiO2 in the syn-
thesis of different itaconate esters, such as dimethyl itaconate,
Table 2
Esterification of itaconic acid using La3+∼SO42−/TiO2–SiO2 as catalyst.a
Product
Reaction time/h
n(acid):n(alcohols)
w(catalysts):w(reactant)/%
Conversion/%
Yield/%b
Dimethyl
3
4
5
6
7
6
6
6
6
6
6
6
6
1:10
1:10
1:10
1:10
1:10
1:7
4
4
4
4
4
4
4
4
4
2.5
3
3.5
4.5
76.67
85.92
90.08
94.31
95.21
89.17
90.84
91.65
90.28
82.84
85.5
71.96
81.13
87.62
92.27
93.07
85.75
87.97
89.81
88.91
78.36
83.19
89.51
92.95
1:8
1:9
1:11
1:10
1:10
1:10
1:10
91.36
95.02
Dibutyl
1.5
2
2.5
3
3.5
3
3
3
3
3
3
1:3
1:3
1:3
1:3
1:3
1:2
1:2.5
1:3.5
1:4
1:3
1:3
1:3
1:3
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
3
84.73
89.56
92.45
96.76
97.51
69.24
93.19
84.31
83.23
85.95
89.79
92.13
97.99
80.81
87.25
91.07
94.65
95.02
57.8
87.5
82.3
82.29
81.26
86.68
89.77
94.88
3.5
4
5
3
3
Diisooctyl
0.25
0.5
0.75
1
1.25
1
1
1
1
1
1:3
1:3
1:3
1:3
1:3
1:2.5
1:4
1:4.5
1:3
1:3
1:3
1:3
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
3
61.91
78.42
91.87
99.15
99.09
95.49
92.99
90.65
75.31
81.75
93.02
99.05
53.23
72.35
86.19
97.61
97.25
92.35
89.05
87.71
70.21
77.95
90.89
97.38
3.5
4
5
1
1
a
The molar ratio of Ti/Si = 25:1, the concentration of La3+ = 0.07 mol/L, all solid catalysts were calcined at 500 ◦C.
Yield: dimethyl itaconate, dibutyl itaconate or diisooctyl itaconate.
b

30
L. Li et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 24–30
w(La3+∼SO42−/TiO2–SiO2):w(reactant) = 4.5:100, 115 ◦C for 1 h;
95
90
85
80
75
70
95
90
85
80
75
70
under the above conditions, the conversion of itaconic acid and
yield of diisooctyl itaconate were 99.15% and 97.61%, respectively,
and the purity of diisooctyl itaconate could reach 99.87%. This
illuminates that La3+∼SO42−/TiO2–SiO2 is an excellent catalyst in
the esterification of itaconic acid with different chain alcohols.
4. Conclusions
conversion
yield
La3+∼SO42−/TiO2–SiO2 solid acids was prepared and character-
ized in the present work. It is suggested that La3+∼SO42−/TiO2–SiO2
catalyst prepared in the present work is practical in the ester-
ification of itaconic acid. The excellent activity and stability of
La3+∼SO42−/TiO2–SiO2 attribute to the combination of Si and La3+
ion, which hinders the leaching of sulfur species from the surface
and is favorable to increasing the amount of acid sites, strength-
ening the acidity, and then enhancing the activity and stability of
catalyst.
15:1
20:1
25:1
30:1
35:1
Fig. 10. The effect of molar ratio of Ti/Si on activity of La3+∼SO42−/TiO2–SiO2. Con-
centration of La3+ = 0.07 mol/L, all solid catalysts were calcined at 500 ◦C. Reaction
conditions: 4 wt.% of catalyst based on all reactants, itaconic acid 0.1 mol, molar ratio
of methanol/itaconate acid = 10/1, and reaction for 6 h at 120 ◦C in 100 mL autoclave.
Yield: dimethyl itaconate.
Acknowledgements
The work described was supported by “11th National 5-year
R&D plan in rural areas” (2011BAD22B05) and the National Natural
Science Foundation of China (31100521).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2012.11.008.
35:1
30:1
References
25:1
20:1
[1] L. Dwiarti, M. Otsuka, S. Miura, Bioresour. Technol. 98 (2007) 3329–3337.
[2] K. Eleni, L. Elena, P. Lionel, S.P. Costas, Eur. Polym. J. 47 (2011) 816–822.
[3] K. Jiang, D. Tong, J. Tang, R. Song, C. Hu, Appl. Catal. A: Gen. 389 (2010) 46–51.
[4] J.L. Ropero-Vega, A. Aldana-Perez, R. Gomez, M.E. Nino-Gomez, Appl. Catal. A:
Gen. 379 (2010) 24–29.
[5] Y. Liao, X. Huang, X. Liao, B. Shi, J. Mol. Catal. A: Chem. 347 (2011) 46–51.
[6] M. Khodadadi Moghaddam, M.R. Gholami, Mater. Lett. 60 (2006) 715–719.
[7] D.E. López, J.G. Goodwin Jr., D.A. Bruce, E. Lotero, Appl. Catal. A: Gen. 295 (2005)
97–105.
15:1
2000
1500
1000
500
[8] K. Takao, Catal. Today 81 (2003) 57–63.
Wavenumber(cm-1)
[9] B.C. Huang, Z.T. Huang, Z.F. Ma, J. Mol. Catal. 13 (1999) 383–387.
[10] Y. Li, X.D. Zhang, L. Sun, J. Zhang, H.P. Xu, Appl. Energy 87 (2010) 156–159.
[11] B. Deng, L.P. Chen, Q. Yu, China Condiment (2008) 848–851.
[12] G.X. Yu, X.L. Zhou, C.L. Li, L.F. Chen, J.A. Wang, Catal. Today 148 (2009) 169–173.
[13] W.S. Li, Z.Q. Shen, Y.F. Zhang, Eur. Polym. J. 37 (2001) 1182–1190.
[14] X.L. Cui, M.L. lin, H.F. Guo, Chem. World China 1 (2003) 27–30.
[15] M. Hino, S. kobayashi, K. Arata, J. Am. Chem. Soc. 101 (1979) 6439–6440.
[16] C. Cativiela, F. Figueras, J.M. Fraile, J.I. Garcia, J.A. Mayoral, L.C. de Ménorval, E.
Pires, Appl. Catal. A: Gen. 101 (1993) 253–267.
Fig. 11. NH3-FTIR spectra of La3+∼SO42−/TiO2–SiO2 prepared by different molar
ratio of Ti/Si. Concentration of La3+ = 0.07 mol/L, all solid catalysts were calcined
at 500 ◦C.
w(La3+∼SO42−/TiO2–SiO2):w(reactant) = 4:100, 120 ◦C for 6 h;
under the above conditions, the conversion of itaconic acid and
yield of dimethyl itaconate were 94.31% and 92.27%, respectively,
and the purity of dimethyl itaconate could reach 99.85%. The
technological conditions of synthesis of dibutyl itaconate were as
follows: itaconic acid 0.1 mol, n(itaconic acid):n(1-butanol) = 1:3,
w(La3+∼SO42−/TiO2–SiO2):w(reactant) = 4.5:100, 120 ◦C for 3 h;
under the above conditions, the conversion of itaconic acid and
yield of dibutyl itaconate were 96.76% and 94.65%, respectively, and
the purity of dibutyl itaconate could reach 99.88%.The technologi-
cal conditions of synthesis of diisooctyl itaconate were as follows:
itaconic acid 0.1 mol, n(itaconic acid):n(2-isooctanol) = 1:3,
[17] X.L. Cui, H.F. Guo, M.L. Lin, J.W. Guo, Y.N. Wu, J. Rare Earths 21 (2003) 460–464.
[18] S.V. Donk, J.H. Bitter, K.P. Jong, Appl. Catal. A: Gen. 212 (2001) 97–116.
[19] Y. Sun, Q.W. Sun, F.K. Jiang, J.S. Liu, Z.S. Zhang, J. Fuel Chem. Technol. 40 (2012)
54–58.
[20] A. Corma, A. Martinez, C. Martinez, Appl. Catal. A: Gen. 144 (1996) 249–268.
[21] B.M. Reddy, B. Chowdhury, E.P. Reddy, A. Fernández, J. Mol. Catal. A: Chem. 162
(2000) 431–441.
[22] J. Zhao, Y.H. Yue, W.M. Hua, Appl. Catal. A: Gen. 336 (2008) 133–139.
[23] T. Yamaguchi, T. Jin, K. Tanabe, J. Phys. Chem. 90 (1986) 3148–3152.
[24] T. Jin, T. Yamaguchi, K. Tanabe, J. Phys. Chem. 90 (1986) 4794–4796.
[25] H.P. Yan, Y. Yang, X. Xiang, C.W. Hu, Catal. Commun. 10 (2009) 1558–1563.
[26] J.H. Wang, C.Y. Mou, Appl. Catal. A: Gen. 286 (2005) 128–136.
[27] G.D. Fan, M. Shen, Z. Zhang, F.R. Jia, J. Rare Earths 27 (2009) 437–442.
[28] G.C. Dong, R.C. Zhang, R.R. Zhan, Y.F. Zhan, J. North Normal Univers.: Nat. Sci.
Ed. China 36 (2004) 27–31.