5770 Ji et al.
Asian J. Chem.
General procedure: In a typical preparation, nano-TiO2
was carried out as follows. At room temperature, 19 mL tetra-
butyl titanate (TBOT) was dissolved in 86 mL anhydrous
ethanol under stirring in a beaker. Then, 5 mL acetic acid and
1 mL distilled water were added into the reaction mixture,
respectively. After it was stirred under room temperature for
about 2 h, white TiO2 formed as suspension. Subsequently,
the solution was put into an oven at 100 ºC for 10 h and a dried
sol-gel nano-TiO2 was obtained.
101
200
103
105
213
Nano-SO42-/TiO2 solid acid catalysts were prepared by
impregnation method. 12 g dry sol-gel nano-TiO2 was added
into 12 mL H2SO4 (1 mol/L) at room temperature. After being
stirred for 1 h, the solution was dried at 100 ºC for 5 h. Finally,
the products were calcined at different temperature (350, 400,
450, 500 and 550 ºC) for 3 h to obtain the catalyst, designated
as nano-SO42-/TiO2.
107
116
70
10
20
30
40
50
60
80
2θ (°)
Fig. 1. XRD pattern of nano-SO42-/TiO2
TABLE-1
SPECIFIC SURFACE AREA (BET), PORES
MEAN DIAMETER (BJH) AND PORES VOLUME
The catalytic activities of the catalysts were tested by the
esterification of sebacic acid with 2-ethyl hexanol and a series
of other dicarboxylic acid. The experiment was performed in
a three-neck flask equipped with a thermometer, a refluxing
condenser and a water separator. The experimental conditions
are the following: 15 mL xylene was used as water-carrying
agent and the molar ratio of sebacic acid to 2-ethyl hexanol
was from 1:3.5 to 1:2 and the weight of catalyst was from 3-8
wt % of the total weight of sebacic acid and 2-ethyl hexanol
and the reaction temperature and the reaction time were 90-
170 ºC and 2-4 h, respectively. After cooling to room tempe-
rature, the resulting solution was filtrated and washed with
saturated solution carbonate and distilled water for at least
3 times, respectively. Then the solution was dried by anhydrous
magnesium sulfate for 24 h. The solution was filtrated and
distilled under reduced presser at 160 ºC to remove water,
2-ethyl hexanol and xylene from the solution and get the
product.
Specific
surface area
(m2/g)
174.01
157.52
152.39
125.20
72.36
Average pores
Pores
volume
(cm3/g)
0.16
Catalysts
diameter
(nm)
3.4
4.3
4.2
Nano-SO42-/TiO2-350a
Nano-SO42-/TiO2-400a
Nano-SO42-/TiO2-450a
Nano-SO42-/TiO2-500a
Nano-SO42-/TiO2-550a
aCalcination temperature.
0.19
0.21
0.21
0.16
5.5
7.5
FE-SEM and HR-TEM analysis of the catalysts: The
morphologies and sizes of the catalysts calcined at 450 ºC
were examined by FE-SEM and HR-TEM. The FE-SEM image
of the nano-SO42-/TiO2 catalyst shown in Fig. 2a confirms that
the product is agglomerate, which is composed of spherical
nanoparticles. Fig. 2b shows the HR-TEM image of the nano-
SO42-/TiO2 catalyst. It can be seen that the size of the spherical
nanoparticles is about 6-8 nm.
Detection method: X-Ray diffractometer (RigaKu
D/max-RB, Japan) using CuKα radiation (λ = 1.54056 Å) under
40 kV and 30 mA was used to identify the phase of the catalysts.
Specific surface areas were determined through the Brunauer-
Emmett-Teller (BET) isothermic method. Pore diameter and
pore volume were calculated by the Barret-Joyner-Hallenda
(BJH) method. The morphologies and sizes of the products
were determined by field emission scanning electron micro-
scopy (FE-SEM, JSM-6701F type) and high-resolution trans-
mission electron microscopy (HR-TEM, Jeol JEM 2010 type,
accelerating voltage = 200 kV).
Fig. 2. FE-SEM and TEM micrographs of nano-SO42-/TiO2
RESULTS AND DISCUSSION
Sythesis of dioctyl sebacate
XRD analysis of the catalysts: The XRD pattern of nano-
SO42-/TiO2 solid acid catalysts in Fig. 1 shows that the diffrac-
tion peaks match well with literature patterns (JCPDF Card
No. 01-0562), indicating that the phase of nano-SO42-/TiO2 is
anatase.
BET surface area and pore size of the catalysts: The
specific surface areas, pores mean diameter and pores volume
of the catalysts calcined at different temperatures are listed in
Table-1. It can be seen that with the increase of calcination
temperature, the specific surface areas becomes lower, while
the pores mean diameter becomes higher.
Influence of the calcination temperature of nano-
SO42-/TiO2 catalysts on the conversion of sebacic acid: Fig. 3
presents the influence of the different calcination temperature
of nano-SO42-/TiO2 catalysts on the conversion of the sebacic
acid. It can be observed that the catalytic activity of the pre-
pared nano-SO42-/TiO2 calcined at 450 ºC is the highest and
the conversion reached to 99.1%. The suitable calcination
temperature was 450 ºC.
Reaction condition optimization: Fig. 4a presents the
influence of the reaction temperature on the reaction. The