Y. Liang et al.
MolecularCatalysis465(2019)16–23
Scheme 1. The main products of reaction between BPA and DMC.
Lithium-Ion Battery [33], Nanosensors [34], photocatalytic [35,36].
However, the transesterification of DMC with BPA over Li/TiO2 have
not been studied. In this work, lithium doped TiO2 was prepared by
simple impregnation method, and the catalysts were used for the
transesterification of DMC with BPA. The results showed that Li+ re-
acted with TiO2 to form surface Ti-O-Li species at 400 ℃, and the
synthesized catalysts displayed the high catalytic activity in transes-
terification of BPA with DMC. In addition, the effects of lithium doping
amount, calcination temperature and reusability of catalysts were in-
vestigated, and the possible reaction mechanism was provided.
X-ray photoelectron spectroscopy (XPS) with Mg kα (1253.6 e V) X-ray
source from Thermo Fisher Company, USA.
The basicity active site of the catalysts was characterized by CO2
Temperature-programmed desorption (CO2-TPD) using Micromeritics
TPD/TPR 2900 apparatus. Typically, 200 mg of sample was pretreated
by flowing 35 mL/min He at 250 ℃ for 60 min to dry the catalysts, then,
pretreated catalyst cooled to 100 ℃ and exposed to pure CO2 for
90 min. Subsequently, He (35 ml/min) was passed for 40 min at 100 ℃
to remove physically adsorbed CO2. The CO2-TPD measurement was
performed from100 to 800 ℃ at a rate of 10 ℃/min. A thermal con-
ductivity cell was used for recording the desorbed amount of CO2.
2. Experimental
2.4. Reaction procedure
2.1. Chemical reagents
Reactions were carried out in a three neck flask, equipped with a
thermometer, a controlled volume pump and fractionating column
connected to a liquid dividing head. BPA and catalysts were charged
into flask under nitrogen atmosphere. When mixture was heated to 170
℃ under rigorous stirring, DMC was added drop-wise by a controlled
volume pump and the reaction temperature was kept at 160–180 °C
under refluxing condition. During the reaction, the mixture of DMC and
methanol was collected slowly in a receiver flask. After reaction, mix-
ture was cooled and analyzed by GC–MS. The products were mainly
one-methylcarbonate-ended-BPA (MmC(1)) and two-methylcarbonate-
ended-BPA (DmC(1)), O-methylation of BPA (A), fromortho-methyla-
tion of BPA with DMC (B and C). The selectivity of products to MmC(1)
and DmC(1) were defined as the moles of MmC(1) and DmC(1) pro-
duced per 100 mol of consumed BPA, and the yields of MmC(1) and
DmC(1) were obtained from multiplication of BPA conversion by the
selectivity of products to MmC(1) and DmC(1) (Scheme 1).
TiO2 powder was provided by Tianjin Chemical Reagent Co.
Lithium nitrate (LiNO3) was obtained from Aladdin Corp. Dimethyl
carbonate (DMC) (99.9 wt%) was purchased from Macklin Biochemical
Co., Ltd., Shanghai, China. Analytical BPA was provided by Tianjin
Chemical Reagent Company. Polyvinyl pyrrolidone (PVP, K90) was
obtained from Tianjin Guangfu Chemical Co., Ltd.
2.2. Sample preparation
Li-doped TiO2 catalysts were prepared by a simple wet impregna-
tion method. To prepare Li doped TiO2 catalysts, 2 g Polyvinyl pyrro-
lidone (PVP) was dissolved in 100 mL water, after that 4.8 g ordinary
grade TiO2 was added to the above solution by ultrasonic treatment for
60 min to obtain uniformly distributed suspension A. Then, 0.69 g li-
thium nitrate was loaded into suspension A, and it was aged for 24 h at
room temperature to obtain suspension B. Then suspension B was
transferred into a reactor with polytetrafluorine at 160 ℃ for 3 h. After
cooling, lithium doped TiO2 was obtained. The lithium doped TiO2
catalyst was then calcined at different temperatures in muffle furnace
for 4 h. The obtained catalyst was named as Ti/Li-n-T, where n and T
were the molar ratio and calcination temperature, respectively. Such as,
Ti/Li-6-400 indicated that Ti/Li molar ratio was 6 and calcined at 600
℃.
(initial moles of BPA− final moles of BPA)*100
Conversion %=
(1)
inital moles of BPA
( moles of product formed)*100
Selectivity of products %=
(2)
(3)
moles of BPA reacted
Yield %= conversion of BPA*selectivity of products
3. Results and discussions
2.3. Characterization
Fig. 1 depicted the FTIR spectrum of catalysts with the different Li
doped amounts and calcination temperatures in the range of 400-
4000 cm−1. A peak at 1640 cm−1 and a strong broad at 3400 cm−1
were ascribed to the H − O binding vibration. The intensity of these
peaks became weaken with the increase of calcination temperature
(Fig. 1b). The strong peaks at 500-800 cm−1 were attributed to Ti-O-Ti
and Ti-O bonds. The absorption peaks at 1390 cm−1 was found in
sample with calcination temperature at 300 ℃, which could be attrib-
uted to the stretching vibration peak of NeO bond in LiNO3. However,
the stretching vibration peak of NeO bond disappeared while a new
peak at 1512 cm−1 appeared together with the calcination temperature
increase. Because the atomic mass of lithium was lower than titanium,
X-ray diffraction Spectra of Catalysts measured by Cu K α radiation
to Bruker AXS (Germany) with a scan range of 20-70° (2θ). FT-IR
spectrum was obtained from the range of 4000–400 cm−1 wave num-
bers with resolution of 4 cm−1
a
BRUKER FT-IR Analyzer.
Thermogravimetric analysis was measured by Setaram TGA-92 ther-
mogravimetric analyzer at a heating rate of 10 °C/min and N2 flow of
90 mL/min. Gemini SEM500 high resolution scanning selection micro-
scope working under 10 kV was obtained from ZEISS Inc. Transmission
electron micrographs (TEM) were provided by a Hitachi instrument H-
7650 with an accelerating voltage of 120 kV. The surface chemical in-
formation and elemental analysis of the catalysts were characterized by
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