Published on the web April 5, 2013
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CoreShell Catalyst CuOZnOAl O @Al O for Dimethyl Ether Synthesis from Syngas
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Yan Wang, Wenli Wang, Yuexian Chen, Jinghong Ma, Jiajun Zheng, and Ruifeng Li*
Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, P. R. China
(
Received October 29, 2012; CL-121099; E-mail: rfli@tyut.edu.cn)
Coreshell structure catalyst CuOZnOAl2O3@Al2O3 was
prepared using glucose as template. This novel preparation
procedure and the specific coreshell structure contributed to
excellent performance for dimethyl ether (DME) direct synthesis
from syngas. This catalyst showed higher CO conversion and
DME selectivity compared with the physically mixed catalyst.
synthesis catalyst. The methanol synthesis catalyst CZA was
first calcined at 350 °C for 3 h. Before the following utilization,
the raw CZA catalyst was granulated into grains with a size of
0.851.70 mm. For the coreshell structure catalyst CuOZnO
Al O @Al O synthesis, 4 g of glucose was first dissolved in
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40 mL of deionized water, and then 2 g of aluminum nitrate was
added to the solution to form a clear solution. The solution was
poured into an autoclave vessel. Subsequently, 1 g of CZA
catalyst particles was immersed into the solution. The autoclave
vessel was sealed and hydrothermal synthesis was carried out
under autogenous pressure at 120 °C for 6 h. A rinsing process
involving five cycles of centrifugation and washing was
performed with water or ethanol. The samples were obtained
after drying at room temperature overnight. The samples were
calcined at 330 and 440 °C for 3 h under nitrogen atmosphere
and then under oxygen atmosphere at 500 °C for another 3 h.
At the calcination stage, the heating rate was controlled at
In addition to utilization as an important chemical inter-
mediate,1 dimethyl ether (DME) has been widely known as
clean alternative fuel with handling characteristics similar to
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those of liquefied petroleum gas (LPG). Conventionally, DME
has been produced by methanol dehydration using acid catalyst.
Recently, one-step synthesis of DME from syngas has attracted
more and more interest because of lower thermodynamic
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limitation and investment. The preparation of hybrid bifunc-
tional catalysts is a complex process and needs special attention
for the proper control of the preparation conditions. Since the
hybrid bifunctional catalyst is composed of methanol synthesis
and methanol dehydration catalysts, the preparation conditions
of the hybrid catalyst could deactivate either function due to the
covering of the acidic dehydration center by part of the methanol
synthesis catalyst, the formation of new species, or low
dispersion of the active component.5 Consequently, the hybrid
catalyst is deactivated.
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3 °C min . For comparison, the methanol synthesis catalyst
CZA was physically mixed with methanol dehydration catalyst
£-Al2O3 (China Research Institute of Daily Chemical Industry)
with a weight ratio of 10:1. The BET surface area of £-Al2O3 is
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143 m g . The physically mixed hybrid catalyst was named
CZA-M.
,6
In Figure 1, the characteristic peaks of CuO and ZnO
existed in the XRD patterns of CZA, CZA-M, and CZA@Al O ,
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Yang et al. have reported a millimeter-sized zeolite capsule
but the graphite peak disappeared and no diffractive peaks of
Al2O3 were observed obviously in CZA@Al2O3. Using glucose
as template to synthesize the coreshell catalyst CZA@Al O ,
catalyst possessing a special coreshell with methanol synthesis
catalyst CuZnOAl O as core. This special coreshell catalyst
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was applied to syngas to DME (STD) reaction and presented
higher selectivity than traditional physically mixed hybrid
catalyst with zero formation of unexpected hydrocarbon
various chemical reactions could take place under hydrothermal
condition, resulting in a complex mixture of the organic acid,
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such as levulinic acid, acetic acid, and formic acid. After
hydrothermal treatment, the pH of the solution was 3.3, and the
pH of the original solution before hydrothermal treatment was
3.5. The formation of organic acid could cause the CZA core to
partially dissolve during the synthesis procedure, which led to
the decreased crystallinity of ZnO on CZA@Al2O3.
(HC) by-products. However, during the hydrothermal synthesis
process of the coreshell structure catalyst the use of amine
template TPAOH (tetrapropylammonium hydroxide) damages
the core CuZnOAl O and causes the deactivation the core
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shell catalyst.
Recently, carbon material obtained from carbonaceous
polysaccharide has been used as template for the synthesis of
a series of metal oxides.8 This carbon material has an external
surface densely functionalized with polar functional groups such
as carboxylic, hydroxy, or quinone groups. These functional
groups are amendable to anchorage of hydrophilic or hydro-
phobic materials for synthesis of the coreshell structure
As shown in Figure 2A, the Al2O3 shell had enwrapped the
CZA core uniformly. The average thickness of the Al O shell
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CuO
ZnO
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Graphite
CZA
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catalyst.
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In this work, we report a facile route to synthesize the core
shell structure catalyst CuOZnOAl2O3@Al2O3 using glucose
as template. The coreshell structure catalyst CuOZnO
Al O @Al O exhibited high catalytic performance and stability
CZA@Al O
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CZA-M
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in the STD reaction.
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In this study, a commercial catalyst CuOZnOAl2O3
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(C302, Southwest Research & Design Institute Chemical
Industry, China, denoted as CZA) was used as methanol
Figure 1. XRD patterns of CZA, CZA-M, and CZA@Al2O3.
Chem. Lett. 2013, 42, 335337