Implanting Copper?Zinc Nanoparticles into the Matrix of Mesoporous Alumina as a Highly Selective Bifunctional Catalyst for Direct Synthesis of Dimethyl Ether from Syngas

Article abstract of DOI:10.1002/cctc.201902166

Dimethyl ether (DME) is an industrially important intermediate and clean alternative fuel. Thus, developing an efficient bifunctional catalyst for syngas-to-DME is practically important but remains a challenge. In this paper, a copper?zinc implanting into matrix of mesoporous alumina (CuZn@m?Al₂O₃) catalyst was prepared by introducing the as-prepared Cu?Zn oxalate nanoparticles into the Al(_i-OPr)₃-containing precursor solution for preparing mesoporous Al₂O₃ (m-Al₂O₃) through evaporation-inducing assembly method. The preparation of Cu?Zn oxalate in advance for synthesizing CuZn@m?Al₂O₃ can intensify the Cu?ZnO interaction, confirmed by XRD and H₂-TPR. Thanks to the unique CuZn-implanting closed structure, CuZn@m?Al₂O₃ shows 89.0 % of higher selectivity with comparable CO conversion (15.5 %) than the previously reported supported-type CuZn catalyst on m-Al₂O₃ (CuZn/m?Al₂O₃, 75.2 %) for hydrogenation of syngas to DME. Over the developed CuZn@m?Al₂O₃ catalyst, 0.16 mmol g^?1 _cat h^?1 of high DME rate can be achieved. CuZn@m?Al₂O₃ also shows higher methanation resistance (2.7 % CH₄) compared to CuZn/m?Al₂O₃ (6.3 %), ascribed to intensified Cu?Zn interaction owing to the as-formation of Cu?Zn oxalate in advance. Moreover, Both CuZn@m?Al₂O₃ and CuZn/m?Al₂O₃ exhibit high stability. The outstanding catalytic performance of CuZn@m?Al₂O₃ allows it to be a promising catalyst for DME synthesis from syngas.

Full text of DOI:10.1002/cctc.201902166

Accepted Article
Title: Implanting Copper-Zinc Nanoparticles into the Matrix of
Mesoporous Alumina as a Highly Selective Bifunctional Catalyst
for Direct Synthesis of Dimethyl Ether from Syngas
Authors: Yingqi Sun and Zhongkui Zhao
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of the final Version of Record (VoR). This work is currently citable by
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published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201902166
Link to VoR: http://dx.doi.org/10.1002/cctc.201902166
A Journal of
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ChemCatChem
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COMMUNICATION
Implanting Copper-Zinc Nanoparticles into the Matrix of
Mesoporous Alumina as a Highly Selective Bifunctional Catalyst
for Direct Synthesis of Dimethyl Ether from Syngas
Yingqi Sun and Zhongkui Zhao*
Abstract: Dimethyl ether (DME) is an industrially important
intermediate and clean alternative fuel. Thus developing an efficient
bifunctional catalyst for syngas-to-DME is practically important but
remains a challenge. In this paper, a copper-zinc implanting into
DME and other acidic catalysis processes.[11,14,19,20] Previous
studies have paid more attention to the simple mechanical
mixing of the two catalysts.[22-27] However, some deficiencies like
copper sintering and far distance between active sites of
syngas-to-methanol and solid acidic sites cannot be avoided in
matrix of mesoporous alumina (CuZn@m-Al
prepared by introducing the as-prepared Cu-Zn oxalate
nanoparticles into the Al(-OPr) -containing precursor solution for
preparing mesoporous Al (m-Al ) through evaporation-inducing
assembly method. The preparation of Cu-Zn oxalate in advance for
2 3
O ) catalyst was
one-pot transformation process over this kind of mixed hybrid
catalyst.[28-32]
i
3
O
2 3
2 3
O
Many efforts have been done to overcome the above
problems.[33-41] The confinement of Cu-Zn into the pores of high
synthesizing CuZn@m-Al
2
O
3
can intensify the Cu-ZnO interaction,
-TPR. Thanks to the unique CuZn-
2 3
thermal stability mesoporous Al O can efficiently enhance the
confirmed by XRD and H
2
catalytic stability by suppressing the aggregation of Cu
nanopartilces,[33-35] but the selectivity of DME remains to be
improved owing to the as-formed methanol on the Cu catalyst
easily leaving the catalyst through the mesopores before it to be
converted into DME by dehydration. In order to address this
implanting closed structure, CuZn@m-Al
selectivity with comparable CO conversion (15.5%) than the
previously reported supported-type CuZn catalyst on m-Al
CuZn/m-Al , 75.2%) for hydrogenation of syngas to DME. Over
the developed CuZn@m-Al
DME rate can be achieved. CuZn@m-Al
methanation resistance (2.7% CH ) compared to CuZn/m-Al
6.3%), ascribed to intensified Cu-Zn interaction owing to the as-
formation of Cu-Zn oxalate in advance. Moreover, Both CuZn@m-
Al and CuZn/m-Al exhibit high stability. The outstanding
catalytic performance of CuZn@m-Al allows it to be a promising
catalyst for DME synthesis from syngas.
2 3
O shows 89.0% of higher
2 3
O
(
2 3
O
-
1
-1
2
O
3
catalyst, 0.16 mmol g cat
h of high
issue, various core-shell catalysts with Cu-Zn as core and
zeolite as shell have been reported.[36-41] Thanks to the
2 3
O
also shows higher
4
2 3
O
confinement effect of core-shell structure, thus catalysts have
shown much high DME selectivity since the as-formed methanol
must pass through the zeolite shell before it leaves from the
catalyst. Unfortunately, the process of coating zeolite shell on
the CuZn core inevitably etches the Cu-based core, which would
deteriorate the catalytic activity of CuZn@zeolite core-shell
although it shows outstanding selectivity of DME. Therefore,
pursuing a new and highly efficient Cu-based bifunctional
catalyst with high active and selectivity still remains a challenge.
In this work, we design and prepare CnZn embedding-type
(
2
O
3
2 3
O
2 3
O
Nowadays, dimethyl ether (DME) has attracted more and more
attention concerning its application acting as both an industrially
important chemical materials and a clean alternative fuel.[1-5]
DME was generally produced by two routes: one is methanol
dehydration catalyzed by an acidic catalyst, in which methanol is
previously synthesized by catalyzed hydrogenation of syngas;
the other is a direct synthesis route from one-pot transformation
of syngas over a bifunctional catalyst.[5-11] The latter is regarded
as a promising pathway for DME production. The generally used
bifunctional catalyst for the one-step synthesis of DME from
syngas is composed of two types of active sites: one is methanol
synthesis transition metallic catalyst, and the other is methanol
dehydration solid acid catalyst. Regarding methanol synthesis
process, Cu-ZnO catalysts have been extensively studied for
decades. Traditionally, impregnation, co-precipitation, chemical
vapor deposition, sol–gel and other wet-chemical methods have
been widely used to prepare Cu-ZnO based catalysts.[11-18] For
bifunctional catalyst into the matrix of m-Al
formed CuZn oxalate into the precursor solution in the
preparation process of m-Al . The developed CuZn@Al
catalyst shows much higher selectivity of DME than the
2 3
O by adding the as-
2
O
3
2 3
O
previously reported CuZn/m-Al
impregnating CuZn on the m-Al
CuZn@Al and CuZn/m-Al
stability. The outstanding catalytic performance of CuZn@m-
Al catalyst allows it to be a promising candidate for direct
2
O
3
catalyst prepared by
2
3
O support. Moreover, both
2
O
3
2 3
O catalysts show high activity and
2
O
3
DME production from syngas. This work not only creates a novel
and highly efficient bifunctional syngas-to-DME catalyst, but also
presents
bifunctional catalysts for other consecutive reactions.
Scheme depicts the schematic illustration for the
preparation of the developed CuZn@m-Al bifunctional
catalyst. Typically, the CuZn@m-Al catalyst was prepared by
a new conception for designing highly efficient
1
solid acid catalysts, H-ZSM-5 and γ-Al
considered excellent candidates for methanol dehydration to
2
O
3
are generally
2 3
O
2
O
3
the following 4 steps: (1) The CuZn oxalate was prepared by co-
precipitation method with oxalic acid as precipitant as well as the
Cu(NO
(2) Pluronic P123, aluminum isopropoxide and HNO
dissolved in ethanol solvent under strong stirring at ambient
temperature for 6 hours to form precursor solution of m-Al
3) The CuZn oxalate powder were added to the above
3
)
2
and Zn(NO
3
)
2
as Cu and Zn precursors, respectively;
[
a]
Yingqi Sun, and Prof. Zhongkui Zhao
State Key Laboratory of Fine Chemicals Department of Catalysis
Chemistry and Engineering School of Chemical Engineering Dalian
University of Technology Dalian 116024, P.R. China
E-mail: zkzhao@dlut.edu.cn
3
were
2
3
O ;
(
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
precursor solution; (4) The solvent was evaporated and then
o
transferred to an drying oven, and finally calcined at 400 C and
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ChemCatChem
10.1002/cctc.201902166
COMMUNICATION
corresponding mapping images (Figure 1c and 1d). The textural
properties of the two catalysts were characterized by N
adsorption-desorption experiments, and the bare m-Al is also
included for comparison. Figure 2 shows the isotherms and
2
2
O
3
Scheme 1. Schematic illustration of the preparation of implanting-type
CuZn@m-Al O bifunctional catalyst.
2 3
then 600 oC for oxalate decomposition and mesoporous Al
formation. As a consequence, the implanting-type CuZn@m-
O
3
2
Al
Al
2
O
O
3
was prepared. Moreover, the supporting-type CuZn/m-
was prepared by incipient wetness impregnation method
Figure 2. Nitrogen adsorption-desorption isotherms of m-Al
2 3
O , CuZn@m-
2
3
Al and CuZn/m-Al . Inset: pore size distributions from adsorption branch
2
O
3
2 3
O
for comparison.
Figure 1 shows TEM images of as-synthesized CuZn@m-
and CuZn/m-Al . From Figure 1, CuZn nanoparticles
Al
2
O
3
2
O
3
the pore size distribution regarding mesopores, and the
quantitative data are listed in Table 1. The mesoporous
Table 1. Characterization data of the CuZn@m-Al
m-Al catalysts.
O
2 3
, CuZn/m-Al
O
2 3
and
2 3
O
[
a]
[b]
[c]
[d]
Catalyst
S
BET
V
P
D
P
S
Cu
[
m2 g-1]
[cm3 g-1]
[nm]
[m2 g-1cat
]
CuZn@m-Al
CuZn/m-Al
m-Al
2
O
3
108
55
0.62
0.11
0.72
14.9
6.0
8.35
9.59
2
O
3
2
O
3
201
9.5
[
a] BET specific surface area from N
2
adsorption desorption. [b] Total pore
volume (cm g-1). [c] Average pore diameter (nm). [d] Surface area of Cu
3
2 2
were determined from by H -TPR after oxidation of the samples by N O.
structures of the solid acid m-Al
2
O
3
2 3
and CuZn@m-Al O
catalysts were confirmed by the typical type IV adsorption–
desorption isotherms.[33] However, the typical type IV adsorption-
desorption isotherm cannot be observed on the CuZn/m-Al
catalyst although the m-Al support has typical
ssmesoporous structure, might be ascribed to the blockage of
mesopores of m-Al by a large amount of CuZn nanoparticles.
2 3
O
2
O
3
a
2 3 2 3
Figure 1. a,b) TEM images of CuZn@m-Al O (a) and CuZn/m-Al O (b). c,d)
STEM image (c) and the corresponding mapping image (d) of CuZn@m-Al O
2 3
catalyst.
2
O
3
Moreover, the CuZn@m-Al
2
O
3
catalyst shows higher surface
area (108 m2 g ) and mesoporous volume (0.62 cm g )
-1
3
-1
2
-1
3
-1
2 3
compared to CuZn/Al O catalyst (55 m g , 0.11 cm g ).
To acquire the crystalline structure of these materials, this
work used X-ray diffraction (XRD) to obtain the result. As
isshown in Figure 3, the characteristic diffractions peaks of CuO
are located at 35.6, 38.8, 58.3, 61.6, and 66.3o and the XRD
peaks at 34.2 and 48.1o corresponding to ZnO phase can be
with the size of 30-60 nm are implanted into the matrix of
CuZn@m-Al while the smaller CuZn dispersed into the m-
Al of CuZn/m-Al catalyst. The bigger CuZn size in the
CuZn@m-Al catalyst than that of CuZn/m-Al leads to its
lower surface area of exposed Cu (8.35 vs. 9.59 m g .).
Furthermore, the unique implanting-type CuZn@m-Al
catalyst featuring the CuZn nanoparticles to be embedded into
the matrix of m-Al is confirmed by the STEM and the
2
O
3
2
O
3
2 3
O
2
O
3
2 3
O
2
-1
resolved [40-42]. Furthermore, the characteristic X-ray diffraction
2
O
3
o
peaks at 66.1 corresponding to m-Al
2
O
3
of the CuZn@m-Al
2
O
3
samples can be resolved, presenting an evidence for the
2
O
3
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ChemCatChem
10.1002/cctc.201902166
COMMUNICATION
Figure 4. H
and the Cu/m-Al
2
-TPR profiles of the CuZn@m-Al
2 3 2 3
O and CuZn/m-Al O catalysts,
2 3 2 3 2 3
Figure 3. XRD patterns of m-CuZn@Al O , CuZn/m-Al O , CuZn@m-Al O -s,
and CuZn/m-Al O -s.
2 3
2 3
O
is included for comparison.
The acidic properties of the as-prepared CuZn@m-Al
CuZn/m-Al bifunctional catalysts were measured by NH
TPD technique, and the spent catalysts (CuZn@m-Al -s and
CuZn/m-Al -s) were also included for comparison. Figure 5
2 3
O and
successful coating m-Al
obviously weaker and wider diffraction peaks assigned to CuO
and ZnO compared to those of CuZn/m-Al , suggesting
smaller crystalline size of CuO and ZnO. The average crystalline
size of CuO was estimated by Scherrer Equation (Table S1),
2 3 2 3
O . Moreover, CuZn@m-Al O shows
2
O
3
3
-
2
O
3
2
O
3
2
O
3
presents the NH3-TPD profiles, and the quantitative results are
CuZn@m-Al
size (29.7 nm) compared CuZn/m-Al
2
O
3
catalyst shows lower CuO average crystalline
(41.6 nm), although the
2
O
3
former shows larger particle size confirmed by TEM images
shown in Figure 1. After reduction, the CuO can be transformed
into metallic Cu. The smaller crystalline size of Cu and ZnO
leads to the intensified Cu-ZnO interaction. According to the
reference,[5] ZnO can maintain high copper dispersion through
2 3
Cu-ZnO interaction in CuZn@m-Al O catalyst, which can
promote methanol synthesis and inhibit methane formation. The
ZnO peaks after the reaction of the two catalysts all shifted to
the right, indicates that the crystal structure of the ZnO changed
after the reaction.
The H
behavior and the interaction of Cu particles with Zn species of
the m-CuZn/Al and CuZn@m-Al catalysts, and Cu/m-
Al was included for comparison. From Figure 4, the
reference supported single Cu catalyst on m-Al exhibits two
-consumption peaks appearing at 188 and 220 oC,
corresponding to the reduction of highly dispersed CuO in
copper-zinc oxide and the reduction of bulk CuO crystals with
larger grain sizes dispersed among ZnO particles, respectively.
2
-TPR was carried out to investigate the redox
2
O
3
2 3
O
2
O
3
2
O
3
Figure 5. NH -TPD profiles of the CuZn@m-Al O , CuZn/m-Al O , CuZn@m-
3
2
3
2
3
H
2
Al
2
O
3 2 3
-s and CuZn/m-Al O -s.
listed in Table S1. From Figure 5, all of the samples show a
strong peak according to weak acid sites with a broadened peak
concerning medium-strength acid sites. Moreover, both of the
spent catalysts show a slightly decreasing amount of acidic sites
compared to that of the two fresh catalysts, ascribed to the
dehydration of surface hydroxyl groups in the reaction process.
2 3 2 3
Compared with Cu/m-Al O , the CuZn/m-Al O shows similar
reduction peaks, but the reduction peak at high temperature
becomes more obvious. Furthermore, the reduction peaks of
CuZn@m-Al
to those of CuZn/m-Al
featuring the CuZn nanoparticles implanted into the matrix of m-
Al
, besides the intensified Cu-ZnO interaction.[26] According
to Table S1, the H consumption of CuZn@m-Al (24.2 mmol
g ) is lower than that of CuZn/m-Al , which might be an
indicator for the embedding Cu-Zn into the matrix of m-Al
2
O
3
shift to higher reduction temperature compared
2
O
3
, might be ascribed to unique structure
The catalytic performance of CuZn@m-Al
is presented in Table 2 and S1. The CuZn@m-Al
catalyst shows slightly higher TOF than CuZn/m-Al for direct
2 3
O and CuZn/m-
2
O
3
Al
2
O
3
2 3
O
2
2 3
O
2
O
3
-1
2
O
3
synthesis of DME from syngas, ascribed to the stronger
promotion of ZnO by the intensified Cu-ZnO interaction.[33]
2
O
3
.
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COMMUNICATION
2 3 2 3
Table 2. Catalytic performance of the CuZn@m-Al O and CuZn/m-Al O
[
a]
catalysts for direct synthesis of dimethyl ether from syngas.
product distribution[b]
(mol %)
CO-to-
CO
TOF
Con.
%)
2
catalyst
-
1
(
min )
(
(%)
MeOH
18.2
7.9
DME
75.2
89
CH
4
CuZn/m-Al
CuZn@m-Al
Cu@m-Al
2
O
3
17.4
15.5
13.2
2.1
3.2
2.9
-
6.3
3.1
1.74
2
O
3
1.78
2
O
3
8.6
87.2
48.5
5.1
4.2
-
-
-
2 3
Zn@m-Al O
0.8
22.5
93.4
29.0
1.4
CuZnAl[c]
24.7
0.8
[
1
a] Reaction condition: 0.5 g catalyst, P = 3.0 MPa, T = 250 oC, H
2
/CO
2
/N
2
=
0/5/5, GHSV = 1800 ml g-1 h , obtained at 4 h of TOS. [b] Based on the
-1
2 3 2 3
Figure 6. Catalytic stability of CuZn@Al O and CuZn/Al O for direct
synthesis of dimethyl ether from syngas.
as-formed total hydrocarbons and oxygenates. [c] Standard methanol
synthesis catalyst.
[
43]
Interestingly, CuZn@m-Al
distribution (selectivity) with promoted dehydration of methanol
to DME than the traditional supported-type CuZn/m-Al
catalyst although the former shows much more acidic sites
Figure 5), which can be ascribed to the unique implanting-type
structure of the developed CuZn@m-Al catalyst. In
comparison with the standard CuZnAl methanol synthesis
catalyst (93.4% methanol selectivity),[43] our CuZn@m-Al
2 3
O catalyst shows much higher DME
comparing the product distributions of the initial and last points
listed in Table S2 (TOS = 4 and 28 h), the decreased selectivity
mainly comes from the greater amount of methanol (7.9 vs.
2
O
3
13%). The no obvious increase in CH4 can be observed (3.1%
(
vs 3.9%). The slight decrease in DME selectivity can be
ascribed to the lowering amount of acidic sites in the reaction
2
O
3
process confirmed by the NH -TPD profiles presented in Figure
3
2
O
3
5. In a word, this work develops an efficient bifunctional catalyst
catalyst can efficiently convert the as-formed methanol from
syngas over the implanted CuZn nanoparticles in the matrix of
for direct synthesis of DME from syngas.
In summary, we report a practical CuZn implanted-type
m-Al
be ascribed to the unique implanting-type structure of CuZn@m-
Al catalyst and the higher Al content (60% vs. 10%).
Moreover, CuZn@m-Al
content than CuZn/m-Al
2 3 2 3
O into DME while it passes through the m-Al O . This can
catalyst in the matrix of mesoporous Al
addition of the as-prepared CuZn oxalate nanoparticles into the
precursor solution according to the preparation of m-Al . This
2 3
O simply prepared by
2
O
3
O
3
catalyst shows lower methane
3
O catalyst, originating from the
2
O
3
2
produces a superior bifunctional catalyst for one-pot DME
synthesis from syngas with higher selectivity towards DME from
the as-formed methanol over Cu-ZnO to the previously reported
2
[
33]
suppressed formation of methane
conversion of the as-formed methane to methanol[5] by
or the promoted
supported CuZn catalyst on m-Al
implanting-type structure. The prior formation of Cu-Zn oxalate
for the preparation of CuZn@m-Al catalyst can intensify the
2 3
O , resulting from its unique
intensified Cu-ZnO interaction. For another, we compared the
catalytic performance of the implanted single component
catalysts (Cu@m-Al O and Zn@m-Al O ) to present a further
2 3 2 3
2
O
3
Cu-ZnO interaction, which can subsequently stabilize the Cu
and also suppress the formation of methane. As a result, the
insight. From the results listed in Table 2, the addition of Zn
shows a promoting effect on the catalytic performance of the
supported Cu catalyst in some degree, although only 0.8%
developed CuZn@m-Al
2
O
3
catalyst shows 15.5% of CO
conversion with 89% DME content. This work not only presents
highly selective bifunctional catalyst for syngas-to-DME, but also
opens up a simple method for designing other bifunctional
catalysts for diverse consecutive reactions.
2 3
conversion over Zn@m-Al O can be seen. From XRD and TPR,
there is no evidence for the formation of Cu-Zn alloy. From our
previous work concerning the CuZnAl prepared by the same
method,[40] the Cu-ZnO interaction promotes the catalysis of Cu-
based catalyst. Therefore, we proposed that the Cu is the active
sites for CO hydrogenation to methanol, and the promoting
effect of added Zn into the implanted Cu catalyst in this work Experimental Section
might come from the Cu-ZnO interaction at the interface.
Furthermore, CuZn@m-Al
2
O
3
2
catalyst shows slight higher DME
2 3
Catalysts preparation: CuZn@m-Al O catalyst was prepared by the
-
-1
following procedure: Firstly, binary metal CuZn oxalate particles were
prepared by co-precipitation method using oxalate as precipitant.
Typically, 1.8 g of oxalic acid in ethanol was added rapidly to a mixed
ethanol solution consisting of 1.09 g of copper nitrates and 0.59 g of zinc
nitrates in the desired ratio at room temperature under vigorous stirring.
The gel-like precipitate was aged for 4 h at room temperature and then
separated by centrifugation. The drying process was carried out at 105
oC for 6 h. The obtained CuZn catalyst is crushed into a powder before
subsequent use. After that, 2 g of Pluronic P123 was dissolved in 40 mL
formation rate (0.16 μmol m Cu h ) than the traditional CuZn/m-
catalyst (0.15 μmol m- Cu h ).
2
-1
2 3
Al O
The catalytic stability of the bifunctional catalysts of two
different structures is shown in Figure 6. Both of these catalysts
show outstanding catalytic stability, and no visible decrease in
CO conversion can be observed along with the extending time
on stream, although there is a slight decrease in selectivity. By
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ChemCatChem
10.1002/cctc.201902166
COMMUNICATION
o
-1
of ethanol at room temperature. Then, 2 mL of 67 wt % nitric acid and 4.8
g of aluminum iso-propoxide were added into the above solution with
vigorous stirring. The mixture was covered with PE film, stirred at room
temperature for about 5 h, and then the as-formed CuZn powder was
added into the above solution, and then put into a 60 oC water bath to
undergo the solvent evaporation crystallization for 24 h. After aging for 1
day, the as-prepared light blue powder was calcined, the temperature
was slowly raised from room temperature to 400 oC (2 oC min-1 heating
reduction was performed in situ at 250 C by a mixture gas (10 ml min
hydrogen with 20 ml min-1 nitrogen) at atmospheric pressure for 2 h. The
effluent products from the reactor were transported to the gas
chromatography (FULI 9790 II) with tubing warm 160 C. The GC was
equipped with Porapak N and 5A molecular sieve packed columns, which
2 2 4
, CO, CO ) and organic (CH ,
CH OCH , CH OH) gaseous species, respectively. The CO conversion
o
were used to separate inorganic (N
3
3
3
(XCO) and organic product distribution were calculated using an internal
standard method via Eq. 2 and 3, respectively:
o
rate) and heated at 400 C for 4 h. The high temperature treatment was
carried out in air at a ramp rate of 10 C min-1 at 600 C for 2 h. Finally,
o
o
the CuZn@m-Al catalyst was obtained. For comparison, the CuZn/m-
O
2 3
COout
CO conversion (mol%) = (1 − COin ) × 100 % (Eq. 2)
Al (Cu/m-Al O ) catalyst was prepared by loading the same amount of
2
O
3
2 3
CuZn (Cu) with incipient wetness impregnation method on the m-Al
support that prepared by the similar method to that for CuZn@m-Al
catalyst except for no CuZn was introduced.
2
O
3
3
i
Mꢀle ꢀf C ×ꢁ
i
C distribution (mol%) = ∑n
× 100 % (Eq. 3)
2
O
i
Mꢀle ꢀf C ×ꢁ
iꢂꢃ
Where COin and COout stands for the molar fraction of CO at the inlet
i
Catalysts characterization: JEM-2000EX TEM instrument was used to
obtain the Transmission electron microscopy (TEM) images. X-ray
diffraction (XRD) patterns of the samples were collected in the 2θ range
and outlet, respectively. C represents the organic product of CH
3
OH,
CH
4
, DME, and i is for the carbon number in the molecules.
The formation of CO via the water–gas shift reaction of CO was
evaluated by the conversion of CO to CO (mol%). Furthermore, the
2
o
o
of 5–80 with a step of 0.02 on a Rigaku D/max-2400 apparatus with Cu
Kα radiation. NH temperature-programmed desorption (NH -TPD) data
were acquired on a Builder Chemisorption (PCA-1200) instrument with a
thermal conductivity detector (TCD) to measure the desorbed NH . The
2
3
3
turnover frequency (TOF) of CO was calcu-lated as the transferred CO
per min per surface Cu atom. The intrinsic activity was calculated as the
number of moles of as-formed DME per h per m2 surface area of the
exposed Cu atoms. TOF and intrinsic activity were calculated by
employing equations 4 and 5, respectively:
3
catalyst sample with the amount of 0.1 g was firstly pretreated in flowing
argon at 500 oC for 1 h, and then cooled to room temperature. The
pretreated sample was saturated with ammonia at 100 oC via pulse
injection of ammonia. Desorption profiles were obtained with the flowing
argon from 100 oC to 500 oC at a heating rate of 10 oC min . Nitrogen
-1
-1
Fco×Xco
TOF (min ) =
(Eq. 4)
adsorption-desorption
analysis
was
applied
to
measure
ꢄꢅꢅꢅ×Vm×nCu
Brunauer−Emmett−Teller (BET) surface area, pore volume, and
Barrett−Joyner−Halenda (BJH) pore size distribution from the desorption
nDME×MDME
Intrinsic activity RDME
=
(Eq. 5)
Cu cat
S W
branch on the as-prepared Al
and CuZn/Al catalysts using
000PS1 at -196 oC. H
-TPR experiments were performed on a Builder
PCA-1200 automated system. 0.03 g of catalyst was placed in a U-shape
quartz tube in a temperature‐controlled oven. The catalyst was first
2
O
3
supports and bifunctional CuZn@Al
2 3
O
V
m
is the molar volume of an ideal gas at 298 K (24.5 L mol−1), FCO
O
2 3
a
Beishide apparatus Model 3H-
2
2
represents the CO flow rate (ml min−1), nCu is the number of moles of
exposed Cu atom of the loaded catalyst for the performance test, MDME is
the molecular mass of DME, nDME represents the as-formed DME per min,
o
o
purged under Ar flow at 250 C for 60 min (using a heating rate of 10 C
S
Cu is the Cu surface area of samples, and Wcat is the mass of catalyst.
-
1
min ) and then cooled down to room temperature. After that, it was
-
1
DME productivity is defined as the number of moles of as-formed DME
per h per g catalyst.
reduced with a 10% H
2
‐90% Ar mixture (50 mL min ) by heating to 400
C at a heating rate of 2 C min . The amount of hydrogen consumption
was measured using a thermal conductivity detector. Cu surface areas of
o
o
-1
samples were determined by H
2
-TPR after oxidation of the samples by
o
2
N O at 50 C. The procedure was as follows: the catalyst sample with the
Acknowledgements
-
1
o
amount of 0.1 g was reduced under 10 % H
2
/Ar (30 ml min ) at 250 C
for 2 h, and then cooled down to room temperature. After purging with He
This work was financially supported by the National Natural
Science Foundation of China (U1610104).
for 30 minutes to remove excess H
through the sample to oxidize metallic copper at 50 C for 1 hour. Finally,
2
/Ar, the 10% N
2
O/He was passed
o
1
0% H
sample temperature was raised to 400 C at a heating rate of 10 C min .
The H consumption is obtained by integrating and converting the TPR
peak area. The number of surface area copper atom is twice the number
of H molecules consumed. The surface area of the exposed surafce Cu
2
/Ar (30 ml min-1 ) was passed through the sample and the
o
o
-1
Keywords: Cu-Zn catalyst • implantation • syngas • dimethyl
ether • bifunctional catalyst • Cu-ZnO interaction
2
2
per gram catalyst (SCu) was calculated by atopting the Eq. 1:
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1
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10.1002/cctc.201902166
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10.1002/cctc.201902166
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
Implanting-type bifunctional
Yingqi Sun and Zhongkui Zhao*
catalyst: This work reports a practical
CuZn implanted-type catalyst in the
Page No. – Page No.
2 3
matrix of mesoporous Al O .This
Implanting Copper-Zinc
produces a superior bifunctional
catalyst for one-pot DME synthesis
from syngas with higher selectivity
towards DME from the as-formed
methanol over Cu-ZnO sites to the
previously reported supported CuZn
Nanoparticles into the Matrix of
Mesoporous Alumina as a Highly
Selective Bifunctional Catalyst for
Direct Synthesis of Dimethyl Ether
from Syngas
catalyst on m-Al
2 3
O , resulting from its
unique implanting-type structure.
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