A High-Performance Nanoreactor for Carbon-Oxygen Bond Hydrogenation Reactions Achieved by the Morphology of Nanotube-Assembled Hollow Spheres

Article abstract of DOI:10.1021/acscatal.7b03026

Hydrogenation of carbon-oxygen bonds is extensively used in organic synthesis. However, a high partial pressure of hydrogen or the presence of excess hydrogen is usually essential to achieve favorable conversions. In addition, because most hydrogenations are consecutive reactions, the selectivity is difficult to manipulate, leading to an unsatisfactory distribution of products. Herein, a copper silicate nanoreactor with a nanotube-assembled hollow sphere (NAHS) hierarchical structure is proposed as a solution to these problems. In the case of dimethyl oxalate (DMO) hydrogenation, the NAHS nanoreactor achieves remarkable catalytic activity (the yield of ethylene glycol is 95%) and stability (>300 h) when the H₂/DMO molar ratio is as low as 20 (in comparison to typical values of 80-200). For further investigation, nanotubes and lamellar-shaped Cu/SiO₂ catalysts with similar surface areas of active sites of NAHSs were investigated as contrasts. By a combination of high-pressure hydrogen adsorption and Monte Carlo simulation, it is demonstrated that hydrogen can be enriched on the concave surface of nanotubes and hollow spheres, leading to a favorable activity in such a low H₂ proportion. Furthermore, because of the spatial restriction effect of reactants, adjusting the diffusion path is an effective route for manipulating the selectivity and product distribution of the hydrogenation reactions. By variation in the length of nanotubes on NAHS, the yields of methyl glycolate and ethylene glycol are easily controlled. The NAHS nanoreactor, with insights into the effect of morphology on hydrogen enrichment and spatial restriction of reactant diffusion, offers inspiring possibilities in the rational design of catalysts for hydrogenation reactions.

Full text of DOI:10.1021/acscatal.7b03026

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Article
A High-Performance Nanoreactor for Carbon-Oxygen
Bonds Hydrogenation Reactions Achieved by the
Morphology of Nanotube-Assembled Hollow Sphere
Dawei Yao, Yue Wang, Ying Li, Yujun Zhao, Jing Lv, and Xinbin Ma
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b03026 • Publication Date (Web): 27 Dec 2017
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A HighꢀPerformance Nanoreactor for CarbonꢀOxygen Bonds
Hydrogenation Reactions Achieved by the Morphology of
NanotubeꢀAssembled Hollow Sphere
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‡
‡
Dawei Yao , Yue Wang , Ying Li, Yujun Zhao, Jing Lv and Xinbin Ma*
Key Laboratory for Green Chemical Technology of Ministry of Education, Collaborative
Innovation Center of Chemical Science and Engineering
School of Chemical Engineering and Technology, Tianjin University
Tianjin 300072 (P. R. China)
ABSTRACT: Hydrogenation of carbonꢀoxygen bonds are extensively used in organic synthesis.
However, a high partial pressure of hydrogen or the presence of excess hydrogen is usually
essential to achieve favorable conversions. In addition, because most hydrogenations are
consecutive reactions, the selectivity is difficult to manipulate, leading to an unsatisfactory
distribution of product. Herein, a copper silicate nanoreactor with a nanotubeꢀassembled hollow
sphere (NAHS) hierarchical structure is proposed as a solution to these problems. In the case of
dimethyl oxalate (DMO) hydrogenation, the NAHS nanoreactor achieves remarkable catalytic
activity (the yield of ethylene glycol is 95%) and stability (> 300 h) when the H /DMO molar
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ratio is as low as 20 (compared to typical values of 80 to 200). For further investigation,
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nanotubes and lamellarꢀshaped Cu/SiO catalysts with similar surface areas of active sites of
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NAHS were investigated as contrasts. Combining the highꢀpressure hydrogen adsorption and
Monte Carlo simulation, it is demonstrated that hydrogen can enrich on the concave surface of
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nanotube and hollow sphere, leading to a favorable activity in such a low H proportion.
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Furthermore, because of the spatial restriction effect of reactants, adjusting the diffusion path is
an effective route for manipulating the selectivity and product distribution of the hydrogenation
reactions. By varying the length of nanotubes on NAHS, the yields of methyl glycolate and
ethylene glycol are easily to control. The NAHS nanoreactor, with insights into the effect of
morphology on hydrogen enrichment and spatial restriction of reactants diffusion, offers
inspiring possibilities in the rational design of catalysts for the hydrogenation reactions.
Keywords: enrichment • heterogeneous catalysis • hydrogenation • copperꢀbased catalyst •
spatial restriction
INTRODUCTION
Hydrogenation of carbonꢀoxygen (C=O/CꢀO) bonds (for example, esters, ethers, furfural and
CO ), as a versatile fundamental reaction, has been extensively used in chemical synthesis.
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Numerous attractive chemical products, fuels and polymers can be obtained by the
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hydrogenation of C=O/CꢀO from coalꢀderived resources or biomass. However, two common
issues are desiderating to be overcome in these hydrogenation reactions, especially for industrial
applications. First, a high partial pressure of H or the presence of excess H (much higher than
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the stoichiometric ratio) is an essential requirement for obtaining favorable conversion and/or
selectivity in the reaction. For example, the H2 pressures required in most biomass
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hydrogenations are as high as 4ꢀ10 MPa, some even reaching 100 MPa. In the synthesis of
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ethylene glycol (EG) from syngas via the hydrogenation of dimethyl oxalate (DMO), the
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H /DMO ratio is typically higher than 80 to generate favorable space time yield of EG.
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Although a few cases were conducted at the H /DMO ratio of 50, the space velocities of DMO
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were all very low. Consequently, recycling large amounts of highꢀpressure H is necessary in
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these processes, which leads to massive energy consumption and requires highꢀcost industrial
devices. Second, because most hydrogenations are consecutive reactions, such as hydrogenation
of furfural, DMO or biomassꢀderived glyceride compounds, the selectivity of product is difficult
to manipulate. As a result, the cost of separation is increased and the yields of products are
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reduced, which greatly hinders the application of these hydrogenations in industry.
Therefore, developing innovative and practical methods to overcome these two problems is
imperative.
One direction toward finding a solution to these challenges is the rational design of catalysts. A
unique morphology that enables the enrichment of H may provide a way to maintain the
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catalytic performance with reduced H concentrations in feed. Small molecules such as H , CO
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or CO can be effectively adsorbed by materials with a nanotube or hollow structure.
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Additionally, specific morphologies, such as the coreꢀshell structure, have been used to isolate
active sites and for sequential channeling of reactants and intermediates, resulting in direct
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synthesis of products in a consecutive reaction. Such results demonstrate the importance of
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spatial restriction for product control.
Thus, designing and fabricating catalysts with a
particular morphology with the aforementioned characteristics may be a promising strategy to
simultaneously address both of the problems associated with hydrogenation.
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Herein, we report a facile and efficient approach for the fabrication of a nanoreactor with
unique morphology of nanotubeꢀassembled hollow sphere (NAHS), attempting to solve both of
the aforementioned issues. DMO as the simplest diꢀester containing C=O, CꢀO and CꢀC bonds,
becomes a typical case to understand the hydrogenation of these bonds. Moreover, this reaction
not only comprises two continuous hydrogenations (Scheme 1), including the hydrogenation of
DMO to methyl glycolate (MG) followed by a further hydrogenation to EG, but also typically
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, 15
needs a high H /DMO ratio of 80ꢀ200 to reach satisfied activity and selectivity.
Thus, DMO
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hydrogenation became a showcase to allow us to investigate the effect of morphology on activity
and selectivity. We here demonstrate the product distribution can be simply controlled by
adjusting the length of nanotubes on NAHS, as well as remarkable efficiency and stability at
H /DMO ratio of 20 is achieved by this NAHS nanoreactor. The superior activity and adjustable
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selectivity is attributed to the effect of unique morphology on enrichment of hydrogen within the
nanoreactor and spatial restriction of reactants, respectively.
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Scheme 1. Scheme of nanotubeꢀassembled hollow sphere nanoreactor for DMO hydrogenation.
EXPERIMENTAL SECTION
Materials
All the chemicals and reagents were analytical grade and used without any purification.
Cu(NO ) ·3H O (99 %) was purchased from Sinopharm Chemical Reagent Co. Tetraethyl
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orthosilicate (98 %), ammonia (25 wt. % in water), HNO (68 wt. %), NH NO (99.8 %),
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dehydrated methanol (99.8 %) and dehydrated ethanol (99.8 %) were all purchased from Tianjin
Kemiou Chemical Reagent Co.
Catalyst preparation
Given mesoporous copper silicate has been reported as an excellent catalyst precursor for
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DMO hydrogenation , the copper silicate NAHS materials was fabricated here by using the
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modified hydrothermal method
(Scheme 2).
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Synthesis of the silica spheres: Monodispersed silica spheres were fabricated according to the
Stöber method. Briefly, 9 mL ammonia was added into 25 mL deionized water, followed by the
addition of a mixture of 8 mL tetraethyl orthosilicate (TEOS) and dehydrated ethanol. The
mixture was then stirred at 313 K for 2 h to obtain the silica sphere solution. The silica spheres
were separated by centrifugation and washed with ethanol and deionized water. Finally, the silica
spheres were dispersed into 60 mL deionized water again for the copper silicate materials
preparation process.
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Fabrication of the copper silicate NAHS: Typically, 2.42 g copper nitrate and 13 mL ammonia
were added into 200 mL deionized water, followed by dropꢀwise addition of 60 mL silica
spheres solution with stirring and then aged at 313 K for 3 h. The mixture was transferred into an
autoclave, heated at 413 K for 5 h to prepare the NAHS materials with approximately 63
nmꢀlength nanotubes (denoted as NAHSꢀ63nm). The NAHSꢀ70nm, NAHSꢀ92nm, NAHSꢀ119nm
materials were fabricated by increasing the hydrothermal treatment time to 10 h, 15 h and 20 h,
respectively. Likewise, the NAHSꢀ120nm and NAHSꢀ232nm were similarly fabricated with an
increased mass of copper nitrate addition to 7.11 g, and by modifying the hydrothermal treatment
time to 5 h and 20 h, respectively. The obtained materials were separated by centrifugation,
washed with deionized water until the pH value reached 7.0, and dried under vacuum at 355 K
for 6 h. These asꢀsynthesized samples were calcined in static air at 723 K for 4 h, tableted,
crushed, and sieved to 40−60 meshes.
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Preparation of the copper silicate nanotubes (NTs): Typically, 7.11 g copper nitrate and 13 mL
ammonia with calculated proportion were mixed into deionized water, followed by dropꢀwise
addition of 60 mL silica spheres solution with stirring. After aging at 313 K for 3 h, the 5 g
NH NO was added. Then, the mixture was transferred into an autoclave and heated at 413 K for
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several hours. The product was separated by centrifugation, washed until the pH value reached
.0 and dried under vacuum at 355 K for 6 h. This asꢀsynthesized sample was calcined in static
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air at 723 K for 4 h, tableted, crushed, and sieved to 40−60 meshes.
Preparation of the lamellarꢀstructured Cu/SiO : The lamellarꢀstructured Cu/SiO was prepared
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by using the ammonia evaporation (AE) method. Typically, copper nitrate and ammonia with
calculated proportion were mixed into deionized water and stirred for 10 min, followed by a
dropꢀwise addition of silica sol while stirring. Then, the suspension was stirred at room
temperature for 6 h. The initial pH value of the suspension was 11ꢀ12. The suspension was
subsequently heated in a 353 K water bath to allow the evaporation of ammonia, the decrease of
pH, and the consequent deposition of copper species on silica. When the pH value decreased to
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, the evaporation process was terminated. The product was washed, filtrated and dried under
vacuum at 355 K for 6 h. This asꢀsynthesized sample was calcined in static air at 723 K for 4 h,
tableted, crushed, and sieved to 40−60 meshes.
Catalytic activity test
The catalytic evaluation was carried out in a fixedꢀbed reaction system. A sample of 0.4 g of
catalyst (40ꢀ60 meshes) was placed in the certain zone of the reaction tube where the temperature
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could maintain constant. Before the reaction, the catalyst was first reduced by hydrogen at 573 K
for 4 h. Then, the feed (20 wt. % DMO, dissolved in methanol) was injected into the fixedꢀbed
reaction system contiguously with a certain weight liquid hourly space velocity (WLHSV). The
catalytic performance was tested at 473 K under 2.5 MPa. The reaction products were
condensed, then analyzed on the Agilent Micro GC 6820, which is equipped with a
HPꢀINNOWAX capillary column (HewlettꢀPackard Company, 30 m×0.32 mm×0.50 ꢁm), as
well as a flame ionization detector (FID).
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Characterization
Pore structure of the catalysts was determined at 77 K by a N adsorptionꢀdesorption method
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using a Micromeritics Tristar II 3000 Analyzer. Poreꢀsize distribution was estimated by the
BarrettꢀJoynerꢀHalenda (BJH) method from adsorption isotherm branch of the isotherms, and the
specific surface area was calculated from the isotherms using Brunauer−Emmett−Teller (BET)
method.
The copper content of catalyst was analyzed by using an Inductively Coupled Plasma Optical
Emission Spectrometer (ICPꢀOES, Varian VistaꢀMPX), and was determined by the Cu
characteristic peak at 324.754 nm.
Transmission electron microscopy (TEM) image was analyzed by using a Philips TECNAI G2
F20 system electron microscope. The 40ꢀ60 meshes sample was crushed and dispersed in
ethanol, dropped onto a copper gridꢀsupported carbon membrane and dried. For each NAHS
material and NTs material, 100ꢀ200 nanotubes were measured to obtain the length distribution of
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nanotubes. Likewise, for each catalyst, 200ꢀ300 copper nanoparticles were processed to calculate
the average particle size.
Scanning electron microscopy (SEM) image was analyzed by using a Hitachi Sꢀ4800 system
electron microscope. The calcined sample was severely crushed and dispersed in ethanol,
dropped onto small pieces of quartz glass.
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The copper dispersion and metallic copper surface area were measured by N O titration using a
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Micromeritics Autochem II 2920 apparatus. Briefly, 50 mg sample was pretreated in Ar for 1 h
at 473 K, followed by its reduction in 10% H /Ar flow for 2 h at 573 K. Subsequently, the
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sample was exposed to N O for 1 h at 363 K, which could ensure that the surface metallic copper
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was completely oxidized to Cu O. After purging the remaining N O with a flow of Ar for 30
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min, the sample was reduced again at 573 K by pulse titration using 10% H /Ar.
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Xꢀray diffraction (XRD) was conducted with a Rigaku C/maxꢀ2500 diffractometer, employing
the graphiteꢀfiltered Cu Kα radiation (λ=1.5406 Å) at room temperature. The particle size of
copper was calculated according to the Scherrer equation. The reduced catalyst powder was
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scanned with a rate of 8 /min from 2θ ranging from 10 to 90 .
Fourierꢀtransform Infrared (FTIR) spectra was recorded by a Nicolet 6700 spectrometer
ꢀ1
equipped with a DTGS detector in the range of 400ꢀ4000 cm . The sample was ground,
ꢀ1
dispersed in KBr, and pelletized. The spectral resolution was 4 cm , and 32 scans were recorded
for each spectrum.
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The in situ FTIR of CO adsorption was performed to determine the surface area of Cu species
using the Nicolet 6700 spectrometer equipped with a MCT/A detector and a vacuum system.
Briefly, the sample (16ꢀ17 mg) was tableted and placed into the in situ cell. Subsequently, the
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sample disk was reduced under a 10% H /Ar flow at 573 K for 1 h, then exposed to the flow of
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CO at 303 K for 30 min. In order to remove CO molecules in the gas phase and the ones that
were weakly adsorbed on the sample, an evacuation was performed until the scanned spectra no
longer changed.
Xꢀray photoelectron spectra (XPS) and Auger electron spectroscopy (AES) were detected on a
Kratos XSAM 800 spectrometer with Al Kα Xꢀray radiation source (hν = 1486.6 eV). The
sample was tableted to a small disk, reduced in H at 573 K for 4 h, immediately transferred into
2
ꢀ8
the chamber, and vacuumed under 10 Torr. The obtained binding energy was calibrated using
the Si 2p peak at 103.2 eV as the reference. The experimental error was within ±0.2 eV.
The highꢀpressure hydrogen adsorption was carried out on a pressure composition isothermal
system (Micromeritics ASAP 2050). Before the measurement, the sample was tableted, crushed,
weighed and reduced at 573 K in a flow of hydrogen for 4 h. A stainless steel tube was loaded
with 2 g of the reduced sample in a glovebox, and subsequently connected to the manometric
instrument. After pretreated under vacuum at 573 K for 2 h to remove water and other adsorbed
molecules, the sample was cooled down to the reaction temperature (473 K). Then, the H was
2
injected into the sample tube to increase the pressure gradually to 5 MPa, for measuring the
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pressureꢀcompositionꢀisotherms. The pressure was measured by a capacitance manometer with
an error of 1%.
Computational details
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Monte Carlo simulations were carried out with the Adsorption Locator module implemented in
®18
Materials Studio . The adsorption configurations were identified by conducting Monte Carlo
1
9
searches of the configurational space of the substrateꢀadsorbate system as the temperature
20,21
slowly decreased according to a simulated annealing schedule.
This process was repeated
several times to identify further local energy minima. Further details of Monte Carlo simulations
is shown in Supporting Information.
RESULTS AND DISCUSSION
Morphology of NAHS materials with different nanotube-length
The NAHS is formed by a dissolutionꢀprecipitation mechanism, which is shown in Figure S1.
At the early stage of hydrothermal treatment, the silica spheres dissolve and react with copper
ions to generate copper silicate. As the time of hydrothermal treatment increases, silica sphere
core continues to dissolve and more copper silicate generates, which prolongs the nanotubes.
And the nanotube would not stop growing until the copper ions were exhausted. Consequently,
nanotubes openꢀended on both sides form a radial array on the surface of a hollow sphere,
providing the only connection between the space inside and outside of the hollow sphere (as
shown in Figure 1). The SEM images of cracked samples in Figure S4 shows that there is no
isolated nanotube existed inside the hollow spheres. According to the dissolutionꢀprecipitation
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mechanism, we modulated the time of hydrothermal treatment and adjusted the copper content to
fabricate a series of NAHS materials with nanotubes of different lengths. The obtained samples
were characterized by TEM (Figure 1, corresponding largeꢀscale TEM images and
highꢀmagnification TEM images are shown in Figure S2 and S3). The length of the resulting
nanotubes varies from 63 nm to 119 nm as the hydrothermal time is increased from 5 h to 20 h.
As the amount of copper ions increases, the nanotube length further increases to 120 nm and 232
nm. The NAHS assembled with x nm nanotubes is denoted as NAHSꢀxnm. Additionally, copper
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silicate nanotubes (NTs) and lamellarꢀstructured Cu/SiO were prepared as contrasting catalysts.
2
Notably, the nanotubes of NAHSꢀ232nm are as long as the NTs, which enables a separate
discussion of the effect of nanotubes and hollow spheres. The copper silicate composition of all
the materials was verified by FTIR spectroscopy, as shown in Figure S5.
Figure S6 shows the nitrogen adsorptionꢀdesorption isotherms of copper silicate materials. All
the samples exhibit type IV isotherms with a hysteresis loop, corresponding to a typical
mesoporous material. The hysteresis loops of NAHS and NTs are attributed to the
2
2
cylinderꢀshaped pore, which is consisted with the shape of nanotube. Meanwhile, the hysteresis
loop of lamellarꢀstructured Cu/SiO is a standard H3 type loop, corresponding to the
2
2
3
lamellarꢀshaped pore. These structures are also agreed with the structures shown in TEM
images (Figure 1). Furthermore, the specific surface area of the copper silicate materials (Table
S1) with same copper loadings is similar. The average pore size calculated by BJH method is
also shown in Table S1, indicating the pore size of all the materials is around 4.2 nm. This is also
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confirmed by the highꢀmagnification TEM images (Figure S3), where inner diameters of the
nanotubes in both the NAHS and NTs are approximately 4 nm. We also counted the diameter of
hollow sphere in all NAHS materials from lots of TEM images, which is all around 280 nm
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(Table S1). Thus, except for the length of nanotubes, all the NAHS samples display nearly the
same pore structural properties, size of hollow spheres as well as diameter of nanotubes.
Figure 1. TEM images of calcined copper silicate materials. AꢀG: NAHS materials, H: NTs and
I: lamellarꢀstructured Cu/SiO . Copper contents: 20 wt. % (AꢀE), 43 wt. % (FꢀI). Hydrothermal
2
treatment time: 5 h (B, F), 10 h (A, C), 15 h (D, H), 20 h (E, G). Corresponding largeꢀscale TEM
images and nanotubeꢀlength distributions are show in Figure S2.
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Morphology of NAHS nanoreactors
All the NAHS materials, NTs, and lamellarꢀstructured Cu/SiO were first reduced at 573 K in a
2
H flow for 4 h before the reaction. It can be seen from Figure 2 and Figure S7, although some of
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the lamellarꢀshaped Cu/SiO turns to amorphous form, the structures of NAHS and NTs are not
2
collapsed during reduction and there is no obvious pore on the nanotube wall. Meanwhile, the
small nanoparticles generated in all the catalysts after reduction. The regular lattice with a
interplanar spacing of 0.202 nm in Figure 2I can be ascribed to the Cu(111) phase of metallic Cu
o
(
JPCDS 65ꢀ9743), which is also consisted with the diffraction peak at 43.3 in XRD patterns
(Figure 3(a)). The diameters of Cu nanoparticles are around 3 nm, which are calculated from the
XRD patterns by Scherrer equation (Table 1). We also counted the metallic Cu particle sizes
based on the TEM images (Table S2), which agree with the results from XRD patterns.
Moreover, the magnified TEM image (Figure 2H) shows that most copper nanoparticles socket
on the wall of nanotubes. In this case, part of the nanoparticle is exposed to the inside of
nanotube and narrows the diameter of nanotube, which is consisted with the decreasing of the
pore size of the NAHS nanoreactor after the reduction (Figure S9).
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Figure 2. TEM images of reduced copper silicate materials. A, B: NAHSꢀ63nm; C:
NAHSꢀ70nm; D: NAHSꢀ92nm; E: NAHSꢀ119nm; F: NAHSꢀ120nm; G, H, I: NAHSꢀ232nm, J:
NTs and H: Cu/SiO . Corresponding large scale and high resolution TEM images are shown in
2
Figure S7.
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Characterization of active species
Considering the components, pore structure and copper particle size of all the catalysts are
similar, the number of exposed active species may be the key factor influencing the catalytic
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performance, in addition to the morphology. The synergy between Cu and Cu species on the
surface of catalysts has been reported to remarkably enhance the catalytic performance in DMO
0
+
hydrogenation, where Cu facilitates decomposition of H and Cu adsorbs and activates the
2
24ꢀ26
0
methoxy or acyl species.
Hence, we sequentially measured the surface amounts of Cu and
+
0
Cu sites qualitatively and quantitatively. The Cu surface areas (SCu(0)) of all the catalysts were
27,28
determined by N O titration;
the results are listed in Table 1. Notably, catalysts with the same
2
0
Cu content display similar Cu surface areas. The absence of the Cu 2p satellite peak at 942ꢀ944
2
+
eV in XPS (Figure 3) demonstrates that all of the surface Cu species are reduced to a lower
2
+
0
+
valence. In the absence of surface Cu species, the surface area of Cu and Cu species could be
distinguished and calculated by deconvoluting the two overlapping peaks at binding energies of
5
69.8 eV and 573.1 eV respectively in the Cu LMM AES (Figure 3). The ratio of
+
+
0
Cu /(Cu +Cu ), denoted as XCu(I), was calculated from the integrated areas of the corresponding
2
5
+
peaks, as listed in Table 1. The Cu surface area (SCu(I)) was calculated on the basis of SCu(0) and
+
+
0
XCu(I). Notably, the Cu /(Cu +Cu ) ratios of all the samples are similar, irrespective of their
morphology. To further verify the fitting results of XCu(I), in situ FTIR of CO adsorption was also
0
conducted after CO adsorption (Figure S10). Given the weak interaction between CO and Cu or
2
+
2+
Cu , and the absence of Cu of all the catalysts proved by XPS, the bands after longꢀtime
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ꢀ
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+
26, 29
evacuation at 2100ꢀ2200 cm should be assigned to the Cu ꢀCO species.
The integral areas
+
of the Cu ꢀCO peaks are consistent with the calculated SCu(I), verifying the reliability of the
0
+
characterizations of Cu and Cu species (Figure S10). In summary, considering that the
resemblance textural structure and activeꢀsite distribution of these catalysts, the contribution of
the morphology becomes the most important fact in catalyzing the hydrogenation reaction.
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Figure 3. (a) XRD patterns (b) XPS spectra and (c) AES spectra of reduced copper silicate
materials. A: NAHSꢀ63nm; B: NAHSꢀ70nm; C: NAHSꢀ92nm; D: NAHSꢀ119nm; E:
NAHSꢀ120nm; F: NAHSꢀ232nm, G: NTs and H: Cu/SiO2.
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Table 1. Characterization of Cu species on catalysts.
a
b
c
d
e
Cu content
wt. %)
Crystallite size
SCu(0)
SCu(I)
XCu(I)
Catalysts
2
2
(
(nm)
3.2
3.1
3.0
3.1
3.2
3.3
(m /g)
27.1
26.1
25.7
25.8
42.9
45.6
(m /g)
7.9
(%)
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NAHSꢀ63nm
NAHSꢀ70nm
NAHSꢀ92nm
19.8
21.0
20.3
22.6
21.5
22.2
23.7
23.0
25.0
6.6
7.3
NAHSꢀ119nm 20.5
NAHSꢀ120nm 41.7
NAHSꢀ232nm 43.0
NAHSꢀ232nmꢀu
8.1
12.9
16.7
4
2.8
3.4
45.0
15.2
25.3
f
sed
NTs
42.7
43.9
3.3
3.8
43.2
45.0
13.0
14.6
23.0
24.2
Cu/SiO2
a
Determined by Inductively Coupled Plasma Optical Emission Spectrometry.
b
c
Calculated from XRD patterns by using the Scherrer equation. Determined by N O
2
d
+
+
0
titration. Calculated on the basis of S
and Cu /(Cu +Cu ) and verified by inꢀsitu
Cu(0)
e
f
FTIR spectra of CO adsorption. Calculated from Cu LMM AES spectra. The
NAHSꢀ232nmꢀused catalyst is characterized after the 300 h longꢀtime stability test.
Catalytic performance
To reveal the effects of morphology, the reduced NAHSꢀ232nm nanoreactor, NTs and Cu/SiO2
were evaluated in DMO hydrogenation under different H /DMO ratios (Figure 4 and S11). At
2
the H /DMO ratio from 70 to 80, all three catalysts present nearly the same EG yields. When the
2
H /DMO ratio is decreased from 70 to 50, the EG yield of Cu/SiO decreases to 42% but that of
2
2
the NAHSꢀ232nm nanoreactor and NTs are maintained at 95%. As the H /DMO ratio is further
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decreased below 50, a sharp decline of the EG yield appears in the activity tests of NTs. In
contrast, the NAHSꢀ232nm nanoreactor continues to exhibit a high performance, with an EG
yield of 95% until the H /DMO ratio is decreased to 20. Moreover, the NAHSꢀ232nm displays
2
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excellent stability at H /DMO of 20, which is demonstrated by the 95% EG yield in 300 h
2
reaction (Figure 4C). During this longꢀtime reaction, neither the structure of nanotubes nor the
hollow spheres of NAHS is obviously changed, which is demonstrated by the TEM image of the
used NAHSꢀ232nm catalyst in Figure 4D. Furthermore, XRD (Figure S12A), XPS (Figure S12B,
C) and N O titration analysis of the used NAHSꢀ232nm catalyst demonstrate that the copper
2
particle size and the surface areas of copper active species haven’t changed as well after 300 h
reaction. These results of copperꢀspecies characterization of the used NAHSꢀ232nm catalysts are
also summarized in Table 1.
For further understanding these different performance of catalysts, we used the WeiszꢀPrater
3
0
criterion to evaluate the diffusion influence on this reaction. When the WeiszꢀPrater criterion is
30
less than 0.3, the effect of mass transfer of the reactant on reaction is negligible. The calculated
Nwꢀp of DMO over NAHSꢀ232nm, NTs and Cu/SiO catalysts is much lower than the limit value
2
of 0.3, which is shown in Table S3. Thus the catalytic performance of these catalyst is not
limited by the mass transfer. As demonstrated before, the NAHSꢀ232nm nanoreactor, NTs and
Cu/SiO are all very similar in terms of their textural properties as well as the number of exposed
2
active sites, the diffusion limitation is also excluded by calculating the WeiszꢀPrater criterion
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(
Table S3) . The unique morphology of NAHS is the only key factor influencing catalytic
performance in DMO hydrogenation.
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Figure 4. Comparison of catalytic performance. A: Effect of H /DMO ratio on the catalytic
2
ꢀ1
performance of different catalysts. Reaction conditions: 473 K, 2.5 MPa, WLHSV = 2.0 h B:
.
Reaction rates of different catalysts at H /DMO = 20, 473 K, 2.5 MPa. The data for calculation
2
of reaction rates were obtained under much more severe conditions, where the DMO conversions
were kept below 20%. C: Stability test of NAHSꢀ232nm nanoreactor. Reaction conditions: 473
ꢀ1
K, 2.5 MPa, WLHSV = 2.0 h , H /DMO = 20. D: TEM image of NAHSꢀ232nm before and after
2
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00 h reaction.
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To further analyze the effect of morphology, we calculated the reaction rates as shown in
Figure 4B. The reactant concentration must be the main reason for the difference in reaction rates
because the three catalysts have identical distribution of active sites and reaction conditions.
Meanwhile, the TOF values (Figure S13) also show the same trend to the reaction rate because
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the similar ratio of Cu /Cu in these catalysts. Therefore, the morphology effect of the catalyst
results from its ability to be enriched by small molecules, as intended by our design.
Additionally, the reason of the slightly lower EG yield of NAHSꢀ232nm is a further
hydrogenation of EG to other byꢀproducts. Compared against the current stateꢀofꢀtheꢀart
performance of the Cu/SiO catalysts, this NAHS nanoreactor exhibits an excellent performance
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in an extremely low H /DMO ratio (Table S4). Besides DMO hydrogenation, the NAHS
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nanoreactor also exhibits an excellent performance under a low H proportion in other C=O/CꢀO
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hydrogenation reactions, which is shown in Figure S14. The results indicate that the morphology
of NAHS could be generalized into other hydrogenation reactions.
Enrichment of H inside NAHS
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To gain further insight into the morphology effect, the H ꢀadsorption volumes of the three
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catalysts were investigated at the reaction temperature of 473 K. The relation between the H2
pressure and the adsorption volumes of the reduced NAHSꢀ232nm nanoreactor, NTs and
Cu/SiO catalysts is shown in Figure 5. At the reaction pressure of 2.5 MPa, the H ꢀadsorption
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volume of the NAHSꢀ232nm nanoreactor is 51.80 mL/g, higher than the adsorption volumes of
the NTs (39.20 mL/g) and Cu/SiO (21.47 mL/g). The difference between the H ꢀadsorption
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volumes of these catalysts becomes much larger as the pressure is increased. The results indicate
that both nanotube and hollowꢀsphere morphologies can enhance the adsorption of H . This
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in an accelerated reaction rate and an improved catalytic performance.
Figure 5. H ꢀadsorption isotherms of the NAHS materials, NTs and Cu/SiO catalysts.
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Adsorption temperature: 473 K.
Furthermore, Monte Carlo simulations were also employed to further elucidate the
phenomenon of H ꢀenrichment in the nanotube morphology. A silica nanotube was modeled with
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a nanotube morphology in NAHS nanoreactors and NTs, whereas a planar counterpart was
selected to represent the surface of the Cu/SiO catalyst (Figure 6BꢀC, Figures S15 and S16).
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concentrations of H molecules inside/outside of the nanotube, or around the planar surface were
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calculated. Results obtained in the reaction temperature of 473 K, and with different H2
pressures, are shown in Figure 6A. Local concentrations of H molecules decrease in the
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following order: inside the nanotube, around the planar surface, in the gas phase, and outside the
nanotube. This order implies the significant enrichment effect inside the nanotube structure. Due
to the unique geometry of curved surface of nanotubes, the Si and O atoms on the concave side
are denser than those on the convex side. Thus, the H molecules interact more strongly with the
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ability on the concave side probably causes the enrichment effect of H on the nanotubes.
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Moreover, the silica hollow sphere structure has previously been shown to store more guest
molecules (like CO , ibuprofen or hexane) than conventional mesoporous materials such as
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MCMꢀ41, SBAꢀ15 or HMS.
In the present study, the NAHS nanoreactors, which contain
both nanotube and hollowꢀsphere structures, exhibit a much superior H ꢀenrichment effect than
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the NTs and Cu/SiO . Consequently, the H /DMO ratio inside the NAHS nanoreactors is
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probably higher than that in the gas phase, which is the reason that the nanoreactor maintains
excellent activity even at a low H /DMO ratio in the feed.
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Figure 6. A: Local concentrations of H inside nanotubes, outside nanotubes and around planar
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surface, calculated by Monte Carlo simulations at 473 K. B: Model of silica nanotube. C: Model
of silica planar surface. The H molecules within 2 nm of the silica surface, which is equal to the
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radius of the nanotube, are considered as the molecules near the planar surface.
Spatial restriction of reactants inside NAHS
To explore the spatial restriction of nanotubes, NAHS nanoreactors with identical Cu contents,
but different nanotube lengths, were also evaluated in DMO hydrogenation. To ensure the
presence of sufficient H and to exclude the enrichment effect, a H /DMO ratio of 70 was used.
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As shown in Figure 7, as the nanotube length is increased from 63 to 119 nm, the conversion of
DMO increases and more MG is hydrogenated to EG, which exhibits an increase of EG
selectivity. Due to the similarity of the textural properties, number of exposed active sites and
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morphologies of these nanoreactors (Table 1), the variation in nanotube length must be the
reason for the difference in product distribution. This spatial restriction, due to the nanotube
shell, may enhance the probability of contact between the molecules and the active sites. Thus,
the NAHS nanoreactor with longer nanotubes would catalyze the hydrogenation reaction with a
higher performance. Taking into account this spatial restriction effect of NAHS nanoreactors,
control of the nanotube length could be an effective way to manipulate the selectivity and
product distribution in hydrogenation.
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Figure 7. Comparison of product distribution of NAHS nanoreactors with different lengths of
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nanotubes. Reaction conditions: 473 K, 2.5 MPa, WLHSV = 2.0 h , H /DMO = 70.
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CONCLUSIONS
In this work, we propose a novel nanoreactor with a unique morphology of
nanotubeꢀassembled hollow sphere, which can exhibit remarkable activity and stability when the
H dosage in C=O/CꢀO hydrogenation reaction is significantly decreased. To obtain an EG yield
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of 95%, the NAHS nanoreactor could allow the H /DMO ratio to be decreased to 20, while the
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NTs and Cu/SiO require at least a H /DMO ratio of 50 and 70, respectively. Given the similar
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textural structure and activeꢀsite distribution of these catalysts, the contribution of the
morphology in catalyzing the hydrogenation reaction is revealed. Both the experimental and
computational results demonstrate that the structure of nanotube and hollow sphere could
increase the hydrogen concentration within the nanoreactor, resulting in the excellent activity of
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NAHS at low H proportion in DMO hydrogenation, as well as other hydrogenations. Moreover,
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when the nanotubes on the NAHS are lengthened, DMO is hydrogenated to a further stage,
resulting in selective production of EG. Therefore, the NAHS nanoreactor proposed here
provides a promising solution for both of the imperative issues in hydrogenation reactions:
excess H consumption and the control of product selectivity. Based on these insights into the
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effect of morphology on hydrogen enrichment and the effect of spatial restriction on catalytic
performance, new possibilities can be introduced for the rational design of catalysts.
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AUTHOR INFORMATION
Corresponding Author
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Eꢀmail: xbma@tju.edu.cn
Author Contributions
D. Y. and Y. W. contributed equally to this whole work.
‡
Notes
The authors declare no competing financial interest.
ASSOCIATED CONTENT
Details of experiments, catalyst characterization and evaluation, Monte Carlo simulations are
included in Supporting Information. The Supporting Information is available free of charge on
the ACS Publications website.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (21325626,
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1434127).
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REFERENCES
1) Klankermayer, J.; Wesselbaum, S.; Beydoun, K.; Leitner, W. Angew. Chem. Inter. Ed.
016, 55, 7296ꢀ7343.
(
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(2)
(3)
(4)
Ruppert, A.; Weinberg, K.; Palkovits, R. Angew. Chem. Inter. Ed. 2012, 51, 2564ꢀ2601.
Yue, H.; Ma, X.; Gong, J. Acc. Chem. Res. 2014, 47, 1483ꢀ1492.
Zhao, S.; Yue, H.; Zhao, Y.; Wang, B.; Geng, Y.; Lv, J.; Wang, S.; Gong, J.; Ma, X. J.
Catal. 2013, 297, 142ꢀ150.
(5)
Yin, A.; Wen, C.; Guo, X.; Dai, W.; Fan, K. J. Catal. 2011, 280, 77ꢀ88.
(6)
Zhao, L.; Zhao, Y.; Wang, S.; Yue, H.; Wang, B.; Lv, J.; Ma, X. Ind. Eng. Chem. Res.
2
012, 51, 13935ꢀ13943.
(7)
Chen, L.; Guo, P.; Qiao, M.; Yan, S.; Li, H.; Shen, W.; Xu, H.; Fan, K. J. Catal. 2008,
257, 172ꢀ180.
(
8)
9)
Hollak, S.; Gosselink, R.; van Es, D.; Bitter, J. ACS Catal. 2013, 3, 2837ꢀ2844.
(
MaligalꢀGanesh, R.; Xiao, C.; Goh, T.; Wang, L.; Gustafson, J.; Pei, Y.; Qi, Z.;
Johnson, D.; Zhang, S.; Tao, F.; Huang, W. ACS Catal. 2016, 6, 1754ꢀ1763.
(10) Bai, S.; Liu, J.; Gao, J.; Yang, Q.; Li, C. Microporous Mesoporous Mater. 2012, 151,
474ꢀ480.
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(
11) Wang, X.; Zhuang, J.; Chen, J.; Zhou, K.; Li, Y. Angew. Chem. Inter. Ed. 2004, 43,
2
4
017ꢀ2020.
1
1
1
1
1
1
1
1
1
1
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2
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0
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2
3
4
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0
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2
3
4
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0
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0
1
2
3
4
5
6
7
8
9
0
(12) Yue, H.; Zhao, Y.; Zhao, S.; Wang, B.; Ma, X.; Gong, J. Nat. Commun. 2013, 4, 2339.
(13) Bao, J.; He, J.; Zhang, Y.; Yoneyama, Y.; Tsubaki, N. Angew. Chem. Inter. Ed. 2008,
7, 353ꢀ356.
(14) Yang, Y.; Liu, X.; Li, X.; Zhao, J.; Bai, S.; Liu, J.; Yang, Q. Angew. Chem. Inter. Ed.
2012, 51, 9164ꢀ9168.
(15) Gong, J.; Yue, H.; Zhao, Y.; Zhao, S.; Zhao, L.; Lv, J.; Wang, S.; Ma, X. J. Am. Chem.
Soc. 2012, 134, 13922ꢀ13925
(16) Wang, Y.; Wang, G.; Wang, H.; Cai, W.; Zhang, L. D., Chem. Commun. 2008,
6
555ꢀ6557.
(17) Sheng, Y.; Zeng, H. C. Chem. Mat. 2015, 27, 658ꢀ667.
(
18) Metropolis, N.; Rosenbluth, A. W.; Rosenbluth, M. N.; Teller, A. H.; Teller, E. J. Chem.
Phys. 1953, 21, 1087.
(19) Frenkel, D.; Smit, B. In Understanding Molecular Simulation: From Algorithms to
Applications, 2nd ed.; Academic Press: San Diego, 2002.
(
20) Kirkpatrick, S.; Gelatt, C. D.; Vecchi, M. P. Science, 1983, 220, 671ꢀ680.
21) Cerný, V. J. Optim. Theor. Appl., 1985, 45, 41ꢀ51.
(
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