Metal–Organic-Framework-Derived Co3S4 Hollow Nanoboxes for the Selective Reduction of Nitroarenes

Article abstract of DOI:10.1002/cssc.201801641

MOF-derived Co₃S₄/CN hollow nanoboxes (CN=nitrogen-doped carbon) was used to catalyze the chemoselective reduction of nitroarenes to anilines under mild reaction conditions with H₂ as the reducing agent. The catalyst provides high conversion efficiencies and selectivities for a variety of nitroarene substrates that contain electron-donating or electron-withdrawing substituents under mild reaction conditions (in methanol at 60 °C). Further, the nanobox inhibits both dehalogenation and vinyl hydrogenation reactions, which are common limitations of state-of-the-art Pd-based catalysts. Because the reactions result in pure aniline products, the need for separation by column chromatography is eliminated. The resulting anilines are easily separated from the methanolic reaction solution in just three simple steps (centrifugation, decantation, and drying). If employed in industrial processes, catalysts of this kind would significantly reduce the amount of waste organic solvent generated and thus satisfy the need for sustainable chemical processes.

Full text of DOI:10.1002/cssc.201801641

Accepted Article
Title: A Metal-Organic Framework Derived Co3S4 Hollow Nanobox for
the Selective Reduction of Nitroarenes
Authors: Shuliang Yang, Li Peng, Daniel T. Sun, Emad Oveisi, Safak
Bulut, and Wendy L. Queen
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To be cited as: ChemSusChem 10.1002/cssc.201801641
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10.1002/cssc.201801641
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A Metal-Organic Framework Derived Co3S4 Hollow Nanobox for
the Selective Reduction of Nitroarenes
Shuliang Yang,[a] Li Peng,[a] Daniel T. Sun,[a] Emad Oveisi,[b] Safak Bulut,[a] and Wendy L. Queen*[a]
Dedication ((optional))
Abstract: In this work, we report a new MOF-derived Co3S4/CN
hollow nanobox (CN = nitrogen-doped carbon), which is used to
catalyze the chemoselective reduction of nitroarenes to anilines
under mild reaction conditions using H2 as the reducing agent. The
catalyst is shown to provide high conversion efficiencies and
selectivities for a variety of nitroarene substrates that contain
electron-donating or withdrawing substituents and under mild
reaction conditions (in methanol at 60 °C). Further, the newly
prepared nanobox inhibits both dehalogenation and vinyl
hydrogenation reactions, which are common limitations of state of
the art Pd-based catalysts. Because the reactions result in pure
aniline products, the need for separation via column chromatography
is eliminated. The resulting anilines are easily separated from the
methanolic reaction solution in just three simple steps including
centrifugation, decantation, and subsequent drying. If employed in
industrial processes, catalysts of this kind will significantly reduce the
amount organic solvent waste generated, satisfying the needs for
sustainable chemical processes.
the metal building blocks are well-defined and more often than
not, highly dispersed. This, combined with the presence of Lewis
base functionality on the organic ligands can inhibit metal
diffusion, yielding large numbers of homogenously distributed
nanoparticles (NPs) upon heat treatment.[5] If compared to
traditional methods for the impregnation of porous supports with
NPs, whose dispersity and homogeneity is not often well
controlled, MOF-derived materials promote the creation of small,
homogeneous, catalytically active species inside of the resulting
mesoporous carbon networks. As an example, recent work of Li
et al reported highly dispersed single cobalt atoms and Fe-Co
dual sites embedded in a N-doped porous carbon. This material,
created through the pyrolysis of a predesigned bimetallic Zn/Co
MOF,[6] was shown to be highly efficient in the electrochemical
oxygen reduction reaction. Similarly, Han et al artfully
synthesized Ni/SiO2 and Co/SiO2 catalysts with metal NPs of
sizes less than 1 nm using Ni-BTC and Co-BTC MOFs as
precursors, respectively (BTC3-: 1,3,5-benzenetricarboxylate).
The Ni-Co/SiO2 catalysts exhibit excellent catalytic activity in the
thermally-driven hydrogenation of benzene to cyclohexane.[7]
While numerous works show exceptional catalytic properties
of MOF-derived carbons containing metal or metal oxide NPs,
the use of MOF-derived transition-metal sulfides, phosphides
and carbides for thermally driven organic transformation is only
recently making a debut.[8] Mounting interest is the result of their
low cost, robust stability, corrosion resistance, high melting
points and good mechanical properties. Moreover, transition-
metal chalcogenides, phosphides and carbides are shown to be
outstanding catalysts in several electrochemically driven
processes.[9] While there is an increasing amount of work
published related to their electrochemical properties, these
materials are seldom explored in traditional thermally-driven
organic transformations.[8, 10]
Herein, we report a MOF-derived cobalt sulfide hollow
nanobox and show its high activity in the chemoselective
reduction of nitroarenes to anilines. The as-prepared Co3S4/CN
catalyst exhibits excellent activity and outstanding selectivity for
nitroarenes with a wide range of electron withdrawing or
donating functional groups, including alkenyl, amino, ketone,
ester, bromo, iodo, chloro, methyl, methoxyl, methylthio, cyano
and quinolyl. Moreover, the reaction conditions are mild,
employing a sustainable and low boiling point solvent, methanol,
and H2 as the reducing agent. After the reactions, pure aniline
products are readily separated by simply removing the catalyst
via centrifugation and drying. There is no need for tedious steps
such as silica gel column chromatography for the separation of
the product, and hence will decrease consumption of organic
solvents immensely. To the best of our knowledge, this is the
first report of a MOF-derived cobalt sulfide catalyst that is active
in the chemoselective reduction of nitroarenes with H2 as the
hydrogen source. This material exhibits improved performance
Introduction
Metal-organic frameworks (MOFs) have sparked immense
scientific interest due to their potential application in a host of
fields such as adsorption/separation, catalysis, drug delivery,
CO2 conversion, water remediation or harvesting, and so on.[1]
While this attention is in part due to their high internal surface
areas, MOFs also offer unprecedented chemical tunability. For
example, predefined organic building blocks, which control MOF
pore size, shape, and the types of accessible chemical
functionality on their internal surface, command the nature of the
interactions between the frameworks and incoming guest
species.[2] Also, MOF chemistry can be further manipulated by
tuning the metal-containing building blocks, metal coordination
environments, nuclearity, and identity are also proven highly
versatile.[3]
In recent years, interest in MOF-derived materials, particularly
for use in catalysis, has soared.[4] This is driven by the fact that
[a]
[b]
Dr. S. Yang, Dr. L. Peng, D. Sun, Dr. S. Bulut, Prof. Dr. W. L. Queen
Institute of Chemical Sciences and Engineering
École Polytechnique Fédérale de Lausanne (EPFL)
EPFL-ISIC-Valais, Sion, 1950, Switzerland
E-mail: wendy.queen@epfl.ch
Dr. E. Oveisi
Interdiciplinary Center for Electron Microscopy, École Polytechnique
Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Supporting information for this article is given via a link at the end of
the document. ((Please delete this text if not appropriate))
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10.1002/cssc.201801641
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when compared to recently published work on MOF-derived
cobalt phosphide nanocubes and other CoS2/porous carbon
systems derived from sulfur power.[8b, 11]
amount of Co (0.45 mmol), the process continues until the inside
ZIF-67 core is completely consumed, leaving behind a uniform
hollow structure.
It should be noted that the amount of thioacetamide used in
the reaction has a significant effect on the resulting morphology.
The reaction was left incomplete when only half of the amount of
thioacetamide was used, yet the resulting nanostructures
exhibited cracking when the amount of thioacetamide was
doubled (Figure S5). This implies that an appropriate
thioacetamide concentration is very important for the formation
of ideal hollow structures.
Results and Discussion
The synthesis of Co3S4@CN nanoboxes takes place in three
steps as shown in Scheme 1. Firstly, zeolitic imidazolate
framework (ZIF-67) nanocubes were prepared with cobalt nitrate
hexahydrate and 2-methylimidazole as the precursors in the
presence of hexadecyltrimethylammonium bromide (CTAB)
surfactant, which is used as a capping agent. Then, ZIF-67 was
converted to Co3S4/CN hollow nanoboxes with low crystallinity
by adopting thioacetamide as the sulphur source. In the final
step, a simple thermal treatment resulted in the formation of the
Co3S4/CN hollow nanoboxes.
To further improve the crystallinity and increase the stability of
the Co3S4 phase during the catalysis process, a low-temperature
o
thermal annealing was carried out under argon at 350 C. From
Figure 1c and 1f, it is seen that the mild thermal treatment
maintains the cubic morphology. Moreover, High-angle annular
dark field scanning TEM (HAADF-STEM) imaging coupled with
energy dispersive X-ray spectroscopy STEM-EDX mapping
reveals Co3S4 NPs of about 3 nm in size are distributed through
the Co3S4 nanoboxes, and that Co and S elements are
distributed uniformly in the Co3S4 NPs (Figs. 1g-1l). Further,
reciprocal plane spacing, determined by the selected area
electron diffraction pattern (SAEDP), also matched well with the
simulated electron diffraction pattern of Co3S4 (Figure 1k). EDX
analysis shows the Co to S ratio, 0.75, is equivalent to the
theoretical value of Co3S4. Further, the broad peaks in the XRD
pattern imply that the Co3S4 particles do not undergo significant
aggregation (Figure 2a).
Scheme 1. The synthetic process used to make Co3S4/CN hollow nanoboxes.
After each step in the reaction, the morphology of the
resulting material was characterized by SEM and TEM. Figs. 1a,
1d and S1 show that the prepared ZIF-67 nanocubes are
uniform with an average size of about 190 nm, an X-ray
diffraction pattern confirmed the successful formation of the ZIF-
67 phase (Figure S2). The CTAB molecules change the growth
rate of different crystal facets and hence promotes the formation
of uniform ZIF-67 nanocubes.[12] In the second sulfurization step,
thioacetamide was chosen as the sulphur source. During the
solvothermal treatment, thioacetamide reacts with ethanol to
form CH3(NH2)C(OC2H5)-SH, which further reacts with another
ethanol molecule to produce CH3(NH2)C(OC2H5)2 and
subsequently releasing one H2S molecule.[13] The in-situ
generated H2S molecule reacts with the cobalt source in ZIF-67
to form the Co3S4 phase.[14] From the XRD pattern in Figure S3,
the Co3S4 phase has broad diffraction peaks. SEM images
shown in Figures 1b, 1e and S4 reveal that hollow Co3S4
nanoboxes were formed.
The hollow, cubic morphology is thought to form in the
following steps: (i) First, S2- produced from the decomposition of
the thioacetamide, diffuses into the ZIF due to a concentration
gradient. (ii) Then, because the bond strength of Co2+ and S2− is
larger than Co2+ and 2-methylimidazole,[15] the S2- displaces the
ligand forming an outer Co3S4 phase maintaining the cubic
morphology. (ii) Last, during solvothermal treatment, Co2+ is
released from inside the ZIF-67 core. Due to the smaller ionic
radius of Co2+ (74 pm) compared to S2− (184 pm),[13b] the cation
Figure 1. BF-TEM (top row) and SEM (middle row) images of ZIF-67
nanocubes (a,d), hollow Co3S4 nanoboxes (b,e) and hollow Co3S4/CN
nanoboxes after 350 oC thermal treatment (c,f). HAADF-STEM and BF-TEM
images (g,j) of a hollow Co3S4/CN nanoboxes after 350 oC thermal treatment
and corresponding EDX elemental maps of S and Co (h,i) . SAED pattern (k)
from the nanocube of figure (j). Simulated electron diffraction ring pattern of
Co3S4 is shown in the right panel. Dark-field TEM image showing Co3S4
particles in the nanobox (l). The red circle on the SAED pattern marks the
reflection used for dark-field imaging.
diffuses out faster than the anion can diffuse inward,[13b, 15-16]
a
phenomenon called the Kirkendall effect.[17] Further, because the
added thioacetamide (1.6 mmol) is in excess compared to the
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The valence state of the Co3S4 hollow nanobox was
investigated by X-ray photoelectron spectroscopy (XPS). XPS
full spectrum reveals that the nanostructures consist of C, O, N,
Co and S elements. Further high-resolution XPS analysis of Co
shows that the Co peaks could be deconvoluted into two spin-
orbit doublets. The first doublet with positions at 778.6 eV and
793.6 eV is ascribed to Co 2p3/2 and Co 2p1/2 of Co3+; meanwhile
the second doublet with location at 781.1 eV and 797.2 eV is the
Co 2p3/2 and Co 2p1/2 of Co2+. The other two peaks located at
786.2 eV and 802.3 eV are due to shake-up satellites (Figure
MOFs and MOF-derived materials have been widely used as
catalysts for a series of organic transformations such as
hydrogenation reactions,[19] oxidation reaction,[20] condensation
reactions,[21] cascade reactions[22] and so on.[23] As one of them,
nitroarene hydrogenation to anilines is of vital importance as the
latter are widely used as building blocks for the synthesis of
polymers, agrochemicals, dyes, pigments, and pharmaceuticals
in various industries.[24] While a few MOF-derived Co-based
materials have been explored for the hydrogenation of
nitroarenes using H2 as hydrogen source,[25] to the best of our
knowledge, there are no reports of MOF-derived CoSx materials.
Compared to bulk catalysts and solid nanostructured materials,
hollow nanostructures have obvious advantages because of the
shorter substrate diffusion distance. As such, we chose the
2c).[15]
A high-resolution S 2p XPS spectrum shows a
pronounced doublet with binding energies at 161.8 eV and 163.0
eV, which correspond to the S 2p3/2 and S 2p1/2 of S2-,
respectively.[13a] The higher energy peak at 168.9 eV is due to
an oxidized sulphur species such as sulfate.[18] All peak positions
match well with the reported characteristic peaks of Co3S4,
which further confirms the formation of the Co3S4 phase.
Co3S4/CN hollow nanobox as
hydrogenation.
a catalyst for nitroarene
First, the simplest nitroarene substrate, nitrobenzene, was
used to optimize the reaction conditions (Table 1). Control
experiments showed that nitrobenzene could not be reduced to
aniline without a catalyst nor with the ZIF-67 nanocube as
catalyst (entries 1-2). Delightfully, the nitrobenzene could be
converted to the aniline completely with >99% selectivity when
the Co3S4/CN hollow nanobox was selected as the catalyst
(entry 3). Furthermore, when the temperature was decreased to
o
60 C, complete conversion could still be reached (entry 4). It is
noteworthy that this condition is significantly milder than our
recently reported MOF-derived cobalt phosphide nanocube
catalyst, as the Co3S4/CN nanobox realizes total conversion with
less cobalt loading, lower hydrogen pressure, and shorter
reaction time.[8b] Also, Co3S4/CN exhibits much better
performance when compared to Co9S8 NPs (entry 5). For this
test, we carried out a reaction containing the same amount of Co
as employed for the nanobox; however, Co9S8 only promotes a
4% conversion under the same reaction conditions. Next, for the
reaction containing the Co3S4/CN nanobox, efforts were also
made to further reduce the temperature to 25 oC, but this
decreased the conversion to 28% (entry 6). Additionally, solvent
and hydrogen pressure were also varied; however, the
conversion and selectivity never exceeded the values in entry 4
(entries 7-9). So, the optimized reaction conditions include a 60
oC reaction temperature over a 3 h period, 3.0 MPa H2, with 5
mg of catalyst and 0.5 mmol of substrate. Last, we also
prepared ZIF-8 derived ZnS/CN and ZnO/CN as a comparison.
These two materials did not show any activity, confirming that
cobalt is the active species (entries 10-11). In addition, hot
filtration experiments revealed that no conversion occurred when
the catalyst was separated from the reaction solution, which
confirmed that the reaction process is exclusively
heterogeneous (Table S1).
Figure 2. XRD pattern of Co3S4/CN nanobox (a), full XPS spectrum (b) and
high resolution XPS spectra of Co 2p (c) and S 2p (d) of Co3S4 nanobox.
The porosity of the synthesized materials was investigated by
N2 adsorption measurements taken at 77 K. The original ZIF-67
nanocubes display a type I curve with a surface area of 1134
m2/g, which is indicative of the intrinsic microporosity (Figure
S6a). Pore size analysis revealed that ZIF-67 possesses two
types of pores with diameters of ~1.2 nm and 1.6 nm (Figure
S6b). However, after thermal treatment, N2 isotherms of the
Co3S4/CN hollow nanobox displayed a type IV curve, indicative
of mesoporosity (Figure 7a). The hollow nanobox has a BET
surface area of 108 m2/g, and an irregular mesopore size
distribution ranging from 2 nm to 19 nm and a micropore size
centred at 1.7 nm (Figure S7c). The decreased surface area is
ascribed to the collapse of well-organized micropores in ZIF-67
and the structural reconstruction during the sulfurization process.
It is thought the induced mesoporosity of the Co3S4/CN nanobox
will improve the diffusion of reactants for catalysis when
compared to its microporous counterpart.
Table 1 Optimization of the reaction conditions for the hydrogenation of
nitroarenes.[a]
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For heterogeneous catalysts, another important aspect is
recyclability and long-term stability. From Figure S8, the
prepared Co3S4/CN catalyst exhibits good stability and is readily
reused over at least three cycles with nitrobenzene as the
substrate. After that, the conversion decreases to 77% while the
selectivity maintains >99% for the aniline product. After 5 runs,
the XRD pattern confirms that there is no change in the Co3S4
crystal phase (Figure S9). ICP-AES analysis reveals that the
recovered catalyst maintains the Co content, 44.7 wt% Co, when
compared to the fresh one with 46.5 wt% Co. This implies that
the cobalt loss is negligible during the 5 consecutive runs. The
low metal leaching is highly important for products to be applied
in applications related to life sciences. The morphology of the
recovered catalyst was also well maintained from SEM and TEM
images (Figure S10). Moreover, the active Co species shows no
change according to XPS analysis (Figure S11). SEM-EDX
analysis also indicates that the Co:S ratio is still ~0.75 (Figure
S12) after 5 catalytic cycles. After the above-mentioned analysis,
the partial loss of catalytic activity is ascribed to slight
agglomeration of the smaller active particles and unavoidable
catalyst loss during the recycling procedure.
[a] Reaction conditions: catalyst (5.0 mg), nitrobenzene (0.5 mmol), methanol
(3.0 mL), 3.0 MPa H2, desired temperature, 3.0 h. [b] Determined by GC-FID
and GC-MS using mesitylene as internal standard. [c] The amount of Co9S8
catalyst used is equivalent to the amount of cobalt used in entry 4. [d] EtOH as
solvent. [e] 2.0 MPa H2 used.
With the optimized condition, the reaction was extended to
other substrates with different functional groups (Table 2). It can
be seen that nitroarenes with either electron-donating or
electron-withdrawing substituents afforded the targeted anilines
products (entries 2-4, 16-17). The sterically hindered substrate
1,3-dimethyl-2-nitrobenzene also provided satisfying conversion
Table 2 Hydrogenation of substituted nitroarenes to anilines with Co3S4/CN
hollow nanobox as the catalyst.[a]
o
and selectivity when the temperature was increased to 110 C
(entry 5). Moreover, the halogen substitute substrates that
include chloro-, bromo- and iodo-, proceed to produce the
desired anilines with excellent activity and selectivity and without
any dehalogenated products detected by GC-MS. The reaction
also proceeds regardless of halogen location in the the ortho-,
meta- or para- positions (entries 6-9). Further, in the case of 1-
nitro-3-vinylbenzene, which has a highly active alkene carbon-
carbon double bond, only the nitro group was reduced with the
vinyl group remaining untouched (entry 10). This strongly implies
that the ZIF-67 derived Co3S4/CN hollow nanobox is an ideal
catalyst for the selective reduction of nitroarenes to anilines. For
Pd-based catalysts, which are currently employed in industry,
both dehalogenation and vinyl hydrogenation reactions often
take place.[26] Moreover, substrates containing thioether, cyano,
quinoline N or amino groups are known to coordinate to Pd-
based catalysts and poison them;[27] however, for the Co3S4/CN
catalyst, all targeted anilines are achieved with excellent
selectivities (entries 11-15, 17). Last, polycyclic 2-nitrofluorene
was also well tolerated (entry 18). All these data strongly support
that the Co3S4/CN catalyst has a high tolerance for substrates
with a broad distribution of different functional groups. Moreover,
the synthesized Co3S4/CN catalyst exhibits better catalytic
performance than the latest CoS2 catalyst (Table S2) derived
from sulphur powder.[11] The excellent activity of our nanobox is
ascribed to the following: (i) the hollow catalyst structure likely
endows the Co3S4/CN catalyst with more exposed active sites
while also shortening the substrate diffusion distance, making it
effectively superior to existing solid, nonhollow catalysts;[28] (ii)
o
the low temperature thermal treatment (350 C) likely alleviates
NP aggregation and hence maintains a larger number of active
sites compared to catalysts prepared at significantly higher
temperatures, 500-800 oC.[8b, 11]
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mixture. For this, methanol, which is considered to be a “green
choice” for sustainable, chemical transformations,[30] was
employed as
a low-boiling point solvent. To verify easy
separation of the products, 3-aminobenzoate was chosen as the
model. Indeed, in three simple steps including centrifugation,
decantation, and drying, a colorless oil was obtained with a 99%
isolated yield. NMR and GC analysis of the final product showed
no detectable impurities peaks (Figs. S13-15), and an
electrospray ionization (ESI) mass spectrum also revealed a
peak at an m/z =151.0 that corresponds to [M+] of the 3-
aminobenzoate product (Figure S16). Following the same
procedure, 4-(methylthio) aniline and 9H-fluoren-2-amine were
also readily separated with 97% and 99% isolated yield,
respectively. NMR, GC and MS further confirmed the purity of
the targeted products (Figs. S17-24). These results strongly
indicate that the highly active and selective hollow Co3S4/CN
catalyst could simplify the product separation and significantly
reduce the consumption of organic solvents and hence aid the
development of sustainable, green chemical processes.
Figure 3. Pictorial representation of the separation of methyl 3-aminobenzoate.
Conclusions
In summary, by taking advantage of the differences in the
diffusion rates of Co2+ and S2-, a Co3S4/CN hollow nanobox was
prepared using ZIF-67 nanocubes and thioacetamide as a
precursor. Due to the short distance required for the diffusion of
the reactants to the catalyst surface, combined with the small
particle size of the Co3S4 particles and a large number of active
sites, the as-prepared Co3S4/CN exhibits outstanding activity
and selectivity for the chemoselective reduction of nitroarenes.
Moreover, when compared to the state of the art CoSx and Pd-
catalysts, the hydrogenation of nitroarenes in this work is carried
out under milder reaction conditions, and the nanobox is shown
to inhibit dehalogenation reactions and the hydrogenation of
vinyl groups, which are known to plague Pd-based materials. To
the best of our knowledge, this is the first report of a MOF-
derived Co3S4/CN composite that promotes this reaction with H2
as the hydrogen source. Last, thanks to the ideal conversion and
selectivity, the obtained anilines are easily separated from the
reaction solution in three simple steps including centrifugation,
decantation, and methanol evaporation. The reactions yield pure
aniline products eliminating any need for additional purification
processes, which often generate exorbitant amounts of organic
waste. We believe that this simple method could be extended to
cheaper and more environmentally friendly iron-based catalytic
systems that are derived from Fe-based MOFs, work that is
currently underway in our laboratory.
[a] reaction conditions: catalyst (5.0 mg), nitroarenes (0.5 mmol), methanol
(3.0 mL), 3.0 MPa H2, desired temperature. [b] Determined by GC-FID and
GC-MS using mesitylene as internal standard. [c] 0.7% 4-ethylaniline by-
product was detected.
When developing sustainable chemical processes, it is highly
important to reduce or avoid the intensive purification/separation
steps, which require the use of organic solvents. In typical
organic transformations, tedious product separations are often
carried out via column chromatography, which invariably
produces large amounts of organic waste. In fact, it is predicted
that up to 85% of the waste produced in drug syntheses are
solvents.[29] Considering the outstanding activity and selectivity
of the presented catalysts, there was interest in determining if
the resulting anilines could easily be separated from the reaction
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performed on a FEI Osiris in scanning transmission electron microscopy
mode (STEM) at an accelerating voltage of 200 kV. This microscope is
equipped with a high brightness X-FEG gun and silicon drift Super-X
EDX detectors. STEM-EDX elemental maps were acquired using a beam
current of ∼ 250 pA. XPS measurements were performed using a
Physical Instruments AG PHI VersaProbe II scanning XPS microprobe.
Analysis was performed using a monochromatic Al Kα X-ray source of
24.8 W power with a beam size of 100 μm. Nitrogen adsorption-
desorption isotherms were obtained on a Micromeritics instrument at 77
K. The surface area of the materials was measured by the Brunauer-
Emmett-Teller (BET) method. The samples were degassed at 120 oC for
12 h under vacuum. The metal contents in the samples were measured
on an Agilent 5110 Synchronous Vertical Dual View ICP-AES. The
spectra of all target compounds were observed as [M+] using Agilent
7890B-5977A GC-MS.
Experimental Section
Preparation of ZIF-67 nanocubes
The ZIF-67 nanocubes were prepared using slightly modified conditions
that were taken from a previous report.[12] In a typical experiment, 580 mg
of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 30 mg of hexadecyl
trimethyl ammonium bromide (CTAB) were dissolved into 20 mL of water
to obtain a clear solution. Then 9.08 g of 2-methylimidazole was
dissolved in 140 mL of water. Next the cobalt-containing solution was
poured into the 2-methylimidazole solution. After stirring for 20 min, the
resulting purple solid precipitate was centrifuged, washed thoroughly with
ethanol three times and dried under vacuum at room temperature for 12
h.
Preparation of cobalt sulphide hollow nanoboxes
100 mg of the as-synthesized ZIF-67 nanocubes was dispersed in 32 mL
ethanol. After 15 min of sonication, 120 mg of thioacetamide was added
into the suspension and the sonication was continued for another 15 min.
Then the solution was transferred to a 45 mL Teflon autoclave and was
put in an oven at 120 oC for 4 h. After cooling to room temperature, the
black precipitate was washed with ethanol three times and subsequently
dried under vacuum at room temperature for 6 h. Then the product was
treated at 350 oC for 2 h under argon using a tube furnace with a heating
rate of 2 oC/min. The recovered black material was denoted as Co3S4/CN.
Acknowledgements
We thank the financial supports from the Swiss National Science
Foundation under grant PYAPP2_160581.
Keywords: metal-organic framework
•
cobalt sulfide
•
hydrogenation • nitroarene • heterogeneous catalysis
General procedure for catalytic test
Substrate (0.5 mmol), catalyst (5.0 mg), and solvent (3.0 mL) were
introduced into a 75 mL Parr stainless-steel autoclave. The autoclave
was purged three times with H2 and then charged with the desired H2
pressure and the reaction mixture was stirred (400 rpm) for the required
time at given temperature. When the reaction time was reached, the
autoclave was immediately cooled using ice-water. After releasing the H2
slowly, 50 μL mesitylene was added to the system as an internal
standard. Next, 5 mL ethyl acetate was added to dilute the reaction
solution. After removing the catalyst by centrifugation, the organic phase
was analyzed by a gas chromatograph (Agilent 7890B) equipped with a
flame ionization detector (FID) and MS detector (5977A), and a HP-5ms
capillary column (0.25 mm in diameter, 30 m in length). The recyclability
of Co3S4/CN was tested using nitrobenzene as the substrate. In the
context of the recyclability tests, after completion of each reaction, the
Co3S4/CN catalyst was separated by centrifugation, washed with
methanol three times and reused directly in the next run.
[1]
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Shuliang Yang, Li Peng, Daniel T. Sun,
Emad Oveisi, Safak Bulut, and Wendy L.
Queen*
((Insert TOC Graphic here; max. width: 11.5 cm; max. height: 2.5 cm))
Page No. – Page No.
A Metal-Organic Framework Derived
Co3S4 Hollow Nanobox for
Selective Reduction Reaction of
Nitroarenes
the
A MOF-derived Co3S4/CN hollow nanobox could catalyze the chemoselective
reduction reaction of nitroarenes to anilines with excellent conversion and selectivity
using H2 as hydrogen source, which could simplify the product separation and
reduce the amount organic solvent waste generated efficiently.
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