Transfer hydrogenation of nitroarenes to arylamines catalysed by an oxygen-implanted MoS2 catalyst

Article abstract of DOI:10.1016/j.apcata.2016.07.008

We present an efficient approach for chemoselective synthesis of various functionalized arylamines from nitroarenes over an oxygen-implanted MoS₂ catalyst (O-MoS₂). The HRTEM, XRD, XPS, Raman, EXAFS and NH₃-TPD characterizations show the existence of Mo^IVO_x structure and abundant coordinative unsaturated (CUS) Mo sites in the 2D-layer structure of O-MoS₂. In the transfer hydrogenation of nitroarenes with hydrazine hydrate, the Mo^IVO_x structure works as the catalytic active center. The N₂H₄ selectively decomposes to the active hydrogen species in polar electronic states (H^δ? and H^δ+), which show high chemoselectivity toward the nitro reduction over [Formula presented], [Formula presented], and [Formula presented] groups. The O-MoS₂ catalyst can be recovered in a facile manner from the reaction mixture and recycled four times without any significant loss of activity.

Full text of DOI:10.1016/j.apcata.2016.07.008

Accepted Manuscript
Title: Transfer hydrogenation of nitroarenes to arylamines
catalysed by an oxygen-implanted MoS2 catalyst
Author: Chaofeng Zhang Zhixin Zhang Xu Wang Mingrun Li
Jianmin Lu Rui Si Feng Wang
PII:
S0926-860X(16)30363-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2016.07.008
APCATA 15945
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
22-4-2016
28-6-2016
14-7-2016
Please cite this article as: Chaofeng Zhang, Zhixin Zhang, Xu Wang, Mingrun Li,
Jianmin Lu, Rui Si, Feng Wang, Transfer hydrogenation of nitroarenes to arylamines
catalysed by an oxygen-implanted MoS2 catalyst, Applied Catalysis A, General
http://dx.doi.org/10.1016/j.apcata.2016.07.008
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Transfer hydrogenation of nitroarenes to arylamines catalysed by an
oxygen-implanted MoS2 catalyst
Chaofeng Zhang,a, b Zhixin Zhang,a Xu Wang,c Mingrun Li,a Jianmin Lua, Rui Si,c and
Feng Wanga*
a State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy,
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023,
Liaoning, China
b Graduate University of Chinese Academy of Sciences, Beijing 100049, China
c Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics,
Chinese Academy of Sciences, Shanghai 201204, China
*Corresponding author.
Tel: +86-411-84379762; Fax: +86-411-84379762; E-mail: wangfeng@dicp.ac.cn

Graphical Abstract
NH2H
(2)
N2H4
N2
Hd- + Hd+
MoIVOx cluster
surrounded by
MoS2 structure
(Active site)
N2H4
(1)
O-MoS2
MoIV(6)
S
O
MoIV(4), MoIV(5)
We present an efficient approach for chemoselective synthesis of various
functionalized arylamines from nitroarenes with hydrazine hydrate. The oxygen-
implanted MoS2 catalyst (O-MoS2) can be recovered in a facile manner from the
reaction mixture and recycled four times without any significant loss of activity.
Highlights
 An oxygen-implanted MoS2 catalyst (O-MoS2) is prepared, characterizations show
the existence of MoIVOx structure consisted of MoIV-O bonds and abundant
coordinatively unsaturated (CUS) Mo sites in the 2D-layer structure of O-MoS2.
 The O-MoS2 works an efficient catalyst in chemoselective synthesis of various
functionalized arylamines from nitroarenes with N2H4.
 The O-MoS2 selectively catalyzes the N2H4 decomposition to generate active
hydrogen species in polar electronic states (Hδ– and Hδ+).
 The MoIVOx structure works as the active center.

Abstract
We present an efficient approach for chemoselective synthesis of various functionalized
arylamines from nitroarenes over an oxygen-implanted MoS2 catalyst (O-MoS2). The
HRTEM, XRD, XPS, Raman, EXAFS and NH3-TPD characterizations show the
existence of MoIVOx structure and abundant coordinative unsaturated (CUS) Mo sites
in the 2D-layer structure of O-MoS2. In the transfer hydrogenation of nitroarenes with
hydrazine hydrate, the MoIVOx structure works as the catalytic active center. The N2H4
selectively decomposes to the active hydrogen species in polar electronic states (Hδ–
and Hδ+), which show high chemoselectivity toward the nitro reduction over C=C, C=C,
and C≡N groups. The O-MoS2 catalyst can be recovered in a facile manner from the
reaction mixture and recycled four times without any significant loss of activity.
Keywords
MoS2, MoOx, N2H4, transfer hydrogenation, nitro reduction
1 Introduction
Functionalized arylamines prepared from its corresponding nitroarenes are very
important industrial intermediates for pharmaceuticals, functional polymers,
herbicides, dyestuffs and other fine chemicals.[1] Previous studies on nitroarene
reduction majorly focused on oxide-supported catalysts containing d6-d10
metals.[2-16] Besides their oxidizable nature in the air, the selectivity of the
corresponding amines was not high enough when other reducible functional
groups were present in the same molecules. Regarding the storage and
availability, robust non-precious metal oxides have attracted attentions for
nitroarene reduction, but oxide catalysts with high activity are still rarely
used.[17-23] So, researches on new catalytic methods and the intrinsic
mechanism should be done.
Recently, in the nitroarenes catalytic transformation, numbers of effective
and selective approaches with various oxide-supported Au,[24-33] Pt[34] and

Ag[35] catalysts have been developed. Besides the catalytic approaches
exploitation, Corma and co-workers found the cooperative effects between gold
and the support played crucial roles in the selective activation of substrates[26]
and hydrogenation route control.[36] Kaneda and co-workers found that the
metal-oxide interfacial structure played crucial roles in the hydrogenation of nitro
and alkynyl groups with active hydrogen species in polar electronic states.[35, 37,
38] The metal-oxide interfacial structure can dynamically stabilize the in-situ
generated hydride and proton via a cooperative effect of metallic and basic
sites.[35]
Since most of the pure metal oxides lack the required metallic properties, the
redox character of central metal plays crucial roles in the catalysis.[19] It is
understandable that most pure metal oxide catalysts are inactive in nitroarenes
catalytic reduction. Recently, Beller and co-workers found that Fe2O3 and CoOx
particles surrounded by nitrogen-doped carbon layers were efficient catalysts for
the selective hydrogenation [39-41] and transfer hydrogenation [42-44] of
nitroarenes to anilines. The nitrogen-doped carbon layers and MNx (M=Co, Fe)
species of the oxide catalysts account for the high activity.
Without doping or other modification methods, we recently found that the
crystalline MoO2, with inherent bifunctional metallic-basic character, was an
effective catalyst for the transfer hydrogenation of nitrobenzene with N2H4.[23]
Density functional theory (DFT) calculations suggest that the stepwise hydrogen
transfer via the prior cleavage of N–H bond than N–N bond is the key step to
create the dissociated hydride and proton species on the surface MoIVOx center.
However, the MoO2 surface can be oxidized, and the adsorbed ammonia can
prevent the oxidized sites reduction with N2H4, which causes the catalyst
deactivation. The used catalyst needs calcination regeneration in recycle using.
In this work, we prepared an oxygen-implanted MoS2 catalyst (O-MoS2) via
an incomplete sulfidation and reduction method. The ammonium molybdate was
used as the precursor, and some MoIVOx structure was left to O-MoS2. The O-
MoS2 can efficiently catalyse nitroarenes reduction to the corresponding

arylamines with N2H4 under air condition, and the used catalyst can be easily
recovered and reused four times without any significant loss of activity. Different
from previous MoS2-based catalysts with MoS2 skeleton as the active center for
the nitroarenes reduction,[45-50] results of this work propose that the MoIVOx
structure implanted in O-MoS2 works as the active center. The O-MoS2 can
catalyse the N2H4 selective decomposition to the active hydrogen species in polar
electronic states (Hδ– and Hδ+), which show high chemoselectivity toward the
nitro reduction. The MoS2 skeleton with metallic character around the MoIVOx
structure can also catalyse N2H4 decomposition to create active H*, which has
the potential ability to promote the antioxidant properties of MoIVOx structure.
This cooperative effect makes O-MoS2 an effective and robust catalyst.
2 Experimental
2.1 Chemicals and reagents
All chemicals were of analytical grade and used as purchased without further
purification.
2.2 General procedure for catalyst preparation
O-MoS2 and O-MoS2-Ar preparation: Typically, 3.70 g (NH4)6Mo7O24·4H2O (3
mmol, AHM) and 6.85 g thiourea (90 mmol) were dissolved in 105 mL distilled
water. The autoclave was tightly sealed in air and then placed in an oven
thermally stabilized at 180 oC for 24 h, after which the autoclave was taken out
and naturally cooled down to room temperature. The solid at the bottom of the
reactor was centrifuged, washed with distilled water and ethanol, and dried at 60
oC under vacuum. The final solid was O-MoS2. O-MoS2-Ar was obtained by
treating O-MoS2 in Ar flow at 250 oC for 3 h.
The chemical exfoliation of commercial 2H-MoS2 (designated as ceMoS2)
was adapted from Chou et al.[51] 700 mg of 2H-MoS2 powder was immersed in
10 mL of n-butyllithium (1.6 M in hexane) and stirred for 48 h under Ar

protection. After the stirring, 20 mL hexane was added into the mixture, then
0.36 mL H2O was added dropwisely in 10 min under Ar flow. After 0.5 h, 200
mL of H2O was added into the mixture. The mixture was sonicated at 25~30 oC
for 2 h with a KUDOS ultrasonic cleaner (53 kHz) to achieve exfoliation. The
ceMoS2 nanosheets were centrifuged and washed with water and ethanol for five
times over a HITACHI CR21G
Ⅲ centrifuge (15000 rpm, 5 min at room
temperature). The final product was obtained after vacuum drying at room
temperature.
2.3 Characterization
The high-resolution transmission electron microscopy (HRTEM) was observed
on a FEI Tecnai F30 electron microscope at an accelerating voltage of 300 kV.
X-ray diffraction (XRD) characterizations were conducted on a Rigaku D/Max
3400 powder diffraction system with Cu Kα radiation (λ=1.542Å). The X-ray
photoelectron spectroscopy (XPS) measurements were carried out on a
VGESCALAB MK2 spectrometer equipped with an Al Kα X-ray source (hυ =
1486.6 eV) at an operation voltage of 12.5 kV. The binding energy (BE) was
calibrated with the C1s signal (284.6 eV) as a reference. Raman spectra were
recorded on a micro-Raman spectrometer (Renishaw) equipped with a CCD
detector using a He/Ne laser with a wavelength of 532 nm.
X-ray absorption fine structure (XAFS) spectra at Mo K-edge (E0 = 20000
eV) were performed at BL14W1 beam line of Shanghai Synchrotron Radiation
Facility (SSRF) operated at 3.5 GeV under “top-up” mode with a constant current
of 240 mA. The XAFS datas were recorded under transmission mode with ion
chambers. The energy was calibrated according to the absorption edge of pure
Mo foil. Athena and Artemis codes were used to extract the data and fit the
profiles. For the X-ray absorption near edge structure (XANES) part, the
experimental absorption coefficients as function of energies μ(E) were processed
by background subtraction and normalization procedures, and reported as
“normalized absorption”. For the extended X-ray absorption fine structure
(EXAFS) part, the Fourier transformed (FT) data in R space were analyzed by

applying MoS2 model for the Mo-S or Mo-Mo shell. The passive electron factors,
2
S0 , were determined by fitting the experimental Mo foil data and fixing the Mo-
Mo coordination number (CN) to be 8+6, then fixed for further analysis of the
measured samples. The parameters describing the electronic properties (e.g.,
correction to the photoelectron energy origin, E0) and local structure environment
including CN, bond distance (R) and Debye Waller (D.W.) factor around the
absorbing atoms were allowed to vary during the fit process.
The CUS Mo sites of MoS2 were probed and quantitatively analyzed by
temperature-programmed desorption of ammonia (NH3-TPD). Milligrams of
MoS2 sample was loaded into a quartz tubular reactor, which was heated in a
vertical electronic furnace. The desorption gas mixture was analyzed by an online
mass spectrometer (THERMOStar gas analysis system). The sample was initially
o
pretreated at 100 C under an Ar gas flow (30 mL·min–1) for 1 h to remove the
adsorbed impurities, and then cooled down to room temperature. Then the flow
gas was switched to ammonia gas (99.9%) for 30 min at room temperature, and
then back to Ar gas. The reactor temperature was increased to 400 oC at a ramp
rate of 10 oC· min–1. The m/z 17 was recorded for NH3 and HO* from H2O. The
pure NH3 mass signal was the subtracted value between m/z 17 (NH3 and HO*)
and the HO* mass signal based on the reference mass spectrum of H2O (m/z 18).
The quantification results were calculated by referring an ammonia standard
curve.
2.4 Catalytic reactions and product analyses
Nitrobenzene 0.5 mmol, solvent 2.0 mL and 50 μL p-xylene as an internal
standard were added into a 15 mL pressure bottle with magnetic stirring. Then
the hydrazine hydrate and catalyst were added into the reactor, and the reaction
time was set as zero. The samples were obtained by hot filtration and analyzed
by GC-MS (GC: Agilent 7890 A, MS: Agilent 5975 C) and GC (Agilent 7890
A).

3 Results and discussion
3.1 The characterization of the O-MoS2 material
The morphology of MoS2 materials are observed by TEM and HRTEM. Both
2H-MoS2 (Figure 1A and 1B) and ceMoS2 (Figure 1C and 1D) have a lamellar
structure, and preferentially expose the basal planes with Mo and S atoms orderly
arranged along (0001) crystal plane, indicating a well-crystallized phase. In
contrast, the O-MoS2 is featured with the twisted ultrathin sheets (Figure 1E),
whose atomic surface is short-range ordered but long-range disordered as
illustrated in high resolution images (Figure 1F). Except the lattice-distorted
zones, a number of subnano-sized defected zones with additional edge sites are
also observed on O-MoS2. For the O-MoS2-Ar, the thermal treatment of O-MoS2
o
in Ar flow at 250 C reforms the O-MoS2. Consequently, its surface becomes
ordered without agglomeration (Figure 1G and Figure 1H). EDX result shows
that the O content was 3.7 atom% in the O-MoS2 (Figure S1) and the TPD-MS
results (Figure S2) show that there is no lattice oxygen species released from the
O-MoS2 as O2 or SO2 below 250 oC in the Ar flow.
XRD characterizations show that O-MoS2 has two distinct peaks in the low-
angle region with the d-spacings of 9.52 Å and 4.76 Å, respectively (Figure 2),
indicating the formation of a new lamellar structure with enlarged interlayer
spacing. Thermal treatment of O-MoS2 in Ar gas at 250 oC for 3 h results in the
XRD pattern which resembles that of commercial 2H-MoS2, signifying that the
thermal treatment reforms O-MoS2. It should be noted that no molybdenum
oxides (MoO2 or MoO3) crystallites are present in O-MoS2 as revealed by XRD.
As shown in XPS spectra of Mo, S and O in the O-MoS2, two characteristic
peaks arising from Mo 3d5/2 and Mo 3d3/2 orbitals are located at 229.1 and 232.2
eV (Figure 3A), suggesting the dominance of Mo(IV) in the O-MoS2.[52] The S

2p region (Figure 3B) exhibits primarily a single doublet with the 2p3/2 peak at
161.7 eV, which is consistent with −2 oxidation state of sulfur.[52] Furthermore,
as shown in Figure 3C, the O 1s peak located at 530.7 eV is corresponding to the
oxygen bonding with Mo ion,[53] suggesting the existence of Mo(IV)−O bonds,
thus verifying the oxygen incorporation. The peak located at 532.0 eV can be
attributed to adsorbed water. Because the molybdate precursor has Mo6+, it is
very reasonable that the sulfidation and reduction process is incomplete, and
some Mo−O bonds are left to O-MoS2. The existence various Mo−O bonds in
the O-MoS2 lattice structure are further revealed by the Raman spectra (Figure
S3). These characterizations show the existence of MoIVOx structure consisted of
MoIV-O bonds in O-MoS2.
For more information about the MoS2-based materials structure, the EXAFS
fitting method was adopted to check the influence of the coordination shell of the
Mo atom in the O-MoS2 crystal structure (Figure S4). As shown in Table 1, the
Mo-Mo structure distance (R) is 3.17 Å with a coordination number (CN) of
6.91.3 in 2H-MoS2, which are very close to the theoretical values (RMo-Mo =
3.15 Å, CNMo-Mo = 6) and show the commercial 2H-MoS2 is in well-crystallized
phase. However, when 3.7 atom% oxygen (Figure S1) is implanted into the MoS2
structure via a hydrothermal synthesis method, the distance of Mo-Mo structure
reduces to 2.77 Å from 3.15 Å, the CN of Mo-Mo in O-MoS2 changes more
obviously from 6.91.3 to 0.60.2, which indicates the Mo-Mo structure on the
second shell almost disappears and O-MoS2 has a prominent disorder degree.
When the O-MoS2 is treated in the Ar at 250 oC, the Mo-Mo distance in the O-
MoS2-Ar returns to 3.16
the lattice structure and increases the layer structure crystallinity. While the CN
of Mo-Mo in O-MoS2-Ar is 2.9 1.1, which also shows the existence of a
0.01 Å, which indicates the thermal treatment reforms

disordered structure. For the Mo-S structure in the MoS2-based materials, Mo-S
distance is almost in conformity to the theoretical value (Mo-S bond, 2.41 Å) and

the CN of Mo-S structure in all materials is between 4.2 and 5.2 with a narrower
range than the one of Mo-Mo structure. These results show the interaction
between Mo and S in this material is strong and stable. Taking into account the
facts that the oxygen content in the O-MoS2 is almost ~3 atom%, the CN is
4.20.5 for the Mo-S structure and 0.60.2 for the Mo-Mo structure in O-MoS2,
O-MoS2 should contain more CUS Mo sites than 2H-MoS2 or O-MoS2-Ar.
3.2 The performance of the O-MoS2 in the nitrobenzene reduction
o
Our initial efforts focused on the nitrobenzene reduction at 50 C, O-MoS2 gave
99% aniline yield in 1 h (Table 2, Entry 1). Besides the O-MoS2, we also
employed different MoS2-based material as the reference catalysts. As shown in
Table 2, commercial 2H-MoS2 offered a 41.8% conversion (Entry 2), ceMoS2
(Entry 3) obtained by chemical exfoliation of commercial 2H-MoS2 gave a
o
65.4% conversion. The O-MoS2 treated in the Ar flow at 250 C (O-MoS2-Ar)
offered a 87.3% conversion (Entry 4). No obvious reaction was observed without
catalyst or without N2H4 (Entries 5 and 6). When Mo metal was used as a catalyst
(Entry 7) or as a reductant (Entry 8), no obvious reaction was observed,
suggesting a non-redox route.[54] Taking into account the fact that hydrazine
would decompose to H2,[55-58] employing H2 gas in replace of N2H4 (Entry 9)
to test whether H2 was hydrogen donor gave no product, indicating O-MoS2 had
no ability of activating molecule hydrogen under this condition. This suggests
the active hydrogen species (H*) is in-situ generated during the N2H4
decomposition on the surface of the O-MoS2, nitroarenes reduction occurred via
a transfer hydrogenation route.
Hot filtration tests showed the reaction was a heterogeneous reaction (Table 2,
Entry 10). ICP analysis showed no obvious leaching of the catalyst. When the reaction
scale was enlarged to 30 times with 1.85 g PhNO2, >99% aniline GC yield was obtained
(Table 2, Entry 11). The spent catalyst was filtered out, washed with ethanol, dried

under vacuum, and then used in a new reaction. It can be reused for four cycles without
any significant loss in activity (Table 2, Entry 12), which showed the stability of O-
MoS2 in liquid phase reactions (Figure S5).
3.3 The substrate scope of the O-MoS2 catalyst
With the excellent catalyst in hand, the substrate scope was evaluated (Table 3).
4-Chloro-aniline was synthesized in 99% GC yield and 87% isolated yield. No
dehalogenation occurred (Entry 1). The substituents like -CH3, -CH2OH, -OCH3,
-OH, -COCH3 and -COOH were all unaffected and well-tolerated (Entries 2–7),
the products were the corresponding arylamines, respectively. The ester group of
4-nitrophenyl acetate could react with N2H4, its product was 4-nitrophenol (Entry
8). The nitroaniline reduction gave the 99% yield phenyl diamine in the presence
o
of 3 equivalent hydrazine at 50 C in 1.5 h (Entry 9). And the multiamino
aromatic compounds could also be efficiently and selectively produced in the
chemoselective reduction of corresponding nitroarenes (Entry 10). Notably, the
O-MoS2 catalyst could promote the heterocyclic nitroaromatics reduction
without being deactivated by N atom (Entries 11-12). Besides the aromatic
nitroarenes, the O-MoS2 could also promote the nitrocyclohexane reduction
(Entry 13).
However, O-MoS2 had low activity towards catalysing the reduction of olefin,
alkyne and nitrile compounds with hydrazine at 50 oC (Entries 14-16). The feature was
advantageous because it could achieve the selective reduction of nitro-group in the
presence of other reducible functionalities. For example, in the 1:1 molar ratio of
nitrobenzene and styrene mixture, >99% aniline was obtained and ethylbenzene was
only at the detectable level (<1%) (Entry 17). When the 4-nitrostyrene was used as the
substrate, 4-aminostyrene was the main product with a >99% GC yield (Entry 18).
3.4 The main reaction route of nitrobenzene reduction

Having demonstrated the utility of this method, we then focused on our interests
in answering a question why O-MoS2 is an efficient and robust catalyst in the
chemoselective synthesis of arylamines from corresponding nitroarenes. For the
nitroarenes reduction to arylamines, Haber proposed the reaction network,[59]
and there were two main routes to get the final products (Scheme S1): the direct
route and the condensation route with N–N bonds formation and cleavage. In this
work, besides the nitrobenzene, we also used azoxybenzene and azobenzene as
the substrate to check the reaction route.
As shown in Figure 4A, in the nitrobenzene reduction, besides the main
product aniline, nitrosobenzene, azoxybenzene and azobenzene were detected.
After the reaction, the only product was the aniline. In this process, the aniline
generation rate kept at 3.5~7.0 mmol·L–1·min–1 (Figure 4D). In the azoxybenzene
reduction (Figure 4B), the azoxybenzene was firstly reduced to the azobenzene,
and the aniline generation rate reached ~4.0 mmol·L–1·min–1 at 30 min (Figure
4D). In the azobenzene reduction (Figure 4C), the products were 1,2-
diphenylhydrazine and aniline, before the 25 min, the aniline generation rate kept
at 1.5~3 mmol·L–1·min–1 (Figure 4D). Then, the aniline generation rate decreased
significantly and the azobenzene conversion reached 53.8% at 30 min and did
not obviously increase in the following 30 min.
Taking into account the different aniline generation rates from nitrobenzene,
azoxybenzene and azobenzene (Figure 4D), in the nitrobenzene reduction with
N2H4 over the O-MoS2, the direct route was the main route. And, small amount
of by-product generated from condensation route could also be reduced to aniline
over the O-MoS2. In addition, when the PhNO was used as the substrate, its
conversion was 94.0% in 10 min under the same condition showed in the caption
of Figure 4, and the 79.3% selectivity to PhNH2 indicated the average generation
rate of aniline was 18.6 mmol·L–1·min–1. Taking into account the reduction rate
of PhNO2 to PhNH2 (5.9~6.9 mmol·L–1·min–1), the PhNO→PhNH2 should occur
faster than the PhNO2→PhNO under a condition without competitive adsorption

between PhNO2 and PhNO on the catalyst (Scheme S2). Based on the generation
rates of aniline from various substrate, PhNO2→PhNO was the rate determining
step in the nitrobenzene reduction catalysed with the O-MoS2.
3.5 The electronic state of active hydrogen species
For most of hydrogenation reactions with substrates containing polar bonds, the
heterolysis of H2 molecule or other hydrogen donors to generate and stabilize
hydride and proton is a premise, which often occurs over catalysts with metallic
site and acid or basic sites.[35, 37, 60, 61] As we discussed before, the
nitrobenzene reduction over the O-MoS2 with N2H4 is a transfer hydrogenation
process. For the electronic state of active hydrogen species (H*) generated from
N2H4, they can be in polar (hydride and proton, Hδ– and Hδ+) or nonpolar (radical,
Hδ0) state.
If the H* exists in a nonpolar state, Hδ0 may escape from the reaction system
as H2 gas. However, H2 gas was not detected (Figure S6A) and it was not an
effective hydrogen donor (Table 2, Entry 9). Further experiment, adding 2,6-di-
tert-butyl-4-methylphenol (BHT, 0.2 mmol) as the radical scavenger had no
effect on catalytic result, indicated a non-radical reaction path. Considering the
fact that only Mo, S and O species exist on the O-MoS2 surface, if the H*
combined with the O-MoS2 surface, the polar electronic state might be in the
lower energy state. Previous researches also showed the existence of Mo–H (Hδ–
) intermediate in transfer hydrogenation of nitroarenes with Mo-cluster or MoO2
catalysts.[23, 47]
A linear relationship between log(kX/kH) and Brown–Okamoto constant

(Figure 5) was established for the reduction of substituted nitroarenes (X = p-Cl,
p-H, p-CH3, p-OCH3 and p-NH2). The Hammett parameter ρ is 0.68, suggesting
that the reaction is substituent-sensitive and an anion intermediates is involved.

As showed in Figure 5, we proposed that the negative H* species (hydride, Mo–
Hδ–) participated in the slow reaction step PhNO2→PhNO. The Hδ– attacked the
Nδ+ atom in the -N=O bond and generated an anion intermediate.[61] The anion
intermediate reacted with another Hδ+ species and released a H2O to PhNO.
As discussed above, both Hδ– and Hδ+ were necessary for the reduction of the
N-O or N=O bond. The base or basic sites on the catalyst could promote the
heterolysis of the N-H bond in the N2H4 to generated active hydrogen
species,[58, 62] but the extra base (OH–) adding would increase the system pH
and affect the Hδ+ concentration. As shown in proposed nitrobenzene reduction
network with active hydrogen species in polar electronic states (Scheme 1), the
low Hδ+ concentration would inhibit the PhNHOH from further reduction to
aniline (Step 3a and 3b), PhNHOH would tend to react with PhNO to
azoxybenzene.[59] Azoxybenzene was then reduced to azobenzene, which had a
neutral N=N bond and was hard reduced with polar H* directly.[63] And, in this
step, adding OH– could not only change the Hδ+ concentration but also affect the
performance of acid sites to activate the N=N bond in polar state (step 6a),
azobenzene further reduction would be inhibited. From this perspective, the Hδ+
concentration change can affect the products distribution, and low Hδ+
concentration is in favor of the generation of azobenzene. This should be the part
reasons that azobenzene synthesis from nitrobenzene usually needs base additive
or the catalysts with basic support. [28, 33, 64-66]
For further supporting the conclusion that H* should exist in polar electronic
states as Hδ– and Hδ+, an inhibition experiment with extra base (NaOH) was
carried out (Figure 6). When OH– (NaOH) was added to the system, the ratio of
aniline as the direct-route product decreased, and the ratio of condensation route
product increased. When 3.0 mmol NaOH was added, almost 50% yield of

azoxybenzene and azobenzene was obtained without dynamics optimization.
This result further confirmed the suggestion that the H* should be in polar
electronic states as Hδ– and Hδ+.
3.6 The reaction mechanism of nitroarenes reduction
In order to further study the reaction mechanism, we analyzed gas product with
mass spectrometry. As shown in Figure S6, N2 (m/z=28) was detected in the gas
phase with or without nitrobenzene. No H2 (m/z=2) was detected in both cases.
With the reaction proceeding, m/z=17 (NH3 and HO*) signal line was higher than
the m/z=18 (H2O) one, which showed the generation of NH3 in the gas phase.
Generally speaking, the typical reaction route for hydrazine decomposition was
3N2H4→4(1−x)NH3 +(1+2x)N2 + 6xH2.[58, 67] So, hydrazine decomposition
over O-MoS2 occurred according to the equation of 3N2H4→N2+4NH3. Two
N2H4 were reduced to four NH3 with four active H*,[68, 69] and the other N2H4
molecular should transform into one N2 molecular and four H*.[23]
Based on the above discussion, the H* could exist as Hδ– and Hδ+, and
nitrobenzene reduction with N2H4 occurred via a transfer hydrogenation route.
The reaction process might be that (Scheme 2): the active H* in polar electronic
states (Hδ– and Hδ+) were generated from N2H4 via N-H bond activation on the
O-MoS2, then Hδ– and Hδ+ species reacted with nitro to amine or with hydrazine
to NH3, and the catalytic active sites restored to the original state.

3.7 The catalytic active structure of the O-MoS2
As a typical 2D-layer material, the coordinative unsaturated (CUS) edge Mo sites
in the MoS2 structure usually played crucial roles in the catalysis process.[47, 52,
70-76] We used the NH3-TPD characterization to estimate the amount of CUS
Mo sites on the Mo based catalyst. As shown in Figure 7, the NH3 desorption
capacity of 2H-MoS2 was only 10.7 μmol·g–1, chemical exfoliation method made
ceMoS2 a higher one and the value reached 34.8 μmol·g–1. In comparison, the O-
MoS2 NH3 desorption capacity was 7 times (226.4 μmol·g–1) of ceMoS2. After
treatment in Ar at 250 oC, the value was remarkably decreased to 11.2 μmol·g–1
for the O-MoS2-Ar. In the nitrobenzene reduction over various catalysts, the
conversions over 2H-MoS2, ceMoS2 and O-MoS2 were 4.3%, 16.3% and 32.0%,
respectively. The relationship between conversion and NH3 desorption capacity
or the CUS Mo site was not a positive correlation (Figure 7). These results
showed the promotion of CUS Mo sites in nitrobenzene conversion was limited.
The nitrobenzene conversion over O-MoS2-Ar with few CUS Mo sites
reached 27.0% at 10 min (Figure 7), which was as good as O-MoS2 (31.8 %) with
abundant CUS Mo sites and much better than the 2H-MoS2 (4.3 %) with
approximate amount CUS Mo sites. Given the fact that there was about 3.7 atom%
O in the O-MoS2-Ar, the difference between the conversions of 2H-MoS2 and O-
MoS2-Ar indicated that MoIVOx structure connecting to the MoS2 skeleton in the
O-MoS2 or O-MoS2-Ar structure obviously promoted the reaction.
As we had reported,[23] crystalline MoO2 shows high chemoselectivity
toward the nitro reduction with N2H4, >99% aniline yield was obtained in 30 min
o
at 30 C. Under the same condition, the nitrobenzene conversion over O-MoS2
was just 17% (Figure S7). However, the MoO2 catalyst deactivated in the reuse
experiment (Figure S8), and the active MoO2 surface could be partly oxidized to
the worse MoO3 (Figure S9) phase and NH3 generated in this reaction adsorbed

on this generated MoO3, which prevents the reaction of MoO3 and N2H4 to
produce the active MoO2 (Figure S10). However, O-MoS2 could be reused four
times without any loss in its catalytic performance and did not need regeneration
operations (Figure S5). The MoS2 skeleton around the MoIVOx structure should
have a promoting effect on the stability of the O-MoS2.
As shown in Figure 7, the 2H-MoS2 or ceMoS2 could activate N2H4 to the active
H* in the nitrobenzene reduction, which indicated that the MoS2 skeleton around the
MoIVOx structure should have the potential ability to achieve the oxidized Mo center
reduction with the generated active H*. In addition, the heteroatom (S2-) around the
MoIVOx structure could improve metal property of the active sites,[77, 78] which was
favorable in Hδ– species stabilization. Based on these discussions, the cooperative effect
between the active MoIVOx structure and connecting MoS2 skeleton made O-MoS2 an
efficient and robust catalyst, which efficiently catalysed chemoselective synthesis of
arylamines from corresponding nitroarenes with N2H4.
4. Conclusions
In summary, we present an efficient approach for chemoselective synthesis of
various functionalized arylamines from corresponding nitroarenes by an oxygen-
implanted MoS2 catalyst. The robust O-MoS2 catalyst can be easily separated and
reused four times without any loss in its catalytic performance under the air
condition, which is attributed to the cooperative effect between the active MoOx
structure and its surrounding MoS2 skeleton. Furthermore, in this transfer
hydrogenation reaction, the active hydrogen species in polar electronic states as
Hδ– and Hδ+ are generated by N-H bond activation of N2H4, which is beneficial
for nitroarenes reduction. We believe that our findings will broaden the
application of MoS2 and MoOx catalysts in the mild liquid-phase reactions.
Acknowledgements

This work was supported by the National Natural Science Foundation of China
(21303189, 21403216, 21422308), and Dalian Excellent Youth Foundation
(2014J11JH126).
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(A)
(E)
(B)
(F)
(D)
(H)
(C)
(G)
d(100)
0.272 nm
d(101)
d(112)
d(100)
d(103)
d(008)
d(100)
d(110)
d(107)
d(101)
Figure 1. The TEM and HRTEM images of 2H-MoS2 (A, B), ceMoS2 (C, D), O-
MoS2 (E, F) and O-MoS2-Ar (G, H).

d=9.52 Å
d=4.76 Å
O-MoS2
O-MoS2-Ar
ceMoS2
d=6.15 Å
Commericial 2H-MoS2
JCPDS Card No. 37-1492
10
20
30
40
50
60
70
2 Theta (o)
Figure 2. The XRD patterns of the MoS2 materials.

MoIV 3d5/2
(C)
(A)
(B)
S 2p3/2
O 1s
MoIV 3d3/2
S 2p1/2
S 2s
236 232 228 224
166 164 162 160 158 538 536 534 532 530 528 526
B.E.(eV)
B.E.(eV)
B.E.(eV)
Figure 3. XPS spectra showing the binding energies of molybdenum (A),
sulfur (B), and oxygen (C) in the O-MoS2.

Conversion
PhNO
PhNH2
PhN=NPh
PhNO=NPh
(A)100
100
80
60
40
20
0
80
60
40
20
0
0
10
20
30
40
50
60
Reaction Time (min)
Conversion
PhNH2
(B)100
100
PhN=NPh
PhNHNHPh
80
60
40
20
0
80
60
40
20
0
0
10
20
30
40
50
60
Reaction Time (min)
Conversion
PhNH2
(C) 60
60
PhNHNHPh
50
40
30
20
10
0
50
40
30
20
10
0
0
10
20
30
40
50
60
Reaction Time (min)
PhNO2 as the substrate (a)
PhN=NPh as the substrate (b)
PhNO=NPh as the substrate (c)
(D) 7
6
5
4
3
2
1
0
(a)
(b)
(c)
10
20
30
40
50
Reaction Time (min)
Figure 4. The conversion-time curves of nitrobenzene (A), azoxybenzene (B),
azobenzene (C) and their aniline generation rate (D). Reaction conditions:
substrate n(N)=0.5 mmol, N2H4 1.5 mmol, ethanol 2.0 mL, O-MoS2 20 mg, 50
oC.

0.2
0.1
p-Cl
p-H
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
p-CH3
p-OCH3
p-NH2
=0.68
0.2
-0.8
-0.6
-0.4
-0.2
0.0

Figure 5. Hammett plot for the nitroarenes reduction catalysed by O-MoS2 with
N2H4. The inset is the proposed way for the reduction of the N=O bond by Hδ–
species.

PhNO=NPh
PhN=NPh
PhNH2
100
75
50
25
0
100
75
50
25
0
0
2
3
N1aOH (mmol)
Figure 6. The effect of the NaOH on the products distribution. Reaction
condition: nitrobenzene 0.5 mmol, ethanol 2.0 mL, hydrazine hydrate (80 w%)
1.5 mmol, catalyst 20 mg, Air, 50 oC, 1 h.

40
30
20
10
0
250
200
150
100
50
PhNO=NPh
PhN=NPh
PhNH2
PhNO
0
2H-MoS2 O-MoS2-Ar
ceMoS2
O-MoS2
Figure 7. The effect of the CUS Mo site on the nitrobenzene with N2H4 over the
MoS2-based catalyst. Reaction condition: nitrobenzene 0.5 mmol, ethanol 2.0
mL, hydrazine hydrate (80 w%) 1.5 mmol, catalyst 20 mg, Air, 50 oC for 10 min.
CUS Mo sites was estimated with the NH3-TPD results.

Scheme 1. The proposed nitrobenzene reduction network with active hydrogen
specieses in polar electronic state. Cat-Astands for the acid sites on the O-MoS2 catalyst.