Ni-W2C/mpg-C3N4 as a promising catalyst for selective hydrogenation of nitroarenes to corresponding aryl amines in the presence of Lewis acid

Article abstract of DOI:10.1016/j.molcata.2014.12.014

The selective hydrogenation of nitroarenes to their corresponding aryl amines has been investigated over the supported nickel propoted tungsten carbide catalyst on polymeric mesoporous graphitic carbon nitride (Ni-W₂C/mpg-C₃N₄) in the presence of Lewis acid. The Ni-W₂C/mpg-C₃N₄ is demonstrated much higher catalytic activity and selectivity for the selective hydrogenation of nitrobenzene than the supported Ni-W₂C catalyst on activated carbon (Ni-W₂C/AC) and mesoporous carbon (Ni-W₂C/CMK-3), and the developed Ni-W₂C/mpg-C₃N₄ also exhibits excellent catalytic properties for the selective hydrogenation of various substrates comprising the extra reducible functionalized groups besides nitro group to diverse functionalized arylamines, industrially important compounds, offering more than 92% of yield with 100% selectivity, which may be ascribed to the strengthened mass transfer by using mesoporous support, intentified synergistic effect between Ni-W₂C/mpg-C₃N₄ and Lewis acid owing to the basicity of mpg-C₃N₄, as well as the improved reducibility of NiO-WO₃ and the dispersion of Ni-W₂C. It can be also found that the developed catalyst could be easily recovered by filtration and recycled many times without visible loss in its catalytic performance. The significantly improved catalytic properties of supported Ni-W₂C catalyst fabricated by using mpg-C₃N₄ as a superior carrier in the presence of Lewis acid allows it to be a promising candidate for the clean and highly-efficient synthesis of diverse functionalized arylamines through the selectivie hydrogenation of substituted nitroarenes.

Full text of DOI:10.1016/j.molcata.2014.12.014

Accepted Manuscript
Title: Ni-W C/mpg-C N as a promising catalyst for selective
2
3
4
hydrogenation of nitroarenes to corresponding aryl amines in
the presence of Lewis acid
Author: Zhongkui Zhao Hongling Yang
PII:
S1381-1169(14)00574-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.12.014
MOLCAA 9376
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
20-9-2014
13-11-2014
21-12-2014
Please cite this article as: Zhongkui Zhao, Hongling Yang, Ni-W2C/mpg-C3N4 as a
promising catalyst for selective hydrogenation of nitroarenes to corresponding aryl
amines in the presence of Lewis acid, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2014.12.014
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Ni-W C/mpg-C N as a promising catalyst for selective hydrogenation of
2
3
4
nitroarenes to corresponding aryl amines in the presence of Lewis acid
Zhongkui Zhao* and Hongling Yang
State Key Laboratory of Fine Chemicals, Department of Catalysis Chemistry and
Engineering, School of Chemical Engineering, Dalian University of Technology, 2
Linggong Road, Dalian 116024, China
*
Corresponding Author
Tel. +86-411-84986354
Fax. +86-411-84986354
E-mail: zkzhao@dlut.edu.cn
Highlights
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Ni-W C/mpg-C N shows promising catalytic properties for selective
2 3 4
hydrogenation.
The superior catalytic properties are ascribed to synergism of
catalyst/Lewis acid.
The mpg-C N efficiently strengthens the synergism between catalyst and
3
4
Lewis acid.
Support type notably affects the dispersion and reducibility of supported
NiO-WOx.
Ni-W C/mpg-C N can be a practical catalyst for synthesis of diverse
2
3
4

arylamines.
Graphical abstract
Abstract
The selective hydrogenation of nitroarenes to their corresponding aryl amines has
been investigated over the supported nickel propoted tungsten carbide catalyst on
polymeric mesoporous graphitic carbon nitride (Ni-W C/mpg-C N ) in the presence
2
3
4
of Lewis acid. The Ni-W C/mpg-C N is demonstrated much higher catalytic activity
2
3
4
and selectivity for the selective hydrogenation of nitrobenzene than the supported
Ni-W C catalyst on activated carbon (Ni-W C/AC) and mesoporous carbon
2
2
(
Ni-W C/CMK-3), and the developed Ni-W C/mpg-C N aslo exhibits excellent
2 2 3 4
catalytic properties for the selctive hydrogenation of various substrates comprising the
extra reducble functionalized groups besides nitro group to diverse functionalized
arylamines, industrially improtants compounds, offering more than 92% of yield with
1
00% selectivity, which may be ascribed to the strengthened mass transfer by using
mesoporous support, intentified synergistic effect between Ni-W C/mpg-C N and
2
3
4

Lewis acid owing to the basicity of mpg-C N , as well as the improved reducibility
3
4
of NiO-WO and the dispersion of Ni-W C. It can be also found that the developed
3
2
catalyst could be easily recovered by filtration and recycled many times without
visible loss in its catalytic performance. The significantly improved catalytic
properties of supported Ni-W C catalyst fabricated by using mpg-C N as a superior
2
3
4
carrier in the presence of Lewis acid allows it to be a promising candidate for the
clean and highly-efficient synthesis of diverse functionalized arylamines through the
selectivie hydrogenation of substituted nitroarenes.
Keywords: Selective hydrogenation; Metal carbide; Support effect; mpg-C N ; Aryl
3
4
amines
1
. Introduction
Aryl amines, as the key intermediates for fine chemical, agrochemical, and
pharmaceutical industries [1-3], are generally produced by the selective
hydrogenation of nitroarenes [4-9]. However, selective hydrogenation of the extra
reducible moieties-containing nitroarenes remains challenging. The sustainable
development demands highly active and selective catalysts for the hydrogenation of
substituted nitroarenes. Unfortunately, the existing catalysts have often failed to meet
the dual requirements of activity and selectivity. On one hand, the most common
commercially available Raney nickel and palladium catalysts are broadly employed
[
10-13], although they show high activity and selectivity for nitrobenzene
hydrogenation, the selectivity towards the hydrogenation of many functionalized

nitroarenes, especially chloronitrobenzene, still remains quite low owing to the
co-existing dehalogenation reaction in the hydrogenation process. On the other hand,
platinum, rhodium and ruthenium based catalysts have also been extensively
investigated [14-18], they have shown fascinating catalytic performance under mild
reaction conditions, but they are still not suitable for an industrial application due to
their high cost and very limited availability.
Recently, the transition-metal carbides, especially molybdenum carbide and
tungsten carbide, as Pt-like metals have attracted much attention as promising
material for their outstanding bulk and surface physicochemical properties [19,20],
therefore it’s a promising approach to employ transition metal carbide catalyst in the
hydrogenation of nitroarenes with excellent activity and high selectivity. According to
the reported literatures that transition metal carbide had been attempted as additives or
supports for precious metal catalysts to catalyze the hydrogenation of nitroarenes
using hydrazine hydrate as a hydrogen source, but the usage of precious metals is
indispensable [21,22]. Many reports have demonstrated that the supported metal
carbide exhibits higher catalytic performance compared with the unsupported carbide
catalysts, ascribed to high surface area, high sintering-tolerrance stability, and the
possible metal-support interaction [23-27]. In our precious report, we have employed
supported transition metal molybdenum carbide catalysts in the hydrogenation of
functionalized nitroarenes using hydrazine hydrate as hydrogen source [28], therefore,
transition metal carbide has great potential for the hydrogenation of nitroarenes under
the condition of hydrogen. From the viewpoint of economic and clean process, the

replacement of hydrazine hydrate by hydrogen is highly desirable.
We previously demonstarted that the supported Ni-W C catalyst on AC can be
2
promising candidate for selective hydrogenation of diverse nitroarenes to their
coppesponding aryl amines by using hydrogen to replace hydrazine hydrate as H
source, and also the promoting effect of the synergism between the Ni-W C (Lewis
2
base) and Lewis acid on the reaction was established [10]. However, the relatively
high reaction temperature and pressure is indispensible to obtain satisfactory reaction
results. To develop highly efficient and highly selective catalytic systems for aryl
amine production under relatively low reaction and presure is highly desirable, but it
still remains challenge. mpg-C N materials with two-dimension pore architecture
3
4
possess higher specific surface area and larger pore volume, which results in
enhanced catalytic performances in catalysis due to higher surface density of active
sites exposed on the surface, their easier accessibility by strengthened diffusion, and
the basicity [14,15,29-37]. Hopefully the offered base sites from mpg-C N may
3
4
strengthen the synergistic effect between the supported Ni-W C catalyst and Lewis
2
acid that was established in our previous report [10].
In this work, the supported Ni-W C catalyst on mpg-C N is firstly prepared and
2
3
4
used in chemoselective hydrogenation of functionalized nitroarenes to their
corresponding aryl amines in the presence of Lewis acid. The Ni-W C/mpg-CN
2
x
catalyst shows fascinating catalytic properties, ascribed to the strengthened synergistic
effect between the supported Ni-W C catalyst and the added Lewis acid, besides to
2
the support effect on the dispersion of Ni-W C, the reducibility of NiO-WO of the
2
3

precursor of Ni-W C, as well as the improved mass transfer during catalysis owing to
2
the well-ordered mesoporous structure of the mpg-C N support. The possible
3
4
meahcnism was also discussed. It can be also found that the developed catalyst could
be easily recovered by filtration and recycled many times without visible loss in its
catalytic performance. The improved catalytic properties of supported Ni-W C
2
catalyst fabricated by using mpg-C N as a superior carrier in the presence of Lewis
3
4
acid allows it to be a promising and practical candidate for the clean and
highly-efficient synthesis of diverse functionalized arylamines through the selectivie
hydrogenation of substituted nitroarenes.
2
. Experimental Section
2
.1. Preparation of catalysts
Mesoporous silica SBA-15 powder was synthesized according to the previous
paper [38,39]: In a typical synthesis, 4.0 g of Pluronic P123 purchased from
Sigma-Aldrich Cor. was dissolved in 30 g of distilled water and 120 g of 2 M HCl
solution under vigorous stirring. After the complete dissolution, 8.50 g of TEOS
(Acros, Purity 98 %) was added into above solution. The mixture was further stirred
o
at 35 C for 20 h. The resulting mixture was aged at 80 °C overnight. The achieved
solid product was recovered, washed, and then dried at 105 °C, followed by
calcination at 500 °C for 6 h.
The mpg-C N was prepared according to the reported procedure [40]: 0.5 g of
3
4
calcined SBA-15 was added to a mixture of ethylenediamine (2.2 g) and carbon

o
tetrachloride (5.4 g). The resultant mixture was refluxed and stirred at 90 C for 6 h.
o
Then, the dark-brown solid mixture was heated in a nitrogen flow at 600 C to
carbonize the polymer. The mesoporous carbon nitride was recovered after
dissolution of the silica framework in 5 wt.-% hydrofluoric acid, followed by filtration,
o
washing several times with ethanol, and drying at 105 C. CMK-3 was also prepared
as follows: Briefly, 1 g of calcined SBA-15 was added to a solution containing 1.25 g
of sucrose, 0.14 g of H SO and 5 g of H O. The mixture was placed in a drying oven
2
4
2
o
o
for 6 h at 100 C, and then the temperature was increased to 160 C and kept this
temperature for 6 h. The resultant solid, containing silica template, partially
o
o
polymerized and carbonized sucrose, was treated again at 100 C, and then at 160 C
using the same drying oven after the addition of the solution containing 0.8 g of
sucrose, 0.09 g of H SO and 5 g of H O. The carbonization was performed by
2
4
2
pyrolysis in nitrogen atmosphere. The obtained carbon-silica composite was washed
with 5 wt% HF at room temperature to remove the silica template. The template-free
o
carbon product was obtained by filtering, washing with ethanol, and drying at 120 C.
The as-received activated carbon derived from coconut shells (Aladdin, special for
catalyst support, China) was ground and sieved into powders with grain size less than
6
2 µm for preparing catalyst support.
The Ni-W C/mpg-C N (5% Ni and 25%W C) was prepared as follows: an
2
3
4
2
aqueous solution of nickel nitrate and ammonium tungstate solution containing
desired amount of Ni and W were impregnated onto the prepared mpg-C N support
3
4
using incipient wetness impregnation (IWI) method reported in literatures [41,42],

followed by drying overnight and calcinating at a certain temperature in N2
atmosphere to obtain NiO-WO /mpg-CN . Subsequently, the NiO-WO /mpg-C N
4
x
x
x
3
were carburized in CH /H mixture according to references [43-46]. Finally, the
4
2
Ni-W C/mpg-C N catayst was obtained after it suffered from passivating in 1%
2
3
4
O /N . For comparison, the two samples Ni-W C/CMK-3 and Ni-W C/AC were
2
2
2
2
prepared by using the similar procedure as above except for the use of different
support.
2
.2. Characterization of catalysts
Nitrogen adsorption–desorption isotherms were measured at -196 °C using a
Builder 4300 analyzer. The specific surface areas were calculated according to the
Brunauer-Emmet-Teller (BET) method and the pore size distributions were calculated
from an adsorption branch of the iotherm by the (Barrett-Joyner-Halenda) BJH
o
method. X-ray diffraction patterns were collected from 10 to 80 at a step width of
o
0
.02 using Rigaku Automatic X-ray Diffractometer (D/Max 2400) equipped with a
CuKα source (λ=1.5406 Å). H temperature-programmed reduction (H -TPR)
2
2
experiments were performed in an in-house constructed system equipped with a TCD
thermal conductivity detector) to measure H consumption. In a typical H -TPR
(
2
2
experimental procedure, a quartz tube was loaded with 100 mg of sample which was
o
pretreated by calcination in Ar at 300 C for 30 min and then was cooled to ambient
temperature in Ar. After that, it was reduced with a 10 vol.% H /Ar mixture (30 ml
2
-1
o
o
-1
min ) by heating up to 800 C at a ramp rate of 10 C min .

2
.3. Catalytic performance measurement
Catalytic measurements were performed according to the literature [10]: In a
typical procudure, a certain amount of the as-prepared catalyst, cyclohexane as
solvent (Tianjin Fuyu Chemials Corp., Ltd) and 4.1 mmol of nitrobenzene (Tianjin
Beilian Fine Chemcials Corp., Ltd) were put into the in a 50 mL stainless steel
autoclave batch reactorreactor and purged 3 times with N to replace the air in the
2
reactor and purged 3 times with H to replace the N for 3 times at room temperature
2
2
respectively. In our experiments, all the reagents were analytical grade and used
without further purification. The reaction was then performed at the desired
temperature and H pressure under vigorous stirring (1000 rpm). After appropriate
2
reaction time, the temperature was lowered quickly in an ice-water bath and the
hydrogen pressure was released, then the catalyst systems including FeCl were
3
separated from the products by easily filtration, washed with cyclohexane, and then
reused in the next cycle under the same reaction conditions. The filtrate and washing
liquid were combined to obtain the mixture for chromatography analysis. The mixture
was quantitatively analyzed by gas chromatography (GC) and liquid chromatography
(
LC). The molecular structures of the synthesized arylamines were confirmed by mass
spectrometer (MS) and 1H NMR (ESI†). The conversion was calculated by weight
percent of the consumed aromatic nitro compounds in the added total amount; the
selectivity to arylamines was calculated by weight percent of the desired product in
the total products. The yields included in this paper are the GC or LC yield, except for
the scaled-up experiment. The seperated and washed catalyst was dried and reused for

recyclability measurement without extra catalyst being added. In order to probe the
perspective of practical application in industrial production towards the developed
catalyst, the scaled-up experiment by factor 10 was performed on the basis of above
procedure, and the isolated yield was calculated by the percentage of the seperated
aniline through evaporation method to the theoretical value based on the amount of
added nitrobenzene.
3
. Results and discussion
3
.1. Characterization of catalyst
By using established procedure [47], we prepared the mpg-C N . The structure
3
4
of the mpg-C N support and the as-prepared Ni-W C/mpg-C N catalyst were firstly
3
4
2
3
4
characterized by X-ray diffraction analysis (XRD). The XRD patterns (Fig. 1a)
o
indicate a characteric peak at 25.9 of (002) packing of graphite-like carbon nitride
[
47]. The shaper and stronger peak corresponding to graphitic C N on the XRD
3 4
pattern of Ni-W C/mpg-C N catalyst than that on the mpg-C N can be clearly
2
3
4
3
4
observed, ascribed to the further graphitization of the mpg-C N support in the
3
4
carburization procedure of supported NiO-WOx precursor for preparing
o
Ni-W C/mpg-C N catalyst. Besides the diffraction peak at 25.9 corresponding to
2
3
4
mpg-C N , the XRD peaks of the Ni-W C/mpg-C N at 34.2, 37.9, 39.3, 52.1, 61.7,
3
4
2
3
4
o
6
9.8, and 74.6 were well resolved, assigned to the diverse planes of W C phases
2
with hexagonal structure (JCPDS 20-1315), as well as the diffraction peaks at 31.4,

o
3
4.2, 48.2, 64.1, and 65.7 in the XRD patterns can be assigned to the (001), (100),
(101), (110), and (002) planes of WC crystal phase (JCPDS 03-1096),
o
respectively. Moreover, the three diffraction peaks at 27.2, 40.3 and 43.9 can be
clearly observed, asigned to WO , W, and Ni phases, repectively [28,48-50]. The
2
above XRD results show the supported Ni and W C catalyst on mpg-C N was
2
3
4
successfully prepared [10,28], besides the existence of W and WO phase on the
2
catalyst. The BET technique was employed to investigate the textural properties of the
catalysts, and the nitrogen adsorption-desorption isotherms are presented in Fig. 1b.
2
-1
The isotherm curves of mpg-C N reveals a higher surafce area of 451.6 m g and
3
4
some micropores of the parent mpg-C N . After supporting Ni-W C, the obvious
3
4
2
change in isotherm towards Ni-W C/mpg-C N catalyst can be observed, ascribed to
2
3
4
the partial collapse of mpg-C N framework at higher calcination temperature in the
3
4
process of carburization of W C precursor or to the possible blocked pores by
2
Ni-W C particles.
2
Furthermore, we investigate the effect of support type on the crystalline phases
of supported Ni-W C and the reducibility of the supported NiO-WO , the precursor of
2
x
Ni-W C, by performing the XRD characterization experiment of Ni-W C/mpg-C N ,
2
2
3
4
Ni-W C/CMK-3, and Ni-W C/AC samples at the same analytical conditions, as well
2
2
as the H -TPR measurement on the NiO-WO /mpg-C N , NiO-WO /CMK-3, and
2
x
3
4
x
NiO-WO /AC samples, respectively. The XRD patterns and H -TPR profiles are
x
2
presented in Fig. S1 and S2, respectively. From Fig. S1, the support type have

obvious influence on the dominant crystalline planes and crystalline size of the
supported Ni-W C catalysts, and further about 30, 34, 37 nm average crystalline size
2
of W C phase on the Ni-W C/mpg-C N , Ni-W C/CMK-3, and Ni-W C/AC,
2
2
3
4
2
2
respectively, can be obtained (Table S1). The H -TPR profiles of the
2
NiO-WO /mpg-C N , NiO-WO /CMK-3, and NiO-WO /AC samples reveals that the
x
3
4
x
x
reducibility of the supported NiO-WO is affected by the support type, and the lower
x
reducing temperature of NiO-WO /mpg-C N allows it to be easily carbothermally
x
3
4
reduced to Ni-W C, which may be one of the reasons for high catalytic performance
2
of the Ni-W C/mpg-C N for selective hydrogenation [10,28].
2
3
4
3
.2. Effect of support type on the supported Ni-W C catalysts
2
We previously demnstrated that the supported Ni-W C catalyst on AC to be a
2
promising candidate for the selective hydrogenation of nitroarenes in the presence of
Lewis acid [10], but the catalytic activity is not high enough for commercial
application, and the development of more efficient catalyst for this industrially
important reaction is highly desirable. Herein, the selective hydrogenation of
nitrobenzene to aniline was used as a probe reaction to investigate the effect of
support type of supported Ni-W C catalysts. The reaction results are summarized in
2
Table 1.
The results show that the catalytic performance of the supported Ni-W C catalyst
2
are notably dependent on the support type. By using mesoporous carbon or carbon
o
nitride as support, more than 60% of yield of aniline can be obtained at 220 C of the

lower reaction temperature. However, only 52% of yield can be obtained even if the
o
reaction temperature is increased to 240 C. In conbination of reaction results with
characterization results shown as above, the strengthened mass transfer by using
mesoporous support, as well as the improved reducibility of NiO-WO and the
3
dispersion of Ni-W C of the Ni-W C/mpg-C N makes it a superior catalyst for the
2
2
3
4
desired reaction. Furthermore, the yield is dramatically increased from 73 up to 100%
o
at 220 C for 2.5 h by introducing Lewis acid FeCl into the reaction systems,
3
ascribed to the strengthened synergistic effect between Ni-W C/mpg-C N and Lewis
2
3
4
acid [10,40,47]. Furthermore, the compared results of the supported Ni-W C catalysts
2
on diverse supports demonstrate that the support type and structure have significant
influence on their catalytic performance. Among the three supported catalysts, the
Ni-W C/mpg-C N shows the best catalytic performance for the catalytic
2
3
4
hydrogenation of nitrobenzene in the presence of FeCl , possibly ascribed to both the
3
enhanced synergism between Ni-W C/mpg-C N catalyst and Lewis acid by the
2
3
4
alkalinity of support, besides the strengthened mass trasferring by the use of
mesoprous support.
3
.3. Possible reaction mechanism
A plausible reaction mechanism for the strengthened synergistic is proposed as
Fig. 2. In our previously report [10], the synergistic effect from the Lewis acid and the
Ni-W C/AC with weak basicity was established. mpg-C N has been used as excellent
2
3
4
base catalysts for diverse reactions [40,47]. Metal carbide is most active catalyst for

hydrogen-concerned reactions [19-22], Ni-W C/AC can activate H to produce active
2
2
H for the reaction. The Lewis base (Ni-W C/mpg-C N ) [21,22] and acid (FeCl ) may
2
3
4
3
interact with the substrate and the intermediates to weaken the NO , N=O and N-O
2
bonds, and then they are hydrogenated by the active H. As a result, the
chemsoselective hydrogenation of nitroarenes can be efficiently enhanced by the
catalytic systems containing Ni-W C/mpg-C N catalyst and Lewis acid. In details,
2
3
4
firstly, the N-O of NO is activated by the coordination of Ni-W C/mpg-C N with N
2
2
3
4
atom and the Lewis acid with O, and the activated H by Ni-W C/mpg-C N interacts
2
3
4
with the actvated N-O bond, and as a result, the intermediate Ar-NO is formed. The
Ni-W C/mpg-C N and Lewis acid synergistically catalyze the above porcess.
2
3
4
Secondly, the Ar-NO is further activated and hydrogenated to Ar-NHOH, and then the
formed Ar-NH-OH is further activated and hydrogenated to produce the final product
Ar-NH though the similar activation process as above. Owing to the application of
2
basic mpg-C N , the synergism between supported Ni-W C catalyst and Lewis acid
3
4
2
would be stengthened, and therefore, the improved catalytic performance can eb
achieved.
3
.4. Scope of the substrates
From above, the catalytic systems comprising Ni-W C/mpg-C N and Lewis acid
2
3
4
with the improved catlytic performance in selective hydrogenation of nitrobenzene to
aniline has been primarily established, and herein, the scope of the developed catalytic
system is investigated by performing catalytic hydrogenation of diverse nitroarenes

with extra reducible groups under their optimized reaction conditions. The reaction
results are sumarrized in Table 2.
From Table 2, the developed Ni-W C/mpg-C N catalyst
demonstrates
2
3
4
excellent catalytic properties for the diverse substrates in the presence of Lewis acid,
and many etra reducible substitued groups-containing aromatic amine compounds can
o
be obtained with the 100% of high selectivity at 210-220 C of lower temperature [10].
More interesting point is that the halogen substitued nitrobenzenes are selectively
hydrogenated into their corresponding chloroanilines in a high yield and without any
dehalogenation (Table 2, Entries 2-4, 13). The reaction results indicate that the
developed Ni-W C/mpg-C N is a much superior catalyst for selective hydrogenation
2
3
4
of extensive scope of nitroarenes than the previosuly established Ni-W C/AC catalyst.
2
The new catalytic system comprised of Ni-W C/mpg-C N and Lewsi acid could be
2
3
4
considered as a fascinating approach for efficient and selective hydrogenation of
many nitroarenes and even extra reducible groups containing nitroaromatic substrates
for the clean production of the industrially significant functionalized aromatic amines.
3
.5. The large-scale catalytic transformtion
As an industrially important process, the scaled-up catalytic properties and
isolated yield are essential. Therefore, by using nitrobenzene as a probe substrate, the
scaled-up experiment by factor 10 was performed, and the GC yield and isolated yield
are presented in Table 3. Reaction results show that no difference in selectivity and
GC yield take palce if the reaction is scaled-up by factor 10, as well as 99.3% of

isolated yield can be achieved, which is very close to the GC yield.
3
.6. The resuability of the catalyst
In industrialized production process, the catalyst recovery and recycling is
definitely significant. Therefore, we investigated the recyclability of our developed
catalytic system for chemoselective hydrogenation by using nitrobenzene as a model
substrate. In our previous report [28], it was found that the transition metal modified
carbide on AC is so stable in the reduction systems that no leaching may be detected.
Thereore, the seperated spent catalyst was used only by washing with solvent and
drying before use, but without extra fresh catalyst being added. Figure 3 presents the
reaction results for eight times’ recycling. From the reaction results, we can observe
that the developed catalytic system containing Ni-W C/AC and Lewis acid can be
2
reused by simply separation without losing its activity for more than eight runs of the
used catalyst, and there is no loss in the yields of aromatic anilines, suggesting the
potential catalyst for the chemoselective hydrogenation of nitroarenes in practical
applications.
4
. Conclusion
In summary, we develop a novel and efficient Ni-W C/mpg-C3N4 catalyst for
2
selective hydrogenation of diverse nitroarenes in the presence of Lewis acid, which
demonstrates much superior catalytic performance. be ascribed to the strengthened
mass transfer by using mesoporous support, intentified synergistic effect between

Ni-W C/mpg-C N and Lewis acid owing to the basicity of mpg-C3N4, as well as the
2
3
4
improved reducibility of NiO-WO and the dispersion of Ni-W C. It can be also
3
2
found that the developed catalyst could be easily recovered by filtration and
recycled many times without visible loss in its catalytic performance. The improved
catalytic properties of supported Ni-W C catalyst fabricated by using mpg-C N as a
2
3
4
superior carrier in the presence of Lewis acid allows it to be a promising candidate for
the clean and highly-efficient production of many industrially important
functionalized arylamines through the selectivie hydrogenation of their correspnding
substituted nitroarenes.
Acknowledgements
This work is financially supported by the Joint Fund of Coal, set up by National
Natural Science Foundation of China and Shenhua Co., Ltd. (U1261104), the Chinese
Ministry of Education via the Program for New Century Excellent Talents in
University (NCET-12-0079) and the Fundamental Research Funds for the Central
Universities (DUT12LK51).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at
doi:10.1016/j.apcata.2011.xx.xxx.

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Figures and Tables:
Fig. 1 XRD patterns (a) and nitrogen adsorption-desorption isotherms (b) of the
as-prepared Ni-W C/mpg-C N catalyst and mpg-C N carrier.
2
3
4
3
4

Fig. 2 Plausible mechanism of the selective hydrogenation of nitrogen to aniline over
the Ni-W C/mpg-C N catalyst in the presence of Lewis acid.
2
3
4
Fig. 3 Recyclability test of the develoepd 5%Ni25%W C/AC catalyst-Lewis acid
2
catalytic system for chemoselective hydrogenation of nitrobenzene to yield aniline.
o
Reaction conditions: 50 mg catalyst, 4.1 mmol nitrobenzene, P =2.5 MPa, T=220 C,
H2
t=2.5 h.
Table 1 Catalytic performance of the supported Ni-W C catalysts on the diverse
2
supports for selective hydrogenation of nitrobenzene.
Entry
Catalyst
Lewis acid Conversion (%)
73
Selectivity (%)
1
2
Ni-W C/mpg-CNx
100
100
100
100
100
100
2
Ni-W C/CMK-3
FeCl3
FeCl3
60
52
2
a
3
Ni-W C/AC
2
4
5
6
Ni-W C/mpg-CNx FeCl3
100
79
2
Ni-W C/AC
2
Ni-W C/CMK-3
88
2
o
Reaction conditions: 50 mg catalyst, 0.5g nitrobenzene, P =2.5 MPa, T=220 C,
H2
a
o
t=2.5 h. From reference, T=240 C [10].
Table 2 Catalytic performance of the Ni-W C/mpg-C N catalyst for selective
2
3
4
hydrogenation of diverse nitroarenes.
PH2
Time
Conversion Selectivity
Entry
Substrate
Product
(MPa)
(h)
(%)
(%)

1
2
3
4
5
6
7
8
9
2.5
3.0
3.0
3.0
3.0
3.5
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.5
6.0
6.0
6.0
6.0
5.5
6.0
5 .0
6.0
6.0
6
100
100
98
100
100
100
100
100
100
100
100
100
100
100
100
100
a
a
a
92
100
98
a
a
b
a
100
98.2
100
100
100
94
10
11
1
2
3
6
1
6
100
o
Reaction conditions: 50 mg catalyst, 4.1 mmol substrates, 0.02 g FeCl ; T=220 C;
3
a
o
b
o
T=210 C; T=215 C.
Table 3 Catalytic performance of the Ni-W C/mpg-C N catalyst for the large scale
2
3
4
selective hydrogenation of nitrobenzene and the isolated yield.
PH2
MPa)
2.5
Time
(h)
Conversion Selectivity
Entry
1
Substrate
Product
(
(%)
100
(%)
100
2.5

a
2
2.5
2.5
2.5
2.5
100
100
100
b
3
99.3
o
a
Reaction conditions: 50 mg catalyst, 4.1 mmol substrates, 0.02 g FeCl ; T=220 C;
3
b
Scaled up by factor 10; separated yield for a.

fx1 .

gr1 .

gr2 .

gr3 .