Activated carbon supported bimetallic catalysts with combined catalytic effects for aromatic nitro compounds hydrogenation under mild conditions

Article abstract of DOI:10.1016/j.apcata.2019.03.017

Non-noble nickel catalysts have been widely studied and tried in hydrogenation, however the problem of nickel particle sintering is more and more common in high-loaded nickel catalysts. A series of highly dispersed bimetallic Ni-M/AC (M = Cu, Co, Fe or Zn) catalysts were prepared by incipient wetness impregnation methods and applied in 1-nitronaphthalene hydrogenation to 1-naphthylamine under mild reaction conditions. The prepared catalysts were characterized by XRD, BET, H₂-TPR, TEM, HRTEM, HAADF-STEM, XPS, ICP, FT-IR and H₂ chemisorption. The results show that the introduction of the metal promoter inhibits the sintering of the nickel and enhances the reducibility of the catalysts, leading to higher ratio of effective Ni° on the surface of the support, especially for Ni-Zn/AC sample. Moreover, the results of XPS indicate that the electron donating effect of Cu promoter increases surface electronic density of Ni, as a result, the electron-rich Ni might be produced because of the interfacial electronic effect, which favors the desorption and further impedes the hydrogenation of N-naphthylhydroxylamine. Ni-Zn/AC-350 with smaller nickel particles, better dispersion and larger content of effective Ni° presents the best catalytic performance in 1-nitronaphthalene hydrogenation to 1-naphthylamine under mild reaction conditions, it gives 100% conversion of 1-nitronaphthalene and 96.82% selectivity to 1-naphthylamine under 0.6 MPa and 90℃ for 5 h. Additionally, superior performances are also obtained in hydrogenation reactions of nitrobenzene, chloronitrobenzene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene over Ni-Zn/AC catalysts. With good hydrogenation activity the catalyst shows, the application prospect in industrial production of aromatic amine from aromatic nitro compounds has been becoming more and more extension.

Full text of DOI:10.1016/j.apcata.2019.03.017

AppliedCatalysisA,General577(2019)76–85
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Activated carbon supported bimetallic catalysts with combined catalytic
effects for aromatic nitro compounds hydrogenation under mild conditions
⁎
⁎
Lei Huanga, Yang Lva, Shengtao Wua, Pingle Liua,b,c, , Wei Xionga,b, , Fang Haoa,c, He’an Luoa,b,c
a College of Chemical Engineering, Xiangtan University, Xiangtan 411105, China
b National & Local United Engineering Research Centre for Chemical Process Simulation and Intensification, Xiangtan University, China
c Engineering Research Centre for Chemical Process Simulation and Optimization, Ministry of Education, Xiangtan University, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Non-noble nickel catalysts
Metal promoter
Hydrogenation
Aromatic nitro compounds
Aromatic amine
Non-noble nickel catalysts have been widely studied and tried in hydrogenation, however the problem of nickel
particle sintering is more and more common in high-loaded nickel catalysts. A series of highly dispersed bi-
metallic Ni-M/AC (M = Cu, Co, Fe or Zn) catalysts were prepared by incipient wetness impregnation methods
and applied in 1-nitronaphthalene hydrogenation to 1-naphthylamine under mild reaction conditions. The
prepared catalysts were characterized by XRD, BET, H2-TPR, TEM, HRTEM, HAADF-STEM, XPS, ICP, FT-IR and
H2 chemisorption. The results show that the introduction of the metal promoter inhibits the sintering of the
nickel and enhances the reducibility of the catalysts, leading to higher ratio of effective Ni° on the surface of the
support, especially for Ni-Zn/AC sample. Moreover, the results of XPS indicate that the electron donating effect
of Cu promoter increases surface electronic density of Ni, as a result, the electron-rich Ni might be produced
because of the interfacial electronic effect, which favors the desorption and further impedes the hydrogenation
of N-naphthylhydroxylamine. Ni-Zn/AC-350 with smaller nickel particles, better dispersion and larger content of
effective Ni° presents the best catalytic performance in 1-nitronaphthalene hydrogenation to 1-naphthylamine
under mild reaction conditions, it gives 100% conversion of 1-nitronaphthalene and 96.82% selectivity to 1-
naphthylamine under 0.6 MPa and 90℃ for 5 h. Additionally, superior performances are also obtained in hy-
drogenation reactions of nitrobenzene, chloronitrobenzene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene
over Ni-Zn/AC catalysts. With good hydrogenation activity the catalyst shows, the application prospect in in-
dustrial production of aromatic amine from aromatic nitro compounds has been becoming more and more
extension.
1. Introduction
formation of massive undesired by-products due to the use of stoi-
chiometric reducing agents, such as NaBH4 or hydrazine hydrate [16].
Aromatic nitro compounds are one of the most beautiful raw ma-
terials in the organic synthesis industry [1]. It can be reduced to aro-
matic amines, which are intermediates of various industrial reaction,
such as the synthesis reaction of dyes and pigments, rubber anti-
oxidants, pesticides, bio-chemicals and pharmaceuticals [2–8]. The
traditional method for aromatic amines preparation is the reduction of
aromatic nitro compounds, which is catalyzed by metal powder or al-
kali sulfide [9]. Unfortunately, it has such disadvantages as low yield, a
large amount of waste water and residue [10]. Some researches were
concerned with the production of aromatic amines by direct reduction
of the corresponding aromatic nitro compounds [11–15]. Despite the
considerable achievements that have been made, these catalytic sys-
tems are unfortunately associated with environmental issues and the
Hence, many researchers are focused on new method of liquid phase
catalytic hydrogenation to prepare aromatic amines over supported
noble and non-noble metal catalysts. Various supported noble metal
nanoparticles of Pd [17–19], Ru [20,21], Ag [22], Au [23–25] and Pt
[26] were applied in the hydrogenation reaction of aromatic nitro
compounds to aromatic amines and presented perfect catalytic perfor-
mance. However, these noble metal catalysts have the problems of high
cost, scarce resources and un-stability, which restrict their extensive
application in industry. Many researches have been contributed to ex-
ploit the catalytic hydrogenation of aromatic nitro compounds to cor-
responding amines over non-noble metal catalysts such as Raney Ni, Co-
Mo-S, NiFeP and Ni-B amorphous alloys [27–32]. However, it requires
large loading amount of metals or the reaction must be carried out
⁎ Corresponding authors at: College of Chemical Engineering, Xiangtan University, Xiangtan 411105, China.
E-mail addresses: liupingle@xtu.edu.cn (P. Liu), happy.xiongw@163.com (W. Xiong).
https://doi.org/10.1016/j.apcata.2019.03.017
Received 17 January 2019; Received in revised form 21 March 2019; Accepted 22 March 2019
Availableonline23March2019
0926-860X/©2019ElsevierB.V.Allrightsreserved.

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
under higher H2 pressure, higher temperature and for longer time
[28–31]. Carbon nanotube supported nickel catalyst was developed by
Xiong et al. [33], which gave 92.04% selectivity to 1,5-diamino-
naphthalene and 100% conversion of 1,5-dinitronaphthalene under
mild conditions, nevertheless the leaching of monometallic Ni catalyst
will lead to poor reusability. Moreover, large loading amount of nickel
will result in agglomeration and sintering, which will bring bad effects
on catalyst activity and reusability. Active metals doped with other
metal promoter to obtain non-noble bimetallic catalysts have been ex-
tensively studied, which present high stability, activity and selectivity
in comparison with monometallic catalysts for its better particle dis-
persion and synergistic catalytic effects among different metals
[34–49]. Liu et al. [41] found that doping Cu in Ni-based catalyst will
decrease Ni particle size and promote its dispersion, and thus enhance
the alkynes hydrogenation activity, and the selectivity to ethene in-
creases because of the electron transfer from Cu to Ni and thus favors
ethene species desorption. Lv et al. [42] reported that the addition of
copper in MgO-Cu-Ni/MWCNT can lead to better nickel nanoparticles
dispersion, larger metallic surface area and facilitate the reduction of
nickel oxide at lower temperature, hence improve the catalytic per-
formance for adiponitrile hydrogenation under mild conditions. In ad-
dition, Shen and Chen [43] showed that addition of Co in NiB decreased
the particle size and improved the stability of NiCoB nanoalloy catalysts
in p-chloronitrobenzene hydrogenation. Several studies [44–47] also
showed that introduction of Co in Ni-based catalyst decreased the
particle size and reduced the reduction temperature of NiO species. The
most efficient Ni-Fe bimetallic catalyst for guaiacol hydrodeoxygena-
tion was reported by Fang et al. [48]. It showed that incorporation of Fe
in Ni/CNT formed Ni-Fe alloys, reduced the crystallite size and in-
hibited the sintering of metal nanoparticles. Moreover, ZnO has also
been used as the promoter in Ni/ZnO/Al2O3 in partial hydrogenation of
Sunflower oil [49] and it was found that ZnO acted as the spacer in Ni
crystallites to impede the sintering of Ni particles, leading to higher Ni
surface area and better dispersion. Thus, it is worth to develop non-
noble Ni-based bimetallic catalysts with high dispersion and combined
catalytic effects.
0.5 h and impregnated for 12 h, followed by drying at 110℃ for 12 h.
Finally, the obtained solids were calcined at 350℃ for 4 h under ni-
trogen and reduced under hydrogen at 350℃ for 2 h. In addition, in
order to study the effect of reduction temperature on catalytic perfor-
mance, the bimetallic Ni-Zn/AC catalyst and monometallic Ni/AC cat-
alyst were reduced at different temperature and the catalysts were
marked as Ni-Zn/AC-T and Ni/AC-T (T = 300℃, 350℃, 400℃).
2.3. Catalytic reaction
The liquid phase hydrogenation of 1-nitronaphthalene was carried
out in a 50 mL Teflon-lined stainless-steel autoclave reactor with 0.1 g
catalyst, 2 g 1-nitronaphthalene and 20 mL N,N-dimethylformamide
(DMF), then the reaction was conducted at 80℃ and 0.6 MPa H2 pres-
sure under 400 rpm for 5 h. After the reaction, the catalysts were se-
parated by filtration. The reactant and the product were analyzed by
high performance liquid chromatography method. Additionally, the
catalysts were filtered from the reaction solution and used for the next
run without any other treatment to test the reusability.
2.4. Catalysts characterizations
The Powder X-ray diffraction (XRD) measurements were carried out
using a Japan Rigaku D/Max 2550 VB+ 18 kw X-ray diffract meter with
Cu Kα radiation operating at 40 kV and 30 mA, with a scanning speed of
10° min−1 in the range of 2θ = 10-90°.
Nitrogen adsorption-desorption was performed on a NOVA-2200e
automated gas sorption system to measure the specific surface area,
pore size distribution and pore volume of the samples. Specific surface
area was determined by Brunauer-Emmett-Teller (BET) method, pore
size distribution and pore volume were evaluated from the desorption
isotherm branch using the Barrette-Joyner-Halenda (BJH) method.
Fourier transform infrared (FT-IR) spectra of the activated carbon
was recorded on a Nicolet 380 spectrometer.
The quantitative elemental analysis of active metals was determined
by IRIS 1000 ICP-AES (Thermo Elemental, USA).
Activated carbon is widely used as support to load active metals
because of its chemical stability, tailored pore size distribution, high
specific surface area and capacity to be functionalized [50]. In this
work, bimetallic Ni-M/AC (M = Cu, Co, Fe or Zn) catalysts were pre-
pared by incipient wetness impregnation method and applied in 1-ni-
tronaphthalene hydrogenation, among all the catalysts studied, the Ni-
Zn/AC-350 shows the best catalytic performance under very mild
conditions. Such activated carbon supported nickel-based bimetallic
catalysts with lower cost are expected to replace the present noble
metal catalysts in industry.
The hydrogen chemisorption of the samples were examined on
Micromeritics 2920. Before starting the hydrogen chemisorption pro-
cedure, the samples were reduced in a stream of 10% H2/Ar, and then
Ar stream was used to remove the adsorbed hydrogen on the nickel
surface. The samples were then cooled down to room temperature
under Ar stream, and injected with hydrogen pulses until the eluted
areas of consecutive pulses became constant. The stoichiometric ad-
sorption of hydrogen was assumed to calculate the amount of nickel
atoms, and nickel surface area was calculated from the nickel atomic
cross section area.
The X-ray photoelectron spectroscopy (XPS) was carried out on a
Kratos Axis Ultra DLD spectrometer equipped with a monochromatic
Al-Kα radiation, and operated at a invariable transmission energy pass
(80 eV). The peak corresponding to carbon 1 s (at 284.6 eV with an
2. Experimental
2.1. Materials
accuracy of
0.05 eV) was taken to refer to correct binding energy
The activated carbon with specific surface area range from 1200-
1400 m2 g−1 were bought from Fujian Xinsen carbon Co., Ltd. Aromatic
nitro compounds was obtained from Beijing Bailingwei Co., Ltd. Nickel
nitrate (Ni(NO3)2·6H2O), Zinc nitrate (Zn(NO3)2·6H2O), Copper nitrate
(Cu(NO3)2·3H2O), Iron nitrate (Fe(NO3)3·9H2O), Cobalt nitrate (Co
(NO3)2·6H2O) and 5% Pd/C with 40–60 % H2O were bought from
Shanghai Aibi Chemistry Reagent Co., Ltd. The aromatic amine (99 wt.
%) standard sample was purchased from Beijing Bailingwei Co., Ltd.
(BE) values of different elements in the samples.
The temperature programmed H2 reduction (TPR) profiles of the
samples were obtained from ChemBET-3000 equipped with a TCD de-
tector to monitor the H2 consumption. For each TPR measurement,
60 mg of sample was placed in a quartz tube, heated to 200℃ with the
rate of 10℃/min under 100 mL/min Ar for 120 min. The sample was
then cooled down to 70℃ and then heated from 70℃ to 700℃ at the
rate of 10℃/min under a stream of 10% H2/Ar at the speed of 100 mL/
min.
2.2. Catalyst preparation
Transmission electron microscopy (TEM) was carried on a
Jem2100 F electron microscope with an accelerating voltage of 200 kV.
Before starting the TEM characterization, the powder samples were
treated under ultrasonic in anhydrous ethanol, and then dripped on
copper grids covered with a porous carbon film. The different elements
mapping of the samples were conducted under STEM mode with the
Ni-base bimetallic catalysts were prepared by impregnation method.
To prepare the Ni-Zn/AC, 1.5 g activated carbon was impregnated in
5 mL of aqueous solution including 0.75 g of Ni(NO3)2·6H2O and
0.069 g of Zn(NO3)2·6H2O, the slurry was treated under ultrasonic for
77

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
Fig. 1. FT-IR spectra of activated carbon.
EDX detector as recorder.
3. Results and discussion
Fig. 3. XRD patterns of (a) Ni-Zn/AC, (b) Ni-Fe/AC, (c) Ni-Co/AC, (d) Ni-Cu/
AC, (e) Ni/AC.
3.1. Characterization of catalyst
3.1.1. FT-IR
attributed to (111), (220) reflections of the NiO phase. No obvious
diffraction peaks of promoter metal species are observed, probably due
to the lower amount and better dispersion. It must be noted that the
peaks of metal Ni in bimetallic catalysts were much broader than that of
Fig. 1 presents the FT-IR spectra of the activated carbon. The peaks
of 3450 cm−1 and 1633 cm−1 are attributed to the tensile and flexural
vibration of OeH bond in water, and the peaks of 1400 cm−1 and
1070 cm−1 are attributed to the existence of the carboxylic acids [33].
It indicates that the activated carbon support contains a small amount
of oxygen-containing species, which could improve the dispersibility of
activated carbon in water and enhance the specific nucleation sites for
the anchoring of metal particles [33].
monometallic nickel catalysts, indicating that promoter metal
M
(M = Cu, Co, Fe or Zn) can effectively inhibit nickel sintering and form
smaller nickel crystallite with better dispersion on the catalyst surface
[42,47,48,52]. And it can be seen from Table 1 that the average Ni
crystallite sizes are listed in the following order: Ni-Cu > Ni-Co > Ni-
Fe > Ni-Zn.
The effects of reduction temperature on the property of bimetallic
Ni-Zn/AC and monometallic Ni/AC are investigated. The XRD diffrac-
tion patterns of the samples are displayed in Fig. 4. It can be seen that
the samples reduced at 300℃ show five characteristic diffraction peaks
at 2θ = 23°, 37.2°, 44°, 62.5°, and 77°, the samples reduced at 350℃
display six distinct diffraction peaks at 2θ = 23°, 37.2°, 44°, 52°, 62.5°,
and 77°, the samples reduced at 400℃ reveal four obvious diffraction
peaks at 2θ = 23°,44°, 52° and 77°. As we can see, metal Ni nano-
particles are formed even at relatively low temperature of 300℃, the
diffraction peak of metal Ni becomes strong and the crystallinity is
improved with the increment of reduction temperature, meanwhile the
nickel particle size increases, and more NiO species are reduced when
the reduction temperature increases to 400℃.
3.1.2. XRD
The samples were calcined at 350℃ for 4 h under nitrogen and re-
duced at 350℃ for 2 h under hydrogen before XRD characterization.
Fig. 2 shows XRD patterns of Ni/AC with different Ni loading amount.
The peak at 2θ = 23° is corresponded to carbon [51], the peaks at
2θ = 44°, 52°, and 77° (JCPDS #04-0850) are ascribed to (111), (200),
and (220) lattice planes of the metal Ni and the peak of 37.2° and 62.5°
(JCPDS #47-1049) are indexed to NiO (111) and NiO (220). However,
no obvious diffraction peaks of NiO species are observed in 3 wt % Ni/
AC and 5 wt % Ni/AC, probably due to high dispersion when Ni loading
is low. And the characteristic diffraction peak of nickel becomes sharp
with the increment of Ni loading amount, which indicates that larger
nickel particle size is obtained.
The XRD patterns of the reduced Ni-based bimetallic catalysts with
10 wt % Ni and 1 wt % promoter metal M (M = Cu, Co, Fe or Zn) are
shown in Fig. 3. As we can see, diffraction peak at 2θ = 23° for all the
samples is correspond to carbon [51], the significant diffraction peaks
observed at 2θ = 44°, 52°, and 77° (JCPDS #04-0850) are ascribed to
(111), (200), and (220) lattice planes of the metal Ni, respectively, and
the diffraction peaks at 2θ = 37.2°, and 62.5° (JCPDS #47-1049) are
3.1.3. N2 adsorption-desorption
The N2 adsorption/desorption isotherm and BJH pore size dis-
tribution patterns of the samples are shown in Fig. 5, it presents type Ⅳ
adsorption isotherm, which indicates that the samples have micropore
and mesoporore structure [53,54]. The specific surface area, average
pore diameter and pore volume of the samples are summarized in
Table 1. N2 adsorption/desorption data indicates that the activated
carbon support has the specific surface area of 1438.3 m2 g−1, pore
volume of 0.18 cm3 g−1 and pore size of 2.8 nm. After adding 10 wt%
Ni and 1 wt% promoter metal M (M = Cu, Co, Fe or Zn) to activated
carbon, the specific surface area and pore volume of the samples de-
crease probably due to the presence of small metal particles in the pore
of activated carbon [54], while the pore size remains almost unchanged
[55,56].
3.1.4. H2 chemisorption
The hydrogen chemisorption data are shown in Table 2. It can be
seen that Ni/AC-400 shows the lowest H2 uptake quantity, the lowest
metallic surface area and dispersion. And bimetallic Ni-M/AC-350
(M = Cu, Co, Fe or Zn) catalysts present better results than Ni/AC-350.
Some researchers have found that the introduction of promoter metal M
(M = Cu, Co, Fe or Zn) helps to enhance the hydrogen uptake quantity
and metal dispersion [41,42,47,49,57]. And Ni-Zn/AC-350 exhibits the
largest H2 uptake quantity, metallic surface area and the best nickel
Fig. 2. XRD patterns of (a) 15% Ni/AC, (b) 10% Ni/AC, (c) 5% Ni/AC, (d) 3%
Ni/AC.
78

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
Table 1
Textural properties of the samples.
Sample
Ni(wt %)a
M1a(wt %)
SBET(m2. g−1
)
Vpore(cm3. g−1
)
Dpore(nm)
DNi(nm)b
DNi(nm)c
AC
Ni/AC
Ni-Cu/AC
Ni -Co/AC
Ni -Fe/AC
Ni -Zn/AC
–
–
–
1.02
0.96
1.01
0.92
1438.3
1198.8
1190.2
1199.4
1095.5
1186.7
0.18
0.14
0.13
0.13
0.11
0.12
2.8
2.8
2.7
2.8
2.8
2.7
–
–
9.95
10.10
9.92
10.00
10.03
8.3
7.2
6.8
6.3
5.7
7.2
6.5
5.9
5.3
4.6
M1: promoter metal (Cu, Co, Fe or Zn), a: Determined with ICP-AES, b: Calculated from XRD, c: Calculated by TEM images.
Table 2
H2 chemisorption data of the samples.
Catalyst
H2 chemisorption data
H2 uptake quantity
Metallic surface
Metal dispersion
(%)
(μLg−1
)
areas (m2 g−1
)
Ni/AC-350
Ni/AC-400
95.32
54.72
2.31
1.76
2.52
2.61
2.83
3.12
2.01
4.40
2.85
6.01
7.34
7.65
8.05
4.23
Ni-Cu/AC-350
Ni-Co/AC-350
Ni-Fe/AC-350
Ni-Zn/AC-350
Ni-Zn /AC-400
133.74
139.32
147.21
163.45
81.74
Fig. 4. XRD patterns of (a) Ni/AC-400, (b) Ni-Zn/AC-400, (c) Ni/AC-350, (d)
Ni-Zn/AC-350, (e) Ni/AC-300, (f) Ni-Zn/AC-300.
dispersion, which might favor the hydrogenation process of aromatic
nitro compounds.
3.1.5. H2-TPR
Fig. 6 shows the H2-TPR characterization patterns of the samples
calcined at 350℃ for 4 h under flowing nitrogen. It can be seen that all
the samples possess two broad hydrogen consumption peaks, the one is
located at lower temperature of 650–700 K, which is attributed to the
reduction of nickel oxide, the other around 750–850 K is corresponded
to the reduction of amorphous C species in the presence of nickel
[58,59]. Bian et al. reported that nickel can promote the methanation of
carbon nanotubes when the temperature surpassed 773 K [60]. Com-
pared with monometallic catalyst precursor NiO/AC, the bimetallic
catalysts make the reduction peaks of nickel oxide shift toward lower
temperature, indicating that promoter metals (M = Cu, Co, Fe or Zn)
aid in NiO reduction. The reason may be that the synergic effect be-
tween nickel and promoter metals (M = Cu, Co, Fe or Zn) will decrease
the reduction activation energy of NiO [34,41,50,54,55].
Fig. 6. H2-TPR profiles of (a) 10% Ni/AC, (b) Ni-Cu/AC, (c) Ni-Co/AC, (d) Ni-
Fe/AC, (e) Ni-Zn/AC.
3.1.6. XPS
Fig. 7 exhibits the Ni 2p3/2 spectra of the samples. The peaks in Ni
2p3/2 XPS spectra are located at the BE of 852.8 eV to 853.1 eV,
854.8 eV to 855.1 eV, and 856.4 eV to 856.7 eV, which are attributed to
Ni°, Ni2+, and Ni3+, respectively [48]. Additionally, the shake-up
Fig. 5. N2 adsorption-desorption isotherm and BJH pore size distribution of (a) AC, (b) Ni/AC, (c) Ni-Cu/AC, (d) Ni-Co/AC, (e) Ni-Fe/AC, (f) Ni-Zn/AC.
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L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
Table 4
Surface composition of the samples.
Catalyst
XPS Peak area ratio (%)
Ni°
Ni2+
Ni3+
Ni/AC-300
Ni/AC-350
Ni/AC-400
Ni-Zn/AC-300
Ni-Zn /AC-350
Ni-Zn /AC-400
10.2
20.3
25.1
14.5
27.5
31.7
41.2
37.5
39.2
40.6
37.4
35.2
48.6
42.2
35.7
44.9
35.1
33.1
In addition, the covalent of Ni in bimetallic Ni-Zn/AC and monometallic
Ni/AC under different reduction temperature was characterized by XPS.
The Ni 2p3/2 spectra of the samples are shown in Fig. 8. The results
indicate that a certain proportion of nickel oxides still exist even the
reduction temperature increases to 400℃, the content of Ni° in Ni-Zn/
AC is greater than that of Ni/AC under the same reduction temperature
(Table 4), hence, Ni-Zn/AC presents higher catalytic activity.
Fig. 7. XPS patterns of (a) Ni/AC, (b) Ni-Cu/AC, (c) Ni-Co/AC, (d) Ni-Fe/AC,
(e) Ni-Zn/AC.
Table 3
Surface composition of samples.
Catalyst
XPS Peak area ratio (%)
Ni°
3.1.7. TEM
Fig. 9 shows the TEM images of the samples. It can be seen from
Fig. 9 a that obvious agglomeration exists in Ni/AC, and the mean
particle size is about 7.1 nm. As for promoter metal doped Ni-based
catalysts Ni-M/AC (M = Cu, Co, Fe or Zn) in Fig. 9 b, c, d and e, the
doped metal can prevent nickel sintering in a certain degree [50,68,62],
thus smaller Ni nanoparticles with mean particle sizes of 6.5 nm,
5.9 nm, 5.3 nm and 4.6 nm disperse uniformly on the surface of the
support, this is in agreement with the XRD results. In addition, uniform
dispersion of metallic particles is beneficial to the exposure of catalytic
active sites, hence improves catalytic performance [69].
Fig. 9 a, e and Fig. 10 a, b presents TEM images of Ni-Zn/AC and Ni/
AC reduced under 350℃ and 400℃. It was observed that Ni-Zn/AC and
Ni/AC reduced at 350℃ show highly dispersed metal particles with an
average size of 4–7 nm. However, relatively larger particles with an
average size of 7–9.5 nm were observed when the reduction tempera-
ture increases to 400℃, the particles sintering and agglomeration may
occur under higher temperature. In addition, compared with Ni/AC, Ni-
Zn/AC shows well dispersion under the same reduction temperature,
which further prove that introduction of promoter metal Zn favors Ni
particles dispersion.
Ni2+
Ni3+
Ni/AC
20.3
22.1
23.4
24.5
27.5
37.5
40.5
39.6
38.8
37.4
42.2
37.4
37.0
36.7
35.1
Ni-Cu/AC
Ni-Co/AC
Ni-Fe/AC
Ni-Zn/AC
satellites peak appears at 861.3 eV, which is accompanied by multiple
division of binding energy of the oxidized nickel [61]. Compared with
monometallic catalyst, the intensity of Ni° increases with the in-
troduction of promoter metals (Table 3), indicating that the synergic
effect between nickel and promoter metals (M = Cu, Co, Fe or Zn) aids
in NiO reduction [42,49,62–64]. This is consistent with the result of H2-
TPR in Fig. 6. Furthermore, compared with Ni/AC, the binding energy
of Ni° in Ni-Cu/AC (Fig. 7 b) shifts towards lower binding energy (BE)
(-0.3 eV), the reason may be the charge transfer from Cu to the adjacent
Ni since stronger electronic interactions take place between copper and
nickel species [41,65,66], and it proves that doping of Cu can lead to
the formation of Ni-Cu alloy [41,42]. According to the electron-band
theory, nickel has free d-orbitals delocalized in the conductivity band,
while copper has free d-electrons. The interaction between Ni and Cu
will result in the filling of the d-zone of Ni [67]. As for promoter metals
(M = Co, Fe or Zn), the results of XPS show that there is no obvious
charge transfer to nickel. Typically, Liu et al. reported that the char-
acteristic peak of metallic nickel species in Ni-Cu/MMO shifted towards
lower binding energy (BE) (-0.4 eV) in comparison with Ni/MMO [41].
Ni-Zn/AC-350 was characterized by using high-resolution trans-
mission electro microscope (HRTEM), scanning transmission electro
microscope-energy dispersive X-ray (STEM-EDX) and elemental map-
ping. Meanwhile, the crystal lattice of Ni-Cu alloy in Ni-Cu/AC-350 was
measured by HRTEM. It presents that the lattice distance of 0.205 nm
(Fig. 11 a) is assigned to (111) plane spacing of Ni-Cu alloy [42]. It can
be seen from Fig. 11 b that there exists the lattice distance of 0.204 nm,
which is ascribed to (111) plane spacing of Ni (JCPDS #04-0850), and
Fig. 8. XPS patterns of (a) Ni/AC-300, (b) Ni/AC-350, (c) Ni/AC-400, (a1) Ni-Zn/AC-300, (b1) Ni-Zn/AC-350, (c1) Ni-Zn/AC-400.
80

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AppliedCatalysisA,General577(2019)76–85
Fig. 9. TEM pictures (a) Ni/AC, (b) Ni-Cu/AC, (c) Ni-Co/AC, (d) Ni-Fe/AC, (e) Ni-Zn/AC.
the lattice distance of 0.190 nm is assigned to (102) plane spacing of
ZnO (JCPDS #36-1451). The small amount of ZnO served as the spacer
between Ni crystallites is to prevent the formation of bulky Ni particles.
Similarly, Wong et al. found that bimetallic Ni/ZnO/Al2O3 presented
less sintering and better dispersion than that of monometallic Ni/Al2O3
because ZnO acts as the physical spacer between Ni crystallites [49].
The elemental mapping analysis based on EDS indicates that nickel and
zinc are dispersed homogeneously on the activated carbon support
(Fig. 11 e, f).
product is 1-naphthylamine. Other intermediates such as ni-
trosonaphthalene (NSN), N-naphthylhydroxylamine (HN), azox-
ynaphthalene (AON), azonaphthalene (AN) and hydrazonaphthalene
(HAN) will appear in this reaction (Scheme 1). In “routeⅠ”, the rate of
HN hydrogenation to 1-naphthylamine is relatively slow, hence the
NSN and HN is accumulated during this process [70]. Therefore, in
“routeⅡ”, NSN reacts with HN to form AON, and AON can be reduced to
AN, and then AN can be hydrogenated to HAN and finally to 1-naph-
thylamine.
Since the reaction takes place on the surface of the catalyst, it fol-
lows the classical Langmuir–Hinshelwood model [71]. Hydrogen mo-
lecules and 1-nitronaphthalene can be adsorbed onto the surface of the
bimetallic nanoparticles, and both of the adsorptions are reversible.
Under the catalysis of the bimetallic nanoparticles, the hydrogen mo-
lecules may dissociate, then active surface hydrogen species are thus
3.2. Catalytic performance
The prepared catalysts were applied in 1-nitronaphthalene hydro-
genation and the results are shown in Fig. 12. The main intermediates
include hydroxynaphthalene and hydrazonaphthalene, while the main
81

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
Fig. 10. TEM pictures (a) Ni/AC-400, (b) Ni-Zn/AC-400.
Fig. 11. (a) HRTEM of Ni-Cu/AC, (b) HRTEM of Ni-Zn/AC, (c) HAADF-STEM image of Ni-Zn/AC, (d–f) the corresponding elemental mappings of Ni-Zn/AC.
Fig. 12. Catalytic performance; Reaction conditions:1-nitronaphthalene, 2 g; DMF, 20 mL; Catalyst, 0.1 g; Temperature, 80℃; H2 pressure, 0.6 MPa; Time, 5 h, a 4 h.
82

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
XRD in Fig. 3 and TEM in Fig. 9 that the promoter metals can inhibit
nickel nanoparticles agglomeration so as to obtain smaller nickel par-
ticles and improve its dispersion. The selectivity to 1-naphthylamine is
more than 90% over Ni-Co/AC, Ni-Fe/AC and Ni-Zn/AC, which in-
dicates that deoxygenation of HN to 1-naphthylamine is prone to take
place on smaller nickel particles [73,74]. However, bimetallic Ni-Cu/
AC gives only 80.12% selectivity to 1-naphthylamine, the reason may
be the transfer of charge from Cu to the adjacent Ni, which results in
disadvantage of electron-rich nickel to the adsorption of N-naphthyl-
hydroxylamine, and thus prevent further hydrogenation of N-naph-
thylhydroxylamine to 1-naphthylamine. Similarly, Chen et al. found
that the interfacial electronic effects can control the reaction selectivity
in nitrobenzene hydrogenation over platinum catalysts, furthermore,
high selectivity to N-hydroxylaniline was obtained by adjusting the
surface electron of platinum nanowires with ethylenediamine, and the
adsorption of electron-deficient nitrobenzene was favoured by electron-
rich Pt, thus preventing further hydrogenation of N-hydroxylaniline to
aniline [75].
Scheme 1. The possible reaction routes of the 1-nitronaphthalene hydrogena-
tion.
The reduction temperature has great influence on the micro-
structure and surface composition of the catalyst, hence affects the
catalytic performance [33,35]. Too low or too high reduction tem-
perature is not good for either monometallic Ni/AC or bimetallic Ni-Zn/
AC catalyst, lower content of Ni° is obtained under relatively lower
reduction temperature of 300℃, while it appears Ni sintering and ag-
glomeration when the reduction temperature increases to 400℃
(Fig. 12 c). 1-nitronaphthalene hydrogenation occurs on the surface of
the active metal nanoparticles, hence the catalyst with good metal
dispersion generally presents good catalytic activity. However, high
temperature will cause the sintering of nanoparticles, which may result
in a decrease in the amount of the exposed Ni°. Although the total Ni°
content of Ni-Zn/AC-400 is higher than that of Ni-Zn/AC-350, the
amount of effective Ni° involved in the reaction is less than that of Ni-
Zn/AC-350. It can be seen from Table 2 that Ni-Zn/AC-350 exhibits
better metal dispersion (8.05%) than that of Ni-Zn/AC-400 (4.23%) and
the highest H2 uptake quantity of 163.45μLg−1. Hence, Ni-Zn/AC-350
presents better catalytic performance than that of Ni-Zn/AC-400. The
similar results are obtained in monometallic Ni/AC. And Ni/AC-350
gives 77.15% conversion of 1-nitronaphthalene and 87.03% selectivity
to 1-naphthylamine, while Ni-Zn/AC-350 gives 92.20% conversion of
1-nitronaphthalene and 91.70% selectivity to 1-naphthylamine.
Bimetallic Ni-Zn/AC-350 presented good catalytic performance in
1-nitronaphthalene hydrogenation, it was tried in other aromatic nitro
compounds hydrogenation such as 1,5-dinitronaphthalene, 1,8-dini-
tronaphthalene, nitrobenzene, o-chloronitrobenzene, m-chloroni-
trobenzene and p-chloronitrobenzene. It can be seen from Table 5 that
95.63% yield of 1,5-diaminonaphthalene, 97.25% yield of 1,8-diami-
nonaphthalene, 98.36% yield of aniline, 93.57% yield of o-chloroani-
line, 93.54% yield of m-chloroaniline and 94.02% yield of p-chlor-
oaniline are obtained under mild conditions.
generated and bonded to the surfaces of the bimetallic nanoparticles.
The adsorbed 1-nitronaphthalene can be reduced to 1-naphthylamine
by these active hydrogen species derived from the hydrogen molecules.
Because of the much weaker adsorb ability of the amino groups than
that of the nitro groups, 1-naphthylamine may desorb readily from the
catalyst surface once generated [72]. So the reaction is proceed spon-
taneously.
It can be seen from Fig. 12 a that AC without active metal does not
show catalytic activity in 1-nitronaphthalene hydrogenation, while
high cost noble metal catalyst 5% Pd/C shows 100% 1-ni-
tronaphthalene conversion and 98.48% selectivity to 1-naphthylamine
under 80℃, 0.6 MPa H2 pressure and 4 h. The unreduced 10% NiO/AC
and 1% M/AC (M = Cu, Co, Fe or Zn) reduced under 350℃ are also
tested in 1-nitronaphthalene hydrogenation, but these catalysts do not
show catalytic activity. For Ni/AC catalyst, as the Ni loading amount
increases from 3% to 15%, 1-nitronaphthalene conversion increases
from 30.50% to 80.03% and the selectivity to 1-naphthylamine in-
creases from 79.00% to 88.21%. The conversion of 1-nitronaphthalene
and the selectivity to 1-naphthylamine present unconspicuous increase
with the increment of the Ni loading amount from 10 wt % to 15 wt %,
therefore 10% Ni loading amount was adopted.
In order to cut catalyst cost, non-noble bimetallic Ni-M/AC
(M = Cu, Co, Fe or Zn) catalysts are prepared and tried in 1-ni-
tronaphthalene hydrogenation, and the results are shown in Fig. 12 b.
Notably, in the case of monometallic 10% Ni/AC, 77.05% conversion of
1-nitronaphthalene and 87.03% selectivity to 1-naphthylamine are
obtained. However, in bimetallic Ni-M/AC (M = Cu, Co, Fe or Zn)
catalysts, the catalytic activity is greatly improved and Ni-Zn/AC gives
92.20% 1-nitronaphthalene conversion under the same reaction con-
ditions. The reason may be the strong interaction between promoter
metals and nickel, H2-TPR in Fig. 6 shows that the promoter metals can
enhance the nickel oxide reduction. What is more, it can be seen from
XPS in Fig. 7 that the promoter metals can promote much more Ni°
exposure on the surface of the support, moreover, it can be seen from
3.3. Influence of the reaction conditions
The effects of reaction temperature on the reaction catalyzed by Ni-
Zn/AC-350 at 0.6 MPa H2 pressure and reaction time of 5 h are shown
Table 5
The hydrogenation of aromatic nitro compounds to corresponding aromatic amine over Ni-Zn/AC-350.
Reactant
Product
Time(h)
T(℃)
P(Mpa)
Conversion (%)
Yield(%)
1,5-dinitronaphthalene
1,8-dinitronaphthalene
Nitrobenzene
o-chloronitrobenzene
m-chloronitrobenzene
p-chloronitrobenzene
1,5-diaminonaphthalene
1,8-diaminonaphthalene
Aniline
o-chloroaniline
m-chloroaniline
p-chloroaniline
5
6
4
4
4
4
110
110
80
80
80
0.6
0.6
1
1
1
100
100
100
100
100
100
95.63
97.25
98.36
93.57
93.54
94.02
80
1
Reaction conditions: reactant, 2 g, DMF, 20 mL, Catalyst, 0.1 g.
83

L. Huang, et al.
AppliedCatalysisA,General577(2019)76–85
Fig. 13. Influence of the reaction conditions and reusability of
catalyst; (a) Reaction conditions:1-nitronaphthalene, 2 g; DMF,
20 mL; Catalyst, 0.1 g; H2 pressure, 0.6 MPa; Time, 5 h; (b)
Reaction conditions:1-nitronaphthalene, 2 g; DMF, 20 mL;
Catalyst, 0.1 g; Temperature, 90℃; Time, 5 h; (c) Reaction condi-
tions:1-nitronaphthalene, 2 g; DMF, 20 mL; Catalyst, 0.1 g;
Temperature, 90℃; H2 pressure, 0.6 MPa; (d) Reaction condi-
tions:1-nitronaphthalene, 2 g; DMF, 20 mL; Catalyst, 0.1 g;
Temperature, 90℃; H2 pressure, 0.6 MPa;Time, 5 h.
catalyzed by Ni-Zn/AC-350 under 90℃ and reaction time of 5 h. It can
be seen that the conversion of 1-nitronaphthalene reaches to 100% and
selectivity to 1-naphthylamine is up to 96.82% when H2 pressure in-
creases to 0.6 MPa.
Fig. 13 c presents the effects of reaction time on the reaction cata-
lyzed by Ni-Zn/AC-350 under 90℃ and 0.6 MPa H2 pressure. It can be
seen that 1-nitronaphthalene cannot be totally converted when the
reaction time is less than 5 h. As the reaction time increases to 5 h, 1-
nitronaphthalene conversion increases to 100% and the selectivity to 1-
naphthylamine is up to 96.82%. In a word, bimetallic Ni-Zn/AC-350
gives the best catalytic performance under mild conditions of 90℃,
0.6 MPa H2 pressure and 5 h.
3.4. The reusability of catalyst
The recycle of the bimetallic Ni-Zn/AC-350 is carried out by using
the filtrated catalyst without other treatment for the next run. It can be
seen from Fig. 13 d that the catalytic performance remains almost un-
changed for the second run, but the yield of 1-naphthylamine decreases
a little for the third and the fourth run, which is attributed to the
leaching of the Ni on the surface proved by the ICP-AES analysis of the
nickel loading amount of the recycled catalyst, it decreases from 10% to
9% after the fourth run and ICP-AES analysis shows that 0.95% nickel is
leaked to the reaction solution. In addition, the XRD and TEM char-
acterization results of the catalyst after the fourth run show that the
Fig. 14. XRD and TEM patterns of Ni-Zn/AC of after four runs.
in Fig. 13 a. The conversion of 1-nitronaphthalene and the selectivity to
1-naphthylamine increases with the increment of reaction temperature
from 70 to 90℃, it gives 100% 1-nitronaphthalene conversion and the
selectivity to 1-naphthylamine is up to 96.82% under 90℃.
Fig. 13 b indicates the effects of hydrogen pressure on the reaction
Fig. 15. XPS patterns of Ni-Zn/AC of after four runs.
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AppliedCatalysisA,General577(2019)76–85
diffraction peaks of metallic nickel become more sharper and the nickel
nanoparticles tend to agglomerate (Fig. 14), as for the XPS character-
ization results, it shows that the oxidation state of nickel has little
change after the fourth run (Fig. 15).
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4. Conclusion
In conclusion, a series of highly dispersed bimetallic Ni-M/AC
(M = Cu, Co, Fe or Zn) catalysts were prepared by incipient wetness
impregnation method and applied in 1-nitronaphthalene hydrogenation
to 1-naphthylamine under mild reaction conditions. The prepared cat-
alysts were characterized by XRD, BET, H2-TPR, TEM, HRTEM, HAADF-
STEM, XPS, ICP, FT-IR and H2 chemisorption. The results show that
introduction of the metal promoter inhibits the sintering of the nickel
and enhances the reducibility of the catalysts, leading to higher ratio of
effective Ni° on the surface of the support, especially for Ni-Zn/AC-350.
The results of XPS indicate that the electron donating effect of Cu
promoter increases surface electronic density of Ni, which favors N-
naphthylhydroxylamine desorption, thus impedes its further hydro-
genation to 1-naphthylamine. Ni-Zn/AC-350 presents the best catalytic
performance in 1-nitronaphthalene hydrogenation to 1-naphthylamine
under mild reaction conditions, it gives 100% conversion of 1-ni-
tronaphthalene and 96.82% selectivity to 1-naphthylamine under
0.6 MPa and 90℃ for 5 h. Furthermore, it also shows good catalytic
performance in hydrogenation reaction of nitrobenzene, chloroni-
trobenzene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene.
In summary, with good hydrogenation activity the activated carbon
supported Ni doped with Zn promoter catalyst shows, the application
prospect in industrial production of aromatic amine from aromatic nitro
compounds has been becoming more and more extension.
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Acknowledgments
This work was supported by NSFC (U1662127), Project of education
department of Hunan Province (17A209), Project of Hunan Provincial
Natural Science Foundation of China (2016JJ2123, 2018JJ3497),
Project of Hunan Provincial Science and Technology Department
(2015GK1060) and Supported by Hunan Provincial Innovation
Foundation for Postgraduate (CX2017B304), Environment-friendly
Chemical Process Integration Technology Hunan Province Key labora-
tory and Collaborative Innovation Center of New Chemical
Technologies for Environmental Benignity and Efficient Resource
Utilization.
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