Hydrogenation of Aliphatic Nitriles to Primary Amines over a Bimetallic Catalyst Ni25.38Co18.21/MgO–0.75Al2O3 Under Atmospheric Pressure

Article abstract of DOI:10.1007/s10562-021-03532-9

Abstract: A mixed oxide supported bimetallic catalyst Ni_25.38Co_18.21/MgO–0.75Al₂O₃ was readily prepared and found to be efficient in the hydrogenation of valeronitrile (VN) to amylamine (AA) under atmospheric pressure. Under the optimal conditions: H₂ to VN molar ratio of 4:1, NH₃ to VN molar ratio of 3:1, reaction temperature of 130?°C and residence time of 5?s, the conversion of VN reached 100% with a AA yield of 70.8%, and a diamylamine (DAA) yield of 25.9%. This catalyst was also active in the hydrogenation of other low carbon aliphatic nitriles to their corresponding primary amines. The characterization results revealed that the catalyst had the properties of large surface area, uniform and fine dispersion of metal particles in the form of Ni/Co alloy with synergy effect between the two metals, which endowed the catalyst with good catalytic performances in the hydrogenation reaction of aliphatic nitriles. Graphic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-021-03532-9

Catalysis Letters
https://doi.org/10.1007/s10562-021-03532-9
Hydrogenation of Aliphatic Nitriles to Primary Amines
over a Bimetallic Catalyst Ni25.38Co18.21/MgO–0.75Al2O3 Under
Atmospheric Pressure
Dongxu Shi1 · He Zhu1 · Yaping Han1 · Yuecheng Zhang1,3 · Jiquan Zhao1,2
Received: 23 November 2020 / Accepted: 4 January 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
A mixed oxide supported bimetallic catalyst Ni25.38Co18.21/MgO–0.75Al2O3 was readily prepared and found to be efcient in
the hydrogenation of valeronitrile (VN) to amylamine (AA) under atmospheric pressure. Under the optimal conditions: H2 to
VN molar ratio of 4:1, NH3 to VN molar ratio of 3:1, reaction temperature of 130 °C and residence time of 5 s, the conversion
of VN reached 100% with a AA yield of 70.8%, and a diamylamine (DAA) yield of 25.9%. This catalyst was also active in
the hydrogenation of other low carbon aliphatic nitriles to their corresponding primary amines. The characterization results
revealed that the catalyst had the properties of large surface area, uniform and fne dispersion of metal particles in the form
of Ni/Co alloy with synergy efect between the two metals, which endowed the catalyst with good catalytic performances in
the hydrogenation reaction of aliphatic nitriles.
Graphic Abstract
Keywords Ni/Co bimetallic catalyst · Nitrile hydrogenation · Valeronitrile · Amylamine · Mixed MgO–Al2O3 support
Supplementary Information The online version contains
supplementary material available at https://doi.org/10.1007/s1056
1 Introduction
2-021-03532-9.
Amines are widely used in the production of agrochemicals,
pharmaceuticals, dyestufs, polymers, pigments, plasticizing
agents, and emulsifers [1–3]. Among which, the primary
amines are the most versatile intermediates or precursors in
industrial synthesis due to their ease of functionalization.
* Yuecheng Zhang
yczhang@hebut.edu.cn
* Jiquan Zhao
zhaojq@hebut.edu.cn
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

D. Shi et al.
Accordingly, the selective synthesis of primary amines is of
signifcant importance. Several protocols have been devel-
oped to synthesize primary amines, such as reductive amina-
tion of carbonyl compounds [4, 5], nucleophilic substitution
of ammonia on haloalkanes [6], direct amination of alcohols
with ammonia [7–9], and hydrogenation of nitro compounds
[10–12], nitriles [13], and amides [14]. Among all the meth-
ods, the direct amination of alcohols with ammonia over
heterogeneous catalysts is the most recommended proto-
col for commercial production of amines because of ready
availability and low cost of alcohols compared to carbonyl
compounds as raw materials in general. Moreover, water
is the only by-product in the process in principle, which is
consistent with the concept of green chemistry. However,
most of the developed heterogeneous processes were not
compatible to the direct amination of primary aliphatic
alcohols to the terminal primary amines [15]. Therefore,
the selective hydrogenation of aliphatic nitriles to terminal
primary amines might be a good alternative, because ali-
phatic nitriles can be obtained from primary alcohols and
ammonia via dehydrogenation–amination over heterogene-
ous catalysts, being a green chemical process [16–20]. Nev-
ertheless, the selective hydrogenation of aliphatic nitriles to
the terminal primary amines is a complicated process due
to the inevitable side reactions [13]. As shown in Scheme 1,
the hydrogenation of nitrile 1 generates an imine intermedi-
ate 2. Due to the high reactivity of 2, a set of consecutive
and parallel reactions takes place and leads to a mixture
of primary 3, secondary 5 and tertiary amines 7 via imine
intermediates 4 and 6. The key issue in the hydrogenation
of nitriles to primary amines is to prevent the formation of
secondary and tertiary amines. Generally, the introduction
of ammonia is often used to increase the selectivity of the
primary amine [13].
from catalytic hydrogenation of nitriles is generally real-
ized in the liquid phase over heterogeneous catalysts such
as Raney® nickel or cobalt [13]. It is well known that the
hydrogenation in gas phase has the advantages of easy oper-
ation, safety, and stable product quality. However, only a
few catalysts especially the non-noble metal based catalysts
have been found to be efcient in the gas phase hydrogena-
tion of nitriles to primary amines [27–29]. Among the cata-
lysts, a serious of Co–Ni bimetallic catalysts derived from
layered double hydroxides (LDHs) with a hydrotalcite-like
structure and containing Ni2+, Co2+, Mg2+, Al3+ showed
good performances in the hydrogenation of acetonitrile to
ethylamine in gas phase [29]. However, the preparation pro-
cesses of these catalysts were too complicated. Therefore, it
is of great importance to develop a catalyst with characters
of high activity, low cost, and ease of preparation for the
selective gas phase hydrogenation of aliphatic nitriles to the
corresponding primary aliphatic amines.
Herein, we report the preparation, characteriza-
tion, and catalysis of a bimetallic catalyst Ni25.38Co18.21
/
MgO–0.75Al2O3 in the hydrogenation of aliphatic nitriles
to terminal primary aliphatic amines. The catalyst showed
good catalytic performances in the gas phase hydrogena-
tion of several aliphatic nitriles in a fxed bed reactor under
atmospheric pressure.
2 Experimental
2.1 Catalyst Preparation
All reagents were analytical grade and used as received with-
out further purifcation. Metal nitrates and reagents for cata-
lyst preparation were purchased from Tianjin Keruisi Chem-
ical Reagent Cooperation. Nitriles and standard amines were
provided by Tianjin Hengshan Chemical Technology Coop-
eration. Valeronitrile (VN) with a purity higher than 99%
was prepared in our laboratory from amyl alcohol over a
catalyst FeZn/γ-Al2O3 in a fxed bed reactor.
Both homogeneous and heterogeneous catalysts have
been developed for the hydrogenation of nitriles to primary
amines [13, 21–31], and heterogeneous catalysts are more
suitable for the production of bulk primary amines. Up till
now, the industrial production of terminal primary amines
Scheme 1 Reaction pathways in the catalytic hydrogenation of nitriles
1 3

Hydrogenation of Aliphatic Nitriles to Primary Amines over a Bimetallic Catalyst…
The designed catalysts are denoted as NixCoy/
mMgO–nAl2O3, where the subscripts x and y are respective
mass contents of nickel and cobalt in a bimetallic catalyst;
m:n is the molar ratio of MgO to Al2O3, and m is 0 or 1. If
m or n is 1, 1MgO or 1Al2O3 is directly written as MgO or
Al2O3. The catalysts were obtained from their precursors
by in situ calcination in a fxed bed reactor, and the catalyst
precursors were prepared by a coprecipitation method as
illustrated by the following examples.
adsorption–desorption was performed on a Micromeritics
ASAP 2020 at 77 K to determine the surface area, total pore
volume and pore size distribution of the samples. The specifc
surface areas and pore sizes of the samples were calculated by
Brunauer–Emmett–Teller (BET) method. The transmission
electron micrographs (TEM) images were taken on a JEM
2100F instrument at accelerating voltage of 200 kV. The sam-
ples were dispersed ultrasonically in ethanol to prepare the
specimens for TEM analysis, where a drop of the suspension
was evaporated on a lacey-carbon/copper grid.
(1) The precursor of mixed oxide supported bimetallic
catalyst Ni25.38Co18.21/MgO–0.75Al2O3:
2.3 Catalytic Test
Into 200 mL of deionized water in a beaker
were added 20.36 g of Ni(NO3)2·6H2O, 14.55 g of
Co(NO3)2·6H2O, 20.51 g of Mg(NO3)2·6H2O and
45.02 g of Al(NO3)3·9H2O successively. The mixture
was stirred at room temperature for a while to give a
clean solution A. Next, 12.00 g of NaOH and 15.90 g of
Na2CO3 were dissolved in 200 mL of deionized water
in another beaker to obtain a solution B. The solution B
was added dropwise into the solution A under stirring
until the pH of the mixture reached 9.0. The mixture
was stirred strongly for another 2 h, then, the solid was
collected by centrifugation, and thoroughly washed
with deionized water under stirring until the pH of the
supernatant reached 7.0. The solid was separated by
vacuum fltration and dried in an oven at 80 °C for
12 h. The dried solid was ground in a ball crusher to
give a powder with a particle size < 200 mesh. Into a
beaker, 30.0 g of the resulted powder, 0.1 g of sesbania
powder and an appropriate amount of deionized water
were added successively. The mixture was kneaded in
a kneader thoroughly to give a paste which was pro-
cessed in an extruder to obtain extrudates with a diam-
eter of 2 mm. The extrudates were dried in air at room
temperature for 12 h, and then moved into an oven to
dry at 80 °C for 10 h. The dried extrudates were cut into
columns with a length of 2 mm to yield the precursor
of catalyst Ni25.38Co18.21/MgO–0.75Al2O3.
The catalytic hydrogenation of valeronitrile (VN) to amyla-
mine (AA) was conducted in a fxed-bed reactor with an inner
diameter of 20 mm and a length of 1000 mm installed in an
electric furnace. The furnace consists of four heating zones
equipped with four temperature controllers. Before catalytic
test, the thermocouple, mass fow controller and advection
pump in the equipment system were calibrated precisely, and
the gas tightness of the device was checked carefully.
In a typical process, 25 mL of the catalyst precursor was
loaded into the center a fx-bed reactor, while the bottom and
top of the reactor were flled with inert Pyrex glass chips.
The temperature of the catalyst bed was increased to 600 °C
with a ramp rate of 5 °C/min under N2 atmosphere. Thus, the
catalyst precursor was converted to the catalyst. Then, H2 was
introduced at rate of 100 mL/min to reduce the catalyst for
2 h. After the reduction, the temperature was adjusted to the
required temperature under a nitrogen atmosphere. The con-
trolled fows of VN, ammonia and hydrogen were introduced
separately into a vaporizer where the three reactants were
preheated, vaporized and mixed thoroughly. Then the mixed
gaseous reactants were fed into the catalyst bed under atmos-
pheric pressure. The reaction mixture was passed through a
condenser, and collected in a fask. The collected reaction
mixture was subjected to GC analysis.
2.4 Product Analysis
(2) The precursor of mixed oxide supported monometallic
catalyst Ni43.55/MgO–0.5Al2O3: See Supporting Infor-
mation.
Reaction mixture was analyzed by a gas chroma-
tography equipped with a SE-54 capillary column
(30 m × 0.32 mm × 0.50 μm) using the internal standard
method. The content of each liquid product was calculated
using calibration curves, with butanol as an internal standard.
The GC temperature program was set to 80 °C for 1 min, 3 °C/
min up to 110 °C and 30 °C/min up to 250 °C.
(3) The precursor of mono oxide supported monometallic
catalyst Ni46.63/MgO: See Supporting Information.
2.2 Characterization of Catalysts
The X-ray difraction (XRD) patterns of the samples were
moles of VN reacted
taken on a Bruker D8 X-ray diffractometer with Ni-fil-
tered Cu Kα radiation (150 mA, 40 kV) in the 2θ range of
5°–90°. The spectra of X-ray photoelectron spectroscopy
(XPS) were recorded using a Thermo ESCALAB 250XI
spectrometer with monochromatic Mg Kα radiation. N2
VN conversion (%) =
× 100%
moles of VN fed
moles of VN consumed to produce AA
moles of VN reacted
AA selectivity (%) =
× 100%
1 3

D. Shi et al.
moles of VN consumed to produce AA
moles of VN reacted
Generally, bimetallic catalysts exhibited good catalytic
performances compared to monometallic ones in the hydro-
genation of nitriles [37–40]. Next, a series of Ni–Co bime-
tallic catalysts with diferent nickel to cobalt molar ratios
but a constant total metal molar percent were prepared, and
evaluated in the hydrogenation of VN under the same reac-
tion conditions. As shown in the Table 1 (Entries 5–9), the
catalyst Ni25.38Co18.21/MgO–0.5Al2O3, in which the nickel to
cobalt molar ratio is 1.4:1, exhibited the best results among
all the tested bimetallic catalysts, and also performed bet-
ter than the monometallic catalyst Ni43.55/MgO–0.5Al2O3
in view of both the conversion of VN and the yield of AA.
Either increase or decrease in nickel to cobalt molar ratio
led to the reduction of both the conversion of VN and the
yield of AA.
DAA selectivity (%) = 2 ×
× 100%
Yield (%) = conversion × selectivity × 100%.
3 Results and Discussion
3.1 Screen of the Catalysts
It was reported that oxide supported nickel catalysts were
active in the hydrogenation of nitriles to amines either in gas
phase or liquid phase [24, 29]. Besides, the oxide supports
such as Al2O3 and MgO had strong efects on the perfor-
mances of the catalysts [32, 33]. Therefore, three oxide sup-
After determining the molar ratio of nickel to cobalt, the
MgO to Al2O3 molar ratio was then screened, too. Several
catalysts were prepared with diferent MgO to Al2O3 ratios
but constant contents of nickel and cobalt. As shown in
Table 1 (Entries 6, 10–13), no big diference was observed
in either the conversion of VN or the yield of AA in the
screened MgO to Al2O3 molar ratio range of 1:0.41–1: 0.75,
which indicated that the MgO to Al2O3 molar ratio had no
major efects on the catalysis of the catalysts. Taking into
account a slightly higher AA yield of 50.8% received in the
MgO to Al2O3 molar ratio of 1: 0.75, as well as the lower
cost of Al2O3 than MgO, Ni25.38Co18.21/MgO–0.75Al2O3 was
fnally chosen as the best catalyst.
ported monometallic nickel catalysts Ni46.63/MgO, Ni40.85
/
Al2O3, and Ni43.55/MgO–0.5Al2O3 were frstly prepared,
and evaluated in the hydrogenation of VN to AA under
atmospheric pressure in the presence of ammonia in a fxed
bed reactor. As shown in Table 1 (Entries 1–4), the catalyst
Ni46.63/MgO gave the lowest VN conversion of 58.2%, but
the highest AA selectivity of 64.4%. Compared to Ni46.63
/
MgO, Ni40.85/Al2O3 exhibited a good VN conversion of
72.3%, but a poor AA selectivity of 55.3%. The mixed oxide
supported catalyst Ni43.55/MgO-0.5Al2O3 showed the best
result in view of the yield of AA as high as 45.1%. These
results indicated that the catalytic performances of the cata-
lysts were related to the properties of the supports [28, 29,
34–36]. For comparation, a mixed oxide supported cobalt
catalyst Co43.65/MgO–0.5Al2O3 was also prepared, but very
poor results were received over this catalyst, indicating the
necessity of nickel in the catalysts.
3.2 Optimization of Reaction Conditions
After the catalyst Ni25.38Co18.21/MgO–0.75Al2O3 was cho-
sen, the reaction parameters afecting the hydrogenation
Table 1 Catalysis of various
Entry Catalyst
Ni:Co
MgO:Al2O3 Con. AA
AA
DAA
oxide supported nickel catalysts
in the hydrogenation of VN
(molar ratio) (molar ratio) (%)
Sel. (%) yield (%) Sel. (%)
1
2
3
4
5
6
7
8
Ni46.63/MgO
Ni40.85/Al2O3
Ni43.55/MgO–0.5Al2O3
Co43.65/MgO–0.5Al2O3
Ni29.00Co14.57/MgO–0.5Al2O3 2:1
Ni25.38Co18.21/MgO–0.5Al2O3 1.4:1
Ni22.00Co22.00/MgO–0.5Al2O3 1:1
Ni18.13Co25.49/MgO–0.5Al2O3 0.71:1
Ni14.92Co28.88/MgO–0.5Al2O3 0.5:1
Ni25.38Co18.21/MgO–0.33Al2O3 1.4:1
Ni25.38Co18.21/MgO–0.41Al2O3 1.4:1
Ni25.38Co18.21/MgO–0.61Al2O3 1.4:1
Ni25.38Co18.21/MgO–0.75Al2O3 1.4:1
–
–
–
–
–
–
58.2 64.4
72.3 55.3
78.0 57.9
4.3 16.4
82.3 49.4
84.5 56.9
81.3 58.0
74.5 53.4
69.2 49.5
79.6 54.8
84.4 56.0
85.4 58.7
86.6 58.7
37.5
40.0
45.1
0.7
40.7
48.1
47.2
39.8
34.2
43.6
47.3
50.1
50.8
22.5
26.1
26.4
13.7
40.7
33.4
29.6
26.9
26.5
31.5
32.4
30.8
30.1
1:0.5
1:0.5
1:0.5
1:0.5
1:0.5
1:0.5
1:0.5
1:0.33
1:0.41
1:0.61
1:0.75
9
10
11
12
13
Reaction conditions: temperature 130 °C, NH3 to VN molar ratio=4:1, H2 to VN molar ratio=2:1, resi-
dence time 4.5 s, time on stream 6–8 h, atmospheric pressure
1 3

Hydrogenation of Aliphatic Nitriles to Primary Amines over a Bimetallic Catalyst…
of VN were studied systematically to improve the yield of
AA. First, the efect of reaction temperature on the reac-
tion was investigated under atmospheric pressure, residence
time of 4.5 s, NH3 to VN molar ratio of 4:1, and H2 to VN
molar ratio of 2:1. As shown in Fig. 1, the VN conversion
increased from 63.9 to 86.6% with increase in reaction tem-
perature from 110 to 130 °C, then changed slightly with a
further increase in reaction temperature. The AA yield also
increased with temperature initially and reached its maxi-
mum of 50.9% at 130 °C, and then turned to slight decrease
with a further increase in reaction temperature due to the
formation of more DAA. Besides, the total yield of AA and
DAA was 77.0% at 130 °C.
DAA
AA
Conversion of VN
100
80
60
40
20
100
80
60
40
20
0
1.5:1
2:1
3:1
4:1
5:1
6:1
Next, the efect of the molar ratio of H2 to VN on the
reaction was studied in the range of 1.5:1–6:1 at 130 °C
under atmospheric pressure, residence time of 4.5 s, and
molar ratio of NH3 to VN of 4:1. As shown in Fig. 2, both
the conversion of VN and the yield of AA increased with
H /valeronitrile (mol/mol)
2
Fig. 2 Efect of H2 to VN molar ratio on the catalysis of
Ni25.38Co18.21/MgO–0.75Al2O3. Reaction conditions: ammonia to VN
molar ratio=4:1, temperature 130 °C, residence time 4.5 s, atmos-
pheric pressure, time on stream 6–8 h
increase in H2 to VN molar ratio from 1.5:1 to 4:1, and then
remained almost constant. When the molar ratio of H2 to
VN was equal to or higher than 4:1, the conversion of VN
was always close to 100%, and the yield of AA was 65.7%.
Meanwhile, the total yield of AA and DAA reached 89.4%.
The results indicated that a high fraction of hydrogen in
the gaseous mixture favored the transformation of VN to
amines.
with increase in NH3 to VN molar ratio from 2:1 to 3:1, and
reached its maximum of 68.7% at the molar ratio of 3:1.
Instead, a further increase in NH3 to VN molar ratio led to
the decrease of the yield of AA. Meanwhile, the total yield
of AA and DAA reached its maximum of 94.0% at the NH3
to VN molar ratio of 2:1. As shown in Scheme 1, dialkylim-
ine (4) undergoes transimination with NH3 to give alkylim-
ine (2) and alkylamine (3). Ammonia is in favor of a shift
of the transimination equilibrium to the side of the primary
imine and amine [41]. Therefore, an appropriate amount of
ammonia enhanced the selectivity of primary amine in the
Then, the efect of the molar ratio of NH3 to VN on the
reaction was investigated in the range of 2:1–6:1 at 130 °C
under atmospheric pressure, residence time of 4.5 s, and H2
to VN molar ratio of 4:1. As shown in Fig. 3, the VN conver-
sion was always close to 100% in the screened molar ratio
range of NH3 to VN. However, the yield of AA increased
AA
DAA
AA
DAA
Conversion of VN
100
80
60
40
20
0
100
80
60
40
20
0
Conversion of VN
100
80
60
40
20
0
100
80
60
40
20
0
110
130
140
150
160
120
2:1
3:1
4:1
5:1
6:1
Reaction temperature (°C)
NH /valeronitrile (mol/mol)
3
Fig. 1 Efect of the temperature on the catalysis of Ni25.38Co18.21
/
Fig. 3 Efect of NH3 to VN molar ratio on the catalysis of
Ni25.38Co18.21/MgO–0.75Al2O3. Reaction conditions: temperature
130 °C, H2 to VN molar ratio=4:1, time on stream 6–8 h, atmos-
pheric pressure, residence time 4.5 s
MgO–0.75Al2O3. Reaction conditions: NH3 to VN molar ratio=4:1,
H2 to VN molar ratio of=2:1, atmospheric pressure, residence time
4.5 s, time on stream 6–8 h
1 3

D. Shi et al.
hydrogenation of VN. However, much excessive ammonia
could dilute the concentration of hydrogen, which deterio-
rated the hydrogenation of alkylimine to AA.
hydrogenation of C6–C8 aliphatic nitriles. In these cases the
conversions of three nitriles were higher than 81%, and the
yields of the corresponding primary amines were 62.5%,
58.0% and 60.1%, respectively. However, the catalyst per-
formed poorly in the hydrogenation of lauronitrile. In this
case the conversion of lauronitrile was only 61.3% with a
laurylamine yield of 47.3%. It was noted that the longer the
carbon chain of aliphatic nitrile, the lower the conversion of
the substrate, as well as the yield of the primary amine. The
results could be ascribed to the big inner difusion resistance
of long carbon chain substrates in the catalyst. The results
will be improved if the hydrogenation reaction is conducted
under the optimal conditions of the specifc substrate. It is
expected that the catalyst Ni25.38Co18.21/MgO–0.75Al2O3
will has wide applications in the hydrogenation of aliphatic
nitriles to primary amines.
Residence time is another important parameter afecting a
gas phase reaction in a fxed bed reactor, therefore, its efect
on the hydrogenation of VN over the catalyst Ni25.38Co18.21
/
MgO–0.75Al2O3 was studied at 130 °C under atmospheric
pressure, H2 to VN molar ratio of 4:1, and NH3 to VN molar
ratio of 3:1. As shown in Fig. 4, both the conversion of VN
and the yield of AA increased with increase in residence
time from 3.5 to 5.0 s, and reached their maxima of 100%
and 70.8% at the residence time of 5.0 s, respectively. Mean-
while, the total yield of AA and DAA reached its maxi-
mum of 96.7%. With a further increase in residence time of
longer than 5.0 s, the conversion of VN maintained 100%,
but the yield of AA decreased. Meanwhile, the yield of DAA
increased. The results indicated that a longer residence time
led to the transformation of more AA to DAA.
3.4 Lifetime and Regeneration of the Catalyst
Based on the above experimental results, the opti-
mal parameters for the hydrogenation of VN to AA were
obtained, which are atmospheric pressure, H2 to VN molar
ratio of 4:1, NH3 to VN molar ratio of 3:1, reaction tempera-
ture of 130 °C, and residence time of 5 s. Under the optimal
conditions, the conversion of VN reached 100% with an AA
yield of 70.8%, and a total yield of AA and DAA of 96.7%.
The lifetime and the regeneration of Ni25.38Co18.21
/
MgO–0.75Al2O3 were then studied in the hydrogenation of
VN under the optimal reactions. As shown in Fig. 5, the
conversion of VN was always close to 100% in the frst 30 h
of the catalyst on stream, and then decreased slightly from
30 to 60 h. Meanwhile, the yield of AA decreased slowly,
and dropped from 70.8 to 66.5% from 5 to 60 h of the cata-
lyst on stream. The used catalyst was regenerated by on-line
hydrogenation at 600 °C for 2 h, and then tested again on
the reaction. As shown in Fig. 5, both the conversion of
VN and the yield of AA over the regenerated catalyst were
close to those over the fresh catalyst. The results indicated
that the catalyst was stable on stream and could be easily
regenerated.
3.3 Hydrogenation of Other Aliphatic Nitriles
Under the optimal conditions of VN hydrogenation, the cata-
lyst Ni25.38Co18.21/MgO–0.75Al2O3 was then applied to the
hydrogenation of several other aliphatic nitriles. As shown
in Table S1 the catalyst showed good performances in the
AA
DAA
Conversion of VN
100
80
100
80
60
40
20
0
100
80
60
40
20
0
60
40
Conversion of valeronitrile
Yield of amylamine
Yield of total amine
Regenerated
20
0
3.5
4.0
4.5
5.0
5.5
0
15
30
45
60 0
15
30
45
60
Residence time (s)
Reaction time (h)
Fig. 4 Efect of the residence time on the catalysis of Ni25.38Co18.21
/
Fig. 5 Catalytic results of the fresh and the used Ni25.38Co18.21/MgO–
0.75Al2O3 with time on stream. Reaction conditions: NH3 to VN
molar ratio=3:1, H2 to VN molar ratio=4:1, atmospheric pressure
temperature 130 °C, residence time 5 s
MgO–0.75Al2O3. Reaction conditions: NH3 to VN molar ratio=3:1,
atmospheric pressure, H2 to VN molar ratio=4:1, temperature
130 °C, reaction time 6–8 h
1 3

Hydrogenation of Aliphatic Nitriles to Primary Amines over a Bimetallic Catalyst…
the binding energies between 845 and 895 eV, including the
peaks Ni 2p1/2 and Ni 2p3/2 for nickel, are shown in Fig. 7B.
The Ni 2p3/2 binding energies of 852.41 eV and 852.75 eV
correspond to the metallic nickel [44, 45] in the samples
of Ni46.63/MgO and Ni40.85/Al2O3, respectively, whereas the
binding energy of about 855.1 eV is assigned to the Ni2+
species [46] in both the samples. It should be noted that
the Ni2+ species found in all the catalyst samples is due to
the oxidation of Ni0 species during analysis. The Ni 2p3/2
binding energy of Ni0 in Ni46.63/MgO is lower than that
in Ni40.85/Al2O3 due to more electron transfer from MgO
to Ni0 species [47], indicating the stronger metal-support
interaction between Ni0 species and MgO than that between
Ni0 species and Al2O3. In the mixed oxide supported cata-
lyst Ni43.55/MgO–0.5Al2O3, the binding energy of Ni 2p3/2
for Ni0 is 852.59 eV between the ones in Ni46.63/MgO and
Ni40.85/Al2O3.
3.5 Catalyst Characterization
The reduced catalysts were characterized by XRD, XPS,
N2 adsorption and desorption, and TEM to reveal the
relationship between catalytic performance and micro-
structure. The XRD patterns of the samples of the reduced
Ni46.63/MgO, Ni40.85/Al2O3, Ni43.55/MgO–0.5Al2O3,
Ni25.38Co18.21/MgO–0.75Al2O3, as well as the Ni25.38Co18.21
/
MgO–0.75Al2O3 after on stream for 20 h are shown in
Fig. 6. The characteristic difraction peaks of Ni0 phase are
clearly observed in the patterns of frst three samples, and
the peaks of Ni0/Co0 phases are found in the patterns of
the last two ones at 2θ = 44.5°, 51.8° and 76.4°, which are
ascribed to the planes (111), (200) and (220) [42]. Overlap-
ping of the difraction peaks of Ni0 (JCPDS no. 87-0712)
and Co0 (JCPDS no. 15-0806) phases impeded their sepa-
rate identifcation in the bimetallic catalyst samples. The
peaks ascribed to NiO (JCPDS no. 73–1523) phase at
2θ=43.1° and 62.8° were clearly observed in the pattern of
Ni46.63/MgO, which was ascribed to the oxidation of Ni0 to
NiO in analysis [43]. Importantly, the patterns of the used
Ni25.38Co18.21/MgO–0.75Al2O3 are virtually identical to
those of the fresh one, also indicating the stability of the
catalyst on stream.
The binding energy of Ni 2p3/2 for Ni0 in the catalyst
Ni25.38Co18.21/MgO–0.75Al2O3 was 853.72 eV, much big-
ger than that in the Ni43.55/MgO–0.5Al2O3, suggesting the
formation of Ni/Co alloy. This result seems contradictory,
because the electronegativity of Ni0 is greater than that of
Co0, upon the Ni/Co alloy formed, more electrons of Co0
will fow to Ni0, leading to lower binding energy of Ni 2p3/2
for Ni0. However, the shifting of Ni 2p3/2 binding energy for
Ni0 in the Ni/Co alloy to higher energy rather than lower
energy was due to the fact that Co0 species were almost
completely oxidized to cobalt oxides during the analysis
process as revealed in Fig. 7C, which led to more electrons
transfer from Ni0 to cobalt oxides, resulting in bigger bind-
ing energy of Ni 2p3/2 for Ni0 in the catalyst. The formation
of Ni/Co alloy endowed a synergy efect between nickel and
cobalt in the catalytic reaction, which enhanced the selectiv-
ity towards primary amines in the hydrogenation of aliphatic
nitriles [29, 42, 48]. The ftted Co 2p XPS spectra for the
To reveal the states of surface Co and Ni in the catalysts,
the reduced catalysts were characterized by X-ray photo-
electron spectra (XPS). As exhibited in the wide scan XPS
spectra of the samples (Fig. 7A), distinct peaks of Ni 2p, Mg
1s, Co 2p, O 1s, C 1s and Al 2p were observed clearly. The
XPS spectrum of the used Ni25.38Co18.21/MgO–0.75Al2O3
was almost identical to that of the fresh one, further con-
frming its stability of the catalyst in the catalytic run. The
ftted Ni 2p XPS spectra for the catalysts corresponding to
reduced catalysts Co43.65/MgO–0.5Al2O3 and Ni25.38Co18.21
/
MgO–0.75Al2O3 were shown in Fig. 7C. The Co 2p3/2 bind-
ing energy of 777.6 eV was corresponds to the Co0 spe-
cies, and the Co 2p3/2 binding energies of 779.6 eV and
780.4 eV are attributed to the Co2+and Co3+ oxide species
in the catalysts Co43.65/MgO–0.5Al2O3 and Ni25.38Co18.21
/
MgO–0.75Al2O3 [49–51]. The results indicated that the Co0
species in the reduced catalysts were very easily oxidized, so
the catalysts must be reduced in situ in application.
The textural properties of the reduced catalysts Ni46.63
MgO, Ni40.85/Al2O3, Ni43.55/MgO–0.5Al2O3, Ni25.38Co18.21
MgO–0.75Al2O3, as well as the used Ni25.38Co18.21
/
/
/
MgO–0.75Al2O3 were determined by N2 adsorption–des-
orption analysis. As shown in Fig. 8, all the samples showed
standard type IV isotherms, indicating the existence of
mesopores in the catalysts. Besides, the presence of hys-
teretic loops similar to the type H4 is indicative of slit-like
pores [52]. The similarity of the isotherms of the samples
Fig. 6 XRD patterns of catalyst samples (a) Ni46.63/MgO; (b)
Ni40.85/Al2O3; (c) Ni43.55/MgO–0.5Al2O3; (d) Ni25.38Co18.21/MgO–
0.75Al2O3; (e) Ni25.38Co18.21/MgO–0.75Al2O3 (used)
1 3

D. Shi et al.
B
O 1s
A
Ni 2p
Ni 2p1/2
Ni0
869.10 eV
Ni 2p3/2
852.41 eV
Ni0
Mg 1s
e
Ni2+
Co 2p
Ni2+
C 1s Al 2p
a
d
c
852.75 eV
871.68 eV
b
c
871.70 eV
852.59 eV
853.72 eV
b
a
871.95 eV
d
1400
1200
1000
800
600
400
200
0
885
880
870
865
860
855
850
845
875Binding Energy (eV)
Binding Energy(eV)
C
780.45 eV
3+
Co2+ or Co
777.60 eV
Co0
f
780.70 eV
779.60 eV
Co2+
d
792
790
788
786
784
782
780
778
776
Binding Energy (eV)
Fig. 7 The wide scan XPS spectra (A), Ni 2p XPS spectra of sam-
ples (B) and Co2p3/2 XPS spectra (C) of the samples (a) Ni46.63/MgO;
(b) Ni40.85/Al2O3; (c) Ni43.55/MgO–0.5Al2O3; (d) Ni25.38Co18.21/MgO–
0.75Al2O3; (e) Ni25.38Co18.21/MgO–0.75Al2O3 (used); (f) Co43.65
MgO–0.5Al2O3
/
of the fresh and used Ni25.38Co18.21/MgO–0.75Al2O3 again
confrmed the stability of the catalyst in catalytic run.
The specific surface areas and the range of the pore
structural parameters of the catalyst samples are presented
in Table 2. As seen, the surface areas of the catalysts were
related to the supports. For the three mono nickel catalysts,
the surface area, pore volume, and pore diameter are all in
TEM, which endowed this catalyst good performances in
the hydrogenation of VN to AA.
After the catalyst Ni25.38Co18.21/MgO–0.75Al2O3 was
on stream for 20 h, both the surface area and the pore vol-
ume decreased slightly as shown in Table 2, which could be
ascribed to the slight deposition of carbon and nonvolatile
amine condensates on the pores of the catalyst. On the con-
trary, the mean pore diameter of the used catalyst increased
slightly compared to that of the fresh one because of the
deposition of substances on the small pores, leading to the
shift in the pore size distributions to large ones. The depo-
sition of some nonvolatile substances on the pores of the
catalyst impeded reactants access to the active centers of
the catalyst in the catalytic run, leading to a decrease in the
yield of AA as shown in Fig. 5.
the order of Ni40.85/Al2O3 >Ni43.55/MgO–0.5Al2O3 >Ni46.63
/
MgO. The bimetallic catalyst Ni25.38Co18.21/MgO–0.75Al2O3
showed higher surface area, pore volume, and pore diam-
eter compared to Ni43.55/MgO–0.5Al2O3. It also had big-
ger surface area and pore volume than Ni40.85/Al2O3. The
big surface area of Ni25.38Co18.21/MgO–0.75Al2O3 could
be ascribed to the doping of nickel with cobalt leading
to decrease in the sizes of metal particles as disclosed by
1 3

Hydrogenation of Aliphatic Nitriles to Primary Amines over a Bimetallic Catalyst…
hydrogenation of VN to AA. In addition, HRTEM images
of the Ni25.38Co18.21/MgO–0.75Al2O3 sample clearly mani-
fested lattice fringes of 0.203 nm (Fig. 9e), which could
be assigned to the 111 crystal plane of Ni and Co or Ni/
Co alloy [10, 53, 54].
e
The EDX elemental mapping revealed that the areas of
nickel and cobalt species overlapped well (Fig. 9f–i), also
indicating the formation of Ni/Co alloy. Besides, magne-
sium and aluminum also located in the same zone, which
confrmed the perfect mixing of Al2O3 and MgO in the
catalyst, afording good dispersion of active centers on
the support.
d
c
b
a
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
4 Conclusion
Fig. 8 Adsorption–desorption isotherms of the catalyst samples
(a) Ni46.63/MgO; (b) Ni40.85/Al2O3; (c) Ni43.55/MgO–0.5Al2O3; (d)
Ni25.38Co18.21/MgO–0.75Al2O3; (e) Ni25.38Co18.21/MgO–0.75Al2O3
(used)
The screened bimetallic catalyst Ni25.38Co18.21
/
MgO–0.75Al2O3 showed good catalytic performances
in the hydrogenation of VN as well as other low carbon
aliphatic nitriles to their corresponding primary amines
under atmospheric pressure in the presence of ammonia in
a fxed bed reactor. The conversion of VN reached 100%
with a AA yield of 70.8% and a total yield of AA and DAA
of 96.7% under the optimal conditions. The catalyst also
showed good stability and ease of regeneration. The good
performances of the catalyst could be ascribed to the large
surface area of the catalyst, uniform and fne dispersion
of metal nanoparticles on the mixed oxide support, and
formation of Ni/Co alloy with synergy efect between the
two metals in the reduced Ni25.38Co18.21/MgO–0.75Al2O3.
The transmission electron micrograph (TEM) of
the catalysts Ni43.55/MgO–0.5Al2O3 and Ni25.38Co18.21
/
MgO–0.75Al2O3 were taken fnally. As shown in Fig. 9,
nickel and nickel–cobalt nanoparticles are dispersed on
MgO–Al2O3 support with diameters of 22.45–29.75 nm
(Fig. 9a and c) and 11.65–19.89 nm (Fig. 9b and d),
respectively. The results revealed that the doping of nickel
with cobalt led to decrease in average sizes and uniform
dispersion of Ni/Co nanoparticles, which were the main
reasons for the good performances of Ni25.38Co18.21
/
MgO–0.75Al2O3 compared to the other ones in the
Table 2 Textural properties of
Entry
Catalyst
SBETa (m2/g)
Vb (cm3/g)
dpc (nm)
catalysts
1
2
3
4
5
Ni46.63/MgO
Ni40.85/Al2O3
Ni43.55/MgO–0.5Al2O3
Ni25.38Co18.21/MgO–0.75Al2O3
Ni25.38Co18.21/MgO–0.75Al2O3 (used)
98.21
156.70
123.26
168.10
152.50
0.13
0.30
0.22
0.33
0.27
2.30
4.91
4.62
4.85
5.22
aBET surface area
bBJH cumulative desorption pore volume
cMean pore diameter=4V/SBET
1 3

D. Shi et al.
Fig. 9 TEM images of
Ni43.55/MgO–0.5Al2O3 (a, c),
Ni25.38Co18.21/MgO–0.75Al2O3
(b, d, e), and correspond-
ing element mappings of
Ni25.38Co18.21/MgO–0.75Al2O3
(f–i)
Acknowledgements We thank the fnancial support from the National
Natural Science Foundation of China (Grant No. 21476057), the Cen-
tral Government Guides Local Science and Technology Development
Project (Grant No. 206Z4001G) and the Natural Science Foundation
of Hebei Province of China (Grant No. B2016202393).
6. Aubin Y, Fischmeister C, Thomas CM, Renaud J (2010) Chem
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Compliance with Ethical Standards
11. Peng Y, Geng Z, Zhao S, Wang L, Li H, Wang X, Zheng X, Zhu
J, Li Z, Si R, Zeng J (2018) Nano Lett 18:3785
12. Zhang G, Tang F, Wang X, An P, Wang L, Liu YN (2020) ACS
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Conflict of interest The authors declare that they have no confict of
interest.
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Authors and Afliations
Dongxu Shi1 · He Zhu1 · Yaping Han1 · Yuecheng Zhang1,3 · Jiquan Zhao1,2
1
3
School of Chemical Engineering and Technology, Hebei
University of Technology, Tianjin 300131, China
Tianjin Key Laboratory of Chemical Process Safety,
Tianjin 300131, China
2
Hebei Provincial Key Laboratory of Green Chemical
Technology and High Efcient Energy Saving,
Tianjin 300131, China
1 3