Research on the direct amination of benzene to aniline by NiAlPO4–5 catalyst

Article abstract of DOI:10.1002/aoc.4828

A series of NiAlPO₄–5 molecular sieves have been hydrothermally synthesized and shown high and stable activity in the direct amination of benzene to aniline with hydroxylamine hydrochloride as aminating agent. The as-synthesized and calcined samples were investigated with XRD, SEM, TG, BET, NH₃-TPD and FT-IR to explore the crystalline, coordination and location of the incorporated transition metal ions. The results indicated that nickel ions were incorporated into the framework of AlPO₄–5 and the as-synthesized catalysts were highly crystalline, and possessed good thermal stability. Among them, Ni(0.3)AlPO₄–5 showed the highest catalytic activity for the direct amination of benzene with the highest aniline yield of 73.2% and 100.0% selectivity to aniline. After the catalyst was reused for 5 times, the activity remained little change.

Full text of DOI:10.1002/aoc.4828

Received: 27 August 2018
DOI: 10.1002/aoc.4828
Revised: 13 December 2018
Accepted: 7 January 2019
F U L L P A P E R
Research on the direct amination of benzene to aniline by
NiAlPO –5 catalyst
4
Wei Wang | Yan Yang | Long Zhang
Jilin Provincial Engineering Laboratory
A series of NiAlPO –5 molecular sieves have been hydrothermally synthesized
for the Complex Utilization of Petro‐
resources and Biomass, School of
Chemical Engineering, Changchun
University of Technology, Changchun
4
and shown high and stable activity in the direct amination of benzene to aniline
with hydroxylamine hydrochloride as aminating agent. The as‐synthesized and
130012, People's Republic of China
calcined samples were investigated with XRD, SEM, TG, BET, NH ‐TPD and
3
FT‐IR to explore the crystalline, coordination and location of the incorporated
Correspondence
transition metal ions. The results indicated that nickel ions were incorporated
Long Zhang, Jilin Provincial Engineering
Laboratory for the Complex Utilization of
Petro‐resources and Biomass, School of
Chemical Engineering, Changchun
University of Technology, Changchun
into the framework of AlPO –5 and the as‐synthesized catalysts were
4
highly crystalline, and possessed good thermal stability. Among them, Ni(0.3)
AlPO –5 showed the highest catalytic activity for the direct amination of ben-
4
1
30012, People's Republic of China.
zene with the highest aniline yield of 73.2% and 100.0% selectivity to aniline.
After the catalyst was reused for 5 times, the activity remained little change.
Email: zhanglongzhl@163.com
Funding information
Changchun University of Technology
KEYWORDS
aluminophosphate molecular sieves, aniline, benzene, catalytic amination, hydrothermally synthesis
1
| INTRODUCTION
But C‐H bond activation is an important and difficult
[
8–11]
problem to overcome.
Therefore, exploring efficient
Aniline as an important organic chemical raw material
catalyst system for the direct amination of benzene has
attracted more and more attentions in chemical industry
[1]
and a fine chemical intermediate is widely used in the
fields of pesticide, dye, pharmaceutical, explosive, spice,
resin, rubber additive, special conductive polymer raw
materials and the others, especially as the raw material
of MDI production. At present, the industrial production
of aniline is mainly in three ways, that is, catalytic
hydrogenation of nitrobenzene, phenol amination and
nitrobenzene iron reduction method, its production
capacity is about 85.0%, 10.0% and 5.0% of the total pro-
duction capacity of aniline, respectively. However, these
methods characterized of higher cost, harsh operating
[
12–14]
[15]
recently.
Mantegazza
has reported the direct syn-
thesis of hydroxylamine with high yield by the oxidation
of ammonia with hydrogen peroxide in the presence of
Ti‐silicate at low temperature and atmospheric pressure.
It provided a potential benign supply of hydroxylamine
[
16]
for the amination of benzene. Kuznetsova
investigated
the amination of benzene and toluene with hydroxyl-
amine sulfate in the presence of transition metal redox
catalysts in a closed system. The reaction was carried out
in acetic acid–water or sulfuric acid–acetic acid–water
media, and a maximum aniline yield of about 27% was
[2]
conditions and environmental pollution, these do not
accord with the concept of green chemistry and sustain-
[
2,17]
obtained. Zhu
studied on direct synthesis of aniline
[3–5]
able development.
Through the activation of C‐H
with hydroxylamine as aminating agent, inorganic
vanadium salts (NaVO or VOSO ) and several typical
bond in benzene, amino groups will be directly introduced
3
4
[6]
into the benzene ring to form aniline. By doing it, the
multi‐step reactions go into a one‐step reaction, the entire
reaction process can significantly improve the atom utili-
vanadium complexes as catalysts, respectively, with the
maximum aniline yield up to 64% and the highest selectiv-
[
18]
ity up to 95.8%; Parida
studied on the direct amination
[
7]
zation, with hydrogen and/or water as by‐products.
of benzene to aniline by optimizing the reaction
Appl Organometal Chem. 2019;e4828.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.4828

2
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WANG ET AL.
conditions with hydroxylamine as aminating agent,
Mn‐MCM‐41 as catalyst, the conversion and selectivity
to aniline are respectively up to 68.5% and 100%.
1 hr. Finally, triethylamine as template was dropwise
introduced to the above mixture. This mixture was
further stirred for 2.5 hr. The resultant gel was sealed in
Teflon‐lined stainless steel autoclaves in a convection
oven and crystallized under autogenous pressure at
200 °C for 16 hr. The as‐synthesized solids were filtered,
washed with deionized water to neutral, and further
dried in air at 90 °C. Then the solid was calcined in an
oven in air at 550 °C (at the rate of 3 °C/min rise) for
16 hr, the calcined samples were stored for further use.
Aluminophosphates (AlPO or AlPO ‐n) molecular
s
4
[19,20]
sieves, as one of microporous zeolite family
have
attracted wide attention since their first synthesis by
[
21]
Wilson et al. in 1982,
which is used to describe the
1:1 aluminium‐to‐
3
D
oxide frameworks with
a
phosphorus ratio (n refers to the specific crystallographic
structure). In this sense, the modification of AlPO frame-
s
work with transition metal (Fe, Co, Ni, Cu and so on) can
lead to the elaboration of novel materials with enhanced
[22–27]
2.3 | Characterization of the catalyst
sample
acidic and/or redox properties.
AlPO –5 is a typical
4
aluminophosphate molecular sieve with 3D structure
[
21,22,28,29]
with hexagonal symmetry.
Ajayan Vinu et al.
Yoshihiro Sugi and
The crystalline phase of the as‐synthesized solids was
identified with a D/Max 2000/PC X‐ray diffractometer
with Cu Ka radiation, pipe voltage is 60 kV, electric
current is 330 mA. The spectra were collected stepwise
[30]
reported the isopropylation of
biphenyl to 4,4´‐DIPB with Co(5)APO‐5 and Ni(5)APO‐5
as catalysts, giving the high selectivity to 4,4´‐DIPB of
6
5–75%. Till now there is no report on the direct
o
o
o
−1
in the range of 5 ≤ 2θ ≤ 50 , scan rate 4 ·min .
amination of benzene to aniline with modified AlPO –5
4
Thermal gravimetric analysis was carried out in a STA
molecular sieves as the catalyst.
−
1
6000, under the nitrogen atmosphere at 20 mL·min ,
In this paper, Ni doped AlPO –5 catalyst is explored
4
observing the weight loss while the temperature heated
from room temperature to 800 °C at the rate of
for one‐step amination of benzene to aniline with hydrox-
ylamine hydrochloride as aminating agent in acetic acid
aqueous solution, with better results achieved.
−
1
1
0 °C·min . The nitrogen adsorption/desorption mea-
surement was performed on a Micromeritics ASAP
020 M surface area and porosity analyzer. SEM was
2
2
2
| EXPERIMENTAL
.1 | Materials
conducted in a JSM‐5500LV high resolution scanning
electron microscope, accelerating voltage 0 to 30 kV,
resolution of 3.0 nm, 300000–350000 times magnification.
The acidities of the catalysts were measured by
temperature‐programmed desorption using ammonia as
Aluminum isopropoxide, phosphoric acid (wt. 85% in
aqueous solution), triethylamine, nickel nitrate hexahy-
drate, benzene, and hydroxylamine hydrochloride, acetic
acid, sodium hydroxide, ether and aniline, phenol, nitro-
the probe molecule (NH ‐TPD, Micromeritics AutoChem
3
II 2920). 0.1 g of the sample was placed in a quartz sam-
ple tube and heated to 500 °C for 1 hr in helium atmo-
sphere, then cooling to 110 °C. When the temperature
benzene, NH OH·HCl and benzene were all of analytical
2
grade and used without further purification.
was decreased to 110 °C, NH was introduced to attain
3
adsorption saturation. Then, the sample was purged by
helium for 1 hr to remove the physically absorbed NH3.
Finally, the TPD experiment started with a heating rate
2.2 | Catalyst preparation
of 10 °C/min, and the NH desorption signal was detected
3
The catalyst was prepared by static hydrothermal method
by a thermal conductivity detector (TCD). Fourier trans-
form infrared (FT‐IR) spectra of catalysts were recorded
on a NICOLET IS10 (Thermo SCIENTIFIC Company)
[31–35]
according to literature
after modifications,
isopropanol aluminum, phosphoric acid and nickel
nitrate hexahydrate as a source of Al, P and metal source,
triethylamine as the template. The gel started from the
mixture of 1.0 TEA: (0–0.4) NiO: 0.95 Al O : 1 P O : 40
−
1
in the spectral range of 4000–450 cm with a resolution
−
1
of 4 cm using the conventional KBr pellet technique.
2
3
2 5
H O.
2
The preparation procedure is as follows: metal salts
were added to a solution of ortho‐phosphoric acid in dis-
tilled water at 20 °C. Then, after the transition metal salts
were completely dissolved, the above solution was slowly
added into the solution of aluminum isopropanol which
was per dissolved in water under continuous stirring for
2.4 | Catalytic amination of benzene
To a 100 ml three‐necked flask with reflux condenser,
stirrer and a thermometer. The catalyst and NH OH·HCl
2
in proportion were loaded into the flask containing acetic
acid aqueous solution, after stirring for 20 min at 30 °C,

WANG ET AL.
3 of 12
2
2.5 mmol benzene was introduced, and the mixture was
doping. According to Bragg formula, when the value of
the crystal plane spacing (d) is increased, it indicates that
the small ion of the crystal structure is replaced by a large
ion. For the same type of metal ions, the migration extent
of d values reflects the amount of nickel substitution into
the molecular sieve. The greater increasing of d is, the
more of metal ions go into the molecular sieve frame-
work, as shown in Figure 1, angle shifting to a small
heated to the required temperature under agitation. After
the reaction was carried out for 4 hrs, the resulting
mixture was cooled to room temperature and neutralized
by a 30% NaOH solution. The organic compounds were
extracted with ether and analyzed by GC–MS (Agilent
GC6890) equipped with a HP‐5 capillary column (film
thickness, 0.25 μm; i.d., 0.25 mm; length, 30 m) and flame
ionization detector (FID) using n‐butyl alcohol as an
internal standard, and further identified by gas
chromatography–mass spectrometry (Agilent, 5973
Network 6890 N) by comparing retention times and
fragmentation patterns with authentic samples. The
temperature of the GC column was set at 60 °C for
angle of Ni (0.3) AlPO –5 sample (100) is the most
4
obvious, it shows that the amount of Ni metal ions which
5+[32]
isomorphously substitute P
in molecular sieve skele-
ton is the largest. This has been verified by the fact that,
when the doping amount of Ni is 0.3, the catalyst shows
the highest activity.
3
min and then was programmed to rise to 80 °C at the
Figure 2 shows that the molecular sieve samples
before and after calcination, the characteristic diffraction
peaks (110), (200), (210) have the corresponding peak
intensity. After calcination, the intensity of the (110)
diffraction peak is enhanced, while the intensity of (100)
and (210) is relatively weaker than that of the uncalcined
due to the lattice distortion induced by the organic
template. They all keep a typical topological structure of
rate of 5 °C/min, and further reached 220 °C at the rate
of 10 °C/min and remained at that temperature for 3 min.
3
3
3
| RESULTS AND DISCUSSION
.1 | Catalyst characterization
[
36]
AFI.
.1.1 | X‐ray powder diffraction (XRD)
studies
3
.1.2 | TG
XRD diffraction peaks of the samples are shown in
Figure 1. It can be seen that all the samples have typical
AFI topology, the peaks of 100, 110, 200, 210, 002, 211,
The TG data of the as‐synthesized AlPO –5 and calcined
AlPO –5 in various nickel doping samples synthesized
4
4
2
20 were characterized of AlPO –5, and the crystallinity
are presented in Figure 3 and Figure 4. The TG data of
4
was high, and no diffraction peaks for other crystalline
the calcined AlPO –5 and AlPO –5 samples presented in
4
4
phases were found, which indicated that a single
Figure 4 indicated that the largest amount of total weight
NiAlPO –5 crystal was obtained in a given range of nickel
loss during heating to 800 °C is 18.0%.
4
FIGURE 1 XRD spectra of NiAlPO4–5
with various nickel doping

4
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WANG ET AL.
FIGURE 2 XRD spectra of AlPO4–5 and NiAlPO4–5 before and after calcination
FIGURE 3 TG spectra of as‐synthesized AlPO4–5 in various
nickel doping
FIGURE 4 TG spectra of calcined AlPO4–5 in various nickel
doping
The weight loss of the as‐synthesized AlPO –5 and
are attributed to the oxidative decomposition of organic
template, suggesting that the template of TEA in the
channel of AlPO –5 and nickel containing AlPO –5
4
nickel substituted AlPO –5 samples mainly includes the
4
desorption of water molecules adsorbed in the molecular
sieve and the depletion of the organic template agent. The
first weight loss in the low temperature range
4
4
samples may have different chemical environment. The
template decomposition can be related to the dimensions
of the channel system, the nature of the template, and the
9
0 °C–100 °C with an endothermic process is assigned
[
37–39]
to the water desorption. Since the as‐synthesized powders
were dried at 90 °C for 16 hr, it is not obvious enough to
observe this change from the figure. The second and third
weight losses, both accompanied by an exothermic effect,
template–framework interaction.
By considering
the strong template–framework interaction between pro-
tonated template and negatively charged framework, the
second weight loss can be attributed to the removal of

WANG ET AL.
5 of 12
neutral template molecule. While the third weight loss
may be due to the decomposition of charged template
molecule in the channel of as‐synthesized molecular
the weight loss rate of Ni(0.3)AlPO –5 is the least, only
4
about 10.0%. This shows that Ni(0.3)AlPO –5 molecular
4
sieve has the best thermal stability among the AlPO –5
4
[37,40]
sieves.
It is concluded from the comparison that
with various nickel doping.
FIGURE 5 BET spectra of the as‐synthesized and calcined AlPO4–5
FIGURE 6 BET spectra of the as‐synthesized and calcined Ni(0.3)AlPO4–5

6
of 12
WANG ET AL.
3.1.3 | Bet
The adsorption and desorption isothermal curves for var-
ious catalysts were shown in Figure 5, 6 after calcination,
the adsorption capacity increased rapidly in a relatively
low pressure, characterizing of the single molecule layer
adsorption. With the increasing of the relative pressure,
the adsorption capacity increases slowly. As the pores
were gradually filled by absorbed molecules, the adsorp-
tion capacity gradually decreased to show a platform‐like
area. This belongs to a typical monolayer or quasi mono-
layer adsorption characteristics. Capillary condensation
phenomena occurred at P/P = 0.2 in the AlPO –5 and
0
4
P/P0 = 0.7 in the Ni(0.3)AlPO –5. The adsorption
4
isothermal line and the desorption isothermal curve is
no longer coincides with to result in the occurrence of
hysteresis. For the samples, the narrowing of the
hysteresis loop may be induced by the accumulation of
particles in the framework of the molecular sieve for
the partial nickel institution to change the structure of
inner channel.
We also obtained the data of the molecular sieve
surface area and the micro pore volume, the surface area
of as‐synthesized AlPO –5 and Ni(0.3)AlPO –5 were
4
4
2
−1
2 −1
6
7.1 m .g and 38.6 m .g , respectively, and the micro-
pore volume was almost 0, with the pores to be occupied
by water and organic template. After calcination, specific
surface area of AlPO –5 and Ni(0.3)AlPO –5 was
4
4
2
−1
2 −1
increased to 194.7 m .g and 123.4 m .g , and the
micropore volume increased to 0.07 cm .g
.03 cm .g , respectively.
3
−1
and
3
−1
0
FIGURE 7 (a) Scanning electron micrographs of AlPO4–5. (b)
Scanning electron micrographs of Ni(0.3)AlPO4–5
3.1.4 | SEM
The scanning electron microscopy (SEM) images of
existence of weak acidic cites. It is seen that the peak
intensity increased when the Ni is incorporated to
AlPO –5 and Ni(0.3)AlPO –5 are shown in Figure 7.
4
4
Both the particles of Ni(0.3)AlPO –5 and AlPO –5
4
4
the AlPO –5 structure, this phenomenon is consistent
4
samples are presented in the form of small crystals aggre-
gation. Despite they have slight difference in the degree
of aggregation, the size and shape of the crystals are
with the results of our catalytic experiments, conversion
of benzene, yield to aniline and selectivity to
aniline increased in Ni content, among the catalysts,
nearly of no difference. The particles of Ni(0.3)AlPO –5
4
Ni(0.3) AlPO –5 had the best effect. Continue to
4
appear as clusters of hexagonal‐shaped crystals with
increase nickel content, the yield to byproduct biphenyl
increased.
5
–10 μm in size. And this morphology has been observed
[21]
[41]
before in both the AlPO –5
and CuAlPO –5
4
4
systems.
3
.1.6 | Ft‐IR
3
.1.5 | NH ‐TPD
3
Figure 9 represents the FT‐IR spectra of the catalysts. The
−
1
The acidity of the catalysts is evaluated via NH ‐TPD
measurements. The results regrouped in Figure 8 shown
a large peak located at 147 °C characterized to the
vibration band at 3500–3400 cm observed in all samples
is assigned to H–O–H bending motion of adsorbed water.
As can be discerned, the spectra of all samples exhibit
3

WANG ET AL.
7 of 12
FIGURE 8 NH3‐TPD of AlPO4–5 in
various nickel doping
FIGURE 9 FTIR of AlPO4–5 in various nickel doping
−
1
broad absorption bands in the range of 1100–1130 cm ,
3.2 | Amination activity evaluation of the
which correspond to the asymmetric vibration of
catalyst
[
42]
phosphate (triply degenerate P‐O stretching vibration).
−
1
−1
Besides, the bands at 470–490 cm , 640–650 cm ,
3.2.1 | The influence of nickel doping
amount
−
1
8
60–875 cm for the catalysts are the Al‐O‐P stretching
vibrations as well as the O‐P‐O bending mode of the
3
−
[43]
PO4
tetrahedral, respectively,
indicating the
Various nickel‐doped AlPO –5 catalysts were tested for
4
presence of crystalline AlPO that is also corroborated
the direct amination of benzene, the results are summa-
4
by the XRD analysis.
rized in Table 1.

8
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WANG ET AL.
TABLE 1 Catalyst performance over NiAlPO
n (NH OH•HCl)/
4
–5 catalysts
Yield
2
Acetic acid
(vol.%)
C
(%)
6
H
6
a
Conv.
Aniline
Selec (%)
b
c
d
Catalyst
n(C
6
H
6
)
Aniline (%)
Byproduct (%)
lPO –5
4
1/1
1/1
1/1
1/1
1/1
1/1
1/1
1/1
70.0
70.0
70.0
70.0
70.0
50.0
60.0
80.0
70.0
70.0
70.0
4.7
39.5
52.8
73.2
75.5
50.5
58.8
80.2
59.9
75.6
82.4
3.5
33.4
49.7
73.2
69.6
43.2
54.2
59.1
57.2
65.1
58.0
0.8
0.4
0.4
0.0
1.1
0.2
0.3
8.2
0.1
0.2
5.5
78.4
90.1
94.2
100.0
92.2
85.4
92.2
73.8
95.8
86.5
70.4
Ni(0.1)AlPO
Ni(0.2)AlPO
Ni(0.3)AlPO
Ni(0.4)AlPO
Ni(0.3)AlPO
Ni(0.3)AlPO
Ni(0.3)AlPO
Ni(0.3)AlPO
Ni(0.3)AlPO
Ni(0.3)AlPO
4
4
4
4
4
4
4
4
4
4
–5
–5
–5
–5
–5
–5
–5
–5
–5
–5
0.5/1
1/1.5
2/1
Reaction condition: Benzene: 22.5 mmol (2.0 ml), time: 4 hr, temperature: 80 °C, catalyst input: 0.1 g.
a
Conversion of benzene (%) = [converted benzene amount (mol) /initial amount (mol) of benzene] × 100%;
b
Yield of aniline (%) = [amount (mol) of aniline/ initial amount (mol) of benzene] × 100%;
c
Yield of byproduct (%) = [amount (mol) of byproduct/initial amount (mol) of benzene] × 100% and the by‐product was detected as biphenyl;
d
Selectivity to aniline (%) = {converted amount (mol) of benzene to aniline/initial amount of benzene)} × 100%.
When AlPO –5 was used as a catalyst, the conver-
doping will make the particles accumulate in the
catalyst to block its pores, hindering the diffusion and
reaction. Therefore, the catalysts used in the following
4
sion of benzene is 4.7%, and the selectivity to aniline
was 78.4%. The conversion of benzene and the selectivity
to aniline with nickel doped catalysts were significantly
experiments were Ni(0.3)AlPO –5.
4
higher than those of AlPO –5 catalyst, this is due
4
to introduction of nickel ions in the framework of
AlPO –5. When the nickel doping increased from 0.1
4
to 0.3, the conversion of benzene increased from 39.5%
to 73.2%, with further increasing in nickel doping, the
conversion increases to 75.5%, but the selectivity
decreases to 92.2%. Combined with XRD, BET and
FI‐IR analysis, it can be concluded that excess nickel
3.2.2 | The influence of reaction
temperature
The effect of the reaction temperature on amination of
benzene was shown in Figure 10.
FIGURE 10 Effect of reaction
temperature on the amination

WANG ET AL.
9 of 12
When the temperature was 50 °C, there was no
aniline, it indicated that the catalyst was not active. When
the reaction temperature rose from 60 to 80 °C, the yield
of aniline increased from 33.7% to 67.2%, further temper-
ature increasing makes the yield decrease to 43.8%.
Higher temperature could accelerate the decomposition
[2]
of hydroxylamine and benzene volatilization, it is also
possible that aniline was further oxidized to form by‐
products, witnessed by the nitrobenzene's presence in
the product. It can be determined that the appropriate
reaction temperature is 80 °C.
3
.2.3 | Kinetics of aniline synthesis by
FIGURE 11 Relation between integrals ln and time at various
temperatures
amination of benzene
In aniline synthesis from benzene with hydroxylamine
hydrochloride, Ni(0.3)AlPO –5 as catalyst, the
4
reaction process could be described by following expres-
sion:
(
1)
The reaction rate equation could describe as:
ꢂ
ꢀ
ꢁꢃ
β
dcA
1
2
a
A
β
B
a
r ¼ − dt ¼ kc c ¼ k½c ð1−xÞꢀ cA0 1− x
: (2)
A0
FIGURE 12 Effect of temperature on apparent reaction rate
Where r is the reaction rate in terms of the rate of
consumption of benzene, cA0 is the initial concentration
of benzene, c and c represent the instantaneous molar
concentrations of benzene and hydroxylamine hydrochlo-
ride, respectively. The α and β are the reaction order of
the corresponding concentration factor, t is the reaction
time, k is the reaction rate constant, x is the measured
conversion of benzene.
constant
A
B
dcA
101389
RT
À
Á
13
−1
r ¼ − dt ¼ 2:258x10 e −
cA min
3.2.4 | The influence of the acidity of the
reaction medium
The reaction kinetics of aniline synthesis was investi-
gated at three temperatures of 313.15 K, 323.15 K and
3
33.15 K. The conversion x of the reaction system at each
The effect of the acidity of the reaction medium on
amination of benzene is shown in Table 1.
time is substituted into the integral formula, and the time
t is plotted as Figure 11.
+
[42]
The pK of the •NH3 is 3.75 and 6.7,
cates that in a relative acidic reaction system, •NH3 is
which indi-
a
+
The linear relationship in the figure is obvious, that
is, the direct catalyzed synthesis of aniline by benzene
shows a grade 1 for benzene. The slope of each line in
the figure is the apparent rate constant k at that temper-
ature. The Arrhenius equation to k rate constant into lnk
and Plot 1/T and the result is shown in Figure 12.
From the obtained parameters, the kinetic equations are
sorted out:
the dominant position comparing to neutral amino acid
[
16]
group. Kuznetsova
put forward a free‐radical mecha-
nism, considering the protonation of amino radical
+
(•NH ) as the activity group for amination by an initio
3
quantum mechanics calculations for the amination of
benzene and toluene. In acetic acid solution, hydroxyl-
+
3
amine exists in the form of HONH , acting as a reducing

10 of 12
WANG ET AL.
[
43]
agent,
the reduction of hydroxylamine by the catalyst
3.2.5 | The influence of the ratio of raw
materials
+
will generate •NH3 and then, it reacts with benzene to
form protonated aminocyclohexadienyl intermediates.
Due to its instability, it is easily oxidized into aniline. This
shows that a relative acidic condition is favorable to the
amination of benzene. No aniline was generated when
only water or only acetic acid was used as the solvent.
When acetic acid aqueous solution is employed, as
hydroxylamine can easily dissolve in it, the increasing of
concentration of acetic acid make selectivity to aniline
increase, when the concentration is vol. 70.0%, aniline
selectivity reached 100%, continuing to increase the
concentration of acetic acid, the conversion of benzene
and selectivity to aniline both decreased. This shows that
vol. 70.0% acetic acid solution is an appropriate reaction
medium.
The effect of the ratio of raw materials on the amination
is shown in Table 1.
When the molar ratio of the reactants nNH2OH·HCL
/
nbenzene increased from 0.5: 1 to 1: 1, selectivity to aniline
rose from 95.8% to 100%, benzene conversion increased
from 59.9% to 73.2%, and when the reactant ratio increased
from 1: 1 to 2: 1, benzene conversion increased slowly from
73.2% to 75.6%, while selectivity to aniline significantly
reduced from 100% to 86.5%, which may be the reason that
excess amount of hydroxylamine in the solution led to
accelerate its decomposition to produce N O by nickel
2
[
2]
catalyst and the yield to byproduct biphenyl increased.
When the reactant ratio nNH2OH·HCL/nbenzene is 1:1, the
FIGURE 13 Effect of catalyst input on
amination of benzene
FIGURE 14 Recyclability of the
catalyst on amination

WANG ET AL.
11 of 12
selectivity to aniline reaches the maximum, so it is chosen
as a suitable ratio of raw materials.
AlPO –5 as the catalyst, with aniline yield of 73.2% and
4
100% selectivity to aniline. And this catalyst can be used
up to five cycles with little activity declining. This process
has great potential in industry exploration.
3.2.6 | The influence of catalyst input
ACKNOWLEDGEMENTS
The influence of catalyst input on the amination is shown
in Figure 13.
When no catalyst was added, no aniline was gener-
ated, as the catalyst input was increased from 0.025 g to
The authors gratefully acknowledge Changchun
University of Technology for all of the support that was
provided.
0
7
8
.1 g, the benzene conversion increased from 34.9% to
3.2%, and the selectivity to aniline increased from
9.4% to 100%. Continuing to increase the catalyst input,
ORCID
the conversion of benzene increased from 73.2% to 76.7%,
while the selectivity to aniline decreased from 100% to
Long Zhang https://orcid.org/0000-0002-5719-135X
8
7.1%. The analysis of the reaction products shows that
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