Colloid and Nanosized Catalysts in Organic Synthesis: XXI. Reduction of Nitroarenes Catalyzed by Immobilized Nickel Nanoparticles

Article abstract of DOI:10.1134/S1070363219080012

It has been found that nickel nanoparticles on NaX zeolite, γ-alumina, activated carbon, or magnesium oxide support catalyze the reduction of nitrobenzene and its homologs affording aniline and its derivatives in high yield. The effect of the substrate on

Full text of DOI:10.1134/S1070363219080012

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 8, pp. 1549–1553. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Obshchei Khimii, 2019, Vol. 89, No. 8, pp. 1151–1156.
Colloid and Nanosized Catalysts in Organic Synthesis:
1
XXI . Reduction of Nitroarenes Catalyzed
by Immobilized Nickel Nanoparticles
a
a
a
a
V. M. Mokhov , Yu. V. Popov *, D. N. Nebykov , E. V. Nishchik ,
a
a
K. V. Shcherbakova , and Yu. L. Zotov
a
Volgograd State Technical University, pr. Lenina 28, Volgograd, 400131 Russia
e-mail: tons@vstu.ru
*
Received March 12, 2019; revised March 12, 2019; accepted March 14, 2019
Abstract―It has been found that nickel nanoparticles on NaX zeolite, γ-alumina, activated carbon, or magnesium
oxide support catalyze the reduction of nitrobenzene and its homologs affording aniline and its derivatives in high
yield. The effect of the substrate on the process in a continuous reactor at atmospheric hydrogen pressure has been
investigated. The use of activated carbon or magnesium oxide as a carrier аllows proceeding of the reaction at
8
0–100°С.
Keywords: catalysis, nanoparticles, nickel, reduction, nitroarenes, aniline
DOI: 10.1134/S1070363219080012
Aniline and its C-substituted homologs, which are
widely used in the production of dyes, polyurethanes, and
pharmaceuticals [2–6], are synthesized via hydrogena-
tion of nitrobenzene in a liquid or gas phase. Most of the
related industrial processes are performed under harsh
conditions: high pressure or temperature.
100%) [18], and Cu/MgO (280°С, conversion 94%,
selectivity 100%) [19].
The use of colloidal solution of nickel nanoparticles
as a catalyst of the nitro group reduction in nitroarenes
has been reported. For example, nitrobenzene and its
homologs have been reduced into the corresponding sub-
stituted anilines under conditions of catalysis with nickel
nanoparticles obtained via reduction of Ni(II) salts with
hydrazine hydrate [20]. Hydrogenation of 4-nitrophenol
with hydrogen in the presence of colloid nickel nanopar-
ticles in an autoclave (100°С, 8 atm) has been performed
as well [21]. The catalyst activity has been affected by
the size of nickel nanoparticles, determined by the nature
of the solvent. For example, the decrease in the particles
size from 300 to 60 nm has led to the increase in the re-
action yield after 2 h from 14 to 80%. It has been shown
that the conversion of nitrobenzene in the presence of
nickel nanoparticles is 8 times higher in comparison with
Raney nickel, other conditions being the same. Nickel
nanoparticles with size of 4 nm applied on silica gel
have catalyzed the reduction of nitrobenzene at 90°С and
Selective reduction of nitroarenes into aniline de-
rivatives has been accomplished under catalysis with a
series of metal catalysts such asAu/TiO [7] Pd/C or Pt/C
2
[
8–10], PtO [11], Raney nickel [12], or Ni/TiO [13].
2
2
Nickel sulfide has been used as catalyst of hydrogenation
at 250–350°С as well [14].
Nitrobenzene reduction has been catalyzed by nickel
nanoparticles applied onto ZrO or TiO surface via reduc-
2
2
tion of the adsorbed salts with hydrazine hydrate. Nickel
content in the catalyst was of 5%, nickel nanoparticles
size being of 2–8 nm. The Ni/TiO has revealed high
2
activity (conversion up to 99% at high selectivity) [15],
whereas the Ni/ZrO has lost activity upon prolonged use
2
at 250°С. Other catalysts which have been tested in gas-
phase hydrogenation of nitrobenzene involve Ru/SBA15
(275°С, conversion 94%, selectivity 100%) [16], Pd on
10 atm of hydrogen, with conversion 100% and selectivity
hydrotalcite (225°С, conversion 99%, selectivity 100%)
with respect to aniline 99% [22].
[
17], Ni/SBA-15 (250°С, conversion 97%, selectivity
Reduction of nitroarenes catalyzed by ferromagnetic
nanoparticles have been widely studied [23]. For example,
the use of palladium nanoparticles (3 nm) applied on
1
For communication XX, see [1].
1
549

1550
MOKHOV et al.
Fe O (11 nm) for the reduction of nitrobenzene with hy-
Scheme 1.
3
4
drogen at 1 atm and room temperature has been reported
24]. The catalyst has been used repeatedly without a
NO2
NH2
[
loss in activity.
1 atm, 80ꢀ240qɋ
R + 3H2
R + 2H O
2
Ni0
We have previously shown that nickel nanoparticles
applied on a support are catalytically active in a series
of hydrogenation reactions at atmospheric pressure of
hydrogen [25, 26]. This study aimed to investigate the
reduction of nitroarenes at atmospheric pressure of hy-
drogen in a continuous reactor in the presence of nickel
submicro- and nanoparticles immobilized on various
supports: NaХ zeolite, γ-alumina, activated carbon, and
magnesium oxide.
1
ɚꢀ1f
ꢀ
2ɚ 2f
R = H (а), 2-CH (b), 3-CH (c), 4-CH (d), 2-OCH (e),
3
3
3
3
4
-OCH (f).
3
equaled 100%. However, the decrease in the activity of
nickel particles on NaX zeolite and fast deactivation of
the catalyst were observed at temperature below 180°С.
When the substrate supply was stopped and the reactor
was purged with hydrogen at 240°С during 30 min, the
catalyst activity was fully restored.
The catalysts were prepared via impregnation of the
supports (the 1–1.5 mm fraction) with an aqueous solution
of nickel(II) chloride hexahydrate during a day, filtration,
and treatment with an aqueous solution of sodium boro-
hydride at room temperature. The reactor was charged
with moist catalyst which was dried in a hydrogen stream
immediately prior to the reaction. The size of supported
nickel nanoparticles was of 40–120 nm [27].
In the cases of weakly acidic or basic carriers, the
catalyst activity was retained with the decrease in tem-
perature. For example, nickel nanoparticles applied on
compressed magnesium oxide powder reduced nitroarene
1
a at 100–120°С. However, the catalytic activity was also
decreased after 1 h operation in that temperature range,
likely due to strong adsorption of nitrobenzene hamper-
ing its reduction with hydrogen. The catalyst activity was
retained upon the increase in temperature to 180–200°С
and purging with hydrogen (deblocking of active sites),
that process was accompanied by desorption of up to
2.5 g of a mixture of compounds 1a and 2a from 3 g of
the catalyst.
Nitroarenes 1a–1f were reduced at 160–240°С in the
presence of nickel nanoparticles applied on NaX zeolite
at the substrate supply 0.6 or 0.9 L/(kgcat h) depending
on the amount of the catalyst and specific hydrogen
supply 300–1700 L/(kgcat h) (Scheme 1) Yield of the
products was 91–100%, starting nitroarenes being the
major admixtures.
The effects of temperature on the conversion of ni-
troarenes and the yield of anilines was investigated for the
case of 2-nitrotoluene 1b conversion into 2-methylaniline
To prolong the catalyst activity at 100–120°С, ni-
troarene 1a was diluted with an inert component (toluene),
which allowed uniform distribution of the nitroarene and
toluene molecules at the catalyst surface. Being more
fugitive, toluene was easier desorbed from the catalyst
surface, liberating the active sites for hydrogen adsorption
and thus facilitating the reduction of nitroarene 1a. The
dilution at the nitrobenzene : toluene ratio 1 : 5 afforded
aniline in quantitative yield at 120–180°С, the catalyst
remaining active during 10 h of continuous operation. The
catalyst was also active at temperature 80–100°С, allow-
ing reduction of nitrobenzene with conversion of 94–96%.
2b. The yield of compound 2b was decreased from 99.9 to
97.2% with the increase in temperature in the 160–240°С
range, due to side reaction occurring at temperature above
80°С. The decrease in temperature from 140 to 100°С
led to the decrease in conversion of the starting nitroarene
b and yield of 2-methylaniline 2b from 82.2 to 29.5%,
the selectivity being 100%. In the case of 3-nitrotoluene
c, the yield of compound 2c was decreased from 99.3
1
1
1
to 98.4% when the process temperature was decreased
from 240 to 200°С.
As in the case of magnesium oxide, nickel nanopar-
ticles applied on activated carbon (Norit RX 3 EXTRA)
were active over wide temperature range (80–240°С),
conversion of nitrobenzene being complete. In contrast
to magnesium oxide, neither diffusion nor adsorption
processes hindered the catalyst activity at 80–140°С, and
the dilution of nitrobenzene was not needed. However, the
catalyst on carbon exhibited lower selectivity with respect
The effect of the carrier nature was demonstrated using
reduction of nitrobenzene as example. It was found that
the studied catalysts exhibited high catalytic activity at
specific supply of nitrobenzene 0.6 L/(kgcat h), specific
supply of hydrogen 1330 L/(kg h), hydrogen : nitroben-
zene molar ratio (10–15) : 1, and temperature 140–200°С;
cat
the conversion of nitrobenzene under those conditions
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 8 2019

COLLOID AND NANOSIZED CATALYSTS IN ORGANIC SYNTHESIS: XXI.
1551
Scheme 2.
NH
NH2
NH2
H
NH2
N
H
N
+
+
3H2
+ H2
NH3
ꢀ
+
2H2
ꢀH2
+H2
NH
O
OH
HO NH2
+
H2
H O
2
ꢀ
NH3
NH2
+
H
NH2
N
H
N
+
H2
NH3
ꢀ
to the target product. For example, gas-liquid chroma-
tography (GLC) and mass spectrometry analyses of the
reaction mixture obtained at 200°С revealed the pres-
ence of aniline (91.3 wt %), cyclohexylamine (1 wt %),
cyclohexanone (1.6 wt %), cyclohexanol (0.4 wt %),
phenylcyclohexylamine (2 wt %), and dicyclohexylamine
[1.08 kg /(kg h) when using non-diluted nitrobenzene],
nb cat
thus evidencing the prospects of further studies and op-
timization of such catalysts.
In summary, we found that nickel nanoparticles
immobilized on magnesium oxide, activated carbon,
γ-alumina, or NaX zeolite exhibited catalytic activity
towards reduction of nitroarenes. The experimental data
revealed that the use of magnesium oxide as the carrier
allowed aniline with selectivity up to 100%, whereas up
to 20% of side products of aromatic ring hydrogenation
were formed when using other carriers (NaX zeolite,
γ-Al O , or activated carbon)
(3.7 wt %) When the reaction temperature was increased
to 300°С, the fraction of high-boiling side products was
up to 20 wt %. The low selectivity could not be avoided
even at 80–100°С: the content of aniline was as high as
9
3 wt %, but derivatives of cyclohexane were present
as well.
The formation of side products (1–9 wt % in total)
was also revealed when NaX zeolite or γ-Al O were
2
3
EXPERIMENTAL
2
3
used as the catalyst carriers. On the other hand, aniline
was formed with selectivity up to 100% using magnesium
oxide as the carrier.
Chromato–mass spectroscopy analysis was performed
using a Saturn 2100 T/GC3900 instrument (EI, 70 eV)
Quantitative GLC analysis of the reaction mixtures was
performed using a Kristallyuks-4000M chromatograph
(t = 100–210°С, tevap = 250°С, polar column HP-5, l =
50 m, d = 0.32 mm, carrier gas—nitrogen, flame ion-
ization detector, tdet = 250°C, solvent—acetonitrile)
Scanning electron microscopy studies were performed
using a FEI Versa 3D DualBeam instrument (working
distance 10 mm, secondary electrons detector ETD,
backscattered electrons detector CBS, elemental analysis
method—EDS.
Hence, partial hydrogenation of the aromatic ring
occurred under the probed conditions. The formation
of cyclohexanone could be explained by hydrolysis of
the imine intermediate (Scheme 2), and the presence of
dicyclohexylamine could be due to the disproportionation
of cyclohexylamine and cross-coupling with aniline,
as had been observed earlier in the presence of nickel
nanoparticles on a carrier [28].
It should be noted that the industrial catalysts such
as NTK-4 and LOK exhibit the productiveness of
Catalyst preparation. The catalysts were prepared
via impregnation of a carrier (fraction 1–1.5 mm) with
an aqueous solution of nickel(II) chloride hexahydrate
0
.24 kg /(kg h) (nb = nitrobenzene) which is
nb cat
lower than that of the catalysts used in this study
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 8 2019

1552
MOKHOV et al.
during a day (0.7 g of nickel chloride per 2 g of NaХ
zeolite, 1 g of nickel chloride per 3 g of γ-Al O or С ,
or 3 g of nickel chloride per 3 g of MgO) The saturated
carrier was filtered off, washed with distilled water, and
treated with an aqueous solution of sodium borohydride
240°С. Conversion 100%, selectivity and yield 99.3%.
+
Mass spectrum, m/e (I , %): 107.9 (7) [M + 2] , 107.0
2
3
act
rel
+
+
(69) [M + 1] , 106.0 (100) [M] , 79.0 (17), 77.0 (17),
51.0 (8)
4
-Methylaniline (2d) Hydrogen [300 L/(kgcat h)]
and a mixture of 4-nitrotoluene 1d {0.6 L/(kgcat h)
molar ratio 1d : toluene = 1 : 3]} 0.6 L/(kgcat h)
(
3×0.1 g) at room temperature. Reduction with each
portion was performed during 2 min. The reduced moist
catalyst was loaded in a reactor and dried in a hydrogen
stream at 300°С just prior to the reaction.
[
uniflow with respect to hydrogen] were supplied on the
Ni/NaX catalyst (3 g) at 200°С. Conversion 96.9%, se-
General procedure of the reaction. The reaction
was performed in a continuous reactor plug-flow reactor
at atmospheric pressure and temperature 80–240°С. At
that temperature range, the reaction could occur either in
the gas phase or in the gas–liquid–solid catalyst system,
depending on the boiling point of the starting nitroarene.
The laboratory reactor was made of a 12Х18Н10Т steel
tube (inner diameter 9 mm, heating zone height 50 mm)
in an electric oven. Specific supply rate of the liquid
mixture was of 0.6 or 0.9 L/(kgcat h) depending on the
catalyst amount. Hydrogen supply rate was of 300–
lectivity 97.5%, yield 94.5%. Mass spectrum, m/e (I ,
отн
+
+
%): 108.0 (6) [M + 2] , 107.0 (83) [M + 1] , 106.0 (100)
+
[M] , 79.0 (11), 78.1 (7), 77.0 (13)
2
-Methoxyaniline (2e) Hydrogen [1100 L/(kgcat h)]
and 2-nitroanisole 1e [0.6 L/(kg h), uniflow with respect
cat
to hydrogen] were supplied on the Ni/NaX catalyst (3 g)
at 200°С. Conversion 100%, selectivity and yield 99.3%.
+
Mass spectrum, m/e (I , %): 123.9 (15) [M + 1] , 123.0
(
rel
+
76) [M] , 108.0 (88), 80.1 (100), 53.0 (26), 52.1 (13),
51.1 (8)
4
-Methoxyaniline (2f) Hydrogen [1100 L/(kgcat h)]
1
700 L/(kg h) (10–15-fold molar excess)
cat
and a mixture of 4-nitroanisole 1f {0.6 L/(kgcat h)
[molar ratio 1d : toluene = 1 : 3]} 0.6 L/(kgcat h)
uniflow with respect to hydrogen] were supplied on the
Ni/NaX catalyst (3 g) at 200°С. Conversion 99.8%, se-
Aniline (2a) a. Hydrogen [1330 L/(kgcat h)] and
nitrobenzene 1a [0.6 L/(kgcat h), uniflow with respect to
hydrogen] were supplied on the Ni/NaX catalyst (3 g) at
2
00°С. Conversion 100%, selectivity and yield 90.7%.
lectivity 97.4%, yield 97.2%. Mass spectrum, m/e (I ,
rel
+
Mass spectrum, m/e (I , %): 93.9 (13) [M + 1] , 93.0
+
+
rel
%): 123.9 (51) [M + 1] , 123.0 (100) [M] , 108.0 (63),
0.1 (66), 53.0 (14)
+
(100) [M] , 92.0 (9), 66.0 (35), 65.0 (20), 63.0 (5)
8
b. Hydrogen [1330 L/(kgcat h)] and nitrobenzene 1a
0.6 L/(kgcat h), uniflow with respect to hydrogen] were
CONFLICT OF INTEREST
[
supplied on the Ni/Cact catalyst (3 g) at 200°С. Conver-
sion 100%, selectivity and yield 91.3%.
No conflict of interest was declared by the authors.
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