Selective Liquid Phase Hydrogenation of Aromatic Nitro Compounds in the Presence of Fe–Cu Nanoparticles

Article abstract of DOI:10.1134/S0036024420060217

Abstract: Fe–Cu bimetallic oxide nanoparticles supported on silica gel that catalyze the hydrogenation of nitrobenzene to aniline and of dinitrobenzenes to phenylenediamines under relatively mild reaction conditions (200°C, p_H2 1.3 MPa, 4 h, and 700 rpm) are synthesized. The catalytic properties of supported bimetallic Fe–Cu catalysts depend on the synthesis procedure, sample composition, and conditions of thermal treatment. There is a synergistic effect of interaction between Cu and Fe in the hydrogenation of nitrobenzene, 1,3-dinitrobenzene, and 1,4-dinitrobenzene in the presence of a bimetallic Fe–Cu catalyst obtained via coprecipitation.

Full text of DOI:10.1134/S0036024420060217

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2020, Vol. 94, No. 6, pp. 1180–1183. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Fizicheskoi Khimii, 2020, Vol. 94, No. 6, pp. 888–892.
PHYSICAL CHEMISTRY
OF NANOCLUSTERS AND NANOMATERIALS
Selective Liquid Phase Hydrogenation of Aromatic Nitro Compounds
in the Presence of Fe–Cu Nanoparticles
a,b
a,b,
a,b,c
A. A. Shesterkina , A. A. Strekalova *, and L. M. Kustov
a
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119334 Russia
b
National University of Science and Technology (MISIS), Moscow, 119049 Russia
c
Department of Chemistry, Moscow State University, Moscow, 119991 Russia
*e-mail: anastasiia.strelkova@mail.ru
Received July 5, 2019; revised July 5, 2019; accepted September 3, 2019
Abstract—Fe–Cu bimetallic oxide nanoparticles supported on silica gel that catalyze the hydrogenation of
nitrobenzene to aniline and of dinitrobenzenes to phenylenediamines under relatively mild reaction condi-
tions (200°C, р 1.3 MPa, 4 h, and 700 rpm) are synthesized. The catalytic properties of supported bimetal-
Н2
lic Fe–Cu catalysts depend on the synthesis procedure, sample composition, and conditions of thermal treat-
ment. There is a synergistic effect of interaction between Cu and Fe in the hydrogenation of nitrobenzene,
1
,3-dinitrobenzene, and 1,4-dinitrobenzene in the presence of a bimetallic Fe–Cu catalyst obtained via
coprecipitation.
Keywords: Fe–Cu/SiO2 catalysts, selective hydrogenation, nitrobenzene, dinitrobenzene, bimetallic
nanoparticles
DOI: 10.1134/S0036024420060217
INTRODUCTION
The catalytic reduction of nitro groups in aromatic
mono- and dinitro compounds on heterogeneous cat-
90 min), ~100% selectivity towards aniline and 95%
conversion of nitrobenzene were achieved.
Metallic iron immobilized in an ionic liquid
alysts is a key method of preparation of aromatic (ImmFe-IL) was used as a catalyst in the hydrogena-
amines in laboratories and industry [1–3]. Aromatic tion of p-dinitrobenzene. The resulting product was
amines are also widely used to synthesize different fine p-nitroaniline with a selectivity of 99% at 88% conver-
chemicals, dyes, urethanes, and pharmaceuticals [4, sion of p-DNB [18]. The reaction proceeded for 12 h
5
]. The most effective heterogeneous catalysts for the at 110°C in ethylene glycol in the presence of hydra-
hydrogenation of mono and dinitro compounds are zine hydrate.
systems based on noble metals, particularly Pt [6–8],
It is therefore of interest to obtain iron-containing
Pd [9–11], Ru [12], and others (e.g., Ni) [13–16].
Despite their high efficiency, these catalysts have con-
siderable disadvantages (large amounts of active com-
ponents, high costs, and rapid deactivation of an active
surface). Nickel-containing systems require high tem-
peratures, high hydrogen pressures, and long reaction
times [15, 16].
catalytic systems that would be active in the liquid-
phase reduction of nitro compounds using hydrogen
as a reducting agent under relatively mild reaction
conditions.
The aim of this work was to study the catalytic
properties of bimetallic iron-copper catalysts in the
selective reduction of nitro groups in nitrobenzene,
Despite the growing scientific interest in the tran-
sition from precious metals to more affordable, effi-
cient and environmentally friendly iron-based cata-
lytic systems, currently there are only few publications
on hydrogenation of nitro compounds on iron-con-
taining systems [17–19]. It should be noted that
hydrazine hydrate was used as a reducing agent in
these studies.
1
,3-dinitrobenzene, and 1,4-dinitrobenzene to form
corresponding amines.
EXPERIMENTAL
Bimetallic Fe–Cu catalysts supported on a SiO
2
−1
2
−1
3
(KSKG silica, S = 108 m g , V = 1.05 cm g ,
sp
pore
For example, 8% Fe O /C supported catalysts were
Dpore = 26 nm, Khimmed, Russia) were synthesized in
2
3
used for the selective reduction of nitrobenzene [17]. two different ways: via the co-deposition of Cu and Fe
Hydrazine hydrate was used as a source of hydrogen. precursors (Cu(NO
) and Fe(NO ) ) by deposition–
3 2 3 3
Under mild conditions (atmospheric pressure, 60°C, precipitation with urea (DPU), and the sequential
1180

SELECTIVE LIQUID PHASE HYDROGENATION
1181
Fe-Cu/SiO2
Table 1. Catalytic properties of Fe–Cu/SiO catalysts in the hydrogenation of nitro compounds R–NO ⎯ ⎯ ⎯ ⎯ → R–NH
2
2
2
No.
Catalyst
X, %
Product
γ, %
Nitrobenzene as a substrate
1
2
3
4
5
6
7
8
9
6Fe-DPU-300C
6Fe-SI-300C
3Cu-DPU-300C
6Fe-3Cu-SI-300С
6Fe-3Cu-DPU-300С
6Fe-3Cu-DPU-300Н
3Fe-6Cu-DPU-300С
6Fe-6Cu-DPU-300С
6Fe-1Cu-DPU-300С
1
20
17
73
56
98
72
45
52
23
Aniline
100
100
100
100
100
100
100
100
100
Aniline
Aniline
Aniline
Aniline
Aniline
Aniline
Aniline
Aniline
,3-Dinitrobenzene as a substrate
1
0
6Fe-DPU-300C
3Cu-DPU-300C
6Fe-3Cu-DPU-300С
6Fe-3Cu-SI-300С
1
54
27
100
100
Nitroaniline
Nitroaniline
Phenylenediamine
Phenylenediamine
55
34
82
45
1
1
1
2
13
,4-Dinitrobenzene as a substrate
1
4
6Fe-DPU-300C
3Cu-DPU-300C
6Fe-3Cu-DPU-300С
6Fe-3Cu-DPU-300Н
6Fe-3Cu-SI-300С
60
20
100
57
Nitroaniline
Nitroaniline
Phenylenediamine
Nitroaniline
Phenylenediamine
44
30
87
80
55
1
5
1
6
1
7
18
100
Reaction conditions: 200°C, pH2 = 1.3 MPa, 700 rpm, 4 h, THF, and nsub : nΣMe = 9; S is the selectivity; X is conversion of substrate.
impregnation onto the outer surface of a carrier from a
solution of (NH ) [Fe(C O ) ] · 3H O and then
nNO2 : n
= 9) was studied at an initial hydrogen pres-
ΣMe
4
3
2
4 3
2
sure of 1.3 MPa, a temperature of 200°C, and intensive
Cu(NO ) with intermediate drying of an iron-con-
3
2
stirring at 700 rpm. The reaction time was 4 h.
taining sample (SI). The procedure for synthesizing
the samples was thoroughly described in [20]. The
samples were dried at 80–100°C and then calcined in
air for 4 h at 300°C after deposition of the precursors.
The temperature of calcination was chosen according
to the results from thermal analysis of the samples.
The calcined samples were reduced at 300°C for 2 h in
a hydrogen flow. The reduction temperature was
selected according to the results of temperature-pro-
RESULTS AND DISCUSSION
The synthesized monometallic and bimetallic
iron-copper catalysts were studied in the liquid-phase
hydrogenation of nitro compounds to obtain amines
under relatively mild reaction conditions. Table 1
shows the results from catalytic tests.
Our results indicate that the calcined monometallic
iron-containing samples have low acivity: the maxi-
mum conversion of nitrobenzene was only 17–20%
after 4 h of the reaction (Table 1, entries 1 and 2). The
efficiency of the monometallic copper catalyst
obtained via deposition was several times higher: the
conversion of nitrobenzene was 73% for the same
reaction time.
grammed reduction with hydrogen (TPR-H ).
2
Fe/SiO and Cu/SiO monometallic catalysts were
2
2
also synthesized by similar procedures to compare
their catalytic properties.
The copper content in the bimetallic samples was 1,
3
, and 6 wt %, while those of iron were 3 and 6 wt %.
The calcined samples are denoted as C; the reduced,
as H. The catalysts were characterized using TEM,
DRIFTS-CO, and XRD.
The catalytic properties of Fe–Cu bimetallic sam-
ples depend mainly on the synthesis method. A syner-
gistic effect of the interaction between Cu and Fe in
hydrogenation of nitrobenzene was observed for the
The catalytic activity of the synthesized catalysts in
the reaction of liquid-phase hydrogenation of aro-
matic nitro compounds (СNO2 = 0.16 M in THF and sample obtained via co-precipitation and hydrolysis of
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 6 2020

1182
SHESTERKINA et al.
urea (6Fe–3Cu–DPU-300C). Its efficiency was
approximately two times higher than that of the cata-
lysts prepared by sequential impregnation (–6Fe–
6
4
2
0
CO, 20°C, 12 mmHg
126
3Cu–SI-300С). The conversion of nitrobenzene on
2
the 6Fe–3Cu–DPU-300С sample was 98% with a
quantitative yield of aniline. The same tendency is typ-
ical of hydrogenation of dinitrobenzenes. The samples
obtained via DPU were the ones most effective in the
hydrogenation of 1,3-dinitrobenzene and 1,4-dinitro-
benzene. There was full conversion of the initial sub-
strates with high selectivity for phenylenediamines
2128
1
2
(
82 and 87%, respectively) after 4 h of the hydrogena-
tion of 1,3-dinitrobenzene and 1,4-dinitrobenzene on
Fe–3Cu–DPU-300С catalyst (Table 1, entries 12
6
and 16). The low selectivity of the samples obtained
via SI, determined internal standard method, in the
hydrogenation of dinitrobenzenes, was probably due
to side reactions with formation of condensation prod-
ucts not detectable via GLC. The differences in the
catalytic activity of the Fe–Cu samples depending on
the method of synthesis can be matched to the physi-
cochemical characterization data for these samples.
2
300
2200
2100
2000
1900
11800
ν, сm−
Fig. 1. (Color online) DRIFT spectra of Fe–Cu/SiO
2
samples near valence vibrations of adsorbed CO:
1) 6Fe–3Cu–SI-300C and (2) 6Fe–3Cu–DPU-300C.
(
TPR-H and SEM-EMF studies indicate that the
2
Our study showed that the conditions of heat treat-
ment also have a strong effect on the activity and selec-
tivity of formation of the target product. The reduction
of the 6Fe–3Cu–DPU-300C calcined sample in
hydrogen sharply lowers its activity in the hydrogena-
tion of nitrobenzene and 1,4-dinitrobenzene (Table 1,
entries 6 and 17). The activity of the 6Fe–3Cu–DPU-
preparation Fe–Cu–SI samples leads to weakly inter-
acting particles of iron and copper oxides, while the
DPU method allows the preparation of Fe–Cu–O
bimetallic mixed oxide phases [20, 21]. As a result, the
best way to obtain active and highly selective iron-cop-
per catalysts is the coprecipitation of metal precursors
via urea hydrolysis.
3
00Н reduced sample was halved, but no target prod-
uct (phenylenediamine) formed. TPR–H data for
Our catalytic tests also showed that the catalytic
2
properties of bimetallic catalysts depend on the com- Fe–Cu bimetallic samples [20] indicate that the
position and heat treatment conditions. A bimetallic reduction of calcined samples with hydrogen at 300°C
sample with 6 wt % iron and 3 wt % (6Fe–3Cu– results in the full reduction of copper-containing
DPU-300C) shows the best catalytic properties in the oxide phase particles. A comparison of physicochem-
hydrogenation of nitrobenzene. Changing the compo- ical properties and data on catalytic activity shows that
0
sition of the samples sharply reduced their activity in the reduction to Cu is undesirable. The phases most
the hydrogenation of nitrobenzene.
active in hydrogenation of nitro group are obviously
100 nm
100 nm
(a)
(b)
Fig. 2. TEM micrographs of (a) 6Fe–3Cu–SI-300C and (b) 6Fe–3Cu–DPU-300C samples.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94
No. 6
2020

SELECTIVE LIQUID PHASE HYDROGENATION
ACKNOWLEDGMENTS
1183
highly dispersed copper oxide nanoparticles, which
have a developed area of contact with iron oxide
nanoparticles or copper ions stabilized in the phases of
the Cu–Fe–O system.
USU_588494 experimental equipment was used in this
work. The authors are grateful to Dr. O.P. Tkachenko for the
DRIFTS-CO measurements and to Dr. O.A. Kirichenko for
her assistance in the preparation of the studied catalysts.
The state of metals in the Fe–Cu/SiO bimetallic
2
samples was studied via the IR spectroscopy of
adsorbed CO. A comparative analysis showed that the
DRIFT-CO spectra at 20°C of the samples synthe-
sized via sequential impregnation and DPU contained
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CONCLUSIONS
1
1
We showed for the first time that Fe–Cu oxide
nanoparticles deposited on silica gel catalyze the
hydrogenation of nitrobenzene to aniline and of dini-
trobenzenes to phenylenediamines under relatively
mild conditions: 200°С and an initial hydrogen pres-
sure of 1.3 MPa. The catalytic properties of deposited
Fe–Cu bimetallic catalysts depend on the synthesis
procedure, sample composition, and conditions of
heat treatment. Catalysts reduced in hydrogen are less
active. A sample synthesized via the coprecipitation of
metal precursors and the hydrolysis of urea with sub-
sequent calcination in air at 300°C with 6 wt % iron
and 3 wt % copper had the best selectivity towards ani-
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This work was supported by the Russian Foundation for
Basic Research, project no. 18-33-00040.
Translated by A. Tulyabaev
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 6 2020