Highly Efficient Pt-Catalyst Supported on Mesoporous Ceria-Zirconia Oxide for Hydrogenation of Nitroaromatic Compounds to Anilines

Article abstract of DOI:10.1134/S0036024418120336

Abstract: In this work, we have prepared a new catalytic system based on highly dispersed Pt nanoparticles supported on mesoporous ceria-zirconia oxide. The unique ability of the synthesized catalyst to activate hydrogen in the temperature range from –50 to 25°C allows us to provide selective hydrogenation of nitro-aromatic compounds to anilines at room temperature and atmospheric pressure of H₂.

Full text of DOI:10.1134/S0036024418120336

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2018, Vol. 92, No. 12, pp. 2374–2378. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © E.A. Redina, K.V. Vikanova, 2018, published in Zhurnal Fizicheskoi Khimii, 2018, Vol. 92, No. 12, pp. 1846–1850.
PHYSICAL CHEMISTRY OF HYBRID NANOMATERIALS
AND MULTICOMPONENT SYSTEMS
Highly Efficient Pt-Catalyst Supported on Mesoporous
Ceria-Zirconia Oxide for Hydrogenation of Nitroaromatic
1
Compounds to Anilines
a,
a
E. A. Redina * and K. V. Vikanova
a
N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
Moscow, 119991 Russia
*
e-mail: redinaea@ioc.ac.ru
Received May 21, 2018
Abstract—In this work, we have prepared a new catalytic system based on highly dispersed Pt nanoparticles
supported on mesoporous ceria-zirconia oxide. The unique ability of the synthesized catalyst to activate
hydrogen in the temperature range from –50 to 25°C allows us to provide selective hydrogenation of nitro-
aromatic compounds to anilines at room temperature and atmospheric pressure of H .
2
Keywords: anilines, amines, Pt nanoparticles, hydrogenation, mesoporious ceria-zirconia oxide
DOI: 10.1134/S0036024418120336
ics at temperatures of 30–60°C under 3–6 bar of H2.
Hydrogenation of nitroaromatics to the corre-
sponding anilines is the simplest way to obtain this The Pt nanoparticles deposited on the MFI zeolite
important class of organic compounds, which are also showed activity in the selective hydrogenation of
actively used in synthesis of pharmaceuticals, dyes nitroaromatic compounds, but a long reaction time
and plastics [1]. For the synthetic purposes, the
reduction of nitroaromatics is usually performed with
the use of metallic Zn in an excess of HCl. This
method requires additional stages of product purifi-
cation, removing the excess of reagents, and, in addi-
tion, the process is not scalable. According to the
modern organic synthesis concept that implies the
principles of “green chemistry,” heterogeneous
hydrogenation is the most perspective methodology
to obtain anilines from nitroaromatics [2]. The het-
erogeneous systems based on non-noble metals like
Co, Ni, Ag [3, 4] and supported Pt, Pd, Au nanopar-
ticles are now used as hydrogenation catalysts [5–7].
Furthermore, the catalysts containing non-noble
(
8–10 h) was required to achieve high yields, as well as
rather stringent process conditions: 80°C, hydrogen
pressure 10 bar [11].
To increase the selectivity of hydrogenation of
nitroaromatic compounds to anilines, in particular,
containing other reducible groups, and also for the
simplicity of the process, it becomes promising to cre-
ate a catalytic system that provides high yields of ani-
lines of different structures under normal conditions:
at atmospheric pressure and room temperature. In this
paper, we propose a new catalytic system based on
supported Pt nanoparticles on a mesoporous cerium-
metals show a much lower activity compared to the zirconium oxide as a carrier. As shown in [12], oxygen
systems with noble metals [8].
vacancies of cerium oxide are the centers of adsorption
The ability of Pt nanoparticles to activate hydrogen and activation of the nitro group. The number of these
has attracted the attention to the synthesis of hydroge- centers can be increased by doping cerium oxide with
nation catalysts with this active metal. Among the pro- zirconium cations, which facilitates the redox cycle of
posed systems, Pt nanoparticles supported on reduc-
ible oxide systems are of high interest. Thus, by using
3+
CeO and the formation of a number of Ce centers
[
2
13, 14]. The deposition of Pt nanoparticles on a
CeO –ZrO substrate also promotes an additional
reduction of Ce to Ce , with Pt being the center of
hydrogen activation. Another important factor of the
high activity of the catalyst is its developed surface,
which in the present work is achieved by creating a
mesoporous oxide support structure.
a Pt/FeO catalyst, it was possible to obtain a wide
x
2
2
range of anilines with yields up to 90%, yet the reac-
4+
3+
tion was performed under H pressure (3 bar) and tem-
2
o
perature 40 C [9]. Corma et al. [10] used a Pt/TiO
catalyst for hydrogenation of substituted nitroaromat-
2
1
The article was translated by the authors.
2374

HIGHLY EFFICIENT Pt-CATALYST SUPPORTED ON MESOPOROUS
2375
EXPERIMENTAL
Support Synthesis
the analytic measurements [16–18]. Before measure-
ments, the samples were mounted on a 3 mm copper
grid and fixed in a grid holder. The samples morphol-
ogy was studied using a Hitachi HT7700 transmission
electron microscope. Images were acquired in a
bright-field TEM mode at a 100 kV accelerating volt-
age.
The preparation of mixed oxide substrates CeO –
2
ZrO was carried out by a coprecipitation method [15].
2
The precursor for the zirconium solution was
ZrO(NO ) · xH O (99.5%; Acros Organics) and
3
2
2
(
NH ) Ce(NO ) (98+%, Alfa Aesar) was used as a
4 2 3 6
Energy-dispersive X-ray spectroscopy (EDS-
SEM). The samples morphology was studied under
native conditions to exclude metal coating surface
precursor for the cerium containing solution. For the
synthesis of cerium-zirconium supports with the
molar ratio Ce : Zr = 0.8 : 0.2, simultaneous co-pre-
cipitation of cerium and zirconium hydroxides from effects. The observations were carried out using a
working solutions in the presence of ammonium Hitachi SU8000 field-emission scanning electron
hydroxide was performed.
microscope (FE-SEM). Images were acquired in a
secondary electron mode at a 10, 15, and 20 kV accel-
erating voltage and at a working distance 15 mm. EDX
A solution containing 0.73 mol of the cerium pre-
cursor was prepared by dissolving the sample in water
and then diluted with isopropanol (99%) in a 1.7 : 1 studies were carried out using an Oxford Instruments
ratio. After dilution, the resulting solution was stirred X-max EDX system.
at room temperature for 1 h.
X-ray diffraction analysis (XRD). The phase com-
position of the samples and the size of the primary
To obtain a solution containing 0.19 mol of the zir-
conium precursor, the sample was dissolved in a 2.3 M
crystals of crystalline phases were determined by the
solution of oxalic acid. The resulting solution was
XRD method. X-ray diffraction patterns were
diluted with isopropanol (99%) in a 1 : 1 (v/v) ratio.
recorded on a DRON-2 device in Ni-filtered CuK
α
After dilution, the solution was stirred at room tem-
radiation (λ = 0.1542 nm) in a step-scan mode (in
perature for 1 hour. To co-precipitate cerium and zir-
0.02° increments) in the range 2θ = 10°–80°. The
conium hydroxides, the working solutions were
poured off under vigorous stirring and an ammonia
solution (23 wt %) was added until pH reached 9.15.
identification of the phase composition was carried
out by matching the position and intensity of the lines
The resulting suspension was stirred for 30 min, after on the X-ray diffraction pattern with the ICDD data
which the precipitate was separated, washed with (International Data Center for X-ray Diffraction).
deionized H O and dried for 12 h at 70°C, followed by The coherent scattering domain size was calculated
2
calcination at 400°C in a closed crucible for 4 h.
from the broadening of the X-ray diffraction lines in
accordance with the Scherer equation.
Catalyst Synthesis
Temperature-programmed reduction with hydrogen
(ТPR-Н ). TPR measurements were carried out on a
2
Synthesis of a catalyst with a platinum content of
laboratory constructed flow-system equipped with a
gas purification system, a quartz U-shaped reactor, a
water vapor trap, and a thermal conductivity detector.
The detector was calibrated by reduction of a CuO
sample (Aldrich-Chemie GmbH, 99%) treated in an
Ar flow at 300°C. All experiments were conducted
with a water vapor trap, which was cooled to –100°C.
A sample of 1% Pt/CZ-N with a weight of 150 mg was
treated in an Ar flow at 250°C for 90 min. The catalyst
was then cooled to –50°C using a mixture of ethanol
and liquid nitrogen as a cooling mixture and thermo-
1
wt % was performed by the method of pH-controlled
precipitation of the precursor. An aqueous solution of
H PtCl (50 mL) with a concentration of 0.46 mM was
2
6
prepared, after that an aqua solution of Na CO
2
3
(
0.1 M) was added until pH 7. Then, a sample of
CeO –ZrO was added and the suspension was stirred
2
2
for 30 min without heating and then the suspension
was stirred for 3 h at 60°C. The completeness of Pt
deposition was checked by the qualitative reaction of
n+
Pt ions in the parent solution with KI and HCl. In all
cases, we observed a complete Pt deposition onto the
support surface. The precipitate was then separated statted at this temperature for 60–90 min. Heating
and washed with deionized H O, dried under vacuum from –50 to 25°C was carried out in a flow of a gas
2
using a rotary evaporator until complete removal of mixture of 4.6% H /Ar (30 mL/min) at a heating rate
2
moisture. The resulting catalyst was reduced in a flow of 10 deg/min. The sample was kept at room tempera-
of hydrogen at 250°C for 2 h. The catalyst was desig- ture (25°C) until the uptake of hydrogen ceased.
nated as 1Pt/CZ-N.
Specific surface area and porosity. N adsorption-
2
desorption isotherms were obtained on an ASAP 2020
Physicochemical Characterization
Plus “Micromeritics” sorptometer at 77 K. The BET
Transmission electron microscopy (TEM). A target- method was used to calculate the specific surface area
oriented approach was utilized for the optimization of (SBET) of the sample. The total pore volume (V) was
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 12 2018

2376
REDINA, VIKANOVA
calculated at p/p = 0.99. The t-plot method was used
0
to control the volume of micropores. The pore size
distribution (PSD) was calculated from the isotherm
desorption branch by the BJH method.
0.04
CZ-N
Dispersion of Pt nanoparticles. The metal disper-
sion was determined by irreversible chemisorption of
CO at 35°C on ASAP 2020 Plus Micromeritics. The
samples of the reduced catalysts before the measure-
ment of chemisorption were additionally reduced in
the ASAP unit with hydrogen at a temperature of
0.02
2
50°C for 30 min in a flow of pure H (300 mL/min).
2
0
0
1
2
Catalytic Experiment
logD [nm]
In this work, the following of nitroaromatic com-
pounds were used:
Fig. 1. The pore size distribution of the support CeO –
2
ZrO , D is pore diameter.
2
NO2
NO2
NO2
of the experimentally obtained retention times of indi-
vidual compounds (nitrobenzene, o-dinitrobenzene,
p-dinitrobenzene, p-hydroxynitrobenzene, p-nitroac-
etophenone, nitrocyclohexane, aniline, o-phenylene-
diamine, p-phenylenediamine, p-hydroxyaniline,
p-nitrophenylethanol, aminocyclohexane). The
structure and purity of the products obtained were
O N
2
NO2
(III)
(
I)
(II)
O
NO2
1
13
confirmed by NMR spectroscopy. The H and
C
NMR spectra were recorded on a Bruker Avance 300
spectrometer in solvents CDCl and DMSO-d .
HO
3
6
NO2
(V)
(IV)
RESULTS AND DISCUSSIONS
The liquid-phase hydrogenation reaction of nitroaro-
matic compounds can be presented as:
The method used for the synthesis of the oxide car-
rier CeO -ZrO made it possible to obtain a mixed
2
2
R
NO2
R
NH2
oxide with the CeO cubic fluorite structure (a =
2
It was carried out at room temperature under an atmo- 5.41 Å) with a coherent scattering domain size of
spheric pressure of H . A sample of the catalyst 5 nm, with ZrO being the X-ray amorphous phase. It
2
2
(
50 mg) was placed in a round-bottomed three- should be noted that the surface area of the obtained
2
necked flask and the system was purged with hydrogen mixed oxide is as high as 104 m /g; the sample has a
for 30 min. A solution of the substrate in ethanol 0.2 M
mesoporous structure with a narrow pore size distri-
bution and an average diameter of 3 nm (Fig. 1). The
microstructure of the sample is shown in Fig. 2a.
(
or in tetrahydrofuran in the case of using o- and
p-dinitrobenzene as a substrate) was then poured into
the reactor by means of a feed cock of the reaction
mixture. The concentration of platinum in the reac-
The deposition of Pt nanoparticles (NPs) on the
tion mixture was 0.85 mol %. The reaction was carried mixed oxide made it possible to obtain nanoparticles
out with vigorous stirring on a magnetic stirrer at a rate with an average size of 4 nm according to the TEM
of 900 rpm in the monitoring mode by means of gas- data (Fig. 2b). However, according to the CO adsorp-
liquid chromatography until the peak of the starting tion data, the dispersion of the deposited metal
compound disappeared on the chromatogram. At the exceeds 50%, and the average size of the Pt nanoparti-
end of the experiment, the stirring was stopped; the
catalyst was separated from the reaction mixture by
centrifugation.
cles is 2 nm.
The SEM-EDX micrographs of the obtained
1
% Pt/CZ-N catalyst confirmed a uniform distribu-
Analysis of the reaction products was performed
using GC with a Chromatek Crystal 5000.2 chromato-
graph with a flame ionization detector (FID) and a
tion of CeO and ZrO in the sample, as well as Pt NPs
2
2
on the surface of the mixed-oxide support (Fig. 3).
capillary column CR-5 (2 mm × 25 m) at a tempera- The study of the reduced catalyst sample of
ture of 190°C. The peaks were identified on the basis 1% Pt/CZ-N by the TPR-H method showed an
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 92
No. 12
2018

HIGHLY EFFICIENT Pt-CATALYST SUPPORTED ON MESOPOROUS
2377
1
μm
50 nm
(а)
(b)
Fig. 2. Micrographs of the prepared samples: (a) the SEM image of the CZ-N support, (b) the TEM image of the 1% Pt/CZ-N
catalyst.
CeLα1
OKα1
5
μm
5 μm
ZrLα1
PtLα1
5
μm
5 μm
Fig. 3. The SEM-EDX images of the 1% Pt/CZ-N catalyst.
anomalously high hydrogen uptake in the temperature
The catalytic system used allows the production of
amines with quantitative yields. Complete hydrogena-
tion of nitrobenzene proceeded within 2 h. Hydroge-
range from –50 to 25°C (Fig. 4); the molar ratio of H :
2
Pt exceeded the stoichiometric one by 11 times.
The intensive hydrogen absorption at low tempera- nation of m- and p-dinitrobenzene resulted in
tures on the catalytic system under study can be diamines with a quantitative yield in 3 h. When hydro-
explained by the appearance of the hydrogen spillover
genating p-nitrophenol, the mild reaction conditions
did not affect the substituent in the benzene ring and
produce the corresponding p-aminophenol in 2 h. By
varying the reaction time, it is possible to obtain both
the corresponding m-aminoacetophenone (in 2 h) and
effect, and, consequently, H activation in the investi-
2
gated temperature region leading to a partial reduction
3+
of the carrier and the formation of Ce centers on
which the nitro group can be adsorbed [12]. The
resulting “active” hydrogen is capable of hydrogenat-
ing the nitro group under normal conditions: at room
temperature and atmospheric pressure.
1-(3-aminophenyl)ethanol (in 5 h) from m-nitroace-
tophenone.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 12 2018

2378
REDINA, VIKANOVA
REFERENCES
. H. U. Blaser, A. Baiker, and R. Prins, in Heterogeneous
Catalysis and Fine Chemicals, Ed. by H. U. Blaser and
E. Schmidt (Elsevier, Amsterdam, 1997), Vol. 4, p. 17.
8
6
4
2
000
000
000
000
0
1
2
. I. P. Beletskaya and L. M. Kustov, Russ. Chem. Rev.
7
9, 441 (2010).
3
. H. Huang, X. Wang, Y. Sheng, et al., RSC Adv. 8, 8898
2018).
4. Y. Chen, C. Wang, H. Liu, et al., Chem. Commun.,
298 (2005).
. C. C. Torres, J. B. Alderete, G. Pecchi, et al., Appl.
Catal., A 517, 110 (2016).
(
5
5
−50
−30
−10
10
30
T, °C
6. D. He, X. Jiao, P. Jiang, et al., Green Chem. 14, 111
2012).
(
7
. F. Wang, J. Liu, and X. Xu, Chem. Commun., 2040
Fig. 4. TPR-H profile of the reduced 1% Pt/CZ-N cata-
2
(2008).
lyst.
8
9
. L. M. Kustov, Russ. J. Phys. Chem. A 89, 2006 (2015).
. H. Wei, X. Liu, A. Wang, et al., Nat. Commun. 5, 5634
For comparison, in [19] the use of a stoichiometric
(2014). doi 10.1038/ncomms6634
reductant, hydrazine hydrate, allowed to reach the
1
0. A. Corma, P. Serna, P. Concepcion, and J. J. Calvino,
J. Am. Chem. Soc. 9, 8748 (2008).
1. J. Gu, Z. Zhang, P. Hu, et al., ACS Catal. 5, 6893
2015).
2. S. Zhang, C.-R. Chang, Z.-Q. Huang, et al., J. Am.
Chem. Soc. 138, 2629 (2016).
quantitative yield of 4-hydroxyaniline only at 100°C in
5
h. In the other work [20], it was reported on the
1
hydrogenation of nitrobenzene on a homogeneous
(
catalyst γ-Fe O @HAP-Pd (ω (Pd) = 2.5%): the yield
2
3
1
of aniline at room temperature in 3 h was 76%.
Thus, the synthesized catalyst with a 1% platinum
content supported on the mesoporous cerium-zirco-
nium oxide exhibited a high catalytic activity in the
hydrogenation of various nitroaromatic compounds to
anilines at an atmospheric pressure and room tem-
perature. The unusual activity of the 1% Pt/CZ-N
catalyst is associated with the hydrogen spillover effect
observed even at sub-ambient temperatures, which
results in the formation of active hydrogen and a par-
tial reduction of the cerium-zirconium carrier with the
formation of adsorption and activation sites for the
substrate.
1
3. S. Damyanova, B. Pawelec, K. Arishtirova, et al., Appl.
Catal., A 337, 86 (2008).
1
4. N. Kakuta, Y. Kudo, H. Rachi, et al., Top. Catal. 42–
3, 377 (2007).
5. O. A. Kirichenko, G. W. Graham, W. Chun, et al.,
Stud. Surf. Sci. Catal. 118, 411 (1998).
4
1
16. V. V. Kachala, L. L. Khemchyan, A. S. Kashin, et al.,
Russ. Chem. Rev. 82, 648 (2013).
17. V. P. Ananikov, E. G. Gordeev, M. P. Egorov, et al.,
Mendeleev Commun. 26, 365 (2016).
18. V. P. Ananikov, D. B. Eremin, S. A. Yakukhnov, et al.,
Mendeleev Commun. 27, 425 (2017).
1
9. Y. Jiang, H. Suo, D. Zhang, X. Li, et al., J. Chem. Res.
ACKNOWLEDGMENTS
41, 401 (2017).
The work was carried out with the financial support 20. L. Jiang and Z. Zhang, Int. J. Hydrogen Energy 41,
of the RSCF (grant no. 17-73-20282).
22983 (2016).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 92
No. 12
2018