Hydrogenation of substituted aromatic nitrobenzenes over 1% 1.0 wt.%Ir/ZrO2 catalyst: Effect of meta position and catalytic performance

Article abstract of DOI:10.1016/j.cattod.2013.03.037

This study is based on 1%Ir/ZrO₂ catalyst which was studied in the hydrogenation of aromatic meta-substituted nitrobenzene in liquid phase. The catalyst was prepared by traditional impregnation method using IrCl₃ and it has been characterized in terms of temperature-programmed reduction (TPR), ICP-MS, BET area, X-ray diffraction, HR-TEM and XPS measurements. The hydrogenation was evaluated in a batch type reactor at 298 K using ethanol like a solvent. The catalyst showed the formation of zero valent and partially oxidized Iridium (Ir^δ+) is established post-TPR and XPS characterization. The metal particle size exhibited a wide distribution with mean size 1.8 nm. Ir/ZrO₂ was active in all the hydrogenation reactions with elevated conversion and promoted exclusive NO₂ group reduction, resulting in the sole formation of the corresponding amino-compound except for CHO and CHCH₂ meta-substituted nitrobenzene. We associate this response to a reducible group competition between NO₂ and CHO or CHCH₂. Reactant activation on the catalyst generates a negatively charged intermediate, consistent with a nucleophilic mechanism. The presence of electron-donating substituents is shown to decrease NO₂ reduction rate. This effect is quantified in terms of the Hammett relationship where a linear correlation between the substituent constant (σ_i) and rate is established and a reaction constant (ρ) 0.639. The data generated provide the first report of the catalytic action of supported Ir in the hydrogenation of meta-substituted nitroarenes and establish the nature of the hydrogenation en liquid phase.

Full text of DOI:10.1016/j.cattod.2013.03.037

Catalysis Today 213 (2013) 93–100
Contents lists available at SciVerse ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Hydrogenation of substituted aromatic nitrobenzenes over 1%
1.0 wt.%Ir/ZrO2 catalyst: Effect of meta position and catalytic
performance
Cristian Camposa, Cecilia Torresa, Marcelo Oportusa, Miguel A. Pen˜ab, J.L.G. Fierrob,
Patricio Reyesa,∗
a Grupo de Catálisis por Metales, Facultad de Ciencias Químicas, Universidad de Concepción, Edmundo Larenas 129, Concepción, Chile
b Instituto de Catálisis y Petroleoquímica (ICP-CSIC), Grupo de Energía y Química Sostenible (EQS), c/Marie Curie s/n Cantoblanco Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
This study is based on 1%Ir/ZrO2 catalyst which was studied in the hydrogenation of aromatic meta-
substituted nitrobenzene in liquid phase. The catalyst was prepared by traditional impregnation method
using IrCl3 and it has been characterized in terms of temperature-programmed reduction (TPR), ICP-MS,
BET area, X-ray diffraction, HR-TEM and XPS measurements. The hydrogenation was evaluated in a batch
type reactor at 298 K using ethanol like a solvent. The catalyst showed the formation of zero valent and
partially oxidized Iridium (Irı+) is established post-TPR and XPS characterization. The metal particle size
exhibited a wide distribution with mean size 1.8 nm. Ir/ZrO2 was active in all the hydrogenation reactions
with elevated conversion and promoted exclusive NO2 group reduction, resulting in the sole formation of
the corresponding amino-compound except for CHO and CH CH2 meta-substituted nitrobenzene. We
associate this response to a reducible group competition between NO2 and CHO or CH CH2. Reactant
activation on the catalyst generates a negatively charged intermediate, consistent with a nucleophilic
mechanism. The presence of electron-donating substituents is shown to decrease NO2 reduction rate.
This effect is quantified in terms of the Hammett relationship where a linear correlation between the
substituent constant (ꢀi) and rate is established and a reaction constant (ꢁ) 0.639. The data generated
provide the first report of the catalytic action of supported Ir in the hydrogenation of meta-substituted
nitroarenes and establish the nature of the hydrogenation en liquid phase.
Received 11 December 2012
Received in revised form 12 March 2013
Accepted 14 March 2013
Available online 17 May 2013
Keywords:
Iridium
Nitrobenzene
Hydrogenation
Heterogeneous catalyst
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
The role of catalysis in the development of clean chemical
production with limited hazardous and toxic by-products is now
The arylamines include a number of bulk organic chemicals,
including aniline itself, diphenylamine and the phenylenediamines.
For the production of aniline and other bulk arylamines, catalytic
hydrogenation of nitroarenes has long displaced the traditional
Bechamp reduction employing iron and hydrochloric acid [1,2]. Ini-
tially the production of this kind of product has been approached
by three different procedures: (i) by stoichiometric reduction of
the corresponding aromatic nitro compounds using iron, tin, zinc
or a metal sulfide such as Na2S. However, this method displays low
selectivity for nitro group, and the major disadvantages are toxic-
ity, odor of most reducing agents and sulfur containing organic side
products and formation of elemental sulfur [2]. (ii) Catalytic hydro-
genation of nitro compounds by transfer hydrogenation processes
[3–7] or using H2 over supported noble metal catalysts [1,2,8].
well-established as using catalytic reduction with molecular hydro-
gen because it is a clean production process, high atom economy,
cheap operations, easy product separation and can offer high
selectivities to the desired product with a significantly lower envi-
ronmental impact [9,10].
Many studies regarding this hydrogenation reaction have been
made both in gas [11–13] and in liquid phase [14–17], emerging
the last as the cleanest and the most sustainable alternative. Most
researches were focused on heterogeneous metal catalysts such as
Pd [18], Pt [19], Rh [20], Ir [21], Ni [17,22], Raney Ni [23], Au [24],
Ru [25] and poly-metallic catalysts [26,27].
Palladium catalysts are the more widely employed, but though
they show high activities for nitrobenzene hydrogenation, but
the selectivity to other nitroarenes, in particular for chloroni-
trobenzene, remains low because of the dehalogenation reaction
[28]. Platinum based catalysts have been also deeply investigated:
although they show interesting catalytic performances under mild
reaction conditions, now they are not suitable for an industrial
∗
Corresponding author.
E-mail address: preyes@udec.cl (P. Reyes).
0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.03.037

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C. Campos et al. / Catalysis Today 213 (2013) 93–100
Scheme 1. Proposed pathways for the reduction of nitroarenes suggested by Auer et al. [21].
expansion due to the high price of platinum [29,30]. Some attempts
were performed using ruthenium and gold catalysts which, despite
promising selectivities, are scarcely active [25,31].
In the present work, we studied ZrO2 (commercial oxide)
like a support of Ir catalyst in the hydrogenation of a series of
meta-substituted nitroarenes, because in previous works it has
shown that this support confers good stability to the active phase
when deposited on the surface either by impregnation of a precur-
sor of metal or metallic nanoparticles [14,39,40].
In other way, hydrogenation of nitrocompounds is a difficult
reaction and in the presence of substituents such as CH3 [41],
OCH3 [42], OH [15] among others, the reaction becomes more
complicated because certain substituents can eventually be hydro-
genated e.g. CHO, CN, CH CH2 [43] or hydrogenolysis of
carbon–halogen bond in chloronitrobenzenes.
The Hammett [44,45] equation evaluates the effect of a -meta
or -para substituent on reaction kinetics and can be used to predict
rate and equilibrium constants without prior experimental deter-
mination [46–48]. Furthermore, it is a useful tool for the elucidation
of reaction mechanisms. In this approach, the rate constants for the
substituted reactants (ki) can be related to that obtained for the
non-substituted (or reference) benzene derivate (ko) according to
Iridium catalysts which, despite promising selectivities in cat-
alytic hydrogenations, are thoroughly active [32–34], but are rarely
used in the hydrogenation of nitro arenes compounds, because
the hydrogenation catalyzed by iridium is accompanied by the
direct rout (hidroxilamine – nitrosobenzene derivates) or the indi-
rect rout (azoxy–azo–hydrazo derivates) as shown in Scheme 1. In
this case the catalytic property of iridium must be modified with
the second metal component and special additives (promoters or
inhibitors). In the hydrogenation of substituted nitrobenzenes can
be proceeded via intermediaries such hydroxylamines which are
highly unstable and can reach disproportionation with an increase
in temperature, and subsequent explosions [35]. The accumulation
of these compounds is usually diminished by using catalysts mod-
ified by Fe or V, or by using additives based on vanadium, or by
optimizing the reaction conditions [36]. Due to the large amount
of secondary product it is of great importance to find the most
direct possible route in order to avoid the formation of these com-
pounds.
In order to improve the catalytic performance, Auer et al. [21]
used supported iridium catalysts for the synthesis of toluenedi-
amine and the supports studied was Al2O3, TiO2, SiO2 or activated
carbon also they use promoters (Fe, Co, V, Ni and Cu). Bimetallic
Ru–Ir catalyst was reported by Xu et al. [37] for hydrogenation of p-
chloronitrobenzene. Synergism between Ru and Ir and the effect of
organic amine modifiers on the hydrogenation over Ir, Ru and Ru–Ir
catalyst supported on ␥-Al2O3 was investigated for improving the
selectivity to p-chloroaniline. Fan et al. found that the hydrous
zirconia supported iridium nanoparticles (Ir/ZrO2xH2O), prepared
by co-precipitation method, exhibited an excellent activity and
selectivity for the hydrogenation of haloaromatic nitro compounds
[38].
ꢀ
ꢁ
ki
log
= ꢁ × ꢀi
ko
The ꢁ term (reaction constant) is an estimation of the charge
development during the course of the reaction and provides a mea-
sure of the susceptibility to substituent electronic effects [49]. The
ꢀ term is Hammett substituent constant.
In this work, we have studied the selective hydrogenation
of
a series of meta-substituted nitroarenes on 1 wt.%Ir/ZrO2
catalyst where the catalytic response has been correlated to
characterization measurements. The use of Ir has been pointed
out in preliminary researches to interact with NO2 groups
providing the catalysts the unique ability to produce a fast
and selective controlled hydrogenation of the nitrocompounds
to the corresponding anilines, without accumulation of nitroso

C. Campos et al. / Catalysis Today 213 (2013) 93–100
95
and hydroxylamines intermediates and their potential exother-
mic decomposition. Furthermore, the catalytic reduction for a
series or meta-substituted nitroarenes has been investigated and
the catalytic data have been subjected to a Hammett treat-
ment.
2. Experimental
2.1. Reagents
Nitrobenzene (Fluka), absolute ethanol (Merck), ZrO2
(SBET = 96 m2/g,
chloronitrobenzene
m-nitrobenzaldehyde
Alfa
Aesar),
(Aldrich),
(Merck),
IrCl3xH2O
m-nitrotoluene
m-nitrostyrene
(Aldrich),
m-
(Merck),
(Aldrich),
m-nitrobenzonitrile (Fluka), m-nitroanisole (Merck) and m-
dinitrobenzene (Aldrich) and H2 by AGA, Chile.
2.2. Catalyst preparation
Fig. 1. TPR profiles of Ir-supported catalyst.
The catalyst was prepared by traditional wet impregnation [50]
using IrCl3xH2O as metal precursor. The appropriate amount of
support ZrO2 is placed in a round bottom flask together with
50 mL of water. The solution containing the required amount of
the precursor, IrCl3xH2O, needed to obtain the desired metal load-
ing (1 wt.% loading) is also added to the support suspension. The
solid obtained by impregnation was calcined under air at 500 ◦C and
reduced at 500 ◦C under H2, both thermal treatments were carried
in situ.
3. Results and discussion
3.1. Catalysts characterization
Fig. 1 shows the TPR profiles of the studied catalyst. In the
first treatment, the catalyst shows three reduction peak (centred
at 360 K and 460 K) attributed to the reduction of iridium precur-
sor and elimination of chlorine from the surface of the catalyst,
in agreement with results found by Reyes and co-workers [51].
The second reduction profile exhibited only two reduction peak
at 360 K attributed to the reduction of highly dispersed iridium
species, appears a second peak at temperatures close to 460 K which
corresponds to the reduction of larger iridium oxide particle. With
these results we can assume that all the chlorine is removed in the
process of calcination and reduction.
Fig. 2 shows the nitrogen adsorption isotherms at 77 K on the
studied support. The isotherm corresponds to type IV in the BDDT
classifcation [52]. It displays a hysteresis loop indicative of transi-
tional cylindrical bottle pores, mainly in the range 4–10 nm being
the surface area of 96 m2/g.
2.3. Characterization
The characterization of the catalytic systems was conducted
using the several techniques. X-ray diffraction (XRD) was per-
formed on a Rigaku X-ray Geigerflex using a Ni filter and Cu
K ␣ radiation within 2–80◦ 2ꢂ range. N2 adsorption–desorption
isotherms were carried out in an ASAP 2010 Micromeitics appa-
ratus. The interaction of hydrogen with the iridium catalysts
was studied in temperature-programmed reduction experiments
(TPR) under continuous flow and atmospheric pressure (TPR/TPD
2900 Micromeritics system). HR-TEM was performed using a
Philips CM200 model high resolution electron microscope with
energy dispersive analyzer and digital camera coupled to
a
Fig. 3 shows the X-ray diffraction patterns of the prepared
Ir/ZrO2 catalyst. All the characteristic reflexions due to monoclinic
and tetragonal phases of the ZrO2 can be observed [14,53]. No
diffraction lines corresponding to Ir were detected indicative of
high speed TVIPS FastScan F-114 model of 1024 × 1024 pixels
and 12 bits. Chemical analysis was performed by inductively
coupled plasma-mass spectrometry on an ICP-MS Spectrometer
PerkinElmer Elas 6000. Photoelectron spectra (XPS) were recorded
using an Escalab 200R spectrometer provided with a hemispher-
ical analyzer, operated in a constant pass energy mode and
Mg K␣ X-ray radiation (hꢃ 1253.6 eV) operated at 10 mA and
12 kV.
˚
metal particle sizes smaller than 50 A.
2.4. Hydrogenation reaction
Catalytic evaluation was carried out in liquid phase in a Parr
stainless steel batch reactor at 298 K using 50.0 mg of catalyst and
0.1 mol L−1 of the model molecule (nitrobenzene) and the others
substrates, under 20 bar hydrogen pressure. All the components
(catalyst, solvent and substrate) were fed to the reactor and stirred
at 700 rpm. Liquid samples were taken periodically from the
reactor and analyzed in a GC-MS Shimadzu GCMS-QP5050 with
a capillary column ␤-Dex 225 (Supelco). The compounds are:
m-chloronitrobenzene, m-nitrotoluene, m-nitrobenzaldehyde,
m-nitrostyrene, m-nitrobenzonitrile, m-nitroanisole and m-
dinitrobenzene and the effect on the activity and selectivity
in function of the effects conferred by the substituents was
studied.
Fig. 2. Nitrogen adsorption–desorption isotherms at 77 K on ZrO2 support.

96
C. Campos et al. / Catalysis Today 213 (2013) 93–100
Fig. 3. XRD patterns of catalyst Ir/ZrO2.
Iridium particle size was evaluated by HR-TEM studies. Fig. 4
shows a representative micrograph of the prepared Ir/ZrO2 catalyst.
It can be seen that a narrow metal particle size distribution is having
an average particle size of 1.8 nm. These features are favorable for
the hydrogenation reaction, allowing more active sites to adsorb
the nitroarene and to dissociate the H2 molecule.
Fig. 5. XPS spectra of catalyst Ir/ZrO2.
XPS core-level spectra of the catalyst is shown in Fig. 5 and the
energy values are in Table 1. The peak corresponding to Ir4f7/2 has
been analyzed; two types of energies are found one correspond-
ing to Ir0 at 60.9 eV in larger proportion and the other at 62.1 eV
corresponding to Irı+. The presence of Irı+ is attributed to a super-
ficial oxidation due to the Ir cluster. In addition for Ir/ZrO2, the O1s
core level spectra indicate that the presence of two types of oxy-
only detected the corresponding aniline without the formation of
nitrosobenzene or hydroxylamine, undesired compounds due to
the explosion characteristics that they present.
For m-nitrostyrene hydrogenation, the formation of m-
ethylnitrobenzene [54] and the total hydrogenation product
m-ethylaniline [55] was detected, due to competition of hydro-
genation between the NO2 and CH CH2 group (see Scheme 2).
In this case the active phase showed a higher selectivity to
the desired product m-vynilaniline at conversion higher than 90%
(see Table 2), due to a kinetic compensation factor similar to
that reported in hydrogenation reaction of ␣-carbonyl compounds
[56–58].
gen species are present in these catalysts, assigned to Zr
O Zr and
surface oxygen groups interacting with Ir species on the support.
The observed Ir/Zr surface ratio are in good agreement, with XRD
and HR-TEM results.
3.2. Catalytic activity
Fig. 7 shows the distribution of products on time for the
hydrogenation of m-nitrostyrene. At the beginning the selectivity
towards the desired product is very low, prevailing the hydro-
genation of CH CH2 due to the activation that the NO2 group
provides to the polarization of the doble bond (see Scheme 3). Delo-
calization of positive charge in the benzene ring promotes the C2
electrophilicity and at the same time stabilized the NO2 group
disfavoring the hydrogenation and the formation of m-vynilaniline.
The kinetics parameters for this reaction are compiled in Table 3.
The pseudo first order rate constant can be calculated for the
different stages, taking into account that the nitroso and hydroxil-
amines intermediate reduction products were not detected such
Catalytic activity shows that the catalyst is active in the
hydrogenation of NB and more important in the chemoselec-
tive hydrogenation of substituted nitroarenes. All the curves were
pseudo first order with respect to the reactant as shown in Fig. 6(A)
and (B). The catalyst has different behavior dependent on the kind
of substituent groups in -meta position, withdrawing or donat-
ing electron density substituent in its ability to supply/withdraw
electrons to/from the reaction site. For donating substituent the
catalytic activity was lower than the nitrobenzene curve, due to the
stabilization of resonance and inductive effects to the NO2 group.
The hydrogenation reaction of m-nitrotoluene and m-nitroanisole
Fig. 4. HR-TEM image and size distribution for catalyst Ir/ZrO2.

C. Campos et al. / Catalysis Today 213 (2013) 93–100
97
Table 1
ICP-MS, metal particle size and binding energies for Ir4f7/2, Zr3d5/2, O1s and atomic surface ratio for reduced Ir-supported catalyst.
Catalyst
Ir/ZrO2
Ir (%)
0.91
dHR-TEM (nm)
Ir4f7/2 (eV)
Zr3d5/2(eV)
182.2
O1s (eV)
Ir/Zr Atomic
0.0058
Ir/Zr bulk
0.0070
1.8
60.9 (70)
62.1 (30)
530.0 (82)
531.9 (18)
Table 2
Yield, selectivity, rate constant and ꢀmeta parameters for nitroarenes hydrogenation
on 1%Ir/ZrO2 catalyst.
a
Substrate
Yied (%)
Selectivity (%)
kg (min−1 g−1
)
ꢀmeta
Nitrobenzene
m-Nitrotoluene
m-Nitroanisole
m-Nitrostyrene
m-Chloronitrobenzene
m-Nitrobenzonitrile
m-Dinitrobenzene
m-Nitrobenzaldehyde
100
97
84
93
99
–
100
100
52
100
100
100a
11
0.092
0.078
0.090
0.098
0.168
0.198
0.266
0.0008
–
−0.07
0.05
0.02
0.37
0.56
0.71
0.36
91
100**
29
**Data at 90 min of reaction after the hydrogenation of the second NO2 group.
a
Data extracted from Ref. [45].
Table 3
Kinetic parameters for m-nitrostyrene hydrogenation on 1%Ir/ZrO2 catalyst.
*kg
k1 (min−1 g−1
)
k2 (min−1 g−1
0.0364
)
k3 (min−1 g−1
0.246
)
0.098
0.0616
*kg = k1 + k2 and k3 = k3.1 + k3.2
.
deactivation that the NH2 group confers to the CH CH2 to obtain
m-ethylaniline assuming k3.1 ꢀ k3.2. (See Scheme 2).
Scheme 2. Diagram for 3-nitrostyrene’s hydrogenation.
For withdrawing substituents the behavior is completely
different; the chemoselective hydrogenation reaches higher val-
ues than NB hydrogenation. These groups do not stabilize the
charge density of the N O bonds of the NO2 group favoring
the hydrogenation as it is shown in Fig. 6(B). The follow-
ing activity sequence was established: m-dinitrobenzene > m-
nitrobenzonitrile > m-chloronitrobenzene > nitrobenzene. In the
case of m-dinitrobenzene the activity increases due to the sym-
metry plane that the molecule possesses, thus, both NO2 groups
as Scheme 2 shows. At 120 min m-ethylaniline product of total
hydrogenation is detected and the curves of m-vynilaniline and
m-ethylnitrobenzene reach a maximum at 300 min and at higher
times the production of m-vynilaniline is maintained and the con-
centration of m-ethylnitrobenzene decreases. This explain why
52% of selectivity at 420 min, due to the higher activation that
the CH2CH3 shows in the reduction of NO2 compared to the
Scheme 3. Resonant structures of m-nitrostyrene or m-nitrobenzaldehyde.

98
C. Campos et al. / Catalysis Today 213 (2013) 93–100
Fig. 8. Products distribution in m-nitrobenzaldehyde hydrogenation on 1%Ir/ZrO2
catalyst.
C
O bond is far more reducible than the N O bond, the products
detected were m-nitrosobenzaldehyde and m-aminobenzaldehyde
products derived from the hydrogenation of the NO2 and
m-(hydroxymethyl)nitrobenzene and m-(hydroxymethyl)aniline
coming from for the CHO group were detected (see Scheme 4).
Fig. 8 displays the distribution of products in the hydro-
genation of m-nitrobenzaldehyde. It shows a similar trend than
m-nitrostyrene counterpart. In spite of NO2 group is more elec-
trodrawing than CHO (see ꢀmeta values in Table 2) the stabilization
of resonant structures are more favored when the NO2 group
resonates with the benzene ring unlike the
C O group (see
Scheme 4), and therefore the hydrogenation of the carbonyl group
is easier. Thus, 3-nitrosobenzaldehyde until 300 min was detected.
In the reduction of NO2 it was found intermediates ( NO and
NHOH), indicative that the rate constants of the hydrogenation of
the NO2 and NO groups are lower than the reaction constant
in the hydrogenation of CHO group. This is a demonstration that
the hydrogenation of NO2 group is highly unfavorable when the
substituent in meta position is CHO.
Fig. 6. Nitroarenes hydrogenation over Ir/ZrO2 (A) donating substrates and (B) with-
drawing substrate. Reaction conditions: Nitroarene concentration: 0.10 mol L−1
PH2: 20 bar, stirring speed: 700 rpm.
,
can be hydrogenated. Over 70% of yield 1,3-diaminebenzene was
detected
The conversion shows values until 30% due to the molar rate
conditions substrate/active phase lower for the hydrogenation of
Selectivity (see Table 2) shows for m-nitrobenzenitrile and
m-chloronitrobenzene hydrogenation only the detection of the
corresponding anilines, whereas in the m-nitrobezaldehyde hydro-
genation the behavior is very different, the curve is presented
below NB, which is an exception due to withdrawing character-
istic. This conduct is attributed to the higher competition between
NO2 and CHO. The active phase presents a high polarizabil-
ity on the nanocrystal surface which promotes the hydrogenation
phase of heteroaromatic bonds. In this case the electronic nature of
C
O group [33,51,56]. The higher contribution to the pseudo rate
constant (in the interval of time studied) comes from the hydro-
genation of the carbonyl group.
The dependence of the nature of the meta-substituent on the
reaction rate was studied applying the Hammett correlation (see
Fig. 9). In this approach, the rate constants for the substituted reac-
tants (ki) can be related to that obtained for the non-substituted (or
reference) benzene derivate (ko) according to Hammett equation.
Table 2 displays the rate constant determined for the different
substrates considering pseudo first order dependence in respect to
the reactant. Hammett correlation is given in Fig. 7 for the studied
catalyst. The ꢁ term is an estimation of the charge development
during the course of the reaction and provides a measure of the
susceptibility of the system to substituent electronic effects [12,26].
In a nucleophilic attack, the reaction rate is enhanced by electron-
withdrawing substituents and ꢁ > 0, while ꢁ values close to 0 are
indicative of a partially charged transition state. This equation was
initially conceived for homogeneous systems where good linear
correlations have been established for aromatic nitro-compounds
using heterogeneous catalyst [59,60].
We provide, in this report, the first example of its application
to the liquid phase hydrogenation of substituted meta-nitroarenes
using catalytic reduction with molecular hydrogen. The catalyst
generated positive reaction constants (ꢁ), consistent with a nucleo-
philic reaction mechanism and greater dependence of rate on
the electronic character of the substituent and that the electrons
Fig. 7. Products distribution in m-nitrostyrene hydrogenation on 1%Ir/ZrO2 catalyst.

C. Campos et al. / Catalysis Today 213 (2013) 93–100
99
Scheme 4. 3-Nitrobenzaldehyde hydrogenation.
Acknowledgments
The authors thank to FONDECYT 1100259 and for financial sup-
port.
References
[1] R.S. Downing, P.J. Kunkeler, H.v. Bekkum, Catalysis Today 37 (1997) 121–136.
[2] K. Nomura, Journal of Molecular Catalysis A: Chemical 130 (1998) 1–28.
[3] S.M. Auer, J.-D. Grunwaldt, R.A. Köppel, A. Baiker, Journal of Molecular Catalysis
A: Chemical 139 (1999) 305–313.
[4] S. Farhadi, F. Siadatnasab, Journal of Molecular Catalysis A: Chemical 339 (2011)
108–116.
[5] A.S. Kulkarni, R.V. Jayaram, Journal of Molecular Catalysis A: Chemical 223
(2004) 107–110.
[6] M. Kumarraja, K. Pitchumani, Applied Catalysis A 265 (2004) 135–139.
[7] H.S. Wilkinson, G.J. Tanoury, S.A. Wald, C.H. Senanayake, Tetrahedron Letters
41 (2001) 167–170.
[8] S. Radl, A. Koynov, G. Tryggvason, J.G. Khinast, Chemical Engineering Science
63 (2008) 3279–3291.
[9] F.T. Zangeneh, S. Sahebdelfar, M.T. Ravanchi, Journal of Natural Gas Chemistry
20 (2011) 219–231.
[10] H.-U. Blaser, M. Studer, Applied Catalysis A: General 189 (1999) 191–204.
[11] F. Cárdenas-Lizana, S. Gómez-Queroa, C.J. Baddeley, M.A. Keane, Applied Catal-
ysis A 387 (2010) 155–165.
Fig. 9. Hammett plot for the selective NO2 group reduction of meta-substituted
nitroarenes over Ir/ZrO2 at 25 ◦C.
[12] F. Cárdenas-Lizana, Z.M.d. Pedro, S. Gómez-Quero, M.A. Keane, Journal of
Molecular Catalysis A: Chemical 326 (2010) 48–54.
[13] P. Sangeetha, P. Seetharamulu, K. Shanthi, S. Narayanan, K.S. Rama Rao, Journal
of Molecular Catalysis A: Chemical 273 (2007) 244–249.
[14] S. Gomez, C. Torres, J.L.G. Fierro, C.R. Apesteguia, P. Reyes, Journal of the Chilean
Chemical Society 57 (2012) 1194–1198.
[15] M.A. Harrad, B. Boualy, L.E. Firdoussi, A. Mehdi, C. Santi, S. Giovagnoli, M. Noc-
chetti, M.A. Ali, Catalysis Communications 32 (2013) 92–100.
[16] K.J.A. Raj, M.G. Prakash, R. Mahalakshmy, T. Elangovan, B. Viswanathan, Chinese
Journal of Catalysis 33 (2012) 1299–1305.
move into the aromatic ring in the determining step reaction. This
effect promotes the hydrogenation of the NO2 in the presence
of withdrawing substrates, on the contrary with donating sub-
strates ( CH CH2, OCH3, CH3) the hydrogenation reaction is
not favored.
[17] J. Relvas, R. Andrade, F.G. Freire, F. Lemos, P. Araújo, M.J. Pinho, C.P. Nunes, F.R.
Ribeiro, Catalysis Today 133–135 (2008) 828–835.
[18] P. Sangeetha, K. Shanthi, K.S.R. Rao, B. Viswanathan, P. Selvam, Applied Catalysis
A 353 (2009) 160–165.
4. Conclusions
The catalytic system Ir/ZrO2 was active in the chemoselective
hydrogenation in liquid phase. The catalysts promoted the reduc-
tion of NO2 for a range of meta-substituted ( H, CHO, OCH3,
CH3, Cl, CN, CH CH2 and NO2) nitrobenzenes. The reac-
tion in the presence of electron-withdrawing ring substituents,
increases the rate as was demonstrated by the linear Hammett rela-
tionship. The high ꢀ value of the reaction (0.64) indicates a strong
dependence of the reaction rate on the electronic character of the
substituent and that the electrons move into the aromatic ring in
the step limiting eaction. The use of Ir as active phase allowed a good
control on the reaction paths and in the formation of secondary
products. The study of the electronic nature of aromatics substi-
tuted nitrobenzene’s with different characteristics promotes the
design of a large amount of catalysts for their used in fine chemistry.
[19] G.C. Torres, E.L. Jablonski, G.T. Baronetti, A.A. Castro, S.R. de Miguel, O.A. Scelza,
M.D. Blanco, M.A. Pena Jimenez, J.L.G. Fierro, Applied Catalysis A 161 (1997)
213–226.
[20] R.M. Magdalene, E.G. Leelamani, N.M. Nanje Gowda, Journal of Molecular Catal-
ysis A: Chemical. 223 (2004) 17–20.
[21] E. Auer, M. Gross, P. Panster, K. Takemoto, Catalysis Today 65 (2001) 31–37.
[22] H. Li, Q. Zhao, H. Li, Journal of Molecular Catalysis A: Chemical 285 (2008) 29–35.
[23] G.S. Samuelsen, V.L. Garik, G.B.L. Smith, Journal of the American Chemical Soci-
ety 72 (1950) 3872–3874.
[24] F. Cárdenas-Lizana, S. Gómez-Quero, N. Perret, M. Keane, Gold Bulletin 42
(2009) 124–132.
[25] A. Tijani, B. Coq, F.o. Figueras, Applied Catalysis 76 (1991) 255–266.
[26] F. Cárdenas-Lizana, D. Lamey, S. Gómez-Quero, N. Perret, L. Kiwi-Minsker, M.A.
Keane, Catalysis Today 173 (2011) 53–61.
[27] T. Joseph, K. Vijay Kumar, A.V. Ramaswamy, S.B. Halligudi, Catalysis Commu-
nications 8 (2007) 629–634.
[28] C. Su, X.-N. Li, Q.-F. Zhang, L. Ma, C.-S. Lu, F. Feng, Chinese Chemical Letters.
[29] R. Nie, J. Wang, L. Wang, Y. Qin, P. Chen, Z. Hou, Carbon 50 (2012) 586–596.

100
C. Campos et al. / Catalysis Today 213 (2013) 93–100
[30] B. Sreedhar, D.K. Devi, D. Yada, Catalysis Communications 12 (2011)
1009–1014.
[46] F. Cárdenas-Lizana, Dissertation submitted for the degree of Doctor of Philos-
ophy, Heriot-Watt University (2009).
[31] Y. Chen, W. Peng, S. Wang, F. Zhang, G. Zhang, X. Fan, Dyes and Pigments 95
(2012) 215–220.
[47] M. Lauwiner, P. Rys, J.r. Wissmann, Applied Catalysis A: General 172 (1998)
141–148.
[32] L. Zhu, G.-S. Hu, J.-Q. Lu, G.-Q. Xie, P. Chen, M.-F. Luo, Catalysis Communications
21 (2012) 5–8.
[48] P.S. Kumbhar, J. Sanchez-Valente, J.M.M. Millet, F.o. Figueras, Journal of Catal-
ysis 191 (2000) 467–473.
[33] T. Marzialetti, J.L.G. Fierro, P. Reyes, Catalysis Today 107–108 (2005) 235–243.
[34] P.B. Wells, A.G. Wilkinson, Topics in Catalysis 5 (1998) 39–50.
[35] F. Visentin, G. Puxty, O.M. Kut, K. Hungerbühler, Industrial & Engineering Chem-
istry Research 45 (2006) 4544–4553.
[36] L.M. Sikhwivhilu, N.J. Coville, B.M. Pulimaddi, J. Venkatreddy, V. Vishwanathan,
Catalysis Communications 8 (2007) 1999–2006.
[37] Q. Xu, L. Wang, J. Chen, X. Li, R. Li, Chinese Journal of Catalysis 28 (2007)
579–581.
[38] G.Y. Fan, L. Zhang, H.Y. Fu, M.L. Yuan, R.X. Li, H. Chen, X.J. Li, Catalysis Commu-
nications 11 (2010) 451–455.
[39] N.G. Willis, J. Guzman, Applied Catalysis A: General 339 (2008) 68–75.
[40] M.L. Kantam, R.S. Reddy, K. Srinivas, R. Chakravarti, B. Sreedhar, F. Figueras, C.
Venkat Reddy, Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101.
[41] P. Selvam, S.K. Mohapatra, S.U. Sonavane, R.V. Jayaram, Tetrahedron Letters 45
(2004) 2003–2007.
[42] A. Corma, C. González-Arellano, M. Iglesias, F. Sánchez, Applied Catalysis A 356
(2009) 99–102.
[43] S.-i. Fujita, H. Yoshida, K. Asai, X. Meng, M. Arai, Journal of Supercritical Fluids
60 (2011) 106–112.
[49] J. Shorter, Chemicke Listy 94 (2000) 210–214.
[50] J. Haber, J.H. Block, B. Delmon, Pure and Applied Chemistry 67 (1995)
1257–1306.
[51] T. Marzialetti, M. Oportus, D. Ruiz, J.L. García-Fierro, P. Reyes, Catalysis Today
133–135 (2008) 711–719.
[52] S.J. Gregg, K.S.W. Sing, Adsorption, Surface Area, & Porosity, Academic Press,
New York, 1967.
[53] G.-Y. Fan, Z.L. Fu, H.-Y. Yuan, M. Lin, R.-X.C. Li, H. Li, X. Jun, Catalysis Communi-
cations 11 (2010) 451–455.
[54] N.J. Creamer, K. Deplanche, T.J. Snape, I.P. Mikheenko, P. Yong, D. Samyahumbi,
J. Wood, K. Pollmann, S. Selenska-Pobell, L.E. Macaskie, Hydrometallurgy 94
(2008) 138–143.
[55] A. Corma, P. Serna, Nature Protocols 1 (2007) 2590–2595.
[56] C.H. Campos, M. Oportus, C. Torres, C. Urbina, J.L.G. Fierro, P. Reyes, Journal of
Molecular Catalysis A: Chemical 348 (2011) 30–41.
[57] E. Toukoniitty, P. Mäki-Arvela, J. Wärnå, T. Salmi, Catalysis Today 66 (2001)
411–417.
ˇ
[58] E. Toukoniitty, B. Sevcˇíková, P. Mäki-Arvela, J. Wärnå, T. Salmi, D.Y. Murzin,
Journal of Catalysis 213 (2003) 7–16.
[44] L.P. Hammett, Journal of the American Chemical Society 59 (1937) 96–103.
[45] H.H. Jaffé, Chemical Reviews 53 (1953) 191–261.
[59] B. Coq, A. Tijani, F. Figuéras, Journal of Molecular Catalysis 68 (1991) 331–345.
[60] P. Lu, N. Toshima, Bulletin of the Chemical Society of Japan 73 (2000).