Chemoselective hydrogenation of halonitroaromatics over γ-Fe 2O3-supported platinum nanoparticles: The role of the support on their catalytic activity and selectivity

Article abstract of DOI:10.1016/j.molcata.2012.10.007

Solvated platinum atoms, obtained by metal vapour synthesis (MVS), were conveniently used to prepare γ-iron oxide and γ-alumina supported Pt catalysts containing small metal nanoparticles of controlled size, ranging 0.5-3.0 nm in diameter (HR-TEM). The γ-Fe₂O₃- supported Pt system showed higher catalytic activity and selectivity than those of a similarly prepared γ-Al₂O₃-supported system in the selective hydrogenation reactions of p- and o-chloronitrobenzene to the corresponding haloanilines, in mild reaction conditions (25°C, 0.1 MPa hydrogen pressure) (p-chloronitrobenzene: specific activity (SA) = 59.5 min ^-1, Selectivity (Sel.) = 99.9%; o-chloronitrobenzene: SA = 42.8 min^-1, Sel. = 99.2%). The Pt/γ-Fe₂O₃ system also showed high catalytic efficiency (Sel. > 98%, at 100% of conversion) in the selective hydrogenations of m-chloro-, p- and o-bromo- and p- and o-iodonitrobenzenes. XPS structural studies performed on a pristine Pt/γ-Fe₂O₃ sample as well as on a sample recovered after the reaction, indicate that the catalytic process did not induce permanent modification in the chemical and/or electronic structure of the catalyst according with the high reusability of the system.

Full text of DOI:10.1016/j.molcata.2012.10.007

Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Chemoselective hydrogenation of halonitroaromatics over ␥-Fe O -supported
2
3
platinum nanoparticles: The role of the support on their catalytic activity and
selectivity
a,∗
b
c
c
Claudio Evangelisti , Laura Antonella Aronica , Maria Botavina , Gianmario Martra ,
d
d
Chiara Battocchio , Giovanni Polzonetti
CNR, Institute of Molecular Science and Technologies (CNR-ISTM), Via G. Fantoli 16/15, 20138 Milano, Italy
Department of Chemistry and Industrial Chemistry, Via Risorgimento 35, 56126 Pisa, Italy
Department of Chemistry IFM & NIS Interdipartimental Centre of Excellence, Via P. Giuria 7, 10125 Torino, Italy
Department of Physics, INSTM e CISDiC, University of Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
a
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Solvated platinum atoms, obtained by metal vapour synthesis (MVS), were conveniently used to prepare
Received 27 August 2012
Received in revised form 8 October 2012
Accepted 9 October 2012
␥-iron oxide and ␥-alumina supported Pt catalysts containing small metal nanoparticles of controlled
size, ranging 0.5–3.0 nm in diameter (HR-TEM). The ␥-Fe2O3-supported Pt system showed higher cat-
alytic activity and selectivity than those of a similarly prepared ␥-Al2O3-supported system in the
selective hydrogenation reactions of p- and o-chloronitrobenzene to the corresponding haloanilines,
Available online 23 October 2012
◦
in mild reaction conditions (25 C, 0.1 MPa hydrogen pressure) (p-chloronitrobenzene: specific activity
Keywords:
Platinum catalyst
Iron oxide
Hydrogenation
Halonitrobenzenes
Metal vapour synthesis
−
1
−
1
(
SA) = 59.5 min , Selectivity (Sel.) = 99.9%; o-chloronitrobenzene: SA = 42.8 min , Sel. = 99.2%). The Pt/␥-
Fe2O3 system also showed high catalytic efficiency (Sel. > 98%, at 100% of conversion) in the selective
hydrogenations of m-chloro-, p- and o-bromo- and p- and o-iodonitrobenzenes. XPS structural studies
performed on a pristine Pt/␥-Fe2O3 sample as well as on a sample recovered after the reaction, indi-
cate that the catalytic process did not induce permanent modification in the chemical and/or electronic
structure of the catalyst according with the high reusability of the system.
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
such as Au [11,12] or Ag [13], which showed high selectivity but
low catalytic activity, were proposed and developed. Despite that,
Pt-based catalysts continue to receive a particular attention due
to their fast reaction rate and low yield of de-halogenation prod-
ucts (<20%) [14]. Their performances were shown to be strongly
related to different parameters including reaction conditions (tem-
perature, pressure, stirring rate, . . .) [15], the presence of specific
promoters or additives [16], the platinum particle size distri-
bution [3,17] or the kind of catalyst support [18–20]. Among
them metal/support interaction can have a great influence on the
electronic density of metal particles by charge transfer or polar-
ization by partially reducible supports, generating special active
sites at the metal–support boundary regions. Recently, it has been
reported that a Pt–iron oxide nanocomposite, prepared by co-
precipitation of iron hydroxide colloid and Pt colloid in ethylene
glycol, exhibits high selectivity (>99%) in the hydrogenation of o-
chloronitrobenzene and bromonitrobenzenes [21,22].
Aromatic haloamine derivatives are valuable intermediates
in the synthesis of pharmaceuticals, agrochemicals, perfumes
and dyes [1,2]. The catalytic hydrogenation of aromatic nitro-
compounds over supported metal catalysts provides a clean route
to the corresponding aromatic amines, with lower economical and
environmental impact than alternatives non-catalytic processes
[
3,4]. Nevertheless, the catalytic reduction of halogen-substituted
nitroaromatic compounds is often problematic because of the
extensive hydrogenolysis of carbon–halogen bond which affords
a mixture of haloaniline and de-halogenated aniline products [5].
De-halogenation reactions have been reported to occur also with
palladium [6], platinum [7], rhodium [8], nickel [9] and copper
chromite [10]. Recently, the application of new supported metals,
In order to get a deeper insight into the role of the support and
the influence of the preparative route on the catalytic activity and
selectivity of the catalyst we report here the preparation of new
∗ Corresponding author at: Istituto di Scienze e Tecnologie Molecolari (ISTM-
CNR), Via Fantoli, 16/15, 20138 Milano, Italy. Tel.: +39 02 50995632/23.
E-mail address: claudio.evangelisti@istm.cnr.it (C. Evangelisti).
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.10.007

C. Evangelisti et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
289
Pt system, obtained following the metal vapour synthesis (MVS)
procedure [23–25], containing small Pt nanoparticles deposited on
16-channel detector giving a total instrumental resolution of
1.0 eV as measured at the Ag 3d5/2 core level. Mg K␣ non-
monochromatised X-ray radiation (hꢁ = 1253.6 eV) was used for
acquiring core level spectra of all samples (C1s, Pt4f, O1s and Fe2p).
The spectra were energy referenced to the C1s signal of aliphatic C
atoms having a binding energy BE = 285.00 eV, due to surface con-
tamination, as expected for XPS measurements performed on solid
samples exposed to air. Atomic ratios were calculated from peak
intensities by using Scofield’s cross-section values and calculated
ꢂ factors [27]. Curve-fitting analysis of the C1s, Pt4f, O1s and Fe2p
spectra was performed using Voigt profiles as fitting functions, after
subtraction of a Shirley-type background [28].
commercially available ␥-Fe O3 support.
2
The catalytic activity and selectivity of the Pt/␥-Fe O3 in p- and
2
o-chlorobenzene hydrogenations, performed in mild reaction con-
ditions (298 K, 0.1 MPa H ), were compared with that of a similarly
2
prepared Pt/␥-Al O3 system, which was previously demonstrated
2
as a valuable catalyst in this reaction [26], as well as a commercial
Pt/␥-Al O catalyst. The high catalytic efficiency of the ␥-Fe O -
2
3
2
3
supported system was confirmed in the selective hydrogenation of
bromo- and iodonitrobenzene derivatives. The structural features
of the ␥-Fe O and ␥-Al O -supported systems were investigated
2
3
2
3
by transmission electron microscopy (TEM) analyses. Moreover, in
order to obtain more information on the electronic and chemical
2.2. Preparation of platinum catalysts
properties of the Pt/␥-Fe O3 system, X-ray photoelectron spec-
2
troscopy (XPS) studies on a pristine sample and on a recovered
sample after a catalytic test, were performed.
According to a previously reported preparation [25], Pt vapour
−2
generated at 10 Pa by resistive heating of a tungsten wire
surface coated with electrodeposited platinum (105 mg), was co-
condensed at liquid nitrogen temperature with mesitylene (60 mL)
in a glass reactor described elsewhere [23,24]. The reactor chamber
2
. Experimental
◦
was heated to the melting point of the solid matrix (−40 C), and
2.1. Materials and apparatus
the resulting yellow-brown solution (55 mL) was worked up under
argon atmosphere with the use of the standard Schlenk technique
All operations involving the MVS products were performed
under a dry argon atmosphere. Mesitylene was purified by
conventional methods, distilled and stored under argon.
◦
and kept at low temperature (−30/−40 C). The platinum content
of the mesitylene solvated platinum solution, measured by ICP-
OES, was 1.6 mg/mL. 10 mL of DVS were added to the Pt/mesitylene
1
,3-divinyl-1,1,3,3-tetramethyldisiloxane
nitrobenzene, 1-chloro-2-nitrobenzene, 1-chloro-3-nitrobenzene,
-bromo-4-nitrobenzene, 1-bromo-2-nitrobenzene, 1-iodo-2-
(DVS),
1-chloro-4-
solution and the resulting thermally stable solution was stirred at
◦
2
1
5 C for 15 min. The DVS-stabilized Pt/mesitylene solution (7.4 mL,
1
0 mg Pt) was added to a dispersion of ␥-Al O3 and ␥-Fe O3 (1 g),
2
2
nitrobenzene were supplied from Aldrich and used as received.
respectively, in mesitylene (20 mL). The mixture was stirred for
2 h at room temperature. The colourless mesitylene was removed
and the light-brown solid, containing 1 wt.% Pt, was washed with
Commercial ␥-Al O (Chimet product, type 49, surface area
2
3
1
2
1
(
10 m /g, mean particle diameter 31 ␮m), ␥-Fe O3 powder
Aldrich products, surface area 50–245 m /g, particles < 50 nm)
2
2
n-pentane and dried under reduced pressure.
was dried in a static oven before use.
Commercial platinum on ␥-Al O (1 wt.% of Pt, surface area
2
3
2
2.3. Catalytic hydrogenations
2
50 m /g) was an Aldrich product.
The amount of platinum in the solvated Pt atoms solutions
Hydrogenation of halonitrobenzene was carried out in a 50-mL
round-bottomed flask fitted a with magnetic stirring bar (stir-
was determined by Inductively Coupled Plasma-Optical Emission
Spectrometers (ICP-OES) with a Spectro-Genesis instrument, with
a software Smart Analyzer Vision. The metal-containing mesity-
lene solution (1 mL) was heated over a heating plate in a porcelain
crucible, in the presence of aqua regia (2 mL), six times. The solid
residue was dissolved in 0.5 M aqueous HCl, and the solution was
analyzed by ICP-OES spectrometer.
ring rate = 1250 rpm) and under atmospheric hydrogen pressure
◦
(
(
0.1 MPa) at 25 C. Prior to the reaction, 20 mg of Pt catalyst
containing 1 wt.% Pt, 0.001 mmol) was activated under hydro-
gen for 15 min, then 2.56 mmol of halonitrobenzene (404 mg for
1
3
1
1
-chloro-4-nitrobenzene, 1-chloro-2-nitrobenzene and 1-chloro-
-nitrobenzene; 517 mg for 1-bromo-4-nitrobenzene and of
-bromo-2-nitrobenzene; 637 mg for 1-iodo-2-nitrobenzene and
-iodo-4-nitrobenzene) in 10 mL of methanol was added to the
The GLC analyses were performed on a Perkin-Elmer Auto Sys-
tem gas chromatograph, equipped with a flame ionization detector
(
FID), using a SiO2 column (BP-1, 12 m × 0.3 mm, 0.25 ␮m) and
reaction system to start the reaction.
helium as carrier gas.
Reactants and products are identified by comparison of their
GLC retention times with those of authentic samples. The semi-
quantitative analysis of trace aniline (AN) in the reaction mixture
was conducted by comparing the AN peak area in GC with those of
standard solutions with ratios of AN to haloaniline (XAN) less than
High resolution transmission electron microscopy (HR-TEM)
images of the materials were obtained using a JEOL 3010-UHR with
an acceleration potential of 300 kV. To obtain a good dispersion and
avoid any contamination, lacey carbon Cu grids were briefly con-
tacted with the powders, resulting in the adhesion of some particles
to the sample holders by electrostatic interactions.
0
.1%. Where reported the Pt/␥-Fe O system was magnetically sep-
2 3
arated from the reaction mixture at the bottom of round-bottomed
flask, washed with methanol, and further reused by adding a new
amount of halonitrobenzene substrate and methanol as solvent.
Histograms of the particle size distribution were obtained by
considering at least 500 particles on the TEM images, and the mean
particle diameter (dm) was calculated as dm = ꢀd n /ꢀn , where n
i
i
i
i
was the number of particles of diameter d . The counting was car-
i
ried out on electron micrographs obtained starting from 300,000
magnification, where Pd particles well contrasted with respect to
the support were clearly detected. The graduation of the particle
size scale was 0.5 nm.
XPS analysis was performed in an instrument of our own
design and construction, consisting of a preparation and an analysis
UHV chamber, equipped with a 150 mm mean radius hemispher-
ical electron analyser with a four-elements lens system with a
3. Results and discussion
It has been recently reported that the addition of 1,3-divinyl-
1,1,3,3-tetramethyldisiloxane (DVS) ligand to mesitylene solvated
Pt atoms, obtained by MVS, is a suitable way to quench the growth
processes of Pt particle in solution making them stable at 25 C and
valuable starting materials for the deposition of Pt nanoparticles of
controlled size on solid supports [25]. Following that procedure,
◦

2
90
C. Evangelisti et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
Fig. 1. TEM images and histograms of the particle size distributions obtained for MVS-derived Pt/␥-Al2O3 (section A), Pt/␥-Fe2O3 (section B) and Pt/␥-Al2O3 commercial
sample (section C), original magnification: 30,000×.
nanostructured Pt systems deposited on ␥-Al O3 and ␥-Fe O ,
evaluation of the Pt particles size was carried out. In the case of
2
2
3
respectively, containing 1 wt.% of Pt, were prepared.
Pt/␥-Al O3 (Fig. 1, section A) a large part of the particles were
2
Representative TEM images of the Pt/␥-Al O3 and Pt/␥-Fe O3
monitored in the interval of 0.8–3.0 nm with a more abundant pop-
2
2
systems are given in Fig. 1. For obtained samples a statistical
ulation around 2 nm (dm = 1.9 ± 1.2 nm). The Pt particles resulted

C. Evangelisti et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
291
pair of spin–orbit components found at higher BE values (Pt4f7/2
BE = 72.66 eV) is related to oxidized Pt atoms, and, as suggested
by literature data, is indicative of Pt(OH)2 species at least on the
nanoparticles surface [31]. The semi-quantitative analysis indicates
that Pt(OH)2 species are nearly 16% of the total Pt amount.
As reported in Table 1, the measured XPS Fe2p signal shows
a single spin–orbit pair with the main Fe2p3/2 component at
7
11.60 eV BE, as expected for Fe O ; iron oxide stoichiometry is
2 3
also confirmed by the estimated Fe/Ooxide atomic ratio of about
/3. The O1s spectrum appears structured, and three main spectral
2
components can be detected by curve fitting [32]. The main con-
tribution at about 530 eV is related to iron oxide; the small peak at
about 532 eV is attributed to OH groups bonded to metals (Pt(OH)2)
as well as to OH groups of surface contaminants adsorbed on the
sample surface, as expected for XPS measurements performed on
solid samples exposed to air; the third component at nearly 534 eV
BE arises by physisorbed H O molecules. In conclusion, XPS analy-
sis results indicate that a weak interaction occurs between Pt atoms
2
Fig. 2. Pt4f spectra of MVS-derived Pt/␥-Fe2O3 system pristine and recovered after
the catalytic process.
and ␥-Fe O3 support, resulting in an electron-deficient state of the
2
Pt nanoparticles in the catalyst, due to an electron transfer from Pt
atoms to the iron oxide.
well separated, but located very close to each other. As concerns
Pt/␥-Fe O the obtained particle size distribution was very narrow
The results obtained in the hydrogenation of halonitroben-
2
3
as well (0.8–3.3 nm) (Fig. 1, section B) and small Pt particles were
well separated and well dispersed on the support surface with a
more abundant population also around 2 nm (± 1.2). It is neces-
sary to take into the consideration that the detection limit of the
TEM technique is around 1 nm and the aggregation phenomena of
sub-nanometric metal particles under the electron beam during
HR-TEM observation cannot be excluded as well. As a conse-
quence the real mean size of MVS Pt particles could be even
smaller.
zene compounds over the Pt/␥-Fe O3 system compared with the
2
analogous ␥-Al O -supportedsystem and a commercial Pt/␥-Al O
2
3
2
3
catalyst are summarized in Table 2. The reactions were performed
◦
under mild reaction conditions (25 C, 0.1 MPa hydrogen pressure)
using a molar ratio substrate/Pt = 2560.
The MVS-derived Pt/␥-Fe O3 and Pt/␥-Al O3 systems showed
2
2
considerably higher catalytic activity than commercial Pt/␥-Al O ,
2
3
having the same metal loading, in the hydrogenation of p- and o-
chloronitrobenzene (runs 1–6). The differences in catalytic activity
can be strictly related to the higher platinum surface area of MVS-
derived samples as evidenced from the particle size distributions
obtained from TEM analyses (Fig. 1).
On the other hand, the commercial Pt/␥-Al O3 sample showed
2
broader particle size distribution (2.0–9.0 nm) with a mean diam-
eter at 4.8 nm (± 3.0).
In Pt/␥-Al O and Pt/␥-Fe O catalysts (sections A and B of Fig. 1,
The Pt/␥-Fe O3 system showed the highest catalytic activity
2
3
2
3
2
respectively), the size of the metal particles was so small to prevent
the attainment at high magnification of a contrast high enough to
allow a clear observation of lattice fringes. Conversely, in the case
of the examined systems and comparable with other reported
Pt–iron oxide systems [21] in hydrogenation of p- and o-
−
1
−1
chloronitrobenzene (SA = 59.5 min , run 1, and SA = 42.8 min ,
of the commercial Pt–␥-Al O3 catalyst (C), which exhibited larger
run 4, respectively). This system showed also higher selectivity
2
metal particles, in some cases lattice fringes 0.23 nm apart, corre-
sponding to the (1 1 1) interplanar distance for Pt crystals with fcc
structure (File ASTM 4-0802).
than both ␥-Al O -supported systems leading top-chloroaniline as
2
3
unique product (>99.9%, run 1) in the hydrogenation of the cor-
responding nitro-compound and a very high selectivity (99.2%,
run 4) to o-chloroaniline in the hydrogenation reaction of o-
chloronitrobenzene. In any cases, as easily predictable, the increase
of steric hindrance (from p- to o-) determines a slight decrease of
reaction rate which in turn could be the cause of a small decrease
of selectivity [2,14].
X-ray photoelectron spectroscopy (XPS) results obtained from
studies on the Pt/␥-Fe O3 pristine system are collected and com-
2
pared in Fig. 2 and in Table 1.
The core level binding energy (BE), the full width at half-maxima
(
FWHM) and atomic ratio N(Pt )/N(Pttot) values were analyzed with
i
particular attention to the Pt4f signal components, which are of
major interest for the study of the nanostructured catalyst, and for
The MVS-derived Pt/␥-Al O3 system, whose containing Pt par-
2
ticle sizes was significantly smaller than those of the commercial
sample (see HR-TEM analyses), showed slightly lower selectivity
both in p-chloronitrobenzene (96.2%, run 2 vs. 97.3%, run 3) and o-
chlorobenzene (93.4%, run 6 vs. 96.0%, run 7) hydrogenations. These
results agree with previously reported studies on the role of Pt par-
ticle sizes in alumina-supported systems on their selectivity in of
p-chloronitrobenzene hydrogenation [18].
the assessment of the Pt/Fe O3 interaction. Pt4f is usually used as
2
reference signal for the XPS study of Pt atoms, since it has the high-
est photoemission cross-section among other Pt signals (i.e., the
highest signal intensity) [29,30].
The Pt4f spectrum of the system is reported at the top of Fig. 2; by
means of a curve-fitting analysis, each Pt4f spin–orbit component
of the experimental spectrum results from the combination of two
peaks as associated to two platinum atoms involved in different
chemical environments. The main Pt4f7/2 peak is found at 71.40 eV
BE and has been attributed to metallic platinum (Pt(0)) interacting
with ␥-Fe O oxide. In fact, the Pt4f7/2 BE value expected for bulk
The Pt/␥-Fe O3 system used in run 1 was magnetically recov-
2
ered from the reaction mixture and reused till to 5 catalytic
cycles showing no appreciable decline of its activity and selectivity
(Fig. 3).
XPS measurements of the Pt4f (Fig. 2, bottom), Fe2p and O1s
2
3
Pt metal on the basis of previous measurements and in agreement
with literature reports is 71.00 eV; as extensively discussed in [21],
the BE positive shift of about 0.4 eV observed in the Pt-supported
catalysts indicates that an electron transfer occurs from the Pt
particles to the iron oxide supports, leading to Pt nanoparticles
of an electron-deficient state in the heterogeneous catalysts. The
core levels (Fig. 2, bottom) performed on the recovered Pt/␥-Fe O3
2
system after run 1 do not show appreciable BE shifts neither
FWHM variation compared to the pristine sample (Fig. 2, top),
as shown in Table 1,thus indicating that the chemical and elec-
tronic structure of the catalyst were not modified by the catalytic
process.

2
92
C. Evangelisti et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
Table 1
BE, FWHM, qualitative and semi-quantitative analysis of Pt/␥-Fe2O3 system pristine and recovered after the catalytic process.
Signal
BE (eV)
FWHM (eV)
Group/chemical specie
Atomic ratio
Pti/Pttot
C1s
O1s
285.00
1.84
1.64
1.64
1.64
1.85
1.85
4.99
C C
Fe2O3
OH
529.80
532.22
533.49
Pt/␥-Fe2O3 (pristine)
H2O
7
7
1.29
2.66
Pt(0)
Pt(OH)2
Fe2O3
0.84
0.16
Pt4f7/2
Fe2p3/2
C1s
711.60
285.00
1.89
1.75
1.75
1.75
1.61
1.61
4.25
C C
Fe2O3 + PtO
OH
H2O
Pt(0)
530.28
O1s
531.99
533.49
Pt/␥-Fe2O3 (recovered)
7
7
1.41
2.67
0.72
0.28
Pt4f7/2
Pt(OH)2
Fe2O3
Fe2p3/2
711.36
Considering its good catalytic efficiency in the hydrogenation
a decrease in reaction rates occurred (runs 10 and 11,
of p- and o-chloronitrobenzene, the Pt/␥-Fe O3 system was also
respectively).
2
tested in the hydrogenations of m-chloro-, bromo- and iodo-
substituted nitrobenezenes (runs 8–11). The hydrogenation rates
of p- and o-bromonitrobenzene (runs 8 and 9, respectively) over
Pt/␥-Fe O system were higher than those of the correspond-
The selectivity achieved towards the aniline derivatives were
in any case very high (98.0–99.5%), that is higher than those of
previously reported catalytic systems [33] and in agreement with
the order of susceptibility to hydrogenolysis for aromatic halo-
gens: Cl < Br < I; due to the increase of atomic number as well as
2
3
ing chloro-derivatives while, with p- and o-iodonitrobenzene,
Table 2
Catalytic properties of supported Pt systems in hydrogenation of halonitrobenzenes.
NO2
NH2
NH2
Pt/Support
X
+ H2 (g)
X
+
+ HX
MeOH, 25 °C
X: Cl, Br, I
XAN
AN
Run
Substrate
Catalyst
Reaction timea (min)
Specific activity (SA)b (min−1
)
Selectivity (%)
XAN
AN
1
2
3
Pt/␥-Fe2O3
Pt/␥-Al2O3
Pt/␥-Al2O3 commercial
48
60
330
59.5
44.2
8.7
99.9
96.2
97.3
0
3.8
2.7
Cl
NO
2
4
Pt/␥-Fe2O3
60
42.8
99.2
0.8
NO
2
5
6
Pt/␥-Al2O3
Pt/␥-Al2O3 commercial
126
510
29.8
5.1
93.4
96.0
6.6
4.0
Cl
NO
2
Cl
Br
7
8
Pt/␥-Fe2O3
Pt/␥-Fe2O3
72
35
39.2
85.3
99.5
99.2
0.5
0.8
NO
2
NO
2
Br
9
Pt/␥-Fe2O3
Pt/␥-Fe2O3
45
64.2
8.25
98.6
98.8
1.4
1.2
I
NO2
1
0
320
NO
2
I
1
1
Pt/␥-Fe2O3
380
6.6
98.0
2.0
Reaction conditions: solvent = MeOH (10 mL), temperature = 25 ◦C, 20 mg of Pt catalyst (containing 1 wt.% Pt), 1 × 10−3 mmol), 2.56 mmol of halonitrobenzene.
a
Time at 100% conversion of halonitrobenzene.
Specific activity is calculated as (mol converted substrate)/(mol Pt × min)) at about 50% of conversion.
b

C. Evangelisti et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 288–293
293
Pt/␥-Fe O3 catalyst respect to the analogous sample supported on
2
␥
-Al O [34].
2 3
Moreover, the catalytic system can be magnetically recovered
from the reaction mixture and used for at least five catalytic
cycles without appreciable decline of its catalytic efficiency and,
as evidenced by XPS analyses, without permanent modification of
its chemical and/or electronic structure.
References
[
[
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[
[
[
[
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4
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1
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[
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Mesitylene solvated Pt atoms, obtained by metal vapour synthe-
◦
sis and stabilized at 25 C, provide a valuable precursor to prepare
highly active supported platinum catalysts. TEM analysis confirms
the efficiency of MVS method in the preparation of higly dispersed
supported platinum catalysts containing metal nanoparticles with
size controlled ranging 0.5–3.0 nm in diameter.
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[
metal particle size: indeed, the Pt/␥-Fe O3 system was signifi-
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[
[
cantly more active and selective than analogous ␥-Al O supported
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3
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Fe O system exhibited considerable selectivity to haloaniline
2
3
◦
products under mild reaction conditions (25 C, 0.1 MPa hydro-
gen pressure), leading to obtain p-chloroaniline as unique product
in the hydrogenation of the corresponding p-chloronitrobenzene
and very high selectivities (≥98%) with bromo- and iodobenzene
derivatives.
[
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2
3
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