Selective hydrogenation of nitrocyclohexane to cyclohexanone oxime with H2 on decorated Pt nanoparticles

Article abstract of DOI:10.1016/j.jcat.2009.02.025

A Pt catalyst has been designed to convert nitrocyclohexane into cyclohexanone oxime under mild hydrogenation conditions (4 bar of H₂, 383 K, and solvent-free media). It has been found that the partial reduction of the nitro group to the oxime

Full text of DOI:10.1016/j.jcat.2009.02.025

Journal of Catalysis 263 (2009) 328–334
Contents lists available at ScienceDirect
Journal of Catalysis
www.elsevier.com/locate/jcat
Selective hydrogenation of nitrocyclohexane to cyclohexanone oxime with H2
on decorated Pt nanoparticles
Pedro Serna a, M. López-Haro b, J.J. Calvino b, Avelino Corma a,∗
a
Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Avda. de los Naranjos s/n, 46022 Valencia, Spain
Departamento Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Universidad de Cádiz, Campus Río San Pedro, Puerto Real, 11510 Cádiz, Spain
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A Pt catalyst has been designed to convert nitrocyclohexane into cyclohexanone oxime under mild
hydrogenation conditions (4 bar of H2, 383 K, and solvent-free media). It has been found that the partial
reduction of the nitro group to the oxime function is promoted by Pt nanoparticles decorated with TiOx
species, being cyclohexanone the main undesired by-product. A reaction scheme has been proposed that
explains the process and active sites involved with the formation of the different reaction products. Based
on that, a further chemical modification of the catalyst with sodium cations has allowed to increase the
selectivity to cyclohexanone oxime to ∼85% at 95% conversion. The final catalyst can be recycled and
TON values of, at least, 13,000 can be obtained.
Received 16 December 2008
Revised 17 February 2009
Accepted 20 February 2009
Available online 24 March 2009
Keywords:
Hydrogenation of nitrocycloalkanes
Synthesis of cyclohexanone oxime
Platinum catalysts
© 2009 Elsevier Inc. All rights reserved.
Decoration of metal nanoparticles
1. Introduction
tion of cyclohexanone oxime was reported by DuPont [13,14]. It
was based on the one step hydrogenation of nitrocyclohexane into
cyclohexanone oxime at 35 bar and 413 K with a supported Pd cat-
alyst in the presence of PbO salts. In this process, relatively high
pressures and environmentally unfriendly PbO salts were required
to produce moderated yields (∼70%) of cyclohexanone oxime. Nev-
ertheless, for carrying out this interesting process nitrocyclohex-
ane has to be produced. Recent publications [15,16] have taught
the possibility to nitrate cyclohexane under mild conditions (343–
356 K) giving up to 91% selectivity to nitrocyclohexane. The ad-
vances in nitration technology has made us to reconsider the direct
transformation of nitrocyclohexane into cyclohexanone oxime and
have designed an easy recyclable lead free (Pt–Na)/TiO2 solid cat-
alyst which works in a solvent free media under milder reaction
conditions (4 bar) than the DuPont process [13,14]. This objective
represents an important scientific challenge since the Pb additive,
which can give toxic by-products, seems to be responsible for the
low activity of the Pd catalysts (high reaction pressures required),
but at the same time is responsible for raising the catalyst selec-
tivity from less than 25% to ∼70%.
Nylon-6 has become an important reference in the industrial
production of polymers, and the demand has expanded in the last
years. ε-caprolactame, precursor of Nylon-6, is currently manufac-
tured using cyclohexanone as starting reactant, which is converted
into cyclohexanone oxime and finally rearranged to give the lactam
in a three step process [1,2]. Based on this approach, much effort
has been done on the study of Beckmann rearrangement reactions
of oximes to the corresponding lactams [3–8]. Though cyclohex-
anone can be obtained by hydrogenation of phenol, the preferred
industrial route involves the direct oxidation of cyclohexane. How-
ever, the aerobic oxidation of cyclohexane to cyclohexanone limits
the whole efficiency of the process owing to the low yields per
pass achieved (∼8%) using homogeneous cobalt catalysts [9] or
up to ∼10% with Co-HZSM-5 [10]. Furthermore, the need of hy-
droxylamine to produce cyclohexanone oxime introduces another
sensitive reaction step in the classical process, which can be im-
proved by in situ generation of hydroxylamine [11].
Alternative processes for the production of ε-caprolactame have
been searched and recently [12] a different route has been pro-
posed that involves the hydrogenation of nitrobenzene to cyclo-
hexylamine followed by controlled oxidation of the amine to pro-
duce the cyclohexanone oxime. This clever method becomes lim-
ited by the long reaction times required (10 days) and the yield
of oxime achieved (∼60%). An alternative method for the produc-
2. Experimental
2.1. Catalysts preparation
A commercial sample of 5% Pd on active charcoal was provided
by Sigma-Aldrich. 1.5% Au on TiO2 was synthesized by the World
Gold Council using a deposition–precipitation procedure [17]. On
the other hand, 0.2% Pt/C, 1% Pt/Al2O3, and 0.2% Pt/TiO2 catalysts
were prepared by the incipient wetness technique, using H2PtCl6
Corresponding author. Fax: +34 96 3877809.
E-mail address: acorma@itq.upv.es (A. Corma).
*
0021-9517/$ – see front matter © 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2009.02.025

P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
329
Table 1
Catalytic results in the hydrogenation of nitrocyclohexane using different metal-based catalysts.a
Treduction
(K)
Catalyst
(mg)
Time
(min)
%Conversion
(NCH)
%Selectivity
CHA
Catalysts
CHO
CHone
CHCHA
DCHA
CHCHone
673e
723
723
723
473
723
723
723
150
100
15
100
150
250
200
200
105
40
195
80
100
80
900
880
9
70
97
85
97
95
96
95
35.2
80.1
84.9
70.0
31.8
5.0
22.8
2.0
4.9
18.0
5.4
65
43.0
8.9
4.7
1.0
3.0
2.5
6.5
4.0
5.0
3.1
2.0
n.d
4.0
n.d
2.0
3.0
0.5
4.0
2.0
2.0
1.5
b
1.5% Au/TiO2
a
1% Pt/Al2O3
5% Pd/Cb
n.d
n.d
40.6
n.d
n.d.
n.d.
0.2% Pt/Cb
5.0
b
0.2% Pt/TiO2
0.2% Pt/TiO2
0.2% Pt/TiO2
0.2% Pt/TiO2
14.2
23.0
21.8
8.6
b
c
3.5
3.4
69.6
84.5
c,d
NCH—nitrocyclohexane; CH—cyclohexylamine; CHO—cyclohexanone oxime; CHone—cyclohexanone; CHCHA—cyclohexyl-cyclohexylidene amine; DCHA—dicyclohexylamine;
CHCHone—2-cyclohexylidene-cyclohexanone.
a
Reaction conditions: T = 393 K, PH = 10 bar; feed composition: 75% ethanol, 25% nitrocyclohexane (mol%).
2
b
T = 413 K; PH = 15 bar; feed composition: 75% ethanol, 25% nitrocyclohexane (mol%).
2
c
T = 383 K; PH = 4 bar; feed composition: 100% nitrocyclohexane (mol%).
2
d
Catalyst doped with 6000 ppm of Na.
e
Catalyst calcined at 373 K under flow air.
hexahydrate as Pt. As an example, 20 mL of an aqueous solution
containing 53.1 mg of H2PtCl6·6H2O were impregnated on 10 g of
TiO2 (Degussa, P-25) to prepare the 0.2 wt% Pt/TiO2 catalyst. After
a perfect mixing of the corresponding slurry, the sample was dried
at 373 K during 5 h.
All the catalysts, with the exception of the Au/TiO2 system,
were treated under H2 flow (50 mL/min) at a selected tempera-
ture before performing the catalytic tests (see Table 1).
The sodium containing titanium decorated Pt/TiO2 catalyst was
prepared by impregnating the 0.2% Pt/TiO2 sample reduced at
723 K with different amounts of Na (sodium acetate as pre-
cursor). As an example, to prepare 10 g of the material doped
with 6000 ppm of Na, 20 mL of an aqueous solution containing
214.1 mg of CH3COONa must be used. After homogenizing the re-
sulting gel, the material was dried at 373 K during 6 h before the
catalytic test.
source and an objective lens with Cs value of 0.5 mm. Operating
this microscope at 200 kV allows recording HREM images with a
point-to-point resolution of 0.19 nm. These images were digitally
recorded on a 1024 × 1024 CCD camera. HREM image analysis was
performed using routines implemented in the software plugins of
Digital Micrograph. High Angle Annular Dark Field Images (HAADF)
were obtained using an electron probe with a diameter of 0.5 nm
and diffraction camera length of 10 cm. For the HAADF detector
mounted on this microscope this would correspond to effective de-
tector radii of 60 mrad (inner radius) and 160 mrad (outer radius).
Under these conditions the image contrasts in the HAADF images
would allow detecting the presence of subnanometer-sized plat-
inum particles supported on titania.
To reveal subtle details of the surface composition of the Pt
nanoparticles in the Pt/TiO2 catalysts, nanoanalysis by STEM-EELS
has been performed. Electron Energy Loss spectra were acquired in
the so-called spectrum-line mode using a GIF2000 spectrometer.
For these experiments a fine, 0.5 nm diameter, electron probe was
scanned along predefined paths of the catalysts, starting at posi-
tions located on the supports, passing through the particle–support
interface, then bulk positions in the particle and particle surface
and ending in vacuum. At specific points of each path, separated at
a distance slightly larger than the probe size, i.e. 0.7 nm, Electron
Energy Loss spectra covering the range of energy losses character-
istic of the elements present in the support were collected (O-K
and Ti-L2,3 edges). Acquisition times in the range 3–5 s per spectra
and a dispersion value of 0.3 eV were used.
The simultaneous analysis of the collection of EELS spectra ob-
tained in this way and the HAADF signal allows establishing the
spatial distribution of Ti species in the catalysts and, more in par-
ticular, the presence of submonolayer TiOx species on the surface
of the metal particles, which could have eventually migrated dur-
ing the synthesis or activation of the catalysts.
Electron microscopy specimens were prepared by depositing
small amounts of the catalyst powders onto holey-carbon coated
3-mm Cu-grids. To avoid contamination problems, the grids were
dipped directly into the catalyst powders and excess sample re-
moved by gentle blowing.
2.2. Kinetic experiments
Catalytic experiments were performed in reinforced glass re-
actors equipped with temperature and pressure control. For each
reaction, 1 mL mixture of reactants and solvent, if required, was
placed into the reactor (2 mL capacity) together with an appro-
priate amount of catalyst. Nitrocyclohexane comes from Sigma-
Aldrich Company with purities above 96%. 1,3,5-trimethylbenzene
was always used as external standard for the determination of con-
versions and yields. Details on the composition of the feed and
amount of catalyst for the different experiments can be found in
Table 1. After sealing the reactor, air was purged by flushing twice
with 10 bar of hydrogen. Then, the autoclave was heated up to
the required temperature and finally it was pressurized with H2
at the selected set point. During the experiment, the pressure was
maintained constant and the stirring rate was fixed at 1000 rpm
(magnetic stirring). Aliquots (∼50 μL) were taken from the reactor
at different reaction times. The product composition was deter-
mined by means of gas chromatography, once the catalyst particles
were removed from the solution by centrifuging at 12,000 rpm.
The products were identified by GC-MS and also by comparison
with commercially pure products (Sigma-Aldrich Company).
For recycling experiments, the catalyst was recovered, washed
with ethanol, and dried at 373 K during 12 h. Only experiments
with mass balances >95% were considered.
3. Results and discussion
3.1. Partial hydrogenation of nitrocyclohexane to cyclohexanone oxime
on Pt and Pt decorated nanoparticles
2.3. TEM measurements
We have recently found that the adsorption and reactivity of
nitro compounds on metal catalysts is strongly dependent not only
on the nature of the metal [18], but also on the crystallite size
Electron Microscopy data were collected in a JEOL2010-FEG
TEM/STEM microscope, equipped with a Field Emission electron

330
P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
Fig. 1. HRTEM images of Pt/TiO2 samples treated at 723 K (a) and 473 K (b) under H2 flow. TiOx species can be observed decorating the surface of Pt particles when the
reduction process is carried out at 723 K, as also evidenced by a STEM-EELS analysis (c).
and the way the reactant interacts with the support [19,20]. More
specifically, it was reported that Au/TiO2 was able to transform
1-nitro-1-cyclohexene into cyclohexanone oxime with excellent se-
lectivity (∼90%) in the presence of H2 [18,21]. However, as far as
we know, there is not yet any feasible process to produce this
starting reactant at an industrial scale and it would be highly de-
sirable to develop an equivalent green and profitable route using a
more accessible substrate such as nitrocyclohexane. Unfortunately,
we have seen (Table 1) that Au/TiO2 is inactive when reacting ni-
trocyclohexane. Thus, when more active hydrogenation catalysts
such as Pt/Al2O3, Pt/C or Pd/C were used, very low selectivities
to cyclohexanone oxime were obtained, and the complete reduc-
tion of the nitro group to the corresponding amine was the main
reaction occurring (see Table 1).
It is known [19,20,22–27] that the activation of nitroaromat-
ics onto metallic nanoparticles strongly depends on the nature of
the support, the metal crystallite size, and the presence of other
additives, which become decisive for the final activity and selec-
tivity of the catalyst. Taking into account that an improvement in
the selective hydrogenation of nitrocyclohexane to cyclohexanone
oxime was observed when depositing PbO on Pd in the DuPont
process [13,14], we thought that TiOx decorated Pt could also be
used as a more active and selective catalyst for producing cy-
clohexanone oxime by hydrogenation of nitrocyclohexane, while
avoiding the use of lead.
the material at 723 K with H2. Thus, we have prepared Pt/TiO2
treated at two different temperatures (473 and 723 K) under H2
flow. The presence of TiOx moieties on the top of Pt crystals was
evidenced on the sample reduced at 723 K by means of HRTEM
measurements (see Fig. 1a). This fact was confirmed with a STEM-
EELS analysis (Fig. 1c), which shows that a partial coverage of the
active phase has been produced. On the contrary, Ti features were
completely absent on the Pt nanoparticles of the sample reduced
a 473 K, indicating that no decoration has occurred in this case
(Fig. 1b).
The catalytic reduction of nitrocyclohexane on the Pt/TiO2 cat-
alysts treated at low (473 K) and high (723 K) temperatures shows
that selectivity to cyclohexanone oxime increases from 5% to 65%
when the Pt particles are decorated with TiOx species (see Table 1),
indicating that the partial coverage of Pt nanoparticles strongly de-
creases the complete hydrogenation of the substrate to the amine
compound (cyclohexylamine). With this catalyst, and after opti-
mizing the reaction conditions, it was possible to reach the se-
lectivity levels of the DuPont process (70%) at high conversions
of the nitrocycloalkane, but working under much milder reaction
conditions, i.e. 4 instead of 35 bar of H2, in a solvent-free media,
and avoiding the use of unfriendly PbO salts. The resultant Pt/TiO2
−1
catalyst is recyclable (see Table 2) and gives a TOF ∼ 300 h
(molconverted molP−t1 h−1, calculated with respect to total Pt atoms
It is well known in the literature [28–32] that the surface of Pt
particles in Pt/TiO2 can be decorated with TiOx species by treating
in the sample) and TON > 13,000.

P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
331
Table 2
unique stable product, formed at high conversion levels (Fig. 3).
On the contrary, cyclohexanone oxime, cyclohexylamine, and cy-
clohexanone appear as primary unstable products, and cyclohexyl-
cyclohexylidene amine as secondary unstable products. Neverthe-
less it should be thought that, from a mechanistic point of view,
cyclohexylamine and cyclohexanone require several reaction steps
to be produced from nitrocyclohexane and they were expected
to appear as secondary products, unless the intermediates react
before desorbing from the catalyst surface. In fact, one could con-
sider that while cyclohexylamine could be produced by consec-
utive hydrogenation reactions [33,34] through cyclohexylhydroxy-
lamine as intermediate (see Scheme 2a), cyclohexanone could be
produced by hydrolysis of cyclohexanone oxime [35–38] with the
water formed during the first hydrogenation step (see Scheme 2b).
After this, and when the amine and ketone compounds are pro-
duced, the formation of cyclohexyl-cyclohexylidene amine, dicyclo-
hexylamine, and small traces of 2-cyclohexylidene could be easily
explained taking into account the sequence of reactions given in
Scheme 3.
When Pt nanoparticles were decorated by TiO2 species (cata-
lyst reduced at 723 K), a drastic decrease of the concentration of
cyclohexylamine (inhibition of the complete hydrogenation of ni-
trocyclohexane) can be observed, but important amounts of the
cyclic ketone are still produced (Table 1 and Fig. 4). The forma-
tion of larger amounts of cyclohexanone by using Pt/TiO2 (either
decorated or not) in comparison with catalysts based on Al2O3 or
C suggests that the presence of TiO2 promotes the hydrolysis of
cyclohexanone oxime. In fact, it is well known that this reaction
Catalytic results during the nitrocyclohexane hydrogenation (TON, TOF, and selectiv-
ity to the oxime at complete conversion of nitrocyclohexane) using the decorated
Pt/TiO2 after two consecutive recycles.
Experiment
Selectivityoxime
(%)
TOF
(h
Accumulated TON
(molconverted molPt)
−1
)
1st use
2nd use
3rd use
70
68
65
303
291
274
3328
7741
13289
3.2. Reaction scheme
Results from Table 1 and Scheme 1 shows that besides cyclo-
hexanone oxime (CHO), other products such as cyclohexylamine
(CHA), cyclohexanone (CHone), cyclohexyl-cyclohexylidene amine
(CHCHA), dicyclohexylamine (DCHA), and 2-cyclohexylidene-cyclo-
hexanone (CHCHone) are usual by-products of the nitrocyclohex-
ane hydrogenation. Results from Fig. 2 indicate that, when using
1% Pt/Al2O3 catalyst, cyclohexanone appears as a primary unsta-
ble product, while the shape of the curves for cyclohexanone
oxime (CHO), cyclohexylamine (CHA), dicyclohexylamine (DCHA),
and cyclohexyl-cyclohexylidene amine (CHCHA) indicates that they
are secondary unstable products, being cyclohexylamine the pre-
dominant. However, the relative proportion of the different prod-
ucts is not only a function of the level of conversion, but also
depends on the nature of the catalysts (Table 1). Then, while sam-
ples based on Al2O3 or C produce cyclohexylamine as the main
reaction product, large amounts of cyclohexanone and dicyclo-
hexylamine are observed with the undecorated Pt/TiO2 catalyst. In
this later case, it is possible to see that dicyclohexylamine is the
Fig. 3. Distribution of products as a function of the conversion level during the
hydrogenation of nitrocyclohexane using the undecorated 0.2% Pt/TiO2 catalyst (re-
duced at 473 K).
Fig. 2. Distribution of products as a function of the conversion level during the hy-
drogenation of nitrocyclohexane using the 1% Pt/Al2O3 catalyst.
Scheme 1. Principal reaction products detected during the hydrogenation of nitrocyclohexane with different Pt, Pd, and Au catalysts.

332
P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
when this reaction was carried out with the decorated Pt/TiO2 cat-
alyst, low conversion of the oxime is observed after 5 h, indicating
that this compound is stable against hydrolysis when in absence
of H2. Thus, we can conclude that the formation of cyclohex-
anone during the hydrogenation of nitrocyclohexane must occur
through a catalytic route other than the direct hydrolysis of cyclo-
hexanone oxime by water given in Scheme 2. To this respect, it has
been reported that cyclohexanone oxime can also be reduced with
H2 in the presence of certain metal-based catalysts, forming ei-
ther cyclohexylamine or cyclohexanone [42–44]. In this alternative
mechanism (see Scheme 4), cyclohexanone would be initially re-
duced to an unstable intermediate (cyclohexylimine), which could
be a further hydrogenated to give the amine, or hydrolyzed giv-
ing the cyclic ketone as reaction product. In our case, we believe
that the formation of large amounts of cyclohexylamine, and cyclo-
hexanone, as well as the formation of the corresponding conden-
sation products, observed when cyclohexanone oxime is reacted
with H2 in the presence of water and the decorated Pt/TiO2 cat-
alyst (see Fig. 5), will be in favor of the reaction scheme given in
Scheme 4. Furthermore, the fact that cyclohexylhydroxylamine has
not been detected in any experiment, clearly suggests that, in our
case, Scheme 4 can also explain the formation of cyclohexylamine,
better than the reaction route proposed in Scheme 2a.
Scheme 2. Potential reaction pathway to form cyclohexylamine and cyclohexanone
oxime during the hydrogenation of nitrocyclohexane.
may be catalyzed either by Brönsted or Lewis acid sites [35–37],
and TiO2 can support certainly introduce certain acid character
into the reaction media [39–41]. In order to check if the formation
of cyclohexanone is directly formed by hydrolysis of cyclohexane
oxime on decorated Pt/TiO2, cyclohexanone oxime was reacted,
in the presence of decorated Pt/TiO2 and stoichiometric amounts
of water, and in absence of H2. Then results in Fig. 5 show that
Taking into account the above discussion we can propose a gen-
eral reaction scheme (Scheme 5) that can explain the products
observed and the potential reaction intermediates.
Fig. 4. Distribution of products as a function of the conversion level during the hy-
drogenation of nitrocyclohexane using the decorated 0.2% Pt/TiO2 catalyst (reduced
at 723 K).
Fig. 5. Stability of cyclohexanone oxime in the presence of the decorated Pt/TiO2
catalyst, and water (molar ratio oxime/H2O = 1). No hydrolysis of the oxime is ob-
served in absence of H2.
Scheme 3. Formation of condensation by-products through binary reactions involving cyclohexylamine and cyclohexanone.

P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
333
Scheme 4. Reaction Scheme proposed by Rylander et al. for the catalytic hydrogena-
tion of cyclohexanone oxime with Nickel Raney Catalysts.
3.3. Improving the catalytic behavior of decorated Pt/TiO2 catalysts by
decreasing the formation of cyclohexanone
Fig. 6. Effect of Na content on the surface of decorated Pt/TiO2 catalysts for the
selective hydrogenation of nitrocyclohexane to cyclohexanone oxime.
The practical absence of cyclohexylamine when nitrocyclohex-
ane is reduced with the decorated Pt/TiO2 catalyst (see Table 1),
indicates that though cyclohexanone oxime can be further hydro-
genated through the route suggested in Scheme 4, this is strongly
inhibited in the presence of a nitro functionality. This fact is in
complete agreement with previous literature about the role of the
metal-TiO2 interphases for preferential activation of the NO2 group
in the presence of other chemical functions [19,25] owing to the
preferential adsorption of the nitro group. Thus, while TiO2 is re-
quired to decorate the Pt and in this way to control the hydro-
genation of nitrocyclohexane avoiding further reduction of cyclo-
hexanone oxime, TiO2 is responsible for the hydrolysis of cyclohex-
anone oxime leading to cyclohexanone. At this point, it becomes
then necessary to preserve the desired hydrogenation sites of the
titanium decorated Pt, while removing the acid sites of the sup-
port responsible for the formation of cyclohexanone. To do this,
we have doped the catalyst an alkali cation [45–48]. Then the dec-
orated Pt/TiO2 catalyst was impregnated with increasing amounts
of CH3COONa (from 1500 to 15,000 ppm Na) and the resultant
samples were tested for the hydrogenation of nitrocyclohexane.
Catalytic results in Fig. 6 show that, for the optimun Na content
(∼6000 ppm), selectivity to cyclohexanone oxime can be increased
from 69% (no Na doping) to 85% at high conversion levels. A fur-
decrease in the selectivity to cyclohexanone oxime. In other words,
it appears that when the Na content is too high, the efficiency of
the titanium decoration effect to promote the partial reduction of
the nitro group is partially lost. Thus, it can be speculated that the
doping method must be accurately controlled to reach an optimal
balance between a low number of acid Ti4+ species (to avoid hy-
drolysis reactions), and a sufficient number of Pt/Ti boundaries (to
avoid a complete hydrogenation of the nitro group). As a result of
the optimization process, the selectivity to cyclohexanone oxime
can be raised to ∼85%, improving the previous results reported
by DuPont with Pd/Pb catalyst, while working under greener and
much milder reaction conditions (and 4 bar of instead of 35 bar)
and in a solvent free media.
4. Conclusion
We have shown that it is possible to selectively reduce nitro-
cyclohexane to cyclohexanone oxime with a titanium decorated Pt
catalyst containing an optimized level of alkaline. In this catalyst
the TiOx decoration avoid the complete hydrogenation of nitrocy-
clohexane to cyclohexylamine, while the alkaline avoids the for-
mation of cyclohexanone by inhibiting the hydrolysis of the cyclo-
hexanone oxime intermediate. These results can give a new chance
+
ther increase in Na decreases the yield of cyclohexanone while
produces an increase in cyclohexylamine formation, with a final
Scheme 5. General reaction scheme during the hydrogenation of nitrocyclohexane with H2 using different metal-based catalytic systems.

334
P. Serna et al. / Journal of Catalysis 263 (2009) 328–334
to the DuPont process that was used at demonstration scale, but
which had to be operated at lower yields, harder reaction condi-
tions and a less environmentally friendly catalyst.
[20] M. Boronat, P. Concepción, A. Corma, S. González, F. Illas, P. Serna, J. Am. Chem.
Soc. 129 (2007) 16230.
[21] A. Corma, P. Serna, H. García, J. Am. Chem. Soc. 129 (2007) 6358.
[22] A. Corma, P. Serna, P. Concepción, J.J. Calvino, J. Am. Chem. Soc. 130 (2008)
8748.
[23] U. Siegrist, P. Baumeister, H.-U. Blaser, Chem. Ind. (Dekker) 75 (1998) 207.
[24] H. U Blaser, U. Siegrist, H. Steiner, M. Studer, in: R.A. Sheldon, H. van Bekkum
(Eds.), Fine Chemicals Through Heterogeneous Catalysis: Aromatic Nitro Com-
pounds, Wiley, New York, 2001, p. 389.
[25] B. Coq, A. Tijani, R. Dutartre, F. Figueras, J. Mol. Catal. 79 (1993) 253.
[26] B. Coq, A. Tijani, F. Figueras, J. Mol. Catal. 68 (1991) 331.
[27] B. Coq, A. Tijani, F. Figuéras, J. Mol. Catal. 71 (1992) 317.
[28] M. Englisch, A. Jentys, J.A. Lercher, J. Catal. 166 (1997) 25.
[29] A.K. Datye, D.S. Kalakkad, M.H. Yao, D.J. Smith, J. Catal. 155 (1995) 148.
[30] T.M. Salama, H. Hattori, H. Kita, K. Ebitani, T. Tanaka, J. Chem. Soc. Faraday
Trans. 89 (1993) 2067.
Acknowledgments
We thank the Spanish government (Project MAT 2006-14274-
C02-01) and PROMETEO Project of the Generalitat Valenciana for
financial support.
References
[1] H. Ichihashi, H. Sato, Appl. Catal. A Gen. 221 (2001) 359.
[2] G. Dahlhoff, J.P.M. Niederer, W.F. Hoelderich, Catal. Rev. Sci. Eng. 43 (2001) 381.
[3] H. Kajikuri, M. Kitamura, US Patent 5304643 (1994), to Suminomo Chemical
Co.
[4] L.X. Dai, R. Hayasaka, Y. Iwaki, K.A. Koyano, T. Tatsumi, Chem. Commun. (1996)
1071.
[31] M.A. Vannice, B. Sen, J. Catal. 115 (1989) 65.
[32] P. Claus, P.S. Schimpf, R. Schödel, P. Kraak, W. Mörke, D. Hönicke, Appl. Catal.
A 165 (1997) 429.
[33] A. Bose, C.R. Saha, J. Mol. Catal. 49 (1989) 271.
[34] S.M. Islam, C.R. Saha, J. Mol. Catal. A Chem. 212 (2004) 131.
[35] C. Ngamcharussrivichai, P. Wu, T. Tatsumi, J. Catal. 227 (2004) 448.
[36] M.A. Camblor, A. Corma, H. García, V. Semmer-Herlédan, S. Valencia, J. Catal.
177 (1998) 267.
[37] N.C. Marzianomaltese, L. Ronchin, C. Tortato, A. Vavasori, C. Badettia, J. Mol.
Catal. A Chem. 277 (2007) 221.
[38] K. You, L. Mao, D. Yin, P. Liu, H. Luo, Catal. Commun. 9 (2008) 1521.
[39] E. Farfan-Arribas, R.J. Madix, J. Phys. Chem. B 107 (2003) 3225.
[40] B. Bonelli, M. Cozzolino, R. Tesser, M. Di Serio, M. Piumetti, E. Garrone, E. San-
tacesaria, J. Catal. 246 (2007) 293.
[41] A.P. Kulkarni, D.S. Muggli, Appl. Catal. A Gen. 302 (2006) 274.
[42] D.P. Curran, J.F. Brill, D.M. Rakiewicz, J. Org. Chem. 49 (1984) 1654.
[43] E. Breitner, E. Roginski, P.N. Rylander, J. Chem. Soc. (1959) 2918.
[44] P.N. Rylander, Catalytic Hydrogenation in Organic Synthesis, Academic Press,
New York, 1979, p. 153.
[5] P. Botella, A. Corma, S. Iborra, J. Catal. 250 (2007) 161.
[6] H. Sato, K. Hirose, M. Kitamura, Y. Nakamura, Stud. Surf. Sci. Catal. 49 (1989)
1213.
[7] P.S. Singh, R. Bandopadhyay, S.G. Hegde, B.S. Rao, Appl. Catal. A Gen. 136 (1996)
249.
[8] S.F. Yin, F.Z. Zhang, B.Q. Xu, Chin, J. Catal. 23 (2002) 321.
[9] K. Takagi, T. Ishida, US Patent 3644526 (1972), to Suminomo Chemical Co.
[10] H.X. Yuan, Q.H. Xia, H.J. Zhan, X.H. Lu, K.X. Su, Appl. Catal. A Gen. 304 (2006)
178.
[11] M.A. Mantegazza (IT), M. Padovan, US Patent 5320819 (1994), to ENICHEM
ANIC SRL.
[12] S.K. Klitgaard, K. Egeblad, U.V. Mentzel, A.G. Popov, T. Jensen, E. Taarning, I.S.
Nielsen, C.H. Christensen, Green Chem. 10 (2008) 419.
[13] GB Patent 860340 (1961), to DuPont.
[14] GB Patent 857902 (1958), to DuPont.
[45] R. Hutter, T. Mallat, A. Peterhans, A. Baiker, J. Mol. Catal. A Chem. 138 (1999)
241.
[15] S. Sakaguchi, Y. Nishiwaki, T. Kitamura, Y. Ishii, Angew. Chem. Int. Ed. 40 (2001)
222.
[46] M.G. Clerici, P. Ingallina, J. Catal. 140 (1993) 71.
[16] K. Yamaguchi, S. Shinachi, N. Mizuno, Chem. Commun. (2004) 424.
[17] M. Haruta, Catal. Today 36 (1997) 153.
[18] A. Corma, P. Serna, Science 313 (2006) 332.
[19] A. Corma, P. Concepción, P. Serna, Angew. Chem. Int. Ed. 46 (2007) 7266.
[47] G.J. Hutchings, D.F. Lee, J. Chem. Soc. Ser. Chem. Commun. (1994) 1095.
[48] T. Sato, J. Dakka, R.A. Sheldon, J. Chem. Soc. Ser. Chem. Commun. (1994)
1887.