Catalysts based on filamentous carbon in the hydrogenation of aromatic compounds

Article abstract of DOI:10.1134/S0023158411050181

In order to extend the area of application of the base catalytic system metal-filamentous carbon, the catalytic properties of Ni-filamentous carbon catalysts have been tested in the hydrogenation of aromatic compounds (benzene, benzyl cyanide, benzophenon

Full text of DOI:10.1134/S0023158411050181

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 5, pp. 770–773. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.A. Zaitseva, V.V. Goidin, V.V. Molchanov, V.V. Chesnokov, R.A. Buyanov, V.A. Utkin, 2011, published in Kinetika i Kataliz, 2011, Vol. 52, No. 5, pp. 787–791.
Catalysts Based on Filamentous Carbon in the Hydrogenation
of Aromatic Compounds
N. A. Zaitseva, V. V. Goidin, V. V. Molchanov†, V. V. Chesnokov, R. A. Buyanov, and V. A. Utkin
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
eꢀmail: zaitseva@catalysis.ru
Received November 13, 2010
Abstract—In order to extend the area of application of the base catalytic system metal–filamentous carbon,
the catalytic properties of Ni–filamentous carbon catalysts have been tested in the hydrogenation of aromatic
compounds (benzene, benzyl cyanide, benzophenone, and nitrobenzene). The selectivity of the catalysts
depends on the outer faceting of the active metal particles. The benzene ring is hydrogenated on the (111)
face of the metal nanoparticles, whereas the selective hydrogenation of functional groups in substituted aroꢀ
matic compounds occurs on the surface of active component nanoparticles in which the (111) face is blocked.
DOI: 10.1134/S0023158411050181
†
We observed an interesting feature of these catalysts
Over several decades, researchers have been expressꢀ
that could not be explained on the basis of available
ing persistent interest in carbon nanofilaments resultꢀ
published data: the benzene ring was hydrogenated on
ing from the catalytic decomposition of various hydroꢀ
none of the catalysts, while it was known that the
carbons on iron subgroup metals or on their alloys.
nickel catalysts, including those on carbon supports,
Such systems are usually studied and used in catalysis
are fairly active in these reactions. We also demonꢀ
as sorbents and supports. We were the first to study
strated that the catalytic systems examined here are
metal particles fixed on the ends of carbon filaments
rather efficient in the hydrogenation of various funcꢀ
(figure), for we concluded that they can serve as active
tional groups in substituted aromatic compounds [5]
components of catalysts for some reactions. As a
(Table 1).
result, radically new metal–filamentous carbon cataꢀ
The selective hydrogenations of substituents at the
benzene ring is of great practical significance because
their products are widely used in the chemical industry
for the synthesis of various organic compounds,
including dyes, drugs, fertilizers, pesticides, and many
other substances. In this work, we present the results of
our study of the prospects of use of the Ni–filament
carbon catalysts in industrially important reactions,
namely, the selective hydrogenation of benzyl cyanide,
benzophenone, and nitrobenzene. The selective
hydrogenation of benzyl cyanide yields important
intermediate products of fine organic synthesis and of
the synthesis of physiologically active substances (pheꢀ
nylethylamines). Benzhydrol and diphenylmethane,
which are used in pharmaceutics, are obtained from
benzophenone. The selective hydrogenation of
nitrobenzene to aniline is an intermediate step in the
production of more complex intermediates, dyes,
chemical additives for polymers, pharmaceuticals,
pesticides, etc. The selective hydrogenation of substitꢀ
uents at the benzene ring is carried out most frequently
on catalysts containing nickel, platinum, or palladium
[8–11]. As a rule, the hydrogenation of functional
groups is accompanied by the hydrogenation of the
benzene ring, which results in the loss of valuable
starting compounds and in difficulties in isolating the
target products. The eplacement of the platinum and
palladium catalysts with the Ni–filamentous carbon
lytic systems were discovered. These systems are active
in the reactions that are usually accelerated by metallic
catalysts. The properties of Ni–filamentous carbon
catalysts were studied most thoroughly in the selective
hydrogenation of dienic and acetylenic hydrocarbons
into olefins [1–7]. The selectivity of these catalysts
depends on what the outer faces of the metal particles
are. The outer face type can be controlled by varying
the catalytic hydrocarbon decomposition conditions
and the nature of the carbon source. Examination of
samples with differently faceted particles of the active
metal made it possible to evaluate the properties of
particular crystallographic faces. For example, it was
shown that the hydrogenation of dienic and acetylenic
hydrocarbons into olefins occurs on the nickel (110)
faces and that these hydrocarbons are totally hydrogeꢀ
nated to alkanes on the (111) and (100) faces.
The purpose of this work was to provide a deeper
insight into the new base metal–carbon catalytic sysꢀ
tem. With the aim of extending the area of application
of such systems, we studied the possibility of their use
in the selective hydrogenation of substituents at the
benzene ring. The study of the catalytic properties of
the Ni/C catalysts in the reductive dechlorination of
chlorobenzene [2] showed that this area is promising.
†
Deceased.
770

CATALYSTS BASED ON FILAMENTOUS CARBON
771
(110)
(100)
(110)
(110)
(100)
(110)
400
Å
(а)
(110)
(110)
400
Å
(b)
Micrographs of the Ni–carbon catalysts with C/Ni = (a) 1.5 and (b) 10.
system reduces the cost of the process and enhances its
selectivity. In addition, the method proposed for the
synthesis of metal–carbon catalysts is environmenꢀ
tally friendly, since its use is not accompanied by the
formation of wastewater or harmful gas emissions.
Table 1. Hydrogenation of functional groups in the substiꢀ
tuted aromatic compounds on the 6.4% Ni/C catalyst based
on filamentous carbon [5]
Starting
compound
Product yield,
mol %
Target product
We assumed that the crystallographic features of
active metal nanoparticles located at the ends of carꢀ
bon filaments can exert a substantial effect on the
selectivity of hydrogenation of aromatic compounds.
We believe that the catalysts in which the surface of
paraꢀBenzoquinone Hydroquinone
90
100
74
Nitrobenzene
Benzamide
Aniline
Benzylamine
KINETICS AND CATALYSIS Vol. 52
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2011

772
ZAITSEVA et al.
active metal nanoparticles has no (111) faces are the of a 10% solution of benzyl cyanide, a 2% solution of
most promising for the selective hydrogenation of subꢀ benzophenone, and a 10% solution of nitrobenzene in
stituents at the benzene ring.
isopropyl alcohol was carried out at pressures of 50,
70, and 50 atm and temperatures of 100, 100, and
120 С, respectively. The hydrogenation time was 4.5,
6, and 5 h, respectively. The reaction products were
analyzed by gas chromatography coupled with mass
spectrometry (GCꢀMS) on a Saturnꢀ200 system.
°
EXPERIMENTAL
Catalysts were synthesized in the Laboratory of
Dehydrogenation of the Boreskov Institute of Catalyꢀ
sis (Siberian Branch, Russian Academy of Sciences)
by the catalytic decomposition of hydrocarbons
according to a standard procedure [1, 5, 6].
RESULTS AND DISCUSSION
According to the data obtained, cyclohexane is the
single product of benzene hydrogenation. The results
of testing of the nickel–filamentous carbon catalyst in
this reaction are given in Table 2.
According to GCꢀMS data, the products of benzyl
cyanide hydrogenation on the 30% Ni/C catalyst at
20% substrate conversion contain the starting comꢀ
Benzene was hydrogenated in a flow reactor. The
testing conditions were as follows: the flow rate of benꢀ
zene at room temperature was 2 g/h, the flow rate of
the benzene–hydrogen vapor mixture fed into the
reactor was 6 l/h, the reaction temperature was 100 or
200 С, and the composition of the catalyst was 41.3%
Ni/C. The reaction products were analyzed chroꢀ
matographically using alumina as the adsorbent.
°
pounds and secondary amines: diꢀ(
β
ꢀphenylꢀ
The catalytic properties of the Ni/C samples conꢀ ethyl)amine and
β
ꢀphenylethylꢀ ꢀaminoꢀ
α
βꢀphenylꢀ
taining 7 to 30% Ni were tested in benzyl cyanide, ethylamine in a 9 : 1 ratio. To obtain primary amines
benzophenone, and nitrobenzene hydrogenation in a by nitrile hydrogenation, the reaction should be carꢀ
static reactor at an elevated hydrogen pressure. In all ried out at a low pressure in an acidic solvent [12, 13].
cases, 0.8 g of the catalyst was placed in an autoclave No products of benzene ring hydrogenation were
equipped with a magnetic stirrer. The hydrogenation observed under our experimental conditions.
CH2
CH2
CH2 CH NH
NH2
CH2 C N
Benzyl cyanide
+H
+H
2
2
βꢀ
Phenylethylamine
CH2
+
CH2
NH2
CH2 CH NH
CH2
NH CH CH2
NH2
ꢀ ꢀaminoꢀ ꢀphenylethylamine
CH2
β
ꢀ
Phenylethyl
α
β
–NH
3
CH2
CH2
CH2
N CH CH2
NH CH2
CH2
CH2
Diꢀ(
+H
2
βꢀphenylethyl)amine
Along with the target product (benzhydrol, 78% 28.3 wt % Ni at 83.1% substrate conversion. The prodꢀ
yield), diphenylmethane (5%) resulted from benꢀ uct of benzene ring hydrogenation (cyclohexylbenꢀ
zophenone hydrogenation on the catalyst containing zene) was present only in trace amounts.
O
C
OH
CH
+
CH2
Benzophenone
Benzhydrol
Diphenylmethane
KINETICS AND CATALYSIS Vol. 52
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2011

CATALYSTS BASED ON FILAMENTOUS CARBON
773
Table 2. Catalytic properties of 41.3% Ni/C in benzene hyꢀ
Aniline was the only product of nitrobenzene
hydrogenation on the 7% Ni/C catalyst. Under the
above conditions, the reaction occurred with 100%
conversion.
drogenation
Reaction
temperature, C6H12 selectivity, %
°C
Conversion, %
NO2
NH2
+H
100
200
100
100
32
42
2
Nitrobenzene
Aniline
As was mentioned above, the selectivity of the
metal–filamentous carbon catalysts in the selective
hydrogenation of unsaturated hydrocarbons is deterꢀ
mined by the types of crystallographic faces on the surꢀ
face of metal particles. The (111) face is the most
active, and the total hydrogenation of dienic and acetꢀ
ylenic hydrocarbons into alkanes occur on it. The set
of crystallographic faces on the surface of metal nanoꢀ
particles can be controlled by varying the catalyst
preparation conditions and the nature of the carbon
source [2–4]. We assumed that the nature of the crysꢀ
tallographic faces of the active component accessible
to reacting molecules and the size of the metal partiꢀ
cles have an effect on the selectivity of the catalyst in
the hydrogenation of substituents at the benzene ring
as well. For benzene ring activation, it is necessary that
the size of the active metal particles and the geometry
of the crystallographic faces on their surface correꢀ
spond to the benzene ring parameters. Our experiꢀ
mental results confirmed this assumption. For examꢀ
ple, the samples in which the (111) face of the nanomꢀ
eterꢀsized particles of the active component was
blocked exhibited no activity in benzene hydrogenaꢀ
tion. In our opinion, this is due to the fact that the benꢀ
zene molecule is activated just on these faces, because
the sizes and geometric structure of the benzene ring
match well with those of the (111) face of the nickel
nanoparticles. The micrographs of two samples are
shown in the figure.
The above assumption is also confirmed by the fact
that nickel alloys with other metals, for example, copꢀ
per are inactive in benzene hydrogenation. In this
case, nickel atoms are diluted with an inactive or lowꢀ
active component and even the (111) face has no sites
whose configuration could ensure activation of benꢀ
zene molecules. Magnesium intermetallide hydrides
are also inactive in this reaction, while other unsaturated
compounds are hydrogenated on them even at room
temperature [14]. This is explained by the specific crystal
structure of these compounds: their surface also has no
areas resembling the structure of the (111) face. Thereꢀ
fore, among the hydrogenation catalysts based on filaꢀ
mentous carbon, the nickel catalysts are the most promꢀ
ising for the selective hydrogenation of substituents in the
benzene ring, because the surface of their active metal
nanoparticles contains no (111) faces.
Thus, we have discovered a new promising area of
application of the metal–carbon catalysts based on filꢀ
amentous carbon, namely, the selective hydrogenation
of substituents in the benzene ring. Such catalysts can
be useful in several processes of fine organic synthesis.
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2011