Platinum- and palladium-containing carbon nanomaterials as catalysts for hydrogenation and hydrogenating amination

Article abstract of DOI:10.1007/s11172-011-0171-2

The catalytic activity of the carbon nanomaterials containing platinum and palladium in the model reactions of liquid-phase hydrogenation of nitrobenzene and hydrogenating amination was investigated. The catalytic systems based on nanodiamonds are more ef

Full text of DOI:10.1007/s11172-011-0171-2

Russian Chemical Bulletin, International Edition, Vol. 60, No. 6, pp. 1085—1089, June, 2011
1085
Platinumꢀ and palladiumꢀcontaining carbon nanomaterials as catalysts
for hydrogenation and hydrogenating amination
N. A. Magdalinova,a M. V. Klyuev,a T. G. Volkova,a N. N. Vershinin,b V. A. Bakaev,b O. N. Efimov,b and I. I. Korobovb
aIvanovo State University,
39 ul. Ermaka, 153025 Ivanovo, Russian Federation.
Fax: +7 (493 2) 32 4677. Eꢀmail: mn2408@mail.ru, klyuev@inbox.ru
bInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, Moscow Region, 142432 Chernogolovka, Russian Federation.
Fax: +7 (496) 517 8910. Eꢀmail: vernik@icp.ac.ru
The catalytic activity of the carbon nanomaterials containing platinum and palladium in
the model reactions of liquidꢀphase hydrogenation of nitrobenzene and hydrogenating aminaꢀ
tion was investigated. The catalytic systems based on nanodiamonds are more efficient than
platinumꢀcontaining fullerene black, multiꢀwalled nanotubes, and carbon nanofibers.
Key words: carbon nanomaterials, Pt and Pd catalysts, hydrogenation of nitrobenzene,
hydrogenating amination, catalytic activity.
70 °С. The oxidized CNM were filtered off, washed with bidisꢀ
tilled water to the neutral pH, and dried in air. Fullerene black
(FB) was used without preliminary preparation. The suspensions
of the oxidized CNM (the concentration of the CNM was
≤ 5 g L–1) for 20 min were treated by sonication. Then a solution
of H2PtCl6•xH2O (the platinum concentration was lower than
4 g L–1) was added to the CNM suspension with continuous
stirring in the presence of pyridine (0.5 mL) for 2—3 h, and the
mixture was refluxed for 0.5—1 h. For platinum reduction, forꢀ
mic acid (10 mL) and a solution of sodium carbonate (∼10 g in
50 mL of water) were added to the reaction mixture. The mixꢀ
ture was stored for 12 h, and the precipitate was filtered off,
washed with water to the neutral pH, and dried in air. The comꢀ
mercial catalyst Pt/C 20% EꢀTEK was used for comparison.
Nanodiamonds containing Pd or Pt were synthesized acꢀ
cording to the patented method.2 Detonation ND with the speꢀ
cific surface 307—314 m2 g–1 (the average size of the crystalline
diamond core of the ND particles was ∼4 nm) and the total
content of nonꢀcarbon admixtures ≤0.5 wt.%. The samples of
the Pdꢀ and Ptꢀcontaining ND were mixed with active carbon in
a weight ratio of 18 : 82 (the total weight was 1 g).
The average sizes of metal crystallites were calculated using
the Sherrer equation from the powder diffraction patterns of
the samples (ThermoARL diffractometer, CuꢀKα radiation,
λ = 1.5406 Å).
The composition of samples Pt/ND and Pd/ND was deterꢀ
mined by electron probe Xꢀray microanalysis, and the specific
surface was determined by the BET method. Electron probe
Xꢀray microanalysis was carried out on a VEGA TS 5130MM
fully PCꢀcontrolled scanning electron microscope (CamScan
MV2300)TP1PT) equipped with secondary electron (SE) and
backscatter electron (BSE) detectors of YAGꢀcrystals and an
energy dispersive Xꢀray (EDX) microanalyzer with an INCA
Energy2 semiconducting Si(Li) detector. The electron probe
Xꢀray microanalysis results were calculated using the INCA Enꢀ
Presently, studies of the synthesis of efficient catalysts
based on carbon nanomaterials (CNM) for many practiꢀ
cal applications are carried out in many countries. In orꢀ
der to prepare catalytic systems with the highly developed
catalytically active surface, it is necessary to obtain nanoꢀ
sized particles with an optimum porous structure. Thereꢀ
fore, the use of CNM as supports for Platinum Group
metals seems promising for the development of new cataꢀ
lytically active materials and catalytic systems. The cataꢀ
lytically active carbon nanomaterials containing platinum
and palladium clusters with the crystallites in the 1 to
1.2 nm range were produced over the past several years.1—18
We have shown19,20 for the first time that the use of detoꢀ
nation nanodiamonds (ND) as supports for the Platinum
Group metal makes it possible to obtain platinum clusters
with the characteristic dimensions: 5 nm in diameter and
the thickness from 0.4 to 1.2 nm. Such catalysts can find
use in systems of air purification from carbon monoxide.20
In this work, we consider the possibility to use the
CNMꢀbased catalysts in liquidꢀphase reactions of hydroꢀ
genation and hydrogenating amination. These reactions
play an important in pharmaceutical industry to manuꢀ
facture drugs of new generations using economical ecoꢀ
logically safe wasteless technologies.
Experimental
Synthesis of metalꢀcontaining carbon nanomaterials. For
the anchoring of Pt clusters, a suspension of multiꢀwalled nanoꢀ
tubes was preliminarily subjected to sonicationꢀassisted in an
H2SO4—HNO3 mixture at 40 °С for 4 h. Nanofibers were oxiꢀ
dized on prolong (24 h) heating in concentrated nitric acid at
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1060—1064, June, 2011.
1066ꢀ5285/11/6006ꢀ1085 © 2011 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
Magdalinova et al.
Scheme 1
ergy 200 program followed by the recalculation of the obtained
data by the TP3PT program package developed at the Institute
of Experimental Mineralogy, Russian Academy of Sciences. The
studies were carried out at an accelerating voltage of 20 kV. The
absorbed electron current on the standard cobalt sample was
516—565 pA and that on the studied sample was 540—620 pA.
The size of the electron probe on the sample surface was
157—200 nm. Admixtures of titanium were ≤0.3 wt.%, and those
of chlorine were ≤0.1%. The sol content of the initial nanoꢀ
diamond was ≤2 wt.%.
Procedure of studying the reactions of hydrogenation of nitroꢀ
benzene and hydrogenating amination of propanal with 4ꢀaminoꢀ
benzoic acid. Experiments for the hydrogenation of nitrobenzene
were performed with the catalyst (30 g) and NaBH4 (10 mg)
were placed in the reactor under the solvent (10 mL of ethanol)
layer and activated for 10 min. Nitrobenzene (1 mmol) was inꢀ
troduced in a flowing hydrogen (Т = 318 K, РH2 = 0.1 MPa).
After hydrogenation of one nitrobenzene portion conducted in
the presence of Pt/ND and Pd/ND, another portion was introꢀ
duced and the hydrogenation was carried out. All in all five
portions of nitrobenzene were used.
Experiments for the hydrogenating amination of propanal
with 4ꢀaminobenzoic acid (Scheme 1) were performed with the
catalyst (30 mg) and NaBH4 (10 mg) placed in the reactor under
the solvent layer (5 mL) and activated for 10 min. Then 4ꢀaminoꢀ
benzoic acid (2 mmol, 0.274 g) and propanal (2 mmol, 0.15 mL)
dissolved in ethanol (20 mL) were introduced, the reactor was
swept with hydrogen, and the process was carried out under the
same conditions. Under the studied conditions, the reactions
were zero order to the substrate and first order to the catalyst and
hydrogen.
The apparent reaction rate constant was measured using
the volumetric method from hydrogen absorption measureꢀ
ments. For comparison of the catalytic activity of the
studied objects, we used the turnover number of the catalyst
(TON/mol gꢀat.–1 min–1), which shows the number of moles of
the substrates transformed per 1 gꢀat. of metal per 1 min
rate was 1.60 0.02 L h–1, and the volume of the introduced
sample was 0.1—0.5 μL).
Results and Discussion
The specific surface area of the obtained samples of the
platinumꢀ and palladiumꢀcontaining CNM varies from 22
to 295 m2 g–1. The metal clusters of the catalyst supported
on ND have higher specific surface area than other
metal—carbon catalysts. When the metal is dispersed on
fullerene black and ND, the average size of Pt and Pd
particles is 4—5 nm. For Pt supporting on carbon nanoꢀ
fibers (Pt/NF) and multiꢀwalled carbon nanotubes
(Pt/MNT), the average metal particle size is independent
of the nature of CNM and the amount of supported Pt,
being 6—8 nm (Table 1). If the metal is supported on
carbon fibers 100—200 nm in diameter, the surface area of
the catalyst decreases slightly as the metal concentration
increases from 5 to 24.1 wt.% (see Table 1, entries 6 and 7).
However, in an analogous experiment with CNM, no reꢀ
duction of the surface is observed (see Table 1, entries 3
and 4). The fivefold increase in the diameter of the carbon
nanofibers increases the surface area of the catalyst by
a factor of two (see Table 1, entries 5 and 7).
It follows from the experimental data that the nature
of CNM depends on the catalyst surface area rather than
on the particle size of the supported metal. Since the size
of metallic crystallites does not increase with an increase
in the total metal content in the CNM, it can be assumed
that a considerable number of free functional groups caꢀ
pable of participating in catalysis, for example, favoring
the orientation of substrate molecules, remain on the CNM
surface.
An analysis of the obtained experimental data (see
Table 1) showed that all studied platinumꢀ and palladiꢀ
umꢀcontaining CNM exhibit catalytic activity in the both
model reactions. Under the same conditions, the rate of
aniline formation in the reaction of nitrobenzene (NB)
hydrogenation is substantially higher than the rate of forꢀ
mation of secondary amine (4ꢀ(propylamino)benzoic acid)
in the reaction of hydrogenating amination of propanal
with 4ꢀaminobenzoic acid (PABA) (see Table 1). This
regularity can be explained by either different mechanisms
of hydrogenation of the nitro group and >С=N– bond, or
TON = W/(VmolM),
where W is the hydrogen consumption rate, mL min–1; Vmol is
the molar volume, mL mol–1; and М is the amount of the metal,
gꢀat.
The hydrogenation products were analyzed using a chroꢀ
matograph with a flameꢀionization detector and a chromatoꢀ
graphic glass column (diameter 3 mm, length 2000 mm) packed
with Lucopren Gꢀ1000 (5%) on Chromaton NꢀAWꢀDMCS with
argon as a carrier gas (the evaporation temperature was 200 °С,
the temperature of the column was 230 °С, the carrier gas flow

Platinum and palladium carbon nanomaterials
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
1087
Table 1. Characteristics of the catalysts and the rates of amine formation in the reactions of hydrogenation
and hydrogenating amination
Entry
Catalyst
da/nm
Sb/m2 g–1
Wan•104
Wsec•106
mol L–1 s–1
1
2
3
4
5
6
7
8
Pt(20%)/C (ЕꢀТЕК)
Pt(10%)/FB
Pt(4.4%)/MNT
Pt(22.6%)/MNT
Pt(26.6%)/NF (d = 20—40 nm)
Pt(5%)/NF (d = 100—200 nm)
Pt(24.1%)/NF (d = 100—200 nm)
Pt(15%)/ND
Pt(20%)/ND
Pt(25%)/ND
Pd(6%)/ND
Pd(10%)/ND
2.5
4—5
6—8
6—8
6—8
6—8
6—8
5.0
5.0
5.0
5.0
5.0
181
280
22
24
42
3.80
0—
1.10
1.90
2.00
0—
3.20
3.09
2.97
2.96
2.82
5.16
7.96
37.5
16.0
7.5
24.8
16.3
10.4
22.6
4.7
116
97
295
288
277
284
267
263
9
9.1
10
11
12
13
18.0
11.0
18.0
17.0
Pd(15%)/ND
5.0
a Average size of the metal particles.
b Specific surface area of the catalyst surface.
by spatial factors: the nitro group is more accessible to
activated hydrogen than the >С=N– bond screened from
two sides.
reduced portions are presented in Fig. 1. It is seen that for
the hydrogenation of the second portion of nitrobenzene
the value of Wan is slightly higher than that for the hydroꢀ
genation of the first portion, and then Wan remains unꢀ
changed upon the introduction of the next portion of nitroꢀ
benzene, indicating stability of catalytic performance of
the studied samples.
Since the catalysts differ both in the metal content and
the surface area, we compared the turnover numbers for
the reaction (Table 2). It turned out that the activity of the
Ptꢀ and PdꢀCNM catalysts in nitrobenzene hydrogenaꢀ
tion is 4—25 times higher than in the hydrogenating aminaꢀ
tion of propanal with 4ꢀaminobenzoic acid. Taking into
The maximum rate for aniline formation (Wan) is charꢀ
acteristic of the catalysts Pd(10%)/ND and Pd(15%)/ND
(see Table 1, entries 12 and 13). In hydrogenating aminaꢀ
tion, the highest rate for secondary amine formation is
observed for the catalyst Pt/C (trade mark ЕꢀТЕК, see
Table 1).21 The fivefold increase in the content of Pt supꢀ
ported on the MNT results only in a threefold increase in
the rate of formation of 4ꢀ(propylamino)benzoic acid
(Wsec) and less than twofold increase in the rate for aniline
formation (see Table 1, entries 3 and 4). For Pt supporting
on the carbon nanofibers 100—200 nm in diameter, it was
found that as the metal content increases nearly fivefold
the formation of secondary amine increases by a factor
of 2.2. For the catalyst Pt/NF with 26.6% Pt supported on
the nanofibers with a diameter of 20—40 nm, the value of
Wsec is 1.4 times lower than the rate obtained on the cataꢀ
lyst Pt(24.1%)/NF with a diameter of the nanofibers of
100—200 nm. In the presence of the NDꢀbased catalysts,
with the increasing metal content, a 1.5—1.8 time inꢀ
crease was observed for the rate of aniline formation in the
case of Pd/ND (see Table 1, entries 11—13) and almost
no change in the rate in the case of Pt/ND was observed
(see Table 1, entries 8—10). The situation is opposite for
hydrogenating amination: the rate for secondary amine
formation for Pt/ND doubles with an increase in the supꢀ
ported metal content (see Table 1, entries 8—10), whereas
no direct dependence is observed for Pd/ND (see Table 1,
entries 11–13).
Wan•104/mol–1 L–1 s–1
1
2
3
4
5
6
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
1
2
3
4
5
N
Fig. 1. Rate of aniline formation in nitrobenzene hydrogenation
using various catalysts: Pd(6%)/ND (1), Pd(10%)/ND (2),
Pd(15%)/ND (3), Pt(15%)/ND (4), Pt(20%)/ND (5), and
Pt(25%)/ND (6); N is the number of portions of nitrobenzene.
The values of the rate for aniline formation in the reacꢀ
tion of nitrobenzene hydrogenation for five successively

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Magdalinova et al.
Table 2. Efficiency of the Ptꢀ and PdꢀCNM* in the hydrogenation of nitrobenzene and the
hydrogenating amination of propanal with 4ꢀaminobenzoic acid
Entry
TON/mol gꢀat.–1 min–1
TON/S/mol gꢀat.–1 min–1 m–2
NB
PABA
NB
PABA
1
2
3
4
5
6
7
8
11.2
0—
14.6
04.9
04.5
0—
07.7
42.2
32.2
25.7
55.5
59.9
65.0
1.8
1.6
1.7
1.1
0.6
2.0
0.9
1.7
2.5
3.9
5.4
5.2
3.3
2.1
0—
22.1
6.8
3.6
0—
0.3
0.2
2.6
1.5
0.5
0.6
0.3
1.1
1.6
2.6
3.5
3.6
2.3
2.6
26.5
20.7
17.2
36.2
41.5
45.5
9
10
11
12
13
* The characteristics of the CNMꢀbased catalysts used in various experiments are given
in Table 1.
account the surface area of the catalyst (see Table 2) does
not change this trend.
ferent weight contents of supported platinum and pallaꢀ
dium. It was shown that the Ptꢀ and PdꢀND in the studied
reactions have higher catalytic activity and efficiency than
other metalꢀcontaining CNM.
Among the catalysts based on multiꢀwalled nanotubes,
the catalyst Pt(4.4%)/MNT has the highest efficiency of
the use of platinum: it is almost 3 times more efficient
than the catalyst Pt(22.6%)/MNT in nitrobenzene hydroꢀ
genation and 1.5 times more efficient than this catalyst in
hydrogenating amination (see Table 2, entries 3 and 4).
A comparison of the catalysts based on carbon nanofibers
shows that a high efficiency is observed for Pt/NF with
a diameter of nanofibers of 100—200 nm and a smaller
weight content of platinum (see Table 2, cf. entries 5—7).
With an increase in the content of palladium supportꢀ
ed on ND the activity of the catalysts increases in nitroꢀ
benzene hydrogenation and decreases in hydrogenating
amination. The dependence is inverse for Pt/ND: with an
increase in the platinum content the efficiency of the catꢀ
alysts decreases for nitrobenzene hydrogenation and inꢀ
creases for hydrogenating amination. In this case, the
hydrogenation and hydrogenating amination in the presꢀ
ence of Pd/ND are 1.4—2.6 and 1.3—2.3 times faster than
those in the presence of Pt/ND.
The authors are grateful to B. P. Tarasov (Institute of
Problems of Chemical Physics, Russian Academy of Sciꢀ
ences) for kindly presented samples of platinumꢀcontainꢀ
ing nanomaterials based on multiꢀwalled carbon nanoꢀ
tubes, nanofibers, and fullerene black.
This work was carried out in the framework of the
program "Development of Basic Research in the Area of
Creation of Functional Nanomaterials at the Educational
Scientific Complex "Chemical Physics" of the Ivanovo
State University and the Institute of Problems of Chemical
Physics, Russian Academy of Sciences" (Project Nos
2.2.1.1.2820 and 2.2.1.1/11465).
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