Hydrogenation of unsaturated compounds in the presence of palladium-containing modified carbon nanofibers

Article abstract of DOI:10.1134/S1070363213050071

Palladium-containing carboxylated carbon nanofibers were studied as catalysts for hydrogenation of double bond >C=C< in olefins, unsaturated alcohols, and acids, as well as for hydrogenation of nitroarenes. The developed catalyst is 7 times more efficient than the industrial analog (Pd/C).

Full text of DOI:10.1134/S1070363213050071

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 5, pp. 928–931. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © N.N. Osipov, M.V. Klyuev, 2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 5, pp. 791–794.
Hydrogenation of Unsaturated Compounds in the Presence
of Palladium-Containing Modified Carbon Nanofibers
N. N. Osipov and M. V. Klyuev
Ivanovo State University, ul. Ermaka 39, Ivanovo, 153025 Russia
e-mail: nicolay-00@yandex.ru
Received April 19, 2012
Abstract―Palladium-containing carboxylated carbon nanofibers were studied as catalysts for hydrogenation
of double bond >C=C< in olefins, unsaturated alcohols, and acids, as well as for hydrogenation of nitroarenes.
The developed catalyst is 7 times more efficient than the industrial analog (Pd/C).
DOI: 10.1134/S1070363213050071
Development and the reduced cost of production of
carbon nanomaterials allows extention of their range of
use. New opportunities of application of carbon
nanomaterials may be opened by modifying their
surface with various functional groups [1, 2]. For
example, the modified carbon nanomaterials can attach
on their surface the transition metals, and the obtained
material can be used as the catalysts for organic
synthesis [3–6]. In this work we investigated the use of
palladium-containing carboxylated carbon nanofibers
as a catalyst for the liquid-phase hydrogenation of
double bond >C=C< in olefins, unsaturated alcohols
and acids, as well as for nitroarenes hydrogenation.
presence of carboxy groups [7, 8], whereas in the
spectrum of the initial sample this peak is not present.
In the Raman spectra (Fig. 2) there is an increase in
the intensity of the D and G modes at 1362 and
–1
1
584 cm , which indicates a violation of the hexagonal
symmetry of graphene caused by the appearance of a
covalent bond on the nanofibre sidewall [7, 8].
According to X-ray diffraction, the sample contains
the allotropic carbon which is common for the carbon
nanofibers (26.15 eV) (Fig. 3).
In the X-ray photoelectron spectrum C1s there is a
2
peak at 285 eV corresponding to the sp -hybridized
Carbon nanofibers were obtained by pyrolysis of
propane-butane mixture on a copper-nickel catalyst at
carbon, which is typical for the flat nets of graphite,
graphene and nanotubes [9], as well as the signal at
288 eV, indicating the presence of carboxy groups on
the surface of carbon nanofibers. This is also con-
firmed by the presence of peaks of O1s line at 532 and
534 eV. Thus, the formation of carboxy groups on the
surface of the carbon nanofibres was confirmed.
5
(
00°C. According to the scanning electron microscopy
Fig. 1), carbon nanofibers range in diameter from 40
to 500 nm and in length from 100 nm to 5 microns.
2
–1
The specific surface area of the material is 124 m g ,
and the content of the carbon nanofibers in it is
approximately 90%.
С1s
O1s
532, 534
Pd3d 5/2
335, 338
335, 338
335, 338
Cl1s
198
–
The functionalization of carbon nanofibers was
performed by treatment with concentrated sulfuric acid
at 70°C with vigorous stirring for 24 h after which the
material was filtered off, washed successively with
water, ethanol, and dried in air. The resulting material
was investigated by a complex of physicochemical
methods.
2
85, 288
285, 288
85, 288
526, 532, 534
526, 532, 534
2
–
Fixing palladium on the oxidized carbon nanofibers
was carried out by treating them in 1 N solution with
2
% solution of PdCl while stirring for 60 min at 20°C.
2
The IR spectra of the functionalized carbon nano-
fibers contain the signal at 1713 cm , confirming the
The material was then filtered off, washed successively
with water, ethanol, and dried in air. The presence of
–
1
9
28

HYDROGENATION OF UNSATURATED COMPOUNDS
a) (b)
929
(
4
0 μm
20 μm
(
c)
(d)
1
0 μm
6 μm
Fig. 1. Scanning electron microscopy image of the carbon nanofibers: (а) ×2950, (b) ×6300, (c) ×7100, and (d) ×21500.
2
+
0
2+
0
fixed palladium was confirmed by the appearance of a
small peak at 40 eV in the diffraction pattern (Fig. 3).
Amount (wt %) of palladium fixed was estimated by
XPS.
Total Pd content
Pd
Pd
Pd /Pd
1.15
1.55
1.48
1.38
0.83
0.95
0.85
0.72
0.53
0.53
1.79
1.60
As seen from the above data, the total amount of
the metal in the carbon nanofibers is about 1.5 wt %,
the palladium is fixed initially in the form of Pd(II)
(338 eV) and Pd(0) (335 eV), and their ratio is close to
1:1. Simultaneously, the sample contains chlorine as
indicated by the signal at 198 eV.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 5 2013

9
30
OSIPOV, KLYUEV
–
1
cm
–
1
cm
b
E , eV
Fig. 3. XRD pattern of palladium-containing carboxylated
carbon nanofibers.
Fig. 2. Raman spectra of the modified carbon nanofibers
1) and carbon nanofibers without treating with acid (2).
(
The obtained material was activated before using as
25 ml) was placed 40 mg of a catalyst (Pd/carbon
a hydrogenation catalyst. The material was placed into
a reactor, equipped with a stirrer and a jacket for
heating, under a layer of ethanol (25 ml) and treated
nanofibers) and NaBH (10 mg); the mixture was
4
stirred under a hydrogen atmosphere at 45°C for 10 min.
Then 1 mmol of substrate was added, and its hydro-
genation was carried out with molecular hydrogen at
45°C at the atmospheric pressure. According to GLC
analysis of the reaction mixture [3], the conversion
was complete. Byproducts were not detected. The
results are shown in the table. XPS analysis of the
catalyst samples after hydrogenation revealed that the
with 10 mg of NaBH in a hydrogen atmosphere at 45°C
4
for 60 min. It was then filtered off, washed suc-
cessively with water, ethanol and dried in air. The XPS
analysis of the obtained material at this stage indicates
that the Pd–Cl bonds are absent, since there is no
signal in the region of 198 eV. However, the total
content of Pd somewhat decreases (presumably due to
losses during the activation), and the ratio of Pd(II):Pd(0)
is 1.79, which can be explained by the palladium
oxidation in air (appearance of a peak at 529 eV on
O1s line corresponding to the Pd–О bond).
2
+
content of Pd decreases slightly, and the ratio of Pd
(II):Pd(0) becomes equal to 1.6. This can be explained
by loss of the palladium in the reaction, separation and
washing of the catalyst.
The rate of hydrogenation of 1-hexene is almost
3 times higher than that of cyclohexene (see the table).
This can be explained by the fact that the terminal
The hydrogenation reaction was carried out as
follows: into a reactor under a layer of solvent (ethanol,
a
Data on hydrogenation of organic compounds in the presence of palladium-containing carbon nanofibers (CNF)
–
5
–1 b
–1
–1
Substrate
Allyl alcohol
Cartalyst
Reaction rate 10 mol min
TN, mol g-at Pd min
Pd/CNF
Pd/CNF
Pd/CNF
Pd/CNF
Pd/CNF
Pd/C
20.0
17.0
18.0
6.5
35.5
30.0
32.0
12.0
30.0
4.0
Acrylic acid
Hexene-1
Cyclohexene
Nitrobenzene
Nitrobenzene
p-Nitrophenol
p-Nitrobenzoic acid
17.0
1.5
Pd/CNF
Pd/CNF
15.0
8.5
27.0
15.0
a
b
Conditions: Pd/CNF (40 mg), ethanol (25 ml), substrate (1 mmol), atmospheric pressure, 45°С. The error in the measurement of the
reaction rate was no more than 13%.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 5 2013

HYDROGENATION OF UNSATURATED COMPOUNDS
931
double bond is sterically more accessible than the
internal. The presence of functional groups in the case
of hydrogenation of acrylic acid and allyl alcohol does
not influence the reaction rate, and it is comparable
with the rate of hydrogenation of 1-hexene (see the
table), apparently due to the fact that in these cases we
are dealing with the reduction of the terminal bond
fluorescence microscopy and spectroscopy (Nano-
Laboratory Integra Spectra), and X-ray powder diffrac-
tometer DRON-1 using X-ray tube with a copper
anode. Surface analysis of the samples was performed
by X-ray photoelectron spectroscopy (XPS) on a LAS-
3000 instrument (Riber) equipped with a hemispherical
analyzer with retarding potential OPX-150. For
excitation of photoelectrons was used X-ray irradiation
>C=C<.
of an aluminum anode (AlK 1486.6 eV) with tube
a
It should be noted that the hydrogenation of
voltage of 12 kV and an emission current of 20 mA.
nitrobenzene takes place almost at the same rate as the
terminal double bond (see the table). This circum-
stance requires further studying because usually nitro
compounds are hydrogenated with lower rates than
olefins. Apparently, in the case of such catalysts
different mechanisms of activation of hydrogen and
hydrogenation are realized compared with the com-
monly used commercial catalyst Pd/C.
–
9
The vacuum in the chamber was 5×10 Torr. The
calibration of the photoelectron peaks was performed
by the carbon C1s line with the binding energy of
2
85 eV.
ACKNOWLEDGMENTS
The authors are grateful to V.E. Vaganov (Sci-
entific Education and Innovation Centre “Nano-
technologies and Nanomaterials”) and K.S. Khor’kov
(Stoletovs Vladimir State University) for the samples
of carbon nanomaterials and the registration of the
Raman spectra.
The rate of hydrogenation of the nitro group in the
molecule of nitrobenzene is almost two times higher
than that of p-nitrobenzoic acid. The rates of hydro-
genation of nitrobenzene and p-nitrophenol are vir-
tually similar (see the table). This effect can be ex-
plained by the different effect of carboxy and hydroxy
groups on the electron density in the substrate
molecules.
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(
turnover number, TN) on a Pd/C catalyst was below
by factors 11 and 7, respectively (see the table).
Thus, the carboxylated palladium-containing carbon
nanofibers are of interest as catalysts for liquid-phase
hydrogenation of organic compounds of different
structure.
EXPERIMENTAL
In the work the following instruments were used:
Perkin-Elmer Spectrum 100 Fourier spectrometer
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 5 2013