Nitrocyclohexane hydrogenation to cyclohexanone oxime over mesoporous carbon supported Pd catalyst

Article abstract of DOI:10.1016/j.catcom.2014.02.020

Mesoporous carbon materials (MC) were prepared by soft template, hard template and hydrothermal synthesis methods. And mesoporous carbon supported palladium catalysts were obtained from incipient impregnation method. The prepared samples were characterize

Full text of DOI:10.1016/j.catcom.2014.02.020

Catalysis Communications 50 (2014) 9–12
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Nitrocyclohexane hydrogenation to cyclohexanone oxime over
mesoporous carbon supported Pd catalyst
⁎
Yanhua Yan, Sihua Liu, Fang Hao, Pingle Liu , He'an Luo
College of Chemical Engineering, Xiangtan University, Xiangtan 411105, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 January 2014
Received in revised form 19 February 2014
Accepted 21 February 2014
Available online 28 February 2014
Mesoporous carbon materials (MC) were prepared by soft template, hard template and hydrothermal synthesis
methods. And mesoporous carbon supported palladium catalysts were obtained from incipient impregnation
method. The prepared samples were characterized by nitrogen adsorption–desorption, X-ray diffraction, transmis-
sion electron microscopy and hydrogen chemisorption. Palladium supported on mesoporous carbon prepared by
hard template method shows better catalytic performance, it gives the 82.2% selectivity to cyclohexanone oxime
at the nitrocyclohexane conversion of 99.4% under the mild reaction conditions of 0.5 MPa and 323 K.
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Nitrocyclohexane
Hydrogenation
Mesoporous carbon
Palladium supported catalyst
Cyclohexanone oxime
1. Introduction
an alternative promising method [10,11], especially cyclohexane
nitration process has made significant progress [12,13]. Serna et al.
Oximes are highly valuable organic intermediates because of their
wide application for polymer, perfumes and paint, and particularly
more attention has been given to the synthesis of cyclohexanone
oxime in view of its usage as the precursor for the production of
ε-caprolactam and Nylon-6. The current commercial production
method for cyclohexanone oxime is mainly based on the traditional
route that cyclohexane is oxidized to cyclohexanone through a very
low efficient process with per pass yield of 4–5% without catalyst or
8–10% catalyzed by cobalt catalyst [1,2], and then cyclohexanone
oxime is obtained by cyclohexanone–hydroxylamine or ammoximation
of cyclohexanone [3,4]. However, the above route is less desirable for
large scale production owing to its low atom economy, complex tech-
nology, serious environmental problems and equipment corrosion [5].
To overcome the above-mentioned disadvantages, there have been
many attempts to find novel and environmentally friendly methods for
the production of cyclohexanone oxime [6,7]. The ammoximation of
cyclohexanone to cyclohexanone oxime over TS-1 in an isopropanol-
based solvent system with high yield has improved atom economy
greatly. However, process optimization, reactor design and cata-
lyst improvement have been restricted due to non-depth re-
search of the reaction mechanism and kinetics behavior [8,9].
Nitrocyclohexane hydrogenation process developed by DuPont is
[14] have prepared a sodium decorated Pt/TiOx catalyst, which could re-
duce nitrocyclohexane to cyclohexanone oxime with the selectivity of
84.5% at 95.0% conversion under 4.0 MPa and 383 K. Shimizu et al.
[15] have developed a heterogeneous Au/Al2O3 catalyst, and the cata-
lyst with smaller size gold particles gives a high cyclohexanone oxime
yield under 0.6 MPa and 373 K. Liu et al. [16] have found that single
walled carbon nanotube (SWCNT) supported Pd is effective for the
reaction and it gives 97.7% conversion of nitrocyclohexane and 97.4%
selectivity toward cyclohexanone oxime for its mesoporous structure
with pore size range from 2 to 50 nm, while activated carbon (AC)
with microporous structure supported palladium only gives a cyclohex-
anone oxime yield of 64.1%. However, carbon nanotube especially
SWCNT is extremely difficult to prepare on large scale and is quite
expensive.
Mesoporous carbon has attracted rapidly growing attention and
has been intensively studied for its remarkable functional proper-
ties, which make it one of the most promising catalyst support
materials for heterogeneous catalytic reaction. The methods including
catalytic gasification, carbon aerogel through sol–gel process and tem-
plate method have been proposed to introduce mesopores in activated
carbon [17–19].
In this paper, mesoporous activated carbon was prepared and used
as support to obtain Pd/MC catalyst, and it presents better catalytic per-
formances in nitrocyclohexane hydrogenation to cyclohexanone oxime
than microporous activated carbon.
⁎
Corresponding author. Tel.: +86 731 58298005; fax: +86 731 58298172.
E-mail address: liupingle@xtu.edu.cn (P. Liu).
http://dx.doi.org/10.1016/j.catcom.2014.02.020
1566-7367/© 2014 Elsevier B.V. All rights reserved.

10
Y. Yan et al. / Catalysis Communications 50 (2014) 9–12
2. Experimental
2.1. Materials
Nitrocyclohexane (95 wt.%) was purchased from Tokyo Chemical
Industry Corporation Limited. Commercial activated coal carbon (ACC)
was purchased from Baoji Rock New Materials Corporation Limited.
PdCl2 and ethylenediamine were analytical grade and purchased from
Sinopharm Chemical Reagent Corporation Limited. H2 (99.9%) was
provided by Zhuzhou Diamond Gas Company.
2.2. Catalyst preparation
Mesoporous carbons prepared by soft template method [20] from
different raw materials are labeled as SMC-1 and SMC-2, mesoporous
carbons prepared by hard template method are marked as HMC-1 and
HMC-2 [21], and the sample prepared by triblock copolymer and phenolic
resin precursor via hydrothermal synthesis method is signed as HTMC
[22].
Fig. 1. N2 adsorption–desorption isotherms and BJH pore size distribution (inset) of
5% Pd/HMC-1, 5% Pd/SMC-1 and 5% Pd/ACC.
The catalysts are prepared as the following steps. MC and ACC were
pretreated in concentrated nitric acid (68 wt.%) overnight, and the
sample was filtrated and washed by distilled water, and then dried
in vacuum at 383 K for 10 h. Pd/MC catalyst was prepared by incipient
impregnation method. 0.14 g PdCl2 was dissolved into a solution of
1.1 g concentrated hydrochloric acid (38 wt.%) and 10 g ultrapure
water under ultrasonication for 5 min. Then the sodium hydroxide solu-
tion (10 wt.%) was dropped into the above solution to adjust the pH to
5–6. Afterwards, the pretreated support was impregnated into the
above prepared H2PdCl4 solution for 10 h at 298 K under magnetic stir-
ring, and then the mixture was dried at 383 K for 10 h under vacuum.
Finally, the sample was calcinated at 473 K for 4 h under 40 mL/min
of nitrogen flow and reduced at 523 K for 3 h under 40 mL/min of
hydrogen.
3. Results and discussions
3.1. Characterization of catalysts
Fig. 1 shows the nitrogen adsorption–desorption curves of Pd/HMC-
1, Pd/SMC-1 and Pd/ACC. The isotherm of Pd/ACC shows an adsorption
isotherm of type I according to the IUPAC classification and has a H4 hys-
teresis loop, representing capillary condensation of nitrogen within the
uniform slit-shaped microporous structure. Pd/HMC-1 shows an ad-
sorption isotherm of type IV with a H4 hysteresis loop, the volume
absorbed for nitrogen increase at relative pressure (p/p0) of approxi-
mately 0.4–0.8, which indicates capillary condensation of nitrogen
within the uniform mesoporous structure. Pd/SMC-1 shows a typical
type IV isotherm and has a H1 hysteresis loop, indicating the mesopo-
rous structures of the materials. It's known that bigger area of the hys-
teresis loop indicates more pores from the geometrical effect and
Kelvin equation, which is in good agreement with the pore volume in
Table 1 that Pd/SMC-1 has the largest volume. Meanwhile, higher rela-
tive pressure at the closure point of the hysteresis loops indicates bigger
pore diameter, which is also consistent with the result in Table 1 that
the pore sizes of Pd/HMC-1 and Pd/SMC-1 calculated from the desorp-
tion branch by the BJH model are respectively 3.4 and 4.4 nm. While
Pd/ACC shows a narrow pore size distribution with the average pore
size of 1.7 nm. The textural properties of the supports have a great effect
on their catalytic performance. The results indicate that mesoporous
carbon-supported palladium catalysts with suitable surface area and
volume show better catalytic performance.
2.3. Catalyst characterization
Specific surface area, pore volume and pore size distribution of the
samples were obtained from the nitrogen adsorption–desorption on a
Quantachrome NOVA-2200e automated gas sorption system. Powder
X-ray diffraction (XRD) patterns were determined under an Aolong
Y-2000 diffractometer using Cu Kα radiation (λ = 1.542 Å). The
tube voltage was 40 kV, the current was 30 mA, and the scan range
was 2θ = 5–90° with a scanning rate of 1°min−1. The microstructure
of the catalysts was observed by transmission electron microscopy
(TEM) on a Tecnai G220 ST electron microscope working under
200 kV. The instrumental magnification ranged from 2 × 104 to
10 × 106. The sample was deposited on a copper grid and coated with
a holey carbon film. Hydrogen chemisorption was measured on a
TP-5080 automated sorption system. The sample had been previously
reduced under the same conditions as the catalyst preparation and
the hydrogen chemisorption was performed at 323 K.
The TEM images of Pd/ACC, Pd/HMC-1 and Pd/HTMC are shown in
Fig. 2. The TEM micrographs of the catalysts show that palladium parti-
cles are well dispersed on the surface of the supports. Statistical results
indicate that palladium particles in Pd/ACC range from 2.9 to 11.4 nm.
Palladium particles in Pd/HTMC range from 4.5 to 11.1 nm, palladium
particles in Pd/HMC-1 range from 3.6 to 10.4 nm. We can find that
2.4. Typical procedures for the catalytic test
The catalytic process was performed in a 50 mL Teflon-lined
stainless-steel autoclave equipped with magnetic stirring. Briefly, 0.56
g nitrocyclohexane (95 wt.%), 5 mL ethylenediamine solvent and 0.1 g
catalyst were added into the autoclave. The reactor was sealed and the
hydrogen was used for replacing the air, then the autoclave was heated
to 323 K and pressurized to the required pressure under continuous stir-
ring. The catalysts were separated from the reaction solution by vacuum
filtration when the reaction was completed. The products were identi-
fied by GC–MS (SHIMADZU, QP2010 PLUS). The content of the products
was determined by GC (GC-14C, SHIMADZU) with a flame ionization
detector (FID) using dimethyl phthalate (DMP) as the internal standard.
Table 1
Textural properties of different catalysts.
Catalysts
Surface area
(m2g−1
Average pore
size (nm)
Pore volume
)
(cm3g−1
)
5% Pd/HMC-1
5% Pd/HMC-2
5% Pd/HTMC
5% Pd/ACC
5% Pd/SMC-1
5% Pd/SMC-2
421.63
649.24
4.30
456.23
1186.80
455.12
3.43
3.43
3.81
1.70
4.35
3.84
0.42
0.70
0.01
0.31
1.00
0.13

Y. Yan et al. / Catalysis Communications 50 (2014) 9–12
11
Fig. 2. TEM images of 5% Pd/ACC (a), 5% Pd/HMC-1 (b) and 5% Pd/HTMC (c).
Pd/HMC-1 (Fig. 2 (b)) presents lamellar structure and Pd/HTMC
presents nutty structure.
reason may be that the surface channel of the AAC is easier to be
blocked. And better dispersion of Pd particle and higher Pd surface
area on MC are in favor of producing cyclohexanone oxime. Moreover,
too high surface area or too small pore volume is unfavorable for cyclo-
hexanone oxime formation.
Furthermore, the effect of reaction temperature and pressure was
discussed. The results are shown in Figs. 4 and 5. Firstly, nitrocyclohexane
hydrogenation over 5% Pd/HMC-1 at different reaction temperatures was
carried out at 6 h and 0.3 MPa. It can be seen from Fig. 4 that a little higher
temperature can promote the selectivity to cyclohexanone oxime, but the
selectivity to cyclohexanone oxime starts to decrease if the temperature
is higher than 323 K. And Fig. 5 shows that the effect of the pressure on
the selectivity to cyclohexanone oxime has the similar tendency as reac-
tion temperature. The suitable pressure is about 0.5 MPa. Under the
optimum reaction conditions, 5% Pd/HMC-1 gives 82.2% selectivity to
cyclohexanone oxime at the nitrocyclohexane conversion of 99.4%.
Fig. 3 shows the XRD patterns of the prepared catalysts. The catalysts
exhibit characteristic diffraction peaks of carbon's crystalline plane
around 2θ = 26°, and the peaks at 2θ = 40 and 47° are ascribed to
the characteristic diffraction peak of palladium. Pd/HMC, Pd/HTMC
and Pd/ACC exhibit three strong and characteristic peaks at 2θ = 32,
45, and 57° which are corresponding to sodium chloride. There are
very weak peaks of Pd with different directions around 2θ = 40° and
2θ = 46° respectively in Pd/HMC-1, Pd/HMC-2 and Pd/HTMC which
demonstrates that Pd particles are well dispersed on carbon. Moreover,
Pd/ACC does not present obvious characteristic diffraction peaks of Pd
particles, which also indicates that the Palladium particles are well dis-
persed on carbon. Table 2 shows the hydrogen chemisorption measure-
ments of Pd/HMC-1, Pd/HMC-2, Pd/HTMC and Pd/ACC. The results
demonstrate that the dispersion of palladium particles on mesoporous
carbon is better than that on microporous coal carbon.
4. Conclusion
3.2. Catalytic performance
In this paper, mesoporous carbons were prepared by different
methods, and the prepared mesoporous carbons were used as the
support to obtain the palladium supported catalyst by incipient impreg-
nation method. Mesoporous structure carbon supported palladium
catalysts show better catalytic performance. 5% Pd/HMC-1 gives 82.2%
selectivity to cyclohexanone oxime at the nitrocyclohexane conversion
of 99.4% under the mild reaction condition of 0.5 MPa and 323 K. It
may provide a low cost catalyst for nitrocyclohexane hydrogenation to
cyclohexanone oxime.
The results of nitrocyclohexane hydrogenation to cyclohexanone
oxime over different catalysts are shown in Table 3. It can be seen
from Table 3 that 5% Pd/HMC-1 gives the best result of nitrocyclohexane
conversion of 99.1% and cyclohexanone oxime selectivity of 78.8%, and
5% Pd/HTMC presents the highest selectivity to cyclohexanone oxime,
however, the catalytic activity is influenced by its very small surface
area and pore volume, while the nitrocyclohexane conversion is only
71.4% at the same reaction conditions. The surface area, pore size, pore
volume and the metal crystallite size have great effects on the activity
and selectivity of the catalyst [23,24]. Mesoporous structure material
supported palladium catalysts show higher selectivity to cyclohexanone
oxime than microporous coal carbon supported palladium catalyst. The
Table 2
Hydrogen chemisorption data of different catalysts.
Catalysts
H
2 uptake
Metallic surface
Dispersion
(%)
(μmolg−1
)
areas (m2g−1
)
5% Pd/HMC-1
5% Pd/HMC-2
5% Pd/HTMC
5% Pd/ACC
10.04
16.55
5.84
19.04
31.40
0.55
4.27
7.05
2.49
1.74
4.09
7.75
Table 3
The results of nitrocyclohexane hydrogenation over different catalysts.
Catalyst
% Conversion (NCH)
% Selectivity
CHO
CHA
CHN
5% Pd/HMC-1
5% Pd/HMC-2
5% Pd/HTMC
5% Pd/ACC
5% Pd/SMC-1
5% Pd/SMC-2
99.08
99.72
71.41
99.14
99.77
99.87
78.81
61.88
82.87
53.74
59.43
58.22
9.10
1.48
1.96
0.25
0.76
0.56
0.38
1.514
1.318
4.314
1.379
9.878
NCH—nitrocyclohexane; CHO—cyclohexanone oxime; CHA—cyclohexylamine; CHN—
cyclohexanone.
Fig. 3. XRD patterns of 5% Pd/ACC, 5% Pd/HMC-1, 5% Pd/HMC-2 and 5% Pd/HTMC.
Reaction conditions: T = 323 K, PH2 = 0.3 MPa, t = 6 h, n = 1100 pm.

12
Y. Yan et al. / Catalysis Communications 50 (2014) 9–12
Acknowledgments
This work was supported by the NSFC (21276218), Program for
New century Excellent Talents in University (NCET-10-0168),
SRFDP (2012430110007), Scientific Research Fund of Hunan Provincial
Education Department (13k043) and Project of Hunan Provincial
Science & Technology Department (2012Fj1001).
References
[1] H.X. Yuan, Q.H. Xia, H.J. Zhan, X.H. Lu, K.X. Su, Appl. Catal. A Gen. 304 (2006)
178–184.
[2] K. Takagi, T. Ishida, US Patent 3644526 (1972) to Sumitomo Chemical Company.
[3] P. Roffia, M. Padovan, G. Leofanti, M. Maria A, G.D. Alberti, G.R. Tauszik, US Patent
4794198 (1988) to Montedipe S.p.A.
[4] T. Sooknoi, V. Chitranuwatkul, J. Mol. Catal. A Chem. 236 (2005) 220–226.
[5] J.F. Knifton, J. Catal. 33 (1974) 289–298.
[6] S. Sakaguchi, Y. Nishiwaki, T. Kitamura, Y. Ishii, Angew. Chem. Int. Ed. 113 (2001)
228–230.
[7] T.T. J.N., J. Catal. 161 (1996) 570–576.
Fig. 4. Effect of reaction temperature on nitrocyclohexane hydrogenation.
[8] X. Liang, Z. Mi, Y. Wang, L. Wang, X. Zhang, W. Wu, E. Min, S. Fu, J. Chem. Technol.
Biotechnol. 79 (2004) 658–662.
[9] X. Liang, Z. Mi, Y. Wang, L. Wang, X. Zhang, T. Liu, Chem. Eng. Technol. 27 (2004)
176–180.
[10] GB Patent 860340 (1961) to DuPont.
[11] GB Patent 857,902 (1961) to DuPont.
[12] S. Isozaki, Y. Nishiwaki, S. Sakaguchi, Y. Ishii, Chem. Commun. (2001) 1352–1353.
[13] K. Yamaguchi, S. Shinachi, N. Mizuno, Chem. Commun. (2004) 424–425.
[14] P. Serna, M. López-Haro, J.J. Calvino, A. Corma, J. Catal. 263 (2009) 328–334.
[15] K.-i. Shimizu, T. Yamamoto, Y. Tai, A. Satsuma, J. Mol. Catal. A Chem. 345 (2011)
54–59.
[16] P.-L. Liu, H.-K. Zhang, S.-H. Liu, Z.-J. Yao, F. Hao, H.-G. Liao, K.-Y. You, H.-A. Luo,
ChemCatChem (2013) 2932–2938.
[17] H. Tamon, H. Ishizaka, T. Araki, M. Okazaki, Carbon 36 (1998) 1257–1262.
[18] T. Otowa, Y. Nojima, T. Miyazaki, Carbon 35 (1997) 1315–1319.
[19] Y. Meng, D. Gu, F. Zhang, Y. Shi, L. Cheng, D. Feng, Z. Wu, Z. Chen, Y. Wan, A. Stein,
Chem. Mater. 18 (2006) 4447–4464.
[20] Y. Huang, H. Cai, T. Yu, F. Zhang, F. Zhang, Y. Meng, D. Gu, Y. Wan, X. Sun, B. Tu, D.
Zhao, Angew. Chem. Int. Ed. 46 (2007) 1089–1093.
[21] S. Jun, S.H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna, O. Terasaki, J. Am.
Chem. Soc. 122 (2000) 10712–10713.
[22] C. Vercaemst, M. Ide, B. Allaert, N. Ledoux, F. Verpoort, P.V.D. Voort, Chem. Commun.
(2007) 2261–2263.
[23] K. Lee, M. Kim, H. Kim, J. Mater. Chem. 20 (2010) 3791–3798.
[24] G.A. Somorjai, J.Y. Park, Top. Catal. 49 (2008) 126–135.
Fig. 5. Effect of reaction pressure on nitrocyclohexane hydrogenation.