DOI: 10.1002/cctc.201600126
Communications
Solvent-Free Selective Hydrogenation of Nitroarenes Using
Nanoclusters of Palladium Supported on Nitrogen-Doped
Ordered Mesoporous Carbon
[
a]
[a, b]
[a]
[b]
[b]
Haigen Huang, Xueguang Wang,*
Mingwu Tan, Chenju Chen, Xiujing Zou,
[a, b]
[a, b]
Weizhong Ding,
and Xionggang Lu*
[
8–10]
The selective hydrogenation of nitroarenes is a key transforma-
tion for the production of aromatic amines, which are primary
intermediates in the synthesis of pharmaceuticals, agrochemi-
cals, and dyes. However, most reaction processes require toxic
organic solvents and suffer from poor selectivity in the pres-
ence of other reducible groups. Herein, we report a successful
example of nanoclusters of ultrafine Pd supported on N-modi-
fied ordered mesoporous CMK-3 carbon (Pd/N-CMK-3) pre-
pared by a facile two-step impregnation route with aqueous
solutions of 1,10-phenanthroline and H PdCl that hydrogenat-
as alkenes, ketones, and aldehydes
for practical applica-
tions. The most desirable production of aromatic amines is the
direct and quantitative hydrogenation of nitroarenes over
highly efficient solid metal catalysts with hydrogen either in
[
11]
the absence of solvent or in an aqueous medium. To date,
the development of new and efficient supported metal cata-
lysts remains a big challenge for the green production of aro-
matic amines.
Mesoporous carbon materials have attracted much interest
as catalytic supports because of their improved properties in
the conversion of larger substrate molecules in their defined
2
4
ed various nitroarenes highly efficiently and selectively to the
corresponding aromatic amines with hydrogen in the absence
of solvent. The Pd/N-CMK-3 catalyst could be recovered easily
for multiple recycling reactions without a loss of catalytic
performance.
[
12–14]
channels with uniform pore size distributions.
The catalytic
performance is strongly dependent on the structure and sur-
face properties of the mesoporous carbon and metal particles,
the metal particle sizes, and the interaction between the sup-
port and metal, which could be modulated by preparation
[
15–17]
method, thermal treatment, and element doping.
Aromatic amines are important organic intermediates in the
Herein, we report that clusters of Pd supported on N-doped
ordered mesoporous CMK-3 carbon (Pd/N-CMK-3), which were
prepared by impregnating CMK-3 powder with aqueous solu-
tions of 1,10-phenanthroline and H PdCl in two steps, show
[
1]
synthesis of dyes, agrochemicals, and pharmaceuticals. The
reduction of nitroarenes is a fundamental transformation for
the production of aromatic amines in organic chemistry. The
typical reduction routes are performed over transition-metal-
based catalysts using reducing agents such as hydrosilanes,
sodium borohydride, and hydrazine derivatives, which cause
2
4
unprecedented intrinsic activity and selectivity to aromatic
amines for the hydrogenation of various substituted nitroar-
enes with H in the absence of solvent.
2
[2–4]
serious environmental problems.
Recently, much attention
The N sorption analysis (Figure S1) of Pd/CMK-3 and Pd/N-
2
has been directed towards the selective hydrogenation of ni-
troarenes to aromatic amines over supported metal catalysts,
such as Pt, Pd, Au, and Ru, using hydrogen as a reducing
CMK-3 showed typical type IV isotherms with clear hysteresis
loops of H1-type and narrow pore size distributions, similar to
those of pure CMK-3. This result indicated that the mesopo-
rous structure and the relatively uniform mesopores of CMK-3
were still preserved in Pd/CMK-3 and Pd/N-CMK-3. The low-
angle XRD patterns (Figure S2a) of Pd/CMK-3 and Pd/N-CMK-3
further confirmed the presence of the ordered mesoporous
structures by the strong (100) reflections at 2q= ~1.058. How-
ever, the disappearance of the (110) and (200) reflections of
CMK-3 revealed that the incorporation of Pd, N, and C resulted
[
5–7]
agent.
However, these systems often require complicated
catalyst preparation and the use of expensive toxic solvents to
facilitate heat and mass transfer in liquid-phase reaction sys-
tems. Besides, the relatively low catalytic activity and poor
nitro group chemoselectivity also severely limit the hydrogena-
tion of nitroarenes, especially with other reducible groups such
[
18]
[
a] Dr. H. Huang, Prof. X. Wang, Dr. M. Tan, Prof. W. Ding, Prof. X. Lu
State Key Laboratory of Advanced Special Steel
Shanghai University
in the decrease of structural ordering in the samples.
The wide-angle XRD patterns (Figure S2b) of both Pd/CMK-3
and Pd/N-CMK-3 showed two remarkable peaks as a result of
the (002) and (101) reflections of graphitic carbon, which was
Shanghai 200072 (China)
Fax: (+86)21-56338244
E-mail: wxg228@shu.edu.cn
[
14b,18b]
an indication of crystallization of the carbon walls.
In the
case of Pd/CMK-3, three strong diffraction peaks of Pd were
[
b] Prof. X. Wang, Dr. C. Chen, Dr. X. Zou, Prof. W. Ding, Prof. X. Lu
Shanghai Key Laboratory of Advanced Ferrometallurgy
School of Materials Science and Engineering
Shanghai University
observed at 2q=40.1, 46.6, and 68.18, whereas for Pd/N-CMK-
[9]
3
, only a very weak Pd peak at 2q=40.18 was observed. This
result implied that N-CMK-3 treated with 1,10-phenanthroline
facilitated the dispersion of Pd species significantly to form
smaller Pd clusters on the surface, likely because of the cap-
ChemCatChem 2016, 8, 1485 – 1489
1485
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim