A novel type of nanoporous carbon material supporting high
dispersion of rhodium nanoparticles
Fengbo Li, Jin Zou, and Guoqing Yuan
Ã
Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, China
Received 21February 2003; accepted 6 May 2003
Nanoporous carbon (NC) was prepared by the controlled pyrolysis of copolymer of vinylidene chloride and acrylonitrite. These
organic–inorganic hybrid polymers were synthesized by suspending polymerization. After gradually controlled pyrolysis at
180–300
C under nitrogen stream, the resulting material was carbonized at 1000
C for 3 h under argon stream. In this way,
nanoporous carbon was obtained, which has uniform pore size in the range of 0.8–1.6 nm and specific surface area of
900–1000 m
2
g
À1
. The surface morphology and chemical composition were characterized by scanning electron microscopy (SEM)
and X-ray photoelectron spectroscopy (XPS). Rhodium particles kept in a highly dispersed state over it were prepared and
characterized by XPS and transmission electron microscopy (TEM). The expected high catalytic activity of the final material for
methanol carbonylation was observed experimentally.
KEY WORDS: copolymer; carbonization; nanoporous carbon; supported metal; catalytic activity.
1. Introduction
Nanostructured carbon materials are potentially of
great theoretical and technological importance for the
development of catalysis [1,2]. Dispersion of metal
particles determines the final catalyst activity and
other properties [3]. Ordered nanoporous carbon made
high dispersion of metal particles feasible, exceeding
that of other common microporous carbon materials
such as charcoal, activated carbon and carbon black [4].
The nanocasting process is the only route developed so
far to produce ordered nanoporous carbon materials
[4,5]. Here we describe an economical and easily
operated strategy for obtaining a type of nanoporous
material having uniform pore size in the range of
0.8–1.6 nm and specific surface area of 900–1000 m
2
g
À1
.
The final nanoporous material supports a high disper-
sion of rhodium nanoparticles, which are characterized
by X-ray photoelectron spectroscopy (XPS) and trans-
mission electron microscopy (TEM). High metal disper-
sion is an important design factor for the catalyst and is
useful in practice, not only because it saves expensive
metal but also because it controls structure sensitivity.
2. Experimental section
2.1. Preparation of nanoporous carbon and supported
rhodium nanoparticles
Nanoporous carbon in this work is derived from
organic–inorganic hybrid polymers, which are synthe-
sized by suspending polymerization. Purified vinylidene
chloride and acrylonitrile (2 : 1, mole ratio) were
copolymerized in saturated Na
2
SO
4
aqueous solution.
The initiator was azobisisobutylvaleronitrile (ABVN)
(1% (mole ratio) of monomers). Bentonite was used as
the inorganic template and the dispersion phase.
Copolymerization was kept at a constant temperature
of 45
C for 24 h, agitated with proper speed (200–250 r/
min) in the first 12 h and then kept static. The polymeric
materials were washed with hot water ð80–95
CÞ to
remove excessive bentonite and purified in acetone
stream to remove remaining monomers. The final
copolymer was carbonized in a controlled manner to
obtain ordered nanoporous carbon, heated at 180
C for
12 h. Then the temperature was elevated to 300
C by
1:0
C min
À1
and kept constant for 12 h, all in nitrogen
stream. After removal of volatile molecules, the
temperature was elevated from 300–1000 8C gradually
and kept constant for 3 h in an argon stream. In this
way, nanoporous carbon was obtained.
The precursor of rhodium nanoparticles was a binuc-
lear rhodium carbonyl complex ðRh
2
Cl
2
ðCOÞ
4
Þ,which
was introduced by impregnating the nanoporous carbon in
methanol solution of the complex for about 40 min,
followed by drying in vacuum at ambient temperature.
The dried fresh samples were reduced in a hydrogen stream
at 400
C for 75 min and then treated at experimentally
designed temperature under an argon stream for 1h. The
metal loading was in the range of 1.0–1.2 wt%.
2.2. Characterization of the resulting materials
Prepared nanoporous carbons and supported rho-
dium were characterized by SEM, XPS and TEM. The
Ã
To whom correspondence should be addressed.
E-mail: Yuangq@iccas.ac.cn
Catalysis Letters Vol. 89, Nos. 1–2, July 2003 ( # 2003) 115
1011-372X/03/0700–0115/0 # 2003 Plenum Publishing Corporation