Carbon nanofiber supported palladium catalyst for liquid-phase reactions. An
active and selective catalyst for hydrogenation of CNC bonds
C. Pham-Huu,a N. Keller,a L. J. Charbonniere,b R. Ziesselb and M. J. Ledoux*a
a Laboratoire de Chimie des Matériaux Catalytiques, ECPM-ULP, UMR 7504 CNRS, 25, rue Becquerel, 67087
Strasbourg Cedex 02, France. E-mail: ledoux@cournot.u-strasbg.fr
b Laboratoire de Chimie, d’Electronique et de Photonique Moléculaire, ECPM-ULP, UPRES-A 7008 CNRS, 25, rue
Becquerel, 67087 Strasbourg Cedex 02, France
Received (in Oxford, UK) 30th June 2000, Accepted 21st August 2000
First published as an Advance Article on the web 18th September 2000
Carbon nanofibers with a mean diameter of about 50 nm
were successfully used as support for a palladium catalyst in
the liquid phase selective hydrogenation of the CNC bond in
an a,b-unsaturated molecule: a less critical problem of mass-
transfer limitation led to the obtention of a highly active and
chemo-selective catalyst compared to a commercial high
surface area activated charcoal supported palladium cata-
lyst.
broad, ranging in size from 1.5 to 43.5 nm, with an average size
of the metal particles of ca. 7–10 nm.
The hydrogenation of cinnamaldehyde was carried out at
atmospheric pressure and low temperature, i.e. < 100 °C, with
bubbling hydrogen. For the test, 10 ml of cinnamaldehyde
(Athos, > 99.95 vol%) were dissolved in 40 ml of dioxane (RP,
> 99.95 vol%). The catalyst (loading 1.05 3 1023 g Pd) was
added to the liquid under vigorous stirring (400 rpm) and
subsequently, the reaction temperature was increased from rt to
80 °C, under continuous hydrogen bubbling through the liquid
phase. The cinnamaldehyde concentration and the product
distribution were followed by gas chromatography analysis
(PONA capillary column equipped with a FID detector) of
microsamples periodically withdrawn, and diluted with diox-
ane.
The catalytic results obtained over the Pd supported on
carbon nanofibers and the commercial catalyst (Aldrich), are
reported in Figs. 2 and 3. The superiority in terms of reaction
rate of the nanofiber based catalyst was clear when the slopes of
disappearance of CALD were compared. This performance was
quite surprising as the literature reports that a relatively low
surface area (45 m2 g21 instead of 900 m2 g21 for the
Since their discovery at the beginning of the last decade,1
carbon nanotubes and nanofibers seemed to be promising
candidates for use as catalyst supports for heterogeneous
catalytic reactions.2–4 Such materials were expected to be
efficient in liquid phase media due to their high external
surfaces which can allow a significant decrease in critical mass
transfer limitations,5,6 also leading to an increase in the rate and
the selectivity of the reactions.7–10
The aim of the present communication is to report the
preparation of a highly dispersed palladium catalyst supported
on carbon nanofibers, which is active and chemo-selective in
the liquid phase hydrogenation of the CNC bond of cinnamalde-
hyde, at atmospheric pressure. The reaction rate and the product
distribution are compared with those obtained on a commer-
cially available activated charcoal supported palladium catalyst
under the same reaction conditions.
The carbon nanofibers (CNF) were synthesized by a gas
phase catalytic decomposition of a mixture of ethane and
hydrogen over a high surface area alumina supported nickel
catalyst at 650 °C. This nickel catalyst was prepared by
incipient wetness impregnation of an alumina support with an
aqueous solution of nickel nitrate containing 20 vol% of
glycerol as viscous agent. After synthesis and sonication the
carbon nanofibers were subsequently purified by acid treatment
at 80 °C for 2 h in order to dissolve any residual nickel catalyst
that they might have contained. The carbon nanofibers had a
mean diameter of around 50 nm and lengths up to several
micrometers and they were built with graphene planes in a
herringbone pattern, sometimes connected in the middle of the
fiber, forming a closed angle of about 75°. The distance between
the planes was found to be 0.34 ± 0.01 nm.
The palladium deposition (5 wt%) onto the support was
achieved by incipient wetness impregnation with an aqueous
solution of palladium nitrate. The solid was dried overnight at
110 °C and subsequently reduced under flowing hydrogen at
350 °C for 2 h. Transmission Electron Microscopy (TEM)
images evidenced the high and homogeneous dispersion of
spheroidal palladium metal particles, with a narrow particle size
distribution centered at around 3–5 nm diameter (Fig. 1). This
homogeneous dispersion was attributed to a relatively strong
metal-support interaction between the metal salt precursor and
the graphite edges of the carbon nanofibers, increasing the
resistance to the growth of the palladium particle. A similar
observation has also been reported by Baker and co-workers2–4
for graphite nanofibers supported on a nickel catalyst. However
the distribution profile of the metal particles was relatively
Fig. 1 A Transmisson Electron Microscopy image of the carbon nanofibers
supported palladium catalyst and the particle distribution.
DOI: 10.1039/b005306f
Chem. Commun., 2000, 1871–1872
This journal is © The Royal Society of Chemistry 2000
1871
Pham-Huu
