COMMUNICATION
TiO2-supported Rh nanoparticles: From green catalyst preparation to
application in arene hydrogenation in neat water
Claudie Hubert,a,b Audrey Denicourt-Nowicki,*a,b Patricia Beaunierc and Alain Roucoux*a,b
Received 10th March 2010, Accepted 21st May 2010
First published as an Advance Article on the web 7th June 2010
DOI: 10.1039/c004079g
TiO2-supported Rh(0) nanoparticles were prepared by an
easy method under mild conditions in neat water. They
proved to be highly active catalysts for arene hydrogenation
in water with TOFs up to 33 333 h-1.
of TiO2-supported rhodium(0) nanoparticles and their efficient
use in model arene hydrogenation. Titania materials offer many
advantages such as good stability, low cost and nontoxicity,15
and are widely used in oxidative reactions and photocatalysis
due to their wide gap band. Metal-doped TiO2 are also described
in hydrogenation of various substrates, such as olefins, alkynes
or nitro groups, but to our knowledge there is scarcely any
report on arene reduction. Moreover, contrary to classical routes
for the synthesis of supported nanocatalysts, which requires
repeated oxidation and reduction steps under severe conditions,
our approach relies on an impregnation methodology which
consists of wetting the titania support with an aqueous solution
containing preformed rhodium nanoparticles. Among the three
main crystalline forms (brookite, rutile and anatase), the anatase
form was chosen, offering the possibility to apply the method to
photocatalysis.
Based on the method we have developed for silica-supported
nanoparticles, the immobilization of rhodium(0) nanoparticles
on titania has been performed from our previously reported
aqueous colloidal rhodium(0) suspension prepared by chemical
reduction of an aqueous solution of rhodium chloride salt in
the presence of highly hydrosoluble ammonium chloride salts
as stabilizing agents (Fig. 1).16–18 Then, the addition of an
adequate amount of titania under vigorous stirring leads to
the nanoparticle adsorption on the support. The color change
from black to colorless evidences the total adsorption of the
metallic nanospecies on the titania surface. After filtration, the
grey powder was washed several times with clean water and dried
overnight at 60 ◦C. The metal loading of the nanomaterials was
determined by ICP analysis as 0.09 wt% and corresponds to
the expected one. Our method combines a one pot stabilization
of metallic nanospecies and their deposition onto the inorganic
support at room temperature, under air, without gas treatment
or calcination step.
The use of metallic nanoparticles in catalysis has attracted
a growing interest over the last few decades owing to their
unique properties such as a large surface-to-volume ratio and
tunable shapes.1 The control of their size, shape and dispersity
is essential for selective and enhanced activity in a desired
application. Among the various catalytic applications, noble
metal nanospecies are reference catalysts for the hydrogenation
of arene derivatives,2,3 thus leading to the formation of key
intermediates for fine chemistry. In the drive towards sustainable
and environmentally-friendly chemistry, catalyst recovery is a
crucial parameter. The combination of metal nanoparticles with
an heterogeneous support provides a powerful means for the
development of new, highly active and recyclable catalysts,4,5
leading to specific applications in catalysis. Supported metal
nanoparticles are a mainstay of commercial heterogeneous
catalysts with applications in various industrial reactions.6,7
Different preparation routes have been developed over the last
few years and are subdivided into physical (e.g. sonication, mi-
crowaves, UV) or chemical (e.g. electrochemical, impregnation,
fluidized bed).4,8 However, with respect to the sustainability
criterion, the design and synthesis of supported nanomaterials
is still an ongoing challenge.9,10 In this context, the particles
should ideally be prepared with less toxic precursors in green
solvents in mild conditions and with few synthetic steps.11
Among the various supports, metal oxides offer high thermal
and chemical stabilities with a well-developed porous structure
and high surface areas (>100 m2 g-1). Our approach relies
on the deposition onto an inorganic support of pre-stabilized
nanoparticles in aqueous suspensions, which have been well-
characterized in terms of size and organization.12 Interest-
ing results in terms of catalytic activity and recycling have
been obtained in arene hydrogenation using silica-supported
rhodium(0) nanoparticles prepared by wet impregnation or in
fluidized beds.13,14 In this paper, we describe the easy synthesis
aEcole Nationale Supe´rieure de Chimie de Rennes, CNRS, UMR 6226,
Avenue du General Leclerc, CS 50837, 35708, Rennes Cedex 7, France.
E-mail: Alain.Roucoux@ensc-rennes.fr; Fax: +33 (0)2 23 23 80 46;
Tel: +33 (0)2 23 23 80 37
Fig. 1 One pot synthesis of TiO2-supported Rh(0) nanoparticles.
bUniversite´ Europe´enne de Bretagne
cLaboratoire de Re´activite´ de Surface, UPMC, Universite´ Pierre et
Marie Curie - Paris 6, CNRS - UMR 7197, 75252, Paris Cedex 05,
France
The obtained Rh@TiO2 materials were characterized by High
Resolution Transmission Electron Microscopy (HRTEM) and
This journal is
The Royal Society of Chemistry 2010
Green Chem., 2010, 12, 1167–1170 | 1167
©
Hubert, Claudie
