II International Symposium on Carbon for Catalysis ABSTRACTS

OP-<strong>II</strong>-6
AVOIDING MASS TRANSFER LIMITATIONS IN CARBON SUPPORTED
CATALYSIS BY USING CARBON XEROGEL TYPE SUPPORTS
Job N., Heinrichs B., Léonard A., Colomer J.-F. 1 , Marien J., Pirard J.-P.
Université de Liège, Laboratoire de Génie Chimique (B6a), B-4000 Liège, Belgium
1 Laboratoire de Résonance Magnétique Nucléaire, Facultés Universitaires Notre-Dame
de la Paix, rue de Bruxelles 61, B-5000 Namur, Belgium
e-mail: Nathalie.Job@ulg.ac.be
Porous carbon xerogel with tailored texture can be obtained by evaporative drying and
pyrolysis of resorcinol-formaldehyde aqueous gels [1-2]. The pore texture is controllable by
varying the pH of the precursors solution in a narrow range: depending on the pH, micromacroporous,
micro-mesoporous, microporous or non porous carbons are obtained. Solvent
removal can be performed by the convective air drying process, which is commonly used in
industry and very suitable to large-scale applications [3-4]. The pore texture is not influenced
by the drying conditions. Due to their pore texture flexibility and mechanical resistance, these
materials are suitable for many applications, among which catalyst supports. Moreover, the
synthesis method is very simple and relatively cheap: industrial production can be envisaged.
The ability to control at will the pore size in carbon xerogels is a great advantage
compared to classical active charcoals, whose textural parameters are mainly fixed by the
origin of the raw material. Indeed, the pore texture of active charcoals obtained after thermal
treatment strongly depends on the nature of the precursor. Moreover, these supports are
mainly microporous, with low meso- or macropore volume. Even if the metal is well
dispersed in micropores, mass transfer limitations decrease the performances of the catalyst.
On the contrary, the presence of large amounts of meso- or macropores should minimize
diffusional limitations inside carbon supports synthesized by sol-gel process, and these
supports could be designed according to the considered reaction.
In this study, mass transfer inside carbon xerogels was analysed during a well known
chemical reaction. The aim of this work is to show that it is possible to completely eliminate
diffusional limitations inside the catalyst pellets provided that the carbon xerogel texture is
adequately adjusted through an appropriate choice of synthesis variables values. Three carbon
xerogels with various pore size were selected: one micro-mesoporous sample with small
mesopores (maximum pore size = 10 nm), one micro-mesoporous sample with large
mesopores (maximum pore size = 40 nm) and one micro-macroporous sample (maximum
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