Carbon xerogels as supports for catalysts and electrocatalysts
Résumé
In order to improve mass transport in the pore texture of carbon supported catalysts, the widely used supports (activated carbons or carbon blacks) can be replaced by carbon gels, i.e. texture-tailored materials obtained by drying and pyrolysis of organic gels. Carbon xerogels issued from resorcinol-formaldehyde aqueous gels were used as metal catalyst supports both in gas phase heterogeneous catalysis and in PEM fuel cell electrodes. These materials, composed of very pure carbon, allow for excellent metal dispersion via impregnation methods. Pd-Ag/C catalysts were obtained by impregnation and tested for hydrodechlorination reactions in gaseous phase. Pt loaded carbon xerogels were tested as electrocatalysts in PEM fuel cell cathodes. In both cases, the well-adapted structure of the support proved to be a great advantage compared to classical activated carbons or carbon blacks: (i) in the gas phase reaction, diffusional limitations encountered with activated carbon supports were completely eliminated; (ii) in fuel cells, Pt loaded catalysts enabled decreasing the effect of diffusion in the catalytic layer on potential loss and led to increasing the global metal utilization ratio.
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