Investigations of palladium catalysts on different carbon supports

Pd-catalysts (5 wt%) were prepared on various supports: powdered and pelletized activated carbon derived from pine wood or beech wood, carbon black, and graphitized carbon black. The supports were palladized in the original condition or after HCl-treatment. The catalysts were characterized with CO-chemisorption, transmission electron micrographs, and X-ray photoelectron spectrometry. The precious metal dispersion and the catalytic activity are improved by the acid treatment of activated carbon as well as carbon black supports. A selection of samples were also characterized by means of inelastic neutron scattering (INS) to study the hydrogen-related features of the acid modification of the carbon supports. Indications for different sensitivities of the final Pd/C-catalysts to catalytically driven hydrogasification effects of the supports and the impact of these effects on the precious metal dispersion and the formation of Pd-hydrides were obtained. The formation of molecular-like polyaromatic structures was observed especially on HCl-treated activated carbon due to enhanced spillover of active hydrogen from the Pd-particles to adjacent sites on the support. The generation and accessability of these sites on the support seems to be promoted by the removal of ash and adsorbed species. (C) 1999 Academic Press.