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.