The surface modifications of activated carbon catalyst supports due to HCl treatment were measured in investigations combining X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The surface properties of carbons derived from beech wood, pine wood, and bitumen were qualitatively characterized by analyzing selected positively and negatively charged fragment ions in SIMS experiments. Surface modification and lot-to-lot variations were found with respect to surface oxygen, aliphatic and aromatic/graphitic carbon, and surface C/H ratios. The surface characteristics of the supports correlated partly with properties of catalytic interest such as the valency and dispersion of precious metals which were deposited on these supports. The interaction between the activated carbon surfaces and precious metal compounds is apparently governed not only by the redox behavior of C/O and heterofunctional groups but also by the concentration of surface hydrogen. The surface hydrogen seems to enhance redox processes in the precious metal impregnation step of catalyst preparation. Therefore, surface hydrogen is an important parameter for controlling catalyst properties in catalyst preparation and should be carefully monitored.