SIMS XPS INVESTIGATIONS ON ACTIVATED CARBON CATALYST SUPPORTS

The surface modifications of activated carbon catalyst supports due to HCl treatment were measured in investigations combining X-ray photoel ectron 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 pos itively and negatively charged fragment ions in SIMS experiments. Surf ace 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 part ly with properties of catalytic interest such as the valency and dispe rsion of precious metals which were deposited on these supports. The i nteraction between the activated carbon surfaces and precious metal co mpounds is apparently governed not only by the redox behavior of C/O a nd heterofunctional groups but also by the concentration of surface hy drogen. The surface hydrogen seems to enhance redox processes in the p recious metal impregnation step of catalyst preparation. Therefore, su rface hydrogen is an important parameter for controlling catalyst prop erties in catalyst preparation and should be carefully monitored. (C) 1994 Academic Press, Inc.