Particle size dependent CO dissociation on alumina-supported Rh: a model study

Via deposition of Ph from the gas phase onto a thin, well-ordered alumina film we have prepared various of alumina-supported Rh particle systems. The morphologies and particle sizes have been characterised with spot profile analysis LEED and STM measurements. The probabilities for thermally induced dissociation of adsorbed CO at temperatures between 350 and 500K were determined from Cls photoelectron spectra. For small aggregates the dissociation activity increases with increasing average particle size. After reaching a maximum for particles containing an average of 500 to 1000 Rh atoms, the fraction of dissociated CO decreases to values closer to those observed on well-prepared Rh single crystal surfaces. (C) 1997 Published by Elsevier Science B.V.