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 alum ina film we have prepared various of alumina-supported Rh particle sys tems. The morphologies and particle sizes have been characterised with spot profile analysis LEED and STM measurements. The probabilities fo r thermally induced dissociation of adsorbed CO at temperatures betwee n 350 and 500K were determined from Cls photoelectron spectra. For sma ll aggregates the dissociation activity increases with increasing aver age particle size. After reaching a maximum for particles containing a n average of 500 to 1000 Rh atoms, the fraction of dissociated CO decr eases to values closer to those observed on well-prepared Rh single cr ystal surfaces. (C) 1997 Published by Elsevier Science B.V.