SURFACE RESTRUCTURING OF PALLADIUM PARTICLES INDUCED BY CO ADSORPTION

In order to characterize chemisorption induced reconstruction the surface of supported palladium particles (model catalyst) has been investigated during CO adsorption by SSIMS (static secondary ion mass spectrometry). The SSIMS signal ratio SIGMA(n) Pd(n)CO+/Pd(n)+ has been used to monitor the CO adsorption kinetics. The relative occupancy of linear and bridged CO sites has been determined by the value of PdCO+/(SIGMA(n) Pd(n)CO+) and the variation of the Pd-Pd next neighbour distance by plotting Pd2+/Pd+ during CO exposure. It has been shown that CO chemisorption induces a surface restructuring by increasing the Pd-Pd distance in the particle surface. This phenomenon has the features of a cooperative phenomenon. On the reconstructed particle one bonding state has been identified which appeared to be a precursor of the CO dissociation.