RECONSTRUCTION OF PD PARTICLES SUPPORTED ON SILICA IN THE PRESENCE OFCO AS STUDIED BY C-13 NMR

The C-13 NMR spectrum of (CO)-C-13 adsorbed on Pd particles varies dra matically depending on dispersion. The spectrum of highly dispersed Pd particles supported on silica is a powder pattern similar to 800 ppm wide with a first moment of 410 ppm. A low dispersion sample has a mot ionally narrowed line centered at 750+/-10 ppm and only similar to 85 ppm full width at half height (FWHH). Over several years, high dispers ion samples show an increase in the intensity near 750 ppm. These obse rvations are interpreted as an increase of mobile bridging CO on high dispersion Pd surfaces of particles which resulted from smoothing of t he metal particle surfaces in the presence of CO.