SURFACE-CHEMISTRY ON COLLOIDAL METALS - REVERSIBLE ADSORBATE-INDUCED SURFACE-COMPOSITION CHANGES IN COLLOIDAL PALLADIUM-COPPER ALLOYS

Carbon monoxide adsorbs reversibly into organic suspensions of a serie s of colloidal poly(vinylpyrrolidone) stabilized bimetallic palladium- copper alloys with particle sizes of ca. 45 Angstrom, binding to both copper and palladium sites. The relative intensities of the [CuCO] and [PdCO] infrared absorptions of the as-prepared bimetallic colloids in the presence of saturated solutions of CO reveal the preference of pa lladium for surface sites on the alloy particles, in contrast to the m ore commonly observed surface segregation of copper in the bulk alloy. The IR spectrum of adsorbed CO at room temperature is time dependent over several days, in a manner suggesting a rearrangement of the surfa ce atomic layers of the particles with further enrichment in palladium .