DECARBONYLATION OF MGO-SUPPORTED PTRH5 CLUSTERS CHARACTERIZED BY INFRARED AND EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPIES

[PtRh5(CO)(15)](-) was synthesized from RhCl3, Na2PtCl6, and CO in met hanol slurried with MgO powder; after removal of the methanol, [PtRh5( CO)(15)](-) remained adsorbed on the MgO surface. In addition to the m etal carbonyl clusters, X-ray absorption near edge spectra indicated t he presence of cationic rhodium species on the MgO surface. When the s ample was treated in He or H-2, decarbonylation took place, accompanie d by temperature-dependent aggregation of the metals, as indicated by infrared spectra and EXAFS spectra measured at both the Ph K and Pt L- III edges. The resultant decarbonylated clusters and aggregates were b imetallic and not significantly segregated into separate metals. The s mallest supported bimetallic clusters incorporated only about 6-10 ato ms each; on average-these are among the smallest supported bimetallic clusters yet reported. The smallest supported clusters were not fully decarbonylated; complete decarbonylation resulted in aggregation of th e metal without significant segregation of the metal. The EXAFS data i ndicate that the aggregates had rhodium-rich cores, with the platinum concentrated near the surfaces.