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 methanol slurried with MgO powder; after removal of the methanol, [PtRh5(CO)(15)](-) remained adsorbed on the MgO surface. In addition to the metal carbonyl clusters, X-ray absorption near edge spectra indicated the presence of cationic rhodium species on the MgO surface. When the sample was treated in He or H-2, decarbonylation took place, accompanied 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 bimetallic and not significantly segregated into separate metals. The smallest supported bimetallic clusters incorporated only about 6-10 atoms 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 the metal without significant segregation of the metal. The EXAFS data indicate that the aggregates had rhodium-rich cores, with the platinum concentrated near the surfaces.