| Abstract
| - Highly dispersed γ-Al2O3-supported PtRu clusters were prepared by decarbonylation of molecularly adsorbed[Pt2Ru4(CO)18] in He or H2 at temperatures in the range of 300−400 °C. Infrared (IR) and extended X-rayabsorption fine structure (EXAFS) spectroscopies were used to characterize the supported species before andafter removal of the CO ligands. The IR and EXAFS spectra show that most of the [Pt2Ru4(CO)18] interactedweakly through its CO ligands with the surface hydroxyl groups of γ-Al2O3 and could be extracted intoCH2Cl2, but a small fraction of the [Pt2Ru4(CO)18] interacted strongly with the support and could not beextracted. The strongly bonded species, characterized by a νco band at 2063 cm-1, formed as a result ofnucleophilic attack of some support hydroxyl groups on carbonyl ligands, leading to the removal of theseligands as CO2 and formation of covalent bonds between the clusters and the oxygen atoms of the support.The EXAFS data show that after decarbonylation in He or H2 at 300−400 °C, the Pt−Ru cluster frame waschanged relative to that of the supported [Pt2Ru4(CO)18]. The average Pt−Pt bond distance increased from2.66 to 2.69 Å, and the Ru−Ru distance decreased from 2.83 to 2.64 Å. The corresponding Pt−Pt and Ru−Ru coordination numbers were found to be 2.0 and 4.0, respectively, indicating that slight agglomeration ofthe metal took place upon decarbonylation. The EXAFS data show that the Pt−Ru interactions were largelymaintained after decarbonylation, so that highly dispersed Pt−Ru structures were present on the support.From the Pt−Pt and Ru−Ru coordination numbers it follows that decarbonylated clusters incorporate, onaverage, less than three and six Pt and Ru atoms, respectively, being the smallest such supported bimetallicclusters of platinum-group metals yet reported.
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