A stable site-isolated mononuclear platinum catalyst with a well-defined structure is presented. Platinum complexes supported in zeolite KLTL were synthesized from [Pt(NH3)4](NO3)2, oxidized at 633 K, and used to catalyze CO oxidation. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the platinum complexes in the zeolite pores, demonstrate the platinum-support bonding, and show that the platinum remained site isolated after oxidation and catalysis.

A stable site-isolated mononuclear platinum catalyst with a well-defined structure is presented. Platinum complexes supported in zeolite KLTL were synthesized from [Pt(NH 3 ) 4 ]-(NO 3 ) 2 , oxidized at 633 K, and used to catalyze CO oxidation. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the platinum complexes in the zeolite pores, demonstrate the platinumsupport bonding, and show that the platinum remained site isolated after oxidation and catalysis.

Extremely small supported rhodium clusters were prepared from rhodium complexes on the surfaces of solids with contrasting electron-donor properties. The samples were characterized by infrared and extended X-ray absorption fine structure spectroscopies to determine the changes occurring in the rhodium species resulting from treatments in hydrogen. Rhodium cluster formation occurred in the presence of H2, and the first steps are controlled by the electron-donor properties of the support--which acts as a ligand--and the other ligands bonded to the rhodium. The cluster formation begins at a lower temperature when the support is zeolite HY than when it is the better electron-donor MgO, provided that the other ligands on rhodium are ethene. In contrast, when these other ligands are CO, the pattern is reversed. The choice of ligands including the support also allows regulation of the stoichiometry of the surface transformations in H2 and the stability of the structures formed in the presence of other reactants. The combination of MgO as the support and ethene as a ligand allows restriction of the rhodium cluster size to the smallest possible-and these were formed in high yields. The data presented here are among the first characterizing the first steps of metal cluster formation.

A family of supported bimetallic samples was prepared by the reactions of Rh(C2H4)(acac) (acac = acetylacetonate) and Os3(CO)12 with MgO. The samples were characterized by infrared and extended X-ray absorption fine structure spectroscopies, before and after various treatments with hydrogen at temperatures up to 393 K. The spectra identify the following combinations of supported species: (a) [Os3(CO)11](2-) + Rh(C2H4)2, (b) [Os3(CO)11](2-) + Rh(CO)2, and (c) [Os3(CO)11](2-) + rhodium clusters containing approximately 4 to 6 atoms each, on average. No bimetallic clusters formed. The triosmium frame remained intact while the rhodium surface species were reduced in the presence of H2. The samples were tested as catalysts for ethylene hydrogenation at 298 K, and the catalytic activity matched that of the rhodium complexes alone; evidently the rhodium complexes were responsible for all the catalysis, with the osmium clusters remaining inactive because of the presence of the carbonyl ligands on them.

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