| Abstract
| - Anion ligands-preserved cationic giant Pd clusters were prepared by treatment of palladium carbonylacetate cluster, Pd4(CO)4(OAc)4·2AcOH (PCA), with metal nitrates, e.g. Cu(NO3)2, and Fe(NO3)3, in thepresence of 1,10-phenanthroline (phen). Extensive characterization of the Pd clusters was made by XRD,XPS, XAFS, TPD, FE-SEM, ion-chromatography, and CO adsorption. It was revealed that the inner partof the clusters was an exclusively metallic form, whereas both Pd cations (Pd2+ and Pd+) and Pd0 specieswere located on the same surface of the clusters to form specific ensemble sites. Further, the particle sizeand surface fraction of Pd0, Pd+, and Pd2+ of the giant Pd clusters could be tuned by changing the amountof the metal nitrate; the largest particle size of about 35 Å and the highest surface fraction of the Pd2Ocould be obtained when the Cu(NO3)2/PCA ratio was 0.10. The 8-shell giant Pd clusters of about 35 Å indiameter having a large number of surface Pd cations showed a high catalytic activity for the oxidativeacetoxylation of toluene to give benzyl acetates in the presence of molecular oxygen. Furthermore, the Pdcluster could be immobilized on a neutral TiO2 surface by keeping its original cluster size and high catalyticactivity. The prominent catalysis of this Pd cluster can be ascribed to the ensemble sites composed ofmetallic Pd atoms and neighboring Pd cations on its surface.
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