Palladium (0) metal clusters: Novel Krebs type polyoxoanions stabilized, extremely active hydrogenation catalyst

One-pot synthetic route has been applied for successful synthesis and stabilization of Pd, Au and Ag metal-clusters (Metal-clusters can be defined as nanoparticles of size less than 10 nm.) using Krebs type polyoxoanions [(TBA)(4)H-4[M-4(H2O)(10)(XW9O33)(2)], where M = Mn, Ni, Zn, X = Te, Se; M = Fe, X = Sb, As] as stabilizers. These polyoxoanions falls under the category of heteropolyanions and possess Krebs structure. All the polyoxoanion-metal colloidal systems were found to be stable for approximately three/six months in solution media. It was found that, due to some kind of structural transformation, polyoxoanions loose their stabilizing capability. Polyoxoanions stabilized Pd metal-clusters was found to be extremely active toward hydrogenation reaction of cyclohexene and 1-hexene. The Pd-Mn4Se2W18 system demonstrated the longest lifetime of up to 250,000 for 1-hexene and 100,000 for cyclohexene hydrogenation. The catalytic activity is found to vary with transition metal ions like Mn, Fe, Ni, Zn, As, Sb, Te, Se which are present in the polyoxoanions. All the metal-cluster systems were characterized using various instrumental techniques such as UV-vis spectroscopy, FTIR spectroscopy, X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy.