STRUCTURES AND CATALYTIC ACTIVITY OF PT-MO BIMETALLIC ENSEMBLES DERIVED FROM A NEW PLANAR [PTMO6O24]8- HETEROPOLYANION SUPPORTED ON AL2O3 AND SIO2

PtMo bimetallic ensembles active for ethene hydrogenation and ethane hydrogenolysis were prepared on silica and alumina using a new Anderson-type plane [PtMo6O24]8- heteropolyanion as a precursor. The structures of the supported bimetallic ensembles were determined by H2-chemisorption, TEM (transmission electron microscopy), analytical TEM, XRD (X-ray diffraction), EXAFS (extended X-ray absorption fine structure), and XANES (X-ray absorption near edge structure). The heteropolyanion framework was maintained when it was supported on silica, but was broken when on alumina. After reduction at 773-823 K, dispersed particles with an "eggshell" structure (3.0 ± 0.5 nm) were formed on silica, where a small platinum cluster (ca. 1.0 nm) located in the center was covered with partially oxidized Mo-oxide layers. On alumina bimetallic clusters of 2.0 ± 0.5 nm were formed, and part of the molybdenum was involved in the bimetallic particle in zero valency and the remaining molybdenum atoms were dispersed in low valence states on the Al2O3 surface. © 1992.