Abstract
The electronic state of platinum in the K4[SiW11PtO39]/Al2O3 supported system and its thermal stability in redox cycles were investigated by diffuse-reflectance IR spectroscopy using CO as a probe molecule. The bulk sample of the K4[SiW11PtO39]·13H2O heteropolycompound (HPC) was studied for comparison. It was shown that platinum is present in the oxidized HPC mainly as the Pt1+ and Pt0 species. In the supported system, the ratio of these species strongly depends on the temperature of oxidative pretreatment. The reduced HPC contains mainly metallic platinum in the form of Pt0 complexes with the bridged CO ligands. Supporting of the bulk sample HPC increases the thermal stability of its structure in an oxidative medium from ∼600 to ≥820 K. The supported K4[SiW11PtO39]/Al2O3 system exhibits a higher stability in the redox cycles compared to that of the bulk sample of individual HPC and preserves the Keggin structure and highly dispersed state of platinum up to T ≥ 670 K.
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