diffuse reflectance IR spectroscopy

The state of platinum in the potassium platinum-11-tungstosilicate system on alumina studied by diffuse-reflectance IR spectroscopy

P. A. Korovchenko, N. A. Vladimirov, R. A. Gazarov, and L. M. Kustov

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]?3H₂O 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.