Investigation of the state of palladium in the potassium palladium-11-tungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

The influence of redox treatments on the state of palladium in the K-6[SiW11PdO39]. 11H(2)O/gamma-Al2O3 system was investigated by diffuse-reflectance IR (DRIFT) spectroscopy using CO as a probe molecule. The K-6[SiW11PdO39]. H2O heteropoly-compound (HPC) and starting gamma-Al2O3 support were studied for comparison. It was shown that palladium is present in HPC mainly in the form of Pd2+ ions. Treatment of HPC in an H-2 flow results in complete reduction of palladium to Pd-0. The HPC is unstable in redox cycles at temperatures above 373 K. When the HPC was supported on alumina, the Keggin units were stabilized on the support surface and Pd+ formed in the oxidized sample. The supported K-6[SiW11PdO39]. 11H(2)O/gamma-Al2O3 catalyst displays higher thermal stability and does not decompose during redox treatments at temperatures up to 723 K.