Decomposition and migration behavior of Pt salt on Al2O3 and SiO2 upon calcination studied by XAFS and UV–visible spectroscopy using a laboratory-type spectrometer

Thermal decomposition behavior of two kinds of Pt salts, namely, H₂PtCl₆ and Pt(NH₃)₄Cl₂, on amorphous SiO₂ and γ-Al₂O₃ under air to prepare supported platinum catalysts up to 773 K was investigated by in-situ laboratory X-ray absorption fine structure (XANES/EXAFS) and UV–Vis spectroscopy. Changing the oxidation state of platinum species and the coordination environment, the migration to vacant sites or aggregation process on the surface were discussed. The supported H₂PtCl₆ was reduced to Pt²⁺ species under air flow around 573 K by eliminating Cl/O ligand atoms until 573 K. High-temperature treatment caused the re-oxidation of the supported Pt species on Al₂O₃, but it did not affect the oxidation state of SiO₂-supported species. The formed platinum oxychloride on Al₂O₃ was stable under air, but it partly decomposed to atomic-like species above 673 K, followed by migration on the surface, trapping at the cation vacant site because of its defect spinel structure. The lattice oxygen atoms of Al₂O₃ adjacent to Pt atom captured might cause the re-oxidation, and molecular oxygen was not the oxidant. The partly formed atomic-like species migrates on the SiO₂ surface, followed by aggregation to form metallic Pt particles above 573 K.