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

Abstract

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.