Phase-Dependent Formation of Coherent Interface Structure between PtO2 and TiO2 and Its Impact on Thermal Decomposition Behavior

Abstract

This study investigated the thermal decomposition behaviors of platinum oxide (PtO2) nanoparticles deposited on polycrystalline TiO2 in different crystal phases. The dissociation of PtO2 to metallic platinum in air occurred at 400 °C on anatase TiO2 (Pt/TiO2-A), but required 650 °C or higher on rutile TiO2 (Pt/TiO2-R). The higher thermal stability of PtO2 on rutile TiO2 is caused by thermodynamic effect and rather than kinetic effect. In contrast to the thermodynamic prediction, metallic Pt (Pt0) on TiO2-R was reversibly oxidized to PtO2 (Pt4+) at 650 °C. This behavior was attributed to the coherent interface structure formed by strong interactions between PtO2 and rutile TiO2, as revealed by combined extended X-ray adsorption spectroscopy (EXAFS) and density functional theory (DFT) studies. At the optimized interface structure, between the (100) planes of α-PtO2 and rutile TiO2, the interface formation energy was −17.04 kJ mol–1 Å–2 versus −9.84 kJ mol–1 Å–2 in the anatase TiO2 model. The larger interface formation energy provides a stabilizing effect against PtO2 dissociation. Therefore, the widely used Pt-loaded rutile TiO2 typifies the interfacial interactions under an oxidizing atmosphere, which differ from the strong metal–support interactions prevailing under a reducing atmosphere.