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.

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The catalytic NH 3 combustion properties and local structures of copper oxides (CuO x ) supported on aluminum oxide borates (Al 20 B 4 O 36 , 10Al 2 O 3 •2B 2 O 3 : 10A2B) were studied by means of high-angle annular dark-field scanning transmission electron microscopy, energy dispersive X-ray mapping, X-ray absorption fine structure, X-ray photoelectron spectroscopy, gas adsorption techniques, etc. Among the CuO x supported on various metal oxide materials, CuO x / 10A2B exhibited high catalytic NH 3 combustion activity, highest N 2 (lowest N 2 O•NO) selectivity, and high thermal stability. Because the combustion activity is closely associated with the reducibility and dispersion of CuO x , highly dispersed CuO x nanoparticles on supports are considered to play a key role in the low temperature light-off of NH 3 . For NO and N 2 O selectivities, the oxidation state of CuO x and the dissociative species of adsorbed NH 3 are suggested to be important catalytic combustion properties, respectively. On the basis of these discussions, the reaction mechanism of catalytic NH 3 combustion over CuO x /10A2B is described.

The local structures and catalytic NH 3 combustion properties of copper oxides (CuO x ) and silver (Ag) catalysts supported on aluminum oxides (Al 2 O 3 ) were studied. In order to achieve high catalytic NH 3 combustion activity and high N 2 (low N 2 O/NO) selectivity, the preparation conditions for impregnated binary catalysts were optimized. In comparison with the single CuO x /Al 2 O 3 and Ag/Al 2 O 3 , binary CuO x −Ag supported on Al 2 O 3 showed high performance for catalytic NH 3 combustion. Among the binary catalysts, sequentially impregnated CuO x /Ag/Al 2 O 3 exhibited the highest activity and N 2 selectivity. Because the combustion activity is closely associated with the Ag−Ag coordination number estimated from Ag K-edge XAFS, highly dispersed Ag nanoparticles supported on Al 2 O 3 are considered to play a key role in the lowtemperature light-off of NH 3 . CuO x /Ag/Al 2 O 3 also showed higher N 2 (lower NO) selectivity for temperatures at which NH 3 conversion reached approximately 100%, indicating that the N 2 is directly produced from the NH 3 combustion reaction over CuO x /Ag/Al 2 O 3 . Based on several analyses, a reaction mechanism for catalytic NH 3 combustion over CuO x /Ag/Al 2 O 3 was finally suggested.

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