The states of components of highly efficient Pt/CeO2 catalysts for low-temperature oxidation of carbon monoxide are studied in detail by X-ray photoelectron spectroscopy (XPS). Using the precise calib

Low-temperature oxidation of the polycrystalline surface of bulk metallic gold with radio-frequency activated oxygen is used to obtain oxide films, which are investigated by a combination of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). The XPS estimate for the composition and thickness of the oxide films is close to Au₂O₃ and is 6–10 nm. The analysis of the Au4f and O1s lines reveals only one state of the oxidized gold, which is described by E _b(Au4f) = 85.5 eV, and two nonequivalent states of oxygen with E _b(O1s) = 529.3 eV and 530.3 eV, which are uniformly distributed over the oxide film and may be attributed to nonequivalent oxygen states in the gold oxide structure. The thermal stability study shows that the gold oxide decomposes in one stage into metal at a temperature of T _des = 530 K. According to the TPD data, the desorption activation energy is E _des = 140 kJ/mol. The high-temperature oxidation of the gold surface reveals the formation of dissolved oxygen in bulk gold. This oxygen is characterized by a broad TPD peak with a maximum at T _des = 800 K. This oxygen state is not detected by XPS. The concentration of dissolved oxygen is supposed to be below the XPS sensitivity threshold and is estimated at about 1% or less.

A set of physicochemical methods, including X-ray photoelectron spectroscopy (XPS), X-ray diraction, electron microscopy and X-ray absorption spectroscopy, was applied to study Pt/TiO2 catalysts prepared by impregnation using a commercial TiO2-P25 support and a support produced by pulsed laser ablation in liquid (PLA). The Pt/TiO2-PLA catalysts showed increased thermal stability due to the localization of the highly dispersed platinum species at the intercrystalline boundaries of the support particles. In contrast, the Pt/TiO2-P25 catalysts were characterized by uniform distribution of the Pt species over the support. Analysis of Pt4f XP spectra shows that oxidized Pt2+ and Pt4+ species are formed in the Pt/TiO2-P25 catalysts, while the platinum oxidation state in the Pt/TiO2-PLA catalysts is lower due to stronger interaction of the active component with the support due to strong interaction via Pt-O-Ti bonds. The Pt4f XP spectra of the samples after reaction show Pt2+ and metallic platinum, which is the catalytically active species. The study of the catalytic properties in ammonia oxidation showed that, unlike the catalysts prepared with a commercial support, the Pt/TiO2-PLA samples show higher stability during catalysis and significantly higher selectivity to N2 in a wide temperature range of 200–400 C.

The photocatalytic activity of TiO₂ depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO₂ in the gas-phase reduction of CO₂ is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO₂ and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO₂ in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.