Influence of Titania Synthesized by Pulsed Laser Ablation on the State of Platinum during Ammonia Oxidation

A set of physicochemical methods, including X-ray photoelectron spectroscopy (XPS), X-ray diffraction, electron microscopy and X-ray absorption spectroscopy, was applied to study Pt/TiO$_{2}$ catalysts prepared by impregnation using a commercial TiO$_{2}$-P25 support and a support produced by pulsed laser ablation in liquid (PLA). The Pt/TiO$_{2}$-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/TiO$_{2}$-P25 catalysts were characterized by uniform distribution of the Pt species over the support. Analysis of Pt4f XP spectra shows that oxidized Pt$^{2+}$ and Pt$^{4+}$ species are formed in the Pt/TiO$_{2}$-P25 catalysts, while the platinum oxidation state in the Pt/TiO$_{2}$-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 Pt$^{2+}$ 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/TiO$_{2}$-PLA samples show higher stability during catalysis and significantly higher selectivity to N$_{2}$ in a wide temperature range of 200–400 °C.