Photocatalytic and photochemical processes on the surface of uranyl-modified oxides: An in situ XPS study

[Display omitted] •The lability of uranium on the surface of porous supports correlates with the photocatalytic activity under visible light.•A fast and reversible two-electron transition (U6+ ↔ U4+) occurs on TiO2 under visible light and exposure to oxygen.•A slower and only one-electron transition (U6+ ↔ U5+) occurs on the surface of Al2O3 or SiO2 oxides.•The TiO2 supported with uranyl ions has a high stability and oxidizes organic compounds with a high photonic efficiency. The development of photocatalysts active under visible light attracts great attention due to the prospect for the utilization of solar radiation. The modification of porous supports with uranyl ions results in the ability for oxidation of organic compounds under visible light up to 500 nm in wavelength. In this study, the titania, alumina, and silica were modified with 5 wt.% of uranyl nitrate using the impregnation method and tested in the oxidation of acetone vapor under visible light (450 nm) in a continuous-flow setup. The catalyst based on TiO2 revealed a substantially higher activity compared to other oxides. X-ray photoelectron spectroscopy was employed to elucidate the processes occurring on the surface of uranyl-modified catalysts and explain the effect of support on the photocatalytic activity. New data about the uranium transformations on the surface of titania, alumina, and silica under X-rays and visible light were received using the XPS method. On the Al2O3 and SiO2 surfaces, the uranium was slowly reduced from U6+ to the U5+ but a faster reduction to the U4+ state was observed on the TiO2 surface. The conclusion about the influence of uranium lability on the different surfaces on the photocatalytic activity under visible light is made.