Optimization of cerium doping of TiO2 for photocatalytic reduction of CO2 and photocatalytic decomposition of N2O

The cerium-doped TiO2 photocatalysts (0–0.8 mol% Ce) were prepared by using a sol–gel method. Textural, structural, optical and electronic properties of Ce/TiO2 photocatalysts were characterized in detail by using nitrogen physisorption, powder X-ray diffraction, diffuse reflectance UV–Vis spectroscopy and contact potential difference measurements. It was proved that increasing amount of cerium ions in TiO2 (1) decreased the anatase crystallite size, which corresponded to the increase in specific surface area of the photocatalysts, and (2) decreased the absorption edge (shifting the spectral response toward the visible light region). The prepared photocatalysts were tested for CO2 photocatalytic reduction in a stirred batch annular reactor, and methane was a main product. The photocatalytic decomposition of nitrous oxide was carried out in batch reactor with circulation, and only oxygen and nitrogen were detected as reaction products. It was found out that the energies of electrons and holes played the key role in both photocatalytic reactions and can be markedly affected by doping of TiO2 by cerium.