Low-cerium-content catalysts supported on silica and alumina for the photocatalytic decomposition of methyl red

The photocatalytic degradation of azo dyes in wastewater presents a critical environmental challenge, particularly given the persistence and toxicity of compounds such as methyl red (MR). In this study, CeO₂-based catalysts were synthesized by dispersing 5 wt% cerium nitrate onto silica gel and α-alumina supports via incipient wetness impregnation, followed by controlled calcination at 110, 200, and 400 °C. Comprehensive characterization by XRD, TGA, Raman spectroscopy, BET, UV–Vis diffuse reflectance, and XPS confirmed the formation of highly dispersed, non-stoichiometric cerium oxide species with variable Ce³⁺/Ce⁴⁺ ratios and surface oxygen vacancy densities, dependent on the support and thermal treatment. Photocatalytic performance was evaluated through the degradation of MR in aqueous solution under 365 nm LED irradiation. Alumina-supported catalysts exhibited the highest activity, with 5CeAl200 achieving up to 51 % MR conversion in one hour, outperforming both pure CeO₂ at equivalent Ce loading and the silica-supported series. Optimal activity correlated not with surface area or Ce³⁺ content alone, but with the coexistence of Ce³⁺/Ce⁴⁺ species and the associated formation of oxygen vacancies, as evidenced by Raman and XPS analysis. These findings demonstrate that rational dispersion of cerium on inert oxide supports combined with mild thermal activation provides a sustainable and efficient alternative to more complex multicomponent or chemically assisted systems, enabling significant cerium savings without sacrificing catalytic performance.