BACKGROUND Photoreduction of 4-nitrophenol (4-NP) photocatalytically to 4-aminophenol (4-AP) is considered a promising treatment of this recalcitrant pollutant. 4-aminophenol is widely applied as an intermediate in the pharmaceutical and agricultural industries. In this work, iridium/cerium dioxide (Ir/CeO2) photocatalysts with different Ir contents (0.5, 1.0 and 2.0 wt%) were studied in the photoreduction of 4-NP using Na2SO3 as hole scavengers under UV irradiation. In order to identify their physicochemical properties, the materials were studied by several techniques and photoactivity was monitored by UV-visible spectroscopy. RESULTS The characterization results provided evidence that the modification of CeO2 by impregnation of Ir causes a decrease in CeO2 textural properties and its band gap energy. The photocatalytic reduction of 4-nitrophenol was enhanced by 26.1% using Ir/CeO2 1.0 wt% in comparison with CeO2 support. The phrase is related with the comparison between the photocatalytic behavior of Ir/CeO2 1.0 wt% photocatalyst in regard the results evidenced with CeO2 unmodified. An effect of the metal loading over photoactivity was observed and the optimal Ir content was 1.0 wt%. A reduction of 84% was obtained using 1.0 wt%Ir/CeO2, whereas for higher metal loading (2.0 wt%) 4-NP reduction decreased by 72%. CONCLUSION The enhancement in the photocatalytic behavior of the Ir/CeO2 series could be related to the presence of Ir delta+ and Ir-0 species evidenced by X-ray photoelectron spectroscopy (XPS), thus, Ir delta+ species could favor the adsorption of the pollutant and Ir-0 particles could act as trap of the photogenerated electrons that are responsible for reduction of the nitrocompound. The decrease in photoactivity when 2.0 wt% Ir/CeO2 was used as photocatalyst could be associated with partial blockage of the surface active sites by increasing amounts of metal. (c) 2019 Society of Chemical Industry