Doped with up to 70 different metal salts, three semiconductor oxides (TiO2, SnO2, and WO3) formed the basis of three libraries of mixed oxides. From a high-throughput method, over 30 oxides were found to have activities similar to the well-studied Pt-doped TiO2 towards the catalyzed decomposition of a model pollutant 4-chlorophenol in water on irradiation with visible light. Two of the new materials (Ir-doped WO3 and Ce-doped SnO2) have been reproduced by conventional synthesis, and their catalytic activity was confirmed.