BACKGROUND Advanced oxidation processes are an interesting alternative for wastewater treatment. The classic Fenton process, involving ferrous ions and hydrogen peroxide, requires strict pH adjustment and further iron removal. To overcome these difficulties, heterogeneous reaction with solid catalysts has been proposed. Until now, the solid catalysts have been employed as powders in agitated batch reactors. In this work, the application of structured catalysts for processes in flow is proposed. Nano-FeO x/Al2O3/cordierite monolithic catalysts were prepared making firstly an alumina coating, and then impregnation with aqueous solution of iron nitrate at various concentrations. The synthesized catalysts were characterized using various techniques and then they were studied for the dark Fenton reaction. RESULTS The coating adherence in the structured catalysts was better than 93%. Also, high homogeneity of the coating was confirmed. From results of physicochemical characterization, it was deduced that the active phase would consist of oligonuclear (FeO)( n) nanoclusters highly dispersed on the surface of the alumina support. The catalytic activity was evaluated in phenol peroxidation in aqueous phase (without light, pH 3, 30 degrees C), as a model reaction. The monolithic catalysts were active and chemically stable. The most active catalyst (phenol conversion > 90% at 80 min of reaction) was reused 12 times. CONCLUSIONS The monolithic catalysts show a high potential for application in heterogeneous dark Fenton-type reactions. Then, wastewater treatment by means of advanced oxidation processes could be carried out in continuous mode without further operation to separate the catalyst. (c) 2020 Society of Chemical Industry