The degradation of diclofenac in a like Fenton system, FeCeOx-H2O2, was studied in details. The influencing factors, reaction kinetics, reaction mechanism and degradation pathways of diclofenac were investigated. The optimum conditions were at a solution pH of 5.0, H2O2 concentration of 3.0 mmol/L, diclofenac initial concentration of 0.07 mmol/L, FeCeOx dosage of 0.50 g/L, and 84% degradation of diclofenac was achieved within 40 min. The kinetics of FeCeOx catalyzed H2O2 process involved adsorption-dominating and degradation-dominating stages and fitted pseudo-second order model and pseudo-first order model, respectively. Singlet oxygen O-1(2) was the primary intermediate oxidative species in the degradation process; superoxide radical anion O-2(center dot-) also participated in the reaction. The surface cerium and iron sites and the oxygen vacancies in the FeCeOx catalyst were proposed to play an important role in H2O2 decomposition and active species generation. The detected intermediates were identified as hydroxylated derivatives (m/z of 310,326 and 298), quinone imine compounds (m/z of 308, 278 and 264) and hydroxyl phenylamine (m/z of 178). The majority intermediates were hydroxylated derivatives and the minority was hydroxyl phenylamine. The degradation pathways were proposed to involve hydroxylation, decarboxylation, dehydrogenation and C-N bond cleavage. (C) 2017 Elsevier B.V. All rights reserved.