<p>CeO₂/chitosan/expanded graphite (CeO₂/CS/EG) was prepared by hydrothermal synthesis and used for the heterogeneous catalytic ozonation of 4-chlorophenol (4-CP) in wastewater. The catalysts were characterized by XRD, SEM, EDS, BET, XPS and FT-IR. In order to study the catalytic activity of CeO₂/CS/EG, the catalytic performance of CeO₂/CS/EG/O₃ system was compared with other reaction systems, and the effects of catalyst dosage, pH, initial 4-CP concentration, O₃ concentration and co-existing ions on the degradation of 4-CP in this system were investigated. The results showed that CeO₂/CS/EG/O₃ system showed high catalytic activity for 4-CP degradation. Under the optimal conditions (pH &gt; 6.5, catalyst dosage 1.0 g L^–1, initial concentration of 4-CP 100 mg L^–1, ozone concentration 2.5 mg L^–1, reaction time 30 min), the removal rate and mineralization rate of 4-CP reached 99.4% and 70.2%, respectively. This degradation process conformed to first-order reaction kinetics. After five consecutive catalytic cycles, the removal rate of 4-CP was still above 97%, showing the excellent stability and reusability of CeO₂/CS/EG. The ·OH was identified as the main reactive species causing 4-CP degradation through free radical scavenging experiments. According to the main intermediates measured by the HPLC-MS technique, five possible degradation processes of 4-CP catalytic ozonation were deduced.</p> Graphical abstract <p>CeO₂/chitosan/expanded graphite (CeO₂/CS/EG) were prepared by hydrothermal synthesis and used for heterogeneous catalytic ozonation of 4-chlorophenol (4-CP) in wastewater. The results showed that the removal efficiency of 4-CP and total organic carbon (TOC, a key parameter representing the total carbon content in organic compounds that indicates mineralization degree) reached 99.4 and 70.2% under optimal conditions. Besides, OH^⋅ was identified as the main substance causing 4-CP degradation.</p> <p></p>