Mn (Ce_x)/γ-Al₂O₃ Catalysts with Notably Improved Performances for Catalytic Ozonation of Pollutants in Petroleum Refinery Wastewater

In this work, Ce-doped Mn/γ-Al₂O₃ catalysts (Mn (Ce_x)/γ-Al₂O₃) with different Ce/Mn molar ratios were prepared for catalytic ozonation of pollutants in petroleum refinery wastewater (PRW). Results showed that compared to Mn/γ-Al₂O₃ catalyst, the performances of Mn (Ce_x)/γ-Al₂O₃ catalysts were notably improved, especially Mn (Ce_0.20)/γ-Al₂O₃ catalyst demonstrated the highest activity and improved stability for the degradation of PRW (> 97% of chemical oxygen demand (COD) in PRW was removed and the molecules of petroleum-derived pollutants were almost completely degraded in 1.5 h treatment, and the catalyst showed no obvious decrease in activity after 5 cycles). The results of catalyst characterization confirmed that doping Ce changed the growth characteristics of the catalysts, increased the content of active phase α-MnO₂ in the catalysts and led to the growth of α-MnO₂ along crystal planes (310) preferentially, prevented catalyst particles from growing, and also enhanced the dispersion of those catalyst particles. Moreover, electron paramagnetic resonance (EPR) experiments revealed that Mn (Ce_0.20)/γ-Al₂O₃ catalyst promoted the production of more hydroxyl radicals (•OH) and superoxide anion (•O₂⁻). The influences of catalyst dose, O₃ concentration and pH on the degradation were also investigated. This work provided a theoretical basis and an experimental reference for the preparation of highly active Mn-based catalysts for deep ozonation of PRW by HCOP.