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

In this work, Ce-doped Mn/gamma-Al2O3 catalysts (Mn (Ce-x)/gamma-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/gamma-Al2O3 catalyst, the performances of Mn (Ce-x)/gamma-Al2O3 catalysts were notably improved, especially Mn (Ce-0.20)/gamma-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 alpha-MnO2 in the catalysts and led to the growth of alpha-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)/gamma-Al2O3 catalyst promoted the production of more hydroxyl radicals (center dot OH) and superoxide anion (center dot O-2(-)). The influences of catalyst dose, O-3 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.