Preparation of Mn-Ce oxide-loaded Al2O3 by citric acid-assisted impregnation for enhanced catalytic ozonation degradation of dye wastewater

Abstract

The performance of supported catalysts is significantly affected by the dispersion degree of the active components on the support. In this study, citric acid (CA) was used as a modifier to prepare Al₂O₃ supported Mn-Ce oxides (Mn-Ce/CA-Al₂O₃) by the impregnation-calcination method. The characterization results showed that adding citric acid enhanced the dispersion of Mn-Ce oxides on the support, rendering Mn-Ce/CA-Al₂O₃ with a larger specific surface area and abundant surface hydroxyl groups, thereby providing more reaction sites for catalytic ozonation. The Mn-Ce/CA-Al₂O₃ exhibited excellent catalytic ozonation performance in degrading Reactive Black 5 (RB5) dye. It achieved nearly complete decolorization of RB5 within 60 min, with a COD removal efficiency of 60%, which was superior to the sole ozonation (30%). Furthermore, the Mn-Ce/CA-Al₂O₃ system demonstrated significant degradation of RB5 over a wide pH range of 3–11. Based on the XPS and EPR analysis results, a preliminary mechanism of catalytic ozonation over the Mn-Ce/CA-Al₂O₃ was proposed. The redox cycle of Mn³⁺/Mn⁴⁺ and Ce³⁺/Ce⁴⁺ effectively accelerated the electron transfer process, thus promoting the generation of reactive oxygen species (ROS) and improving the degradation of RB5. Meanwhile, the Mn-Ce/CA-Al₂O₃ exhibited superior catalytic stability and effective treatment capabilities for real dye wastewater.