Effect of impregnation strategy on structural characteristics of Ce–Mn/Al2O3 and its catalytic ozonation of benzoic acid

Abstract

Ce–Mn binary oxides supported on Al₂O₃ (Ce–Mn/Al₂O₃), with enhanced activity and stability for catalytic ozonation of benzoic acid, were synthesized using a facile impregnation method. The competitive synergetic effects between cerium and manganese significantly influenced the structural characteristics and catalytic performance of the catalysts depending on the impregnation sequence. Catalysts prepared via the one-step impregnation process exhibited a higher concentration of homogeneous Ce³⁺ species on the catalyst surface. This led to an increase in surface oxygen vacancies, thereby enhancing catalytic activity. In contrast, the two-step impregnation process resulted in fewer oxygen vacancies due to reduced competitive effects between cerium and manganese. Overall, the optimized Ce–Mn/Al₂O₃ catalysts demonstrated improved catalytic performance in ozonation reactions, highlighting the importance of impregnation method and calcination conditions in tailoring catalyst properties for enhanced activity and stability. Oxygen vacancies play a crucial role as active sites for ozone adsorption and dissociation into *O₂ and *O, facilitated by the reduction of Mn⁴⁺ to Mn³⁺ and the oxidation of Ce³⁺ to Ce⁴⁺. This process forms an electron closed loop that maintains electron balance. The synergistic interactions between cerium and manganese enable rapid electron transfer between Ce⁴⁺ and Mn³⁺, facilitating the regeneration of Ce³⁺ and Mn⁴⁺. Due to the increase of the dual redox conjugate pairs and the surface reactive oxygen species, the catalytic ozonation activity and stability of Ce–Mn/Al₂O₃ was enhanced.