Promoting the Catalytic Ozonation of Toluene by Introducing SO₄^2– into the α-MnO₂/ZSM-5 Catalyst to Tune Both Oxygen Vacancies and Acid Sites

Mn-based catalysts hold the promise of practical applications in catalytic ozonation of toluene at room temperature, yet improvement of toluene conversion and COx selectivity remains challenging. Here, an innovative α-MnO2/ZSM-5 catalyst modified with SO42- was successfully prepared, and both characterizations and density functional theory (DFT) calculations showed that SO42- introduction facilitated the formation of oxygen vacancies, Lewis and Brönsted acid sites, and active oxygen species and enhanced the adsorption ability of toluene on α-MnO2/ZSM-5. Characterizations also showed that SO42- introduction made the catalyst possess larger specific surface area, superior reducibility, and stronger surface acidity. As a result, α-MnO2/ZSM-5 with a S/Mn molar ratio of 0.019 exhibited the best toluene conversion and COx selectivity, 87 and 94%, respectively, after the reaction for 8 h at 30 °C under an initial concentration of 5 ppm toluene and 45 ppm ozone, relative humidity of 45%, and space velocity of 32,000 h-1, far superior to those of non-noble catalysts reported to date under comparable reaction conditions. The synergistic role of increased oxygen vacancies and acid sites of α-MnO2/ZSM-5 modified with SO42- resulted in excellent toluene conversion and COx selectivity. The findings represented a critical step toward the rational design and synthesis of highly efficient catalysts for catalytic ozonation of toluene.