Preparation of MnO_x-Al₂O₃ aerogels and synergistic catalytic oxidation of toluene via ozone

At present, it is challenging to improve the activity and humidity resistance of ozone catalysts. Herein, an integrated MnO_x-Al₂O₃ aerogel was prepared by a sol-gel method in this study, and its application in catalytic ozonation of toluene was explored preliminarily. Compared with the MnO_x-SiO₂ aerogel and impregnation catalysts (MnO_x-silicalite-1 and MnO_x-γ-Al₂O₃), the MnO_x-Al₂O₃ aerogel exhibited superior performance in toluene removal and enhanced ozone utilization efficiency under optimal conditions (room temperature, O₃ : C₇H₈ = 14 : 1, GHSV = 45 000 h⁻¹ and 120 ppm C₇H₈). After reacting for 360 min, the 5 wt% MnO_x-Al₂O₃ aerogel still showed stable catalytic ability, with the efficiency of toluene removal and ozone degradation maintained at 64.1% and 62.7%, respectively. Based on SEM characterization, the MnO_x-Al₂O₃ aerogel demonstrated low MnO_x agglomeration. From XPS and NH₃-TPD analyses, it was found that the catalyst had a high content of Mn³⁺/Mn, O_β/O, oxygen vacancies and acid sites, which was positively related to ozone degradation. Among them, an increase in the number of weak acid and moderately strong acid sites could prolong the life of active oxygen, which was the key to promoting the deep oxidation of toluene effectively. In addition, the MnO_x-Al₂O₃ aerogel exhibited remarkable load-adjustability and humidity resistance. Therefore, the development of aerogel catalysts for catalytic ozonation of toluene is an effective strategy to alleviate the current ozone catalyst problem.