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 MnOx-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 MnOx-SiO2 aerogel and impregnation catalysts (MnOx-silicalite-1 and MnOx-gamma-Al2O3), the MnOx-Al2O3 aerogel exhibited superior performance in toluene removal and enhanced ozone utilization efficiency under optimal conditions (room temperature, O-3 : C7H8 = 14 : 1, GHSV = 45 000 h(-1) and 120 ppm C7H8). After reacting for 360 min, the 5 wt% MnOx-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 MnOx-Al2O3 aerogel demonstrated low MnOx agglomeration. From XPS and NH3-TPD analyses, it was found that the catalyst had a high content of Mn3+/Mn, O-beta/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 MnOx-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.