Synergistic promotion effects of surface hydroxyl groups (-OH) and nitrate groups (-NO₃) on catalytic ozonation of toluene over MnFe catalyst

A series of MnFe catalysts were prepared by hydrothermal synthesis combined with heat treatment at different temperatures. The characterizations demonstrated that MnFe-120 with both surface -OH and -NO₃, MnFe-175 with surface -OH, MnFe-300 containing neither surface -OH nor -NO₃, and MnFe-300-NO₃ containing surface -NO₃ were gained by drying or calcination and impregnation. The activity evaluation showed that the order of catalytic activity was MnFe-120 > MnFe-175 > MnFe-300-NO₃ > MnFe-300. Further, characterizations and experiment results revealed that O₃ adsorbed on the surface of the catalyst can interact with surface -OH and generated hydroxyl radicals (·OH). The presence of surface -NO₃ provided more Lewis acid sites, thereby promoting H₂O adsorption and conversion to the surface -OH, which supplemented the surface -OH consumed by the interaction with O₃. It was deduced that the coexistence of surface -OH and -NO₃ improved the production of·OH, which synergistically promoted the catalytic ozonation of toluene.