Role of Frustrated Lewis Pairs in α-MnO2 for Low-Temperature Toluene Oxidation with Ozone

Abstract

The catalytic performance of α-MnO2 in the ozonation of volatile organic compounds (VOCs) is highly synthesis-dependent, which determines surface defects, redox properties, and active site distribution. To investigate this, we prepared three α-MnO2 catalysts through precipitation (MnO2–P), hydrothermal synthesis (MnO2–H), and the crystal transformation approach (MnO2–C). The superior performance of MnO2–C is attributed to its abundant oxygen vacancies and favorable Mn3+/Mn4+ ratio, whereas the efficiency of MnO2–P and MnO2–H is limited by their coordination-saturated Mn sites and insufficient oxygen vacancies, leading to poor O3 activation. In contrast, the crystal transformation approach induces structural defects in MnO2–C, creating abundant oxygen vacancy clusters and an optimized Mn3+/Mn4+ ratio. This unique configuration forms frustrated Lewis pairs (FLPs) between Mn cations (LA) and oxygen anions (LB), synergistically activating O3 to generate reactive oxygen species. As a result, MnO2–C achieves 100% toluene conversion with 85% CO2 selectivity at 30 °C, far surpassing MnO2–P and MnO2–H. This work demonstrates that defect engineering via crystal transformation is an effective strategy for designing highly active catalysts for VOC removal.