Dynamic Evolution of Mn–O Site and ROS Formation in Room-Temperature Formaldehyde Oxidation over Phase-Dependent MnO ₂

Formaldehyde (HCHO) is a hazardous indoor carcinogen that poses significant risks to air quality and human health. Manganese dioxide catalysts demonstrate extensive excellence and broad prospects for formaldehyde removal. However, the dynamic evolution of active sites and the formation of reactive oxygen species (ROS) in MnO 2 catalysts, particularly under room-temperature conditions, still remain poorly understood. In this work, δ-MnO 2 exhibited outstanding catalytic potential among various MnO 2 crystal phases, achieving nearly complete HCHO conversion and stable performance over 48 h at ambient conditions. In situ Raman, EPR, in situ TPD-MS, and in situ DRIFTS techniques were employed to systematically monitor the tension dynamics of [MnO 6 ] octahedra, ROS, and reaction intermediates. Complementary DFT calculations further elucidated the changes in the electronic structure and orbital interactions. This study deepens the mechanistic understanding of active site dynamics and ROS formation, and offers theoretical guidance for the rational design of high-performance MnO 2 -based catalysts.