Background Formaldehyde (HCHO) and ozone (O-3) are seriously hazardous materials to human health, especially in the indoor environment, and need to be inhibited. Manganese dioxide (MnO2) catalysts have been extensively studied in the field of environmental pollution owing to their various morphologies and crystal structures. In this study, one-dimensional rod-like MnO2 catalysts were prepared by a hydrothermal method. The crystal form and other factors affecting the activity were explored through an activity test and various characterization methods. The decomposition process of HCHO and O-3 on the most active catalyst was analyzed by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Results alpha-MnO2 displayed the best catalytic performance and achieved 90% HCHO conversion, 100% carbon dioxide (CO2) yield and 100% O-3 decomposition under different experimental conditions. The characterization results illustrated that the crystal phase of alpha-MnO2 has a suitable tunnel structure for HCHO adsorption, also leading to greater mobility of adsorbed oxygen species, abundant oxygen vacancies and active surface oxygen species, which could be the reason for the superior catalytic performance of alpha-MnO2. Formate and dioxymethylene (DOM) species were identified as the dominant intermediates by in situ DRIFTS. The surface hydroxyl (OH) group was confirmed to play an essential role in the complete oxidation of carbonaceous intermediates into harmless CO2 and water (H2O). Conclusion alpha-MnO2 exhibited the best catalytic performance among the as-prepared samples and can efficiently eliminate HCHO and O-3 in the environment. (c) 2019 Society of Chemical Industry