Spontaneous generation of singlet oxygen on microemulsion-derived manganese oxides with rich oxygen vacancies for efficient aerobic oxidation.

Developing innovative catalysts for efficiently activating O 2 into singlet oxygen ( 1 O 2 ) is a cutting-edge field with the potential to revolutionize green chemical synthesis. Despite its potential, practical implementation remains a significant challenge. In this study, we design a series of nitrogen (N)-doped manganese oxides (N y -MnO 2 , where y represents the molar amount of the N precursor used) nanocatalysts using compartmentalized-microemulsion crystallization followed by post-calcination. These nanocatalysts demonstrate the remarkable ability to directly produce 1 O 2 at room temperature without the external fields. By strategically incorporating defect engineering and interstitial N, the concentration of surface oxygen atoms (O s ) in the vicinity of oxygen vacancy (O v ) reaches 51.1% for the N 55 -MnO 2 nanocatalyst. This feature allows the nanocatalyst to expose a substantial number of O v and interstitial N sites on the surface of N 55 -MnO 2 , facilitating effective chemisorption and activation of O 2 . Verified through electron paramagnetic resonance spectroscopy and reactive oxygen species trapping experiments, the spontaneous generation of 1 O 2 , even in the absence of light, underscores its crucial role in aerobic oxidation. Density functional theory calculations reveal that an increased O v content and N doping significantly reduce the adsorption energy, thereby promoting chemisorption and excitation of O 2 . Consequently, the optimized N 55 -MnO 2 nanocatalyst enables room-temperature aerobic oxidation of alcohols with a yield surpassing 99%, representing a 6.7-fold activity enhancement compared to ε-MnO 2 without N-doping. Furthermore, N 55 -MnO 2 demonstrates exceptional recyclability for the aerobic oxidative conversion of benzyl alcohol over ten cycles. This study introduces an approach to spontaneously activate O 2 for the green synthesis of fine chemicals.