Frenkel defects facilitate oriented 1O2 formation in birnessite for enhanced catalytic oxidation of formaldehyde.

Defect strategy is one of the most effective approaches for enhancing the efficiency of Mn-based catalysts in removing formaldehyde (HCHO) under ambient conditions. Herein, the interlayer Mn-O octahedra in birnessite synergistically form with Mn vacancies through proton exchange in acidic solutions, creating surface Frenkel defects. As evidenced by highly combined physicochemical characterization and density functional theory calculations, surface Frenkel defects are highly active sites on the surface of birnessite. The surface Frenkel defects can induce surface electronic reconstruction, generating strong electrophilicity, which promotes the evolution of superoxide radicals (O 2 •−) into singlet oxygen (1O 2). In-situ quenching DRIFTS indicates that 1O 2 is the most important ROS in the oxidation process of HCHO. Additionally, the surface Frenkel defects enhance the adsorption of HCHO, promoting the dehydrogenation of HCHO to form CO, which is then rapidly oxidized to CO 2 and H 2 O under the action of 1O 2. This provide a more effective kinetic and thermodynamic catalytic pathway. The defect-rich birnessite (R-Bir) achieved complete HCHO removal in the dynamic test at 10 ppm within 10 hours, significantly outperforming defect-free birnessite (F-Bir) and most previously reported catalysts. This study precisely reveals the catalytic mechanism of HCHO over R-Bir and provides valuable insights for the design of high-performance environmental catalysts. [Display omitted] • Frenkel defects enhance birnessite's catalytic activity for HCHO oxidation. • Frenkel defects promote formation of reactive singlet oxygen 1O 2. • 1O 2 plays a crucial role in the catalytic oxidation of HCHO. • Electrophilic defects improve HCHO adsorption and conversion efficiency. [ABSTRACT FROM AUTHOR]