Oxygen Defect Engineering of β‐MnO2 Catalysts via Phase Transformation for Selective Catalytic Reduction of NO

Abstract The catalysts for low‐temperature selective catalytic reduction of NO with NH 3 (NH 3 ‐SCR) are highly desired due to the large demand in industrial furnaces. The characteristic of low‐temperature requires the catalyst with rich active sites especially the redox sites. Herein, the authors obtain oxygen defect‐rich β‐MnO 2 from a crystal phase transformation process during air calcination, by which the as‐prepared γ‐MnO 2 nanosheet and nanorod can be conformally transformed into the corresponding β‐MnO 2 . Simultaneously, this transformation accompanies oxygen defects modulation resulted from lattice rearrangement. The most active β‐MnO 2 nanosheet with plentiful oxygen defects shows a high efficiency of > 90% NO conversion in an extremely wide operation window of ≈120–350 °C. The detailed characterizations and density functional theory (DFT) calculations reveal that the introduction of oxygen defects enhances the adsorption properties for reactants and decreases the energy barriers of *NH 2 formation more than 0.3 eV (≈0.32–0.37 eV), which contributes to a high efficiency of low‐temperature SCR activity. The authors finding provides a feasible approach to achieve the oxygen defect engineering and gains insight into manganese‐based catalysts for low‐temperature NO removal or pre‐oxidation.