Oxygen Defect Engineering of beta-MnO2 Catalysts via Phase Transformation for Selective Catalytic Reduction of NO

The catalysts for low-temperature selective catalytic reduction of NO with NH3 (NH3-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 beta-MnO2 from a crystal phase transformation process during air calcination, by which the as-prepared gamma-MnO2 nanosheet and nanorod can be conformally transformed into the corresponding beta-MnO2. Simultaneously, this transformation accompanies oxygen defects modulation resulted from lattice rearrangement. The most active beta-MnO2 nanosheet with plentiful oxygen defects shows a high efficiency of > 90% NO conversion in an extremely wide operation window of approximate to 120-350 degrees 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 *NH2 formation more than 0.3 eV (approximate to 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.