Structural and Surface Effect of MnO2 for Low Temperature Selective Catalytic Reduction of NO with NH3

α- and β-MnO2 with different phase structures were prepared by hydrothermal method and investigated for low temperature SCR. The α-MnO2 catalyst showed higher activity than the β-MnO2 catalyst at low temperature region. Characterization results revealed that the activity predominately depended on the tunnel (or layer) structure and surface chemisorbed oxygen rather than BET surface area, crystallinity, surface Mn4+/Mn3+ ratio and redox property. α-MnO2 showed the highest activity on account of [2 × 2] tunnel and the most surface oxygen to promote the NH3 adsorption and activation. β-MnO2 exhibited less activity because of [1 × 1] tunnel structure and little surface absorbed oxygen. Further, DFT calculations were used to model the clean and defect surface as well as the NH3 adsorptions on the tunnels of α- and β-MnO2 model surfaces.