Fig. 5.
Electronic structure of the activated catalyst based on an oxidized α-Mn3O4 hausmannite structure as a model system containing both octahedral and tetrahedral Mn–O environments. (A) Schematic representation of the α-Mn3O4 hausmannite and δ-MnO2 structures illustrating their common underlying face-centered cubic oxygen framework and similarity in octahedral Mn structure. The unique tetrahedral Mn sites in α-Mn3O4 are highlighted. (B) Evolution of oxidation states of Mn and O as electrons are removed from the α-Mn3O4 model system. Oxidation states are derived from the values of characteristic atom-projected magnetic moments according to typical values observed for computed manganese oxides and hydroxides. (C) Schematic of the band structure of the activated catalyst system derived from the “α-Mn3O4– 3e−” model. The Td and Oh sections of the band diagram represent tetrahedral and octahedral Mn environments, while the Jahn–Teller orbital depicts the relative position of the Oh LUMO accounting for structural relaxation through Jahn–Teller distortion. (D) Average valence of Mn and O as a function of oxidation level as indicated by the electronically titrated α-Mn3O4 model.