Rational design of MnO 2 @MnO 2 hierarchical nanomaterials and their catalytic activities.

Hierarchically structured materials have special properties and possess potential in applications in the catalytic and electrochemical fields. Herein, two kinds of hierarchical core-shell nanostructures, lavender-like α-MnO2 @α-MnO2 and balsam pear-like α-MnO2 @γ-MnO2 , were prepared by a facile room-temperature method using α-MnO2 nanowires as a backbone under acidic and alkaline conditions, respectively. When being used as a catalyst for dimethyl ether combustion, α-MnO2 @γ-MnO2 exhibited a better performance than α-MnO2 @α-MnO2 (T10 = 171 vs. 196 °C; T90 = 220 vs. 258 °C, SV = 30, 000 mL g-1 h-1 ). It is concluded that the larger surface area, higher reducibility/oxygen mobility, richer surface oxygen species, and the relatively smaller apparent activation energy are responsible for the superior performance of α-MnO2 @γ-MnO2 .