Effect of Phase Structure of MnO2 Nanorod Catalyst on the Activity for CO Oxidation

The α-, β-, γ-, and δ-MnO 2 nanorods were synthesized by the hydrothermal method. Their catalytic properties for CO oxidation were evaluated, and the effects of phase structures on the activities of the MnO 2 nanorods were investigated. The activities of the catalysts decreased in the order of α- ≈ δ- > γ- > β-MnO 2 . The mechanism of CO oxidation over the MnO 2 nanorods was suggested as follows. The adsorbed CO was oxidized by the lattice oxygen, and the MnO 2 nanorods were partly reduced to Mn 2 O 3 and Mn 3 O 4 . Then, Mn 2 O 3 and Mn 3 O 4 were oxidized to MnO 2 by gaseous oxygen. CO chemisorption, the Mn−O bond strength of the MnO 2, and the transformation of intermediate oxides Mn 2 O 3 and Mn 3 O 4 into MnO 2 can significantly influence the activity of the MnO 2 nanorods. The activity for CO oxidation was mainly predominated by the crystal phase and channel structure of the MnO 2 nanorods.