The R-, 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 R-≈ 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.

La 0.5 Sr 0.5 MnO 3 cube and nanoparticle catalysts were synthesized by the hydrothermal and coprecipitation method, respectively. The catalytic performances for CO and CH 4 oxidation were evaluated, and the effect of Jahn-Teller distortion on the catalytic performance was elucidated. La 0.5 Sr 0.5 MnO 3 nanoparticle catalyst showed a higher activity than the cube catalyst for CO oxidation at a lower temperature. While the catalytic activity of the cubes significantly increased at higher temperature, the complete conversion temperatures for CO were both the same at 210 °C. The trend for CH 4 oxidation activity was similar to the trend observed for CO oxidation activity. The catalytic mechanism of CO oxidation over La 0.5 Sr 0.5 MnO 3 cubes is proposed that the adsorbed CO was oxidized by the lattice oxygen. Then, the chemisorbed oxygen over La 0.5 Sr 0.5 MnO 3 cubes was transformed into the lattice oxygen by MnO 6 octahedra to reinforce the consumed lattice oxygen. The catalytic performances of La 0.5 Sr 0.5 MnO 3 cubes and nanoparticles were mainly predominated by Jahn-Teller distortion of the catalysts.

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