Effect of phase structure of MnO2 nanorod catalyst on the activity for CO oxidation

The alpha-,beta-,gamma-, and delta-MnO2 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 MnO2 nanorods were investigated. The activities of the catalysts decreased in the order of alpha- approximate to delta- > gamma- > beta-MnO2. The mechanism of CO oxidation over the MnO2 nanorods was suggested as follows. The adsorbed CO was oxidized by the lattice oxygen, and the MnO2 nanorods were partly reduced to Mn2O3 and Mn3O4. Then, Mn2O3 and Mn3O4 were oxidized to MnO2 by gaseous oxygen. CO chemisorption, the Mn-O bond strength of the MnO2, and the transformation of intermediate oxides Mn2O3 and Mn3O4 into MnO2 can significantly influence the activity of the MnO2 nanorods. The activity for CO oxidation was mainly predominated by the crystal phase and channel structure of the MnO2 nanorods.