Effect of the crystal plane figure on the catalytic performance of MnO2 for the total oxidation of propane

Abstract

Nanosized MnO₂ particles with α-, β-, γ-, and δ-crystal phases were synthesized hydrothermally, and characterized by XRD, SEM, HR-TEM, low temperature N₂ adsorption, TPR, TPD, FT-IR and Raman spectroscopy. The density functional theory (DFT) method was used to calculate the adsorption of propane and O₂ on MnO₂ catalysts. The effect of the crystal phases or crystal plane figure on the catalytic properties of MnO₂ for the total oxidation of propane was evaluated. The results showed that α-, β- and γ-MnO₂ exhibited a 1D structure, and δ-MnO₂ was a 2D layered-structure material. For deep oxidation of propane, the catalytic activities of the MnO₂ samples decreased in the order of α- ≈ γ- > β- > δ-MnO₂. Compared with the other three MnO₂ samples, α-MnO₂ exhibited the highest catalytic activity and stability for propane oxidation, its T₁₀ and T₉₀ were 204 °C and 290 °C, respectively. For the different crystal phases of MnO₂, there are distinct differences in the chemical bonds (Mn–O–Mn and Mn–O) and linking modes of [MnO₆] octahedra, the adsorption energies of propane on the surface of MnO₂ are varied in the order of (310) facet of α- > (120) of γ- > (110) of β- > (001) of δ-MnO₂, and the presence of translational motion in α-MnO₂ along with its stronger deformation and stretching modes may lead to its better catalytic activity for propane oxidation.