Enhancing the catalytic activity of MnO₂ via structural phase transition for propane combustion: Promotional role of ionic liquid

A series of manganese dioxide have been synthesized by ionic liquid assisted hydrothermal method and used for propane combustion. 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM-BF₄] was selected as the structure-directing agent, which could generate extended hydrogen bonds under hydrothermal conditions. These hydrogen bonds could be used for entropy driving of nanostructures self-assembly, thus regulating the growth of crystal. Meanwhile, the existence of [BMIM-BF₄] could interact with [MnO₆] octahedron in MnO₂ through electrostatic and π-π stacking interactions, eventually leading to the transformation from α-MnO₂ to β-MnO₂ after calcination. A series of characterization results further indicated that with the assistance of ionic liquid, the morphology of the precursor evolved from nanoflowers to nanorods attached with nanofibers, and the specific surface areas and redox properties were also enhanced. When the molar ratio of KMnO₄ to ionic liquid reached 8:1, the obtained Mn-1–500 exhibited the highest catalytic activity for propane combustion. The T₉₀ of propane on Mn-1–500 was about 310 °C, which was nearly 110 °C lower than that of Mn-0–500 prepared without the assistance of ionic liquid. These results could offer a novel strategy for the development of high-performance catalysts.