Effects of the Morphology of MnO2 Nanostructures on the Catalytic Oxidation of Toluene

Three MnO2 samples with flower (F-MnO2), rod (R-MnO2), and tube (T-MnO2) morphologies were constructed herein for catalytic toluene oxidation. T-MnO2 is superior to the other two in terms of catalytic performance and water resistance stability for toluene combustion. Overall structural and physicochemical properties characterized by X-ray diffraction, Raman spectroscopy, N2 adsorption–desorption, H2 temperature-programmed reduction, O2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and toluene temperature-programmed desorption verified that T-MnO2 exhibited larger specific surface area, stronger reducibility, and more plentiful surface oxygen species than F-MnO2 and R-MnO2, which could greatly enhance the activation and mobility of oxygen species. Notably, in situ diffuse-reflectance infrared Fourier transform spectroscopy was conducted to investigate the relationship between the activity and surface oxygen species on these catalysts. It was found that the surface lattice oxygen played an important role in the activation–oxidation process of toluene, and the difference in the surface oxygen species on the catalysts led to obvious activity changes due to their different morphologies.