Assembly of sphere-structured MnO2 for total oxidation of propane: Structure-activity relationship and reaction mechanism determination

Through morphology control and structure construction of manganese catalyst to improve the conversion of VOCs is still a significant challenge in the field of environmental catalysis. Herein, secondary sphere structured delta-type manganese oxide (MnO2-SS) was synthesized via a simple room temperature two-step method. Compared with other sphere-type MnO2 samples, MnO2-SS exhibited a higher propane oxidation activity (T-90 = 238 degrees C), turnover frequency (14.54 x 10(-7) s(-1) at 240 degrees C), and stability in H2O, NO2, and CO atmospheres. Experimental results indicated that MnO2-SS exhibited an ultrahigh specific surface area, a high surface concentration of active Mn4+ species and superior surface oxygen mobility. In-situ DRIFTs revealed that active oxygen species exhibit a key role in formation and dissociation of intermediate carboxylates. Electron paramagnetic resonance, O K-edge results and density functional theory calculation revealed that numerous oxygen vacancies existed on MnO2-SS. These vacancies can facilitate adsorption and activation of O-2 to generate active reactive oxygen species, which lead to superior propane and intermediate carboxylates oxidation activity. This work provides new strategy to enhance the surface oxygen activity of manganese oxide.