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 δ-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 (T₉₀ = 238 ℃), turnover frequency (14.54 × 10⁻⁷ s⁻¹ at 240 ℃), 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 O₂ 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.