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

Abstract

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.