Defective perovskite LaMnO3 catalysts for ventilation air methane combustion

The emission of ventilation air methane causes serious air pollution.owing to 21 times higher greenhouse potential in comparison to CO2. Catalytic combustion of methane has received considerable attention due to its effectiveness in eliminating the trace amount of methane in the ventilation air. The key scientific problems and difficulties of the methane combustion reaction are the determination of active sites and elucidation of reaction mechanism. A series of defective rhombohedral perovskite LaMnO3 materials with different La/Mn molar ratios were prepared using the modified Pechini method.and tested in methane combustion. The as-synthesized perovskite samples were characterized by means of X-ray diffraction.N2 physisorption.transmission electron microscopy.and H2-temperature programmed reduction. In addition.the kind and relative content of oxygen species in the samples were measured by X-ray photoelectron spectroscopy.O2-temperature programmed desorption.and Raman spectroscopy techniques. The XRD results evidenced that the pure perovskite phase was simply synthesized for all the samples. The results showed that the perovskite LaMnO3-90 possessed a mesoporous structure with larger specific surface area. Moreover.the Raman.XPS.and O2-TPD results exhibited that the perovskite LaMnO3-90 had more surface lattice oxygen sites.endowing the highest methane combustion activity. The perovskite LaMnO3-90 delivered stable run without obvious deactivation owing to its structural stability. It is found that the methane conversion had a positive correlation with the concentration of surface lattice oxygen among the series LaMnO3-x catalysts. Hence.the authors speculate that the lattice oxygen in the perovskite surface may be responsible for the methane activation during the methane combustion.