Investigation of the ozone-induced oxidation of soot over LaMnO3 catalyst using O3/O2 temperature-programmed desorption experiments

In this study, we investigated how the catalytic redox cycle occurs over a lanthanum manganese oxide (LaMnO3) catalyst when applied to the ozone-induced oxidation of soot. This was accomplished by tracking the catalysis using O-3/O-2 temperature-programmed desorption coupled with X-ray photoelectron spectroscopy (XPS). We prepared the catalyst by the citric acid sol-gel method to obtain a catalyst with a uniform perovskite phase and improved specific surface area. The catalyst was remarkably active in promoting ozone-induced soot oxidation within the temperature range of 25-125 degrees C. The active oxygen species were superoxide ions combined with Mn4+ ions on the catalyst surface. It was presumed the superoxide ion migrates over the surface Mn4+ sites and either desorbs as molecular oxygen or oxidizes the soot particles if it reaches the interface between soot and catalyst particles. The redox cycle was completed by the Mn4+-to-Mn3+ transition, which accompanied the detachment of superoxide ions. No evidence was found to support the involvement of the bulk phase of the catalyst with the redox cycle. The ozone-induced redox cycle was presumed to exclusively occur on the surface of the catalyst.