Manganese Oxide-Based Catalysts for Soot Oxidation: A Review on the Recent Advances and Future Directions

Soot particles generated by combustion engines, such as gasoline direct injection engines (GDIs) and diesel engines, must be removed from the exhaust to meet the tightened emissions standards. The particulate filters with coated catalysts are common and successful techniques for the oxidation and removal of soot, during which the catalytic performance of the used catalyst plays a critical role. This review aims to discuss the soot oxidation behavior using manganese oxides as catalysts considering their beneficial natures of high catalytic oxidation activities, cost effectiveness, and environmental friendliness. This review begins with a brief discussion on how the various influential factors (e.g., soot composition, soot–catalyst mixing ratios, contact conditions, and gaseous reactions) could affect the soot catalyst activities. After that, a detailed introduction to various kinds of manganese oxide-based catalysts, including pure manganese oxides and types of perovskites, composites, and mixed, as well as manganese oxides decorated by nanoparticles or doped with metals, was provided, with the focus on the catalytic performances of each kind of catalyst and the catalytic mechanisms. The thermal stabilities of different manganese oxide-based catalysts were then briefly introduced. Finally, remarkable results and interesting findings were summarized, which are expected to provide valuable guidance for the synthesis, design, and performance optimization of manganese oxide-based catalysts for soot catalytic combustion.