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

Abstract

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.

Controllable Synthesis of Porous and Hollow Nanostructured Catalyst Particles and Their Soot Oxidation

“…Thus, the CO gas penetrated the hollow and porous structures, resulting in a similar CO conversion performance. Internal combustion engine emissions also comprise soot particles, which originate from carbon solidification combustion that must be oxidized. − During oxidation, soot particles react with O 2 to produce CO 2 . Thus, the effectiveness of the hollow and porous TWC particles in oxidizing soot particles was evaluated by measuring the rate of CO 2 formation, which served as an expression of their catalytic performance.…”

Advancements in In-Cylinder and After-Treatment Strategies for Mitigating Pollutants from Diesel Engines: A Critical Review

“…A catalyst providing the possibility of producing peroxides and superoxide species or even the presence of oxygen radicals in the reaction atmosphere could hasten reaction kinetics. Moreover, addition of value-added impurity ions into the lattice of solid solutions creates additional oxygen vacancies which is the fundamental catalytic requirement for soot oxidation . Complete soot oxidation is not feasible at temperatures suited for the LTC combustion modes.…”

“…Moreover, addition of value-added impurity ions into the lattice of solid solutions creates additional oxygen vacancies which is the fundamental catalytic requirement for soot oxidation. 279 Complete soot oxidation is not feasible at temperatures suited for the LTC combustion modes. However, the amount of soot produced in LTC is already negligible; hence, existing methods with some refinements could suffice.…”

Manganese oxide-based catalysts for the sustainable synthesis of value-added chemicals through oxidation processes: a critical review and perspectives for the future

“…1,2,4,7,12 They have proved to be versatile and effective at promoting various reactions, resulting in the development of efficient and environmentally friendly synthesis routes. Extensive reviews have been conducted to assess the catalytic effectiveness of Mn-based heterogeneous catalysts in various reactions such as NH 3 -SCR, 13 gaseous reactions, 14 soot oxidation, 15 water oxidation, 16 removal of air pollutants, 17 oxygen evolution reaction, 18,19 alkane hydroxylation, 20 electrocatalytic water splitting, 21 and oxidation/acceptorless dehydrogenation of alcohols. 22,23 Nonetheless, there are still no reports sum-marizing MnO x -based heterogeneous catalysts for the sustainable synthesis of value-added chemicals.…”