Manganese Based Perovskites in Soot Oxidation: Far from Noble Metals?

Mn-based catalysts for soot oxidation have been developed without noble metals. The compositions are LaMn0.9Co0.1O3, La0.9K0.1Mn0.9Co0.1O3 (LKMC), Sr0.9K0.1Mn0.9Co0.1O3 and 0.1 K/La0.9Mn0.9Co0.1O3: Mn provides stability to the structure both in oxidizing and reducing atmospheres and efficiently exchanges oxygen. Moreover, Co doping enhances soot oxidation. Adding La or Sr as A-site cation in the perovskite composition allows comparing the behaviors of the so-obtained perovskites, and K doping was chosen to increase catalytic activity both in soot and NOx removal. After the wet synthesis, the catalysts were tested for soot oxidation in presence of oxygen and nitrogen monoxide in overstoichiometric oxygen content. Temperature Programmed Oxidation tests were performed and double doping increases the oxidative catalytic activity: LKMC shows the lowest soot conversion temperature (306 °C, soot in tight contact with the catalyst). Sr doping results in worse performances, due to the formation of SrCO3. K incorporation helps oxygen vacancies formation, beneficial to the catalytic activity, through the Mars-van Krevelen mechanism