Experimental and theoretical study on La_0.5K_0.5Mn_1−xFe_xO₃ perovskite catalysts for mild temperature soot combustion and simultaneous removal of soot and NO

In order to control high emissions of soot and NOx from diesel engines, this research utilizes highly efficient perovskite oxide catalysts to simultaneously remove soot and NO. A series of La_0.5K_0.5Mn_1-xFe_xO₃ catalysts were prepared by citric acid complexation method, and the active sites and structure stability of LaMnO₃ perovskite catalyst were investigated according to the first principle. Research results show that K⁺ doping causes the transformation of Mn³⁺ into Mn⁴⁺ in LaMnO₃ catalyst system and forms more oxygen vacancies. Meanwhile, Fe³⁺ doping leads to the octahedron distortion of MnO₆ and FeO₆ in catalyst system, which enhances the stability of catalyst structure. The oxygen vacancy formed by doping K⁺ and Fe³⁺ accelerates the migration rate of lattice oxygen and improves the catalytic activity of perovskite catalyst for soot oxidation. With the increase of Fe³⁺ doping, the proportion of adsorbed oxygen and high valence active ions in catalyst system increases. Moreover, the alkaline sites on the catalyst surface are favorable for the adsorption of acid gas NO. The La_0.5K_0.5Mn_0.67Fe_0.33O₃ catalyst has the highest catalytic activity, the ignition temperature of soot oxidation drops to 291 °C, and CO₂ selectivity exceeds 99.9%. At 370 °C, the conversion rate of NO reaches the maximum value of 61.7%.