Investigation of sodium–manganese oxides with various crystal phases for the efficient catalytic removal of diesel soot particles

Abstract

Sodium–manganese oxides with various crystal phases (Na2Mn5O10, Na2Mn3O7, and Na4Mn9O18) were synthesized using a facile sol-gel method, and applied in the catalytic purification of soot particles from diesel engines. In this study, as-prepared samples with a single Na2Mn3O7 phase exhibited higher soot oxidation activity, with the lowest T10, T50, and T90 values of 279 ℃, 320 ℃, and 349 ℃, respectively. Numerous characterization techniques reveal that the Na2Mn3O7 catalysts have superior reducibility, NO oxidation, and storage capacity compared with the other crystal phases. In the meantime, the Na2Mn3O7 catalyst surface possesses a greater abundance of oxygen vacancies because of the emergence of Mn3+, which serve as crucial active sites during the dynamic cycling process of gaseous oxygen adsorption and activation. Moreover, the E-R reaction mechanism for soot combustion over the steps of (100) crystal plane of Na2Mn3O7 catalysts is proposed based on density functional theory (DFT) calculations and multiple characterization results. This study presents a facile and cost-efficient method for designing and preparing superior performance sodium–manganese composite oxides for soot combustion.