Pivotal role of MnOx physicochemical structure in soot oxidation activity

Abstract

Arising an interest in climate and health problems, catalytic soot oxidation and its mechanism need to be understood, in order to effectively reduce PM (particulate matter) emissions from industry and transportation. Here, a synergistic effect of the Mn physicochemical structure on the soot oxidation activity of Ti-based oxide catalysts is investigated. To unravel the structural change and role of different Mn species, a comparison of different Mn loading and pretreatment conditions was done. While a fine loading with different Mn arrangements is observed by XRD analysis, a comparative XPS study of these Mn catalysts reveals the predominant presence of Mn3+ oxidation state and optimal combination of surface adsorbed and lattice oxygen species (ratio of 1.07) imparts a promotional role in soot oxidation activity. Furthermore, the TPR, O2-TPD, and TEM analysis represent that the increased Mn amount with different configurations led to a decreased reducibility, difficulty in lattice oxygen accessibility, and changed the morphology of MnOx species from cubic to hexapod and/or truncated octahedra associated with the presence of α-Mn2O3-C, β-MnO2 and/or α-Mn2O3-TO, respectively. The presence of smaller segregated cubic particles, ease of reducibility, and predominant presence of Mn3+ species led to superior performance even at lower 10 %Mn supported TiO2 catalyst and was revealed with an activation energy of 112.9 kJ mol−1. This proves the consequence of a proper design of an optimum Mn structure on oxide supports for an efficient soot oxidation reaction.