Revealing the promoting effect of multiple Mn valences on the catalytic activity of CeO2 nanorods toward soot oxidation.

Abstract

Mn-modified CeO2 nanomaterials have attracted extensive attention as efficient and promising catalysts for soot combustion due to their low cost and high catalytic activity. However, a detailed mechanism of how Mn promotes soot oxidation over CeO2 is still not clearly elucidated, which is crucial to further optimize the catalyst for achieving its practical applications. We here report a Mn-doped CeO2 catalyst with tunable surface Mn chemical valence states to study the Mn-promoting mechanism for improving CeO2 catalyst activity in soot oxidation. Experimental results show that Mn-doped CeO2 nanorods with surface Mn chemical valence states being optimized (Mn0.19Ce0.81O2) can lower the eliminating temperature of soot to 410 °C (T90) when in a loose contact and exhibit a strong resistance towards water molecules. The catalytic performances of Mn0.19Ce0.81O2 nanorods are comparable with those of other reported oxide catalysts both in the mimetic realistic and ideal reaction environments. Detailed characterization and theoretical calculation results demonstrate that balanced multiple Mn valences can dramatically enhance the catalysts' redox properties and their ability to activate O2 molecules, as well as improve the dynamic contact efficiency during the oxidation, which synergistically result in superior catalytic performances. This work might provide insight for the future design and preparation of catalysts to efficiently eliminate soot particles.