Unveiling the Surface Chemical Reactions during Multi-Phase Catalytic Oxidation of Soot on...

The aerosol pyrolysis method from nitrate precursors was used to prepare the Mn-CeO₂ catalyst containing Mn₂O₃, CeO₂, and Mn-doped CeO₂ nanoparticles for catalyzing carbonous soot oxidation. The prepared Mn-CeO₂ catalysts have high specific surface areas, Ce³⁺ ratio, and oxygen vacancy defects; these are a benefit for soot oxidation. The T₅₀ for soot oxidation on the 0.57Mn-CeO₂ catalyst is as low as 355 °C, which is 329 °C lower than that for soot oxidation without a catalyst. The catalysts were characterized using XRD, SEM-EDS, HRTEM, XPS, Raman spectroscopy, H₂-TPR-MS, O₂-TPD-MS, soot-TPR-MS, and operando DRIFTS-MS. The functions of Mn₂O₃, CeO₂, and Mn-doped CeO₂ in the 0.57Mn-CeO₂ catalyst are unveiled. Mn-doped CeO₂ plays a key role and CeO₂ participates in soot oxidation, while Mn₂O₃ is used to enhance higher ratios of Ce³⁺, via the reaction of Mn³⁺ + Ce⁴⁺ = Mn⁴⁺ + Ce³⁺. The mechanism of soot oxidation on Mn-CeO₂ was proposed.