Diesel soot oxidation over Mn–Pr–Ce oxide catalysts: structural changes and the impact of Mn doping

Abstract

The soot oxidation activity of manganese-doped ceria-praseodymium catalysts, synthesized via solution combustion synthesis, was evaluated. The analyses performed with XRD and Raman spectroscopy indicated that the Mn-doped CP catalysts displayed the typical fluorite structure of CeO₂. The addition of Mn to CP led to a reduction in crystallite size from 14 nm to below 10 nm. The F_2g Raman active mode of fluorite-structured Ce and the oxygen vacancies resulting from the addition of Mn and Pr (bands ∼ 560 cm⁻¹ to 580 cm⁻¹) were consistently observed across all Mn-doped CP catalysts. 15 and 20 Mn-CP exhibited an additional secondary phase identified as Mn₂O₃. The analysis of BET surface area and BJH pore size revealed that the Mn-doped CP catalysts exhibited both micro and mesoporous characteristics. The H₂-TPR and O₂-TPD profiles indicated enhanced reducibility resulting from the incorporation of Mn and Pr into CeO₂-doped catalysts. The improved T₅₀ (365 ± 1 °C) for the 5 Mn-CP catalytic system is primarily due to its increased specific surface area of 45 m² g⁻¹ and the presence of active surface adsorbed oxygen species identified in the XPS and O₂-TPD studies. 5 Mn-CP exhibited the lowest activation energy value compared to all other Mn-doped catalysts.