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

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 CeO ₂. 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 B 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 Mn ₂O ₃. The analysis of BET surface area and BJH pore size revealed that the Mn-doped CP catalysts exhibited both micro and mesoporous characteristics. The H ₂-TPR and O ₂-TPD profiles indicated enhanced reducibility resulting from the incorporation of Mn and Pr into CeO ₂-doped catalysts. The improved T ₅₀ (365 ± 1 1C) for the 5 Mn-CP catalytic system is primarily due to its increased specific surface area of 45 m ² g ^–1 and the presence of active surface adsorbed oxygen species identified in the XPS and O ₂-TPD studies. 5 Mn-CP exhibited the lowest activation energy value compared to all other Mn-doped catalysts.