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 CeO2. The addition of Mn to CP led to a reduction in crystallite size from 14 nm to below 10 nm. The F2g Raman active mode of fluorite-structured Ce and the oxygen vacancies resulting from the addition of Mn and Pr (bands similar to 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 degrees 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.