Nanostructured Ce_(0.7)Mn_(0.3)O_(2-δ) and Ce_(0.7)Fe_(0.3)O_(2-δ) solid solutions for diesel soot oxidation

摘要

Nanostructured Ce_(0.7)Mn_(0.3)O_(2-δ) and Ce_(0.7)Fe_(0.3)O_(2-δ) (CF) solid solutions were prepared by a facile coprecipitation method and evaluated for soot oxidation. The structural, morphological, and surface properties were investigated by various techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM-HRTEM, UV-vis DRS, Raman, FT-IR, XPS, H2-TPR, and TGA-DTA. XRD and TEM results confirmed formation of nanocrystalline solid solutions with the incorporated Mn and/or Fe cations in the ceria lattice. SEM studies ensured nanoparticle nature of Ce-Mn-0 and Ce-Fe-0 solid solutions with homogeneous distribution. ICP-OES and EDX analysis confirmed actual amount of metal loadings in the respective catalysts. UV-vis DRS and Raman results revealed the formation of more oxygen vacancies, which lead to the creation of more surface active species (Ce~(4+)/Ce~(3+) and 0*). XPS results revealed that the doping of Mn and/or Fe into the ceria lattice makes some Ce~(4+) transferred into Ce~(3+) in order to maintain the electrical neutrality, thereby facilitate the reduction of Ce~(4+) ->Ce~(3+) and the formation of oxygen vacancies. TPR results showed that the mixed oxides reduce at lower temperatures than pure ceria. This observation confirmed that there is a synergetic interaction between Ce-0 and M-0 (M = Mn, Fe). The catalytic activity of CM and CF samples towards soot oxidation has been evaluated under tight contact conditions and compared with the well-established CeO2-ZrO2 (CZ) catalyst. Among the investigated catalysts, the Mn and/or Fe doped ceria solid solutions showed improved catalytic activity. The order of activity is as follows: CM >CF >CZ >C. Further, the CM and CF catalysts were found to be thermally quite stable compared to pure ceria. In particular, the CM sample exhibited superior catalytic activity (T_(50) = ~665 K) and thermal stability towards soot oxidation.