Attempts at an in-situ Raman study of Ceria / Zirconia catalysts in PM combustion

CexZr1−xO2 catalysts with various Ce/Zr contents were studied using Raman spectroscopy under different gaseous atmospheres, at different temperatures and in the presence of a model soot. Catalysts with high concentrations of Zr fluoresced at elevated temperatures making analysis of their spectra impossible. This effect became even more pronounced at higher temperatures. CeO2 and solid solutions with relatively low concentrations of Zr showed a red shift and a decrease in intensity of the characteristic F2g peak at high temperatures under different atmospheres. The magnitude of the latter effect was higher under reducing atmospheres. These changes are reversible upon cooling, showing that they relate to a lattice expansion effect rather than any major chemical change to the material. In the presence of the model soot the Raman spectra of all materials was much decreased due to the absorption of the incident and scattered radiation by the soot particles. The presence of soot does not change the relative intensities or positions of the peaks in the spectra of the solid solutions. Evidence is shown for the production of a Ce3+–CO species following interaction between the soot and the surface at high temperature in an inert atmosphere.