To protect the environment, more stringent regulations for automotive exhausts are periodically enacted in the developed countries. In order to comply with them, a development effort is required, notably to depollute lean burn or Diesel engine emissions (in particular during the cold start) at the lowest possible cost (without noble metals).In this perspective, two ceria-based mixed oxides, Ce0.8Gd0.2O2-d (CGO) and Ce0.64 Y0.32Ti0.04O2-d (CeYTiO) have been investigated to unravel the mechanism for storage and decomposition of NOx species (NO2 and NO) by different spectroscopic techniques. Representative amounts of NOx (350 ppm) have been sent on the oxidized or reduced samples at various temperatures in the (423 � 623 K range). Phenomena of both NOx reduction and nitrate/nitrite formation can be observed, according to the material oxidation state and to the nitrogen oxide speciation. The presence and the amount of the different surface and bulk species, as well as oxygen vacancies, have been quantitatively correlated to the nitrogen oxide dissociation and to the N2 yield. The combined use of operando FTIR spectroscopy, Raman and impedance spectroscopy under different atmospheres have allowed a thorough investigation of the redox steps affecting the system, providing a complete description of the mechanism leading to the anionic vacancies formation, diffusion and filling through the surface and the bulk of the materials. A formal dynamic description of the process and the calculation of the relevant kinetic parameters are in progress.A secondary phenomenon has also been observed: because of the presence of residual carbonate impurities on the basic samples (eventually competing with nitrous adsorbed species), a carbon deposit can be generated on the material surface upon a reducing pretreatment. This deposit is then reoxidized by NOx leading to carbonates on the surface and to N2 in the gas phase, so playing a role in NOx reduction and storage.

NO<sub>x</sub> storage and reduction on ceria-based mixed oxides

246th National Meeting (2013)

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NOx storage and reduction on ceria-based mixed oxides

NO_x storage and reduction on ceria-based mixed oxides