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International audienceThe textural and structural properties of high specific surface area (HS) CexZr1-xO2 mixed oxides (CeZrMO) and their modification upon thermal aging have been investigated. Results from BET area determination and complete porosity analysis, as well as high-resolution electron microscopy, XRD, Raman and FTIR spectroscopies are presented. Some relationships between the molar composition of the binary systems and their textural and structural properties are presented. In addition, it has been possible to propose an explanation for structural features of the mixed oxides (solid-solution structures and possible phase segregation) as a function of Ce content, a point of great interest for the knowledge of phase composition and stability of CeZrMO

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This is the final report of a three-year, Laborato~-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Our objectives were to develop a multidisciplinary team and capabilities to develop a fundamental understanding of homogeneous, heterogeneous, and heterogenized catalysts. With the aid of theoretical chemistry approaches we explored and characterized the chemical reactivity and physical properties of a large number of catalytic systems.

The redox behaviour of a Ce 0.68 Zr 0.32 O 2 mixed oxide is reversibly modified by alternating high temperature (1223 K) reduction with either mild (823 K) or high temperature (1223 K) re-oxidation treatments.

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Abstract-At radioactive sites, at least two mechanisms may affect the genetic diversity of populations of a given species. Increased mutation rates due to radiation exposure may increase the amount of genetic diversity in a population. Alternatively, population bottlenecks exacerbated by environmental degradation may lead to a reduction of diversity. The relationship between these two contradictory forces is complex. To explore this relationship, long-term monitoring of a genetic marker within a population is needed. To provide baseline data on the population genetics of the bank vole (Clethrionomys glareolus) living in the most contaminated regions at Chornobyl, Ukraine, we have sequenced 291 base pairs of the mitochondrial DNA control region. Bank voles were chosen as a model system because they have the highest levels of internal dose of cesium-134, cesium-137, and strontium-90 within the Chornobyl exclusion zone. We sampled three geographic sites, which were Oranoe, a reference site with virtually no radioactive contamination (Ͻ2 Ci/km 2 ), and two highly contaminated sites, Glyboke Lake and the Red Forest (both 1,000 Ci/ km 2 ). Genetic diversity in the population from Red Forest (0.722 Ϯ 0.024) was significantly greater than at the Oranoe reference site (0.615 Ϯ 0.039), while genetic diversity at Glyboke Lake (0.677 Ϯ 0.068) was intermediate. It is concluded that long-term studies of historical and demographic characteristics for experimental and reference populations are required in order to employ population genetics to understand the biological impact of environmental contaminants on the genetics of natural populations.

Pt and Pd particles supported on a texturally stable Ce 0.68 Zr 0.32 O 2 mixed oxide were investigated by means of H 2 chemisorption and high-resolution transmission electron microscopy (HRTEM). The comparison of the metal dispersion data as determined by HRTEM with those estimated from H 2 volumetric adsorption reveals that, in the case of Pt catalysts reduced at temperatures below 350 °C, the chemisorption isotherms recorded at -80 °C provide reliable dispersion data. For catalysts reduced at, or above, 350 °C, some platinum deactivation occurred. However, H 2 chemisorption capability was recovered by reoxidation at 427 °C and further reduction at 150 °C. For catalysts reduced at 700 °C or 900 °C, the recovery of the platinum chemisorptive capability was only partial, even if a more severe reoxidation treatment (700 °C) was applied. To prevent hydride formation, H 2 chemisorption on the Pd/Ce 0.68 Zr 0.32 O 2 was investigated at low H 2 pressures and at room temperature. Under these experimental conditions, which are often employed for characterizing Pd catalysts, hydrogen spillover cannot be blocked, thus preventing a reliable estimate of the metal dispersion in our ceria-zirconia -supported palladium catalysts.