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In situ Raman spectroscopy at temperatures up to 450 °C is used to probe the structural and redox properties of Ce 1−x Zr x O 2−δ solids (x = 0−0.8) prepared by the citrate sol−gel and coprecipitation with urea methods. The anionic sublattice structure of the solids is dependent on the preparation route. The composition effects exhibited by the Raman spectra are adequate for characterizing the phases present and/or eventual phase segregations. For x = 0.5 the pseudocubic t″ phase occurs for the solid prepared by the citrate sol−gel method, while phase segregation (cubic, tetragonal) is evidenced for the corresponding material prepared by the coprecipitation with urea method. A larger extent of defects and interstitial O atoms is evidenced for the materials prepared by the citrate sol−gel method. The well-known "defect" ("D") band around 600 cm −1 for CeO 2 as well as for Ce 1−x Zr x O 2−δ consists of at least two components: "D1" above 600 cm −1 and "D2" below 600 cm −1 . Doping of Ce 0.8 Zr 0.2 O 2−δ with rare earth cations (La 3+ , Nd 3+ , Y 3+ , Pr 3+ ) results in strengthening of the "D2" band that, however, is found to be insensitive under reducing conditions of flowing 5% H 2 /He at 450 °C. A novel approach based on sequential in situ Raman spectra under alternating oxidizing (20% O 2 /He) and reducing (5% H 2 /He) gas atmospheres showed that the "D1" band is selectively attenuated under reducing conditions at 450 °C and is therefore assigned to a metal−oxygen vibrational mode involving interstitial oxygen atoms that can be delivered under suitable conditions. A reversible temperature-dependent evolution of the anionic sublattice structures of Ce 1−x Zr x O 2−δ solids is evidenced by in situ Raman spectroscopy. The results are corroborated by powder XRD and oxygen storage capacity measurements, and observed structure/function relationships are discussed. It is shown that at low temperatures (e.g., 450 °C) the function of oxygen release and refill is based on a mechanism involving oxygen atoms in interstitial sites rather than on defects induced by hetrovalent M 4+ → RE 3+ doping, the latter improving the pertinent function at high (e.g., >600 °C) temperatures.

Pt nanoparticles (1.2−2.0 nm size) supported on Ce 1−x Ti x O 2−δ (x = 0, 0.2, 0.5, 0.8, and 1.0) carriers synthesized by the citrate sol−gel method were tested toward the water−gas shift (WGS) reaction in the 200−350 °C range. A deep insight into the effect of two structural parameters, the chemical composition of support (Ce/Ti atom ratio), and the Pt particle size on the catalytic performance of Pt-loaded catalysts was realized after employing in situ X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and HAADF/STEM, scanning electron microscopy (SEM), in situ Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies under different gas atmospheres, H 2 temperature-programmed reduction (H 2 -TPR), and temperature-programmed desorption (NH 3 -TPD and CO 2 -TPD) techniques. The 0.5 wt % Pt/Ce 0.8 Ti 0.2 O 2−δ solid (d Pt = 1.7 nm) was found to be by far the best catalyst among all the other solids investigated. In particular, at 250 °C the CO conversion over Pt/Ce 0.8 Ti 0.2 O 2−δ was increased by a factor of 2.5 and 1.9 compared to Pt/TiO 2 and Pt/CeO 2 , respectively. The catalytic superiority of the Pt/Ce 0.8 Ti 0.2 O 2−δ solid is the result of the support's (i) robust morphology preserved during the WGS reaction, (ii) moderate acidity and basicity, and (iii) better reducibility at lower temperatures and the significant reduction of "coking" on the Pt surface and of carbonate accumulation on the Ce 0.8 Ti 0.2 O 2−δ support. Several of these properties largely influenced the reactivity of sites (k, s −1 ) at the Pt−support interface. In particular, the specific WGS reaction rate at 200 °C expressed per length of the Pt−support interface (μmol CO cm −1 s −1 ) was found to be 2.2 and 4.6 times larger on Pt supported on Ce 0.8 Ti 0.2 O 2−δ (Ti 4+ -doped CeO 2 ) compared to TiO 2 and CeO 2 alone, respectively.

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