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In this article, a facile solid state mixing of precursors with citric acid was employed for the synthesis of mesoporous ceria–zirconia solid solution (CZ), which further require a thermal treatment alone for the material development. The ceria and zirconia nanocrystals were also prepared by the same solid state mixing method. The as-synthesized samples were characterized by means of various structural and textural studies. The results depicted that the presence of citric acid is desired for the formation of a perfect CZ solid solution with microflake like morphology. It has an enhanced role in the determination of crystalline size, phase purity, morphology, surface area and pore parameters of the as-synthesized samples. The active phase over the CZ samples was found to be tetragonal. The selective vapour phase oxidation of benzyl alcohol (BzOH) to benzaldehyde was effectively carried in a fixed bed reactor in moderate air flow over the redox catalysts with a maximum BzOH conversion of 80 % with substantial durability and reusability.

Bulk ceria-zirconia solid solutions (Ce1−xZrxO2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO2 in the range of 10−24–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO2-ZrO2 as compared to CeO2−δ and ZrO2 were observed. A comparison of temperature- and pO2-dependences of the non-stoichiometry of thin films with literature data for bulk Ce1−xZrxO2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce0.8Zr0.2O2−δ, whereas Ce0.5Zr0.5O2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO2 of 10−14 bar. The defect interactions in Ce1−xZrxO2−δ are analyzed in the framework of defect models for ceria and zirconia.

Local administration of drug effectively following cochlear implantation is highly challenging, which imposes limitations such as insufficient drug, poor distribution and need for additional surgical procedures. Recent research is focused on integrating the drug with the silicone encasing of the electrode in cochlear implanted patients to overcome these limitations. The objective of the study is to assess the delivery of Ce 0.5 Zr 0.5 O 2 antioxidant through silicone encasing and the suitability of the nanocomposites as an electrode encasing material. The proposed strategy is expected to overcome the issues associated with poor dispersion stability of the Ce 0.5 Zr 0.5 O 2 based nanofluid and its corresponding long term effect, while utilizing its regenerative ability. Liquid silicone rubber (LSR)/Ce 0.5 Zr 0.5 O 2 nanocomposites are prepared and characterized using suitable techniques. The reinforcement of nanoparticles up to 5 wt.% did not affect the modulus and electrical conductivity significantly. The hydroxyl radicals are scavenged by 36% in artificial perilymph fluid. The Ce 3+ concentration is reduced from 45 to 9% after adding H 2 O 2 and then it is regenerated to 35% after 13 days due to its ability to switch between Ce 3+ and Ce 4+ . From this study, LSR/ Ce 0.5 Zr 0.5 O 2 nanocomposites are proposed as electrode encasing material inside cochlea for scavenging hydroxyl radicals and its regeneration potential.

We studied the spectral-luminescent properties of (ZrO2)0.805(Y2O3)0.188(Pr2O3)0.007 and (ZrO2)0.802(Y2O3)0.195(Pr2O3)0.003 crystals grown by directional melt crystallization in a cold skull. Analysis of the absorption spectra of the crystals suggested the presence of Pr3+ and Pr4+ ions. Measurement of the relative intensities of the luminescence bands corresponding to the 3P0 → 3H4,5, 3P0 → 3F2,3,4, 3P1 → 3H5 and 1D2 → 3H4 optical transitions of the Pr3+ ions, and analysis of luminescence extinction kinetics for the 3P0 and 1D2 levels of the Pr3+ ions, suggests the presence of cross-relaxation (1D2 → 1G4) → (3H4 → 3F4) of the Pr3+ ions in the ZrO2-Y2O3-Pr2O3 crystals.

Using first principle calculations, the effect of Ce with different doping concentrations in the network of Zirconium dioxide (ZrO2) is studied. The ZrO2 cell volume linearly increases with the increasing Ce doping concentration. The intrinsic band gap of ZrO2 of 5.70 eV reduces to 4.67 eV with the 2.08% Ce doping. In 4.16% cerium doped ZrO2, the valence band maximum and conduction band minimum come closer to each other, about 1.1 eV, compared to ZrO2. The maximum band gap reduction of ZrO2 is observed at 6.25% Ce doping concentration, having the value of 4.38 eV. No considerable shift in the band structure is found with further increase in the doping level. The photo-response of the ZrO2 is modulated with Ce insertion, and two distinct modifications are observed in the absorption coefficient: an imaginary part of the dielectric function and conductivity. A 2.08% Ce-doped ZrO2 modeled system reduces the intensities of peaks in the optical spectra while keeping the peaks of intrinsic ZrO2. However, the intrinsic peaks related to ZrO2 completely vanish in 4.16%, 6.25%, 8.33%, and 12.5% Ce doped ZrO2, and a new absorption hump is created.

Solid solution CeO 2 –ZrO 2 has long been used as a non-noble metal oxide promoter for three-way catalysts owing to its high oxygen storage capacity. However, the stability issue of the CeO 2 –ZrO 2 has been controversial for a long time. In particular, the phenomena observed by phase instability are so diverse and inconsistent that the related causal analysis is still a matter of debate. In this study, for the first time, it was demonstrated theoretically and experimentally that a Ce 0.75 Zr 0.25 O 2 (CZO) solid solution must be completely separated into CeO 2 and ZrO 2 phases owing to its inherent thermodynamic instability. According to an extensive evaluation via defect chemical calculations and well-controlled model experiments with grain-boundary-free epitaxial thin film samples, CZO materials undergo phase separation until they are completely separated, and the separation rate is particularly high in a reducing atmosphere. The underlying inherent stability problem and enhanced phase separation kinetics of the CZO material are attributed to the enhanced cation diffusion in a reducing atmosphere, where more mobile cationic defects (interstitial cations) are generated and an easier pathway with a lower migration energy is available.

A series of ceria-zirconia solid solutions were synthesized using tobacco leaves, stems and stem-silks as biotemplates. A combination of physicochemical techniques such as powder X-ray diffraction (XRD), N2 adsorption/desorption measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the as-synthesized samples. The results show that the morphologies of the templates were well replicated in the obtained ceria-zirconia solid solutions. Catalytic oxidation activities of CO over the ceria-zirconia solid solutions were then investigated. The catalyst templated by tobacco stem-silk exhibited higher conversion of CO at lower temperature than that of ceria-zirconia solid solutions templated by tobacco leaves and stems or without templates due to its special morphology. The catalyst even showed similar CO conversion when compared to ceria-zirconia solid solutions doped with 1.0 wt % noble metals such as Pt, Ag and Au. The results highlighted the advantages of using tobacco as biotemplate.

The paper reports the synthesis and the investigation of the phase formation in M x O y –ZrO 2 nanosized systems the temperature range 360–850 °С, performed via simultaneous thermal analysis, X-ray diffraction analysis and particle size distribution analysis. Nanosized MO-ZrO 2 precursors with MO content 5–10 mol.% and Bi 2 O 3 –ZrO 2 precursors with Bi 2 O 3 content 5–14 mol.% were obtained by reversed co-precipitation from diluted salts solutions with following drying under exceeded pressure. In contrast to microsized systems,nanosized powders exhibit exothermic effects corresponding to crystallization at 360–570 °С in DSC curves. Metastable cubic zirconia solid solutions are present after annealing for all zirconia based precursors studied phase evolution study innanosized M x O y –ZrO 2 systems (M = Zn 2+ , Cd 2+ , Pb 2+ , Bi 3+ ) except 10PbO–90ZrO 2 composition. Cubic zirconia solid solution with no admixture of monoclinic phase is formed only in case of 14Bi 2 O 3 –96ZrO 2 . The stability of cubic solid solutions formed in time and temperature range was studied by X-ray diffraction. Crystalline size estimated from Scherrer’s equation is 17–25 nm. The main agglomerate size calculated from particle size distribution analysis lie in the range 234–590 nm. Nanocrystallinity and high dispersity of powders favor phase stability of cubic solid solutions formed. Graphical Abstract

This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan.Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La4+ or Zr4+. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term “partial OSC” was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the “total OSC”. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the “diffusion barrier concept”, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air.Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper.For ceriazirconia solid solutions composed of equimolar CeO2 and ZrO2(Ce/Zr=1), the total or partial OSC of the κ-phase CeZrO4, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value.For a ceriazirconia solid solution composed of non-equimolar CeO2 and ZrO2(Ce/Zr ≠ 1), the partial OSC of a ceria-κ-phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a κ-phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O2/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%.The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis.

— A process has been demonstrated for the preparation of precursor powders and nanocrystalline (60–90 nm) alumina-based ceramics in the Al 2 O 3 –ZrO 2 〈Y 2 O 3 〉 system. We have studied the influence of mechanochemical activation (MA) on the structure and particle size of precursor powders and found the most effective MA time. MA has been shown to lower the α-Al 2 O 3 formation temperature and accelerate the powder sintering process. We have optimized powder consolidation conditions for the fabrication of dense nanoceramics and studied their physicochemical and mechanical properties.