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It is known that both the type and possibilities of application of cerium molybdates(VI) largely depend on the methods of their synthesis. Despite this, information on the type of molybdates(VI) formed as a result of a waste-free and environmentally friendly reaction occurring in the solid state between CeO.sub.2 and MoO.sub.3 in the air atmosphere, are divergent. The conducted research indicates that CeO.sub.2 and MoO.sub.3 react in air and in the temperature range of 500-650 °C to form two compounds, i.e. Ce.sub.5Mo.sub.8O.sub.32 and/or Ce.sub.2Mo.sub.4O.sub.15. Only the Ce.sub.5Mo.sub.8O.sub.32 compound, for the first time, was obtained as a pure phase. The synthesis of Ce.sub.5Mo.sub.8O.sub.32 takes place through an intermediate stage. In this stage, with the evolution of oxygen, the compound Ce.sub.2Mo.sub.4O.sub.15 is formed, which then reacts with excess CeO.sub.2 to Ce.sub.5Mo.sub.8O.sub.32. The obtained compound was characterized by XRD, DTA-TG, FTIR and UV-Vis/DRS methods. Ce.sub.5Mo.sub.8O.sub.32 has a green-olive colour and a density of 4.82 ± 0.05 g cm.sup.-3. It was found that this compound melts incongruently at the temperature of 960 ± 5 °C with the separation of solid CeO.sub.2. The value of the energy gap E.sub.g ~ 2.59 eV allows the Ce.sub.5Mo.sub.8O.sub.32 compound to be classified as a semiconductor. The previously unknown properties of the compound with mixed cerium valence (Ce43+Ce.sup.4+Mo86+O.sub.32), characterized in this work, will constitute the basis for its application research.

The spin–Hamiltonian parameters g–factors (g[sub.||] and g[sub.⊥]) of the Ce[sup.3+] paramagnetic centers in BaWO[sub.4]: Ce and BaWO[sub.4]: Ce, Na single crystals with axial symmetry are investigated using the superposition model (SPM) via complete diagonalization procedure of energy matrix (CDM method). The calculated g–factors are in reasonable agreement with the experimental values. The fitted intrinsic parameters are comparable with data from other publications for rare-earth paramagnetic centers in a similar environment. The angular distortions of the cerium dodecahedron [CeO[sub.8]] are also studied. Structural analysis of paramagnetic centers with axial symmetry through the postulated cerium barium tetrahedron [CeBa[sub.4]] connected via oxygens bridges was carried out. The mechanism of the charge compensation and the role of the second dopant (Na[sup.+]) is also discussed.

Suspensions of cerium(IV) oxide (CeO.sub.2) particles in molten chloride salts were found to be active for molecular oxygen activation when doped with the larger Lanthanides, gadolinium (Gd), praseodymium, (Pr), and samarium, (Sm). The activity for O.sub.2 oxidation of gas phase CO on suspended doped ceria in molten mixtures of LiCl-LiBr-KBr and NaCl-KCl is significantly higher than undoped ceria or the salt mixtures alone in the temperature ranges of 350-600 °C, and 700-800 °C, respectively. Surface tension measurements show that the solid doped ceria particles suspended in the melt are contacting the gas-liquid interface of the bubbles. The activity for O.sub.2 oxidation of liquid phase MgCl.sub.2 in molten MgCl.sub.2-KCl to produce Cl.sub.2 and solid MgO was also observed to be significantly increased on suspended CeO.sub.2 doped with 5 wt% or 10 wt% Gd. The rates of oxidation were observed to increase with catalyst loading.

In this paper, we report an ultralow thermal conductivity and a high-temperature phase stability of the (Nd.sub.1-xCe.sub.x).sub.2Zr.sub.2O.sub.7+x system over the temperature range from room temperature to 1600 °C and over a wide composition range (0.2 [less than or equal to] x [less than or equal to] 0.8), and the (Nd.sub.1-xCe.sub.x).sub.2Zr.sub.2O.sub.7+x system is therefore considered a strong candidate material for the fabrication of next-generation high-temperature thermal barrier coatings. The observed thermal conductivities (0.65-1.0 W/mK) are about 60-40% lower than those of undoped Nd.sub.2Zr.sub.2O.sub.7 over the same temperature range (100-700 °C) and indicate a glass-like behavior. For comparison, the variation in the thermal conductivity with the temperature of the (Gd.sub.1-xCe.sub.x).sub.2Zr.sub.2O.sub.7+x system with similar point defects was also measured, and the observed behavior was almost the same as that of undoped Gd.sub.2Zr.sub.2O.sub.7 and was mostly determined by phonon-phonon scattering ([lambda] [proportional to] 1/T). The effect of point defect scattering and strong phonon scattering sources (rattlers) on the thermal conductivity is also discussed in this paper. The results of this study suggest that the ultralow thermal conductivity of (Nd.sub.1-xCe.sub.x).sub.2Zr.sub.2O.sub.7+x can be attributed to the presence of rattlers because of the large difference between the ionic radii of the Nd.sup.3+ and Ce.sup.4+ ions.

Nanoceria or cerium oxide nanoparticles characterised by the co-existing of Ce3+ and Ce4+ that allows self-regenerative, redox-responsive dual-catalytic activities, have attracted interest as an innovative approach to treating cancer. Depending on surface characteristics and immediate environment, nanoceria exerts either anti- or pro-oxidative effects which regulate reactive oxygen species (ROS) levels in biological systems. Nanoceria mimics ROS-related enzymes that protect normal cells at physiological pH from oxidative stress and induce ROS production in the slightly acidic tumour microenvironment to trigger cancer cell death. Nanoceria as nanozymes also generates molecular oxygen that relieves tumour hypoxia, leading to tumour cell sensitisation to improve therapeutic outcomes of photodynamic (PDT), photothermal (PTT) and radiation (RT), targeted and chemotherapies. Nanoceria has been engineered as a nanocarrier to improve drug delivery or in combination with other drugs to produce synergistic anti-cancer effects. Despite reported preclinical successes, there are still knowledge gaps arising from the inadequate number of studies reporting findings based on physiologically relevant disease models that accurately represent the complexities of cancer. This review discusses the dual-catalytic activities of nanoceria responding to pH and oxygen tension gradient in tumour microenvironment, highlights the recent nanoceria-based platforms reported to be feasible direct and indirect anti-cancer agents with protective effects on healthy tissues, and finally addresses the challenges in clinical translation of nanoceria based therapeutics.

We studied the mechanism of NO reduction as well as its selectivity and reactivity in the presence of excess [O.sub.2]. Results show that fuel injection and/or pretreatment are important for ceria catalyst reduction and carbon deposition on the catalyst surface. Oxygen defects of reduced ceria are the key sites for the reduction of NO into [N.sub.2]. The deposited carbon acts as a buffer reductant, i.e., the oxidation of carbon by lattice oxygen recreates oxygen defects to extend the NO reduction time interval. A small amount of NO showed a full conversion into only [N.sub.2] both on the reduced Zr-La doped ceria and reduced Pt-Zr-La doped ceria. Only when the catalyst is oxidised NO is converted into N[O.sub.2]. CITATION: Makkee, M. and Wang, Y., \"Reaction Mechanism Study of the Di-Air System and Selectivity and Reactivity of NO Reduction in Excess O2,\" SAE Int. J. Engines 10(4):2017, doi:10.4271/2017-01-0910.

CeO nanoparticles (NPs) have shown promising approaches as therapeutic agents in biology and medical sciences. The physicochemical properties of CeO -NPs, such as size, agglomeration status in liquid, and surface charge, play important roles in the ultimate interactions of the NP with target cells. Recently, CeO -NPs have been synthesized through several bio-directed methods applying natural and organic matrices as stabilizing agents in order to prepare biocompatible CeO -NPs, thereby solving the challenges regarding safety, and providing the appropriate situation for their effective use in biomedicine. This review discusses the different green strategies for CeO -NPs synthesis, their advantages and challenges that are to be overcome. In addition, this review focuses on recent progress in the potential application of CeO -NPs in biological and medical fields. Exploiting biocompatible CeO -NPs may improve outcomes profoundly with the promise of effective neurodegenerative therapy and multiple applications in nanobiotechnology.

Cerium is the most abundant of rare-earth metals found in the Earth’s crust. Several Ce-carbonate, -phosphate, -silicate, and -(hydr)oxide minerals have been historically mined and processed for pharmaceutical uses and industrial applications. Of all Ce minerals, cerium dioxide has received much attention in the global nanotechnology market due to their useful applications for catalysts, fuel cells, and fuel additives. A recent mass flow modeling study predicted that a major source of CeO2 nanoparticles from industrial processing plants (e.g., electronics and optics manufactures) is likely to reach the terrestrial environment such as landfills and soils. The environmental fate of CeO2 nanoparticles is highly dependent on its physcochemical properties in low temperature geochemical environment. Though there are needs in improving the analytical method in detecting/quantifying CeO2 nanoparticles in different environmental media, it is clear that aquatic and terrestrial organisms have been exposed to CeO2 NPs, potentially yielding in negative impact on human and ecosystem health. Interestingly, there has been contradicting reports about the toxicological effects of CeO2 nanoparticles, acting as either an antioxidant or reactive oxygen species production-inducing agent). This poses a challenge in future regulations for the CeO2 nanoparticle application and the risk assessment in the environment.

Cu/ZnO/CeO.sub.2 nanocomposite was supported on metal organic framework (MOF-5) to enhance active sites dispersion and control the nanoparticles agglomeration during synthesis through strong metal-support interactions. The incorporation of MOF-5 alleviated the obstacle facing the commercial ternary Cu/ZnO/Al.sub.2O.sub.3 regarding low surface area due to nanoparticles agglomeration. In addition, Cu/ZnO/CeO.sub.2@MOF-5 gave higher methanol selectivity than the commercial catalyst which can be accounted for by the interfacial sites generated between MOF-5 and Cu/ZnO which favour methanol synthesis over carbon monoxide through regulating the intermediates bonding energies. CeO.sub.2 as support for Cu/ZnO nanoparticles was also compared with commercial support and showed to have led to smaller particle size and superior dispersion of Cu active sites as well. Cu/ZnO/CeO.sub.2@MOF-5 resulted in methanol STY of 23.3 mg g.sub.cat h.sup.-1 and selectivity of 79% at mild reaction temperature (260 °C) and pressure (10 bar). Two different MOFs including cerium based MOF and ZIF-8 demonstrated inferior performance compared to MOF-5.