Papers by Keyword: Ceria

Abstract: Ceria-based materials are widely used in industrial applications such as catalyst supports, catalysts and electrolytes. Various applications require different morphological particles. Spray pyrolysis (SP) is a well-known process for ceria particle fabrication because SP has the advantages of simple and continuous process. Although various studies have discussed the particle morphology formation of SP, some questions are still unclear. In order to solve these questions, this study investigates the morphology of ceria particles from various precursors using SP. By combining the experimental data of scanning electron microscopy, transmission electron microscopy and focused ion beam, the result suggests that the particle formation mechanism is highly correlated with factors of hydrophilic-hydrophobic properties of precursors. Therefore, the morphology mechanism of SP for the ceria particles is proposed .

Abstract: Monodispersed ceria nanocrystals have been synthesized by an oleate-modified precipitation method combined with a hydrothermal treatment at 200°C. TEM observation indicated that ceria nanoparticles with low-crystallinity were produced by synthesis at room temperature, which were crystallized by subsequent heat treatment to form nanocrystals. Produced ceria nanocrystals were well dispersed in a nonpolar solvent and were hardly agglomerated. TEM observation and Raman spectroscopy clarified that the size of ceria nanocrystals was in the range of 2-7 nm. Interparticle distance of cerium nanocrystals two-dimensionally aligned was in the range of 1.5-4 nm, which corresponds to the exclusive distance of oleic chains. Oleate-modified ceria nanocrystals exhibited strong fluorescence by green-laser excitation. Fluorescent behavior of ceria nanocrystals indicated that oleate detachment from the ceria surface and particle growth of ceria nanocrystals could be induced by laser irradiation.

Abstract: CeO₂-SiO₂ (C-S) Binary Oxides Were Prepared by Deposition Precipitation as Modified Support. Nanoparticle Nickel Catalysts (5 Wt.%), Supported on SiO₂ and CeO₂-SiO₂ Were Prepared by Impregnation. Catalysts Were Identified by Several Characterizations (XRD, BET, TPR, TPD and TEM). the Analyses Showed that Nanoparticle Ni Supported on CeO₂-SiO₂ Catalysts Gave Better Properties in Reducibility, Basicity, Ni Metal Dispersion and Size Compared to the Nickel Catalysts Supported on the Single Oxide SiO₂. the Catalytic Test of Dry Reforming of CH₄ with CO₂ (DRMC) Reaction Was Conducted Using Temperature Programmed Reaction (TPRn) Technique which Connected to an Online Mass Spectrometer. the Catalytic Test Showed that Ceria (CeO₂) Loading Influenced the Activity, Mainly the Hydrogen Production. Ni Catalyst with 9 Wt.% of Ceria Exhibited the Highest Hydrogen Production and it Was Suggested to Be the Optimum Value of Ceria Loading. in Addition, the Lower Amount of Carbon Was Observed on the Ni/9C-S Catalyst. this Revealed that the Addition of an Appropriate Amount of Ceria Increased the Hydrogen Production and Reduced the Carbon Formation.

Abstract: This work reported that porous flower-like CeO2 microspheres have been successfully synthesized via a controlled template-free precipitation method and were used as catalyst support for the oxidation of CO and benzene. The scanning electron microscopy results showed that ceric concentration has great influence on the morphology of CeO2 micro and nanostructures. This flower-like CeO2 microstructure exhibited a superior low-temperature catalytic activity used as catalyst support compared with conventional CeO2 nanoparticles. The enhanced catalytic activity of flower-like CeO2 microspheres could be attributed to its porous structure and the abundant oxygen vacancies on the surface.

Abstract: CeO₂ nano-sized crystalline powders were prepared by sol-gel combustion method from ammonium cerium nitrate and citric acid, and the dependences of the particle size of synthesized powder on the precursor gel were investigated. The precursor gels and the synthesized powders were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray scattering (XRD). The colloid particle with nanometer size was firstly observed by FE-SEM, and its size variation had the same tendency as that of CeO₂ powders with the varying of the ratio of metal ions to citric acid. Furthermore, the probable reasons for the effect of gel structure on properties of nano-sized ceria powders prepared by sol-gel combustion were explained.

Abstract: Spherical samarium doped ceria (Ce_0.8Sm_0.2O_1.9, SDC) powders having high specific surface area (SSA) were successfully synthesized by carbon-assisted spray pyrolysis (CASP). Saccharides, such as monosaccharides and disaccharides, or organic acids were used as carbon sources. The physical and chemical properties of these powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Thermo gravimetry-Differential Thermal Analysis (TG-DTA), and BET. Decarbonized powders obtained by this method exhibit spherical morphologies and nano- and submicron-sizes. The SSA of SDC obtained from CASP was more than seven times higher than that obtained from conventional spray pyrolysis (CSP). The SSA of the decarbonized SDC powders obtained by calcination at 900 °C was estimated to be approximately 70 m²/g by using the BET method. The relative density of SDC obtained from CASP was higher than that obtained from CSP. The relative density of the SDC pellet was highest (96 %) when it was sintered at 1400 °C.

Abstract: By pretreatment of Pt/CeO₂ catalysts with high temperature reduction and subsequent low temperature reoxidation, the concentration of Ce³⁺ species in the Pt/CeO₂ catalysts could be adjusted, while at the same time the Pt particle size remained constant. Thus the pure effect of Ce³⁺/Ce⁴⁺ couples on the selective hydrogenation of crotonaldehdye could be explored. The investigation provided direct proofs supporting that Ce³⁺ species favors the crotyl alcohol selectivity.

Abstract: In the present study, nanocrystalline ceria powder and 10 mol% zirconia-doped ceria (10ZDC) powder were prepared by co-precipitation method from cerium nitrate and zirconium nitrate precursors. The resulting particles with irregular shapes were printed onto alumina substrate for the investigation of oxygen gas sensing behavior. The coating morphology of 10ZDC with a network structure revealed a better connection enhancing the sensing properties. Zirconia doping tended to inhibit the grain growth and decrease the lattice constant of ceria. Such effects may improve the electrical conductivity of 10ZDC under different oxygen partial pressures and shorten the response time of 10ZDC to the change of oxygen partial pressure.

Abstract: First-principles electronic structures calculations of the adsorption properties of Cu and Ni on the ceria(111) surface are presented. The adatoms (Cu, Ni) are adsorbed strongly at the hollow site on the CeO2(111) support. Metal induced gap states (MIGS) appear in the O2p-Ce4f gaps and the Cu and Ni adatoms are oxidized to Cu+ and Ni+ mainly by their next nearest neighbor Ce ion, which experiences a conversion of Ce4+→Ce3+. The bonding mechanisms for the Cu-ceria(111) and Ni-ceria(111) systems are proposed.

Abstract: Three different CeO2 sphere nanomaterials (hollow sphere, flowerlike sphere, spherical cluster) were controllably synthesized by carbon sphere template method, hydrothermal and solvothermal method respectively. Then 2.5 wt% Au was doped on the supports by the deposition precipitation method and Au/CeO2 catalysts with three different morphologies were obtained. Composition, morphology and structure of these catalysts were characterized by the techniques of XRD, Raman, TPR, SEM and TEM, and the activity for CO oxidation of the catalysts was investigated. The catalytic test results indicated that the addition of Au could remarkably improve catalytic performance on CO oxidation. The activities of the three catalysts differ largely, the flowerlike Au/CeO2 catalyst had the highest activity for CO oxidation and its T100% was 29°C. The mechanism for the different activity of the catalysts was investigated. H2-TPR result indicated flowerlike had a more intensive peak at 125°C than others and it implied more reducible Au species in this case, that plays a vital role in the CO oxidation.