• Journal of the Korean Ceramic Society
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• v.54 no.1
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• pp.23-27
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• 2017

A series of $CeO_2-TiO_2$ composite samples with different Ce/Ti molar ratios were prepared by the paper template. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm a face-centered cubic lattice of $CeO_2$ with Ce/Ti =8:2 or 9:1 and a two phase mixture of anatase titania and face-centered cubic ceria with Ce/Ti = 7 : 3. The field emission scanning electron microscopy (FESEM) results suggest that the products are micron braid structures consisting of fibers with diameters in a range of $1-6{\mu}m$ and lengths of several hundred micrometers. $N_2$ absorption-desorption testing shows that the composite at Ce/Ti molar fraction of 8 : 2 has the largest BET surface area (about $81m^2{\cdot}g^{-1}$). Compared to the pure $CeO_2$ sample, the composites show superior catalytic activity for $H_2$ reduction and CO oxidation. For the micron braid structure $CeO_2-TiO_2$ composite (Ce/Ti = 8 : 2), due to the high surface area and the solid solution with appropriate $Ti^{4+}$ incorporation, the CO conversion at about $280^{\circ}C$ was above 50% and at $400^{\circ}C$ was 100%.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.451-453
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• 2013

Porous ceramic membranes consisting of $Ce_{1-x}Y_xO_{2-{\delta}}$ were developed for hydrogen permeation tests. Various amounts (x = 0, 0.05, 0.1, 0.2) of yttrium were doped to ceria to study the effect of yttrium doping on ceria membranes on various properties, including hydrogen permeability. $Ce_{1-x}Y_xO_{2-{\delta}}$ powder was synthesized by the sol-gel method. These membranes were fabricated by pressing and sintering at $1300^{\circ}C$ for 6 h. As the amount of yttrium increased, the grain size of the membrane decreased. Hydrogen permeability was improved as the yttrium content increased. Selective permeability of hydrogen compared to CO is explained by electric conductivity. As the temperature rose, both the hydrogen perm-selectivity and electric conductivity on $Ce_{0.8}Y_{0.2}O_{1.9}$ improved.

• Clean Technology
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• v.16 no.4
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• pp.284-291
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• 2010

Nitrous oxide ($N_2O$) is a greenhouse material which is hard to remove. Even with a catalytic process it requires a reaction temperature, at least, higher than 670 K. This study has been performed to see the effects of Ce addition to the mixed oxide catalyst which shows the highest activity in decomposing $N_2O$ completely at temperature as low as 473 K when CO is used as a reducing agent. Mixed metal oxide(MMO) catalyst was made through co-precipitation process with small amount of Ce added to the base components of Co, Al and Rh or Pd. Consequently, the surface area of the catalyst decreased with the contents of Ce, and the catalytic activity of direct decomposition of $N_2O$ also decreased. However, in the presence of CO, the activity was found high enough to compensate the portion of activity decrease by Ce addition, so that it can be ascertained that the catalytic activity and stability can be maintained in the CO involved $N_2O$ reduction system when Ce is added for the physical stability of the catalyst.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1224-1228
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• 2003

The crystallization behavior of a luster glaze containing ceria has been investigated. When glazed specimens were sintered at 110$0^{\circ}C$, crystalline ceria particles were preferentially precipitated with (100) planes parallel to the specimen surface with the size of around 200 nm. The particle population in the surface region was much higher than inside glaze, covering over 60% of the specimen surface area. Crystallization of the particles with preferred orientation was promoted, after the removal of internal interface through complete melting of the fit particles. The luster effect seems to result from CeO$_2$ particles of high refractive index, their strong light scattering at visible rage due to fine crystalline size 200 nm and their planar arrangement in the surface region.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.376-382
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• 2020

CeO₂ nanoparticles, employed in a lot of fields due to their excellent oxidation and reduction properties, are synthesized through a solvothermal process, and a high specific surface area is shown by controlling, among various process parameters in the solvothermal process, the type of solvent. The synthesized CeO₂ nanoparticles are about 11~13 nm in the crystallite size and their specific surface area is about 65.38~84.65 ㎡/g, depending on the amount of ethanol contained in the solvent for the solvothermal process; all synthesized CeO₂ nanoparticles shows a fluorite structure. The dispersibility and microstructure of the synthesized CeO₂ nanoparticles are investigated according to the species of dispersant and the pH value of the solution; an improvement in dispersibility is shown with the addition of dispersants and control of the pH. Various dispersing properties appear according to the dispersant species and pH in the solution with the synthesized CeO₂ nanoparticles, indicating that improved dispersing properties in the synthesized CeO₂ nanoparticles can be secured by applying dispersant and pH control simultaneously.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.160-166
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• 2019

Cerium oxide ($CeO_2$, often called as Ceria) is one of the valuable rare earth oxide materials, which has been widely used for high temperature applications such as solid oxide fuel cells, automotive three-way catalysts and oxygen storage capacity. Considering those application, it is important to improve high redox and thermal stability with high surface morphology because the high surface area of $CeO_2$ could improve the catalytic reactivity at high temperature conditions. Herein we successfully fabricated hierarchical flower-like $CeO_2$ deposited via controlling pathway of precipitation reaction to supply carbonate ion lead to the flower-like morphology. The hexagonal lattice system of precipitated precursor shows better thermal stability then orthorhombic one during thermal cycling condition.

• Journal of the Korean Ceramic Society
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• v.30 no.11
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• pp.941-948
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• 1993

The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{\circ}C$ for 2h in N2 to prepare $\alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $\alpha$-Sialon ceramics were investigated. At 120$0^{\circ}C$, oxidation resistance was best for the Y2O3 added $\alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $\alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3＋CeO2) added $\alpha$-Sialon ceramics was higher than Y2O3 added $\alpha$-Sialon ceramics.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.719-727
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• 1989

By using commercial zirconia powder CeO2-ZrO2 ceramics containing 8~16mol% CeO2 was made by heat treatment at 1350~155$0^{\circ}C$ for 1~10hr. The minimum amount of CeO2 for obtaining complete tetragonal phase was 12mol%, and in the tetragonal phase region fracture toughness of Ce-TZP was decreased with increasing CeO2 content and the maximum value was obtained when 12mol% CeO2 was added. The bending strength goes through maximum at 14mol% CeO2. Fracture mode of Ce-TZP transformed from intergranular to transgranular fracture with increasing CeO2 content, so the morphology of fracture surface of 16mol% Ce-TZP was wholly transgranular and this tendency was independent on grain size. The crystal structure of the 12mol% Ce-TZP was monoclinic with fringes along the grain boundaries which are lying in the particular plane from the TEM observation. The chemical composition of the sintered body was homogeneous as a whole and some amorphism or air pocket was observed at the triple junction.

• Clean Technology
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• v.21 no.3
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• pp.200-206
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• 2015

In order to investigate the effect of cerium oxide addition, Cu-ZnO-CeO₂ catalysts were prepared using co-precipitation method for water gas shift (WGS) reaction. A series of Cu-ZnO-CeO₂ catalyst with fixed Cu Content (50 wt%, calculated as CuO) and a given ceria content (e.g., 0, 5, 10, 20, 30, 40 wt%, calculated as CeO₂) were tested for catalytic activity at a GHSV of 95,541 h^-1, and a temperature range of 200 to 400 ℃. Cu-ZnO-CeO₂ catalysts were characterized by using BET, SEM, XRD, H₂-TPR, and XPS analysis. Varying composition of Cu-ZnO-CeO₂ catlysts led the difference characteristics such as Cu dispersion, and binding energy. The optimum 10 wt% doping of cerium facilitated catalyst reduction at lower temperature and improved the catalyst performance greatly in terms of CO conversion. Cerium oxide added catalyst showed enhanced activities at higher temperature when it compared with the catalyst without cerium oxide. Consequently, ceria addition of optimal composition leads to enhanced catalytic activity which is attributed to enhanced Cu dispersion, lower binding energy, and hindered Cu metal agglomeration.

• Clean Technology
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• v.29 no.4
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• pp.313-320
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• 2023

In order to increase the usability of H₂-SCR, the NOx removal characteristics with catalyst powder of PtNi/CeO₂-W-TiO₂ using Ce as a co-catalyst was synthesized and coated on a porous metal structure (PMS) were evaluated. Catalyst powder of PtNi/CeO₂-W-TiO₂(PtNi nanoparticles onto W-TiO₂, with the incorporation of ceria (CeO₂) as a co-catalysts) was synthesized and coated onto a porous metal structure (PMS) to produce a Selective Catalytic Reduction (SCR) catalyst. H₂-SCR with CeO₂ as a co-catalyst exhibited higher NOx removal efficiency compared to H₂-SCR without CeO₂. Particularly, at a 10wt% CeO₂ loading ratio, the NOx removal efficiency was highest at 90℃. As the amount of catalyst coating on PMS increased, the NOx removal efficiency was improved below 90℃, but it was decreased above 120℃. When the space velocity was changed from 4,000 h^-1 to 20,000 h^-1, the NOx removal efficiency improved at temperatures above 120℃. It was expected that the use of the catalyst could be reduced by applying the PMS with excellent specific surface area as a support.