• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.822-828
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• 2018

P-type Ce/Yb-filled skutterudites were synthesized, and their charge transport and thermoelectric properties were investigated with partial double filling and charge compensation. In the case of $(Ce_{1-z}Yb_z)_{0.8}Fe_4Sb_{12}$ without Co substitution, the marcasite ($FeSb_2$) phase formed alongside the skutterudite phase, but the generation of the marcasite phase was inhibited by increasing Co concentration. The electrical conductivity decreased with increasing temperature, exhibiting degenerate semiconductor behavior. The Hall and Seebeck coefficients were positive, which confirmed that the specimens were p-type semiconductors with holes as the major carriers. The carrier concentration decreased as the concentration of Ce and Co increased, which led to decreased electrical conductivity and increased Seebeck coefficient. The thermal conductivity decreased due to a reduction in electronic thermal conductivity via Co substitution, and due to decreased lattice thermal conductivity via double filling of Ce and Yb. $(Ce_{0.25}Yb_{0.75})_{0.8}Fe_{3.5}Co_{0.5}Sb_{12}$ exhibited the greatest dimensionless figure of merit (ZT = 0.66 at 823 K).

• 한국초전도학회:학술대회논문집
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• v.16
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• pp.36-36
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• 2006

• Journal of Korean Society of Environmental Engineers
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• v.22 no.12
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• pp.2263-2273
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• 2000

Catalytic wet air oxidation of acetic acid over Mn-Ce based catalysts deposited on various supports ($SiO_2$, $TiO_2$, $ZrO_2$), $ZrSiO_4$, $ZrO_2(10wt%)/TiO_2$) have been carried out in high pressure microreactors. Also, promotional effects by small addition(O.5~1.0 wt%) of p-type semiconductors (CoO, $Ag_2O$, SnO) have been investigated. From the screening tests for initial activity ranking, both Mn(2.8)-Ce(7.2 wt%) and Ru(O.4)Mn(2.7)-Ce(6.9 wt%) supported on $TiO_2$ were selected as the promising reference candidates. In $Mn-Ce/TiO_2$ reference catalyst, addition of small amount of each p-type semiconductor (Co, Sn and Ag) resulted in activity promotional effect and the degree of the increase was in the following order: Co> Ag > Sn. Especially, $Mn-Ce/TiO_2$ promoted with 0.5 wt% Co gave the 2.6 folds activity increase compared to the reference case attributing to the surface area increase as well as synergy effect. In $Ru-Mn-Ce/TiO_2$ reference catalyst, only Co(1.0 wt%) promoted case showed a little reaction rate increase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.73-77
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• 2012

Co-(0.8 wt%) and Ce-(0.4 wt%) doped cubic zirconia ($ZrO_2$ : $Y_2O_3$ = 80 : 20, 70 : 30, 60 : 40, 50 : 50 wt%) single crystals grown by a skull melting method were heat-treated in $N_2$ at $1000^{\circ}C$ for 5 hrs. The orange, yellowish brown and brown colored as-grown single crystals were changed into either brownish red, yellow and green color after the heat treatment. Before and after the heat treatment, the YSZ (yttria-stabilized zirconia) single crystals were cut for wafer form (${\phi}6.5mm{\times}t2mm$). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by $Ce^{3+}(^2F_{5/2,7/2}(4f){\rightarrow}^2T_g(5d^1))$, $Co^{2+}(^4A_2(^4F){\rightarrow}^4T_1(^4F)$ or $^4T_1(^4P))$ and $Co^{3+}$, change of ionization energy and lattice parameter were confirmed.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.312-317
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• 2014

Catalytic combustion of benzene over CuO-$CeO_2$ mixed oxides prepared by co-precipitation method were investigated. The CuO-$CeO_2$ mixed oxides were also prepared using different precipitant and CuO precursor. They were characterized by XRD, BET, XPS and $H_2-TPR$. In the CuO-$CeO_2$ catalysts, characteristic copper oxide peaks were shown at $2{\Theta}=35.5^{\circ}$ and $38.5^{\circ}$ regardless of the precipitant. The Cu0.35 catalyst prepared using $NH_4OH$ as a precipitant revealed the highest activity on the combustion of benzene. In addition, the pretreatment with hydrogen enhanced the catalytic activity and the catalyst reduced at $400^{\circ}C$ showed the highest activity on the combustion of benzene.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.226.1-226.1
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• 2010

본연구에서는 GTL(gas to liquids)공정의 합성가스 생산을 위해 수증기-이산화탄소 복합개질반응(Combined Steam and Carbon dioxide Reforming of Methane, CSCRM)을 수행하였다. CSCRM은 수증기와 이산화탄소의 공급비 조절을 통해 $H_2$/CO비를 2로 맞추기 용이한 장점을 지니고 있어 다른 단일 개질 반응과 달리 합성가스 생산 시 $H_2$/CO 비율을 조절하기 위한 부가적인 공정이 필요하지 않아 경제적인 공정이다. 일반적으로 사용되는 Ni개질촉매는 가격대비 우수한 성능을 보이지만 S/C비가 낮은 CSCRM의 경우 촉매표면의 탄소침적에 의한 비활성화가 야기되는 문제점이 있다. 따라서 본 연구에서는 산소저장능력과 산소전달능력이 우수한 $CeO_2$를 조촉매로 첨가하여 표면에 형성된 코크 제거가 용이하도록 하였다. Ni-Ce/$MgAl_2O_4$촉매는 동시함침법(co-impregnation)으로 제조하였으며, Ni의 함량을 10wt%로 고정한 상태에서 Ce의 함량을 조절하여 Ce/Ni 최적비를 찾고자 하였다. XRD, TPR, BET, $H_2$-Chemisorption과 같은 촉매의 특성분석을 통해 촉매의 비표면적, 환원특성과 Ni입자의 분산도 등을 확인하였다. Ce를 첨가함에 따라 Ce2.5wt%까지는 비표면적이 증가하다가 이후 점차 줄어드는 경향성을 보였다. 또한, $H_2$-Chemisorption 결과 역시 비표면적과 유사한 경향성을 보였는데, Ce5.0wt%까지 Ni 분산도가 증가 하다가 다시 감소하는 것을 확인할 수 있었다. 반응실험은 $H_2O:CO_2:CH_4:N_2$ = 0.8:0.4:1:1의 공급조건에서 수행하였으며, 질소와 수소 환원분위기로 $700^{\circ}C$에서 1시간 환원 후 $650^{\circ}C$에서 $550^{\circ}C$범위로 온도를 떨어뜨려가면서 반응을 수행하였다. Ce를 첨가함에 따라 $CH_4$ 전환율이 증가를 하다가 Ce2.5wt% 이후 감소하는 것을 확인할 수 있었다. 이러한 높은 촉매 활성은 Ce 첨가로 인해 환원특성이 좋아지고 Ni분산도가 증가하여 담체와 강한 상호작용(SMSI)을 형성함으로 탄소침적 저항성 강화에 기인한 것이다.

• Corrosion Science and Technology
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• v.22 no.1
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• pp.1-9
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• 2023

This work studied the inhibitory effect of the combination of benzoate-intercalated hydrotalcite (HT-BZ) and Ce³⁺-loaded clay (Clay-Ce) on carbon steel (CS). HT-BZ was prepared by the co-precipitation method and Clay-Ce was fabricated by a cation exchange reaction. HT-BZ and Clay-Ce were assessed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) coupled with zeta potential measurement. Electrochemical measurements coupled with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) were used for studying the inhibitory action of the mixture of HT-BZ and Clay-Ce on steel electrodes immersed in 0.1 M NaCl. For comparison, the inhibitory effect of HT-BZ or Clay-Ce alone was also evaluated. The results showed that HT-BZ combined with Clay-Ce provided synergistic inhibition of the CS substrate. The mixture of 0.5 g/L HT-BZ + 0.5 g/L Clay-Ce provided 93.5% inhibition efficiency. The protective mechanism of the HT-BZ + Clay-Ce mixture consisted of the reaction of released BZ and Ce³⁺ and the deposition of HT-BZ and Clay-Ce structures on the CS substrate.

• Journal of Environmental Science International
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• v.28 no.1
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• pp.65-73
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• 2019

The catalytic activity of Ni-0.2%YSZ (Yttria-Stabilized Zirconia) with different promoters was evaluated for $CO_2$ methanation. The catalysts were weighed for mixing and they were dried at $110^{\circ}C$ for molding into disks. The concentration of $CO_2$ and $CH_4$ for conducting of $CO_2$ methanation were analyzed by gas chromatography and the physical characteristics of the disk-type catalyst formed were analyzed by X-ray diffraction, scanning electron microscope and energy dispersive x-ray spectrometer. The addition of $CeO_2$ as a promoter for Ni-0.2%YSZ (denoted as Ni-5%Ce-0.2%YSZ) resulted in the highest $CO_2$ methanation. It also showed catalytic activity at a low temperature($200^{\circ}C$). Following this, $ZrO_2$, $SiO_2$, $Al_2O_3$ and $TiO_2$ were added to Ni-5%Ce-0.2%YSZ to compare the $CO_2$ methanation, and the highest efficiency was found for. Ni-1%Ti-5%Ce-0.2%YSZ Then, the concentration of Ti was increased to 10% and the catalytic activity was estimated using seven different types of commercial $TiO_2$. In conclusion, ST-01 $TiO_2$ showed the highest efficiency for $CO_2$ methanation.

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.118-123
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• 2012

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized from Ce and Gd nitrate solutions using ammonium carbonate($(NH_4)_2CO_3$) as a precipitant. Attrition-milling of the powder, which had been calcined at $700^{\circ}C$ for 4 h, decreased an average particle size of 2.2 ${\mu}m$ to 0.5 ${\mu}m$. The milled powder consisted of nano-sized spherical primary particles. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 80% at 1000 $^{\circ}C$ and 96.5% at $1200^{\circ}C$, respectively. Densification was found to almost complete at $1300^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%. The grains of ~0.2 ${\mu}m$ in size at $1200^{\circ}C$ grew to ~1 ${\mu}m$ in size at $1300^{\circ}C$ as a result of a rapid grain growth.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.230.1-230.1
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• 2010

조촉매(Promotor)인 Na은 수성가스전이(Water Gas Shift, WGS) 반응 시 생성된 포름산염의 C-H결합을 쉽게 분해하는 역할을 한다. 본 연구에서는 $Pt/CeO_2$ 촉매의 성능 향상을 위해 Na의 담지량을 변화시켜 촉매적 활성을 비교하여 보았다. 제조된 담체는 침전법(Precipitation)을 사용하여 제조하였으며 $500^{\circ}C$에서 6시간 소성하였다. Pt 담지량은 1wt%로 고정하였고 Na 담지량은 1 wt%~5 wt%로 변화를 주어 동시(공)-함침법(Co-incipient wetness method)으로 담지 시켰다. 반응 실험은 공간속도(Gas Hourly Space Velocity, GHSV) $45,385h^{-1}$에서 수행하였다. WGS 반응 결과 3 wt%의 Na이 담지된 $Pt/CeO_2$ 촉매의 경우를 제외하고 나머지 Na이 담지된 촉매들은 비교적 높은 CO의 전환율을 나타내었다. 특히 2 wt%의 Na이 담지된 $Pt/CeO_2$ 촉매는 가장 높은 CO의 전환율을 나타내었다. 따라서 Na 담지량의 변화가 포름산염의 C-H결합 분해에 영향을 미친다는 것을 알 수 있다.