• Title/Summary/Keyword: $CeO_2/ZrO_2$

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Order-disorder structural tailoring and its effects on the chemical stability of (Gd, Nd)2(Zr, Ce)2O7 pyrochlore ceramic for nuclear waste forms

  • Wang, Yan;Wang, Jin;Zhang, Xue;Li, Nan;Wang, Junxia;Liang, Xiaofeng
    • Nuclear Engineering and Technology
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    • v.54 no.7
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    • pp.2427-2434
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    • 2022
  • Series of unequal quantity Nd/Ce co-doped ceramic nuclear waste forms, (Gd, Nd)2(Zr, Ce)2O7, were prepared to tailor its ordered pyrochlore or disordered fluorite structure. The phase transition, microtopography, and elemental composition of the ceramic samples were systematically investigated, especially the effect of order-disorder structure on the chemical stability. It was confirmed that unequal quantity of Nd/Ce could synchronously replace the Gd/Zr-sites of Gd2Zr2O7. And the phase transition of order-disorder structure could be successfully tailored by regulating the average cationic radius ratio of (Gd, Nd)2(Zr, Ce)2O7 series. The elements of Gd, Nd, Zr, and Ce are uniformly distributed in the ordered or disordered structures. The MCC-1 leaching results showed that (Gd, Nd)2(Zr, Ce)2O7 pyrochlore ceramic nuclear waste forms had excellent chemical stability, whose elements' normalized leaching rates were as low as 10-4-10-7 g·m-2·d-1 after 7 days. In particular, the chemical stability of disordered structure was superior to that of ordered structure. It was proposed that the force constant and the closest packing were changed with the structure transformation resulting the chemical stability difference.

Preparation and Characterization of Ceria Stabilized Tetragonal Zirconia Polycrystals(I) : Effect of CeO2 Contents on the Mechanical Properties of Ce-TZP (세리아 안정화 지르코니아의 제조 및 특성(I) : CeO2첨가량 변화에 따른 Ce-TZP의 기계적 특성)

  • Jung, Seung-Hwa;Kang, Jong-Bong
    • Korean Journal of Materials Research
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    • v.20 no.7
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    • pp.379-384
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    • 2010
  • The usual ceramic process of mixing and milling in state of oxides $ZrO_2$ and $CeO_2$ was adopted in this study in a wet process to manufacture Ce-TZP. $CeO_2$-$ZrO_2$ ceramics containing 8~20 mol% $CeO_2$ were made by heat treatment at $1250\sim1500^{\circ}C$ for 5hr. The maximum dispersion point of every slurry manufactured with a mixture of $ZrO_2$ and $CeO_2$ was neat at pH10. A stable slurry with average particle size of 90 nm can be manufactured when it is dispersed with the use of ammonia water and polycarboxylic acid ammonium. The sintered Ce-TZP ceramics manufactured with the addition of $CeO_2$ in a concentration of less than 10 mol% progressed to the fracture of the specimen due to the existence of a monoclinic phase of more than 30% at room temperature. More than 99% of the tetragonal phase was created for the sintered body with the addition of $CeO_2$ beyond 18 mol%, but the degradation of the mechanical properties on the entire specimen was brought about due to the $CeO_2$ existing in a percentage above 3%. Consequently, the optimal Ce-TZP level combined in the oxide state was identified to be 16 mol% of $CeO_2$ contents.

The Effect of Cu Loading on the Performance of Cu-Ce0.8Zr0.2O2 Catalysts for Single Stage Water Gas Shift Reaction (컴팩트 개질기용 수성가스전이 반응에서 Cu-Ce0.8Zr0.2O2 촉매에 Cu 담지량이 미치는 영향)

  • KIM, HAK-MIN;JEON, KYUNG-WON;NA, HYUN-SUK;JANG, WON-JUN;JEONG, DAE-WOON
    • Journal of Hydrogen and New Energy
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    • v.28 no.4
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    • pp.345-351
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    • 2017
  • Single stage water-gas shift reaction has been carried out at a gas hourly space velocity of $150,494h^{-1}$ over $Cu-Ce_{0.8}Zr_{0.2}O_2$ catalysts prepared by a co-precipitation method. Cu loading was optimized to obtain highly active co-precipitated $Cu-Ce_{0.8}Zr_{0.2}O_2$ catalysts for single stage water-gas shift reaction. 80 wt.% $Cu-Ce_{0.8}Zr_{0.2}O_2$ exhibited the excellent catalytic performance as well as 100% $CO_2$ selectivity (CO conversion = 27% at $240^{\circ}C$ for 50 h). The high activity and stability of 80 wt.% $Cu-Ce_{0.8}Zr_{0.2}O_2$ are correlated to low activation energy and large amount of surface Cu atoms.

Autothermal Reforming of Propane over Ni/CexZr1-xO2 Catalysts (Ni 담지 CexZr1-xO2 촉매상에서 프로판의 자열개질반응)

  • Kong, Jin-Hwa;Park, Nam-Cook;Kim, Young-Chul
    • Korean Chemical Engineering Research
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    • v.51 no.1
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    • pp.47-52
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    • 2013
  • In this study, the catalytic performance and characterization of $Ni/Ce_xZr_{1-x}O_2$ were investigated using an autothermal reforming (ATR) process for hydrogen production. The $Ni/Ce_xZr_{1-x}O_2$ catalysts were prepared using the following methods: the water method (CZ-W), urea water method (CZ-UW) and urea, water and ethanol method (CZ-UWA). The performance of $Ni/Ce_xZr_{1-x}O_2$ catalysts in autothermal reforming of propane for hydrogen production was studied in a fixed-bed flow reactor. Reaction tests were conducted by using a feed of $H_2O/C_3H_8/O_2$=3/1/0.37 and $300{\sim}700^{\circ}C$. The CZ-UW and CZ-UWA catalysts showed higher propane conversion and hydrogen yield than the CZ-W catalyst. The activity test confirmed that the improvement in the water-ethanol catalyst was due to the low level of carbon deposition. SEM showed that the surface carbon consisted of clusters on the used CZ-UW catalyst, which is incontrast to the nano-fiber morphology observed on the used CZ-UWA catalyst. It was found that the amount of carbon deposition depends on the preparation method. Especially the $Ni/Ce_{0.75}Zr_{0.25}O_2$ was showed higher propane conversion and hydrogen yield than the other catalysts. Also TGA showed that the resistance of carbon deposition increase to Co addition.

Syngas and Hydrogen Production from $CeO_2/ZrO_2$ coated foam device under concentrated solar radiation (고온 태양열을 이용한 합성가스 및 수소 생산에서 $CeO_2/ZrO_2$가 코팅된 다공성 폼의 영향)

  • Jang, Jong-Tak;Yoon, Ki-June;Han, Gui-Young
    • 한국태양에너지학회:학술대회논문집
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    • 2011.11a
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    • pp.307-313
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    • 2011
  • 금속산화물을 이용한 2단계 산화/환원 반응은 GTL, CTL 의 반응원료인 합성가스 및 수소 생산기술이다. 이 기술은 메탄을 환원제로 사용함으로써 비교적 저온에서 산화/환원 반응을 할 수 있는 장점이 있다. 하지만 반복 사이클의 시연에서 금속산화물의 소결현상으로 인한 활성저하가 이 기술의 문제점 중의 하나이다. 본 연구에서는 2.5 kW Xenon arc lamp 가 설치된 solar simulator를 사용 하였으며, 무기물 다공성 폼 (SiC foam)및 유기물 다공성 폼 (Ni, Cufoam)에 $CeO_2/ZrO_2$ 를 코팅하여 연속적인 합성가스 및 수소 생산 가능성을 알아보았다. 반응 전 후의 $CeO_2/ZrO_2$ 의 결정 구조를 SEM 과 XRD 를 통해 분석하였다.

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A Study on the Ceria Stabilized Tetragonal Zirconia Polycrystals (Ce-TZP) (IV) ; Effect of MgO Addition on 12 Ce-TZP Ceramics (CeO2 안정화 정방정 Zirconia 다결정체(Ce-TZP)에 관한 연구(IV) : 12 Ce-TZP 세라믹스에 미치는 MgO 첨가 영향)

  • 김문일;박정현;강대석;이현권;문성환
    • Journal of the Korean Ceramic Society
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    • v.27 no.2
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    • pp.233-243
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    • 1990
  • For theinvestigation of MgO addition effect on 12Ce-TZP ceramics, MgO-CeO2-ZrO2 ceramics was fabricated using commercial powders under sintering condition of 130$0^{\circ}C$-1$600^{\circ}C$ for 2hr. Fully tetragonal phase could be obtained by proper heat treatment and MgO addition amount. Minor cubic phase was appeared in relatively high MgO content composition at each sintering temperature. As alloying amount of MgO increased, tetragonal stability increased and grain size decreased. Grain size dependence on MgO content was verified by SEM observation of fractured surface. Surface bloating was observed from the 2 m/o to 6m/o in the temperature range of 150$0^{\circ}C$ to 1$600^{\circ}C$. In spite of very porous microstructure owing to surface bloating, 100% TZP could be maintained in 2.0m/o MgO composition by heat treatment of 150$0^{\circ}C$. This result indicated that MgO was more powerful stabilizer than CeO2. Mechanical proprties of MgO-CeO2-ZrO2 ceramics were consistent with the stability observation of tetragonal phase very well.

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Catalytic Behavior of Ni/CexZr1-xO2-Al2O3 Catalysts for Methane Steam Reforming: The CexZr1-xO2 Addition Effect on Water Activation (메탄 습식 개질 반응용 Ni/CexZr1-xO2-Al2O3 촉매의 반응 특성: CexZr1-xO2 첨가에 의한 물 활성화 효과)

  • Haewon Jung;Huy Nguyen-Phu;Mingyan Wang;Sang Yoon Kim;Eun Woo Shin
    • Korean Chemical Engineering Research
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    • v.61 no.3
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    • pp.479-486
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    • 2023
  • In this study, we investigated the effect of the CexZr1-xO2 (CZ) addition onto Ni/Al2O3 catalysts on the catalytic performance in methane steam reforming. In the reaction results, the CZ-added Ni/Al2O3 catalyst showed higher CH4 conversion and H2 yield under the same reaction conditions than Ni/Al2O3. From the characterization data, the two catalysts had similar support porosity and Ni dispersion, confirming that the two properties could not determine the catalytic performance. However, the oxygen vacancy over the CZ-added Ni/Al2O3 catalyst induced an efficient steam activation at low reaction temperatures, resulting in an increase in the catalytic activity and H2 yield.

Synthesis, Characterization and Catalytic Application of MoO3/CeO2-ZrO2 Solid Heterogeneous Catalyst for the Synthesis of Benzimidazole Derivatives

  • Rathod, Sandip B.;Lande, Machhindra K.;Arbad, Balasaheb R.
    • Bulletin of the Korean Chemical Society
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    • v.31 no.10
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    • pp.2835-2840
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    • 2010
  • A series of $MoO_3/CeO_2-ZrO_2$ catalysts with different Mo content (8 - 20 wt %) were prepared by simple co-precipitation followed by impregnation method and were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), energy dispersive spectroscopic (EDS) techniques. The prepared materials were tested for catalytic activity by the synthesis of benzimidazole derivatives using condensation of aromatic aldehydes and o-phenylenediamine by conventional and microwave method. Obtained results reveal that the catalytic activity increases with increase in Mo wt % loading. The best catalytic activity was obtained with 20 wt % $MoO_3/CeO_2-ZrO_2$. The particle size or crystallite size was estimated using Debye-Scherrer equation. After completion of reaction, the catalyst can be recovered efficiently and reused with consistent activity.

Activity of Ni/Ce-ZiO2 Catalyst on the Steam Reforming Reaction with Pretreatment Conditions (전처리 조건에 따른 Ni/Ce-ZiO2촉매의 수증기 개질반응 활성)

  • Oh, Young-Sam;Song, Taek-Yong;Baek, Young-Soon;Jun, Ki-Won
    • Journal of Hydrogen and New Energy
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    • v.14 no.1
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    • pp.1-7
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    • 2003
  • In this study, activity changes of $Ni/Ce-ZrO_2$ catalyst for steam reforming reaction in the various steam treatment condition were investigated and BET, XRD and XPS analysis were introduced to characterize the catalyst before and after treatment. Activity test showed that $Ni/Ce-ZrO_2$ catalyst had good activity after reduction in steam reforming reaction but deactivated rapidly after steam treatment at high temperature. Activities of deactivated catalyst by steam was recovered to die previous activity level after reduction using hydrogen rich gas. It was observed that catalytic activity was preserved after repeated steam treatment, too. It showed that change of catalytic activity due to steam treatment is perfectly reversible. From the BET, XRD and XPS analysis, deactivation of $Ni/Ce-ZrO_2$ catalyst was due to the transition from Ni, that is activity site for steam reforming reaction, to $NiAl_2O_4$ in steam treatment at high temperature.