Phase Analysis and Oxygen Storage Capacity of Ceria-Lanthana-Based TWC Promoters Prepared by Sol-Gel Routes

Ceria-lanthana-based promoters of three-way catalysts are synthesized by two different sol-gel routes, involving nitrate precursors. The oxygen uptake ability of these compounds is measured by O₂ chemisorption. The specific surface area is determined by N₂ adsorption (BET). X-ray diffraction data are analyzed by Rietveld refinement, demonstrating that lanthanum forms solid solution with CeO₂; its total amount in ceria depends on the competitive formation of La-Al mixed oxides and on the synthetic method. The O₂ uptake ability is essentially determined by the La content in the ceria-lanthana solid solution, while it is independent on the surface area and on the CeO₂ particle size. The O₂ uptake ability increases with the La:Ce relative amount in the ceria-lanthana solid solution, but decreases beyond a La:Ce molar ratio greater than ?0.18. This behavior is ascribed to the stable association of vacancy-vacancy or vacancy dopant cation.     

阳离子聚氨酯/CeO2纳米复合材料的制备

二氧化铈;阳离子聚氨酯/CeO2纳米复合材料的制备     

On the Flocculation and Agglomeration of Ceria Dispersion

The ceria dispersions displayed a maximum in the yield stress at the isoelectric point (pI) at pH ～ 7. At pH below pI, the flocculated dispersions at solids concentration of 30 wt% and above produced a smooth and homogeneous appearance. However, at pH above pI, phase separation was observed to occur quite quickly forming a clear layer of liquid supernatant. Upon examination, relatively large discrete aggregates had formed. This behavior can be explained by the surface chemical model proposed by Nabavi et al.^{[ 1} Nabavi , M. , Spalla , O. , and Cabane , B. ( 1993 ) J. Colloid Interface Sci. , 160 : 459 – 471 . [Google Scholar] ^] According to Nabavi et al., nitrate anion, normally an indifferent electrolyte, is both adsorbed and bounded covalently to the surface of the ceria particles at pH below pI. A steric layer is formed preventing particle agglomeration. Such agglomeration was also prevented at high pH with the adsorption of pyrophosphate additive added at 1dwb% concentration. The model proposed by Nabavi et al also explained the agglomeration of ceria particles at pH > pI. Both the covalently bounded and adsorbed nitrates were displaced by the hydroxyl group forming this surface ?OH group that on the interacting particles condenses to form ?Ce?O?Ce? bridging bond and caused particle agglomeration. The yield stress-DLVO force model was obeyed by the ceria dispersion at pH below pI. A critical zeta potential of 56 mV was obtained and this gives an estimate value for its Hamaker constant in water of 82 zJ.     

Auto-combustion synthesis and properties of Ce0.85Gd0.15O1.925 for intermediate temperature solid oxide fuel cells electrolyte

A typical composition of the system Ce_1 − xGd_xO_2 − δ with x = 0.15 (CGO15) has been synthesized by auto-combustion method. DTA/TGA of the precursor compound indicated the completion of reaction at about 270 °C. Greater than 95% of the theoretical density has been achieved by sintering at 1300 °C for 10 h. Single phase formation in as-burnt stage has been confirmed by its powder X-ray diffraction (XRD) pattern. The structural morphology was studied employing bright field transmission electron micrograph (BFTEM) and high resolution transmission electron micrograph (HRTEM). BFTEM image indicates that particles are highly agglomerated and appear to be dispersed in amorphous matrix. Also BFTEM image reveals that the average particle size is 26 ± 5 nm. The presence of amorphous phase in as-prepared ash was also confirmed by HRTEM and selected area diffraction (SAD). The scanning electron micrograph (SEM) of the thermally etched system shows grains having an average size of 400 nm. Impedance measurements have been made in the frequency range 1 Hz to 1.3 MHz between 200 and 500 °C and the total conductivity was measured. An enhanced conductivity value is observed which may make this system suitable for application as a solid electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs).     

Nanostructure and conductivity study of yttria doped zirconia films deposited on samaria doped ceria

Yttrium doped zirconia (YSZ) film was deposited on poly-crystalline 10 at.% samaria doped ceria (SDC) and YSZ plate (doped with 8 at.% yttria) by electron beam evaporation deposition. For electrolyte application in solid oxide fuel cells, YSZ can be used with SDC and act as an electron barrier. The conductivity of YSZ and SDC was measured after sintering at 1000 °C. Results indicated that YSZ film became columnar structure, and a new layer formed between the YSZ film and SDC, due to the inter-diffusion between zirconium ions and cerium ions.     

Preparation of CeO2-ZrO2 Mixed Oxide Powders by the Coprecipitation Method for the Purification Catalysts of Automotive Emission

Influence of CeO₂ content on the specific surface area (SA), oxygen storage capacity (OSC) and crystalline structure of the powders in the CeO₂-ZrO₂ system were investigated. The change of SA value by heat-treatment is almost proportional to that of OSC. The lattice parameters of the powders had a linear relationship with the OSC value. In the CeO₂-ZrO₂ system, powders with 20 mol% CeO₂ was found to show the highest OSC value and the highest durability of SA value after calcined at high temperatures.     

Influence of Pd-Ce interaction and chlorine ion on hydrodesulfurization reaction: The activity and sulfur tolerance of the Pd-Ceo2/Al2O3 catalyst

CeO₂ promoted palladium catalysts supported on Al₂O₃ were prepared using the impregnation (IM) and the deposition-precipitation (DP) methods. The activities and sulfur tolerance of the catalysts for hydrodesulfurization (HDS) were detected with thiophene HDS as probe reaction. H₂ adsorption, XRD, FTIR, NH₃-TPD, XPS were used to characterize the catalysts. The Pd-CeO₂/Al₂O₃ (IM) catalyst was highly active for the HDS reaction, and it had much stronger sulfur tolerance than the Pd/Al₂O₃ catalyst. Pd-CeO₂/Al₂O₃ (DP) showed excellent sulfur tolerance while its initial activity decreased. It was observed that with the chlorine bridge, the interfacial structure of Pd-Cl⁻¹-Ce³⁺ was responsible for the high activity of the Pd-CeO₂/Al₂O₃ (IM) catalyst, at the same time the interaction of Pd with Ce was weakened by Cl₋₁ ions. The enhanced sulfur tolerance over the Pd-CeO₂/Al₂O₃ (IM) catalyst was attributed to the weakened Pd-S bond caused by the competitive adsorption of H₂S on Ce³⁺ ions. As to the Pd-CeO₂/Al₂O₃ (DP) catalyst, a strong interaction of Pd with Ce put Pd at an electron-deficient state, the creation of sulfided palladium was therefore inhibited.     

分子动力学与第一原理研究二氧化铈(CeO2)n (n=1～5)纳米粒子的结构性质

二氧化铈纳米粒子(CeO2)n(n=1～5)材料为固态氧化燃料电池中的催化剂,因此了解其不同尺寸结构的性质是非常重要的.在本论文中使用分子动力学(molecular dynamics)模拟结合火焰算法(FIRE algorithm)计算得到二氧化铈的最小能量结构.再应用密度泛函理论方法(density functional theory)对这些结构进一步计算,得到更精确的最低能量结构.     

微乳液法制备的CuO-CeO2/Al2O3/FeCrAl整体式催化剂催化CO优先氧化反应

采用微乳液法将CuO-CeO2负载于FeCrAl整体式载体上,以超声波和热振荡考察了催化剂在载体表面的粘附稳定性,并测试了CuO-CeO2/Al2O3/FeCrAl整体式催化剂对一氧化碳优先氧化反应的催化性能.使用扫描电子显微镜、X射线衍射和X射线光电子能谱等手段对所制备的催化剂进行了表征.结果表明,CuO-CeO2可以以良好的稳定性粘附于FeCrAl载体表面,且以纳米粒子形式在载体表面分布均匀.载体对催化剂的化学状态没有显著影响,制得的整体式催化剂对一氧化碳优先氧化具有较高的催化活性和高选择性,并且有良好的稳定性.