杂化材料的制备、性能及应用

较详细地介绍了杂化材料的概念及其制备方法、性能和应用。重点是有机高分子－无机杂化材料的制备、性能及应用。     

K/CeO2催化剂上碳黑催化燃烧性能及稳定性（英文）

采用不同的钾盐前体制备了一系列K/CeO2催化剂,利用热重和程序升温氧化(TPO)等技术考察了其催化性能及稳定性.结果表明,K/CeO2催化剂可使碳黑完全燃烧温度降低近200oC.钾盐前体对催化活性和稳定性具有较大影响,由于硝酸钾熔点低,金属在载体上的流动性强,有利于催化剂与碳黑的有效接触,因而表现了较高的活性,三次TPO循环试验中催化活性稳定.碳酸钾的熔点高且碱性较强,使碳黑燃烧生成的CO2不可逆吸附在其表面,导致反应活性低,TPO循环实验表明其反应速率降低,失活明显.     

颗粒可控分散技术在CeO2抛光粉生产中的应用研究

通过高能湿法球磨与低温喷雾干燥联用技术对传统沉淀法氧化铈抛光粉后处理工艺进行改进,从而实现生产过程中颗粒的可控分散.通过XRD确定产品晶型,采用SEM,BET和激光粒度仪对改进前后颗粒度变化进行了分析.将该产品与进口产品在ZF7和K9玻片抛光生产线上比较使用,良品率高于进口产品.结果表明该颗粒可控分散技术有效降低了颗粒的团聚程度,提高了颗粒均匀性,改善了抛光性能.     

Nanosized CeO2–SiO2, CeO2–TiO2, and CeO2–ZrO2 Mixed Oxides: Influence of Supporting Oxide on Thermal Stability and Oxygen Storage Properties of Ceria

The influence of SiO₂, TiO₂, and ZrO₂ on the structural and redox properties of CeO₂ were systematically investigated by various techniques namely, X-ray diffraction (XRD), Raman spectroscopy (RS), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HREM), BET surface area, and thermogravimetry methods. The effect of supporting oxides on the crystal modification of ceria was also mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahigh dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO₂–SiO₂ sample primarily consists of nanocrystalline CeO₂ on the amorphous SiO₂ surface. Both crystalline CeO₂ and TiO₂-anatase phases were noted in the case of CeO₂–TiO₂ sample. Formation of cubic Ce_0.75Zr_0.25O₂ and Ce_0.6Zr_0.4O₂ (at 1073 K) were observed in the case of CeO₂–ZrO₂ sample. The cell ‘a’ parameter estimations revealed an expansion of the ceria lattice in the case of CeO₂–TiO₂, while a contraction is noted in the case of CeO₂–ZrO₂. The DRS studies suggest that the supporting oxides significantly influence the band gap energy of CeO₂. Raman measurements disclose the presence of oxygen vacancies, lattice defects, and displacement of oxide ions from their normal lattice positions in the case of CeO₂–TiO₂ and CeO₂–ZrO₂ samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation states, Si(IV), Ti(IV), and Zr(IV) at the surface of the materials. Cerium is present in both Ce⁴⁺ and Ce³⁺ oxidation states. The HREM results reveal well-dispersed CeO₂ nanocrystals over the amorphous SiO₂ matrix in the case of CeO₂–SiO₂, isolated CeO₂ and TiO₂ (A) nanocrystals and some overlapping regions in the case of CeO₂–TiO₂, and nanosized CeO₂ and Ce–Zr oxides in the case of CeO₂–ZrO₂ sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO₂ is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of mixed oxides is more than that of pure CeO₂ and the CeO₂–ZrO₂ exhibits highest OSC.     

天然气中温SOFC阳极材料铒掺杂的氧化铈的制备与性能研究

采用溶胶-凝胶法合成了新型中温固体氧化物燃料电池(IT-SOFC)阳极材料Ce_1-xEr_xO_y(x=0.00,0.10,0.15,0.20,0.25,0.30)(EDC),并采用共压-共烧结法制备了以NiO-EDC复合阳极为支撑、以Ce_0.8Gd_0.2O_2-δ(GDC)为电解质、以La_0.8Sr_0.2Co_0.8Fe_0.2O_3-δ(LSCF)-GDC为复合阴极的单电池。利用XRD和SEM等方法对阳极材料EDC进行了晶相结构、微观形貌和化学相容性等分析。在400~700 ℃范围内,以加湿天然气(3% H₂O)为燃料气,氧气为氧化气测试了电池的电化学性能。结果表明：EDC阳极材料具有良好的孔道结构;11种不同阳极组成的单电池中50%(质量分数)NiO-50%(质量分数)Ce_0.85Er_0.15O_y(E15C85)阳极支撑的单电池具有最佳的电化学性能,在650 ℃时其最大电流密度为117.84 mA·cm^-2和最大比功率为24.37 mW·cm^-2。     

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).