Preparation of Compound Ultrafine CeO2 by Wet-Solid-Phase Mechanochemical Modification

To satisfy practical requirements from industrial applications, an alternate route for synthesis compound ultrafine CeO2 powders by wet-solid-phase mechanochemical modification using industrial grade hydrated cerium carbonate as raw material was proposed.The effect of modifier reaction percentage, reaction time, calcining temperature and modifier amount on particle size, density, suspensibility, and hardness of compound CeO2 powder was investigated.The phase evolutions of preparation process were characterized by XRD.SEM micrograph of the final product shows that compound CeO2 powders obtained are well-dispersed, spherically-shaped, uniformly-sized and submicron-sized particles.The method is readily available in raw material, low in cost, simple in process, and has great potential for industrialization.The compound CeO2 powders of different physical properties can be synthesized by controlling the above-mentioned influence factors in preparation process.     

Effects of ZrO2 Content on Structure and Performance of Cu/CeO2-ZrO2 Catalysts for Water-Gas Shift Reaction

Water-gas shift(WGS)is a critical step in fuelprocessors for preli minary COclean-up and additionalhydrogen generation prior to the CO clean-up stage,which opened up new potential applications for WGScatalysts.Recently several formulations of noble-met-al…     

掺杂氧化铈钡钨阴极的结构和发射性能的研究

采用CeO2与钨粉机械混合,制备了满足大功率微波器件要求的高性能掺杂CeO2钡钨阴极,利用扫描电镜、压汞仪等测试手段分析了阴极的微观结构.用水冷阳极二极管检测了阴极的发射性能.研究表明,掺杂CeO2钡钨阴极孔径分布较窄,为0.4～3.6um,平均孔径为2um.在阳极正常工作温度1050。C下,掺杂CeO2钡钨阴极的直流发射电流密度和脉冲发射电流密度分别为6.33,17.48A·cm-2,明显优于传统钡钨阴极,满足大功率微波器件要求.     

Effect of CeO2 on Electrical Properties of （Nb, Mn）-Doped TiO2 Varistor Ceramics

Varistor ceramics are a class of semiconductor de-vices with high non-linearity in their current-voltage(V-I)characteristics.Among these,ZnO varistor isthe most typical material and is commercially used asvoltage suppressor to protect electronic componentsand power systems[1~4].However,ZnOis a kind ofpure resistance component and has low permittivity,high dielectric dissipation,lowresponse speed,andpoor ability to absorb high frequency noise and pulsesurge.Soits applicationis restrictedin el…     

Controllable preparation of CeO2 nanostructure materials and their catalytic activity

Well-crystalline CeO2 nanostructures with the morphology of nanorods and nanocubes were synthesized by a template-free hydro-thermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) nitrogen adsorp-tion-desorption measurements were employed to characterize the synthesized materials. The reducibility and catalytic activity of nanostruc-tured CeO2 were examined by hydrogen temperature-programmed reduction (H2-TPR) and CO oxidation. The results showed that CeO2 nanorods could be converted into CeO2 nanocubes with the increasing of the reaction time and the hydrothermal temperature, CeO2 nanorods became longer gradually with the increasing of the concentrations of NaOH. H2-TPR characterization demonstrated that the intense low-temperature reduction peak in the CeO2 nanorods indicated the amount of hydrogen consumed is larger than CeO2 nanocubes. Meantime the CeO2 nanorods enhanced catalytic activity for CO oxidation, the total conversion temperature was 340 oC. The reasons were that CeO2 nanorods have much smaller crystalline sizes and higher surface areas than CeO2 nanocubes.     

Preparation and Characterization of Graphite Powder Covered with CeO2

In order to improve the wetting properties of graphite with Al melt and reduce the oxidation of the graphite, by which the segregation of components during the liquid-stir-casting process could be prevented. In this paper, a uniform thin nano-film of CeO2, about 20 nm thick, was successfully prepared onto graphite powder surface by heterogeneous nucleation process. The results show that an obvious chemical reaction did exit between CeO2 film and graphite with the formation of Ce-O-C bond, leading to a shift of the binding energy of C and Ce. The cover with CeO2 film illustrates a distinct change of surface state of graphite with a decrease of angle of contact.     

Sol-Gel Assembly and Luminescence of SiO2／PEMA Hybrid Material Incorporated with Terbium Complex

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Synthesis and Luminescent Properties of Superfine Sr2CeO4 Phosphors by Sol-Gel Auto- Combustion Method

Citric acid complexing sol-gel auto-combustion method was explored to synthesize superfine Sr2CeO4 phosphors using the inorganic salts Sr（NO3）2 and Ce（NO3）3 as raw materials together with citric acid （CA） as a chelating agent. TGDTA, XRD, SEM and photoluminescence spectra were used to investigate the formation process, microstructure and luminescent properties of the synthesized Sr2CeO4. The results show that the crystallization of Sr2CeO4 begins at about 800 ℃ and completes around 900 ℃ with an orthorhombic structure. When the calcination temperature is above 1000 ℃, Sr2CeO4 partly decomposes into SrCeO3. SEM studies show that the particles of Sr2CeO4 obtained at 900 ℃ are sphericallike shape and superfine with diameter below 100 nm. The excitation spectrum of the superfine Sr2CeO4 phosphors displays a broad band with two peaks around 290 and 350 nm respectively. The former peak is stronger than the latter one. This broad band is due to the charge transfer （CT） band of the Ce^4＋ ion. Excited by a radiation of 290 nm, the superfine phosphors emit a strong blue-white fluorescence, and the emission spectrum shows a broad band with a peak around 470 nm, which can be assigned to the f→t1g transition of Ce^4＋ . It is found that the emission intensity is affected by the calcination temperature.     

Improved sulfur-resistant ability on CO oxidation of Pd/Ce0.75Zr0.25O2 over Pd/CeO2-TiO2 and Pd/CeO2

The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction(XRD), CO chemisorption, X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR) and X-ray fluorescence(XRF). After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/Ce O2-Ti O2 and Pd/Ce O2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/Ce O2-Ti O2 exhibited less sulfur accumulation compared to Pd/Ce O2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.     

Preparation, Characterization of CuO／CeO2 and Cu／CeO2 Catalysts and Their Applications in Low-Temperature CO Oxidation

CeO2 was synthesized via sol-gel process and used as supporter to prepare CuO/CeO2, Cu/CeO2 catalysts by impregnation method. The catalytic properties and characterization of CeO2, CuO/CeO2 and Cu/CeO2 catalysts were examined by means of a microreactor-GC system, HRTEM, XRD, TPR and XPS techniques. The results show that CuO has not catalytic activity and the activity of CeO2 is quite low for CO oxidation. However, the catalytic activity of CuO/CeO2 and Cu/CeO2 catalysts increases significantly. Furthermore, the activity of CuO/CeO2 is higher than that of Cu/CeO2 catalysts.     

Study on Mg PSZ Ceramics Doped with Y_2O_3 and CeO_2

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Effect of CeO2 on Microstructure and Bond Strength of Fe-Ni-Cr Alloy

The more extreme conditions in which metallicmaterials are required to work lead to the developmentof different surface modification materials, such asnickel based alloy, Fe based alloy and Co based al loy, etc. In general, these …     

Distribution of Cerium Ion in Cordierite Ceramics and Its Effect on Structure of Cordierite Crystal

Cerium addition plays an important role in sintering, transformation and phasicochemical properties of cordierite ceramics. The present work aims at studying the distribution of Ce4+ in cordierite ceramics and its effect on the structure of cordierite crystal by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electronic microscope (SEM) so as to clarify the behavior of Ce4+. Results show that Ce4+ can exist in two forms of CeO2 particles and solid solution in Ce4+ -modified cordierite ceramics by the sol-gel method. The CeO2 particles separately distribute in the cordierite matrix. Ce4+ dissolves little into cordierite crystal, resulting in a decrease of lattice constants ofthe crystal. This kind of distribution behavior of Ce4+ makes us to easily tailor the properties of the cordieritc ceramics.     

稀土三元配合物的合成、结构表征及荧光性能研究

合成了铈-草酸-丙烯酸三元固体配合物。利用元素分析、红外光谱（FT-IR）、紫外．可见光谱（UV-Vis）、热重分析（TGA）和荧光光谱等手段研究了配合物的结构和性质。结果表明配合物的组成为[Ce（OOC-COO）（CH2=CH-COO）]·3H2O，荧光光谱表明，配合物中的有机配体能够有效地把吸收的能量传递给中心Ce^3＋离子，强烈敏化Ce^3＋发光，且发射谱线很窄，主发射峰为Ce^3＋的5d→^2F7/2跃迁，这对寻找新型稀土配合物发光材料和制备有机电致发光器件具有一定的价值。     

Fluorescent Comparison of Sr2CeO4 Prepared from Carbonate and Oxalate Precursor

A blue-emitting phosphor powder, SrECeO4, was synthesized after heat-treatment to carbonate and oxalate precursors, which were obtained by co-precipitation reactions with respective ammonium compounds as precipitants. The phase formation and chemical purity of SrECeO4 powders were studied on XRD, TGA and XPS techniques. Their fluorescent performances were investigated and compared. The photoluminescence emission spectra for the phosphor prepared from respective precursors are similar, having a broad band with the peak at about 470nm. However, their fluorescent intensities are different after heat-treatment at same conditions. The optimum condition to achieve superior SrECeO4 phosphor is confirmed.     

Luminescent Thin Film of Doped Terbium Complex Obtained by Sol-Gel Method

The transparent luminescent thin films of doped terbium complex were obtained by sol-gel method. The result indicates that rare earth carboxylates with poor solubility can be homogeneously doped into sol matrix in situ. The fluorescence spectra show that the thin film material emits the characteristic narrow band emission of Tb3 under the UV excitation.     

Catalytic Reduction of SO2 on CeO2-La2O3 Rare Earth Mixed Compounds

Adding rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. By means of dipping CeO2, La2O3 and their mixture, whose carriers were all γ-Al2O3, were used as the catalyst for the reduction of SO2 by CO. The activation process of this catalyst and the impact of temperature and reactant concentration on the activation process were investigated. Using X-ray diffraction, the structure characteristics of catalyst before and after reaction were analyzed to reveal the change of phase structure. The result shows that the rare earth oxide mixtures composing of CeO2 and La2O3, as the catalyst for the reduction of SO2 by CO, diminish activation temperature 50～100℃ less and have higher activity than a single oxide CeO2 or La2O3. The reason possibl is that La2O3 goes into in the lattice of CeO2 to form solid phase complex CeO2-La2O3 and increases the capability of CeO2-La2O3/γ-Al2O3 catalyst to store oxygen, which supplies the redox of CeO2 reaction with a better condition. At the same time, elemental sulfur formed in the redox reaction impels La203 to be transformed to activation phase La2O2S in a lower temperature, which can be explained with the synergism between redox reaction and COS intermediate mechanism reaction.     

Preparation and Characterization of CeO2-ZrO2 Solid Solution Ultrafine Particles Using Reversed Microemulsion

The development of the TWCs (three-way cata-lysts) was dictated bythe need to si multaneously con-vert the three main pollutants inthe exhaust gases ,i .e .,hydrocarbons (HCs) ,COand NOxpresent in theautomotive exhaust to H2O, CO2and N2[1]. Highestconvers…     

Effects of CeO2 on structure and properties of Ni-Mn-K/bauxite catalysts for water-gas shift reaction

Multiple-metal catalysts (Ni-Mn-Ce-K/bauxite) for Water-Gas Shift (WGS) reaction were prepared by impregnation, and the catalytic structure and properties were investigated by N2 physical, XRD, H2-TPR, and CO-TPD. The results indicated that the addition of 7.5% CeO2 improved the activity of the WGS reaction obviously, and also increased the specific surface area and pore volume of the catalysts. The addition of CeO2 decreases the reduction temperature, enhanced the adsorption and activation of H2O, and improved the adsorption content of CO. Besides, active sites were not changed and the number of active sites on catalysts did not increase obviously.     

LaCo_(0.9)Cu_(0.1)O_3的葡萄糖溶胶—凝胶法合成及二甲苯催化氧化性能研究

本文以葡萄糖溶胶—凝胶法合成了稀土钙钛矿型复合氧化物 L a Co0 .9Cu0 .1 O3,并对其进行了 XRD、BET、TPR表征和二甲苯催化氧化性能测试 ,同时与柠檬酸溶胶—凝胶法作了比较。结果表明 ,葡萄糖作为络合剂成胶和干胶容易 ,粒径较小 ,具有进一步降低 L a Co0 .9Cu0 .1 O3形成温度的作用 ,以葡萄糖作为络合剂在 70 0℃所制备的催化剂 L a Co0 .9Cu0 .1 O3低温活性较好