CO_2 Reforming of CH_4 over Ni/CeO_2-ZrO_2-Al_2O_3 Prepared by Hydrothermal Synthesis Method

The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity.     

氧化铈和氧化镧在汽车尾气净化催化剂中的应用

阐述了稀土元素应用于汽车尾气净化催化剂的意义，讨论了氧化铈和氧化镧的催化作用机制及其影响因素，并对其发展前景进行了展望。汽车尾气净化普遍使用铂铑基贵金属三元催化剂。为了解决Pt，Rh的供需矛盾，应用稀土(氧化铈和氧化镧)作为添加剂，降低Pt，Rh用量、扩大Pd基催化剂应用是研究开发的热点。据研究，氧化铈和氧化镧催化作用机制主要是提高活性涂层的催化活性，自动调节空气燃料比和助催化作用，并能提高载体的热稳定性和机械强度等性能。影响氧化铈和氧化镧催化性能的因素主要为共助作用、添加方法、ZrO2，CuO，AgO等其他氧化物的协同作用。     

氯化钠在球形纳米氧化铈形成过程中的作用

以水合碳酸铈为原料, 以氯化钠作为助磨剂和阻聚剂, 采用机械活化法制备了球形纳米氧化铈, 用XRD法研究了水合碳酸铈与氯化钠质量比、球磨时间、煅烧温度对CeO2粉体晶粒度的影响, 用TEM对最终产物粒子进行形貌观察. 结果表明: 在碳酸铈的球磨过程及其随后的煅烧过程中, 氯化钠的存在起到了很好的助磨和阻聚作用, 所得CeO2为类球形粒子, 分散性较好, 晶粒度约为30～50 nm.     

Y2O3 and MgO co-doped ceria based electrolytes

Electrolytes of Ce_1-x-y Y _x Mg _y O_2-0.5x-y were prepared with citrate method and were characterized by inductively coupled plasma-atomic emission spectrometry, energy dispersive spectrometry, powder X-ray diffraction, and impedance spectroscopy. The effect of composition on the structure, conductivity, and stability of the electrolytes were investigated. When 0≤x≤ about 0.2 and 0≤y≤ about 0.05, the electrolytes were all single phase materials of ceria-based solid solution. However, when y> about 0.05, the electrolytes became two-phase materials, Y³⁺ and Mg²⁺ co-doped ceria-based solid solution and free MgO. The sample with nominal composition of Ce_0.815Y_0.065Mg_0.12O_2-d showed ionic conductivity at 973 K close to or even a little higher than that of similarly prepared Ce_0.9Gd_0.1O_1.95, but had lower cost of raw materials and a little better stability in reducing atmosphere. The existing of free MgO improved the stability of the electrolytes in reducing atmosphere, but too much free MgO reduced the conductivity.     

Cellulose-precursor synthesis of nanocrystalline Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2−δ</Subscript> for SOFC anodes

Developments of intermediate-temperature solid oxide fuel cells (IT SOFCs) require novel anode materials with a high electrochemical activity at 800–1070 K. The polarization of cermet anodes, made of nickel, ceria and yttria-stabilized zirconia (YSZ) and applied onto a YSZ solid electrolyte, can be significantly reduced by catalytically active ceria additions, the relative role of which increases with decreasing temperature. Further improvement is observed when using Ce_0.8Gd_0.2O_2– (CGO) having a high oxygen ionic conductivity instead of undoped ceria, owing to enlargement of the electrochemical reaction zone. Nanocrystalline CGO powders with grain sizes of 8–35 nm were thus synthesized via the cellulose-precursor technique and introduced into Ni–CGO–YSZ cermets, and tested in contact with a (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3– (LSGM) electrolyte at 873–1073 K. The results showed that the anode performance can be enhanced by additional surface activation, in particular by impregnation with a Ce-containing solution, and also by incorporation of YSZ, which probably acts as a cermet-stabilizing component. The overpotential of the surface-modified Ni–CGO (25 wt%–75 wt%) anode in a 10% H₂/90% N₂ atmosphere was approximately 110 mV at 1073 K with a current density of 200 mA/cm².Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Effect of Addition of Base on Ceria and Reactivity of CuO/CeO2 Catalysts for Low-Temperature CO Oxidation

In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.     

水合醋酸铈直接热分解制备超细氧化铈及其抛光性能

Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and the removal rate of optical glasses polishing by ceria was determined. The results show that with the increase of pyrolysis temperature, the loose deposit density and crystallinity increases and the specific surface area decreases, however, the particle size decreases firstly and then increases, the minimum medium particle size D₅₀ is 0.47 μm at pyrolysis temperature of 1 000 ℃. The SEM images of ceria prepared by the decomposition at 800 ℃ or at 1 100 ℃ show porous powders or quasi-sphere small particles with loosely agglomeration, respectively. It was found that the removal rate varied with pyrolysis temperature in preparation of ceria and the property of glass polished. The removal rate for three kinds of glasses was in the order of ZF7> F1> K9, and the maximum value appeared at around 1 000 ℃ for ZF7 and F1, and at around 1 100 ℃ for K9.     

用脉冲D2反应研究CeO2在Co-CeO2/SiO2费托合成催化剂中的促进作用机理

 采用脉冲D2反应研究了CeO2在Co-CeO2/SiO2费托合成催化剂中的作用机理. 通过比较在Co-CeO2/SiO2和Co/SiO2催化剂上的脉冲D2反应实验结果发现, CeO2可以提高载体表面 Si-OH 的H-D同位素交换活性和 Si-OH 中H参与CO加氢反应的活性; CeO2不仅增加了催化剂表面活性碳物种的总量,而且活性碳物种以链增长单体-CH2-为主,因而有利于增加费托合成反应速率和链增长几率; CeO2的加入明显提高了催化剂表面碳原子的加氢反应速率,从而减少了碳沉积.     

Transport in ceria electrolytes modified with sintering aids: effects on oxygen reduction kinetics

Small (2 mol%) cobalt oxide additions to ceria-gadolinia (CGO) materials considerably improve sinterability, making it possible to obtain ceramics with 95–99% density and sub-micrometre grain sizes at 1,170–1,370 K. The addition of Co causes a significant shift of the electrolytic domain to lower pO₂. This modification to the minor electronic conductivity of the electrolyte material has influence on the cathodic oxygen reduction reaction. The impedance technique is shown to provide information not only about polarisation resistance, but also about the active electrode area from analysis of the current constriction resistance. It is demonstrated that this current constriction resistance can be related to the minor electronic contributions to total conductivity in these materials. A simple imbedded grid approach gives control of the contact area allowing the properties of the electrolyte materials to be studied. A much lower polarisation resistance for the Co-containing CGO electrolyte is observed, which can be clearly attributed to an increased three-phase reaction area in the Co-containing material, as a consequence of elevated p-type conductivity.     

介孔CeO2负载的Co3O4催化剂催化富氢气体中的CO优先氧化反应

采用溶胶-凝胶法制备出介孔氧化铈(meso-CeO2)及其负载的氧化钴(Co3O4/meso-CeO2)催化剂,并将其应用于富氢气体中CO的优先氧化反应.通过N2物理吸附及X射线衍射表征考察了meso-CeO2和Co3O4/meso-CeO2的结构性质.活性评价结果表明,在高空速下,Co3O4/meso-CeO2催化剂上的CO优先氧化性能很好,但水和CO2对CO的氧化有一定的负作用.Co3O4/meso-CeO2催化剂的CO完全氧化温度窗口远大于沉淀法制备CeO2负载的氧化钴催化剂.