Synthesis of MgAl2O4 Spinel Nanometer Powder via Biology Polysaccharide Assisted Sol-Gel Process

A novel and cost-effective sol-gel process for preparation of MgAl₂O₄ spinel nanometer powders has been developed in this study. A solution of magnesium and aluminum nitrates in stoichiometric proportion was successfully embraced in the biology polysaccharide gel network, formed by the synergistic interaction between xanthan gum (XG) and locust bean gum (LBG) utilizing their broad-spectrum stability of salt tolerance and character of transformation from sol to gel on the condition of proper temperature and relative proportion of polymeric components. Dry gel could be obtained by vacuum dehydration of aqueous gel at low temperatures. Monolithic MgAl₂O₄ spinel nanometer powders were produced by calcining the dry gel above 800°C, with average crystallite size of 20 nanometers.     

尖晶石锂锰氧化物锂离子嵌脱过程的交流阻抗谱研究

用粉末微电极研究了尖晶石锂锰氧化物在不同嵌锂状态下嵌脱锂过程的交流阻 抗图谱，提出了新的等效电路模型。描述锂离子在固体中扩散的Warburg阻抗与累 积或消耗的嵌入电容在Lix MnO4中的x≤0．5时串联，0．5＜x≤1时并联。用提出 的等效电路模型分阶段拟合了实验所得的交流阻抗谱，拟合值与实验值相当吻合， 由拟合结果得到不同电位下锂离子在表面膜中的迁移电阻和电容，界面电荷传递电 阻，双层电容，锂离子在固体中扩散系数和累积或消耗的嵌入电容。     

SnO2-Nb2O5/MgAl2O4/α-Al2O3催化环氧乙烷水合制乙二醇

采用水热稳定的MgAl2O4尖晶石对-αAl2O3载体表面进行修饰,采用具有较强亲水性能的SnO2对活性组分Nb2O5进行修饰,制备了SnO2-Nb2O5/MgAl2O4/-αAl2O3催化剂,并用于环氧乙烷水合制乙二醇反应.采用X射线衍射、红外光谱和程序升温脱附研究了Sn/Nb摩尔比对催化剂酸性、环氧乙烷在催化剂表面的吸附状态和吸附强度以及催化剂性能的影响.结果表明,Sn/Nb摩尔比明显影响催化剂的组成和结构;催化剂的结构不同,环氧乙烷在催化剂表面的吸附强度存在明显差别,催化剂的催化性能明显不同.     

Thermal study of CoxZn7-xSb2O12 spinel obtained by pechini method using different alcohols

With the aim of obtaining materials with applications in pigments, Co_xZn_7-xSb₂O₁₂ spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for the synthesis of a zinc antimoniate spinel, Co_xZn_7-xSb₂O₁₂ (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two alcohols - both presented the spinel phase (Co, Zn)_2.33Sb₀.₆₇O₄. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb₂O₆. This revised version was published online in August 2006 with corrections to the Cover Date.     

负载型无铬超细铁基变换催化剂的制备和催化性能

 以镁铝尖晶石为载体，以过渡金属氧化物为助剂，用吸附γ－Fe2O3胶体法制备了负载型无铬铁基变换催化剂．TEM，XRD，BET和活性测试结果表明，采用胶体负载法制备的变换催化剂，其活性组分Fe3O4以分立的超细微颗粒分布在镁铝尖晶石载体表面上，颗粒之间存在一定的间隔．过渡金属氧化物NiO或V2O5能够进入Fe3O4晶格形成固溶体，起到代替氧化铬的作用，提高催化活性．负载型催化剂FeNi／MgAl2O4（m（NiO）／m（Fe2O3）＝3％）在汽／气比为1和空速为2000h－1的反应条件下，CO转化率在400和350℃时分别为95％和80％；在高空速和低汽／气比条件下也具有很好的催化性能．稳定性实验结果表明，该催化剂 具有良好的热稳定性和一定的抗硫能力．与非负载型催化剂相比，负载型催化剂具有更为优越的催化性能．     

LiMg0.5Mn1.5O4的合成及对Li+的离子交换选择性

锂及其化合物在航空航天、化工、医药、空调、高能电池和热核反应等方面都有广泛应用，对锂及其化合物的需求与日俱增。我国液体锂资源非常丰富，开发利用其中的锂资源具有重要意义。从盐湖水、地下卤水、盐田母液、油气田水等咸水资源中提取锂的方法有碳酸盐沉淀法、离子交换法、萃取法等。离子     

A study of the formation of silica-supported mixed magnesium-manganese spinel oxides from multicomponent gels

The effects of thermal treatment on composite materials prepared by the gelation of sols comprising large concentrations of metal oxide precursor salts have been investigated, in order to determine the compositional and thermal requirements for forming spinel magnesium manganates in such systems. The preparative technique has been found to give rise to derived gel materials in which the metal oxide phase, in the form of regular spherical particles, is dispersed throughout a continuous silica matrix. Silica-supported mixed magnesium and manganese spinel oxide phases were obtained for systems comprising at least 30 wt% metal nitrate after heating to temperatures between 700 and 850°C, but not without concomitant formation of Mn₂O₃ and modification of the silica network by magnesium.     

Mg改性对Co/γ-Al2O3-TiO2催化燃烧丙烷性能影响

采用分步浸渍法制备了系列Mg改性的Co/γ-Al_2O_3-TiO_2催化剂,通过X射线衍射(XRD)、紫外可见漫反射光谱(DR-UV-vis)、N_2吸附-脱附(BET)、X射线光电子能谱(XPS)和H_2程序升温还原(H_2-TPR)等技术对催化剂进行表征,并考察了其对丙烷燃烧的催化性能。结果表明,Co在原始γ-Al_2O_3-TiO_2载体和Mg改性MgO/γ-Al_2O_3-TiO_2载体上均以Co_3O_4的形式存在;Mg掺入后与Al_2O_3作用形成MgAl_2O_4尖晶石,改善了载体的织构性质,提升了Co_3O_4在催化剂载体表面的暴露数量和分散程度。此外,MgAl_2O_4与Co_3O_4相互作用提升了Co_3O_4颗粒表面Co~(3+)/Co~(2+)和O_(ads)/O_(latt)的比例,并削弱了Co-O键键能,从而提升了其对丙烷的催化燃烧活性。当Mg负载量为15%(质量分数)时,在Co/MgO(15%)/γ-Al_2O_3-TiO_2催化剂上进行丙烷燃烧,丙烷90%转化率的温度比无Mg掺杂的Co/γ-Al_2O_3-TiO_2催化剂的降低了45℃,并且连续反应40 h其活性保持稳定。     

Defect clusters and precipitation/oxidation of MgO-Co1−xO solid solution

MgO and Co_1−xO powders in 9:1 and 1:9 molar ratio (denoted as M₉C₁ and M₁C₉, respectively) were sintered and homogenized at 1600°C followed by annealing at 850°C and 800°C, respectively to form defect clusters and precipitates. Analytical electron microscopic observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M₉C₁ sample, however with spinel paracrystal precipitated from the M₁C₉ sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e., four octahedral vacant sites surrounding one Co³⁺-filled tetrahedral interstitial site. The spacing of such defect clusters is 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co_3−δO₄, indicating a higher defect cluster concentration than undoped Co_3−δO₄. The {111} faulting of Mg-doped Co_3−δO₄/Co_1−xO in the annealed M₁C₉ sample implies the possible presence of zinc blend-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane.     

New data on the thermal analysis of diphasic mullite gel

A diphasic mullite gel has been synthesized by using Ludox and Al(NO₃)₃-9H₂O in ammoniacal solution. Both DTA and DDTA studies have been performed with a sensitive differential thermal analyzer system. Besides usual exotherm due to mullite formation, a pronounced exotherm between 800–1300°C has been noted. Considering previous XRD data, it is explained as due to formation of Si-Al spinel phase, which is subsequently transformed exothermally at 1320°C to mullite.