BaY_2F_8∶Ce,Eu中Ce~(3+)→Eu~(2+)的能量传递和Ce~(3+)→Eu~(3+)的电子转移

采用高温固相反应法制备了 Ba Y2 F8∶ Ce3 + ,Ba Y2 F8∶ Eu2 + 和 Ba Y2 F8∶ Ce,Eu,测定了它们的激发、发射和漫反射光谱 .首次发现并研究了在 Ba Y2 F8共掺 Ce F3 和 Eu F3 体系中存在 Ce3 + → Eu2 + 的能量传递和Ce3 +→ Eu3 +的电子转移两种过程及其竞争 .根据光谱数据 ,讨论了 Ce4 +的可能取代格位

KMgF_3∶Eu和KMgF_3∶Eu-Ce单晶体中Eu~(2+)与Ce~(3+)的格位取代和能量传递

在 77K测定了两个晶体的高分辨发射光谱 ,讨论了单掺杂 Eu2 + 和双掺杂 Eu2 + 及 Ce3+ 的 KMg F3中的格位取代问题 .在 KMg F3∶ Eu-Ce中观察到了 Eu2 + 的 6P5/ 2 能级到 Ce3+ 的 4 f 5 d能级间的间接能量传递 ,讨论了能量传递机理

KMgF_3∶Eu,X(X=Ce,Cr,Gd,Cu)体系中Eu~(2+)振动光谱和共掺离子的格位取代

测定了一系列单掺杂 Eu2 +和双掺杂 Eu,X( X=Ce,Cr,Gd,Cu)的 KMg F3晶体在 30 0 K和 77K的高分辨发射光谱以及伴随的振动光谱 ,据此研究了 Eu2 + 在这些体系中的振动跃迁特征 ,并指认了每一振动峰所对应的正则振动模式 .首次发现了在共掺杂体系中 Eu2 +振动频率与其它掺杂离子格位取代间的相关性

取代茚基的茂金属Ti、Zr化合物的合成及其催化乙烯聚合活性

合成了 4种取代茚基均配及混配型的茂金属化合物 ( 1 -C6 H5 CH2 Ind) 2 MCl2 ( M=Ti( 1 ) ,Zr( 2 ) )、( 1 -C6 H5 CH2 Ind) Cp MCl2 ( M=Ti( 3) ,Zr( 4) ) .通过 IR、1 H NMR、EI-MS和元素分析对化合物进行了表征 .用所合成的茂金属化合物与 MAO所组成的催化体系 ,研究了乙烯的聚合 .发现金属为 Ti的催化剂没有聚合活性或活性极低 .金属为 Zr的催化剂有一定的催化活性 ,不同的催化剂得到的聚合物性质有一定的差异 .

茂金属催化剂Cp_2~tMCl_2(Cp~t=~tBuC_5H_4,M=Ti、Zr、Hf)聚合丁烯-1的研究

探讨了茂金属催化剂 Cpt2 MCl2 ( Cpt=t Bu C5 H4,M=Ti,Zr,Hf)的合成以及用于聚合丁烯 -1的研究 ,研究了几种不同的茂金属催化剂和不同聚合条件下的催化行为 ,并通过 IR、1 H NMR、EI-MS、DSC、粘度法测分子量和正庚烷抽提等测试手段对催化剂和聚合物进行了表征 .结果表明 ,叔丁基取代的茂金属催化剂催化丁烯 -1聚合具有较高的催化活性 ,叔丁基的引入提高了聚合物的等规度和分子量

掺Eu~(3+)、Tb~(3+)或Ce~(3+)的InBO_3的合成与光谱

采用固相反应法合成了InBO_3:Re(Re=Eu,Tb,Ce),研究了InBO_3基质中稀土离子的光谱特性,观察到电荷迁移带位于255 nm附近,Eu~(3+)离子在InBO_3 中产生极强的~5D_0→~7F_1 的跃迁表明Eu~(3+)离子在该基质中占据对称性格位。Tb~(3+)的4f-5d 允许跃迁位于240 nm附近,而4f-5d 禁戒跃迁位于267 nm附近,Tb~(3+)离子呈现出极强的~5D_4→~7F_5 发射。Ce~(3+)离子在InBO_3 中不发光。

Co-Cu-Al mixed oxides derived from hydrotalcite-like compound for NO reduction by CO

Various hydrotalcite based catalysts were prepared for catalytic removal of NO (NO reduction by CO). The general formula of hydrotalcite compounds (HTLc) was Co-Cu-Al-HTLc. Precalcination of these materials at 450 degrees C for NO reduction by CO, was necessary for catalytic activity. All catalysts except Co-A1 and Cu-Al have very good activity at lower temperature for NO reduction by CO. All samples were characterized by XRD and BET. The tentative reaction mechanism was also proposed.

The electrical and magnetic properties of lanthanide alkaline-earth transition-metal oxides

Five Ln(2)SrMCuO(6.5) oxides (M = Co, Ln = Y and Ho; M = Fe, Ln = Y, Ho, and Dy) were synthesized, and their crystal structures, IR spectra, and physical properties were studied. They have almost the same structure and crystallize in orthorhombic systems. Below room temperature, Y2SrFeCuO6.5, a known layered oxide, shows antiferromagnetic behavior, but the four new oxides are paramagnetic. Y2SrFeCuO6.5 fits the Curie-Weiss law in the temperature range 300-100 K, but Y2SrCoCuO6.5 shows complex magnetic behavior because of the disproportion of some Co+3 to Co+2 and Co+4 The five oxides are all p-type semiconductors in the measured temperature range and have large electrical resistivities at room temperature.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.

Preparation, charactreization, and catalytic properties of Co-M-Al (M = transition metal) mixed oxides derived from hydrotalcite-like compound

Hydrotalcite-like compounds (HTLcs) CoMAlCO3, where M stands for Cr, Mn, Ni, Cu, or Fe, were synthesized by coprecipitation. After calcination at 450 degrees C, they became mixed oxides with spinel-like structure. The mixed oxides were characterized by XRD, BET, chemical analysis and the adsorption of NO. The catalytic decomposition of NO and its reduction by CO were studied over these mixed oxides. The study showed that the catalytic activity for removal of NO, was very high. The reaction mechanism is proposed and the effects of d-electrons of the transition metals on catalytic activity are elucidated.

Valence stability and change of Eu(II)in oxides

Valence stability and change of Eu(II) in oxides have been studied by luminescence spect a. The results show that the valence stability and change of Eu(II)in oxides is closely related to the radius and electric charge of positive ions substituted by Eu(II) and crystal structure of the host such as Al2O3 which can form alpha-Al2O3 single phase and alpha-Al2O3 and gamma-Al2O3 mixed phases under different reaction temperatures. A, fairly good explanation is made by the proposed relation between energy coefficient and crystal structure for the first time to the observed experiment results. if the energy coefficients of substitution ions is more than that of Eu(II), the lattice substitution of Eu(II)for these ions is not occured generally and valence stare of Eu(II)is not stable and be easily changed into Eu(III). The lattice of gamma-Al2O3 can stablize the valence state of Eu(II)within certain coped concentration and in alpha-Al2O3 crystal lattice Eu(II)can be easily changed into Eu(III).

Catalytic reduction of NO by CO with hydrotalcite derived mixed oxides

Catalysts with spinel structure derived from Hydrotalcite-like Compounds (HTLcs) containing cobalt have been investigated in NO catalytic reduction by Co. It was found that catalysts with spinel structures derived from HTLcs had obviously higher activity than that prepared from general methods. A two-step reaction was observed during the reaction curse: NO was first reduced to N2O by Co, and with the increase of temperature, the N2O was reduced to N-2. The reactivity of the catalysts studied increased with the amount of cobalt-content in the catalyst, and decreased with the calcination temperature. The crystal defect would play an important role in the reaction.

Catalytic combustion of CH4 and CO on La1-xMxMnO3 perovskites

The activities of perovskites depend on compositions and preparation methods. Various perovskites, La1-xMxMnO3 (M=Ag, Sr, Ce, La), have been prepared by two different methods (co-precipitation and spray decomposition). The new preparation method, spray decomposition, produced perovskites of a high surface area of over 10 m(2)/g. The catalytic activities for CH4 and CO oxidation have been studied on a series of catalysts, La1-xMxMnO3. The perovskite-type oxide, La0.7Ag0.3MnO3, shows the highest catalytic activity: the complete conversion of CO and CH4 at 370 and 825 K, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.

KZnF_3中Ce~(3+)→Eu~(2+)的能量传递

研究了KZnF3中Ce3+和Eu2+的光谱特性，在共掺Ce3+和Eu2+的体系中，观察到了Ce3+对Eu2+的能量传递过程．计算了能量传递的鼻子效率，探讨了能量传递机理．研究发现，Ce3+的存在有利于Eu2+的f-f跃迁线状发射.

Crystal growth and TG-DTA properties of K(2)Ln(NO3)(5).2H(2)O (Ln = La, Ce, Pr, Nd, Sm)

Single crystals of KLnN(Ln=La, Ce, Pr, Nd, Sm) can be grown in water solution with pH approximate to 1 similar to 2 at about 40 degrees C. Crystals of KLnN (Ln=La, Ce, Pr, Nd) are orthorhombic with space group Fdd2. KPrN crystal was grwon and its crystal structure was determined for the first time. The KPrN crystal parameters obtained by the direct method are as follows: a=21.411(3) Angstrom, b=11.2210(10)Angstrom, c=12.208(2) Angstrom, Z=6, R=0.0240. The TG-DTA curves of KLnN(Ln=La,Ce, Pr, Nd, Sm) demonstrate that the processes of dehydration, melt, irreversible phase transition and decomposition of NO3- take place in sequence with the temperature increasing(except KCN). There are three steps in the decomposition of NO3- in KLnN(Ln=La, Nd, Sm) while two steps in KLnN (Ln=Ce, Pr). K(2)Ln(NO3)(5). 2H(2)O are formed at about 225 degrees C by the reaction of the starting materials of KNO3 and Ln(NO3)(3). nH(2)O.