类溶胶-凝胶法制备LiMn_2O_(4-δ)Cl_δ正极材料

本文以水合氢氧化锂 (LiOH .H2 O)、水合硝酸锰 (Mn(No3) 2 .6H2 O) ,水合氯化锂 (LiCl.H2 O)为原料 ,用类溶胶 凝胶法制备了LiMn2 O4 δClδ,并且以此作正极进行了电化学测试 .结果表明 ,掺氯的尖晶石LiMn2 O4 正极材料具有优异的稳定性 ,且循环稳定后 ,容量几乎没有衰减 .     

Oxygen permeability and CO_2-tolerance of Ce_(0.8)Gd_(0.2)O_(2-δ)-Ln BaCo_2O_(5+δ) dual-phase membranes

A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2-δ-40 wt% Ln Ba Co2O5+δ(CGO-LBCO, Ln = La, Pr, Nd,Sm, Gd and Y) were synthesized through a sol-gel route and effects of the Ln3+cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3+cations(La3+, Pr3+and Nd3+) successfully stabilized the double-layered perovskite structure of sintered LBCO,while the smaller ones(Sm3+, Gd3+, and Y3+) resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8×10-7mol s-1 cm-2at 925?C with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.     

Oxidation kinetics of nitrogen doped TiO(2-δ) thin films

The oxidation kinetics of nitrogen doped, oxygen deficient titanium dioxide thin films has been studied in atmospheres of pure oxygen or nitrogen at 500 °C, 550 °C, and 600 °C, respectively, by means of in situ optical spectroscopy. The thin films show high electronic absorbance in the visible and NIR region, accompanied by a red shift of the absorption edge of about 0.4 eV, e.g., from about 2.9 to 2.5 eV at 600 °C. The time dependent decrease of absorbance due to oxidation is found to follow a parabolic rate law. An activation energy of about 1.96 eV can be obtained from the temperature dependence of the parabolic oxidation rate constant. In the framework of a microscopic oxidation model, this energy barrier is attributed to the diffusion of titanium interstitials in the re-oxidized part of the thin films as a rate-determining process. In addition, an attempt is made to evaluate the kinetics of nitrogen release from the time dependent blue shift of the absorption edge during re-oxidation.     

Enhanced CO_2 Electrolysis with Mn-doped SrFeO_(3-δ) Cathode

Solid oxide carbon dioxide electrolysers are expected to play a key role in carbon-neutral energy landscape. However, the limited activity of traditional ceramic cathodes still restricts the electrochemical performance. Here we report the doping of Mn at the B site of SrFeO_(3-δ) cathode to improve CO_2 electrolysis. The oxygen vacancy concentration is increased by ～30% with Mn doping while the surface oxygen exchange coefficients are enhanced by ～10 times. The chemisorption of CO_2 indicates the presence of chemical intermediate state between CO_2 molecule and carbonate ion on the oxygen-deficient cathode surface which therefore leads to the desorption temperature of ～800 ℃. The Mn-doped SrFeO_(3-δ) enhances CO_2 electrolysis with no performance degradation being observed even after high-temperature operation of 100 hours.     

Nd_(1 x)Ba_(2-x)Cu_3O_(7-δ)超导体的热处理

通过对Nd1 xBa2 -xCu3O7-δ的两种样品 (烧结样品和区域熔炼样品 )的XRD谱图分析 ,研究了高温氩气氛下热处理对样品中Nd对Ba的取代值x的影响 ,同时比较了不同样品的Tc 和Jc 值。研究表明 ,氩气下 95 0℃热处理可以减少Nd对Ba的取代 ,Tc 和Jc 都有不同程度的提高。对不同固溶度x值的Nd1 xBa2 -xCu3O7-δ进行吸氧热处理 ,样品在热处理前后分别作XRD分析。从XRD谱图可以看出 :当x <0 4时 ,样品经吸氧后可以从四方相转变为正交相 ,而当x >0 4时 ,样品虽经长时间吸氧也不能使其从四方相转变为正交相     

Hydrothermal Synthesis and Characterization of Ce_(1-x)Mn_xO_(2-δ) Solid Solutions

Nanocrystals of Ce1-xMnxO2-δ(x=0.00,0.05,0.10,0.15,and 0.20) were synthesized by a hydrothermal reaction route.The solid solutions crystallized in a cubic fluorite structure with a particle size in the range of 11～15 nm.The incorporation of Mn ions in CeO2 resulted in a lattice volume reduction.Mn ions showed a mixed valence state of +2,+3 and +4 in CeO2 lattice.An obvious red-shift of the absorption threshold edge was observed from the UV-visible spectrum.Compared with the bulk CeO2,Ce1-xMnxO2-δ nanocrystals exhibited a lower releasing oxygen temperature as indicated by TPR technique.     

Convergent asymmetric synthesis of indolizidines from (S)-5-(tosylmethyl)-2-pyrrolidinone: synthesis of (−)-δ-coniceine

The enantiomerically pure (S)-5-(tosylmethyl)-2-pyrrolidinone 2, prepared from commercially available (S)-pyroglutaminol, is dialkylated at the nitrogen atom and the α-sulfonyl position using several dielectrophiles using sodium hydride as the base to diastereoselectively afford indolizidine derivatives 5 and the less common hexahydropyrrolo[1,2-a]azepin-3-one 6 in moderate to good yield. This domino process has been applied to the synthesis of (−)-δ-coniceine.     

γ(δ)-内酯氧化合成4(5)-氧代羧酸

以γ(δ)-内酯(1或2)为原料,次氯酸钠(NaC lO)为氧化剂,分别合成了具有不同碳链长度的4(5)-氧代羧酸(3或4),其结构经NMR和MS表征。考察了NaC lO用量,pH值和反应温度对产率的影响。较适宜的反应条件为:1(或2)15 mmol,NaC lO 35 mL,pH 8~9,冰水浴下反应,3(或4)的产率35%~92%。     

MgO掺杂Ce_(0.9)Sm_(0.1)O_(2-δ)固体电解质的结构和电性能

采用溶胶-凝胶法合成SiO2含量为5.0×10-4(w)的Ce0.9Sm0.1O2-δ(SDC)粉体(SDCSi),并将0-3.0%(x)MgO分别加入到SDCSi陶瓷粉体中,用X射线衍射(XRD)和场发射扫描电子显微镜(FE-SEM)对材料进行表征,用交流阻抗谱(AC)测试材料的电性能.结果表明:MgO掺杂能使SDCSi的烧结温度降低100-200℃,提高陶瓷材料的致密度;清除或降低陶瓷材料晶界处SiO2杂质的有害影响,显著提高晶粒/晶界电导率和总电率;MgO掺杂到SDCSi具有烧结助剂和晶界杂质清除剂的双重作用.     

YBa_2Cu_(3-x)Fe_xO_(7-δ)陶瓷样品的超声特性研究

本文研究了YBa_2Cu_(3-x)Fe_xO_(7-δ)(0≤x≤0.4)高温氧化物多晶超导体系的电阻,超声声速和超声衰减随温度的变化特性。对于超导样品,声速-温度曲线出现三次明显异常,首先是在超导转变温度附近声速呈现一极小值,表明样品中出现声子软化现象,其次分别在170K和240K附近声速发生两次大的突变,同时超声衰减曲线也相应地出现两个峰,而不超导的样品(x=0.40)只有170K和240K两处出现超声异常,而低温下无明显的声子软化现象,这说明,高温超导相变的发生会导致样品的弹性性质发生变化,而240K处体系发生的相变同高温超导电性无必然的联系,文中还初步讨论了170K超声异常的起因。     

Spectrum and Electrochemical Properties of Nanosized Ce_(1-x)Bi_xO_(2-δ) Solid Solutions

Ce1-xBixO2-δ(x = 0.00, 0.03, 0.05, 0.07, 0.10, 0.15, 0.30) solid solutions were synthesized via a hydrothermal method. The structure, spectra and electrochemical transport properties of the samples were characterized systematically. The powder X-ray diffraction analysis showed that all of the doped samples exhibited single phase fluorite structure. The particle sizes decreased from 18 to 9 nm and the lattice parameters increased gradually with the dopant content increasing from x = 0.03 to x = 0.30. The Bi3+ doping also induced the F2 g Raman peak to shift from 463 to 455 cm-1, and caused a red shift of the band gap energies calculated from UV-Vis spectra. The impedance plots at different temperature demonstrated that the boundary resistance was much larger than the grain resistance, and two activation energy values were obtained in different temperature range.     

纳米微晶Y_2Sn_(2-x)FexO_(7-δ)的制备及其催化选择性能研究

采用共沉淀并加法制备了Ｂ位掺杂烧绿石型稀土复合氧化物纳米微晶Ｙ２Ｓｎ２－ｘＦｅｘＯ７－δ（ｘ＝００～１０）。制备的纳米微晶属于立方晶系，Ｆｄ３ｍ，晶胞参数与掺杂量呈线性关系。通过Ｍｓｂａｕｅｒ、ＴＧＤＴＡ，气相色谱和γ射线辐照等技术研究了纳米微晶对ＣＯ的催化选择性能。结果表明，纳米微晶对ＣＯ的催化选择性明显高于一般粉料对ＣＯ的选择性；纳米微晶对ＣＯ的选择性与掺杂量有关；未辐照的纳米微晶，当掺杂量ｘ＝０６时，其对ＣＯ的选择性为最高，辐照后的纳米微晶，当掺杂量ｘ＝０４时，其对ＣＯ的选择性为最高     

Ti_(100-δ)Cu_δ(δ=0.02,0.28,1.39,5.65)阴极的制备及电催化还原NO_3~-机理

以Ti板为基体,采用异位电沉积法通过调控电镀时间制备了质量分数(δ)分别为0.02,0.28,1.39和5.65的Ti_(100-δ)Cuδ阴极;利用扫描电子显微镜(SEM)、X射线衍射(XRD)、电化学测试及NO_3~-处理实验等手段对其微观形貌、物相组成、电催化活性、抗腐蚀性能和产物选择性等进行了表征.结果表明,δ≥0.28时Ti_(100-δ)Cuδ电极表面的Cu镀层呈现(111)晶面择优取向,可有效提高电极稳定性;Cu活性层的形成为NO_3~-的吸附提供了活性点位,增强了电极的电催化性能,但Cu的加入会降低电极抗腐蚀性能;在一定的载铜量范围内,单质Cu对NO_3~-降解产物NO-2的吸附有一定的抑制作用,但会增强NO-2的还原反应活性,提高N2选择系数.应用Ti_(100-δ)Cuδ(δ=5.65)阴极在电流密度为20 m A/cm2、电解时间6 h条件下对NO_3~-进行处理,结果表明,NO_3~-去除率和N2选择系数分别高达75.47%和32.65%,与Ti电极的NO_3~-去除率(39.89%)和N2选择系数(2.19%)相比有显著提高.     

固溶体Ce_(1-x)Eu_xO_(2-δ)的~(151)Eu Mssbauer谱和电性能研究

利用溶胶-凝胶方法在800℃灼烧10h后,合成了固溶体Ce1-xEuxO2-δ(x=0.05~0.5),晶粒平均尺寸为60nm左右,XRD分析表明固溶体的结构为单相立方萤石结构。Mssbauer谱测试表明固溶体Ce1-xEuxO2-δ中Eu离子价态为+3价,同质异能移IS值随掺杂量x增加而增大。Eu3+的四极劈裂QS值小于零,表明Eu3+周围的晶体场是非对称的,QS的绝对值随掺杂量x增加而增大,说明随掺杂量x增加,晶体场对称性越差。阻抗谱测试表明通过掺杂使固溶体Ce1-xEuxO2-δ的导电率得到很大提高,电导率在x=0.2时达到最大值σ800℃=1.28×10-2S·cm-1,电导活化能达到最小值为Ea=0.72eV。     

质子导体(Ce_(0.8)La_(0.2))_(1-x)Ca_xO_(2-δ)在合成氨中的应用

利用溶胶-凝胶法合成了萤石型稀土复合氧化物(Ce_(0.8)La_(0.2))_(1-x)Ca_xO_(2-δ),利用XRD、TEM和SEM对样品进行表征.电化学方法研究表明,合成样品在400～800℃温度范围内具有质子导电特性.将(Ce_(0.8)La_(0.2))_(1-x)Ca_xO_(2-δ)高温烧结体用于固态质子传导电池,在常压下以氮气和氢气为原料合成氨气,并确定了合成氨的适宜条件.650℃时Ce0.8La0.2O2-δ和(Ce_(0.8)La_(0.2))_(1-x)Ca_xO_(2-δ)对应的氨产率分别达7.2×10-9和7.5×10-9mol·s-·1cm-2.     

Sonochemical synthesis of Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) nanocrystallites: oxygen storage material, CO oxidation and water gas shift catalyst

Nanocrystalline Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) of ~4 nm sizes were synthesized by a sonochemical method using diethyletriamine (DETA) as a complexing agent. Compounds were characterized by powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and transmission electron microscopy (TEM). Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) crystallize in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe(3+) ion in CeO(2), lattice oxygen is activated and 33% Fe substituted CeO(2)i.e. Ce(0.67)Fe(0.33)O(1.835) reversibly releases 0.31[O] up to 600 °C which is higher or comparable to the oxygen storage capacity of CeO(2)-ZrO(2) based solid solutions (Catal. Today 2002, 74, 225-234). Due to interaction of redox potentials of Pd(2+/0)(0.89 V) and Fe(3+/2+) (0.77 V) with Ce(4+/3+) (1.61 V), Pd ion accelerates the electron transfer from Fe(2+) to Ce(4+) in Ce(0.65)Fe(0.33)Pd(0.02)O(1.815), making it a high oxygen storage material as well as a highly active catalyst for CO oxidation and water gas shift reaction. The activation energy for CO oxidation with Ce(0.65)Fe(0.33)Pd(0.02)O(1.815) is found to be as low as 38 kJ mol(-1). Ce(0.67)Fe(0.33)O(1.835) and Ce(0.65)Fe(0.33)Pd(0.02)O(1.815) have also shown high activity for the water gas shift reaction. CO conversion to CO(2) is 100% H(2) specific with these catalysts and conversion rate was found to be as high 27.2 μmoles g(-1) s(-1) and the activation energy was found to be 46.4 kJ mol(-1) for Ce(0.65)Fe(0.33)Pd(0.02)O(1.815).     

溶胶-凝胶法制备二元稀土掺杂(Sm2O3)0.04 (Gd2O3)0.06 Ce0.8O2-δ纳米粉体

以Sm2O3、Gd2O3与Ce2(CO3)3.nH2O为原料,采用Sol-Gel法制备了二元稀土掺杂(Sm2O3)0.04(Gd2O3)0.06Ce0.8O2.δ纳米粉体.测定了pH值对0.80Ce(OH)4·0.08Sm(OH)3·0.12Gd(OH)3水溶胶体系zeta电位的影响.pH值约为7.0时,体系的Zeta电位为0,即体系的等电点(IEP)为7.0.pH值为10.0时,Zeta电位达到最大值-18.5my,说明此时该体系的稳定性最好.DTA/TG热分析表明,0.80Ce(OH)4·0.08Sm(OH)3·0.12Gd(OH)3粉体的热分解温度约为232℃.由粉末XRD分析可知,经750℃焙烧的二元稀土掺杂CeO2粉末为立方萤石结构,说明Sm2O3与Gd2O3已完全固溶到CeO2中形成了CeO2基固溶体.由TEM照片可以看出,粉末具有良好的分散性,呈软团聚状态,粒径在5-10nm之间.经BET测试计算的平均颗粒尺寸为11nm,与TEM结果是一致的.     

One-pot synthesis of 4,4-difluoro-3-oxo-2-(triphenylphosphoranylidene)-δ-lactones by Reformatsky reaction

In th presence of zinc and a catalytic amount of cuprous chloride, ethyl 4-bromo-4,4-difluoro-3-oxo-2-(triphenylphosphoranylidene)butanoate 1 reacted with carbonyl compounds to give the gem-difluoromethylenated 2-(triphenylphosphoranylidene)-δ-lactones 4 in moderate to high yields.     

Mixed-conducting perovskite-type Sr_xBi_(1-X)FeO_(3-δ)oxygen-permeating membranes

SrxBi1-xFeO3- (SBF) series mixed conductors were synthesized using Standard ceramic method. The properties of such materials were characterized by XRD, O2-TPD techniques. Ab-normal crystal phenomena were found and explained and correlated with the oxygen permeation results. By analysis of the critical radius (rc), the degree of openness of the lattice (Fv) and the average metal-oxygen bonding energy of the perovskite lattice (ABE), it was proposed that the oxygen permeation flux is determined mainly by the oxygen diffusion rate in bulk when 1-x≤0.5, and by the concentration of oxygen vacancy when 1-x≥ 0.5. The stability of Sr0.5Bi0.5FeO3- was also investigated, and the high stability of it was attributed to the stable BO6 octahedra.