SEELFS对Mg-Al复合氧化物结构的研究

应用EXAFS类似原理,对MgO和Mg-Al复合氧化物[Mg(Al)O]中Mgk-边的SEELFS(SurfaceExtendedenergyLossFineStructure)一阶微分谱进行数据处理,得到了Mg近邻原子的配位距离。研究发现,同MgO比较,由于Al^3^+的引入,使[Mg(Al)O]中的Mg－mg配位距离增加,配位数降低,而Mg－O的配位环境基本不变。     

Li~+,Na~+,K~+,Mg~(2+)/Cl~-,SO_4~(2-)-H_2O体系Pitzer热力学模型

介绍了描述25℃Li+,Na+,K+,Mg2+/Cl-,SO42--H2O体系的热力学Pitzer模型.给出了为获得Pitzer混合参数而测定的Li+/Cl-,SO42--H2O,Li+,K+/Cl--H2O,Li+,Na+/Cl--H2O等三元体系和Li+,Mg2+/Cl-,SO42--H2O四离子体系溶液的渗透系数.详细叙述如何利用热力学数据和溶解度数据,获得Li+,Mg2+/Cl-,SO42--H2O,Li+,K+/Cl-,SO42--H2O,Li+,Na+/Cl-,SO42--H2O体系全部混合参数及7种锂盐Gibbs标准生成自由能.进而通过数据对比,介绍了本模型在含Li+多组分溶液25℃热力学性质计算、含Li+多组分体系25℃溶解相平衡预测等方面的应用.     

尖晶石对β／β″—Al2O3膜相组成和离子导电性的影响

以wag／P”－AI。O。为固体电解质的CO。、SO。、NO。等气体传感器的研究已有很多报道［‘－‘］，多采用的是个AI。O。结构的电解质。AI刀。和p”－AI刃。的结构具有一定的相似性，但后者具有更高的迁移离子浓度和更开放的晶体结构，表现出更好的离子导电性‘’‘．由于卢”－AI。O。为介稳结构，需要加入如Li。O、MgO等作为稳定剂才能稳定存在．以Li对稳定的产”－al。O。烧结较容易，P”－AI。O。相转化率高，但以MsO为稳定剂制备的”－AI刃。其显微结构和抗吸湿性能更为优越．LJLi对和MgO共同稳定的产”－AI。O。可以…     

水溶液交换法制备的(Li,Na)-LSX沸石骨架中Li~+分布

采用水溶液交换法对Na-LSX沸石进行Li+交换,通过改变交换次数制备出不同交换度的低硅铝比X型[(Li,Na)-LSX]沸石分子筛,并对其进行XRD、FT-IR、TG-DSC、SEM和NMR等表征和分析,重点考察了Na-LSX分子筛在Li+交换前后的结构变化情况,以及不同交换度的(Li,Na)-LSX沸石分子筛骨架中Li+的分布。结果表明随着Li+交换度的增加,LSX分子筛的晶胞常数减小,热稳定性有所下降,Li+进入骨架中的顺序依次为S2>S3>S5。     

Li含量对Li/MgO丙烷氧化脱氢制烯烃反应催化性能的影响

采用浸渍法制备了不同Li含量的Li/MgO催化剂,并通过TG-DTA、N_2吸附及XRD等手段对其进行了表征;对丙烷在Li/MgO催化剂表面的两种吸附状态所占据的空间体积大小进行了计算,研究了Li含量对其丙烷氧化脱氢制烯烃反应催化性能的影响。结果表明,随着Li/MgO催化剂中Li含量的增加,丙烷转化率与乙烯、甲烷、乙烷和COx的选择性均先增加,在Li物质的量分数为3%时达到最高,然后随Li含量增加而降低,而丙烯选择性则出现相反的变化趋势。丙烷在Li/MgO催化剂上的吸附和反应同时受动力学和热力学两个因素的制约;Li负载量不同,反应活性位Li+O-分散状态也不同,导致产物分布发生变化。活性位分散度高时受热力学因素影响,有利于生成丙烯;活性位分散度低时受吸附动力学影响,更趋向于生成乙烯等其他产物。     

富锂正极材料Li[Li0.2Mn0.4Fe0.4]O2的表面包覆改性

用共沉淀法合成了富锂正极材料Li[Li0.2Mn0.4Fe0.4]O2,并对其表面进行Al2O3包覆。采用XRD、SEM和电化学测试等方法对样品进行表征。结果表明,与Li[Li0.2Mn0.4Fe0.4]O2相比,包覆改性后的Li[Li0.2Mn0.4Fe0.4]O2具有较好的电化学性能,其初始放电容量未明显降低,而循环寿命大大提高,4.0%Al2O3包覆处理的富锂正极材料经50次充放电循环后,容量衰减量在9%左右。     

环糊精接枝聚硅氧烷气相色谱固定相的手性拆分性能

用环糊精接枝聚硅氧烷（二环[2，6－二－O－戊基－3－O－己烯基（－5）]五环[2，6－二－O－戊基－3－O－甲基－β－CD聚硅氧烷]作气相色谱固定相成功地拆分具有两个手性中心的物质－－2，6－二乙酰氧基庚烷；考察了色谱条件对手性拆分的影响。     

Cu/MgO催化剂上NO-TPO和CO-NO反应性能

采用TPD技术考察了Cu/MgO催化剂表面NO的脱附和分解。载体MgO表面有两类NO吸附中心,为MgO表面碱中心。负载Cu后,由于Cu覆盖了MgO表面碱中心,使Cu/MgO(>1%)催化剂表面只有吸附在Cu上的NO。热脱附过程伴有明显的分解,产物为N~2,N~2O和O~2。CO-NO反应低温有利于N~2O生成,而高温有利于N~2生成,反应活性与NO-TPD峰温有较好的对应关系。NO在催化剂表面解离(NO~a→N~a+O~a)是CO-NO反应的速控步。     

CaO-MgO-Fe2O3-Al2O3-SiO2玻璃晶化机理

玻璃晶化动力学对于理解玻璃的稳定性和制备微晶玻璃十分重要．目前，通过DTA或DSC等简单技术去研究非等温过程和等温过程的动力学已取得一定的进展[1]．这些方法虽然方便，但需要事先知道晶化机理或借助XRD等技术确定Avrami参数[2]才能得到活化能．根据动力学理论，晶体生长速度与晶体生长活化能尽有直接关系[3]，通过理论计算晶体生长速度（U）可以确定玻璃体系的活化能，再结合DTA技术和Kissinger修正方程就可能确定晶体生长机理，这方面研究还未见报导．CaO－MgO－Fe2O3－AI2O3－SiO2（CMFAS）是本文综合利用废渣和尾矿制…     

亮氨酸-脑啡肽结合H~+和Li~+的氢氘交换实验与理论研究

气相氢氘交换质谱(HDX-MS)实验与量子化学计算结合,比较了亮氨酸-脑啡肽(YGGFL)结合H~+和Li~+的反应和结构差异性。HDX-MS结果表明,在相同的实验条件下,[YGGFL+Li]~+在交换5个氢原子后,氢氘同位素反应趋于停止,而[YGGFL+H]~+上的9个可交换氢原子均可发生交换。这表明Li~+会降低脑啡肽的氢氘交换率。理论计算发现,两种离子具有不同的最稳定结构:Li~+与脑啡肽肽上的4个羰基氧原子结合能量最低,而脑啡肽氨基端发生质子化后产生最稳定的[YGGFL+H]~+。基于此稳定结构,实验进一步从离子结构差异性和质子亲和势等方面对HDX实验结果进行了分析。     

Li^＋／MgO上乙烷氧化脱氢制乙烯的研究（Ⅱ）：催化作用机理

借助ＸＲＤ、ＩＲ、ＴＧ等技术对Ｌｉ＾＋／ＭｇＯ进行了表征，结果表明，酸、碱中心的数目，强度、催化性与Ｌｉ＾＋的添加量相关 ，起酸碱作用的表面金属离子、表面低配位氧集团、Ｏ（Ｌ ｉ＾＋Ｏ＾－）是其反应的活性物种，反应机理可能由离子基、游离基协同完成。     

激光促进甲醇氧化偶联表面反应的规律

用沉淀法制备了Ｌｉ３ＰＯ４、ＢｉＰＯ４和Ｌｉ３ＰＯ４、ＢｉＰＯ４三种固体表面材料,并用ＸＲＤ、ＩＲ、ＴＰＤ和激光促进表面反应（ＬＳＳＲ）等技术研究了这些固体表面上甲醇氧化偶联生成乙二醇的反应规律。实验结果表明：甲醇在固体材料表面的Ｐ＝９键上产生Ｃ－Ｈ端的分子态吸附,在表面的Ｌｅｗｉｓ酸位（金属离子）上产生解离态吸附。Ｌｉ３ＰＯ４和ＢｉＰＯ４的相互作用可促进甲醇在固体表面上的分子态吸附而抑制解离态吸     

Defect models of the three trigonal Ti3+ centers in LiF:Ti3+ and LiF:Ti3+:Mg2+ crystals

The EPR g factors of the trigonal Ti3+ center A in LiF:Ti3+ and two additional trigonal Ti3+ centers B and C in LiF:Ti3+:Mg2+ crystals are calculated from the third-order perturbation formulas based on the cluster approach. From the calculations and by considering the Ti3+ displacement along 111 axis obtained by ENDOR experiment, the defect models for the three Ti3+ centers are suggested. For center A, there are two possible models: (i) [Ti3+F3-O3(2-)] cluster and (ii) [Ti3+F6-] cluster with the Ti3+ off-center caused by a neighboring Li+ vacancy (VLi+) at <111> axis. The latter seems the more likely. The defect models of centers B and C are the [Ti3+F3-O(3)2-] clusters associated with a neighboring: Mg2+ ion at the Li+ site along 111 axis in the vicinity of three F- ions and three O2- ions, respectively. The reasonableness of these models is discussed.     

Na^+/CaO催化剂上的甲烷氧化偶联

研究了不同碱金属离子对CaO的促进作用,发现以Na~+的添加效果最好。在此基础上,研究了不同含钠化合物对CaO的促进作用,并用脉冲反应技术研究Na~+/CaO催化剂表面氧物种的特性及其作用。CaO表面上存在非选择性氧化的氧物种。Na~+对CaO的修饰作用是抑制非选择性氧化。当表面上的非选择性氧化的氧物种消耗后,体相的晶格氧会向表面迁移,以补充消耗掉的表面氧物种。消耗掉的表面氧物种也可由气相氧补充。CH_4脉冲和混合气脉冲说明仅靠[Na~+O~-]中心不足以使甲烷转化成C_2产物,必须有气相氧的参与才能使甲烷转化成C_2产物。     

添加Li+对MgO催化性能的影响

本文以IR、TPD、丁烯异构化及直接脱氢反应为手段,对不同Li⁺添加量的MgO催化剂进行了研究。结果表明,表面低配位氧集团是催化剂的主要活性物种,起碱中心作用;表面金属离子起L酸中心作用。酸、碱中心的数目、强度随Li⁺添加量不同而呈规律性变化。这种变化影响了酸、碱中心的协同作用,从而影响其催化活性。     

在Li2O／MgO上以脉冲法研究甲烷氧化偶联

在Ｌｉ_２Ｏ／ＭｇＯ上以脉冲法研究甲烷氧化偶联戚蕴石，卫上方（华东理工大学工业催化研究所，上海，２００２３７）关键词甲烷氧化偶联，晶格氧，脉冲法对甲烷氧化偶联（ＯＣＭ）的研究已有较多报道［１～４］，对其反应机理的研究亦取得了较大的进展．Ｏｔｓｕｋａ［?..     

Identification of defect sites on MgO(100) thin films by decoration with Pd atoms and studying CO adsorption properties.

CO adsorption on Pd atoms deposited on MgO(100) thin films has been studied by means of thermal desorption (TDS) and Fourier transform infrared (FTIR) spectroscopies. CO desorbs from the adsorbed Pd atoms at a temperature of about 250 K, which corresponds to a binding energy, E(b), of about 0.7 +/- 0.1 eV. FTIR spectra suggest that at saturation two different sites for CO adsorption exist on a single Pd atom. The vibrational frequency of the most stable, singly adsorbed CO molecule is 2055 cm(-)(1). Density functional cluster model calculations have been used to model possible defect sites at the MgO surface where the Pd atoms are likely to be adsorbed. CO/Pd complexes located at regular or low-coordinated O anions of the surface exhibit considerably stronger binding energies, E(b) = 2-2.5 eV, and larger vibrational shifts than were observed in the experiment. CO/Pd complexes located at oxygen vacancies (F or F(+) centers) are characterized by much smaller binding energies, E(b) = 0.5 +/- 0.2 or 0.7 +/- 0.2 eV, which are in agreement with the experimental value. CO/Pd complexes located at the paramagnetic F(+) centers show vibrational frequencies in closest agreement with the experimental data. These comparisons therefore suggest that the Pd atoms are mainly adsorbed at oxygen vacancies.     

甲烷氧化偶联催化剂Li/MgO的结构及表面性质的研究

本文用XRD、TEM、XPS和荧光光谱等方法研究了一组不同Li~+含量的Li/MgO催化剂的结构及表面性质,并与它们的氧化偶联甲烷的催化性能相关联。结果表明,低配位O~(2-)(O_(3c)~(2-))是使甲烷活化的活性中心。O_(1s)结合能为531.9eV的氧物种是对甲烷氧化偶联反应的C_2选择性起作用的活性氧物种。     

Mechanism of heterogeneous reaction of carbonyl sulfide on magnesium oxide

Heterogeneous reaction of carbonyl sulfide (OCS) on magnesium oxide (MgO) under ambient conditions was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), quadrupole mass spectrometer (QMS), and density functional theory (DFT) calculations. It reveals that OCS can be catalytically hydrolyzed by surface hydroxyl on MgO to produce carbon dioxide (CO2) and hydrogen sulfide (H2S), and then H2S can be further catalytically oxidized by surface oxygen or gaseous oxygen on MgO to form sulfite (SO3(2-)) and sulfate (SO4(2-)). Hydrogen thiocarbonate (HSCO2-) was found to be the crucial intermediate. Surface hydrogen sulfide (HS), sulfur dioxide (SO2), and surface sulfite (SO3(2-)) were also found to be intermediates for the formation of sulfate. Furthermore, the surface hydroxyl contributes not only to the formation of HSCO2- but also to HSCO2- decomposition. On the basis of experimental results, the heterogeneous reaction mechanism of OCS on MgO was discussed.     

Screening of MgO——and Ce02-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C2＋ Hydrocarbons

The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM)have been investigated over ternary and binary metal oxide catalysts.The catalysts are prepared by doping MgO-and CeO2-based solids with oxides from alkali(Li2O),alkaline earth (CaO),and transition metal groups (WO3 or MnO).The presence of the peroxide (O2^2-)active sites on the Li2O2,revealed by Raman spectroscopy,may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts.The high reducibility of the CeO2 catalyst,an important factor in the CO2-OCM catalyst activity,may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobitity and oxygen vacancies in the CeO2 catalyst.raman and Fourier Transform Infra Red (FT-IR)spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks carresponding to the buld crystalline structures of Li2O,CaO,WO2 and MnO are detected.The performance of 5%MnO/15?O/CeO2 catalyst is the most potential among the CeO2-based catalysts,although lower than the 2%Li2O/MgO catalyst.The 2%Li2O/MgO catalyst showed the most promising C2 hydrocarbons selectivity and yield at 98.0%and 5.7%,respectively.