碳前驱体CH3ArCH2NH2热解反应的热力学和动力学DFT研究

在实验研究基础上 ,通过量子化学理论计算对碳前驱体 CH3 Ar CH2 NH2 的热裂解机理作了进一步的研究 .利用 Gaussian98程序包中 AM1方法及 DFT UB3 LYP/3 -2 1 G*方法 ,对化合物 5种可能热裂解路径的热力学和动力学计算结果表明 ,CH3 Ar CH2 NH2 热裂解的主反应路径为生成自由基 CH3 Ar CH2 ·和 NH2 · ,其主反应路径 AM1计算的活化能 Ea=2 3 0 .78k J/mol,DFT计算的活化能 Ea=3 2 1 .1 8k J/mol;比较键焓计算的数据与相应的实验数据 ,发现 DFT计算结果与实验结果吻合得较好 ;通过分析优化的反应物及产物自由基的部分结构参数 ,了解了理论支持主反应的原因 ;计算的产物自由基的空间构型表明主反应路径生成的产物自由基相互间若进行稠环缩合反应 ,将获得分子平面取向性很好的稠环芳烃产物     

碳源甲基苯热裂解机理的密度泛函动力学研究

在热力学研究的基础上,用UB3LYP/3-21G^*方法对甲苯热裂解机理进行了动力学研究。计算得到了甲苯的5种热裂解路径的活化能。用过渡状态理论,计算得到了这些路径在298～1223K温度范围内的速率常数。动力学计算结果表明：甲苯在热解温度低于963K时的主反应路径为甲苯热裂解生成苄基自由基的反应,其速控步的活化能△E~0^θ^≠=402.27kJ/mol;当温度高于963K达1223K左右时,主反应路径转为苯环上脱甲基生成苯基和甲基自由基的路径,该路径的活化能△E~0^θ^≠=456.91kJ/mol。以上研究结果与实验结果相一致。     

碳前驱体CH3ArCH2NH2的热解性能及动力学研究

通过密闭压力容器法、常压DSC、高压DSC及紫外分光光度定量分析法等实验手段,对液相沉积法制碳／碳复合材料用碳前驱体CH3ArCH2NH2的热裂解行为进行了研究,获得不同温度、不同压力下该碳前驱体的热分解温度和残碳率,用等温动力学和非等温动力学方法获得了热裂解反应的表观活化能,实验结果表明,常压热裂解温度大约为530．15－556．55K,1－3MPa的高压范围内的热裂解温度大约在618．34－675．49K,密闭压力容器中的残碳率为56．23％,常压下的残碳率为28．96％－36．47％,而高压下残碳率可达59．11％,根据基辛格等方法获得了等温条件下和非等温条件下热裂解反应的表观活化能Ea分别为206．78kJ/mol和183．93kJ/mol, 反应级数N~1.     

甲苯热裂解机理的AM1研究(Ⅱ)动力学分析

在（Ⅰ）报热力学的基础上,本文用Gaussian98程序包中AM1法UHF计算,对碳材料用碳前驱体甲苯热裂解机理进行了动力学研究,通过用QST2方法寻找过渡态并经过内禀反应坐标IRC验证。计算得到了甲苯5种热裂解路径的活化能;用过渡态理论,计算了得到了这些路径在298－1073K温度范围内的速率常数。动力学计算结果表明：甲苯在热解温度低于963K时的主反应路径为甲苯热裂解生成苄基自由基的反应;该主反应路径又是经过由反应物→中间体→产物而完成,速控步为反应物→中间体,速控步的活化能△E^O=E(TS1′）-E（R）=227.20kJ.mol^-1;当温度高于963K或1073K左右时,主反应路径转为苯环上脱甲基生成苯基和甲基自由基的路径。以上研究结果与实验结果相一致。     

环己烷的热裂解机理

用Gaussian 98程序包中AM1法和DFT方法,对液相沉积法制碳/碳（C/C）复合材料的碳源化合物环己烷的热解机理做了量子化学理论研究.通过对化合物6种可能的热裂解路径的热力学和动力学计算,找到了环己烷热裂解的主反应路径.结果表明：(1) AM1与DFT计算均显示,断裂C－C键,最终生成乙烯和2 丁烯的反应通道是环己烷的主要裂解通道,与质谱数据吻合; (2) 除主反应路径外,余下的由易到难生成化合物的顺序为甲基环戊烷 >环己烯 >4 甲基环戊烯 >1,3 丁二烯; (3) AM1方法可以很好地推测较大分子体系的热裂解机理,而DFT方法计算的热力学量更接近实验数据.     

自由基HO2与C2H2反应势能面的理论研究

应用量子化学从头计算和密度泛函理论(DFT)对HO2+C2H2反应体系的反应机理进行了研究.在B3LYP/6-311G**和CCSD(T)/6-311G**水平上计算了HO2+ C2H2反应的二重态反应势能面.计算结果表明,主要反应方式为自由基HO2的H原子和C2H2分子中的C原子结合,经过一系列异构化,最后分解得到主要产物P1 (CH2O+ HCO).此反应是放热反应,化学反应热为-321.99 kJ·mol-1.次要产物为P2 (CO2 +CH3),也是放热反应.     

高密度烃燃料四氢环戊二烯三聚体的合成及热裂解

以双环戊二烯为原料,经D-A反应及催化加氢合成了高密度烃燃料四氢环戊二烯三聚体(THTCPD).该三聚体的密度为1.082 g/cm3,体积热值为47.5 MJ/L,闪点为120℃,凝固点为48~49℃.采用裂解器与色谱-质谱联用技术,对THTCPD的热裂解进行了在线监测,结果表明温度对裂解反应影响较大.对裂解产物的结构进行了分析,产物以甲烷、乙烯、丙烯、环戊烯、环戊二烯、苯和甲苯为主.依据产物结构及单分子自由基反应模型,推测得到了9种路径的裂解机理.采用X3LYP法进行了各自由基的热力学计算,得到各反应路径的相对能量及路径比.通过不同温度下的裂解转化率,计算得到热裂解反应动力学方程,经线性拟合得到活化能Ea=6.67×104kJ/mol,指前因子A=133.75.     

Co-Pd催化剂上CH4/CO2合成乙酸反应中CO2与表面金属物种作用的密度泛函理论研究

采用广义梯度近似(GGA)的密度泛函理论(DFT)(DFT-GGA)对Co-Pd催化剂上CH4/CO2两步法合成乙酸反应中CO2与金属表面物种M—H(M=Co,Pd)和Pd—CH3的插入反应机理进行了研究, 给出了CO2与M—H和Pd—CH3的插入反应机理. 计算结果表明, 在CO2与M—H和Pd—CH3相互作用的4个反应路径中, 反应以CO2与Co—H作用生成产物HCOO—Co为动力学优先路径, 但由于HCOO以双齿形式与金属Co结合, 其结合能较大, 导致HCOO在金属表面不易脱附, 故较难形成甲酸; 反应生成H3CCOO—Pd产物路径次之, H3CCOO和Pd之间结合能较小, H3CCOO容易脱附形成主产物乙酸; 生成H3COOC—Pd反应为动力学最不利路径, 故甲酸甲酯为动力学禁阻产物; 计算结果与实验结果吻合得很好.     

吡啶气相光氯化反应机理的理论研究──夺氢机理过渡态和IRC解析

氯自由基与吡啶分子发生夺氢反应生成2-氯吡啶、3-氯吡啶和4-氯吡啶等不同产物主要由两个连续的基元反应组成.研究了生成不同氯代产物的每一个基元反应过渡态,计算比较了不同反应路径活化能的高低,结果表明,不同产物以生成2-氯吡啶的活化能最低,生成2-氯吡啶两个连续基元反应的活化能分别为8.33kJ/mol和1.51kJ/mol,反应优先生成2-氯吡啶,并对邻位反应路径进行了键级、净电荷密度和IRC解析.     

铂催化2-烯炔苯甲醛水合环化反应的机理及化学选择性的理论研究

采用密度泛函理论(DFT)的计算方法, 研究了铂催化2-烯炔基苯甲醛水合环化反应的微观机理及化学选择性的根源. 计算结果表明, 首先炔基被催化活化而发生亲核环化生成吡喃铂中间体; 接着吡喃铂中间体与烯烃双键发生[3+2]环加成生成铂-碳卡宾复合物; 之后, 反应将沿2条路径进行, 得到产物3a或4a, 其中4a的生成需经两步水分子辅助的质子转移过程. 生成产物3a需要克服的活化能垒为146.5 kJ/mol; 对4a的生成, 烯醇式和酮式互变异构是决速步聚, 当一个水分子参与反应时, 对应的能垒为185.8 kJ/mol, 当2个和3个水分子参与反应时, 能垒分别降低到128.1和64.9 kJ/mol. 因此, 水分子参与催化得到产物4a的路径是有利的. 另外, 反应的选择性与在异构化过程中水的共催化作用有关. 以上结果很好地解释了实验现象, 并为铂催化水环化反应提供新的见解.     

KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems

phase diagrams of KCl-KBO₂-K₂CO₃, K₂MoO₄-KBO₂-K₂CO₃, and K₂WO₄-KBO₂-K₂CO₃ ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E ₁: 622°C, 8.5 mol % KBO₂, 56.5 mol % KCl, and 35 mol % K₂CO₃; E ₂: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂MoO₄; E ₃: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂WO₄. The specific heats of melting of the eutectics were determined.     

Solubility in the Na2Cr2O7-(NH4)2Cr2O7-K2Cr2O7-H2O system

Solubility in the Na₂Cr₂O₇-(NH₄)₂Cr₂O₇-K₂Cr₂O₇-H₂O four-component water-salt system at 25, 50, and 75°C was studied for the first time. Phase field boundaries for individual salts and potassium and ammonium dichromate solid solutions, monovariant lines, and invariant points were determined. Experimental data were used to optimize the looped isohydric process of potassium dichromate preparation involving additional salts.     

Li2O-TiO2-SiO2-P2O5和Li2O-TiO2-Al2O3-P2O5体系锂离子固体电解质的制备及性能研究

一些具有NASICON型网格结构的固体电解质具有高的电导率和好的稳定性,NASICON的意思是Na Super Ionic Conductor[1]。当NaZr2(PO4)3中P5 被Si4 部分取代时便可以得到具有NASICON结构的Na1 xZr2SixP3-xO12体系,其具有高的钠离子电导率。然而有相同结构的Li1 xZr2SixP3-xO12体系的离子电导率却很低,这是因为Li 半径太小,而NASICON三维网格结构的离子通道太大,两者不匹配而使电导率下降[2]。但当LiZr2(PO4)3中Zr4 被离子半径小些的Ti4 取代,所得LiTi2(PO4)3的通道就与Li 半径相匹配,适合于锂离子的迁移,从而使其电导率…     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

NaBO2-NaCl-Na2CO3, NaBO2- Na2CO3-NaMoO4, NaBO2- Na2CO3-NaWO4, and NaBO2-NaCl-Na2WO4 ternary systems

The phase diagrams of the NaBO₂-NaCl-Na₂CO₃, NaBO₂-Na₂CO₃-Na₂MoO₄, NaBO₂- Na₂CO₃-Na₂WO₄, and NaBO₂-NaCl-Na₂WO₄ ternary systems were studied by a calculation-experimental method and differential thermal analysis. The coordinates of ternary eutectics were determined: E ₁: 612°C, 16 mol % NaBO₂, 42 mol % NaCl, and 42 mol % Na₂CO₃; E ₂: 568°C, 12 mol % NaBO₂, 28 mol % Na₂CO₃, and 60 mol % Na₂MoO₄; E ₃: 575°C, 12 mol % NaBO₂, 32 mol % Na₂CO₃, and 56 mol % Na₂WO₄; E ₄: 628°C, 8 mol % NaBO₂, 20 mol % NaCl, and 72 mol % Na₂WO₄; and E ₅: 655°C, 9 mol % NaBO₂, 53 mol % NaCl, and 38 mol % Na₂WO₄.     

Li2SO4-Na2SO4-H2O和Li2SO4- K2SO4-H2O溶液的体积性质

本文用高精度数字式振荡管密度计测定了288K至318K温度范围内Li₂SO₄ + Na₂SO₄ + H₂O和 Li₂SO₄ + K₂SO₄ + H₂O三元体系的密度。混合溶液的离子强度范围从0.1到4.5 mol.kg_–1,混合溶液中Na₂SO₄和K₂SO₄的离子强度分数为0.2,0.4,0.6和0.8。用密度实验值拟合得到了不同温度下Pitzer离子相互作用模型混合参数θ_V和 ψ_V,模型的计算值与实验值的偏差在±0.002 g.cm_–3以内。用Pitzer模型计算了不同离子强度下三元体系的混合体积。     

(H2NC4H8NCH2CH2NH2)(HNCH2CH2NH2)3Zn2Ge2Se8: A new,templated one-dimensional ternary semiconductor stabilized by mixed organic cations

The novel, 1D semiconductor (H₂NC₄H₈NCH₂CH₂NH₂)(HNCH₂CH₂NH₂)₃Zn₂Ge₂Se₈ has been synthesized under solvothermal conditions using N-(2-aminoethyl)piperazine as solvent and templating agent at 200 °C. The material was characterized by single crystal and powder X-ray diffraction, IR and Raman spectroscopy and thermogravimetric analysis. The compound consists of 1D anionic [Zn₂Ge₂Se₈]⁴⁻ chains made of alternating edge-shared [ZnSe₄] and [GeSe₄] tetrahedra that charged balanced by one N-(2-aminoethyl)piperazinium and three piperazinium cations. The optical properties were investigated with solid state UV–Vis/near IR spectroscopy and the results show that the solid is a medium gap semiconductor with an absorption edge at 1.8 eV.     

Polymorphism in the Sc2Si2O7-Y2Si2O7 system

This paper examines the structural changes with temperature and composition in the Sc₂Si₂O₇-Y₂Si₂O₇ system; members of this system are expected to form in the intergranular region of Si₃N₄ and SiC structural ceramics when sintered with the aid of Y₂O₃ and Sc₂O₃ mixtures. A set of different compositions have been synthesized using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1750 °C during different times. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the β-RE₂Si₂O₇ polymorph, with γ-RE₂Si₂O₇ and δ-RE₂Si₂O₇ showing very reduced stability fields. Isotherms at 1300 and 1600 °C have been analysed in detail to evaluate the solid solubility of the components. Although, the XRD data show a complete solid solubility of β-Sc₂Si₂O₇ in β-Y₂Si₂O₇ at 1300 °C, the ²⁹Si MAS-NMR spectra indicate a local structural change at x ca. 1.15 (Sc_2−xY_xSi₂O₇) related to the configuration of the Si tetrahedron, which does not affect the long-range order of the β-RE₂Si₂O₇ structure. Finally, it is interesting to note that, although Sc₂Si₂O₇ shows a unique stable polymorph (β), Sc³⁺ is able to replace Y³⁺ in γ-Y₂Si₂O₇ in the compositional range 1.86?x?2 (where x is Sc_2−xY_xSi₂O₇) as well as in δ-Y₂Si₂O₇ for compositions much closer to the pure Y₂Si₂O₇.     

Synthesis and characterization of inorganic solid electrolytes of Li2O-SiO2-P2O5 and Li2O-TiO2-SiO2-P2O5 systems

The lithium-ion-conducting inorganic solid electrolytes in the oxide systems Li₂O-SiO₂-P₂O₅ and Li₂O-TiO₂-SiO₂-P₂O₅ were prepared by the solid-state reaction, and the electrolyte pellet made by cold-pressing method had diameter of 13 mm and was about 1 mm thick. Phase identification and surface morphology of the products were carried out by X-ray diffraction and scanning electron microscopy. Ionic conductivity of the pellets was investigated through ac impedance. The results show that the adding of other cations can improve the ionic conductivity of the solid electrolyte, and the sintering temperature and duration can influence the ionic conductivity. The maximum ionic conductivity in the samples is 9.9 × 10⁻⁴ S/cm in the Li₂O-TiO₂-SiO₂-P₂O₅ system. Original Russian Text ? W. Li, M. Wang, Z.H. Li, X.F. Shang, H. Wang, Y.W. Wang, Y.B. Xu, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 11, pp. 1341–1345.     

Tl2S-Sb2S3-Bi2S3 quasi-ternary system

The Tl₂S-Sb₂S₃-Bi₂S₃ quasi-ternary system (system A) was studied using DTA, X- ray powder diffraction, microstructure examination, and microhardness measurements. TlSbS₂-Tl₄Bi₂S₅(TlBiS₂, Bi₂S₃), Sb₂S₃-TlBiS₂, Tl₃SbS₃-TlBiS₂(Bi₂S₃), and [TlSb_0.5Bi_0.5S₂]-Tl₂S isopleths; isothermal sections at 500 K; and liquidus surface projection of system A were constructed. Characteristic features of the title system are extensive fields of solid solutions extended along the TlSbS₂-TlBiS₂ quasi-binary section and a continuous solubility belt 1–2 mol % wide extended along the Sb₂S₃-Bi₂S₃ binary subsystem. Primary separation fields of phases and the types and coordinates of invariant and monovariant equilibria in system A were determined.