气相中W~+活化CO_2分解的自旋禁阻反应机理

用密度泛函理论中的UB3LYP方法,对W采用相对论校正赝势基组(SDD),对C、O采用6-311+G(3d)基组,研究了气相中不同自旋态W+活化CO2分解的反应机理.计算结果表明,W+活化CO2分解反应以六重态进入反应通道,经过六重态势能面到四重态势能面的系间窜越(ISC),最后产物WO+和CO以四重态离开反应通道.运用Harvey方法优化出最低能量交叉点(MECP),并计算了MECP处的自旋-轨道耦合(SOC)常数(494.95cm-1),势能面的交叉和在MECP处较强的自旋-轨道耦合作用降低了自旋禁阻反应能垒,为反应提供了一条低能反应路径,反应总放热量为122.33kJ.mol-1.     

MH~+(M=Fe,Co,Ni)催化二氧化碳的氢化反应

在密度泛函理论的B3LYP水平下计算了MH~+(M=Fe,Co,Ni)催化二氧化碳的氢化反应.研究表明,氢转移至C上要比转移至O上容易得多.探讨不同泛函方法对反应的影响,从CCSD(T)的计算结果可见,与Co H~+和Ni H~+相比,Fe H~+对H转移至C上的活性较高.电子结构分析表明,反应过程中氢转移为氢负离子转移.     

Time-dependent density functional study of the electronic spectra of oligoacenes in the charge states −1, 0, +1, and +2

We present a systematic theoretical study of the five smallest oligoacenes (naphthalene, anthracene, tetracene, pentacene, and hexacene) in their anionic, neutral, cationic, and dicationic charge states. We used density functional theory (DFT) to obtain the ground-state optimised geometries, and time-dependent DFT (TD-DFT) to evaluate the electronic absorption spectra. Total-energy differences enabled us to evaluate the electron affinities and first and second ionisation energies, the quasiparticle correction to the HOMO–LUMO energy gap and an estimate of the excitonic effects in the neutral molecules. Electronic absorption spectra have been computed by combining two different implementations of TD-DFT: the frequency–space method to study general trends as a function of charge-state and molecular size for the lowest-lying in-plane long-polarised and short-polarised π → π^* electronic transitions, and the real-time propagation scheme to obtain the whole photo-absorption cross-section up to the far-UV. Doubly ionised PAHs are found to display strong electronic transitions of π → π^* character in the near-IR, visible, and near-UV spectral ranges, like their singly charged counterparts. While, as expected, the broad plasmon-like structure with its maximum at about 17–18 eV is relatively insensitive to the charge-state of the molecule, a systematic decrease with increasing positive charge of the absorption cross-section between 6 and 12 eV is observed for each member of the class.     

ZrO2基复合金属氧化物催化剂上CO2温和氧化乙苯制苯乙烯

苯乙烯(SM)是聚合物化学中最重要的单体之一,由其生产的聚合物产品(如PS,SBR和ABS等)具有独特的性能,因而SM的需求逐年增加.乙苯(EB)催化脱氢工艺提供了90％的SM需求,该过程在K促进的氧化铁催化剂上于600-650℃进行.这是一个吸热且体积增大的反应,因此需要绝热反应器和大量的过热过饱和蒸汽以提供热量和降低反应分压,从而有利于反应平衡向SM方向移动,也可避免或消除积碳.同时,也造成大量潜热被浪费;热点也降低了整个反应活性和催化剂寿命.在蒸汽中加入空气或富氧空气,使得副产H2与O2反应,产生的热量可供随后乙苯脱氢反应,同时H2的移除也有利于提高EB单程转化率,并保持高的SM选择性.但是,该过程需要2个催化剂,反应器的设计和催化剂的装填比较复杂,且存在爆炸的危险.因此,人们尝试了多种氧化剂和新型的催化剂.最近也有人提出软氧化剂的概念.这为开发新催化体系提供了可能.相对于O2,CO2的氧化性很弱,但可用作温和氧化剂去除脱氢单元中副产的H2,降低了反应温度,且不影响反应活性和选择性;同时,具有较大的经济性和环保性,在工业上也是切实可行的.除了负载型的碱金属促进的氧化铁催化剂外,各种金属或金属氧化物也用于催化CO2氧化EB脱氢反应中,如Fe,Cr,V和La的氧化物为活性金属,碳材料、MgO、SiO2、Al2O3、Ga2O3、ZrO2、TiO2、水滑石类化合物及分子筛为载体.Park课题组研究了Fe,V和Cr基催化剂,即设计氧化还原的催化剂表面以解离CO2,产生的O用于逆水汽反应.其中以Al2O3负载的V和V-Sb氧化物催化剂性能最为突出;但存在积碳失活和V物种的深度还原等问题.为了进一步提高催化剂性能,该课题组开发了多种ZrO2基复合氧化物催化剂,包括MnO2-ZrO2,TiO2-ZrO2,CeO2-ZrO2和SnO2-ZrO2.这些催化剂具有酸碱特性,在反应中表现出较高的催化性能.因此,本文简要总结了用于CO2氧化EB脱氢反应的ZrO2基催化剂最新研究进展.研究发现,在CO2氧化EB脱氢制SM反应中,CO2在提高催化剂活性和稳定性方面起着非常重要的作用,可被定义为软氧化剂:氧化催化剂表面以保持其表面氧含量,移除催化剂表面产生的积碳和副产物H2,为反应体系提供较高的热容以克服反应平衡限制,从而达到较高的转化率.ZrO2基复合金属氧化物是具有改善的织构特性的纳米粒子,且具有酸碱两性和氧化还原性能.改性可提高催化体系的热稳定性和活性.其中CeO2-V2O5/TiO2-ZrO2催化剂具有恰当的氧化还原性和酸碱两性,二者协同作用,因而催化性能最佳.氧化还原稳定剂Sb的添加进一步提高了其催化性能.碱金属和碱土金属可优化其酸碱性,增加比表面积,从而提高反应活性和选择性以及CO2转化率.继续加强抑制积碳和促进CO2活化方面的研究,可有望进一步提高单程转化率(75％以上)、选择性(98％)和CO2转化率(30％).总之,CO2氧化EB脱氢制SM是一个高度经济性和环境友好的新过程,在未来有望满足SM日益增长的需求.另外,该过程的开发可减少CO2排放,其副产的CO还可用于多种化工过程.然而,该过程仍面临诸多挑战:如何抑制积碳,单程转化率和催化剂寿命有待进一步提高.这些挑战也给我们未来的研究提供了方向.深入理解反应机理、积碳机理和CO2的活化过程也有利于我们开发出更适合工业应用的催化剂.     

接枝羟基对有限长碳纳米管电子结构的影响

基于局域密度泛函理论, 采用第一原理方法, 建立了(5, 5)型和(8, 0)型有限长碳纳米管的原子模型, 并在两个端口接枝1～8个羟基官能团, 先用DMol3中BLYP方法对其结构进行优化, 再利用CASTEP软件计算其电子分布和态密度的变化, 从而讨论羟基官能团对碳纳米管电子结构和电子输运特性的影响. 计算表明, 接枝羟基的碳纳米管的电子结构明显改变, 费米能级上的电子态密度下降, 最高占据轨道上电子的非定域程度减弱, 致使电子输运性能呈下降趋势.     

Thermal Ethane Activation by Bare [V2O5]+ and [Nb2O5]+ Cluster Cations: on the Origin of Their Different Reactivities

The gas‐phase reactivity of [V₂O₅]⁺ and [Nb₂O₅]⁺ towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room‐temperature conversions C₂H₆→C₂H₅OH or C₂H₆→CH₃CHO are brought about solely by [V₂O₅]⁺. In distinct contrast, for the couple [Nb₂O₅]⁺/C₂H₆, one observes only single and double hydrogen‐atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C?H bond activation together with quite different bond‐dissociation energies of the M?O bonds cause the rather varying reactivities of [V₂O₅]⁺ and [Nb₂O₅]⁺ towards ethane. The gas‐phase generation of acetaldehyde from ethane by bare [V₂O₅]⁺ may provide mechanistic insight in the related vanadium‐catalyzed large‐scale process.     

气相中Y^＋活化CS2中的C—S键

以Y+与CS2反应作为第二行前过渡金属离子与CS2反应的范例体系.采用密度泛函UB3LYP方法,对于Y+采用Stuttgart赝势基组,对于CS2采用6-311+G(2d)基组,计算研究了Y+离子在基态和激发态时与CS2气相反应的机理.并用UCCSD(T)方法在相同的基组水平上对各驻点作了单点能量校正.结果表明Y+离子与CS2的反应是插入-消去反应,在反应过程中会发生系间窜越,并且找到了两个势能面的能量最低交义点.     

锰配合物催化CO2加氢生成甲酸的理论研究

采用密度泛函理论(DFT)对锰配合物催化二氧化碳加氢生成甲酸的反应进行了理论研究. 整个催化循环主要包括氢气活化和二氧化碳氢化2个阶段. 计算结果表明, 甲酸的参与明显降低了氢气活化的反应能垒; 二氧化碳的氢化过程遵循外层机理并且氢转移是分步进行的, 决速步骤为氢负离子的转移过程, 自由能垒为21.0 kJ/mol. 对配合物中硫原子上的取代基R进行了调变, 研究结果表明, 当R为吸电子基团时能降低氢气裂解和二氧化碳氢化过程中质子转移的能垒, 而当R为推电子基团时有利于氢负离子的转移,当R=CF₃时整个反应的能量跨度(80.4 kJ/mol)最小.     

COS Activation by Zr~＋ in the Gas Phase：A Case of Two-state Reactivity Process

To elucidate the mechanisms of Zr + reacting with COS,both the quartet and doublet potential energy surfaces (PESs) for reactions of Zr + (4 F,2 D) with COS in the gas phase have been investigated in detail by means of density functional method (B3LYP).To obtain more accurate results,the coupled cluster single-point calculations (CCSD(T)) using B3LYP optimized geometries were performed.For the C-O bond activation,the calculated results indicate that both the quartet and doublet states proceed via an insertion-elimination mechanism.For the C-S bond activation,the quartet reaction has an insertion-elimination mechanism,but the doublet reaction is a direct abstraction of the sulfur atom by Zr +.The C-S bond activation is found to be energetically more favorable than the C-O bond activation.It is found that the reaction of the 4 F gound state of Zr + to yield ZrO + is spin-forbidden (Zr + (4 F) + COS (1 Σ) → ZrO + (2) + CS (1 Σ)) and the crossing points were approximately determined.All the results have been compared with the existing experimental and theoretical data.     

Activation of C-H, C-C and C-I bonds by Pd and cis-Pd(CO)2I2. Catalyst-substrate adaptation

We have studied the oxidative addition reactions of methane and ethane C-H, ethane C-C and iodomethane C-I bonds to Pd and cis-Pd(CO)₂I₂ at the ZORA-BP86/TZ(2)P level of relativistic density functional theory (DFT). Our purpose, besides exploring these particular model reactions, is to understand how the mechanism of bond activation changes as the catalytically active species changes from a simple, uncoordinated metal atom to a metal-ligand coordination complex. For both Pd and cis-Pd(CO)₂I₂, direct oxidative insertion (OxIn) is the lowest-barrier pathway whereas nucleophilic substitution (S_N2) is highly endothermic, and therefore not competitive. Introducing the ligands, i.e., going from Pd to cis-Pd(CO)₂I₂, causes a significant increase of the activation and reaction enthalpies for oxidative insertion and takes away the intrinsic preference of Pd for C-I over C-H activation. Obviously, cis-Pd(CO)₂I₂ is a poor catalyst in terms of activity as well as selectivity for one of the three bonds studied. However, its exploration sheds light on features in the process of catalytic bond activation associated with the increased structural and mechanistic complexity that arises if one goes from a monoatomic model catalysts to a more realistic transition-metal complex. First, in the transition state (TS) for oxidative insertion, the C-X bond to be activated can have, in principle, various different orientations with respect to the square-planar cis-Pd(CO)₂I₂ complex, e.g., C-X or X-C along an I-Pd-CO axis, or in between two I-Pd-CO axes. Second, at variance to the uncoordinated metal atom, the metal complex may be deformed due to the interaction with the substrate. This leads to a process of mutual adjustment of catalyst and substrate that we designate catalyst-substrate adaptation. The latter can be monitored by the Activation Strain model in which activation energies ΔE^≠ are decomposed into the activation strain of and the stabilizing TS interaction between the reactants in the activated complex: .     

Encapsulations of La@C82 and La2@C80 inside single-walled boron nitride nanotubes

Possibility of encapsulations of metallofullerenes inside single-walled boron nitride nanotubes (BNNTs) is studied by using first-principles calculations. We find that both La@C₈₂ and La₂@C₈₀ can be exothermically encapsulated inside the (17, 0) and (14, 7) BNNTs. The minimum diameters of exothermically encapsulating both La@C₈₂ and La₂@C₈₀ inside BNNTs are predicated to be about 13.4 Å.     

气相中2Sr+和2Ba+催化N2O与CO还原反应的理论研究

用密度泛函理论DFT-UB3LYP方法,对2Sr+,2Ba+采用相对论校正赝势基组SDD,对C,N,O采用6-311+G(2d)基组,计算研究了气相中碱土金属离子2Sr+,2Ba+催化N2O(X1∑+)+CI(X1∑+)→N2(X1∑+g)+CO2(X1∑+g)反应的微观机理.优化了二重态势能面上各反应物、中间体和过渡...     

Quinoline-based highly selective and sensitive fluorescent probe specific for Cd2+ detection in mixed aqueous media

Quinoline-based fluorescent probe as a recognition unit was designed and synthesized in this study. The probe R1 displayed excellent selectivity and sensitivity for cadmium ions (Cd²⁺) over a wide range of metal ions in acetonitrile-water (MeCN-H₂O) mixed solution. In order to better understand the recognition mechanism between probe and Cd²⁺, the density functional theory calculations were performed. Finally, the colorimetric experiment result was observed and conveniently monitored by the naked eye, and a visual detection limit of 4 × 10^?6 mol L^?1 was achieved. These experimental results indicated the promising potential of the probe to detect Cd²⁺ in biological system. Furthermore, the probe R1 was successfully used for the highly sensitive detection of Cd²⁺ in living cells.     

Potentials of Silver and Gold Electrodes of ZrO2-Based Cells in N2+ O2+ CO2+ CO Gas Mixtures

Steady-state electrode potentials in cells with a ZrO₂+ 10 mol % Y₂O₃electrolyte are measured at 400 to 500°C in nonequilibrium N₂+ O₂+ CO₂+ CO gas mixtures containing 0–3 and 0–10 vol % of CO and O₂, respectively. In CO-free mixtures, the potentials obey the Nernst equation. The CO-caused deviation of the potential from its equilibrium value depends on the O₂content and temperature and is due mainly to the CO adsorption at electrodes.     

CeO2(100)极性面结构与活性的密度泛函理论研究

CeO2是一类使用非常广泛的稀土氧化物催化材料,在许多重要的催化反应过程,如机动车尾气净化、水汽转换、石油裂解等,表现出很高的活性.大量研究表明,CeO2的高活性来源于其表面晶格氧,正是由于这些晶格氧能够直接参与氧化反应,同时反应留下的氧空位又能够被气相氧分子吸附填补,因而体现出很好的储放氧催化性能.目前多数研究采用CO氧化为模型反应,研究了CeO2常见的(111)和(110)晶面的晶格氧活性,但对于其另外一种重要低指数晶面(100)的结构和活性研究却非常有限.需要指出的是,CeO2(100)是一种极性表面,这给该表面的模型构建和理论研究带来了困难.为了深入了解这种极性表面的结构稳定性和催化活性,本文运用在位库仑力校正的密度泛函理论(DFT+U)方法系统研究了CeO2(100)极性面的可能结构及相关稳定性,并且深入分析了CO在该表面上的吸附和反应.本文首先利用板层模型尝试构建稳定的CeO2(100)极性面结构,方法是在保证整个板层化学计量配比完整的前提下,在表层或体相去除氧原子,同时使得整个板层上下对称不存在极性以利于计算.通过计算发现,在CeO2(100)表层分布氧空位的结构比体相中分布氧空位的结构要稳定,同时,氧空位的分布越接近表面,CeO2(100)面的结构稳定性就会越高,其最稳定的结构是将表层满覆盖氧离子移除一半.对CeO2(100)面不同结构的稳定性及相关电子结构分析表明,CeO2(100)表层满覆盖的氧离子间存在很强的相互排斥作用,因此倾向于降低表面氧浓度来提高表面的稳定性.另外,这种相互作用会降低相邻氧离子的价态,并能引起体相铈离子在整体表面维持完整的化学计量比的情况下,仍能出现局域4?电子而被还原为三价铈.随后我们研究了CO在CeO2(100)最稳定和次稳定表面上的氧化反应.发现CO在不同CeO2(100)表面的氧空位处吸附较强,另外,CO在CeO2(100)最稳定结构上可与表面晶格氧反应形成吸附的CO2中间物种,中间物种可直接解离成气相CO2,也可以继续与表面晶格氧反应形成碳酸盐.而在CeO2(100)次稳定表面上,CO很难与表面晶格氧形成吸附的CO2中间态,而直接产生气态CO2.     

La+活化NH3的自旋禁阻反应机理

采用密度泛函理论的UB3LYP方法,计算研究了气相中La+活化NH3的两态反应机理。为了理解由La+活化NH3过程中自旋翻转行为,对自旋态分别为单重态和三重态两个反应势能面进行了计算研究,其结果表明,La+活化NH3的过程是通过自旋态势能面交叉产生的自旋禁阻反应,单、三重态势能面最低能量交叉点(MECP)附近的系间窜越导致H向La+转移和脱H2反应能垒的降低。此外,运用自然键轨道(NBO)布居分析,研究了反应中各个物种的成键特性。所确定的最低能量反应路径为:3La++NH3→3IM1→MECP→1TS12→1IM2→1TS23→1IM3→1LaNH++H2。     

铜催化内炔的硅羧基化反应机理及区域选择性的密度泛函理论研究

用CO₂作为原料,在过渡金属催化下生成新的碳碳键是很重要的.在这类反应中,杂原子官能团和CO₂同时与不饱和的底物被催化生成高功能化的羧酸衍生物已经越来越受到人们的关注.本文采用密度泛函理论(DFT)方法,研究了金属铜催化剂催化内炔的硅羧基化反应机理.根据炔烃上甲基和苯环两个取代基的相对位置,提出了两条反应路径(path I:甲基和path II:苯环).计算结果表明炔烃插入Cu－Si键既是速率决速步骤也是区域选择决速步骤.在path I中,炔烃插入Cu－Si键的自由能为112.8 kJ·mol^-1,而在path II中为127.6kJ·mol^-1.显然, path I比path II在动力学上更有利,这与实验上两条路径对应产物的产率97: 3是一致的.分析表明区域选择性是由炔烃取代基甲基和苯环的电子效应决定的.     

CO2二聚体分子弱结合作用的DFT计算

用密度泛函理论(DFT)的Becke 3LYP方法,在不同基集合（6 31G和6 311G系列）下对平行结构（C 2h）和T形结构(C2v)的CO2二聚体进行ab initio计算.通过计算,得到了CO2二聚体C2h和C2v两种构型的结构参数和离解能,并给出了CO2二聚体相对稳定构型C2h的12个正则振动分析图.结果表明,CO2二聚体的离解能为2 kJ•mol－1,CO2分子之间振动频率很小,从而说明CO2二聚体是弱结合分子.     

Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes

The first sulfite [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ¹:κ²‐SO₃)] (tacn=triazacyclononane) and dithionite [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ²:κ²‐S₂O₄)] complexes of uranium from reaction with gaseous SO₂ have been prepared. Additionally, the reductive activation of CO₂ was investigated with respect to the rare oxalate [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ²:κ²‐C₂O₄)] formation. This ultimately provides the unique S₂O₄^2?/C₂O₄^2? and SO₃^2?/CO₃^2? complex pairs. All new complexes were characterized by a combination of single‐crystal X‐ray diffraction, elemental analysis, UV/Vis/NIR electronic absorption, IR vibrational, and ¹H NMR spectroscopy, as well as magnetization (VT SQUID) studies. Moreover, density functional theory (DFT) calculations were carried out to gain further insight into the reaction mechanisms. All observations, together with DFT, support the assumption that SO₂ and CO₂ show similar (dithionite/oxalate) to analogous (sulfite/carbonate) activation behavior with uranium complexes.