纳米金催化一氧化碳氧化反应的理论研究

近年来,纳米金催化剂独特的催化性质,特别是其优异的低温催化氧化活性,引起了人们极大的研究热情.除低温选择氧化外,在精细化学品合成、大气污染物消除、氢能的转换和利用等领域也开发出了一系列有广泛应用前景的金催化反应.此外,体相金的化学惰性和纳米金的超高活性之间差异的“鸿沟”也引起了理论工作者浓厚兴趣,试图从原理上理解体相金和纳米金活性差异的根源. CO催化氧化是最具有代表性的研究金催化活性的化学反应,本文主要综述了近十多年来金催化 CO氧化反应理论计算方面的研究工作.一般认为, CO在纳米金表面的吸附是 CO氧化反应的初始步骤.密度泛函理论研究表明, CO在金表面的吸附强度主要与被吸附金原子的配位数有关：金配位数越低, CO的吸附能越强,部分研究结果表明两者之间存在近似的线性关系.我们研究发现, CO吸附强度也与被吸附金周围配位金原子的相对位置有关,其中位于正下方的配位金原子加强 CO吸附,而位于侧位的配位金原子则弱化 CO吸附,这显然削弱了 CO吸附与金配位数线性关系的可靠性.理论研究表明,在纯金表
　　面上 O2吸附强度一般很弱,只有在一些特殊结构的金团簇上才有较强的吸附,但在 Au/TiO2界面及 CeO2表面上 O2吸附较强.金表面原子氧的吸附和金的表面结构有关.我们发现,原子氧倾向于在金的表面形成一种线性的 O–Au–O结构以增加其稳定性.当金表面的氧覆盖度增大时,会形成一种金氧化物薄膜结构,其结构依赖于氧的化学势和金的表面结构.纳米金催化 CO氧化反应机理可能因体系、载体等的差异而不同.大部分理论计算结果表明,在纯金表面上 O2很难直接解离形成原子氧,因此反应机理可能是吸附的 CO先与 O2反应形成了一种 CO–O2中间体,然后解离形成 CO2.在 Au/TiO2和 Au/CeO2催化剂上 CO催化氧化机理争议很大,均有计算结果支持 LH机理和 M–vK机理.另外,根据实验上观察到了负载型纳米金能直接活化分子氧的结果,理论上也提出了分子氧先解离为原子氧再与 CO反应的氧解离机理.针对如何解离分子氧问题,人们分别提出了低配位金模型、正方形金结构模型、Ti5c模型及 Au/Ti5c模型等.我们也提出了一种独特的双直线 O–Au–O模型来理解 Au/TiO2或 Au/CeO2界面解离活化分子氧.理论计算结果表明,低配位的金,金和载体之间的电荷转移,以及金所表现出的强相对论效应对于纳米金的活性影响很大.需要特别指出的是,金的强相对论效应有助于理解金表面的 CO吸附与金配位的关系、金表面原子氧的吸附特性、金氧化物薄膜的结构和分子氧的活化等过程.我们认为,金的强相对论作用导致了体相金的化学惰性以及纳米金的活性,因此相对论效应的深入研究将有助于理解金催化 CO氧化反应机理,从而有助于深层次理解纳米金催化活性来源.     

聚合物稳定的金簇合物上卤素吸附质：质谱检测及其对催化的影响

聚(N-乙烯基-2-吡咯烷酮)稳定的金簇合物(Au：PVP)的质谱结果表明,来源于合成前驱体的Cl吸附质主要存在于Au34和Au43簇合物上。金簇合物上Cl吸附质的数量不影响其催化有氧苯甲醇氧化性能,表明Cl原子与Au簇合物间存在较弱的键合作用。相反,用Br替代Au34和Au43簇合物上Cl显著抑制了其催化活性,但对其电子结构没有任何影响。这表明, Br原子与金簇合物的键合较强,在空间上堵塞了活性位。因Br吸附质而导致活性显著下降表明, Au34和Au43簇合物对Au：PVP催化活性起主要贡献。     

聚合物稳定的金纳米簇催化:理论计算与实验的相互影响（英文）

平均粒径为2–10 nm的聚合物稳定的Au纳米簇(NCs)表现出独特的催化性能.多个研究表明,影响聚合物稳定的AuNCs催化活性的主要因素为:AuNC尺寸的控制、聚合物的选择以及反应条件的优化.这是由于聚合物稳定的AuNCs在多个催化反应中表现出明显的尺寸效应,其催化活性也因所采用的聚合物和反应条件的不同而不同.为了阐明影响聚合物稳定的AuNCs催化活性的内在原因,众多研究者关注于聚合物稳定的AuNCs催化中的理论计算与实验的相互影响.本文主要总结了聚合物稳定的AuNCs中这种相互影响的研究进展.     

沉积-沉淀-微波干燥法制备金属氧化物负载的金簇合物及其在CO氧化和 硫化物氧化反应中的催化性能

采用沉积-沉淀法再辅以微波干燥和焙烧制备了金属氧化物负载的金簇合物和小的金纳米粒子.干燥方法影响了金颗粒尺寸.在炉干燥过程中Au(III)因部分还原而致使Au聚集.相反,在微波干燥下,因快速和加热均一而使Au(III)得以保持,在Al2O3上负载的Au颗粒尺寸小至1.4 nm.该法可用于具有几种不同微波吸收效率的金属氧化物载体,如MnO2,Al2O3和TiO2.这些催化剂在低温CO氧化和硫化物选择有氧氧化反应中的催化活性比常规方法制备的更高.     

基于金纳米簇检测碘单质的荧光分析方法研究

以蛋白质保护的金纳米簇Au NCs@BSA作为荧光探针,高灵敏地检测碘含量。结果表明,碘单质可引起金纳米簇的荧光猝灭,在2.0 nmol/L~35μmol/L浓度范围内具有良好的线性响应关系,检出限为1.8nmol/L。利用建立的方法对水样中的碘单质进行定量测定,并与ICP-MS检测结果进行对比,结果证明该方法在实际样品的检测中具有应用潜力。同时基于Au NCs@BSA与碘浓度的依赖效应,改变温度,诱导荧光响应变化,利用热力学计算,深入探讨了Au NCs@BSA与碘单质之间的作用机理,圆二色谱与红外光谱的结果表明碘单质引起的配体BSA的蛋白二级结构变化,诱导了Au NCs@BSA的荧光猝灭。该文的机理研究为无机小分子与蛋白质保护的金纳米簇之间的相互作用提供了参考。     

金红石纳米团簇与铀酰离子界面作用理论研究

为探索无机氧化物矿物质与锕系物种的界面作用和成键本质,设计优化了实验已知稳定的金红石(110)表面纳米团簇(SNCs).计算表明中性和弱酸性溶液中的sol模型比pH较小情况下的sat模型吸附更有利,与实验观察到的提高溶液pH导致铀酰吸附速率降低的结果相一致.能量分解表明,界面吸附主要以轨道吸引作用为主,并伴有少量空间效...     

基础实验:金纳米粒子的制备及其光学性质

围绕金纳米粒子前沿内容,设计了一个简易的本科生基础实验,利用柠檬酸钠还原氯金酸法制备分散性好的金纳米粒子溶液,讨论了其尺寸与颜色的关系,探究了不同电解质和非电解质对金纳米粒子团聚及其颜色的影响,初步了解金纳米粒子的光学特性和探针效应基本原理。     

基于纳米金与纳米银簇间表面等离子增强能量转移效应特异性检测microRNA

microRNAs(miRNAs)的灵敏检测对临床诊断具有十分重要的意义.本研究采用偶联DNA聚合酶和核酸内切酶介导的恒温扩增反应实现靶标循环再生的策略,利用纳米金(AuNPs)与纳米银簇(AgNCs)间表面等离子增强能量转移效应,开发了一种miRNA定量检测方法.在AuNPs表面组装两种探针(Probe a和Probe b)制备响应元件Probe b-Probe a-AuNP,其中Probe a通过3′端巯基共价偶联到AuNPs表面,此外具有靶标miRNA互补序列、核酸内切酶酶切序列和Probe b互补序列,Probe b为荧光AgNCs合成模板.靶标miRNA存在时,启动酶级联恒温扩增反应,导致Probe b脱离AuNPs表面,抑制了Probe b为模板合成的AgNCs与AuNPs间表面等离子增强能量转移效应,使得反应体系荧光信号增强.本方法的检出限为2.5×10-11 mol/L,与miRNAs商业化检测试剂盒相比,避免了逆转录反应,而且操作简单,检测成本低,可应用于生物样本中miRNAs分析.     

两亲性杂壳聚合物粒子的高效制备及以其作为模板合成金纳米簇合物

将等质量的嵌段聚合物聚乙烯基萘聚丙烯酸和聚氧化乙烯聚丙烯酸（P2VN-b-PAA和PEO-b-PAA）溶解于N,N′-二甲基甲酰胺(DMF)中,加入小分子二元胺（1,2-丙二胺,PDA）,制备出均匀的两亲性杂壳聚合物纳米粒子(MSNPs)。 该粒子以PEO和P2VN混合嵌段为壳层,非共价键交联的PAA嵌段为核,在水相及有机相中均可稳定分散,具有典型的两亲性特点。 扫描电子显微镜和光散射测试结果表明,该杂壳聚合物粒子(MSNPs)的粒径在300 nm左右,分布较均匀,并显示出壳层可塌缩变形的疏松核（软粒子）特征。 以该聚合物粒子(MSNPs)为模板,可以方便制备出金纳米粒子簇合物。     

Theoretical study of correlations between the coordination structures and catalytic activities in polymer-stabilized au nanocluster catalysts

Au nanoclusters (Au NCs) stabilized by poly(N-vinyl-2-pyrrolidone) and poly(allylamine), abbreviated to Au:PVP and Au:PAA, catalyze the aerobic oxidation of p-hydroxybenzyl alcohols, but the catalytic activity of Au:PVP is much higher than that of Au:PAA. To elucidate the correlations between the catalytic activities and coordination structures of the stabilizing polymer, the substrate accessibility on Au NCs was estimated by density functional theory (DFT) and molecular dynamics (MD) calculations. For MD simulations, we applied a systematic method to optimize the temperature parameters in temperature replica exchange molecular dynamics (T-REMD), and the coordination structures were comprehensively classified by multivariate analysis. The results show that the number of open active sites on the Au NCs is a good index for predicting the catalytic activities. © 2018 Wiley Periodicals, Inc.     

Quantum-chemical calculations of the dissociation energy of the C-H bond in hydrocarbons,alcohols, and ethers

The dissociation energy of the C-H bonds in hydrocarbons, alcohols, and ethers were calculated by semiempirical MNDO, AM1, and PM3 methods. The average error of calculations of theD(C-H) values by using various quantum-chemical methods is 1.3 kcal mol^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2858–2861, December, 1996.     

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (2S1/2 electron state)

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (²S_1/2 electron state) were carried out by the Becke-Lee-Yang-Parr density functional method using the Dunning-Hay LanL2DZ basis set. Optimum geometric parameters and electronic characteristics of MCl _n (H₂O) _m ⁿ (n=1–4 andm=0,4,5) complexes were determined. In each of the considered series the spin, population on the central metal atom decreases as its atomic number increases. The energy of transition of the unpaired electron to the lowest unoccupied MO decreases in the same order. The unpaired electron occupies an orbital that is mostly a linear combination of the s-orbital of the metal atom and the p-orbital of the Cl atom (the antibonding σ-orbital of the M−Cl bond). Distinctions in the changes in spectral properties of aquacomplexes and chloride complexes in isoelectronic series, observed as the degree of oxidation of the metal atom increases, were explained. The results of calculations are in agreement with the experimental data obtained by ESR and optical spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1049–1055, June, 1999.     

Characterization of additives in plastics: From MS to MS10 multistep mass analysis and theoretical calculations of tris(2,4‐di‐tert‐butylphenyl)phosphate

In the analysis by electrospray (+) of an extract of hemp sprouts put in a polypropylene vial, we found a large contamination of a plastic additive. It was characterized by multiple‐stage MSⁿ experiments (MS ÷ MS¹⁰) and identified as tris(2,4‐di‐tert‐butylphenyl)phosphate, also known with the synonyms F32IRS6B46, oxidized Naugard 524, and others. The MS² ÷ MS⁷ spectra are characterized by consecutive eliminations of six isobutene molecules from the tert‐butyl moieties, some of them also occurring in the ion source. The first three are calculated to occur preferentially from the ortho positions, whereas eliminations from the para positions are estimated to be less favored at about 5–6 kcal/mol in each step. Once the first three isobutene molecules are eliminated, the remaining three are lost from the tert‐butyl moieties in para positions (MS⁵ ÷ MS⁷), yielding protonated triphenylphosphate, whose structure has been confirmed by the MS² spectrum of triphenylphosphate standard: the latter spectrum is almost superimposable with the MS⁸ spectrum of the analyte under investigation. MS⁸ and MS⁹ spectra show main losses of water and C₆H₄ molecules. The MS¹⁰ spectrum of precursor ions at m/z 215 shows the gas‐phase addition of water and methanol and ions at m/z 168, attributable to the loss of a phosphorus oxide radical. Density functional theory (DFT) calculations (Becke 3LYP [B3LYP] 6‐311+G(2d,2p)) have been used to evaluate structure and stability of different ionic and neutral species involved in the decomposition pathways and to calculate thermochemical data of the decomposition reactions. This multistep mass analysis combined with theoretical calculations resulted to be particularly useful and effective, yielding chemical, thermochemical, and mechanistic data of significant utility in the structural characterization and identification of the unknown analyte as well as to define its gas‐phase reactivity under a multistep low‐energy collision‐induced dissociation regime.     

Convergence of the Rayleigh—Ritz method in self-consistent-field and multiconfiguration self-consistent-field calculations

We investigate the analytical convergence of SCF and MCSCF calculations, when the dimension of the subspaces to which the orbitals are restricted tends to infinity. We show that the completeness only inL ²(R ³;C ²) of the orbital bases does not ensure the convergence of the Ritz-energy, neither in SCF nor in MCSCF calculations, but that this convergence — as well as the convergence of the Ritz-orbitals in SCF calculations — is on the contrary guaranteed if the orbital bases are complete in the Sobolev spaceW ^1,2(R ³;C ²). Some consequences on the choice of the orbital exponents of Slater and Gauss functions are also discussed.     

ChemInform Abstract: Structures and Bonding of Auropolyboroenes [Au2(B4)xB3]‐, [Au2(B4)xB2]2‐ and [Au2(B4)xB]+(x = 2, 3): Comparison with Dihydride Polyboroenes.

Equilibrium structures of title ions are determined by DFT calculations (TPSS with the τ‐dependent gradient‐corrected functional as implemented in the GAUSSIAN09 code).     

Peculiarities of atomic interaction in organic molecules of 3- and 4-coordinated phosphorus using ab initio calculations and Cl NQR

The results of ab initio calculations at the MP2/6-31G(d) level of molecules of the series ClPXX′ (X, X′=C₂H₅, N(CH₃)₂, OCH₃) and ClP(M)XX′ (M=O, S; X=CH₃, ?CH₃; X′=C₂H₅, OCH₃) with total optimization of their geometry were presented. They were compared with the obtained earlier results of such calculations at the RHF/6-31G(d) level and with experimental ³⁵Cl nuclear quadrupole resonance (NQR) spectra for these compounds. MP2/6-31G(d) calculations confirm non-inductive influence of heteroatoms on the geminal Cl atom in the non-linear three-atomic Cl–P–M groups. They agree to the conclusion that the abnormal correlation of the ³⁵Cl NQR frequencies for the compounds studied at different X, X′ and M is caused, in general, by the P–Cl bond polarization under the action of the geminal atom partial charges directly through the field. The satisfactory conformity between the experimental ³⁵Cl NQR frequencies and those estimated from 3p-components of the Cl atom valence p-orbitals calculated at the MP2/6-31G(d) level was obtained.     

ChemInform Abstract: Interplay of Orbital and Relativistic Effects in Bismuth Oxyhalides: BiOF,BiOCl, BiOBr,and BiOI.

Study by using hybrid DFT with explicit treatment of spin—orbit coupling effects and dispersion interactions.     

Effect of intramolecular interaction between polar and polarizable bonds on13C shielding constants in different conformations of 2-methoxy- and 2-vinyloxynaphthalene molecules: Anab initio study

Shielding constants of¹³C nuclei calculated for different conformations of 2-methoxynaphthalene and 2-vinyloxynaphthalene molecules by the GIAOab initio method in the D95^** basis set indicate a strong shielding effect of the intramolecular interaction between the polar O−C bond of the substituent and the polarizable π-bond of the naphthyl moiety on the C atom incis-position. The results obtained are in agreement with the experimentally found trends of changes in the chemical shifts of¹³C nuclei and are in reasonable quantitative agreement with experimental data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1066–1069, June, 1999.