Ni3Al合金液态与非晶中的原子团簇

采用常温常压分子动力学模拟技术，模拟了液态Ni3Al中原子团簇在快速凝固条件下的演变过程，模型采用的是TB(tight binding)作用势.用偶分布函数、键对和多面体等结构参数来描述快速凝固条件下团簇种类和数量的变化，并将团簇结构可视化.在2 000 K下，液态Ni3Al中团簇数量较少，且都是由缺陷二十面体构成；在4×1013 K•s－1的冷速下，团簇的数量随温度的降低不断增加，且出现完整二十面体团簇，体系最终形成了由二十面体和缺陷二十面体团簇网络所组成的非晶结构.     

[BxAl13-x]-(x=0～13)二元团簇的密度泛函理论研究

采用遗传算法（Genetic algorithm,GA）对B-Al二元团簇[B_xAl_13-x]^-（x=0～13）进行了全局结构搜索,并在密度泛函理论（Density Functional Theory,DFT）下对其进行了优化计算. 结果表明在二元团簇中,随着硼原子的数量逐渐增加,团簇的结构由二十面体（3D）逐渐转化为准平面（2D）且团簇结构由B与Al原子的比例所决定的. 当x=0～7时,Al原子占多数,团簇保持3D结构;反之团簇呈现2D构型;在x=7～8时,团簇的结构发生由3D向2D的转变. 能量决定着团簇的稳定性（例如相对能量）. 能量越小,其结构越稳定. 在计算相对能量E_rel,当x=1时,其相对能量最低,团簇结构最稳定. 为了进一步了解团簇的稳定性,计算了[B_xAl_13-x]^- 团簇的HOMO-LUMO能级差（E_H-L）和垂直电离能（Vertical Detachment Energies,VDE）,并且发现它们的值在整体上是随着B原子数量的增加而减小,表明其团簇的稳定性逐渐减弱. 在所有的团簇中,BAl₁₂^-的能级差最大,结构最稳定. 因此文章中对其进行了分子轨道分析,发现当一个B原子替代了Al₁₃^-团簇中的中心Al原子时,所得到的BAl₁₂^-的电子壳层结构的1s²和1p⁶几乎和Al₁₃^-团簇保持一致. 此外,对于x=13时的准平面全硼团簇B₁₃^-,文章中用适应性自然密度划分（Adaptive Natural Density Partitioning,AdNDP）对其化学成键进行了分析,结果显示B₁₃^-有8个π电子,具有π反芳香性.     

液态Ca7Mg3合金快速凝固过程中团簇结构的形成特性

采用分子动力学方法对液态Ca7Mg3合金凝固过程中团簇结构的形成特性进行了模拟研究. 采用双体分布函数、Honeycutt-Andersen(HA)键型指数法、原子团类型指数法(CTIM)以及遗传跟踪等方法对凝固过程中团簇结构的形成演变特性进行了分析. 结果表明: 在以冷速为1×1012 K·s-1 的快速凝固条件下, 系统形成以1551、1541、1431键型为主的非晶态结构; 二十面体基本原子团(12 0 12 0)在快速凝固过程中对非晶态结构的形成起决定性作用; 在合金凝固过程中, 团簇的稳定性不仅与构成团簇的基本原子团类型有关, 还与中心原子类型以及中心原子之间的连接方式有关. 由于(12 0 12 0)基本原子团能量较低并且在低温具有较好的遗传特性, 基本原子团之间很容易连接在一起组成更大的团簇. 所形成的团簇结构显著不同于那些由气相沉积、离子溅射等方法所获得的团簇结构.     

Au_(5~25)Pd团簇结构与性质的理论研究

用basin-hopping算法结合密度泛函PBE方法系统搜索了Au5~25Pd团簇的全局稳定结构,并对团簇几何结构,稳定性,Fermi能级,化学硬度和前线轨道进行了分析。计算结果表明,Au5Pd,Au7Pd和Au11Pd团簇为平面结构,其他团簇均为立体结构,与相同原子数纯金团簇结构类似。所有团簇中,Pd原子均位于配位数较高位置。团簇平均结合能随金原子数增大而逐渐增大,并有收敛到某点的趋势。偶数金原子团簇较相邻的奇数金原子团簇稳定。团簇的Fermi能级随团簇增大呈奇偶振荡,偶数金原子团簇的Fermi能级较相邻奇数金原子团簇的低,与金团簇Fermi能级变化类似。Au7Pd,Au12Pd,Au16Pd和Au18Pd团簇化学活性较高。Au5~19Pd团簇中Pd原子优先与CO,烯烃,炔烃等分子形成配位键。CO等小分子仍然吸附到Au20~25Pd团簇的顶点或面中心的金原子。     

Sc12Co和Sc12Ni团簇的几何结构、磁性和光谱特性的理论研究

基于密度泛函理论和卡利普索结构预测方法,在B3PW91/LanL2DZ水平下,系统研究了Sc₁₃,Sc₁₂Co和Sc₁₂Ni团簇的几何结构、磁性和光谱特性.结果表明,Sc₁₃基态拥有高对称性的二十面体I_h点群对称结构,Sc₁₂Co和Sc₁₂Ni团簇基态结构是分别以Co和Ni为中心的畸变二十面体结构.基于上述基态结构,电荷转移分析发现电荷从Sc原子向Ni或Co原子转移.磁性分析表明Sc₁₃团簇的高磁性主要源于Sc—Sc之间的铁磁性耦合和较大的自旋劈裂.对于Sc₁₂Co和Sc₁₂Ni团簇,Sc—Ni和Sc—Co各原子之间的反铁磁性耦合、较小的自旋劈裂及原子间的电荷转移量是磁性偏低的原因.而且,总磁矩主要来源于Sc-3d轨道上的自旋磁矩贡献,4s和4p轨道上的自旋磁矩贡献非常小.最后,研究发现Sc₁₂Co和Sc₁₂Ni团簇的红外和拉...     

正二十面体Au13和Pt13团簇上肉桂醛的吸附

运用广义梯度近似(GGA)密度泛函理论的Perdew-Burke-Ernzerh (PBE)方法, 研究了肉桂醛在正二十面体Au₁₃和Pt₁₃团簇上的吸附行为. 通过分析不同吸附模式的吸附能和几何构型发现: 同一金属团簇, 顺式肉桂醛的吸附能强于反式肉桂醛的吸附能. 对于Au₁₃团簇, 肉桂醛的稳定吸附构型为C＝C和C＝O共吸附模型; 对于Pt₁₃团簇, 肉桂醛的稳定吸附构型为C＝O吸附. 比较二者发现, 肉桂醛在Pt₁₃团簇的吸附能力强于Au₁₃团簇.分析Au₁₃和Pt₁₃团簇上肉桂醛最稳定吸附构型的电子结构表明, 电子由肉桂醛原子的2s、2p轨道向金属表面转移, 同时金属部分电子反馈到肉桂醛的反键轨道, 最终肉桂醛稳定吸附于金属团簇. 此外, 肉桂醛在团簇模型上的吸附能大于其在平板模型上的吸附能.     

锗分族元素二元团簇及其与Co形成的团簇离子

通过比较激光烧蚀E1/E2 (代表Ge/Sn， Ge/Pb和Sn/Pb) 和Co/E (E为Ge、Sn、Pb)混合样品形成的二元团簇负离子飞行时间质谱分布和谱峰的相对强度及形成的幻数团簇离子峰，发现E1/E2二元团簇离子中原子量大的锗分族元素在团簇离子中占主要组分，而原子量小的元素则少量掺杂，其组成和分布特点说明其结构和性质与纯E团簇离子相似，可能的结构为该类负离子团簇所有原子都在笼结构的骨架上；对于二元团簇离子GeSn9－、GePb9－和SnPb9－其结构可能是双帽反四棱柱构型，只是每个原子均为骨架的一部分.而对激光烧蚀过渡金属钴与锗分族元素的混合物的研究发现，反应形成了丰富的Co/E二元合金团簇负离子，分析发现该类簇离子为钴内包覆于E(锗分族元素)笼状结构.幻数离子CoGe10－、CoSn10－和CoPb10－可能具有双帽四角反棱柱结构，而CoPb12－可能具有二十面体构型，钴原子均为笼状结构的中心.     

银团簇结构与特性的分子动力学研究

用分子动力学方法模拟了银团簇的结构与力能学.计算模拟中使用了一种基于第一性原理的原子间互作用多体势函数.通过分子动力学模拟确定了银微团簇(原子个数3～13)的稳态结构;模拟了原子个数为13～141的银FCC晶体结构理想球形团簇的力能学,发现球形银团簇形成三雏紧密结构;计算了平均结合能,给出了结合能随团簇原子数N的变化图,发现随N增大团簇结合能逐渐接近块材的数值.     

金团簇二十面体结构融合过程中其催化活性的演变（英文）

近年来,由有机配体保护的原子精确金属团簇在合成方面已取得了重要进展,其独特的原子结构对一些化学反应产生独特的催化效果.原子精确的团簇催化剂明显不同于纳米颗粒催化剂和单原子催化剂,是一种关联均相和多相的、原子数目确定、尺寸均一、结构精确的新型催化剂.从原子尺度上精确构筑团簇催化剂,探究亚纳米尺度的微观结构对催化性能的影响,为常规催化剂所未能解决的关键科学问题提供解决的机会,为在分子尺度上揭示催化作用机制以及准确关联催化剂结构与催化性能提供新的研究体系,具有重要的科学研究意义.本文设计和使用了三种结构精确的金团簇催化剂,即Au_(25)(PPh_3)_(10)(SC_2H_4Ph)_5Cl_2, Au_(38)(SC_2H_4Ph)_(24)和Au_(25)(SC_2H_4Ph)_(18),分别由二十面体结构的Au_(13)单元通过中心顶点融合、面融合、体相融合形成的(简写为Au_(vf)、Au_(ff)和Au_(bf)),详细研究了这三个金团簇催化剂在二十面体Au_(13)单元的结构融合过程中,其催化活性的演变规律.在催化吡咯烷与O_2反应制备γ-丁内酰胺反应中,金团簇催化剂的催化活性顺序为Au_(bf)Au_(ff)Au_(vf),表明这三个金团簇中Au_(13)单元的结构随着点、面、体的融合,其催化活性随之增加.同时研究发现,对于同一个Au团簇催化剂,其表面硫醇配体的烷基链越短,其催化活性越高,这主要是由于短链硫醇分子的空间位阻较小,吡咯烷分子更容易进入催化剂的金表面,接触到活性位点,进行催化反应.实验表明,三个团簇金原子均带正电荷,正价金物种可能是催化吡咯烷与O_2反应的催化活化物种.研究发现, Au_(bf)团簇表面的活性位数目高于Au_(ff)和Au_(vf)团簇的,因此Au_(bf)的催化活性最高;同时,团簇表面配体的烷基链越短,其表面活性位数目也越多,这也进一步解释了表面硫醇配体的烷基链越短,其相应的金团簇催化剂的催化活性越高的原因.吡咯烷与O_2在金团簇上反应的可能路径为O_2在Au活性位上裂解的O原子和吡咯烷β-H转移至Au活性位的β-H反应脱水后形成亚胺,亚胺经过水解进一步氧化得到产物.这项研究将为在原子层次上调变金属团簇催化剂的结构进而改变其催化性能提供新的思路,对精准设计和构筑高效催化剂具有一定的科学指导意义.     

荷电(±1)对二十面体X_(13)(X=Cr,Mn,Fe,Co)团簇的稳定性与磁性的影响

采用基于密度泛函理论的计算方法,对正二十面体金属X13(X=Cr,Mn,Fe,Co)中性和荷电团簇进行了全面的结构优化计算,研究了荷电对团簇的稳定性和磁性的影响.结果表明:荷负电能够使团簇的稳定性增强;荷电对不同团簇的原子间距离的影响不同;同时荷电对不同团簇磁性的影响也是不一样的,尤其是荷负电能够使Fe13和Co13团簇的磁性大大增强;荷电对不同团簇磁性的影响不是通过原子间距离的变化来实现的,而是受到原子内部电荷的转移和杂化程度的影响.     

Stability of small Pdn (n=1-7) clusters on the basis of structural and electronic properties: a density functional approach

Density functional calculations within the generalized gradient approximation have been used to investigate the lowest energy electronic and geometric structures of neutral, cationic, and anionic Pd(n) (n=1-7) clusters in the gas phase. In this study, we have examined three different spin multiplicities (M=1, 3, and 5) for different possible structural isomers of each neutral cluster. The calculated lowest energy structures of the neutral clusters are found to have multiplicities, M=1 for Pd(1), Pd(3), Pd(5), Pd(6), and Pd(7), while M=3 for Pd(2) and Pd(4). We have also determined the lowest energy states of cationic and anionic Pd(n) (n=1-7) clusters, formed from the most stable neutral clusters, in three spin multiplicities (M=2, 4, and 6). Bond length, coordination number, binding energy, fragmentation energy, bond dissociation energy, ionization potential, electron affinity, chemical hardness, and electric dipole moment of the optimized clusters are compared with experimental and other theoretical results available in the literature. Based on these criteria, we predict the four-atom palladium cluster to be a magic-number cluster.     

嵌入Y型分子筛中钯簇合成与结构的研究

Pd clusters encaged in Y-zeolite (Pd0Y) have been prepared by means of exchanging zeolite HY with [Pd(NH3)4]2+ under microwave radiation. The product formed was deaminized by heating, washed sufficiently with de-ionized water and reduced with hydrogen. The crystal phase diffraction of Pd was not found in the XRD spectrogram of Pd0y. According to polycrystal X-ray diffraction data. Radial Electron Distribution Function (REDF) of Pd0Y was calculated to elucidate the structure of Pd cluster. The results show that the Pd clusters are of the Al type closely packed arrangement. The dimension of them is about 12 Å. They are encaged in the supercage of zeolite Y. Their occupancy on the supercage is as small as 0.06 so that the framework structure of zeolite Y is unchanged. Therefore, the high dispersing Pd cluster aggregating in supercage exhibit strong catalytic effect. The CO-conversion of Pd0Y with Pd 0.72% and 6.13% (in mass fraction) is 67 % and 100 % (in volume fraction) respectively. Evaluation conditions:
mixed gas containing 0.02% CO and air,
space velocity 3000 h-1,
reaction temperature 0 ℃.     

Influence of phosphorus concentration on the state of the surface layer of Pd–P hydrogenation catalysts

Phase composition and surface layer state of the Pd–P hydrogenation catalyst formed at various P/Pd ratios from Pd(acac)₂ and white phosphorus in a hydrogen atmosphere were determined. Palladium on the catalyst surface is mainly in two chemical states: as Pd(0) clusters and as palladium phosphides. As the P/Pd ratio increases, the fraction and size of palladium clusters decrease, and also the phase composition of formed palladium phosphides changes: Pd₃P_0.8 → Pd₅P₂ → PdP₂. The causes of the modifying action of phosphorus on the properties of palladium catalysts for hydrogenation of unsaturated compounds were considered.     

Reactions of carbon monoxide with free palladium oxide clusters: strongly size dependent competition between adsorption and combustion

The gas phase reactions of carbon monoxide with small mass-selected clusters of palladium, Pd(x)(+) (x = 2-7), and their oxides, Pd(x)O(+) (x = 2-7) and Pd(x)O(2)(+) (x = 4-6), have been investigated in a radio frequency ion trap operated under multi-collision conditions. The bare palladium clusters were found to readily adsorb CO yielding a highly size dependent product pattern. Most interestingly, the reactions of the pre-oxidized palladium clusters with CO lead to very similar product distributions of Pd(x)(CO)(z)(+) complexes as in the case of the corresponding pure Pd(x)(+) clusters. Consequently, it has been concluded that the investigated palladium oxide clusters efficiently oxidize CO under formation of the bare clusters, which further adsorb CO molecules yielding the previously observed Pd(x)(CO)(z)(+) product complex distributions. This CO combustion reaction has been observed even at temperatures as low as 100 K. However, for Pd(2)O(+), Pd(6)O(+), Pd(6)O(2)(+), and Pd(7)O(+) a competing reaction channel yielding palladium oxide carbonyls Pd(x)O(CO)(z)(+) could be detected. The latter adsorption reaction may even hamper the CO combustion under certain reaction conditions and indicates enhanced activation barriers involved in the CO oxidation and/or the CO(2) elimination process on these clusters.     

Formation of nanoarchitectures including subnanometer palladium clusters and their use as highly active catalysts

Subnanometer Pd clusters stabilized within micelles of random copolymers were formed by direct immobilization of Pd(0) via ligand exchange. The clusters were estimated to contain approximately seven Pd atoms on average (cluster diameter approximately 0.7 nm). Several Pd-containing micelle morphologies could be obtained by polymer cross-linking. These micelles containing Pd clusters were demonstrated to be efficient catalysts for hydrogenations and Heck reactions.     

Oxidation state and symmetry of magnesia-supported Pd13O(x) nanocatalysts influence activation barriers of CO oxidation

Combining temperature-programmed reaction measurements, isotopic labeling experiments, and first-principles spin density functional theory, the dependence of the reaction temperature of catalyzed carbon monoxide oxidation on the oxidation state of Pd(13) clusters deposited on MgO surfaces grown on Mo(100) is explored. It is shown that molecular oxygen dissociates easily on the supported Pd(13) cluster, leading to facile partial oxidation to form Pd(13)O(4) clusters with C(4v) symmetry. Increasing the oxidation temperature to 370 K results in nonsymmetric Pd(13)O(6) clusters. The higher symmetry, partially oxidized cluster is characterized by a relatively high activation energy for catalyzed combustion of the first CO molecule via a reaction of an adsorbed CO molecule with one of the oxygen atoms of the Pd(13)O(4) cluster. Subsequent reactions on the resulting lower-symmetry Pd(13)O(x) (x < 4) clusters entail lower activation energies. The nonsymmetric Pd(13)O(6) clusters show lower temperature-catalyzed CO combustion, already starting at cryogenic temperature.     

The Pb12(2-) and Pb10(2-) zintl ions and the M@Pb12(2-) and M@Pb10(2-) cluster series where M = Ni, Pd, Pt

Ethylenediamine (en) solutions of K4Pb9 react with toluene solutions of ML4 (M = Pt, Pd, L = PPh3; M = Ni, L2= COD) and 2,2,2-crypt to give M@Pb12(2-) cluster anions (M = Pt (1), Pd (2), Ni (3)) as the [K(2,2,2-crypt)]+ salts in low (Ni) to good (Pt) yields. The ions have near perfect Ih point symmetry and have been characterized by X-ray diffraction, 207Pb NMR and LDI-TOF mass spectrometry studies. For M = Ni, the primary product formed is the D4d Ni@Pb10(2-) cluster that has also been structurally characterized. The M@Pb10(2-) clusters (M = Pd, Pt) and the new Zintl ions closo-Pb10(2-) and closo-Pb12(2-) were formed in the gas phase but have not been detected in solution or the solid state. The structural trends of these series of clusters have been investigated through DFT calculations. The Ni@Pb10(2-) cluster is dynamic on the 207Pb NMR time scale at -45 degrees C and 104.7 MHz. The M@Pb12(2-) ions show unusually deshielded 207Pb NMR chemical shifts that presumably arise from sigma-aromatic effects associated with their high symmetries. In the solid state, the salts form superlattices of cations and anions (e.g. the AlB2 lattice of [K(2,2,2-crypt)](2)[Pt@Pb12]) and are prototypes for "assembled cluster materials".     

Energy-Dispersive XAFS Studies on the Spontaneous Dispersion of PdO and the Formation of Stable Pd Clusters in Zeolites

Spontaneous dispersion and clustering processes of Pd were measured by means of the energy-dispersive EXAFS method. The spontaneous dispersion of bulky metal Pd into highly dispersed PdO was directly observed on the H-type zeolite in the atmosphere of O2. In contrast to H-type zeolites, simple oxidation of the agglomerated Pd was observed on Na-ZSM-5. The structural change of Pd was followed in the atmosphere of hydrogen. The clustering processes of metal Pd depended on the kind of zeolite, and these were categorized into three groups. The first group, i.e., Na-ZSM-5 and H-beta, showed monotonic agglomeration of metal Pd by increasing the reduction temperature. The second group consisted of H-ZSM-5 and H-mordenite where the formation of Pd6 clusters was found. On these zeolites, the generation of Pd6 clusters was reversibly observed upon the repetition of reduction and oxidation treatments. The third group consisted of H-Y and USY zeolites where the formation of Pd13 clusters was observed. From these findings, it was concluded that the crystal structure and acid sites of zeolites had profound influences on the dynamic behavior and the genesis of Pd clusters with various structures.     

One-pot, high-yield synthesis of titanate nanotube bundles decorated by Pd (Au) clusters for stable electrooxidation of methanol

Titanate nanotube bundles assembled by several simple nanotubes were synthesized through a simple reaction between TiO₂ crystallites and highly concentrated NaOH in the presence of Au or Pd sols. Due to the unique scrolling growth mechanism of titanate nanotubes (TNTs), Au or Pd clusters were encapsulated in situ by TNTs, and titanate/Au and titanate/Pd nanotube bundles were formed. In comparison with carbon nanotubes (CNTs) or active carbon that was widely used as carriers to support metal clusters, TNTs bundles can immobilize the metal clusters tightly and overcome the shortcoming of exfoliation of metal clusters from the carriers. The as-prepared titanate/metal hybrids possess mesoporosity and high surface area. The electrochemical oxidation of methanol demonstrates that titanate/Pd hybrids exhibit high electrocatalytic activity and excellent stability, and hence they should be ideal catalyst candidates in direct methanol fuel cells (DMFCs).     

Evidence for Pdx(CO)y compound formation on an alumina substrate

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 × 10¹³ atoms s⁻¹ cm⁻² onto an alumina substrate (90 K) at a pressure of 2 × 10⁻⁶ mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 × 10¹⁴ Pd atoms cm⁻² and 1.4 × 10¹⁶ Pd atoms cm⁻². The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.