Preparation of gold clusters on metal oxides by deposition-precipitation with microwave drying and their catalytic performance for CO and sulfide oxidation

Gold clusters and small nanoparticles supported on metal oxides could be prepared by deposition‐precipitation followed by microwave irradiation as a drying method and then calcination.The drying method influenced the size of the Au particles.Au(III)was partly reduced during conventional oven drying,resulting in Au aggregates.In contrast,Au(III)was preserved during microwave drying owing to rapid and uniform heating,and the Au diameter was minimized to1.4nm on Al2O3.This method can be applied to several metal oxide supports having different microwave absorption efficiencies,such as MnO2,Al2O3,and TiO2.These catalysts exhibited higher catalytic activities for CO oxidation at low temperature and for selective aerobic oxidation of sulfide than those prepared by conventional methods.

Evolution of catalytic activity driven by structural fusion of icosahedral gold cluster cores

Atomically precise gold cluster catalysts have emerged as a new frontier in catalysis science,owing to their unexpected catalytic properties.In this work,we explore the evolution of the catalytic activity of clusters formed by the structural fusion of icosahedral Au13 units,namely Au25(SR)18,Au38(SR)24,and Au25(PPh3)10(SC2H4Ph)5Cl2,in the oxidation of pyrrolidine toγ-butyrolactam.We demonstrate that the structural fusion of icosahedral Au13 units,forming vertex-fused(vf),face-fused(ff),and body-fused(bf)clusters,can induce a decrease in the catalytic activity in the following order:Aubf>Auff>Auvf.The structural fusion of icosahedral Au13 units in the clusters does not distinguish the adsorption modes of pyrrolidine over the three clusters from each other,but modulates the chemical adsorption capacity and electronic properties of the three clusters,which is likely to be the key reason for the observed changes in catalytic reactivity.Our results are expected to be extendable to study and design atomically defined catalysts with elaborate structural patterns,in order to produce desired products.

Halogen adsorbates on polymer-stabilized gold clusters: Mass spectrometric detection and effects on catalysis

The mass spectrometry of gold clusters stabilized by poly（N‐vinyl‐2‐pyrrolidone） （Au：PVP） re‐vealed the presence of Cl adsorbates derived from synthetic precursors, mainly on the Au34 and Au43 clusters. Changes in the amount of Cl adsorbates on the Au clusters did not affect the catalytic prop‐erties for the aerobic oxidation of benzyl alcohol, suggesting that the Cl atoms were only weakly bound to the Au clusters. In contrast, the replacement of Cl with Br on the Au34 and Au43 clusters significantly suppressed activity, without any influence on the electronic structure. This result indi‐cated that the Br atoms were strongly bound to the Au clusters and sterically blocked their active sites. The substantial reduction of the catalytic activity by the Br adsorbates suggested that the Au34 and Au43 clusters made a major contribution to the catalytic activity of the Au：PVP.

Artificial neural network potential for gold clusters

In cluster science, it is challenging to identify the ground state structures(GSS) of gold(Au) clusters. Among different search approaches, first-principles method based on density functional theory(DFT) is the most reliable one with high precision. However, as the cluster size increases, it requires more expensive computational cost and becomes impracticable.In this paper, we have developed an artificial neural network(ANN) potential for Au clusters, which is trained to the DFT binding energies and forces of 9000 Au N clusters(11 ≤ N ≤ 100). The root mean square errors of energy and force are 13.4 meV/atom and 0.4 eV/A, respectively. We demonstrate that the ANN potential has the capacity to differentiate the energy level of Au clusters and their isomers and highlight the need to further improve the accuracy. Given its excellent transferability, we emphasis that ANN potential is a promising tool to breakthrough computational bottleneck of DFT method and effectively accelerate the pre-screening of Au clusters’ GSS.

DFT Study of Charge Effect on the Odd-even Oscillatory Behavior in Stabilities for Gold Clusters

The comparative study of charge effect on the size-dependence stabilities of gold clusters Aun^z （n = 2-12, z = 0/±1） in gas phase is performed at the M06-L/Lanl2dz level. The lowest-energy structures charged by -1, 0 and ＋1 are optimized. The result shows that the geo- metries of the clusters with over 7 atoms tend to be cake-like. From the two- to three-dimensional geometries, the oscillatory behaviors are exhibited in the structural and electronic properties with the most pronounced in energy gap. The amplitude for the positive clusters is bigger than both the neutral and negative clusters. The neutral clusters with even number of even-coordinated atoms are more stable than the neighbors with odd number of even-coordinated atoms, as is completely reversed for the charged clusters. The oscillatory behaviors for the charged clusters are opposite to that for the neutral clusters, as is attributed to the electron-paired effect.

Design of Support Effect in the Catalytic Application of Ligand-Protect Gold Clusters

Ligand-protected gold(Au_(n))clusters sometimes need the removal of organic ligands to expose more active sites and reduce steric hindrance in catalytic reactions,and large amount of organic and inorganic materials usually need to be employed as supports to anchor Aun clusters through different interaction mechanisms.Whereas,less comprehensive summaries have been provided about the crucial contribution of various supports to the catalytic performance of the supported Aun clusters.Herein,this review firstly summarizes synthesis methods(e.g.,impregnation and encapsulation processes)for the supported Aun cluster catalysts,and then mainly points out specific contributions of support effect in a great diversity of catalytic reactions,as well as deep interaction mechanisms.Besides,opportunities and challenging issues will be stated towards supported Aun clusters,in terms of improving catalytic performance and structural stability of Aun clusters inthedemand of catalysis.

Size hierarchy of gold clusters in nanogold-catalyzed acetylene hydrochlorination

Size hierarchy is a distinct feature of nanogold-catalysts as it can strongly affect their performance in various reactions. We developed a simple method to generate Au n S m nanoclusters of different sizes by thermal treatment of an Au144(PET)60 (PET: phenylethanethiol) parent cluster. These clusters, deposited on activated carbon, exhibit excellent catalytic performance in the hydrochlorination of acetylene. In-situ ultraviolet laser dissociation high-resolution mass spectrometry of the parent cluster in the presence of acetylene revealed a remarkable cluster size-dependence of acetylene adsorption, which is a crucial step in the hydrochlorination. Systematic density functional theory calculations of the reaction pathways on the differently-sized clusters provide deeper insight into the cluster size dependence of the adsorption energies of the reactants and afforded a scaling relationship between the adsorption energy of acetylene and the co-adsorption energies of the reactants (C_(2)H_(2) and HCl), which could enable a qualitative prediction of the optimal Au n S m cluster for the hydrochlorination of acetylene.

Intercluster aurophilicity-driven aggregation lighting circularly polarized luminescence of chiral gold clusters

Herein,we prepared two novel pairs of enantiomeric gold cluster complexes,AU4PL4/Au4PD4 and(Au4L4)n/(Au4D4)n with atomic precision.In Au4PL4/Au4PD4,the discrete chiral Au4-based aggregation-induced emission(AIE)luminogens are separated by bulky substitutes.The corresponding aggregates are cyan-emitting with a photoluminescence quantum yield(PLQY)of 14.4%.Upon decreasing the size of the substituents,these chiral Au4 clusters are strung together by inter-cluster Au-Au interactions,which cause a low-energy green emission from the aggregated(Au4L4)n/(Au4D4)n with a much higher PLQY of 41.4%and more intense circularly polarised photoluminescence(CPL)with a dissymmetry factor|gPL|of 7.0×10^−3.Using(Au4L4)n/(Au4D4)n,circularly polarised organic light-emitting diodes(CP-OLEDs)were for the first time fabricated with|gEL|=|gPL|.These findings signify that inter-cluster metallophilic interactions are a new and important type of driving force for AIE and crystallization-induced emission(CIE),suggesting great potential of CPL-active metal clusters in CP-OLEDs.

Broken electron transfer pathway in enzyme:Gold clusters inhibiting TrxR1/Trx via cell studies and theory simulations

Thioredoxin reductase 1(TrxR1)is over activity in tumor cell to maintain their redox balance.Although gold clusters have great potential in antitumor drug as they could well inhibit TrxR1,the molecular mechanism has not been disclosed yet.In this work,we revealed gold clusters can well inhibit the activity of TrxR1 in lung tumor cells and further disclosed the inhibition mechanism by using computational simulation methods.We firstly inferred the binding sites of gold in the hydrophobic cavities on TrxR1.The simulation results show that the gold ion(released from Au cluster)interact with–SH of Cys189 in TrxR1,this greatly increase the distance between the C-terminal redox center of TrxR1 and the Trx redox center,thereby destroy the electron transfer pathway between them.Our electron transfer destroying mechanism is different from the previous hypothesis that gold binds to the Sec498 of TrxR1 which has never been proved by experimental and theory studies.This work provides a new understanding of the gold clusters to inhibit TrxR1 activity.

One-dimensional chains of gold clusters on the surface of highly oriented pyrolytic graphite

We have investigated the growth of gold nanoclusters on the surface of highly oriented pyrolytic graphite in ultrahigh vacuum. Studies of ultrahigh vacuum scanning tunneling microscopy revealed that the size distribution of gold clusters was very narrow and quasi-one-dimensional chains of gold nanoclusters of approximately 2 nm diameter were produced after being annealed at 74°C. Unlike the results obtained by previous workers, these chains of gold clusters were not formed along steps on the substrate surface, and some of them could even go across monoatomic steps. The orientation of chains of gold clusters was also dependent on the size of gold nanoclusters. These results suggest the viability of a new route to the creation of ordered nanoscale structures.

Ion-Pairing Chirality Transfer in Atropisomeric Biaryl-Centered Gold Clusters

The stereocontrol of chiral metal clusters and nanoclusters has become a focus of interest in metal cluster chemistry due to their promising applications in asymmetric catalysis.Despite being a general chirality transfer strategy,the ion-pairing process is still ambiguous in the course of bestowing chirality to metal clusters.Here we construct a biaryl-centered axially chiral gold-cluster system to study an outside-in ion-pairing chirality transfer process.Four hexanuclear gold(I)clusters,centered by two types of biaryl ligands[(2-indolyl)aniline(L^(1))and biindole(L^(2))],were synthesized via in situ cyclization reactions.In the crystalline state,the biaryl centers showed axial chirality in which the gold atoms were in an asymmetric arrangement.In solution,the chiral phosphates induced an outside-in chirality transfer by significant interactions with the periphery of the biaryl-centered gold clusters.Finally,the chiral resolution of hexa-aurated biindoliums was accomplished via an efficient outside-in chirality transfer process relying on strong aurophilic interaction and extra peripheral coordination.This study not only deepens the understanding of the outside-in ion-pairing chirality transfer process but also provides a new approach for fabricating desired chiral metal clusters by a combination of organometallic transformation and chirality transfer.

Synthesis of Subnanometer-Sized Gold Clusters by a Simple Milling- Mediated Solid Reduction Method

An effective solvent-free method based on a solid-reduction process was developed to fabricate ultrafine gold catalysts. By this method we revealed a strong size-dependent activity of Au species in which subnanometer-sized clusters exhibited the best activity in the hydrogenation of CO_2 to formate, with a turnover number of up to 9278 over 7 h at 90 ℃.

Geochemical and Geostatistical Studies for Estimating Gold Grade in Tarq Prospect Area by K-Means Clustering Method

Tarq geochemical 1:100,000 Sheet is located in Isfahan province which is investigated by Iran’s Geological and Explorations Organization using stream sediment analyzes. This area has stratigraphy of Precambrian to Quaternary rocks and is located in the Central Iran zone. According to the presence of signs of gold mineralization in this area, it is necessary to identify important mineral areas in this area. Therefore, finding information is necessary about the relationship and monitoring the elements of gold, arsenic, and antimony relative to each other in this area to determine the extent of geochemical halos and to estimate the grade. Therefore, a well-known and useful K-means method is used for monitoring the elements in the present study, this is a clustering method based on minimizing the total Euclidean distances of each sample from the center of the classes which are assigned to them. In this research, the clustering quality function and the utility rate of the sample have been used in the desired cluster (S(i)) to determine the optimum number of clusters. Finally, with regard to the cluster centers and the results, the equations were used to predict the amount of the gold element based on four parameters of arsenic and antimony grade, length and width of sampling points.

Density functional study on structural and electronic properties of bimetallic gold-yttrium clusters: comparison with pure gold and yttrium clusters

Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Aun-1Y（n≤9） bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au-Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Aun-1Y structures are found in an early appearance starting at n=5 （Au4Y）. Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO LUMO gap of Au3Y is the biggest in all the doped Aun-1Y（n≤9） bimetallic clusters.

O_(2)在金团簇阳离子上的吸附:键合强度和活化程度的分析

本文结合团簇反应动力学实验和量子化学计算,研究了O_(2)在金团簇阳离子上的吸附与活化.实验发现,在温和条件下,Au_(10)^(+)能快速吸附单个O_(2)分子形成Au_(10)O_(2)^(+);Au_(2)^(+)和Au_(4)^(+)的反应性则较低,但相应的氩络合物Au_(2)ArO_(2)^(+)和Au_(4)Ar_(1,2)O_(2)^(+)很容易形成;除此之外,其他尺寸的团簇都表现出反应惰性.理论计算表明,O_(2)倾向于以端接的方式吸附在具有线型或平面型结构的Au_(n)^(+)(n=2~7)簇和Au_(8)^(+)的平面异构体上,并表现出极低的活化程度吸附在具有三维结构的Au_(n)^(+)(n=9,11,13)簇上的O_(2)也呈现出类似的特征。与此形成鲜明对比的是,在Au_(8)^(+)的三维异构体和n=10,12,14的偶数大尺寸Au_(n)^(+)上,O_(2)倾向于以侧向桥接的方式吸附并被高度活化.理论预测的O_(2)在团簇上的键合强度结合动力学因素影响,合理地解释了实验中观察到的反应产物Au_(2,4,10)O_(2)^(+),Au_(2)ArO_(2)^(+)和Au_(4)ArO_(2)^(+).

Effective removal of the protective ligands from Au nanoclusters by ambient pressure nonthermal plasma treatment for CO oxidation

We used a dielectric barrier discharge(DBD)plasma technique to eliminate the protective ligand of ZnAl-hydrotalcite-supported gold nanoclusters.We used X-ray powder diffraction,ultraviolet-visible spectrophotometry,thermogravimetric analysis,and high angle annular dark-field-scanning transmission electron microscopy characterization to show that the samples pretreated with/without DBD-plasma displayed different performances in CO oxidation.The enhanced activity was obtained on the plasma-treated samples,implying that the protective ligand was effectively removed via the plasma technique.The crystal structure of the plasma-treated samples changed markedly,suggesting that the plasma treatment could not only break the chemical bond between the gold and the protective agent but could also decompose the interlayer ions over the hydrotalcite support.The particle sizes of the gold after DBD-plasma treatment implied that it was a good way to control the size of the gold nanoparticles under mild conditions.

Density-functional investigation of 3d,4d,5d impurity doped Au_6 clusters

The general features of the geometries and electronic properties for 3d, 4d, and 5d transition-metal atom doped Au6 clusters are systematically investigated by using relativistic all-electron density functional theory in the generalized gradient approximation （CGA）. A number of structural isomers are considered to search the lowest-energy structures of M@Au6 clusters （M=3d, 4d and 5d transition-metal atoms）, and the transition metal atom locating in the centre of an Au6 ring is found to be in the ground state for all the M@Au6 clusters. All doped clusters, expect for Pd@Au6, show large relative binding energies compared with a pure Au7 cluster, indicating that doping by 3d, 4d, 5d transition-metal atoms could stabilize the Au6 ring and promote the formation of a new binary alloy cluster.

Machine learning potential aided structure search for low-lying candidates of Au clusters

A machine learning(ML)potential for Au clusters is developed through training on a dataset including several different sized clusters.This ML potential accurately covers the whole configuration space of Au clusters in a broad size range,thus expressing a good performance in search of their global minimum energy structures.Based on our potential,the low-lying structures of 17 different sized Au clusters are identified,which shows that small sized Au clusters tend to form planar structures while large ones are more likely to be stereo,revealing the critical size for the two-dimensional(2D)to three-dimensional(3D)structural transition.Our calculations demonstrate that ML is indeed powerful in describing the interaction of Au atoms and provides a new paradigm on accelerating the search of structures.

Application of K-means and PCA approaches to estimation of gold grade in Khooni district(central Iran)

Grade estimation is an important phase of mining projects, and one that is considered a challenge due in part to the structural complexities in mineral ore deposits.To overcome this challenge, various techniques have been used in the past. This paper introduces an approach for estimating Au ore grades within a mining deposit using k-means and principal component analysis(PCA). The Khooni district was selected as the case study. This region is interesting geologically, in part because it is considered an important gold source. The study area is situated approximately 60km northeast of the Anarak city and 270km from Esfahan. Through PCA, we sought to understand the relationship between the elements of gold,arsenic, and antimony. Then, by clustering, the behavior of these elements was investigated. One of the most famous and efficient clustering methods is k-means, based on minimizing the total Euclidean distance from each class center. Using the combined results and characteristics of the cluster centers, the gold grade was determined with a correlation coefficient of 91%. An estimation equation for gold grade was derived based on four parameters: arsenic and antimony content, and length and width of the sampling points. The results demonstrate that this approach is faster and more accurate than existing methodologies for ore grade estimation.

Synthesis and Crystal Structure of a New Mo/Au/S Cluster [Et_4N][Mo_2S_4(AuPPh_3)(edt)_2]· 0.25Et_2O·0.25MeOH(edt=Ethanedithiolate)

Reactions of the preformed cluster precursor [Et4N]2[Mo2S2（μ-S）2（edt）2] （edt = ethanedithiolate） （1） with [Au（PPh3）Cl] in MeOH/MeCN gave rise to a new heterobimetallic Mo/Au/S cluster [Et4N][Mo2S4（AuPPh3）（edt）2]·0.25Et2O·0.25MeOH （2·0.25Et2O·0.25MeOH）. It was characterized by elemental analysis, IR spectrum and X-ray analysis. 2·0.25Et2O·0.25MeOH crystallizes in the monoclinic system, space group C2/c with a = 20.117（4）, b = 9.2705（19）, c = 44.418（9） A^°, β= 93.19（3）°, V = 8271（3） A^°^3, Z = 8, Dc = 1.794 g/cm^3, T = 193 K, C31.25H43AuMo2NO0.50PS8, Mr = 1116.96, F（000） = 4380, μ（MoKa） = 4.603 mm^-1, S = 1.019, R = 0.0672 and wR = 0.1708 for 7243 observed reflections with I 〉 2σ（I）. The anion of 2 consists of a butterfly-shaped Mo2S4Au core in which one [AuPPh3]^＋ cation is coordinated by one bridging S and two terminal S atoms of the [（edt）2Mo2（S）2（μ-S）2] moiety. The Au（I） center adopts a pseudo-tetrahedral coordination geometry, and the Au-S bond lengths vary from 2.425（2） to 2.898（3）A^°.