Atoms In Cluster Research Articles

Host–Guest Ensemble Effect on Dual-Pt atom-on-Rh Nanosheets Enables High-Efficiency and Anti-CO Alkaline Hydrogen Oxidation

Explicit atomic coordinations of binary metal atoms on low-dimensional host–guest-type bimetallic nanomaterials can arouse unique ensemble effects and significantly improve the catalysis performances, but they confront a formidable challenge in chemical synthesis. Here, we draw on a thermoinduced secondary crystallization process of preprepared amorphous/crystalline hybrid ultrathin Rh nanosheets (NSs) to capture Pt atoms into the two-dimensional (2D) Rh lattice, by which precisely controlled Pt atomic dispersions from a single atom to dual atoms and to clustered atoms can be facilely elected and embedded into the ultrathin Rh hosts. Among them, the dual-Pt atom-on-Rh (denoted as Pt2–Rh) NSs exhibit an extremely high activity and an excellent CO tolerance for the alkaline hydrogen oxidation reaction (HOR), achieving a 18.5 times higher mass activity at 50 mV overpotential than that of commercial Pt/C. Theoretical studies indicate that the host–guest ensemble effect aroused by the specific pairwise Pt2-on-Rh coordination feature can moderately enhance both the surface *H and *OH bindings, which synergistically lower the free energy of the rate-determining Volmer step and thus promote the combination of neighboring *H and *OH to form H2O. Enhanced *H adsorption can also prevent the main available sites from being occupied by hydroxyl groups in alkaline conditions. The free energy diagram and anti-CO experiments coherently indicate that the oxidation of *CO by neighboring *OH to form *COOH is kinetically more favorable to proceed on the Pt2–Rh NSs, effectively preventing the catalysts from being poisoned. This work sheds light on the ensemble effect of host–guest heteroatom coordinations for designing high-efficiency alkaline HOR catalysts.

Quantum chemical study of structural, linear, and nonlinear optical response of pure silver clusters Agn (n = 2–10)

In this study, pure silver clusters Agn (n = 2–10) through a density functional method is explored to analyze the structure-property relationship with the linear and nonlinear optical response. The total density of state (TDOS), photoelectron spectra (PES) and non-covalent interaction (NCI) analyses are also performed to get structural information regarding the bonding environment. New energy levels developed as the silver atoms in higher clusters which are indicated by lowering the HOMO energy level. Among these clusters, Ag5 and Ag9 showed unusual behaviour with higher first hyperpolarizability values (1076 and 2223 au, respectively). The results of hyperpolarizability are compared with the external reference molecule para-nitroaniline (p-NA). Additionally, a two-level model has been applied to rationalize the first hyperpolarizability. The primary outcomes of this study enable the scientist to use silver clusters for photovoltaic applications or as a dopant to enhance the nonlinear optical response.

Bifunctional photocatalyst with tailored interface scale for cooperative glycerol selective oxidation and H2 evolution

AbstractWe propose to fabricate a bifunctional photocatalyst for cooperative glycerol selective oxidation and H2 evolution. The key role of interface scale (nanometer, subnanometer, or atomic level) on tuning catalysis performance was revealed. Specifically, series Pt/defective TiO2 with tailored interface scale were constructed by loading Pt nanoparticle, cluster, and single atom on VTi‐enriched TiO2. It was uncovered that reducing interface scale could largely improve the visible‐light utilization efficiency, the photoexcited electron–hole separation, and well tuned the band structure. It could also enhance the metal–support interaction and thus adjust the chemical behavior toward reactant molecules. The optimized isolated Pt/defective TiO2 with atomic‐level interface achieved 90.6% glycerol conversion and 87.2% C3 products selectivity, accompanied by 7250.4 μmol g−1 H2 accumulative yield. It also exhibited long‐term stability of 36 h without performance loss. Besides, the dominate active site was identified and the possible reaction mechanism was illustrated combined with Density Functional Theory (DFT) calculation and quasi in situ experiments.

On the angular distributions of atoms sputtered by gas cluster ion beam

The angular distributions of atoms sputtered by the noble gas cluster ion beam from metal surfaces are studied. The experimental results on the angular distributions of Cu and W atoms sputtered by 10 keV Ar, Kr, and Xe GCIB are presented. The deviation from the conventional « lateral » angular distribution, found in previous works was studied in detail with new experimental data.The molecular dynamics simulations are performed for the detailed study of the mechanisms that affect the angular distributions. The simulation of consequent impacts considered the effects of the bombarding cluster ion fluence and cluster size distribution. The significant effect of energy per cluster atom on the angular distributions was revealed and explained. Both the cluster size distribution and the surface topography were found to affect the angular distributions of sputtered atoms. The mechanisms of these effects were analyzed.

The highest oxidation state observed in graphene-supported sub-nanometer iron oxide clusters

Size-selected iron oxide nanoclusters are outstanding candidates for technological-oriented applications due to their high efficiency-to-cost ratio. However, despite many theoretical studies, experimental works on their oxidation mechanism are still limited to gas-phase clusters. Herein we investigate the oxidation of graphene-supported size-selected Fen clusters by means of high-resolution X-ray Photoelectron Spectroscopy. We show a dependency of the core electron Fe 2p3/2 binding energy of metallic and oxidized clusters on the cluster size. Binding energies are also linked to chemical reactivity through the asymmetry parameter which is related to electron density of states at the Fermi energy. Upon oxidation, iron atoms in clusters reach the oxidation state Fe(II) and the absence of other oxidation states indicates a Fe-to-O ratio close to 1:1, in agreement with previous theoretical calculations and gas-phase experiments. Such knowledge can provide a basis for a better understanding of the behavior of iron oxide nanoclusters as supported catalysts.

Analysis of Metal Clusters Based on Graph-Theoretic Interpretation of the Lowest Occupied Molecular Orbital

Molecules can be regarded as a kind of graph with atoms as vertices and bonds as edges. Therefore, it is possible to discuss the physical properties and reactivity of various molecules by applying the ideas of graph theory and network theory. Such research has flourished in the field of chemical graph theory. In this manuscript, it is shown that the lowest occupied molecular orbital (LOMO) can be interpreted graph theoretically as eigenvector centrality. This is one measure of centrality that characterizes the importance or influence of a node on a network. As such, LOMO coefficient can be regarded as a manifestation of centrality in an aggregate of atoms, indicating which atom plays the most important role in that aggregate or has the greatest influence on the atom network. Using such properties of LOMO, an analysis of the network of metal atoms in metal clusters is performed. The predictability of the binding energies of the constituent atoms of the metal clusters using LOMO coefficients is discussed.

Quantification of the atomic surfaces and volumes of a metal cluster based on the molecular surface model

The atomic volume and surface are important geometric quantities for calculating various macroscopic physical quantities from atomistic models. This paper proposes a new analytical method to calculate the atomic volumes and surfaces of a metal cluster. This method adopts metallic radii to describe atom sizes and constructs the overall volume/surface by the molecular surface (MS) model. It divides cluster atoms into two types: interior atoms and boundary atoms. For an interior atom, the method defines a variational Voronoi cell as its volume. For a boundary atom, the method defines the intersection of the overall cluster volume and its variational Voronoi cell as its volume. The atomic surfaces are calculated along with the volume calculations. Compared with other methods, the new method considers the effect of atom sizes and does not rely on the size and location of the simulation box. Therefore, the new method can accurately calculate the overall volume of a metal cluster of arbitrary shape and the individual atomic volumes. This method provides computational support for multiscale coupled calculations from the microscale to macroscale.

Electronic properties and adsorption mechanism of Ru-doped copper clusters towards CH3OH molecule: A DFT investigation

In this study, we have investigated the stability and electronic properties of the CunRu (n = 2–10) nanoclusters and their interaction with the CH3OH molecule without and with the presence of O2 molecule by using DFT calculations with TPSS/SDD/6-311g(d,p) level of theory. Based on the second energy difference (Δ2E), the results reveal that the CunRu (n = 4, 6 and 8) clusters are relatively more stable than their neighboring clusters. The values obtained for the Fukui function (f-) proves that the Ru atom in the CunRu clusters is an excellent adsorption site for the molecules. The interaction of the CunRu clusters with CH3OH molecule exhibits that the Ru atom is the preferred adsorption site for the CH3OH molecule, where the O atom of the CH3OH molecule is strongly chemisorbed onto the Ru site of the clusters, forming a strong bond between the Ru and O atoms. The copper sites of the clusters were found less preferred for the adsorption of CH3OH, and the complexes formed between both species are less stable than those obtained from the CH3OH chemisorption over the Ru site of the clusters. The interaction of CH3OH with the clusters was also evaluated in an oxidizing environment, and the results obtained reveal that the molecule is greatly chemisorbed over the ruthenium site with adsorption energies which vary from – 1.18 to – 2.05 eV. In the presence of the oxygen, the gap energy of the clusters was sharply changed after their interactions with the CH3OH molecule, suggesting that these clusters can easily detect the above molecule with great sensitivity. Therefore, the presence of the oxygen not only does not prevent the adsorption process, but it considerably promotes the CH3OH chemisorption onto the ruthenium site of the clusters and therefore significantly rises their sensitivity performance. In conclusion, the CunRu clusters could be employed as effective nanosensors for the CH3OH molecule detection.

Electronic State of Arsenic <i>endo</i>-atom and indices of interatomic bonds in[As@Ni<sub>12</sub>As<sub>20</sub>]<sup>3-/0</sup>, As<sub>20</sub>, Ni<sub>12</sub>As<sub>20</sub>, As@C<sub>60</sub>, and As@C<sub>70</sub> Clusters

The DFT PBE0/SDD method was used to calculate bond lengths and bond indices in As20, Ni12As20, [As@Ni12As20]3-, As@C60 and As@C70 clusters. The degrees of oxidation and reduction of the endo -atom and the shell are expressed in terms of the populations of one-electron states localized in these components of the complexes. Each As atom in clusters has a entirely localized lone electron pair. The arsenic atom inside fullerenes retains the electronic configuration and spin of the ground state of the free As atom. Inside the [Ni12As20]6- shell, it has an oxidation state of 3+. There is no covalent bond between the endo -atom and the shell in clusters. The bond indices refute the opinion about the “onion” structure of [As@Ni12@As20]3-: the nickel atoms are not bonded to each other, the As-As bond indices are three times lower than in As20.

A comparative ab initio study of acetylene activation over Au9 cluster and Au9 supported over ZnO monolayer

A plane wave density functional theory has been employed to investigate acetylene activation over Au9 cluster and the same supported over single layer ZnO. Adsorption of C2H2 over gold clusters adopts the π mode and σ mode. The σ mode of adsorption is preferable as two C atoms bind to least coordinated Au atoms in Aun cluster. Adsorption energy of C2H2 over Au9 is increases from 0.47 eV to 0.87 eV when Au9 is supported on the ZnO single layer.Significantly lower activation energy barrier for acetylene activation (0.08 eV) has been found for Au9/ZnO in comparison to the same over Au9 cluster (2.14 eV). The lowering in the activation energy barrier is attributable to the reduction of Au9: The underlying ZnO monolayer transfers electronic charge to Au9 and thereby reduces it. It is supported by upshift in the Fermi level of the ZnO single layer by 0.47 eV towards higher energies upon hosting Au9. These results provide useful pointers in optimizing the catalytic processes via an appropriate choice of support for metal clusters serving as catalysts.

First principles study of coherent electron/spin transport across metallothionein: A cadmium-binding protein

Metallothioneins (MTs) play an important role in controlling the concentration of heavy metals in the body by forming metal-thiolate clusters. In addition, the proteins can scavenge free radicals, to exhibit an antioxidant effect. To clarify the precise physiological function of these proteins, it is necessary to examine the non-equilibrium state of electron/spin transport in the molecule. In this study, coherent spin transport in MTs connected to metal electrodes has been calculated to examine the behavior of the molecule toward spin flow (radicals) in the body. The estimated values of conductance were found to be very low, while the spin polarization appears to derive considerable spin filtering. Furthermore, spin polarization did not localize on cadmium but on the sulfur atoms of cadmium-thiolate clusters. These results confirmed that cysteine plays an important role in the scavenging of free radicals even when forming the cadmium-thiolate cluster.Significance Statement.The purpose of this study is to better understand how spin polarization (induced radical) flows in metallothionein, even if it forms cadmium-thiolate clusters. This is important because it can be known where the radical is stored and processed in the body. Our results provide a guide to examine non-equilibrium electron transient in the metallothionein by observing the single-molecule electric conduction with scanning tunneling microscope.

States of silicon nanoclusters containing carbon impurities

The structural and electronic states of defective complexes in the Si29 cluster with the participation of carbon and hydrogen atoms were determined by the method of non-conventional strong binding (MNSB) in combination with the method of molecular dynamics. It is shown that carbon atoms in silicon clusters form a bridge bond with two silicon atoms and localized in a hexagonal position at the center of the cell, forming a defect of the Si29 : Ci type. The introduction of hydrogen into a silicon cluster results in the formation of a defective Ci-H-Si complex and a decrease of binding energy of the Si29 : Ci defect. Based on the calculations, it was found that presence of leads to carbon gives shallow levels in the band gap of nano-silicon, and the defective carbon-hydrogen complex in a hydrogenated cluster, depending on the charge state of the defective complex. Moreover this exhibits both deep and shallow levels. Keywords: MD and MNSB methods, silicon nano-clusters, hydrogenated cluster, structural defects, ab initio methods, carbon and hydrogen atoms, spatial structure, shallow and deep levels.

Состояния кремниевых нано-кластеров, содержащих примеси углерода

Abstract The structural and electronic states of defective complexes in the Si29 cluster with the participation of carbon and hydrogen atoms were determined by the method of non-conventional strong binding (MNSB) in combination with the method of molecular dynamics. It is shown that carbon atoms in silicon clusters form a bridge bond with two silicon atoms and localized in a hexagonal position at the center of the cell, forming a defect of the Si29:Ci type. The introduction of hydrogen into a silicon cluster results in the formation of a defective Ci-H-Si complex and a decrease of binding energy of the Si29:Ci defect. Based on the calculations, it was found that presence of leads to carbon gives shallow levels in the band gap of nano-silicon, and the defective carbon-hydrogen complex in a hydrogenated cluster, depending on the charge state of the defective complex. Moreover this exhibits both deep and shallow levels.

In English

It is known that the addition of a small amount of carbon nanomaterials significantly improves the mechanical properties of composites with a metal matrix. One of the most important, promising and available metals as a matrix for such modification is aluminum. However, at the interface between the carbon material and Al, aluminum carbides of different composition are formed, which are brittle and have the main disadvantage - solubility in water. Therefore, the appearance of aluminum carbide is a serious problem, since it contributes to the formation of defects, which, when the composite is deformed, leads to cracking of the composite due to the presence of microneedles. In this regard, in order to predict the features of the interaction of aluminum itself with the surface of carbon nanomaterials, it is advisable to model such processes using quantum chemistry methods. The aim of the work was to reveal the effect of temperature on the chemical interaction of aluminum clusters with native, boron-, silicon-, and nitrogen-containing graphene-like planes (GLP). All the calculated by three methods (B3LYP/6-31G(d,p), MP2/6-31G(d,p) and PВЕ0/6-31G(d,p)) values of the dependence of the Gibbs free energy on temperature for different cluster sizes of aluminum and graphene-like clusters are the highest for native graphene-like planes. In all cases, the values of the Gibbs free energy increase with temperature. The lowest values of the temperature dependence of the Gibbs free energy vary as dependent on the size of the reactant models and research methods, this is especially characteristic of the presence of boron and silicon atoms in the graphene-like clusters. Therefore, the absence of heteroatoms in the composition of the nanocarbon matrix contributes to the fact that aluminum carbide islands should not be formed in the carbon-containing nanocomposite with aluminum, which negatively affects the physical and chemical characteristics of the resulting nanocomposite.

Atomically dispersed Pt in ordered PtSnZn intermetallic with Pt−Sn and Pt−Zn pairs for selective propane dehydrogenation

With the surge of shale gas, propane dehydrogenation becomes increasingly important to synthesize propylene. Herein, a new type of ordered PtSnZn intermetallic clusters (∼0.9 nm) supported on Al2O3 was synthesized by a stepwise approach including electrostatic adsorption and temperature-programmed reduction. The structure of the PtSnZn clusters results from a kinetically controlled process, and Pt atoms in the PtSnZn clusters are well isolated by Sn and Zn with Pt−Sn and Pt−Zn pairs. The PtSnZn/Al2O3 catalyst exhibits excellent catalytic performance for propane dehydrogenation, which achieves ∼100% propylene selectivity and keeps a high propane conversion (>40%) during stability testing. The catalytic performance of PtSnZn/Al2O3 is also significantly higher than that of Pt/Al2O3, PtSn/Al2O3, and PtZn/Al2O3. Experiments and theoretical calculations indicate that the Sn 5p and Zn 4s orbitals are hybridized with Pt 5d by forming Pt−Sn and Pt−Zn pairs, which leads to the d band center of Pt deviating from Fermi level (−2.81 eV). The shift of the Pt d band center significantly decreases the adsorption energy of propylene and prohibits further dehydrogenation, resulting in high propylene selectivity and stability.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2 (Ag52, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5 (Ag53, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52 and Ag53 have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

Small palladium clusters and their adducts with atomic oxygen

A systematic investigation on small Pdn clusters (n = 1 ÷ 8) and their interaction with atomic oxygen was conducted at DFT level. A model to describe cohesive energy for small sized clusters based on a topological approach was proposed and validated. On the basis of the bond length, the stabilisation electronic energy and the second electronic energy difference variation analysis, Pd4 and Pd6 were identified as the most stable clusters. The Natural Bond Orbital (NBO) analysis and the plot of the Molecular Electrostatic Potential (MEP) – both performed for the first time – indicated that the Pd atoms in clusters were not equivalent in terms of atomic charge, population and electron configuration. The plots of the MEP mapped on the electron density also revealed its non-uniform character; areas of positive MEP were found around the Pd atoms, which may undertake nucleophilic attacks. Subsequently, the interaction of atomic oxygen with Pdn clusters was systematically studied, accounting for different possible anchoring positions. The hollow site was revealed to be the most favourable one. The increase in number of Pd atoms favoured higher spin states. Pd6O was identified as the most oxidised and energetically stable cluster. The calculated binding energy value of oxygen (3.5 eV) was in agreement with the Temperature Programmed Desorption (TPD) experimental results conducted on Pd(1 1 0) single-crystal surface. The NBO analysis evidenced that the occupancy of 2 s (2p) orbital of O decreased (increased) as the number of Pd atom increased. The negatively charged Pd atoms had a larger population of 4d orbitals than the neutral or positively charged ones. The interactions between O and Pd atoms were dominated by d-type orbitals.

Controlling sintering and carbon deposition with post-coated MgO confined group VIII metal-based catalysts towards durable high-temperature steam reforming

Metal-sintering and carbon-deposition are two bottlenecks in hydrocarbon (e.g., n-dodecane) steam reforming for hydrogen production. Effective inhibition of carbon-deposition by MgO-pre-coating support was intensively confirmed. Unfortunately, we found that weak interaction between Rh-NPs and MgO-pre-coating-CZO induced serious metal-sintering (4→47 nm). To materialize bifunctional suppression, MgO-post-coating confined metal-NPs strategy is proposed. Under the conditions of 700 °C, WHSV = 10 h−1, and S/C = 3 for 50 h, negligible metal-sintering (4→7 nm) and carbon-deposition (0.7 mg C/g cat.) occurred for 5%MgO-1%Rh-Ce0.75Zr0.25O2, whereas Rh-NPs grew to 36 nm and carbon-deposition was 25.6 mg C/g cat. for 1%Rh-Ce0.75Zr0.25O2. Owing to enhanced metal-support-interaction, formed MgO/Rh/CZO interfaces, and increased proportion of Rh0, 5%MgO-1%Rh-Ce0.75Zr0.25O2 showed superior performance. DFT-based calculation results unveiled that MgO-post-coating increased the desorption energies of Rh cluster (0.21→3.29 eV) and individual atoms (3.89→4.35 eV). This study provides an efficient route for realizing sintering resistances of supported metal catalysts in high-temperature hydrothermal atmosphere.

Sm cluster on hexagonal boron nitride supported by Ir(111): Formation of magnetic cluster superlattice Sm13[formula omitted]h-BN[formula omitted]Ir(111)

The goal toward the ultimate density limit of magnetic information storage is now focused on the creations of identical magnetic clusters as well as their arrangements on a template surface for obtaining an equidistant, monodisperse and equally oriented pattern. To achieve this goal, the combination of rare-earth (RE) cluster and specific template is a viable route, e.g., h-BN monolayer on Ir(111) surface within a corrugated moiré structure (h-BN|Ir(111)) can act as a promising template to steer the intrinsically magnetic RE cluster in a well-defined orientation. Combining abinito molecular dynamic (AIMD) simulation and spin–orbital coupling density function theory (DFT) calculations, we report that magnetic Sm13 cluster can be stably deposited at the pore region of h-BN|Ir(111) template. The low-lying moiré region potential of h-BN|Ir(111) template, stable icosahedron structure of Sm13 cluster, and strong hybridization of Sm-5d6s orbitals with B/N-sp orbitals, play the synergetically roles to form Sm13@h-BN|Ir(111) cluster superlattice. The local magnetic moments of Sm atoms in Sm13 cluster are found to be robust against the structural configuration, localized site and inter-atom magnetic coupling, because their highly localized 4f states hybridize less with the spd states. Nevertheless, different deposition orientations and consequently the altered bonding interactions between Sm atoms and h-BN monolayer lead to different magnetic orders among Sm atoms. The appearances of large magnetic moment and giant magnetic anisotropy energy (MAE) of Sm13 cluster as well as its high deposition stability render Sm13@h-BN|Ir(111) for potential application of magnetic storage.

Geopolymer Stabilization as Novel Technique of Reducing Carbon Dioxide Emissions

The paper discusses geopolymerisation which is a chemical reaction within an alkaline solution as well as a solid reaction of both aluminium and silicon. It highlights the origin of silicates, pozzolanic composite or alumino-silicates that could be melted within alkaline solution that may be utilized as a source of geopolymers creation. Materials that possess plenty aluminium, silicon and others such as metakaolin, microsilica, pozzolanas, ashes, red mud, kaolin clay and slags can be used as raw materials with the activators to create geopolymers. Also geopolymer end product after the exothermic procedure carried out via oligomers, as well as three stages of geopolymerisation which are suspension, when hard or solid alumino-silicates matter and stuff is dissolved because of the occurrence of water together with alkali activator. After jettisoning a small quantity of water, the reorientation outsets, and then the cluster atoms take their position in the structure. In the course of the solidification at 200C (twenty Celsius degree) or higher temperature of roughly 10000C, the water (H2O) is almost absolutely jettisoned and the material displays his final look.