Interaction Of Metal Clusters Research Articles

Modulation of graphene and graphdiyne by metaln (n = 1–5) adsorption and nucleation and the effect on hydrogen evolution reaction

Comprehending the interaction of metal clusters with two-dimensional (2D) carbon materials at the atomic level is important for the rational design of relative materials for various applications. The geometrical and electronic modulation of graphene and graphdiyne (GDY) by the adsorption and nucleation of Cun, Irn, and Pdn (n = 1–5) and the effect on hydrogen evolution reaction (HER) were studied employing dispersion-corrected density functional theory methods. The bonding strength between the metal Mn (n = 1–5) clusters and the considered 2D materials generally followed the order of Irn-substrate > Pdn-substrate > Cun-substrate. The modified electronic properties induced by the metal decoration affected the H adsorption. According to the Sabatier’s principle, the Mn@graphene present better HER catalytic properties than the pristine graphene, while the Mn@GDY depends. Based on the calculated ΔG0(H) and H diffusion barrier, H can easily diffuse from the C site of graphene to the metal site and show better HER activities. The reverse H diffusion from the metal site to the carbon site of GDY for GDY supported Pd1, Pd5, and Ir5 could happen at room temperature, thereby improving the HER activity at pH = 0. A series of linear relationships are found, revealing the possible structure–activity relations.

Hyper-Cross-Linked Polystyrene as a Stabilizing Medium for Small Metal Clusters

Among different polymers nanostructured cross-linked aromatics have the greatest potential as catalytic supports due to their exceptional thermal and chemical stability and preservation of the active phase morphology. This work studies the ability of hyper-cross-linked polystyrene (HPS) to stabilize small Pdn and Ptn (n = 4 or 9) clusters. Unrestricted DFT calculations were carried out for benzene (BZ) adsorption at the BP level of theory using triple-zeta basis sets. The adsorption of BZ rings (stepwise from one to four) was found to result in noticeable gain in energy and stabilization of resulting adsorption complexes. Moreover, the interaction of metal clusters with HPS micropores was also addressed. For the first time, the incorporation of small clusters in the HPS structure was shown to influences its geometry resulting in the stabilization of polymer due to its partial relaxation.

Statistical analysis of homogeneous nucleation of metallic nanoparticles during gas-phase synthesis

In this work, we set out to develop a model of gas-phase nucleation in a mixture of copper and argon atoms, which can be further used for analysing macro-systems. Processes occurring at the atomic level are described using coefficients obtained by statistical analysis of molecular dynamic (MD) data on interactions of metal clusters with metal and argon atoms. The MD simulation results are compared with those obtained using the proposed macroscopic model. It is found that the coefficients obtained by averaging the interaction data suitably represent the integral value of the heat of condensation, although result in the smoothing of the energy distribution functions of the clusters. Analysis of the evolution of the number of clusters has shown that the values of their increase rate were lower than those obtained by MD simulation. The conclusion is made, that in order to improve the precision of the developed gas-phase condensation model, it should be supplemented by cluster coagulation.

The structure and activity of Pt 6 particles in ZSM-5 type zeolites

Density functional theory was applied to investigate the nature of active sites formed by the interaction of a Pt 6 guest particle with the silicalite and H-form of ZSM-5 as the host zeolites. Interaction of metal cluster with silicalite shows a slight stabilization (36 kJ/mol) and formation of a negatively charged Pt entity. When a metal particle is arranged in the channel of H-form substantial stabilization (187 kJ/mol) and generation of an oxidized Pt 6H + species are observed. The formation of an active site includes interaction between a platinum particle and an acid site accompanied by the suppression of zeolite acidity. The suggestion is made that the alkane transformation on supported platinum particles proceeds via metal–cyclobutane and metal–carbene intermediates and does not need the direct involvement of acid sites. The difference in catalytic behavior of the Pt 6/HZSM-5 and Pt 6/ZSM-5 systems is discussed.

Bonding interactions of metal clusters [Mn (M= Cu, Ag, Au; n=1-4)] with ammonia. Are the metal clusters adequate as a model of surfaces?

Density Functional (B3LYP/LANL2DZ) calculations for ammonia metal clusters were done in order to obtain bond lengths, M-N stretching vibrational modes, binding energies, Mulliken atomic charges and adiabatic ionization potentials. The results indicate that copper atom forms stronger bonds with ammonia than silver or gold. The bond interaction between Ag n and ammonia is the weakest of all the systems. The bond of the ammonia molecule to the metal clusters can be compared with the pyridine-Mn systems. Both molecules present a donation interaction from the lone-pair of electrons on the nitrogen atom. Mulliken atomic charges show a small charge transfer from the NH3 molecule to the metal atom or cluster, suggestive of a dative bond formation. After the charge transfer from the ammonia molecule, the metal clusters undergo a redistribution of the charge and this could be important for the stabilization of the system. In a surface, the redistribution of the charge should be less significant. In this sense, the use of metal clusters as a model of the surface may be an inadequate model.

Surface Defect-mediated Reactivity of Au/TiO2(110)

AbstractMetal clusters supported by transition metal oxides, as exemplified by the Au/TiO2 system, have found broad applications as catalytic and sensor materials. The unusual properties of these systems originate from the specific interactions of metal clusters mediated by an oxide substrate, including local reduction below the cluster. In this work, we present recent results on the local interactions between one-dimensional defects on a TiO2 surface and their reactivity with oxygen and Au nano-clusters studied by a combination of Scanning Tunneling Microscopy and Spectroscopy (STM/S). High-resolution STM images, interpreted with first-principles theory, show that the observed one-dimensional strands have partially reduced Ti atoms coordinated above three-coordinated, surface oxygen atoms. When strands are exposed to 5 x 10-7 Torr O2 at 300 K, oxygen is adsorbed and randomly nucleated on and along the strands. The results indicate the presence of exposed Ti that act as an active site for oxygen adsorption even at room temperature. Gold nano-particles of diameters 5 nm and less have also been deposited on the sub-stoichiometric rows of TiOx and characterized by STM. Like point defects and step edges on TiO2(110), the strands serve as nucleation sites for gold nano-clusters. The 1D defects of the surface are interpreted in terms of a surface crystallographic shear type structure, in contrast to the proposed Ti2O3 added row model by Onish and Iwasawa [Phys. Rev. Lett. 76, (1996) 791]. The implications of this behavior and specific interaction between gold clusters, defects and gas molecules for catalytic activity of the Au/TiO2 system are discussed.

Shape Variations and Control in Self-Assembled Metal Nanoclusters

ABSTRACTThe selective interaction of metal clusters with various polymers constitutes the basis for the self-assembly approach to the synthesis of organic-inorganic hybrid materials, that leads to the control of particle size, geometry and dispersion gradient. Metal particles were synthesized by the thermal decomposition of an organometallic precursor, in this case, iron pentacarbonyl, in the presence of a polymer matrix. Under the conditions utilized for these reactions, the aggregation of the metallic clusters competed with the interactions between the growing metal fragments and the polymer matrix. The dominance of one reaction route as compared to the other, ultimately determined the equilibrium particle shape, size and distribution for each metal-polymer system. In this work, we attempted to analyze the formation of iron oxide nanoclusters in several structurally-distinct polymers, and developed a general mechanistic view to explain the characteristics of the polymer-metal oxide hybrid materials that were obtained.

An exploration of the surfaces of some Pt/SiO2 catalysts using CO as an infrared spectroscopic probe

Infrared spectra in the bond-stretching, ν CO, region have been measured for CO adsorbed on an impregnated Pt/SiO2 catalyst (16% Pt) with the aim of characterizing the adsorption sites present. This catalyst has previously been widely used for the study of the spectra from adsorbed hydrocarbons. It has relatively large metal particles, typically in the diameter range of 5 to 15 nm. Samples were studied which were hydrogen-covered, hydrogen-depleted, oxygen-covered and “mature”, the latter in the sense that the catalyst had undergone a number of repeated adsorption/desorption/re-reduction cycles. The spectra were interpreted in terms of the adsorption sites available by using recent correlations between ν CO wavenumbers and different patterns of CO metal interactions in metal clusters of structures known from X-ray crystallography. The strongest ν CO absorptions were from linearly adsorbed OCPt species, but these were relatively uninformative (maxima in the region 2087 to 2084 cm−1 in all cases at saturation coverage) because strong dipolar coupling causes intensity-distortion and the merging-together of absorptions from different types of sites. Small proportions of sites, probably of an atomically rough nature from curved areas of the crystallites, gave weaker absorptions near 2050 and 2030 cm−1. On the oxygen-covered surface a sharp absorption at 2099 cm−1 denoted CO adsorption adjacent to sites of adsorbed oxygen. The weaker absorption bands in the ν CO bridged region were more informative. The strongest, near 1850 cm−1 was correlated with 2-fold bridged species adsorbed on (111) surfaces. Weaker, overlapping features near 1880 and 1795 cm−1 (separated from an overall contour with the aid of computer analysis) were correlated, respectively with 2-fold bridged species on (100) or (110) planes, and 3-fold bridged species on (111) planes. Weaker absorptions near 1700 cm−1 were considered to correspond to different types of adsorption sites involving unequal interactions of CO with at least two metal atoms. The “mature” Pt/SiO2 samples gave notably different spectra in both regions and this was tentatively attributed to the effect of residual carbon atoms on or near the Pt surface. A comparison was made of the present spectra with those previously published from similar experiments on a small-particle (ca 2 nm) Pt/SiO2 catalyst, EUROPT-1. The spectral differences could be well accounted for in terms of the reported raft-like (111)-based morphology of the small metal particles of the EUROPT-1 catalyst.

Interaction of metal clusters with surface steps

A survey is given about the experimental results on the localization of metal clusters at alkali halide surface steps. Depending on the temperature, step height, nature of the metal as well as of the substrate both, the lower and the upper level of a step can be the stable positions of the cluster. The observed phenomena are discussed in terms of the elastic interaction between cluster and step. The interaction energy is found to depend on the strengths of the elastic dipoles of the substrate and of the cluster and to vary with the cluster-step distance r as 1/r. Es wird ein Überblick gegeben über die experimentellen Ergebnisse zur Lokalisierung von Metallclusten and Alkalihalogenid-Oberflächenstufen. In Abhängigkeit von der Temperatur, der Stufenhöhe, der Natur des Metalls und des Substrats kann die stabile Position des Clusters sowohl das obere als auch das untere Niveau der Stufe sein. Die beobachteten Erscheinungen werden auf der Grundlage der elastischen Wechselwirkung zwischen Cluster und Stufe diskutiert. Es zeigt sich, daß die Wechselwirkungsenergie von den Dipolstärken des Substrats und des Clusters abhängt und mit dem Cluster-Stufenabstand r gemäß 1/r variiert.

Interaction of metal clusters with substrate steps

Gold clusters vapour grown at KCl surface steps have been localized with respect to the step level by a combined coarse and fine decoration. In comparison with earlier results obtained on NaCl substrates the position of the clusters has been found to depend in a systematic way on substrate temperature, step height, type of metal deposited and type of substrate.

Interactions in metal clusters : III. Racemization barriers and reversible hydrogen addition of a series of chiral clusters

The barriers to racemization in C 2D 4Cl 2 of [Ir{Fe(P( p-tolyl) 2)(CO) 2(η 5-C 5H 5)} 2] + BF 4 − and [Ir{Ru(P( p-tolyl) 2)(CO) 2(η 5-C 5H 5)} 2] + BF 4 − are 17.5 and 17.8 kcal/mol respectively. Both clusters add H 2 reversibly at 1 atmosphere and room temperature. The former also forms an adduct with H 2 and CO when exposed to both gases simultaneously.

Interactions in metal clusters. Acceleration of substitution by prior substitution at adjacent metal centers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInteractions in metal clusters. Acceleration of substitution by prior substitution at adjacent metal centersKarin J. Karel and Jack R. NortonCite this: J. Am. Chem. Soc. 1974, 96, 21, 6812–6813Publication Date (Print):October 1, 1974Publication History Published online1 May 2002Published inissue 1 October 1974https://doi.org/10.1021/ja00828a072RIGHTS & PERMISSIONSArticle Views94Altmetric-Citations70LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (225 KB) Get e-Alerts Get e-Alerts