共查询到20条相似文献,搜索用时 31 毫秒
1.
Dr. Hristiyan A. Aleksandrov Dr. Francesc Viñes Wiebke Ludwig Dr. Swetlana Schauermann Prof. Dr. Konstantin M. Neyman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1335-1345
Palladium is crucial for industry‐related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near‐surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties. Density functional calculations of the interplay of C and H atoms at various concentrations and sites on suitable Pd NPs have been performed, accompanied by catalysis‐relevant experiments on oxide‐supported bare and C‐modified Pd NPs. It is shown that on a Pd79 NP a subsurface C atom destabilizes nearby atoms H at low coverage. Our experiments confirm that H atoms bind more weakly on C‐containing Pd NPs than on C‐free NPs. Various factors related to the presence of both H and C atoms on a Pd79 surface, which may influence the penetration of H atoms from the surface into the subsurface area, have been investigated. Carbon atoms facilitate the subsurface penetration of atomic H both thermodynamically and kinetically when the surface is densely covered by H atoms. Moreover, subsurface H atoms are also energetically favored, even in the absence of C atoms, when several facets of the NP are covered by H atoms. 相似文献
2.
Xiaobo He Jinghui Lyu Hu Zhou Guilin Zhuang Xing Zhong Jian‐Guo Wang Xiaonian Li 《International journal of quantum chemistry》2014,114(14):895-899
The adsorption mode of aromatic molecules on transition metal surfaces plays a key role in their catalytic transformation. In this study, by means of density functional theory calculations, we systematically investigate the adsorption of p‐chloroaniline on a series of Pd surfaces, including stepped surfaces, flat surfaces, and clusters. The adsorption energies of p‐chloroaniline on these substrates [Pd(221), Pd(211), Pd(111), Pd(100), Pd13‐icosahedral, Pd13‐cubo‐octahedron, Pd55] are ?1.90, ?2.13, ?1.70, ?2.11, ?2.53, ?2.65, ?2.23 eV, respectively. Benzene ring is adsorpted on catalyst rather than amine group in p‐chloroaniline molecular. A very good linear relationship is further found between the adsorption energies of p‐chloroaniline and the d‐band center of both Pd surfaces and clusters. The lower of d‐band center of Pd models, the stronger adsorption of p‐chloroaniline on catalysts. In addition, the frontier molecular orbital and density of states analysis explain the adsorption energy sequence: cluster Pd13 > stepped Pd(221) surface > flat Pd(111) surface. © 2014 Wiley Periodicals, Inc. 相似文献
3.
Robert Grybos Lubomir Benco Tomas Bučko Jürgen Hafner 《Journal of computational chemistry》2009,30(12):1910-1922
The adsorption of NO molecules on small Pdn (n = 1?6) clusters has been studied using first‐principles density‐functional theory. Three adsorption sites were considered: vertex (on–top), bridge, and hollow. Adsorption is strong, ranging from 2 to 3 eV. In all cases NO adsorbs in a bent configuration. Calculated shifts in N–O bond vibration frequencies (with anharmonic corrections) agree very well with available experimental data. In contrast to metallic Pd surfaces, adsorption of NO on palladium clusters causes considerable changes in geometry around adsorption site because palladium d‐orbitals rehybridize to maximize the overlap with NO orbitals (mainly the antibonding π*). Thus, the overall energetic effect of NO adsorption is the result of two competing processes: lowering of the total energy through tighter bonding with NO and rising the energy due to cluster deformation. The Pdn–NO bond creation is governed by electron transfer from Pd–d orbitals into the NO π*. As a result, the Pd cluster becomes locally demagnetized (with total magnetic moment of 1 μB located at Pd atoms not connected to NO) and the NO molecule is activated: the N–O bond length is increased and the vibration frequency is redshifted. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
4.
Kento Shimamoto Prof. Dr. Yusuke Sunada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3761-3765
The construction of well-defined transition-metal clusters has attracted substantial attention due to their unique chemical and/or physical properties. Metal clusters with 1D or 2D structures are now accessible by template-synthesis methods, in which multiple metal atoms are arranged with the aid of template molecules and their 1D or 2D structures. However, the rational synthesis of 3D clusters remains challenging, mostly due to a lack of appropriate template molecules. Herein, we report the rational synthesis of a 2D butterfly shaped Pd4 framework ( 2 ) and 3D edge-sharing Pd6 tetrahedra ( 5 ) by treatment of easily available organosilicon compounds with Pd(CNtBu)2. The diphenylsilylene moiety thereby serves as the key component to generate the butterfly structure of the Pd4 clusters in 2 . A dimensionality expansion, induced by two Cl atoms, of two butterfly shaped Pd4 subunits supported by two diphenylsilylene moieties afforded the edge-sharing tetrahedral architecture of the Pd6 cluster in 5 . 相似文献
5.
Ab initio molecular dynamics calculations were performed to study H2 dissociation mechanisms on Cu13 and defective graphene-supported Cu13 clusters. The study reveals that seven types of corresponding dissociation processes are found on the two clusters. The average dissociation energy barriers are 0.51 eV on the Cu13 cluster and 0.12 eV on the defective graphene-supported Cu13 cluster, which are lowered by ~19 % and ~81 % compared with the pristine Cu(111) surface, respectively. Furthermore, compared with the pure Cu13 cluster, the average dissociation energy barrier on the defective graphene-supported Cu13 cluster is substantially reduced by about 76 %. The preferred dissociation mechanisms on the two clusters are H2 located at a top-bridge site with the barrier heights of 0.30 eV on the Cu13 cluster and −0.31 eV on the defective graphene-supported Cu13 cluster. Analysis of the H−Cu bond interactions in the transition states shows that the antibonding-orbital center shifts upward on the defective graphene-supported Cu13 cluster compared with the one on the Cu13 cluster, which explains the reduction of the dissociation energy barrier. The average adsorption energy of dissociated H atoms is also greatly enhanced on the defective graphene-supported Cu13 cluster, about twice that on the Cu13 cluster. 相似文献
6.
Sauli Vuoti Matti Haukka Jouni Pursiainen 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(12):m601-m603
The dichloromethane solvates of the isomers tetrakis(μ‐1,3‐benzothiazole‐2‐thiolato)‐κ4N:S;κ4S:N‐dipalladium(II)(Pd—Pd), (I), and tetrakis(μ‐1,3‐benzothiazole‐2‐thiolato)‐κ6N:S;κ2S:N‐dipalladium(II)(Pd—Pd), (II), both [Pd2(C7H4NS2)4]·CH2Cl2, have been synthesized in the presence of (o‐isopropylphenyl)diphenylphosphane and (o‐methylphenyl)diphenylphosphane. Both isomers form a lantern‐type structure, where isomer (I) displays a regular and symmetric coordination and isomer (II) an asymmetric and distorted structure. In (I), sitting on an centre of inversion, two 1,3‐benzothiazole‐2‐thiolate units are bonded by a Pd—N bond to one Pd atom and by a Pd—S bond to the other Pd atom, and the other two benzothiazolethiolate units are bonded to the same Pd atoms by, respectively, a Pd—S and a Pd—N bond. In (II), three benzothiazolethiolate units are bonded by a Pd—N bond to one Pd atom and by a Pd—S bond to the other Pd atom, and the fourth benzothiazolethiolate unit is bonded to the same Pd atoms by, respectively, a Pd—S bond and a Pd—N bond. 相似文献
7.
David Evrard Daniel Meilleur Marc Drouin Yves Mugnier Pierre D. Harvey 《无机化学与普通化学杂志》2002,628(11):2286-2292
The recently discovered and characterized [Pd4(dppm)4(H)]2+ cluster catalyst ( 1 ; dppm = Ph2PCH2PPh2), slowly evolves in the presence of the reducing tetraphenylborate anion, to generate a new diamagnetic cluster [Pd4(dppm)4(H)]+ ( 2 ). The evolution of this starting material 1 , has been monitored using NMR (1H and 31P), UV‐vis and ESR spectroscopy. This new 56‐electron Pd cluster has been characterized from X‐ray crystallography, and consists of a cyclic species exhibiting an approximate puckered square structure. The Pd2 bond distances are 2.7367(10) and 2.7495(11)Å and indicate the presence of weak bonding. The diagonal Pd···Pd separations are 3.646(10) and 3.590(10)Å indicating that the square is relatively symmetric. Such a structure is unprecedented for “Pdx(dppm)x” species. Although not formally observed from the X‐ray data, the hydride is assumed to be fluxional as found in 1 . The cyclic voltammogram for 2 exhibits an irreversible reduction wave at —1.65V vs SCE which is greater than that found for 1 , and corroborates the lower oxidation state for Pd (+1/2). The Pd‐H bonding scheme and MO symmetry for a model cluster where the hydride has been placed at the center of the Pd4 frame, have been addressed qualitatively using the EHMO model. These calculations demonstrate clearly that the Pd‐H bonding is strong. 相似文献
8.
Quantum calculations of interaction of the molecular hydrogen with transition-metal clusters have been performed. The aim of the project is to compare the results for different metals and different methods of calculations. The calculations have been mostly based on the gradient-corrected methods of the density functional theory. The list of the exchange-correlation functionals includes: the gradient corrected functional BP86, the hybrid functionals B3P86, B3LYP, B3PW9, and the local SVWN functional. The calculations of the potential energy surface (PES) for the hydrogen molecule positioned over the planar Pd5 clusters have been performed. It was found that the H–H bond activation is without barrier for most of the functionals used. However, the results obtained for the B3LYP functional suggest very small potential barrier, of the order of 0.003 eV. The calculations of the PES for dihydrogen in contact with metal clusters have been performed for Ni5, Ag5, Cu5 clusters and for mixed clusters Ag4Pd, AgPd4, NiCu4, and NiPd4. The dissociation paths for all the cases with the exception of Ag5 and Cu5 have been found and the dissociation energies and activation barriers have been estimated. 相似文献
9.
We present the results of a density functional calculation on adsorption of O2, CO, and their coadsorption at various sites of neutral, cationic, and anionic Pd4 clusters. For all the clusters, the dissociative adsorption of oxygen sitting on Pd bridge sites is found to be preferable. Both O2 and CO binding energies are found to be higher for the anionic Pd4 cluster followed by cationic and neutral cluster. However, binding energies of O2 or CO in the coadsorption complexes follow the trend: anionic > neutral > cationic. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
10.
Density functional theory has been performed to investigate the interaction of H2 and Pdn clusters (n = 1–7). The local minima configurations for different H2 molecule approach modes towards Pdn clusters are presented. Our results show that in some cases H2 is physically adsorbed around Pd atom, and in other cases H2 is dissociated to be H atoms. Except for PdH2, Pdn clusters with H atoms dissociatively adsorbed are most stable. For these most stable PdnH2 clusters (n 2), the binding energy of hydrogen atom decreases as the number of Pd atom increases until n = 4, and when n 4, the binding energy almost keeps constant with the H atoms bound sites changing from Pd–Pd bonds to Pd triangle planes. Besides, the adsorption of H2 on other low-lying isomers of Pdn clusters is also discussed. 相似文献
11.
B3LYP/LANL2DZ and B3LYP/6-31G(d)-restricted and -unrestricted calculations are employed to calculate energies and adsorption forms of formaldehyde adsorbed on planar and on tetrahedral Pd4 clusters and on a Pd4 cluster supported on Al10O15. Formaldehyde adsorbs on planar Pd4 in the eta(2)(C,O)-di-sigma adsorption mode, while on tetrahedral Pd4, it adsorbs in the eta(2)(C,O)-pi adsorption mode. The adsorption energy on planar Pd4 is -21.4 kcal x mol(-1), whereas for the tetrahedral Pd4 cluster, the adsorption energy is -13.2 kcal x mol(-1). The latter value is close to experimental findings (-12 to -14 kcal x mol(-1)). Adsorption of formaldehyde on Pd4 supported on an Al10O15 cluster leads essentially to the same result as that found for adsorption on the tetrahedral Pd4 cluster. Charge density analysis for the interaction between formaldehyde and the Pd4 clusters indicates strong backdonation in the eta(2) adsorption mode, leading to positive charge on the Pd4 cluster. NBO analysis shows that the highly coordinated octahedral aluminum atoms of Al10O15 donate electron density to the supported Pd4 cluster, while tetrahedral aluminum atoms with lower coordination number have acidic nature and therefore act as electron acceptors. 相似文献
12.
Hydrogen spillover, involving the surface migration of dissociated hydrogen atoms from active metal sites to the relatively inert catalyst support, plays a crucial role in hydrogen-involved catalytic processes. However, a comprehensive understanding of how H atoms are driven to spill over from active sites onto the catalyst support is still lacking. Here, we examine the atomic-scale perspective of the H spillover process on a Pt/Cu(111) single atom alloy surface using machine-learning accelerated molecular dynamics calculations based on density functional theory. Our results show that when an impinging H2 dissociates at an active Pt site, the Pt atom undergoes deactivation due to the dissociated hydrogen atoms that attach to it. Interestingly, collisions between H2 and sticking H atoms facilitate H spillover onto the host Cu, leading to the reactivation of the Pt atom and the realization of a continuous H spillover process. This work underscores the importance of the interaction between gas molecules and adsorbates as a driving force in elucidating chemical processes under a gaseous atmosphere, which has so far been underappreciated in thermodynamic studies. 相似文献
13.
The effect of alloying on the adsorption of atomic hydrogen was studied using density functional theory (DFT). In the study
the (100) surfaces of Pd-Ag, Pd-Pt, Pd-Au, Pt-Ag, and Pt-Au alloys were considered by means of a cluster model. The structural
and energetic properties of the H atom adsorbed on the Pd4Me (Me = Ag, Pt, Au) and Pt4Me (Me = Pd, Ag, Au) clusters were calculated and compared with the H-atom adsorption on monometallic clusters. The effect
of alloying on the H-atom adsorption is evident for all the investigated bimetallic systems. However, it strongly depends
on the second metal atom, Me, is placed in the surface layer or in the subsurface one. In general, the H atom adsorbed in
a site containing the second metal exhibits different properties from those characteristic of its adsorption on Pd(100) and
Pt(100). Hence, the modified interaction between atomic hydrogen and the alloyed surfaces may increase the selectivity of
the catalytic hydrogenation reactions on such surfaces. 相似文献
14.
V. A. Matsura N. S. Panina V. V. Potekhin V. B. Ukraintsev K. A. Khokhryakov V. V. Platonov O. M. Tatsenko A. I. Panin 《Russian Journal of General Chemistry》2004,74(7):975-979
The mechanism of the reaction of Pd
n
clusters with an H2 molecule was suggested on the basis of DFT B3LYP/HW calculations. The catalytic center in an elementary event of the process is one of the vertices of the Pd
n
cluster; spillover of hydrogen atoms along the cluster edges results in the formation of a stable Pd
n
H2 complex with a significant energy gain in the case of the singlet reaction channel. In such a mechanism, the cluster size should not significantly affect the reaction up to a certain moment; therefore, when simulating processes involving large clusters, we can restrict ourselves to relatively small sites of their surface. 相似文献
15.
Mitsutaka Okumura Satoshi Sakane Yasutaka Kitagawa Takashi Kawakami Naoki Toshima Kizashi Yamaguchi 《Research on Chemical Intermediates》2008,34(8-9):737-742
It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd13, Pt13, Pt/Pd12, Pd/Pt12 Pd38 and Pd6/Pt32 clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them. 相似文献
16.
Jorge M. Seminario Anglica G. Zacarías Miguel Castro 《International journal of quantum chemistry》1997,61(3):515-523
A systematic study has been carried out for the determination and characterization of the lowest states of Pd, Pd2, and Pd3 using some of the best ab initio tools available at present (conventional and DFT). Full electron ab initio calculations using the HF, MP2, MP3, MP4, and QCI methods were compared with DFT methods using several gradient-corrected functionals as well as the hybrid B3LYP functional that performed very well for the energetics studies of these small clusters. A suitable basis set has been found to perform considerably well with palladium atoms, another of double-ζ quality has been found insufficient to reproduce basic characteristics of the smallest palladium clusters. The results indicate that the ground state for Pd is a singlet. The dimer is a triplet; however, it is very difficult to ascertain due to the closeness between singlet and triplet states (0.9 kcal/mol). The trimer ground state was found to be a triplet with a separation from the lowest singlet of 3.2 kcal/mol. The lowest triplet and singlet of Pd3 were practically equilateral triangles. © 1997 John Wiley & Sons, Inc. 相似文献
17.
Er3Pd7P4 — Crystal Structure Determination and Extended Hückel Calculations Er3Pd7P4 was prepared by heating the elements (1050°C) and investigated by means of single-crystal X-ray methods. The compound crystallizes in a new structure (C2/m; a = 15.180(3) Å, b = 3.955(1) Å, c = 9.320(1) Å, β = 125,65(1)°; Z = 2) with a three-dimensional framework of Pd and P atoms and with Er atoms in the holes. The Pd atoms are surrounded tetrahedrally, trigonally or linearly by P atoms, which are coordinated by nine metal atoms in the form of a tricapped trigonal prism. Therefore the atomic arrangement of Er3Pd7P4 is related to the structures of ternary transition metal phosphides with a metal: phosphorus ratio of 2:1. Band calculations using the Extended Hückel method show strong covalent Pd? P bonds and weak bonding interactions between Pd atoms with Pd? Pd distances shorter than 2.9 Å. 相似文献
18.
Self‐assembly properties of Salamo‐type trinuclear Cu(II) and Co(II) complexes based on the regulation of H+/OHˉ
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A novel naphthalenediol‐based bis(salamo)‐type tetraoxime compound (H4L) was designed and synthesized. Two new supramolecular complexes, [Cu3(L)(μ‐OAc)2] and [Co3(L)(μ‐OAc)2(MeOH)2]·4CHCl3 were synthesized by the reaction of H4L with Cu(II) acetate dihydrate and Co(II) acetate dihydrate, respectively, and were characterized by elemental analyses and X‐ray crystallography. In the Cu(II) complex, Cu1 and Cu2 atoms located in the N2O2 sites, and are both penta‐coordinated, and Cu3 atom is also penta‐coordinated by five oxygen atoms. All the three Cu(II) atoms have geometries of slightly distorted tetragonal pyramid. In the Co(II) complex, Co1 and Co3 atoms located in the N2O2 sites, and are both penta‐coordinated with geometries of slightly distorted triangular bipyramid and distorted tetragonal pyramid, respectively, while Co2 atom is hexa‐coordinated by six oxygen atoms with a geometry of slightly distorted octahedron. These self‐assembling complexes form different dimensional supramolecular structures through inter‐ and intra‐molecular hydrogen bonds. The coordination bond cleavages of the two complexes have occurred upon the addition of the H+, and have reformed again via the neutralization effect of the OH?. The changes of the two complexes response to the H+/OH? have observed in the UV–Vis and 1H NMR spectra. 相似文献
19.
氢和硫原子在Pd、Au和Cu及PdAu、PdCu合金(111)表面吸附的密度泛函研究 总被引:1,自引:0,他引:1
用密度泛函理论研究了氢和硫原子在金属Pd、Au、Cu以及合金PdM3、Pd2M2 和Pd3M(111)表面的吸附(M=Au, Cu), 得到了覆盖率为0.25时最稳定的吸附位、结合能以及吸附前后表面的驰豫情况. 结果表明, 氢和硫均与Pd形成最稳定的吸附, Cu次之, Au的吸附最弱, 其在三种纯金属(111)表面的最稳定吸附位均为fcc位. 由于PdAu合金具有较大的晶格常数, Pd3Au 合金吸附氢的结合能甚至较纯Pd更大, 除此之外, 氢和硫在PdM合金表面的吸附基本随M组分的增加而减弱, 而最稳定的吸附位随金属种类和组成变化而变化. 根据计算得到的吸附结合能, 发现与PdCu合金相比, PdAu合金在Au含量较低(约25%, 摩尔分数)时, 氢和硫吸附的结合能下降较慢, 而Au含量较高(跃50%)时, 结合能迅速下降, 这表明含金量为25%-50%的PdAu合金有可能在保持相近透氢性能的同时, 比PdCu合金具有更好的抗硫毒性. 相似文献
20.
Edward D. Cross Kristen L. MacDonald Robert McDonald Matthias Bierenstiel 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(1):23-27
The reaction of dichlorido(cod)palladium(II) (cod = 1,5‐cyclooctadiene) with 2‐(benzylsulfanyl)aniline followed by heating in N,N‐dimethylformamide (DMF) produces the linear trinuclear Pd3 complex bis(μ2‐1,3‐benzothiazole‐2‐thiolato)bis[μ2‐2‐(benzylsulfanyl)anilinido]dichloridotripalladium(II) N,N‐dimethylformamide disolvate, [Pd3(C7H4NS2)2(C13H12NS)2Cl2]·2C3H7NO. The molecule has symmetry and a Pd...Pd separation of 3.2012 (4) Å. The outer PdII atoms have a square‐planar geometry formed by an N,S‐chelating 2‐(benzylsulfanyl)anilinide ligand, a chloride ligand and the thiolate S atom of a bridging 1,3‐benzothiazole‐2‐thiolate ligand, while the central PdII core shows an all N‐coordinated square‐planar geometry. The geometry is perfectly planar within the PdN4 core and the N—Pd—N bond angles differ significantly [84.72 (15)° for the N atoms of ligands coordinated to the same outer Pd atom and 95.28 (15)° for the N atoms of ligands coordinated to different outer Pd atoms]. This trinuclear Pd3 complex is the first example of one in which 1,3‐benzothiazole‐2‐thiolate ligands are only N‐coordinated to one Pd centre. The 1,3‐benzothiazole‐2‐thiolate ligands were formed in situ from 2‐(benzylsulfanyl)aniline. 相似文献