Cu5 Cluster Research Articles

Mechanism study on CO2 hydrogenation to methanol on Cu5/TiO2 catalyst

Copper clusters supported on TiO2 have demonstrated exceptional performance in catalyzing the reduction of CO2. However, there is a lack of detailed studies on the underlying mechanism. In this study, we employ first-principles thermodynamics and kinetic calculations to unveil the catalytic reduction mechanism of CO2 to C1 product on the Cu5/TiO2 catalyst. Our calculations reveal that the interaction between the cluster and the support significantly enhances the chemical adsorption of CO2 and lowers the dissociation barrier of H2, creating favorable conditions for hydrogenation reduction of CO2. Additionally, our findings suggest that the Cu5 cluster also significantly enhances the adsorption of *CO intermediates, resulting in a preference for the RWGS pathway over the formate pathway for CO2 reduction. The rate-determining barrier for CH3OH formation is considerably lower than that for CH4 formation, indicating that Cu5/TiO2 exhibits remarkable CO2 conversion performance with nearly 100 % selectivity towards CH3OH production.

Constructing a square-like copper cluster to boost C–C coupling for CO2 electroreduction to ethylene

By DFT computations, we proposed Cu5@MoS2—an anchored Cu5 cluster on defective MoS2—as a promising catalyst for CO2-to-ethylene conversion. With distinctive square-like sites, Cu5@MoS2 demonstrates remarkable activity and selectivity, particularly in alkaline conditions.

Mechanism of heteroatom-doped Cu5 catalysis for hydrogen evolution reaction

Developing high-performance hydrogen evolution reaction (HER) electrocatalysts is of great significance for solving the global energy crisis. Cluster has great application potential in the field of catalysis due to their unique quantum size effect and high specific surface area. Herein, the HER catalytic performance of Cu5 cluster were regulated and optimized by doping heteroatoms. The Gibbs free energy calculation shows that the catalytic activity of Cu5Ni and Cu5Pt is comparable to that of Pt-based catalysts, and the Gibbs free energy value of Cu5C can even reach 0.005 eV, indicating its much higher catalytic performance than that of other catalysts. Thus, the catalytic activity of Cu5 clusters is optimized by doping non-metal and transition metal atoms to regulate the geometric and electronic structure of Cu5. It was found that Cu5Ni, Cu5Pt and Cu5C are potential catalysts to replace Pt-based catalysts for reducing the cost and achieving large-scale hydrogen production. This work provides a new avenue to regulate the catalytic performance of clusters, which is helpful for the further development and application of clusters in the field of catalysis.

On the Stability of Cu5 Catalysts in Air Using Multireference Perturbation Theory.

An ab initio study of the interaction of O2, the most abundant radical and oxidant species in the atmosphere, with a Cu5 cluster, a new generation atomic metal catalyst, is presented. The open-shell nature of the reactant species is properly accounted for by using the multireference perturbation theory, allowing the experimentally confirmed resistivity of Cu5 clusters toward oxidation to be investigated. Approximate reaction pathways for the transition from physisorption to chemisorption are calculated for the interaction of O2 with quasi-iso-energetic trapezoidal planar and trigonal bipyramidal structures. Within the multireference approach, the transition barrier for O2 activation can be interpreted as an avoided crossing between adiabatic states (neutral and ionic), which provides new insights into the charge-transfer process and gives better estimates for this hard to localize and therefore often neglected first intermediate state. For Cu5 arranged in a bipyramidal structure, the O–O bond cleavage is confirmed as the rate-determining step. However, for planar Cu5, the high energy barrier for O2 activation, related to a very pronounced avoided crossing when going from physisorption to chemisorption, determines the reactivity in this case.

Increasing the optical response of TiO2 and extending it into the visible region through surface activation with highly stable Cu5 clusters.

The decoration of semiconductors with subnanometer-sized clusters of metal atoms can have a strong impact on the optical properties of the support. The changes induced differ greatly from effects known for their well-studied, metallic counterparts in the nanometer range. In this work, we study the deposition of Cu5 clusters on a TiO2 surface and investigate their influence on the photon-absorption properties of TiO2 nanoparticles via the computational modeling of a decorated rutile TiO2 (110) surface. Our findings are further supported by selected experiments using diffuse reflectance and X-ray absorption spectroscopy. The Cu5 cluster donates an electron to TiO2, leading to the formation of a small polaron Ti3+ 3d1 state and depopulation of Cu(3d) orbitals, successfully explaining the absorption spectroscopy measurements at the K-edge of copper. A monolayer of highly stable and well fixated Cu5 clusters is formed, which not only enhances the overall absorption, but also extends the absorption profile into the visible region of the solar spectrum via direct photo-induced electron transfer and formation of a charge-separated state.

Syntheses, Structure, and 2/5 Magnetization Plateau of a 2D Layered Fluorophosphate Na3Cu5(PO4)4F·4H2O

A new two-dimensional (2D) fluorophosphate compound Na3Cu5(PO4)4F·4H2O with a Cu5 cluster has been synthesized using a conventional hydrothermal method. The compound crystallizes in the orthorhombic crystal system with space group Pnma. The 2D layered structure is formed by cap-like {Cu5(PO4)4F} building units consisting of a Cu4O12F cluster plus a residual cap Cu2+ ion. Magnetic susceptibility exhibits a broad maximum at T2 = 19.2 K due to low-dimensional character followed by a long-range antiferromagnetic ordering at T1 = 11.5 K, which is further confirmed by the specific heat data. High-field magnetization measurement demonstrates a 2/5 quantum magnetization plateau above 40 T. The ESR data indicate the presence of magnetic anisotropy, in accordance with the 2D structure of the system.

Exploration of the Structural, Electronic and Tunable Magnetic Properties of Cu₄M (M = Sc-Ni) Clusters.

The structural, electronic and magnetic properties of Cu4M (M = Sc-Ni) clusters have been studied by using density functional theory, together with an unbiased CALYPSO structure searching method. Geometry optimizations indicate that M atoms in the ground state Cu4M clusters favor the most highly coordinated position. The geometry of Cu4M clusters is similar to that of the Cu5 cluster. The infrared spectra, Raman spectra and photoelectron spectra are predicted and can be used to identify the ground state in the future. The relative stability and chemical activity are investigated by means of the averaged binding energy, dissociation energy and energy level gap. It is found that the dopant atoms except for Cr and Mn can enhance the stability of the host cluster. The chemical activity of all Cu4M clusters is lower than that of Cu5 cluster whose energy level gap is in agreement with available experimental finding. The magnetism calculations show that the total magnetic moment of Cu4M cluster mainly come from M atom and vary from 1 to 5 μB by substituting a Cu atom in Cu5 cluster with different transition-metal atoms.

The synthesis of three new Cu5, Cu8 and Cu12 clusters via the use of a semi-flexible aminotriazine-based bis-methylpyridine ligand.

The synthesis of three new polynuclear Cu5, Cu8 and Cu12 clusters has been achieved using a semi-flexible aminotriazine-based bis-methylpyridine ligand, N2,N2-dibenzyl-N4,N6-di(pyridylmethyl)-1,3,5-triazine-2,4,6-triamine (H2dpmta). The reaction of Cu(ClO4)2·6H2O with H2dpmta in i-PrOH afforded the complex [Cu5(OH)4(H2dpmta)2(ClO4)4(H2O)4](ClO4)2·Et2O·5i-PrOH (1). A similar reaction of Cu(ClO4)2·6H2O and H2dpmta in the presence of PhCO2Na in i-PrOH/CH2Cl2 gave the complex [Cu8(OH)6(O2CPh)4(H2dpmta)2(ClO4)4(i-PrOH)2](ClO4)2·2CH2Cl2·2i-PrOH (2). The complex [Cu12O3(OH)2(Hdpmta)2(dpmta)2(O2CMe)8](ClO4)2·2MeCN (3) was produced from the reaction of [Cu2(O2CMe)4]·2H2O with H2dpmta and NaClO4 in MeCN/CH2Cl2. Single-crystal X-ray diffraction measurements were carried out on these complexes. The Cu5 cluster of 1 consisted of a planar [Cu5(μ-OH)4]6+ core in a rectangle-like arrangement. The Cu12 cluster of 2 represented a [Cu8(μ3-OH)4(μ-OH)2]10+ core infusion of two [Cu4(OH)2]6+ butterfly subunits. Complex 3 possesses a bent [Cu12(μ4-O)3(μ-OH)2]16+ core structure, in which a central [Cu4(μ4-O2-)] square planar moiety was fused with two butterfly-like [Cu4(μ4-O)(μ3-OH)] subunits. The magnetic properties of these three complexes were characterized by the measurements of variable-temperature and field magnetic susceptibility. The magnetic analysis showed that a strong antiferromagnetic interaction was mediated between Cu(ii) ions by the single OH- bridge in 1 and resulted a S = 3/2 spin ground state. In complex 2, both intramolecular antiferro- and ferromagnetic interactions were dominated between Cu(ii) ions resulting a spin ground state of S = 2. Indeed, complex 3 displayed an overall antiferromagnetic coupling.

Five copper(ii) metal–organic coordination complexes with micro-channels based on flexible bis(imidazole) and carboxybenzaldehyde ligands; structural influence of experimental conditions on their frameworks

Five new copper(II) metal–organic coordination complexes, [Cu2(1,2-bix)2(L)4] (1), [Cu(1,3-bix)(L)2]n·nCH3OH·3H2O (2), [Cu(1,3-bix)(L)2]n·nH2O (3), [Cu5(1,3-bix)2(L)6(NO3)2(H2O)2(OH)2]·2H2O (4) and [Cu(1,4-bix)(L)2]n (5), have been synthesized using 4-carboxybenzaldehyde (HL) and 1,n-bis(imidazol-l-ylmethyl)benzene (1,n-bix; n = 2, 3, 4) as ligands. These complexes were structurally characterized by single-crystal X-ray crystallography and further characterized by FT-IR spectroscopy and thermogravimetric analysis (TGA). Complex 1 is a symmetrical binuclear structure, and in compound 2 the 1D ladders are entangled through π–π stacking interactions to generate a 3D network with one-dimensional micro channel. A 3D coordination framework 2 converted to network 3 by just increasing the reaction temperature. Metal–organic polymer 3 is comprised of 1D corrugated double chains structure. Complex 4 has a pentanuclear (Cu5) cluster structure and compound 5 shows a 1D zigzag chain. The magnetic properties of the complexes 1 and 3 are reported briefly.

Isomers of the Cu5 cluster: a density function theory study**Project supported by the National Natural Science Foundation of China (Grant No. 10375028).

In this work, a systematic study of some possible isomer structures of the Cu5 cluster obtained from density functional theory methods is presented. The polarisation and pseudopotential basis sets are employed in the calculations. The results show that the binding energies, frequencies, coordination numbers and average bond lengths are in reasonable agreement with reported experimental data. Moreover, four isomers of the Cu5 cluster are obtained according to calculations, in which the most stable configuration is the planar structure. Meanwhile, two three-dimensional structures of the Cu5 cluster are obtained in this work, which might be valuable for further theoretical and experimental studies. In addition, our study proves the possibility of the isomer structures of the Cu5 cluster.

Isomers of Cu5 cluster: a density functional theory study

Isomers of Cu5 cluster: a density functional theory study

非経験的分子軌道法を用いた六塩化ベンゼンの銅クラスターへの吸着構造における理論的解明

In this study, we have clarified the structural and electronic properties of Cl6Benzene onto Cu5(100) cluster using ab initio molecular orbital method. The results obtained in this study are as follows: (1) the result of Mulliken Charge analysis shows that a large number of electrons are transfered from the Cu cluster to the adsorbent, (2) with single-point calculation, transition state exists 4×10-2 nm away from the adsorption state and this potential energy curve is valid untile 5×10-2 nm away from the adsorption state, and. (3) Homo-1 and Homo-2 at adsorption state are resulted from orbital interaction between Cu5 cluster and Cl6Benzene due to this smallest cluster model.

Ionic and covalent electronic states for K adsorbed on Cu5 and Cu25 cluster models of the Cu(100) surface

The chemisorption of K on the fourfold hollow site of the Cu(100) surface has been theoretically investigated by means of Cu5–K and Cu25–K cluster models. We have analyzed Hartree–Fock self-consistent field (SCF) wave functions for various electronic states of the two clusters. Four different measures have been used to establish the degree of ionicity of each state: (1) the analysis of the dipole moment curve for the variation of the Cu–K distance; (2) a constrained variation of the SCF orbitals to separate electrostatic, polarization, and charge transfer contributions; (3) the projection of the K valence orbitals onto the cluster wave function to measure the orbital occupancies, and (4) an energetic analysis of the cost and benefit of forming an ionic bond. We found different properties for the two clusters. All the considered electronic states of Cu25–K show large ionic character, suggesting that the bonding of K to a Cu(100) surface is indeed ionic at low coverage. The bonding character of the lowest states of Cu5–K is different, ranging from dominantly ionic to dominantly covalent. This behavior for Cu5–K is related to the small size of the cluster but it can be useful for modeling the transition from ionic to metallic bonding as the coverage of the alkali metal increases.

All electron versus pseudopotentials in a b i n i t i o chemisorption cluster model calculations

The interaction of atomic oxygen with a Cu5 cluster model simulating chemisorption on the fourfold site is studied at the ab initio SCF level. Three different levels of approximation were tested. In the first one all the electrons were explicitly included while in the other two only the 3d104s1 or the 4s1 electrons were explicitly included, the corresponding Cu cores were treated by means of a nonempirical pseudopotential. We have obtained Cu5O wave functions where only the Cu 4sp or the 4sp plus the 3d electrons are varried and deeper core electrons are frozen as well as wave functions where all the Cu electrons are varied. This allows us to separately examine the effect of the pseudopotentials on the Cu 4sp and Cu 3d contributions to the Cu–O bond. It is found that the pseudopotential errors for these individual contributions are about 0.25–0.50 eV. These uncertainties are sufficiently large so that they limit the use of pseudopotentials to providing qualitative rather than quantitative information about the bond. Finally, a proposal is made for the proper way to obtain the Cu–O binding energy with SCF wave functions for clusters.

Reliability of one-electron approaches in chemisorption cluster model studies: Role of core-polarization and core–valence correlation effects

Interaction of atomic oxygen with a Cu5 (Ag5) cluster model simulating the fourfold chemisorption of oxygen on Cu(100) and Ag(100) has been studied at the self-consistent-field (SCF) and configuration interaction (CI) levels using one-electron pseudopotentials to describe the inner shells of the cluster metal atoms. Core-polarization effects are introduced by means of a second-order perturbation method. Results show the method to be reliable and that there is no need for any molecular adjustment of the pseudopotential. Nondynamical and dynamical valence correlation effects are found to be very important. The separability of valence correlation effects is analyzed by comparison with previous calculations explicitly including the d electrons of the cluster metal atoms. Core–valence correlation effects decrease the interaction energy calculated at the valence CI level and are shown to be very important not only from the quantitative point of view but also from the qualitative one because different electronic states are differently affected, leading to a change in the ordering of the electronic states with respect to that found at the CI valence calculation level.

Cu 3d covalency in chemisorption?

Two problems are addressed in the present study: the degree of copper 3d covalency involved in the chemisorption of oxygen at the fourfold hollow site of Cu(100) and the separability of the correlation energy into contributions from the 3d shells on copper and from the valence sp band. The investigation was carried out at the all-electron level using a Cu5 cluster as a model of the Cu(100) surface. The analysis shows that the 3d covalency is of practically no importance in the system considered, contributing only 1–3 kcal/mol to the total chemisorption energy of 89 kcal/mol. The correlation energy was found to be separable to within 5 kcal/mol. A configuration-interaction calculation on the Cu5O system using the one-electron effective core potential developed previously yielded a correlation energy in close agreement with the all-electron results.

Dynamical and nondynamical correlation effects in a b i n i t i o chemisorption cluster model calculations. Ground and low lying states of H on Cu(100) and Ag(100)

The nondynamical correlation effects for the interaction between an adsorbate and a surface cluster model can be recovered by means of a simple and accurate method. A projection localization procedure permits to distinguish between cluster and adsorbate MOs and between lone pairs or bonds. Valence virtual MOs are obtained by an inexpensive method. Once the valence space is defined CASCI calculations account for these correlation effects, the results being in good agreement with CASSCF calculations. The dynamical correlation effects are taken into account by using a perturbative approach in which the CAS wave function is taken as the zeroth order one. Results, thus obtained, are also in agreement with accurate CIPSI calculations. The overall procedure is illustrated by means of calculations on the ground and low lying electronic states of the on top chemisorption of atomic hydrogen on the Cu5 and Ag5 cluster models simulating the (100) metal surface. The main effects of nondynamical correlation in the electronic ground state are a slight increase on the internuclear equilibrium distance of the adsorbate to the surface model and a considerable contribution to the binding energy (≊20% of the total binding energy). The dynamical effects tend to cancel the effect on the equilibrium distance and left almost unchanged the binding energy. Since these effects are quite small valence CASCI can lead to an accurate enough description of the chemisorption bonds. These general trends also hold for the excited states studied here.

On the Nature of the Bonding of Lone Pair Ligands to Small Metal Clusters

AbstractWe analyse the interaction and bonding between CO, NH3 and PF3 molecules and a Cu5 cluster in detail. From a constrained space orbital variation (CSOV) study, we are able to determine the energetic importance of different contributions to the metal‐ligand interaction, such as intra‐unit, Cu5 and ligand, polarization and inter‐unit donation. The results show that the Cu5–NH3 bonding is determined to a large part by the electrostatic interaction between the units with little charge transfer. The Cu5–CO bonding is characterized mainly by a metal to ligand π donation. The Cu5–PF3 bonding has metal to ligand π and ligand to metal s̀ donation of comparable importance. The free PF3 dipole leads to a repulsive interaction with the Cu5 and this affects the intra‐unit polarization.