Bimetallic Dimers Research Articles

Atomic Phosphorus Sites for Anchoring Platinum–Tungsten Dimers to Facilitate Proton Transfer in All‐pH Hydrogen Evolution

AbstractBimetallic single‐atom‐dimer (SAD) with unique electronic structures and adsorption properties presents exceptional catalytic performance owing to atomic‐level synergistic effects from direct bonding between different metal atoms. However, inherent characteristics of substrate present great challenges in their synthesis and mechanism investigation. Herein, a unique phosphorus modified atomic layer deposition (P‐ALD) strategy is designed to synthesize P‐anchored Pt–W dimers, overcoming substrate limitation (Pt1W1–P/C). Motivated introduction of atomic P site via ALD can effectively anchor one‐to‐one AB bimetallic dimer structure on various substrates, confirmed by X‐ray absorption spectroscopy (XAS). Density functional theory reveals an interatomic synergistic adsorption mechanism, with W as primary hydrogen adsorption site extending to Pt, optimizing hydrogen coverage, leading to 60‐fold increase in mass activity compared to commercial Pt/C in both acidic and alkaline electrolytes. Anion exchange membrane water electrolyzer with ultra‐low loading Pt1W1–P/C (50 µgPt cm−2) catalyst operates durability at 1000 mA cm−2 for 550 h with ultra‐low degradation of 38 µV h−1. Operando XAS confirms hydrogen adsorption pathway between atoms and remarkable self‐healing ability of P–Pt–W–O sites under all‐pH conditions. These findings extend the application domain of SAD to catalytic manufacturing methods and aid in designing advanced materials with multi‐atomic active sites.

Mechanisms for deNOx and deN2O Processes on FAU Zeolite with a Bimetallic Cu-Fe Dimer in the Presence of a Hydroxyl Group-DFT Theoretical Calculations.

In this paper, a detailed mechanism is discussed for two processes: deNOx and deN2O. An FAU catalyst was used for the reaction with Cu-Fe bimetallic adsorbates represented by a dimer with bridged oxygen. Partial hydration of the metal centres in the dimer was considered. Ab initio calculations based on the density functional theory were used. The electron parameters of the structures obtained were also analysed. Visualisation of the orbitals of selected structures and their interpretations are presented. The presented research allowed a closer look at the mechanisms of processes that are very common in the automotive and chemical industries. Based on theoretical modelling, it was possible to propose the most efficient catalyst that could find potential application in industry-this is the FAU catalyst with a Cu-O-Fe bimetallic dimer with a hydrated copper centre. The essential result of our research is the improvement in the energetics of the reaction mechanism by the presence of an OH group, which will influence the way NO and NH3 molecules react with each other in the deNOx process depending on the industrial conditions of the process. Our theoretical results suggest also how to proceed with the dosage of NO and N2O during the industrial process to increase the desired reaction effect.

Ultrahigh Bifunctional Photocatalytic CO2 Reduction and H2 Evolution by Synergistic Interaction of Heteroatomic Pt-Ru Dimerization Sites.

Diatomic-site catalysts (DASCs) inherit the excellent performance of single-atom catalysts (SACs) by utilizing two adjacent atomic metal species to achieve functional complementarity and synergistic effects that improve the carbon dioxide reduction reaction (CO2RR) and H2 evolution reaction (HER) kinetics. Herein, we report a method to further improve the catalytic efficiency of Pt by using Pt and Ru single atoms randomly anchored on a g-C3N4 surface, yielding partial Pt-Ru dimers. The synthesized catalyst exhibits extraordinary photocatalytic activity and stability in both the CO2RR and HER processes. In-depth experimentation, the pH-dependent chemical exchange saturation transfer (CEST) imaging nuclear magnetic resonance (NMR) method, and theoretical analyses reveal that the excellent performance is attributed to orbital coupling between the Pt atoms and the neighboring Ru atoms (mainly dxy and dxz), which decreases the orbital energy levels and weakens the bond strength with intermediates, resulting in improved CO2RR and HER performance. This study successfully applies the pH-dependent CEST imaging NMR method to catalytic reactions, and CO2 adsorption is directly observed using CEST 2D imaging maps. This work presents significant potential for a variety of catalytic reaction applications by systematically designing bimetallic dimers with higher activity and stability.

Comparison of the Mechanisms of deNOx and deN2O Processes on Bimetallic Cu–Zn and Monometallic Cu–Cu Dimers in Clinoptilolite Zeolite—A DFT Study Simulating Industrial Conditions

This paper presents two mechanisms for the deNOx process and for the deN2O process (in two variants). The processes were carried out on a clinoptilolite zeolite catalyst with a deposited Cu–Cu monometallic dimer and Cu–Zn bimetallic dimer with bridged oxygen between the metal atoms. Analyses were performed for hydrated forms of the catalyst with a hydrated bridging oxygen on one of the metal atoms. Calculations were performed using DFT (density functional theory) based on an ab initio method. The analyses included calculations of the energies of individual reaction steps and analysis of charges, bond orders and bond lengths as well as HOMO, SOMO and LUMO orbitals of selected steps in the mechanism. Based on the results obtained, it was determined that the most efficient catalyst for both processes is a Cu–Zn bimetallic catalyst with a bridged hydroxyl group. It shows higher efficiency in the limiting step (formation of the -N2H intermediate product) than the previously studied FAU and MFI zeolites with a Cu–Zn bimetallic dimer. In addition, the possibility of using the catalytic system from the deNOx process in the deN2O process was presented, which can benefit SCR installations. In addition, it was proved that the order of adsorption of NO and N2O has significance for further steps of the deN2O process. In order to improve the comparison of FAU, MFI and CLI zeolite catalysts with a Cu–Zn dimer, further studies on the deN2O mechanism for the first two zeolites are needed. This study allows us to propose a bimetallic catalyst for the deNOx and deN2O processes.

Asymmetric electronic occupation in bimetallic single-atom dimers to accelerate spin-resolved oxygen evolution reaction

The catalytic performance of single-atom catalysts (SACs) strongly depends on their electronic occupation at 3d-orbitals and spin exchange interaction. However, the correlation between catalytic activity and the optimal spin configuration in accelerating oxygen evolution reaction (OER) still needs to be understood. Herein, we suggest a bimetallic single-atom dimer with asymmetric spin polarization to eliminate the antiferromagnetic contribution, in which the bonding interaction and charge transfer between active sites and reactants can be effectively optimized by this intriguing residual ferromagnetic behavior. As a result, the activation barrier of OER at rate-limiting step reduces effectively due to this asymmetric spin occupation. This work provides a new insight into accelerating the OER by regulating spin electron occupation in SACs.

Facile and efficient ligand-directed asymmetric growth of Au–Ag bimetallic dimer nanostructures

Facile and efficient ligand-directed asymmetric growth of Au–Ag bimetallic dimer nanostructures

The effect of the presence of a hydroxyl group on the vibration frequencies of NO and NH3 adsorbates on Cu-Zn bimetallic nanoparticles in ZSM-5 and FAU zeolite – a DFT study

The objective of this study was to propose a more promising catalyst for the deNOx process to effectively eliminate harmful nitrogen oxides from the environment. In the present study we considered bimetallic dimers of copper and zinc deposited in zeolites. The study was performed with a computer calculation using DFT based on ab initio method and a cluster model. Two zeolite catalysts, FAU and ZSM-5, were selected with an additional Cu-O-Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of adsorption of nitric oxide and ammonia in a different environment was selected. Two types of adsorption were proposed: with only a bridging oxygen of the dimer and with a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with the bimetallic dimer and the OH group behave differently than ZSM-5, regarding both NO and NH3 adsorption. A full vibrational analysis of the adsorbates was developed. The obtained anharmonic vibrations can be used to improve the interpretation of comprehensive experimental data of the deNOx process on bimetallic systems.

Theoretical Studies on the Mechanism of deNOx Process in Cu-Zn Bimetallic System-Comparison of FAU and MFI Zeolites.

In the present study we propose a more promising catalyst for the deNOx process to eliminate harmful nitrogen oxides from the environment. The study was performed with a computer calculation using density functional theory (DFT) based on an ab initio method. Two zeolite catalysts, FAU and MFI, were selected with additional Cu–O–Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of co-adsorption of nitric oxide and ammonia was selected, which became the initial configuration for the reaction mechanism. Two types of mechanisms were proposed: with hydroxyl groups on a bridged position of the dimer or a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with a bimetallic dimer and an OH group on the zinc atom was the most efficient configuration with a relatively low energy barrier. The real advantage of the Cu–Zn system over FAU and MFI in hydrothermal conditions has been demonstrated in comparison to a conventional Cu–Cu catalyst.

Adsorption and dissociation of dinitrogen on mono-metallic and bimetallic dimers

This paper deals with Density Functions Theory (DFT) based theoretical investigation of the dissociation of strong N–N triple bond of dinitrogen (N2). Mono-metallic and bimetallic dimers of selected transition metals (Zr, Nb, Hf, and Ta) are used as adsorbent. The dissociation of N–N bond is found to be strongly dependent on orientation of N–N axis with respect to the axis of the adsorbent dimer. N–N axis perpendicular to dimer axis has been found to be suitable for dissociative adsorption of dinitrogen. Apart from orientation the combination of two different transition metal atoms in the dimer also has significant effect in the elongation and dissociation of N–N bond. Our study shows even 2-atom clusters (dimers) of these transition metals are capable of breaking N–N triple bond.

Color Routing via Cross-Polarized Detuned Plasmonic Nanoantennas in Large-Area Metasurfaces.

Bidirectional nanoantennas are of key relevance for advanced functionalities to be implemented at the nanoscale and, in particular, for color routing in an ultracompact flat-optics configuration. Here we demonstrate a novel approach avoiding complex collective geometries and/or restrictive morphological parameters based on cross-polarized detuned plasmonic nanoantennas in a uniaxial (quasi-1D) bimetallic configuration. The nanofabrication of such a flat-optics system is controlled over a large area (cm2) by a novel self-organized technique exploiting ion-induced nanoscale wrinkling instability on glass templates to engineer tilted bimetallic nanostrip dimers. These nanoantennas feature broadband color routing with superior light scattering directivity figures, which are well described by numerical simulations and turn out to be competitive with the response of lithographic nanoantennas. These results demonstrate that our large-area self-organized metasurfaces can be implemented in real-world applications of flat-optics color routing from telecom photonics to optical nanosensing.

Catalytic Oxidation of NO on [Au–M]− (M = Pd and Pt) Bimetallic Dimers: An Insight from Density Functional Theory Approach

Escalation of nitrogen monoxide (NO) concentration into the atmosphere has caused severe environmental problems. So, it is important to prepare or design a suitable catalytic system to understand t...

Atomic layer deposited Pt-Ru dual-metal dimers and identifying their active sites for hydrogen evolution reaction

Single atom catalysts exhibit particularly high catalytic activities in contrast to regular nanomaterial-based catalysts. Until recently, research has been mostly focused on single atom catalysts, and it remains a great challenge to synthesize bimetallic dimer structures. Herein, we successfully prepare high-quality one-to-one A-B bimetallic dimer structures (Pt-Ru dimers) through an atomic layer deposition (ALD) process. The Pt-Ru dimers show much higher hydrogen evolution activity (more than 50 times) and excellent stability compared to commercial Pt/C catalysts. X-ray absorption spectroscopy indicates that the Pt-Ru dimers structure model contains one Pt-Ru bonding configuration. First principle calculations reveal that the Pt-Ru dimer generates a synergy effect by modulating the electronic structure, which results in the enhanced hydrogen evolution activity. This work paves the way for the rational design of bimetallic dimers with good activity and stability, which have a great potential to be applied in various catalytic reactions.

Graphene-Supported Monometallic and Bimetallic Dimers for Electrochemical CO2 Reduction

Bimetallic catalysts are attractive alternatives to extend the parameter space that can be tuned for support interactions and catalytic performance. In this study, we have investigated the smallest bimetallic catalysts—dimers—supported on defective graphene for the electrochemical reduction of CO2 to CH4 based on a first-principles approach and the computational hydrogen electrode model. The monometallic and bimetallic dimers formed from Group 10 (Ni, Pd, Pt) and group 11 (Cu, Ag, Au) elements are characterized by a positively charged anchoring atom occupying the vacancy site of graphene and a neutral or slightly negatively charged antenna atom sticking out from the graphene surface. The strong selective binding of these dimers ensures their high stability. Possible rate-limiting steps are identified from the full reaction pathways to generate CH4. Overall, Pt2, AgNi, Pd2, and AgPt are the best candidates with the lowest overpotential values of 0.37, 0.69, 0.69, and 0.76 V, respectively. It is found that ...

Theoretical analysis of bimetallic nanorod dimer biosensors for label-free molecule detection

In this work, we theoretically analyze a gold (Au) core within silver (Ag) shell (Au@Ag) nanorod dimer biosensor for label-free molecule detection. The incident light on an Au@Ag nanorod strongly couples to localized surface plasmon modes, especially around the tip region. The field enhancement around the tip of a nanorod or between the tips of two longitudinally aligned nanorods as in a dimer can be exploited for sensitive detection of biomolecules. We derive analytical expressions for the interactions of an Au@Ag nanorod dimer with the incident light. We also study the detail dynamics of an Au@Ag nanorod dimer with the incident light computationally using finite difference time domain (FDTD) technique when core-shell ratio, relative position of the nanorods, and angle of incidence of light change. We find that the results obtained using the developed analytical model match well with that obtained using FDTD simulations. Additionally, we investigate the sensitivity of the Au@Ag nanorod dimer, i.e., shift in the resonance wavelength, when a target biomolecule such as lysozyme (Lys), human serum albumin (HSA), anti-biotin (Abn), human catalase (CAT), and human fibrinogen (Fb) protein molecules are attached to the tips of the nanorods.

Cobalt complexes of the chelating dicarboxylate ligand "esp": a paddlewheel-type dimer and a heptanuclear coordination cluster.

The coordination chemistry of Co(ii) with the chelating dicarboxylate ligand esp (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropionate) is explored. We report here the bimetallic paddlewheel-type dimer, Co2(esp)2(EtOH)2 (1), and a bowl-shaped, heptanuclear coordination cluster, Co7(OH)4(Hesp)2(esp)4(MeCN)2·4MeCN (2). Crystal structures of both complexes are reported as well as their magnetic properties, which indicate antiferromagnetic interactions among the Co(ii) ions.

(ZnSb6)2]4-: a new structure type for coupled norbornadiene-like subunits.

The norbornadiene-like bimetallic dimer [(ZnSb6)2]4- anion (1) was prepared by direct extraction from a ternary alloy with nominal composition "K6ZnSb5" in ethylenediamine/toluene/2,2,2-crypt solutions. The structure represents a new type for coupled norbornadiene subunits, however, distortions around the Zn2+ ions degrade the overall symmetry. The Zn2+ ions achieve a 16e- configuration and reside in near perfect ZnSb3 triangular coordination environments. DFT calculations reveal a 2.35 eV HOMO-LUMO gap and suggest covalent bonding between the Zn and Sb atoms.

Effects of gold based dimers on structural and electronic properties of MoS2

In view of first principles calculations, we investigate the electronic structure redecoration of monolayer MoS2 upon adsorptions of AuAg, AuPt, AuPd, AuCu, and AuAl bimetallic dimers. Geometrical structure, band structures, electronic density of states, charge density differences of dimer adsorbed MoS2 systems are presented and discussed. All the systems studied have non-magnetic ground states. Charge transfers occur from dimer to surface except for AuPt adsorption. Our results indicate that the semiconductor MoS2 maintains its semiconductor character with decreased band gaps upon AuAg, AuCu, and AuAl adsorptions. However, MoS2 shows metallic behaviour by AuPt and AuPd adsorptions, so Pt-d and Pd-d states cross Fermi level yielding metallic character. AuPt adsorbed system has the highest Eads value of 3.15eV indicating the most stable structure energetically among the dimer adsorbed MoS2 systems considered.

Bimetallic dimers adsorbed on a defect-free MgO(001) surface: bonding, structure and reactivity.

A large number of computational studies have been devoted to the investigation of monometallic clusters supported by MgO. However, in practice, catalysis shows that multicomponent catalytic systems often win in catalytic performance over single component systems. In this study, the geometrical and electronic structure, stability and chemisorption properties of M1M2 metal dimers (M1, M2 = Ru, Rh, Pd, Ir, Pt) supported by defect free MgO(001) have been investigated in the framework of density functional theory. The oxygen sites of MgO(001) are the preferred adsorption sites for all the studied clusters, the majority of them adsorbing parallel to the surface with metal atoms attached to two surface oxygen atoms. The energetics of M1M2 + MgO(001) formation shows that the adsorption complexes are stable and benefit from metal-oxygen and metal-metal interaction. The chemisorption properties of Pd and Pt atoms in PdM2 and PtM2 dimers are studied using CO as a probe molecule. A linear relationship between the CO chemisorption and the d-band center position of the reacting atom in the dimer is observed, extending the d-band center model to the case of highly under-coordinated metal atoms supported by a non-conductive material.

Shape-defined nanodimers by tailored heterometallic epitaxy.

The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.

Excitation of Multiple Fano-Like Resonances Induced by Higher Order Plasmon modes in Three-Layered Bimetallic Nanoshell Dimer

The presence of plasmonic Fano-like resonances in the optical response of isolated and dimer metal-dielectric-metal nanostructures are investigated theoretically. The nanostructures are engineered in such a way to support multiple Fano-like resonances that are induced by the interference of bright and dark plasmon modes. It is found that the dimer resonators exhibit different types of Fano resonances for both the transverse and longitudinal polarizations unlike conventional nanodimers. Several configurations of the dimer Fano resonator are analyzed with special emphasis on the Fano spectral line shape. Breaking the symmetry of the dimer nanostructure in various directions control the asymmetric line shape and provides different kinds of unique Fano resonances. In certain cases, the Fano resonators exhibit multiple Fano resonances that are particularly significant for plasmon line shaping and can serve as platforms for multi-wavelength sensing applications.