Ru Atoms Research Articles

First-principles study of the magnetic exchange forces between the RuO2 (110) surface and Fe tip.

Magnetic exchange force microscopy (MExFM) is an important experimental technique for mapping the magnetic structure of surfaces with atomic resolution relying on the spin-dependent short-range exchange interaction between a magnetic tip and a magnetic surface. RuO2 is a significant compound with applications in heterogeneous catalysis and electrocatalysis. It has been characterized recently as an antiferromagnetic (AFM) material, and its magnetism has been predicted somewhat surprisingly to play an important role in its catalytic properties. In the current study, we explore theoretically whether MExFM can visualize the magnetic surface structure of RuO2 . We use density functional theory (DFT) calculations to extract the exchange interactions between a ferromagnetic Fe tip interacting with an AFM RuO2 (110) surface, as a function of tip-surface distance and the position of the tip over the surface. Mimicking the MExFM experiment, these data are then used to calculate the normalized frequency shift of an oscillating cantilever tip versus the minimum tip-surface distance, and construct corrugation height line profiles. It is found that the exchange interaction between tip and surface is strongest for a parallel configuration of the spins of the tip and of the surface; it is weakest for an anti-parallel orientation. In a corrugation profile, this gives rise to a sizable height difference of 25 pm between the spin-up and spin-down Ru atoms in the RuO2 (110) surface at a normalized frequency shift =-10.12 fNm1/2 . The O atoms in the surface are not or hardly visible in the corrugation profile.

Crystal Structure and Electrical Properties of Ruthenium-Substituted Calcium Copper Titanate.

This paper reports a detailed study of crystal structure and dielectric properties of ruthenium-substituted calcium-copper titanates (CaCu3Ti4-xRuxO12, CCTRO). A series of three samples with different stoichiometry was prepared: CaCu3Ti4-xRuxO12, x = 0, 1 and 4, abbreviated as CCTO, CCT3RO and CCRO, respectively. A detailed structural analysis of CCTRO samples was done by the Rietveld refinement of XRPD data. The results show that, regardless of whether Ti4+ or Ru4+ ions are placed in B crystallographic position in AA'3B4O12 (CaCu3Ti4-xRuxO12) unit cell, the crystal structure remains cubic with Im3¯ symmetry. Slight increases in the unit cell parameters, cell volume and interatomic distances indicate that Ru4+ ions with larger ionic radii (0.62 Å) than Ti4+ (0.605 Å) are incorporated in the CaCu3Ti4-xRuxO12 crystal lattice. The structural investigations were confirmed using TEM, HRTEM and ADF/STEM analyses, including EDXS elemental mapping. The effect of Ru atoms share in CaCu3Ti4-xRuxO12 samples on their electrical properties was determined by impedance and dielectric measurements. Results of dielectric measurements indicate that one atom of ruthenium per CaCu3Ti4-xRuxO12 unit cell transforms dielectric CCTO into conductive CCT3RO while preserving cubic crystal structure. Our findings about CCTO and CCT3RO ceramics promote them as ideal tandem to overcome the problem of stress on dielectric-electrode interfaces in capacitors.

Ruthenium ion modification of glassy carbon: Implication on the structural evolution and migration behaviour of implanted Ru atoms

Glassy carbon samples were implanted with ruthenium ions to a fluence of 1 × 1016 cm−2 at room temperature (at 150 keV). The implanted samples were annealed isochronally in vacuum from 1000 to 1300 °C for 5 h. The resulting microstructural changes were investigated using X-ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The diffusion behaviour of ruthenium in glassy carbon was investigated using secondary-ion mass spectrometry (SIMS). Raman results showed that the implantation of ruthenium into glassy carbon caused amorphization and increase the tensile stress in the implanted region. XRD showed that the amount of tensile stress in virgin glassy carbon increased from 0.016 GPa to 0.19 GPa after ion implantation which is in qualitative agreement with the Raman results. Annealing of the samples exhibited more recrystallization and changed the tensile stress to compressive stress. SIMS results showed that annealing of the as-implanted samples at 1000 °C caused aggregation of the ruthenium atoms, while annealing at higher temperatures led to some segregation of ruthenium atoms at a depth of 155 nm below the glassy carbon surface. The aggregation of ruthenium atoms after annealing (as observed by SIMS) played a role in the surface roughness as observed by AFM.

Selective Hydrodeoxygenation of Aromatics to Cyclohexanols over Ru Single Atoms Supported on CeO2.

Cyclohexanols are widely used chemicals, which are mainly produced by oxidation of fossil feedstocks. Selective hydrodeoxygenation of lignin derivatives has great potential for producing these chemicals but is challenging to obtain high yields. Here, we report that CeO2-supported Ru single-atom catalysts (SACs) enabled the hydrogenation of the benzene ring and catalyzed etheric C-O(R) bond cleavage without changing the C-O(H) bond, which could afford 99.9% yields of cyclohexanols. As far as we know, this is the first to report that SACs catalyze hydrogenation of the aromatic ring. The reaction mechanism was studied by control experiments and density functional theory calculations. In the catalysts, the Ru-O-Ce sites were formed and one Ru atom was coordinated with about four O atoms. These catalytic sites could realize both the hydrogenation and deoxygenation reactions efficiently, and thus desired cyclohexanols were generated. This work pioneers the single-atom catalysis in aromatic transformation and provides a novel route for synthesis of cyclohexanols.

Ruthenium doped commercial carbon cloth for efficient electrocatalytic hydrogen evolution reaction

The heterogenous electrochemical catalyst of activated carbon cloth coupled with Ru doping was fabricated via a facile hydrothermal method. The obtained activated carbon cloth coupled with Ru catalyst possesses outstanding hydrogen evolution reaction performance even superior than 40 % Pt/C catalyst in alkaline system. • Commercial carbon cloth was activated via facile hydrothermal process for the first time. • The Ru atoms anchored on carbon cloth act as the new active centers. • Ru/CC exhibited excellent HER activity and strong stability in alkaline solution. • Low overpotential of 24 mV and Tafel slope of 51.5 mV dec −1 was delivered at 10 mA cm −2 . Ru atoms are doped on the surface of commercial carbon cloth (Ru/CC) through a simple and facile hydrothermal process and the catalytic inert surface of CC is activated. The activated Ru/CC exhibit excellent HER electrocatalytic activity in 1 M KOH solution. The Ru/CC-0.1 catalyst has a small overpotential of 24 mV at 10 mA cm −2 and low Tafel slope of 51.5 mV dec −1 .

Syntheses and Applications of Symmetrical Dinuclear Half-Sandwich Ruthenium(II)–Dipicolinamide Complexes as Catalysts in the Transfer Hydrogenation of Ketones

The treatment of [Ru(η6-p-cymene)Cl2]2 with N,N’-(1,2-phenylene)dipicolinamide (H2L1) afforded the double salt complex [{Ru(η6-p-cymene)2-µ-Cl}L1][Ru(η6-p-cymene)Cl3], (Ru1) in moderate yields. Separately, the reactions of ligands (H2L1), N,N’-(4,5 dimethyl-1,2-phenylene)dipicolinamide (H2L2), and N,N’-(4-methoxy-1,2-phenylene)dipicolinamide (H2L3) with the [Ru(η6-p-cymene)Cl2]2 in the presence of KPF6 afforded the respective dinuclear half-sandwich Ru(II) complexes [{(Ru(η6-p-cymene)2--µ-Cl}L1][PF6] (Ru2), [{(Ru(η6-p-cymene)2-µ-Cl}L2][PF6] (Ru3), and [{(Ru(η6-p-cymene)2-µ-Cl}L3][PF6] (Ru4). NMR and FT-IR spectroscopies, ESI-MS spectrometry, and elemental analyses were used to establish the molecular structures of the new dinuclear ruthenium(II) complexes. Single crystal X-ray crystallography was used to confirm the piano-stool geometry of the dinuclear complexes Ru1 and Ru4, as containing N^N chelated ligand and bridging chlorido ligands in each Ru(II) atom. The complexes (Ru1-Ru4) showed good catalytic activities at low catalyst concentrations of 0.005 mol% in the transfer hydrogenation of a wide range of ketone substrates.

Ru Single Atoms on One-Dimensional CF@g-C3N4 Hierarchy as Highly Stable Catalysts for Aqueous Levulinic Acid Hydrogenation.

Herein, we report a stable catalyst with Ru single atoms anchored on a one-dimensional carbon fiber@graphitic carbon nitride hierarchy, by assembling wet wipes composed of fiber-derived carbon fiber (CF), melamine-derived graphitic carbon nitride (g-C3N4) and RuCl3 before NaBH4 reduction. The atomically dispersed Ru species (3.0 wt%) are tightly attached via N-coordination provided by exterior g-C3N4 nanosheets, and further stabilized by the interior mesoporous CF. The obtained CF@g-C3N4-Ru SAs catalyst can be cycled six times without notable leaching of Ru or loss of GVL yield in the acidic media. This catalyst is more stable than Ru nanoparticles supported on CF@g-C3N4, as well as Ru single atoms anchored on CF and g-C3N4, and proves to be one of the most efficient metal catalysts for aqueous LA hydrogenation to γ-valerolactone (GVL). The isolated Ru atoms by strong N-coordination, and their enhanced electron/mass transfer afforded by the one-dimensional hierarchy, can be responsible for the excellent durability of CF@g-C3N4-Ru SAs under harsh reaction conditions.

Atomically dispersed single ruthenium sites anchored on bismuth tungstate with synergistic geometric and electronic effects for epoxidation of trans-stilbene

The feasibility of elegantly tuned geometric structures and electronic environments of metal active sites in single atom catalysts (SACs) is crucial for developing highly robust and efficient catalytic materials. Here we report a straightforward and efficient approach to accessing single ruthenium (Ru) atoms over a Bi2WO6 assemblage, with each Ru atom coordinated with four neighboring oxygen atoms. This Ru catalyst, exhibits synergistic geometric and electronic effects, resulting in a significantly enhanced catalytic performance for epoxidation of trans-stilbene to give trans-stilbene oxide. The reaction takes place under mild conditions, with high conversion (>99 %) and selectivity (>99 %) within a mere 2 h and a high turnover frequency (TOF) of 558 h−1. The theoretical calculations demonstrate that the high catalytic activity originates from the strong electronic metal-support interaction and the charge state of ruthenium sites in Bi2WO6. This work opens an avenue to engineer SACs on Aurivillius (perovskite) phase materials at the atomic level and serves as a promising platform for further studies of many other organic transformations.

Mo3ReRuC: A Noncentrosymmetric Superconductor Formed in the MoReRu-Mo2C System.

A quaternary compound with the composition Mo3ReRuC is obtained in a previously unexplored MoReRu-Mo2C system. According to X-ray structural analysis, Mo3ReRuC crystallizes in the noncentrosymmetric space group P4132 [cubic β-Mn-type structure, a = 6.8107(1) Å]. Below 7.7 K, Mo3ReRuC becomes a bulk type-II superconductor with an upper critical field close to the Pauli paramagnetic limit. The specific heat data give a large normalized jump ΔCp/γTc = 2.3 at Tc, which points to a strongly coupled superconducting state. First-principles calculations show that its electronic states at the Fermi level are mainly contributed by Mo, Re, and Ru atoms and strongly increased by the spin-orbit coupling. Our finding suggests that the intermediate phase between alloys and carbides may be a good place to look for β-Mn-type noncentrosymmetric superconductors.

Construction of Ru–N Single Sites for Effective Acetylene Hydrochlorination: Effect of Polyethyleneimine Modifiers

Several single-site catalysts have been synthesized through the chelation of polyethyleneimine (PEI) with Ru precursors because of the lack of durable active sites in Ru catalysts for acetylene hydrochlorination. Proper thermal activation successfully constructed the local active domains of Ru–N. Ru species were stabilized in their active states by coordinating N in PEI with the central atom Ru in the Ru/activated carbon (AC) catalyst. The metal and highly electronegative heteroatomic sites in the Ru–N domains augmented the activation ability of reactant molecules synergistically. The synthetic strategy developed led to the dispersion of active metal at the level of a single site. Additionally, more Ru–N–C interfaces formed after appropriate pyrolysis of the catalyst (Ru/AC@PEI-T), increasing the contact area to reactants and improving the catalytic efficiency. The modified Ru/AC@PEI catalyst has significantly enhanced catalytic stability over time, allowing for possible industrial applications.

Structural and magnetic properties of Ca3Mn2−xRuxO7(0<x≤0.9)

We here report on the study of the crystallographic and magnetic properties of layered perovskites ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{7}$ ($x\ensuremath{\le}0.9$). We observe a solid solution between Mn and Ru atoms in the whole series and all samples present the same orthorhombic structure independently of the Ru content. Different magnetic structures, depending on the Ru content in the sample, have been determined using neutron powder diffraction. For low Ru doping ($x\ensuremath{\le}0.1$), there is a dominant $G$-type antiferromagnetic ordering in the perovskite bilayers but, differently from undoped ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$, the magnetic moments are located on the $ab$ plane. For higher Ru concentration ($x\ensuremath{\ge}0.3$), the predominant $G$-type ordering is preserved along the $y$ axis while an $A$-type component is developed along the $x$ axis and its intensity increases as Ru content does. This component is characterized by a ferromagnetic ordering in the $a$ direction of one of the $Mn(\mathrm{Ru}){\mathrm{O}}_{6}$ layers, coupled antiferromagnetically with the neighbor $\mathrm{Mn}(\mathrm{Ru}){\mathrm{O}}_{6}$ layer within the same bilayer. The study of the macroscopic magnetic properties shows that ferromagneticlike correlations are enhanced with increasing Ru content as deduced from the shift to higher temperature of the onset of the magnetic transition temperature. The magnetic transitions take place in two steps. At higher temperatures (140--200 K), short-range magnetic correlations are established. Tiny spontaneous magnetization is observed in the hysteresis loops with small coercive field. At ${T}_{\mathrm{N}}\ensuremath{\approx}115--125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, long-range antiferromagnetic ordering is developed. The ferromagnetic component remains with a strong increase of coercivity. We discuss in the paper the possible origins of this ferromagnetic contribution.

Catalase-Mimetic Artificial Biocatalysts with Ru Catalytic Centers for ROS Elimination and Stem-Cell Protection.

Exploring high-efficiency reactive oxygen species (ROS)-elimination materials is of great importance for combating oxidative stress in diverse diseases, especially stem-cell-based biotherapeutics. By mimicking the FeN active centers of natural catalase, here, an innovative concept to design ROS-elimination artificial biocatalysts with Ru catalytic centers for stem-cell protection is reported. The experimental studies and theoretical calculations have systematically disclosed the activity merits and structure diversities of different Ru sites when serving as ROS-elimination artificial biocatalysts. Benefiting from the metallic electronic structures and synergetic effects of multiple sites, the artificial biocatalysts with Ru cluster centers present exceptional ROS-elimination activity; notably, it shows much higher catalytic efficiency per Ru atom on decomposing H2 O2 when compared to the isolated single-atom Ru sites, which is more efficient than that of the natural antioxidants and recently reported state-of-the-art ROS-scavenging biocatalysts. The systematic stem-cell protection studies reveal that the catalase-like artificial biocatalysts can provide efficient rescue ability for survival, adhesion, and differentiation functions of human mesenchymal stem cells in high ROS level conditions. It is suggested that applying these artificial biocatalysts with Ru cluster centers will offer a new pathway for engineering high-performance ROS-scavenging materials in stem-cell-based therapeutics and many other ROS-related diseases.

Mott Insulator Ca2RuO4 under External Electric Field.

We have investigated the structural, electronic and magnetic properties of the Mott insulator Ca2RuO4 under the application of a static external electric field in two regimes: bulk systems at small fields and thin films at large electric fields. Ca2RuO4 presents S- and L-Pbca phases with short and long c lattice constants and with large and small band gaps, respectively. Using density functional perturbation theory, we have calculated the Born effective charges as response functions. Once we break the inversion symmetry by off-centering the Ru atoms, we calculate the piezoelectric properties of the system that suggest an elongation of the system under an electric field. Finally, we investigated a four-unit cell slab in larger electric fields, and we found insulator–metal transitions induced by the electric field. By looking at the local density of states, we have found that the gap gets closed on surface layers while the rest of the sample is insulating. Correlated to the electric-field-driven gap closure, there is an increase in the lattice constant c. Regarding the magnetic properties, we have identified two phase transitions in the magnetic moments with one surface that gets completely demagnetized at the largest field investigated. In all cases, the static electric field increases the lattice constant c and reduces the band gap of Ca2RuO4, playing a role in the competition between the L-phase and the S-phase.

Stacking-mediated diffusion of ruthenium nanoclusters in bilayer graphene and graphite

The diffusion, penetration and intercalation of metallic atomic dopants is an important question for various graphite applications in engineering and nanotechnology. We have performed systematic first-principles calculations of the behaviour of ruthenium nanoclusters on a graphene monolayer and intercalated into a bilayer. Our computational results show that at a sufficiently high density of single Ru atom interstitials, intercalated atoms can shear the surrounding lattice to an AA stacking configuration, an effect which weakens with increasing cluster size. Moreover, the interlayer stacking configuration, in turn, has a significant effect on cluster diffusion. We therefore find different trends in diffusivity as a function of cluster size and interlayer stacking. For monolayer graphene and an AA graphene bilayer, the formation of small clusters generally lowers diffusion barriers, while the opposite behaviour is found for the preferred AB stacking configuration. These results demonstrate that conditions of local impurity concentration and interlayer disregistry are able to regulate the diffusivity of metallic impurities in graphite.

Catalytic Descriptor Exploration for Ru-Based Fischer–Tropsch Catalysts: Effect of Chlorine and Sulfur Addition

As an important factor in the design of catalysts, catalytic descriptor exploration has emerged as a novel frontier in heterogeneous catalysis. Here, the underlying structure-activity relationships of Ru-based catalysts are theoretically studied to shed light on this area. Calculations of different competing reaction paths suggest that the HCO*-mediated path─because of two synergistic active sites─is more favorable than others. In addition, compared to unadulterated Ru catalysts, the presence of Cl enhances the hydrocarbon production, whereas the presence of S decreases it. After a systematic examination of a series of structure-activity relationships (42 in total), we found that both charge transfer and average charge difference of active Ru atoms are good descriptors for the binding stability of reactants. However, for reactivity the Gibbs free energy of the reactants performs better. More interestingly, due to the quite different catalytic processes of the dissociation and hydrogenation steps, their correlations have opposite slopes.

Catalytic Synergies in Bimetallic RuPt Single–Atom Catalysts via Speciation Control

AbstractBimetallic single–atom catalysts (b–SACs) have recently gained prominence by virtue of the unique catalytic cooperative interactions they can exhibit, intertwining electronic and geometric effects. To date, research efforts have exclusively focused on direct mechanisms such as electron density transfer or sequential reactivity. Herein, the first study on indirect, coordination–induced catalytic synergies in carbon‐supported RuPt SACs is conducted. To this end, a holistic approach is developed, combining i) precision synthesis, ii) advanced characterization, iii) exploration of single–site adsorption properties via the hydrogen evolution reaction, and iv) modeling through density functional theory. Despite the lack of both intermetallic coordination in the first or second shell and charge redistribution effects, the RuPt SACs exhibit a H2 formation rate enhanced up to 15–fold compared with their monometallic counterparts. To unfold the origin of the intermetallic cooperativity, modifications of the structural and catalytic properties induced by the integration of a second metal species are investigated. Thus, Pt atoms are found to selectively occupy the most energeticallyfavorable cavities in the support, prompting Ru atoms to assume a distinct, more active, configuration. This contribution unveils a novel principle of bimetallic cooperativity, demonstrating the key role of integrative experimental and computational analyses in studying b–SACs.

Single Atom Ru Monolithic Electrode for Efficient Chlorine Evolution and Nitrate Reduction.

Fabricating single-atom electrodes via atomic dispersion of active metal atoms into monolithic metal supports is of great significance to advancing the lab-to-fab translation of the electrochemical technologies. Here, we report an inherent oxide anchoring strategy to fasten ligand-free isolated Ru atoms on the amorphous layer of monolithic Ti support by regulating the electronic metal-support interactions. The prepared Ru single atom electrode exhibited exceptional electrochemical chlorine evolution activity, three orders of magnitude higher mass activity than that of commercial dimensionally stable anode, and also selectively reduced nitrate to ammonia with an unprecedented ammonia yield rate of 22.2 mol g-1 h-1 at -0.3 V. Furthermore, the Ru single atom monolithic electrode can be scaled up from 2×2 cm to 25×15 cm at least, thus demonstrating great potential for industrial electrocatalytic applications.

Strong electronic coupling between single Ru atoms and cobalt-vanadium layered double hydroxide harness efficient water splitting

Atomic coordination modulation and electronic structure engineering are appealing routes to develop versatile electrocatalysts targeting high-performance water electrolysis. Herein, atomically dispersed Ru sites are successfully anchored on the surface of CoV layered double hydroxide (LDH), affording a vertically aligned and interconnected nanosheet array architecture. Benefitting from the strong electronic coupling, fast charge transfer capability and well-defined morphology of as-prepared catalyst, ultralow overpotentials for hydrogen evolution reaction (HER, η10 = 28 mV) and oxygen evolution reaction (OER, η25 = 263 mV) are required. The two-electrode configuration cell only requires a cell voltage of 1.52 V to reach 10 mA cm−2, which is lower than that of commercialized Pt/C||RuO2 couple. Synchrotron X-ray absorption spectroscopy studies in combination with density functional theory calculations reveal that the strong electronic coupling between monatomic Ru with CoV LDH induces spatial charge redistribution and a distorted coordination environment around V atoms, thereby accelerating the hydrogen release for HER and reducing the rate-determining step (O* → OOH*) free energy for OER.

Single Atom Ru Monolithic Electrode for Efficient Chlorine Evolution and Nitrate Reduction

AbstractFabricating single‐atom electrodes via atomic dispersion of active metal atoms into monolithic metal supports is of great significance to advancing the lab‐to‐fab translation of the electrochemical technologies. Here, we report an inherent oxide anchoring strategy to fasten ligand‐free isolated Ru atoms on the amorphous layer of monolithic Ti support by regulating the electronic metal‐support interactions. The prepared Ru single atom electrode exhibited exceptional electrochemical chlorine evolution activity, three orders of magnitude higher mass activity than that of commercial dimensionally stable anode, and also selectively reduced nitrate to ammonia with an unprecedented ammonia yield rate of 22.2 mol g−1 h−1 at −0.3 V. Furthermore, the Ru single atom monolithic electrode can be scaled up from 2×2 cm to 25×15 cm at least, thus demonstrating great potential for industrial electrocatalytic applications.

Ru single atom catalyst with dual reaction sites for efficient fenton-like degradation of organic contaminants

Recently, Fenton-like reaction based on peroxymonosulfate (PMS) has been recognized as a potential alternative for the degradation of organic pollutants. Herein, a high-efficiency and stable catalyst comprised of single Ru atoms dispersed on N-doped carbon (RuSA-N-C) is synthesized by solvothermal strategy. RuSA-N-C could effectively activate PMS for the degradation of azide dyes (Orange Ⅱ), compared with Ru-nanoparticle-loaded catalysts. Free radical scavenging experiments and density functional theory have displayed that singlet oxygen (1O2) produced by Ru-N4 sites are the main reactive oxygen species for the degradation of Orange Ⅱ. Meanwhile, the adjacent pyridinic N acts as the adsorption sites to anchor Orange Ⅱ. The ultra-high catalytic activity of RuSA-N-C mainly derivate from its distinctive dual reaction sites, which significantly shorten the migration distance from 1O2 to the adsorbed Orange Ⅱ molecules. This study provides a potential RuSA-N-C/PMS system for the high-efficiency sewage treatment.