Bulk Ru Research Articles

The Effect of pH on Slurry Erosion–Corrosion of Tungsten Carbide Overlays Alloyed with Ru

The aim of the study was to determine the effect of Ru additions to WC-Fe overlays when exposed to low pH slurry erosion conditions. These overlays were applied through Plasma Transferred Arc, and the original bulk Ru powder concentrations varied from 0.5 to 5 wt.%. A slurry jet impingement erosion–corrosion test rig was used to evaluate wear, and electrochemical measurements were performed to characterize the corrosion properties. The slurry mixtures contained silica sand and synthetic mine water. The pH was varied between 3 and 6.5 for the slurry erosion tests and lowered further for the corrosion characterization. Samples were examined optically and with a scanning electron microscope using energy-dispersive x-ray spectroscopy. X-ray diffraction analysis was used to determine the phases present. For the slurry erosion–corrosion results at the pH of 6.5, addition of Ru did not show a decrease in erosion–corrosion rates. However, when the pH was decreased to 3, by the addition of HCl, Ru improved the resistance. From the electrochemistry, it was also clear that Ru additions improved the corrosion resistance, but more than 1 wt.% Ru was required. At very low pH levels, the presence of Ru was not able to prevent corrosion.

Facile Synthesis of Ru-Based Octahedral Nanocages with Ultrathin Walls in a Face-Centered Cubic Structure

Noble-metal nanocages with ultrathin (less than 2 nm) walls and well-defined facets have received great interest owing to their remarkable utilization efficiency of atoms and facet-dependent catalytic activities toward various reactions. Here, we report the synthesis of Ru-based octahedral nanocages covered by {111} facets, together with ultrathin walls in a face-centered cubic (fcc) structure rather than the hexagonal close-packed (hcp) of bulk Ru. The involvement of slow injection for the Ru(III) precursor, the introduction of KBr, and the use of elevated temperature were all instrumental to the formation of Pd@Ru core–shell octahedra with a conformal, uniform shell and a smooth surface. The {111} facets were well preserved during the selective removal of the Pd cores via wet etching, even when the Ru walls were only five atomic layers in thickness. Through in situ XRD, we demonstrated that the fcc structure of the Ru nanocages was stable up to 300 °C. We also used first-principles, self-consistent dens...

Unexpected Odd–Even Oscillation in the Enhanced Chemical Activities of the Run (n = 2–14) Nanoclusters for H2O Splitting

Nanoclusters usually display exotic physical and chemical properties due to their intriguing geometric structures in contrast to their bulk counterparts. In general, the more energetically stable the nanocluster, the weaker the reagent reacts with it; however, to date, it is still open whether all reactions are subject to such a fundamental constraint. Here, using first-principles calculations within density functional theory in consideration of van der Waals corrections and Gaussian 09 program, we investigate the energetic and kinetic properties of water molecules adsorption on small Run (n = 2–14) clusters. It is found that almost all of the studied Run clusters possess superior activities toward H2O adsorption and dissociation, due to the enlarged desorption energies and reduced dissociation barriers when compared with the bulk Ru(0001) counterpart. More interestingly, though the stabilities of Run clusters exhibit significant odd–even oscillation behavior, i.e., the even-numbered nanoclusters are dist...

Synthesis and Characterization of Ru Cubic Nanocages with a Face-Centered Cubic Structure by Templating with Pd Nanocubes.

Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core-shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6-18 nm, with smaller seeds being more favorable for the formation of Ru shells with a flat, smooth surface due to shorter distance for the surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N2 dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts.

Evolution of supercurrent path inNb/Ru/Sr2RuO4dc-SQUIDs

Phase-sensitive measurements of direct-current superconducting quantum interference devices (dc-SQUIDs) composed of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$-Ru eutectic crystals have been performed to temperatures below a bulk Ru superconducting transition temperature at 0.49 K. A SQUID with $\mathrm{Nb}/\mathrm{Ru}/{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ junctions fabricated on one Ru inclusion exhibits two distinct transitions due to the Ru superconducting transition and competition of proximity-induced superconducting gaps at the junctions. At sufficiently low temperatures, the SQUID interference patterns start to collapse with large phase shifts of the Fraunhofer patterns. This result indicates the influence of magnetic fluxes induced by large bias currents flowing in a strongly asymmetric supercurrent path. Such a large change in supercurrent path suggests superconducting phase mismatch between the $s$-wave and chiral $p$-wave states at the $\mathrm{Ru}/{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ interface.

Formation of a Cu@RhRu core-shell concave nanooctahedron via Ru-assisted extraction of Rh from the Cu matrix and its excellent electrocatalytic activity toward the oxygen evolution reaction.

A facile one step route has been developed for the synthesis of trimetallic Cu@RhRu core-shell concave nanooctahedra by co-decomposition of Ru, Rh and Cu precursors. A mechanistic study reveals that nanoparticles with a CuRh alloy core and a Ru shell are initially formed and a subsequent migration of Rh to the shell results in the Cu@RhRu core-shell concave nanooctahedron. The shell exhibits atomically mixed Ru and Rh phases with an fcc atomic structure, although the hcp atomic structure is commonly found for the bulk Ru. We also report an unusually high catalytic activity of the Cu@RhRu octahedral nanocrystals toward the oxygen evolution reaction in alkaline solution.

Density functional theory analysis of methanation reaction of CO2 on Ru nanoparticle supported on TiO2 (1 0 1)

The methanation reaction of CO2 on a Ru nanoparticle supported on TiO2 catalyst has been investigated by density functional theory (DFT) using the generalized gradient approximation with periodic boundary conditions. Two plausible reaction paths were found for the transformation of CO2 to CH4 on TiO2-supported Ru nanoparticles. The origin of the high activity of the catalyst is discussed based on the overall reaction energy diagram obtained from DFT calculations. The CO2 is readily and stably adsorbed on Ru cluster at moderate temperature as compared with that on bulk Ru surface. It is due to the difference of the Ru structure between the Ru nanoparticle and the bulk Ru surface. The elementary reactions of the hydrogenation of adsorbed CO and of the production of CH4 are possible to become the rate-determining steps over the methanation reaction, because these two reactions have a higher potential energy barrier than that of other elementary reactions in the overall reaction path. These potential energy barriers for the hydrogenation of CO and the production of CH4 on TiO2-supported Ru nanoparticles were lower than those on bulk Ru surface, which explains the high activity of the Ru nanoparticle-loaded TiO2 catalyst. The lowering of these potential energy barriers can be caused by weak charge transfer between Ru atoms and adsorbed species on the TiO2-supported Ru nanoparticles. As the results, the catalytic activity of the Ru nanoparticles supported on TiO2 catalyst is characterized by the structure of Ru nanoparticles and by the weak charge transfer between Ru atoms and adsorbed species.

Reverse Monte Carlo study of spherical sample under non-periodic boundary conditions: the structure of Ru nanoparticles based on x-ray diffraction data

A new method to fit experimental diffraction data with non-periodic structure models for spherical particles was implemented in the reverse Monte Carlo simulation code. The method was tested on x-ray diffraction data for ruthenium (Ru) nanoparticles approximately 5.6 nm in diameter. It was found that the atomic ordering in the ruthenium nanoparticles is quite distorted, barely resembling the hexagonal structure of bulk Ru. The average coordination number for the bulk decreased from 12 to 11.25. A similar lack of structural order has been observed with other nanoparticles (e.g. Petkov et al 2008 J. Phys. Chem. C 112 8907–11) indicating that atomic disorder is a widespread feature of nanoparticles less than 10 nm in diameter.

Deactivation of Ru Catalysts under Catalytic CO Oxidation by Formation of Bulk Ru Oxide Probed with Ambient Pressure XPS

The surface science approach of using model catalysts in conjunction with the development of in situ spectroscopic tools, such as ambient pressure X-ray photoelectron spectroscopy (AP-XPS), offers a synergistic strategy for obtaining a substantially better understanding of deactivation phenomena. In this study, we investigated the nature of Ru oxides on a Ru polycrystalline film under oxidizing, reducing, and catalytic CO oxidation reaction conditions. Thus, bulk Ru oxide was easily formed on such Ru catalysts, the growth of which was dependent on reaction temperature. Once formed, such an oxide is irreversible and cannot be completely removed even under reducing conditions at elevated temperatures (200 °C). Our reaction studies showed substantial deactivation of the Ru film during catalytic CO oxidation, and its activity could be partially recovered after reduction pretreatment. Such continuous deactivation of a Ru film is correlated with irreversibly formed bulk Ru oxide, as shown by AP-XPS. Such in situ spectroscopic evidence of the transition of oxides to a catalytically inactive state can enable more effective design of catalysts with less deactivation.

Discovery of Face-Centered-Cubic Ruthenium Nanoparticles: Facile Size-Controlled Synthesis Using the Chemical Reduction Method

We report the first discovery of pure face-centered-cubic (fcc) Ru nanoparticles. Although the fcc structure does not exist in the bulk Ru phase diagram, fcc Ru was obtained at room temperature because of the nanosize effect. We succeeded in separately synthesizing uniformly sized nanoparticles of both fcc and hcp Ru having diameters of 2-5.5 nm by simple chemical reduction methods with different metal precursors. The prepared fcc and hcp nanoparticles were both supported on γ-Al2O3, and their catalytic activities in CO oxidation were investigated and found to depend on their structure and size.

Optimising the synthesis, polymer membrane encapsulation and photoreduction performance of Ru(ii)- and Ir(iii)-bis(terpyridine) cytochrome c bioconjugates

Ruthenium(II) and iridium(III) bis(terpyridine) complexes were prepared with maleimide functionalities in order to site-specifically modify yeast iso-1 cytochrome c possessing a single cysteine residue available for modification (CYS102). Single X-ray crystal structures were solved for aniline and maleimide Ru(II) 3 and Ru(II) 4, respectively, providing detailed structural detail of the complexes. Light-activated bioconjugates prepared from Ru(II) 4 in the presence of tris(2-carboxyethyl)-phosphine (TCEP) significantly improved yields from 6% to 27%. Photoinduced electron transfer studies of Ru(II)-cyt c in bulk solution and polymer membrane encapsulated specimens were performed using EDTA as a sacrificial electron donor. It was found that membrane encapsulation of Ru(II)-cyt c in PS140-b-PAA48 resulted in a quantum efficiency of 1.1 ± 0.3 × 10(-3), which was a two-fold increase relative to the bulk. Moreover, Ir(III)-cyt c bioconjugates showed a quantum efficiency of 3.8 ± 1.9 × 10(-1), equivalent to a ∼640-fold increase relative to bulk Ru(II)-cyt c.

Structural phase transition of Ru at high pressure and temperature

The magnetism, stabilities and phase transition of Ru in hcp, fcc, bct and bcc structures are investigated with detailed first-principles calculations based on density-functional theory and quasiharmonic lattice dynamics approximation. Magnetic ground states and stability ranges of various phases are obtained. Calculated results indicate that the non-magnetic (NM)-hcp structure is the most stable in the entire pressure range at zero temperature, and the structural transition cannot be induced by pressure alone. NM-fcc structure is a metastable phase of bulk Ru, while both the NM-bcc and ferromagnetic (FM)-bct structures are dynamically unstable. At high pressure and temperature, a transformation from NM-hcp to NM-fcc structure will occur. Finally, the pressure-temperature phase diagram of Ru is presented.

Electrocatalytic Oxygen Evolution Reaction (OER) on Ru, Ir, and Pt Catalysts: A Comparative Study of Nanoparticles and Bulk Materials

A comparative investigation was performed to examine the intrinsic catalytic activity and durability of carbon supported Ru, Ir, and Pt nanoparticles and corresponding bulk materials for the electrocatalytic oxygen evolution reaction (OER). The electrochemical surface characteristics of nanoparticles and bulk materials were studied by surface-sensitive cyclic voltammetry. Although basically similar voltammetric features were observed for nanoparticles and bulk materials of each metal, some differences were uncovered highlighting the changes in oxidation chemistry. On the basis of the electrochemical results, we demonstrated that Ru nanoparticles show lower passivation potentials compared to bulk Ru material. Ir nanoparticles completely lost their voltammetric metallic features during the voltage cycling, in contrast to the corresponding bulk material. Finally, Pt nanoparticles show an increased oxophilic nature compared to bulk Pt. With regard to the OER performance, the most pronounced effects of nanosca...

Water Dispersible Ru (0) Nanorods: A Highly Efficient Heterogeneous Catalyst for the Hydrogen Generation from Sodium Borohydride Solutions

Water-dispersible Ru (0) nanorods stabilized by Poly (N-vinyl-2-pyrrolidone) (PVP) were employed as catalyst in the hydrolysis of sodium borohydride (NaBH4). The hydrogen generation rate was determined as a function of solution temperature, NaBH4 concentration, and catalyst amount. Ru (0) nanorods were found to be highly active catalysts even at room temperature. Kinetics study indicated that the hydrolysis reaction was first order in catalyst concentration and zeroth order in substrate concentration. The activation parameters of the hydrolysis reaction were also determined from the evaluation of the kinetic data. The PVP-stabilized Ru (0) nanorods provided a lower apparent activation energy (Ea = 33.4 ± 1 kJ/mol) than bulk Ru(0) metal and other reported Ru-based supported catalysts for the hydrolysis of NaBH4.

Electronic state of ruthenium deposited onto oxide supports: An XPS study taking into account the final state effects

The electronic state of ruthenium in the supported Ru/EOx (EOx=MgO, Al2O3 or SiO2) catalysts prepared by with the use of Ru(OH)Cl3 or Ru(acac)3 (acac=acetylacetonate) and reduced with H2 at 723K is characterized by X-ray photoelectron spectroscopy (XPS) in the Ru 3d, Cl 2p and O 1s regions. The influence of the final state effects (the differential charging and variation of the relaxation energy) on the binding energy (BE) of Ru 3d5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/EOx samples with the corresponding characteristics of the bulk Ru metal. It is found that the negative shift of the Ru 3d5/2 peak which is observed in the spectrum of ruthenium deposited onto MgO (BE=279.5–279.7eV) with respect to that of Ru black (BE=280.2eV) or ruthenium supported on γ-Al2O3 and SiO2 (BE=280.4eV) is caused not by the transfer of electron density from basic sites of MgO, as considered earlier, but by the differential charging of the supported Ru particles compared with the support surface. Correction for the differential charging value reveals that the initial state energies of ruthenium in the Ru/EOx systems are almost identical (BE=280.5±0.1eV) irrespectively of acid–base properties of the support, the mean size of supported Ru crystallites (within the range of 2–10nm) and the surface Cl content. The results obtained suggest that the difference in ammonia synthesis activity between the Ru catalysts supported on MgO and on the acidic supports is accounted for by not different electronic state of ruthenium on the surface of these oxides but by some other reasons.

Methanol oxidation on carbon supported Pt–Ru catalysts prepared by electrodeposition – Evaluation of Nafion ® 117 film effect

Diverse electrochemical techniques were performed in order to obtain meaningful information about the methanol oxidation reaction on nanostructured planar carbon supported Pt–Ru electrodes prepared by electrodeposition, on which a layer of Nafion ionomer was incorporated. A metallic deposit consisting of dendritic agglomerates (between 50 and 200 nm) constituted by smaller particles (6 nm) was obtained. The average bulk Ru content obtained by EDX analysis was between 23 and 25 at. %. A decrease of the activity in the electrodes for methanol oxidation was determined when the thickness of the Nafion 117 film was increased. These results may be associated with the partial blocking of the surface active sites by hydrophobic domains of the polymer, and the presence of CO 2 molecules retained within the Nafion hydrophilic microchannels. EIS results indicated that methanol electro-oxidation mechanism does not change with Nafion presence.

Atomic Layer Deposition of TiO2 Films on Ru Buffered TiN Electrode for Capacitor Applications

This study examined the effect of a Ru buffer layer growth on a TiN electrode on the structural and electrical properties of a dielectric film grown by atomic layer deposition. The growth of a film directly on TiN resulted in the formation of a mixture of anatase and rutile with a dielectric constant of only 42. However, interposing a thin Ru layer altered the crystal structure of from a mixed phase to almost pure rutile, which was accompanied by an abrupt increase in the dielectric constant to . This is a much better result compared with the film deposited on a bulk Ru film, which showed a dielectric constant of . This improvement was attributed to a change in the preferred growth direction of a film on the Ru/TiN layer compared with that on a thicker Ru film.

Interaction of polyols with ruthenium metal surfaces in aqueous solution

The irreversible adsorption and decomposition of glycerol and other polyhydric alcohols over ruthenium metal at 298–353 K has been examined in a recirculating microreactor system. The quantity of glycerol (GO), propylene glycol (1,2-propanediol, herein PG), ethylene glycol (EG), or 1,3-propanediol (1,3-PDO) adsorbed on a reduced and evacuated bulk Ru metal powder at saturation is 0.8 ± 0.2 μmol/g, a value approximately one-tenth that of CO adsorbed (9.0 μmol/g) on the same material. The quantity of polyol adsorbed is independent of temperature, but is strongly affected by the condition of the Ru surface—saturating the metal surface with hydrogen prior to exposure to the polyol significantly reduces the quantity of polyol adsorbed. When they are present together in solution, GO adsorbs more readily than PG, to the point of excluding PG from adsorbing when excess GO is present. Removal of adsorbed species in their original form by heating or flushing with water is not possible, but all carbon is accounted for as desorbed methane when the Ru catalyst is heated under hydrogen.

3-D Structure of Nanosized Catalysts by High-Energy X-ray Diffraction and Reverse Monte Carlo Simulations: Study of Ru

Ruthenium exhibits a high catalytic activity that is further enhanced when the material is used as nanosized particles. The origin of the enhanced performance lies in the highly increased surface to volume ratio and, often, to the surface/environment-driven structural relaxation taking place at the nanoscale. In this paper, we show how high-energy X-ray diffraction, atomic pair distribution function analysis, and reverse Monte Carlo simulations may be used to determine the 3-D structure of nanoparticle catalysts such as Ru with sizes less than 5 nm. Ruthenium particles that are 4 nm in size are found to possess a hexagonal close packed-type structure, similar to that found in bulk Ru. Particles that are only 2 nm in size are heavily disordered and consist of a Ru core and a Ru−S skin due to the usage of thiol-based capping agents. This work is the first application of an approach for determining the atomic-scale structure of nanosized catalysts based entirely on experimental diffraction data. The new structural information is a starting point for a better understanding of the structure−property relationship and, hence, for the design of improved nanosized catalysts, including Ru.

Towards a determination of the active surface area of polycrystalline and nanoparticle electrodes by Cu upd and CO oxidation

Methods for the determination of the surface area for Pt, Ru and Se modified Pt and Ru are compared, in view of their possible application for technical and nanoparticle electrodes. The hydrogen adsorption charge can hardly be used as a reliable measure for the surface area for Ru because it is paralleled by anion adsorption. The charge necessary for the oxidation of adsorbed CO also contains a large contribution due to anion or oxygen adsorption, which amounts to approx. 45% of the charge in the case of Ru. The mass spectrometrically determined amount of CO2 formed gives a more reliable measure for the surface area, provided that the maximum coverages are constant and independent of the particular surface. Values obtained in this way agree to within 20% with surface area values obtained from measuring the charge needed for the desorption of a complete monolayer of Cu upd on Pt(111) and polycrystalline Pt, polycrystalline Ru, submonolayers of Ru on polycrystalline Pt and on Pt(111) and for nanoparticle, carbon supported electrodes. Se modified Ru has recently found attention as a methanol tolerant cathode material for oxygen reduction. CO does not adsorb on Pt or Ru saturated by Se. For surfaces partially covered by Se, a comparison of the charge measured by cyclic voltammetry in the hydrogen region and of the mass spectrometrically determined amount of CO2 suggests that the latter can be used for a determination of the area not covered by Se. Cu upd, on the other hand, also takes place on surfaces completely covered by Se; the Cu desorption charge is independent of the Se coverage on Pt and Ru modified Pt as long as it does not exceed 70% of full coverage. In the presence of multilayers of Se, CuxSe is formed. On Se modified bulk Ru the amount of Cu upd decreases with increasing Se coverage, approaching only 105 μC m−2 for full Se coverage.