Pure Ru Research Articles

An Investigation into Methanol Oxidation Reactions and CO, OH Adsorption on Pt-Ru-Mo Catalysts for a Direct Methanol Fuel Cell

The electrochemical performance of pure Pt and Pt-based alloy nanoparticle catalysts with various Pt, Ru and Mo concentrations is investigated. Pure Pt, Ru, and Mo are first deposited on multi-walled carbon nanotubes (MWCNTs) using a E-beam evaporator (MEP5000, SNTEK), and Pt-based alloy nanoparticles are subsequently formed on the MWCNTs via flash light irradiation. Several microscopic and spectroscopic techniques, including X-ray diffractometry, scanning electron microscopy, and Raman spectroscopy are employed to characterize the catalysts. Cyclic voltammetry experiments are also performed to measure the electrochemical reactions of the Pt-based alloy nanoparticle/MWCNT catalysts. To verify the experimental results, a computational simulation analysis is conducted using molecular dynamics and the application of density functional theory. From the experimental and analytical findings, it is concluded that the Pt43-Ru43-Mo14/MWCNT structure exhibits the best electrochemical performance for the oxidation of methanol.

Ziegler's Indecomposability Criterion

Abstract.Ziegler’s Indecomposability Criterion is used to prove that a totally transcendental, i.e., ∑-pure injective, indecomposable left module over a left noetherian ring is a directed union of finitely generated indecomposable modules. The same criterion is also used to give a sufficient condition for a pure injective indecomposable module RU to have an indecomposable local dual

Kinetically Limited CO Adsorption: Spill-Over as a Highly Effective Adsorption Pathway on Bimetallic Surfaces

We demonstrate that the (local) adsorbed carbon monoxide, COad , coverage on the Pt-free areas of bimetallic Pt/Ru(0001) surfaces (a Ru(0001) substrate partly covered by Pt monolayer islands) can be increased to ∼0.80 monolayers (ML), well above the established saturation COad coverage of 0.68 ML, even under ultrahigh vacuum conditions by using spill-over of CO adsorbed on the Pt islands to the Ru areas as an highly effective adsorption channel. The apparent COad saturation coverage of 0.68 ML on pure Ru(0001) is identified as due to kinetic limitations, hindering further uptake from the gas phase, rather than being caused by thermodynamic reasons. This spill-over mechanism is proposed to be a general phenomenon for adsorption on bimetallic surfaces.

Effect of heat treatment on the electrocatalytic properties of nano-structured Ru cores with Pt shells

Ru@Pt core–shell particles are relevant for application as electrocatalysts in fuel cells. The Ru core is expected to influence the activity of the Pt in the shell through a compression of bond lengths and electronic interaction with the core. In this work Ru@Pt core–shell (Ru core and Pt shell) and pure Ru nanoparticles of diameter below less than 5nm were synthesized and supported on carbon black (Vulcan XC-72). The supported catalysts were heat-treated at temperatures up to 500°C. Analysis of the catalysts by TEM, EXAFS, XRD, and CO-stripping indicates a strongly segregated architecture with Ru in the core of the particles. Upon heat-treatment we observed moderate particle growth, increased extent of alloying, and a decrease of the Pt–Pt bond lengths. The Pt–Pt bond lengths decreased uniformly with heat-treatment temperature in the entire range. The extent of alloying and particle growth were significant (i.e. beyond measurement uncertainties) only at a heat-treatment temperature of 500°C. The electrocatalytic activity for oxidation of adsorbed CO (CO-stripping) increased in the entire temperature interval. The activity for methanol oxidation only increased when catalysts were heated to 500°C. The results indicate that the surface concentration of ruthenium in the pristine Ru@Pt catalysts is small.

Hydrogen electrosorption into Pd-rich Pd–Ru alloys

Hydrogen electrosorption into Pd-rich (>90% Pd in the bulk) Pd–Ru alloys obtained by electrodeposition was studied at 298K in 0.5M H2SO4 solution using cyclic voltammetry and chronoamperometry. Cyclic voltammograms for pure Pd, pure Ru and a Pd–Ru alloy in a wide range of potentials are compared. Pd–Ru electrodeposits with a small Ru content in the bulk (0.5–2%) can absorb more hydrogen than pure Pd, with the maximum hydrogen-to-metal atomic ratio above 0.80 (as compared with 0.74 for Pd). The maximum absorption capacity of Pd–Ru electrodes containing less than 97% Pd gradually decreases and the H/M ratio drops to ca. 0.40 for electrodes with 90% Pd. The potential of absorbed hydrogen oxidation peak is shifted negatively with decreasing Pd bulk content. The amounts of electrosorbed hydrogen for α and β phase boundaries, i.e. αmax and βmin have been determined from the integration of the initial parts of current–time responses in hydrogen absorption and desorption processes. The influence of electrode potential on the amount of electrosorbed hydrogen is presented. On the plot of H/M vs. potential the regions of α↔β phase transitions are shifted to lower potentials in comparison with pure Pd. The thermodynamic stability of β-phase decreases with decreasing Pd content. The hysteresis effect is observed in chronoamperometric absorption and desorption experiment. The values of maximum, normalized time needed for electrode saturation with hydrogen and its removal with the exception of region containing 97.9–99.6% Pd decrease with increasing Ru bulk content. Hydrogen absorption properties of Pd–Ru electrodes may be explained taking into account changes in electronic and geometric factors probably resulting from alloy formation between Pd and Ru.

Hydrothermal Synthesis of Co-Ru Alloy Particle Catalysts for Hydrogen Generation from Sodium Borohydride

We report the synthesis ofμm and sub-μm-sized Co, Ru, and Co-Ru alloy species by hydrothermal approach in the aqueous alkaline solutions (pH ≥ 13) containing CoCl2and/or RuCl3, sodium citrate, and hydrazine hydrate and a study of their catalytic properties for hydrogen generation by hydrolysis of sodium borohydride solution. This way provides a simple platform for fabrication of the ball-shaped Co-Ru alloy catalysts containing up to 12 wt% Ru. Note that bimetallic Co-Ru alloy bowls containing even 7 at.% Ru have demonstrated catalytic properties that are comparable with the ones of pure Ru particles fabricated by the same method. This result is of great importance in view of the preparation of cost-efficient catalysts for hydrogen generation from borohydrides. The morphology and composition of fabricated catalyst particles have been characterized using scanning electron microscopy, energy dispersive X-ray diffraction, and inductively coupled plasma optical emission spectrometry.

Catalytic combustion of chlorobenzene over Ru-doped ceria catalysts: Mechanism study

To investigate the mechanism of the catalytic combustion of chlorobenzene over pure CeO2 and Ru doped CeO2 catalysts, we examined the oxidation reaction in depth by temperature-programmed surface reaction (TPSR) technique and a series of supplementary experiments. The results suggest that the CCl bond in chlorobenzene molecule can be dissociated easily on Ce3+/Ce4+ active sites, and the dissociated chlorobenzene can be rapidly oxidized into CO2 and H2O by surface reactive oxygen or lattice oxygen. The chlorine species dissociatively adsorbed on the active sites can result in the rapid deactivation of catalysts and be removed in form of Cl2 via the Deacon Reaction catalyzed by RuO2 or CeO2, which would improve the catalyst stability. Additionally, the partial chlorination of RuO2 or CeO2 possibly occurs during the long reaction, which is responsible for the production of dichlorobenzene by-products.

Dynamical Properties of a Ru/MgAl2O4 Catalyst during Reduction and Dry Methane Reforming

Combined in situ small- and wide-angle X-ray scattering (SAXS/WAXS) studies were performed in a new laboratory setup to investigate the dynamical properties of a ruthenium/spinel (Ru/MgAl2O4) catalyst, w(Ru) = 4 wt %, during the reduction and subsequent dry methane reforming. The Ru particles in the fresh catalyst sample were found to be partially oxidized. High-resolution transmission electron microscopy (HRTEM) indicated a coexistence of pure Ru and RuO2 nanoparticles. Reduction in hydrogen occurred at a temperature between 373 and 393 K. The mean particle diameter as refined from SAXS of the size regime attributed to scattering from Ru/RuO2-particles decreases slightly by about 0.2 nm during the reduction. Dry methane reforming experiments were performed in a temperature interval from 723 to 1023 K by applying a gas mixture of carbon dioxide and methane in molar ratio of 3:1. The catalyst did not show any deactivation during the experiment of overall 32 h, indicated by stable turnover frequencies for m...

Spectroscopy and Photophysics in Cyclometalated RuII–Bis(bipyridyl) Complexes

AbstractA series of cyclometalated RuII coordination compounds of the general structural formula [Ru(bpy)2(C∧N)]PF6 {C∧N = 2‐phenylpyridine (1), 2‐(2,4‐difluorophenyl)pyridine (2), 2‐(4‐methoxyphenyl)‐5‐methylpyridine (3), benzo[h]quinoline (4); bpy = 2,2′‐bipyridine} have been synthesized, structurally and electrochemically characterized, and examined by using a battery of spectroscopic techniques. The combination of static and dynamic photoluminescence at room temperature and 77 K, resonance Raman spectroscopy, cyclic voltammetry, spectroelectrochemistry, and ultrafast transient absorption spectroscopy reveal that – although the nature of the cyclometalating ligand substantially affects the oxidation potential at the metal center – the lowest‐energy metal‐to‐ligand charge‐transfer excited state always retains pure Ru→bpy character across this series of molecules, and the cyclometalating subunit plays the role of ancillary ligand.

Effect of the Pt/Ru intermetallic boundary on the carbon monoxide electrooxidation: Excess electrocatalytic activity

The carbon monoxide oxidation reaction was studied on smooth Pt, Ru and Pt/Ru (Ru partially covered by Pt islands) rotating disc electrodes on acid solution saturated with CO gas (PCO = 1 atm) through steady state measurements. The current density vs. overpotential plot of the Pt/Ru electrode shows a profile qualitatively similar to the sum of both curves corresponding to pure Pt and Ru. On this basis, the excess electrocatalytic activity was defined as the difference between the current densities of the bimetallic electrode and those corresponding to the pure metals, which allowed evaluating the contribution of the intermetallic region to the reaction. It was verified that this property depends on overpotential, defining two ranges of positive excess values, 0.6 ≤ η/V < 0.82 and 0.88 < η/V ≤ 1.0, separated by the range 0.82 ≤ η/V ≤ 0.88, where the contribution of the boundary region is negligible. A simple model was developed, which explains the experimental results on the basis of the spillover of the adsorbed reaction intermediates, while the reaction between adsorbed species on both sides of the intermetallic edge is not feasible.

Atomic layer deposition of Ru thin film using N2/H2 plasma as a reactant

Ruthenium (Ru) thin films were grown by atomic layer deposition using IMBCHRu [(η6-1-Isopropyl-4-MethylBenzene)(η4-CycloHexa-1,3-diene)Ruthenium(0)] as a precursor and a nitrogen–hydrogen mixture (N2/H2) plasma as a reactant, at the substrate temperature of 270°C. In the wide range of the ratios of N2 and total gas flow rates (fN2/N2+H2) from 0.12 to 0.70, pure Ru films with negligible nitrogen incorporation of 0.5at.% were obtained, with resistivities ranging from ~20 to ~30μΩcm. A growth rate of 0.057nm/cycle and negligible incubation cycle for the growth on SiO2 was observed, indicating the fast nucleation of Ru. The Ru films formed polycrystalline and columnar grain structures with a hexagonal-close-packed phase. Its resistivity was dependent on the crystallinity, which could be controlled by varying the deposition parameters such as plasma power and pulsing time. Cu was electroplated on a 10-nm-thick Ru film. Interestingly, it was found that the nitrogen could be incorporated into Ru at a higher reactant gas ratio of 0.86. The N-incorporated Ru film (~20at.% of N) formed a nanocrystalline and non-columnar grain structure with the resistivity of ~340μΩcm.

Ultrathin Cr added Ru film as a seedless Cu diffusion barrier for advanced Cu interconnects

A 5nm thick Cr added Ru film has been extensively investigated as a seedless Cu diffusion barrier. High-resolution transmission electron microscopy micrograph, X-ray diffraction (XRD) pattern and Fourier transform-electron diffraction pattern reveal that a Cr contained Ru (RuCr) film has a glassy microstructure and is an amorphous-like film. XRD patterns and sheet resistance data show that the RuCr film is stable up to 650°C, which is approximately a 200°C improvement in thermal stability as compared to that of the pure Ru film. X-ray photoelectron spectroscopy depth profiles show that the RuCr film can successfully block Cu diffusion, even after a 30-min 650°C annealing. The leakage current of the Cu/5nm RuCr/porous SiOCH/Si stacked structure is about two orders of magnitude lower than that of a pristine Ru sample for electric field below 1MV/cm. The RuCr film can be a promising Cu diffusion barrier for advanced Cu metallization.

New insights into the synergistic effect in bimetallic-boron catalysts for hydrogen generation: The Co–Ru–B system as a case study

Catalysed sodium borohydride hydrolysis is a high-potential method to produce hydrogen for portable applications. Co–B catalysts are the most chosen because they are easily prepared, cheap and efficient. The addition of small amounts of Ru produces a significant enhancement in catalytic activity.In the present work a series of Co–Ru–B catalysts with variable Ru content was prepared, isolated and characterized. The comprehension of the synergistic effect was achieved trough the incorporation of the nanostructural dimension to the study of surface and bulk chemical states of the involved atoms along the series. It was found that up to 70% (of total metal) atomic content of Ru the catalysts can be considered isostructural to the single Co–B catalyst in the nanoscale. A structural transition occurs in the case of the pure Ru–B material to produce a boron deficient material with higher nanoparticle size. This structural transition together with Co segregation and Ru dispersion play a key role when explaining a [OH−] dependent effect.The inexistence of borate layers in Ru rich catalysts is suggestive in the research for non deactivating catalysts.

Thermal stability of RuO2 thin films prepared by modified atomic layer deposition

Thermal stability of RuO2 thin films formed by modified atomic layer deposition on SiO2 substrate was investigated. Rapid thermal annealing was conducted for 2 min under NH3 and N2 ambient. It was demonstrated that NH3 gas can completely reduce RuO2 to pure Ru at a relatively low annealing temperature of 500 °C, while partial reduction of RuO2 into Ru at the outmost surface was observed after N2 annealing. Agglomeration of the NH3 annealed film was not observed due to high quality of the as-deposited film that was dense and had low level of impurities such as hydrogen and carbon.

Anodic Hydrogen Oxidation at Bare and Pt-modified Ru(0001) in Flowing Electrolyte – Theory versus Experiment

ABSTRACTThis paper reports on electrochemical hydrogen oxidation at atomically smooth single crystal surfaces. These surfaces are considered as planar models for (bi)metallic nanoparticles that are commonly used as catalytically active electrode materials in low-temperature fuel cells. These samples are prepared in ultrahigh vacuum but are characterized under conditions of enhanced mass transport in hydrogen saturated electrolyte. The two examples shown in this paper are Ru(0001) with or without an atomically thin layer of Pt. The Pt thin layer turns out to be more active than pure Ru(0001) by three orders of magnitude and also more active than bulk Pt electrodes. We show that those findings agree very well with predictions based on density functional theory in combination with a simple kinetic model.

Selective hydrogenation of cyclohexenone on iron–ruthenium nano-particles suspended in ionic liquids and CO2-expanded ionic liquids

Iron and ruthenium mono- and bimetallic nanoparticles (NPs) with different metal ratios (Fe–Ru 9 : 1, Fe–Ru 3 : 1, and Fe–Ru 1 : 1) have been prepared in imidazolium ionic liquids (ILs) via decarbonylation of the corresponding metal carbonyl precursors. The as-prepared ionic liquid suspended nanoparticles were tested as catalysts for the selective hydrogenation of cyclohexenone to cyclohexanone at 50 °C in a high pressure batch reactor equipped for in situ Attenuated Total Reflection (ATR) infrared spectroscopy. After reaction, supercritical carbon dioxide was applied to extract the products from the reaction mixture, thus facilitating a green approach to solventless transition metal catalysis. The course of the reaction and extraction was followed by ATR-IR spectroscopy. From the IL suspended monometallic NPs, Ru showed much higher activity than Fe. Addition of 50 at% iron to Ru (Fe–Ru 1 : 1) resulted in a remarkable decrease of the average particle size of the NPs from 2.9 nm to 1.6 nm. Among the different NPs prepared, the bimetallic Fe–Ru 1 : 1 was most active followed by the pure Ru. Addition of CO2 to the reaction mixture greatly increased the reaction rate (4 times faster with 60 bar of CO2 than without), as demonstrated for the highly active Fe–Ru 1 : 1 NPs suspended in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]). At 60 bar of CO2 high selectivity >95% to cyclohexanone, at a TOF of ca. 300 h−1, was achieved and the catalyst could be reused 5 times without noticeable deactivation.

Robust ultra-thin RuMo alloy film as a seedless Cu diffusion barrier

This study investigated the properties of 5 nm-thick RuMo film as a Cu diffusion barrier. The sheet resistance variation and X-ray diffraction patterns show that the RuMo alloy film has excellent barrier performance and that it is stable upon annealing at 725 °C against Cu. The transmission electron microscopy micrograph and diffraction patterns show that the RuMo film is an amorphous-like structure, whereas pure Ru film is a nano-crystalline structure. The elements’ depth profiles, analyzed by X-ray photoelectron spectroscopy, indicate no inter-diffusion behavior between the Cu and Si layer, even annealing at 700 °C. Lower leakage current has been achieved from the Cu/barrier/insulator/Si test structure using RuMo film as the barrier layer. A 5 nm ultrathin RuMo film provided two orders of magnitude improvement in leakage current and also exhibited a 175 °C improvement in thermal stability than that of the pure Ru film. It is a potential candidate as a seedless Cu diffusion barrier for advanced Cu interconnects.

Synthesis of Copper and Copper-Ruthenium Nanoparticles in Ionic Liquids for the Metallization of Advanced Interconnect Structures

Bimetallic nanoparticles can be used in a variety of applications such as catalysis, in advanced magnetic or optical devices or as starting materials to form continuous metallic layers. In this study, we report the synthesis of bimetallic ruthenium-copper (Ru-Cu) nanoparticles in ionic liquids. For this purpose, solutions of ionic liquids containing a mixture of precursors of Ru and Cu were decomposed under dihydrogen. Small, crystalline and well dispersed Ru-CuNPs (2.5 ± 0.6 nm) were obtained, which are significantly smaller than the pure Ru or pure CuNPs formed under the same conditions. Our analyses suggest that these NPs have a Ru core - Cu shell structure. This structure is expected from thermodynamical and kinetics data. Moreover, this could explain the dramatic size reduction observed when mixing the two metals.

Structural and magnetic properties of FemYn (m + n = 7, Y = Ru, Rh, Pd, and Pt) nanoalloys

The structural and magnetic properties of the small binary clusters Fe m Y n (with m + n = 7, Y = Ru, Rh, Pd, Pt) were studied through extensive ab initio calculations, by means of the fully unconstrained version of the density-functional method, as implemented in the SIESTA code, within the generalized gradient approximation. The lowest energy state geometries, the chemical ordering, and the electronic and the magnetic structures were calculated. We found that the lowest energy geometrical structures for the pure Ru, Rh, Pd, Pt, and Fe heptamers, are a cube without an apex, a triangular prism capped on a square face, a decahedron, a side capped double square, and a decahedron, respectively. Starting from these geometries of the pure element heptamers, we followed the changes in the geometric structure as a function of the chemical composition. We analyzed all the different chemical arrangements, which depend on the particular geometry, and magnetic moment orientations, in the whole range of compositions. In general, there are important modifications to the magnetic moment of the Y atoms as soon as one of them is substituted by an Fe atom in the cluster. In contrast, under the same circumstances, the Fe magnetic moment takes values larger than 3 μ B and keeps almost this value, insensitive to the structure, composition and chemical order of the system.

Preparation and characterization of Co–Ru/TiO 2/MWCNTs electrocatalysts in PEM hydrogen electrolyzer

The subject of this study is preparation and characterization of hypo–hyper d-electrocatalysts with reduced amount of precious metals aimed for water electrolysis. The studied electrocatalysts contain 10% mixed metallic phase (Co:Ru = 1:1 wt., Co:Ru = 4:1 wt. and Co:Ru:Pt = 4:0.5:0.5 wt.), 18% TiO 2 as a crystalline anatase deposited on multiwalled carbon nanotubes (MWCNTs). Previously, MWCNTs were activated in 28% nitric acid. As a reference electrocatalyst for hydrogen evolution reaction, corresponding electrocatalysts with pure Pt metallic phase and mixed CoPt (Co:Pt = 1:1 wt.) metallic phase were prepared. Also, as a reference electrocatalyst for oxygen evolution reaction, electrocatalyst with pure Ru metallic phase was prepared. The prepared electrocatalysts were structurally characterized by means of XPS, XRD, TEM, SEM and FTIR analysis. Electrochemical characterization was performed by means of cyclic voltammetry and potentiodynamic method in the PEM hydrogen electrolyzer. The range of the catalytic activity for hydrogen evolution of studied electrocatalysts was the following: CoRuPt (4:0.5:0.5) > CoPt (1:1) > Pt > CoRu (1:1) > CoRu (4:1). The order of the catalytic activity for oxygen evolution was the following: CoRu (1:1) > Ru > CoRu (4:1) > Pt > CoRuPt (4:0.5:0.5) > CoPt (1:1).