Ru Oxidation Research Articles

Oxidation of Ru(III)-Bound Thiocyanate with Peroxomonosulfate: Kinetic and Mechanistic Studies

The reaction of [RuIII(edta)(SCN)]2− (edta4− = ethylenediaminetetraacetate; SCN− = thiocyanate ion) with the peroxomonosulfate ion (HSO5−) has been studied by using stopped-flow and rapid scan spectrophotometry as a function of [RuIII(edta)], [HSO5−], and temperature (15–30oC) at constant pH 6.2 (phosphate buffer). Spectral analyses and kinetic data are suggestive of a pathway in which HSO5− effects the oxidation of the coordinated SCN− by its direct attack at the S-atom (of SCN−) coordinated to the RuIII(edta). The high negative value of entropy of activation (ΔS≠ = −90 ± 6 J mol−1 deg−1) is consistent with the values reported for the oxygen atom transfer process involving heterolytic cleavage of the O-O bond in HSO5−. Formation of SO42−, SO32−, and OCN− was identified as oxidation products in ESI-MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented.

Synthesis, single crystal structure and efficient catalysis for alcohol oxidation of a novel Ru(II) complex with both a N,N,N-tridentate ligand and a pyridinedicarboxylate

A novel N,N,N-tridentate ligand known as 2-(2-pyridylmethylamino)ethylbenzimidazole (pymaeb) was designed and synthesized. This ligand in combination with disodium pyridine-2,6-dicarboxylate (pydic) reacted with RuCl3 to afford a novel complex Ru[2-(2-pyridymethylimino)ethylbenzimidazole]pyridinedicarboxylate [Ru(pymieb)(pydic)] which was characterized by NMR, IR, HR-MS and single crystal X-ray diffraction. Crystal structure analysis revealed that the complex has a distorted octahedral geometry. The complex showed excellent activity for the oxidation of various alcohols with TBHP as oxidation under mild and solvent-free conditions.

A Sensitive Electrochemiluminescence Immunosensor for Celiac Disease Diagnosis Based on Nanoelectrode Ensembles.

We report here the design of a novel immunosensor and its application for celiac disease diagnosis, based on an electrogenerated chemiluminescence (ECL) readout, using membrane-templated gold nanoelectrode ensembles (NEEs) as a detection platform. An original sensing strategy is presented by segregating spatially the initial electrochemical reaction and the location of the immobilized biomolecules where ECL is finally emitted. The recognition scaffold is the following: tissue transglutaminase (tTG) is immobilized as a capturing agent on the polycarbonate (PC) surface of the track-etched templating membrane. It captures the target tissue transglutaminase antibody (anti-tTG), and finally allows the immobilization of a streptavidin-modified ruthenium-based ECL label via reaction with a suitable biotinylated secondary antibody. The application of an oxidizing potential in a tri-n-propylamine (TPrA) solution generates an intense and sharp ECL signal, suitable for analytical purposes. Voltammetric and ECL analyses evidenced that the ruthenium complex is not oxidized directly at the surface of the nanoelectrodes; instead ECL is generated following the TPrA oxidation, which produces the TPrA•+ and TPrA• radicals. With NEEs operating under total overlap diffusion conditions, high local fluxes of these reactive radicals are produced by the nanoelectrodes in the immediate vicinity of the ECL labels, so that they efficiently generate the ECL signal. The radicals can diffuse over short distances and react with the Ru(bpy)32+ label. In addition, the ECL emission is obtained by applying a potential of 0.88 V versus Ag/AgCl, which is about 0.3 V lower than when ECL is initiated by the electrochemical oxidation of Ru(bpy)3(2+). The immunosensor provides ECL signals which scale with anti-tTG concentration with a linearity range between 1.5 ng·mL–1 and 10 μg·mL–1 and a detection limit of 0.5 ng·mL–1. The sensor is finally applied to the analysis of anti-tTG in human serum samples, showing to be suitable to discriminate between healthy and celiac patients.

Nature of Activated Manganese Oxide for Oxygen Evolution.

Electrodeposited manganese oxide films (MnOx) are promising stable oxygen evolution catalysts. They are able to catalyze the oxygen evolution reaction in acidic solutions but with only modest activity when prepared by constant anodic potential deposition. We now show that the performance of these catalysts is improved when they are "activated" by potential cycling protocols, as measured by Tafel analysis (where lower slope is better): upon activation the Tafel slope decreases from ∼120 to ∼70 mV/decade in neutral conditions and from ∼650 to ∼90 mV/decade in acidic solutions. Electrochemical, spectroscopic, and structural methods were employed to study the activation process and support a mechanism where the original birnessite-like MnOx (δ-MnO2) undergoes a phase change, induced by comproportionation with cathodically generated Mn(OH)2, to a hausmannite-like intermediate (α-Mn3O4). Subsequent anodic conditioning from voltage cycling or water oxidation produces a disordered birnessite-like phase, which is highly active for oxygen evolution. At pH 2.5, the current density of activated MnOx (at an overpotential of 600 mV) is 2 orders of magnitude higher than that of the original MnOx and begins to approach that of Ru and Ir oxides in acid.

Carbon monoxide and methanol oxidations on carbon nanofibers supported Pt–Ru electrodes at different temperatures

ABSTRACT The current work focuses on the mechanistic and kinetic study of CO and methanol oxidation reactions in acidic medium for Pt–Ru nanoparticles (atomic ratio 1:1) supported on carbon nanofibers (CNFs) in an intermediate temperature range (20 [1] . Activation energies ( E act ) and apparent activation energies ( E ap ) for the CO and methanol electrooxidation were determined by potentiodynamic and potentiostatic experiments and correlated with the physicochemical properties of the catalysts previously reported [1] . The rate-determining step was established for the different materials. Main results revealed a great decrease of E a with the introduction of Ru in the Pt-based catalysts during the CO stripping experiments. In order to evaluate the catalyst performance, the materials synthesized were tested as anodes in a direct methanol fuel cell station operating at 40 and 60 °C. In agreement with the results achieved at the three-electrode system, the catalyst reduced with formate ions developed the best performance toward the methanol oxidation reaction. Surface crystalline Ru oxides, high density of suitable surface sites for methanol adsorption and elevated conductivity of the catalyst support appeared to be responsible for the catalyst performance.

Activity and stability of the oxygen evolution reaction on electrodeposited Ru and its thermal oxides

The activity and stability of Ru metal and its thermal oxide films for the oxygen evolution reaction (OER) were investigated. The metallic Ru films were prepared by electrodeposition on a Ti substrate and then thermally oxidized at various temperatures under atmospheric conditions. During long-term operation of the OER with cyclic voltammetry (CV) in H2SO4 electrolyte, changes in the properties of the Ru and its thermal oxides were monitored in terms of their morphology, crystal structure, and electronic structure. In the initial stages of the OER, all of the Ru thermal oxide films underwent an activation process that was related to the continuous removal of low-activity Ru oxides from the surface. With further cycling, the OER activity decreased. The rate of decrease was different for each Ru film and was related to the annealing temperatures. Monitoring of material properties indicates that the amount of stable anhydrous RuO2 is important for OER stability because it prevents both the severe dissolution of metallic Ru beneath the oxide surface and the formation of a less active hydrous RuO2 at the surface.

Anodic Electrogenerated Chemiluminescence of Ru(bpy)3(2+) with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA.

In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)32+ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)32+. Ru(bpy)32+ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)32+ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)32+, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

Metal-centered oxidation decreases nitrile hydration activity of bioinspired (N2S3)Ru-PPh3 precatalysts

A series of ruthenium(II) nitrile hydration catalysts based on the pentadentate ligand 4,7-bis(2′-methyl-2′-mercaptopropyl)-1-thia-4,7-diazacyclononane and its sulfur-oxidized derivatives has been oxidized at the metal center yielding their ruthenium(III) counterparts. Metal-centered oxidation results in complete loss of nitrile hydration activity for the dithiolato (RS−/RS−) parent complex. The sulfur-oxidized thiolato/sulfinato (RS−,RSO2−) derivative displays a decrease in turnover number from 238±23 to 3±1 upon oxidation of Ru(II) to Ru(III). A similar decrease in turnover number from 242±23 to 7±3 is observed upon metal-centered oxidation of the sulfenato/sulfinato (RSO−, RSO2−) derivative. The inactive complex [(4,7-bis(2′-methyl-2′-mercaptopropyl)-1-thia-4,7-diazacyclononane)(triphenyl-phosphine)ruthenium(III)]hexafluorophosphate has been synthesized and characterized by electronic spectroscopy, electron paramagnetic resonance, and single crystal X-ray diffraction studies.

Antiferromagnetism atT>500Kin the layered hexagonal ruthenateSrRu2O6

We report an experimental and computational study of the magnetic and electronic properties of the layered Ru(V) oxide $\mathrm{SrR}{\mathrm{u}}_{2}{\mathrm{O}}_{6}$ (hexagonal, $P\overline{3}1m)$, which shows antiferromagnetic order with a N\'eel temperature of 563(2) K, among the highest for $4d$ oxides. Magnetic order occurs both within edge-shared octahedral sheets and between layers and is accompanied by anisotropic thermal expansivity that implies strong magnetoelastic coupling of Ru(V) centers. Electrical transport measurements using focused-ion-beam--induced deposited contacts on a micron-scale crystallite as a function of temperature show $p$-type semiconductivity. The calculated electronic structure using hybrid density functional theory successfully accounts for the experimentally observed magnetic and electronic structure, and Monte Carlo simulations reveal how strong intralayer as well as weaker interlayer interactions are a defining feature of the high-temperature magnetic order in the material.

Performance and Stability of the Ru–Re/γ-Al2O3 Catalyst in the Total Oxidation of Propane: Influence of the Order of Impregnation

Ru–Re/γ-Al2O3 catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H2 chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/γ-Al2O3 catalyst with dispersion of 0.52, the Ru dispersion was improved by the presence of Re going from 0.64 for the catalyst with Re deposited on Ru/γ-Al2O3, to 0.70 for the sample with Ru deposited on Re/γ-Al2O3. The O2 adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/γ-Al2O3 catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/γ-Al2O3 exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/γ-Al2O3, but activity of Re-modified catalysts was not improved as compared to the Ru/γ-Al2O3 catalyst. On the other hand, bimetallic Ru–Re/γ-Al2O3 catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 °C. TEM and XRD data showed that oxidized rhenium species strongly interacted with γ-alumina prevented large agglomeration of the Ru phase under O2-rich reaction conditions. The used monometallic Ru catalyst contained RuO2 oxide with crystallite size of 26 nm, while in the used bimetallic catalysts with size of 6–7 nm. Thus, in the consecutive catalytic tests Re-promoted Ru/γ-Al2O3 catalysts present higher activity and extended resistance to deactivation.

Water Oxidation by Ru-Polyoxometalate Catalysts: Overpotential Dependency on the Number and Charge of the Metal Centers

Water oxidation is efficiently catalyzed by several Ru-based polyoxometalate (POM) molecular catalysts differing in the number, local atomistic environment and oxidation state of the Ru sites. We employ density functional theory calculations to rationalize the dependency of the reaction overpotential on the main structural and electronic molecular properties. In particular, we compare the thermodynamics of the water oxidation cycle for single-site Ru-POM and multiple-site Ru4-POM complexes. For the Ru-POM case, we also investigate the reaction free energy as a function of the Ru oxidation state. We find that the overpotential of these molecular catalysts is primarily determined by the oxidation state of the metal center and is minimum for Ru(IV). In solution, the number of active sites is shown to play a minor role on the reaction energetics. The results are rationalized and discussed in terms of the local structure around the active sites and of the electrostatic screening due to the molecular structure or the solvent.

Effects of functional group modification on the thermal properties of nano-carbon clusters

In this paper, the thermal properties including thermal stability, thermal decomposition activation energy and the thermal enthalpy of nano-carbon clusters (NCCs, including fullerene[60](C60, with a diameter of 0.71 nm), multi-walled carbon nanotubes(MWCNTs, with a diameter of 10–30 nm and a length of 1–2 µm), single-walled carbon nanotubes (SWCNTs, with a diameter of ~2 nm and a length of 5–15 µm), ligands of NCC-based terpyridine (NCC-tpy), and NCC-based ruthenium complexes (NCC-tpyRuCl3) were systematically studied by method of simultaneous thermogravimetric and differential thermal analysis. The results show that the modification of NCCs with terpyridine leads to a decrease in the thermal stability and in the thermal decomposition activation energy (the thermal decomposition activation energy decreased from 174.4 for C60, 144.9 for MWCNTs and 161.2 kJ/mol for SWCNTs to 166.2 for C60-tpy, 119.7 for MWCNT-tpy and 85.0 kJ/mol for SWCNT-tpy). But the modification of NCCs with terpyridine results in an increase in the enthalpy change of NCC thermal decomposition reaction. The introduction of the metal ions through complexation further decreases the thermal stability and the thermal decomposition activation energy of NCC-tpyRuCl3 due to the catalytic oxidation of Ru(III) ions (the activation energy decreases to 124.1 for C60-tpyRuCl3, 106.4 for MWCNT-tpyRuCl3 and 41.2 kJ/mol for SWCNT-tpyRuCl3). The introduction of the metal ions also leads to a decrease in the enthalpy change of the thermal decomposition reaction.

Catalytic wet hydrogen peroxide oxidation of p-hydroxybenzoic acid over Fe/TiO2 and 0.5Ru–3Fe/TiO2

p-Hydroxybenzoic acid (p-HBZ) degradation was achieved using catalytic wet hydrogen peroxide oxidation over Fe/TiO2 and Ru–Fe/TiO2 under mild conditions. The results showed that 71 % of p-HBZ conversion was obtained after 10 min of reaction over the 0.5Ru–3Fe/TiO2 catalyst calcined under oxygen. The influence of the H2O2/p-HBZ molar ratio (5:1, 10:1 and 15:1), reaction temperature (25, 40 and 60 °C), Fe loading (1, 2 and 3 wt%) and thermal treatment was studied. Characterization studies were performed by X-ray diffraction, N2 physisorption at 77 K, H2-TPR and elemental analysis, showing that close interaction between Ru and iron oxide species is necessary to obtain active and stable catalysts. 0.5Ru–3Fe/TiO2 C catalyst shows a high activity for the degradation of p-HBZ at 60 °C by CWHPO in the presence of H2O2. The system could be considered as a Fenton-like reaction due to the generation of radicals from H2O2 as well as the presence of iron sites on the catalyst.

Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries

A chelating benzimidazolylidene–carboxylate ligand (1) was transferred from [Ag(1)] to [RuCl2(dmso)4] to afford trans(C)-[Ru(1)2(bpy)] (2), but all attempts to incorporate 1 into cis(Cl)-[RuCl2(bpy)2] were unsuccessful. Alternatively, reaction of [RuCl(1)(η6-cymene)] (3) with bpy and AgOTf successfully produced [Ru(1)(bpy)2][OTf] (4). Methylation of 2 and 4 with MeOTf yielded trans(C)-[Ru(1-Me)2(bpy)][OTf]2 (5) and [Ru(1-Me)(bpy)2][OTf]2 (6), accompanied by a +2 and +1 increase in net charge, respectively. Cyclic voltammetry indicated that the increase in Ru(II)/Ru(III) oxidation potential from 2 to 5 was twice the increase from 4 to 6. UV–Vis spectroscopy also revealed that transitions in 5 occurred at higher energy than in 2 by double the difference between 6 and 4. Crystallographic analysis demonstrated that the coordination environment of Ru did not differ significantly between 2 and 5, suggesting that the observed shifts in oxidation potentials and absorption wavelengths are not due to changes in coordination chemistry or formal oxidation state. Collectively, these results show that 5 and 6 feature Ru centers more electron deficient than those in 2 and 4, respectively, by amounts linearly proportional to the difference in net charge.

Effect of FA/O complexing agents and H2O2 on chemical mechanical polishing of ruthenium in weakly alkaline slurry**Project supported by the Special Project Items No. 2 in National Long-Term Technology Development Plan (No. 2009ZX02308), the Natural Science Foundation of Hebei Province (No. E2013202247), the Science and Technology Plan Project of Hebei Province (Nos. Z2010112, 10213936), the Hebei Provincial Department of Education

This paper investigated the effect of FA/O and hydrogen peroxide (H2O2) on ruthenium (Ru) removal rate (RR) and static etching rate (SER). It was revealed that Ru RR and SER first linearly increased then slowly decreaseed with the increasing H2O2 probably due to the formation of uniform Ru oxides on the surface during polishing. Their corrosion behaviors and states of surface oxidation were analyzed. In addition, FA/O could chelate Ru oxides (such as (RuO4)2– and RuO4− changed into soluble amine salts [R(NH3)4] (RuO4)2) and enhance Ru RR. The non-ionic surfactant AD was used to improve the Ru CMP performance. In particular, the addition of AD can lead to significant improvement of the surface roughness.

Heavy fermions, metal-to-insulator transition, and quantum criticality in La y Cu3Ru x Ti4−x O12

In this work we investigate the solid-solution series La y Cu3Ru x Ti4−x O12. The titanate La2/3Cu3Ti4O12 (x = 0) is an antiferromagnetic insulator exhibiting colossal dielectric constants, while the ruthenate LaCu3Ru4O12 (x = 4) is known as a rare d-electron derived heavy-fermion compound. Detailed structural investigations, AC- and DC-magnetization measurements, resistivity, specific-heat, and magnetic-resonance investigations have been performed for all polycrystalline compounds prepared by solid-state synthesis. These experiments have been accompanied by band-structure calculations. Close to the Ru concentration x = 2 we identify a quantum-critical point coinciding with a metal-to-insulator transition. The quantum-critical point separates an insulating spin glass from a paramagnetic metal. Interestingly, there is no evidence for a divergence of the effective mass upon reaching the quantum-critical point from the metallic side. In the paramagnetic metal, Ru behaves like a canonical Kondo ion. While the Ru oxidation state remains stable at + 4 for the whole concentration regime, the Cu valence seems to decrease from + 2 in the insulating antiferromagnet with localized copper spins to a significantly lower value in the metallic heavy-fermion compounds.

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

Bilayer silicate films grown on metal substrates are weakly bound to the metal surfaces, which allows ambient gas molecules to intercalate the oxide/metal interface. In this work, we studied the interaction of oxygen with Ru(0001) supported ultrathin silicate and aluminosilicate films at elevated O2 pressures (10−5–10mbar) and temperatures (450–923K). The results show that the silicate films stay essentially intact under these conditions, and oxygen in the film does not exchange with oxygen in the ambient. O2 molecules readily penetrate the film and dissociate on the underlying Ru surface underneath. The silicate layer does however strongly passivate the Ru surface towards RuO2(110) oxide formation that readily occurs on bare Ru(0001) under the same conditions. The results indicate considerable spatial effects for oxidation reactions on metal surfaces in the confined space at the interface. Moreover, the aluminosilicate films completely suppress the Ru oxidation, providing some rationale for using crystalline aluminosilicates in anti-corrosion coatings.

Spectroelectrochemical investigation of electrocatalytic water oxidation by a mononuclear ruthenium complex in a homogeneous solution

Abstract Electrochemical water oxidation by [Ru(EtOtpy)(bpy)OH 2 ] 2+ ( 1 ) (EtOtpy = 4′-ethoxy-2,2′:6#6°6#′-terpyridine, bpy = 2,2′-bipydidine) was investigated in a homogeneous solution under weakly acidic conditions (pH 5.3). The cyclic voltammogram of a 1 aqueous solution showed that successive proton-coupled electron transfer reactions of Ru II OH 2 / Ru III OH and Ru III OH/Ru IV O redox pairs and high anodic current above 1.1 V vs SCE. Electrocatalytic water oxidation was corroborated by the bulk electrolysis at 1.5 V; the significant amount of O 2 was evolved compared with the blank during the electrolysis. Potential-step chronocoulospectrometry (PSCCS) from 0.0 V to 1.52 V vs SCE was conducted to observe the change of 1 in solution during the electrocatalysis. The in situ UV visible spectral change showed oxidation of 1 (Ru II OH 2 ) to Ru III OH and to further oxidation of Ru III OH to Ru IV O, and that the Ru IV O species mainly exists in a steady state after 200 s in the electrocatalysis. The in situ UV–vis spectral change in a reverse potential step from 1.52 V to 0.22 V vs SCE exhibited that Ru II OH 2 completely recovers by two electron re-reduction process from the steady state in the electrocatalysis. The observation of Ru IV O in a steady state suggests that a rate determining step in the catalytic cycle is oxidation of Ru IV O to Ru V O rather than the O O bonding formation by nucleophilic attack of water to Ru V O in the electrocatalysis in a homogeneous solution.

Phase equilibrium experiments on the simulated high-level waste glass containing platinum group elements

Phase equilibrium experiments for the simulated high-level waste (HLW) glass containing palladium, rhodium and ruthenium discharged from a full scale mock up melter have been carried out between 1073 and 1473 K under air and CO2 atmosphere. The chemical compositions of Pd–Rh–Ru–Te (Pd metal phase) and (Ru, Rh)O2 (Ru oxide phase) solid solutions and glass matrix were measured by electron probe micro analysis. Palladium content in the Pd metal phase decreased and ruthenium content in the Ru oxide phase increased with increasing temperature and decreasing oxygen fugacity due to progressive reduction of rhodium. The chemical compositions of these crystalline phases are independent of that of borosilicate glass matrix. Partition coefficient of rhodium between Pd metal phase and Ru oxide phase (KRh) can be expressed bywhere T and represent absolute temperature and oxygen fugacity. Based on the comparison of crystal compositions in the HLW glass with experimental results, it can be expected that the HLW glass examined in this study had been equilibrated in the temperature range from 1273 to 1373 K and oxygen fugacity close to that of air just before discharging from the melter.

Vapor synthesis and thermal modification of supportless platinum-ruthenium nanotubes and application as methanol electrooxidation catalysts.

Metallic, mixed-phase, and alloyed bimetallic Pt-Ru nanotubes were synthesized by a novel route based on the sublimation of metal acetylacetonate precursors and their subsequent vapor deposition within anodic alumina templates. Nanotube architectures were tuned by thermal annealing treatments. As-synthesized nanotubes are composed of nanoparticulate, metallic platinum and hydrous ruthenium oxide whose respective thicknesses depend on the sample chemical composition. The Pt-decorated, hydrous Ru oxide nanotubes may be thermally annealed to promote a series of chemical and physical changes to the nanotube structures, including alloy formation, crystallite growth, and morphological evolution. Annealed Pt-Ru alloy nanotubes and their as-synthesized analogs demonstrate relatively high specific activities for the oxidation of methanol. As-synthesized, mixed-phase Pt-Ru nanotubes (0.39 mA/cm(2)) and metallic alloyed Pt64Ru36NTs (0.33 mA/cm(2)) have considerably higher area-normalized activities than PtRu black (0.22 mA/cm(2)) at 0.65 V vs RHE.