Ru Oxidation Research Articles

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.

Photoinduced oxidation of a tris(2,2'‐bipyridyl)ruthenium(II)–peroxodisulfate chemiluminescence system for the analysis of mebeverine HCl pharmaceutical formulations and biological fluids using a two‐chip device

A new method for the analysis of mebeverine hydrochloride (MEB) has been developed using a two-chip device. The method is highly selective, sensitive, rapid and consumes minute amount of reagents. The developed method is free of interference from the degradation products of MEB and from common ingredients present in pharmaceutical formulations. The limit of detection was 0.043 µg/mL, and the limit of quantification was 0.138 µg/mL. The short analysis time per sample (20 s) allowed a large number of analyses to be performed within a very short time. Various samples were analyzed, including two different pharmaceutical formulations and a uniformity of content analysis for 20 tablets from a known batch and two biological samples at different concentrations. In addition, the method was compared with a validated high-performance liquid chromatography (HPLC) method and the results clearly indicated the suitability of the developed method for routine analyses. A new mechanism for the tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3 (2+) )-peroxodisulfate (S2 O8 (2-) ) chemiluminescence (CL) system has also been proposed. The mechanism is based on photoinduced oxidation of Ru(bpy)3 (2+) to Ru(bpy)3 (3+) via the formation of Ru(bpy)3 (2+) * upon irradiation with visible light. S2 O8 (2-) then oxidizes Ru(bpy)3 (2+) * to Ru(bpy)3 (3+) and the analyte subsequently reduces the resultant Ru(bpy)3 (3+) to Ru(bpy)3 (2+) *, which then produces the CL signal.

Separation and recovery of ruthenium: a review

The chemistry of the noble metal fission product, ruthenium is very complex due to the existence of many oxidation states in addition to forming a large number of co-ordination complexes. In the PUREX process for the separation of U and Pu from the spent nuclear fuels from fast breeder reactors, owing to the high volatile nature of RuO4 problems arise not only during the extraction stages but also in the treatment of high active liquid waste and subsequent vitrification. As this volatile RuO4 can deposit in cooler parts, there is an increase in the radiation field due to the presence of 106Ru. The problem is very acute in the reprocessing of fast reactor fuels due to the increased concentration of ruthenium in the spent fuel. In nitric acid medium Ru can exist in various nitroso nitrate complexes and nitroso complexes are more stable than nitrates. The nitrates are non-extractable by the solvent TBP; however, they are extractable to a higher degree by DBP (the primary degradation product of TBP). The extractability of Ru nitrates into the solvent is inhibited by high acid content, temperature and prolonged hold-up time. Nevertheless, these factors promote the volatilization of Ru as RuO4. The volatilization is enhanced by the addition of phosphate ions, but is suppressed by phosphite or hypophosphite ions. Thus, it would be advantageous if ruthenium is removed so that not only the purity of the product (Pu) is improved, but also the problem related to volatilisation can be resolved. High molecular weight amines (tertiary amines) capable of forming co-ordinate bonds are reported to be ideal extractants for Ru. Gas phase separation is an effective method for the recovery of Ru from catalysts, lead button and from other platinum group metals. Separation and pre-concentration of noble metals can be accomplished from non-metals by simple sorbents like coconut shell activated carbon to complicated chelating resins, aromatic polymers and zeolites. In the electro-oxidation of active Ru from nitroso salts, Pd was found to interfere and removal of Pd prior to oxidation of Ru is recommended. Redox catalysts such as Ag2+ and Ce4+ are found to play a prominent role in the electro-oxidation of Ru. Though, various methods and extractants are reported in the literature for the separation of Ru, R&D is being pursued for the removal of Ru during aqueous reprocessing of spent fuels using extractants and methods which are conducive to plant conditions. Hence, an exhaustive survey of literature was made and the different methods reported for the removal of Ru with emphasis towards reprocessing applications are discussed in this report as a review. Attempts made by the authors in separating Ru from simulated waste solution are also included in this review.

Following the Evolution of Ru/Activated Carbon Catalysts during the Decomposition–Reduction of the Ru(NO)(NO3)3 Precursor

AbstractOxygen surface groups, which are typically present on the surface of activated carbon, have a decisive effect on the achieved dispersion of active phases, which affects the electronic properties of the surface sites and stabilizes the materials against sintering phenomena. Therefore, the desorption of oxygen surface groups during the decomposition–reduction of the metal salt precursors of the fresh carbon‐based catalysts can lead to surface reconstruction of the metal nanoparticles, which can significantly affect their catalytic activity. In this work, the oxidation states of Ru atoms supported on both an activated carbon thermally treated to remove all oxygen groups and the untreated material were studied during the reduction process. The precursor to prepare these catalysts is Ru(NO)(NO3)3. The main results were obtained by using in situ X‐ray absorption near‐edge structure analysis of the Ru K‐edge under conditions comparable to the temperature‐programmed reduction experiments. The different reduction mechanism observed in each of the catalysts, of a multistep nature if oxygen surface groups are present and single‐step in the case of clean graphitic surfaces, can be regarded as a typical metal–support interaction. Moreover, differences in both the final Ru oxidation state and the subsequent interaction of the active phase with the support are the main cause of the five‐times higher catalytic activity observed in the presence of the catalyst without surface oxygen groups for the NH3 decomposition reaction.

Metal oxides nanoparticles from complexes on SBA-15 for glycerol conversion

Metal oxides nanoparticles dispersed on SBA-15 were synthesized by functionalization of metalloporphyrins onto modified SBA-15, for confining the growth of Ru, Cu, Zn or Co oxides nanocrystals. The composites were evaluated in the dehydration of glycerol at 250°C and 1atm. Among the solids studied, best results were achieved for RuSBA-15 and CoSBA-15 due to the resistance shown by nanoparticles to sintering. On the other hand, ZnSBA-15 and CuSBA-15, which possessed a lesser basic strength, led to parallel reaction instead of the dehydration of glycerol, by forming heavy compounds; this resulted in the catalysts deactivation by coking.

Effect of the Structural Characteristics of Binary Pt–Ru and Ternary Pt–Ru–M Fuel Cell Catalysts on the Activity of Ethanol Electrooxidation in Acid Medium

In view of their possible use as anode materials in acid direct ethanol fuel cells, the electrocatalytic activity of Pt-Ru and Pt-Ru-M catalysts for ethanol oxidation has been investigated. This minireview examines the effects of the structural characteristics of Pt-Ru, such as the degree of alloying and Ru oxidation state, on the electrocatalytic activity for ethanol oxidation.

Influence of bias voltage on the switching behaviour of CoCrPt–SiO2 perpendicular recording media

A systematic investigation of the influence of negative substrate bias on the microstructure and magnetic switching behaviour of CoCrPt : SiO2 perpendicular recording media is performed by varying the negative bias voltage from 0 to 600 V during the deposition of a bottom Ru (or Ru : TiO2SiO2) intermediate layer. The microscopic structures and the surface morphology are studied by a transmission electron microscope and an atomic force microscope. The crystallographic properties are studied by an x-ray diffractometer. Our observation shows that high biasing is at work to favour the formation of low-energy hexagonal close packed (0 0 2) planes, resulting in high crystallinity of Ru. Addition of oxide to the Ru intermediate layer leads to an increase in grain segregation, which results in a small grain diameter, but broad standard deviation and large surface roughness. Utilization of a bias voltage on the Ru oxide intermediate layer successfully improves the crystal texture of CoCrPt : SiO2 and induces high Hc, a narrow intrinsic switching field distribution and low Hcr45/Hcr0, while maintaining isolated grains and small grain size.

New rock salt-related oxides Li3M2RuO6 (M=Co, Ni): Synthesis, structure, magnetism and electrochemistry

We describe the synthesis, crystal structure, magnetic and electrochemical characterization of new rock salt-related oxides of formula, Li 3 M 2 RuO 6 ( M =Co, Ni). The M =Co oxide adopts the LiCoO 2 ( R- 3 m ) structure, where sheets of LiO 6 and (Co 2 /Ru)O 6 octahedra are alternately stacked along the c -direction. The M =Ni oxide also adopts a similar layered structure related to Li 2 TiO 3 , where partial mixing of Li and Ni/Ru atoms lowers the symmetry to monoclinic ( C 2 /c ). Magnetic susceptibility measurements reveal that in Li 3 Co 2 RuO 6 , the oxidation states of transition metal ions are Co 3+ (S=0), Co 2+ (S=1/2) and Ru 4+ (S=1), all of them in low-spin configuration and at 10 K, the material orders antiferromagnetically. Analogous Li 3 Ni 2 RuO 6 presents a ferrimagnetic behavior with a Curie temperature of 100 K. The differences in the magnetic behavior have been explained in terms of differences in the crystal structure. Electrochemical studies correlate well with both magnetic properties and crystal structure. Li-transition metal intermixing may be at the origin of the more impeded oxidation of Li 3 Ni 2 RuO 6 when compared to Li 3 Co 2 RuO 6 . Interestingly high first charge capacities (between ca. 160 and 180 mAh g −1 ) corresponding to ca. 2/3 of theoretical capacity are reached albeit, in both cases, capacity retention and cyclability are not satisfactory enough to consider these materials as alternatives to LiCoO 2 . Two new rock salt related oxides of formula, Li 3 M 2 RuO 6 , ( M =Co, Ni) have been prepared. The M =Co oxide adopts the LiCoO 2 ( R- 3 m ) structure and the M =Ni oxide adopts a similar layered structure related to Li 2 TiO 3, monoclinic ( C 2 /c ), with partial mixing of Li and Ni/Ru atoms. For Li 3 Co 2 RuO 6 , oxidation state for Ru is 4+ and antiferromagnetic (AFM) order is found below 10 K while for the analogous Li 3 Ni 2 RuO 6 , Ru oxidation state is 5+ and a ferrimagnetic (FM) behavior with a Curie temperature of 100 K is found. Electrochemical studies correlate well with both magnetic properties and crystal structure. • New Ruthenium rock salt-related oxides of formula, Li 3 M 2 RuO 6 ( M =Co, Ni) were studied. • Structurally different: rhombohedral α-NaFeO 2 -type (Co) and monoclinic Li 2 TiO 3 -type (Ni) • Magnetic behavior is different: the Co sample is AFM while the Ni one is ferrimagnetic. • Ruthenium oxidation states are different: 4+ in the Co sample and 5+ in the Ni one. • Electrochemical studies correlate well with magnetic properties and crystal structures.

Kinetics and Mechanism of Aquachlororuthenium (III) Catalyzed Oxidation of Tartaric Acid by Acid Bromate

The kinetics of the oxidation of Ru (III) catalyzed oxidation of tartaric acid by potassium bromate in aqueous perchloric acid medium at constant ionic strength was investigated in the temperature range 303- 318 K. The reactions exhibit first order kinetics at low concentration of bromate, tending to zero order at high concentration. Zero order kinetics with respect to (tartaric acid) and first order kinetics in (Ru (III)) were observed in the oxidation of tartaric acid. A positive effect on the rate of reaction has been found on the successive addition of (H + ) and (Cl - ). Variation in mercuric acetate concentration, (Hg(OAc)2) and ionic strength of the medium did not bring any significant change on the rate of reaction. The first order rate constant increases with decrease in the dielectric constant of the medium. The values of rate constants observed at four different temperatures were utilized to calculate the activation parameters. Formic acid and carbon dioxide have been identified as main oxidation products of the reaction. A plausible mechanism from the results of kinetic studies, reaction stoichiometry and product analysis has been proposed.

Simultaneous determination of ascorbic acid and rutin in pharmaceutical preparations with electrochemical method based on multi-walled carbon nanotubes–chitosan composite film modified electrode

In this paper, the simultaneous voltammetric determination of ascorbic acid (AA) and rutin (Ru) has been achieved at an acetylene black paste electrode modified with multi-walled carbon nanotubes–chitosan composite film (denoted as MWCNTs–CHIT/ABPE). Compared with bare electrode, the peak currents of AA and Ru at MWCNTs–CHIT/ABPE increased greatly and the anodic peak potential difference (ΔEpa) between AA and Ru are up to 342mV, which is undoubtedly attributed to the unique characteristics of AB and MWCNTs such as excellent electric conductivity, high surface area and strong adsorptive abilities, resulting in higher accumulation efficiency to AA and Ru. The influences of some experimental conditions on the oxidation of AA and Ru were tested and the calibration plot was examined. Under the optimized condition, a good linearity was obtained in the concentration range of 1μM–0.4mM for AA in the presence of 10μM Ru and 20nM–10μM for Ru in the presence of 1mM AA. The detection limits (S/N=3) of AA and Ru are 0.8μM and 10nM, respectively. The proposed method was successfully applied to the simultaneous determination of AA and Ru in pharmaceutical samples with reliable recovery.

Oxygen Evolution during Water Electrolysis from Thin Films Using Bimetallic Oxides of Ir-Pt and Ir-Ru

Catalysts are required for both the oxidation of water and the reduction of oxygen. Blended oxides of Ir and Ru are superior for water oxidation whereas mixtures of Pt and Ir perform better when both oxidation of water and reduction of oxygen are required on the same electrode. A strategy for rationing these elements is explored by the formation of a thin film using a dry, flame process. IrxPt1-xO2-y and IrxRu1-xO2-y were both deposited from the vapor phase, as thin films, onto substrates of glassy carbon, polypropylene, and quartz. Elemental analysis of the Ir-Pt electrode suggests a stoichiometry of Ir0.56Pt0.44O2-y. Bulk diffraction of the film shows two separate phases consisting of Pt metal and IrO2. The sample showed signs of spallation after 10 cycles when scanned between 1.2 and 1.7 V. A weak oxygen evolution current of 0.8–0.4 mA/mg was measured at 1.6 V. Elemental analysis of the Ru-Ir film suggests a ratio of Ru0.41Ir0.59O2-y. Phases of a homogeneous solid-solution of IrO2 and RuO2 and to a lesser extent Ru metal are shown by bulk X-ray diffraction. An exceptional oxygen evolution current of 25–40 mA/cm2 was observed for the Ru0.41Ir0.59O2-y sample corresponding to a normalized mass activity of 400 mA/mg.

Electron transfer dynamics of peptide‐derivatized RuII‐polypyridyl complexes on nanocrystalline metal oxide films

The performance of dye-sensitized solar and photoelectrochemical cells is strongly dependent on the electron transfer events at the electrode-sensitizer interface. Surface-bound peptides derivatized with chromophores have not been used in dye-sensitized solar and photoelectrochemical cells, but they have properties for these applications that could be advantageous by exploiting secondary structure and the attachment of multiple chromophores. In this manuscript, we have investigated structure-property relationships for three metallopeptide-based assemblies to solution and chemically bound to nanocrystalline MO(2) (M = Ti, Zr) films. A particular interest was exploring the influence of increasing separation distance between a common chromophore, [Ru(bpy)(2) (4-Me-4'-(NHCO)bpy)](2+) , and the underlying oxide substrate on excited and ground state electron transfer. Rates of Ru(II) oxidation to Ru(III) at the interface were measured by cyclic voltammetry on fluorine-doped tin oxide and cross-surface electron transfer on TiO(2) . Excited state injection by [Ru(III) (bpy)(2) (bpy(-) )](2+) was monitored by transient absorption and time-resolved emission. There are discernible trends in the electron transfer rate data with approximated, fully extended distances between the [Ru(bpy)(2) (4-Me-4'-(NHCO)bpy)](2+) sites and the interface. However, the distance dependences that are observed are smaller than anticipated, a result consistent with a lack of ordered secondary structure in the surface-bound peptide chains and a distribution of local orientations. For the surface-bound excited states, only a small fraction undergo quenching by electron transfer to TiO(2) , presumably from those oriented near the surface.

Role of Guanidine Carbonate and Crystal Orientation on Chemical Mechanical Polishing of Ruthenium Films

Ruthenium (Ru) films deposited on either TiN or TaN/Ta have been proposed as a barrier stack in advanced interconnects. Here, we investigated their polishing behavior using colloidal silica-based slurries containing guanidine carbonate (GC) or hydrogen peroxide (H2O2) or both. Neither GC nor H2O2 alone enhanced the Ru removal rates (RRs) but their combination did, presumably, due to the formation of Ru oxide-guanidinium complexes which can be polished by silica abrasives suggesting that the oxidation of Ru to its oxides is a crucial first step. Ethylenediamine and 2, 2–bipyridine that were reported to form complexes with halides of Ru in various oxidation states also enhanced the RRs of Ru films, similar to GC. Furthermore, even though both types of Ru films were deposited at same conditions, RRs of Ru on TiN were enhanced more compared to those on TaN/Ta, likely a consequence of the difference in the crystalline structure of the oxide films formed due to a difference in the structure of the Ru films themselves. Using X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentation, zeta potential measurements, thermo gravimetric analysis and contact angle measurements, the role of GC and crystalline structure in enhancing the RRs of the films is discussed.

Synthesis, characterization, electronic structure and catalytic activity of new ruthenium carbonyl complexes of N-[(2-pyridyl)methylidene]-2-aminothiazole

Reaction of ruthenium carbonyls, [Ru(CO)2Cl2]n/[Ru(CO)4I2] with bidentate Schiffs base ligands derived by the condensation of pyridine-2-carboxaldehyde with 2-aminothiazole in a 1:1 mole ratio in acetonitrile led to the formation of complexes having general formula [Ru(CO)2(L)X2] (X=Cl (1) and I (2)) (L=N-[(2-pyridyl)methylidene]-2-aminothiazole). The compounds have been characterized by various analytical and spectroscopic (IR, electronic and 1H NMR) studies. In acetonitrile solution the complexes exhibit a weak broad metal–ligand to ligand charge transfer (MLLCT) band along with ILCT transitions. The compounds are emissive in room temperature upon excitation in the ILCT band. The complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 1.44V for 1 and 0.94V for 2. Catalytic activity of these compounds is investigated to the oxidation of PhCH2OH to PhCHO, 2-butanol (C4H9OH) to 2-butanone, 1-phenylethanol (PhC2H4OH) to acetophenone, cyclopentanol (C5H9OH) to cyclopentanone, cyclohexanol to cyclohexanone, cycloheptanol to cycloheptanone and cycloctanol to cycloctanone using N-methylmorpholine-N-oxide (NMO) as oxidant. The catalytic efficiency of 2 is greater than complex 1 and well correlate with the metal oxidation potential of the complexes. DFT, NBO and TDDFT calculations are employed to explain the structural and electronic features and to support the spectroscopic assignments.

Effect of Oxidizers on Chemical Mechanical Planarization of Ruthenium with Colloidal Silica Based Slurry

We investigated effect of oxidizers on chemical mechanical planarization (CMP) of ruthenium (Ru). Several commonly used oxidizers with different standard reduction potentials were used in the Ru CMP test, and their corrosion behaviors and states of surface oxidation were analyzed. We found that Ru only had a high polishing rate with slurries containing sodium periodate and sodium hypochlorite. We also observed that Ru film underwent severe pitting corrosion with these slurries, and formed a porous RuO3/RuO2 oxide layer. Ru film was unable to achieve high corrosion current density as well as form a porous RuO3/RuO2 oxide layer except for these two oxidizers. Both the corrosion and oxidation (formation of RuO3/RuO2 layer) processes influenced the Ru polishing rate, but the oxidation process was assumed to play a more decisive role in the Ru CMP. The mechanism for the types of oxidizers in Ru corrosion and oxidation processes is discussed and explained through a diagram of the equilibrium electronic band of Ru metal electrodes and oxidizers in an aqueous solution.

Atomic Scale Insights into the Initial Oxidation of Ru(0001) Using Molecular Oxygen: A Scanning Tunneling Microscopy Study

The initial oxidation of Ru(0001) has been studied by scanning tunneling microscopy (STM) using molecular oxygen as the oxidizing agent. The initial oxidation process reveals a complex behavior in which three-dimensional RuO2 domains (clusters) are exclusively formed at multiple steps, and only few of these clusters are able to initiate the growth of flat RuO2 domains with its (110) orientation along the (0001) direction of the Ru substrate. The oxide formation requires a minimum temperature of 500 K and a minimum pressure of about 1 × 10–5 mbar of oxygen. Below 1 × 10–5 mbar, oxide growth is very slow, although even at pressure of 10–6 mbar oxidation in step bunching regions is occasionally observed. The modified nucleation and growth mode of Ru(0001) oxidation is corroborated by growing the oxide in two separate steps: Starting with oxygen exposure of 1.5 × 10–5 mbar of O2 for 960 s at a sample temperature of 680 K, RuO2 nuclei are preferably formed. Subsequently, the further growth of flat oxide domain...

Insights into the deactivation and reactivation of Ru/TiO2 during Fischer–Tropsch synthesis

The catalytic performance of Ru/TiO2 for the production of hydrocarbons via Fischer–Tropsch synthesis (FTS) has been evaluated in this work. Ru/TiO2 exhibits high CO conversion rates (523K, 2.5MPa H2, 1.25MPa CO) that decrease significantly with time-on-stream. To recover the initial catalytic performance, different treatments using H2 or air have been tested. The evolution of the catalyst structure during FTS and after the re-activation protocols have been explored by a combination of ex situ and in situ techniques. Ru agglomeration, oxidation, and formation of Ru–volatile species are not responsible for the observed deactivation. However, Raman and infrared (FTIR) spectroscopy have confirmed the presence of coke and alkyl chains on the spent catalysts. These species hinder the adsorption of the reactants on the active sites and are the primary reason for the observed decrease in the catalytic activity. These carbonaceous species can be removed by severe thermal treatments in air. However, this latter treatment drastically alters the morphology of the Ru/TiO2, which leads to a substantial loss of catalytic activity.

Carbon monoxide, methanol and ethanol electro-oxidation on Ru-decorated carbon-supported Pt nanoparticles prepared by spontaneous deposition

Carbon-supported Pt nanoparticles (Pt/C) were modified by spontaneous deposition of Ru species in 0.1 M HClO4 solutions with different Ru concentrations and treatment duration. Cyclic voltammetry (CV) of thin-layer electrodes in 0.5 M H2SO4 allowed determining the coverage θ of Pt by the Ru deposits. The CO oxidation activity of the Ru-decorated Pt specimens (Ru(Pt)/C) was evaluated by CO stripping measurements in the same background electrolyte. The activity towards methanol and ethanol oxidation was tested using CV in 0.5 M H2SO4 with 1.0 M CH3OH or 1.0 M CH3CH2OH. A promotional effect of all the anodic reactions due to the introduction of Ru species was detected, with a significant reduction of the overpotential in all cases. The optimum coverage for achieving the best CO oxidation activity and the highest current for the oxidation of these alcohols was found around θ = 0.20–0.30, indicating the involvement of CO as intermediate in the oxidation pathway of both, methanol and ethanol. The observed activation was mainly assigned to the deposited hydrous Ru oxide (RuOxHy). The Tafel slopes were analyzed and discussed on the basis of the presence of Ru species and the proposed mechanism for each oxidation reaction.

Intrinsic Relation between Catalytic Activity of CO Oxidation on Ru Nanoparticles and Ru Oxides Uncovered with Ambient Pressure XPS

Recent progress in colloidal synthesis of nanoparticles with well-controlled size, shape, and composition, together with development of in situ surface science characterization tools, such as ambient pressure X-ray photoelectron spectroscopy (APXPS), has generated new opportunities to unravel the surface structure of working catalysts. We report an APXPS study of Ru nanoparticles to investigate catalytically active species on Ru nanoparticles under oxidizing, reducing, and CO oxidation reaction conditions. The 2.8 and 6 nm Ru nanoparticle model catalysts were synthesized in the presence of poly(vinyl pyrrolidone) polymer capping agent and deposited onto a flat Si support as two-dimensional arrays using the Langmuir-Blodgett deposition technique. Mild oxidative and reductive characteristics indicate the formation of surface oxide on the Ru nanoparticles, the thickness of which is found to be dependent on nanoparticle size. The larger 6 nm Ru nanoparticles were oxidized to a smaller extent than the smaller Ru 2.8 nm nanoparticles within the temperature range of 50-200 °C under reaction conditions, which appears to be correlated with the higher catalytic activity of the bigger nanoparticles. We found that the smaller Ru nanoparticles form bulk RuO(2) on their surfaces, causing the lower catalytic activity. As the size of the nanoparticle increases, the core-shell type RuO(2) becomes stable. Such in situ observations of Ru nanoparticles are useful in identifying the active state of the catalysts during use and, hence, may allow for rational catalyst designs for practical applications.

Synthesis, X-ray structure, spectroscopic and DFT study of cis-[Ru(PPh3)(L)X2] complexes (X = Cl−, Br−, I− and NCS−) (L = 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole)

The complex cis-[Ru(PPh3)(L)Cl2] (1) has been synthesized by the reaction between Ru(PPh3)3Cl2 and thioether containing azo ligand (L) (L=1-methyl-2-{(o-thiomethyl)phenylazo}imidazole). The Cl atoms have been exchanged with Br−, I− and NCS− leading to the formation of cis-[Ru(PPh3)(L)Br2] (2), cis-[Ru(PPh3)(L)I2] (3) and cis-[Ru(PPh3)(L)(NCS)2] (4), respectively. The complexes have been characterized by spectroscopic techniques (IR, NMR and UV–Vis) and geometries have been confirmed by X-ray crystal structures of 1 and 3. The electronic spectra of the complexes show moderately intense MLCT band along with intense ILCT transitions. Cyclic voltammetric studies show one quasi reversible Ru(III)/Ru(II) oxidation couple and two successive one electron reductions leading to the formation of L− and L2−, respectively. The electronic structure, redox and absorption properties of the complexes have been explained based on DFT and TDDFT results.