Ru Composition Research Articles

Supported catalyst characterization

Small Ru- and Pt-containing mono- and bimetallic particles supported on silica were characterized using both theoretical thermodynamic simulations and experimental nuclear magnetic resonance (NMR) of chemisorbed hydrogen. The thermodynamic Monte Carlo simulations have provided detailed information on the morphologies, surface structures, and surface compositions of Ru–Cu and Pt–Cu bimetallic particles. For small Ru and Pt crystallites, a significant fraction of surface atoms populate defect-like edge and corner sites (e.g., 20% of total surface atoms for a particle with a dispersion of 0.31). These sites are preferentially occupied by copper. NMR of chemisorbed hydrogen is a surface-sensitive technique and has been used to measure the overall surface composition of the bimetallic particles and reveal subtle changes in the surface electronic environments due to addition of a second metal (copper) or a surface contaminant (chlorine or sulfur). The surface composition results determined from thermodynamic simulations are in agreement with those from proton NMR measurements for a series of 4% Ru–Cu/SiO2 and a series of 5% Pt–Cu/SiO2 bimetallic catalysts. Chlorine and sulfur are capable of inhibiting hydrogen chemisorption on Ru surfaces at a less-than-monolayer coverage. This observation and also the observed decrease in proton Knight shifts with increasing Cl coverage (less pronounced for S) on Ru surfaces were attributed to a short-ranged, ‘‘through-the-surface’’ electronic effect.

Electrochemical Oxidation of Methanol at Chemically Prepared Platinum‐Ruthenium Alloy Electrodes

Chemically prepared Pt‐Ru alloy catalysts were investigated to study the effects of temperature, Pt loading, and heat‐treatment on the kinetics of methanol oxidation in acid electrolyte. The maximum current density obtained for the Pt‐Ru catalyst, dispersed on Vulcan XC‐72R carbon, was about 600 mA/cm2 at 60°C and a Pt loading of 2.05 mg/cm2. The maximum catalytic shift due to the Ru modification of Pt was 200 mV at a current density of 160 mA/cm2. The activation energy for methanol oxidation is similar for both Pt and Pt‐Ru. The Ru composition of the electrode stabilized at higher levels when the electrode was heat‐treated. The oxidation current per mg of Pt decreased with an increase in the Pt loading. A phenomenological analysis of the catalytic shift for methanol oxidation at Pt‐Ru electrodes favored the bifunctional catalyst model over models based on geometric and electronic factors.

On the isotopic composition of ruthenium in the Allende and Leoville carbonaceous chondrites

The isotopic composition of Ru has been measured mass spectrometrically in an acid resistant residue of the Allende meteorite and in one magnetic and three non-magnetic portions of type-B inclusions, two from Allende and one from Leoville. Normalized to 96Ru101Ru = 0.324851, all 98Ru101Ru and 99Ru101Ru ratios were found to be indistinguishable from the terrestrial values within 1.6 permil and 0.4 permil (3σ), respectively. Thus, in the sampled reservoirs we find no evidence for different relative amounts of radiogenic 98Ru and 99Ru from the decay of now extinct 4.2 Myr-98Tc and 0.21 Myr-99Tc. 100Ru101Ru and 104Ru101Ru were found to deviate from the terrestrial norm by more than 2σ (≤0.6 permil) in one and two cases, respectively. Since terrestrial ratios were occasionally compromised by molecular interferences to an even larger extent, these overabundances cannot be unambiguously attributed to nonlinear isotope anomalies in the samples. The 102Ru101Ru ratio is normal in two aliquants of the acid resistant Allende residue but higher than normal by up to 0.35 permil in all four inclusion samples. There is a possibility, although very remote, that these excesses are due to contamination by a 102Ru spike. A less conservative interpretation of the data and normalization to 104Ru101Ru rather than to 96Ru101Ru results in overabundances of the light p-process isotopes 96Ru and 98Ru in the non-magnetic portions of all three inclusions.

Enhancement of catalytic activity by effect of graphite on Ru−Pt/C catalysts

Surface composition and catalytic activity of Ru−Pt/C catalysts were determined. A surface enrichment in Pt was found over the entire composition range. Catalytic activity showed a maximum value (1∶40) on 66% Ru bimetallic catalyst. These results are correlated with the nature of the impregnating salts and with the conductive properties of graphite.

Fluorescence of clay-intercalated methylviologen

The elucidation of the effect of structure and composition of Ru(bpy)/sub 3//sup 2 +/ and of the function of each component on the photochemical processes may be assisted by a variety of spectroscopic studies. With this in mind the authors investigated the fluorescence behavior of methylviologen (MV). To the best of their knowledge fluorescence from MV at ambient temperatures has not been reported previously. However, fluorescence of MV/sup 2 +/ could be observed when it was incorporated into the lamellae of colloidal hectorite and montmorillonite suspensions. No fluorescence could be detected in the case of nontronite. Time-resolved fluorescence measurements as well as the fluorescence intensity variation with the ratio MV/sup 2 +//clay suggest different types of binding sites for MV/sup 2 +/ adsorbed on the clay colloidal particles.

A photoemission study of the oxidation of platinum in Pt-based alloys: PtPd, PtRu, PtIr

Photoemission technique was used to study the surface composition of PtPd, PtRu and PtIr alloys in a wide range of bulk compositions. The samples were submitted to in-situ oxygen exposures at atmospheric pressure and various temperatures in the 200 to 600°C range. Oxygen induced changes of surface composition were followed. Special attention was paid to the various oxidation states of the metals characterized by high-binding energies shifts of the core-levels. Oxidation properties of platinum but also of Pd, Ru and Ir drastically changed by alloying. The Pt-based alloys could be oxidized provided the impurity (i.e. Pd, Ru or Ir) surface concentration was higher than a limit situated between 13% and 20% for all three systems. Above this limit, the impurity and the platinum atoms were both oxidized. Three different Pt oxidation states were detected and identified with PtO, α-PtO 2 and β-PtO 2, the occurrence of which depended on the composition and the temperature of oxidation treatment. In the low impurity content range, neither the impurity nor platinum could be oxidized. Several hypotheses (kinetics of oxidation, oxygen spill-over, percolation effects, changes in local electronic states) are discussed to elucidate this phenomenon.

A photoemission study of the oxidation of platinum in Pt-based alloys: Pt-Pd, Pt-Ru, Pt-Ir

Abstract Photoemission technique was used to study the surface composition of PtPd, PtRu and PtIr alloys in a wide range of bulk compositions. The samples were submitted to in-situ oxygen exposures at atmospheric pressure and various temperatures in the 200 to 600°C range. Oxygen induced changes of surface composition were followed. Special attention was paid to the various oxidation states of the metals characterized by high-binding energies shifts of the core-levels. Oxidation properties of platinum but also of Pd, Ru and Ir drastically changed by alloying. The Pt-based alloys could be oxidized provided the impurity (i.e. Pd, Ru or Ir) surface concentration was higher than a limit situated between 13% and 20% for all three systems. Above this limit, the impurity and the platinum atoms were both oxidized. Three different Pt oxidation states were detected and identified with PtO, α-PtO 2 and β-PtO 2 , the occurrence of which depended on the composition and the temperature of oxidation treatment. In the low impurity content range, neither the impurity nor platinum could be oxidized. Several hypotheses (kinetics of oxidation, oxygen spill-over, percolation effects, changes in local electronic states) are discussed to elucidate this phenomenon.

The physical metallurgy and electrical contact resistance of mechanically alloyed CuRu composites

Mechanical alloying (high energy attrition milling) has been used to create a novel type of electrical contact material, a Cu-15vol.%Ru composite consisting of a fine (micron-scale) distribution of ruthenium in copper. Because these elements are mutually insoluble, mechanical alloying is one of the only ways of creating such a non-equilibrium microstructure. Consolidation of the composite powders into strip was carried out by warm and cold rolling, to preserve the metastable microstructure. The removal of surface copper from the consolidated strip gives rise to a “sandpaper” structure in which the hard, refractory and conductive ruthenium particles, now protruding from the surface, serve as the electrical contacts, whereas the copper matrix supports these particles and provides electrical continuity. The fact that this is so is borne out by the observation that in contact resistance versus exposure time tests, the Cu-15vol.%Ru composite behaves much more like pure ruthenium than like pure copper. Thus, we have developed a procedure for producing a base metal-ruthenium composite with electrical contact properties similar to those of ruthenium, without the difficulties (i.e. hot forging) or expense of working with pure ruthenium. This processing is applicable to an unlimited number of alloy systems.

Methanation studies over well-characterized silica-supported Pt-Ru bimetallic clusters

A methanation study over a well-characterized series of silica-supported Pt-Ru bimetallic clusters has been completed. Surface compositions, determined by O 2-CO titration using a pulse technique, show considerable surface enrichment in Pt. Turnover numbers and activation energies for CH 4 formation were determined for Pt-Ru bimetallic cluster catalysts having the following Pt surface compositions: 17.9, 50, 73, and 99%. The results suggest that Ru ensembles are necessary to catalyze the methanation reaction as Pt-Ru dual sites show a catalytic behavior characteristic of Pt. When the surface composition of Ru is high, the observed turnover number for CH 4 formation is in good agreement with the sum total of the corresponding turnover numbers for methanation on the separate metals. For low surface concentrations of Ru, the reverse is true. A temperature-programmed pulse technique was used to study carbon formation by pulsing CO over each catalyst as the temperature was increased in flowing He. The temperature of incipient carbon formation, as determined by measuring CO 2 formation gas chromatographically, increased as the surface concentration of Pt was increased.

Surface characterization of supported PtRu bimetallic clusters using infrared spectroscopy

The feasibility of determining the surface composition of a series of supported PtRu bimetallic cluster catalysts using infrared spectroscopy has been explored. The nominal bulk compositions of Ru in these samples were 10, 22, 38, 62, and 80 atom%; total metal content of each sample was 6% by weight. The infrared absorption bands of CO (g) selectively adsorbed on Pt sites and those of NO(g) selectively adsorbed on Ru sites were stable in vacuo at room temperature. As the concentration of Ru was increased, there was a gradual shift in the frequencies of these bands indicating the weakening of the CO bond and strengthening of the NO bond. Prolonged exposure of each bimetallic catalyst (fully covered by both CO and NO) to NO(g) resulted in reaction between NO(g) and CO (ads) yielding CO 2(g) and N 2O(g). As the content of Ru was increased, there was a corresponding increase in the NO-band intensity and a decrease in the CO-band intensity. If both extinction coefficients and stoichiometric coefficients are taken to be independent of surface composition, a simple linear correlation between the absorbance ratio and the bulk metal composition was obtained, suggesting that the composition of the surface changed in the same way as that of the bulk. Such a plot provides a quick and inexpensive method of determining surface compositions of supported PtRu cluster catalysts.

Displacive transformations in near-equiatomic Nb-Ru alloys—II. Energetics and mechanism

The transformation distortions during the β→β′ and β′→β′′ transformations in near eluiatomic Nb-Ru allols produce phases that have progressivell loler slmmetrl than the CsCl tlpe β phase and approach the packing of the hexagonal close packed structure. Bl the use of a simple approximation—the superposition approximation—a model is developed lhich explains all of the experimental measurements on this allol slstem. The driving force for these transformations is electronic in nature. The Fermi energl μ of the β phase allols is near a sharp peak in the densitl of status. ρ( E). The transformations broaden this peak, lolering ρ(μ) and the energl of the phase. The significant experimental measurements accounted for bl this model are the variation of magnetic susceptibilitl lith phase and Ru content, the variation of transformation temperatures and transformation distortion lith Ru composition, and distortion in the β phase lith temperature and Ru composition.