Ru Ratio Research Articles

Degradation, Cleanup, and Reusability of Octylphenyl- N, N′-diisobutylcarbamoylmethyl Phosphine Oxide (CMPO) during Partitioning of Minor Actinides from High Level Waste (HLW) Solutions

ABSTRACT The radiolytic degradation of the extractant mixture 0.2 M octylphenyl-N,N′-diiso-butylcaibamoylmethyl phosphine oxide (CMPO) + 1.2 M tributyl phosphate in n- dodecane [to be utilized for the partitioning of minor actinides from high level waste (HLW) solutions of PUREX origin] has been investigated in contact with 3 M HNO3 or synthetic pressurized heavy water reactors (PHWR)-HLW solution under dynamic conditions. The distribution ratios of Am, Zr, Fe, and Ru with the irradiated extractant mixture at varying doses have been determined under various aqueous phase conditions and correlated with the formation of degradation products. Various cycles ofloading the extractant mixture with Am from PHWR-HLW, irradiating at a fixed gamma dose, and then primary and secondary clean-up of the solvent has been carried out to illustrate its reusability during partitioning of minor actinides from actual HLW solutions. The degradation products of CMPO have been identified by employing GC and GC-MS techniques.

A new trial to search for isotopically anomalous osmium and ruthenium in fine-grained Ca, Al-rich Allende inclusions by radiochemical neutron activation analysis

The ratios of 184Os 190Os and 96Ru 102Ru in five fine-grained Ca, Al-rich Allende inclusions (CAIs) were determined simultaneously and precisely by radiochemical neutron activation analysis (RNAA). The results show that their deviations relative to the terrestrial chemical reagent are within −1.5%v and 1.9%v for 184Os 190Os and 96Ru 102Ru , respectively. It seems unlikely that the isotopic anomalies of Os and Ru exist at a magnitude of more than ±2% in bulk fine-grained Allende CAIs. Whereas the possibility that the fine-grained Allende CAIs measured in this work do not contain presolar components and thus have normal isotopic compositions cannot be excluded, we believe that our data may most plausibly be interpreted as the anomalies carried by submicron-size metal alloys thought to be the presolar grains were homogenized during the processes of sample digestion and chemical separation. Os and Ru concentrations in five fine-grained CAIs were determined by comparison with the activities of the known amounts of Os and Ru standards, respectively. In contrast to the coarse-grained Allende CAIs, Os and Ru were greatly depleted in these five fine-grained CAIs. The mean enrichment factors of Os and Ru relative to C1 chondrite were 2.82 and 2.99, respectively. In addition, Os is depleted relative to Ru in four of five fine-grained Allende CAIs, and a large fractionation between Os and Ru is observed. The C1 chondrite-normalized Os Ru enrichment factor ranges from 0.23 to 2.50 in five fine-grained Allende CAIs. These results support the non-equilibrium incomplete condensation model for the origin of fine-grained Allende CAIs. It suggests that the fine-grained Allende CAIs probably contain much less hcp alloy grains, and thus the primordial signatures of isotope and Os Ru ratio might more readily survive the equilibrium process than those in coarse-grained Allende CAIs. Consequently, it is undeniable that the fine-grained Allende CAI is one of the most promising hunting grounds to search for isotopically anomalous Os and Ru.

Suppressed hydrogen chemisorption of zeolite encaged metal clusters: discrimination between theoretical models on the basis of Ru/NaY

The effects of thermal treatment and zeolite proton concentration on the chemical state and metal particle size of zeolite Y supported ruthenium (3.0 wt%) have been investigated using H2-TPR, H2-TPD, TPMS, FTIR, TEM, and EXAFS. Heating in Ar of the precursor after ion exchange, [Ru(NH3)6]3+/NaY, up to 400°C leads to nearly 100% autoreduction of the ruthenium, as evidenced by H2-TPR and TPMS. Heating in O2 results in the formation of volatile ruthenium oxides. After autoreduction, the Ru clusters are extremely small, their coordination numbers, derived from EXAFS, are 0.6 for Ru/HY and 0.8 for Ru/NaY. Subsequent treatment at 500°C in flowing H2 induces Ru agglomeration to particles which are about the size of the zeolite Y supercages, as indicated by TEM and EXAFS. The Ru-Ru distances are contracted compared to bulk Ru metal. Washing of autoreduced Ru/NaY with NaOH, thus removing the protons formed during autoreduction, results in Ru agglomeration to large particles (60-100 A). Comparison of the hydrogen adsorption of Ru clusters with similar sizes of 10-15 A reveals a marked interaction of the Ru clusters with zeolite protons. Increasing the H+/Ru ratio from 3 for Ru/NaY to 10 for Ru/HY, results in a suppression of hydrogen chemisorption per Ru atom by 75%. The conclusion that formation of metal-proton adducts affects the electronic structure of the Ru clusters, thus being one of the main causes of the lowering of the heat of hydrogen chemisorption, is supported by FTIR data of adsorbed CO. The most pronounced C-O vibration band in Ru/HY is located at 2099 cm-1; this band is absent in Ru/NaY. Significant blue-shifting of the IR bands is in conformity with electron-deficiency of the Ru clusters in Ru/HY. The results confirm that adsorptive properties of zeolite encaged metal clusters can be "tuned" by other ions sharing the same cavities.

The activity of carbonyl cluster derived [formula omitted] and [formula omitted] catalysts in CO hydrogenation

We studied systematically the use of tetranuclear cobalt, cobalt-ruthenium, cobalt-rhodium and rhodium carbonyl clusters as catalyst precursors. The catalytic activities and the product distributions of the hydrogenation of carbon monoxide over Co 4−nRu n SiO 2 and Co 4−nRh n SiO 2 catalysts (where n = 0−4) and (Co 4 + Ru 4) SiO 2 and (Co 4 + Rh 4) SiO 2 catalysts derived from the transition-metal carbonyl clusters were compared. Activities were highest for the catalysts derived from homometallic clusters, and lowest for catalysts with 1:1 ratio of Co Ru or Co Rh . Interestingly enough, the highly active homometallic cobalt catalyst was the most resistant to deactivation. On Co 4−nRh n SiO 2 catalysts the deactivation was stronger on bimetallic sites and on the Co 4−nRu n SiO 2 catalysts the deactivation was closely related to the presence of ruthenium. The selectivities for oxygenated compounds were clearly promoted by the bimetallic sites of Co-Rh catalysts. This result is very plausible since the probability to find dual active sites responsible for the formation of oxygenates is greater in bimetallic than in homometallic catalysts.

Formula omitted] X-ray intensity ratios of Fe, Co, Ni, Cu, Mo, Ru, Rh and Pd in equiatomic aluminides

K β K α X-ray intensity ratios of Fe, Co, Ni, Cu, Mo, Ru, Rh and Pd transition metals in equiatomic aluminides have been measured following excitation by 59.54 keV γ-rays from a 200mCi 241Am point-source. In the case of 3 d metal aluminides we find significant deviation in the K β K α ratio from the pure metal value. The maximum deviation observed in the case of cobalt can be accounted by the transfer of 2.48 ± 0.19 electrons both from the (4 s, 4 p) states of the transition metal as well as (3 s, 3 p) states of aluminium to the 3 d state of cobalt. For Fe, Ni and Cu the charge transfer amounts to 1.58 ± 0.20, 0.79 ± 0.21 and 1.08 ± 0.33 respectively. For the 4 d metal aluminides we find an increase in the K β K α ratio by about 4% for Mo and Ru whereas for Rh and Pd almost no difference from the pure metal value is observed. Fresh calculations are needed for explaining the observed increase in the K β K α ratios of Mo and Ru.

Surface studies of Pt-Ru electrodeposits on gold

Auger electron spectroscopy, energy dispersive X-ray techniques and X-ray diffraction were used for the characterization of platinum-ruthenium electrodeposits prepared on gold. SEM-EDAX analysis showed that the gold surface is totally covered by a homogeneous electrodeposit after 30 min of potentiostatic electrodeposition at 0.05 V vs. rhe. The AES analysis of the low kinetic energy peaks revealed that the electrodeposits with more Pt, presented more oxygen on the surface and those deposits with higher intensity ratio of Ru showed more oxygen in bulk. The composition of the deposits calculated from MNN transitions showed that the surface is enriched in Pt. On the basis of the XRD spectra, the electrodeposits, with solPt Ru ratio higher than 1.5, form alloys. The catalytic activity was observed in 3.5 NH 2 SO 4 + 2 M methanol solution at 70 °C. The electrodeposit with 80% Pt and 19% Ru and 1% O (at 5 nm) exhibited the highest apparent current density at 450 mV vs. rhe, for the oxidation of methanol.

Structure and Chemical Composition of a Supported Pt-Ru Electrocatalyst for Methanol Oxidation

High resolution electron microscopy and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of Pt-Ru particles with nominal Pt:Ru ratios of 1:1 and 3:1, supported on carbon black. The particles are predominantly single nanocrystals with diameters in the order of 2.0 to 2.5 nm. Occasionally, twinned particles are also observed. All investigated particles represent solid solutions of Pt and Ru with compositions very close to the nominal one. Based on two-dimensional projection in high resolution images, it is suggested that the well-resolved particles are of cubooctahedral shape. In addition to {200} and {111} facets, {113} facets are also observed.

Catalytic and structural properties of ruthenium monometallic and bimetallic catalysts: characterization by EXAFS and XRD

This work presents an extensive structural study of Ru monometallic ( Ru Al 2O 3 ) and bimetallic ( RuM Al 2O 3 , M = Ge, Sn, Pb) catalysts by means of extended X-ray absorption fine structure (EXAFS) at the Ru K-edge, and X-ray powder diffraction. Samples prepared by the controlled surface reaction (CSR) technique and by the classical impregnation method with different Ru loadings and different Ru M weight ratios were studied. The results show that monometallic catalysts contain small Ru clusters whose degree of dispersion, measured from the average Ru coordination numbers, decreases with the Ru loading. The clusters are formed by metallic ruthenium. The Ru 1% weight sample, prepared by the controlled surface reaction technique, is the most highly dispersed, comprising small clusters of no more than 12 atoms. The samples prepared by this latter technique are in general better dispersed than those prepared by the impregnation method. Addition of germanium produces an increase of Ru dispersion, and in the case of the highest Ge Ru ratio, bimetallic clusters formed. The degree of dispersion is higher in some Sn-containing catalysts while lead does not induce any structural change.

Characterization of carbon-supported ruthenium–tin catalysts by high-resolution electron microscopy

Ruthenium and bimetallic ruthenium–tin catalysts supported on high-surface-area carbon are characterized by high-resolution electron microscopy (HREM) and CO chemisorption. The characterization results give important insights into the reasons for the remarkable catalytic properties of Ru–Sn bimetallic catalysts in selective hydrogenation reactions of α,β-unsaturated aldehydes. In the monometallic Ru/C sample, ruthenium is present as small particles, showing no variation in the crystalline structure and lattice parameters with respect to the bulk state. At low Sn : Ru ratios, the average metal particle size is smaller than for monometallic Ru/C, whereas at higher Sn: Ru ratios Ru particles agglomerate on the surface of the support. According to HREM observations, most metal particles in the bimetallic catalysts possess a structure consistent with that of elemental ruthenium. CO chemisorption results indicate that the surface of the ruthenium particles is partially covered by tin species. Only in the samples with high tin loading are a few Ru–Sn only particles found, in addition to a majority of particles having the structure of pure ruthenium. The high selectivity of Ru–Sn/C catalysts for selective hydrogenation of the CO group in α,β-unsaturated aldehydes can thus be attributed to the presence of small ruthenium particles whose surface is covered with tin species which are most likely in ionic form. Ru–Sn alloy particles do not appear to make a significant contribution to the catalytic activity.

Rate constants for intramolecular electron-transfer reactions of ruthenium-modified histidine mutants of cytochrome b2

The cytochrome b2 core derived from flavocytochrome b2 has been expressed in Escherichia coli and four mutants Lys-56→His, Lys-51→His, Asn-42→His and Pro-41→His have been generated by site-directed mutagenesis. Ruthenium modification of the first three mutants with [Ru(NH3)5(H2O)]2+ led to the formation of singly modified His-56[Ru(NH3)5], His-51 [Ru(NH3)5] and His-42[Ru(NH3)5] derivatives in 30–45% yield. However no modification was observed with Pro41His. Moreover no evidence was obtained for the formation of His-19[Ru(NH3)5], where His-19 is the unco-ordinated histidine present in wild-type and mutant cytochrome b2 forms. Characterisation of the singly modified products by inductively coupled plasma analyses indicates an Fe : Ru ratio of 1 : 1 for all three derivatives. The NMR spectra of the Ru-modified proteins reveal specific broadening by the paramagnetic RuIII of the characteristically sharp CIµH and CδH resonances assigned to His-56, His-51 and His-42, while the CIµH resonance due to His-19 is unaffected. Whereas the titration of unmodified His-56, His-51, His-42 and His-41 residues by 1H NMR spectroscopy gave pKa 6.4, 6.2, 6.5 and 6.4 respectively, His-19 did not similarly titrate in the pH 4.8–10.0 range, which is attributed to hydrogen bonding to a nearby residue. Using pulse radiolysis to generate the methyl viologen radical, MV˙+, the metastable iron(II)ruthenium(III) form of the protein was obtained. Rate constants for intramolecular electron transfer from FeII to RuIII were determined; 3.5 (His-56), 2.8 (His-51) and 78 s–1(His-42) at I= 0.100 M. Edge-to-edge distances, from the nearest point on one or other of the axial haem ligands to the nearest point on the imidazole ring, are 10.8 (His-56), 9.8 (His-51) and 8.5 A(His-42), and the driving force is close to 145 mV. Using the Beratan–Onuchic approach the most favourable pathways for electron transfer have been identified. For His-42 a direct through-bond pathway via axial His-43 to the haem Fe is indicated. In the case of the His-56 and His-51 derivatives, pathways that include through-space interactions appear to be dominant.

Transmission electron microscopy of stearic acid Langmuir-Blodgett films with incorporated ruthenium(II) tris(2,2′-bipyridyl) complex

Monolayer Langmuir-Blodgett (LB) films of stearic acid and Ru(bpy) 3(ClO 4) 2 (bpy is 2,2′-bipyridyl), Ru(tmbpy) 3(ClO 4) 2 (tmbpy is 4,4′,6,6′-tetramethyl-2,2′-bipyridyl) of varying ratios and of an amphiphilic Ru(II) complex have been produced. Comparison of pressure-area isotherms for pure stearic acid with the mixed films of stearic acid with metal complexes indicates that the molecular area is determined only by the fatty acid. The absence of any contribution of the metal complex to the molecular area for the mixed film suggests that the metal complex may reside beneath the stearic acid film (ion paired with the hydrophilic head group). Transmission electron microscopy and the cyclic voltammogram for the LB films of varying concentration indicate the presence of the Ru(II) complex in mixed LB films of different molar ratios of stearic acid and Ru(bpy) 3(ClO 4) 2 and in a pure amphiphilic Ru(II) complex film. The atomic force microscopy images, on the contrary, support the close packing of the stearic acid in the mixed films implying that the metal complex does not disturb the stearic acid packing.

Pulse radiolysis and related studies on the Ru-modified his 16 derivative of Anabaena variabilis [2Fe-2S] ferredoxin

The preparation and characterisation of a Ru-modified derivative of the [2Fe-2S] ferredoxin FdI component of A. variabilis by attachment of Ru(NH 3) 5 to a surface histidine has been carried out. Metal analyses by ICP gave an Fe Ru ratio of 1.97:1. From NMR the attachment is confirmed as a modification at His-16 and not His-92. No Ru-modification of the [2Fe-2S] FdI component of spinach, which has His-92 but no His-16, was observed. Histidine p K a values have been determined and anomalously low values for A. variabilis (5.3) and spinach (< 5.0) His-92 residues are noted, whereas His-16 gives a p K a of 6.95. Pulse radiolysis techniques with e aq − as reductant have been used to generate the metastable Fe(II)Fe(III)Ru(III) state from Fe(III) 2Ru(III), k = 8.8 · 10 10 M − s −1. Intermolecular, k inter = 4.3 · 10 6 M −1 s −1 at approx. 19°C, but no intramolecular electron-transfer (ET) Fe(II)Fe(III) to Ru(III) contribution was observed with Fe(III) 2Ru(III) in the range 7–30 μM. The driving force for ET is approx. 500 mV, and the edge to edge distance from the C γ of His-16 to the nearest cysteinyl S-atom attached to the Fe 2S 2 cluster is 16.1 Å. Using the Beratan-Onuchic pathway approach, the most favourable ET intramolecular route consists of 20 covalent and 3 Hbonds, with a total distance from the S of Cys-49 to the C γ of His-16 of 37.1 Å. We note that the reduced Fe is on the remote side of the [2Fe-2S] cluster from the site of Ru-attachment.

Refractory inclusions from the Leoville, Efremovka, and Vigarano c3v chondrites: Major element differences between types A and B, and extraordinary refractory siderophile element compositions

We have measured the bulk major and trace element compositions often CAIs from Leoville, Efremovka, and Vigarano, members of the reduced subgroup of C3V chondrites, by INAA. Like CAIs from the reduced subgroup studied previously and unlike CAIs from Allende, a member of the oxidized subgroup, nine of the ten CAIs studied here possess only small amounts of secondary phases and, hence, preserve their pre-alteration bulk major element compositions. Using those compositions and model pre-alteration compositions of Allende CAIs, we cannot distinguish Type B1s clearly from B2s, nor some CTAs from FTAs. All Type As and most Type Bs have superchondritic CaO Al 2O 3 ratios, suggesting that their precursors condensed from a solar gas after ~20% of the Al was removed by high-temperature, Al-rich phases. Type Bs possess higher concentrations of MgO and SiO 2 than do Type As because the precursor phases of Type Bs reacted with the cooling nebular gas to form fassaite, while those of Type As did not. Eight of the ten CAIs have unusual or unique refractory trace element characteristics compared to those seen in Allende inclusions. Vig1, L2, Ef1, and Ef2 have remarkably high concentrations of Re and Os (~57–145 × Cl) because they sampled 4–9 times more hcp condensate metal alloy than did most Allende inclusions. Vig1, L2, Ef1, Ef2, L1, and Vig2 have unusually large Os Ru ratios (up to 6.9 × Cl) because the removal temperatures of their hcp alloy precursors were unusually high (up to ~ 1655 K at 10 −3atm). L2 and L4 have low Zr Hf ratios (~0.4 × Cl); L1 and Ef2, low V/Yb ratios (~0.25 × Cl); Ef2, high Th La (~1.6 × Cl), and Sr Yb (~-2.4 × Cl) ratios; and ED, high Hf Lu (~2.6 × Cl), Sc Lu (~3.1 × Cl), and Zr Lu (~2.8 × Cl) ratios. Most of these fractionations are explained by non-representative nebular sampling of one or more of hibonite, zirconium oxide, perovskite, and melilite, which may be condensates or evaporation residues. Of twenty-five inclusions from the reduced subgroup now studied in this laboratory, seventeen have at least one pair of refractory trace elements which are more fractionated relative to one another compared to Cl chondrites than are the same elements in Allende CAIs, indicating that the host phases of these elements were not as thoroughly mixed together in the nebular region where CAIs of the reduced subgroup accreted as where those in Allende did. Parts of the nebula sampled by C3V chondrites of the reduced subgroup were not well sampled by Allende, and vice versa. Like most coarse-grained inclusions from the reduced subgroup studied previously, most of those analyzed here have lower concentrations of Na, Au, Fe, Zn, and Mn than their Allende counterparts, consistent with the idea that they experienced secondary alteration at a higher temperature or for a shorter time than did Allende inclusions.

Preparation and intramolecular electron-transfer rate constant for the ruthenium-modified selenium-substituted [4Fe–4Se] high-potential protein from Chromatium vinosum and related studies

The Se-substituted [4Fe–4Se] form of the high-potential iron–sulfur protein from Chromatium vinosum(Mr≈9500, 85 amino acids) has been prepared and Ru-modified (68% yield) at the single histidine residue His 42. The purified product gives and Fe: Ru ratio close to 4:1 consistent with a single stoichiometric modification. The His 42 of the Ru-modified protein no longer reacts with O(CO2Et)2 and the sharp 1H NMR C2H resonance for His 42 at δ 8.38 is no longer present due to paramagnetic line broadening by the attached RuIII. The His 42 is bonded via Cys 43 to the active site, with an edge-to-edge distance close to 7.9 Å. Pulse-radiolysis reduction of the fully oxidised Fe4Se43+–RuIII protein with eaq– gives the metastable product Fe4Se3+–RuII. A second slower stage, corresponding to conversion of the Fe4Se43+–RuII to Fe4Se42+–RuIII is made up of intramolecular (1.30 s–1) and intermolecular (2.65 × 105 M–1 s–1) electron-transfer steps. The kintra step is of interest alongside the earlier value (18 s–1) for native [4Fe–4S] protein. The smaller reduction potential for the Fe4Se43+/2+(285 mV) as compared to Fe4S43+/2+(350 mV) couple is believed to be the major contributing factor to the slower intramolecular electron-transfer process. The Beratan–Onuchic pathways program has been used and indicates through-bond electron transfer from the Ru at His 42 to the cluster as the most favourable route. The rate constant at 25 °C (M–1 s–1) for the [Fe(CN)6]3– oxidation of the Fe4Se42+ protein has also been determined (4.5 × 103 M–1 s–1), and is less than that for native Fe4S42+ protein (2.0 × 103 M–1 s–1) at pH 7.0, /= 0.100 M (NaCl).

Use of CO as probe molecule for characterization of mixed Ru-Ni sulphide phases supported over alumina

Infrared spectroscopy was used to characterize mixed ruthenium-nickel sulphides prepared by step-wise impregnation over alumina and further sulphidation. The hydrogenation of biphenyl was compared over samples containing different amounts of nickel and ruthenium and a large increase was observed for a catalyst with an atomic Ni /(Ni + Ru) ratio near 0.4. Infrared spectra of adsorbed CO indicate that the increase in catalytic activity is ascribed to the presence of a very large number of Ru-Ni sites.

7th international symposium on heterogeneous catalysis

Mono- and bimetallic Pt-, Ru- and Pt-Ru catalysts with various Pt to Ru ratio for process of selective catalytic oxidation of methane to synthesis-gas at short contact time are developed. Precious metals were supported on alumina which was modified by cerium to enhance dispersion over carrier. Pt-Ru/2%Ce/(θ + α)-Al2O3, reduced by H2 at 1023 K, presents a mixture of nano-particles of Pt0 (7.5–15.0 nm), Ru0 (5.0–30.0 nm), its alloy in the mixed catalysts and intermetallic compounds of Pt13Ru27 (3.0 < d < 18.0 nm). Semi-transparent Ce6O11 particles (3.0–10.0 nm) and CeAlO3 (3.0–5.0 nm) are present on the surface of Al2O3. Such phase composition provides for optimum selective oxidation of CH4 to synthesis-gas.

Distribution of platinum-group elements and gold within the Vourinos chromitite ores, Greece

A geochemical study of chromite ores and host rocks of the Vourinos ophiolite complex leads to the distinction of three geotectonic units, corresponding to the North Vourinos, South Vourinos, and Kissavos geographic areas. This is based on the range and variability of Cr/(Cr + Al), (Pt + Pd)/(Os + Ir + Ru), and Pd/Ir ratios and the relative abundance of compatible platinum-group elements (PGE, Os, Ir, and Ru) within the three blocks. The platinum-group element and gold contents are low. Average concentrations (in ppb) are Os = 23, Ir = 19, Ru = 58, Rh = 12, Pt = 5.9, Pd = 3.3, and Au = 2.7. However, a few PGE-enriched chromite samples (up to 3,030 ppb) were also found. The South Vourinos area differs from North Vourinos as far as its remarkably constant chemical composition (major and trace elements), its lower Pd/Ir and (Pt + Pd)/(Os + Ir + Ru) ratios, its greater abundance of the (Os + Ir) sum relative to Ru, and its absence of PGE-enriched chromite ores.There is no significant correlation between chromite composition and PGE data throughout the complex. The only exception is the Kissavos area, where the PGE content is higher and the Pd/Ir ratio lower in Cr-rich ores than in Al-rich ones, showing a strong negative correlation between the Cr/(Cr + Al) and Pd/Ir ratios (r = -0.8).The low PGE content in the majority of the Vourinos chromite ores may reflect a lack of sulfur saturation during an early stage of their crystallization, whereas PGE enrichment may suggest a mixing of primitive and partially fractionated magmas. Assuming that the Vourinos complex formed in a suprasubduction zone environment, it seems likely that South Vourinos chromitites formed directly above the spreading center, whereas the North Vourinos chromitites formed at a distance from the spreading center. In addition, the strong depletion of PGE in the Kissavos Cr-rich ores, particularly Os, Ir, and Ru, may suggest that these chromitites were crystallized from magmas derived by partial melting of an already-depleted mantle source.The geochemical trend throughout the Vourinos complex seems to provide valuable confirmation of a stratigraphic orientation in the mantle sequence of the complex.

Studies on ruthenium catalysts Part 2: Oxides of the first row transition elements as modifiers of a Ru/SiO 2 catalyst

The addition of the oxides of Ca, Sc and Ti to a Ru/SiO 2 catalyst increases its activity for n-butane hydrogenolysis to an extent which depends on the type of pretreatment applied; product selectivities and turnover frequencies are essentially unchanged. Adding the oxides of V, Cr and Mn, which are partially reduced under reaction conditions, leads to decreases in rate which are much more marked after high-temperature reduction (HTR; 758 K) than after low-temperature reduction (LTR; 433 K), but only modest changes in product selectivities are seen; the effectiveness in deactivation decreases with increasing atomic number. Activation energies decrease progressively with increasing modifier concentration. Numerous variables in catalyst composition, preparation and pretreatment affect the extent of interaction between modifier and metal. Failure to detect an SMSI-like effect with TiO 2 is attributed to the use of a low Ti:Ru ratio (0.25). The addition of V oxide can lead to either selective or non-selective deactivation, significant changes in product selectivities occurring only in the former case. The non-selective mode was the main one in the present work.

Chemical compositions of siderophile element-rich opaque assemblages in an Allende inclusion

Ten opaque assemblages, or Fremdlinge, weighing 0.17–19 μg, from an Allende Type B, Ca-, Al-rich, coarse-grained inclusion were analyzed by INAA for Ca, Na, Mn, Sc, Ta, Ti, V, Cr, Fe, Ni, Co, W, Re, Os, Ir, Mo, Ru, Pt, Rh, Au, As, Sb and Se. Refractory siderophiles are usually enriched by factors of 10 3–10 4 relative to Cl chondrites, but not uniformly. From sample to sample, C1 chondrite-normalized Re Os , Ir Pt , Os Ru and Pt Rh ratios vary from 0.81–1.03, 0.70–>2.25, 0.67–3.32 and 0.45–1.43, respectively. Attempts to model the abundances of refractory siderophiles by condensation from the solar nebula into a single phase, assuming ideal solution, fail to match the observed combination of subchondritic Re Os and Ir Pt ratios, even allowing for fractionation of the highest-temperature condensates. A different model, in which all metals whose high-temperature crystal structures are hcp condense into one alloy, bcc into another and fcc into a third, is capable of matching virtually all refractory siderophile fractionations in these Fremdlinge. In this model, all isostructural metals are assumed to form ideal solutions with one another and metals of different structure are assumed to be insoluble in one another. After fractionation of high-temperature hcp and fcc alloys, individual proto-Fremdlinge formed by mixing of high- and low-temperature varieties of each of the three alloys, either in the nebula before and during CAI accretion, or during later partial melting of the silicate, oxide and metal components of CAIs.

Studies on ruthenium-tin boride catalysts II. Hydrogenation of fatty acid esters to fatty alcohols

Hydrogenation of methyl hexadecanoate, methyl-9-octadecenoate, and dimethyl succinate was studied as a function of catalyst composition as well as various reaction parameters. It was found that an atomic ratio of Ru to Sn of 1 : 1 gave maximum activity and selectivity for alcohol formation from methyl hexadecanoate and dimethyl succinate. Methyl-9-octadecenoate gave the best yield of 9-octadecen-1-ol (the unsaturated alcohol) at an atomic ratio of Ru to Sn of 1 : 2. The hydrogenation of dimethyl succinate was found to depend delicately on the temperature of the reaction, with the diol yields reaching a maximum at 200°C. Based on the characterization of the catalysts and the catalytic activity data, the nature of the active species responsible for the selective hydrogenation and the mode of activation of the ester are discussed.