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Showing papers on "Molybdenum published in 1996"


Journal ArticleDOI
TL;DR: In this article, Molybdenum adsorption behavior was investigated on various crystalline and x-ray amorphous Al and Fe oxide minerals, clay minerals, CaC@, and arid-zone calcareous and non-calcareous ssoils.
Abstract: Molybdenum adsorption behavior was investigated on various crystalline and x-ray amorphous Al and Fe oxide minerals, clay minerals, CaC@, and arid-zone calcareous and noncalcareou s ssoils. Molybdenum adsorption on botb Al and Fe oxides exhibited a maximum at low pH extending to about pH 4 to 5. Above pH 5 adsorption decreased rapidly, with little adsorptio noccurring above pH 8. Molybdenum adsorption was higher for the oxide minerals having higher specific surface area and lower crystallinity. Molybdenum adsorption on the clay minerals exhibited a peak near pH 3 and then decreased rapidly with increasing pH until adsorption was virtually zero near pH 7. The magnitude of MO adsorption on clays increased in the order: kaolinite < illite < montmorillonite. Shifts in point of zero charge were observed on Al and Fe oxides and kaolinite following MO adsorption, indicating an inner-sphere adsorption mechanism for MO on these surfaces. Molybdenum adsorption behavior on three arid-zone noncalcareous soils resembled that on clays, exhibiting a peak near pH 3 to 4 and decreasing with increasing pH up to pH 7. This behavior is expected since the oxide content of these soils is low. Molybdenum adsorption on calcite and tw ocalcareous arid-zone soils was low, indicating that CaCOJ is not a significant sink for MO in soils.

295 citations


Journal ArticleDOI
TL;DR: In this paper, a simple sonochemical synthesis of nanostructured molybdenum carbide from the ultrasonic irradiation of hexacarbonyl was presented.
Abstract: The preparation of nanophase materials has been the focus of intense study in materials science1,2 A variety of chemical and physical preparative methods have been applied to produce materials with nanometer structure, including metal evaporation,3 decomposition of organometallic compounds,4 and reduction of metal salts5,6 Sonochemical decomposition of transition metal carbonyl compounds has also been proven to be a useful technique to generate nanophase transition metals7,8 Recently, molybdenum and tungsten carbides have been examined as heterogeneous catalysts because their activity is often similar to that of the platinum group metals9-11 For catalytic applications, high surface area materials are generally needed; the preparation of interstitial carbides of molybdenum and tungsten with high surface areas, however, is very difficult We present here a simple sonochemical synthesis of nanostructured molybdenum carbide from the ultrasonic irradiation of molybdenum hexacarbonyl In addition, we have examined the catalytic activity and selectivity of these materials for the dehydrogenation of alkanes The chemical effects of ultrasound arise from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid12,13 The collapse of bubbles generates localized hot spots through adiabatic compression or shock wave formation within the gas of the collapsing bubble This local heating produces a wide range of high-energy chemistry The conditions formed in these hot spots have been experimentally determined, with transient temperatures of ∼5000 K, pressures of∼1800 atm, and cooling rates in excess of 1010 K/s14,15 Using these extreme conditions, we have explored a variety of applications of ultrasound to materials chemistry16 A slurry of molybdenum hexacarbonyl (1 g in 50 mL of hexadecane) was sonicated with a high-intensity ultrasonic horn (Sonic and Materials, model VC-600, 05 in Ti horn, 20 kHz, 100 W cm-2) at 90 °C for 3 h under argon to yield a black powder The powder was filtered inside an inert atmosphere box (Vacuum Atmospheres, <1 ppm O2), washed several times with purified, degassed pentane, and heated at 100 °C under vacuum X-ray powder diffraction17 (XRD) showed extremely broad peaks centered at a d spacing of 24, 15, and 13 A (Figure 1), which did not match body-centered cubic (bcc) lines of molybdenum metal After the heat treatment at 450 °C under helium flow for 12 h, sharper peaks in the XRD were observed at d spacing values of 239, 149, and 127 A which accurately correspond to face-centered cubic (fcc) molybdenum carbide, Mo2C (Figure 1) The synthesis of Mo2C is particularly prone to substantial oxygen contamination9 Even after heat treatment at 450 °C under helium, oxygen was still present at about 4 wt % Since the presence of oxygen could poison the catalytic activity, it was removed prior to catalytic studies by heating in a flowing 1:1 CH4/H2 mixture at 300 °C for 1 h, then at 400 °C for 1 h, and finally at 500 °C for 48 h The flow rate of the CH4/H2 mixture was 275 cm3 (STP)/min After this carburization, excess carbon, hydrogen, and oxygen had been largely removed The elemental analysis results showed the sample was very pure (theoretical for Mo2C, 9411 % Mo, 589 % C; exptl, 9386 % Mo, 568 % C, 008 % H, 006 % N), which corresponds to a stoichiometry of Mo2C097 The XRD was essentially unchanged by carburization

256 citations


Journal ArticleDOI
TL;DR: The periplasmic dimethyl sulfoxide reductase (DMSOR) from the photosynthetic purple bacterium Rhodobacter capsulatus functions as the terminal electron acceptor in its respiratory chain, which catalyzes the reduction of highly oxidized substrates like dim methyl sulfoxide toDimethyl sulfide.

242 citations


Journal ArticleDOI
TL;DR: In this paper, the philosophy of the development and the resulting properties of a new austenitic stainless steel was presented, which contains 15-18% chromium, 3-6% molybdenum, 10-12% manganese, and 0.9% nitrogen.
Abstract: The paper presents the philosophy of the development and the resulting properties of a new austenitic stainless steel. The steel contains 15-18% chromium, 3-6% molybdenum, 10-12% manganese, and about 0.9% nitrogen. The most important feature of this steel is the complete absence of nickel as alloying element. The austenitic microstructure is obtained exclusively by adding nitrogen. Besides being nickel free, the steel is further characterized by an excellent corrosion resistance, the absence of ferromagnetism, and outstanding mechanical properties. The unique combination of these properties makes this steel most interesting for its use in items which are in direct contact with the human body. By using these new steels, nickel allergy can be prevented.

231 citations


Journal ArticleDOI
TL;DR: The crystal structure of the xanthine oxidase-related molybdenum-iron protein aldehyde oxido-reductase from the sulfate reducing anaerobic Gram-negative bacterium Desulfovibrio gigas (Mop) was analyzed in its desulfo-, sulfo-, oxidized, reduced, and alcohol-bound forms at 1.8-A resolution as mentioned in this paper.
Abstract: The crystal structure of the xanthine oxidase-related molybdenum-iron protein aldehyde oxido-reductase from the sulfate reducing anaerobic Gram-negative bacterium Desulfovibrio gigas (Mop) was analyzed in its desulfo-, sulfo-, oxidized, reduced, and alcohol-bound forms at 1.8-A resolution. In the sulfo-form the molybdenum molybdopterin cytosine dinucleotide cofactor has a dithiolene-bound fac-[Mo, = O, = S, ---(OH2)] substructure. Bound inhibitory isopropanol in the inner compartment of the substrate binding tunnel is a model for the Michaelis complex of the reaction with aldehydes (H-C = O,-R). The reaction is proposed to proceed by transfer of the molybdenum-bound water molecule as OH- after proton transfer to Glu-869 to the carbonyl carbon of the substrate in concert with hydride transfer to the sulfido group to generate [MoIV, = O, -SH, ---(O-C = O, -R)). Dissociation of the carboxylic acid product may be facilitated by transient binding of Glu-869 to the molybdenum. The metal-bound water is replenished from a chain of internal water molecules. A second alcohol binding site in the spacious outer compartment may cause the strong substrate inhibition observed. This compartment is the putative binding site of large inhibitors of xanthine oxidase.

212 citations


Journal ArticleDOI
TL;DR: In this article, the mass-transport limiting species were identified for different operating conditions and electrolyte compositions in order to study the rate-limiting steps of induced codeposition.
Abstract: The electrodeposition of nickel-molybdenum alloys was studied on rotating cylinder electrodes. The current density, electrode rotation rate, electrolyte temperature, and species concentrations were shown to influence alloy composition. The mass-transport limiting species were identified for different operating conditions and electrolyte compositions in order to study the rate-limiting steps of induced codeposition. If the concentration of nickel in the electrolyte was much larger than that of molybdate the molybdenum content in the alloy increased with rotation rate. On the other hand, if the concentration of molybdate in the electrolyte was larger than that of nickel the alloy composition was found to be independent of rotation rate. These results were applied to the deposition of compositionally modulated Ni-Mo alloys exhibiting larger periodic variations in Mo concentration than hitherto reported.

208 citations


Journal ArticleDOI
TL;DR: In this paper, the alignment of energy bands in polycrystalline thin films starting with the molybdenum coated soda lime glass was analyzed with photoelectron spectroscopy techniques.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the catalytic performance of molybdenum nitride (Mo2N), supported on alumina (Mo 2 C Al 2 O 3 ) was compared with commercial sulfided MoS 2Al 2O 3 > and NiMoS Al 2O3 > for hydrotreating coal-derived gas oil and residuum at 633 K (360°C) and 13.7 MPa (2000 psig).
Abstract: Unsupported molybdenum nitride (Mo2N) and molybdenum carbide supported on alumina ( Mo 2 C Al 2 O 3 ) were compared against commercial sulfided MoS 2 Al 2 O 3 > and NiMoS Al 2 O 3 for hydrotreating coal-derived gas oil and residuum at 633 K (360°C) and 13.7 MPa (2000 psig). When the catalytic rates were compared on the basis of active sites measured by chemisorption, the nitrides and carbides were estimated to have activities as much as five times that of NiMoS Al 2 O 3 and MoS 2 Al 2 O 3 . The comparison was based on sites titrated by CO on the carbide and nitride and by O2 on the sulfided catalysts. The gas oil and resid product quality from the carbide and nitride catalysts was significantly better than the thermal blank, indicating that the materials were active under practical hydrotreating conditions. X-ray photoelectron spectroscopy analysis after reaction of the Mo2N and Mo 2 C Al 2 O 3 catalysts indicated that surface sulfiding was not extensive.

158 citations


Journal ArticleDOI
TL;DR: In this article, a direct bandgap of 1.78 eV was found for the annealed films of MoS 2 with the van der Waals planes parallel to the substrate.

138 citations


Journal ArticleDOI
TL;DR: In this paper, annealing at 500°C in air, the layers consist of rhombic molybdenum trioxide with a (010) texture, and electrical conductivity measurements with different test gases show that MoO3 layers are suitable for NH3 detection at operating temperatures between 400 and 450°C.
Abstract: Thin films of MoO3 for gas sensing applications have been deposited by reactive sputtering using a metallic molybdenum target. After annealing at 500°C in air, the layers consist of rhombic molybdenum trioxide with a (010) texture. The morphology of the layers considerably depends on the film thickness. Electrical conductivity measurements with different test gases show that MoO3 layers are suitable for NH3 detection at operating temperatures between 400 and 450°C.

130 citations


Journal ArticleDOI
TL;DR: In this paper, a combination of tungstic acid, molybdenum and vanadium pentoxide with the surfactant template dodecyltrimethylammonium bromide (DTABr) yielded one compound with a Keggin type structure, [C12H25N(CH3)3]6(H2W12O40)·xH2O, and two new layered compounds.
Abstract: Hydrothermal reaction of tungstic acid, molybdic acid, and vanadium pentoxide with the surfactant template dodecyltrimethylammonium bromide (DTABr) yielded one compound with a Keggin type structure, [C12H25N(CH3)3]6(H2W12O40)·xH2O, and two new layered compounds, [C12H25N(CH3)3]0.5(MoO3.25) and [C12H25N(CH3)3]2/3V2O5.33·H2O. The tungsten salt produced needlelike crystals of a hexagonal shape while the molybdenum and vanadium salts formed layered structures. FTIR analysis of the tungsten salt was consistent with materials containing Keggin anions. The X-ray powder diffraction data of this material were indexed to a monoclinic cell with a = 50.56(4) A, b = 54.41(4) A, c = 13.12(1) A, and β = 99.21°. The observed reflections are consistent with space group C2/m. Diffraction data obtained from the molybdenum salt showed a between layer d spacing of ca. 22 A. The vanadium salt was indexed to a triclinic cell with a = 9.813(3) A, b = 11.512(3) A, c = 21.725(5) A, α = 95.30(1)°, β = 93.82(6)°, and γ = 101.12(8)°,...

Journal ArticleDOI
TL;DR: In this paper, the extraction of molybdenum(VI) and vanadium(IV) from sulfuric acid solution in the presence of various other metals, such as aluminum(III), cobalt(H), nickel(II), and iron(III).

Journal ArticleDOI
TL;DR: In this article, the influence of a second metal oxide (tungsten oxide, molybdenum oxide, nickel oxide, cobalt oxide) upon a V2O5/Al2O3 catalyst has been investigated by a combined Raman and IR study under dehydrated conditions.
Abstract: The influence of a second metal oxide (tungsten oxide, molybdenum oxide, nickel oxide, cobalt oxide) upon a V2O5/Al2O3 catalyst has been investigated by a combined Raman and IR study under dehydrated conditions. The presence of tungsten or molybdenum oxide was found to increase the concentration of polymerized surface vanadium oxide species, and this reflects the higher surface coverages of the metal oxides on the alumina support. This is probably caused by competition between vanadium and molybdenum oxide (or vanadium and tungsten oxide) species for reaction with the alumina hydroxy groups, since the IR spectra showed that on addition of these metal oxides the same type of alumina hydroxy groups are consumed. The presence of nickel or cobalt oxide on alumina increases the concentration of polymerized vanadium oxide species dramatically, which indicates that the presence of these oxides is also experienced by the surface vanadium oxide. However, the hydroxy groups are not affected as they are for the molybdenum and tungsten oxide systems.

Journal ArticleDOI
TL;DR: A notable development in mild (≤ 200°C) hydrothermal synthesis in the past few years has been the extension of the synthesis technique from zeolites and metal phosphates to binary and ternary transition metal oxides as mentioned in this paper.
Abstract: A notable development in mild (≤ 200°C) hydrothermal synthesis in the past few years has been the extension of the synthesis technique from zeolites and metal phosphates to binary and ternary transition metal oxides. This low-temperature technique is critical to the formation of metastable phases not obtainable using traditional high-temperature methods. New phases, as well as known materials, of the oxides of tungsten, molybdenum, vanadium and manganese have been formed, often in highly crystalline form. One enhancement of the technique is microwave heating, which appears to accelerate nucleation, producing very uniform particles in a few hours.

Journal ArticleDOI
TL;DR: In this paper, surface science models of silica and alumina-supported CoMoS catalysts have been made by impregnating thin SiO2 and Al2O3 films with a solution of nitrilotriacetic acid (NTA) complexes of cobalt and molybdenum.
Abstract: Surface science models of silica- and alumina-supported CoMoS catalysts have been made by impregnating thin SiO2 and Al2O3 films with a solution of nitrilotriacetic acid (NTA) complexes of cobalt and molybdenum. XPS spectra indicate that the order in which cobalt and molybdenum transfer to the sulfided state is reversed with respect to oxidic Co and Mo systems prepared by conventional methods, implying that NTA complexation retards the sulfidation of cobalt to temperatures where MoS2 is already formed. Catalytic tests show that the CoMoS model catalysts exhibit activities for thiophene desulfurization and product distributions similar to those of their high surface area counterparts.

Journal ArticleDOI
TL;DR: The data suggest that the major features in the absorption spectrum of the native molybdenum domain arise from the binding of Cys-207 to the molyBdenum and indicate that this residue functions as a ligand of the metal.

Journal ArticleDOI
TL;DR: In this paper, the XPS spectra of bulk MoO2 and MoO3 are reported and the presence of multilayers of MoO 3 covering bulk Mo O2 is revealed.
Abstract: The XPS spectra of bulk MoO2 and MoO3 are reported. Commercial MoO2 reveals the presence of multilayers of MoO3 covering bulk MoO2. In situ reduction of bulk MoO3 by H2 at temperatures equal to 623 K and less than 673 K reduces the superficial layer(s) to mainly MoO2. Such phase is characterised by a certain density of states in terms of the free 4d, 5s electrons localised mainly on the Mo atoms and observed in the valence band energy region at the Fermi-level in the XP spectrum of this system. Catalytic reactions on the MoO2 phase of 2-methylpentane at atmospheric pressure using a mixture of the hydrocarbon (5 Torr) with hydrogen (755 Torr) yield 3-methylpentane andn-hexane as the main products in roughly equal amounts. These results are interpreted in terms of dual sites on the MoO2 surface.

Journal ArticleDOI
TL;DR: In this article, a comparative analysis of the surface reaction of ethylene with clean Mo(110) and carbide-modified Mo (110) has been carried out using high-resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD).
Abstract: A comparative investigation of the surface reaction of ethylene with clean Mo(110) and carbide-modified Mo(110) has been carried out using high-resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). As typically observed for early transition metals, the clean Mo(110) surface interacts very strongly with ethylene, as indicated by the decomposition of ethylene to produce C2H2 surface species at temperatures as low as 80 K. The surface acetylene species further decompose to atomic carbon and hydrogen at higher temperatures. The strong reactivity of the Mo(110) surface can be modified by the formation of carbide. The surface reactivity is modified in such a way that the reaction mechanism of ethylene on C/Mo(110) is very similar to those typically observed on Pt-group metal surfaces: At 80 K, ethylene molecules bond to the C/Mo(110) surface in the di-σ bonded configuration; a new surface reaction intermediate, which can be best described as ethylidyne species, is d...

Journal ArticleDOI
TL;DR: It is concluded that cysteine 207 is a ligand of molybdenum in wild-type human sulfite oxidase, and that, in the mutant, the Mo is ligated to an extra oxo group rather than the hydroxyl of the substituent serine 207.
Abstract: X-ray absorption spectroscopy at the molybdenum and sulfur K-edges has been used to probe the active site of wild-type and cysteine 207 → serine mutant human sulfite oxidases. We compare the active site structures in the Mo(VI) oxidation states: the wild-type enzyme possesses two MoO ligands at 1.71 A and three Mo−S ligands at 2.41 A. The mutant molybdenum site is a novel trioxo site with MoO bond lengths of 1.74 A, with two Mo−S ligands at 2.47 A. We conclude that cysteine 207 is a ligand of molybdenum in wild-type human sulfite oxidase, and that, in the mutant, the Mo is ligated to an extra oxo group rather than the hydroxyl of the substituent serine 207.

Patent
04 Nov 1996
TL;DR: In this article, a capacitor is defined as a capacitor with an anode including a metal selected from tantalum, aluminum, niobium, zirconium, and titanium, spaced from the coating, and an electrolyte in contact with the coating and the anode.
Abstract: A capacitor includes a cathode having a coating including an oxide of one of cobalt, molybdenum, and tungsten, a nitride of a metal selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, and tungsten, a carbide of a metal selected from the group consisting of vanadium, niobium, molybdenum, and tungsten, an intercalation carbon cathode, or an electrically conducting polymer selected from polyacetylene, polypyrrole, poly-p-phenylene, polythiophene, poly-3-phenylthiophene, and poly-3-(4-fluorophenyl)-thiophene, an anode including a metal selected from tantalum, aluminum, niobium, zirconium, and titanium, spaced from the coating, and an electrolyte in contact with the coating and the anode.

Journal ArticleDOI
TL;DR: A preconcentration procedure, using a short column filled with Amberlite XAD-8, is proposed for the Spectrophotometric determination of traces of molybdenum in steel as mentioned in this paper.



Journal ArticleDOI
TL;DR: In this article, X-ray absorption spectroscopy at the molybdenum K-edge has been used to probe the coordination of Rhodobacter sphaeroides dimethyl sulfoxide reductase.
Abstract: X-ray absorption spectroscopy at the molybdenum K-edge has been used to probe the molybdenum coordination of Rhodobacter sphaeroides dimethyl sulfoxide reductase. The molybdenum site of the oxidized protein possesses a novel Mo(VI) mono-oxo site (MoO at 1.68 A) with additional coordination by approximately four thiolate ligands at 2.44 A and probably one oxygen or nitrogen at 1.92 A. The reduced Mo(IV) form of the enzyme is a des-oxomolybdenum with 3−4 thiolates at 2.33 A and two different Mo−O/N ligands at 2.16 A and 1.92 A. Similarly, the stable Mo(V) glycerol-inhibited species is found to be a des-oxomolybdenum with approximately four thiolate ligands at 2.40 A and (probably) two similarly coordinated oxygen or nitrogen ligands at 1.96 A.

Patent
09 Dec 1996
TL;DR: In this paper, the authors present a process to produce a high surface area niobium oxynitride, tantalum oxide, vanadium oxide, zirconium oxide, titanium oxide, or molybdenum oxide substrate for use as an electrical energy storage component.
Abstract: The present invention concerns a process to produce a high surface area niobium oxynitride, tantalum oxynitride, vanadium oxynitride, zirconium oxynitride, titanium oxynitride or molybdenum oxynitride coated substrate for use as an electrical energy storage component in a capacitor or a battery configuration. The process relates to: (a) coating one or both flat etched surfaces of a solid substrate, in the form of a thin sheet, with a solution or a slurry of a metal halide in a liquid volatile carrier to produce a thin surface film; (b) contacting the metal halide surface film-carrier coated substrate of step (a) with oxygen, air, or combinations thereof at a temperature to convert the metal halide to metal oxide, respectively, as a thin film and to remove the liquid volatile carrier; (c) repeating steps (a) and (b) to obtain a desired thickness; (d) heating the metal oxide film coated substrate of step (c) in oxygen, air or combinations thereof to convert at least about 95% of the metal chloride to metal oxide; (e) increasing the temperature of the metal oxide coated substrate to elevated temperatures; (f) contacting the oxide coated substrate produced in step (e) with a nitrogen source selected from excess flowing gaseous ammonia, a mixture of ammonia gas and hydrogen gas, or a mixture of hydrogen gas and nitrogen gas at elevated temperatures to convert about 95% or greater of the oxide coating to the corresponding metal oxynitride on the substrate, which metal oxynitride layer has a high surface area and is electrically conductive; and (g) cooling to ambient temperature and recovering the high surface area metal oxynitride coated substrate produced in step (f).

Journal ArticleDOI
TL;DR: A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al, to give a Mo(VI) species.
Abstract: The reaction mechanism of the molybdoenzyme xanthine oxidase has been further investigated by 13C and 17O ENDOR of molybdenum(V) species and by kinetic studies of exchange of oxygen isotopes. Three EPR signal-giving species were studied: (i) Very Rapid, a transient intermediate in substrate turnover, (ii) Inhibited, the product of an inhibitory side reaction with aldehyde substrates, and (iii) Alloxanthine, a species formed by reaction of reduced enzyme with the inhibitor, alloxanthine. The Very Rapid signal was developed either with [8-13C]xanthine or with 2-oxo-6-methylpurine using enzyme equilibrated with [17O]H2O. The Inhibited signal was developed with 2H13C2HO and the Alloxanthine signal by using [17O]H2O. Estimates of Mo-C distances were made, from the anisotropic components of the 13C-couplings, by corrected dipolar coupling calculations and by back-calculation from assumed possible structures. Estimated distances in the Inhibited and Very Rapid species were about 1.9 and less than 2.4 A, respectively. A Mo-C bond in the Inhibited species is very strongly suggested, presumably associated with side-on bonding to molybdenum of the carbonyl of the aldehyde substrate. For the Very Rapid species, a Mo-C bond is highly likely. Coupling from a strongly coupled 17O, not in the form of an oxo group, and no coupling from other oxygens was detected in the Very Rapid species. No coupled oxygens were detected in the Alloxanthine species. That the coupled oxygen of the Very Rapid species is the one that appears in the product uric acid molecule was confirmed by new kinetic data. It is concluded that this oxygen of the Very Rapid species does not, as frequently assumed, originate from the oxo group of the oxidized enzyme. A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al. [Coucouvanis, D., Toupadakis, A., Lane, J. D., Koo, S. M., Kim, C. G., Hadjikyriacou, A. (1991) J. Am. Chem. Soc. 113, 5271-5282]. It involves formal addition of the elements of the substrate (e.g., xanthine) across the Mo = S double bond, to give a Mo(VI) species. This is followed by attack of a "buried" water molecule (in the vicinity of molybdenum and perhaps a ligand of it) on the bound substrate carbon, to give an intermediate that on intramolecular one-electron oxidation gives the Very Rapid species. The latter, in keeping with the 13C, 17O, and 33S couplings, is presumed to have the 8-CO group of the uric acid product molecule bonded side-on to molybdenum, with the sulfido molybdenum ligand retained, as in the oxidized enzyme.

Journal ArticleDOI
TL;DR: In this paper, the effect of molybdenum on the electronic structure of the passive films formed on ferritic (Fe-Cr and Fe-Cr-Mo) stainless steels is examined by capacitance and photoelectrochemical measurements.
Abstract: The effect of molybdenum on the electronic structure of the passive films formed on ferritic (Fe-Cr and Fe-Cr-Mo) stainless steels is examined by capacitance and photoelectrochemical measurements. The capacitance study is supported by a mathematical analysis of the Schottky barrier developed at the semiconductor-electrolyte interface in the case of a semiconductor with multiple bulk electronic states in the bandgap. The numerical simulations, based on the more general Mott-Schottky relation proposed, are in good agreement with the experimental results. It can be concluded that the capacitance behavior of the passive films is related to the contributions of a shallow donor level very close to the conduction band and a deep donor level at about 0.4 eV below the conduction band. The addition of molybdenum decreases the donor density of the deep level. Photoeffects observed for subbandgap photon energies reveal that this deep donor level behaves like a trapping electronic state situated in the space-charge zone of the passive film. On the basis of the results obtained, the crystallographic factors determining the nature of the donor species are discussed.

Journal ArticleDOI
TL;DR: In this article, the molybdenum(II) chloride cluster Mo6Cl12 has been immobilized on 2% cross-linked poly(4-vinylpyridine) (PVP-Mo6Cl 12) by the axial ligation of two pendant pyridines of the polymer to the hexanuclear metal core.
Abstract: The molybdenum(II) chloride cluster Mo6Cl12 has been immobilized on 2% cross-linked poly(4-vinylpyridine) (PVP-Mo6Cl12) by the axial ligation of two pendant pyridines of the polymer to the hexanuclear metal core. Polymers with different cluster loadings exhibit the characteristic broad band emission of Mo6Cl12 at λmax = 765 ± 3 nm, and luminescence decays are composed of short- and long-lifetime components, which are consistent with the presence of cis- and trans-disubstituted cluster species, respectively. The lifetime of the cis form is too short to permit its bimolecular reaction with oxygen. However, the long-lifetime component is quenched efficiently by O2, and Stern−Volmer analyses of emission lifetimes yield quenching rate constants of (2−10) × 105 M-1 s-1 for cluster loadings in the range (3.5−0.3) × 10-3 g/g of PVP, respectively. The quenching rate constant increases to ∼50 × 105 M-1 s-1 for all polymers in MeOH regardless of cluster loading. In aqueous solutions (pH 3−6) intermediate quenching r...

Patent
01 Nov 1996
TL;DR: In this article, a mixture of molybdenum and diarylamine was proposed for use as a crankcase lubricant, which provided improved oxidation control and friction modifier performance.
Abstract: There is disclosed a lubricating oil composition which contains from about 100 to 450 parts per million of molybdenum from a molybdenum compound which is substantially free of active sulfur and about 750 to 5,000 parts per million of a secondary diarylamine. This combination of ingredients provides improved oxidation control and friction modifier performance to the lubricating oil. The composition is particularly suited for use as a crankcase lubricant.

Journal ArticleDOI
TL;DR: A series of six-coordinate compounds containing a chelating dithiolate coordinated to the [LMo(V)O](2+) unit (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) have been characterized by EPR spectroscopy as models for the molybdenum centers of pterin-containing molyBdenum enzymes.
Abstract: A series of six-coordinate compounds containing a chelating dithiolate coordinated to the [LMoVO]2+ unit (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) have been characterized by EPR spectroscopy as models for the molybdenum centers of pterin-containing molybdenum enzymes. The structure of LMoO(bdt) (1) (bdt = 1,2-benzenedithiolate) has been determined by X-ray crystallography; the space group is P21/n with a = 10.727(1) A, b = 14.673(2) A, c = 15.887(2) A, β = 100.317(4)° and Z = 4. Compound 1 exhibits distorted octahedral stereochemistry; the terminal oxo group and the sulfur atoms are mutually cis to one another. The MoO distance is 1.678(4) A, and the average Mo−S distance is 2.373(2) A. The EPR parameters for 1, determined from simulation of the frozen-solution spectrum, are g1 = 2.004, g2 = 1.972, g3 = 1.934 and A1(95,97Mo) = 50.0 × 10-4, A2 = 11.4 × 10-4, A3 = 49.7 × 10-4 cm-1. The EPR parameters for several LMoVO{S(CH2)xS} compounds (x = 2−4) with saturated chelate skeletons are similar to those ...