Showing papers on "Molybdenum published in 1969"
225 citations
TL;DR: In this paper, the structure determination of the cobalt molybdate on alumina catalyst has been studied and it is shown that the cobalo-molybdenum is distributed throughout the bulk of the alumina as CoAl 2 O 4, whereas the molybenzenum is spread over the carrier surface, probably as a monomolecular layer.
112 citations
TL;DR: Electron paramagnetic resonance spectra of native and arsenite- and cyanide-treated xanthine dehydrogenase have provided more definitive evidence for the binding of these inhibitors to enzymic molybdenum.
84 citations
TL;DR: In this paper, two modifications of CoMoO4 were prepared and two transition temperatures of the modifications into each other were shown to be octahedrally surrounded by oxygen.
83 citations
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70 citations
TL;DR: Further electron-paramagnetic-resonance studies relating to the role of molybdenum in the enzymic mechanisms of xanthine oxidase were carried out, and the origin of the protons is discussed in the light of the direct hydrogen-transfer mechanism implicated earlier for the enzyme.
Abstract: Further electron-paramagnetic-resonance studies relating to the role of molybdenum in the enzymic mechanisms of xanthine oxidase were carried out. The classification of the various molybdenum signals obtained on reducing the enzyme is briefly discussed. The group of ;Rapidly appearing' signals, which are obtained with all substrates within the turnover time and which show interaction with exchangeable protons, were studied in detail. Signals with salicylaldehyde, purine and xanthine in H(2)O and in 95% D(2)O were examined at 9 and 35GHz and interpreted with the help of computer simulation. Molybdenum atoms in a number of different chemical environments are involved, each substrate giving rise to two superimposed spectra with slightly different parameters; g values and proton splittings were determined. The spectrum with salicylaldehyde is believed to represent the reduced enzyme alone not in the form of a complex with substrate and its two constituents are believed to represent the two molybdenum atoms bonded slightly differently within the enzyme molecule. With purine and xanthine the spectra are thought to represent complexes of reduced enzyme with substrate molecules. With xanthine one signal-giving species shows coupling to two equivalent protons, whereas in all the other species observed two non-equivalent protons are involved. The origin of the protons is discussed in the light of the direct hydrogen-transfer mechanism implicated earlier for the enzyme. It is concluded that the proton derived from the substrate is located at least 3a from the molybdenum atom with which it interacts.
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TL;DR: In this article, the mechanism of ammonia synthesis over molybdenum nitride has been studied by means of 15 N tracer, deuterium isotope effect, and kinetics.
TL;DR: The nitrogenase of Azotobacter chroococcum was fractionated into two essential components by anaerobic chromatography and elution with MgCl2 and the ratio of these fractions, giving maximum rate of nitrogen fixation, acetylene reduction or ATP-dependent hydrogen evolution was about 2:1 but for isocyanide or cyanide reduction the optimum ratio was about 6:1.
TL;DR: In this paper, the ESR signals ascribed to Mo 5+ have been found when bismuth molybdate or Molybdenum oxide catalysts were exposed to propene at temperatures between 225 and 500 °C.
TL;DR: The difference in response patterns between deficient and non-deficient plants, induced by molybdenum treatment could form the basis for a plant test for molyBdenum deficiency.
Abstract: The effect of molybdenum on nitrate reductase was assessed by incubating wheat leaf fragments with potassium nitrate, with or without molybdenum, under lights supplying 2000 f.c. Enzyme activity was then estimated by measuring the nitrite produced by the fragments and released into the solution during 1 hr in total darkness. Light stimulated the induction of nitrate-reducing activity while darkness was essential to obtain accumulation of nitrite. Molybdenum deficiency in wheat depressed nitrate reductase activity and dry matter yield. Molybdenum caused a rapid increase in nitrate reductase in tissue from deficient plants but had no such effect on tissue from non-deficient plants. The difference in response patterns between deficient and non-deficient plants, induced by molybdenum treatment could form the basis for a plant test for molybdenum deficiency.
TL;DR: A trans-dinitrogen complex of molybdenum was prepared by the use of 1,2-bisdiphenylphosphinoethane as discussed by the authors.
Abstract: A trans-dinitrogen complex of molybdenum was prepared by the use of 1,2-bisdiphenylphosphinoethane.
TL;DR: In this article, the parent hexacarbonyls of molybdenum and tungsten have been prepared for the first time by the direct interaction of the parenthexacarbonyls with iodine at room temperature under the influence of ultraviolet radiation.
Abstract: Diiodotetracarbonyls of molybdenum and tungsten(II) have been prepared for the first time by the direct interaction of the parent hexacarbonyls with iodine at room temperature under the influence of ultraviolet radiation. Reaction of the iodocarbonyls with donor ligands such as triphenylphosphine, triphenylarsine, and triphenylstibine generally gives neutral substitution products, but the reaction between the molybdenum compound and triphenylphosphine yielded the previously reported triphenylphosphonium salt of the triiodotricarbonyl(triphenylphosphine)-molybdate(II) ion. Diiodotricarbonylbis(triphenylphosphine)tungsten(II) loses carbon monoxide on heating under vacuum to give the corresponding blue dicarbonyl compound. The dicarbonyl dissolved in dichloromethane readily absorbs carbon monoxide to reform the tricarbonyl and the compounds therefore represent a further carbon monoxide carrying system.
TL;DR: In this paper, a study was made of the solubility and diffusivity of nitrogen in high purity zone refined molybdenum making use of liquid helium resistivity measurements to monitor the presence of the gas.
TL;DR: In this article, a method was described for the determination of trace amounts of phosphorus, arsenic or silicon by atomic absorption spectrometry, and the heteropoly-molybdo acids were formed and selectively separated by means of solvent extraction.
TL;DR: In this paper, the incorporation of cobalt and molybdenum(VI) into γ-alumina from aqueous solutions and the magnetic and spectroscopic properties of γ alumina containing cobalt(II) and MBLV have been studied.
Abstract: The incorporation of cobalt(II) and molybdenum(VI) into γ-alumina from aqueous solutions and the magnetic and spectroscopic properties of γ-alumina containing cobalt(II) and molybdenum(VI) have been studied. At low concentrations cobalt(II) is adsorbed as an octahedral aquo-species which on dehydration at 130° enters tetrahedral sites of the alumina. At higher concentrations cobalt(II) is incorporated mainly by occlusion of the aqueous phase in the alumina pores. Occluded cobalt(II) remains octahedral after dehydration. On calcining cobalt–alumina samples in air, octahedral cobalt(II) is partially oxidised to cobalt(III), but tetrahedral cobalt(II) is not oxidised. On oxidation the magnetic moments of the samples decrease and a new u.v. band at 20,000–30,000 cm.–1 appears. Molybdenum(VI) is adsorbed from solutions of ammonium paramolybdate mainly as the tetrahedral MoO42– ion. In the presence of molybdenum(VI), the incorporation of cobalt(II) and the proportion of octahedral cobalt(II) both increase. In the presence of cobalt(II), the incorporation of molybdenum(VI) increases. In the presence of molybdenum(VI), aerial oxidation of octahedral cobalt(II) does not occur. There is an interaction between cobalt(II) in the solution and/or at the alumina surface. The relevance of the results to the preparation of the catalyst is discussed.
TL;DR: A model which indicates the probable function of the molybdenum is presented, and it is shown that the iron in this model probably picks up the nitrogen molecule (dinitrogen) to form a dinitrogen complex.
Abstract: NITROGENASE is a metalloenzyme containing molybdenum and iron, and both metals are considered to be directly involved in nitrogen fixation. The iron probably picks up the nitrogen molecule (dinitrogen) to form a dinitrogen complex, but the role of molybdenum is uncertain1. We now present a model which indicates the probable function of the molybdenum.
TL;DR: In this article, an initial clean surface was made at reaction temperatures between room temperature and 850°C, and four ordered structures were formed on the surface with increasing oxygen coverage at 750°C.
Abstract: Oxygen adsorption on the (100) surface of molybdenum single crystals was examined by low‐energy electron‐diffraction (LEED) in a display‐type apparatus. Continuous diffraction‐pattern observations from an initially clean surface were made at reaction temperatures between room temperature and 850°C. Below 650°C, no new ordered structures were observed. At 750°C, four ordered structures were formed on the surface with increasing oxygen coverage. The thermal characteristics and kinetics of formation of these oxides are discussed. In addition, models of surface structure with less than a monolayer oxygen coverage are presented.
TL;DR: In this article, the desorption kinetics of the atomic and oxide phases 1,2 ) have been studied to determine the composition of the surface film formed upon interaction of oxygen at low pressure with the surface of W and Mo single crystals.
TL;DR: A combined ion exchange spectrophotometric method was developed for the determination of molybdenum and tungsten in sea water as discussed by the authors, where the two elements were adsorbed quantitatively on Dowex 1-X8 (SCN-form) from sea water adjusted to 0.1 M in hydrochloric acid and ammonium thiocyanate.
TL;DR: The behavior of iron(III) hydroxide was studied in this article in order to clarify its role as a collector of the trace element molybdenum in sea water.
Patent•
15 Oct 1969
TL;DR: In this article, the authors describe a set of methods for the selective DEMETALLZATION and MOLECULAR WEIGHT REDUCTION and/or REMOVAL of ASPHALTENES and RESINS.
Abstract: HYDROCARBONS ARE HYDROCRACKED,HYDROFINED, HYDROGENATED AND/OR DEMETALLIZERD BY INTIMATE CONTACTING AT ELEVATED TEMPERATURES IN THE PRESENCE OF HYDROGEN WITH AN AQUEOUS DISPERSION OF A SULFIDE OF MOLYBDENUM, VANADIUM AND/OR RHENIUM. THE CATALYTICALLY ACTIVE COMPONENTS ARE CONVENIENTLY PRODUCED IN THE AQUEOUS PHASE BY REDUCTION AND/OR SULFURIZATION OF THE CORRESPONDING WATER SOLUBLE SULFIDES, OXIDES, ACIDS OR SALTS. THESE METHODS ARE PARTICULARLY ATTRACTIVE FOR THE SELECTIVE DEMETALLZATION AND MOLECULAR WEIGHT REDUCTION AND/OR REMOVAL OF ASPHALTENES AND RESINS.
TL;DR: In this article, the ultraviolet and visible spectra of Mo 2 O 3 (C 5 H 7 O 2 ) 4 and MoO 2 (C 7 O 3 ) 2 have been obtained in a variety of solvents and the electronic transitions assigned.
Patent•
02 Sep 1969TL;DR: OLEFINs are converted into other OLEFINS having different numbers of carbon atoms by contact with a CATALYST, ACTIVE FOR DISPROPORTIONATING PROPYLENE into ETHYLENE and BUTENE, COMPRISING ALUMINA PROMOTED with a COMPOUND OF MOLYBDENUM, TUNGSTEN OR RHENIUM and FURTHER TREATED with a MODIFYING AMOUNT of a COMPound of an ALKALI METAL OR AN ALkaline EAR
Abstract: OLEFINS ARE CONVERTED INTO OTHER OLEFINS HAVING DIFFERENT NUMBERS OF CARBON ATOMS BY CONTACT WITH A CATALYST, ACTIVE FOR DISPROPORTIONATING PROPYLENE INTO ETHYLENE AND BUTENE, COMPRISING ALUMINA PROMOTED WITH A COMPOUND OF MOLYBDENUM, TUNGSTEN OR RHENIUM AND FURTHER TREATED WITH A MODIFYING AMOUNT OF A COMPOUND OF AN ALKALI METAL OR AN ALKALINE EARTH METAL.