Showing papers on "Molybdenum published in 1981"
TL;DR: Several series of nickel (or Co) molybdenum oxide catalysts supported on X-ray photoelectron and Raman spectroscopy have been studied by as discussed by the authors, where the combination of these two techniques is a complementary approach to the alumina coverage, the nature of the deposited species, and the interaction between these species.
Abstract: Several series of nickel (or Co) molybdenum oxide catalysts supported on ..gamma..-Al/sub 2/O/sub 3/ have been studied by X-ray photoelectron and Raman spectroscopy. The combination of these two techniques is a complementary approach to the alumina coverage, the nature of the deposited species, and the interaction between these species. In particular, the characteristics of the monolayer coverage by the nickel species appear somewhat different from cobalt in systems without molybdenum. When molybdenum is present, formation of a phase similar to (a) NiMoO/sub 4/ is observed. No bulk NiO or Ni(OH)/sub 2/ phases are detected. Comparison with Co-Mo or Ni-Mo-..gamma..-Al/sub 2/O/sub 3/ industrial catalysts is also presented.
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206 citations
TL;DR: Several molybdenum compounds were prepared and their catalytic properties in the methanation of CO at 350 °C were investigated and compared with those of nickel and iron as mentioned in this paper.
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173 citations
TL;DR: In this paper, the authors used radiometrically-dated molybdenum stockwork data to classify calc-alkalic and calc-calcic calcine stockwork deposits.
Abstract: Molybdenum deposits are classified by using magma series chemistry expressed as K (sub 57.5) (i.e., the K 2 O content at 57.5% SiO 2 in a magma series); the F, Nb, Rb, and Sr contents of the source pluton; and the abundance of F and Sn in the hydrothermal system. By plotting K (sub 57.5) values against the Nb, Rb, and F contents of the granitic source pluton, a natural dividing line emerges separating igneous rocks with K (sub 57.5) values below 2.5 from rocks with K (sub 57.5) values above 2.5. This metallogenically significant break forms the basis for our proposed classification.No molybdenum deposits have been found in calcic magma series. Calc-alkaline stockwork molybdenum deposits are associated with calc-alkalic and high K calc-alkalic magma series (K (sub 57.5) 2.5), alkali-calcic, and alkalic magma series. Source plutons contain from 25 to in excess of 250 ppm Nb, 200 to 800 ppm Rb, less than 125 ppm Sr, and less than 0.2 percent TiO 2 and are enriched in F, Sn, and Mo. The hydrothermal system commonly contains molybdenite grades above 0.30 percent and is characterized by intense K metasomatism and an abundance of fluorite and/or topaz. Tungsten is common and occurs as huebnerite or wolframite. The deposits are enriched in tin. The alkali-calcic to alkalic deposit category has been subdivided into: (1) transitional deposits cogenetic with granitic differentiates of high K calc-alkalic (K (sub 57.5) > 2.5) and alkali-calcic magma series characterized by moderate enrichment in Nb, Rb, and F (Questa, Mount Hope); (2) Climax-type deposits associated with highly differentiated granites of alkali-calcic magma series (e.g., Climax, Urad-Henderson, Mount Emmons); and (3) alkalic deposits found with alkali-calcic and alkalic magma series. The alkalic molybdenum deposits are subdivided into (a) deposits cogenetic with metaluminous quartz-deficient syenitic and monzonitic stocks (e.g., Nogal Peak) and (b) deposits related to granites (e.g., Malmbjerg).Calc-alkaline molybdenum deposits occur in continents and older island arcs in volcanoplutonic arcs associated with plate convergence. Climax-type deposits are found in areas of crustal relaxation and extension above the deepest part of a subduction zone. Alkalic deposits are present in areas of back-arc spreading associated with converging plate margins, in intracratonic rifts, and in rifts associated with the opening of oceanic basins. Magmatism responsible for the formation of calc-alkaline molybdenum stockwork deposits may be a product of partial fusion of subducted oceanic lithosphere. Partial melting of enriched upper mantle in response to pressure release in areas of back-arc spreading and intracratonic rifting could form magmas related to Climax-type and alkalic deposits. We propose that the chemical differences between source plutons and hydrothermal systems in the two categories indirectly reflect the phlogopite stability field in the subducted slab and the overlying mantle wedge. We also propose that, based on the data presented, molybdenum contained in all stockwork deposit types is of subcrustal origin.The validity of the proposed classification has been tested by plotting radiometrically dated molybdenum deposits of the western United States on maps showing the distribution and magma chemistry of arc magmatism for the appropriate time span. The location of the deposit accurately predicts the type of deposit as determined independently by igneous trace element data and hydrothermal system characteristics. Our findings suggest that at any time during the development of the magma arc each molybdenum deposit category has its unique position within the arc. Geochemical data presented also show that a continuum exists between calc-alkaline molybdenum stockwork deposits and porphyry coppers. Calc-alkaline molybdenum deposits grade into Climax-type deposits through the intermediate transitional deposit type. No deposits transitional between alkalic porphyry copper deposits and Climax-type molybdenum deposits are known to us.The striking differences between calc-alkaline and Climax-type molybdenum deposits are a consequence of original magma chemistry, molybdenum concentration levels in the parent magma, and the behavior of molybdenum in the melt and hydrothermal system. The high K, F, Rb, and low Ti and Fe contents of granitic rocks associated with Climax-type deposits create conditions ideal for molybdenum concentration, initially through crystal fractionation and liquid state thermogravitational diffusion and later by means of volatile transfer or the formation of a hydrous alumina-deficient K-rich silicate melt. Following vapor saturation of this residual melt, molybdenum will be introduced into the hydrothermal system. Decomposition of the K silicate component in response to cooling and a pH decrease results in addition of potassium to the hydrothermal fluid or the wall rocks and the precipitation of quartz and molybdenite. The striking correlation between added K 2 O and MoS 2 grades in the deposits lends credence to this concentration mechanism. No quantitative correlation between fluorine and molybdenum introduced in the hydrothermal system has been documented. In our estimation, the importance of fluorine principally lies in its capability of altering magma characteristics that help to enhance molybdenum concentration processes. Differentiates of calc-alkaline magma series have lower initial molybdenum concentrations and this factor combined with the higher Ti and Fe levels, and the less extreme K and Rb and low F contents, prohibits extreme molybdenum concentration during the late magmatic stage. Consequently, most calc-alkaline molybdenum deposits are less intensely mineralized.The relationship between magma chemistry and metallogeny as exemplified by the metallogeny of molybdenum deposits may be extended to include other metals and could prove to be a valuable exploration tool.
169 citations
TL;DR: In this article, a new treatment of EXAFS amplitudes has been developed which allows the extraction of meaningful Debye-Waller factors using experimentally derived functions, and a search profile procedure has also been developed to aid in the treatment of minor exafS components.
Abstract: The molybdenum enzymes sulfite oxidase and xanthine dehydrogenase have been investigated by fluorescence-detected EXAFS using synchrotron radiation, and the results have been interpreted with improved EXAFS analysis procedures. A new treatment of EXAFS amplitudes has been developed which allows the extraction of meaningful Debye-Waller factors using experimentally derived functions. A search profile procedure has also been developed to aid in the treatment of minor EXAFS components. These methods have been used for a more detailed analysis of sulfite oxidase molybdenum EXAFS. They have also been used for analysis of the EXAFS of intact and cyanolyzed xanthine dehydrogenase, in both oxidized and reduced forms. Although the results are in qualitative agreement with recent work by Bordas et al., some significant quantitative differences are found. For oxidized sulfite oxidase, the analysis revealed two oxygens at 1.68 A and two or three sulfurs at 2.41 A, changing to one oxygen at 1.69 8, and three sulfurs at 2.38 A upon reduction. For oxidized, intact xanthine dehydrogenase the prediction was one oxygen at 1.70 A, one sulfur at 2.15 A, and two sulfurs at 2.47 A, changing to one oxygen at 1.68 8, and three sulfurs at 2.38 A upon reduction. Finally, in cyanolyzed xanthine dehydrogenase, two oxygens at 1.67 8, and two sulfurs at 2.46 A were found, which upon reduction changed to one oxygen at 1.66 A and two or three sulfurs at 2.33 A. In all cases there may be extra ligands which complete the molybdenum coordination sphere but contribute only weakly to the EXAFS. Molybdenum enzymes exhibit a broad range of chemical and spectroscopic behavior,’ and comprehending the structural basis for this diversity is a prerequisite for understanding and synthetically modeling their catalytic mechanisms. Previous results from X-ray absorption spectroscopy have suggested that the Mo sites of these enzymes can be classified as either “cluster” type such as in nitrogenase2-‘ or “oxo” t pe such as contained in xanthine Specifically, the EXAFS studies of nitrogenase have shown that the molybdenum is present in an Fe,Mo,S cluster, whereas the other Mo enzymes appear to have a Mo site with both sulfur donor and terminal oxo ligands. The structural differences between these two types of sites may be related to the fact that nitrogenase possesses an iron-molybdenum cofactor (“FeMo-co”),’O whereas the other enzymes cited contain a molybdenum cofactor (“Moa”) which is free of iron but contains a novel pterin component.” Even within the class of oxo-type Mo proteins there are substantial differences in properties. Xanthine oxidase, xanthine dehydrogenase, and aldehyde oxidase all have relatively low Mo redox potentialsI2 and a unique “cyanolyzable” sulfur.’ Upon treatment of these enzymes with cyanide, SCNis released and “desulfo” Mo proteins are formed which have no catalytic activity and even lower redox potentials. A molybdenum protein from Desulfovibrio gigas has properties similar to these desulfo proteins.” In contrast, sulfite oxidaseI4 and nitrate red~ctase’~ have substantially higher Mo redox potentials, and although they are inhibited by cyanide in their reduced states, this process is re* To whom correspondence should be addressed at the Exxon Research and sulfite oxidase, P and nitrate r e d ~ c t a s e . ~ Engineering Co. versible by oxidation and no SCNis released.16 Thus, a distinction can be made between low potential and high potential (1) For a recent review of molybdenum biochemistry, see: “Molybdenum and Molybdenum-Containing Enzymes”, M. P. Coughlan, Ed., Pergamon Press: New York, 1980. (2) S. P. Cramer, K. 0. Hodgson, W. 0. Gillum, and L. E. Mortenson, J . Am. Chem. Soc., 100, 3398-3407 (1978). (3) S. P. Cramer, W. 0. Gillum, K. 0. Hodgson, L. E. Mortenson, E. I. Stiefel, J. R. Chisnell, W. J. Brill, and V. K. Shah, J . Am. Chem. Soc., 100, ( 4 ) T. E. Wolff, J. M. Berg, C. Warrick, K. 0. Hodgson, and R. H. Holm, J. Am. Chem. SOC., 100, 4630-4632 (1978). (5) T. D. Tullius, D. M. Kurtz, Jr., S. D. Conradson, and K. 0. Hodgson, J . Am. Chem. Soc., 101, 2776-2779 (1979). (6) J. Bordas, R. C. Bray, C. D. Garner, S. Gutteridge, and S. S. Hasnain, J . Inorg. Biochem., 11, 181-186 (1979). (7) J. Bordas, R. C. Bray, C. D. Garner, S. Gutteridge, and S. S. Hasnain, Biochem. J. 191,499-508 (1980). (8) S. P. Cramer, H. B. Gray, and K. V. Rajagopalan, J . Am. Chem. Soc., (9) S. P. Cramer, L. E. Solomonson, M. W. W. Adams, and L. E. Mortenson, submitted to Biochem. Biophys. Res. Commun. (10) P. T. Pienkos, V. K. Shah, and W. J. Brill in “Molybdenum and Molybdenum-Containing Enzymes”, M. P. Coughlan, Ed., Pergamon Press, New York, 1980, pp 385-401. (1 1) J. L. Johnson in “Molybdenum and Molybdenum-Containing Enzymes”, M. P. Coughlan, Ed., Pergamon Press, New York, 1980, pp 345-383. (12) M. J. Barber, M. P. Coughlan, M. Kanda, and K. V. Rajagopalan, Arch. Biochem. Biophys., 201, 468-475 (1980). (13) J. J. G. Moura, A. V. Xavier, R. Cammack, D. 0. Hall, M. Bruschi, and J. LeGall, Biochem. J., 173,419-425 (1978). (14) S. P. Cramer, H. B. Gray, N. S. Scott, M. Barber, and K. V. Rajagopalan in “Molybdenum Chemistry of Biological Significances”, W. E. Newton and S. Osaka, Eds., Plenum Press, New York, 1980, pp 157-168. 3814-3819 (1978). 101, 2772-2774 (1979). 0002-7863/8l/l503-7721$01.25/0
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149 citations
TL;DR: In this paper, the electron transfer characteristics of molybdenum(VI) complexes of the type MoO 2 (L). where L is a tridentate dianionic Schiff base ligand, are reported.
Abstract: Molybdenum(VI) complexes of the type MoO 2 (L). where L is a tridentate dianionic Schiff base ligand, are reported. Infrared data suggest oligomerization via a Mo=0→Mo bridge which is cleaved by a wide variety of donors (D): aldehyde, amide, amine. N-oxide, sulfoxide, phosphine oxide, water, alcohol, and phosphinetroducing Mo0 2 (L)(D). The tendency of adduct formation by the molybdenyl systems increases in a particular way as L is changed. Mo0 2 (L)(D) usually shows two IR absorptions attributable to cis-Mo0 2 stretches, and on the average, species with oxygen donors vibrate at higher frequencies than those with nitrogen donors. On the basis of ligand displacement reactions D binding increases in the order CH 3 CHO 6 H 5 CHO 2 S0 2 (L)(D) is readily converted to Mo0 2 (L) in a single endothermic step. Thermal analysis data together with NMR data support the weak binding of the D ligands. The electron transfer characteristics of a number of the MoO 2 (L)(dmf) species are studied with use of voltarmmetric techniques. In general two to three reduction waves are obsened, all !mated at potentials more negative than —0.9 V vs. SCE. The chemistry and electrochemistry of a dinuclear molybdenum V) species resulting from hydrazine reduction of one Mo0 2 (L) is also briefly described.
121 citations
TL;DR: In this paper, a literature review of Mo as an alloying element in stainless steels, with particular reference to crevice corrosion, is presented, and the role of soluble Mo species in corrosion inhibition is discussed.
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104 citations
TL;DR: In this paper, a pyrolytic hydrogen reduction of MoO2Cl2 in the temperature range 550-710°C on both quartz and metal substrates is described.
TL;DR: In this article, the potential-pH diagrams of chromium, molybdenum, titanium, and platinum in water at temperatures from 25 to 300 C are presented.
Abstract: This paper describes the potential-pH diagrams of chromium, molybdenum, titanium, and platinum in water at temperatures from 25 to 300 C. The diagrams can be utilized to predict the stability of these metals in aqueous solutions over this temperature range. A computer program written by D. D. Macdonald, et al, was utilized to perform the thermodynamic calculations and to construct the diagrams. In general, the diagrams indicate that the metals are more active at higher temperatures and that the area of the stable metal oxide domains decreases with increasing temperature.
TL;DR: In this paper, the authors report the deposition of refractory metals chromium, molybdenum, and tungsten through the laser-induced gas phase photolysis of their respective hexacarbonyls.
Abstract: We report the deposition of the refractory metals chromium, molybdenum, and tungsten through the laser‐induced gas‐phase photolysis of their respective hexacarbonyls A copper, hollow cathode laser was used at ultraviolet wavelengths matched to peaks in the absorption spectra of the carbonyl molecules Localized room‐temperature metal deposition was achieved by focusing the beam into a cell containing the carbonyl gas and helium as a buffer No major differences were noted for deposition on a polished silicon wafer, a thermally oxidized silicon wafer, and a quartz flat
TL;DR: In this paper, the long-term ageing characteristics of Ni-Mo-Cr alloys (the high-temperature HASTELLOY alloy S and the corrosion resistant hasselloy alloys C-4 and C-276) at 810 K were investigated.
Abstract: The long-term ageing characteristics of some commercial Ni-Mo-Cr alloys (the high-temperature HASTELLOY alloy S and the corrosion resistant HASTELLOY alloys C-4 and C-276) at 810 K were investigated. It was found that the three alloys undergo the following long-range ordering reaction: disordered f c c lattice → ordered orthorhombic, Pt2Mo-type superlattice. Ordering was found to cause considerable strengthening without severe loss of tensile elongation. Deformation in the ordered state occurred predominantly by twinning. The corrosion rates of alloys C-4 and C-276 in boiling sulphuric-ferric sulphate solution did not seem to be greatly affected by the long-range ordering reaction. In addition to ordering, the three alloys were also found to undergo grain boundary reactions. The resulting phase in alloys S and C-4 assumed a dispersed morphology and was identified as carbide, probably of the Type M12C. In alloy C-276, however, which contains higher amounts of iron and tungsten, the boundary precipitate was in the form of a continuous layer consisting of M12C and Mu-phase. This could account for the reduced tensile elongation of alloy C-276 relative to alloys S and C-4 and also to its high corrosion rate.
01 Jun 1981
TL;DR: It was observed from ESR spectrum that the biological reduction of Mo(VI) to Mo(V) or Mo(III) occurs intracellularly and the efficiency at which molybdenum was accumulated was species specific in the following order.
Abstract: SummaryThe accumulation of molybdenum from aqueous systems by various green microalgae in particular,Chlorella regularis, as it is known to concentrate large amounts of heavy metals such as uranium, copper, manganese and cadmium, was investigated. Molybdenum was absorbed rapidly byChlorella cells during the first 2 h after exposure to molybdenum and thereafter more slowly. the uptake of molybdenum byChlorella was not markedly affected by the pH or temperature of the solution or by the presence of metabolic inhibitors. The amount of molybdenum absorbed byChlorella cells (μg Mo/g dry cells) increased as the molybdenum concentration of the solution increased but decreased as the algal concentration increased. The capacity ofChlorella cells to accumulate molybdenum was increased by heat treatment.Chlorella cells could not accumulate such large amounts of molybdenum from sea water as they did from fresh water. It was observed from ESR spectrum that the biological reduction of Mo(VI) to Mo(V) or Mo(III) occurs intracellularly.The efficiency at which molybdenum was accumulated was species specific in the following order:Scenedesmus chlorelloides > Chlamydomonas reinhardtii > Chlorella regularis > Scenedesmus bijuga > Chlamydomonas angulosa > Scenedesmus obliquus.
TL;DR: In this article, arc-melted molybdenum was fully recrystallized and annealed below 1100 K under various atmospheres and they were tested by bending.
TL;DR: Molybdenum cofactor was synthesized in all the chl mutants, but additional processing steps may be missing in chlA and chlE mutants for proper insertion of cofactor in the membrane.
Abstract: Experiments were performed to determine whether defects in molybdenum cofactor metabolism were responsible for the pleiotropic loss of the molybdoenzymes nitrate reductase and formate dehydrogenase in chl mutants of Escherichia coli. In wild-type E. coli, molybdenum cofactor activity was present in both the soluble and membrane-associated fractions when the cells were grown either aerobically or anaerobically, with and without nitrate. Molybdenum cofactor in the soluble fraction decreased when the membrane-bound nitrate reductase and formate dehydrogenase were induced. In the chl mutants, molybdenum cofactor activity was found in the soluble fraction of chlA, chlB, chlC, chlD, chlE, and chlG, but only chlB, chlC, chlD, and chlG expressed cofactor activity in the membrane fraction. The defect in the chlA mutants which prevented incorporation of the soluble cofactor into the membrane also caused the soluble cofactor to be defective in its ability to bind molybdenum. This cofactor was not active in the absence of molybdate, and it required at least threefold more molybdate than did the wild type in the Neurospora crassa nit-1 complementation assay. However, the cofactor from the chlA strain mediated the dimerization of the nit-1 subunits in the presence and absence of molybdate to yield the 7.9S dimer. Growth of chlA mutants in medium with increased molybdate did not repair the defect in the chlA cofactor nor restore the molybdoenzyme activities. Thus, molybdenum cofactor was synthesized in all the chl mutants, but additional processing steps may be missing in chlA and chlE mutants for proper insertion of cofactor in the membrane.
Patent•
03 Apr 1981
TL;DR: In this paper, an antioxidant additive combination for lubricating oils is prepared by combining a sulfur containing molybdenum compound, a basic nitrogen compound, and a sulfur compound, with an organic sulfur compound.
Abstract: An antioxidant additive combination for lubricating oils is prepared by combining (a) a sulfur containing molybdenum compound prepared by reacting an acidic molybdenum compound, a basic nitrogen compound, and a sulfur compound, with (b) an organic sulfur compound
TL;DR: In this article, several reduced ternary and quaternary oxides of molybdenum are reported, each containing moly bdenum in an average oxidation state 2 sealed in Mo tubes held at 1100°C for ca 7 days.
TL;DR: In this article, the authors measured the deuterium permeation rate and reemission rate during the implantation of 20 keV deuteron with use of a quadrupole mass-spectrometer.
Patent•
07 Aug 1981
TL;DR: In this paper, an antioxidant additive combination for lubricating oils is prepared by combining a sulfur containing molybdenum compound and a basic nitrogen compound, with an organic sulfur compound, and it is shown that the combination can improve the performance of the oils.
Abstract: An antioxidant additive combination for lubricating oils is prepared by combining (a) a sulfur containing molybdenum compound prepared by reacting an acidic molybdenum compound, a basic nitrogen compound, and carbon disulfide, with (b) an organic sulfur compound.
TL;DR: This study utilizes the known tungsten sensitivity of molybdoenzymes to demonstrate directly that pyridoxal oxidase is also a molyBdoenzyme.
Abstract: The molybdenum hydroxylases are a ubiquitous class of enzymes which contain molybdenum in association with a low molecular weight cofactor. Genetic evidence suggests that the Drosophila loci, ma--1, cin and lxd are concerned with this cofactor because mutants for any one of these loci simultaneously interrupt activity for two molybdenum hydroxylases, XDH and A0. A third enzyme activity, P0, is also absent in each of the three mutants but evidence classifying P0 as a molybdoenzyme has been lacking. This study utilizes the known tungsten sensitivity of molybdoenzymes to demonstrate directly that pyridoxal oxidase is also molybdoenzyme. The low molecular weight molybdenum cofactor is found to be severely reduced in extracts of the 1xd and cin mutants but ma--1 mutants have high levels of cofactor. A partially purified preparation of XDH crossreacting material from ma--1 was also shown to contain the molybdenum cofactor. These results, considered with data from other workers are taken to indicate that the functions of all three of the loci examined could be concerned with some aspect of cofactor biosynthesis.