Molybdenum Salt Research Articles

Solution combustion synthesis and physicochemical characterization of ZrO 2–MoO 3 nanocomposite oxides prepared using different fuels

A series of MoO 3–ZrO 2 nanocomposite oxides with MoO 3 content in the range of 2–20 mol% were prepared by solution combustion method. Three different fuels namely urea, glycine and hexamethylenetetramine (HMTA) were used for the preparation of MoO 3–ZrO 2 oxides. For the sake of comparison, the MoO 3–ZrO 2 composite oxides were also prepared by impregnation of zirconia with molybdenum salt precursor and subsequent heat treatment. The synthesized nanomaterials were characterized by XRD, SEM, TEM and UV–vis spectroscopic technique. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of MoO 3. The method of preparation was found to be crucial for the phase composition of zirconia in the composite oxide. The crystallite size and rms stain were calculated from the Fourier line shape analysis of the broadened X-ray diffraction profiles. With increase in the MoO 3 content, the crystallite size of the tetragonal zirconia phase was found to be decreased. TEM study indicated the presence of small nanoparticles with size in the 5–10 nm range. UV–vis study of the composite oxide materials revealed well dispersion of the molybdenum oxide component in the form of monomer, dimers and nanoclusters in the zirconia matrix. The nature of fuel was found to be crucial in determining the morphology and shape of the particles.

The electrochemical dissolution of molybdenum in non-aqueous media

Electrochemical dissolution of molybdenum in 1.0 M solution of ammonium nitrate in liquid ammonia at − 35 °C was investigated. The electrolyte has good conductivity and it showed corrosive ability to great extent. The galvanostatic method was used to investigate the anodic dissolution of molybdenum in NH 4NO 3/NH 3 system with a cell potential difference of + 4.0 V. The dissolution efficiency of 79% was noted, while electrodeposition efficiency of molybdenum at parent cathode went up to 76%. No new molybdenum salt was added to the solution; only the dissolved molybdenum was redeposited on parent cathode. Later the residue left was analyzed for possible molybdenum complex and XRF analysis showed the presence of molybdenum in the residue. Cyclic voltammetry was used to investigate kinetic parameters of Mo in NH 4NO 3/NH 3 system. Electrochemical behavior of molybdenum in 1-butyl-3-methyl-imidazolium/trifluoromethansulfonat was also investigated and it was noticed that molybdenum dissolves in NH 4NO 3/NH 3 system at faster rates.

Thermal Spreading As an Alternative for the Wet Impregnation Method: Advantages and Downsides in the Preparation of MoO3/SiO2−Al2O3 Metathesis Catalysts

Silica alumina-supported MoO3 catalysts are classically prepared via impregnation of the support with a molybdenum salt solution, usually ammonium heptamolybdate, and subsequent drying and calcination (three steps). The downsides of such a route for the synthesis of heterogeneous metathesis catalysts are linked to the limited control on the nature of the Mop, stabilized at the surface, to the uneven distribution of the deposit in the pores of the support, and to the build up of inactive species that find their origin in the wet step of the preparation. In opposition, the direct thermal spreading of molybdenum oxide onto the support is a straightforward (one step) method involving no wet stage. It allows the conversion of bulk MoO3 crystals to amorphous molybdate species dispersed at the surface of the silica alumina support. This contribution shows that the catalysts obtained via both methods exhibit similar performances in the self-metathesis of propene to butene and ethene. However, based on XRD, XPS, Raman spectroscopy, ICP-AES, N-2 physisorption, TEM, and MAS-NMR spectroscopy, it is shown that the origin of active and inactive species in the two systems is different. Whereas the activity of wet-made catalysts is limited by the formation of bulky MoO3 crystals and of aluminum molybdate, the performances of dry-made catalysts are limited by the incomplete spreading of MoO3 nanocrystallites.

Extraction of Mo from solutions in HNO3 and other mineral acids with solutions of dibutyl hydrogen phosphate in a diluent

Extraction of Mo from HNO3 solutions with solutions of HDBP in xylene and CCl4 in a wide range of Mo concentrations was studied. The Mo distribution ratios are considerably higher with CCl4 diluent compared to xylene, but the extractant capacity in both cases is the same and corresponds to the ratio HDBP: Mo = 2. The active species in the Mo extraction is the HDBP dimer. In the first step, an acidic molybdenyl salt with HDBP of the composition MoO2(DBP)2(HDBP)2, exhibiting certain secondary extraction properties toward rare-earth elements, is formed in all the cases. The dependence of the Mo extraction on the aqueous solution acidity passes through a minimum at 3–4 M HNO3. The subsequent increase in the Mo distribution ratios is associated with the simultaneous extraction of HNO3 (or nitrate ion) whose concentration in the extract is considerably lower than the Mo concentration. With an increase in the loading of the extract with molybdenum, the acidic molybdenum salt of HDBP undergoes restructurization, probably associated with additional coordination of H2MoO4 to it. The dependence of the Mo distribution ratio on the acid concentration in the extraction from sulfuric acid solutions passes through a minimum at 3–4 M H2SO4, which correlates with the first step of the acid dissociation, and in the extraction from HClO4 the dependence passes through a minimum and a maximum. In the extraction from hydrochloric acid solutions, the Mo extractability decreases with an increase in the acid concentration, owing to complexation in the aqueous phase. The nature of processes occurring at various loadings of the extract with molybdenum are discussed.

Silicate determination in sea water: Toward a reagentless electrochemical method

Silicate has been determined in sea water by four different electrochemical methods based on the detection of the silicomolybdic complex formed in acidic media by the reaction between silicate and molybdenum salts. The first two methods are based on the addition of molybdate and protons in a seawater sample in an electrochemical cell. Cyclic voltammetry presents two reduction and two oxidation peaks giving four values of the concentration and therefore increasing the precision. Then chronoamperometry is performed on an electrode held at a constant potential. A semi-autonomous method has been developed based on the electrochemical anodic oxidation of molybdenum, the complexation of the oxidation product with silicate and the detection of the complex by cyclic voltammetry. This method is tested and compared with the classical colorimetric one during ANT XXIII/3 cruise across Drake Passage (January–February 2006). The detection limit is 1 μM and the deviation between both methods is less than 3% for concentrations higher than 10 μM. Finally a complete reagentless method with a precision of 2.6% is described based on the simultaneous formation of the molybdenum salt and protons in a divided electrochemical cell. This latter method should be very useful for developing a reagentless sensor suitable for long term in situ deployments on oceanic biogeochemical observatories.

New Method To Minimize High-Temperature Corrosion Resulting from Alkali Sulfate and Chloride Deposition in Combustion Systems. II. Molybdenum Salts

The use of fuels other than natural gas in gas turbine generators still is fraught with blade corrosion problems that result from the formation of sodium sulfate or potassium sulfate, in the presence of chlorine. The present work illustrates that the addition of molybdenum salts to synthetic fuels (synfuels) modifies this deposition process and benign protective coatings of alkali polymolybdates are produced instead. This study is a follow-up to research published earlier in this journal that showed closely similar behavior with tungsten salt additives. In the case of molybdenum, a new preferential ranking of product formation on the surface is established that is closely related to the thermodynamic stabilities, namely, Na2Mo2O7 > Na2SO4 > Na2MoO4 > NaCl and K2Mo4O13 > K2Mo3O10 > K2Mo2O7 > K2SO4 > K2MoO4 > KCl. This chemistry exists under fuel-lean conditions and is otherwise not sensitive to the fuel, combustion conditions, surface temperature, or material. The required additive trace levels of molybdenum salt are on the order of twice that of the gaseous alkali, on an atomic basis. Consequently, when used as a final pre-gas turbine polishing technique and following other fuel precleaning methods, the approach offers a very practical and inexpensive solution.

Modification of Electroless Nickel-Plating Coatings with Sol-Gel Film

Four Sol-Gel films were developed by dip-coating electroless nickel-plated samples in different Sols, followed by heat treatment. The effects of the coating times and heat treatment temperature on the corrosion, oxidation resistance and wearing quality of the modified coating were examined. Results show that, after six coating, Sol-Gel films obtained can provide good corrosion and oxidation resistance, and their anti-corrosion quality remains high even after being oxidized at 500 °C for 60 hours. Addition of inorganic molybdenum salt or chromate into the Ti Sol also makes the wearing quality of the Sol-Gel film better.

Hypersensitivity to metals in orthodontics

To study the incidence of hypersensitivity to orthodontic metals, patch tests were carried out before and 2 months after the placement of orthodontic appliances in 38 patients (17 male, 21 female). The tested substances were cobalt chloride, copper sulfate, potassium dichromate, iron sulfate, manganese chloride, molybdenum salt, nickel sulfate, and titanium oxide. Eight strips containing the test substances were positioned on the patients' backs. They were removed after 48 hours and assessed by a dermatologist at 48 and 72 hours after antigen application. The obtained data were analyzed by the chi-square test and McNemar's chi-square test. Statistically significant positive reactions were observed for nickel sulfate (21.1%), potassium dichromate (21.1%), and manganese chloride (7.9%); reactions to nickel sulfate had the greatest intensity. No differences were observed between the reactions before and after placement of the orthodontic appliances; this indicates that they did not sensitize the patients or affect their tolerance to these metals during the study period. No statistical difference was observed regarding sex for any evaluated substance, although a greater tendency to positivity to nickel sulfate was observed among female patients and to potassium dichromate in male patients.

Homogeneous and Polymer-Supported Catalysts in the Oxidation of α-Pinene with Oxygen

The catalytic activities of nitrogen-containing cobalt complexes, polymer (AN-251 anion exchanger)-supported cobalt complex, and a polymer–salt composition containing molybdenum salt and nonionogenic water-soluble polymers were compared in the oxidation of α-pinene.

Application of liquid emulsion membrane (LEM) process for enrichment of molybdenum from aqueous solutions

A comprehensive study pertaining to liquid emulsion membrane (LEM) extraction process to enrich dilute aqueous solutions of molybdenum salt is presented here. The liquid membrane is made up of Aliquat 336 as a carrier, organic diluent and an emulsifying agent. The selection of extractant, Aliquat 336 was made on the basis of conventional liquid–liquid extraction studies. The role of pH is very important in the LEM process for extraction of molybdenum. The important variables affecting the LEM permeation process, including the residence time for LEM extraction, membrane viscosity (surfactant concentration), extractant concentration, internal strip phase concentration, organic solvents, level of agitation and the phase ratio between emulsion phase ( V m) and feed phase ( V l) were systematically investigated. When the strip phase concentration was 0.5 M (NaOH) and dodecane was used as a diluent, better extraction of molybdenum was obtained. Higher V m/ V l gave higher extraction of molybdenum.

Synthesis and redox characterization of the polyoxo anion, gamma*-[S2W18O62]4-: a unique fast oxidation pathway determines the characteristic reversible electrochemical behavior of polyoxometalate anions in acidic media.

The synthesis and characterization of (Bu4N)4[S2W18O62].1.23MeCN.0.27H2O are reported. It crystallizes in the monoclinic space group C2/c with a = 22.389(6) A, b = 22.104(3) A, c = 25.505(5) A, beta = 95.690(15) degrees, V = 12560(5) A3, and Z = 4. The anion exists as the gamma* isomer, the second example of this isomer type to be characterized structurally. The equivalent molybdenum salt occurs as the alpha isomer. gamma*-[S2W18O62]4- in MeCN solution displayed four electrochemically reversible one-electron redox processes at E1/2 values of -0.24, -0.62, -1.18, and -1.57 V versus the Fc+/Fc couple. Upon addition of acid in MeCN/H2O (95/5 v/v), the two most cathodic processes converted to an overall two-electron process at -0.71 V. The total data suggested that this process actually comprises two one-electron transfer processes, occurring at different potentials, with associated proton-transfer reactions. The interpretation is supported by simulation of the effect of acid titration upon the cyclic voltammetry. While multiple pathways for correlated reduction and protonation are present in both the molybdenum and tungsten systems, only a single fast oxidation pathway is available. As the reduced forms of [S2W18O62]4- are much weaker bases than those of [S2Mo18O62]4-, the individual oxidation pathways are not the same. However, their existence determines the highly reversible electrochemical behavior that is characteristic of these anions, and that of polyoxometalate systems in general.

Novel Tungsten, Molybdenum, and Vanadium Oxides Containing Surfactant Ions

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) Å, b = 54.41(4) Å, c = 13.12(1) Å, 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 Å. The vanadium salt was indexed to a triclinic cell with a = 9.813(3) Å, b = 11.512(3) Å, c = 21.725(5) Å, α = 95.30(1)°, β = 93.82(6)°, and γ = 101.12(8)°, with a layer spacing of 21.6 Å.

Kinetics and mechanism of maleic acid hydroxylation by hydrogen peroxide. Part I: Formal kinetic studies by immobilized catalysis in a pseudo‐homogeneous system

AbstractFormal kinetic studies of the epoxidation and hydroxylation of maleic acid by hydrogen peroxide (H2O2) have been carried out in the presence of a molybdenum salt, as catalyst, immobilized on Amberlite IRA‐400 polymer resin in the chloride form. Immobilization of the catalyst on the resin was by a sorption process. Hydroxylation by immobilized catalysis afforded higher H2O2 selectivity and increased product yield in excess of 85%. Analysis of kinetic results shows that the reaction in the pseudo‐homogeneous system follows the typical pseudo‐zero order dependence on H2O2 concentration and is first order with respect to maleic acid concentration. However, the rate model developed for the immobilized catalyst fits the experimental data smoothly and parameter estimation using the Lineweaver–Burk plot fulfils the kinetic consistency tests without additional mathematical manipulation. The problem of activity and stability of the present catalyst was also investigated.

Synthesis of the complexes [N(PPH 3) 2][M(CO) 2(η 3-C 3H 5)-(η 6-7, 9-C 2B 10H 10Me 2)](M = Mo or W): crystal structure of [N(PPH 3) 2][WBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)

Treatment of the compounds [MBr(CO) 2(NCMe) 2(η 3-C 3H 5)] (M = Mo or W) with Na 2[7,9-C 2B 10H 10Me 2] in tetrahydrofuran, followed by addition of [N(PPh 3) 2]Cl, affords the salts [N(PPh 3) 2][M(CO) 2(η 3-C 3H 5)(η 6-7,9-C 2 B 10H 10Me 2)]. Reactions of [N(PPh 3) 2] 2[M(CO) 3(η 6-7,9-C 2B 10H 10Me 2)] with an excess of allyl bromide generate the complexes [N(PPh 3) 2][MBr(CO) 3 (η 6-7,9-C 2B 10H 10Me 2)] via an allyl-coupling process. The structure of the latter (M = W) has been determined by X-ray diffraction. The preparation of the molybdenum salt [N(PPh 3) 2] [MoBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)] by this route was accompanied by the formation of small amounts of the complex [N(PPh 3) 2][MoBr(CO) 3(η 5-7,9-C 2B 9H 9Me 2)] resulting from ejection of a BH vertex from the cage. Indeed, it was observed that in CH 2Cl 2 solutions, the former species was slowly converted into the latter at ambient temperatures. Protonation (aqueous HBr) of the salts [N(PPh 3) 2][M(CO) 2(η 3-C 3H 5)(η 6-7,9-C 2B 10H 10Me 2)] in the presence of an atmosphere of CO also yields the compounds [N(PPh 3) 2][MBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)], but if the molybdenum compound is protonated in the absence of CO the complex [N(PPh 3) 2][MoBr(CO) 3(η 5-7,9-C 2B 9H 9Me 2)] is formed directly. The NMR data for the new compounds are reported and discussed, as are the possible pathways of their formation.

カーボンブラックの添加効果を利用した混合モリブデン塩の示差原子吸光分析

カーボンブラックの添加効果を利用した混合モリブデン塩の示差原子吸光分析

Six-coordinate molybdenum(II) complexes of 2,2′-bipyridine containing thiolate, nitrate, nitrite and pentane-2,4-dionate ligands

Substitution of 2,2′-bipyridine (bipy) in the seven-coordinate molybdenum(II) salt cis-[Mo(CO)2(bipy)2(NCMe)][BF4]2 by sodium 1,1-dimethylethanethiolate gives six-coordinate red trans,cis-[Mo(SCMe3)2(CO)2(bipy)] and by sodium N,N-diethyldithiocarbamate gives purple cis-[Mo(CO)2(S2CNEt2)(bipy)][BF4]. Tetrabutylamonium nitrate also displaces bipy to form green cis-[Mo(η2-NO3)(CO)2(bipy)][BF4]. Substitution of CO in the same seven-coordinate molybdenum(II) salt by nitrite produces green [Mo(ONO)(CO)(bipy)2][BF4], and by pentane-2,4-dione (acacH) gives purple [Mo(acac)(bipy)2][BF4]. The products of the reactions have been characterised by microanalysis and IR,1H NMR, and electronic absorption spectroscopy.

Coal liquefaction with encapsulated catalyst

The liquefaction of a bituminous coal has been studied in the presence of ammonium heptamolybdate catalyst added in the form of microcapsules. These were prepared by in situ encapsulation of an emulsion of the molybdenum salt in tetralin. The average diameter of the polymeric microcapsules (resulting from reaction between a diisocyanate and a polyfunctional amine) was about 6 ..mu..m. Autoclave testing of the catalytic effect on liquefaction showed, both for coal conversion and hydrogen consumption, that at 450/sup 0/C the microencapsulated catalyst is at least as good as ammonium heptamolybdate pre-impregnated on the coal from aqueous solution, and far better than powdered ammonium heptamolybdate. Microencapsulated catalysts of this kind appear to offer some advantages of convenience in use, stability in storage, and flexibility.

Molybdic and tungstic heteropolyanions for "ionic fixation" of acetylcholine in cholinergic motor nerve terminals.

The treatment of neuromuscular junctions with phosphomolybdic acid (PMA) and silicotungstic acid (STA) heteropolyanions permits the visualization of electron dense precipitates in the synaptic vesicles of the cholinergic motor nerve terminals. At the light microscopic level, the uncolored molybdenum salt is visualized after reduction to molybdenum blue. The blue coloration is confined to the nerve terminals. Since PMA and STA are known as strong precipitating agents of quaternary ammonium compounds (cations) it is supposed that they have insolubilized in situ the acetylcholine (Ach) of the synaptic vesicles by means of a rapid ionic interaction. Furthermore, in spite of the strong acidity of PMA and STA solutions, the ultrastructure of the treated tissue is not significantly altered but on the contrary seems to be well preserved. The ionic insolubilization of Ach, added to the good preservation of the ultrastructure prompted us to use the term "ionic fixation".

An assay for inorganic orthophosphate in the presence of alkaloids and related drugs

There have been many reported techniques for the determination of inorganic orthophosphate, largely utilising the formation of a yellow complex between the phosphate and a molybdenum salt, and the formation of a blue chromophore on reduction of the complex. The method of Fiske and Subbarow (1) employs l-amino-Znaphthol-Csulphonic acid as the reducing agent, and this technique is still widely used. Modifications to the basic procedure have included the direct measurement of the yellow phosphomolybdate complex to avoid reduction of susceptible compounds (2) and the extraction of the phosphomolybdate complex with organic solvents to prevent interference by inorganic ions (3, 4). Atkinson et al. (5), reported that incorporation of the non-ionic detergent Cirrasol ALN-WF, formerly called Lubrol-W, into the acid ammonium molybdate reagent prevented the interference in the phosphate assay by a number of simple compounds that adversely affect the conventional methods. Our studies on the effects of certain pharmacological agents on the active transport of calcium in muscle tissue, have led us to look for a reliable and simple method of determining levels of inorganic phosphate in the presence of alkaloids and related methyl xanthines, since these compounds form a white precipitate in the presence of phosphate and acid ammonium molybdate which renders the conventional assay inoperable.

STRAIN SELECTION BRADYRHIZOBIUM JAPONICUM AND SINORHIZOBIUM FREDII TO RESISTANT TO AMMONIUM MOLYBDATE IN GROWING MEDIUM

The article presents the results of the study of the resistance of Bradyrhizobium japonicum (Jordan, 1982) and Sinorhizobium fredii (Scholla, Elkan, 1984) strains, selection of the FSBSI ARSRI of Soybean, to ammonium molybdate in a nutrient medium. In the variant without introducing a molybdenum salt, from 47 strains of rhizobia of the B. japonicum species, 37 strains showed good growth, 3 strains-abundant and 7 strains-moderate growth of the bacterial mass stroke. When 1 g/l of ammonium molybdate was introduced into the nutrient medium, the growth intensity of the bacterial mass stroke of all tested B. japonicum decreased slightly; the number of moderately growing strains increased to 11, and one poorly growing strain appeared. When 10 g/l of ammonium molybdate was introduced into the nutrient medium, the strains of B. japonicum, showing abundant and good growth of bacterial mass, were not detected. 31 strains of rhizobia of this species have stopped their growth. In the variants with a nutrient medium MRS without a molybdenum salt and with 1 g/l molybdenum salt from 44 strains of rhizobia of the species S. fredii 93-95 % of pure cultures showed abundant and good bacterial mass stroke growth. When 10 g/l of ammonium molybdate was introduced into the nutrient medium, no rhizobia strains of the S. fredii species were found with abundant and good growth of the bacterial mass, 12 rhizobia strains of this species showed poor growth, and 4 strains stopped growing at this concentration of molybdenum salt in the nutrient environment. It was established that ammonium molybdate at a concentration of 1 g/l in a nutrient medium, practically does not affect the growth intensity of the bacterial mass stroke of strains B. japonicum and S. fredii.