Thermal activation of hydrocarbon C-H bonds by Cp*M(NO) complexes of molybdenum and tungsten

Gentle thermolysis of appropriate CpM(NO)(hydrocarbyl)(2) complexes (Cp = eta(5)-C(5)Me(5)) of molybdenum and tungsten results in loss of hydrocarbon and the transient formation of 16-electron CpM(NO)-containing complexes such as CpM(NO)(alkylidene), CpM(NO)(eta(2)-benzyne), CpM(NO)(eta(2)-acetylene), and CpM(NO)(eta(2)-allene) (M = Mo, W). These intermediates effect the single, double, or triple activation of hydrocarbon C-H bonds intermolecularly, the first step of these activations being the reverse of the transformations by which they were generated. This Account summarizes the various types of C-H activations that have been effected with these nitrosyl complexes and also describes the results of kinetic, mechanistic, and theoretical investigations of these processes.     

Alumina-supported catalysts for propane oxidative dehydrogenation from mixed VXM(6−X)O19 (M=W, Mo) hexametalate precursors

γ-Al₂O₃ supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW₅O₁₉⁵⁻, V₂W₄O₁₉⁴⁻, VMo₅O₁₉⁵⁻ and V₂Mo₄O₁₉⁴⁻) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and ⁵¹V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state ⁵¹V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VO_x/γ-Al₂O₃ was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al₂O₃ surface.     

含氧酸根检测方法的研究现状及质谱法在钨钼分离中的应用前景

溶剂萃取法具有操作简单、回收率高、产品纯度高等优点，被广泛应用于钨钼分离。分离过程中钨钼离子形态会影响与萃取剂的结合方式及萃取历程，因而研究钨钼的离子形态变化有助于深入了解钨钼分离机理，进而指导工业生产。在水溶液中，钨钼的离子形态以钨钼含氧酸根形式存在，研究钨钼离子形态的本质即研究不同钨钼含氧酸根形式对萃取分离过程的影响。本工作综述了水溶液中含氧酸根离子形态的仪器分析方法，发现ESI-MS(电喷雾质谱法)在监测萃取过程中钨钼离子形态转化路径中具有潜在应用，并对ESI-MS在湿法冶金领域中监测钨钼离子形态及其转化规律的应用进行了展望，旨在为今后深入了解钨钼分离机理、定向调控钨钼分离过程及工业生产提供理论指导。     

酸性溶液中钨钼离子的电化学行为

为加大钨钼电化学性质的差异实现钨钼分离,使钨钼形成钨磷、钼磷杂多酸,采用循环伏安法研究酸性条件下含钨钼溶液及钨磷、钼磷杂多酸的电化学行为,获得多种溶液体系的循环伏安曲线. 结果表明,研究体系中钨的还原电位较钼高,但二者电位差小于0.1 V,无法利用电化学性质差异高效分离;而将钨和钼形成杂多酸体系后,钼磷杂多酸还原峰电位为0.401 V,钨磷杂多酸为0.1949 V,加入磷酸增大了钨钼离子电位差,可优先将钼还原.     

合成高比表面氮（碳）化钼（钨）研究综述

高比表面的氮化钼（钨）和碳化钼（钨）在催化加氢脱氢反应中表现出高的活性，成为催化领域中一种新型催化材料而受到重视。本文从高比表面氮化钼（钨）和碳化钼（钨）的合成和表征方面系统地综述了这一新材料的研究情况，对存在的问题给予了分析。     

The impact of solvent extraction and ion exchange on the hydrometallurgy of tungsten and molybdenum

This paper is concerned with the impact that solvent extraction and/or ion exchange has on the design of hydrometallurgical processes for the recovery of tungsten and molybdenum. The chemistries of tungsten and molybdenum will be discussed and flowsheets for the commercially important products will be presented.     

用离子交换树脂回收钼酸根离子、钨酸根离子的研究

分别采用静态和动态的方法,对W305-C钨钼吸附专用树脂吸附钨、钼的最佳条件及最大吸附容量进行了深入地研究。采用静态的方法研究的各种条件如pH值等对树脂吸附钨、钼的影响,测定了最适宜的条件及最大静态吸附量;采用动态的方法测定了树脂的吸附容量,研究了流速对钨、钼离子在W305-C树脂上的吸附量的影响,同时也研究了氨水浓度对树脂解吸的影响。结果表明,在pH=3.74,流速为3mL／min树脂对钨的吸附量最大;pH=3,流速为3mL/min时,树脂对钼的吸附量最大。     

High-temperature electrochemical synthesis of carbides, silicides and borides of VI-group metals in ionic melts

Possible systems and conditions have been determined for the electrosynthesis of carbides, silicides and borides of chromium, molybdenum and tungsten on the basis of thermodynamic analysis of chemical and electrochemical reactions involved in high temperature electrochemical synthesis. Electrosynthesis of powdered molybdenum and tungsten carbides has been carried out under thermodynamic conditions from halide–oxide, under excess CO₂ pressure, and tungstate–molybdate–carbonate melts. Electrosynthesis of powdered silicides and borides of chromium, molybdenum and tungsten has been realized under kinetic conditions. Oxide and halide–oxide electrolytes have been developed for the electrodeposition of molybdenum and tungsten carbide coat ings.     

Phase transformation in the synthesis of Ba(Ti1-xMx)O3-based PTCR ceramic

Systems based on BaTiO₃ with aliovalent substitutions of titanium by niobium, tantalum, molybdenum and tungsten have been investigated. The effect of substitution on the microstructure and electrophysical properties of ceramic is shown. Novel compounds with perovskite structure have been synthesized.     

Ring-Opening Metathesis Polymerization of 5,6-Bis(Chloromethyl)-Norbornene by Tungsten(II) and Molybdenum(II) Complexes

The reaction of endo,endo-5,6-bis(chloromethyl)bicyclo[2.2.1]hept-2-ene in the presence of seven-coordinate tungsten(II) and molybdenum(II) complexes of the type [MCl(M'Cl₃)(CO)₃(NCMe)₂] (M'=W, Mo; M=Sn, Ge) leads to ring-opening metathesis polymerization and to the formation of high-molecular-weight soluble polymers with dispersity index in the range 1.4-2.0 and number average molecular weights in the range 300 000-790 000 g mol^-1. The geometric structure of these polymers was determined by means of ¹H- and ¹³C-NMR spectroscopy. Molybdenum catalysts gave polymers with lower cis vinylene content (20-50%), whereas tungsten catalysts gave polymers with higher cis vinylene content (84-95%).     

地质化探样品中微量钨、钼的光谱定量测定

本文对微量钨、钼光谱定量测定作了改进。采用浅孔电极．以氯化镉酸性溶液作载体．以分析线旁背景作内标,定量测定钨、钼。适应1：5万区域化探样品的测定要求。本法有效地改善了微量钨、钼元素的蒸发行为。该方法快速．简捷,准确．成本低。适合于大批量的地质化探样品的测定。     

Novel phosphorus-doped alumina-supported molybdenum and tungsten carbides: synthesis, characterization and hydrogenation properties

The effect of atomically dispersed phosphorus on Mo₂C- and WC-supported -Al₂O₃ has been studied. Phosphorus was introduced via molybdenum or tungsten heteropolyanions. Mo- and W-based heteropolyanions were used to synthesize supported materials. Propene and tetralin hydrogenation were used as molecular probe reactions to test the activity and selectivity of the alumina-supported molybdenum or tungsten carbides. The effect of phosphorus on the hydrogenation activity of materials was also considered. Catalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and CO chemisorption. Phosphorus was found to increase significantly the activity of molybdenum and tungsten carbides. Supported molybdenum carbides are highly dispersed. Tungsten carbide particles are well dispersed with sizes ranging from 2 to 4 nm. To check the stability of carbides they were characterized after catalytic runs.     

利用离子交换树脂提取钨、钼的技术进展

对近年来利用离子交换树脂回收钨、钼离子进行了综述,分别讨论了回收钨、回收钼的树脂选用与使用条件,并且对分离含钨溶液中微量钼的技术进行了讨论。     

Interaction of certain oxides,carbides and high-melting metals at high temperatures

Conclusions The greatest stability in contact with BeO is shown by tungsten: with MgO, by molybdenum and tungsten; and with stabilized zirconium oxide, by molybdenumThe most resistant material in contact with the molybdenum up to 2100° is tantalum carbide, and the interaction between molybdenum and zirconium, hafnium and niobium carbide begins at 1800–2200°.     

卡尔曼滤波分光光度法同时测定钼(Ⅵ)钨(Ⅵ)钒(Ⅴ)三组分混合体系

在研究了Tiron与钼(Ⅵ)、钨(Ⅵ)、钒(Ⅴ)的显色反应基础上,对采用卡尔曼滤波分光光度法(简称KF法)同时测定钼、钨、钒三组分混合体系进行了探讨。对10份不同比例的钼、钨、钒标准混合液的测定,平均回收率分别为103.4％、102.0％和99.31％。标准偏差分别为3.48％、1.15％及2.16％。应用于工具钢标样及杂多酸合成样的分析,获得满意结果。     

二茂二氯化钛或锆与二茂基氯化钐复合催化乙烯聚合

分别以二茂二氯化钛(Cp2TiCl2)和二茂二氯化锫(Cp2ZrCl2)与钐茂金属催化剂复合组成催化体系，并以甲基铝氧烷为助催化剂，进行宽分子量分布聚乙烯合成研究。研究发现与使用Cp2TiCl2和二(甲基茂基)氯化钐复合体系相比，使用其与二(特丁基茂基)氯化钐[(t—BuCp)2SmCl]复合体系能得到具有较高粘均分子量的聚乙烯。同样，使用Cp2ZrCl2与(t—BuCp)2SmCl复合体系也能得到具有较高粘均分子量的聚乙烯。且使用含(t-BuCp)2SmCl复合体系得到分子量分布指数达3．5以上的聚乙烯。     

金属矿中钨钼铋检测方法研究综述

我国多金属矿中钨钼铋能否高效率的开发利用,提高其检测水平是至关重要的一部分。对金属矿中钨、钼及铋的检测方法进行了综述,为其检测提供有效参考。     

Prospects for using Mo- and W-containing catalysts in hydroisomerization: A patent review. II: Catalysts based on molybdenum and tungsten carbides

Patent information on the production of catalytic systems containing molybdenum and tungsten carbides and their application in the hydroisomerization of paraffinic hydrocarbons is reviewed. Analysis shows that modifying acid supports with molybdenum and tungsten carbides solves the problem of creating a stable catalyst for the hydroisomerization of paraffinic fractions. The resulting catalyst is resistant to sulfurcontaining impurities in hydroisomerization feedstock.     

Rhenium,tungsten and molybdenum as substitutes for plantinum in aromatics hydrogenation catalysts

Three metal substitutes for platinum on alumina-supported catalysts have been investigated. These metals are rhenium, tungsten and molybdenum. In the absence of platinum, these metals are catalytically inactive. At high hydrogenation temperatures (≥100°C) rhenium, tungsten and molybdenum appear to substitute platinum up to at least 66.7, 50 and 33.3% of the platinum atoms, respectively, providing almost the same conversion as platinum. At low hydrogenation temperatures (～50°C), the catalyst containing 0.6 wt% Pt is more active than those containing metallic combinations. At low reaction temperatures, in particular for high platinum substitution ratios, tungsten appears functionless whereas molybdenum may act as an inhibitor for platinum.     

Prospects for using Mo- and W-containing catalysts in hydroisomerization. a patent review. Part 1: Catalysts based on molybdenum and tungsten phosphides

Patent information on methods used for preparing catalytic systems containing molybdenum and tungsten phosphides and employing these systems in the hydroisomerization of paraffinic hydrocarbons are analyzed. Analysis of the patent information shows that modifying acidic supports with molybdenum and tungsten phosphides allows us to create a catalyst for the hydroisomerization of paraffinic fractions that is stable and resistant to sulfur impurities contained in the hydroisomerization feedstock.