Tungsten oxide, mixture

Alkyne metathesis is a curious reaction in view of the fact that two alkyne triple bonds are cleaved and reconstructed simultaneously leading to different triple bonds. The first reported effective catalyst is a heterogeneous mixture of tungsten oxide and silica. Then Mortreux found that a catalytic system that consisted of Mo(CO)6 and resorcinol was effective for alkyne metathesis. As reported, the added alkynes come into equilibrium with different product... 

OCP (3) [Olefins Conversion Process] A process for making propylene by reacting ethylene with mixed refinery C4 streams. The catalyst is a mixture of tungsten oxide on silica (the actual metathesis... 

The influence of the laser and plasma parameters (such as wavelength, laser power density, pulse length, plasma temperature, electron and ion density and others) on the physical and chemical processes in a laser induced plasma with respect to the formation of polyatomic and cluster ions has been investigated for different materials (e.g. graphite, boron nitride, boron nitride/graphite mixture, boron carbide, tungsten oxide/graphite mixture and superconductors ). 

The introduction of an inert liquid may have an advantage in equilibrium-controlled reversible reactions. Tf the product is selectively more soluble in the liquid than the reactant, then the composition of the reacting mixture shifts from the equilibrium composition and better conversions are obtained. Zabor et al.58 have shown this to be the case during equilibrium conversion of propylene to isopropanol in the presence of an excess of water and tungsten oxide catalyst. Isopropanol is selectively more soluble in water than propylene, causing reduction of product concentration at the catalyst surface and resulting in better conversions of propylene. 

The reactivity of tungsten oxide is also slightly increased after it mechanical activation. In the case of activated WO3, 10 % of oxide reacts with the solution of phosphoric acid, while in the case of activated WO3 -V2O5 mixtures, the yield increases up to 13 %. 

Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO)6 in diphenylmethane (DPhM) in the presence of an Ar (80%) and O2 (20%) gaseous mixture at 90 °C [137]. Heating this amorphous powder at 550 °C under Ar yields snowflake-like dendritic particles consisting of a mixture of monodinic and orthorhombic WO2 crystals. Annealing... 

Molten Carbonate Fuel Cells (MCFCs) The development of molten carbonate fuel cells (MCFCs) started in 1951, when Boers and Ketlaar built a fuel cell with a mixture of sodium carbonate and tungsten oxide as electrolyte later they changed it to a mixture of lithium,... 

The oxidation of benzene to phenol can also be achieved using nitrous oxide as an oxidant in the presence of a catalytic system such as vanadium, molybdenum or tungsten oxides at 550 °C, and after addition of 30% of water to afford phenol in 10% yield . More effective catalytic systems have been investigated and zeolites show promise to be good catalysts for the oxidation of benzene to phenol with nitrous oxide . The use of zeolite catalysts has led to a reduction in the reaction temperature to 300-400°C, to the exclusion of water addition to the reaction mixture and to an increase in the yields up to 25-30% . Recently, direct oxidation of benzene to phenol by nitrous oxide has been commercialized . 

Only recently was a new caibothermal reduction process developed in which the WC is synthesized by a rapid carbothermal reduction of tungsten oxides in a vertical graphite transport reactor (RCR entrainment process) [3.49]. Rapid heating of the WO3/C mixture driven by thermal radiation allows conversion of the mixture into a carbide precursor (WCi. c) within very short reaction times (a matter of seconds). In a second step, additional carbon is added to the carbide precursor to form a mixture, which then imdergoes a second heat treatment to convert the precursor into substantially pure WC. 

Carbothermal reduction of tungsten oxides with carbon monoxide [3.47], or gas mixtures of CO/CO2, CO/H2, CH4/H2 [3.50], C2H4/H2, and C2H4/H2 [3.51], as well as by reaction between metal oxide vapor and solid carbon [3.52] have recently attracted attention for producing high surface area tungsten carbides (up to lOOm /g), for use as catalyst (see Section 10.4), and for nanophase WC/Co composite powders (see also Section 9.2.1.4) [3.53]. 

Mixtures containing 65% of tungsten with organic binders were developed as priming charges for surface flares [1]. Ignition of the dual metal-oxidant mixtures by IR irradiative heating was studied [2]. 

Although little experimental data is available, numerous patents have been issued for the vapor phase catalytic oxidation of various other derivatives containing the benzene nucleus, as well as heterocyclic compounds Thus, fluorene (diphenyl methane) is oxidized to fluorenone with air in the presence of a catalyst containing iron vanadate or other suitable metal salt of the fifth or sixth group of the periodic system at a temperature of 360° to 400°.1,2 Maleic acid and anhydride are formed by the catalytic oxidation of compounds of the furan series, such as furan, furfural alcohol, furfural, methyl furfural, hydroxymethylfurfural, pyromucic acid or mixtures, with air over catalysts of molybdenum, vanadium, or other metals.133 Dimethyl benzaldehyde is formed by oxidizing pseudocumene with air at 550° C. in the presence of a tungsten oxide catalyst. Molybdenum, vanadium, or tantalum oxide catalysts may also be used to form aromatic aldehydes from o-, m-, or p-xylenes, mesitylene, p-cymene, or o-chlorotoluene by air oxidation. Times of contact of 0.3 to 0.4 seconds... 

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