Vanadium trioxide, preparation

Vanadium Carbide. Vanadium pentoxide [1314-62-17, V2O5, or vanadium trioxide [1314-34-7] VO3, are the most satisfactory oxides for the preparation of VC. Vanadium pentoxide is best prepared by igniting chemically pure ammonium vanadate [7803-55-6] NH VO, in the presence of moist oxygen to avoid reaction with nitrogen V2O3 is obtained by reduction of V2O3 with hydrogen (see Vanadium compounds). 

Vanadium Disilicide, VSia, is prepared by reducing a mixture of vanadium trioxide and silicon with magnesium vanadium pentoxide can also be employed with the addition of fluorspar to the mixture.12 Gin used a mixture of the pentoxide, silica, and coke.18 Vanadium disilicide is a very stable compound it forms metallic prisms which melt at 1655° C., have a specific gravity of 4-42, and are hard enough to scratch glass. It is attacked by hydrofluoric acid, hydrogen chloride gas, and fused alkalis. 

Vanadium powder can be prepared by substituting V2O2 for the V20 as the vanadium source. The heat generated during the reduction of the trioxide is considerably less than for the pentoxide, so that only soHd products are obtained. The powder is recovered from the product by leaching the slag with dilute acid. 

The active phase, which is soHd at room temperature, is comprised of mixed potassium and sodium vanadates and pyrosulfates, whereas the support is macroporous siUca, usually in the form of 6—12 mm diameter rings or pellets. The patent Hterature describes a number of ways to prepare the catalyst a typical example contains 7 wt % vanadium pentoxide, 8% potassium added as potassium hydroxide or carbonate, 1% sodium, and 78 wt % siUca, added as diatomaceous earth or siUca gel, formed into rings, and calcined in the presence of sulfur dioxide or sulfur trioxide to convert a portion of the alkah metal salts into various pyrosulfates (81,82). 

Vanadium Oxytrichloride, VOCl3, commonly known as vanadyl chloride, is the easiest to prepare of all the halogen or oxyhalogen compounds of vanadium. It distils over as a yellow liquid when vanadium pentoxide is strongly heated, or when vanadiun trioxide is gently heated, in a current of chlorine. Addition of charcoal accelerates the reactions 9... 

However, this reaction is very slow in the absence of a catalyst. One of the mysteries during early research on air pollution was how the sulfur dioxide produced from the combustion of sulfur-containing fuels is so rapidly converted to sulfur trioxide in the atmosphere. It is now known that dust and other particles can act as heterogeneous catalysts for this process (see Section 15.9). In the preparation of sulfur trioxide for the manufacture of sulfuric acid, either platinum metal or vanadium(V) oxide (V205) is used as a catalyst, and the reaction is carried out at approximately 500°C, even though this temperature decreases the value of the equilibrium constant for this exothermic reaction. 

To obtain a high yield, it is important to use the right catalyst and the right material for containing the catalyst. With vanadium pentoxide in pyrex tubes, the yield is only 25 percent of the input furfural, but with a vanadium pentoxide/molybdenum trioxide/iron molybdate catalyst in nickel tubes, the yield is in the order of 75 percent. Interestingly, the best yields are obtained when the catalyst, prepared from appropriate ammonium salts, is cured with air at 300 °C in situ, and when it is then used directly at the reaction temperature of 270 °C without allowing it to cool down. 

By reduction of the trioxide with carbon.2 (5) By the thermite reduction process.3 A product which was 99 per cent pure has been obtained by this method or by reduction with vanadium carbide. (6) By electrolysis of a solution of the trioxide in fused calcium vanadate.4 The anode is made of carbon and the cathode is prepared by pulverizing ferro-vanadium and pressing the powder into a cone-shaped form. The current density used is 4.5 amperes per square inch of anode surface. 

Sulphur trioxide is prepared by the oxidation of sulphur dioxide with oxygen in the presence of a vanadium (V) oxide catalyst. It maybe prepared in the laboratory by distilling a mixture of concentrated sulphuric acid and phosphorus(V) oxide. It reacts violently with water to give sulphuric(VI) acid and is an important intermediate in the preparation of sulphuric acid and oleum. 

For the catalyst preparation REACHIM vanadium pentoxide, pure for analysis, and POCH antimony trioxide, of the same grade of purity, were used. The grounded mixture of vanadia and antimony trloxide in quartz ampoule sealed without any evacuation was placed in a cool oven, then it was heated slowly up to 973 K for 7 hours, annealed at this temperature for 30 hours and slowly cooled down to room temperature for 10 hours. One part of black powder obtained by this procedure was xidized at 673 K in air atmosphere for 30 hours another onewas reduced at the same temperature in vacuum (10 Torr) for 4 hours. 

In Fig. 5 X-ray diffraction patterns (XRDPs) of the used antimony trioxide (a), of antimony trioxide slowly heated from room temperature to 973 K for 5 hours (b), and of the freshly prepared catalyst are presented. As it is seen, slow heating of of antimony trioxide from room temperature to 973 K causes oxidative transformation of the antimony trloxide into a-antimony tetroxide containing traces of /9-antimony tetroxide. While, the similar heating of the mixture of vanadia and antimony trioxide followed by its annealing at 973 K results in formation of the mixture of crystals of vanadium antimonate, a—antimony tetroxide, and /3-antimony tetroxide. Vanadium antimonate is the base phase of this mixture. There are not lines of the starting oxides in XRDP of the catalyst. 

During the commercial preparation of sulfuric acid, sulfur dioxide reacts with oxygen in an exothermic reaction to produce sulfur trioxide. In this step, sulfur dioxide mixed with oxygen-enriched air passes into a reaction tower at about 420°C, where reaction occurs on a vanadium(V) oxide catalyst. Discuss the conditions used in this reaction in terms of its effect on the yield of sulfur trioxide. Are there any other conditions that you might explore in order to increase the yield of sulfur trioxide ... 

Sulfuric acid, one of the most important industrial chemicals, is prepared by a similar method. The acid anhydride of H2SO4 is sulfur trioxide, SO3, Direct oxidation of sulfur produces sulfur dioxide, SOj, which can be subsequently oxidized in the presence of a vanadium pentoxide (VjO ) catalyst to SO3 (see page 420 for discussion of catalysis). The hydration reaction of SO3 is very exothermic. The heat liberated vaporizes the water, and the steam cloud carries away much of the SO3 in the form of a sulfuric acid mist. For more efiectlve results, the SOj is dissolved in concentrated H2SO4 to form disulfiiric acid, 1 38307, while water is added continuously to maintain a constant con-... 

Besides the use of vanadium-based catalysts, a wide variety of other catalyst compositions were reported. A recent review focussed on FeSbO based catalysts promoted by appropriate additives as suitable for the ammoxidation of alkyl-substituted aromatics and hetero aromatic compounds. A unique preparation method of a fluid-bed catalyst is presented using nitric acid oxidation of antimony trioxide catalyzed with iron ions. The catalysts thus prepared have superior catalytic and physical properties. [78]. In addition, some unique compositions were reported by different research groups. For instance, new ammoxidation catalysts based on rhenium carbonyl cluster complexes containing antimony and bismuth ligands were reported by Adam et al. [79]. Single-site multifunctional catalysts based on [Cu RUj C ] nanocluster anchored to inner walls of mesoporous silica were also used in the ammoxidation of 3P [80]. 

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