Vanadium pentoxide as catalyst

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

With vanadium pentoxide as catalyst in an acidic medium, sodium chlorate oxidizes hydroquinone to quinone. A procedure by Underwood and Walsh calls for stirring a mixture of the reactants in 1 I. of 2% sulfuric acid until the green... 

Graebe and Liebermann378 converted anthracene into anthraquinone by oxidation with chromic acid in glacial acetic acid, although it is preferable379 to use sodium chlorate and vanadium pentoxide as catalysts. However, anthraquinone can also be prepared in good yield by use of potassium permanganate ... 

Modem converter systems have cesium promoted ring type vanadium pentoxide as catalyst in the first and the last (fourth/fifth) passes and conventional vanadium pentoxide catalyst (also ring type) in the other two/three passes. A second waste heat boiler is provided to recover additional heat after the first pass of catalyst. A steam superheater can be provided in the waste heat recovery system, if required by the client in order to export the steam to nearby industry or to generate superheated steam for captive use. 

The sulfuric acid industry got a head start in the 1940s due to the invention of vanadium pentoxide as catalyst to convert sulfur dioxide to sulfur trioxide, popularly known as the contact process. This enabled large sulfuric acid plants of high capacity to be built to produce phosphoric acid for the manufacture of phosphatic fertilizers. 

Benzoselenadiazoles are aminated by treatment with equimolar quantities of hydroxylamine sulphate in concentrated sulphuric acid in the presence of vanadium pentoxide as catalyst the appropriate amines, e.g. (236), are isolated in moderate yields (9—37%). ... 

Phthalic anhydride is prepared by oxidizing o-xylene. The oxidation may be performed either in the gas phase with vanadium pentoxide as a catalyst or in the liquid phase with dissolved manganese, molybdenum, or cobalt salts as catalysts ... 

A third option involves oxidizing naphthalene, possibly with vanadium pentoxide as a catalyst. 

The most important starting materials for process A are 4,4, 4"-triamino-triphenylmethane, pararosaniline (119), and parafuchsin (118). Aniline and formaldehyde are treated at 170°C to form, apart from some formaldehyde-aniline intermediates, 1,3,5-triphenylhexahydrotriazine as the main component. Subsequent treatment with an acidic catalyst, for instance with hydrochloric acid, in excess aniline as a solvent initially affords 4,4 -diaminodiphenylmethane, which is finally oxidized to yield parafuchsin (118). Iron(III)chloride and nitrobenzene, which in the past were used as oxidants, are no longer used. The reaction is now performed by air oxidation in the presence of vanadium pentoxide as a catalyst. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

Maleic acid and anhydride are recovered as by-products of the oxidation of xylenes and naphthalenes to form phthalic acids, and are also made specifically by the partial oxidation of benzene over a vanadium pentoxide (V205) catalyst. This is a highly exothermic reaction, and several modifications of the basic process exist, including one using butylenes as the starting materials. 

As discussed above the preferred technology for NOx removal in nitric add plants is selective catalytic reduction (SCR) using ammonia as a reductant and in many cases vanadium-pentoxide-type catalysts. Unfortunately, this process does not remove of N2O (nitrous oxide)221. 

By oxidizing butyl alcohol with sodium chlorate and dilute sulfuric add, using vanadium pentoxide as a catalyst. Milas, J. Amer. Chem. Soc. 50, 493 (1928). 

A wide variety of catalysts have been tested for their behaviour in the SCR of NOi using NHa as reductant [7-10]. Most of the commercially utilized catalyst formulations contain vanadium pentoxide as the active component and titanium dioxide as the support material. However, the titania as a support presents some disadvantages, such as a lack of abrasion resistance, a low specific surface area and a high price. In addition, the anatase phase of titania has a poor thermal... 

Deactivation of SCR catalysts also occurs by solid-state reactions between the reagents or poisons and the catalytically active surface. The active metal oxides are thus reduced (or over oxidized) to inactive oxidation states. As an example, if, as often presumed, is the active form of vanadium, then the formation of vanadium pentoxide (as a separate phase) would result in a loss of activity. Alternately, vanadium may be reduced to vanadium +3 or less which, again, may be inactive. 

Benzene oxidation using a vanadium pentoxide/pumice catalyst was first studied at the time that the phthalic anhydride process was being developed. Weiss and Downs discovered that maleic anhydride was formed in significant amounts. They concluded that the maleic anhydride was produced via benzoquinone as the intermediate. The yields of maleic anhydride were not high with the unselec-tive vanadium or molybdenum oxide catalysts being tested at that time. 

C. Fumaric acid from furfural. Place in a 1-litre three-necked flask, fitted with a reflux condenser, a mechanical stirrer and a thermometer, 112 5 g. of sodium chlorate, 250 ml. of water and 0 -5 g. of vanadium pentoxide catalyst (1), Set the stirrer in motion, heat the flask on an asbestos-centred wire gauze to 70-75°, and add 4 ml. of 50 g. (43 ml.) of technical furfural. As soon as the vigorous reaction commences (2) bvi not before, add the remainder of the furfural through a dropping funnel, inserted into the top of the condenser by means of a grooved cork, at such a rate that the vigorous reaction is maintained (25-30 minutes). Then heat the reaction mixture at 70-75° for 5-6 hours (3) and allow to stand overnight at the laboratory temperature. Filter the crystalline fumaric acid with suction, and wash it with a little cold water (4). Recrystallise the crude fumaric acid from about 300 ml. of iif-hydrochloric acid, and dry the crystals (26 g.) at 100°. The m.p. in a sealed capillary tube is 282-284°. A further recrystaUisation raises the m.p. to 286-287°. 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

About 80% of the vanadium now produced is used as ferrovanadium or as a steel additive. Vanadium foil is used as a bonding agent in cladding htanium to steel. Vanadium pentoxide is used in ceramics and as a catalyst. 

Chemically, 2,2,2-trifluoroethanol behaves as a typical alcohol. It can be converted to trifluoroacetaldehyde [75-90-1] or trifluoroacetic acid [76-05-1] by various oxidi2iag agents such as aqueous chlorine solutions (51) or oxygen ia the preseace of a vanadium pentoxide catalyst (52). Under basic conditions, it adds to tetrafluoroethylene and acetylene to give, respectively, 1,1,2,2-tetrafluoroethyl 2/2/2 -trifluoroethyl ether [406-78-0] (53) and... 

Monosaccharides such as glucose and fmctose are the most suitable as starting materials. When starch is used, it is first hydrolyzed with oxahc acid or sulfuric acid into a monosaccharide, mainly glucose. It is then oxidized with nitric acid in an approximately 50% sulfuric acid solution at 63—85°C in the presence of a mixed catalyst of vanadium pentoxide and iron(III) sulfate. 

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

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). 

The most popular SCR catalyst formulations are those that were developed in Japan in the late 1970s comprised of base metal oxides such as vanadium pentoxide [1314-62-1J, V20, supported on titanium dioxide [13463-67-7] Ti02 (1). As for low temperature catalysts, NO conversion rises with increasing temperatures to a plateau and then falls as ammonia oxidation begins to dominate the SCR reaction. However, peak conversion occurs in the temperature range between 300 and 450°C, and the fah-off in NO conversion is more gradual than for low temperature catalysis (44). 

Selective catalytic reduction (SCR) is cmrently the most developed and widely applied FGT technology. In the SCR process, ammonia is used as a reducing agent to convert NO, to nitrogen in the presence of a catalyst in a converter upstream of the air heater. The catalyst is usually a mixture of titanium dioxide, vanadium pentoxide, and hmgsten trioxide. SCR can remove 60-90% of NO, from flue gases. Unfortunately, the process is very expensive (US 40- 80/kilowatt), and the associated ammonia injection results in an ammonia slip stream in the exhaust. In addition, there are safety and environmental concerns associated with anhydrous ammonia storage. 

Vanadium pentoxide and mercuric oxide were used as catalysts for the hydrogen peroxide oxidation of bis(phenylthio)methane to its monooxide 17a31 (equation 5). From the synthetic point of view, it is interesting to note that vanadium pentoxide, in addition to its catalytic action, functions also as an indicator in this reaction. In the presence of hydrogen peroxide, the reaction mixture is orange while in the absence of hydrogen peroxide a pale yellow colour is observed. Thus, it is possible to perform the oxidation process as a titration ensuring that an excess of oxidant is never present. 

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