Vanadium pentoxide, catalyst with oxygen

The ethyl ester is prepared in 60 per cent yield by passing ethyl lactate with air or oxygen over a vanadium pentoxide catalyst. Boehringer Sohn, U. S. pat. 1,614,195 (1927). [C. A. ai, 746 (1927).]... 

Sulfur dioxide combines with oxygen on heating and in the presence of a catalyst. This reaction proceeds at temperatures between 400 to 700°C with vanadium pentoxide catalyst to make sulfuric acid ... 

Roiter and co-workers have investigated with the aid of 0 , the participation of vanadium pentoxide oxygen in reactions of oxidation. In the oxidation of naphthalene (51) on vanadium pentoxide enriched with 0 , no decrease of the content of this isotope in catalyst was discovered within the accuracy of measurements ( 10%). If all oxygen required for oxidation of naphthalene was removed from the vanadium pentoxide surface and the intermixing of oxygen inside catalyst were full, then the final content of in vanadium pentoxide should decrease to up to 10-30% of the original content. The authors have concluded from this... 

When reaction of oxidation of sulfur dioxide (32) is realized on vanadium pentoxide enriched with 0 , one could observe the decrease in the content of this isotope in catalyst, but it is still not a greater decrease than in the exchange with oxygen in similar conditions. If the oxidation of sulfur dioxide proceeded at the expense of surface oxygen of vanadium pentoxide then the extraction of from catalyst should be considerably accelerated in the process of reaction. The doubt as to the insufficient mobility of catalyst oxygen, in this case, due to high temperature of experiments (500-610°) is out of the question. The data obtained by Kasatkina for the transition in the process of catalysis of O - from vanadium pentoxide into the formed sulfur trioxide are in some contradiction to these results. 

Ortho-xylene may be oxidized directly by air in vapor phase over vanadium pentoxide catalysts under conditions resembling those used in oxidation of naphthalene to phthalic anhydride. The stability of the cyclic anhydride structure of phthalic anhydride at the temperatures required and in the presence of oxidizing conditions is, of course, the distinctive feature. Since the oxidation of o-xylene to phthalic anhydride requires the theoretical interaction of only six atoms of oxygen relative to the nine required by naphthalene, the amount of heat generated per unit of product is less, and the volume of diluent gases in the product stream may be lower. Because of decreased formation of quinones and color bodies, product purification should be easier. Very little is available by way of information relative to commercial operating conditions. Some laboratory results of early work showed a maximum conversion to total acids of 18.2 per cent when commercial xylene was oxidized in vapor phase over unfused vanadium oxide catalyst. Recent work with o-xylene showed a conversion of 42.7 per cent to phthalic anhydride over unfused vanadium oxide catalyst and conversions up to 61.7 per cent to phthalic anhydride plus fi.6 per cent to maleic... 

Selective Catalytic Reduction catalysts are similar to the vanadium pentoxide-anatase catalysts introduced by BASF and von Hayden in the 1960s for the oxidation of methyl groups in ortho-xylene. They were also coated onto cordierite supports. Vanadium pentoxide reacts with surface hydroxyl groups on the tita-nia to form active surface sites. In the case of oxidation catalysts, the monovanadyl species are active. However, for NOX reduction, at least two vanadyl groups, linked by an oxygen atom, form the selective site. These sites must be maximized. ... 

In the process (Fig. 1), sulfur and oxygen are converted to sulfur dioxide at 1000°C and then cooled to 420°C. The sulfur dioxide and oxygen enter the converter, which contains a catalyst such as vanadium pentoxide (V205). About 60 to 65% of the sulfur dioxide is converted by an exothermic reaction to sulfur trioxide in the first layer with a 2 to 4-second contact time. The gas leaves the converter at 600°C and is cooled to 400°C before it enters the second layer of catalyst. After the third layer, about 95% of the sulfur dioxide is converted into sulfur trioxide. The mixture is then fed to the initial absorption tower, where the sulfur trioxide is hydrated to sulfuric acid after which the gas mixture is reheated to 420°C and enters the fourth layer of catalyst that gives overall a 99.7% conversion of sulfur dioxide to sulfur trioxide. It is cooled and then fed to the final absorption tower and hydrated to sulfuric acid. The final sulfuric acid concentration is 98 to 99% (1 to 2% water). A small amount of this acid is recycled by adding some water and recirculating into the towers to pick up more sulfur trioxide. 

Vanadium pentoxide, VjOj (mp 690 °C), is one of the strongest catalysts used for dehydrogenations [478] and oxidations with air or oxygen 479], especially in the gas phase and at very high temperatures. It also catalyzes the hydroxylation of alkenes with aqueous hydrogen peroxide 34]. 

Vanadium Pentoxide Promoted by the Sulfates of Alkali Metals, The additions of sulfates of alkali metals are used as promoters for a number of industrial vanadium catalysts, e.g., vanadium catalysts for the industrial production of sulfuric acid, phthalio acid, and others (22). They essentially increase catalytic activity in relation to the exchange of molecular oxygen 4) (Table II) with the increase of promoting action in the series... 

For this reaction the comparison of activity of various oxides cannot be carried out because most of them transform in reaction conditions into nonactive sulfates. The exception is vanadium pentoxide whose activity strongly increases when promoted by sulfates of alkali metals. As is clear from Fig. 15, the catalytic activity of vanadium catalysts, with the addition of different sulfates of alkali metals, changes identically in reactions of isotopic exchange in molecular oxygen and in the oxidation of sulfur dioxide. 

The position of equilibrium in a reversible reaction is not changed by the presence of the catalyst. This conclusion has been verified experimentally in several instances. For example, the oxidation of sulfur dioxide by oxygen has been studied with three catalysts platinum, ferric oxide, and vanadium pentoxide. In all three cases the equilibrium compositions were the same. 

Because sulfur dioxide reacts slowly with excess oxygen, a catalyst, either vanadium pentoxide (V2O5) or finely divided platinum at a temperature of 400°C, is used. The reaction produces sulfur trioxide. 

The next step in the process is called the contact method because the sulfur dioxide and oxygen molecules are in contact with a catalyst, usually vanadium pentoxide, V2O5. When the sulfur dioxide and oxygen gases pass through a heated tube that contains layers of the pellet-size catalyst, the sulfur dioxide is converted to sulfur trioxide. To make sure the reaction is complete, contact with the catalyst takes place twice. 

Electrolytic oxidation of anthracene in 20 per cent sulfuric acid solution with 1 per cent of vanadium pentoxide present is carried out at 80° C. with lead electrodes and a current density of 300 amperes per square meter at 1.6 volts. Good yields have been claimed 10 for this process. Air under pressure has been used for the oxidation of anthracene in the form of dispersions in aqueous ferric sulfate solutions,20 or as a solution iu pyridine or dispersion in aqueous alkaline solutions preferably in the presence of catalysts 21 of copper, cobalt, nickel or lead compounds. Vanadium compounds have been found more active than chromium compounds for use as oxidation catalysts in the form of suspensions in the liquid phase, as in the preparation of aniline black.22 Anthracene suspended in water or dilute sulfuric arid or dissolved in a solvent as acetone is oxidized with ozone, or ozonized oxygen at ordinary temperatures.28... 

Maleic anhydride production. The oxidation of benzene to maleic anhydride over a vanadium pentoxide electrode has been studied by Pizzini et ai 90,91 Unfortunately, the quantities of benzene and maleic anhydride were not determined experimentally. Breckner et al. have studied the partial oxidation of butene to produce maleic anhydride over a vanadium phosphate catalyst. Reaction rate and oxygen activity were monitored in order to correlate catalyst selectivity with oxygen activity. The selectivity of the catalyst was found to increase as the oxygen activity of the catalyst decreased. Both the catalyst reactivity and oxygen activity were found to be dependent upon prior treatments. 

Removal of heat from the reaction. In the vapor phase catalytic oxidation of naphthalene to phthalic anhydride, the heat of reaction is so great that unless it is rapidly and thoroughly dissipated the temperature of the catalyst mass rises to a point where complete combustion only occurs. Further, there is a tendency for the pentoxide of vanadium to be reduced to lower oxides at the high temperatures used, particularly if the oxygen supply is limited. These lower oxides tend to combine with the phthalic anhydride and subsequently decompose to destroy the anhydride, so that simple limitations of the oxygen supply to prevent further oxidation of the hydrocarbon is not effective. 

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