Tungsten Oxide Catalysts Research Articles

Catalytic properties of supported tungsten oxide catalysts

Catalytic properties of the WO3-MgF2 preparations obtained by the impregnation (I-series) and coprecipitation (C-series) method have been determined in acid environment. Various tungsten complexes causing the Lewis and Broensted acidity have been observed by IR spectroscopy. For catalysts of the I-series the isolated tungsten species were responsible for the activity in acid reactions, whereas for the C-series preparations the polymerized oxide was also involved.

Activation of tungsten oxide catalyst on SiO 2 surface by low-temperature plasma

The disproportionation of alkenes, in particular propene, promotes an improvement in the balance of crude oil processing and is one of the possibilities of gaining a new raw-material source for petrochemical syntheses. The disproportionation processes comprising conversion of alkenes into the two qualitatively new ones proceed only in the presence of the catalysts. As the catalyst, tungsten oxide which is applicable on the silica gel carrier may be used. It was a practical effort which led the authors to study the plasma interaction with the WO{sub 3}/SiO{sub 3} catalyst to accelerate and achieve the more effective preparation of the catalyst needed for heterogeneous catalysis of propene, and thus to positively influence the catalyst quality. On the basis of investigation carried out on the catalyst's activity, selectivity, and lifetime - in relation to propene disproportionation - it may be stated that: the equilibrium degree of conversion is attainable with lower W/F values (W = mass of catalysts, F = feed rate); the composition of disproportionation products is shifted more to the ethylene formation; the lifetime of the catalyst remains unchanged; and for both dimerization and cracking no active centers are formed.

Comparison of the acidities of [formula omitted] and ultrastable faujasite catalysts

The acidity of WO 3 on γ-alumina is compared with that of ultrastable faujasite using both base adsorption techniques and model compound conversion studies. The addition of WO 3 to γ-alumina introduces Brønsted acidity, and the density of Brønsted sites is increased by high-temperature calcination. The acid sites displayed by the supported tungsten oxide catalyst are considerably weaker than those found in ultrastable faujasite.

Formation of 2-ethyl acrolein by gas phase aldol condensation

The gas phase aldol condensation between n-butyraldehyde and formaldehyde to give 2-ethyl acrolein, CH 2 C(C 2H 5) CHO, over a silica supported tungsten oxide catalyst, by feeding formaldehyde as hemiformal or trioxane, over a wide range of operating conditions has been studied. A maximum selectivity of about 95% to 2-ethyl acrolein based on n-butyraldehyde, at 275–300°C, by using a feeding molar ratio of formaldehyde (supplied as hemiformal) to n-butyraldehyde of about 2 to 1, with 50% n-butyraldehyde conversion, was found. The reaction studied could provide a viable alternative to the usual liquid phase process for the synthesis of 2-ethyl acrolein.

Activity of supported tungsten oxide catalysts for the metathesis of propene

The activity of several supported tungsten oxide catalysts for the metathesis of propene has been studied under temperature-programmed conditions. WO3/TiO2 was found to be active at moderate temperatures; its activity passes through a maximum when the reaction temperature is decreased from 670 to 450 K. WO3/ZnO is less active and its activity as a function of the reaction temperature goes through a maximum under certain conditions. In contrast to these catalysts and to the earlier reported behaviour of the well known WO3/Al2O3 catalyst, the activity of the WO3/SiO2 catalyst steadily increases for reaction temperatures up to 860 K. In this respect the WO3/SiO2–Al2O3 catalyst behaves like the WO3/SiO2 catalyst and not like the WO3/Al2O3 catalyst.

Catalytic liquefaction of various coals using a mixture of carbon monoxide and water

In a batch-autoclave, twenty coals were liquefied using a cobalt-molybdenum oxide catalyst with a mixture of CO and H 20 at 400 °C with or without vehicle oil. Furthermore, lignite and peat were liquefied on tungsten oxide catalyst at 300 °C in the absence of CO. The reactivity of coal in this liquefaction is found to depend strongly on its rank. The vehicle oil significantly influences the extent of the water-gas shift reaction, especially when bituminous coals are liquefied, by dissolving such coals. Liquefaction of coal by this process is considered to take place via three routes: hydrogenolysis by the nascent hydrogen produced from the shift reaction; dissolution of coal into the vehicle oil which is an initial stage of hydrogenolysis; and a solvolytic reaction with H 2O, such as hydrolysis.

Methyl methacrylate by gas phase catalytic condensation of formaldehyde with methyl propionate

The gas phase catalytic condensation of formaldehyde with methyl propionate to methyl methacrylate over niobium, tantalum or tungsten oxide catalysts by feeding formaldehyde as hemiformal or trioxane has been studied. Experiments were carried out over a wide range of reaction temperatures, contact times and reagent molar ratios to find the most favourable conditions for high methyl methacrylate yields and selectivities. The best results were obtained over: a) the niobium oxide catalyst by feeding formaldehyde as hemiformal and b) the tungsten oxide catalyst by feeding formaldehyde as trioxane. The influence of the formaldehyde source on the reaction products and the mechanism of the catalysis are also discussed.

Activity of supported tungsten oxide catalysts for the metathesis of propene

A high-temperature activation under inert gas of a WO 3 SiO 2 catalyst greatly increases the break-in rate and the catalytic activity for the metathesis of propene. During activation oxygen atoms and hydroxyl groups are eliminated from a tungsten oxide surface compound. As a result, tungsten ions become more exposed; some of these also undergo a change in oxidation state. The results suggest that the level of catalytic activity as well as the break-in rate depend on the number of these ions and on the rate of their formation. For a given catalyst type and structure, it depends primarily on the conditions of the activation whether a break-in appears or not. WO 3 Al 2O 3 catalysts are characterized by a maximum in the reaction rate as a function of the reaction temperature. They attain, under the conditions of the proposed activation, high activity in a very short time and, under certain circumstances, are affected by product hindrance.

Polymerization and Disproportionation of Lower Olefins over Tungsten Oxide on Alumina

The reaction of ethylene or propylene over alumina supported tungsten oxide catalyst has been investigated at 200eC, using a onventional closed circulation apparatus with reference to the nature of active site.Formation propylene, butene and polymerized products were obserbed in the re. action of ethylene, in P propylene was assumed to be produced bytdispr opor-tion ation of ethyleRe witradsorbed butene formed by dimerization of ethylene. On the other hand, propylene gave ethylene and butenes in almost the same amount. This fact indicatcd that b. ot. h. were prodgceq thr6ugh disproportionation of propylene, Propylene also gave polymers which were retained on the catalyst.According to the ehange of pretreatment temperature of the catalyst, both activity of the catalyst and distribution of the products changed remarkably. The activity of the catalyst fer the three types of reaction, i. e., disproportionation and polymerization of ethylene and disproportionation of propylene, was increased extensively by the evacuation above 400eC. Analysis by TPD method revealed that reduced tungsten appeared on the surface of the catalyst and it played a role of active site in these reactions.A close relationship was obserbed between the activity of propylene polymerization and the amount of pyridine adsorbed on the catalyst. This result suggested that polymerization of propylene proceeded on acidic site of the catalyst.

A Study of Catalysis by Uranium Oxide and Its Mixed Catalysts. III. A Comparison of the Uranium Oxide Catalyst with Vanadium Oxide, Molybdenum Oxide and Tungsten Oxide Catalysts for the Catalytic Oxidation of Carbon Monoxide

A Study of Catalysis by Uranium Oxide and Its Mixed Catalysts. III. A Comparison of the Uranium Oxide Catalyst with Vanadium Oxide, Molybdenum Oxide and Tungsten Oxide Catalysts for the Catalytic Oxidation of Carbon Monoxide