Tungsten Oxide Catalysts

The four doped tungsten oxide catalysts (noted above) were synthesized and used in this study. The catalysts were analyzed by scanning electron microscopy (SEM), x-ray difBaction (XRD), and electron... 

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. 

Nozaki F, Ohki K (1972) A study of catalysis by uranium oxide and its mixed catalysis, 3. Comparison of uranium oxide catalysts with vanadium oxide, molybdenum oxide and tungsten oxide catalysts for catalytic oxidation of carbon monoxide. Bull Chem Soc Jap 45 9473... 

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... 

In the early literature it was reported that Si02-Al203 [10,11] and supported tungsten oxide [11] had high activity and selectivity for -caprolactam. Tungsten oxide catalysts prepared from the hydrolysis of WClg and supported on silica gel were more caprolactam selective than the catalyst prepared from ammonium tungstate... 

The apparatus was later modified so that the products from reactor 1 passed through a cooling coil to trap hydrocarbons greater than Cg. The remaining products were passed over the tungsten oxide catalyst in reactor 2. The product distribution was that which would be expected from isomerization alone, with little cracking, and the lifetime of the catalyst was much greater. 

Mace and Bonilla have established a rate equation for the direct hydration of ethylene over supported tungsten oxide catalyst which uuhcates that hydration proceeds by a surface reaction without preferential adsorption of either ethylene or water and without retardation by strong adsoiption of ethyl alcohol. 

The disproportionation of propylene on supported tungsten oxide catalysts is thought to proceed via a cyclobutane intermediate as follows. 

The number of available surface sites for isopropanol adsorption of bulk tungsten trioxide and monolayer supported tungsten oxide catalysts, even mesoporous nanoparticles, is orders of magnitude (0.9-6 pmol/m ) lower than the heteropolyacids (8-55 pmol/m ). This observation cannot be attributed to the surface structure because all these materials possess polymerized WOg species with octahedral coordination (see Table 5.1). Moreover, no correlation is observed with the specific surface area and the pore diameter because high surface area, mesoporous monolayer supported catalysts possess lower Ns than HPAs. In fact. Table 5.1 shows that those materials do not possess microporosity the specific surface area is only external surface area. This observation shows that the adsorption of alcohol occurs exclusively at the outermost surface layer of WO3 and monolayer supported tungsten oxide catalysts. 

C. D. Baertsch, K.T. Komala, Y.H. Chua and E. Iglesia, Genesis of Brpnsted acid sites during dehydration of 2-butanol on tungsten oxide catalysts, J. Catal, 205(1), 44-57, 2002. 

D.S. Kim, M. Ostromecki and I.E. Wachs, Surface stractures of supported tungsten oxide catalysts under dehydrated conditions, J. Mol Catal. A-Chem., 106(1-2), 93-102, 1996. 

Gutierrez-Alejandre, A., Ramirez, J., and Busca, G. The electronic structure of oxide supported tungsten oxide catalysts as studied by UV spectroscopy. Catal Lett. 1998, 56, 29-33. 

Basrur, A.G., Patwardhan, S.R., and Vyas, S.N. Propene metathesis over silica-supported tungsten oxide catalyst—Catalyst induction mechanism. J. Catal. 1991, 127, 86-95. 

Andreini, A. and Mol, J.C. Activity of supported tungsten oxide catalysts for the metathesis of propene. J. Chem. Soc., Faraday Trans. 1 1985,81,1705-1714. 

Extensively used in the polyethylene industry, ethene can be obtained, along with 2-butene, by metathesis disproportionation of propene in the presence of alumina- or silica-supported molybdenum or tungsten oxide catalysts [1] ... 

Thus, 1,6-heptadiene is readly produced by cyclo-pentene ethenolysis in the presence of molybedenum or tungsten oxide catalysts ... 

Other related cyclic olefins, 1,3-cyclohexadiene and vinylcyclohexene, are reported to be formed as main products from butadiene over tungsten oxide catalysts [24]. Under the reaction conditions, hexatriene, resulting from the intermolecular metathesis of butadiene, underwent subsequent cyclization to 1,3-cyclohexa-diene ... 

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