Tungsten oxide alumina supported

Studies related to alumina-supported tungsten oxide metathesis catalysts also continue.Unsupported alumina tungstate, Al2(W04)3, has metathesis activity between 100 and 200° C it has been proposed that this difficult-to-reduce compound is a reasonable precursor to the active metathesis sites for tungsten oxide supported on 7-alumina. However, a controversy exists as to the presence of Al2(W04)3 as a major component on the surface of these catalysts Raman spectra do not show bands that can be attributed to Al2(W04)3. Evidence reported in the literature for the formation of aluminium tungstate on the surface is not valid because of impurities in the reference compounds used. The conclusion that this compound is not a major surface component does not completely rule out the possibility that it is involved in the catalytic active phase,especially since the number of active sites is extremely small, e.g., 10 sites per gram of... 

An unanticipated catalytic reaction of olefinic hydrocarbons was described in 1964 by Banks and Bailey.1 2 They discovered that C3-C8 alkenes disproportionate to homologs of higher and lower molecular weight in the presence of alumina-supported molybdenum oxide [Eq. (12.1)], cobalt oxide-molybdenum oxide, molybdenum hexacarbonyl, or tungsten hexacarbonyl at 100-200°C, under about 30 atm pressure ... 

Table 18.4 Selectivity (%) of tungsten carbide on alumina compared to the supported tungsten oxide precursor in FT reaction...

The response of the supported nickel oxide on alumina to an in situ experiment is very different from that presented earlier for the supported tungsten oxide, as shown in Figure 13. The Raman band of the supported nickel oxide on alumina is not affected by the removal of the moisture present on the sample surface (compare Figures 13(a) and 13(d)) and suggests that water molecules do not coordinate to the supported nickel oxide. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

The raw materials needed to supply about ten million new automobiles a year do not impose a difficult problem except in the case of the noble metals. Present technology indicates that each car may need up to ten pounds of pellets, two pounds of monoliths, or two pounds of metal alloys. The refractory oxide support materials are usually a mixture of silica, alumina, magnesia, lithium oxide, and zirconium oxide. Fifty thousand tons of such materials a year do not raise serious problems (47). The base metal oxides requirement per car may be 0.1 to 1 lb per car, or up to five thousand tons a year. The current U.S. annual consumption of copper, manganese, and chromium is above a million tons per year, and the consumption of nickel and tungsten above a hundred thousand tons per year. The only important metals used at the low rate of five thousand tons per year are cobalt, vanadium, and the rare earths. 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

Application of Raman spectroscopy to a study of catalyst surfaces is increasing. Until recently, this technique had been limited to observing distortions in adsorbed organic molecules by the appearance of forbidden Raman bands and giant Raman effects of silver surfaces with chemisorbed species. However, the development of laser Raman instrumentation and modern computerization techniques for control and data reduction have expanded these applications to studies of acid sites and oxide structures. For example The oxidation-reduction cycle occurring in bismuth molybdate catalysts for oxidation of ammonia and propylene to acrylonitrile has been studied in situ by this technique. And new and valuable information on the interaction of oxides, such as tungsten oxide and cerium oxide, with the surface of an alumina support, has been obtained. 

The reaction of u-butenes to give isobutylene is cataly zed by a wide variety of solid acids but requires relatively high temperature. Typical catalysts include alumina, halogenated alumina, amorphous silica-alumina, supported phosphoric acid, and supported tungsten or molybdemmi oxide. The most characteristic features of the skeletal isomerization of n-butenes... 

These catalysts consist of the oxides of vanadium, chromium, molybdenum or tungsten deposited by co-precipitation or by impregnation on a silica or silica—alumina support. The catalysts require an activation process before use, and for those containing chromic oxide this consists of... 

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