Rhenium dispersion

Cost. The catalytically active component(s) in many supported catalysts are expensive metals. By using a catalyst in which the active component is but a very small fraction of the weight of the total catalyst, lower costs can be achieved. As an example, hydrogenation of an aromatic nucleus requires the use of rhenium, rhodium, or mthenium. This can be accomplished with as fittie as 0.5 wt % of the metal finely dispersed on alumina or activated carbon. Furthermore, it is almost always easier to recover the metal from a spent supported catalyst bed than to attempt to separate a finely divided metal from a liquid product stream. If recovery is efficient, the actual cost of the catalyst is the time value of the cost of the metal less processing expenses, assuming a nondeclining market value for the metal. Precious metals used in catalytic processes are often leased. 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

The rhenium interacts strongly with the oxygen atoms of the support and also with platinum platinum interacts less strongly with the support than rhenium. One is tempted to generalize that when one of the metals in a supported bimetallic cluster is noble and the other oxophihc, the oxophUic metal interacts more strongly with the support than the noble metal if the bimetalhc frame of the precursor is maintained nearly intact, then this metal-support interaction helps keep the noble metal highly dispersed. 

Reference has been made earlier to scattered rare metals, the five most important members of this particular group being gallium, indium, thallium, rhenium, and germanium. A common feature of these metals is that they do not form commercially significant mineral sources of their own, but are invariably produced from the processing of other mineral sources. The description given here pertains to rhenium, and serves as one example of these dispersed metals. 

Iodine-131-labeled Lipiodol, a polyiodinated poppy seed oil which becomes particulate on dispersion in aqueous media, has been used for some time in treatment of hepatocellular carcinoma by arterial injection. This targeting approach has been coupled with the superior radioactivity properties of rhenium radioisotopes by exploiting the lipid solubility of... 

Rhenium complex (37) has been used in the ring-opening metathesis polymerization of strained alkenes such as norbornene.37 The alkenes of the polymer backbone are predominantly Z, the polymer exhibiting high molecular weight and poly-dispersity. 

The reduction of rhenium salt in a PAN matrix and the formation of the polyconjugated polymer system proceed simultaneously and interdependently during IR-pyrolysis of a film. As result the thin film of carbon with ultra dispersed metal particles is formed on a surface of porous support (Fig. 2). The thickness of defectless Re-containing carbon film was 300 - 500 nm. The size of metallic particles was proved to be from 3 to 10 nm. The average content of rhenium in a metal-carbon composition was about 5 mass %. 

Elucidation of the structure of a solid catalyst is paramount to any understanding of its activity. Without such information, inferences about its activity would be speculation. Often it is instructive to determine the structure of a catalyst after a treatment such as oxidation, reduction, or exposure to a reactant, or with the catalyst in a particular state it may be helpful to compare a fresh catalyst with a spent or a regenerated catalyst. XAFS spectroscopy used in this manner is "static the structure of the catalyst is determined in a specific well-defined state determined by the treatment and gas environment during the measurement. Two such examples are discussed here the determination of the location of the isomor-phous substitution of a heteroatom (tin) into a zeolite framework (zeolite beta), and the structure of dispersed rhenium oxide supported on y-Al203. 

The chemistry of rhenium supported on alumina is of technological importance in heterogeneous catalysis. Rhenium oxide dispersed on... 

The most active catalysts are APR with 0.36 wt% Pt - 0.36 wt % Re ratio, usually used in industry. These catalysts has been prepared by method III, using Y-AI2O3 with preferential pore radius 6.0 - 10.0 nm. Average dispersity of the Pt sole was 1.5 nm. The activity of platinum-rhenium catalysts depends on the methods of preparation and increase in the raw I < II < III. The activity of catalysts was shown 1.61, 1.70, and 2.25 mol C6Hi2/mol Pt s, respectively, at this range (Tables 5 6). 

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