Rhenium catalytic

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. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

The use of rhenium-based systems for the epoxidation of olefins has increased considerably during the last ten years [87]. In 1989, Jgrgensen stated, the catalytic... 

The first catalytic study of Reaction 1 was published in 1902 by Sabatier and Senderens (1) who reported that nickel was an excellent catalyst. Since that time, the active catalysts were identified as the transition elements with unfilled 3d, 4d, and 5d orbitals iron, cobalt, nickel, ruthenium, rhenium, palladium, osmium, indium, and platinum, as well as some elements that can assume these configurations (e.g., silver). These are discussed later. For practical operation of this process,... 

Immediately upon addition of the urea-hydrogen peroxide adduct to the solution containing methyltrioxorhenium, a yellow color develops due to formation of the catalytically active rhenium peroxo complexes.3... 

The catalytic system used in the Pacol process is either platinum or platinum/ rhenium-doped aluminum oxide which is partially poisoned with tin or sulfur and alkalinized with an alkali base. The latter modification of the catalyst system hinders the formation of large quantities of diolefins and aromatics. The activities of the UOP in the area of catalyst development led to the documentation of 29 patents between 1970 and 1987 (Table 6). Contact DeH-5, used between 1970 and 1982, already produced good results. The reaction product consisted of about 90% /z-monoolefins. On account of the not inconsiderable content of byproducts (4% diolefins and 3% aromatics) and the relatively short lifetime, the economics of the contact had to be improved. Each diolefin molecule binds in the alkylation two benzene molecules to form di-phenylalkanes or rearranges with the benzene to indane and tetralin derivatives the aromatics, formed during the dehydrogenation, also rearrange to form undesirable byproducts. 

The reactions of olefins with non-organometallic Tc(VII) compounds behaved similarly. In a recent study, [Tc03C1(AaA)] (86a) (in which AA stands for aromatic diamine derivatives) was shown to react quantitatively with olefins, and produce the corresponding Tc(V) diolato-complex [TcOC1(OaO)(AaA)] (87a). The process could not be run catalytically, as Tc(V) complexes tend to undergo disproportionation rather than reoxidation in the presence of water [97]. These alkene-glycol interconversions could not be performed with the analog Re(VII) compound. Rhenium displays completely contrary behaviour, in that alkenes can... 

Figure 3.53 shows the volume of CO produced, and the turnover number of the rhenium catalyst, as a function of the charge passed. Over 14 hours of electrolysis the Re catalyst underwent 300 catalytic cycles without loss of activity and showed no degradation, as seen by isolation and characterisation... 

Das, T.K., Jacobs, G., Patterson, P.M., Conner, W.A., Li, J., and Davis, B.H. 2003. Fischer-Tropsch synthesis Characterization and catalytic properties of rhenium promoted cobalt alumina catalysts. Fuel 82 805-15. 

Rheniforming [Rhenium reforming] A catalytic reforming process developed by Chevron Research Company. The catalyst formulation includes rhenium. First announced in 1967 and first commercialized in 1970 by 1988, 73 units had been licensed. 

Ultraforming A catalytic reforming process developed by Standard Oil of Indiana and licensed by Amoco Oil Company. The catalyst contains platinum and rhenium, contained in a swing reactor - one that can be isolated from the rest of the equipment so that the catalyst can be regenerated while the unit is operating. The first unit was commissioned in 1954. 

The regioselective borylation of alkanes can be achieved either catalytically or stoichiometrically using a host of metal complexes such as rhenium analogs. Such processes can be photochemically or thermally induced (Equation (19)).30 30a 30c... 

According to the general postulates presented, a dioxorhenium(VII) species intervenes along the reaction pathway. Attempts to detect it under the conditions of the catalytic experiments were not successful. Indeed, species A and B were not seen either 1 was the only rhenium species found by NMR spectroscopy. In an attempt to provide other validation for a rhenium(VII) intermediate, other experiments were carried out. 

The catalytic cycle can be considered in two parts. First, a rhenium(V) species is generated from MeRe(NAr)20 as (MeO)3PO is formed. This step has been studied independently, because 22 has been independently isolated and characterized. A reaction occurs between 22 and PMe2Ph... 

The catalytic capabilities of rhenium compounds burst on the scene about one decade ago, featuring MeRe03 as a catalyst for reactions of hydrogen peroxide. It was quickly verified that peroxorhenium(VII) compounds were the active intermediates. With them, practical reactions and fundamental questions of mechanism could then be resolved. 

---