Catalysts containing rhenium

The data on the catalyst containing rhenium alone indicate signficant chemisorption of carbon monoxide, but no chemisorption of hydrogen. As expected, the platinum catalyst chemisorbs both carbon monoxide and hydrogen, and the values of CO/M and H/M are nearly equal. The platinum-rhenium catalyst exhibits a value of CO/M about twice as high as the value of H/M. This result approximates what one would expect if hydrogen chemisorbed on only the platinum component of the catalyst. While this chemisorption behavior is consistent with the possibility that the platinum and rhenium are present as two separate entities in the catalyst, they do not rule out the possibility that bimetallic clusters of platinum and rhenium are present. 

US patent 5,864,047 claims alkaline earth metal compound-supported silver catalysts containing rhenium and potassium promoters. 

Catalysts containing rhenium are generally based on Re207, ReCls, or a carbonyl or other complex compound. Some typical examples are listed in Table 2.5. 

A new generation of bifunctional catalysts was introduced in 1967. The catalyst containing rhenium in addition to platinum provides greater stability.In 1975, the process using a catalyst containing platinum and iridium was commercialized. These catalysts are called bimetallic catalysts. The bimettillic catalysts are typically 3 to 4 times more active than the all-platinum catalyst. A bimetallic catalyst with rhenium typically contains about 0.3% platinum and 0.3% rhenium. The reasons for the effectiveness of these bimetallic catalysts are beyond the scope of this volume and the readers should refer to the appropriate monographs or reviews. ... 

Survey of the patent Hterature reveals companies with processes for 1,4-butanediol from maleic anhydride include BASF (94), British Petroleum (95,96), Davy McKee (93,97), Hoechst (98), Huels (99), and Tonen (100,101). Processes for the production of y-butyrolactone have been described for operation in both the gas (102—104) and Hquid (105—108) phases. In the gas phase, direct hydrogenation of maleic anhydride in hydrogen at 245°C and 1.03 MPa gives an 88% yield of y-butyrolactone (104). Du Pont has developed a process for the production of tetrahydrofuran back-integrated to a butane feedstock (109). Slurry reactor catalysts containing palladium and rhenium are used to hydrogenate aqueous maleic acid to tetrahydrofuran (110,111). 

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

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. 

Re) for the preparation of solid catalysts refer to bimetallic catalysts containing manganese or rhenium. These systems are covered in the Section 8.2.3.1 (Pt-Re) and Section 8.3.1.1 (Fe-Mn). 

The granulated catalyst containing up to 7 mass, per cent of rhenium in a porous carbon matrix was obtained for the first time by high-temperature destruction of copolymers. 

For catalysts that were simply dried in air at 110°C after impregnation of the alumina with H2PtClfe and Re207, it was concluded that a platinum-rhenium alloy formed on reduction. This conclusion was based on the observation that the presence of platinum accelerated the reduction of oxygen chemisorbed on the rhenium and on results showing that the frequencies of the infrared absorption bands of carbon monoxide adsorbed on platinum and rhenium sites in platinum-rhenium catalysts were different from those found with catalysts containing only platinum or rhenium. However, for catalysts calcined in air at 500°C prior to reduction in hydrogen, it was concluded that the platinum exhibited much less interaction with the rhenium (66,71). 

Studies by a group at the Shell Laboratories in Amsterdam (73) have been reported as evidence of interaction between platinum and rhenium in catalysts containing these two elements. These workers, on the basis of infrared spectroscopy studies of carbon monoxide chemisorbed on platinum-rhenium catalysts, and also of X-ray photoelectron spectroscopy measurements on the catalysts, concluded that platinum-rhenium bonds are present in the surface. 

In the X-ray photoelectron spectroscopy studies on the platinum-rhenium catalyst, it was observed that the binding energies of the platinum 4/7/2 and rhenium 4dm core electrons were higher than they were in the catalysts containing platinum or rhenium alone. 

Data on rates of dehydrocyclization rD and cracking rc of n-heptane at 495°C and 14.6 atm are given in Table 5.2 for platinum-iridium on alumina and platinum-rhenium on alumina catalysts, and also for catalysts containing platinum or iridium alone on alumina (33). The rate rD refers to the rate of production of toluene and C7 cycloalkanes, the latter consisting primarily of methylcyclohexane and dimethylcyclopentanes. The rate of cracking is the rate of conversion of n-heptane to C6 and lower carbon number alkanes. 

The reaction rates were determined at low conversion levels (7-12%) in an attempt to minimize the effects of secondary reactions. The inlet stream to the reactor contained five moles of hydrogen per mole of n-heptane. The n-heptane contained 0.5 ppm sulfur, and the reaction rates were determined after 40 hours on stream. The catalysts contained 0.9 wt% chlorine as charged. Prior to the runs the catalysts were contacted with an H2S-containing gas until H2S was detected at the reactor outlet (34). This step is routinely employed with platinum-rhenium and platinum-iridium catalysts to suppress hydrogenolysis activity (33). 

The selectivity to benzene is much lower for the iridium catalyst than for any of the other catalysts except rhenium on alumina. The platinum-iridium catalyst is clearly more selective than the iridium catalyst with respect to benzene formation. However, it is less selective for benzene formation than the catalyst containing platinum alone, although it is possible that this debit may disappear as the catalyst ages during a run. Also, except for the initial reaction period, the platinum-iridium catalyst is less selective for benzene formation than the platinum-rhenium catalyst. 

The studies of n-heptane and methylcyclopentane conversion provide insight into the advantages of platinum-iridium and platinum-rhenium catalysts over catalysts containing only one of the transition metal components, that is, platinum, iridium, or rhenium. If, for example, we consider an iridium-alumina catalyst for the reforming of a petroleum naphtha fraction, we find that it produces a substantially higher octane number reformate than a platinum on alumina catalyst under normal reforming conditions. The iridium-alumina catalyst will also exhibit a lower rate of formation of carbonaceous residues on the surface, with the result that the maintenance of activity with time will be much superior to that of a platinum-alumina catalyst. 

Catalyst contains 0.3 wt% each of platinum and rhenium on alumina. 

Besides Re-Pt/AbOs reforming catalysts other rhenium-containing systems... 

A series of five supported catalysts containing 12 or 20 wt.% cobalt and 0.5 wt.% rhenium were prepared by one-step incipient wetness co-impregnation of the different supports with aqueous solutions of Co(N03)2 6H20 (Acros Organics, 99%) and HRe04 (Alfa Aesar, 75-80%). 

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