Platinum-rhenium catalysts

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. 

Platinum loadings, reducing, 19 628 Platinum metals plating, 9 822-823 Platinum oxides, volatilized, 17.T80 Platinum-palladium thermocouple, 24 461 Platinum reforming catalysts, rhenium and, 21 695-696... 

A typical process flow diagram of a catalytic reformer is shown in Figure 3.17. Desulfurized naphtha is heated in feed-effluent exchangers and then passed to a fired heater, where it is heated to 850 to 1,000° F (455 to 540° C) at 500 psia (3,450 kPa) in a series of reactors and fired heaters. In the reactors, the hydrocarbon and hydrogen are passed over a catalyst (often platinum/rhenium based) to produce rearranged molecules, which are primarily aromatics with some isoparaffins. The reactor effluent is cooled by exchange and then passed to a separator vessel. The gas from the separator is recycled to the reactors. The liquid is fed to a fractionator. 

Monochloroanilines are made by reduction of chloronitrobenzenes with either iron/acid or, nowadays, mainly catalytic hydrogenation. Catalysts include platinum, copper chromite and rhenium in conjunction with palladium38. The chloroanilines are used in the manufacture of colorants, agricultural products, pharmaceuticals and polymers. For example, o-chloronitrobenzene (29) is a source of o-nitroanilinc, o-phenylenediamine (1,2-benzenediamine) (30), o-aminophenol (19b), o-chloroaniline and 3,3 -dichlorobenzidine (31a). The o-phenylenediamine (30) is a particularly versatile intermediate, used to prepare thioureidoformates. Ring-substituted o-phenylenediamines with cyanoesters yield benzimidazoles that, on condensation with an aldehyde, followed by treatment with H2S, give a range of thioureas. 

Hydrogenation Copper chromite (Lazier catalyst). Copper chromium oxide (Adkins catalyst). Lindlar catalyst (see also Lithium ethoxyacetylide, Malealdehyde, Nickel boride). Nickel catalysts. Palladium catalysts. Palladium hydroxide on carbon. Perchloric acid (promoter). Platinum catalysts. Raney catalysts, Rhenium catalysts. Rhodium catalysts. Stannous chloride. Tributylborane. Trifluoroicetic acid, Tris (triphenylphosphine)chlororhodium. 

In considering the nature of platinum-rhenium catalysts, we begin with a comparison of the chemisorption properties of alumina-supported rhenium, platinum, and platinum-rhenium catalysts (40). Data on the chemisorption of carbon monoxide and hydrogen at room temperature are given in Table 4.4 for catalysts with platinum and/or rhenium contents in the range of interest for reforming applications. 

The physical and chemical nature of the rhenium in platinum-rhenium catalysts has been considered by a number of investigators. Johnson and Leroy (63) concluded that the rhenium is present as a highly dispersed oxide at typical reforming conditions. They studied a series of alumina-supported platinum-rhenium catalysts with platinum contents ranging from 0.31 to 0.66 wt% and rhenium contents ranging from 0.20 to 1.18 wt%. Their conclusions were based on measurements of hydrogen consumption during reduction of the catalysts at 482°C and on X-ray diffraction studies of the metal component of the catalyst after the alumina had been leached from the catalyst by treatment with a solution of fluoboric acid. 

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 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. 

Kariya et al. performed dehydrogenation of methylcyclohexane and other cycloalkanes over platinum, palladium and rhodium monometallic and platinum/palladium, platinum/rhodium, platinum/molybdenum, platinum/tungsten, platinum/rhenium platinum/osmium and platinum/iridium catalysts supported on both petroleum coke active carbon and on alumina between 375 and 400 °C [279]. The platinum catalyst supported by petroleum active carbon showed the highest activity. While platinum was the most active monometallic catalyst, its activity could be increased by addition of molybdenum, tungsten and rhenium. 

Typical reforming catalysts contain platinum as the metal component and modified 7-AI2O3 for acidity. Rhenium is used as promoter to decrease coke formation, which increases the cycle time between regenerations. The (internal) surface area of a reforming catalyst is about 200m g , and commonly 1-6 mm diameter spheres or extrudates are used. 

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. ... 

The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired reformate. The catalysts used are principally platinum or platinum—rhenium on an alumina base. The purpose of platinum on the catalyst is to promote dehydrogenation and hydrogenation reactions. Nonplatinum catalysts are used in regenerative processes for feedstocks containing sulfur, although pretreatment (hydrodesulfurization) may permit platinum catalysts to be employed. 

Another synthesis of pyrogaHol is hydrolysis of cyclohexane-l,2,3-trione-l,3-dioxime derived from cyclohexanone and sodium nitrite (16). The dehydrogenation of cyclohexane-1,2,3-triol over platinum-group metal catalysts has been reported (17) (see Platinum-GROUP metals). Other catalysts, such as nickel, rhenium, and silver, have also been claimed for this reaction (18). 

Low pressure operation became routine with the appHcation of new catalysts that are resistant to deactivation and withstand the low pressures. The catalysts are bimetallic most incorporate rhenium as well as platinum (95). The stmctures of these catalysts are stiU not well understood, but under some conditions the two metals form small alloylike stmctures, which resist deactivation better than the monometallic catalyst. 

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. 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Palladium and platinum (5—10 wt % on activated carbon) can be used with a variety of solvents as can copper carbonate on siHca and 60 wt % nickel on kieselguhr. The same is tme of nonsupported catalysts copper chromite, rhenium (VII) sulfide, rhenium (VI) oxide, and any of the Raney catalysts, copper, iron, or nickel. 

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