Rhenium-alumina catalyst

Complete reforming kinetics have been developed for several commercial catalysts, including those used in Mobil reformers. Since KINPTR affects Mobil s business strategy, the complete reforming kinetics are proprietary. However, as an example, KINPTR C6 kinetics will be presented for UOP s R16H platinum-rhenium-alumina catalyst. Both the hydrocarbon conversion and the deactivation equations [Eqs. (36), (40)] can be directly applied to the C6 system. For the C6 hydrocarbon conversion, Eq. (40) becomes... 

Bolivar, C. Charcosset, H. Frety, R. Primet, M. Tournayan, L. Betizeau, C. Leclercq, G. and Maurel, R. "Platinum-rhenium-alumina catalysts. II. Study of the metallic phase after reduction." /. Catal 45 163-178 1976. 

Figure 11. Variation in relative activity for a cobalt/rhenium/ alumina catalyst by adding traces of an impurity component.

To avoid using expensive hydrogen, a process has been developed to convert toluene into benzene with steam at a temperature of around 430 °C and pressures of from 5 to 15 bar on rhenium/alumina catalysts. This produces carbon monoxide, carbon dioxide and hydrogen. Benzene selectivity of this process, which has not yet been applied on a large scale, is 87%, with 46% toluene conversion. 

The catalytic carbon monoxide clean-up worked with a two-stage water-gas shift in tubular reactors cooled by steam generation. The kinetics for a rhenium-alumina catalyst for high temperature water-gas shift and for a copper/alumina catalyst for low temperature shift had been extracted from the literature. 

However, precious metal based catalysts without an oxygen carrier or additive, such as the rhenium/alumina catalyst as used here for the calculations, are known to have much lower activity compared with catalytic systems, such as platinum/ceria (see Section 4.5.1). 

The reformate left the reformer with a temperature of 814 °C and entered a zinc oxide trap. However, this would he not feasible in a practical system, because zinc oxide adsorbent materials cannot tolerate temperatures exceeding 450 °C. The reformate, which was cooled to 440 °C in heat-exchanger E-2 was then passed to the water-gas shift reactor. This reactor was cooled by steam generation at 15-bar pressure and a temperature of200 °C in a counternoble metal based rhenium/alumina catalyst at the inlet section followed by a copper/zinc oxide catalyst at the outlet section. Despite the fact that a water-gas shift catalyst of fairly low activity had been chosen for the... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Pt-Re-alumina catalysts were prepared, using alumina containing potassium to eliminate the support acidity, in order to carry out alkane dehydrocyclization studies that paralleled earlier work with nonacidic Pt-alumina catalysts. The potassium containing Pt-Re catalyst was much less active than a similar Pt catalyst. It was speculated that the alkali metal formed salts of rhenic acid to produce a catalyst that was more difficult to reduce. However, the present ESCA results indicate that the poisoning effect of alkali in Pt-Re catalysts is not primarily due to an alteration in the rhenium reduction characteristics. 

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. 

T. K. Das, G. Jacobs, P. M. Patterson, W. A. Conner, J. Li and B. H. Davis, Fischer-Tropsch synthesis characterization and catalytic properties of rhenium promoted cobalt alumina catalysts, Fuel, 2003, 82, 805-815. 

FEAST (further exploitation of advanced shell technology), another Shell process142-144 commercialized in 1986, utilizes a highly active promoted rhenium-on-alumina catalyst (100°C, 2 atm) to synthesize 1,5-hexadiene from 1,5-cyclo-octadiene [Eq. (12.30)] and 1,9-decadiene from cyclooctene [Eq. (12.31)] ... 

Table 3. Preparation of rhenium oxide-alumina catalysts...

Mol, Visser, and Boelhouwer 741 subjected 1,2-dimethyl-butane (ring structure of the suggested transition state for disproportionation of propylene) to rhenium oxide-alumina catalyst under conditions which propylene gives high disproportionation conversions. This compound was stable only at high temperatures (730 °C), where thermal cracking occurred, were olefins found. 

Rhenium oxide-alumina catalysts are reduced at ambient temperatures and sub-atmospheric pressure by propene and higher alkenes, generating metathesis activity. Ethylene at these conditions did not show any reduction capabilities. Reduction with CO or NH3 at 300-500° C did not result in metathesis activity. At room temperature CO did not adsorb on reduced catalysts however, NO adsorbs and is a poison for the olefin metathesis reaction. Water generated in reducing catalysts with alkenes is mainly associatively adsorbed and, at ambient temperatures, exchanges hydrogen atoms with propene and butene. Activity for double-bond isomerization is partly accounted for by associatively adsorbed water, which generates acidity. ... 

In contrast to the X-ray diffraction pattern of alumina-supported rhenium oxide, the pattern for the silica-supported samples gives diffraction lines characteristic of metallic rhenium. The metal particle size is about 75 A. Initial kinetic studies with propylene indicated that the silica-supported samples were inactive for the disproportionation reactions up to 180°C. X.p.s. studies of rhenium-supported catalysts show that the state of the initial and reduced rhenium on silica surface is quite different from that on 7-alumina and is dependent on the rhenium compound used to prepare the catalysts. Because of a stronger interaction of Re with the alumina surface, the reducibility of rhenium on alumina is much less than on silica. 

The kinetics of the metathesis of propene over a rhenium oxide-alumina catalyst (5.8% Rea07) have been studied by Kapteijn and Mol. The data correlate with a model based on the carbene mechanism and are in agreement with infrared and adsorption studies. Hsu has developed a kinetic model to express the time-on-stream profile of activity during catalyst break-in and deactivation. 

Bimetallic platinum-rhenium catalysts can be prepared in aqueous acid medium, under hydrogen flow, by a redox reaction between hydrogen activated on a parent platinum-alumina catalyst and the perrhenate ion ReO4. ... 

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