Rhenium oxide metathesis catalyst

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. ... 

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. 

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. 

In catalyst preparation, one can use this knowledge to determine the relative contributions of various hydroxyl groups before and after application of the active phase onto the support. In this way Sibeijn etal. [31] established that rhenium oxide attached to acidic sites of the alumina support exhibits higher activity for the metathesis of olefins than rhenium oxide on neutral or basic sites. As, however, rhenium species preferentially exchange with basic hydroxyls, one needs to increase the loading above a certain value (6 wt% for an alumina of 200 m2/gram) before the catalyst exhibits appreciable activity [31]. 

Meta-4 A process for converting ethylene and 2-butene into propylene by metathesis. The process operates in the liquid phase at low temperatures in the presence of heterogeneous catalyst based on rhenium oxide on alumina. The catalyst is constantly regenerated by coke combustion. Developed by IFP and the Chinese Petroleum Corporation of Taiwan. A demonstration plant was operated from 1988 to 1990 and the process was demonstrated at Kaohsiung, Taiwan, in 1999. Now offered by Axens. 

Warwel et al. [27] synthesized 1,8-nonadiene in 75 % yield via ethenolysis of cy-cloheptene over a Rc207/Al203 catalyst (at 60 °C and an ethene pressure of 80 bar). The diene was subsequently subjected to intermolecular metathesis (release of ethene), again over a rhenium oxide catalyst (at 35 °C and 15 torr vacuum), giving 80% yield of 1,8,15-hexadecatriene. The latter was converted, via oxidation, intramolecular aldol condensation, and hydrogenation, to muscone (3-methylcyclo-pentadecanone), an important perfume ingredient. 

The selectivity of cross-metathesis reactions has been demonstrated by the reaction of trans-3-hexene with vinyl acetate or a,yff-unsaturated esters (e. g. methyl rran -crotonate) in the presence of a supported rhenium oxide catalyst (Eq. 14). 

Mol, J.C. (1999) Olefin Metathesis over Supported Rhenium Oxide Catalysts, Catalysis Today 51, 289-299 52. 377. 

Heterogeneous catalysts for the metathesis of acyclic unsaturated esters are mainly based on rhenium. The rhenium oxide catalysts (Table 7.2) not only have the advantage that they are active at room temperature, but they are also highly selective, and can be easily recovered (Mol 1991). Mo03/Si02, that has been photoreduced in a CO atmosphere and subsequently treated with cyclopropane, has an even higher activity (Berezin 1991, Mol 1994b). Several well-defined metal... 

In 1998, Ookoshi and Onaka reported remarkable increase in activity of M0O3 when this was supported on hexagonal mesoporous silica instead of conventional one. With this catalyst (7 wt % Mo) they achieved high conversion of 1-octene into 7-tetradecene at 50°C. Similarly in 2002, Onaka and Oikawa found rhenium oxide dispersed on mesoporous alumina with uniform pore size (7 wt % Re) to be more active in 1-octene metathesis than rhenium oxide on conventional y-alumina. Although both works lacked detailed characterization of supports and prepared catalysts, they clearly showed the positive effect of organized mesoporous siqrport on catalyst activity in alkene metathesis. 

Mol, J.C. Olefin metathesis over snpported rhenium oxide catalysts. Catal. Today 1999, 51, 2S9-299. 

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