The present invention also relates to the use of said catalyst in the metathesis reaction of olefins.

Metathesis reactions, also known as dismutation and disproportioning of olefins, are reactions of great practi- cal interest which can be used, for example, for rebalanc- ing the weight of olefins deriving from steam cracking.

When olefins are treated in the presence of suitable catalysts, they are converted to other olefins in a reac- tion inn which the (R1R2C=) alkylidene groups are inter-

changed with a process with is schematically represented by the following equation: Heterogeneous catalysts essentially consisting of rhe- nium derivatives carried on inert materials (for example silica or alumina) are known to be active in the metathesis of olefins. For example, U. S. patents 3,641, 189 and 3,676, 520 describe the preparation of these materials and their use in the metathesis of olefins.

In the preparation of this catalyst, the active compo- nent is usually laid on the surface of the carrier medium by means of impregnation. In this reaction, the carrier is mixed with a solution in which the active component has been dissolved. When the solvent is removed by evaporation, the active component remains inside the particles of the carrier.

With these catalysts, however, it is necessary for the active component to be present in quantities ranging from 5 to 7% and, in spite of this, not particularly high conver- sions have been observed, and also, in the case of higher olefins, low selectivities which can often be attributed to secondary isomerization reactions of the double bonds (J. <BR> <BR> <P>Mol. Cat: 46, 1988, 119-130 and App. Catal. , 70,1991, 295-

306).

It has now been found that it is possible to overcome the above disadvantages and obtain optimum catalyst per- formances, using much lower quantities of active component, by means of the catalyst of the present invention contain- ing rhenium and an inert carrier such as alumina, charac- terized in that said carrier is subjected to a prior si- lanization treatment with a compound containing chlorine, before impregnation with the active component, and the ac- tivation of the heterogeneous catalyst takes place by means of thermal treatment followed by a rapid final cooling.

This catalyst is active in metathesis reactions even when used without a co-catalyst and reduces problems relat- ing to the formation of isomers or secondary reactions ob- taining a high selectivity.

In accordance with what is specified above, an object of the present invention therefore relates to a process for the preparation of a heterogeneous catalyst active in me- tathesis reactions of olefins containing rhenium as active component and alumina as inert carrier medium, character- ized in that the inert carrier medium is treated with a si- lanizing agent having the general formula RnSiClm (I) wherein R represents an amine or a Cl-ces (iso) alkyl, C5-C25 cyclo-alkyl, C6-C18 aromatic or C7-C25 alkyl aromatic radi-

cal, optionally containing at least one heteroatom selected from 0, S and N; n is an integer so that 1 < n < 3; m is an integer so that 1 < m < 3.

Examples of silanizing agents having general formula (I) are: trimethyl chloro silane, allyl trichloro silane, triphenyl chloro silane, tributyl chloro silane.

The treatment of the carrier is carried out using the silanizing agent as such or, preferably, by dissolution of the silanizing agent itself in a solvent selected from an alkyl or aromatic hydrocarbon such as hexane, heptane, oc- tane, decane, toluene or xylenes; an alkyl or cyclic ether such as ethyl ether, dimethyl ether or tetrahydrofuran; a chlorinated product such as methylene chloride, carbon tet- rachloride or chloroform.

The alumina is maintained in the presence of the solu- tion of silanizing agent for a time ranging from 0.5 to 24 hours, preferably from 8 to 15 hours, at a temperature ranging from-10 to 100°C. At the end of the impregnation, after evaporation of the solvent, the alumina can be op- tionally subjected to thermal treatment ranging from 400 to 600°C.

According to the present invention, the alumina is preferably used with a surface area ! 50 m2/g, preferably from 100 to 200 m2/g, and with a total cumulative pore vol- ume greater than 0.1 ml/g, preferably from 0.3 to 0.8 ml/g.

The rhenium compound can be laid on the carrier pre- treated as described above, by means of precipitation or impregnation starting from precursors consisting for exam- ple of solutions of its salts or soluble complexes.

The precursors of the rhenium compound are selected from rhenium heptoxide, ammonium perrenate, tetra-alkyl am- monium perrenate, perrenic acid or from other compounds known to experts in the art.

Impregnation of the inert carrier is generally pre- ferred, using a saturated solution of the rhenium compound, in a solvent selected from water or an organic solvent, for example a hydrocarbon, an alcohol or an ether.

The impregnation is preferably effected at a tempera- ture ranging from 20 to 70°C in order to increase the solu- bility of the rhenium salt; in this case the carrier is also heated to the same temperature.

After impregnation of the carrier with the metal, the catalyst is activated with a pre-calcination at a tempera- ture ranging from 100 to 200°C in a stream of dry air and a subsequent calcination at a temperature ranging from 300 to 600°C, first in a stream of dry air and then nitrogen. The cooling is effected in a stream of nitrogen over a period of time ranging from 5 to 30 minutes, preferably from 10 to 20 minutes.

In these catalysts, the rhenium is normally present

in a quantity ranging from 1 to 20% by weight, preferably from 3 to 10% by weight with respect to the carrier.

In order to obtain a further improvement of the cata- lyst, it is possible, after the treatment described above, to wet it with a quantity of water equal to the porosity of the carrier and calcine it again according to the method described above.

The catalysts of the present invention can be used in metathesis reactions of olefins.

These reactions can be homo-metathesis (two equal ole- fins) or co-metathesis (two different olefins).

Olefins which can be subjected to the metathesis reac- tion are mono-olefins with from 2 to 30 carbon atoms such as, for example, ethylene, propylene, butene, pentene, hex- ene; cyclo-olefins with from 5 to 20 carbon atoms, for ex- ample cyclo-pentene, cyclo-octene, norbornene; olefins with two or more unsaturations containing from 4 to 30 carbon atoms, for example 1,4-hexadiene, 1,7-octadiene, cyclo- olefins containing two or more unsaturations containing from 6 to 30 carbon atoms, for example 1,5-cyclo-octadiene, norbordiene, dicyclopentadiene.

Other olefins can be mono-olefins or olefins contain- ing several unsaturations, linear or cyclic, carrying func- tional groups such as, for example, halogens or ester groups such as methyl oleate.

The metathesis reaction can be carried out either batchwise or in continuous by feeding the materials into a fluid bed or fixed bed reactor. The reaction conditions such as temperature, pressure and streams are selected in relation to the material fed and the end-product desired.

The metathesis reaction is generally carried out at a temperature ranging from 0 to 100°C, preferably from 25 to 60°C, and at a pressure of up to 10 MPa, preferably from 0.1 to 6 MPa, and can be carried out in gas phase or in liquid phase, with or without an organic solvent.

When a solvent is used, this is selected from ethers, aliphatic and aromatic hydrocarbons. Examples of these sol- vents are ethyl ether, hexane, heptane, toluene, etc.

The catalyst is normally dispersed in the reaction me- dium at a concentration ranging from 1 to 50% by weight, preferably from 1 to 10% by weight with respect to the re- action mixture.

The metathesis reaction can be optionally carried out in the presence of co-catalysts selected from metal alkyls such as, for example, tin tetra-alkyls (tin tetramethyl, tin tetra-ethyl, tin tetrabutyl) or other metal alkyls such as lead tetramethyl, lead tetra-ethyl, aluminum triethyl, chloro aluminum diethyl, as described in patent U. S.

3,855, 338.

The following examples are illustrative but non-

limiting of the invention described.

EXAMPLE 1 Preparation of catalyst A 10 g of y-alumina with a surface of 180 m2/g and a po- rosity of 0.5 ml/g, are pre-calcined in a muffle at 110°C for 1 hour in a stream of air and subsequently at 550°C for 4 hours in a stream of air.

The carrier is then wet with 5 ml of a hexane solution containing 0.087 g of SiMe3Cl and is maintained at 25°C for 18 hours. The hexane is then evaporated maintaining the sample in an oven at 60°C for 2 hours.

The carrier thus treated is calcined first at 110°C for 1 hour in a stream of dry air and then at 550°C for 3 hours in a stream of dry air and for 1 hour in a stream of nitrogen. After cooling for 15 minutes in a stream of ni- trogen, the carrier is then wet four times with 5 ml of an aqueous solution containing 0.126 g of NH4ReO4, the water is evaporated, between one impregnation and the next, by keeping the sample in an oven at 60°C.

The catalyst thus prepared has a rhenium content of 3. 5% by weight.

EXAMPLE 2 Use of catalyst A in metathesis.

358 mg of catalyst A prepared as described in example 1 and 12 ml of a solution consisting of 10 1 of co-

catalyst SnMe4 in 100 ml of hexane, are charged, in an ar- gon atmosphere, into a 150 ml tailed flask.

The resulting mixture is maintained under light stir- ring, at 25°C for 10 minutes and 13 ml of 1-hexene are then added.

After 10 minutes, the reaction mixture is analyzed via gas chromatography using an internal standard. The follow- ing results are obtained: conversion of 1-hexene 55% selectivity of 5-decene 100% EXAMPLE 3 (Comparative) Preparation of catalyst B 10 g of y-alumina with a surface of 180 m2/g and a po- rosity of 0.5 ml/g, are pre-calcined in a muffle at 110°C for 1 hour in a stream of air and subsequently at 550°C for 4 hours in a stream of air.

The carrier is then wet four times with 5 ml of an aqueous solution containing 0.28 g of NE4ReO4, the water is evaporated, between one impregnation and the next, by keep- ing the sample in an oven at 60°C.

The carrier is calcined first at 110°C for 1 hour in a stream of dry air and then at 550°C for 3 hours in a stream of dry air and for 1 hour in a stream of nitrogen. The re- actor is then extracted from the muffle and cooled for 15 minutes in a stream of nitrogen

The catalyst thus prepared has a rhenium content of 7. 5% by weight.

EXAMPLE 4 (Comparative) Use of catalyst B in metathesis 358 mg of catalyst B prepared as described in example 3 and 23 ml of a solution consisting of 10 ll of co- catalyst SnMe4 in 100 ml of hexane, are charged, in an ar- gon atmosphere, into a 150 ml tailed flask.

The resulting mixture is maintained under light stir- ring, at 25°C for 10 minutes and 26 ml of 1-hexene are then added.

After 30 minutes, the reaction mixture is analyzed via gas chromatography using an internal standard. The follow- ing results are obtained: conversion of 1-hexene 70% selectivity of 5-decene 95% EXAMPLE 5 (Comparative) Preparation of catalyst C 10 g of y-alumina with a surface of 180 m2/g and a po- rosity of 0.5 ml/g, are pre-calcined in a muffle at 110°C for 1 hour in a stream of air and subsequently at 550°C for 4 hours in a stream of air.

The carrier is then wet four times with 5 ml of an aqueous solution containing 0.126 g of NH4ReO4, the water is evaporated, between one impregnation and the next, by

keeping the sample in an oven at 60°C.

The carrier is calcined first at 110°C for 1 hour in a stream of dry air and then at 550°C for 3 hours in a stream of dry air and for 1 hour in a stream of nitrogen. The re- actor is then extracted from the muffle and cooled for 15 minutes in a stream of nitrogen The catalyst thus prepared has a rhenium content of 3. 5% by weight.

EXAMPLE 6 (Comparative) Use of catalyst C in metathesis 358 mg of catalyst C prepared as described in example 5 and 23 ml of a solution consisting of 10 ll of co- catalyst SnMe4 in 100 ml of hexane, are charged, in an ar- gon atmosphere, into a 150 ml tailed flask.

The resulting mixture is maintained under light stir- ring, at 25°C for 10 minutes and 26 ml of 1-hexene are then added.

After 10 minutes, the reaction mixture is analyzed via gas chromatography using an internal standard. The follow- ing results are obtained: conversion of 1-hexene 15% selectivity of 5-decene 85% EXAMPLE 7 (Compatative) Preparation of catalyst D 10 g of y-alumina with a surface of 180 m2/g and a po-

rosity of 0.5 ml/g, are pre-calcined in a muffle at 110°C for 1 hour in a stream of air and subsequently at 550°C for 4 hours in a stream of air.

The carrier is then wet four times with 5 ml of an aqueous solution containing 0.260 g of Me3SiOSiMe3, and is maintained at 25°C for 18 hours. The hexane is then evapo- rated maintaining the sample in an oven at 60°C for 2 hours.

The carrier medium thus treated is calcined first at 110°C for 1 hour in a stream of dry air and then at 550°C for 3 hours in a stream of dry air and for 1 hour in a stream of nitrogen. After cooling for 15 minutes in a stream of nitrogen, the carrier is then wet four times with 5 ml of an aqueous solution containing 0.126 g of NH4ReO4, the water is evaporated, between one impregnation and the next, by keeping the sample in an oven at 60°C.

The catalyst thus prepared has a rhenium content of 3. 5% by weight.

EXAMPLE 8 (Comparative) Use of catalyst D in metathesis 358 mg of catalyst D prepared as described in example 7 and 23 ml of a solution consisting of 10 Al of co- catalyst SnMe4 in 100 ml of hexane, are charged, in an ar- gon atmosphere, into a 150 ml tailed flask.

The resulting mixture is maintained under light stir-

ring, at 25°C for 10 minutes and 26 ml of 1-hexene are then added.

After 10 minutes, the reaction mixture is analyzed via gas chromatography using an internal standard. The follow- ing results are obtained: - conversion of 1-hexene 35% - selectivity of 5-decene 98%