Supported Catalyst Comprising Delta- Or Theta-Modified Aluminium Oxide Supports

Abstract

Process for producing a supported catalyst which comprises at least 75% by weight of Al2O3, whose proportion of Al2O3 in the delta or theta modification is, based on the proportion of Al2O3, at least 1% and which comprises a rhenium compound and, if appropriate, a promoter as active component (A), which comprises a) converting a customary support (S) which comprises at least 75% by weight of Al2O3 and to which a promoter may, if appropriate, have been applied is converted into a modified support (S) whose proportion of Al2O3 in the delta or theta modification is, based on the proportion of Al2O3, at least 1% by calcining the customary support (S) at a temperature of from 750 to 1100°C.,b) producing a supported catalyst precursor from the modified support (S) by applying the active component (A) comprising the rhenium compound to the modified support (S) andc) calcining the supported catalyst precursor at a temperature of from 500 to 750° C.

Description

EXAMPLE 1

Production of a Catalyst According to the Invention (A-85999)

Commercial D10-21 extrudates (1.5 mm gamma-Al₂O₃ extrudates from BASF AG) were heated at 850° C. in air for 2 hours (during their production, the extrudates had been exposed to temperatures of not more than 600° C.). The extrudates were subsequently impregnated with an aqueous perrhenic acid solution to 90% of the water absorption and dried at 120° C. in air for 6 hours. The temperature was subsequently increased to 520° C. over a period of 2 hours, then to 550° C. over a further period of 15 minutes and the catalyst was calcined at this temperature for 2 hours. The catalyst was cooled and stored in air. The finished catalyst comprised 9.5% by weight of Re₂O₇. The pore volume determined by means of mercury porosimetery was 0.53 ml/g, and the surface area was 129 m²/g. The maximum in the distribution function over the pore size distribution in the mesopore range was 13 nm. A mixture of delta- and theta-Al₂O₃ phases was identified by means of X-ray diffraction (FIG. 1). Reflections having maxima at 2 theta=32.76° and 2 theta=37.05° can be seen. The intensity ratio (counts/counts) of the two reflections to the main reflection at 67.07° is 0.36 and 0.45, respectively. An additional, very weak reflection could be seen at 2 theta=50.6°. The Cs content of this sample is <10 ppm (detection limit). The K and Na contents were in each case <30 ppm (detection limit).

EXAMPLE 2

Production of a Catalyst According to the Invention (B-86000)

A catalyst was produced as described in example 1, but the support extrudates were in this case pretreated at 1000° C. in air for 2 hours.

The finished catalyst comprised 9.9% by weight of Re₂O₇. The pore volume determined by means of mercury porosimetery was 0.44 ml/g, and the surface area was 89 m²/g. The maximum in the distribution function over the pore size distribution in the mesopore range was 15 nm. A mixture of delta- and theta-Al₂O₃ phases was identified by means of X-ray diffraction (FIG. 2). Reflections having maxima at 2 theta.=32.79° C. and 2 theta=36.73° can be seen. The intensity ratio (counts/counts) of the two reflections to the main reflection at 67.34° is 0.51 and 0.45, respectively.

A gamma phase could no longer be seen in the XRD. In addition, a distinct reflection could be seen at 2 theta=50.7°. The Cs content of this sample is <10 ppm (detection limit). The K and Na contents were in each case <30 ppm (detection limit).

EXAMPLE 3

Production of a Comparative Example (C-85850)

A catalyst was produced as described in example 1, but the support extrudates were not additionally pretreated.

The finished catalyst comprised 9.0% by weight of Re₂O₇. The pore volume determined by means of mercury porosimetery was 0.52 ml/g, and the surface area was 158 m²/g. The maximum in the distribution function over the pore size distribution in the mesopore range was at 9.8 nm. Pure γ-Al₂O₃ is identified by means of X-ray diffraction (FIG. 3). All reflection maxima were outside the 2 theta range from 32.5° to 37.4°. Even in the range from 2 theta>50.0° and 2 theta<53.0°, no reflection was to be seen under the measurement conditions chosen. The Cs content of this sample was <10 ppm (detection limit). The K and Na contents were in each case <30 ppm (detection limit).

EXAMPLES 4-6

Comparison of the Performance of the Catalysts A-C

9 g of catalyst were in each case installed in a tube reactor. The feed consists of 162 g/h of a mixture of about 85-90% of linear butenes, about 2.5% of isobutene and butanes as balance (raffinate II). To compensate for the somewhat lower rhenium content of the sample C, the feed rate was reduced by about 5% in this measurement. The reaction conditions are in each case 35° C. and 35 bar. The composition of the stream leaving the reactor is monitored by means of on-line GC. As representatives of the numerous components, the amounts of the most important or largest products, i.e. propene, trans-2-pentene and trans-3-hexene, at different measurement times are shown in the following table. All products not shown (ethylene, cis-2-pentene, cis-3-hexene, 2-methyl-2-butene and 2-methyl-2-pentene) have in principle a similar time profile and comparable differences at prolonged running times.

	Ex. A (85999)	Ex. B (86000)
	Propene			Propene
T	[% by	trans-2-Pentene	trans-3-Hexene	[% by	trans-2-Pentene	trans-3-Hexene
[h]	weight]	[% by weight]	[% by weight]	weight]	[% by weight]	[% by weight]
4	13.1	15.1	3.5	14.1	15.8	4.0
9	10.4	11.6	2.2	11.5	12.3	2.6
17	7.7(−42%)	8.2(−46%)	1.1(−69%)	8.6(−39%)	8.6(−46%)	1.3(−67%)
	Comp. Ex. C (85850)
	Propene
T	[% by	trans-2-Pentene	trans-3-Hexene	—
[h]	weight]	[% by weight]	[% by weight]	—	—	—
4	11.5	12.6	2.5	—	—	—
9	8.8	8.9	1.5	—	—	—
17	6.1(−47%)	6.7(−47%)	0.8(−67%)	—	—	—

It can be seen that the catalysts according to the invention have higher initial activities throughout (differences up to about 40%) and specifically in respect of the lighter products (here: propene) deactivate somewhat more slowly, so that higher conversions are still achieved after a prolonged running time, which significantly increases the total yield.

EXAMPLE 7, 8

Transmission Electron Micrographs of Catalysts Containing Alkali Metals (Comparative Examples)

Catalyst D (84325) was produced by impregnation of an aluminum oxide support containing about 250 ppm of Na (based on the metal) as impurity with perrhenic acid. Examination by means of TEM (transmission electron microscopy, FIG. 4) showed coarse Na-Re-containing crystals. In contrast, pure rhenium oxide formed a highly disperse phase on Al₂O₃ supports. These units were usually smaller than 4 nm and mostly could not be seen by means of TEM.

A further Re₂O₇/Al₂O₃ sample, catalyst E (MS33) was subsequently impregnated with a Cs(NO₃) solution, dried and the catalyst was calcined again at 550° C. The catalyst comprised 600 ppm of Cs. Here too, rod-shaped, coarse Cs—Re-containing crystallites could be seen by means of TEM (FIG. 5).

As a person skilled in the art will know, catalytic reactions proceed on the surface of such catalysts. Thus, less noble metal will be required, the higher the dispersion of the active substance. The formation of coarsely crystalline alkali metal perrhenates greatly reduces the dispersion of the Re₂O₇ phase on Al₂O₃-containing support materials, so that a higher total loading with rhenium is generally necessary in order to achieve the same catalytic activity.

Claims

1-11. (canceled)

12. A process for producing a supported catalyst which comprises at least 75% by weight of Al2O3, whose proportion of Al2O3 in the delta or theta modification is, based on the proportion of Al2O3, at least 1% and which comprises a rhenium compound and optionally a promoter as active component (A), which comprises a) converting a support (S) whlich comprises at least 75% by weight of Al2O3 and optionally a promoter has been applied is converted into a modified support (S) whose proportion of Al2O3 in the delta or theta modification is, based on the proportion of Al2O3, at least 1% by calcining the support (S) at a temperature of from 750 to 1000° C.,b) producing a supported catalyst precursor from the modified support (S) by applying the active component (A) comprising the rhenium compound to the modified support (S) andc) calcining the supported catalyst precursor at a temperature of from 500 to 750° C.

13. The process according to claim 12, wherein the total proportion of Al2O3 in the delta or theta modification is, based on the proportion of Al2O3, at least 10%.

14. The process according to claim 12, wherein the proportion of Al2O3 in the theta modification is, based on the proportion of Al2O3, at least 10%.

15. The process according to claim 12, wherein the support (S) comprises Al2O3 together with components selected from the group consisting of SiO2, aluminosilicates, TiO2, ZrO2, MgO, CeO2 and ZnO.

16. The process according to claim 12, wherein the amount of rhenium compound used as active component (A) in step b) is selected so that the catalyst comprises from 0.01 to 1 mmol of rhenium per gram of catalyst.

17. The process according to claim 12, wherein the supported catalyst has an XRD spectrum in which the maximum of the most intense reflection (main reflection) is in the range from 2 theta >66° to 2 theta <68° and the maximum of one additional reflection or the maxima of a plurality of additional reflections (secondary reflection) are in the range from 2 theta >32.5° to 2 theta <37.4° and the intensity ratio of the respective secondary reflection to the main reflection is at least 0.05.

18. The process according to claim 12, wherein the starting materials are selected so that the total amount of alkali metal compounds, calculated as alkali metal, in the supported catalyst is less than 1000 ppm by weight.

19. The process according to claim 12, wherein the starting compounds are selected so that the total amount of cesium compounds, calculated as elemental cesium, in the supported catalyst is less than 50 ppm by weight.

20. A process for preparing a compound having a nonaromatic C—C double bond or C—C triple bond (compound A) from another compound or mixture of other compounds having a nonaromatic C—C double bond or C—C triple bond (compound B), which comprises bringing the compound (B) into contact with a supported catalyst according to claim 12 at a temperature of from 50 to 500° C.

21. The process according to claim 20, wherein compound (B) is 1-butene or a mixture of butenes comprising 1-butene.

22. A supported catalyst obtainable according to the process as described in claim 18.

23. A supported catalyst obtainable according to the process as described in claim 19.