NO308989B1 - New catalyst, process for its preparation and use of the catalyst for dehydrogenation of dehydrogenatable hydrocarbons - Google Patents

Description

The present invention relates to a new catalyst, a method for producing the catalyst and uses of the catalyst for dehydrogenation of dehydrogenable C2-C30 hydrocarbons, preferably C2-C5 paraffins.

Dehydrogenation of paraffins to olefins is of great commercial importance due to the need for olefins for the production of products such as e.g. high octane petrols, synthetic elastomers, detergents, plastic materials, ion exchange resins and pharmaceutical products. In order for a dehydrogenation process to be commercially applicable, it is necessary to use catalysts which show high activity and which give a high turnover, have good selectivity for the formation of olefins and show good stability.

For the dehydrogenation of paraffins, a large number of catalysts of the type comprising a solid support material based on inorganic oxide and various catalytic metals and promoter metals deposited on the support material or incorporated into the support material in another way are known. Aluminum oxide-based carrier materials have been widely used in such dehydrogenation catalysts.

US Patent No. 4,788,371 describes such a catalyst and a method for steam dehydrogenation of dehydrogenable hydrocarbons with oxidative heating. A dehydrogenable C2-C30 hydrocarbon, steam and an oxygen-containing gas are contacted in a reaction zone with a catalyst comprising a Group VIII noble metal, one or more constituents selected from lithium, potassium, rubidium, cesium and francium, and a component selected from boron, gallium, indium, germanium, tin and lead, deposited on a carrier material consisting of inorganic oxide. Aluminum oxide with a surface area of 1-500 m<2>/g, preferably 5-120 m<2>/g, is preferred as carrier material. In all the design examples of the patent document, aluminum oxide is used as a catalyst carrier. A preferred catalyst according to the US patent contains approx. 0.70 wt% platinum, approx. 0.50 wt% tin and approx. 3.86 wt% cesium and has a surface area of approx. 85 m<2>/g.

Mixtures of magnesium oxide MgO and aluminum oxide A1203 and mixed oxides of Mg and Al have also been used as catalysts and as carrier materials for catalysts. In international patent application PCT/JP89/00053, an alkylation catalyst comprising a magnesium oxide which has been modified through the addition of at least one trivalent metal ion, preferably chosen from Al<3+> and Ga3+, is described. In British patent application GB 2,225,731, a catalyst for hydrogen treatment is described, e.g. hydrodemetallization or hydrodesulfurization, comprising, in an essentially homogeneous phase, magnesium oxide and aluminum oxide where the molar ratio Mg/Al is preferably from 3:1 to 10:1, as well as a metal from Group VI and/or at least one metal from Group VIII .

It has now been shown that if, together with a mixed oxide of Mg and Al, a noble metal from Group VIII and certain promoters of the type described in the above-mentioned US patent document No. 4,788,371 is used, a catalyst can be obtained which exhibits improved activity values and better stability when dehydrogenating dehydrogenable hydrocarbons.

The invention thus provides a catalyst comprising a combination of a carrier consisting of magnesium, aluminum and oxygen; a Group VIII precious metal; a metal from Group IVA and possibly an alkali metal from Group IA. The catalyst is characterized by the fact that the carrier essentially consists of a mixed oxide of magnesium and aluminum Mg(Al)0 which generally has an MgO structure where Al<3+-> cation ions have replaced part of the Mg2+ cation ions, in which mixed oxide the molar ratio between magnesium and aluminum is in the range from 1:1 to 10:1.

It is preferred that the catalyst has been subjected to a pretreatment comprising a reduction, preferably in hydrogen, a subsequent oxidation, preferably in air possibly mixed with nitrogen, and finally a new reduction, preferably in hydrogen (ROR pretreatment; ROR = Reduction Oxidation-Reduction).

The noble metal from Group VIII is preferably chosen from platinum and palladium, platinum being the most preferred. The metal from Group IVA is preferably chosen from among tin and germanium. Most preferred is tin.

It has been shown that the new catalyst's selectivity during dehydrogenation is further improved by the fact that it also contains an alkali metal from Group IA, preferably cesium or potassium, most preferably cesium.

It is remarkable that the new catalyst exhibits very good activity in the dehydrogenation of hydrocarbons even with a low content of noble metal from Group VIII of e.g. 0.2-0.4% by weight.

The catalyst according to the invention can suitably contain:

0.05 - 5.0% by weight precious metal from Group VIII,

0.05 - 7.0% by weight metal from Group IVA,

0 - 5.0% by weight metal from Group IA,

calculated on the total weight of the catalyst.

Preferably, the catalyst according to the invention contains:

0.1 - 1.0% by weight precious metal from Group VIII,

0.1 - 3.0 wt% metal from Group IVA,

0 - 0.7% by weight metal from Group IA,

calculated on the total weight of the catalyst.

Most preferably, the catalyst according to the invention contains:

0.2 - 0.4% by weight precious metal from Group VIII,

0.3 - 1.5% by weight metal from Group IVA,

0 - 0.6% by weight metal from Group IA,

calculated on the total weight of the catalyst.

When the catalyst according to the invention contains a metal from Group IA, the amount of this is usually 0.1-1.0% by weight, preferably 0.3-0.7% by weight and most preferably 0.4-0.6% by weight. The Group VIII metal, the Group IVA metal and the optional Group IA metal can be incorporated into the carrier in any manner known in the art. A preferred method involves impregnating the oxide carrier with solutions or suspensions of fissile compounds of the metals to be incorporated.

Below, the catalyst and its manufacture will be described in more detail with reference to embodiments where platinum, tin and possibly cesium are deposited on the support material, but the explanation also applies to cases where other metals are deposited within the scope of the invention, with possible adaptations that will be obvious to a person skilled in the art in the area.

The mixed oxide of magnesium and aluminum, Mg(Al)0, which is used as carrier material in the catalyst according to the invention, can be prepared by adding a solution of sodium hydroxide and sodium carbonate to a solution of magnesium nitrate and aluminum nitrate according to the method described in Journal of Catalysis 94, (1985 ), pp. 547-557. Instead of sodium hydroxide and sodium carbonate, potassium hydroxide and potassium carbonate can be used, see Applied Catalysis 54 (1989), p.p. 79-90. By evaporation (drying) of the above-mentioned mixtures, the compound hydrotalcite, Mg6Al2 (OH) 16C034H20, is formed, which after calcination at 500-800°C gives Mg(Al)0. However, it is preferred to modify this method somewhat by using ammonium hydroxide and ammonium carbonate instead of the respective compounds sodium hydroxide/potassium hydroxide and sodium carbonate/potassium carbonate, as a larger and more stable surface area is thereby obtained. The obtained Mg(Al)0 is characterized by a magnesium oxide structure where part of the magnesium atoms have been replaced by aluminum atoms. The molar ratio Mg/Al is typically in the range from 1:1 to 10:1, and the surface area is typically in the range from 100 to 300 m<2>/g, preferably in the range from 140 to 210 m<2>/g. The grain size can range from 100 µm to 20 mm.

The deposition of platinum and tin on the Mg(Al)O support material can advantageously be carried out in one step, e.g. using stannous chloride and hexachloroplatinic acid dissolved in ethanol. A method for the deposition of platinum and tin in one step is described in J. Catalysis, vol. 128, 1991, page 1. By simultaneously depositing tin and platinum on the Mg(Al)O material, the number of necessary calcination steps is reduced, which gives better possibilities for achieving a large surface area on the Mg(Al)O material. Other applicable impregnation procedures are described in the above-mentioned US Patent No. 4,788,371, in US Patent No. 4,962,265 and in EP 0,098,622.

When the catalyst is to contain cesium, after the deposition of tin and platinum and subsequent calcination, the deposition of cesium can be carried out in a separate step using cesium nitrate dissolved in water. The impregnation with cesium nitrate can be carried out as described in US Patent No. 4,788,371.

The ROR pre-treatment of the catalyst is suitably carried out by reducing the catalyst in hydrogen, a subsequent oxidation in air which is optionally mixed with nitrogen, and finally a further reduction in hydrogen. The pre-treatment can be carried out at a temperature in the range 500-700°C and using volume velocities GHSV for the treatment gases of 10-100,000 N ml g"1h"<1>, preferably 100-5000 N ml g"1 h"<1>. The initial reduction of the catalyst with hydrogen is carried out for a period of from 1 minute to 10 hours, usually for approx. 2 hours. The subsequent oxidation of the reduced catalyst in air, which may optionally be mixed with nitrogen, is also carried out for a period of from 1 minute to 10 hours, normally for approx. 2 hours. The oxidation can advantageously be carried out by first treating the catalyst for approx. 1 hour in a stream of nitrogen containing approx. 20 vol% air and then for approx. 1 hour in clean air. The final reduction with hydrogen is carried out under similar conditions as the initial reduction.

The invention thus also relates to a method for producing a catalyst for the dehydrogenation of dehydrogenable C2-C30 hydrocarbons, where a noble metal from Group VIII, a metal from Group IVA and optionally an alkali metal from Group IA. The method is characterized by the fact that a carrier consisting essentially of a mixed oxide of magnesium and aluminum Mg(Al)0 is used, in which mixed oxide the molar ratio between magnesium and aluminum is in the range from 1:1 to 10:1, preferably from 2: 1 to 5:1, and that the material obtained is subjected to a pre-treatment (ROR pre-treatment) comprising a reduction, preferably in hydrogen, a subsequent oxidation, preferably in air possibly mixed with nitrogen, and finally a second reduction, preferably in hydrogen.

Furthermore, the invention concerns an application of the new catalyst for dehydrogenation of dehydrogenable C2-C30 hydrocarbons, preferably C2-C5 paraffins.

In accordance with common practice in the dehydrogenation of hydrocarbons, it is preferred to bring the hydrocarbons into contact with the solid catalyst in gas phase, in admixture with common additives such as water vapour, nitrogen and hydrogen. The feed mixture containing the hydrocarbons is preferably fed to a reactor with one or more stationary catalyst beds, and the dehydrogenation is preferably carried out at a temperature in the range from 500 to 700°C, at a pressure in the range from 0.5 to 1.5 bar absolute and using a volume velocity GHSV in the range from 10 to 10,000 N ml g"<1> h"<1>.

The new catalyst has also proven to be very suitable in cases where the dehydrogenation of hydrocarbons is carried out in combination with the mixing of oxygen and the combustion of hydrogen, as the new catalyst also has a selective catalytic effect on the oxidation of hydrogen to water.

It is well known that when dehydrogenating dehydrogenable hydrocarbons it is advantageous to oxidize the hydrogen formed in the reaction with an oxygen-containing gas. Because the dehydrogenation process is endothermic, oxidation of the hydrogen formed can be used to maintain the desired reaction temperature during the dehydrogenation. For this heating purpose, it will also often be appropriate to add a supplementary amount of recycled hydrogen to the reaction mixture. In addition to the heat balance that can thus be achieved, the reduction in the hydrogen concentration in the reaction mixture that is achieved by combustion will also shift the equilibrium of the desired dehydrogenation reactions towards a higher yield of unsaturated hydrocarbons. Although a high hydrogen turnover would therefore be beneficial, it is important to avoid accompanying oxidation of hydrocarbons, which would reduce the overall yield of the process. It is therefore important to achieve the most selective oxidation of the hydrogen that is formed during the dehydrogenation process. Such selective oxidation has been shown to be achieved with the new catalyst.

The invention thus also relates to an application of the new catalyst for dehydrogenation of dehydrogenable C2-C30 hydrocarbons, preferably C2-C5 paraffins, in combination with the mixing of oxygen-containing gas, preferably oxygen, and combustion of hydrogen.

In accordance with common practice for this type of dehydrogenation of hydrocarbons, the hydrocarbons are brought into contact with the solid catalyst in gas phase, in a mixture with an oxygen-containing gas and with usual additives such as water vapour, any supplementary amounts of hydrogen and nitrogen. The feed mixture containing the hydrocarbons is preferably fed to a reactor with one or more stationary catalyst beds, where oxygen-containing gas is also supplied between the catalyst beds when several of these are used. The dehydrogenation is preferably carried out at a temperature in the range from 400 to 700°C, at a pressure in the range from 0.5 to 3 bar absolute and using a volume velocity GHSV in the range from 10 to 10,000 N ml g<1> h"< 1.>

In both types of dehydrogenation process, the activity of the catalyst will decrease with time. When the activity has become undesirably low, the catalyst can be regenerated, e.g. in the same reactor. Regeneration can be carried out by burning off coke formed on the catalyst with oxygen-containing gas for a period of from 1 minute to 10 hours, preferably in a stream of air which is optionally mixed with nitrogen. The catalyst is then subjected to a reduction treatment for a period of from 1 minute to 10 hours in a stream of hydrogen. The treatments are conveniently carried out at 300-700°C, using volume velocities GHSV for the treatment streams of 10-10,000 N ml g"<1> h"<1>, preferably 100-5000 N ml g"<1>h"<1> . Optionally, a redispersion of the precious metal can be carried out, e.g. platinum, in the catalyst, with a chlorine-containing gas after the coke burning, but before the reduction treatment is carried out.

Through the regeneration of the catalyst, the original catalyst properties are restored to a significant extent. The restoration of the catalyst's activity and selectivity occurs more completely in the temperature range from 300°C to 400°C than at the higher temperatures. Also mixing nitrogen into the air flow used in the oxidation tends to improve the restoration of the catalyst properties.

Compared to the previously known dehydrogenation catalysts based on aluminum oxide, the new catalyst exhibits improved activity values and improved stability.

The invention is explained in more detail in the examples below.

Example 1

A Mg(Al)0 material with an atomic ratio Mg/Al of from 2:1 to 3:1 was prepared by the following procedure: An aqueous solution of 1.13 mol NaOH and 0.045 mol Na2CO3 was mixed with a solution of 0 .91 mol Mg (N03) 26H20 and 0.09 mol Al(N03) 39H20 at approx. 75°C (pH = 9.5). After filtering, washing and drying at approx. 100°C for approx. 15 hours, hydrotalcite, Mg6Al2 (OH)16C034H20, was formed. The structure was confirmed by X-ray diffraction analysis. The obtained material was calcined at 700°C for approx. 15 hours, whereby Mg(Al)0 was formed. The structure was confirmed by X-ray diffraction analysis, and the surface area was measured to be 156 m<2>/g.

Example 2

A Mg(Al)O material with an atomic ratio Mg/Al of from 2:1 to 3:1 was prepared by the following procedure: An aqueous solution of 1.13 mol NH4OH and 0.045 mol (NH4)2CO3 was mixed with an aqueous solution of 0.91 mol Mg(N03) 26H20 and 0.09 mol A1(N03) 39H20 at a temperature of approx. 75°C (pH = 9.5). After filtering, washing and drying at approx. 10 0°C for approx. 15 hours, hydrotalcite, Mg6Al2 (OH)16C034H20, was formed. The obtained material was calcined at 700°C for approx. 15 hours, whereby Mg(Al)0 was formed. The structure was confirmed by X-ray diffraction analysis, and the surface area was measured to be 198 m<2>/g.

Example 3

A Mg(Al)O material with a grain size of 300-400 (im) produced according to Example 1 was impregnated with a solution containing stannous chloride and hexachloroplatinic acid and with a solution of cesium nitrate according to the following procedure: 0.1150 g of SnCl22H20 and 0. 0805 g of H 2 PtCl 6 6 H 2 O was dissolved in 60 ml of ethanol, and the mixture was added to 10.1 g of Mg(Al) 0. When the impregnation was complete, the obtained material was evaporated to dryness in vacuo and then dried at about 100°C for about . 15 hours. The dried material was then calcined at 560°C for about 3 hours in air supplied at a rate of 100 cm<3>/min. 0.0711 g of CsN03 dissolved in 25 ml of water was then added to the calcined material. When the impregnation was complete, the obtained material was dried at about 100°C for about 15 hours. The dried material was calcined at 560°C for about 3 hours in air supplied in an amount of 100 cm<3> /min 3 g of the calcined product was then reduced at 600°C for 2 hours in a stream of H2 supplied in an amount of 20 cm<3>/min.

The reduced product was then oxidized at 600°C for approx. 1 hour in a stream of N2 containing 20 vol% air, supplied at a rate of 50 cm<3>/min, and for approx. 1 hour in clean air supplied at a rate of 50 cm<3>/min. The oxidized product was then reduced in the same way as before the oxidation.

A catalyst was obtained with the chemical composition:

0.3 wt% Pt

0.6 wt% Avg

0.5 wt% Cs

98.6 wt% Mg(Al)0.

The catalyst was tested in the dehydrogenation of propane in a microreactor with a stationary catalyst bed under the following conditions:

The results obtained are shown in table 1.

Example 4 - Comparative example.

The procedure according to Example 3 was followed, except that after the first reduction of the calcined product with H 2 , the oxidation in gaseous N 2 and the subsequent second reduction with H 2 were omitted.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 5

The procedure of Example 3 was followed, including the post-treatment consisting of reduction and subsequent oxidation and re-reduction (ROR pre-treatment) of the calcined catalyst, but the impregnation with CsN0 3 for the incorporation of cesium was omitted. The impregnation with a solution containing stannous chloride and hexachloroplatinic acid was carried out with such amounts of stannous chloride and hexachloroplatinic acid present that a catalyst with the chemical composition was obtained:

0.3 wt% Pt

0.6 wt% Avg

99.1 wt% Mg(Al)O.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 6

A Mg(Al)O material with a grain size of 300-400 (am prepared according to Example 2 was impregnated with a solution containing stannous chloride and hexachloroplatinic acid according to the following procedure: 0.1150 g of SnCl22H20 and 0.0805 g of H2PtCl66H20 were dissolved in 60 ml ethanol, and the mixture was added to 10.1 g of Mg(Al)O. When the impregnation was complete, the material obtained was evaporated to dryness in vacuo and then dried at about 100°C for about 15 hours. The dried material was then calcined at 56 0°C for about 3 hours in air supplied at a rate of 100 cm<3>/min.

The calcined product was then reduced at 600°C for 2 hours in a stream of H2 supplied at a rate of 20 cm<3>/min.

The reduced product was then oxidized at 60 0°C for approx. 1 hour in a stream of N2 containing 20 vol% air, supplied at a rate of 50 cm<3>/min, and for approx. 1 hour in clean air supplied at a rate of 50 cm<3>/min. The oxidized product was then reduced in the same way as before the oxidation.

A catalyst was obtained with the chemical composition:

0.3 wt% Pt

0.6 wt% Avg

99.1% by weight Mg(Al)0.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 7

The procedure of Example 6 was followed, including the post-treatment consisting of reduction and subsequent oxidation and re-reduction (ROR pre-treatment) of the calcined catalyst, but the impregnation with a solution containing stannous chloride and hexachloroplatinic acid was carried out with such amounts of stannous chloride and hexachloroplatinic acid present that it was obtained a catalyst with chemical composition:

0.3 wt% Pt

0.9% by weight Avg

98.8% by weight Mg(Al)0.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 8

The procedure of Example 6 was followed, including the post-treatment consisting of reduction and subsequent oxidation and re-reduction (ROR pre-treatment) of the calcined catalyst, but the impregnation with a solution containing stannous chloride and hexachloroplatinic acid was carried out with such amounts of stannous chloride and hexachloroplatinic acid present that it was obtained a catalyst with chemical composition:

0.3 wt% Pt

1.2 wt% Avg

98.5% by weight Mg(Al)0.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 9 - Comparative example.

A known dehydrogenation catalyst was prepared according to the method described in US Patent No. 4,788,371. 0.179 g of SnCl22H20 dissolved in 14 ml of water was added to 18.8 g

6-alumina with a grain size of 100 - 400 (am. When the impregnation was complete, the resulting material was dried at about 100°C for about 6 hours. The dried material was calcined for about 3 hours at 600° C in a stream of air supplied at a rate of 100 cm<3>/min.

0.349 g of H 2 PtCl 6 6 H 2 O dissolved in 14 ml of water was added to the calcined material. When the impregnation was complete, the resulting material was dried at approx. 10 0°C for approx. 15 hours. The dried material was calcined for approx. 3 hours at 570°C in a stream of air containing 10% water vapour, added in a quantity of approx. 100 cm<3>/min.

1.06 g of CsNO 3 dissolved in 14 ml of water was added to the calcined material. When the impregnation was complete, the resulting material was dried at approx. 100°C for approx. 30 hours. The dried material was calcined for approx. 3 hours at 570°C in an air flow supplied in a quantity of approx. 100 cm<3>/min. 3 g of the catalyst obtained was then reduced at 600°C for approx. 2 hours in a stream of H2 supplied at a rate of 20 cm<3>/min.

A catalyst was obtained with the chemical composition:

0.7 wt% Pt

0.5% by weight Avg

3.9 wt% Cs

94.9% by weight 0-alumina.

The catalyst was used for dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1.

Example 10 - Comparative example.

The catalyst preparation according to example 9 was repeated, after which 3 g of the reduced catalyst was oxidized at 600°C for approx. 1 hour in a stream of N2 containing 20 vol% air, supplied at a rate of 50 cm<3>/min, and for approx. 1 hour in clean air supplied at a rate of 50 cm<3>/min. The oxidized product was then reduced in the same way as before the oxidation, i.e. at 600°C for 2 hours in a stream of H2 supplied at a rate of 20 cm<3>/min.

The post-treatment of the catalyst after the calcination thus corresponded to an ROR pre-treatment as prescribed for the catalysts according to the invention.

The catalyst was used for the dehydrogenation of propane under the same conditions as in example 3. The results obtained are shown in table 1. The results in table 1 show that an ROR-pretreated catalyst according to the invention gives a large increase in the turnover of propane compared to a corresponding catalyst which has not been subjected to such pre-treatment (Example 3 compared to Example 4). The selectivity for the formation of propene is maintained at approximately the same level, whereby the total yield of propene is substantially increased.

The results in table 1 also show that with an increase in the surface area of the Mg (Al)O material from 156 m<2>/g to 198 m<2>/g, a somewhat more stable catalyst is obtained and thus an increase in the yield of propene after 25 hours (Example 6 compared to Example 5).

Increasing the catalyst's content of Sn from 0.6 wt% to 0.9 wt% appears to give a further increase in the yield of propene (Example 7 compared to Example 6).

The known catalyst according to example 9 gives a substantially lower yield of propene than the new catalysts (examples 3, 5, 6, 7, 8). When the known catalyst according to example 9 is subjected to a complete ROR pretreatment as prescribed according to the invention (example 10), the yield is also improved for the known catalyst. However, the ROR pretreatment does not have nearly as good an improving effect on the known catalyst as on the new catalysts, so that the new catalysts also give a significantly better yield of propene than the ROR pretreated catalyst according to example 10.

Example 11.

The performance of one of the new catalysts according to the invention was compared with the performance of a known catalyst in the dehydrogenation of propane carried out in combination with the combustion of hydrogen with oxygen-containing gas. The combination of dehydrogenation and hydrogen combustion was carried out in a reactor comprising two catalyst zones and an intermediate oxygen mixing zone. In addition to oxygen being added to the feed to the first catalyst zone, oxygen was also introduced into the oxygen mixing zone between the two catalyst zones.

The new catalyst (I) consisted of 0.3 wt% Pt and 1.2 wt% Sn on Mg(Al)0 and was a catalyst like that of Example 8 above, except that it was prepared with a grain size of 1-2 mm .

The known catalyst (II) was a catalyst according to US 4,788,371, consisting of 0.65 wt% Pt, 1.15 wt% Sn and 2.18 wt% Cs on 9-alumina. Catalyst (II) had been prepared according to US 4,788,371, in a similar way as described in example 9 above, except that, like the new catalyst (I), it had been prepared with a grain size of 1-2 mm.

The conditions used in the combined dehydrogenation and hydrogen combustion, and the results obtained, are listed in Table 2 below. The results in Table 2 show that both the new catalyst I and the known catalyst II, both of which are described in Example 11, do possible to achieve a selective oxidation of the hydrogen in the gas mixture.

The turnover of propane C3H8, and thus the yield of propene C3H6, is significantly higher for the new catalyst than for the known catalyst, namely 57% versus 45% after 5 hours and 55% versus 30% after 20 hours of operation respectively. The higher propene yield was achieved despite the fact that the gas space velocity per grams of catalyst and per hour (GHSV) was higher when using the new catalyst (2100 N ml g"<1>h"<1> against 1400 N ml g"<1>h"1 for the known catalyst) and despite the fact that the content of active noble metal (platinum) was significantly lower in the new catalyst (0.3% by weight compared to 0.65% by weight in the known catalyst). The higher GHSV used for the new catalyst was due to the fact that this catalyst had a lower volume weight than the known catalyst. Due to the lower volume weight of the new catalyst, the advantage of a low content of platinum was even greater than the percentage content alone indicates. A low platinum content is economically important in a commercial reactor.

The selectivity for oxidation of hydrogen to water is somewhat higher for the known catalyst than for the new catalyst, namely 88% versus 80% after 5 hours and 95% versus 87% after 20 hours of operation. This is at least partly explained by the fact that the lower propane conversion for the known catalyst led to the formation of smaller quantities of the desired dehydro-generated product, propene. With the known catalyst, the oxidation of hydrogen to water was therefore less susceptible to competitive oxidation of propene to carbon oxides.

Claims (18)

1. Catalyst comprising a combination of a support consisting of magnesium, aluminum and oxygen; a Group VIII precious metal; a metal from Group IVA and possibly an alkali metal from Group IA, characterized in that the carrier essentially consists of a mixed oxide of magnesium and aluminum Mg(Al)0 which generally has an MgO structure where Al<3+-> cations have replaced part of the Mg2+ cations, in which mixed oxide the molar ratio between magnesium and aluminum are in the range from 1:1 to 10:1, 2. Catalyst according to claim 1, characterized in that the molar ratio between magnesium and aluminum in the Mg(Al)O carrier is in the range from 2:1 to 5:1. 3. Catalyst according to claim 1 or 2, characterized in that the surface area of the Mg (Al) O carrier is from 10 to 400 m<2>/g, preferably from 100 to 300 m<2>/g, more preferably from 140 to 210 m<2>/g. 4. Catalyst according to one of claims 1 - 3, characterized in that it contains: 0.05 - 5.0% by weight noble metal from Group VIII, 0.05 - 7.0% by weight metal from Group IVA, 0 - 5.0 wt% metal from Group IA, calculated on the total weight of the catalyst. 5. Catalyst according to claim 4, characterized in that it contains 0.1-1.0% by weight metal from Group IA. 6. Catalyst according to claim 4, characterized in that it contains: 0.1 - 1.0% by weight precious metal from Group VIII, 0.1 - 3.0% by weight metal from Group IVA, 0 - 0.7% by weight metal from Group IA, calculated on the total weight of the catalyst. 7. Catalyst according to claim 6, characterized in that it contains 0.3-0.7% by weight metal from Group IA. 8. Catalyst according to claim 6, characterized in that it contains: 0.2 - 0.4% by weight precious metal from Group VIII, 0.3 - 1.5% by weight metal from Group IVA, 0 - 0.6% by weight metal from Group IA, calculated on the total weight of the catalyst. 9. Catalyst according to claim 8, characterized in that it contains 0.4-0.6% by weight of metal from Group IA. 10. Catalyst according to one of claims 1-9, characterized in that the metal from Group IVA is tin or germanium, preferably tin. 11. Catalyst according to one of claims 1-10, characterized in that the noble metal from Group VIII is platinum or palladium, preferably platinum. 12. Catalyst according to one of claims 1-11, characterized in that the alkali metal from Group IA is cesium or potassium, preferably cesium. 13. Process for producing a catalyst for the dehydrogenation of dehydrogenable C2-C30 hydrocarbons, where a noble metal from Group VIII, a metal from Group IVA and optionally an alkali metal from Group IA is incorporated into a carrier consisting of magnesium, aluminum and oxygen, characterized in that a carrier consisting essentially of a mixed oxide of magnesium and aluminum Mg(Al)0 is used, in which mixed oxide the molar ratio between magnesium and aluminum is in the range from 1:1 to 10:1, preferably from 2:1 to 5:1, and that it obtained material is subjected to a pre-treatment (ROR pre-treatment) comprising a reduction, preferably in hydrogen, a subsequent oxidation, preferably in air which is optionally mixed with nitrogen, and finally a second reduction, preferably in hydrogen. 14. Method according to claim 13, characterized in that the ROR pre-treatment is carried out at a temperature from 500 to 700°C. 15. Use of a catalyst according to one of claims 1-12, for dehydrogenation of dehydrogenable C2-C30 hydrocarbons, preferably C2-C5 paraffins. 16. Use according to claim 15, where the dehydrogenation is carried out at a temperature in the range from 500 to 700°C, a pressure in the range from 0.5 to 1.5 bar absolute and using a volume velocity (GHSV) of from 10 to 10,000 N ml g"<1> h"<1>. 17. Use of a catalyst according to one of claims 1-12, for dehydrogenation of dehydrogenable C2-C30 hydrocarbons, preferably C2-C5 paraffins, in combination with the mixing of an oxygen-containing gas, preferably oxygen, and combustion of hydrogen. 18. Use according to claim 17, where the dehydrogenation is carried out at a temperature in the range from 400 to 700°C, a pressure in the range from 0.5 to 3 bar absolute and using a volume velocity (GHSV) of from 10 to 10,000 N ml g"<1> h"<1>.