Catalyst Ta-Nb for the production of 1,3-butadiene

Abstract

The invention relates to a catalyst that comprises a mesoporous oxide matrix, with said matrix comprising at least one oxide of an element X that is selected from among silicon and titanium, taken by itself or in a mixture, with said catalyst comprising at least the tantalum element and the niobium element, with the tantalum mass representing between 0.1 to 30% by weight of the mass of the mesoporous oxide matrix, the niobium mass representing between 0.02 to 6% by weight of the mass of the mesoporous oxide matrix, the content by mass of the tantalum element being greater than or equal to the content by mass of the niobium element. The invention also relates to the use of this catalyst in a method for the production of 1,3-butadiene from a feedstock that comprises at least ethanol.

Claims

1. A catalyst comprising a mesoporous oxide matrix, said matrix comprising at least one oxide of an element X that is silicon or titanium, alone or in a mixture, said catalyst comprising tantalum and niobium, having a tantalum mass of 0.1 to 30% of the mass of the mesoporous oxide matrix, a niobium mass of 0.02 to 6% of the mass of the mesoporous oxide matrix, the content by mass of the tantalum element in said catalyst being greater than or equal to the content by mass of the niobium element in said catalyst, said catalyst being prepared by consecutive introduction of the niobium element and then the tantalum element.

2. The catalyst according to claim 1, in which said oxide matrix is mesostructured.

3. The catalyst according to claim 1, in which said oxide matrix is a silicon oxide that has a specific surface area of 100 to 1,200 m.sup.2/g, a mesopore volume of between 0.2 and 1.8 ml/g and a mesopore diameter of between 4 and 50 nm.

4. The catalyst according to claim 3, in which said oxide matrix contains an alkaline metal content that is expressed in terms of % by weight of metal in relation to the mass of the mesoporous matrix of less than 1% by weight.

5. The catalyst according to claim 1, further comprising at least one element of groups 1, 2, 3, 4 of the periodic table, or mixtures thereof, with the mass of said element representing between 0.01 and 5% of the mass of said mesoporous oxide matrix.

6. The catalyst according to claim 5, further comprising at least one element of groups 1 or 2 of the periodic table, or mixtures thereof, with the mass of said element representing between 0.01 and 5% of the mass of said mesoporous oxide matrix.

7. The catalyst according to claim 6, comprising at least one element that is Cs, Ca, Ba, or mixtures thereof, with the mass of said element representing between 0.01 and 5% of the mass of said mesoporous oxide matrix.

8. The catalyst according to claim 1, further comprising at least one element of groups 11 or 12 of the periodic table, or mixtures thereof, with the mass of said element representing between 0.5 and 10% of the mass of said mesoporous oxide matrix.

9. The catalyst according to claim 8, comprising at least Zn, with the mass of Zn representing between 0.5 and 10% of the mass of said mesoporous oxide matrix.

10. A process for the production of 1,3-butadiene from a feedstock that comprises at least ethanol, comprising contacting said feedstock with a catalyst according to claim 1, at a temperature of between 300 and 400 C., a pressure of between 0.15 and 0.5 MPa, and a volumetric flow rate of between 0.5 and 5 h.sup.1.

11. The process according to claim 10, in which the temperature is between 320 C. and 380 C.

12. The process according to claim 10, in which the pressure is between 0.15 and 0.3 MPa.

13. The process according to claim 10, in which the volumetric flow rate is between 1 and 4 h.sup.1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents a curve showing the relationship between tantalum content of the catalyst and butadiene productivity

(2) The invention is illustrated by means of the following examples.

EXAMPLES

Example 1: Preparation of the Catalyst a Based on 0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum Precursor that is Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(3) 0.67 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst A is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 2: Preparation of the Catalysts B, B and B Based on 0.5% Nb/SiO.SUB.2..SUP.., 0.25% Nb/SiO.SUB.2..SUP. and 1% Nb/SiO.SUB.2..SUP. (0.5%, 0.25% and 1% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium Precursor that is Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(4) 1.06 g of niobium oxalate and pentahydrated ammonium oxolate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst B is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(5) The catalyst B is prepared in a similar way with a precursor content that is 2 smaller (0.53 g of niobium oxalate and pentahydrated ammonium oxalate).

(6) The catalyst B is prepared in a similar way with a precursor content that is 2 larger (2.12 g of niobium oxalate and pentahydrated ammonium oxalate).

Example 3: Preparation of the Catalyst C Based on 0.5% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Nb and Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium and Tantalum Precursors Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Calcination (for Comparison Purposes)

(7) 1.05 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the catalyst A until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst C is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 4: Preparation of the Catalyst D Based on 0.5% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Nb and Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Drying (for Comparison Purposes)

(8) 0.67 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. 1.27 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 96 ml of water. This solution is quickly added drop by drop and mixed with the dried solid until wettability of the surface of the latter (dry impregnation) is observed. The latter is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst D is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 5: Preparation of the Catalyst E Based on 0.5% Ta/0.5% Nb/SiO.SUB.2..SUP. (0.5% by Weight of Nb and Ta in Relation to the Silica Mass) Obtained by Successive Dry Impregnations of the Niobium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Calcination (According to the Invention)

(9) 0.33 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 48 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the catalyst B until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst E is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 6: Preparation of the Catalyst F Based on 0.25% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.25% By Weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium and Tantalum Precursors Attached to the Surface of the Davisil 636 Commercial Slica () (for Comparison Purposes)

(10) 0.53 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the catalyst A until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst F is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 7: Preparation of the Catalysts F and F Based on 1% Nb/0.5% Ta/SiO.SUB.2..SUP. (1% by Weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (Outside of the Invention)

(11) 2.12 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the catalyst A until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst F is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(12) 2.54 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and =7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid that is obtained is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours.

(13) 0.67 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with the solid that is obtained until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst F is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 8: Preparation of the Catalyst G Based on 1% Ta/SiO.SUB.2..SUP. (1% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum Precursor that is Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(14) 1.34 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst G is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 9: Preparation of the Catalyst H 0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum Precursor that is Attached to the Surface of a Synthesized Silica () Along the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(15) Preparation of the Silica:

(16) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol and then dried at 100 C. for 24 hours. The silica powder that is obtained is then calcined in air at 550 C. for 4 hours.

(17) Preparation of the Catalyst:

(18) 0.11 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is dissolved in 31.7 ml of ethanol. This solution is added drop by drop and mixed with 10 g of silica until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst H is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 10: Preparation of the Catalyst I 0.5% Nb/SiO.SUB.2..SUP. (0.5% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium Precursor that is Attached to the Surface of a Synthesized Silica () Along the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(19) Preparation of the Silica:

(20) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The silica powder that is obtained is then calcined in air at 550 C. for 4 hours.

(21) Preparation of the Catalyst:

(22) 0.17 g of niobium oxalate and ammonium oxalate is dissolved in 18 ml of water. This solution is added drop by drop and mixed with 10 g of silica until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst I is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 11: Preparation of the Catalyst J 0.5% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium and Tantalum Precursors that are Attached to the Surface of a Synthesized Silica () Along the Metallo-Organic Modern Sol-Gel Path (According to the Invention)

(23) Preparation of the Silica:

(24) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The silica powder that is obtained is then calcined in air at 550 C. for 4 hours.

(25) Preparation of the Catalyst:

(26) 0.17 g of niobium oxalate and ammonium oxalate is dissolved in 18 ml of water. This solution is added drop by drop and mixed with 10 g of silica until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. 0.11 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is dissolved in 31.7 ml of ethanol. This solution is added drop by drop and mixed with 10 g of the solid NbSiO.sub.2 until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst J is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(27) Preparation of the Catalyst J 0.5% Nb/0.5% Ta/SiO.sub.2.sup. (0.5% by weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium and Tantalum Precursors that are Attached to the Surface of a Synthesized Silica () Along the Metallo-Organic Modern Sol-Gel Path on which 1,000 ppm of Sodium was Deposited (According to the Invention)
Preparation of the Silica:

(28) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The silica powder that is obtained is then calcined in air at 550 C. for 4 hours.

(29) Preparation of the Sodium-Doped Silica:

(30) 37 mg of sodium nitrate is dissolved in 18 ml of water. This solution is added drop by drop and mixed with 10 g of silica until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours, and then calcined in air at 550 C. for 4 hours.

(31) Preparation of the Catalyst:

(32) 0.17 g of niobium oxalate and ammonium oxalate is dissolved in 18 ml of water. This solution is added drop by drop and mixed with 10 g of silica until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. 0.11 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is dissolved in 31.7 ml of ethanol. This solution is added drop by drop and mixed with 10 g of the NbSiO.sub.2 solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst J is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 12: Preparation of the Catalyst K Based on 2% Ta/SiO.SUB.2..SUP. (2% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum Precursor that is Attached to the Surface of the Evonik Aerolyst 3041 Commercial Silica () (for Comparison Purposes)

(33) 1.35 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 28 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of Evonik extrudates (SBET160 m.sup.2/g, Vp0.9 ml/g and , 25 nm) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst K is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 13: Preparation of the Catalyst L Based on 0.5% Nb/SiO.SUB.2..SUP. (0.5% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium Precursor that is Attached to the Surface of the Evonik Aerolyst 3041 Commercial Silica () (for Comparison Purposes)

(34) 0.63 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 28 ml of water. This solution is quickly added drop by drop and mixed with 30 g of Evonik extrudates (SBET160 m.sup.2/g, Vp0.9 ml/g and 25 nm) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst L is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 14: Preparation of the Catalyst M Based on 0.5% Nb/2% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Nb and 2% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium and Tantalum Precursors that are Attached to the Surface of the Evonik Aerolyst 3041 Commercial Silica () (for Comparison Purposes)

(35) 0.63 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 28 ml of water. This solution is quickly added drop by drop and mixed with 30 g of catalyst K until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst M is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 15: Preparation of the Catalysts N, N and N Based on 0.5% Zr/SiO.SUB.2..SUP.., 0.25% Zr/SiO.SUB.2..SUP. and 0.05% Zr/SiO.SUB.2..SUP. (0.5%, 0.25% and 0.05% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Zirconium Precursor that is Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(36) 0.88 g of octahydrated zirconyl chloride is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst N is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(37) The catalyst N is prepared in a similar way with a precursor content that is 2 smaller (0.44 g of octahydrated zirconyl chloride).

(38) The catalyst N is prepared in a similar way with a precursor content that is 10 smaller (0.04 g of octahydrated zirconyl chloride).

Example 16: Preparation of the Catalyst O Based on 0.5% Zr/0.5% Ta/SiO.SUB.2..SUP. (0.5% by Weight of Zr and Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Zirconium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Calcination (for Comparison Purposes)

(39) 0.18 g of octahydrated zirconyl chloride is diluted in 15 ml of water. This solution is quickly added drop by drop and mixed with 10 g of the catalyst A until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst 0 is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 17: Preparation of the Catalysts P and P Based on 1% Nb/0.5% Zr/SiO.SUB.2..SUP. and 1% Nb/0.25% Zr/SiO.SUB.2..SUP. (0.5% or 0.25% by Weight of Zr and 1% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium and Zirconium Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Calcination (for Comparison Purposes)

(40) 0.42 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 15 ml of water. This solution is quickly added drop by drop and mixed with 10 g of the catalyst N until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst P is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(41) The same operation is repeated on the catalyst N to obtain the catalyst P.

Example 18: Preparation of the Catalyst R Based on 0.5% Nb/2% Ta/SiO.SUB.2..SUP. .(0.5% and 2% by Weight of Nb and Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () with Intermediate Drying (for Comparison Purposes)

(42) 2.68 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. 1.27 g of niobium oxalate and pentahydrated ammonium oxalate is then diluted in 96 ml of water. This solution is quickly added drop by drop and mixed with the dried solid until wettability of the surface of the latter (dry impregnation) is observed. The latter is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst R is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 19: Preparation of the Catalyst S Based on 0.75% Ta/SiO.SUB.2..SUP. (0.75% by Weight of Ta in Relation to the Silica Mass) that is Obtained Via the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(43) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 0.25 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The catalyst S is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 20: Preparation of the Catalyst T Based on 0.25% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.25% by Weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Synthesis of the Nb/SiO.SUB.2 .Solid Via the Metallo-Organic Modern Sol-Gel Path and Dry Impregnation of the Latter By the Associated Tantalum Precursor (According to the Invention)

(44) Preparation of the NbSiO.sub.2 Solid:

(45) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 0.13 g of niobium ethoxide (Nb(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The NbSiO.sub.2 powder that is obtained is then calcined in air at 550 C. for 4 hours.

(46) Preparation of the Catalyst:

(47) 0.11 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is dissolved in 31.7 ml of ethanol. This solution is added drop by drop and mixed with 10 g of the NbSiO.sub.2 solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst T is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 21: Preparation of the Catalyst U Based on 0.25% Nb/0.5% Ta/SiO.SUB.2..SUP. (0.25% by Weight of Nb and 0.5% by Weight of Ta in Relation to the Silica Mass) that is Obtained Via the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(48) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. A solution that contains 0.13 g of niobium ethoxide (Nb(OCH.sub.2CH.sub.3).sub.5), 0.25 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5), 5 ml of ethanol and 0.4 ml of 68% (by volume) nitric acid is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The catalyst U is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 22: Preparation of the Catalyst V Based on 10% Ta/SiO.SUB.2..SUP. (10% by Weight of Ta in Relation to the Silica Mass) that is Obtained Via the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(49) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 3.31 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The catalyst X is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 23: Preparation of the Catalyst W Based on 7% Nb/SiO.SUB.2..SUP. (10% by Weight of Ta in Relation to the Silica Mass) that is Obtained Via the Metallo-Organic Modern Sol-Gel Path (for Comparison Purposes)

(50) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 3.37 g of niobium ethoxide (Nb(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The catalyst X is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 24: Preparation of the Catalyst X Based on 7% Nb/10% Ta/SiO.SUB.2..SUP. (7% by Weight of Nb and 10% by Weight of Ta in Relation to the Silica Mass) that is Obtained Via the Metallo-Organic Modern Sol-Gel Path (Outside of the Invention)

(51) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. A solution that contains 3.37 g of niobium ethoxide (Nb(OCH.sub.2CH.sub.3).sub.5), 3.31 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5), 20 ml of ethanol and 1.6 ml of 68% (by volume) nitric acid is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The system is disturbed, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100 C. for 24 hours. The catalyst X is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 25: Preparation of the Catalyst Y Based on 5% Zn/1% Ta/SiO.SUB.2..SUP. (5% by Weight of Zn and 1% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of Zinc and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(52) 11.37 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(53) 0.67 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 48 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the solid that was previously prepared until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst V is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 26: Preparation of the Catalyst Z Based on 5% Zn/0.25% Nb/SiO.SUB.2..SUP. (5% by Weight of Zn and 0.25% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Zinc and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(54) 11.37 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(55) 0.53 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the solid that was previously prepared until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst W is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 27: Preparation of the Catalyst AA Based on 10% Zn/0.25% Nb/1% Ta/SiO.SUB.2..SUP. (10% by Weight of Zn, 0.25% Nb and 1% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Zinc, Niobium and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (According to the Invention)

(56) 22.74 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(57) 0.53 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 76 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(58) 0.67 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 45 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst X is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 28: Preparation of the Catalyst AB Based on 10% Zn/1.7% Ta/SiO.SUB.2..SUP. (10% by Weight of Zn and 1.7% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Zinc and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (for Comparison Purposes)

(59) 22.74 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(60) 1.14 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 48 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst Y is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 29: Preparation of the Catalyst AC Based on 10% Zn/0.5% Nb/0.8% Ta/SiO.SUB.2..SUP. (10% By Weight of Zn, 0.5% by Weight of Nb and 0.8% By Weight of Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium, Zinc and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (According to the Invention)

(61) 22.74 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(62) 1.06 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 76 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(63) 0.54 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 48 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst Y is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

Example 30: Preparation of the Catalyst AD Based on 10% Zn/0.2% Nb/1.4% Ta/SiO.SUB.2..SUP. (10% by Weight of Zn, 0.2% by Weight of Nb and 1.4% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Successive Dry Impregnations of the Niobium, Zinc and Tantalum Precursors that are Attached to the Surface of the Davisil 636 Commercial Silica () (According to the Invention)

(64) 22.74 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET500 m.sup.2/g, Vp0.9 ml/g and 7 nm, granulometry: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550 C. for 4 hours.

(65) 0.42 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 76 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The intermediate solid is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(66) 0.95 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 48 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100 C. for 24 hours. The catalyst Y is obtained by calcination of the solid that is dried in air at 550 C. for 4 hours.

(67) Definition of the Terms

(68) pph (g/g.sub.cat/h):

(69) $\mathrm{pph}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{the}\mathrm{feedstock}\left(g/h\right)}{\mathrm{catalyst}\mathrm{mass}\left(\mathrm{gcat}\right)}$
Conversion (% by weight):

(70) $\mathrm{conversion}=100*\left(1-\frac{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{exiting}\mathrm{ethanol}+\\ \mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{exiting}\mathrm{acetaldehyde}\end{array}}{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{entering}\mathrm{ethanol}+\\ \mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{entering}\mathrm{acetaldehyde}\end{array}}\right)$
Productivity (g.sub.c/g.sub.cat/h)

(71) $\mathrm{productivity}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\mathrm{belonging}\mathrm{to}\mathrm{butadiene}\left(\mathrm{gc}\text{/}h\right)}{\mathrm{catalyst}\mathrm{mass}\left(\mathrm{gcat}\right)}$
Selectivity (% C):

(72) $\mathrm{selectivity}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\mathrm{belonging}\mathrm{to}\mathrm{butadiene}\left(\mathrm{gc}\text{/}h\right)}{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\\ \mathrm{belonging}\mathrm{to}\mathrm{the}\mathrm{converted}\mathrm{feedstock}\end{array}}$
{A+B} represents the weighted activity of the catalysts A and B in the absence of any interaction between these two catalysts.

(73) $\mathrm{pph}\left\{A+B\right\}=\mathrm{pph}\left(A\right)+\mathrm{pph}\left(B\right)$$\mathrm{productivity}\left\{A+B\right\}=\mathrm{productivity}\left(A\right)+\mathrm{productivity}\left(B\right)$$\mathrm{selectivity}\left\{A+B\right\}=\frac{\begin{array}{c}\mathrm{productivity}\left(A\right)*\mathrm{selectivity}\left(A\right)+\\ \mathrm{productivity}\left(B\right)*\mathrm{selectivity}\left(B\right)\end{array}}{\mathrm{productivity}\left(A\right)+\mathrm{productivity}\left(B\right)}$

(74) If a better result is obtained during the combination of A and B, synergetic interaction may be said to have taken place. If a less good result is obtained, this is an antagonistic interaction.

(75) Description of the Catalytic Test Unit

(76) The reactor that is used in the following examples consists of a stainless steel tube that is 20 cm long and 10 mm in diameter. The reactor is first loaded with carborundum and then with the catalyst that is diluted in carborundum and finally with carborundum. The carborundum is inert relative to the feedstock and does not influence the catalytic results; it makes it possible to position the catalyst in the isothermal zone of the reactor and to limit the risks of material and heat transfer problems. The temperature of the reactor is controlled with a tubular furnace with three heating zones. The liquid feedstock (mixture of ethanol and acetaldehyde in a ratio R) is injected via a double-piston HPLC pump. The liquid stream is evaporated in the lines that are heated by a tracer before entering into the reactor and is homogenized by passing into a static mixer. The products that are formed during the reaction are kept in the vapor phase so that they can be analyzed on-line by gas chromatography (PONA and Carboxen 1010 capillary columns) to make possible the most precise identification of the hundreds of products formed. The catalyst is activated in situ under nitrogen at the test temperature. The specific operating conditions are described in the following examples.

(77) Catalytic Test 1: Demonstration of the Nb/Ta Synergy EffectEtOH/AcH Feedstock

(78) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C., and the pressure at 1.5 bar. For each catalyst, the pph and therefore the feedstock flow rate are adjusted to obtain a conversion of the feedstock of 35%.

(79) The values of carbon productivity and butadiene selectivity are measured at this operating point.

(80) TABLE-US-00001 Ta Nb pph Butadiene Con- Con- (g/ Productivity Selectivity Catalyst tent tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) A 0.5 0.9 0.11 68 B 0.5 0.9 0.10 61 {A + B} 0.5 0.5 1.8 0.21 65 Outside of C 0.5 0.5 2.0 0.26 73 the Invention Outside of D 0.5 0.5 1.7 0.22 73 the Invention According E 0.5 0.5 3.0 0.39 74 to the Invention Outside of F 0.5 0.25 1.6 0.21 74 the Invention

(81) The catalyst E according to the invention has a selectivity and a productivity that are greater than those of the catalysts outside of the invention.

(82) TABLE-US-00002 Ta Nb pph Butadiene Con- Con- (g/ Productivity Selectivity Catalyst tent tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) A 0.5 0.9 0.11 68 B 1 1.9 0.20 59 {A + B} 0.5 1 2.8 0.31 63 Outside F 0.5 1 2.0 0.24 67 of the Invention Outside F 0.5 1 2.0 0.26 67 of the Invention

(83) The catalyst F with a niobium content that is greater than that of tantalum does not make it possible to improve selectivity and productivity in comparison to the sum of the performances of the catalysts A and B, even by modifying the order of addition of tantalum and niobium (F).

(84) Catalytic Test 2: Demonstration of the Nb/Ta Synergy EffectEtOH/AcH Feedstock

(85) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C. and the pressure at 1.5 bar. For each catalyst, the pph and therefore the feedstock flow rate are adjusted to obtain a conversion of the feedstock of 25%.

(86) The values of carbon productivity and butadiene selectivity are measured at this operating point.

(87) The feedstock flow rate is regulated to obtain a conversion of the feedstock of 25%.

(88) TABLE-US-00003 Nb pph Butadiene Ta Con- (g/ Productivity Selectivity Catalyst Content tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) H 0.5 1.7 0.16 70 I 0.5 2.7 0.20 53 {H + 0.5 0.5 4.4 0.36 61 I}.sub.50/50 According J 0.5 0.5 9.5 1.02 71 to the Invention According J 0.5 0.5 6.8 0.75 73 to the Invention

(89) The catalysts J and J according to the invention have a selectivity and a productivity that are greater than those of the catalysts H and I.

(90) TABLE-US-00004 Ta Nb pph Butadiene Con- Con- (g/ Productivity Selectivity Catalyst tent tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) V 10 25 2.35 71 W 7 20 1.06 40 {V + W} 10 7 45 3.41 61 Outside X 10 7 32 2.37 56 of the Invention

(91) The catalyst X with a niobium content that is greater than 6% does not make it possible to improve selectivity and productivity in comparison to the sum of performances of the catalysts V and W.

(92) Catalytic Test 3: Demonstration of the Absence of Ta/Zr SynergyEtOH/AcH Feedstock

(93) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C. and the pressure at 1.5 bar. For each catalyst, the pph and therefore the feedstock flow rate are adjusted to obtain a conversion of the feedstock of 35%.

(94) The values of carbon productivity and butadiene selectivity are measured at this operating point.

(95) TABLE-US-00005 Ta Zr pph Butadiene Con- Con- (g/ Productivity Selectivity Catalyst tent tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) A 0.5 0.9 0.11 68 N 0.5 2.4 0.28 64 {A + N} 0.5 0.5 3.3 0.39 65 Outside O 0.5 0.5 1.9 0.25 65 of the Invention

(96) In contrast to the tantalum/niobium association, the association between tantalum and zirconium does not make it possible to improve the selectivity of the reaction and even has an antagonistic effect on the productivity of the catalyst.

(97) Catalytic Test 4: Demonstration of the Absence of Nb/Zr SynergyEtOH/AcH Feedstock

(98) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C. and the pressure at 1.5 bar. For each catalyst, the pph and therefore the feedstock flow rate are adjusted to obtain a conversion of the feedstock of 35%.

(99) The values of carbon productivity and butadiene selectivity are measured at this operating point.

(100) The feedstock flow rate is regulated to obtain a conversion of the feedstock of 35%.

(101) TABLE-US-00006 Zr pph Butadiene Nb Con- (g/ Productivity Selectivity Catalyst Content tent g.sub.cat/h) (g.sub.C/g.sub.cat/h) (% C) B 1 1.8 0.20 59 N 0.5 2.2 0.28 64 {B + 1 0.5 4.2 0.48 62 N} Outside P 1 0.5 2.7 0.38 66 of the Invention B 1 1.8 0.20 59 N 0.25 1.2 0.16 65 {B + 1 0.25 3.0 0.36 62 N} Outside P 1 0.25 1.6 0.23 66 of the Invention

(102) In contrast to the tantalum/niobium association, the association between niobium and zirconium makes it possible to improve the selectivity of the reaction, but it has an antagonistic effect on the productivity of the catalyst.

(103) Catalytic Test 5: Demonstration of the Substitution EffectEtOH/AcH Feedstock

(104) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C., the pph at 2.5 h.sup.1 and the pressure at 1.5 bar. The values of carbon productivity and butadiene selectivity are measured at this operating point.

(105) A standard curve of the relationship between the tantalum content and butadiene productivity is plotted by causing the tantalum content to vary between 0.25% and 5%, with the catalysts being prepared by following the preparation protocol for the catalyst A. This curve is presented in FIG. 1.

(106) The curve that is presented in FIG. 1 makes it possible, according to the productivity that is obtained under the test conditions with each catalyst based on Ta and Nb, to estimate the tantalum content that would be necessary to obtain this productivity if a catalyst containing only Ta was used. The amount of tantalum saved represents the difference between this value and the actual tantalum content of the tested catalyst.

(107) TABLE-US-00007 Equivalent of Ta by Ta Itself Saved Conversion Butadiene (Depending g/g.sub.cat Ta Nb (% by Productivity Selectivity on (% Catalyst Content Content Weight) (g/g.sub.cat/h) (% C) Production) Ta) C 0.5 0.5 31 0.31 73 1 0.5 (49%) D 0.5 0.5 29 0.28 72 0.9 0.4 (41%) E 0.5 0.5 37 0.36 74 1.4 0.9 (62%) R 2 0.5 47 0.43 72 2.3 0.3 (9%)

(108) The table shows that it is possible to obtain the same performances as a catalyst that is based on tantalum with catalysts based on niobium and tantalum, but with smaller contents of tantalum. The catalyst E that is prepared by introducing in succession the niobium element and then the tantalum element makes it possible to achieve a much more significant savings in tantalum.

(109) Catalytic Test 6: Demonstration of the Substitution EffectEtOH/AcH Feedstock

(110) In this test, the ethanol/acetaldehyde ratio is set at 2.6 (mol/mol), the temperature at 350 C., the pph at 3 h.sup.1 and the pressure at 1.4 bar. The values of carbon productivity and butadiene selectivity are measured at this operating point.

(111) TABLE-US-00008 Ta Nb Conversion Butadiene Cat- Con- Con- (% by Productivity Selectivity alyst tent tent Weight) (g/g.sub.cat/h) (% C) S 0.75 29 0.34 71 According T 0.5 0.25 32 0.37 70 to the Invention Outside of U 0.5 0.25 28 0.34 73 the Invention

(112) The table shows that it is possible to obtain the same performances as a catalyst that is based on tantalum with catalysts based on niobium and tantalum but with smaller contents of tantalum, the catalyst prepared by introducing consecutively the niobium and then the tantalum making possible a significant gain in productivity in relation to the catalyst U in which tantalum and niobium have been added simultaneously.

(113) Catalytic Test 7: Demonstration of the Synergy EffectEtOH Feedstock

(114) In this test, the feedstock contains only ethanol, the temperature is set at 375 C., and the pressure at 1.4 bar. For each catalyst, the pph and therefore the feedstock flow rate are adjusted to obtain a conversion of the feedstock of 55%.

(115) The values of carbon productivity and butadiene selectivity are measured at this operating point.

(116) TABLE-US-00009 Ta Nb Content Content Butadiene Zn (% by (% by Productivity Selectivity Catalyst Content Weight) Weight) pph (g/gcat/h) (% C) V 5 1 0 0.5 0.11 63 W 5 0 0.25 0.2 0.03 45 {V + W} 10 1 0.25 0.7 0.14 59 According X 10 1 0.25 0.8 0.18 64 to the Invention

(117) The catalyst X according to the invention has a selectivity and a productivity that are greater than those of the catalysts V and W.

(118) Catalytic Test 8: Demonstration of the Substitution EffectEtOH Feedstock

(119) In this test, the feedstock contains only ethanol, the temperature is set at 350 C., the pph at 3 h.sup.1 and the pressure at 1.4 bar. The values of carbon productivity and butadiene selectivity are measured at this operating point.

(120) TABLE-US-00010 Ta Nb Content Content Conversion Butadiene Zn (% by (% by (% by Productivity Selectivity Catalyst Content Weight) Weight) Weight) (g/gcat/h) (% C) Y 10 1.7 55 0.34 63 According Z 10 0.8 0.5 53 0.29 61 to the Invention According Z 10 1.4 0.2 55 0.30 63 to the Invention

(121) The table shows that it is possible within the framework of a method for producing butadiene in one step from ethanol to obtain the same performances as a catalyst based on tantalum with catalysts based on niobium and tantalum but with smaller contents of tantalum.