METHOD FOR THE INDIRECT ADDITION OF AN ORGANIC COMPOUND TO A POROUS SOLID

Abstract

The present invention relates to a process for adding an organic compound to a porous solid wherein, in an open or closed chamber, a first batch of porous solid rich in an organic compound is brought together with a second batch of porous solid low in said organic compound. The step of bringing the porous solids together is carried out under temperature, pressure and time conditions such that a fraction of said organic compound is transferred gaseously from the first batch of porous solid to the second batch of porous solid.

Claims

1. A process for adding an organic compound to a porous solid comprising a step a) wherein, in an open or closed chamber, a first batch of porous solid rich in an organic compound is brought together with a second batch of porous solid low in said organic compound, step a) being carried out under temperature, pressure and time conditions such that a fraction of said organic compound is transferred gaseously from the first batch of porous solid to the second batch of porous solid.

2. The process as claimed in claim 1, wherein the temperature of step a) is below the boiling point of the organic compound.

3. The process as claimed in claim 1 2, wherein the amount of said organic compound of the second batch of porous solid is zero.

4. The process as claimed in claim 1, wherein step a) is carried out by placing the first and second batches of porous solid in physical contact.

5. The process as claimed in claim 4, wherein step a) is carried out in a storage or transport chamber. process as claimed in claim 1, wherein step a) of bringing said batches together is carried out in a chamber comprising two separate compartments that are in gaseous communication, said compartments being suitable for containing, respectively, the first and second batches of porous solid so that the bringing together of the batches of support takes place without physical contact.

7. The process as claimed in claim 1, comprising the following steps: a′) providing an initial batch of porous solid, b′) heterogeneously impregnating the initial batch of porous solid with the organic compound in the liquid state so as to provide a first batch of porous solid rich in organic compound and a second batch of porous solid low in organic compound, c′) leaving together, according to step a), said batches of porous solids resulting from step b′) under temperature, pressure and time conditions such that a fraction of said organic compound is transferred gaseously from the first batch of porous solid to the second batch of porous solid.

8. The process as claimed in 1, comprising the following steps: a″) providing an initial batch of porous solid, b″) separating said initial batch into first and second separate fractions, c″) introducing the organic compound in the liquid state into the first fraction of solid resulting from step b″) so as to provide the first batch of solid rich in organic compound, d″) bringing, according to step a), the first batch of support rich in organic compound resulting from step c″) together with the second fraction of solid resulting from step b″) under temperature, pressure and time conditions such that a fraction of said organic compound is transferred gaseously from the first batch of porous solid to the second batch of porous solid.

9. The process as claimed in claim 1, wherein step a) is carried out at an absolute pressure of between 0 and 1 MPa.

10. The process as claimed in claim 1, wherein step a) is carried out in the presence of a flow of a carrier gas.

11. The process as claimed in claim 1, wherein at least one fraction of the porous solid resulting from step a) is separated and said fraction is recycled to step a).

12. The process as claimed in claim 1, wherein the porous solid is chosen from a porous catalyst support and a porous catalyst support further comprising at least one metal from group VIB and/or at least one metal from group VIII.

13. The process as claimed in claim 12, wherein the porous support is based on an oxide of a metal and/or of a metalloid.

14. The process as claimed in claim 1, wherein the organic compound is chosen from organic molecules containing oxygen and/or nitrogen and/or sulfur.

15. A process for preparing a catalyst comprising a porous support, at least one metal from group VIB and/or at least one metal from group VIII and at least one organic compound, the process comprising at least the following steps: i) carrying out the process for adding at least one organic compound as claimed in claim 1 by bringing the porous support together with a porous solid containing said organic compound so as to provide a batch of porous support containing said organic compound, ii) depositing at least one metal from group VIB and/at least one metal from group VIII on the porous support by bringing the support into contact with a solution containing at least one precursor of at least one metal from group VIII and/or at least one precursor of at least one metal from group VIB, iii) drying the porous support resulting from step ii), step i) being carried out separately before or after steps ii) and iii).

16. The preparation process as claimed in claim 15, wherein the solution of step ii) further comprises at least one additional organic compound different from the organic compound used in step i).

17. The preparation process as claimed in claim 15, further comprising at least one step of impregnating the porous support with a solution comprising an organic compound different from the organic compound used in step i).

18. A process for hydrotreating a hydrocarbon feedstock wherein hydrogen, the hydrocarbon feedstock and a catalyst are brought into contact at a temperature between 180° C. and 450° C., at a pressure between 0.5 and 30 MPa, with an hourly space velocity of between 0.1 and 20 h.sup.−1 and with a hydrogen/feedstock ratio expressed as volume of hydrogen, measured under normal temperature and pressure conditions, per volume of liquid feedstock of between 50 l/l to 5000 l/l, said catalyst having been prepared by a process as claimed in claim 15 and subjected to at least one sulfiding step.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0081] FIG. 1 is a diagram illustrating the principle of adding an organic compound according to standard practice known to a person skilled in the art;

[0082] FIG. 2 is a diagram illustrating the process according to the invention for adding an organic compound according to a first embodiment;

[0083] FIG. 3 shows a diagram of the process for adding an organic compound according to another embodiment;

[0084] FIG. 4 is a diagram of the process for adding an organic compound according to a third embodiment.

[0085] Generally, similar elements are denoted by identical references in the figures.

[0086] FIG. 1 corresponds to a block diagram presenting a known process for adding an organic compound to a porous catalyst support or a catalyst precursor as described previously that is denoted hereinbelow by the generic term “porous solid”.

[0087] The batch of solid 1 is subjected to an optional pretreatment in a unit 2 for pretreatment of the solid 1 intended, if need be, to condition the solid before the step of impregnation of the organic compound. This pretreatment step may, for example and depending on the desired effect, be a preliminary drying step in order to adjust the residual moisture content.

[0088] This pretreatment may also be an addition by controlled addition of the same solvent, introduced through the line 3, as the one which is used during the impregnation of the organic compound in order to avoid too lively a reaction of the solid during the organic compound impregnation phase. The type of reaction that it is desired to avoid is for example a great release of heat linked to the sudden adsorption of the solvent (such as water for example) on the active sites of the solid.

[0089] The batch of solid 4 resulting from the pretreatment step is sent to a unit 5 for impregnation of the organic compound. According to the prior art, this step uses a solution containing a solvent, for example water, in which the organic compound to be impregnated is dissolved. In FIG. 1, the impregnation solution is conveyed by the line 6. The impregnation is carried out according to any method known to a person skilled in the art and for example by a dry impregnation. In this impregnation method, the solid set in motion is subjected to a jet of the impregnation solution, the volume of solution sprayed generally being equivalent to the whole of the pore volume of the solid to be impregnated which is accessible to the solution. In accordance with prior art practice, the impregnated solid is discharged via the line 7 into a drying unit 8 in order to eliminate the solvent which was incorporated in the solid at the same time as the organic compound. The stream 9 represents the hot utility that is used to dry the solid, which is for example hot air. This results in a dry solid 10 impregnated with the chosen organic compound. Depending on the organic compound chosen and its solubility in the solvent used during the impregnation step, it is possible that the amount introduced is not sufficient at the end of a single impregnation step. In which case, use may be made of several impregnation and drying steps described above.

[0090] After impregnation of the organic compound, the solid may undergo one or more steps of impregnation of one or more metals from group VIB and/or from group VIII in order to deposit a metal catalytic phase. The impregnation step(s) may be followed, optionally after a maturing step, by a step of drying at a moderate temperature, generally below 200° C.

[0091] FIG. 2 depicts the process according to the invention for adding an organic compound according to a first embodiment. The solid 1 having been, if necessary, conditioned in a pretreatment unit 2 is transferred via the line 4 into the unit 5 for introducing the organic compound. In accordance with the invention, this impregnation step is carried out with the organic compound which is in the liquid state introduced via the line 6. The volume of liquid organic compound which is used is chosen so that it is strictly less than the pore volume of the total batch of porous solid 1 and of porous solid 2 which is accessible to the liquid organic compound.

[0092] The solid rich in organic compound is discharged from the unit 5 for introducing the organic compound via the line 7 to a unit 20 in which said solid is brought together, preferably under controlled conditions (pressure/temperature/composition of the gaseous atmosphere), with another batch of porous solid 2 low in said organic compound, for example the amount of organic compound of the batch of porous solid 2 is zero. The objective of the step of bringing together the solids in the unit 20 is to carry out the gaseous transfer of a portion of the organic compound contained in the solid rich in organic compound to the solid low in organic compound in order to provide, at the end of the balancing, the batch of solid 22 impregnated with said organic compound. The nature and the pore structure of the solid rich in organic compound and of the solid low in organic compound are also parameters which may be taken into account. Thus the chemical composition of the solid rich in organic compound may be such that its adsorptivity with respect to the organic compound is lower than that of the solid to be additivated. A similar effect may be obtained by adapting the porous structure of the solid rich in organic compound so that it has a mean pore opening that is greater than that of the solid to be impregnated so as to favor the transfer to the solid low in organic compound, particularly in the case of a mechanism involving capillary condensation.

[0093] As indicated in FIG. 2, when the solids are of the same nature, the solid low in organic compound may be chosen from the solid 23 before pretreatment or the pretreated solid 24.

[0094] The step of bringing together the solids according to the invention may be carried out with or without physical contact of the two batches of solids. When said step of bringing together the solids is carried out with physical contact of the solids, the solids may be mixed before or during the bringing-together step.

[0095] According to the invention, the bringing-together step a) is carried out at a temperature below the boiling point of the organic compound at the chosen pressure. For example, the temperature may be below 150° C. and for a range of absolute pressure between 0 and 1 MPa. The duration of this step is chosen so as to obtain a balance as described previously. Generally, the higher the temperature and the lower the pressure, the shorter this time will be, which will be favorable for integrating this step into a rapid production line. Typically, the duration is less than 24 hours, preferentially less than 5 hours and preferably less than 1 hour.

[0096] Within the context of the invention, the unit 20 enabling the solids to be brought together is for example a chamber, preferably a closed chamber. To enable the solids to be brought together without physical contact between the solids, it is possible to use a compartmentalized chamber so as to receive, in two respective compartments, the solid rich in organic compound and the solid low in organic compound, the compartments being configured to allow the passage of the organic compound in the gaseous state between the two compartments.

[0097] According to the invention, the bringing-together step may also be carried out in a suitable storage or transport container into which the mixed solids are placed in bulk. This type of use may be practiced when the balancing time is not critical. The pressure and temperature conditions may then be close to ambient and the time for bringing together the solids (from several days to several weeks) corresponds to the time needed for transporting the solids from the production site to the site of use of the solids, optionally with an additional storage time at the end user's premises.

[0098] FIG. 3 represents another embodiment of the process for adding the organic compound according to the invention which differs from that of FIG. 2 by the fact that the batches of solid rich in organic compound and of solid low in organic compound are obtained at the same time at the end of the step of impregnating a fraction of an initial batch of porous solid.

[0099] With reference to FIG. 3, a stream of conditioned solid withdrawn from the unit 2 for pretreatment of the solid is sent via the line 4 to the step of introducing the organic compound in the liquid state. The introduction step which is carried out in the unit 5 differs from that of FIG. 2 in that it is carried out so that only a fraction of the solid is bought into contact with the liquid organic compound introduced by the line 6. At the end of this step, two fractions of solids A and B having different contents of organic compound are obtained. By way of nonlimiting example, the impregnation step according to the embodiment of FIG. 3 may consist in spreading the organic compound in the liquid state, for example by means of a dispersion device, on the surface of the batch of solid so as to provide a fraction of solid A rich in organic compound and a fraction of solid B low in organic compound. For example, this step of impregnating the batch of solid may be carried out in a unit 5 comprising a belt conveyor for conveying the solid and which unit is equipped with the liquid dispersion device. At the end of the impregnation step, the batches of solids A and B are left together with one another. For example, they are brought together in the unit 5 for introducing the liquid organic compound or in a dedicated unit 20 as indicated in FIG. 3. Preferably, the fractions A and B are mixed after the step of introducing the liquid organic compound.

[0100] Another embodiment of the process for adding an organic compound to a solid (a porous catalyst support or a catalyst precursor) is depicted in FIG. 4. This embodiment according to the invention corresponds to the case where the porous solid containing the organic compound acts as a reservoir of organic compound for the step of bringing the solids together. As indicated in FIG. 4, a so-called “carrier” porous solid 4, optionally pretreated in a conditioning unit 2 as described above, is impregnated in the impregnation unit 5 with a liquid organic compound introduced via the line 6. The carrier solid 7 rich in said organic compound is transferred into the unit 20 in which said carrier solid is brought together with a so-called porous solid “of interest” low in organic compound conveyed via the line 21. For example, the porous solid may have a zero amount of said organic compound.

[0101] At the end of the step of bringing the solids together, a mixture of carrier solid and solid of interest, each containing said organic compound, is withdrawn from the unit via the line 22. The mixture of solids is then sent to a separation unit 25 which carries out a physical separation of the carrier solid and solid of interest. Owing to the use of the separation, two streams of solids are obtained, namely the carrier solid 26 containing the organic compound and the solid of interest 27 also containing the organic compound.

[0102] In accordance with this embodiment, the carrier solid still containing the organic compound 26 is recycled to the unit for introducing the liquid organic compound for subsequent use. In this embodiment, the carrier solid has at least one discriminating physical feature with respect to the solid of interest in order to enable the separation thereof. For example and nonlimitingly, this physical feature may be: [0103] the size of the particles of the solid: the separation may be carried out through a screen [0104] magnetism: the separation is carried out by the application of a magnetic field [0105] the density of the solid: optionally in conjunction with the size of the particles, this difference in density may for example be used for a separation via elutriation.

[0106] The nature and the porous structure of the carrier solid and of the solid of interest are also parameters to be taken into account. Thus, the carrier solid has a chemical composition suitable for disfavoring the adsorption of the compound to be impregnated relative to the adsorption of the compound to be impregnated on the solid of interest. A similar effect may be obtained by adapting the porous structure of the carrier solid so that it has a mean pore opening that is greater than that of the solid of interest so as to favor the transfer of the organic compound to the solid of interest, particularly in the case of a mechanism involving capillary condensation.

EXAMPLES

[0107] The following examples specify the advantage of the invention without however limiting the scope thereof.

Example 1: Preparation of CoMoP Catalysts on Alumina without Organic Compound C1 and C2 (According to the Prior Art)

[0108] To an alumina support in “extrudate” form, having a BET surface area of 230 m.sup.2/g, a mesopore volume measured by mercury porosimetry of 0.78 ml/g and a volume median diameter by mercury porosimetry of 11.5 nm, cobalt, molybdenum and phosphorus are added. The impregnation solution is prepared by dissolving, at 90° C., molybdenum oxide (21.1 g) and cobalt hydroxide (5.04 g) in 11.8 g of an 85 wt % aqueous solution of phosphoric acid. After drying, the extrudates are left to mature in a water-saturated atmosphere for 24 h at ambient temperature, then they are dried at 90° C. for 16 hours. The dried catalytic precursor thus obtained is denoted by C1. The calcination of the catalytic precursor C1 at 450° C. for 2 hours leads to the calcined catalyst C2. The metal composition of the catalyst precursor Cl and of the calcined catalyst C2 is: MoO.sub.3=19.5±0.2 wt %, CoO=3.8±0.1 wt % and P.sub.2O.sub.5=6.7±0.1 wt %, the percentages being expressed relative to the weight of dry catalyst.

Example 2: Preparation of the CoMoP Catalyst Additivated with Citric Acid on Alumina C3 (According to the Prior Art) by Co-Impregnation

[0109] To the alumina support described in example 1 and which is in the “extrudate” form, cobalt, molybdenum and phosphorus are added. The impregnation solution is prepared by dissolving, at 90° C., molybdenum oxide (28.28 g) and cobalt hydroxide (6.57 g) in 15.85 g of an 85 wt % aqueous solution of phosphoric acid. After homogenization of the preceding mixture, 38 g of citric acid were added before adjusting the volume of solution to the total pore volume of the support by addition of water. The amount of citric acid used is such that the (citric acid)/Mo molar ratio is equal to 1 mol/mol and the (citric acid)/Co molar ratio is equal to 2.7 mol/mol. After dry impregnation, the extrudates are left to mature in a water-saturated atmosphere for 24 h at ambient temperature, then they are dried at 120° C. for 16 hours. The catalyst additivated with citric acid thus obtained is denoted by C3. The final metal composition of the catalyst C3 relative to the mass of dry catalyst is then the following: MoO.sub.3=19.6±0.2 wt %, CoO=3.7±0.1 wt % and P.sub.2O.sub.5=6.7±0.1 wt %.

Example 3: Preparation of the CoMoP Catalyst Additivated with 2-methoxyethyl 3-oxobutanoate on Alumina C4 (According to the Prior Art) by Post-Impregnation

[0110] Added to 18 g of catalyst Cl described in example 1 and which is in the form of extrudates, are 3.2 g of 2-methoxyethyl 3-oxobutanoate diluted in water so as to obtain a solution having a total volume equal to the pore volume of the catalyst. The amount of organic compound added is such that the (2-methoxyethyl 3-oxobutanoate)/Mo molar ratio is 0.8 mol/mol or is 2.2 mol of 2-methoxyethyl 3-oxobutanoate per mole of cobalt. The extrudates are left to mature in a water-saturated atmosphere for 16 h at ambient temperature. The catalyst is then dried at 120° C. for 2 hours. The final metal composition of the catalyst C4 expressed in the form of oxides is: MoO.sub.3=19.5±0.2 wt %, CoO=3.8±0.1 wt % and P.sub.2O.sub.5=6.7±0.1 wt % relative to the weight of dry catalyst.

Example 4: Preparation of the CoMoP Catalyst on Alumina C5 (According to the Invention) by Introduction, After the Impregnation of the Metals, of a Solvent-Free Organic Compound at a Volume Less than that of the Porosity of the Solid to be Impregnated

[0111] Arranged in a closed chamber is a batch of 12 g of the catalyst precursor C1. 2.3 g (i.e. 1.9 ml) of 2-methoxyethyl 3-oxobutanoate in liquid form are dispersed on the surface of the batch of catalyst precursor Cl at ambient temperature and pressure. As in example 3, the amount of 2-methoxyethyl 3-oxobutanoate added is such that the (2-methoxyethyl 3-oxobutanoate)/Mo molar ratio is 0.8 mol/mol, i.e. 2.2 mol of 2-methoxyethyl 3-oxobutanoate per mole of cobalt. It will furthermore be noted that the volume of 1.9 ml of organic compound introduced is less than the total pore volume of the batch of catalyst precursor Cl used which is around 6.5 ml. Thus, at the end of the dispersion step, a batch of catalyst precursor rich in organic compound and a batch of catalyst precursor low in organic compound are obtained.

[0112] The closed chamber is placed in an oven at 120° C. for 6 hours. 14.1 g of catalyst C5 impregnated with the organic compound are thus obtained. The final metal composition of the catalyst C5 is: MoO.sub.3=19.5±0.2 wt %, CoO=3.8±0.1 wt % and P.sub.2O.sub.5=6.7±0.1 wt % relative to the weight of dry catalyst. The catalyst C5 moreover has a (2-methoxyethyl 3-oxobutanoate)/Mo molar ratio of 0.8 mol/mol.

Example 5: Preparation of the CoMoP Catalyst on Alumina C6 (According to the Invention) by Introduction, before the Impregnation of the Metals, of a Solvent-Free Organic Compound at a Volume Less than that of the Porosity of the Solid to be Impregnated

[0113] Arranged in a closed chamber is a batch of 8.4 g of the same support in the form of extrudates as the one used in example 1. 2.3 g (i.e. 1.9 ml) of 2-methoxyethyl 3-oxobutanoate in liquid form are dispersed on the surface of the batch of support at ambient temperature and pressure. In this example, the volume of organic compound introduced is less than the total pore volume of the batch of support which is around 7.4 ml. Thus, at the end of the dispersion step, a batch of catalyst precursor rich in organic compound and a batch of precursor low in organic compound are obtained.

[0114] The closed chamber is placed in an oven at 120° C. for 6 hours. At the end of this step,10.5 g of support impregnated with organic compound are thus obtained. As in example 4, the amount of 2-methoxyethyl 3-oxobutanoate introduced on the support is fixed so as to obtain, after impregnation of the metals, a (2-methoxyethyl 3-oxobutanoate)/Mo molar ratio of 0.8 mol/mol, i.e. 2.2 mol of (2-methoxyethyl 3-oxobutanoate) per mole of cobalt.

[0115] The support with the added 2-methoxyethyl 3-oxobutanoate is then impregnated with an impregnation solution prepared by dissolving, at high temperature, molybdenum oxide (2.4 g) and cobalt hydroxide (0.6 g) in 1.4 g of an 85 wt % aqueous solution of phosphoric acid. Water is added to the solution for impregnation of the metals so that its volume is equal to the total pore volume of the batch of additivated support. After dry impregnation, the extrudates were left to mature in a water-saturated atmosphere for 24 h at ambient temperature, then dried at 120° C. for 16 hours to result in the catalyst C6. The final metal composition of the catalyst C6 expressed in the form of oxides is the following: MoO.sub.3=19.6±0.2 wt %, CoO=3.9±0.1 wt % and P.sub.2O.sub.5=6.8 ±0.1 wt % relative to the weight of dry catalyst. The catalyst C6 moreover has a (2-methoxyethyl 3-oxobutanoate)/Mo molar ratio of 0.8 mol/mol.

Example 6: Evaluation in Hydrodesulfurization (HDS) of Diesel Fuel of the Catalysts C1, C2, C3 and C4 (Prepared According to the Prior Art) and C5 and C6 (Prepared by the Process According to the Invention)

[0116] The catalysts C1, C2, C3 and C4 (comparative) and C5 and C6 (prepared according to the invention) were tested in hydrodesulfurization of a diesel fuel feedstock.

[0117] The features of the diesel fuel feedstock used are the following: [0118] Density at 15° C.: 0.8522 g/cm.sup.3, [0119] Total sulfur content: 1.44% by weight. [0120] Simulated distillation: [0121] IP: 155° C. [0122] 10%: 247° C. [0123] 50%:315° C. [0124] 90%: 392° C. [0125] FP: 444° C.

[0126] The test is carried out in an isothermal crossed fixed-bed pilot reactor, the fluids circulating from bottom to top. The catalysts are first sulfided in situ at 350° C. in the unit under pressure by means of the diesel fuel of the test to which 2 wt % of dimethyl disulfide are added.

[0127] The tests of hydrodesulfurization of the diesel fuel feedstock were carried out under the following operating conditions: a total pressure of 7 MPa, with a catalyst volume of 30 cm.sup.3, at a temperature of between 330 to 360° C. and with a hydrogen flow rate of 24 l/h and a feedstock flow rate of 60 cm.sup.3/h.

[0128] The catalytic performances of the catalysts tested are given in table 1. There are expressed in degrees Celsius starting from a comparative catalyst chosen as a reference (catalyst C2): they correspond to the temperature difference to be applied in order to attain 50 ppm of sulfur in the effluent. A negative value signifies that the target sulfur content is attained for a lower temperature and that there is therefore an increase in activity. A positive value signifies that the target sulfur content is attained for a higher temperature and that there is therefore a loss of activity.

TABLE-US-00001 TABLE 1 Catalyst (comparative Organic or according Organic compound/ to the compound Mo molar Method of introducing HDS invention) used ratio the organic compound activity C1 (comp) — — — Base +1.0° C.  C2 (comp) — — — Base C3 (comp) Citric acid 1.0 Co-impregnation of the organic Base- compound 2.9° C. C4 (comp) 2-methoxyethyl 0.8 Post-impregnation of the organic Base- 3-oxobutanoate compound 5.7° C. C5 (inv) 2-methoxyethyl 0.8 Post-impregnation of the solvent-free Base- 3-oxobutanoate organic compound at a volume less 6.9° C. than that of the porosity of the solid to be impregnated C6 (inv) 2-methoxyethyl 0.8 Pre-impregnation of the solvent-free Base- 3-oxobutanoate organic compound at a volume less 6.5° C. than that of the porosity of the solid to be impregnated

[0129] Table 1 clearly shows that the method of introducing the organic compound according to the invention makes it possible to avoid the use of a solvent and consequently of a drying step while introducing the adequate amount of organic compound to obtain catalysts that are at least as efficient as those prepared according to the prior art. Specifically, the catalysts C5 and C6 according to the invention are more efficient than all the other comparative catalysts. The increase is very significant in comparison with the catalysts that do not use an organic molecule (C1 and C2) or citric acid (C3) commonly used by a person skilled in the art. Furthermore, the catalysts C5 and C6 are more efficient than the catalyst C4 using the same organic molecule introduced according to a protocol well known to a person skilled in the art based on a post-additivation in aqueous solution. The organic compound may therefore be introduced according to the invention both before and after the impregnation of the metals. These examples therefore indeed show the feasibility and the relevance of the method of introducing an organic compound according to the invention in particular for preparing catalysts that may have performances at least as high as those of the catalysts of the prior art.