BRPI0714962A2 - palladium / carbon catalysts and their preparations - Google Patents

Abstract

Patent of Invention for "PALADIUM / CARBON CATALYZERS AND THEIR PREPARATIONS". The present invention relates to a palladium / carbon catalyst in which palladium maintained on activated carbon support is present as crystallites, in which particle size crystals less than 2.5 nm comprise at least 80% by weight of the total palladium crystallites. The present invention further relates to a process for preparing the palladium / carbon catalyst, wherein a solution used to impregnate or spray the activated carbon support contains a palladium compound and a compound of formula I, wherein n and m are independently. 0 or an integer from 1 to 5; and R 1, R 2 and R 3 are independently selected from the group consisting of H, CH 3, NH 2, OH and COOH.

Description

Patent Descriptive Report for "PALADIUM / CARBON CATALYZERS AND THEIR PREPARATIONS" Cross Reference to Related Requests

This application claims the benefit of Chinese Patent Application No. 200610029964.4 filed August 11, 2006, incorporated herein by reference in its entirety and for all purposes. Field of Invention

The present invention relates to palladium metal maintained on the activated carbon catalyst (referred to as palladium / carbon catalyst) and to a process for preparing it and in particular to a palladium / carbon catalyst used in the refinement of crude terephthalic acid by selective hydrogenation and a process for its preparation.

Palladium / carbon catalysts are widely used in the selective hydrogenation of unsaturated organic compounds. In particular, palladium / carbon catalysts are useful in refining crude terephthalic acid, where some impurities in crude terephthalic acid such as 4-carboxybenzaldehyde (4-CBA) are converted by hydrogenation to other compounds, and the terephthalic acid product. It can then be isolated by crystallization. Since palladium / carbon catalysts typically contain an individual active component, known prior art research to improve these catalysts has primarily emphasized the support structure and the distribution of metallic Pd [palladium] on the support, and these aspects actually considerably affect properties of catalysts.

As the terephthalic acid hydro-refinement reaction is a first order reaction and the reaction rate is rapid, the reactants are difficult to diffuse into the catalyst particles during the reaction, so the active component within the Catalyst particles may not work well. Thus, to make full use of the noble metal, catalysts are generally prepared as one of the types of eggshell in which the active component, ie the noble metal, is kept mainly on the surface of the support.

As the hydrogenation reaction is performed on the surface of metallic Pd, as a rule for catalysts containing the same amount of metallic Pd charge, the greater the degree of dispersion of metallic Pd in a catalyst and / or the higher the metallic Pd content. maintained in the catalyst and / or the better the thermal stability of the catalyst, the greater the catalyst activity and the longer the catalyst life.

If the solution containing a Pd compound (such as sodium chloropaladate or palladium chloride) is loaded directly onto an activated carbon, a very thin, shiny layer of metallic palladium will appear quickly on the surface of activated carbon. The reason is mainly due to the fact that the surface of activated carbon has reduction groups such as aldehyde group and free electrons, which will easily reduce the Pd ion to the zero valence metallic Pd. As a result, the catalysts thus prepared have very low degrees of dispersion of metallic Pd. One method to overcome this problem is to convert the Pd ion into the impregnating liquid containing Pd compound into an insoluble compound prior to impregnation. For example, a water-soluble Pd compound may be hydrolyzed at room temperature to insoluble Pd (OH) 2 or PdO H 2 O, which is then kept in an activated carbon and then reduced with a reducing agent such as formaldehyde, sodium formate, glucose, formic acid and hydrogen gas. Thus, Pd migration and growth of palladium crystallites can be prevented. For example, US 3,138,560 demonstrates that hydrogen peroxide is added in an impregnation liquid to hydrolyze a water-soluble Pd compound to an insoluble compound, and impregnation is then performed. US 4,476,242 suggests the preparation of an impregnating liquid containing Pd compound using an organic solvent such as methanol, pyridine and the like. It is reported that this is also effective in preventing Pd migration and the increase of palladium crystallites. In addition, there are patents reporting that a chloropaladic acid solution is converted to a colloidal solution containing Pd by adjusting the pH value, and it is said that this can prevent reducing groups on the surface of an activated carbon from directly reducing Pd ions to a zero valence metal Pd.

CN1698952A discloses the addition of nitrogen-containing polycarboxylic acids in an impregnation liquid used to prepare a palladium / carbon catalyst. An object of the present invention is to provide an innovative palladium maintained on an activated carbon catalyst. The metal Pd in the catalyst has a high degree of dispersion, a higher crystallite content and better thermal stability. When used in the crude refinement of crude terephthalic acid, the catalyst can provide a greater conversion of 4-carboxybenzaldehyde (4-CBA).

Another object of the invention is to provide a process for preparing the palladium / carbon catalyst.

Detailed Description of the Invention

In the first aspect, the present invention provides a palladium / carbon catalyst in which palladium held on an activated carbon support is present as nanometer size crystals, and in which particle size crystals of less than 2.5 nm constitute in the 80% by weight, preferably at least 85% by weight, more preferably at least 88% by weight and more preferably at least 90% by weight of the total palladium crystallites.

In the palladium / carbon catalyst according to the invention, a metallic Pd content preferably is in the range of 0.05 to 5% by weight, and more preferably in the range of 0.2 to 3.5% by weight based on total weight of catalyst.

In a preferred embodiment, the maintained palladium is enriched in an activated carbon support surface layer such that, in the case where the palladium / carbon catalyst has a Pd content of 0.50 ± 0.10 wt%. Palladium crystallites in a 5 nm depth layer under the surface of the activated carbon support comprise at least 30 wt.%, preferably at least 40 wt.% and more preferably at least 50 wt. total weight of all atoms in this layer; and palladium crystallites in a layer at 300 nm depth under the surface of the activated carbon support comprise at least 5 wt%, preferably at least 10 wt%, more preferably at least 15 wt% and more preferably at least 20% by weight of the total weight of all atoms in this layer.

In the palladium / carbon catalyst according to the invention, the maintained palladium is highly dispersed on the surface of the activated carbon support, with a minimum dispersion degree of 5%, preferably at least 10%, more preferably at least 15% and more. preferably at least 20%. After calcining the catalyst in a nitrogen stream, which bubbled in water (at 25 ° C) at 500 ° C for hours, the palladium maintained has an average particle size of at most 10 nm, preferably at most 8.0. nm, more preferably at most 7.0 nm, and more preferably at most 7.0 nm.

In the second aspect, the present invention provides a process for preparing the palladium / carbon catalyst, which process consists of the following steps:

a) washing an activated carbon with an aqueous solution of an inorganic acid, and then with water to neutralize, and then drying the washed activated carbon to obtain an activated carbon support;

b) impregnating or spraying the activated carbon support with an aqueous solution containing a Pd compound and an additive to support the Pd compound on an activated carbon support to provide a catalytic precursor, where a molar ratio of the additive with Pd in the Pd compound in the solution is in the range 0.01: 1 to 2.0: 1; The additive is selected from the compounds represented by the general formula I:

R1 - (CH2) n - CHCOOH I

R2 - (CH2) m - CCOOH I

R3 - (CH2), - CHCOOH I

Where n, m and I are independently 0 or an integer from 1 to 5; and R1, R2 and R3 are independently selected from the group consisting of H, CH3, NH2, OH and COOH; and the palladium containing solution is adjusted to a pH value of 7 + 3; and

c) treating the catalytic precursor with a reducing agent to provide the palladium / carbon catalyst.

In a preferred embodiment, the above process further comprises catalytic precursor aging at a temperature of 0 to 80 ° C for 1 to 50 hours prior to catalytic precursor reduction treatment.

There are no specific limitations on the activated carbon used in the invention. An example of activated carbon is coconut shell activated carbon with a specific surface area above 900 m2 / g and particle size in the range of 4 to 8 mesh. The aqueous inorganic acid solution useful in the process according to the invention may have an acid concentration of 0.01 to 5 M (mole / liter), preferably 0.01 to 3.0 M. Examples of inorganic acid include, but are not limited to, hydrochloric acid, nitric acid and phosphoric acid. The time period for acid washing is not crucial, but preferably within a range of 0.5 to 8 hours, and more preferably within a range of 0.5 to 4 hours.

After washing with the aqueous inorganic acid solution, the activated carbon is washed with water to neutrality and then allowed to dry. Drying is generally performed at a temperature of 80 to 150 ° C for 0.5 to 10 hours, and preferably for 0.5 to 6 hours.

Examples of the Pd compound useful in the invention include, but are not limited to, palladium halides, palladium acetate, palladium nitrate, chloropaladic acid, basic chloropaladic acid salts, palladium amino complexes and mixtures thereof. Preferably the Pd compound is chloropaladic acid or palladium acetate. The solution containing the compound Pd and the additive preferably has a pH value between 4 and 9. The concentration of compound Pd in terms of Pd in the solution is preferably in the range 0.01 to 20% by weight, more preferably. in a range of 0.1 to 10% by weight and more preferably in a range of 0.2 to 3.6% by weight.

The amount of additive used in the solution containing Pd may vary depending on the compound Pd used as well as the additive used. In general, however, a molar ratio of the additive to Pd in the Pd compound in the solution in the range of 0.01: 1 to 2: 1 is feasible, and the molar ratio of the additive to Pd in the compound Pd is preferably in the ranges. from 0.05: 1 to 1.5: 1, and more preferably in a range from 0.1: 1 to 1.0: 1.

Some examples of the compound of general formula I useful in the invention include:

R1 - (CH2) n - CHCOOH I

R2 - (CH2) m - CCOOH I

Rs - (CH2), - CHCOOH I Additive A R -) = R2 = R3 = H n = m = 1 = 0__ Additive B R1 = R3 = HjR2 = NH2 n = 5; m = 1 = 1 - Additive C R 1 = CH 3; R2 = R3 = H n = 4; m = 1 = 0 _ Additive D R1 = R2 = H; R 3 = OH n = m = 3; 1 = 1 __ Additive E R1 = R3 = H; R2 = COOH n = m = 1 = 0 Additive F R1 = R3 = H; R2 = OH N = m = 1 = 0

Examples of reducing agent used to reduce the catalyst precursor include, but are not limited to, formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, hydrogen gas and mixtures thereof. Preferably, the reducing agent is sodium formate or hydrazine hydrate. The amount of reducing agent used is determined according to the amount of active component, Pd, and is generally in the range of 1 to 10 times, and preferably 2 to 5 times of the theoretical amount required by the reduction reaction. The catalytic precursor reduction treatment may be performed according to procedures and under conditions well known to those skilled in the art. For example, the reduction treatment may be performed at a temperature of from 0 to 200 ° C, preferably from 20 to 120 ° C for 0.5 to 24 hours, preferably for 1 to 10 hours and more preferably for 1 to 4 hours. .

In a preferred embodiment, the process for preparing the palladium / carbon catalyst according to the invention consists of the following steps:

i) washing an activated carbon support of particulate or particulate material with an aqueous acid solution for 0.5 to 8 hours, the aqueous acid solution having an acid concentration of 0.01 to 3.0 mole / liter, and at least acid is selected from the group consisting of hydrochloric acid, nitric acid and phosphoric acid;

ii) washing the acid washed activated carbon support with water to neutral, and then drying at a temperature of 80 to 150 ° C for 0.5 to 10 hours to provide a treated activated carbon support;

(iii) soak or spray the activated carbon support treated with an aqueous solution containing a water-soluble Pd compound and an additive of the general formula I: R1 - (CH2) n - CHCOOH I

R2 - (CH2) m - CCOOH i

Ra - (CH2), - CHCOOH I

Where n, m and I are independently O or an integer from 1 to 5; and R 1, R 2 and R 3 are independently selected from the group consisting of OH, H 1 CH 3, NH 2 and COOH to support the Pd compound on the treated activated carbon support to provide a catalytic precursor, where a Pd compound content in terms of Pd in the aqueous solution is in the range 0.1 to 10 wt.%, a molar ratio of the additive to Pd is in the range 0.05: 1 to 1.5: 1, and the aqueous solution is adjusted to a pH value of 7 ± 3;

iv) aging the catalytic precursor obtained from step iii) at a temperature of 0 to 80 ° C for 1 to 50 hours; and

v) treating the aged catalytic precursor with a reducing agent, thereby reducing the Pd ion in the Pd compound to the metallic Pd to obtain the palladium carbon catalyst.

Compared to the state of the art, the present invention has advantages that the prepared catalyst has a higher degree of metallic Pd dispersion and a higher crystallite content, and that the catalyst exhibits high activity and long service life. Examples:

The following examples are provided to further illustrate the invention, but without limitation of the invention.

In the examples, the following test methods are used:

(1) Degree of dispersion of metallic palladium:

The degree of dispersion of metallic palladium was measured by the hydrogen-oxygen titration method using a chemical adsorption equipment. The degree of dispersion was calculated according to the following equation:

Dispersion degree = ((2xVads. X Mpd) / (3 χ 22400 χ Wam0Stra x Cpd)) x 100% Where: VacJs- Represents the amount of hydrogen gas adsorbed by the sample,

Mpd represents the atomic weight of Pd,

Wamostra represents the weight of the sample and

Opd represents the content of Pd in the sample.

(2) Content of crystallites:

As used herein, the term "crystallite content" is intended to mean a crystallite content having a particle size of less than 2.5 nm.

The palladium content in the catalysts was measured by X-ray fluorescence spectrograph, and the particle sizes of the metallic Pd crystallites by X-ray diffractometer (XRD). Then the crystallite content was calculated as:

Crystallite content = ((Weight of metallic Pd crystallites with particle size below 2.5 nm) / (Total weight of metallic Pd)) χ 100%.

(3) Thermal Stability:

An average particle diameter of Pd crystallites from a palladium / carbon catalyst was measured by X-ray diffractometer (XRD). After calcining the catalyst in a nitrogen stream, which bubbled in water (at 25 ° C) at 500 ° C for 10 hours, an average particle diameter of the Pd crystallites was measured again by X-ray diffractometer. (XRD). The average particle diameter of Pd crystallites after calcination as well as the change in mean particle diameter of Pd crystallites before and after calcination indicate the thermal stability of the catalyst. The smaller the average particle diameter of Pd crystallites, the better the thermal stability of the catalyst. And the smaller the change in mean particle diameter of Pd crystallites before and after calcination, the better the thermal stability of the catalyst.

(4) Pd content in layers of various depths below the catalyst surface:

The surface of a catalyst was etched in argon. After recording at a certain depth, the surface layer Pd content revealed by the recording was measured by X-ray photoelectron spectrometry (XPS) and Auger electron spectroscopy (AES), and thus the Pd content was obtained. in the layers at various depths below the catalyst surface. Example 1:

A 100 g volume of activated carbon from the coconut shell, which was passed through a 4 mesh screen but retained in an 8 mesh screen and with a specific surface area of 1100 m2 / g, was washed with 200 ml of 0.4 M aqueous nitric acid solution for 2 hours. After removing the acidic solution, the activated carbon was washed with deionized water to neutrality and then dried at 120 ° C for 6 hours.

To 3.2 g of aqueous chloropaladic acid solution containing 16 wt% palladium, deionized water was added to a total volume of 40 ml. Then, 2.16 g of 10 wt% solution of additive A in water was added, followed by the addition of deionized water until the total volume of the solution reached 60 ml. Aqueous 3% NaOH solution was added to adjust the pH value of the Pd-containing solution to approximately 7. After aging for 180 minutes, the Pd-containing solution was used to impregnate the activated carbon treated above for 3 hours to provide a precursor. catalytic The catalytic precursor was aged at room temperature for 24 hours, and then soaked in a reducing liquid consisting of 20 g of 5% by weight aqueous hydrazine hydrate solution and 200 g of pure water at 20 ° C for 3 hours. After removing the liquid by filtration, the solids were washed with pure water to neutrality and then dried to provide a catalyst product.

Examples 2 to 24:

The procedure as described in Example 1 was followed, but different Pd compounds and different additives were used to prepare the Pd containing solution. The Pd compounds used, Pd compound content in terms of Pd in the Pd-containing solution, the additives used and the molar ratios of the Pd additives are shown in Table 1 below.

Examples 25 to 30:

The procedure as described in Example 1 was followed except that different additives (the additives used are shown in Table 1) were used to prepare the Pd containing solution, the Pd containing solutions were sprayed on activated carbon to provide catalytic precursors, and that inorganic acids, inorganic acid concentrations, acid wash times, drying times, temperatures, pH values of solutions containing additives and Pd compound reducing agents were employed. , temperatures for reduction treatment and time periods for reduction treatment as shown in Table 2 below.

Comparative Example:

The procedure as described in Example 1 was followed except that no additives were used in the preparation of the Pd containing solution.

The degrees of dispersion, crystallite content, thermal stability and Pd content of the layers at various depths below the catalyst surface were measured on the catalysts prepared in the Examples and Comparative Example. Catalysts were better evaluated under the evaluation conditions as shown below. Results are shown in Tables 3 and 4 below.

Catalyst evaluation conditions:

4-CBA conversion = quant. of 4-CBA added - quant. Residual χ 100%

Catalyst Amount: Amount of Crude Terephthalic Acid: Amount of 4-CBA: Reaction Pressure: Gas Partial Pressure

2.0 g 30.0 g 1.0g 70 kg 5.0 kg

hydrogen:

Reaction Time: Reaction Temperature:

1.0 hour 270 ° C

Amount of 4-CBA Added Table 1

Example Pd Compound Additive Pd charged / active carbon (wt%) Additive / Pd (mol / mol) Example 1 Additive chloropaladic acid A 0.51 0.20 Example 2 Additive chloropaladic acid A 0.51 0.30 Example 3 Additive Chloropaladic Acid A 0.22 0.60 Example 4 Additive Palladium Acetate A 0.08 1.50 Example 5 Additive Chloropaladic Acid B 0.51 0.20 Example 6 Additive Chloropaladic Acid B 0.62 0 , 40 Example 7 Additive Chloropaladic Acid B 0.51 0.60 Example 8 Palladium Acetate Additive B 3.55 0.80 Example 9 Additive Chloropaladic Acid C 0.51 0.20 Example 10 Additive Chloropaladic Acid C 0 .51 0.40 Example 11 Additive Chloropaladic Acid C 0.51 0.60 Example 12 Palladium Acetyl Additive C 0.15 1.00 Example 13 Additive Chloropaladic Acid D 0.51 0.20 Example 14 Adil Chloropaladic Acid D = 0.41 0.40 Example 15 Additive chloropaladic acid D 0.51 0.60 Example 16 Palladium acetate Additive D 0.51 0.80 Example 17 Additive chloropaladic acid E 0.51 0.20 Ex Example 18 Additive Chloropaladic Acid E 1.00 0.40 Example 19 Additive Chloropaladic Acid E 0.51 0.60 Example 20 Additive Palladium Acetate E 0.51 0.80 Example 21 Additive Chloropaladic Acid F 4.50 0.05 Example 22 Additive Chloropaladic Acid F 0.51 0.40 Example 23 Additive Chloropaladic Acid F 0.51 0.60 Example 24 Additive Palladium Acetate F 0.51 0.80 Example 25 Additive Chloropaladic Acid A 0.51 0.20 Example 26 Additive chloropaladic acid B 0.51 0.40 Example 27 Additive chloropaladic acid C 0.51 0.60 Example 28 Additive chloropaladic acid D 0.51 0.80 Example 29 Adil chloropaladic acid E 0.51 0.50 Example 30 Chloropaladic Acid Additive F 0.51 0.50 Comparative Example Chloropaladic Acid / 0.51 / ο

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Example Catalyst Pd content (% weight) Dispersion degree (%) Crystallite content (%) Size average particle size (nm) Size average particle size after calcination at 500 ° C (nm) Change in average particle size before and after calcination (%) 4-CBA conversion (%) Example 1 0.50 20 90 3.5 5.9 69 99.5 Example 2 0.50 23 91 3.6 6.0 67 99.7 Example 3 0.20 29 90 3.4 5.3 56 89.2 Example 4 0.08 21 92 2.7 5.3 96 - Example 5 0.50 20 90 3.5 5.9 69 99.4 Example 6 0.60 26 90 3.6 6.0 67 99.8 Example 7 0.50 28 93 3.8 5.8 53 99.5 Example 8 3.50 20 92 3.3 5.9 79 99.6 Example 9 0.50 20 91 2.9 5.7 97 99.6 Example 10 0.50 22 92 3.8 5.6 47 99.8 Example 11 0, 49 25 90 3.6 5.8 61 99.7 Example 12 0.15 28 91 3.0 5.7 90 ~ Example 13 0.50 20 90 3.6 5.9 64 99.5 Example 14 0.40 21 92 3.3 5.6 70 99.5 Example 15 0.50 26 91 3.4 5.8 71 99.8 Example 16 0.49 25 90 3.2 5.9 84 99.9 Example 17 0, 50 30 94 3.6 6.0 67 99.7 Example 18 0.98 27 90 3.7 5.9 59 100 Example 19 0.50 27 91 3.4 5.8 71 99.7 Example 20 0.50 28 91 3.5 5.7 63 99.8 Example 21 4.48 27 90 3.7 6.0 62 100 Example 22 0.50 28 92 3 , 6.9 64 99.7 Example 23 0.50 30 90 3.8 5.9 55 99.9 Example 24 0.50 28 91 3.3 5.9 79 99.7 Example 25 0.50 20 91 3.3 6.0 82 99.6 Example 26 0.50 20 90 3.5 5.9 69 99.7 Example 27 0.50 22 90 3.4 6.0 76 99.8 Example 28 0.49 26 91 3.7 5.9 59 99.9 Example 29 0.50 27 90 3.8 6.0 58 99.8 Example 30 0.50 28 92 3.0 5.7 90 99.6 Comparative Example 0 , 50 4 52 4.6 11.1 141 66.2 Table 4

Example Pd content of Pd content in layer Pd content in catalyst layer with depth of 5 with depth of 300 (wt%) nm under surface of nm under surface of catalyst (% weight) catalyst (% weight) 0.50 50.2 22.3 Example 2 0.50 51.2 23.7 Example 3 0.20 43.1 11.8 Example 4 0.08 30.1 5.9 Example 5 0.50 52.6 20.4 Example 6 0.60 57.8 28.0 Example 7 0.50 60.1 23.5 Example 8 3.50 63.4 29.3 Example 9 0.50 54.3 24.2 Example 10 0 , 50 51.4 23.6 Example 11 0.49 50.3 23.2 Example 12 0.15 40.6 11.3 Example 13 0.50 52.3 23.7 Example 14 0.40 50.4 20 .5 Example 15 0.50 52.9 24.9 Example 16 0.49 50.4 23.1 Example 17 0.50 56.3 23.0 Example 18 0.98 70.1 30.3 Example 19 0, 50 57.8 23.6 Example 20 0.50 53.5 23.8 Example 21 4.48 83.2 40.2 Example 22 0.50 56.1 21.2 Example 23 0.50 50.6 24, 7 Example 24 0.50 53.4 25.3 Example 25 0.50 54.5 23.0 Example 26 0.50 55.6 27.4 Example 27 0.50 56.4 23.7 Example 28 0.49 53.3 23.9 Example 29 0.50 50.1 20.1 Example 30 0.50 56.5 24.7 E Example 0.50 30.6 12.5 Comparative Patents, patent applications, non-patent literature, and test methods cited in the report are incorporated herein by reference.

While the invention has been described with respect to embodiments of the examples, it will be understood by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the invention is not limited to the particular embodiments disclosed as the best contemplated embodiment of this invention, but will include all embodiments within the scope of the appended claims.

Claims (16)

Palladium / carbon catalyst characterized by the fact that palladium kept on an activated carbon support is present as crystallites; and crystallites with particle size less than 2.5 nm comprise at least 80% by weight of the total palladium crystallites. Palladium / carbon catalyst according to claim 1, characterized in that the maintained palladium is enriched in a surface layer of the active carbon support such that, in the case where the palladium on the carbon catalyst has a content Pd of 0.50 ± 0.10% by weight of the total catalyst weight, the metallic palladium in a layer at a depth of 5 nm below the surface of the active carbon support consists of at least 30% by weight of the total carbon weight. all atoms in this layer; and metal palladium in a layer 300 nm deep under the surface of the active carbon support consists of at least 5% by weight of the total weight of all atoms in this layer. Palladium / carbon catalyst according to claim 2, characterized in that, where the palladium on the carbon catalyst has a Pd content of 0.50 ± 0.10% by weight of the total weight of the catalyst, the metallic palladium on the layer at a depth of 5 nm below the surface of the active carbon support consists of at least 40% by weight of the total weight of all atoms in this layer; and metal palladium in a layer 300 nm deep under the surface of the active carbon support consists of at least 10% by weight of the total weight of all atoms in this layer. Palladium / carbon catalyst according to any one of claims 1 to 3, characterized in that, in the case where the maintained palladium is highly dispersed on the surface of the active carbon support, with a dispersion degree of at least 5 %. Palladium / carbon catalyst according to claim 4, characterized in that the degree of dispersion of palladium maintained is at least 10%. Palladium / carbon catalyst according to any of claims 1 to 5, characterized in that the maintained palladium has an average grain size of at most 6.0 nm after the catalyst is calcined in a nitrogen stream, which bubbled in water (at 25 ° C) at 500 ° C for 10 hours. Palladium / carbon catalyst according to any one of claims 1 to 6, characterized in that the catalyst consists of 0.05 to 5% by weight of the metal palladium, based on the total weight of the catalyst. Palladium / carbon catalyst according to claim 7, characterized in that the catalyst consists of 0.2 to 3.5% by weight of the metal palladium, based on the total weight of the catalyst. A process for preparing the palladium / carbon catalyst according to claim 1, consisting of the steps of: (a) washing an activated carbon with an aqueous solution of an inorganic acid, and then with water to neutralize, and then drying washed activated carbon to obtain activated carbon support; (b) impregnating or spraying the activated carbon support with an aqueous solution containing a Pd compound and an additive to support the Pd compound on an activated carbon support to provide a catalytic precursor, wherein a molar ratio of Pd additive in the Pd compound in solution is in the range 0.01: 1 to 2.0: 1; the additive is selected from the compounds represented by the general formula I: wherein n, m and I are independently 0 or one of the compounds represented by the formula I: R 1 - (CH 2) n - CHCOOH I R 2 - (CH 2) m integer from 1 to 5; and R1, R2 and R3 are independently selected from the group consisting of H, CH3, NH2, OH and COOH; and the palladium containing solution is adjusted to a pH value of 7D3; and c) treating the catalytic precursor with a reducing agent to provide the palladium / carbon catalyst. Process according to Claim 9, characterized in that the inorganic acid is at least that selected from the group consisting of hydrochloric acid, nitric acid and phosphoric acid; the acid wash time is in the range of 0.5 to 8 hours; the inorganic acid solution has an acid concentration of 0.01 to 5.0 mole / liter; and drying is performed at a temperature of 80 to 150 ° C for 0.5 to 10 hours. Process according to Claim 9 or 10, characterized in that the Pd compound is selected from palladium halide, palladium acetate, palladium nitrate, chloropaladic acid, chloropaladic acid basic salts, amino acid complexes. palladium and mixtures thereof; the palladium concentration in the solution containing Pd is in the range 0.01 to 20% by weight; and a molar ratio of the palladium additive to compound Pd in solution is in the range 0.01: 1 to 2.0: 1. Process according to Claim 11, characterized in that the compound Pd is chloropaladic acid or palladium acetate, the solution containing the compound Pd and the additive has a pH value of 4 to 9; the palladium concentration in the solution is in the range 0.1 to 10 wt%; and the molar ratio of the palladium additive to the Pd compound in the solution is in the range 0.05: 1 to 1.5: 1. A process according to any one of claims 9 to 12 further comprising aging the catalytic precursor at a temperature of 0 to 80 ° C for 1 to 50 hours prior to the reduction treatment. Process according to any one of claims 9 to 13, characterized in that the reducing agent is selected from the group consisting of formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, hydrogen gas and mixtures thereof. ; and the reduction treatment is performed at a temperature of 0 to 200 ° C for 0.5 to 24 hours. Process according to Claim 14, characterized in that the catalytic precursor is aged at a temperature of 0 to 80 ° C for 1 to 24 hours before carrying out the reduction treatment; The reducing agent is sodium formate or hydrazine hydrate and the reducing treatment is conducted at a temperature of 20 to 120 ° C for 1 to 10 hours. A process for preparing palladium on the carbon catalyst according to claim 1, consisting of the following steps: (i) washing an activated carbon support of particulate or particulate material with an aqueous acid solution for 0 5 to 8 hours, the aqueous acid solution having an acid concentration of 0.01 to 3.0 mole / liter, and at least the acid selected from the group consisting of hydrochloric acid, nitric acid and phosphoric acid; (ii) washing the acid-washed activated carbon support with water to neutrality, and then drying at a temperature of 80 to 150 ° C for 0.5 to 10 hours to provide a treated activated carbon support; (iii) impregnating or spraying the activated carbon support treated with an aqueous solution containing a water-soluble Pd compound and an additive of the general formula I: R1 - (CH2) n - CHCOOH I R2 - (CH2) m-CCOOH I R3 - (CH2), -CHCOOH I wherein n, m and I are independently 0 or an integer from 1 to 5; and R1, R2 and R3 are independently selected from the group consisting of OH, H, CH3, NH2 and COOH to support the Pd compound on the treated activated carbon support, to provide a catalytic precursor, where a content of the compound of Pd in terms of Pd in the aqueous solution is in the range 0.1 to 10% by weight, a molar ratio of the additive to Pd is in the range 0.05: 1 to 1.5: 1, and the aqueous solution is adjusted at a pH value of 7 ± 3; (iv) aging the catalytic precursor obtained from operation iii) at a temperature of 0 to 80 ° C for 1 to 50 hours; and (v) treating the aged catalytic precursor with a reducing agent, thereby reducing the Pd ion in the Pd compound to the metallic Pd to provide palladium on the carbon catalyst.