DE102007038045B4 - Process for the production of a palladium / carbon catalyst - Google Patents

Abstract

Process for the production of a palladium / carbon catalyst in which: a) an activated carbon is washed neutral with an aqueous solution of an inorganic acid and then with water and then the washed activated carbon is dried to obtain an activated carbon carrier; b) the activated carbon carrier with an Pd compound and an additive-containing aqueous solution impregnated or sprayed in order to support the Pd compound on the activated carbon support, a catalyst precursor being obtained, the molar ratio of additive to Pd in the Pd compound in the solution being in the range of 0, 01: 1 to 2.0: 1; the additive among the compounds of the general formula I: in which n, m and 1 independently of one another represent 0 or an integer from 1 to 5 and R1, R2 and R3 independently of one another are selected from the group consisting of H, CH3, NH2, OH and COOH is selected and the palladium-containing solution is adjusted to a pH of 7 ± 3; andc) treating the catalyst precursor with a reducing agent to obtain the palladium / carbon catalyst.

Description

Cross reference to related application

This application claims priority from the Chinese patent application filed on August 11, 2006 200610029964.4 , to which reference is hereby made in full and for all purposes.

Field of the invention

The present invention relates to a process for producing a carbon-supported metallic palladium catalyst (hereinafter referred to as a palladium-carbon catalyst) which is used in the refining of crude terephthalic acid by selective hydrogenation.

Background of the invention

Palladium / carbon catalysts are widely used in the selective hydrogenation of unsaturated organic compounds. In particular, palladium / carbon catalysts are suitable for use in the refining of crude terephthalic acid, in which some impurities in the crude terephthalic acid such as 4-carboxybenzaldehyde (4-CBA) are converted to other compounds by hydrogenation and the terephthalic acid product can then be isolated by crystallization . Since the palladium-on-carbon catalysts typically contain a single active component, the prior art efforts to improve such catalysts have focused primarily on the structure of the support and the distribution of metallic Pd on the support, and these have aspects indeed great influence on the properties of the catalysts.

Since the hydrorefining reaction of terephthalic acid is a first order reaction and proceeds at a high reaction rate, diffusion of reactants into the inside of catalyst particles is difficult during the reaction, so that the active component in the catalyst particles cannot work well. In order to fully utilize the noble metal, the catalysts are therefore generally produced as coated catalysts in which the active component, d. H. the precious metal is mainly carried on the surface of the support.

Since the hydrogenation reaction is carried out on the surface of metallic Pd, it applies to catalysts with the same loading of metallic Pd that the higher the degree of dispersion of metallic Pd in a catalyst, the higher the activity of the catalyst and the longer the service life of the catalyst / or the higher the content of supported crystallite of metallic Pd in the catalyst and / or the better the thermal stability of the catalyst.

When a solution containing a Pd compound (such as sodium tetrachloropalladate or palladium chloride) is loaded directly onto an activated carbon, a very thin, shiny layer of metallic palladium quickly appears on the surface of the activated carbon. This is mainly because the surface of the activated carbon has reducing groups such as aldehyde groups or free electrons, which easily reduce Pd ions to zero-valent metallic Pd. As a result, catalysts produced in this way have very low degrees of dispersion of metallic Pd. One approach to overcoming this problem is to convert the Pd ion in the impregnating liquid containing a Pd compound into an insoluble compound prior to impregnation. For example, a water-soluble Pd compound can be _{reduced to insoluble Pd (OH) 2} or PdO · H ₂ O at room temperature, which is then supported on an activated carbon and then reduced with a reducing agent such as formaldehyde, sodium formate, glucose, formic acid or hydrogen gas . In this way one can prevent the migration of Pd and the growth of Pd crystallites. For example, the U.S. 3,138,560 A adding hydrogen peroxide to an impregnating liquid to hydrolyze a water-soluble Pd compound to an insoluble compound, followed by impregnation. In the U.S. 4,476,242 A it is proposed to prepare an impregnating liquid containing a Pd compound by using an organic solvent such as methanol, pyridine and the like. It is stated that this is also quite effective in preventing the migration of Pd and the growth of palladium crystallites. In addition, there are patents which report that a solution of tetrachloropalladium (II) acid is converted into a Pd-containing colloidal solution by adjusting the pH, and it is stated that this results in the direct reduction of Pd ions Zero-valent metallic Pd can be prevented by reducing groups on the surface of an activated carbon.

In the CN1698952A describes the addition of nitrogen-containing polycarboxylic acids to an impregnation liquid used for the production of a palladium / carbon catalyst.

The CN1457922A discloses a hydrogenation catalyst for processing terephthalic acid.

In the DE 698 15 754 T2 discloses a hydrogenation catalyst containing palladium on an activated carbon support and a process for its preparation.

Summary of the invention

One object of the invention is to provide a method for producing the palladium / carbon catalyst, in particular a palladium catalyst supported on activated carbon. Metallic Pd in the catalyst has a higher degree of dispersion, a higher crystallite content and a better thermal stability. When used in the hydro refining of crude terephthalic acid, the catalyst can provide high conversion of 4-carboxybenzaldehyde (4-CBA).

Detailed description of the preferred embodiments

In the first aspect, the present invention provides a palladium / carbon catalyst in which the palladium supported on an activated carbon support is in the form of nanometer-sized crystals and crystallites with a particle size of less than 2.5 nm at least 80% by weight, preferably at least 85% by weight, particularly preferably at least 88% by weight and very particularly preferably at least 90% by weight of all palladium crystallites.

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

In a preferred embodiment, the supported palladium is enriched in a surface layer of the activated carbon support, so that in the event that the palladium / carbon catalyst has a Pd content of 0.50 +/- 0.10% by weight of the total weight of the catalyst comprises palladium crystallites in a layer at a depth of 5 nm below the surface of the activated carbon support at least 30% by weight, preferably at least 40% by weight and particularly preferably at least 50% by weight of the total weight of all atoms in this layer and palladium crystallites in one Layer at a depth of 300 nm below the surface of the activated carbon support at least 5% by weight, preferably at least 10% by weight, particularly preferably at least 15% by weight and very particularly preferably at least 20% by weight of the total weight of all atoms in this layer include.

In the palladium / carbon catalyst prepared according to the invention, the supported palladium is highly dispersed on the surface of the activated carbon support, the degree of dispersion being at least 5%, preferably at least 10%, particularly preferably at least 15% and very particularly preferably at least 20%. After calcination of the catalyst in a stream of nitrogen blown through water (at 25 ° C) at 500 ° C for a period of 10 hours, the supported palladium has an average particle size of at most 10 nm, preferably at most 8.0 nm, particularly preferably at most 7, 0 nm and very particularly preferably at most 6.0 nm.

1. a) eine Aktivkohle mit einer wäßrigen Lösung einer anorganischen Säure und dann mit Wasser neutral wäscht und dann die gewaschene Aktivkohle trocknet, wobei man einen Aktivkohleträger erhält;
2. b) den Aktivkohleträger mit einer eine Pd-Verbindung und ein Additiv enthaltenden wäßrigen Lösung imprägniert oder besprüht, um die Pd-Verbindung auf dem Aktivkohleträger zu trägern, wobei man eine Katalysatorvorstufe erhält, wobei das Molverhältnis von Additiv zu Pd in der Pd-Verbindung in der Lösung im Bereich von 0,01:1 bis 2,0:1 liegt; das Additiv aus Verbindungen der allgemeinen Formel I ausgewählt ist:
   
   worin n, m und 1 unabhängig voneinander für 0 oder eine ganze Zahl von 1 bis 5 stehen und R₁, R₂ und R₃ unabhängig voneinander aus der Gruppe bestehend aus H, CH₃, NH₂, OH und COOH ausgewählt sind, und die Palladium enthaltende Lösung auf einen pH-Wert von 7±3 eingestellt wird; und
3. c) die Katalysatorvorstufe mit einem Reduktionsmittel behandelt, wobei man den Palladium/Kohle-Katalysator erhält.

The present invention provides a process for the preparation of the palladium / carbon catalyst which comprises:

1. a) washing an activated carbon with an aqueous solution of an inorganic acid and then with water until neutral and then drying the washed activated carbon to obtain an activated carbon support;
2. b) the activated carbon support is impregnated or sprayed with an aqueous solution containing a Pd compound and an additive in order to support the Pd compound on the activated carbon support, a catalyst precursor being obtained, the molar ratio of additive to Pd in the Pd compound in the solution ranges from 0.01: 1 to 2.0: 1; the additive is selected from compounds of the general formula I:
   
   wherein n, m and 1 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, and the palladium-containing solution is adjusted to a pH of 7 ± 3; and
3. c) treating the catalyst precursor with a reducing agent, the palladium / carbon catalyst being obtained.

In a preferred embodiment, in the above process, the catalyst precursor is aged before the reduction treatment of the catalyst precursor at a temperature of 0 to 80 ° C. for a period of 1 to 50 hours.

There are no particular restrictions on the activated carbon used in the present invention. An example of the activated carbon is coconut shell activated carbon having a specific surface area of more than 900 m ² / g and a particle size of 4 to 8 mesh.

The aqueous solution of the inorganic acid which can be used in the process of the present invention may have an acid concentration of 0.01-5M (mol / liter), and preferably 0.01-3.0M. Examples of the inorganic acid include: Hydrochloric acid, nitric acid and phosphoric acid. The period of time for the acid wash is not critical, but is preferably in the range from 0.5 to 8 hours and particularly preferably in the range from 0.5 to 4 hours.

After washing with the aqueous solution of the inorganic acid, the activated carbon is washed neutral with water and then dried. The drying is generally carried out at a temperature of 80 to 150 ° C. over a period of 0.5 to 10 hours and preferably 0.5 to 6 hours.

Examples of the Pd compound which can be used in the invention include: Palladium halides, palladium acetate, palladium nitrate, palladium (IV) hydrogen chloride, basic salts of palladium (IV) hydrogen chloride, palladium-amino complexes and mixtures thereof. The Pd compound is preferably palladium (IV) hydrogen chloride or palladium acetate. The solution containing the Pd compound and the additive preferably has a pH of 4 to 9. The Pd concentration of the Pd compound in the solution is preferably in the range from 0.01 to 20% by weight, particularly preferably in the range from 0.1 to 10% by weight and very particularly preferably in the range from 0.2 up to 3.6% by weight.

The amount of the additive used in the Pd-containing solution may vary depending on the Pd compound and additive used. In general, however, a molar ratio of additive to Pd in the Pd compound in the solution in the range from 0.01: 1 to 2: 1 is possible, and the molar ratio of additive to Pd in the Pd compound is preferably in the range of 0 .05: 1 to 1.5: 1 and particularly preferably in the range from 0.1: 1 to 1.0: 1.

Additiv A R₁=R₂=R₃=H n=m=1=0 Additiv B R₁= R₃=H; R₂=NH₂ n = 5; m = 1=1 Additiv C R₁= CH₃; R₂=R₃=H n=4; m=1=0 Additiv D R₁=R₂= H; R₃=OH n=m=3; 1=1 Additiv E R₁=R₃=H; R₂=COOH n=m=1=0 Additiv F R₁= R₃=H; R₂=OH n=m=l=0 Some examples of the compound of general formula I which can be used in the invention are the following compounds:

Additive A R ₁ = R ₂ = R ₃ = H n = m = 1 = 0 Additive B R ₁ = R ₃ = H; R ₂ = NH ₂ n = 5; m = 1 = 1 Additive C R ₁ = CH ₃ ; R ₂ = R ₃ = H n = 4; m = 1 = 0 Additive D R ₁ = R ₂ = H; R ₃ = OH n = m = 3; 1 = 1 Additive E R ₁ = R ₃ = H; R ₂ = COOH n = m = 1 = 0 Additive F. R ₁ = R ₃ = H; R ₂ = OH n = m = l = 0

Examples of the reducing agent used to reduce the catalyst precursor include: Formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, hydrogen gas and mixtures thereof. The reducing agent is preferably sodium formate or hydrazine hydrate. The amount of the reducing agent depends on the amount of the active component, Pd, and is generally in the range from 1 to 10 times and preferably from 2 to 5 times the theoretical amount required for the reduction reaction. The reduction treatment of the catalyst precursor can be carried out according to methods and under conditions well known to those skilled in the art. For example, the reduction treatment can be carried out at a temperature of 0 to 200 ° C. and preferably 20 to 120 ° C. over a period of 0.5 to 24 hours, preferably 1 to 10 hours and particularly preferably 1 to 4 hours.

1. i) einen teilchenförmigen oder geformten Aktivkohleträger über einen Zeitraum von 0,5 bis 8 Stunden mit einer wäßrigen Lösung einer Säure wäscht, wobei die wäßrige Lösung der Säure eine Säurekonzentration von 0,01 bis 3,0 mol/Liter aufweist und es sich bei der Säure um mindestens eine Säure aus der Gruppe bestehend aus Salzsäure, Salpetersäure und Phosphorsäure handelt;
2. ii) den mit Säure gewaschenen Aktivkohleträger mit Wasser neutral wäscht und dann bei einer Temperatur von 80 bis 150 °C über einen Zeitraum von 0,5 bis 10 Stunden trocknet, wobei man einen behandelten Aktivkohleträger erhält;
3. iii) den behandelten Aktivkohleträger mit einer eine wasserlösliche Pd-Verbindung und ein Additiv der allgemeinen Formel I:
   

worin n, m und 1 unabhängig voneinander für 0 oder eine ganze Zahl von 1 bis 5 stehen und R₁, R₂ und R₃ unabhängig voneinander aus der Gruppe bestehend aus H, CH₃, NH₂, OH und COOH ausgewählt sind, enthaltenden wäßrigen Lösung imprägniert oder besprüht, um die Pd-Verbindung auf dem behandelten Aktivkohleträger zu trägem, wobei man eine Katalysatorvorstufe erhält, wobei der Pd-Gehalt der Pd-Verbindung in der wäßrigen Lösung im Bereich von 0,1 bis 10 Gew.-% liegt, das Molverhältnis von Additiv zu Pd im Bereich von 0,05:1 bis 1,5:1 liegt und die wäßrige Lösung auf einen pH-Wert von 7±3 eingestellt wird;

• iv) die aus Schritt iii) erhaltene Katalysatorvorstufe bei einer Temperatur von 0 bis 80 °C über einen Zeitraum von 1 bis 50 Stunden altert und
• v) die gealterte Katalysatorvorstufe mit einem Reduktionsmittel behandelt, wodurch das Pd-Ion in der Pd-Verbindung zu metallischem Pd reduziert wird, wobei man den Palladium/Kohle-Katalysator erhält.

In a preferred embodiment, the process for preparing the palladium / carbon catalyst according to the invention is carried out in such a way that:

1. i) washing a particulate or shaped activated carbon support for a period of 0.5 to 8 hours with an aqueous solution of an acid, the aqueous solution of the acid having an acid concentration of 0.01 to 3.0 mol / liter and the Acid is at least one acid from the group consisting of hydrochloric acid, nitric acid and phosphoric acid;
2. ii) the acid-washed activated carbon support was washed neutral with water and then dried at a temperature of 80 to 150 ° C. for a period of 0.5 to 10 hours, a treated activated carbon support being obtained;
3. iii) the treated activated carbon carrier with a water-soluble Pd compound and an additive of the general formula I:
   

wherein n, m and 1 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 aqueous solution impregnated or sprayed in order to support the Pd compound on the treated activated carbon support, whereby a catalyst precursor is obtained, the Pd content of the Pd compound in of the aqueous solution is in the range from 0.1 to 10% by weight, the molar ratio of additive to Pd is in the range from 0.05: 1 to 1.5: 1 and the aqueous solution is adjusted to a pH of 7 ± 3 is set;

• iv) the catalyst precursor obtained from step iii) ages at a temperature of 0 to 80 ° C. for a period of 1 to 50 hours and
• v) treating the aged catalyst precursor with a reducing agent, whereby the Pd ion in the Pd compound is reduced to metallic Pd, whereby the palladium / carbon catalyst is obtained.

Compared with the prior art, the present invention has the advantages that the catalyst produced has a higher degree of dispersion of metallic Pd and a higher crystallite content and that the catalyst has a high activity and a long service life.

Examples

The following examples serve to further illustrate the invention, but do not restrict the invention in any way.

The following test methods were used in the examples:

Degree of dispersion of metallic palladium:

worin: V_ads. für die von der Probe adsorbierte Wasserstoffmenge steht,
M_Pd für das Atomgewicht von Pd steht,
W_Probe für das Gewicht der Probe steht und
C_Pd für den Pd-Gehalt in der Probe steht.The degree of dispersion of metallic palladium was measured by the hydrogen-oxygen titration method on a chemical adsorption device. The degree of dispersion was calculated according to the following equation: $$\begin{array}{l}\text{Degree of dispersion}=\left(\left(2\times {\text{V}}_{\text{ads}\text{.}}\times {\text{M.}}_{\text{Pd}}\right)\text{/}\left(3\times 22400\times {\text{W.}}_{\text{sample}}\times {\text{C.}}_{\text{Pd}}\right)\right)\\ \times 100\text{\%}\end{array}$$

where: V _ads . represents the amount of hydrogen adsorbed by the sample,
M _{Pd stands} for the atomic weight of Pd,
W _{sample stands} for the weight of the sample and
C _{Pd stands} for the Pd content in the sample.

Crystallite content:

• Die Palladiumgehalte in den Katalysatoren wurden auf einem Röntgenfluoreszenzspektrographen gemessen, und die Teilchengrößen von Kristalliten von metallischem Pd wurden auf einem Röntgendiffraktometer (XRD) gemessen. Dann wurde der Kristallitgehalt berechnet als:
  • Kristallitgehalt = ((Gewicht von Kristalliten von metallischem Pd mit einer Teilchengröße von weniger als 2,5 nm) /(Gesamtgewicht von metallischem Pd))x100%

In the context of the present invention, the term “crystallite content” is to be understood as meaning the content of crystallites with a particle size of less than 2.5 nm.

• The palladium contents in the catalysts were measured on an X-ray fluorescence spectrograph, and the particle sizes of crystallites of metallic Pd were measured on an X-ray diffractometer (XRD). Then the crystallite content was calculated as:
  • Crystallite content = ((weight of crystallites of metallic Pd with a particle size of less than 2.5 nm) / (total weight of metallic Pd)) x100%

Thermal stability:

The average particle diameter of Pd crystallites of a palladium / carbon catalyst was measured on an X-ray diffractometer (XRD). After calcination of the catalyst in a stream of nitrogen blown through water (at 25 ° C.) at 500 ° C. for a period of 10 hours, the average particle diameter of the Pd crystallites was measured again on the X-ray diffractometer (XRD). The average particle diameter of Pd crystallites after calcination and the change in the average particle diameter of the Pd crystallites before and after calcination indicate the thermal stability of the catalyst. The smaller the average particle diameter of the Pd crystallites, the better the thermal stability of the catalyst. And the smaller the change in the average particle diameter of the Pd crystallites before and after calcination, the better the thermal stability of the catalyst.

Pd contents in layers at different depths under the surface of the catalysts:

The surface of a catalyst was etched with argon. After etching to a certain depth, the content of the Pd exposed by the etching in the surface layer was measured by means of X-ray photoelectron spectrometry (XPS) and Auger electron spectroscopy (AES), whereby the Pd contents in layers at different depths below the surface of the catalysts were obtained .

example 1

100 g of coconut shell activated carbon which had passed through a 4-mesh sieve but retained on an 8-mesh sieve and had a specific surface area of 1100 m ² / g was treated with 200 ml of 0.4 M aqueous solution of for 2 hours Washed nitric acid. After removing the acid solution, the activated carbon was washed neutral with deionized water and then dried at 120 ° C. for 6 hours.

3.2 g of an aqueous solution of palladium (IV) hydrogen chloride containing 16% by weight of palladium were admixed with deionized water until the total volume was 40 ml. 2.16 g of a 10% strength by weight solution of Additive A in water were then added to the solution, after which deionized water was added until the total volume of the solution reached 60 ml. The pH of the Pd-containing solution was adjusted to about 7 with 3% strength aqueous NaOH solution. After aging for 180 minutes, the Pd-containing solution was used to impregnate the above treated activated carbon over a period of 3 hours, yielding a catalyst precursor. The catalyst precursor was aged for 24 hours at room temperature and then impregnated at 20 ° C. for 3 hours in a reducing liquid consisting of 20 g of aqueous 5% strength by weight hydrazine hydrate solution and 200 g of pure water. After filtering off the liquid, the solids were washed neutral with pure water and then dried to give a catalyst product.

Examples 2 to 24

The procedure was analogous to Example 1, except that other Pd compounds and other additives were used to prepare the Pd-containing solution. The Pd compounds used, the Pd contents of Pd compound in the Pd-containing solution, the additives used and the molar ratios of the additives to Pd are listed in Table 1 below.

Examples 25 to 30

The procedure was analogous to Example 1, except that other additives were used to prepare the Pd-containing solution (the additives used are listed in Table 1), the Pd-containing solutions were sprayed onto the activated carbon in order to obtain catalyst precursors, and the inorganic acids, the concentrations of the inorganic acids, the periods of time for acid washing, the periods of time for drying, the temperatures, the pH values of the solutions containing the additives and the Pd compounds, the reducing agents, the temperatures for the reduction treatment and the periods of time for the reduction treatment were used in accordance with Table 2 below.

Comparative example

The procedure was analogous to Example 1, except that no additive was used to prepare the Pd-containing solution.

The degrees of dispersion, crystallite contents, thermal stabilities and Pd contents in layers at various depths below the surface of the catalysts were measured on the catalysts prepared in the examples and the comparative example. The catalysts were also evaluated under the evaluation conditions listed below. The results are shown in Tables 3 and 4 below.

Tabelle 1 Beispiel Pd-Verbindung Additiv Zugegebenes Pd /Aktivkohle (Gew.-%) Additiv/Pd (mol/mol) Beispiel 1 PalladiumIV-chlorwasserstoff Additiv A 0,51 0,20 Beispiel 2 Palladium(IV)-chlorwasserstoff Additiv A 0,51 0,30 Beispiel 3 Palladium(IV)-chlorwasserstoff Additiv A 0,22 0,60 Beispiel 4 Palladi umacetat Additiv A 0,08 1,50 Beispiel 5 Palladium(IV-chlorwasserstoff Additiv B 0,51 0,20 Beispiel 6 Palladium(IV)-chlorwasserstoff Additiv B 0,62 0,40 Beispiel 7 Palladium(IV)-chlorwasserstoff Additiv B 0,51 0,60 Beispiel 8 Palladiumacetat Additiv B 3,55 0,80 Beispiel 9 Palladium(IV)-chlorwasserstoff Additiv C 0,51 0,20 Beispiel 10 Palladium(IV)-chlorwasserstoff Additiv C 0,51 0,40 Beispiel 11 Palladium(IV-chlorwasserstoff Additiv C 0,51 0,60 Beispiel 12 Palladiumacetat Additiv C 0,15 1,00 Beispiel 13 PalladiumIV)-chlorwasserstoff Additiv D 0,51 0,20 Beispiel 14 Palladium(IV)-chlorwasserstoff Additiv D 0,41 0,40 Beispiel 15 Palladium(IV)chlorwasserstoff Additiv D 0,51 0,60 Beispiel 16 Palladiumacetat Additiv D 0,51 0,80 Beispiel 17 Palladium(IV-chlorwasserstoff Additiv E 0,51 0,20 Beispiel 18 Palladium(IV)-chlorwasserstoff Additiv E 1,00 0,40 Beispiel 19 PalladiumIV)-chlorwasserstoff Additiv E 0,51 0,60 Beispiel 20 Palladiumacetat Additiv E 0,51 0,80 Beispiel 21 PalladiumIV)-chlorwasserstoff Additiv F 4,50 0,05 Beispiel 22 Palladium(IV)-chlorwasserstoff Additiv F 0,51 0,40 Beispiel 23 Palladium(IV)-chlorwasserstoff Additiv F 0,51 0,60 Beispiel 24 Palladiumacetat Additiv F 0,51 0,80 Beispiel 25 Palladium(IV)-chlorwasserstoff Additiv A 0,51 0,20 Beispiel 26 Palladium(IV)-chlorwasserstoff Additiv B 0,51 0,40 Beispiel 27 PalladiumIV)-chlorwasserstoff Additiv C 0,51 0,60 Beispiel 28 Palladium(IV)-chlorwasserstoff Additiv D 0,51 0,80 Beispiel 29 Palladium(IV)-chlorwasserstoff Additiv E 0,51 0,50 Beispiel 30 Palladium(IV)-chlorwasserstoff Additiv F 0,51 0,50 Vergleichsbeispiel Palladium(IV)-chlorwasserstoff / 0,51 / Tabelle 2 Bsp. 25 Bsp.26 Bsp.27 Bsp.28 Bsp.29 Bsp.30 Anorganische Säure Salzsäure Salpetersäure Phosphorsäure Salpetersäure Salpetersäure Salpetersäure Konzentration der anorganischen Säure (M) 0,4 0,1 3 0,4 0,01 0,4 Zeit für die Säurewäsche (h) 4 8 0,5 4 4 4 Trocknungstemperatur (°C) 150 120 120 80 120 120 Trocknungszeit (h) 1 6 6 10 6 6 pH-Wert der Additiv und Pd-Verbindung enthaltenden Lösung 9 7 6 7 4 10 Reduktionsmittel Formaldehyd Formaldehyd Natriumformiat Wasserstoffgas Glucose Hydrazinhydrat Reduktionstemperatur (°C) 50 80 120 200 120 80 Reduktionszeit (h) 3 3 2 1 24 3 Evaluation conditions for the catalysts: Amount of catalyst: 2.0 g Amount of raw terephthalic acid: 30.0 g Amount of 4-CBA: 1.0 g Reaction pressure: 70 kg Hydrogen gas partial pressure: 5.0 kg Reaction time: 1.0 hours Reaction temperature: 270 ° C $$\text{Sales of 4-CBA}=\frac{\text{Amount of remaining 4-CBA added}}{\text{Amount of 4-CBA added}}\times 100\text{\%}$$

Table 1 example Pd connection Additive Added Pd / activated carbon (wt .-%) Additive / Pd (mol / mol) example 1 Palladium IV hydrogen chloride Additive A 0.51 0.20 Example 2 Palladium (IV) hydrogen chloride Additive A 0.51 0.30 Example 3 Palladium (IV) hydrogen chloride Additive A 0.22 0.60 Example 4 Palladium acetate Additive A 0.08 1.50 Example 5 Palladium (IV-hydrogen chloride Additive B 0.51 0.20 Example 6 Palladium (IV) hydrogen chloride Additive B 0.62 0.40 Example 7 Palladium (IV) hydrogen chloride Additive B 0.51 0.60 Example 8 Palladium acetate Additive B 3.55 0.80 Example 9 Palladium (IV) hydrogen chloride Additive C 0.51 0.20 Example 10 Palladium (IV) hydrogen chloride Additive C 0.51 0.40 Example 11 Palladium (IV-hydrogen chloride Additive C 0.51 0.60 Example 12 Palladium acetate Additive C 0.15 1.00 Example 13 Palladium IV) hydrogen chloride Additive D 0.51 0.20 Example 14 Palladium (IV) hydrogen chloride Additive D 0.41 0.40 Example 15 Palladium (IV) hydrogen chloride Additive D 0.51 0.60 Example 16 Palladium acetate Additive D 0.51 0.80 Example 17 Palladium (IV-hydrogen chloride Additive E 0.51 0.20 Example 18 Palladium (IV) hydrogen chloride Additive E 1.00 0.40 Example 19 Palladium IV) hydrogen chloride Additive E 0.51 0.60 Example 20 Palladium acetate Additive E 0.51 0.80 Example 21 Palladium IV) hydrogen chloride Additive F. 4.50 0.05 Example 22 Palladium (IV) hydrogen chloride Additive F. 0.51 0.40 Example 23 Palladium (IV) hydrogen chloride Additive F. 0.51 0.60 Example 24 Palladium acetate Additive F. 0.51 0.80 Example 25 Palladium (IV) hydrogen chloride Additive A 0.51 0.20 Example 26 Palladium (IV) hydrogen chloride Additive B 0.51 0.40 Example 27 Palladium IV) hydrogen chloride Additive C 0.51 0.60 Example 28 Palladium (IV) hydrogen chloride Additive D 0.51 0.80 Example 29 Palladium (IV) hydrogen chloride Additive E 0.51 0.50 Example 30 Palladium (IV) hydrogen chloride Additive F. 0.51 0.50 Comparative example Palladium (IV) hydrogen chloride / 0.51 / Table 2 Ex. 25 Ex. 26 Ex. 27 Ex. 28 Ex. 29 Ex. 30 Inorganic acid hydrochloric acid nitric acid phosphoric acid nitric acid nitric acid nitric acid Inorganic Acid Concentration (M) 0.4 0.1 3 0.4 0.01 0.4 Acid wash time (h) 4th 8th 0.5 4th 4th 4th Drying temperature (° C) 150 120 120 80 120 120 Drying time (h) 1 6th 6th 10 6th 6th pH of the solution containing additive and Pd compound 9 7th 6th 7th 4th 10 Reducing agent formaldehyde formaldehyde Sodium formate Hydrogen gas glucose Hydrazine hydrate Reduction temperature (° C) 50 80 120 200 120 80 Reduction time (h) 3 3 2 1 24 3

Table 3 example Pd content in catalyst (% by weight) Degree of dispersion (%) Crystallite content (%) Average particle size (nm) Average particle size after calcination at 500 ° C (nm) Change in average particle size before and after calcination (%) 4-CBA Sales (%) example 1 0.50 20th 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 21st 92 2.7 5.3 96 - Example 5 0.50 20th 90 3.5 5.9 69 99.4 Example 6 0.60 26th 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 20th 92 3.3 5.9 79 99.6 Example 9 0.50 20th 91 2.9 5.7 97 99.6 Example 10 0.50 22nd 92 3.8 5.6 47 99.8 Example 11 0.49 25th 90 3.6 5.8 61 99.7 Example 12 0.15 28 91 3.0 5.7 90 - Example 13 0.50 20th 90 3.6 5.9 64 99.5 Example 14 0.40 21st 92 3.3 5.6 70 99.5 Example 15 0.50 26th 91 3.4 5.8 71 99.8 Example 16 0.49 25th 90 3.2 5.9 84 99.9 Example 17 0.50 30th 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 5.9 64 99.7 Example 23 0.50 30th 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 20th 91 3.3 6.0 82 99.6 Example 26 0.50 20th 90 3.5 5.9 69 99.7 Example 27 0.50 22nd 90 3.4 6.0 76 99.8 Example 28 0.49 26th 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 4th 52 4.6 11.1 141 66.2 Table 4 example Pd content of the catalyst (% by weight) Pd content in the layer at a depth of 5 nm below the catalyst surface (% by weight) Pd content in the layer at a depth of 300 nm below the catalyst surface (% by weight) example 1 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 Comparative example 0.50 30.6 12.5

Reference is hereby expressly made to the patent specifications, patent applications, non-patent literature and test methods cited in the description.

While the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes and modifications can 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 mode for carrying out the present invention, but includes all embodiments falling within the scope of the appended claims.

Claims (8)

Process for the preparation of a palladium / carbon catalyst in which: a) an activated carbon is washed neutral with an aqueous solution of an inorganic acid and then with water and then the washed activated carbon is dried to obtain an activated carbon support; b) the activated carbon support is impregnated or sprayed with an aqueous solution containing a Pd compound and an additive in order to support the Pd compound on the activated carbon support, a catalyst precursor being obtained, the molar ratio of additive to Pd in the Pd compound in the solution ranges from 0.01: 1 to 2.0: 1; the additive among the compounds of general formula I:

wherein n, m and 1 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 and the palladium-containing solution is adjusted to a pH of 7 ± 3; and c) treating the catalyst precursor with a reducing agent to obtain the palladium / carbon catalyst. Procedure according to Claim 1 in which the inorganic acid is at least one acid from the group consisting of hydrochloric acid, nitric acid and phosphoric acid and the time for the acid wash is in the range from 0.5 to 8 hours; the inorganic acid solution has an acid concentration of 0.01 to 5.0 mol / liter and the drying is carried out at a temperature of 80 to 150 ° C. for a period of 0.5 to 10 hours. Procedure according to Claim 1 or 2 wherein the Pd compound is selected from the group consisting of palladium halides, palladium acetate, palladium nitrate, tetrachloropalladium (II) acid, basic salts of tetrachloropalladium (II) acid, palladium-amino complexes and mixtures thereof; the palladium concentration in the Pd-containing solution is in the range from 0.01 to 20% by weight and the molar ratio of additive to palladium in the Pd compound in the solution is in the range from 0.01: 1 to 2.0: 1 . Procedure according to Claim 3 in which the Pd compound is tetrachloropalladium (II) acid or palladium acetate; the solution containing the Pd compound and the additive has a pH of 4 to 9; the palladium concentration in the solution is in the range from 0.1 to 10% by weight and the molar ratio of additive to palladium in the Pd compound in the solution is in the range from 0.05: 1 to 1.5: 1. Method according to one of the Claims 1 to 4th , in which the catalyst precursor is further aged at a temperature of 0 to 80 ° C. for a period of 1 to 50 hours before the reduction treatment. Method according to one of the Claims 1 to 5 , in which 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 carried out at a temperature of 0 to 200 ° C for a period of 0.5 to 24 hours. Procedure according to Claim 6 , in which the catalyst precursor is aged before the reduction treatment at a temperature of 0 to 80 ° C for a period of 1 to 24 hours; sodium formate or hydrazine hydrate is used as the reducing agent and the reduction treatment is carried out at a temperature of 20 to 120 ° C. for a period of 1 to 10 hours. Process for the preparation of a palladium / carbon catalyst, in which: i) a particulate or shaped activated carbon support is washed for a period of 0.5 to 8 hours with an aqueous solution of an acid, the aqueous solution of the acid having an acid concentration of 0, 01 to 3.0 mol / liter and the acid is at least one acid from the group consisting of hydrochloric acid, nitric acid and phosphoric acid; ii) the acid-washed activated carbon support was washed neutral with water and then dried at a temperature of 80 to 150 ° C. for a period of 0.5 to 10 hours, a treated activated carbon support being obtained; iii) the treated activated carbon carrier with a water-soluble Pd compound and an additive of the general formula I:

wherein n, m and 1 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 is, containing aqueous solution impregnated or sprayed in order to support the Pd compound on the treated activated carbon support, whereby a catalyst precursor is obtained, the Pd content of the Pd compound in the aqueous solution in the range from 0.1 to 10 wt. -%, the molar ratio of additive to Pd is in the range from 0.05: 1 to 1.5: 1 and the aqueous solution is adjusted to a pH of 7 ± 3; iv) the catalyst precursor obtained from step iii) ages at a temperature of 0 to 80 ° C. for a period of 1 to 50 hours and v) treating the aged catalyst precursor with a reducing agent, thereby reducing the Pd ion in the Pd compound to metallic Pd to give the palladium-on-carbon catalyst.