Preparation method of palladium-carbon catalyst for dehalogenation coupling reaction

Abstract

The invention relates to the technical field of preparation of noble metal catalysts, and discloses a preparation method of a palladium-carbon catalyst for dehalogenation coupling reaction, which specifically comprises the following steps: 1, preparing nitric acid modified activated carbon: heating and refluxing activated carbon with nitric acid at 80 DEG C for 1 hour, and washing the activated carbon to be neutral to obtain the nitric acid modified activated carbon; 2, slurry preparation: adding nitric acid modified activated carbon into a sodium carbonate solution, mixing to prepare slurry, and stirring at room temperature for 0.5 h; 3, stirring and mixing treatment: adding a chloropalladic acid solution into the slurry while stirring, and continuously stirring for 0.5 h after dropwise adding; according to the palladium-carbon catalyst for the dehalogenation coupling reaction, provided by the invention, the conversion rate is increased, and the defects that the selectivity is not high, the catalytic activity is not strong and the catalyst is inactive and difficult to use mechanically in the preparation of 3, 3 ', 4, 4'-biphenyl tetraformate in the dehalogenation coupling reaction are overcome.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal catalyst preparation, and in particular to a method for preparing a palladium-carbon catalyst for a dehalogenation coupling reaction. Background Art

[0002] Biphenyl polyimide (PI for short) is called a high-performance material in engineering plastics. There are many methods for its synthesis. Among them, the performance of PI synthesized from biphenyl dianhydride is the most superior, especially the PI obtained by polymerization of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a monomer is a very good super heat-resistant resin. The polyimide film formed by stretching has almost the same thermal expansion coefficient as the copper foil, and can be well laminated with the copper foil under long-term high and low temperature conditions without peeling. It is widely used in flexible circuit boards and ultra-high power 5G signal transmitters. There are many literatures and patent reports on the synthesis of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). Among them, the dehalogenation coupling reaction using palladium carbon as a catalyst and halogenated phthalic anhydride as a raw material is currently a relatively excellent catalytic reaction. Patent CN111620769A uses palladium-copper loaded on activated carbon as a catalyst, which is reduced by a hydrazine reducing agent to undergo a dechlorination coupling reaction, and then heated and dehydrated to finally obtain BPDA. Patent CN114315555A uses zinc chloride as a promoter and activated carbon loaded with palladium and manganese as a catalyst to improve the conversion rate of 4-chlorophthalic anhydride and the selectivity of 3,3',4,4'-biphenyltetracarboxylic acid, and improve the reaction efficiency. The current problem is that the yield of 3,3',4,4'-biphenyltetracarboxylic acid is low, and there is still a lot of room for improvement in industrial production. Most of the dehalogenation coupling reactions reported in the literature are currently carried out in the presence of a reducing agent. There are coupling reactions and hydrogenation dehalogenation reactions at the same time, and these two reactions are competitive reactions. The generally accepted reaction mechanism is that the first step is an oxidative addition reaction of halogenated aromatics with zero-valent palladium. The second step is a coupling reaction, during which zero-valent palladium is converted into positive divalent palladium, and at the same time, due to the presence of a reducing agent in the reaction system, it is reduced to zero-valent palladium in situ. The third step is mainly a side reaction, that is, after the first step of the addition process, the catalyst activity is too strong, and it is easy to dehalogenate first during the coupling process, and then the coupling product decreases.

[0003] However, in the dehalogenation coupling reaction, divalent palladium is easily reduced to zero-valent palladium under in-situ reaction conditions. The catalyst after the in-situ reaction can also undergo coupling reaction, with high product selectivity but low conversion rate. The selectivity for preparing 3,3',4,4'-biphenyl tetracarboxylate in the dehalogenation coupling reaction is not high, the catalytic activity is not strong, and the catalyst deactivation is difficult to apply.

[0004] To this end, we propose a method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction. Summary of the invention

[0005] The present invention mainly solves the technical problems existing in the above-mentioned prior art and provides a method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme, a method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, specifically comprising the following steps:

[0007] Step 1: Preparation of nitric acid-modified activated carbon: reflux the activated carbon with nitric acid at 80°C for 1 hour, wash the activated carbon to neutrality, and obtain nitric acid-modified activated carbon;

[0008] Step 2: Prepare slurry: Add nitric acid-modified activated carbon into sodium carbonate solution and mix to prepare slurry, and stir at room temperature for 0.5h;

[0009] Step 3: Stirring and mixing: Add the chloropalladium acid solution to the slurry while stirring, and continue stirring for 0.5h after the addition is complete;

[0010] Step 4: Reduction and heating treatment: Add reducing agent and heat to 90°C, keep warm for 2 hours, then filter and wash until no chloride ions are detected by AgNO3 solution to obtain the dehalogenation coupling palladium carbon catalyst.

[0011] Preferably, the weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:(525-2100).

[0012] Preferably, the mass percentage of the sodium carbonate solution in the second step is 5wt%, and the concentration of the chloropalladic acid solution is 10g / L.

[0013] Preferably, in the third step, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon is 5:100.

[0014] Preferably, the specific material of the activated carbon in the first step is wood charcoal.

[0015] Preferably, the specific surface area of ​​the wood charcoal is not less than 1200 m2 / g.

[0016] Preferably, the particle size of the wood charcoal is 200-300 meshes.

[0017] Preferably, the specific material of the reducing agent in the fourth step is sodium formate.

[0018] Preferably, the molar ratio of sodium formate to palladium metal is not greater than 1.

[0019] Beneficial Effects

[0020] The present invention provides a method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction. It has the following beneficial effects:

[0021] 1. A method for preparing a palladium-carbon catalyst for a dehalogenation coupling reaction. The present invention provides a palladium-carbon catalyst for a dehalogenation coupling reaction, which improves the conversion rate and solves the shortcomings of low selectivity, weak catalytic activity and difficulty in applying the catalyst deactivated in the preparation of 3,3',4,4'-biphenyltetracarboxylate in the dehalogenation coupling reaction.

[0022] 2. A method for preparing a palladium-carbon catalyst for a dehalogenation coupling reaction. The present invention provides a method for preparing a palladium-carbon catalyst for a dehalogenation coupling reaction. The palladium particles prepared by the sodium carbonate buffer solution system are uniform in size. The temperature-raising aging process improves the interaction strength between the palladium and the carrier. The addition of a small amount of a reducing agent is beneficial to controlling the ratio of Pd0 / Pd2+ in the catalyst, and the activity of the catalyst is changed by adjusting the ratio.

[0023] 3. A method for preparing a palladium-carbon catalyst for a dehalogenation coupling reaction. The present invention prepares a palladium-carbon catalyst for a dehalogenation coupling reaction, thereby greatly reducing the dehalogenation rate of the reaction, reducing the emission of pollutants in the solution, and further improving the economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0025] Example 1: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: preparing a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is complete; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution to obtain a dehalogenation coupling palladium carbon catalyst. The weight ratio of the activated carbon, nitric acid and sodium carbonate solution in the first and second steps is 10 The invention discloses a palladium-carbon catalyst for dehalogenation coupling reaction, which improves the conversion rate and solves the problems of low selectivity, low catalytic activity and difficulty in applying the deactivated catalyst in the preparation of 3,3',4,4'-biphenyl tetracarboxylate in the dehalogenation coupling reaction. The invention discloses a palladium-carbon catalyst for dehalogenation coupling reaction, which improves the conversion rate and solves the problems of low selectivity, low catalytic activity and difficulty in applying the deactivated catalyst in the preparation of 3,3',4,4'-biphenyl tetracarboxylate in the dehalogenation coupling reaction.

[0026] Example 2: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is complete; the fourth step: reduction and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution to obtain a dehalogenated coupling palladium carbon catalyst. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first and second steps is 100:5:525, and the sodium carbonate solution in the second step is 1:10 ... The mass percentage of is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of palladium metal to nitric acid modified activated carbon in the chloropalladic acid solution in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200㎡ / g, and the particle size of the wood charcoal is 200-300 meshes, the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 0.3. The present invention provides a preparation method for a palladium carbon catalyst for a dehalogenation coupling reaction, and the prepared palladium particles are uniform in size through a sodium carbonate buffer solution system, and the heating aging process improves the interaction strength between palladium and a carrier, and the addition of a small amount of reducing agent is beneficial to controlling the ratio of Pd0 / Pd2+ in the catalyst, and the activity of the catalyst is changed by adjusting the ratio.

[0027] Example 3: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is complete; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution to obtain a dehalogenated coupling palladium carbon catalyst. In the first and second steps, the activated carbon and nitric acid are mixed. The weight ratio of the palladium metal to the sodium carbonate solution is 100:5:525, the mass percentage of the sodium carbonate solution in the second step is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of the palladium metal to the nitric acid modified activated carbon in the chloropalladic acid solution in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200 square meters / g, and the particle mesh number of the wood charcoal is 200-300 meshes, the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of the sodium formate to the palladium metal is 0.5. The present invention prepares the palladium carbon catalyst for the dehalogenation coupling reaction, so that the reaction dehalogenation rate is greatly reduced, the discharge of pollutants in the solution is reduced, and the economic benefit is further improved.

[0028] Example 4: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1 As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is completed; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution A dehalogenation coupling palladium carbon catalyst can be obtained. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:525, the mass percentage of the sodium carbonate solution in the second step is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200 m2 / g, and the particle mesh number of the wood charcoal is 200-300 meshes, and the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 0.7.

[0029] Example 5: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1 As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is completed; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chlorine ions are detected by AgNO3 solution The dehalogenation coupling palladium carbon catalyst can be obtained. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:525, the mass percentage of sodium carbonate solution in the second step is 5wt%, the concentration of chloropalladic acid solution is 10g / L, the weight ratio of palladium metal in chloropalladic acid solution and nitric acid modified activated carbon in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200㎡ / g, and the particle size of the wood charcoal is 200-300 meshes, and the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 1.

[0030] Example 6: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1 As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is completed; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution A dehalogenation coupling palladium carbon catalyst can be obtained. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:525, the mass percentage of the sodium carbonate solution in the second step is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200 m2 / g, and the particle mesh number of the wood charcoal is 200-300 meshes, and the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 0.3.

[0031] Example 7: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is completed; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution A dehalogenation coupling palladium carbon catalyst can be obtained. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:1050, the mass percentage of the sodium carbonate solution in the second step is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200 square meters / g, and the particle mesh number of the wood charcoal is 200-300 meshes, and the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 0.5.

[0032] Embodiment 8: A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, such as Figure 1 As shown, it specifically includes the following steps: the first step: preparing nitric acid-modified activated carbon: heating the activated carbon with nitric acid at a temperature of 80°C for 1h, washing the activated carbon to neutrality, and obtaining nitric acid-modified activated carbon; the second step: making a slurry: adding the nitric acid-modified activated carbon to a sodium carbonate solution and mixing to form a slurry, and stirring at room temperature for 0.5h; the third step: stirring and mixing treatment: adding chloropalladic acid solution to the slurry while stirring, and continuing to stir for 0.5h after the addition is completed; the fourth step: reducing and heating treatment: adding a reducing agent, and heating to 90°C, keeping warm for 2h, and then filtering and washing until no chloride ions are detected with an AgNO3 solution A dehalogenation coupling palladium carbon catalyst can be obtained. The weight ratio of activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:2100, the mass percentage of the sodium carbonate solution in the second step is 5wt%, the concentration of the chloropalladic acid solution is 10g / L, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon in the third step is 5:100, the specific material of the activated carbon in the first step is wood charcoal, the specific surface area of ​​the wood charcoal is not less than 1200 square meters / g, and the particle mesh number of the wood charcoal is 200-300 meshes, and the specific material of the reducing agent in the fourth step is sodium formate, and the molar ratio of sodium formate to palladium metal is 0.5.

[0033] Example 9: This example is a conventional method for a palladium carbon catalyst, and the steps are as follows: Step 1: Preparation of modified activated carbon, the activated carbon is heated to reflux at 80°C for 1h with 5% by mass nitric acid, and then the activated carbon is washed to neutral; Step 2: The above-mentioned activated carbon is prepared into a slurry, and a chloropalladic acid solution is added, and the pH is adjusted to about 9 with an alkali solution; Step 3: Add a reducing agent such as formaldehyde, sodium formate, etc., wherein the molar ratio of the reducing agent to metallic palladium is about 3, reduce for 2h, and then filter and wash until there is no chloride ion detected with an AgNO3 solution.

[0034] The conventional palladium-carbon catalyst Example 9 and the catalysts of Examples 1 to 8 were used for dehalogenation coupling reaction to evaluate the catalytic performance of the prepared catalysts. The specific process is as follows: a certain mass of water, 4-chlorophthalic anhydride and catalyst mass ratio of 200:1 were added, sodium hydroxide was used to adjust the solution pH to 11, then the temperature was raised to 90°C, hydrazine hydrochloride was added, and the reaction was kept warm for 4 hours. After the liquid was taken, it was analyzed by liquid chromatography. The results of the catalyst in the dehalogenation coupling reaction are shown in Table 1:

[0035] Table 1

[0036]

[0037] As can be seen from Table 1, the activity of the palladium carbon catalyst prepared by soaking the carrier in sodium carbonate solution and reducing it with a small amount of reducing agent is improved compared with the conventionally prepared palladium carbon, especially the selectivity of the product is significantly improved. Further use of the catalyst in Example 7 found that it can be applied multiple times.

[0038] Working principle of the present invention: The preparation method of the dehalogenation coupling palladium carbon catalyst described in the present invention lies in the step of modifying the activated carbon with nitric acid and the subsequent soaking in sodium carbonate solution and the use of an appropriate amount of reducing agent. The step of modifying the activated carbon with nitric acid not only increases the active sites on the surface of the activated carbon, but also improves its adsorption capacity for palladium metal, and the soaking in sodium carbonate solution further adjusts the surface charge state of the activated carbon, so that the palladium metal can be more evenly loaded on the activated carbon to form a stable palladium carbon complex. In the reduction and heating treatment step, the use of an appropriate amount of reducing agent ensures the uniform distribution and high dispersion of palladium metal on the surface of the activated carbon, while avoiding the degradation of catalyst performance caused by excessive reducing agent. The molar ratio of the reducing agent is controlled within an appropriate range to ensure the high efficiency and stability of the catalyst. For the dehalogenation coupling reaction, the palladium-carbon catalyst of the present invention exhibits excellent catalytic performance. It can be seen from the data in Table 1 that, compared with the conventionally prepared palladium-carbon catalyst, the catalyst of the present invention has significantly improved conversion rate and product selectivity, which is mainly attributed to the nitric acid modification of the activated carbon surface, the immersion in the sodium carbonate solution and the use of an appropriate amount of reducing agent. These factors work together to form highly dispersed and stable active centers of palladium metal on the activated carbon surface, thereby improving the catalytic activity and stability of the catalyst. In particular, the catalyst in Example 7 exhibits extremely high conversion rate and selectivity, and can be used multiple times, indicating that it has good reusability and stability, which further proves the feasibility and effectiveness of the dehalogenation coupling palladium-carbon catalyst preparation method described in the present invention.

[0039] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction, characterized in that: The specific steps include: Step 1: Preparation of nitric acid-modified activated carbon: reflux the activated carbon with nitric acid at 80°C for 1 hour, wash the activated carbon to neutrality, and obtain nitric acid-modified activated carbon; Step 2: Prepare slurry: Add nitric acid-modified activated carbon into sodium carbonate solution and mix to prepare slurry, and stir at room temperature for 0.5h; Step 3: Stirring and mixing: Add the chloropalladium acid solution to the slurry while stirring, and continue stirring for 0.5h after the addition is complete; Step 4: Reduction and heating treatment: Add reducing agent and heat to 90°C, keep warm for 2 hours, then filter and wash until no chloride ions are detected by AgNO3 solution to obtain the dehalogenation coupling palladium carbon catalyst.

2. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 1, wherein: The weight ratio of the activated carbon, nitric acid and sodium carbonate solution in the first step and the second step is 100:5:(525-2100).

3. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 1, wherein: The mass percentage of the sodium carbonate solution in the second step is 5wt%, and the concentration of the chloropalladic acid solution is 10g / L.

4. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 1, wherein: In the third step, the weight ratio of palladium metal in the chloropalladic acid solution to nitric acid-modified activated carbon is 5:

100.

5. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 1, wherein: The specific material of the activated carbon in the first step is wood charcoal.

6. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 5, characterized in that: The specific surface area of ​​the wood charcoal is not less than 1200 m2 / g.

7. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 5, characterized in that: The particle size of the wood charcoal is between 200 and 300 meshes.

8. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 1, wherein: The specific material of the reducing agent in the fourth step is sodium formate.

9. The method for preparing a palladium-carbon catalyst for dehalogenation coupling reaction according to claim 8, characterized in that: The molar ratio of the sodium formate to the palladium metal is not greater than 1.

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