Catalyst for synthesizing 2, 3-dichloropyridine as well as preparation method and application of catalyst

Abstract

The invention relates to the technical field of catalysts and particularly discloses a catalyst for synthesizing 2, 3-dichloropyridine as well as a preparation method and application of the catalyst. The catalyst for synthesizing 2, 3-dichloropyridine provided by the invention comprises a carrier, an active component and an auxiliary agent which are loaded on the carrier, and a coating layer which coats the outside of the carrier, the carrier is a SiO2 (silicon dioxide) modified Al2O3 carrier or a TiO2 (titanium dioxide) modified Al2O3 carrier; in the TiO2 modified alpha-Al2O3 or the SiO2 modified alpha-Al2O3, the mass fraction of the TiO2 or the SiO2 is 0.5 to 5 percent; the active component is Pd; the auxiliary agent is selected from one or more of compounds of Mg, Ni, Rh and Ru; the invention further provides a preparation method of the catalyst for synthesizing the 2, 3-dichloropyridine. The catalyst for synthesizing the 2, 3-dichloropyridine, provided by the invention, can be used for synthesizing the 2, 3-dichloropyridine by hydrodechlorination of polychloropyridine, so that the reaction conversion rate and the yield of the 2, 3-dichloropyridine are greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of catalysts, and particularly relates to a catalyst for synthesizing 2,3-dichloropyridine, a preparation method thereof, and an application thereof. Background Art

[0002] 2,3-Dichloropyridine is an important fine chemical intermediate, which can be used to synthesize new insecticides such as chlorantraniliprole and cyantraniliprole. Its environmentally friendly characteristics and specific effects on Lepidoptera pests have made it a research hotspot in the field of agricultural chemicals; in addition, 2,3-dichloropyridine is also widely used in multiple fields such as dyes, pharmaceuticals, and rubber, and has good industrial value.

[0003] Currently, the synthesis of 2,3-dichloropyridine is mainly carried out by using 2,3,6-trichloropyridine as a raw material and performing a hydrodechlorination reaction under the action of a catalyst. Its process is simple, the product yield is high, and the environmental pollution is small, and it has become the most promising method for synthesizing 2,3-dichloropyridine. However, there are still some problems in the currently used catalytic systems; for example: a Pd / C catalyst has been reported in the related art, which lacks a selectivity regulation mechanism, resulting in side reaction competition and causing excessive dechlorination, and the yield of the target product is less than 80%; there is also a literature report on a Pd-Mg / C system catalyst, although the selectivity of the reaction is improved to a certain extent, its noble metal loading is too high and it is easily dissolved out; there is also a report on a Co / Pt-Al 2 O 3 catalyst, although it achieves good stability through strong metal-support interaction, there is a problem of limited reaction efficiency caused by insufficient dispersion of the active component.

[0004] Therefore, the currently disclosed catalysts seriously restrict the cost-effectiveness and process sustainability of the industrial production of 2,3-dichloropyridine, and there is an urgent need to develop a new catalytic material system with high activity, high selectivity, and excellent stability. Summary of the Invention

[0005] In order to overcome the problems of low activity, poor selectivity, and easy deactivation of the existing catalysts for preparing 2,3-dichloropyridine, the present application provides a catalyst for synthesizing 2,3-dichloropyridine, a preparation method thereof, and an application thereof.

[0006] In the first aspect, the present application provides a catalyst for synthesizing 2,3-dichloropyridine, and adopts the following technical solution: A catalyst for synthesizing 2,3-dichloropyridine, comprising a carrier, an active component and an auxiliary agent loaded on the carrier, and a coating layer wrapped outside the carrier; The carrier is SiO 2 modified Al 2 O 3Carrier or TiO 2 Modified Al 2 O 3 Carrier; the SiO 2 Modified α - Al 2 O 3 Or TiO 2 Modified α - Al 2 O 3 In, the mass fraction of SiO 2 Or TiO 2 Is 0.5 - 5%; The active component is Pd; The promoter is selected from one or more of the compounds of Mg, Ni, Rh and Ru.

[0007] This application provides a nitrogen - doped carbon - material - coated SiO 2 Modified Al 2 O 3 Or TiO 2 Modified Al 2 O 3 Supported Pd catalyst, which has good reaction activity and stability. When used in the hydrogenation and dechlorination of polychloropyridine to synthesize 2,3 - dichloropyridine, it can greatly improve the selectivity and yield of the product. Specifically: In this application, by using SiO 2 Modified Al 2 O 3 Or TiO 2 Modified Al 2 O 3 As the carrier and controlling the mass fraction of TiO 2 Or SiO 2 In the modified carrier within the above - specified range, the dispersion of Pd can be further improved, the acid - base properties of the catalyst surface can be improved, and thus a catalyst with more stable and excellent catalytic performance for synthesizing 2,3 - dichloropyridine can be obtained; in addition, the addition of the above - mentioned Mg, Ni, Rh or Ru compounds can further optimize the distribution state of Pd and its synergistic effect with the carrier, enhancing the selectivity and conversion efficiency of the catalyst for the hydrogenation and dechlorination reaction of polychloropyridine. Therefore, the catalyst for synthesizing 2,3 - dichloropyridine provided by this application effectively solves the problems of poor reaction selectivity and low product yield caused by uneven dispersion of the active component or poor stability in the prior art, and significantly improves the production efficiency of the target product 2,3 - dichloropyridine.

[0008] In some embodiments, in the SiO 2 Modified α - Al 2 O 3 In, SiO 2The mass fraction can be 0.5 - 1%, 0.5 - 1.5%, 0.5 - 2%, 0.5 - 5%, 1 - 1.5%, 1 - 2%, 1 - 5%, 1.5 - 2%, 1.5 - 5% or 2 - 5%.

[0009] In a specific embodiment, the SiO 2 modified α-Al 2 O 3 In, the mass fraction of SiO 2 can also be 0.5%, 1%, 1.5%, 2% or 5%.

[0010] In some embodiments, the TiO 2 modified α-Al 2 O 3 In, the mass fraction of TiO 2 can be 0.5 - 1%, 0.5 - 1.5%, 0.5 - 2%, 0.5 - 5%, 1 - 1.5%, 1 - 2%, 1 - 5%, 1.5 - 2%, 1.5 - 5% or 2 - 5%.

[0011] In a specific embodiment, the TiO 2 modified α-Al 2 O 3 In, the mass fraction of TiO 2 can also be 0.5%, 1%, 1.5%, 2% or 5%.

[0012] In this application, the compound of Mg can be magnesium nitrate, the compound of Ni can be nickel nitrate hexahydrate, the compound of Rh can be rhodium chloride, and the compound of Ru can be ruthenium chloride.

[0013] Optionally, in the SiO 2 modified α-Al 2 O 3 In, the mass fraction of SiO 2 is 0.5 - 1.5%; in the TiO 2 modified α-Al 2 O 3 In, the mass fraction of TiO 2 is 1 - 2%.

[0014] Optionally, the loading amount of Pd is 0.005 - 1 wt% of the carrier, and the loading amount of the promoter is 0.01 - 0.5 wt% of the carrier.

[0015] Optionally, the promoter is a mixture of a compound of Ni and a compound of Rh.

[0016] Optionally, the weight ratio of the compound of Ni to the compound of Rh is 1:(0.2 - 0.4).

[0017] In this application, when a compound of Ni and a compound of Rh are used in combination as promoters in a specific ratio, the dispersion of the active component Pd can be significantly optimized. Through experimental exploration, it is found that when the weight ratio of the compound of Ni and the compound of Rh is further controlled within the range of 1:(0.2 - 0.4), not only can the small-size distribution of Pd particles be further promoted, reducing their agglomeration phenomenon, but also the ability to regulate the acid-base balance on the catalyst surface can be enhanced, thereby effectively improving the selectivity and yield of the target product 2,3-dichloropyridine. In addition, the synergistic effect of the promoters under this ratio helps to improve the overall stability and anti-poisoning performance of the catalyst, and prolong the service life of the catalyst.

[0018] In some embodiments, the weight ratio of the compound of Ni and the compound of Rh can be 1:(0.1 - 0.2), 1:(0.1 - 0.3), 1:(0.1 - 0.4), 1:(0.1 - 0.5), 1:(0.2 - 0.3), 1:(0.2 - 0.4), 1:(0.2 - 0.5), 1:(0.3 - 0.4), 1:(0.3 - 0.5), or 1:(0.4 - 0.5).

[0019] In a specific embodiment, the weight ratio of the compound of Ni and the compound of Rh can also be 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5.

[0020] Optionally, the coating layer is a nitrogen-doped carbon material, and the weight of the coating layer is 0.05 - 2 wt% of the weight of the carrier.

[0021] In a second aspect, this application provides a method for preparing a catalyst for synthesizing 2,3-dichloropyridine.

[0022] A method for preparing a catalyst for synthesizing 2,3-dichloropyridine includes the following steps: (1) First, immerse the carrier in a solution containing a Pd salt and a promoter salt, adsorb for 2 - 24 h, filter, dry, and calcine at 400 - 600 °C for 2 - 6 h to obtain a catalyst loaded with the active component and the promoter; (2) Add m-xylene to the catalyst loaded with the active component and the promoter, then add ethylenediamine and carbon tetrachloride, stir at 50 - 90 °C for 3 - 5 h, and then stir at 120 - 160 °C for 3 - 5 h; dry the resulting solid compound at 100 - 150 °C for 10 - 15 h, grind and screen the solid compound with a particle size of 50 - 100 μm, and then calcine it in a nitrogen atmosphere at 400 - 650 °C for 2 - 6 h and reduce it in a hydrogen atmosphere at 200 - 450 °C for 2 - 6 h to obtain a catalyst for synthesizing 2,3-dichloropyridine.

[0023] Third aspect, the present application provides the use of the catalyst for synthesizing 2,3-dichloropyridine in the reaction of hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine.

[0024] Fourth aspect, the present application provides a method for synthesizing 2,3-dichloropyridine, characterized in that the catalyst for synthesizing 2,3-dichloropyridine according to any one of claims 1-6 is used in the synthesis method.

[0025] In summary, the present application has the following beneficial effects: 1. By using SiO 2 modified Al 2 O 3 or TiO 2 modified Al 2 O 3 as the carrier, Pd as the active component and using a nitrogen-doped carbon material for coating, a Pd catalyst supported on nitrogen-doped carbon material-coated SiO 2 modified Al 2 O 3 or TiO 2 modified Al 2 O 3 is obtained. This catalyst has good reaction activity and stability, can be used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, and greatly improves the selectivity and yield of the product.

[0026] 2. The nitrogen-doped carbon material coating layer of the present application can effectively inhibit the poisoning, loss and aggregation of the Pd active component, and greatly improve the stability and cyclic service life of the catalyst; 3. By adjusting the mass fraction of SiO 2 in SiO 2 modified α-Al 3 O 2 to be in the range of 0.5-1.5%; and the mass fraction of TiO 2 in TiO 2 modified α-Al 3 O 2 to be in the range of 1-2%, the obtained catalyst has better stability and higher catalytic efficiency. When used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, the conversion rate can reach more than 99.5%, and the yield of 2,3-dichloropyridine can reach more than 95%.

[0027] 4. The present application further uses a mixture of a Ni compound and a Rh compound as an auxiliary agent, which can further optimize the dispersion performance of the active component Pd, thereby improving the stability of the catalyst and making its catalytic performance more excellent. It is used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, and the yield of 2,3-dichloropyridine can reach more than 96%. Detailed implementation mode

[0028] The present application provides a catalyst for synthesizing 2,3-dichloropyridine, which includes a carrier, an active component and an auxiliary agent loaded on the carrier, and a coating layer wrapped outside the carrier; the carrier is SiO 2 modified Al 2 O 3 carrier or TiO 2 modified Al 2 O 3 carrier; in the SiO 2 modified α-Al 2 O 3 or TiO 2 modified α-Al 2 O 3 , the mass fraction of SiO 2 or TiO 2 is 0.5-5%; the active component is Pd; the auxiliary agent is selected from one or more of compounds of Mg, Ni, Rh and Ru; the coating layer is a nitrogen-doped carbon material, and the weight of the coating layer is 0.05-2 wt% of the weight of the carrier. Further, in the SiO 2 modified α-Al 2 O 3 , the mass fraction of SiO 2 is 0.5-1.5%; in the TiO 2 modified α-Al 2 O 3 , the mass fraction of TiO 2 is 1-2%; the loading amount of Pd is 0.005-1 wt% of the carrier, and the loading amount of the auxiliary agent is 0.01-0.5 wt% of the carrier. The auxiliary agent is a mixture of a Ni compound and a Rh compound; still further, the weight ratio of the Ni compound to the Rh compound is 1:(0.2-0.4) The preparation method of the above-mentioned catalyst for synthesizing 2,3-dichloropyridine includes the following steps: (1) Dissolve the Pd salt and the auxiliary agent salt in water at 30-80 °C, then immerse the carrier in the above solution, filter after adsorption for 2-24 h, and place the solid in sequence at 100-150 °C for drying for 6-16 h and calcining at 400-600 °C for 2-6 h to obtain a catalyst loaded with the active component and the auxiliary agent; (2) Add m-xylene to the catalyst loaded with active components and promoters, then add ethylenediamine and carbon tetrachloride, stir at 50-90 °C for 3-5 h, and then stir at 120-160 °C for 3-5 h; dry the resulting solid compound at 100-150 °C for 10-15 h, grind and screen the solid compound of 50-100 μm, and calcine it in a nitrogen atmosphere at 400-650 °C for 2-6 h and reduce it in a hydrogen atmosphere at 200-450 °C for 2-6 h in sequence to obtain a catalyst for synthesizing 2,3-dichloropyridine.

[0029] In this application, TiO 2 modified α-Al 2 O 3 support and SiO 2 modified α-Al 2 O 3 support is prepared according to the method provided in ZL 202410357906.2; in SiO 2 modified α-Al 2 O 3 the mass fraction of SiO 2 can be 0.5%, 1%, 1.5%, 2%, 5%; in TiO 2 modified α-Al 2 O 3 the mass fraction of TiO 2 can be 0.5%, 1%, 1.5%, 2%, 5%. The raw materials, reagents, solvents, etc. used in this application can all be obtained through commercial purchase.

[0030] The following further elaborates on this application in combination with examples and performance detection tests. Examples 1-10

[0031] Examples 1-10 respectively provide a catalyst for synthesizing 2,3-dichloropyridine.

[0032] The differences between the above examples lie in the type of support, as shown in Table 1 below.

[0033] The preparation method of the catalyst for synthesizing 2,3-dichloropyridine provided in Examples 1-10 includes the following steps: (1) Dissolve 0.11 g of palladium nitrate and 0.05 g of nickel nitrate hexahydrate in 50 g of water at 50 °C, then immerse 100 g of the support in the above solution, filter after adsorption for 3 h, dry at 130 °C for 12 h, and calcine at 500 °C for 5 h to obtain PdNi / SiO 2 -Al 2 O 3 catalyst or PdNi / TiO 2 -Al 2O 3 Catalyst; (2) Take 5 g of PdNi / SiO 2 -Al 2 O 3 catalyst or 5 g of PdNi / TiO 2 -Al 2 O 3 catalyst, add 160 g of m-xylene, then add 4 g of ethylenediamine and 8 g of carbon tetrachloride, stir at 90 °C for 4 h, then raise the temperature to 140 °C and stir for 4 h; dry the resulting solid compound at 120 °C for 12 h, grind and screen the solid compound of 50 - 100 μm, calcine in a nitrogen atmosphere at 500 °C for 2 h and reduce in a hydrogen atmosphere at 300 °C for 4 h to obtain CN-coated PdNi / SiO 2 -Al 2 O 3 catalyst or CN-coated PdNi / TiO 2 -Al 2 O 3 catalyst.

[0034] Table 1 Types of carriers in the catalysts for synthesizing 2,3-dichloropyridine provided in Examples 1 - 10 Examples 11 - 16

[0035] Examples 11 - 16 respectively provide a catalyst for synthesizing 2,3-dichloropyridine.

[0036] The difference between the above examples and Example 2 lies in: the type and ratio of the additives, as shown in Table 2 below.

[0037] Table 2 Types and ratios of additives in the catalysts for synthesizing 2,3-dichloropyridine provided in Examples 11 - 16 Comparative Example 1

[0038] Comparative Example 1 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0039] The difference between the above comparative example and Example 2 lies in: the carrier uses Al 2 O 3 carrier. Comparative Example 2

[0040] Comparative Example 2 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0041] The difference between the above comparative example and Example 2 lies in: the carrier uses 10% SiO2 Modified Al 2 O 3 support Comparative Example 3

[0042] Comparative Example 3 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0043] The difference between the above comparative example and Example 8 is that the support used is 10% TiO 2 Modified Al 2 O 3 support Comparative Example 4

[0044] Comparative Example 4 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0045] The difference between the above comparative example and Example 2 is that the promoter used is tin tetrachloride. Comparative Example 5

[0046] Comparative Example 5 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0047] The difference between the above comparative example and Example 2 is that the PdNi / SiO is prepared only through step (1). 2 -Al 2 O 3 catalyst Comparative Example 6

[0048] Comparative Example 6 provides a catalyst for synthesizing 2,3-dichloropyridine.

[0049] The difference between the above comparative example and Example 2 is that the PdNi / TiO is prepared only through step (1). 2 -Al 2 O 3 catalyst Performance detection test

[0050] (I) Catalyst performance detection The catalysts obtained in Examples 1-16 and Comparative Examples 1-6 were used to synthesize 2,3-dichloropyridine, and the conversion rate and mass yield of the above reaction were calculated to evaluate the performance of each catalyst. The results are shown in Table 3 below.

[0051] The evaluation method is as follows: Mix 50 g of 2,3,6-trichloropyridine, 150 g of methanol, 6 g of 15% ammonia in methanol, 20 g of deionized water, and 0.02 g of catalyst, and place the mixture in a high-pressure reactor. After replacing the air in the reactor with nitrogen, introduce hydrogen. React at 37 °C and 1.0 MPa for 2.5 h to obtain a crude product; filter the catalyst from the crude product, and separate the filtrate by distillation to obtain 2,3-dichloropyridine.

[0052] The calculation formulas for conversion rate and mass yield are as follows: Conversion rate = { (feed amount of 2,3,6-trichloropyridine - discharge amount × mass fraction of 2,3,6-trichloropyridine in the discharge) / feed amount of 2,3,6-trichloropyridine} × 100% Mass yield = (discharge amount × mass fraction of 2,3-dichloropyridine in the discharge / feed amount of 2,3,6-trichloropyridine) × 100% Table 3 Detection results of the performance of the catalysts obtained in Examples 1-16 and Comparative Examples 1-6

[0053] According to the detection results in Table 3, when synthesizing 2,3-dichloropyridine using the catalysts provided in Examples 1-16 of the present application, the conversion rate of the raw material 2,3,6-trichloropyridine is 99.2 - 99.9%, and the mass yield of 2,3-dichloropyridine is 94.1 - 96.9%. Therefore, it shows that the catalyst provided by the present application can be used for the hydrogenation and dechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, and has high catalytic activity and stable catalytic performance.

[0054] From the detection results of Examples 1-10 and Comparative Examples 1-3, it can be seen that in Examples 1-10, SiO 2 modified Al 2 O 3 or TiO 2 modified Al 2 O 3 is used as the carrier, and in SiO 2 modified α-Al 2 O 3 or TiO 2 modified α-Al 2 O 3 the mass fraction of SiO 2 or TiO 2 is 0.5 - 5%. The obtained catalyst is used for the hydrogenation and dechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, with a conversion rate of 99.2 - 99.7% and a yield of 94.1 - 95.7%; while in Comparative Example 1, unmodified Al 2 O 3As a carrier, the obtained catalyst is used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, with a conversion rate of 99.5% and a yield of 92.7%. Comparative Example 2 uses 10% SiO 2 modified Al 2 O 3 As a carrier, the obtained catalyst is used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, with a conversion rate of 99.5% and a yield of 93.3%. Comparative Example 3 uses 10% TiO 2 modified Al 2 O 3 As a carrier, the obtained catalyst is used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, with a conversion rate of 99.2% and a yield of 93.1%. Therefore, it shows that the present application uses SiO 2 modified Al 2 O 3 or TiO 2 modified Al 2 O 3 as a carrier, and in SiO 2 modified α-Al 2 O 3 or TiO 2 modified α-Al 2 O 3 the mass fraction of SiO 2 or TiO 2 is controlled within the range of 0.5 - 5%, and a catalyst for synthesizing 2,3-dichloropyridine with good catalytic stability and high catalytic efficiency can be obtained. Further comparison shows that the catalysts obtained in Examples 1 - 3 and Examples 7 - 8 are used for the hydrodechlorination of polychloropyridine to synthesize 2,3-dichloropyridine, with a conversion rate of 99.5 - 99.7% (≥99.5%) and a yield of 95.2 - 95.7% (≥95%). It shows that in the present application, in SiO 2 modified α-Al 2 O 3 the mass fraction of SiO 2 is controlled to be 0.5 - 1.5%; in TiO 2 modified α-Al 2 O 3 the mass fraction of TiO 2 is controlled to be 1 - 2%, and the obtained catalyst has better stability and higher catalytic efficiency.

[0055] From the detection results of Example 2 and Examples 11 - 16, it can be seen that in Example 2 and Example 11, only Ni or Rh was used as the promoter, and the obtained catalyst was used for the hydrodechlorination of polychloropyridine to synthesize 2,3 - dichloropyridine, with a yield of only 95.1 - 95.7%; while in Examples 12 - 16, Ni and Rh were used as the promoters, and the obtained catalyst was used for the hydrodechlorination of polychloropyridine to synthesize 2,3 - dichloropyridine, with a yield of 96.2 - 96.9% (≥96%). Therefore, it shows that further using a mixture of a Ni compound and a Rh compound as the promoter in this application results in a more excellent performance of the obtained catalyst. Further comparison found that the catalysts obtained in Examples 13 - 15 were used for the hydrodechlorination of polychloropyridine to synthesize 2,3 - dichloropyridine, with a yield as high as 96.6 - 96.9% (≥96.5%), indicating that further controlling the weight ratio of the Ni compound and the Rh compound within the range of 1:(0.2 - 0.4) gives a higher catalytic efficiency of the obtained catalyst.

[0056] (II) Catalyst performance detection The catalysts provided in Example 2 and Comparative Examples 1 - 2 were respectively re - added to new raw materials after use to continue the catalytic reaction to investigate the reusability.

[0057] The conversion rate and mass yield of the reused catalyst are shown in Table 4.

[0058] Table 4 Reusability effects of the catalysts provided in Example 2, Example 8, and Examples 1 - 3

[0059] From the detection results in Table 4, it can be seen that the catalytic performance of the catalyst obtained in Example 2 of this application decreased slightly after being reused 5 times, while the catalytic performance of the catalysts provided in Comparative Examples 1 - 2 decreased significantly after being used 2 times. Therefore, it shows that the catalyst provided in this application can significantly improve the activity and stability of the catalyst and extend its service life.

[0060] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope claimed by the present invention.

Claims

1. A catalyst for synthesizing 2,3-dichloropyridine, characterized in that: It includes a carrier, an active component and an auxiliary agent loaded on the carrier, and a coating layer wrapped around the outside of the carrier; The carrier is a SiO2-modified Al2O3 carrier or a TiO2-modified Al2O3 carrier; in the SiO2-modified α-Al2O3 or TiO2-modified α-Al2O3, the mass fraction of SiO2 or TiO2 is 0.5-5%; The active component is Pd; The auxiliary agent is selected from one or more compounds of Mg, Ni, Rh and Ru.

2. The catalyst for synthesizing 2,3-dichloropyridine according to claim 1, characterized in that: In the SiO2-modified α-Al2O3, the mass fraction of SiO2 is 0.5-1.5%; in the TiO2-modified α-Al2O3, the mass fraction of TiO2 is 1-2%.

3. The catalyst for synthesizing 2,3-dichloropyridine according to claim 1, characterized in that: The loading amount of Pd is 0.005-1wt% of the carrier, and the loading amount of the auxiliary agent is 0.01-0.5wt% of the carrier.

4. The catalyst for synthesizing 2,3-dichloropyridine according to claim 1, characterized in that: The auxiliary agent is a mixture of a Ni compound and a Rh compound.

5. The catalyst for synthesizing 2,3-dichloropyridine according to claim 4, characterized in that: The weight ratio of the Ni compound to the Rh compound is 1:(0.2-0.4).

6. The catalyst for synthesizing 2,3-dichloropyridine according to claim 1, characterized in that: The coating layer is a nitrogen-doped carbon material, and the weight of the coating layer is 0.05-2wt% of the weight of the carrier.

7. The method for preparing a catalyst for synthesizing 2,3-dichloropyridine according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) First, immersing the support in a solution containing Pd salt and auxiliary salt, adsorbing for 2-24 hours, filtering, drying, and calcining at 400-600°C for 2-6 hours to obtain a catalyst loaded with active components and auxiliary agents; (2) Add m-xylene to the catalyst loaded with active components and auxiliary agents, then add ethylenediamine and carbon tetrachloride, stir at 50-90°C for 3-5h, and then stir at 120-160°C for 3-5h; dry the generated solid compound at 100-150°C for 10-15h, grind and screen the solid compound of 50-100 μm, and place it in a nitrogen atmosphere at 400-650°C for calcination for 2-6h, and reduce it in a hydrogen atmosphere at 200-450°C for 2-6h to obtain a catalyst for synthesizing 2,3-dichloropyridine.

8. Use of the catalyst for synthesizing 2,3-dichloropyridine as claimed in any one of claims 1 to 6 in the reaction of hydrodechlorination of polychlorinated pyridine to synthesize 2,3-dichloropyridine.

9. A method for synthesizing 2,3-dichloropyridine, characterized in that: The synthesis method uses the catalyst for synthesizing 2,3-dichloropyridine described in any one of claims 1 to 6.

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