Preparation of palladium monatomic catalyst and application of palladium monatomic catalyst in Suzuki-Miyaura cross-coupling reaction
Carbon support was prepared by SiO2@PANI and pyrolysis, combined with H2PdCl4 and formaldehyde reaction, and a high-activity and low-load palladium single-atom catalyst Pd@N-MCNs was prepared, which solved the cost and separation of high-content palladium catalysts in Suzuki-Miyaura reaction. The problem has achieved efficient and economical catalytic effects.
Patent Information
- Application Number
- CN202411324097.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-23
- Publication Date
- 2024-12-20
AI Technical Summary
In the prior art, the high content of palladium catalyst used in the Suzuki-Miyaura cross-coupling reaction leads to high cost, difficult to separate and recover, limiting its wide application in the industry, and the synthesis process of low content of palladium catalysts is complex. , it is difficult to achieve high activity and low loading of palladium single atom catalyst.
Carbon support N-MCNs were prepared by preparation, pyrolysis and pickling of SiO2@PANI, and high-activity, low-load palladium single-atom catalyst Pd@N-MCNs were prepared by the reaction of H2PdCl4 solution and formaldehyde. In the Suzuki-Miyaura coupling reaction, the use of high-loaded palladium and special ligands is avoided.
The preparation of a high-activity and low-load palladium single-atom catalyst is achieved, which simplifies the reaction process, reduces costs, has good catalytic effect, and is easy to separate and recover, with good industrial prospects.
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Figure CN119158567A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of preparation of noble metal palladium catalyst materials, and specifically relates to the preparation and application of a palladium single-atom catalyst. Background Art
[0002] In recent years, single atom catalysts (SACs) have become a powerful tool for achieving highly selective organic synthesis. Compared with other catalysts, SACs have the advantages of reusability, easy separation, and efficient atom utilization. Therefore, people are committed to developing various SACs for industrial and fine chemical production.
[0003] Traditional effective strategies for synthesizing SACs include spatial confinement, in which porous materials with uniform and regular structures, such as zeolites, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), metal alloys and metal oxides are used as supports to encapsulate appropriate mononuclear metal complexes, thereby confining metal precursors and preventing their migration and agglomeration. In addition, creating defects on the support surface is another way to enhance the stability of single atoms. However, supports such as MOFs, COFs, metal alloys and metal oxides require additional synthesis steps and additional metal sources, which increases the cost.
[0004] The Suzuki-Miyaura cross-coupling reaction has a wide range of substrate adaptability, mild reaction conditions and high yields. It has developed into one of the most effective methods for constructing CC bonds and is widely used in organic chemistry, medicinal chemistry and materials chemistry. At present, the reaction usually uses precious metal palladium as the catalytic active center and requires a high content of palladium, but the reserves and prices of palladium greatly limit their large-scale application in industry. Therefore, more and more chemists are committed to developing low-content palladium and high-activity catalysts. Although some low-content palladium catalysts have been reported, special ligands such as organophosphorus ligands or N-heterocyclic carbene ligands are usually required. However, these catalysts usually involve cumbersome synthesis processes, and in some cases, additional additives are required, and it is difficult to separate and recover the precious metal palladium component from the system, which increases the total cost of the reaction.
[0005] Therefore, developing effective supports from cheap and abundant chemicals, preparing a highly active, low-loading PdSAC, and developing a simple, green, and economical catalyst remain the research focuses in the Suzuki–Miyaura coupling reaction. Summary of the invention
[0006] The purpose of the present invention is to disclose a method for preparing a palladium single-atom catalyst to solve the problems existing in the above-mentioned background technology.
[0007] The method for preparing the palladium single-atom catalyst of the present invention comprises the following steps: (1) Preparation of SiO2@PANI: First, colloidal SiO2 is uniformly dispersed in a hydrochloric acid solution, and then aniline and ammonium persulfate are added. The mixture is reacted in an ice bath for 12 to 24 hours. When the reaction system gradually changes from colorless and transparent to dark green, the precipitate is collected by centrifugation, washed with distilled water and ethanol respectively, and dried to obtain a dark green solid, namely SiO2 polyaniline nanomaterial, denoted as SiO2@PANI. Among them, the concentration of colloidal SiO2 is 39~41wt.%, the specific gravity is 1.28~1.3; the concentration of hydrochloric acid is 1 mol / L; the mass ratio of colloidal SiO2: aniline: ammonium persulfate is (3~3.5):1:(2~2.5), preferably 3.25:1:2.5.
[0008] (2) Preparation of carbon carrier: The SiO2@PANI obtained in step (1) was placed in a nitrogen atmosphere and heated to 850-950°C for pyrolysis to obtain a black solid, i.e., a carbon carrier precursor, denoted as N-MCNs-SiO2; N-MCNs-SiO2 was then dissolved in an HF aqueous solution for 10-12 h, filtered, washed, and dried to obtain a carbon carrier, denoted as N-MCNs; The pyrolysis condition is to increase the temperature to 900°C at a heating rate of 5°C / min and keep the temperature constant for 2 hours. The desiliconization treatment is to treat with a 10wt.% HF aqueous solution for 10-12 hours at room temperature.
[0009] (3) Preparation of Pd@N-MCNs: The N-MCNs obtained in step (2) were dispersed in distilled water, and then H2PdCl4 solution was added and stirred at 35°C for 1-3 h. The pH of the reaction system was adjusted to 8-9, and formaldehyde was added for reduction reaction for 1-2 h to obtain a palladium single atom catalyst, which was recorded as Pd@N-MCNs.
[0010] The concentration of N-MCNs is 0.01-0.05 g / mL, the concentration of palladium ions in the H2PdCl4 solution is 0.005 g / mL, and the volume ratio of the H2PdCl4 solution to formaldehyde is 2:1-1:1.
[0011] The preparation method of H2PdCl4 solution is as follows: Weigh 0.1666 g of palladium chloride and dissolve it in 10 mL of concentrated hydrochloric acid to obtain a reddish-brown clear solution. Add distilled water to a 20 mL volumetric flask to prepare an H2PdCl4 solution.
[0012] Another object of the present invention is to disclose the application of the above palladium single atom catalyst in the Suzuki-Miyaura cross-coupling reaction.
[0013] Specifically, a reaction system consisting of 0.6 mmol p-methoxyphenylboronic acid, 0.5 mmol halogenated aromatic hydrocarbon or substituted halogenated aromatic hydrocarbon, 1.0 mmol anhydrous Na2CO3, 2 mL distilled water and 2 mL ethanol is prepared, and then 20 mg of palladium single atom catalyst is weighed and added to the above system, reacted at 90°C for 8 to 12 h, the catalyst was separated by filtration, the filtrate was extracted with dichloromethane, and the product was separated by column chromatography to obtain biphenyl or a biphenyl derivative.
[0014] Wherein, the structural formula of halogenated aromatic hydrocarbon or substituted halogenated aromatic hydrocarbon is R1-X, and the structural formula of biphenyl or biphenyl derivative is ; R1 is , , , , , , , or , X is I, Br or Cl.
[0015] The developing solvent used in the column chromatography is pure petroleum ether or a mixture of ethyl acetate and petroleum ether, wherein the volume ratio of ethyl acetate to petroleum ether is 1:20.
[0016] Compared with the prior art, the present invention has the following advantages: The invention uses aniline as a precursor and silicon dioxide as a porogen, and prepares a low-load palladium single-atom catalyst through self-assembly, pyrolysis, pickling and impregnation. The catalyst has high catalytic activity and is easy to separate. The catalyst is applied to the Suzuki-Miyaura coupling reaction of halogenated hydrocarbons and phenylboronic acid, which can avoid the use of high-load palladium and special ligands. The reaction is simple, green and economical, and has good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 It is a SEM image of Pd@N-MCNs in an embodiment of the present invention.
[0018] Figure 2 It is a TEM image of Pd@N-MCNs in an embodiment of the present invention.
[0019] Figure 3 : is the XRD pattern of Pd@N-MCNs in the embodiment of the present invention.
[0020] Figure 4 It is the EDS graph of Pd@N-MCNs in the embodiment of the present invention. DETAILED DESCRIPTION
[0021] The present invention will be further explained below in conjunction with specific embodiments. Example
[0022] (1) Preparation of SiO2@PANI: Weigh 6.5g colloidal SiO2 and dissolve it in 100mL distilled water, add 25mL hydrochloric acid solution (1mol / L), stir at room temperature for 10min, then add 2.0g aniline monomer; dissolve 5.0g ammonium persulfate in 10mL 1M HCl, add dropwise to the above mixed solution under vigorous stirring, and polymerize in an ice bath for 24h. The reaction system gradually changes from colorless and transparent to dark green. After the reaction is completed, wash with 30mL distilled water and 15mL ethanol respectively, and dry to obtain a dark green solid, which is SiO2 polyaniline nanomaterial (SiO2@PANI); (2) Preparation of carbon carrier: The SiO2@PANI obtained in step (1) was pyrolyzed in a tube furnace under a nitrogen atmosphere, and the temperature was programmed to 900°C at a heating rate of 5°C / min and kept constant for 2 h to obtain a black solid (N-MCNs-SiO2); then 3.0 g of N-MCNs-SiO2 was dissolved in an HF aqueous solution and treated for 12 h to remove SiO2, and the filter cake was washed with 30 mL of distilled water and 15 mL of ethanol, respectively, and vacuum dried to obtain 1.12 g of a black solid, which is N-MCNs; (3) Preparation of Pd@N-MCNs: 1 g of N-MCNs obtained in step (2) was weighed and dispersed in 50 mL of distilled water. Then, 1 mL of H2PdCl4 solution was added and stirred at 35 °C for 2 h. The pH of the reaction system was adjusted to 8 with 1 mol / L NaOH. Then, 0.5 mL of formaldehyde was added to reduce the palladium ions to obtain a palladium single atom catalyst, which was recorded as Pd@N-MCNs.
[0023] Product structure characterization and performance evaluation Structural characterization: Figure 1 : is a SEM image of Pd@N-MCNs in an embodiment of the present invention. From the SEM image, it can be seen that the catalyst has a porous structure.
[0024] Figure 2 TEM image of Pd@N-MCNs in the embodiment of the present invention. From the TEM image, it can be seen that the palladium atoms in the catalyst exist in some pores.
[0025] Figure 3 : This is the XRD spectrum of Pd@N-MCNs in the embodiment of the present invention. From the XRD pattern, it can be seen that there are two broad peaks at 24° and 44° in the catalyst, corresponding to graphite carbon (002) and (004), respectively, indicating that N-MCNs are partially graphitized.
[0026] Figure 4: is the EDS graph of Pd@N-MCNs in the embodiment of the present invention. From the EDS graph, it can be seen that the catalyst is carbonized at a relatively high temperature of 900°C, and the four elements of C, N, O and Pd are evenly distributed.
[0027] Performance evaluation: The above-mentioned Pd@N-MCNs catalyst was applied to the Suzuki-Miyaura cross-coupling reaction to investigate its catalytic performance.
[0028] A reaction system consisting of 0.6 mmol of p-methoxyphenylboronic acid, 0.5 mmol of bromobenzene, 1.0 mmol of a base, and 4 mL of a solvent was prepared, and then 20 mg of a Pd@N-MCNs catalyst was added. The reaction was carried out at 90° C. for 8 h to obtain biphenyl. The specific reaction conditions and yields are shown in Table 1.
[0029] Table 1 Performance study of Pd@N-MCNs catalysts in different solvent systems As shown in Table 1, under the conditions of potassium carbonate, sodium carbonate, triethylamine as base or without adding base, it was found that sodium carbonate was used as base with a yield of 86%. In addition, the effects of different solvents and temperatures on the reaction rate were explored. When THF was used as solvent, the yield dropped significantly. During the reaction, the catalyst was observed to agglomerate. We speculate that the oxygen atom of THF combined with the active center, resulting in the deactivation of the catalyst. In water, a small amount of raw materials can also be promoted for conversion, so we chose the greener mixed solvent EtOH: H2O=1:1 as the optimal reaction solvent.
[0030] Furthermore, a reaction system consisting of 0.6 mmol of p-methoxyphenylboronic acid, 0.5 mmol of substituted halogenated aromatic hydrocarbon, 1.0 mmol of anhydrous Na2CO3, 2 mL of distilled water and 2 mL of ethanol was prepared, and then 20 mg of Pd@N-MCNs catalyst was added and reacted at 90 °C for 8 h to obtain biphenyl and substituted biphenyl with the following yields: It can be seen that the catalyst still has a good catalytic effect on substituted halogenated aromatics, and its yield is basically maintained at above 70%.
[0031] Finally, the catalyst was separated from the reaction system by centrifugation and washed three times with ethanol and deionized water respectively. Then, the system consisting of the recovered catalyst, 0.6 mmol p-methoxyphenylboronic acid, 0.5 mmol substituted halogenated aromatic hydrocarbon (X=I), 1.0 mmol anhydrous Na2CO3, 2 mL distilled water and 2 mL ethanol was reacted at 90 °C for 8 h. After eight recovery tests, the yield was still above 70%, which was 76.9%.
Claims
1. A method for preparing a palladium single-atom catalyst, characterized in that: The following steps are involved: (1) Preparation of SiO2@PANI: First, colloidal SiO2 is uniformly dispersed in a hydrochloric acid solution, and then aniline and ammonium persulfate are added. The mixture is reacted in an ice bath for 12 to 24 hours. When the reaction system gradually changes from colorless and transparent to dark green, the precipitate is collected by centrifugation, washed with distilled water and ethanol respectively, and dried to obtain a dark green solid, namely SiO2 polyaniline nanomaterial, denoted as SiO2@PANI. (2) Preparation of carbon carrier: The SiO2@PANI obtained in step (1) was placed in a nitrogen atmosphere and heated to 850-950°C for pyrolysis to obtain a black solid, i.e., a carbon carrier precursor, denoted as N-MCNs-SiO2; N-MCNs-SiO2 was then dissolved in an HF aqueous solution for 10-12 h, filtered, washed, and dried to obtain a carbon carrier, denoted as N-MCNs; (3) Preparation of Pd@N-MCNs: The N-MCNs obtained in step (2) were dispersed in distilled water, and then H2PdCl4 solution was added and stirred at 35°C for 1-3 h. The pH of the reaction system was adjusted to 8-9, and formaldehyde was added for reduction reaction for 1-2 h to obtain a palladium single atom catalyst, which was recorded as Pd@N-MCNs.
2. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (1), the concentration of colloidal SiO2 is 39-41 wt.%, the specific gravity is 1.28-1.3; and the concentration of hydrochloric acid is 1 mol / L.
3. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (1), the mass ratio of colloidal SiO2:aniline:ammonium persulfate is (3-3.5):1:(2-2.5).
4. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (2), the pyrolysis condition is to increase the temperature to 900°C at a heating rate of 5°C / min and maintain the temperature for 2h.
5. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (2), the reaction mixture is treated with a 10 wt.% HF aqueous solution at room temperature for 10 to 12 h.
6. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (3), the concentration of N-MCNs is 0.01~0.05g / mL.
7. A method for preparing a palladium single-atom catalyst as claimed in claim 1, characterized in that: In step (3), the concentration of palladium ions in the H2PdCl4 solution is 0.005 g / mL, and the volume ratio of the H2PdCl4 solution to formaldehyde is 2:1 to 1:
1.
8. Use of a palladium single-atom catalyst prepared by the method of claim 1 in a Suzuki-Miyaura cross-coupling reaction, characterized in that: A reaction system consisting of 0.6 mmol p-methoxyphenylboronic acid, 0.5 mmol halogenated aromatic hydrocarbon or substituted halogenated aromatic hydrocarbon, 1.0 mmol anhydrous Na2CO3, 2 mL distilled water and 2 mL ethanol is prepared, and then 20 mg of palladium single atom catalyst is weighed and added to the above system, and the reaction is carried out at 90°C for 8-12 h. The catalyst is separated by filtration, the filtrate is extracted with dichloromethane, and the product is separated by column chromatography to obtain biphenyl or a biphenyl derivative.
9. The use of a palladium single atom catalyst in a Suzuki-Miyaura cross-coupling reaction as claimed in claim 8, characterized in that: The structural formula of halogenated aromatic hydrocarbon or substituted halogenated aromatic hydrocarbon is R1-X, and the structural formula of biphenyl or biphenyl derivative is ; R1 is , , , , , , , or , X is I, Br or Cl.
10. The use of the palladium single atom catalyst in the Suzuki-Miyaura cross-coupling reaction as claimed in claim 8, characterized in that: The developing solvent used in the column chromatography is pure petroleum ether or a mixture of ethyl acetate and petroleum ether, wherein the volume ratio of ethyl acetate to petroleum ether is 1:20.