A supported AuPd bimetallic catalyst and its application in catalytic methoxylation reaction

Abstract

This invention relates to a supported AuPd bimetallic catalyst, which is obtained by uniformly mixing chloroauric acid (HAuCl4·3H2O) and sodium chloropalladium (Na2PdCl4) solutions, adding graphene oxide (GO) solution, neutralizing and adjusting the pH of the mixture with alkali solution, heating and stirring the mixture, cooling and aging it, then removing the upper layer, and repeatedly centrifuging and washing the lower precipitate, followed by drying and crushing to obtain the supported bimetallic Au3Pd2@rGO catalyst. The Au / Pd bimetallic synergistic catalyst exhibits high catalytic activity, can be repeatedly recycled, and reduces catalyst costs. Supporting the metal on graphene oxide can effectively improve the dispersibility of nanoparticles, reduce their aggregation during the catalytic process, improve catalytic activity and efficiency, and also increase the recyclability of the catalyst in the reaction.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a supported AuPd bimetallic catalyst and its application in catalytic methoxylation reactions. Background Technology

[0002] Currently, most methoxylation reactions are catalyzed by palladium, which is too costly and presents many other problems. For example, in 2014, Novak's group reported the methoxylation of aryl chlorides using KB(OMe)4 and NaB(OCD3)4 as methoxylating agents. This reaction was short, taking only 3 hours, but heteroaryl halides were not suitable for this system. In 2018, Furong Li's group reported the methylation of quinolinamides using PtCl2 as a catalyst, triethylamine as an additive, PhI(OAc)2 as an oxidant, and CH3OH as a methylating agent, reacting for 2 hours at room temperature in air. In 2019, Pengfei Zhang's group also reported the methylation of pyridine amides using PtCl2 as a catalyst, iodobenzene as an additive, PhI(OAc)2 as an oxidant, and CH3OH as a methylating agent, reacting for 3 hours at room temperature in air. However, the catalyst PtCl2 is expensive, cannot be recycled, and causes significant environmental pollution.

[0003] Therefore, considering the high cost of catalysts, developing a methoxylation reaction catalyst with high catalytic activity and efficiency, and good recyclability has become an important research topic in recent years. Summary of the Invention

[0004] This invention relates to a supported AuPd bimetallic catalyst and its preparation method, specifically a supported bimetallic Au3Pd2@rGO catalyst. The method involves uniformly mixing chloroauric acid (HAuCl4·3H2O) and sodium chloropalladium (Na2PdCl4) solutions, then adding graphene oxide (GO) solution and mixing them uniformly. The pH of the mixture is adjusted by neutralization with an alkaline solution to obtain a mixed solution. The mixed solution is heated and stirred, cooled and matured, then the upper layer is removed. The lower precipitate is repeatedly centrifuged and washed, and then dried and crushed to obtain the final product. The Au / Pd bimetallic synergistic catalyst exhibits high catalytic activity, can be repeatedly recycled, and reduces catalyst cost. Supporting the metal on graphene oxide can effectively improve the dispersibility of nanoparticles, reduce their aggregation during the catalytic process, improve catalytic activity and efficiency, and also increase the recyclability of the catalyst in the reaction.

[0005] This invention relates to a method for preparing a supported bimetallic Au3Pd2@rGO catalyst, the method comprising the following steps:

[0006] 1) Take chloroauric acid (HAuCl4·3H2O) and sodium chloropalladium (Na2PdCl4) solution, and stir to mix them evenly;

[0007] 2) Add the graphene oxide (GO) solution dropwise and sonicate to mix the graphene oxide solution with the above solution uniformly;

[0008] 3) Neutralize and adjust the pH of the above mixed solution to 7-9 with alkali solution;

[0009] 4) Heat and stir the above mixed solution to carry out the reaction; after the reaction is completed, cool to room temperature and let it stand to mature;

[0010] 5) Remove the upper layer solution, centrifuge the lower layer precipitate, remove the upper layer solution after centrifugation, retain the precipitate at the bottom of the centrifuge tube, and wash the precipitate; then centrifuge and wash several times to remove impurities from the precipitate, thus obtaining the supported bimetallic Au3Pd2@rGO catalyst;

[0011] 6) The catalyst prepared by vacuum drying is crushed into fine black powder particles.

[0012] In steps 1) and 2), the mass ratio of chloroauric acid (HAuCl4·3H2O) to sodium chloropalladium (Na2PdCl4) and graphene oxide (GO) is (80-140):(40-80):(60-100); the concentration ranges of chloroauric acid (HAuCl4·3H2O), sodium chloropalladium (Na2PdCl4), and graphene oxide (GO) are 0.005-0.03 mol / L, 0.005-0.03 mol / L, and 1.0-4.0 mg / mL, respectively. In step 3), the alkaline solution is a sodium hydroxide solution with a concentration of 0.2-1.0 mol / L; the pH value is adjusted to 8. In step 4), the mixture is heated from room temperature to 80℃-90℃ at a heating rate of 1-3℃ / min, and the solution gradually changes from reddish-brown to black, and stirring is continued until the reaction is complete. In step 5), remove the supernatant solution, place the lower precipitate in a centrifuge tube and centrifuge for 10-30 minutes at a speed of 10,000-16,000 rpm. After centrifugation, remove the supernatant solution from the centrifuge tube, retain the precipitate at the bottom of the centrifuge tube, wash the precipitate with deionized water, and sonicate it in an ultrasonic bath for 10-20 minutes to ensure that the precipitate is completely dispersed in the deionized water. Centrifuge again for 10-30 minutes, and repeat the above steps at least 3 times. Then wash with anhydrous ethanol at least 3 times, centrifuge for 10-30 minutes, remove the supernatant solution, and remove other impurities from the precipitate to obtain the supported bimetallic Au3Pd2@rGO catalyst. In step 6), the vacuum drying process includes: placing the obtained catalyst in a vacuum drying oven, and when the vacuum degree of the vacuum drying oven is 0, gradually increasing the temperature from room temperature to 50-80℃ and vacuum drying for 18-30 hours; when the vacuum drying oven cools to room temperature, take out the prepared catalyst, grind it thoroughly into a fine black powder with a quartz grinder, weigh it, and set it aside.

[0013] This invention also relates to a supported bimetallic Au3Pd2@rGO catalyst prepared by the method described above.

[0014] The above describes the application of the supported bimetallic Au3Pd2@rGO catalyst in the catalytic methoxylation reaction.

[0015] As described above, the supported bimetallic Au3Pd2@rGO catalyst achieved a catalytic reaction yield of over 80% after six cycles.

[0016] Beneficial effects:

[0017] The supported bimetallic Au3Pd2@rGO catalyst of the present invention has the following advantages: (1) Compared with single metal nanoparticles, it has more tunability. The particle size and morphology of the nanoparticles can be controlled by controlling the relative ratio of the two metals, and a synergistic effect is generated between the two metal atoms; (2) Electrons will not only be transferred between the two metal atoms, but also compete for transfer at the interface between the two atoms and the reduced graphene oxide, which is beneficial to control the electronic state of the active atoms and improve its catalytic activity; (3) The introduction of transition metal ions can induce different exposure surfaces of the nanocatalyst, thereby controlling its catalytic activity; (4) Doping transition metals into single noble metal nanoparticles can effectively reduce the amount of noble metals used and further reduce the cost of the catalyst; (5) The catalyst has strong magnetism and can be separated by centrifugation or magnetic force, with a high recycling rate. The advantages of graphene oxide (GO) as a supported substrate are as follows: GO has a large surface area and numerous hydroxyl (-OH), carbonyl (-C=O), and carboxyl (-COOH) groups on its surface, making it an excellent dispersion carrier. It provides significant support and anchoring for alloy nanoparticles, helping to control the size and distribution of metal particles formed during synthesis, thus achieving excellent monodispersion. Therefore, loading metals onto graphene oxide can significantly improve the dispersibility of nanoparticles, reduce their aggregation during catalysis, enhance their catalytic activity and efficiency, and also improve the recyclability of the catalyst in the reaction.

[0018] The supported bimetallic Au3Pd2@rGO catalyst obtained in this invention is used to catalyze methoxylation reactions. The catalyst has good catalytic activity, stability and recyclability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 Transmission electron microscopy image of Au3Pd2@rGO;

[0021] Figure 2 High-resolution transmission electron microscope image of Au3Pd2@rGO;

[0022] Figure 3 X-ray powder diffraction patterns of Au3Pd2@rGO, Au@rGO, and Pd@rGO;

[0023] Figure 4 The energy-dispersive X-ray spectrum of Au1Pd1@rGO;

[0024] Figure 5 The graph shows the catalytic recycling performance of Au3Pd2@rGO. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0026] Example 1: Preparation of supported bimetallic Au3Pd2@rGO nanocatalysts

[0027] (1) Preparation method of supported bimetallic Au3Pd2@rGO nanocatalyst:

[0028] 1. Take 30 mL of 0.01 mol / L chloroauric acid (HAuCl4·3H2O) and 20 mL of 0.01 mol / L sodium chloropalladate (Na2PdCl4) solution and add them to a round-bottom flask. Stir magnetically to mix the chloroauric acid and sodium chloropalladate completely and evenly. The solution should be a clear, deep yellow color.

[0029] 2. Add 40 mL of 2.0 mg / mL graphene oxide (GO) solution dropwise into the round-bottom flask mentioned above, while sonicating. Add 60-80 drops per minute. After the addition is complete, continue sonicating for 2 hours to ensure that the graphene oxide solution is completely and uniformly mixed with the chloroauric acid and sodium chloropalladium solution.

[0030] 3. Neutralize and adjust the pH of the mixed solution in the flask to 8 with 0.5 mol / L sodium hydroxide solution. At this point, the solution will turn into a thick, reddish-brown color.

[0031] 4. Place the round-bottom flask in an oil bath and heat with magnetic stirring. Gradually increase the temperature from room temperature to 85°C at a rate of 2°C / min. The solution will gradually change from reddish-brown to black. Maintain the magnetic stirring at 85°C for 4 hours at a speed of 1200 rpm. After the reaction is complete, allow it to cool naturally to room temperature and let it stand for 12 hours to mature.

[0032] 5. Use a dropper to remove the upper layer of solution from the round-bottom flask, place the lower precipitate in a centrifuge tube, and centrifuge for 20 min at 14000 rpm. After centrifugation, remove the upper layer of solution from the centrifuge tube, retaining the precipitate at the bottom. Wash the precipitate with deionized water, and sonicate it for 15 min to ensure that the precipitate is completely dispersed in the deionized water. Centrifuge again for 20 min, and repeat the above steps 3 times. Finally, wash the precipitate 3 times with anhydrous ethanol, centrifuge for 20 min, and remove the upper layer of solution to ensure that organic impurities in the precipitate are removed, thus obtaining the supported bimetallic Au3Pd2@rGO catalyst.

[0033] 6. Place the catalyst in a vacuum drying oven. When the vacuum level in the oven reaches 0, gradually increase the temperature from room temperature to 60°C and vacuum dry for 24 hours. After the vacuum drying oven cools to room temperature, remove the prepared catalyst, grind it thoroughly into a fine black powder using a quartz grinder, weigh it, and set it aside.

[0034] (2) Characterization of supported bimetallic Au3Pd2@rGO nanocatalysts

[0035] The Au3Pd2@rGO catalyst was characterized using transmission electron microscopy (TEM), such as... Figure 1 As shown, the catalyst particles are uniformly dispersed and of uniform size, with no obvious agglomeration, and their particle size is approximately 5 nm.

[0036] The Au3Pd2@rGO catalyst was characterized using high-resolution transmission electron microscopy (HRTEM), such as... Figure 2 As shown, its lattice spacing is 0.221 nm, located between the (111) plane spacing of Au (0.210 nm) and the (111) plane spacing of Pd (0.225 nm).

[0037] X-ray powder diffraction (XRD) characterization was performed on Pd@rGO, Au3Pd2@rGO, and Au@rGO, such as... Figure 3 As shown, the characteristic peak of Au3Pd2@rGO is located between Pd@rGO and Au@rGO, indicating that Au and Pd elements are loaded onto the reduced graphene oxide.

[0038] Energy-dispersive X-ray spectroscopy (EDS) was performed on Au3Pd2@rGO, such as... Figure 4 As shown. Figure 4 It can be seen that the ratio of Au (0.86%) to Pd (0.67%) loaded on reduced graphene oxide is 3:2.

[0039] Example 2: Au3Pd2@rGO-catalyzed methoxylation reaction

[0040] (1) Optimization of reaction conditions for Au3Pd2@rGO catalytic methoxylation reaction

[0041] The steps for applying Au3Pd2@rGO to the catalytic methoxylation reaction are as follows: 7 mg of Au3Pd2@rGO catalyst was accurately weighed and added to a 100 mL reaction tube, followed by 2 mL of methanol as a solvent. The tube was then sonicated for 20 min to ensure that Au3Pd2@rGO was fully dispersed in the methanol. 0.2 mmol of 4-methyl-N-(8-quinolinyl)benzamide was then added, and the mixture was magnetically stirred at 1200 rpm for 3 h at room temperature. After the reaction was complete, the reaction product was extracted with ethyl acetate. Qualitative and quantitative analysis was performed using gas chromatography-mass spectrometry (GC-MS). The yield of Au3Pd2@rGO in the catalytic methoxylation reaction was 90%.

[0042] The experimental factors such as catalyst type, oxidant type, solvent type, and reaction temperature were screened and optimized. The optimal conditions were: 7 mg Au3Pd2@rGO as catalyst, 2 mL methanol as solvent, 0.2 mmol iodobenzene acetate (PhI(OAc)2) as oxidant, and reaction at room temperature in air for 1.5 h. The yield of the catalytic methoxylation reaction was 92%. The experimental results are shown in Table 1.

[0043]

[0044] Table 1. Optimization of methoxylation reaction conditions for Au3Pd2@rGO catalytic reaction

[0045]

[0046]

[0047] Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), oxidant (0.4 mmol), solvent (2 mL), catalyst (7 mg), reaction at room temperature for 1.5 h.

[0048] (2) Substrate expansion for Au3Pd2@rGO catalytic methoxylation reaction

[0049] Under optimal conditions (7 mg Au3Pd2@rGO as catalyst, 2 mL methanol as solvent, 0.2 mmol iodobenzene acetate (Ph I(OAc)2) as oxidant, reaction at room temperature in air for 1.5 h), we expanded the substrates for the methoxylation reaction, and the experimental results are shown in Table 2.

[0050] Table 2. Expansion of methoxylation reaction substrates

[0051]

[0052] (3) Investigation on the recyclability of Au3Pd2@rGO catalytic coupling reaction

[0053] The catalytic recycling performance of Au3Pd2@rGO for methoxylation was investigated. As shown in Table 1, after 6 cycles, the yield of this catalyst was 82%. Figure 5 As shown, this indicates that the catalyst has good catalytic activity, stability, and recyclability.

[0054] Supporting the bimetallic catalyst on graphene oxide as described in this invention can effectively improve the dispersibility of nanoparticles, reduce their aggregation during the catalytic process, achieve good dispersion, enhance catalytic activity and efficiency, and also improve the recyclability of the catalyst in the reaction. Therefore, the supported bimetallic Au3Pd2@rGO catalyst obtained in this invention exhibits good catalytic activity, stability, and recyclability in the methoxylation reaction.

[0055] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. The application of a supported bimetallic Au3Pd2@rGO catalyst in the catalytic methoxylation reaction, characterized in that, The preparation method of the supported bimetallic Au3Pd2@rGO catalyst includes the following steps: 1) Take chloroauric acid (HAuCl4·3H2O) and sodium chloropalladium (Na2PdCl4) solution, and stir to mix them evenly; 2) Add the graphene oxide (GO) solution dropwise and sonicate to mix the graphene oxide solution with the above solution uniformly; 3) Neutralize and adjust the pH of the above mixed solution to 7-9 with alkali solution; 4) Heat and stir the above mixed solution to carry out the reaction; after the reaction is completed, cool to room temperature and let it stand to mature; 5) Remove the upper layer of solution, centrifuge the lower layer of precipitate, and after centrifugation, remove the upper layer of solution from the centrifuge tube, retain the precipitate at the bottom of the centrifuge tube, and wash the precipitate. After multiple centrifugation and washing processes, impurities in the precipitate are removed, thus obtaining the supported bimetallic Au3Pd2@rGO catalyst. 6) The catalyst prepared by vacuum drying is crushed into fine black powder particles; In steps 1) and 2), the mass ratio of chloroauric acid (HAuCl4·3H2O) to sodium chloropalladium (Na2PdCl4) and graphene oxide (GO) is (80-140):(40-80):(60-100); the concentration ranges of chloroauric acid (HAuCl4·3H2O) to sodium chloropalladium (Na2PdCl4) and graphene oxide (GO) are 0.005-0.03 mol / L, 0.005-0.03 mol / L, and 1.0-4.0 mg / mL, respectively. In step 4), the mixture is heated from room temperature to 80℃-90℃ at a rate of 1-3℃ / min, and the solution gradually changes from reddish-brown to black. Stirring continues until the reaction is complete.

2. The application as described in claim 1, characterized in that, In step 3) of the preparation method of the supported bimetallic Au3Pd2@rGO catalyst, the alkaline solution is a sodium hydroxide solution with a concentration of 0.2-1.0 mol / L; the pH value is adjusted to 8.

3. The application as described in claim 1, characterized in that, In step 5) of the preparation method of the supported bimetallic Au3Pd2@rGO catalyst, the upper layer solution is removed, and the lower precipitate is placed in a centrifuge tube and centrifuged for 10-30 min at a speed of 10000-16000 rpm. After centrifugation, the upper layer solution is removed, and the precipitate at the bottom of the centrifuge tube is retained. The precipitate is washed with deionized water and ultrasonically treated for 10-20 min to ensure that the precipitate is completely dispersed in deionized water. The precipitate is then centrifuged for another 10-30 min. The above steps are repeated at least 3 times. The precipitate is then washed with anhydrous ethanol at least 3 times and centrifuged for 10-30 min. The upper layer solution is removed, and other impurities in the precipitate are removed to obtain the supported bimetallic Au3Pd2@rGO catalyst.

4. The application as described in claim 1, characterized in that, In step 6) of the preparation method of the supported bimetallic Au3Pd2@rGO catalyst, the vacuum drying process includes: placing the obtained catalyst in a vacuum drying oven, and when the vacuum degree of the vacuum drying oven is 0, gradually increasing the temperature from room temperature to 50-80℃, and vacuum drying for 18-30h; when the vacuum drying oven cools to room temperature, take out the prepared catalyst, grind it thoroughly into a fine black powder with a quartz mill, weigh it, and set it aside.

5. As described in claim 1, the supported bimetallic Au3Pd2@rGO catalyst achieves a catalytic reaction yield of over 80% after 6 cycles.

Images