Method for converting sugar into 2, 5-hexanedione by single atom catalysis

Abstract

The invention discloses a method for converting sugar into 2, 5-hexanedione by monatomic catalysis, which comprises the following steps: taking glucose as a raw material, and reacting under the synergistic catalysis of a monatomic catalyst Pd-N-C and an auxiliary agent to prepare 2, 5-hexanedione; during the reaction, the hydrogen pressure is 1-2MPa, the reaction temperature is 120-160 DEG C, and the reaction time is 15-60 minutes; the preparation method of the monatomic catalyst Pd-N-C comprises the following steps: mixing palladium nitrate, phenanthroline and absolute ethyl alcohol to react; and heating to 300-700 DEG C at a heating rate of 2 DEG C / min in an N2 atmosphere, calcining for 1-2 hours, naturally cooling, carrying out acid etching for 6-8 hours in a water bath of 60-80 DEG C by using a 0.5 M H2SO4 solution, and carrying out suction filtration, washing and drying to obtain the monatomic catalyst Pd-N-C, and the auxiliary agent is AlCl3 and / or SnCl4. According to the method, the reaction conditions are effectively reduced, and the selectivity of the 2, 5-hexanedione is improved.

Description

Technical Field

[0001] This invention relates to a method for converting sugars into 2,5-hexanedione using single-atom catalysis, belonging to the field of biomass resource development and utilization technology. Background Technology

[0002] With increasing public awareness of environmental issues and the gradual depletion of fossil fuels, the development and utilization of renewable energy has become a major challenge facing the world today. Research and utilization of renewable energy can not only reduce dependence on traditional fossil fuels but also contribute to achieving the important goals of "carbon neutrality and carbon peaking." Renewable energy refers to resources that can be regenerated in nature within a human lifespan. Biomass energy is considered an important bridge in the transition from fossil fuels to renewable energy, and in recent years, the production of high-value-added intermediates and products from biomass resources has gradually attracted attention.

[0003] Glucose is an abundant and inexpensive biomass resource with significant conversion value. 2,5-Hexanedione (HD) is an important organic chemical intermediate (Li et al., 2016), widely used in pharmaceuticals, fragrances, pesticides, electroplating, and painting. Furthermore, HD is also an important precursor for aviation kerosene and can be converted into aviation kerosene through specific methods (Woodroffe et al., 2020), demonstrating significant application and development potential, and its market size has steadily increased in recent years.

[0004] With the development of biomass production, the catalytic synthesis of HD from biomass has gradually become a research hotspot both domestically and internationally. In recent years, methods for preparing HD using inexpensive biomass such as cellulose have emerged. For example, Li et al. (2016) showed that using cellulose in a biphase catalytic system, the yield of cellulose reached a maximum of 99%. Although this reaction system has a high yield, the strong acidity in the system is not conducive to the industrialization of this process (Li et al., 2016). Yang et al. (2024) used cellulose as a raw material in a multiphase system formed by organic solvents, inorganic salts, and water, using an A / B supported catalyst, to directly convert cellulose to HD in a one-pot process, achieving a maximum HD yield of 62%. Li Ning et al. (2022) showed that using glucose as a raw material, under conditions of 2 MPa and 190°C, with Pd / C as a catalyst, HD was catalytically prepared, achieving a raw material conversion rate of up to 99% and an HD yield of 69%. Most of the above systems suffer from problems such as low raw material concentration, acid corrosion, and high production costs. Therefore, there is an urgent need to find a new catalyst and catalytic system to significantly reduce its production cost and promote the production and application of HD.

[0005] In addition, due to differences in structure and performance among different biomass resources, the catalytic performance of the same catalyst varies greatly for different biomass resources. Currently, the preparation of 2,5-hexanedione from glucose has problems such as low yield, high reaction temperature, and long reaction time. Summary of the Invention

[0006] This invention provides a method for converting sugars into 2,5-hexanedione using single-atom catalysis, which effectively reduces reaction conditions and improves the selectivity of 2,5-hexanedione.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for converting sugar into 2,5-hexanedione using a single-atom catalyst involves using glucose as a raw material and reacting it under the synergistic catalysis of a single-atom catalyst Pd-NC and an auxiliary agent to obtain 2,5-hexanedione. During the reaction, the hydrogen pressure is 1-2 MPa, the reaction temperature is 120-160℃, and the reaction time is 15-60 min. The mass ratio of glucose, single-atom catalyst Pd-NC, and auxiliary agent is (10-15):(0.5-2):(1-5). The preparation method of the single-atom catalyst Pd-NC includes the following steps: 1) Mix palladium nitrate, o-phenanthroline, and anhydrous ethanol, add magnesium oxide, sonicate for 5-10 min, then stir and reflux at 50-60°C for 2-4 h, remove the ethanol by rotation, and obtain a pink solid. Dry in an oven at 40-60°C for 6-12 h. The mass ratio of palladium nitrate, o-phenanthroline, and magnesium oxide is 1:(58-62):(22-26), preferably 1:(60-61):(23.5-24.5). 2) The material obtained in step 1) is heated to 300~700℃ for 1~2 hours under N2 atmosphere at a heating rate of 2~3°C / min, and then naturally cooled to obtain a black solid powder; 3) Using 0.5 M H2SO4 solution, the material obtained in step 2) was acid etched in a water bath at 60~80°C for 6~8 hours, filtered, washed 2~3 times with anhydrous ethanol, washed with deionized water until neutral, and dried in an oven at 60~80°C for 1~2 hours to obtain the single-atom catalyst Pd-NC. The additives are AlCl3 and / or SnCl4.

[0008] This application significantly improves the yield of 2,5-hexanedione by using a specific single-atom catalyst, Pd-NC, to catalyze the preparation of 2,5-hexanedione from glucose, while reducing the amount of catalyst used, lowering the reaction temperature, and shortening the reaction time.

[0009] To improve the yield of 2,5-hexanedione, the optimal reaction temperature is 115–125 °C and the reaction time is 25–35 min. Excessive temperature or time will trigger too many side reactions, affecting the product yield.

[0010] To further improve the yield of 2,5-hexanedione, the auxiliary agent AlCl3 was used.

[0011] In step 1) above, the amount of anhydrous ethanol used is the solvent volume. Preferably, the mass ratio of palladium nitrate and o-phenanthroline to the volume ratio of anhydrous ethanol is (40~50) mg: 5 mL.

[0012] To further improve the yield of 2,5-hexanedione, the mass ratio of glucose, single-atom catalyst Pd-NC, and auxiliaries was (10~15):(0.8~1.2):(2.5~3.5). Through experiments, the inventors unexpectedly discovered that the addition of specific auxiliaries had a significant positive promoting effect on the reaction, but excessive amounts could lead to more side reactions, thus reducing the HD yield.

[0013] As a specific implementation scheme, the method of converting sugar into 2,5-hexanedione by single-atom catalysis is as follows: glucose, organic solvent, inorganic salt aqueous solution, single-atom catalyst Pd-NC and auxiliary agent are mixed and reacted for 15-60 min under the conditions of hydrogen pressure of 1~2MPa and reaction temperature of 120~160℃. After cooling to room temperature, the mixture is allowed to stand and separate into layers. 2,5-hexanedione is obtained by separation of the organic phase. The organic solvent is one or more of tetrahydrofuran (THF), toluene (TOL), and methyl isobutyl ketone (MIBK); the inorganic salt aqueous solution has a mass concentration of 25-35%, and the inorganic salt is at least one of NaCl, NaBr, or NH4Br. The catalyst in this application can be recycled. The specific method is as follows: after the reaction is completed, the catalyst is recovered by centrifugation, washed with deionized water and anhydrous ethanol in sequence, and then dried at 50~60℃ to constant weight for recycling.

[0014] Different organic solvents can have a significant impact on the yield of 2,5-hexanedione. In order to improve the yield of 2,5-hexanedione, the preferred organic solvent in this application is tetrahydrofuran.

[0015] The volume ratio of the organic solvent to the inorganic salt aqueous solution is (1~4):1. More preferably, the volume ratio of the organic solvent to the inorganic salt aqueous solution is 2:1. Through experiments, the inventors unexpectedly discovered that an excessive amount of organic solvent would actually lead to a decrease in the HD yield.

[0016] To achieve a better synergistic effect with the single-atom catalyst Pd-NC of this application, the inorganic salt is preferably NaCl.

[0017] Any techniques not mentioned in this invention are based on existing technologies.

[0018] This invention relates to a method for converting sugars into 2,5-hexanedione using a single-atom catalyst. By preparing a specific single-atom catalyst, Pd-NC, the yield of 2,5-hexanedione prepared from glucose is significantly improved, and the reaction conditions are effectively reduced, which is beneficial for production and promotion. Attached Figure Description

[0019] Figure 1 The image shows the gas chromatogram of 2,5-hexanedione.

[0020] Figure 2 This is the HR-TEM image of Pd-NC-600.

[0021] Figure 3 The isotherms for the physical adsorption of nitrogen in Pd-NC gas are shown in Figure 1 (a: Pd-NC-500, b: Pd-NC-600, c: Pd-NC-700). Specific Implementation

[0022] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0023] Unless otherwise specified, all examples were conducted at room temperature (15~25℃); unless otherwise specified, all examples were conducted at 200 r / min. Preparation of single-atom catalysts: Weigh 0.5 mmol palladium nitrate (133.2 mg), 43.8 mmol o-phenanthroline (8.09 g), and 50 mL anhydrous ethanol into a 100 mL round-bottom flask and stir at room temperature for 0.5 h. Then weigh 3.2 g magnesium oxide and add it to the above solution, sonicate (200 W) for 10 min, and then reflux at 60°C for 4 h. Remove the ethanol from the refluxed catalyst solution using a rotary evaporator at 45°C to obtain a pink solid, which is then dried in an oven at 60°C for 8 h. Subsequently, grind the catalyst, place it in a quartz boat, and calcine it to 500°C for 2 h at a gas flow rate of 100 mL / min under a N2 atmosphere with a heating rate of 2 °C / min. After natural cooling, a black solid powder is obtained. Then, using 200 mL of 0.5 M H₂SO₄ solution, acid etching was performed at 80°C in a water bath for 8 hours, followed by filtration. Finally, the catalyst was washed twice with anhydrous ethanol and then washed with deionized water until neutral. It was then dried in an oven at 80°C for 2 hours to obtain the single-atom Pd-NC-500 catalyst. ICP analysis showed that the Pd mass content in the catalyst was 0.95%.

[0024] By changing the calcination temperature to 600℃ and following the same procedure as described above, a single-atom Pd-NC-600 catalyst was obtained. ICP measurement showed that the Pd mass content in the catalyst was 0.93%. HR-TEM images are shown below. Figure 2 As shown.

[0025] By changing the calcination temperature to 700℃ and following the same procedure as described above, a single-atom Pd-NC-700 catalyst was obtained. ICP measurement showed that the Pd mass content in the catalyst was 0.92%.

[0026] Example 1

[0027] A method for converting sugars to 2,5-hexanedione using single-atom catalysis: 0.1 g of glucose, 16 mL of THF organic solvent, 12 mL of 30% NaCl aqueous solution, 0.01 g of Pd-NC-600, and 0.03 g of AlCl3 were mixed and reacted for 30 min at a hydrogen pressure of 2 MPa, a stirring speed of 800 r / m, and a reaction temperature of 120 °C. After cooling to room temperature and allowing to stand, the mixture separated into layers. The organic phase was 2,5-hexanedione. The organic phase was analyzed by gas chromatography (using an HP-FFAP capillary column (30 m, 0.25 mm ID, film thickness 0.25 μm)) to determine the content of 2,5-hexanedione. The gas chromatogram is shown below. Figure 1 As shown.

[0028] Examples 2-9 The effects of different organic phases (THF, MIBK, TOL) and different volume ratios of organic phases to 30% NaCl aqueous solution (1.3:1, 2:1 and 3:1) on the HD yield were compared. The results are shown in Table 1. Unless otherwise specified in Table 1, all conditions are based on Example 1.

[0029] Table 1. Conversion results of 2,5-hexanedione under different organic phases.

[0030] As shown in Table 1, when the volume ratio of organic solvent to inorganic salt solution is 1.3:1, 2:1, and 3:1, the yields obtained with MIBK and TOL as organic solvents are lower than those with THF. For all three organic solvents, the highest HD yield occurs when the volume ratio of organic phase to aqueous phase is 2:1, with the highest HD yield (86.25%) achieved when THF is used as the organic phase.

[0031] Examples 10-12 The effects of different inorganic salt solutions on the HD yield were compared. The difference from Example 1 was that NaCl was replaced with NaB and NH4Br, respectively. The results are shown in Table 2. Conditions not listed in Table 2 were all the same as in Example 1.

[0032] Table 2. Conversion results of 2,5-hexanedione in different inorganic salt solutions.

[0033] As shown in Table 2, NaCl solution has the best promoting effect on the reaction for inorganic salt solutions with a mass fraction of 30%.

[0034] Note: Example 10 in Table 2 is actually Example 4 in Table 1. The representation in Table 1 is only for the convenience of intuitive comparison and sequential numbering.

[0035] Examples 13-21 The effects of different catalysts and different amounts of catalyst on the HD yield were compared. The difference from Example 1 is that Pd-NC-600 was replaced with Pd-NC-500 and Pd-NC-700 respectively, and the amount was replaced with 0.01g and 0.03g respectively. The results are shown in Table 3. The conditions not listed in Table 3 are all the same as in Example 1.

[0036] Table 3. Conversion results of 2,5-hexanedione under different catalyst dosages.

[0037] As shown in Table 3, the experiments on the self-made Pd-NC-500 / 600 / 700 catalysts show that the catalytic effect of the Pd-NC-600 single-atom catalyst is significantly better than the other two (Pd-NC-500 and Pd-NC-700), with the highest HD yield reaching 86.25%. Furthermore, the catalytic effect can be improved by changing the amount of catalyst used.

[0038] Note: Example 14 in Table 3 is actually Example 4 in Table 1. The representation in Table 3 is only for the convenience of intuitive comparison and sequential numbering.

[0039] Examples 22-30 The effects of different additives on HD yield were compared. The difference from Example 1 is that AlCl3 was replaced with SnCl4. The effects of different additive dosages were also compared. The results are shown in Table 4. Unless otherwise specified in Table 4, all conditions are the same as in Example 1.

[0040] Table 4. Conversion results of 2,5-hexanedione with different catalysts and their contents.

[0041] The results in Table 4 show that the addition of aluminum chloride and tin chloride as auxiliaries promotes the reaction. Aluminum chloride has a significant effect as an auxiliary, with the highest HD yield reaching 86.25%. However, the amount of auxiliary added needs to be controlled. Adding too much auxiliary will lead to more side reactions, thereby reducing the HD yield.

[0042] Note: Example 24 in Table 4 is actually Example 4 in Table 1. The representation in Table 4 is only for the convenience of intuitive comparison and sequential numbering.

[0043] Examples 31-43 The effects of different reaction times, reaction temperatures, glucose contents, and reaction pressures on the yield of HD were compared, and the results are shown in Table 5. Conditions not listed in Table 5 refer to Example 1 of this embodiment.

[0044] Table 5 Results of Process Condition Optimization

[0045] The catalysts used in Examples 31-43 were all Pd-NC-600. As shown in Table 5, when the reaction conditions are: glucose content of 0.1 g, reaction pressure of 2 MPa, reaction temperature of 120 °C, and reaction time of 30 min, the glucose conversion rate is the highest (>99%) and the HD yield reaches the maximum of 86.25%.

[0046] Note: Examples 32, 36, 38, and 42 in Table 5 are actually Example 4 in Table 1. The representation in Table 5 is only for easy and intuitive comparison and sequential numbering.

[0047] Examples 44-48 After each reaction, the separated aqueous phase was centrifuged at high speed to recover the catalyst. It was then washed three times each with deionized water and anhydrous ethanol to remove surface adsorbates, followed by treatment in a vacuum drying oven at 60°C for 6 hours until constant weight. This was used for the next reaction, with reaction conditions as in Example 4. This cycle was repeated five times to systematically evaluate the catalyst's stability. To minimize experimental error, three parallel samples were set up for each cycle experiment, and the average value was taken as the final result. Table 6 shows the evaluation results of the recycling of Pd-NC-600.

[0048] Table 6. Stability test results of the catalyst

[0049] The results of the catalyst stability test are shown in Table 6. After five cycles of reaction, the Pd-NC / 600 catalyst still maintains excellent catalytic performance, and the glucose conversion rate and 2,5-hexanedione selectivity do not show significant decrease.

[0050] Comparative Example 1 The catalyst used in this example was prepared according to the following method: Weigh 0.5 mmol palladium nitrate (133.2 mg), 43.8 mmol o-phenanthroline (8.09 g), and 50 mL anhydrous ethanol into a 100 mL round-bottom flask and stir at room temperature for 0.5 h. Then weigh 3.2 g magnesium oxide and add it to the above solution, sonicate (200 W) for 10 min, and then reflux at 60°C for 4 h. Remove the ethanol from the refluxed catalyst solution using a rotary evaporator at 45°C to obtain a pink solid, which is then dried in an oven at 60°C for 8 h. Subsequently, grind the catalyst, place it in a quartz boat, and calcine it to 500°C for 2 h at a gas flow rate of 100 mL / min under a N2 atmosphere with a heating rate of 2 °C / min. After natural cooling, a black solid powder is obtained.

[0051] All other steps were performed in accordance with Example 4. The difference between this example and Example 4 is that the catalyst was not subjected to acid etching treatment with 0.5M H2SO4 solution during preparation. The results are shown in Table 7.

[0052] Comparative Example 2 The difference from Example 4 is that, in the preparation of the catalyst, palladium nitrate was replaced with an equimolar amount of palladium chloride, while the rest were the same as in Example 4.

[0053] Comparative Example 3 The difference from Example 4 is that, in the preparation of the catalyst, palladium nitrate was replaced with an equimolar amount of tetraamminepalladium nitrate, while the rest were the same as in Example 4.

[0054] Comparative Example 4 The difference from Example 4 is that, in the preparation of the catalyst, palladium nitrate was replaced with an equimolar amount of sodium chloropalladate, while the rest were the same as in Example 4.

[0055] Comparative Example 5 The difference from Example 4 is that, in the preparation of the catalyst, palladium nitrate was replaced with an equimolar amount of palladium acetate, while the rest were the same as in Example 4.

[0056] Comparative Example 6 The catalyst used in this example was prepared according to the following method: The preparation of nitrogen-doped graphene-encapsulated heterogeneous Pd catalyst Pd@N / C-2 includes the following steps: (1) 0.03 mol citric acid, 0.003 mol palladium nitrate dihydrate, 0.03 mol melamine and 50 mL anhydrous ethanol were heated and stirred at 70 °C and 300 rpm for 4 h to form a brownish-yellow uniform gel. The gel was dried in a drying oven at 100 °C for 24 h to obtain the catalyst precursor Pd-N.

[0057] (2) The catalyst precursor Pd-N obtained in step (1) was placed in a gas flow of N2 with a gas flow rate of 40 mL / min, heated to 700℃ at a heating rate of 2℃ / min and calcined at 700℃ for 3h. After cooling in the N2 gas flow, the catalyst was obtained. The catalyst was placed in a 1 mol / L sulfuric acid aqueous solution and heated and washed at 70℃ until no bubbles were generated and the acid solution was clear. After washing with deionized water at room temperature until neutral, it was freeze-dried, ground thoroughly, and sieved through a 1000-mesh stainless steel sieve to obtain the nitrogen-doped graphene-encapsulated heterogeneous Pd catalyst Pd@N / C-2.

[0058] The rest are the same as in Example 4.

[0059] Comparative Example 7 The catalyst used in this example was prepared according to the following method: NH3 (30 ml / min) was passed through a flow tube containing 30 g of coconut shell activated carbon and treated at 800 °C for 6 h. 0.17 g of PdCl2 was dissolved in 15 ml of deionized water, and then 10 g of the treated coconut shell activated carbon was added. After impregnation and stirring until no bubbles were generated, the solvent was evaporated in a 90 °C water bath, dried in an oven at 120 °C for 8 h, calcined under nitrogen protection at 300 °C for 4 h, and then reduced with hydrogen at 300 °C for 2 h to obtain activated carbon-supported Pd / AC nanoparticles. These nanoparticles were then treated with a mixture of CO and CH3I (molar ratio 1:1) at 100 °C for 0.5 h to obtain an N-modified carbon-supported single-atom Pd catalyst.

[0060] The rest are the same as in Example 4.

[0061] Comparative Example 8 The catalyst used in this example was prepared according to the following method: Weigh 0.90 g of N-CNTs with a N content of 10 wt.% and disperse them evenly in 200 ml of deionized water. Stir for 30 min, then add 10 ml of chloropalladium acid solution (0.094 mol / L) with a concentration of 0.01 g / ml (palladium) dropwise, stirring for 2 h. Then add 10 wt.% sodium carbonate solution dropwise to slowly increase the pH to 11-13, then heat to 60 °C and maintain the temperature for 3 h. Then add 1.00 g of sodium borohydride (0.026 mol) for reduction for 1 h. Finally, filter, wash with deionized water until neutral, and dry in a vacuum oven at 80 °C for 12 h.

[0062] The rest are the same as in Example 4.

[0063] Table 7

[0064] The results of the comparative examples are shown in Table 7. Compared with the other comparative examples, the Pd-NC of the present invention has better catalytic effect and significantly improved HD yield.

[0065] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for converting sugars to 2,5-hexanedione using single-atom catalysis, characterized in that: 2,5-hexanedione was prepared by reacting glucose as a raw material under the synergistic catalysis of single-atom catalyst Pd-NC and auxiliary agent; wherein, the hydrogen pressure was 1~2 MPa, the reaction temperature was 120~160℃, and the reaction time was 15~60 min; the mass ratio of glucose, single-atom catalyst Pd-NC and auxiliary agent was (10~15):(0.5~2):(1~5). The preparation method of the single-atom catalyst Pd-NC includes the following steps: 1) Mix palladium nitrate, o-phenanthroline and anhydrous ethanol, add magnesium oxide, sonicate for 5-10 min, then stir and reflux at 50-60°C for 2-4 h, remove the ethanol by rotation, and obtain a pink solid, which is dried in an oven at 40-60°C for 6-12 h; the mass ratio of palladium nitrate, o-phenanthroline and magnesium oxide is 1:(58-62):(22-26); 2) The material obtained in step 1) is heated to 300~700℃ for 1~2 hours under N2 atmosphere at a heating rate of 2 °C / min, and then naturally cooled to obtain a black solid powder; 3) Using 0.5 M H2SO4 solution, the material obtained in step 2) was acid etched in a water bath at 60~80°C for 6~8 hours, filtered, washed 2~3 times with anhydrous ethanol, washed with deionized water until neutral, and dried in an oven at 60~80°C for 1~2 hours to obtain the single-atom catalyst Pd-NC. The additives are AlCl3 and / or SnCl4.

2. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 1, characterized in that: Additive AlCl3.

3. The method for converting 2,5-hexanedione using single-atom catalysis according to claim 1 or 2, characterized in that: The mass ratio of palladium nitrate and o-phenanthroline to anhydrous ethanol was (40~50) mg: 5 mL.

4. The method for converting 2,5-hexanedione to sugar using single-atom catalysis according to claim 1 or 2, characterized in that: The mass ratio of glucose, single-atom catalyst Pd-NC, and auxiliary agent is (10~15):(0.8~1.2):(2.5~3.5).

5. The method for converting 2,5-hexanedione by single-atom catalysis according to claim 1 or 2, characterized in that: Glucose, organic solvent, inorganic salt aqueous solution, single-atom catalyst Pd-NC and auxiliary agent are mixed and reacted for 15-60 min under hydrogen pressure of 1-2 MPa and reaction temperature of 120-160℃. After cooling and standing, the mixture separates into layers, and the organic phase is 2,5-hexanedione. The organic solvent is one or more of tetrahydrofuran, toluene, and methyl isobutyl ketone; the inorganic salt aqueous solution has a mass concentration of 25-35%, and the inorganic salt is at least one of NaCl, NaBr, or NH4Br.

6. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 5, characterized in that: After the reaction is complete, the catalyst is recovered by centrifugation, washed successively with deionized water and anhydrous ethanol, dried at 50-60°C to constant weight, and then recycled.

7. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 5, characterized in that: The organic solvent is tetrahydrofuran.

8. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 5, characterized in that: The volume ratio of organic solvent to inorganic salt aqueous solution is (1~4):

1.

9. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 8, characterized in that: The volume ratio of organic solvent to inorganic salt aqueous solution is 2:

1.

10. The method for converting sugars to 2,5-hexanedione using single-atom catalysis according to claim 5, characterized in that: The inorganic salt is NaCl.

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