Method for preparing dihydroxyacetone based on hairpin structure directional catalytic oxidation glycerol

Abstract

The invention belongs to the technical field of chemical catalysis, and particularly relates to a method for preparing dihydroxyacetone by directionally catalyzing and oxidizing glycerol based on a hairpin structure. Comprising the following steps: taking a conductive substrate loaded with a catalyst Ce-coated Fe2O3 as a photo-anode, and assembling the conductive substrate, a cathode and an electrolyte into a photoelectric catalytic reaction device; and adding glycerol and glutaraldehyde into the electrolyte, and selectively oxidizing the glycerol into dihydroxyacetone under the conditions of illumination and voltage application. According to the invention, hydrogen bond acceptor molecule glutaraldehyde with a specific spatial configuration is selected to form a hairpin composite structure with hydroxyl groups at two ends of glycerol, and accurate activation and directional oxidation of intermediate hydroxyl groups are realized under the action of a catalyst Ce-coated Fe2O3, so that glycerol is directionally and efficiently oxidized into 1, 3-dihydroxyacetone, and the yield of 1, 3-dihydroxyacetone is improved. And an innovative solution is provided for high-selectivity conversion of the biomass-derived polyol.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical catalysis, and particularly relates to a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure. BACKGROUND

[0002] Biomass platform molecule-glycerol oxidation can obtain a variety of oxygen-containing high-value chemicals. Among them, 1,3-dihydroxyacetone (DHA) has significant economic value due to its wide application in the field of cosmetics (such as sunscreen, etc.), with an annual growth rate of 8% in global market demand and a market price of up to 150 US dollars / kg. However, there are three hydroxyl groups (two primary hydroxyl groups and one secondary hydroxyl group) in the glycerol molecule, which have similar reactivity. In the traditional catalytic system, the following competitive reactions will occur simultaneously: (1) primary hydroxyl group oxidation to generate glycerol aldehyde; (2) secondary hydroxyl group oxidation to generate DHA; (3) C-C bond cleavage to generate small molecules such as formic acid or glycolic acid, resulting in the selectivity of the target product DHA generally maintained at 60%.

[0003] At present, the main methods for preparing dihydroxyacetone by directional oxidation of glycerol include thermal catalysis, electrocatalysis and photocatalysis. Among them, the thermal catalysis method usually relies on active sites of >3wt% noble metals (such as Au, Pt, Pd, etc.), and needs to overcome the high activation energy barrier of C-H / O-H bond under high temperature and high pressure (80-120℃, 0.5-3 MPa oxygen) conditions, resulting in high energy consumption and expensive catalyst cost. The electrocatalysis method has the advantages of green economy, without external heat source and oxidant, but needs to apply high potential in a strong alkaline environment, and there is a strong mutual exclusion balance between conversion rate and selectivity. Although the photocatalysis method can be carried out under mild conditions, it still needs to introduce oxidants (such as O2, H2O2), and is limited by the rapid recombination of photo-generated carriers, resulting in low glycerol conversion efficiency.

[0004] It is particularly worth noting that the prior art has not effectively solved the key problem of selective recognition of primary and secondary hydroxyl groups of glycerol, making it difficult to achieve directional activation oxidation. The selectivity of hydroxyl groups can be controlled by steric hindrance, but there has been no successful report on the control of glycerol molecular configuration. Therefore, it is of important scientific significance, economic and application value to develop a photoelectrocatalytic method which is mild in reaction conditions, green and low in energy consumption, and does not rely on noble metals, and can realize efficient directional oxidation of glycerol to dihydroxyacetone. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the first purpose of the present application is to provide a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure. The synergistic effect of the anode and the electrolyte enables the directional and efficient oxidation of glycerol to 1,3-dihydroxyacetone.

[0006] In order to achieve the above object, the technical scheme adopted by the present application is: A method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure, comprising the following steps: (1) The conductive substrate loaded with catalyst Ce@Fe2O3 is used as a photoanode, and a cathode and an electrolyte are assembled into a photoelectrocatalytic reaction device; (2) Glycerol and glutaraldehyde are added to the electrolyte, and glycerol is selectively oxidized to dihydroxyacetone under the conditions of light and applied voltage.

[0007] Further, the molar ratio of glycerol and glutaraldehyde is 1:1.

[0008] The above scheme is used to construct the hairpin structure: the distance between H-H on the two end hydroxyl groups of the glycerol molecule is 5.74 Å, and by using the "molecular hairpin" confinement strategy, glutaraldehyde with a matching spatial structure is selected to combine with glycerol in an equimolar amount, and the distance between O-O on the two end aldehyde groups is 6.23 Å, which fixes the two end primary hydroxyl groups of glycerol through bidentate hydrogen bonding interaction to form a hairpin structure, so that only the secondary hydroxyl group is exposed to participate in the reaction, and the schematic diagram is shown in Figure 1 .

[0009] Further, the catalyst Ce@Fe2O3 is prepared by the following preparation process: Ce nitrate, FeCl3 and NaNO3 are added to water and stirred to obtain a mixed solution; then the conductive glass is placed in the mixed solution with the conductive surface facing upwards to form a hydrothermal reaction system, and after the reaction is completed, the conductive glass is taken out and washed, dried and calcined to obtain the catalyst Ce@Fe2O3.

[0010] Further, the mass ratio of NaNO3, FeCl3 and Ce(NO3)3 is 0.85:2.43:(0.025-0.1).

[0011] Further, the temperature of the hydrothermal reaction is 90-120 ℃, and the time is 2-12 h; the temperature of the calcination is 500-580 ℃, and the time is 1-4 h.

[0012] Further, the temperature of the hydrothermal reaction is preferably 100 ℃, and the time is preferably 4 h.

[0013] Further, the temperature of the calcination is preferably 550 ℃, and the time is preferably 2 h.

[0014] Further, the electrolyte is a NaCl solution or a NaBr solution, and the concentration is 0.05-0.5 mol / L; the dosage ratio of the electrolyte to glycerol and glutaraldehyde is 10 mL:1 mmol:1 mmol.

[0015] Further, the cathode is Pt wire; the conductive substrate is ITO or FTO.

[0016] Further, a naphthol 117 proton film is arranged between the photoanode and the cathode.

[0017] Further, the intensity of the light is 100 mW / cm 2 ; the voltage is 0.2-1.4 V.

[0018] Further, the light direction is the non-conductive surface of the anode.

[0019] The beneficial technical effects of the present application are: 1. The present application forms a bidentate hydrogen bond complex structure by designing a hydrogen bond acceptor molecule (glutaraldehyde) with a specific spatial configuration and glycerol, accurately fixes the primary hydroxyl groups at both ends of glycerol, and makes the intermediate secondary hydroxyl group directional exposure to the active site. At the same time, the catalyst Ce@Fe2O3 promotes the separation of photo-generated carriers under light, enhances the electron transport efficiency by applying a given voltage, and cooperates with the bidentate hydrogen bond complex structure to efficiently catalyze the active site exposed by glycerol, improve the conversion rate of glycerol, and have high selectivity and higher reactivity, thereby significantly improving the selectivity of DHA (which can reach >75%), effectively avoiding the problem of side reactions caused by the competitive oxidation of primary hydroxyl groups and the rupture of C-C bonds in the catalytic system, providing an efficient and economical new path for biomass refining, and providing an innovative solution for the high-selectivity conversion of biomass-derived polyols.

[0020] 2. The present application has mild and green reaction conditions without pollution, uses photoelectrocatalytic technology (0.8 V vs. RHE, normal temperature and pressure, combined with simulated light), does not require high temperature and pressure or strong alkaline environment, and the photoelectrode used does not involve noble metals, reducing energy consumption and catalyst cost, and meeting the requirements of green chemistry and sustainable development. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The present application is a schematic diagram of the hairpin structure formed by glycerol and glutaraldehyde; Figure 2 The X-ray diffraction pattern of the catalyst Ce@Fe2O3 prepared in Example 1 is shown in the figure; Figure 3 The reaction principle diagram of the photoelectrocatalytic oxidation coupling cathode hydrogen production of glycerol and glutaraldehyde in Example 1 is shown in the figure; Figure 4 The corresponding relationship between the glycerol conversion rate and the selectivity of each product after photoelectrocatalysis of Example 1 and Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0022] The following further describes the present application in connection with specific preferred embodiments, which should not be construed as limiting the present application to these descriptions. Those ordinarily skilled in the art to which the present application pertains can make several simple deductions or substitutions without departing from the concept of the present application, which should be considered as falling within the scope of the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturers. The reagents or instruments used, if not specifically mentioned, are the conventional products obtained through the commercial channels.

[0023] (I) Examples Example 1 Example 1 provides a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure, and the specific steps are as follows: (1) The FTO conductive glass is immersed in a toluene solution and ultrasonicated for 5 min to remove organic impurities, and then ultrasonicated in an ethanol solution for 5 min, followed by ultrasonication in a 5% hydrogen peroxide solution for 5 min. The glass is washed with deionized water and then ultrasonicated in acetone for 5 min. The glass is then placed in a 60°C air-drying oven for 1 h to obtain a pretreated FTO conductive glass; (2) 0.05 g of cerium nitrate, 2.43 g of iron chloride, and 0.85 g of sodium nitrate are added to 100 mL of deionized water and stirred for 5 min. The resulting solution is transferred to a high-pressure reaction kettle liner, and the pretreated FTO conductive glass is placed in the liner with the conductive side tilted upward at 45°. The glass is hydrothermally reacted at 100°C for 4 h, and then naturally cooled. The electrode is removed and washed with deionized water three times, each time using 10 mL. After washing, the electrode is dried in a 60°C oven for 1 h, and then calcined in a muffle furnace at 550°C for 2 h, with a heating rate of 10°C / min. A photoelectrode loaded with a catalyst Ce@Fe2O3 is obtained. (3) Prepare 10 mL of sodium bromide electrolyte with a pH of 7.04 and a concentration of 0.5 mol / L. Then, use a Ce@Fe2O3 photoelectrode as the anode, a Pt wire as the cathode, and Ag / AgCl as the reference electrode, and use a naphthol 117 proton exchange membrane to separate the anode and cathode to assemble a three-electrode system. Add 1 mmol of glycerol and 1 mmol of glutaraldehyde to the electrolyte, and stir magnetically at 300 r / min for 20 min. Then, under nitrogen protection, apply voltage using an electrochemical workstation (CHI 760F) and use the current-time (it) mode to irradiate the reaction for 4 h at a given voltage of 0.8 V vs. RHE (RHE represents reversible hydrogen electrode) to prepare 1,3-dihydroxyacetone. A xenon lamp with an AM 1.5G filter is used to simulate sunlight irradiation of the anode, with the irradiation direction being the non-conductive surface of the anode, and the irradiation intensity being 100 mW / cm². 2 .

[0024] This embodiment provides an X-ray diffraction pattern of the catalyst Ce@Fe2O3, such as... Figure 2 As shown, the mass fraction of cerium atoms in the catalyst Ce@Fe2O3 was determined to be 1.0 wt% using inductively coupled plasma mass spectrometry. This embodiment also provides a schematic diagram of the photoelectrocatalytic oxidation of glycerol and glutaraldehyde coupled to a cathode for hydrogen production, as shown below. Figure 3 As shown.

[0025] Example 2 Example 2 provides a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure. The specific steps are as follows: (1) Soak the FTO conductive glass in toluene solution and sonicate for 5 min to remove organic impurities. Then sonicate with ethanol solution for 5 min, then sonicate with 5% hydrogen peroxide solution for 5 min, wash with deionized water, and then sonicate with acetone for 5 min. Finally, place it in a 60 ℃ forced-air drying oven and dry for 1 h to obtain the pretreated FTO conductive glass. (2) 0.10 g cerium nitrate, 2.43 g iron chloride, 0.85 g sodium nitrate were added into 100 mL deionized water and stirred for 5 min, the obtained solution was transferred into a high-pressure reaction kettle liner, the pre-processed FTO conductive glass was placed in the high-pressure reaction kettle liner with the conductive side tilted upward by 45°, and hydrothermal reaction was carried out at 100°C for 4 h, after the reaction was completed, the electrode was naturally cooled, washed with 10 mL deionized water for 3 times, and then placed in a 60°C oven for drying for 1 h, after being taken out, high-temperature calcination was carried out in a muffle furnace at 550°C for 2 h, wherein the heating rate of the muffle furnace was 10°C / min, thereby obtaining a photoelectrode loaded with catalyst Ce@Fe2O3; at the same time, inductively coupled plasma mass spectrometry was used to determine that the mass fraction of cerium atoms in the catalyst Ce@Fe2O3 was 2.0 wt%.

[0026] (3) 10 mL sodium bromide electrolyte with a pH value of 7.06 and a concentration of 0.1 mol / L was configured, a photoelectrode loaded with catalyst Ce@Fe2O3 was used as an anode, a Pt wire was used as a cathode, Ag / AgCl was used as a reference electrode, and a naphthol 117 proton membrane was used between the anode and the cathode to assemble a three-electrode system; 1 mmol glycerol and 1 mmol glutaraldehyde were added to the electrolyte, and magnetic stirring was carried out at a speed of 300 r / min for 20 min, then under the protection of nitrogen, a voltage was applied by using an electrochemical workstation (CHI 760F), a current-time (i-t) mode was used, and a light reaction was carried out at a given voltage of 0.4 V vs. RHE (RHE represents a reversible hydrogen electrode) for 4 h to prepare 1,3-dihydroxyacetone, wherein in the light reaction, a xenon lamp light source with an AM 1.5G filter was used to simulate sunlight to irradiate the anode, the light direction was the non-conductive surface of the anode, and the light intensity was 100 mW / cm 2 .

[0027] Example 3 Example 3 provides a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure, and the specific steps are as follows: (1) The FTO conductive glass was immersed in a toluene solution and ultrasonicated for 5 min to remove organic impurities, then ultrasonicated in an ethanol solution for 5 min, and then ultrasonicated in a 5% hydrogen peroxide solution for 5 min, washed with deionized water, and then ultrasonicated in acetone for 5 min, and then placed in a 60°C air drying oven for drying for 1 h to obtain pre-processed FTO conductive glass; (2) 0.025 g cerium nitrate, 2.43 g iron chloride, 0.85 g sodium nitrate were added into 100 mL deionized water and stirred for 5 min, the obtained solution was transferred into a high-pressure reaction kettle liner, the pre-processed FTO conductive glass was placed in the high-pressure reaction kettle liner with the conductive side tilted upward by 45°, and hydrothermal reaction was carried out at 100 ℃ for 4 h, after the reaction was completed, the electrode was naturally cooled, washed with deionized water for 3 times, each time with 10 mL, after the washing was completed, it was placed in a 60 ℃ oven for drying for 1 h, and after being taken out, it was calcined in a muffle furnace at 550 ℃ for 2 h, wherein the heating rate of the muffle furnace was 10 ℃ / min, thereby the photoelectrode loaded with catalyst Ce@Fe2O3 was obtained; at the same time, inductively coupled plasma mass spectrometry was used to determine that the mass fraction of cerium atoms in the catalyst Ce@Fe2O3 was 0.5 wt%.

[0028] (3) 10 mL sodium bromide electrolyte with a pH value of 7.05 and a concentration of 0.2 mol / L was configured, then the photoelectrode loaded with catalyst Ce@Fe2O3 was used as an anode, a Pt wire was used as a cathode, Ag / AgCl was used as a reference electrode, and a naphthol 117 proton membrane was used between the anode and the cathode to assemble a three-electrode system; 1 mmol glycerol and 1 mmol glutaraldehyde were added to the electrolyte, and magnetic stirring was carried out at a speed of 300 r / min for 20 min, then a voltage was applied to the electrolyte under nitrogen protection by using an electrochemical workstation (CHI 760F), a current-time (i-t) mode was used, and anode irradiation was carried out under simulated sunlight of a given voltage of 1.4 V vs. RHE (RHE represents a reversible hydrogen electrode) for 4 h to prepare 1,3-dihydroxyacetone, wherein a xenon lamp light source with an AM 1.5G filter was used for simulated sunlight irradiation of the anode, the irradiation direction was the non-conductive surface of the anode, and the irradiation intensity was 100 mW / cm 2 .

[0029] Example 4 Example 4 provides a method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on a hairpin structure, and the specific steps are as follows: (1) The FTO conductive glass was immersed in a toluene solution and ultrasonicated for 5 min to remove organic impurities, then ultrasonicated in an ethanol solution for 5 min, and then ultrasonicated in a 5% hydrogen peroxide solution for 5 min, washed with deionized water, and then ultrasonicated in acetone for 5 min, and then placed in a 60 ℃ air drying oven for drying for 1 h to obtain pre-processed FTO conductive glass. (2) 0.075 g cerium nitrate, 2.43 g iron chloride, 0.85 g sodium nitrate were added into 100 mL deionized water and stirred for 5 min, the obtained solution was transferred into a high-pressure reaction kettle liner, the pre-processed FTO conductive glass was placed in the high-pressure reaction kettle liner with the conductive side tilted upward by 45°, and hydrothermal reaction was carried out at 100 ℃ for 4 h, after the reaction, the electrode was naturally cooled, washed with deionized water for 3 times, each time with 10 mL, and then placed in a 60 ℃ oven for drying for 1 h, and after taking out, calcination was carried out in a muffle furnace at 550 ℃ for 2 h, wherein the heating rate of the muffle furnace was 10 ℃ / min, thereby the photoelectrode loaded with catalyst Ce@Fe2O3 was obtained; at the same time, inductively coupled plasma mass spectrometry was used to determine that the mass fraction of cerium atoms in the catalyst Ce@Fe2O3 was 1.5 wt%.

[0030] (3) 10 mL sodium bromide electrolyte with a pH value of 7.04 and a concentration of 0.4 mol / L was configured, then the photoelectrode loaded with catalyst Ce@Fe2O3 was used as the anode, Pt wire was used as the cathode, Ag / AgCl was used as the reference electrode, and naphthol 117 proton membrane was used between the anode and the cathode to assemble a three-electrode system; 1 mmol of glycerol and 1 mmol of glutaraldehyde were added to the electrolyte, and magnetic stirring was carried out at a speed of 300 r / min for 20 min, then under the protection of nitrogen, a voltage was applied by using an electrochemical workstation (CHI 760F), a current-time (i-t) mode was used, and light reaction was carried out at a given voltage of 0.8 V vs. RHE (RHE represents a reversible hydrogen electrode) for 4 h to prepare 1,3-dihydroxyacetone, wherein a xenon lamp light source with an AM 1.5G filter was used to simulate sunlight to irradiate the anode, the light direction was the non-conductive side of the anode, and the light intensity was 100 mW / cm 2 .

[0031] (II) Comparative Examples Comparative Example 1 Comparative Example 1 and Example 1 are basically the same, except that glutaraldehyde is not added to the electrolyte.

[0032] Comparative Example 2 Comparative Example 2 and Example 1 are basically the same, except that in step (2), cerium nitrate is not used when preparing the photoelectrode.

[0033] Comparative Example 3 Comparative Example 3 and Example 1 are basically the same, except that in step (2), the amount of cerium nitrate is adjusted to 0.005 g, and inductively coupled plasma mass spectrometry is used to determine that the mass fraction of cerium atoms in the catalyst Ce@Fe2O3 is 0.1 wt%.

[0034] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that the amount of glutaraldehyde added in the electrolyte is replaced by 0.1 mmol, and no voltage is applied when preparing 1,3-dihydroxyacetone.

[0035] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that the amount of glutaraldehyde added in the electrolyte is replaced by 0.5 mmol, and no light is applied when preparing 1,3-dihydroxyacetone.

[0036] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that the electrolyte and the amounts of glycerol and glutaraldehyde added are different, specifically: 10 mL of a mixed solution of sodium chloride and sodium bromide with a concentration of 0.5 mol / L and a pH value of 6.94 is used as the electrolyte, and 1 mmol of glycerol and 2 mmol of glutaraldehyde are added.

[0037] Comparative Example 7 Comparative Example 7 is basically the same as Example 1, except that the electrolyte and the amounts of glycerol and glutaraldehyde added are different, specifically: 10 mL of a sodium chloride solution with a concentration of 0.5 mol / L and a pH value of 6.86 is used as the electrolyte, and 1 mmol of glycerol and 2 mmol of glutaraldehyde are added.

[0038] (Three) Test Examples The electrolytes after reaction in Examples 1-4 and Comparative Examples 1-7 are taken as the samples to be tested, a small amount of dilute sulfuric acid is added to each sample to be tested for dilution, and then filtered with a nylon 66 filter membrane and placed in a sample bottle for liquid chromatography test: the molar concentrations of glycerol, dihydroxyacetone, glycerol, and glutaric acid are analyzed by liquid chromatography. The external standard analysis method is used, and Shimadzu LC-20AT type liquid chromatography is used for testing, with a sample size of 20 μL. According to the liquid chromatography results, the main products of glycerol selective oxidation and the selectivity of each product and the yield of glutaric acid, the oxidation product of glutaraldehyde, are determined, and the results are shown in Table 1.

[0039] This test example also provides the corresponding relationship between the glycerol conversion rate and the selectivity of each product after photoelectrocatalysis of Example 1 and Comparative Example 1, and the results are shown in Table 1. Figure 4

[0040] Table 1: Catalytic product results of examples and comparative examples As can be seen from Table 1, the method of Examples 1-3 of the present application can effectively improve the selectivity of photoelectrocatalytic glycerol oxidation to 1,3-dihydroxyacetone, and the glutaraldehyde used in the present application can be oxidized to high-value chemical glutaric acid, and the products are all value-added chemicals.​

[0041] Compared with example 1, the glutaraldehyde in the electrolyte is omitted in comparative example 1, the cerium nitrate is omitted in comparative example 2, the amount of cerium nitrate is adjusted to 0.005 g in comparative example 3, the amount of glutaraldehyde in the electrolyte is adjusted to 0.1 mmol and 0.5 mmol in comparative examples 4-5, sodium bromide is replaced by sodium chloride and the amount of glutaraldehyde in the electrolyte is adjusted to 2 mmol in comparative examples 6-7, and the selectivity of 1,3-dihydroxyacetone is obviously decreased. Specific analysis shows that: according to the H-H distance of 5.74 Å on the two ends of the hydroxyl group of glycerol molecule, the space structure matching glutaraldehyde is selected by the “molecular hairpin” confinement strategy, and the O-O distance on the two ends of the aldehyde group is 6.23 Å, which fixes the two primary hydroxyl groups of glycerol through bidentate hydrogen bond interaction to form a hairpin structure, so that only the secondary hydroxyl group is exposed to participate in the reaction. At the same time, the Ce@Fe2O3 photoelectrode promotes the separation of photo-generated carriers under light, enhances the electron transport efficiency by applying a given voltage, and cooperates with the bidentate hydrogen bond complex structure to efficiently catalyze the active sites exposed by glycerol, realizes the efficient selective oxidation of glycerol, effectively avoids the problem of side reactions caused by the competitive oxidation of primary hydroxyl group and the rupture of C-C bond in the catalytic system, and significantly improves the selectivity of DHA (which can reach >75%).

[0042] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it. The basic principles and main features of the present application have been described above with specific embodiments, and some modifications or replacements can be made on the basis of the present application, but these modifications or replacements do not make the corresponding technical solutions deviate from the scope of the present application.

Claims

1. A method for preparing dihydroxyacetone from glycerol based on a hairpin structure directed catalytic oxidation, characterized in that, The method comprises the following steps: (1) an electrically conductive substrate loaded with catalyst Ce@Fe2O3 is used as a photoanode to assemble a photoelectrocatalytic reaction device together with a cathode and an electrolyte; (2) glycerol and glutaraldehyde are added to the electrolyte, and glycerol is selectively oxidized into dihydroxyacetone under the conditions of light irradiation and voltage application.

2. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, The molar ratio of glycerol to glutaraldehyde is 1:

1.

3. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, The catalyst Ce@Fe2O3 is prepared by the following preparation process: Ce(NO3)3, FeCl3 and NaNO3 are added to water and stirred to obtain a mixed solution; then the electrically conductive glass is placed in the mixed solution with the electrically conductive surface facing upwards to undergo a hydrothermal reaction, and after the reaction is completed, the electrically conductive glass is taken out and washed, dried and calcined to obtain the catalyst Ce@Fe2O3.

4. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 3, characterized in that, The mass ratio of NaNO3, FeCl3 to Ce(NO3)3 is 0.85:2.43:(0.025-0.1).

5. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 3, characterized in that, The temperature of the hydrothermal reaction is 90-120 ℃, and the time is 2-12 h; the temperature of the calcination is 500-580 ℃, and the time is 1-4 h.

6. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, The electrolyte is a sodium chloride solution or a sodium bromide solution, and the concentration is 0.1-0.5 mol / L; the dosage ratio of the electrolyte to glycerol and glutaraldehyde is 10 mL:1 mmol:1 mmol.

7. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, The cathode is Pt wire; and the electrically conductive substrate is ITO or FTO.

8. The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, A naphthol 117 proton membrane is arranged between the photoanode and the cathode. 9.The method for preparing dihydroxyacetone by directional catalytic oxidation of glycerol based on hairpin structure according to claim 1, characterized in that, The light has an intensity of 100 mW / cm 2 ; and the voltage is 0.2-1.4 V.

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