Catalyst for isomerizing glucose into fructose as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for isomerizing glucose into fructose as well as a preparation method and application of the catalyst, and belongs to the field of preparation of biomass-based chemicals. The molecular sieve is used as a carrier, bimetal is loaded, and the catalyst with a core-shell structure is obtained through processes such as complex precipitation, roasting, reduction and oxidation. The catalytic performance is improved by utilizing the shape-selective effect of the molecular sieve and the metal-acid synergistic effect, and the catalytic stability is improved by combining reduction-passivation treatment, so that high conversion rate and high selectivity from glucose to fructose are realized. The catalyst provided by the invention is simple in preparation process, mild in reaction condition, high in stability and high in catalytic efficiency, and provides reliable technical support for efficient and green preparation of fructose.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bio-based chemical preparation, in particular to a catalyst for isomerization of glucose into fructose and a preparation method and application thereof. BACKGROUND

[0002] Fructose, as a natural sweetener, has been increasingly demanded in food, beverage and pharmaceutical industries due to its high sweetness and specific metabolic pathway. Traditional industrial production of fructose mainly relies on hydrolysis of natural raw materials (such as inulin) or enzymatic isomerization of starch-based syrup. However, the enzymatic catalyst has the disadvantages of high cost and poor stability. Chemical catalytic isomerization of glucose has attracted much attention due to its independence on biological enzymes and wide process adaptability. However, there are still significant bottlenecks in the existing technology.

[0003] In recent years, enzyme method (such as immobilized glucose isomerase) has become the mainstream due to its high selectivity, but it has significant drawbacks: high enzyme cost, poor operational stability (sensitive to pH and temperature), and long reaction period which limits the production capacity. Therefore, it is of great significance to develop efficient, stable and environmentally friendly chemical catalytic system to realize the directional conversion of glucose into fructose, which can improve the yield and reduce the production cost, and promote green manufacturing.

[0004] Currently, chemical isomerization method mainly uses alkaline catalysts (such as sodium hydroxide, carbonate) or metal-based catalysts (such as tin, aluminum compounds). Although alkaline conditions can promote the conversion of glucose into fructose, they can easily cause side reactions (such as decomposition to generate carboxylic acids or pigment substances), resulting in decreased product purity and complex post-processing. Meanwhile, the strong alkaline environment intensifies equipment corrosion and increases maintenance costs. Although metal catalysts can improve selectivity, they generally have problems such as easy deactivation of active sites and metal leaching to contaminate products. Moreover, high-temperature reaction conditions (> 120℃) result in high energy consumption and significant carbon footprint. In addition, the fructose yield of existing processes is generally less than 45%, which is difficult to meet the economic demand of large-scale production.

[0005] CN106563495A discloses a glucose isomerization molecular sieve catalyst and a preparation method thereof. The glucose isomerization molecular sieve catalyst is obtained by Al-Beta zeolite dealumination, tin source loading and twice hydrothermal crystallization. The molecular sieve catalyst is used for the isomerization reaction of glucose, and the conversion rate of glucose is only 43.4%-62.4%, and the yield of fructose is only 22.3%-47.6%. CN112028949A discloses a method for preparing fructose from glucose by catalysis. The modified HY molecular sieve catalyst is obtained by impregnating the HY molecular sieve in a sodium salt solution, and then calcining the impregnated HY molecular sieve after drying. The fructose yield is only 33.6%-42.7%.

[0006] Therefore, it is of great practical significance to develop an efficient and stable catalytic system to realize the directional conversion of glucose into fructose, so as to improve the product yield and reduce the production cost. SUMMARY

[0007] In order to solve the problems of low conversion rate, poor selectivity and insufficient stability of the catalyst in the existing glucose isomerization technology, the main purpose of the present application is to provide a catalyst for isomerization of glucose into fructose and its preparation method and application. The catalyst preparation process is simple, the reaction conditions are mild, the catalyst has high stability and high catalytic efficiency, and a new technical scheme is provided for the efficient and green preparation of fructose.

[0008] In order to solve the above technical problems, the technical scheme adopted by the present application is:

[0009] A preparation method of a catalyst for isomerization of glucose into fructose, comprising the following steps: (1) After the molecular sieve is subjected to acid pickling treatment and then activated by high-temperature calcination, a pretreated molecular sieve is obtained; (2) The metal compound and the pretreated molecular sieve are dissolved in water, and the metal is precipitated on the carrier by adjusting the pH and temperature of the solution to obtain a precursor; (3) The precursor obtained in step (2) is sequentially subjected to low-temperature calcination, high-temperature reduction and high-temperature oxidation treatment to obtain the catalyst.

[0010] Preferably, the molecular sieve in step (1) is selected from one or more than two of ZSM-5 type, Y type molecular sieve, Beta type, TS-1 molecular sieve and mordenite.

[0011] Preferably, the acid used in the acid pickling in step (1) is selected from one or more than two of sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid and hydrofluoric acid; the acid concentration of the acid pickling treatment is 0.01-10 mol / L, the acid pickling time is 0.01-10 h, the calcination temperature is 300-800℃, and the calcination time is 2-5 h.

[0012] Preferably, the metal compound in step (2) is selected from at least one of lanthanum salt, antimony salt, tin salt, lithium salt, platinum salt, indium salt, niobium salt and magnesium salt.

[0013] More preferably, the molar ratio of the two metals in the metal compound is 1:0.2-5, and the total metal loading is 0.01-50% of the mass of the carrier.

[0014] Preferably, the metal compound is selected from one or more than two of nitrate, carbonate, sulfate and halide.

[0015] Preferably, in the step (2), the pH value of the solution is adjusted to 1-14 by using ammonia water, ammonium chloride, sodium hydroxide, formic acid, acetic acid or phosphate, under which conditions the high-valence metal salt and the low-valence metal salt are precipitated in turn.

[0016] Preferably, in the step (2), after the metal salt is dissolved in water, a complexing agent is added, which is selected from one or more than two of citric acid, EDTA, N,N-dimethylformamide, pyridine, N-methylpiperidine, N-acyl amino acid and 4-sulfonamino pyridine.

[0017] Preferably, in the step (2), the metal precipitation process specifically comprises: precipitating the high-valence metal by stirring at 30-50℃ for 1-4h, and then precipitating the low-valence metal by stirring at 50-70℃ for 2-6h.

[0018] Preferably, the step (3) specifically comprises: first, under N2 atmosphere, increasing the temperature to 200-300℃ at a rate of 0.1-5℃ / min and calcining for 0.5-5h to remove the crystal water of the precursor; then, under H2 / N2 atmosphere, increasing the temperature to 400-800℃ and reducing for 1-6h, and then replacing with N2 and then with O2 to oxidize for 1-3h, so as to passivate the metal on the surface of the catalyst into a stable oxidation state, thereby enhancing the stability of the catalyst, and then naturally cooling to room temperature to obtain the desired catalyst.

[0019] The second aspect of the present application provides a catalyst for isomerizing glucose into fructose, which is prepared by the preparation method.

[0020] The third aspect of the present application provides the application of the catalyst in the reaction of isomerizing glucose into fructose.

[0021] Preferably, the application comprises: adding the catalyst into a glucose solution to perform isomerization reaction, so as to obtain a fructose product.

[0022] More preferably, the application specifically comprises: dissolving glucose in a solvent to obtain a glucose solution; adding the catalyst into the glucose solution to perform isomerization reaction under a reaction temperature of 50-180℃ and a self-generated pressure, so as to obtain a fructose product.

[0023] Preferably, the solvent is selected from one or more of pure water, methanol, ethanol, glycerol and alcohol-water mixture.

[0024] Preferably, the reactor for the isomerization reaction is selected from one of a reaction kettle, a tower reactor, a fixed bed and a slurry bed.

[0025] Preferably, the isomerization reaction is controlled according to the reactor type using the following parameters: when using a reactor vessel, the mass ratio of glucose to catalyst is 5-10:1; when using a tower reactor, fixed bed reactor, or slurry bed reactor, the mass hourly space velocity (HHSV) is controlled to be 0.5-2.0 h⁻¹. -1 .

[0026] This invention uses molecular sieves as a carrier to support bimetallic compounds, which are then processed through complexation precipitation, calcination, reduction, and oxidation to obtain a catalyst with a core-shell structure. The shape-selective effect of the molecular sieve restricts the diffusion of glucose and fructose, promoting glucose reaction within a specific space. The Lewis acid-metal synergistic sites formed by the bimetallic combination can both catalyze glucose ring-opening via Lewis acid and promote isomerization via metal sites, while suppressing side reactions such as dehydration to form 5-hydroxymethylfurfural (5-HMF), thereby improving the selectivity and yield of fructose. Stepwise precipitation of the metal via co-precipitation achieves atomic-level dispersion of the metal, resulting in a more uniform distribution of active sites on the molecular sieve surface, improving the contact efficiency between metal atoms and glucose, and thus enhancing catalytic activity. Reduction and oxidation treatments are used to form a stable oxidation state of the metal, preventing metal particle aggregation or precipitation during the reaction and ensuring the long-term stability of the catalyst.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. The catalyst of the present invention utilizes the shape-selective effect of molecular sieves and the synergistic effect of metal-acid to enhance catalytic performance, and combines reduction-passivation treatment to enhance catalytic stability, significantly improving the conversion rate (>80%), selectivity (>80%), and fructose yield (>65%) of glucose isomerization reaction. Compared with traditional catalysts or single metal catalysts, it has obvious advantages and provides technical support for the efficient preparation of fructose.

[0028] 2. This invention uses a post-treatment process of "calcination, reduction and oxidation" to form a stable oxidation state on the surface of the catalyst, thereby enhancing its stability during the reaction process and extending its service life.

[0029] 3. The catalyst preparation process of this invention is simple and the reaction conditions are mild, which reduces the energy consumption and equipment requirements for industrial production; the catalyst has strong stability and high catalytic efficiency, providing a new technical solution for the efficient and green preparation of fructose. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a SEM image of the catalyst Mg-0.5Sn-TS-1 prepared in Example 2 of this invention. Detailed Implementation

[0031] The technical solution and technical effects of the present invention will be further described in detail below with reference to the embodiments. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0033] Example 1: (1) Take 10g of ZSM-5 and treat it with 2ml of 0.3M oxalic acid at 60℃ for 2h, then wash, dry, and calcine at 500℃ for 3h to obtain the acid-washed ZSM-5 carrier; (2) MgCl2·H2O and SbCl3 (total metal loading 5wt%) with a molar ratio of 1:0.4 and ZSM-5 support were dissolved in water. Citric acid was added at 40℃ to complex and prevent hydrolysis. NH3·H2O was slowly added dropwise until the pH was 5.0. The mixture was stirred and aged for 1 h, and the Sb layer precipitated preferentially. The temperature was then raised to 60℃, and NH3·H2O was slowly added dropwise until the pH was 9.0. The mixture was stirred and aged for 4 h to coat the Sb core with Mg layers. After aging, the support was filtered, washed, and dried at 120℃ to obtain the precursor. (3) The precursor was first calcined at 250°C for 2h under N2 atmosphere at a heating rate of 2°C / min to remove the water of crystallization in the precursor. Then it was reduced at 550°C for 3h under H2 / N2 atmosphere. Finally, O2 was introduced for oxidation for 2h to passivate the metal on the catalyst surface into a stable oxidation state and enhance the stability of the catalyst. The catalyst was then naturally cooled to room temperature to obtain the catalyst Mg-0.4Sb-ZSM-5. (4) Prepare a 30wt% glucose aqueous solution. Place 5g of Mg-0.4Sb-ZSM-5 catalyst in a fixed-bed reactor. Set the reaction temperature to 90℃, the reaction pressure to 1MPa, and the mass hourly space velocity to 1.0h. -1 Under certain conditions, an isomerization reaction was carried out by passing a 30% glucose aqueous solution through the solution, yielding a product containing fructose. The product was analyzed by HPLC, and the results are shown in Table 1.

[0034] Example 2: (1) Take 20g of TS-1 and treat it with 2ml of 0.1M nitric acid at 60℃ for 1h, then wash, dry, and calcine at 500℃ for 3h to obtain the acid-washed TS-1 carrier; (2) Mg(NO3)2·6H2O and SnCl4 (total metal loading 6wt%) with a molar ratio of 1:0.5 and TS-1 support were dissolved in water. EDTA was added at 40℃ to complex and prevent hydrolysis. NH4Cl was slowly added dropwise until the pH was 5.0. The mixture was stirred and aged for 2h, and the Sn layer precipitated preferentially. The temperature was then raised to 60℃, and NH4Cl was slowly added dropwise until the pH was 9.0. The mixture was stirred and aged for 4h, so that the Mg layered material coated the Sn core. After aging, the support was filtered, washed, and dried at 120℃ to obtain the precursor. (3) The precursor was first calcined at 250°C for 2 hours under N2 atmosphere at a heating rate of 2°C / min to remove the water of crystallization in the precursor. Then it was reduced at 550°C for 3 hours under H2 / N2 atmosphere. Finally, O2 was introduced for oxidation for 2 hours to passivate the metal on the catalyst surface into a stable oxidation state. The catalyst was then naturally cooled to room temperature to obtain catalyst Mg-0.5Sn-TS-1. (4) Weigh 100g of glucose and dissolve it in 100g of water. Add 134g of ethanol to prepare a 30wt% glucose solution. Add the solution to a high-pressure reactor, then add 15g of Mg-0.5Sn-TS-1 catalyst. Seal the reactor and heat it to 100℃. After isomerization reaction at 300rpm for 2h, cool it to room temperature and release the pressure to obtain a product containing fructose. HPLC analysis of the product is shown in Table 1.

[0035] Figure 1 SEM image of the catalyst Mg-0.5Sn-TS-1 prepared in this example. Figure 1 It can be seen that the catalyst particles exhibit a polydisperse spherical or near-spherical morphology, indicating that through co-precipitation, pH gradient control, and subsequent calcination, reduction, and oxidation treatments, the metal components (Mg, Sn) exhibit good dispersion on the TS-1 molecular sieve support, providing sufficient active sites for the glucose isomerization reaction and improving the catalytic performance of the glucose isomerization reaction.

[0036] Example 3: (1) Take 10g of β molecular sieve and treat it with 2ml of 0.1M nitric acid at 60℃ for 0.5h, then wash, dry, and calcine at 500℃ for 3h to obtain the acid-washed β molecular sieve carrier; (2) LiCl2 and In(NO3)3 (total metal loading 8wt%) with a molar ratio of 1:0.3 and β molecular sieve support were dissolved in water. N,N-dimethylformamide was added at 40℃ to complex and prevent hydrolysis. NaOH was slowly added dropwise until the pH was 5.0. The mixture was stirred and aged for 1 h, and the In layer precipitated preferentially. The temperature was then raised to 60℃, and NaOH was slowly added dropwise until the pH was 9.0. The mixture was stirred and aged for 2 h to coat the In core with Li layer. After aging, the support was filtered, washed, and dried at 120℃ to obtain the precursor. (3) The precursor was first calcined at 250°C for 2h under N2 atmosphere at a heating rate of 2°C / min to remove the water of crystallization in the precursor. Then it was reduced at 550°C for 3h under H2 / N2 atmosphere. Finally, O2 was introduced for oxidation for 2h to passivate the metal on the catalyst surface into a stable oxidation state. The catalyst was then naturally cooled to room temperature to obtain the catalyst Li-0.3In-β. (4) Take 5g of Li-0.3In-β catalyst and place it in a fixed-bed reactor. Set the reaction temperature to 90℃, the reaction pressure to 1MPa, and the mass hourly space velocity to 2.0h. -1 Under certain conditions, an isomerization reaction was carried out by passing a 15% glucose aqueous solution through the solution, yielding a product containing fructose. The product was analyzed by HPLC, and the results are shown in Table 1.

[0037] Example 4: (1) Take 15g of Y-type molecular sieve and treat it with 2ml of 0.3M oxalic acid at 60℃ for 1h, then wash, dry, and calcine at 500℃ for 3h to obtain the acid-washed Y-type molecular sieve carrier; (2) Pt(NH3)4Cl2 and La2(NO3)3·6H2O (total metal loading 4wt%) with a molar ratio of 1:0.7 and Y-type molecular sieve support were dissolved in water. Pyrrole complexation was added at 40℃ to prevent hydrolysis. NH3·H2O was slowly added dropwise until the pH was 5.0. The mixture was stirred and aged for 1.5h, and the La layer precipitated preferentially. The temperature was then raised to 60℃, and NH3·H2O was slowly added dropwise until the pH was 9.0. The mixture was stirred and aged for 3h to allow the Pt layered material to coat the La core. After aging, the support was filtered, washed, and dried at 120℃ to obtain the precursor. (3) The precursor was first calcined at 250°C for 2h under N2 atmosphere at a heating rate of 2°C / min to remove the water of crystallization in the precursor. Then it was reduced at 550°C for 3h under H2 / N2 atmosphere. Finally, O2 was introduced for oxidation for 2h to passivate the metal on the catalyst surface into a stable oxidation state. The catalyst was then naturally cooled to room temperature to obtain the catalyst Pt-0.7La-Y. (4) Take 5g of Pt-0.7La-Y catalyst and place it in a fixed-bed reactor. Set the reaction temperature to 90℃, the reaction pressure to 1MPa, and the mass hourly space velocity to 2.0h. -1 Under certain conditions, an isomerization reaction was carried out by passing a 20% glucose aqueous solution through the solution, yielding a product containing fructose. The product was analyzed by HPLC, and the results are shown in Table 1.

[0038] Example 5: (1) Take 20g of ZSM-5 and treat it with 2ml of 0.1M oxalic acid at 60℃ for 1h, then wash, dry, and calcine at 500℃ for 3h to obtain the acid-washed ZSM-5 carrier; (2) MgCl2·H2O and In(NO3)2 (total metal loading 5wt%) with a molar ratio of 1:0.6 and ZSM-5 support were dissolved in water. EDTA was added at 40℃ to complex and prevent hydrolysis. NH3·H2O was slowly added dropwise until the pH was 5.0. The mixture was stirred and aged for 2h, and the In layer precipitated preferentially. The temperature was then raised to 60℃, and NH3·H2O was slowly added dropwise until the pH was 9.0. The mixture was stirred and aged for 4h, so that the Mg layered material coated the In core. After aging, the support was filtered, washed, and dried at 120℃ to obtain the precursor. (3) The precursor was first calcined at 250°C for 2h under N2 atmosphere at a heating rate of 2°C / min to remove the water of crystallization in the precursor. Then it was reduced at 550°C for 3h under H2 / N2 atmosphere. Finally, O2 was introduced for oxidation for 2h to passivate the metal on the catalyst surface into a stable oxidation state. The catalyst was then naturally cooled to room temperature to obtain the catalyst Mg-0.6In-ZSM-5. (4) Weigh 100g of glucose and dissolve it in 100g of water, then add 300g of methanol to prepare a 20wt% glucose solution. Add the solution to a high-pressure reactor, then add 15g of Mg-0.6In-ZSM-5 catalyst, seal the reactor, heat to 100℃ for isomerization reaction for 2h, cool to room temperature, and release the pressure to obtain a product containing fructose. The product was analyzed by HPLC, and the results are shown in Table 1.

[0039] Comparative Example 1: Fructose was prepared using the method of Example 1, except that step (2) was not performed.

[0040] Comparative Example 2: Fructose was prepared using the method of Example 2, the difference being that step (2) only precipitated Mg metal, and the catalyst prepared was denoted as Mg-TS-1.

[0041] Comparative Example 3: Fructose was prepared using the method of Example 2, the difference being that step (2) only precipitated Sn metal, and the prepared catalyst was denoted as Sn-TS-1.

[0042] Comparative Example 4: This comparative example uses an impregnation method to prepare Pt-La-Y catalysts, and the specific steps are as follows: (1) Take 15g of Y-type molecular sieve, treat it with 0.3M oxalic acid at 60℃ for 1h, wash and dry it, and calcine it at 500℃ for 3h to obtain pretreated molecular sieve; (2) Dissolve Pt(NH3)4Cl2 and La2(NO3)3·6H2O in water at a molar ratio of 1:1, add the pretreated Y-type molecular sieve, stir at 60℃ for 2h, and then dry at 120℃; (3) Heat the catalyst to 250℃ / 2h at a heating rate of 2℃ / min to remove the water of crystallization from the precursor, then heat it to 550℃ / 3h to form a stable metal oxidation state on the catalyst surface, and then cool it naturally to room temperature to obtain the catalyst.

[0043] (4) Weigh 100g of glucose and dissolve it in 100g of water, then add 300g of methanol to prepare a 20wt% glucose solution. Add the solution to a high-pressure reactor, then add 15g of Mg-0.6In-ZSM-5 catalyst, seal the reactor, heat to 100℃ for isomerization reaction for 2h, cool to room temperature, and release the pressure to obtain a product containing fructose. The product was analyzed by HPLC, and the results are shown in Table 1.

[0044] Table 1. Catalyst reaction results of the examples and comparative examples.

[0045] As shown in Table 1, the catalysts prepared by the co-precipitation method in Examples 1-5 exhibited better conversion rates, selectivity, and fructose yields in the glucose isomerization to fructose reaction than those in Comparative Examples 1-4. This indicates that the core-shell structured bimetallic coated modified molecular sieve of this invention can significantly improve the catalytic performance of the glucose isomerization to fructose reaction. In Example 5, the catalyst with ZSM-5 as the support and Mg-In (molar ratio of 1:0.6) as the active component showed the best performance, with a glucose conversion rate of 86.4%, a selectivity of 84.2%, and a fructose yield of 72.75%.

[0046] Examples 1 and 1 (Comparative Example 1) show that the activity of the molecular sieve without any metal modification is lower than that of the modified molecular sieve. Examples 2 and 2-3 (Comparative Examples 2-3) show that the catalyst prepared by single-metal deposition performs worse than the bimetallic catalyst. Examples 4 and 4 (Comparative Example 4) show that the catalyst prepared by impregnation method has poorer performance because the metal on the support surface is not as well dispersed as that precipitated by co-precipitation method. These results indicate that the core-shell structure design and bimetallic synergy significantly improve the catalytic performance of the catalyst.

[0047] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for the isomerization of glucose to fructose, characterized in that, Includes the following steps: (1) After acid washing, the molecular sieve is activated by high-temperature calcination to obtain a pretreated molecular sieve; (2) Dissolve the metal compound and pretreated molecular sieve in water, and adjust the pH and temperature of the solution to precipitate the metal onto the carrier to obtain the precursor; (3) The precursor obtained in step (2) is subjected to low-temperature calcination, high-temperature reduction and high-temperature oxidation treatment in sequence to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, The molecular screening in step (1) is selected from one or more of ZSM-5 type, Y type molecular sieve, Beta type, TS-1 molecular sieve and mordenite; the acid concentration of the acid washing treatment is 0.01-10 mol / L, the acid washing time is 0.01-10 h, the calcination temperature is 300-800℃, and the calcination time is 2-5 h.

3. The preparation method according to claim 1, characterized in that, The metal compound in step (2) is selected from at least two of lanthanum salt, antimony salt, tin salt, lithium salt, platinum salt, indium salt, niobium salt and magnesium salt; the total metal loading is 0.01 to 50% of the carrier mass.

4. The preparation method according to claim 1, characterized in that, In step (2), ammonia, ammonium chloride, sodium hydroxide, formic acid, acetic acid, or phosphate are used to adjust the pH of the solution to 1-14.

5. The preparation method according to claim 1, characterized in that, In step (2), after the metal salt is dissolved in water, a complexing agent is added. The complexing agent is selected from one or more of citric acid, EDTA, N,N-dimethylformamide, pyridine, N-methylpiperidine, N-acyl amino acid, and 4-sulfonamide.

6. The preparation method according to claim 1, characterized in that, In step (2), the metal precipitation process specifically includes: stirring at 30-50℃ for 1-4 hours to precipitate high-valence metals, and then heating to 50-70℃ and stirring for 2-6 hours to precipitate low-valence metals.

7. The preparation method according to claim 1, characterized in that, The specific steps (3) include: first, calcining at 200-300℃ for 0.5-5h under N2 atmosphere at a heating rate of 0.1-5℃ / min; then reducing at 400-800℃ for 1-6h under H2 / N2 atmosphere, then oxidizing with O2 after N2 replacement for 1-3h, and finally naturally cooling to room temperature to obtain the desired catalyst.

8. A catalyst for the isomerization of glucose to fructose, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the catalyst according to claim 8 in the reaction of glucose isomerization to fructose.

10. The application according to claim 9, characterized in that, A catalyst was added to a glucose solution to carry out an isomerization reaction, yielding a fructose product.

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