A method for electrochemical synthesis of hexanediamine from acrylonitrile

Abstract

The present application relates to a kind of method for synthesizing hexanediamine by electrochemistry of acrylonitrile, wherein electrolysis is divided into two stages, lead electrode is used in cathode in the first stage electrolysis, nanometer titanium dioxide array tube electrode is used in cathode in the second stage electrolysis, the anode used in two stage electrolysis is all DSA anode of iridium tantalum coating, electrolyte includes acrylonitrile, phosphate and quaternary ammonium base, electrolyte is injected into electrolytic cell to carry out two stage electrolysis reaction, and hexanediamine, a small amount of propylamine and a small amount of 1,3,6-hexane triamine are obtained.The process uses electrochemistry method to directly synthesize hexanediamine from acrylonitrile, process is simple, three wastes are little, and it has higher practical value.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical synthesis, specifically a method for the electrochemical synthesis of hexamethylenediamine from acrylonitrile. Background Technology

[0002] The only traditional methods for producing hexamethylenediamine are the adiponitrile process, the hexanediol process, and the caprolactam process. Among these, the adiponitrile hydrogenation method for producing hexamethylenediamine is almost a global industrial consensus, while the main production methods for adiponitrile are the butadiene process, the acrylonitrile electrolytic dimerization process, and the adipic acid catalytic amination process.

[0003] For a long time, China has relied entirely on imports for adiponitrile, resulting in persistently high prices that severely impact the economic benefits and international competitiveness of my country's nylon industry, hindering the development of nylon 66 and related industries. However, since 2022, China has overcome the challenges in preparing adiponitrile, leading to a surge in both domestic and planned adiponitrile production capacity. It is foreseeable that the hexamethylenediamine industry will soon enter a phase of intense competition based on cost and technology. To cope with this fierce competition, we need to find a new, lower-cost, and shorter process for synthesizing hexamethylenediamine.

[0004] CN109647419A discloses a method for catalytic hydrogenation of adiponitrile to hexamethylenediamine in a batch reactor using a nickel-based catalyst supported on alumina as the active component. Based on existing literature and technologies, the industrialized route for hydrogenating adiponitrile to hexamethylenediamine involves adiponitrile with high toxicity and complex steps. Therefore, finding a one-step direct synthesis of hexamethylenediamine from low-cost raw materials is a highly valuable research direction.

[0005] US5266731A discloses a method for preparing amines by electrochemical reduction of nitrile substances, but it faces problems such as the need for a diaphragm in electrolysis, cumbersome process, and difficulty in electrode preparation. We urgently need to find a simple series method, that is, a diaphragm-free electrolysis method that can reduce acrylonitrile to hexamethylenediamine in two steps without changing the electrolyte. Summary of the Invention

[0006] This invention provides an electrochemical synthesis method for preparing hexamethylenediamine. The process of preparing hexamethylenediamine using this method is simple, produces very little waste, and has high practical value.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for the electrochemical synthesis of hexamethylenediamine from acrylonitrile, the method comprising the following steps:

[0009] (1) Prepare an electrolyte by mixing acrylonitrile, quaternary ammonium base, phosphate and water;

[0010] (2) The electrolyte is passed into two diaphragmless electrolytic cells A and B to carry out a two-stage electrolysis reaction to obtain hexamethylenediamine.

[0011] In this invention, the quaternary ammonium base in step (1) is one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltriethylammonium hydroxide, and adamantyl ammonium hydroxide.

[0012] In this invention, the content of quaternary ammonium base in the electrolyte prepared in step (1) is 0.01wt%-5wt%.

[0013] In this invention, the phosphate mentioned in step (1) is one or more of dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate;

[0014] In this invention, the phosphate content in the electrolyte prepared in step (1) is 5wt%-12wt%.

[0015] In this invention, the acrylonitrile content in the electrolyte in step (1) is 1wt%-20wt%, preferably 5wt%-15wt%;

[0016] The two electrolytic cells A and B used in this invention are both single-chamber diaphragm-free electrolytic cells. They use DC power and employ a constant current method to electrolyze the electrolyte. The voltage is strictly controlled below 10V to prevent the side reaction of hydrogen evolution during water electrolysis from intensifying.

[0017] In this invention, when the reactant conversion rate in electrolytic cell A reaches 60-100% in step (2), the process is switched to electrolytic cell B, and electrolysis is stopped when the reactant conversion rate in electrolytic cell B reaches 60-100%. Preferably, the process is switched to electrolytic cell B when the reactant conversion rate in electrolytic cell A reaches 70-90%, and electrolysis is stopped when the reactant conversion rate in electrolytic cell B reaches 70-90%.

[0018] In this invention, the electrolysis reaction temperature in electrolytic cells A and B in step (2) is 20-50℃.

[0019] In this invention, the current density in electrolytic cell A in step (2) is 500 A / m. 2 -3000A / m 2 The current density in electrolytic cell B is 1500 A / m 2 -3000A / m 2 In electrolytic cell A, the electrodes are lead cathodes and DSA anodes with iridium-tantalum coatings.

[0020] In this invention, in step (2), the electrolytic anode in electrode cell B is an iridium-tantalum coated DSA electrode, and the electrolytic cathode is a nano-titanium dioxide array electrode, preferably a metal-doped modified titanium-based titanium dioxide array electrode. The doping metal is one or more of In, Ir, Zn, Sn, Pb, Ce, Zr, Fe, and Cu, and the doping amount is 1-50 mg / cm³. 2 ;

[0021] The preparation method is as follows: titanium sheet is anodized to obtain nano-titanium dioxide array tube electrode, and then other metals are loaded by impregnation method to obtain metal-doped modified titanium-based titanium dioxide array tube electrode.

[0022] In one specific embodiment, the method for preparing the metal-doped modified titanium-based titanium dioxide array electrode includes:

[0023] a) Using pure titanium plate as the substrate and hydrofluoric acid solution as the anodic oxidation solution, anodize it to obtain nano-titanium dioxide array tube electrodes;

[0024] Preferably, the concentration of the hydrofluoric acid solution is 0.01wt%-10wt%, the anodizing voltage is 5-50V, and the time is 0.5-2h.

[0025] b) Impregnate nano-titanium dioxide array electrodes with metal salt solution and calcine to obtain metal-doped modified titanium dioxide array electrodes.

[0026] The metal salt is one or more nitrates selected from In, Ir, Zn, Sn, Pb, Ce, Zr, Fe, and Cu;

[0027] Preferably, the total mass fraction of metal salt in the impregnation solution is 2-15 wt%, the impregnation time is 1-4 h, the calcination temperature is 400-600℃, and the calcination time is 1-3 h.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention employs a two-stage electrolysis process to synthesize hexamethylenediamine from acrylonitrile in one step. The synthesis route is short, the process is simplified, and it generates almost no wastewater, resulting in high molecular utilization and making it environmentally friendly. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention. While not exhaustive, representative detailed implementation methods and specific operating procedures are provided based on experimental results. The scope of protection of the present invention is not limited to the following embodiments.

[0031] Iridium-tantalum coated DSA electrode: Iridium-tantalum DSA electrode from Suzhou Fenggang Titanium Materials Co., Ltd.

[0032] All other ingredients mentioned in this article are commercially available.

[0033] The analytical method used gas chromatography (GC) to analyze the products. Conditions: Agilent GC column, HP-5, online analysis, two-stage temperature program: initial temperature 20°C, held for 1 minute, then increased to 50°C at a rate of 5°C / min; then increased to 280°C at a rate of 10°C / min. High-purity N2 was used as the carrier gas with a split ratio of 100:1. Injection temperature was 180°C, and the detector was an FID with a detector temperature of 280°C.

[0034] Example 1

[0035] Electrode preparation:

[0036] After polishing the pure titanium substrate with 600, 1500, and 5000 grit sandpaper, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes and then dried in an oven for later use.

[0037] Prepare 100g of an aqueous solution containing 0.05wt% hydrofluoric acid. Use the treated pure titanium substrate as the anode and a graphite electrode as the cathode. Oxidize at 5V for 1 hour to obtain a nano-titanium dioxide array electrode. Remove the electrode and immerse it in deionized water for 5 minutes. Then, place it in an oven and dry for 20 minutes until completely dry before weighing.

[0038] 2g of indium nitrate and 1g of zirconium nitrate were weighed and added to deionized water to prepare 100g of impregnation solution. The dried nano-titanium dioxide array electrode was immersed in the impregnation solution for 4 hours, then removed and rinsed in deionized water for 30 seconds. It was then calcined in a muffle furnace at 400℃ for 2 hours, followed by furnace cooling. The metal doping amount was determined to be 11 mg / cm³ by differential gravity method. 2 Modified titanium-based titanium dioxide array tube electrode.

[0039] Electrolysis reaction:

[0040] Weigh 2g of acrylonitrile, 20g of dipotassium hydrogen phosphate, and 1g of tetraethylammonium hydroxide, add them to deionized water to prepare 200g of electrolyte, and pour it into a container with a 4cm laminar flow rate. 2 The lead electrode is the cathode, 4cm 2 In a single-chamber electrolytic cell (Cell A) with an iridium-tantalum coated DSA electrode as the anode, the cell is equipped with a serpentine condenser and an oil bath for temperature control. Electrolysis begins when the electrolyte temperature reaches 30°C. The current density is controlled at 500 A / m during the reaction. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 5.05h, and the power is cut off after 4h of reaction.

[0041] Pour the reaction solution from tank A into tank B, where tank B is filled with a solution at a depth of 4 cm.2 Metal-doped modified titanium-based titanium dioxide array tube electrode as cathode, 4cm 2 The iridium-tantalum coated DSA electrode forms the anode of a single-chamber electrolytic cell. Cell B is also equipped with a serpentine condenser, and an oil bath is used to control the temperature of the electrolytic cell. Electrolysis begins when the electrolyte temperature reaches 40°C. The controlled current density is 1500 A / m. 2 The condenser temperature is 15℃, and the maximum voltage is controlled to not exceed 10V for constant current electrolysis. The theoretical reaction time required for complete reaction is calculated to be 6.73h, and the power supply is cut off after 6h of reaction.

[0042] Sampling analysis revealed that the conversion rate of the raw material acrylonitrile was 80%, the selectivity of the product hexamethylenediamine was 83%, the selectivity of the main byproduct adiponitrile was 5%, the selectivity of propylamine was 8%, and the selectivity of hexanetriamine was 2%.

[0043] Example 2

[0044] Electrode preparation:

[0045] After polishing the pure titanium substrate with 600, 1500, and 5000 grit sandpaper, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes and then dried in an oven for later use.

[0046] Prepare 100g of an aqueous solution containing 1wt% hydrofluoric acid. Use the treated pure titanium substrate as the anode and a graphite electrode as the cathode. Oxidize at 25V for 0.5h to obtain a nano-titanium dioxide array electrode. Remove and immerse in deionized water for 5min, then place in an oven to dry for 20min until completely dry, and weigh.

[0047] 10g of zirconium nitrate, 0.5g of iridium nitrate, and 1g of lead nitrate were weighed and added to deionized water to prepare 100g of impregnation solution. The dried nano-titanium dioxide array electrode was immersed in the impregnation solution for 4 hours. After removal, it was rinsed in deionized water for 30 seconds, then calcined in a muffle furnace at 450℃ for 3 hours. After furnace cooling, the metal doping amount was determined to be 35mg / cm³ by differential gravity method. 2 Modified titanium-based titanium dioxide array tube electrode.

[0048] Electrolysis reaction:

[0049] Weigh out 10g of acrylonitrile, 24g of dipotassium hydrogen phosphate, 0.5g of tetrabutylammonium hydroxide, and 0.4g of adamantyl ammonium hydroxide, add them to deionized water to prepare 200g of electrolyte, and pour it into a container with a 4cm laminar flow rate. 2 The lead electrode is the cathode, 4cm 2 In a single-chamber electrolytic cell (Cell A) with an iridium-tantalum coated DSA electrode as the anode, the electrolytic cell is equipped with a serpentine condenser and an oil bath is used for temperature control. Electrolysis begins when the electrolyte temperature reaches 40°C. The current density is controlled at 1500 A / m during the reaction. 2The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 8.62h, and the power supply is cut off after 6.90h of reaction.

[0050] Pour the reaction solution from tank A into tank B, with tank B having a 4cm gap. 2 Metal-doped modified titanium-based titanium dioxide array tube electrode as cathode, 4cm 2 The iridium-tantalum coated DSA electrode forms the anode of a single-chamber electrolytic cell. Cell B is also equipped with a serpentine condenser, and an oil bath is used to control the temperature of the electrolytic cell. Electrolysis begins when the electrolyte temperature reaches 30°C. The controlled current density is 2500 A / m³. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 20.10h, and the power is cut off after 18h of reaction.

[0051] Sampling analysis revealed that the conversion rate of the raw material acrylonitrile was 90%, the selectivity of the product hexamethylenediamine was 88%, and the main byproducts adiponitrile had a selectivity of 3%, propylamine a selectivity of 4%, and hexanetriamine a selectivity of 4%.

[0052] Example 3

[0053] Electrode preparation:

[0054] After polishing the pure titanium substrate with 600, 1500, and 5000 grit sandpaper, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes and then dried in an oven for later use.

[0055] Prepare 100g of an 8wt% hydrofluoric acid aqueous solution. Use the treated pure titanium substrate as the anode and a graphite electrode as the cathode. Oxidize at 50V for 1.5h to obtain a nano-titanium dioxide array electrode. Remove and immerse in deionized water for 5min, then place in an oven to dry for 20min until completely dry, and weigh.

[0056] 2g of zirconium nitrate, 5g of cerium nitrate, 1g of tin nitrate, and 1g of ferric nitrate were weighed and added to deionized water to prepare 100g of impregnation solution. The dried nano-titanium dioxide array electrode was immersed in the impregnation solution for 4 hours. After removal, it was rinsed in deionized water for 30 seconds, then calcined in a muffle furnace at 500℃ for 2 hours. After furnace cooling, the metal doping amount was determined to be 29mg / cm³ by differential gravity method. 2 Modified titanium-based titanium dioxide array tube electrode.

[0057] Electrolysis reaction:

[0058] Weigh out 20g of acrylonitrile, 15g of dipotassium hydrogen phosphate, 2g of tetrabutylammonium hydroxide, 0.5g of benzyltriethylammonium hydroxide, and 0.5g of tetrapropylammonium hydroxide, and add them to deionized water to prepare 200g of electrolyte. Pour the electrolyte into a container with a flow rate of 4cm.2 The lead electrode is the cathode, 4cm 2 In a single-chamber electrolytic cell (Cell A) with an iridium-tantalum coated DSA electrode as the anode, the electrolytic cell is equipped with a serpentine condenser and an oil bath for temperature control. Electrolysis begins when the electrolyte temperature reaches 25°C. The current density is controlled at 3000 A / m during the reaction. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 8.62h, and the power supply is cut off after 6.90h of reaction.

[0059] Pour the reaction solution from tank A into tank B, with tank B having a 4cm gap. 2 Metal-doped modified titanium-based titanium dioxide array tube electrode as cathode, 4cm 2 The iridium-tantalum coated DSA electrode forms the anode of a single-chamber electrolytic cell. Cell B is also equipped with a serpentine condenser, and an oil bath is used to control the temperature of the electrolytic cell. Electrolysis begins when the electrolyte temperature reaches 40°C. The control current is 3000 A / m. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 33.50h, and the power is cut off after 30.02h of reaction.

[0060] Sampling analysis revealed that the conversion rate of the raw material acrylonitrile was 85%, the selectivity of the product hexamethylenediamine was 85%, the selectivity of the main byproduct adiponitrile was 4%, the selectivity of propylamine was 0.8%, and the selectivity of hexanetriamine was 9%.

[0061] Example 4

[0062] Electrode preparation:

[0063] After polishing the pure titanium substrate with 600, 1500, and 5000 grit sandpaper, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes and then dried in an oven for later use.

[0064] Prepare 100g of an aqueous solution containing 1wt% hydrofluoric acid. Use the treated pure titanium substrate as the anode and a graphite electrode as the cathode. Oxidize at 25V for 0.5h to obtain a nano-titanium dioxide array electrode. Remove and immerse in deionized water for 5min, then place in an oven to dry completely for 20min.

[0065] The electrode was placed in a muffle furnace and calcined at 450°C for 2 hours, then cooled with the furnace to obtain a common titanium dioxide array electrode without metal doping modification.

[0066] Electrolysis reaction:

[0067] Weigh 10g acrylonitrile, 15g dipotassium hydrogen phosphate, 5g tetrabutylammonium hydroxide, and 0.4g adamantyl ammonium hydroxide, add them to deionized water to prepare 200g of electrolyte, and pour into a container with a 4cm laminar flow rate. 2 The lead electrode is the cathode, 4cm 2 In a single-chamber electrolytic cell (Cell A) with an iridium-tantalum coated DSA electrode as the anode, the electrolytic cell is equipped with a serpentine condenser and an oil bath is used for temperature control. Electrolysis begins when the electrolyte temperature reaches 40°C. The current density is controlled at 1500 A / m during the reaction. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 8.62h, and the power supply is cut off after 6.90h of reaction.

[0068] Pour the reaction solution from tank A into tank B, with tank B having a 4cm gap. 2 Ordinary titanium dioxide array tube electrodes are cathodes, 4cm 2 The iridium-tantalum coated DSA electrode forms the anode of a single-chamber electrolytic cell. Cell B is also equipped with a serpentine condenser, and an oil bath is used to control the temperature of the electrolytic cell. Electrolysis begins when the electrolyte temperature reaches 30°C. The controlled current density is 2500 A / m³. 2 The condenser temperature is 15℃, constant current electrolysis is used, and the maximum voltage is controlled not to exceed 10V. The theoretical reaction time required for complete reaction is calculated to be 20.10h, and the power is cut off after 18h of reaction.

[0069] Sampling analysis revealed a 77% conversion rate of acrylonitrile, a 35% selectivity for hexamethylenediamine, a 45% selectivity for the main byproduct adiponitrile, a 10% selectivity for propylamine, and a 4% selectivity for hexanetriamine.

[0070] Comparative Example 1

[0071] Compared to Example 2, a two-stage electrolysis was still used, the only difference being that the cathode in electrolytic cell B was a pure titanium electrode. Sampling analysis revealed that the conversion rate of the raw material acrylonitrile was 85%, the selectivity of the products hexamethylenediamine was 0%, the selectivity of propylamine was 0%, the selectivity of hexanetriamine was 0%, and the selectivity of the main byproduct adiponitrile was 84%.

[0072] Comparative Example 2

[0073] Compared with Example 2, the difference is that only the electrodes in Electrolytic Cell A are used for the first stage of electrolysis reaction. After reaching the endpoint, the sample is analyzed and the conversion rate of the raw material acrylonitrile is 87%, the selectivity of the products hexamethylenediamine is 0%, the selectivity of propylamine is 0%, the selectivity of hexanetriamine is 0%, and the selectivity of the main by-product adiponitrile is 85%.

[0074] Comparative Example 3

[0075] Compared to Example 2, the difference lies in that only the first stage of electrolysis in electrolytic cell A is performed, and the cathode of electrolytic cell A is the prepared metal-doped modified titanium-based titanium dioxide array electrode, with the electrode preparation method being the same as in Example 2. After reaching the endpoint, sample analysis revealed a 66% conversion rate for the raw material acrylonitrile, a 60% selectivity for the products hexamethylenediamine, a 4% selectivity for propylamine, a 2% selectivity for hexanetriamine, and a 26% selectivity for the main byproduct adiponitrile.

[0076] Table 1. Raw material conversion rate and selectivity of each product

[0077] serial number Acrylonitrile (%) Hexamethylenediamine (%) Adiponitrile (%) Acetylmethane (%) Hexanetriamine (%) Example 1 80 83 5 8 2 Example 2 90 88 3 4 4 Example 3 85 85 4 0.8 9 Example 4 77 35 45 10 4 Comparative Example 1 85 0 84 0 0 Comparative Example 2 87 0 85 0 0 Comparative Example 3 66 60 26 4 2

Claims

1. A process for the electrochemical synthesis of hexanediamine from acrylonitrile, characterized in that, The method comprises the following steps: (1) mixing acrylonitrile, quaternary ammonium base, phosphate, and water to prepare an electrolyte; (2) passing the electrolyte into two electrolytic cells A and B to perform two-stage electrolysis reaction to prepare hexanediamine; The two electrolytic cells A and B are both single-chamber diaphragm-free electrolytic cells; in the electrolytic cell A, the cathode is a lead electrode, and the anode is a DSA electrode coated with iridium and tantalum; in the electrolytic cell B, the cathode is a nano-titanium dioxide array tube electrode or a metal-doped modified titanium-based titanium dioxide array tube electrode, the doped metal is one or more of In, Ir, Zn, Sn, Pb, Ce, Zr, Fe, and Cu, and the anode is a DSA electrode coated with iridium and tantalum.

2. The method of claim 1, wherein, The quaternary ammonium base in step (1) is one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltriethylammonium hydroxide, and adamantylammonium hydroxide.

3. The method of claim 2, wherein, The content of the quaternary ammonium base in the electrolyte is 0.01wt%-5wt%.

4. The method of claim 1, wherein, The phosphate in step (1) is one or more of dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate.

5. The method of claim 4, wherein, The content of the phosphate in the electrolyte is 5wt%-12wt%.

6. The method of claim 1, wherein, The content of acrylonitrile in the electrolyte in step (1) is 1wt%-20wt%.

7. The method of claim 6, wherein, The content of acrylonitrile in the electrolyte is 5wt%-15wt%.

8. The method of claim 1, wherein, In step (2), the two electrolytic cells A and B use a direct current power source, and the electrolyte is subjected to electrolysis reaction by a constant current method.

9. The method of claim 1, wherein, The current density in the A electrolytic cell of step (2) is 500 A / m 2 - 3000 A / m 2 .

10. The method of claim 1, wherein, The current density in the B electrolytic cell of step (2) is 1500 A / m 2 - 3000 A / m 2 .

11. The method of claim 1, wherein, The nano-titanium dioxide array tube electrode is prepared by an anodic oxidation method using a hydrofluoric acid solution as an anodic oxidation solution.

12. The method of claim 11, wherein, The concentration of the hydrofluoric acid solution is 0.01wt%-10wt%, the anodic oxidation voltage is 5-50V, and the time is 0.5-2h.

13. The method of claim 1, wherein, The metal doping amount in the metal-doped modified titanium-based titanium dioxide array tube electrode is 1-50 mg / cm 2 .

14. The method of claim 1, wherein, The metal-doped modified titanium-based titanium dioxide array tube electrode in the electrolytic cell B is obtained by impregnating a nano-titanium dioxide array tube electrode in an aqueous metal salt solution and then calcining.

15. The method of claim 14, wherein, The total mass fraction of the aqueous metal salt solution is 2-15wt%, and the impregnation time is 1-4h; and / or: the calcination temperature after doping is 400-600℃, and the time is 1-3h.