Preparation method of magnesium modified porous material catalyst and application thereof to catalytic production of hydrogen peroxide

Abstract

The application provides a preparation method of a magnesium-modified porous material catalyst and application of the magnesium-modified porous material catalyst in catalysis of hydrogen peroxide production. A porous covalent triazine framework containing 2,2'-bipyridine units and a soluble magnesium salt are dispersed in a water polar solvent in sequence, then a certain amount of an acid and a chelating agent are added, a chelation reaction is carried out at a certain temperature, and finally, after filtration, washing and drying, the target product of the magnesium salt chelated in the inner hole of the covalent triazine framework is obtained. The preparation process of the magnesium-modified porous material is simple, has little pollution to the environment, and has excellent performance of catalyzing oxygen reduction into hydrogen peroxide. The magnesium-modified porous material exhibits 85-88% two-electron selectivity (the rest is reduced into water, no pollution) and high reaction activity.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of an electrocatalyst, which is applied to the field of green industrial synthesis represented by electrocatalytic production of hydrogen peroxide. BACKGROUND

[0002] Hydrogen peroxide (H2O2) is an important chemical product, which has the advantages of high active oxygen content, strong oxidation and green environmental protection, and has a wide range of applications in chemical synthesis, paper bleaching, wastewater treatment, disinfection and sterilization, fuel cells and many other fields. At present, hydrogen peroxide is generally prepared by anthraquinone method in industry, which has the disadvantages of high energy consumption and high pollution, and needs to use hydrogen as hydrogen source, which cannot meet the requirements of green and sustainable development. In contrast, the two-electron oxygen reduction reaction (2e - ORR) can use protons in water as the source of hydrogen, and realize the synthesis of hydrogen peroxide under the drive of electric energy, which is energy-saving and environmentally friendly, and has great development potential. Therefore, 2e - ORR electric synthesis of hydrogen peroxide has attracted widespread attention. In the process of 2e - ORR reaction, the catalyst plays a very key role, and an efficient catalyst can effectively reduce the overpotential of the reaction and improve the activity and selectivity of the reaction. Covalent triazine framework (CTF) is a nitrogen-containing aromatic polymer framework with triazine ring. The highly porous nature provides a large specific surface area for itself, thereby providing a large number of adsorption sites for gallium salt. The excellent stability endows CTF with great potential as an ORR electrocatalyst base material. It is reported that magnesium monatomic material with Mg-N x as the central unit can be used as a high-activity catalyst for oxygen reduction reaction (Nature Communications, DOI:10.1038 / s41467-020-14565-w), but the catalyst in the report is prepared by pyrolysis, and the preparation process is complex and the reaction conditions are harsh. The selectivity of the reaction of oxygen to hydrogen peroxide is low. In contrast, the solvent thermal method is selected in the present application, which not only has simple operation and mild preparation conditions, but also can obtain the target product in one step. The designed material has good selectivity of oxygen two-electron reduction to hydrogen peroxide. SUMMARY

[0003] In view of the above technical problems, the present application provides a method for preparing magnesium-modified porous material by non-pyrolysis method and catalyzing hydrogen peroxide production, which comprises the following steps:

[0004] Step 1: uniformly disperse covalent triazine framework CTF and soluble magnesium salt in deionized water to obtain a dispersion liquid.

[0005] The mass ratio of CTF and soluble magnesium salt is 1:0.5-1:5, and the dispersion degree of CTF in deionized water is 1-3 g / L -1 .

[0006] The CTF is [2,2'-bipyridyl]-5,5'-diylmethanol, and the benzene monomer biphenyl-4,4'-dimethylformamidine or p-phenylenediamine is mixed, cesium carbonate is added, and the obtained solid product is washed, freeze-dried, and obtained.

[0007] The soluble magnesium salt includes magnesium acetate, magnesium nitrate hexahydrate, magnesium sulfate, and the like.

[0008] The second step is to add a pH adjuster and a chelating agent to the dispersion liquid in batches and multiple times, and after ultrasonic homogenization, the reaction is carried out by heating and stirring.

[0009] The pH value of the dispersion liquid is 0-6, and the pH adjuster used includes nitric acid, acetic acid, and the like. The chelating agent added in the application is a stable ligand that can provide oxygen atom coordination. The CTF contains a large number of bidentate nitrogen binding sites, and the entire environment is negatively charged; the chelating agent contains oxygen coordination sites, and some of them are weakly acidic (ionized and negatively charged). Therefore, the positively charged magnesium ions are well combined with the CTF and the chelating agent, and the prepared complex has a stable structure.

[0010] The heating temperature is 30-100°C, and the time is 6-24 h.

[0011] The third step is to filter, wash, and dry to obtain the catalyst.

[0012] In some embodiments, one or more non-aqueous polar solvents such as methanol, tetrahydrofuran, N-N-dimethylformamide (DMF), and the like are repeatedly washed at least three times, and after filtration, the sample is placed in a vacuum drying oven for drying for 6-24 h to obtain the catalyst. Taking phenanthrenequinone as an example, the preparation process of the prepared magnesium-modified porous material and the corresponding structural formula are shown in the following formula:

[0013]

[0014] The above preparation process is simple, has little pollution to the environment, and the prepared magnesium-modified porous material has excellent performance of electrocatalytic oxygen reduction to hydrogen peroxide. It shows 85-89% two-electron selectivity and high reaction activity. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 , a is the ORR graph of the sample of Example 1, b is the hydrogen peroxide selectivity of the sample of Example 1, and c is the number of transferred electrons of the sample of Example 1.

[0016] Figure 2, a is the ORR graph of the sample of Example 2, b is the hydrogen peroxide selectivity of the sample of Example 2, c is the number of transferred electrons of the sample of Example 2.

[0017] Figure 3 , a is the ORR graph of the sample of Example 3, b is the hydrogen peroxide selectivity of the sample of Example 3, c is the number of transferred electrons of the sample of Example 3.

[0018] Figure 4 , a is the ORR graph of the sample of Example 4, b is the hydrogen peroxide selectivity of the sample of Example 4, c is the number of transferred electrons of the sample of Example 4.

[0019] Figure 5 , a is the ORR graph of the sample of Example 5, b is the hydrogen peroxide selectivity of the sample of Example 5, c is the number of transferred electrons of the sample of Example 5.

[0020] Figure 6 , is the XRD graph of Examples 1, 2. DETAILED DESCRIPTION

[0021] Characterization conditions:

[0022] The ORR test method in the embodiments of the present application: take 980 μL of water, 980 μL of ethanol and 40 μL of Nafion, mix well, then take 1 mg of the sample, add it to the solution, ultrasonic for 2 h, so that it is uniformly dispersed. Then the obtained slurry is dropped on the rotating ring-disk electrode, and the loading is 0.02 mg cm -2 Then a reference electrode (mercury oxide), a counter electrode (carbon rod), and a working electrode three-electrode system are used to test in an oxygen-saturated 0.1 M KOH solution.

[0023] Preparation of covalent triazine framework (CTF):

[0024] In a round-bottom flask, add [2,2'-bipyridyl]-5,5'-diylmethanol, benzene monomer biphenyl-4,4'-diimidazole or p-phenylenediamine and cesium carbonate yellow suspension to the dimethyl sulfoxide solution, wash the precipitate in dilute hydrochloric acid to remove residual cesium carbonate, then wash with water, ethanol and tetrahydrofuran several times. The filtered solid is freeze-dried to obtain a yellow CTF.

[0025] Example 1:

[0026] In a round-bottom flask (25 mL), add 1.2 ml Mg(CH3COO)2 solution (120.32 mg Mg(CH3COO)2 dissolved in 100 ml water), 5 mg CTF, 2 ml deionized water, and ensure that the dispersity of Mg(CH3COO)2, CTF in up water is 0.36 g L-1 1.25 g L -1 Then add 0.5 ml of nitric acid to adjust the pH of the solution to 0-3, and the dispersion of nitric acid in the system is 0.02 g / L. -1 The mixture was then sonicated until homogeneous, heated and stirred at 65°C for 2 hours, and then the ligand o-naphthol was added. 100 μl of o-naphthol solution (2.03 mg o-naphthol dissolved in 900 μl of water) was added every 30 minutes, and the cycle was repeated three times. Heating and stirring at 65°C continued for 6 hours. After the reaction was complete, the precipitate was obtained by filtration. The precipitate was washed several times with methanol and ethanol to remove residual Mg(CH3COO)2. Finally, it was dried in a vacuum drying oven for 12 hours to obtain the covalent triazine framework / magnesium salt complex.

[0027] Figure 1 a shows the ORR curve of the sample from Example 1, with an initial potential of 0.74 V vs RHE and a limiting current density of 1.04 mA cm⁻¹. -2 The half-wave potential is 0.54 V vs RHE. Figure 1 b represents the hydrogen peroxide selectivity of the sample from Example 1, which shows a selectivity of 88.42%. Figure 1 c represents the number of transferred electrons in the sample of Example 1, which can be calculated to be 2.23.

[0028] Figure 6 The XRD pattern of the sample in Example 1, combined with the standard card, shows that magnesium did not form compounds such as oxide salts, and the presence of magnesium salts and magnesium acetate indicates that magnesium is chelated with CTF and small molecule chelating agents in the form of single atoms, thus largely maintaining the crystal structure of CTF. This also indicates the successful preparation of the covalent triazine framework / magnesium salt complex.

[0029] Example 2:

[0030] Add 1.2 ml of Mg(CH3COO)2 solution (120.32 mg Mg(CH3COO)2 dissolved in 100 ml of water), 5 mg CTF, and 2 ml of deionized water to a 25 mL round-bottom flask; then add 0.5 ml of nitric acid to adjust the pH of the solution to 0-3. The dispersion of nitric acid in the system is 0.02 g / L. -1 The mixture was then sonicated until homogeneous, heated and stirred at 65°C for 2 hours, and then the ligand phenanthrenequinone was added. 100 μL of phenanthrenequinone solution (7.92 mg dissolved in 900 μL of water) was added every 30 minutes, and the cycle was repeated three times. Heating and stirring at 65°C continued for 6 hours. After the reaction was complete, the precipitate was obtained by filtration. The precipitate was washed several times with methanol and ethanol to remove residual Mg(CH3COO)2. Finally, it was dried in a vacuum oven for 12 hours to obtain the covalent triazine framework / magnesium salt complex.

[0031] Figure 2 a shows the ORR curve of the sample from Example 2, with an initial potential of 0.73 V vs RHE and a limiting current density of 1.11 mA / cm². -2 The half-wave potential is 0.56 V vs RHE. Figure 2 b represents the hydrogen peroxide selectivity of the sample from Example 2, which shows a selectivity of 87.82%. Figure 2 c represents the number of transferred electrons in the sample of Example 2, which can be calculated to be 2.24.

[0032] Figure 6 The XRD pattern of the sample in Example 1, combined with the standard card, shows that magnesium did not form compounds such as oxide salts. This indicates that magnesium is chelated with CTF and small molecule chelating agents in the form of single atoms, thus largely maintaining the crystal structure of CTF. This also shows the successful preparation of the covalent triazine framework / magnesium salt complex.

[0033] Example 3:

[0034] Add 1.2 ml of Mg(CH3COO)2 solution (120.32 mg Mg(CH3COO)2 dissolved in 100 ml of water), 5 mg CTF, and 2 ml of deionized water to a 25 mL round-bottom flask; then add 0.5 ml of nitric acid to adjust the pH of the solution to 0-3. The dispersion of nitric acid in the system is 0.02 g / L. -1 The mixture was then sonicated until homogeneous, heated and stirred at 65°C for 2 hours, and then the ligand salicylic acid was added. 100 μL of salicylic acid solution (5.25 mg dissolved in 900 μL of water) was added every 30 minutes, and the cycle was repeated three times. Heating and stirring at 65°C continued for 6 hours. After the reaction was complete, the precipitate was obtained by filtration. The precipitate was washed several times with methanol and ethanol to remove residual Mg(CH3COO)2. Finally, it was dried in a vacuum drying oven for 12 hours to obtain the covalent triazine framework / magnesium salt complex.

[0035] Figure 3 a shows the ORR curve of the sample from Example 3, with an initial potential of 0.78 V vs RHE and a limiting current density of 1.71 mA cm⁻¹. -2 The half-wave potential is 0.78 V vs RHE. Figure 3 b represents the hydrogen peroxide selectivity of the sample in Example 3, which shows a selectivity of 65.7%. Figure 3 c represents the number of transferred electrons in the sample of Example 3, which can be calculated to be 2.67.

[0036] Example 4:

[0037] Add 1.2 ml of Mg(CH3COO)2 solution (120.32 mg Mg(CH3COO)2 dissolved in 100 ml of water), 5 mg CTF, and 2 ml of deionized water to a 25 mL round-bottom flask; then add 0.5 ml of nitric acid to adjust the pH of the solution to 0-3. The dispersion of nitric acid in the system is 0.02 g / L. -1 The mixture was then sonicated until homogeneous, heated and stirred at 65°C for 2 hours, and then benzoic acid ligand was added. 100 μL of benzoic acid solution (4.8 mg dissolved in 900 μL of water) was added every 30 minutes, and the cycle was repeated three times. Heating and stirring at 65°C continued for 6 hours. After the reaction was complete, the precipitate was obtained by filtration. The precipitate was washed several times with methanol and ethanol to remove residual Mg(CH3COO)2. Finally, it was dried in a vacuum oven for 12 hours to obtain the covalent triazine framework / magnesium salt complex.

[0038] Figure 4 a shows the ORR curve for sample 4, with an initial potential of 0.74 V vs. RHE and a limiting current density of 1.14 mA / cm². -2 The half-wave potential is 0.51V vs RHE. Figure 4 b represents the hydrogen peroxide selectivity of the sample in Example 4, which shows a selectivity of 78.16%. Figure 4 c represents the number of transferred electrons in the sample of Example 4, which can be calculated to be 2.44.

[0039] Example 5:

[0040] Add 1.2 ml of Mg(CH3COO)2 solution (120.32 mg Mg(CH3COO)2 dissolved in 100 ml of water), 5 mg CTF, and 2 ml of deionized water to a 25 mL round-bottom flask; then add 0.5 ml of nitric acid to adjust the pH of the solution to 0-3. The dispersion of nitric acid in the system is 0.02 g / L. -1 The mixture was then sonicated until homogeneous, heated and stirred at 65°C for 2 hours, and then the ligand salicylol was added. 100 μL of salicylol solution (4.72 mg dissolved in 900 μL of water) was added every 30 minutes, and the cycle was repeated three times. Heating and stirring at 65°C continued for 6 hours. After the reaction was complete, the precipitate was obtained by filtration. The precipitate was washed several times with methanol and ethanol to remove residual Mg(CH3COO)2. Finally, it was dried in a vacuum drying oven for 12 hours to obtain the covalent triazine framework / magnesium salt complex.

[0041] Figure 5 a shows the ORR curve for sample 5, with an initial potential of 0.7 V vs. RHE and a limiting current density of 0.99 mA / cm². -2The half-wave potential is 0.57 V vs RHE. Figure 5 b represents the hydrogen peroxide selectivity of the sample from Example 5, which shows a selectivity of 72.5%. Figure 5 c represents the number of transferred electrons in the sample of Example 5, which can be calculated to be 2.55.

Claims

1. A method for preparing a magnesium-modified porous material catalyst, characterized in that, The preparation steps include the following: S1. A covalent triazine framework CTF and a soluble magnesium salt are uniformly dispersed in deionized water to obtain a dispersion. The soluble magnesium salt is selected from any one of magnesium acetate, magnesium nitrate, and magnesium sulfate. The CTF is [2,2'-bipyridyl]-5,5'-dimethylmethanol. After mixing benzene monomer biphenyl-4,4'-dimethylamidine or terephthalamide, cesium carbonate is added. After precipitation, the resulting solid product is washed and freeze-dried. S2. Add a pH adjuster to the dispersion described in S1, followed by a chelating agent. After ultrasonic homogenization, heat and stir the mixture to induce a reaction. The chelating agent is selected from one or two of phenanthrenequinone and o-naphthol. S3. After filtration, washing and drying, the catalyst is obtained. The magnesium-modified porous material catalyst is a covalent triazine framework / magnesium salt complex.

2. The preparation method according to claim 1, characterized in that, The mass ratio of CTF to soluble magnesium salt in S1 is 1:0.5 to 1:5, and the dispersibility of CTF in deionized water is 1 to 3 g / L. -1 .

3. The preparation method according to claim 1, characterized in that, The molar ratio of the chelating agent to the magnesium metal atoms in the soluble magnesium salt is 1.0~2.0:

1.

4. The preparation method according to claim 1, characterized in that, The heating temperature in S2 is 30~100℃, and the time is 6~24 h.

5. The covalent triazine framework / magnesium salt complex prepared by the preparation method according to any one of claims 1-4 is used as a catalyst for the production of hydrogen peroxide.

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