Preparation and application of a covalent organic framework-supported catalyst

Abstract

The invention relates to the technical field of catalysts and provides a preparation method and application of a covalent organic skeleton-supported catalyst. The covalent organic skeleton-supported catalyst comprises: a covalent organic framework synthesized by an aldehyde-amine condensation reaction, and a noble metal supported on the covalent organic framework, wherein the loading amount of the noble metal is 4.1-5.7%. The catalyst of the invention has high catalytic activity in rubber hydrogenation, is particularly suitable for hydrogenation of nitrile rubber, and achieves a catalytic efficiency of more than 90% at a relatively low addition amount. Meanwhile, the catalyst can achieve a recovery rate of up to 98.5% of the noble metal after magnetic modification, and the catalytic activity will not be significantly reduced after recovery.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to the preparation and application of a covalent organic framework-supported catalyst. Background Art

[0002] Nitrile rubber has excellent mechanical properties and oil resistance due to the cyanide group in its molecular chain, but its aging resistance is poor due to the unsaturated carbon-carbon double bonds on its main chain. Therefore, we perform hydrogenation reaction on it to increase the saturation of the main chain of nitrile rubber, so that the mechanical properties and oil resistance of hydrogenated nitrile rubber are still excellent, and the aging resistance and oil resistance are greatly improved.

[0003] The hydrogenation catalysts of nitrile rubber are mainly divided into two categories: homogeneous catalysts and heterogeneous catalysts. Heterogeneous catalysts are popular because they are easy to recycle and reuse. Heterogeneous catalysts are catalysts that load precious metal catalysts on porous carrier materials by impregnation. However, heterogeneous catalysts often have the problem of precious metal shedding after one experiment. For example, patent application CN110756225A discloses a metal / MOFs nanocatalyst and its preparation method and application. At 30°C, its hydrogenation degree can be as high as more than 90%, but this catalyst cannot achieve repeated hydrogenation experiments. The reason is that after hydrogenation, the precious metal will fall off in large quantities, resulting in a significant reduction in the activity of the catalyst during the second hydrogenation, and thus it is impossible to achieve a high hydrogenation degree during the second hydrogenation. In order to improve the recycling rate of precious metals, patent application CN114797991A discloses a rubber hydrogenation catalyst and its preparation method, recycling method and application. In the scheme, in view of the problem of a large amount of precious metals falling off, a scheme of using an adsorbent to recycle the fallen precious metals and then load them is proposed, which can improve the utilization rate of precious metals, but this method is too complicated and the experimental steps are cumbersome. In addition, in the early research of this research group, the technical scheme disclosed in patent application CN103537304A is specifically: by modifying the silane coupling agent, the falling of precious metals can be better avoided, and the catalytic activity of the recovered catalyst is retained. When the catalyst is reused for 3 times, it can still achieve 90% hydrogenation degree, but the activity of the catalyst is low, and the recovery rate of the catalyst is not high, which is less than 80%.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The invention provides a preparation method and application of a covalent organic framework-supported catalyst, which are used to solve the defects of the heterogeneous catalyst used for the catalytic hydrogenation of nitrile rubber in the prior art, that is, it is difficult to recover the precious metal and it is difficult to balance the catalytic activity. A covalent organic framework with a polyphenyl ring structure of C=N is synthesized by an aldehyde-amine condensation reaction, and the precious metal is supported on COFs by a simple impregnation method to realize the preparation of the heterogeneous catalyst. The catalyst has high catalytic activity, and can achieve a hydrogenation degree of more than 90% when the addition amount is more than 0.8%. At the same time, the catalyst can be efficiently recovered after magnetic modification, and the recovery efficiency of the catalyst is as high as 98.5%, and the catalytic activity will not be significantly reduced after recovery.

[0006] Specifically, the present invention provides a covalent organic framework supported catalyst, comprising: a covalent organic framework synthesized by an aldehyde-amine condensation reaction, and a noble metal supported on the covalent organic framework, wherein the loading amount of the noble metal is 4.1-5.7%.

[0007] The present invention has been found in experiments that in order to overcome the defects of the heterogeneous catalyst used for the catalytic hydrogenation of nitrile rubber, namely, the difficulty in recovering the precious metals and the difficulty in maintaining the catalytic activity, the covalent organic framework synthesized by the aldehyde-amine condensation reaction and the precious metal loading amount of 4.1-5.7% achieved thereon play a key role in the recovery rate of the precious metals and the catalytic activity of the recovered catalyst.

[0008] According to the covalent organic framework-supported catalyst provided by the present invention, the covalent organic framework is synthesized by a solvent thermal method from a precursor containing an aldehyde group and a precursor containing an amino group;

[0009] Preferably, the precursor containing an aldehyde group is one or more of p-nitrobenzaldehyde, terephthalaldehyde and 1,4-di(4-aldehydephenyl)benzene; and / or, the precursor containing an amino group is one or more of 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetrakis(4-aminophenyl)methane and melamine;

[0010] More preferably, the molar ratio of the precursor containing an aldehyde group to the precursor containing an amino group is 0.2-0.4:0.5-0.7.

[0011] More preferably, the aldehyde-containing precursor is terephthalaldehyde, and the amino-containing precursor is tetrakis(4-aminophenyl)methane; tetrakis(4-aminophenyl)methane with a three-dimensional structure and simple terephthalaldehyde are used as monomers to synthesize three-dimensional COFs materials with superior performance; in order to minimize impurities in the synthesized product, the molar ratio of the two monomers is controlled to be 1:2.

[0012] According to the covalent organic framework-supported catalyst provided by the present invention, the noble metal is supported on the covalent organic framework by an impregnation method.

[0013] Preferably, the noble metal is Pd, Rh, Ru or Ir;

[0014] More preferably, the noble metal is Pd.

[0015] According to the covalent organic framework-supported catalyst provided by the present invention, the covalent organic framework and Fe3O4 form a core-shell structure with Fe3O4 as the core;

[0016] The present invention also provides a method for preparing the covalent organic framework-supported catalyst as described above, wherein the noble metal is supported on the covalent organic framework synthesized by the aldehyde-amine condensation reaction.

[0017] According to the preparation method of the covalent organic framework-supported catalyst provided by the present invention, the preparation process of the covalent organic framework comprises: mixing a precursor containing an aldehyde group and a precursor containing an amino group with a solvent, and synthesizing the covalent organic framework by a solvothermal method under the catalysis of an acid and a nitrogen atmosphere;

[0018] Wherein, the solvent is one or more of mesitylene, 1,4-dioxane and N-methylpyrrolidone; preferably, the solvent is a mixed solution of mesitylene and 1,4-dioxane, which exhibits better crystallinity and thermal stability than other single solvents and other co-solvent combinations; more preferably, the solvent is a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 7:3;

[0019] And / or, the acid is one or more of acetic acid, hydrochloric acid and nitric acid; preferably, the acid is acetic acid; more preferably, the ratio of the amount of acetic acid added to the molar amount of the precursor containing an aldehyde group is 2 to 18:6, and further preferably, the concentration of the acetic acid is 4 to 10:6;

[0020] And / or, the temperature of the solvothermal method is 90-140°C; preferably, the temperature of the solvothermal method is 110-120°C;

[0021] And / or, the solvent thermal method lasts for 60 to 120 hours; preferably, the solvent thermal method lasts for 60 to 80 hours.

[0022] According to the covalent organic framework supported catalyst provided by the present invention, the preparation process of the covalent organic framework comprises: using an aldehyde-containing precursor, an amino-containing precursor and Fe3O4 as raw materials, synthesizing by a solvent thermal method to obtain a core-shell structure with Fe3O4 as the core; Fe3O4 can also be replaced by a magnetic material such as ferric oxide;

[0023] Preferably, the molar ratio of the precursor containing aldehyde groups, the precursor containing amino groups and Fe3O4 is 0.2-0.4:0.5-0.7:0.1-0.2;

[0024] According to the covalent organic framework-supported catalyst provided by the present invention, the process of loading the precious metal onto the covalent organic framework comprises: mixing the precious metal with the covalent organic framework in the form of acetate, then adding deionized water and stirring evenly, then adding NaBH4 aqueous solution, continuing to stir, and finally vacuum drying to obtain the covalent organic framework-supported catalyst.

[0025] The present invention also provides an application of the above-mentioned covalent organic skeleton-supported catalyst in rubber hydrogenation.

[0026] The application of the covalent organic skeleton-supported catalyst provided by the present invention comprises: adding the covalent organic skeleton-supported catalyst to hydrogenation of nitrile rubber to prepare hydrogenated nitrile rubber;

[0027] Preferably, chlorobenzene or xylene is used as a solvent, the catalyst having a mass content of 0.8% or more is added to the nitrile rubber solution, hydrogen with a pressure of 2 to 7 MPa is introduced, and the reaction is carried out at 40 to 150° C. for more than 60 to 600 minutes to obtain the hydrogenated nitrile rubber.

[0028] The present invention provides a preparation method and application of a covalent organic framework-supported catalyst. A covalent organic framework having a C=N polyphenyl ring structure is synthesized by an aldehyde-amine condensation reaction. The covalent organic framework has stable properties, high crystallinity, and a large specific surface area. Furthermore, the present invention adopts a simple impregnation method to load precious metals on COFs to achieve the preparation of a heterogeneous catalyst. The catalyst has high catalytic efficiency in a hydrogenated nitrile rubber experiment. The catalyst has high catalyst recovery efficiency, high reusability, and high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is a schematic structural diagram of the magnetic COFs / Fe3O4 with a core-shell structure obtained in Example 30 provided by the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1 Covalent Organic Framework

[0033] A preparation method of a covalent organic framework comprises the following specific steps: weighing 0.3 mmol of tetrakis(4-aminophenyl)methane and 0.6 mmol of terephthalaldehyde, dissolving them in a mixed solvent consisting of 4 mL of mesitylene and 4 mL of 1,4-dioxane solution, and ultrasonically dispersing them for 30 minutes, then adding 0.2 mL of 3 mol / L acetic acid, reacting in a high-pressure reactor, adding nitrogen for protection, the reaction temperature being 120 DEG C, the reaction time being 72 hours, cooling to room temperature, washing with anhydrous ethanol for 4 times, and drying at 100 DEG C for 12 hours to obtain a yellow powder, which is the covalent organic framework.

[0034] Example 2 Covalent Organic Framework

[0035] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 8 mL of mesitylene.

[0036] Example 3 Covalent Organic Framework

[0037] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 8 mL of 1,4-dioxane.

[0038] Example 4 Covalent Organic Framework

[0039] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 4 mL of mesitylene and 4 mL of N-methylpyrrolidone to form a mixed solvent.

[0040] Example 5 Covalent Organic Framework

[0041] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 7.2 mL of mesitylene and 0.8 mL of 1,4-dioxane to form a mixed solvent.

[0042] Example 6 Covalent Organic Framework

[0043] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 5.6 mL of mesitylene and 2.4 mL of 1,4-dioxane to form a mixed solvent.

[0044] Example 7 Covalent Organic Framework

[0045] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 2.4 mL of mesitylene and 5.6 mL of 1,4-dioxane to form a mixed solvent.

[0046] Example 8 Covalent Organic Framework

[0047] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 1, except that the mixed solvent is replaced with 0.8 mL of mesitylene and 7.2 mL of 1,4-dioxane solution to form a mixed solvent.

[0048] The yield and thermal stability (testing the thermal decomposition temperature of the covalent organic frameworks prepared in Examples 1 to 8) were compared, and the results are as follows:

[0049]

[0050]

[0051] It can be seen that the co-solvent of mesitylene and 1,4-dioxane as a mixed solvent has a better effect, and when the ratio of mesitylene to 1,4-dioxane is 7:3, the effect is the best. In addition, the covalent organic framework prepared in each embodiment has stable properties, and the covalent organic framework prepared in each embodiment is highly crystalline as determined by XRD testing.

[0052] Example 9 Covalent Organic Framework

[0053] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the concentration of acetic acid is replaced with 6 mol / L.

[0054] Example 10 Covalent Organic Framework

[0055] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the concentration of acetic acid is replaced with 9 mol / L.

[0056] The yield and thermal stability of the covalent organic frameworks prepared in Examples 6, 9 and 10 were compared, and the results are as follows:

[0057] Example No. Yield Thermal decomposition starting temperature 6 53.6％ 320℃ 9 50.4％ 300℃ 10 48.2％ 300℃

[0058] It can be seen that when the concentration of acetic acid is 3 mol / L, the effect is better.

[0059] Example 11 Covalent Organic Framework

[0060] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the reaction temperature is reduced to 90°C.

[0061] Example 12 Covalent Organic Framework

[0062] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the reaction temperature is raised to 140°C.

[0063] The yield and thermal stability of the covalent organic frameworks prepared in Examples 6, 11 and 12 were compared, and the results are as follows:

[0064] Example No. Yield Thermal decomposition starting temperature 6 53.6％ 320℃ 11 51.2％ 320℃ 12 49.3％ 180℃

[0065] It can be seen that when the reaction temperature is 120°C, the effect is better.

[0066] Example 13 Covalent Organic Framework

[0067] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the reaction time is extended to 120 h.

[0068] The yield and thermal stability of the covalent organic framework prepared in Example 13 were tested, and the results were as follows: the yield was 50.6%, and the initial thermal decomposition temperature was 240°C.

[0069] Comparative Example 1

[0070] A method for preparing a covalent organic framework, wherein the specific steps are substantially the same as those of Example 6, except that the reaction time is shortened to 24 h, and the reaction is unsuccessful.

[0071] It can be seen that the effect is better when the reaction time is 72h.

[0072] Examples 14-26 Covalent organic framework supported catalyst

[0073] A preparation method of a covalent organic framework-supported catalyst, the specific steps of which are: placing 100 mg of the covalent organic framework prepared in Examples 1 to 13 and 20 mg of Pd(CH3COO)2 in a beaker, dripping 20 mL of deionized water into the beaker, placing the beaker on a magnetic stirrer and stirring at a rate of 300 r / min at room temperature for 12 hours, adding a NaBH4 aqueous solution, continuing to stir for 12 hours, and placing in a vacuum oven at 100°C for drying for 12 hours to obtain a covalent organic framework-supported catalyst (Pd@COFs catalyst).

[0074] The obtained Pd@COFs catalyst was tested, and the Pd content was tested as follows:

[0075]

[0076]

[0077] Example 27 Hydrogenated nitrile rubber

[0078] The Pd@COFs catalyst prepared in Example 19 was further used to prepare hydrogenated nitrile rubber. The specific process was as follows: the nitrile rubber was dissolved in xylene to prepare a 7% NBR solution by mass, the NBR solution was placed in a 30 mL high-pressure reactor, and a Pd@COFs catalyst with a mass ratio (mass ratio of the catalyst mass to the total system) of 0.8% was added, hydrogen with a pressure of 3 MPa was introduced, the temperature was 120°C, and the reaction was carried out for 8 hours (the agitator speed was 300 r / min). The hydrogenation results are shown in Table 2.

[0079] Example 28 Hydrogenated nitrile rubber

[0080] It is basically the same as Example 27, except that the addition amount of Pd@COFs catalyst is adjusted to 1.2%.

[0081] Example 29 Hydrogenated nitrile rubber

[0082] It is basically the same as Example 27, except that the time is adjusted to 10 hours.

[0083] Comparative Examples 2 to 5

[0084] It is basically the same as Example 27, except that the addition amount of Pd@COFs catalyst is adjusted to 0.4%, 0.2%, 0.1% and 0.05% respectively.

[0085] The hydrogenation results in Example 27, Example 28 and Comparative Examples 2 to 5 are compared as follows:

[0086] Catalyst dosage / % Hydrogenation degree / % Comparative Example 5 0.05 23.1 Comparative Example 4 0.10 25.8 Comparative Example 3 0.20 26.2 Comparative Example 2 0.40 44.6 Embodiment 27 0.80 92.8 Embodiment 28 1.20 92.6

[0087] As can be seen from the table above, as the amount of catalyst increases, the degree of hydrogenation gradually increases. When the amount of catalyst reaches 0.8%, the degree of hydrogenation reaches the maximum. If the amount of catalyst is further increased, the degree of hydrogenation will not increase significantly. This is because the content of precious metals required for hydrogenation of NBR rubber has reached saturation, and adding more will have no effect on hydrogenation.

[0088] Comparative Examples 6 to 9

[0089] It is basically the same as Example 27, except that the temperature is adjusted to 60°C, 80°C, 100°C and 140°C respectively.

[0090] The hydrogenation results in Example 27 and Comparative Examples 6 to 9 are compared as follows:

[0091] Temperature / ℃ Hydrogenation degree / % Comparative Example 6 60 54.2 Comparative Example 7 80 60.6 Comparative Example 8 100 80.4 Embodiment 27 120 92.8 Comparative Example 9 140 82.8

[0092] It can be seen from the above table that with the increase of reaction temperature, the degree of hydrogenation first gradually increases and then decreases. This is because the activity of hydrogen molecules increases with the increase of temperature, making it easier to collide with metal Pd. When the temperature is higher than 120°C, the activity begins to decrease and the degree of hydrogenation also decreases accordingly.

[0093] Comparative Examples 10 to 12

[0094] It is basically the same as Example 27, except that the time is adjusted to 2h, 4h and 6h respectively.

[0095] The hydrogenation results in Example 27, Example 29 and Comparative Examples 10 to 12 are compared as follows:

[0096] Time / h Hydrogenation degree / % Comparative Example 10 2 40.6 Comparative Example 11 4 52.3 Comparative Example 12 6 73.5 Embodiment 27 8 92.8 Embodiment 29 10 92.0

[0097] It can be seen from the above table that as the reaction time increases, the degree of hydrogenation gradually increases. During the period of 2 to 8 hours, the degree of hydrogenation increases dramatically, from 40% to 90%. As the reaction time continues to increase, the degree of hydrogenation remains almost unchanged.

[0098] Example 30 Covalent organic framework supported catalyst

[0099] A method for preparing a covalent organic framework-supported catalyst, the specific steps of which are:

[0100] (1) 0.3 mmol of tetrakis(4-aminophenyl)methane, 0.6 mmol of terephthalaldehyde, and 0.15 mmol of Fe3O4 were weighed and dissolved in a mixed solvent consisting of 5.6 mL of mesitylene and 2.4 mL of 1,4-dioxane. The mixture was ultrasonically dispersed for 30 min and reacted at 120°C for 72 h. After cooling, the mixture was washed with anhydrous ethanol for 4 times and dried at 100°C for 12 h to obtain a black powder. The core-shell structure of COFs / Fe3O4 with magnetic properties was synthesized (the schematic diagram of the structure is shown in FIG. 2 ). Figure 1 ).

[0101] (2) is basically the same as Example 19, except that the covalent organic framework is replaced with COFs / Fe3O4 obtained in the above step (1) to obtain Pd@COFs / Fe3O4 catalyst.

[0102] The Pd content in the Pd@COFs / Fe3O4 catalyst is 4.24%.

[0103] Example 31 Hydrogenated nitrile rubber

[0104] It is basically the same as Example 27, except that the Pd@COFs catalyst prepared in Example 19 is replaced by the Pd@COFs / Fe3O4 catalyst prepared in Example 30. After the reaction is completed, the tested degree of hydrogenation is 92.8%, and the catalyst is recovered using a magnet with a recovery rate of up to 98.5%, achieving efficient recovery of the catalyst, and the Pd content in the recovered catalyst is still as high as 4.15%.

[0105] Furthermore, the recovered catalyst was subjected to catalytic hydrogenation reaction again under the same conditions, the degree of hydrogenation was tested, and it was recycled and reused multiple times. The catalytic number of times of the catalyst and the corresponding degree of hydrogenation are shown in the table below.

[0106] Hydrogenation times Hydrogenation degree / % 1 92.8 2 92.0 3 91.6 4 90.5 5 88.4

[0107] It can be seen from the above table that the catalytic efficiency of NBR rubber hydrogenation is still high after the catalyst is recovered, and the achieved hydrogenation degree remains almost unchanged, still as high as 88.4% after being reused 5 times.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Application of a covalent organic framework supported catalyst in rubber hydrogenation, characterized in that: The covalent organic framework supported catalyst comprises: a covalent organic framework synthesized by an aldehyde-amine condensation reaction, and a noble metal supported on the covalent organic framework, wherein the covalent organic framework and Fe3O4 form a core-shell structure with Fe3O4 as the core; the loading amount of the noble metal is 4.1-5.7%; the noble metal is Pd, Rh, Ru or Ir; The covalent organic framework is synthesized by a solvothermal method from a precursor containing an aldehyde group and a precursor containing an amino group; The precursor containing aldehyde groups is one or more of p-nitrobenzaldehyde, terephthalaldehyde and 1,4-di(4-aldehydephenyl)benzene; and / or the precursor containing amino groups is one or more of 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetrakis(4-aminophenyl)methane and melamine; the molar ratio of the precursor containing aldehyde groups to the precursor containing amino groups is 0.2~0.4:0.5~0.

7.

2. The use according to claim 1, characterized in that: include: The covalent organic skeleton-supported catalyst is added into the hydrogenation of nitrile rubber to prepare hydrogenated nitrile rubber.

3. The use according to claim 2, characterized in that: Using chlorobenzene or xylene as solvent, adding the catalyst with a mass content of 0.8% or more into the nitrile rubber solution, introducing hydrogen with a pressure of 2-7 MPa and reacting at 40-150° C. for more than 60-600 minutes to obtain the hydrogenated nitrile rubber.

4. The use according to claim 1, characterized in that: The precursor containing an aldehyde group is terephthalaldehyde, and the precursor containing an amino group is tetrakis(4-aminophenyl)methane.

5. The use according to claim 1 or 4, characterized in that: The noble metal is loaded onto the covalent organic framework by an impregnation method.

6. The use according to claim 5, characterized in that: The noble metal is Pd.

7. The use according to claim 1, characterized in that: The preparation method of the covalent organic framework-supported catalyst is to support the noble metal on the covalent organic framework synthesized by aldehyde-amine condensation reaction.

8. The use according to claim 7, characterized in that: The preparation process of the covalent organic framework comprises: mixing a precursor containing an aldehyde group and a precursor containing an amino group with a solvent, and synthesizing the covalent organic framework by a solvothermal method under the catalysis of an acid and a nitrogen atmosphere; Wherein, the solvent is one or more of mesitylene, 1,4-dioxane and N-methylpyrrolidone.

9. The use according to claim 8, characterized in that: The solvent is a mixed solution of mesitylene and 1,4-dioxane.

10. The use according to claim 9, characterized in that: The solvent is a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 7:

3.

11. The use according to claim 8, characterized in that: The acid is one or more of acetic acid, hydrochloric acid and nitric acid.

12. The use according to claim 11, characterized in that: The acid is acetic acid.

13. The use according to claim 12, characterized in that: The molar ratio of the added amount of the acetic acid to the molar amount of the precursor containing the aldehyde group is 2-18:

6.

14. The use according to claim 13, characterized in that The molar ratio of the added amount of the acetic acid to the molar amount of the precursor containing the aldehyde group is 4-10:

6.

15. The use according to claim 8, characterized in that: The temperature of the solvothermal method is 90-140°C.

16. The use according to claim 15, characterized in that The temperature of the solvothermal method is 110-120°C.

17. The use according to claim 8, characterized in that The time of the solvothermal method is 60 to 120 hours.

18. The use according to claim 17, characterized in that The time of the solvothermal method is 60 to 80 hours.

19. The use according to claim 7, characterized in that: The preparation process of the covalent organic framework comprises: using an aldehyde-containing precursor, an amino-containing precursor and Fe3O4 as raw materials, and synthesizing a core-shell structure with Fe3O4 as the core through a solvent thermal method.

20. The use according to claim 19, characterized in that The molar ratio of the precursor containing aldehyde groups, the precursor containing amino groups and Fe3O4 is 0.2~0.4:0.5~0.7:0.1~0.

2.

21. The use according to claim 7, characterized in that: The process of loading the precious metal onto the covalent organic framework includes: mixing the precious metal with the covalent organic framework in the form of acetate, then adding deionized water and stirring evenly, then adding NaBH4 aqueous solution, continuing stirring, and finally vacuum drying to obtain the covalent organic framework-loaded catalyst.

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