A TEMPO-based catalyst and its synthesis method and application

Abstract

The present invention relates to the field of electrochemical technology, and discloses a TEMPO-based catalyst, its synthesis method and application. The present invention first prepares a polymer PEDOT-N3 as a preparatory step before catalyst synthesis, and then grafts 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidine nitroxide free radical onto the polymer PEDOT-N3 by reaction to obtain the catalyst PEDOT-T-TEMPO. In the catalyst PEDOT-T-TEMPO, it uses the polymer PEDOT-N3 as a carrier, has the characteristics of good conductivity and good environmental stability, and is verified in one embodiment that the catalyst PEDOT-T-TEMPO still has a high catalytic activity after 100 repeated uses. In the catalyst PEDOT-T-TEMPO, the role of the 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidine nitroxide free radical is to bring catalytic activity similar to that of the 2,2,6,6-tetramethylpiperidine nitroxide free radical to the catalyst PEDOT-T-TEMPO.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and in particular to a TEMPO-based catalyst and a synthesis method and application thereof. Background Art

[0002] Hydroxymethylfurfural (HMF) is an important biomass platform chemical that can be produced by acid-catalyzed dehydration of carbohydrates such as fructose, glucose and cellulose. The presence of aldehyde and hydroxymethyl groups in the 5-hydroxymethylfurfural molecule allows it to be converted into a series of high-value-added furan derivatives such as 2,5-diformylfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) through various chemical reactions. Among them, 2,5-diformylfuran is one of the most important derivatives of 5-hydroxymethylfurfural and can be used as a synthetic antifungal agent, fluorescent material and pharmaceutical intermediate. In the traditional method of preparing DFF from HMF, it is mainly achieved by using metal catalysts.

[0003] 2,2,6,6-Tetramethylpiperidinyl nitroxide (TEMPO), a mild, green catalyst, is a promising method for the oxidation of HMF to DFF. However, the current application of TEMPO as a catalyst in the HMF-based DFF reaction is plagued by difficulties in catalyst recovery and product purification.

[0004] Fixing the organic small molecule catalyst TEMPO on the surface of inorganic materials to realize the recycling of catalyst and reduce post-processing costs has always been a hot topic of people's attention. For example, the invention patent with application publication number CN112159515A discloses a method and application of preparing TEMPO free radical functionalized hollow conjugated microporous polymer based on SiO2 template, which realizes the recycling of catalyst and facilitates post-processing by loading TEMPO on porous material coated SiO2 functionalized conjugated microporous polymer material. However, the method of loading TEMPO in this patent involves realizing the hollowing of supported materials through hydrofluoric acid, and this process easily causes the activity of TEMPO to be destroyed after fixing, resulting in low catalytic efficiency. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a TEMPO-based catalyst and a synthesis method and application thereof.

[0006] The specific technical solutions of the present invention are:

[0007] In a first aspect, the present invention provides a TEMPO-based catalyst having the structural formula: Wherein, n=8-300.

[0008] In a second aspect, the present invention provides a method for synthesizing a TEMPO-based catalyst, characterized in that it comprises the following steps:

[0009] Step S1: using EDOT-N3 as a monomer to perform a polymerization reaction to prepare a polymer PEDOT-N3;

[0010] Step S1: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto the polymer PEDOT-N3 to obtain PEDOT-T-TEMPO;

[0011] The structural formula of the PEDOT-T-TEMPO is:

[0012] Wherein, n=8-300.

[0013] The reaction process of step S1 to step S2 is as follows:

[0014]

[0015] As a preferred embodiment of the above synthesis method, in step S1, the polymerization reaction is carried out by electrochemical polymerization.

[0016] As a preferred embodiment of the above-mentioned synthesis method, the polymerization reaction is an electropolymerization reaction, and the electropolymerization adopts a three-electrode system, wherein the working electrode is a Pt electrode, the auxiliary electrode is a Pt electrode, and the Ag / Ag+ electrode is a reference electrode; the electropolymerization reaction is carried out at 20-40° C. in an acetonitrile solution of tetrabutylammonium perchlorate.

[0017] More preferably, the molar concentration of tetrabutylammonium perchlorate in acetonitrile is 0.05 to 0.2 mol / L.

[0018] More preferably, the electropolymerization potential is -0.2 to 1.5 V, the electropolymerization scanning speed is 25 to 75 mV / s, and the number of scanning cycles is 3 to 15 cycles.

[0019] As a preferred embodiment of the above synthesis method, in step S2, the grafting method is: immersing the polymer PEDOT-N3 in an acetonitrile solution containing 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide free radical, using cuprous iodide as a catalyst, and reacting at 20-50°C.

[0020] More preferably, the molar concentration of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide in the acetonitrile solution of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide is 0.005 to 0.02 mol / L.

[0021] More preferably, the reaction time is 8 to 16 hours.

[0022] In a third aspect, the present invention provides use of the TEMPO-based catalyst PEDOT-T-TEMPO in catalyzing the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] The PEDOT-T-TEMPO prepared by the present invention has a catalytic activity similar to that of 2,2,6,6-tetramethylpiperidinyl nitroxide (TEMPO). It is used in the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran. The results show that it has excellent catalytic oxidation performance.

[0025] The PEDOT-T-TEMPO prepared by the present invention can be fixed on the carrier polymer PEDOT-N3 under the premise of high catalytic activity, and exists in a state where the PEDOT-T-TEMPO as a whole is attached to the electrode. It can be easily separated after electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran. The catalyst can be separated by directly removing the electrode. The PEDOT-T-TEMPO attached to the electrode can be repeatedly used after washing, and can still maintain a high catalytic activity after repeating 100 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The infrared spectra of polymer PEDOT-N3 and polymer PEDOT-T-TEMPO;

[0027] Figure 2 This is the cyclic voltammetry characteristic curve of the polymer PEDOT-T-TEMPO. DETAILED DESCRIPTION

[0028] In one aspect, the present invention provides a TEMPO-based catalyst having the structural formula: Wherein, n=8-300.

[0029] On the other hand, the present invention provides a method for synthesizing a TEMPO-based catalyst, characterized in that it comprises the following steps:

[0030] Step S1: using EDOT-N3 as a monomer to perform a polymerization reaction to prepare a polymer PEDOT-N3;

[0031] Step S1: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto the polymer PEDOT-N3 to obtain PEDOT-T-TEMPO;

[0032] The structural formula of the PEDOT-T-TEMPO is:

[0033] Wherein, n=8-300.

[0034] This synthesis method synthesizes the PEDOT-T-TEMPO catalyst through steps S1 and S2. In this synthesis method, the polymer PEDOT-N3 is first prepared as a preparatory step before catalyst synthesis. Then, the 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide radical is grafted onto the polymer PEDOT-N3 via a reaction to obtain the PEDOT-T-TEMPO catalyst. The PEDOT-T-TEMPO catalyst, which uses the polymer PEDOT-N3 as a carrier, exhibits excellent electrical conductivity and environmental stability. In one example, it was demonstrated that the PEDOT-T-TEMPO catalyst maintained high catalytic activity after 100 cycles of reuse. In the catalyst PEDOT-T-TEMPO, the role of the 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide free radical is to bring catalytic activity similar to that of the 2,2,6,6-tetramethylpiperidinylnitroxide free radical (TEMPO) to the catalyst PEDOT-T-TEMPO.

[0035] The reaction process of step S1 to step S2 is as follows:

[0036]

[0037] Existing catalysts are typically synthesized and supported by functionalization followed by polymerization. This pre-functionalization approach not only makes polymerization difficult but also leads to poor support stability and reduced catalyst activity. The present preparation method utilizes electropolymerization and pre-functionalization to prepare the catalyst PEDOT-T-TEMPO, successfully producing a catalyst with high catalytic activity and excellent stability.

[0038] As a preferred embodiment of the above synthesis method, in step S1, the polymerization reaction is carried out by electrochemical polymerization.

[0039] As a preferred embodiment of the above-mentioned synthesis method, the polymerization reaction is an electropolymerization reaction, and the electropolymerization adopts a three-electrode system, wherein the working electrode is a Pt electrode, the auxiliary electrode is a Pt electrode, and the Ag / Ag+ electrode is a reference electrode; the electropolymerization reaction is carried out at 20-40° C. in an acetonitrile solution of tetrabutylammonium perchlorate.

[0040] In one embodiment, it is shown that when tetrabutylammonium perchlorate is used as the electrolyte and its molar concentration in acetonitrile is 0.05 to 0.2 mol / L, the catalytic activity of the finally prepared catalyst PEDOT-T-TEMPO is relatively high.

[0041] As a preferred embodiment of the above synthesis method, the electropolymerization potential is -0.2 to 1.5 V, the electropolymerization scanning speed is 25 to 75 mV / s, and the number of scanning cycles is 3 to 15 cycles.

[0042] As a preferred embodiment of the above synthesis method, in step S2, the grafting method is: immersing the polymer PEDOT-N3 in an acetonitrile solution containing 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide free radical, using cuprous iodide as a catalyst, and reacting at 20-50°C.

[0043] In one embodiment, it is shown that in an acetonitrile solution of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical, when the molar concentration of the 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical is 0.005 to 0.02 mol / L, the catalytic activity of the finally prepared catalyst PEDOT-T-TEMPO is relatively high.

[0044] In one embodiment, it is shown that when the reaction time is 8 to 16 hours, the catalytic activity of the finally prepared catalyst PEDOT-T-TEMPO is higher.

[0045] Furthermore, the present invention also provides the use of the above-mentioned TEMPO-based catalyst PEDOT-T-TEMPO in catalyzing the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

[0046] In one embodiment, the PEDOT-T-TEMPO prepared by the present invention has catalytic activity similar to that of 2,2,6,6-tetramethylpiperidinyl nitroxide (TEMPO), and is used in the electrocatalytic oxidation of 5-hydroxymethylfurfural to produce 2,5-diformylfuran, exhibiting excellent catalytic oxidation performance.

[0047] In another embodiment, the PEDOT-T-TEMPO prepared by the present invention can be easily separated after the electrocatalytic oxidation of 5-hydroxymethylfurfural to produce 2,5-diformylfuran. The separation of the catalyst in the electrocatalytic oxidation of 5-hydroxymethylfurfural to produce 2,5-diformylfuran can be achieved by directly removing the electrode. The removed PEDOT-T-TEMPO attached to the electrode can be rinsed and reused repeatedly, and can still maintain a high catalytic activity after repeating 100 times.

[0048] The present invention will be further described below with reference to the embodiments and accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below generally represent only a portion of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0049] Example 1 Preparation of PEDOT-N3 In this example, PEDOT-N3 was prepared by electropolymerization. The electropolymerization reaction was performed on an electrochemical workstation using a three-electrode system with a Pt working electrode, a Pt auxiliary electrode, and an Ag / Ag+ (0.1 mol / L silver nitrate acetonitrile solution) electrode as the reference electrode. The specific steps are as follows:

[0050] A 0.2 mol / L tetrabutylammonium perchlorate acetonitrile solution (15 mL) and 1.5 mmol of EDOT-N3 were added to a 25 mL beaker and electropolymerization was carried out at room temperature; the polymerization potential was 0-1.2 V, the scan rate was 50 mV / s, and after scanning 5 circles, the electropolymerization was terminated, the working electrode was removed, and the electrode surface was rinsed with acetonitrile to obtain the polymer PEDOT-N3 attached to the surface of the Pt electrode.

[0051] Example 2 Synthesis of PEDOT-T-TEMPO

[0052] In this example, PEDOT-T-TEMPO was prepared in the following steps:

[0053] An electrode with the polymer PEDOT-N3 attached to its surface (prepared according to Example 1) was immersed in 5 mL of acetonitrile containing 0.05 mmol of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide and 0.5 mmol of cuprous iodide. The reaction was allowed to proceed at room temperature for 10 hours. After the reaction, the electrode surface was rinsed with acetonitrile to obtain the polymer PEDOT-T-TEMPO attached to the Pt electrode surface. The structural formula of PEDOT-T-TEMPO is as follows:

[0054] Wherein, n=8-300.

[0055] The polymer PEDOT-N3 attached to the electrode surface prepared in Example 1 and the polymer PEDOT-T-TEMPO attached to the electrode surface prepared in this example were tested by infrared spectroscopy. The results are shown in FIG. Figure 1 .

[0056] By comparison Figure 1From the infrared spectra of PEDOT-N3 and PEDOT-T-TEMPO, it can be found that the infrared spectrum peak (2103cm -1 ), indicating that a click reaction occurred between PEDOT-N3 and 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide radical.

[0057] At the same time, the cyclic voltammetry characteristic curve of the polymer PEDOT-T-TEMPO attached to the electrode surface prepared in this example was tested, and the results are shown in FIG. Figure 2 .

[0058] Depend on Figure 2 It can be seen that the polymer PEDOT-T-TEMPO can observe the cyclic voltammetric response belonging to TEMPO.

[0059] Example 3 Synthesis of PEDOT-T-TEMPO

[0060] In this example, PEDOT-T-TEMPO was prepared. Compared with Example 2, this example differed in that the amount of cuprous iodide used was 0.75 mmol and the reaction time was 8 h.

[0061] Example 4 Synthesis of PEDOT-T-TEMPO

[0062] In this example, PEDOT-T-TEMPO was prepared. Compared with Example 2, this example differed in that the amount of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinylnitroxide free radical used was 0.075 mmol, and the reaction time was 8 h.

[0063] Example 5 Electrocatalytic Performance of PEDOT-T-TEMPO

[0064] The PEDOT-T-TEMPO-attached Pt electrode prepared in Example 2 was coated with 10 μL of a Nafion-ethanol solution (Nafion:ethanol volume ratio of 1:9), dried, and then used. The Pt electrode was labeled PEDOT-T-TEMPO / Pt. The electrocatalytic reaction steps were as follows:

[0065] The electrocatalytic oxidation reaction was carried out on an electrochemical workstation using a three-electrode system. The working electrode was the PEDOT-T-TEMPO / Pt prepared above, the auxiliary electrode was a Pt electrode, and the reference electrode was an Ag / Ag+ (0.1 mol / L silver nitrate in acetonitrile) electrode. A 25 mL beaker was added with 0.1 mmol of 5-hydroxymethylfurfural, 0.2 mmol of 1-methylimidazole, and 15 mL of a 0.1 mol / L tetrabutylammonium tetrafluoroborate solution in acetonitrile. Constant current electrolysis was performed at room temperature and 3 mA. After 6 hours of electrolysis, the electrolyte was analyzed by gas chromatography. The conversion of 5-hydroxymethylfurfural was 92%, and the selectivity for the product 2,5-diformylfuran was 97%.

[0066] Example 6 Electrocatalytic Performance of PEDOT-T-TEMPO

[0067] The PEDOT-T-TEMPO-attached Pt electrode prepared in Example 3 was coated with 10 μL of a Nafion-based ethanol solution (Nafion:ethanol volume ratio of 1:9), dried, and then used. This Pt electrode was labeled PEDOT-T-TEMPO / Pt. The electrocatalytic performance was tested using the same experimental procedures as in Example 5. The conversion of 5-hydroxymethylfurfural was 95%, and the selectivity for the product 2,5-diformylfuran was 98%.

[0068] Example 7 Electrocatalytic Performance of PEDOT-T-TEMPO

[0069] The PEDOT-T-TEMPO-attached Pt electrode prepared in Example 4 was coated with 10 μL of a Nafion-based ethanol solution (Nafion:ethanol volume ratio of 1:9), dried, and then used. This Pt electrode was labeled PEDOT-T-TEMPO / Pt. The electrocatalytic performance was tested using the same experimental procedures as in Example 5. The conversion of 5-hydroxymethylfurfural was 96%, and the selectivity for the product 2,5-diformylfuran was 98%.

[0070] Example 8 Repeated Electrocatalytic Performance of PEDOT-T-TEMPO

[0071] The surface of the PEDOT-T-TEMPO-attached Pt electrode prepared in Example 4 was coated with 10 μL of a Nafion ethanol solution (Nafion:ethanol volume ratio of 1:9), dried, and set aside. The Pt electrode was labeled PEDOT-T-TEMPO / Pt. The electrocatalytic reaction was repeated 100 times. The electrocatalytic oxidation reaction was carried out as follows: on an electrochemical workstation, a three-electrode system was used: the working electrode was the PEDOT-T-TEMPO / Pt prepared above, the auxiliary electrode was a Pt electrode, and an Ag / Ag+ (0.1 mol / L silver nitrate in acetonitrile) electrode served as the reference electrode. In a 25 mL beaker, 0.1 mmol of 5-hydroxymethylfurfural, 0.2 mmol of 1-methylimidazole, and 15 mL of a 0.1 mol / L tetrabutylammonium tetrafluoroborate in acetonitrile solution were added. Constant current electrolysis was performed at room temperature and 3 mA. After 6 h of electrolysis, the PEDOT-T-TEMPO / Pt electrode was removed. The PEDOT-T-TEMPO / Pt was rinsed with ethanol and dried, and the electrocatalytic oxidation reaction was repeated 100 times. After the 100th electrocatalytic oxidation reaction, the electrolyte was tested using gas chromatography. At this time, the conversion of 5-hydroxymethylfurfural was 95%, and the selectivity for the product 2,5-diformylfuran was 98%.

[0072] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0073] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A TEMPO-based catalyst, characterized in that: The structural formula of the catalyst is: Among them, n=8-300.

2. A method for synthesizing a TEMPO-based catalyst, characterized in that: The following steps are involved: Step S1: using EDOT-N3 as a monomer to perform a polymerization reaction to prepare a polymer PEDOT-N3; Step S2: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto the polymer PEDOT-N3 to obtain PEDOT-T-TEMPO; The structural formula of the PEDOT-T-TEMPO is: Among them, n=8-300.

3. The synthesis method according to claim 2, wherein: In step S1, the polymerization reaction is performed by electrochemical polymerization.

4. The synthesis method according to claim 2 or 3, wherein: The polymerization reaction is an electropolymerization reaction, which adopts a three-electrode system, wherein the working electrode is a Pt electrode, the auxiliary electrode is a Pt electrode, and the Ag / Ag+ electrode is a reference electrode; the electropolymerization reaction is carried out at 20-40° C. in an acetonitrile solution of tetrabutylammonium perchlorate.

5. The synthesis method according to claim 4, wherein: The molar concentration of tetrabutylammonium perchlorate in acetonitrile is 0.05-0.2 mol / L.

6. The synthesis method according to claim 4, wherein: The electropolymerization potential is -0.2 to 1.5 V, the electropolymerization scanning speed is 25 to 75 mV / s, and the number of scanning circles is 3 to 15 circles.

7. The synthesis method according to claim 4, wherein: In step S2, the grafting method is: immersing the polymer PEDOT-N3 in an acetonitrile solution containing 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical, using cuprous iodide as a catalyst, and reacting at 20-50°C.

8. The synthesis method according to claim 7, wherein: In the acetonitrile solution of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical, the molar concentration of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical is 0.005 to 0.02 mol / L.

9. The synthesis method according to claim 7, wherein: The reaction time is 8 to 16 hours.

10. Use of the TEMPO-based catalyst according to claim 1, or the PEDOT-T-TEMPO synthesized by the synthesis method according to any one of claims 2 to 9, in catalyzing the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

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