TEMPO-based catalyst as well as synthesis method and application thereof

Abstract

The invention relates to the technical field of electrochemistry, and discloses a TEMPO-based catalyst as well as a synthesis method and application thereof. The preparation method comprises the following steps: firstly, preparing a polymer PEDOT-N3 as a preparation step before synthesis of a catalyst, and then grafting 4-(2-propinyloxy)-2, 2, 6, 6-tetramethylpiperidine nitroxide free radicals on the polymer PEDOT-N3 through a reaction, so as to obtain the catalyst PEDOT-T-TEMPO. In the catalyst PEDOT-T-TEMPO, a polymer PEDOT-N3 is used as a carrier, the catalyst has the characteristics of good conductivity, good environmental stability and the like, and it is verified in one embodiment that the catalyst PEDOT-T-TEMPO still has high catalytic activity after being repeatedly used for 100 times. In the catalyst PEDOT-T-TEMPO, the effect of the 4-(2-propinyloxy)-2, 2, 6, 6-tetramethylpiperidine nitroxide free radical is to bring catalytic activity similar to the catalytic activity 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), as a mild and green catalyst, is a promising method for catalytic oxidation of HMF to prepare DFF. However, currently, the use of TEMPO as a catalyst in the preparation of DFF from HMF has the problems of difficulty in catalyst recovery and product purification.

[0004] Fixing the organic small molecule catalyst TEMPO on the surface of inorganic materials to achieve the recycling of the catalyst and reduce the post-processing cost has always been a hot topic of concern. 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 the catalyst and facilitates post-processing by loading TEMPO on the functionalized conjugated microporous polymer material coated with SiO2 by porous material. However, the method of loading TEMPO in the patent involves hollowing the loading material through hydrofluoric acid, which easily leads to the destruction of the activity of TEMPO after fixation, 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 scheme of the present invention is: In a first aspect, the present invention provides a TEMPO-based catalyst having the structural formula: Among them, n=8-300.

[0007] In a second aspect, the present invention provides a method for synthesizing a TEMPO-based catalyst, characterized in that it comprises the following steps: Step S1: using EDOT-N3 as a monomer to perform a polymerization reaction to prepare a polymer PEDOT-N3; Step S1: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto polymer PEDOT-N3 to obtain PEDOT-T-TEMPO; The structural formula of the PEDOT-T-TEMPO is: Among them, n=8-300.

[0008] The reaction process of step S1 to step S2 is as follows: As a preferred embodiment of the above synthesis method, in step S1, the polymerization reaction is carried out by electrochemical polymerization.

[0009] As a preferred embodiment of the above synthesis method, the polymerization reaction is an electropolymerization reaction, and the electropolymerization adopts a three-electrode system, 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.

[0010] More preferably, the molar concentration of tetrabutylammonium perchlorate in acetonitrile is 0.05 to 0.2 mol / L.

[0011] 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.

[0012] As a preferred embodiment of the above-mentioned 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-tetramethylpiperidinyl nitroxide free radical, using cuprous iodide as a catalyst, and reacting at 20 to 50°C.

[0013] More preferably, 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.

[0014] More preferably, the reaction time is 8 to 16 hours.

[0015] In a third aspect, the present invention provides the use of the above TEMPO-based catalyst PEDOT-T-TEMPO in catalyzing the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

[0016] Compared with the prior art, the present invention has the following technical effects: The PEDOT-T-TEMPO prepared by the present invention has a catalytic activity similar to that of 2,2,6,6-tetramethylpiperidinyl nitroxide free radical (TEMPO), and is used in the reaction of preparing 2,5-diformylfuran by electrocatalytic oxidation of 5-hydroxymethylfurfural. The results show that the PEDOT-T-TEMPO has excellent catalytic oxidation performance.

[0017] The PEDOT-T-TEMPO prepared by the present invention can be fixed on a carrier polymer PEDOT-N3 under the premise of high catalytic activity, and exists in a state where the PEDOT-T-TEMPO is attached to the electrode as a whole. It can be easily separated after electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran, and the catalyst can be separated by directly taking out 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 being repeated 100 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the infrared spectra of polymer PEDOT-N3 and polymer PEDOT-T-TEMPO; Figure 2 This is the cyclic voltammetric characteristic curve of the polymer PEDOT-T-TEMPO. DETAILED DESCRIPTION

[0019] In one aspect, the present invention provides a TEMPO-based catalyst having the structural formula: Among them, n=8-300.

[0020] On the other hand, the present invention provides a method for synthesizing a TEMPO-based catalyst, characterized in that it comprises the following steps: Step S1: using EDOT-N3 as a monomer to perform a polymerization reaction to prepare a polymer PEDOT-N3; Step S1: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto polymer PEDOT-N3 to obtain PEDOT-T-TEMPO; The structural formula of the PEDOT-T-TEMPO is: Among them, n=8-300.

[0021] The present synthesis method realizes the synthesis of the catalyst PEDOT-T-TEMPO through steps S1 to S2. In the present synthesis method, the polymer PEDOT-N3 is first prepared as a preparatory step before the catalyst synthesis, and then the 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical is grafted onto the polymer PEDOT-N3 through reaction to obtain the catalyst PEDOT-T-TEMPO. In the catalyst PEDOT-T-TEMPO, the polymer PEDOT-N3 is used as a carrier, and has the characteristics of good conductivity and good environmental stability, and it is verified in an embodiment that the catalyst PEDOT-T-TEMPO still has a high catalytic activity after being reused 100 times. In the catalyst PEDOT-T-TEMPO, the role of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical is to bring similar catalytic activity of 2,2,6,6-tetramethylpiperidinyl nitroxide free radical (TEMPO) to the catalyst PEDOT-T-TEMPO.

[0022] The reaction process of step S1 to step S2 is as follows: The synthesis and loading of existing catalysts are mostly carried out by functionalization first and then polymerization. Functionalization first will not only cause the problem of difficult polymerization, but also lead to the problem of poor stability of the carrier and reduced catalyst activity. The preparation method of the present invention uses electropolymerization reaction and first functionalization to prepare the catalyst PEDOT-T-TEMPO, and successfully prepares a catalyst with high catalytic activity and good stability.

[0023] As a preferred embodiment of the above synthesis method, in step S1, the polymerization reaction is carried out by electrochemical polymerization.

[0024] As a preferred embodiment of the above synthesis method, the polymerization reaction is an electropolymerization reaction, and the electropolymerization adopts a three-electrode system, 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.

[0025] In one embodiment, it is shown that when tetrabutylammonium perchlorate is used as an 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.

[0026] 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.

[0027] As a preferred embodiment of the above-mentioned 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-tetramethylpiperidinyl nitroxide free radical, using cuprous iodide as a catalyst, and reacting at 20 to 50°C.

[0028] 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 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.

[0029] 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 relatively high.

[0030] Furthermore, the present invention also provides the use of the above TEMPO-based catalyst PEDOT-T-TEMPO in catalyzing the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

[0031] In one embodiment, the PEDOT-T-TEMPO prepared by the present invention has a catalytic activity similar to that of 2,2,6,6-tetramethylpiperidinyl nitroxide (TEMPO), and is used in the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran, and has excellent catalytic oxidation performance.

[0032] In another embodiment, the PEDOT-T-TEMPO prepared by the present invention can be easily separated after the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran. The separation of the catalyst in the electrocatalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran can be achieved by directly taking out the electrode. The 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.

[0033] The present invention is further described below in conjunction with the embodiments and the accompanying drawings. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0034] Example 1 Preparation of PEDOT-N3 In this example, PEDOT-N3 was prepared by electropolymerization reaction. The electropolymerization reaction was carried out on an electrochemical workstation using a three-electrode system, with a Pt electrode as the working electrode, a Pt electrode as the 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: A 0.2 mol / L tetrabutylammonium perchlorate acetonitrile solution (15 mL) and 1.5 mmol 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, and the scanning speed was 50 mV / s. After scanning for 5 circles, the electropolymerization was terminated, the working electrode was taken out, and the electrode surface was rinsed with acetonitrile to obtain the polymer PEDOT-N3 attached to the surface of the Pt electrode.

[0035] Example 2 Synthesis of PEDOT-T-TEMPO In this example, PEDOT-T-TEMPO is prepared, and the specific steps are as follows: The electrode with the polymer PEDOT-N3 attached to the surface (prepared according to the method of Example 1) was immersed in 5 mL of acetonitrile solution containing 0.05 mmol 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical and 0.5 mmol cuprous iodide, and reacted for 10 hours at room temperature. After the reaction, the electrode surface was rinsed with acetonitrile to obtain the polymer PEDOT-T-TEMPO attached to the surface of the Pt electrode. The structural formula of PEDOT-T-TEMPO is as follows: Among them, n=8-300.

[0036] 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 .

[0037] By comparison Figure 1 From the infrared spectra of PEDOT-N3 and PEDOT-T-TEMPO, it can be found that the infrared spectrum peak (2103cm2) belonging to the N3 group in PEDOT-N3 is not observed in the infrared spectrum of PEDOT-T-TEMPO. -1 ), indicating that a click reaction occurred between PEDOT-N3 and 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide radical.

[0038] At the same time, the polymer PEDOT-T-TEMPO prepared in this example and attached to the electrode surface was tested for cyclic voltammetry characteristic curves. The results are shown in Figure 2 .

[0039] Depend on Figure 2 It can be seen that the polymer PEDOT-T-TEMPO can observe the cyclic voltammetric response belonging to TEMPO.

[0040] Example 3 Synthesis of PEDOT-T-TEMPO In this example, PEDOT-T-TEMPO was prepared. Compared with Example 2, the difference between this example and Example 2 is that the amount of cuprous iodide used is 0.75 mmol and the reaction time is 8 h.

[0041] Example 4 Synthesis of PEDOT-T-TEMPO In this example, PEDOT-T-TEMPO was prepared. Compared with Example 2, the difference between this example and Example 2 is that the amount of 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical used is 0.075 mmol, and the reaction time is 8 h.

[0042] Example 5 Electrocatalytic performance of PEDOT-T-TEMPO 10 μL of Nafion ethanol solution (the volume ratio of Nafion to ethanol is 1:9) is coated on the surface of the Pt electrode with PEDOT-T-TEMPO attached prepared in Example 2, and dried for later use. The Pt electrode is marked as PEDOT-T-TEMPO / Pt. The steps of the electrocatalytic reaction are as follows: The electrocatalytic oxidation reaction was carried out on an electrochemical workstation using a three-electrode system, with the working electrode being the PEDOT-T-TEMPO / Pt prepared above, the auxiliary electrode being a Pt electrode, and the Ag / Ag+ (0.1 mol / L silver nitrate acetonitrile solution) electrode as a reference electrode. 0.1 mmol of 5-hydroxymethylfurfural, 0.2 mmol of 1-methylimidazole, and 15 mL of 0.1 mol / L tetrabutylammonium tetrafluoroborate acetonitrile solution were added to a 25 mL beaker, and constant current electrolysis was performed at room temperature and 3 mA. After 6 h of electrolysis, the electrolyte was detected using gas chromatography, and the conversion rate of 5-hydroxymethylfurfural was 92%, and the selectivity of the product 2,5-diformylfuran was 97%.

[0043] Example 6 Electrocatalytic performance of PEDOT-T-TEMPO 10 μL of Nafion ethanol solution (volume ratio of Nafion to ethanol is 1:9) was coated on the surface of the Pt electrode attached with PEDOT-T-TEMPO prepared in Example 3, and dried for use. The Pt electrode was marked as PEDOT-T-TEMPO / Pt. The electrocatalytic performance test experimental steps were the same as those in Example 5. The conversion rate of 5-hydroxymethylfurfural was 95%, and the selectivity of the product 2,5-diformylfuran was 98%.

[0044] Example 7 Electrocatalytic Performance of PEDOT-T-TEMPO 10 μL of Nafion ethanol solution (volume ratio of Nafion to ethanol is 1:9) was coated on the surface of the Pt electrode attached with PEDOT-T-TEMPO prepared in Example 4, and dried for later use. The Pt electrode was marked as PEDOT-T-TEMPO / Pt. The electrocatalytic performance test experimental steps were the same as those in Example 5. The conversion rate of 5-hydroxymethylfurfural was 96%, and the selectivity of the product 2,5-diformylfuran was 98%.

[0045] Example 8 Repeated electrocatalytic performance of PEDOT-T-TEMPO 10 μL of Nafion ethanol solution (the volume ratio of Nafion to ethanol is 1:9) is coated on the surface of the Pt electrode attached with PEDOT-T-TEMPO prepared in Example 4, and then dried for standby use. The Pt electrode is marked as PEDOT-T-TEMPO / Pt. The electrocatalytic reaction is repeated 100 times. The electrocatalytic oxidation reaction is as follows: It is carried out on an electrochemical workstation, using a three-electrode system, the working electrode is the PEDOT-T-TEMPO / Pt prepared above, the auxiliary electrode is a Pt electrode, and the Ag / Ag+ (0.1 mol / L silver nitrate acetonitrile solution) electrode is used as a reference electrode. 15 mL of acetonitrile solution of 0.1 mmol of 5-hydroxymethylfurfural, 0.2 mmol of 1-methylimidazole and 0.1 mol / L of tetrabutylammonium tetrafluoroborate is added to a 25 mL beaker, and constant current electrolysis is performed at room temperature and 3 mA. After 6 hours of electrolysis, the electrode PEDOT-T-TEMPO / Pt is taken out. The PEDOT-T-TEMPO / Pt was rinsed with ethanol and dried, and the above electrocatalytic oxidation reaction was repeated 100 times. After the 100th electrocatalytic oxidation reaction, the electrolyte was detected by gas chromatography. At this time, the conversion rate of 5-hydroxymethylfurfural was 95%, and the selectivity of the product 2,5-diformylfuran was 98%.

[0046] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0047] 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 falls within the protection scope 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 S1: grafting 4-(2-propynyloxy)-2,2,6,6-tetramethylpiperidinyl nitroxide free radical onto 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, characterized in that: In step S1, the polymerization reaction is performed by electrochemical polymerization.

4. The synthesis method according to claim 2 or 3, characterized in that: 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, characterized in that: The molar concentration of tetrabutylammonium perchlorate in acetonitrile is 0.05-0.2 mol / L.

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

7. The synthesis method according to claim 4, characterized in that: 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, characterized in that: 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, characterized in that: The reaction time is 8 to 16 hours.

10. Use of the TEMPO-based catalyst according to claim 1, or 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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