Organic electrocatalyst for converting co 2 into c 3, c 2 and c 1 products and preparation method therefor

Abstract

An organic electrocatalyst for converting CO2 into C3, C2 and C1 products and a preparation method therefor. The organic electrocatalyst is a metal-free azo ligand 2,2'-((1E,1'E)-1,2-phenylenebis(diazen-2,1-diyl))diphenylamine and can be used for converting CO2 into C1, C2 and C3 products. The preparation method for the catalyst comprises: (1) degassing o-phenylenediamine in toluene using argon vapor, then adding PbO2, carrying out a reflux reaction on the solution, and purifying the reaction product to obtain 2,2'-diaminoazobenzene; and (2) degassing 2,2'-diaminoazobenzene in toluene using an argon flow, adding 2-nitroacetanilide and acetic acid, heating, stirring and reacting these materials, and purifying the reaction product by means of column chromatography; and dissolving the purified product in a solvent, adding KOH, heating the mixture for reaction, and purifying the reaction product to obtain a target product.

Description

Organic electrocatalyst for converting CO2 into C3, C2 and C1 products and preparation method thereof Technical Field

[0001] The present invention relates to a catalyst and a preparation method thereof, and in particular to an organic electrocatalyst for converting CO2 into C3, C2 and C1 products and a preparation method thereof. Background Art

[0002] The world needs to convert carbon dioxide into value-added fuels and chemicals to meet the demand for sustainable renewable energy. To date, high-FE C1 and C2 products have been reported, but metal-free C3 products remain largely unexplored. For example, Chinese invention patent CN 112251766 A discloses a method for the electrochemical reduction of carbon dioxide to produce carbon monoxide with high selectivity and efficiency. Chinese invention patent CN 114672846 A discloses the preparation and application of a bimetallic catalytic material for electrocatalytic CO2 reduction. The prepared Cu / Ni-NC catalytic material can increase metal utilization, reduce costs, inhibit the hydrogen evolution reaction, and improve the Faradaic efficiency of electrocatalytic CO2 reduction to CO. Chinese patent CN 114381747 A discloses a method for preparing an electrocatalytic electrode for the electrochemical reduction of carbon dioxide to produce ethylene. However, catalytic materials that can simultaneously and efficiently and selectively convert carbon dioxide into C3, C2, and C1 products remain scarce.

[0003] Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide a synergistic flow organic electrocatalyst for the efficient conversion of CO2 into C3, C2 and C1 products.

[0005] Technical solution: The organic electrocatalyst for converting CO2 into C3, C2 and C1 products described in the present invention is 2,2'-((1E, 1'E)-1,2-phenylenebis(diazene-2,1-diyl)diphenylamine, with the following structural formula:

[0006] Preferably, the products include formic acid as a C1 product, acetic acid and ethanol as C2 products, and acetone as a C3 product.

[0007] Preferably, during the electrocatalytic process, the organic electrocatalyst is dissolved in an organic solvent and dripped onto carbon paper as a working electrode.

[0008] The method for preparing the organic electrocatalyst for converting CO2 into C3, C2 and C1 products comprises the following steps:

[0009] (1) degassing o-phenylenediamine in toluene with argon steam, then adding PbO2, and reflux the solution for reaction. After the reaction is completed, filtering and collecting the filtrate, and purifying to obtain 2,2'-diaminoazobenzene;

[0010] (2) 2,2′-diaminoazobenzene is degassed in toluene with an argon stream, and then 2-nitroacetanilide and acetic acid are added, heated and stirred to react, and purified by column chromatography; the purified product is dissolved in a solvent, KOH is added, and the mixture is heated to react. After the reaction is completed, purification is performed to obtain the target product.

[0011] Furthermore, the synthetic route of the above reaction is as follows:

[0012] Preferably, in step (1), the molar ratio of o-phenylenediamine to PbO2 is 1:1 to 1:10, and the reflux reaction time is 1.5 to 6 hours.

[0013] Preferably, in step (2), the molar ratio of 2,2′-diaminoazobenzene, 2-nitroacetanilide and acetic acid is 1:1-4:1-15, the temperature during heating and stirring reaction is 40-90° C., and the reaction time is 24-72 hours.

[0014] Preferably, in step (2), the molar ratio of mono-protected o-bisaminobisazobenzene to KOH is 1:40 to 1:70, the heating reaction temperature is 60 to 100° C., and the reaction time is 1 to 5 hours; the KOH is pre-dissolved in a mixed solution of ethanol and water.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the organic electrocatalyst is the first of its kind to easily and efficiently convert CO2 into C1, C2, and especially C3 products. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 shows (a) the geometry of the catalyst optimized using DFT; (b) the cyclic voltammogram of the catalyst in homogeneous medium and over the full range (oxidation and reduction regions), with acetonitrile as solvent, carbon paper as working electrode, Ag / AgCl reference electrode, and supporting electrolyte = 0.1 M NaClO4; (c) the spin density of [1 ●● ] 2- Catalyst state; (d) Schematic diagram of the formation of two electron-reduced species [1 ●● ] 2- From 1; (e) Combined with the in situ UV-Vis map without CO2, the spectrum was recorded every 10 minutes (other colors), and the UV-Vis spectrum of [1 was calculated using DFT ●● ] 2- ;

[0017] Figure 2 shows (a) homogeneous cyclic voltammograms of a carbon paper electrode modified with an azo ligand in Ar (black) and saturated with CO2 (red) at a scan rate of 50 mV / s; (b) homogeneous cyclic voltammograms of a carbon paper electrode modified with an azo ligand in Ar (black) and CO2 (red) at a scan rate of 50 mV / s at a scan rate of 50 mV / s; (c) heterogeneous linear sweep voltammograms of a carbon paper electrode modified with an azo ligand in Ar (black) and CO2 (red) at pH 5.5; (d) heterogeneous linear sweep voltammograms of a carbon paper electrode modified with an azo ligand in Ar (black) and CO2 (red) at pH 6.7.

[0018] Figure 3 shows (a) controlled potential electrolysis at -0.28 V vs. Ag / AgCl on a carbon paper electrode modified with a catalyst in CO2-saturated phosphate buffer solutions at pH 5.5 and pH 6.7; (b) the analyte concentrations after 5 h of CPE in CO2-saturated buffer solutions. 1 H NMR spectra, with phenol and DMSO used as internal standards; (c) low-temperature EPR spectra of the analytes after 1 h of CPE; (d) DFT-optimized structure of the catalyst forming an adduct with CO2; (e) FE% versus potential for acetone and acetic acid;

[0019] Figure 4 shows the analytes after the addition of formic acid to CPE. 1 H NMR spectrum;

[0020] Figure 5 shows the analytes after adding glyoxal to CPE. 1 H NMR spectrum;

[0021] Figure 6 shows the analytes after addition of acetyl chloride and formic acid to CPE. 1 H NMR spectrum;

[0022] FIG7 is a diagram showing the hypothetical mechanism for the electrocatalytic formation of acetic acid and acetone;

[0023] FIG8 is a schematic diagram of the conversion of CO2 into C1, C2 and C3 products;

[0024] Figure 9 shows the catalyst 1 H NMR spectrum;

[0025] Figure 10 shows the catalyst 13 C NMR spectrum;

[0026] FIG11 is a HRMS spectrum of the catalyst;

[0027] FIG12 is an infrared spectrum of the catalyst;

[0028] FIG13 is a UV-Vis spectrum of the catalyst. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0030] Example 1

[0031] Synthesis of catalyst:

[0032] A solution of o-phenylenediamine (1.00 equivalent) in dry toluene (15 ml / mmol) was degassed with argon steam for 15 minutes. PbO (4.00 equivalent) was then added in a portion (1.00 equivalent / hour) and the solution was refluxed for 4 hours. After the reaction was complete, the dark red solution was filtered through a bed of diatomaceous earth 545 to remove excess PbO . The filtrate was collected and the solvent was removed under reduced pressure. Silica gel and toluene were used as eluents to carry out column chromatography on the residue to obtain the red, shiny crystals of 2,2'-diaminoazobenzene.

[0033] A solution of 2,2'-diaminoazobenzene (1.00 equivalent) in dry toluene (10 mL / mmol) was degassed with an argon stream for 15 minutes. 2-Nitroacetanilide (1.00 equivalent) and acetic acid (12.00 equivalent) were then added. The reaction mixture was stirred at 70°C for 72 hours and the solvent was removed under reduced pressure. The dark red oily residue was purified by column chromatography using silica gel and 2:1 hexane / EtOAc (v / v) as eluents.

[0034] The purified product was dissolved in ethanol, KOH (57.7 equivalents) was dissolved in a mixed solution of ethanol (20 mL) and water (15 mL), the two were mixed, and the mixture was heated to 90°C for about 1.5 hours. The mixture was poured onto crushed ice (300 g), extracted with CH2Cl2, dried over Na2SO4, and concentrated to produce a red oil, which was stored in a refrigerator overnight to obtain a solid product. Suitable crystals were grown from the heated hexane solution by slow evaporation. Product yield: 65%; HRMS [M + H] + : M / z 317.1533 (calculated 317.1515); 1 H NMR (300MHz, CDCl3) δ7.88 (dd, J=8.1, 1.6Hz, 2H. 13 C NMR (75 MHz, CDCl3) δ 116.71, 117.20, 117.33, 130.24, 130.51, 132.51, 137.97, 142.27, 148.04. The hydrogen spectrum, carbon spectrum, mass spectrum, infrared and ultraviolet spectrum of the catalyst are shown in Figures 9-13.

[0035] Example 2

[0036] Catalytic conditions for CO2RR:

[0037] Preparation of working electrode

[0038] By 0.5cm 2 The working electrode was prepared by dropping 50 mM acetonitrile solution containing catalyst onto carbon paper. The catalyst loading was 1.02 mg / cm 2 The electrodes were dried at room temperature for 1 h to remove excess acetonitrile. These electrodes were used for all inhomogeneous electrochemical measurements.

[0039] Linear sweep voltammetry (LSV), cyclic voltammetry (CV), and controlled potential electrolysis (CPE)

[0040] All heterogeneous and homogeneous LSV, CV and CPE experiments for CO2 reduction were performed in a three-neck airtight cell in a CHI400A model workstation, where the counter electrode was a Pt wire and an Ag / AgCl reference filled with 1M KCl was used. Phosphate buffer was used to maintain the pH of the solution, and 0.3M (pH = 5.5) and 0.15M (pH = 6.7) NaClO4·2H2O were used as supporting electrolytes in all cases. All controlled potential electrolysis was performed for 5 hours with continuous CO2 purge. In the homogeneous electrolysis, cyclic voltammetry was performed with a non-aqueous Ag reference electrode, 0.1M NaClO4·2H2O loaded electrolyte, Pt wire as the counter electrode and carbon paper as the working electrode, as shown in Figure 2.

[0041] Spectroelectrochemical UV-Visible Experiment (SEC UV-Vis)

[0042] Spectroelectrochemical measurements were performed on an Ocean Mini Probe using a quartz cuvette. In situ UV-Vis spectroscopy was performed for 90 minutes during the CPE, with UV-Vis spectra recorded every 10 minutes.

[0043] EPR

[0044] Electron paramagnetic resonance spectroscopy measurements were performed on a Bruker EMX CW microX-band EPR spectrometer equipped with an ER4119HS high-sensitivity resonator, with a microwave power of Ca 6.9 mW and a modulation frequency and amplitude of 100 kHz and 5 G, respectively. EPR spectra of CPE samples were recorded at low temperatures. One hour after CPE, the analytes in the cells were placed in capillary tubes, stored in EPR tubes, and immersed in liquid nitrogen to maintain low temperatures.

[0045] Product testing and 1 H-NMR quantification

[0046] The CO2 reduction products after CPE were detected and quantified using a Neo Advance Bruker 500MHz NMR spectrometer. Equal amounts of 20mM phenol and 10mM DMSO were mixed to prepare the internal standard. NMR samples were prepared by extracting 350μl of analyte, 50μl of internal standard, and 200μl of D2O in an NMR tube (7 inches high, 5mm diameter). 1 Solvent suppression was used to enhance signal intensity in H NMR spectroscopy. Acetic acid and acetone peaks were detected at 2 ppm and 2.17 ppm, respectively. Product quantification was performed by integrating the DMSO peak at 2.6 ppm.

[0047] Electronic absorption spectroscopy

[0048] UV-visible spectroscopy was performed on a UV-1800 Shimazdu spectrometer to record the spectra of the catalysts. In addition, the spectra of the analytes after CPE and the catalyst concentration loaded after dissolution in ACN were recorded to examine the stability of the catalysts.

[0049] XPS analysis

[0050] XPS was performed using a PHI-VersaProbe4, ULVAc-PHI.INC instrument, using monochromatic Al Kα (1486.7 eV), a spot size of 100 μm, photoelectrons taking off at a 45° angle to the surface plane, and a single flood gun for charge neutralization. The stability of the catalyst was analyzed by XPS analysis of the modified carbon paper electrode before and after CPE.

[0051] As shown in Figure 1, the organic electrocatalyst of the present invention is designed to possess inherent coordination mobility. In the catalyst's structure, two azo groups are embedded at the o-position of the benzene ring. These groups function as two mobile, side-by-side electron pockets to accept electron pairs and can be converted into the corresponding triplet azo anion diradicals as the active catalyst. This ability to behave as diradicals is of great electronic importance, as these individual stereoelectronic azo anion radical centers can further serve as electron sinks and metastable platforms for activating kinetically inert CO2 molecules by providing anchoring sites for them. Notably, the close proximity of the azo functional groups provides a platform for the simultaneous approach of two CO2 molecules, one terminal and the other lateral. This positioning of the azo groups provides scope for stepwise electron transfer from the azo anion radical pockets. Furthermore, the ligand platform possesses two amino functional groups at either end, which can be protonated at slightly acidic pH and serve as proton sources to promote CO2 activation and subsequent valence via a proton-coupled electron transfer (PCET) pathway. The electron-accepting catalyst converts to a triplet diradical state, forming an adduct with a CO2 molecule for CO2RR. These unique features of this metal-free catalyst make it suitable for electrocatalysis, and CO2RR to C2+ products is possible, as well as a cascade catalysis from C1 to C2 to C3 via glyoxal as an intermediate state.

[0052] DFT-optimized triplet diradical structures infer an increased bond length (NN) and a planar structure, bringing the azo groups closer together. CO2 then forms adducts with the azo moiety in both pendant and end-on modes. These adducts transfer electrons to the CO2 molecule in a stepwise manner, forming CO through conformational changes in the ligand framework. This distortion facilitates proton transfer from the -NH2 moiety, promoting proton-coupled electron transfer reactions.

[0053] The mechanism of the present invention for activating the precatalyst by converting diradicals is shown in FIG3(d). Since the azo moiety is electron-deficient and can easily accept 1e - and 2e - Forming [-N=N-] 。 Azo radical anion and 2e - Form [-N=N-] 2-The azodiradical anion further attacks CO2. To verify this claim, the present invention performed uniform electrochemical cyclic voltammetry by adding a precatalyst to an acetonitrile (AcCN) solvent, using a Pt wire as the counter electrode, carbon paper as the working electrode, non-aqueous Ag as the reference electrode, and NaClO4·2H2O as the supporting electrode, with a potential range of -2.5 to -2.5 V. The two reduction peaks at -0.26 V and -1.4 V relative to Ag / AgCl in Figure 2(a) confirm that the azo group accepts two electrons one after another in its π* orbital and redox couple, one of which is reversible and the other irreversible. This irreversible anion creates instability in the catalyst and is active towards CO2 molecules to achieve stability. In addition, cyclic voltammetry was performed in a CO2-saturated system for comparison, as shown in Figure 2(a). The disappearance of the reduction peak at -1.4 V in the voltammogram confirmed the formation of an adduct between the azo moiety of the ligand and the CO2 molecule and also showed the electrochemical activation of the catalyst.

[0054] In addition, the present invention further discloses the role of water. As shown in Figure 2(b), ACN:H2O=5:2 and ACN cyclic voltammogram, the current in water tends to increase significantly compared with the CO2 saturated system, showing the effect of proton-coupled electron transfer CO2 reduction reaction.

[0055] The catalyst described in the present invention is insoluble in water, so it is used as a heterogeneous electrocatalyst by fixing it on carbon paper. The redox couple obtained is the same as that of the homogeneous electrocatalyst. The specific process is: using catalyst-immobilized carbon paper as a working medium, and performing linear sweep voltammetry relative to Ag / AgCl at a potential of 0 to -2 V at pH 5.5 and 6.7 in argon and CO2-saturated media. In this electrochemical device, Pt wire is used as a counter electrode, Ag / AgCl reference electrode, and 0.1M NaClO4·2H2O as a carrier in water. When comparing the voltammograms, the changes in current density in Ar and CO2-saturated media are observed in Figures 2(c) and 2(d). In addition, it is observed that the current increases sharply from -1 to -2 V compared with Ag / AgCl, and gas is released from both the working electrode and the counter electrode, which indicates that the water-retaining charge balance in the battery circuit is oxidized. The difference in current density indicates the activation of CO2 。

[0056] The present invention also performs controlled potential electrolysis (CPE), wherein a change in current density is observed in the voltammogram. The present invention discloses CPE with a potential of 0 to -0.65 vs Ag / AgCl continuously purged in a saturated CO2 solution and using 1H NMR characterized and quantified the analytes. At an onset potential of -0.28 V, C1 (formic acid), C2 (acetic acid and ethanol), and C3 (acetone) were formed. Figure 8 shows a schematic diagram of the conversion of CO2 to C1, C2, and C3 products. The (FE) of C3 ranged from 20% to 30%, that of acetic acid from 20% to 30%, and that of C1 from 5% to 10%. Ethanol content was very low (see Figure 3(e)).

[0057] The pH was maintained between 5 and 7 to suppress the HER and provide excess protons for the proton-electron transfer reaction. The activity of the catalyst was verified by homogeneous cyclic voltammetry experiments. Figure 3(a) shows a schematic diagram of controlled potential electrolysis at a potential of -0.28 V vs. Ag / AgCl on a carbon paper electrode modified with the catalyst in CO2-saturated phosphate buffer solutions at pH 5.5 and pH 6.7. Figure 3(b) shows the analyte after 5 hours of CPE in CO2-saturated buffer solution. 1 H NMR spectrum. Triplet diradicals were also observed in the EPR spectrum recorded during the CPE process, as shown in Figure 3(c). The present invention discloses intermediates for the formation of C3 and C2 products. As we know, formyl radicals are the initial step of the CO2RR process. Therefore, formic acid was added to the buffer solution, CPE was run, and 1 H NMR, acetic acid and acetone peaks were observed in the spectrum shown in Figure 4. In addition, glyoxal was added to the buffer solution and CPE was performed. 1 Acetone and acetic acid were found in the H spectrum, as shown in Figure 5. These two control experiments inferred that formic acid and glyoxal were the key intermediates in the formation of C2 and C3 products. Acetyl chloride and formic acid were added to the buffer solution, and CPE was performed. 1 H NMR, in the spectrum shown in Figure 6 , a peak of acetone was observed when CPE was run by adding acetyl chloride and formic acid to the buffer solution.

[0058] The present invention further discloses the role of formic acid and acetic acid in the formation of acetone. We add acetyl chloride and formic acid under all conditions unchanged and perform CPE. 1 The H NMR spectrum showed the formation of acetone. This indicates that the acetyl and formyl groups were combined with protons in the medium to give acetone, as shown in Figure 7.

Claims

1. An organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that The organic electrocatalyst is 2,2'-((1E,1'E)-1,2-phenylenebis(diazene-2,1-diyl))dianiline, and its structural formula is as follows:

2. The organic electrocatalyst according to claim 1 for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that The product includes C 1 The product formic acid, C 2 The product acetic acid and ethanol, C 3 The product acetone.

3. The organic electrocatalyst according to claim 1 for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that In the electrocatalysis process, the organic electrocatalyst is dissolved in an organic solvent and dripped onto carbon paper as the working electrode.

4. A method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that It includes the following steps: (1) Degas o-phenylenediamine in toluene with argon vapor, and then add PbO 2 , reflux the solution for reaction. After the reaction is completed, filter and collect the filtrate, and obtain 2,2'-diaminoazobenzene after purification; (2) Degas 2,2′-diaminoazobenzene in toluene with an argon stream, then add 2-nitroacetanilide and acetic acid, heat and stir for reaction, and purify by column chromatography; dissolve the purified product in a solvent, add KOH, heat the mixture for reaction, and after the reaction is completed, carry out purification treatment to obtain the target product.

5. The method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products, It is characterized in that The synthetic route is as follows:

6. The method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products as claimed in claim 4 It is characterized in that In step (1), the molar ratio of o-phenylenediamine to PbO 2 is 1:1 to 1:

10.

7. The method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that In step (1), the reflux reaction time is 1.5 to 6 hours.

8. The method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that In step (2), the molar ratio of 2,2′-diaminoazobenzene, 2-nitroacetanilide and acetic acid is 1:1 to 4:1 to 15.

9. The method for preparing an organic electrocatalyst according to claim 4 for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that In step (2), the temperature during the heating and stirring reaction is 40 to 90 °C, and the reaction time is 24 to 72 hours.

10. The method for preparing an organic electrocatalyst for converting CO 2 into C 3 , C 2 and C 1 products It is characterized in that In step (2), the molar ratio of the purified product to KOH is 1:40 to 1:70, the heating reaction temperature is 60 to 100 °C, and the reaction time is 1 to 5 hours.

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