Organic electrocatalysts for conversion of co2 to c3, c2 and c1 products and methods of making the same
CO2 in the prior art was solved by using 2,2'-((1E,1'E)-1,2-phenylene bis(diazane-2,1-diyl)diphenylamine as an organic electrocatalyst The problem of difficulty in converting to C3, C2 and C1 products simultaneously achieves efficient and selective catalytic effects and provides an innovative solution for metal-free catalysts.
Patent Information
- Application Number
- CN202311671188.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-07
- Publication Date
- 2025-01-03
AI Technical Summary
The prior art is difficult to efficiently convert CO2 into C3, C2 and C1 products simultaneously, and there are few researches on catalytic materials for C3 products, especially C3 products.
2,2'-((1E,1'E)-1,2-phenylene bis(diazane-2,1-diyl)diphenylamine is used as an organic electrocatalyst and dissolved by a specific synthetic method. Drip in the organic solvent on carbon paper as a working electrode, and conducts an electrocatalytic process to achieve the conversion of CO2 into C3, C2 and C1 products.
The high selectivity and efficiency of efficient conversion of CO2 into C1, C2 and especially C3 products is achieved, providing a metal-free catalyst solution, which is significantly better than the prior art.
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Figure CN119241389A_ABST
Abstract
Description
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. So far, high FE C1 and C2 products have been reported, but C3 products with metal-free catalysts are still rarely explored. For example, Chinese invention patent CN 112251766 A discloses a method for preparing carbon monoxide with high selectivity and high efficiency by electrochemical reduction of carbon dioxide; Chinese invention patent CN 114672846 A discloses the preparation and application of a bimetallic catalytic material for electrocatalytic CO2 reduction, and the prepared Cu / Ni-NC catalytic material can increase metal utilization, reduce costs, inhibit hydrogen evolution reaction, and improve the Faraday efficiency of electrocatalytic CO2 reduction to CO; Chinese patent CN 114381747 A discloses a method for preparing an electrocatalytic electrode for electrochemical reduction of carbon dioxide to prepare ethylene, but there are still few reports on catalytic materials that can efficiently and selectively convert carbon dioxide into C3, C2 and C1 products at the same time. Summary of the invention
[0003] 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.
[0004] Technical solution: The organic electrocatalyst for converting CO2 into C3, C2 and C1 products of the present invention is 2,2'-((1E, 1'E)-1,2-phenylenebis(diazene-2,1-diyl)diphenylamine, and the structural formula is as follows:
[0005]
[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, in 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 refluxing the solution to react. After the reaction is completed, filtering and collecting the filtrate, and purifying to obtain 2,2'-diaminoazobenzene;
[0010] (2) Degas 2,2′-diaminoazobenzene in toluene with an argon flow, then add 2-nitroacetanilide and acetic acid, heat and stir to react, and purify by column chromatography; dissolve the purified product in a solvent, add KOH, heat the mixture to react, and after the reaction is completed, purify to obtain the target product.
[0011] Further, the synthetic route of the above reaction is as follows:
[0012]
[0013] 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.
[0014] 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.
[0015] Preferably, in step (2), the molar ratio of mono-protected o-bisaminobisazobenzene to KOH is 1:40-1:70, the heating reaction temperature is 60-100° C., and the reaction time is 1-5 hours; the KOH is pre-dissolved in a mixed solution of ethanol and water.
[0016] 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
[0017] Figure 1 (a) The geometry of the catalyst optimized using DFT; (b) Cyclic voltammograms of the catalyst in homogeneous medium and full range (oxidation and reduction region), acetonitrile as solvent, carbon paper as working electrode, Ag / AgCl reference electrode, supporting electrolyte = 0.1M 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 image without CO2, the spectrum was recorded every 10 minutes (other colors), and the UV-Vis spectrum of [1 was calculated using DFT ●● ] 2- ;
[0018] Figure 2(a) Homogeneous cyclic voltammograms of the electrode dissolved in ACN in Ar (black) and saturated with CO2 (red) at a scan rate of 50 mV / s; (b) Homogeneous cyclic voltammograms of the electrode dissolved in ACN:H2O (5:2) in Ar (black) and CO2 (red) at a scan rate of 50 mV / s; (c) Heterogeneous linear sweep voltammograms of the carbon paper electrode modified with azo ligands at pH 5.5 in Ar (black) and CO2 (red); (d) Heterogeneous linear sweep voltammograms of the carbon paper electrode modified with azo ligands at pH 6.7 in Ar (black) and CO2 (red);
[0019] Figure 3 Figure 3 is a graph showing (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 at pH 5.5 and pH 6.7; (b) CPE of the analyte after 5 h in CO2-saturated buffer. 1 H NMR spectra, phenol and DMSO were used as internal standards; (c) low-temperature EPR spectra of the analytes after 1 h of CPE; (d) DFT-optimized structure of the catalyst for adduct formation with CO2; (e) FE% versus potential for acetone and acetic acid;
[0020] Figure 4 For the analytes with formic acid added after CPE 1 H NMR spectrum;
[0021] Figure 5 After adding glyoxal to CPE, the analytes 1 H NMR spectrum;
[0022] Figure 6 For the analytes with acetyl chloride and formic acid added after CPE 1 H NMR spectrum;
[0023] Figure 7 Diagram of the hypothesized mechanism for the electrocatalytic formation of acetic acid and acetone;
[0024] Figure 8 Schematic diagram of the conversion of CO2 into C1, C2 and C3 products;
[0025] Fig. 9 For catalyst 1 H NMR spectrum;
[0026] Fig.10 For catalyst 13 C NMR spectrum;
[0027] Fig.11 is the HRMS spectrum of the catalyst;
[0028] Fig.12 is the infrared spectrum of the catalyst;
[0029] Fig.13 UV-Vis spectrum of the catalyst. DETAILED DESCRIPTION
[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.
[0031] Example 1
[0032] Catalyst synthesis:
[0033]
[0034] A solution of o-phenylenediamine (1.00 equivalent) in dry toluene (15 ml / mmol) was degassed with argon steam for 15 minutes. Then PbO2 (4.00 equivalent) was 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 PbO2. 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.
[0035] A solution of 2,2'-diaminoazobenzene (1.00 equivalent) in dry toluene (10 mL / mmol) was degassed with an argon stream for 15 minutes. Then, 2-nitroacetanilide (1.00 equivalent) and acetic acid (12.00 equivalent) were 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 eluent.
[0036] 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, 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 with 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. 13C NMR (75MHz, CDCl3) δ116.71, 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 Figure 9-13 .
[0037] Example 2
[0038] Catalytic conditions for CO2RR:
[0039] Preparation of working electrode
[0040] By 0.5cm 2 The working electrode was prepared by dropping 50 mM acetonitrile solution containing the 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.
[0041] Linear sweep voltammetry (LSV), cyclic voltammetry (CV), and controlled potential electrolysis (CPE)
[0042] All heterogeneous and homogeneous LSV, CV and CPE experiments for CO2 reduction were performed in a three-neck gastight 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, respectively. All controlled potential electrolysis were performed for 5 h 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 5. Figure 2 shown.
[0043] Spectroelectrochemical UV-Visible Experiment (SEC UV-Vis)
[0044] Spectroelectrochemical measurements were performed on an Ocean Mini Probe using a quartz cuvette. In situ UV-Vis spectroscopy was performed for 90 min during the CPE, with UV-Vis spectroscopy being performed every 10 min. Spectra were recorded.
[0045] EPR
[0046] 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. The EPR spectra of the CPE samples were recorded at low temperatures. One hour after CPE, the analytes in the cells were placed in capillaries, stored in EPR tubes, and immersed in liquid nitrogen to keep them cryogenic.
[0047] Product testing and 1 H-NMR quantification
[0048] 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, 5 mm diameter). 1 Solvent suppression was used to enhance signal intensity in H NMR spectroscopy. Acetic acid and acetone peaks were found at 2 ppm and 2.17 ppm, respectively. Quantification of the product was performed by integrating the DMSO peak at 2.6 ppm.
[0049] Electronic absorption spectroscopy
[0050] UV-visible spectroscopy measurements were performed in 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 check the stability of the catalysts.
[0051] XPS analysis
[0052] 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.
[0053] like Figure 1As shown, the design of the organic electrocatalyst of the present invention has inherent coordination mobility. In the structural formula of the catalyst, two azo groups are embedded in the o position of the benzene ring, which can accept electron pairs as two mobile side-by-side electron pockets and can be converted into corresponding triplet azo anion diradicals as active catalysts. Its ability to behave in the form of diradicals has great electronic importance, because these individual stereoelectronic azo anion radical centers can further act as electron pools and metastable platforms for activating kinetically inert carbon dioxide molecules by providing anchoring sites for kinetically inert carbon dioxide molecules. It is worth noting that the azo functional groups are very close, which provides a platform for the simultaneous approach of two CO2 molecules, one on the end and the other on the side. This positioning of the azo group provides a range for the gradual transfer of electrons from the azo anion radical pocket. In addition, the ligand platform has two amino functional groups at both ends, which can be protonated at weakly acidic pH and can also serve as a proton source to promote CO2 activation, followed by valence through the proton coupled electron transfer (PCET) pathway. The electron-accepting catalyst converts to a triplet diradical state to form an adduct with a CO2 molecule for CO2RR. These unique features of this metal-free catalyst make it suitable for electrocatalysts, and CO2RR to C2+ products is possible, and cascade catalysis from C1 to C2 to C3 is performed via glyoxal as an intermediate state.
[0054] The triplet diradical structure optimized using DFT inferred that the bond length NN increased and the structure was planar, which brought the azo group closer. Thereafter, CO2 formed adducts with the azo moiety in both side- and end-on modes. They transferred electrons to the CO2 molecule in a stepwise manner and formed CO through conformational changes in the ligand framework. This distortion facilitated the transfer of protons from the -NH2 moiety, thereby promoting proton-coupled electron transfer reactions.
[0055] The present invention activates the pre-catalyst by the conversion of two free radicals. Figure 3 As shown in (d), the azo moiety is electron-deficient and readily accepts a 1e in its lower π* orbital. - and 2e - Formation of [-N=N-]° azo radical anion and 2e - Form [-N=N-] 2- Azodiradical anion, which further attacks CO2. In order to verify the above statement, the present invention adds precatalyst in acetonitrile (AcCN) solvent, uses Pt wire as counter electrode, carbon paper as working electrode, non-aqueous Ag as reference electrode, and conducts uniform electrochemical cyclic voltammetry, NaClO4·2H2O as supporting electrode, and the potential range is -2.5 to -2.5V. Figure 2The two reduction peaks at -0.26V and -1.4V relative to Ag / AgCl in (a) confirm that the azo group accepts 2 electrons one by one in its π* orbital and redox couple, one of which is a reversible radical anion and the other is irreversible. This irreversible anion creates instability in the catalyst and is active towards CO2 molecules to gain stability. In addition, cyclic voltammetry was performed in a CO2 saturated system and compared, as shown in Figure 2. Figure 2 (a) The voltammogram with the reduction peak at -1.4 V disappears, confirming the formation of an adduct between the azo moiety of the ligand and the CO2 molecule, and also showing the electrochemical activation of the catalyst.
[0056] In addition, the present invention further discloses the role of water, such as Figure 2 (b) shows the cyclic voltammograms of ACN:H2O=5:2 and ACN. Compared with the CO2-saturated system, the current in water tends to increase significantly, showing the effect of proton-coupled electron transfer CO2 reduction reaction.
[0057] 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 -2V at pH 5.5 and 6.7 in an argon and CO2 saturated medium. In this electrochemical device, Pt wire is used as a counter electrode, Ag / AgCl reference electrode, and 0.1MNaClO4·2H2O as a carrier in water. When comparing the voltammograms, it is observed Figure 2 (c) and Figure 2 (d) Changes in current density in Ar and CO2-saturated media. In addition, a sharp increase in current from -1 to -2 V vs. Ag / AgCl was observed, with gas released from both the working and counter electrodes, indicating that the water-retaining charge balance in the cell circuit was oxidized. The difference in current density indicates the activation of CO2.
[0058] 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 continuous purging from a potential of 0 to -0.65 vs Ag / AgCl in a saturated CO2 solution, and using 1 The analytes were characterized and quantified by H NMR. At an onset potential of -0.28 V, C1 (formic acid), C2 (acetic acid and ethanol), and C3 (acetone) were formed. Figure 8 Schematic diagram of the conversion of CO2 into C1, C2 and C3 products. The (FE) of C3 ranges from 20% to 30%, acetic acid is 20-30%, C1 (FE) ranges from 5-10%, and ethanol content is very low. Figure 3 (e).
[0059] The pH was maintained between 5 and 7 to suppress HER and provide excess protons for proton-electron transfer reactions. The activity of the catalyst was verified by homogeneous cyclic voltammetry experiments. Figure 3 (a) Schematic diagram of controlled potential electrolysis at a potential of −0.28 V relative to Ag / AgCl on a catalyst-modified carbon paper electrode in CO2-saturated phosphate buffer solutions at pH 5.5 and pH 6.7. Figure 3 (b) is the analyte concentration after 5 h of CPE in CO2-saturated buffer solution. 1 HNMR spectroscopy. Triplet diradicals were also observed in the EPR spectra recorded during CPE, such as Figure 3 (c) is shown. The present invention discloses intermediates for forming C3 and C2 products. As we know, formyl radical is the initial step of CO2RR process. Therefore, formic acid is added to the buffer solution, CPE is run, and 1 H NMR, Figure 4 In the spectrum shown, acetic acid and acetone peaks were observed. In addition, glyoxal was added to the buffer solution and CPE was performed. 1 Acetone and acetic acid were found in the H spectrum, such as Figure 5 These two control experiments infer that formic acid and glyoxal are key intermediates in the formation of C2 and C3 products. Acetyl chloride and formic acid were added to the buffer solution, CPE was run, and 1 HNMR, Figure 6 The spectrum shown shows the peak of acetone observed when running CPE by adding acetyl chloride and formic acid in the buffer solution.
[0060] 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 inferred that the acetyl and formyl groups were combined with protons in the medium to give acetone, such as Figure 7 shown.
Claims
1. An organic electrocatalyst for converting CO2 into C3, C2 and C1 products, characterized in that: The organic electrocatalyst is 2,2'-((1E, 1'E)-1,2-phenylenebis(diazene-2,1-diyl)diphenylamine, and the structural formula is as follows:
2. The organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 1, characterized in that The products include C1 product formic acid, C2 products acetic acid and ethanol, and C3 product acetone.
3. The organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 1, characterized in that In the electrocatalytic process, the organic electrocatalyst is dissolved in an organic solvent and dripped onto carbon paper as a working electrode.
4. A method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products as claimed in claim 1, characterized in that: The steps include: (1) degassing o-phenylenediamine in toluene with argon steam, then adding PbO2, and refluxing the solution to react. After the reaction is completed, filtering and collecting the filtrate, and purifying to obtain 2,2'-diaminoazobenzene; (2) Degassing 2,2′-diaminoazobenzene in toluene with an argon flow, then adding 2-nitroacetanilide and acetic acid, heating and stirring to react, and purifying by column chromatography; dissolving the purified product in a solvent, adding KOH, heating the mixture to react, and after the reaction is completed, purifying to obtain the target product.
5. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, characterized in that: The synthetic route is as follows:
6. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, characterized in that: The molar ratio of o-phenylenediamine to PbO2 in step (1) is 1:1 to 1:
10.
7. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, characterized in that: The reflux reaction time in step (1) is 1.5 to 6 hours.
8. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, characterized in that: In step (2), the molar ratio of 2,2′-diaminoazobenzene, 2-nitroacetanilide and acetic acid is 1:1-4:1-15.
9. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, characterized in that: The temperature during the heating and stirring reaction in step (2) is 40 to 90° C., and the reaction time is 24 to 72 hours.
10. The method for preparing an organic electrocatalyst for converting CO2 into C3, C2 and C1 products according to claim 4, 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.