Water-soluble cobalt porphyrin catalyst, preparation method thereof and application of water-soluble cobalt porphyrin catalyst in photocatalytic reduction of pure water phase CO2

Abstract

The embodiment of the invention discloses a water-soluble cobalt porphyrin catalyst, a preparation method of the water-soluble cobalt porphyrin catalyst and application of the water-soluble cobalt porphyrin catalyst in pure water phase CO2 photocatalytic reduction, relates to the technical field of catalysts, and aims to overcome the defects of an existing pure water phase CO2 photocatalytic reduction reaction (CO2RR) technology. The structural general formula of the water-soluble cobalt porphyrin catalyst is shown in the specification, in the structural general formula, when R1 = F, R2 = R3 = H, the water-soluble cobalt porphyrin catalyst is 6F-CoTMPyP; when R1 is equal to Me, R2 is equal to R3 and H is equal to H, the water-soluble cobalt porphyrin catalyst is 6Me-CoTMPyP; when R2 is equal to Me and R1 is equal to R3 and H is equal to H, the water-soluble cobalt porphyrin catalyst is 5Me-CoTMPyP; when R3 is equal to Me and R1 is equal to R2 is equal to H, the water-soluble cobalt porphyrin catalyst is 4Me-CoTMPyP; when R1 = R3 = Me, and R2 = H, the water-soluble cobalt porphyrin catalyst is 4, 6Me-CoTMPyP.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalysts, in particular to a water-soluble cobalt porphyrin catalyst, a preparation method thereof and application thereof in pure water phase CO2 photocatalytic reduction. BACKGROUND

[0002] The acceleration of the globalization process has led to a sharp increase in CO2 emissions, which has become an environmental problem that needs to be addressed urgently. It is essential to develop efficient CO2 conversion technologies. Among them, using solar energy to drive CO2RR can convert CO2 into high-value-added chemicals (such as CO, formic acid, methanol, etc.), which has both environmental benefits and economic value, and is a green technology path with great development potential. However, the inherent reaction inertness and high reduction energy barrier of CO2 make its conversion difficult, and the distribution of reduced products is complex, so it is urgent to design catalysts to overcome the above challenges.

[0003] Metal complexes have been widely used in the field of photocatalytic CO2RR due to their clear structure-activity relationship and easy-to-study reaction mechanism. Among them, complexes based on noble metals (such as Ru, Re, Ir) have shown good performance, but their high cost has limited their large-scale application. Therefore, developing complex catalysts based on inexpensive metals (such as Fe, Co, Ni, Mn, Zn, Cu, etc.) has become an important research direction. However, the above technologies all need to be carried out in organic solvents such as acetonitrile, DMF or organic / water mixed solvents, which essentially still rely on organic medium environment. However, there are relatively few reports on water-soluble molecular catalysts with excellent catalytic performance designed and developed for pure water phase systems.

[0004] Compared with organic solvent-dependent systems, pure water phase photocatalytic systems have shown great application prospects due to their green environmental protection, low cost and sustainability. However, this system puts forward more stringent requirements for the catalyst and faces unique challenges: (1) The hydrogen evolution reaction (HER) competition in the pure water phase system is extremely fierce, which greatly reduces the selectivity of CO2 reduction; (2) The catalyst in this system not only needs to have good water solubility, but also must maintain catalytic activity and molecular structure stability in the water phase environment to avoid catalyst molecular deactivation. The above challenges together result in the common bottleneck problems of low catalytic activity, poor product selectivity and poor catalyst stability when existing catalysts are applied to pure water phase systems, which seriously restricts the practical application and development of pure water phase photocatalytic CO2RR technology.

[0005] In the prior art, a photocatalytic system composed of photosensitizer 4P-DPAIPN and catalyst CoTMPyP has been adopted (Journal of the American Chemical Society, 2024, 146, 17773-17783.), which has realized a high apparent quantum yield of CO, however, the stability of the catalyst CoTMPyP in the system is poor, and it is easy to be deactivated, which seriously restricts the efficiency and long-term use value of the system. Therefore, developing a photocatalytic CO2 reduction catalyst suitable for pure water phase environment, which has excellent water solubility, high catalytic activity, high selectivity and good stability, especially a high-efficiency water-soluble molecular catalyst based on a cheap metal, has become a key problem to be broken through in the current field. SUMMARY

[0006] The main purpose of the present application is to provide a water-soluble cobalt porphyrin catalyst and a preparation method and application thereof, aiming at improving the deficiencies of the existing pure water phase photocatalytic CO2RR technology.

[0007] To achieve the above-mentioned purpose, the technical solutions adopted by the embodiments of the present application are as follows: In a first aspect, the embodiments of the present application provide a water-soluble cobalt porphyrin catalyst, the structure general formula of which is as follows: ; In the above structure general formula: When R1=F, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6F-CoTMPyP; When R1=Me, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6Me-CoTMPyP; When R2=Me, R1=R3=H, the water-soluble cobalt porphyrin catalyst is 5Me-CoTMPyP; When R3=Me, R1=R2=H, the water-soluble cobalt porphyrin catalyst is 4Me-CoTMPyP; When R1=R3=Me, R2=H, the water-soluble cobalt porphyrin catalyst is 4,6Me-CoTMPyP.

[0008] In a second aspect, the embodiments of the present application provide a preparation method of the water-soluble cobalt porphyrin catalyst as described above, comprising the following steps: The pyrrole and the pyridine aldehyde derivative are mixed according to a molar ratio of (1.0-1.3) : 1, then the mixture is heated to the refluxing temperature of the selected solvent under the action of an acid catalyst and in a nitrogen atmosphere to carry out a condensation reaction, the reaction progress is monitored by thin layer chromatography, and generally 4 to 6 hours of reaction is required until the aldehyde raw material point basically disappears, and a porphyrin ligand is generated; The porphyrin ligand is mixed with Co(CH3COO)2·4H2O in a molar ratio of 1:(3-5) in a DMF solvent, the mixture is heated to the reflux temperature of the selected solvent, and the reaction is usually required for 6-10 hours to generate a reaction solution containing a cobalt porphyrin complex intermediate; The reaction solution is cooled to room temperature, an excess of methyl iodide (for example, 16.0-30.0 equivalents, relative to the porphyrin ligand) is added thereto, and the quaternary ammonium saltization reaction is continued by heating to reflux (8-12 hours). After the reaction is completed, the reaction solution is concentrated to remove most of the organic solvent, and a saturated NaPF6 aqueous solution is added to the obtained residue to precipitate the target product. The solid is collected by filtration, washed, and dried to obtain the target water-soluble cobalt porphyrin complex catalyst.

[0009] As some optional embodiments of the present application, the porphyrin ligand includes at least one of 6F-TPyP, 6Me-TPyP, 5Me-TPyP, 4Me-TPyP, and 4,6Me-TPyP.

[0010] As some optional embodiments of the present application, when the porphyrin ligand is 6F-TPyP or 6Me-TPyP, the solvent is xylene, and the acidic catalyst is salicylic acid.

[0011] As some optional embodiments of the present application, when the porphyrin ligand is 5Me-TPyP, 4Me-TPyP, or 4,6Me-TPyP, the solvent and the catalyst are both propionic acid.

[0012] As some optional embodiments of the present application, the cobalt porphyrin complex intermediate includes at least one of 6F-CoTPyP, 6Me-CoTPyP, 5Me-CoTPyP, 4Me-CoTPyP, and 4,6Me-CoTPyP.

[0013] As some optional embodiments of the present application, the reagent used for washing includes ethyl acetate, water, and methanol.

[0014] As some optional embodiments of the present application, the target water-soluble cobalt porphyrin complex catalyst includes at least one of 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, and 4,6Me-CoTMPyP.

[0015] In a third aspect, the embodiments of the present application provide an application of the water-soluble cobalt porphyrin catalyst as described above. The water-soluble cobalt porphyrin catalyst is applied to a pure water phase photocatalytic CO2RR as a catalyst to construct a pure water phase photocatalytic CO2reduction system. The system includes: a photosensitizer: 4P-DPAIPN; Electron sacrificial agent: sodium ascorbate (AscHNa); Catalyst: at least one of 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP and 4,6Me-CoTMPyP; Reaction medium: 0.1M NaHCO3buffer solution.

[0016] As some optional embodiments of the present application, when the water-soluble cobalt porphyrin catalyst is applied as a catalyst in the photocatalytic CO2RR in pure aqueous phase, the method comprises the following steps: The catalyst, the photosensitizer and the electron sacrificial agent are added to the reaction medium to obtain a mixed solution, and the mixed solution is placed in a sealed quartz reactor. CO2gas is continuously introduced into the sealed quartz reactor for bubbling to replace the air in the system until the CO2gas is saturated; then the sealed quartz reactor is irradiated with an LED light source, and at a predetermined time point, the reduced products in the gas above the reactor cavity are quantitatively analyzed by gas chromatography.

[0017] Compared with the prior art, the present application provides a cobalt porphyrin complex with novel structure, excellent water solubility and low cost, and an efficient preparation method thereof, i.e. a series of water-soluble cobalt porphyrin complexes (6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP and 4,6Me-CoTMPyP) with specific pyridine ring substituents (-Me, -F) are successfully synthesized, which have clear structure and good water solubility. The provided preparation method has clear steps and is feasible, which provides a reliable way for the synthesis of such catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Synthesis route of the water-soluble cobalt porphyrin catalyst of the present application; Figures 2-6 Nuclear magnetic resonance hydrogen spectrum of the porphyrin ligand prepared in Example 1-5 of the present application, respectively; Figures 7-11 Nuclear magnetic resonance carbon spectrum of the porphyrin ligand prepared in Example 1-5 of the present application, respectively; Figure 12 Nuclear magnetic resonance fluorine spectrum of the porphyrin ligand prepared in Example 2 of the present application; Figures 13-17 Mass spectrum and mass spectrum fitting diagram of the porphyrin ligand prepared in Example 1-5 of the present application, respectively; Figures 18-22 Mass spectrum and mass spectrum fitting diagram of the water-soluble cobalt porphyrin complex prepared in Example 1-5 of the present application, respectively; Figure 23 FIG. 1 is a performance comparison chart of the photocatalytic CO2 reduction of the water-soluble cobalt porphyrin catalyst of application example 1. DETAILED DESCRIPTION

[0019] It should be understood that the specific embodiments described herein are merely exemplary and not intended to limit the present application.

[0020] As described above, metal complexes are widely used in photocatalytic CO2 reduction reaction (CO2RR) due to their clear structure-activity relationship and easy-to-study reaction mechanism. Among them, noble metal complexes have good performance but high cost, so inexpensive metal complexes have become the focus of research. However, these technologies all rely on organic solvents or organic / water mixed solvents, and there are few reports on excellent water-soluble molecular catalysts in pure aqueous phase systems. Although the pure aqueous phase photocatalytic system has the advantages of green environmental protection, low cost and sustainability, and has great application prospects, it is very demanding for catalysts and faces two major challenges: first, the hydrogen evolution reaction (HER) in the pure aqueous phase system is highly competitive, which reduces the selectivity of CO2 reduction; second, the catalyst needs to have good water solubility, water phase catalytic activity and structural stability to avoid deactivation. This leads to the bottleneck of the existing catalysts in the pure aqueous phase system, which has low activity, poor selectivity and poor stability, and restricts the application of the technology. Therefore, developing a photocatalytic CO2RR catalyst suitable for pure aqueous phase, which has excellent water solubility, high activity, high selectivity and good stability, especially inexpensive metal-based efficient water-soluble molecular catalyst, is a key problem that needs to be broken through in the current field.

[0021] Based on this, the water-soluble cobalt porphyrin catalyst provided by the embodiments of the present application has a synthesis route as shown in FIG. 1, and the general structure thereof is as shown below: Figure 1 In the above general structure: When R1=F, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6F-CoTMPyP; When R1=Me, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6Me-CoTMPyP; When R2=Me, R1=R3=H, the water-soluble cobalt porphyrin catalyst is 5Me-CoTMPyP; When R3=Me, R1=R2=H, the water-soluble cobalt porphyrin catalyst is 4Me-CoTMPyP; When R1=R3=Me, R2=H, the water-soluble cobalt porphyrin catalyst is 4,6Me-CoTMPyP.

[0022] In order to facilitate the understanding of the technical solutions of the present application by those skilled in the art, the technical solutions will be described in more detail below in conjunction with specific embodiments: ​​The instruments involved in the following examples are as follows: nuclear magnetic resonance hydrogen spectrum, carbon spectrum, fluorine spectrum data acquisition are carried out using a Bruker Advance III 400 MHz nuclear magnetic resonance spectrometer. A 470 nm LED is used as the irradiation light source, and the light source is provided with current by a high-precision current controller (from Beijing Zhuoli Han Guang Instrument Co., Ltd., model: MLED-Controller). GC9790Plus gas chromatograph equipped with TCD and FID detectors is used for gas product quantitative analysis. Ultra-high performance liquid chromatography-triple quadrupole mass spectrometry is used for high-resolution mass spectrometry testing.

[0023] In the following examples, the drugs are all commercially available reagents and do not need to be treated before use. The purchase sources are as follows: 3-methyl-2-pyridine aldehyde, 3-fluoro-2-pyridine aldehyde, 5-methyl-2-pyridine aldehyde, 4-methyl-2-pyridine aldehyde, pyrrole, CH3I: analytical pure, Shanghai Bide Pharmaceutical Technology Co., Ltd.; 3, 5-dimethyl-2-pyridine aldehyde: analytical pure, Shanghai Haohong Biological Medicine Science and Technology Co., Ltd.; Co(CH3COO)2•4H2O, sodium ascorbate (AscHNa), NaHCO3: analytical pure, Shanghai Maikelin Biochemical Science and Technology Co., Ltd.

[0024] Example 1: Step 1: 0.9 g (7.5 mmol) of 3-methyl-2-pyridine aldehyde and 0.5 g (7.5 mmol) of pyrrole are added to a 500 mL round-bottom flask containing xylene, 0.42 g (3 mmol) of salicylic acid is added as a catalyst, and the reaction is heated (135-140°C) under argon and light shielding conditions for 2 hours. Then, the xylene solvent in the reaction liquid is removed by reduced pressure distillation, and the product is extracted with water and dichloromethane three times to obtain the crude product of porphyrin ligand 6Me-TPyP. Then, a mixture of methanol and dichloromethane (volume ratio 1:50) is used as the developing agent for column chromatography separation and purification, and then the solvent is removed by reduced pressure rotary evaporation to obtain a purple solid, which is the porphyrin ligand 6Me-TPyP, with a yield of 15%. The nuclear magnetic resonance hydrogen spectrum is shown in Figure 2 , the nuclear magnetic resonance carbon spectrum is shown in Figure 7 , the mass spectrum and mass spectrum fitting diagram are shown in Figure 13 , and the structure characterization is as follows: 1 H NMR (400 MHz, Chloroform- d ) δ 8.91 (dd, J = 5.1, 1.6 Hz, 4H), 8.60(s, 8H), 7.95 (t, J = 6.9 Hz, 4H), 7.66 (dd, J= 7.8, 4.8 Hz, 4H), 2.12 (s,3H), 1.99 (s, 6H), 1.91 (s, 3H), -2.67 (s, 2H). 13 C NMR (101 MHz, Chloroform- d ) δ 159.95, 145.97, 137.39, 135.93,123.51, 117.61, 20.85, 20.61, 20.54. High resolution mass spectrometry HRMS (ESI) m / z: C 44 H 34 N8, 675.29803, [M+H] + , found 675.29792.

[0025] Step 2: Under nitrogen protection, 486 mg (0.72 mmol) of porphyrin ligand 6Me-TPyP and 718 mg (2.88 mmol) of Co(CH3COO)2•4H2O were added to a 100 mL flask, and DMF (3 mL) was added. The above solution was heated (140-153°C) to reflux for 6 hours. The reaction was naturally cooled to room temperature, 3.12 mg (22 mmol) of CH3I was added, and the heating reflux was continued for 12 hours. Most of the organic solvent was removed by distillation under reduced pressure, and a saturated NaPF6 aqueous solution was added to the obtained residue to precipitate the target product. The solid was collected by filtration and washed with 5 mL of ethyl acetate, water and methanol respectively, and then dried to obtain the target water-soluble cobalt porphyrin complex catalyst 6Me-CoTMPyP with a yield of 41%. The mass spectrum and mass spectrum fitting diagram thereof are shown in Figure 18 , and the structure characterization is as follows: High resolution mass spectrometry HRMS (ESI) m / z: CoC 48 H 44 N8, 197.82498, [M] 4+ , found 197.82497.

[0026] Example 2: Step 1: The preparation method of porphyrin ligand 6F-TPyP is basically the same as that in step 1 of example 1, except that 3-methyl-2-pyridine aldehyde in step 1 is replaced by 3-fluoro-2-pyridine aldehyde, and the yield is 10%. The nuclear magnetic resonance hydrogen spectrum of the obtained porphyrin ligand 6F-TPyP is shown in Figure 3 , the nuclear magnetic resonance carbon spectrum is shown in Figure 8 , the nuclear magnetic resonance fluorine spectrum is shown in Figure 12 , the mass spectrum and mass spectrum fitting diagram are shown in Figure 14 , and the structure characterization is as follows: 1 H NMR (400 MHz, Chloroform- d ) δ 8.97 (d, J = 4.9 Hz, 4H), 8.81 (s,8H), 7.89 (d, J = 7.4 Hz, 4H), 7.81 (d, J = 5.3 Hz, 4H), -2.77 (s, 2H). 13 C NMR (101 MHz, Chloroform- d ) δ 161.00, 158.42, 149.03, 148.88,144.77, 125.08, 123.40, 112.52. 19 F NMR (376 MHz, Chloroform- d ) δ -116.40, -116.62. HRMS (ESI) m / z: C 40 H 22 F4N8, 691.19781, [M+H] + The theoretical value is 691.19763.

[0027] Step 2: The preparation method of the water-soluble cobalt porphyrin complex 6F-CoTMPyP is basically the same as step 2 in Example 1, except that the porphyrin ligand is replaced with 6F-TPyP, with a yield of 42%. The mass spectrum and mass spectrum fitting diagram of the obtained cobalt porphyrin complex 6F-CoTMPyP are shown below. Figure 19 As shown, the structure is characterized as follows: HRMS (ESI) m / z: CoC 44 H 32 F4N8, 201.79979, [M] 4+ The theoretical value is 201.79990.

[0028] Example 3: Step 1: 1.0 g (8.2 mmol) of 5-methyl-2-pyridaldehyde and 0.7 g (9.9 mmol) of pyrrole were added to a 500 mL round-bottom flask. 200 mL of propionic acid was added as a catalyst and solvent. Under argon atmosphere and light protection, the mixture was heated (135~140℃) and refluxed for 3 hours. The propionic acid in the reaction solution was removed by vacuum distillation. The mixture was extracted three times with water and dichloromethane to obtain the crude product of porphyrin ligand 4Me-TPyP. Then, using a methanol-dichloromethane mixture (v / v) of 1:25 as the developing solvent, the mixture was purified by column chromatography. The solvent was then removed by rotary evaporation under reduced pressure to obtain a purple solid, which is porphyrin ligand 4Me-TPyP. Its 1H NMR spectrum is shown below. Figure 4 As shown, the carbon NMR spectrum is as follows: Figure 9 As shown, the mass spectrum and the mass spectrum fitting plot are as follows: Figure 15 As shown, the yield was 20%, and the structural characterization is as follows: 1 H NMR (400 MHz, Chloroform- d ) δ 8.99 (d, J = 5.1 Hz, 4H), 8.87 (s,8H), 8.03 (s, 4H), 7.53 (d, J = 5.1 Hz, 4H), 2.65 (s, 12H), -2.82 (s, 2H). 13 C NMR (101 MHz, Chloroform- d ) δ 160.78, 148.65, 132.12, 123.93,119.29, 21.77. HRMS (ESI) m / z: C 44 H 34 N8, 675.29865, [M+H] + The theoretical value is 675.29792.

[0029] Step 2: The preparation method of the water-soluble cobalt porphyrin complex 4Me-CoTMPyP is basically the same as step 2 in Example 1, except that the porphyrin ligand is replaced with 4Me-TPyP, with a yield of 56%. The mass spectrum and mass spectrum fitting diagram of the obtained cobalt porphyrin complex 4Me-CoTMPyP are shown below. Figure 20 As shown, the structure is characterized as follows: HRMS (ESI) m / z: CoC 48 H 44 N8, 197.82509, [M] 4+ The theoretical value is 197.82497.

[0030] Example 4: Step 1: The preparation method of porphyrin ligand 5Me-TPyP is basically the same as step 1 in Example 3, except that the reactant 5-methyl-2-pyridaldehyde in step 1 is replaced with 4-methyl-2-pyridaldehyde, the volume ratio of methanol to dichloromethane as the developing solvent is 1:50, and the yield is 17%. The 1H NMR spectrum of the obtained porphyrin ligand 5Me-TPyP is shown below. Figure 5 As shown, the carbon NMR spectrum is as follows: Figure 10 As shown, the mass spectrum and the mass spectrum fitting plot are as follows: Figure 16 As shown, the structure is characterized as follows: 1 H NMR (400 MHz, Chloroform-d) δ 8.96 (s, 4H), 8.87 (s, 8H), 8.09 (d,J = 7.7 Hz, 4H), 7.89 (d,J = 7.7 Hz, 4H), 2.70 (s, 12H), -2.81 (s, 2H). 13 C NMR (101 MHz, Chloroform-d) δ 157.92, 149.16, 135.53, 132.07,130.14, 118.84, 18.68. HRMS (ESI) m / z: C 44 H 34 N8, 675.29791, [M+H] + The theoretical value is 675.29792.

[0031] Step 2: The preparation method of the water-soluble cobalt porphyrin complex 5Me-CoTMPyP is basically the same as step 2 in Example 1, except that the porphyrin ligand is replaced with 5Me-TPyP, with a yield of 51%. The mass spectrum and mass spectrum fitting diagram of the obtained cobalt porphyrin complex 5Me-CoTMPyP are shown below. Figure 21 As shown, the structure is characterized as follows: HRMS (ESI) m / z: CoC 48 H 44 N8, 197.82500, [M] 4+ The theoretical value is 197.82497.

[0032] Example 5: Step 1: The preparation method of porphyrin ligand 4,6Me-TPyP is basically the same as step 1 in Example 3, except that the reactant 5-methyl-2-pyridaldehyde in step 1 is replaced with 3,5-dimethyl-2-pyridaldehyde, the volume ratio of methanol to dichloromethane as the developing solvent is 3:100, and the yield is 11%. The 1H NMR spectrum of the obtained porphyrin ligand 4,6Me-TPyP is shown below. Figure 6 As shown, the carbon NMR spectrum is as follows: Figure 11 As shown, the mass spectrum and the mass spectrum fitting plot are as follows: Figure 17 As shown, the structure is characterized as follows: 1 H NMR (400 MHz, Chloroform- d ) δ 8.72 (t, J = 8.4 Hz, 4H), 8.60 (s, 8H), 7.75 (d, J = 6.9 Hz, 4H), 2.66 (d, J = 3.0 Hz, 12H), 2.08 (s, 3H), 1.95 (s, 6H), 1.87 (s, 3H), -2.69 (s, 2H). 13 C NMR (101 MHz, Chloroform- d ) δ 157.49, 146.71, 138.30, 135.55,133.24, 117.81, 21.02, 20.77, 20.71, 18.90. HRMS (ESI) m / z: C 48 H 42 N8, 731.36078, [M+H] + The theoretical value is 731.36052.

[0033] Step 2: The preparation method of the water-soluble cobalt porphyrin complex 4,6Me-CoTMPyP is basically the same as step 2 in Example 1, except that the porphyrin ligand is replaced with 4,6Me-TPyP, with a yield of 45%. The mass spectrum and mass spectrum fitting diagram of the obtained cobalt porphyrin complex 4,6Me-CoTMPyP are shown below. Figure 22 As shown, the structure is characterized as follows: HRMS (ESI) m / z: CoC 52 H 52 N8, 211.84068, [M] 4+ The theoretical value is 211.84063.

[0034] Application testing: The water-soluble cobalt porphyrin catalyst was used as a catalyst in a pure aqueous photocatalytic CO2 reduction system to construct a pure aqueous photocatalytic CO2 reduction system. The system includes: photosensitizer: 4P-DPAIPN; electron sacrificial agent: sodium ascorbate (AscHNa); catalyst: at least one of 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, and 4,6Me-CoTMPyP; reaction medium: 0.1M NaHCO3 buffer solution.

[0035] To compare with existing technologies, the catalyst CoTMPyP (when R1=R2=R3=H) was prepared using the method described in the reference (Zhang, X., Cibian, M., Call, A., Yamauchi, K., & Sakai, K.. Photochemical CO2 reduction driven by water-soluble copper(I) photosensitizer with the catalysis accelerated by multi-electronchargeable cobalt porphyrin. ACS Catalysis, 2019, 9, 11263-11273.).

[0036] The 4P-DPAIPN was prepared in-house according to the method described in the literature Ma, F., Luo, ZM, Wang, JW, & Ouyang, G. Highly efficient, noble-metal-free, fully aqueous CO2 photoreduction sensed by a robust organic dye. Journal of the American Chemical Society, 2024, 146, 17773-17783. The NaHCO3 buffer solution was prepared from deionized water.

[0037] Application Example 1: Step 1: System Preparation: Add one of the above-mentioned water-soluble cobalt porphyrin catalysts (preferably 3.0 μM), photosensitizer 4P-DPAIPN (preferably 0.5 mM), and electron sacrificial agent AscHNa (preferably 0.1 M) to a 0.1 M NaHCO3 buffer solution to prepare a 4 mL mixed solution. Place this mixed solution in a self-made quartz reactor with a reaction volume of 23 mL and seal it.

[0038] Step 2: Gas replacement: Continuously bubble CO2 gas into the sealed quartz reactor to replace the air in the system until the CO2 gas is saturated.

[0039] Step 3: Photocatalytic reaction: Irradiate the quartz reactor treated in Step 2 with an LED light source with a wavelength of 470 nm.

[0040] Step 4: Product monitoring: After illumination at specific time points (e.g., 1, 2, 4, 6, 9, 21, 31, 43 hours), 100 μL of gas is taken from the cavity above the reactor using a gas-tight syringe and analyzed for reduction products, including CO and H2, using a GC9790Plus gas chromatograph equipped with TCD and FID detectors.

[0041] The photocatalytic CO2 reduction performance of cobalt porphyrin catalysts 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, 4, 6Me-CoTMPyP, and CoTMPyP was compared and tested according to the method in Example 1. The results are as follows: Figure 23 As shown in Table 1.

[0042] Table 1: Photocatalytic results obtained using different water-soluble cobalt porphyrin catalysts.

[0043] ; All cobalt porphyrin complexes exhibited good CO2 reduction catalytic activity in pure aqueous systems, with 4,6Me-CoTMPyP showing the best stability and most outstanding catalyst performance: CO conversion number (TON) CO Breakthrough 10 4 CO selectivity is as high as 90%.

[0044] Substituent electronic effects: Compared with 6F-CoTMPyP modified with electron-withdrawing groups (-F) on the pyridine ring, the catalysts modified with electron-donating groups (-Me) (6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, 4,6Me-CoTMPyP) showed significantly better catalytic activity and aqueous stability than the CoTMPyP catalyst. This indicates that electron-donating groups can improve the utilization rate of the active center and the structural stability of the catalyst by regulating the electron cloud density of the central metal.

[0045] Substituent position effect: When a substituent (-Me or -F) is introduced at the ortho position (e.g., 6-position) of the pyridine ring, the CO selectivity of the catalysts (6Me-CoTMPyP, 6F-CoTMPyP, 4,6Me-CoTMPyP) is significantly improved, effectively suppressing the hydrogen evolution reaction (HER). However, catalysts with monosubstituted methyl groups at the meta (5-position) or para (4-position) positions of the pyridine ring (5Me-CoTMPyP, 4Me-CoTMPyP) and unmodified CoTMPyP exhibit lower selectivity than ortho-substituted catalysts. This pattern indicates that ortho-substituted groups can regulate the binding mode of CO2 to the active site through steric hindrance, reducing the competitive adsorption of H2O molecules on the active site and thus suppressing the HER.

[0046] The technical solution proposed in this application addresses the core bottleneck of pure aqueous phase photocatalytic CO2RR. Through the design of novel cobalt porphyrin complex catalysts and optimization of the reaction system, it has achieved breakthroughs in several aspects, with the specific beneficial effects as follows: I. Development of novel water-soluble cobalt porphyrin complexes and reliable preparation methods This application successfully synthesized a series of novel, water-soluble, and low-cost cobalt porphyrin complexes, whose molecular structures were identified as derivatives with specific pyridine ring substituents (-Me, -F), specifically including 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, and 4,6Me-CoTMPyP. These complexes not only solve the problem of poor water solubility in traditional catalysts, but also feature clear synthetic steps and strong operational feasibility, providing reliable technical support for the large-scale preparation and application of similar catalysts. Furthermore, the use of inexpensive cobalt effectively reduces catalyst costs, avoiding the economic limitations of precious metal catalysts.

[0047] II. Exhibiting excellent catalytic performance and establishing a clear structure-activity relationship in a pure aqueous system. In the pure aqueous phase photocatalytic CO2RR system, the water-soluble cobalt porphyrin complex developed in this application exhibits excellent comprehensive catalytic performance, and a clear structure-activity relationship has been established through systematic research, providing key guidance for catalyst structure optimization.

[0048] (i) High catalytic activity and CO selectivity All cobalt porphyrin complexes exhibited good CO2 reduction catalytic activity in pure aqueous systems, with the 4,6Me-CoTMPyP catalyst showing the most outstanding performance: the CO conversion number (TON(CO)) exceeded 10. 4 With a CO selectivity of over 90%, it is significantly superior to inexpensive metal molecular catalysts in existing pure aqueous systems, effectively solving the core problems of low catalytic activity and poor product selectivity in pure aqueous environments.

[0049] (ii) Clear structure-function relationship rules By comparing the performance of catalysts modified with different substituents, the regulatory mechanism of catalytic performance by the electronic and positional effects of pyridine ring substituents was revealed: Substituent electronic effects: Compared with 6F-CoTMPyP modified with electron-withdrawing groups (-F) on the pyridine ring, the catalysts modified with electron-donating groups (-Me) (6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP, 4,6Me-CoTMPyP) showed significantly higher catalytic activity and aqueous phase stability than unmodified CoTMPyP. This indicates that electron-donating groups can improve the utilization rate of the active site and the structural stability of the catalyst by regulating the electron cloud density of the central metal.

[0050] Substituent position effect: When a substituent (-Me or -F) is introduced at the ortho position (e.g., 6-position) of the pyridine ring, the CO selectivity of the catalysts (6Me-CoTMPyP, 6F-CoTMPyP, 4,6Me-CoTMPyP) is significantly improved, effectively suppressing the hydrogen evolution reaction (HER). However, catalysts with monosubstituted methyl groups at the meta (5-position) or para (4-position) positions of the pyridine ring (5Me-CoTMPyP, 4Me-CoTMPyP) and unmodified CoTMPyP exhibit lower selectivity than ortho-substituted catalysts. This pattern indicates that ortho-substituted groups can regulate the binding mode of CO2 to the active site through steric hindrance, reducing the competitive adsorption of H2O molecules to the active site and thus suppressing the HER side reaction.

[0051] (III) Theoretical and Practical Guiding Value The discovery of the aforementioned electronic and positional effects clearly elucidates the structure-activity relationship between the properties and positions of pyridine ring substituents and catalyst activity, selectivity, and stability. This provides a clear theoretical basis and structural design strategy for the subsequent design of higher-performance pure aqueous CO2RR molecular catalysts, thereby promoting the development of this field from empirical screening to rational design.

[0052] III. Providing new solutions for the green economy and resource utilization of CO2 This application's technical solution successfully overcomes two key challenges in pure aqueous systems: intense competition from HER and easy catalyst deactivation. It achieves highly efficient CO2 conversion using water as the sole reaction medium. On the one hand, it avoids the use of organic solvents, reducing environmental pollutant emissions and aligning with the principles of green chemistry. On the other hand, it utilizes inexpensive cobalt to construct the catalyst system, lowering reaction costs and demonstrating economic potential for large-scale application. This solution efficiently and selectively converts CO2 into high-value products (such as CO), providing a technological pathway for CO2 resource utilization that is both environmentally friendly and economical.

[0053] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A water-soluble cobalt porphyrin catalyst characterized in that, The structural general formula is as follows: ； In the above structural general formula, When R1=F, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6F-CoTMPyP; When R1=Me, R2=R3=H, the water-soluble cobalt porphyrin catalyst is 6Me-CoTMPyP; When R2=Me, R1=R3=H, the water-soluble cobalt porphyrin catalyst is 5Me-CoTMPyP; When R3=Me, R1=R2=H, the water-soluble cobalt porphyrin catalyst is 4Me-CoTMPyP; When R1=R3=Me, R2=H, the water-soluble cobalt porphyrin catalyst is 4,6Me-CoTMPyP.

2. A method for preparing the water-soluble cobalt porphyrin catalyst as described in claim 1, characterized in that, The method comprises the following steps: The pyrrole and the pyridine aldehyde derivative are mixed in a molar ratio of 1.0-1.3:1, and then the mixture is heated to the refluxing temperature of the selected solvent under the action of an acid catalyst and in a nitrogen atmosphere to perform a condensation reaction. The reaction process is monitored by thin layer chromatography. Generally, 4-6 hours are needed for the reaction until the aldehyde raw material point basically disappears, and a porphyrin ligand is generated. The porphyrin ligand and Co(CH3COO)2·4H2O are mixed in a molar ratio of 1:3-5 in a N,N-dimethylformamide (DMF) solvent, and the mixture is heated to the refluxing temperature of the selected solvent. Generally, 6-10 hours are needed for the reaction to generate a reaction liquid containing a cobalt porphyrin complex intermediate. The reaction liquid is cooled to room temperature, an excess of methyl iodide is added thereto, and the quaternary ammonium saltization reaction is continued for 8-12 hours under heating refluxing. After the reaction is completed, the reaction liquid is concentrated to remove most of the organic solvent, and a saturated NaPF6 aqueous solution is added to the obtained residue to precipitate and separate out the target product. The solid is collected by filtration, washed and dried to obtain the target water-soluble cobalt porphyrin complex catalyst.

3. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, The porphyrin ligand comprises at least one of 6F-TPyP, 6Me-TPyP, 5Me-TPyP, 4Me-TPyP and 4,6Me-TPyP.

4. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, When the porphyrin ligand is 6F-TPyP or 6Me-TPyP, the solvent is xylene, and the acid catalyst is salicylic acid.

5. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, When the porphyrin ligand is 5Me-TPyP, 4Me-TPyP or 4,6Me-TPyP, both the solvent and the catalyst are propionic acid.

6. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, The cobalt porphyrin complex intermediate comprises at least one of 6F-CoTPyP, 6Me-CoTPyP, 5Me-CoTPyP, 4Me-CoTPyP and 4,6Me-CoTPyP.

7. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, The reagent used for the washing comprises ethyl acetate, water and methanol.

8. The method for preparing the water-soluble cobalt porphyrin catalyst according to claim 2, characterized in that, The target water-soluble cobalt porphyrin complex catalyst comprises at least one of 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP and 4,6Me-CoTMPyP.

9. Use of the water-soluble cobalt porphyrin catalyst according to claim 1, characterized in that, The water-soluble cobalt porphyrin catalyst is applied to a pure water phase photocatalytic CO2RR as a catalyst to construct a pure water phase photocatalytic CO2 reduction system; the system comprises: a photosensitizer: 4P-DPAIPN; Electron sacrificial agent: sodium ascorbate (AscHNa); Catalyst: at least one of 6F-CoTMPyP, 6Me-CoTMPyP, 5Me-CoTMPyP, 4Me-CoTMPyP and 4,6Me-CoTMPyP; Reaction medium: 0.1M NaHCO3buffer solution.

10. Use of the water-soluble cobalt porphyrin catalyst according to claim 9, characterized in that, When the water-soluble cobalt porphyrin catalyst is applied as a catalyst in the photocatalytic CO2RR in a pure aqueous phase, the following steps are included: The catalyst, the photosensitizer and the electron sacrificial agent are added to the reaction medium to obtain a mixed solution, and the mixed solution is placed in a sealed quartz reactor; CO2gas is continuously introduced into the sealed quartz reactor for bubbling to replace the air in the system until the CO2gas is saturated; then the sealed quartz reactor is irradiated by using an LED light source, and at a preset time point, the reduced products in the gas in the cavity above the reactor are quantitatively analyzed by using gas chromatography.

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