A method for catalyzing co2 hydrogenation to form formic acid in aqueous solution by a porous organometallic iridium polymer

Abstract

The application develops a kind of porous polyaryl KAPs-PNP-Ph-Ir catalyst and utilizes it as catalyst to catalyze the method for CO2 hydrogenation preparation formic acid.By FeCl3 catalyzed Friedel-Crafts reaction and benzene and dimethoxymethane direct weaving polymerization PNP-Ph-Ir, KAPs-PNP-Ph-Ir catalyst can be synthesized.By adjusting the ratio of PNP-Ph-Ir monomer and benzene, a variety of porous metal organic polymers KAPs-PNP-Ph-Ir are prepared, the polymer has large specific surface area, ultra-low metal loading, good CO2 adsorption capacity and superhydrophobicity, can realize the high TON of CO2 hydrogenation in aqueous solution.The superhydrophobicity of KAPs-PNP-Ph-Ir makes the structure of Ir-H bond very stable in water, which provides guarantee for the continuous activation and hydrogenation of CO2.The application provides a new method for efficient and industrial application potential CO2 hydrogenation preparation formic acid.

Description

Technical Field

[0001] This invention relates to the field of green catalysis, and more specifically, to a novel method for the polymer-catalyzed hydrogenation of CO2 to formic acid. Background Technology

[0002] CO2 is the most abundant carbon resource on Earth. Using CO2 as a raw material, high-value chemicals such as formic acid, methanol, and hydrocarbons can be directly produced through chemical conversion reactions. This not only solves the environmental problems caused by carbon dioxide emissions but also alleviates the pressure of depleting non-renewable fossil fuels to some extent. Therefore, converting CO2 into high-value chemicals has significant economic benefits and strategic importance. Among these, the hydrogenation of CO2 to formic acid has the advantages of 100% atom utilization and being environmentally friendly. The product, formic acid, is also considered the most ideal liquid hydrogen storage medium. However, due to the strong chemical and thermal stability of formic acid, the direct hydrogenation of CO2 to formic acid presents a significant challenge. Therefore, exploring and designing a highly efficient catalyst for the hydrogenation of CO2 to formic acid is of great significance and has broad application prospects.

[0003] Compared to other organic solvents, water has long been considered an ideal green solvent for the hydrogenation of CO2 to formic acid. Water as a solvent offers several advantages: it is non-toxic, the catalyst is easily separated, and it has high CO2 capture efficiency. To date, several publications (ACS Catalysis, 2018, 8, 4346-4353; Chem, 2019, 5, 693-705; ACS Catalysis, 2020, 10, 8557-8566; Journal of CO2 Utilization, 2021, 54) have reported the high efficiency of CO2 hydrogenation to formic acid in aqueous solutions. Conversely, some catalytic systems (JAm Chem Soc, 2017, 139, 14244-14250; ACS Catalysis, 2015, 5, 5301-5305; JAm Chem Soc, 2016, 138, 9968-9977; ACS Catalysis, 2017, 7, 3864-3868) have been reported to exhibit good hydrogenation performance in organic solvents. According to the mechanistic descriptions of these catalysts, H2 activation to form metal-hydrogen bonds (MH) is the key step in the hydrogenation of CO2 to formic acid. MH readily converts to M-OH in the presence of water, but the reverse process is thermodynamically constrained, preventing the timely formation of MH bonds during the reaction and affecting the hydrogenation efficiency. This may be the key to solving the problem of catalyst deactivation in the hydrogenation of CO2 to formic acid in aqueous solutions. Summary of the Invention

[0004] This invention aims to overcome the negative impact of metal-hydrogen bond consumption on the reaction efficiency in existing CO2 hydrogenation to formic acid aqueous solution systems. It develops a method that uses a pincer-shaped phosphine-iridium complex (PNP-Ph-Ir) and its corresponding aryl porous polymer as catalysts. By forming a hydrophobic protective layer, the metal-hydrogen bonds of the active intermediate in CO2 hydrogenation are protected. Water is used as a solvent to achieve highly efficient catalytic CO2 hydrogenation to formic acid salts.

[0005] The catalyst preparation process is shown in the following formula:

[0006]

[0007] The technical solution of the present invention is as follows:

[0008] A heterogeneous polyaryl PNP-Ph-Ir catalyst for the hydrogenation of CO2 to formic acid was designed and synthesized. PNP-Ph-Ir was directly polymerized with benzene and dimethoxymethane via a Friedel-Crafts reaction catalyzed by FeCl3. By adjusting the ratio of PNP-Ph-Ir monomer to benzene, a porous organometallic polymer KAPs-PNP-Ph-Ir was prepared. This polymer exhibits a controllable porous structure and excellent CO2 adsorption capacity. The resulting polymer iridium catalyst showed significantly enhanced hydrophobicity and thermal stability, which is highly beneficial for the protection of the Ir-H bond. The catalyst is characterized by using water as a solvent to convert CO2 to formate at high temperatures and can be recycled up to 15 times without deactivation. This provides an efficient and feasible new method for the hydrogenation of CO2 to formate.

[0009] The key to the realization of this invention is based on the fact that metal-hydrogen bonds in aqueous solution generally have the process shown in the figure below. Metal-hydrogen bonds (MH) are easily converted into M-OH under the action of water. However, the reverse process is constrained by thermodynamics and MH bonds cannot be formed in time during the reaction, which affects the hydrogenation effect.

[0010]

[0011] A method for preparing PNP pincer-shaped phosphine-iridium catalyst (PNP-Ph-Ir) and polymeric PNP iridium catalyst (KAPs-Ph-Ir) using 2,6-chloromethylpyridine, diphenylphosphine, dimethoxymethane, benzene, and 1,5-cyclooctadiene iridium chloride as raw materials to protect the iridium hydrogen intermediate, and using water as a solvent, to catalyze the hydrogenation of CO2 to formate.

[0012] The method for the catalyst is preferably characterized in that the molar ratio of 2,6-chloromethylpyridine, diphenylphosphine, dimethoxymethane, benzene and 1,5-cyclooctadiene iridium chloride is 1:1:1:1:1 to 1:2:10:100:1.

[0013] The method for preparing the catalyst is preferably characterized by a reaction temperature of 60°C to 120°C and a reaction time of 12 to 48 hours.

[0014] The method for producing formate by CO2 hydrogenation is preferably characterized in that the amount of catalyst used is 0.00002-0.0015 mmol based on the molar amount of iridium contained.

[0015] The method for producing formate by CO2 hydrogenation is preferably characterized by a reaction temperature of 100℃ to 150℃.

[0016] The method for producing formate by CO2 hydrogenation is preferably characterized by using DBU, potassium hydroxide, triethylamine and potassium carbonate as alkali.

[0017] The method for producing formate by CO2 hydrogenation is preferably characterized by a total pressure of 1-10 MPa (CO2:H2 = 2:5).

[0018] The method for producing formate by CO2 hydrogenation is preferably characterized by a reaction time of 12h to 48h.

[0019] After the reaction is complete, the TON of the reaction is calculated using the following formula.

[0020]

[0021] Where TON represents the number of substrate conversions per mole of catalyst per unit active site, n1 represents the amount of formate generated, and n cat This indicates the amount of iridium contained in the catalyst used. The amount of formate was determined by 1H NMR with internal standard, using isopropanol as the internal standard and deuterium water lock field. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the porous organometallic iridium polymer structure and its catalytic CO2 hydrogenation to formic acid production according to the present invention.

[0023] Figure 2 Nitrogen adsorption and desorption isotherms of porous organometallic iridium polymers KAPs 2a-2e of this invention.

[0024] Figure 3 Thermogravimetric curves of the porous organometallic iridium polymer KAPs 2a-2e of this invention. Detailed Implementation Plan

[0025] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Variations are included within the technical scope of the present invention without departing from the general spirit and intent.

[0026] As an example, the catalyst structure involved is as follows:

[0027]

[0028] Implementation Case 1

[0029] The PNP-Ph-Ir complex (0.1 mmol, 70 mg) and benzene (0.1 mmol, 8 mg) were dissolved in 5 mL of 1,2-dichloroethane. After stirring for five minutes, anhydrous FeCl3 (2.0 mmol, 324 mg) and dimethoxymethane (2.0 mmol, 152 mg) were added. The resulting mixture was heated to 85 °C and stirred under a nitrogen atmosphere for 24 h. After cooling to room temperature, the precipitate was washed successively with methanol, distilled water, dichloromethane, and acetone. Further purification was carried out by Soxhlet extraction with methanol for 48 h, followed by vacuum drying at 60 °C for 24 h to obtain a dark brown powder, KAPs-PNP-Ph-Ir (2a, yield 58%).

[0030] Implementation Case 2

[0031] The PNP-Ph-Ir complex (0.1 mmol, 70 mg) and benzene (0.5 mmol, 39 mg) were dissolved in 5 mL of 1,2-dichloroethane. After stirring for five minutes, anhydrous FeCl3 (2.0 mmol, 324 mg) and dimethoxymethane (2.0 mmol, 152 mg) were added. The resulting mixture was heated to 85 °C and stirred under a nitrogen atmosphere for 24 h. After cooling to room temperature, the precipitate was washed successively with methanol, distilled water, dichloromethane, and acetone. Further purification was performed by Soxhlet extraction with methanol for 48 h, followed by vacuum drying at 60 °C for 24 h to obtain a dark brown powder, KAPs-PNP-Ph-Ir (2b, yield 63%).

[0032] Implementation Case 3

[0033] The PNP-Ph-Ir complex (0.1 mmol, 70 mg) and benzene (1.0 mmol, 78 mg) were dissolved in 5 mL of 1,2-dichloroethane. After stirring for five minutes, anhydrous FeCl3 (2.0 mmol, 324 mg) and dimethoxymethane (2.0 mmol, 152 mg) were added. The resulting mixture was heated to 85 °C and stirred under a nitrogen atmosphere for 24 h. After cooling to room temperature, the precipitate was washed successively with methanol, distilled water, dichloromethane, and acetone. Further purification was performed by Soxhlet extraction with methanol for 48 h, followed by vacuum drying at 60 °C for 24 h to obtain a dark brown powder, KAPs-PNP-Ph-Ir (2c, yield 77%).

[0034] Implementation Case 4

[0035] The PNP-Ph-Ir complex (0.1 mmol, 70 mg) and benzene (5.0 mmol, 390 mg) were dissolved in 5 mL of 1,2-dichloroethane. After stirring for five minutes, anhydrous FeCl3 (2.0 mmol, 324 mg) and dimethoxymethane (2.0 mmol, 152 mg) were added. The resulting mixture was heated to 85 °C and stirred under a nitrogen atmosphere for 24 h. After cooling to room temperature, the precipitate was washed successively with methanol, distilled water, dichloromethane, and acetone. Further purification was performed by Soxhlet extraction with methanol for 48 h, followed by vacuum drying at 60 °C for 24 h to obtain a dark brown powder, KAPs-PNP-Ph-Ir (2 d, yield 82%).

[0036] Implementation Case 5

[0037] The PNP-Ph-Ir complex (0.1 mmol, 70 mg) and benzene (10.0 mmol, 780 mg) were dissolved in 5 mL of 1,2-dichloroethane. After stirring for five minutes, anhydrous FeCl3 (2.0 mmol, 324 mg) and dimethoxymethane (2.0 mmol, 152 mg) were added. The resulting mixture was heated to 85 °C and stirred under a nitrogen atmosphere for 24 h. After cooling to room temperature, the precipitate was washed successively with methanol, distilled water, dichloromethane, and acetone. Further purification was performed by Soxhlet extraction with methanol for 48 h, followed by vacuum drying at 60 °C for 24 h to obtain a dark brown powder, KAPs-PNP-Ph-Ir (2e, yield 89%).

[0038] Implementation Case 6

[0039] 0.01 μmol (4 × 10⁻⁶) of catalyst PNP-Ir -4 5 mol / L THF solution, 5 mL of solvent water, and 5 mmol KOH were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 120 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 78100.

[0040] Implementation Case 7

[0041] 0.002 μmol (4 × 10⁻⁶) of catalyst PNP-Ir -45 mol / L THF solution, 5 mL of solvent water, and 5 mmol KOH were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 120 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 165900.

[0042] Implementation Case 8

[0043] The catalyst PNP-Ph-Ir was 0.01 μmol (4 × 10⁻⁶). -4 5 mol / L THF solution, 5 mL of solvent water, and 5 mmol DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 120 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 32200.

[0044] Implementation Case 9

[0045] The catalyst PNP-Ph-Ir was 0.01 μmol (4 × 10⁻⁶). -4 5 mol / L THF solution, 5 mL of solvent water, and 5 mmol [C1C2Im][HCO3] were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 60500.

[0046] Implementation Case 10

[0047] The catalyst PNP-Ph-Ir was 0.01 μmol (4 × 10⁻⁶). -45 mol / L THF solution, 5 mL of solvent water, and 5 mmol KOH were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 80400.

[0048] Implementation Case 11

[0049] The catalyst PNP-Ph-Ir was 0.002 μmol (4 × 10⁻⁶). -4 5 mol / L THF solution, 5 mL of solvent water, and 5 mmol DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was complete, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 185900.

[0050] Implementation Case 12

[0051] 1.211 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by 1H NMR analysis. Under these conditions, the obtained TON value was 2000.

[0052] Implementation Case 13

[0053] 0.134 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 17100.

[0054] Implementation Case 14

[0055] 0.039 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 54900.

[0056] Implementation Case 15

[0057] 0.014 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 129200.

[0058] Implementation Case 16

[0059] 0.002 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar of CO2 and 50 bar of H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 585400.

[0060] Implementation Case 17

[0061] 0.002 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 24 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by 1H NMR analysis. Under these conditions, the obtained TON was 941400.

[0062] Implementation Case 18

[0063] 0.002 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 48 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON was 1110800.

[0064] Implementation Case 19

[0065] 0.002 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of KOH were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 150 °C for 24 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing. 1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 813000.

[0066] Implementation Case 20

[0067] 0.002 μmol of catalyst KAPs-PNP-Ph-Ir, 5 mL of solvent water, and 0.5 mmol of DBU were added to a 50 mL high-pressure reactor. Then, 20 bar CO2 and 50 bar H2 were introduced at room temperature, and the reaction was carried out at 120 °C for 12 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was released. Then, 0.2 g of isopropanol was added to the reactor as an internal standard, and 100 μL of the reaction solution was added to 400 μL of D2O for further processing.1 The formic acid content was determined by ¹H NMR analysis. Under these conditions, the obtained TON value was 467300.

[0068] Implementation Case 21

[0069] The described CO2 hydrogenation catalyst recycling method is as follows: 0.01 μmol (10 mg) of KAPs-PNP-Ph-Ir catalyst, 5 mL of water solvent, and 0.5 mmol of DBU are added to a 50 mL high-pressure reactor. CO2 at 20 bar and H2 at 50 bar are introduced, and the reaction is carried out at 150 °C for 12 h. After the reaction, the reactor is cooled to room temperature, and the formic acid content is determined by 1H NMR analysis using isopropanol as an internal standard. The catalyst solid is then separated by centrifugation and added to the reactor for the next hydrogenation reaction.

Claims

1. A method for catalytically hydrogenating CO2 to produce formate, characterized in that... Water was used as the solvent, DBU as the base, and the catalyst was a polyaryl PNP iridium heterogeneous catalyst KAPs-PNP-Ph-Ir. The catalyst was prepared by using 2,6-chloromethylpyridine and diphenylphosphine as raw materials to prepare the catalyst monomer PNP-Ph-Ir, and then directly weaving and polymerizing it with benzene and dimethoxymethane using a FeCl3-catalyzed Friedel-Crafts reaction to obtain a polyaryl PNP iridium heterogeneous catalyst KAPs-PNP-Ph-Ir.

2. The method according to claim 1, characterized in that... The molar ratio of 2,6-chloromethylpyridine, diphenylphosphine, dimethoxymethane, benzene, and 1,5-cyclooctadiene iridium chloride is 1:1 to 2:1 to 10:1 to 100:

1.

3. The method according to claim 1, characterized in that... The reaction temperature for preparing the polyaryl PNP iridium heterogeneous catalyst is 60℃~120℃, and the reaction time is 12~48h.

4. The method according to claim 1, characterized in that... The amount of catalyst used is 0.00002-0.0001 mmol based on the molar amount of iridium it contains.

5. The method according to claim 1, characterized in that... The reaction temperature for preparing formate is 100℃~150℃.

6. The method according to claim 1, characterized in that... The total pressure is 1-10 MPa, and the CO2:H2 ratio is 2:

5.

7. The method according to claim 1, characterized in that... The reaction time for preparing formate is 12h to 48h.

Images