Single-atom catalyst NiSA / ZIF and its application in the cycloaddition reaction of epoxides with CO2

Abstract

The present invention discloses a single-atom catalyst NiSA / ZIF and its application in the catalytic cycloaddition reaction of epoxides with CO2. The single-atom catalyst NiSA / ZIF uses the metal-organic framework ZIF-8 as a carrier and Ni1(Dppp)1(SPhF2)2 as a precursor, and is obtained through wet impregnation and annealing. The synthesis conditions of the single-atom catalyst Ni SA / ZIF of the present invention are mild and do not require dangerous conditions such as high temperature and hydrogen reduction. This material can be used in the catalytic cycloaddition reaction of epoxides with CO2, can effectively convert CO2, has high activity and stability, can maintain high activity and be recycled at least five times, and has good practicability.

Description

Technical Field

[0001] The present invention relates to a single-atom catalyst NiSA / ZIF and its application in the catalytic cycloaddition reaction of epoxides with CO2, belonging to the field of material synthesis. Background Art

[0002] Carbon dioxide (CO2) is an important carbon resource on the earth and also the main gas causing the greenhouse effect. As an inexpensive, abundant, green, non-toxic, and renewable C1 building block, in addition to taking necessary measures to reduce emissions and develop carbon capture and storage technologies, the chemical conversion of CO2 as a synthon into high-value-added chemicals is considered a green method, which can effectively alleviate the greenhouse effect and environmental problems caused by the overuse of fossil energy. Reacting CO2 with epoxides to synthesize polycarbonates can consume CO2 while obtaining completely biodegradable green carbon materials, simultaneously contributing to solving the country's "carbon neutrality" and "plastic restriction / banning order".

[0003] The main challenges in CO2 conversion come from the inherent thermodynamic stability and kinetic inertness of CO2, which require a strong driving force to ensure its effective conversion. Therefore, the key issue in converting CO2 into useful chemicals is the activation of CO2. After activation, the molecular configuration of CO2 changes from linear to bent, enabling more effective chemical conversion. And the key to activation lies in an efficient catalytic system. However, due to the relatively high activation energy of this reaction, most current reaction systems usually require relatively harsh reaction conditions, such as high temperature (≥100 °C), high pressure (≥2 MPa), long reaction time (40 hours), high cost, a large amount of metal residues in the product, and cumbersome separation and recovery. Developing heterogeneous catalysts that are inexpensive, easily available, highly catalytically active, and stable, and developing new heterogeneous catalysts with high activity, high selectivity, and recyclability to achieve the efficient conversion of CO2 and epoxides under mild conditions have become the key core issues for deeply promoting the development and application of this technology. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the present invention provides a single-atom catalyst NiSA / ZIF and its application in the catalytic cycloaddition reaction of epoxides with CO2. Experiments have proved that NiSA / ZIF can efficiently catalyze the cyclization reaction of CO2 under mild conditions, and this catalyst can be recycled multiple times while maintaining high activity.

[0005] The single-atom catalyst NiSA / ZIF of the present invention uses the metal-organic framework ZIF-8 as a carrier and Ni1(Dppp)1(SPhF2)2 (abbreviated as Ni1) as a precursor, and obtains the target catalyst through wet impregnation and low annealing.

[0006] In the single-atom catalyst NiSA / ZIF of the present invention, the structure of the Ni single atom is a NiN3S coordination mode formed by Ni with 3 N atoms and 1 S atom.

[0007] In the single-atom catalyst NiSA / ZIF of the present invention, the loading amount of Ni is 0.0108 wt%.

[0008] The single-atom catalyst NiSA / ZIF of the present invention is prepared by a method comprising the following steps:

[0009] Step 1: Dissolve 30 mg of NiCl2 in a mixed solution of 10 mL of methanol and 10 mL of CH2Cl2, then add 120 mg of 1,3-diphenylphosphinopropane and 100 μL of 2,4-difluorobenzenethiol. After stirring for 20 min, dissolve 30 mg of NaBH4 in 2 mL of ice water and quickly add it to the above reaction solution, and continue stirring for 12 h. After the reaction is completed, the reaction mixture is centrifuged to obtain the upper solution part, which is concentrated by a rotary evaporator to obtain a solid crude product. The crude product is washed three times with methanol (3 × 10 mL) to remove excess thiol. The purified product is dissolved in 3 mL of CH2Cl2, and product crystals are obtained by the two-phase diffusion method (CH2Cl2:hexane = 1:3, V / V). Black crystals of Ni1(Dppp)1(SphF2)2 are formed after 4 - 6 days.

[0010] Step 2: Drop the dichloromethane solution (1 mg, 10 mL) of Ni1(Dppp)1(SPhF2)2 obtained in Step 1 into the dichloromethane suspension (100 mg, 10 mL) of ZIF-8, stir at room temperature for 3 hours, and centrifuge to collect the solid as Ni1 / ZIF-8.

[0011] Step 3: Anneal the Ni1 / ZIF-8 obtained in Step 2 in a tubular furnace to obtain the single-atom catalyst Ni SA / ZIF.

[0012] In Step 3, the annealing is carried out by heating from room temperature to 300 °C in an argon gas stream and holding at 300 °C for 2 hours; the heating rate is 5 °C / min; the flow rate of the argon gas stream is 80 - 200 sccm. When the annealing temperature is greater than 300 °C, the Ni particulate catalyst NiNP / ZIF will be obtained.

[0013] In the present invention, ZIF-8 is synthesized by a conventional method (J. Mater. Chem. A, 2018, 6, 15371).

[0014] The application of the single-atom catalyst NiSA / ZIF of the present invention in the cycloaddition reaction of epoxides with CO2 specifically comprises the following steps:

[0015] Using the single-atom catalyst Ni SA / ZIF, with CO2 and epoxides as raw materials, in the presence of the additive tetrabutylammonium bromide, a one-step reaction is carried out under the conditions of a reaction pressure of 0.1 to 1 MPa and a reaction temperature of 40 to 100 °C for 12 to 24 hours to prepare carbonates. After the reaction is completed, the unreacted CO2 gas is removed. After the reaction solution is cooled to room temperature, 5 mL of ethyl acetate is added, and centrifugation is used to separate the solid from the liquid; the solvent in the liquid is removed using a rotary evaporator to obtain the crude product. Gas chromatography and column chromatography are used to determine its yield and selectivity.

[0016] The types of epoxides in the catalytic reaction include aliphatic epoxides and aromatic epoxides, and are selected from propylene oxide, epichlorohydrin, allyl glycidyl ether, styrene oxide, 4-chlorostyrene epoxide, 4-fluorostyrene epoxide, glycidyl phenyl ether, etc.

[0017] The molar ratio of Ni to epoxide in the single-atom catalyst is 1:3.4×10 2 ~1:2.7×10 3 . The molar ratio of epoxide to the additive tetrabutylammonium bromide is 1:1~1:8.

[0018] Furthermore, the reaction pressure is preferably 0.1 MPa, the reaction temperature is 70 °C, and the reaction time is 12 hours.

[0019] Furthermore, the molar ratio of Ni to epoxide in the catalyst is 1:2.7×10 3 ; the molar ratio of epoxide to the additive tetrabutylammonium bromide is 1:8.

[0020] The atomic catalyst NiSA / ZIF designed and synthesized in the present invention uses Ni1(Dppp)1(SPhF2)2 (abbreviated as Ni1) as the precursor, and Ni1 is loaded on ZIF-8 by the wet impregnation method. The Ni1 / ZIF-8 composite material is annealed in argon at 300 °C to obtain the single-atom catalyst NiSA / ZIF. ZIF-8 has high stability, high porosity and organic functions, and can catalyze, separate, immobilize and activate gases (J. CO2 Util. 2017, 20, 282-291).

[0021] The single-atom catalyst Ni SA / ZIF of the present invention is used to catalyze the one-step reaction of CO2 and propylene oxide to synthesize carbonates. This catalyst has excellent activity and stability for the cycloaddition reaction of epoxides and CO2, thus effectively realizing the conversion and utilization of CO2.

[0022] The beneficial effects of the present invention are reflected in:

[0023] 1. The material synthesis and preparation are simple, and the reaction can be carried out at low temperature.

[0024] 2. The single-atom catalyst prepared by the ligand regulation method has an atomic utilization rate of up to 100%, stable catalyst performance, and a wide range of applications for epoxides.

[0025] 3. This single-atom catalyst adopts the Ni(N)3S coordination mode. Compared with the materials coordinated by Ni-(N)4, NiSA / ZIF of the present invention can catalyze the cycloaddition reaction of epoxides and CO2 under mild conditions, and has excellent catalytic activity and stability. Description of the Drawings

[0026] Figure 1 are the single-crystal structure analysis (a) and ultraviolet-visible spectrum (b) of Ni1(Dppp)1(SphF2)2. Through Figure 1 Figure (a), it can be seen that the central Ni atom is protected by one 1,3-bis(diphenylphosphino)propane and two 2,4-difluorobenzenethiol; through Figure 1 Figure (b), it can be seen that its absorption peaks are at 404, 487, and 587 nm.

[0027] Figure 2 are the TEM (A), AC HAADF-STEM (B), and elemental distribution map (C) of Ni SA / ZIF. Through Figure 2 it can be seen that Ni SA / ZIF has a regular dodecahedron structure, and Ni is uniformly dispersed on the surface of ZIF in the form of single atoms.

[0028] Figure 3 is the performance comparison of the cycloaddition reaction of styrene oxide and CO2 catalyzed by different catalysts. It can be seen from Figure 3 that the yields are 28.4% (ZIF), 30.2% (Ni1), 66.6% (Ni1 / ZIF), 96.9% (NiSA / ZIF), 45.2% (Ni(N)4 / NC), and 42.7% (Ni NP / ZIF), respectively. It can be seen therefrom that among different catalysts, Ni SA / ZIF has the highest catalytic activity.

[0029] Figure 4 is the cyclic test of the cyclization reaction of epichlorohydrin and CO2 catalyzed by NiSA / ZIF. It can be seen from Figure 4 that the stability of this catalyst remains good after 5 cycles. Detailed Embodiments

[0030] The technical solution of the present invention will be further analyzed and described below through specific embodiments.

[0031] Example 1: Preparation of Ni1 Precursor

[0032] 30 mg of NiCl2, 10 mL of methanol, and 10 mL of CH2Cl2 were placed in a round-bottom flask and stirred for 10 min. Then, 120 mg of 1,3-diphenylphosphinopropane and 100 μL of 2,4-difluorobenzenethiol were added, and after stirring for 20 min, 30 mg of NaBH4 was dissolved in 2 mL of ice water and quickly added to the above reaction solution, followed by continued stirring for 12 h. After the reaction was completed, the reaction mixture was centrifuged to obtain the upper solution part, and the solution was concentrated by a rotary evaporator to obtain a crude solid product. The crude product was washed three times with methanol (3 × 10 mL) to remove the excess thiol; the purified product was dissolved in 3 mL of CH2Cl2, and product crystals were obtained by the two-phase diffusion method (CH2Cl2:hexane = 1:3, v / v). Black crystals of Ni1(Dppp)1(SphF2)2 were obtained after 4 - 6 days.

[0033] Figure 1 are the single-crystal structure analysis and UV-visible spectrum of Ni1(Dppp)1(SphF2)2. Through Figure 1 as can be seen from (a) in Figure 1 the central Ni atom is protected by 1 1,3-bis(diphenylphosphino)propane and 2 2,4-difluorobenzenethiols; as can be seen from (b) in

[0034] Example 2: Preparation of ZIF-8

[0035] 2-Methylimidazole (250 mmol) and zinc nitrate hexahydrate (250 mmol) were respectively dissolved in 200 mL of methanol, and then the 2-methylimidazole solution was mixed with the zinc salt solution. The mixed solution was allowed to stand and age at room temperature for 24 h; after the reaction was completed, the reaction mixture was centrifuged to collect the product, centrifuged at 10000 rpm for 5 min, and the solid was washed 5 times with methanol. Finally, ZIF-8 was dried in a vacuum drying oven at 60 °C for 5 h.

[0036] Example 3: Preparation of single-atom catalyst NiSA / ZIF

[0037] 100 mg of ZIF-8 was uniformly dispersed in 10 mL of CH2Cl2, and then 1 mg of Ni1(Dppp)1(SphF2)2 was dissolved in 5 mL of CH2Cl2 and added dropwise to the ZIF-8 solution, followed by stirring at room temperature for 3 h. The solid was collected by centrifugation and dried in a vacuum drying oven at 60 °C for 5 h to obtain Ni1(Dppp)1(SphF2)2 / ZIF (abbreviated as Ni1 / ZIF); subsequently, Ni1 / ZIF was annealed in an Ar atmosphere at 300 °C for 2 h to obtain the single-atom catalyst NiSA / ZIF-300.

[0038] Example 4: Cyclization of styrene oxide and CO2 to synthesize styrene carbonate catalyzed by different catalysts

[0039] Add 4.0 mmol of styrene oxide, 80 mg of different catalysts, and 0.5 mmol of n-Bu4NBr to a 10 mL Schlenk reaction flask in sequence. Seal, evacuate, and connect a carbon dioxide balloon. Stir and react at 70 °C for 12 h. After the reaction is completed, remove the carbon dioxide balloon. Wait for the temperature of the reaction solution to cool to room temperature, add 5 mL of ethyl acetate, and centrifuge to separate the solid from the liquid. The liquid is evaporated to remove the solvent using a rotary evaporator to obtain the product. The yields are as Figure 3 shown. It can be seen from Figure 3 that the yields are 28.4% (ZIF), 30.2% (Ni1), 66.6% (Ni1 / ZIF), 96.9% (NiSA / ZIF), 45.2% (Ni(N)4 / NC), and 42.7% (Ni NP / ZIF), respectively. It can be seen that among different catalysts, the single-atom catalyst Ni SA / ZIF has the highest catalytic activity.

[0040] Example 5: Cycloaddition of propylene oxide and CO2 catalyzed by single-atom catalyst NiSA / ZIF to synthesize propylene carbonate

[0041] Add 4.0 mmol of propylene oxide, 80 mg of NiSA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr to a 10 mL Schlenk reaction flask in sequence. Seal, evacuate, and connect a carbon dioxide balloon. Stir and react at 70 °C for 12 h. After the reaction is completed, remove the carbon dioxide balloon. Wait for the temperature of the reaction solution to cool to room temperature, add 5 mL of ethyl acetate, and centrifuge to separate the solid from the liquid. The liquid is evaporated to remove the solvent using a rotary evaporator to obtain the product. The yield is 98.3%

[0042] Example 6: Cyclization of epichlorohydrin and CO2 catalyzed by single-atom catalyst Ni SA / ZIF to synthesize 4-(chloromethyl)-1,3-dioxolan-2-one

[0043] Add 4.0 mmol of epichlorohydrin, 80 mg of NiSA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr to a 10 mL Schlenk reaction flask in sequence. Seal, evacuate, and connect a carbon dioxide balloon. Stir and react at 70 °C for 12 h. After the reaction is completed, remove the carbon dioxide balloon. Wait for the temperature of the reaction solution to cool to room temperature, add 5 mL of ethyl acetate, and centrifuge to separate the solid from the liquid. The liquid is evaporated to remove the solvent using a rotary evaporator to obtain the product. The yield is 90.2%

[0044] Example 7: The single-atom catalyst Ni SA / ZIF catalyzes the cyclization of allyl glycidyl ether and CO2 to synthesize 4-((allyloxy)methyl)-1,3-dioxolan-2-one.

[0045] 4.0 mmol of allyl glycidyl ether, 80 mg of Ni SA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were successively added to a 10 mL Schlenk reaction flask, sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The yield was 97.0%

[0046] Example 8: The single-atom catalyst Ni SA / ZIF catalyzes the cyclization of styrene oxide and CO2 to synthesize styrene carbonate.

[0047] 4.0 mmol of styrene oxide, 80 mg of Ni SA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were successively added to a 10 mL Schlenk reaction flask, sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The yield was 96.9%

[0048] Example 9: The single-atom catalyst Ni SA / ZIF catalyzes the cyclization of 4-chlorostyrene epoxide and CO2 to synthesize 4-chlorostyrene carbonate.

[0049] 4.0 mmol of 4-chlorostyrene epoxide, 80 mg of Ni SA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were successively added to a 10 mL Schlenk reaction flask, sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The yield was 94.5%

[0050] Example 10: The single-atom catalyst Ni SA / ZIF catalyzes the cyclization of 4-fluorostyrene epoxide and CO2 to synthesize 4-fluorostyrene carbonate.

[0051] To a 10 mL Schlenk reaction flask, 4.0 mmol of 4-fluorostyrene epoxide, 80 mg of NiSA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were added successively. The flask was sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The yield was 91.3%.

[0052] Example 11: Cyclization synthesis of 3-phenoxycyclocarbonate from glycidyl phenyl ether and CO2 catalyzed by single-atom catalyst Ni SA / ZIF.

[0053] To a 10 mL Schlenk reaction flask, 4.0 mmol of glycidyl phenyl ether, 80 mg of NiSA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were added successively. The flask was sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The yield was 81.7%.

[0054] Example 12: Recycling performance test of the cyclization addition of epichlorohydrin and CO2 catalyzed by single-atom catalyst NiSA / ZIF to synthesize 4-(chloromethyl)-1,3-dioxolan-2-one.

[0055] To a 10 mL Schlenk reaction flask, 4.0 mmol of epichlorohydrin, 80 mg of NiSA / ZIF catalyst, and 0.5 mmol of n-Bu4NBr were added successively. The flask was sealed, evacuated, and connected to a carbon dioxide balloon. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the carbon dioxide balloon was removed. When the temperature of the reaction solution cooled to room temperature, 5 mL of ethyl acetate was added, and centrifugation was used to separate the solid from the liquid. The solvent of the liquid was removed using a rotary evaporator to obtain the product. The relationship between the yield of the obtained target product and the number of cycles is as Figure 4 shown, indicating that the stability of the catalyst remains good after 5 cycles.

Claims

1. A single-atom catalyst NiSA / ZIF, characterized in that: The single-atom catalyst NiSA / ZIF uses metal-organic framework ZIF-8 as a carrier and Ni1(Dppp)1(SPhF2)2 as a precursor, and is obtained through wet impregnation and annealing; The single-atom catalyst NiSA / ZIF is prepared by a method including the following steps: Step 1: Dissolve NiCl2 in a mixed solution of methanol and CH2Cl2, then add 1,3-diphenylphosphine propane and 2,4-difluorobenzenethiol. After stirring, dissolve NaBH4 in ice water and quickly add it to the above reaction solution, and continue stirring for 12 h; after the reaction is completed, the reaction mixture is centrifuged to obtain the upper solution part, which is concentrated by a rotary evaporator to obtain a solid crude product; the crude product is washed with methanol to remove excess thiol, and the product crystal Ni1(Dppp)1(SphF2)2 is obtained by the two-phase diffusion method; Step 2: Drop the dichloromethane solution of Ni1(Dppp)1(SPhF2)2 obtained in Step 1 into the dichloromethane suspension of ZIF-8, stir at room temperature for 3 hours, and centrifuge to collect the solid as Ni1 / ZIF-8; Step 3: Anneal the Ni1 / ZIF-8 obtained in Step 2 in a tube furnace to obtain the single-atom catalyst Ni SA / ZIF; In Step 3, the annealing is to heat from room temperature to 300 °C in an argon gas stream and hold at 300 °C for 2 hours; the heating rate is 5 °C / min; the argon gas stream flow rate is 80-200 sccm.

2. The single-atom catalyst NiSA / ZIF according to claim 1, characterized in that: In the single-atom catalyst NiSA / ZIF, the loading amount of Ni is 0.0108 wt%.

3. Use of the single-atom catalyst NiSA / ZIF according to claim 1 or 2 in the catalytic cycloaddition reaction of epoxides and CO2.

4. The use according to claim 3, characterized in that: Using the single-atom catalyst Ni SA / ZIF, with CO2 and epoxide as raw materials, in the presence of the additive tetrabutylammonium bromide, a one-step reaction is carried out under the conditions of a reaction pressure of 0.1-1 MPa and a reaction temperature of 40-100 °C, and the reaction time is 12-24 hours to prepare a carbonate.

5. The use according to claim 4, characterized in that: The epoxide is selected from propylene oxide, epichlorohydrin, allyl glycidyl ether, styrene oxide, 4-chlorostyrene epoxide, 4-fluorostyrene epoxide, glycidyl phenyl ether.

6. The use according to claim 4, characterized in that: The molar ratio of Ni to epoxide in the single-atom catalyst is 1:3.4×10 2 ~1:2.7×10 3 ; the molar ratio of epoxide to the additive tetrabutylammonium bromide is 1:1~1:

8.

7. The use according to claim 6, characterized in that: The molar ratio of Ni to epoxide in the catalyst is 1:2.7×10 3 ; the molar ratio of epoxide to the additive tetrabutylammonium bromide is 1:

8.

8. The use according to claim 4, characterized in that: The reaction pressure is 0.1 MPa, the reaction temperature is 70 °C, and the reaction time is 12 hours.

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