Preparation method and application of bifunctional catalyst based on metal-bipyridine

Abstract

The invention discloses a preparation method and application of a bifunctional catalyst based on metal-bipyridine, and belongs to the technical field of catalyst preparation. The bifunctional catalyst based on metal-bipyridine is prepared by coating a metal-bipyridine polymer generated by condensation reaction on silicon oxide loaded with ionic liquid through a surfactant micelle solution. In the catalyst, the metal-dipyridyl can be fully exposed, and the ionic liquid loaded on the silicon oxide can well cooperate with the metal-dipyridyl. The obtained bifunctional catalyst can catalyze the reaction of carbon dioxide and an epoxy compound to prepare cyclic carbonate under the conditions of no solvent and no cocatalyst, the catalyst is easy to recover, the product is simple to purify, and the energy consumption is reduced. The invention provides a strategy for preparation of the high-efficiency bifunctional catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method and application based on a metal-bipyridine bifunctional catalyst. Background Art

[0002] Since the Industrial Revolution, the concentration of carbon dioxide in the atmosphere has been increasing year by year. On the other hand, carbon dioxide is an important C1 resource and can be converted into high-value-added chemicals through various methods such as thermal catalysis, photocatalysis, and electrocatalysis. Among them, the reaction of CO 2 with epoxides to prepare cyclic carbonates has an atom utilization rate of 100%, meeting the development requirements of green chemistry, and is one of the ideal ways for the resource utilization of CO 2 .

[0003] Metal-bipyridine is often used as a Lewis acid site in synergy with nucleophiles in the reaction of CO 2 with epoxides to prepare cyclic carbonates. Chen Jian et al. reported in the article "Hierarchical mesoporous organic polymer with an intercalated metal complex for the efficient synthesis of cyclic carbonates from flue gas" (Green Chem., 2016, 18, 6493) that melamine was reacted with Zn-bipyridine dialdehyde to prepare a hierarchically porous Zn-bipyridine polymer and applied it to the cycloaddition reaction of carbon dioxide and epoxides. However, TBAB needs to be added as a cocatalyst, and the product purification is difficult, which is not conducive to industrial production. Xie Yaqiang et al. reported in the article "Poly(ionic liquid)s with high density of nucleophile / electrophile for CO 2 fixation to cyclic carbonates at mild conditions" (J.CO 2In (Util., 2019, 32, 281), it was reported that an ionic polymer containing bipyridine units was obtained by free radical polymerization of an ethylene-functionalized imidazole ionic liquid and bipyridine. Subsequently, through metal coordination, a series of bifunctional catalysts were prepared. The metal-bipyridine sites and the imidazole ionic liquid could synergistically catalyze the cycloaddition reaction of carbon dioxide efficiently. However, the ionic polymer contains abundant charges and needs to be dried under supercritical carbon dioxide to maintain a high specific surface area. The process is complex and the energy consumption is relatively high. In the article "Flexibility matters: cooperative active sites in covalent organic framework and threaded ionic polymer" (J. Am. Chem. Soc. 2016, 138, 15790) by Sun Qi et al., an ionic polymer was introduced onto a covalent organic framework material containing bipyridine units through free radical polymerization of a vinyl-containing phosphonium salt ionic liquid. Subsequently, through metal coordination, a bifunctional catalyst was obtained, which could catalyze the cycloaddition reaction of carbon dioxide at 40 °C and 0.1 MPa CO 2 under the condition. However, the ionic liquid polymer is prone to clogging the pores of the covalent organic framework material, which is not conducive to the exposure of active sites and their contact with reactants, thus restricting its catalytic activity. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a metal-bipyridine-based catalyst. The method is simple to operate, and the prepared catalyst has high catalytic activity, is easy to recycle, saves energy consumption, and can catalyze the reaction of carbon dioxide and epoxide to prepare cyclic carbonate under solvent-free and cocatalyst-free conditions, having good application prospects.

[0005] To achieve the purpose of the invention, the present invention provides a preparation method of a metal-bipyridine-based bifunctional catalyst, including the following steps: (1) Add fumed silica, a silane coupling agent, and a nitrogen-containing monomer to dry toluene, ultrasonicate for 0.5 - 1 h, and then under nitrogen protection, control the temperature at 80 - 120 °C and react for 8 - 24 h. Filter the reaction product, wash the obtained solid, and dry it to obtain silica loaded with ionic liquid ILs-SiO 2 .

[0006] (2) Dissolve cetyltrimethylammonium bromide and sodium dodecyl sulfate in deionized water and ultrasonicate for 0.5 - 1 h to obtain a micelle solution; Dissolve the 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex and the aromatic amine monomer in polar organic solvents respectively, and then add them into micellar solutions of equal volume, and ultrasonicate for 0.5 - 1 h to obtain a first solution and a second solution; Mix the obtained first solution and the obtained second solution, add glacial acetic acid, stir for 0.5 - 1 h, and then let it stand at room temperature for 8 - 24 h to obtain a third solution; (3)Add silica ILs-SiO loaded with ionic liquid to the third solution obtained in (2) 2 , and then stir and react at room temperature for 24 - 48 h. After the reaction, filter by suction and wash. The obtained solid is subjected to Soxhlet extraction for 12 - 48 h, and finally vacuum dried at 60 - 120 °C for 8 - 24 h to obtain a metal-bipyridine-based bifunctional catalyst.

[0007] Further, in the step (1), the silane coupling agent is one of 3-bromopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane or 3-iodopropyltrimethoxysilane, and the nitrogen-containing monomer is one of N-methylimidazole, triethylamine, pyridine; for every 1 g of fumed silica, 1 - 3 mmol of silane coupling agent and 1.5 - 4.5 mmol of nitrogen-containing monomer are added.

[0008] Further, in the step (2), the transition metal in the 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex is one of Cu, Zn or Co; the aromatic amine monomer is one of 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine; the polar organic solvent is one of dimethyl sulfoxide, N,N-dimethylformamide or dioxane.

[0009] Further, in the step (2), the molar concentration ratio of sodium dodecyl sulfate to cetyltrimethylammonium bromide is 1:30 - 40; the dosage of the 2,2'-bipyridine-5,5'-dicarboxaldehyde metal complex is 10 - 30 mmol / L of the first solution; the dosage of the aromatic amine monomer is 6.7 - 20 mmol / L of the second solution; the volume ratio of glacial acetic acid to the third solution is 1 - 3:305.

[0010] Further, in the step (3), the dosage of the silica ILs-SiO loaded with ionic liquid 2 is 6.6 - 16.4 g / L of the third solution, and the solvent used for Soxhlet extraction is one of acetone, ethanol or tetrahydrofuran.

[0011] Another object of the present invention is to provide the application of the above metal-bipyridine-based bifunctional catalyst in the reaction of carbon dioxide with epoxides to prepare cyclic carbonates.

[0012] The beneficial effects of the present invention compared with the prior art are as follows: In the present invention, silica supported ionic liquid is prepared through grafting reaction and quaternization reaction, and metal-bipyridine polymer is prepared through aldehyde-amine condensation reaction in micellar solution and coated on the silica supported ionic liquid to obtain a bifunctional catalyst based on metal-bipyridine. It does not require the use of homogeneous cocatalyst, and the purification is simple, which is conducive to industrial utilization.

[0013] In the present invention, ionic liquid is loaded on silica, and metal-bipyridine polymer is compounded with the former through micellar solution to obtain a bifunctional catalyst of metal-bipyridine. Cetyltrimethylammonium bromide and sodium dodecyl sulfate in the micellar solution are used as template agents, which are beneficial to the formation of pores. After washing and removing the template agents, the material can have a high specific surface area through simple drying. Supercritical carbon dioxide drying is not required, which simplifies the preparation process and saves energy consumption.

[0014] In the present invention, the metal-bipyridine polymer is coated on the silica grafted with ionic liquid. Through the method of in-situ composite in micellar solution, the active sites are fully exposed, solving the problem that the ionic liquid polymer blocks the pores, which is not conducive to the exposure of active sites and their contact with reactants, and limits the catalytic activity.

[0015] The application of the bifunctional catalyst based on metal-bipyridine provided by the present invention is used for catalyzing the reaction of carbon dioxide and epoxide to prepare cyclic carbonate. Under the conditions of solvent-free and cocatalyst-free, the yield of cyclic carbonate can reach 99%. The reaction conditions are simple, the cost is reduced, the catalyst is easy to recycle, and the product purification is simple, which has good application prospects in actual production. Description of the Drawings

[0016] Figure 1 It is the transmission electron microscope photograph of Cat2 obtained in Example 2; Figure 2 It is the infrared spectrum diagram of Cat2 obtained in Example 2; Figure 3 It is the nitrogen isothermal adsorption and desorption curve diagram of Cat2 obtained in Example 2 at 77K. Detailed Embodiments

[0017] The present invention will be described in detail below with reference to the drawings and embodiments. However, the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments will fall within the protection scope of the present invention. Example 1

[0018] (1) Add 1 g of fumed silica, 1 mmol of 3-chloropropyltrimethoxysilane, and 1.5 mmol of pyridine to 50 mL of dry toluene. After ultrasonic treatment for 0.5 h, then under nitrogen protection, react at 80 °C for 24 h. Filter the reaction product by suction, wash the obtained solid, and dry it to obtain silica supported ionic liquid ILs-SiO 2 .

[0019] (2) Dissolve 30 mmol of cetyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water, and ultrasonically treat for 0.5 h to obtain a micellar solution; Dissolve 0.3 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde copper complex and 0.2 mmol of 1,3,5-tris(4-aminophenyl)benzene in 0.5 mL of dimethyl sulfoxide respectively, and then add them to 30 mL of the micellar solution respectively, and ultrasonically treat for 0.5 h to obtain a first solution and a second solution accordingly; Mix the obtained first solution and the obtained second solution, add 0.2 mL of glacial acetic acid, stir for 0.5 h, and then let it stand at room temperature for 8 h to obtain a third solution.

[0020] (3) Add 0.4 g of silica supported ionic liquid ILs-SiO 2 to the third solution obtained in (2), and then stir and react at room temperature for 24 h. After the reaction is completed, filter by suction, wash, extract the obtained solid with acetone in a Soxhlet extractor for 12 h, and finally vacuum dry at 60 °C for 24 h to obtain a bifunctional catalyst based on Cu-bipyridine, named Cat1. Example 2

[0021] (1) Add 1 g of fumed silica, 2 mmol of 3-bromopropyltrimethoxysilane, and 3 mmol of triethylamine to 50 mL of dry toluene. After ultrasonic treatment for 0.75 h, then under nitrogen protection, react at 100 °C for 16 h. Filter the reaction product by suction, wash the obtained solid, and dry it to obtain silica supported ionic liquid ILs-SiO 2 .

[0022] (2) Dissolve 32 mmol of cetyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water, and ultrasonically treat for 0.75 h to obtain a micellar solution; Dissolve 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde zinc complex and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine in 0.5 mL of N,N-dimethylformamide respectively, and then add them to 30 mL of the micellar solution respectively, and ultrasonically treat for 0.75 h to obtain a first solution and a second solution accordingly; Mix the obtained first solution and the obtained second solution, add 0.4 mL of glacial acetic acid, stir for 0.75 h, and then let it stand at room temperature for 16 h to obtain a third solution.

[0023] (3) Add 0.7 g of ionic liquid-supported silica ILs-SiO 2 to the third solution obtained in (2), and then stir and react at room temperature for 36 h. After the reaction is completed, filter by suction and wash. The obtained solid is subjected to Soxhlet extraction with ethanol for 30 h, and finally vacuum dried at 90 °C for 16 h to obtain a bifunctional catalyst based on Zn-bipyridine, named Cat2. Example 3

[0024] (1) Add 1 g of fumed silica, 3 mmol of 3-iodopropyltrimethoxysilane, and 4.5 mmol of N-methylimidazole to 50 mL of dry toluene. After ultrasonic treatment for 1 h, then under nitrogen protection, react at 120 °C for 8 h. Filter the reaction product by suction, wash the obtained solid, and dry it to obtain ionic liquid-supported silica ILs-SiO 2 .

[0025] (2) Dissolve 40 mmol of cetyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water, and ultrasonically treat for 1 h to obtain a micellar solution; Dissolve 0.9 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde cobalt complex and 0.6 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine in 0.5 mL of dioxane respectively, and then add them to 30 mL of the micellar solution respectively, and ultrasonically treat for 1 h to obtain a first solution and a second solution accordingly; Mix the obtained first solution and the obtained second solution, add 0.6 mL of glacial acetic acid, stir for 1 h, and then let it stand at room temperature for 24 h to obtain a third solution.

[0026] (3) Add 1.0 g of ionic liquid-supported silica ILs-SiO 2 to the third solution obtained in (2), and then stir and react at room temperature for 48 h. After the reaction is completed, filter by suction and wash. The obtained solid is subjected to Soxhlet extraction with tetrahydrofuran for 48 h, and finally vacuum dried at 120 °C for 8 h to obtain a bifunctional catalyst based on Co-bipyridine, named Cat3. Example 4

[0027] 10 mmol of propylene oxide and 60 mg of the catalyst Cat1 obtained in Example 1 were placed in a 15 mL stainless steel autoclave, sealed, filled with carbon dioxide at 2 MPa, and then transferred to an oil bath at 120 °C and stirred for 4 h. After the reaction, the autoclave was cooled with an ice-water bath. Subsequently, the unreacted carbon dioxide was released, and the reaction liquid was transferred to a centrifuge tube containing a certain internal standard (biphenyl). After centrifugation, the supernatant was taken for gas chromatography analysis, and the yield of propylene carbonate was 90%. Example 5

[0028] Similar to Example 4, Cat2 obtained in Example 2 was used to replace Cat1 in Example 4, and other reaction conditions and procedures remained unchanged. The yield of propylene carbonate was 99%. Example 6

[0029] Similar to Example 4, Cat3 obtained in Example 3 was used to replace Cat1 in Example 4, and other reaction conditions and procedures remained unchanged. The yield of propylene carbonate was 93%. Example 7

[0030] To test the universality of catalyst Cat2: Similar to Example 6, epichlorohydrin, 1,2-epoxyhexane, and styrene oxide were used as reaction substrates to replace propylene oxide in Example 5, and other conditions remained unchanged. The conversion rates of the substrates used are shown in the following table.

[0031] Table 1. Reaction results of the cycloaddition of other epoxides with carbon dioxide catalyzed by Cat2 in Example 7: Comparative Example 1

[0032] The difference from Example 2 was that no micellar solution was used. The specific experimental protocol was as follows: (1) 1 g of fumed silica, 2 mmol of 3-bromopropyltrimethoxysilane, and 3 mmol of triethylamine were added to 50 mL of dry toluene. After sonication for 0.75 h, the mixture was then reacted at 100 °C for 16 h under nitrogen protection. The reaction product was filtered by suction, and the obtained solid was washed and dried to obtain silica supported ionic liquid ILs-SiO 2 .

[0033] (2) 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde zinc complex and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine were each dissolved in 0.5 mL of N,N-dimethylformamide, and then added to 30 mL of deionized water and sonicated for 0.75 h to obtain a first solution and a second solution, respectively; Mix the obtained first solution and the obtained second solution, add 0.4 mL of glacial acetic acid, stir for 0.75 h, and then let it stand at room temperature for 16 h to obtain a third solution.

[0034] (3)Add 0.7 g of ionic liquid-supported silica ILs-SiO 2 to the third solution obtained in (2), and then stir and react at room temperature for 36 h. After the reaction is completed, filter by suction and wash. The obtained solid is subjected to Soxhlet extraction with ethanol for 30 h, and finally vacuum-dried at 90 °C for 16 h to obtain a bifunctional catalyst based on Zn-bipyridine, named Cat2'. Comparative Example 2

[0035] Do not compound with ILs-SiO 2 , and the specific experimental scheme is as follows: (1)Dissolve 32 mmol of cetyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water, and ultrasonicate for 0.75 h to obtain a micellar solution; Dissolve 0.6 mmol of zinc complex of 2,2'-bipyridine-5,5'-dicarboxaldehyde and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine in 0.5 mL of N,N-dimethylformamide respectively, and then add them to 30 mL of the micellar solution respectively, and ultrasonicate for 0.75 h to obtain a first solution and a second solution accordingly; Mix the obtained first solution and the obtained second solution, add 0.4 mL of glacial acetic acid, stir for 0.75 h, and then let it stand at room temperature for 16 h to obtain a third solution.

[0036] (2)Stir and react the third solution obtained in (1) at room temperature for 36 h. After the reaction is completed, filter by suction and wash. The obtained solid is subjected to Soxhlet extraction with ethanol for 30 h, and finally vacuum-dried at 90 °C for 16 h to obtain a catalyst of Zn-bipyridine-based polymer, named Cat2". Comparative Example 3

[0037] Similar to Example 4, use Cat2' obtained in Comparative Example 1 to replace Cat1 in Example 4, and keep other reaction conditions and processes unchanged. The yield of propylene carbonate is 72%. Comparative Example 4

[0038] Similar to Example 4, use Cat2" obtained in Comparative Example 2 to replace Cat1 in Example 4, and keep other reaction conditions and processes unchanged. The yield of propylene carbonate is 5%.

[0039] Appendix Figure 1 The TEM photo of Cat1 is given, indicating that it is composed of nanospheres of about 20 nm, without impurities, indicating that the metal porphyrin polymer and ILs-SiO2 It can be well compounded.

[0040] Appendix Figure 2 The infrared spectrum of Cat2 obtained in Example 2 is given. A characteristic vibration peak attributed to C=N can be observed at 1660 cm -1 , indicating that the aldol condensation reaction between the 2,2'-bipyridine-5,5'-dicarbaldehyde metal complex and the aromatic amine has successfully occurred, forming a metal bipyridine polymer; the absorption peak at 1000 - 1200 cm -1 can be attributed to the vibration of Si-O-Si in ILs-SiO 2 . The vibrations at 2924 cm -1 , 1462 cm -1 , and 1389 cm -1 can be attributed to the C-H vibrations of methyl and methylene in the ionic liquid in ILs-SiO 2 .

[0041] Appendix Figure 3 The nitrogen isothermal adsorption and desorption curve of Cat2 obtained in Example 2 at 77 K is given. The adsorption amount increases steeply in the low-pressure region and contains a hysteresis loop, indicating that the material has a micro-mesoporous structure. The BET specific surface area is 782 m 2 / g, and the total pore volume is 0.9 cm 3 / g.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bifunctional catalyst based on metal-bipyridine, characterized in that: The following steps are involved: (1) Add fumed silica, silane coupling agent and nitrogen-containing monomer to dry toluene, ultrasonicate for 0.5-1h, then control the temperature at 80-120°C to react for 8-24h under nitrogen protection, filter the reaction product, wash the obtained solid, and dry it to obtain ionic liquid-loaded silicon oxide ILs-SiO2; (2) dissolving hexadecyltrimethylammonium bromide and sodium dodecyl sulfate in deionized water and ultrasonicating for 0.5-1h to obtain a micellar solution; Dissolving the 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex and the aromatic amine monomer in polar organic solvents respectively, and then adding them to equal volumes of micelle solutions respectively, and ultrasonicating for 0.5-1h to obtain a first solution and a second solution respectively; The first solution and the second solution are mixed, glacial acetic acid is added, stirred for 0.5-1h, and then allowed to stand at room temperature for 8-24h to obtain a third solution; (3) ILs-SiO2 loaded with ionic liquid is added to the third solution obtained in step (2), and then stirred at room temperature for reaction for 24-48h; after the reaction is completed, the solid is filtered and washed, and the solid is subjected to Soxhlet extraction for 12-48h, and finally vacuum dried at 60-120°C for 8-24h to obtain a metal-bipyridine based bifunctional catalyst.

2. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (1), the silane coupling agent is one of 3-bromopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane or 3-iodopropyltrimethoxysilane, and the nitrogen-containing monomer is one of N-methylimidazole, triethylamine and pyridine; 1-3 mmol of silane coupling agent and 1.5-4.5 mmol of nitrogen-containing monomer are added to every 1 g of fumed silica.

3. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (2), the molar concentration ratio of sodium dodecyl sulfate to hexadecyltrimethylammonium bromide in deionized water is 1:30-40; the transition metal in the 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex is one of Cu, Zn or Co; the aromatic amine monomer is one of 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine; and the polar organic solvent is one of dimethyl sulfoxide, N'N-dimethylformamide or dioxane.

4. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (2), the amount of 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex used is 10-30 mmol / L of the first solution; the amount of aromatic amine monomer used is 6.6-20 mmol / L of the second solution; and the volume ratio of glacial acetic acid to the third solution is 1-3:

305.

5. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (3), the amount of silicon oxide ILs-SiO2 loaded with ionic liquid is 6.6 g-16.4 g / L of the third solution, and the solvent used for Soxhlet extraction is one of acetone, ethanol or tetrahydrofuran.

6. An application of a bifunctional catalyst based on metal-bipyridine prepared by the preparation method according to claim 1, characterized in that: The metal-bipyridine based bifunctional catalyst was applied to the reaction of carbon dioxide and epoxides to prepare cyclic carbonates.

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