Magnesium oxide modified polystyrene microsphere supported palladium catalyst for high-selectivity preparation of delta-lactone as well as preparation method and application of magnesium oxide modified polystyrene microsphere supported palladium catalyst

Abstract

The invention belongs to the field of high polymer materials and nano catalysis, and discloses a magnesium oxide modified polystyrene microsphere supported palladium catalyst as well as a preparation method and application thereof. A polystyrene microsphere prepared by an SPG membrane emulsification method is used as a carrier, a zero-valent palladium complex is loaded after magnesium oxide modification to obtain the heterogeneous catalyst with rich alkaline sites, the content of an active component Pd is 0.5-5wt%, the structure is spherical, an active center Pd (0) is mainly loaded on the surface of the polystyrene microsphere, and the size of the catalyst is 1.8-9.6 microns. The catalyst synthesized by the method disclosed by the invention shows relatively high catalytic activity on telomerization reaction of delta-lactone synthesized by CO2 and 1, 3-butadiene. The catalyst is simple in preparation process, mild in reaction condition and beneficial to large-scale industrial production. The synthesized catalyst is easy to separate, can be recycled through simple washing and has good stability.

Description

Technical Field

[0001] The present invention belongs to the fields of polymer materials and nanocatalysis, and particularly relates to a palladium catalyst supported on magnesium oxide modified polystyrene microspheres, a preparation method thereof, and an application thereof. Background Art

[0002] At present, carbon-based fossil fuels (coal, natural gas, petroleum, etc.) are still an important part of global energy consumption. With the development of social economy and the increasing demand for energy by humans, the global carbon dioxide emissions related to energy are continuously increasing. This trend not only threatens the global climate stability, but also has a negative impact on the marine ecosystem, agricultural production and human health.

[0003] The utilization of carbon dioxide as a resource is one of the important means to address global climate change. Using carbon dioxide as a raw material is widely used in industry to produce chemicals such as carbonates, salicylic acid, urea, and carbonates. The utilization of carbon dioxide as a resource can not only significantly reduce carbon emissions, but also provide new possibilities for industrial production and energy supply. Among the many chemicals produced from carbon dioxide as a raw material, δ-lactone synthesized by the telomerization reaction of CO2 with 1,3-butadiene has great research value due to the highly functionalized structural characteristics of δ-lactone.

[0004] δ-Lactones contain two different carbon-carbon double bonds and a lactone structure, and can undergo hydroformylation, hydroamination, hydroaminomethylation, and hydrogenation reactions to produce many different products, such as saturated and unsaturated diols and unsaturated hydroxy acids, and can also be used as monomers for polymers. Since this reaction has high requirements for the catalytic system, current research on δ-lactones mainly focuses on the field of homogeneous catalysis. Although homogeneous catalysts have high reaction activity, they have the disadvantage that the catalyst is difficult to recycle. Heterogeneous catalysts have the advantages of easy separation and recyclability of the catalyst. Therefore, it is very meaningful to design a heterogeneous catalyst for the synthesis of δ-lactones. Bao et al. developed a method for generating δ-lactones without an external phosphine ligand. After adding tetrabutylammonium acetate to the catalytic system, palladium nanoparticles will be in-situ generated from palladium acetylacetonate. This catalyst can obtain a yield of 51% and a selectivity of 94% after reacting at 70 °C for 24 h. Although this palladium nanoparticle catalyst can be recycled by extraction, palladium active species are prone to loss during the recycling process (Tetrahedron Letters, 2016, 57: 3163-3166). Bao et al. developed a new type of Pd(acac)2 / PPh3 / TBAOAc catalytic system, which can obtain a yield of up to 86% and a selectivity of 96% after reacting at 30 °C for 21 h. PPh3 can not only act as a ligand and a reducing agent, but also regulate the size of the generated palladium nanoparticles (ChemistrySelect, 2020, 5: 9404-9408). Although this catalyst can obtain good catalytic effects at room temperature, palladium active species are prone to agglomeration and deactivation during the recycling process of the catalyst, resulting in a continuous decrease in the activity of the catalyst. Moreover, the catalyst is also recycled by extraction, which is prone to the loss of active species. Although the in-situ generation of palladium nanoparticles as a catalyst realizes the recycling of the catalyst, due to the lack of protection of the carrier, palladium active species are prone to agglomeration deactivation and loss problems, and the extraction and separation methods used are also relatively troublesome. At the same time, since palladium nanoparticles themselves are a weak Lewis acid and lack basic sites, and their adsorption capacity for carbon dioxide is limited, it is also difficult to modify them to improve their adsorption capacity for CO2.

[0005] Supported catalysts are widely used in the field of catalysis due to their unique structural and performance advantages. Loading the active component onto the support can improve the dispersion of the active component and expose more active sites. The support has electronic and steric effects and can be modified and functionalized to improve catalytic performance. The support can endow the catalyst with solid-phase characteristics, facilitating the separation and recycling of the catalyst. However, when most transition metals are loaded onto the support, due to the chemical influence of the support surface, the activity and selectivity of the catalyst will significantly decrease. For example, Pitter et al. reported that palladium catalysts supported on polystyrene and silica were used to catalyze the telomerization reaction of CO2 and 1,3-butadiene to prepare δ-lactone. However, due to the easy formation of inert complexes of palladium on the catalyst surface, the catalytic effect was poor (Journal of Molecular Catalysis A: Chemical, 1999, 146: 25-36). Therefore, there are few studies on supported catalysts for δ-lactone, and no public content has been found on the structural optimization of the catalyst support to develop the CO2 adsorption capacity and separation and recycling capacity of the catalyst.

[0006] Based on the characteristics of easy modification and functionalization of polymer, the transition metal is loaded into such polymer microspheres through coordination. The presence of ligands enables the highly dispersed active species in the polymer microspheres, making the spatial distribution of the active centers of the heterogeneous catalyst close to that of the homogeneous system. And the polymer microspheres will undergo partial swelling in polar solvents, increasing the pore size of the microspheres, making the contact mode between the active sites of this heterogeneous catalyst and the reactants closer to that of the homogeneous catalytic system, thereby enhancing the reaction activity of the catalyst. The size of the polymer microspheres is usually in the micron size, which is convenient for recycling. The presence of ligands in the microspheres can prevent the loss of active species. At the same time, the CO2 adsorption and activation ability of the catalyst can be further adjusted by modifying the polymer. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a composite catalyst for catalyzing the synthesis of δ-lactone from CO2 and 1,3-butadiene, its preparation method and application. The preparation method has mild reaction conditions, the prepared catalyst has good stability, is easy to separate, has excellent CO2 adsorption and activation ability, and is easy to realize industrialization. Therefore, the present invention has great application value and social and economic benefits.

[0008] Technical solution of the present invention:

[0009] A palladium catalyst supported on magnesium oxide modified polystyrene microspheres for highly selective production of δ-lactone, which is a spherical heterogeneous catalyst with a particle size of 1.8 - 9.6 μm, prepared by the SPG (Shirasu Porous Glass) membrane emulsification method. The palladium catalyst supported on polystyrene microspheres includes polystyrene microspheres containing phosphine ligands, zero-valent palladium active species, and magnesium oxide that increases the basicity of the catalyst. The zero-valent palladium active species and magnesium oxide are loaded on the surface and inside of the polystyrene microspheres containing phosphine ligands. Among them, the loading amounts of both the zero-valent palladium active species and magnesium oxide are 0.5 - 5 wt%. The phosphine ligands in the polymer microspheres can load magnesium acetate and zero-valent palladium complexes through coordination, so the formed magnesium oxide and palladium active species exist on the surface and inside of the microspheres.

[0010] A preparation method of a palladium catalyst supported on magnesium oxide modified polystyrene microspheres for highly selective production of δ-lactone, comprising the following steps:

[0011] (1) Prepare a mixed solution by mixing diphenylphosphine styrene, azobisisobutyronitrile, divinylbenzene, and toluene in a mass ratio of 1:0.03:0.2:3, and add it to an SPG membrane emulsifier. Control the stirring speed at 100 - 600 rpm, and disperse the mixed solution into an aqueous solution containing polyvinyl alcohol and sodium dodecyl sulfate under the extrusion of high-purity nitrogen to prepare uniform emulsion droplets. In the emulsion droplets, the mass ratio of sodium dodecyl sulfate to polyvinyl alcohol is 0.03:1, the volume ratio of water to toluene is 50:3, and the mass percentage of polyvinyl alcohol is 1% - 5 wt%. After emulsification, carry out a suspension polymerization reaction at 60 - 80 °C in nitrogen for 10 - 30 h to prepare polymer microspheres. After polymerization is completed, centrifuge and separate the mixed solution, remove the liquid phase, wash successively with deionized water, absolute ethanol, acetone, and dichloromethane, and then vacuum dry for 4 - 8 h to obtain polystyrene microspheres containing phosphine ligands;

[0012] (2) Under nitrogen protection, add polystyrene microspheres containing phosphine ligands and magnesium acetate to absolute ethanol, and stir for 20 - 36 h to fully load magnesium acetate. Among them, the mass fraction of magnesium acetate in the polystyrene microspheres containing phosphine ligands obtained in step (1) is 10 - 60 wt%, and the mass ratio of the polystyrene microspheres containing phosphine ligands to absolute ethanol is 0.1 - 0.2:1;

[0013] [[ID=I2]](3) Filter and separate the mixed solution obtained in step (2), remove the liquid phase, wash with absolute ethanol, and vacuum dry at 60 - 80 °C for 3 - 6 h;

[0014] (4) After the dried sample obtained in step (3) is cooled to room temperature, it is ground into a powder; under the protection of an inert gas, it is calcined in a tube furnace at a calcination temperature of 200-400 °C for 0.5-4 h, and magnesium acetate decomposes to obtain a sample loaded with magnesium oxide components;

[0015] (5) After the sample obtained in step (4) is cooled to room temperature, Pd2(dba)3 (bis(dibenzylideneacetone)palladium(II)) and dichloromethane are added thereto under the protection of nitrogen. The mass ratio of the sample obtained in step (4) to Pd2(dba)3 and dichloromethane is controlled to be 0.08:0.01-0.07:1, and the mixture is stirred for 4-8 h to fully load zero-valent palladium active species into the polystyrene microspheres;

[0016] (6) The mixture obtained in step (5) is filtered and separated to remove the liquid phase, washed with dichloromethane, and dried in vacuo for 3-6 h to obtain a magnesium oxide-modified polystyrene microsphere-supported palladium catalyst.

[0017] In the above method, the heating rate in step (4) is 1-6 °C / min, preferably 2-3 °C / min.

[0018] In the above method, in step (4), the inert gas includes but is not limited to nitrogen, helium, and argon, and the volume fraction ≥ 99%.

[0019] In the above method, the rate of introducing the inert gas in step (4) is 20-100 mL / min.

[0020] In the above method, the size of the polystyrene microspheres in step (1) is 1.8-9.6 μm.

[0021] A method for synthesizing δ-lactone by the reaction of CO2 and 1,3-butadiene, comprising the following steps:

[0022] The magnesium oxide-modified polystyrene microsphere-supported palladium catalyst and triphenylphosphine are added to a solvent according to a mass ratio of 1:0.25-0.60. After nitrogen replacement, triethylamine is added. The mass ratio of the magnesium oxide-modified polystyrene microsphere-supported palladium catalyst to triethylamine is 1:1.6-10. It is sealed and cooled to -10 °C to -60 °C, and acetonitrile and 1,3-butadiene are added in sequence. The mass ratio of acetonitrile to 1,3-butadiene is 4.7:1, and the mass ratio of 1,3-butadiene to the catalyst is 27:1; then 0.5-3 Mpa of CO2 is introduced; it is sealed and placed in an oil bath at 30-80 °C for reaction for 12-48 h. After the reaction is completed, the reaction kettle is cooled to room temperature. Then the remaining gas is slowly released.

[0023] In the above method, the solvents used include one or more mixtures of toluene, n-hexane, tetrahydrofuran, N,N-dimethylformamide, dichloromethane, N-methylpyrrolidone, and acetonitrile. Acetonitrile and N-methylpyrrolidone are preferred. The molar ratio of the solvent to 1,3-butadiene is 0.1:1 to 100:1.

[0024] In the above method, the reaction temperature is preferably 40 to 70 °C.

[0025] In the above method, the reaction time is preferably 15 to 45 h.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) In the process of synthesizing δ-lactone from CO2 and 1,3-butadiene using the palladium catalyst supported on magnesium oxide-modified polystyrene microspheres of the present invention, the catalyst particles are in the micron size range and have uniform size. They can be recovered by simple filtration and reused after simple washing, greatly simplifying the catalyst recovery process. The presence of phosphine ligands in the polymer microspheres can not only load zero-valent palladium active species and magnesium oxide through coordination, but also stabilize the zero-valent palladium active species to prevent their loss. The catalyst can still maintain almost unchanged catalytic activity after being recycled multiple times. At the same time, the catalyst also has certain catalytic activity and selectivity, which is suitable for the synthesis of δ-lactone.

[0028] (2) The palladium catalyst supported on magnesium oxide-modified polystyrene microspheres of the present invention has abundant medium-strong basic sites, greatly improving its performance in adsorbing and activating carbon dioxide and enhancing the catalytic performance of the catalyst. The loading of magnesium oxide on the surface of the microspheres improves the mechanical strength of the catalyst and reduces the inactivation caused by catalyst fragmentation, which is beneficial to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 TEM image of the palladium catalyst supported on magnesium oxide-modified polystyrene microspheres prepared in Example 1; wherein, (a) is the overall TEM image of the catalyst, (b) is the distribution of C element in the catalyst, (c) is the distribution of O element in the catalyst, (d) is the distribution of P element in the catalyst, (e) is the distribution of Mg element in the catalyst, and (f) is the distribution of Pd element in the catalyst;

[0030] Figure 2 SEM image of the palladium catalyst supported on magnesium oxide-modified polystyrene microspheres prepared in Example 1;

[0031] Figure 3FT-IR spectra of the magnesium oxide-modified polystyrene microsphere-supported palladium catalyst prepared in Example 1; (a) is the FT-IR spectra of the catalyst before and after magnesium oxide modification, and (b) is a partially enlarged FT-IR spectrum;

[0032] Figure 4 The compound δ-lactone prepared in Example 1 1 H NMR spectrum;

[0033] Figure 5 CO2-TPD diagram of magnesium oxide modified polystyrene microspheres loaded palladium catalyst prepared at different calcination temperatures in Example 1. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to implementation cases. Of course, the present invention is not limited to the following specific implementation cases.

[0035] Example 1

[0036] A mixed solution of 1.20 g of 4-diphenylphosphinostyrene, 0.36 g of divinylbenzene, 36 mg of azobisisobutylnitrile, and 3.6 mL of toluene was added as the dispersed phase to an SPG membrane emulsifier. The mixture was stirred at 400 rpm and dispersed into 60 mL of an aqueous solution containing 1.0 wt% polyvinyl alcohol and 0.03 wt% sodium lauryl sulfate under high-purity nitrogen to form uniform emulsion droplets. After emulsification, the mixture was suspended and polymerized at 60°C in nitrogen for 24 hours to produce polymer microspheres. After polymerization, the mixture was centrifuged, the liquid phase removed, and the mixture was washed sequentially with deionized water, anhydrous ethanol, acetone, and dichloromethane, followed by vacuum drying for 4 hours to obtain polystyrene microspheres containing phosphine ligands.

[0037] Under nitrogen protection, 1.0 g of polystyrene microspheres and 380 mg of magnesium acetate were added to 5 mL of anhydrous ethanol. The resulting mixture was stirred at room temperature for 25 h, filtered, and washed with anhydrous ethanol. The resulting sample was placed in a vacuum drying oven and dried at 60°C for 4 h. After the dried sample was cooled to room temperature, it was ground into a powder. Under nitrogen protection, the polymer microspheres loaded with magnesium acetate were calcined in a tube furnace at 300°C for 1 h at a heating rate of 2°C / min. After the resulting sample was cooled, 0.02 mmol of Pd2(dba)3 complex was added and stirred in 10 mL of dichloromethane for 6 h. The mixture was filtered, washed, placed in a vacuum drying oven and dried for 4 h. It was then transferred to a Schleck bottle and sealed for storage.

[0038] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (15 mg) and add them successively to a 25 mL autoclave. After purging with nitrogen, add triethylamine (154 mg). After the autoclave is sealed and cooled to -25 °C, add refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol), and CO2 (1 Mpa) successively. Seal the autoclave and place it in an oil bath at 70 °C for reaction for 24 h. After the reaction is completed, cool the autoclave to room temperature, and then slowly release the remaining gas. Using dodecane as an internal standard, through gas chromatography analysis, the yield of δ-lactone is 67% and the selectivity is 96%.

[0039] Appendix Figure 1 Figure 1 TEM image of the palladium catalyst supported on magnesium oxide modified polystyrene microspheres prepared in Example 1. It can be seen that the catalyst presents a regular spherical shape, and the spatial distributions of P, Mg, and Pd elements highly coincide and are evenly dispersed, proving that the active sites in the catalyst are highly dispersed and the phosphine ligand has a stabilizing effect on MgO and Pd active species.

[0040] Appendix Figure 2 Figure 2 SEM image of the palladium catalyst supported on magnesium oxide modified polystyrene microspheres prepared in Example 1. It can be seen that the particle size of the catalyst is very uniform.

[0041] Appendix Figure 3 Figure 3 FT-IR image of the palladium catalyst supported on magnesium oxide modified polystyrene microspheres prepared in Example 1. It can be seen that the characteristic peak of the Mg-O bond appears in the catalyst modified by magnesium oxide, indicating that magnesium acetate is successfully calcined to magnesium oxide and loaded onto the surface of the catalyst.

[0042] Appendix Figure 4 1H NMR spectrum of the compound δ-lactone prepared in Example 1 1 The NMR data is consistent with the results reported in the literature, proving that δ-lactone is successfully synthesized.

[0043] Appendix Figure 5 Figure 4 CO2-TPD image of the palladium catalyst supported on magnesium oxide modified polystyrene microspheres prepared in Example 1 at different calcination temperatures. It can be seen from the figure that when calcined at 300 °C, the catalyst has abundant basic sites, and different calcination temperatures will affect the number of basic sites. Abundant basic sites are beneficial for the catalyst to adsorb and activate CO2.

[0044] Example 2

[0045] On the basis of Example 1, the content of magnesium acetate was replaced from 380 mg to 160 mg, and the temperature of vacuum drying was replaced from 60 °C to 80 °C, obtaining a magnesium oxide modified catalyst. Using this catalyst to catalyze the telomerization reaction of CO2 and 1,3-butadiene, the yield of δ-lactone was 54% and the selectivity was 96%.

[0046] Example 3

[0047] On the basis of Example 1, the addition amount of Pd2(dba)3 was replaced from 0.02 mmol to 1.0 mmol, and the vacuum drying time was replaced from 4 h to 3 h, obtaining a magnesium oxide modified catalyst.

[0048] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (15 mg) and add them into a 25 mL reaction kettle in sequence. After purging with nitrogen, add triethylamine (154 mg). After the autoclave is sealed and cooled to -60 °C, add refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol) and CO2 (3 Mpa) in sequence. Seal the reaction kettle and place it in an 80 °C oil bath for reaction for 48 h. After the reaction is completed, cool the reaction kettle to room temperature, and then slowly release the remaining gas. Using dodecane as an internal standard, through gas chromatography analysis, the yield of δ-lactone was 60% and the selectivity was 93%.

[0049] Example 4

[0050] On the basis of Example 1, the content of magnesium acetate was replaced from 380 mg to 600 mg, the stirring time was replaced from 24 h to 20 h, the drying time was replaced from 4 h to 3 h, and the calcination time was replaced from 1 h to 0.5 h, obtaining a magnesium oxide modified catalyst.

[0051] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (12.5 mg) and add them into a 25 mL reaction kettle in sequence. After purging with nitrogen, add N,N-diisopropylethylamine (154 mg). After the autoclave is sealed and cooled to -25 °C, add refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol) and CO2 (1 Mpa) in sequence. Seal the reaction kettle and place it in a 60 °C oil bath for reaction for 24 h. After the reaction is completed, cool the reaction kettle to room temperature. Then slowly release the remaining gas. Using dodecane as an internal standard, through gas chromatography analysis, the yield of δ-lactone was 63% and the selectivity was 89%.

[0052] Example 5

[0053] On the basis of Example 1, the calcination time was replaced from 1 h to 3 h, obtaining a magnesium oxide modified catalyst.

[0054] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (30 mg), and add them into a 25 mL reaction kettle in sequence. After purging with nitrogen, add triethylamine (500 mg). After the autoclave is sealed and cooled to -30 °C, add refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol) and CO2 (0.5 Mpa) in sequence. Seal the reaction kettle and place it in an oil bath at 30 °C for reaction for 12 h. After the reaction is completed, cool the reaction kettle to room temperature, and then slowly release the remaining gas. Using dodecane as the internal standard, through gas chromatography analysis, the yield of δ-lactone is 56% and the selectivity is 96%.

[0055] Example 6

[0056] On the basis of Example 1, replace the calcination temperature from 300 °C with 400 °C to obtain a catalyst modified with magnesium oxide.

[0057] Example 7

[0058] On the basis of Example 1, replace the calcination time from 1 h with 4 h to obtain a catalyst modified with magnesium oxide.

[0059] Example 8

[0060] On the basis of Example 1, replace the addition amount of Pd2(dba)3 from 0.02 mmol with 0.06 mmol, and replace the vacuum drying time from 4 h with 6 h to obtain a catalyst modified with magnesium oxide.

[0061] Example 9

[0062] On the basis of Example 1, replace the polymerization time from 24 h with 10 h, replace the polymerization temperature from 70 °C with 60 °C, and replace the drying time from 4 h with 8 h to obtain a catalyst modified with magnesium oxide.

[0063] Example 10

[0064] On the basis of Example 1, replace the mass percentage of polyvinyl alcohol from 1.0 wt% with 1.5 wt%, and replace the mass percentage of sodium dodecyl sulfate from 0.03 wt% with 0.045 wt% to obtain a catalyst modified with magnesium oxide.

[0065] Example 11

[0066] On the basis of Example 1, replace the mass percentage of polyvinyl alcohol from 1.0 wt% with 5.0 wt%, replace the mass percentage of sodium dodecyl sulfate from 0.03 wt% with 0.15 wt%, and replace the polymerization time from 24 with 30 h to obtain a catalyst modified with magnesium oxide.

[0067] Example 12

[0068] On the basis of Example 1, the nitrogen gas used during the calcination of the polymer microspheres loaded with magnesium acetate was replaced with argon gas to obtain a catalyst modified with magnesium oxide.

[0069] Example 13

[0070] On the basis of Example 1, the nitrogen gas used during the calcination of the polymer microspheres loaded with magnesium acetate was replaced with helium gas to obtain a catalyst modified with magnesium oxide.

[0071] Example 14

[0072] On the basis of Example 1, the stirring speed during the emulsification process was replaced from 400 rpm to 600 rpm, and the calcination time of the polymer microspheres loaded with magnesium acetate was replaced from 1 h to 4 h to obtain a catalyst modified with magnesium oxide.

[0073] Example 15

[0074] On the basis of Example 1, the calcination temperature of the polymer microspheres loaded with magnesium acetate was replaced from 300 °C to 250 °C to obtain a catalyst modified with magnesium oxide.

[0075] Example 16

[0076] On the basis of Example 1, the content of magnesium acetate was replaced from 380 mg to 100 mg, the stirring time was replaced from 24 h to 36 h, and the calcination time was replaced from 1 h to 0.5 h to obtain a catalyst modified with magnesium oxide.

[0077] Example 17

[0078] On the basis of Example 1, the calcination temperature was replaced from 300 °C to 200 °C to obtain a catalyst modified with magnesium oxide.

[0079] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (30 mg) and add them sequentially into a 25 mL reaction kettle. After purging with nitrogen, add triethylamine (80 mg). After the autoclave is sealed and cooled to -10 °C, add refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol), and CO2 (1 Mpa) in sequence. Seal the reaction kettle and place it in an oil bath at 30 °C for reaction for 24 h. After the reaction is completed, cool the reaction kettle to room temperature, and then slowly release the remaining gas. Using n-dodecane as an internal standard, through gas chromatography analysis, the yield of δ-lactone is 63% and the selectivity is 93%.

[0080] Comparative Example 1

[0081] A mixed solution of 1.20 g of 4-diphenylphosphinostyrene, 0.36 g of divinylbenzene, 36 mg of azobisisobutyronitrile and 3.6 mL of toluene was added as the dispersed phase to an SPG membrane emulsifier. The stirring speed was controlled at 400 rpm, and it was dispersed into 60 mL of an aqueous solution containing 1 wt% of polyvinyl alcohol and 0.3 wt% of sodium dodecyl sulfate under the extrusion of high-purity nitrogen to prepare uniform emulsion droplets; after emulsification, polymerization was carried out by suspension polymerization at 80 °C in nitrogen for 24 h to prepare polymer microspheres; after polymerization was completed, the mixed solution was centrifuged to remove the liquid phase, and it was washed successively with deionized water, absolute ethanol, acetone and dichloromethane, and then vacuum dried for 4 h to obtain polystyrene microspheres containing phosphine ligands; 0.020 mmol of Pd2(dba)3 complex was added to the obtained sample, and it was stirred in 10 mL of dichloromethane for 6 h. After the mixture was filtered and washed, it was placed in a vacuum drying oven and dried for 4 h, and then transferred to a Schleck bottle and sealed for storage.

[0082] Application of the catalyst in this example: Accurately weigh the prepared catalyst (50 mg) and triphenylphosphine (15 mg) and add them successively to a 25 mL autoclave. After purging with nitrogen, triethylamine (154 mg) was added. After the autoclave was sealed and cooled to -25 °C, refined acetonitrile (8.0 mL), 1,3-butadiene (1.35 g, 25 mmol) and CO2 (1 Mpa) were added successively. The autoclave was sealed and placed in an oil bath at 70 °C for reaction for 24 h. After the reaction was completed, the autoclave was cooled to room temperature, and then the remaining gas was slowly released. Using n-dodecane as the internal standard, through gas chromatography analysis, the yield of δ-lactone was 36% and the selectivity was 86%.

[0083] Compared with the catalyst modified with magnesium oxide, the yield of δ-lactone of the polymer microspheres containing phosphine ligands directly loaded with palladium complex is lower, which is mainly because there are no basic sites in the catalyst. The lack of basic sites leads to insufficient adsorption and activation ability of the catalyst for CO2, resulting in low catalytic activity. And compared with the polystyrene microspheres modified with magnesium oxide, its mechanical strength is lower, and the catalyst is prone to fragmentation during the reaction. After the catalyst is fragmented, the active species are prone to agglomeration inactivation and loss, and the fragmented catalyst fragments will also adhere to the surface of the catalyst, hindering the contact between the reaction substrate and the active species, resulting in a decrease in the yield and selectivity of the catalyst.

[0084] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as stipulated, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A magnesium oxide modified polystyrene microsphere supported palladium catalyst for highly selective production of δ-lactone, characterized in that, The magnesium oxide modified polystyrene microsphere supported palladium catalyst is prepared by the SPG membrane emulsification method; the polystyrene microsphere supported palladium catalyst includes polystyrene microspheres containing phosphine ligands, zero-valent palladium active species, and magnesium oxide that increases the basicity of the catalyst. Zero-valent palladium active species and magnesium oxide are loaded on the surface and inside of the polystyrene microspheres containing phosphine ligands; among them, the loading amounts of both the zero-valent palladium active species and magnesium oxide are 0.5-5 wt%.

2. The palladium catalyst supported on magnesium oxide modified polystyrene microspheres according to claim 1, wherein The polystyrene microsphere supported palladium catalyst described above is a spherical heterogeneous catalyst with a particle size of 1.8-9.6 μm.

3. A preparation method of a palladium catalyst supported on magnesium oxide modified polystyrene microspheres for highly selective production of δ-lactone, characterized in that, It includes the following steps: (1) Prepare a mixed solution of diphenylphosphine styrene, azobisisobutyronitrile, divinylbenzene, and toluene, and add it to an SPG membrane emulsifier; stir, and disperse the mixed solution into an aqueous solution containing polyvinyl alcohol and sodium dodecyl sulfate under the extrusion of high-purity nitrogen to prepare uniform emulsion droplets; after emulsification, carry out a suspension polymerization reaction at 60-80 °C in nitrogen for 10-30 h to prepare polymer microspheres; after polymerization is completed, centrifuge the mixed solution to separate, remove the liquid phase, wash successively with deionized water, absolute ethanol, acetone, and dichloromethane, and then vacuum dry to obtain polystyrene microspheres containing phosphine ligands; (2) Under nitrogen protection, add polystyrene microspheres containing phosphine ligands and magnesium acetate to absolute ethanol, and stir for 20-36 h to fully load magnesium acetate; (3) Filter and separate the mixed solution obtained in step (2), remove the liquid phase, wash with absolute ethanol, and vacuum dry at 60-80 °C for 3-6 h; (4) After the dried sample obtained in step (3) is cooled to room temperature, grind it into a powder; under the protection of an inert gas, carry out calcination in a tube furnace, the calcination temperature is 200-400 °C, and keep it for 0.5-4 h, and magnesium acetate decomposes to obtain a sample loaded with magnesium oxide components; (5) After the sample obtained in step (4) is cooled to room temperature, add Pd2(dba)3 (tris(dibenzylideneacetone)dipalladium) and dichloromethane to it under nitrogen protection, and stir the mixture for 4-8 h to fully load the zero-valent palladium active species into the polystyrene microspheres; (6) Filter and separate the mixed solution obtained in step (5), remove the liquid phase, wash with dichloromethane, and vacuum dry for 3-6 h to obtain the magnesium oxide modified polystyrene microsphere supported palladium catalyst.

4. According to the preparation method described in claim 3, characterized in that, In step (1), in the emulsion droplets, the mass ratio of polyvinyl alcohol to sodium dodecyl sulfate is 30:1, the volume ratio of water to toluene is 1:0.06, and the mass percentage of polyvinyl alcohol is 1%-5 wt%; Diphenylphosphine styrene, azobisisobutyronitrile, divinylbenzene, and toluene are configured into a mixed solution according to the mass ratio of 1:0.03:0.2:

3.

5. According to the preparation method described in claim 3, characterized in that, In step (2), the mass fraction of magnesium acetate in the polystyrene microspheres containing phosphine ligands obtained in step (1) is 10-60 wt%, and the mass ratio of the polystyrene microspheres containing phosphine ligands to absolute ethanol is 0.1-0.2:

1.

6. The preparation method according to claim 3, characterized in that in step (5), the mass ratio of the sample obtained in step (4), Pd2(dba)3 and dichloromethane is controlled to be 0.08:0.01 - 0.07:

1.

7. A method for synthesizing δ-lactone by the reaction of CO2 and 1,3-butadiene, characterized in that, It includes the following steps: Add the magnesium oxide modified polystyrene microsphere supported palladium catalyst and triphenylphosphine to the solvent, replace with nitrogen, then add triethylamine, seal and cool to -10°C to -60°C, and successively add acetonitrile and 1,3-butadiene; Subsequently, introduce 0.5 - 3 Mpa of CO2; seal and place in an oil bath at 30 - 80°C for reaction for 12 - 48 h; after the reaction is completed, cool the reaction kettle to room temperature, and then slowly release the remaining gas.

8. The preparation method according to claim 7, characterized in that the mass ratio of the magnesium oxide modified polystyrene microsphere supported palladium catalyst to triphenylphosphine is 1:0.25 - 0.60; the mass ratio of the magnesium oxide modified polystyrene microsphere supported palladium catalyst to triethylamine is 1:1.6 - 10; the mass ratio of acetonitrile to 1,3-butadiene is 4.7:1, and the mass ratio of 1,3-butadiene to the catalyst is 27:

1.

9. The preparation method according to claim 7, characterized in that the solvent includes one or more mixtures of toluene, n-hexane, tetrahydrofuran, N,N-dimethylformamide, dichloromethane, N-methylpyrrolidone, acetonitrile; the molar ratio of the solvent to 1,3-butadiene is 0.1:1 - 100:

1.

10. The preparation method according to claim 7, characterized in that the reaction temperature is 40 - 70°C, and the reaction time is 15 - 45 h.

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