Preparation method and application of quaternary ammonium salt supported zinc-aluminum hydrotalcite nanosheet material

Abstract

The invention relates to a preparation method and application of a quaternary ammonium salt supported zinc-aluminum hydrotalcite nanosheet material. According to the method, a hydrotalcite-like structure and quaternary ammonium salt are integrated, alkyl sulfate ions are inserted into the hydrotalcite-like structure to increase the interlayer spacing of LDH so that the LDH can be more easily stripped in methylbenzene, silane coupling agent grafting is carried out on the stripped LDH structure, the loading capacity of LDH on the silane coupling agent is improved to a greater extent, and the preparation process is simplified. Finally, the introduction of an interlayer quaternary ammonium salt unit is realized through quaternization. According to the present invention, with the application of the catalyst as the heterogeneous catalyst in the catalysis of the cycloaddition reaction of CO2 and butylene oxide, the excellent epoxy conversion rate and the excellent butylene carbonate selectivity are provided under the condition of no solvent and no co-catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of carbon dioxide conversion and utilization, and specifically relates to a preparation method of a quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material X-SiR / ZnAl LDHs-(X = Cl, Br, I) and its application in the catalytic cycloaddition reaction of CO2 and epoxide. Background Art

[0002] The cycloaddition reaction of carbon dioxide and epoxide is an important technical route for the resource utilization of carbon dioxide. Its product, cyclic carbonate, is widely used in fields such as lithium battery electrolytes, organic solvents, and polycarbonate synthesis. The existing catalytic systems for this technology mainly rely on homogeneous catalysts (such as organic bases, ionic liquids, metal complexes, etc.), which have problems such as difficult catalyst recovery and poor stability. Developing efficient, stable, and easily recyclable heterogeneous catalysts is the current main technical breakthrough direction. Layered double hydroxide intercalation materials (LDHs) have a two-dimensional layered structure, and the metal hydroxide surface and interlayer anions on them can provide the Lewis acid-base sites required for the cycloaddition reaction of carbon dioxide and epoxide, and have the potential to catalyze this reaction as heterogeneous catalysts.

[0003] Due to the van der Waals force between the layers and the electrostatic force between the anions and the layers in traditional LDHs, the hydroxyl groups on the layer board tend to be stable and it is not easy to form oxygen vacancies. This results in a small number of Lewis acid sites on the layer board. At the same time, the small layer spacing makes it difficult for the internal hydroxyl groups to participate in the reaction, and the reaction diffusion is also limited, resulting in poor catalytic activity. For the MgAl LDH structure intercalated with iodide ions reported in the literature DOI: 10.1016 / j.mcat.2023.112994, even when the catalyst needs to react at 80 °C and 2 MPa of CO2 for 24 h under the condition of using MEK as a solvent, the conversion rate of propylene oxide is still less than 50%. This material is a bulk LDH structure with a small layer spacing, which is not conducive to the exposure of active sites on the layer board.

[0004] Therefore, it is very crucial to develop single-layer or ultrathin LDHs nanosheet materials with a large enough layer spacing and high-activity catalytic sites. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method and application of a quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material in view of the above deficiencies existing in the current prior art. This material is a thin-layer or single-layer zinc-aluminum layered double hydroxide nanosheet, with rich oxygen vacancies on the surface of the layer board, a quaternary ammonium salt structural unit between the layer boards, and a relatively large layer spacing; in the preparation, the layered double hydroxide structure and the quaternary ammonium salt are integrated, alkyl sulfate ions are inserted into the layered double hydroxide (LDH) structure to increase the layer spacing of the LDH, making it easier to exfoliate in toluene, and the exfoliated LDH structure is grafted with a silane coupling agent, which greatly improves the loading amount of the silane coupling agent on the LDH. Finally, the introduction of the interlayer quaternary ammonium salt unit is realized through quaternization. The present invention has excellent epoxy conversion rate and product selectivity as a heterogeneous catalyst under the conditions of no solvent and co-catalyst.

[0006] In order to achieve the above object, the present invention provides the following specific technical solutions:

[0007] A preparation method of a quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material, the method comprising the following steps:

[0008] (1) Preparation of intercalated zinc-aluminum layered double hydroxide RS-ZnAl LDHs:

[0009] Using the co-precipitation method, selecting alkyl sulfate ions (RS - ) as the intercalating ions, at 50-100 °C, in an inert atmosphere, with stirring, dropping solution A into the sodium alkyl sulfate (SRS) solution, and simultaneously dropping the NaOH solution to keep the pH of the reaction system at 9.0-11.0; after solution A is added dropwise, maintaining this pH value for 10-60 min by continuing to drop the NaOH solution; keeping this temperature and continuously stirring for 4-12 h; then filtering, washing the solid, and drying to obtain RS-ZnAl LDHs;

[0010] Among them, the solvent of the SRS solution is a mixed solvent, and the composition of the mixed solvent is water and ethanol, and the volume ratio of ethanol to water is 1-5; 5-30 mmol of SRS is added to every 50-150 mL of the mixed solvent;

[0011] The solute of solution A is Zn(NO3)2 and Al(NO3)3; the sum of the concentrations of Zn(NO3)2 and Al(NO3)3 in solution A is 0.1-0.3 mol / L, and the molar ratio s of Zn / Al is 2-5; the volume of solution A is 0.5 to 1.5 times the volume of the SRS solution;

[0012] The concentration of the NaOH solution is 0.5-3 mol / L.

[0013] The stirring rate is 200-500 rpm.

[0014] The inert atmosphere is nitrogen, argon or helium.

[0015] (2) Preparation of silane coupling agent modified zinc-aluminum layered double hydroxide nanosheets SiR / ZnAl LDHs:

[0016] Add RS-ZnAl LDHs to toluene, ultrasonically disperse for 30 - 120 min, then add an amino-containing silane coupling agent, heat at 60 - 120 °C under a nitrogen atmosphere, reflux for 4 - 12 h, after cooling to room temperature, centrifuge, wash, and dry to obtain silane coupling agent modified SiR / ZnAl LDHs;

[0017] Among them, 0.1 - 1 g of RS-ZnAl LDHs and 1 - 40 mmol of amino-containing silane coupling agent are added to every 500 - 200 mL of toluene;

[0018] (3) The preparation scheme of quaternary ammonium salt supported zinc-aluminum layered double hydroxide nanosheets X-SiR / ZnAl LDHs is as follows:

[0019] Dissolve the quaternization reagent in ethanol, then add SiR / ZnAl LDHs, heat and reflux at 50 - 90 °C for 12 - 24 h. After cooling to room temperature, centrifuge, wash, and dry, then collect the solid to obtain quaternary ammonium salt supported zinc-aluminum layered double hydroxide nanosheets X-SiR / ZnAl LDHs (X = Cl, Br, I) ZnAl LDH nanosheet materials.

[0020] Among them, 10 - 40 mmol of quaternization reagent and 0.1 g - 1 g of SiR / ZnAl LDHs are added to every 20 - 50 mL of ethanol;

[0021] In step (1), the sodium alkyl sulfate is one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium octyl sulfate, and sodium benzenesulfonate;

[0022] In step (2), the amino-containing silane coupling agent is one or two of 3-aminopropyltriethoxysilane (KH-550), γ-aminopropyltriethoxysilane (KH-792), diethylenetriaminepropyltrimethoxysilane (NQ-62), and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (HD-602), and the addition amount is 5 - 25 mmol.

[0023] In step (3), the quaternization reagent is one or more of 1,2-dichloroethane, 3-chloro-1-propanol, potassium chloride, 1,2-dibromoethane, 2-bromoethanol, potassium bromide, 1,2-diiodoethane, 2-iodoethanol, and potassium iodide.

[0024] The quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material obtained by the described method is a quaternized silane coupling agent-modified zinc-aluminum layered double hydroxide X-SiR / ZnAl-LDHs, where X = Cl, Br or I, and it includes a halogenated quaternary ammonium salt ion pair, a silane coupling agent, and a zinc-aluminum layered double hydroxide; among them, the mass ratio of the halogen pair in the material is 1-40%, the loading amount of the silane coupling agent is 0.1-5 mmol / g, and the Zn / Al ratio in the zinc-aluminum layered double hydroxide is 2-5.

[0025] Preferably, in the X-SiR / ZnAl-LDHs nanosheet material, the halogen is bromide ion, the mass ratio of the bromide ion in the material is 20-35%, the loading amount of the silane coupling agent is 0.5-3.5 mmol / g, and the Zn / Al ratio in the zinc-aluminum layered double hydroxide is 2-5.

[0026] The structure of the X-SiR / ZnAl-LDHs material is a thin layer or a single layer of zinc-aluminum layered double hydroxide nanosheets, and the layer spacing is 2-3 nm, which is beneficial for exposing more catalytic active sites and facilitating the diffusion of reactants and products.

[0027] The so-called room temperature refers to 28 ± 5°C.

[0028] The application of the quaternary ammonium salt-supported ZnAl LDH nanosheets, that is, for the activity evaluation of the catalytic cycloaddition reaction of CO2 and epoxy butane, specifically includes the following steps:

[0029] Place the obtained quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheets X-SiR / ZnAl-LDHs in a reaction kettle, then add epoxy butane and seal the reaction kettle. Open the inlet valve to fill the reaction kettle with 0.1-5 MPa of CO2 gas. The reaction temperature is 25-120°C. After reacting for 1-12 h, stop the reaction to obtain the target product butylene carbonate.

[0030] Among them, 1-10 mL of epoxy butane is added to every 1 g of the obtained X-SiR / ZnAl-LDHs nanosheet catalyst.

[0031] The substantial features of the present invention are:

[0032] The present invention integrates the layered double hydroxide structure with the quaternary ammonium salt. On the one hand, it increases the layer spacing of the layered double hydroxide structure, exposing more active sites. In addition, the formation of a quaternary ammonium salt unit between the layers successfully fixes the halogen ions between the layers. When the present invention is applied to the catalytic cycloaddition reaction of CO2 and epoxy, the abundant oxygen vacancies on the surface of the layer board increase the surface acidity and basicity, thereby improving the adsorption of epoxy and carbon dioxide. The quaternary ammonium salt immobilized between the layer boards provides halogen ions to enable the rapid ring-opening of epoxy, and the large layer space promotes the diffusion of reactants and products.

[0033] The beneficial effects of the present invention are:

[0034] 1. There are no literature and patent reports on this organic-inorganic hybrid material integrating hydrotalcite-like and quaternary ammonium salt units designed in the present invention. This material makes full use of the layered structure of LDH. By using long-chain alkyl sulfate ions (RS - ) as intercalating ions and exfoliating the hydrotalcite-like lamellar by ultrasonic treatment in toluene, the bulk hydrotalcite structure is made into thin or single-layer hydrotalcite-like nanosheets, which can expose more silane grafting sites. The loading amount of the silane coupling agent in Example 1 can reach up to 3.1 mmol / g at most, showing a significant improvement compared with the highest loading amount of 0.5 mmol / g of the bulk ZnAl LDH2 in Comparative Example 1.

[0035] 2. In the present invention, alkyl sulfate ions are intercalated between the layers of zinc-aluminum hydrotalcite-like, greatly expanding the layer spacing of zinc-aluminum hydrotalcite-like compared with traditional bulk LDH materials; silane coupling agents are grafted to the layers of zinc-aluminum hydrotalcite-like and further quaternized. While introducing quaternary ammonium cation / halide anion pairs, the layer spacing of zinc-aluminum hydrotalcite-like can be further expanded, making the layer spacing of the X-SiR / ZnAl-LDHs nanosheet material expand from less than 1 nm of the traditional bulk material to 2 - 3 nm, and this thin nanosheet structure can exist stably. Comparing Example 1 and Example 3, when the quaternary ammonium salt loading amounts are 1.28 mmol / g and 3.1 mmol / g respectively, the layer spacing of the material calculated by XRD in Example 9 expands from 2.45 nm to 2.54 nm. Compared with 2.32 nm of DS-ZnAl LDH2 in Example 1 before organic modification, the layer spacing of both has been improved to a certain extent. Compared with 0.78 nm of the bulk material ZnAl LDH2 in Comparative Example 1, the layer spacing has been significantly improved.

[0036] 3. There are no patent reports on the application of hydrotalcite-like materials in the catalytic cycloaddition of CO2 and epoxides, and only a small amount of literature research. In the present invention, the expansion of the layer spacing of zinc-aluminum hydrotalcite-like supported by quaternized silane coupling agents makes the original hydroxyl groups on the surface of the zinc-aluminum hydrotalcite-like lamellae easily desorb to form surface oxygen vacancies, generating more Lewis acid-base sites, which is conducive to the adsorption and activation of CO2 and epoxides, overcoming the problems of low utilization rate of the layer structure, small content of active sites, and small layer spacing in bulk LDH materials, which are not conducive to diffusion and result in low activity in the catalytic cycloaddition reaction of CO2 and epoxides. B described in Example 1 of the present invention 20-KH550 / ZnAl-LDHs material can react for 10 h at 100 °C and 3 MPa CO2 without solvent and cocatalyst, and the highest yield of butylene carbonate can reach 94%. Compared with the existing LDH materials, the activity has been significantly improved. For example, the iodide-intercalated MgAl LDH material reported in the literature DOI: 10.1016 / j.mcat.2023.112994, under the condition of MEK as the solvent, reacts at 80 °C and 2 MPa CO2 for 24 h, and the conversion rate of propylene oxide is less than 50%. The ultrathin ZnAl layered double hydroxide synthesized by the reverse micelle method in the literature DOI: 10.1002 / adsc.201801223 requires the addition of tetrabutylammonium bromide (TBAB), reacts at 25 °C and 1 MPa CO2 for 24 h, and the yield of propylene carbonate is only 74%. In addition, compared with the recently reported metal oxide materials loaded with quaternary ammonium halide units, the performance of this invention is also better. For example, in DOI: 10.1007 / s10562-023-04427-7, the performance of the material of this invention is improved by more than 10% under the same reaction conditions when flower-like copper oxide is loaded with tetrabutylammonium iodide.

[0037] 4. The present invention proposes a strategy for exfoliating and stabilizing thin-layer / monolayer zinc-aluminum layered double hydroxide nanosheets, which can be used to prepare layered double hydroxide materials with large interlayer spacing and stability; the thin-layer structure can expose more catalytic sites, which is conducive to improving the catalytic reaction activity. At the same time, the thin-layer structure can expose more structural modification sites, which is conducive to the modification of the surface of the layered double hydroxide layer board; the preparation method of the present invention has the advantages of simple operation and easy large-scale production. Brief Description of the Drawings

[0038] Figure 1 X-ray powder diffraction patterns of Example 1, Example 3, and Comparative Example 1.

[0039] Figure 2 FTIR spectra of Example 1 and Comparative Example 1.

[0040] Figure 3 O1s X-ray photoelectron spectra of Example 1 and Comparative Example 1.

[0041] Figure 4 SEM images of Example 1 and Comparative Example 1.

[0042] Figure 5 AFM images of Example 1 and Comparative Example 1.

[0043] Figure 6 TEM image of Example 1. Detailed Description of the Invention

[0044] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the following embodiments are illustrative and not restrictive, and the protection scope of the present invention cannot be limited by the following embodiments. The raw materials required in the following examples and comparative examples are all commercially available.

[0045] In this embodiment, XRD crystal structure analysis was carried out using a Rigaku-Smartlab X-ray diffractometer from Japan.

[0046] In this embodiment, FTIR molecular backbone structure analysis was carried out using an INVENIOR infrared spectrometer from Bruker Corporation, Germany.

[0047] In this embodiment, XPS elemental chemical state analysis was carried out using an AXIS Supra+ X-ray photoelectron spectrometer from Shimadzu Corporation.

[0048] In this embodiment, SEM morphology analysis was carried out using an IT800-SHL scanning electron microscope from Japan.

[0049] In this embodiment, AFM morphology analysis was carried out using a Dimension Icon atomic force microscope from Bruker Corporation, Germany.

[0050] In this embodiment, TEM morphology analysis was carried out using a TF-20 scanning electron microscope from FEI Company, USA.

[0051] In this embodiment, XRF quantitative analysis was carried out using an S8 TIGER X-ray fluorescence spectrometer from Bruker Corporation, Germany.

[0052] Example 1

[0053] Sample B 20 - The preparation steps of KH550 / ZnAl LDH2 are as follows:

[0054] (1) Preparation of DS-ZnAl LDH2:

[0055] Dissolve 12 mmol of sodium dodecyl sulfate (SDS) in a 100 mL mixed solution of ethanol and water with a volume ratio of ethanol to water of 1:1. Ultrasonic for 30 min to ensure complete dissolution, and keep it warm in an oil bath at 65 °C for 30 min. Dissolve 20 mmol of Zn(NO3)2 and 10 mmol of Al(NO3)3 in 100 mL of deionized water, denoted as solution A. Prepare 100 mL of 1 mol / L NaOH solution. Under the condition of 65 °C, add solution A and NaOH solution dropwise into the SDS solution. Nitrogen is continuously introduced during this process, and the pH of the system is maintained at 10.0 by controlling the dropping rate, with a stirring rate of 300 rpm. After adding solution A, continue to add NaOH solution within 30 min to make the pH of the system = 10. Then continue to stir at 65 °C for 8 h. Then separate the solid by filtration, and wash it repeatedly 5 times with a mixed solution of ethanol and water with a volume ratio of 1:1, consuming a total of 2 L of the solution. Freeze-dry under vacuum for 12 h, collect the solid, and name it DS-ZnAl LDH2.

[0056] (2) Preparation of KH550 / ZnAl LDH2:

[0057] Take 0.5 g of DS-ZnAl LDH2 and disperse it in 200 mL of toluene. Ultrasonic for 60 min to uniformly disperse and exfoliate the ZnAl LDH2 nanosheets. An obvious light column can be seen through laser irradiation. Add 20 mmol of silane coupling agent KH550 to the exfoliated toluene solution respectively, heat the solution to 110 °C, and carry out condensation reflux for 8 h under a nitrogen atmosphere. After cooling to room temperature, obtain KH550 / ZnAl LDH2 by centrifugation, wash it 5 times with ethanol, 50 mL each time, and vacuum dry at 60 °C for 12 h.

[0058] (3) B 20 - Preparation of KH550 / ZnAl LDH2:

[0059] Take 0.5 g of the dried solid and add it to 30 mL of absolute ethanol containing 20 mmol of 2-bromoethanol. Carry out condensation reflux at 75 °C for 24 h. Cool to room temperature and collect the solid by centrifugation. Wash it 5 times with ethanol, 50 mL each time, and vacuum dry at 60 °C for 12 h. Name it B 20 - KH550 / ZnAl LDH2.

[0060] B 20 - The performance evaluation method of KH550 / ZnAl LDH2 is as follows:

[0061] Take 0.2 g of catalyst B 20-KH550 / ZnAl LDH2 and 22 mmol of epoxybutane were loaded into a 25 mL stainless-steel autoclave. The autoclave was placed in an ice-water bath. When the temperature dropped to 8 °C, the autoclave was purged with CO2 at 0.2 MPa for 5 times to remove air, then filled with 0.2 MPa CO2, the inlet valve was closed, and the autoclave was heated to 100 °C. Subsequently, the CO2 pressure in the autoclave was increased to 3 MPa at one time and maintained at 3 MPa during the reaction. The mixture was reacted at 100 °C for 10 h under magnetic stirring at 600 rpm. After the reaction, the reactor was quickly cooled to room temperature in an ice-water bath, and the excess CO2 was discharged. The liquid in the autoclave was filtered and collected. A certain mass of biphenyl was dissolved in DMF and added to the liquid, and ultrasonicated for 30 min to mix evenly, and qualitative and quantitative analysis was carried out using Shimadzu GC-2030. The conversion rate of epoxybutane was 95%, the yield of butylene carbonate was 94%, and the selectivity was 99%.

[0062] Comparative Example 1

[0063] Sample B 20 The preparation steps of -KH550 / B-ZnAl LDH2 are as follows:

[0064] (1) The preparation method of bulk ZnAl LDH2 is as follows: 20 mmol of Zn(NO3)2 and 10 mmol of Al(NO3)3 were dissolved in 100 mL of deionized water, denoted as solution A. 100 mL of 1 mol / L NaOH solution was prepared. Under the condition of 65 °C, solution A and the NaOH solution were added dropwise into 100 mL of deionized water, and the pH of the system was maintained at 10.0 by controlling the dropping rate, and the stirring rate was 300 rpm. After adding solution A dropwise, the NaOH solution was continuously added dropwise within 30 min to make the system pH = 10. Subsequently, under 65 °C, continuous stirring was carried out for 12 h. Then the solid was separated by filtration and washed repeatedly with 2 L of deionized water for 5 times. Vacuum dried at 60 °C for 8 h, and the solid was collected and named ZnAl LDH2.

[0065] (2) Bulk B 20-The preparation method of KH550 / B-ZnAl LDH2 is as follows: Take 0.5 g of bulk ZnAl LDH2 and disperse it in 200 mL of toluene, and sonicate for 60 min. Add 20 mmol of silane coupling agent KH550 to the dispersed suspension, heat the solution to 110 °C, and carry out condensation reflux under a nitrogen atmosphere for 8 h. After cooling to room temperature, KH550 / B-ZnAl LDH2 is obtained by centrifugation, washed 5 times with ethanol, 50 mL each time. Then dry it in vacuo at 60 °C for 12 h. Weigh 0.5 g of the dried solid and add it to 30 mL of absolute ethanol containing 20 mmol of 2-bromoethanol. Under the condition of 75 °C, carry out condensation reflux for 24 h. Cool to room temperature and collect the solid by centrifugation. Wash it 5 times with ethanol, 50 mL each time. Then dry it in vacuo at 60 °C for 12 h. Name it B 20 -KH550 / B-ZnAl LDH2.

[0066] B 20 -The performance evaluation method of KH550 / B-ZnAl LDH2 is as follows:

[0067] B 20 -The performance evaluation method of KH550 / B-ZnAl LDH2 refers to Example 1, change the catalyst to B 20 -KH550 / B-ZnAl LDH2, and the rest of the process remains unchanged. The conversion rate of epoxybutane is 48%, the yield of butenyl carbonate is 48%, and the selectivity is 99%.

[0068] Example 2

[0069] Sample B 20 -The preparation steps of NQ62 / ZnAl LDH2 are as follows:

[0070] B 20 -The preparation steps of NQ62 / ZnAl LDH2 refer to Example 1, the difference is that the silane coupling agent used in Example 1 is changed from KH-550 to NQ-62, and the prepared sample is denoted as B 20 -NQ62 / ZnAl LDH2.

[0071] B 20 -The performance evaluation method of NQ62 / ZnAl LDH2 is as follows:

[0072] B 20 -The performance evaluation method of NQ62 / ZnAl LDH2 refers to Example 1, change the catalyst to B 20 -NQ62 / ZnAl LDH2, and the rest of the process remains unchanged. The conversion rate of epoxybutane is 50%, the yield of butenyl carbonate is 94%, and the selectivity is 47%.

[0073] Example 3

[0074] The preparation steps of sample B5-KH550 / ZnAl LDH2 are as follows:

[0075] The preparation steps of B5-KH550 / ZnAl LDH2 refer to Example 1, except that the addition amount of the silane coupling agent used in Example 1 is changed to 5 mmol, and the prepared sample is denoted as B5-KH550 / ZnAl LDH2.

[0076] The performance evaluation method of B5-KH550 / ZnAl LDH2 is as follows:

[0077] The performance evaluation method of B5-KH550 / ZnAl LDH2 refers to Example 1. The catalyst is changed to B5-KH550 / ZnAl LDH2, and the rest of the process remains unchanged to discuss the influence of the quaternary ammonium salt loading. The conversion rate of epoxybutane is 50%, the yield of butenyl carbonate is 47%, and the selectivity is 96%.

[0078] Example 4

[0079] Sample B 10 -KH550 / ZnAl LDH2 The preparation steps are as follows:

[0080] B 10 -KH550 / ZnAl LDH2 The preparation steps refer to Example 1, except that the addition amount of the silane coupling agent used in Example 1 is changed to 10 mmol, and the prepared sample is denoted as B 10 -KH550 / ZnAl LDH2.

[0081] B 10 -KH550 / ZnAl LDH2 The performance evaluation method is as follows:

[0082] B 10 -KH550 / ZnAl LDH2 The performance evaluation method refers to Example 1. The catalyst is changed to B5-KH550 / ZnAl LDH2, and the rest of the process remains unchanged to discuss the influence of the quaternary ammonium salt loading. The conversion rate of epoxybutane is 77%, the yield of butenyl carbonate is 74%, and the selectivity is 97%.

[0083] Example 5

[0084] Sample B 15 -KH550 / ZnAl LDH2 The preparation steps are as follows:

[0085] B 15 -KH550 / ZnAl LDH2 The preparation steps refer to Example 1, except that the addition amount of the silane coupling agent used in Example 1 is changed to 15 mmol, and the prepared sample is denoted as B15 -KH550 / ZnAl LDH2.

[0086] Sample B 15 The performance evaluation method of -KH550 / ZnAl LDH2 is as follows:

[0087] B 15 The performance evaluation method of -KH550 / ZnAl LDH2 refers to Example 1, with the catalyst changed to B 15 -KH550 / ZnAl LDH2, with the rest of the process unchanged, to discuss the influence of the quaternary ammonium salt loading. The conversion rate of epoxybutane is 77%, the yield of butenyl carbonate is 76%, and the selectivity is 98%.

[0088] Example 6

[0089] Sample B 25 The preparation steps of -KH550 / ZnAl LDH2 are as follows:

[0090] B 25 The preparation steps of -KH550 / ZnAl LDH2 refer to Example 1, except that the addition amount of the silane coupling agent used in Example 1 is changed to 25 mmol, and the prepared sample is denoted as B 25 -KH550 / ZnAl LDH2.

[0091] Sample B 25 The performance evaluation method of -KH550 / ZnAl LDH2 is as follows:

[0092] B 25 The performance evaluation method of -KH550 / ZnAl LDH2 refers to Example 1, with the catalyst changed to B 25 -KH550 / ZnAl LDH2, with the rest of the process unchanged, to discuss the influence of the quaternary ammonium salt loading. The conversion rate of epoxybutane is 94%, the yield of butenyl carbonate is 93%, and the selectivity is 99%.

[0093] Example 7

[0094] Sample C 20 The preparation steps of -KH550 / ZnAl LDH2 are as follows:

[0095] C 20 The preparation steps of -KH550 / ZnAl LDH2 refer to Example 1, except that the quaternization reagent used in Example 1 is changed from 2-bromoethanol to 3-chloro-1-propanol, and the prepared sample is denoted as C 20 -KH550 / ZnAl LDH2.

[0096] Sample C 20The performance evaluation method of -KH550 / ZnAl LDH2 is as follows:

[0097] C 20 The performance evaluation method of -KH550 / ZnAl LDH2 refers to Example 1, and the catalyst is changed to C 20 -KH550 / ZnAlLDH2, and the rest of the process remains unchanged. The conversion rate of epoxybutane is 32%, the yield of butenyl carbonate is 30%, and the selectivity is 94%.

[0098] Example 8

[0099] Sample I 20 The preparation steps of -KH550 / ZnAl LDH2 are as follows:

[0100] I 20 The preparation steps of -KH550 / ZnAl LDH2 refer to Example 1, except that the quaternization reagent used in Example 1 is changed to 2-iodoethanol, and the prepared sample is denoted as I 20 -KH550 / ZnAl LDH2

[0101] Sample I 20 The performance evaluation method of -KH550 / ZnAl LDH2 is as follows:

[0102] I 20 The performance evaluation method of -KH550 / ZnAl LDH2 refers to Example 1, and the catalyst is changed to I 20 -KH550 / ZnAlLDH2, and the rest of the process remains unchanged. The conversion rate of epoxybutane is 84%, the yield of butenyl carbonate is 83%, and the selectivity is 99%.

[0103] Comparative Example 2

[0104] Set the sample without quaternization as Comparative Example 1

[0105] The preparation steps of KH550 / ZnAl LDH2 refer to Example 1, except that the subsequent quaternization treatment of KH550 / ZnAl LDH2 in Example 1 is not carried out, and the rest of the steps are the same as those in Example 1

[0106] The performance evaluation method of KH550 / ZnAl LDH2 refers to Example 1, and the catalyst is changed to KH550 / ZnAl LDH2, and the rest of the process remains unchanged. The conversion rate of epoxybutane is less than 2%, the yield of butenyl carbonate is less than 1%, and the selectivity is 38%.

[0107] Example 9

[0108] The crystal structures of DS-ZnAl LDH2 in Example 1, ZnAl LDH2 in Comparative Example 1, and the organically modified zinc-aluminum layered double hydroxide Example 3B5-KH550 / ZnAl LDH2 and Example 1B were characterized by powder X-ray diffraction, and the results are as follows 20 -KH550 / ZnAl LD H2 are shown as follows Figure 1 Compared with ZnAl LDH2, the structure of DS-ZnAl LDH2 changed significantly after the DS ion exfoliation. By calculating the interplanar spacing of the (003) crystal plane using the Bragg equation, the interlayer spacing of ZnAl LDH2 was d(003) = 0.78 nm. When DS - was used as the interlayer anion, the interlayer spacing of DS-ZnAl LDH2 was d(003) = 2.32 nm. Therefore, DS - successfully entered the crystal structure of ZnAl LDH2 as an intercalated anion, increasing the interlayer spacing of ZnAl LDH2. After exfoliation and organic surface modification, the crystallinity of the catalyst decreased significantly, especially for the (00n) crystal plane of the catalyst. As the content of the quaternary ammonium salt increased, the diffraction peak intensity of the (00n) crystal plane of this material gradually decreased. At the same time, the diffraction peak shifted towards a lower angle, indicating that the expansion of the crystal interlayer spacing increased from 2.45 nm for B5-KH550 / ZnAl LDH2 to - 2.54 nm for B 20 -KH550 / ZnAl LDH2.

[0109] Example 10

[0110] The framework structures of DS-ZnAl LDH2, KH550 / ZnAl LDH2, and B 20 -KH550 / ZnAl LDH2 in Example 1 and ZnAl LDH2 in Comparative Example 1 were characterized by Fourier transform infrared spectroscopy, and the results are as follows Figure 2 shown. Compared with the bulk-phase structure of ZnAl LDH2, the DS-intercalated ZnAl LDH2 showed stretching vibration peaks of methyl and methylene groups at 2922 cm -1 and 2850 cm -1 . In addition, 1200 cm -1 was ν(SO3 - ). Combining with the XRD results, this indicates that DS - successfully intercalated into the lattice of ZnAl LDH2 as an interlayer anion. KH550 / ZnAl LDH2 showed δ(-NH2) at 1595 cm -1 and the stretching vibration peak of N-H at 3200 cm -1 . At the same time, in the range of 1000 - 1100 cm -1The broad peak that appears is the stretching vibration peak of Si-O, indicating that the silane coupling agent is loaded onto ZnAl LDH2 in a covalent bond manner. Quaternization of KH550 is carried out to achieve the loading of quaternary ammonium salts, and it is found that the peak of -NH2 is somewhat weakened, indicating that -NH2 is successfully quaternized.

[0111] Example 11

[0112] The surface O species of DS-ZnAl LDH2 and B 20 -KH550 / ZnAl LDH2 in Example 1 and ZnAl LDH2 in Comparative Example 1 were analyzed by X-ray photoelectron spectroscopy, and the O1s spectrum was fitted by XPS, as Figure 3 shown. The peaks at 531.4, 532.5, and 533.3 are O Ⅰ , O Ⅱ , O Ⅲ , representing the hydroxyl species (-OH) in the LDH structure, oxygen vacancies (O V ), and surface adsorbed water, respectively. Compared with the bulk phase and the LDH structure before organic modification, the oxygen vacancy content of B 20 -KH550 / ZnAl LDH has increased significantly, from 29% and 30% of ZnAl LDH2 and DS-ZnAl LDH2 to 45% of B 20 -KH550 / ZnAl LDH2.

[0113] Example 12

[0114] SEM was used to characterize the microtopography of DS-ZnAl LDH2, B 20 -KH550 / LDH2 in Example 1 and ZnAl LDH2 in Comparative Example 1, and the results are as Figure 4 shown. ZnAl LDH2 has a relatively regular hexagonal flake structure. After intercalation with DS - , obvious changes have occurred in this structure, the rigidity of the flake structure has decreased, and the thickness has become thinner. For B 20 -KH550 / LDH2 after loading quaternary ammonium salts, the layered structure of this LDH has not changed, but the thickness has increased, and there is obvious agglomeration.

[0115] Example 13

[0116] AFM was used to analyze the layer thickness of DS-ZnAl LDH2 in Example 1 and ZnAl LDH2 in Comparative Example 1, and the results are as Figure 5 shown. After being exfoliated and dispersed in toluene, the thickness of DS-ZnAl LDH2 has significantly thinned, from 13 nm in the bulk material to 1.2 nm. The morphology is consistent with the results of SEM.

[0117] Example 14

[0118] The micro-morphology and elemental distribution of DS-ZnAl LDH2 and B 20 -KH550 / LDH2 in Example 1 were characterized by TEM, and the results are as Figure 6 shown. DS-ZnAl LDH2 dispersed in toluene presents an ultrathin irregular nanosheet structure. Selective electron diffraction indicates that the nanosheet has a close-packed hexagonal lattice of LDH, which is a single-crystal nanosheet. After organic modification, the B 20 -KH550 / LDH2 nanosheets show obvious aggregation, but the elemental distribution is uniform.

[0119] Example 15

[0120] The elemental compositions of B5-KH550 / ZnAl LDH2, B 10 -KH550 / ZnAl LDH2, B 15 -KH550 / ZnAl LDH2, B 20 -KH550 / ZnAl LDH2, B 25 -KH550 / ZnAl LDH2 and B 20 -KH550 / B-ZnAl LDH2 were analyzed by X-ray fluorescence spectrometer. The loading amount of the silane coupling agent and the mass percentage of Br in the materials are shown in Table 1. The results indicate that the loading of the silane coupling agent in B 20 -KH550 / ZnAl LDH2 has reached saturation.

[0121] Table 1 Loading amount of silane coupling agent and mass percentage of Br in each catalyst

[0122]

[0123] Example 16

[0124] The cyclic performance of B 20 -KH550 / ZnAl LDH2 was tested. The experimental scheme is as follows:

[0125] The test process refers to Example 1. The tested catalyst was washed with 100 mL of ethanol, dried under vacuum at 60 °C, and the dried solid was collected for the next test. The cyclic test was carried out 5 times, and the activity of the catalyst is shown in Table 2.

[0126] Table 2 Cyclic performance test of catalyst B 20 -KH550 / ZnAl LDH2

[0127] Number of cycles Yield / % Selectivity / % 0 93 99 1 88 98 2 87 98 3 85 97 4 85 97

[0128] Matters not covered by this invention are well-known techniques.

Claims

1. A preparation method of a quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material, characterized in that, The method comprises the following steps: (1) Preparation of intercalated zinc-aluminum layered double hydroxides RS-ZnAl LDHs: By the coprecipitation method, at 50-100 °C, in an inert atmosphere and with stirring, solution A is added dropwise to the sodium alkyl sulfate (SRS) solution, and at the same time, a NaOH solution is added dropwise to keep the pH of the reaction system at 9.0-11.0; after solution A is added dropwise, the pH value is maintained for 10-60 min by continuously adding the NaOH solution; the temperature is maintained and continuous stirring is carried out for 4-12 h; then filtration is carried out, the solid is washed and dried to obtain RS-ZnAl LDHs; Among them, the solvent of the sodium alkyl sulfate solution is a mixed solvent, and the composition of the mixed solvent is water and ethanol, and the volume ratio of ethanol to water is 1-5; 5-30 mmol of SRS is added to every 50-150 mL of the mixed solvent; The solute of solution A is Zn(NO3)2 and Al(NO3)3; the sum of the concentrations of Zn(NO3)2 and Al(NO3)3 in solution A is 0.1-0.3 mol / L, and the molar ratio s of Zn / Al is 2-5; the volume of solution A is 0.5 to 1.5 times the volume of the SRS solution; (2) Preparation of silane-coupled zinc-aluminum layered double hydroxide nanosheets SiR / ZnAl LDHs: RS-ZnAl LDHs is added to toluene and ultrasonically dispersed for 30-120 min, then an amino-containing silane coupling agent is added, and it is heated at 60-120 °C under a nitrogen atmosphere and refluxed for 4-12 h. After cooling to room temperature, centrifugation, washing and drying are carried out to obtain silane-coupled SiR / ZnAl LDHs; Among them, 0.1-1 g of RS-ZnAl LDHs and 1-40 mmol of the amino-containing silane coupling agent are added to every 500-200 mL of toluene; (3) The preparation scheme of quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheets X-SiR / ZnAl LDHs is as follows: The quaternization reagent is dissolved in ethanol, and then SiR / ZnAl LDHs is added, and it is heated under reflux at 50-90 °C for 12-24 h; after cooling to room temperature, centrifugation, washing and drying are carried out, and the solid is collected to obtain the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material; Among them, 10-40 mmol of the quaternization reagent and 0.1-1 g of SiR / ZnAl LDHs are added to every 20-50 mL of ethanol.

2. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, In step (1), the concentration of the NaOH solution is 0.5-3 mol / L; the stirring rate is 200-500 rpm; The inert atmosphere is nitrogen, argon or helium.

3. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, In step (1), the sodium alkyl sulfate is one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium n-octyl sulfate, and sodium benzenesulfonate.

4. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, In step (2), the amino group-containing silane coupling agent is one or two of 3-aminopropyltriethoxysilane (KH-550), γ-aminopropyltriethoxysilane (KH-792), diethylenetriaminepropyltrimethoxysilane (NQ-62), N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (HD-602), and the addition amount is 5-25 mmol.

5. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, In step (3), the quaternization reagent is one or more of 1,2-dichloroethane, 3-chloro-1-propanol, potassium chloride, 1,2-dibromoethane, 2-bromoethanol, potassium bromide, 1,2-diiodoethane, 2-iodoethanol, and potassium iodide.

6. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, The nanosheet material is a quaternized silane coupling agent-modified zinc-aluminum layered double hydroxide, including a quaternary ammonium halide ion pair, a silane coupling agent, and a zinc-aluminum layered double hydroxide; wherein, the mass ratio of the halogen pair in the material is 1-40%, the loading amount of the silane coupling agent is 0.1-5 mmol / g, and the Zn / Al ratio in the zinc-aluminum layered double hydroxide is 2-5; The structure is a thin-layer or single-layer zinc-aluminum layered double hydroxide nanosheet, and the interlayer spacing is 2-3 nm.

7. The preparation method of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material according to claim 1, characterized in that, In this nanosheet material, the halogen is a bromide ion, the mass ratio of the bromide ion in the material is 20-35%, the loading amount of the silane coupling agent is 0.5-3.5 mmol / g, and the Zn / Al ratio in the zinc-aluminum layered double hydroxide is 2-5.

8. The application of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material prepared by the method according to claim 1, characterized in that it is used for the catalytic cycloaddition reaction of CO2 and epoxybutane.

9. The application of the quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material prepared by the method according to claim 8, characterized by including the following steps: Placing the obtained quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material in a reaction kettle, then adding epoxybutane and sealing the reaction kettle, opening the inlet valve to fill the reaction kettle with 0.1-5 MPa of CO2 gas, the reaction temperature is 25-120 °C, stopping the reaction after reacting for 1-12 h to obtain the target product butylene carbonate; Among them, 1-10 mL of epoxybutane is added to every 1 g of the obtained quaternary ammonium salt-supported zinc-aluminum layered double hydroxide nanosheet material.

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