Metal organic framework catalyst based on flexible connection as well as preparation method and application of metal organic framework catalyst

Abstract

The invention discloses a flexible connection-based metal organic framework catalyst preparation method, which comprises: (1) mixing terephthalaldehyde, 1-(3-aminopropyl) imidazole, a basic catalyst and a solvent I, and carrying out an imidization reaction to prepare an intermediate product; and (2) mixing the intermediate product, metal bromide and a solvent II at room temperature to obtain the metal organic framework catalyst, the metal bromide is selected from indium bromide and / or zinc bromide. The invention discloses a preparation method of a metal organic framework catalyst based on flexible connection, the preparation process is mild in condition and short in time, and the prepared product is used for catalyzing CO2 cycloaddition reaction, has high catalytic activity and can realize high conversion of a substrate under normal pressure (CO2 pressure is 0.1 MPa) and mild conditions (70-100 DEG C).

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular, to a metal-organic framework catalyst based on flexible connection, its preparation method and application in the cycloaddition reaction of carbon dioxide. Background Art

[0002] In the past century, due to the widespread use of fossil fuels, the concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere has been continuously increasing, leading to global warming and climate change problems. Converting CO2 into high-value-added chemicals is an effective way to realize the resource utilization of CO2. In this context, the cycloaddition reaction of CO2 with epoxides to form cyclic carbonates (as an important industrial chemical) has attracted extensive attention in the scientific community.

[0003] Generally, due to the thermodynamic stability of CO2, the CO2 cycloaddition reaction requires a catalyst. Many catalysts, including ionic liquids (ILs), metal halides, and metal-organic frameworks (MOFs), have been developed for this cycloaddition reaction. Among them, MOFs such as MIL-101(Cr), MIL-53(Al), UiO-66, and zeolitic imidazolate frameworks (ZIFs) similar to zeolites have proven to be a popular choice due to their unique pore structures and chemical properties. In this regard, ZIFs, as a subclass of MOFs, composed of transition metal ions and imidazole-type linkers, are promising catalysts for the CO2 cycloaddition reaction because they have dual active sites of Lewis acid (metal ions)-base (imidazole), which can synergistically enhance the catalytic activity.

[0004] For example, Timofeeva et al. (M.N. Timofeeva, I.A. Lukoyanov, V.N. Panchenko, K.I. Shefer, M.S. Mel’gunov, B.N. Bhadra, S.H. Jhung, Tuning the catalytic properties for cycloaddition of CO2 to propylene oxide on zeolitic-imidazolate frameworks through variation of structure and chemical composition, Mol. Catal. 529 (2022) 112530.) studied the catalytic performance of Zn, Co, and Zn-Co mixed ZIFs for the cycloaddition reaction of CO2 / propylene oxide (PO) in the presence of a co-catalyst (tetrabutylammonium bromide ([n-Bu4N]Br)) and found that Zn-ZIFs exhibited the highest catalytic activity under the conditions of 80 °C and 0.8 MPa CO2 due to its larger pore size.

[0005] For another example, Zhou et al. (M. Zhou, J. Chen, Z. Qu, Y. Du, J. Zhang, H. Jiang, R. Chen, Dimension and shape controllable ZIFs for highly-efficient chemical fixation of CO2 without solvent and co-catalyst, Sep. Purif. Technol. 320 (2023) 124120.) designed a two-dimensional Co-based ZIF (ZIF-(80)-Co), which exhibited excellent catalytic activity for the cycloaddition reaction of CO2 and epichlorohydrin (ECH) under the conditions of 0.9 MPa CO2 and 120 °C without a co-catalyst.

[0006] The above studies all indicate that ZIFs have great potential as catalysts for the CO2 cycloaddition reaction. However, most ZIFs still face the problem of insufficient Lewis acidity, resulting in unsatisfactory catalytic performance. Therefore, there is an urgent need to design new ZIFs to improve their catalytic activity for the CO2 cycloaddition reaction under mild conditions. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention discloses a preparation method of a metal-organic framework catalyst based on flexible connection, with mild preparation process conditions and short time. The prepared product is used for catalyzing the CO2 cycloaddition reaction, having high catalytic activity, and can achieve high conversion of the substrate under normal pressure (CO2 pressure is 0.1 MPa) and mild conditions (70 - 100 °C).

[0008] The specific technical solution is as follows:

[0009] A preparation method of a metal-organic framework catalyst based on flexible connection, comprising the following steps:

[0010] (1) Mix terephthalaldehyde, 1-(3-aminopropyl)imidazole, a basic catalyst and solvent I, and prepare an intermediate product through an imidization reaction;

[0011] (2) Mix the intermediate product, a metal bromide and solvent II, and obtain the metal-organic framework catalyst after mixing at room temperature;

[0012] The metal bromide is selected from indium bromide and / or zinc bromide.

[0013] The present invention discloses a preparation method of a metal-organic framework catalyst based on flexible connection, with mild process conditions and short time. The prepared metal-organic framework catalyst has a novel structure and high catalytic activity in the catalysis of the CO2 cycloaddition reaction.

[0014] In step (1):

[0015] Preferably:

[0016] The basic catalyst is selected from one or more of p-toluenesulfonic acid and trifluoroacetic acid;

[0017] The solvent I is selected from one or more of 1,4-dioxane and toluene.

[0018] Preferably:

[0019] The molar ratio of terephthalaldehyde to 1-(3-aminopropyl)imidazole is 1:(1.0 - 3.0);

[0020] Further preferably, the molar ratio of terephthalaldehyde to 1-(3-aminopropyl)imidazole is 1:2.

[0021] Preferably:

[0022] The molar ratio of the basic catalyst to terephthalaldehyde is (1.0 - 6.5)%.

[0023] Preferably:

[0024] The dosage ratio of terephthalaldehyde to solvent I is 1.0 - 2.5 mol / L.

[0025] Preferably:

[0026] The imidization reaction is carried out at the reflux temperature of Solvent I.

[0027] Preferably:

[0028] After the imidization reaction, the solvent is removed by distillation, and then the intermediate product is obtained through post-treatments such as washing and drying.

[0029] In step (2):

[0030] Preferably:

[0031] The Solvent II is selected from one or more of ethanol, methanol, and N,N-dimethylformamide.

[0032] Preferably:

[0033] The molar ratio of the metal bromide to the intermediate product is selected from 1:(1 / 3 - 3);

[0034] Further preferably:

[0035] The metal bromide is selected from indium bromide, and the molar ratio of the metal bromide to the intermediate product is selected from 1:(1 - 3); more preferably 1:3.

[0036] Or, the metal bromide is selected from zinc bromide, and the molar ratio of the metal bromide to the intermediate product is 1:3.

[0037] Preferably:

[0038] The dosage ratio of the metal bromide to Solvent II is 1 - 25 mmol / L;

[0039] Further preferably, the dosage ratio of the metal bromide to Solvent II is 2.5 - 22.5 mmol / L.

[0040] Preferably:

[0041] Stir at room temperature for 10 - 60 min, and the obtained crude product is dried to obtain the metal-organic framework catalyst.

[0042] The present invention also discloses a metal-organic framework catalyst prepared according to the above method.

[0043] The present invention also discloses a carbon dioxide cycloaddition reaction, using carbon dioxide and epoxide as raw materials and adopting the above-mentioned metal-organic framework catalyst.

[0044] Preferably, the metal bromide used in preparing the metal-organic framework catalyst is selected from indium bromide.

[0045] It has been found through experiments that the metal-organic framework prepared using indium bromide as a raw material has higher catalytic activity in the catalytic carbon dioxide cycloaddition reaction.

[0046] Preferably, the carbon dioxide cycloaddition reaction is carried out under atmospheric pressure, the reaction temperature is 70 - 100 °C, and the reaction time is 3 - 9 h.

[0047] Preferably, the epoxide is selected from one or more of epichlorohydrin (ECH), styrene oxide (SO), benzyl glycidyl ether (BZGE), glycidyl phenyl ether (GPE), butyl glycidyl ether (BGE).

[0048] More preferably, the epoxide is selected from ECH, BZGE, GPE; even more preferably ECH.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention discloses a preparation method of a metal-organic framework catalyst based on flexible connection. The preparation process is simple, the process conditions are mild and the time is short. The prepared metal-organic framework catalyst has a novel structure and is used for catalyzing the CO2 cycloaddition reaction, having high catalytic activity, and can achieve high conversion of substrates under atmospheric pressure (CO2 pressure is 0.1 MPa) and mild conditions (70 - 100 °C, 3 - 9 h); moreover, the metal-organic framework catalyst can be recycled and has good recycling stability. Description of the Drawings

[0051] Figure 1 1H NMR spectrum of the intermediate PBIM prepared in Example 1;

[0052] Figure 2 High-resolution XPS spectra of the product prepared in Example 1, C 1s (a), N 1s (b), Br 3d (c) and In 3d (d);

[0053] Figure 3 SEM images (a - b) and EDS mapping images (c - f) of the product prepared in Example 1;

[0054] Figure 4 High-resolution XPS spectra of the product prepared in Example 4, C 1s (a), N 1s (b), Br 3d (c) and Zn 2p (d);

[0055] Figure 5 SEM images (a - b) and EDS mapping images (c - f) of the product prepared in Example 4;

[0056] Figure 6 X-ray diffraction (XRD) patterns of the products prepared in Examples 1 - 6 respectively;

[0057] Figure 7 FT-IR spectra of the products were prepared for Examples 1-6 respectively;

[0058] Figure 8 Thermogravimetric (TGA) curves of the products were prepared for Examples 1-6 respectively;

[0059] Figure 9 N2 adsorption-desorption isotherms of the products prepared for Examples 1-6 respectively;

[0060] Figure 10 Bar graphs of CPC yields in Application Examples 1-6;

[0061] Figure 11 Bar graphs of CPC yields in Application Examples 1, 7-21;

[0062] Figure 12 Bar graphs of CPC yields in Application Example 1, Comparative Application Example 1, Application Examples 22-23;

[0063] Figure 13 Bar graphs of product yields in Application Examples 24-27. Detailed implementation manners

[0064] In order to make the objectives, features, and advantages of the present invention more obvious, the following further list embodiments to illustrate the present invention in detail. The following embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention all fall within the protection scope of the present invention.

[0065] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0066] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0067] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those of ordinary skill in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0068] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. If descriptions such as "first", "second", etc. are involved throughout the text, such "first", "second", etc. descriptions are only used to distinguish similar objects, and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly indicating the quantity of the technical features indicated. It should be understood that the data described by "first", "second", etc. can be interchanged under appropriate circumstances.

[0069] The raw materials used in the present invention are described as follows:

[0070] p-Toluenesulfonic acid monohydrate (TA, ≥98.5%) and phenyl glycidyl ether (GPE, >99.0%) were provided by Aladdin Scientific Corp. (Shanghai, China).

[0071] Indium bromide (InBr3, 99.9%), terephthalaldehyde (PA, ≥99%), 1-(3-aminopropyl)imidazole (API, ≥97%), styrene oxide (SO, 98%), zinc bromide (ZnBr2, 99%), 1,4-dioxane (≥99%), epichlorohydrin (ECH, ≥99.5%), butyl phenyl glycidyl ether (BGE, 98%) and benzyl phenyl glycidyl ether (BZGE, 99%) were purchased from Macklin Inc. (Shanghai, China).

[0072] Example 1

[0073] (1) Synthesis of PBIM

[0074] 0.06 mol of PA, 0.12 mol of API and 0.17 g of TA (0.89 mmol) were dissolved in 35 mL of 1,4-dioxane, and the resulting solution was refluxed at 100 °C for 12 h. The solvent was removed by distillation to obtain a viscous liquid, which was then washed with ethyl acetate and water respectively. It was dried at 70 °C to obtain an orange solid PBIM with a yield of 77%.

[0075]

[0076] The chemical structure of PBIM was characterized by proton nuclear magnetic resonance ( 1 1H NMR, 400 MHz, DMSO-d6) spectroscopy, and the results are shown inFigure 1 .

[0077] (2) Preparation of MOFs

[0078] Weigh 0.75 mmol of InBr3 and 0.75 mmol of PBIM (InBr3:PBIM = 1:1) and dissolve them in 100 mL of ethanol. Stir the resulting mixture at room temperature for 30 min to form a yellow precipitate. After drying the precipitate at 100 °C for 8 h, indium-based MOFs, denoted as InPBIMBr-1, are obtained with a yield of 73.6%.

[0079] Figure 2 This is the high-resolution XPS spectrum of the product prepared in this example, C 1s (a), N 1s (b), Br 3d (c) and In 3d (d). The C 1s spectrum can be deconvoluted into two peaks with binding energies of 284.8 eV and 286.1 eV, attributed to C-C / C═C and C-N respectively; the N 1s spectrum shows two peaks located at 401.1 eV and 399.2 eV, corresponding to the N atoms from C–N and M–N═C (M = In 3+ ) in the imidazole ring of PBIM. In addition, the binding energy of M–N═C is located at 399.2 eV, indicating the presence of M-N2 coordination form (i.e., two nitrogen atoms coordinate with one metal ion) in MOFs. In the Br 3d spectrum, the peak at 68.8 eV is attributed to Br 3d. The high-resolution In 3d spectrum shows two peaks at 452.8 eV and 445.2 eV, corresponding to In 3d3 / 2 and In 3d5 / 2 respectively.

[0080] Figure 3 This is the SEM image (a–b) and EDS mapping image (c–f) of the product prepared in this example. It is observed that the product shows a typical flake structure, and the elements C, N, Br and metal In are uniformly distributed in the MOF.

[0081] Example 2

[0082] The preparation process is basically the same as that of Example 1, except that in step (2), the molar amount of InBr3 is replaced with 0.25 mmol, and the initial molar ratio of InBr3 to PBIM is 1:3.

[0083] The product prepared in this example is denoted as InPBIMBr-2, and the yield is 62.9%.

[0084] After XPS testing, the product prepared in this example is similar to Figure 2 that.

[0085] After SEM and EDS testing, the product prepared in this example is similar to Figure 3 that.

[0086] Example 3

[0087] The preparation process is basically the same as that of Example 1, except that in step (2), the number of moles of InBr3 is replaced with 2.25 mmol, and the initial molar ratio of InBr3 to PBIM is 3:1.

[0088] The product prepared in this example is denoted as InPBIMBr-3, and the yield is 24.2%.

[0089] After XPS testing, the product prepared in this example is similar to Figure 2 that.

[0090] After SEM and EDS testing, the product prepared in this example is similar to Figure 3 that.

[0091] Example 4

[0092] The preparation process is basically the same as that of Example 1, except that in step (2), InBr3 is replaced with an equimolar amount of ZnBr3, and the initial molar ratio of ZnBr3 to PBIM is 1:1.

[0093] The product prepared in this example is denoted as ZnPBIMBr-1, and the yield is 81.3%.

[0094] Figure 4 is the high-resolution XPS spectrum of the product prepared in this example, C 1s (a), N 1s (b), Br 3d (c) and Zn2p (d). The C 1s spectrum can be deconvoluted into two peaks with binding energies of 284.8 eV and 286 eV, attributed to C-C / C═C and C-N, respectively; the N 1s spectrum shows two peaks located at 401.2 eV and 399.3 eV, corresponding to the N atoms from C–N and M–N═C (M = Zn 2+ ) in the imidazole ring of PBIM. In addition, the binding energy of M–N═C is located at 399.3 eV, indicating the presence of M-N2 coordination form in MOFs (i.e., two nitrogen atoms coordinate with one metal ion). In the Br 3d spectrum, the peak located at 68.8 eV is attributed to Br3d. The high-resolution Zn2p spectrum shows two peaks at 1045.3 eV and 1022.4 eV, corresponding to Zn 2p1 / 2 and Zn2p3 / 2, respectively.

[0095] Figure 5 is the SEM image (a–b) and EDS mapping (c–f) of the product prepared in this example. It is observed that the product shows a typical flake structure, and the elements C, N, Br, and metal Zn are evenly distributed in the MOF.

[0096] Example 5

[0097] The preparation process is basically the same as that of Example 4, except that in step (2), the number of moles of ZnBr3 is replaced with 0.25 mmol, and the initial molar ratio of ZnBr3 to PBIM is 1:3.

[0098] The product obtained in this example is denoted as ZnPBIMBr-2, and the yield is 51.2%.

[0099] Example 6

[0100] The preparation process is basically the same as that of Example 4, except that in step (2), the number of moles of ZnBr3 is replaced with 2.25 mmol, and the initial molar ratio of ZnBr3 to PBIM is 3:1.

[0101] The product obtained in this example is denoted as ZnPBIMBr-3, and the yield is 42.1%.

[0102] Figure 6 X-ray diffraction (XRD) patterns of the products were prepared for Examples 1 to 6 respectively. It was observed that the synthesized MOFs exhibited broad diffraction peaks, indicating their amorphous nature. At the same time, the diffraction peaks located at 10.9° - 11.9° (2θ) and 21.5° - 24.0° were consistent with the characteristic diffraction peaks of ZIFs, suggesting that the synthesized MOFs were ZIF-like analogues.

[0103] Since it is difficult to obtain detailed structural information of amorphous MOFs, high performance liquid chromatography (HPLC), ion chromatography (IC) and inductively coupled plasma optical emission spectrometry (ICP-OES) techniques were further used to gain in-depth understanding of the structural information of the building units of the synthesized MOFs. The specific test conditions are as follows:

[0104] The synthesized product was dissolved in 0.1 mol L –1 HCl aqueous solution, and the metal content (In 3+ and Zn 2+ ) was measured by inductively coupled plasma optical emission spectrometry (ICP-OES, model 5110, Agilent Technologies, Santa Clara, California, USA).

[0105] The content of PBIM was determined by a high performance liquid chromatograph (HPLC, model Alliance 2695, Waters, Milford, Massachusetts, USA) equipped with a photodiode array detector and an autoinjector under the following chromatographic conditions: separation column, Amethyst C18-H column (4.6 mm × 150 mm, 5 μm, Sepax Technologies Inc., Newark, Delaware, USA); mobile phase, a mixture of methanol (65%, V / V) and water, and the flow rate was 0.6 mL min–1 ; Detection wavelength, 270 nm; Column temperature, 25 °C; Injection volume, 10 μL.

[0106] Br – The content of Br was measured by an ion chromatograph (IC, model ICS-2100, Thermo Fisher Scientific Inc., Waltham, Massachusetts, USA) equipped with a conductivity detector. The chromatographic conditions were as follows: Separation column, IonPac AS11-HC (250 mm × 4 mm); Guard column, IonPac AG11-HC (50 mm × 4 mm); Eluent, 20 mmol L–1 NaOH, flow rate 1.0 mL min–1; Suppression current, 80 mA; Column temperature, 35 °C; Injection volume, 25 μL; Detection cell temperature, 30 °C.

[0107] It was found that the chemical compositions of the synthesized MOFs were as follows: InPBIMBr3 (InPBIMBr-1), InPBIM 1.5 Br3 (InPBIMBr-2), InPBIM 0.5 Br3 (InPBIMBr-3), ZnPBIMBr2 (ZnPBIMBr-1), ZnPBIMBr2 (ZnPBIMBr-2), and ZnPBIM 0.8 Br2 (ZnPBIMBr-3).

[0108] All MOFs were amorphous structures, and their chemical compositions were determined by separately measuring the contents of Zn, PBIM, and Br. Among them, although ZnPBIMBr-1 and ZnPBIMBr-2 had the same chemical formula (ZnPBIMBr2), they were two different MOF products, possibly due to the structural differences caused by the differences in synthesis conditions.

[0109] Figure 7 FT-IR spectra of the products prepared for Examples 1–6 were obtained. It was observed that the peaks at 3402–3517 cm –1 corresponded to the –OH stretching vibration of residual water, and the band at 3117 cm –1 was attributed to the C-H stretching vibration mode of the aromatic / imidazole ring. The peaks at 2932 cm –1 and 2841 cm –1 represented the asymmetric and symmetric stretching vibrations of aliphatic C-H, respectively. The bands in the range of 1096 cm –1 to 1694 cm –1 were related to the stretching and bending vibrations of the aromatic / imidazole ring, and the absorption peak at approximately 507 cm – 1 could be attributed to the stretching vibration of In-N / Zn-N.

[0110] Figure 8 Thermogravimetric (TGA) curves of the products were prepared for Examples 1 to 6 respectively. It was observed that all the synthesized MOFs showed good thermal stability, and their initial decomposition temperatures were approximately between 242 and 260 °C, approaching the decomposition temperature of ZIFs.

[0111] The porosity of the synthesized MOFs was studied by measuring the N2 adsorption - desorption isotherms of the products prepared in Examples 1 to 6 at 77 K. The measured curves are as Figure 9 shown. The results indicate that the synthesized MOFs exhibit type IV isotherms and H3 - type hysteresis loops, suggesting a mesoporous structure with slit - like pores as the main pore morphology. In addition, the calculated Brunauer - Emmett - Teller (BET) specific surface area, pore diameter (Barrett - Joyner - Halenda (BJH) method), and pore volume (BJH method) are listed in Table 1. It can be seen from this that the synthesized MOFs show a relatively small specific surface area (2.2 - 9.9 m 2 g –1 ), which is in line with the characteristics of amorphous MOFs.

[0112] Table 1

[0113]

[0114]

[0115] Application Example 1: Cycloaddition reaction of CO2 and epichlorohydrin (ECH)

[0116] Using InPBIMBr - 1 prepared in Example 1 as a catalyst, 10 mmol of ECH and 50 mg (the mass ratio of the catalyst to ECH is 5.4%) of the catalyst were added to a 50 mL Schlenk reaction tube. The tube was purged with CO2 gas three times, and then a CO2 balloon was connected to maintain a pure CO2 atmosphere (CO2 pressure was 0.1 MPa); then the reaction was stirred at 80 °C for 5 h. After the cycloaddition reaction was completed, the catalyst solid was separated by centrifugation, and the yield and selectivity of chloropropylene carbonate (CPC) were determined by 1 1H NMR spectroscopy.

[0117] After the catalyst solid obtained by centrifugation was washed with acetone and dried under vacuum at 100 °C for 2 h, the recovered catalyst was obtained. The recovered catalyst was used to catalyze the cycloaddition reaction of CO2 and epichlorohydrin (ECH) under the conditions of Application Example 1. After testing, the yield was 92.3%.

[0118] Application Examples 2 - 6

[0119] The preparation process is basically the same as that of Application Example 1, except that the catalyst is sequentially replaced with the products prepared in Examples 2-6 respectively, and the dosage of each catalyst is 50 mg.

[0120] Figure 10 It is a bar chart of the CPC yields in Application Examples 1-6. It is observed that all the synthesized catalysts have high selectivity (exceeding 90%). At the same time, although the CO2 adsorption capacity of Zn-based MOFs is stronger (see Table 1), In-based MOFs show higher catalytic activity.

[0121] The CPC yield data in Application Examples 1-6 are listed in Table 2 below.

[0122] Table 2

[0123]

[0124] Application Examples 7-21

[0125] The preparation process is basically the same as that of Application Example 1, except that the temperature and time of the cycloaddition reaction are adjusted.

[0126] The specific reaction conditions and the bar chart of the CPC yield in each application example are as Figure 11 shown. It is observed that as the temperature or reaction time increases, the yield of CPC increases (selectivity > 98%). Although the yield of CPC increases slightly under higher temperature or longer reaction time conditions, considering factors such as the energy consumption, time cost, and experimental operation efficiency of the reaction, 80 °C and a reaction time of 5 hours are finally selected as the optimal reaction conditions. Under these conditions, the selectivity of CPC remains above 98%, taking into account both the yield and the feasibility of practical applications.

[0127] Application Examples 22-23

[0128] The preparation process is basically the same as that of Application Example 1, except that the mass of the catalyst is sequentially replaced with 10 mg (the mass ratio of the catalyst to ECH is 1.1%) and 30 mg (the mass ratio of the catalyst to ECH is 3.2%).

[0129] Comparative Application Example 1

[0130] The preparation process is basically the same as that of Application Example 1, except that no catalyst is added.

[0131] Figure 12It is a bar chart showing the CPC yields at different catalyst dosages in Application Example 1, Comparative Application Example 1, and Application Examples 22 and 23. It is observed that in the absence of a catalyst, the conversion rate of ECH is zero. When the catalyst dosage is increased to 5.4%, the yield increases to 97.2% (selectivity > 98%). This is because a higher catalyst dosage means more active sites. Given that a 5.4% catalyst can provide a CPC yield as high as 97.2%, it is selected as the optimal catalyst dosage and used in subsequent experiments.

[0132] Application Examples 24 - 27

[0133] The preparation process is basically the same as that of Application Example 1, except that the types of epoxides are sequentially replaced with butyl glycidyl ether (BGE), styrene oxide (SO), benzyl glycidyl ether (BZGE), and glycidyl phenyl ether (GPE), and the dosage of each epoxide is 10 mmol.

[0134] The bar charts of the yields in each application example are as shown in Figure 13 It can be observed that the catalyst disclosed in the present invention shows high catalytic activity towards BZGE and GPE; while when SO and BGE are used as substrates, the yields of the corresponding cyclic carbonates decrease to 66.3% and 53.5% respectively, which can be attributed to the steric hindrance brought by the aromatic ring (SO) and the longer alkyl chain length (BGE). These results indicate that the catalyst disclosed in the present invention has size selectivity for epoxides in the catalytic CO2 cycloaddition reaction.

[0135] The yield data in Application Examples 22 - 27 are listed in Table 3 below.

[0136] Table 3

[0137]

[0138] The above are only several specific embodiments of the present invention. It should be noted that many variations and improvements can be made by those of ordinary skill in the art. All variations or improvements that do not exceed the scope of the claims shall be regarded as within the protection scope of the present invention.

Claims

1. A preparation method of a metal-organic framework catalyst based on flexible connection, characterized in that, It includes the following steps: (1) Mix terephthalaldehyde, 1-(3-aminopropyl)imidazole, a basic catalyst and solvent I, and prepare an intermediate product through an imidization reaction; (2) Mix the intermediate product, a metal bromide and solvent II, and obtain the metal-organic framework catalyst after mixing at room temperature; The metal bromide is selected from indium bromide and / or zinc bromide.

2. The preparation method of the metal-organic framework catalyst based on flexible connection according to claim 1, characterized in that In step (1): The basic catalyst is selected from one or more of p-toluenesulfonic acid and trifluoroacetic acid; The solvent I is selected from one or more of 1,4-dioxane and toluene.

3. The preparation method of the metal-organic framework catalyst based on flexible connection according to claim 1, wherein, In step (1): The molar ratio of terephthalaldehyde to 1-(3-aminopropyl)imidazole is 1:(1.0 - 3.0); The molar ratio of the basic catalyst to terephthalaldehyde is (1.0 - 6.5)%; The dosage ratio of terephthalaldehyde to solvent I is 1.0 - 2.5 mol / L.

4. The preparation method of the metal-organic framework catalyst based on flexible connection according to claim 1, characterized in that, In step (1), the imidization reaction is carried out at the reflux temperature of solvent I.

5. The preparation method of the metal-organic framework catalyst based on flexible connection according to claim 1, wherein In step (2): The solvent II is selected from one or more of ethanol, methanol, and N,N-dimethylformamide.

6. The preparation method of the metal-organic framework catalyst based on flexible connection according to claim 1, wherein, In step (2): The molar ratio of the metal bromide to the intermediate product is selected from 1:(1 / 3 - 3); The dosage ratio of the metal bromide to solvent II is 1 - 25 mmol / L.

7. The preparation method of the metal-organic framework catalyst based on flexible connection according to any one of claims 1 to 6, characterized in that, In step (2): The metal bromide is selected from indium bromide, and the molar ratio of the metal bromide to the intermediate product is selected from 1:(1 - 3); Or, the metal bromide is selected from zinc bromide, and the molar ratio of the metal bromide to the intermediate product is selected from 1:

3.

8. A metal-organic framework catalyst based on flexible connection prepared by the method according to any one of claims 1 to 7.

9. A carbon dioxide cycloaddition reaction uses carbon dioxide and epoxide as raw materials, characterized in that, Use the metal-organic framework catalyst based on flexible connection according to claim 8.

10. The carbon dioxide cycloaddition reaction according to claim 9, characterized in that: The carbon dioxide cycloaddition reaction is carried out under atmospheric pressure, the reaction temperature is 70 - 100 °C, and the reaction time is 3 - 9 h; The epoxide is selected from one or more of epichlorohydrin, styrene oxide, benzyl glycidyl ether, phenyl glycidyl ether, and butyl glycidyl ether.

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