Catalyst for carbon dioxide cycloaddition comprising core-shell zeolitic imidazolate framework

Abstract

This specification discloses a ZIF (Zeolitic imidazolate framework)-based catalyst for the cyclic addition reaction of carbon dioxide, comprising a core in which Co metal and Zn metal exist in a core-shell form, and a method for manufacturing the same. Furthermore, this specification discloses a method for manufacturing a cyclic organic carbonate using the said catalyst. The catalyst according to this disclosure exhibits a synergistic effect in the cyclic addition reaction of carbon dioxide, showing a high carbon dioxide conversion rate and excellent stability, allowing for multiple reuses. Additionally, since it contains Co and Zn metals in a core-shell form, it has the advantage of allowing for the quantitative evaluation of each effect.

Description

Technology Field

[0001] This specification relates to metal-organic framework compounds and catalysts containing the same. Background Technology

[0002] Since carbon dioxide (CO2) causes global warming originating from fossil fuel-based power plants, various technologies for CO2 capture, storage, and utilization have been developed to reduce anthropogenic CO2 emissions. The chemical conversion of CO2 is attracting attention as an eco-friendly and inexpensive C1 building block that produces non-flammable, non-toxic, and useful chemicals; however, due to CO2's low reactivity, catalysts are required to convert it efficiently.

[0003] One of the most interesting CO2 fixation strategies is the cyclization of CO2 into epoxides to produce cyclic organic carbonates, which can be used in various industrial applications such as degreasing agents, polar aprotic solvents, electrolytes for lithium-ion batteries, and intermediates for polymer materials. Epoxide-derived cyclic carbonates are prepared using various homogeneous and heterogeneous catalysts containing Lewis acidic metal ions such as Zn(II) and Co(II). Additionally, solvents or co-catalysts with Lewis base sites or nucleophilic properties are commonly used to open the epoxide ring and enhance catalytic activity. Metal-organic frameworks (MOFs), a new class of crystalline porous materials, have been considered a potential heterogeneous catalyst for the cyclization of CO2 into epoxides due to their unique characteristics of high surface area, large porosity, well-ordered porous structure, and ease of functionalization; however, there has been a problem in that their catalytic application in liquid phases is limited because most are unstable when exposed to water / moisture or air.

[0004] In this regard, zeolitic imidazolate frameworks (ZIFs), a sub-concept of MOFs, consist of metal centers coordinated to imidazolate linker tetrahedra (typically, Zn in ZIF-8 or Co in ZIF-67). However, according to previous reports on CO2 cyclization addition reactions, although ZIF-8, a complex of Zn metal ions and imidazole ligands, exhibits higher conversion rates in shorter time periods, there is a problem of very low selectivity and reusability due to the breakdown of the Zn-imidazole binding-induced structure, which has weaker binding forces, caused by stronger interactions between the Zn atoms and the substrate (see Non-Patent Literature 1). ZIF-67, a complex of Co metal ions and imidazole ligands, showed poor CO2 conversion efficiency in CO2 cyclization addition reactions without solvents or co-catalysts due to weak interactions between the substrate and the Co atoms, a metal with relatively low Lewis acidity (see Non-Patent Literature 2). Accordingly, bimetallic ZIFs of random form generated by mixing Zn and Co metals were developed, improving CO2 conversion rate, selectivity, and reusability; however, there were limitations in that the effects of each metal ion (Zn and Co) on structural properties such as acidity / basicity, pore size, and particle size could not be quantitatively evaluated because Co and Zn metals were irregularly coordinated, and the structural stability of the catalyst was poor due to low stability in moisture / air (see Non-Patent Literature 3). Prior art literature

[0005] C. M. Miralda, E. E. Macias, M. Zhu, P. Ratnasamy, and M. A. Carreon, ACS Catal. 2(1) (2012) 180-183B. Mousavi, S. Chaemchuen, B. Moosavi, Z. Luo, N. Gholampour, and F. Verpoort, New J. Chem.40 (6) (2016) 5170-5176R. R. Kuruppathparambil, R. Babu, H. M. Jeong, G. Y. Hwang, G.S. Jeong, M-Il. Kim, DW. Kim and DW. Park, Green Chem. 18 (2016), 6349-6356 The problem to be solved

[0006] The problem that the present disclosure aims to solve is to provide a carbon dioxide cycloaddition catalyst comprising a novel zeolite imidazolate framework (ZIFs) exhibiting excellent conversion rate, selectivity, and reusability. means of solving the problem

[0007] To solve the above problem, one embodiment of the present disclosure provides a catalyst for a cyclic addition reaction of carbon dioxide having a core-shell structure comprising a core and a shell surrounding the core, wherein the core-shell particles comprise ZIF (Zeolitic imidazolate framework)-8 in the core and ZIF-67 in the shell, or comprise ZIF-67 in the core and ZIF-8 in the shell.

[0008] Another embodiment of the present disclosure is a method for manufacturing the catalyst for the carbon dioxide cycloaddition reaction,

[0009] (i) a step of dissolving a cobalt salt, a zinc salt, and 2-methylimidazole in a solvent, respectively; a step of injecting the cobalt salt solution into the 2-methylimidazole ligand solution and then adding the zinc salt solution to react; and a step of heat-treating the reaction mixture to produce a catalyst comprising ZIF-67 in the core and ZIF-8 in the shell, or

[0010] (ii) a step of adding a solution in which ZIF-8 is dispersed to an alcohol solution in which cobalt chloride is dispersed and mixing; a step of adding a solution in which 2-methylimidazole is dispersed to the mixture and reacting; and a step of heat-treating the reaction product to produce a catalyst comprising ZIF-8 in the core and ZIF-67 in the shell;

[0011] A method for manufacturing a catalyst for a carbon dioxide cycloaddition reaction comprising

[0012] Another embodiment of the present disclosure provides a method for producing a cyclic organic carbonate, comprising the steps of: placing an epoxide-based compound substrate and a carbon dioxide cyclic addition reaction catalyst into an autoclave; and injecting a gas containing carbon dioxide into the autoclave and then performing a carbon dioxide cyclic addition reaction in an oil bath to produce a cyclic organic carbonate. Effects of the invention

[0013] One embodiment of the present disclosure relates to a ZIF-based catalyst in which Co metal and Zn metal exist in a core-shell form. It exhibits a synergistic effect in the cycloaddition reaction of carbon dioxide, showing a high carbon dioxide conversion rate, and simultaneously possesses excellent stability, allowing for multiple reuses. Furthermore, according to the present disclosure, since Co and Zn metals are included in a core-shell form, there is an advantage in that the respective effects can be quantitatively evaluated. Brief explanation of the drawing

[0014] FIG. 1 is a schematic diagram illustrating the synthesis procedure of (A) core-shell ZIF-67@ZIF-8 and (B) core-shell ZIF-8@ZIF-67 according to one embodiment of the present disclosure. Figure 2a shows the particle size distribution and SEM image of Comparative Example 1 (ZIF-8). Figure 2b shows the particle size distribution and SEM image of Comparative Example 2 (ZIF-67). Figure 2c is a figure showing the particle size distribution and SEM image of Example 1 (ZIF-67@ZIF-8). Figure 2d shows the particle size distribution and SEM image of Example 2 (ZIF-8@ZIF-67). Figure 2e shows the particle size distribution and SEM image of Comparative Example 3 (bimetallic Zn / Co-ZIF). Fig. 3a is The XRD patterns of Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) are shown. FIG. 3b is a figure showing the FT-IR spectra of Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67). FIG. 3c is a figure showing the TGA graphs of Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67). FIG. 3d is a figure showing the differential thermal gravity of Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67). FIG. 4 is a figure showing STEM images corresponding to EDX elemental mappings (Zn: green, Co: pink) and EDX-line scanning of (A) Example 1 (ZIF-67@ZIF-8), (B) Example 2 (ZIF-8@ZIF-67), and (C) Comparative Example 3 (bimetallic Zn / Co-ZIF) (right graph) and EDX elemental mappings (left image; Zn: green, Co: pink). Figure 5a shows the wide-scan XPS spectrum for Comparative Example 3 (bimetallic Zn / Co-ZIF). Figure 5b shows the high-resolution XPS spectrum of the Co 2p band for Comparative Example 3 (bimetallic Zn / Co-ZIF). Figure 5c shows the high-resolution XPS spectrum of the Zn 2p band for Comparative Example 3 (bimetallic Zn / Co-ZIF). FIG. 5d is a figure showing the wide-scan XPS spectrum for Example 1 (ZIF-67@ZIF-8). Figure 5e shows the high-resolution XPS spectrum of the Co 2p band for Example 1 (ZIF-67@ZIF-8). Figure 5f shows the high-resolution XPS spectrum of the Zn 2p band for Example 1 (ZIF-67@ZIF-8). Figure 5g shows the wide-scan XPS spectrum for Example 2 (ZIF-8@ZIF-67). Figure 5h shows the high-resolution XPS spectrum of the Co 2p band for Example 2 (ZIF-8@ZIF-67). Figure 5i shows the high-resolution XPS spectrum of the Zn 2p band for Example 2 (ZIF-8@ZIF-67). Figure 6 shows the epichlorihydrin conversion rate and D for catalysts of various sizes. SEM / DXRD This is a diagram showing the correlation between them (4 h, 7 bar, 100℃). Figure 7 is a figure showing a comparison of catalytic performance using an epichlorohydrin substrate for Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67), which have similar particle sizes. Figure 8 is a figure comparing the catalytic performance of epichlorohydrin substrates for Comparative Example 3 (bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) when using 100% pure CO2 gas and mixed gas (85% CO2 / 15% N2, v / v). FIG. 9 is a figure comparing the catalytic performance of Comparative Example 3 (bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) on a styrene oxide substrate (Reaction conditions: 25 mmol styrene oxide, 50 mg catalyst, 4 hours, 7 bar, and 140°C). Figure 10 shows the CO2 adsorption isotherms of Comparative Example 3 (bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) measured at various temperatures. Figure 11a is a figure showing the results of the reusability test of Example 1 (ZIF-67@ZIF-8). Figure 11b is a figure showing the XRD pattern according to the number of reuses of Example 1 (ZIF-67@ZIF-8). FIG. 11c is a figure showing the FT-IR spectrum according to the number of reuses of Example 1 (ZIF-67@ZIF-8). Figure 11d shows SEM images according to the number of reuses of Example 1 (ZIF-67@ZIF-8). Figure 12 shows the concentration of metal elements in the reaction mixture through the conversion of epichlorohydrin using the catalyst of Example 1 (ZIF-67@ZIF-8). Figure 13 shows the results of a hot-filtration test of the catalyst of Example 1 (ZIF-67@ZIF-8) in a carbon dioxide cycloaddition reaction using epichlorohydrin. Figure 14 shows the DFT calculation configuration for the partial structure of the crystals of Example 1 (ZIF-67@ZIF-8) and Example 2 (ZIF-8@ZIF-67) with styrene epoxide-derived oxygen bonding within the open Zn or Co metal parts of the shell, and the Gibbs free energy calculation results after the reaction of the CO2 ring portion. Specific details for implementing the invention

[0015] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the attached drawings.

[0016] The embodiments of the present disclosure disclosed herein are illustrative for illustrative purposes only, and the embodiments of the present disclosure may be practiced in various forms and should not be interpreted as being limited to the embodiments described herein. As the present disclosure is subject to various modifications and may take various forms, the embodiments are not intended to limit the present disclosure to a specific form and should be understood to include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and do not exclude the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0017] One embodiment of the present disclosure provides a catalyst for a carbon dioxide cycloaddition reaction having a core-shell structure comprising a core and a shell surrounding the core, wherein the core-shell particles may comprise ZIF (Zeolitic imidazolate framework)-8 in the core and ZIF-67 in the shell, or comprise ZIF-67 in the core and ZIF-8 in the shell.

[0018] In this specification, the catalyst comprising ZIF-8 in the core and ZIF-67 in the shell is named “ZIF-8@ZIF-67”, and the catalyst comprising ZIF-67 in the core and ZIF-8 in the shell is named “ZIF-67@ZIF-8”.

[0019] In this specification, 'metal-organic framework (MOF)' refers to a porous material in which inorganic nodes of metal ions or metal oxide clusters are interconnected by coordinate bonding of multitopic organic linkers to form a one-dimensional, two-dimensional, or three-dimensional framework.

[0020] In this specification, zeolitic imidazolate frameworks (ZIFs) are a type of metal-organic framework (MOF) and consist of metal centers coordinated to imidazolate linker tetrahedra.

[0021] In the present disclosure, the ZIF-8 may be a ZIF having the chemical formula Zn(2-methylimidazole)2, where the metal center (M) is Zn. The ZIF-67 may be a ZIF having the chemical formula Co(2-methylimidazole)2, where the metal center is Co.

[0022] In this specification, the 'carbon dioxide cycloaddition reaction (CO2cycloaddition)' is a reaction capable of producing a cyclic organic carbonate by adding carbon dioxide to an epoxy compound, and is also referred to as a carbon dioxide conversion reaction, a carbon dioxide cyclization reaction, or a carbon dioxide cycloaddition reaction.

[0023] The attached FIG. 1 illustrates an exemplary embodiment of the present disclosure. Referring to FIG. 1, FIG. 1 (A) schematically illustrates the synthesis procedure of core-shell ZIF-67@ZIF-8 and FIG. 1 (B) schematically illustrates the synthesis procedure of core-shell ZIF-8@ZIF-67, in which the shell of each catalyst surrounds and encloses the core.

[0024] In one embodiment, the average particle size of the catalyst may be 100 to 500 nm. Specifically, the average particle size may refer to the average particle size of at least 50%, 60%, 70%, 80%, or 90% of the catalyst particles. Additionally, the average particle size may be the maximum diameter of the catalyst particles. Specifically, the average particle size may be 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 310 nm or more, 320 nm or more, 330 nm or more, 340 nm or more, 350 nm or more, 360 nm or more, 370 nm or more, 380 nm or more, 390 nm or more, 400 nm or more, or 450 nm or more, and may be 500 nm or less, 450 nm or less, 400 nm or less, 390 nm or less, 380 nm or less, 370 nm or less, 360 nm or less, 350 nm or less, 340 nm or less, 330 nm or less, 320 nm or less, 310 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, or 150 nm or less. If the average particle size of the above catalyst is less than 100 nm, it may be difficult to stably form a core-shell structure, and if it exceeds 500 nm, the catalytic activity may be reduced.

[0025] In addition, according to one embodiment, the molar ratio of the Co element contained in each ZIF-67 of the core-shell ZIF-67@ZIF-8 and the Zn element contained in the ZIF-8 of the core-shell ZIF-8@ZIF-67 may be 3:1 to 1:3. Specifically, the molar ratio of the Co element contained in ZIF-67 to the Zn element contained in ZIF-8 may be 1:0.33 or more, 1:0.4 or more, 1:0.5 or more, 1:0.6 or more, 1:0.7 or more, 1:0.8 or more, 1:0.9 or more, 1:1 or more, 1:1.1 or more, 1:1.2 or more, 1:1.3 or more, 1:1.4 or more, 1:1.5 or more, 1:1.6 or more, 1:1.7 or more, 1:1.8 or more, 1:1.9 or more, 1:2 or more, or 1:2.5 or more, and may be 1:3 or less, 1:2.5 or less, 1:2 or less, 1:1.9 or less, 1:1.8 or less, or 1:1.7 It may be less than or equal to, 1: 1.6 or less, 1: 1.5 or less, 1: 1.4 or less, 1: 1.3 or less, 1: 1.2 or less, 1: 1.1 or less, 1: 1 or less, or 1: 0.5 or less.

[0026] The present disclosure is distinguished from conventional technologies, such as random heterometal ZIFs in which Zn and Co metals are randomly included, in that it includes a bimetal of Zn and Co and incorporates them in a core-shell ZIF structure, thereby enabling control over the thickness of the core or shell that affects the catalytic activity of the CO2 cyclization addition reaction. Furthermore, since the present disclosure allows for the control of surface roughness, such as surface area and porosity, which are known to increase the absorption of gases like carbon dioxide through the growth of the shell on the core surface, the CO2 adsorption capacity is improved compared to conventional single-metal ZIFs or random heterometal ZIFs, as confirmed in the test examples described below, thereby significantly enhancing the efficiency of the CO2 cyclization addition reaction.

[0027] In the above view, the thickness ratio of the core to the shell of the core-shell ZIF-67@ZIF-8 and core-shell ZIF-8@ZIF-67 according to one embodiment may be 50 to 300: 50 to 200, specifically 120 to 300: 80 to 150, more specifically 180 to 300: 100 to 120.

[0028] In the above view, the catalyst according to one embodiment may have an average pore size (diameter) of 0.3 to 0.7 nm, but is not limited thereto. In this case, the average pore size may mean an average pore size of at least 50%, 60%, 70%, 80%, or 90% of the particles. Specifically, the average pore size of the catalyst may be 0.3 nm or more, 0.4 nm or more, 0.5 nm or more, or 0.6 nm or more, and may be 0.7 nm or less, 0.6 nm or less, 0.5 nm or less, or 0.4 nm or less.

[0029] In addition, the catalyst according to one embodiment is 500 to 3000 m 2 It may have a specific surface area of ​​ / g, but is not limited thereto. In addition, in the above view, the porosity of the catalyst according to one embodiment may be 30 to 90%, but is not limited thereto. Specifically, the specific surface area of ​​the catalyst is 500 m² 2 / g or more, 1000 m 2 / g or more, 1500 m 2 / g or more, 2000 m 2 / g or more or 2500 m 2 It may be greater than / g, and 3000 m 2 / g or less, 2500 m 2 / g or less, 2000 m 2 / g or less, 1500 m 2 / g or less or 1000 m 2 It may be less than / g.

[0030] In one embodiment, the shape of the core-shell particles may be a rhombic dodecahedron or a sphere, but is not limited thereto. In addition, the catalyst according to one embodiment may be provided in the form of granules, powder, film, or membrane.

[0031] In one embodiment, the catalyst may have a second peak among the peaks for binding energy indicating the formation of Zn-OH in X-ray photoelectron spectroscopy (XPS) analysis appearing at 700 to 800 eV. In addition, in one embodiment, the catalyst may have a second peak among the peaks for binding energy indicating the formation of Co-OH appearing at 900 to 1200 eV.

[0032] The present disclosure may also provide a method for manufacturing a catalyst for a carbon dioxide cycloaddition reaction described above as one embodiment.

[0033] As one embodiment, the manufacturing method may include: (i) dissolving a cobalt salt, a zinc salt, and 2-methylimidazole in a solvent, respectively; injecting the cobalt salt solution into the 2-methylimidazole ligand solution and then adding the zinc salt solution to react; and heat-treating the reaction product to produce a catalyst (ZIF-67@ZIF-8) that includes ZIF-8 in the core and ZIF-67 in the shell.

[0034] As another embodiment, the manufacturing method may include: (ii) a step of adding a solution in which ZIF-8 is dispersed to a solution in which cobalt chloride is dispersed and mixing them; a step of adding a solution in which 2-methylimidazole is dispersed to the mixture and reacting them; and a step of heat-treating the reaction mixture to produce a catalyst (ZIF-8@ZIF-67) in which ZIF-67 is contained in the core and ZIF-8 is contained in the shell.

[0035] In the preparation of the above ZIF-67@ZIF-8 catalyst, if the core-shell ZIF-67@ZIF-8 is prepared using a ZIF-67 seed that is a combination of Co / imidazole without using the above method (i), heterogeneous seed-induced nucleation does not occur on the surface of the ZIF-67 seed due to the rapid nucleation process of the ZIF-8 crystal that is a combination of Zn / imidazole, it may be difficult to synthesize the ZIF-67 core and ZIF-8 shell forms.

[0036] As an example, each solvent used in the methods (i) and (ii) may be one or more selected from the group consisting of water, methanol, dimethylformamide, tetrahydrofuran, etc.

[0037] As an example, in the method of (i) and (ii) above, the heat treatment temperature in each step may be 100 to 150°C. Specifically, the temperature may be 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher, and may be 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, or 110°C or lower. If the heat treatment temperature falls outside the above range, problems such as irregular crystal growth or reduced crystallinity may occur.

[0038] In one embodiment, each of the above heat treatment times may be 12 to 36 hours. Specifically, the above heat treatment time may be 12 hours or more, 18 hours or more, 24 hours or more, or 30 hours or more, and may be 36 hours or less, 30 hours or less, 24 hours or less, or 18 hours or less.

[0039] In addition, the present disclosure may provide a method for producing a cyclic organic carbonate, comprising, as one embodiment, the step of placing an epoxide-based compound substrate and the catalyst for the carbon dioxide cyclic addition reaction described above into an autoclave; and the step of injecting a gas containing carbon dioxide into the autoclave and then producing a cyclic organic carbonate by carrying out a carbon dioxide cyclic addition reaction in an oil bath.

[0040] Chemical Formula 1 below illustrates the mechanism of a carbon dioxide ring addition reaction using a ZIF-67@ZIF-8 catalyst, which is an embodiment of the present disclosure. Referring to Chemical Formula 1, an epoxide substrate is bonded to the shell layer of the catalyst according to an embodiment of the present disclosure, and one or two CO2 molecules are adsorbed at the N base position. Subsequently, the reaction is activated at the Lewis acid site of the Zn / Co metal ion between the core and the shell, attacking and breaking the weak bond (βC-O) of the carbon within the epoxide, and continuous ring-opening occurs. Afterward, ring-closing occurs, forming a carbonate complex via two possible pathways (one or two CO2 molecules), and finally, the catalyst is regenerated. Specifically, the adsorption of a single activated CO2 molecule can attack the epoxide ring via an SN2-nucleophilic reaction to form a primary carbonate complex, and then the ring of the carbonate complex is closed to produce a cyclic carbonate and generate a catalyst. In the case of two activated CO2 adsorptions, the first activated CO2 forms a primary carbonate complex through the ring-opening of the epoxide in sequence, and then in the next step, the second activated CO2 adsorption is introduced at the Lewis base site to react with the primary carbonate complex to form a second intermediate complex. Finally, one CO2 molecule is released through the ring-closing of the second intermediate complex to produce a cyclic carbonate, and a catalyst for further reactions is generated.

[0041] [Chemical Formula 1]

[0042]

[0043] In one embodiment, the epoxide compound may be one or more selected from the group consisting of epichlorohydrin (ECH), ethylene oxide (EO), styrene oxide (SO), propylene oxide (PO), allyl glycidyl ether (AGE), cyclohexene oxide (CO), 1,2-epoxybutane (EB), and 1,2-epoxyhexane, but is not limited thereto.

[0044] For example, as shown in Chemical Formula 2 below, when epichlorohydrin is reacted with carbon dioxide using a catalyst as an epoxide-based compound, the carbon dioxide is cyclized to produce a cyclic organic carbonate.

[0045] [Chemical Formula 2]

[0046]

[0047] In one embodiment, the cyclic organic carbonate prepared according to the method may vary depending on the type of alkyl group of the epoxide-based compound used as the substrate. For example, the cyclic organic carbonate may include, but is not limited to, propylene carbonate, styrene carbonate, glycerol-1,2-carbonate.

[0048] In one embodiment, the gas containing carbon dioxide may be carbon dioxide; or a mixed gas of carbon dioxide and nitrogen.

[0049] In one embodiment, the method may involve the step of placing the two materials into a reactor with a magnetic rod and ultrasonically treating them before placing the epoxide-based compound substrate and catalyst into the autoclave, and then transferring them to the autoclave.

[0050] As an example, the reaction of the carbon dioxide ring addition reaction may be carried out at 80 to 120°C for 1 to 10 hours. Specifically, the reaction temperature may be 80°C or higher, 90°C or higher, 100°C or higher, or 110°C or higher, and may be 120°C or lower, 110°C or lower, 100°C or lower, or 90°C or lower. Specifically, the reaction time may be 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, or 9 hours or more, and may be 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, or 2 hours or less. If the above ranges are not satisfied, the reaction efficiency may decrease.

[0051] In addition, as one embodiment, the supply pressure of the gas containing carbon dioxide may be 1 bar to 20 bar. Specifically, the supply pressure may be 1 bar or more, 3 bar or more, 5 bar or more, 6 bar or more, 7 bar or more, 8 bar or more, 9 bar or more, 10 bar or more, 12 bar or more, or 15 bar or more, and may be 20 bar or less, 18 bar or less, 15 bar or less, 13 bar or less, 10 bar or less, 9 bar or less, 8 bar or less, 7 bar or less, 6 bar or less, 4 bar or less, or 2 bar or less. The pressure may be maintained while the reaction proceeds. If the pressure falls outside the above pressure range, the reaction efficiency may decrease or the yield of the cyclic organic carbonate may decrease.

[0052] The present disclosure will be explained in more detail below through examples. These examples are solely for the purpose of illustrating the present disclosure, and it will be obvious to those skilled in the art that the scope of the present disclosure is not to be interpreted as being limited by these examples.

[0053] [Preparation Example]

[0054] Preparation Example 1: Synthesis of Core-Shell ZIF-67@ZIF-8

[0055] First, 2.196 g (7.5 mmol) of Co(NO3)2·6H2O and 1.232 g (15 mmol) of 2-methylimidazole were added to 30 mL of methanol, respectively, and dissolved at room temperature using ultrasound for 10 minutes. Then, the imidazole ligand solution was injected into the zinc salt solution and stirred at room temperature for 2 hours. The purple particles (ZIF-67) prepared after the reaction were centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours. The 160 mg of ZIF-67 particles obtained in this way were added to 30 mL of methanol and dispersed through mixing and ultrasonic treatment. Subsequently, 2.232 g (7.5 mmol) of Zn(NO3)2·6H2O and 1.232 g (15 mmol) of 2-methylimidazole were added to 30 mL and 30 mL of methanol, respectively, and dissolved at room temperature using ultrasound for 10 minutes. Then, the cobalt salt solution was injected into the 2-methylimidazole ligand solution, followed by the addition of the zinc salt solution and stirring for 2 hours. After the reaction, the prepared purple solution was centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours. As a result, core-shell ZIF-67@ZIF-8 (~389 nm) was synthesized (see (A) in Fig. 1).

[0056] Preparation Example 2: Synthesis of Core-Shell ZIF-8@ZIF-67

[0057] Solution A was prepared by adding 160 mg of ZIF-8 (~120 nm) to 20 mL of methanol, mixing, and dispersing it through sonication. At this time, the ZIF-8 was synthesized using the same method as in Preparation Example 1. Specifically, 2.232 g (7.5 mmol) of Zn(NO3)2·6H2O and 1.232 g (15 mmol) of 2-methylimidazole were added to 30 mL and 30 mL of methanol, respectively, and dissolved at room temperature for 10 minutes using ultrasound. Subsequently, the imidazole ligand solution was injected into the zinc salt solution and stirred at room temperature for 2 hours. The white particles produced after the reaction were centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours to obtain ZIF-8.

[0058] Next, 1.061 g (8.17 mmol) of cobalt chloride was dissolved in 18 mL of methanol and stirred for 5 minutes to prepare a clear solution (Solution B). Solution B was poured into Solution A and mixed under vigorous mixing conditions at room temperature. 5.37 g (65.4 mmol) of 2-methylimidazole was dissolved in 18 mL of methanol and poured into the mixture of Solution A and Solution B. After stirring continuously for 20 minutes, the mixture was transferred to an autoclave at 100°C in an oven. After the reaction time, the pale purple precipitate was washed several times with methanol, and the purple powder was dried in a vacuum oven at 120°C for 24 hours to synthesize core-shell ZIF-8@ZIF-67 (244 nm; Example 2) (see (B) in Fig. 1).

[0059] Core-shell ZIF-8@ZIF-67 (~318 nm; Example 3) was prepared in the same manner as above, except that a ZIF-8 core having a particle size of 250 nm was used.

[0060] [Comparative Manufacturing Example]

[0061] Comparative Manufacturing Example 1

[0062] 2.232 g (7.5 mmol) of Zn(NO3)2·6H2O and 1.232 g (15 mmol) of 2-methylimidazole were added to 30 mL of methanol, respectively, and dissolved at room temperature for 10 minutes using ultrasound. Then, the imidazole ligand solution was injected into the zinc salt solution and stirred at room temperature for 2 hours. The white particles produced after the reaction were centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours to obtain ZIF-8.

[0063] Comparative Manufacturing Example 2

[0064] 2.196 g (7.5 mmol) of Co(NO3)2·6H2O and 1.232 g (15 mmol) of 2-methylimidazole were added to 30 mL of methanol, respectively, and dissolved at room temperature for 10 minutes using ultrasound. Then, the imidazole ligand solution was injected into the zinc salt solution and stirred at room temperature for 2 hours. The white particles produced after the reaction were centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours to obtain ZIF-67.

[0065] Comparative Manufacturing Example 3

[0066] A catalyst having random heterometals Zn / Co (bimetallic Zn / Co-ZIF) was prepared according to the following method.

[0067] First, 2.196 g (7.5 mmol) of Co(NO3)2·6H2O, 2.232 g (7.5 mmol) of Zn(NO3)2·6H2O, and 2.464 g (30 mmol) of 2-methylimidazole were added to 30 mL, 30 mL, and 60 mL of methanol, respectively, and dissolved at room temperature using ultrasound for 10 minutes. Next, the cobalt salt solution was injected into the 2-methylimidazole ligand solution, followed by the addition of the zinc salt solution and stirring for 2 hours. After the reaction, the prepared purple solution was centrifuged with methanol, washed three times, and dried in a vacuum oven at 120°C for 24 hours.

[0068] [Test Example 1] Analysis of Catalyst Characteristics

[0069] Prior to the test example, ZIF-8 was prepared as Comparative Example 1 and ZIF-67 as Comparative Example 2, and the particle size of each was approximately 300 nm (300-400 nm). In addition, to reduce the influence of catalyst particle size on catalyst performance, Example 1 (ZIF-67@ZIF-8), Example 2 (ZIF-8@ZIF-67), and Comparative Example 3 (Bimetallic Zn / Co-ZIF) were prepared by the same method as Preparation Examples 1 to 3 above, but with the particle size of each controlled to approximately 300 nm. At this time, the particle sizes of Example 1 (ZIF-67@ZIF-8) and Example 2 (ZIF-8@ZIF-67), which are core-shell type catalysts according to one embodiment of the present disclosure, were controlled through a seed mediation method that adjusts the particle size of each core ZIF. The particle size of Comparative Example 3 (bimetallic Zn / Co-ZIF) was controlled through the nucleation and growth process by adjusting the concentration of the 2-methylimidazole linker while maintaining a constant concentration of the metal nodes. By doubling the concentration of the 2-methylimidazole linker, the particle size of Zn / Co-ZIF increased from 146 nm to 340 nm. ZIF-8 is white, ZIF-67 is dark purple, and Examples 1 and 2 and Comparative Example 3 are light purple.

[0070] Morphology and particle size distribution of ZIF catalyst

[0071] The morphology and particle size distribution of all ZIF catalysts were investigated by FE-SEM (Field Emission Scanning Electron Microscopy) analysis (Manufacturer: FEI, Product Name: Inspect F50) as shown in Fig. 1, and their microstructural characteristics are summarized in Table 1. As shown in Fig. 1, the ZIF nanocrystals of Examples 1 and 2 and Comparative Example 3 were all observed to have a rhombohedral dodecahedral shape, and the particle size was similar at approximately 300 nm.

[0072] Crystallinity of ZIF catalyst

[0073] The crystallinity of the ZIF catalysts was investigated by X-ray diffraction (XRD) analysis (Manufacturer: Bruker, Product Name: D8 Advance) (see Fig. 3a). Comparative Example 1 (ZIF-8), Comparative Example 2 (ZIF-67), Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) exhibited sharp characteristic peaks at 2θ–7.2°, 10.2°, 12.6°, and 18.0°, indicating that ZIF crystals with high crystallinity were successfully formed. Their porosity was determined by analyzing N2 adsorption-desorption isotherms, and the results are shown in Table 1. All of the above ZIF catalysts had similar surface areas (~1750 m²). 2 / g) and pore volume (~0.71cm²) 3 It shows a Type I isotherm corresponding to a microporous material having (g). Specifically, in the low pressure range (0 <P / P0<0.02)에서 서로 다른 흡착 단계가 관찰되는데, 이는 골격체의 유연성과 관련된다. 비교예 1(ZIF-8)은 흡착 등온선 한 단계가 나타난 반면, 비교예 2(ZIF-67)는 링커의 이동과 대칭성 변화로 인해 두 개의 추가 단계를 나타낸다. 링커와 골격체의 금속 노드 사이의 구조와 결합 형성을 분석하기 위해 FT-IR(Fourier-transform infrared spectroscopy)(제조사: Thermo-fisher, 제품명: Nicolet iS10)을 측정하였으며, 그 결과를 도 3b에 나타내었다. 도 3b에서 볼 수 있듯이 코어-쉘 구조인 실시예 1 및 2와 비교예 1(ZIF-8) 또는 비교예 2(ZIF-67) 사이에는 큰 변화가 없다. 모든 물질의 FT-IR 스펙트럼에서 ~1579cm -1 A peak was observed, which corresponds to the C=N bond stretching vibration of the imidazole linker. Also, ~418–427 cm⁻¹ -1The nearby peak indicates the formation of metal-N stretch bonds (Co-N, Zn-N) between the metal node and the imidazole linker. As can be seen in Figs. 3c and 3d, Comparative Example 1 (ZIF-8) and Comparative Example 2 (ZIF-67), which are single metal-based ZIFs, Comparative Example 3 (bimetallic Zn / Co-ZIF), which is a hybrid ZIF, and Example 1 (ZIF-67@ZIF-8) and Example 2 (ZIF-8@ZIF-67) exhibited high thermal stability up to 540°C to 600°C. In general, the decomposition temperature of Comparative Example 1 (ZIF-8) was slightly higher than that of Comparative Example 2 (ZIF-67). Specifically, the decomposition temperatures upon significant weight loss of these materials were in the order of Comparative Example 1 (ZIF-8) (616°C) > Comparative Example 3 (Bimetallic Zn / Co-ZIF) (585°C) > Example 1 (ZIF-67@ZIF-8) (564°C) > Comparative Example 2 (ZIF-67) (545°C) > Example 2 (ZIF-8@ZIF-67) (542°C). The hybrid ZIFs Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) exhibited thermal stability located between the decomposition temperatures of Comparative Example 1 (ZIF-8) and Comparative Example 2 (ZIF-67), and these results suggest that increasing the thickness of ZIF-8 improves the thermal stability of the hybrid ZIF.

[0074] Analysis of Zn and Co elemental distribution

[0075] The rhombohedral dodecahedral shapes of the hybrid ZIFs Comparative Example 3 (bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67) were examined using a scanning transmission electron microscope (STEM), and the chemical composition with Zn and Co elemental distributions was analyzed using EDX (Energy Dispersive X-ray Microanalysis)-line scanning with elemental mapping (Manufacturer: AMETEK, Product Name: Inspect S) (Fig. 4). In the case of Comparative Example 3 (bimetallic Zn / Co-ZIF), it can be seen that Zn and Co elements are randomly distributed in the framework. On the other hand, in Example 1 (ZIF-67@ZIF-8), a distinct distribution of Co elements in the core and Zn elements in the shell was observed, and in Example 2 (ZIF-8@ZIF-67), the opposite distribution was observed, which means that the core-shell shape was successfully formed. Co via ICP (Inductively Coupled Plasma)-OES (Optical Emission Spectrometry) analysis (Manufacturer: Perkin-Elmer, Product Name: Nexlon 350D) 2+ / Zn 2+ It was confirmed that the molar ratios were Example 2 (ZIF-8@ZIF-67) (Co / Zn = 1.09), Example 1 (ZIF-67@ZIF-8) (Co / Zn = 1.29), and Comparative Example 3 (Bimetallic Zn / Co-ZIF) (Co / Zn = 1.05), and this is shown in Table 1.

[0076] X-ray photoelectron spectroscopy (XPS) analyze

[0077] XPS analysis was performed to investigate the chemical bonding characteristics and state of each catalyst.

[0078] As a result, as shown in FIGS. 5a to 5i, the Co 2p (~1021 eV) and Zn 2p (~781 eV) spectra of Examples 1 and 2, which are core-shell type ZIFs according to one embodiment of the present disclosure, are Zn 2+ and Co 2+ It matched well with the spectrum of the oxidation state. Metal ions (Zn) in the core 2+ or Co 2+ The signal of ) is due to the metal ions in the shell, i.e., in the case of Example 2 (ZIF-8@ZIF-67), Co, because of the encapsulation of the core by the shell. 2+ , in the case of Example 1 (ZIF-67@ZIF-8), Zn 2+ It appeared at a lower intensity than ).

[0079] catalyst particle size a (nm) Core thickness b (nm) Shell thickness b (nm) S BET c (m 2 g -1 ) V total d (cm 3 g -1 ) V micro e (cm 3 g -1 ) V micro / V total (%) Co / Zn f ZIF-8(S1) 120 - - 1735 0.790 0.710 89.9 - ZIF-8(S2) 252 - - 1704 0.718 0.641 89.3 - Comparative Example 1 ZIF-8 308 - - 1663 0.923 0.756 81.9 - ZIF-67(S) 175 - - 1820 0.718 0.694 96.7 - Comparative Example 2 ZIF-67 310 - - 1752 0.735 0.680 92.5 - Zn / Co-ZIF(S) 146 - - 1748 0.752 0.723 96.1 - Comparative Example 3 Zn / Co-ZIF 340 - - 1751 0.694 0.594 85.5 1.05 ZIF-8@ZIF-67(S) 244 150 94 1752 0.704 0.681 96.7 - Example 1 ZIF-67@ZIF-8 389 280 110 1804 0.727 0.681 93.7 1.29 Example 2 ZIF-8@ZIF-67 318 200 118 1794 0.722 0.672 93.1 1.09

[0080] ( a Determined by SEM; b Determined by STEM; c Specific surface area determined by the BET method; d Total pore volume (V total ); e Micropore volume (V) calculated by the BHJ method micro ), f molar ratio detected by inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis)

[0081] [Test Example 2] Cyclic addition reaction of carbon dioxide

[0082] Comparison of catalytic activity according to catalyst particle size

[0083] To investigate the effect of particle size of ZIFs catalysts on catalytic performance, a carbon dioxide cycloaddition reaction was performed under identical conditions using metal-based ZIF catalysts of various particle sizes as shown in Table 1 above. Specifically, an epoxy substrate (25 mmol) and the catalyst (50 mg) were placed in a 100 mL reactor equipped with a magnetic rod, sonicated for 5 minutes, and then transferred to a Teflon-lined stainless steel autoclave. The reactor was purged three times with CO2 gas to remove moisture and impurities. The reactor was pressurized with CO2 gas (7 bar), and the mixture of the epoxy substrate and catalyst was stirred in an oil bath at a target temperature. After the reaction, the reactor was cooled to room temperature. The catalyst used was separated by centrifugation, and the collected supernatant was dissolved in chloroform-d, and 1 The conversion rate and selectivity of the reaction product, the epoxide substrate, to cyclic carbonate were analyzed using an H NMR (nuclear magnetic resonance) analyzer (Manufacturer: Bruker, Product Name: NMR 400 MHz HD). 1 It was calculated through H NMR analysis.

[0084] As a result, the catalysts of Comparative Example 1 (ZIF-8) and Comparative Example 2 (ZIF-67), which have relatively large particle sizes, exhibited low conversion rates of the epoxide substrate, and a similar trend was observed in Example 2 (ZIF-8@ZIF-67) and Comparative Example 3 (bimetallic Zn / Co-ZIF). This may be due to the decrease in the diffusion resistance of the substrate and the number of active sites where reactions can occur as the particle size of the catalyst increases. According to reports, D SEM / D XRD The ratio is considered an important parameter regarding the relationship between the regular and imperfect structural regions of the catalyst, and it is shown that the particle size decreases as the size of the imperfect structural region increases. Therefore, DSEM / D XRD By calculating and analyzing the correlation between the average particle size, structural bonding, and catalytic activity of the ZIF catalyst, the results are as follows.

[0085] D of each of the above catalysts XRD The values ​​change in the following order:

[0086] -ZIF-8(S1) (36.3 nm) < ZIF-8(S2) (54.7 nm) < ZIF-8 (58.4 nm)

[0087] -ZIF-67(S) (69.0 nm) < ZIF-67 (99.2 nm), Zn / Co-ZIF(S) (53.9 nm) < Zn / Co-ZIF (60.4 nm)

[0088] -ZIF-8@ZIF-67 (S) (52.0 nm) < ZIF-8@ZIF-67 (59.9 nm)

[0089] The order of the incomplete structural regions of each of the above catalysts is as follows:

[0090] -ZIF-8(S1) (3.3) > ZIF-8(S2) (4.6) > ZIF-8 (5.3), ZIF-67(S) (2.5) > ZIF-67 (3.1)

[0091] -Zn / Co-ZIF(S) (2.7) > Zn / Co-ZIF (5.6)

[0092] -ZIF-8@ZIF-67 (S) (4.7) > ZIF-8@ZIF-67 (5.3)

[0093] FIG. 6 shows the particle size of each catalyst and the conversion rate of epichlorohydrin and styrene oxide by the catalyst and D SEM / D XRDAs shown in the relationship, it can be confirmed that the conversion rate of epichlorohydrin decreases as the particle size of the ZIF catalyst increases. This shows a trend similar to that observed with styrene oxide substrates, implying that diffusion is restricted by the increase in catalyst particle size, and that the number of defects and active sites resulting from incomplete structures decreases.

[0094] Comparison of catalytic activity according to catalyst type

[0095] In order to exclude the difference in catalytic activity according to catalyst particle size confirmed in the above experiment, Comparative Example 1 (ZIF-8) and Comparative Example 2 (ZIF-67), which are single-metal-based ZIF catalysts with sizes controlled to approximately 300-400 nm, and Comparative Example 3 (Bimetallic Zn / Co-ZIF), Example 1 (ZIF-67@ZIF-8), and Example 2 (ZIF-8@ZIF-67), which are hybrid ZIFs, were subjected to the same method as described above. 1 H NMR analysis was performed and is shown in Fig. 7.

[0096] In the case of a single metal-based ZIF catalyst, Comparative Example 2 (ZIF-67) showed a relatively lower conversion rate than Comparative Example 1 (ZIF-8) at the same reaction time, which may be because Comparative Example 1 (ZIF-8) structurally collapsed due to the relatively stronger interaction between the Zn site and CO2 compared to the interaction between the Co site and CO2.

[0097] In addition, it was observed that as the reaction time increased, the catalytic activity was enhanced in the order of Example 1 (ZIF-67@ZIF-8) > Example 2 (ZIF-8@ZIF-67) > Comparative Example 3 (Bimetallic Zn / Co-ZIF) > Comparative Example 1 (ZIF-8) > Comparative Example 2 (ZIF-67) (see Fig. 7). Specifically, regarding the initial catalytic activity for epichlorohydrin conversion, Example 1 (ZIF-67@ZIF-8) was significantly higher than other catalysts in the same reaction time range of 1 to 4 hours. Although Comparative Example 3 (Bimetallic Zn / Co-ZIF) had higher catalytic performance than Comparative Examples 1 and 2, which are single metal-based ZIFs, Example 1 (ZIF-67@ZIF-8) and Example 2 (ZIF-8@ZIF-67) exhibited even higher activity than Comparative Example 3 (Bimetallic Zn / Co-ZIF). This is because the advantageous properties of high catalytic activity by Zn metal and low leaching and high selectivity by Co metal are combined, and it contains a larger amount of acid-base sites as seen in the TPD-NH3 and TPD-CO2 results confirmed in Test Example 1.

[0098] In the case of Example 1 (ZIF-67@ZIF-8), the larger window pore size of ZIF-8 (3.42 Å) located in the shell compared to ZIF-67 (3.3 Å) allows the epoxide substrate to diffuse more easily into the shell surface and can promote the rapid reaction between the core ZIF-67 and the shell ZIF-8. The stronger binding ability of CO2 molecules and Zn metal requires more reaction time to release the adsorbed reactants, but instead, the substrate molecules are rapidly desorbed due to the weak coordination behavior of the Co metal. Additionally, in Example 1 (ZIF-67@ZIF-8), the hydrophobic properties of the ZIF-8 shell can enhance the interaction between the substrate and the shell, thereby improving catalytic performance. Therefore, the high catalytic activity of Example 1 (ZIF-67@ZIF-8) may be due to differences in structural and organizational properties, such as the Lewis acidity / basicity and hydrophobic properties of the ZIF-8 shell, as well as the improved carbon dioxide adsorption efficiency, in addition to the diffusion effect.

[0099] [Test Example 3]

[0100] Since larger pores increase accessibility to the active site and lower the diffusion limit, a CO2 cycloaddition reaction was carried out using a mixed gas (85% CO2 / 15% N2) to investigate how pore size affects the diffusion and selective adsorption of CO2 in mixed gases with different kinetic diameters. At this time, the CO2 cycloaddition reaction of an epichlorohydrin substrate was performed in the same manner as in Test Example 2, except that a mixed gas (a mixture of 85 v / v% CO2 and 15 v / v% N2) was used, and the catalytic performance when using pure CO2 gas is also shown in Figure 8.

[0101] As a result, as shown in Fig. 8, Example 1 (ZIF-67@ZIF-8) exhibited high catalytic performance of 92.5%. When using pure 100% CO2 gas, Comparative Example 3 (bimetallic Zn / Co-ZIF) and Example 2 (ZIF-8@ZIF-67) showed a decrease in catalytic activity of 6% (from 76.4% to 73%) and 10% (from 88% to 78%), respectively, compared to Example 1 (ZIF-67@ZIF-8). This result implies that the relatively large pore size of the ZIF-8 shell in Example 1 (ZIF-67@ZIF-8) can increase accessibility to the active site by CO2 gas passing through ZIF-8 and lower the diffusion limit for selective CO2 adsorption. Furthermore, it suggests that the catalyst of the present disclosure can also be utilized as a conversion catalyst using CO2 from actual air.

[0102] Next, a CO2 ring addition reaction was performed using pure CO2 gas in the same manner as above, with styrene oxide as the substrate. As a result, as shown in Fig. 9, catalytic behavior was observed similar to that of the CO2 ring addition reaction of the epichlorohydrin substrate described above. At a reaction time (4 hours), Example 1 (ZIF-67@ZIF-8) showed a higher catalytic conversion rate (82%) compared to Example 2 (ZIF-8@ZIF-67) (79.4%) and Comparative Example 3 (bimetallic Zn / Co-ZIF) (67%), which is supported by the CO2 adsorption capacity results in Fig. 10. As shown in Fig. 10, the CO2 adsorption amount increased in the order of Comparative Example 3 (Bimetallic Zn / Co-ZIF) < Example 2 (ZIF-8@ZIF-67) < Example 1 (ZIF-67@ZIF-8), and Example 1 (ZIF-67@ZIF-8) was found to have the highest potential for catalytic activity for CO2 conversion. This indicates that Example 1 (ZIF-67@ZIF-8) exhibited the highest catalytic performance for CO2 ring addition due to the large pore size of the shell, which facilitates reactant diffusion, and the appropriate binding strength resulting from the weak acidity / basicity that plays a crucial role in catalytic activity. At a reaction time of 8 hours, as shown in Figure 9, Examples 1, 2 and Comparative Example 3 all exhibited high catalytic activity of over 90%, which is because the Zn and Co metals acting as Lewis acid sites and the -NH group acting as Brønsted acid sites coexist with the base sites (OH group and the N(-) portion of the imidazole ligand).

[0103] [Test Example 4]

[0104] The performance of Example 1 (ZIF-67@ZIF-8) was verified using various epoxide substrates. At this time, the same carbon dioxide cyclic addition reaction as in Test Example 2 was performed, except that the substrates in Table 2 were used, and the results are shown together in Table 2.

[0105] Comparison of CO2 cycloadaptive catalyst performance of Example 1 (ZIF-67@ZIF-8) with various substrates Entry Substrate a Time (h) Temperature (°C) Conversion rate (%) 1 PO 4 100 84.7 2 ECH 4 100 93.5 3 EB 8 140 84.7 4 SO 8 140 91.7 5 AGE 8 140 99 6 CO 24 140 77.5

[0106] ( a Reaction conditions: 25 mmol epoxide, 50 mg catalyst, pressure 7 bar)

[0107] As a result, various catalytic activities were observed due to the influence of steric hindrance, molecular size, length, and the polarity of the epoxide substrate, and the optimal reaction conditions also differed. Specifically, the long chain length or large molecular size of the epoxide substrate required harsh reaction conditions, including high temperatures and longer reaction times. For example, the difference in effect depending on the epoxide substituent can be seen in the results using PO and ECH substrates. In the case of ECH with -Cl terminal substituents, conversion was more active at 93.5% compared to PO (84.7%) due to the nucleophilic chloride group (-Cl), which weakened the βC-O bond, making it easier to open the ring and change the structure. When comparing PO and EB, a higher reaction temperature was required for EB (140°C) than for PO (100°C) to obtain nearly the same epoxide conversion rate because the molecular size of EB is larger than that of PO. This trend can also be observed in AGE, SO, and CO, which is attributed to steric hindrance that takes more time to pass through the pores and channels of the catalyst.

[0108] [Test Example 5]

[0109] In the experiment below, the activity of the catalyst according to the present disclosure was compared with other previously reported catalysts. The carbon dioxide cycloaddition reaction was carried out in the same manner as in Test Example 2 above.

[0110] As a result, as shown in Table 3 below, compared to other materials, the catalyst according to the present disclosure demonstrated better performance with high conversion rate and high selectivity without the need for co-catalysts and co-solvents. For example, the catalyst in Example 1 (ZIF-67@ZIF-8) achieved a high conversion rate (93.5%) with >98% selectivity for ECH under the same conditions (100°C, 7 bar, 4 h) using a smaller amount of catalyst (50 mg catalyst for a 25 mmol substrate), whereas Comparative Example 3 (Bimetallic Zn / Co-ZIF), Comparative Example 1 (ZIF-8), and Comparative Example 2 (ZIF-67) achieved conversion rates of 79%, 40%, and 50%, respectively, using 50 mg catalyst for a 9 mmol substrate.

[0111] In addition, when the catalytic activity was measured in the same manner as above under harsher conditions (18.1 mmol styrene substrate 20 mg), the catalyst of Example 1 (ZIF-67@ZIF-8) showed a carbon dioxide conversion rate of 82%, which was significantly improved compared to 67% of Comparative Example 3 (bimetallic Zn / Co-ZIF).

[0112] temperament catalyst. Time (h) pressure (bar) Temperature (°C) Conversion rate (%) Selectivity (%) EPC ZIF-8 Comparative Example 1 4 7 100 40 - EPC ZIF-67 Comparative Example 2 4 7 100 50 - EPC ZIF-8@ZIF-67 Example 2 4 7 100 88 >98 EPC ZIF-67@ZIF-8 Example 1 4 7 100 93.5 >98 EPC Zn / Co-ZIF Comparative Example 3 4 7 100 79.4 >98 SO ZIF-8@ZIF-67 Example 2 4 7 140 79.4 >98 SO ZIF-67@ZIF-8 Example 1 4 7 140 82 >98 SO Zn / Co-ZIF Comparative Example 3 4 7 140 67 >98

[0113] (EPC: epichlorohydrin substrate, SO: styrene oxide substrate)

[0114] [Test Example 6]

[0115] In this experiment, the structural stability of the catalyst according to the present disclosure upon reuse was analyzed, and it was confirmed that the catalyst of the present disclosure is a catalyst with stability capable of being applied multiple times to CO2 cycloaddition reactions. Example 1 (ZIF-67@ZIF-8) was used in the experiment, and in the same manner as Test Example 2, an epichlorohydrin substrate was used to perform a carbon dioxide cycloaddition reaction under reaction conditions of 4 hours, 100°C, and 7 bar. Afterward, the catalyst was separated by centrifugation, washed with methanol, and then dried under vacuum at 120°C for 24 hours for each repeated use.

[0116] The catalyst was used 10 times repeatedly, and the structural stability of the reused catalyst was confirmed through XRD, FT-IR, SEM, and TGA analysis, with the results shown in Fig. 11. As can be seen in Fig. 11a, the catalytic performance of Example 1 (ZIF-67@ZIF-8) maintained catalytic activity without significant loss during 7 consecutive cycles, but gradually decreased to 70% in the 10th cycle. The used Example 1 (ZIF-67@ZIF-8) was recovered after 5 and 10 cycles and characterized by an XRD pattern (Fig. 11b) to confirm its structural stability. According to the XRD pattern, both the new Example 1 (ZIF-67@ZIF-8) catalyst and the used catalyst were observed to maintain high crystallinity up to 5 reuses, indicating no structural collapse. However, after 5 and 10 cycles, the intensity of the XRD peaks gradually decreased, indicating a reduction in the crystallinity of the catalyst. This may be attributed to the appearance of defects and impurities on the substrate located on the surface of the reused Example 1 (ZIF-67@ZIF-8) catalyst. TGA analysis performed after 5 and 10 cycles, during which the reaction conversion rate decreased somewhat, confirmed the structural stability of the catalyst. The Example 1 (ZIF-67@ZIF-8) catalyst remained stable up to a maximum of 438°C, and above this temperature, it was observed that the weight of the used catalyst decreased slightly compared to the new catalyst. This may be due to the presence of impurities, including unreacted substrates and products, on the catalyst surface that remained even after the vigorous washing process.

[0117] In addition, as shown in Fig. 11c, the FT-IR spectra after 5 and 10 cycles of Example 1 (ZIF-67@ZIF-8) show 1047 cm⁻¹ with very small intensities corresponding to the untuned linker and NH…N bending and NH stretching vibrations, respectively. -1 and 1796 cm -1Two new peaks appeared with very low intensity. This indicates that defects may have formed in the catalyst due to the elution of metal ions (Co, Zn) from the structure of Example 1 (ZIF-67@ZIF-8) during the reaction and uncoordinated bonding. The SEM image in Fig. 11d shows that Example 1 (ZIF-67@ZIF-8), reused three times, maintains a rhombic dodecahedral shape compared to the new Example 1 (ZIF-67@ZIF-8). Although some particles appear partially broken after five cycles, it can be confirmed that the CO2 ring exhibits excellent reusability for the reaction without severe structural collapse during 10 reuses.

[0118] [Test Example 7]

[0119] In this experiment, a high-temperature filtration test of the catalyst according to the present disclosure was performed.

[0120] First, the reaction was carried out using the catalyst of Example 1 (ZIF-67@ZIF-8) in the same manner as the reaction of the carbon dioxide ring portion of Test Example 2, but the reaction was stopped after 1 hour, rapidly cooled with ice water, and the unreacted excess CO2 was released. Next, the catalyst of Example 1 (ZIF-67@ZIF-8) was separated using a syringe filter (0.45 μm), the collected supernatant was transferred to a new reactor, and the reaction was carried out under the same reaction conditions without the catalyst. The metal (Co) leached into the reaction mixture 2+ and Zn 2+) was detected through ICP analysis. As a result, as shown in Figure 12, only trace amounts of cobalt and zinc elements were detected in the reaction mixture during the initial reaction stage until the conversion rate of epichlorohydrin reached 60%. Subsequently, the concentrations of cobalt and zinc in the reaction mixture began to increase until the conversion rate reached 95.3%, at which point the leaching amounts of cobalt and zinc were 17.9 ppm and 55.7 ppm, respectively. Although metal leaching was present, the amount was reduced compared to previous reports.

[0121] In addition, the reaction was carried out in the same manner as the reaction of the carbon dioxide ring portion of Test Example 2 using the catalyst of Example 1 (ZIF-67@ZIF-8), but the reaction was stopped at 1 hour and the reaction was carried out without the catalyst. As a result, no progress of the reaction was observed in the absence of the catalyst even after 18 hours, and only trace amounts of metal (CO2+ and Zn2+) were detected in the filtrate confirmed by ICP analysis (see FIG. 13). This means that the catalyst according to the present disclosure exhibits high structural stability and heterogeneity.

[0122] [Test Example 8]

[0123] The distance between the open metal sites in each shell layer and the oxygen atoms originating from the styrene epoxy substrate having binding energy in the catalysts of Example 1 (ZIF-67@ZIF-8) and Example 2 (ZIF-8@ZIF-67), which are embodiments of the present disclosure, was analyzed using the spatially periodic density functional theory (DFT) as shown in Fig. 14.

[0124] As a result, it was found that oxygen atoms were absorbed at the open metal sites of the shell layers of each catalyst: Zn in Example 1 (ZIF-67@ZIF-8) and Co in Example 2 (ZIF-8@ZIF-67), exhibiting different binding energies of 103.56 kcal / mol and 82.23 kcal / mol, respectively. The relatively shorter distance between Zn and O (2.248 Å) in Example 2 (ZIF-67@ZIF-8) compared to Co and O (2.319 Å) in Example 1 (ZIF-67@ZIF-8) also supports the high binding energy results with oxygen originating from the styrene epoxide of the Zn metal in Example 1 (ZIF-67@ZIF-8). These results are also in good agreement with experimental results showing that Example 1 (ZIF-67@ZIF-8) exhibits higher catalytic performance than Example 2 (ZIF-8@ZIF-67) due to stronger interactions between the metal atoms of the shell layer and the oxygen of the substrate molecules in the test examples described above.

[0125] From the above tests, it was confirmed that a ZIF catalyst having a core-shell structure of heterometals Zn and Co according to one embodiment of the present disclosure exhibits higher catalytic performance in the carbon dioxide ring addition reaction than a heterometal ZIF catalyst containing a single metal of Zn or Co, or containing them randomly, while also having excellent reusability. In addition, among the catalysts according to the present disclosure, the catalyst containing ZIF-67 in the core and ZIF-8 in the shell exhibited the highest carbon dioxide adsorption capacity and high selectivity (> 98%), and was confirmed to exhibit excellent catalytic performance with an epoxide conversion rate of > 93% and reusability of more than 10 times.

Claims

Claim 1 A catalyst for a cyclic addition reaction of carbon dioxide having a core-shell structure comprising a core and a shell surrounding the core, wherein the core-shell particles include ZIF (Zeolitic imidazolate framework)-8 in the core and ZIF-67 in the shell, or include ZIF-67 in the core and ZIF-8 in the shell, wherein the molar ratio of the Co element included in ZIF-67 and the Zn element included in ZIF-8 is 3:1 to 1:3, the thickness ratio of the core and the shell is 50 to 300: 50 to 200, and the catalyst includes pores having an average diameter of 0.3 to 0.7 nm. Claim 2 A catalyst for a carbon dioxide cycloaddition reaction according to claim 1, wherein the average particle size of the catalyst is 100 to 500 nm. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A catalyst for a carbon dioxide cycloaddition reaction according to claim 1, wherein the porosity of the catalyst is 30 to 90%. Claim 7 In claim 1, the catalyst is 500 to 3000 m 2 A catalyst for a cyclic addition reaction of carbon dioxide having a specific surface area of ​​ / g. Claim 8 A method for preparing a catalyst for a carbon dioxide cyclic addition reaction according to any one of claims 1, 2, 6 and 7, comprising: (i) dissolving a cobalt salt, a zinc salt, and 2-methylimidazole in a solvent, respectively; injecting the cobalt salt solution into the 2-methylimidazole solution and then adding the zinc salt solution to react; and heat-treating the reaction mixture to prepare a catalyst comprising ZIF-67 in the core and ZIF-8 in the shell; or (ii) introducing a solution in which ZIF-8 is dispersed into a solution in which cobalt chloride is dispersed and mixing; introducing a solution in which 2-methylimidazole is dispersed into the mixture and reacting; and heat-treating the reaction mixture to prepare a catalyst comprising ZIF-8 in the core and ZIF-67 in the shell. Claim 9 A method of preparation according to claim 8, wherein each solvent of (i) and (ii) is one or more selected from the group consisting of water, methanol, dimethylformamide, and tetrahydrofuran. Claim 10 A manufacturing method according to claim 8, wherein each of the heat treatments of (i) and (ii) is performed at a temperature of 100 to 150°C for 12 to 36 hours. Claim 11 A method for producing a cyclic organic carbonate, comprising: a step of placing an epoxide-based compound substrate and a carbon dioxide cyclic addition reaction catalyst of any one of claims 1, 2, 6 and 7 into an autoclave; and a step of injecting a gas containing carbon dioxide into the autoclave and then producing a cyclic organic carbonate by carrying out a carbon dioxide cyclic addition reaction in an oil bath. Claim 12 A method for producing a cyclic organic carbonate according to claim 11, wherein the gas containing carbon dioxide is carbon dioxide; or a mixed gas of carbon dioxide and nitrogen. Claim 13 A method for producing a cyclic organic carbonate according to claim 11, wherein the epoxide-based compound is one or more selected from the group consisting of epichlorohydrin (ECH), ethylene oxide (EO), styrene oxide (SO), propylene oxide (PO), allyl glycidyl ether (AGE), cyclohexene oxide (CO), 1,2-epoxybutane (EB), and 1,2-epoxyhexane. Claim 14 A method for producing a cyclic organic carbonate according to claim 11, wherein the carbon dioxide ring addition reaction is carried out at 80 to 120°C for 1 to 10 hours.

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