Metal organic framework material taking multiphase hindered Lewis acid-base pair as catalytic site, preparation and catalytic application

Abstract

The invention belongs to the field of inorganic and organic material design and catalysts, and discloses a metal organic framework material taking a multiphase hindered Lewis acid-base pair as a catalytic site, and preparation and catalytic application of the metal organic framework material. The structural formula of the metal organic framework material taking the multiphase hindered Lewis acid-base pair as the catalytic site is M3 (OH) (L1) 3 (L2) 1; wherein M3 is a three-metal cluster node; l1 is a parent framework composed of carboxylic acid ligands; l2 is a bipyridyl ligand containing a Lewis base; and the Lewis base on the L2 and the metal node form an FLP structure. The method has high capability of activating small molecules. The catalyst has high stability, and can be recycled for multiple times in the semi-hydrogenation reaction of phenylacetylene to maintain the performance. According to the invention, metal nodes, high specific surface area and high porosity in the MOF are fully utilized.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic and organic material design and catalysts, and relates to a metal organic framework material for constructing high-density Lewis acid-base pair catalytic sites by selective coordination of soft and hard acids and bases, and its preparation and catalytic application. Background Art

[0002] Frustrated Lewis acid-base pairs (FLPs) have emerged as promising catalysts in modern catalysis due to their ability to activate small molecules under mild conditions, regulate reaction pathways, promote challenging chemical transformations, and their potential to achieve efficient catalysis without reliance on precious metals. FLPs are composed of Lewis acids (LA) and Lewis bases (LB) that are unable to form stable adducts due to steric hindrance. These unadducted Lewis acids and Lewis bases can activate small molecules, allowing FLPs to catalyze a range of reactions including hydrogenation, hydroboration, and CO2 activation. Although FLPs have demonstrated excellent catalytic activity and product selectivity in homogeneous systems, their practical application is often limited by the problem of catalyst recovery and reuse. To address this limitation, recent efforts have focused on developing heterogeneous FLP catalysts by immobilizing FLPs on solid supports. This approach not only facilitates the separation and recovery of the catalyst, thereby improving the practical usability of FLPs, but also provides a platform for the rational design of new FLP structures.

[0003] Among the various heterogeneous catalysts designed, metal organic frameworks (MOFs) have attracted much attention due to their structural diversity, tunability and high specific surface area. In the past decade, FLP has been loaded in the MOF framework to achieve heterogeneity, and the performance is excellent. There are four types of MOF-loaded FLP methods: ligand modification, node functionalization, node LA and node FLP itself. Most of these methods use traditional FLP loading, which is easy to lose FLP and cause catalytic deactivation. In addition, traditional FLP is difficult to control the LA-LB distance regulation performance. Individual reports have the ability to accurately control the distance and orientation between FLPs, using a three-organoboron linker as LA and a monomer linker as LB to separate metal oxide clusters in a tetrahedral geometry, and the distance between LA and LB can be precisely controlled (see Hexiang, D., et al. Precise Distance Control and Functionality Adjustment of Frustrated. Lewis Pairs in Metal-Organic Frameworks. J. Am. Chem. Soc. 2024, 146, 12215-12224). However, by using partial replacement of ligands, the proportion of FLP in MOF is not high and it affects the stability of the metal-organic framework.

[0004] In the present invention, a soft and hard acid-base selection coordination strategy is used, a carboxylic acid ligand is used as the ligand L1 of the parent framework, and a pyridyl ligand containing a Lewis base site is used as the second ligand L2 introduced into the metal organic framework. Due to different coordination abilities, the two ligands coordinate with the metal to form a metal organic framework material with FLP sites. Since each metal node can be used as a FLP catalytic site composed of LA and the second ligand LB, the content of FLP catalytic sites in MOF is very high. Summary of the invention

[0005] One of the purposes of the present invention is to provide a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, wherein the acidity and alkalinity of the Lewis acid and base are adjustable and the distance between the Lewis acid-base pairs is adjustable.

[0006] The second object of the present invention is to provide a method for preparing a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, which has a simple preparation process and is easy to adjust.

[0007] The third object of the present invention is to provide an application of a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site.

[0008] The technical solution of the present invention:

[0009] A metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, named MOF-FLP, has a structural formula of M3(OH)(L1)3(L2)1; wherein M3 is a trimetallic cluster node, and the metal node in the trimetallic cluster node is a single metal or a mixture of two metals; when it is a mixture of two metals, the high-valent metal and the low-valent metal are mixed in a molar ratio of 1:2; L1 is a parent framework composed of carboxylic acid ligands; L2 is a bipyridyl ligand containing a Lewis base; the Lewis base on L2 forms a FLP structure with the metal node; the basicity of the Lewis base and the distance from the metal node are changed by replacing L2, and the regulation of Lewis acids of different acidities is achieved by replacing the metal node; the carboxylic acid ligand, the bipyridyl ligand containing the Lewis base and the metal cluster are spatially coordinated in an orderly manner to form an M3 trimetallic cluster node, wherein each metal node forms a FLP with a Lewis base in L2, thereby achieving the construction of a high-content FLP.

[0010] A method for preparing a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, comprising the following steps:

[0011] (1) mixing a carboxylic acid ligand and a solvent, stirring and dissolving; adding a bipyridyl ligand containing a Lewis base until dissolved under stirring; continuing to add a metal salt until dissolved under stirring, stirring at room temperature for 1 hour, and then performing a hydrothermal synthesis;

[0012] (2) After the reaction is completed, the mixture is cooled to room temperature and filtered to obtain a powder; the powder is washed with a synthetic solvent for one day and then filtered, and then washed with dichloromethane (DCM), and the solvent is changed every three hours for one day;

[0013] (3) The powder in step (2) was activated by vacuum heating at 65° C. for 10 hours to obtain a MOF material having a large number of evenly distributed FLP catalytic sites, which was named MOF-FLP.

[0014] Wherein, the metal salt is one or two of alkaline earth metal salts and transition metal salts. When two metal salts are mixed, the molar ratio of high-valent metal (+3, +4 valence) to low-valent metal (+2 valence) needs to be controlled to be 1:2.

[0015] The carboxylic acid ligand is a parent framework ligand, specifically, polycarboxylic acids of different lengths such as fumaric acid, terephthalic acid, biphenyl dicarboxylic acid, 3,5-pyridine dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, and polycarboxylic acids modified with different types and numbers of functional groups, and its concentration in the reaction system is 0.1-0.3 mol / L.

[0016] The bipyridyl ligand containing a Lewis base is a ligand containing two pyridyl groups and additional Lewis base sites, such as 3,5-bis(4-pyridyl)pyridine, 3,5-di-4-pyridylaniline, 3,5-di(pyridin-4-yl)phenol and di(pyridin-4-yl)amine.

[0017] The molar ratio of the metal salt, the carboxylic acid ligand and the bipyridyl ligand containing a Lewis base is 3:3:1.

[0018] The solvent is a solvent that can dissolve non-polar and polar substances, such as N,N-dimethylformamide, N,N-dimethylacetamide or N,N-dimethylacetamide.

[0019] The hydrothermal reaction temperature is 100-150°C and the time is 12-120h.

[0020] An application of a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, wherein the metal organic framework material with a multiphase Lewis acid-base pair as a catalytic site is used as a catalyst for gas-solid phase and gas-liquid-solid phase alkyne hydrogenation reaction; the gas-solid phase reaction steps are as follows: the catalyst and quartz sand are mixed and filled into a fixed bed, reacted in a gas mobile phase containing alkyne hydrogen, and the reaction conversion rate is calculated by detecting the alkyne content before and after the reaction by gas chromatography. The gas-liquid-solid phase reaction steps are as follows: the substrate phenylacetylene, the solvent isopropanol and the n-dodecane internal standard equal to the amount of phenylacetylene are added to the reactor. The reaction is carried out in a normal pressure hydrogen atmosphere. After a period of reaction, the reaction solution is filtered and diluted, and then qualitatively and quantitatively analyzed using a gas chromatography-mass spectrometer.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention adopts adjustable metal MOF materials, in which the metal type and ligand type are adjustable. The electronic state of the metal can be adjusted by changing the metal cluster composition to change the acidity of LA in FLP, and the regulation of different alkalinity and different distances can be achieved by changing the Lewis base ligand.

[0023] 2. The present invention uses the framework itself to limit the formation of FLP, and uses mixed ligands to introduce Lewis base sites and open metal sites of metal nodes to form FLP, which reasonably limits the distance of FLP and can achieve full coverage of FLP catalytic sites in MOF.

[0024] 3. The present invention has a high ability to activate small molecules and is highly active in the hydrogenation of alkynes.

[0025] 4. The present invention has high catalytic stability and can be recycled for multiple times while maintaining performance.

[0026] 5. The present invention makes full use of the metal nodes, high specific surface area and high porosity in MOF. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a synthetic schematic diagram;

[0028] Figure 2 Schematic diagram of the structure; (a) is MOF-FLP, (b) is MOF-LA;

[0029] Figure 3 is a schematic diagram of XRD of MOF-FLP and MOF-LA powders;

[0030] Figure 4 is the nitrogen adsorption graph of MOF-FLP and MOF-LA;

[0031] Figure 5 is the thermogravimetric analysis graph of MOF-FLP and MOF-LA;

[0032] Figure 6 are scanning electron microscopy images; (a) is MOF-FLP, (b) is MOF-LA;

[0033] Figure 7 is the performance diagram of the semi-hydrogenation of phenylacetylene catalyzed by MOF-FLP and MOF-LA;

[0034] Figure 8 This is a test diagram of the catalytic cycle stability of MOF-FLP catalyst. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0036] Figure 1 The synthesis route and structural formula of MOF-FLP are shown. Figure 2 The structures of MOF-FLP and MOF-LA are shown. The high catalytic activity of the FLP structure can be seen by comparing it with the comparison sample containing only LA sites. In the constructed MOF-FLP material, the metal nodes are Figure 1 The three-metal node structure shown in the figure has adjustable metal nodes, which are composed of one or two transition metals and alkaline earth metals, and have a large adjustable space. At the same time, the carboxylic acid ligand L1 that constitutes the framework and the pyridine ligand L2 with Lewis base sites can also be reasonably replaced, which makes MOF-FLP materials have a wide range of regulation and research space.

[0037] Example 1

[0038] Synthesis steps of MOF-FLP:

[0039] (1) In a 15 mL glass vial, 100 mg of terephthalic acid, 46.6 mg of 3,5-bis(4-pyridyl)pyridine and 3 g of N,N-dimethylformamide were added, and then 120 mg of cobalt nitrate hexahydrate and 32 mg of vanadium trichloride were added in sequence.

[0040] (2) After stirring for 1 hour, the magnet was removed and the vial was placed in an oven at 130°C for three days.

[0041] (3) After cooling to room temperature, filter the sample and rinse with N,N-dimethylformamide to obtain a dark red powder. Add the powder into a beaker containing 80 mL of N,N-dimethylformamide and stir for one day; filter again and add the powder into 80 mL of dichloromethane, replace the dichloromethane every three hours, and filter one day later to obtain the MOF-FLP sample.

[0042] Example 2

[0043] Based on Example 1, 46.6 mg of 3,5-bis(4-pyridyl)pyridine was replaced with 46.4 mg of 1,3-di(4-pyridyl)benzene, and other treatments were the same.

[0044] The materials obtained in Examples 1 and 2 were characterized by X-ray powder diffraction. Figure 3 As shown, the two materials have almost identical XRD patterns. Figure 4 These are the nitrogen adsorption diagrams of the two materials, both showing the characteristics of micropores. Figure 5 These are the thermogravimetric analysis curves of the two samples. Both materials have high thermal stability. Figure 6These are scanning electron microscope images of the two materials. The two materials have similar morphologies. The above four characterizations basically verify that the materials have been successfully synthesized and have the same structure.

[0045] Example 3

[0046] On the basis of Example 1, 120 mg of cobalt nitrate hexahydrate was replaced with 116 mg of nickel nitrate hexahydrate, and other treatments were the same to obtain MOF-FLP (Ni2V).

[0047] Example 4

[0048] (1) In a 20 mL glass vial, 50 mg of terephthalic acid, 23.3 mg of 3,5-bis(4-pyridyl)pyridine, 4 g of N,N-dimethylformamide, and 0.5 g of deionized water were added, and then 80 μL of concentrated hydrochloric acid and 87 mg of nickel nitrate hexahydrate were added.

[0049] Steps (2) and (3) are the same as those in Example 1.

[0050] Example 5

[0051] Experiments on hydrogenation of phenylacetylene catalyzed by catalysts with FLP catalytic sites and those with only LA.

[0052] Add 2mL of isopropanol, 22μL of phenylacetylene and 22μL of n-dodecane to the test tube, and add 10mg of catalyst. Then plug the test tube with a stopper and put it in an oil bath at 80°C. Tie a hydrogen balloon on the stopper to provide hydrogen, and react while stirring at 800 rpm. The reaction is basically complete after 4 hours. Use a syringe to take a sample, use a filter to filter out the solid catalyst, add the reaction solution to a gas chromatography-mass spectrometer, dilute with isopropanol, and use a gas chromatography-mass spectrometer for qualitative and quantitative analysis to test the phenylacetylene conversion rate and styrene selectivity. The catalytic results are as follows: Figure 7 As shown in the figure, under the same reaction conditions, the MOF-FLP material constructed with FLP showed a 100% phenylacetylene conversion rate and 89% styrene selectivity, while the MOF-LA sample only had a 3% phenylacetylene conversion rate. By using metal nodes as Lewis acid sources and ligands as Lewis base sources, FLP catalytic sites were successfully introduced at each metal node, and a large number of FLP catalytic sites showed excellent activity and reaction selectivity for phenylacetylene semi-hydrogenation. In addition, due to the framework restrictions, the constructed FLP catalytic sites are fixed and clear, and the catalytic mechanism is easy to study.

[0053] Another advantage of this FLP construction is stability. The MOF-FLP was tested for its cyclic stability. Figure 8 It can be seen that the catalyst's activity for the semi-hydrogenation of phenylacetylene has not decreased after five reactions.

[0054] Embodiment 6-13

[0055] The MOF-FLP catalyst was used to catalyze the semi-hydrogenation of different alkynes, namely 4-ethynylaniline, 4-tert-butylphenylacetylene, 4-fluorophenylacetylene, 4-chlorophenylacetylene, 4-methoxyphenylacetylene, 2-acetylenonaphthalene, 1-octyne and 4-octyne. Under the same conditions, they all achieved high alkyne conversion rates and high olefin selectivity.

[0056] Embodiment 14

[0057] 0.1g MOF-FLP catalyst and 1g quartz sand were mixed evenly, loaded into a fixed bed reactor, and reacted at 80°C in a mixture of 50% ethylene, 44.5% helium, 0.5% acetylene and 5% hydrogen at a flow rate of 20mL / min. The conversion rate was calculated by using gas chromatography to detect the alkyne content before and after the reaction. 100% alkyne conversion rate can be achieved at 80°C.

[0058] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A metal organic framework material with a heterogeneous hindered Lewis acid-base pair as a catalytic site, characterized in that: The metal organic framework material is named MOF-FLP, and its structural formula is M3(OH)(L1)3(L2)1; Among them, M3 is a trimetallic cluster node, and the metal node in the trimetallic cluster node is a single metal or a mixture of two metals; L1 is a parent framework composed of carboxylic acid ligands; L2 is a bipyridyl ligand containing a Lewis base; the Lewis base on L2 forms a FLP structure with the metal node; The carboxylic acid ligands and Lewis base-containing bipyridyl ligands are spatially coordinated with the metal clusters in an orderly manner to form M3 trimetallic cluster nodes, in which each metal node forms a FLP with a Lewis base in L2, achieving the construction of a high-content FLP.

2. The metal organic framework material according to claim 1, characterized in that: When the metal node in the trimetallic cluster node is a mixture of two metals, the high-valent metal and the low-valent metal are mixed in a molar ratio of 1:

2.

3. The metal organic framework material according to claim 1, characterized in that: By replacing L2, the basicity of the Lewis base and the distance from the metal node can be changed, and by replacing the metal node, the regulation of Lewis acids with different acidities can be achieved.

4. A method for preparing a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, characterized in that: Here are the steps: (1) mixing a carboxylic acid ligand and a solvent, stirring and dissolving; adding a bipyridyl ligand containing a Lewis base until dissolved under stirring; continuing to add a metal salt until dissolved under stirring, stirring at room temperature for 1 hour, and then performing a hydrothermal synthesis; (2) After the reaction is completed, the mixture is cooled to room temperature and filtered to obtain a powder; the powder is washed with a synthetic solvent for one day and then filtered, and then washed with dichloromethane (DCM), and the solvent is changed every three hours for one day; (3) The powder in step (2) was activated by vacuum heating at 65° C. for 10 hours to obtain a MOF material having a large number of evenly distributed FLP catalytic sites, which was named MOF-FLP.

5. The preparation method according to claim 4, characterized in that: The metal salt is one or two of an alkaline earth metal salt and a transition metal salt. When the metal salt is a mixture of two metal salts, it is necessary to control the molar ratio of the high-valent metal (+3, +4) to the low-valent metal (+2) to be 1:2, the high-valent metal is +3 or +4, and the low-valent metal is +2.

6. The preparation method according to claim 4, characterized in that: The carboxylic acid ligand is a parent framework ligand, which is fumaric acid, terephthalic acid, biphenyl dicarboxylic acid, 3,5-pyridine dicarboxylic acid or 2,6-naphthalene dicarboxylic acid, and its concentration in the reaction system is 0.1-0.3 mol / L.

7. The preparation method according to claim 4, characterized in that: The bipyridyl ligand containing a Lewis base is 3,5-bis(4-pyridyl)pyridine, 3,5-di-4-pyridylaniline, 3,5-di(pyridin-4-yl)phenol or di(pyridin-4-yl)amine; the molar ratio of the metal salt, the carboxylic acid ligand and the bipyridyl ligand containing a Lewis base is 3:3:

1.

8. The preparation method according to claim 4, characterized in that: The solvent is N,N dimethylformamide, N,N dimethylacetamide or N,N dimethylacetamide.

9. The preparation method according to claim 4, characterized in that: The hydrothermal reaction temperature is 100-150°C and the time is 12-120h.

10. An application of a metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site, characterized in that: A metal organic framework material with a multiphase hindered Lewis acid-base pair as a catalytic site is used for gas-solid phase and gas-liquid-solid phase alkyne hydrogenation reaction; the gas-solid phase reaction steps are as follows: the catalyst and quartz sand are mixed and loaded into a fixed bed, and the reaction is carried out in a gas mobile phase containing alkyne hydrogen; the gas-liquid-solid phase reaction steps are as follows: the substrate phenylacetylene, the solvent isopropanol and the n-dodecane internal standard equal to the amount of phenylacetylene are added to the reactor, and the reaction is carried out in a normal pressure hydrogen atmosphere.

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