A ligand-functionalized MOF confined metal catalyst, its preparation method and application

Abstract

This invention discloses a ligand-functionalized MOF-confined metal catalyst, its preparation method, and its applications. The catalyst uses UiO-66-X (where X represents the functionalized group) as a support, and loads metal Pd via an impregnation reaction. The functionalized group plays two roles in regulating the microenvironment of metal Pd: adjusting the electronic properties of Pd and altering the hydrophilicity / hydrophobicity surrounding Pd, thereby affecting catalytic activity and selectivity. In the continuous catalytic synthesis of higher alcohols from ethanol, the metal Pd in ​​the Pd@UiO-66-CH3 catalyst exhibits high electron density and a hydrophobic microenvironment, thus demonstrating excellent ethanol conversion and higher alcohol yield (47.7%), the highest yield reported to date. This catalyst holds promise for industrial continuous production of higher alcohols from ethanol and provides important insights for developing more efficient catalysts for this process.

Description

Technical Field

[0001] This invention relates to a ligand-functionalized MOF confined metal catalyst and its preparation method, as well as its application in the continuous catalytic synthesis of higher alcohols from ethanol. Background Technology

[0002] Due to the increasing depletion of fossil resources and the greenhouse effect and environmental pollution caused by their use, the development and utilization of renewable biomass resources are receiving increasing attention. Higher alcohols (including butanol, 2-ethylbutanol, hexanol, and octanol) can be used not only as antifoaming agents, plasticizers, antifreeze agents, gasoline additives, and lubricant additives, but also in the manufacture of fragrances, cosmetics, and pharmaceuticals. Industrially, the production of higher alcohols mainly employs the carbonyl synthesis method. This method uses non-renewable petroleum as raw material and employs precious metal catalysts, making the process complex. The technical route for synthesizing higher alcohols from renewable ethanol (…) Figure 1 It has received increasing attention.

[0003] Over the past few decades, both homogeneous and heterogeneous catalysts have been used to achieve the synthesis of higher alcohols from ethanol. Homogeneous catalysts are typically composed of noble metals (iridium and ruthenium) and non-noble metals (manganese) [Chemistry Letters, 2009, 38(8): 838-839; Chemical Communications, 2016, 52(14): 2901-2904; Journal of the American Chemical Society, 2017, 139(34): 11941-11948]. These catalysts exhibit excellent catalytic activity under mild reaction conditions. However, most homogeneous catalysts require the use of strong bases such as sodium ethoxide to create an alkaline environment, which limits their applicability in continuous reaction systems. In addition, the high cost of homogeneous catalysts also poses a challenge to their widespread application. Therefore, heterogeneous catalysts are considered more suitable for the continuous catalytic synthesis of higher alcohols from ethanol.

[0004] Traditional heterogeneous catalysts include alkaline earth metal oxides, alkali metal-modified molecular sieves, hydrotalcite, and hydroxyapatite. Although the reaction conditions for these catalysts are relatively harsh (typically requiring temperatures above 300°C), the butanol yield is generally less than 10%. In our previous study [ACS Catalysis, 2018, 8(12): 11973-11978], we encapsulated Pd nanoparticles in UiO-66 cages to prepare a Pd@UiO-66 catalyst. Due to the confinement effect of the UiO-66 cages and the electrostatic interaction between the metal Pd and Zr nodes, the Pd nanoparticles were highly dispersed and stable. In a 200-hour catalytic performance evaluation, this catalyst consistently and stably achieved a butanol yield of 25%.

[0005] Recent literature reports [Accounts of Materials Research, 2021, 2(5): 327-339] that the microenvironment in metal-organic frameworks (MOFs) has a significant impact on catalytic activity and selectivity. One strategy for modulating the microenvironment in MOFs is to post-treat them with hydrophobic substrates [Journal of Catalysis, 2016, 333: 1-7; Angewandte Chemie International Edition, 2016, 55(26): 7379-7383; Advanced Science, 2020, 7(4): 1901758; Chem, 2021, 7(3): 686-698], forming a hydrophobic microenvironment around the encapsulated metal nanoparticles. Compared to untreated catalysts, these modified catalysts exhibit better catalytic performance because the hydrophobic microenvironment promotes the enrichment of hydrophobic reactants around the metal nanoparticles. Another strategy for regulating the microenvironment is to select suitable ligands containing functionalized groups to synthesize MOFs [Angewandte Chemie International Edition, 2012, 51(20): 4887-4890; Catalysis Science & Technology, 2020, 10(12): 4002-4009; National Science Review, 2020, 8(1): nwaa224; ChemCatChem, 2021, 13(10): 2517-2529; Angewandte Chemie International Edition, 2022, 61(36): e202205077]. The functionalized groups in these ligands will change the electron density of the encapsulated metal nanoparticles, thereby affecting the catalytic activity and selectivity. Inspired by this, we used terephthalic acid containing functionalized groups to synthesize UiO-66-X, and further loaded metal Pd to form Pd@UiO-66-X catalyst ( Figure 2 ). Summary of the Invention

[0006] This invention provides a ligand-functionalized MOF confined metal catalyst, its preparation method, and its application.

[0007] The technical solution of the present invention is as follows:

[0008] A ligand-functionalized MOF confined metal catalyst, consisting of palladium as the active metal component and UiO-66-X as the support;

[0009] Based on the total mass of the catalyst, the mass percentage of palladium is 0.05–10% (particularly preferred 1%), with the balance being the support;

[0010] In the carrier UiO-66-X, X represents a functionalized group such as -NH2, -CH3, -OCH3, -COOH, -F, -Cl, -Br or -NO2; during the synthesis of the carrier UiO-66-X, X is introduced by a terephthalic acid ligand containing the above functionalized groups;

[0011] The carrier UiO-66-X is a white powdery solid with a specific surface area of ​​900–1200 m². 2 / g, pore size 0.4~0.7nm, pore volume 0.4~0.7cm³ 3 / g, which belongs to the typical microporous materials (Table 2).

[0012] The ligand-functionalized MOF-confined metal catalyst of this invention can be prepared by impregnation reaction, and the amount of raw materials can be calculated based on the mass percentage of the catalyst components; the specific preparation method is as follows:

[0013] (1) ZrCl4 and terephthalic acid containing functional groups were added to N,N-dimethylformamide, then acetic acid and water were added and stirred thoroughly to dissolve. The resulting mixture was transferred to a hydrothermal reactor and allowed to stand at 100-150℃ for 12-24 h. After cooling to room temperature, the mixture was collected by centrifugation and dried to obtain UiO-66-X solid.

[0014] In terephthalic acid containing functionalized groups, the functionalized groups are -NH2, -CH3, -OCH3, -COOH, -F, -Cl, -Br or -NO2, etc., and the synthesized UiO-66-X are, for example: UiO-66-NH2, UiO-66-CH3, UiO-66-OCH3, UiO-66-NO2, etc.

[0015] The preferred terephthalic acid containing functionalized groups is 2-methylterephthalic acid, 2-aminoterephthalic acid, or 2-nitroterephthalic acid;

[0016] (2) Dissolve the palladium precursor in a solvent, then add UiO-66-X and completely submerge it, stir and react at 20-100℃ for 2-48h, then stir and evaporate to dryness at 100-160℃ to obtain a solid powder; place the obtained solid powder at 70-300℃ for 2-24h (to remove residual solvent and moisture in the catalyst channels), and cool to room temperature to obtain the target catalyst;

[0017] The palladium precursor is selected from one or more of palladium chloride, palladium nitrate, palladium acetate, palladium propionate, palladium sulfate, palladium cyanide, palladium iodide, palladium dibromide, potassium chloropalladate, palladium trifluoroacetate, palladium acetylacetonate, bis(acetonitrile) chloride, palladium tetraaminonitrate, and palladium hexafluoroacetylacetonate.

[0018] The solvent is selected from one or more of methanol, ethanol, toluene, xylene, chloromethane, dichloromethane, trichloromethane, deionized water, N,N-dimethylformamide, and acetylacetone.

[0019] The ligand-functionalized MOF-confined metal catalyst described in this invention can be applied to the continuous catalytic synthesis of higher alcohols from ethanol. The specific application method is as follows:

[0020] Ligand-functionalized MOFs confined metal catalysts were loaded into a fixed-bed reactor and reduced for 2–8 h (preferably 4 h) under a mixed atmosphere of H2 / N2 (H2 volume fraction 10%), at 250–300 °C (preferably 270 °C) and atmospheric pressure. Ethanol was then introduced (N2 / ethanol = 250:1 (v / v), LHSV = 1–6 h). -1 Higher alcohols are synthesized by reacting at 200–300°C and 1–4 MPa (preferably 2 MPa).

[0021] The reaction liquid products were analyzed by gas chromatography using a gas chromatograph equipped with a flame ionization detector (FID) and an EN-20 column (30 m, 0.25 mm inner diameter, 0.25 μm film thickness).

[0022] The products, including higher alcohols, include n-butanol, 2-ethylbutanol, and n-hexanol.

[0023] The technical principle of this invention is as follows:

[0024] The active metal component of the catalyst in this invention is palladium, and the ligand is terephthalic acid containing functionalized groups such as -NH2, -CH3, -OCH3, -COOH, -F, -Cl, -Br, and -NO2. These functionalized groups can regulate the electronic properties of metallic Pd and change the hydrophilicity or hydrophobicity around metallic Pd, thereby affecting the catalyst's activity in the synthesis of higher alcohols from ethanol (Table 1). It can be seen that as the electron density of metallic Pd increases (BE value decreases), the TOF value of the reaction also increases.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention provides a ligand-functionalized MOF-confined metal catalyst. When this catalyst is applied to the continuous catalytic synthesis of higher alcohols from ethanol, the catalytic performance results show that the yield of higher alcohols can reach up to 47.7%, which is the highest yield reported in the literature to date. Attached Figure Description

[0027] Figure 1 : Reaction mechanism diagram for the synthesis of higher alcohols from ethanol.

[0028] Figure 2 Transmission electron microscopy (TEM) images and elemental distribution diagrams of Pd@UiO-66-X catalysts: A. Pd@UiO-66-NH2; B. Pd@UiO-66-CH3; C. Pd@UiO-66-NO2; D. Pd@UiO-66.

[0029] Figure 3 Schematic diagram of a fixed-bed reactor for continuous catalytic synthesis of higher alcohols from ethanol: 1-metering pump, 2-vaporizer, 3-fixed-bed reactor, 4-catalyst bed, 5-temperature measuring point, 6-condenser, A-liquid feed inlet, B-nitrogen inlet, C-top of reactor, D-bottom of reactor, E-product outlet.

[0030] Figure 4 Evaluation results of the Pd@UiO-66-CH3 catalyst in Example 1 for the continuous catalytic synthesis of higher alcohols from ethanol in a fixed bed; reaction conditions were: temperature 250℃, pressure 2.0 MPa, and liquid hourly space velocity (LHSV) 4.0 h⁻¹. -1 Nitrogen / ethanol = 250:1 (v / v). Detailed Implementation

[0031] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] In the following embodiments,

[0033] The preparation method of UiO-66 support is as follows: Anhydrous zirconium chloride (5.25 g) and terephthalic acid (3.71 g) were dissolved separately in 256 mL of N,N-dimethylformamide. The solutions were magnetically stirred for 20 min until zirconium chloride and terephthalic acid were completely dissolved. The two solutions were mixed and 2 mL of deionized water and 38.4 mL of glacial acetic acid were added. The mixture was stirred again for 20 min to form a crystallization mother liquor. The crystallization mother liquor was poured into a 500 mL hydrothermal reactor with a polytetrafluoroethylene liner and statically crystallized at 120 °C for 24 h. After crystallization, the obtained solid product was collected by centrifugation. The solid product was washed multiple times with N,N-dimethylformamide and anhydrous methanol to remove unreacted zirconium chloride, terephthalic acid, and residual solvent molecules from the pores. Finally, the obtained support was dried in a forced-air oven at 80 °C for 12 h and then transferred to a vacuum drying oven for vacuum activation at 150 °C for 12 h to obtain the UiO-66 support.

[0034] The UiO-66-CH3 support was prepared as follows: Anhydrous zirconium chloride (5.25 g) and 2-methylterephthalic acid (4.02 g) were dissolved separately in 256 mL of N,N-dimethylformamide. The solutions were magnetically stirred for 20 min until both zirconium chloride and 2-methylterephthalic acid were completely dissolved. The two solutions were then mixed, and 2 mL of deionized water and 38.4 mL of glacial acetic acid were added. The mixture was stirred again for 20 min to form a crystallization mother liquor. The crystallization mother liquor was poured into a 500 mL hydrothermal reactor lined with polytetrafluoroethylene and statically crystallized at 120 °C for 24 h. After crystallization, the resulting solid product was collected by centrifugation. The solid product was washed multiple times with N,N-dimethylformamide and anhydrous methanol to remove unreacted zirconium chloride, 2-methylterephthalic acid, and residual solvent molecules from the pores. Finally, the obtained support was dried in a forced-air oven at 80°C for 12 hours, and then transferred to a vacuum drying oven at 150°C for 12 hours to obtain the UiO-66-CH3 support.

[0035] The preparation method of the UiO-66-NH2 support is as follows: Anhydrous zirconium chloride (5.25 g) and 2-aminoterephthalic acid (4.05 g) were dissolved separately in 256 mL of N,N-dimethylformamide. The solutions were magnetically stirred for 20 min until zirconium chloride and 2-aminoterephthalic acid were completely dissolved. The two solutions were mixed, and 2 mL of deionized water and 38.4 mL of glacial acetic acid were added. The mixture was stirred again for 20 min to form a crystallization mother liquor. The crystallization mother liquor was poured into a 500 mL hydrothermal reactor with a polytetrafluoroethylene liner and statically crystallized at 120 °C for 24 h. After crystallization, the obtained solid product was collected by centrifugation. The solid product was washed multiple times with N,N-dimethylformamide and anhydrous methanol to remove unreacted zirconium chloride, 2-aminoterephthalic acid, and residual solvent molecules from the pores. Finally, the obtained support was dried in a forced-air oven at 80°C for 12 hours, and then transferred to a vacuum drying oven at 150°C for vacuum activation for 12 hours to obtain the UiO-66-NH2 support.

[0036] The preparation method of UiO-66-NO2 support is as follows: Anhydrous zirconium chloride (5.25 g) and 2-nitroterephthalic acid (4.71 g) were dissolved separately in 256 mL of N,N-dimethylformamide. The solutions were magnetically stirred for 20 min until zirconium chloride and 2-nitroterephthalic acid were completely dissolved. The two solutions were mixed, and 2 mL of deionized water and 38.4 mL of glacial acetic acid were added. The mixture was stirred again for 20 min to form a crystallization mother liquor. The crystallization mother liquor was poured into a 500 mL hydrothermal reactor with a polytetrafluoroethylene liner and statically crystallized at 120 °C for 24 h. After crystallization, the obtained solid product was collected by centrifugation. The solid product was washed multiple times with N,N-dimethylformamide and anhydrous methanol to remove unreacted zirconium chloride, 2-nitroterephthalic acid, and residual solvent molecules from the channels. Finally, the obtained support was dried in a forced-air oven at 80°C for 12 hours, and then transferred to a vacuum drying oven at 150°C for vacuum activation for 12 hours to obtain the UiO-66-NO2 support.

[0037] Example 1

[0038] 28.6 mg Pd(acac)2 was added to a round-bottom flask containing 57.3 mL acetylacetone and stirred at 50 °C for 0.5 h to completely dissolve it. Then, 1.0 g UiO-66-CH3 support was added and stirred at 50 °C for 24 h. The mixture was then transferred to an oil bath at 120 °C and stirred to evaporate. The resulting pale yellow solid was repeatedly ground in an agate mortar and pestle. Finally, it was dried in an oven at 150 °C for 12 h.

[0039] 0.5 g of Pd@UiO-66-CH3 catalyst was immobilized in the isothermal zone of the reaction tube bed using quartz wool. Figure 3 Before the reaction, the Pd@UiO-66 catalyst was reduced at 270℃ for 4 h using a 10% H2 / N2 mixture. After reduction, N2 was introduced (10 mL / min) to 2 MPa. When the reactor temperature dropped to 250℃, anhydrous ethanol (N2 / ethanol = 250:1 (v / v), LHSV = 4 h) was added. -1 The catalyst is pumped into the preheating furnace, where it undergoes gasification before entering the reactor to participate in the reaction. Catalyst evaluation results are shown in Table 3 and... Figure 4 As shown.

[0040] Comparative Example 1

[0041] 28.6 mg of Pd(acac)₂ was added to a round-bottom flask containing 57.3 mL of acetylacetone and stirred at 50 °C for 0.5 h to ensure complete dissolution. Then, 1.0 g of UiO-66 support was added, and the mixture was stirred at 50 °C for 24 h. The mixture was then transferred to an oil bath at 120 °C and stirred until evaporated. The resulting pale yellow solid was repeatedly ground using an agate mortar and pestle. Finally, it was dried in an oven at 150 °C for 12 h. The catalyst evaluation method was the same as in Example 1, and the evaluation results are shown in Table 3.

[0042] Comparative Example 2

[0043] 28.6 mg of Pd(acac)₂ was added to a round-bottom flask containing 57.3 mL of acetylacetone and stirred at 50 °C for 0.5 h to ensure complete dissolution. Then, 1.0 g of UiO-66-NH₂ support was added, and the mixture was stirred at 50 °C for 24 h. The mixture was then transferred to an oil bath at 120 °C and stirred until evaporated. The resulting pale yellow solid was repeatedly ground using an agate mortar and pestle. Finally, it was dried in an oven at 150 °C for 12 h. The catalyst evaluation method was the same as in Example 1, and the evaluation results are shown in Table 3.

[0044] Comparative Example 3

[0045] 28.6 mg of Pd(acac)₂ was added to a round-bottom flask containing 57.3 mL of acetylacetone and stirred at 50 °C for 0.5 h to ensure complete dissolution. Then, 1.0 g of UiO-66-NO₂ support was added, and the mixture was stirred at 50 °C for 24 h. The mixture was then transferred to an oil bath at 120 °C and stirred until evaporated. The resulting pale yellow solid was repeatedly ground using an agate mortar and pestle. Finally, it was dried in an oven at 150 °C for 12 h. The catalyst evaluation method was the same as in Example 1, and the evaluation results are shown in Table 3.

[0046] Table 1. Relationship between the electronic properties and hydrophilicity / hydrophobicity of catalysts and their reactivity in the synthesis of higher alcohols from ethanol.

[0047]

[0048] Table 2. Structural properties of UiO-66-X support and Pd@UiO-66-X catalyst

[0049]

[0050] [a]BET surface area;

[0051] [b]The volume of a single-point orifice at P / P0 = 0.99;

[0052] [c] Average aperture calculated by DFT method;

[0053] [d] Pd particle size determined by TEM.

[0054] Table 3 Catalytic performance of different catalysts in the synthesis of higher alcohols from ethanol.

[0055]

[0056] [a] Conversion, selectivity, and yield under steady-state conditions; Reaction conditions: 0.5 g catalyst, 250 °C, 2 MPa, LHSV = 4 h -1 N2 / ethanol (v / v) = 250:1.

[0057] [b]AcH = Acetaldehyde; Ether = Diethyl ether; EA = Ethyl acetate; BuH = Butyraldehyde; BuOH = Butanol; >C6 alcohols mainly include 2-ethylbutanol, 1-hexanol, 2-ethyl-1-hexanol, octanol, etc.; others include 2-ethylbutanol, hexanal, 1,1-dioxane, butyl acetate, etc.

[0058] As shown in Tables 1-3, in the continuous catalytic synthesis of higher alcohols from ethanol, the Pd@UiO-66-CH3 catalyst exhibits high electron density and a hydrophobic microenvironment, thus demonstrating the highest ethanol conversion and higher alcohol yield among all Pd@UiO-66-X catalysts. The higher alcohol yield of this catalyst reached 47.7%, which is the highest yield reported to date.

Claims

1. Application of a ligand-functionalized MOF confined metal catalyst in the continuous catalytic synthesis of higher alcohols from ethanol; The catalyst is composed of the active metal component palladium and the support UiO-66-X; Based on the total mass of the catalyst, the mass percentage of palladium is 0.05~10%, with the remainder being the support; In the carrier UiO-66-X, X represents the functionalized group -CH3; during the synthesis of the carrier UiO-66-X, X is introduced by a terephthalic acid ligand containing the above-mentioned functionalized group; The products, higher alcohols, include n-butanol, 2-ethylbutanol, and n-hexanol.

2. The application as described in claim 1, characterized in that, The carrier UiO-66-X is a white powdery solid with a specific surface area of ​​900~1200 m². 2 / g, pore size 0.4~0.7 nm, pore volume 0.4~0.7 cm³ 3 / g, which belongs to the typical microporous materials.

3. The application as described in claim 1, characterized in that, The catalyst is prepared as follows: (1) ZrCl4 and terephthalic acid containing functional groups were added to N,N-dimethylformamide, then acetic acid and water were added, and the mixture was stirred and dissolved. The resulting mixture was transferred to a hydrothermal reactor and allowed to stand at 100~150 °C for 12~24 h. After cooling to room temperature, the mixture was collected by centrifugation and dried to obtain UiO-66-X solid. In terephthalic acid containing functionalized groups, the functionalized group is -CH3; (2) Dissolve the palladium precursor in a solvent, then add UiO-66-X and completely submerge it, stir and react at 20~100 °C for 2~48 h, then stir and evaporate to dryness at 100~160 °C to obtain a solid powder; place the obtained solid powder at 70~300 °C for 2~24 h, and cool to room temperature to obtain the target catalyst.

4. The application as described in claim 3, characterized in that, In step (2), the palladium precursor is selected from one or more of palladium chloride, palladium nitrate, palladium acetate, palladium propionate, palladium sulfate, palladium cyanide, palladium iodide, palladium dibromide, potassium chloropalladium, palladium trifluoroacetate, palladium acetylacetonate, bis(acetonitrile)palladium chloride, tetraaminopalladium nitrate, and hexafluoroacetylacetonate.

5. The application as described in claim 3, characterized in that, In step (2), the solvent is selected from one or more of methanol, ethanol, toluene, xylene, dichloromethane, chloroform, deionized water, N,N-dimethylformamide, and acetylacetone.

6. The application as described in claim 1, characterized in that, The application method is as follows: Ligand-functionalized MOFs confined metal catalysts were loaded into a fixed-bed reactor and reduced for 2–8 h under a mixed H2 / N2 atmosphere, 250–300 °C, and atmospheric pressure. Then, ethanol was introduced and the reaction was carried out at 200–300 °C and 1–4 MPa to synthesize higher alcohols.

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