A core-shell metal-organic framework-based UiO-66@SiO2-CN@Pd stabilized Pickering emulsion and its application in catalytic tandem reactions.
By preparing a core-shell structure-based UiO-66@SiO2-CN@Pd stabilized Pickering emulsion, the activity and stability issues of nano-MOFs in organic catalytic reactions were solved, achieving efficient catalyst recovery and stability, suitable for Suzuki-Knovenagel tandem reactions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LIAONING UNIVERSITY
- Filing Date
- 2026-03-12
- Publication Date
- 2026-06-19
AI Technical Summary
Existing homogeneous catalysts cannot be recycled in Suzuki-Knovenagel tandem reactions, and the synthesis of hydrophobic shells of nano-MOFs has not been effectively solved, affecting their activity and stability in organic catalytic reactions.
A stable Pickering emulsion was prepared using a core-shell metal-organic framework UiO-66@SiO2-CN@Pd emulsifier through surface modification and nanoparticle modification. This emulsion provides alkali-metal bifunctional active sites for catalyzing the Suzuki-Knovenagel tandem reaction.
It improves the hydrophobicity and stability of nanomaterials, enables efficient recycling of catalysts, maintains high catalytic activity and stability, and is suitable for Suzuki-Knovenagel tandem reactions.
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Figure CN122230804A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, specifically to a core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion and its application in catalytic tandem reactions. More specifically, it relates to the preparation and application of a metal-organic framework material-stabilized Pickering emulsion for catalyzing the Suzuki-Knoevenagel tandem reaction. Background Technology
[0002] Tandem reactions, a highly efficient, energy-saving, and environmentally friendly method of chemical synthesis, are increasingly attracting the interest of chemical researchers. The Suzuki cross-coupling reaction is one of the most effective methods for forming C-C bonds and generating asymmetric biaryl groups. Meanwhile, the Knovenagel condensation reaction is a method for producing α,β-unsaturated carbonyl compounds, widely used in the synthesis of chemicals, bioproducts, and pharmaceuticals. However, Knovenagel condensation reactions are generally catalyzed by homogeneous catalysts, which have the disadvantage of not being able to recycle the catalyst. Therefore, from both environmental and economic perspectives, developing heterogeneous catalysts capable of realizing these reactions is highly desirable.
[0003] Metal-organic frameworks (MOFs) have attracted widespread research interest due to their ultra-high specific surface area, tunable porosity, and adjustable composition. However, to ensure their practical application, many key issues, such as surface properties and structural stability, must be addressed. Layering mesoporous silica (mSiO2) shells can significantly improve the mechanical properties of encapsulated nano-MOFs. However, since mSiO2 is typically highly hydrophilic, synthesizing hydrophobic shells around nanocrystals remains a significant challenge. Organically modifying mSiO2 to make its surface hydrophobic greatly enhances its catalytic activity and stability in organocatalytic reactions.
[0004] Pickering emulsions are emulsions obtained using ultrafine solid particles as emulsifiers. These particles self-assemble at the interface of two immiscible liquids, preventing droplet coalescence and forming numerous water or oil microdroplets, significantly increasing the interfacial area between water and oil. Compared to traditional emulsions, Pickering emulsions have advantages such as low toxicity and high stability. Pickering interfacial catalysis shows broad application prospects in acid-catalyzed transesterification, oxidation, and acetal reactions. Summary of the Invention
[0005] To address the problems existing in the prior art, one of the objectives of this invention is to provide a UiO-66@SiO2-CN@Pd emulsifier that simultaneously possesses alkali-metal bifunctional active sites.
[0006] The technical solution adopted in this invention is as follows: a metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure, and the preparation method is as follows:
[0007] 1) Disperse UiO-66@SiO2, 3-aminopropyltriethoxysilane, and methyltriethoxysilane in toluene solution, heat for surface modification, centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2-CN;
[0008] 2) Take UiO-66@SiO2-CN and slowly add sodium chloropalladium solution dropwise while stirring vigorously. Stir and mix evenly. Add sodium borohydride to methanol. Sodium borohydride and methanol release hydrogen gas. Quickly pick up the upper layer of bubbly liquid and add it to the mixed solution of UiO-66@SiO2-CN and sodium chloropalladium. Continue stirring for 30 min. Centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2-CN@Pd powder.
[0009] In the above-mentioned metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure, step 1) involves heating at 110-120°C for 6-12 hours.
[0010] In the aforementioned metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure, in step 1), the mass ratio of UiO-66@SiO2, 3-aminopropyltriethoxysilane, and methyltriethoxysilane is 100:7.9:117.5.
[0011] In the aforementioned core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd emulsifier, step 1) involves the following preparation method for UiO-66@SiO2:
[0012] Step 1: Disperse ZrCl4 and terephthalic acid in DMF, add glacial acetic acid, and react in a hydrothermal reactor at 493 K for 24 h. Separate the resulting precipitate by centrifugation, wash, and vacuum dry to obtain UiO-66.
[0013] Step 2: Disperse UiO-66 in a mixed solution of water and ethanol, add hexadecyltrimethylammonium bromide under vigorous stirring, heat and add ammonia to adjust to alkalinity, add ethanol solution of tetraethyl orthosilicate dropwise, centrifuge, add the solid powder to anhydrous ethanol containing ammonium nitrate, heat and stir, centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2.
[0014] In step 2) of the above-mentioned metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure, the solid-liquid ratio is: UiO-66@SiO2-CN: sodium chloropalladium solution = 50 mg: 60 μL; sodium borohydride: methanol = (8.5-9.0) mg: 5 mL.
[0015] The second objective of this invention is to provide a method for preparing a core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion, comprising the following steps: ultrasonically dispersing UiO-66@SiO2-CN@Pd material in deionized water, adding ethyl acetate under stirring conditions, and shaking for 5-6 min to obtain the UiO-66@SiO2-CN@Pd Pickering emulsion.
[0016] According to the solid-liquid ratio, the volume of UiO-66@SiO2-CN@Pd: deionized water and ethyl acetate is (30-50) mg : 5 mL; according to the volume ratio, deionized water: ethyl acetate is (1-4) : (4-1); preferably, according to the solid-liquid ratio, the volume of UiO-66@SiO2-CN@Pd: deionized water and ethyl acetate is 40 mg : 5 mL; according to the volume ratio, deionized water: ethyl acetate is 3 : 2.
[0017] The third objective of this invention is to provide a core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion as a catalyst in the catalytic Suzuki-Knovenagel reaction.
[0018] Further, the method is as follows: Iodobenzene, phenylboronic acid, potassium carbonate, and a catalyst are placed in a reaction vessel and reacted at 313-353 K for 2-3 h; the catalyst is a UiO-66@SiO2-CN@Pd Pickering emulsion. After the first step of the reaction is completed, malononitrile is added and the reaction continues for 1 h.
[0019] Furthermore, in the molar ratio, iodobenzene: phenylboronic acid: malononitrile: potassium carbonate = 1 : (1-2) : (1-2) : (2-4).
[0020] In the UiO-66@SiO2-CN@Pd stabilized Pickering emulsion of this invention, palladium provides metal sites to catalyze the first step of the Suzuki reduction reaction, while functionalized SiO2 provides abundant basic sites to catalyze the second step of the Knovenagel reaction, thus synergistically catalyzing a tandem reaction. The reaction formula is as follows:
[0021]
[0022] The beneficial effects of this invention are as follows: In the Pickering emulsion UiO-66@SiO2-CN@Pd provided by this invention, the silica shell greatly improves the stability of UiO-66 and enriches the pore size of UiO-66, allowing chemical reactants and Pd nanoparticles to easily penetrate it, effectively preventing the aggregation of nanoparticles. Organic modification of the silica layer surface results in improved hydrophobic surface properties of the nanomaterial, enhancing its catalytic activity and stability in the Suzuki-Knovenagel reaction process. Furthermore, after five cycles, UiO-66@SiO2-CN@Pd still maintains high catalytic activity, exhibiting high stability and recyclability. The UiO-66@SiO2-CN@Pd of this invention demonstrates excellent catalytic performance in the Suzuki-Knovenagel tandem reaction. Attached Figure Description
[0023] Figure 1 This is an optical microscope image of the formed UiO-66@SiO2-CN@Pd Pickering emulsion.
[0024] Figure 2 This is a TEM image of UiO-66@SiO2-CN@Pd in the Picklein emulsion of the present invention.
[0025] Figure 3 This is the PXRD pattern of the UiO-66@SiO2-CN@Pd material in the Pickering emulsion of the present invention.
[0026] Figure 4 This is a catalytic activity diagram of the UiO-66@SiO2-CN@Pd Pickering emulsion of the present invention undergoing five cycles of catalytic reaction.
[0027] Figure 5 This is an optical micrograph of the emulsion formed by the catalyst recovered after five cycles of catalytic reaction of the UiO-66@SiO2-CN@Pd Pickering emulsion of the present invention. Detailed Implementation
[0028] Example 1: A core-shell metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion
[0029] (a) The preparation method is as follows:
[0030] 1. Synthesis of UiO-66 powder
[0031] Zirconium chloride (0.372 g, 1.60 mmol) and terephthalic acid (0.266 g, 1.60 mmol) were added to an 80 mL hydrothermal synthesis reactor. Then, 40 mL of DMF and 11 mL of 99.95% glacial acetic acid were accurately pipetted into the reactor. The mixture was stirred at room temperature for 30 min. The reactor was then placed in a 493 K oven for hydrothermal reaction for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The resulting precipitate was separated by centrifugation, washed three times with DMF, then three times with anhydrous ethanol, and finally dried in a vacuum drying oven at 353 K for 12 h to obtain the precursor UiO-66.
[0032] 2. Preparation of sodium chloropalladium solution
[0033] Accurately weigh 0.12 g of palladium chloride solid and 0.044 g of sodium chloride solid into a 10 mL glass bottle. Add 4 mL of methanol to the bottle, heat slightly until completely dissolved, and stir overnight. A 0.17 mol / L brown sodium chloropalladium solution is obtained.
[0034] 3. Synthesis of UiO-66@SiO2-CN powder
[0035] Accurately weigh 100 mg of UiO-66 and place it in a 250 mL three-necked reaction vessel. Use a pipette to accurately add 100 mL of deionized water and 20 mL of anhydrous ethanol. Then add hexadecyltrimethylammonium bromide (1.250 g, 3.40 mmol) to the three-necked reaction vessel and stir at room temperature for 1 h. Heat to 323 K, add 0.5 mL of ammonia water, and adjust the pH of the solution to 10. Then, using a syringe pump, slowly add 10 mL of a 5.8 g / L tetraethyl orthosilicate ethanol solution at a rate of 2 mL / h, and stir for 6 h. Centrifuge the resulting precipitate (6000 rpm, 3 min) to disperse the lower precipitate in 40 mL of anhydrous ethanol, add 2 g of ammonium nitrate, and stir at 353 K for 24 h. Centrifuge the resulting precipitate (6000 rpm, 3 min), wash three times with anhydrous ethanol and twice with acetone. Then, vacuum dry at 353 K for 24 h. UiO-66@SiO2 powder was obtained. 100 mg UiO-66@SiO2, 7.9 mg 3-aminopropyltriethoxysilane, and 117 mg methyltriethoxysilane were dispersed in 5 mL of toluene solution, and surface modification was performed by heating at 110 °C for 6 h. After centrifugation, washing, and vacuum drying, UiO-66@SiO2-CN was obtained.
[0036] 4. Synthesis of UiO-66@SiO2-CN@Pd powder
[0037] Accurately weigh 40 mg of UiO-66@SiO2-CN and place it in a 5 mL glass bottle. Use a pipette to accurately transfer 58.82 μL of a 0.17 mol / L sodium chloropalladium solution into the glass bottle in multiple portions to ensure more uniform dispersion. Accurately weigh 8.62 mg of sodium borohydride solid and add it to 5 mL of methanol solution. The reaction of sodium borohydride and methanol releases hydrogen gas. Quickly pipette the bubbly upper layer of liquid and add it to the glass bottle. Continue stirring for 0.5 h until the final solution turns black. Wash three times with methanol and finally place in a 353 K vacuum drying oven for 6 h to obtain black crystals, which is the UiO-66@SiO2-CN@Pd material.
[0038] 5. Preparation of UiO-66@SiO2-CN@Pd stabilized Pickering emulsion
[0039] Add 2 mL of ethyl acetate and 3 mL of deionized water to 40 mg of UiO-66@SiO2-CN@Pd, respectively, sonicate at 100 W for 5 min, and then shake vigorously for 5 min to obtain a UiO-66@SiO2-CN@Pd stable Pickering emulsion.
[0040] (II) Testing
[0041] Figure 1 This is an optical microscope image of the formed UiO-66@SiO2-CN@Pd Picklerm emulsion. It can be seen that the stable UiO-66@SiO2-CN@Pd Picklerm emulsion droplets are uniformly dispersed and of uniform size.
[0042] Figure 2 The image is a transmission electron microscope (TEM) image based on UiO-66@SiO2-CN@Pd material, showing that Pd nanoparticles are uniformly dispersed in UiO-66@SiO2-CN@Pd material.
[0043] Figure 3 The X-ray diffraction (PXRD) pattern of the UiO-66@SiO2-CN@Pd material shows that the UiO-66@SiO2-CN@Pd material has good crystallinity during the synthesis and preparation process.
[0044] Example 2: Catalytic function of UiO-66@SiO2-CN@Pd material for the Suzuki-Knovenagel tandem reaction
[0045] (i) The Suzuki-Knovenagel tandem reaction was catalyzed using a Pickering emulsion based on a core-shell metal-organic framework UiO-66@SiO2-CN@Pd prepared in Example 1 as a catalyst.
[0046] The method is as follows:
[0047] 40 mg of the UiO-66@SiO2-CN@Pd Pickering emulsion obtained in step 5 of Example 1 was added to a 10 mL three-necked reaction vessel, followed by the sequential addition of 1 mmol iodobenzene, 1.5 mmol phenylboronic acid, and 3 mmol K2CO3. The reaction was carried out at 333 K for 2 h, and then 1.5 mmol malononitrile was added, followed by a further 1 h of reaction to generate an N-benzylide aniline derivative. The yield of the product was monitored by gas chromatography (GC).
[0048] During the reaction, the catalytic performance of the UiO-66@SiO2-CN@Pd stabilized Pickering emulsion on the tandem reaction was detected by GC. As the reaction proceeded, the yield of the reaction gradually increased, and the yield of the reaction reached 99% after 4 h.
[0049] (II) Reuse of Pickering emulsion based on UiO-66@SiO2-CN@Pd
[0050] After the reaction was completed, the reaction mixture was centrifuged and filtered to separate it from UiO-66@SiO2-CN@Pd. The mixture was then washed with ethanol, filtered, and dried. The UiO-66@SiO2-CN@Pd material was recovered.
[0051] The specific operation of the cyclic experiment: the recycled UiO-66@SiO2-CN@Pd material was used to prepare the Pickering emulsion-catalyzed Suzuki-Knovenagel tandem reaction again.
[0052] Figure 4 This is a catalytic activity graph of the UiO-66@SiO2-CN@Pd Pickering emulsion after five cycles of catalytic reaction. After five cycles, the yield and conversion rates were both above 95%, indicating that the catalyst activity did not decrease significantly. Figure 5 The image shows an optical micrograph of the emulsion formed after five cycles of catalytic reaction of the UiO-66@SiO2-CN@Pd Pickering emulsion. The image demonstrates that the recovered catalyst can still stably form the Pickering emulsion. This indicates that UiO-66@SiO2-CN@Pd in this Pickering emulsion can be recycled as a catalyst for the Suzuki-Knovenagel tandem reaction.
Claims
1. A metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure, characterized in that, The preparation method is as follows: 1) Disperse UiO-66@SiO2, 3-aminopropyltriethoxysilane, and methyltriethoxysilane in toluene solution, heat for surface modification, centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2-CN; 2) Take UiO-66@SiO2-CN and slowly add sodium chloropalladium solution dropwise while stirring vigorously. Stir and mix evenly. Add sodium borohydride to methanol. Sodium borohydride and methanol release hydrogen gas. Quickly pick up the upper layer of bubbly liquid and add it to the mixed solution of UiO-66@SiO2-CN and sodium chloropalladium. Continue stirring for 30 min. Centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2-CN@Pd powder.
2. The metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure according to claim 1, characterized in that, In step 1), the heating is carried out at 110-120℃ for 6-12 hours.
3. The metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure according to claim 1, characterized in that, In step 1), the mass ratio of UiO-66@SiO2, 3-aminopropyltriethoxysilane, and methyltriethoxysilane is 100:7.9:117.
5.
4. The metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure according to claim 1, characterized in that, In step 1), the preparation method of UiO-66@SiO2 is as follows: Step 1: Disperse ZrCl4 and terephthalic acid in DMF, add glacial acetic acid, and react in a hydrothermal reactor at 493 K for 24 h. Separate the resulting precipitate by centrifugation, wash, and vacuum dry to obtain UiO-66. Step 2: Disperse UiO-66 in a mixed solution of water and ethanol, add hexadecyltrimethylammonium bromide under vigorous stirring, heat and add ammonia to adjust to alkalinity, add ethanol solution of tetraethyl orthosilicate dropwise, centrifuge, add the solid powder to anhydrous ethanol containing ammonium nitrate, heat and stir, centrifuge, wash, and vacuum dry to obtain UiO-66@SiO2.
5. The metal-organic framework UiO-66@SiO2-CN@Pd emulsifier based on a core-shell structure according to claim 1, characterized in that, In step 2), according to the solid-liquid ratio, UiO-66@SiO2-CN: sodium chloropalladium solution = 50 mg : 60 μL; sodium borohydride: methanol = (8.5-9.0) mg : 5 mL.
6. A core-shell metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion, characterized in that, It is prepared by shaking and mixing the UiO-66@SiO2-CN@Pd emulsifier as described in any one of claims 1-5 with deionized water and ethyl acetate.
7. A core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion according to claim 6, characterized in that, According to the solid-liquid ratio, the volume of UiO-66@SiO2-CN@Pd: deionized water and ethyl acetate is (30-50) mg : 5 mL; according to the volume ratio, deionized water: ethyl acetate is (1-4) : (4-1); preferably, according to the solid-liquid ratio, the volume of UiO-66@SiO2-CN@Pd: deionized water and ethyl acetate is 40 mg : 5 mL; according to the volume ratio, deionized water: ethyl acetate is 3 :
2.
8. The application of the core-shell structured metal-organic framework UiO-66@SiO2-CN@Pd stabilized Pickering emulsion as described in claim 6 or 7 as a catalyst in the catalytic Suzuki Knoevenagel reaction.
9. The application according to claim 8, characterized in that, The method is as follows: Iodobenzene, phenylboronic acid, malononitrile, potassium carbonate and catalyst are placed in a reaction vessel and reacted at 313-353 K for 2-3 h; the catalyst is the UiO-66@SiO2-CN@Pd Pickering emulsion as described in any one of claims 1-6.
10. The application according to claim 9, characterized in that, The molar ratio is iodobenzene: phenylboronic acid: malononitrile: potassium carbonate: catalyst = 1 : (1-2) : (1-2) : (2-4).