Method for preparing one-shell multi-core watermelon seed type core-shell structure catalyst by one-pot method

Abstract

The invention discloses a method for in-situ synthesis of a one-shell and multi-core watermelon seed type core-shell structure catalyst by a one-pot method. The metal salt aqueous solution A, the oil phase reagent B and the surface reagent C are mixed to form the water-in-oil microemulsion. And adding a reagent F formed by mixing a back-extractant D and a silane reagent E into the microemulsion. Under the extraction action of the back extraction solvent D, the metal salt is gradually separated out in the micro-droplets in the form of tiny crystal grains due to the gradual removal of water. And the water extracted to the phase interface reacts with a silane reagent E to generate hydrolysis reaction to generate Si (OH) x to form a shell structure. The small crystalline particles coated with the Si (OH) x are bonded through the Si (OH) x to form a multi-core core-shell structure product G. And drying and roasting the solid product G to obtain the core-shell structure material. The method is simple in preparation process and can be applied to the field of preparation of high-temperature anti-sintering thermal catalysts.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and technology, and specifically relates to a one-pot method for preparing a core-shell structure catalyst of a multi-core watermelon seed type, which belongs to the field of core-shell structured nanomaterials and catalyst preparation. Background Technology

[0002] Core-shell materials are encapsulated structural materials consisting of an inner active metal core and an outer porous shell. They are ideal for stabilizing metal nanoparticles and minimizing metal sintering at high temperatures, and are widely used in biomedicine and catalysis. In a core-shell structure, active nanoparticles may be encapsulated or partially embedded in a shell-stabilized material, which acts as a physical barrier to inhibit particle migration and aggregation. Based on the number of cores, they are further classified into mononuclear and multinuclear core-shell materials. Multinuclear core-shell materials, with their greater number of cores, exhibit stronger drug delivery capabilities and catalytic activity in biomedicine and catalysis. Therefore, the preparation of multinuclear core-shell materials has received extensive research and attention.

[0003] Current methods for preparing multi-core-shell nanomaterials mainly include hydrolysis, precipitation, hydrothermal methods, and sol-gel methods. These synthetic processes typically involve two steps: first, synthesizing core nanoparticles, and then coating them through hydrolysis, precipitation, or hydrothermal processes. However, in the second coating step, the core nanoparticles dispersed in the solvent agglomerate significantly, making precise control over the core of the multi-core nanoparticles difficult. Existing methods for preparing core-shell nanomaterials are two-step processes, characterized by cumbersome procedures and poor reproducibility. These methods fall far short of meeting the current requirements for preparing core-shell nanomaterials. Therefore, there is an urgent need for a simple, controllable method for preparing core-shell nanomaterials that can achieve multi-core coating. Summary of the Invention

[0004] The purpose of this invention is to simplify the preparation process of multi-core core-shell materials and provide a one-pot method for synthesizing multi-core core-shell structured materials. This method utilizes the simultaneous hydrolysis of silane reagents to form the shell and the precipitation of metal precursor salts to form nuclei, resulting in a core-shell material with a uniformly dispersed core and a multi-core structure.

[0005] The specific preparation steps are as follows: (1) A water-in-oil microemulsion system is formed by stirring a metal salt aqueous solution A with a mass fraction of 0.1%~5%, an oil phase reagent B with a mass fraction of 30%~80%, and a surface reagent C with a mass fraction of 3%~30% at 15-60℃. (2) Mix and stir 50%~85% of the back-extraction agent D and 15%~50% of the silane reagent E to form reagent F; (3) Add reagent F slowly to the microemulsion system and react at 15-80℃ for 4-10 hours; (4) The solid product was obtained by filtration. The solid product was dried and calcined to obtain a core-shell structure catalyst with a multi-core coated shell.

[0006] The metal salt in the aqueous solution A is a mixture of one or more salts selected from acetate, oxalate, nitrate, and sulfate, and the metal is copper (Cu), zinc (Zn), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), calcium (Ca), or lanthanum (La). The oil phase reagent B is n-hexane, cyclohexane, n-heptane, or n-octane.

[0007] The surface reagent C is a mixture of a surfactant and a co-surfactant; the surfactant is polyethylene glycol hexadecyl ether, polyethylene glycol p-isooctylphenyl ether, hexadecyltrimethylammonium bromide, fatty alcohol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether; the co-surfactant is ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, 1-hexanol, 2-hexanol, 1-heptanol, 2-heptanol, 1-octanol, or 2-octanol.

[0008] The stripping agent D is acetone, ethyl acetate, acetonitrile, or tetrahydrofuran.

[0009] The silane reagent E is a mixture of one or more components selected from methyl orthosilicate, 3-aminopropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane.

[0010] Compared with the prior art, the present invention has the following advantages and beneficial effects: The core-shell structured catalyst prepared by the invention has strong metal-support interaction, high dispersion of active sites, significantly improved catalytic activity, simple preparation method, easy operation, easy control, and wide applicability. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the in-situ one-pot synthesis method for multinuclear core-shell structure catalysts according to an embodiment of the present invention.

[0012] Figure 2 This is a TEM image of the in-situ one-pot synthesis of a multinucleated core-shell catalyst according to an embodiment of the present invention.

[0013] Figure 3 This invention presents a comparison of the catalytic activity of a multinucleated core-shell structure catalyst synthesized in situ using a one-pot method with that prepared by a conventional impregnation method.

[0014] Figure 4This invention presents a comparison of the anti-sintering properties of catalysts synthesized by the in-situ one-pot method for multi-core core-shell structure in this embodiment of the invention with those prepared by the traditional impregnation method.

[0015] Figure 5 This is a comparison of XPS characterization results between the in-situ one-pot synthesis of multinuclear core-shell structure catalysts according to embodiments of the present invention and catalysts prepared by the traditional impregnation method.

[0016] Figure 6 This is a TEM image of the in-situ one-pot synthesis of a bimetallic one-shell multinucleate core-shell structure catalyst according to an embodiment of the present invention. Detailed Implementation

[0017] Example 1 The synthesis process of core-shell Ni@SiO2, and its preparation steps are as follows: A water-in-oil microemulsion system was formed by stirring at 50°C with 200 mL of cyclohexane as the organic phase, 3 mL of saturated nickel acetate (0.65 g) aqueous solution as the aqueous phase, and 25 g of polyethylene glycol hexadecyl ether as the surfactant. Then, 20 mL of acetone, 1 g of 3-aminopropyltrimethoxysilane, and 7 g of methyl orthosilicate were added to the microemulsion system via a syringe pump. After reacting at 50°C for 8 h, 100 mL of isopropanol was added, resulting in a green suspension. The solid was separated by filtration and dried overnight at 60°C to obtain a solid powder. Finally, the solid powder was calcined in air at 550°C for 2 h, and the resulting sample was labeled Ni@SiO2.

[0018] Example 2 Ni / (C)SiO2 catalyst was prepared by impregnation. The commercial SiO2 support was named (C)SiO2. In the synthesis process, 0.45 g of Ni(CH3COO)2·4H2O was dissolved in 40 mL of deionized water, then 1.9044 g of (C)SiO2 was added, and the mixture was sonicated for 30 min. After impregnation at 80 °C for 8 h, 100 mL of isopropanol was added, resulting in a green suspension in the system. The solid was separated by filtration and dried overnight at 60 °C to obtain a solid powder. Finally, the solid powder was calcined in air at 550 °C for 2 h, and the resulting sample was labeled Ni / (C)SiO2.

[0019] from Figure 2 As can be seen, the Ni@SiO2 catalyst prepared by the method of the present invention has a one-shell multi-core core-shell structure, with the core uniformly dispersed in the shell, and the metal particle size is 5 nm.

[0020] from Figure 3As can be seen, the Ni@SiO2 catalyst prepared by the method of this invention exhibits catalytic activity 35% higher than that of the corresponding impregnated Ni / (C)SiO2 catalyst in the methane dry reforming probe reaction test. The Ni@SiO2 catalyst maintained stable activity during the 25-hour activity test, while the Ni / (C)SiO2 catalyst showed a 20% decrease in activity during the 25-hour activity test.

[0021] from Figure 4 As can be seen, the Ni@SiO2 catalyst prepared by the method of this invention exhibits higher anti-sintering performance than the corresponding impregnation catalyst in the methane dry reforming probe reaction test, and the core metal particles maintain a size of 5 nm before and after use. The metal particles of the Ni / (C)SiO2 catalyst grow to more than 20 nm after use.

[0022] Figure 5 XPS characterization data analysis shows that the binding energy of Ni element in the Ni@SiO2 catalyst prepared by the method of the present invention has been significantly shifted to a higher position in XPS testing. This indicates that there is a strong interaction between the active sites of the core-shell structure catalyst and the support in this sample.

[0023] Example 3 The synthesis process of the core-shell Ni-M / (C)SiO2 bimetallic catalyst is as follows: A water-in-oil Co(NO3)2-Ni(NO3)2 / cyclohexane microemulsion was formed by stirring at 50 °C with 200 mL cyclohexane as the organic phase, 3 mL of a saturated aqueous solution (0.31 g Ni(NO3)2·6H2O, 0.312 g Co(NO3)2·6H2O) at a nickel-cobalt molar ratio of 1:1 as the aqueous phase, and 25 g polyethylene glycol hexadecyl ether as the surfactant. Then, 20 mL acetone, 1 g 3-aminopropyltrimethoxysilane, and 7 g methyl orthosilicate were added to the microemulsion system via a syringe pump. After reacting at 50 °C for 8 h, 100 mL isopropanol was added, resulting in a green suspension. The solid was separated by filtration and dried overnight at 60 °C to obtain a solid powder. Finally, the solid powder was calcined in air at 550 °C for 2 h, and the resulting sample was labeled NiCo@SiO2. Compared with the single-metal Ni@SiO2 catalyst, the size of the bimetallic core particles is also maintained at 5 nm, which indicates that the method of the present invention has universality and can also be used for the synthesis of multi-metal multi-core-shell materials.

Claims

1. A method for one-pot preparation of a core-shell structured catalyst of a multi-core watermelon seed type, characterized in that... Water in water-in-oil microdroplets is extracted to the microdroplet interface using an antisolvent. Silane reagents hydrolyze at the microdroplet interface to generate Si(OH)x, forming a shell. Metal salt precursors in the microdroplets precipitate out as multiple fine particles due to water loss. The precipitated fine particles constitute the multi-core of the core-shell structured material. The obtained solid is then calcined to form a core-shell structured material with one shell and multiple cores.

2. According to claim 1, the specific steps include: (1) A water-in-oil microemulsion system is formed by stirring a metal salt aqueous solution A with a mass fraction of 0.1%~5%, an oil phase reagent B with a mass fraction of 30%~80%, and a surface reagent C with a mass fraction of 3%~30% at 15-60℃. (2) Mix and stir 50%~85% of the back-extraction agent D and 15%~50% of the silane reagent E to form reagent F; (3) Add reagent F slowly to the microemulsion system and react at 15-80℃ for 4-10 hours; (4) The solid product is obtained by filtration and separation. The solid product is dried and calcined to obtain a core-shell structure catalyst with a multi-core coated shell.

3. The preparation method according to claim 1 or 2, characterized in that, The metal salt in the aqueous solution A is one or a mixture of more than one of the following: acetate, oxalate, nitrate, and sulfate; the metal is copper (Cu), zinc (Zn), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), calcium (Ca), or lanthanum (La).

4. The preparation method according to claim 1 or 2, characterized in that, The oil phase reagent B is n-hexane, cyclohexane, n-heptane, or n-octane.

5. The preparation method according to claim 1 or 2, characterized in that, The surface reagent C is a mixture of a surfactant and a co-surfactant; the surfactant is polyethylene glycol hexadecyl ether, polyethylene glycol p-isooctylphenyl ether, hexadecyltrimethylammonium bromide, fatty alcohol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether; the co-surfactant is ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, 1-hexanol, 2-hexanol, 1-heptanol, 2-heptanol, 1-octanol, or 2-octanol.

6. The preparation method according to claim 1 or 2, characterized in that, The stripping agent D is acetone, ethyl acetate, acetonitrile, or tetrahydrofuran.

7. The preparation method according to claim 1 or 2, characterized in that, The silane reagent E is a mixture of one or more components selected from methyl orthosilicate, 3-aminopropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane.

Images