CN104815685A - A kind of magnetic multilevel core@shell structure nano-palladium catalyst and preparation method thereof - Google Patents

Abstract

A magnetic multilevel core-shell structure nano-palladium catalyst and a preparation method thereof belong to the field of magnetic nano-catalysis materials. The general formula of the material is Fe ₃ O ₄ MAl-LDHxPd ⁰ ; where MAl-LDH is shell hydrotalcite, M is one or two divalent metal elements, and x is the loading amount of palladium in mass percentage. LDH nanocrystals were assembled on the surface of Fe ₃ O ₄ magnetic core by low-temperature double-drop co-precipitation method, and the shell layer of LDH hexagonal nanocrystals grew interlacedly in the form of ab-plane perpendicular to the surface of the magnetic core, showing a honeycomb-like morphology. Palladium nanoparticles were supported on the magnetic multi-level core-shell structure carrier by impregnation reduction method, and a class of magnetic multi-level core-shell structure nano-palladium catalyst was obtained, and the palladium nanoparticles were evenly distributed on the edge and interlaced parts of LDH nanocrystals. The obtained catalyst was used in the Heck coupling reaction of iodobenzene and styrene, and showed good catalytic activity, with the highest TOF value of 160.5h ^-1 . It was recovered by an external magnetic field, and the catalytic activity did not decrease significantly after being used for 10 times.

Description

A kind of magnetic multilevel core-shell structure nano-palladium catalyst and preparation method thereof

technical field

The invention belongs to the technical field of magnetic nano-catalysis materials, and in particular relates to a magnetic multi-level core-shell structure nano-palladium catalyst and a preparation method thereof. The magnetic nano-palladium catalyst can be applied to the fields of carbon-carbon coupling, olefin hydrogenation, alcohol oxidation, etc. .

Background technique

In the field of organic synthesis, carbon-carbon coupling reaction is a kind of chemical reaction with good substrate applicability, which is widely used in the synthesis of organic intermediates. Common carbon-carbon coupling reaction catalysts mainly use transition metals such as copper, nickel, and palladium as active species. Among them, homogeneous palladium catalysts, especially palladium catalysts containing organophosphine ligands, have attracted much attention due to their excellent catalytic activity, but there are also problems such as sensitivity to air and moisture and difficulty in recovery. Therefore, it is of great practical significance to select suitable support materials to prepare green and efficient heterogeneous palladium catalysts.

Anionic clay hydrotalcite (Layered double hydroxides) is a typical two-dimensional layered material. Hydrotalcite materials can be directly bonded to metal palladium nanoparticles to form supported palladium catalysts through hydrogen-like hydrogen bonds acting on the surface, such as Pd-HO bonds between metal bonds and covalent bonds, which can be applied to carbon-carbon coupling , olefin hydrogenation and alcohol oxidation and other fields. Choudary et al. (BMChoudary, Sattesh Madhi, NSChowdari, et al., J.Am.Chem.Soc., 2002, 124, 14127-14136) used magnesium aluminum hydrotalcite intercalated with chloride ions as a precursor, and ion exchange PdCl ₄ ^2- is introduced into the interlayer, and then PdCl ₄ ^2- is reduced with hydrazine hydrate in ethanol to obtain a zero-valent palladium catalyst supported by magnesium aluminum hydrotalcite, and the palladium nanoparticle size is 4-6 nm. The catalytic activity of ether-styrene Heck coupling reaction is obviously better than that of Pd/C and Pd/Al ₂ O ₃ . Li et al. (P.Li, PPHuang, FFWei, et al., J.Mater.Chem.A, 2014, 2, 12739-12745) synthesized flower-shaped cobalt-aluminum hydrotalcite with urea as the base by hydrothermal method, and then passed through the layer The in-situ redox process of plate Co ²⁺ and PdCl ₄ ^2- supports palladium nanoclusters on the surface of the carrier to obtain a palladium catalyst with a hierarchical flower structure, and the palladium nanoparticle size is about 2nm. Suzuki coupling reaction, the product yield reached 98% after 5 minutes of reaction. Although a single hydrotalcite-supported palladium catalyst can be recycled by conventional solid-liquid separation methods such as centrifugation and filtration, it still consumes a lot of time and manpower. Magnetically functionalized heterogeneous nanocatalysts can be rapidly separated by means of an external magnetic field, thus effectively solving the problems of low separation efficiency and time-consuming of conventional palladium catalysts. Ay et al. (ANAy, NVAbramova, Deniz Konuk, et al., Inorg.Chem.Commun., 2013, 27, 64-68) intercalated NO ₃ ^-ions into magnesium aluminum hydrotalcite and ferroferric oxide magnetic nanoparticles (15 ~25nm) mechanically mixed for more than 48h to prepare magnetic magnesium aluminum hydrotalcite carrier, and then directly support Pd ₂ (dba) ₃ species in toluene, the obtained catalyst is close to spherical, but most of the hydrotalcite nanosheets and ferroferric oxide magnetic nanoparticles It is isolated in a free state, and its specific saturation magnetization is only 2.53emu/g. It is used to catalyze the Heck coupling reaction of iodobenzene and ethyl acrylate. The conversion rate of iodobenzene reaches 100% in 10 minutes, but its recycling performance has not been reported. Zhang et al. (Chinese invention patent: ZL 201010224523.6) reported a novel class of "honeycomb" magnetic multilevel core-shell structure MgAl hydrotalcite-based nano-gold catalysts. Loaded on the surface of hydrotalcite nanosheets, the catalyst is used to catalyze the oxidation reaction of 1-phenylethanol, and the conversion rate can reach 100% after 3 hours of reaction, and the catalyst has good superparamagnetism, and there is no activity reduction after 5 times of recycling. However, so far, there is no report on a magnetic hierarchical core-shell structured hydrotalcite-based nano-palladium catalyst with clear structure and controllable morphology.

Therefore, this patent intends to use the improved double-drop co-precipitation method to orderly assemble hydrotalcite nanocrystals of different compositions on the surface of Fe ₃ O ₄ magnetic nanoparticles to obtain a series of magnetic multi-level core-shell structure hydrotalcite composite carriers. A simple impregnation reduction method is used to load palladium nanoparticles on the above-mentioned composite carrier to prepare a class of ligand-free nano-palladium heterogeneous catalyst with magnetic multilevel core-shell structure. The material combines the basic characteristics of the hydrotalcite material itself, the dispersing effect of the laminates on the palladium complex anions (such as PdCl ₄ ^2- ions) and the excellent superparamagnetism of the Fe ₃ O ₄ magnetic nanoparticles, and realizes the precious metal palladium. use efficiently. This type of catalyst is expected to be used in organic synthesis fields such as carbon-carbon coupling catalysis, olefin hydrogenation and alcohol oxidation.

Contents of the invention

The object of the present invention is to provide a magnetic multilevel core-shell structure nano-palladium catalyst and a preparation method thereof, a "honeycomb" magnetic multi-level core-shell structure hydrotalcite-based nano-palladium catalyst and a preparation method thereof.

This type of catalyst uses Fe ₃ O ₄ magnetic nanoparticles as the core, CO ₃ ^{2- intercalated} MgAl, CoAl, NiAl, NiMgAl, CoMgAl and NO ₃ -intercalated CaMgAl-LDH as the shell structure, without ligand zero Palladium nanoparticles are uniformly loaded on the edge and interlaced parts of the shell hydrotalcite hexagonal sheets; the chemical formula of this type of catalyst is Fe ₃ O ₄ MAl-LDHxPd ⁰ , where the ab-plane of MAl-LDH is perpendicular to Fe ₃ O ₄ surface and interlaced growth shell layer hydrotalcite hexagonal nanocrystals, Pd ⁰ is ligand-free zero-valent palladium nanoparticles evenly distributed on the edge and staggered parts of MAl-LDH hexagonal nanocrystals, x is the mass percentage loading of palladium, The unit is wt%; wherein, the mass percentages of each component are:

_Fe3O4 : 35.3～49.8% _;

MAl-LDH: 47.7～61.5%;

Pd ⁰ : 0.18 to 3.43%.

Where M is one or two divalent metals, which can be Mg, Ni, Co, NiMg, CoMg and CaMg; the interlayer anion of shell MAl-LDH can be CO ₃ ^2- or NO ₃ ^- anion.

The overall particle size of the magnetic palladium catalyst is 400-600nm, the specific saturation magnetization is 38.6-54.9emu/g, the specific surface area is 63-74m ² /g; the thickness of the hydrotalcite shell is 80-120nm, and the single hydrotalcite nanocrystal The size of the palladium nanoparticles is 65-100nm, the thickness is 8-10nm, the size of the pores between the hydrotalcite nanocrystals is 55-110nm; the size of the palladium nano-particles is 3.9-12.1nm.

This type of catalyst has good catalytic activity for the Heck coupling reaction of iodobenzene and styrene, especially Fe ₃ O ₄ CoAl-LDH0.80Pd ⁰ when the catalyst usage is 0.601mol%, the reaction temperature is 120°C, and the reaction medium is Under the reaction conditions of N,N-dimethylformamide, the TOF value is as high as 160.5h ^-1 , and the activity does not decrease significantly after being recycled for 10 times.

The present invention uses laboratory self-made Fe ₃ O ₄ magnetic nanoparticles as the core, and assembles a MAl-LDH shell structure on its surface by a double-drop co-precipitation method in an ice-water bath or at room temperature (wherein, M is one or two kinds of two Valence metals, which can be Mg, Ni, Co, CaMg, NiMg and CoMg), without additional heating crystallization process, and then load zero-valent palladium nanoparticles on the above-mentioned magnetic hydrotalcite by impregnation reduction method to obtain a class of multi-level core-shell Structure and "honeycomb"-like morphology of hydrotalcite-based ligand-free nano-palladium magnetic catalysts. The specific process steps are as follows:

(1) Preparation of magnetic nanoparticles

The preparation of ferroferric oxide magnetic nanoparticles by a surfactant-free solvothermal method is the same as the Chinese invention patent: ZL201110344754.5.

Weigh 2.16g FeCl ₃ 6H ₂ O and dissolve in 80mL ethylene glycol in a water bath at 30-50°C to obtain a uniform and stable orange solution with a concentration of 0.1mol/L; add 5.76g NaAc 3H ₂ O, slowly Stir until completely dissolved to avoid bubbles, the molar ratio of NaAc·3H ₂ O to FeCl ₃ ·6H ₂ O is 5.29; transfer to a 100mL self-generating pressure vessel lined with polytetrafluoroethylene, and react at 200°C for 8h. Naturally cool to room temperature, use NdFeB permanent magnets for magnetic separation, wash with ethanol and deionized water for 5 times, and dry at 60°C for 24-48 hours to obtain black powdery magnetic nanoparticles, which are recorded as Fe ₃ O ₄ .

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

The magnetic multi-level core-shell structure hydrotalcite carrier was prepared by an improved double-drop co-precipitation method.

Step 1: Divalent metal salts and aluminum salts are formulated with water at a molar concentration ratio of M ²⁺ /Al ³⁺ = 3 to form a mixed salt solution with a concentration of 0.03-0.09 mol/L; additionally prepare NaOH and Na ₂ CO ₃ , the concentration of NaOH is 0.2mol/L, and the concentration of Na ₂ CO ₃ is 0.06mol/L (the only solute in the alkali solution in the magnetic CaMgAl-LDH system is NaOH); weigh 1.042g Fe ₃ O ₄ Magnetic nanoparticles (prepared by solvothermal method without surfactant, about 400nm) are ultrasonically dispersed in 100mL water for 20min to form a black suspension, in which the molar ratio of the divalent element M in the hydrotalcite laminate to the Fe element in the magnetic core is 0.25-0.75 ;

Where M is one or more divalent metals, which can be Mg, Ni, Co, CaMg, NiMg or CoMg, and the anion of the soluble M salt and Al salt is NO ₃ ^- or Cl ^- .

The second step: put the Fe ₃ O ₄ suspension in a 500mL four-neck flask, and stir it mechanically rapidly (the magnetic CaMgAl-LDH system needs to be protected with a nitrogen atmosphere). In an ice-water bath (magnetic CoAl and CoMgAl-LDH systems) or room temperature (magnetic MgAl, NiAl, NiMgAl and CoMgAl-LDH systems), slowly adjust the pH value of the Fe ₃ O ₄ suspension to the desired value ( For the magnetic MgAl, NiAl, CoAl, NiMgAl and CoMgAl-LDH systems, the precipitation pH is adjusted to 10; for the magnetic CaMgAl-LDH system, the precipitation pH is adjusted to 11.5), and it is stable for 5-10 minutes, then the mixed salt solution and the mixed alkali solution are simultaneously Slowly add dropwise to the above suspension at a rate of 1-1.5mL/min. During the dropwise addition, keep the pH of the slurry constant. After the mixed salt solution is added dropwise, stop adding the mixed lye and continue to stir the slurry for 5 minutes. .

Step 3: Use NdFeB permanent magnets to magnetically separate the black solid product, wash the above solid with deionized water for several times until the pH of the supernatant is neutral, and dry at 60°C for 24-48h (the magnetic CaMgAl-LDH system requires vacuum drying ), and ground to obtain a black powdery magnetic multi-level core-shell structure hydrotalcite carrier, which is denoted as Fe ₃ O ₄ MAl-LDH.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

The zero-valent palladium nanoparticles are loaded on the above-mentioned magnetic multilevel core-shell structure hydrotalcite carrier by impregnation reduction method.

Weigh 1 g of the above-mentioned magnetic multi-level core-shell structure hydrotalcite carrier Fe ₃ O ₄ MAl-LDH and disperse it in 100 mL of ethanol, and stir it rapidly mechanically. Add 0.17-8.33mL potassium tetrachloropalladate aqueous solution (0.56mol/L) into the above suspension. Subsequently, 1 mL of hydrazine hydrate was added and reduced at 25° C. for 3 h. Use NdFeB permanent magnets to magnetically separate the black solid, wash it with ethanol and deionized water several times until neutral, dry it in vacuum at 60°C for 24-48 hours, and grind it to obtain a black powdery magnetic multi-level core-shell structure nano-palladium catalyst. It is Fe ₃ O ₄ MAl-LDHxPd ⁰ (x=0.18～3.43).

Among them, in the synthesis steps of Fe ₃ O ₄ CaMgAl-LDHxPd ⁰ , all experimental water was deionized water boiled and decarbonated.

The advantages of the present invention are:

[1] For the first time at room temperature, magnesium-aluminum, nickel-aluminum, nickel-magnesium-aluminum and calcium-magnesium with magnetic multi-level core-shell structure and "honeycomb" shape were prepared by double-drop co-precipitation method without additional heating crystallization process Aluminum hydrotalcite carrier material; wherein, the magnetic CaMgAl-LDH carrier material needs to be protected by a nitrogen atmosphere during the synthesis process, and the required alkaline solution only uses NaOH as the solute.

[2] For the first time, cobalt-aluminum and cobalt-magnesium-aluminum hydrotalcite carrier materials with magnetic multi-level core-shell structure and "honeycomb" morphology were prepared by double-drop co-precipitation method without additional heating crystallization process under ice-water bath conditions.

[3] For the first time, potassium tetrachloropalladate was used as the palladium source, and the above six kinds of magnetic hydrotalcite carrier materials were loaded with ligand-free zero-valent palladium nanoparticles by a simple impregnation reduction method, and six kinds of magnetic multi-level core-shell materials were obtained respectively. Structure and "honeycomb"-like morphology of magnetic nano-palladium catalysts.

[4] Using the green solvent—water as the co-precipitation medium, by adjusting the conditions for the vertical orientation growth of hydrotalcite on the surface of the magnetic core, such as the type and concentration of metal nitrate/chloride salt, nucleation temperature and precipitation pH, etc., the Control of parameters such as chemical composition, morphology and structural characteristics, and magnetic properties of magnetic nano-palladium catalysts.

[5] Using magnetic cobalt-aluminum hydrotalcite with a magnetic multi-level core-shell structure and a "honeycomb" shape as a carrier to support ligand-free zero-valent palladium nanoparticles, the obtained catalyst has a palladium loading of 0.80% and a usage amount of 0.601 Under the conditions of mol %, reaction temperature of 120℃ and reaction medium of N,N-dimethylformamide, the TOF value of conversion frequency in the heck coupling process of catalytic iodobenzene and styrene is up to 160.5h ^-1 .

Description of drawings

Fig. 1 is a TEM spectrum of Fe ₃ O ₄ magnetic nanoparticle samples in Examples 1-7.

Fig. 2 is the SEM spectrum of the magnetic hierarchical structure hydrotalcite carrier Fe ₃ O ₄ MgAl-LDH in Example 1 and Example 7.

FIG. 3 is the SEM spectrum of the magnetic hierarchical nano-palladium catalyst Fe ₃ O ₄ MgAl-LDH3.32Pd ⁰ in Example 1.

Fig. 4 is the SEM spectrum of the magnetic hierarchical structure hydrotalcite carrier Fe ₃ O ₄ NiAl-LDH in Example 3 and Example 6.

FIG. 5 is the SEM spectrum of the magnetic hierarchical nano-palladium catalyst Fe ₃ O ₄ NiAl-LDH3.17Pd ⁰ in Example 3.

Detailed ways

Example 1

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ . Transmission electron microscopy results (accompanying drawing 1) show that gained Fe ₃ O ₄ magnetic nanoparticles are spherical particles with a particle diameter of about 400nm; the magnetic strength test results of the vibrating sample show that it has typical superparamagnetism, and the specific saturation magnetization is 76.5emu/g .

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. Dissolve 2.310 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 1.125 g of Al(NO ₃ ) ₃ ·9H ₂ O in 100 mL of water to obtain a mixed salt solution. Dissolve 0.640g of Na ₂ CO ₃ and 0.800g of NaOH in 100mL of water as an alkaline solution. In a water bath at 25°C, slowly drop a small amount of alkali solution into the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multilevel core-shell structure hydrotalcite carrier, which was designated as Fe ₃ O ₄ MgAl-LDH. The results of scanning electron microscopy (attached figure 2) and transmission electron microscopy show that the shell hydrotalcite nanosheets grow interlaced with each other and the ab-plane is perpendicular to the surface of the magnetic core. , the size of a single hydrotalcite nanosheet is about 100nm, and the thickness is about 10nm; the test results of the magnetic strength of the vibrating sample show that its specific saturation magnetization is 36.1emu/g.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above Fe ₃ O ₄ MgAl-LDH and disperse it in 100 mL of ethanol. 8.33 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ MgAl-LDH3.32Pd ⁰ . The composition mass percentage of this magnetic nano-palladium catalyst after characterization is: Fe ₃ O ₄ nanoparticles are 37.1%, hydrotalcites are 59.6%, and palladium is 3.32%; Scanning electron microscope (accompanying drawing 3) shows that its shell hydrotalcite nanosheets interact Staggered growth and the ab-plane is perpendicular to the surface of the magnetic core, the overall surface morphology is "honeycomb" and the dispersion is good; high-resolution transmission electron microscopy shows that the average size of palladium nanoparticles is 12.1nm; the test results of the magnetic strength of the vibrating sample show that the catalyst is The specific saturation magnetization is 38.6emu/g; the specific surface area-pore size analysis shows that the specific surface area of the catalyst is 63.5m ² /g.

Example 2

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. 2.622g Co(NO ₃ ) ₂ ·6H ₂ O and 1.125g Al(NO ₃ ) ₃ ·9H ₂ O were dissolved in 100 mL of water to obtain a mixed salt solution. Dissolve 0.640g of Na ₂ CO ₃ and 0.800g of NaOH in 100mL of water as an alkaline solution. In an ice-water bath at 0°C, slowly drop a small amount of alkali solution to the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was designated as Fe ₃ O ₄ CoAl-LDH. The test results of the magnetic strength of the vibrating sample show that its specific saturation magnetization is 43.3emu/g; the results of scanning and transmission electron microscopy show that the shell hydrotalcite nanosheets grow interlaced and the ab-plane is perpendicular to the surface of the magnetic core, showing a "honeycomb" shape as a whole The surface morphology and dispersion are good, the thickness of the hydrotalcite shell is about 100nm, the size of a single hydrotalcite nanosheet is about 76nm, and the thickness is about 10nm.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above Fe ₃ O ₄ CoAl-LDH and disperse it in 100 mL of ethanol. 8.33 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ CoAl-LDH3.43Pd ⁰ . The composition mass percentage of the magnetic nano _- palladium catalyst is characterized as follows: 48.9% of _Fe3O4 nanoparticles, 47.7% of hydrotalcite, and 3.43% of palladium; scanning and transmission electron microscopy results show that the shell hydrotalcite nanosheets are interlaced and grown And the ab-plane is perpendicular to the surface of the magnetic core, showing a "honeycomb" surface morphology and good dispersion; the results of high-resolution transmission electron microscopy show that the average size of palladium nanoparticles is 7.5nm; the test results of the magnetic strength of the vibrating sample show that the ratio The saturation magnetization is 54.9emu/g; the specific surface area-pore size analysis shows that the specific surface area of the catalyst is 64.1m ² /g.

Example 3

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. 2.620g Ni(NO ₃ ) ₂ ·6H ₂ O and 1.125g Al(NO ₃ ) ₃ ·9H ₂ O were dissolved in 100mL water to obtain a mixed salt solution. Dissolve 0.640g of _Na2CO3 and 0.800g of _NaOH in 100mL of water as an alkaline solution. In a water bath at 25°C, slowly drop a small amount of alkali solution into the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was denoted as Fe ₃ O ₄ NiAl-LDH. The test results of the magnetic strength of the vibrating sample show that its specific saturation magnetization is 43.4emu/g; the results of scanning electron microscopy (figure 4) and transmission electron microscopy show that the shell hydrotalcite nanosheets are interlaced and the ab-plane is perpendicular to the surface of the magnetic core. The overall surface morphology is "honeycomb" shape, the thickness of the hydrotalcite shell is about 80nm, the size of a single hydrotalcite nanosheet is about 65nm, and the thickness is about 8nm.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above-mentioned Fe ₃ O ₄ NiAl-LDH and disperse it in 100 mL of ethanol. 8.33 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ NiAl-LDH3.43Pd ⁰ . The composition mass percent of this magnetic nano-palladium catalyst through characterization is: Fe ₃ O ₄ nanoparticles are 35.3%, hydrotalcites are 61.5%, and palladium is 3.17%; Scanning electron microscope (accompanying drawing 5) and transmission electron microscope result show that its shell water The talc nanosheets grow alternately and the ab-planes are perpendicular to the surface of the magnetic core, showing a "honeycomb" surface morphology and good dispersion; the results of high-resolution transmission electron microscopy show that the average size of palladium nanoparticles is 6.7nm; the magnetic strength of the vibration sample The test results show that the specific saturation magnetization of the catalyst is 44.3emu/g; the specific surface area-pore size analysis shows that the specific surface area of the catalyst is 74.1m ² /g.

Example 4

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. 2.622g Co(NO ₃ ) ₂ ·6H ₂ O and 1.125g Al(NO ₃ ) ₃ ·9H ₂ O were dissolved in 100 mL of water to obtain a mixed salt solution. Dissolve 0.640g of Na ₂ CO ₃ and 0.800g of NaOH in 100mL of water as an alkaline solution. In an ice-water bath at 0°C, slowly drop a small amount of alkali solution to the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was denoted as Fe ₃ O ₄ CoAl-LDH, and its structure The morphology and magnetic properties are the same as in Example 2.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above Fe ₃ O ₄ CoAl-LDH and disperse it in 100 mL of ethanol. 1.67 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ CoAl-LDH0.80Pd ⁰ . It is characterized that the palladium content of the magnetic nano palladium catalyst is 0.80%, and the palladium particle size is 3.9nm.

Example 5

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. 2.622g Co(NO ₃ ) ₂ ·6H ₂ O and 1.125g Al(NO ₃ ) ₃ ·9H ₂ O were dissolved in 100 mL of water to obtain a mixed salt solution. Dissolve 0.640g of Na ₂ CO ₃ and 0.800g of NaOH in 100mL of water as an alkaline solution. In an ice-water bath at 0°C, slowly drop a small amount of alkali solution to the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was denoted as Fe ₃ O ₄ CoAl-LDH, and its structure The morphology and magnetic properties are the same as in Example 2.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above Fe ₃ O ₄ CoAl-LDH and disperse it in 100 mL of ethanol. 5.00 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ CoAl-LDH2.51Pd ⁰ . It is characterized that the palladium content of the magnetic nano palladium catalyst is 2.51%, and the palladium particle size is 5.8nm.

Example 6

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. 2.620g Ni(NO ₃ ) ₂ ·6H ₂ O and 1.125g Al(NO ₃ ) ₃ ·9H ₂ O were dissolved in 100mL water to obtain a mixed salt solution. Dissolve 0.640g of _Na2CO3 and 0.800g of _NaOH in 100mL of water as an alkaline solution. In a water bath at 25°C, slowly drop a small amount of alkali solution into the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by NdFeB permanent magnets, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was denoted as Fe ₃ O ₄ NiAl-LDH, and its structure The morphology and magnetic properties are the same as in Example 3.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above-mentioned Fe ₃ O ₄ NiAl-LDH and disperse it in 100 mL of ethanol. 5.00 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ NiAl-LDH2.51Pd ⁰ .

Example 7

(1) Preparation of magnetic nanoparticles

Dissolve 2.16g FeCl ₃ 6H ₂ O in 80mL ethylene glycol in a 40°C water bath to obtain a uniform and stable solution; add 5.76g NaAc 3H ₂ O and stir slowly until completely dissolved to avoid bubbles; transfer to 100mL Lined with polytetrafluoroethylene self-generated pressure bomb, 200 ° C for 8 hours. Cool naturally to room temperature, magnetically separate with NdFeB permanent magnets, wash with ethanol for 5 times, then wash with deionized water until neutral, and dry at 60°C for 24 hours to obtain black powdery magnetic nanoparticles, denoted as Fe ₃ O ₄ , Its size and magnetic properties are the same as in Example 1.

(2) Preparation of magnetic multi-level core-shell structure hydrotalcite carrier

Weigh 1.042g Fe ₃ O ₄ nanoparticles and place in 100mL water for ultrasonic dispersion for 20min. Dissolve 2.310 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 1.125 g of Al(NO ₃ ) ₃ ·9H ₂ O in 100 mL of water to obtain a mixed salt solution. Dissolve 0.640g of Na ₂ CO ₃ and 0.800g of NaOH in 100mL of water as an alkaline solution. In a water bath at 25°C, slowly drop a small amount of alkali solution into the Fe ₃ O ₄ suspension until the pH is 10 and stabilize for 5 min. Then add the lye and the mixed salt solution dropwise at the same time, stir vigorously, and keep the pH at 10 until the dropwise addition of the mixed salt solution is completed. The product was magnetically separated by an NdFeB permanent magnet, washed five times with deionized water, and dried in vacuum at 60°C for 24 hours to obtain a magnetic multi-level core-shell structure hydrotalcite carrier, which was denoted as Fe ₃ O ₄ MgAl-LDH, and its structure The morphology and magnetic properties are the same as in Example 1.

(3) Preparation of magnetic multilevel core-shell structure nano-palladium catalyst

Weigh 1 g of the above Fe ₃ O ₄ MgAl-LDH and disperse it in 100 mL of ethanol. 1.67 mL of potassium tetrachloropalladate aqueous solution (0.56 mol/L) was added to the above suspension. Subsequently, 1 mL of hydrazine hydrate was added, reacted at 25°C for 3 hours, and the product was magnetically separated by an NdFeB permanent magnet, washed with ethanol and water several times to neutrality, and vacuum-dried at 60°C for 24 hours to obtain a black powder magnetic multi-stage The nano palladium catalyst with core-shell structure is recorded as Fe ₃ O ₄ MgAl-LDH0.80Pd ⁰ .

Claims (2)

1. a magnetic multistage core shell structure hydrotalcite nano Pd catalyst, is characterized in that: with Fe ₃o ₄magnetic nano particle is core, with CO ₃ ^2-mgAl, CoAl, NiAl, NiMgAl, CoMgAl and NO of intercalation ₃ ^-the CaMgAl-LDH of intercalation is shell structurre, without part zeroth order Pd nano particle uniform load in the edge of shell hydrotalcite six square piece and staggered position; The chemical general formula of material is Fe ₃o ₄@MAl-LDH@xPd ⁰, wherein MAl-LDH is that ab-face is perpendicular to Fe ₃o ₄surface and the shell hydrotalcite hexagonal nano of interlaced growth is brilliant, Pd ⁰for be uniformly distributed in MAl-LDH hexagonal nano crystal edge edge and staggered position without part zeroth order Pd nano particle, x is the mass percent load capacity of palladium, and unit is wt%; Wherein, the mass percentage of each component is respectively:

Fe ₃O ₄：35.5～49.8％；

MAl-LDH：47.7～61.5％；

Pd ⁰：0.18～3.43％；

Wherein M is one or both divalent metals, can be Mg, Ni, Co, NiMg, CoMg and CaMg; The interlayer anion of shell MAl-LDH can be CO ₃ ^2-or NO ₃ ^-anion;

Monolith particle is of a size of 400 ~ 600 nm, and specific saturation magnetization is 38.6 ~ 54.9emu/g, and specific area is 63 ~ 74m ²/ g; Hydrotalcite shell thickness is 80 ~ 120nm, and single hydrotalcite nano crystalline substance is of a size of 65 ~ 100nm, and thickness is 8 ~ 10nm, and the pore-size between hydrotalcite nano crystalline substance is 55 ~ 110nm; Palladium nanoparticle is of a size of 3.9 ~ 12.1nm.

2. a preparation method for magnetic according to claim 1 multistage core shell structure hydrotalcite nano Pd catalyst, is characterized in that, comprises following three steps:

(1) preparation of magnetic nano particle

Surfactant-free solvent-thermal method is adopted to prepare ferroferric oxide magnetic nano grain;

Take 2.16 g FeCl ₃6H ₂o is dissolved in 80mL ethylene glycol in 30 ~ 50 DEG C of water-baths, obtained stable homogeneous orange solution, and concentration is 0.1mol/L; Add 5.76 g NaAc3H ₂o, is slowly stirred to and dissolves completely, avoids producing bubble, NaAc3H ₂o and FeCl ₃6H ₂the mol ratio of O is 5.29; Being transferred to 100mL liner is in the self-generated pressure bullet appearance of polytetrafluoroethylene (PTFE), in 200 DEG C of reaction 8h; Naturally cool to room temperature, adopt Nd-Fe-B permanent magnet magnetic to be separated, wash 5 times respectively by ethanol and deionized water, in 60 DEG C of drying 24 ~ 48h, obtain black powder magnetic nano particle, be designated as Fe ₃o ₄;

(2) preparation of magnetic multistage core@shell structure hydrotalcite supports

The two coprecipitations of dripping improved are adopted to prepare magnetic multistage core@shell structure hydrotalcite supports;

The first step: M pressed by divalent metal salt and aluminium salt ²⁺/ Al ³⁺the molar concentration rate of=3, is made into mixing salt solution with water; Another preparation contains NaOH and Na ₂cO ₃aqueous slkali (in magnetic CaMgAl-LDH system, the solute of aqueous slkali only has NaOH; Take 1.042g Fe ₃o ₄magnetic nano particle, with the preparation of surfactant-free solvent-thermal method, size is about 400nm, and in 100mL water, ultrasonic 20min forms suspension, and wherein the molal quantity ratio of hydrotalcite laminate divalent metal element and magnetic core Fe element is 0.25 ~ 0.75;

Wherein M is one or more divalent metals, is Mg, Ni, Co, NiMg, CoMg and CaMg;

Second step: by Fe ₃o ₄suspension is placed in 500mL four-hole boiling flask; mechanical agitation; magnetic CaMgAl-LDH system need be protected with nitrogen atmosphere, under ice-water bath magnetic CoAl or CoMgAl-LDH system or room temperature magnetism MgAl, NiAl, NiMgAl and CaMgAl-LDH system, with mixed ammonium/alkali solutions by Fe ₃o ₄the pH value of suspension is slowly adjusted to required numerical value, and for magnetic MgAl, NiAl, CoAl, NiMgAl and CoMgAl-LDH system, precipitation pH is adjusted to 10; For magnetic CaMgAl-LDH system, precipitation pH is adjusted to 11.5, stablizes 5 ~ 10min; Mixing salt solution and mixed ammonium/alkali solutions are slowly dripped wherein subsequently simultaneously, keep slurries pH constant, after mixing salt solution drips off, slurries continue to keep rapid stirring 5min;

3rd step: be separated black solid product with Nd-Fe-B permanent magnet magnetic, with deionized water washing repeatedly to supernatant pH in neutral, in 60 DEG C of drying 24 ~ 48h, magnetic CaMgAl-LDH system needs vacuum drying, grinding obtains black powder magnetic multistage core@shell structure hydrotalcite supports, is designated as Fe ₃o ₄@MAl-LDH;

(3) preparation of magnetic multistage core@shell structure hydrotalcite loaded nanometer palladium catalyst

Adopt immersion reduction method load zeroth order palladium nanoparticle in above-mentioned magnetic multistage core@shell structure hydrotalcite supports;

Take the above-mentioned magnetic of 1g multistage core@shell structure hydrotalcite supports Fe ₃o ₄@MAl-LDH is scattered in 100mL ethanol, mechanical agitation, and 0.17 ~ 8.33mL tetrachloro-palladium acid aqueous solutions of potassium 0.56mol/L is joined above-mentioned suspension; Subsequently, add 1mL hydrazine hydrate, room temperature reduction 3h at 25 DEG C; Be separated to obtain magnetic black solid with Nd-Fe-B permanent magnet, wash repeatedly to neutral with ethanol and deionized water, in 60 DEG C of vacuum drying 24 ~ 48h, grinding obtains black powder magnetic multistage core@shell structural nano palladium catalyst, is designated as Fe ₃o ₄@MAl-LDH@xPd ⁰, wherein, x is the mass percent load capacity of palladium, and unit is wt%, and scope is 0.18 ~ 3.43.