CN114192164A - Au @ silicate core-shell nano-structure catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses an Au @ silicate core-shell nano-structured catalyst and a preparation method thereof, which utilize the confinement effect of a silicate shell on nanogold to improve the dispersity of nanogold particles and the interaction between the nanogold particles and a carrier, thereby achieving the purpose of improving the reaction activity and stability, and simultaneously, other metal active sites are selectively introduced into a catalyst system to contribute to the partial oxidation reaction activity of ethanol. The invention effectively solves the problem that gold nanoparticles are easy to sinter in the partial oxidation reaction of ethanol, realizes the problem that the thickness of the silicate nanoshell is adjustable, and has larger gas contact area than the common core-shell structure catalyst. According to the proportion of the amount of the nano gold and the addition amount of the soluble silicon source, the wrapping SiO can be adjusted₂Is measured.

Description

Au @ silicate core-shell nano-structure catalyst and preparation method thereof

Technical Field

The invention relates to an Au @ silicate core-shell nano-structure catalyst and a preparation method thereof, belonging to the technical field of hydrogen production.

Background

The ethanol used as a hydrogen production raw material has the advantages of wide source, no pollution and no toxicity in the process, and the hydrogen production approaches mainly comprise ethanol partial oxidation reforming, ethanol steam reforming, ethanol cracking, ethanol partial oxidation and the like. The partial oxidation hydrogen production of ethanol has the advantages of fast start, high efficiency, convenient miniaturization and the like, has wide application prospect when being used as the hydrogen source of the fuel cell, and is also an important way for realizing vehicle-mounted hydrogen production. The ethanol partial oxidation catalyst can be mainly divided into a supported catalyst with copper, noble metal and bimetal as active components. The patent number CN201510741794.1 discloses a catalyst for hydrogen production by partial oxidation of ethanol and a preparation method thereof, wherein the chemical formula of the catalyst for hydrogen production by partial oxidation of ethanol prepared by a hydrothermal-coprecipitation method is as follows: PrNixCo1-xO 3. The patent number CN01145252.8 discloses a catalyst for hydrogen production by partial oxidation of ethanol, and provides a catalyst prepared by a coprecipitation method, wherein the active component of the catalyst is Ni-Fe-La, and the general formula of the catalyst is Ni (x) Fe (100-x) La (y) O (z).

The gold nano catalyst has better low-temperature catalytic activity on the partial oxidation reaction of the ethanol, however, because the partial oxidation reaction of the ethanol is an exothermic reaction and the temperature is generally 200-400 ℃, the problems of low reaction activity, poor stability and the like are caused by grain migration, sintering and instability of Au active components easily caused in the reaction process. Therefore, the novel Au-based catalyst with special morphology structure and surface chemical property is designed and constructed, Au nano particles are highly dispersed through the structure confinement effect, and the metal and the carrier form strong interaction, which is the key for obtaining high activity and high stability in the partial oxidation hydrogen production reaction of ethanol.

Disclosure of Invention

The invention overcomes the defects of the prior art and provides an Au @ silicate core-shell nano-structured catalyst and a preparation method thereof, the limit effect of a silicate shell on nanogold is utilized to improve the dispersity of nanogold particles and the interaction between the nanogold particles and a carrier, so that the aim of improving the reaction activity and the stability is fulfilled, and other metal active sites are selectively introduced into a catalyst system to contribute to the partial oxidation reaction activity of ethanol.

A preparation method of a noble metal catalyst with an Au @ silicate core-shell nano structure comprises the following steps:

1) preparing chloroauric acid solution, adding PVA, stirring, adding NaBH₄Solution, when the solution turns into wine red, gold nanoparticles are obtained;

2) adjusting the pH value of the gold nanoparticle aqueous solution formed in the step 1) to 9-10, adding a soluble silicon source, stirring and hydrolyzing to form Au @ SiO₂A nanoparticle;

3) dissolving metal salt in water, adding 25% ammonia water, adding ethanol, stirring, and adding into the Au @ SiO prepared in step 2)₂And uniformly stirring the nano particles, transferring the nano particles into a hydrothermal kettle, performing hydrothermal treatment for 12-36h in an oven at 273-473K, washing and drying after the reaction is finished, and calcining for 3-4h at 380-400 ℃ to obtain the Au @ silicate core-shell nano-structured catalyst.

Further, the concentration of the chloroauric acid solution in the step 1) is 90-100 mg/L.

Further, the addition amount of the PVA in the step 1) is that according to the mass ratio of the Au to the PVA in the solution, the ratio is (1.2-1.5): 1 in a ratio of 1.

Further, NaBH described in the above step 1)₄The concentration of the solution is 0.1-0.2 mol/L; the NaBH₄The addition amount of the solution is Au and NaBH₄The molar ratio is 1: (4-5) mixing.

Further, the addition amount of the soluble silicon source in the step 2) is 1 to 10mmol/100 ml.

Further, the soluble silicon source in the step 2) refers to one of sodium silicate, potassium silicate and ethyl orthosilicate.

Further, the method for adjusting the pH of the gold nanoparticle aqueous solution in the step 2) is to use ammonia water for adjustment.

Further, the metal salt in the step 3) is one of nitrates, sulfates or oxalates of metal copper, magnesium, zinc, nickel and aluminum.

Further, the concentration of the metal salt dissolved by adding water in the step 3) is 0.1-0.5 mol/L.

Further, the amount of the 25% ammonia water added in the step 3) is 1 to 5 mL.

Further, the adding amount of the ethanol in the step 3) is 1:1-1:2 according to the water-alcohol ratio.

Has the advantages that:

(1) the effective limited area of the gold nanoparticles is in the silicate shell, so that the problem that the gold nanoparticles are easy to sinter in the partial oxidation reaction of ethanol is effectively solved;

(2) the adjustable loading of the active component Au is realized;

(3) the problem that the thickness of the silicate nanoshell is adjustable is solved, and the gas contact area is larger than that of a common core-shell structure catalyst. According to the proportion of the amount of the nano gold and the addition amount of the soluble silicon source, the wrapping SiO can be adjusted₂Is measured.

Drawings

Au @ SiO prepared in FIG. 1₂TEM images of the nanocatalyst.

3% Au @ CuSiO prepared in FIG. 2₃TEM image of nanocatalyst

Detailed Description

In order to make the technical solutions in the present application better understood, the present invention is further described below with reference to examples, which are only a part of examples of the present application, but not all examples, and the present invention is not limited by the following examples.

Examples 1,

Preparation of Au @ CuSiO₂Catalyst and process for preparing same

Firstly synthesizing Au nano-particles, dispersing the Au nano-particles in 100mL of water, adding about 2mL of ammonia water to adjust the pH to 9-10, and adjusting the pH to Au @ SiO₂The content of Au in the solution accounts for 3 percent, 3mmol of tetraethoxysilane is added into the solution, and the solution is stirred and fully reacted. Filtered, washed and dispersed in 10mL of aqueous solution for use.

1.5 g Cu (NO)₃)₂·6H₂Dissolving O in water, adding 25% ammonia water to precipitate, dissolving, adding ethanol, stirring for 10min, and mixing with the above prepared Au @ SiO₂The solution is prepared by mixing a solvent and a solvent,stirring for 180min, transferring to a 150mL hydrothermal kettle, moving to an oven 473K for hydrothermal treatment for 12-36 hours, taking out, cooling, filtering, washing, drying and roasting to obtain the Au @ CuSiO2 catalyst.

Second, result analysis

The gold nanoparticles synthesized by the method have the diameter of 3-5nm and pass through SiO₂After coating, Au @ SiO with uniform particle size of about 15-20nm is formed as shown in figure 1₂The structure is that the effective limited domain of the gold nano-particles is in a core-shell structure. Introduction of Cu²⁺Through hydrothermal reaction, SiO of the inner layer₃²⁺Continuously migrate outward and Cu²⁺React to form CuSiO₃. Finally, Au @ CuSiO shown in figure 2 is formed₃A core-shell nano-catalyst. The catalyst is applied to partial oxidation reaction of ethanol, and after 50 hours of reaction, the diameter of Au nano-particles is kept between 5 and 8nm, thus the Au @ CuSiO₃The core-shell nano-catalyst can effectively prevent Au nano-particles from sintering.

Example 2

This example is to change the loading amount of the active component loaded on the basis of example 1.

Firstly synthesizing Au nano-particles, dispersing the Au nano-particles in 100mL of water, adding about 2mL of ammonia water to adjust the pH to 9-10, and adjusting the pH to Au @ SiO₂The content of Au in the solution is 5%, 5mmol of ethyl orthosilicate is added into the solution, and the solution is stirred and fully reacted. Filtered, washed and dispersed in 10mL of aqueous solution for use.

0.78 g CuC₂O₄Dispersing in water, adding 25% ammonia water to precipitate, dissolving, adding ethanol, stirring for 10min, and mixing with the above prepared Au @ SiO₂Stirring the solution for 180min, transferring the solution to a 150mL hydrothermal kettle, transferring the solution to a drying oven at 473K for hydrothermal treatment for 12-36 hours, taking out the solution, cooling, filtering, washing, drying and roasting to obtain Au @ CuSiO₂A catalyst.

Example 3

This example is based on example 1 with a change in the composition of the silicate.

Firstly synthesizing Au nano-particles, and dispersing the Au nano-particlesTo 100mL of water, about 2mL of aqueous ammonia was added as Au @ SiO₂The content of Au in the solution is 3%, 3mmol of ethyl orthosilicate is added into the solution, and the solution is stirred and fully reacted. Filtered, washed and dispersed in 10mL of aqueous solution for use.

1.3 g Mg (NO)₃)₂·2H₂Dispersing O in water, adding 25% ammonia water to precipitate, dissolving, adding ethanol, stirring, and mixing with the above prepared Au @ SiO solution for 10min₂Stirring the solution for 180min, transferring the solution to a 150mL hydrothermal kettle, transferring the solution to a drying oven at 473K for hydrothermal treatment for 12-36 hours, taking out the solution, cooling, filtering, washing, drying and roasting to obtain Au @ MgSiO₂A catalyst.

Claims (10)

1. A preparation method of a noble metal catalyst with an Au @ silicate core-shell nano structure is characterized by comprising the following steps:

1) preparing chloroauric acid solution, adding PVA, stirring, adding NaBH₄Solution, when the solution turns into wine red, gold nanoparticles are obtained;

2) adjusting the pH value of the gold nanoparticle aqueous solution formed in the step 1) to 9-10, adding a soluble silicon source, stirring and hydrolyzing to form Au @ SiO₂A nanoparticle;

3) dissolving metal salt in water, adding ammonia water, adding ethanol, stirring, and adding into the Au @ SiO prepared in step 2)₂And uniformly stirring the nano particles, transferring the nano particles into a hydrothermal kettle, performing hydrothermal treatment for 12-36h in an oven at 273-473K, washing and drying after the reaction is finished, and calcining for 3-4h at 380-400 ℃ to obtain the Au @ silicate core-shell nano-structured catalyst.

2. The method according to claim 1, wherein the concentration of the chloroauric acid solution in step 1) is 90 to 100 mg/L.

3. The method according to claim 1, wherein the amount of PVA added in step 1) is such that the mass ratio of Au to PVA in the solution is (1.2-1.5): 1 in a ratio of 1.

4. The method of claim 1, wherein the NaBH of step 1) is prepared by₄The concentration of the solution is 0.1-0.2 mol/L; the NaBH₄The addition amount of the solution is Au and NaBH₄The molar ratio is 1: (4-5) mixing.

5. The method according to claim 1, wherein the amount of the soluble silicon source added in step 2) is 1 to 10mmol/100 ml.

6. The method according to claim 1, wherein the soluble silicon source in step 2) is one of sodium silicate, potassium silicate and ethyl orthosilicate.

7. The method according to claim 1, wherein the method for adjusting the pH of the aqueous solution of gold nanoparticles in step 2) is adjustment using ammonia water.

8. The method according to claim 1, wherein the metal salt in step 3) is one of nitrates, sulfates or oxalates of copper, magnesium, zinc, nickel, aluminum.

9. The method according to claim 1, wherein the concentration of the metal salt dissolved in water in the step 3) is 0.1 to 0.5 mol/L.

10. The production method according to any one of claims 1 to 9, wherein the aqueous ammonia in the step 3) is 25% aqueous ammonia, and is added in an amount of 1 to 5 mL; the adding amount of the ethanol is 1:1-1:2 according to the water-alcohol ratio.

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