CN112023977A - Y-type molecular sieve packaged platinum group noble metal nanoparticle catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a Y-type molecular sieve-encapsulated platinum group noble metal nanoparticle catalyst and a preparation method thereof. The preparation method comprises: dispersing the Y-type molecular sieve in an ethanol solvent, and then adding a platinum group precursor in which platinum group elements exist in the form of cations, the Y-type Molecular sieves carry out intrapore adsorption of platinum group precursors, and the adsorbed samples are reduced in an ethanol solvent under a hydrogen atmosphere to prepare Y-type molecular sieve-encapsulated platinum group noble metal nanoparticle catalysts. The invention is based on the capillary force and electrostatic adsorption force of the Y-type molecular sieve micropores, utilizes the electronegativity characteristic of the Y molecular sieve framework, and realizes the normal-pressure hydrogen atmosphere under liquid phase conditions by selecting the precursor in which the platinum group elements exist in the form of cations. Uniform encapsulation of platinum group noble metal nanoparticles by medium Y molecular sieves.

Description

Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst and preparation method thereof

technical field

The invention belongs to the field of heterogeneous catalyst preparation, in particular to a preparation method of a Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst.

Background technique

Noble metal nanocatalysts have good catalytic activity due to their small particle size and high specific surface area, and have shown good application prospects in the fields of fine chemical production and pharmaceutical preparation. In contrast, affected by particle size and specific surface area, noble metal nanocatalysts are prone to agglomeration or sintering during the catalytic process, resulting in a decrease in catalytic activity. How to improve the stability of noble metal nanocatalysts has become a key problem that needs to be solved urgently in this field.

Molecular sieve is a crystalline silicate or aluminosilicate, which is composed of silicon-oxygen tetrahedron or aluminum-oxygen tetrahedron connected by oxygen bridge bonds. Has excellent thermal and hydrothermal stability. Using the confinement effect of molecular sieve channels, noble metal nanoparticles encapsulated in molecular sieve crystals can exhibit very good stability, and are not prone to agglomeration and growth under high temperature conditions.

The current method for encapsulating precious metals in molecular sieve channels is mainly in-situ encapsulation. The self-assembly process in molecular sieve synthesis encapsulates precious metal precursors into molecular sieve crystals, and then prepares the desired molecular sieve-encapsulated precious metal nanoparticles through steps such as high-temperature calcination and reduction. Typically, Enrique Iglesia's research group used SOD-type molecular sieve, GIS-type molecular sieve and ANA-type molecular sieve as the carrier, and chose Pt(NH ₃ ) ₄ (NO ₃ ) ₂ as the precursor, and successfully encapsulated platinum nanoparticles through in situ synthesis. In the above molecular sieve crystals (J.Am.Chem.Soc. 2012, 134, 17688), the encapsulated platinum particles showed good thermal stability. However, such a preparation method involves a high-temperature calcination process in the later stage, and the encapsulated particles may grow slightly during the calcination process.

The impregnation method is a traditional method of supporting precious metals on molecular sieves. For example, chloroplatinic acid or chloropalladium acid is supported on various molecular sieve carriers by the method of impregnation, and then the molecular sieve-supported precious metal catalysts are finally obtained by drying, calcining and other steps. However, the unavoidable noble metal precursors during the impregnation process may be adsorbed on the outer surface of the molecular sieve, which will lead to the agglomeration or deactivation of noble metals when such supported catalysts are used at high temperatures. How to optimize the traditional impregnation method to avoid the adsorption and diffusion of noble metal precursor salts on the outer surface of the molecular sieve, but to diffuse into the molecular sieve pores as much as possible is an effective way to solve the problem of the easy agglomeration and deactivation of such noble metal-supported catalysts.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst and a preparation method thereof, which are used to improve the thermal stability of platinum group noble metal nanoparticles. The Y molecular sieve itself has good high temperature stability. The precious metal particles are encapsulated into the Y molecular sieve channels, and the high temperature agglomeration of the precious metal particles can be suppressed by using the confinement effect of the Y molecular sieve channels.

To achieve the above object, the technical scheme adopted in the present invention is:

A preparation method of Y-type molecular sieve encapsulated platinum group nanoparticles, comprising:

Disperse Y-type molecular sieve in ethanol solvent, then add platinum group precursor in the form of cationic platinum group element, Y-type molecular sieve carries out intrapore adsorption of platinum group precursor, and the adsorption completed sample is carried out in ethanol solvent under hydrogen atmosphere reduction to obtain Y-type molecular sieve encapsulated platinum group nanoparticles.

Further, the concentration of the Y-type molecular sieve in the ethanol solvent is 4-10 mg/ml, the platinum group precursor is calculated according to the platinum group element, and the mass ratio of the platinum group element to the Y-type molecular sieve: 0.5-4.0:100; The platinum group precursor is obtained by dissolving the platinum group precursor salt in ethanol; the platinum group precursor is added dropwise.

Further, the processes of dispersing the Y-type molecular sieve in ethanol and adding the platinum group precursor are carried out at room temperature; the platinum group precursor is added and stirred for 4 to 24 hours for adsorption.

Further, the temperature conditions for the reduction of the adsorbed sample under a hydrogen atmosphere are 40-70° C., the hydrogen pressure is 1-2.5 atmospheres, and the reduction time is 24-36 hours.

Further, the sample after the reduction is washed and vacuum dried to obtain platinum group nanoparticles encapsulated by Y-type molecular sieve.

Further, the molar silicon-alumina ratio of the Y-type molecular sieve is 2-7.

Further, the molar silicon-alumina ratio of the Y-type molecular sieve is 2-5.

Further, the platinum group precursor salt is platinum acetylacetonate or palladium acetylacetonate.

A Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst.

A preparation method of a Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst of the present invention comprises:

Using ethanol as a solvent, at 20°C to 30°C, the precursors of platinum group elements in the form of cations use the electrostatic adsorption force and capillary force of the molecular sieve to adsorb and diffuse the platinum group precious metal precursors into the Y-type molecular sieve pores. After completion, the precursors diffused into the molecular sieve channels are reduced to corresponding nanoparticles under a hydrogen atmosphere.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention utilizes the negative charge characteristic of the Y molecular sieve framework to carry out adsorption and diffusion by selecting a precursor in which platinum group elements exist in the form of cations, the Y molecular sieve framework is negatively charged, and the dissolved precursor dissociates from the platinum group element cation (positively charged), Through electrostatic adsorption combined with the capillary effect of the molecular sieve channel, the platinum group elements can diffuse into the molecular sieve channel as much as possible, avoiding adsorption on the outer surface of the molecular sieve to the greatest extent, and then through the hydrogen reduction, washing and drying processes to obtain Y Molecular sieve encapsulated platinum group nanoparticles. High temperature calcination shows that the size of platinum group particles does not agglomerate and grow significantly after calcination at high temperature of 500 ℃, 600 ℃ and 700 ℃.

Description of drawings

The accompanying drawings forming a part of the present application are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

Fig. 1 is the XRD pattern after Y molecular sieve encapsulates Pd particle;

Fig. 2 is the TEM image of Y molecular sieve after Pd particles are encapsulated;

Figure 3 is a TEM image of Y molecular sieve encapsulated with Pd particles and calcined at 500°C;

Figure 4 is a TEM image of Y molecular sieve encapsulated with Pd particles and calcined at 600°C;

Figure 5 is a TEM image of Y molecular sieve encapsulated with Pd particles and calcined at 700°C;

FIG. 6 is a TEM image of Y molecular sieve encapsulated Pd particles using sodium chloropalladate as a precursor.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict.

The following detailed descriptions are all exemplary descriptions and are intended to provide further detailed descriptions of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention.

Example 1

Take 50 mg of dry HY molecular sieve, the silicon-aluminum ratio of HY molecular sieve (SiO ₂ /Al ₂ O ₃ ) is 3:1, add 10 mL of absolute ethanol, and mix uniformly by ultrasonic. Weigh 2.74mg of palladium acetylacetonate and dissolve it in 1.12mL of absolute ethanol, ultrasonicate until the palladium acetylacetonate powder is completely dissolved, slowly add the dissolved solution dropwise to the HY molecular sieve ethanol solution, stir at room temperature or in a water bath (25-30°C) for 10 Hour.

Take the sample after stirring overnight, discard the supernatant by centrifugation, add 10 mL of absolute ethanol to wash the sample, repeat three times, then add 10 mL of absolute ethanol for ultrasonic dispersion, slowly stir in a water bath at 60 °C, and reduce under 0.1 MPa H ₂ for 24 h. The reduced samples were taken, the supernatant was discarded by centrifugation, 5 mL of absolute ethanol and 5 mL of deionized water were added, and 5 mL of deionized water was added for ultrasonic washing. This washing step was repeated three times, and the samples were placed in a vacuum drying box to dry overnight. The HY molecular sieve Pd@HY encapsulated with palladium nanoparticles was obtained.

From the XRD data in Figure 2, it can be concluded that the structure of the Y-type molecular sieve after the catalyst encapsulation process is not significantly affected, and the molecular sieve after the loading has not observed obvious palladium element characteristic peaks in the XRD data, indicating that the molecular sieve The supported nanoparticles have smaller particle size and no obvious agglomeration. From the TEM data in Figure 2, it can be seen that the palladium nanoparticles are reduced and supported on the HY molecular sieve, and the reduced nanoparticles have a relatively uniform particle size distribution, with an average particle size of 1.6 nm, and there is no obvious agglomeration on the molecular sieve carrier.

Figure 4 is a TEM image of Y molecular sieve encapsulated with Pd particles and calcined at 500 °C. It can be seen that the particle size distribution of nanoparticles is still uniform after calcination, and there is no obvious agglomeration on the molecular sieve carrier.

Figure 4 is a TEM image of Y molecular sieve encapsulated with Pd particles and calcined at 600°C. It can be seen that there is no obvious agglomeration of Pd particles on the molecular sieve carrier after calcination.

Figure 5 is a TEM image of the Pd particles encapsulated by Y molecular sieve and calcined at 700°C, and the agglomeration and size growth of the Pd particles are also not observed.

Example 2

Take 45 mg of dry HY molecular sieve, the silicon-alumina ratio of HY molecular sieve is 3, add 10 mL of absolute ethanol, and mix uniformly by ultrasonic. Weigh 2.74mg of palladium acetylacetonate and dissolve it in 1.12mL of absolute ethanol, ultrasonicate until the palladium acetylacetonate powder is completely dissolved, slowly add the dissolved solution dropwise to the HY molecular sieve ethanol solution, stir at room temperature or in a water bath (25-30°C) for 15 Hour.

Take the sample after stirring overnight, discard the supernatant by centrifugation, add 8 mL of anhydrous ethanol to wash the sample, repeat three times, then add 10 mL of anhydrous ethanol for ultrasonic dispersion, slowly stir in a water bath at 63 °C, and reduce under 0.1 MPa H ₂ for 26 h. The reduced samples were taken, the supernatant was discarded by centrifugation, 5 mL of absolute ethanol and 5 mL of deionized water were added, and 5 mL of deionized water was added for ultrasonic washing. This washing step was repeated three times, and the samples were placed in a vacuum drying box to dry overnight. The HY molecular sieve Pd@HY encapsulated with palladium nanoparticles was obtained.

Example 3

Take 50 mg of dry HY molecular sieve, the silicon-alumina ratio of HY molecular sieve is 4, add 10 mL of absolute ethanol, and mix uniformly by ultrasonic. Weigh 2.74mg of palladium acetylacetonate and dissolve it in 1.12mL of absolute ethanol, ultrasonicate until the palladium acetylacetonate powder is completely dissolved, slowly add the dissolved solution dropwise to the HY molecular sieve ethanol solution, stir at room temperature or in a water bath (25-30°C) for 10 Hour.

Take the sample after stirring overnight, discard the supernatant by centrifugation, add 10 mL of absolute ethanol to wash the sample, repeat three times, then add 10 mL of absolute ethanol for ultrasonic dispersion, slowly stir in a water bath at 60 °C, and reduce under 0.1 MPa H ₂ for 24 h. The reduced samples were taken, the supernatant was discarded by centrifugation, 5 mL of absolute ethanol and 5 mL of deionized water were added, and 5 mL of deionized water was added for ultrasonic washing. This washing step was repeated three times, and the samples were placed in a vacuum drying box to dry overnight. The HY molecular sieve Pd@HY encapsulated with palladium nanoparticles was obtained.

Example 4

Take 50 mg of dry HY molecular sieve, the silicon-alumina ratio of HY molecular sieve is 5, add 10 mL of absolute ethanol, and mix uniformly by ultrasonic. Weigh 2.74mg of palladium acetylacetonate and dissolve it in 1.12mL of absolute ethanol, ultrasonicate until the palladium acetylacetonate powder is completely dissolved, slowly add the dissolved solution dropwise to the HY molecular sieve ethanol solution, stir at room temperature or in a water bath (25-30°C) for 10 Hour.

Take the sample after stirring overnight, discard the supernatant by centrifugation, add 10 mL of absolute ethanol to wash the sample, repeat three times, then add 10 mL of absolute ethanol for ultrasonic dispersion, slowly stir in a water bath at 60 °C, and reduce under 0.1 MPa H ₂ for 24 h. The reduced samples were taken, the supernatant was discarded by centrifugation, 5 mL of absolute ethanol and 5 mL of deionized water were added, and 5 mL of deionized water was added for ultrasonic washing. This washing step was repeated three times, and the samples were placed in a vacuum drying box to dry overnight. The HY molecular sieve Pd@HY encapsulated with palladium nanoparticles was obtained.

Example 5

Take 50 mg of dry HY molecular sieve, the silicon-to-aluminum ratio of HY molecular sieve is 3, add 10 mL of anhydrous ethanol, and mix uniformly by ultrasonic. Weigh 3.00 mg of platinum acetylacetonate and dissolve it in 1.12 mL of absolute ethanol, ultrasonicate until the platinum acetylacetonate powder is completely dissolved, slowly add the dissolved solution dropwise to the HY molecular sieve ethanol solution, and stir at room temperature or in a water bath (25-30 ° C) for 10 Hour.

Take the sample after stirring overnight, discard the supernatant by centrifugation, add 10 mL of absolute ethanol to wash the sample, repeat three times, then add 10 mL of absolute ethanol for ultrasonic dispersion, slowly stir in a water bath at 60 °C, and reduce under 0.1 MPa H ₂ for 24 h. The reduced samples were taken, the supernatant was discarded by centrifugation, 5 mL of absolute ethanol and 5 mL of deionized water were added, and 5 mL of deionized water was added for ultrasonic washing. This washing step was repeated three times, and the samples were placed in a vacuum drying box to dry overnight. The HY molecular sieve Pt@HY encapsulated with platinum nanoparticles was obtained.

Comparative Example 1

Sodium chloropalladate was used as the precursor and prepared by traditional impregnation method as a comparative example. Weigh 1.18mg sodium chloropalladate powder and dissolve it in 300ul of deionized water, disperse by ultrasonic, add dropwise to 100mg HY molecular sieve after being completely dissolved, make the molecular sieve completely evenly immersed in the sodium chloropalladate solution to reach a wet state, and let stand overnight After that, the samples were placed in an oven, dried at 100 °C for 4 h, and the heating and cooling times were both 30 min. After the samples were cooled, the dried samples were taken and placed in a muffle furnace, calcined at 300 °C for 4 h in an air environment, and the heating rate was 0.5 °C/min. After roasting, the samples were prepared by impregnation method. It can be seen from the TEM in Fig. 6 that the Pd particles supported on the Y molecular sieve using sodium chloropalladate as the precursor are larger in size, and their particle size distribution is uneven.

It is known from the technical common sense that the present invention can be realized by other embodiments without departing from its spirit or essential characteristics. Accordingly, the above-disclosed embodiments are, in all respects, illustrative and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims (9)

1. A preparation method of a Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst is characterized by comprising the following steps:

dispersing a Y-type molecular sieve in an ethanol solvent, adding a platinum group precursor of platinum group elements in a cation form, carrying out in-hole adsorption on the platinum group precursor by the Y-type molecular sieve, and reducing the adsorbed sample in the ethanol solvent under a hydrogen atmosphere to prepare the Y-type molecular sieve packaged platinum group noble metal nanoparticle catalyst.

2. The preparation method of claim 1, wherein the concentration of the Y-type molecular sieve in the ethanol solvent is 4-10 mg/ml, the mass ratio of the platinum group elements to the Y-type molecular sieve is calculated according to the platinum group elements in the platinum group precursor: 0.5-4.0: 100, respectively; the platinum group precursor is obtained by dissolving platinum group precursor salt in ethanol; the platinum group precursor is added dropwise.

3. The preparation method according to claim 2, wherein the dispersion of the Y-type molecular sieve in ethanol and the addition of the platinum group precursor are carried out at room temperature; and adding the platinum group precursor, and stirring for 4-24 hours for adsorption.

4. The method according to claim 1, wherein the temperature for reducing the adsorbed sample in a hydrogen atmosphere is 40 to 70 ℃, the hydrogen pressure is 1 to 2.5 atm, and the reduction time is 24 to 36 hours.

5. The preparation method of claim 4, wherein the sample after the reduction is washed and vacuum-dried to obtain Y-type molecular sieve encapsulated platinum group nanoparticles.

6. The preparation method of claim 1, wherein the molar silica-alumina ratio of the Y-type molecular sieve is 2-7.

7. The preparation method of claim 1, wherein the molar silica-alumina ratio of the Y-type molecular sieve is 2-5.

8. The method according to claim 2, wherein the platinum group precursor salt is platinum acetylacetonate or palladium acetylacetonate.

9. A Y-type molecular sieve encapsulated platinum group noble metal nanoparticle catalyst, characterized by being prepared by the preparation method of any one of claims 1 to 8.

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