Preparation method and application of ultra-small platinum rare earth alloy nanoparticle catalyst packaged in pore channel of mesoporous material

Abstract

The invention relates to a preparation method and application of an ultra-small platinum rare earth alloy nanoparticle catalyst packaged in a mesoporous material pore channel. The preparation method comprises the following steps: (1) synthesizing a mesoporous material with regular pore channels; (2) selectively modifying the inner surface of the pore channel of the mesoporous material; and (3) loading and alloying the metal active center. Equipment required by the preparation process is simple, the synthesis steps are simple and convenient, and the large-scale application potential is large. The obtained platinum rare earth alloy nano-particles are uniform in size and ultra-small (smaller than 5 nm), the thermal stability is excellent, metal components are easy to regulate and control, the catalytic activity is high, the problem of synthesizing the ultra-small platinum rare earth alloy nano-particles in a mesoporous material channel is solved, and a brand new scheme is provided for preparing a propane direct dehydrogenation catalytic material with excellent performance.

Description

Technical Field

[0001] This invention relates to the field of supported metal catalyst preparation technology, specifically to a method for preparing and applying an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated within the pores of a mesoporous material. Background Technology

[0002] Propylene, as an important olefin monomer, is widely used in the production of high-value-added chemical products such as polypropylene and acrylonitrile. Compared with olefin technologies such as petroleum catalytic cracking, direct propane dehydrogenation (PDH) technology offers a simpler operation process, high propylene selectivity, and environmental friendliness, making it an important pathway for industrial propylene production. Platinum-based catalysts, especially platinum-tin systems, dominate the commercial PDH catalyst market due to their efficient activation of CH bonds and resistance to carbon deposition. However, the PDH reaction is a strongly endothermic process involving an increase in the number of molecules, and to achieve high propane conversion, the reaction typically needs to be carried out at high temperatures. However, these harsh high-temperature conditions not only pose a serious challenge to the structural stability of the catalyst but also exacerbate side reactions such as coking and hydrogenolysis, which are extremely detrimental to achieving efficient and stable propylene production.

[0003] Existing research indicates that the controllable synthesis of ultrafine metal catalysts can be achieved by functionalizing the surface of non-porous supports with heteroatoms. However, the surface-modified heteroatoms are easily lost under high-temperature reaction conditions, making it difficult to maintain the size and structure of the metal particles in their initial state, which greatly limits their industrial applications.

[0004] Zeolite supports with sub-2 nm microporous structures can effectively stabilize metal nanoparticles and inhibit their high-temperature sintering due to the confinement effect of the pores. However, the narrow micropore windows of zeolite supports inevitably hinder mass transfer kinetics, making it difficult for reactants to effectively contact the active metal sites. In contrast, mesoporous supports have more open pore structures, making the preparation of thermally stable and uniformly distributed metal catalysts within these pores a better choice for achieving efficient catalysis. However, achieving precise loading of ultra-small metal nanoparticles within mesoporous channels is extremely difficult. Furthermore, due to the lack of pore confinement, metal nanoparticles encapsulated in mesopores are prone to migration and aggregation within the pores, thus significantly reducing their catalytic performance. Therefore, developing a universal synthesis strategy for the precise synthesis of highly dispersed, ultra-small, and thermally stable platinum-based catalysts within the pores of mesoporous materials is of great significance for promoting the development of PDH processes towards higher efficiency, stability, and lower cost. Summary of the Invention

[0005] Based on the above-mentioned prior art, the present invention provides a method for preparing an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated in the pores of a mesoporous material, and uses it to achieve efficient catalytic production of propylene from propane.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated within the pores of a mesoporous material includes the following steps: (1) The surfactant P123, tetraethyl silicate, hydrochloric acid and n-butanol were mixed in deionized water in a certain proportion. After stirring for 24 h, the mixture was allowed to stand for 24 h. The product was collected by filtration, washed and dried, and the resulting solid powder was placed in a muffle furnace for calcination to obtain a mesoporous silica carrier. (2) The mesoporous silica support obtained in step (1) is mixed with urea, ground and then transferred to a muffle furnace for open calcination. After the reaction is completed, the product is washed and dried to obtain a mesoporous support with selective nitrogen modification on the inner surface of the pores. (3) The selective nitrogen-modified mesoporous support obtained in step (2), potassium chloroplatinate solution and rare earth metal salt solution are stirred and impregnated for 10-14 h. The product is collected by centrifugation and washed with deionized water. It is then dried at 50°C overnight. Finally, a two-stage heating reduction is carried out in H2 / Ar atmosphere to obtain an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated in the pores of the mesoporous material.

[0007] Furthermore, in step (1), the ratio of surfactant P123, tetraethyl silicate, hydrochloric acid and n-butanol is 6.5g:14.9mL:10.6mL:8mL.

[0008] Furthermore, the roasting temperature in step (1) is 500~600℃ and the time is 4~8 h.

[0009] Furthermore, the mass ratio of the mesoporous silica carrier and urea in step (2) is 1:1 to 1:3.

[0010] Furthermore, the roasting temperature in step (2) is 200~400℃ and the time is 10 h.

[0011] Furthermore, the rare earth metals in the rare earth metal salt solution in step (3) include one or more of Sm, La, Ce, Pr, Nd and Er; the molar ratio of platinum to rare earth metals in the potassium chloroplatinate solution and the rare earth metal salt solution is 2:5.

[0012] Furthermore, the H2 / Ar atmosphere described in step (3) is 5% H2 / 95% Ar, and the flow rate is 50~100 sccm.

[0013] Furthermore, in step (3), the reduction temperature of the first stage of the two-stage temperature program is 400℃ and the reduction time is 2 h. The second stage increases the temperature from 400℃ to 650~900℃ and the reduction time is 1~6 h. The heating rate at both ends is 5℃ / min.

[0014] The particle size of the ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated in the pores of the mesoporous material prepared by the above method is <5 nm.

[0015] The above-mentioned application of ultra-small platinum rare earth alloy nanoparticle catalysts encapsulated in the pores of mesoporous materials in the dehydrogenation of propane to propylene.

[0016] The advantages of this invention are: This invention provides a method for preparing ultra-small platinum-rare earth alloy nanoparticle catalysts encapsulated within the pores of mesoporous materials. Compared with existing technologies, this method is simple to operate, has a convenient preparation process, high reproducibility, strong universality, and possesses the potential for large-scale synthesis. Furthermore, when the theoretical platinum loading is 3% and the molar ratio of platinum to lanthanum is 2:5, the prepared ultra-small platinum-lanthanum alloy nanoparticle catalyst encapsulated within the pores of mesoporous silica exhibits excellent catalytic performance in the direct dehydrogenation reaction of propane, significantly outperforming other platinum-lanthanum ratios and commercially available platinum-tin composite metal catalysts. This represents a preferred method for the efficient catalytic production of propylene from propane using platinum-based catalysts. Attached Figure Description

[0017] Figure 1 The X-ray diffraction pattern of the ultra-small platinum-lanthanum alloy nanoparticle catalyst (platinum to lanthanum molar ratio of 2:5) encapsulated in mesoporous silica channels in Example 1 is shown.

[0018] Figure 2 This is a scanning transmission electron microscope image of the ultra-small platinum-lanthanum alloy nanoparticle catalyst (platinum to lanthanum molar ratio of 2:5) encapsulated in mesoporous silica channels in Example 1.

[0019] Figure 3 The elemental distribution diagram is shown for the ultra-small platinum-lanthanum alloy nanoparticle catalyst (platinum to lanthanum molar ratio of 2:5) encapsulated in mesoporous silica channels in Example 1.

[0020] Figure 4 The X-ray photoelectron spectra of the platinum 4f orbitals and lanthanum 3d orbitals of the ultra-small platinum-lanthanum alloy nanoparticle catalyst (platinum to lanthanum molar ratio of 2:5) encapsulated in mesoporous silica channels in Example 1 are shown.

[0021] Figure 5 The image shows a scanning transmission electron microscope image of the catalyst obtained in Comparative Example 1 (calcination time of support and urea was 4 h).

[0022] Figure 6 The image shows a scanning transmission electron microscope image of the catalyst obtained in Comparative Example 2 (calcination time of support and urea was 14 h).

[0023] Figure 7The image shows a scanning transmission electron microscope image of the catalyst obtained in Comparative Example 3 (centrifuged 3 times after impregnation).

[0024] Figure 8 The image shows a scanning transmission electron microscope image and elemental distribution of the catalyst obtained in Comparative Example 4 (platinum and lanthanum metals were loaded via a secondary impregnation method).

[0025] Figure 9 Comparison of platinum 4f orbital X-ray photoelectron spectra of Example 1 (platinum to lanthanum molar ratio of 2:5) and Comparative Example 8 (single metal platinum).

[0026] Figure 10 The performance of the catalyst obtained in Example 1 (platinum to lanthanum molar ratio of 2:5) in the direct dehydrogenation reaction of propane is shown.

[0027] Figure 11 The performance of the catalyst obtained in Comparative Example 5 (platinum to lanthanum molar ratio of 2:2) in the direct dehydrogenation reaction of propane is shown.

[0028] Figure 12 The performance of the catalyst obtained in Comparative Example 6 (platinum to lanthanum molar ratio of 2:8) in the direct dehydrogenation reaction of propane is shown.

[0029] Figure 13 The performance of the catalyst (platinum-tin metal catalyst) obtained in Comparative Example 7 in the direct dehydrogenation reaction of propane is shown.

[0030] Figure 14 The performance of the catalyst (single metal platinum) obtained in Comparative Example 8 in the direct dehydrogenation reaction of propane is shown.

[0031] Figure 15 This is a comparison graph showing the change of propane conversion rate with reaction time in the direct dehydrogenation reaction of propane in Examples 1, 5, 6, 7, and 8. Detailed Implementation

[0032] To further describe the present invention, preferred embodiments are described below with reference to examples. It should be noted that the described embodiments are merely illustrative of the features and advantages of the present invention and should not be construed as limiting the scope to these embodiments.

[0033] Example 1 (1) 6.5 g of surfactant P123 (i.e., polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer), 8 mL of n-butanol, 10.6 mL of hydrochloric acid and 14.9 mL of tetraethyl silicate were dissolved in 234 mL of deionized water. The mixture was stirred at 500 r / min for 24 h and then allowed to stand for 24 h. The product was collected by filtration and washed several times with deionized water. Then it was transferred to an oven at 90 °C and dried overnight. After drying, the resulting solid powder was placed in a muffle furnace and heated to 550 °C at a heating rate of 5 °C / min and calcined for 6 h to obtain mesoporous SiO2, denoted as m-SiO2.

[0034] (2) 2.0 g m-SiO2 and 4.0 g urea were thoroughly ground and then transferred to a muffle furnace and calcined at 300 °C for 10 h with an open opening. The heating rate was 3 °C / min. After cooling to room temperature, the resulting mixture was washed with deionized water and dried at 50 °C for 12 h to obtain nitrogen-modified m-SiO2.

[0035] (3) 154 μL of 0.1M potassium chloroplatinate aqueous solution, 154 μL of 0.25 M lanthanum nitrate hexahydrate aqueous solution, and 100 mg of nitrogen-modified m-SiO2 were added sequentially to 20 mL of deionized water (i.e., the theoretical loading of platinum was 3%, and the molar ratio of platinum to lanthanum was 2:5). The mixture was stirred at 700 r / min for 12 h, centrifuged at 9000 r / min for 4 min and repeated 6 times, and then dried overnight in an oven at 50℃. Finally, the obtained solid powder was reduced at 400℃ for 2 h in a 5% H2 / 95% Ar atmosphere, and then directly heated to 850℃ for 2 h, with a heating rate of 5℃ / min. After naturally cooling to room temperature, ultra-small platinum-lanthanum rare earth alloy nanoparticle catalyst encapsulated in mesoporous silica channels was obtained.

[0036] Figure 1 The image shows the X-ray diffraction pattern of the ultrasmall platinum-lanthanum alloy nanoparticle catalyst encapsulated within mesoporous silica channels. The pattern indicates that no diffraction peaks appear except for the amorphous silica diffraction peak at approximately 23°, suggesting that the platinum-lanthanum rare-earth alloy nanoparticles encapsulated within mesoporous silica channels prepared in Example 1 are extremely small in size. Scanning transmission electron microscopy characterization results show that their average particle size is only 2.1 nm. Figure 2 The overall EDS elemental distribution map of Example 1 shows that platinum and lanthanum are uniformly distributed on the mesoporous silica support, with no local enrichment signals. Furthermore, the platinum and lanthanum signals of a single, slightly larger particle overlap, indicating that the particle composition is platinum and lanthanum. Figure 3 Furthermore, the X-ray photoelectron spectroscopy (XPS) spectra of the platinum 4f orbital and lanthanum 3d orbital in Example 1 show that the valence states of platinum and lanthanum are primarily metallic. Figure 4The results indicate that ultra-small platinum-lanthanum rare-earth alloy nanoparticles encapsulated within mesoporous silica channels have been successfully synthesized.

[0037] Comparative Example 1 Repeat steps (1) and (3) of Example 1, except that in step (2) the open-top roasting time of the muffle furnace at 300°C is changed to 4 hours; the rest of the operation is the same as in Example 1. Figure 5 As shown, when the calcination time of the mesoporous silica support and urea is short, a large number of nitrogen-containing species will remain on the outer surface of the pores of the mesoporous silica support. The platinum and lanthanum ions coordinated with the nitrogen atoms on the outer surface of the pores will form platinum and lanthanum nanoparticles in the subsequent high-temperature reduction due to the lack of pore confinement effect, resulting in obvious agglomeration and exhibiting characteristics of wide size distribution and poor thermal stability.

[0038] Comparative Example 2 Repeat steps (1) and (3) of Example 1, except that the open-top calcination time of the muffle furnace at 300°C was changed to 14 h in step (2), and the rest of the operation was the same as in Example 1. When the calcination time of the mesoporous silica support and urea was extended to 14 h, even though the nitrogen species on the inner surface of the pores were more easily retained than those on the outer surface of the pores due to the longer diffusion path, the 14 h calcination time left very few nitrogen species on the inner surface of the pores. Due to the lack of coordination of N atoms, not only did the density of metal nanoparticles in the pores decrease sharply, but they were also more likely to migrate and aggregate in the pores (e.g., Figure 6 (As shown).

[0039] Comparative Example 3 Repeat steps (1) and (2) of Example 1, except that the number of centrifugations after immersion in step (3) is reduced from 6 to 3, and the rest of the operation is the same as in Example 1. Figure 7 As shown, reducing the number of centrifugation cycles after impregnation makes it impossible to completely remove the platinum and lanthanum metal precursors physically adsorbed on the inner and outer surfaces of the mesoporous silica channels, resulting in a wide size distribution and agglomeration of the synthesized platinum-lanthanum alloy nanoparticles.

[0040] Comparative Example 4 Steps (1) and (2) of Example 1 were repeated, except for the impregnation method of the platinum and lanthanum metal precursors in step (3). Specifically, 154 μL of 0.1M potassium chloroplatinate aqueous solution and 100 mg of nitrogen-modified m-SiO2 were first added to 20 mL of deionized water, stirred at 700 r / min for 12 h, centrifuged at 9000 r / min for 4 min and repeated 6 times, and then dried in an oven at 50 °C overnight. Then, the powder was reduced at 400 °C for 2 h in a 5% H2 / 95% Ar atmosphere to obtain platinum seed crystals. Subsequently, 0.1 g of platinum seed crystals and 154 μL of 0.25 M lanthanum nitrate hexahydrate aqueous solution were added to 20 mL of deionized water. After repeating the first impregnation operation, the dried powder was directly reduced at 850 °C for 2 h in a 5% H2 / 95% Ar atmosphere to obtain the sample of Comparative Example 4. Figure 8 As shown, the platinum-lanthanum metal catalyst prepared by the secondary impregnation method not only exhibited obvious local agglomeration, but also showed phase separation between platinum and lanthanum metals through EDS elemental analysis, indicating that this impregnation method cannot obtain uniform platinum-lanthanum alloy nanoparticles.

[0041] As can be seen from Examples 1 and Comparative Examples 1-4, in the process of preparing ultra-small platinum-lanthanum rare earth alloy nanoparticle catalysts encapsulated in mesoporous silica channels, the calcination time of mesoporous silica and urea, the number of centrifugation times after impregnation, and the loading mode of platinum and lanthanum precursors have important effects on the synthesis of ultra-small platinum-lanthanum alloy nanoparticles.

[0042] Comparative Example 5 Repeat steps (1) and (2) of Example 1, except that in step (3) the volume of lanthanum nitrate hexahydrate is changed to 62 μL, that is, the molar ratio of platinum to lanthanum is 2:2, and the rest of the operation is the same as in Example 1.

[0043] Comparative Example 6 Repeat steps (1) and (2) of Example 1, except that in step (3) the volume of lanthanum nitrate hexahydrate is changed to 247 μL, that is, the molar ratio of platinum to lanthanum is 2 to 8, and the rest of the operation is the same as in Example 1.

[0044] Comparative Example 7 Repeat steps (1) and (2) of Example 1, except that in step (3), the lanthanum nitrate hexahydrate solution is replaced with stannous chloride dihydrate, wherein the concentration of stannous chloride dihydrate is 0.25 M and the molar ratio of platinum to tin is 2:5. The rest of the operation is the same as in Example 1. Since stannous chloride dihydrate has poor solubility in deionized water, a small amount of hydrochloric acid was added when preparing the 0.25 M stannous chloride dihydrate solution in this comparative example. The amount added was 100 mg stannous chloride dihydrate / 5 μL hydrochloric acid.

[0045] Comparative Example 8 Repeat steps (1) and (2) of Example 1, except that lanthanum nitrate hexahydrate solution is not added in step (3), and the rest of the operation is the same as in Example 1.

[0046] Figure 9 The image shows a comparison of the X-ray photoelectron spectra of the platinum 4f orbitals in Example 1 and Comparative Example 8. The results indicate that the addition of lanthanum significantly modulates the electronic structure of the platinum active sites. Compared to single-metal platinum, the platinum 4f orbitals in the platinum-lanthanum alloy shift significantly towards lower binding energies, indicating electron transfer from lanthanum sites to platinum sites, thereby effectively controlling the adsorption intensity of key intermediates. Consequently, the ultra-small platinum-lanthanum rare-earth alloy nanoparticle catalyst prepared in Example 1, encapsulated within mesoporous silica channels, exhibits a propane conversion rate as high as 26% in the direct propane dehydrogenation reaction at a reaction temperature of 550°C. After 50 hours of continuous testing, the conversion rate only decreased by 16.2%, and it consistently maintained nearly 100% propylene selectivity. Figure 10 This is significantly superior to Comparative Example 5 (propane conversion rate 15.5%, 50-hour decay 72.2%), Comparative Example 6 (propane conversion rate 19.8%, 50-hour decay 35.1%), Comparative Example 7 (propane conversion rate 21.7%, 50-hour decay 28.8%), and Comparative Example 8 (propane conversion rate 8.2%, 3-hour decay 96.0%). See details... Figure 11-15 The propane dehydrogenation performance of the above catalysts was tested under the following conditions: activation conditions: atmospheric pressure, 550℃, 10% H2 / He, 10 mL / min; reaction conditions: C3H8 / Ar = 1 / 3, WHSV = 2.5 h. -1 50 mg catalyst, reaction temperature 500℃, feed gas is mass-produced mixed gas.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any equivalent substitutions or modifications made by those skilled in the art in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. A method for preparing an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated within the pores of a mesoporous material, characterized in that: Includes the following steps: (1) The surfactant P123, tetraethyl silicate, hydrochloric acid and n-butanol were mixed in deionized water in a certain proportion. After stirring for 24 h, the mixture was allowed to stand for 24 h. The product was collected by filtration, washed and dried, and the resulting solid powder was placed in a muffle furnace for calcination to obtain a mesoporous silica carrier. (2) The mesoporous silica support obtained in step (1) is mixed with urea, ground and then transferred to a muffle furnace for open calcination. After the reaction is completed, the product is washed and dried to obtain a mesoporous support with selective nitrogen modification on the inner surface of the pores. (3) The selective nitrogen-modified mesoporous support obtained in step (2), potassium chloroplatinate solution and rare earth metal salt solution are stirred and impregnated for 10-14 h. The product is collected by centrifugation and washed with deionized water. It is then dried at 50°C overnight. Finally, a two-stage temperature-programmed reduction is carried out in H2 / Ar atmosphere to obtain an ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated in the pores of the mesoporous material.

2. The preparation method according to claim 1, characterized in that: In step (1), the ratio of surfactant P123, tetraethyl silicate, hydrochloric acid and n-butanol is 6.5g:14.9mL:10.6mL:8mL.

3. The preparation method according to claim 1, characterized in that: The roasting temperature in step (1) is 500~600℃ and the time is 4~8 h.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the mesoporous silica carrier and urea in step (2) is 1:1 to 1:

3.

5. The preparation method according to claim 1, characterized in that: The roasting temperature in step (2) is 200~400℃ and the time is 10 h.

6. The preparation method according to claim 1, characterized in that: The rare earth metals in the rare earth metal salt solution mentioned in step (3) include one or more of Sm, La, Ce, Pr, Nd and Er; the molar ratio of platinum to rare earth metals in the potassium chloroplatinate solution and the rare earth metal salt solution is 2:

5.

7. The preparation method according to claim 1, characterized in that: The H2 / Ar atmosphere mentioned in step (3) is 5% H2 / 95% Ar, and the flow rate is 50~100 sccm.

8. The preparation method according to claim 1, characterized in that: In step (3), the first stage of the two-stage temperature program has a reduction temperature of 400℃ and a reduction time of 2 h. The second stage increases the temperature from 400℃ to 650~900℃ and the reduction time is 1~6 h. The heating rate for both stages is 5℃ / min.

9. The ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated within the pores of a mesoporous material, prepared by the method according to any one of claims 1-8, is characterized in that: The particle size of the ultra-small platinum rare earth alloy nanoparticles encapsulated in the pores of the mesoporous material is <5nm.

10. The application of the ultra-small platinum rare earth alloy nanoparticle catalyst encapsulated in the pores of a mesoporous material as described in claim 9 in the dehydrogenation of propane to propylene.

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