Pt-loaded hierarchical porous ZSM-5 molecular sieve and preparation method thereof
By constructing single-atom, nanoparticle, and single-atom-nanoparticle coupled noble metal active centers on ZSM-5 molecular sieves, the problem of low diffusion efficiency of molecular sieve catalysts was solved, and efficient catalytic conversion was achieved.
Patent Information
- Application Number
- CN202511029682.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-25
- Publication Date
- 2025-11-11
AI Technical Summary
The microporous structure of molecular sieve catalysts reduces diffusion performance and metal site accessibility, limiting their catalytic performance in reactions such as hydrogenation, dehydrogenation, and oxidation.
A hierarchical porous ZSM-5 molecular sieve loaded with Pt was constructed using an in-situ ligand protection method. By controlling the synthesis conditions, single-atom, nanoparticle, and single-atom-nanoparticle coupled noble metal active centers were constructed to improve the molecular diffusion capacity.
The catalytic performance of the catalyst was improved, especially in the hydrogenation reaction of nitrobenzene, where it exhibited high conversion and selectivity.
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Figure CN120920050A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, specifically relating to a method for preparing a Pt-supported hierarchical porous ZSM-5 molecular sieve. Background Technology
[0002] Molecular sieves possess unique micropores, a uniform cage-like structure, and excellent chemical stability, ion exchange capacity, shape selectivity, and corrosion resistance, making them the most promising support materials for confining small-sized, especially smaller than 2 nm, metal particles. Many microporous molecular sieve materials, such as MFI, Beta, and Y, have been used as supports for the confined synthesis of supported clusters and even single-atom noble metal catalysts. However, the micropores of molecular sieve supports can reduce molecular diffusion performance and metal site accessibility, significantly limiting catalytic performance.
[0003] Hierarchical porous molecular sieves not only constrain metal size, but their hierarchical structure also improves molecular diffusion and the accessibility of active sites, making them ideal support materials. The acidity of hierarchical ZSM-5 molecular sieves makes them highly efficient acid catalysts in reactions such as methanol conversion and catalytic cracking. However, their low activity in hydrogenation, dehydrogenation, and oxidation reactions prevents their solo application in important industrial reactions such as propane dehydrogenation, Fischer-Tropsch synthesis, and C1 conversion. As a support material, they can be used to synthesize bifunctional catalysts supported on molecular sieves, applicable to hydrogenation reactions (such as CO / CO2 hydrogenation, unsaturated compound hydrogenation, and nitrogen-containing compound hydrogenation); dehydrogenation reactions (such as alkane dehydrogenation and dehydrogenation of chemical hydrogen storage materials); and oxidation reactions (CO oxidation, methane oxidation, and olefin epoxidation). Encapsulating noble metal atoms within hierarchical porous molecular sieves is an effective way to prepare metal catalysts with controllable size distribution and stability. Noble metal clusters and nanoparticles can also adjust the acidity of the molecular sieve support, which is beneficial for improving catalytic performance.
[0004] Noble metal (Pt, Pd, Au, Ru, etc.) catalysts are widely used in homogeneous or heterogeneous catalysis due to the following advantages: (1) the outermost d electron orbitals of noble metal atoms are not filled and there are defect sites on the surface, which are easy to form covalent bonds with H, O atoms, etc., which is very beneficial for forming the "active intermediate" or "transition state" required for catalytic reaction; (2) compared with other catalysts, noble metals are more resistant to oxygen, sulfur, chlorine, etc.; (3) their high catalytic activity and selectivity, non-toxicity and safety are widely used in homogeneous or heterogeneous catalysis and are widely studied. However, the reserves of noble metals are limited and the price is high. Therefore, the research focus of noble metal catalysts is to reduce the amount used and improve the utilization rate. Synthesizing small-sized nanoparticles, clusters or single-atom catalysts is the most effective method. However, reducing the particle size will lead to an increase in the unsaturated coordination environment and surface free energy of the metal, which will make it easy to aggregate and sinter under reaction conditions. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing Pt-loaded hierarchical ZSM-5 molecular sieves using an in-situ ligand protection method. By controlling the synthesis conditions, three types of noble metal active centers are constructed: single atoms, nanoparticles, and single atoms coupled with nanoparticles. This method delays the problem of carbon deposition in microporous molecular sieves, improves the flow and diffusion capacity of molecules, and thus enhances catalytic performance.
[0006] To achieve the above objectives, the following technical solution is adopted: A method for preparing Pt-loaded hierarchical ZSM-5 molecular sieves includes the following steps: (1) Polystyrene microspheres, colloidal silica, sucrose and dilute sulfuric acid solution were mixed evenly and transferred into an oven for deposition self-assembly process to obtain polystyrene microsphere / silica / carbon mixed precursor; (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and then washed, filtered, and dried to obtain a graded macroporous-mesoporous carbon template material. (3) A precursor solution was prepared using deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, chloroplatinic acid, ethylenediamine and tetraethyl orthosilicate, mixed with the macroporous-mesoporous carbon template material of the above grade, dried and transferred to a reaction vessel for crystallization treatment, centrifuged, washed and dried to obtain the crystallized product; (4) The crystallized product is placed in a muffle furnace for calcination treatment; (5) The product obtained in step (4) is reduced under a hydrogen atmosphere to obtain a single crystal of graded pore ZSM-5 molecular sieve loaded with Pt.
[0007] According to the above scheme, the size of the polystyrene microspheres in step (1) is 400~600nm, the colloidal silica is a silica suspension with a concentration of 40wt%, and the concentration of the sulfuric acid solution is 10wt%; the mass ratio of polystyrene microspheres, silica, sucrose and sulfuric acid solution is 100 : (10-20) : (10-20) : (10-20).
[0008] According to the above scheme, the calcination treatment in step (2) includes holding at 400℃ for 1 hour, raising the temperature to 500℃ and holding for 6 hours, raising the temperature to 650℃ and holding for 4 hours, with a heating rate of 1℃ / min.
[0009] According to the above scheme, in step (2), the calcined product is added to hydrofluoric acid and stirred for more than 4 hours to dissolve; the drying temperature is 80℃ and the drying time is 24 hours.
[0010] According to the above scheme, the preparation of the precursor solution in step (3) includes the following steps: deionized water and structure directing agent tetrapropylammonium hydroxide are stirred and dissolved, aluminum source aluminum isopropoxide is added and stirred and dissolved, and then silicon source tetraethyl orthosilicate (TEOS) and ethylenediamine are added dropwise and stirred and dissolved to obtain a clear and transparent precursor solution.
[0011] According to the above scheme, the molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, tetraethyl orthosilicate, chloroplatinic acid and ethylenediamine in step (3) is 15:(0.4-0.5):(0.01-0.015):(0.9-1.1):(0.0003-0.015):(0.03-0.19).
[0012] According to the above scheme, in step (3), the carbon template material is completely soaked in the precursor solution and then dried and aged at 40°C for 12 hours to remove water molecules.
[0013] According to the above scheme, the crystallization temperature in step (3) is 180℃ and the time is 5~6h.
[0014] According to the above scheme, the calcination treatment in step (4) includes heating to 550℃ and calcining for 7~8 hours, with a heating rate of 2℃ / min.
[0015] The present invention also provides a Pt-loaded hierarchical porous ZSM-5 molecular sieve, which is prepared using the above-described method.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: To address the problems of low diffusion efficiency and easy pore blockage and deactivation in molecular sieve catalysts, resulting in low catalyst yield, this invention introduces a hierarchical pore structure, with interconnected layers, to give the molecular sieve a higher specific surface area and diffusion efficiency. The morphology and active site distribution of the molecular sieve significantly affect its catalytic performance. This invention designs and controls the structure and microscopic placement of highly efficient diffusion hierarchical pores and noble metal sites to develop a novel hierarchical molecular sieve coupled with a noble metal catalyst, achieving highly efficient catalytic conversion.
[0017] Metallic Pt was loaded onto a hierarchical porous ZSM-5 single-crystal molecular sieve using an in-situ ligand protection method, forming active sites in the catalyst. By modulating the amount of platinum source and organic ligand added during synthesis, three types of noble metal active centers were constructed: single atom, nanoparticle, and single atom and nanoparticle coupling. The resulting hierarchical porous Pt@HZSM-5 coupled catalyst was used to optimize the catalytic hydrogenation process of nitrobenzene hydrogenation. Attached Figure Description
[0018] Figure 1 : Process data table for controlling the particle size of polystyrene microspheres.
[0019] Figure 2SEM images of the products obtained in Examples 2, 3, and 4.
[0020] Figure 3 HAADF-STEM and elemental distribution maps of Examples 2, 3, and 4.
[0021] Figure 4 High-resolution transmission electron microscope images of the products obtained in Examples 2, 3, and 4.
[0022] Figure 5 XRD patterns of the products obtained in Examples 1, 2, 3, and 4.
[0023] Figure 6 Catalytic performance of the products obtained in Examples 2, 3, and 4. Detailed Implementation
[0024] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.
[0025] A specific embodiment provides a method for preparing polystyrene microspheres: A certain amount of styrene solution and a pre-prepared 1 mol / L sodium hydroxide solution were mixed and stirred at room temperature for 1 hour. The mixture was allowed to stand, and the supernatant was collected and added to a 500 mL three-necked round-bottom flask equipped with a reflux condenser. Then, 360 g of deionized water and a certain amount of sodium dodecyl sulfate were added. The mixture was stirred in an oil bath at room temperature for 10 minutes. Under an inert atmosphere of argon or nitrogen, the temperature was raised to the desired temperature, and then potassium persulfate was added. By controlling the mass ratio of water, sodium dodecyl sulfate, styrene, and potassium persulfate, as well as the reaction time and temperature, the particle size of polystyrene microspheres can be controlled. Specific reaction conditions are detailed in the appendix. Figure 1 As shown.
[0026] Example 1 (1) Polystyrene microspheres, silica microspheres, sucrose, and sulfuric acid solution were mixed evenly and then transferred to an oven for deposition and drying to obtain a polystyrene microsphere / silica microsphere / carbon mixed precursor; the size of the polystyrene microspheres was 400-600 nm. The colloidal silica solution was Sigma-Aldrich brand LUDOX / AS-40 colloidal silica with a concentration of 40 wt% H2O; the mass ratio of polystyrene microspheres, silica, sucrose, and sulfuric acid solution was 100 : 15 : 15 : 15; the concentration of the sulfuric acid solution was 10 wt%.
[0027] (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and stirring. After washing, filtering and drying, a graded macroporous-mesoporous carbon template material is obtained. The calcination process is carried out at 400°C for 1 hour, then at 500°C for 6 hours, and then at 650°C for 4 hours. The heating rate is 1°C / min. Hydrofluoric acid is added and stirred for more than 4 hours to dissolve. The drying temperature is 80°C and the drying time is 24 hours.
[0028] (3) Deionized water and structure-directing agent tetrapropylammonium hydroxide were stirred and dissolved, aluminum source aluminum isopropoxide was added and stirred and dissolved, and silicon source tetraethyl orthosilicate (TEOS) was added dropwise. After stirring and dissolving thoroughly, a clear and transparent precursor solution was obtained. This solution was mixed with the macroporous-mesoporous carbon template material of the specified grade, dried, and then transferred to a reaction vessel for crystallization treatment. After centrifugation, washing, and drying, the crystallized product was obtained. The molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, and tetraethyl orthosilicate was 15:0.44:0.01:1. After the carbon template material was completely wetted by the precursor solution, it was dried and aged at 40°C for 12 hours to remove water molecules. The crystallization temperature was 180°C and the time was 6 hours.
[0029] (4) The crystallized product is placed in a muffle furnace for calcination treatment, and the temperature is increased to 550°C at 2°C / min for 7 hours.
[0030] (5) The product obtained in step (4) is reduced in a hydrogen atmosphere to obtain unloaded graded pore HZSM5 molecular sieve single crystals.
[0031] Example 2 (1) Polystyrene microspheres, silica microspheres, sucrose, and sulfuric acid solution were mixed evenly and then transferred to an oven for deposition and drying to obtain a polystyrene microsphere / silica microsphere / carbon mixed precursor; the size of the polystyrene microspheres was 400-600 nm. The colloidal silica solution was Sigma-Aldrich brand LUDOX / AS-40 colloidal silica with a concentration of 40 wt% H2O; the mass ratio of polystyrene microspheres, silica, sucrose, and sulfuric acid solution was 100 : 15 : 15 : 15; the concentration of the sulfuric acid solution was 10 wt%.
[0032] (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and stirring. After washing, filtering and drying, a graded macroporous-mesoporous carbon template material is obtained. The calcination process is carried out at 400°C for 1 hour, then at 500°C for 6 hours, and then at 650°C for 4 hours. The heating rate is 1°C / min. Hydrofluoric acid is added and stirred for more than 4 hours to dissolve. The drying temperature is 80°C and the drying time is 24 hours.
[0033] (3) Deionized water and structure-directing agent tetrapropylammonium hydroxide were stirred and dissolved, aluminum source aluminum isopropoxide was added and stirred and dissolved, and silicon source tetraethyl orthosilicate (TEOS), chloroplatinic acid and ethylenediamine were added dropwise. The mixture was stirred and dissolved thoroughly to obtain a clear and transparent precursor solution. The precursor solution was mixed with the macroporous-mesoporous carbon template material of the specified grade, dried and transferred to a reaction vessel for crystallization treatment. The product was obtained by centrifugation, washing and drying. The molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, tetraethyl orthosilicate, chloroplatinic acid and ethylenediamine was 15:0.44:0.01:1:0.000315:0.0375. The carbon template material was completely wetted by the precursor solution and then dried and aged at 40°C for 12 hours to remove water molecules. The crystallization temperature was 180°C and the time was 6 hours.
[0034] (4) The crystallized product is placed in a muffle furnace for calcination treatment, and the temperature is increased to 550°C at 2°C / min for 7 hours.
[0035] (5) The product obtained in step (4) is reduced under a hydrogen atmosphere to obtain graded porous Pt. 0.1% @HZSM5 single crystal.
[0036] Example 3 (1) Polystyrene microspheres, silica microspheres, sucrose, and sulfuric acid solution were mixed evenly and then transferred to an oven for deposition and drying to obtain a polystyrene microsphere / silica microsphere / carbon mixed precursor; the size of the polystyrene microspheres was 400-600 nm. The colloidal silica solution was Sigma-Aldrich brand LUDOX / AS-40 colloidal silica with a concentration of 40 wt% H2O; the mass ratio of polystyrene microspheres, silica, sucrose, and sulfuric acid solution was 100 : 15 : 15 : 15; the concentration of the sulfuric acid solution was 10 wt%.
[0037] (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and stirring. After washing, filtering and drying, a graded macroporous-mesoporous carbon template material is obtained. The calcination process is carried out at 400°C for 1 hour, then at 500°C for 6 hours, and then at 650°C for 4 hours. The heating rate is 1°C / min. Hydrofluoric acid is added and stirred for more than 4 hours to dissolve. The drying temperature is 80°C and the drying time is 24 hours.
[0038] (3) Deionized water and structure-directing agent tetrapropylammonium hydroxide were stirred and dissolved, aluminum source aluminum isopropoxide was added and stirred and dissolved, and silicon source tetraethyl orthosilicate (TEOS), chloroplatinic acid and ethylenediamine were added dropwise. The mixture was stirred and dissolved thoroughly to obtain a clear and transparent precursor solution. The precursor solution was mixed with the macroporous-mesoporous carbon template material of the specified grade, dried and transferred to a reaction vessel for crystallization treatment. The product was obtained by centrifugation, washing and drying. The molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, tetraethyl orthosilicate, chloroplatinic acid and ethylenediamine was 15:0.44:0.01:1:0.0009:0.1125. The carbon template material was completely wetted by the precursor solution and then dried and aged at 40°C for 12 hours to remove water molecules. The crystallization temperature was 180°C and the time was 6 hours.
[0039] (4) The crystallized product is placed in a muffle furnace for calcination treatment, and the temperature is increased to 550°C at 2°C / min for 7 hours.
[0040] (5) The product obtained in step (4) is reduced under a hydrogen atmosphere to obtain graded porous Pt. 0.3% @HZSM5 single crystal.
[0041] Example 4 (1) Polystyrene microspheres, silica microspheres, sucrose, and sulfuric acid solution were mixed evenly and then transferred to an oven for deposition and drying to obtain a polystyrene microsphere / silica microsphere / carbon mixed precursor; the size of the polystyrene microspheres was 400-600 nm. The colloidal silica solution was Sigma-Aldrich brand LUDOX / AS-40 colloidal silica with a concentration of 40 wt% H2O; the mass ratio of polystyrene microspheres, silica, sucrose, and sulfuric acid solution was 100 : 15 : 15 : 15; the concentration of the sulfuric acid solution was 10 wt%.
[0042] (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and stirring. After washing, filtering and drying, a graded macroporous-mesoporous carbon template material is obtained. The calcination process is carried out at 400°C for 1 hour, then at 500°C for 6 hours, and then at 650°C for 4 hours. The heating rate is 1°C / min. Hydrofluoric acid is added and stirred for more than 4 hours to dissolve. The drying temperature is 80°C and the drying time is 24 hours.
[0043] (3) Deionized water and structure-directing agent tetrapropylammonium hydroxide were stirred and dissolved, aluminum source aluminum isopropoxide was added and stirred and dissolved, and silicon source tetraethyl orthosilicate (TEOS), chloroplatinic acid and ethylenediamine were added dropwise. The mixture was stirred and dissolved thoroughly to obtain a clear and transparent precursor solution. The precursor solution was mixed with the macroporous-mesoporous carbon template material of the specified grade, dried and transferred to a reaction vessel for crystallization treatment. The product was obtained by centrifugation, washing and drying. The molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, tetraethyl orthosilicate, chloroplatinic acid and ethylenediamine was 15:0.44:0.01:1:0.0015:0.1875. The carbon template material was completely wetted by the precursor solution and then dried and aged at 40°C for 12 hours to remove water molecules. The crystallization temperature was 180°C and the time was 6 hours.
[0044] (4) The crystallized product is placed in a muffle furnace for calcination treatment, and the temperature is increased to 550°C at 2°C / min for 7 hours.
[0045] (5) The product obtained in step (4) is reduced under a hydrogen atmosphere to obtain graded porous Pt. 0.5% @HZSM5 single crystal.
[0046] SEM images of the products obtained in Examples 2, 3, and 4 are attached. Figure 2 The a, b, and c series correspond to Examples 2, 3, and 4, respectively. As shown in the figure, the Pt@HSCZ5(430, 200) series samples all exhibit a highly regular and ordered hexagonal coffin-plate-level single-crystal morphology with a size of approximately 3 μm. The b-axis thickness of the samples decreased after loading, which is attributed to the effect of a small amount of ethylenediamine ligand. Typically, the growth of the b-axis of MFI-type molecular sieves is controlled by adding structure-directing agents (quaternary ammonium salts) or growth inhibitors such as urea ammonium fluoride. The ammonium ions in urea and the generated ammonia gas inhibit the growth of the molecular sieve b-axis. Ethylenediamine is also a strongly alkaline structure-directing agent, which reduces the growth rate of the molecular sieve b-axis.
[0047] The HAADF-STEM and elemental distribution maps for Examples 2, 3, and 4 are attached. Figure 3 The a, b, and c series correspond to Examples 2, 3, and 4, respectively. Further analysis of the distribution of Pt elements is conducted. Figure 3 EDS-mapping results showed that the in-situ synthesized Pt w% In sample @HSCZ5(430, 200), the Pt element (yellow) is very uniformly distributed within the molecular sieve structure, without any aggregation.
[0048] High-resolution transmission electron microscope images of the products obtained in Examples 2, 3, and 4 are attached. Figure 4 As shown, series a, b, and c correspond to Examples 2, 3, and 4, respectively. Figure 4 Pt can be observed in high-resolution transmission electron microscopy images. 0.1%The @HSCZ5 (430, 200) sample did not contain any metallic Pt nanoparticles or clusters. 0.3% The Pt sample in @HSCZ5 (430, 200) is composed of nanoparticles with an average size of approximately 3.3 nm. 0.5% The Pt nanoparticles in the @HSCZ5 (430, 200) sample are approximately 4.5 nm in size. Organic ligand protection and the pore confinement of the hierarchical ZSM-5 molecular sieve are beneficial for obtaining small-sized Pt nanoparticles.
[0049] The HZSM5 and Pt obtained in Examples 1, 2, 3, and 4 0.1% @HZSM5, Pt 0.3% @HZSM5 and Pt 0.5% The XRD pattern of @HZSM5 is attached. Figure 5 As shown in the figure, the samples all exhibit characteristic diffraction peaks of the MFI type structure and have no other impurity peaks, indicating that the ZSM-5 molecular sieve was successfully synthesized. Furthermore, the increased intensity of the diffraction peaks after loading with Pt indicates an increase in the crystallinity of the samples. Figure 5 In the magnified XRD pattern of b, it can be seen that as the Pt loading increases, the diffraction peak of metallic Pt (PDF#04-0802) gradually appears at 2Theta of 39.8°, indicating that the size of metallic Pt particles gradually increases with the increase of loading.
[0050] The catalytic performance of the product was evaluated by using the hydrogenation reaction of nitrobenzene to support noble metals in the prepared ZSM-5 molecular sieve. 10 mL of deionized water, 20 μL of nitrobenzene, and 20 μL of dodecane were placed in a glass bottle and stirred for 10 minutes. Then, 20 mg of catalyst and a certain amount of sodium borohydride solution were added, and after stirring for a certain time, dichloromethane was added for extraction. The lower layer was collected, filtered through a 0.2 μm filter, and analyzed on a gas chromatograph (Agilent 7890B GC) equipped with a methylsiloxane capillary column (HP-5) connected to a flame ionization detector.
[0051] Cyclic stability test: After the reaction is completed, the mixed liquid is centrifuged, precipitated, dried in an oven at 60°C, and then the same catalytic test is performed, repeated 5 times.
[0052] The conversion C and selectivity S were calculated using n-dodecane as an internal standard. The conversion of nitrobenzene was calculated using Equation 5-1: Equation (1) A s1 , , These represent the peak areas of the initial reactant, post-reaction reactant, initial internal standard, and post-reaction internal standard in the chromatographic determination, respectively.
[0053] The selectivity of the product aniline was calculated using Equation 5-2: Equation (2) , These represent the peak areas of aniline and all products as determined by chromatography, respectively.
[0054] The catalytic performance of the products obtained in Examples 1, 2, 3, and 4 is shown in the appendix. Figure 6 As shown in the figure, the catalytic performance of Pt-based catalysts for the hydrogenation of nitrobenzene shows that single-atom Pt... 0.1% The nitrobenzene conversion rate of the @HSCZ5 (430, 200) catalyst was 82.6%, compared to Pt. 0.3% The 82.7% selectivity of the @HSCZ5 (430, 200) sample is close to that of the Pt sample, and the aniline selectivity is even higher than that of the Pt sample. 0.3% The @HSCZ5 (430, 200) sample demonstrates that when the size of metallic Pt is reduced to the single-atom level, the utilization rate of catalytic active sites increases significantly, and the performance is comparable to that of a high-load 3 nm Pt catalyst.
Claims
1. A method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieves, characterized in that... Includes the following steps: (1) Polystyrene microspheres, colloidal silica, sucrose and dilute sulfuric acid solution were mixed evenly and transferred into an oven for deposition self-assembly process to obtain polystyrene microsphere / silica / carbon mixed precursor; (2) The mixed precursor is calcined under an inert atmosphere. The calcined product is dissolved by adding hydrofluoric acid and then washed, filtered, and dried to obtain a graded macroporous-mesoporous carbon template material. (3) A precursor solution was prepared using deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, chloroplatinic acid, ethylenediamine and tetraethyl orthosilicate, mixed with the macroporous-mesoporous carbon template material of the above grade, dried and transferred to a reaction vessel for crystallization treatment, centrifuged, washed and dried to obtain the crystallized product; (4) The crystallized product is placed in a muffle furnace for calcination treatment; (5) The product obtained in step (4) is reduced under a hydrogen atmosphere to obtain a single crystal of graded pore ZSM-5 molecular sieve loaded with Pt.
2. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... The polystyrene microspheres in step (1) have a size of 400~600nm, the colloidal silica is a silica suspension with a concentration of 40wt%, and the sulfuric acid solution has a concentration of 10wt%. The mass ratio of polystyrene microspheres, silica, sucrose and sulfuric acid solution is 100 : (10-20) : (10-20) : (10-20).
3. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... The calcination process in step (2) includes holding at 400℃ for 1 hour, raising the temperature to 500℃ and holding for 6 hours, raising the temperature to 650℃ and holding for 4 hours, with a heating rate of 1℃ / min.
4. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... In step (2), the calcined product is added to hydrofluoric acid and stirred for more than 4 hours to dissolve; the drying temperature is 80℃ and the drying time is 24 hours.
5. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... The preparation of the precursor solution in step (3) includes the following steps: deionized water and structure-directing agent tetrapropylammonium hydroxide are stirred and dissolved, aluminum source aluminum isopropoxide is added and stirred and dissolved, and then silicon source tetraethyl orthosilicate and ethylenediamine are added dropwise and stirred and dissolved to obtain a clear and transparent precursor solution.
6. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... In step (3), the molar ratio of deionized water, tetrapropylammonium hydroxide, aluminum isopropoxide, tetraethyl orthosilicate, chloroplatinic acid and ethylenediamine is 15:(0.4-0.5):(0.01-0.015):(0.9-1.1):(0.0003-0.015):(0.03-0.19).
7. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... In step (3), the carbon template material is completely soaked in the precursor solution and then dried and aged at 40°C for 12 hours to remove water molecules.
8. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... In step (3), the crystallization temperature is 180℃ and the time is 5~6h.
9. The method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve as described in claim 1, characterized in that... The calcination process in step (4) includes heating to 550℃ and calcining for 7-8 hours at a rate of 2℃ / min.
10. A Pt-loaded hierarchical porous ZSM-5 molecular sieve, prepared by the method for preparing Pt-loaded hierarchical porous ZSM-5 molecular sieve according to any one of claims 1-9.