Method for synthesizing hierarchical pore ZSM-5 molecular sieve with assistance of metal salt

Abstract

The invention belongs to the technical field of molecular sieves and porous materials, and particularly relates to a method for synthesizing a hierarchical pore ZSM-5 molecular sieve under the assistance of metal salt. The method comprises the following steps: mixing a metal salt, water and a synthesis mother solution of the ZSM-5 molecular sieve, carrying out hydrothermal crystallization, separating, washing and drying a crystallization product, and calcining to obtain the hierarchical pore ZSM-5 molecular sieve. Compared with the prior art, the method has the advantages that the metal salt is used for replacing a long-chain organic matter or a carbon material to serve as the hierarchical pore guiding agent, and the production cost of the hierarchical pore ZSM-5 can be effectively reduced. Meanwhile, the hierarchical pore degree of ZSM-5 can also be regulated and controlled through the adding proportion of the metal salt, so that the hierarchical pore ZSM-5 molecular sieve has a wide application prospect in the fields of catalysis, separation and the like.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve and porous materials technology, specifically relating to a method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salts. Background Technology

[0002] Molecular sieves are a class of microporous materials widely used in industrial catalysis processes, with ZSM-5 molecular sieve being a typical example. ZSM-5 molecular sieve was first synthesized by Mobil in 1972 (US4954325). According to results published by the International Zeolite Association (IZA), ZSM-5 molecular sieve belongs to the MFI topology, possessing a three-dimensional ten-membered ring pore structure with pore diameters ranging from 0.5 to 0.6 nm.

[0003] ZSM-5 possesses regular and ordered micropores and acidic active centers within these pores, making it widely applicable in catalytic reactions and separations, such as hydrocracking, alkylation, and isomerization. However, the small size of the micropores increases the resistance to molecular diffusion, leading to side reactions and reducing its performance and lifetime as a catalyst. Therefore, it is crucial to prepare ZSM-5 molecular sieves that simultaneously contain hierarchical pores.

[0004] Traditional methods for preparing hierarchical porous ZSM-5 include post-treatment methods and template methods. For example, J. Pérez-Ramírez et al. treated ZSM-5 molecular sieves with NaOH solution (J. Phy. Chem. C, 2011, 115: 1, 4193-14203), but the product yield was low and the crystallinity was poor. Template methods include hard template methods and soft template methods. The hard template method uses various carbon materials as templates to directly grow molecular sieves on the surface of the carbon materials, and removes the template by calcination after crystallization (Inorg. Chem. 2000, 39, 2279-2283; Microporous Mesoporous Mater. 2003, 65, 59-75; Chem. Mater. 2004, 16, 3168-3175). The soft template method uses long-chain organic compounds as soft templates for synthesis, such as using bisquaternary ammonium surfactant C. 22-6-6 (OH)₂ (Nature 2009, 461, 246-249), CTAB (Catal. Commun. 2011, 12, 1201-1205), silanized seed crystals (Chem. Mater. 2009, 21, 641-654), etc. Template methods generally suffer from relatively high costs and are difficult to industrialize. Therefore, developing a cost-effective and easy-to-implement strategy for synthesizing hierarchical porous ZSM-5 molecular sieves is crucial. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for synthesizing hierarchical pore ZSM-5 zeolite assisted by metal salts. This method is simple and economical and is of great significance for regulating the morphology, catalytic and separation properties of the zeolite.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a method for synthesizing hierarchical pore ZSM-5 zeolite assisted by metal salts. Mix metal salts, water and the synthesis mother liquor of ZSM-5 zeolite, carry out hydrothermal crystallization, then separate, wash and dry the crystallization product, and then calcine to obtain hierarchical pore ZSM-5 zeolite; the metal salts include at least one of titanium salts, tin salts, gallium salts, vanadium salts, copper salts, zirconium salts, chromium salts, nickel salts, niobium salts, yttrium salts, scandium salts.

[0008] In the above technical solution, further, the synthesis mother liquor of ZSM-5 zeolite consists of a silicon source, an aluminum source, an organic template R and an alkali source; wherein, the silicon source is selected from at least one of silicic acid, silica gel, silicon sol, tetraalkyl orthosilicate, water glass, silicon dioxide, the aluminum source is selected from at least one of aluminum hydroxide, sodium metaaluminate, aluminum nitrate, aluminum chloride, aluminum isopropoxide, aluminum sulfate, pseudo-boehmite, kaolin, montmorillonite, the organic template R is selected from at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, and the alkali is selected from one of hydroxides of alkali metals, hydroxides of alkaline earth metals, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide.

[0009] In the above technical solution, further, the titanium salts include titanium tetrachloride, tetrabutyl titanate, tetraethyl titanate, the tin salts include tin tetrachloride, sodium stannate, tin dioxide, the gallium salts include gallium nitrate, gallium oxide, gallium chloride, the vanadium-containing salts include vanadyl sulfate, ammonium metavanadate, the copper salts include copper acetylacetonate, copper nitrate, copper chloride, copper sulfate, the zirconium salts include zirconium oxychloride, zirconium nitrate, zirconium oxynitrate, the chromium salts include chromium chloride, chromium oxide, chromium nitrate, chromium sulfate, the nickel salts include nickel chloride, nickel nitrate, nickel acetate, the niobium salts include niobium ethoxide, niobium pentachloride, the yttrium salts include yttrium nitrate, and the scandium salts include scandium nitrate.

[0010] In the above technical solution, further, the molar ratio of the silicon source, aluminum source, alkali, organic template R, metal salt M and water is: SiO2:Al2O3:OH - :R:M:H2O = 1:(0.00001 - 0.4):(0.01 - 1):(0.01 - 1):x:(1 - 200), 0 < x < 0.5, preferably SiO2:Al2O3:OH -:R:M:H2O=1:(0.005-0.1):(0.01-1):(0.01-1):x:(10-100),0 <x<0.5。

[0011] In the above technical solution, the hydrothermal crystallization conditions are further defined as follows: crystallization temperature of 130-190℃ and crystallization time of 3-240 hours.

[0012] In the above technical solution, the calcination temperature is 400-600℃ and the calcination time is 2-10 hours.

[0013] Another aspect of the present invention provides a hierarchical porous ZSM-5 molecular sieve prepared by the above method, characterized in that the proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared and 2,6-di-tert-butylpyridine adsorption infrared, is higher than 10%.

[0014] When the mother liquor system for synthesizing ZSM-5 molecular sieve contains alkali metals or alkaline earth metals, if sodium aluminate is used as the aluminum source and alkali metal hydroxides or alkaline earth metal hydroxides are used as the alkali source, the resulting hierarchical porous ZSM-5 molecular sieve will convert the framework equilibrium ions into H+. + Subsequently, the results were determined by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy.

[0015] The skeletal equilibrium ions are converted into H. + The method involves placing the molecular sieve in an aqueous solution of ammonium chloride, ammonium sulfate, ammonium acetate, or ammonium nitrate at 60-80℃, wherein NH4+... + The concentration is 0.05-2 mol / L. The mixture is stirred for 1-3 hours for exchange, and the exchange is repeated 1-5 times. The separated product is then dried and calcined.

[0016] The measurement procedures and methods for the percentage of acid sites on the outer surface determined by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy are as follows:

[0017] Pyridine adsorption infrared spectroscopy was performed in an in-situ transmission cell. Typically, approximately 20 mg of sample was pressed into a self-supported sample sheet on a 14 mm mold and placed in the in-situ cell. The sample was degassed under vacuum at 450 °C for 1 h, then cooled to 150 °C for spectral acquisition. The sample was then exposed to pyridine vapor at 150 °C for 5 min, followed by vacuum degassed for 1 h to remove excess pyridine. The resulting spectrum was then acquired. The two spectra were subtracted to obtain the pyridine adsorption infrared spectrum. The total Brønsted acid density was calculated using methods referenced in the literature (J. Catal. 1991, 141, 347-354 or J. Chem. Soc., Faraday Trans. 1997, 93, 1661-1665), denoted as B. Py .

[0018] 2,6-Di-tert-butylpyridine adsorption infrared spectroscopy was performed in an in-situ transmission cell. Typically, approximately 20 mg of sample was pressed onto a 14 mm mold to prepare a self-supported sample sheet, which was then placed in the in-situ cell. The sample was degassed under vacuum at 450 °C for 1 h, followed by cooling to 150 °C for spectral acquisition. The sample was then exposed to 2,6-di-tert-butylpyridine vapor at 150 °C for 10 min, followed by vacuum degassed for 1 h to remove excess 2,6-di-tert-butylpyridine before acquiring the adsorbed spectrum. The two spectra were subtracted to obtain the pyridine adsorption infrared spectrum. The method used to calculate the Brønsted acid density on the outer surface was based on the literature (J. Phy. Chem. C, 2014, 118, 12266-12274), denoted as Brønsted acid. 2,6-DT BPy ;

[0019] The proportion of acid sites on the outer surface is B 2,6-DTBPy / B Py ×100%.

[0020] The beneficial effects of this invention are as follows:

[0021] Compared with existing technologies, this invention uses metal salts instead of long-chain organic materials or carbon materials as hierarchical pore guiding agents, which can effectively reduce the production cost of hierarchical ZSM-5. Furthermore, the degree of hierarchical porosity of ZSM-5 can be controlled by the proportion of metal salt added, making this hierarchical ZSM-5 molecular sieve promising for broad applications in catalysis and separation.

[0022] The method of this invention has the advantages of simple operation, good economy and high product yield, which is of great significance for controlling the morphology and catalytic and separation performance of the molecular sieve. Attached Figure Description

[0023] Figure 1 The NLDTF pore size distribution diagram of the hierarchical porous ZSM-5 molecular sieve prepared in Example 1;

[0024] Figure 2 The images show TEM images of the hierarchical porous ZSM-5 molecular sieve prepared in Example 2 and the ZSM-5 molecular sieve prepared in Comparative Example 1. a is Example 2 and b is Comparative Example 1. Detailed Implementation

[0025] The present invention will be further illustrated below by way of embodiments, but the scope of the claims of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Weigh 7.75g of 40wt% tetrapropylammonium hydroxide solution, 28.3g of water and 0.12g of aluminum isopropoxide and stir to dissolve. Add 12.71g of tetraethyl orthosilicate and stir for 2h to obtain a clear solution. Add 0.42g of tetrabutyl titanate and stir for 2h. The reactant ratio is SiO2:Al2O3:TPAOH:Ti:H2O=1:0.005:0.25:0.02:30.

[0028] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 170℃ for 1 day. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0029] The proportion of acid sites on the outer surface to the total acid sites, as determined by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 31%.

[0030] The pore size distribution of the ZSM-5 molecular sieve prepared in Example 1, measured by NLDFT, is shown in the figure. Figure 1 .Depend on Figure 1 The clearly visible hierarchical porous components (indicated by the arrows) indicate that the synthesized material is a hierarchical ZSM-5 molecular sieve.

[0031] Example 2

[0032] Weigh 10.15g of 40wt% tetrapropylammonium hydroxide solution, 11.3g of water, 0.1631g of aluminum isopropoxide, and 2.0g of gallium nitrate and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2 hours to obtain a clear solution. The reactant ratio is SiO2:Al2O3:TPAOH:Ga:H2O = 1:0.05:0.25:0.01:10.

[0033] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 170℃ for 3 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0034] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 28%.

[0035] The TEM image of the ZSM-5 molecular sieve obtained in Example 1 is shown below. Figure 2 The ZSM-5 particles clearly exhibit visible porosity, indicating that they are hierarchical ZSM-5 molecular sieves.

[0036] Example 3

[0037] Weigh out 5.32 g of tetrapropylammonium bromide, 0.64 g of NaOH, 143.9 g of water, 3.24 g of aluminum isopropoxide, and 0.28 g of SnCl4, and stir to dissolve. Add 16.64 g of tetraethyl orthosilicate and stir for 2 hours to obtain a clear solution. The reactant ratio is SiO2:Al2O3:TPABr:OH - :Sn:H2O=1:0.1:0.25:0.2:0.015:100;

[0038] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner, and the temperature was increased to 170℃ at 0.5℃ / min for 3 days for crystallization. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0039] The obtained molecular sieve was placed in a 1 mol / L ammonium acetate solution with a volume of 50 ml / g of molecular sieve. The solution was placed in an 80°C water bath for ammonium exchange for 2 h. After the exchange was completed, the solid was obtained by filtration. This process was repeated 3 times. The obtained solid was dried at 110°C for 10 h and calcined at 500°C for 4 h to obtain the H-type molecular sieve product.

[0040] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 24%.

[0041] Example 4

[0042] Weigh 10.15g of 40wt% tetrapropylammonium hydroxide solution, 22.6g of water and 0.326g of aluminum sulfate and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2h to obtain a clear solution. Add 13.5g of niobium ethoxy and stir for 2h. The reactant ratio is SiO2:Al2O3:TPAOH:Nb:H2O=1:0.01:0.25:0.5:20.

[0043] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 140℃ for 4 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0044] The proportion of acid sites on the outer surface to the total acid sites, as determined by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 35%.

[0045] Example 5

[0046] Weigh out 22.6g of water, 0.326g of aluminum sulfate and 0.29g of vanadium sulfate and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2 hours. Quickly add 40.6g of 40wt% tetrapropylammonium hydroxide solution and stir for 2 hours. The reactant ratio is SiO2:Al2O3:TPAOH:V:H2O=1:0.01:1:0.01:20.

[0047] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 140℃ for 4 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0048] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 24%.

[0049] Example 6

[0050] Weigh 0.82 g of 40 wt% tetrapropylammonium hydroxide solution, 79.6 g of water, 0.16 g of aluminum isopropoxide, and 0.6 g of yttrium nitrate and stir to dissolve. Add 32.3 g of tetraethyl orthosilicate and stir for 5 h. The reactant ratio is SiO2:Al2O3:TPAOH:Y:H2O = 1:0.0025:0.01:0.01:30.

[0051] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 170℃ for 4 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0052] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 18%.

[0053] Example 7

[0054] Weigh 16g of 30% silica sol, 10.15g of 40wt% tetrapropylammonium hydroxide solution, 11.4g of water, 0.1631g of aluminum isopropoxide, and 0.21g of chromium chloride hexahydrate. Stir and dissolve the solutions for 2 hours to obtain a clear solution. The reactant ratio is SiO2:Al2O3:TPAOH:Cr:H2O = 1:0.005:0.25:0.01:20.

[0055] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 150℃ for 4 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0056] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 15%.

[0057] Example 8

[0058] Weigh 10.15g of 40wt% tetrapropylammonium hydroxide solution, 8.3g of water and 0.326g of aluminum sulfate and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2h to obtain a clear solution. Add 0.21g of copper acetylacetonate and stir for 2h. The reactant ratio is SiO2:Al2O3:TPAOH:Cu:H2O=1:0.01:0.25:0.01:10.

[0059] The reactants were placed in a 100ml reactor lined with polytetrafluoroethylene and crystallized at 130℃ for 5 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve. The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 22%.

[0060] Example 9

[0061] Weigh out 22.6g of water, 0.213g of aluminum chloride, and 0.77g of zirconium oxychloride octahydrate and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2 hours. Add 10.15g of 40wt% tetrapropylammonium hydroxide solution and stir for 2 hours. The reactant ratio is SiO2:Al2O3:TPAOH:Zr:H2O = 1:0.01:0.25:0.03:20.

[0062] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 175℃ for 2 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0063] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 14%.

[0064] Example 10

[0065] Weigh out 16.5g of water, 0.42g of aluminum chloride and 0.40g of nickel acetate tetrahydrate and stir to dissolve. Add 12.16g of tetramethyl orthosilicate and stir for 2 hours. Add 16.24g of 25wt% tetrapropylammonium hydroxide solution and stir for 2 hours. The reactant ratio is SiO2:Al2O3:TPAOH:Ni:H2O = 1:0.02:0.25:0.02:20.

[0066] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 145℃ for 4 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0067] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 12.5%.

[0068] Example 11

[0069] Weigh out 4.8g of fumed silica, 10.15g of 40wt% tetrapropylammonium hydroxide solution, 37g of water, 0.652g of aluminum isopropoxide, and 0.21g of scandium chloride hexahydrate. Stir and dissolve the solutions for 2 hours to obtain a clear solution. The reactant ratio is SiO2:Al2O3:TPAOH:Sc:H2O = 1:0.02:0.25:0.01:30.

[0070] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 180℃ for 1 day. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0071] The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was 21.5%.

[0072] Comparative Example 1

[0073] Weigh 10.15g of 40wt% tetrapropylammonium hydroxide solution, 22.6g of water and 0.1631g of aluminum isopropoxide and stir to dissolve. Add 16.64g of tetraethyl orthosilicate and stir for 2h to obtain a clear solution. The reactant ratio is SiO2:Al2O3:TPAOH:H2O=1:0.005:0.25:20.

[0074] The reactants were placed in a 100ml reaction vessel with a polytetrafluoroethylene liner and crystallized at 170℃ for 3 days. After crystallization, the mixture was filtered, washed, and dried to obtain the molecular sieve precursor, which was then calcined in air at 540℃ for 6 hours to obtain ZSM-5 molecular sieve.

[0075] The proportion of acid sites on the outer surface, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was only 9.4% of the total acid sites.

[0076] TEM images of the molecular sieves prepared in Comparative Example 1 are shown below. Figure 2 The morphology is regular and there are no visible mesopores, indicating that hierarchical ZSM-5 cannot be obtained without the addition of other metal salts.

[0077] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salt-assisted synthesis, characterized in that, Metal salts, water and the synthesis mother liquor of ZSM-5 molecular sieve were mixed and hydrothermally crystallized. The crystallized products were separated, washed and dried, and then calcined to obtain hierarchical porous ZSM-5 molecular sieve. The metal salt includes at least one of titanium salt, tin salt, gallium salt, vanadium salt, copper salt, zirconium salt, chromium salt, nickel salt, niobium salt, yttrium salt, and scandium salt.

2. The method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salts as described in claim 1, characterized in that, The synthesis mother liquor of the ZSM-5 molecular sieve is composed of a silicon source, an aluminum source, an organic template agent R, and an alkali source. The silicon source is selected from at least one of silicic acid, silica gel, silica sol, tetraalkyl silicate, water glass, and silica. The aluminum source is selected from at least one of aluminum hydroxide, sodium aluminate, aluminum nitrate, aluminum chloride, aluminum isopropoxide, aluminum sulfate, boehmite, kaolin, and montmorillonite. The organic template agent R is selected from at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and tetrapropylammonium chloride. The alkali is selected from one of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, alkali metal hydroxides, and alkaline earth metal hydroxides.

3. The method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salts as described in claim 1, characterized in that, The molar ratio of the silicon source, aluminum source, alkali, organic template agent R, metal salt M, and water is: SiO2:Al2O3:OH. - :R:M:H2O=1:(0.00001-0.4):(0.01-1):(0.01-1):x:(1-200),0 <x<0.5。 4. The method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salts as described in claim 1, characterized in that, The hydrothermal crystallization conditions are: crystallization temperature of 130-190℃ and crystallization time of 3-240 hours.

5. The method for synthesizing hierarchical porous ZSM-5 molecular sieves using metal salts as described in claim 1, characterized in that, The calcination temperature is 400-600℃, and the calcination time is 2-10 hours.

6. A hierarchical porous ZSM-5 molecular sieve prepared by the method according to any one of claims 1-5, characterized in that, The proportion of acid sites on the outer surface to the total acid sites, as measured by pyridine adsorption infrared spectroscopy and 2,6-di-tert-butylpyridine adsorption infrared spectroscopy, was higher than 10%.

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