Nanoscale zsm-5 molecular sieve and method for synthesizing the same

Abstract

The application discloses a kind of nano ZSM-5 molecular sieve and synthesis method thereof.Synthesis method includes: (1) the silicon source, aluminum source, template agent and water are mixed, adjust solution pH value, keep 1~72 hours under 20~120 DEG C, and material I is obtained;Control source is added to material I and is reacted, hydrothermal crystallization, and the crystallization product is obtained;The obtained crystallization product is acid treated, and control source element is removed, and the nano ZSM-5 molecular sieve is obtained.The synthesis method of the application can effectively control the size of nano ZSM-5 molecular sieve, and it is simple and feasible to operate.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, and more specifically, to a nano ZSM-5 molecular sieve and its synthesis method. Background Technology

[0002] Microporous zeolite molecular sieves are inorganic silicon-containing crystals with a framework containing regularly ordered channels similar in size to molecules. They are widely used in catalysis, ion exchange, and separation, especially ZSM-5 molecular sieves. ZSM-5 zeolite has a three-dimensional channel system composed of 10-membered rings, with a size comparable to the aromatic rings of monocyclic aromatic hydrocarbons. In the early 1970s, US5672331A disclosed a method for synthesizing ZSM-5 molecular sieves. Since then, ZSM-5 molecular sieves have been widely used in reactions such as alkylation, isomerization, disproportionation, selective cracking, and the synthesis of gasoline from methanol.

[0003] CN106698463A employs a specific macroporous carbon synthesis method, mixing different macroporous carbons, inorganic bases, water, template agents, aluminum sources, and silicon sources to form a gel, and then synthesizing ZSM-5 nanomolecular sieves using a gas-phase synthesis method. This method is complex, with significant challenges in gel evaporation, making reproducibility difficult to guarantee. CN108793185A synthesizes ZSM-5 molecular sieve catalysts by adding polymers. The polymers include polyvinylpyrrolidone, polyacrylamide, polystyrene, polyurethane, and other high-molecular-weight compounds.

[0004] CN109694086A and CN112047847A were synthesized using a conventional hydrothermal synthesis method, but specific template agents were employed. These template agents have complex structures, resulting in high synthesis costs and making them unsuitable for large-scale production.

[0005] CN100364890A uses a surfactant, which is added to an acidified aluminum salt solution. Then, an alkaline solution formed by water glass, template agent, and seed crystal is slowly added dropwise to the aluminum salt solution. After crystallization, ZSM-5 molecular sieve is obtained.

[0006] CN102671693A discloses a method for synthesizing high silica-to-alumina ratio nano-ZSM-5 molecular sieves. The method uses an organic template method, in which organosilanes are directly added to the original molecular sieve solution, and silanes are grafted onto ZSM-5 molecular sieve seed crystals under reflux conditions. The organic template and organosilanes are removed by calcination to obtain the ZSM-5 molecular sieve.

[0007] Currently, there are many methods for synthesizing nano-ZSM-5 molecular sieves, but many problems still need to be solved in the synthesis process. The preparation process of nano-ZSM-5 molecular sieves is complex, requiring the addition of a large number of auxiliary agents. Furthermore, the synthesized molecular sieves require post-processing to obtain the final nano-molecular sieves, and the excessively small particle size makes separation difficult, limiting its industrial applications. How to effectively control the crystallite size of nano-ZSM-5 molecular sieves has become a major challenge in molecular sieve synthesis. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies for synthesizing nano-ZSM-5 molecular sieves by providing a nano-ZSM-5 molecular sieve and its synthesis method. This method effectively controls the crystal size of the nano-ZSM-5 molecular sieve, has a simple preparation process, and can be used for industrial production.

[0009] The first aspect of this invention provides a method for synthesizing nano-ZSM-5 molecular sieves, comprising the following steps:

[0010] (1) Mix silicon source, aluminum source, template agent and water, adjust the pH value of the solution, and keep it at 20-120℃ for 1-72 hours to obtain material I;

[0011] (2) Add the control source to the material I obtained in step (1) to react, and perform hydrothermal crystallization to obtain the crystallized product;

[0012] (3) The crystallized product obtained in step (2) is subjected to acid treatment to obtain the nano ZSM-5 molecular sieve.

[0013] Further, in step (1), the silicon source is at least one of silica sol, water glass, and tetraethyl orthosilicate. The aluminum source is at least one of aluminum sulfate, aluminum nitrate, aluminum hydroxide, and sodium aluminate.

[0014] Further, in step (1), the template agent is an organic amine template agent, and the organic amine is one or more of alkylamine (monoalkylamine) and polyalkylamine, wherein the number of carbon atoms in the alkyl group is 1 to 6, and the number of alkyl groups is 1 to 4; preferably at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tri-n-propylamine, and cyclohexylamine.

[0015] Further, in step (1), the pH value is 9.0 to 11.5, and the pH of the solution can be adjusted by adding an acid or a base. The base used is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and cesium hydroxide, and the acid used is selected from one or more of sulfuric acid, hydrochloric acid, acetic acid, phosphoric acid, formic acid, propionic acid, oxalic acid, and amino acids.

[0016] Further, in step (1), the silicon source is SiO2 and the aluminum source is Al2O3. The molar ratio of each substance is SiO2:Al2O3:template agent:H2O=a:1:b:c, where the value of a ranges from 15 to 900, the value of b ranges from 0 to 500, and the value of c ranges from 100 to 50000.

[0017] Further, in step (1), preferably, the value range of a is 18 to 200, the value range of b is 0.1 to 300, and the optimized value range of c is 180 to 8000.

[0018] Further, in step (1), the molar ratio of the template agent to the silicon source (calculated as SiO2) is 0 to 1.0 and 0.001 to 0.3.

[0019] Furthermore, ZSM-5 seed crystals may be added in step (1). The amount of ZSM-5 seed crystals added is 0.2% to 5.0% based on the weight of SiO2 contained in the silicon source, preferably 0.2% to 1.0%.

[0020] Furthermore, the SiO2 / Al2O3 molar ratio of the ZSM-5 seed crystal is 12 to 500.

[0021] Furthermore, in step (1), the mixture can be kept at a temperature of 50 to 120°C for 2 to 60 hours under static or dynamic conditions, with a gauge pressure of 0.1 to 0.3 MPa.

[0022] Further, in step (2), the control source can be a soluble compound. The control source element is selected from one or more elements among B, Ge, V, Fe, Co, Ni, Ga, Sn, and Zn, preferably one or more elements among Fe and Zn. For example, the B source can be at least one of sodium tetraborate and boric acid; the Ge source can be one or more alkali metal germanates; the V source can be at least one of ammonium vanadate and sodium vanadate; the Fe source can be at least one of ferric sulfate, ferric halide, and ferric nitrate; the Co source can be at least one of cobalt sulfate, cobalt halide, and cobalt nitrate; the Ni source can be at least one of nickel sulfate, nickel halide, and nickel nitrate; the Ga source can be at least one of gallium halide, gallium nitrate, sodium gallate, and potassium gallate; the Sn source can be at least one of its corresponding sulfate, halide, and nitrate; and the Zn source can be at least one of its corresponding sulfate, halide, nitrate, and water-soluble zincate (such as group IA salts).

[0023] Further, in step (2), the mass ratio of the silicon source (SiO2) to the control source (oxide) is 15 to 2000, preferably 15 to 200.

[0024] Furthermore, in step (2), the concentration of the source element ions is controlled to be 0.01–10 mol / L.

[0025] Further, in step (2), the reaction is carried out under stirring, the reaction temperature is below 50°C, preferably 0 to 30°C, and the reaction time is 0.5 to 72 hours, preferably 0.5 to 20 hours; wherein, the reaction temperature in step (2) is 10 to 115°C lower than the temperature in step (1), preferably 20 to 70°C.

[0026] Furthermore, in step (2), the conditions for hydrothermal crystallization are: crystallization at 90-180°C for 2-96 hours, preferably at 120-180°C for 12-72 hours.

[0027] Furthermore, in step (2), after hydrothermal crystallization, the crystallized solid product can be separated from the obtained mixture by any conventionally known separation method, such as filtration or washing.

[0028] Further, in step (3), the acid used for acid treatment is one or more of hydrochloric acid, sulfuric acid, and nitric acid, wherein the concentration of the acid used is 0.01 to 5 mol / L, and the ratio of the mass of the acid to the mass of the crystallized product is 0.001 to 5, preferably 0.01 to 0.5.

[0029] Further, in step (3), the acid treatment conditions are: acid treatment temperature of 20-95℃, treatment time of 1-48h, and treatment times of 1-4 times.

[0030] Further, in step (3), after the acidification treatment, the ZSM-5 molecular sieve product can be separated from the obtained mixture by any conventionally known separation method, such as filtration, washing, and drying. The drying temperature can be selected from 30 to 280°C, preferably 60 to 180°C, and the drying time can be selected from 0.1 to 72 hours, preferably 5 to 48 hours. The drying can be carried out under normal pressure or under reduced pressure; to save energy, it is usually carried out under normal pressure.

[0031] A second aspect of the present invention provides a nano-ZSM-5 molecular sieve synthesized by the above-described synthesis method, wherein the crystal size of the nano-ZSM-5 molecular sieve is 20-200 nm, preferably 20-100 nm.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This invention provides a novel method for synthesizing nano-ZSM-5 molecular sieves. The synthesis process involves first preparing a crystallization solution, maintaining it under static or dynamic conditions for a period of time, then adding a control source, and finally removing the impurities through acid treatment to obtain pure-phase nano-ZSM-5 molecular sieves. This method effectively controls the size of the nano-ZSM-5 molecular sieves; the crystal size gradually decreases with increasing control source content. This synthesis method significantly reduces the difficulty of synthesizing nano-molecular sieves, is simple to operate, and allows for large-scale production. Attached Figure Description

[0034] Figure 1 The XRD pattern of the nano ZSM-5 molecular sieve prepared in Example 1 of this invention;

[0035] Figure 2 This is a SEM image of the nano ZSM-5 molecular sieve prepared in Example 1 of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] In this invention, XRD characterization was performed on a Pert PRO X-ray diffractometer. The experimental parameters were: tube voltage 40 kV, tube current 40 mA, Cu(Kα) (λ = 5.1540589 nm). Before testing, the sample was thoroughly ground in a mortar and scanned at a speed of 2° / min, with a 2θ angle scanning range of 5°–50°.

[0038] In this invention, ZSM-5 molecular sieve crystals with a size greater than 100 nm were characterized by scanning electron microscopy (SEM) using a Hitachi S-4800P II scanning electron microscope. ZSM-5 molecular sieve crystals with a size less than 100 nm were characterized by analytical transmission electron microscopy (TEM) using a Hitachi JEM-2010 analytical transmission electron microscope at a test voltage of 200 kV.

[0039] Example 1

[0040] (1) Mix silica sol (silicon source), aluminum sulfate (aluminum source), tetrapropylammonium bromide (template agent) and deionized water evenly, and add sodium hydroxide to adjust the pH value to 10. Add 0.5% ZSM-5 seed crystals (SiO2 / Al2O3 molar ratio is 15) based on the weight of SiO2 contained in the silicon source. The final molar ratio of each substance in the mixture is SiO2:Al2O3:template agent:H2O = 50:1:0.5:3000. Keep it under static conditions at 80℃ for 50 hours to obtain material I;

[0041] (2) The temperature of the above material I was lowered to 30℃, and a 0.05mol / L ferric sulfate solution was added and stirred for 8 hours. The mass ratio of silicon source (SiO2) to ferric sulfate (Fe2O3) was 20:SiO2:Fe2O3. Then, the mixture was crystallized at 120℃ under hydrothermal conditions for 72 hours, filtered and washed to obtain the crystallized product.

[0042] (3) The crystallized product was treated with 0.1 mol / L sulfuric acid at 80°C for 6 h, with the mass ratio of sulfuric acid to crystallized product being 0.01. After filtration and washing, the acid treatment was repeated once more, and the product was dried at 80°C for 80 h to obtain nano ZSM-5 molecular sieve. The crystal size was 70–120 nm.

[0043] Example 2

[0044] (1) Water glass (silicon source, mass content 22.0% SiO2, 6.8% Na2O), aluminum sulfate (aluminum source), tetrapropylammonium bromide (template agent) and deionized water are mixed evenly, and sulfuric acid is added to adjust the pH value to 10.5. Based on the weight of SiO2 contained in the silicon source, 1.0% ZSM-5 seed crystals (SiO2 / Al2O3 molar ratio is 56) are added. The final molar ratio of each substance in the mixture is SiO2:Al2O3:template agent:H2O = 30:1:0.5:3000. The mixture is kept under static conditions at 50℃ for 60 hours to obtain material I.

[0045] (2) The temperature of the above material I was lowered to 30℃, and a zinc sulfate solution with a concentration of 0.1mol / L was added. The mixture was stirred for 1 hour, wherein the mass ratio of silicon source (SiO2) to zinc sulfate (ZnO) was 1:5. Then, the mixture was crystallized at 130℃ under hydrothermal conditions for 48 hours, filtered and washed to obtain the crystallized product.

[0046] (3) The crystallized product was treated with 0.6 mol / L hydrochloric acid at 80 °C for 4 h, with the mass ratio of hydrochloric acid to crystallized product being 0.1. This process was repeated twice. After filtration and washing, the product was dried at 120 °C for 19 h to obtain nano ZSM-5 molecular sieve. The crystal size was 30–50 nm.

[0047] Example 3

[0048] (1) Tetraethyl orthosilicate (silicon source), aluminum nitrate (aluminum source), tri-n-propylammonium (template agent) and deionized water were mixed evenly, and sodium hydroxide was added to adjust the pH value to 10.5. Based on the weight of SiO2 contained in the silicon source, 1.0% ZSM-5 seed crystals were added (SiO2 / Al2O3 molar ratio of 210). The final molar ratio of each substance in the mixture was SiO2:Al2O3:template agent:H2O = 200:1:0.5:3000. The mixture was kept under static conditions at 100℃ and 0.1MPa for 16 hours to obtain material I.

[0049] (2) The temperature of the above material I was lowered to 30℃, and a 0.05mol / L ferric sulfate solution was added and stirred for 16 hours. The mass ratio of silicon source (SiO2) to ferric sulfate (Fe2O3) was 203. Then, the mixture was crystallized at 150℃ under hydrothermal conditions for 60 hours, filtered and washed to obtain the crystallized product.

[0050] (3) The above crystallized product was treated with 0.2 mol / L nitric acid at 80 °C for 4 h, with the mass ratio of nitric acid to crystallized product being 0.3. After filtration and washing, the process was repeated 3 times, and the product was dried at 180 °C for 6 h to obtain nano ZSM-5 molecular sieve. The crystal size was 20–90 nm.

[0051] Example 4

[0052] (1) Mix silica sol (silicon source), aluminum sulfate (aluminum source), tetrapropylammonium bromide (template agent) and deionized water evenly, and add sodium hydroxide to adjust the pH value to 10. Add 0.5% ZSM-5 seed crystals (SiO2 / Al2O3 molar ratio of 50) based on the weight of SiO2 contained in the silicon source. The final molar ratio of each substance in the mixture is SiO2:Al2O3:template agent:H2O = 50:1:0.5:3000. Keep it under static conditions at 80℃ for 50 hours to obtain material I;

[0053] (2) The temperature of the above material I was lowered to 30℃, and a 0.05mol / L ferric sulfate solution was added and stirred for 8 hours. The mass ratio of silicon source (SiO2) to ferric sulfate (Fe2O3) was 5:1. Then, the product was crystallized at 120℃ under hydrothermal conditions for 72 hours, filtered and washed to obtain the crystallized product.

[0054] (1) The above crystallized product was acidified with 0.1 mol / L sulfuric acid at 80 °C for 6 h, wherein the mass ratio of sulfuric acid to crystallized product was 0.1. The acidification treatment was repeated once, filtered and washed, and dried at 80 °C for 80 h to obtain nano ZSM-5 molecular sieve. The average grain size was 120-190 nm.

[0055] Example 5

[0056] (1) Water glass (silicon source, mass content 22.0% SiO2, 6.8% Na2O), aluminum sulfate (aluminum source), tetrapropylammonium bromide (template agent) and deionized water are mixed evenly, and sulfuric acid is added to adjust the pH value to 10.5. Based on the weight of SiO2 contained in the silicon source, 1.0% ZSM-5 seed crystals (SiO2 / Al2O3 molar ratio is 56) are added. The final molar ratio of each substance in the mixture is SiO2:Al2O3:template agent:H2O = 30:1:0.5:3000. The mixture is kept under static conditions at 50℃ for 60 hours to obtain material I.

[0057] (2) The temperature of the above material I was lowered to 30℃, and a zinc sulfate solution with a concentration of 0.1mol / L was added. The mixture was stirred for 1 hour, wherein the mass ratio of silicon source (SiO2) to zinc sulfate (ZnO) was 50. Then, the mixture was crystallized at 130℃ under hydrothermal conditions for 48 hours, filtered and washed to obtain the crystallized product.

[0058] (3) The crystallized product was treated with 0.6 mol / L hydrochloric acid at 80 °C for 4 h, with the mass ratio of hydrochloric acid to crystallized product being 0.1. This process was repeated twice. The product was then filtered, washed, and dried at 120 °C for 19 h to obtain nano ZSM-5 molecular sieve. The crystal size was 90–150 nm.

[0059] Examples 6-11

[0060] (1) Mix silicon source, aluminum source, template agent and deionized water evenly, and add sodium hydroxide to adjust the pH value to 10.5. Based on the weight of SiO2 contained in silicon source, add ZSM-5 seed crystals (SiO2 / Al2O3 molar ratio is 45). The final molar ratio of each substance in the mixture is SiO2:Al2O3:template agent:H2O=a:1:b:c. Keep under static conditions of T1 and P1 for H1 hours to obtain material I.

[0061] (2) The temperature of the above material I is lowered to T2, and a salt solution containing the control source element of a specified concentration C1 is added and stirred for H2 hours. The mass ratio of the silicon source (SiO2) to the salt containing the control source element (oxide) is Q1. Then, the product is crystallized under hydrothermal conditions at a specified temperature T3 and a specified time H3, filtered and washed to obtain the crystallized product;

[0062] (3) The crystallized product was acidified with a specified concentration of C2 acid solution R, with the ratio of acid mass to crystallized product mass being Q2, at a specified temperature T4 for a specified time H4, filtered and washed, and the above acidification treatment steps were repeated. The product was then dried at 80°C for 80 hours to obtain nano ZSM-5 molecular sieve.

[0063] The reaction conditions, reactant composition, and molecular sieve size for each step are detailed in Tables 1 and 2.

[0064] Table 1

[0065] T1 / ℃ P1 / MPa H1 / h T2 / ℃ H2 / h T3 / ℃ H3 / h T4 / ℃ H4 / h frequency Example 6 90 0 18 40 0.5 130 40 70 5 3 Example 7 120 0.3 60 5 30 160 80 80 4 2 Example 8 100 0.1 40 30 3 150 60 30 28 2 Example 9 90 0 30 50 72 180 50 95 3 2 Example 10 120 0.15 60 30 12 140 60 80 8 1 Example 11 120 0.25 72 30 60 135 65 50 48 1

[0066] Table 2

[0067]

[0068]

[0069] Comparative Example 1

[0070] Compared with Example 1, the difference is that step (1) does not include the step of maintaining the mixture at 80°C under static conditions for 50 hours. Amorphous molecular sieves are obtained.

[0071] Comparative Example 2

[0072] Compared with Example 1, the difference is that no control source ferric sulfate was added in step (2), and the resulting ZSM-5 molecular sieve size was 0.5 micrometers.

[0073] Comparative Example 3

[0074] Compared with Example 1, the difference is that in step (2), the material is not cooled and stirred before the reaction, that is, the ferric sulfate solution is directly added to the material I obtained in step (1) to react and obtain an amorphous molecular sieve.

[0075] The embodiments described above are merely detailed descriptions of the technical solutions of the present invention, but the present invention is not limited to the above embodiments, that is, the present invention does not depend on the steps described in the above embodiments to be implemented. In summary, any improvements made to the present invention by those skilled in the art, including the substitution of the raw materials and additives described in the present invention, the selection of specific implementation methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for synthesizing nano ZSM-5 molecular sieve, comprising the following steps: (1) mixing a silicon source, an aluminum source, a template agent and water, adjusting the pH value of the solution, and keeping at 20-120 ℃ for 1-72 hours to obtain material I; (2) adding a control source to the material I obtained in step (1) to react and hydrothermally crystallize to obtain a crystallization product; (3) acid treating the crystallization product obtained in step (2) to obtain the nano ZSM-5 molecular sieve; in step (2), the control source element is selected from one or more elements of B, Ge, V, Fe, Co, Ni, Ga, Sn and Zn; in step (2), the reaction temperature is below 50 ℃, and the reaction time is 0.5-72 hours. In step (1), the silicon source is at least one of silica sol, water glass and tetraethyl orthosilicate, and the aluminum source is at least one of aluminum sulfate, aluminum nitrate, aluminum hydroxide and sodium aluminate. In step (1), the template agent is an organic amine template agent, and the organic amine is one or more of alkyl amine and polyalkyl amine, wherein the number of carbon atoms in the alkyl group is 1-6, and the number of alkyl groups is 1-4. The organic amine is at least one of tetrapropyl ammonium hydroxide, tetrapropyl ammonium bromide, tri-n-propyl amine and cyclohexylamine. In step (1), the pH value is 9.0-11.

5. In step (1), the molar ratio of the silicon source (calculated as SiO2) to the aluminum source (calculated as Al2O3) and each substance is SiO2: Al2O3: template agent: H2O = a: 1: b: c, wherein the value range of a is 15-900, the value range of b is 0-500, and the value range of c is 100-50000. In step (1), the molar ratio of the silicon source (calculated as SiO2) to the aluminum source (calculated as Al2O3) and each substance is SiO2: Al2O3: template agent: H2O = a: 1: b: c, wherein the value range of a is 18-200, the value range of b is 0.1-300, and the value range of c is 180-8000. In step (1), the molar ratio of the template agent to the silicon source (calculated as SiO2) is 0-1.

0. In step (1), the molar ratio of the template agent to the silicon source (calculated as SiO2) is 0.001-0.

3. In step (1), ZSM-5 seeds are added, and the addition amount of the ZSM-5 seeds is 0.2%-5.0% based on the weight of SiO2 contained in the silicon source. The addition amount of the ZSM-5 seeds is 0.2%-1.0%. In step (1), the mixture is kept at 50-120 ℃ for 2-60 hours under static or dynamic conditions, and the gauge pressure is 0-0.3 MPa. In step (2), the control source element is one or more elements of Fe and Zn; the concentration of the control source is 0.01-10 mol / L; and / or, in step (3), the acid used for acid treatment is one or more of hydrochloric acid, sulfuric acid and nitric acid, the acid concentration is 0.01-5 mol / L, and the mass ratio of the acid to the crystallization product is 0.001-5. The mass ratio of the acid to the crystallization product is 0.01-0.

5. ​ ​ ​ ​ ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 1, wherein, ​ 4. The method of claim 3, wherein, ​ 5. The method of claim 1, wherein, ​ 6. The method of claim 1, wherein, ​ 7. The method of claim 6, wherein, ​ 8. The method of claim 1, wherein, ​ 9. The method of claim 8, wherein, ​ 10. The method of claim 1, wherein, ​ 11. The method of claim 1, wherein, ​ 12. The method of claim 1, wherein, ​ 13. The method of claim 1, wherein, ​ ​ 14. The method of claim 13, wherein, ​ 15. The method of claim 1, wherein, In step (2), the mass ratio of the silicon source calculated as SiO2 to the control source calculated as oxide is 15-2000.

16. The method of claim 15, wherein, In step (2), the mass ratio of the silicon source calculated as SiO2 to the control source calculated as oxide is 15-200.

17. The method of claim 1, wherein, In step (2), the reaction temperature is 0-30°C, and the reaction time is 0.5-20 hours; and / or, The hydrothermal crystallization is performed at 90-180°C for 2-96 hours; and / or, In step (3), the acid treatment is performed at 20-95°C for 1-48 hours, 1-4 times.

18. The method of claim 17, wherein, In step (2), the hydrothermal crystallization is performed at 120-180°C for 12-72 hours.

19. The nano-ZSM-5 molecular sieve synthesized by the method of any one of claims 1-18.

20. The molecular sieve of claim 19, wherein, The nano-ZSM-5 molecular sieve has a crystal grain size of 20-200 nm.

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