Alkyl phosphine directed nanosheet p@zsm-5 molecular sieve, preparation method and application thereof

Abstract

The application discloses an alkyl phosphine oriented nanosheet P@ZSM-5 molecular sieve and a preparation method and application thereof, and belongs to the technical field of molecular sieves. The nanosheet P@ZSM-5 molecular sieve provided by the application contains phosphorus in crystals, has an MFI structure and presents a regular nanosheet crystal form. The preparation method of the nanosheet P@ZSM-5 molecular sieve comprises the following steps: mixing a silicon source, an aluminum source, a phosphorus source, a solvent and MFI type seeds, stirring, then crystallizing the obtained initial solution, and washing, drying and calcining the obtained product to obtain the nanosheet P@ZSM-5 molecular sieve material containing phosphorus in crystals. The MFI type seeds and alkyl phosphine are used as a template agent and a phosphorus source in the application, and the phosphorus-containing nanosheet ZSM-5 molecular sieve is synthesized in one step. The preparation process of the application is simple, environment-friendly, the obtained molecular sieve material has a uniform and regular hexagonal prismatic crystal structure, and the molecular sieve material exhibits good catalytic effect and service life.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, and in particular to the one-step synthesis of nanosheet P@ZSM-5 molecular sieves, their preparation method, and their applications. Background Technology

[0002] ZSM-5 molecular sieves, due to their unique three-dimensional pore structure, tunable acidity, and excellent shape selectivity, are widely used in numerous catalytic reaction systems such as catalytic cracking, aromatization, methanol-to-propylene, and biomass conversion. However, in practical applications, the acidity and hydrothermal stability of conventional ZSM-5 molecular sieves cannot meet the performance requirements of these catalytic reactions. Phosphating of molecular sieves is the most critical technology for controlling the acidity of ZSM-5 and increasing the olefin selectivity of catalytic reaction products. Industrially, it has been successfully applied to processes such as alcohol-to-olefins, toluene and methanol alkylation, and catalytic cracking to increase propylene production. Post-modification of the parent ZSM-5 molecular sieve using phosphorus-containing compounds is currently the most widely used method in phosphorus modification research. Specifically, phosphoric acid or phosphate is introduced into the molecular sieve through impregnation, followed by calcination to obtain P-ZSM-5, and then the product slurry is ground to prepare the catalyst. The entire process is environmentally polluting, complex, and energy-intensive, and large phosphorus molecules do not easily enter the interior of the molecular sieve, resulting in low phosphorus utilization.

[0003] Patent application CN102311130A discloses a method for obtaining a phosphorus-containing ZSM-5 molecular sieve by gelling, crystallizing, filtering, drying, and calcining a silicon source, an aluminum source, an organophosphorus surfactant as a template agent, and water in a certain proportion. However, the synthesized material has low phosphorus utilization, resulting in a waste of phosphorus source. Patent document CN116216734B uses quaternary phosphorus bases as template agents, and after synthesis, calcination is performed to obtain a phosphorus-containing ZSM-5 molecular sieve. However, quaternary phosphorus bases are usually prepared by reacting alkylphosphine with halogenated hydrocarbons, which is expensive and the preparation process is relatively cumbersome. Patent application CN116216734A reports a method for directly synthesizing phosphorus-containing molecular sieves, but the synthesized material does not possess the excellent properties of nanosheets, i.e., it lacks a short b-axis and does not have good mass transfer performance.

[0004] Currently, the prepared P@ZSM-5 molecular sieves contain sodium, and the preparation process is complex, energy-intensive, and the molecular sieve crystals are irregular. Therefore, designing a simple preparation route that can effectively introduce phosphorus species and synthesize molecular sieves with a regular crystal form is the key issue in the current preparation of P@ZSM-5 molecular sieves. Summary of the Invention

[0005] The purpose of this invention is to provide an alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve with the chemical formula: xSiO2:Al2O3:yP2O5, where x = 10~100 and y = 0.01~10. It possesses an MFI structure and exhibits a regular nanosheet crystal form. This molecular sieve not only has a regular short b-axis nanosheet crystal structure, demonstrating excellent mass transfer performance and product selectivity in catalytic applications, but also improves the dispersibility and utilization of phosphorus, enhances the interaction between phosphorus and aluminum, and allows the phosphorus species within the synthesized molecular sieve material to efficiently stabilize the framework aluminum structure.

[0006] Another objective of this invention is to provide a method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieves, specifically including the following steps:

[0007] (1) Stir the alkylphosphine, aluminum source, silicon source, MFI seed crystal and solvent required to dissolve the alkylphosphine at room temperature to obtain an initial mixed solution.

[0008] (2) The initial mixed solution was subjected to hydrothermal crystallization, and the crystallized product was recovered to obtain the initial gel.

[0009] (3) The initial gel was washed, dried and calcined to obtain MFI type seed nanosheets P@ZSM-5 molecular sieve.

[0010] Preferably, the preparation method of the MFI type seed crystal is as follows: tetraethyl orthosilicate and tetrapropylammonium hydroxide are mixed at a mass ratio of 1:0.36, stirred at 35°C for 6 hours, then heated to 45°C and stirred for 4 hours, and then transferred to a crystallization box for hydrothermal crystallization at 170°C for 3 days to synthesize the MFI type seed crystal.

[0011] Preferably, in the initial mixed solution of the present invention, the molar ratio of Si:Al is (10-100):1; the molar ratio of P:Al is (0.01-10):1; the mass ratio of alcohol solvent to alkylphosphine is (1-10):1; and the mass of MFI type seed crystals accounts for 0.1-20 wt.% of the total mass of the initial mixed solution.

[0012] Preferably, the alkylphosphine of the present invention is one or more of trimethylphosphine, triethylphosphine, tripropylphosphine, and tributylphosphine.

[0013] Preferably, the aluminum source of the present invention is one or more of sodium aluminate, boehmite, aluminum hydroxide, and aluminum isopropoxide.

[0014] Preferably, the silicon source of the present invention is one or more of solid silica gel, alkaline silica sol, tetraethyl orthosilicate, and precipitated silica.

[0015] Preferably, the solvent of the present invention is one or more of ethanol, n-propanol, glycerol, n-hexanol, isopropanol, and n-hexanol.

[0016] Preferably, the hydrothermal crystallization of the present invention is a dynamic temperature-variable crystallization method, which includes two stages of temperature-variable crystallization: the crystallization temperature of the first stage is 50-90℃ and the time is 1-10h; the crystallization temperature of the second stage is 110-190℃ and the time is 24-72h.

[0017] Preferably, the calcination conditions of the present invention are as follows: the calcination atmosphere is one or more of nitrogen, argon, and air; the calcination temperature is 200-700℃, the heating rate is 1-10℃ / min, and the time is 5-20h.

[0018] Another objective of this invention is to provide the application of the prepared nanosheet P@ZSM-5 molecular sieve in catalytic cracking, aromatization, methanol-to-propylene, and biomass conversion reaction systems.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) This invention provides a seed method for synthesizing nanosheet P@ZSM-5 molecular sieves by combining alkyl phosphorus as a phosphorus source. It not only has a regular short b-axis nanosheet crystal structure, but also effectively regulates the acidity of the molecular sieve by using phosphorus species inside the molecular sieve. The resulting nanosheet P@ZSM-5 molecular sieve material significantly improves the mass transfer performance and product selectivity during the catalytic reaction.

[0021] (2) This invention uses alkylphosphine as a phosphorus source and introduces MFI type seed crystals to synthesize nanosheet P@ZSM-5 molecular sieve in one step, which improves the dispersibility and utilization of phosphorus, enhances the interaction between phosphorus and aluminum, simplifies the phosphorus modification steps in traditional methods, reduces phosphorus loss, and the process is environmentally friendly and efficient. In addition, in this technology, phosphorus and aluminum in the framework interact directly to form phosphorus-aluminum coordination in situ, which enables the material to efficiently stabilize the framework aluminum structure.

[0022] (3) The preparation method of the present invention has many advantages such as being simple, easy to operate, low energy consumption, short crystallization time, and the ability to introduce phosphorus in situ. Attached Figure Description

[0023] Figure 1 The XRD pattern of the nanosheet P@ZSM-5 molecular sieve prepared in Example 1.

[0024] Figure 2 The XRD pattern of the nanosheet P@ZSM-5 molecular sieve prepared in Example 2 is shown.

[0025] Figure 3 The NMR phosphorus spectra of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 before and after calcination.

[0026] Figure 4The NMR aluminum spectra of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 before and after calcination.

[0027] Figure 5 The image shows the XRD pattern of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3.

[0028] Figure 6 The image shows a SEM image of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3.

[0029] Figure 7 The XRD pattern of the nanosheet ZSM-5 molecular sieve prepared for Comparative Example 1.

[0030] Figure 8 A comparison of methanol conversion rates in the methanol-to-propylene reaction between the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 and the nanosheet ZSM-5(75) molecular sieve prepared in Comparative Example 1.

[0031] Figure 9 The graph shows a comparison of olefin selectivity in the methanol-to-propylene reaction between the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 and the nanosheet ZSM-5 molecular sieve prepared in Comparative Example 1.

[0032] Figure 10 The graph shows a comparison of propylene selectivity in the methanol-to-propylene reaction between the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 and the nanosheet ZSM-5 molecular sieve prepared in Comparative Example 1. Detailed Implementation

[0033] To further illustrate the present invention, the nanosheet P@ZSM-5 molecular sieve, its preparation method, and its application are described in detail below with reference to examples. However, the scope of protection of the present invention is not limited to the content described herein.

[0034] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field, and all percentages are by weight.

[0035] Example 1

[0036] A method for preparing nanosheet P@ZSM-5 molecular sieves, with the chemical structural formula: 20SiO2:Al2O3:1.2P2O 5， Includes the following steps:

[0037] (1) Tributylphosphine, boehmite, alkaline silica sol, MFI seed crystals and isopropanol were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 20:1; the molar ratio of P:Al was 1.2:1; the mass ratio of isopropanol to tributylphosphine was 2:1; and the mass of MFI seed crystals accounted for 5 wt.% of the initial mixed solution.

[0038] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 50℃ and the time is 10h; the second stage crystallization temperature is 110℃ and the time is 72h.

[0039] (3) The initial gel was washed with deionized water, dried at 80℃ overnight, and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was air; the calcination temperature was 550℃, the heating rate was 10℃ / min, and the time was 8h. Its XRD pattern is shown in [reference needed]. Figure 1 ,according to Figure 1 It can be seen that the sample exhibits the characteristic diffraction peaks of MFI type molecular sieve.

[0040] Example 2

[0041] A method for preparing nanosheet P@ZSM-5 molecular sieves, with the chemical structural formula: 50SiO2:Al2O3:1.2P2O 5， Includes the following steps:

[0042] (1) Tributylphosphine, boehmite, alkaline silica sol, MFI seed crystals, and isopropanol were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 50:1; the molar ratio of P:Al was 1.2:1; the mass ratio of alcohol solvent to alkylphosphine was 2:1; and the mass of MFI seed crystals accounted for 5 wt.% of the initial mixed solution.

[0043] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 90℃ and the time is 5h; the second stage crystallization temperature is 190℃ and the time is 24h.

[0044] (3) The initial gel was washed with deionized water, dried at 80℃ overnight, and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was argon; the calcination temperature was 600℃, the heating rate was 5℃ / min, and the time was 5h. Its XRD pattern is shown below. Figure 2 ,from Figure 2 It can be seen that the sample exhibits the characteristic diffraction peaks of MFI type molecular sieve.

[0045] Example 3

[0046] A method for preparing nanosheet P@ZSM-5 molecular sieves, with the chemical structural formula: 75SiO2:Al2O3:1.2P2O 5， Includes the following steps:

[0047] (1) Tripropylphosphine, boehmite, alkaline silica sol, MFI seed crystals, and isopropanol (the solvent required to dissolve alkylphosphine) were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 75:1; the molar ratio of P:Al was 1.2:1; the mass ratio of alcohol solvent to alkylphosphine was 2:1; and the mass of MFI seed crystals accounted for 5 wt% of the initial mixed solution.

[0048] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 80℃ and the time is 3h; the second stage crystallization temperature is 170℃ and the time is 48h.

[0049] (3) The initial gel was washed with deionized water, dried at 80°C overnight, and calcined to obtain MFI type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was air; the calcination temperature was 550°C, the heating rate was 10°C / min, and the time was 6h.

[0050] Phosphorus spectra before and after calcination are shown in the figure. Figure 3 The NMR spectra of aluminum before and after calcination are shown in [reference needed]. Figure 4 XRD pattern can be found Figure 5 See SEM Figure 6 .according to Figure 3 It can be seen that before calcination, P@ZSM-5 molecular sieve, 31 PMAS NMR showed signals at 32 ppm and 12 ppm. The 32 ppm signal was attributed to phosphorus atoms in the TBP (isopropanol) molecule bonded to three butyl groups. The 12 ppm signal likely originated from hydrogen bonding interactions between TBP and silanol groups (Si-OH) on the molecular sieve surface, forming a weakly bonded P-OH···Si complex. In contrast, [the signal was obtained from...]. Figure 4 It can be seen that a new [molecule] was observed when TBP in the calcined P@ZSM-5 molecule decomposed. 31 The P MAS NMR signal, located at -18 ppm, corresponds to a resonance peak belonging to a tetrahedral phosphorus species. Its chemical shift is highly consistent with the characteristic of phosphorus atoms substituting silicon sites in the molecular sieve framework (forming PO-Si bonds). This result indicates that some phosphorus has successfully embedded into the MFI framework, forming a stable PO-Si-Al network structure tetrahedral coordinated phosphorus (PIV) species.

[0051] Figure 4 PZ-75 molecular sieve before and after calcination 27 Al MAS NMR spectrum comparison; a dominant peak is observed at δ = 54 ppm, corresponding to a typical four-coordinated aluminum framework (AlIV), indicating good integrity of the initial molecular sieve framework; a new signal appears at δ = 46 ppm, attributed to a distorted four-coordinated aluminum species; combined with31 P and 27 The results of Al MAS suggest that at least one combination of PIV and AlIV atoms exists within the P@ZSM-5 molecular sieve, forming a PO-Al structure; based on Figure 5 The XRD results show that the sample exhibits the characteristic diffraction peaks of MFI type molecular sieves, and the crystallinity is more complete.

[0052] from Figure 6 SEM images show that all samples exhibit typical MFI topological characteristics—highly crystalline hexagonal prism-shaped crystals with sharp edges (angle ~60°) and smooth surfaces, forming three-dimensional crystal aggregates through directional stacking, with phosphorus species uniformly distributed on the nanosheets.

[0053] Example 4

[0054] A method for preparing nanosheet P@ZSM-5 molecular sieves, with the chemical structural formula: 10SiO2:Al2O3:0.01P2O 5， Includes the following steps:

[0055] (1) Tripropylphosphine, sodium aluminate, precipitated silica, MFI seed crystals and n-propanol were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 10:1; the molar ratio of P:Al was 0.01:1; the mass ratio of isopropanol to tributylphosphine was 1:1; and the mass of MFI seed crystals accounted for 0.1 wt% of the initial mixed solution.

[0056] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 50℃ and the time is 10h; the second stage crystallization temperature is 110℃ and the time is 72h.

[0057] (3) The initial gel was washed with deionized water, dried at 80°C overnight, and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was air; the calcination temperature was 200°C, the heating rate was 1°C / min, and the time was 20h. According to its XRD spectrum, the sample showed the characteristic diffraction peaks of MFI-type molecular sieve.

[0058] Example 5

[0059] A method for preparing nanosheet P@ZSM-5 molecular sieves, with the chemical structural formula: 100SiO2:Al2O3:10P2O 5， Includes the following steps:

[0060] (1) Trimethylphosphine, boehmite, tetraethyl orthosilicate, MFI seed crystals and hexanol were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 100:1; the molar ratio of P:Al was 10:1; the mass ratio of isopropanol to tributylphosphine was 10:1; and the mass of MFI seed crystals accounted for 20 wt% of the initial mixed solution.

[0061] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 90℃ and the time is 1h; the second stage crystallization temperature is 190℃ and the time is 24h.

[0062] (3) The initial gel was washed with deionized water, dried at 80°C overnight, and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was air; the calcination temperature was 700°C, the heating rate was 10°C / min, and the time was 5h. According to its XRD spectrum, the sample showed the characteristic diffraction peaks of MFI-type molecular sieve.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that no phosphorus source was introduced; its chemical structural formula is: 75SiO2:Al2O3:1.2P2O 5， The specific steps are as follows:

[0065] (1) Boehmite, alkaline silica sol, and MFI seed crystals were stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al was 75:1; and the mass of the MFI seed crystals accounted for 5 wt% of the initial mixed solution.

[0066] (2) The mixed product is placed in the polytetrafluoroethylene liner of the crystallization vessel and subjected to hydrothermal crystallization. The crystallized product is recovered to obtain the initial gel. The hydrothermal crystallization includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 80℃ and the time is 3h; the second stage crystallization temperature is 170℃ and the time is 48h.

[0067] (3) The initial gel was washed with deionized water, dried at 80°C overnight, and calcined to obtain MFI type seed nanosheets P@ZSM-5 molecular sieve; the calcination atmosphere was air; the calcination temperature was 550°C, the heating rate was 10°C / min, and the time was 6h.

[0068] The nanosheet ZSM-5 molecular sieve was thus prepared and named ZSM-5(75). Its XRD pattern is shown in [reference needed]. Figure 7 ,according to Figure 7 The XRD pattern shows that the crystallinity of the material is not as good as that of Example 3 when no phosphorus source is introduced.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 2 is that the MFI type seed crystal is replaced with a template agent, and the preparation is carried out using the same method. The specific steps are as follows:

[0071] 0.31 g TPAOH, 13.33 g alkaline silica sol, 0.072 g boehmite (AlOOH·nH2O), 0.22 g tributylphosphine (TBPO, 96%), and 0.44 g isopropanol were added to beakers and stirred until homogeneous. The resulting aluminosilicate gel was then transferred to a 25 mL stainless steel autoclave lined with polytetrafluoroethylene and aged in an 80 °C electric heating drying oven for 72 h. The temperature was then raised to 170 °C for crystallization for 48 h. After crystallization, the autoclave was cooled to room temperature, and the bottom precipitate was collected, centrifuged, washed, and then dried overnight in an 80 °C electric heating drying oven. The dried sample was calcined in air at 550 °C for 6 h to obtain ordinary P-ZSM-5 molecular sieve. The prepared catalyst was used for the methanol-to-propylene reaction. The high methanol conversion rate was maintained for 5.5 h before decreasing sharply, and the propylene selectivity was only 30%. This may be related to whether the material structure is nanosheet-type. The catalyst in the comparative example exhibits a spherical structure composed of stacked small sheet structures, which does not possess the excellent mass transfer performance of nanosheet structures.

[0072] Application examples

[0073] The catalytic performance of catalyst PZ-75 prepared in Example 3 and catalyst ZSM-5(75) prepared in Comparative Example 1 on methanol-to-propylene was tested.

[0074] The reaction was carried out at a methanol feed rate of 12.6 μL / min, a catalyst of 0.1 g, and a reaction space velocity of 6 h⁻¹. -1 The reaction was carried out at a temperature of 480℃, and the propylene selectivity comparison chart is shown below. Figure 10 See the olefin selectivity comparison chart. Figure 9 The reaction stability comparison chart is shown below. Figure 8 .

[0075] The results show that, according to Figure 8 It can be seen that in the methanol-to-propylene reaction, as the reaction time is extended to 30h, the conversion rate of the nanosheet PZ-75 molecular sieve prepared in Example 3 to methanol is stably maintained at 100%, while the high conversion rate of the ZSM-5(75) molecular sieve prepared in Comparative Example 1 to methanol can only be maintained for a short time of 5-7h. Figure 9 The propylene selectivity of the PZ-75 nanosheet molecular sieve after phosphating by the seed crystal method was approximately 54%, which was higher than the propylene selectivity of the ZSM-5(75) molecular sieve prepared in Comparative Example 1, which was approximately 35%. Figure 10It can be seen that the reaction stability of PZ-75 molecular sieve (33.5h) is greater than that of ZSM-5 (75) molecular sieve (6.5h); therefore, it can be further explained that the nanosheet P@ZSM-5 molecular sieve synthesized by the seed method combined with alkyl phosphorus as phosphorus source in this invention can significantly improve the mass transfer performance, product selectivity and efficient framework structure stability during the catalytic reaction.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way.

[0077] It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve, characterized in that, Includes the following steps: (1) Mix and stir alkyl phosphorus, aluminum source, silicon source, MFI type seed crystal and solvent to obtain an initial mixed solution; (2) The initial mixed solution was subjected to hydrothermal crystallization, and the crystallized product was recovered to obtain the initial gel; (3) The initial gel was washed, dried and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve; The chemical formula of the alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve is: xSiO2: Al2O3: yP2O5, where x=10~100 and y=0.01~10. It has an MFI structure and exhibits a regular nanosheet crystal form.

2. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The initial mixed solution has the following molar ratios: Si:Al = (10~100):1; P:Al = (0.01~10):1; alcohol solvent to alkylphosphine mass ratio = (1~10):1; and MFI type seed crystals account for 0.1~20 wt.% of the total mass of the initial mixed solution.

3. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The alkylphosphine is one or more of trimethylphosphine, triethylphosphine, tripropylphosphine, and tributylphosphine.

4. The method for preparing alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The aluminum source is one or more of sodium aluminate, boehmite, aluminum hydroxide, and aluminum isopropoxide.

5. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The silicon source is one or more of solid silica gel, alkaline silica sol, tetraethyl orthosilicate, and precipitated silica.

6. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The solvent is one or more of ethanol, n-propanol, glycerol, n-hexanol, isopropanol, and n-hexanol.

7. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The hydrothermal crystallization is a dynamic temperature-variable crystallization method, which includes two stages of temperature-variable crystallization: the first stage crystallization temperature is 50~90℃ and the time is 1~10 h; the second stage crystallization temperature is 110~190℃ and the time is 24~72 h.

8. The method for preparing alkylphosphine-directed nanosheets P@ZSM-5 molecular sieve according to claim 1, characterized in that: The calcination conditions are as follows: the calcination atmosphere is one or more of nitrogen, argon, and air; the calcination temperature is 200~700℃, and the heating rate is 1-10. o C / min, time is 5~20 h.

9. The application of the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve prepared by the method of claim 1 in catalytic cracking, aromatization, methanol-to-propylene, and biomass conversion reaction systems.

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