Alkylphosphine-guided nanosheet P-coated ZSM-5 molecular sieve as well as preparation method and application thereof

Abstract

The invention discloses an alkylphosphine-guided nanosheet P-coated ZSM-5 molecular sieve as well as a preparation method and application thereof, and belongs to the technical field of molecular sieves. According to the nanosheet P-coated ZSM-5 molecular sieve provided by the invention, the crystal contains phosphorus, and the nanosheet P-coated ZSM-5 molecular sieve has an MFI structure and presents a regular nanosheet crystal form; the preparation method of the nanosheet P-coated ZSM-5 molecular sieve comprises the following steps: mixing and stirring a silicon source, an aluminum source, a phosphorus source, a solvent and an MFI type seed crystal, then crystallizing the obtained initial solution, and washing, drying and roasting the obtained product to obtain a nanosheet P-coated ZSM-5 molecular sieve material containing phosphorus in the crystal, according to the method, the phosphorus-containing nanosheet ZSM-5 molecular sieve is synthesized by using an MFI type seed crystal and alkyl phosphorus as a template agent and a phosphorus source in a one-step oriented manner; the preparation process is simple and environment-friendly, and the obtained molecular sieve material has a uniform and regular hexagonal prismatic crystal structure and shows a good catalytic effect and long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a one-step synthesis of nanosheet P@ZSM-5 molecular sieves, a preparation method and an application thereof. Background Art

[0002] ZSM-5 zeolites, due to their unique three-dimensional pore structure, tunable acidity, and excellent shape selectivity, are widely used in numerous catalytic reaction systems, including catalytic cracking, aromatization, methanol-to-propylene, and biomass conversion. However, in practical applications, the acidity and hydrothermal stability of conventional ZSM-5 zeolites do not meet the performance requirements of these catalytic reactions. Phosphation of zeolites is a key technology for regulating ZSM-5 acidity and increasing olefin selectivity in catalytic reactions. It has been successfully applied in industrial processes such as alcohol-to-olefin conversion, alkylation of toluene and methanol, and catalytic cracking to increase propylene production. Post-modification of the parent ZSM-5 zeolite with phosphorus-containing compounds is the most widely used method in phosphorus modification research. Specifically, phosphoric acid or phosphates are introduced into the zeolite via an impregnation method, followed by calcination to obtain P-ZSM-5. The resulting slurry is then ground to prepare the catalyst. This entire process is environmentally hazardous, complex, and energy-intensive. Furthermore, large phosphorus species are difficult to enter the zeolite interior, resulting in low phosphorus utilization.

[0003] Patent application CN102311130A discloses a method of forming a phosphorus-containing ZSM-5 molecular sieve by combining a silicon source, an aluminum source, and an organic phosphorus-oxygen surfactant as a template with water in a certain proportion, followed by gelation, crystallization, filtration, drying, and calcination. However, the phosphorus utilization rate of the synthesized material is low, resulting in waste of the phosphorus source. Patent document CN116216734B uses a quaternary phosphatic base as a template and calcines the synthesized material to obtain a phosphorus-containing ZSM-5 molecular sieve. However, quaternary phosphatic bases are usually prepared by reacting alkyl phosphines with halogenated hydrocarbons, are expensive, and have a relatively complicated preparation process. Patent application CN116216734A reports a method of directly synthesizing a phosphorus-containing molecular sieve, but the synthesized material does not have the excellent properties of nanosheets, i.e., it has no short b-axis and does not have good mass transfer effect.

[0004] Currently, the prepared P@ZSM-5 zeolite contains sodium, and the preparation process is complex, energy consumption is high, and the zeolite crystal shape is irregular. Therefore, designing a preparation route with a simple process and the ability to effectively introduce phosphorus species to synthesize a zeolite with a single crystal form is a key issue in the current preparation of P@ZSM-5 zeolite. Summary of the Invention

[0005] The purpose of the present invention is to provide an alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve, which has the chemical formula: xSiO2:Al2O3:yP2O5, wherein x=10-100, y=0.01-10, has an MFI structure, and presents a regular nanosheet crystal form. The molecular sieve not only has a regular short b-axis nanosheet crystal structure, but also exhibits excellent mass transfer performance and product selectivity in catalytic applications; at the same time, it also improves the dispersibility and utilization rate of phosphorus, enhances the interaction between phosphorus and aluminum, and the phosphorus species within the synthesized molecular sieve material can efficiently stabilize the skeleton aluminum structure.

[0006] Another object of the present invention is to provide a method for preparing alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve, which specifically comprises the following steps:

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

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

[0009] (3) The initial gel is 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 in a mass ratio of 1:0.36, stirred at 35°C for 6 hours, then heated to 45°C and stirred for 4 hours, transferred to a crystallization box and hydrothermally crystallized at 170°C for 3 days to synthesize MFI type seed crystals.

[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 alkyl phosphine is (1-10):1; and the mass of the 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 metaaluminate, pseudo-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 white carbon black.

[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 variable temperature crystallization method, which includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 50-90°C and the time is 1-10 hours; the crystallization temperature of the second stage is 110-190°C and the time is 24-72 hours.

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

[0018] Another object of the present 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) The present invention provides for the first time a nanosheet P@ZSM-5 molecular sieve synthesized by a seed crystal method combined with alkyl phosphorus as a phosphorus source, which not only has a regular short b-axis nanosheet crystal structure, but also uses phosphorus species to effectively regulate the acidity of the molecular sieve inside the molecular sieve. The obtained nanosheet P@ZSM-5 molecular sieve material significantly improves the mass transfer performance and product selectivity during the catalytic reaction.

[0021] (2) The present invention uses alkyl phosphine as a phosphorus source and introduces MFI type crystal seeds to synthesize nanosheet P@ZSM-5 molecular sieve in one step, which improves the dispersibility and utilization rate of phosphorus, enhances the interaction between phosphorus and aluminum, simplifies the phosphorus modification steps in traditional methods, and reduces the loss of phosphorus. The process is environmentally friendly and efficient. In addition, phosphorus in this technology directly reacts with the skeleton aluminum to form phosphorus-aluminum coordination in situ, so that the material can efficiently stabilize the skeleton aluminum structure.

[0022] (3) The preparation method of the present invention has many advantages, such as simplicity, easy operation, low energy consumption, short crystallization time, and the ability to introduce phosphorus in situ. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0025] Figure 3 This is the nuclear magnetic phosphorus spectrum of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 before and after calcination.

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

[0027] Figure 5 This is the XRD spectrum of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3.

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

[0029] Figure 7 This is the XRD spectrum of the nanosheet ZSM-5 molecular sieve prepared in Comparative Example 1.

[0030] Figure 8 This is a comparison chart of the methanol conversion rates of the methanol to propylene reaction of 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 This is a comparison chart of olefin selectivity in the methanol to propylene reaction of 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 This is a comparison chart of propylene selectivity in the methanol to propylene reaction of the nanosheet P@ZSM-5 molecular sieve prepared in Example 3 and the nanosheet ZSM-5 molecular sieve prepared in Comparative Example 1. DETAILED DESCRIPTION

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

[0034] In the present invention, unless otherwise specified, the raw materials used are commercially available products in the field, and all percentages are by mass.

[0035] Example 1

[0036] A method for preparing nanosheet P@ZSM-5 molecular sieve, the chemical structure of which is: 20SiO2:Al2O3:1.2P2O 5， The following steps are involved:

[0037] (1) Tributylphosphine, pseudoboehmite, alkaline silica sol, MFI seed crystals and isopropyl alcohol 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 isopropyl alcohol to tributylphosphine was 2:1; and the mass of the MFI seed crystals accounted for 5 wt.% of the initial mixed solution.

[0038] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 50°C and the time is 10 hours; the crystallization temperature of the second stage is 110°C and the time is 72 hours.

[0039] (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 8 h. The XRD spectrum is shown in FIG. Figure 1 ,according to Figure 1 It can be seen that the sample exhibits characteristic diffraction peaks of MFI type molecular sieve.

[0040] Example 2

[0041] A method for preparing nanosheet P@ZSM-5 molecular sieve, the chemical structure of which is: 50SiO2:Al2O3:1.2P2O 5， The following steps are involved:

[0042] (1) Tributylphosphine, pseudoboehmite, alkaline silica sol, MFI seed crystals, and isopropyl alcohol are stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al is 50:1; the molar ratio of P:Al is 1.2:1; the mass ratio of the alcohol solvent to the alkyl phosphine is 2:1; and the mass of the MFI seed crystals accounts for 5 wt.% of the initial mixed solution.

[0043] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 90°C and the time is 5 hours; the crystallization temperature of the second stage is 190°C and the time is 24 hours.

[0044] (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 argon; the calcination temperature was 600 °C, the heating rate was 5 °C / min, and the time was 5 h. The XRD spectrum is shown in FIG. Figure 2 ,from Figure 2 It can be seen that the sample exhibits characteristic diffraction peaks of MFI molecular sieve.

[0045] Example 3

[0046] A method for preparing nanosheet P@ZSM-5 molecular sieve, the chemical structure of which is: 75SiO2:Al2O3:1.2P2O 5， The following steps are involved:

[0047] (1) Tripropyl phosphine, pseudo-boehmite, alkaline silica sol, MFI seed crystals, and isopropyl alcohol, a solvent required for dissolving alkyl phosphines, are stirred at room temperature to obtain an initial mixed solution; wherein the molar ratio of Si:Al is 75:1; the molar ratio of P:Al is 1.2:1; the mass ratio of the alcohol solvent to the alkyl phosphine is 2:1; and the mass of the MFI seed crystals accounts for 5 wt% of the initial mixed solution.

[0048] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 80°C and the time is 3 hours; the crystallization temperature of the second stage is 170°C and the time is 48 hours.

[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 6 h.

[0050] Phosphorus spectra before and after calcination Figure 3 , the aluminum NMR images before and after calcination are shown in Figure 4 , XRD spectrum see Figure 5 , SEM see Figure 6 .according to Figure 3 It can be seen that before calcination, P@ZSM-5 molecular sieve 31 PMAS NMR has signals at 32 ppm and 12 ppm respectively. The 32 ppm is attributed to the phosphorus atom bonded to three butyl groups in the TBP (isopropyl alcohol) molecule, and the 12 ppm may be due to the hydrogen bond interaction between TBP and the silanol (Si-OH) on the surface of the molecular sieve, forming a weakly bound P-OH···Si complex. Figure 4 It can be seen that a new 31 The P MAS NMR signal is located at -18 ppm, and the resonance peak there is attributed to the tetrahedral coordinated framework phosphorus species. Its chemical shift is highly consistent with the characteristics of phosphorus atoms replacing silicon sites in the molecular sieve framework (forming PO-Si bonds); this result indicates that part of the phosphorus is successfully embedded in the MFI framework to form a stable PO-Si-Al network structure tetrahedral coordinated phosphorus (PIV) species.

[0051] Figure 4 PZ-75 molecular sieve before and after calcination 27 Comparison of Al MAS NMR spectra; a dominant peak appears at δ = 54 ppm, corresponding to a typical tetracoordinated aluminum framework (AlIV), indicating that the initial molecular sieve framework is well intact; a new signal appears at δ = 46 ppm, attributed to a distorted tetracoordinated aluminum species; combined with31 P and 27 The results of Al MAS indicate that there is at least one combination of PIV and AlIV atoms in the P@ZSM-5 molecular sieve, forming a PO-Al structure. Figure 5 XRD shows that the sample presents the characteristic diffraction peaks of MFI molecular sieve and the crystallinity is more complete.

[0052] from Figure 6 SEM analysis shows that all samples exhibit typical MFI topological structural characteristics - highly crystalline hexagonal prism-shaped crystal morphology with sharp edges (angle ~60°), smooth surface, and three-dimensional crystal aggregates formed by directional stacking, with phosphorus species evenly distributed on the nanosheets.

[0053] Example 4

[0054] A method for preparing nanosheet P@ZSM-5 molecular sieve, the chemical structure of which is: 10SiO2:Al2O3:0.01P2O 5， The following steps are involved:

[0055] (1) Tripropyl phosphine, sodium metaaluminate, 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 isopropyl alcohol to tributyl phosphine was 1:1; and the mass of the MFI seed crystals accounted for 0.1 wt% of the initial mixed solution.

[0056] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 50°C and the time is 10 hours; the crystallization temperature of the second stage is 110°C and the time is 72 hours.

[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, it can be seen that the sample exhibits the characteristic diffraction peaks of MFI-type molecular sieve.

[0058] Example 5

[0059] A method for preparing nanosheet P@ZSM-5 molecular sieve, the chemical structure of which is: 100SiO2:Al2O3:10P2O 5， The following steps are involved:

[0060] (1) Trimethylphosphine, pseudoboehmite, 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 the MFI seed crystals accounted for 20 wt% of the initial mixed solution.

[0061] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 90°C and the time is 1 hour; the crystallization temperature of the second stage is 190°C and the time is 24 hours.

[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, it can be seen that the sample exhibits 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 is introduced, and its chemical structure is: 75SiO2:Al2O3:1.2P2O 5， The specific steps are as follows

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

[0066] (2) The mixed product is placed in the polytetrafluoroethylene lining of a crystallization kettle for hydrothermal crystallization, and the crystallized product is recovered to obtain the initial gel; the hydrothermal crystallization includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 80°C and the time is 3 hours; the crystallization temperature of the second stage is 170°C and the time is 48 hours.

[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 6 h.

[0068] The nanosheet ZSM-5 molecular sieve was obtained and named ZSM-5(75). Its XRD spectrum is shown in Figure 7 ,according to Figure 7 It can be seen from the XRD pattern that when no phosphorus source is introduced, the crystallinity of the material is not as good as that in Example 3.

[0069] Comparative Example 2

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

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

[0072] Application Examples

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

[0074] The reaction was carried out at a methanol feed rate of 12.6 μl / min, 0.1 g of catalyst, and a reaction space velocity of 6 h. -1 , the reaction temperature is 480℃, and the propylene selectivity comparison chart is shown in Figure 10 , see the comparison chart of olefin selectivity Figure 9 , reaction stability comparison chart see 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 methanol by the nanosheet PZ-75 molecular sieve prepared in Example 3 is stably maintained at up to 100%, while the high conversion rate of methanol by the ZSM-5(75) molecular sieve prepared in Comparative Example 1 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 medium seed method is ≈54%, which is higher than the propylene selectivity of the ZSM-5 (75) molecular sieve prepared in Comparative Example 1, which is ≈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 is further explained that the nanosheet P@ZSM-5 molecular sieve synthesized by the seed method combined with alkyl phosphorus as a phosphorus source in the present invention can significantly improve the mass transfer performance and product selectivity during the catalytic reaction and the efficient skeleton structure stability.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form.

[0077] It is pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. An alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve, characterized by: The chemical formula is: xSiO2:Al2O3:yP2O5, wherein x=10-100, y=0.01-10, and it has an MFI structure and presents a regular nanosheet crystal form.

2. The method for preparing the alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve according to claim 1, characterized in that: The following steps are involved: (1) mixing an alkylphosphorus, an aluminum source, a silicon source, an MFI type seed crystal, and a solvent, and stirring to obtain an initial mixed solution; (2) subjecting the initial mixed solution to hydrothermal crystallization, and recovering the crystallized product to obtain an initial gel; (3) The initial gel is washed, dried, and calcined to obtain MFI-type seed nanosheets P@ZSM-5 molecular sieve.

3. The method for preparing the alkylphosphine-guided nanosheet P@ZSM-5 molecular sieve according to claim 2, characterized in that: The molar ratio of Si to Al in the initial mixed solution is (10-100):1; the molar ratio of P to Al is (0.01-10):1; the mass ratio of the alcohol solvent to the alkyl phosphine is (1-10):1; and the mass of the MFI seed crystals accounts for 0.1-20 wt.% of the total mass of the initial mixed solution.

4. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, characterized in that: The alkylphosphine is one or more of trimethylphosphine, triethylphosphine, tripropylphosphine and tributylphosphine.

5. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, characterized in that: The aluminum source is one or more of sodium metaaluminate, pseudo-boehmite, aluminum hydroxide, and aluminum isopropoxide.

6. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, characterized in that: The silicon source is one or more of solid silica gel, alkaline silica sol, tetraethyl orthosilicate, and precipitated white carbon black.

7. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, characterized in that: The solvent is one or more of ethanol, n-propanol, glycerol, n-hexanol, isopropanol, and n-hexanol.

8. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, characterized in that: The hydrothermal crystallization is a dynamic variable temperature crystallization method, which includes two stages of variable temperature crystallization: the crystallization temperature of the first stage is 50-90° C. and the time is 1-10 hours; the crystallization temperature of the second stage is 110-190° C. and the time is 24-72 hours.

9. The method for preparing the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 2, 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° C., the heating rate is 1-10° C. / min, and the calcination time is 5-20 hours.

10. Use of the alkylphosphine-guided nanosheets P@ZSM-5 molecular sieve according to claim 1 in catalytic cracking, aromatization, methanol to propylene and biomass conversion reaction systems.

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