Modified core-shell molecular sieve, its preparation method and application in co-pyrolysis for producing aromatics

Abstract

The present invention discloses a modified core-shell molecular sieve, a preparation method thereof, and an application thereof in co-pyrolysis for producing aromatic hydrocarbons, belonging to the technical field of catalysts and applications. The preparation method of the modified core-shell molecular sieve provided includes the following steps: mixing a structure modifier, deionized water, an aluminum source, and a silicon source to obtain a first mixed gel, and performing first hydrothermal crystallization to obtain a first premix; mixing sodium hydroxide, deionized water, an Fe source, and a silicon source to obtain a second mixed gel, mixing the first premix with the second mixed gel, and performing hydrothermal crystallization to obtain a molecular sieve catalyst loaded with transition metal nanoparticles; performing ammonia exchange, separating to obtain a second solid product, drying to obtain a catalyst core, and sequentially adding the catalyst core and a silicon source into a mixed solution of P123 and hydrochloric acid, and performing hydrothermal treatment at a constant temperature to obtain the modified core-shell molecular sieve. The modified core-shell molecular sieve prepared by the present invention has a unique core-shell structure with catalytic activity and a synergistic catalytic effect with transition metals, improving the catalytic performance and the selectivity of aromatic hydrocarbons.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts and their applications, and particularly relates to a modified core-shell molecular sieve, a preparation method thereof, and an application thereof in co-pyrolysis for producing aromatics. Background Art

[0002] Biomass energy is the only renewable energy containing a carbon source. According to statistics, the total annual biomass energy in China is higher than the sum of photovoltaic, wind energy, and geothermal energy, and has extremely high utilization value. Biomass is currently the only source that can provide a sustainable organic carbon source. Lignin has the second-highest content in biomass. Structurally, lignin has aromatic characteristics and is a three-dimensional polymer network compound formed by the connection of three phenylpropane structural units, namely p-hydroxyphenyl, guaiacyl, and syringyl, through ether bonds and carbon-carbon bonds. It is the most abundant natural renewable aromatic polymer and a good source of aromatic compounds.

[0003] Due to the limitation of the low effective hydrogen-carbon ratio of lignin, the bio-oil derived from it has some adverse characteristics, such as low energy density, high viscosity, instability leading to polymerization reactions, relatively low content of hydrocarbon fuels, and corrosion of contact surfaces during storage and transportation. Therefore, co-pyrolysis of biomass and hydrogen-rich raw material plastics can increase the yield and quality of bio-oil through the synergistic effect of the two raw materials. Catalytic fast pyrolysis is an effective method for directly converting the two raw materials into high-value chemicals with aromatic structures.

[0004] Catalytic fast pyrolysis largely depends on the pyrolysis catalyst. The addition of the catalyst helps reduce the generation of oxygen-containing compounds (such as acids and carbonyl compounds) and maximize the proportion of hydrocarbons in the bio-oil. Patent CN114956946A discloses a method for catalytic fast pyrolysis of cassava residue to prepare monocyclic aromatics using a modified molecular sieve, with a pyrolysis temperature as high as 750 °C and a mass ratio of raw material to catalyst as high as 1:20, which requires too much catalyst in pyrolysis. Patent CN112439446A reports using H-Beta molecular sieve as a carrier and then loading active metals Ru and Re for the C-C bond depolymerization reaction of model compounds. The results show that the conversion rate of the C-C bond of the model compounds is improved. This report only studied model compounds and failed to illustrate the depolymerization effect of the Ru-ReOx / H-Beta catalyst on lignin.

[0005] Molecular sieve catalysts have strong surface acidity, but too strong acidity will cause side reactions during the reaction and easily coke. The core-shell molecular sieve with a mesoporous catalyst as the shell and a microporous catalyst as the core fully combines their advantages, maintains strong acidity and large pore size, and allows small molecules to enter. This alleviates the problem that traditional composite catalysts are easily deactivated due to coking during pyrolysis, and enhances the synergistic effect between core-shell catalysts. Patent CN116062763A discloses a method for preparing a core-shell molecular sieve, but the preparation process is long and has not been used in practical applications. Patent CN112705248A reports a core-shell MFI / MFI molecular sieve and its preparation method, which has good molecular shape selectivity in catalytic reactions and can be used in catalytic reactions with high requirements for reaction selectivity, such as for the production of para-xylene and the production of ethylbenzene, etc., with high selectivity and conversion rate. The report only studied model compounds and failed to explain the catalytic effect of the catalyst used in actual raw materials. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a modified core-shell molecular sieve, a preparation method thereof and an application in co-pyrolysis to produce aromatics. By utilizing the unique core-shell structure with catalytic activity of the prepared modified core-shell molecular sieve and the synergistic catalytic effect with transition metals, lignin and plastic are co-pyrolyzed to produce aromatics at 650°C and a raw material to catalyst mass ratio of 1:2, thereby improving the catalytic performance and the selectivity of aromatics.

[0007] To achieve the above object, the present invention provides a method for preparing a modified core-shell molecular sieve, comprising the following steps:

[0008] (1) mixing a structure modifier, deionized water, an aluminum source, and a silicon source in sequence, first stirring to obtain a mixed gel 1, and first hydrothermally crystallizing the mixed gel 1 to obtain a premix 1;

[0009] (2) mixing sodium hydroxide, deionized water, an Fe source and a silicon source in sequence, stirring for a second time to obtain a mixed gel 2, mixing the premix 1 described in step (1) with the mixed gel 2, performing a second hydrothermal crystallization, separating to obtain a solid product 1, and drying for a first time to obtain a molecular sieve catalyst loaded with transition metal nanoparticles;

[0010] (3) taking the molecular sieve catalyst loaded with transition metal nanoparticles described in step (2) and performing ammonia exchange 3 to 5 times to separate a second solid product, and drying the solid product to obtain a catalyst core;

[0011] (4) adding the catalyst core and silicon source described in step (3) to the mixed solution of P123 and hydrochloric acid in sequence, stirring for the third time, heating at a constant temperature, separating the solid product for the third time, and drying for the third time to obtain the modified core-shell molecular sieve.

[0012] Preferably, in step (1), the structure modifier is tetrapropylammonium hydroxide; in step (1), the aluminum source is aluminum isopropoxide; the mixing ratio of the structure modifier, deionized water, aluminum source and silicon source in step (1) is calculated according to the molar ratio of Al 2 O 3 :SiO 2 :TPAOH:H 2 O of 1:30 - 60:5 - 15:400 - 1000.

[0013] Preferably, in step (1), the temperature of the first stirring is 35°C, and the time of the first stirring is 4 - 5 h; in step (1), the temperature of the first hydrothermal crystallization is 120 - 140°C, and the time of the first hydrothermal crystallization is 6 - 10 h.

[0014] Preferably, in step (2), the Fe source is iron nitrate; the mixing ratio of sodium hydroxide, deionized water, Fe source and silicon source in step (2) is calculated according to the molar ratio of SiO 2 :FeNO 3 :NaOH:H 2 O of 30 - 60:1:6 - 9.6:90 - 200; the mixing ratio of the first premix and the second mixed gel in step (2) is calculated according to the proportion of the transition metal Fe loading of 1 - 10 wt%.

[0015] Preferably, in step (2), the temperature of the second stirring is 35°C, and the time of the second stirring is 6 - 8 h; in step (2), the temperature of the second hydrothermal crystallization is 140 - 180°C, and the time of the second hydrothermal crystallization is 20 - 30 h; in step (2), the temperature of the first drying is 100 - 120°C, and the time of the first drying is 10 - 15 h.

[0016] Preferably, in step (3), the ammonia exchange uses an ammonium chloride aqueous solution, the temperature of the ammonia exchange is 60°C, and the time of each ammonia exchange is 1 h; in step (3), the temperature of the second drying is 60 - 80°C, and the time of the second drying is 20 - 24 h.

[0017] Preferably, in step (4), the mass ratio of the catalyst core to the silicon source is 2:1; in step (4), the temperature of the third stirring is 35°C, and the time of the third stirring is 4 - 6 h; in step (4), the temperature of the constant temperature hydrothermal is 90 - 140°C, and the time of the constant temperature hydrothermal is 20 - 30 h; in step (4), the temperature of the third drying is 70 - 90°C, and the time of the third drying is 8 - 10 h.

[0018] Preferably, in steps (1), (2) and (4), the silicon source is tetraethyl orthosilicate.

[0019] The present invention also provides a modified core-shell molecular sieve prepared by the above preparation method.

[0020] The present invention also provides the application of the modified core-shell molecular sieve prepared by the above preparation method in the reaction of co-pyrolysis of lignin and plastic to prepare aromatics, and the modified core-shell molecular sieve is used as a catalyst.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] The present invention provides a catalyst prepared by substituting a part of aluminum with Fe in a core-shell molecular sieve as a modified core-shell molecular sieve. The Fe-modified core-shell molecular sieve catalyst is applied to the co-pyrolysis of lignin and plastic to prepare aromatics, so as to improve the catalytic performance and the selectivity of aromatics. In the co-pyrolysis products of lignin and plastic catalyzed by the molecular sieve catalyst produced industrially in batches, most of the aromatics are polycyclic aromatics, and serious carbon deposition occurs in the catalyst during the pyrolysis process. In the aromatics products of the co-pyrolysis of the Fe-modified core-shell molecular sieve catalyst of the present invention, there are more monocyclic aromatics, and the carbon deposition is significantly better than that of general molecular sieve catalysts. Utilizing its unique core-shell structure with catalytic activity and the synergistic catalytic effect with transition metals, lignin and plastic are co-pyrolyzed to prepare aromatics under the conditions of 650 °C and a mass ratio of raw material to catalyst of 1:2. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a TEM image of the modified core-shell molecular sieve of the present invention, and the scale bar is 10 nm. DETAILED DESCRIPTION OF THE INVENTION

[0025] The various exemplary embodiments of the present invention will be described in detail below. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention.

[0026] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0028] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0029] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0030] Example 1

[0031] (1) Dissolve 2 g of aluminum isopropoxide in a solution prepared from 8.46 mL of tetrapropylammonium hydroxide and 42.35 mL of deionized water, stir at 35 °C for 30 min, then add 33.52 mL of tetraethyl orthosilicate. After stirring the mixture at 35 °C for 4 h, obtain mixed gel 1. Transfer the obtained mixed gel 1 to a stainless steel autoclave and perform the first hydrothermal crystallization at 140 °C for 9 h to obtain premix 1. The feeding ratio of each material is calculated according to the molar ratio of Al 2 O 3 :SiO 2 :TPAOH:H 2 O of 1:30:8.5:480.

[0032] (2) Take 3.4237 g of Fe(NO 3 ) 3 ·9H 2O was added to the solution prepared by adding 2.373 g of NaOH and 14.644 mL of deionized water, and stirred for 2 h until homogeneous. Then, 57.956 mL of tetraethyl orthosilicate was added at 35 °C, and stirred for 5 h to obtain mixed gel II. Subsequently, mixed gel II was transferred to a stainless-steel autoclave. Premix I and mixed gel II were hydrothermally crystallized at 180 °C for 24 h according to the calculated ratio with a transition metal Fe loading of 1 wt%. The product was collected, separated by centrifugation at 9000 rpm for 8 min, and washed by filtration to obtain solid product I. It was dried at 110 °C for the first 12 h, placed in a muffle furnace, and calcined at 550 °C for 3 h to obtain a molecular sieve catalyst loaded with transition metal nanoparticles. The feeding ratio of each material was calculated according to the molar ratio of SiO 2 :FeNO 3 :NaOH:H 2 O of 30:1:7:96.

[0033] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was taken and subjected to 4 times of ammonia exchange in 1 M NH 4 Cl aqueous solution. The temperature of ammonia exchange was 60 °C, and the time of each ammonia exchange was 1 h; separated by centrifugation at 9000 rpm for 10 min, washed with deionized water to obtain solid product II, dried at 60 °C for the second 24 h, and calcined in a muffle furnace at 540 °C for 12 h to obtain the catalyst core;

[0034] (4) The catalyst core and tetraethyl orthosilicate were added successively according to a mass ratio of 2:1 to the mixed solution of P123 and hydrochloric acid (2 g of P123 was added to 100 mL of 2 M HCl aqueous solution and stirred at 35 °C for 2 h to completely dissolve). Stirred at 35 °C for the third 5 h, hydrothermally treated at 100 °C for 24 h, separated the solid product III by filtration, dried at 80 °C for the third 10 h, and calcined in a muffle furnace at 550 °C for 5 h to obtain the modified core-shell molecular sieve Fe-30H / S.

[0035] Example 2

[0036] (1) 1.8 g of aluminum isopropoxide was dissolved in the solution prepared by mixing 12.789 mL of tetrapropylammonium hydroxide and 34.38 mL of deionized water, stirred at 35 °C for 30 min, and then 40.23 mL of tetraethyl orthosilicate was added. After stirring the mixture at 35 °C for 4 h, mixed gel I was obtained. The obtained mixed gel I was transferred to a stainless-steel autoclave and hydrothermally crystallized at 140 °C for the first 9 h to obtain premix I. The feeding ratio of each material was Al 2 O 3 :SiO 2 :TPAOH:H 2 O molar ratio of 1:40:14.28:433 was calculated.

[0037] (2) 1.67 g of Fe(NO 3 ) 3 ·9H 2 O was added to the solution prepared by adding 1.587 g of NaOH and 7.442 mL of deionized water, and stirred for 2 h until homogeneous. Then, 37.7 mL of tetraethyl orthosilicate was added at 35 °C, and the mixture was stirred for 5 h to obtain mixed gel II. Subsequently, mixed gel II was transferred to a stainless-steel autoclave. Premix I and mixed gel II were hydrothermally crystallized at 180 °C for 24 h according to the calculated ratio of the transition metal Fe loading of 1 wt%. The product was collected, separated by centrifugation at 9000 rpm for 8 min, and washed by filtration to obtain solid product I. It was dried at 110 °C for 12 h for the first time, placed in a muffle furnace, and calcined at 550 °C for 3 h to obtain the molecular sieve catalyst loaded with transition metal nanoparticles. The feeding ratio of each material was calculated according to the molar ratio of SiO 2 :FeNO 3 :NaOH:H 2 O of 40:1:9.6:100.

[0038] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was taken and subjected to three ammonia exchanges in 1 M NH 4 Cl aqueous solution. The temperature of the ammonia exchange was 60 °C, and the time of each ammonia exchange was 1 h; it was separated by centrifugation at 9000 rpm for 10 min, washed with deionized water to obtain solid product II, dried at 60 °C for 24 h for the second time, and calcined in a muffle furnace at 540 °C for 12 h to obtain the catalyst core;

[0039] (4) The catalyst core and tetraethyl orthosilicate were added to the mixed solution of P123 and hydrochloric acid (2 g of P123 was added to 100 mL of 2 M HCl aqueous solution and stirred at 35 °C for 2 h to completely dissolve) in a mass ratio of 2:1, stirred at 35 °C for 5 h for the third time, hydrothermally treated at 90 °C for 20 h, the solid product III was separated by filtration, dried at 80 °C for 10 h for the third time, and calcined in a muffle furnace at 550 °C for 5 h to obtain the modified core-shell molecular sieve Fe-40H / S.

[0040] Example 3

[0041] (1) 1.2 g of aluminum isopropoxide was dissolved in the solution prepared by adding 5.672 mL of tetrapropylammonium hydroxide and 42.353 mL of deionized water, stirred at 35 °C for 30 min, and then 35.924 mL of tetraethyl orthosilicate was added. After stirring the mixture at 35 °C for 4 h, mixed gel I was obtained. The obtained mixed gel I was transferred to a stainless-steel autoclave and hydrothermally crystallized at 140 °C for 9 h for the first time to obtain premix I. The feeding ratio of each material was Al 2 O 3 :SiO 2 :TPAOH:H 2Calculated according to the molar ratio of 1:50:9.5:800.

[0042] (2) Add 1.114 g of Fe(NO 3 ) 3 ·9H 2 O to the solution prepared by adding 0.882 g of NaOH and 7.718 mL of deionized water, stir for 2 h until homogeneous, then add 31.418 mL of tetraethyl orthosilicate at 35 °C, stir for 5 h to obtain mixed gel two. Subsequently, transfer mixed gel two to a stainless-steel autoclave. Premix one and mixed gel two are in the calculated ratio according to the transition metal Fe loading of 1 wt%, and hydrothermally crystallize at 180 °C for 24 h. Collect the product, centrifuge at 9000 rpm for 8 min for separation, and use filtration and washing to obtain solid product one. Dry at 110 °C for the first time for 12 h, place it in a muffle furnace, and calcine at 550 °C for 3 h to obtain the molecular sieve catalyst loaded with transition metal nanoparticles. The feeding ratio of each material is calculated according to the molar ratio of SiO 2 :FeNO 3 :NaOH:H 2 O as 50:1:8:160.

[0043] (3) Take the molecular sieve catalyst loaded with transition metal nanoparticles and perform three ammonia exchanges in 1 M NH 4 Cl aqueous solution. The temperature of the ammonia exchange is 60 °C, and the time of each ammonia exchange is 1 h; centrifuge at 9000 rpm for 10 min for separation, and use deionized water for washing to obtain solid product two. Dry at 60 °C for the second time for 24 h, and calcine in a muffle furnace at 540 °C for 12 h to obtain the catalyst core;

[0044] (4) Add the catalyst core and tetraethyl orthosilicate in a mass ratio of 2:1 successively to the mixed solution of P123 and hydrochloric acid (2 g of P123 is added to 100 mL of 2 M HCl aqueous solution and stirred at 35 °C for 2 h to completely dissolve). Stir at 35 °C for the third time for 5 h, carry out hydrothermal treatment at 90 °C for 20 h, separate the solid product three by filtration, dry at 80 °C for the third time for 10 h, and calcine in a muffle furnace at 550 °C for 5 h to obtain the modified core-shell molecular sieve Fe-50H / S.

[0045] Example 4

[0046] (1) Dissolve 1 g of aluminum isopropoxide in the solution prepared by adding 2.488 mL of tetrapropylammonium hydroxide and 44.118 mL of deionized water, stir at 35 °C for 30 min, then add 33.524 mL of tetraethyl orthosilicate, and stir the mixture at 35 °C for 4 h to obtain mixed gel one. Transfer the obtained mixed gel one to a stainless-steel autoclave and hydrothermally crystallize at 140 °C for the first time for 9 h to obtain premix one. The feeding ratio of each material is Al 2 O3 :SiO 2 :TPAOH:H 2 The molar ratio of O is calculated as 1:60:5:1000.

[0047] (2) Add 0.929 g of Fe(NO 3 ) 3 ·9H 2 O to the solution prepared by adding 0.551 g of NaOH and 8.269 mL of deionized water, stir for 2 h until homogeneous, then add 31.418 mL of tetraethyl orthosilicate at 35 °C, stir for 5 h to obtain mixed gel II. Subsequently, transfer mixed gel II to a stainless steel autoclave. The pre-mixture I and mixed gel II are in a calculated ratio according to a transition metal Fe loading of 1 wt%, and hydrothermally crystallized at 180 °C for 24 h. Collect the product, centrifuge at 9000 rpm for 8 min for separation, and use filtration and washing to obtain solid product I. Dry at 110 °C for the first time for 12 h, place it in a muffle furnace, and calcine at 550 °C for 3 h to obtain a molecular sieve catalyst loaded with transition metal nanoparticles. The feeding ratio of each material is calculated according to the molar ratio of SiO 2 :FeNO 3 :NaOH:H 2 O of 60:1:6:200.

[0048] (3) Take the molecular sieve catalyst loaded with transition metal nanoparticles and perform three ammonia exchanges in 1 M NH 4 Cl aqueous solution. The temperature of ammonia exchange is 60 °C, and the time of each ammonia exchange is 1 h; centrifuge at 9000 rpm for 10 min for separation, and use deionized water for washing to obtain solid product II. Dry at 60 °C for the second time for 24 h, and calcine in a muffle furnace at 540 °C for 12 h to obtain the catalyst core;

[0049] (4) Add the catalyst core and tetraethyl orthosilicate in a mass ratio of 2:1 to the mixed solution of P123 and hydrochloric acid (2 g of P123 is added to 100 mL of 2 M HCl aqueous solution and stirred at 35 °C for 2 h to completely dissolve) in sequence, stir at 35 °C for the third time for 5 h, perform hydrothermal at 90 °C for 20 h, separate the solid product III by filtration, dry at 80 °C for the third time for 10 h, and calcine in a muffle furnace at 550 °C for 5 h to obtain the modified core-shell molecular sieve Fe-60H / S.

[0050] Experimental Example 1

[0051] Use lignin and plastic with a mass ratio of 1:1 uniformly mixed as raw materials for non-in-situ pyrolysis in a vertical pyrolysis furnace. The specific experimental conditions are as follows: the mass ratio of raw materials to catalyst is 1:2, the heating rate is 10 °C / s to 650 °C, the residence time is 30 min, and the pyrolysis oil is sent to GC-MS for analysis.

[0052] The catalyst is any one of the modified core-shell molecular sieves prepared in Examples 1 to 4. The four catalysts are the catalysts prepared in the examples and are named Fe-30H / S, Fe-40H / S, Fe-50H / S, and Fe-60H / S according to the silicon-aluminum ratio.

[0053] Table 1 Product Selectivity

[0054]

[0055]

[0056] The results are shown in Table 1, indicating that using the catalyst of Example 3 can reduce the alcohol yield from 33.625% to 14.11%, increase the aromatic hydrocarbon yield from 7.285% to 26.885%, and increase the monocyclic aromatic hydrocarbon from 1.605% to 10.83%.

[0057] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a modified core-shell molecular sieve, characterized in that: The following steps are involved: (1) mixing a structure modifier, deionized water, an aluminum source, and a silicon source in sequence, first stirring to obtain a mixed gel 1, and first hydrothermally crystallizing the mixed gel 1 to obtain a premix 1; (2) mixing sodium hydroxide, deionized water, an Fe source and a silicon source in sequence, stirring for a second time to obtain a mixed gel 2, mixing the premix 1 described in step (1) with the mixed gel 2, performing a second hydrothermal crystallization, separating to obtain a solid product 1, and drying for a first time to obtain a molecular sieve catalyst loaded with transition metal nanoparticles; (3) taking the molecular sieve catalyst loaded with transition metal nanoparticles described in step (2) and performing ammonia exchange 3 to 5 times to separate a second solid product, and drying the solid product to obtain a catalyst core; (4) adding the catalyst core and silicon source described in step (3) to the mixed solution of P123 and hydrochloric acid in sequence, stirring for the third time, heating at a constant temperature, separating the solid product for the third time, and drying for the third time to obtain the modified core-shell molecular sieve; The Fe source in step (2) is ferric nitrate; the mixing ratio of the sodium hydroxide, deionized water, Fe source and silicon source in step (2) is calculated according to the molar ratio of SiO2:FeNO3:NaOH:H2O of 30-60:1:6-9.6:90-200; the mixing ratio of the premix 1 and the mixed gel 2 in step (2) is calculated according to the ratio of transition metal Fe loading of 1-10wt%; The structure modifier described in step (1) is tetrapropylammonium hydroxide; the aluminum source described in step (1) is aluminum isopropoxide; the mixing ratio of the structure modifier, deionized water, aluminum source and silicon source described in step (1) is calculated according to the molar ratio of Al2O3:SiO2:TPAOH:H2O of 1:30-60:5-15:400-1000; In step (1), the temperature of the first stirring is 35° C., and the time of the first stirring is 4 to 5 hours; in step (1), the temperature of the first hydrothermal crystallization is 120 to 140° C., and the time of the first hydrothermal crystallization is 6 to 10 hours.

2. The preparation method according to claim 1, characterized in that: In step (2), the temperature of the second stirring is 35°C, and the time of the second stirring is 6 to 8 hours; the temperature of the second hydrothermal crystallization in step (2) is 140 to 180°C, and the time of the second hydrothermal crystallization is 20 to 30 hours; the temperature of the first drying in step (2) is 100 to 120°C, and the time of the first drying is 10 to 15 hours.

3. The preparation method according to claim 1, characterized in that: The ammonia exchange in step (3) uses an aqueous solution of ammonium chloride, the temperature of the ammonia exchange is 60° C., and the time of each ammonia exchange is 1 hour; the temperature of the second drying in step (3) is 60-80° C., and the time of the second drying is 20-24 hours.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the catalyst core and the silicon source in step (4) is 2:1; the temperature of the third stirring in step (4) is 35°C, and the time of the third stirring is 4 to 6 hours; the temperature of the constant temperature hydrothermal in step (4) is 90 to 140°C, and the time of the constant temperature hydrothermal is 20 to 30 hours; the temperature of the third drying in step (4) is 70 to 90°C, and the time of the third drying is 8 to 10 hours.

5. The preparation method according to claim 1, characterized in that: The silicon source in step (1), step (2) and step (4) is tetraethyl orthosilicate.

6. The modified core-shell molecular sieve prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the modified core-shell molecular sieve prepared by the preparation method according to any one of claims 1 to 5 in the co-pyrolysis of lignin and plastic to prepare aromatic hydrocarbons, characterized in that: The modified core-shell molecular sieve is a catalyst.

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