Modified core-shell molecular sieve, preparation method thereof and application of modified core-shell molecular sieve in preparation of aromatic hydrocarbon through co-pyrolysis

Abstract

The invention discloses a modified core-shell molecular sieve, a preparation method thereof and application of the modified core-shell molecular sieve in preparation of aromatic hydrocarbon through co-pyrolysis, and belongs to the technical field of catalysts and application, and the preparation method of the modified core-shell molecular sieve comprises the following steps: mixing a structure modifier, deionized water, an aluminum source and a silicon source to obtain mixed gel I, and performing first hydrothermal crystallization to obtain a premix I; mixing sodium hydroxide, deionized water, a Fe source and a silicon source to obtain a mixed gel II, mixing the premix I with the mixed gel II, and performing hydrothermal crystallization to obtain a transition metal nanoparticle-loaded molecular sieve catalyst; and carrying out ammonia exchange, separating to obtain a solid product II, drying to obtain a catalyst core, sequentially adding the catalyst core and a silicon source into a mixed solution of P123 and hydrochloric acid, and carrying out constant-temperature hydrothermal treatment to obtain the modified core-shell molecular sieve. The modified core-shell molecular sieve prepared by the method has a unique core-shell structure with catalytic activity and a synergistic catalysis effect with transition metal, so that the catalytic performance and the aromatic hydrocarbon selectivity are improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst and application technology, and particularly relates to modified core-shell molecular sieves, their preparation methods, and their application in co-pyrolysis to produce aromatics. Background Technology

[0002] Biomass energy is the only renewable energy source containing carbon. Statistics show that my country's annual biomass energy output exceeds the combined output of photovoltaic, wind, and geothermal energy, demonstrating its extremely high utilization value. Biomass is currently the only sustainable source of organic carbon. Lignin is the second most abundant organic carbon source in biomass after cellulose. Structurally, lignin possesses aromatic properties and is a three-dimensional polymeric network compound formed by three phenylpropane structural units—p-hydroxyphenyl, guaiacol, and syringyl—linked by ether and carbon-carbon bonds. It is the richest natural renewable aromatic polymer and an excellent source of aromatic compounds.

[0003] Due to its low hydrogen-to-carbon ratio, lignin-derived bio-oils exhibit several undesirable properties, such as low energy density, high viscosity, instability in polymerization reactions, relatively low hydrocarbon content, and corrosive effects on contact surfaces during storage and transportation. Therefore, co-pyrolysis of biomass with hydrogen-rich plastic feedstocks can increase the yield and quality of bio-oils through the synergistic effect of the two feedstocks. Catalytic rapid pyrolysis is an effective method for directly converting these two feedstocks into high-value chemicals with aromatic structures.

[0004] Catalytic rapid pyrolysis largely depends on the pyrolysis catalyst. The addition of the catalyst helps reduce the production of oxygen-containing compounds (such as acids and carbonyl compounds) and maximizes the proportion of hydrocarbons in bio-oils. Patent CN114956946A discloses a method for the rapid pyrolysis of cassava residue to prepare monocyclic aromatics using modified molecular sieves, with a pyrolysis temperature as high as 750℃ and a feed-to-catalyst mass ratio as high as 1:20, placing excessive demands on the amount of catalyst used in the pyrolysis. Patent CN112439446A reports on using H-Beta molecular sieves as a support, then loading active metals Ru and Re, to depolymerize model compounds via C / C bonds, showing an improved conversion rate of the C / C bonds in the model compounds. However, this report only studied the model compounds and failed to explain the depolymerization effect of the Ru-ReOx / H-Beta catalyst on lignin.

[0005] Molecular sieve catalysts possess strong surface acidity, but excessive acidity can lead to side reactions and coking during the reaction process. Core-shell molecular sieves, with mesoporous catalysts as the shell and microporous catalysts as the core, fully combine their advantages, maintaining strong acidity and large pore size to allow small molecules to enter. This alleviates the problem of deactivation due to coking during pyrolysis of traditional composite catalysts and enhances the synergistic effect between the core and shell catalysts. Patent CN116062763A discloses a method for preparing a core-shell molecular sieve, but the preparation process is lengthy and has not been used in practical applications. Patent CN112705248A reports a core-shell type MFI / MFI molecular sieve and its preparation method, which exhibits good molecular shape selectivity in catalytic reactions and can be used in catalytic reactions requiring high selectivity, such as in the production of p-xylene and ethylbenzene, showing high selectivity and conversion rates. This report only studies model compounds and fails to demonstrate the catalytic effect of the catalyst in actual feedstocks. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a modified core-shell molecular sieve, its preparation method, and its application in co-pyrolysis for aromatic hydrocarbon production. Utilizing the unique catalytically active core-shell structure of the prepared modified core-shell molecular sieve, as well as its synergistic catalytic effect with transition metals, lignin and plastics are co-pyrolyzed at 650°C with a raw material to catalyst mass ratio of 1:2 to produce aromatic hydrocarbons, thereby improving catalytic performance and the selectivity of aromatic hydrocarbons.

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

[0008] (1) The structural modifier, deionized water, aluminum source and silicon source are mixed sequentially and stirred for the first time to obtain mixed gel one. The mixed gel one is then subjected to first hydrothermal crystallization to obtain premix one.

[0009] (2) Sodium hydroxide, deionized water, Fe source and silicon source are mixed sequentially, and stirred for a second time to obtain mixed gel II. The premix I described in step (1) is mixed with the mixed gel II, and hydrothermal crystallization is performed for a second time to separate solid product I. After drying, a molecular sieve catalyst loaded with transition metal nanoparticles is obtained.

[0010] (3) Take the molecular sieve catalyst loaded with transition metal nanoparticles described in step (2) and perform ammonia exchange 3 to 5 times to separate solid product II. After drying, the catalyst core is obtained.

[0011] (4) The catalyst core and silicon source described in step (3) are added sequentially to a mixed solution of P123 and hydrochloric acid, stirred for a third time, and hydrothermally heated at a constant temperature to separate the solid product three times. Then, the product is dried to obtain the modified core-shell molecular sieve.

[0012] Preferably, the structural modifier in step (1) is tetrapropylammonium hydroxide; the aluminum source in step (1) is aluminum isopropoxide; and the mixing ratio of the structural modifier, deionized water, aluminum source and silicon source in step (1) is calculated according to the molar ratio of Al2O3:SiO2:TPAOH:H2O of 1:30~60:5~15:400~1000.

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

[0014] Preferably, the Fe source in step (2) is ferric 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 SiO2:FeNO3:NaOH:H2O of 30-60:1:6-9.6:90-200; the mixing ratio of premix one and mixed gel two in step (2) is calculated according to the ratio of transition metal Fe loading of 1-10 wt%.

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

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

[0017] Preferably, the mass ratio of the catalyst core to 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 treatment in step (4) is 90 to 140°C, and the time of the constant temperature hydrothermal treatment 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.

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

[0019] The present invention also provides a modified core-shell molecular sieve prepared by the aforementioned 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 lignin and plastic co-pyrolysis to prepare aromatics, wherein the modified core-shell molecular sieve is a catalyst.

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

[0022] This invention provides a modified core-shell molecular sieve catalyst prepared by partially substituting Fe with aluminum. The Fe-modified core-shell molecular sieve catalyst is applied to the co-pyrolysis of lignin and plastics to produce aromatics, improving catalytic performance and selectivity for aromatics. Industrially produced molecular sieve catalysts often produce polycyclic aromatic hydrocarbons (PAHs) in the co-pyrolysis products of lignin and plastics, and suffer from severe catalyst coking during pyrolysis. The Fe-modified core-shell molecular sieve catalyst of this invention produces more monocyclic aromatic hydrocarbons in the co-pyrolysis products, and exhibits significantly better coking performance than conventional molecular sieve catalysts. Utilizing its unique catalytically active core-shell structure and synergistic catalytic effect with transition metals, the co-pyrolysis of lignin and plastics to produce aromatics is achieved at 650°C with a feed-to-catalyst mass ratio of 1:2. Attached Figure Description

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a TEM image of the modified core-shell molecular sieve of the present invention, with a scale bar of 10 nm. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0028] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0029] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0030] Example 1

[0031] (1) Dissolve 2g of aluminum isopropoxide in a solution prepared by 8.46mL of tetrapropylammonium hydroxide and 42.35mL of deionized water. Stir at 35℃ for 30min, then add 33.52mL of tetraethyl orthosilicate. Stir the mixture at 35℃ for 4h to obtain mixed gel one. Transfer the obtained mixed gel one to a stainless steel autoclave and perform first hydrothermal crystallization at 140℃ for 9h to obtain premix one. The feeding ratio of each material is calculated as Al2O3:SiO2:TPAOH:H2O molar ratio of 1:30:8.5:480.

[0032] (2) 3.4237 g Fe(NO3)3·9H2O was added to a solution prepared with 2.373 g NaOH and 14.644 mL deionized water. The mixture was stirred for 2 h until homogeneous. Then, 57.956 mL tetraethyl orthosilicate was added at 35 °C and stirred for 5 h to obtain mixed gel II. Mixed gel II was then transferred to a stainless steel reactor. The premix I and mixed gel II were subjected to a second hydrothermal crystallization at 180 °C for 24 h, based on a calculated ratio of 1 wt% Fe loading. The product was collected, centrifuged at 9000 rpm for 8 min, and filtered to obtain solid product I. Solid product I was dried at 110 °C for 12 h and then calcined in a muffle furnace 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 a molar ratio of SiO2:FeNO3:NaOH:H2O of 30:1:7:96.

[0033] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was subjected to ammonia exchange 4 times in 1M NH4Cl aqueous solution. The temperature of ammonia exchange was 60℃ and the time of each ammonia exchange was 1h. The catalyst was separated by centrifugation at 9000rpm for 10min, washed with deionized water to obtain solid product II, dried at 60℃ for 24h, and calcined in a muffle furnace at 540℃ for 12h to obtain the catalyst core.

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

[0035] Example 2

[0036] (1) Dissolve 1.8 g of aluminum isopropoxide in a solution prepared by 12.789 mL of tetrapropylammonium hydroxide and 34.38 mL of deionized water. Stir at 35 °C for 30 min, then add 40.23 mL of tetraethyl orthosilicate. 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 perform first hydrothermal crystallization at 140 °C for 9 h to obtain premix one. The feeding ratio of each material is calculated as Al2O3:SiO2:TPAOH:H2O molar ratio of 1:40:14.28:433.

[0037] (2) 1.67 g Fe(NO3)3·9H2O was added to a solution prepared by 1.587 g NaOH and 7.442 mL deionized water, and stirred for 2 h until homogeneous. Then, 37.7 mL tetraethyl orthosilicate was added at 35 °C, and stirred for 5 h to obtain mixed gel II. Mixed gel II was then transferred to a stainless steel reactor. The premix I and mixed gel II were subjected to a second hydrothermal crystallization at 180 °C for 24 h according to a calculated ratio of 1 wt% Fe loading. The product was collected, centrifuged at 9000 rpm for 8 min, and filtered and washed to obtain solid product I. Solid product I was dried at 110 °C for 12 h and then 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 a molar ratio of SiO2:FeNO3:NaOH:H2O of 40:1:9.6:100.

[0038] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was subjected to ammonia exchange three times in 1M NH4Cl aqueous solution. The ammonia exchange temperature was 60℃ and the ammonia exchange time was 1h each time. The catalyst was separated by centrifugation at 9000rpm for 10min, washed with deionized water to obtain solid product II, dried at 60℃ for 24h, and calcined in a muffle furnace at 540℃ for 12h to obtain the catalyst core.

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

[0040] Example 3

[0041] (1) Dissolve 1.2 g of aluminum isopropoxide in a solution prepared by 5.672 mL of tetrapropylammonium hydroxide and 42.353 mL of deionized water. Stir at 35 °C for 30 min, then add 35.924 mL of tetraethyl orthosilicate. 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 perform first hydrothermal crystallization at 140 °C for 9 h to obtain premix one. The feeding ratio of each material is calculated as Al2O3:SiO2:TPAOH:H2O molar ratio of 1:50:9.5:800.

[0042] (2) 1.114 g Fe(NO3)3·9H2O was added to a solution prepared with 0.882 g NaOH and 7.718 mL deionized water. The mixture was stirred for 2 h until homogeneous. Then, 31.418 mL tetraethyl orthosilicate was added at 35 °C and stirred for 5 h to obtain mixed gel II. Mixed gel II was then transferred to a stainless steel reactor. The premix I and mixed gel II were subjected to a second hydrothermal crystallization at 180 °C for 24 h, based on a calculated ratio of 1 wt% Fe loading. The product was collected, centrifuged at 9000 rpm for 8 min, and filtered and washed to obtain solid product I. Solid product I was dried at 110 °C for 12 h and then calcined in a muffle furnace 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 a molar ratio of SiO2:FeNO3:NaOH:H2O of 50:1:8:160.

[0043] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was subjected to ammonia exchange three times in 1M NH4Cl aqueous solution. The ammonia exchange temperature was 60℃ and the ammonia exchange time was 1h each time. The catalyst was separated by centrifugation at 9000rpm for 10min, washed with deionized water to obtain solid product II, dried at 60℃ for 24h, and calcined in a muffle furnace at 540℃ for 12h to obtain the catalyst core.

[0044] (4) The catalyst core and tetraethyl orthosilicate were added to a mixed solution of P123 and hydrochloric acid in a mass ratio of 2:1 (2g of P123 was added to 100mL of 2M HCl aqueous solution and stirred at 35℃ for 2h to completely dissolve). The mixture was stirred at 35℃ for 5h, and then hydrothermally heated at 90℃ for 20h. The solid product was separated by filtration, dried at 80℃ for 10h, and calcined in a muffle furnace at 550℃ for 5h to obtain the modified core-shell molecular sieve Fe-50H / S.

[0045] Example 4

[0046] (1) Dissolve 1g of aluminum isopropoxide in a solution prepared by 2.488mL of tetrapropylammonium hydroxide and 44.118mL of deionized water. Stir at 35℃ for 30min, then add 33.524mL of tetraethyl orthosilicate. Stir the mixture at 35℃ for 4h to obtain mixed gel one. Transfer the obtained mixed gel one to a stainless steel autoclave and perform first hydrothermal crystallization at 140℃ for 9h to obtain premix one. The feeding ratio of each material is calculated as Al2O3:SiO2:TPAOH:H2O molar ratio of 1:60:5:1000.

[0047] (2) 0.929 g Fe(NO3)3·9H2O was added to a solution prepared with 0.551 g NaOH and 8.269 mL deionized water, and stirred for 2 h until homogeneous. Then, 31.418 mL tetraethyl orthosilicate was added at 35 °C, and stirred for 5 h to obtain mixed gel II. Mixed gel II was then transferred to a stainless steel reactor. The premix I and mixed gel II were subjected to a second hydrothermal crystallization at 180 °C for 24 h according to a calculated ratio of 1 wt% Fe loading. The product was collected, centrifuged at 9000 rpm for 8 min, and filtered and washed to obtain solid product I. Solid product I was dried at 110 °C for 12 h and then placed in a muffle furnace for calcination 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 a molar ratio of SiO2:FeNO3:NaOH:H2O of 60:1:6:200.

[0048] (3) The molecular sieve catalyst loaded with transition metal nanoparticles was subjected to ammonia exchange three times in 1M NH4Cl aqueous solution. The ammonia exchange temperature was 60℃ and the ammonia exchange time was 1h each time. The catalyst was separated by centrifugation at 9000rpm for 10min, washed with deionized water to obtain solid product II, dried at 60℃ for 24h, and calcined in a muffle furnace at 540℃ for 12h to obtain the catalyst core.

[0049] (4) The catalyst core and tetraethyl orthosilicate were added to a mixed solution of P123 and hydrochloric acid in a mass ratio of 2:1 (2g of P123 was added to 100mL of 2M HCl aqueous solution and stirred at 35℃ for 2h to completely dissolve). The mixture was stirred at 35℃ for 5h, and then hydrothermally heated at 90℃ for 20h. The solid product was separated by filtration, dried at 80℃ for 10h, and calcined in a muffle furnace at 550℃ for 5h to obtain the modified core-shell molecular sieve Fe-60H / S.

[0050] Experimental Example 1

[0051] Using a uniform mixture of lignin and plastic at a mass ratio of 1:1 as raw material, non-in-situ pyrolysis was performed in a vertical pyrolysis furnace. The specific experimental conditions were: a raw material to catalyst mass ratio of 1:2, a heating rate of 10℃ / s to 650℃, a retention time of 30 min, and the pyrolysis oil was sent to GC-MS for analysis.

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

[0053] Table 1 Product Selectivity

[0054]

[0055]

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

[0057] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined 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.

2. The preparation method according to claim 1, characterized in that: 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.

3. The preparation method according to claim 1, characterized in that: 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.

4. The preparation method according to claim 1, characterized in that: 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 the transition metal Fe loading of 1-10wt%.

5. 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.

6. 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.

7. 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.

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

9. The modified core-shell molecular sieve prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the modified core-shell molecular sieve prepared by the preparation method according to any one of claims 1 to 8 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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