Core-shell molecular sieve ZSM-5 / silicalite-1 as well as preparation method and application thereof

Abstract

The invention provides a preparation method of a core-shell molecular sieve ZSM-5 / silicalite-1, which comprises the following steps: (1) carrying out first hydrothermal treatment on a feed liquid A containing a template agent and a silicon source to obtain a feed liquid B; and (2) mixing the feed liquid B with a ZSM-5 molecular sieve, and carrying out second hydrothermal treatment. The ZSM-5 / silicalite-1 molecular sieve prepared by the method disclosed by the invention is regular in morphology and high in core molecular sieve coating rate, and has relatively high light aromatic hydrocarbon selectivity in a reaction of preparing aromatic hydrocarbon by a CO2 hydrogenation one-step method.

Description

Technical Field

[0001] The invention belongs to the field of porous materials, and in particular relates to a core-shell molecular sieve ZSM-5 / silicalite-1 and a preparation method and application thereof. Background Art

[0002] Aromatics are important platform chemicals that are often used as raw materials for synthetic petrochemicals and pharmaceuticals. The growing global demand for products such as polyester fibers, resins, and benzene derivatives has driven the continued expansion of the aromatics market. Traditional methods of producing aromatics include steam cracking and naphtha reforming. However, the industrial production of aromatics is both energy intensive and heavily dependent on oil and natural gas. In recent years, coal pyrolysis and methanol to aromatics (MTA) have also been gradually developed as potential process technologies. Alternative strategies for synthesizing aromatics from CO2 provide important opportunities to reduce emissions and develop low-cost ways to produce high-value-added chemicals.

[0003] In recent years, the new strategy of "coupled catalysis" has provided an important basis for the direct conversion of CO2 to aromatics. In the oxide-molecular sieve bifunctional catalytic system, the oxide is the main active component of CO2 hydrogenation. The above work explores the application of different oxide systems in the CO2 hydrogenation reaction to aromatics. ZSM-5 zeolite is a commonly used active component for converting intermediates such as methanol into aromatics. ZSM-5 zeolite has a ten-membered ring structure, and the basic structural unit is composed of eight five-membered rings. The crystal structure belongs to the orthorhombic system and the structure is very stable. Under the action of the acidic site of ZSM-5, the methanol intermediate is first converted into olefins, and then converted into aromatics through continuous oligomerization, cyclization and dehydrogenation reactions.

[0004] Since there are 3 to 5 acid sites on the outer surface of ZSM-5 molecular sieve, these acid sites are not spatially confined and do not have shape-selective catalytic properties. Core-shell molecular sieve ZSM-5 / Silicalite-1, as one of the effective methods to change the acid properties of the outer surface, achieves the modification of the outer surface without affecting the diffusion properties of the zeolite pores, and can greatly improve its selectivity without significantly reducing the catalytic activity of the core phase molecular sieve. Its structural characteristics are that the crystal structure of ZSM-5 and silicalite-1 molecular sieves is completely similar, the core-shell interface is very tight and firm, and the mechanical properties are good; there are few shell defects; the shell thickness can be adjusted and has good hydrophobicity, which greatly enhances the life of the molecular sieve.

[0005] Currently, the most common method for synthesizing core-shell molecular sieves ZSM-5 / Silicalite-1 is hydrothermal synthesis. However, hydrothermal synthesis often has the problem of uneven shell coating. In the reaction of CO2 hydrogenation to aromatics, the selectivity of light aromatics is not significantly improved, and the selectivity of total aromatics is low, resulting in excessive by-products. Summary of the invention

[0006] In order to solve one of the above-mentioned technical problems existing in the prior art, the present invention provides a method for preparing ZSM-5 / Silicalite-1 molecular sieve. The ZSM-5 / Silicalite-1 molecular sieve prepared by the method has a regular morphology and improves the selectivity of light aromatics in the one-step CO2 hydrogenation process for producing aromatics.

[0007] In a first aspect, the present invention provides a method for preparing a core-shell molecular sieve ZSM-5 / silicalite-1, comprising the following steps:

[0008] (1) subjecting a liquid A containing a template and a silicon source to a first hydrothermal treatment to obtain a liquid B;

[0009] (2) Mixing the feed solution B with the ZSM-5 molecular sieve and performing a second hydrothermal treatment.

[0010] In some embodiments, in step (1), the temperature of the first hydrothermal treatment is 150-180°C, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or any value therebetween.

[0011] In some embodiments, in step (1), the time of the first hydrothermal treatment is 1 to 12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0012] In some embodiments, step (1) further comprises the step of cooling the liquid A after the first hydrothermal treatment. In some specific embodiments, the cooling step comprises: directly placing the liquid A after the first hydrothermal treatment in water at 15 to 40° C. to cool to room temperature. In some specific embodiments, the cooling step comprises: naturally cooling the liquid A after the first hydrothermal treatment to room temperature.

[0013] In some embodiments, in step (1), the template is selected from at least one of silicon tetrafluoride, tetrapropylammonium hydroxide, ammonium fluorosilicate or tetrapropylammonium bromide.

[0014] In some embodiments, the silicon source is selected from at least one of silica sol, white black carbon, and tetraethyl orthosilicate.

[0015] In some embodiments, the feed liquid A further contains a solvent. In some specific embodiments, the solvent includes at least one of alcohol and water, preferably alcohol and water. In some specific embodiments, the alcohol is selected from C1 to C5 alcohols, such as methanol, ethanol, isopropanol, n-butanol, etc., preferably ethanol.

[0016] In some embodiments, in the slurry A, the silicon source is calculated as SiO2, and the molar ratio of the silicon source to the template is 1:(0.1-1), for example 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1 or any value therebetween.

[0017] In some embodiments, in the slurry A, the silicon source is calculated as SiO2, and the molar ratio of the silicon source to the alcohol is 1:(2-10), for example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or any value therebetween.

[0018] In some embodiments, in the slurry A, the silicon source is calculated as SiO2, and the molar ratio of the silicon source to water is 1:(50-150), for example 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, 1:110, 1:120, 1:130, 1:140, 1:150 or any value therebetween.

[0019] In some embodiments, in step (2), the mass ratio of the feed liquid B to the ZSM-5 molecular sieve is (10-30):1, for example, 10:1, 15:1, 20:1, 25:1, 30:1 or any value therebetween.

[0020] In some embodiments, in step (2), the silicon-aluminum ratio of the ZSM-5 molecular sieve is 25-150.

[0021] In some embodiments, in step (2), the ZSM-5 molecular sieve is in the hydrogen type.

[0022] In some embodiments, in step (2), the particle size of the ZSM-5 molecular sieve is 0.1-5 μm.

[0023] In some embodiments, in step (2), the temperature of the second hydrothermal treatment is 150-180°C, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or any value therebetween.

[0024] In some embodiments, in step (2), the time of the second hydrothermal treatment is 48 to 96 hours, for example, 48 hours, 54 hours, 60 hours, 65 hours, 70 hours, 72 hours, 75 hours, 80 hours, 85 hours, 90 hours, 96 hours or any value therebetween.

[0025] In some embodiments, the step (2) further comprises: performing solid-liquid separation after the second hydrothermal treatment, and drying and calcining the solid to obtain a core-shell molecular sieve ZSM-5 / silicalite-1. In some specific embodiments, the drying temperature is 60 to 100° C., preferably 70 to 90° C. In some specific embodiments, the calcining temperature is 450 to 650° C., preferably 500 to 600° C.

[0026] In the preparation method of the present invention, the operation of mixing the ZSM-5 molecular sieve with the feed liquid B prepared in step (1) and hydrothermally treating the ZSM-5 molecular sieve can be performed multiple times, so that silicon is deposited on the ZSM-5 molecular sieve multiple times to achieve a better coating effect. In the method of the present invention, silicon can be deposited on the ZSM-5 molecular sieve 2 to 3 times to achieve complete coating of the outer surface of the core phase molecular sieve, and the obtained core-shell type molecular sieve has a regular morphology.

[0027] In some embodiments, the method further comprises step (3):

[0028] The core-shell molecular sieve obtained in step (2) is mixed with the feed liquid B and subjected to a third hydrothermal treatment.

[0029] In some specific embodiments, step (3) further comprises: performing solid-liquid separation after the third hydrothermal treatment, and drying and calcining the solid to obtain a core-shell molecular sieve ZSM-5 / silicalite-1. In some specific embodiments, in step (3), the drying temperature is 60 to 100° C., preferably 70 to 90° C. In some specific embodiments, in step (3), the calcination temperature is 450 to 650° C., preferably 500 to 600° C.

[0030] In some embodiments, the temperature of the third hydrothermal treatment is 150-180° C., such as 150° C., 155° C., 160° C., 165° C., 170° C., 175° C., 180° C., or any value therebetween. Preferably, the time of the third hydrothermal treatment is 48-96 h, such as 48 h, 54 h, 60 h, 65 h, 70 h, 72 h, 75 h, 80 h, 85 h, 90 h, 96 h, or any value therebetween.

[0031] The solid obtained by solid-liquid separation in the above step (3) of the present invention can also be mixed with the feed liquid B again without being dried and calcined, and subjected to hydrothermal treatment to allow silicon to continue to be deposited on the ZSM-5 molecular sieve.

[0032] In some preferred embodiments, the method further comprises step (4): mixing the core-shell molecular sieve obtained in step (3) with the feed liquid B and performing a fourth hydrothermal treatment. Optionally, after the fourth hydrothermal treatment, solid-liquid separation is performed and the solid is dried and calcined.

[0033] In some specific embodiments, step (4) further comprises: mixing the core-shell molecular sieve obtained in step (3) with the feed liquid B, performing a fourth hydrothermal treatment, and then separating the solid and the liquid, and drying and calcining the solid to obtain the core-shell molecular sieve ZSM-5 / silicalite-1. In some specific embodiments, in step (4), the drying temperature is 60 to 100° C., preferably 70 to 90° C. In some specific embodiments, in step (4), the calcining temperature is 450 to 650° C., preferably 500 to 600° C.

[0034] In some embodiments, the temperature of the fourth hydrothermal treatment is 150-180° C., such as 150° C., 155° C., 160° C., 165° C., 170° C., 175° C., 180° C., or any value therebetween. Preferably, the time of the fourth hydrothermal treatment is 48-96 h, such as 48 h, 54 h, 60 h, 65 h, 70 h, 72 h, 75 h, 80 h, 85 h, 90 h, 96 h, or any value therebetween.

[0035] In a second aspect, the present invention provides a core-shell molecular sieve ZSM-5 / silicalite-1 obtained by the preparation method described in the first aspect.

[0036] In a third aspect, the present invention provides a catalyst comprising the core-shell molecular sieve ZSM-5 / silicalite-1 described in the second aspect and a metal oxide.

[0037] The metal oxide of the present invention is selected from metal oxides having a catalytic CO2 hydrogenation effect, including one or more of ZnO, Cr2O3, Fe2O3, Y2O3, Ga2O3, MnO2, CuO, ZrO2 and CeO2.

[0038] In some embodiments, the catalyst is prepared by the following method:

[0039] The core-shell molecular sieve ZSM-5 / Silicalite-1 is mixed with the metal oxide, ground, tableted and sieved, preferably sieved to 20-40 mesh, to obtain the catalyst.

[0040] In a fourth aspect, the present invention provides the use of the core-shell molecular sieve ZSM-5 / silicalite-1 described in the second aspect or the catalyst described in the third aspect in the reaction of hydrogenating CO2 to produce aromatics.

[0041] In some embodiments, the reaction temperature is 320°C to 350°C.

[0042] In some embodiments, the reaction pressure is 2.5 MPa to 3.5 MPa.

[0043] In some embodiments, the space velocity of the reaction is 1200 mL / g·h to 6000 mL / g·h.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The preparation method of the molecular sieve ZSM-5 / Silicalite-1 provided by the present invention is to obtain a ZSM-5 / Silicalite-1 core-shell structure molecular sieve with a relatively regular morphology by first subjecting the shell liquid used for coating the core phase molecular sieve to hydrothermal treatment and then mixing it with the core phase molecular sieve for coating. After 2 to 3 times of coating, the outer surface of the core phase molecular sieve is basically completely coated, and the one-step CO2 hydrogenation method for aromatics has achieved good light aromatics selectivity. The preparation method of the present invention is simple, the raw materials are low-cost, and it is easy to promote, and it is convenient to optimize the existing one-step CO2 hydrogenation method for aromatics, making it more commercially valuable. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application, but do not constitute a limitation to the present application.

[0047] Figure 1 It is a SEM picture of the ZSM-5 molecular sieve used in Examples 1-14 of the present invention.

[0048] Figure 2 This is the SEM image of the product prepared in Comparative Example 2.

[0049] Figure 3 This is a SEM image of the ZSM-5 / Silicalite-1 molecular sieve prepared in Example 1 of the present invention.

[0050] Figure 4 This is a SEM image of the secondary coated ZSM-5 / Silicalite-1 molecular sieve prepared in Example 2 of the present invention.

[0051] Figure 5 This is a SEM image of the secondary coated ZSM-5 / Silicalite-1 molecular sieve prepared in Example 4 of the present invention.

[0052] Figure 6 It is the XRD diagram of the molecular sieve of comparative example 1 of the present invention and the molecular sieve prepared in examples 1-2. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described herein are only used to explain the present invention and are not intended to constitute any limitation to the present invention.

[0054] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0055] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless the weight basis does not conform to the common understanding of those skilled in the art.

[0056] Unless otherwise specified, the "silicon to aluminum ratio" mentioned in the present invention refers to the molar ratio of SiO2 to Al2O3.

[0057] Unless otherwise specified, the "space velocity" mentioned in the present invention refers to the unit amount of reactants passing through a unit volume of catalyst per unit time.

[0058] Unless otherwise specified, the reagents used in the following examples and comparative examples of the present invention can be obtained through commercial channels.

[0059] Example 1

[0060] (1) Preparation of shell solution

[0061] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 170°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0062] (2) Preparation of core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1

[0063] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed until neutral; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1.

[0064] Example 2

[0065] (1) Preparation of shell solution

[0066] The same method as step (1) of Example 1 was used to obtain a shell solution.

[0067] (2) Preparation of secondary coated core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-2a

[0068] 4 g of the Z5@S1 molecular sieve obtained in Example (1) was added to the shell solution and stirred for 1 h. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 h. After being taken out, it was centrifuged and washed until neutral. It was then dried in an oven at 80°C overnight and finally calcined in a muffle furnace at 550°C for 6 h to obtain a solid product, which was recorded as Z5@S1-2a.

[0069] Example 3

[0070] (1) Preparation of shell solution

[0071] The same method as step (1) of Example 1 was used to obtain a shell solution.

[0072] (2) Preparation of triple-coated core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-3a

[0073] 4 g of the Z5@S1-2a molecular sieve obtained in Example (2) was added to the shell solution and stirred for 1 h. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 h. After being taken out, it was centrifuged and washed until neutral. It was then dried in an oven at 80°C overnight and finally calcined in a muffle furnace at 550°C for 6 h to obtain a solid product, which was recorded as Z5@S1-3a.

[0074] Example 4

[0075] (1) Preparation of shell solution

[0076] The same method as step (1) of Example 1 was used to obtain a shell solution.

[0077] (2) Preparation of secondary coated core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-2b

[0078] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermaled in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed three times to obtain a wet base.

[0079] The wet base mass M1 after centrifugal washing, a certain mass of wet base m1 = 4 × M1 / 7.04 was added to the reconfigured shell solution, and stirring was continued for 1 hour. The solution was transferred to an autoclave with a liner, and hydrothermal in a 170°C oven for 72 hours; after taking it out, it was centrifuged and washed until neutral; then dried in an 80°C oven overnight, and finally calcined in a 550°C muffle furnace for 6 hours to obtain a solid product, which was recorded as Z5@S1-2b.

[0080] Example 5

[0081] (1) Preparation of shell solution

[0082] The same method as step (1) of Example 1 was used to obtain a shell solution.

[0083] (2) Preparation of triple-coated core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-3b

[0084] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 μm was added to the shell solution and stirred for 1 h. The solution was transferred to an autoclave with an inner liner and hydrothermaled in an oven at 170°C for 72 h; after being taken out, it was centrifuged and washed three times to obtain a wet base 1.

[0085] The mass of wet base 1 after centrifugal washing is M1. A certain mass m1 of wet base 1 (m1 = 4 × M1 / 7.04) is added to the reconfigured shell solution and stirred for 1 hour. The solution is transferred to an autoclave with an inner liner and hydrothermal in an oven at 170°C for 72 hours; after taking it out, it is centrifuged and washed 3 times to obtain wet base 2.

[0086] The mass of wet base 2 after centrifugal washing is M2. A certain mass m2 of wet base 2 (m2 = 4 × M2 / 7.04) is added to the reconfigured shell solution and stirred for 1 hour. The solution is transferred to an autoclave with a liner and hydrothermally heated in a 170°C oven for 72 hours; after being taken out, it is centrifuged and washed until neutral; then dried in an 80°C oven overnight, and finally calcined in a 550°C muffle furnace for 6 hours to obtain a solid product, which is recorded as Z5@S1-3b.

[0087] Example 6

[0088] (1) Preparation of shell solution

[0089] Weigh 3.05 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 5.27 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 170°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0090] (2) Preparation of core-shell molecular sieve ZSM-5 / silicalite-1, denoted as Z5@S1-0.5

[0091] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed until neutral; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-0.5.

[0092] Example 7

[0093] (1) Preparation of shell solution

[0094] Weigh 4.58 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 7.02 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 170°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0095] (2) Preparation of core-shell molecular sieve ZSM-5 / silicalite-1, denoted as Z5@S1-0.75

[0096] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; centrifuged and washed three times after removal; dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-0.75.

[0097] Example 8

[0098] (1) Preparation of shell solution

[0099] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 170°C for 3 h, take it out and cool it to room temperature to obtain a shell solution.

[0100] (2) Preparation of core-shell molecular sieve ZSM-5 / silicalite-1, denoted as Z5@S1-3

[0101] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; centrifuged and washed three times after removal; dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-3.

[0102] Example 9

[0103] (1) Preparation of shell solution

[0104] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 170°C for 6 h, take it out and cool it to room temperature to obtain a shell solution.

[0105] (2) Preparation of core-shell molecular sieve ZSM-5 / silicalite-1, denoted as Z5@S1-6

[0106] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; centrifuged and washed three times after removal; dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-6.

[0107] Example 10

[0108] (1) Preparation of shell solution

[0109] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, and hydrothermally treat it in an oven at 170°C for 9 h. Then take it out and cool it to room temperature to obtain a shell solution.

[0110] (2) Preparation of core-shell molecular sieve ZSM-5 / silicalite-1, denoted as Z5@S1-9

[0111] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; centrifuged and washed three times after removal; dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-9.

[0112] Embodiment 11

[0113] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 150°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0114] (2) Preparation of core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-150

[0115] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifugally washed to neutrality; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-150.

[0116] Example 12

[0117] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 180°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0118] (2) Preparation of core-shell molecular sieve ZSM-5 / Silicalite-1, denoted as Z5@S1-180

[0119] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed until neutral; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product, which was recorded as Z5@S1-180.

[0120] Embodiment 13

[0121] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 120°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0122] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed to neutrality; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product.

[0123] As in Comparative Example 2, only a small amount of Silicalite-1 was observed to be attached to ZSM-5.

[0124] Embodiment 14

[0125] Weigh 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) to prepare a mixed solution, transfer the mixed solution to an autoclave, hydrothermally treat it in an oven at 200°C for 1 h, take it out and cool it to room temperature to obtain a shell solution.

[0126] 4 g of ZSM-5 molecular sieve with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added to the shell solution and stirred for 1 hour. The solution was transferred to an autoclave with an inner liner and hydrothermally heated in an oven at 170°C for 72 hours; after being taken out, it was centrifuged and washed to neutrality; then dried in an oven at 80°C overnight, and finally calcined in a muffle furnace at 550°C for 6 hours to obtain a solid product.

[0127] Only the self-growth phenomenon of Silicalite-1 was observed.

[0128] Comparative Example 1

[0129] The ZSM-5 molecular sieve used in Comparative Example 2 and Examples 1-14 of the present invention has a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns. The SEM spectrum is as follows: Figure 1 shown.

[0130] Comparative Example 2

[0131] 6.10 g of tetrapropylammonium hydroxide solution (TPAOH, 25 wt%), 9.21 g of ethanol, 54.0 g of deionized water, and 10.53 g of tetraethyl orthosilicate (TEOS) were weighed to prepare a mixed solution, and the solution was stirred at 40°C overnight. Then 4 g of ZSM-5 powder with a silicon-aluminum ratio (SiO2 / Al2O3) of 100 and a particle size of 2 microns was added and fully mixed, and Silicalite-1 was grown by hydrothermal treatment at 170°C for 72 h. Centrifuged three times, the collected crystals were dried at 80°C for 24 h. Finally, CS1 was obtained by calcining in a muffle furnace at 550°C for 6 h.

[0132] Observe the SEM spectrum of the solid product (see Figure 2 ), there is only a small amount of Silicalite-1 attached to ZSM-5, and a large amount of Silicalite-1 self-growth phenomenon occurs.

[0133] The SEM images of the core-shell molecular sieves prepared in Example 1, Example 2 and Example 4 are as follows: Figure 3 , Figure 4 and Figure 5 As shown. Figures 3 to 5 It can be seen that the ZSM-5 / Silicalite-1 prepared by the method of the present invention grows a dense shell layer on the outer surface of ZSM-5 with regular morphology.

[0134] The XRD patterns of the molecular sieves of Comparative Example 1 and the molecular sieves prepared in Examples 1-2 are as follows: Figure 6 shown. Figure 6 No amorphous peaks were observed in the XRD patterns of the zeolite in the 20-30° region, and typical MFI zeolite structure characteristic peaks were shown, indicating that after shell coating, the crystallinity of the molecular sieve was still high and the core / shell were both MFI structures.

[0135] The core-shell molecular sieves prepared in Examples 1 to 14 and the molecular sieves in Comparative Examples 1 to 2 were evaluated for catalytic activity.

[0136] Test method: The synthesized core-shell molecular sieve ZSM-5 / Silicalite-1 powder was mixed with Zn-Cr oxide particles and ground in an agate mortar. The mixture was pressed into tablets and sieved to 20-40 mesh to obtain a bifunctional coupling catalyst.

[0137] The obtained bifunctional coupled catalyst was loaded into a stainless steel reaction tube lined with a quartz tube, reduced in reducing gas H2, and then switched to a CO2 / H2 / N2 mixed gas for reaction at 320°C and 3.0 MPa with a reaction space velocity of 1200 mL / g·h. The results are listed in Table 1.

[0138] Table 1

[0139]

[0140]

[0141] It can be seen from Table 1 that, compared with the molecular sieves of Comparative Examples 1 and 2, the ZSM-5 / Silicalite-1 prepared by the preparation method of the present invention, when applied to the reaction of one-step preparation of aromatics by CO2 hydrogenation, achieves a higher selectivity for light aromatics without substantially changing the CO2 conversion rate and aromatics selectivity. When the pressure is increased, a higher CO2 conversion rate can be achieved; increasing the temperature and flow rate can further increase the selectivity for C6-C8 aromatics. When reacting at 350°C and 3.0MPa, the reaction space velocity is 6000mL / g·h, and the selectivity for C6-C8 aromatics in Example 3 reaches 60.7%.

[0142] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a core-shell molecular sieve ZSM-5 / silicalite-1, comprising the following steps: (1) subjecting a liquid A containing a template and a silicon source to a first hydrothermal treatment to obtain a liquid B; (2) The feed solution B is mixed with ZSM-5 molecular sieve and subjected to a second hydrothermal treatment.

2. The preparation method according to claim 1, characterized in that: In step (1), the temperature of the first hydrothermal treatment is 150 to 180° C., and / or the time of the first hydrothermal treatment is 1 to 12 hours.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the template is selected from at least one of silicon tetrafluoride, tetrapropylammonium hydroxide, ammonium fluorosilicate or tetrapropylammonium bromide; and / or, The silicon source is selected from at least one of silica sol, white black carbon, and tetraethyl orthosilicate; and / or, The feed liquid A further contains a solvent. Preferably, the solvent includes alcohol and water. Preferably, the alcohol is selected from C1 to C5 alcohols, preferably methanol, ethanol, isopropanol and n-butanol.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In the feed solution A, the silicon source is calculated as SiO2, and the molar ratio of the silicon source to the template is 1: (0.1-1); and / or, The molar ratio of silicon source to alcohol is 1:(2-10); and / or, The molar ratio of the silicon source to water is 1:(50-150).

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step (2), the mass ratio of the feed liquid B to the ZSM-5 molecular sieve is (10-30):1; and / or, The silicon-aluminum ratio of the ZSM-5 molecular sieve is 25 to 150; and / or, The ZSM-5 molecular sieve is in the hydrogen type.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step (2), the temperature of the second hydrothermal treatment is 150 to 180° C.; the time of the second hydrothermal treatment is 48 to 96 hours; and / or, The step (2) further comprises: performing solid-liquid separation after the second hydrothermal treatment, and drying and calcining the solid to obtain a core-shell molecular sieve.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The method further comprises: Step (3): mixing the core-shell molecular sieve obtained in step (2) with the feed liquid B, and performing a third hydrothermal treatment. Optionally, after the third hydrothermal treatment, solid-liquid separation is performed, and the solid is dried and calcined; Optionally, the method further comprises: Step (4): mixing the core-shell molecular sieve obtained in step (3) with the feed liquid B, and performing a fourth hydrothermal treatment. Optionally, after the fourth hydrothermal treatment, solid-liquid separation is performed, and the solid is dried and calcined; Preferably, the temperature of the third hydrothermal treatment is 150-180° C., and the time of the third hydrothermal reaction is 48-96 hours; Preferably, the temperature of the fourth hydrothermal treatment is 150-180° C., and the time of the fourth hydrothermal reaction is 48-96 hours.

8. The core-shell molecular sieve ZSM-5 / silicalite-1 obtained by the preparation method according to any one of claims 1 to 7.

9. A catalyst comprising the core-shell molecular sieve ZSM-5 / silicalite-1 according to claim 8 and a metal oxide, Preferably, the metal oxide includes one or more of ZnO, Cr2O3, Fe2O3, Y2O3, Ga2O3, MnO2, CuO, ZrO2 and CeO2; Preferably, the catalyst is prepared by the following method: The core-shell molecular sieve ZSM-5 / Silicalite-1 is mixed with the metal oxide, ground, tableted and sieved, preferably sieved to 20-40 mesh, to obtain the catalyst.

10. Use of the core-shell molecular sieve ZSM-5 / silicalite-1 according to claim 8 or the catalyst according to claim 9 in the reaction of preparing aromatics by hydrogenation of CO2.

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