Zn-modified hierarchical pore molecular sieve with nanosheet self-supporting structure as well as preparation method and application of Zn-modified hierarchical pore molecular sieve

Abstract

The invention discloses a Zn-modified hierarchical pore molecular sieve with a nanosheet self-supporting structure as well as a preparation method and application thereof, and belongs to the technical field of preparation of carbon dioxide hydrogenation catalysts. The preparation method provided by the invention comprises the following steps: mixing a Si source, tetrabutyl ammonium hydroxide and water, and carrying out hydrolysis reaction to obtain a first mixed solution; mixing and dissolving a Zn source and an Al source in water to obtain a second mixed solution; and mixing the first mixed solution and the second mixed solution, performing crystallization treatment, and roasting a product obtained after crystallization treatment to obtain the catalyst. The preparation method is simple and low in production cost, and when the obtained hierarchical pore molecular sieve serves as a catalyst to be applied to a carbon dioxide hydrogenation reaction, high selectivity can be achieved on target products C5 and above high-carbon hydrocarbon while the high carbon dioxide conversion rate is maintained, and good catalytic stability is shown.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide hydrogenation catalyst preparation technology, and in particular to a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In the field of catalytic materials, developing multi-level porous molecular sieves is a common strategy to improve the mass transfer and diffusion of reactants. Among them, self-supporting zeolites constructed from nanosheets through orthogonal connections are considered a promising catalytic material because they possess both microporous and mesoporous open systems.

[0004] Catalytic hydrogenation of carbon dioxide to convert high-carbon hydrocarbons (C 5+ Carbon dioxide (CO2) is a crucial pathway for obtaining liquid fuels and achieving carbon resource recycling, possessing significant environmental and energy strategic value. However, when applying the aforementioned self-supporting zeolite structures to such reactions, the synergistic optimization of their catalytic performance faces significant challenges. The reaction process is complex, involving multiple conversion steps and carbon chain growth, placing high demands on catalyst performance. Currently, catalysts based on this structure often struggle to simultaneously achieve high CO2 conversion rates and ideal selectivity for high-carbon hydrocarbon products. Pursuing high conversion rates often leads to the aggravation of side reactions such as cracking, resulting in reduced selectivity for the target product and catalyst deactivation due to carbon deposition; conversely, focusing on improving selectivity often limits overall reaction activity. This contradiction restricts the practical application of such materials in the efficient resource utilization of CO2.

[0005] Therefore, how to effectively modify self-supporting zeolites to synergistically enhance their activity and selectivity for high-carbon hydrocarbons in carbon dioxide hydrogenation is an urgent problem to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention provides a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, its preparation method and application. The hierarchical porous molecular sieve prepared by the present invention exhibits high activity, high selectivity and high stability in the reaction of carbon dioxide hydrogenation to produce high carbon hydrocarbons.

[0007] In a first aspect, the present invention provides a method for preparing a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, comprising the following steps: Si source, tetrabutylammonium hydroxide and water were mixed and hydrolyzed to obtain the first mixed solution; The Zn source and the Al source were mixed and dissolved in water to obtain a second mixed solution; The first and second mixed solutions are mixed and then crystallized. The crystallized product is then calcined to obtain the final product.

[0008] Preferably, the ratio of the molar amount of Si to the total molar amount of Zn and Al is controlled to be (90~110):1.

[0009] Furthermore, the molar ratio of Zn to Al is (2~6): (4~8).

[0010] Preferably, the molar ratio of the tetrabutylammonium hydroxide to the Si element in the Si source is (0.2~0.4):1.

[0011] Preferably, the Si source is selected from at least one of organosilicon esters or silica sol; the Al source is selected from at least one of aluminum alkoxides or soluble aluminum salts; and the Zn source is selected from soluble zinc salts.

[0012] Preferably, the hydrolysis reaction temperature is 30~40℃ and the hydrolysis reaction time is 2~8h; the mixing and dissolving temperature is 30~40℃ and the mixing and dissolving time is 1~5h.

[0013] Preferably, the crystallization treatment is performed using a hydrothermal method, with a crystallization temperature of 120~140℃ and a crystallization time of 60~84h.

[0014] Preferably, the calcination temperature is 500~600℃, the calcination time is 4~10h, and the calcination is carried out in an air atmosphere.

[0015] Secondly, the present invention provides a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, which is prepared by the above-described preparation method.

[0016] Thirdly, the present invention provides the application of the above-mentioned Zn-modified hierarchical porous molecular sieve with nanosheet self-supporting structure in the production of C5 and above high carbon hydrocarbons by carbon dioxide hydrogenation.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The preparation method provided by the present invention uses tetrabutylammonium hydroxide as a template agent. By mixing Si source, Zn source and Al source in a specific step and then performing hydrothermal crystallization and calcination in one step, the in-situ introduction of Zn species into the self-supporting nanosheet molecular sieve framework is successfully achieved. This process route avoids the use of expensive template agents and complex post-processing steps, and the preparation method is simple and has a low production cost.

[0018] (2) The Zn-modified hierarchical porous molecular sieve prepared by the above method of the present invention has a stable three-dimensional hierarchical channel structure formed by mutual support of its nanosheets. This structure significantly shortens the diffusion path between reactants and products and exposes abundant accessible active surfaces, providing excellent mass transfer conditions for catalytic reactions. At the same time, the co-introduction of Zn and Al in the synthesis process realizes the synergistic regulation of the type, intensity and distribution of acidic sites of the molecular sieve, optimizing its surface acidity.

[0019] (3) When the hierarchical porous molecular sieve obtained in this invention is used as a catalyst in the hydrogenation reaction of carbon dioxide, its unique structure and the synergistic effect of modulated acidity effectively promote the conversion of reaction intermediates and the growth of carbon chains. This enables the catalyst to significantly improve the selectivity for the target product C5 and above high carbon hydrocarbons while maintaining a high carbon dioxide conversion rate, and exhibits good catalytic stability. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 These are scanning electron microscope images of the hierarchical porous molecular sieve Zn2Al8-SPP(100) prepared in Example 1 of this invention; Figure 2 These are the XRD patterns of the hierarchical porous molecular sieves prepared in Examples 1-3 and Comparative Examples 1-2 of this invention; Figure 3 The thermogravimetric curves are those of the Si / Al=100 SPP hierarchical porous molecular sieve catalyst (A) of Comparative Example 2 and the Zn6Al4-SPP(100) hierarchical porous molecular sieve catalyst (B) of Example 3 after catalytic reaction for 24 hours. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. 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.

[0023] This invention provides a method for preparing a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, comprising the following steps: Si source, tetrabutylammonium hydroxide and water were mixed and hydrolyzed to obtain the first mixed solution; The Zn source and the Al source were mixed and dissolved in water to obtain a second mixed solution; The first and second mixed solutions are mixed and then crystallized. The crystallized product is then calcined to obtain the final product.

[0024] The preparation method provided by this invention enables the construction of self-supporting nanosheet structures and the in-situ introduction of Zn species. First, a Si source and tetrabutylammonium hydroxide (TBAOH) are mixed in water and hydrolyzed. In this step, TBAOH not only acts as an alkaline catalyst to promote the hydrolysis and oligomerization of the Si source, forming active silicate species, but its molecular structure also serves as a key structure-directing agent. The cationic groups of TBAOH, through electrostatic and spatial interactions with silicate species, guide the assembly of silicon-oxygen tetrahedra in a specific direction, laying the foundation for the subsequent formation of sheet-like nanostructure units. This step pre-forms a clear and homogeneous first mixed solution, ensuring sufficient activation of the silicon species and effective binding with the template agent molecules.

[0025] Subsequently, the Zn and Al sources are pre-mixed and dissolved in water to form a homogeneous second mixed solution. This step aims to achieve uniform mixing of zinc and aluminum ions at the molecular level, preventing localized precipitation or segregation upon subsequent direct contact with the highly alkaline silicate solution. This pre-homogenization design creates conditions for zinc and aluminum elements to participate in the lattice construction of the molecular sieve in a highly dispersed state.

[0026] When a silicate solution containing a structure-directing agent is mixed with a solution containing zinc and aluminum ions, TBAOH continues to guide the self-assembly of silicon-aluminum-zinc species under a hydrothermal environment of heating and high pressure. Due to its specific ionic radius and coordination characteristics, zinc ions can participate in the construction of the inorganic framework alongside silicon and aluminum species. This process is not a simple physical mixing or post-loading; rather, zinc species are embedded in the vicinity of the forming framework structure or specific lattice sites during the early stages of molecular sieve crystal growth. Finally, the organic template agent is removed by high-temperature calcination. This stabilizes the multi-level self-supporting three-dimensional structure with micropores and mesopores formed by the cross-linking of nanosheets. Furthermore, it immobilizes the introduced zinc species, forming active sites that interact closely with the framework, thereby enabling the regulation of properties such as acidity in the final product.

[0027] This invention differs from the complex dual-templating agents, seed crystals, or post-treatment pore-forming processes commonly used to obtain nanosheet structures, and also from conventional post-impregnation modification on pre-formed molecular sieves. Instead, it innovatively integrates the guided growth of self-supporting nanosheet structures and the in-situ introduction of zinc species into a single continuous and controllable chemical process through a one-step hydrothermal synthesis strategy. The resulting hierarchical porous molecular sieve with a self-supporting nanosheet structure, when used as a catalyst, exhibits high activity, high selectivity, and high stability in the carbon dioxide hydrogenation reaction to produce higher carbon hydrocarbons.

[0028] In an optional embodiment of the present invention, the molar ratio of Si to the total molar ratio of Zn and Al is controlled to be (90~110):1, more preferably (95~105):1. A ratio that is too high will result in too few acid sites and insufficient catalytic activity; a ratio that is too low will result in excessively dense acid sites, easily leading to the aggregation of strong acid sites, causing excessive cracking and carbon deposition in reactions such as CO2 hydrogenation, and may also affect the stability of the crystal structure.

[0029] In an optional embodiment of the present invention, the molar ratio of Zn to Al is (2~6):(4~8), for example, 2:8, 3:7, 4:6, 5:5, 6:4, etc., and more preferably (4~6):(4~6). Al provides the necessary Brønsted acid active sites, and an appropriate amount of Zn optimizes the acid environment, jointly promoting the dehydrogenation, coupling, and cyclization of intermediates in the CO2 hydrogenation process, while inhibiting cracking.

[0030] In an optional embodiment of the present invention, the molar ratio of the tetrabutylammonium hydroxide to the Si element in the Si source is (0.2~0.4):1, more preferably (0.25~0.35):1.

[0031] In optional embodiments of the present invention, the Si source is selected from at least one of organosilicon esters or silica sols, such as tetraethyl orthosilicate or propyl orthosilicate. The Al source is selected from at least one of aluminum alkoxides or soluble aluminum salts; aluminum alkoxides include aluminum isopropoxide and aluminum ethoxide; soluble aluminum salts include aluminum nitrate, aluminum sulfate, and aluminum chloride, or their hydrated salts. The Zn source is selected from soluble zinc salts, such as zinc nitrate, zinc acetate, zinc chloride, zinc sulfate, and zinc acetylacetonate, or their hydrated salts. In one or more embodiments of the present invention, the Si source is tetraethyl orthosilicate, the Al source is aluminum nitrate, and the Zn source is zinc nitrate.

[0032] In an optional embodiment of the present invention, the hydrolysis reaction temperature is 30-40°C, more preferably 33-37°C, and the hydrolysis reaction time is 2-8 hours, more preferably 2-5 hours. The mixing and dissolving temperature is 30-40°C, more preferably 33-37°C, and the mixing and dissolving time is 1-5 hours. Both the hydrolysis reaction and the mixing and dissolving process are carried out under continuous stirring to ensure uniform heat and material transfer, forming a homogeneous solution. The present invention does not impose any special limitations on the amount of water used in the hydrolysis reaction and the mixing and dissolving process; commonly used water amounts in the art can be used.

[0033] In an optional embodiment of the present invention, the crystallization treatment employs a hydrothermal method, where the hydrothermal environment provides the necessary temperature and pressure to drive the inorganic species to self-assemble and crystallize around the template agent. The crystallization treatment temperature is 120~140℃, more preferably 125~135℃, and the crystallization treatment time is 60~84h, more preferably 66~78h.

[0034] This invention further includes washing and drying the crystallization product after the crystallization treatment. Washing is preferably performed using deionized water to thoroughly remove residual alkaline ions and soluble salts remaining in the pores and on the surface. This invention does not impose special limitations on the drying method; it can be atmospheric pressure drying or vacuum drying, etc., to remove physically adsorbed water and prevent material structural damage due to rapid vaporization of moisture during subsequent high-temperature calcination.

[0035] In an optional embodiment of the present invention, the calcination temperature is 500-600℃, more preferably 520-560℃, and the calcination time is 4-10h, more preferably 5-8h; the calcination is carried out in an air atmosphere. The calcination process can remove the organic template agent (TBAOH), releasing the molecular sieve channels; and it can stabilize the inorganic framework and convert the introduced zinc species into a stable oxidized state or a specific coordination state.

[0036] This invention also provides a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, which is prepared by the above-described method. The nanosheet self-supporting structure endows it with an extremely high specific surface area and an interconnected mesoporous system, greatly improving mass transfer; the in-situ introduction of Zn modulates its acidity at the atomic level.

[0037] This invention also provides the application of the above-mentioned Zn-modified hierarchical porous molecular sieve with nanosheet self-supporting structure in the production of C5 and above high carbon hydrocarbons by carbon dioxide hydrogenation.

[0038] A specific application method is as follows: In the reaction of catalytic carbon dioxide hydrogenation to prepare C5 and above high carbon hydrocarbons, the Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure is used as a catalyst in a fixed-bed reactor at a reaction temperature of 280~320℃ and a reaction pressure of 2~4 MPa. The feed gas composed of H2 and CO2 at a volume ratio of (2~4):1 is fed at a rate of 3400~3800 mL·g. -1 ·h -1 The space velocity passes through the catalyst bed for reaction.

[0039] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0040] Example 1 This embodiment provides a method for preparing Zn-modified hierarchical porous molecular sieve Zn2Al8-SPP(100) with a nanosheet self-supporting structure. In this embodiment, n Zn / n Al =2:8,n Si / n (Al+Zn) =100.

[0041] (1) Weigh 19.166 g of tetraethyl orthosilicate (TEOS, 92.0 mmol), add 28.646 g of 25wt% tetrabutylammonium hydroxide (TBAOH, 27.6 mmol) aqueous solution dropwise with stirring, and stir in a water bath at 35℃ for 3 hours to obtain a clear first mixed solution.

[0042] (2) Weigh 0.2761 g aluminum nitrate nonahydrate (0.736 mmol) and 0.0547 g zinc nitrate hexahydrate (0.184 mmol), dissolve them together in 31.5 g deionized water, and stir in a water bath at 35°C for 3 hours to obtain a homogeneous second mixed solution.

[0043] (3) Add the solution obtained in step (2) to the solution obtained in step (1) and stir at 35°C for 0.5 hours to form a homogeneous mother liquor.

[0044] (4) Transfer the homogenized mother liquor from step (3) to a crystallization vessel with a polytetrafluoroethylene liner and perform hydrothermal crystallization at 130°C for 72 hours.

[0045] (5) After the crystallized product is cooled, centrifuged, washed with water until neutral, dried and ground, it is then calcined at 540°C for 6 hours in air at a heating rate of 2°C / min to obtain the in-situ synthesized Zn2Al8-SPP(100) molecular sieve.

[0046] Example 2 This embodiment provides a method for preparing Zn-modified hierarchical porous molecular sieve Zn4Al6-SPP(100) with a nanosheet self-supporting structure. In this embodiment, n Zn / n Al =4:6,n Si / n (Al+Zn) =100.

[0047] (1) Weigh 19.166 g of tetraethyl orthosilicate (TEOS, 92.0 mmol), add 28.646 g of 25wt% tetrabutylammonium hydroxide (TBAOH, 27.6 mmol) aqueous solution dropwise with stirring, and stir in a water bath at 35℃ for 3 hours to obtain a clear first mixed solution.

[0048] (2) Weigh 0.2071 g aluminum nitrate nonahydrate (0.552 mmol) and 0.1095 g zinc nitrate hexahydrate (0.368 mmol), dissolve them together in 31.5 g deionized water, and stir in a water bath at 35°C for 3 hours to obtain a homogeneous second mixed solution.

[0049] (3) Add the solution obtained in step (2) to the solution obtained in step (1) and stir at 35°C for 0.5 hours to form a homogeneous mother liquor.

[0050] (4) Transfer the homogenized mother liquor from step (3) to a crystallization vessel with a polytetrafluoroethylene liner and perform hydrothermal crystallization at 130°C for 72 hours.

[0051] (5) After the crystallized product is cooled, centrifuged, washed with water until neutral, dried and ground, it is then calcined at 540°C for 6 hours in air at a heating rate of 2°C / min to obtain the in-situ synthesized Zn4Al6-SPP(100) molecular sieve.

[0052] Example 3 This embodiment provides a method for preparing Zn-modified hierarchical porous molecular sieve Zn6Al4-SPP(100) with a nanosheet self-supporting structure. In this embodiment, n Zn / n Al =6:4, n Si / n (Al+Zn) =100.

[0053] (1) Weigh 19.166 g of tetraethyl orthosilicate (TEOS, 92.0 mmol), add 28.646 g of 25wt% tetrabutylammonium hydroxide (TBAOH, 27.6 mmol) aqueous solution dropwise with stirring, and stir in a water bath at 35℃ for 3 hours to obtain a clear first mixed solution.

[0054] (2) Weigh 0.1381 g aluminum nitrate nonahydrate (0.368 mmol) and 0.1642 g zinc nitrate hexahydrate (0.552 mmol), dissolve them together in 31.5 g deionized water, and stir in a water bath at 35°C for 3 hours to obtain a homogeneous second mixed solution.

[0055] (3) Add the solution obtained in step (2) to the solution obtained in step (1) and stir at 35°C for 0.5 hours to form a homogeneous mother liquor.

[0056] (4) Transfer the homogenized mother liquor from step (3) to a crystallization vessel with a polytetrafluoroethylene liner and perform hydrothermal crystallization at 130°C for 72 hours.

[0057] (5) After the crystallized product is cooled, centrifuged, washed with water until neutral, dried and ground, it is then calcined at 540°C for 6 hours in air at a heating rate of 2°C / min to obtain the in-situ synthesized Zn6Al4-SPP(100) molecular sieve.

[0058] Comparative Example 1 This comparative example provides a method for preparing Zn-modified hierarchical porous molecular sieve Zn8Al2-SPP(100) with a nanosheet self-supporting structure. In this comparative example, n Zn / n Al =8:2, n Si / n (Al+Zn) =100.

[0059] (1) Weigh 19.166 g of tetraethyl orthosilicate (TEOS, 92.0 mmol), add 28.646 g of 25wt% tetrabutylammonium hydroxide (TBAOH, 27.6 mmol) aqueous solution dropwise with stirring, and stir in a water bath at 35℃ for 3 hours to obtain a clear first mixed solution.

[0060] (2) Weigh 0.069 g aluminum nitrate nonahydrate (0.184 mmol) and 0.2189 g zinc nitrate hexahydrate (0.736 mmol), dissolve them together in 31.5 g deionized water, and stir in a water bath at 35°C for 3 hours to obtain a homogeneous second mixed solution.

[0061] (3) Add the solution obtained in step (2) to the solution obtained in step (1) and stir at 35°C for 0.5 hours to form a homogeneous mother liquor.

[0062] (4) Transfer the homogenized mother liquor from step (3) to a crystallization vessel with a polytetrafluoroethylene liner and perform hydrothermal crystallization at 130°C for 72 hours.

[0063] (5) After the crystallized product is cooled, centrifuged, washed with water until neutral, dried and ground, it is then calcined at 540°C for 6 hours in air at a heating rate of 2°C / min to obtain the in-situ synthesized Zn8Al2-SPP(100) molecular sieve.

[0064] Comparative Example 2 This comparative example provides a method for preparing a hierarchical porous molecular sieve with a nanosheet self-supporting structure, Si / Al=100 SPP. In this comparative example, n Si / n Al =100.

[0065] (1) Weigh 19.166 g of tetraethyl orthosilicate (TEOS, 92.0 mmol), add 28.646 g of 25wt% tetrabutylammonium hydroxide (TBAOH, 27.6 mmol) aqueous solution dropwise with stirring, and stir in a water bath at 35℃ for 3 hours to obtain a clear first mixed solution.

[0066] (2) Weigh 0.3451 g of aluminum nitrate nonahydrate (0.92 mmol) and dissolve it in 31.5 g of deionized water. Stir in a water bath at 35°C for 3 hours to obtain a homogeneous second mixed solution.

[0067] (3) Add the solution obtained in step (2) to the solution obtained in step (1) and stir at 35°C for 0.5 hours to form a homogeneous mother liquor.

[0068] (4) Transfer the homogenized mother liquor from step (3) to a crystallization vessel with a polytetrafluoroethylene liner and perform hydrothermal crystallization at 130°C for 72 hours.

[0069] (5) After the crystallized product is cooled, centrifuged, washed with water until neutral, dried and ground, it is then calcined at 540°C for 6 hours in air at a heating rate of 2°C / min to obtain a multi-level porous molecular sieve Si / Al=100 SPP with a nanosheet self-supporting structure.

[0070] Comparative Example 3 This comparative example uses the Si / Al=100 SPP molecular sieve prepared in Comparative Example 2 as a support, and loads 0.1wt% Zn using a conventional impregnation method. The steps include: (1) Weigh 1.0 g Si / Al=100 SPP carrier, add 1 mL of deionized water, and ultrasonically disperse for 30 minutes.

[0071] (2) Add 0.0046 g of zinc nitrate hexahydrate (approximately 0.001 g of Zn element) and continue ultrasonic dispersion for 30 minutes to allow the zinc salt to be initially adsorbed.

[0072] (3) Dry the above mixture at 80°C for 12 hours.

[0073] (4) The dried precursor was heated to 500°C for 3 hours in air at a heating rate of 2°C / min to obtain a catalyst with a zinc loading of about 0.1 wt%, which was denoted as 0.1% Zn / SPP(100).

[0074] Comparative Example 4 This comparative example uses the Si / Al=100 SPP molecular sieve prepared in Comparative Example 2 as a support, and loads a low content of zinc (0.1 wt%) using a conventional impregnation method. The steps include: (1) Weigh 1.0 g Si / Al=100 SPP carrier, add 1 mL of deionized water, and ultrasonically disperse for 30 minutes.

[0075] (2) Add 0.0455 g of zinc nitrate hexahydrate (approximately 0.01 g of Zn element) and continue ultrasonic dispersion for 30 minutes to allow the zinc salt to be initially adsorbed.

[0076] (3) Dry the above mixture at 80°C for 12 hours.

[0077] (4) The dried precursor was heated to 500°C for 3 hours in air at a heating rate of 2°C / min to obtain a catalyst with a zinc loading of about 1 wt%, denoted as 1% Zn / SPP(100).

[0078] Test case 1. Morphological characteristics Figure 1 The image shows a scanning electron microscope (SEM) image of the hierarchical porous molecular sieve Zn2Al8-SPP(100) prepared in Example 1. The SEM image shows a typical orthogonally connected nanosheet structure within each particle of the catalyst, confirming the formation of SPP. The sample has a uniform particle size distribution with an average size of 150-200 nm.

[0079] 2. Characterization by X-ray diffraction (XRD) patterns Figure 2 The XRD patterns of the hierarchical porous molecular sieves prepared in Examples 1-3 and Comparative Examples 1-2 are shown. SPP is composed of MFI and MEL topologies, wherein the nanosheets have an MFI topology and the intersections of the nanosheets have a MEL topology. As can be seen from the XRD patterns, SPP molecular sieves with different Al / Zn ratios all showed obvious characteristic diffraction peaks at 7.9°, 8.8°, 23.3°, and 23.9°, which are consistent with the SPP zeolite reported in the literature and correspond to the 101, 020, 501, and 301 crystal planes of SPP zeolite, respectively, further confirming the synthesis of Zn / Al-SPP.

[0080] 3. Hierarchical porous molecular sieves in the hydrogenation of carbon dioxide to produce C5 and higher carbon hydrocarbons (C6H5 and above). 5+ Applications in ) The hierarchical porous molecular sieves prepared in Examples 1-3 and Comparative Examples 1-4 were used as catalysts for the hydrogenation of carbon dioxide to produce C5 and higher carbon hydrocarbons (C5 and above). 5+ The reaction performance was evaluated in a fixed-bed reactor under uniform reaction conditions: a hydrogen to carbon dioxide volume ratio of 3:1 in the feed gas and a reaction space velocity (GHSV) of 3600 mL·g⁻¹. -1 ·h -1The reaction temperature was 300℃, and the reaction pressure was 3 MPa. The CO2 conversion rate (%) and C2 concentration were recorded after 24 hours of reaction. 5+ Selectivity (%), the results are shown in Table 1.

[0081] Table 1 Performance of hierarchical porous molecular sieve catalysts in the examples and comparative examples

[0082] Note: C in Table 1 5+ Selectivity refers to C 5+ The molar percentage of high-carbon hydrocarbons in all hydrocarbon products.

[0083] As can be seen from Table 1, the ZnAl-SPP(100) series catalysts (Examples 1-3) prepared by the in-situ synthesis method of this invention exhibit superior overall performance. A comparison between Examples 1-3 and Comparative Example 1 shows that their performance exhibits a clear Zn / Al ratio dependence; excess Zn leads to lower CO2 conversion and lower C content. 5+ Selectivity decreased across the board, especially for C. 5+ The selectivity is worse than that of the unmodified Si / Al=100 SPP catalyst.

[0084] During the reaction, a counter-current gas reaction occurred. The inventors discovered that introducing 1% Zn via impregnation (Comparative Example 4) exacerbated the counter-current gas reaction, thus affecting the yield of gasoline products. The CO selectivity of Zn2Al8-SPP(100) was 38%, while that of 1% Zn / SPP(100) was 47.6%. Therefore, the overall performance of Zn2Al8(100) synthesized in situ through the embodiments of the present invention is superior to that of 1% Zn / SPP(100) prepared by the traditional impregnation method.

[0085] The in-situ synthesis method of this invention, by precisely controlling the ratio of Zn to Al, successfully optimizes the intrinsic properties of the molecular sieve catalyst, enabling it to synergistically achieve higher catalytic activity and product selectivity in the CO2 hydrogenation to high-carbon hydrocarbon reaction. Its effect is superior to that of unmodified samples and traditional post-impregnation modified samples.

[0086] Thermogravimetric analysis was performed on the Zn6Al4-SPP(100) hierarchical porous molecular sieve catalyst of Example 3 and the Si / Al=100 SPP hierarchical porous molecular sieve catalyst of Comparative Example 2 after 24 h of reaction. The thermogravimetric curves are shown in the figure. Figure 3 As shown, the carbon deposition of the catalyst in Example 3 is 1.03 wt%, which is significantly lower than that of the molecular sieve in Comparative Example 2 (1.93 wt%) without Zn doping, indicating that Example 3 has better catalytic stability than Comparative Example 2.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, characterized in that, Includes the following steps: Si source, tetrabutylammonium hydroxide and water were mixed and hydrolyzed to obtain the first mixed solution; The Zn source and the Al source were mixed and dissolved in water to obtain a second mixed solution; The first and second mixed solutions are mixed and then crystallized. The crystallized product is then calcined to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The ratio of the molar amount of Si to the total molar amount of Zn and Al is controlled to be (90~110):

1.

3. The preparation method according to claim 2, characterized in that, The molar ratio of Zn to Al is (2~6): (4~8).

4. The preparation method according to claim 1, characterized in that, The molar ratio of the tetrabutylammonium hydroxide to the Si element in the Si source is (0.2~0.4):

1.

5. The preparation method according to claim 1, characterized in that, The Si source is selected from at least one of organosilicone esters or silica sols; the Al source is selected from at least one of aluminum alkoxides or soluble aluminum salts; and the Zn source is selected from soluble zinc salts.

6. The preparation method according to claim 1, characterized in that, The hydrolysis reaction is carried out at a temperature of 30-40°C for 2-8 hours; the mixing and dissolving reaction is carried out at a temperature of 30-40°C for 1-5 hours.

7. The preparation method according to claim 1, characterized in that, The crystallization process is performed using a hydrothermal method, with a crystallization temperature of 120~140℃ and a crystallization time of 60~84h.

8. The preparation method according to claim 1, characterized in that, The calcination treatment is carried out at a temperature of 500~600℃ for 4~10 hours in an air atmosphere.

9. A Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the Zn-modified hierarchical porous molecular sieve with a nanosheet self-supporting structure as described in claim 9 in the production of C5 and higher carbon hydrocarbons by carbon dioxide hydrogenation.

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