A method for preparing a hierarchical pore MFI molecular sieve

Abstract

The application belongs to the technical field of molecular sieve preparation, and particularly relates to a preparation method of a multi-level pore MFI structure molecular sieve material. The application uses tetrapropylammonium hydroxide micropore template agent and biomass as a mesopore template agent, only needs to use a trace amount of the low-cost mesopore template agent, the operation is simple and green, and the application is low in cost. The application only needs to add a trace amount of biomass to synthesize the MFI multi-level pore molecular sieve with good crystallinity, avoids subsequent complex acid treatment, alkali treatment or steam treatment operation, and is simpler in method. The multi-level pore molecular sieve obtained by the application has multi-level pores with micropore and mesopore channel structures, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation technology, specifically relating to a method for preparing multi-level porous MFI structured molecular sieve materials. Background Technology

[0002] Zeolite molecular sieves are a class of microporous aluminosilicate crystals with regular channel structures. Due to their large specific surface area, strong hydrothermal stability, and tunable acidity, they have long held a crucial position in catalysis, adsorption separation, and ion exchange. MFI-structured molecular sieves possess unique channel structures, including ten-membered ring straight channels with a pore size of 5.6 × 5.3 nm and sinusoidal channels with a pore size of 5.5 × 5.1 nm. However, precisely because of the unique microporous structure of MFI-structured molecular sieves, they cannot be used for the transport and diffusion of large molecules. Even with smaller molecules, the catalyst activity deteriorates or even deactivates due to diffusion resistance of reactants. Therefore, it is necessary to synthesize hierarchical porous molecular sieve catalysts with micropores, mesopores, and / or macropores to solve the above problems and improve catalyst utilization.

[0003] The preparation methods of hierarchical porous molecular sieves can be summarized into two strategies: "top-down" and "bottom-up." The "top-down" strategy constructs the hierarchical structure by post-processing the synthesized molecular sieve, with mainstream methods including desilication, dealumination, and recrystallization. However, this method is complex and may cause the molecular sieve framework to collapse. Therefore, the "bottom-up" strategy is preferred. The "bottom-up" strategy requires understanding the formation of the molecular sieve topology at the crystal growth level. Common methods can be categorized as soft-templating, hard-templating, and template-free self-assembly methods. However, hard-templating methods rely on the use of microporous and mesoporous templates, but mesoporous templates are typically expensive, significantly increasing the preparation cost of hierarchical porous molecular sieves.

[0004] In the prior art (as shown in References 1 and 2 below), the synthesis of molecular sieves is usually carried out by synthesizing silicate or aluminosilicate gels in an alkaline medium at a temperature of 60°C to 200°C for 1-20 days under high temperature and pressure. This is an energy-intensive and time-consuming process.

[0005] [1] Guodong Feng, PC, 1*Wenfu Yan, 1Mercedes Boronat, 2Xu Li, 1Ji-Hu Su, 3Jianyu Wang, 1Yi Li, 1Avelino Corma, 2Ruren Xu, 1Jihong (2016).Acceleratedcrystallization ofzeolites via hydroxyl free radicals.Science

[0006] [2] Zhang, B., Li, acidicsites via a nanocrystalline cellulose template.Green Chemistry,18(11),3315-3323.https: / / doi.org / 10.1039 / c5gc03077c

[0007] Therefore, it is essential to provide a new method for preparing hierarchical porous MFI molecular sieves, and to reduce costs, shorten the synthesis time, and lower the synthesis temperature. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing multi-level porous MFI structured molecular sieves under mild conditions.

[0009] The preparation method provided by this invention only requires the addition of trace amounts of hydroxyl radicals and inexpensive mesoporous template agents. It is simple to operate, green and environmentally friendly, and the prepared multi-level porous molecular sieve has microporous and mesoporous channel structures; the mesoporous template agent is biomass.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] In a first aspect of the present invention, a method for preparing a hierarchical porous MFI molecular sieve is provided, comprising the following steps:

[0012] 1) Mix the microporous template agent and deionized water in a certain proportion to obtain a mixed solution. Depending on the molecular sieve to be synthesized, selectively add one, two, or neither of the titanium source compound and aluminum source compound. Stir under sealed room temperature conditions.

[0013] 2) Add the silicon source compound to the mixed solution in step 1) while stirring, and continue stirring the solution for 2 to 24 hours;

[0014] 3) Add biomass mesoporous template agent to the mixed solution in step 2), and continue stirring for 1-5 hours under sealed room temperature conditions to obtain the initial sol mixture of the required proportion.

[0015] 4) A trace amount of hydroxyl radicals is introduced into the sol mixture of step 3) by thermal initiation with sodium persulfate, so that the concentration of sodium persulfate in the solution is 0.03 mol / L. The mixture is then transferred to a hydrothermal reactor for hydrothermal crystallization at a temperature of 60-150°C for 12-48 h.

[0016] 5) After crystallization, collect the product from the hydrothermal reactor in step 4), centrifuge, wash, and dry the product, and finally calcine it to obtain the molecular sieve catalyst. The calcination temperature is 450–600℃, the calcination time is 15–20 h, and the calcination is carried out in an air atmosphere. The template agent contained in the molecular sieve will be removed by calcination. Molecular sieve powder is obtained.

[0017] 6) Weigh the molecular sieve powder obtained in step 5) and uniformly disperse it in Cu(NO3)2 solution. The mass ratio of molecular sieve powder to Cu(NO3)2 is 1:46.9. Stir at room temperature for 2 hours. The powder is collected by filtration, washed three times with deionized water to complete one ion exchange, and repeated three times. The powder is dried at 120℃ overnight, calcined at 200℃ for 4 hours, and finally reduced at 300℃ in a hydrogen flow environment (~0.5MPa) for 4 hours to obtain the precursor powder.

[0018] 7) The precursor powder obtained in step 6) was dispersed in a Zn(NO3)2 solution at a mass ratio of 1:23.7. The mixture was stirred at room temperature for 2 hours, filtered and washed three times with deionized water to complete the ion exchange process. The residue was dried overnight at 120°C, calcined at 200°C for 4 hours, and then reduced again at 300°C for 4 hours in a positive pressure hydrogen flow environment (~0.5MPa) to obtain the Cu-ZnO molecular sieve catalyst.

[0019] Furthermore,

[0020] The Cu-ZnO molecular sieve catalyst is Cu / ZnO / Silicalite-1 molecular sieve, titanium-silicon Cu / ZnO / TS-1 molecular sieve, or silica-alumina Cu / ZnO / Na-ZSM-5 molecular sieve.

[0021] When the molecular sieve is Cu / ZnO / Silicalite-1 molecular sieve, neither titanium source nor aluminum source compound is added during synthesis.

[0022] When the molecular sieve is a titanium-silicon Cu / ZnO / TS-1 molecular sieve, a titanium source compound is added during synthesis;

[0023] When the molecular sieve is a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, an aluminum source compound is added during synthesis.

[0024] Furthermore, the titanium source compound is one or more of titanium tetrachloride, tetraethyl titanate, and tetrabutyl titanate.

[0025] Furthermore, the aluminum source compound is one or more of aluminum isopropoxide, aluminum oxide, aluminum hydroxide, and sodium aluminate.

[0026] Furthermore, the silicon source compound is one or more of silica sol, tetraethyl orthosilicate, and tetrabutyl orthosilicate.

[0027] Furthermore, the microporous template agent is a 25 wt% tetrapropylammonium hydroxide solution.

[0028] Furthermore, the biomass mesoporous template agent is one or more of cellulose, sugarcane bagasse, and carbonized starch.

[0029] Furthermore,

[0030] When the molecular sieve is a pure silicon Cu / ZnO / Silicalite-1 molecular sieve, the molar ratio of silicon source, microporous template agent, and water is 1:0.1-0.4:1-100; more preferably, the molar ratio is 1:0.2:19.

[0031] When the molecular sieve is a titanium-silicon Cu / ZnO / TS-1 molecular sieve, the molar ratio of the silicon source, titanium source, microporous template agent, and water is 1:0.001-0.5:0.1-0.4:1-100; more preferably, the molar ratio is 1:0.02-0.3:0.2:19.

[0032] When the molecular sieve is a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, the molar ratio of the silicon source, aluminum source, microporous template agent, and water is 1:0.001~2:0.1~0.4:1~100; more preferably, the molar ratio is 1:0.02~0.3:0.2:19.

[0033] In step 3), the amount of biomass mesoporous template agent added to the system is 3 wt% or 6 wt%.

[0034] In a second aspect of the invention, the application of a hierarchical porous molecular sieve prepared by the method described in the first aspect as a gas adsorbent is provided. In this invention, the gas adsorbed by the gas adsorbent is nitrogen.

[0035] In a third aspect of the invention, a method is provided for using a hierarchical porous molecular sieve prepared by the method described in the first aspect as a catalyst for the hydrogenation of carbon dioxide to methanol, specifically comprising the following steps: reducing the catalyst in situ at 350°C under pure H2 conditions for 4 h at a flow rate of 30 mL·min. -1 After cooling to the target reaction temperature, CO2 / H2 / N2 gases were introduced at a rate of 50 mL / min under a pressure of 3.0 MPa. -1 The catalyst was passed through at a flow rate of 6 h, and the molar ratio of the three gases was 23.5 / 71.5 / 5.0 to ensure the stability of the reaction.

[0036] The present invention has the following technical effects:

[0037] 1) This invention uses tetrapropylammonium hydroxide as a microporous template agent and biomass as a mesoporous template agent, eliminating the need for expensive mesoporous templates and offering advantages such as low cost, environmental friendliness, and simple operation.

[0038] 2) This invention can produce high-quality multi-level porous MFI structure molecular sieves. The molecular sieves produced, such as silicalite-1 molecular sieve, titanium-silicon TS-1 molecular sieve, and silicon-aluminum ZSM-5 molecular sieve, all have large specific surface area and mesopore volume, which is beneficial to solving the problems of diffusion restriction and easy deactivation in the reaction process, and improving their catalytic stability and product selectivity.

[0039] 3) The MFI structured molecular sieve prepared by this invention has high crystallinity, good structural stability, and wide range of applications, which is of great significance for practical industrial applications. Attached Figure Description

[0040] Figure 1 The XRD pattern is shown in Example 1 of this invention.

[0041] Figure 2 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / Silicalite-1 molecular sieve prepared in Example 1 of this invention.

[0042] Figure 3 The XRD pattern is shown in Example 2 of this invention, which is a multi-level porous Cu / ZnO / Silicalite-1 molecular sieve.

[0043] Figure 4 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / Silicalite-1 molecular sieve prepared in Example 2 of this invention.

[0044] Figure 5 The image shows the XRD pattern of the hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve prepared in Example 3 of this invention.

[0045] Figure 6 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve prepared in Example 3 of this invention.

[0046] Figure 7 The image shows the XRD pattern of the hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve prepared in Example 4 of this invention.

[0047] Figure 8 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve prepared in Example 4 of this invention.

[0048] Figure 9 The image shows the XRD pattern of the hierarchical porous Cu / ZnO / TS-1 molecular sieve prepared in Example 5 of this invention.

[0049] Figure 10 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / TS-1 molecular sieve prepared in Example 5 of this invention.

[0050] Figure 11 The image shows the XRD pattern of the hierarchical porous Cu / ZnO / TS-1 molecular sieve prepared in Example 6 of this invention.

[0051] Figure 12 The nitrogen adsorption-desorption curves are for the hierarchical porous Cu / ZnO / TS-1 molecular sieve prepared in Example 6 of this invention.

[0052] Figure 13 The figures show the methanol selectivity and temperature curves of the hierarchical porous molecular sieve samples prepared in Examples 1-6 of this invention during the methanol production reaction via carbon dioxide hydrogenation. Figures 1-6 correspond to the hierarchical porous molecular sieve samples prepared in Examples 1-6, respectively.

[0053] Figure 14 The figures show the carbon dioxide conversion rate and temperature curves of the hierarchical porous molecular sieve samples prepared in Examples 1-6 of this invention during the carbon dioxide hydrogenation to methanol reaction. Figures 1-6 correspond to the hierarchical porous molecular sieve samples prepared in Examples 1-6, respectively. Detailed Implementation

[0054] As analyzed in the background section of this application, existing methods for preparing hierarchical porous MFI molecular sieves suffer from high cost, high energy consumption, and long preparation time. To address these issues, this application provides a method for preparing hierarchical porous MFI molecular sieves.

[0055] 1) Mix the microporous template agent and deionized water in a certain proportion to obtain a mixed solution. Depending on the molecular sieve to be synthesized, selectively add one, two, or neither of the titanium source compound and aluminum source compound. Stir under sealed room temperature conditions.

[0056] 2) Add the silicon source compound to the mixed solution in step 1) while stirring, and continue stirring the solution for 2 to 24 hours;

[0057] 3) Add biomass mesoporous template agent to the mixed solution in step 2), and continue stirring for 1-5 hours under sealed room temperature conditions to obtain the initial sol mixture of the required proportion.

[0058] 4) A trace amount of hydroxyl radicals is introduced into the sol mixture of step 3) by thermal initiation with sodium persulfate, so that the concentration of sodium persulfate in the solution is 0.03 mol / L. The mixture is then transferred to a hydrothermal reactor for hydrothermal crystallization at a temperature of 60-150°C for 12-48 h.

[0059] 5) After crystallization, collect the product from the hydrothermal reactor in step 4), centrifuge, wash, and dry the product, and finally calcine it to obtain the molecular sieve catalyst. The calcination temperature is 450–600℃, the calcination time is 15–20 h, and the calcination is carried out in an air atmosphere. The template agent contained in the molecular sieve will be removed by calcination. Molecular sieve powder is obtained.

[0060] 6) Weigh the molecular sieve powder obtained in step 5) and uniformly disperse it in Cu(NO3)2 solution. The mass ratio of molecular sieve powder to Cu(NO3)2 is 1:46.9. Stir at room temperature for 2 hours. The powder is collected by filtration, washed three times with deionized water to complete one ion exchange, and repeated three times. The powder is dried at 120℃ overnight, calcined at 200℃ for 4 hours, and finally reduced at 300℃ in a hydrogen flow environment (~0.5MPa) for 4 hours to obtain the precursor powder.

[0061] 7) The precursor powder obtained in step 6) was dispersed in a Zn(NO3)2 solution at a mass ratio of 1:23.7. The mixture was stirred at room temperature for 2 hours, filtered and washed three times with deionized water to complete the ion exchange process. The residue was dried overnight at 120°C, calcined at 200°C for 4 hours, and then reduced again at 300°C for 4 hours in a positive pressure hydrogen flow environment (~0.5MPa) to obtain the Cu-ZnO molecular sieve catalyst.

[0062] The method of this invention uses tetrapropylammonium hydroxide as a microporous template agent and biomass as a mesoporous template agent, eliminating the need for expensive mesoporous templates and offering advantages such as low cost, environmental friendliness, and simple operation. Compared to existing technologies, it has the following improvements: First, it uses inexpensive biomass instead of expensive mesoporous template agents to prepare hierarchical porous molecular sieves. Second, it prepares hierarchical porous molecular sieves in the presence of hydroxyl radicals and biomass at a relatively low temperature (60-150℃) and in a relatively short time (12-48h).

[0063] In this invention,

[0064] The Cu-ZnO molecular sieve catalyst is Cu / ZnO / Silicalite-1 molecular sieve, titanium-silicon Cu / ZnO / TS-1 molecular sieve or silica-alumina Cu / ZnO / Na-ZSM-5 molecular sieve.

[0065] When the molecular sieve is Cu / ZnO / Silicalite-1 molecular sieve, no titanium or aluminum source compounds are added during synthesis.

[0066] When the molecular sieve is a titanium-silicon Cu / ZnO / TS-1 molecular sieve, a titanium source compound is added during synthesis;

[0067] When the molecular sieve is a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, an aluminum source compound is added during synthesis.

[0068] The titanium source compound is one or more of titanium tetrachloride, tetraethyl titanate, and tetrabutyl titanate.

[0069] The aluminum source compound is one or more of aluminum isopropoxide, aluminum oxide, aluminum hydroxide, and sodium aluminate.

[0070] The silicon source compound is one or more of silica sol, tetraethyl orthosilicate, and tetrabutyl orthosilicate.

[0071] The microporous template agent is a 25 wt% tetrapropylammonium hydroxide solution.

[0072] The biomass mesoporous template agent is one or more of cellulose, sugarcane bagasse, and carbonized starch.

[0073] When the molecular sieve is a pure silicon Cu / ZnO / Silicalite-1 molecular sieve, the molar ratio of silicon source, microporous template agent, and water is 1:0.1-0.4:1-100; more preferably, the molar ratio is 1:0.2:19.

[0074] When the molecular sieve is a titanium-silicon Cu / ZnO / TS-1 molecular sieve, the molar ratio of the silicon source, titanium source, microporous template agent, and water is 1:0.001-0.5:0.1-0.4:1-100; more preferably, the molar ratio is 1:0.02-0.3:0.2:19.

[0075] When the molecular sieve is a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, the molar ratio of the silicon source, aluminum source, microporous template agent, and water is 1:0.001~2:0.1~0.4:1~100; more preferably, the molar ratio is 1:0.02~0.3:0.2:19.

[0076] In step 3), the amount of biomass mesoporous template agent added to the system is 3 wt% or 6 wt%.

[0077] The synthesis process of this invention only requires the addition of trace amounts of inexpensive mesoporous template agents and hydroxyl radicals to synthesize hierarchical porous molecular sieves. This effectively reduces synthesis costs, is simple to operate, and is suitable for industrial-scale production.

[0078] Using the method provided by this invention, Ti and Al catalytic active sites can be effectively and uniformly anchored within the molecular sieve channels. The resulting hierarchical porous molecular sieves, including silicalite-1, titanium-silicon TS-1, and silica-alumina ZSM-5, possess large external specific surface areas and mesopore volumes. During the reaction process, they can effectively overcome diffusion limitations and suppress carbon deposition and secondary reactions, thereby improving their catalytic stability and product selectivity.

[0079] The preparation method provided by this invention involves mixing silicon, aluminum, metal, organic template agents, and biomass, followed by a crystallization reaction. During the crystallization reaction, the silicon and aluminum sources crystallize into nuclei under the induction of molecular sieve seeds and the action of the organic template agent. Biomass, as a linear macromolecule, can thicken, emulsify, and directionally regulate the mixing of raw materials during the crystallization reaction. Furthermore, it self-assembles to form micelles that interact with silicon / aluminum species. As the crystallization reaction proceeds, the biomass micelles gradually decompose and coke to form colloidal or nano-carbon particles, which mix with the molecular sieve structure and are ultimately removed by calcination, providing support for the production of mesoporous and macroporous molecular sieve products. Therefore, this preparation method successfully achieves the preparation of hierarchical porous molecular sieves and effectively improves their catalytic performance, which is of great significance for the design and preparation of molecular sieve catalysts with high catalytic activity. In addition, this preparation method is simple to operate, environmentally friendly, and widely applicable on an industrial scale.

[0080] This invention provides the application of the hierarchical porous molecular sieve prepared by the above method as a gas adsorbent. In this invention, the gas adsorbed by the gas adsorbent is nitrogen.

[0081] This invention also provides a method for using a hierarchical porous molecular sieve prepared by the above method as a catalyst for the hydrogenation of carbon dioxide to methanol, specifically comprising the following steps: reducing the catalyst in situ at 350°C under pure H2 conditions for 4 h at a flow rate of 30 mL·min. -1 After cooling to the target reaction temperature, CO2 / H2 / N2 gases were introduced at a rate of 50 mL / min under a pressure of 3.0 MPa. -1 The catalyst was passed through at a flow rate of 6 h, and the molar ratio of the three gases was 23.5 / 71.5 / 5.0 to ensure the stability of the reaction.

[0082] To make the objectives and technical solutions of this invention clearer, the following embodiments provide a more detailed and clear description of the multi-level porous molecular sieve, its preparation method, and applications. However, these descriptions should not be construed as limiting the scope of protection of this invention. All modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0083] Unless otherwise specified, all raw materials used in the embodiments of the present invention were purchased commercially. Specifically, the tetraethyl orthosilicate used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; the tetrapropylammonium hydroxide solution (TPAOH, 25wt%) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; and the sodium persulfate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0084] Example 1

[0085] Weigh 8.465g of water and 4.0235g of tetrapropylammonium hydroxide solution (concentration 25%), mix thoroughly, and stir at room temperature for 10 min to obtain a mixed solution; then add 5.156g of tetraethyl orthosilicate, stir for 5 hours, and introduce 3wt% cellulose mesoporous template agent into the mixed system to obtain a sol mixture; the molar ratio of silicon source material, tetrapropylammonium hydroxide, and water in the sol mixture in the reaction system is 1:0.2:19; introduce hydroxyl radicals into the mixed solution through thermal initiation with sodium persulfate, so that the concentration of sodium persulfate in the solution is 0.03mol / L, and then put the mixed solution into a hydrothermal reactor with a 100mL polytetrafluoroethylene liner, and then place the reactor in an oven for constant temperature hydrothermal crystallization at 90℃ for 24 hours. The resulting product was then centrifuged, repeatedly washed with deionized water until the solution was neutral, dried in an oven at 100°C, and calcined in air at 600°C to remove the template agent from the molecular sieve. 0.2 g of the obtained molecular sieve powder was weighed and uniformly dispersed in 50 mL of 0.1 mol / L Cu(NO3)2 solution, and stirred at room temperature for 2 h. The powder was harvested by centrifugation, washed three times with deionized water to complete one ion exchange, and repeated three times. The powder was dried overnight at 120°C, calcined at 200°C for 4 h, and finally reduced for 4 h at 300°C in a hydrogen-filled environment (~0.5 MPa) to obtain the precursor powder. The precursor powder was dispersed in 50 mL of 0.15 mol / L Zn(NO3)2 solution and stirred at room temperature for 2 h. It was then filtered and washed three times with deionized water to complete the ion exchange process. The obtained residue was dried overnight at 120°C, calcined at 200°C for 4 hours, and then reduced again at 300°C for 4 hours in a positive pressure hydrogen flow environment (~0.5MPa) to obtain a hierarchical porous Cu / ZnO / Silicalite-1 sample, numbered 1.

[0086] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / Silicalite-1 molecular sieve 1 is shown below. Figure 1 As shown, by Figure 1 It can be seen that the Cu / ZnO / Silicalite-1 molecular sieve obtained in this embodiment has high metal dispersion and good crystallinity.

[0087] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 2 It can be seen that the Cu / ZnO / Silicalite-1 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 527.4 m². 2 / g.

[0088] Example 2

[0089] The raw materials and steps used in Example 2 were basically the same as those in Example 1, except that the amount of biomass introduced into the mixed system was 6 wt%. A hierarchical porous Cu / ZnO / Silicalite-1 sample was obtained, numbered 2.

[0090] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / S-1 molecular sieve 1 is shown below. Figure 3 As shown, by Figure 3 It can be seen that the Cu / ZnO / Silicalite-1 molecular sieve obtained in this embodiment has high metal dispersion and good crystallinity.

[0091] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 4 It can be seen that the Cu / ZnO / Silicalite-1 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 413.9 m². 2 / g.

[0092] Example 3

[0093] The raw materials and steps used in Example 3 are basically the same as those in Example 1. The only difference is that after adding tetraethyl orthosilicate for 3 hours, 0.030 g of sodium aluminate needs to be added to the reaction system to obtain a hierarchical porous Cu / ZnO / Na-ZSM-5 sample, numbered 3.

[0094] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve 3 is shown below. Figure 5 As shown, by Figure 5 As can be seen, the Cu / ZnO / Na-ZSM-5 molecular sieve obtained in this embodiment is a pure phase with high metal dispersion and good crystallinity.

[0095] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 6 It can be seen that the Cu / ZnO / Na-ZSM-5 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 503.7 m². 2 / g.

[0096] Example 4

[0097] The raw materials and steps used in Example 4 were basically the same as those in Example 3, except that the amount of biomass introduced into the mixed system was 6 wt%. A hierarchical porous Cu / ZnO / Na-ZSM-5 sample was obtained, numbered 4.

[0098] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / Na-ZSM-5 molecular sieve 4 is shown below. Figure 7 As shown, by Figure 7It can be seen that the Cu / ZnO / Na-ZSM-5 molecular sieve obtained in this embodiment has high metal dispersion and good crystallinity.

[0099] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 8 It can be seen that the Cu / ZnO / Na-ZSM-5 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 469.3 m². 2 / g.

[0100] Example 5

[0101] The raw materials and steps used in Example 5 were basically the same as those in Example 1, except that after adding tetraethyl orthosilicate, 0.283 g of tetraethyl titanate was added to the reaction system. A hierarchical porous Cu / ZnO / TS-1 sample was obtained, numbered 5.

[0102] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / TS-1 molecular sieve 5 is shown below. Figure 9 As shown, by Figure 9 It can be seen that the Cu / ZnO / TS-1 molecular sieve obtained in this embodiment has high metal dispersion and good crystallinity.

[0103] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 10 It can be seen that the Cu / ZnO / TS-1 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 480.41 m². 2 / g.

[0104] Example 6

[0105] The raw materials and steps used in Example 6 are basically the same as those in Example 5, except that the amount of biomass introduced into the mixed system is 6 wt%, and a multi-level porous Cu / ZnO / TS-1 sample, numbered 6, is obtained.

[0106] The X-ray diffraction pattern of hierarchical porous Cu / ZnO / TS-1 molecular sieve 6 is shown below. Figure 11 As shown, by Figure 11 It can be seen that the Cu / ZnO / TS-1 molecular sieve obtained in this embodiment has high metal dispersion and good crystallinity.

[0107] Furthermore, the molecular sieve obtained in this embodiment underwent total pore surface area analysis, which... Figure 12 It can be seen that the Cu / ZnO / TS-1 molecular sieve obtained in this embodiment exhibits hysteresis loops, indicating the presence of mesoporous / macroporous structures. Its total specific surface area was measured to be 441.4 m². 2 / g.

[0108] Example 7

[0109] The catalytic performance of the hierarchical porous molecular sieve samples prepared in Examples 1-6 was tested, as follows:

[0110] The hierarchical porous molecular sieve samples prepared in Examples 1-6 were used in the carbon dioxide hydrogenation to methanol reaction:

[0111] 0.5 g of catalyst powder (diluted with 1.0 g of silica sand) was loaded in the center of a stainless steel reactor. Before the reaction, the catalyst was reduced in situ at 350 °C under pure H2 conditions for 4 h at a flow rate of 30 mL·min⁻¹. After cooling to the target reaction temperature, the catalyst was passed through a CO₂ / H₂ / N₂ (23.5 / 71.5 / 5.0 molar ratio, 50 mL·min⁻¹) at 3.0 MPa for 6 h to ensure reaction stability. The product was quantified by online gas chromatography.

[0112] Figure 13 The graphs show the methanol selectivity and temperature effect of the hierarchical porous molecular sieve samples prepared in Examples 1-6 in the carbon dioxide hydrogenation to methanol reaction. Figure 13 It can be seen that, regardless of whether it is at low temperature or high temperature, the methanol selectivity (up to 98%) of the Cu / ZnO / Na-ZSM-5 molecular sieve sample prepared in Example 4 is higher than that of other molecular sieve samples (up to 95%).

[0113] Figure 14 The graphs show the carbon dioxide conversion rate and temperature effect of the hierarchical porous molecular sieve samples prepared in Examples 1-6 in the carbon dioxide hydrogenation to methanol reaction. Figure 14 It can be seen that, regardless of whether it is at low temperature or high temperature, the carbon dioxide conversion rate of the Cu / ZnO / Na-ZSM-5 molecular sieve sample prepared in Example 4 (up to 11%) is higher than that of other molecular sieve samples (up to 8%).

[0114] As can be seen from the above embodiments, the preparation method provided by the present invention uses a low-cost mesoporous template agent, which is not only simple and low-cost, but also produces a multi-level porous molecular sieve with high catalytic activity, which can efficiently catalyze the hydrogenation of carbon dioxide to methanol.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical-pore MFI molecular sieve, characterized in that, The method comprises the following steps: 1) mixing microporous template agent and deionized water in a certain proportion to obtain a mixed solution, and selectively adding one, both or none of a titanium source compound and an aluminum source compound according to the molecular sieve to be synthesized, and stirring under airtight room temperature conditions; 2) adding a silicon source compound to the mixed solution of step 1) under stirring, and continuing to stir the solution for 2-24 hours; 3) adding a biomass mesoporous template to the mixed solution of step 2), and continuing to stir under airtight room temperature conditions for 1-5 hours to obtain an initial sol mixture with a desired proportion; 4) introducing trace hydroxyl radicals into the sol mixture of step 3) by thermal initiation of sodium persulfate, so that the concentration of sodium persulfate in the solution is 0.03 mol / L, and then transferring the mixture to a hydrothermal reaction kettle for hydrothermal crystallization, wherein the hydrothermal temperature is 60-150 DEG C, and the time is 12-48 hours; 5) after the crystallization is completed, collecting the product in the hydrothermal reaction kettle of step 4), and centrifuging, washing, drying and finally calcining the obtained product to obtain a molecular sieve catalyst, wherein the calcination temperature is 450-600 DEG C, the calcination time is 15-20 hours, and the calcination is carried out in an air atmosphere; the template contained in the molecular sieve is removed by calcination to obtain a molecular sieve powder; 6) weighing the molecular sieve powder obtained in step 5) and uniformly dispersing it in a Cu(NO3)2 solution, wherein the mass ratio of the molecular sieve powder to Cu(NO3)2 is 1:46.9, and stirring at room temperature for 2 hours; filtering and harvesting the powder, washing it with deionized water for 3 times to complete an ion exchange process, repeating the process for 3 times, drying the powder at 120 DEG C overnight, calcining it at 200 DEG C for 4 hours, and finally reducing it at 300 DEG C in a hydrogen flow environment for 4 hours to obtain a precursor powder; 7) dispersing the precursor powder obtained in step 6) in a Zn(NO3)2 solution, wherein the mass ratio of the precursor powder to Zn(NO3)2 is 1:23.7, and stirring at room temperature for 2 hours; filtering and washing the powder with deionized water for 3 times to complete the ion exchange process, drying the obtained residue at 120 DEG C overnight, calcining it at 200 DEG C for 4 hours, and then reducing it at 300 DEG C in a positive pressure hydrogen flow environment for 4 hours to obtain a Cu-ZnO molecular sieve catalyst.

2. The method according to claim 1, characterized in that: the Cu-ZnO molecular sieve catalyst is a Cu / ZnO / Silicalite-1 molecular sieve, a titanium-silicon Cu / ZnO / TS-1 molecular sieve or a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve; when the molecular sieve is a Cu / ZnO / Silicalite-1 molecular sieve, no titanium source compound or aluminum source compound is added during synthesis; when the molecular sieve is a titanium-silicon Cu / ZnO / TS-1 molecular sieve, a titanium source compound is added during synthesis; when the molecular sieve is a silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, an aluminum source compound is added during synthesis.

3. The method of claim 2, wherein, the titanium source compound is one or more of titanium tetrachloride, tetraethyl titanate and tetrabutyl titanate.

4. The method of claim 2, wherein, The aluminum source compound is one or more of aluminum isopropoxide, aluminum trioxide, aluminum hydroxide, and sodium metaaluminate.

5. The method of claim 1, wherein, The silicon source compound is one or more of silica sol, tetraethyl orthosilicate, and tetra-n-butyl orthosilicate.

6. The method of claim 5, wherein, The micropore template agent is tetrapropylammonium hydroxide solution with a concentration of 25wt%.

7. The method of claim 1, wherein, The biomass mesopore template agent is one or more of cellulose, bagasse, and carbonized starch.

8. The method of claim 6, wherein, when the molecular sieve is pure-silicon Cu / ZnO / Silicalite-1 molecular sieve, the molar ratio of the silicon source, the micropore template agent, and water is 1: 0.1-0.4: 1-100; when the molecular sieve is titanium-silicon Cu / ZnO / TS-1 molecular sieve, the molar ratio of the silicon source, the titanium source, the micropore template agent, and water is 1: 0.001-0.5: 0.1-0.4: 1-100; when the molecular sieve is silicon-aluminum Cu / ZnO / Na-ZSM-5 molecular sieve, the molar ratio of the silicon source, the aluminum source, the micropore template agent, and water is 1: 0.001-2: 0.1-0.4: 1-100; In the step 3), the biomass mesopore template agent is added in an amount of 3wt% or 6wt% in the system.

9. Use of the hierarchical-pore molecular sieve prepared by the method of any one of claims 1-8 as a gas adsorbent.

10. A process for the hydrogenation of carbon dioxide to methanol using the hierarchical porous molecular sieve prepared according to the process of any one of claims 1 to 8 as catalyst, characterized in that, Specifically comprising the following steps: reducing the catalyst in situ under pure H2condition at 350℃ for 4 h, the flow rate is 30 mL·min −1 After cooling to the target reaction temperature, flow CO2 / H2 / N2three gases through the catalyst at a flow rate of 50 mL·min −1 6 h under 3.0 MPa, the molar ratio of the three gases is 23.5 / 71.5 / 5.0 to ensure the stability of the reaction.

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