Synthesis method of two-dimensional nanosheet SSZ-39 molecular sieve

Abstract

The invention discloses a synthesis method of a two-dimensional nanosheet SSZ-39 molecular sieve, and belongs to the field of molecular sieve synthesis. The preparation method comprises the following steps: mixing and dissolving an alkali source and water, adding a template agent and a silicon source, continuously stirring until the template agent and the silicon source are completely dissolved, then adding an aluminum source, a seed crystal and a surfactant, and continuously stirring and aging at 25-80 DEG C to obtain alkaline gel; transferring the alkaline gel into a reaction kettle for sealed crystallization, cooling after crystallization is finished, separating mother liquor, centrifugally washing a solid product to be neutral, drying and roasting to obtain the SSZ-39 molecular sieve. The two-dimensional nanosheet SSZ-39 molecular sieve with a high silica-alumina ratio is obtained under the condition that the silica-alumina ratio of initial gel is high, the crystal thickness is within the range of 10-20 nanometers, and diffusion limitation can be effectively reduced. The key of the invention lies in the introduction of the surfactant, so that the synthesized two-dimensional nanosheet SSZ-39 molecular sieve has a relatively high specific surface area, and can be used in the fields of catalytic reduction, gas adsorption and the like.

Description

A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis, specifically relating to a method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve. Background Technology

[0002] SSZ-39 is an eight-membered ring microporous molecular sieve with an AEI topological configuration. In the AEI structure, the double six-membered ring (d6r) structural units are linked by four-membered rings (4mr) to form chains. The chains are connected in a plane, and the plane is rotated 180 degrees. o The layers were then stacked along the c-axis, ultimately forming a pear-shaped cage and eight-membered ring channels. The cage dimensions were 0.85 × 0.99 nm, and the channel dimensions were 0.38 × 0.38 nm. Due to the unique pore structure of SSZ-39 molecular sieve, it exhibits excellent methanol-to-olefins (MTO) performance and low nitrogen oxide (NOx) content. x Its selective catalytic reduction properties make it one of the most promising small-pore zeolites in recent years.

[0003] Compared with micron-sized SSZ-39 molecular sieves, nano-sized SSZ-39 molecular sieves have a higher specific surface area and a shorter mass transfer path, thus the catalytic and adsorption efficiency of two-dimensional nanosheet molecular sieves is higher.

[0004] The published literature (Reaction Kinetics, Mechanisms and Catalysis (2024) 137: 1885-1897) discloses a solvent-free seed-assisted method for preparing relatively dispersed SSZ-39 zeolite nanosheets with an aspect ratio of 10, but it requires pretreatment of raw materials and consumes a lot of energy, making it difficult to implement in industry.

[0005] A high aspect ratio nanosheet SSZ-39 was disclosed in the published literature (Chem. Mater. 2015, 277, 2695-2702), but its silicon-aluminum ratio is low and the sheets are tightly connected with low dispersion, which limits its catalytic and adsorption separation.

[0006] A published paper (Catal.Sci.Technol., 2021, 11, 5839-5848) discloses a method for preparing ultra-large sheet-like SSZ-39 molecular sieves, but the sheets are tightly connected and thick, which reduces the exposed area to some extent.

[0007] CN119143144A successfully prepared SSZ-39 molecular sieves with a crystal length of 300 nm and a thickness of 30 nm by using a crystal transfer method and evaporating the water in the gel to a water-silica ratio of 0.1. However, the excessively low water-silica ratio increased the complexity of its synthesis process. Summary of the Invention

[0008] The purpose of this invention is to provide a method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieves. The SSZ-39 molecular sieves synthesized by this method have both an AEI structure and a high aspect ratio nanosheet morphology. This controllable morphology feature provides an effective way to meet the differentiated requirements for catalyst morphology in chemical production.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve, comprising the following steps: 1) mixing an alkali source with water, stirring in a water bath at 25-80°C until the alkali source is completely dissolved, adding a template agent and a silicon source, continuing to stir until completely dissolved, then adding an aluminum source, seed crystals and a surfactant, continuing to stir and age at 25-80°C to obtain an alkaline gel; 2) transferring the alkaline gel to a reaction vessel with a polytetrafluoroethylene liner for sealed crystallization, cooling after crystallization, separating the mother liquor, centrifuging and washing the solid product until neutral, drying and calcining to obtain SSZ-39 molecular sieve.

[0010] Furthermore, the alkali source is one or a mixture of sodium hydroxide and potassium hydroxide.

[0011] Further, the template agent is one or a mixture of several of the following: 1,1,3,5-tetramethylpiperidine hydroxide, 1,1,2,6-tetramethylpiperidine hydroxide, tetraethylphosphine hydroxide, tetrapropylphosphine hydroxide, tetrabutylphosphine hydroxide, and tetraethylammonium hydroxide.

[0012] Furthermore, the silicon source is one or a mixture of several of the following: silica sol, water glass, tetraethyl orthosilicate, silica gel, solid silica gel, and sodium silicate.

[0013] Furthermore, the aluminum source is one or a mixture of several of sodium aluminate, aluminum hydroxide, metallic aluminum, boehmite, and aluminum nitrate.

[0014] Furthermore, the surfactant is one or a mixture of several of the following: Span 60, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, dodecyl phosphate, fatty acid glycerides, and polyethylene glycol octylphenyl ether.

[0015] Furthermore, the molar ratio of each component in the alkaline gel is: SiO2:Al2O3:MOH:ROH:H2O:seed crystal:surfactant = 1:0.005~0.02: 0.4~0.6: 0.08-0.2: 10-30:0.03-0.1: 0.03-0.05, where MOH represents the alkali source and ROH represents the template agent.

[0016] Furthermore, the aging time is 1~24 hours, and the crystallization temperature is 150~170℃, with a crystallization time of 24~120 hours. Crystallization can be static or dynamic.

[0017] Furthermore, the calcination temperature is 550~700℃, the calcination time is 4~8 hours, and the heating rate during calcination is 2~5℃ / min.

[0018] Compared with the existing SSZ-39 synthesis scheme, the beneficial effects of the present invention are as follows: 1. The raw materials used in the present invention do not require additional pretreatment steps, and readily available sodium aluminate is used as the aluminum source. Compared with the traditional synthesis system that uses USY molecular sieve as the sole aluminum source, the present invention uses a lower template agent, which greatly reduces the synthesis cost.

[0019] 2. Compared with conventional SSZ-39 molecular sieves, the two-dimensional nanosheet SSZ-39 molecular sieve synthesized in this invention has extremely high dispersibility, aspect ratio and smaller thickness.

[0020] 3. The key to this invention lies in the introduction of surfactants, which enable the synthesized two-dimensional nanosheet SSZ-39 molecular sieve to have a high specific surface area and a nanosheet structure, and can be used in fields such as catalytic reduction and gas adsorption. Attached Figure Description

[0021] Figure 1 is a scanning electron microscope image of the SSZ-39 molecular sieve obtained in Example 1.

[0022] Figure 2 shows the X-ray diffraction pattern of the SSZ-39 molecular sieve obtained in Example 1.

[0023] Figure 3 is a scanning electron microscope image of the SSZ-39 molecular sieve obtained in Example 2.

[0024] Figure 4 is a scanning electron microscope image of the SSZ-39 molecular sieve obtained in Example 3.

[0025] Figure 5 is a scanning electron microscope image of the SSZ-39 molecular sieve obtained in Example 4.

[0026] Figure 6 is a scanning electron microscope image of the SSZ-39 molecular sieve obtained in Comparative Example 1. Detailed Implementation

[0027] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention. All reagents used in the present invention are commercially available reagents.

[0028] The seed crystals used in Examples 1-4 were the SSZ-39 molecular sieve prepared in Comparative Example 1. Example 1

[0029] A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve includes the following steps: 3.744 g of sodium hydroxide is added to 15.4782 g of deionized water and stirred to dissolve. The mixture is stirred and homogenized at 25-35°C. Then, 14.8824 g of a 25% (w / w) solution of 1,1,3,5-tetramethylpiperidine hydroxide (DMDMPOH) is added. After stirring for ten minutes, 36 g of a 30% (w / w) silica sol is added dropwise until the silica sol is completely hydrolyzed and homogenized. Then, 0.3111 g of sodium aluminate and 0.54 g of seed crystals are added, followed by 2.1168 g of octadecyltrimethylammonium bromide. The mixture is stirred and aged for 2 hours to finally obtain an alkaline gel with a molar ratio of SiO2:Al2O3:NaOH:DMDMPOH:H2O:seed:OTAB = 1:0.009:0.52:0.13:16:0.05:0.03.

[0030] The alkaline gel was transferred to a reaction vessel lined with polytetrafluoroethylene (PTFE) and crystallized at 160°C for 72 hours. After crystallization, the product was subjected to solid-liquid separation. The solid product was washed with deionized water, centrifuged until neutral, and dried overnight in an oven at 100°C. The dried solid was then calcined in a muffle furnace at 600°C with a heating rate of 2°C / min to remove the template agent. After natural cooling, two-dimensional nanosheet SSZ-39 molecular sieve was obtained. XRD analysis determined that it belongs to SSZ-39 molecular sieve (Figure 2). Scanning electron microscopy (Figure 1) showed that the thickness distribution of the obtained crystallized sample was in the range of 10-20 nm, and the specific surface area of ​​the sample was 501 m². 2 / g. Example 2

[0031] A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve includes the following steps: 3.744 g of sodium hydroxide is added to 18.054 g of deionized water and stirred to dissolve. The mixture is stirred and homogenized at 25-35°C. Then, 11.448 g of a 25% (w / w) solution of 1,1,3,5-tetramethylpiperidine hydroxide (DMDMPOH) is added. After stirring for ten minutes, 36 g of a 30% (w / w) silica sol is added dropwise until the silica sol is completely hydrolyzed and homogenized. Then, 0.3111 g of sodium aluminate and 0.54 g of seed crystals are added, followed by 3.5285 g of octadecyltrimethylammonium bromide. The mixture is stirred and aged for 2 hours to finally obtain an alkaline gel. The molar ratio of the components is SiO2:Al2O3:NaOH:DMDMPOH:H2O:seed:OTAB = 1:0.009:0.52:0.1:16:0.05:0.05.

[0032] The above-mentioned alkaline gel was transferred to a reaction vessel lined with polytetrafluoroethylene and crystallized in a sealed container at 160°C for 72 hours. After crystallization, the product was subjected to solid-liquid separation. The solid product was washed with deionized water, centrifuged until neutral, and dried overnight in an oven at 100°C. The dried solid was then calcined in a muffle furnace at 600°C with a heating rate of 2°C / min to remove the template agent. After natural cooling, two-dimensional nanosheet SSZ-39 molecular sieve was obtained. Scanning electron microscopy (Figure 3) shows that the thickness of the obtained crystallized sample is mainly distributed in the range of 6-20 nm. Example 3

[0033] A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve includes the following steps: 3.744 g of sodium hydroxide is added to 5.094 g of deionized water and stirred to dissolve. The mixture is stirred and homogenized at 25-35°C. Then, 11.448 g of a 25% (w / w) solution of 1,1,3,5-tetramethylpiperidine hydroxide (DMDMPOH) is added. After stirring for ten minutes, 36 g of a 30% (w / w) silica sol is added dropwise until the silica sol is completely hydrolyzed and homogenized. Then, 0.3111 g of sodium aluminate and 0.54 g of seed crystals are added, followed by 2.1194 g of octadecyltrimethylammonium bromide. The mixture is stirred and aged for 2 hours to obtain the final gel component with a molar ratio of SiO2:Al2O3:NaOH:DMDMPOH:H2O:seed:OTAB = 1:0.009:0.52:0.1:12:0.05:0.03.

[0034] The above-mentioned alkaline gel was transferred to a reaction vessel lined with polytetrafluoroethylene and crystallized in a sealed container at 160°C for 72 hours. After crystallization, the product was subjected to solid-liquid separation. The solid product was washed with deionized water, centrifuged until neutral, and dried overnight in an oven at 100°C. The dried solid was then calcined in a muffle furnace at 600°C with a heating rate of 2°C / min to remove the template agent. After natural cooling, two-dimensional nanosheet SSZ-39 molecular sieve was obtained. Scanning electron microscopy (Figure 4) shows that the thickness of the obtained crystallized sample is mainly distributed in the range of 10-20 nm. Example 4

[0035] A method for synthesizing two-dimensional nanosheet SSZ-39 molecular sieve includes the following steps: 3.744 g of sodium hydroxide is added to 18.054 g of deionized water and stirred to dissolve. The mixture is stirred and homogenized at 25-35°C. Then, 11.448 g of a 25% (w / w) solution of 1,1,3,5-tetramethylpiperidine hydroxide (DMDMPOH) is added. After stirring for ten minutes, 36 g of a 30% (w / w) silica sol is added dropwise until the silica sol is completely hydrolyzed and homogenized. Then, 0.3111 g of sodium aluminate and 1.08 g of seed crystals are added, followed by 2.1194 g of octadecyltrimethylammonium bromide. The mixture is stirred and aged for 2 hours to finally obtain an alkaline gel with a molar ratio of SiO2:Al2O3:NaOH:DMDMPOH:H2O:seed:OTAB = 1:0.009:0.52:0.1:16:0.1:0.03.

[0036] The alkaline gel was transferred to a reaction vessel lined with polytetrafluoroethylene and crystallized in a sealed container at 160°C for 72 hours. After crystallization, the product was separated into solid and liquid phases. The solid product was washed with deionized water, centrifuged until neutral, and dried overnight in an oven at 100°C. The dried solid was then calcined in a muffle furnace at 600°C with a heating rate of 2°C / min to remove the template agent. After natural cooling, two-dimensional nanosheets SSZ-39 molecules were obtained. Scanning electron microscopy (Figure 5) showed that the thickness of the obtained crystallized sample was mainly distributed in the range of 6-50 nanometers.

[0037] Comparative Example 1: SSZ-39 molecular sieve was prepared using the crystallization method. The specific preparation steps are as follows: 1.6 g of sodium hydroxide was added to 10.812 g of a 25% (w / w) solution of 1,1,3,5-tetramethylpiperidine hydroxide (DMDMPOH) and stirred until dissolved. The mixture was stirred evenly at 25-35°C. Then, 0.7762 g of deionized water was added, and after stirring for ten minutes, 18.164 g of a 30% (w / w) silica sol was added dropwise until the silica sol was completely hydrolyzed and the mixture was evenly mixed. Finally, 0.7242 g of sodium hydroxide was added. USY molecular sieve with a silicon-to-aluminum ratio of 5.4 was continuously stirred and aged for 2 hours to obtain a gel with a molar ratio of SiO2:Al2O3:NaOH:DMDMPOH:H2O=1:0.017:0.4:0.17:12. The gel was transferred to a reaction vessel with a polytetrafluoroethylene liner and crystallized at 160℃ for 72 hours. After crystallization, the product was separated into solid and liquid phases. The solid product was washed with deionized water, centrifuged until neutral, and dried overnight in an oven at 100℃. The dried solid was calcined in a muffle furnace at 600℃ with a heating rate of 2℃ / min to remove the template agent. After natural cooling, SSZ-39-C was obtained. The scanning electron microscope image (Figure 6) shows that the obtained crystallized sample is a cubic crystal.

Claims

1. A method for preparing two-dimensional nanosheet SSZ-39 molecular sieve, characterized in that, Includes the following steps: 1) Mix the alkali source with water and stir in a water bath at 25-80℃ until the alkali source is completely dissolved. Then add the template agent and silicon source and continue stirring until completely dissolved. Then add the aluminum source, seed crystal and surfactant and continue stirring and aging at 25-80℃ to obtain an alkaline gel. 2) Transfer the alkaline gel to a reaction vessel with a polytetrafluoroethylene liner and seal it for crystallization. After crystallization, cool it, separate the mother liquor, centrifuge and wash the solid product until neutral, and dry and calcine to obtain SSZ-39 molecular sieve.

2. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The alkaline source is one or a mixture of sodium hydroxide and potassium hydroxide.

3. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The template agent is one or a mixture of several of the following: 1,1,3,5-tetramethylpiperidine hydroxide, 1,1,2,6-tetramethylpiperidine hydroxide, tetraethylphosphine hydroxide, tetrapropylphosphine hydroxide, tetrabutylphosphine hydroxide, and tetraethylammonium hydroxide.

4. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The silicon source is one or a mixture of several of the following: silica sol, water glass, tetraethyl orthosilicate, silica gel, solid silica gel, and sodium silicate.

5. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The aluminum source is one or a mixture of several of the following: sodium aluminate, aluminum hydroxide, metallic aluminum, boehmite, and aluminum nitrate.

6. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The surfactant is one or a mixture of several of the following: Span 60, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, dodecyl phosphate, fatty acid glycerides, and polyethylene glycol octylphenyl ether.

7. The method for preparing two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The molar ratio of each component in the alkaline gel is: SiO2:Al2O3:MOH:ROH:H2O:seed crystal:surfactant = 1:0.005~0.02:0.4~0.6:0.08-0.2:10-30:0.03-0.1:0.03-0.05, where MOH represents the alkali source and ROH represents the template agent.

8. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The aging time is 1 to 24 hours.

9. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The crystallization temperature is 150~170℃, the crystallization time is 24~120 hours, and the crystallization can be static or dynamic.

10. The method for preparing a two-dimensional nanosheet SSZ-39 molecular sieve according to claim 1, characterized in that, The calcination temperature is 550~700℃, the calcination time is 4~8 hours, and the heating rate during calcination is 2~5℃ / min.

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