Self-supporting MFI nanosheet molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molecular sieves, in particular to a self-supporting MFI nanosheet molecular sieve as well as a preparation method and application thereof.The preparation method of the self-supporting MFI nanosheet molecular sieve comprises the following steps: 1) mixing a silicon source, an aluminum source, an alkali source, a template agent and water to obtain a gel mixture; and 2) crystallizing the gel mixture prepared in the step 1) to obtain the self-supporting MFI nanosheet molecular sieve, wherein the template agent is an imidazolyl quaternary ammonium salt compound. The self-supporting MFI nanosheet molecular sieve prepared by the method does not need an expensive surfactant, phosphorus species cannot remain in pores after roasting, the silica-alumina ratio range is wide, and the operation is simple and easy to repeat.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieves, and in particular to a self-supporting MFI nanosheet molecular sieve and a preparation method and application thereof. Background Art

[0002] Since Argauer and Landelt et al. used tetrapropylammonium hydroxide to synthesize ZSM-5 molecular sieve (MFI topology) for the first time in 1972, MFI molecular sieve has been widely used in many fields such as petrochemicals, environmental catalysis, fine chemicals, adsorption separation, etc., and is one of the most important molecular sieves with the widest application range. With the growing demand for deep processing of heavy oil and fine chemical products, the requirements for mass transfer and diffusion efficiency of molecular sieve catalysts have increased accordingly. Nanosheet molecular sieves have attracted the attention of researchers due to their advantages such as shortened mass transfer path, improved diffusion capacity, and increased exposure of active sites.

[0003] In recent years, there have been more and more reports on MFI nanosheet molecular sieves. For example, in 2009, Ryoo et al. designed a quaternary ammonium salt surfactant template [C 22 H 45 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 Br2 2- ], in which the quaternary ammonium salt part guides the MFI molecular sieve structure and the surfactant part separates the MFI molecular sieve layer, and a single unit cell thickness MFI nanosheet molecular sieve is synthesized for the first time (Nature 2009, 461, 246.); Che Shunai et al. designed a new surfactant template [C6H5-C6H4-OC 10 H 20 -N + (CH3)2-C6H 13 ·Br -], using the π-π interaction between the hydrophobic benzene rings at the tail of the template to limit the growth of the MFI molecular sieve layer (Nat. Commun. 2014, 5, 4262.). However, due to the high synthesis cost of the surfactant template, the MFI nanosheet molecular sieve synthesized by this method is difficult to promote to industrial applications. In 2012, Tsapatsis et al. used the small molecule template tetrabutylphosphine hydroxide to synthesize a self-supporting five-membered ring chain molecular sieve with a house of cards morphology and a thickness of 2nm for the first time, referred to as SPP (Science 2012, 336, 1684.), but the phosphorus species remaining in the pores after calcination affected the catalytic reaction performance, and only high-silicon SPP could be synthesized. Rimer et al. synthesized self-supporting MFI nanosheet molecular sieves without templates (Adv. Mater. 2021, 33, 2100897.), but could only synthesize low-silicon molecular sieves, which limited its application to a certain extent. The synthesis of self-supporting MFI nanosheet molecular sieves needs to be further optimized. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a self-supporting MFI nanosheet molecular sieve and a preparation method and use thereof, so as to solve the problems in the prior art.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides a method for preparing a self-supporting MFI nanosheet molecular sieve, the preparation method comprising the following steps:

[0006] 1) mixing a silicon source, an aluminum source, an alkali source, a template and water to obtain a gel mixture, wherein the template is an imidazolyl quaternary ammonium salt;

[0007] 2) Crystallizing the gel mixture obtained in step 1) to obtain the self-supporting MFI nanosheet molecular sieve.

[0008] The present invention also provides a self-supporting MFI nanosheet molecular sieve, which is prepared by the preparation method.

[0009] The present invention also provides the use of the self-supporting MFI nanosheet molecular sieve as a catalyst.

[0010] As described above, the self-supporting MFI nanosheet molecular sieve and its preparation method and use of the present invention have the following beneficial effects:

[0011] 1) The present invention uses R1: 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide or R2: 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide or R3: 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide or R4: 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide as a template agent. Compared with surfactant template agents, tetrabutylphosphine hydroxide or template-free methods, the single template agent of the present application can synthesize all-silicon, silicon-aluminum controllable self-supporting MFI nanosheet molecular sieves in one step, without the need for expensive surfactants, no residual phosphorus species in the pores after calcination, a wide range of silicon-aluminum ratios, and simple and easy-to-repeat operations;

[0013] 2) The self-supporting MFI nanosheet molecular sieve prepared by the method of the present invention has a larger silicon-aluminum ratio, which is not less than 15. The adjustable aluminum content makes the amount of Bronsted acid in the self-supporting MFI nanosheet molecular sieve controllable. Therefore, the self-supporting MFI nanosheet molecular sieve obtained in this application has a broader application space;

[0014] 3) The self-supporting MFI nanosheet molecular sieve prepared by the method of the present invention has excellent activity in methanol to propylene (MTP), Beckmann rearrangement, and 1-hexene catalytic cracking reactions;

[0015] 4) The self-supporting MFI nanosheet molecular sieve prepared by the method of the present invention has a shorter b-axis and a shorter diffusion path, so that it has a longer life and propylene selectivity in the methanol to propylene reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Shown is the XRD spectrum of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention.

[0017] Figure 2 Shown is a SEM image of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention.

[0018] Figure 3 Shown is a TEM image of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention.

[0019] Figure 4 Shown is the N2 adsorption curve of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention.

[0020] Figure 5 Shown is the solid aluminum nuclear magnetic resonance spectrum of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention.

[0021] Figure 6 Shown is the MTP reaction activity diagram of the self-supporting MFI nanosheet molecular sieve obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0022] The present invention first provides a method for preparing a self-supporting MFI nanosheet molecular sieve, the preparation method comprising the following steps:

[0023] 1) mixing a silicon source, an aluminum source, an alkali source, a template and water to obtain a gel mixture, wherein the template is an imidazole quaternary ammonium salt compound;

[0024] 2) Crystallizing the gel mixture obtained in step 1) to obtain the self-supporting MFI nanosheet molecular sieve.

[0025] In certain embodiments of the present invention, in step 1), the imidazolyl quaternary ammonium salt compound is selected from:

[0026] 1,1-(Hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide,

[0027] or 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide,

[0028] or 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium) hydroxide,

[0029] or one or more of 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium) hydroxide.

[0030] In certain embodiments of the present invention, the 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide. The structural formula of the 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide is as follows:

[0031]

[0032] In certain embodiments of the present invention, the 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide is 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide. The structural formula of the 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide is as follows:

[0033]

[0034] In certain embodiments of the present invention, the 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide, and the structural formula of the 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide is as follows:

[0035]

[0036] In certain embodiments of the present invention, the 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide, and the structural formula of the 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide is as follows:

[0037]

[0038] In certain embodiments of the present invention, in step 1), the mass of the silicon source is converted into the mole number of SiO2 based on the mole number of silicon element; the mass of the aluminum source is converted into the mole number of Al2O3 based on the mole number of aluminum element, and the silicon source, aluminum source, alkali source, template and water are mixed in a molar ratio of 1: (0-0.033): (0.1-0.3): (0.15-0.25): (20-40).

[0039] In certain embodiments of the present invention, in step 1), the molar ratio of the silicon source, aluminum source, alkali source, template and water is selected from any of the following ranges: 1: (0-0.01): (0.1-0.3): (0.15-0.25): (20-40), 1: (0.01-0.02): (0.1-0.3): (0.15-0.25): (20-40), 1: (0.02-0.033): (0.1-0. 3): (0.15~0.25): (20~40), 1: (0~0.033): (0.1~0.15): (0.15~0.25): (20~40), 1: (0~0.033): (0.15~0.2): (0.15-0.25): (20~40), 1: (0~0.033): (0.2~0.25): (0.15~0.25): (20~40), 1: ( 0~0.033):(0.25~0.3):(0.15~0.25):(20~40),1:(0~0.033):(0.1~0.3):(0.15~0.2):(20~40),1:(0~0.033):(0.1~0.3):(0.2~0.25):(20~40),1:(0~0.033):(0.1~0.3):(0.15~0.25) :(20~30), 1:(0~0.033):(0.1~0.3):(0.15~0.25):(30~40), 1:0:(0.1~0.15):(0.15~0.25):(20~40), 1:0:(0.15~0.2):(0.2~0.25):(20~40), 1:0:(0.2~0.25):(0.15~0.25):(20~40).

[0040] In certain embodiments of the present invention, in step 1), the molar ratio of the silicon source, aluminum source, alkali source, template and water is selected from any of the following ranges: 1: 0.033: 0.1: 0.15: 20, 1: 0.017: 0.15: 0.20: 30, 1: 0.005: 0.10: 0.20: 26, 1: 0.005: 0.25: 0.25: 40, 1: 0.033: 0.10: 0.15: 20, 1: 0.10: 0.20: 0.25: 40, 1: 0: 0.10: 0.20: 26, 1: 0: 0.15: 0.20: 30, 1: 0: 0.25: 0.25: 40, 1: 0: 0.25: 0.25: 40.

[0041] For example, in certain embodiments of the present invention, the silicon source is 10 g of tetraethyl orthosilicate (TEOS). It is known that the chemical formula of TEOS is Si(OC2H5)4 and its molar mass is 208.33 g / mol. The molar number of TEOS is 0.048 mol. Since each TEOS and SiO2 molecule contains one silicon atom, each mole of TEOS can be converted to each mole of SiO2. Therefore, 10 g of TEOS is equivalent to 0.048 mol of SiO2.

[0042] For example, in certain embodiments of the present invention, the aluminum source is 10 g of aluminum sulfate 18hydrate [Al2(SO4)3·18H2O]. It is known that the molar mass of Al2(SO4)3·18H2O is 666.43 g / mol, and the molar number of Al2(SO4)3·18H2O is 0.015 mol. Since one Al2(SO4)3·18H2O and Al2O3 molecule both contain two aluminum atoms, each mole of Al2(SO4)3·18H2O can be converted into one mole of aluminum oxide. Therefore, 10 g of Al2(SO4)3·18H2O is equivalent to 0.015 mol of Al2O3.

[0043] In certain embodiments of the present invention, in step 1), the silicon source is selected from one or more of white carbon black, silica sol, tetramethyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS).

[0044] In a preferred embodiment of the present invention, in step 1), the silica sol is selected from 40 wt.% silica sol or 30.5 wt.% silica sol.

[0045] In the present invention, the 40wt.% silica sol or 30.5wt.% silica sol refers to a silica sol with a SiO2 solid content of 40% (weight percentage) or a SiO2 solid content of 30.5% (weight percentage).

[0046] In certain embodiments of the present invention, in step 1), the aluminum source is selected from one or more of sodium aluminate, pseudo-boehmite, aluminum nitrate, aluminum sulfate 18hydrate or aluminum isopropoxide.

[0047] In a preferred embodiment of the present invention, in step 1), the aluminum source is selected from aluminum sulfate 18hydrate.

[0048] In certain embodiments of the present invention, in step 1), the alkali source is selected from one or more of sodium hydroxide, potassium hydroxide or cesium hydroxide.

[0049] In certain embodiments of the present invention, in step 2), the crystallization is performed in a closed reactor, such as in a sealed reactor.

[0050] In certain embodiments of the present invention, in step 2), the crystallization temperature is 110-180° C. The crystallization temperature is selected from any of the following ranges: 110-120° C., 120-140° C., 140-160° C., 160-180° C.

[0051] In a preferred embodiment of the present invention, in step 2), the crystallization temperature is 120°C or 160°C.

[0052] In the present invention, the crystallization temperature should be neither too high nor too low. If it is too high (such as above 180° C.), the template will decompose and form a heterogeneous zeolite; if it is too low (such as 100° C.), amorphous powder will be produced and the molecular sieve cannot be formed.

[0053] In certain embodiments of the present invention, in step 2), the crystallization time is 24 to 168 hours. The crystallization time is selected from any of the following ranges: 24 to 50 hours, 50 to 80 hours, 80 to 110 hours, 110 to 140 hours, and 140 to 168 hours.

[0054] In a preferred embodiment of the present invention, in step 2), the crystallization time is 48 h, 96 h or 168 h.

[0055] In the present invention, the crystallization time should be neither too short nor too long. If it is too long (such as 180 h), a dense phase without a pore structure may be formed; if it is too short (such as 12 h), it will result in the coexistence of self-supporting MFI nanosheet molecular sieve and amorphous products.

[0056] In certain embodiments of the present invention, in step 2), the state of the crystallization is dynamic crystallization or static crystallization.

[0057] In a preferred embodiment of the present invention, in step 2), the dynamic crystallization is rotational dynamic crystallization.

[0058] In certain embodiments of the present invention, step 2) further comprises post-processing the obtained product after crystallization.

[0059] The post-treatment includes washing, drying and calcining, which are conventional technical means in the art.

[0060] The drying temperature is 80-120° C. The drying temperature is selected from any one of the following ranges: 80-90° C., 90-100° C., 100-110° C., 110-120° C.

[0061] The calcination temperature is 550-600° C. The calcination temperature is selected from any of the following ranges: 550-560° C., 560-570° C., 570-580° C., 580-590° C., 590-600° C.

[0062] The present invention also provides a self-supporting MFI nanosheet molecular sieve, which is prepared by the preparation method.

[0063] In certain embodiments of the present invention, the self-supporting MFI nanosheet molecular sieve is an all-silicon molecular sieve.

[0064] In certain embodiments of the present invention, the silicon-aluminum ratio of the self-supporting MFI nanosheet molecular sieve is ≥15.

[0065] In a preferred embodiment of the present invention, the silicon-aluminum ratio of the self-supporting MFI nanosheet molecular sieve is ≥30.

[0066] In a more preferred embodiment of the present invention, the silicon-aluminum ratio of the self-supporting MFI nanosheet molecular sieve is 30, 50 or 100.

[0067] The present invention also provides the use of the self-supporting MFI nanosheet molecular sieve as a catalyst.

[0068] In certain embodiments of the present invention, the catalyst is a catalyst used in one or more of the following chemical reactions: methanol to propylene, nitrobenzene hydrogenation, Beckmann rearrangement or 1-hexene catalytic cracking.

[0069] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0070] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0071] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0072] Example 1

[0073] In this embodiment 1, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0074] 1) 40wt.% silica sol, aluminum nitrate, sodium hydroxide and R1: 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed to obtain a gel mixture. The molar ratio of the silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Na2O:R1:H2O=1.0:0.033:0.1:0.15:20;

[0076] 2) Transfer to a reactor and crystallize at 110° C. for 168 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0077] Example 2

[0078] In this embodiment 2, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0079] 1) 40wt.% silica sol, aluminum isopropoxide, cesium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Cs2O:R1:H2O=1.0:0.017:0.15:0.20:30;

[0081] 2) Transfer to a reaction kettle and crystallize at 160° C. for 24 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 600° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0082] Example 3

[0083] In this embodiment 3, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0084] 1) 40wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R1:H2O=1.0:0.005:0.10:0.20:26;

[0087] 2) Transfer to a reactor and crystallize at 120° C. for 144 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0088] The prepared self-supporting MFI nanosheet molecular sieve was characterized by XRD, SEM, TEM, N2 adsorption and solid aluminum NMR. Figure 1 , 2 , 3, 4 and 5.

[0089] The XRD characterization results of the product show that the self-supporting MFI nanosheet molecular sieve obtained in this application has the characteristic diffraction peaks of MFI molecular sieves; SEM shows that the crystal size obtained in this application is below 200nm; TEM results show that the self-supporting MFI nanosheet molecular sieve is a nanocrystal with a "house of cards" morphology and the thickness of the nanosheet is below 30nm, and the nitrogen adsorption results show that its BET is 380.9m 2 / g, micropore volume is 0.11cm 3 / g. Solid aluminum NMR results show that the prepared self-supporting MFI nanosheet molecular sieve mainly contains 4-coordinated framework aluminum species. In summary, the characterization results prove that the method of the present application can prepare a self-supporting MFI nanosheet molecular sieve with high crystallinity.

[0090] Example 4

[0091] In this embodiment 4, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0092] 1) 40wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R1:H2O=1.0:0.005:0.10:0.25:40;

[0095] 2) Transfer to a reactor and crystallize at 140° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0096] Example 5

[0097] In this embodiment 5, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0098] 1) Tetraethyl silicate, pseudo-boehmite, sodium hydroxide and 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Na2O:R2:H2O=1.0:0.033:0.10:0.15:20;

[0101] 2) Transfer to a reactor and crystallize at 110° C. for 168 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0102] Example 6

[0103] In this Example 6, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0104] 1) Mix white carbon black, aluminum isopropoxide, cesium hydroxide and 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Cs2O:R2:H2O=1.0:0.017:0.15:0.20:30;

[0106] 2) Transfer to a reaction kettle and crystallize at 160° C. for 24 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 600° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0107] Example 7

[0108] In this Example 7, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0109] 1) 40wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R2:H2O=1.0:0.01:0.10:0.25:40;

[0112] 2) Transfer to a reactor and crystallize at 120° C. for 120 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0113] Example 8

[0114] In this Example 8, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0115] 1) 30.5wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R2:H2O=1.0:0.005:0.10:0.25:40;

[0118] 2) Transfer to a reactor and crystallize at 140° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0119] Example 9

[0120] In this Example 9, the preparation of a self-supporting MFI nanosheet molecular sieve comprises the following steps:

[0121] 1) 40wt.% silica sol, aluminum nitrate, sodium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Na2O:R3:H2O=1.0:0.033:0.1:0.15:20;

[0124] 2) Transfer to a reactor and crystallize at 110° C. for 168 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0125] Example 10

[0126] In this embodiment 10, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0127] 1) 40wt.% silica sol, aluminum isopropoxide, cesium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Cs2O:R3:H2O=1.0:0.017:0.15:0.20:30;

[0129] 2) Transfer to a reaction kettle and crystallize at 160° C. for 24 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 600° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0130] Embodiment 11

[0131] In this embodiment 11, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0132] 1) 40wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R3:H2O=1.0:0.01:0.10:0.25:40;

[0135] 2) Transfer to a reactor and crystallize at 120° C. for 120 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0136] Example 12

[0137] In this embodiment 5, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0138] 1) 30.5wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R3:H2O=1.0:0.005:0.10:0.25:40;

[0141] 2) Transfer to a reactor and crystallize at 140° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0142] Embodiment 13

[0143] In this Example 13, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0144] 1) 40wt.% silica sol, aluminum nitrate, sodium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Na2O:R4:H2O=1.0:0.033:0.10:0.15:20;

[0147] 2) Transfer to a reactor and crystallize at 110° C. for 168 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0148] Embodiment 14

[0149] In this Example 14, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0150] 1) Tetramethyl orthosilicate, aluminum isopropoxide, cesium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:Cs2O:R4:H2O=1.0:0.017:0.15:0.20:30;

[0153] 2) Transfer to a reaction kettle and crystallize at 160° C. for 24 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 600° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0154] Embodiment 15

[0155] In this Example 15, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0156] 1) 40wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R4:H2O=1.0:0.01:0.15:0.25:40;

[0159] 2) Transfer to a reactor and crystallize at 120° C. for 120 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0160] Example 16

[0161] In this Example 16, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0162] 1) 30.5wt.% silica sol, aluminum sulfate 18hydrate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, aluminum source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, aluminum source, alkali source, template and water is as follows: SiO2:Al2O3:K2O:R4:H2O=1.0:0.005:0.10:0.25:40;

[0165] 2) Transfer to a reactor and crystallize at 140° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0166] Embodiment 17

[0167] In this Example 17, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0168] 1) 40wt.% silica sol, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, alkali source, template and water is as follows: SiO2:K2O:R1:H2O=1.0:0.10:0.20:26;

[0169] 2) Transfer to a reactor and crystallize at 120° C. for 168 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0170] Embodiment 18

[0171] In this Example 18, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0172] 1) Tetramethyl orthosilicate, aluminum isopropoxide, cesium hydroxide and 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, alkali source, template and water is as follows: SiO2:Cs2O:R2:H2O=1.0:0.15:0.20:30;

[0174] 2) Transfer to a reaction kettle and crystallize at 160° C. for 24 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 600° C. to obtain a self-supporting MFI nanosheet molecular sieve.

[0175] Embodiment 19

[0176] In this Example 19, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0177] 1) 30.5wt.% silica sol, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, alkali source, template and water is as follows: SiO2:K2O:R3:H2O=1.0:0.15:0.25:40;

[0178] 2) Transfer to a reactor and crystallize at 140° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain an all-silicon self-supporting MFI nanosheet molecular sieve.

[0179] Embodiment 20

[0180] In this Example 20, the preparation of self-supporting MFI nanosheet molecular sieves includes the following steps:

[0181] 1) Tetraethyl silicate, potassium hydroxide and 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium)ammonium hydroxide are mixed as silicon source, alkali source and template respectively to obtain a gel mixture. The molar ratio of silicon source, alkali source, template and water is as follows: SiO2:K2O:R4:H2O=1.0:0.25:0.25:40;

[0182] 2) Transfer to a reaction kettle and crystallize at 120° C. for 96 h. After the crystallization is completed, cool, filter, wash, dry at 80° C., and calcine at 550° C. to obtain an all-silicon self-supporting MFI nanosheet molecular sieve.

[0183] Application Example 1

[0184] In this Application Example 1, the self-supporting MFI nanosheet molecular sieve obtained in Example 3 was used to test the catalytic performance of methanol to propylene (MTP) using a fixed bed catalytic reaction device line analyzer.

[0185] The test conditions are as follows: weigh 0.5g of 20-40 mesh catalyst and load it into the reaction tube. Pre-treat it in a N2 (30ml / min) atmosphere at 500℃ at normal pressure for 120min. After cooling to 480℃, pump methanol into the vaporization chamber through a high-pressure pump, mix it with nitrogen and pass it into the reaction tube. The space velocity of methanol is 2h -1 The products were analyzed by gas chromatograph equipped with FID detector and HP-PLOT-Q.

[0186] Methanol conversion and product selectivity in MTP reaction Figure 6 As shown, the self-supporting MFI nanosheet molecular sieve can maintain high methanol conversion and propylene selectivity for a long time.

[0187] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limiting the present invention. In addition, the various modifications listed herein and the variations of the methods in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for preparing a self-supporting MFI nanosheet molecular sieve, characterized in that: The preparation method comprises the following steps: 1) mixing a silicon source, an aluminum source, an alkali source, a template and water to obtain a gel mixture, wherein the template is an imidazole quaternary ammonium salt compound; 2) Crystallizing the gel mixture obtained in step 1) to obtain the self-supporting MFI nanosheet molecular sieve.

2. The preparation method according to claim 1, characterized in that: In step 1), any one or more of the following conditions are included: 11) The imidazolyl quaternary ammonium salt compound is selected from one or more of 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide, 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide, 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium) hydroxide or 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium) hydroxide; preferably, the 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-ethyl-1H-imidazol-3-ium ) ammonium hydroxide; preferably, the 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium) hydroxide is 1,1-(pentane-1,5-diyl)bis(3-ethyl-1H-imidazol-3-ium) ammonium hydroxide; preferably, the 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-propyl-1H-imidazol-3-ium) ammonium hydroxide; preferably, the 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium) hydroxide is 1,1-(hexane-1,6-diyl)bis(3-butyl-1H-imidazol-3-ium) ammonium hydroxide; 12) The silicon source is selected from one or more of white carbon black, silica sol, tetramethyl orthosilicate or tetraethyl orthosilicate; 13) The aluminum source is selected from one or more of sodium aluminate, pseudo-boehmite, aluminum nitrate, aluminum sulfate 18hydrate or aluminum isopropoxide; 14) The alkali source is selected from one or more of sodium hydroxide, potassium hydroxide and cesium hydroxide.

3. The preparation method according to claim 1, characterized in that: In step 1), the mass of the silicon source is converted into the mole number of SiO2 based on the mole number of silicon element; the mass of the aluminum source is converted into the mole number of Al2O3 based on the mole number of aluminum element, and the silicon source, aluminum source, alkali source, template and water are mixed in a molar ratio of 1:0-0.033:0.1-0.3:0.15-0.25:20-40.

4. The preparation method according to claim 1, characterized in that: In step 2), any one or more of the following conditions are included: 1) The crystallization is completed in a reactor; 2) The crystallization temperature is 110-180°C; 3) The crystallization time is 24 to 168 hours; 4) The state of the crystallization is dynamic crystallization or static crystallization.

5. The preparation method according to claim 1, characterized in that: Step 2) also includes post-processing the obtained product after crystallization.

6. The preparation method according to claim 5, characterized in that: The post-treatment includes washing, drying and calcining; preferably, the drying temperature is 80-120°C; preferably, the calcining temperature is 550-600°C.

7. A self-supporting MFI nanosheet molecular sieve, characterized in that: The self-supporting MFI nanosheet molecular sieve is prepared by the preparation method described in any one of claims 1 to 6.

8. The self-supporting MFI nanosheet molecular sieve according to claim 7, characterized in that: The molecular sieve includes any one or more of the following features: I. The self-supporting MFI nanosheet molecular sieve is an all-silicon molecular sieve; II. The silicon-to-aluminum ratio of the self-supporting MFI nanosheet molecular sieve is ≥15.

9. Use of the self-supporting MFI nanosheet molecular sieve according to any one of claims 7 to 8 as a catalyst.

10. The use according to claim 9, characterized in that The catalyst is a catalyst used in one or more of the following chemical reactions: methanol to propylene, nitrobenzene hydrogenation, Beckmann rearrangement or 1-hexene catalytic cracking.

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