Nano beta molecular sieve with high crystallinity and low unit cell composition as well as preparation method and application of nano beta molecular sieve

Abstract

The invention discloses a nano beta molecular sieve with high crystallinity and low unit cell composition as well as a preparation method and application thereof, and belongs to the technical field of molecular sieve material preparation. A single nanocrystal of the nano beta molecular sieve comprises, preferably, no more than 20 cells of the beta molecular sieve; the crystal belongs to a tetragonal crystal system; the space group of the crystal is P4122; the cell parameters comprise: # imgabs0 # # imgabs1 # alpha = 90 degrees; beta is equal to 90 degrees; gamma is equal to 90 degrees; # imgabs2 # RDLS is equal to 0.0022, and the RDLS is equal to According to the preparation method disclosed by the invention, the self-made silicon powder with a structural memory effect is adopted as a silicon source, and the nano beta molecular sieve with relatively high stability is obtained under an optimized hydrothermal synthesis condition. According to the technical scheme, the problem of structural stability of the nano beta molecular sieve is well solved, the obtained nano beta molecular sieve has the characteristics of uniform particle size, high crystallinity, high dispersion and the like, and due to stable nanocrystallization (20-50 nm) and reservation of the high crystallinity effect, the nano beta molecular sieve can be more efficiently used for solid acid catalytic reaction.

Description

Technical Field

[0001] The invention relates to a nanometer beta molecular sieve with high crystallinity and low unit cell composition and a preparation method and application thereof, belonging to the technical field of molecular sieve material preparation. Background Art

[0002] Molecular sieves are often used as key catalytic materials due to the effective effect of the skeleton atomic force field on aromatic molecules. Ideal acid centers and mass transfer channels are necessary prerequisites for their catalytic effect. The performance of molecular sieves is closely related to their structure. The pore type can determine the spatial restriction and electrostatic stabilization effect, and play different catalytic roles (Studies in Surface Science & Catalysis, 1991, 65 (9): 603-612). The β molecular sieve with *BEA topological structure is the only high-silicon zeolite material with a three-dimensional twelve-membered ring pore structure. The pore opening is suitable for aromatic molecules to diffuse in and maintain a suitable adsorption state concentration, with high conversion efficiency and high reaction selectivity. The mass transfer and diffusion of β molecular sieve usually relies on the straight channels (diameters are 0.66nm×0.67nm) that intersect vertically along the a-axis and b-axis directions; at the same time, because the energy of different connection modes between structural units is the same, the lattice is similar, and the stacking fault direction of tetragonal and monoclinic polymorphs, the irregular channel diameter of the crystal along the c-axis direction is small, and its tortuosity further reduces the diffusion coefficient. For aromatic molecules, such as: the kinetic diameter of benzene Its configuration diffusion coefficient in micropores is much lower than that of mesopore Knudsen diffusion and macropore molecular diffusion, which easily leads to secondary side reactions (Applied Catalysis A: General, 2020, 591: 117379). Based on the goal of optimizing the material diffusion path, a higher apparent reaction rate constant is achieved; among them, nano-sizing is an effective way to improve the diffusion performance of β molecular sieves. In theory, the Taylor modulus will decrease with the decrease in particle size (shortening the internal diffusion distance), thereby improving the accessibility and utilization of the active center, and further optimizing its comprehensive reaction performance of synergistic catalysis.

[0003] To The catalytic activity of the carbon ion reaction with acid as the active center increases with the increase of the silicon-aluminum ratio within a certain range; however, the thermodynamic process of sol-gel hydrothermal formation of ionic silicon clusters conforms to the LOWE equilibrium model, and the difficulty of effective activation of the silicon source increases with the increase of the silicon-aluminum ratio (J. Phys. Chem. C, 2011, 115 (20): 9879-9888). TEA +Tetraethylammonium (TEA) polymers play a comprehensive role in the synthesis of β molecular sieves, such as OSDA (organic structural directing agent) directional synthesis, significantly reducing the crystallization barrier (from 102.3 kJ / mol to 53.1 kJ / mol), and filling the pores to stabilize the structure and balance the charge (Journal of the American Chemical Society, 2015, 137(45): 14533-14544). However, the higher the mold-to-silicon ratio (TEA) + / SiO2) and the amount of organic templates limit the application and development of nano-β molecular sieves; at the same time, the synthesized nano-molecular sieves usually have the defects of low crystallinity and poor thermal stability. Even if crystal seeds or directing agents are added, the utilization rate of silicon source is low (the silicon-aluminum ratio of the product is low) under high alkalinity system, the adjustable range of silicon-aluminum ratio is narrow, and the crystal size controllability is poor (Microporous and Mesoporous Materials, 2022, 329: 111557.). In the crystallization process of molecular sieves, the silicon source has a great influence on both kinetics and thermodynamics, and its dissolution and activation is the rate-controlling step of crystallization; usually, liquid silica sol has poor activity and water glass easily induces the formation of impurity crystals. As a crystalline substance, the molecular sieve material is long-range ordered, and the three-dimensional size requires at least 5 to 10 unit cells. The unit cell parameters (CellParameters) of β molecular sieve are The three-dimensional size of a single crystal of β molecular sieve is directly related to the number of constituent unit cells. The polymorph reduces disordered stacking faults and has less than 20 unit cells, which is close to the growth limit of nano β crystals. It has high crystallinity and uniform high dispersion, and its synthesis is relatively difficult. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the existing technology has low crystallinity of nano β molecular sieves and uneven unit cell composition. Due to the special polymorphic stacking symbiosis, disordered growth and different stacking methods of β molecular sieves, their crystal dispersion and uniformity are poor, and the stacking faults and defect sites are uncontrollable. At the same time, there are technical problems such as defects in crystallinity and structural stability after nano-scaling.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is to provide a nano-β molecular sieve with high crystallinity and low unit cell composition. A single nanocrystal of the nano-β molecular sieve is composed of ≤20 unit cells of β molecular sieve; the crystal belongs to the tetragonal system; the space group of the crystal is P4122 (#91); the unit cell parameters include: α=90°; β=90°; γ=90°; RDLS = 0.0022; skeleton density The nano-β molecular sieve is shown on the official website of the International Zeolite Association IZA (https: / / asia.iza-structure.org / IZA-SC) as the β molecular sieve with BEA topology, and its cell parameters are The crystalline material has a long-range order, and the size of the molecular sieve grains (which can be calculated by electron microscopy, by the Debye-Scherrer formula based on the characteristic peaks of XRD, or by the external specific surface area S ext The estimated and mutually confirmed data can be used to infer the number of unit cell components of a single crystal of β molecular sieve.

[0006] Optionally, the solid state nuclear magnetic resonance silicon spectrum of the nano-β molecular sieve 29 Si MAS NMR detection has a chemical shift of δ>-108~-118 (attributed to the zeolite framework silicon Q 4 The characteristic peak area of ​​the coordination characteristic signal) accounts for more than 90% (the signal peak area of ​​the nuclear magnetic resonance is obtained from the spectrum, the proportion = the peak area of ​​the characteristic signal / the sum of the peak areas of the signals with Σδ>40*100%).

[0007] Optionally, the solid state nuclear magnetic resonance aluminum spectrum of the nano-β molecular sieve is 27 Al MAS NMR detection has two characteristic signals (representing two types of coordination forms) at chemical shift δ>40 (characteristic signal of tetracoordinated aluminum in zeolite framework), and the signal peak area of ​​the two characteristic signals located at chemical shift δ>40 accounts for ≥45%.

[0008] In addition, a single nanocrystal of low unit cell composition nano-β molecular sieve is composed of ≤20 β molecular sieve unit cells (by Parameter calculation size ≤52.4nm) composition, specific surface area S BET 700~950m 2 / g, of which the micropore specific surface area S micro 450~1000m 2 / g.

[0009] The silicon-aluminum ratio of the nano-β molecular sieve, the molar ratio of SiO2 / Al2O3 is 4 to ∞ (pure silicon), preferably 9 to 220.

[0010] The second technical problem to be solved by the present invention is to provide a method for preparing a nano-β molecular sieve with high crystallinity and low unit cell composition, which solves the first technical problem.

[0011] The preparation method of nanometer beta molecular sieve comprises: S1 obtaining solution I containing metal ion source, obtaining solution II containing template agent, S2 mixing aluminum source and silicon source with solution I and solution II to obtain gel solution; S3 hydrothermally crystallizing the gel solution to obtain product containing the beta molecular sieve.

[0012] Optionally, in the gel solution, in terms of molar ratio, template / SiO2=0.2-0.8, metal ion / SiO2=0.001-0.2, SiO2 / Al2O3=15-220; preferably, template / SiO2=0.25-0.55, metal ion / SiO2=0.01-0.15, SiO2 / Al2O3=25-120.

[0013] Optionally, the solvent in the solution I is selected from at least one of water, imidazolium-type ionic liquids, and [bimm]PF6 anionic ionic liquids; and the concentration of metal ions in the solution I is 0.1 wt% to 40 wt%.

[0014] Optionally, the solvent in the solution II is alcohol or water, preferably at least one of water, methanol, ethanol, glycerol, n-butanol or isopropanol; the concentration of the template in the solution II is 0.05wt% to 50wt%.

[0015] Optionally, the hydrothermal crystallization conditions include: temperature of 120-170° C., and crystallization time of 2-12 hours; preferably, a pre-crystallization step is also included, and the pre-crystallization conditions include: temperature of 50-120° C., and time of 0.5-12 hours.

[0016] Optionally, the method further comprises the steps of cooling, washing, drying and calcining after crystallization.

[0017] Optionally, the cooling conditions include: cooling to below 50°C, preferably cooling to 20-0°C; preferably cooling by natural cooling at room temperature or rapid cooling to below 50°C with room temperature water.

[0018] Optionally, the drying conditions include: drying at a temperature of 50-200° C. until there is no free water or solvent adsorbed on the surface.

[0019] Optionally, the calcination conditions include: a temperature of 200 to 1000° C., a treatment time of 10 minutes to 10 hours; and removal of the organic template and adsorbed solvent or water.

[0020] Optionally, after the drying step and before the calcination step, a molecular sieve precursor is obtained, and the molecular sieve precursor is subjected to magic angle solid nuclear magnetic resonance or two-dimensional multi-quantum magic angle spinning aluminum nuclear magnetic resonance ( 27 Al MAS NMR or 2D 27 Al MQ-MAS NMR) characterization showed that there was no obvious characteristic signal peak near the chemical shift δ=0 (attributed to six-coordinated non-framework aluminum).

[0021] Optionally, the organic template is selected from at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, lysine, arginine, ornithine, and histidine.

[0022] Optionally, the metal ion is selected from at least one of sodium ion, potassium ion, rubidium ion and cesium ion.

[0023] Optionally, the metal ion source is selected from alkali or alkali metal halogen salts.

[0024] Optionally, the base is selected from at least one of ammonia water, sodium hydroxide, potassium hydroxide, cesium hydroxide, and rubidium hydroxide;

[0025] Optionally, the alkali metal halogen salt is selected from potassium bromide, sodium bromide, cesium chloride, rubidium bromide, sodium chloride;

[0026] Optionally, the metal oxide is selected from at least one of rubidium oxide, cesium oxide, magnesium oxide, calcium oxide, strontium oxide, yttrium oxide, lanthanum oxide and cerium oxide;

[0027] Optionally, the aluminum source is selected from at least one of pretreated aluminum hydroxide monohydrate and sodium aluminate;

[0028] Optionally, the pretreatment of aluminum hydroxide monohydrate is performed by peptization pretreatment using at least one reagent selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, and formic acid, and the mixture is diluted with deionized water to a concentration of 5% to 35%, and the acid-aluminum molar ratio is adjusted to 0.005 to 0.5.

[0029] The silicon source is selected from silicon aluminum powder. The silicon aluminum powder provided by the present invention can be applied to the synthesis of crystalline materials, and has the characteristics of easy activation and crystallization, low dependence on organic templates, and shortened crystallization induction period. The silicon / aluminum atomic molar ratio (silicon aluminum ratio) is not less than 1 (such as 1 to ∞), preferably 2 to 500; the surface hydroxyl concentration of the silicon aluminum powder is not less than 20 μmol / g, preferably not less than 30 μmol / g.

[0030] In some embodiments of the present invention, the surface hydroxyl concentration of the silicon aluminum powder is 20 to 60 μmol / g, preferably 30 to 60 μmol / g.

[0031] In some embodiments of the present invention, the silicon aluminum powder is measured by solid nuclear magnetic resonance aluminum spectroscopy. 27 According to Al MAS NMR detection, the signal peak area of ​​hexacoordinated non-framework aluminum accounts for ≤50% of the total area of ​​all signal peaks, preferably ≤20%.

[0032] In the present invention, solid state NMR aluminum spectroscopy 27The “total area of ​​all signal peaks” in the Al MAS NMR detection results refers to the sum of the signal peak area of ​​hexacoordinated non-framework aluminum and the signal peak area of ​​tetracoordinated framework aluminum.

[0033] In some embodiments of the present invention, the silicon aluminum powder is measured by solid nuclear magnetic resonance aluminum spectroscopy. 27 There are two types of characteristic signals in the Al MAS NMR detection, which are signal peaks near δ=0 and near δ=40-80.

[0034] In the present invention, the signal peak near δ=0 represents the hexacoordinated non-framework aluminum of the silicon aluminum powder, and the signal peak near δ=40-80 represents the tetracoordinated framework aluminum of the silicon aluminum powder.

[0035] In the present invention, by solid state nuclear magnetic resonance aluminum spectrum 27 The results of Al MAS NMR detection indicate that in the silicon-aluminum powder obtained by the present invention, more than 50% of the aluminum atoms in the composition form a framework four-coordinate structure.

[0036] In some embodiments of the present invention, the silicon aluminum powder is measured by solid nuclear magnetic resonance silicon spectroscopy. 29 Si MAS NMR detection, the presence of Q 3 Coordination and Q 4 The characteristic signal of coordination, and Q 3 Coordination and Q 4 The ratio of the peak area of ​​the coordinated characteristic signal peak to the total area of ​​all signal peaks is ≥30%, preferably ≥60% (eg, 60-100%).

[0037] In the present invention, solid-state NMR silicon spectroscopy 29 The “total area of ​​all signal peaks” in Si MAS NMR test results refers to Q 1 The peak area of ​​the characteristic signal peak of coordination, Q 2 The peak area of ​​the characteristic signal peak of coordination, Q 3 The peak area and Q of the characteristic signal peak of coordination 4 The sum of the peak areas of the characteristic signal peaks of the coordination. 1 Coordination, Q 2 Coordination, Q 3 Coordination and Q 4 The difference in coordination lies in the number of -OH groups directly connected to Si. 1 Coordination refers to the direct connection between Si and 3 -OH groups, Q 2 Coordination refers to the direct connection between Si and two -OH groups, Q 3 Coordination refers to the direct connection between Si and one -OH group. 4 Coordination means that Si is not directly connected to -OH.

[0038] In the present invention, Q 3 The characteristic signal of coordination is around δ = -110 ~ -100, Q 4 The characteristic signal of coordination is around δ=-120~-110.

[0039] In the present invention, solid-state nuclear magnetic resonance silicon spectroscopy 29 The results of Si MAS NMR detection show that the corresponding proportion of Q 3 , Q 4 Coordination.

[0040] In some embodiments of the present invention, the silicon aluminum powder is detected by ultraviolet Raman spectroscopy at a vibration frequency of 240 cm -1 There is a characteristic peak nearby; at the vibration frequency 335cm -1 、400cm -1 or 480cm -1 There is at least one characteristic peak near the vibration frequency of 335cm -1 、400cm -1 or 480cm -1 There is at least one characteristic peak with a peak intensity greater than the vibration frequency 240cm -1 The peak intensity of the characteristic peaks near .

[0041] The present invention provides a silicon aluminum powder with a "structural memory effect". The silicon aluminum powder of the present invention is detected to have structural units such as four-membered rings, five-membered rings or six-membered rings by UV-Raman Raman spectroscopy structural characterization means, which is consistent with the TOT skeleton structural units in the synthesized molecular sieve and other silicon-containing crystalline materials. Therefore, the silicon aluminum powder of the present invention can be called a silicon aluminum powder with a structural memory effect.

[0042] According to the present invention, in the ultraviolet Raman spectrum of silicon aluminum powder, the vibration frequency is 240cm -1 The characteristic peaks near the 8-membered ring (8MR) represent the bending vibration signal of TOT in the silicon-containing 8-membered ring (TOT bending vibration). -1 In the characteristic region of the structural unit, the smaller rings correspond to higher vibration frequencies, not 240 cm -1 Among the characteristic peaks nearby, 335cm -1 、400cm -1 and 480cm -1 The characteristic peaks near the ring represent the bending vibration of TOT in the six-membered ring (6MR), five-membered ring (5MR) and four-membered ring (4MR) containing silicon, respectively. -1 、400cm -1 or 480cm-1 The presence of at least one characteristic peak nearby indicates the presence of at least one structural unit of 6MR, 5MR or 4MR. Vibration frequency 335cm -1 、400cm -1 or 480cm -1 The peak intensity of the characteristic peak near the vibration frequency is greater than 240cm -1 The peak intensity of the characteristic peak near φ indicates that the number of 6MR, 5MR or 4MR structural units in the silicon-aluminum powder is greater than the number of 8MR structural units.

[0043] As for the expression "near" in the above content, those skilled in the art will know that each characteristic peak (signal peak) usually has a displacement, so the position of the characteristic peak defined in the present invention may have deviations. -1 The nearby characteristic peak is at 450cm -1 ~500cm -1 However, the deviation represented by each characteristic peak (signal peak) can be determined by those skilled in the art.

[0044] In some embodiments of the present invention, the specific surface area of ​​the silicon aluminum powder is 500m 2 / g~1200m 2 / g.

[0045] In some embodiments of the present invention, the pore volume of the silicon aluminum powder is 0.05 cm 3 / g~5cm 3 / g.

[0046] The present invention also provides a method for preparing the above silicon aluminum powder, comprising the following steps:

[0047] S11, providing a mixed solution I containing a treatment reagent I and a solvent I; the treatment reagent I comprises a halogen-containing compound, preferably at least one selected from silicon tetrafluoride, silicon tetrachloride, ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, sodium fluoride, sodium chloride, sodium bromide, sodium iodide, hydrofluoric acid, hydrochloric acid and hydrobromic acid;

[0048] Providing a mixed solution II containing a treatment reagent II and a solvent II; the treatment reagent II includes an acidic reagent, preferably at least one selected from ammonium nitrate, nitric acid, ammonium fluoride, ammonium chloride, hydrochloric acid, ammonium bromide, perbromic acid, carbonic acid, acetic acid, phosphoric acid, oxalic acid, formic acid, acetic acid, citric acid, ammonium iodide, iodine-containing acid, hydrofluoric acid and hydrobromic acid;

[0049] S12, performing a first mixing process on the silicon-containing raw material and the mixed solution I to obtain a mixed solution III;

[0050] Performing a second mixing process on the aluminum-containing raw material and the mixed solution II to obtain a mixed solution IV;

[0051] S13, after mixing the mixed solution III with the mixed solution IV, sequentially subjecting the mixed solution to a standing treatment, a de-impurity treatment and a calcination treatment to obtain the silicon-aluminum powder.

[0052] In some embodiments of the present invention, a small amount of alkaline substance may be added to the mixed solution I to further promote the activation of the silicon-containing raw material.

[0053] In some embodiments of the present invention, in step S11, the solvent I and the solvent II are the same or different, and are independently selected from at least one of water, alcohols and ionic liquids; preferably selected from at least one of deionized water, methanol, ethanol, isopropanol, n-butanol, ethylene glycol, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0054] In some embodiments of the present invention, in step S12, the silicon-containing raw material is selected from at least one of silicates (such as tetramethyl silicate TMOS, tetraethyl silicate TEOS or tetrapropyl silicate TPOS), isobutylene triethoxysilane, tetramethylsilane (Si(CH3)4, silicon tetrachloride, methyltrimethoxysilane (MTMS), trichlorosilane (SiHCl3), hexamethyldisilazane and hexamethyldisiloxane.

[0055] In some embodiments of the present invention, the aluminum-containing raw material is selected from at least one of aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydrogen phosphate, aluminum sol, pseudo-boehmite, alumina powder prepared by alcohol aluminum process, boehmite, α-alumina, β-alumina, γ-alumina and θ-alumina.

[0056] In some embodiments of the present invention, the molar ratio of the treatment reagent I to SiO2 in the silicon-containing raw material (hereinafter referred to as the treatment reagent I / SiO2 molar ratio) is 0.0001 to 2:1, preferably 0.001 to 0.2:1.

[0057] In some embodiments of the present invention, the molar ratio of the solvent I to SiO2 in the silicon-containing raw material is 0.5 to 100:1 (hereinafter referred to as the solvent I / SiO2 molar ratio) is 0.5 to 100:1, preferably 1 to 10:1.

[0058] In some embodiments of the present invention, the mass ratio of the treatment reagent II to Al2O3 in the aluminum-containing raw material is 0.0001 to 2:1, preferably 0.001 to 0.25:1.

[0059] In some embodiments of the present invention, in the aluminum-containing mixed solution II, the mass fraction of Al2O3 is 0.1% to 60%, preferably 1% to 31%.

[0060] In some embodiments of the present invention, the conditions for the first mixing treatment include: a stirring speed of 0 to 5000 rpm, preferably 2 to 100 rpm; a temperature of 0 to 50° C., preferably 5 to 30° C. The mixing treatment time is 1 s to 10 h.

[0061] In some embodiments of the present invention, the conditions for the second mixing process include: a stirring speed of 0 to 5000 rpm, preferably 2 to 100 rpm; a temperature of 0 to 50° C., preferably 5 to 30° C. The mixing process is performed for 1 second to 10 hours.

[0062] In some embodiments of the present invention, in step S3, the conditions for the static treatment include: a temperature of -30 to 50°C; and / or a time of 10 to 2000 min. The static treatment is completed by sealed curing at -30 to 50°C for 10 to 2000 min.

[0063] In some embodiments of the present invention, the temperature of the impurity removal treatment is 20-100° C. The solvent and volatile substances are removed at 20-100° C. The impurity removal treatment method includes an oven, a muffle furnace / mesh belt kiln, an infrared lamp, irradiation, vacuum filtration, natural light exposure, etc.

[0064] In some embodiments of the present invention, the calcination treatment conditions include: a temperature of 200 to 1200° C.; and a time of 0.1 to 100 h.

[0065] In some embodiments of the present invention, the calcination conditions include: in the temperature range of 250 to 1100° C., at least two calcination temperatures are selected from low to high in an air atmosphere for 0.01 to 2 h, preferably 0.1 to 2 h.

[0066] In some embodiments of the present invention, the calcination conditions include: performing the calcination at 250-350°C, 350-500°C, and 500-1100°C for 0.01-2h, preferably 0.1-2h.

[0067] In the present invention, the calcination treatment is used to remove the skeleton crystal water (the desorption temperature is usually ≥ 200°C at normal pressure), sublimable fluoride, sulfur or MoO x It can also completely decompose organic matter by high-temperature oxidation.

[0068] In some embodiments of the present invention, in step S13, after the mixed liquid III is mixed with the mixed liquid IV, a sol-gel is obtained, and the sol-gel is then subjected to a standing treatment and a de-impurity treatment (removal of solvent and volatile substances) until a solid block is precipitated, and the solid is powdered to obtain an intermediate powder; the intermediate powder is calcined to obtain the silicon-aluminum powder.

[0069] The preparation method of silicon aluminum powder of the present invention selects silane-based silicon-rich substances and aluminum-containing substances as initial raw materials, and uses halogen-containing compounds and acidic reagents as treating agents respectively, so as to highlight the hydrolysis and mineralization of silicon species, form rich surface silanol species, and form aluminum-containing substances with H + The protons represented by are acted on alumina, and through a simple and controllable treatment method, the solvent is recovered and the gel is obtained, which is then purified by high-temperature calcination to obtain solid silicon-aluminum powder with structural memory effect.

[0070] The present invention also provides the use of the silicon-aluminum powder as described above or the silicon-aluminum powder prepared by the preparation method as described above in the preparation of crystalline materials.

[0071] In the present invention, the crystalline material refers to silicon-aluminum microporous zeolite molecular sieve, silicon-phosphorus-aluminum molecular sieve, borosilicate molecular sieve, titanium-silicon molecular sieve, pure silicon porous material and the like.

[0072] According to the present invention, after the silicon-aluminum powder is used to synthesize the crystalline material, the crystalline material (catalytic material) can be used in a highly efficient catalytic carbonium ion reaction.

[0073] In some embodiments of the present invention, the crystalline material is at least one of β molecular sieve, ZSM-4 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, ZSM-35 molecular sieve, MCM-22 molecular sieve, MCM-68 molecular sieve, EU-1 molecular sieve, mordenite molecular sieve, SSZ-33 molecular sieve, NU-87 molecular sieve, IM-5 molecular sieve, SSZ-39 molecular sieve, SSZ-35 molecular sieve, and TNU-9 molecular sieve.

[0074] In some embodiments of the present invention, the silicon aluminum powder selected when synthesizing ZSM-5 molecular sieve, mordenite, β molecular sieve, EU-1, SSZ-33 or MCM-22 (rich five-membered ring molecular sieve) is 400cm -1 preferably, at 400cm -1 The characteristic peaks nearby are the main characteristic peaks (with the largest peak area).

[0075] In some embodiments of the present invention, the silicon aluminum powder selected when synthesizing β molecular sieve, ZSM-4, ZSM-12, NU-87, etc. (molecular sieves marked by the formation of a four-membered ring structure during the induction period) is 480 cm -1preferably, at 480cm -1 The characteristic peaks nearby are the main characteristic peaks (with the highest peak intensity).

[0076] In the present invention, when preparing synthetic crystal materials (such as molecular sieves), the synthesis methods of crystalline materials of different configurations are different, and the silicon aluminum powder of the present invention can be applied. As for the amount of silicon aluminum powder, those skilled in the art can add an appropriate amount according to different requirements of the target product.

[0077] The silicon-aluminum powder provided by the present invention has a large concentration of surface active hydroxyl groups and high structure-directed activity, and can solve the problem of poor crystallization activity of conventional silicon-aluminum raw materials; and the silicon-aluminum powder helps to shorten the induction period when acting on synthetic crystalline materials;

[0078] The preparation method of silicon aluminum powder provided by the present invention selects silane-based silicon-rich substances and aluminum-containing substances as initial raw materials, respectively, and uses halogen-containing compounds and acidic reagents as treating agents, respectively, to highlight the hydrolysis and mineralization of silicon species, to form rich surface silanol species, and to form aluminum-containing substances with H + The protons represented by are acted on alumina, and a mixed gel is obtained through a controllable process, and an intermediate powder is formed after the solvent is recovered, and then the silicon aluminum powder is purified by high-temperature roasting; the preparation method of the present invention avoids the use of excessive solvents and the generation of waste water, and the process route can be used for industrial efficient production, which provides the possibility for its application in a wider field of efficient synthesis of crystal catalytic materials with silicon aluminum as the main skeleton composition;

[0079] The silicon-aluminum powder with a structural memory effect of the present invention can be used for the synthesis of crystal materials with silicon-aluminum as the main skeleton composition, especially for the efficient production of beta molecular sieve, ZSM-4 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, ZSM-35 molecular sieve, MCM-22 molecular sieve, MCM-68 molecular sieve, EU-1 molecular sieve, mordenite molecular sieve, SSZ-33 molecular sieve, NU-87 molecular sieve, IM-5 molecular sieve, SSZ-39 molecular sieve, SSZ-35 molecular sieve, TNU-9 molecular sieve and the like, and plays a role in shortening the crystallization induction period and the corresponding structure guidance, saving the time required for synthesis, and improving the efficiency of the seed induction method or the guiding agent solution synthesis method.

[0080] In the above technical scheme, the obtained nano-β molecular sieve with high crystallinity and low unit cell composition has the characteristics of uniform particle size, high crystallinity and high dispersion, and can be used for more efficient solid acid catalytic reaction. It is preferably and efficiently applied to aromatic production technologies such as toluene disproportionation and transalkylation, lightening of heavy aromatics, and catalytic cracking of light cycle oil LCO to aromatics.

[0081] The present invention obtains a highly efficient activated silicon source through simple and controllable pretreatment, explores nucleation and growth dynamics, constructs a charge density environment of cations and alkalinity, and obtains a nano-β molecular sieve with high diffusion performance under optimized hydrothermal synthesis conditions, achieving the goal of uniform high crystallinity and low unit cell composition of the product. This technical solution effectively solves the problem that the β molecular sieve in the prior art has poor crystal dispersion and uniformity, and stacking faults and defect sites are very common due to the special polymorph stacking symbiosis, disordered growth and different stacking methods. Nano-sizing simultaneously achieves the improvement and optimization of crystallinity and structural stability, and can be used for more efficient solid acid catalytic reactions.

[0082] The present invention uses self-made silicon powder with structural memory effect as silicon source to obtain nanometer β molecular sieve with high stability under optimized hydrothermal synthesis conditions. This technical solution solves the structural stability problem of nanometer β molecular sieve well, and the obtained nanometer β molecular sieve has the characteristics of uniform particle size, high crystallinity and high dispersion. Because of its stable nanometerization (20-50nm) and the retention of high crystallinity, it can be used for solid acid catalytic reaction more efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1a , Figure 1b is a HR-TEM image of sample DJ1 prepared in Example 1;

[0084] Figure 2 is the XRD pattern of sample DJ1 prepared in Example 1;

[0085] Figure 3 is the solid magic angle NMR of sample DJ1 prepared in Example 1 ( 29 Si MAS NMR) spectrum, Figure 3 Middle Q 3 —(SiO)3Si(OH);Q 4 (0Al)—(SiO)4Si;Q 4 (1Al)—(SiO)3Si(1Al);

[0086] Figure 4 are the crystallization kinetic curves of sample DJ1 prepared in Example 1 and sample DB1 prepared in Comparative Example 1;

[0087] Figure 5 The Fourier transform infrared spectra of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention and the sample DBJ01 prepared in Preparation Comparative Example 1 in the hydroxyl region are shown;

[0088] Figure 6 The UV-Raman spectra of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention and the sample DBJ01 prepared in Preparation Comparative Example 1 under 244 nm ultraviolet excitation light are shown;

[0089] Figure 7 The skeleton Fourier transform infrared spectrum of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention is shown;

[0090] Figure 8 The scanning electron microscope (SEM) image of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention is shown;

[0091] Fig. 9 The solid magic angle aluminum nuclear magnetic resonance spectrum (27AlMAS NMR) of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention is shown;

[0092] Fig.10 The solid magic angle silicon nuclear magnetic resonance spectrum (29SiMAS NMR) of the silicon aluminum powder SAJ01 prepared in Preparation Example 1 of the present invention is shown;

[0093] Fig.11 The solid magic angle aluminum nuclear magnetic resonance spectrum (27AlMAS NMR) of the sample DBJ01 prepared in Comparative Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0094] The technical solution adopted by the present invention comprises the following steps:

[0095] a. Use organic base or organic salt (OSDA) and inorganic base to adjust the system cation composition and control the charge density environment;

[0096] b. Adding aluminum source and self-made silicon powder with structural memory effect to the above solution in sequence to form a gel;

[0097] The c gel solution is subjected to low-temperature pre-crystallization, high-temperature hydrothermal crystallization, rapid cooling, filtration, cleaning and drying to obtain a solid product.

[0098] In the above technical scheme, the organic base or organic salt in step a) is selected from at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, lysine, arginine, ornithine, and histidine.

[0099] In the above technical solution, the inorganic base or compound in step a) is selected from at least one of ammonia water, sodium hydroxide, potassium hydroxide, and alkali metal halogen salts.

[0100] In the above technical solution, the aluminum source in step b) is selected from at least one of pretreated aluminum hydroxide monohydrate and sodium aluminate. The pretreatment of aluminum hydroxide monohydrate adopts peptization pretreatment using at least one reagent selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, and formic acid, and is diluted with deionized water to a concentration of 5% to 35%, and the acid-aluminum molar ratio is 0.005 to 0.5. The further preferred condition is 10% to 20% concentration, and the acid-aluminum molar ratio is adjusted to 0.01 to 0.1.

[0101] In the above technical solution, the silicon powder with structural memory effect prepared in step b) is detected by UV-Raman spectroscopy to have a vibration frequency of 335 cm -1 、400cm -1 or 480cm -1 There is at least one obvious characteristic signal peak nearby; at the same time, its specific surface area is greater than 500m 2 / g, SiO2 purity>95%.

[0102] In the above technical scheme, OSDA / SiO2=0.2~0.8, inorganic cation / SiO2=0.001~0.2, SiO2 / Al2O3=15~220, and further preferred conditions are OSDA / SiO2=0.25~0.55, inorganic cation / SiO2=0.01~0.15, SiO2 / Al2O3=25~120.

[0103] In the above technical solution, in step c), the low-temperature pre-crystallization temperature is 50-120° C. and the time is 0.5-12 hours. A further preferred condition is that the pre-crystallization temperature is 60-90° C. and the time is 2-6 hours.

[0104] In the above technical solution, in step c), the high temperature hydrothermal crystallization temperature is 120-170°C and the time is 2-12 days. A further preferred condition is that the hydrothermal crystallization temperature is 140-165°C and the time is 3-6 days.

[0105] In the present invention, the surface hydroxyl concentration of the silicon aluminum powder is measured by analyzing the hydroxyl region of the molecular sieve using a Nexus 670 Fourier transform infrared spectrometer (FT-IR) produced by Nicolet Company of the United States. For the test of the hydroxyl vibration region of the molecular sieve, 50 mg of the molecular sieve sample powder is pressed into a thin sheet with a diameter of 1 cm, placed in a vacuum cell, and vacuumed and dehydrated at 450° C. for 1.5 hours, and then tested after the temperature is lowered to room temperature.

[0106] The Fourier transform infrared spectrum of the skeleton vibration area was also analyzed and tested using the Nexus 670 Fourier transform infrared spectrometer (FT-IR) produced by Nicolet Company in the United States, with a test resolution of 4 cm -1, scanning times 32 times, test range 400~4000cm -1 ; Dilute the sample powder with KBr to a mass fraction of about 3%, grind and mix evenly with a mortar, press into tablets, and scan;

[0107] The crystal morphology was observed using a Nova Nano SEM 450 field emission scanning electron microscope produced by FEI Company with an operating voltage of 2.0 kV.

[0108] Solid-state magic angle NMR spectroscopy was performed using a Bruker Avance III / WB-400 spectrometer. 29 Si MAS NMR and 27 Al MAS NMR test, 27 Al MAS NMR test standard KAl(SO4)2.12H2O, rotation speed 12kHz, resonance frequency 79.50MHz, relaxation time 4s; 29 Si MAS NMR Test Standard Q8M8([(CH3)3SiO]8SiO 12 ), rotation speed 3kHz, resonance frequency 79.43MHz, relaxation time 60s.

[0109] The specific surface area and pore volume were analyzed by low-temperature N2 adsorption-desorption analysis of the samples using a Tristar3000 specific surface analyzer produced by Micrometrics. The samples were pretreated at 300°C for 6 hours by vacuum activation before testing. The test temperature was -196°C. The pore structure data such as specific surface area and pore volume of the test samples were obtained by analyzing the isotherms.

[0110] The molecular sieve samples were analyzed by Raman spectroscopy using a Jobin-Yvon T6400 triplet ultraviolet-Raman spectrometer (UV-Raman) developed by the Dalian Institute of Physical Chemistry with a resolution of 2 cm -1 , the excitation light source wavelength is 244nm.

[0111] The dry basis mass fraction of silicon aluminum powder was measured by thermogravimetric TG-DTA analysis of the sample using TGA Q500analyzer instrument (test conditions were air atmosphere, heating rate 10°C / min).

[0112] In the following examples, all chemical reagents used are commercially available products and, unless otherwise specified, have not been specially purified.

[0113] Preparation Example 1

[0114] Weigh 0.1g of sodium hydroxide and 0.4g of sodium fluoride, add them into 200ml of deionized water, stir and mix until dissolved evenly, then add 500g of methanol and place in a constant temperature water bath at 10°C; under stirring at 30rpm, take 520g of tetramethyl silicate (TMOS) and add it to the above solution, stir evenly; wherein the molar ratio of the treatment reagent I / SiO2 is 0.0026; the molar ratio of the solvent I / SiO2 is 7.3.

[0115] A certain amount of pseudo-boehmite was weighed according to the Si / Al atomic molar ratio of 35, and slurried with water to obtain a slurry with an Al2O3 mass content of 16%. Under stirring conditions of 25°C and 30rpm, hydrochloric acid was added at a hydrochloric acid / Al2O3 mass ratio of 0.05 and stirred evenly.

[0116] The aluminum liquid was quickly added to the silicon-containing material and mixed evenly, and then placed in a container in a constant temperature water bath at 10°C for 2 hours to obtain a sol-gel. The solvent methanol and water were evaporated in a vacuum at 55°C until a solid block was precipitated, and then the solid was taken out and powdered to obtain an intermediate powder. The temperature was then raised to 550°C at 3°C / min, and the intermediate powder was calcined at a constant temperature for 3 hours to obtain sample SAJ01.

[0117] The surface hydroxyl concentration of sample SAJ01 is 39 μmol / g silicon aluminum powder, and the specific surface area is S BET =620m 2 / g, pore volume = 0.55cm 3 / g.

[0118] Figure 5 In the FT-IR spectrum, 3580-3600, 3680-3700 and 3720-3730 cm -1 The characteristic vibration peaks nearby correspond to the bridge hydroxyl group, internal hydroxyl group and terminal hydroxyl group (external hydroxyl group), and the areas of the above characteristic peaks of the SAJ01 sample are larger, indicating that its hydroxyl group distribution is richer.

[0119] Figure 6 In the UV-Raman spectrum, the vibration frequency is less than 600cm -1 The structural unit characteristic area of ​​DBJ01 is only amorphous TOT at 240 cm -1 As the TOT bond angle decreases and the force constant increases, the active Al atoms activate and ionize the Si-O bonds, increase the skeleton flexibility and reduce the skeleton stress. The SAJ01 sample has a peak at 335cm -1 , especially 400cm -1 and 480cm -1 Signal peaks belonging to specific structural units appeared near the positions of 335cm -1 、400cm -1and 480cm -1 The characteristic peaks near the surface overlap partially. It can be seen that the vibration frequency is around 335cm -1 、400cm -1 and 480cm -1 The peak area of ​​the characteristic peak near 240 cm -1 The peak area of ​​the characteristic peak nearby.

[0120] Figure 7 In the FT-IR spectrum of sample SAJ01, the -1 The vibration peaks nearby correspond to silanols species.

[0121] Depend on Figure 8 From the scanning electron microscope photograph, it can be seen that the nanoparticles of sample SAJ01 are uniform in size and highly dispersed.

[0122] Depend on Fig. 9 It can be seen that sample SAJ01 shows tetracoordinated framework aluminum (δ>50), and there is no obvious characteristic peak attributable to hexacoordinated non-framework aluminum at δ=0, indicating that more than 50% of the aluminum atoms in sample SAJ01 form framework tetracoordinates.

[0123] Depend on Fig.10 It can be seen that the sample SAJ01 has Q corresponding to (SiO)4Si species and (SiO)3Si(1Al) near the chemical shifts -115 and -111, respectively. 4 The strong signal vibration peak of the structural species; the broadened NMR vibration peak signal of the sample at -104 is attributed to the (SiO)3Si(OH) species in the molecular sieve (Q 3 ), indicating that there are a certain amount of coordination defect (SiO)3Si(OH) species, and there are no obvious silicon species with other coordination numbers.

[0124] Preparation Comparative Example 1

[0125] Weigh white carbon black and pseudo-boehmite, and stir them mechanically to make them uniform; wherein the Si / Al atomic molar ratio is 35.

[0126] The obtained silicon and aluminum oxides form a powder mixture, and the comparative sample is marked as DBJ01.

[0127] In the FT-IR spectrum of Figure 1, 3580-3600, 3680-3700 and 3720-3730 cm -1 The characteristic vibration peaks nearby correspond to the bridge hydroxyl group, internal hydroxyl group and terminal hydroxyl group (external hydroxyl group), respectively. The above characteristic peak areas of DBJ01 sample are all small, indicating that its surface hydroxyl distribution is not as rich as that of SAJ01.

[0128] Depend on Fig.11 It can be seen that sample DBJ01 has an obvious characteristic peak attributable to hexacoordinated non-framework aluminum near δ=0, indicating that in this sample, the framework coordination of aluminum atoms mainly comes from the mechanical mixing composition of pseudo-boehmite, which is dominated by amorphous hexacoordinated non-framework aluminum.

[0129] Figure 6 In the UV-Raman spectrum, the vibration frequency is less than 600cm -1 The structural unit characteristic area of ​​DBJ01 is only amorphous TOT at 240 cm -1 characteristic peaks.

[0130] Using the sample of this comparative example as the synthetic raw material of the molecular sieve is not conducive to the formation of molecular sieve supercages or 10-membered ring and 12-membered ring microporous channels, and is likely to lead to the formation of dense phase small-pore zeolite impurities. At the same time, the crystallinity of the product will be significantly lower than the crystallinity of the product synthesized using SAJ01 as the raw material under the same synthetic conditions.

[0131] Example 1

[0132] Measure 1200 ml of deionized water, dissolve 55 g of sodium hydroxide (metal ion source) and 2500 g of 35 wt% tetraethylammonium hydroxide (template R) aqueous solution. Weigh 35 g of aluminum hydroxide monohydrate powder (aluminum source), and use 20% diluted hydrochloric acid, aluminum hydroxide and sodium hydroxide to dissolve. + After being mixed uniformly to form gel at a molar ratio of 0.10, the mixture was added to the above solution. 1400 g of the silicon powder SAJ01 prepared in Preparation Example 1 was weighed and uniformly added to the above solution to obtain a gel solution.

[0133] The gel solution was transferred into a tetrafluoroethylene-lined pressure bomb, pre-crystallized at 90°C for 4 hours, then hydrothermally synthesized at 165°C for 4 days, naturally cooled to below 40°C in air, filtered and washed, and dried at 120°C for 12 hours to obtain a solid product, which was labeled as DJ1.

[0134] like Figure 1a , Figure 1b High-resolution transmission electron microscopy (HR-TEM) shows that the high structural stability of sample DJ1 is reflected in the clear lattice fringes, and it is relatively stable under transmitted light radiation, forming a β-zeolite crystal array similar to a "townhouse" form, and has the characteristics of uniform and high dispersion.

[0135] like Figure 2 As shown, the XRD pattern shows that sample DJ1 is a pure phase β molecular sieve material. *BEA (β molecular sieve) unit cell parameters are Therefore, it is inferred that the β molecular sieve is composed of approximately eight unit cells; the crystalline material has long-range order, and the β molecular sieve meets the limit range that a single nanocrystal contains at least 5 to 10 unit cells.

[0136] like Figure 3 As shown, the solid-state NMR silicon spectrum of sample DJ1 29 Si MAS NMR detection has a chemical shift of δ>-108~-118 (attributed to the zeolite framework silicon Q 4 The characteristic peak area of ​​coordination characteristic signal) accounts for 93%; solid nuclear magnetic resonance aluminum spectrum 27 AlMAS NMR detection shows that there are two types of coordination forms when the chemical shift δ>40 (characteristic signal of tetracoordinated aluminum in the zeolite framework), and the signal peak at high chemical shift (δ>40) accounts for about 51%; before calcination, there is no obvious characteristic signal peak near δ=0 (attributed to hexacoordinated non-framework aluminum). In addition, a single nanocrystal is composed of about 12 β molecular sieve unit cells, with a specific surface area S BET =709m 2 / g, of which the micropore specific surface area S micro =455m 2 / g.

[0137] Comparative Example 1

[0138] The beta molecular sieve was hydrothermally synthesized according to the method and conditions of Example 1, except that gas phase silica sol (A200 product of Degussa) was used as the silicon source to replace the silicon powder TFS with structure memory effect in Example 1. Sample DB1 was obtained by hydrothermal synthesis under the same conditions. The solid NMR silicon spectrum of the sample 29 Si MAS NMR detection has a chemical shift of δ>-108~-118 (attributed to the zeolite framework silicon Q 4 The characteristic peak area of ​​coordination characteristic signal) accounts for 74%; solid nuclear magnetic resonance aluminum spectrum 27 AlMAS NMR detection shows that there are two types of coordination forms when the chemical shift δ>40 (characteristic signal of tetracoordinated aluminum in the zeolite framework), and the proportion of the signal peak at high chemical shift (δ>40) is ≥21%; before calcination, there is a characteristic signal peak near δ=0 (attributed to hexacoordinated non-framework aluminum). In addition, a single nanocrystal is composed of about 45 β molecular sieve unit cells, and the uniformity of the grain size is poor, with a specific surface area S BET =509m 2 / g, of which the micropore specific surface area S micro =335m 2 / g. DB1 cannot meet the requirements of high crystallinity and low unit cell composition of nano-β molecular sieve.

[0139] like Figure 4 is the crystallization kinetic curve of sample DJ1 prepared in Example 1 and sample DB1 prepared in Comparative Example 1. Figure 4It can be seen that different silicon sources have an important influence on the induction period of the crystallization of β molecular sieve: the induction period of white carbon black A200 as a silicon source is longer, which is consistent with the characteristics of β molecular sieve that it is not easy to nucleate and has a long crystallization period. After 120 hours, its crystallization growth curve slows down, and the final DB sample has a low relative crystallinity (less than 80%). The obvious difference is that when the self-made silicon powder TFS with structural memory effect is used as the silicon source, the induction period of DJ1 is significantly shortened, which not only breaks through the crystallization temperature phase region of the synthetic pure phase β molecular sieve (increased to 165°C), but also further shortens the crystallization induction period (around 10 hours), and reaches a relative crystallinity of >95% in 48 hours. Due to the Si-O bond length Smaller than Al-O bond length TEA + With AlO4 - There are differences in the interactions. The five-coordinate aluminum with weaker bond energy can be connected to each other through hydroxyl Al-O bonds, dehydroxylated and induce a topological transformation to four-coordinate. As the silicon-aluminum ratio increases, the unit cell shrinks, which shortens the induction period and crystallization period. A high silicon-aluminum ratio is more conducive to nucleation.

[0140] The crystallization kinetics of β molecular sieves conform to the cooperative crystallization mechanism and its crystal growth theory: (1) The role of the solvent (liquid phase) is limited to organic OSDA such as TEA + and activation of aluminum species; (2) due to the alkalinity sensitivity of silicate, the mineralization and dissolution of silicon species under the action of alkali heat is the rate-controlling step of crystallization. Organic cations further enhance the activation and nucleation ability of silicon species and co-condense with the balanced incorporated liquid phase activated species to form TEA + -aluminosilicate composite micro-nano species (sol-gel); (3) the above-mentioned micro-nano species undergo solid-phase condensation and structural rearrangement, gradually forming a ring-shaped secondary structural unit and a microporous skeleton, through the inorganic Na + NH4 + The size effect of hydrated ions plays a role in inducing skeleton bending, stabilizing pores, balancing charges, and increasing the force constant of the structure. The synergistic effect of coupled cations promotes a suitable charge density environment and controls the anisotropy of crystal growth; (4) At the same time, TEA + Migration and aggregation form molecular clusters, and further accelerate the interfacial polycondensation process of inorganic species. Under the structural guidance of hydrated cations, the structural units form polyhedrons and have a certain network connectivity (four-membered rings, five-membered rings and six-membered rings are connected to form the twelve-membered ring channels of β molecular sieves. The five-membered rings are connected in pairs through oxygen bridges, and the rearrangement and promotion of the formation of four-membered rings are the key to the crystallization of β zeolite); (5) The crystallinity gradually increases with the synergistic promotion of the two close processes, and the regular microporous structure and nanocrystals of H-β molecular sieves are grown.

[0141] Embodiments 2 to 13

[0142] Examples 2 to 13 are nano-β molecular sieves prepared according to the method of Example 1 (the molar amounts of R, M and Al2O3 in the aluminum source are consistent with those in Example 1). The samples are marked as DJ2 to DJ13. The difference lies in the organic matter (OSDA), inorganic base, aluminum source and its pretreatment acid-aluminum ratio. The specific conditions are shown in Table 1.

[0143] Table 1

[0144]

[0145] Examples 14 to 22

[0146] Examples 14 to 22 are nano-β molecular sieves prepared according to the method of Example 5 (the molar amount of R, M and Al2O3 in the aluminum source is consistent with that of Example 5). The corresponding samples are marked as DJ14 to DJ22. The difference lies in the composition of the initial gel mixture, OSDA / SiO2, inorganic I / SiO2 and SiO2 / Al2O3, and thus the product skeleton silicon Q 4 The coordination ratio (corresponding to the relative crystallinity of β molecular sieve) and the crystal unit cell composition parameters are different, see Table 2 for details.

[0147] Table 2

[0148] Example Sample No. <![CDATA[OSDA / SiO2]]> <![CDATA[I / SiO2]]> <![CDATA[SiO2 / Al2O3]]> <![CDATA[Q 4 Silicon Proportion]]> Number of unit cells 14 DJ14 0.45 0.02 85 95.5％ 10 15 DJ15 0.26 0.12 35 93％ 15 16 DJ16 0.55 0.10 106 95％ 9 17 DJ17 0.05 0.15 25 96％ 20 18 DJ18 0.52 0.05 112 97％ 11 19 DJ19 0.30 0.13 60 92％ 16 20 DJ20 0.35 0.15 85 96％ 14 21 DJ21 0.40 0.08 90 94％ 12 22 DJ22 0.65 0.01 120 95％ 7.5

[0149] Embodiment 23

[0150] Example 23: The gel was formed according to the method of Example 5. The above gel was transferred into a pressure bomb lined with tetrafluoroethylene. First, pre-crystallization was carried out at 110°C for 2 hours, and then hydrothermal synthesis was carried out at a crystallization temperature of 165°C for 3 days. The solid product was rapidly cooled, filtered, cleaned, and dried. The sample was labeled DJ23. The solid NMR silicon spectrum of the sample 29 Si MAS NMR detection has a chemical shift of δ>-108~-118 (attributed to the zeolite framework silicon Q 4 The characteristic peak area of ​​coordination characteristic signal) accounts for 95%; solid nuclear magnetic resonance aluminum spectrum 27 Al MAS NMR detection shows that there are two types of coordination forms at chemical shift δ>40 (characteristic signal of tetracoordinated aluminum in zeolite framework), and the signal peak at high chemical shift (δ>40) accounts for about 60%; before calcination, there is no obvious characteristic signal peak near δ=0 (attributed to hexacoordinated non-framework aluminum). In addition, a single nanocrystal is composed of about 11 β molecular sieve unit cells, with a specific surface area S BET =725m 2 / g, of which the micropore specific surface area S micro =463m 2 / g.

[0151] Embodiments 24 to 32

[0152] Examples 24 to 32 are respectively prepared according to the method described in Example 23 (the amount of each raw material added is consistent with that in Example 23) by nano-β molecular sieves with high crystallinity and low unit cell composition of the present invention. The corresponding samples are marked as DJ24 to DJ32. The difference lies in the different pre-crystallization (Temp1, Time1) and hydrothermal synthesis (Temp2, Time2) conditions, and thus the product skeleton silicon Q 4 The coordination ratio (corresponding to the relative crystallinity of β molecular sieve) and the crystal unit cell composition parameters are different. The specific conditions are shown in Table 3.

[0153] Table 3

[0154] Example Sample No. Temp1 Time1 Temp2 Time2 <![CDATA[Q 4 Silicon Proportion]]> Number of unit cells 24 DJ24 60 5h 145 3 days 94％ 11 25 DJ25 85 3h 140 3.5 days 92％ 8 26 DJ26 90 2h 140 6 days 96％ 10 27 DJ27 75 4.5h 150 5 days 94.5％ 11 28 DJ28 50 6h 165 5.5 days 95.5％ 10.5 29 DJ29 120 1h 160 4 days 93％ 12 30 DJ30 65 4h 155 4.5 days 95％ 9 31 DJ31 80 2.5h 152 4.5 days 96％ 11 32 DJ32 75 5h 170 2 days 97％ 12.5

Claims

1. Nano-β molecular sieve, characterized in that: The single nanocrystal of the nano-β molecular sieve includes, preferably consists of ≤20 unit cells of β molecular sieve; The crystal belongs to the tetragonal system; The space group of the crystal is P4122; The unit cell parameters include: α=90°; β=90°; γ=90°; R DLS =0.0022; 2. The nano-β molecular sieve according to claim 1, characterized in that: The cell parameters of the crystal are And / or, the solid state nuclear magnetic resonance silicon spectrum of the beta molecular sieve 29 The characteristic peak area of ​​Si MAS NMR detection in the chemical shift region of δ>-108~-118 accounts for more than 90%; And / or, the solid state nuclear magnetic resonance aluminum spectrum of the beta molecular sieve 27 Al MAS NMR detection has two characteristic signals at chemical shift δ>40; And / or, the signal peak areas of the two characteristic signals located at the chemical shift δ>40 account for ≥45%.

3. The nano-β molecular sieve according to claim 1 or 2, characterized in that: The specific surface area S of the nano-β molecular sieve BET 700~950m 2 / g; And / or, the micropore specific surface area of ​​the nano-β molecular sieve is S micro 450~1000m 2 / g.

4. A method for preparing a nano-β molecular sieve, comprising: S1 obtains a solution I containing a metal ion source and a solution II containing a template, S2: mixing the aluminum source and the silicon source with solution I and solution II to obtain a gel solution; The S3 gel solution is hydrothermally crystallized to obtain a product containing the β molecular sieve.

5. The preparation method according to claim 4, characterized in that: In the gel solution, template agent / SiO2=0.2-0.8, metal ion / SiO2=0.001-0.2, SiO2 / Al2O3=15-220; preferably, template agent / SiO2=0.25-0.55, metal ion / SiO2=0.01-0.15, SiO2 / Al2O3=25-120; And or, the solvent in the solution I is selected from at least one of water, imidazole type ionic liquid, [bimm]PF6 anionic ionic liquid; the concentration of metal ions in the solution I is 0.1wt% to 40wt%; and / or, the solvent in the solution II is alcohol or water, preferably at least one selected from water, methanol, ethanol, glycerol, n-butanol or isopropanol; the concentration of the template in the solution II is 0.05wt% to 50wt%; And / or, the hydrothermal crystallization conditions include: temperature 120-170° C., crystallization time 2-12 hours; preferably, a pre-crystallization step is also included, and the pre-crystallization conditions include: temperature 50-120° C., time 0.5-12 hours; And / or, the method further comprises the steps of cooling, washing, drying and calcining after crystallization; Preferably, the cooling conditions include: cooling to below 50°C, preferably cooling to 20-0°C; And / or, the drying conditions include: drying at a temperature of 50 to 200° C. until there is no free water or solvent adsorbed on the surface; And / or, the calcination conditions include: a temperature of 200 to 1000° C. and a treatment time of 10 minutes to 10 hours.

6. The preparation method according to claim 5, characterized in that: After the drying step and before the calcination step, a molecular sieve precursor is obtained, and the molecular sieve precursor is subjected to magic angle solid nuclear magnetic resonance or two-dimensional multi-quantum magic angle spinning aluminum nuclear magnetic resonance ( 27 Al MAS NMR or 2D 27 Al MQ-MAS NMR) characterization showed that there was no obvious characteristic signal peak near the chemical shift δ=0 (attributed to six-coordinated non-framework aluminum).

7. The preparation method according to any one of claims 4 to 6, characterized in that: The organic template is selected from at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, lysine, arginine, ornithine, and histidine; And / or, the metal ion is selected from at least one of sodium ion, potassium ion, rubidium ion and cesium ion; Preferably, the metal ion source is selected from alkali or alkali metal halogen salts; Preferably, the base is selected from at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide, cesium hydroxide, and rubidium hydroxide; and / or, the alkali metal halogen salt is selected from potassium bromide, sodium bromide, cesium chloride, rubidium bromide, sodium chloride; And / or, the metal oxide is selected from at least one of rubidium oxide, cesium oxide, magnesium oxide, calcium oxide, strontium oxide, yttrium oxide, lanthanum oxide and cerium oxide; And / or, the aluminum source is selected from at least one of pretreated aluminum hydroxide monohydrate and sodium aluminate; Preferably, the pretreatment of aluminum hydroxide monohydrate is performed by peptization pretreatment using at least one reagent selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, and formic acid, and the mixture is diluted with deionized water to a concentration of 5% to 35%, and the acid-aluminum molar ratio is adjusted to 0.005 to 0.

5.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The silicon source is selected from silicon aluminum powder, the silicon aluminum powder has a silicon / aluminum atomic molar ratio of not less than 1, preferably 2 to 500; the surface hydroxyl concentration of the silicon aluminum powder is not less than 20 μmol / g, preferably not less than 30 μmol / g; Preferably, the silicon aluminum powder is measured by solid state nuclear magnetic resonance aluminum spectroscopy. 27 In Al MAS NMR detection, the signal peak area of ​​hexacoordinated non-framework aluminum accounts for ≤50% of the total area of ​​all signal peaks, preferably ≤20%; And / or, the silicon aluminum powder is measured by solid nuclear magnetic resonance silicon spectroscopy 29 Si MAS NMR detection, the presence of Q 3 and Q 4 The characteristic signal of coordination, and Q 3 Coordination and Q 4 The ratio of the peak area of ​​the coordinated characteristic signal peak to the total area of ​​all signal peaks is ≥30%, preferably ≥60%; And / or, the silicon aluminum powder is detected by ultraviolet Raman spectroscopy at a vibration frequency of 240cm -1 There is a characteristic peak nearby; at the vibration frequency 335cm -1 、400cm -1 or 480cm -1 There is at least one characteristic peak near the vibration frequency of 335cm -1 、400cm -1 or 480cm -1 There is at least one characteristic peak with a peak intensity greater than the vibration frequency 240cm -1 The peak intensity of the nearby characteristic peaks; And / or, the specific surface area of ​​the silicon aluminum powder is 500m 2 / g~1200m 2 / g; And / or, the pore volume of the silicon aluminum powder is 0.05cm 3 / g~5cm 3 / g.

9. The preparation method according to claim 8, characterized in that: The method for preparing the silicon aluminum powder comprises the following steps: S11, providing a mixed solution I containing a treatment reagent I and a solvent I; the treatment reagent I comprises a halogen-containing compound, preferably at least one selected from silicon tetrafluoride, silicon tetrachloride, ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, sodium fluoride, sodium chloride, sodium bromide, sodium iodide, hydrofluoric acid, hydrochloric acid and hydrobromic acid; Providing a mixed solution II containing a treatment reagent II and a solvent II; the treatment reagent II includes an acidic reagent, preferably at least one selected from ammonium nitrate, nitric acid, ammonium fluoride, ammonium chloride, hydrochloric acid, ammonium bromide, perbromic acid, carbonic acid, acetic acid, phosphoric acid, oxalic acid, formic acid, acetic acid, citric acid, ammonium iodide, iodine-containing acid, hydrofluoric acid and hydrobromic acid; S12, performing a first mixing process on the silicon-containing raw material and the mixed solution I to obtain a mixed solution III; Performing a second mixing process on the aluminum-containing raw material and the mixed solution II to obtain a mixed solution IV; S13, after mixing the mixed solution III with the mixed solution IV, sequentially subjecting the mixed solution to a standing treatment, a de-impurity treatment and a calcination treatment to obtain the silicon-aluminum powder.

10. Use of the nano-β molecular sieve according to any one of claims 1 to 3 or the nano-β molecular sieve obtained by the preparation method according to any one of claims 4 to 9 as a solid acid catalytic material.

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