High-crystallinity nano beta molecular sieve as well as synthesis method and application thereof

Abstract

The invention relates to a high-crystallinity nano beta molecular sieve as well as a synthesis method and application thereof, and belongs to the technical field of molecular sieve preparation. The solid nuclear magnetic resonance aluminum spectrum 27AlMASNMR detection of the beta molecular sieve shows that the chemical shift is delta gt; 50, existence of two types of characteristic signals; the synthesis method comprises the following steps: obtaining a solution I containing a metal ion source, and obtaining a solution II containing a template agent; mixing an aluminum source and a silicon source with the solution I and the solution II to obtain a gel solution; and carrying out hydrothermal crystallization on the gel solution to obtain a product containing the beta molecular sieve. The synthesized nano beta molecular sieve has the advantages of good structural stability, high crystallinity and the like, and can be more stably used as a catalytic material for a solid acid catalytic reaction.

Description

Technical Field

[0001] The invention relates to a high-crystallinity nanometer beta molecular sieve and a synthesis method and application thereof, belonging to the technical field of molecular sieve preparation. Background Art

[0002] The properties and functions of a substance are closely related to its multi-level condensed structure. Zeolite molecular sieves are a type of crystalline aluminosilicates with molecular pores or cages. The diffusion performance and adsorption mass transfer of molecular sieves are closely affected by the acid distribution. The location of aluminum and its coordination chemical environment largely determine the type and properties of the acid center. The quantitative information of the skeleton T position is crucial, which further affects the relationship between the spatial structure of the molecular sieve and the adsorption and diffusion behavior of the guest molecules (Applied Catalysis A: General, 2020, 606: 117795). The framework structure of β molecular sieve is a cage-free open system and the only chiral high-silicon zeolite with a three-dimensional staggered twelve-membered ring pore structure. The a-axis and b-axis directions are linear pores with a pore diameter of 0.66nm×0.67nm; the c-axis direction is a curved pore that runs through the a-axis and b-axis with a pore diameter of 0.56nm×0.56nm. The β zeolite synthesized by the conventional system is composed of tetragonal and monoclinic crystals. It is a highly stacked defective mixture obtained by the stacking faults of the two polymorphic structures A and B in the

[001] direction. The different stacking modes, disordered growth and stacking in the c-axis direction make imperfect structures such as stacking faults and defect sites very common. The smaller c-axis pores in the microporous structure of β inhibit the diffusion mass transfer of the catalytic reaction and the heat transfer during the reaction to a certain extent. Highly dispersed nano- and multi-level pore molecular sieves have larger specific surface area, shorter pore length and more exposed catalytic active sites, which can significantly reduce the carbon deposition rate and improve the catalytic efficiency. In recent years, the improvement of β molecular sieves has been studied to better meet the needs of catalytic reactions, mainly through synthetic method control and post-treatment modification (Angew. Chem. Int. Ed. 2020, 59, 19582-19591), shortening the molecular diffusion path and increasing the specific surface area of ​​the molecular sieve. The catalytic activity of the positive 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 silicon source increases with the increase of silicon-aluminum ratio (J.Phys.Chem.C, 2011, 115(20): 9879-9888). Improving the structural stability of high-silicon zeolite is a difficulty in the field of synthesis. *The structural instability of high-silicon zeolites such as BEA stems from defects in their framework (J.Am.Chem.Soc., 2020, 142, 3931-3938). Structural stability is usually based on the high crystallinity of molecular sieves. The introduction of seed radiation strategy in the synthesis of β molecular sieves, its relatively complete ordered structure and the generation of more free radicals, are necessary conditions for the rapid crystallization of β zeolite (Microporous and Mesoporous Materials, 2021, 310: 110633). Low-toxic and easily recyclable pentacyclic lactams were used as "promoters" to rapidly synthesize hollow β zeolites, and the unique species of internally activated aluminosilicates were discovered for the first time (Journal of Materials Chemistry A, 2019, 7: 10795–10804). Homogeneous solvents such as trace amounts of crystalline water promote the rearrangement and connection between five-membered rings and the formation of Al-containing four-membered rings, which is a key factor in the growth of β molecular sieves (Industrial & Engineering Chemistry Research, 2020, 59 (42): 18824-18834). Zhang Qiang and others from Jilin University used an excess amino acid-assisted method to confine the growth of β molecular sieves, and revealed through liquid NMR studies that the addition of amino acids plays an extremely important role in the introduction of framework aluminum atoms in the molecular sieve (Chemistry of Materials, 2020, 32, 751-758); further studies have found that the basic amino acid can promote the formation of single-crystal multi-level pore β molecular sieves (Inorganic Chemistry Frontiers, 2022, 9 (11): 2470-2478). Academician Yu Jihong's team used hydroxyl radicals to achieve Coulomb stabilization of the liquid phase and accelerated the crystallization process of zeolite. However, hydroxyl radicals need to be excited by ultraviolet irradiation or Fenton reaction, which is difficult to achieve in industrial production (Science, 2016, 351 (6278): 1188-1191).

[0003] The discovery of the natural mineral Tschernichite indicates that the pure inorganic synthesis of β molecular sieve is feasible (Chemical Communications, 1991, 6: 363-364.). In view of the defects of low crystallinity and poor thermal stability of β molecular sieve; the CDM (charge density mismatch) principle is to reduce TEA +The influence of decomposition, synthesized high diffusion performance nano β molecular sieve (Microporous & Mesoporous Materials, 2017, 240: 159-168), but the structural stability of its products, especially the thermal stability, has not been substantially improved. In addition, high dielectric constant solvents have activation effects such as hydroxylation of amorphous species, and there are disadvantages such as uneven mass transfer and heat transfer during the crystallization process, and indirectly affect the crystallinity of zeolite (Dalton Transactions, 2020, 49 (21): 6939-6944). Sodium-free synthesis is usually replaced by fluorides and acts as a mineralizer, but limited to the influence of crystallization efficiency, hydrated alkali metal ions are the preferred solution for balancing the negative charge of the β molecular sieve microcrystalline framework, and play a structural guiding role in promoting crystallization to a certain extent, while fluorine easily leads to a sharp reduction in terminal silanols (Microporous & Mesoporous Materials, 2008, 116 (1-3): 188-195). Summary of the invention

[0004] In view of this, existing methods for improving the stability of the framework structure of β molecular sieves have certain defects, which affect their large-scale application. The present invention uses a silicon source containing structural units to explore the nucleation and growth dynamics, construct a suitable charge density environment, and obtain a highly structurally stable nano β molecular sieve by hydrothermal synthesis. This technical solution effectively solves the problem of poor thermal stability of the framework structure of β molecular sieves caused by the disordered stacking symbiosis of polymorphs in the prior art. The obtained product optimizes the coordination morphology of the framework aluminum and promotes higher structural stability, which can be used for more efficient solid acid catalytic reactions.

[0005] The technical problem to be solved by the present invention is that the existing technology has the problem of insufficient stability of the framework structure and coordination of beta molecular sieve.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is to provide a nano-β molecular sieve, the solid nuclear magnetic resonance aluminum spectrum of the nano-β molecular sieve is 27 Al MAS NMR detection has two characteristic signals (representing the coordination forms of two framework aluminum atoms) at chemical shift δ>40 (attributed to the four-coordinated aluminum of the zeolite framework).

[0007] Optionally, the signal peak areas of the two types of characteristic signals located at chemical shift δ>40 account for 45% to 100%, preferably greater than 45% (the signal peak area of ​​nuclear magnetic resonance is obtained from the spectrum, the proportion = the peak area of ​​the characteristic signal / the sum of the signal peak areas of Σδ>40*100%).

[0008] In the above technical solution, optionally, the nano-β molecular sieve has a specific surface area S BET 400~900m 2 / g, preferably greater than 400m 2 / Characteristics of g.

[0009] The silicon-aluminum ratio of the nano-β molecular sieve, the molar ratio of SiO2 / Al2O3, is 5-500, preferably 9-220.

[0010] The second technical problem to be solved by the present invention is to provide a method for synthesizing nano-β molecular sieves to solve the first technical problem. The method for synthesizing nano-β molecular sieves comprises:

[0011] S1 obtains a solution I containing a metal ion source and obtains a solution II containing a template;

[0012] S2: mixing the aluminum source and the silicon source with solution I and solution II to obtain a gel solution;

[0013] The S3 gel solution is hydrothermally crystallized to obtain a product containing the β molecular sieve.

[0014] In the above technical solution, optionally, the gel solution has a molar composition of: template / SiO2=0.01-1, metal ion / SiO2=0.001-2, OH - / SiO2=0.01~1、SiO2 / Al2O3=15~220、H2O / SiO2=2~100;Preferably R / SiO2=0.25~0.55、metal ion / SiO2=0.01~0.5、OH - / SiO2=0.05~0.5、SiO2 / Al2O3=25~120、H2O / SiO2=5~50;

[0015] And / or, the molar ratio of Al2O3 to SiO2 contained in the gel solution is 0.0001 to 1 / 5.

[0016] Optionally, the solvent in the solution I is selected from at least one of water, imidazole ionic liquid, and [bimm]PF6 anionic ionic liquid; the concentration of metal ions in the solution I is 0.1wt% to 40wt%;

[0017] Optionally, the solvent in the solution II is alcohol, preferably at least one of methanol, ethanol, glycerol, n-butanol and isopropanol; the concentration of the template in the solution II is 0.05wt% to 50wt%.

[0018] Optionally, the conditions of the hydrothermal crystallization include: a temperature of 30-200°C and a crystallization time of 0.1-20 days; preferably, a temperature of 140-165°C and a crystallization time of 2-6 days. A hydrothermally synthesized crystal product is obtained, and the product has a zeolite molecular sieve material with a *BEA characteristic structure.

[0019] Optionally, the method further comprises the steps of cooling, washing, drying and calcining after crystallization.

[0020] Optionally, the cooling conditions include: cooling to below 50°C, preferably cooling to 20-30°C; cooling can be done by natural cooling at room temperature or rapid cooling to below 50°C with room temperature water.

[0021] Optionally, 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;

[0022] Optionally, the calcination conditions include: temperature of 200 to 1000° C., time of 10 minutes to 10 hours; and removal of the organic template and adsorbed solvent or water.

[0023] In the above technical scheme, optionally, the template (R) is selected from nitrogen-containing templates, preferably at least one selected from lysine, arginine, ornithine, histidine, citrulline, proline, glutamic acid, aspartic acid, sarcosine, alanine, glycine, tyrosine, cystine, urea, tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, butanediamine, carbamoyl acid, oxaloacetic acid, argininosuccinic acid, dimethyldiallylammonium chloride, dimethyldioctadecylammonium chloride, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, hexamethylenetetramine, HMI, tetrahydropyridine, ethylenediaminetetraacetic acid, and adamantane. More preferably, at least one of lysine, arginine, ornithine, histidine, citrulline, proline, tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, and ethyltrimethylammonium hydroxide is used.

[0024] In the above technical scheme, optionally, the metal ion source (M) is selected from at least one of sodium ion, potassium ion, rubidium ion, cesium ion, magnesium ion, calcium ion, strontium ion, yttrium ion, lanthanum ion and cerium ion; preferably, the metal ion source is selected from alkali, metal oxide or metal halide; preferably, the alkali is selected from at least one of ammonia water, sodium hydroxide and potassium hydroxide; the metal halide is selected from potassium chloride, sodium bromide, sodium iodide and sodium fluoride; 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.

[0025] In the above technical solution, the aluminum source is selected from at least one of aluminum hydroxide (PB pseudo-boehmite, B boehmite), aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide.

[0026] In the above technical solution, optionally, the molecular sieve precursor is obtained after the drying step and before the calcination step, 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 MASNMR or 2D 27 Al MQ-MAS NMR) characterization showed no characteristic signal peak near the chemical shift δ=0 (attributed to hexacoordinated non-framework aluminum).

[0027] The silicon powder provided by the present invention can be applied to the synthesis of silicon-containing crystalline materials and has the characteristics of easy activation and crystallization, low dependence on organic templates, shortened crystallization induction period, etc.

[0028] The present invention provides a method for preparing the silicon powder, using common silicon-containing substances as initial raw materials, and the process adopts The treatment forms such as process, pseudo-foam alkalization or controlled oligomerization highlight the dissolution and mineralization of silicon species by inorganic (OH-, F-, etc.) or organic anions to form rich surface silicon hydroxyl species, and solve the problem of poor crystallization activity of conventional silicon sources through simple and controllable pretreatment methods.

[0029] In the ultraviolet Raman spectrum of the silicon powder, at the vibration frequency of 240cm -1 There are characteristic peaks nearby, with a vibration frequency no greater than 600cm -1 In the characteristic area, there is at least one non-240cm -1 Characteristic peaks near 240cm -1 The sum of the peak areas of the nearby characteristic peaks is no more than 600 cm -1 The total area of ​​the characteristic peaks in the characteristic region is ≥ 20% but not more than 98% (correspondingly, at 240 cm -1 The area of ​​the characteristic peaks near the -1 The total area of ​​characteristic peaks in the characteristic region is ≤80%).

[0030] In some embodiments of the present invention, in the ultraviolet Raman spectrum of the silicon powder, at a vibration frequency of no more than 600 cm -1 In the characteristic region, there is a vibration frequency of 335cm -1 、400cm -1 and 480cm -1 At least one characteristic peak in the vicinity.

[0031] In the present invention, the peak area of ​​each characteristic peak can be obtained by automatic (or manual if necessary) integration in a spectrometer. The present invention does not limit the specific peak area of ​​each characteristic peak. -1 The peak area of ​​the characteristic peaks near 240 cm -1 The relationship between the areas of nearby characteristic peaks has corresponding limitations.

[0032] The silicon powder in the present invention is a silicon powder containing structural units, and the structural unit in "silicon powder containing structural units" refers to a silicon-containing four-membered ring (4MR), five-membered ring (5MR) or six-membered ring (6MR) that can constitute the molecular sieve framework structure.

[0033] According to the present invention, 240cm -1 The characteristic peak near is the characteristic signal of TOT bending vibration of silicon-containing eight-membered ring (8MR). When the ultraviolet Raman spectrum of the silicon powder is at 240cm -1 When there is a characteristic peak nearby, it means that the silicon atoms in the silicon powder have overcome the skeleton stress and formed more active structural units of the aforementioned 4MR, 5MR or 6MR.

[0034] According to the present invention, in the ultraviolet Raman spectrum of silicon powder, 240cm -1 The characteristic peaks near the 8-membered ring (8MR) represent the bending vibration of TOT in the silicon-containing 8-membered ring; the vibration frequency is not more than 600 cm -1 In the characteristic region, the smaller rings correspond to higher vibration frequencies, not 240 cm -1 Among the characteristic peaks nearby, 335cm -1 、400cm -1 or 480cm -1 The characteristic peaks near 240cm represent the bending vibration of TOT in the six-membered ring (6MR), five-membered ring (5MR) and four-membered ring (4MR) containing silicon. -1 The sum of the peak areas of the nearby characteristic peaks is no more than 600 cm -1 The total area of ​​the characteristic peaks in the characteristic region is ≥20% but not more than 98%, indicating that the silicon atoms in the silicon powder have more active structural units such as four-membered rings (4MR), five-membered rings (5MR) or six-membered rings (6MR).

[0035] In some embodiments of the present invention, in the ultraviolet Raman spectrum of the silicon powder, at a vibration frequency of no more than 600 cm -1 In the characteristic area, non-240cm -1 The characteristic peak near is 335cm -1 、400cm -1 and 480cm -1 At least one of the nearby characteristic peaks.

[0036] In some embodiments of the present invention, at a vibration frequency of no more than 600 cm -1 In the characteristic area, non-240cm -1 The characteristic peak near 335cm -1 、400cm -1 and 480cm -1The sum of the peak areas of at least one of the characteristic peaks nearby is no more than 600 cm -1 The total area of ​​characteristic peaks in the characteristic region is ≥50%.

[0037] Regarding the expression “near” in the above content, those skilled in the art will know that since each characteristic peak in the ultraviolet Raman spectrum usually has a displacement, the position of the characteristic peak defined in the present invention may have a deviation, such as 480cm -1 The nearby characteristic peak is at 450cm -1 ~500cm -1 However, the vibration represented by each characteristic peak can be determined by those skilled in the art.

[0038] In the present invention, the above-mentioned “no more than 600cm -1 The characteristic area generally refers to 200cm -1 ~600cm -1 Those skilled in the art will understand that if a characteristic peak appears in a region of silicon powder where it is not easy to have a characteristic peak, it should be verified whether it is an impurity peak formed by contamination.

[0039] In some embodiments of the present invention, the specific surface area of ​​the silicon powder is 200m 2 / g~980m 2 / g, preferably 550m 2 / g~980m 2 / g.

[0040] In some embodiments of the present invention, the mass fraction of SiO2 in the silicon powder is >90%, preferably >95%, and more preferably >98%.

[0041] In some embodiments of the present invention, the pore volume of the silicon powder is 0.2 cm 3 / g~3.0cm 3 / g.

[0042] The method for preparing silicon powder comprises the following steps:

[0043] S11, providing a mixed solution I containing a treatment reagent and a solvent I;

[0044] S12, mixing the silicon-containing raw material with the mixed solution I to obtain a mixed solution II;

[0045] S13, performing activation treatment on the mixed solution II to obtain an activated product;

[0046] S14, calcining the activated product to obtain the silicon powder.

[0047] In some embodiments of the present invention, in step S11, the treatment reagent is selected from at least one of an inorganic base, a fluorine-containing substance, an organic base and an ionic liquid containing an organic anion; preferably at least one of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, hydrofluoric acid, sodium fluoride, ammonium fluoride, silicon tetrafluoride, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0048] In the present invention, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) is an imidazole-type ionic liquid.

[0049] In the present invention, the treatment reagent is preferably an organic quaternary ammonium base or fluoride, that is, at least one selected from hydrofluoric acid, sodium fluoride, ammonium fluoride, silicon tetrafluoride, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0050] In the present invention, when used, the treatment reagent is usually prepared into a solution of a certain concentration using water or alcohol as a solvent. For example, the organic base can be prepared into an aqueous solution or an alcohol solution. Those skilled in the art can make a selection based on actual conditions.

[0051] In some embodiments of the present invention, in step S11, the solvent I is selected from at least one of water, alcohols and ionic liquids; preferably at least one of deionized water, methanol, ethanol, n-butanol, isopropanol, ethylene glycol and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0052] In some embodiments of the present invention, in step S12, the silicon-containing raw material is selected from at least one of diatomaceous earth, water glass, (liquid) silica sol, white carbon black, gas-phase silica sol, silicon powder, silicone resin microspheres, silicates (such as tetramethyl silicate, tetraethyl silicate or tetrapropyl silicate), silicon tetrachloride and silane; wherein the silane is preferably selected from at least one of tetramethylsilane Si(CH3)4, methyltrimethoxysilane MTMS, isobutylene triethoxysilane, trichlorosilane SiHCl3 and tetraethoxysilane Si(OC2H5)4.

[0053] In the present invention, the silicon-containing raw material is preferably liquid silica sol, silicate or silane.

[0054] In the present invention, the optional silicon-containing raw materials mentioned above are all silicon-containing materials commonly used in the art.

[0055] In some embodiments of the present invention, the molar ratio of the treatment reagent to SiO2 in the silicon-containing raw material (hereinafter referred to as the treatment reagent / SiO2 molar ratio) is 0.0001 to 10:1, preferably 0.0001 to 0.1:1.

[0056] In some embodiments of the present invention, the molar ratio of the solvent I to SiO2 in the silicon-containing raw material (hereinafter referred to as the solvent I / SiO2 molar ratio) is 0.5 to 50:1.

[0057] In some embodiments of the present invention, the molar ratio of the total hydroxide anions in the treatment reagent and the solvent I to the SiO2 in the silicon-containing raw material (hereinafter referred to as OH - / SiO2 molar ratio) is 2 to 60:1.

[0058] In some embodiments of the present invention, in step S12, the conditions for the mixing treatment include: a stirring speed of 0 to 5000 rpm, preferably 0 to 50 rpm; and a temperature of 0 to 50°C, preferably 5 to 30°C.

[0059] In some embodiments of the present invention, in step S13, the process for performing the activation treatment (also referred to as the gelling process) is selected from The method comprises at least one of the following steps: preparing monodisperse SiO2 microspheres by alkaline hydrolysis of tetraethyl orthosilicate (TEOS), hydrolysis, oligomer precipitation, alkaline dissolution and hot melting to highlight the mineralization effect on silicon atoms.

[0060] The activated The process includes mixing and hydrolysis steps; the hydrolysis step of the activation treatment is mainly controlled by controlling the hydrolysis catalyst (promoter or inhibitor) and temperature, stirring / ultrasound / irradiation, time and other parameters; the oligomer precipitation of the activation treatment includes the steps of hydrolysis, solvent network bonding and growth; the alkali dissolution of the activation treatment includes adding a certain amount of ammonia water, sodium hydroxide or potassium hydroxide solution with a certain concentration into the above preparation process; the hot melt of the activation treatment refers to a single-stage or segmented high-temperature heat treatment at 300-1000°C for a certain period of time.

[0061] In the present invention, the activation treatment preferably uses an optimized Specifically, the hydrolysis, bonding and SiO2 growth rates can be controlled by the amount of solvent, temperature and stirring speed to achieve uniformity and controllability of silicon powder.

[0062] According to the present invention, The process, hydrolysis, oligomer precipitation, alkali dissolution and hot melting are all conventional methods of the present invention. The present invention does not strictly limit the various parameters involved in the process, and those skilled in the art can determine them according to actual conditions.

[0063] In some embodiments of the present invention, the conditions for activation treatment include: temperature not higher than 200°C (such as 0-200°C), preferably not higher than 100°C (such as 0-100°C); treatment time is 1 hour to 500 days, preferably 12 hours to 12 days; further preferably, the activation treatment is completed at a temperature of 0-10°C, a temperature of 10-30°C, a temperature of 30-80°C, and a temperature of 80-100°C (segmented constant temperature heat treatment) for 0 to 120 hours (such as 1 to 120 hours).

[0064] In some embodiments of the present invention, after obtaining the activated product of step S13, before the calcination treatment of step S4, the activated product may be subjected to impurity removal treatment, and water-soluble impurities and solvents, including all impurities such as physically adsorbed water, alcohols, salts and ionic liquids, may be removed by means of forced air drying, vacuuming, etc. At the same time, a maximum of Si, C, H, O, F, S, Br, Cl or MoO x At least one composition.

[0065] In some embodiments of the present invention, in step S14, the conditions for the calcination treatment include: a temperature of 150 to 1000°C, preferably 400 to 600°C; a time of 0.05 to 500 hours; further preferably, within the temperature range of 150 to 1000°C (preferably 400 to 600°C), at least two calcination temperatures are selected from low to high in an air atmosphere and calcined for 0.05 to 2 hours respectively, for example, in an air atmosphere, calcined at 150 to 200°C, 250 to 350°C, 400 to 500°C, and 500 to 600°C in sequence for 0.05 to 2 hours.

[0066] In some embodiments of the present invention, during the calcination treatment, a programmed temperature increase of 0.5 to 5° C. / min is used to raise the temperature from room temperature to the calcination temperature (ie, 150 to 1000° C., preferably 400 to 600° C.).

[0067] In the present invention, the calcination treatment is used to remove the skeleton crystal water (the desorption temperature is usually ≥ 200°C under normal pressure), sublimable fluoride, sulfur or MoO x Impurities such as alkali or salt molecules of the organic template can be completely decomposed by high temperature oxidation.

[0068] The present invention also provides the use of the silicon powder and / or the silicon powder prepared by the above preparation method in the preparation of silicon-containing crystalline materials, especially in the preparation of titanium silicon molecular sieve, silicon aluminum molecular sieve, germanium silicon molecular sieve or pure silicon porous material. That is, the silicon-containing crystalline material is preferably titanium silicon molecular sieve, silicon aluminum molecular sieve, germanium silicon molecular sieve or pure silicon porous material; the silicon-containing crystalline material is further preferably at least one of TS-1 molecular sieve, β molecular sieve, ZSM-5 molecular sieve, EU-1 molecular sieve, MCM-22 molecular sieve, SCM-4 molecular sieve, Solicalite-2 molecular sieve, mordenite molecular sieve, intergrowth zeolite molecular sieve and SBA-15 molecular sieve.

[0069] According to the present invention, after the silicon-containing crystalline material is synthesized using the silicon powder, the silicon-containing crystalline material (catalytic material) can be used in a highly efficient catalytic carbonium ion reaction.

[0070] In the present invention, when preparing and synthesizing silicon-containing crystalline materials (such as molecular sieves), the synthesis methods of silicon-containing crystalline materials of different configurations are different, and the silicon powder of the present invention can be applied. As for the amount of silicon powder used, those skilled in the art can add an appropriate amount according to different requirements of the target product.

[0071] According to the present invention, after the silicon powder is used to synthesize the silicon-containing crystalline material, the nucleation induction period of the obtained silicon-containing crystalline material at a temperature below 100° C. is less than 24 hours.

[0072] The silicon powder provided by the present invention overcomes the structural stress of forming structural units, has abundant silicon-containing four-membered rings (4MR), five-membered rings (5MR) or six-membered rings (6MR), has a large pore volume and specific surface area, and can thus significantly shorten the nucleation induction period. As an active raw material, it can be efficiently applied to the synthesis process of silicon-containing crystalline materials.

[0073] The method for preparing silicon powder provided by the present invention solves the problem of efficient preparation of silicon powder containing structural units. The key to the technology lies in the control of the pretreatment process. The preparation process avoids the use of excessive water or non-circulating organic matter, and can be used for industrial production.

[0074] The silicon powder containing the structural unit of the present invention can be used for the synthesis of silicon-containing crystalline materials, especially for the synthesis of titanium silicon molecular sieve, silicon aluminum molecular sieve, germanium silicon molecular sieve or pure silicon porous material, and can shorten the crystallization induction period.

[0075] The present invention also provides the use of the nanometer beta molecular sieve as a solid acid catalytic material.

[0076] The nanometer beta molecular sieve synthesized by the invention has the advantages of good structural stability, high crystallinity and the like, and can be used as a catalytic material for solid acid catalytic reactions more stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 is a HR-TEM photograph of sample JWB1 prepared in Example 1 of the present invention;

[0078] Figure 2 The solid magic angle nuclear magnetic resonance ( 27 Al MAS NMR) spectrum;

[0079] Figure 3 It is the two-dimensional multi-quantum magic angle spinning aluminum nuclear magnetic resonance spectrum of sample JWB1 prepared in Example 1 of the present invention;

[0080] Figure 4 is a TEM photograph of silicon powder SG1 containing structural units prepared in Preparation Example 1;

[0081] Figure 5 is the UV-Raman spectra of silicon powder SG1 and white carbon black A200 containing structural units obtained in Preparation Example 1;

[0082] Figure 6 are nitrogen low temperature adsorption-desorption (BET) curves of silicon powder SG1 and white carbon black A200 containing structural units obtained in Preparation Example 1;

[0083] Figure 7 FT-IR spectra of silicon powder SG1 and white carbon black A200 containing structural units obtained in Preparation Example 1;

[0084] Figure 8 It is the XRD pattern of sample JWB1 prepared in Example 1 of the present invention.

[0085] The present invention will be further described below by way of examples. DETAILED DESCRIPTION

[0086] The preparation method of the high structural stability β molecular sieve of the present invention is as follows:

[0087] S1: obtaining a solution I containing a metal ion source (metal compound or oxide), and obtaining a solution II containing a template; mixing solution I with solution II, and using a nitrogen-containing organic substance, i.e., a template, and a metal compound or oxide to regulate the charge density environment of the synthesis system;

[0088] S2: In solution I, aluminum source, silicon powder containing structural units (the silicon source is diatomaceous earth, water glass, silica sol, white carbon black, gas phase silica sol, silicon powder, silicone resin microspheres, silicate, silicon tetrachloride and silane, etc., which are pretreated to form a certain number of four-membered rings, five-membered rings or six-membered rings of TOT molecular sieve skeleton structural units, and the vibration frequency is 335cm by UV-Raman spectroscopy. -1、400cm -1 、480cm -1 and 600cm -1 There are obvious characteristic signal peaks near the positions, etc.), and water is stirred to obtain a gel solution;

[0089] The S3 gel liquid is crystallized by high temperature hydrothermal treatment, rapidly cooled, filtered, cleaned and dried to obtain a solid product.

[0090] In the present invention, the specific surface area and pore volume are analyzed by low-temperature N2 adsorption-desorption analysis of the samples using a Tristar3000 specific surface analyzer produced by Micrometrics. The samples are pretreated at 300°C for 6 hours by vacuum activation before testing. The test temperature is -196°C. The pore structure data such as the specific surface area and pore volume of the test samples are obtained by analyzing the isotherms.

[0091] In the present invention, the mass fraction of SiO2 in silicon powder is measured by thermogravimetric TG-DTA analysis of samples using a TGA Q500analyzer instrument (test conditions are air atmosphere, heating rate 10°C / min). In the following examples, the chemical reagents used are all commercially available products, and no special purification treatment is performed unless otherwise specified.

[0092] In the present invention, the FT-IR spectrum test uses a Nexus670 Fourier transform infrared spectrometer (FT-IR) produced by Nicolet Company of the United States to analyze the skeleton vibration area of ​​the sample; during the test, the sample powder is first diluted with KBr to a mass fraction of about 3%, ground and mixed evenly with a mortar, and then pressed into a tablet to prepare a sample, which is then placed in a vacuum cell for testing, and the test resolution is 4cm- 1 , scanning times 32 times, test range 400~4000cm -1 .

[0093] Preparation Example 1 Preparation of silicon powder containing structural units

[0094] Weigh sodium hydroxide, sodium fluoride, and 25% ammonia solution, add them to deionized water to dissolve evenly, add methanol, and place the solution in a 5°C water bath; weigh methyltrimethoxysilane, add it evenly to the above solution while stirring at 30rpm, stir for another 2 minutes, transfer it to a container and let it stand at 30°C for 5 hours to obtain a sol, and rotary evaporate the solvent under vacuum conditions at 80°C until a solid block is precipitated. The molar ratio of treatment reagent / SiO2 is 0.05; the molar ratio of solvent I / SiO2 is 10; OH - / SiO2 molar ratio 10.

[0095] The solid block obtained in the above preparation was treated with 1% citric acid aqueous solution at a liquid-solid mass ratio of about 6:1, and then acid exchanged at 80°C for 1.5 hours, washed with deionized water until electrically neutral, and dried at 120°C. The temperature was then raised to 600°C at a rate of 3°C / min, and calcined at a constant temperature for 1.5 hours to obtain sample SG1.

[0096] The specific surface area of ​​sample SG1 is S BET 510m 2 / g, pore volume = 2.4 cm 3 / g, SiO2 mass fraction is 99%, Figure 5 It can be seen that compared with silica A200, sample SG1 has a vibration frequency of no more than 600 cm -1 There are more non-240cm areas in the characteristic area -1 Nearby characteristic peaks; UV-Raman detected its vibration frequency at 335cm -1 、400cm -1 and 480cm -1 The peak area of ​​the characteristic peak near 240cm -1 Characteristic peaks near 240cm -1 The sum of the peak areas of the nearby characteristic peaks is no more than 600 cm -1 The total area of ​​the characteristic peaks in the characteristic region is 78%. Figure 5 In the UV-Raman spectrum of sample SG1, due to peak overlap, 335cm -1 、400cm -1 and 480cm -1 Nearby characteristic peaks overlap.

[0097] Depend on Figure 4 It can be seen that the silicon oxide particles in sample SG1 are uniform and dispersed; Figure 6 It can be seen that compared with silica A200, sample SG1 has a larger low-temperature adsorption capacity for nitrogen, and the specific surface area and pore volume obtained from the curve are larger; Figure 7 It can be seen that the signal peak of silanol in the corresponding FT-IR spectrum of sample SG1 is stronger (usually, the larger the peak area at the characteristic position, the higher the surface silanol concentration of the sample).

[0098] Example 1

[0099] Measure 900 ml of deionized water, dissolve 35 grams of potassium chloride (metal ion source M) and 2300 grams of 35wt% tetraethylammonium hydroxide (nitrogen-containing template R) in methanol solution. Weigh 30 grams of sodium aluminate (aluminum source), and add it evenly to the above solution. Weigh 1300 grams of silicon powder SG1 containing structural units obtained in Preparation Example 1, and add it evenly to the above solution to obtain a gel solution. The gel solution is transferred into a pressure bomb lined with tetrafluoroethylene. Hydrothermal synthesis is carried out at a crystallization temperature of 150°C for 6 days, and the solid product is rapidly cooled to below 50°C with room temperature water, filtered and washed, and dried at 100°C for 6 hours. The sample is labeled JWB1. By Figure 2 It can be seen that the solid NMR aluminum spectrum of the sample 27 Al MAS NMR detection shows that there are two types of coordination forms when the chemical shift δ>50 (characteristic signal of tetracoordinated aluminum in the zeolite framework); at the same time, the proportion of the high chemical shift signal peak is 49%; at the same time, there is no obvious characteristic signal peak near δ=0 (attributed to hexacoordinated non-framework aluminum) before calcination. The specific surface area S of the pure phase β molecular sieve is BET =510m 2 / g.

[0100] Depend on Figure 1 It can be seen that high-resolution transmission electron microscopy (HR-TEM) shows that the high structural stability of sample JWB1 is reflected in the clear lattice fringes, and it is relatively stable under transmitted light radiation, forming a β-zeolite crystal array in the form of a "townhouse" and has the characteristics of uniform and high dispersion.

[0101] Depend on Figure 2 It can be seen that sample JWB1 mainly shows (δ>50ppm) tetracoordinate framework aluminum, which contains at least two types of The acid site, crystallinity and high chemical shift peak area are consistent, and the corresponding T9 site is very stable.

[0102] Depend on Figure 3 It can be seen that combined 27 Al MQ-MAS NMR results show that sample JWB has two main stable coordination forms in the four-coordination region, with better crystal order and optimized acid properties and diffusion performance.

[0103] Figure 8 The XRD pattern shows that sample JWB1 is a pure phase β molecular sieve material.

[0104] Comparative Example 1

[0105] Measure 900 ml of deionized water and dissolve 35 g of potassium chloride (metal ion source M) and 2300 g of 35 wt% methanol solution of tetraethylammonium hydroxide (nitrogen-containing template R). Weigh 30 g of sodium aluminate (aluminum source) and add it evenly to the above solution. Weigh white carbon black A200 (commercially available with a specific surface area of ​​about 200 m2) with the same molar amount of SiO2 as in Example 1. 2 / g), and evenly added to the above solution to obtain a gel solution. The gel solution was transferred into a pressure bomb lined with tetrafluoroethylene. The product was hydrothermally synthesized at a crystallization temperature of 150°C for 6 days, rapidly cooled to below 50°C with room temperature water, filtered and washed, and dried at 100°C for 6 hours to obtain a solid product. The sample was labeled DB1.

[0106] Depend on Figure 2 It can be seen that the product synthesized with white carbon black A200 (fumed silica sol), namely sample DB1, has a poor relative crystallinity, and a characteristic peak attributable to hexacoordinated non-framework aluminum appears at 0 ppm.

[0107] Embodiments 2 to 12

[0108] Examples 2 to 12 are nano-β molecular sieves prepared according to the method of Example 1, and the corresponding samples are marked as JWB2 to JWB12. The difference lies in the different nitrogen-containing templates (R), metal ion sources (M), and aluminum sources (the molar amounts of R, M and Al2O3 in the aluminum source are consistent with those in Example 1), and therefore the proportions of high chemical shift signal peaks in the solid nuclear magnetic resonance aluminum spectrum of the β molecular sieve (GR=Peak1 / [Peak1+Peak2]╳100%, corresponding to the structural stability and relative crystallinity of the zeolite) are different. The specific conditions are shown in Table 1.

[0109] Table 1

[0110]

[0111] Examples 13 to 22

[0112] Examples 13 to 22 are nano-β molecular sieves prepared according to the method of Example 5. The corresponding samples are marked as JWB13 to JWB22. The difference lies in the composition of the gel solution, the molar ratio of R / SiO2, M / SiO2, OH - / SiO2, SiO2 / Al2O3 and H2O / SiO2, and thus the 27 The GR of the Al MAS NMR results is different, see Table 2 for details.

[0113] Table 2

[0114]

[0115] Embodiment 23

[0116] Example 23: Prepare a gel solution according to the method of Example 4 (the amounts of R, M and aluminum source are exactly the same as those of Example 4). The gel solution is transferred into a pressure bomb lined with tetrafluoroethylene. The difference is that the hydrothermal crystallization process is carried out at a temperature of 170°C, the hydrothermal synthesis takes 2 days, and the solid product is obtained by rapid cooling, filtration, cleaning and drying. The sample is labeled JWB23. The solid NMR aluminum spectrum of the sample 27 Al MAS NMR detection shows that there are two types of coordination forms when the chemical shift δ>50 (characteristic signal of tetracoordinated aluminum in the zeolite framework), and the proportion of the high chemical shift signal peak is about 51%; before calcination, there is no obvious characteristic signal peak near δ=0 (attributed to hexacoordinated non-framework aluminum); in addition, its specific surface area S BET =525m 2 / g.

[0117] Embodiments 24 to 30

[0118] Examples 24 to 30 are β molecular sieves prepared according to the method of Example 23 (the amounts of R, M and aluminum source are the same as those in Example 23), and the corresponding samples are marked as JWB24 to JWB respectively. The difference lies in their different hydrothermal crystallization conditions, which leads to differences in the performance of the product β molecular sieves, as shown in Table 3 for details.

[0119] Table 3

[0120]

Claims

1. Nano-β molecular sieve, characterized in that: Solid-state NMR aluminum spectrum of the β molecular sieve 27 Al MAS NMR detection has two characteristic signals at chemical shift δ>40.

2. The nano-β molecular sieve according to claim 1, characterized in that: The signal peak areas of the two characteristic signals located at the chemical shift δ>40 account for 45% to 100%.

3. The nano-β molecular sieve according to claim 1 or 2, characterized in that: The specific surface area S of the β molecular sieve BET 400~900m 2 / g.

4. A method for synthesizing 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 synthesis method according to claim 4, characterized in that The gel solution has a molar composition of: template / SiO2=0.01-1, metal ion / SiO2=0.001-2, OH - / SiO2=0.01~1、SiO2 / Al2O3=15~220、H2O / SiO2=2~100;Preferably template agent / SiO2=0.25~0.55、metal ion / SiO2=0.01~0.5、OH - / SiO2=0.05~0.5、SiO2 / Al2O3=25~120、H2O / SiO2=5~50; and / or, the solvent in the solution I is selected from at least one of water, imidazole-type ionic liquid, and [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 an alcohol, preferably at least one of methanol, ethanol, glycerol, n-butanol and isopropanol; the concentration of the template in the solution II is 0.05wt% to 50wt%; And / or, the conditions of the hydrothermal crystallization include: temperature 30-200° C., crystallization time 0.1-20 days; preferably, temperature 140-165° C., crystallization time 2-6 days; 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 20-30°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: temperature of 200 to 1000° C. and time of 10 minutes to 10 hours.

6. The synthesis method according to claim 4 or 5, characterized in that: The template is selected from nitrogen-containing templates; preferably, the nitrogen-containing template is selected from at least one of lysine, arginine, ornithine, histidine, citrulline, proline, glutamic acid, aspartic acid, sarcosine, alanine, glycine, tyrosine, cystine, urea, tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, tetraethylammonium iodide, tetramethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, butanediamine, carbamoyl acid, oxaloacetic acid, argininosuccinic acid, dimethyldiallylammonium chloride, dimethyldioctadecylammonium chloride, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, hexamethylenetetramine, HMI, tetrahydropyridine, ethylenediaminetetraacetic acid, and adamantane; And / or, the metal ion is selected from at least one of sodium ion, potassium ion, rubidium ion, cesium ion, magnesium ion, calcium ion, strontium ion, yttrium ion, lanthanum ion and cerium ion; preferably, the metal ion source is selected from alkali, metal oxide or metal halide; preferably, the alkali is selected from at least one of ammonia water, sodium hydroxide and potassium hydroxide; and / or, the metal halide is selected from at least one of potassium chloride, sodium bromide, sodium iodide and sodium fluoride; 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 aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide.

7. The synthesis method according to claim 5 or 6, characterized in that: The molecular sieve precursor is obtained after the drying process and before the calcination process. 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 no characteristic signal peak near the chemical shift δ=0 (attributed to hexacoordinated non-framework aluminum).

8. The synthesis method according to any one of claims 4 to 7, characterized in that The silicon source is selected from silicon powder containing structural units; In the ultraviolet Raman spectrum of the silicon powder, at the vibration frequency of 240cm -1 There are characteristic peaks nearby, with a vibration frequency no greater than 600cm -1 In the characteristic area, there is at least one non-240cm -1 Characteristic peaks near 240cm -1 The sum of the peak areas of the nearby characteristic peaks is no more than 600 cm -1 The characteristic peak area of ​​the characteristic region is 20% to 98% of the total area; Preferably, in the ultraviolet Raman spectrum of the silicon powder, the vibration frequency is not greater than 600cm -1 In the characteristic region, there is a vibration frequency of 335cm -1 、400cm -1 and 480cm -1 At least one characteristic peak in the vicinity; Preferably, the vibration frequency is not greater than 600cm -1 In the characteristic area, non-240cm -1 The sum of the peak areas of the nearby characteristic peaks is no more than 600 cm -1 The total area of ​​characteristic peaks in the characteristic region is ≥50%; Preferably, the specific surface area of ​​the silicon powder is 200m 2 / g~980m 2 / g; And / or, in the silicon powder, the mass fraction of SiO2 is greater than 90%; And / or, the pore volume of the silicon powder is 0.2 cm 3 / g~3.0cm 3 / g.

9. The synthesis method according to claim 8, characterized in that The method for preparing silicon powder containing structural units comprises: S11, providing a mixed solution I containing a treatment reagent and a solvent I; the treatment reagent is selected from at least one of an inorganic base, a fluorine-containing substance, an organic base and an ionic liquid containing an organic anion; S12, mixing the silicon-containing raw material with the mixed solution I to obtain a mixed solution II; S13, performing activation treatment on the mixed solution II to obtain an activated product; S14, calcining the activated product to obtain the silicon powder; More preferably, the silicon-containing material is selected from at least one of diatomaceous earth, water glass, silica sol, white carbon black, fumed silica sol, silicon powder, silicone resin microspheres, silicate, silicon tetrachloride and silane; wherein the silane is preferably selected from at least one of tetramethylsilane, methyltrimethoxysilane, isobutylenetriethoxysilane, trichlorosilane and tetraethoxysilane.

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 synthesis method according to any one of claims 4 to 9 as a solid acid catalytic material.

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