Preparation method and application of nb-beta molecular sieve

Abstract

The application discloses a preparation method and application of Nb-Beta molecular sieve, and belongs to the field of chemical synthesis and catalysis. The method comprises the following steps: mixing a first silicon source, an organic template agent R1 and water, performing first crystallization, and obtaining a precursor I; mixing a second silicon source, an inorganic salt M, an organic template agent R2 and water, adding the precursor I, and obtaining a precursor II; performing second crystallization on the precursor II, then adding a niobium source, and performing third crystallization, thereby obtaining the Nb-Beta molecular sieve. The method has the advantages of simple synthesis process, fast crystallization rate, high product crystallinity, no use of fluorine ions as a mineralizer, small pollution and high safety.

Description

Technical Field

[0001] This application belongs to the field of chemical synthesis and catalysis, specifically relating to a method for preparing Nb-Beta molecular sieves and their applications. Background Technology

[0002] Nb-Beta molecular sieves are molecular sieves that introduce Lewis acidic centers by implanting niobium (Nb) atoms into the *BEA zeolite framework. These heteroatom-containing molecular sieves have exhibited excellent catalytic activity, water stability, and renewability in many macromolecular catalytic reactions (such as biomass conversion), thus attracting widespread attention from researchers and industry.

[0003] Currently, the synthesis methods for Nb-Beta molecular sieves can be mainly divided into direct synthesis and post-processing methods. The post-processing method (see Catal Today, 2019, 325, 109-116) generally uses commercially available Al-Beta molecular sieves as the parent material. First, framework vacancies are generated through nitric acid dealumination, and then niobium atoms are grafted onto these vacancies using various methods, thus obtaining the Nb-Beta molecular sieve. This method involves lengthy synthesis steps, requires strong acids in the processing, is hazardous, and easily causes environmental pollution. Furthermore, the product has many defect sites, poor hydrophobicity, and difficulty in introducing Nb into the framework, readily forming Nb oxides and extra-framework Nb. The direct synthesis method (see J. Phys. Chem. C, 2009, 113, 11306-11315) mainly uses fluoride ions as mineralizing agents for synthesis. This method yields products with high crystallinity, few internal defects, and strong hydrophobicity, which is beneficial for improving catalytic performance in aqueous systems. However, the synthesis process requires hydrofluoric acid, which easily corrodes equipment, and the crystallization time is long (about 30 days), resulting in limited Nb content and generally large crystal sizes. These problems severely limit the industrial-scale production of the product. Summary of the Invention

[0004] This application provides a method for the direct synthesis of Nb-Beta molecular sieves in a fluorine-free system. This method involves adding a pre-crystallized molecular sieve liquid directing agent to the gel system used for synthesis, introducing alkali metal / alkaline earth metal ions, and adding a niobium source under specific conditions, thereby enabling the rapid, green, and controllable synthesis of Nb-Beta molecular sieves.

[0005] According to one aspect of this application, a method for preparing Nb-Beta molecular sieves is provided, comprising:

[0006] The first silicon source, organic template agent R1 and water are mixed and subjected to first crystallization to obtain precursor I;

[0007] The second silicon source, inorganic salt M, organic template agent R2 and water are mixed and added to the precursor I to obtain precursor II;

[0008] The precursor II is subjected to a second crystallization, and then a niobium source is added for a third crystallization to obtain the Nb-Beta molecular sieve.

[0009] Optionally, the method includes the following steps:

[0010] a) Mix the first silicon source, organic template agent R1, and water to obtain the initial gel A;

[0011] b) The initial gel A is subjected to a first crystallization, which includes crystallization at 80-170°C for 0.5-20 h to obtain precursor I;

[0012] c) Mix the second silicon source, inorganic salt M, organic template agent R2 and water to obtain the initial gel B;

[0013] d) The precursor I is added to the initial gel B to obtain precursor II;

[0014] e) The precursor II is subjected to a second crystallization, the second crystallization comprising crystallization at 110-190°C for 2-66 h to obtain a crystallized mixture;

[0015] f) Adding a niobium source to the crystallization mixture to perform a third crystallization, the third crystallization comprising crystallization at 110-190°C for 42-126 h;

[0016] g) The obtained solid product is separated, washed, and dried to obtain the Nb-Beta molecular sieve.

[0017] Optionally, in step a), the initial gel A has the following component molar ratio:

[0018] R1∶SiO2=(0.10-1.10)∶1,

[0019] H2O∶SiO2=(2.0-21.0)∶1,

[0020] Wherein, the number of moles of the first silicon source is calculated based on the number of moles containing SiO2, and the number of moles of the organic template agent R1 is calculated based on the number of moles of R1 itself.

[0021] Optionally, in step a), the component molar ratio R1:SiO2 of the initial gel A is independently selected from any value or a range between 0.10:1, 0.20:1, 0.30:1, 0.40:1, 0.50:1, 0.60:1, 0.70:1, 0.80:1, 0.90:1, 1.00:1, and 1.10:1, and H2O:SiO2 is independently selected from 2. Any value from 0:1, 3.0:1, 4.0:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, 9.0:1, 10.0:1, 11.0:1, 12.0:1, 13.0:1, 14.0:1, 15.0:1, 16.0:1, 17.0:1, 18.0:1, 19.0:1, 20.0:1, and 21.0:1, or a range of values ​​between any two.

[0022] Preferably, in step a), the initial gel A has the following component molar ratio:

[0023] R1∶SiO2=(0.10-1.00)∶1,

[0024] H2O∶SiO2=(3.0-20.0)∶1.

[0025] More preferably, in step a), the initial gel A has the following component molar ratio:

[0026] R1∶SiO2=(0.40-0.80)∶1,

[0027] H2O∶SiO2=(6.0-18.0)∶1.

[0028] Optionally, in step c), the initial gel B has the following component molar ratio:

[0029] M∶SiO2=(0.05-0.60)∶1,

[0030] R2∶SiO2=(0.05-0.60)∶1,

[0031] H2O∶SiO2=(5.0-35.0)∶1,

[0032] Wherein, the number of moles of the second silicon source is calculated based on the number of moles containing SiO2, the number of moles of the organic template agent R2 is calculated based on the number of moles of R2 itself, and the number of moles of the inorganic salt M is calculated based on the number of moles of M itself.

[0033] Optionally, in step c), the molar ratio of the components M:SiO2 in the initial gel B is independently selected from any value or a range between any two of 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1, 0.30:1, 0.35:1, 0.40:1, 0.45:1, 0.50:1, 0.55:1, and 0.60:1, and R2:SiO2 is independently selected from 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1, and R2:SiO2. The range of H2O:SiO2 is any value selected from 0.30∶1, 0.35∶1, 0.40∶1, 0.45∶1, 0.50∶1, 0.55∶1, and 0.60∶1, or any value between any two of them.

[0034] Preferably, in step c), the initial gel B has the following component molar ratio:

[0035] M∶SiO2=(0.05-0.50)∶1,

[0036] R2∶SiO2=(0.05-0.50)∶1,

[0037] H2O∶SiO2=(5.0-30.0)∶1.

[0038] More preferably, in step c), the initial gel B has the following component molar ratio:

[0039] M∶SiO2=(0.10-0.40)∶1,

[0040] R2∶SiO2=(0.10-0.40)∶1,

[0041] H2O∶SiO2=(10.0-25.0)∶1.

[0042] Optionally, in step d), the precursor I contains 0.8-12% of the mass of SiO2 contained in the initial gel B.

[0043] Optionally, in step d), the mass of SiO2 contained in the precursor I is a percentage of the mass of SiO2 contained in the initial gel B, independently selected from any value or a range between 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, and 12%.

[0044] Preferably, in step d), the precursor I contains 1-10% of the mass of SiO2 contained in the initial gel B.

[0045] Optionally, in step f), the niobium source is at least one selected from niobium ethoxide and niobium pentachloride.

[0046] Optionally, in step f), the molar ratio of the niobium source to the SiO2 contained in the precursor II is 1:(40-160), wherein the number of moles of the niobium source is calculated based on the number of moles of Nb2O5 contained.

[0047] Optionally, in step f), the molar ratio of the niobium source to the SiO2 contained in the precursor II is any value or a range between any two of the following: 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, 1:105, 1:110, 1:115, 1:120, 1:125, 1:130, 1:135, 1:140, 1:145, 1:150, 1:155, and 1:160.

[0048] Preferably, in step f), the molar ratio of the niobium source to the SiO2 contained in the precursor II is 1:(50-150), wherein the number of moles of the niobium source is calculated based on the number of moles of Nb2O5 contained.

[0049] Optionally, in step b), the temperature of the first crystallization is any value or a range between any two of 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, and 170°C, and the time of the first crystallization is any value or a range between any two of 0.5h, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, and 20h.

[0050] Preferably, in step b), the first crystallization includes crystallization at 90-160°C for 0.5-18 hours.

[0051] More preferably, in step b), the first crystallization includes crystallization at 100-140°C for 2-14 hours.

[0052] Optionally, in step e), the temperature of the second crystallization is any value or a range between any two of 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and 190°C, and the time of the second crystallization is any value or a range between any two of 2h, 4h, 6h, 12h, 18h, 24h, 30h, 36h, 42h, 48h, 54h, 60h, and 66h.

[0053] Preferably, in step e), the second crystallization includes crystallization at 120-180°C for 2-60 hours.

[0054] More preferably, in step e), the second crystallization includes crystallization at 120-160°C for 12-48 hours.

[0055] Optionally, in step f), the temperature of the third crystallization is any value or a range between any two of 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and 190°C, and the time of the third crystallization is any value or a range between any two of 42h, 48h, 54h, 60h, 66h, 72h, 78h, 84h, 90h, 96h, 102h, 108h, 114h, 120h, and 126h.

[0056] Preferably, in step f), the third crystallization includes crystallization at 120-180°C for 48-120 hours.

[0057] More preferably, in step f), the third crystallization includes crystallization at 120-160°C for 60-96 hours.

[0058] Optionally, the first crystallization, the second crystallization, and the third crystallization are carried out independently under autogenous pressure.

[0059] Optionally, the first crystallization, the second crystallization, and the third crystallization may be carried out independently under static, dynamic, or a combination of both conditions.

[0060] In one implementation, the first crystallization is performed dynamically.

[0061] In one embodiment, the second crystallization and the third crystallization are performed at the same temperature.

[0062] Optionally, in steps a) and c), the first silicon source and the second silicon source may be the same or different, and are independently selected from at least one of silica sol, silica gel, silica gel for chromatography, fumed silica, methyl orthosilicate and tetraethyl orthosilicate.

[0063] Preferably, in step a), the first silicon source is selected from tetraethyl orthosilicate and silica sol.

[0064] Preferably, in step c), the second silicon source is selected from tetraethyl orthosilicate, silica sol, silica fume, and silica gel for chromatography columns.

[0065] Optionally, in steps a) and c), the organic template agent R1 and the organic template agent R2 may be the same or different, and are independently selected from at least one of N,N-dimethyl-3,5-dimethylpiperidine, N,N-dimethyl-2,6-dimethylpiperidine, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, triethylhydroxymethylammonium hydroxide, triethylhydroxyethylammonium hydroxide, triethylcyclohexylammonium hydroxide, and triethyladamantylammonium hydroxide.

[0066] Preferably, in steps a) and c), the organic template agent R1 and the organic template agent R2 are independently selected from N,N-dimethyl-2,6-dimethylpiperidine, tetraethylammonium hydroxide, methyltriethylammonium hydroxide and triethylhydroxymethylammonium hydroxide.

[0067] Optionally, in step c), the cation of the inorganic salt M is selected from Li + Na + K + Ca2 + and Mg 2+ At least one of the following, wherein the anion is selected from Cl-, Br-, etc. - SO4 2- and NO3 - At least one of them.

[0068] Optionally, in step c), the inorganic salt M is selected from at least one of lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, lithium bromide, sodium bromide, potassium bromide, calcium bromide, magnesium bromide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, lithium nitrate, sodium nitrate, potassium nitrate, calcium nitrate, and magnesium nitrate.

[0069] Preferably, in step c), the inorganic salt M is at least one selected from lithium chloride, sodium chloride, magnesium chloride, lithium bromide, sodium bromide, magnesium bromide, lithium sulfate, sodium sulfate, magnesium sulfate, lithium nitrate, sodium nitrate, and magnesium nitrate.

[0070] According to another aspect of this application, an Nb-Beta molecular sieve is provided, which is prepared by the method described above.

[0071] Optionally, the Nb-Beta molecular sieve includes micropores with a specific surface area of ​​420-660 m². 2 / g, the volume of the micropores is 0.14-0.30 cm³. 3 / g.

[0072] Optionally, the particle size of the Nb-Beta molecular sieve is 100-500 nm.

[0073] According to another aspect of this application, a catalyst is provided, said catalyst comprising the Nb-Beta molecular sieve as described above.

[0074] According to another aspect of this application, a method for preparing the above-mentioned catalyst is provided, the method comprising: calcining the Nb-Beta molecular sieve at 550-660°C for 2-10 hours.

[0075] According to another aspect of this application, the Nb-Beta molecular sieve as described above or the catalyst as described above is provided as a catalyst in, for example, the reaction of glucose dehydration to prepare hydroxymethylfurfural.

[0076] The beneficial effects that this application can produce include:

[0077] 1) The method for preparing Nb-Beta molecular sieves provided in this application involves direct synthesis by adding a liquid directing agent to the gel system used for synthesis and introducing alkali metal / alkaline earth metal ions. The process is simple, the crystallization speed is fast, and the product has high crystallinity.

[0078] 2) The method for preparing Nb-Beta molecular sieves provided in this application does not require the use of fluoride ions as a mineralizing agent, resulting in less environmental pollution and higher safety.

[0079] 3) The Nb-Beta molecular sieve prepared in this application has an adjustable Nb content between 0-8 wt%. Attached Figure Description

[0080] Figure 1 The X-ray diffraction (XRD) spectra of sample 1, control sample 2, and control sample 3 are shown.

[0081] Figure 2 This is a scanning electron microscope (SEM) image of sample 1.

[0082] Figure 3 The image shows the FT-IR spectrum of sample 1. Detailed Implementation

[0083] As mentioned above, the purpose of this application is to provide a method for preparing Nb-Beta molecular sieves. This method involves adding a liquid directing agent to a gel system used for synthesis and introducing alkali metal / alkaline earth metal cations, while controlling the timing of the addition of the niobium source during crystallization, thereby directly synthesizing Nb-Beta molecular sieves.

[0084] The present application is further described below with reference to embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0085] Experimental methods not specified in the following examples are generally performed under standard conditions or as recommended by the manufacturer.

[0086] Unless otherwise specified, all raw materials used in this application were purchased commercially and used directly without special treatment.

[0087] The instruments and methods used for analysis in the embodiments of this application are as follows:

[0088] X-ray powder diffraction (XRD) phase analysis was performed using an X'Pert PRO X-ray diffractometer from PANalytical (Netherlands), with a Cu target, Kα radiation source (λ = 0.15418 nm), voltage 40 kV, and current 40 mA. The relative crystallinity of the samples was calculated based on the peak areas of the main characteristic diffraction peaks (2θ = 7.8°, 22.6°) in the XRD pattern. The specific algorithm is as follows: First, the sample with the largest sum of peak areas (sample 1) was selected as the standard sample, and its crystallinity was set to 100%. The relative crystallinity of the remaining samples was then calculated as a percentage of the sum of the main characteristic diffraction peak areas of the sample compared to the aforementioned standard sample.

[0089] Elemental composition was determined using a Philips Magix 2424 X-ray fluorescence analyzer (XRF).

[0090] Scanning electron microscopy (SEM) tests were performed using a Hitachi SU8020 field emission scanning electron microscope with an accelerating voltage of 2kV.

[0091] The specific surface area and pore size distribution of the samples were determined using an ASAP 2020 physical adsorption analyzer from Micromeritics, USA. Before analysis, the samples were pretreated by vacuum heating at 350℃ for 6 h, and the free volume of the sample tube was measured using He as the medium. During analysis, nitrogen was used as the adsorbate gas, and physical adsorption and desorption were measured at liquid nitrogen temperature (77 K). The specific surface area of ​​the material was determined using the BET formula. The total pore volume of the material was calculated using the amount of N2 adsorbed at a relative pressure (P / P0) of 0.99. The micropore specific surface area and micropore volume were calculated using the t-plot method. In the calculations, the cross-sectional area of ​​the N2 molecule was taken as 0.162 nm. 2 .

[0092] In-situ diffuse reflectance Fourier transform infrared (FT-IR) spectra were acquired using a Bruker Tensor 37. The sample was placed in a diffuse reflectance cell to acquire the diffuse infrared signal. To eliminate water interference with the spectra, the sample was dried at 450 °C under a nitrogen atmosphere (50 mL / min) for 1 h. Spectra were then acquired at 200 °C under a nitrogen atmosphere.

[0093] Example 1

[0094] The proportions of raw materials and crystallization conditions are shown in Table 1. The sample preparation process is as follows:

[0095] 31.98 g of triethylmethylammonium hydroxide (25% aqueous solution) was added to 3.01 g of deionized water, and then 20.83 g of tetraethyl orthosilicate (TEOS, SiO2 content 28.8 wt%) was added. The mixture was stirred overnight at room temperature to obtain initial gel A.

[0096] The initial gel A obtained above was transferred to a stainless steel reactor and crystallized by rotation at 120°C and autogenous pressure for 12 hours to obtain precursor I.

[0097] Add 15.99g of triethylmethylammonium hydroxide and 0.88g of sodium chloride to 7.45g of deionized water and stir until dissolved and clear. Then add 22.06g of silica sol (SiO2 solid content of 27.2wt%) and stir for 0.5h to form initial gel B. Then add 5.58g of precursor I and continue stirring for 0.5h to obtain precursor II.

[0098] The precursor II obtained above was transferred to a stainless steel reactor and crystallized by rotation at 140°C and autogenous pressure for 24 hours. The resulting crystallized mixture was then cooled to room temperature.

[0099] Add 0.35g of niobium ethanol to the crystallization mixture, stir until homogeneous, then seal the stainless steel reactor and continue to crystallize at 140℃ and autogenous pressure for 120h.

[0100] After crystallization, the solid product was centrifuged, washed with deionized water until neutral, and then dried overnight at 100°C. The resulting sample was designated as Sample 1.

[0101] The X-ray powder diffraction (XRD) pattern of sample 1 is shown below. Figure 1 As shown, this indicates that the sample is a molecular sieve with a *BEA framework structure. After calcining sample 1 to remove the template agent, its specific surface area and pore volume were measured. The microporous specific surface area and microporous volume of this sample were calculated using the t-plot method to be 476 m². 2 ·g -1 and 0.18cm 3 ·g -1 Elemental analysis showed that the Nb content in sample 1 on a dry molecular sieve basis was 5.8 wt%. A scanning electron microscope (SEM) image of sample 1 is shown below. Figure 2 As shown, the sample exhibits a plate-like morphology composed of numerous small particles with a size of 200 nm to 500 nm. Figure 3 The infrared diffuse reflectance spectrum (FT-IR) of sample 1 is shown, visible at 960 cm⁻¹. -1A distinct absorption peak appears at this point, indicating that heteroatoms have been successfully introduced into the zeolite framework.

[0102] Example 2-20

[0103] The proportions of raw materials and crystallization conditions are shown in Table 1. Samples were prepared according to the process described in Example 1, and the resulting samples were designated as Samples 2-20.

[0104] XRD and XRF analyses were performed on the above samples. The results showed that samples 2-20 prepared in Examples 2-20 were all high-purity, high-crystallinity Nb-Beta molecular sieves, with Nb2O5 content in the dry molecular sieve basis ranging from 2-8 wt%, and the sample morphology was similar to that of sample 1 prepared in Example 1.

[0105] Comparative Example 1

[0106] Samples were prepared according to the procedure in Example 1, with the difference that initial gel A was not crystallized; after stirring overnight at room temperature, the same amount as in Example 1 was directly added to initial gel B, and the subsequent process was the same as in Example 1. After synthesis, the synthesized system was found to be a clear liquid, and centrifugation under the same conditions as in Example 1 did not yield a solid product. The results indicate that without the first crystallization step, initial gel A cannot obtain Beta zeolite structures / structural units to serve as nuclei for subsequent zeolite formation.

[0107] Comparative Example 2

[0108] Samples were prepared according to the procedure in Example 1, except that inorganic salt M was not added. The resulting sample was designated as Comparative Sample 2. The results of XRD analysis of Comparative Sample 2 are shown below. Figure 1 The results indicate that the sample possesses a BEA* topology, but its crystallinity is quite low, with a relative crystallinity of only about 33% compared to sample 1, indicating that it still contains a large amount of amorphous material. These results confirm that the assistance of inorganic salts is an important factor in the successful synthesis of Nb-Beta molecular sieves.

[0109] Comparative Example 3

[0110] Samples were prepared according to the procedure in Example 1, except that the niobium source was added directly during the preparation of precursor II, instead of adding it after crystallization of precursor II. In this case, the subsequent crystallization temperature of precursor II with added niobium source was the same as in Example 1, and its crystallization time was the sum of the crystallization time of precursor II in Example 1 and the crystallization time of the crystallization mixture with added niobium source. The resulting sample was designated as comparative sample 3. The results of XRD analysis of comparative sample 3 (…) Figure 1The results indicate that this sample possesses a BEA* topology, but its crystallinity is significantly lower than that of sample 1, with a relative crystallinity of only 65% ​​compared to sample 1. These results suggest that the timing of niobium source addition is a crucial factor in the formation of the BEA* zeolite framework.

[0111] Table 1. Raw material types, ratios, precursor addition amounts, and crystallization conditions for samples 1-20

[0112]

[0113]

[0114] The above descriptions are merely several embodiments of this application and are not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, these embodiments are not intended to limit this application. Any modifications or alterations made by those skilled in the art using the disclosed technical content without departing from the scope of the technical solution of this application are equivalent to equivalent implementations and fall within the scope of the technical solution of this application.

Claims

1. A method for preparing Nb-Beta molecular sieves, characterized in that, Includes the following steps: a) Mix the first silicon source, organic template agent R1, and water to obtain the initial gel A; b) The initial gel A is subjected to a first crystallization, which includes crystallization at 80-170°C for 0.5-20 h to obtain precursor I; c) Mix the second silicon source, inorganic salt M, organic template agent R2 and water to obtain the initial gel B; d) The precursor I is added to the initial gel B to obtain precursor II; e) The precursor II is subjected to a second crystallization, the second crystallization comprising crystallization at 110-190°C for 2-66 h to obtain a crystallized mixture; f) Adding a niobium source to the crystallization mixture to perform a third crystallization, the third crystallization comprising crystallization at 110-190°C for 42-126 h; g) Separate, wash, and dry the obtained solid product to obtain the Nb-Beta molecular sieve; in, In step a), the initial gel A has the following component molar ratio: R1∶SiO2=(0.10-1.10)∶1, H2O∶SiO2=(2.0-21.0)∶1; In step c), the initial gel B has the following component molar ratio: M∶SiO2=(0.05-0.60)∶1, R2∶SiO2=(0.05-0.60)∶1, H2O∶SiO2=(5.0-35.0)∶1; The number of moles of the first silicon source and the second silicon source is based on the number of moles of SiO2 each contains, the number of moles of the organic template agent R1 is based on the number of moles of R1 itself, the number of moles of the organic template agent R2 is based on the number of moles of R2 itself, and the number of moles of the inorganic salt M is based on the number of moles of M itself. The organic template agent R1 and the organic template agent R2 may be the same or different, and are independently selected from at least one of N,N-dimethyl-3,5-dimethylpiperidine, N,N-dimethyl-2,6-dimethylpiperidine, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, methyltriethylammonium hydroxide, triethylhydroxymethylammonium hydroxide, triethylhydroxyethylammonium hydroxide, triethylcyclohexylammonium hydroxide, and triethyladamantylammonium hydroxide; The cation of the inorganic salt M is selected from Li + Na + K + Ca 2+ and Mg 2+ At least one of the following, wherein the anion is selected from Cl. - ,Br - SO4 2- and NO3 - At least one of them.

2. The method according to claim 1, characterized in that, In step d), the precursor I contains 0.8-12% of the mass of SiO2 contained in the initial gel B.

3. The method according to claim 1, characterized in that, In step f), the niobium source is at least one selected from niobium ethanol and niobium pentachloride.

4. The method according to claim 1, characterized in that, In step f), the molar ratio of the niobium source to the SiO2 contained in the precursor II is 1:(40-160), wherein the number of moles of the niobium source is calculated based on the number of moles of Nb2O5 contained.

5. The method according to claim 1, characterized in that, In step b), the first crystallization includes crystallization at 100-140°C for 2-14 h.

6. The method according to claim 1, characterized in that, In step e), the second crystallization includes crystallization at 120-160°C for 12-48 h.

7. The method according to claim 1, characterized in that, In step f), the third crystallization includes crystallization at 120-160°C for 60-96 h.

8. The method according to claim 1, characterized in that, In steps a) and c), the first silicon source and the second silicon source may be the same or different, and are independently selected from at least one of silica sol, silica gel, silica gel for chromatography columns, fumed silica, methyl orthosilicate and tetraethyl orthosilicate.

9. An Nb-Beta molecular sieve, characterized in that, Prepared by the method according to any one of claims 1 to 8.

10. The Nb-Beta molecular sieve according to claim 9, characterized in that, The Nb-Beta molecular sieve comprises micropores with a specific surface area of ​​420-660 m². 2 / g, the volume of the micropores is 0.14-0.30 cm³. 3 / g.

11. The Nb-Beta molecular sieve according to claim 9, characterized in that, The particle size of the Nb-Beta molecular sieve is 100-500 nm.

12. A catalyst, characterized in that, Including the Nb-Beta molecular sieve according to claim 9.

13. The application of the Nb-Beta molecular sieve according to claim 9 or the catalyst according to claim 12 as a catalyst in the dehydration of glucose to prepare hydroxymethylfurfural.

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