A hierarchical pore pure silicon molecular sieve, a preparation method and application thereof

Abstract

The present disclosure relates to a hierarchical pore all-silica molecular sieve, a preparation method and application thereof. In the hierarchical pore all-silica molecular sieve 1 In the peak separation result of the spectrum peak in the 1-6 ppm chemical shift range of the H MAS NMR spectrum: the peak area of the spectrum peak in the 1.7-1.9 ppm chemical shift range is recorded as A1, the peak area of the spectrum peak in the 2.0-2.2 ppm chemical shift range is recorded as A2, the peak area of the spectrum peak in the 3.1-3.3 ppm chemical shift range is recorded as A3, the peak area of the spectrum peak in the 4.4-4.6 ppm chemical shift range is recorded as A4, and the sum of the A1-A4 peak areas is recorded as A0; X 1‑1 =A1 / A0×100%, X 1‑2 =A2 / A0×100%, X 1‑3 =A3 / A0×100%, X 1‑4 =A4 / A0×100%, X 1‑1 is 5-20%, X 1‑2 is 12-30%, X 1‑3 is 35-60%, X 1‑4 is 12-32%. The present disclosure can effectively improve the selectivity of caprolactam and the service life of the molecular sieve in the cyclohexanone oxime gas-phase Beckmann rearrangement reaction.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of all-silica molecular sieve preparation, in particular to a hierarchical porous pure-silica molecular sieve, a preparation method and application thereof. BACKGROUND

[0002] In the 1880s, German chemist Ernst Otto Beckmann discovered that aliphatic or aromatic ketoxime molecules could undergo intramolecular rearrangement to generate corresponding amide molecules under the action of an acid catalyst, and named this process as Beckmann rearrangement. Beckmann rearrangement is a stereospecific reaction, and the group undergoing migration in the ketoxime molecule is anti to the leaving hydroxyl group, and the configuration of the carbon atom remains unchanged during the migration process. The most successful commercial application of Beckmann rearrangement is the rearrangement of cyclohexanone oxime (CHO) to caprolactam (CPL). CPL is an important monomer for the production of nylon-6 and polyamide engineering plastics, and with the rapid development of the automobile, electronics and textile industries, the global caprolactam production capacity reached 8.8 million tons in 2021.

[0003] Currently, more than 95% of CPL is prepared by CHO liquid Beckmann rearrangement reaction, using concentrated sulfuric acid (or fuming sulfuric acid) as catalyst and solvent, which has serious problems of equipment corrosion and environmental pollution, etc. After the reaction is completed, liquid ammonia is used to neutralize the waste sulfuric acid, generating a large amount of low-value ammonium sulfate by-product (1.9 t of ammonium sulfate / t of CPL), resulting in poor technical and economic performance of this route. Compared with the traditional liquid phase method, the CHO gas phase Beckmann rearrangement process avoids the use of ammonia and fuming sulfuric acid from the source, with an atomic utilization rate of 100%, and is an environmentally friendly green production process of CPL. At present, a variety of solid catalysts including molecular sieves, metal oxides and mesoporous materials have been applied to the research of CHO gas phase Beckmann rearrangement reaction, among which the all-silica MFI topological structure Silicalite-1 molecular sieve shows excellent catalytic performance. Japan Sumitomo and China Petrochemical have successively carried out industrial demonstration tests of CHO gas phase Beckmann rearrangement using Silicalite-1 molecular sieve catalyst.

[0004] However, the CHO gas phase Beckmann rearrangement route has two difficult problems of poor product CPL selectivity and short single-pass life of the catalyst, which affects the technical and economic performance and the continuous stability of operation, causing the subsequent large-scale industrial scaling-up and commercialization process to be extremely slow. This is because the MFI structure micropore size is small, which is close to the size of the reactant and product molecules, resulting in slow diffusion of guest molecules in the confined channels of the molecular sieve, significantly prolonging the residence time in the crystal, thus exacerbating the generation of by-products and carbon deposition blocking the channels.

[0005] Therefore, people try to improve the diffusion performance of molecular sieves by constructing hierarchical pore structures to achieve the purpose of improving the selectivity of the reaction and the life of the catalyst. However, when the synthesized hierarchical pore Silicalite-1 molecular sieve is used in the gas phase Beckmann rearrangement reaction of cyclohexanone oxime, the improvement effect of the selectivity of caprolactam and the life of the catalyst is not ideal. SUMMARY

[0006] The purpose of the present disclosure is to provide a hierarchical pore pure silicon molecular sieve and a preparation method and application thereof, which can effectively improve the selectivity of caprolactam and the life of the molecular sieve in the gas phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a hierarchical pore all-silicon molecular sieve, which has the following 1 H MAS NMR characteristics:

[0008] In the hierarchical pore all-silicon molecular sieve 1 In the peak separation result of the spectrum peak in the chemical shift range of 1-6 ppm of the H MAS NMR spectrum, the peak area of the spectrum peak in the chemical shift range of 1.7-1.9 ppm is recorded as A1, the peak area of the spectrum peak in the chemical shift range of 2.0-2.2 ppm is recorded as A2, the peak area of the spectrum peak in the chemical shift range of 3.1-3.3 ppm is recorded as A3, the peak area of the spectrum peak in the chemical shift range of 4.4-4.6 ppm is recorded as A4, and the sum of the peak areas of A1-A4 is recorded as A0;

[0009] X as defined in the following formula (1-1) 1-1 is any value between 5-20%:

[0010] X 1-1 =A1 / A0x100% formula (1-1);

[0011] X as defined in the following formula (1-2) 1-2 is any value between 12-30%:

[0012] X 1-2 =A2 / A0x100% formula (1-2);

[0013] X as defined in the following formula (1-3) 1-3 is any value between 35-60%:

[0014] X 1-3 =A3 / A0x100% formula (1-3);

[0015] X as defined in the following formula (1-4) 1-4 is any value between 12-32%:

[0016] X1-4 = A4 / A0 x 100% Equation (1-4).

[0017] Optionally, the X 1-1 is any value between 11-19%, X 1-2 is any value between 16-27%, X 1-3 is any value between 40-50%, X 1-4 is any value between 11-25%.

[0018] Optionally, the nitrogen adsorption / desorption curve of the multi-level pore all-silicon molecular sieve has a double hysteresis loop structure;

[0019] Preferably, the multi-level pore all-silicon molecular sieve has a first hysteresis loop at a first P / P0 of 0.1-0.4, and the adsorption amount of the first hysteresis loop accounts for 10-25% of the total adsorption amount;

[0020] The multi-level pore all-silicon molecular sieve has a second hysteresis loop at a second P / P0 of 0.5-0.9, and the adsorption amount of the second hysteresis loop accounts for 30-40% of the total adsorption amount.

[0021] Optionally, the multi-level pore all-silicon molecular sieve has a hollow structure in the crystal; the size of the hollow structure is 50-200 nm;

[0022] Preferably, the volume of the hollow structure accounts for 50-99% of the total volume of the molecular sieve, and more preferably 65-95%;

[0023] Optionally, the shape of the hollow structure is selected from one or more of a sphere, an ellipsoid, a cube, and an irregular ellipsoid.

[0024] Optionally, the multi-level pore all-silicon molecular sieve has the following FT-IR characteristics:

[0025] In the FT-IR spectrum of the multi-level pore all-silicon molecular sieve, the peak in the 3200-3800 cm -1 In the peak separation result of the peak in the 3200-3800 cm -1 The peak area of the peak in the 3660-3720 cm -1 The peak area of the peak in the 3400-3500 cm -1 The peak area of the peak in the 3400-3500 cm

[0026] X 2-1 is any value between 5-25%:

[0027] X2-1 = B1 / B0 x 100% Equation (2-1);

[0028] X as defined by Equation (2-2) below 2-2 is any value between 15 and 35%:

[0029] X 2-2 = B2 / B0 x 100% Equation (2-2);

[0030] X as defined by Equation (2-3) below 2-3 is any value between 35 and 75%:

[0031] X 2-3 = B3 / B0 x 100% Equation (2-3).

[0032] Optionally, the hierarchical all-silica molecular sieve has 29 Si MAS NMR characteristics:

[0033] The peak area of the spectrum peak in the range of -102 to -104 ppm of the chemical shift of the hierarchical all-silica molecular sieve is denoted as Q 3 , and the peak area of the spectrum peak in the range of -112 to -114 ppm of the chemical shift is denoted as Q 4 X3 as defined by Equation (3) below is any value between 1 and 8%:

[0034] X3 = Q 3 / Q 4 x 100% Equation (3);

[0035] Preferably, X3 is any value between 2 and 6%.

[0036] Optionally, the hierarchical all-silica molecular sieve comprises molecular sieve particles composed of a single crystal grain, and / or molecular sieve particles composed of a plurality of crystal grains aggregated together;

[0037] Preferably, the average particle size of the molecular sieve particles is 0.1 to 0.5 μm, preferably 0.15 to 0.35 μm; the BET specific surface area is 260 to 500 m 2 / g, preferably 280 to 460 m 2 / g; the micropore specific surface area is 220 to 380 m 2 / g, preferably 250 to 360 m 2 / g; the total pore volume is 0.1 to 0.6 cm 3 / g, preferably 0.2 to 0.5 cm 3 / g; the micropore volume is 0.05 to 0.3 cm 3 / g, preferably 0.08 to 0.28 cm 3 / g; the mesopore volume is 0.07-0.4 cm 3 / g, preferably 0.1-0.26 cm 3 / g.

[0038] The second aspect of the present disclosure provides a method for preparing a hierarchical porous all-silicon molecular sieve, comprising the following steps:

[0039] S1, mixing a first silicon source, a first template agent and water to obtain a reaction mixture;

[0040] S2, sequentially performing a first hydrothermal crystallization treatment and a first calcination treatment on the reaction mixture to obtain an intermediate product;

[0041] S3, mixing the intermediate product, a second silicon source, a second template agent and water, and then sequentially performing a second hydrothermal crystallization treatment and a second calcination treatment.

[0042] Optionally, in step S1, the molar ratio of the first silicon source: the first template agent: water is 1:(0.01-2):(1-50); preferably 1:(0.02-0.3):(10-30);

[0043] Optionally, in step S3, the weight ratio of the intermediate product: the second silicon source: the second template agent: water is 1:(0.2-10):(0.1-5):(1-15); preferably 1:(0.5-8):(0.2-3):(2-10).

[0044] Optionally, the first silicon source in step S1 and the second silicon source in step S3 are each independently selected from at least one of an organic silicon grease, a solid silica gel, white carbon black and a silica sol; preferably, the first silicon source and the second silicon source are each independently selected from at least one of an organic silicon grease, a solid silica gel and white carbon black;

[0045] Further preferably, the first silicon source and the second silicon source are each independently selected from an organic silicon grease, and the general formula of the organic silicon grease is shown in the following formula (A):

[0046]

[0047] wherein R a , R b , R c , R d are each independently selected from an alkyl group having 1-6 carbon atoms, which is a branched or straight-chain alkyl group; preferably, R a , R b , R c , R d are each independently selected from a straight-chain alkyl group having 1-4 carbon atoms or a branched alkyl group having 3-4 carbon atoms; further preferably, the Ra R1, R2, R3and R4are each independently selected from one or more of a group consisting of a linear alkyl group having 1-4 carbon atoms and a branched alkyl group having 3-4 carbon atoms; further preferably, R1, R2, R3and R4are each independently selected from one or more of a group consisting of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group; b R1, R2, R3and R4are each independently selected from one or more of a group consisting of a linear alkyl group having 1-4 carbon atoms and a branched alkyl group having 3-4 carbon atoms; further preferably, R1, R2, R3and R4are each independently selected from one or more of a group consisting of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group; c R1, R2, R3and R4are each independently selected from one or more of a group consisting of a linear alkyl group having 1-4 carbon atoms and a branched alkyl group having 3-4 carbon atoms; further preferably, R1, R2, R3and R4are each independently selected from one or more of a group consisting of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group; d R1, R2, R3and R4are each independently selected from one or more of a group consisting of a linear alkyl group having 1-4 carbon atoms and a branched alkyl group having 3-4 carbon atoms; further preferably, R1, R2, R3and R4are each independently selected from one or more of a group consisting of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group;

[0048] Optionally, the first template agent in step S1 and the second template agent in step S3 are each independently selected from one or more of a group consisting of a quaternary ammonium base, an aliphatic amine and an aliphatic alcohol amine;

[0049] Further preferably, the first template agent and the second template agent are each independently selected from one or more of a group consisting of a quaternary ammonium base having a structure shown in the following formula (B):

[0050] R1, R2, R3and R4are each independently selected from one or more of a group consisting of a linear alkyl group having 1-4 carbon atoms and a branched alkyl group having 3-4 carbon atoms; further preferably, R1, R2, R3and R4are each independently selected from one or more of a group consisting of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group;

[0051] Further preferably, the first template agent and the second template agent are each independently selected from one or more of a group consisting of a quaternary ammonium base having a structure shown in the following formula (B):

[0052] Optionally, the silicon source is an organosilicon grease, and step S1 comprises:

[0053] mixing the first silicon source, the first template agent and water to obtain a hydrolytic sol of silicon by hydrolytic alcohol-removing treatment;

[0054] Preferably, the conditions of the hydrolytic alcohol-removing treatment comprise stirring hydrolysis at 40-90°C for 6-12h; preferably, stirring hydrolysis at 60-85°C for 8-10h.

[0055] Optionally, the conditions of the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 are each independently selected from one or more of a group consisting of a hydrothermal crystallization temperature of 130-200°C, a hydrothermal crystallization time of 6-168h, and an autogenous pressure; preferably, a hydrothermal crystallization temperature of 150-180°C, a hydrothermal crystallization time of 24-72h, and an autogenous pressure;

[0056] The conditions of the first calcination treatment in step S2 and the second calcination treatment in step S3 each independently include a calcination temperature of 300-700°C and a calcination time of 1-16h; preferably, the calcination temperature is 400-600°C and the calcination time is 2-5h.

[0057] The third aspect of the present disclosure provides a hierarchical-pore all-silicon molecular sieve prepared by the method according to the second aspect of the present disclosure.

[0058] The fourth aspect of the present disclosure provides an application of the hierarchical-pore all-silicon molecular sieve according to the first aspect and the third aspect of the present disclosure in a catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0059] By the above technical solution, the present disclosure provides a hierarchical-pore all-silicon molecular sieve, a preparation method and an application thereof. The hierarchical-pore all-silicon molecular sieve has a large reaction space and abundant active centers of nest-like silicon hydroxyl groups, and contains a small amount of isolated silicon hydroxyl groups and a large amount of hydrogen-bonded silicon hydroxyl groups. The catalytic activity and the catalytic stability of the hierarchical-pore all-silicon molecular sieve are significantly improved, and in a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the conversion rate of cyclohexanone oxime, the selectivity of caprolactam and the service life of the catalyst can be effectively improved.

[0060] Other features and advantages of the present disclosure will be described in detail in the following specific embodiments section. BRIEF DESCRIPTION OF DRAWINGS

[0061] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, and together with the following specific embodiments, serve to explain the present disclosure but do not constitute a limitation thereof. In the drawings:

[0062] Figure 1 TEM electron micrograph of the hierarchical-pore all-silicon molecular sieve prepared for Example 1 of the present disclosure 1 H MAS NMR spectrum

[0063] Figure 2 TEM electron micrograph of the hierarchical-pore all-silicon molecular sieve prepared for Example 1 of the present disclosure

[0064] Figure 3 BET nitrogen adsorption-desorption curve of the hierarchical-pore all-silicon molecular sieve prepared for Example 1 of the present disclosure

[0065] Figure 4 FT-IR spectrum of the hierarchical-pore all-silicon molecular sieve prepared for Example 1 of the present disclosure

[0066] Figure 5 TEM electron micrograph of the intermediate product prepared for Example 1 of the present disclosure

[0067] Figure 6XRD spectrum of the hierarchical porous all-silicon molecular sieve prepared for Example 1 of the present disclosure 29 Si MAS NMR spectrum;

[0068] Figure 7 XRD spectrum of the hierarchical porous all-silicon molecular sieve prepared for Example 1 of the present disclosure

[0069] Figure 8 SEM electron micrograph of the hierarchical porous all-silicon molecular sieve prepared for Example 1 of the present disclosure

[0070] Figure 9 BET nitrogen adsorption-desorption curve of the molecular sieve prepared for Comparative Example 2 of the present disclosure

[0071] Figure 10 TEM electron micrograph of the molecular sieve prepared for Comparative Example 2 of the present disclosure

[0072] Figure 11 XRD spectrum of the hierarchical porous all-silicon molecular sieve prepared for Example 9 of the present disclosure

[0073] Figure 12 XRD spectrum of the hierarchical porous all-silicon molecular sieve prepared for Example 10 of the present disclosure. DETAILED DESCRIPTION

[0074] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0075] The first aspect of the present disclosure provides a hierarchical porous all-silicon molecular sieve, which has the following 1 H MAS NMR characteristics:

[0076] In the 1-6 ppm chemical shift range of the spectrum peak of the H MAS NMR spectrum of the hierarchical porous all-silicon molecular sieve: 1 In the peak separation result of the spectrum peak in the 1-6 ppm chemical shift range of the H MAS NMR spectrum: the peak area of the spectrum peak in the 1.7-1.9 ppm chemical shift range is recorded as A1, the peak area of the spectrum peak in the 2.0-2.2 ppm chemical shift range is recorded as A2, the peak area of the spectrum peak in the 3.1-3.3 ppm chemical shift range is recorded as A3, the peak area of the spectrum peak in the 4.4-4.6 ppm chemical shift range is recorded as A4, and the sum of the peak areas of A1-A4 is recorded as A0;

[0077] X as defined in the following formula (1-1) 1-1 is any value between 5-20%:

[0078] X 1-1 = A1 / A0 x 100% formula (1-1);

[0079] X as defined in the following formula (1-2) 1-2 is any value between 12 and 30%:

[0080] X 1-2 = A2 / A0 x 100% formula (1-2);

[0081] X as defined in the following formula (1-3) 1-3 is any value between 35 and 60%:

[0082] X 1-3 = A3 / A0 x 100% formula (1-3);

[0083] X as defined in the following formula (1-4) 1-4 is any value between 12 and 32%:

[0084] X 1-4 = A4 / A0 x 100% formula (1-4).

[0085] The present disclosure provides a hierarchical pore all-silicon molecular sieve, which has large reaction space and abundant nest-like silicon hydroxyl active centers, and contains a small amount of isolated silicon hydroxyl and a large amount of hydrogen-bonded silicon hydroxyl, significantly improving the catalytic activity and catalytic stability of the hierarchical pore all-silicon molecular sieve, and in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the conversion rate of cyclohexanone oxime, the selectivity of caprolactam and the service life of the catalyst can be effectively improved.

[0086] The present disclosure finds that in the hierarchical pore all-silicon molecular sieve 1 In the H MAS NMR spectrum, the peak signal in the chemical shift range of 1.7-1.9 ppm represents the isolated silicon hydroxyl, and the peak signal in the chemical shift range of 2-6 ppm (2.0-2.2 ppm, 3.1-3.3 ppm and 4.4-4.6 ppm, respectively) represents the hydrogen-bonded silicon hydroxyl, and the relationship between the peak area of the above four kinds of silicon hydroxyl spectrum peaks and the total peak area can be used to reflect the catalytic activity and catalytic stability of the hierarchical pore all-silicon molecular sieve.

[0087] In a preferred embodiment, X of the hierarchical pore all-silicon molecular sieve 1-1 is any value between 11 and 19%, X 1-2 is any value between 16 and 27%, X 1-3 is any value between 40 and 50%, X 1-4 is any value between 11 and 25%. The hierarchical pore all-silicon molecular sieve satisfying X 1-1 ~ X 1-4 The hierarchical pore all-silicon molecular sieve with the value range of X

[0088] In one embodiment, the nitrogen adsorption / desorption curve of the multi-level pore all-silicon molecular sieve has a double hysteresis loop structure.

[0089] In one preferred embodiment, the multi-level pore all-silicon molecular sieve has a first hysteresis loop at a first P / P0 of 0.1-0.4, and the adsorption amount of the first hysteresis loop accounts for 10-25% of the total adsorption amount.

[0090] The multi-level pore all-silicon molecular sieve has a second hysteresis loop at a second P / P0 of 0.5-0.9, and the adsorption amount of the second hysteresis loop accounts for 30-40% of the total adsorption amount. The multi-level pore all-silicon molecular sieve of the present disclosure has a hysteresis loop at low pressure and high pressure, respectively, and the double hysteresis loop structure indicates that the multi-level pore all-silicon molecular sieve has a very strong effect of adsorbing guest molecules.

[0091] In one embodiment, the multi-level pore all-silicon molecular sieve has a hollow structure in the crystal; the size of the hollow structure is 50-200 nm. In the present disclosure, the hollow structure in the molecular sieve and its size are obtained by transmission electron microscopy. In the present disclosure, the size of the hollow structure refers to the length between two positions on the cavity wall passing through the center of the hollow structure in the transmission electron microscopy photograph of the molecular sieve; for example, "the size of the hollow structure is 50-200 nm" means that the length between two positions on the cavity wall passing through the center of the hollow structure in the molecular sieve is within the range of 50-200 nm.

[0092] In one preferred embodiment, the volume of all the hollow structures accounts for 50-99% of the total volume of the molecular sieve, and further preferably 65-95%.

[0093] Alternatively, the shape of the hollow structure is selected from one or more of a sphere, an ellipsoid, a cube, and an irregular ellipsoid. In the present disclosure, the volume of the hollow structure in the molecular sieve and the total volume of the molecular sieve are calculated according to the calculation method of the volume of a spherical body after obtaining the size (such as the radius) from the transmission electron microscopy photograph.

[0094] The multi-level pore all-silicon molecular sieve of the present disclosure has a large-size hollow structure inside, and the hollow structure has a large number of silicon hydroxyl active centers, the unique hollow structure provides a large number of independent reaction units, and has a large specific surface area and pore volume; in addition, the large-size hollow structure meets the needs of macromolecular reactions, and the reaction products are more easily flowed out of the catalyst, avoiding the phenomenon of reduced catalytic activity of the catalyst due to pore blockage.

[0095] In one embodiment, the multi-level pore all-silicon molecular sieve has the following FT-IR characteristics:

[0096] In the FT-IR spectrum of the multi-level pore all-silicon molecular sieve, the peak at 3200-3800 cm -1The peak area of the spectrum peak in the wave number range of 3730~3750cm -1 The peak area of the spectrum peak in the wave number range of 3660~3720cm -1 The peak area of the spectrum peak in the wave number range of 3400~3500cm -1 The peak area of the spectrum peak in the wave number range of 3400~3500cm

[0097] X as defined in the following formula (2-1) 2-1 is any value between 5~25%:

[0098] X 2-1 =B1 / B0x100% formula (2-1);

[0099] X as defined in the following formula (2-2) 2-2 is any value between 15~35%:

[0100] X 2-2 =B2 / B0x100% formula (2-2);

[0101] X as defined in the following formula (2-3) 2-3 is any value between 35~75%:

[0102] X 2-3 =B3 / B0x100% formula (2-3).

[0103] In the present disclosure, the hierarchical pore full-silica molecular sieve has abundant nested silicon hydroxyl and ortho silicon hydroxyl, and the spectrum peak near 3740cm -1 represents the end silicon hydroxyl, the spectrum peak near 3690cm -1 represents the ortho silicon hydroxyl spectrum peak, and the spectrum peak near 3500cm -1 represents the nested silicon hydroxyl, and the peak area of the above three spectrum peaks satisfies X 2-1 ~X 2-3 , the hierarchical pore full-silica molecular sieve has excellent catalytic activity and catalytic stability.

[0104] In a preferred embodiment, X 2-1 is any value between 8~22%; X 2-2 is any value between 18~32%; X 2-3 is any value between 38~66%.

[0105] In an embodiment, the hierarchical pore full-silica molecular sieve has the following 29 Si MAS NMR characteristics:

[0106] The peak area of the spectrum peak with chemical shift in the range of -102 to -104 ppm of the hierarchical porous all-silicon molecular sieve is recorded as Q 3 The peak area of the spectrum peak with chemical shift in the range of -112 to -114 ppm is recorded as Q 4 X3 is any value between 1 and 8% as defined in the following formula (3):

[0107] X3 = Q 3 / Q 4 × 100% formula (3).

[0108] In the present disclosure, the spectrum peak with chemical shift around -103 ppm represents a three-coordinated silicon group, and the spectrum peak with chemical shift around -113 ppm represents a four-coordinated silicon group, and the hierarchical porous all-silicon molecular sieve has abundant surface silicon hydroxyl groups.

[0109] In a preferred embodiment, X3 is any value between 2 and 6%.

[0110] In an embodiment, the hierarchical porous all-silicon molecular sieve comprises a molecular sieve particle composed of a single crystal grain, and / or a molecular sieve particle composed of a plurality of crystal grains aggregated together.

[0111] Preferably, the average particle size of the molecular sieve particle is 0.1 to 0.5 μm, preferably 0.15 to 0.35 μm; the BET specific surface area is 260 to 500 m 2 / g, preferably 280 to 460 m 2 / g; the micropore specific surface area is 220 to 380 m 2 / g, preferably 250 to 360 m 2 / g; the total pore volume is 0.1 to 0.6 cm 3 / g, preferably 0.2 to 0.5 cm 3 / g; the micropore volume is 0.05 to 0.3 cm 3 / g, preferably 0.08 to 0.28 cm 3 / g; the mesopore volume is 0.07 to 0.4 cm 3 / g, preferably 0.1 to 0.26 cm 3 / g.

[0112] In a specific embodiment, the configuration of the hierarchical porous all-silicon molecular sieve is selected from one or more of MFI topology, MEL topology, BEA topology and SVR topology; preferably MFI topology.

[0113] The second aspect of the present disclosure provides a method for preparing a hierarchical porous all-silicon molecular sieve, comprising the following steps:

[0114] S1, mixing a first silicon source, a first template agent and water to obtain a reaction mixture;

[0115] S2, sequentially performing a first hydrothermal crystallization treatment and a first calcination treatment on the reaction mixture to obtain an intermediate product;

[0116] S3, mixing the intermediate product, a second silicon source, a second template agent and water, and then sequentially performing a second hydrothermal crystallization treatment and a second calcination treatment.

[0117] The present disclosure provides a method for preparing a hierarchical pore full-silica molecular sieve, which is achieved by destroying the existing structure of the molecular sieve crystal through post-treatment to obtain a hierarchical pore structure. In the post-treatment process, the second template agent is dissociated into a large molecular cation (such as TPA + and a small molecule OH - in an aqueous solution. The small molecule OH - can enter the interior of the microporous molecular sieve, starting from the defect site to dissolve the molecular sieve structure to obtain a silica species, and the large molecular cation stays outside the microporous molecular sieve, guiding the dissolved silica species to re-form a topological structure (such as MFI topological structure), and the continuous dissolution-recrystallization process eventually forms a hierarchical pore full-silica molecular sieve with a large intracrystalline cavity. Moreover, the present disclosure introduces a second silicon source, which can provide sufficient silicon source to form a shell outside the original molecular sieve crystal to protect the internal cavity structure.

[0118] In an embodiment, in step S1, the molar ratio of the first silicon source: the first template agent: water is 1:(0.01-2):(1-50); preferably 1:(0.02-0.3):(10-30).

[0119] In an embodiment, in step S1, the first silicon source is selected from at least one of organic silicon grease, solid silica gel, white carbon black and silica sol; preferably selected from at least one of organic silicon grease, solid silica gel and white carbon black;

[0120] Further preferably, the organic silicon grease has a general structure as shown in the following formula (A):

[0121]

[0122] wherein R a , R b , R c , R d are each independently selected from an alkyl group having 1-6 carbon atoms, which is a branched or straight-chain alkyl group; preferably, R a , R b , R c , R deach independently selected from a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms; further preferably, the R a , R b , R c , R d each independently selected from a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms; further preferably, the R

[0123] In a preferred embodiment, the organosilicon ester is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate and dimethyldiethyl silicate.

[0124] In a specific embodiment, the silicon source is an organosilicon ester, and step S1 comprises:

[0125] mixing the first silicon source, the first template agent and water to obtain a hydrolytic sol of silicon by hydrolytic alcohol-removing treatment;

[0126] Preferably, the conditions of the hydrolytic alcohol-removing treatment comprise stirring hydrolysis at 40 to 90 °C for 6 to 12 h; preferably stirring hydrolysis at 60 to 85 °C for 8 to 10 h.

[0127] In an embodiment, the first template agent in step S1 is selected from at least one of a quaternary ammonium base, an aliphatic amine and an aliphatic alcohol amine.

[0128] Further preferably, the first template agent is selected from at least one of a quaternary ammonium base having a structure shown in the following formula (B):

[0129] R1, R2, R3and R4are each selected from one or more of an alkyl group having 1 to 4 carbon atoms, preferably a linear alkyl group having 1 to 4 carbon atoms and a branched alkyl group having 3 to 4 carbon atoms, further preferably R1, R2, R3and R4are each selected from one or more of a methyl group, an ethyl group, a n-propyl group, an iso-propyl group, a n-butyl group, a sec-butyl group, an iso-butyl group and a tert-butyl group.

[0130] In a preferred embodiment, the first template agent is tetrapropyl ammonium hydroxide or a mixture of tetrapropyl ammonium hydroxide and one or more selected from tetrapropyl ammonium chloride and tetrapropyl ammonium bromide.

[0131] In an embodiment, the conditions of the first hydrothermal crystallization treatment in step S2 comprise a hydrothermal crystallization temperature of 130 to 200 °C, a hydrothermal crystallization time of 6 to 168 h; and a pressure of autogenous pressure.

[0132] The conditions of the first calcination treatment in step S2 comprise a calcination temperature of 300 to 700 °C and a calcination time of 1 to 16 h.

[0133] In a preferred embodiment, the first hydrothermal crystallization treatment in step S2 is performed at a temperature of 150-180°C for 24-72 hours.

[0134] The first calcination treatment in step S2 is performed at a temperature of 400-600°C for 2-5 hours. The molecular sieve prepared according to this embodiment has better catalytic performance.

[0135] In one embodiment, the weight ratio of the intermediate product: the second silicon source: the second template agent: water in step S3 is 1:(0.2-10):(0.1-5):(1-15); preferably 1:(0.5-8):(0.2-3):(2-10).

[0136] In one embodiment, the second silicon source in step S3 is selected from the same range as the first silicon source, which is not repeated here. Preferably, the first silicon source and the second silicon source are the same silicon source reagent.

[0137] In a preferred embodiment, when the second silicon source is an organic silicon source, the hydrolysis and alcohol removal step in step S3 is performed by mixing the intermediate product, the second silicon source, the second template agent, and water; wherein the hydrolysis and alcohol removal treatment is performed by stirring at 40-90°C for 6-12 hours; preferably by stirring at 60-85°C for 8-10 hours.

[0138] In one embodiment, the second template agent in step S3 is selected from the same range as the first template agent, which is not repeated here. Preferably, the first template agent and the second template agent are the same template agent.

[0139] In one embodiment, the second hydrothermal crystallization treatment in step S3 is performed at a temperature of 130-200°C for 6-168 hours at autogenous pressure.

[0140] The second calcination treatment in step S3 is performed at a temperature of 300-700°C for 1-16 hours.

[0141] In a preferred embodiment, the second hydrothermal crystallization treatment in step S3 is performed at a temperature of 150-180°C for 24-72 hours.

[0142] The second calcination treatment in step S3 is performed at a temperature of 400-600°C for 2-5 hours. The molecular sieve prepared according to this embodiment has better catalytic performance.

[0143] The third aspect of the present disclosure provides a hierarchical-pore all-silicon molecular sieve prepared by the method according to the second aspect of the present disclosure.

[0144] The fourth aspect of the present disclosure provides an application of the hierarchical-pore all-silicon molecular sieve according to the first aspect and the third aspect of the present disclosure in a catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0145] In a specific embodiment, the gas-phase Beckmann rearrangement reaction conditions of cyclohexanone oxime include: a reaction temperature of 350-400 ℃, a reaction pressure of 0-0.2 MPa, a molar ratio of nitrogen to cyclohexanone oxime of 0.1-30:1, a cyclohexanone oxime content of 5-50% by weight based on the total amount of cyclohexanone oxime and solvent, and a cyclohexanone oxime weight hourly space velocity of 1-10 h -1 .

[0146] The present disclosure is described in detail below through examples.

[0147] The sample's 1 The H MAS NMR spectrum was obtained on a Varian Infinityplus-400 spectrometer, using a 4mm double-resonance probe, a Ф4mm ZrO2 rotor, a resonance frequency of 400.1MHz, a magic angle rotation speed of 10kHz, a pulse width of 3.57μs, a cycle delay time of 1s, and about 4000 scans.

[0148] The sample's transmission electron microscope (TEM) picture was obtained on a FEI Tecnai G2F20S-TWIN transmission electron microscope. The size of the sample's hollow structure and the volume content of the hollow structure in the total volume of the molecular sieve were obtained by measuring the transmission electron microscope picture, specifically: the wall thickness of the molecular sieve was measured by the TEM picture, the inside of the molecular sieve was regarded as a hollow structure, and then the total volume of the molecular sieve and the volume of the hollow structure were calculated according to the spherical volume calculation formula, so as to obtain the volume fraction of the hollow structure in the total volume of the molecular sieve (the average value was taken after 50 molecular sieve hollow structure volume percentages were tested).

[0149] The sample's BET specific surface area and micropore specific surface area, and total pore volume, micropore volume and mesopore volume were determined on a Micromeritics ASAP245 static nitrogen adsorption instrument according to the standard method of ASTM D4222-98. The adsorption isotherm and desorption isotherm of the sample's low-temperature nitrogen adsorption were determined according to the standard method of ASTM D4222-98.

[0150] The sample's Fourier transform infrared (FT-IR) spectrum was determined on a Nicolet 8210 Fourier transform infrared spectrometer, and the test range was 400-4000cm -1 .

[0151] Q of the sample 3 Q 4 The measurement method adopts 29 Si MAS NMR method, on AVANCE III 500WB nuclear magnetic resonance spectrometer, using 7mm double resonance probe, Ф7mm ZrO2 rotor, resonance frequency is 99.3MHz, rotation speed is 5kHz, pulse width is 1.8μs, cycle delay time is 2s, and scanning number is about 3000 times.

[0152] The scanning electron microscope (SEM) picture of the sample is obtained on a Hitachi S4800 high-resolution cold field emission scanning electron microscope. The average particle size of the sample is tested by the method of measuring the SEM electron microscope picture (after testing the particle size of 50 molecular sieves, the average value is taken).

[0153] Example 1

[0154] (1) 104g of tetraethyl orthosilicate, 65g of a 25wt% tetrapropylammonium hydroxide (TPAOH) aqueous solution and 140g of water were sequentially added into a 500mL beaker, placed on a magnetic stirrer with heating and stirring function, mixed uniformly, and stirred at 60℃ for 5h, and the evaporated water was supplemented in time, to obtain a colorless transparent silica gel solution;

[0155] (2) The mixture obtained in step (1) was transferred into a stainless steel sealed reaction kettle, and crystallized at 170℃ for 24h to obtain a sample. The obtained sample was filtered, washed, dried at 110℃ for 3h, and then calcined at 550℃ in a muffle furnace for 3h to obtain an intermediate product S-1-L.

[0156] (3) 10g of S-1-L sample, 20g of tetraethyl orthosilicate, 20g of a 25wt% tetrapropylammonium hydroxide (TPAOH) aqueous solution and 40g of water were uniformly mixed, transferred into a stainless steel sealed reaction kettle, and kept at 170℃ for 24h to obtain a sample. The obtained sample was filtered, washed, dried at 110℃ for 3h, and then calcined at 550℃ in a muffle furnace for 3h to obtain a sample S-1-H.

[0157] The characterization parameters of S-1-H, such as BET specific surface area, micropore specific surface area, total pore volume, micropore volume and mesopore volume, are listed in Table 2.

[0158] The characterization parameters of S-1-H, such as BET specific surface area, micropore specific surface area, total pore volume, micropore volume and mesopore volume, are listed in Table 2. 1 The H MAS NMR spectrum and its peak separation results are as follows Figure 1As shown in the figure, it can be seen that there are spectral peaks at chemical shifts of 1.8 ppm, 2.1 ppm, 3.3 ppm and 4.6 ppm, respectively, and the corresponding spectral peak areas A1-A4 are 33893, 61089, 142592 and 61428, respectively, the total area A0 of A1-A4 is 299002, and X 1-1 ~X 1-4 The values are listed in Table 3.

[0159] The TEM electron micrograph of S-1-H is shown in Figure 1. Figure 2 As shown in the figure, it can be seen that the S-1-H hierarchical porous full-silica molecular sieve particles are uniform in size, and the molecular sieve crystals contain obvious hollow structures, and the size of the hollow structures is about 184 nm (taking the average value of the size of 50 hollow structures); the TEM electron micrograph of the intermediate product S-1-L without dissolution and recrystallization is shown in Figure 2. Figure 5 Comparing the two figures, it can be seen that, Figure 2 the product in Figure 1 has intracrystalline hollow structures after the dissolution and recrystallization treatment of the second template;

[0160] The BET nitrogen adsorption-desorption curve of S-1-H is shown in Figure 3. Figure 3 As shown in the figure, there is an obvious double hysteresis ring structure between the nitrogen adsorption-desorption curves, in which the first P / P0 at low pressure is 0.05, a hysteresis ring appears, and its adsorption amount accounts for 21% of the total adsorption amount; the second P / P0 at high pressure is 0.48, a hysteresis ring appears, and its adsorption amount accounts for 35% of the total adsorption amount.

[0161] The FT-IR spectrum of S-1-H is shown in Figure 4. Figure 4 As shown in the figure, S-1-H has spectral peaks at wave numbers of 3740 cm -1 , 3690 cm -1 and 3500 cm -1 , respectively, and the peak areas of the above three spectral peaks are calculated by integration to be B1 of 9.6, B2 of 13.9 and B3 of 34.2, respectively, and the total area B0 of the three spectral peaks is 57.7, and X 2-1 ~X 2-3 The values are listed in Table 3.

[0162] The 29 Si MAS NMR spectrum of S-1-H is shown in Figure 5. Figure 6 As shown in the figure, S-1-H has spectral peaks at chemical shifts of -103 ppm and -113 ppm, respectively, and the peak areas of the spectral peaks at chemical shifts of -103 ppm and -113 ppm are calculated by integration to be Q 3 of 280724 and Q4 The value of X3, calculated by formula (3), is 8020705 and is listed in Table 3.

[0163] The XRD pattern of S-1-H is as follows: Figure 7 As shown, this indicates that the S-1-H sample has an MFI topology.

[0164] SEM images of S-1-H are as follows: Figure 8 As shown in the figure, the molecular sieve particles have regular shapes and uniform sizes.

[0165] Comparative Example 1

[0166] This comparative example was prepared according to the method of Example 1. The difference from Example 1 is that the post-processing process of step (3) is not performed. The resulting molecular sieve product is denoted as D-1. Its preparation conditions are shown in Table 1, and its characterization results are shown in Tables 2 and 3.

[0167] Comparative Example 2

[0168] This comparative example prepared a conventional all-silica Silicalite-1 molecular sieve according to the method disclosed in patent CN1338427A, specifically including the following steps:

[0169] (1) Add 104g of tetraethyl silicate, 90g of 22.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution and 110g of water to a 500mL beaker, place it on a magnetic stirrer with heating and stirring functions and mix evenly. Stir at 75℃ for 5h, and replenish the evaporated water periodically to obtain a colorless and transparent silica gel solution.

[0170] (2) The above sol was transferred to a stainless steel closed reactor and crystallized at 170°C for 2 days. After filtration and washing, it was dried at 120°C for 24 hours and then calcined at 550°C in a muffle furnace for 5 hours.

[0171] (3) Take 15g of the calcined product and mix it with 55g of a 22.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution. Crystallize at 170℃ for 1 day, filter, wash, dry at 110℃ for 12h, and then calcine at 550℃ for 4h in a muffle furnace. The obtained product is denoted as D-2. The characterization results of the obtained molecular sieve are shown in Tables 2-3.

[0172] The nitrogen adsorption-desorption curve of D-2 is as follows: Figure 9 As shown in the figure, D-2 does not have a double hysteresis loop structure;

[0173] TEM of D-2 Figure 10 As shown in the figure, D-2 molecular sieve does not have an internal cavity structure.

[0174] Examples 2-8

[0175] The hierarchical porous all-silica molecular sieve was prepared according to the method of Example 1, except that the ratio and the synthesis conditions were changed, and the hierarchical porous pure-silica molecular sieve sample was recorded as S-2-H-S-8-H; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Tables 2-3.

[0176] Example 9

[0177] The hierarchical porous all-silica molecular sieve was prepared according to the method of Example 1, except that the template was changed, and the template used was tetrabutylammonium hydroxide (TBAOH), and a MEL topological structure was prepared, and the hierarchical porous molecular sieve sample was recorded as S-9-H; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Tables 2-3. The XRD of S-9-H is shown in Figure 11 , which shows that S-9-H is a MEL structure.

[0178] Example 10

[0179] The hierarchical porous all-silica molecular sieve was prepared according to the method of Example 1, except that the ratio and the template were changed, and the template used was tetraethylammonium hydroxide (TEAOH), and a BEA topological structure was prepared, and the hierarchical porous molecular sieve sample was recorded as S-10-H; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Tables 2-3. The XRD of S-10-H is shown in Figure 12 , which shows that S-10-H is a BEA structure.

[0180] Example 11

[0181] The hierarchical porous all-silica molecular sieve was prepared according to the method of Example 1, except that the ratio was changed, and the hierarchical porous pure-silica molecular sieve sample was recorded as S-11-H; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Tables 2-3.

[0182] Example 12

[0183] The hierarchical porous all-silica molecular sieve was prepared according to the method of Example 1, except that the preparation conditions were changed:

[0184] In step (2), the sample was obtained by crystallization at 130°C for 12h in a stainless steel sealed autoclave, and then the obtained sample was filtered, washed, dried at 110°C for 3h, and then calcined at 300°C for 8h in a muffle furnace to obtain the intermediate product S-1-L.

[0185] In step (3), the sample was obtained by crystallization at 130°C for 12h in a stainless steel sealed autoclave, and then the obtained sample was filtered, washed, dried at 110°C for 3h, and then calcined at 300°C for 8h in a muffle furnace.

[0186] The remaining procedures were the same as in Example 1 to obtain a sample of hierarchical porous pure-silica molecular sieve, which was designated S-12-H; the preparation conditions thereof are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Tables 2-3.

[0187] Table 1

[0188]

[0189] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, and TEAOH is tetraethylammonium hydroxide. The reagents used in the present disclosure can be obtained through conventional purchase channels. In the calculation of "water / first silicon source" in Table 1, the water also includes water from the aqueous solution of the first template; in the calculation of "intermediate product in step (3): second silicon source: second template: water", the water also includes water from the aqueous solution of the second template.

[0190] Table 2

[0191]

[0192] Table 3

[0193]

[0194]

[0195] Test Example

[0196] The molecular sieves prepared in the above examples and comparative examples were evaluated. The prepared molecular sieves were tabletted, then broken, and 20-60 mesh particles were taken as catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime, and the catalytic performance of the obtained molecular sieves was evaluated. The evaluation conditions were as follows:

[0197] The evaluation device was a normal-pressure continuous-flow fixed-bed reactor, the inner diameter of the reactor was 5 mm, and the loading amount of the catalyst was 2 g. After loading the catalyst, the reactor was pretreated in a nitrogen atmosphere at normal pressure and 350°C for 3 hours. The concentration of the raw material cyclohexanone oxime was 35% by weight, and the solvent was methanol. The reaction conditions included: the weight hourly space velocity (WHSV, the flow rate of cyclohexanone oxime in the feedstock / the weight of the catalyst in the reactor) was 2 h -1 -1, the reaction temperature was 380°C, the nitrogen flow rate was 4 L / h, and the reaction time was 24 h and 120 h, respectively.

[0198] The cooled reaction product was collected, and the concentration of each substance was quantitatively analyzed using a gas chromatograph. The gas chromatograph used was a 6890 gas chromatograph produced by Agilent, and the analysis column used was an HP-5 column. The test conditions included: a vaporization chamber temperature of 250°C, a detection chamber temperature of 230°C, and a column temperature of programmed temperature elevation, 110°C constant temperature for 8 minutes, elevation to 230°C at 15°C / min, and constant temperature for 14 minutes. The results are listed in Table 4 below.

[0199] wherein the cyclohexanone oxime conversion rate (mol%) = (molar content of cyclohexanone oxime in the feed - molar content of cyclohexanone oxime in the product) / molar content of cyclohexanone oxime in the feed x 100%;

[0200] the caprolactam selectivity (mol%) = molar percentage content of caprolactam in the product / (100 - molar percentage content of cyclohexanone oxime in the product) x 100%;

[0201] the cyclohexanone oxime conversion rate reduction rate (%) = (24h cyclohexanone conversion rate - 120h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate x 100%;

[0202] the caprolactam selectivity reduction rate = (24h caprolactam selectivity - 120h caprolactam selectivity) / 24h caprolactam selectivity x 100%.

[0203] Table 4

[0204]

[0205] According to the data in the above table, compared with the molecular sieves D-1 and D-2 prepared in Comparative Examples 1-2, the molecular sieves S-1-H to S-12-H prepared by the method provided in the present disclosure have higher cyclohexanone oxime conversion rates and caprolactam selectivities at 24h and 120h of the reaction; and have lower cyclohexanone oxime conversion rate reduction rates and caprolactam selectivity reduction rates under long-time reaction conditions (120h), higher molecular sieve stability, and longer service life.

[0206] Comparing S-11-H with S-1-H, it can be seen that S-1-H satisfies the molar ratio of the first silicon source: the first template agent: water of 1:(0.02-0.3):(10-30) and the weight ratio of the intermediate product: the second silicon source: the second template agent: water of 1:(0.5-8):(0.2-3):(2-10) during preparation, and S-1-H has higher cyclohexanone oxime conversion rate and caprolactam selectivity, and higher molecular sieve stability.

[0207] S-12-H is compared with S-1-H, it can be seen that S-1-H has higher conversion rate of cyclohexanone oxime and higher selectivity of caprolactam and higher stability of molecular sieve in the preparation process under the reaction conditions provided in the preferred embodiments of the present disclosure.

[0208] The above describes the preferred embodiments of the present disclosure, but the present disclosure is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0209] In addition, it should be noted that each specific technical feature described in the above-described specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0210] In addition, various different embodiments of the present disclosure can also be combined in any manner as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed by the present disclosure.

Claims

1. A multi-level porous all-silica molecular sieve, characterized in that, This hierarchical porous all-silica molecular sieve has the following characteristics: 1 HMAS NMR characteristics: The multi-level porous all-silica molecular sieve 1 In the peak separation results of the 1~6 ppm chemical shift range of the H MAS NMR spectrum: the peak area of ​​the peak in the 1.7~1.9 ppm chemical shift range is recorded as A1, the peak area of ​​the peak in the 2.0~2.2 ppm chemical shift range is recorded as A2, the peak area of ​​the peak in the 3.1~3.3 ppm chemical shift range is recorded as A3, the peak area of ​​the peak in the 4.4~4.6 ppm chemical shift range is recorded as A4, and the sum of the peak areas of A1~A4 is recorded as A0. X is defined as follows (1-1) 1-1 Any value between 5% and 20% X 1-1 =A1 / A0×100% (1-1); X is defined as follows (1-2) 1-2 Any value between 12% and 30% X 1-2 =A2 / A0×100% (1-2); X is defined as follows (1-3) 1-3 Any value between 35% and 60% X 1-3 =A3 / A0×100% (1-3); X is defined as follows (1-4) 1-4 Any value between 12% and 32% X 1-4 =A4 / A0×100% (1-4); The hierarchical porous all-silica molecular sieve is prepared by a method including the following steps: S1. Mix the first silicon source, the first template agent, and water to obtain a reaction mixture; S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain an intermediate product; S3. Mix the intermediate product, the second silicon source, the second template agent and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

2. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The X of the multi-level porous all-silica molecular sieve 1-1 X is any value between 11% and 19%. 1-2 X is any value between 16% and 27%. 1-3 X is any value between 40% and 50%. 1-4 It can be any value between 11% and 25%.

3. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The nitrogen adsorption-desorption curve of this hierarchical porous all-silica molecular sieve exhibits a double hysteresis loop structure.

4. The multi-level porous all-silica molecular sieve according to claim 3, characterized in that, The hierarchical porous all-silica molecular sieve exhibits a first hysteresis loop when the first P / P0 ratio is 0.1 to 0.4, and the adsorption capacity of the first hysteresis loop accounts for 10 to 25% of the total adsorption capacity. The hierarchical porous all-silica molecular sieve exhibits a second hysteresis loop when the second P / P0 ratio is 0.5 to 0.9, and the adsorption amount of the second hysteresis loop accounts for 30 to 40% of the total adsorption amount.

5. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The multi-level porous all-silica molecular sieve has a hollow structure within its crystal; the size of the hollow structure is 50~200nm.

6. The multi-level porous all-silica molecular sieve according to claim 5, characterized in that, The volume of the hollow structure accounts for 50-99% of the total volume of the molecular sieve.

7. The multi-level porous all-silica molecular sieve according to claim 6, characterized in that, The volume of the hollow structure accounts for 65-95% of the total volume of the molecular sieve.

8. The multi-level porous all-silica molecular sieve according to claim 5, characterized in that, The shape of the hollow structure is selected from one or more of the following: sphere, ellipsoid, cube, and irregular ellipsoid.

9. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, This hierarchical porous all-silica molecular sieve exhibits the following FT-IR characteristics: The FT-IR spectra of the hierarchical porous all-silica molecular sieve were observed in the 3200–3800 cm⁻¹ range. -1 In the peak fractionation results for the wavenumber range: 3730~3750 cm⁻¹ -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as B1, and the peak area of ​​the spectral peak in the range of 3660~3720 cm⁻¹ is... -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as B2, and the peak area of ​​the 3400~3500 cm⁻¹ range is used for the peak area. -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as B3, and the total area of ​​the above three spectral peaks is denoted as B0; X is defined as follows (2-1) 2-1 Any value between 5% and 25% X 2-1 =B1 / B0×100% (2-1); X is defined as follows (2-2) 2-2 Any value between 15% and 35% X 2-2 =B2 / B0×100% (2-2); X is defined as follows (2-3) 2-3 Any value between 35% and 75% X 2-3 =B3 / B0×100% formula (2-3).

10. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, This hierarchical porous all-silica molecular sieve has the following characteristics: 29 Si MAS NMR characteristics: The peak area of ​​the chemical shift of the hierarchical porous all-silica molecular sieve in the range of -102 to -104 ppm is denoted as Q. 3 The peak area of ​​the spectral peak with a chemical shift in the range of -112 to -114 ppm is denoted as Q. 4 As defined in formula (3), X3 is any value between 1% and 8%. X3=Q 3 / Q 4 ×100% formula (3).

11. The multi-level porous all-silica molecular sieve according to claim 10, characterized in that, X3 is any value between 2% and 6%.

12. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The multi-level porous all-silica molecular sieve includes molecular sieve particles composed of single crystals and / or molecular sieve particles composed of aggregates of multiple crystals.

13. The multi-level porous all-silica molecular sieve according to claim 12, characterized in that, The molecular sieve particles have an average particle size of 0.1~0.5μm and a BET specific surface area of ​​260~500m². 2 / g; Microporous specific surface area is 220~380m² 2 / g; total pore volume is 0.1~0.6cm³. 3 / g; micropore volume is 0.05~0.3cm³ 3 / g; mesopore volume is 0.07~0.4cm³ 3 / g.

14. The multi-level porous all-silica molecular sieve according to claim 13, characterized in that, The molecular sieve particles have an average particle size of 0.15~0.35μm and a BET specific surface area of ​​280~460m². 2 / g; Microporous specific surface area is 250~360m² 2 / g; total pore volume is 0.2~0.5cm³. 3 / g; micropore volume is 0.08~0.28cm³ 3 / g; mesopore volume is 0.1~0.26cm³ 3 / g.

15. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of the first silicon source, the first template agent, and water is 1:(0.01~2):(1~50).

16. The multi-level porous all-silica molecular sieve according to claim 15, characterized in that, In step S1, the molar ratio of the first silicon source, the first template agent, and water is 1:(0.02~0.3):(10~30).

17. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, In step S3, the weight ratio of the intermediate product, the second silicon source, the second template agent, and water is 1:(0.2~10):(0.1~5):(1~15).

18. The multi-level porous all-silica molecular sieve according to claim 17, characterized in that, In step S3, the weight ratio of the intermediate product, the second silicon source, the second template agent, and water is 1:(0.5~8):(0.2~3):(2~10).

19. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The first silicon source mentioned in step S1 and the second silicon source mentioned in step S3 are each independently selected from at least one of silicone grease, solid silicone, silica, and silica sol.

20. The multi-level porous all-silica molecular sieve according to claim 19, characterized in that, The first silicon source and the second silicon source are each independently selected from at least one of silicone grease, solid silicone and silica.

21. The multi-level porous all-silica molecular sieve according to claim 20, characterized in that, The first silicon source and the second silicon source are each independently selected from silicone grease, and the silicone grease has the general formula shown in formula (A): （A）； Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is a branched or straight-chain alkyl group.

22. The multi-level porous all-silica molecular sieve according to claim 21, characterized in that, In formula (A), R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms.

23. The multi-level porous all-silica molecular sieve according to claim 22, characterized in that, In formula (A), R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

24. The multi-level porous all-silica molecular sieve according to claim 21, characterized in that, The silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

25. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The first template agent in step S1 and the second template agent in step S3 are organic bases.

26. The multi-level porous all-silica molecular sieve according to claim 25, characterized in that, The first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcoholic amines.

27. The multi-level porous all-silica molecular sieve according to claim 26, characterized in that, The first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases having the structure shown in formula (B): (B); R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms.

28. The hierarchical porous all-silica molecular sieve according to claim 27, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms.

29. The multi-level porous all-silica molecular sieve according to claim 28, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

30. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

31. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The silicon source is silicone grease, and step S1 includes: The first silicon source, the first template agent and water are mixed and subjected to hydrolysis and alcohol removal treatment to obtain a silicon hydrolysate.

32. The multi-level porous all-silica molecular sieve according to claim 31, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h.

33. The multi-level porous all-silica molecular sieve according to claim 32, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85℃ for 8~10h.

34. The multi-level porous all-silica molecular sieve according to claim 1, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: hydrothermal crystallization temperature of 130~200℃, hydrothermal crystallization time of 6~168h; and pressure of autogenous pressure. The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 300~700℃ and a roasting time of 1~16h.

35. The multi-level porous all-silica molecular sieve according to claim 34, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: a hydrothermal crystallization temperature of 150~180℃ and a hydrothermal crystallization time of 24~72h; The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 400~600℃ and a roasting time of 2~5h.

36. The application of the hierarchical porous all-silica molecular sieve according to any one of claims 1 to 35 in the catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

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