Preparation method and application of sn-beta zeolite catalyst for improving selectivity of caprolactone

Abstract

This invention belongs to the field of zeolite molecular sieve heterogeneous catalyst preparation technology, and relates to a method for preparing Sn-Beta zeolite catalysts to improve caprolactone selectivity. This method uses dimple-modified dealubilized Beta zeolite as a support and prepares the Sn-Beta zeolite catalyst via a solid-solid isomorphous substitution reaction. Specifically, before the solid-solid isomorphous substitution reaction, the hydroxyl dimples of the dealubilized Beta zeolite are dimple-modified with an aqueous solution of a weak organic base to expand the inclusion capacity of the hydroxyl dimples for tin ions. This invention solves the problem that heteroatom tin, due to its large ionic radius, is difficult to enter the hydroxyl dimples of dealubilized Beta zeolite for isomorphous substitution reaction, while avoiding the problem caused by the volume expansion of the hydroxyl dimples due to tin ion implantation. The Sn-Beta zeolite prepared by this invention can be used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide to synthesize caprolactone.

Description

Technical Field

[0001] This invention belongs to the field of zeolite molecular sieve heterogeneous catalyst preparation technology, and relates to a method for preparing Sn-Beta zeolite catalyst to improve caprolactone selectivity and its application. Background Technology

[0002] Sn-Beta zeolite is a fully Lewis acid-type macroporous heteroatom zeolite with a BEA topology, exhibiting unique catalytic activity and important potential applications. Sn-Beta zeolite demonstrates excellent catalytic performance in a series of important reactions, including the Baeyer–Villiger oxidation of ketones, the transfer hydrogenation (MPV) reaction of ketones, glucose isomerization, and the ring-opening hydration reaction of epoxides.

[0003] Sn-Beta zeolite is the most effective catalyst for the Baeyer-Villiger oxidation of ketones. Taking cyclohexanone as an example, Sn-Beta zeolite catalyzes the Baeyer-Villiger oxidation of cyclohexanone to produce caprolactone. Caprolactone is an important chemical intermediate with a wide range of applications. It can be used to produce polycaprolactone and polycaprolactone polyols. Polycaprolactone is a fully biodegradable material with good biodegradability and biocompatibility, and has broad application prospects in biomedical engineering, pharmaceuticals, and environmental protection materials. Polycaprolactone-based polyols with abundant terminal hydroxyl groups exhibit high reactivity and can continue to polymerize with other materials to synthesize more high-value-added functional products. The following literature pertains to the Sn-Beta-catalyzed oxidation of ketones Baeyer–Villiger: Tetrahedron, 2006, 62, 11697–11703; Chem. Eur. J., 2010, 16, 12962–12969; J. Phys. Chem. C., 2011, 115, 3663–3670; Angew. Chem. Int. Ed., 2012, 51, 11736–11739; Chem. Eng. J., 2013, 218, 425–432; ACS. Catal.2015,5,3108-3119, Chem.Commun.,2016,52,6712-6715, J.Phys.Chem.C.,2016,120,23613-23624, Catal.Sci.Technol.,2016, 6, 2787–2795, J. Catal., 2017, 352, 1–12, Micropor. Mesopor. Mat., 2018, 266, 242–251, Micropor. Mesopor. Mat., 2019, 287, 85–92, ACS Catal.2020,10,14135-14146, Micropor.Mesopor.Mat.,2021,320,111090, Fuel.,2023,340,127505, RSC Adv.,2023,13,4835–4842, etc.

[0004] There are two main methods for synthesizing Sn-Beta zeolite. The first method is hydrothermal synthesis. In 1997, a method for hydrothermal synthesis of Sn-Beta zeolite was reported in the published literature Chem. Commun., 1997, 5, 425-426. Its technical features include: first, hydrothermally synthesizing Sn-Al-Beta zeolite using a silicon-aluminum gel containing tin tetrachloride; then, treating the Sn-Al-Beta zeolite with concentrated nitric acid for dealumination; and finally, using the dealumination-treated Sn-Al-Beta zeolite as seed crystals, hydrothermally synthesizing Sn-Beta zeolite using an aluminum-free tin-silicon gel as raw material. Sn-Beta zeolite synthesized by this method has a low Sn content in its framework, and Al atoms inevitably remain in the framework.

[0005] In 2001, the published paper *Nature*, 412(6845), 423-425, first reported a hydrothermal method for the direct synthesis of aluminum-free Sn-Beta zeolite using fluorides as mineralizers with the assistance of highly dealufted Beta zeolite seed crystals. Specifically, this method uses tetraethyl orthosilicate as the silicon source, tin tetrachloride pentahydrate as the tin source, hydrofluoric acid (HF) as the mineralizer, and highly dealufted Beta zeolite as the seed crystal. Crystallization is carried out at 140°C for 20 days, resulting in the hydrothermal synthesis of highly crystalline, completely aluminum-free Sn-Beta zeolite. The obtained Sn-Beta zeolite was applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. Under the conditions of 1,4-dioxane as solvent, a reaction temperature of 90℃, a hydrogen peroxide feed concentration of 35 wt%, and a solvent:ketone:H₂O₂ ratio of 50:1.5:1 (hydrogen peroxide concentration in the reactants was 0.215 mol / L, and water concentration was 0.424 mol / L) for 3 h, the conversion rate of cyclohexanone reached 52% (theoretical conversion rate 66.67%), and the selectivity for caprolactone reached 98%. Although the Sn-Beta reported in this published literature exhibits excellent catalytic performance, the hydrothermal synthesis of Sn-Beta requires a long crystallization time, and the large amount of fluoride added during the synthesis process would cause serious environmental pollution in industrial applications.

[0006] The published paper Chem. Eng. J., 2013, 218, 425–432 reports a relatively simple method for synthesizing Sn-Beta using steam-assisted conversion (SAC). Specifically, this method first prepares a hydrogel using silica, tin tetrachloride pentahydrate, tetraethylammonium hydroxide, and ammonium fluoride as raw materials. The hydrogel is then dried at 60°C for 6 hours to obtain a tin-silicon dry gel. This tin-silicon dry gel is then placed in a synthesis reactor and crystallized at 180°C for 5 hours without contact with water, relying solely on the assistance of steam, to obtain well-crystallized Sn-Beta zeolite (Si / Sn = 93). The obtained Sn-Beta zeolite was applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. The results showed that under the conditions of 1,4-dioxane as solvent, reaction temperature of 90℃, hydrogen peroxide concentration of 30wt%, solvent:ketone:H2O2 = 35:1:1.5 (hydrogen peroxide concentration in the reactants was 0.447 mol / L, and water concentration was 1.66 mol / L), the conversion rate of cyclohexanone reached 36.1% (theoretical conversion rate is 100%), and the selectivity of caprolactone reached 99.48% after 3 h of reaction. This literature shows that the steam-assisted conversion (SAC) method is faster and more convenient than the traditional hydrothermal synthesis method. However, in this method, the Sn content has a significant impact on the synthesis; the higher the Sn content, the longer the required crystallization time and the lower the crystallinity. When Si / Sn ≤ 75, even after 200 h of crystallization, Sn-Beta zeolite could not be obtained using this method. It is also worth noting that this method requires the use of fluorides as mineralizing agents.

[0007] A published paper, J. Catal., 2017, 352, 1–12, reports a method for synthesizing Sn-Beta zeolite using molecular sieve crystallization. Specifically, this method requires first synthesizing ITQ-1 molecular sieve (all-silica MWW-type zeolite) via a hydrothermal method using N,N,N-trimethyl-1-adamantane ammonium hydroxide and hexamethyleneimine as co-structure directing agents. Then, using calcined ITQ-1 molecular sieve as the silicon source, tin tetrachloride pentahydrate as the tin source, ammonium fluoride as the mineralizer, dealulated Beta zeolite as the seed crystal, and tetraethylammonium hydroxide as the structure directing agent, Sn-Beta zeolite is synthesized at 140 °C. The results show that using this method, Sn-Beta zeolite with low tin content (Si / Sn = 203) can be obtained with a short crystallization time (e.g., 1 day); while Sn-Beta zeolite with higher tin content (Si / Sn = 63) can be obtained with a longer crystallization time (e.g., 3 days). The obtained Sn-Beta zeolite was applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. Under the conditions of using fluorobenzene as solvent, reaction temperature of 85℃, hydrogen peroxide feed concentration of 66.9wt%, solvent:ketone:H2O2 = 13:5:1 (hydrogen peroxide concentration in reactants of 0.443mol / L and water concentration of 0.233mol / L) for 40 min, the conversion rate of cyclohexanone reached 19.3% (theoretical conversion rate of 20%), and the selectivity of caprolactone reached 91.2%.

[0008] The following patents and published documents all relate to the hydrothermal synthesis method for Sn-Beta zeolite: CN102249258A (application date 2011-05-06), US9108190B1 (application date 2013-09-12), CN106563495A (application date 2016-10-31), CN107244678B (application date 2017-07-04), CN107311201B (application date 2017-07-04), CN1078277 27A (application date 2017-11-09), CN110422857B (application date 2019-07-25), CN111285381B (application date 2020-03-09), CN112551538A (application date 2020-12-23), CN112645346A (application date 2020-12-23), CN112645347A (application date 2020-12-23), CN112678842A (application date 2020- 12-23), CN112897547A (application date 2021-03-30), CN114572996A (application date 2022-03-23), Chem. Eur. J., 2002, 20, 4708-4717, Collect. Czech. Chem. Commun., 2005, 70, 1727-1736, Mater. Chem. Phys., 2013, 141, 519-529, Micropor .Mesopor.Mat.,2017,239,19-27, Chem.Commun.,2017,53,12516-12519, Micropor.Mesopor.Mat.,2018,2 66,242-251, Micropor.Mesopor.Mat.,2019,287,85-92, Micropor.Mesopor.Mat.,2020,294,109915,Appl Catal A-gen.,2020,590,117370, Micropor.Mesopor.Mat.,2021,320,111090,Master's Thesis "Synthesis, Characterization and Catalytic MPVO Reaction Mechanism of Sn-Beta Molecular Sieves", Lanzhou University (2016);Master's Thesis "Synthesis and Catalytic Performance Study of Sn-Beta Zeolite Molecular Sieves Catalyzing Glucose Isomerization", South China University of Technology (2017);Master's Thesis "Synthesis of Sn-Beta Molecular Sieves by Dry Gel Method and Its Catalytic Performance in Furfural Conversion", China University of Petroleum (2018);Master's Thesis "Aerosol-Assisted Synthesis of Sn-Beta Molecular Sieves and Its Catalytic Performance in Baeyer-Villiger Oxidation Reaction" The following numerous research papers were published: Dalian University of Technology (2019), Master's Thesis "Study on the Preparation of Sn-Beta Molecular Sieves and Their BV Oxidation Reaction Performance by Aerosol-Assisted Post-Synthesis Method"; Dalian University of Technology (2020), Master's Thesis "Study on the Preparation of Sn-Beta Molecular Sieves and Catalytic Conversion of Glucose to Methyl Lactate by Seed-Assisted Hydrothermal Method"; Zhengzhou University (2021), Master's Thesis "Mechanism of Seed in the Crystallization Process of Sn-Beta Molecular Sieves"; Zhengzhou University (2022), Master's Thesis "Effect of Sn Content in Sn-Beta Molecular Sieves on the Catalytic Conversion of Glucose to Methyl Lactate and Fructose"; Zhengzhou University (2022). From these numerous papers, it can be observed that a relatively large amount of fluoride mineralizing agent is required when preparing Sn-Beta zeolite by hydrothermal synthesis. Furthermore, Sn-Beta zeolite prepared by hydrothermal synthesis generally has a low framework Sn content, poor quality reproducibility, and a long crystallization time.

[0009] The published paper Green Chem., 2017, 19, 692–701 reports a method for using F-free... - The system describes a hydrothermal synthesis method for Sn-Beta zeolite. Specifically, this method involves first grinding dried dealubilized Beta zeolite with tin tetrachloride pentahydrate until homogeneous. Then, the solid mixture is brought into contact with TEAOH in a stainless steel high-pressure reactor lined with polytetrafluoroethylene for a hydrothermal reaction. The reaction is carried out under static conditions at 140°C for 24 hours to obtain Sn-Beta zeolite. Under these conditions, dealubilized Beta zeolite undergoes a dissolution-recrystallization reaction in the strongly alkaline TEAOH solution, allowing Sn species to enter the Beta framework during recrystallization. Therefore, the essence of this method is to obtain Sn-Beta zeolite through zeolite framework reconstruction. However, the Sn-Beta zeolite synthesized using this method not only has a low Sn loading but also very low crystallinity, requiring a large amount of template agent, resulting in high manufacturing costs for Sn-Beta.

[0010] The publicly available literature Inorg. Chem. Front., 2018, 5, 2763–2771 also reports a method in the absence of F -A hydrothermal synthesis method for Sn-Beta zeolite in a system. This method uses N-cyclohexyl-N,N-dimethylcyclohexylamine hydroxide as a structure-directing agent, all-silica Beta zeolite as a seed crystal, and sodium hydroxide as a mineralizing agent, crystallizing at 140℃ for 14 days to obtain Sn-Beta zeolite. Although this method can eliminate the need for F... - However, it requires the use of special guiding agents with complex structures, which are expensive and have a long crystallization time of up to 14 days.

[0011] In addition to the aforementioned publicly available documents, patent CN104709920B also discloses a method for synthesizing Sn-Beta zeolite without an F-system. This method employs a boric acid-assisted hydrothermal synthesis method. Specifically, the method involves first preparing a homogeneous gel from dealubilized Beta zeolite, tetraethylammonium hydroxide, tetraethyl orthosilicate, boric acid, and tin tetrachloride, and then crystallizing the gel at 140°C for 25 days to obtain Sn-beta zeolite. Clearly, one of the drawbacks of this method is the excessively long crystallization time.

[0012] In addition, the following patents and documents also involve methods for hydrothermal synthesis of Sn-Beta zeolite under fluorine-free conditions: CN104707649A (application date 2013-12-16), CN110683557A (application date 2019-11-20), Green Chem., 2017, 19, 692–701, Master's thesis "Green Synthesis and Catalytic Performance Study of Heteroatom Beta and CHA Molecular Sieves", East China Normal University (2018), Master's thesis "Fluorine-Free Hydrothermal Synthesis of Pure Silicon Beta and Sn-Beta Zeolite", Zhengzhou University (2021), Master's thesis "Comparative Study on the Rules and Properties of Sn-Beta Zeolite Synthesized by Different Methods", China University of Petroleum (2020).

[0013] In short, without F - The preparation of Sn-Beta zeolite using hydrothermal synthesis in a system is a long-awaited goal. Unfortunately, to date, this hydrothermal synthesis method is not yet practically applicable.

[0014] The second method for preparing Sn-Beta zeolite is the post-synthesis method. The principle of the post-synthesis method is to first perform acid dealumination treatment on the parent silica-alumina Beta zeolite to obtain all-silica Beta zeolite with framework defect sites. Then, tin heteroatoms are introduced into the framework defect sites (hydroxyl holes) of the all-silica Beta zeolite using different methods, giving it four-coordinate framework tin catalytic active sites. Depending on the tin source, the post-synthesis method can be divided into gas-solid isomorphic substitution, liquid-solid isomorphic substitution, and solid-solid isomorphic substitution.

[0015] A post-synthetic method for preparing Sn-Beta zeolite via gas-solid isomorphic substitution was reported in the published literature J. Phys. Chem. C, 2011, 115, 3663–3670. Specifically, this method uses anhydrous SnCl4 as the tin source, and nitrogen gas is bubbled into the anhydrous SnCl4 liquid, thereby allowing the nitrogen-carried SnCl4 gas to contact the dealuminated Beta zeolite and undergo an isomorphic substitution reaction. The reaction is carried out at 500 °C, and Sn-Beta zeolite with a Sn content as high as 6.2 wt% is obtained after 1.5 h. The obtained Sn-Beta zeolite (Sn content 3.5 wt%) was used in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. When using 50 wt% hydrogen peroxide as the oxidant, acetonitrile as the solvent, with a solvent:ketone:H₂O₂ ratio of 61:2:1 (hydrogen peroxide concentration in the reactants was 0.361 mol / L, and water concentration was 0.384 mol / L), a reaction temperature of 75℃, and a reaction time of 3 hours, the cyclohexanone conversion rate was 34.1% (the theoretical conversion rate should be 50%), and the caprolactone selectivity was 57.8%. This demonstrates that catalytically active Sn-Beta zeolite can be obtained from dealuminated Beta zeolite through a gas-solid isomorphic substitution reaction.

[0016] The following literature all involve the preparation of Sn-Beta zeolite using the gas-solid isomorphous substitution method: Dalton Trans., 2014, 43, 8196–8204; J. Catal., 2015, 330, 545-557; Appl Catal A-gen., 2018, 556, 52–63; Master's thesis "Preparation, Characterization and Performance Study of Al-Free Sn-Beta Molecular Sieves in Baeyer-Villiger Catalytic Oxidation", East China Normal University (2011); Master's thesis "Study on the Preparation of Sn-Beta Zeolite Molecular Sieves by Isomorphous Substitution Method for Catalytic Isomerization of Glucose to Fructose", Dalian University of Technology (2013); Master's thesis "Synthesis, Characterization and Catalytic Performance Study of Sn-Beta Zeolite by Gas-Solid Phase Method", Dalian University of Technology (2013); Master's thesis "Synthesis, Characterization and Catalytic MPVO Reaction Mechanism Study of Sn-Beta Molecular Sieves", Lanzhou University (2016). However, in general, the preparation of Sn-Beta zeolite using the gas-solid isomorphic substitution method is subject to harsh conditions and is difficult to scale up. Due to the low volatility of SnCl4, the efficiency of grafting with nitrogen-carried SnCl4 is low, making it difficult to graft a sufficient amount of Sn into the framework vacancies of dealubilized Beta zeolite. Furthermore, and more importantly, Sn-Beta zeolite prepared by the gas-solid isomorphic substitution method forms a large number of inactive extra-framework tin oxide species.

[0017] A literature review revealed that the publicly available paper *Chinese.J.Catal.*, 2012, 33, 898–904, reported the preparation of Sn-Beta zeolite via a liquid-solid isomorphous substitution method. In this reported method, the tin source was tin tetrachloride pentahydrate, and the reflux solvent was water. However, this Sn-Beta zeolite, obtained through a liquid-solid isomorphous substitution reaction based on dealuminated Beta zeolite, exhibited poor reactivity and product selectivity in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. For example, under the reaction conditions of a reaction temperature of 90℃, a hydrogen peroxide feed concentration of 30wt%, and a molar ratio of 1,4-dioxane:cyclohexanone:H₂O₂ = 35:1:1.4 (with a hydrogen peroxide concentration of 0.299 mol / L and a water concentration of 0.742 mol / L in the reactants), the cyclohexanone conversion and caprolactone selectivity were 23.6% (the theoretical conversion should be 100%) and 70.0%, respectively. The preparation of Sn-Beta zeolite using the liquid-solid isomorphous substitution method also suffers from the prominent drawback of high non-framework tin oxide content.

[0018] The following patents and published documents all relate to the liquid-solid isomorphous substitution method for preparing Sn-Beta zeolite: CN103464196A (application date 2013-07-25), CN106861747B (application date 2015-12-10), US10414664B2 (application date 2017-08-25), CN114805284B (application date 2022-05-11), Green Chem., 2013, 15, 2777–2785, J. Catal., 2015, 330, 545-557, ACS Catal., 2015, 5, 928-940, Chem. Commun., 2016, 52, 6712-6715, ACS Catal., 2016, 6, 31-46, ACS Catal., 2017, 7, 3792-3798; Chem. Eng. J., 2017, 307, 868–876; Doctoral dissertation “Synthesis, Characterization and Catalytic Performance Study of Sn-Beta Molecular Sieves”, Dalian University of Technology (2013). These documents reveal that when Sn-Beta zeolite is prepared using the liquid-solid isomorphous substitution method, a large number of extra-framework tin oxide species are formed regardless of the solvent chosen.

[0019] The published paper Angew. Chem. Int. Ed., 2012, 51, 11736–11739 reports a post-synthetic method for preparing Sn-Beta zeolite using a solid-solid isomorphous substitution method. Specifically, this method requires first reacting silica-alumina Beta zeolite with concentrated nitric acid to remove skeletal aluminum atoms. Then, using tin(II) acetate as the tin source, the dealuminized Beta zeolite and tin(II) acetate solid powders are homogenized for 15 min. Finally, the homogenized solid mixture is calcined in air at high temperature (550 °C) to obtain Sn-Beta zeolite. The obtained Sn-Beta zeolite was applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. When 1,4-dioxane was used as solvent, the reaction temperature was 90℃, the hydrogen peroxide concentration was 30wt%, the solvent:ketone:H2O2 ratio was 36:2:3 (the concentration of hydrogen peroxide in the reactants was 0.809mol / L, and the concentration of water was 2.01mol / L), and the reaction time was 4h, the conversion rate of cyclohexanone could reach 41.1% (the theoretical conversion rate was 100%), and the selectivity of caprolactone could reach 93%.

[0020] The following patents and published documents also relate to the solid-solid isomorphic substitution method for preparing Sn-Beta zeolite: CN103920527A (application date 2014-04-24), US2016279621A1 (application date 2014-11-05), US9464022B2 (application date 2015-10-30), CN106984356A (application date 2017-05-05), CN111170982A (application date 2017-08-05). 020-01-09), J. Catal., 2015, 330, 545–557, ChemCatChem., 2015, 7, 3322–3331, ChemCatChem., 201 6,8,1–10, J.Mater.Chem.A.,2016,4,1373–1382, Catal.Sci.Technol.,2017,7,2782–2788, Green Chem., 2017, 19, 692–701; ChemSusChem., 2017, 10, 3652–3659; ACSSustainable Chem.Eng., 2017, 5, 3123-3131; ACS Catal., 2020, 10, 14135-14146; Master's Thesis "Rapid Synthesis of Sn-Beta Molecular Sieves and Catalytic Sugar Conversion to Prepare Lactate", Zhengzhou University (2017); Master's Thesis "Preparation of Sn-Beta Molecular Sieves and Study on Cyclohexanone Oxidation Reaction Performance", Dalian University of Technology (2020); Master's Thesis "Study on Influencing Factors of Cyclohexanone Oxidation Reaction on Sn-β Zeolite", Dalian University of Technology (2022); Master's Thesis "Acid Regulation of Sn-Beta Molecular Sieves and Study on Catalytic Meerwein-Ponndorf-Verley-Oppenauer Reaction Performance", Zhengzhou University (2022). In summary, compared with the other two post-synthetic methods, the solid-solid isomorphic substitution method for preparing Sn-Beta is simple to operate, has less stringent requirements for raw materials and conditions, and is easily implemented industrially. Moreover, this post-synthetic method does not involve solvents, has a short synthesis time, and can be used to prepare Sn-Beta zeolites with high skeletal Sn content, making it a highly practical post-synthetic method for preparing Sn-Beta.

[0021] However, due to the ionic radius of Sn The ionic radius is much larger than that of Al. Therefore, it is difficult for Sn ions to enter the hydroxyl sites generated by dealumination on the Beta zeolite framework. This is a common challenge faced by all three post-synthesis methods. Because of this, all post-synthesis methods suffer from the following problem: regardless of the method used to introduce tin ions into the framework defect sites of all-silica Beta zeolite, the total number of tin ions that can ultimately enter the framework lattice points in the form of isomorphic substitution of framework aluminum ions depends on the "inclusivity" of the hydroxyl sites and the zeolite framework. Hydroxyl sites that are initially isomorphically substituted by tin ions can gain "inclusivity" for implanted tin ions through volume expansion, consuming the "inclusivity" of the zeolite framework. As the "inclusivity" of the zeolite framework is exhausted, the remaining hydroxyl sites can no longer accept tin ions through expansion and deformation. The framework defect sites not occupied by tin ions exist in the form of weakly acidic hydroxyl sites, while the tin ions that cannot enter the framework lattice points become non-catalytically active extra-framework SnO. x Species.

[0022] As is well known, in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, the selectivity of the target product, caprolactone, is mainly affected by the side reaction of caprolactone hydrolysis and ring-opening to generate 6-hydroxyhexanoic acid. On the one hand, in Sn-Beta zeolite prepared by the post-synthetic method, since the defect sites of the all-silica Beta zeolite framework are difficult to be completely replaced by tin ions, weak acidic sites generated by hydroxyl pits at defect sites will exist on the Sn-Beta zeolite catalyst framework. This weak acidic site catalyzes the hydrolysis side reaction of caprolactone, which is an important reason for the low selectivity of Sn-Beta zeolite catalysts prepared by the post-synthetic method for caprolactone. On the other hand, tin atoms that do not enter the framework defect sites are guest species in the zeolite channels. As the tin loading increases, these guest species aggregate into larger particles, blocking the Beta zeolite channels, reducing the accessibility of active sites inside the catalyst, and thus reducing the catalytic activity of the catalyst.

[0023] Currently, there are few effective methods to address the aforementioned problems in post-synthesis methods. The master's thesis, "Study on the Preparation of Sn-Beta Zeolite for the Catalytic Conversion of Glucose to Lactate by an Improved Post-treatment Method," published by Zhengzhou University (2016), provides a solution of further hydrothermal modification of Sn-Beta zeolite prepared by the solid-solid isomorphic substitution method using tetraethylammonium hydroxide (TEAOH) solution. During this modification process, Sn-Beta zeolite crystals undergo partial dissolution and recrystallization, thus yielding hierarchical porous Sn-Beta molecular sieves with fewer defect sites. According to literature reports, this modification method significantly improves the yield of the product (methyl lactate) from the glucose conversion reaction of Sn-Beta zeolite. In fact, this modification method has been widely used in the modification of titanium silicate zeolite TS-1. The difference is that tetrapropylammonium hydroxide (TPAOH) is used in the hydrothermal modification of TS-1. Both TPAOH and TEAOH are commonly used quaternary ammonium base template agents. TPAOH is generally used for the synthesis and modification of MFI family zeolite molecular sieves (ZSM-5, S-1, TS-1), while TEAOH is generally used for the synthesis of BEA family zeolite molecular sieves (Al-Beta, Ti-Beta, and Sn-Beta). However, in principle, this dissolution-recrystallization modification method cannot fundamentally solve the problem that heteroatoms are difficult to integrate into the zeolite framework due to their large ionic radii. Furthermore, this modification method also suffers from significant catalyst loss and high TEAOH template consumption, inevitably leading to a significant increase in catalyst cost.

[0024] The literature review also revealed an ion modification method in the published paper Catal. Sci. Technol., 2016, 6, 2787–2795. This ion modification method involves Li... + Na + K + Cs + and NH4 + Several modified ions. The principle of this modification method is to neutralize and passivate the weakly acidic hydroxyl groups in Sn-Beta zeolite using basic cations. According to literature reports, Sn-Beta zeolite modified by this method exhibits weakly acidic hydroxyl groups that are neutralized by Li. + Na + and NH4 + The basicity of the isocations deactivates them, thus inhibiting the caprolactone hydrolysis side reaction in the Baeyer-Villiger reaction of cyclohexanone and hydrogen peroxide to a certain extent.

[0025] In addition, the master's thesis "Preparation, Characterization and Application of Modified Sn-Beta Catalyst in the Catalytic Production of Lactic Acid from Biomass Derivatives" (Xiamen University, 2018) provides a solution using Na... + K + NH4 + Zn 2+ Ca 2+ Mg 2+ Ion exchange modification was performed on Sn-Beta molecular sieves prepared by the solid-solid isomorphic substitution method. The principle of this modification method is to neutralize and passivate the weakly acidic hydroxyl groups in Sn-Beta zeolite using basic cations. The authors believe that the acidic environment inside the molecular sieve can be controlled through monovalent metal ion exchange and divalent ion exchange, and Lewis bases and... The base center, in conjunction with Lewis acid catalysis, significantly improves the lactic acid selectivity in the conversion of biomass derivatives to lactic acid, thanks to the modification of Sn-Beta zeolite using this method.

[0026] Invention patent CN110575844A (application date 2019-08-16) discloses a method for alkaline earth metal modification of Sn-Beta zeolite. For Sn-Beta zeolite, alkaline earth metal modification aims to eliminate the weakly acidic sites of the Sn-Beta catalyst. Its modification principle is similar to that of alkali metal ion modification. Sn-Beta zeolite modified using this method has also been used in sugar inversion reactions, with the target product being lactic acid.

[0027] Invention patent CN114210362A (application date 2021-11-30) discloses a method for modifying Sn-Beta zeolite with zinc ions. This method utilizes the selective binding of zinc ions to hydroxyl sites by impregnating Sn-Beta zeolite with a zinc salt solution, converting residual hydroxyl sites into weak Lewis acid sites. The zinc-modified Sn-Beta zeolite was used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone to synthesize caprolactone. Results showed that at a 1,4-dioxane:cyclohexanone:H₂O₂ molar ratio of 4:2:1, a reaction temperature of 60℃, and a reaction time of 2 h, the cyclohexanone conversion rate was 27.75% (theoretical conversion rate 50%), and the selectivity of the product caprolactone was 93.80%.

[0028] In addition to the methods mentioned above, invention patent CN108727180A (application date 2018-05-07) also discloses a surface amination modification method. The technical feature of this method is that Sn-Beta, obtained by a solid-solid isomorphic substitution method, is first dispersed in anhydrous ethanol. Then, an amination reagent (3-aminopropyltrimethoxysilane (APTMS) or 3-aminopropyltriethoxysilane (APTES)) is added, and the mixture is refluxed at 80°C for 6 hours. After the reaction, the material is cooled to room temperature and filtered. The filter cake is washed with a large amount of anhydrous ethanol and then dried at 80°C to obtain the amination-modified Sn-Beta zeolite. The principle of surface amination modification is: using an amino-containing silanizing reagent to graft onto the acidic sites on the surface, a Si-OR bridge is formed, grafting the amino-containing silane species onto the acidic sites of Sn-Beta, thereby covering the acidic sites. Using amination-modified Sn-Beta zeolite in the reaction of sugar conversion to lactic acid improves both glucose conversion and lactic acid yield. It is noteworthy that in this method, after the amino-containing silanizing agent is grafted onto Sn-Beta zeolite, only low-temperature drying is performed, without high-temperature calcination. Therefore, the 3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane modifiers form Si-OR bonds with the surface silanol groups (Si-OH) and remain on the modified Sn-Beta zeolite. This modification method is unsuitable for applications requiring frequent char regeneration of the catalyst.

[0029] The published paper ACS Omega., 2018, 3, 17430-17438 also reported a study on the surface amination modification of Sn-Beta zeolite using 3-aminopropyltrimethoxysilane (APTMS). The modified catalyst was used for the conversion of sucrose to lactic acid. Under optimized conditions, complete sucrose conversion was achieved, with a lactic acid yield of up to 58%.

[0030] The published literature RSC Adv., 2019, 9, 18989–18995 also used 3-aminopropyltrimethoxysilane (APTMS) to modify the surface amino functionalization of Sn-Beta zeolite. The modified catalyst was used for the reaction of glucose conversion to lactic acid. While achieving complete glucose conversion, a lactic acid yield of up to 56% was also achieved.

[0031] A surface amination modification method for Sn-Beta zeolite is also reported in the published literature ACS Omega., 2021, 6, 284-293. Specifically, anhydrous ethanol is used as a solvent to modify Sn-Beta zeolite prepared by a post-synthetic method by mixing it with a certain amount of amination reagent. The amination reagents involved in this literature mainly include 3-aminopropyltrimethoxysilane (APTMS), 3-(2-aminoethylamino)propyltrimethoxysilane (AEPTMES), and diethylenetriamine (DETA). The modified Sn-Beta zeolite catalyst obtained by this method was applied to the reaction of Scenedesmus algae to produce lactic acid. The results showed that the yield of lactic acid, the main product, was significantly increased by Sn-Beta zeolite modified with 3-aminopropyltrimethoxysilane (APTMS). Under optimal reaction conditions (190℃ and 5 hours), the lactic acid yield reached a maximum of 37%.

[0032] Clearly, the surface amination modification method for Sn-Beta zeolite described above relies on retaining amino-containing organic groups in the modified catalyst to achieve its modification effect. However, this type of modified catalyst cannot be used in applications where frequent carbonization regeneration is required.

[0033] The published paper Chem. Mater., 2021, 33, 9366-9381 discloses a post-treatment modification method for Sn-Beta zeolite with a Sn content as high as 10 wt% prepared by the solid-solid isomorphic substitution method, involving tandem reduction and re-oxidation. This method requires first placing the prepared Sn-Beta zeolite under a hydrogen atmosphere and heating it at a certain rate (5 °C·min). -1 The catalyst is heated to the required temperature for 2 hours for reduction treatment, and then the reduced catalyst is placed in an air stream at a certain heating rate (5℃·min). -1 The Sn-Beta zeolite, modified by a series of reduction-reoxidation methods, was used as a catalyst for the synthesis of caprolactone via the Baeyer-Villiger oxidation of cyclohexanone and hydrogen peroxide. The modified catalyst exhibited higher Lewis acid density and higher Baeyer-Villiger oxidation activity. This was attributed to the reduction of extra-skeletal tin oxide species into mobile Sn(II)O species during the reduction process. These Sn(II)O species can diffuse within the Sn-Beta zeolite and interact with silanol sites, allowing some extra-skeletal tin oxide species to re-enter the framework. However, the degree of reduction in this modification method is difficult to control, and the reduction result is affected by the amount of SnO. xFactors such as size and content can influence the outcome; excessive reduction can lead to the formation of metallic Sn particles, which is detrimental to achieving the desired modification. It's easy to understand that, due to the limitations of the zeolite framework's "inclusivity," the amount of non-framework tin that can re-enter the framework using this modification method is inevitably limited. Summary of the Invention

[0034] The purpose of this invention is to provide a method for preparing Sn-Beta zeolite that can improve the selectivity of caprolactone in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide.

[0035] Specifically, this invention provides a method for preparing Sn-Beta zeolite via a solid-solid isomorphic substitution reaction using a hollow-modified dealubilized Beta zeolite as a support. The Sn-Beta zeolite prepared by this invention catalyzes the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide, exhibiting high selectivity for the caprolactone product. The hollow-modification refers to the use of organic amines to control desilication on the dealubilized Beta zeolite support, thereby increasing the size of the hydroxyl dimples generated during dealubilization and improving the "containment" of tin ions within the hydroxyl dimples.

[0036] Extensive experimental exploration has led to a profound understanding that, due to the ionic radius of tin... Larger than the ionic radius of aluminum Therefore, it is impossible to implant large amounts of tin ions into the smaller hydroxyl pockets of dealuminolite beta zeolite and form a perfect bond with the zeolite framework containing four Si-O-Sn bonds through isomorphous substitution. The presence of a large number of non-framework tin species in the prepared Sn-Beta zeolite is an unavoidable result.

[0037] Those familiar with this field know that during the hydrothermal synthesis of heteroatom zeolites, especially when the heteroatoms have large ionic radii (such as titanium and tin), the entry of heteroatoms into the zeolite framework inevitably causes expansion of the zeolite unit cell. The greater the number of heteroatoms entering the zeolite framework, the greater the expansion of the zeolite unit cell.

[0038] Similarly, when preparing Sn-Beta zeolite using the post-synthetic method, the introduction of heteroatomic tin into the framework of dealubilized Beta zeolite as tin ions through isomorphous substitution with hydroxyl groups will inevitably cause expansion of the Beta zeolite unit cell. The greater the number of tin ions that enter the dealubilized Beta zeolite framework through isomorphous substitution, the greater the expansion of the Beta zeolite unit cell.

[0039] The difference lies in the process: in the hydrothermal synthesis of heteroatom zeolites, the volume expansion of the heteroatom zeolite unit cells occurs on the growth surface of the zeolite crystal, i.e., the outer surface of the framework, regardless of whether it is during the nucleation or crystal growth stage. This volume expansion on the outer surface of the crystal framework is unimpeded and does not generate compressive stress pointing inwards. Therefore, for the de novo synthesis of Sn-Beta zeolite, the zeolite framework's capacity to contain a large number of tin ions is continuously acquired during the dynamic process of nucleation and crystal growth through the volume expansion of the forming unit cells on the grain surface. However, for the post-synthetic preparation of Sn-Beta zeolite, the overall rigid structure of the zeolite crystal has already been formed, and the framework vacancies (hydroxyl pockets) generated by dealumination are mainly distributed within the zeolite crystal framework. In this case, whenever a tin ion enters a hydroxyl pocket in the framework vacancy through isomorphic substitution, the hydroxyl pocket expands outwards under the pressure of the tin ion to gain sufficient containment to allow the larger tin ion to complete the isomorphic substitution reaction. The result of the extrusion stress being transmitted to the surrounding framework is that the volume of the adjacent hydroxyl dendrites is compressed, making it increasingly difficult for the remaining hydroxyl dendrites on the dealuminized Beta zeolite framework to be isomorphously replaced by tin ions.

[0040] Therefore, when preparing Sn-Beta zeolite using the post-synthesis method, if the volume expansion of the hydroxyl nests caused by the implantation of tin ions into the hydroxyl nests cannot be eliminated, the remaining hydroxyl nests will be squeezed and lose their "containment". It will be impossible to obtain high-quality Sn-Beta zeolite with fully utilized hydroxyl nests and high skeletal tin content rather than low skeletal tin content by the post-synthesis method.

[0041] After careful consideration, it was concluded that if one or two framework silicon atoms could be controllably removed from the hydroxyl nest walls of the dealuminized Beta zeolite (nesting modification), thereby expanding the small hydroxyl nests with only one framework atom defect (acid dealuminization) to larger hydroxyl nests with 2-3 framework atom defects, tin ions could easily enter and become framework tin through isomorphous substitution reactions, while avoiding the problems caused by the volume expansion of hydroxyl nests due to tin ion implantation. Following this line of thought, extensive exploratory research was conducted using weakly alkaline organic base aqueous solutions. Compared with alkali metal hydroxide (inorganic strong base) solutions and quaternary ammonium base solutions (organic strong base), the weakly alkaline organic bases have a weaker desilication ability, only capable of small-scale desilication, thus making it easier to achieve controllable desilication. Simultaneously, because of their weaker desilication ability, the weakly alkaline organic bases also easily achieve selective desilication, primarily targeting the weakest points in the Beta zeolite framework—the hydroxyl nest defects. The study found that aqueous solutions of small-molecule aliphatic amines (methylamine, ethylamine, propylamine, tert-butylamine, isopropylamine, n-butylamine, diethylamine, ethylenediamine, isobutylamine, triethylamine) and small-molecule alcoholic amines (ethanolamine, diethanolamine, triethanolamine, isopropanolamine, diisopropanolamine) exhibit controlled desilication when in contact with dealubilized Beta zeolite, demonstrating a "dimpling" effect on the hydroxyl groups in the dealubilized Beta zeolite. Compared with general organic bases, small-molecule aliphatic amines and alcoholic amines have the advantages of good water solubility and low dosage. As will be seen in the following examples, by applying a solid-solid isomorphic substitution reaction on a dealubilized Beta zeolite support that has undergone appropriate dimple-making modification with aqueous solutions of small-molecule aliphatic amines or alcoholic amines, high-quality Sn-Beta zeolite with fully utilized hydroxyl groups and high framework tin content rather than low framework tin content can be easily obtained. Therefore, in the method for preparing Sn-Beta zeolite catalyst by using hollow-modified dealubilized Beta zeolite as a carrier and utilizing solid-solid isomorphous substitution reaction provided by this invention, the dealubilized Beta zeolite is appropriately treated with an aqueous solution of small molecule aliphatic amines or alcoholic amines. The aim is to controllably remove 1-2 framework silicon atoms from the walls of its hydroxyl dendrites, thereby expanding the small hydroxyl dendrites with only one framework atom defect to larger hydroxyl dendrites with 2-3 framework atom defects. This is the core inventive idea and key technical feature.

[0042] In efforts to selectively synthesize caprolactone by catalyzing the Baeyer-Villiger reaction of cyclohexanone and hydrogen peroxide with the prepared Sn-Beta zeolite, it was found that the Sn-Beta zeolite prepared by the method of this invention can significantly improve the selectivity of caprolactone in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, even with a small amount of solvent (1,4-dioxane). For example, from the specific embodiments and comparative examples provided by the present invention, it can be seen that under the reaction conditions of batch reactor mode (atmospheric pressure, 90°C, reaction for 3 h) and low solvent dosage (the molar ratio of 1,4-dioxane (solvent): cyclohexanone: H2O2 is 5.5:1:0.4), the reaction results of a Sn-Beta zeolite catalyst with a tin content of 6 wt.% obtained by directly carrying out a solid-solid isomorphic substitution reaction on dealubilized Beta zeolite according to known methods are: cyclohexanone conversion of about 40% (theoretical value 40%) and caprolactone selectivity of about 13% (the remainder being 6-hydroxyhexanoic acid generated by the hydrolysis of caprolactone); while the Sn-Beta zeolite catalyst with the same tin content prepared according to the method provided by the present invention has a cyclohexanone conversion of about 38% and a caprolactone selectivity of about 41%.

[0043] It is important to emphasize that in order to controllably remove 1-2 more framework silicon atoms from the hydroxyl cell walls of dealubilized Beta zeolite, thereby expanding the small hydroxyl cell with only one framework atom defect to a larger hydroxyl cell with 2-3 framework atom defects, it is necessary to rationally utilize the combination of factors such as the type of small molecule organic amine or alkanolamine, solution concentration, solution volume, treatment temperature, and time as means to regulate the degree of desilication, and to take into account the difference in the molar ratio of silicon and aluminum oxides in the Beta zeolite parent material and the difference in the number of hydroxyl cells in the dealubilized Beta zeolite carrier.

[0044] The technical solution of the present invention:

[0045] A method for preparing a Sn-Beta zeolite catalyst to improve caprolactone selectivity includes the following steps:

[0046] The first step is to prepare a dealuminated Beta zeolite support.

[0047] Engineers skilled in the art can, according to the requirements of this invention, combine their own work experience with conventional acid dealumination methods in relevant literature, to obtain a dealuminated Beta zeolite support from a Beta zeolite parent material. The requirements of this invention are as follows:

[0048] (1) Select Beta zeolite parent material

[0049] The Beta zeolite matrix referred to herein is ordinary silica-alumina Beta zeolite. This invention does not limit the grain size of the Beta zeolite matrix, nor does it limit the production process of the Beta zeolite matrix. However, to facilitate the implementation of this invention, the following requirements are placed on the Beta zeolite matrix: 1) The Beta zeolite matrix is ​​free of impurities; 2) The Beta zeolite matrix has good crystallinity; 3) The molar ratio of silica-alumina oxides (SiO2 to Al2O3) in the Beta zeolite matrix is ​​appropriate.

[0050] The presence of impurities in the Beta zeolite matrix can be confirmed by X-ray polycrystalline powder diffraction (XRD). Those skilled in the art know that the molar ratio of silicon to aluminum oxide (SiO2 to Al2O3) in Beta zeolite produced by hydrothermal synthesis is typically between 10 and 200 (US3 308 069 (1967)). Beta zeolite products with lower SiO2 to Al2O3 molar ratios generally may contain mordenite (MOR) impurities, while Beta zeolite with higher SiO2 to Al2O3 molar ratios generally may contain ZSM-5 zeolite impurities. By sampling and performing XRD analysis on the Beta zeolite matrix, and comparing the XRD patterns of the samples with standard diffraction cards for Beta zeolite, MOR zeolite, and ZSM-5 zeolite, it can be determined whether the sample's XRD pattern contains characteristic peaks of MOR zeolite and ZSM-5 zeolite impurities, thus determining whether the Beta zeolite matrix is ​​a pure Beta zeolite phase.

[0051] Theoretically, the crystallinity of the Beta zeolite matrix can also be analyzed using XRD, with the relative crystallinity index used as a measure. However, the XRD relative crystallinity index requires comparing the sum of the intensities of the medium-intensity characteristic diffraction peaks in the Beta zeolite matrix located between 2θ = 7.6-8° and the highest-intensity characteristic diffraction peak located between 2θ = 22-23° with the sum of the intensities of the corresponding diffraction peaks in a reference sample (standard Beta zeolite with 100% crystallinity). Furthermore, there is no uniformly defined reference sample. Additionally, the intensities of the medium-intensity characteristic diffraction peaks in the 2θ = 7.6-8° and the highest-intensity characteristic diffraction peak located between 2θ = 22-23° are significantly affected by grain size, post-processing techniques such as calcination, and other conditions. Therefore, using the XRD relative crystallinity index to determine the crystallinity of a purchased or synthesized Beta zeolite matrix has poor general applicability. Therefore, this invention recommends using the specific surface area index of the Beta zeolite matrix to assess whether the crystallinity of the purchased or synthesized Beta zeolite matrix meets the requirements. Based on statistical results of literature reports on the specific surface area of ​​Beta zeolite, the BET specific surface area value of well-crystallized Beta zeolite produced by hydrothermal synthesis is generally not less than 450 m². 2 / g. Engineers skilled in the art can use conventional nitrogen physical adsorption methods to first measure the nitrogen adsorption isotherm data of the Beta zeolite matrix, and then calculate its BET specific surface area value according to the BET model. In summary, this invention requires that the BET specific surface area value of the Beta zeolite matrix used be ≥450m². 2 / g serves as a good criterion for determining crystallization.

[0052] The molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) is a key indicator for the Beta zeolite matrix. This is because, on the one hand, Beta zeolite matrices with a lower molar ratio of silicon-aluminum oxides, i.e., those with a higher skeletal aluminum content, can generate more hydroxyl groups after complete dealumination, which is relatively beneficial for introducing more tin atoms into the framework of dealugenized Beta zeolite in subsequent synthesis. On the other hand, pure-phase Beta zeolites with a very low molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) are more difficult to synthesize using hydrothermal methods. Moreover, Beta zeolite matrices with a very low molar ratio of silicon-aluminum oxides (SiO2 to Al2O3), after being converted into dealugenized Beta zeolite supports by acid dealumination, have poor framework thermal stability, which leads to a loss of crystallinity during the subsequent calcination process for preparing Sn-Beta zeolite catalysts, resulting in deteriorated catalyst performance. Therefore, the suitable range for the molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix required by this invention is between 10 and 200, preferably between 20 and 150, and more preferably between 25 and 100. The analysis of the molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix can be performed using conventional chemical analysis methods (tipping), or using X-ray fluorescence spectrometry (XRF) or inductively coupled plasma atomic emission spectrometry (ICP). This invention recommends the use of the simple and rapid XRF method.

[0053] The Beta zeolite matrix that meets the requirements of this invention can be obtained commercially or synthesized by engineers skilled in the art based on their experience and other literature reports.If synthesizing the Beta zeolite matrix yourself, the following methods reported in patents and publications are available: US3 308 069 (1967), EP187 522A2 (1986), US4847055 (1989), CN1 086 792A (application date 1993.9.20), CN1 108 213A (application date 1994.3.11), CN1 108214A (application date 1994.3.11), CN1 154 341A (application date 1996.1.11), CN1 154 242A (application date 1996.1.9), CN1 154 342A (application date 1996.1.11), CN1 268 545A (application date 1999.3.30), CN1 133497C (application date 1999.3.30), CN1 108 275C (application date 1999.9.10), CN1 100 004C (application date 2000.5.19), CN1 335 258A (application date 2001.2.28), CN1 116 227C (application date 2001.3.12), CN101205 072B (application date 2006.12.18), Chem. Comm., 1996, 625; J. Mater. Chem., 1998, 8(9), 2137-2145; Microporous and Mesoporous Materials 21(1998) 305-313; Applied CatalysisA-GENERAL,166(1998),97–103;Microporous and Mesoporous Materials 48(2001)23-29;Microporous and Mesoporous Materials 56(2002)1–10.;Journal of MolecularCatalysis A:Chemical 252(2006)76–84;Microporous and Mesoporous Materials 94(2006)1–8; J.Mater.Sci.41(2006)1861-1864; Cryst.Res.Technol.44,No.4,379-385(2009)DOI 10.1002 / crat.200800474; Microporous and Mesoporous Materials 143(2011)97-103;RSC Adv. 2019, 9, 3653-3660.

[0054] (2) Preparation of dealuminized Beta zeolite carrier

[0055] As mentioned earlier, conventional acid dealumination methods can be used to prepare dealusion-coated Beta zeolite supports based on a Beta zeolite matrix. This invention requires the dealusion-coated Beta zeolite support to have the highest possible molar ratio of silicon to aluminum oxides (SiO2 to Al2O3), meaning that as much skeletal aluminum as possible should be removed from the Beta zeolite matrix. A suitable range for the molar ratio of silicon to aluminum oxides (SiO2 to Al2O3) of the dealusion-coated Beta zeolite support meeting the requirements of this invention is ≥700, preferably ≥800, and more preferably ≥900. Because the dealusion-coated Beta zeolite has a high molar ratio of silicon to aluminum oxides (SiO2 to Al2O3) and a low aluminum content, accurate determination of this ratio requires inductively coupled plasma atomic emission spectrometry (ICP) or atomic absorption spectrometry (AA). This invention recommends using ICP.

[0056] When performing acid dealumination treatment on the Beta zeolite matrix, efforts should be made to remove all skeletal aluminum. The disadvantage of excessive skeletal aluminum remaining on the dealuminated Beta zeolite support is that the strong acidity of the skeletal aluminum will reduce the catalyst's selectivity for the caprolactone main product.

[0057] Although the skeletal aluminum of Beta zeolite is easy to remove, and dealuminate Beta zeolite carriers that meet the requirements of this invention can be prepared based on the Beta zeolite matrix using high-temperature steam dealumination, dealumination with complexing agents such as EDTA, dealumination with organic acid solutions, dealumination with inorganic acid (concentrated hydrochloric acid, concentrated nitric acid) solutions, or any combination of the above methods, considering the production cost, process complexity, and difficulty in treating the waste liquid generated during dealumination, this invention recommends using concentrated nitric acid aqueous solution dealumination to prepare dealuminate Beta zeolite carriers that meet the requirements of this invention.

[0058] Engineers skilled in the art can, based on their experience or by referring to the specific practices disclosed in the following documents, perform acid dealumination treatment on the Beta zeolite matrix with concentrated nitric acid aqueous solution to prepare a dealuded Beta zeolite support that meets the requirements of this invention: Chemical Communications, 1998, 1: 87-88; Micropor. Mesopor. Mater., 1999, 31: 163-173; Micropor. Mesopor. Mater., 2001, 49: 103–109; Micropor. Mesopor. Mater., 2008, 110: 480–487; Micropor. Mesopor. Mater., 2012, 163: 122-130; ACS Catalysis, 2014, 4(8): 2801-2810.

[0059] Studies have shown that when preparing dealugenized Beta zeolite carriers by acid dealumination of Beta zeolite matrix using concentrated nitric acid aqueous solution, the concentration of the nitric acid aqueous solution, the ratio of acid to zeolite (liquid-solid ratio), and the temperature and time of acid treatment are all important factors affecting the degree of acid dealumination of the Beta zeolite matrix. Ultimately, the influence of these factors on the dealumination of the Beta zeolite matrix is ​​reflected in the residual aluminum content of the dealugenized Beta zeolite carrier. Furthermore, the pretreatment of the Beta zeolite matrix also affects the degree of acid dealumination and the residual aluminum content of the dealugenized Beta zeolite carrier. However, if a dealugenized Beta zeolite carrier with the required silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) cannot be obtained after one dealumination, it is entirely possible to achieve the required silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of the dealugenized Beta zeolite through secondary or even multiple dealumination processes. This invention recommends using 13M concentrated nitric acid as the dealugenizing acid solution, and determining the acid volume according to a liquid-solid ratio of 20 ml / g. Under these conditions, the dealumination reaction was carried out at 95℃ for 20 hours to obtain a satisfactory dealugenized Beta zeolite support. Conventionally, the dealugenized Beta zeolite support prepared by the concentrated nitric acid dealumination method requires routine solid-liquid separation to recover the solid product. The solid product is then washed with water until the pH is neutral, dried at 80-200℃ for 3-24 hours, and finally calcined at 500-600℃ for 3-8 hours to obtain the dealugenized Beta zeolite support. After dealumination, the Beta zeolite matrix generates a large number of hydroxyl lattice defect sites, increasing its water absorption and moisture absorption capacity; therefore, it should be stored in a sealed container for later use.

[0060] The second step involves modifying the hydroxyl groups of the dealuminated Beta zeolite support by using an aqueous solution of small-molecule fatty amines and / or alcoholic amines (weak organic bases).

[0061] The hydroxyl-derived pit modification is carried out using a conventional aqueous solution impregnation method. Pitting modification is essentially an alkaline-catalyzed hydrolysis reaction modification ([(OSi)3-O-SiOH]+3H2O=Si(OH)4+3≡Si-OH). For each skeletal silicon atom released (existing in the form of orthosilicic acid (Si(OH)4)), i.e., for each silicon atom (existing in the form of Si(OH)4) "chiseled" from the hydroxyl-derived pit wall, three silanol groups (≡SiOH) are generated on the new pit wall of the hydroxyl-derived pit.

[0062] The small molecule aliphatic amines mainly refer to methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine, or ethylenediamine. The small molecule alcoholic amines mainly refer to ethanolamine, isopropanolamine, diethanolamine, diisopropanolamine, or triethanolamine. Hole-knocking modification of the hydroxyl groups on the dealubilized Beta zeolite support can be performed using aqueous solutions of any one or more of the above-mentioned small molecule aliphatic amines and alcoholic amines, or aqueous solutions of any combination of the above-mentioned small molecule aliphatic amines and alcoholic amines. However, it should be noted that other aliphatic amines and alcoholic amines, as well as other organic amines (such as alicyclic amines), also have the effect of hole-knocking modification of the hydroxyl groups on the dealubilized Beta zeolite support. However, the advantages of small molecule aliphatic amines and alcoholic amines are their good water solubility, low dosage, and low cost and availability.

[0063] Hollowing modification of dealubilized Beta zeolite carrier was carried out by impregnation in an aqueous solution of small molecule fatty amines and / or alkanolamines. After the hollowing modification was completed, the dealubilized Beta zeolite carrier was obtained by solid-liquid separation, drying and calcination. The concentration of the hollowing solution (aqueous solution of small molecule fatty amines and / or alkanolamines), the ratio of the hollowing solution to the dealubilized Beta zeolite carrier (i.e., the liquid-solid ratio (ml / g), and the desilication reaction temperature and time of the hollowing modification were the main factors affecting the controllable desilication modification of hydroxyl groups of dealubilized Beta zeolite (hollowing modification).

[0064] An aqueous solution of small molecule fatty amines and / or alcoholic amines is called a denting solution, which contains one or more of the aforementioned small molecule fatty amines and / or small molecule alcoholic amines, under the following conditions:

[0065] The suitable concentration range of the denting solution is 0.01M-0.4M, the preferred range is 0.02M-0.3M, and the more preferred range is 0.03M-0.16M.

[0066] The suitable range for the ratio of the denting solution to the dealuminolite Beta zeolite carrier, i.e. the liquid-solid ratio (ml / g), is 1:1-100:1, preferably 2:1-50:1; and more preferably 3:1-20:1.

[0067] The suitable range of desilication reaction temperature for the dent modification is 20℃-100℃; the preferred range is 30℃-90℃; and the more preferred range is 40℃-80℃.

[0068] The suitable range for the desilication reaction time of the dent modification is 0.5h-24h; the preferred range is 0.5h-10h; and the more preferred range is 1h-5h.

[0069] Engineers skilled in the art can refer to the impregnation process commonly used in the preparation of heterogeneous catalysts, and use the small molecule aliphatic amines and alcoholic amines recommended in this invention to prepare a dimerizing solution. Within the above-mentioned conditions, the dealuminolite Beta zeolite support can be dimerized to achieve the purpose of dimerizing the hydroxyl dimers of the dealuminolite Beta zeolite support. Details will not be elaborated further. After dimerizing modification, the liquid-solid mixture can be post-processed according to common practice, mainly including conventional liquid-solid separation, water washing (to neutral pH), drying, and calcination. The dimerized dealuminolite Beta zeolite support after calcination needs to be sealed and stored for later use to prevent water absorption. The drying and calcination conditions can refer to the drying and calcination conditions for the dealuminolite Beta zeolite support in the first step (preparation of dealuminolite Beta zeolite support) of this embodiment of the invention. Further details will not be elaborated further.

[0070] However, it is important to further emphasize that for dealuated Beta zeolite supports with varying numbers of hydroxyl holes prepared from Beta zeolite matrices using different molar ratios of silicon and aluminum oxides (SiO2 to Al2O3), the key to achieving controllable hole-knocking modification of the hydroxyl holes using aqueous solutions of small-molecule aliphatic amines and / or alkanolamines lies in correctly selecting modification conditions composed of four parameters: hole-knocking solution concentration, liquid-to-solid ratio (ml / g), desilication reaction temperature, and time. It is easy to understand that modification conditions composed of the lower limits of the above four parameters have the weakest desilication effect and are suitable for hole-knocking modification of dealuated Beta zeolite supports with a small number of hydroxyl holes; modification conditions composed of the upper limits of the above four parameters have the strongest desilication effect and can be used for hole-knocking modification of dealuated Beta zeolite supports with a large number of hydroxyl holes; and modification conditions composed of other different values ​​of the above five parameters within a specified range will produce different desilication effects between the weakest and strongest. The above explanation of the present invention is intended to provide principled guidance for engineers in the art. For different dealuated Beta zeolite carriers, the impregnation conditions for achieving moderate denting modification with aqueous solutions of small molecule fatty amines and / or alkanolamines are best determined experimentally.

[0071] The third step involves preparing Sn-Beta zeolite via a solid-solid isomorphic substitution reaction using dimpled modified dealuminolite as a carrier.

[0072] Following the solid-solid isomorphic substitution reaction method, the dimpled modified dealuated Beta zeolite support is first mixed with a tin source in a solid phase and ground until homogeneous. Then, the solid mixture is successively calcined in a nitrogen atmosphere and an air atmosphere to obtain Sn-Beta zeolite.

[0073] Because solid-solid isomorphic substitution reactions require hydroxyl holes to occur, the molar ratio of silicon and aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix determines the number of hydroxyl holes in the dealuminated Beta zeolite support and the hollowed-out Beta zeolite support. The number of hydroxyl holes in the zeolite support, in turn, determines the theoretical maximum tin content of the Sn-Beta zeolite catalyst. Therefore, this invention specifies the percentage of hydroxyl holes in the zeolite support as a crucial technical parameter for preparing Sn-Beta zeolite from Beta zeolite matrices with different molar ratios of silicon and aluminum oxides (SiO2 to Al2O3) via solid-solid isomorphic substitution reactions. This parameter can be used to calculate the ratio of zeolite support to tin source.

[0074] This invention requires that, when preparing Sn-Beta zeolite from Beta zeolite parent materials with different molar ratios of silicon-aluminum oxides (SiO2 to Al2O3) via a solid-solid isomorphic substitution reaction, the proportion of zeolite support and tin source is determined by the percentage of the number of moles of tin ions relative to the number of moles of hydroxyl groups in the zeolite support. The suitable range is 5%-100%, the preferred range is 15%-80%, and the more preferred range is 30%-60%. That is, the number of hydroxyl groups is calculated based on the mass of the zeolite support, and the required amount of tin ions is determined according to the proportion, thereby calculating the required mass of the tin source. The number of moles of hydroxyl groups in a given mass of zeolite support is equal to the number of moles of acid-induced aluminum removal when preparing the same mass of zeolite support.

[0075] The solid-solid isomorphic substitution reaction can be carried out according to existing methods. The following references are available: US2016279621(A1) (application date 2014-11-05), CN106984356A (application date 2017-05-05), ACSCatalysis, 2014, 4(8): 2801-2810, Angewandte Chemie International Edition, 2012, 51(47): 11736-11739, Master's thesis "Rapid Synthesis of Sn-Beta Molecular Sieves and Catalytic Sugar Conversion to Prepare Lactate Ester", Zhengzhou University (2017).

[0076] Based on existing methods, the present invention summarizes the following operational steps for preparing Sn-Beta zeolite using a solid-solid isomorphous substitution reaction method:

[0077] (1) Based on the number of hydroxyl holes in the dealuminated Beta zeolite carrier modified by denting, the amount of tin source is calculated according to the percentage of the number of tin ions to the number of hydroxyl holes in the zeolite carrier.

[0078] (2) The dealuminated Beta zeolite carrier that has been modified by denting, dried and calcined and is in a dry state is mixed with a metered tin source and thoroughly ground.

[0079] (3) A solid mixture of thoroughly homogenized zeolite support and tin source is placed in a tubular reactor for a solid-solid substitution reaction. First, high-purity nitrogen is introduced into the reactor to completely replace the air inside. Then, the solid mixture in the reactor is heated to 200°C at a heating rate of 6°C / min in a high-purity nitrogen atmosphere and held at this temperature for 1-3 hours to allow the tin source to diffuse into the zeolite channels. Next, the solid mixture in the reactor is heated to the range of 450°C-550°C at a heating rate of 7°C / min in a high-purity nitrogen atmosphere and held at this temperature for 6-8 hours to complete the solid-solid isomorphic substitution reaction. Midway through the solid-solid isomorphic substitution reaction (when the temperature is held at 450°C-550°C for 3-4 hours), the high-purity nitrogen atmosphere introduced into the reactor is changed to an air atmosphere. After the solid-solid isomorphic substitution reaction is completed, the Sn-Beta zeolite product prepared by the method of this invention is obtained.

[0080] The tin source is a common tin hydrochloride and acetate, specifically including tin tetrachloride pentahydrate, tin chloride dihydrate and tin acetate (II), preferably tin chloride dihydrate and tin acetate (II), more preferably tin acetate (II).

[0081] Engineers skilled in the art can, based on their own experience or by referring to the solid-solid isomorphic substitution method reported in existing literature and patents, prepare Sn-Beta zeolite using dimpled modified dealuded Beta zeolite as a carrier, in accordance with the requirements of this invention.

[0082] The Sn-Beta zeolite prepared by the above method was used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide to synthesize caprolactone.

[0083] The cyclohexanone oxidation reaction with hydrogen peroxide and Baeyer-Villiger peroxide is carried out according to existing methods. The reactor can be a batch reactor, a fixed-bed continuous reactor, or even a catalytic distillation reactor; this invention is not limited in this regard. Engineers skilled in the art can, based on their experience or reports in existing literature and patents, use the Sn-Beta zeolite prepared by the method of this invention as a catalyst to carry out the cyclohexanone oxidation reaction with hydrogen peroxide and Baeyer-Villiger peroxide, thereby improving the selectivity of the target product, caprolactone. The following publicly available documents and patents report Baeyer-Villiger oxidation methods of cyclohexanone with hydrogen peroxide for reference: CN1071923A (application date 1993-10-25), JP2000256348A (application date 1993-03-12), US6531615B (application date 2001-01-30), CN104211675A (application date 2014-09-22), CN104370873A (application date 2014-11-2). 1) CN111170982A (application date 2020-01-09), CN111285381B (application date 2020-03-09), CN112645346A (application date 2020-12-23), CN114210362A (application date 2021-11-30), Nature, 2001, 412, 423-425, Chem. Eur. J. 2002, 8, 4708-4717, J. Phys. Chem. C 2011,115,3663–3670, Chin.J.Catal.,2012,33:898–904, Angew.Chem.Int.Ed.2012,51,11736–11739, Chem.Eng.J .2013,218,425-432, Catal.Sci.Technol.,2016,6,2787–2795, Chem.Commun.,2016,52,6712-6715, J.Phys.Chem.C 2016,120,23613-23624, J. Catal.2017,352,1–12, Micropor.Mesopor.Mat.,2018,266,242–251, Micropor.Mesopor.Mat.,2018,287,85–92, ACS Catal.2020,10,14135-14146, Micropor.Mesopor.Mat.,2021,320,111090, Fuel,2023,340,127505, RSC Adv.,2023,13,4835–4842, ACS Appl.Nano Mater.2024, 7, 9314-9323, Doctoral Dissertation "Synthesis, Characterization and Catalytic Performance Study of Sn-Beta Molecular Sieves", Dalian University of Technology (2012); Doctoral Dissertation "Aerosol-Assisted Synthesis of Sn-Beta Molecular Sieves and Its Catalytic Performance in Baeyer-Villiger Oxidation Reaction", Dalian University of Technology (2019); Master's Thesis "Preparation of Sn-Beta Molecular Sieves and Its Cyclohexanone Oxidation Reaction Performance Study", Dalian University of Technology (2020); Master's Thesis "Preparation of Sn-Beta Molecular Sieves by Aerosol-Assisted Post-Synthesis Method and Its BV Oxidation Reaction Performance Study", Dalian University of Technology (2020); Master's Thesis "Study on Influencing Factors of Cyclohexanone Oxidation Reaction on Sn-β Zeolite", Dalian University of Technology (2022).

[0084] To illustrate the effect of the Sn-Beta zeolite catalyst prepared by the method of this invention on improving the selectivity of the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, this invention employs a batch reactor to conduct the cyclohexanone oxidation reaction with hydrogen peroxide under harsh conditions of relatively small amounts of the reaction solvent (1,4-dioxane). The method is as follows: First, 1,4-dioxane solvent, cyclohexanone, and hydrogen peroxide solution are added sequentially to the batch reactor. Finally, the Sn-Beta zeolite catalyst prepared by the method of this invention is added. The reaction is carried out under atmospheric pressure and stirring. The reaction conditions are: reaction temperature 90℃, reaction time 3 h, catalyst dosage based on cyclohexanone reactant 0.6 g / g, hydrogen peroxide feed concentration 50 wt%, and 1,4-dioxane:cyclohexanone:H2O2 = 12.5:2.5:1.

[0085] Beneficial effects of the present invention

[0086] In summary, this invention provides a method for preparing Sn-Beta zeolite catalysts using hollow-modified dealubilized Beta zeolite as a support via a solid-solid isomorphous substitution reaction. The key to this invention lies in the hollow-modification treatment of the hydroxyl groups in the dealubilized Beta zeolite with an aqueous solution of a small-molecule aliphatic amine or alkanolamine before the solid-solid isomorphous substitution reaction, thereby expanding the inclusion capacity of the hydroxyl groups for tin ions. The key technical method provided by this invention solves the problem that heteroatom tin, due to its large ionic radius, is difficult to enter the hydroxyl groups of dealubilized Beta zeolite for isomorphous substitution reactions, while avoiding the problem caused by the volume expansion of the hydroxyl groups due to tin ion implantation. Using this method, high-quality Sn-Beta zeolite with fully utilized hydroxyl groups and a high skeletal tin content (rather than a low skeletal tin content) can be easily obtained. The Sn-Beta zeolite prepared by this method can significantly improve the selectivity of caprolactone even with a relatively small amount of solvent (1,4-dioxane). Attached Figure Description

[0087] Figure 1 The first type of Beta zeolite carrier (Beta24c) is prepared by acid dealumination treatment of a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3) of 24. The second type of Beta zeolite carrier (Beta24C) is prepared by denting modification treatment based on Beta24c. 44 Comparison of infrared spectra of the hydroxyl region of )

[0088] Figure 2 Before the dented modified dealuminite Beta zeolite support prepared by the method of this invention was replaced by tin ion solid-solid isomorphic substitution (Beta24C) 44 (Beta24C) 44 Comparison of changes in the infrared spectrum of the hydroxyl region (-6Sn).

[0089] Figure 3 This refers to Sn-Beta zeolite catalysts (Beta24c-6Sn) prepared by directly using a dealuminated Beta zeolite support in a solid-solid isomorphic substitution reaction of tin ions, and Sn-Beta zeolite catalysts (Beta24C) prepared by first subjecting a dealuminated Beta zeolite support to a denting modification treatment before using it in a solid-solid isomorphic substitution reaction of tin ions. 44 -6Sn), UV-Vis spectral characterization results of skeletal tin content.

[0090] Figure 4 This is a comparison of the changes in the infrared spectrum of the hydroxyl region of the dealuminated Beta zeolite support before (Beta24c) and after (Beta24c-6Sn) substitution by tin ions for solid-solid isomorphic crystals. Detailed Implementation

[0091] The effectiveness of this invention can be evaluated through two aspects: physicochemical property characterization and catalyst performance testing.

[0092] in:

[0093] (1) The effect of aqueous solutions of small-molecule aliphatic amines or alcoholic amines on the hydroxyl dimple modification of dealubilized Beta zeolite can be characterized by Fourier transform infrared spectroscopy (FT-IR) and evaluated by inductively coupled plasma atomic emission spectroscopy (ICP) to detect the amount of desilication. It should be noted that the most typical characteristic band of hydroxyl dimples in dealubilized zeolite is located in the 3400-3600 cm⁻¹ region. -1 A continuous absorption band within the range, with a maximum value typically around 3500 cm⁻¹. -1(References: RSC Adv., 2023, 13, 4835–4842; ACS Sustainable Chem. Eng. 2022, 10, 4391-4403; ACS Catal. 2020, 10, 14135-14146; ACS Catal. 2016, 6, 31-46). In addition, terminal silanol groups may exist in larger hydroxyl clusters, and their vibrational absorption can occur at 3740 cm⁻¹. -1 At this location, it overlaps with the surface silanol group.

[0094] (2) In the case of tin ions being implanted into hydroxyl nests by solid-solid isomorphic substitution reaction, the intensity attenuation of the hydroxyl nest band of dealuated Beta zeolite can be evaluated by Fourier transform infrared spectroscopy (FT-IR).

[0095] (3) The distribution of framework tin and non-framework tin in Sn-Beta zeolite catalysts with different tin contents prepared by solid-solid isomorphic substitution reaction can be characterized by diffuse reflectance ultraviolet-visible spectroscopy.

[0096] (4) The catalytic performance of Sn-Beta zeolite catalysts with different tin contents prepared by the method of this invention in the Beayer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide was evaluated using a batch reactor. The product solution was analyzed by an Agilent 7890B gas chromatograph with a CP-Wax 52CB column (25m × 0.32mm × 1.2μm), a detector temperature of 240℃, and an injection port temperature of 200℃. The column temperature was initially set at 80℃ and held for 1 min, then increased to 150℃ at a rate of 12℃ / min and held for 2 min, and then increased to 250℃ at a rate of 10℃ / min and held for 20 min. The conversion rate of cyclohexanone and the selectivity of caprolactone were quantitatively calculated using the internal standard method.

[0097] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to these embodiments.

[0098] Example 1: This example illustrates how a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment using an aqueous solution of small-molecule fatty amines and / or alkanolamines. This treatment aims to controllably remove 1-2 skeletal silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one skeletal atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 skeletal atom defects. Then, using the "dimpling-modified" dealuminized Beta zeolite as a support, Sn-Beta zeolite is prepared via a solid-solid isomorphous substitution reaction, which facilitates the isomorphous substitution reaction of tin ions. The Sn-Beta zeolite prepared using this method has a high skeletal tin content, low non-skeletal tin content, and high hydroxyl cell utilization. The prepared Sn-Beta zeolite catalyst exhibits high selectivity for caprolactone products in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide.

[0099] Step 1: Preparation of dealuminolite Beta zeolite support

[0100] (1) Following the hydrothermal crystallization method provided in US Patent 3,308,069 (1967), a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 25 was synthesized as a raw material for preparing a dealuminized Beta zeolite support. After conventional filtration, washing, drying (110°C, 12 h), and calcination to remove the template agent (540°C, 6 h), the synthesized Beta zeolite matrix was observed by TEM to have a grain size of less than 100 nm, classifying it as nano-Beta zeolite. XRD analysis revealed no impurities. Calculations based on its nitrogen physical adsorption data showed a BET specific surface area of ​​approximately 550 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was approximately 24, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0101] (2) The Beta zeolite matrix was treated with concentrated nitric acid to prepare a dealuminized Beta zeolite carrier.

[0102] First, a concentrated nitric acid solution with a molar concentration of 13M was prepared. Then, 20g of the Beta zeolite precursor, which had undergone the above-mentioned drying and calcination treatment, was added to a three-necked flask containing 400ml of 13M concentrated nitric acid solution under stirring, at a liquid-to-solid ratio of 20:1 (ml / g). The dealuminization process was carried out at 95℃ for 20h. During the dealuminization reaction, the three-necked flask was kept under reflux. After the dealuminization reaction was completed, the solution was cooled to room temperature and filtered to recover the solid product. Then, it was washed with water, dried (overnight at 110℃), and calcined (550℃, 3h) to obtain the dealuminated Beta zeolite support Beta24c. The molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) of the dealuminated Beta zeolite support was determined to be 980 by ICP. This is suitable for the purpose of this invention. Store in a sealed container to avoid moisture absorption.

[0103] The second step involves using an aqueous solution of ethanolamine to perform a pitting modification treatment on the hydroxyl groups of the dealuminized Beta zeolite support.

[0104] The denting modification was carried out by atmospheric pressure impregnation. First, a 44 mmol / L (44 mM) aqueous solution of ethanolamine was prepared as the denting modification solution. Then, 20 g of dealuminized Beta zeolite support was added to 120 ml of ethanolamine modification solution at a liquid-to-solid ratio of 6:1 (ml / g). The reactants were heated to 40 °C with stirring and reacted at this temperature with continuous stirring for 1 h. During this period, the dealuminized Beta zeolite support underwent a weak alkaline-catalyzed hydrolysis desilication reaction in the weakly alkaline solution of ethanolamine ([(OSi)3-O-SiOH]+3H2O=Si(OH)4+3≡Si-OH). For each silicon atom removed (existing in the form of orthosilicic acid (Si(OH)4)), three silanol groups (≡Si-OH) were generated on the new dent wall of the hydroxyl group. After reacting for 1 hour, the reactants were filtered to recover the solid product. The solid product was then repeatedly washed with deionized water until neutral, followed by drying (overnight at 110°C) and calcination (550°C, 3 hours) to obtain the dimpled modified dealubilized Beta zeolite support. It was sealed and stored for later use. Based on weight reduction estimates, an average of 1.07 framework silicon atoms (calculated as SiO2) were removed from each hydroxyl lattice defect site of the dealubilized Beta zeolite support. This indicates that the dimpled modification was carried out under controlled conditions with moderate desilication, meeting the requirements for dimpled modification of the dealubilized Beta zeolite support. The dimpled modified support is designated Beta24C. 44 (The capital "C" indicates that the denting modification increases the hydroxyl cavity volume in the dealuminized Beta zeolite). Fourier transform infrared spectroscopy (FT-IR) was used to obtain the dealuminized Beta zeolite support (Beta24c) and its dented-modified sample (Beta24C). 44 The infrared spectrum of hydroxyl vibrations, such as Figure 1 As shown. By Figure 1 It can be seen that after the dealuminated Beta zeolite support is modified by denting, its characteristic hydroxyl dent band (3400 cm⁻¹) is present. -1 -3600cm -1 The significant changes indicate that the dimpling modification does indeed occur at the hydroxyl lattice defect sites of the dealuminated Beta zeolite.

[0105] Step 3: Using tin acetate (II) as the tin source, Sn-Beta zeolite was prepared on a hollowed-out dealuminized Beta zeolite support using a solid-solid isomorphic substitution method.

[0106] (1) Take 10g of the dented modified dealuminolite Beta zeolite carrier Beta24C 44 The total number of hydroxyl clusters in the sample was 13 mmol (estimated using the amount of dealumination from the Beta zeolite matrix). Based on the assumption that 38% of the hydroxyl clusters participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated, resulting in 1.20 g of tin(II) acetate.

[0107] (2) 10g of zeolite carrier Beta24C that has been modified by denting, dried and calcined and is in a dry state 44 Mix with 1.2g of tin(II) acetate and grind thoroughly;

[0108] (3) A thoroughly homogenized solid mixture of zeolite and tin source is placed in a tubular reactor for a solid-solid substitution reaction. First, high-purity nitrogen gas (60 mL / min) is introduced into the reactor to completely replace the air inside. Then, the solid mixture in the reactor is heated to 200°C in a high-purity nitrogen atmosphere at a heating rate of 6°C / min and held at this temperature for 1 hour to allow the tin source to diffuse into the zeolite channels. Next, the solid mixture in the reactor is heated to 550°C in a high-purity nitrogen atmosphere at a heating rate of 7°C / min and held at this temperature for 6 hours to complete the solid-solid isomorphic substitution reaction. Midway through the solid-solid isomorphic substitution reaction (when the temperature is held at 550°C for 3 hours), the high-purity nitrogen atmosphere introduced into the reactor is changed to an air atmosphere. After the solid-solid isomorphic substitution reaction is completed, the Sn-Beta zeolite product prepared by the method of this invention is obtained, designated Beta24C. 44 -6Sn.

[0109] (4) The prepared Sn-Beta zeolite product Beta24C 44 Physicochemical characterization of -6Sn: Beta24C was determined by XRF. 44 The Si / Sn ratio of the -6Sn zeolite catalyst is 33. Fourier transform infrared spectroscopy was used to characterize the changes in the hydroxyl bands of the zeolite support before and after the solid-solid isomorphic substitution reaction. The results are as follows: Figure 2 As shown. Beta24C was characterized by UV-Vis spectroscopy.44 The distribution of tin species in the -6Sn zeolite catalyst is shown in the following results. Figure 3 As shown. From Figure 2 The hydroxyl infrared spectroscopy characterization results show that first, the dealuitized Beta zeolite was subjected to controlled "dimpling modification" with an aqueous solution of ethanolamine to expand the containment capacity of tin ions in the hydroxyl nests. Then, using the "dimpling modified" dealuitized Beta zeolite as a support, Sn-Beta zeolite was prepared by solid-solid isomorphic substitution reaction, which is beneficial for the solid-solid isomorphic substitution reaction of tin ions in the hydroxyl nests. The result is that in the prepared Beta24C... 44 In the -6Sn zeolite catalyst, the intensity of the silanol vibrational infrared absorption band related to the hydroxyl nests on the support is significantly weakened, indicating that the hydroxyl nests are largely occupied by tin ions. Figure 3 As can be seen, Beta24C 44 The 6Sn zeolite catalyst contains a high amount of skeletal tin (characteristic absorption band at 215 nm). In summary, the physicochemical characterization demonstrates the significant effectiveness of this invention.

[0110] Step 4: Use Beta24C 44 -6Sn zeolite catalyst catalyzes the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone to synthesize caprolactone.

[0111] (1) Using a 50mL round-bottom flask as the reactor, according to the molar ratio of 1,4-dioxane:cyclohexanone:H2O2 of 5.5:1:0.4, first add 5g of 1,4-dioxane as a solvent to the reactor, then add 1g of cyclohexanone and 0.2756g of 50wt% hydrogen peroxide, put in the rotor, and connect the condenser.

[0112] (2) Turn on the stirrer and set the oil bath temperature to 90°C to begin heating. Once the reactor reaches the specified reaction temperature, add approximately 0.6g of Beta24C. 44 -6Sn zeolite catalyst was used and the timing was started, with the reaction time set at 3 hours.

[0113] (3) After the reaction was completed, the reactants were centrifuged, and the supernatant was analyzed by gas chromatography. Based on the chromatographic analysis data, the reaction results were calculated as follows: cyclohexanone conversion rate 38.28% (the theoretical conversion rate based on the amount of hydrogen peroxide used is 40%), caprolactone selectivity 40.61%, and hydrogen peroxide conversion rate 92.89%.

[0114] Comparative Example 1: This example illustrates that if the dealuated Beta zeolite support is not first "dimpling modification" with an aqueous solution of small-molecule aliphatic amines and / or alkanolamines, but instead directly prepared as a solid-solid isomorphous substitution reaction using dealuated Beta zeolite as the support, the isomorphous substitution reaction of tin ions is less likely to occur. Therefore, the prepared Sn-Beta zeolite has a low framework tin content, a high non-framework tin content, and low hydroxyl nest utilization. The prepared Sn-Beta zeolite catalyst exhibits poor selectivity for caprolactone products in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide.

[0115] Example 1 was repeated, but after the dealuated Beta zeolite support Beta24c was prepared in the first step, the second step was skipped and the dealuated Beta zeolite support Beta24c was directly used in the third step, that is, Sn-Beta zeolite was prepared by solid-solid isomorphic substitution reaction using dealuated Beta zeolite Beta24c as support. The Sn-Beta zeolite catalyst obtained was designated as Beta24c-6Sn.

[0116] The physicochemical properties of the prepared Sn-Beta zeolite product, Beta24c-6Sn, were characterized: the Si / Sn ratio of the Beta24c-6Sn zeolite catalyst was also determined to be 33 by XRF. The tin species distribution of the Beta24c-6Sn zeolite catalyst was characterized by UV-Vis spectroscopy, and the results are as follows... Figure 3 As shown. Fourier transform infrared spectroscopy was used to characterize the changes in the hydroxyl bands of the zeolite support before and after the solid-solid isomorphic substitution reaction. The results are as follows. Figure 4 As shown. From Figure 3 It is evident that the skeletal tin content (characteristic absorption band at 210 nm) in the Beta24c-6Sn zeolite catalyst is low. From... Figure 4 The infrared spectral characterization results of the hydroxyl groups show that, without first subjecting the dealuated Beta zeolite to a controlled "dimpling modification" treatment with a weak organic base aqueous solution, directly using dealuated Beta zeolite as a support to prepare Sn-Beta zeolite via a solid-solid isomorphic substitution reaction is not conducive to the solid-solid isomorphic substitution reaction of tin ions in the hydroxyl groups. As a result, in the prepared Beta24c-6Sn zeolite catalyst, the intensity of the silanol vibrational infrared absorption band related to the hydroxyl groups on the support is only slightly weakened, indicating that the hydroxyl groups are not extensively utilized by tin ions. This is consistent with the property characterization results of Example 1 (…). Figure 1 and Figure 2The benefits of this invention are readily apparent upon comparison. Furthermore, using the Beta24c-6Sn zeolite catalyst in the fourth step of the hydrogen peroxide and cyclohexanone Beayer-Villiger oxidation reaction yielded a cyclohexanone conversion of 39.66% (theoretical conversion 40%), a caprolactone product selectivity of 12.78%, and a hydrogen peroxide conversion of 96.58%. A comparison with the reaction data of Example 1 clearly shows that the method provided by this invention for preparing the Sn-Beta zeolite catalyst—namely, the controlled "dimpling modification" treatment of the dealuated Beta zeolite with a weak organic base aqueous solution, followed by the use of the "dimpling modified" dealuated Beta zeolite as a support for a solid-solid isomorphic substitution reaction to prepare Sn-Beta zeolite—is beneficial for improving the caprolactone product selectivity in the hydrogen peroxide and cyclohexanone Beayer-Villiger oxidation reaction.

[0117] Example 2: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealubilized Beta zeolite support using an aqueous solution of a small-molecule fatty amine or / and an alkanolamine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealubilized Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The aqueous solution of the small-molecule fatty amine or / and alkanolamine refers to aqueous solutions of different small-molecule fatty amines and any mixtures thereof, aqueous solutions of different small-molecule alkanolamines and any mixtures thereof, and aqueous solutions of any mixture of small-molecule fatty amines and alkanolamines. Changing the type of the small-molecule fatty amine and alkanolamine, or using any mixture thereof, only affects the degree of "dimpling modification" of the hydroxyl cells of the dealubilized Beta zeolite, without altering the benefits of the present invention.

[0118] Example 1 was repeated. However, in the second step of the hollowing modification treatment of the hydroxyl holes in the dealuminolite zeolite support, aqueous solutions of isopropanolamine, diethanolamine, diisopropanolamine, and triethanolamine at 44 mmol / L (44 mM) were used sequentially, while other hollowing modification conditions and procedures remained unchanged. Based on weight reduction estimates, the average number of framework silicon atoms (calculated as SiO2) removed from the hydroxyl hole lattice defect sites of the dealuminolite zeolite support was 1.04, 1.02, 0.99, and 0.95 respectively. This indicates that when using aqueous solutions of isopropanolamine, diethanolamine, diisopropanolamine, and triethanolamine, the hollowing modification was also carried out under controlled conditions with moderate desilication, achieving the requirements for hollowing modification of the dealuminolite zeolite support. The obtained dent-modified dealuminated Beta zeolite support was used in the third step, namely, Sn-Beta zeolite was prepared using tin(II) acetate as the tin source and a solid-solid isomorphous substitution method. The resulting Sn-Beta zeolite catalyst showed cyclohexanone conversion rates of 39.29%, 38.47%, 39.33%, and 38.54% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, respectively; caprolactone product selectivity of 33.30%, 32.56%, 32.00%, and 31.22%, respectively; and hydrogen peroxide conversion rates of 94.70%, 93.68%, 95.83%, and 93.85%, respectively.

[0119] Example 3: This example further illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealuated Beta zeolite support using an aqueous solution of a small molecule fatty amine and / or an alcoholic amine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealuated Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The aqueous solution of the small molecule fatty amine and / or an alcoholic amine refers to aqueous solutions of different small molecule fatty amines and any mixtures thereof, aqueous solutions of different small molecule alcoholic amines and any mixtures thereof, and aqueous solutions of any mixture of small molecule fatty amines and alcoholic amines. Changing the type of the small molecule fatty amine and alcoholic amine, or using any mixture thereof, only affects the degree of "dimpling modification" of the hydroxyl cells of the dealuated Beta zeolite, without altering the benefits of the present invention.

[0120] Repeat Example 1. However, in the second step of the hydroxyl dimple modification treatment of the dealuminized Beta zeolite support, the aqueous solutions of methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine and ethylenediamine at 44 mmol / L (44 mM) were used in sequence, while the other dimple modification conditions and procedures remained unchanged. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) removed from the hydroxyl-hole lattice defect sites of the dealuminized Beta zeolite support were 1.12, 1.10, 1.25, 1.23, 1.19, 1.14, 1.36, 1.33, 1.28, and 1.08, respectively. This indicates that when using aqueous solutions of methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine, and ethylenediamine, the hole-knocking modification was carried out under controlled conditions with moderate desilication, meeting the requirements for hole-knocking modification of the dealuminized Beta zeolite support. The resulting dent-modified dealuminated Beta zeolite support was used in the third step, namely, Sn-Beta zeolite was prepared using tin(II) acetate as the tin source and a solid-solid isomorphic substitution method. The cyclohexanone conversion rates of the obtained Sn-Beta zeolite catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 38.44%, 38.50%, 38.01%, 38.05%, 38.18%, 38.32%, 37.99%, 38.14%, and 37. The selectivity of caprolactone products was 35.52%, 35.43%, 36.11%, 35.89%, 35.74%, 35.61%, 35.33%, 35.02%, 34.89%, and 34.48%, respectively, and the conversion rates of hydrogen peroxide were 94.1%, 94.23%, 93.03%, 93.33%, 93.65%, 93.66%, 92.98%, 93.55%, 93.01%, and 89.90%, respectively.

[0121] Example 4: This example further illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealubilized Beta zeolite support using an aqueous solution of a small molecule fatty amine and / or an alcoholic amine to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls. This expands the small hydroxyl cells, which originally had only one framework atom defect (acid dealumination), into larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealubilized Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The aqueous solution of the small molecule fatty amine and / or an alcoholic amine refers to aqueous solutions of different small molecule fatty amines and any mixtures thereof, aqueous solutions of different small molecule alcoholic amines and any mixtures thereof, and aqueous solutions of any mixture of small molecule fatty amines and alcoholic amines. Changing the type of the small molecule fatty amine and alcoholic amine, or using any mixture thereof, only affects the degree of "dimpling modification" of the hydroxyl cells of the dealubilized Beta zeolite, without altering the benefits of the present invention.

[0122] Example 1 was repeated, but in the second step of the hydroxyl cavity modification treatment of the dealuminized Beta zeolite support, aqueous solutions of the following were used in sequence: a mixture of methylamine-ethylamine-n-butylamine (molar ratio 1:1:1), isopropylamine-isobutylamine-tert-butylamine-diethylamine (molar ratio 1:2:3:0.5), n-propylamine-triethylamine-ethylenediamine (molar ratio 1:3:6), isopropanolamine-diethanolamine (molar ratio 5:1), ethanolamine-diisopropanolamine-triethanolamine (molar ratio 3:1:1), n-butylamine-ethanolamine (1:1), and diethylamine-ethanolamine-diisopropanolamine (molar ratio 4:5:1). The total molar concentration of the above organic amine mixture solutions (the sum of the moles of each fatty amine and / or alcohol amine in 1 liter of solution) was kept at 44 mmol / L (44 mM), and other cavity modification conditions and procedures remained unchanged. The obtained dented modified dealuminated Beta zeolite support was used in the third step, namely, Sn-Beta zeolite was prepared using tin(II) acetate as the tin source and a solid-solid isomorphous substitution method. The cyclohexanone conversion rates of the obtained Sn-Beta zeolite catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 38.39%, 38.11%, 36.84%, 39.22%, 39.09%, 38.21%, and 38.23%, respectively; the caprolactone product selectivity was 35.66%, 35.47%, 35.02%, 33.14%, 39.28%, 38.85%, and 37.79%, respectively; and the hydrogen peroxide conversion rates were 94.08%, 93.38%, 90.30%, 96.15%, 95.83%, 93.64%, and 93.98%, respectively.

[0123] Example 5: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealuated Beta zeolite support using an aqueous solution of a small-molecule fatty amine or / and an alkanolamine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealuated Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The molar concentration of the aqueous solution of the small-molecule fatty amine or / and alkanolamine is adjustable within a certain range. Changing the concentration of the aqueous solution of the small-molecule fatty amine or / and alkanolamine only affects the degree of "dimpling modification" of the hydroxyl cells of the dealuated Beta zeolite, without changing the benefits of the present invention.

[0124] Example 1 was repeated. However, in the second step, when the hydroxyl holes of the dealuminized Beta zeolite support were modified by chiseling an aqueous solution of ethanolamine, the concentration of the ethanolamine aqueous solution was changed sequentially to 11 mmol / L (11 mM), 22 mmol / L (22 mM), 88 mmol / L (88 mM), 177 mmol / L (177 mM), 220 mmol / L (220 mM), and 354 mmol / L (354 mM). Based on the weight reduction estimate, the average number of framework silicon atoms (calculated as SiO2) chiseled out of the hydroxyl hole lattice defect sites of the dealuminized Beta zeolite support were 0.80, 0.95, 1.21, 1.36, 1.51, and 1.77 silicon atoms, respectively. This indicates that the chiseling modification was carried out under controlled conditions with moderate desilication, achieving the requirements for chiseling modification of the dealuminized Beta zeolite support. The chiseling modified support was designated as Beta24C. 11 Beta24C 22、 Beta24C 88、 Beta24C 177、 Beta24C 220 and Beta24C 354 The carriers obtained from the above-mentioned denting modification were used sequentially in the third step, that is, Sn-Beta zeolite was prepared using tin acetate (II) as the tin source and a solid-solid isomorphic substitution method. The resulting Sn-Beta zeolite catalysts were designated as Beta24C. 11 -6Sn, Beta24C 22 -6Sn, Beta24C 88 -6Sn, Beta24C 177 -6Sn, Beta24C 220 -6Sn and Beta24C 354The cyclohexanone conversion rates of -6Sn in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 39.0%, 38.43%, 37.33%, 39.26%, 39.98%, and 38.15%, respectively; the caprolactone product selectivity was 31.2%, 38.25%, 38.06%, 31.89%, 32.19%, and 32.12%, respectively; and the hydrogen peroxide conversion rates were 95.2%, 93.78%, 91.03%, 95.85%, 97.65%, and 93.08%, respectively.

[0125] Example 6: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealuated Beta zeolite support using an aqueous solution of a small-molecule fatty amine or / and an alkanolamine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealuated Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The amount (liquid-to-solid ratio) of the aqueous solution of the small-molecule fatty amine or / and an alkanolamine is adjustable within a certain range. Changing the amount (liquid-to-solid ratio) of the aqueous solution of the small-molecule fatty amine or / and an alkanolamine only affects the degree of "dimpling modification" of the hydroxyl cells of the dealuated Beta zeolite, without changing the benefits of the present invention.

[0126] Example 1 was repeated. However, in the second step, when the hydroxyl holes of the dealuminized Beta zeolite support were modified by chiseling an aqueous solution of ethanolamine, the amount of ethanolamine aqueous solution (liquid-to-solid ratio) was changed to 3:1 (ml / g), 9:1 (ml / g), 12:1 (ml / g), and 15:1 (ml / g) respectively. Based on weight reduction estimation, the average number of framework silicon atoms (calculated as SiO2) chiseled from the hydroxyl hole lattice defect sites of the dealuminized Beta zeolite support were 0.99, 1.10, 1.15, and 1.19 silicon atoms respectively. This indicates that the chiseling modification was carried out under controlled conditions with moderate desilication, meeting the requirements for chiseling modification of the dealuminized Beta zeolite support. The chiseling-modified support was designated as Beta24C. 44-3 Beta24C 44-9、 Beta24C 44-12 and Beta24C 44-15 The carriers obtained from the above-mentioned denting modification were used sequentially in the third step, that is, Sn-Beta zeolite was prepared using tin acetate (II) as the tin source and a solid-solid isomorphic substitution method. The resulting Sn-Beta zeolite catalysts were designated as Beta24C. 44-3 -6Sn, Beta24C 44-9 -6Sn, Beta24C 44-12 -6Sn and Beta24C44-15 The -6Sn groups showed the following cyclohexanone conversion rates in the Baeyer-Villiger oxidation reactions of hydrogen peroxide and cyclohexanone: 39.11%, 38.78%, 38.66%, and 38.56%, respectively; caprolactone product selectivity: 33.10%, 39.15%, 38.97%, and 38.59%, respectively; and hydrogen peroxide conversion rates: 95.68%, 94.85%, 94.65%, and 94.5%, respectively.

[0127] Example 7: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealubilized Beta zeolite support using an aqueous solution of a small-molecule fatty amine or / and an alkanolamine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealubilized Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The temperature of the controllable desilication reaction of the dealubilized Beta zeolite with the aqueous solution of the small-molecule fatty amine or / and an alkanolamine is adjustable within a certain range. Changing the temperature of the controllable desilication reaction of the dealubilized Beta zeolite with the aqueous solution of the small-molecule fatty amine or / and an alkanolamine only affects the degree of "dimpling modification" of the hydroxyl cells of the dealubilized Beta zeolite, without changing the benefits of the present invention.

[0128] Example 1 was repeated. However, in the second step, when the hydroxyl holes of the dealuminized Beta zeolite support were modified by dimpling with an aqueous solution of ethanolamine, the desilication reaction temperature was changed to 50°C, 60°C, and 70°C respectively. Based on weight reduction estimation, the average number of framework silicon atoms (calculated as SiO2) of lattice defect sites of the hydroxyl holes in the dealuminized Beta zeolite support that were dimpled were 1.10, 1.19, and 1.25 respectively. The resulting dimpled modified dealuminized Beta zeolite support was then used in the third step, i.e., Sn-Beta zeolite was prepared using tin(II) acetate as the tin source and a solid-solid isomorphic substitution method. The resulting Sn-Beta zeolite catalyst was designated Beta24C. 44-50 -6Sn, Beta24C 44-60 -6Sn and Beta24C 44-70 -6Sn. The cyclohexanone conversion rates of the above catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 38.16%, 37.99%, and 36.75%, respectively; the caprolactone product selectivity was 39.22%, 38.30%, and 35.45%, respectively; and the hydrogen peroxide conversion rates were 93.9%, 92.98%, and 88.61%, respectively.

[0129] Example 8: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealubilized Beta zeolite support using an aqueous solution of a small-molecule fatty amine or / and an alkanolamine. This treatment aims to controllably remove 1-2 framework silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealubilized Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. The reaction time for the controllable desilication reaction of the dealubilized Beta zeolite with the aqueous solution of the small-molecule fatty amine or / and an alkanolamine is adjustable within a certain range. Changing the reaction time of the controllable desilication reaction of the dealubilized Beta zeolite with the aqueous solution of the small-molecule fatty amine or / and an alkanolamine only affects the degree of "dimpling modification" of the hydroxyl cells in the dealubilized Beta zeolite, without changing the benefits of the present invention.

[0130] Example 1 was repeated. However, in the second step, when the hydroxyl holes of the dealuminized Beta zeolite support were modified by dimpling with an aqueous solution of ethanolamine, the reaction time of the desilication reaction was changed to 2 h, 3 h, and 4 h respectively. Based on weight reduction estimation, the average number of framework silicon atoms (calculated as SiO2) of lattice defect sites of the hydroxyl holes in the dealuminized Beta zeolite support that were dimpled were 1.11, 1.16, and 1.20 respectively. The obtained dimpled modified dealuminized Beta zeolite support was then used in the third step, i.e., Sn-Beta zeolite was prepared using tin(II) acetate as the tin source and a solid-solid isomorphic substitution method. The resulting Sn-Beta zeolite catalyst was designated Beta24C. 44-2h -6Sn, Beta24C 44-3h -6Sn and Beta24C 44-4h -6Sn. The cyclohexanone conversion rates of the above catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 38.33%, 38.15%, and 38.24%, respectively, and the caprolactone product selectivities were 38.33%, 37.99%, and 38.04%, respectively. The hydrogen peroxide conversion rates were 94.23%, 93.78%, and 94.01%, respectively.

[0131] Example 9: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealubilized Beta zeolite support using an aqueous solution of a small-molecule aliphatic amine and / or an alcoholic amine. This treatment aims to controllably remove 1-2 skeletal silicon atoms from the hydroxyl cell walls, thereby expanding the small hydroxyl cells with only one skeletal atom defect (acid dealubilization) to larger hydroxyl cells with 2-3 skeletal atom defects. Then, using the "dimpling modified" dealubilized Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. Different tin sources are permissible when preparing Sn-Beta zeolite using the solid-solid isomorphic substitution reaction. Changing the tin source affects the catalytic performance of the prepared Sn-Beta zeolite catalyst but does not alter the benefits of the present invention.

[0132] Repeat Example 1. However, in the third step, when preparing Sn-Beta zeolite via a solid-solid isomorphic substitution reaction using dimpled modified dealuminol Beta zeolite as a support, tin tetrachloride pentahydrate and stannous chloride dihydrate were used as the tin source sequentially. The resulting Sn-Beta zeolite catalyst is designated Beta24C. 44 -SnCl4-6Sn and Beta24C 44 -SnCl2-6Sn. The above catalyst achieved cyclohexanone conversions of 38.10% and 38.24% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, respectively; caprolactone product selectivities of 35.27% and 38.63%, respectively; and hydrogen peroxide conversions of 93.85% and 94.25%, respectively.

[0133] Example 10: This example illustrates that, according to the method provided by the present invention, a "dimpling modification" treatment is first performed on a dealuated Beta zeolite support using an aqueous solution of a small molecule aliphatic amine or / and an alcoholic amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells, which originally had only one framework atom defect (acid dealumination), into larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealuated Beta zeolite as a support, Sn-Beta zeolite is prepared by a solid-solid isomorphic substitution reaction. In the solid-solid isomorphic substitution reaction step, the amount of tin source can be varied within a certain range to prepare Sn-Beta zeolite catalysts with different framework tin contents.

[0134] Example 1 was repeated. However, in the third step, when Sn-Beta zeolite was prepared via a solid-solid isomorphic substitution reaction using foveated dealubilized Beta zeolite as a support, the amount of tin ions was calculated based on the participation of 30%, 50%, and 60% of hydroxyl groups in the solid-solid isomorphic substitution reaction, resulting in tin(II) acetate amounts of 0.95 g, 1.58 g, and 1.90 g, respectively. Therefore, the resulting Sn-Beta zeolite catalyst was designated Beta24C.44 -4.74Sn, Beta24C 44 -7.9Sn and Beta24C 44 -9.48Sn. The cyclohexanone conversion rates of the above catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 38.68%, 39.28%, and 39.11%, respectively, and the caprolactone product selectivities were 40.97%, 39.86%, and 39.01%, respectively. The hydrogen peroxide conversion rates were 95.66%, 97.12%, and 96.68%, respectively.

[0135] Example 11: This example further illustrates that, according to the method provided by the present invention, the dealuitized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of small molecule aliphatic amines and / or alkanolamines, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealumination) to larger hydroxyl cells with 2-3 framework atom defects. Then, using the "dimpling modified" dealuitized Beta zeolite as a support, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction. In the solid-solid isomorphic substitution reaction step, the amount of tin source can be changed within a certain range to prepare Sn-Beta zeolite catalysts with different framework tin contents.

[0136] Example 1 was repeated. However, in the third step, when Sn-Beta zeolite was prepared via a solid-solid isomorphic substitution reaction using foveated dealubilized Beta zeolite as a support, the amount of tin ions was calculated according to the following parameters: 10%, 20%, 80%, and 100% of the hydroxyl groups participating in the solid-solid isomorphic substitution reaction. This resulted in tin(II) acetate amounts of 0.32 g, 0.63 g, 2.53 g, and 3.16 g, respectively. Therefore, the resulting Sn-Beta zeolite catalyst was designated Beta24C. 44 -1.58Sn, Beta24C 44 -3.16Sn, Beta24C 44 -12.64Sn and Beta24C 44 -15.8Sn. The cyclohexanone conversion rates of the above catalyst in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone were 37.01%, 39.78%, 39.87%, and 39.89%, respectively, and the caprolactone product selectivities were 57.66%, 45.21%, 30.89%, and 28.69%, respectively. The hydrogen peroxide conversion rates were 91.33%, 98.15%, 98.38%, and 98.55%, respectively.

[0137] Example 12: This example illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells, which originally had only one framework atom defect (acid dealuminization), into larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0138] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 60 was synthesized using the hydrothermal crystallization method provided in US Patent 3,308,069 (1967) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (170°C, 3h), and calcination to remove the template agent (500°C, 8h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size close to 100 nm, classifying it as nano-Beta zeolite. XRD analysis revealed no impurities, and its BET specific surface area was calculated to be approximately 530 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was approximately 57, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0139] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding a dealuminized Beta zeolite support (code Beta57c) with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 861 (>800). The degree of dealumination of the support met the requirements of this invention. In the second step, when the hydroxyl groups of the dealuminized Beta zeolite support were modified by hollowing out the hydroxyl groups with an aqueous solution of ethanolamine, the concentration of the aqueous solution of ethanolamine was changed to 20 mmol / L (20 mM). After the hollowing out modification was completed, the reactants were filtered to recover the solid product, and then the solid product was repeatedly washed with deionized water until neutral, followed by drying (overnight at 110°C) and calcination (500°C, 5 h) to obtain the hollowed-out modified dealuminized Beta zeolite. It was sealed and stored for later use. According to the weight reduction estimate, the average number of framework silicon atoms (based on SiO2) hollowed out at the hydroxyl group lattice defect sites of the dealuminized Beta zeolite support was 1.2 silicon atoms. The obtained dented modified dealuminolite Beta zeolite carrier was named Beta57C.

[0140] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 5.84 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the calculation that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated to be 0.525 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta57C. 20 -2.63Sn. The catalyst achieved a cyclohexanone conversion of 38.88%, a caprolactone product selectivity of 48.67%, and a hydrogen peroxide conversion of 96.01% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone.

[0141] Example 13: This example further illustrates that, according to the method provided by the present invention, the dealuitized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of small molecule aliphatic amines and / or alkanolamines, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuitization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuitized Beta zeolite as a support. The dealuitized Beta zeolite support can be obtained by acid dealuitization treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0142] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 40 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (80℃, 24h), and calcination to remove the template agent (600℃, 3h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size at the nanometer level. XRD analysis revealed no impurities, and its BET specific surface area was calculated to be higher than 500 m² / s. 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 38 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0143] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding dealuminized Beta zeolite support Beta38c. Its silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) was 870 (>800), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 160 mmol / L (160 mM), the liquid-to-solid ratio was changed to 20:1, the impregnation temperature was changed to 30℃, and the impregnation time was changed to 5 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral. It was then dried (at 80℃ for 24 h) and calcined (at 600℃ for 3 h) to obtain the dented-modified dealuminized Beta zeolite support, named Beta38C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.0.

[0144] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 8.76 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the calculation that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated to be 0.788 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta38C. 160 -4Sn. This catalyst achieved a cyclohexanone conversion of 39.13% and a caprolactone product selectivity of 32.98% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and a hydrogen peroxide conversion of 96.53%.

[0145] Example 14: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0146] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 80 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (170℃, 6h), and calcination to remove the template agent (520℃, 7h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of small grains (less than 1μm). XRD analysis showed no impurities, and its BET specific surface area was calculated to be higher than 500 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 72 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0147] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding Beta72c, a dealuminized Beta zeolite support with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 855 (>800), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 15 mmol / L (15 mM), the liquid-to-solid ratio was changed to 50:1, the impregnation temperature was changed to 25℃, and the impregnation time was changed to 10 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral, followed by drying (3 h at 200℃) and calcination (3 h at 600℃) to obtain the dented modified dealuminized Beta zeolite support, named Beta72C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.5.

[0148] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 4.62 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the assumption that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated, resulting in 0.416 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta72C. 15 -2.09Sn. The catalyst achieved a cyclohexanone conversion of 39.50%, a caprolactone product selectivity of 42.03%, and a hydrogen peroxide conversion of 96.55% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone.

[0149] Example 15: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0150] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 100 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (90℃, 24h), and calcination to remove the template agent (560℃, 4h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of small grains (less than 1μm). XRD analysis showed no impurities, and its BET specific surface area was calculated to be higher than 500 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was 94, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0151] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding Beta94c, a dealuminized Beta zeolite support with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 932 (>900), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 10 mmol / L (10 mM), the liquid-to-solid ratio was changed to 100:1, the impregnation temperature was changed to 25℃, and the impregnation time was changed to 0.5 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral, followed by drying (5 h at 200℃) and calcination (10 h at 500℃) to obtain the dented modified dealuminized Beta zeolite support, named Beta94C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.0.

[0152] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 3.54 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the assumption that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated, resulting in 0.319 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta94C. 10 -1.6Sn. The catalyst achieved a cyclohexanone conversion of 39.08%, a caprolactone product selectivity of 38.96%, and a hydrogen peroxide conversion of 96.45% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone.

[0153] Example 16: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0154] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 150 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (80℃, 20h), and calcination to remove the template agent (530℃, 8h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of small grains (less than 1μm). XRD analysis showed no impurities, and its BET specific surface area was calculated to be higher than 500 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 136 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0155] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding dealuminized Beta zeolite support Beta136c. Its silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) was 1088 (>900), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the above-mentioned dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 10 mmol / L (10 mM), the liquid-to-solid ratio was changed to 5:1, the impregnation temperature was changed to 20℃, and the impregnation time was changed to 0.5 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral, followed by drying (overnight at 110℃) and calcination (550℃, 3 h) to obtain the dented-modified dealuminized Beta zeolite support, named Beta136C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.6.

[0156] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 2.45 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the assumption that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated, resulting in 0.22 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta136C. 10 -1.1Sn. The catalyst achieved a cyclohexanone conversion of 36.69% and a caprolactone product selectivity of 40.41% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and a hydrogen peroxide conversion of 90.47%.

[0157] Example 17: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells, which originally had only one framework atom defect (acid dealuminization), into larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0158] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 200 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (110℃, 12h), and calcination to remove the template agent (540℃, 6h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of small grains (less than 1μm). XRD analysis showed no impurities, and its BET specific surface area was calculated to be higher than 500 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 189 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0159] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding dealuminized Beta zeolite support Beta189c. Its silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) was 960 (>900), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 10 mmol / L (10 mM), the liquid-to-solid ratio was changed to 5:1, the impregnation temperature was changed to 20℃, and the impregnation time was changed to 0.5 h. After denting modification, the reactants were filtered to recover the solid product. The solid product was then repeatedly washed with deionized water until neutral, followed by drying (overnight at 110℃) and calcination (550℃, 3 h) to obtain the dented modified dealuminized Beta zeolite support, named Beta189C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 2.0.

[0160] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 1.76 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the calculation that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated to be 0.158 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta189C. 10 -0.79Sn. The catalyst achieved a cyclohexanone conversion of 35.55%, a caprolactone product selectivity of 40.82%, and a hydrogen peroxide conversion of 87.78% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone.

[0161] Example 18: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0162] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 15 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (110℃, 12h), and calcination to remove the template agent (540℃, 6h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size at the nanometer level. XRD analysis revealed no impurities, and its BET specific surface area was calculated to be higher than 500 m² / s. 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 14 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0163] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding dealuminized Beta zeolite support Beta14c. Its silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) was 760 (>700), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 300 mmol / L (300 mM), the liquid-to-solid ratio was changed to 100:1, the impregnation temperature was changed to 90℃, and the impregnation time was changed to 0.5 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral. It was then dried (overnight at 110℃) and calcined (550℃, 3 h) to obtain the dented-modified dealuminized Beta zeolite support, named Beta14C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.9.

[0164] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 23.78 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the assumption that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated, resulting in 2.14 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta14C. 300 -10.7Sn. The catalyst achieved a cyclohexanone conversion of 38.13% and a caprolactone product selectivity of 30.01% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and a hydrogen peroxide conversion of 93.53%.

[0165] Example 19: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0166] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 10 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (110℃, 12h), and calcination to remove the template agent (540℃, 6h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size at the nanometer level. XRD analysis revealed no impurities, and its BET specific surface area was calculated to be higher than 500 m² / s. 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 10 by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0167] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, yielding dealuminized Beta zeolite support Beta10c. Its silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) was 710 (>700), meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, following the procedure in step 2 of Example 1, the dealuminized Beta zeolite support was subjected to denting modification treatment with an aqueous solution of ethanolamine. The denting modification conditions were: the concentration of the ethanolamine aqueous solution was changed to 400 mmol / L (400 mM), the liquid-to-solid ratio was changed to 20:1, the impregnation temperature was changed to 100℃, and the impregnation time was changed to 1.0 h. After denting modification, the reactants were filtered to recover the solid product, which was then repeatedly washed with deionized water until neutral. It was then dried (overnight at 110℃) and calcined (550℃, 3 h) to obtain the dented modified dealuminized Beta zeolite support, named Beta10C. It was sealed and stored for later use. Based on weight reduction estimates, the average number of framework silicon atoms (in SiO2) that are chiseled out of hydroxyl-dwelling lattice defect sites in the dealuminated Beta zeolite support is 1.5.

[0168] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 33.29 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the calculation that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated to be 3.00 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta10C. 400 -15Sn. This catalyst achieved a cyclohexanone conversion of 38.69% and a caprolactone product selectivity of 26.63% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and a hydrogen peroxide conversion of 95.73%.

[0169] Example 20: This example further illustrates that, according to the method provided by the present invention, a dealuminized Beta zeolite support is first subjected to a "dimpling modification" treatment with an aqueous solution of a small molecule aliphatic amine and / or an alcohol amine, which aims to controllably remove 1-2 framework silicon atoms from its hydroxyl cell walls. This expands the small hydroxyl cells with only one framework atom defect (acid dealuminization) to larger hydroxyl cells with 2-3 framework atom defects. Then, Sn-Beta zeolite is prepared by solid-solid isomorphic substitution reaction using the "dimpling modification" dealuminized Beta zeolite as a support. The dealuminized Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite parent material with different silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratio). However, when using Beta zeolite with a higher molar ratio of silicon and aluminum oxides (the molar ratio of SiO2 to Al2O3) as the parent material, since the number of hydroxyl holes in the prepared dealuminized Beta zeolite support is relatively small, it is advisable to use a weaker combination of desilication reaction modification conditions for "hole-drilling modification", and vice versa.

[0170] Example 19 was repeated, but in the second step, when the dealuminized Beta zeolite support was modified with an aqueous solution of ethanolamine, the following conditions were used: the concentration of the aqueous ethanolamine solution was changed to 20 mmol / L (20 mM), the liquid-to-solid ratio was changed to 100:1, the impregnation temperature was changed to 40°C, and the impregnation time was changed to 24 h. After the cavity modification was completed, the reactants were filtered to recover the solid product, and then the solid product was repeatedly washed with deionized water until neutral, and then dried (overnight at 110°C) and calcined (550°C, 3 h) to obtain the cavity-modified dealuminized Beta zeolite support, named Beta10C. It was sealed and stored for later use. According to the weight reduction estimate, the average number of framework silicon atoms (calculated as SiO2) of the hydroxyl cavity lattice defect sites of the dealuminized Beta zeolite support was 1.7.

[0171] The obtained pore-modified dealuminated Beta zeolite support was used in the third step, namely, the preparation of Sn-Beta zeolite using tin(II) acetate as the tin source via a solid-solid isomorphous substitution method. The total number of hydroxyl pores in the sample was 33.29 mmol (estimated using the dealuminated amount from the Beta zeolite matrix). Based on the calculation that 38% of the hydroxyl pores participated in the solid-solid isomorphous substitution reaction, the amount of tin ions required was calculated to be 3.00 g of tin(II) acetate. The resulting Sn-Beta zeolite catalyst was designated Beta10C. 20 -15Sn. This catalyst achieved a cyclohexanone conversion of 39.25% and a caprolactone product selectivity of 31.66% in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and a hydrogen peroxide conversion of 96.99%.

Claims

1. A method for preparing a Sn-Beta zeolite catalyst to improve the selectivity of caprolactone, characterized in that, Includes the following steps: The first step is to prepare a dealuminated Beta zeolite support. (1) Select Beta zeolite parent material The aforementioned Beta zeolite matrix refers to silica-alumina Beta zeolite that meets the following requirements: 1) The Beta zeolite matrix is ​​free of impurities; 2) The Beta zeolite matrix has good crystallinity, i.e., the BET specific surface area value of the Beta zeolite matrix measured by nitrogen physical adsorption method is ≥450m². 2 / g; 3) The molar ratio of silicon and aluminum oxides in the Beta zeolite matrix, i.e., the molar ratio of SiO2 to Al2O3, is between 10 and 200; (2) Preparation of dealuminized Beta zeolite carrier A dealuminized Beta zeolite support was prepared by acid dealuminization based on the Beta zeolite matrix; the required molar ratio of silicon-aluminum oxides in the obtained dealuminized Beta zeolite support, i.e., the molar ratio of SiO2 to Al2O3, was ≥700. The second step involves pitting the hydroxyl groups of the dealuminated Beta zeolite support with an aqueous solution of small-molecule fatty amines and / or alcoholic amines. Hole-knocking modification of the hydroxyl holes of the dealuminol Beta zeolite carrier was carried out by impregnation in an aqueous solution of small molecule fatty amines and / or alkanolamines. After the hole-knocking modification was completed, the dealuminol Beta zeolite carrier was obtained by solid-liquid separation, drying and calcination. The small molecule fatty amines are methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine or ethylenediamine, and the small molecule alcohol amines are ethanolamine, isopropanolamine, diethanolamine, diisopropanolamine or triethanolamine; An aqueous solution of small molecule fatty amines and / or alcoholic amines is called a denting solution, which contains one or more of the aforementioned small molecule fatty amines and / or small molecule alcoholic amines, under the following conditions: The concentration of the denting solution ranges from 0.01M to 0.4M; The liquid-solid ratio of the denting solution to the dealuminized Beta zeolite carrier ranges from 1:1 ml / g to 100:1 ml / g. The temperature range for dent modification is 20℃-100℃; The modification time for denting ranges from 0.5h to 24h; The third step involves preparing Sn-Beta zeolite via a solid-solid isomorphic substitution reaction using dimpled modified dealuminolite as a carrier. According to the solid-solid isomorphic substitution reaction method, the hollow-modified dealuated Beta zeolite support was first mixed with the tin source in a solid phase and ground evenly. Then, the solid mixture was successively calcined in a nitrogen atmosphere and an air atmosphere to obtain Sn-Beta zeolite. The ratio of zeolite carrier and tin source is determined by the percentage of the number of moles of tin ions to the number of moles of hydroxyl groups in the zeolite carrier, and its range is 5%-100%. The number of moles of hydroxyl groups in a given mass of zeolite support is equal to the number of moles of acid dealuminate when preparing the same mass of zeolite support.

2. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In step (1), the molar ratio of silicon aluminum oxide in the Beta zeolite matrix, i.e., the molar ratio of SiO2 to Al2O3, is 20-150.

3. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 2, characterized in that, In step (1), the molar ratio of silicon aluminum oxide in the Beta zeolite matrix, i.e., the molar ratio of SiO2 to Al2O3, is 25-100.

4. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In step (2), the molar ratio of silicon aluminum oxide in the dealuminated Beta zeolite support, i.e., the molar ratio of SiO2 to Al2O3, is ≥800.

5. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 4, characterized in that, In step (2), the molar ratio of silicon aluminum oxide in the dealuminated Beta zeolite support, i.e., the molar ratio of SiO2 to Al2O3, is ≥900.

6. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In step (2), the dealuminized Beta zeolite support is prepared using a concentrated nitric acid aqueous solution dealuminization method. The specific steps are as follows: Using 13M concentrated nitric acid as the dealumination acid, the amount of acid was determined according to a liquid-to-solid ratio of 20 ml / g. The dealumination reaction was carried out at 95℃ for 20 h. After the dealumination reaction, the solid product was first recovered by solid-liquid separation, then the solid product was washed with water until the pH value was neutral, then dried at 80-200℃ for 3-24 h, and finally calcined at 500℃-600℃ for 3-8 h to obtain the dealumination Beta zeolite carrier.

7. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In the second step, when impregnating the dealuminized Beta zeolite support with an aqueous solution of small molecule fatty amines and / or alkanolamines for dent modification, the conditions are as follows: The concentration range of the denting solution is 0.02M-0.3M; The liquid-solid ratio of the denting solution to the dealuminolite Beta zeolite carrier ranges from 2:1 ml / g to 50:1 ml / g. The desilication reaction temperature range for dimpling modification is 30℃-90℃; The desilication reaction time for the dent modification ranges from 0.5h to 10h.

8. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 7, characterized in that, In the second step, when impregnating the dealuminized Beta zeolite support with an aqueous solution of small molecule fatty amines and / or alkanolamines for dent modification, the conditions are as follows: The concentration range of the denting solution is 0.03M-0.16M; The liquid-solid ratio of the denting solution to the dealuminolite Beta zeolite carrier ranges from 3:1 ml / g to 20:1 ml / g. The desilication reaction temperature range for dimpling modification is 40℃-80℃; The desilication reaction time for the dimpling modification ranges from 1 hour to 5 hours.

9. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In the third step, the ratio of zeolite carrier to tin source is determined by the percentage of the number of moles of tin ions to the number of moles of hydroxyl groups in the zeolite carrier, and the range is 15%-80%.

10. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 9, characterized in that, In the third step, the ratio of zeolite carrier to tin source is determined by the percentage of the number of moles of tin ions to the number of moles of hydroxyl groups in the zeolite carrier, and the range is 30%-60%.

11. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, In the third step, when preparing Sn-Beta zeolite using the solid-solid isomorphic substitution reaction method, the specific procedure is as follows: (1) Based on the number of hydroxyl holes in the dealuminated Beta zeolite carrier modified by denting, the amount of tin source is calculated according to the percentage of the number of tin ions to the number of hydroxyl holes in the zeolite carrier. (2) The dealuminated Beta zeolite carrier that has been modified by denting, dried and calcined and is in a dry state is mixed with a metered tin source and thoroughly ground. (3) The solid mixture of zeolite carrier and tin source that has been thoroughly ground is placed in a tubular reactor to carry out a solid-solid phase substitution reaction. First, high-purity nitrogen is introduced into the reactor to completely replace the air in the reactor. Then, the solid mixture in the reactor is heated to 200°C in a nitrogen atmosphere at a heating rate of 6°C / min and kept at this temperature for 1-3 hours to allow the tin source to diffuse into the zeolite channels. Next, the solid mixture in the reactor was heated to the range of 450℃-550℃ in a nitrogen atmosphere at a heating rate of 7℃ / min and held at this temperature for 6-8 hours to complete the solid-solid isomorphic substitution reaction. Midway through the solid-solid isomorphic substitution reaction, i.e., when the temperature was held at 450℃-550℃ for 3-4 hours, the high-purity nitrogen atmosphere in the reactor was changed to an air atmosphere. After the solid-solid isomorphic substitution reaction was completed, the Sn-Beta zeolite catalyst was obtained.

12. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, The tin source is tin hydrochloride or acetate, specifically tin tetrachloride pentahydrate, stannous chloride dihydrate, or tin(II) acetate.

13. The Sn-Beta zeolite catalyst prepared by the method for improving caprolactone selectivity according to any one of claims 1-12 is used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide to synthesize caprolactone.

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