Preparation method for sn-beta zeolite catalyst for improving selectivity of caprolactone, and use thereof

Abstract

The present invention belongs to the technical field of preparing zeolite molecular sieve heterogeneous catalyst, and relates to a method for preparing an Sn-Beta zeolite catalyst for improving the selectivity of caprolactone. In the method, a cavity-modified dealuminated Beta zeolite is used as a carrier, and the Sn-Beta zeolite catalyst is prepared by means of a solid-solid phase isomorphic substitution reaction. Specifically, before the solid-solid phase isomorphic substitution reaction, silanol nests of the dealuminated Beta zeolite are subjected to cavity modification by using an aqueous solution of a weak organic base, so as to enlarge the inclusivity of the silanol nests to tin ions. The present invention solves the problem of it being difficult for a tin heteroatom to enter the silanol nests of the dealuminated Beta zeolite to undergo an isomorphic substitution reaction due to having an overly large ionic radius; and also avoids the problem caused by the volume expansion of the silanol nests resulting from the implantation of the tin ions into the silanol nests. The Sn-Beta zeolite prepared by the present invention can be used for catalyzing the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide to synthesize caprolactone.

Description

Preparation method and application of Sn-Beta zeolite catalyst for improving selectivity of caprolactone TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of zeolite molecular sieve heterogeneous catalysts, and relates to a preparation method and application of Sn-Beta zeolite catalyst for improving selectivity of caprolactone. BACKGROUND

[0002] Sn-Beta zeolite is a large-pore heteroatomic zeolite with BEA topology and complete Lewis acid type, and has unique catalytic action and important potential application. The Sn-Beta zeolite exhibits excellent catalytic performance in a series of important reactions such as Baeyer-Villiger oxidation of ketones, transfer hydrogenation (MPV) reaction of ketones, glucose isomerization reaction and ring-opening hydration reaction of epoxides.

[0003] Sn-Beta zeolite is the most effective catalyst for the Baeyer-Villiger oxidation of ketones. For example, Sn-Beta zeolite can catalyze the Baeyer-Villiger oxidation of cyclohexanone to produce caprolactone. Caprolactone is an important chemical intermediate with very wide applications. Caprolactone can be used to produce polycaprolactone and polycaprolactone polyols. Polycaprolactone is a completely biodegradable material with good biodegradability and biocompatibility, and has broad application prospects in biomedical engineering, medicine and health, and environmental protection materials. Polycaprolactone-based polyols with rich terminal hydroxyl groups have high reactivity and can be further polymerized with other materials to synthesize more high-value functional products. The following literatures are related to the study of Sn-Beta catalyzed Baeyer-Villiger oxidation of ketones: 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 mainly two methods for synthesizing Sn-Beta zeolite. The first method is hydrothermal synthesis. In 1997, a hydrothermal synthesis method for Sn-Beta zeolite was reported in the publication Chem. Commun., 1997, 5, 425-426. The technical features of the method are as follows: first, Sn-Al-Beta zeolite is hydrothermally synthesized from silica-alumina gel containing tin tetrachloride; then, the Sn-Al-Beta zeolite is dealuminated by concentrated nitric acid; finally, Sn-Beta zeolite is hydrothermally synthesized from tin-silicon gel containing no aluminum, using the dealuminated Sn-Al-Beta zeolite as a seed crystal. The Sn-Beta zeolite synthesized by the method has a low content of framework Sn, and Al atoms inevitably remain in the framework.

[0005] In 2001, a hydrothermal method for directly synthesizing Sn-Beta zeolite containing no aluminum under the assistance of highly dealuminated Beta zeolite seed crystals and using fluoride as a mineralizer was first reported in the publication Nature, 2001, 412(6845), 423-425. Specifically, the method hydrothermally synthesizes highly crystalline Sn-Beta zeolite containing no aluminum by using tetraethyl orthosilicate as a silicon source, tin tetrachloride pentahydrate as a tin source, hydrofluoric acid (HF) as a mineralizer, and highly dealuminated Beta zeolite as a seed crystal at 140°C for 20 days. The obtained Sn-Beta zeolite is applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. In the reaction, 1,4-dioxane is used as a solvent, the reaction temperature is 90°C, the raw material concentration of hydrogen peroxide is 35wt%, and the solvent: ketone: H2O2 is 50:1.5:1 (the concentration of hydrogen peroxide in the reactants is 0.215 mol / L, and the concentration of water is 0.424 mol / L). After the reaction for 3h, the conversion rate of cyclohexanone can reach 52% (the theoretical conversion rate is 66.67%), and the selectivity of caprolactone can reach 98%. Although the Sn-Beta reported in the publication has excellent catalytic performance, the crystallization time required for hydrothermally synthesizing the Sn-Beta is long, and a large amount of fluoride is added in the synthesis process, which will cause serious environmental pollution in industrialization.

[0006] A relatively simple method of synthesis of Sn-Beta by steam assisted conversion (SAC) is reported in the publication Chem. Eng. J., 2013, 218, 425-432. Specifically, the method first prepares a hydrogel using fumed silica, tin tetrachloride pentahydrate, tetraethylammonium hydroxide and ammonium fluoride as raw materials, then dries the hydrogel at 60 °C for 6 h to obtain a tin-silica xerogel, and then places the tin-silica xerogel in a synthesis kettle, without contacting water, and only relying on the assistance of water vapor, to crystallize at 180 °C for 5 h to obtain well-crystallized Sn-Beta zeolite (Si / Sn = 93). The obtained Sn-Beta zeolite is applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, and the results show that under the conditions of 1,4-dioxane as solvent, reaction temperature of 90 °C, raw material concentration of hydrogen peroxide of 30 wt%, solvent: ketone: H2O2 = 35: 1: 1.5 (concentration of hydrogen peroxide in the reactants is 0.447 mol / L, concentration of water is 1.66 mol / L), and reaction time of 3 h, the conversion rate of cyclohexanone can reach 36.1% (theoretical conversion rate is 100%), and the selectivity of caprolactone can reach 99.48%. It can be seen from this publication that compared with the traditional hydrothermal synthesis method, the steam assisted conversion method (SAC) is faster and more convenient. However, in this method, the content of Sn has a significant effect on the synthesis, the higher the content of Sn, the longer the required crystallization time, and the lower the crystallinity. In the case of Si / Sn ≤ 75, using this method, Sn-Beta zeolite cannot be obtained even if crystallization is performed for 200 h. In addition, it is worth noting that this method also requires fluoride as a mineralizer.

[0007] The publication J. Catal., 2017, 352, 1-12 reports a method for the synthesis of Sn-Beta zeolite using a zeolite transformation. Specifically, the method requires first synthesizing ITQ-1 zeolite (all-silicon MWW type zeolite) using N,N,N-trimethyl-1-adamantammonium hydroxide and hexamethyleneimine as co-structure directing agents by hydrothermal method, and then using the calcined ITQ-1 zeolite as silicon source, using tin tetrachloride pentahydrate as tin source, using ammonium fluoride as mineralizer, using dealuminated Beta zeolite as seed, using tetraethylammonium hydroxide as structure directing agent, to synthesize Sn-Beta zeolite at 140°C. The results show that using this method, Sn-Beta zeolite with low tin content (Si / Sn = 203) can be obtained in a short crystallization time (e.g. 1 day); Sn-Beta zeolite with higher tin content (Si / Sn = 63) can be obtained in a longer crystallization time (e.g. 3 days). The obtained Sn-Beta zeolite is applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, and under the conditions of fluorobenzene as solvent, reaction temperature of 85°C, raw material concentration of hydrogen peroxide of 66.9wt%, solvent: ketone: H2O2 = 13:5:1 (concentration of hydrogen peroxide in the reactants is 0.443mol / L, concentration of water is 0.233mol / L), the reaction is carried out for 40min, the conversion rate of cyclohexanone can reach 19.3% (theoretical conversion rate is 20%), and the selectivity of caprolactone can reach 91.2%.

[0008] The following patents and publications all relate to the hydrothermal synthesis of synthetic Sn-Beta zeolites: CN102249258A (filing date 2011-05-06), US9108190B1 (filing date 2013-09-12), CN106563495A (filing date 2016-10-31), CN107244678B (filing date 2017-07-04), CN107311201B (filing date 2017-07-04), CN107827727A (filing date 2017-11-09), CN110422857B (filing date 2019-07-25), CN111285381B (filing date 2020-03-09), CN112551538A (filing date 2020-12-23), CN112645346A (filing date 2020-12-23), CN112645347A (filing date 2020-12-23), CN112678842A (filing date 2020-12-23), CN112897547A (filing date 2021-03-30), CN114572996A (filing 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, 266, 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 Thesis “Synthesis, Characterization and Catalytic Mechanism of MPVO Reaction of Sn-Beta Zeolite”, Lanzhou University (2016), Master Thesis “Synthesis and Catalytic Performance of Sn-Beta Zeolite for Catalyzing Glucose Isomerization”, South China University of Technology (2017), Master Thesis “Synthesis of Sn-Beta Zeolite by Dry Gel Method and Its Catalytic Performance for Furfural Conversion”, China University of Petroleum (2018), Master Thesis “Aerosol-Assisted Synthesis of Sn-Beta Zeolite and Its Catalytic Performance in Baeyer-Villiger Oxidation Reaction”, Dalian University of Technology (2019), Master Thesis “Aerosol-Assisted Post-Synthesis Method for Preparing Sn-Beta Zeolite and Its Performance in B-V Oxidation Reaction”, Dalian University of Technology (2020), Master Thesis “Seed-Assisted Hydrothermal Method for Preparing Sn-Beta Zeolite and Its Catalytic Performance for Preparing Methyl Lactate from Glucose”, Zhengzhou University (2021), Master Thesis “Mechanism of Seed in Crystallization Process of Sn-Beta Zeolite”, Zhengzhou University (2022), Master Thesis “Effect of Sn Content in Sn-Beta Zeolite on Catalytic Conversion of Glucose to Methyl Lactate and Fructose”, Zhengzhou University (2022). From the above large amount of literature, it can also be found that when Sn-Beta zeolite is prepared by hydrothermal synthesis method, a large amount of fluoride mineralizer needs to be used. In addition, the Sn content in the framework of Sn-Beta zeolite prepared by hydrothermal synthesis method is generally low, the mass repeatability is poor, and the crystallization time is long.

[0009] The publication Green Chem., 2017, 19, 692-701 reports a method for hydrothermal synthesis of Sn-beta zeolite in a F - free system. Specifically, the method first grinds dry dealuminated Beta zeolite and tin tetrachloride pentahydrate uniformly, and then makes the solid mixture contact with TEAOH in a stainless steel high-pressure reaction kettle lined with polytetrafluoroethylene to carry out hydrothermal reaction. The reaction is carried out under static conditions, the reaction temperature is 140°C, and the reaction time is 24h, and Sn-Beta zeolite can be obtained. Since the dealuminated Beta zeolite will undergo dissolution-recrystallization reaction in the strong alkaline TEAOH solution under the above conditions, the Sn species enters the Beta framework by recrystallization opportunity, so the essence of this method is to obtain Sn-Beta zeolite by zeolite framework reconstruction. However, the Sn-Beta zeolite synthesized by this method not only has low Sn loading, but also has very low crystallinity, and the amount of template used is also large, resulting in high manufacturing cost of Sn-Beta.

[0010] The publication Inorg. Chem. Front., 2018, 5, 2763-2771 also reports a method for hydrothermal synthesis of Sn-beta zeolite in a F -A method for hydrothermally synthesizing Sn-Beta zeolite in a system. The method uses N-cyclohexyl-N,N-dimethylcyclohexylamine hydroxide as a structure directing agent, full-silica Beta zeolite as a seed crystal, and sodium hydroxide as a mineralizer, and obtains Sn-Beta zeolite by crystallization at 140°C for 14 days. Although the method can get rid of F - , it needs to use a special directing agent with complex structure, which is expensive, and the crystallization time is too long, up to 14 days.

[0011] In addition to the above-mentioned public documents, patent CN104709920B also discloses a method for synthesizing Sn-Beta zeolite in a F-free system. The method uses a boron acid-assisted hydrothermal synthesis method. Specifically, the method is to first prepare a uniform gel from dealuminated Beta zeolite, tetraethylammonium hydroxide, tetraethyl orthosilicate, boric acid, and tin tetrachloride, and then crystallize the gel at 140°C for 25 days to obtain Sn-beta zeolite. Obviously, one of the disadvantages of this method is that the crystallization time is too long.

[0012] In addition, the following patents and documents also relate to a method for hydrothermally synthesizing Sn-Beta zeolite in a F-free system: 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 of Heteroatom Beta and CHA Zeolites", East China Normal University (2018), Master's Thesis "Fluorine-free Hydrothermal Synthesis of Pure Silica Beta and Sn-Beta Zeolites", Zhengzhou University (2021), Master's Thesis "Comparison of Rules and Properties of Sn-Beta Zeolites Synthesized by Different Methods", China University of Petroleum (2020).

[0013] In summary, it is a dream of people to prepare Sn-Beta zeolite by hydrothermal synthesis in a F - free system. Unfortunately, so far, this hydrothermal synthesis method cannot be practically applied.

[0014] The second method for preparing Sn-Beta zeolite is a 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 a full-silica Beta zeolite with skeletal defect sites. Then, different methods are used to introduce tin heteroatoms into the skeletal defect sites (hydroxyl pits) of the full-silica Beta zeolite, so that it has four-coordinated skeletal tin catalytic active sites. According to the different tin sources, the post-synthesis method can be divided into gas-solid isomorphous substitution method, liquid-solid isomorphous substitution method, and solid-solid isomorphous substitution method.

[0015] The publication J. Phys. Chem. C, 2011, 115, 3663-3670 reports a post-synthesis method for the preparation of Sn-Beta zeolite by gas-solid isomorphous substitution. Specifically, the method uses anhydrous SnCl4 as tin source, and nitrogen gas is bubbled through the liquid of anhydrous SnCl4, so that the nitrogen gas carries SnCl4 gas to contact with the dealuminated Beta zeolite to occur isomorphous substitution reaction. The reaction is carried out at 500°C, and after 1.5h, Sn-Beta zeolite with Sn content as high as 6.2wt% is obtained. The obtained Sn-Beta zeolite (Sn content of 3.5wt%) is used for Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, when using hydrogen peroxide raw material with a concentration of 50wt% as oxidant, acetonitrile as solvent, solvent: ketone: H2O2 = 61:2:1 (the concentration of hydrogen peroxide in the reaction is 0.361 mol / L, and the concentration of water is 0.384 mol / L), the reaction temperature is 75°C, and the reaction time is 3 hours, the conversion rate of cyclohexanone is 34.1% (the theoretical conversion rate should be 50%), and the selectivity of caprolactone is 57.8%. It can be seen that, based on the dealuminated Beta zeolite, Sn-Beta zeolite with catalytic activity can be obtained by gas-solid isomorphous substitution reaction.

[0016] The following documents all relate to the preparation of Sn-Beta zeolite by 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 Thesis “Preparation, Characterization and Performance of Al-Free Sn-Beta Zeolite in Baeyer-Villiger Catalytic Oxidation”, East China Normal University (2011), Master Thesis “Preparation of Sn-Beta Zeolite by Isomorphous Substitution for Catalyzing Isomerization of Glucose to Fructose”, Dalian University of Technology (2013), Master Thesis “Synthesis, Characterization and Catalytic Performance of Sn-Beta Zeolite by Gas-Solid Method”, Dalian University of Technology (2013), Master Thesis “Synthesis, Characterization and Catalytic Mechanism of MPVO Reaction of Sn-Beta Zeolite”, Lanzhou University (2016). However, in general, the preparation of Sn-Beta zeolite by gas-solid isomorphous substitution method is harsh, and it is difficult to scale up. Since the volatility of SnCl4 is low, the grafting efficiency of SnCl4 carried by nitrogen gas is low, and it is difficult to graft sufficient amount of Sn into the framework vacancies of dealuminated Beta zeolite. In addition, and more importantly, a large amount of inactive extra-framework tin oxide species is formed in the Sn-Beta zeolite prepared by gas-solid isomorphous substitution method.

[0017] In the literature research, it was found that the open literature Chinese. J. Catal., 2012, 33, 898-904 reported the preparation of Sn-Beta zeolite by liquid-solid isomorphous substitution method. In the reported method, the tin source was tin tetrachloride pentahydrate, and the refluxing solvent was water. However, the Sn-Beta zeolite prepared by liquid-solid isomorphous substitution reaction on the basis of dealuminated Beta zeolite had poor reactivity and product selectivity in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. For example, the conversion of cyclohexanone and the selectivity of caprolactone of the prepared catalyst were 23.6% (the theoretical conversion should be 100%) and 70.0%, respectively, under the reaction conditions of a reaction temperature of 90°C, a raw material concentration of hydrogen peroxide of 30wt%, and a molar ratio of 1,4-dioxane: cyclohexanone: H2O2 = 35:1:1.4 (the concentration of hydrogen peroxide in the reactants was 0.299 mol / L, and the concentration of water was 0.742 mol / L). When Sn-Beta zeolite was prepared by liquid-solid isomorphous substitution method, there was also the outstanding shortcoming of high content of non-framework tin oxide.

[0018] The following patents and open literature all involve the liquid-solid isomorphous substitution method for preparing Sn-Beta zeolite: CN103464196A (filing date 2013-07-25), CN106861747B (filing date 2015-12-10), US10414664B2 (filing date 2017-08-25), CN114805284B (filing 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, and the doctoral thesis “Synthesis, Characterization and Catalytic Performance of Sn-Beta Zeolite”, Dalian University of Technology (2013). It can be found from these literatures that when Sn-Beta zeolite is prepared by liquid-solid isomorphous substitution method, a large amount of extra-framework tin oxide species will be formed regardless of the solvent selected.

[0019] The publication Angew. Chem. Int. Ed., 2012, 51, 11736-11739 reports a post-synthetic method for the preparation of Sn-Beta zeolite using a solid-solid iso- crystalline substitution method. Specifically, the method requires first reacting a silicon-aluminum Beta zeolite with concentrated nitric acid to remove framework aluminum atoms. Then, tin(II) acetate is used as the tin source, and the de-aluminated Beta zeolite and tin(II) acetate are ground together for 15 min. Finally, the ground mixture of solids is calcined at high temperature (550 °C) in air to obtain Sn-Beta zeolite. The obtained Sn-Beta zeolite is applied to the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide. When 1,4-dioxane is used as the solvent, the reaction temperature is 90 °C, the raw material concentration of hydrogen peroxide is 30 wt%, and the solvent: ketone: H2O2 = 36:2:3 (the concentration of hydrogen peroxide in the reactants is 0.809 mol / L, and the concentration of water is 2.01 mol / L) for 4 h, the conversion of cyclohexanone can reach 41.1% (the theoretical conversion is 100%), and the selectivity of caprolactone can reach 93%.

[0020] 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 2020-01-09), J. Catal., 2015, 330, 545-557, ChemCatChem., 2015, 7, 3322-3331, ChemCatChem., 2016, 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, ACS Sustainable Chem. Eng., 2017, 5, 3123-3131, ACS Catal., 2020, 10, 14135-14146, Master thesis “Rapid synthesis of Sn-Beta zeolite and its catalytic performance for the conversion of sugars to lactate esters”, Zhengzhou University (2017), Master thesis “Preparation of Sn-Beta zeolite and its catalytic performance for the oxidation of cyclohexanone”, Dalian University of Technology (2020), Master thesis “Influence factors of cyclohexanone oxidation reaction over Sn-Beta zeolite”, Dalian University of Technology (2022), Master thesis “Acidity modulation of Sn-Beta zeolite and its catalytic performance for the Meerwein-Ponndorf-Verley-Oppenauer reaction”, Zhengzhou University (2022). In summary, compared with the other two post-synthetic methods, the solid-solid isomorphous substitution method for the preparation of Sn-Beta is simple to operate, has no strict requirements for raw materials and conditions, and is easy to realize in industry. 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 Sn content, and thus is a quite practical post-synthetic method for the preparation of Sn-Beta.

[0021] However, the ionic radius of Sn is much larger than the ionic radius of Al So Sn ions have some difficulty to enter the hydroxyl pockets generated by dealumination on the framework of Beta zeolite, which is a common challenge faced by the three post-synthesis methods. Therefore, various post-synthesis methods have the following problems, that is, no matter which method is used to introduce tin ions into the framework defect sites of the all-silicon Beta zeolite, the total number of tin ions that can enter the framework lattice points in the form of isomorphic substitution of framework aluminum ions depends on the "tolerance" of the hydroxyl pockets and the zeolite framework. The hydroxyl pockets that are isomorphically substituted by tin ions in advance can obtain the "tolerance" for implanting tin ions by volume expansion, consuming the "tolerance" of the zeolite framework. As the "tolerance" of the zeolite framework is consumed, the remaining hydroxyl pockets will not be able to accept tin ions by expansion deformation. The framework defect sites that are not occupied by tin ions exist in the form of weakly acidic hydroxyl pockets, and the tin ions that cannot enter the framework lattice points will become SnO x species.

[0022] It is well known that 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 hydrolytic ring opening of caprolactone to generate 6-hydroxyhexanoic acid. On the one hand, in the Sn-Beta zeolite prepared by post-synthesis method, due to the difficulty of complete isomorphic substitution of tin ions for the defect sites of the all-silicon Beta zeolite framework, there will be weakly acidic sites on the framework of the prepared Sn-Beta zeolite catalyst, which are generated by the defect site hydroxyl pockets. This weakly acidic site catalyzes the hydrolysis side reaction of caprolactone, which is an important reason for the low selectivity of caprolactone in the Sn-Beta zeolite catalyst prepared by post-synthesis method. On the other hand, the tin atoms that do not enter the framework defect sites are guest species in the zeolite pores. With the increase of tin loading, these guest species aggregate into larger particles, block the Beta zeolite pores, and reduce the accessibility of the internal active sites of the catalyst, thereby reducing the catalytic activity of the catalyst.

[0023] There are few effective methods available to solve the above problems existing in the post-synthesis method. The solution provided in the master's thesis "Improved post-treatment method for the preparation of Sn-Beta zeolite catalytic glucose conversion to prepare lactate ester research", Zhengzhou University (2016) is to take further tetraethylammonium hydroxide (TEAOH) solution hydrothermal modification treatment on the Sn-Beta zeolite prepared by the solid-solid isomorphous substitution method. In the modification process described, the Sn-Beta zeolite crystals undergo partial dissolution and recrystallization reaction, so that the modified method can obtain a few defect sites of hierarchical Sn-Beta molecular sieve. According to the literature, this modification method can significantly improve the yield of Sn-Beta zeolite for glucose conversion reaction (methyl lactate). In fact, this modification method has been widely used in the modification of titanium silicate TS-1. The difference is that tetrapropylammonium hydroxide (TPAOH) is used in the hydrothermal modification treatment of TS-1. TPAOH and TEAOH are both commonly used quaternary ammonium base templates. TPAOH is generally used for synthesizing and modifying MFI family zeolite molecular sieves (ZSM-5, S-1, TS-1), while TEAOH is generally used for synthesizing BEA group zeolite molecular sieves (Al-Beta, Ti-Beta and Sn-Beta). However, in principle, this dissolution-recrystallization modification method cannot fundamentally solve the problem that the heteroatom is difficult to enter the zeolite framework due to its too large ionic radius. In addition, this modification method also has the problems of large catalyst loss and large consumption of TEAOH template, which will inevitably cause a significant increase in the cost of the catalyst.

[0024] It is also found from literature research that the ion modification method is provided in the published literature Catal. Sci. Technol., 2016, 6, 2787-2795. The ion modification method involves Li + , Na + , K + , Cs + and NH4 + several modified ions. The principle of the modification method is to neutralize and passivate the weak acidic hydroxyl groups in Sn-Beta zeolite with alkaline cations. According to the literature, the Sn-Beta zeolite modified by the method is passivated by the alkalinity of Li + , Na + and NH4 + , etc. Therefore, the weak B acidity of the hydroxyl pit is passivated, so that the hydrolysis side reaction of caprolactone in the Baeyer-Villiger reaction of cyclohexanone and hydrogen peroxide is inhibited to a certain extent.

[0025] In addition, the solution provided in the master's thesis "Preparation, Characterization of Modified Sn-Beta Catalyst and Its Application in Catalytic Conversion of Biomass Derivatives to Lactic Acid", Xiamen University (2018) is to use Na + , K + , NH4 + , Zn 2+ , Ca 2+ , Mg 2+ to ion exchange modify Sn-Beta zeolite prepared by solid-solid isomorphous substitution method. The principle of this modification method is also to neutralize and passivate the weakly acidic hydroxyl groups in Sn-Beta zeolite with alkaline cations. The author believes that through monovalent metal ion exchange and divalent ion exchange, the acid environment inside the molecular sieve can be regulated, and Lewis base and alkali centers can be constructed to synergize with Lewis acid catalysis. Sn-Beta zeolite modified by this method can significantly improve the selectivity of lactic acid in the reaction of converting biomass derivatives to lactic acid.

[0026] Invention patent CN110575844A (application date 2019-08-16) discloses a method for modifying Sn-Beta zeolite with alkaline earth metals. For Sn-Beta zeolite, alkaline earth metal modification is also to eliminate the weak acid sites of Sn-Beta catalyst. The modification principle is similar to that of alkali metal ion modification. Sn-Beta zeolite modified by this method is also used for sugar conversion reaction, and the target product is to obtain lactic acid.

[0027] Invention patent CN114210362A (application date 2021-11-30) discloses a method for modifying Sn-Beta zeolite with zinc ions. This method takes advantage of the characteristic that zinc ions can selectively bind to hydroxyl pits, and modifies Sn-Beta zeolite by impregnating it with a zinc salt solution, converting the residual hydroxyl pits into weak Lewis acid sites. Sn-Beta zeolite modified with zinc ions is used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone to synthesize caprolactone. The results show that when the molar ratio of 1,4-dioxane: cyclohexanone: H2O2 is 4:2:1, the reaction temperature is 60°C, and the reaction time is 2h, the conversion rate of cyclohexanone is 27.75% (theoretical conversion rate 50%), and the selectivity of the product caprolactone is 93.80%.

[0028] In addition to the above method, the invention patent CN108727180A (application date 2018-05-07) also discloses a surface amination modification method. The technical feature of this method is to first disperse Sn-Beta prepared by solid-solid isomorphous substitution method in anhydrous ethanol, then add amination reagent (3-aminopropyltrimethoxysilane (APTMS) or 3-aminopropyltriethoxysilane (APTES)) to it, and condense and distill at 80°C for 6h. After the reaction is completed, the material is cooled to room temperature and filtered, the filter cake is washed with a large amount of anhydrous ethanol, then dried at 80°C, and finally the aminated Sn-Beta zeolite is obtained. The principle of surface amination modification is: using silanization reagent containing amino group to graft with surface acid site, and grafting silane species containing amino group on the acid site of Sn-Beta through the formation of Si-O-R bridge, so as to cover the acid site. The aminated Sn-Beta zeolite is used for the reaction of converting saccharides into lactic acid, and the conversion rate of glucose and the yield of lactic acid are both improved. It is worth noting that in this method, after the silanization reagent containing amino group is grafted onto the Sn-Beta zeolite, only low-temperature drying is used for post-treatment, and there is no high-temperature calcination post-treatment, so that the 3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane modifier remains on the modified Sn-Beta zeolite through the formation of Si-O-R bond between its 3-aminopropyl group and the surface silicon hydroxyl group (Si-OH). This modification method is not suitable for the use occasions where the catalyst needs to be frequently carbonized and regenerated.

[0029] The published document ACS Omega., 2018, 3, 17430-17438 also reports the research work of surface amination modification of Sn-Beta zeolite using 3-aminopropyltrimethoxysilane (APTMS). The modified catalyst is used for the reaction of converting sucrose into lactic acid. Under the optimized conditions, complete conversion of sucrose is achieved, and the yield of lactic acid can reach 58%.

[0030] The published document RSC Adv., 2019, 9, 18989-18995 also uses 3-aminopropyltrimethoxysilane (APTMS) to modify the surface amino functionalization of Sn-Beta zeolite, and the modified catalyst is used for the reaction of converting glucose into lactic acid. While achieving complete conversion of glucose, a lactic acid yield as high as 56% is also achieved.

[0031] A surface amination modification method of Sn-Beta zeolite is also reported in the publication ACS Omega., 2021, 6, 284-293. The method is to mix the post-synthetic prepared Sn-Beta zeolite with a certain amount of amination reagent in anhydrous ethanol as solvent for modification treatment. The amination reagents involved in the literature mainly include 3-aminopropyltrimethoxysilane (APTMS), 3-(2-aminoethylamino) propyltrimethoxysilane (AEPTMES) and diethylenetriamine (DETA). The modified Sn-Beta zeolite catalyst obtained by this modification method is applied to the study of the reaction of Scenedesmus producing lactic acid. The results show that the Sn-Beta zeolite modified by 3-aminopropyltrimethoxysilane (APTMS) significantly improves the yield of the main product lactic acid. Under the optimal reaction conditions (190°C and 5 hours), the highest lactic acid yield can reach 37%.

[0032] Obviously, the surface amination modification method of Sn-Beta zeolite described above relies on the retention of organic groups containing amino groups in the modified catalyst to achieve the modification effect. However, this modified catalyst cannot be used in applications where the catalyst needs to be frequently regenerated by calcination.

[0033] The publication Chem. Mater., 2021, 33, 9366-9381 provides a post-treatment modification method of Sn-Beta zeolite prepared by solid-solid isomorphous substitution method with Sn content up to 10wt% by a series of reduction and re-oxidation. The method requires that the prepared Sn-Beta zeolite is first placed in a hydrogen atmosphere, heated to the required temperature at a certain heating rate (5°C·min -1 ) for 2h reduction treatment, and then the reduced catalyst is placed in an air stream, heated to the required temperature at a certain heating rate (5°C·min -1 ) for 2h re-oxidation treatment. The Sn-Beta zeolite modified by the series of reduction and re-oxidation method is used for the catalytic reaction of Baeyer-Villiger oxidation of cyclohexanone and hydrogen peroxide to synthesize caprolactone, and it is found that the modified catalyst has higher Lewis acid density and higher Baeyer-Villiger oxidation activity. This is attributed to the fact that during the reduction process, the extra-framework tin oxide species are reduced to mobile Sn(II)O species, which can diffuse inside the Sn-Beta zeolite and interact with the silanol nests, causing a part of the extra-framework tin oxide species to re-enter the framework. However, the reduction degree of this modification method is difficult to control, and the reduction result is affected by the SnO xThe influence of factors such as size and content, if excessive reduction, will form metal Sn particles, which is not conducive to achieve the purpose of modification. It is not difficult to understand that due to the limitation of the "inclusion" of the zeolite framework, the amount of non-framework tin that can be re-entered into the framework using this modification method is necessarily limited. SUMMARY

[0034] The purpose of the present application is to provide a preparation method of Sn-Beta zeolite which can improve the selectivity of caprolactone in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide.

[0035] Specifically, the present application provides a method for preparing Sn-Beta zeolite by solid-solid isomorphous substitution reaction using a delaminated Beta zeolite as a carrier. The Sn-Beta zeolite prepared by the present application has high selectivity of caprolactone product in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide. The delamination modification refers to using organic amine to control the desilication technology to make the hydroxyl pits produced by delamination larger, thereby improving the "inclusion" of tin ions in the hydroxyl pits.

[0036] In a large number of experimental explorations, it is deeply realized that, due to the fact that the ionic radius of tin is much larger than the ionic radius of aluminum Therefore, it is impossible to implant a large amount of tin ions with large volume into the small hydroxyl pits of the delaminated Beta zeolite and form a perfect combination with the zeolite framework through isomorphous substitution reaction to form four Si-O-Sn bonds. It is inevitable that the Sn-Beta zeolite prepared contains a large amount of non-framework tin species.

[0037] As known to those skilled in the art, when synthesizing heteroatomic zeolites by hydrothermal method, especially when the ionic radius of the heteroatom is large (such as titanium and tin), the expansion of the zeolite unit cell will inevitably occur after the heteroatom enters the zeolite framework. The more the number of heteroatoms entering the zeolite framework, the greater the degree of expansion of the zeolite unit cell.

[0038] Similarly, when preparing Sn-Beta zeolite by post-synthesis method, introducing heteroatom tin into the framework of delaminated Beta zeolite in the form of tin ions through isomorphous substitution reaction with hydroxyl pits will also inevitably cause the expansion of the Beta zeolite unit cell. The more the number of tin ions entering the framework of delaminated Beta zeolite through isomorphous substitution reaction, the greater the degree of expansion of the Beta zeolite unit cell.

[0039] The difference is that in the hydrothermal synthesis of heteroatomic zeolites, the expansion of the unit cell volume of the heteroatomic zeolite occurs on the external surface of the zeolite crystal, i.e. on the external surface of the framework, both in the nucleation stage and in the crystal growth stage. The expansion of the unit cell volume on the external surface of the crystal framework is not resisted and does not generate extrusion stress directed to the interior of the crystal. Therefore, for the de novo synthesis of Sn-Beta zeolite, the inclusion capacity of the zeolite framework for a large number of tin ions is constantly obtained through the expansion of the unit cell volume on the external surface of the grain during the dynamic process of nucleation and crystal growth. 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) produced by dealumination are mainly distributed in the interior of the zeolite crystal framework. In this case, whenever a tin ion enters the hydroxyl pocket of the framework vacancy through isomorphous substitution, the hydroxyl pocket at the site will expand around to obtain sufficient inclusion capacity to enable the isomorphous substitution reaction of the tin ion with a larger volume to be completed. The result of the transmission of extrusion stress to the surrounding framework is to cause the volume of the adjacent hydroxyl pocket to be compressed, thereby causing the remaining hydroxyl pockets on the dealuminated Beta zeolite framework to become increasingly difficult for tin ions to continue to isomorphously substitute.

[0040] Therefore, in the post-synthetic preparation of Sn-Beta zeolite, if the expansion of the volume of the hydroxyl pocket caused by the implantation of the tin ion into the hydroxyl pocket cannot be eliminated, the remaining hydroxyl pockets will be extruded and lose "inclusion capacity", and it will not be possible to obtain high-quality Sn-Beta zeolite with a high framework tin content and a low non-framework tin content by the post-synthetic method.

[0041] After deep thought, if 1-2 framework silicons can be controllably removed from the hydroxyl pockets of dealuminated Beta zeolite (pocket modification), so that the small hydroxyl pocket originally with only one framework atom vacancy (acid dealuminated) is expanded to a larger hydroxyl pocket with 2-3 framework atom vacancies, tin ions can easily enter and become framework tin through isomorphous substitution reaction, while problems caused by the volume expansion of the hydroxyl pocket due to the implantation of tin ions into the hydroxyl pocket are avoided. According to this idea, a large number of exploratory research work has been carried out using aqueous solution of weakly basic organic base. Compared with alkali metal hydroxide solution (inorganic strong base) and quaternary ammonium base solution (organic strong base), the desilication ability of weakly basic organic base is weak, and only a small amount of desilication can be achieved, so that controllable desilication can be achieved. At the same time, because of the weak desilication ability of weakly basic organic base, selective desilication can also be achieved, that is, desilication mainly from the weakest part of the framework of dealuminated Beta zeolite, the vacancy site of the hydroxyl pocket. In the study, it is found that the aqueous solution of small molecule aliphatic amine (methylamine, ethylamine, propylamine, tert-butylamine, isopropylamine, n-butylamine, diethylamine, ethylenediamine, isobutylamine, triethylamine) and small molecule alcohol amine (ethanolamine, diethanolamine, triethanolamine, isopropyl alcohol amine, diisopropyl alcohol amine) has controllable desilication effect when contacting with dealuminated Beta zeolite, that is, it shows the "pocket modification" effect on the hydroxyl pocket of dealuminated Beta zeolite. Compared with general organic bases, the advantages of small molecule aliphatic amine and alcohol amine are good water solubility and small dosage. As can be seen from the following examples, using solid-solid isomorphous substitution reaction on the dealuminated Beta zeolite support which has been appropriately modified by the aqueous solution of small molecule aliphatic amine or alcohol amine, high-quality Sn-Beta zeolite with fully utilized hydroxyl pocket, high framework tin content and low non-framework tin content can be easily obtained. Therefore, in the method for preparing Sn-Beta zeolite catalyst provided by the present application, using the aqueous solution of small molecule aliphatic amine or alcohol amine to appropriately treat the dealuminated Beta zeolite, so as to controllably remove 1-2 framework silicons from the hydroxyl pocket, thereby expanding the small hydroxyl pocket originally with only one framework atom vacancy to a larger hydroxyl pocket with 2-3 framework atom vacancies, is the most core idea and key technical feature.

[0042] In an attempt to use the prepared Sn-Beta zeolite to catalyze the Baeyer-Villiger reaction of cyclohexanone and hydrogen peroxide, in an effort to selectively synthesize caprolactone, it was found that the Sn-Beta zeolite prepared by the method of the present application could significantly improve the selectivity of caprolactone in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, even with a smaller amount of solvent (1,4-dioxane). For example, as will be seen from the specific examples and comparative examples provided in the present application, under the reaction conditions of a batch kettle reaction mode (atmospheric pressure, 90°C, reaction for 3h) and a low solvent amount (1,4-dioxane (solvent): cyclohexanone: H2O2molar ratio of 5.5:1:0.4), the reaction results of a Sn-Beta zeolite catalyst with a tin content of 6wt.% obtained by directly performing a solid-solid isomorphous substitution reaction on a dealuminated Beta zeolite according to the known method were: cyclohexanone conversion of about 40% (theoretical value 40%), caprolactone selectivity of about 13% (the rest was 6-hydroxyhexanoic acid generated by hydrolysis of caprolactone); while the Sn-Beta zeolite catalyst with the same tin content prepared according to the method provided in the present application had a cyclohexanone conversion of about 38% and a caprolactone selectivity of about 41%.

[0043] It needs to be emphasized that in order to controllably remove 1-2 framework silicons from the hydroxyl pockets of the dealuminated Beta zeolite, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy to a larger hydroxyl pocket having 2-3 framework atom vacancies, it is necessary to reasonably use the combination of factors such as the type, solution concentration, solution amount, treatment temperature and time of small molecule organic amines or alcohol amines as a means to control the degree of desilication, and to consider the difference in the molar ratio of silicon-aluminum oxide of the Beta zeolite mother body and the number of hydroxyl pockets of the dealuminated Beta zeolite carrier.

[0044] Technical solutions of the present application:

[0045] A preparation method of a Sn-Beta zeolite catalyst for improving the selectivity of caprolactone, comprising the following steps:

[0046] First step, preparation of a dealuminated Beta zeolite carrier

[0047] Engineers familiar with the field can prepare a dealuminated Beta zeolite carrier from a Beta zeolite mother body according to the requirements of the present application, combined with their own work experience and reference to conventional acid dealuminization methods in related literature. The requirements of the present application are as follows:

[0048] (1) Select a Beta zeolite mother body

[0049] The Beta zeolite precursor is a common silicon-aluminum Beta zeolite. The present application does not limit the grain size of the Beta zeolite precursor, nor does it limit the production process of the Beta zeolite precursor. However, in order to facilitate the implementation effect of the present application, the Beta zeolite precursor has the following requirements: 1) the Beta zeolite precursor has no impurity crystals; 2) the Beta zeolite precursor has good crystallization; and 3) the Beta zeolite precursor has a suitable silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3).

[0050] The presence or absence of impurity crystals in the Beta zeolite precursor can be checked and confirmed by X-ray powder diffraction (XRD) method. As is known to those skilled in the art, the silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) of the Beta zeolite produced by hydrothermal synthesis is generally between 10 and 200 (US 3 308 069 (1967)). In Beta zeolite products with a lower silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3), mordenite (MOR) impurity crystals are generally possible, while in Beta zeolite with a higher silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3), ZSM-5 zeolite impurity crystals are generally possible. By sampling the Beta zeolite precursor and performing XRD analysis, and comparing the XRD pattern of the sample with the standard diffraction cards of Beta zeolite, MOR zeolite and ZSM-5 zeolite, it can be determined whether the XRD pattern of the sample has characteristic peaks of MOR zeolite and ZSM-5 zeolite impurity crystals, and thus whether the Beta zeolite precursor is a pure Beta zeolite phase.

[0051] In theory, the crystallization of the Beta zeolite precursor can also be analyzed by XRD, using the relative crystallinity index as a measure. However, the XRD relative crystallinity index requires the sum of the intensities of the medium intensity characteristic diffraction peaks of the Beta zeolite precursor at 2Θ = 7.6-8° and the highest intensity characteristic diffraction peak at 2Θ = 22-23° to be compared with the sum of the intensities of the corresponding diffraction peaks of a reference sample (a standard Beta zeolite with a crystallinity of 100%), and the reference sample is not uniformly defined. Furthermore, the intensities of the medium intensity characteristic diffraction peaks of the Beta zeolite at 2Θ = 7.6-8° and the highest intensity characteristic diffraction peak at 2Θ = 22-23° are greatly affected by the size of the crystallite, post-processing techniques and conditions such as calcination, etc. Therefore, the XRD relative crystallinity index is not generally applicable for determining whether the purchased or synthesized Beta zeolite precursor is well crystallized. For this reason, the present application recommends using the specific surface area index of the Beta zeolite precursor to determine whether the purchased or synthesized Beta zeolite precursor is well crystallized. According to the statistical results of the literature reported values of the specific surface area of the Beta zeolite, the BET specific surface area of a well crystallized Beta zeolite produced by the hydrothermal synthesis method is generally not less than 450 m 2 / g. Engineers familiar with the art can first measure the nitrogen adsorption isotherm data of the Beta zeolite precursor using the conventional nitrogen physical adsorption method, and then calculate the BET specific surface area according to the BET model. In summary, the present application requires that the BET specific surface area of the Beta zeolite precursor used is ≧ 450 m 2 / g, as a criterion for well crystallized.

[0052] The silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) is a key index of the Beta zeolite precursor. This is because, on the one hand, a Beta zeolite precursor with a low silicon-aluminum oxide molar ratio, i.e. a Beta zeolite precursor with a high framework aluminum content, can generate more hydroxyl pockets after complete dealumination, which is relatively conducive to introducing more tin atoms into the framework of the dealuminated Beta zeolite in the subsequent synthesis. On the other hand, a pure-phase Beta zeolite with a very low silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) is more difficult to synthesize by a hydrothermal method. Moreover, after a Beta zeolite precursor with a very low silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) is dealuminated by an acid dealumination method to form a dealuminated Beta zeolite carrier, the framework thermal stability is poor, and the crystallinity will be lost during the subsequent calcination step for preparing a Sn-Beta zeolite catalyst, resulting in poor performance of the catalyst. Therefore, the silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) of the Beta zeolite precursor required by the present application is preferably in the range of 10-200, more preferably in the range of 20-150, and even more preferably in the range of 25-100. The silicon-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) of the Beta zeolite precursor can be analyzed by a traditional chemical analysis method (titration method), or by an X-ray fluorescence spectroscopy (XRF) method or an inductively coupled plasma emission spectroscopy (ICP) method. The simple and fast XRF method is recommended by the present application.

[0053] Beta zeolite precursors meeting the requirements of the present invention can be obtained commercially or synthesized by engineers skilled in the art according to their experience and other literature reports.If the Beta zeolite precursor is synthesized by oneself, the following methods reported in the invention patents and open literature can be selected: US3 308 069(1967), EP187 522 A2(1986), US4 847 055(1989), CN1 086 792 A(September 20, 1993), CN1 108 213 A(March 11, 1994), CN1 108 214 A(March 11, 1994), CN1 154 341 A(January 11, 1996), CN1 154 242 A(January 9, 1996), CN1 154 342 A(January 11, 1996), CN1 268 545 A(March 30, 1999), CN1 133 497 C(March 30, 1999), CN1 108 275 C(September 10, 1999), CN1 100 004 C(May 19, 2000), CN1 335 258 A(February 28, 2001), CN1 116 227 C(March 12, 2001), CN101 205 072 B(December 18, 2006), Chem.Comm., 1996, 625; J.Mater.Chem., 1998, 8(9), 2137-2145; Microporous and Mesoporous Materials 21(1998)305-313; Applied Catalysis A-GENERAL, 166(1998), 97-103; Microporous and Mesoporous Materials 48(2001)23-29; Microporous and Mesoporous Materials 56(2002)1-10.; Journal of Molecular Catalysis 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 the dealuminated Beta zeolite support

[0055] As mentioned above, the dealuminated Beta zeolite support can be prepared from a Beta zeolite precursor by using a conventional acid dealumination method. The present invention requires that the molar ratio of silica to alumina (SiO2 / Al2O3) of the dealuminated Beta zeolite support be as high as possible, i.e. the framework aluminum of the Beta zeolite precursor should be removed as completely as possible. The molar ratio of silica to alumina (SiO2 / Al2O3) of the dealuminated Beta zeolite support according to the present invention is preferably in the range of > 700, more preferably in the range of > 800, and even more preferably in the range of > 900. Because the molar ratio of silica to alumina (SiO2 / Al2O3) of the dealuminated Beta zeolite is very high and the aluminum content is very low, the molar ratio of silica to alumina (SiO2 / Al2O3) of the dealuminated Beta zeolite support should be determined by inductively coupled plasma emission spectroscopy (ICP) or atomic absorption (AA). The present invention recommends the use of ICP.

[0056] When the Beta zeolite precursor is subjected to acid dealumination, the framework aluminum should be removed as completely as possible. The presence of too much residual framework aluminum in the dealuminated Beta zeolite support is disadvantageous because the strong acidity of the framework aluminum will reduce the selectivity of the catalyst for the main product, caprolactam.

[0057] Although the framework aluminum of the Beta zeolite is easily removed so that the dealuminated Beta zeolite support according to the present invention can be prepared from a Beta zeolite precursor by using a high-temperature steam dealumination method, an EDTA complexing agent dealumination method, an organic acid solution dealumination method, an inorganic acid (concentrated hydrochloric acid, concentrated nitric acid) solution dealumination method, or a combination of any of the above methods, the present invention recommends the use of a concentrated nitric acid solution dealumination method for the preparation of the dealuminated Beta zeolite support according to the present invention, taking into account the production cost, the process complexity, and the difficulty of treating the waste liquid resulting from dealumination.

[0058] Engineers skilled in the art can prepare the dealuminated Beta zeolite carrier meeting the requirements of the present application by using concentrated nitric acid aqueous solution to dealuminate the Beta zeolite precursor according to their own experience or referring to the specific methods disclosed in the following documents: 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 dealuminated Beta zeolite carrier is prepared by using concentrated nitric acid aqueous solution to dealuminate the Beta zeolite precursor, the concentration of the nitric acid aqueous solution, the ratio of the acid solution to the zeolite (liquid-solid ratio), and the temperature and time of the acid treatment are important factors affecting the degree of acid dealumination of the Beta zeolite precursor. The effects of the above factors on the dealumination of the Beta zeolite precursor are ultimately reflected in the residual aluminum content of the dealuminated Beta zeolite carrier. In addition, the pretreatment of the Beta zeolite precursor can also affect the degree of acid dealumination and the residual aluminum content of the dealuminated Beta zeolite carrier. However, if the dealuminated Beta zeolite carrier with a required molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) cannot be obtained after one dealumination, the molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of the dealuminated Beta zeolite can be adjusted to meet the requirements of the present application by secondary or even multiple supplemental dealumination. The present application recommends using 13M concentrated nitric acid as the dealumination acid and determining the amount of acid solution according to a liquid-solid ratio of 20ml / g. Under this premise, the dealumination reaction is carried out at 95°C for 20h to obtain the dealuminated Beta zeolite carrier meeting the requirements. Conventionally, the dealuminated Beta zeolite carrier prepared by the concentrated nitric acid dealumination method needs to be subjected to conventional solid-liquid separation to recover the solid product, then the solid product is washed with water until the pH value is neutral, and then the solid product is dried at a temperature of 80-200°C for 3-24h, and finally the dealuminated Beta zeolite carrier is obtained by calcining the dried product at a temperature of 500°C-600°C for 3-8h. After dealumination of the Beta zeolite precursor, a large number of hydroxyl pit lattice defect sites are generated, which enhances the water absorption and moisture absorption capacity of the Beta zeolite carrier, and therefore the dealuminated Beta zeolite carrier should be stored in a sealed manner for later use.

[0060] Second step, using an aqueous solution of a small molecule fatty amine or / and an alcohol amine (weak organic base) to modify the hydroxyl pits of the dealuminated Beta zeolite carrier

[0061] The hydroxyl pocket modification is carried out by using a conventional aqueous solution immersion method. The pocket modification is essentially an alkali-catalyzed hydrolysis reaction modification ([(OSi)3-O-SiOH]+3H2O=Si(OH)4+3≡Si-OH), and for each skeleton silicon atom (in the form of orthosilicic acid (Si(OH)4)) removed, three silicon hydroxyl groups (≡SiOH) are generated on the new pit wall of the hydroxyl pocket.

[0062] The small molecule aliphatic amine mainly refers to methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine or ethylenediamine, and the small molecule alcohol amine mainly refers to ethanolamine, isopropanolamine, diethanolamine, diisopropanolamine or triethanolamine. The pocket modification of the hydroxyl pocket of the dealuminated Beta zeolite carrier can use an aqueous solution of any one or more than two kinds of small molecule aliphatic amine and alcohol amine, or an aqueous solution of any combination of the small molecule aliphatic amine and alcohol amine. However, it should be noted that other aliphatic amines and alcohol amines and other organic amines (such as alicyclic amines) also have the effect of pocket modification on the hydroxyl pocket of the dealuminated Beta zeolite carrier, but the small molecule aliphatic amine and alcohol amine have the advantages of good water solubility, small dosage and low cost.

[0063] The pocket modification of the hydroxyl pocket of the dealuminated Beta zeolite carrier is carried out by immersion in an aqueous solution of a small molecule aliphatic amine or / and alcohol amine. After the pocket modification is completed, the pocket-modified dealuminated Beta zeolite carrier is obtained by solid-liquid separation, drying and calcination. During the modification, the concentration of the pocket modification solution (aqueous solution of a small molecule aliphatic amine or / and alcohol amine), the ratio of the pocket modification solution to the dealuminated Beta zeolite carrier (i.e. the liquid-solid ratio (ml / g)), and the desiliconization reaction temperature and time of the pocket modification are the main factors affecting the controllable desiliconization modification (pocket modification) of the hydroxyl pocket of the dealuminated Beta zeolite.

[0064] The aqueous solution of a small molecule aliphatic amine or / and alcohol amine is referred to as a pocket solution, which contains one or more than two kinds of small molecule aliphatic amine and / or small molecule alcohol amine, and the conditions are limited as follows:

[0065] The suitable range of the concentration of the pocket 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 of the ratio of the pocket solution to the dealuminated Beta zeolite carrier (i.e. the liquid-solid ratio (ml / g)) is 1:1-100:1, the preferred range is 2:1-50:1, and the more preferred range is 3:1-20:1;

[0067] The suitable range of the temperature of the desilication reaction for the cavity modification is 20-100°C; the preferable range is 30-90°C; and the more preferable range is 40-80°C.

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

[0069] The engineers familiar with the art can refer to the impregnation process commonly used in the preparation of heterogeneous catalysts, and prepare the cavity solution with the small molecule fatty amine and the alcohol amine recommended by the present application, and perform the cavity modification treatment on the desilicated Beta zeolite carrier within the above-mentioned condition range, so as to achieve the purpose of the cavity modification on the hydroxyl cavity of the desilicated Beta zeolite carrier, and the details are not described herein again. After the cavity modification is completed, the post-processing treatment can be performed on the liquid-solid mixture according to the common sense, mainly including the conventional liquid-solid separation, water washing (to neutral pH value), drying and calcination treatment. The cavity modification desilicated Beta zeolite carrier after the calcination treatment needs to be sealed and stored for standby, so as to avoid water absorption. The conditions of the drying and calcination treatment can refer to the drying and calcination treatment conditions of the desilicated Beta zeolite carrier in the first step (preparation of the desilicated Beta zeolite carrier) of the embodiment of the present application. The details are not described herein again.

[0070] However, it needs to be further emphasized that for the desilicated Beta zeolite carriers with different numbers of hydroxyl cavities prepared from the Beta zeolite matrix with different molar ratios of silicon aluminum oxide (molar ratio of SiO2 to Al2O3), in order to perform the cavity modification with controllable degree on the hydroxyl cavities by using the aqueous solution of the small molecule fatty amine or / and the alcohol amine, the key lies in the correct selection of the modification conditions combined by the four parameters of the cavity solution concentration, the liquid-solid ratio (ml / g), the desilication reaction temperature and the time. It can be understood that the modification conditions combined by the lower limit values of the above-mentioned four parameters have the weakest desilication effect, and are suitable for the cavity modification of the desilicated Beta zeolite carrier with a small number of hydroxyl cavities; the modification conditions combined by the upper limit values of the above-mentioned four parameters have the strongest desilication effect, and can be used for the cavity modification of the desilicated Beta zeolite carrier with a large number of hydroxyl cavities; and the modification conditions combined by other different values of the above-mentioned five parameters within the specified range will produce different desilication effects between the weakest and the strongest. The above explanation of the present application aims to provide the engineers in the art with the principle guidance, and the impregnation treatment conditions for achieving the moderate cavity modification by using the aqueous solution of the small molecule fatty amine or / and the alcohol amine are preferably determined through the test for the different desilicated Beta zeolite carriers.

[0071] The third step is to prepare the Sn-Beta zeolite by the solid-solid isomorphous substitution reaction with the cavity modification desilicated Beta zeolite as the carrier

[0072] According to the solid-solid isomorphous substitution reaction method, first, the delaminated Beta zeolite carrier modified by drilling holes is mixed with a tin source in a solid phase, and then the solid mixture is calcined in a nitrogen atmosphere and an air atmosphere in sequence, so that the Sn-Beta zeolite can be prepared.

[0073] Because the solid-solid isomorphous substitution reaction needs to occur in the hydroxyl hole, the molar ratio of silicon aluminum oxide (molar ratio of SiO2 to Al2O3) of the Beta zeolite mother body determines the number of hydroxyl holes of the delaminated Beta zeolite carrier and the delaminated Beta zeolite carrier modified by drilling holes, and the number of hydroxyl holes in the zeolite carrier determines the theoretical maximum tin content of the Sn-Beta zeolite catalyst. In view of this, the present application provides the percentage of the hydroxyl hole of the zeolite carrier as an important technical parameter for preparing Sn-Beta zeolite by solid-solid isomorphous substitution reaction starting from Beta zeolite mother bodies with different molar ratios of silicon aluminum oxide (molar ratio of SiO2 to Al2O3). The parameter can be used to calculate the batching ratio of the zeolite carrier and the tin source.

[0074] The present application requires that when Sn-Beta zeolite is prepared by solid-solid isomorphous substitution reaction starting from Beta zeolite mother bodies with different molar ratios of silicon aluminum oxide (molar ratio of SiO2 to Al2O3), the batching ratio of the zeolite carrier and the tin source is determined by the percentage of the number of tin ions in the number of moles of the hydroxyl hole of the zeolite carrier, and 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 holes is calculated according to the mass of the zeolite carrier, the amount of tin ions required is determined according to the proportion, and the mass of the tin source required is calculated. The number of moles of the hydroxyl hole of a certain mass of the zeolite carrier is equal to the number of moles of acid delamination when the same mass of the zeolite carrier is prepared.

[0075] The solid-solid isomorphous substitution reaction can be carried out according to the existing method, and the following documents can be referred to: US2016279621(A1) (filing date 2014-11-05), CN106984356A (filing date 2017-05-05), ACS Catalysis, 2014, 4(8): 2801-2810, Angewandte Chemie International Edition, 2012, 51(47): 11736-11739, Master's Thesis “Rapid Synthesis of Sn-Beta Zeolite and Catalytic Conversion of Sugar to Lactate Ester”, Zhengzhou University (2017).

[0076] According to the existing method, the operation steps for preparing Sn-Beta zeolite by solid-solid isomorphous substitution reaction method are as follows:

[0077] (1) The number of hydroxyl pits of the dealuminated Beta zeolite support modified by the pit-chipping is selected according to the percentage of the molar number of tin ions to the molar number of the hydroxyl pits of the zeolite support, and the amount of tin source is calculated according to the selected percentage;

[0078] (2) The dealuminated Beta zeolite support modified by the pit-chipping and dried and calcined is mixed with the measured tin source and ground thoroughly;

[0079] (3) The solid mixture of the zeolite support and the tin source ground thoroughly is put into a tubular reactor to carry out the solid-solid phase substitution reaction. First, high-purity nitrogen is introduced into the reactor to replace the air in the reactor thoroughly. Then the solid mixture in the reactor is heated to 200℃ at a heating rate of 6℃ / min and kept at the temperature for 1-3h to allow the tin source to diffuse into the pores of the zeolite in the high-purity nitrogen atmosphere. Next, the solid mixture in the reactor is heated to the temperature interval of 450℃-550℃ at a heating rate of 7℃ / min and kept at the temperature for 6-8h to complete the solid-solid isomorphous substitution reaction. In the middle of the solid-solid isomorphous substitution reaction (when kept at the temperature interval of 450℃-550℃ for 3-4h), the high-purity nitrogen atmosphere in the reactor is changed to air atmosphere. After the solid-solid isomorphous substitution reaction is completed, the Sn-Beta zeolite product prepared by the method of the present application is obtained.

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

[0081] The engineers familiar with the art can prepare Sn-Beta zeolite according to the requirements of the present application with the dealuminated Beta zeolite modified by the pit-chipping as the support according to their own experience or referring to the solid-solid isomorphous substitution method reported in the existing published literatures and patents.

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

[0083] The Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide is carried out according to the existing method, and the reactor form can be a batch kettle reactor, a fixed bed continuous reactor, or even a catalytic distillation reactor, and the present application has no limitation on this. Engineers familiar with the field can use the Sn-Beta zeolite prepared by the method of the present application as a catalyst to carry out the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide according to their own experience or according to the reports in the existing published literature and patents, so as to improve the selectivity of the target product caprolactone. The following published literature and patents report the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide, which can be referred to: 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 2014-11-21), 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, Ph.D. Dissertation, “Synthesis, Characterization and Catalytic Performance of Sn-Beta Zeolite”, Dalian University of Technology (2012), Ph.D. Dissertation, “Aerosol-Assisted Synthesis of Sn-Beta Zeolite and Its Catalytic Performance in Baeyer-Villiger Oxidation Reaction”, Dalian University of Technology (2019), Master Dissertation, “Preparation of Sn-Beta Zeolite and Its Performance in Cyclohexanone Oxidation Reaction”, Dalian University of Technology (2020), Master Dissertation, “Preparation of Sn-Beta Zeolite by Aerosol-Assisted Post-Synthesis Method and Its Performance in Baeyer-Villiger Oxidation Reaction”, Dalian University of Technology (2020), Master Dissertation, “Study on Influencing Factors of Cyclohexanone Oxidation Reaction on Sn-β Zeolite”, Dalian University of Technology (2022).

[0084] In order to facilitate the illustration of the effect of the Sn-Beta zeolite catalyst prepared by the method of the present application in improving the selectivity of the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, the present application uses a batch reactor to carry out the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide under harsh conditions with a small amount of solvent (1,4-dioxane). The method is as follows: first, add the solvent 1,4-dioxane, cyclohexanone and hydrogen peroxide solution reactants into the batch reactor in sequence, and finally add the Sn-Beta zeolite catalyst prepared by the method of the present application, and the reaction is carried out under normal pressure and stirring. The reaction conditions are as follows: the reaction temperature is 90℃, the reaction time is 3h, the catalyst dosage is 0.6g / g based on the cyclohexanone reactant, the concentration of hydrogen peroxide raw material is 50wt%, and the molar ratio of 1,4-dioxane: cyclohexanone: H2O2 is 12.5:2.5:1.

[0085] Advantages of the present application

[0086] In general, the present application provides a method for preparing Sn-Beta zeolite catalyst using solid-solid isomorphous substitution reaction with delaminated Beta zeolite as carrier. The key of the present application is to modify the hydroxyl cavity of the delaminated Beta zeolite with a small molecule fatty amine or alcohol amine aqueous solution before the solid-solid isomorphous substitution reaction to expand the inclusion of tin ions by the hydroxyl cavity. The key technical method provided by the present application can solve the problem that the heteroatom tin is difficult to enter the hydroxyl cavity of the delaminated Beta zeolite for isomorphous substitution reaction due to its large ion radius, and can also avoid the problem caused by the volume expansion of the hydroxyl cavity due to the implantation of tin ions into the hydroxyl cavity. Using the method of the present application, high-quality Sn-Beta zeolite with fully utilized hydroxyl cavity, high framework tin content and low non-framework tin content can be easily obtained. The Sn-Beta zeolite prepared by the method of the present application can significantly improve the selectivity of caprolactone even under the condition of less solvent (1,4-dioxane) usage. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 is a comparison of the hydroxyl region infrared spectra of the dealuminated Beta zeolite support (Beta24c) prepared from the acid dealumination treatment of the Beta zeolite mother substance with a silica alumina oxide molar ratio (molar ratio of SiO2 to Al2O3) of 24, and the channeled modified dealuminated Beta zeolite support (Beta24C 44 ) prepared from the channeled modification treatment of the Beta24c.

[0088] Figure 2 is a comparison of the changes in the hydroxyl region infrared spectra of the channeled modified dealuminated Beta zeolite support prepared by the method of the present invention before (Beta24C 44 ) and after (Beta24C 44 -6Sn) solid-solid isomorphous substitution of tin ions.

[0089] Figure 3 is a comparison of the results of the ultraviolet-visible spectroscopy characterization of the tin content of the skeleton of the Sn-Beta zeolite catalyst (Beta24c-6Sn) prepared from the direct use of the dealuminated Beta zeolite support in the solid-solid isomorphous substitution reaction of tin ions, and the Sn-Beta zeolite catalyst (Beta24C 44 -6Sn) prepared from the use of the dealuminated Beta zeolite support after the channeled modification treatment in the solid-solid isomorphous substitution reaction of tin ions.

[0090] Figure 4 is a comparison of the changes in the hydroxyl region infrared spectra of the dealuminated Beta zeolite support (Beta24c) before and after (Beta24c-6Sn) solid-solid isomorphous substitution of tin ions without channeled modification. DETAILED DESCRIPTION

[0091] The implementation effects of the present application can be evaluated in two aspects: the characterization of physicochemical properties and the test of the catalytic performance of the catalyst. Among them:

[0092] (1) The channeled modification effect of the aqueous solution of small molecule fatty amine or alcohol amine on the hydroxyl pockets of the dealuminated Beta zeolite can be evaluated by the changes in the hydroxyl pocket band characterized by Fourier transform infrared spectroscopy (FT-IR) and the amount of desilication detected by inductively coupled plasma emission spectroscopy (ICP). It should be noted that the most typical characteristic band of the hydroxyl pocket of the dealuminated zeolite is a continuous absorption band in the range of 3400-3600 cm -1 , with the maximum generally at 3500 cm -1at 3740 cm-1, which overlaps with the surface silanol vibration at 3740 cm-1(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, there can be terminal silanol groups in the larger hydroxyl pockets, whose vibration absorption can appear at 3740 cm -1

[0093] (2) In the case of implanting tin ions into the hydroxyl pockets by solid-solid isomorphous substitution reaction, the attenuation of the hydroxyl pocket band intensity of the dealuminated Beta zeolite can be evaluated by Fourier transform infrared spectroscopy (FT-IR).

[0094] (3) The distribution of framework tin and non-framework tin in the Sn-Beta zeolite catalysts with different tin contents prepared by solid-solid isomorphous substitution reaction can be characterized by diffuse reflectance ultraviolet-visible spectroscopy.

[0095] (4) The catalytic performance of the Sn-Beta zeolite catalysts with different tin contents prepared by the method of the present application in the Beayer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide was evaluated using a batch reactor. The product liquid was analyzed using an Agilent 7890B gas chromatograph, with a CP-Wax 52CB column (25 m x 0.32 mm x 1.2 μm), a detector temperature of 240 °C, and an injection port temperature of 200 °C. The column temperature was started at 80 °C and maintained for 1 min, then increased to 150 °C at a rate of 12 °C / min and maintained for 2 min, and then increased to 250 °C at a rate of 10 °C / min and maintained for 20 min. The internal standard method was used to quantitatively calculate the conversion of cyclohexanone and the selectivity of caprolactone.

[0096] The present application is further illustrated by the following examples, but the present application is not limited by these examples.

[0097] ​Example 1: This example is used to illustrate that, first, a "pocket modification" treatment aiming at controllably removing 1-2 framework silicons from the hydroxyl pockets of the dealuminated Beta zeolite support is carried out by using an aqueous solution of a small molecular fatty amine or / and alcohol amine, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acid dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then a solid-solid isomorphous substitution reaction is used to prepare Sn-Beta zeolite with the "pocket modified" dealuminated Beta zeolite as the support, so as to make the isomorphous substitution reaction of tin ions easy to occur. The Sn-Beta zeolite prepared by the method of the present application has high framework tin content, low non-framework tin content, and high hydroxyl pocket utilization rate. The Sn-Beta zeolite catalyst prepared has high selectivity of the product of caprolactone in the Baeyer-Villiger oxidation reaction of cyclohexanone and dilute hydrogen peroxide.

[0098] First step: preparation of dealuminated Beta zeolite support

[0099] (1) A Beta zeolite mother substance with a molar ratio of silicon aluminum oxide (molar ratio of SiO2 to Al2O3) of 25 was synthesized by a hydrothermal crystallization method provided in US Patent US3 308 069 (1967) as a raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to a conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template agent (540°C, 6h), it was observed by TEM that the crystal grain size thereof was less than 100 nanometers, belonging to nano-Beta zeolite; it was checked by XRD method that there was no any impurity crystal therein, and the BET specific surface area thereof was calculated to be about 550m 2 / g by using the nitrogen physical adsorption data, and the molar ratio of silicon aluminum oxide (molar ratio of SiO2 to Al2O3) thereof was measured by XRF method to be about 24, meeting the technical requirements of the Beta zeolite mother substance of the present application.

[0100] (2) The dealuminated Beta zeolite support was prepared by using concentrated nitric acid to dealuminate the Beta zeolite mother substance.

[0101] First, prepare a concentrated nitric acid solution with a molar concentration of 13 M. Then, under stirring, add 20 g of the Beta zeolite mother substance that has been dried and calcined as described above to a three-necked flask containing 400 ml of the 13 M concentrated nitric acid solution in a liquid-to-solid ratio of 20:1 (ml / g) to perform the dealumination treatment. The dealumination temperature is 95°C, and the dealumination time is 20 h. During the dealumination reaction, the three-necked flask is kept in a reflux state. After the dealumination reaction is completed, the reaction mixture is cooled to room temperature, and the solid product is recovered by filtration. Then, through conventional water washing, drying (overnight at 110°C), and calcination (550°C for 3 h), the dealuminated Beta zeolite support Beta24c is prepared. The molar ratio of silicon-aluminum oxides (molar ratio of SiO2 to Al2O3) of the dealuminated Beta zeolite support is 980, as determined by ICP. It is suitable for use in the present application. It is stored in a sealed state to avoid moisture absorption and is ready for use.

[0102] Second, the hydroxyl pockets of the dealuminated Beta zeolite support are subjected to pocket-modification treatment using an aqueous solution of ethanolamine

[0103] The pocket-modification is performed by atmospheric pressure impregnation. First, prepare an aqueous solution of ethanolamine with a concentration of 44 mmol / L (44 mM) as the pocket-modification solution. Then, add 20 g of the dealuminated Beta zeolite support to 120 ml of the ethanolamine modification solution in a liquid-to-solid ratio of 6:1 (ml / g). Under stirring, heat the reaction mixture to 40°C, and allow the reaction mixture to react at this temperature for 1 h under continuous stirring. During this period, a weakly basic hydrolytic desilication reaction of the dealuminated Beta zeolite support in the weakly basic solution of ethanolamine occurs, i.e., [(OSi)3-O-SiOH] + 3H2O = Si(OH)4 + 3≡Si-OH, in which for each silicon atom (in the form of orthosilicic acid (Si(OH)4)) removed, three silicon hydroxyl groups (≡Si-OH) are generated on the new pit wall of the hydroxyl pocket. After 1 h of reaction, the reaction mixture is filtered to recover the solid product, which is then repeatedly washed with deionized water until neutral, dried (overnight at 110°C), and calcined (550°C for 3 h) to obtain the pocket-modified dealuminated Beta zeolite support. It is stored in a sealed state and is ready for use. According to the weight loss, on average, 1.07 framework silicon atoms (in terms of SiO2) are chipped out from each hydroxyl pocket lattice defect site of the dealuminated Beta zeolite support, indicating that the pocket modification is a controlled and moderate desilication, which meets the requirements for pocket modification of the dealuminated Beta zeolite support. The pocket-modified support is designated as Beta24C 44 (the capital "C" indicates that the pocket modification increases the volume of the hydroxyl pockets in the dealuminated Beta zeolite). The dealuminated Beta zeolite support (Beta24c) and its pocket-modified sample (Beta24C 44) is shown in Figure 1. As can be seen from Figure 1, after the modification of the dealuminated Beta zeolite support by the channelling method, the characteristic spectrum band (3400 cm -1 -3600 cm -1 ) of the hydroxyl group of the dealuminated Beta zeolite support has changed obviously, which indicates that the modification by the channelling method has indeed occurred at the lattice defect site of the hydroxyl group of the dealuminated Beta zeolite.

[0104] Third step: using tin (II) acetate as the tin source, Sn-Beta zeolite is prepared on the dealuminated Beta zeolite support modified by the channelling method by using the solid-solid isomorphous substitution method

[0105] (1) 10 g of the dealuminated Beta zeolite support modified by the channelling method, Beta24C 44 , has a total amount of hydroxyl group of 13 mmol (estimated by the amount of dealuminated Beta zeolite). According to the calculation of the amount of tin ion used in the solid-solid isomorphous substitution reaction by the participation of 38% of the hydroxyl group, the amount of tin (II) acetate used is 1.20 g;

[0106] (2) 10 g of the dealuminated Beta zeolite support modified by the channelling method and dried and calcined, Beta24C 44 , is mixed with 1.2 g of tin (II) acetate and ground thoroughly;

[0107] (3) the solid mixture of the zeolite and the tin source is put into a tubular reactor for the solid-solid substitution reaction. First, high-purity nitrogen gas is introduced into the reactor to replace the air in the reactor completely. Then, the solid mixture in the reactor is heated to 200℃ at a temperature increasing rate of 6℃ / min under the high-purity nitrogen atmosphere and is kept at this temperature for 1 h to allow the tin source to diffuse into the pores of the zeolite. Next, the solid mixture in the reactor is heated to 550℃ at a temperature increasing rate of 7℃ / min under the high-purity nitrogen atmosphere and is kept at this temperature for 6 h to complete the solid-solid isomorphous substitution reaction. In the middle of the solid-solid isomorphous substitution reaction (when kept at 550℃ for 3 h), the high-purity nitrogen atmosphere in the reactor is changed to air atmosphere. After the completion of the solid-solid isomorphous substitution reaction, the Sn-Beta zeolite product prepared by the method of the present application is obtained, which is designated as Beta24C 44 -6Sn.

[0108] (4) the prepared Sn-Beta zeolite product, Beta24C 44 -6Sn, is characterized for the physicochemical properties: the Si / Sn ratio of the Beta24C 44 -6Sn zeolite catalyst is determined by XRF to be 33. The change of the spectrum band of the hydroxyl group of the zeolite support before and after the solid-solid isomorphous substitution reaction is characterized by the Fourier transform infrared spectroscopy, and the result is shown in Figure 2. The Beta24C 44The tin species distribution of the -6Sn zeolite catalyst is shown in Figure 3. From the results of the hydroxyl infrared spectrum characterization in Figure 2, it can be seen that, after the "pocket modification" treatment of the dealuminated Beta zeolite with an aqueous solution of ethanolamine, the inclusion of tin ions in the hydroxyl pocket is expanded, and then the dealuminated Beta zeolite subjected to the "pocket modification" is used as a carrier to prepare the Sn-Beta zeolite by solid-solid isomorphous substitution reaction, which is conducive to the solid-solid isomorphous substitution reaction of tin ions in the hydroxyl pocket. As a result, the content of the framework tin (characteristic absorption band at 215 nm) in the prepared Beta24C 44 -6Sn zeolite catalyst is large. In summary, the physicochemical property characterization shows that the implementation effect of the present application is remarkable. 44 -6Sn zeolite catalyst is large. In summary, the physicochemical property characterization shows that the implementation effect of the present application is remarkable.

[0109] Fourth step: Beta24C 44 -6Sn zeolite catalyst is used to catalyze the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone to synthesize caprolactone.

[0110] (1) A 50 mL round-bottom flask is used as a reactor, and 1,4-dioxane, cyclohexanone and H2O2 are added in a molar ratio of 5.5:1:0.4. First, 5 g of 1,4-dioxane is added as a solvent, then 1 g of cyclohexanone and 0.2756 g of 50 wt% hydrogen peroxide are added, and the rotor is placed. The condensate water is connected.

[0111] (2) Start stirring and set the oil bath temperature to 90°C. After the reactor reaches the specified reaction temperature, about 0.6 g of Beta24C 44 -6Sn zeolite catalyst is added and the timing starts. The reaction time is set to 3 h.

[0112] (3) After the reaction is completed, the reaction is centrifuged, and the supernatant is analyzed by gas chromatography. According to the chromatographic analysis data, the reaction results are: the conversion rate of cyclohexanone is 38.28% (the theoretical conversion rate based on the amount of hydrogen peroxide used is 40%), the selectivity of the product caprolactone is 40.61%, and the conversion rate of hydrogen peroxide is 92.89%.

[0113] Comparative Example 1: This example is used to illustrate that if the "pocket modification" treatment of the dealuminated Beta zeolite support with an aqueous solution of a small molecule aliphatic amine or / and an aliphatic alcohol amine is not used, but instead the dealuminated Beta zeolite is directly used as the support, and a solid-solid isomorphous substitution reaction is used to prepare the Sn-Beta zeolite, the isomorphous substitution reaction of tin ions does not easily occur, and thus the Sn-Beta zeolite prepared has a low framework tin content, a high non-framework tin content, and a low hydroxyl pocket utilization. The Sn-Beta zeolite catalyst prepared has a poor selectivity to the caprolactone product in the Baeyer-Villiger oxidation reaction of cyclohexanone with dilute hydrogen peroxide.

[0114] Example 1 is repeated, but after the dealuminated Beta zeolite support Beta24c is prepared in the first step, the second step is skipped, and the dealuminated Beta zeolite support Beta24c is directly used in the third step, i.e., the dealuminated Beta zeolite Beta24c is directly used as the support, and a solid-solid isomorphous substitution reaction is used to prepare the Sn-Beta zeolite. The Sn-Beta zeolite catalyst prepared has the code Beta24c-6Sn.

[0115] The prepared Sn-Beta zeolite product Beta24c-6Sn was characterized for physicochemical properties: the Si / Sn ratio of the Beta24c-6Sn zeolite catalyst was also 33 as determined by XRF. The tin species distribution of the Beta24c-6Sn zeolite catalyst was characterized by UV-visible spectroscopy, and the results are shown in Figure 3. The hydroxyl band changes of the zeolite support before and after the solid-solid isomorphous substitution reaction were characterized by Fourier transform infrared spectroscopy, and the results are shown in Figure 4. As can be seen from Figure 3, the content of framework tin (characteristic absorption band at 210 nm) in the Beta24c-6Sn zeolite catalyst is small. As can be seen from the characterization results of the hydroxyl infrared spectrum in Figure 4, in the case where the dealuminated Beta zeolite is not first treated with a weak aqueous organic base solution for controllable "pitting modification", and the dealuminated Beta zeolite is directly used as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, it is not conducive to the solid-solid isomorphous substitution reaction of tin ions in the hydroxyl pits. As a result, in the prepared Beta24c-6Sn zeolite catalyst, the intensity of the silicon hydroxyl vibration infrared absorption band related to the support hydroxyl pits is very small, indicating that the hydroxyl pits have not been largely utilized by tin ions. By comparing the characterization results of Example 1 (Figures 1 and 2), the benefits of the present application can be easily found. In addition, the Beta24c-6Sn zeolite catalyst was used for the fourth step of the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone, and the reaction results were a cyclohexanone conversion rate of 39.66% (theoretical conversion rate of 40%) and a caprolactone product selectivity of 12.78%, and the conversion rate of hydrogen peroxide was 96.58%. By comparing the reaction data of Example 1, it can be clearly seen that the use of the Sn-Beta zeolite catalyst prepared by the method provided in the present application, i.e. first treating the dealuminated Beta zeolite with a weak aqueous organic base solution for controllable "pitting modification", and then using the "pitting modified" dealuminated Beta zeolite as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, is conducive to improving the caprolactone product selectivity of the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone.

[0116] Example 2: This example is used to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite support aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets is first carried out using an aqueous solution of a small molecule aliphatic amine or / and an alcohol amine, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acidic dealumination) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then the Sn-Beta zeolite is prepared by using the "pitting modified" dealuminated Beta zeolite as the support through a solid-solid isomorphous substitution reaction, wherein the aqueous solution of a small molecule aliphatic amine or / and an alcohol amine refers to an aqueous solution of different small molecule aliphatic amines and any mixture thereof, an aqueous solution of different small molecule alcohol amines and any mixture thereof, and an aqueous solution of any mixture of small molecule aliphatic amines and alcohol amines. Changing the types of the small molecule aliphatic amines and alcohol amines, or using any mixture thereof, only affects the degree of "pitting modification" of the hydroxyl pockets of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0117] Example 1 is repeated. However, in the second step of the pitting modification treatment of the hydroxyl pockets of the dealuminated Beta zeolite support, the aqueous solution of 44 mmol / L (44 mM) of isopropyl alcohol amine, diethanol amine, diisopropyl alcohol amine and triethanol amine is sequentially used, and other pitting modification conditions and practices remain unchanged. According to the weight loss estimation, the average number of framework silicon atoms (calculated as SiO2) removed from the lattice defect sites of the hydroxyl pockets of the dealuminated Beta zeolite support is 1.04, 1.02, 0.99 and 0.95, respectively, indicating that when using the aqueous solutions of isopropyl alcohol amine, diethanol amine, diisopropyl alcohol amine and triethanol amine, the pitting modification is also a moderate desiliconization under controllable conditions, achieving the pitting modification requirements of the dealuminated Beta zeolite support. The pitting modified dealuminated Beta zeolite support is used in the third step, i.e. using tin (II) acetate as the tin source, and using the solid-solid isomorphous substitution method to prepare Sn-Beta zeolite. The conversion rate of cyclohexanone in the hydrogen peroxide and cyclohexanone Baeyer-Villiger oxidation reaction of the obtained Sn-Beta zeolite catalyst is 39.29%, 38.47%, 39.33% and 38.54%, respectively, the selectivity of caprolactone product is 33.30%, 32.56%, 32.00% and 31.22%, respectively, and the conversion rate of hydrogen peroxide is 94.70%, 93.68%, 95.83% and 93.85%, respectively.

[0118] Example 3: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom deficiency (acidic dealumination) to a larger hydroxyl pocket having 2-3 framework atom deficiencies, and then using the "pocket modified" dealuminated Beta zeolite as a support to prepare Sn-Beta zeolite by a solid-solid isomorphous substitution reaction, wherein the aqueous solution of a small molecule aliphatic amine or / and an alcohol amine refers to an aqueous solution of different small molecule aliphatic amines and any mixture thereof, an aqueous solution of different small molecule alcohol amines and any mixture thereof, and an aqueous solution of any mixture of small molecule aliphatic amines and alcohol amines. Changing the type of said small molecule aliphatic amines and alcohol amines, or using any mixture thereof, only affects the degree of "pocket modification" of the dealuminated Beta zeolite hydroxyl pockets, but does not change the benefits of the present application.

[0119] Example 1 was repeated. However, in the second step, the hydroxyl pocket of the dealuminated Beta zeolite carrier was subjected to pocket-chiseling modification treatment, in turn, 44 mmol / L (44 mM) aqueous solutions of methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, diethylamine, triethylamine and ethylenediamine were used, and other pocket-chiseling modification conditions and procedures were unchanged. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiseled out from the hydroxyl pocket lattice defect sites of the dealuminated Beta zeolite carrier was 1.12, 1.10, 1.25, 1.23, 1.19, 1.14, 1.36, 1.33, 1.28 and 1.08, respectively, indicating that when using aqueous solutions of methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, diethylamine, triethylamine and ethylenediamine, the pocket-chiseling modification was also a moderate desiliconization under controllable conditions, which met the requirements of pocket-chiseling modification of the dealuminated Beta zeolite carrier. Then, the dealuminated Beta zeolite carrier subjected to pocket-chiseling modification was used for the third step, i.e., Sn-Beta zeolite was prepared by using tin (II) acetate as tin source and applying the solid-solid isomorphous substitution method, and the conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone over the obtained Sn-Beta zeolite catalyst was 38.44%, 38.50%, 38.01%, 38.05%, 38.18%, 38.32%, 37.99%, 38.14%, 37.99% and 36.72%, respectively, the selectivity of caprolactone product 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 rate of hydrogen peroxide was 94.1%, 94.23%, 93.03%, 93.33%, 93.65%, 93.66%, 92.98%, 93.55%, 93.01% and 89.90%, respectively.

[0120] Example 4: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acidic dealumination) to a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the aqueous solution of small molecule aliphatic amine or / and alcohol amine refers to the aqueous solution of different small molecule aliphatic amines and any mixture thereof, the aqueous solution of different small molecule alcohol amines and any mixture thereof, and the aqueous solution of any mixture of small molecule aliphatic amine and alcohol amine. Changing the type of said small molecule aliphatic amine and alcohol amine, or using any mixture thereof, only affects the degree of "pocket modification" of the hydroxyl pockets of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0121] Example 1 was repeated, but in the second step of subjecting the hydroxyl pockets of the dealuminated Beta zeolite support to pocket-modification treatment, aqueous solutions of mixtures 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) were used in turn, with the total molar concentration (sum of moles of each aliphatic amine or / and alcohol amine in 1 liter of solution) of the above organic amine mixture solutions kept at 44 mmol / L (44 mM), and other pocket-modification conditions and procedures unchanged. Then, the pocket-modified dealuminated Beta zeolite support obtained was used in the third step, i.e. solid-solid isomorphous substitution method using tin (II) acetate as tin source to prepare Sn-Beta zeolite, and the conversion of cyclohexanone in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide over the obtained Sn-Beta zeolite catalyst was 38.39%, 38.11%, 36.84%, 39.22%, 39.09%, 38.21% and 38.23% in turn, the selectivity of caprolactone product was 35.66%, 35.47%, 35.02%, 33.14%, 39.28%, 38.85% and 37.79% in turn, and the conversion of hydrogen peroxide was 94.08%, 93.38%, 90.30%, 96.15%, 95.83%, 93.64% and 93.98% in turn.

[0122] Example 5: This example is used to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite support with an aqueous solution of a small molecule aliphatic amine or / and alcohol amine, aiming at controllably removing 1-2 framework silicon atoms from the hydroxyl pockets of the dealuminated Beta zeolite, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acidic dealumination) into a larger hydroxyl pocket having 2-3 framework atom vacancies, is performed first, and then the Sn-Beta zeolite is prepared by using the "pitting modified" dealuminated Beta zeolite as the support through a solid-solid isomorphous substitution reaction, wherein the molar concentration of the aqueous solution of the small molecule aliphatic amine or / and alcohol amine is adjustable within a certain range. Changing the concentration of the aqueous solution of the small molecule aliphatic amine or / and alcohol amine only affects the degree of "pitting modification" of the hydroxyl pockets of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0123] Example 1 is repeated. However, when the hydroxyl pockets of the dealuminated Beta zeolite support are subjected to the pitting modification treatment with the aqueous solution of ethanol amine in the second step, the concentration of the aqueous solution of ethanol amine is changed 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) in turn, and according to the weight loss, the average number of framework silicon atoms (calculated as SiO2) pitted out from the lattice defect sites of the hydroxyl pockets of the dealuminated Beta zeolite support is 0.80, 0.95, 1.21, 1.36, 1.51 and 1.77 silicon atoms in turn, indicating that the pitting modification is a moderate desilication performed under controllable conditions, and the requirement for the pitting modification of the dealuminated Beta zeolite support is reached, and the pitting modification support codes are Beta24C 11 , Beta24C 22、 , Beta24C 88、 , Beta24C 177、 , Beta24C 220 and Beta24C 354 . The above pitting modification obtained support is used in the third step in turn, i.e. the Sn-Beta zeolite is prepared by using tin (II) acetate as the tin source and using the solid-solid isomorphous substitution method, and the obtained Sn-Beta zeolite catalyst codes are Beta24C 11 -6Sn, Beta24C 22 -6Sn, Beta24C 88 -6Sn, Beta24C 177 -6Sn, Beta24C 220 -6Sn and Beta24C 354-6Sn, their cyclohexanone conversion rates in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide are 39.0%, 38.43%, 37.33%, 39.26%, 39.98% and 38.15% respectively, the selectivity of caprolactone product is 31.2%, 38.25%, 38.06%, 31.89%, 32.19% and 32.12% respectively, and the conversion rate of hydrogen peroxide is 95.2%, 93.78%, 91.03%, 95.85%, 97.65% and 93.08% respectively.

[0124] Example 6: This example is used to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite carrier aiming at controllably removing 1-2 framework silicons from the hydroxyl pits of the carrier is first carried out by using an aqueous solution of small molecule fatty amine or / and alcohol amine, so as to expand the small hydroxyl pit originally having only one framework atom vacancy (acid dealuminated) into a larger hydroxyl pit having 2-3 framework atom vacancies, and then the Sn-Beta zeolite is prepared by using the "pitting modified" dealuminated Beta zeolite as the carrier through the solid-solid isomorphous substitution reaction, wherein the amount (liquid-solid ratio) of the aqueous solution of small molecule fatty amine or / and alcohol amine can be adjusted within a certain range. Changing the amount (liquid-solid ratio) of the aqueous solution of small molecule fatty amine or / and alcohol amine only affects the degree of "pitting modification" of the hydroxyl pit of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0125] Example 1 is repeated. However, when the hydroxyl pit of the dealuminated Beta zeolite carrier is subjected to the pitting modification treatment in the second step by using the aqueous solution of ethanol amine, the amount (liquid-solid ratio) of the aqueous solution of ethanol amine is changed to 3:1 (ml / g), 9:1 (ml / g), 12:1 (ml / g) and 15:1 (ml / g) respectively. Then, according to the weight loss estimation, the average number of framework silicon atoms (calculated as SiO2) pitted out from the hydroxyl pit lattice defect site of the dealuminated Beta zeolite carrier is 0.99, 1.10, 1.15 and 1.19 silicon atoms respectively, which indicates that the pitting modification is a moderate desiliconization carried out under controllable conditions, and the pitting modification requirement of the dealuminated Beta zeolite carrier is achieved, and the pitting modification carrier codes are Beta24C 44-3 , Beta24C 44-9、 , Beta24C 44-12 , Beta24C 44-15 respectively. The above pitting modified carriers are used in the third step, i.e. the solid-solid isomorphous substitution method is used to prepare Sn-Beta zeolite by using tin (II) acetate as the tin source, and the obtained Sn-Beta zeolite catalyst codes are Beta24C 44-3 -6Sn, Beta24C 44-9 -6Sn, Beta24C 44-12 -6Sn and Beta24C44-15 -6Sn, their cyclohexanone conversion in the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide are 39.11%, 38.78%, 38.66% and 38.56% respectively, the selectivity of caprolactone product are 33.10%, 39.15%, 38.97% and 38.59% respectively, the conversion of hydrogen peroxide are 95.68%, 94.85%, 94.65% and 94.5% respectively.

[0126] Example 7: This example is to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite support with aqueous solution of small molecule aliphatic amine or / and alcohol amine aiming at controllably removing 1-2 framework silicon from its hydroxyl pit, so as to expand the small hydroxyl pit originally having only one framework atom vacancy (acid dealuminated) to a larger hydroxyl pit having 2-3 framework atom vacancies, and then using the "pitting modified" dealuminated Beta zeolite as the support, Sn-Beta zeolite is prepared by solid-solid isomorphous substitution reaction, wherein the temperature for the controllable dealuminating reaction of the dealuminated Beta zeolite with aqueous solution of small molecule aliphatic amine or / and alcohol amine is adjustable within a certain range. Changing the temperature for the controllable dealuminating reaction of the dealuminated Beta zeolite with aqueous solution of small molecule aliphatic amine or / and alcohol amine only affects the degree of "pitting modification" of the hydroxyl pit of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0127] Example 1 is repeated. However, when the hydroxyl pit of the dealuminated Beta zeolite support is subjected to pitting modification treatment with aqueous solution of ethanol amine in the second step, the temperature for the dealuminating reaction is changed to 50°C, 60°C and 70°C in turn. According to the weight loss estimation, the average number of framework silicon atoms (calculated as SiO2) pitted out from the hydroxyl pit lattice defect site of the dealuminated Beta zeolite support is 1.10, 1.19 and 1.25 in turn. Then, the pitting modified dealuminated Beta zeolite support obtained is used for the third step, i.e. Sn-Beta zeolite is prepared by solid-solid isomorphous substitution method using tin (II) acetate as tin source, and the obtained Sn-Beta zeolite catalyst codes are Beta24C 44-50 -6Sn, Beta24C 44-60 -6Sn and Beta24C 44-70 -6Sn. The above catalysts have cyclohexanone conversion in the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide are 38.16%, 37.99% and 36.75% respectively, the selectivity of caprolactone product are 39.22%, 38.30% and 35.45% respectively, the conversion of hydrogen peroxide are 93.9%, 92.98% and 88.61% respectively.

[0128] Example 8: This example is used to illustrate that according to the method provided by the present application, the "pocket modification" treatment of the dealuminated Beta zeolite support with aqueous solution of small molecular aliphatic amine or / and alcohol amine to controllably remove 1-2 framework silicon atoms from the hydroxyl pockets of the dealuminated Beta zeolite, so as to expand the small hydroxyl pocket with only one framework atom vacancy (acid dealuminated) to a larger hydroxyl pocket with 2-3 framework atom vacancies, and then to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction with the "pocket modified" dealuminated Beta zeolite as the support, wherein the reaction time of the controllable dealumination reaction of the dealuminated Beta zeolite with aqueous solution of small molecular aliphatic amine or / and alcohol amine is adjustable within a certain range. Changing the reaction time of the controllable dealumination reaction of the dealuminated Beta zeolite with aqueous solution of small molecular aliphatic amine or / and alcohol amine only affects the degree of "pocket modification" of the hydroxyl pockets of the dealuminated Beta zeolite, but does not change the benefits of the present application.

[0129] Example 1 was repeated. However, when the hydroxyl pockets of the dealuminated Beta zeolite support were subjected to the pocket modification treatment with aqueous solution of ethanol amine in the second step, the reaction time of the dealumination reaction was changed to 2 h, 3 h and 4 h in turn. According to the weight loss estimation, the average number of framework silicon atoms (calculated as SiO2) removed from the lattice defect sites of the hydroxyl pockets of the dealuminated Beta zeolite support was 1.11, 1.16 and 1.20 in turn. Then, the obtained pocket modified dealuminated Beta zeolite support was used in the third step, i.e. Sn-Beta zeolite was prepared by solid-solid isomorphous substitution method with tin (II) acetate as tin source, and the obtained Sn-Beta zeolite catalyst codes were Beta24C-6Sn, Beta24C-6Sn and Beta24C-6Sn in turn. 44-2h -6Sn, Beta24C 44-3h -6Sn and Beta24C 44-4h -6Sn. The cyclohexanone conversion in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide over the above catalysts was 38.33%, 38.15% and 38.24% in turn, the selectivity of caprolactone product was 38.33%, 37.99% and 38.04% in turn, and the conversion of hydrogen peroxide was 94.23%, 93.78% and 94.01% in turn.

[0130] Example 9: This example is used to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite support with the aqueous solution of small molecular aliphatic amine or / and alcohol amine aiming at controllably removing 1-2 framework silicas from the hydroxyl pockets of the dealuminated Beta zeolite support, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acid dealuminated) to a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pitting modified" dealuminated Beta zeolite as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein different tin sources can be allowed to be used in the preparation of Sn-Beta zeolite by solid-solid isomorphous substitution reaction. Changing the tin source has an influence on the catalytic performance of the prepared Sn-Beta zeolite catalyst, but does not change the benefits of the present application.

[0131] Example 1 is repeated. However, in the third step, the "pitting modified" dealuminated Beta zeolite is used as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, and then the pentahydrate tin tetrachloride and stannous chloride dihydrate are used in turn as the tin source. Then, the obtained Sn-Beta zeolite catalyst codes are Beta24C 44 -SnCl4-6Sn and Beta24C 44 -SnCl2-6Sn. The cyclohexanone conversion rates in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide are 38.10% and 38.24% in turn, the caprolactone product selectivities are 35.27% and 38.63% in turn, and the hydrogen peroxide conversion rates are 93.85% and 94.25% in turn.

[0132] Example 10: This example is used to illustrate that according to the method provided by the present application, the "pitting modification" treatment of the dealuminated Beta zeolite support with the aqueous solution of small molecular aliphatic amine or / and alcohol amine aiming at controllably removing 1-2 framework silicas from the hydroxyl pockets of the dealuminated Beta zeolite support, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acid dealuminated) to a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pitting modified" dealuminated Beta zeolite as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein in the solid-solid isomorphous 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.

[0133] Example 1 is repeated. However, in the third step, the "pitting modified" dealuminated Beta zeolite is used as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, and then the pentahydrate tin tetrachloride and stannous chloride dihydrate are used in turn as the tin source. Then, the obtained Sn-Beta zeolite catalyst codes are Beta24C44 - 4.74 Sn, Beta24C 44 - 7.9 Sn and Beta24C 44 - 9.48 Sn. The above catalysts have the cyclohexanone conversion in the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide of 38.68%, 39.28% and 39.11% respectively, and the selectivity of the caprolactone product of 40.97%, 39.86% and 39.01% respectively. The conversion of hydrogen peroxide is 95.66%, 97.12% and 96.68% respectively.

[0134] Example 11: This example is used to further illustrate the method provided according to the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom deficiency (acid dealuminated) to a larger hydroxyl pocket having 2-3 framework atom deficiencies, and then using the "pocket modified" dealuminated Beta zeolite as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the amount of tin source used in the solid-solid isomorphous substitution reaction step can be varied within a certain range to prepare Sn-Beta zeolite catalysts having different framework tin contents.

[0135] Example 1 is repeated, but in the third step, the dealuminated Beta zeolite modified by pocket modification is used as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, and the amount of tin ions is calculated according to the participation of 10%, 20%, 80% and 100% of the hydroxyl pockets in the solid-solid isomorphous substitution reaction, respectively, so that the amount of tin (II) acetate used is 0.32 g, 0.63 g, 2.53 g and 3.16 g, respectively. Then, the obtained Sn-Beta zeolite catalysts are designated as Beta24C 44 - 1.58 Sn, Beta24C 44 - 3.16 Sn, Beta24C 44 - 12.64 Sn and Beta24C 44 - 15.8 Sn. The above catalysts have the cyclohexanone conversion in the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide of 37.01%, 39.78%, 39.87% and 39.89% respectively, and the selectivity of the caprolactone product of 57.66%, 45.21%, 30.89% and 28.69% respectively. The conversion of hydrogen peroxide is 91.33%, 98.15%, 98.38% and 98.55% respectively.

[0136] Example 12: This example is used to illustrate that according to the method provided by the present application, the "pocket-modification" treatment of the dealuminated Beta zeolite support with aqueous solution of small molecular fatty amine or / and alcohol amine aiming at controllably removing 1-2 framework silicon atoms from the hydroxyl pockets of the dealuminated Beta zeolite, so as to expand the small hydroxyl pocket originally having only one framework atom vacancy (acidic dealumination) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as the support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid dealumination treatment of Beta zeolite mother substance with different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance with higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) is used, since the dealuminated Beta zeolite support obtained has less number of hydroxyl pockets, it is appropriate to use weaker desilication reaction modification condition combination for "pocket modification", and vice versa.

[0137] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, the Beta zeolite mother substance with molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 60 was synthesized by hydrothermal crystallization method provided by US Patent US3 308 069 (1967) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was treated by conventional filtration, washing, drying (170°C, 3h) and calcination for removing template (500°C, 8h), its average crystal size was observed by TEM to be close to 100 nanometers, belonging to nano-Beta zeolite; no any impurity crystal was found in it by XRD method, and its BET specific surface area was calculated to be about 530m 2 / g by nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be about 57 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application.

[0138] The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite support by dealumination with concentrated nitric acid, and a dealuminated Beta zeolite support with a molar ratio of silicon to alumina (SiO2 / Al2O3) of 861 (>800) was obtained (code Beta57c). The degree of dealumination of the support met the requirements of the present application. In the second step, the dealuminated Beta zeolite support was subjected to a channelling modification treatment with an aqueous solution of ethanolamine, and the concentration of the aqueous ethanolamine solution was changed to 20 mmol / L (20 mM). After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (overnight at 110°C) and calcined (500°C for 5 h) to obtain a channelling-modified dealuminated Beta zeolite. The product was sealed and stored for later use. According to the weight loss, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the lattice defect sites of the hydroxyl pockets of the dealuminated Beta zeolite support was 1.2 silicon atoms. The channelling-modified dealuminated Beta zeolite support obtained was designated as Beta57C.

[0139] The channelling-modified dealuminated Beta zeolite support obtained was used in the third step, i.e. to prepare a Sn-Beta zeolite by using tin (II) acetate as the tin source and a solid-solid isomorphous substitution method. The total number of hydroxyl pockets of the sample was 5.84 mmol (estimated according to the amount of dealumination of the Beta zeolite mother substance). According to the calculation of the amount of tin ions involved in the solid-solid isomorphous substitution reaction at a rate of 38% of the hydroxyl pockets, the amount of tin (II) acetate used was 0.525 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta57C 20 -2.63Sn. The conversion of cyclohexanone in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide over the catalyst was 38.88%, the selectivity of the caprolactone product was 48.67%, and the conversion of hydrogen peroxide was 96.01%.

[0140] Example 13: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to subject the dealuminated Beta zeolite support to "pocket-modification" by using a weaker combination of desilication reaction modification conditions, and vice versa.

[0141] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 40 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to the conventional filtration, washing, drying (80°C, 24h) and calcination for removing the template (600°C, 3h), it was observed by TEM that its average crystalline particle size was in the nanometer range. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 38 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2

[0142] ​The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid, and a dealuminated Beta zeolite carrier Beta38c was obtained, which had a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 870 (>800), both of which met the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 160 mmol / L (160 mM), the liquid-solid ratio was changed to 20:1, the impregnation temperature was changed to 30°C, and the impregnation time was changed to 5 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (at 80°C for 24 h) and calcined (at 600°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, which was designated as Beta38C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 1.0.

[0143] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e., a Sn-Beta zeolite was prepared by using tin (II) acetate as a tin source and using a solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 8.76 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions based on the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate was 0.788 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta38C 160 -4Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 39.13%, the selectivity of the caprolactone product was 32.98%, and the conversion rate of hydrogen peroxide was 96.53%.

[0144] Example 14: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicons from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) to a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by subjecting a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) to acid-dealumination treatment. However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" due to the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained, and vice versa.

[0145] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 80 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to conventional filtration, washing, drying (170°C, 6h) and calcination for removing the template (520°C, 7h), it was observed by TEM that its average crystalline particle size belonged to the small particle size (less than 1 μm) category. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500 m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 72 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2

[0146] ​The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta72c, which has a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 855 (> 800), meeting the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 15 mmol / L (15 mM), the liquid-solid ratio was changed to 50:1, the impregnation temperature was changed to 25°C, and the impregnation time was changed to 10 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (at 200°C for 3 h) and calcined (at 600°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, designated as Beta72C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 1.5.

[0147] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e. the preparation of a Sn-Beta zeolite by using tin (II) acetate as the tin source and applying the solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 4.62 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions based on the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate was 0.416 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta72C 15 -2.09Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 39.50%, the selectivity of the caprolactone product was 42.03%, and the conversion rate of hydrogen peroxide was 96.55%.

[0148] Example 15: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" because of the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained therefrom, and vice versa.

[0149] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 100 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to the conventional filtration, washing, drying (90°C, 24h) and calcination for removing the template (560°C, 4h), it was observed by TEM that its average crystallite size belonged to the small crystallite (less than 1 μm) category. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500 m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 94 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2

[0150] ​The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta94c, which had a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 932 (>900), both of which met the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the method of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 10 mmol / L (10 mM), the liquid-solid ratio was changed to 100:1, the impregnation temperature was changed to 25°C, and the impregnation time was changed to 0.5 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (at 200°C for 5 h) and calcined (at 500°C for 10 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, which was named Beta94C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl channelling lattice defect sites of the dealuminated Beta zeolite carrier was 1.0.

[0151] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e., a solid-solid isomorphous substitution method was used to prepare a Sn-Beta zeolite with tin (II) acetate as the tin source. The total number of hydroxyl channelling sites of the sample was 3.54 mmol (estimated according to the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions required for the participation of 38% of the hydroxyl channelling sites in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate required was 0.319 g, and the Sn-Beta zeolite catalyst obtained was named Beta94C 10 -1.6Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 39.08%, the selectivity of the caprolactone product was 38.96%, and the conversion rate of hydrogen peroxide was 96.45%.

[0152] Example 16: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" because of the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained therefrom, and vice versa.

[0153] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 150 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to the conventional filtration, washing, drying (80°C, 20h) and calcination for removing the template (530°C, 8h), it was observed by TEM that its average crystalline particle size belonged to the small particle size (less than 1 μm) category. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500 m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 136 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2 / g, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 136 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application.

[0154] The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta136c, which has a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 1088 (> 900), meeting the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 10 mmol / L (10 mM), the liquid-solid ratio was changed to 5:1, the impregnation temperature was changed to 20°C, and the impregnation time was changed to 0.5 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (overnight at 110°C) and subjected to calcination treatment (550°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, designated as Beta136C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 1.6.

[0155] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e., to prepare a Sn-Beta zeolite by using tin (II) acetate as the tin source and using the solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 2.45 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions based on the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate used was 0.22 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta136C 10 -1.1Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 36.69%, the selectivity of the caprolactone product was 40.41%, and the conversion rate of hydrogen peroxide was 90.47%.

[0156] Example 17: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" because of the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained therefrom, and vice versa.

[0157] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 200 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to the conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template (540°C, 6h), it was observed by TEM that its average crystallite size belonged to the small crystallite (less than 1 μm) category. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500 m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 189 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2 / g, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 189 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application.

[0158] The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta189c, which has a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 960 (> 900), meeting the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 10 mmol / L (10 mM), the liquid-solid ratio was changed to 5:1, the impregnation temperature was changed to 20°C, and the impregnation time was changed to 0.5 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then subjected to drying (overnight at 110°C) and calcination treatment (550°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, designated as Beta189C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 2.0.

[0159] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e. the preparation of a Sn-Beta zeolite by using tin (II) acetate as the tin source and applying the solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 1.76 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions required for the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate required was 0.158 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta189C 10 -0.79Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 35.55%, the selectivity of the caprolactone product was 40.82%, and the conversion rate of hydrogen peroxide was 87.78%.

[0160] Example 18: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" due to the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained, and vice versa.

[0161] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 15 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to the conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template (540°C, 6h), it was observed by TEM that its average crystalline particle size was in the nanometer range. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 14 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2 / g, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 14 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application.

[0162] The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta14c, which has a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 760 (> 700), meeting the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 300 mmol / L (300 mM), the liquid-solid ratio was changed to 100:1, the impregnation temperature was changed to 90°C, and the impregnation time was changed to 0.5 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then subjected to drying (overnight at 110°C) and calcination treatment (550°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, designated as Beta14C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 1.9.

[0163] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e. the preparation of a Sn-Beta zeolite by using tin (II) acetate as the tin source and applying the solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 23.78 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions required for the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate required was 2.14 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta14C 300 -10.7Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 38.13%, the selectivity of the caprolactone product was 30.01%, and the conversion rate of hydrogen peroxide was 93.53%.

[0164] Example 19: This example is used to further illustrate the method provided by the present application, i.e. first subjecting the dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acid-dealuminated) into a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as support to prepare Sn-Beta zeolite by solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by acid-dealuminating a Beta zeolite mother substance having different molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3). However, when the Beta zeolite mother substance has a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3), it is advisable to use a weaker desilication reaction modification condition combination for the "pocket-modification" due to the smaller number of hydroxyl pockets in the dealuminated Beta zeolite support obtained, and vice versa.

[0165] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite support, a Beta zeolite mother substance having a molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) of 10 was first synthesized by hydrothermal crystallization according to the method provided in Chinese Invention Patent CN1108275C (filing date 10 September 1999) as the raw material for preparing the dealuminated Beta zeolite support. After the synthesized Beta zeolite mother substance was subjected to conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template (540°C, 6h), it was observed by TEM that its average crystalline particle size was in the nanometer range. No any impurity crystal was found by XRD method, and its BET specific surface area was calculated to be higher than 500m2 / g from its nitrogen physical adsorption data, and its molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) was measured to be 10 by XRF method, which met the technical requirements of the Beta zeolite mother substance according to the present application. 2

[0166] ​The Beta zeolite mother substance was used to prepare a dealuminated Beta zeolite carrier by dealumination with concentrated nitric acid to obtain a dealuminated Beta zeolite carrier Beta10c, which has a molar ratio of silicon-alumina oxide (molar ratio of SiO2 to Al2O3) of 710 (> 700), meeting the technical requirements of a dealuminated Beta zeolite carrier. On this basis, the dealuminated Beta zeolite carrier was subjected to a channelling modification treatment with an aqueous solution of ethanolamine according to the practice of the second step of Example 1. The channelling modification treatment conditions were as follows: the concentration of the aqueous solution of ethanolamine was changed to 400 mmol / L (400 mM), the liquid-solid ratio was changed to 20:1, the impregnation temperature was changed to 100°C, and the impregnation time was changed to 1.0 h. After the channelling modification was completed, the reaction material was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then subjected to drying (overnight at 110°C) and calcination treatment (550°C for 3 h) to obtain a channelling-modified dealuminated Beta zeolite carrier, designated as Beta10C. It was sealed and stored for later use. According to the weight loss estimation, the average number of framework silicon atoms (in terms of SiO2) chiselled out from the hydroxyl cavity lattice defect sites of the dealuminated Beta zeolite carrier was 1.5.

[0167] The channelling-modified dealuminated Beta zeolite carrier obtained was used in the third step, i.e., to prepare a Sn-Beta zeolite by using tin (II) acetate as the tin source and applying the solid-solid isomorphous substitution method. The total number of hydroxyl cavities of the sample was 33.29 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions required for the participation of 38% of the hydroxyl cavities in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate required was 3.00 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta10C 400 -15Sn. The conversion rate of cyclohexanone in the Baeyer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone was 38.69%, the selectivity of the caprolactone product was 26.63%, and the conversion rate of hydrogen peroxide was 95.73%.

[0168] Example 20: This example is used to further illustrate the method provided according to the present application, i.e. first subjecting a dealuminated Beta zeolite support to a "pocket-modification" treatment aimed at controllably removing 1-2 framework silicon atoms from its hydroxyl pockets, thereby enlarging the small hydroxyl pocket originally having only one framework atom vacancy (acidic dealumination) to a larger hydroxyl pocket having 2-3 framework atom vacancies, and then using the "pocket-modified" dealuminated Beta zeolite as a support to prepare a Sn-Beta zeolite by a solid-solid isomorphous substitution reaction, wherein the dealuminated Beta zeolite support can be obtained by subjecting a Beta zeolite mother substance having different molar ratios of silicon to alumina (molar ratio of SiO2 to Al2O3) to an acid dealumination treatment. However, when a Beta zeolite mother substance having a higher molar ratio of silicon to alumina (molar ratio of SiO2 to Al2O3) is used, since the dealuminated Beta zeolite support obtained has a smaller number of hydroxyl pockets, it is appropriate to use a weaker combination of dealumination reaction modification conditions for the "pocket-modification", and vice versa.

[0169] Example 19 was repeated, but in the second step, the dealuminated Beta zeolite support was subjected to a pocket-modification using an aqueous solution of ethanolamine, and the conditions used were: the concentration of the ethanolamine aqueous solution was changed to 20 mmol / L (20 mM), the liquid-to-solid ratio was changed to 100:1, and the impregnation temperature was changed to 40°C, and the impregnation time was changed to 24 h. After the pocket-modification was completed, the reaction mass was filtered to recover the solid product, which was then repeatedly washed with deionized water until it was neutral, and then dried (overnight at 110°C) and subjected to a calcination treatment (550°C for 3 h) to obtain a pocket-modified dealuminated Beta zeolite support, which was designated as Beta10C. It was stored in a sealed container for later use. According to the weight loss, the average number of framework silicon atoms (in terms of SiO2) removed from the hydroxyl pocket lattice defect sites of the dealuminated Beta zeolite support was 1.7.

[0170] The pocket-modified dealuminated Beta zeolite support obtained was used in the third step, i.e. to prepare a Sn-Beta zeolite using tin (II) acetate as a tin source by a solid-solid isomorphous substitution method. The total number of hydroxyl pockets of the sample was 33.29 mmol (estimated from the dealumination amount of the Beta zeolite mother substance). According to the calculation of the amount of tin ions used based on 38% of the hydroxyl pockets participating in the solid-solid isomorphous substitution reaction, the amount of tin (II) acetate used was 3.00 g, and the Sn-Beta zeolite catalyst obtained was designated as Beta10C 20 -15Sn. The conversion of cyclohexanone in the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide over this catalyst was 39.25%, the selectivity of the caprolactone product was 31.66%, and the conversion of hydrogen peroxide was 96.99%.

Claims

1. A method for preparing a Sn-Beta zeolite catalyst for improving selectivity of caprolactone, characterized by, The method comprises the following steps: First step, preparation of dealuminated Beta zeolite carrier (1) selection of Beta zeolite mother body The Beta zeolite mother phase refers to a silicon-aluminum Beta zeolite meeting the following requirements: 1) the Beta zeolite mother phase contains no impurity crystals; 2) the Beta zeolite mother phase has good crystallization, i.e. the BET specific surface area value of the Beta zeolite mother phase measured by a nitrogen physical adsorption method is ≧450 m 2 / g; 3) the silicon-aluminum oxide molar ratio of the Beta zeolite mother phase, i.e. the molar ratio of SiO2 to Al2O3 is between 10-200; (2) preparation of dealuminated Beta zeolite carrier Dealuminated Beta zeolite carrier is prepared by acid dealuminization method based on Beta zeolite mother body; the obtained dealuminated Beta zeolite carrier has a molar ratio of silicon-aluminum oxide, i.e. a molar ratio of SiO2 to Al2O3, in the range of >= 700; Second step, modification of the dealuminated Beta zeolite carrier by alveolating the hydroxyl pockets with an aqueous solution of small molecule fatty amine or / and alcohol amine The dealuminated Beta zeolite carrier is alveolated by immersion in an aqueous solution of small molecule fatty amine or / and alcohol amine; after the alveolation modification, the dealuminated Beta zeolite carrier is treated by solid-liquid separation, drying and calcination to obtain the alveolated dealuminated Beta zeolite carrier; The small molecule fatty amine is methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, diethylamine, triethylamine or ethylenediamine; the small molecule alcohol amine is ethanolamine, isopropyl alcohol amine, diethanolamine, diisopropyl alcohol amine or triethanolamine; The aqueous solution of small molecule fatty amine or / and alcohol amine is referred to as alveolation solution, which contains one or more than two small molecule fatty amines and / or small molecule alcohol amines; the conditions are limited as follows: The concentration of the alveolation solution is in the range of 0.01M-0.4M; The liquid-solid ratio of the alveolation solution to the dealuminated Beta zeolite carrier is in the range of 1:1ml / g-100:1ml / g; The alveolation modification temperature is in the range of 20℃-100℃; The alveolation modification time is in the range of 0.5h-24h; Third step, preparation of Sn-Beta zeolite by solid-solid isomorphous substitution reaction with the alveolated dealuminated Beta zeolite as carrier According to the solid-solid isomorphous substitution reaction method, the alveolated dealuminated Beta zeolite carrier is first mixed with a tin source in solid phase, ground, and then the solid mixture is treated by calcination in nitrogen atmosphere and air atmosphere in sequence to obtain Sn-Beta zeolite; The proportion of the zeolite carrier and the tin source is determined by the percentage of the molar number of tin ions to the molar number of hydroxyl pockets of the zeolite carrier, which is in the range of 5%-100%; The molar number of the hydroxyl pockets of a certain mass of zeolite carrier is equal to the acid dealuminization molar number when the same mass of zeolite carrier is prepared.

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

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

4. The Sn-Beta zeolite catalyst preparation method for improving the selectivity of caprolactone according to claim 1, characterized in that, In the first step (2), the molar ratio of silica-alumina of the dealuminated Beta zeolite support, i.e. the molar ratio of SiO2 to Al2O3, is in the range of > 800.

5. The method according to claim 4, wherein the molar ratio of silica-alumina of the dealuminated Beta zeolite support, i.e. the molar ratio of SiO2 to Al2O3, is in the range of > 900. In the first step (2), the molar ratio of silica-alumina of the dealuminated Beta zeolite support, i.e. the molar ratio of SiO2 to Al2O3, is in the range of > 900.

6. The method according to claim 1, wherein the molar ratio of silica-alumina of the dealuminated Beta zeolite support, i.e. the molar ratio of SiO2 to Al2O3, is in the range of > 900. In the first step (2), the dealuminated Beta zeolite support is prepared by using a concentrated nitric acid aqueous solution, and the specific steps are as follows: The amount of the acid solution is determined according to a liquid-solid ratio of 20 ml / g by using 13M concentrated nitric acid as the dealumination acid solution; the dealumination reaction is carried out at 95°C, and the dealumination reaction time is 20h; after the dealumination reaction is completed, the solid product is recovered through solid-liquid separation, then the solid product is washed with water until the pH value is neutral, and then the solid product is dried at a temperature of 80-200°C for 3-24h, and finally the solid product is calcined at a temperature of 500°C-600°C for 3-8h to obtain the dealuminated Beta zeolite support.

7. The method according to claim 1, wherein in the second step, when the dealuminated Beta zeolite support is impregnated with a small-molecule fatty amine or / and alcohol amine aqueous solution for the modification of the dealuminated Beta zeolite support, the conditions are limited as follows: The concentration of the solution for the modification of the dealuminated Beta zeolite support is in the range of 0.02M-0.3M; The liquid-solid ratio of the solution for the modification of the dealuminated Beta zeolite support to the dealuminated Beta zeolite support is in the range of 2:1ml / g-50:1ml / g; The desilication reaction temperature for the modification of the dealuminated Beta zeolite support is in the range of 30°C-90°C; The desilication reaction time for the modification of the dealuminated Beta zeolite support is in the range of 0.5h-10h.

8. The method according to claim 7, wherein in the second step, when the dealuminated Beta zeolite support is impregnated with a small-molecule fatty amine or / and alcohol amine aqueous solution for the modification of the dealuminated Beta zeolite support, the conditions are limited as follows: The concentration of the solution for the modification of the dealuminated Beta zeolite support is in the range of 0.03M-0.16M; The liquid-solid ratio of the solution for the modification of the dealuminated Beta zeolite support to the dealuminated Beta zeolite support is in the range of 3:1ml / g-20:1ml / g; The desilication reaction temperature for the modification of the dealuminated Beta zeolite support is in the range of 40°C-80°C; The desilication reaction time for the modification of the dealuminated Beta zeolite support is in the range of 1h-5h. In the third step, the proportioning ratio of the zeolite support to the tin source is determined by the percentage of the number of moles of tin ions to the number of moles of hydroxyl holes of the zeolite support, and the percentage is in the range of 15%-80%. In the third step, the proportioning ratio of the zeolite support to the tin source is determined by the percentage of the number of moles of tin ions to the number of moles of hydroxyl holes of the zeolite support, and the percentage is in the range of 30%-60%. 9.The method for preparing a Sn-Beta zeolite catalyst for improving selectivity of caprolactone according to claim 1, characterized in that, In the third step, when the Sn-Beta zeolite is prepared by using a solid-solid isomorphous substitution reaction method, the specific method is as follows:

10. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 9, characterized in that, (1) The amount of the tin source is selected according to the percentage of the number of moles of tin ions to the number of moles of hydroxyl holes of the dealuminated Beta zeolite support for the modification of the dealuminated Beta zeolite support; 11. The method for preparing a Sn-Beta zeolite catalyst for improving caprolactone selectivity according to claim 1, characterized in that, ​ ​ (2) the dealuminated Beta zeolite carrier after the modification of the chisel cavity, drying and calcination treatment and in the dry state is mixed with a metered tin source and ground thoroughly; (3) the solid mixture of the zeolite carrier and the tin source which is ground thoroughly is put into a tubular reactor to carry out a solid-solid phase substitution reaction; first, high-purity nitrogen is passed into the reactor to replace the air in the reactor thoroughly; then the solid mixture in the reactor is heated to 200℃ at a temperature rising speed of 6℃ / min and kept at this temperature for 1-3h in a nitrogen atmosphere so as to diffuse the tin source into the zeolite channel; Next, the solid mixture in the reactor is heated to the interval of 450℃-550℃ at a temperature rising speed of 7℃ / min and kept at a constant temperature for 6-8h to complete the solid-solid isomorphous substitution reaction; in the middle of the solid-solid isomorphous substitution reaction, i.e. when kept at a constant temperature for 3-4h in the interval of 450℃-550℃, the high-purity nitrogen atmosphere in the reactor is changed to an air atmosphere; after the solid-solid isomorphous substitution reaction is completed, the Sn-Beta zeolite catalyst is prepared.

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 chloride or acetate, specifically tin tetrachloride pentahydrate, stannous chloride dihydrate or tin (II) acetate.

13. The Sn-Beta zeolite catalyst prepared by the preparation method of claim 1-12 is used to catalyze the Baeyer-Villiger oxidation reaction of cyclohexanone with hydrogen peroxide to synthesize caprolactone.

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