Method for realizing stable migration of Lewis acid into molecular sieve skeleton under assistance of B atom and application

Abstract

The invention belongs to the field of molecular sieve preparation, and provides a method for realizing stable migration of Lewis acid into a molecular sieve framework under the assistance of B atoms and application of the Lewis acid, and the method comprises the following steps: adopting a post-treatment method, taking a B-containing molecular sieve as a silicon source, adding a zirconium source, a structure-directing agent and water, uniformly mixing, performing hydrothermal crystallization, centrifuging, washing, drying and calcining to obtain a Zr-G molecular sieve; the preparation method comprises the following steps: fully treating a Zr-G molecular sieve in an acid solution at 100 DEG C by adopting an acid treatment method, centrifuging, washing, drying and calcining to obtain the Zr-M molecular sieve. According to the invention, efficient introduction of Lewis acid in a molecular sieve framework is realized, the problems that weak acidic surface bonded species are mainly formed in post-synthesis construction of L acid sites, agglomeration and loss are easy to occur, confinement effect is lacked and the like are solved, and a new way is developed for comprehensive application of the Lewis acid molecular sieve in sustainable catalysis.

Description

Technical Field

[0001] The present invention belongs to the field of molecular sieve preparation, and particularly relates to a method and application for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms. Background Art

[0002] Lewis acid (L-acid) molecular sieves are characterized by having electron-deficient metal centers such as zirconium (Zr) and tin (Sn), and play a key role in sustainable catalysis. They can activate oxygen-containing substrates in reactions such as biomass valorization through coordination interactions. The traditional method is to introduce metals by direct synthesis to construct Lewis acid sites (Maura Koehle, et al. Lewisacidic zeolite Beta catalyst for the

[0003] Meerwein–Ponndorf–Verley reduction of furfural[J].Catal.Sci.Technol.,2016,6:3018-3026), but due to the limitation of the molecular sieve framework on heteroatoms, the direct synthesis method usually requires a long synthesis period or harsh synthesis conditions. The solid-state ion exchange method (I. Hermans, et al. Simple and Scalable Preparation of Highly Active Lewis Acidic Sn-β[J]. Angew.Chem.Int.Ed.,2012,51(47):11736-11739.) and the post-synthesis method (Daniel T. Bregante, et al. Consequences of Confinement for Alkene Epoxidation with Hydrogen Peroxide on Highly Dispersed Group 4 and 5 Metal Oxide Catalysts[J]. ACS Catal.2018,8(4):2995–3010) can avoid the above problems. However, the state of metal species on the surface of the molecular sieve is unstable, prone to enrichment to form oxide clusters or loss, and cannot well maintain the stable loading of metal species, and lacks the confinement effect. Recent studies have shown that by removing Ge in the BEC molecular sieve to create cavities, the directional construction of metal active sites can be achieved (Y. Román-Leshkov, et al. Selective active site placement in Lewis acid zeolites and implications for catalysis of oxygenated compounds[J]. Chem.Sci.,2020,11(37):10225-10235.). However, this method is limited to specific molecular sieve systems and lacks universality.

[0004] Therefore, it is still challenging to develop a strategy with strong universality and simple process to achieve the efficient anchoring of L acid sites in the molecular sieve framework. Summary of the Invention

[0005] In view of the existing challenges, the present invention provides a method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms.

[0006] The technical solution of the present invention is as follows:

[0007] A method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms, comprising the following steps:

[0008] (1) Synthesis of grafted Lewis acid molecular sieve: Using the post-treatment method, with the boron-containing molecular sieve as the silicon source, adding zirconium source, structure-directing agent and water, mixing evenly to form a first mixed solution; subjecting the first mixed solution to hydrothermal crystallization, centrifuging, washing, drying, and calcining to obtain Zr-G molecular sieve;

[0009] The structure-directing agent is tetrabutylammonium hydroxide (abbreviated as TBAOH); the zirconium source is zirconium sulfate (Zr(SO4)2).

[0010] The addition ratio of the silicon source, zirconium source, structure-directing agent and water in the first mixed solution: the silicon source is calculated as SiO2, the zirconium source is calculated as ZrO2, and the molar ratio of SiO2, ZrO2, structure-directing agent and water is 1:0.02:0.1:10.

[0011] (2) Synthesis of migrated Lewis acid molecular sieve: Using the acid treatment method, treating the Zr-G molecular sieve in an acid solution at a temperature of 100 °C for 24 h, centrifuging, washing, drying, and calcining to obtain Zr-M molecular sieve;

[0012] The acid solution is a 2 mol / L HNO3 solution;

[0013] The addition ratio of the acid solution to the molecular sieve: the mass ratio of the molecular sieve to the acid solution is 1:100.

[0014] The specific implementation steps of step (1) are as follows:

[0015] Using the boron-containing molecular sieve as the silicon source, adding zirconium source, structure-directing agent and water, stirring for 2 h to form a first mixed solution; crystallizing the first mixed solution at a temperature of 120 °C for 2 d; cooling at room temperature, centrifuging to obtain a sample, washing with water until the pH = 7; then drying at a drying temperature of 80 °C for 12 h; calcining the dried sample at a temperature of 550 °C for 6 h with a heating rate of 2 °C / min to obtain Zr-G molecular sieve.

[0016] The specific implementation steps of step (2) are as follows:

[0017] Treating the Zr-G molecular sieve in the acid solution at 100 °C for 24 h, cooling at room temperature, centrifuging to obtain a sample, washing with water until the pH = 7; then drying at a drying temperature of 80 °C for 12 h; calcining the dried sample at a temperature of 550 °C for 6 h with a heating rate of 2 °C / min to obtain Zr-M molecular sieve.

[0018] Advantages of the present invention: The present invention has successfully achieved the efficient introduction of Lewis acid in the molecular sieve framework with the assistance of B atoms, solving the problems that the post-synthesis construction of L acid sites mainly forms weakly acidic surface-bonded species, which are prone to agglomeration, loss, and lack of confinement effect. Among them, B atoms provide a pre-occupation effect, and a large number of silanol nests are generated during the acid treatment process after dropping, providing suitable sites for the migration of Zr. After migration, Zr species are transformed from weakly acidic surface-grafted species into strongly Lewis acidic four-coordinated Zr species, which can stably exist in the molecular sieve framework. The present invention opens up a new way for the comprehensive application of Lewis acid molecular sieves in sustainable catalysis. Brief Description of the Drawings

[0019] Figure 1 It is the pyridine adsorption infrared spectrum of the sample prepared in Example 1.

[0020] Figure 2 It is the pyridine adsorption infrared spectrum of the sample prepared in Example 2.

[0021] Figure 3 It is the pyridine adsorption infrared spectrum of the sample prepared in Comparative Example 3. Detailed Embodiments

[0022] The following further illustrates the specific embodiments of the present invention in combination with the drawings and technical solutions.

[0023] Example 1

[0024] Boric acid, tetraethyl orthosilicate, 40% by mass aqueous solution of tetrabutylammonium hydroxide, and water were mixed evenly and stirred for 12 h to obtain a mixed solution with a molar composition of 10SiO2:1B2O3:3.6TBAOH:120H2O. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle with a polytetrafluoroethylene inner lining and statically crystallized at 140 °C for 5 d. After centrifugation, washing, and drying, B-SPP molecular sieve was obtained.

[0025] Using B-SPP as the silicon source, 40% by mass aqueous solution of tetrabutylammonium hydroxide, zirconium sulfate, and water were added again, and stirred for 2 h to obtain a mixed solution with a molar composition of 1SiO2:0.02Zr(SO4)2:0.1TBAOH:10H2O. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle with a polytetrafluoroethylene inner lining and crystallized at 120 °C for 48 h. After centrifugation, washing, drying, and calcination, Zr-B-SPP-G molecular sieve M1-G was obtained; M1-G was treated in 2M HNO3 aqueous solution at 100 °C for 24 h, and after centrifugation, washing, drying, and calcination, Zr-B-SPP-A molecular sieve M1 was obtained. The pyridine adsorption infrared spectra of M1-G and M1 are as Figure 1 shown, indicating that Zr species were successfully introduced into the molecular sieve framework after acid treatment, bringing more Lewis acid.

[0026] Example 2

[0027] Boric acid, a 25% by mass aqueous solution of tetraethylammonium hydroxide, and water were mixed evenly, and after stirring for 30 min, silica white was added. After stirring for 10 h, a mixed solution with a molar composition of 5SiO2:0.16B2O3:0.65TEAOH:57.5H2O was obtained. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle with a polytetrafluoroethylene liner, and was crystallized dynamically at 140 °C for 6 d. After filtration, washing, and drying, B-BEA molecular sieve was obtained.

[0028] Using B-BEA as the silicon source, and then adding a 40% by mass aqueous solution of tetrabutylammonium hydroxide, zirconium sulfate, and water, and stirring for 2 h, a mixed solution with a molar composition of 1SiO2: 0.02Zr(SO4)2: 0.1TBAOH: 10H2O was obtained. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle with a polytetrafluoroethylene liner, and was crystallized at 120 °C for 48 h. After centrifugation, washing, drying, and calcination, Zr-B-BEA-G molecular sieve M2-G was obtained; M2-G was treated in a 2M HNO3 aqueous solution at 100 °C for 24 h. After centrifugation, washing, drying, and calcination, Zr-B-BEA-A molecular sieve M2 was obtained. The pyridine adsorption infrared spectra of M2-G and M2 are as Figure 2 shown, indicating that Zr species were successfully introduced into the molecular sieve framework after acid treatment, and more Lewis acids were brought.

[0029] Comparative Example 1

[0030] Using B-SPP as the silicon source, and then adding a 40% by mass aqueous solution of tetrabutylammonium hydroxide, zirconium sulfate, and water, and stirring for 2 h, a mixed solution with a molar composition of 1SiO2: 0.01-0.04Zr(SO4)2: 0.1TBAOH: 10H2O was obtained. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle with a polytetrafluoroethylene liner, and was crystallized at 120 °C for 48 h. After centrifugation, washing, drying, and calcination, Zr-B-SPP-G molecular sieve D1-x-G (where x represents the content of Zr, x = 0.01, 0.02, 0.04) was obtained; D1-x-G was treated in a 2M HNO3 aqueous solution at 100 °C for 24 h. After centrifugation, washing, drying, and calcination, Zr-B-SPP-A molecular sieve D1-x was obtained.

[0031] Comparative Example 2

[0032] Using B-SPP as the silicon source, adding an aqueous solution of tetrabutylammonium hydroxide with a mass fraction of 40%, zirconium sulfate, and water, and stirring for 2 h to obtain a mixed solution with a molar composition of 1SiO2:0.02Zr(SO4)2:0.1TBAOH:10H2O. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle lined with polytetrafluoroethylene and crystallized at 120 °C for 48 h. After centrifugation, washing, drying, and calcination, Zr-B-SPP-G molecular sieve D2-G was obtained; D2-G was treated in 1-6M HNO3 aqueous solution at 100 °C for 24 h. After centrifugation, washing, drying, and calcination, Zr-B-SPP-A molecular sieve D2-y (where y represents the nitric acid concentration, y = 1, 2, 6, 12) was obtained.

[0033] Comparative Example 3

[0034] Tetraethyl orthosilicate, an aqueous solution of tetrabutylammonium hydroxide with a mass fraction of 40%, and water were mixed evenly and stirred for 12 h to obtain a mixed solution with a molar composition of 5SiO2:1.8TBAOH:60H2O. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle lined with polytetrafluoroethylene and crystallized at 120 °C for 72 h. After centrifugation, washing, and drying, Si-SPP molecular sieve was obtained.

[0035] Using Si-SPP as the silicon source, adding an aqueous solution of tetrabutylammonium hydroxide with a mass fraction of 40%, zirconium sulfate, and water, and stirring for 2 h to obtain a mixed solution with a molar composition of 1SiO2:0.02Zr(SO4)2:0.1TBAOH:10H2O. The mixed solution was loaded into a 25 mL hydrothermal reaction kettle lined with polytetrafluoroethylene and crystallized at 120 °C for 48 h. After centrifugation, washing, drying, and calcination, Zr-SPP-G molecular sieve D3-G was obtained; D3-G was treated in 2M HNO3 aqueous solution at 100 °C for 24 h. After centrifugation, washing, drying, and calcination, Zr-SPP-A molecular sieve D3 was obtained. The pyridine adsorption infrared spectra of D3-G and D3 are as Figure 3 shown, indicating that Zr species were successfully introduced into the molecular sieve framework after acid treatment, bringing more Lewis acids.

[0036] Application Example 1

[0037] The catalysts obtained in Examples 1-2 and Comparative Examples 1-3 were used as catalysts for the transfer hydrogenation of cyclohexanone to cyclohexanol in the MPV reaction to evaluate the activity of the catalysts.

[0038] 1. Catalyst catalytic performance evaluation method: Using a 0.002M cyclohexanone isopropanol solution as the reaction substrate, using a sealed glass bottle as the reaction vessel, adding the catalyst, cyclohexanone, and isopropanol to it respectively, where the molar ratio of cyclohexanone to the catalyst is 8, and the glass bottle was placed in an oil bath at 100 °C for 8 h.

[0039] 2. Test conditions: The contents of various substances in the solution were analyzed by gas chromatography. The test results are shown in Table 1 below.

[0040] Table 1 Catalyst Activity Evaluation Results of Example 1

[0041]

[0042] The catalyst in Example 1 used B-SPP molecular sieve as the matrix. During the synthesis process, acid treatment caused the shedding of B, bringing a large number of silanol nests, thereby capturing more Lewis acidic Zr species, making cyclohexanone in the MPV reaction almost completely react.

[0043] Table 2 Catalyst Activity Evaluation Results of Example 2

[0044]

[0045] The catalyst in Example 2 used B-BEA as the matrix. During the synthesis process, acid treatment caused the shedding of B, bringing a large number of silanol nests, thereby capturing more Lewis acidic Zr species, achieving a significant improvement in reaction activity. Through the expansion of the molecular sieve types, the generality of the present invention was verified.

[0046] Table 3 Catalyst Activity Evaluation Results of Comparative Example 1

[0047]

[0048] The reaction results of Comparative Example 1 show that when the content of Zr is too low, due to the too small L acid content introduced into the zeolite, it is not sufficient to provide the catalytic sites required for the MPV reaction; when the content of Zr is too high, the reaction activity is low. At this time, the Zr species in the zeolite tend to agglomerate to form ZrO2 clusters with B acid, which is not conducive to the occurrence of the MPV reaction. Therefore, Zr content y = 0.02 is a suitable condition for catalyzing the MPV reaction.

[0049] Table 4 Catalyst Activity Evaluation Results of Comparative Example 2

[0050]

[0051] The reaction results of Comparative Example 2 show that when the concentration of nitric acid is low, the driving force provided by the acid is not enough for all Zr species to migrate into the framework; when the concentration of nitric acid is too high, it will damage the structure of the molecular sieve and is not conducive to the reaction. Therefore, a nitric acid concentration of 2M is a suitable treatment condition for driving Zr migration.

[0052] Table 5 Catalyst Activity Evaluation Results of Comparative Example 3

[0053]

[0054] The reaction results of Comparative Example 3 illustrate the lack of B species. The molecular sieve treated only with acid has fewer Lewis acid species captured due to the smaller number of silanol nests and cannot exhibit good activity in the MPV reaction.

Claims

1. A method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms, characterized in that, It includes the following steps: (1) Synthesis of grafted Lewis acid molecular sieve: Using the post-treatment method, with boron-containing molecular sieve as the silicon source, adding zirconium source, structure-directing agent and water, mixing evenly to form the first mixed solution; subjecting the first mixed solution to hydrothermal crystallization, centrifuging, washing, drying, and calcining to obtain Zr-G molecular sieve; (2) Synthesis of migrating Lewis acid molecular sieve: Using the acid treatment method, treating the Zr-G molecular sieve in an acid solution at 100 °C for 24 h, centrifuging, washing, drying, and calcining to obtain Zr-M molecular sieve.

2. The method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms according to claim 1, characterized in that in step (1), the structure-directing agent is tetrabutylammonium hydroxide; the zirconium source is zirconium sulfate; the addition ratio of silicon source, zirconium source, structure-directing agent and water in the first mixed solution: the silicon source is calculated as SiO2, the zirconium source is calculated as ZrO2, and the molar ratio of SiO2, ZrO2, structure-directing agent and water is 1:0.02:0.1:

10.

3. The method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms according to claim 2, characterized in that the specific implementation steps of step (1) are as follows: Using boron-containing molecular sieve as the silicon source, adding zirconium source, structure-directing agent and water, stirring for 2 h to form the first mixed solution; crystallizing the first mixed solution at 120 °C for 2 d; cooling at room temperature, centrifuging to obtain a sample, washing with water until pH = 7; then drying at a drying temperature of 80 °C for 12 h; calcining the dried sample at 550 °C for 6 h with a heating rate of 2 °C / min to obtain Zr-G molecular sieve.

4. The method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms according to claim 1, characterized in that the specific implementation steps of step (2) are as follows: Treating the Zr-G molecular sieve in an acid solution at 100 °C for 24 h, cooling at room temperature, centrifuging to obtain a sample, washing with water until pH = 7; then drying at a drying temperature of 80 °C for 12 h; calcining the dried sample at 550 °C for 6 h with a heating rate of 2 °C / min to obtain Zr-M molecular sieve.

5. The method for realizing the stable migration of Lewis acid into the molecular sieve framework assisted by B atoms according to claim 4, characterized in that in step (2), the acid solution is a 2 mol / L HNO3 solution; the addition ratio of the acid solution to the Zr-G molecular sieve: the mass ratio of the molecular sieve to the acid solution is 1:

100.

6. Application of the Zr-M molecular sieve obtained by any one of the methods of claims 1-5 in the MPV reaction.

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