Method for passivating acid sites on the external surface of l molecular sieves and use thereof
By using short-chain silanes, long-chain silanes, or sugar derivatives to mix with L-type molecular sieves, the acidic sites on their outer surface are passivated, solving the problems of poor selectivity and structural stability in existing technologies, and improving the selectivity of the catalyst and the yield of the target product.
Patent Information
- Application Number
- CN202211610770.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-12
- Publication Date
- 2026-05-15
- Estimated Expiration
- 2042-12-12
AI Technical Summary
Existing technologies struggle to selectively passivate acidic sites on the outer surface of L-zeolites, leading to reduced catalyst selectivity. Furthermore, traditional methods negatively impact pore structure and stability.
Short-chain silanes, long-chain silanes, or sugars and their derivatives are used as passivating agents. After being mixed with L-type molecular sieves and dispersants, a passivation reaction is carried out. Then, the mixture is centrifuged, dried, and calcined to prepare L-type molecular sieves with passivated acidic sites on the outer surface.
Selective passivation of acidic sites on the outer surface of L molecular sieves was achieved, improving the shape selectivity of catalytic reactions, maintaining the stability of acidic sites and pore structure on the inner surface, and enhancing the selectivity of the catalyst and the yield of the target product.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the fields of materials and catalysis technology, and specifically relates to a method for passivating acidic sites on the outer surface of L molecular sieves and its application. Technical Background
[0002] Molecular sieves, due to their unique acidic properties and pore structure, have wide applications in petrochemical processes and chemical synthesis, primarily in shape-selective catalysis and adsorption separation. The shape-selective catalytic performance of molecular sieves is mainly influenced by surface acidic sites and pore structure; therefore, suitable acidic sites and appropriate pore structure are essential conditions for good reaction performance. Acidic sites located within the micropores of zeolite are called internal surface acidic sites, exhibiting excellent shape selectivity. Acidic sites located at the pore openings or outside the micropores are called external surface acidic sites, which are not limited by the micropores and have almost no shape selectivity, easily leading to reduced reaction selectivity, especially in mesoporous zeolites and nano-zeolite molecular sieves with large external specific surface areas. Therefore, when investigating the influence of the acidity of the inner and outer surfaces of molecular sieve pores on catalytic reaction performance, it is necessary to passivate the acidic sites on the outer surface of the molecular sieve pores beforehand using modification methods.
[0003] L-type molecular sieve is a potassium-containing synthetic zeolite with a twelve-membered ring one-dimensional channel structure, with a pore size of 0.71 nm and a kinetic diameter of 0.81 nm. It is a catalytic material with excellent thermal stability and can be used to prepare catalysts for hydrocarbon conversion processes such as cracking, reforming, isomerization, aromatization, alkylation, and lubricating oil hydrogenation. The catalytically active sites located within the one-dimensional main channels of L-type molecular sieve exhibit excellent shape selectivity in catalytic reactions. Acidity on the outer surface, which lacks shape selectivity, can easily lead to side reactions and reduce catalyst selectivity. Therefore, passivating the acidic sites on the outer surface of L-type molecular sieve is of great significance for improving catalyst selectivity.
[0004] Currently, the main method for passivating acidic sites on the outer surface of zeolites is chemical liquid phase deposition (CLPD). This involves hydrolyzing and calcining a silanizing agent, which is then deposited onto the outer surface of the zeolite molecular sieve. The greater the deposition amount, the more pronounced the passivation of the acidic sites. However, this method requires repeated deposition to achieve the desired passivation effect. Furthermore, the hydrolysis degree of the silanizing agent is relatively low during CLPD, which ultimately severely affects the passivation effect. In addition, most of the molecular sieves passivated in existing reports have small-pore structures with ten- or eight-membered rings. L-zeolite, on the other hand, is a one-dimensional macroporous catalyst with six-, eight-, and twelve-membered rings, and its main pores are twelve-membered rings. It requires passivation treatment with long-chain macromolecular organic compounds, which cannot enter the micropores and thus selectively passivate the acidic sites on the outer surface.
[0005] Current methods for controlling the acidity of L-type molecular sieves mainly employ post-treatment methods, which require strict control over the concentration of the treatment solution and the reaction time. Moreover, this method is a "destructive" treatment, which ultimately has a significant impact on the pore structure and stability of the L-type molecular sieve, and the acidity in the molecular sieve cannot be selectively controlled. Summary of the Invention
[0006] The purpose of this invention is to provide a method for passivating acidic sites on the outer surface of L-zeolite, overcoming the shortcomings of existing synthetic L-zeolite methods, such as numerous defects on the outer surface, pore collapse and blockage, and easy occurrence of side reactions. This invention's method can selectively passivate acidic sites on the outer surface of L-zeolite without affecting the acidic sites on the inner surface or blocking micropores. The synthesis process is simple and easy to operate.
[0007] To achieve the above objectives, the technical solution of the present invention is as follows:
[0008] A method for passivating acidic sites on the outer surface of an L-type molecular sieve, characterized in that the method comprises the following steps:
[0009] (1) Mix L molecular sieve and dispersant thoroughly, add passivating agent to the mixed solution of L molecular sieve and dispersant, stir, and then transfer to a reaction vessel for passivation reaction;
[0010] (2) The reactants obtained in step (1) are centrifuged, filtered to remove the dispersant, dried, and calcined to obtain L molecular sieves with passivated acidic sites on the outer surface.
[0011] In the above technical solution, the passivating agent is further defined as a short-chain silane, a long-chain silane, or a sugar or its derivative.
[0012] Wherein: the short-chain silane is one or a mixture of two or more of vinyltrimethoxysilane (A171), 3-aminopropyltrimethoxysilane (KH-540), 3-aminopropyltriethoxysilane (KH-550), 3-(methylpropyloxy)propyltriethoxysilane (KH-570), and 3-aminoethylaminopropyltrimethoxysilane;
[0013] The long-chain silane is one or a mixture of two or more of methyldodecyl dimethoxysilane (HD-109), dodecyl trimethoxysilane (KH-304), and hexadecyl trimethoxysilane (HDTMS);
[0014] The sugars and their derivatives are one or a mixture of two or more of sucrose, fructose, glucose, cellulose, and 5-hydroxymethylfurfural.
[0015] In the above technical solution, the dispersant is any one of n-hexane, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, and anhydrous ethanol; the solid-liquid ratio of the L molecular sieve to the dispersant is 1:10 to 1:50 g / ml, preferably 1:15 to 1:30 g / ml.
[0016] In the above technical solution, the mass ratio of the L molecular sieve to the passivating agent is 1:1 to 1:10, preferably 1:1 to 1:3; the passivating agent is added to the mixed solution of the L molecular sieve and the dispersant, and stirred at 25°C for 0.5 to 1 hour.
[0017] In the above technical solution, the passivation reaction temperature is 170-200℃ and the reaction time is 4-24h.
[0018] In the above technical solution, the drying temperature is further specified as 100-110℃, and the drying time is further specified as 8-12h.
[0019] In the above technical solution, the calcination temperature is further specified as 400–600°C, and the calcination time is further specified as 1–5 hours.
[0020] In the above technical solution, the synthesis method of the L-zeolite further includes the following steps:
[0021] (1) Mix precipitated silica and potassium hydroxide in a mortar and grind for 10-30 minutes;
[0022] (2) Add aluminum hydroxide to the sample ground in step (1) and continue grinding for 10 to 30 minutes; the molar ratio of each reactant is 3.5K2O:xAl2O3:10SiO2, where x = 0.25 to 2;
[0023] (3) Place the ground sample from step (2) into a reaction vessel and crystallize it at 150-200℃ for 4-24 hours;
[0024] (4) The crystallized sample from step (3) was calcined at 550°C for 4 hours to obtain KL molecular sieve;
[0025] (6) Weigh 0.15g of KL molecular sieve into a 50ml flask, add 30ml of 0.1M~1.0M NH4NO3 solution, stir at 80℃ for 1~6h, centrifuge, dry and calcine at 550℃ for 4h to obtain L molecular sieve.
[0026] In another aspect, the present invention provides an L-type molecular sieve with passivated acidic sites on its outer surface, prepared by the above method.
[0027] In another aspect, this invention provides an application of the L-type molecular sieve with its outer surface acidic sites passivated, for catalytic conversion of chitin-based biomass to prepare 3-acetamido-5-acetylfuran or catalytic conversion of cellulose-based biomass to prepare 5-hydroxymethylfurfural.
[0028] The beneficial effects of this invention are as follows:
[0029] 1. This invention can selectively passivate the acidic sites on the outer surface of L molecular sieves, thereby improving the shape selectivity of molecular sieve catalytic reactions, with almost no impact on the acidic sites on the inner surface or blockage of micropores, providing a new method for controlling the acidity of the inner and outer surfaces of macroporous solid acid catalysts.
[0030] 2. The L-type molecular sieve sample prepared by the present invention, with its acidic sites on the outer surface passivated, showed no impurities and maintained good crystallinity and purity.
[0031] 3. The L-type molecular sieve with passivated acidic sites on its outer surface, prepared by this invention, is used for catalytic conversion of chitin-based biomass to 3-acetamido-5-acetylfuran and catalytic conversion of cellulose-based biomass to 5-hydroxymethylfurfural, exhibiting higher selectivity for the target products. Attached Figure Description
[0032] Figure 1 The XRD pattern of the L molecular sieve in Example 1;
[0033] Figure 2 The XRD pattern of the 3-aminopropyltrimethoxysilane passivated L-zeolite of Example 2 is shown below.
[0034] Figure 3 The XRD pattern of the hexadecyltrimethoxysilane passivated L-zeolite of Example 3 is shown below.
[0035] Figure 4 The image shows the XRD pattern of the 5-hydroxymethylfurfural passivated L-zeolite from Example 4. Detailed Implementation
[0036] The following detailed description is provided in conjunction with the embodiments and accompanying drawings:
[0037] Example 1
[0038] First, weigh 1.8g of solid raw materials, including silica and potassium hydroxide, and grind them in a mortar for 10 minutes. Then, add 0.468g of aluminum hydroxide and grind for another 15 minutes. Add the reaction raw materials to a polytetrafluoroethylene stainless steel reactor and crystallize at 175℃ for 24 hours. The resulting product does not require filtration or washing and is directly calcined at 550℃ for 4 hours in air to obtain the final KL molecular sieve. Weigh 0.15g of KL molecular sieve into a 50ml flask, add 30ml of 1.0M NH4NO3 solution, and stir the sample at 80℃ for 4 hours. After centrifugation and drying, calcine at 550℃ for 4 hours to obtain L molecular sieve.
[0039] X-ray diffraction analysis revealed that its structure is L-zeolite molecular sieve. Figure 1 The XRD pattern synthesized using this method.
[0040] Example 2
[0041] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of n-hexane, stir until it is evenly suspended, and then add 3g of 3-aminopropyltrimethoxysilane; stir the mixed sample at 25℃ for 1h in a heat-collecting constant temperature magnetic stirrer, and then transfer it to a reaction vessel and react at 170℃ for 6h; then centrifuge the obtained sample, put it in a drying oven and heat it at 100℃ for 8h, cool it and then calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0042] Example 3
[0043] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of N,N-dimethylformamide, stir until suspended, and then add 3g of hexadecyltrimethoxysilane (HDTMS); stir the mixed sample at 25℃ for 1h in a heat-collecting constant temperature magnetic stirrer, then transfer it to a reaction vessel and react at 170℃ for 6h; then centrifuge the obtained sample, place it in a drying oven and heat and dry at 100℃ for 8h, cool it and calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0044] Example 4
[0045] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of cyclohexane, stir until suspended, and then add 3g of 5-hydroxymethylfurfural. Stir the mixed sample at 25℃ for 1h in a heat-collecting constant-temperature magnetic stirrer, then transfer it to a reaction vessel and react at 170℃ for 6h. After centrifugation, place the sample in a drying oven and heat at 100℃ for 8h. After cooling, calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0046] Example 5
[0047] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of N,N-dimethylformamide, stir until suspended, and then add 1g of hexadecyltrimethoxysilane (HDTMS); stir the mixed sample at 25℃ for 1h in a heat-collecting constant temperature magnetic stirrer, then transfer it to a reaction vessel and react at 170℃ for 6h; then centrifuge the obtained sample, place it in a drying oven and heat and dry at 100℃ for 8h, cool it and calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0048] Example 6
[0049] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of N,N-dimethylformamide, stir until suspended, and then add 5g of hexadecyltrimethoxysilane (HDTMS); stir the mixed sample at 25℃ for 1h in a heat-collecting constant temperature magnetic stirrer, then transfer it to a reaction vessel and react at 170℃ for 6h; then centrifuge the obtained sample, place it in a drying oven and heat and dry at 100℃ for 8h, cool it and calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0050] Example 7
[0051] Weigh 1g of the L molecular sieve prepared in Example 1 into a 50ml beaker, add 30ml of N,N-dimethylformamide, stir until suspended, and then add 10g of hexadecyltrimethoxysilane (HDTMS); stir the mixed sample at 25℃ for 1h in a heat-collecting constant temperature magnetic stirrer, then transfer it to a reaction vessel and react at 170℃ for 6h; then centrifuge the obtained sample, place it in a drying oven and heat and dry at 100℃ for 8h, cool it and calcine it in a muffle furnace at 550℃ for 4h to obtain the sample.
[0052] Examples 2-7 involve passivating the acidic sites on the outer surface of the L-type molecular sieves prepared in Example 1 with long-chain silanes, short-chain silanes, and sugars and their derivatives, respectively. To verify the structure of the modified molecular sieve surface, Raman spectroscopy was used to measure the samples of Examples 1-7.
[0053] Table 1. Raman spectral characterization results of samples from Examples 1-7
[0054]
[0055] Among them, 225cm -1 and 314cm -1 The peak at 470 cm⁻¹ belongs to the eight-membered and six-membered rings in the topological structure of the L-zeolite. -1 and 500cm-1 The peak at 1060 cm⁻¹ belongs to the TOT bond, while the peak at 1060 cm⁻¹ belongs to the TOT bond. -1 and 1190cm -1 The peak at 1355 cm⁻¹ belongs to the SiO₂ structural unit, which can be considered as the deposition of SiO₂ structured material on the outer surface of the L molecular sieve; -1 and 1592cm -1 The peaks at that point are attributed to the D and G peaks of carbon, indicating the presence of amorphous carbon, which can be considered as carbon elements being deposited on the outer surface of the L molecular sieve.
[0056] Example 8
[0057] L-zeolite passivated with hexadecyltrimethoxysilane catalyzes the preparation of 3-acetamido-5-acetamidofuran from N-acetylglucosamine.
[0058] 0.1 g of N-acetylglucosamine was dissolved in 10 mL of N,N-dimethylacetamide, and 0.025 g of L-molecular sieve passivated with hexadecyltrimethoxysilane prepared in Example 3 was added. The mixture was reacted at 160 °C for 30 minutes. High-performance liquid chromatography analysis showed that the yield of 3-acetamido-5-acetylfuran was 93%.
[0059] Example 9
[0060] L-type molecular sieve passivated with hexadecyltrimethoxysilane catalyzes the preparation of 5-hydroxymethylfurfural from glucose.
[0061] 0.1 g of glucose was dissolved in 10 mL of N,N-dimethylacetamide, and 0.025 g of the L-molecule sieve passivated with hexadecyltrimethoxysilane prepared in Example 3 was added. The mixture was reacted at 160 °C for 30 minutes. High-performance liquid chromatography (HPLC) analysis showed that the yield of 5-hydroxymethylfurfural was 94%.
[0062] Comparative Example 1
[0063] L-zeolite catalysis for the preparation of 3-acetamido-5-acetamidofuran from N-acetylglucosamine
[0064] 0.1 g of N-acetylglucosamine was dissolved in 10 mL of N,N-dimethylacetamide, and 0.025 g of the L molecular sieve prepared in Example 1 was added. The mixture was reacted at 160 °C for 120 minutes. High-performance liquid chromatography (HPLC) analysis showed that the yield of 3-acetamido-5-acetylfuran was 53%.
[0065] Comparative Example 2
[0066] L-molecular sieve catalysis for the preparation of 5-hydroxymethylfurfural from glucose
[0067] 0.1 g of glucose was dissolved in 10 mL of N,N-dimethylacetamide, and 0.025 g of the L-molecular sieve prepared in Example 1 was added. The mixture was reacted at 160 °C for 120 minutes. High-performance liquid chromatography (HPLC) analysis showed that the yield of 5-hydroxymethylfurfural was 65%.
[0068] Examples 8-9 describe the use of L-zeolite molecular sieves passivated with hexadecyltrimethoxysilane prepared in Example 3 for the catalytic conversion of N-acetylglucosamine to 3-acetamido-5-acetylfuran and the catalytic conversion of glucose to 5-hydroxymethylfurfural. Examples 8-9 and Comparative Examples 1-2 present catalytic performance experiments of L-zeolite molecular sieves before and after modification. The yields of 3A5AF and 5-HMF were analyzed by high-performance liquid chromatography, and the results are shown in Table 2.
[0069] Table 2 Catalytic performance of L zeolite molecular sieves before and after modification
[0070]
[0071]
[0072] As shown in Table 2, the selectivity of 3A5AF and 5-HMF was improved after modification by the technical solution of the present invention, indicating that the method of the present invention can effectively passivate the acidic sites on the outer surface of L zeolite molecular sieve and improve the selectivity of the reaction.
[0073] The above descriptions are merely several embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention. However, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A method for passivating acidic sites on the outer surface of an L-type molecular sieve, characterized in that: The method includes the following steps: (1) Mix L molecular sieve and dispersant thoroughly, add passivating agent to the mixed solution of L molecular sieve and dispersant, stir, and then transfer to reaction vessel for passivation reaction; (2) The reactants obtained in step (1) are centrifuged, filtered, dried and calcined to obtain L molecular sieves with passivated acidic sites on the outer surface; The dispersant is any one of n-hexane, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, and anhydrous ethanol; the solid-liquid ratio of the L molecular sieve to the dispersant is 1:10 to 1:50 g / ml. The passivation reaction temperature is 170–200℃, and the reaction time is 4–24 h.
2. The method for passivating acidic sites on the outer surface of L-zeolite according to claim 1, characterized in that: The passivating agent is a short-chain silane, a long-chain silane, or a sugar or its derivative. Wherein: the short-chain silane is one or a mixture of two or more of vinyltrimethoxysilane (A171), 3-aminopropyltrimethoxysilane (KH-540), 3-aminopropyltriethoxysilane (KH-550), 3-(methylpropyloxy)propyltriethoxysilane (KH-570), and 3-aminoethylaminopropyltrimethoxysilane; The long-chain silane is one or a mixture of two or more of methyldodecyldimethoxysilane (HD-109), dodecyltrimethoxysilane (KH-304), and hexadecyltrimethoxysilane (HDTMS); The sugars and their derivatives are one or a mixture of two or more of sucrose, fructose, glucose, cellulose, and 5-hydroxymethylfurfural.
3. The method for passivating acidic sites on the outer surface of L-zeolite according to claim 1, characterized in that: The mass ratio of the L molecular sieve to the passivating agent is 1:1 to 1:10; the passivating agent is added to the mixed solution of the L molecular sieve and the dispersant, and stirred at 25°C for 0.5 to 1 hour.
4. The method for passivating acidic sites on the outer surface of L-zeolite according to claim 1, characterized in that: The drying temperature is 100-110℃, and the drying time is 8-12 hours.
5. The method for passivating acidic sites on the outer surface of L-zeolite according to claim 1, characterized in that: The roasting temperature is 400–600℃, and the roasting time is 1–5 hours.
6. The method for passivating acidic sites on the outer surface of L-zeolite according to claim 1, characterized in that: The synthesis method of the L-molecule sieve includes the following steps: (1) Mix precipitated silica and potassium hydroxide in a mortar and grind for 10-30 minutes; (2) Add aluminum hydroxide to the sample ground in step (1) and continue grinding for 10 to 30 minutes; the molar ratio of each reactant is 3.5K2O:xAl2O3:10SiO2, where x = 0.25 to 2; (3) Place the ground sample from step (2) into a reaction vessel and crystallize it at 150-200℃ for 4-24 hours; (4) The crystallized sample from step (3) was calcined at 550°C for 4 hours to obtain KL molecular sieve; (6) Weigh 0.15g of KL molecular sieve into a 50ml flask, add 30ml of NH4NO3 solution with a concentration of 0.1M to 1.0M, stir the sample at 80℃ for 1 to 6 hours, centrifuge, dry and calcine at 550℃ for 4 hours to obtain L molecular sieve.
7. An L-type molecular sieve with passivated acidic sites on its outer surface, prepared by the method according to any one of claims 1-6.
8. An application of the L-zeolite with passivated acidic sites on its outer surface as described in claim 7, characterized in that: It is used for the catalytic conversion of chitin-based biomass to prepare 3-acetamido-5-acetylfuran or the catalytic conversion of cellulose-based biomass to prepare 5-hydroxymethylfurfural.