Molecular sieve catalyst for direct dehydrogenation of n-butane as well as preparation method and application of molecular sieve catalyst

Abstract

The invention discloses a molecular sieve catalyst for direct dehydrogenation of n-butane and a preparation method and application thereof.The preparation method comprises the steps that a first metal precursor, a second metal precursor, a structure-directing agent and a silicon source are dispersed in water to obtain a first solution, and the first metal precursor is a Pt source; heating and stirring the first solution in a sealed environment to obtain a second solution; dropwise adding a fluorine-containing compound solution into the second solution, heating and stirring to obtain a third solution; transferring the third solution into a hydrothermal reaction kettle for static crystallization; and collecting a crystallized product, washing, drying, and calcining at high temperature to obtain the molecular sieve catalyst. According to the present invention, the molecular sieve catalyst is prepared through the in-situ loading strategy-one pot method, the metal active center can be anchored in the molecular sieve pore channel, the migration and the agglomeration of the metal atoms are strictly limited by using the molecular sieve pore channel and the cage-shaped structure, the sub-nano-scale Pt-M particles are formed, and the utilization rate of the metal active site is high.

Description

Technical Field

[0001] This application belongs to the field of catalyst technology, specifically relating to a molecular sieve catalyst for the direct dehydrogenation of n-butane, its preparation method, and its application. Background Technology

[0002] 1,3-Butadiene is an important petrochemical feedstock, serving as a key structural unit in polymer products such as synthetic rubber, resins, and plastics. Its market demand continues to grow rapidly with the downstream industries. Traditionally, 1,3-Butadiene is mainly extracted from the C4 fraction, a byproduct of naphtha cracking, via cryogenic distillation, or produced through ethanol-catalyzed dimerization. However, these methods are increasingly unable to meet the growing industrial demand. In recent years, with advancements in exploration technologies for light alkane resources such as shale gas, the process of producing 1,3-Butadiene from n-butane via direct dehydrogenation (BDH) has emerged as a promising alternative. However, the BDH process involves a complex reaction pathway and a wide distribution of products, necessitating the development of a catalyst capable of balancing high activity, selectivity, and stability of 1,3-Butadiene at high temperatures.

[0003] Platinum (Pt) has been widely used in alkane dehydrogenation reactions due to its significant affinity for C–H bond activation. Although platinum-based catalysts generally exhibit excellent catalytic activity, their active sites are prone to gradual deactivation due to metal sintering, carbon deposition, and strong adsorption of olefin molecules on metal surfaces, leading to decreased stability and selectivity. Particularly in the dehydrogenation of n-butane, catalyst systems with platinum nanoparticles supported on acidic zeolites face challenges such as excessive acidity, increased side reactions, and unsatisfactory isobutene yields. Summary of the Invention

[0004] The purpose of this application is to provide a molecular sieve catalyst for the direct dehydrogenation of n-butane, its preparation method and application, in order to solve the problems of easy deactivation of active sites and insufficient selectivity and stability of existing platinum-based catalysts for the direct dehydrogenation of n-butane.

[0005] To achieve the above objectives, the first aspect of this application provides a method for preparing a molecular sieve catalyst for the direct dehydrogenation of n-butane, comprising:

[0006] A first metal precursor, a second metal precursor, a structure directing agent, and a silicon source are dispersed in water to obtain a first solution, wherein the first metal precursor is a Pt source.

[0007] The first solution was heated and stirred in a sealed environment to obtain the second solution;

[0008] A fluorine-containing compound solution was added to the second solution, and the mixture was heated and stirred to obtain a third solution.

[0009] The third solution was transferred to a hydrothermal reactor for static crystallization.

[0010] The crystalline product was collected, washed, dried, and then calcined at high temperature to obtain the molecular sieve catalyst.

[0011] In one or more embodiments, the Pt source is ammonium hexachloroplatinate.

[0012] In one or more embodiments, the structure directing agent is N-methyltetrapropylammonium bromide.

[0013] In one or more embodiments, the silicon source is tetraethoxysilane.

[0014] In one or more embodiments, the second metal precursor is selected from one or more combinations of In source, Sn source, Ce source, Zn source and Ga source.

[0015] In one or more embodiments, the In source is selected from one or a combination of indium nitrate and indium chloride.

[0016] In one or more embodiments, the Sn source is selected from one or a combination of two of stannous chloride dihydrate and stannous tetrachloride.

[0017] In one or more embodiments, the Ce source is selected from one or a combination of two of cerium nitrate and cerium chloride.

[0018] In one or more embodiments, the Zn source is selected from one or a combination of two of zinc nitrate hexahydrate and zinc chloride.

[0019] In one or more embodiments, the Ga source is selected from one or a combination of gallium chloride and gallium nitrate hydrate.

[0020] In one or more embodiments, the molar ratio of the first metal precursor, the second metal precursor, the structure directing agent and the silicon source in the first solution is (0.001~0.01): (0~0.009):0.1:1.

[0021] In one or more embodiments, in the step of heating and stirring in a sealed environment, the heating temperature is 90~100 ℃ and the stirring time is 12~14 h.

[0022] In one or more embodiments, the fluorinated compound is ammonium hydrogen fluoride.

[0023] In one or more embodiments, the molar ratio of the fluorinated compound to the silicon source is (1~1.6):1.

[0024] In one or more embodiments, during the heating and stirring step, the stirring temperature is 90~100 ℃ and the stirring time is 12~14 h.

[0025] In one or more embodiments, the static crystallization step involves a crystallization temperature of 90-100 °C and a crystallization time of 72-96 h.

[0026] In one or more embodiments, the high-temperature calcination step specifically involves calcination in a hydrogen atmosphere at a temperature of 550-600 °C.

[0027] To achieve the above objectives, a second aspect of this application provides a molecular sieve catalyst for the direct dehydrogenation of n-butane prepared by the preparation method described in any of the above embodiments.

[0028] To achieve the above objectives, a third aspect of this application provides a method for the direct dehydrogenation of n-butane to prepare 1,3-butadiene, comprising:

[0029] The n-butane feedstock is reacted with a catalyst to obtain a product including 1,3-butadiene;

[0030] The catalyst is a molecular sieve catalyst for direct dehydrogenation of n-butane as described in any of the above embodiments.

[0031] The advantages of this application, which differ from existing technologies, are:

[0032] The catalyst of this application incorporates a second metal other than Pt, which can form bimetallic nanoparticles, promote the isolation of Pt atoms on the support and regulate the electronic structure, and significantly improve the dehydrogenation performance and stability of the catalyst.

[0033] The molecular sieve catalyst prepared by the in-situ loading strategy-one-pot method in this application can anchor the metal active center in the molecular sieve channel, effectively avoiding the deep embedding of metal particles and significantly improving the accessibility of active sites.

[0034] The catalyst of this application utilizes molecular sieve channels and cage-like structures to strictly restrict the migration and aggregation of metal atoms, thereby forming sub-nanometer-scale Pt-M particles, resulting in high utilization of metal active sites.

[0035] The reaction system of the preparation method of this application contains fluorine-containing compounds. Fluorine ions are beneficial to the synthesis of sheet-like molecular sieves, and the pore structure inside the molecular sieve is etched to form a large number of mesopores, which is beneficial to the diffusion of metal ions and the exposure of active sites, resulting in a catalyst with high catalytic stability, high catalytic activity and high 1,3-butadiene selectivity.

[0036] The reaction system of the preparation method of this application contains fluorine-containing compounds. Due to the strong coordination effect between fluorine ions and metal ions, the active center of Pt-M bimetallic ions can be effectively located at a specific position on the growing molecular sieve framework, realizing atomic-level dispersion or confinement of ultra-small nanoclusters, achieving in-situ loading, and perfectly solving the core problem of preventing agglomeration. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This application describes the preparation method of the molecular sieve catalyst for the direct dehydrogenation of n-butane.

[0039] Figure 2 This is a high-resolution scanning transmission electron microscope image of the catalyst in Example 1 of this application;

[0040] Figure 3 These are characterization analysis diagrams of Example 1 of this application, wherein the upper diagram is the diffuse reflectance infrared Fourier transform spectrum of the catalyst of Example 1 and Comparative Example 1, and the lower diagram is the X-ray powder diffraction pattern of the catalyst of Example 1. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0042] Platinum-based catalysts typically exhibit excellent catalytic activity, but their active sites are prone to gradual deactivation due to metal sintering, carbon deposition, and strong adsorption of olefin molecules on metal surfaces, leading to decreased stability and selectivity (such as selectivity for isobutylene). Particularly in the dehydrogenation of n-butane, catalyst systems supporting platinum nanoparticles on acidic zeolites also face problems such as excessive acidity, increased side reactions, and unsatisfactory isobutylene yields.

[0043] To address the aforementioned issues, the applicant developed a novel Pt-M bimetallic catalyst. This bimetallic catalyst incorporates other metals to form customized bimetallic nanoparticles with Pt, and also introduces a support with a high specific surface area to achieve high dispersion of the metal nanoparticles. This significantly improves the catalyst's reactivity, selectivity for 1,3-butadiene, and catalytic stability.

[0044] The catalyst of this application is described in detail below; please refer to [link / reference]. Figure 1 , Figure 1 This application describes the preparation method of the molecular sieve catalyst for the direct dehydrogenation of n-butane.

[0045] like Figure 1 As shown, the preparation method of this catalyst includes:

[0046] S100. The first metal precursor, the second metal precursor, the structure directing agent and the silicon source are dispersed in water to obtain the first solution.

[0047] In this embodiment, the first metal precursor is a Pt source. In one embodiment, the Pt source can be ammonium hexachloroplatinate. In other embodiments, the Pt source can also be other commonly used Pt metal compounds, all of which can achieve the effect of this embodiment.

[0048] The second metal precursor is used to form bimetallic nanoparticles with Pt, which promotes the isolation of Pt atoms on the support and regulates their electronic structure, significantly improving the dehydrogenation performance and stability of the catalyst.

[0049] In one embodiment, the second metal precursor may be selected from one or more combinations of In source, Sn source, Ce source, Zn source and Ga source.

[0050] In one embodiment, the In source can be one or a combination of indium nitrate and indium chloride; the Sn source can be one or a combination of stannous chloride dihydrate and stannous chloride tetrahydrate; the Ce source can be one or a combination of cerium nitrate and cerium chloride; the Zn source can be one or a combination of zinc nitrate hexahydrate and zinc chloride; and the Ga source can be one or a combination of gallium chloride and gallium nitrate hydrate. In other embodiments, the In source, Sn source, Ce source, Zn source, and Ga source can also be other metal compounds commonly used in the art, all of which can achieve the effects of this embodiment.

[0051] The structure-directing agent serves as a template agent, used in conjunction with the silicon source to prepare the all-silicon molecular sieve support S-1 in subsequent steps. In one embodiment, the structure-directing agent can be N-methyltetrapropylammonium bromide; in other embodiments, the structure-directing agent can be a commonly used structure-directing agent such as tetrapropylammonium hydroxide, both of which can achieve the effects of this embodiment.

[0052] In one embodiment, the molar ratio of the first metal precursor, the second metal precursor, the structure directing agent, and the silicon source in the first solution can be: (0.001~0.01): (0~0.009):0.1:1.

[0053] To improve dissolution efficiency, in one embodiment, the first metal precursor, the second metal precursor, and the structure directing agent can be dissolved in water first, and then a silicon source can be added to the solution to obtain a first solution.

[0054] S200. The first solution is heated and stirred in a sealed environment to obtain the second solution.

[0055] The first solution is heated and stirred in a sealed environment to fully hydrolyze the silicon source and initially form a gel system, laying the foundation for molecular sieve crystallization.

[0056] In one embodiment, the heating temperature can be 90~100 ℃, and the stirring time can be 12~14 h.

[0057] S300. Add a fluorine-containing compound solution to the second solution, heat and stir to obtain the third solution.

[0058] S400, the third solution is transferred to a hydrothermal reactor for static crystallization.

[0059] To promote the synthesis of sheet-like molecular sieves and the formation of numerous mesoporous structures, while simultaneously positioning metal nanoparticles within the molecular sieve channels to achieve atomic-level dispersion of the metal nanoparticles and prevent aggregation, this application creatively adds fluorine-containing compounds to the system.

[0060] Firstly, fluoride ions can change the relative growth rate of different crystal planes of molecular sieves, which is beneficial to the synthesis of molecular sieves with plate-like structures. Furthermore, they can etch the pore structure inside the molecular sieve to form a large number of mesopores, which is beneficial to the diffusion of metal ions and the exposure of active sites.

[0061] Secondly, due to the strong coordination effect between fluoride ions and metal ions, the active center of Pt-M bimetallic ions can be effectively located at a specific position on the growing molecular sieve framework, realizing atomic-level dispersion or confinement of ultra-small nanoclusters, achieving in-situ loading, and perfectly solving the core problem of preventing aggregation.

[0062] In one embodiment, the fluorinated compound may be ammonium hydrogen fluoride.

[0063] In one embodiment, the molar ratio of the fluorine-containing compound to the silicon source can be (1~1.6):1.

[0064] In one embodiment, the molar ratio of the first metal precursor, the second metal precursor, the structure directing agent, the silicon source, the fluorine-containing compound, and water in the reaction system can be: (0.001~0.01): (0~0.009):0.1:1:(1~1.6):30.

[0065] In one embodiment, during the heating and stirring step, the stirring temperature can be 90~100 ℃, and the stirring time can be 12~14 h.

[0066] After the reaction system was constructed, the all-silica molecular sieve S-1 was prepared by a one-pot hydrothermal reaction, and the loading of active sites was achieved simultaneously. The preparation of the support and the loading of active sites were completed in one step, which simplified the production process and avoided the losses and uncertainties caused by multiple steps.

[0067] In one embodiment, the crystallization temperature for static crystallization can be 90~100 ℃, and the crystallization time can be 72~96 h.

[0068] S500, collect the crystallized product, wash and dry it, and then calcine it at high temperature to obtain the molecular sieve catalyst.

[0069] After crystallization, the product is washed, dried, and calcined at high temperature to obtain a molecular sieve catalyst.

[0070] In one embodiment, the washing method may be to wash several times with alternating water and acetone, and the drying method may specifically be to filter and then dry at 60~95 ​​℃ for 8~14 h.

[0071] In one embodiment, high-temperature calcination can specifically refer to calcination in a hydrogen atmosphere at a temperature of 550-600°C.

[0072] The molecular sieve catalysts prepared by the in-situ loading strategy-one-pot method based on the above embodiments can anchor the metal active centers within the molecular sieve channels, effectively avoiding deep embedding of metal particles and significantly improving the accessibility of active sites. At the same time, the migration and aggregation of metal atoms are strictly restricted by the molecular sieve channels and cage-like structure, thereby forming sub-nanometer-scale Pt-M particles, resulting in high utilization of metal active sites. Furthermore, the plate-like molecular sieve structure and numerous mesoporous structures facilitate the diffusion of metal ions and the exposure of active sites, resulting in catalysts with high catalytic stability, high catalytic activity, and high 1,3-butadiene selectivity.

[0073] The beneficial effects of the technical solution of this application will be further described in detail below with reference to specific embodiments.

[0074] Example 1:

[0075] A Pt-In@S-1 bimetallic catalyst was prepared using the following steps:

[0076] Step 1: Add 1.56 g of N-methyltetrapropylammonium bromide, 0.34 g of ammonium hexachloroplatinate, 0.21 g of indium nitrate and 16.6 g of deionized water to the reaction vessel in sequence, and stir thoroughly until the mixture is homogeneous;

[0077] Step 2: Add 16 grams of tetraethoxysilane to the above mixture, seal the container, and stir continuously at 90°C for 12 hours; the molar ratios of each component in the reaction system are as follows:

[0078] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: indium nitrate = 1 : 0.1 : 0.01 : 0.009;

[0079] Step 3: Prepare a solution consisting of 4.55 g of ammonium bifluoride and 24.9 g of deionized water, add it dropwise to the above reaction system, and stir at 90°C for 12 hours in an open container until a gel is formed;

[0080] Step 4: Place the obtained gel into a 100 ml hydrothermal reactor and let it stand in a 90℃ oven for 3 days to crystallize;

[0081] Step 5: After the reaction is complete, remove the solid product from the reactor, wash it repeatedly with deionized water and acetone until neutral (pH≈7), dry it overnight at 70°C, grind it into powder, and finally calcine it at 600°C in a 10% hydrogen atmosphere for 5 hours to obtain the target catalyst.

[0082] Example 2:

[0083] A Pt-Sn@S-1 bimetallic catalyst was prepared using a method basically the same as in Example 1, except that:

[0084] Indium nitrate in Example 1 was replaced with stannous chloride dihydrate. The molar ratios of the components in the reaction system are as follows:

[0085] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: stannous chloride dihydrate = 1 : 0.1 : 0.01 : 0.009.

[0086] Example 3:

[0087] A Pt-Ce@S-1 bimetallic catalyst was prepared using a method essentially the same as in Example 1, except that:

[0088] Indium nitrate in Example 1 was replaced with cerium nitrate, and the molar ratios of the components in the reaction system are as follows:

[0089] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: cerium nitrate = 1 : 0.1 : 0.01 : 0.009.

[0090] Example 4:

[0091] A Pt-Zn@S-1 bimetallic catalyst was prepared using a method basically the same as in Example 1, except that:

[0092] Zinc nitrate hexahydrate replaced indium nitrate in Example 1. The molar ratios of the components in the reaction system are as follows:

[0093] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: zinc nitrate hexahydrate = 1 : 0.1 : 0.01 : 0.009.

[0094] Example 5:

[0095] A Pt-Ga@S-1 bimetallic catalyst was prepared using a method basically the same as in Example 1, except that:

[0096] Gallium chloride replaced indium nitrate in Example 1, and the molar ratios of each component in the reaction system are as follows:

[0097] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: gallium chloride = 1 : 0.1 : 0.01 : 0.009.

[0098] Example 6:

[0099] A Pt-In@S-1 bimetallic catalyst was prepared using the following steps:

[0100] Step 1: Add 1.56 g of N-methyltetrapropylammonium bromide, 0.034 g of ammonium hexachloroplatinate, 0.12 g of indium nitrate and 16.6 g of deionized water to the reaction vessel in sequence, and stir thoroughly until the mixture is homogeneous;

[0101] Step 2: Add 16 grams of tetraethoxysilane to the above mixture, seal the container, and stir continuously at 100°C for 14 hours; the molar ratios of each component in the reaction system are as follows:

[0102] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: indium nitrate: deionized water = 1 : 0.1 : 0.001 : 0.005;

[0103] Step 3: Prepare a solution consisting of 7.1 g ammonium bifluoride and 24.9 g deionized water, add it dropwise to the above reaction system, and stir at 100°C for 14 hours in an open container until a gel is formed;

[0104] Step 4: Place the obtained gel into a 100 ml hydrothermal reactor and let it stand in a 100℃ oven for 4 days to crystallize.

[0105] Step 5: After the reaction is complete, remove the solid product from the reactor, wash it repeatedly with deionized water and acetone until neutral (pH≈7), dry it overnight at 70°C, grind it into powder, and finally calcine it at 550°C in a 10% hydrogen atmosphere for 5 hours to obtain the target catalyst.

[0106] Example 7:

[0107] A Pt-In@S-1 bimetallic catalyst was prepared using a method basically the same as in Example 1, except that:

[0108] Step 1: Add 1.56 g of N-methyltetrapropylammonium bromide, 0.17 g of ammonium hexachloroplatinate, 0.12 g of indium nitrate and 16.6 g of deionized water to the reaction vessel in sequence, and stir thoroughly until the mixture is homogeneous;

[0109] Step 2: Add 16 grams of tetraethoxysilane to the above mixture, seal the container and place it at 100°C for 14 hours with continuous stirring.

[0110] The molar ratios of each component in the reaction system are as follows:

[0111] Tetraethoxysilane: N-methyltetrapropylammonium bromide: ammonium hexachloroplatinate: indium nitrate: deionized water = 1 : 0.1 : 0.005 : 0.005 : 30.

[0112] Comparative Example 1:

[0113] A Pt@S-1 metal catalyst was prepared using a method essentially the same as in Example 1, except that:

[0114] Indium nitrate was not added to the reaction system.

[0115] Comparative Example 2:

[0116] A Pt-In@S-1 bimetallic catalyst was prepared using a method basically the same as in Example 1, except that:

[0117] Ammonium hydrogen fluoride was not added to the reaction system.

[0118] Comparative Example 3:

[0119] A Pt-In@S-1 bimetallic catalyst was prepared using the following steps:

[0120] Step 1: Preparation of S-1 molecular sieve

[0121] Add 1.56 g of N-methyltetrapropylammonium bromide (TPAOH) to a container, add 16.6 g of deionized water, and stir until completely dissolved to form a clear solution. While stirring continuously, slowly add 16 g of tetraethoxysilane (TEOS) to the above solution. At this time, the solution will become turbid. Then, stir continuously in a closed environment at 90°C for 12 hours to allow TEOS to be fully hydrolyzed.

[0122] Dissolve 4.55 g of ammonium bifluoride in 24.9 g of deionized water to prepare a solution; add this solution dropwise to the above hydrolyzed mixture at a uniform rate, and continue stirring the system at 90 °C under open conditions for 12 hours to evaporate some of the ethanol and form a homogeneous sol.

[0123] The obtained sol was transferred to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 90 °C for static crystallization for 72 hours. After crystallization, the mixture was cooled to room temperature, and the solid product was removed from the reactor. The solid was repeatedly centrifuged and washed with deionized water until the filtrate was neutral (pH≈7). The obtained solid was dried at 70 °C overnight, and finally calcined in a muffle furnace at 550 °C for 6 hours (heating rate: 2 °C / min) to completely remove the template agent, yielding a pure white S-1 molecular sieve support.

[0124] Step 2: Preparation of Pt-In@S-1 catalyst by impregnation method

[0125] Weigh 0.0007 mol of indium nitrate and dissolve it in deionized water to prepare an impregnation solution; add the S-1 molecular sieve support to the above solution and stir at room temperature for 2 hours to allow the solution to be fully and uniformly absorbed by the support; dry the impregnated sample at 80℃ for 12 hours, and then calcine it in air at 550℃ for 4 hours (heating rate: 2℃ / min) to obtain the In2O3 / S-1 intermediate;

[0126] Weigh 0.00077 mol of chloroplatinic acid (H2PtCl6·6H2O), dissolve it in deionized water, add the In2O3 / S-1 intermediate obtained in the first step to the platinum salt solution, and stir at room temperature for 2 hours to ensure thorough wetting; dry the sample at 80℃ for 12 hours; place the dried powder sample in a tube furnace, and under a 10% H2 / Ar atmosphere, program the temperature to 600℃ at a rate of 2℃ / min, and reduce it at this temperature for 3 hours; after the reduction is completed, cool it to room temperature under an inert atmosphere to obtain the final desired Pt-In@S-1 catalyst.

[0127] Example 1: Characterization Analysis

[0128] The morphology of the Pt-In bimetallic catalyst prepared in Example 1 was analyzed, and the results were obtained. Figure 2 , Figure 2This is a high-resolution scanning transmission electron microscope image of the catalyst in Example 1 of this application.

[0129] like Figure 2 As shown, the Pt-In bimetallic catalyst prepared in Example 1 has an overall elongated elliptical sheet-like structure, which proves that the method of Example 1 successfully formed a sheet-like molecular sieve, which facilitates the exposure of active sites.

[0130] Furthermore, to investigate the dispersion of metal nanoparticles in the catalyst of Example 1, infrared spectroscopy analysis was performed on the catalysts prepared in Example 1 and Comparative Example 1. Simultaneously, X-ray diffraction analysis was performed on the catalyst prepared in Example 1, yielding... Figure 3 , Figure 3 These are characterization analysis diagrams of Example 1 of this application, wherein the upper diagram is the diffuse reflectance infrared Fourier transform spectrum of the catalyst of Example 1 and Comparative Example 1, and the lower diagram is the X-ray powder diffraction pattern of the catalyst of Example 1.

[0131] like Figure 3 As shown, the catalyst of Comparative Example 1 contained a large number of agglomerated Pt particles, while the catalyst of Example 1 did not show obvious agglomeration or large-sized Pt particles. This indicates that the addition of the second metal -In in Example 1 can help improve the dispersion of Pt atoms.

[0132] Example 2:

[0133] The catalytic activity of the catalysts in Examples 1 to 5 and Comparative Examples 1 to 3 was tested using the following methods:

[0134] To ensure the catalyst remained free from air contact after pretreatment, all operations were performed in a fixed-bed microreactor. A 7 mm diameter quartz reaction tube was filled with 50 mg of catalyst diluted with quartz sand (quartz sand to catalyst mass ratio 4:1). Before testing, the catalyst was reduced for 1 h at 600 °C and 0.1 MPa by purging with 50 mL / min of 10% hydrogen (residual gas: 90% argon). After reduction, the bed was purged with inert high-purity argon for 40 min. Finally, the reaction gas was switched to evaluate the catalyst's performance in the dehydrogenation of n-butane to 1,3-butadiene.

[0135] The reaction temperature was 600 °C, and the mass hourly space velocity (HHSV) of n-butane was 5.9 h⁻¹. -1 The pressure was 0.1 MPa, and the volume ratio of n-butane to nitrogen was 1:9. Gas chromatography was used to analyze the composition of the reaction products. Alkanes and alkenes were detected using an FID detector, while carbon dioxide, carbon monoxide, and hydrogen were detected using a TCD detector. Nitrogen was used as an internal standard for parameter correction. The experimental results are shown in the table below.

[0136]

[0137] Based on the data in Table 1, the following conclusions can be drawn:

[0138] Among the catalysts listed, the Pt-In@S-1 catalyst prepared in Example 1 exhibited the best overall performance, with an initial n-butane conversion of 74%, a 1,3-butadiene selectivity of 59%, and an extremely long single-pass lifetime (maintaining 70% conversion after 1500 hours), demonstrating excellent stability and catalytic durability.

[0139] Although the Pt-Sn@S-1 prepared in Example 2 had the highest initial conversion rate (88%), its lifetime was significantly shorter than that of the PtIn system.

[0140] The bimetallic catalysts prepared in Examples 1 to 5 showed significantly better activity, selectivity, and single-pass lifetime than the comparative examples.

[0141] Compared with Example 1, Comparative Example 1 is a single Pt metal catalyst with low activity, selectivity and single-pass lifetime; while in Example 1, In can promote the isolation of Pt atoms on the support and regulate the electronic structure, which can significantly improve the dehydrogenation performance and stability of the catalyst.

[0142] Compared with Example 1 and Comparative Example 2, Comparative Example 2, which did not add ammonium bifluoride, had a significantly lower conversion rate, selectivity, and lifetime than the catalyst in Example 1. This indicates that the introduction of fluorine additives is crucial for constructing a highly active and stable molecular sieve-confined bimetallic structure.

[0143] Compared with Example 1 and Comparative Example 3, Comparative Example 3 first prepared S-1 molecular sieve, and then used an impregnation method to attach metal particles to the surface of the molecular sieve. Its conversion rate, selectivity and lifetime were significantly lower than those of the catalyst in Example 1. This shows that the in-situ supported one-pot method of this application can significantly improve the catalytic activity and stability of the catalyst compared with the traditional impregnation method.

[0144] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0145] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a molecular sieve catalyst for direct dehydrogenation of n-butane, characterized by, The application relates to a preparation method of a molecular sieve catalyst for direct dehydrogenation of n-butane. The first metal precursor, the second metal precursor, the structure directing agent and the silicon source are dispersed in water to obtain a first solution, wherein the first metal precursor is a Pt source; The first solution is heated and stirred in a sealed environment to obtain a second solution; A fluorine-containing compound solution is added to the second solution, and the solution is heated and stirred to obtain a third solution; The third solution is transferred to a hydrothermal reaction kettle for static crystallization; The crystallization product is collected, washed and dried, and then high-temperature calcination is carried out to obtain the molecular sieve catalyst.

2. The molecular sieve catalyst of claim 1, wherein, The Pt source is ammonium hexachloroplatinate; and / or, The structure directing agent is N-methyl tetrapropyl ammonium bromide; and / or, The silicon source is tetraethoxysilane.

3. The molecular sieve catalyst of claim 1, wherein, The second metal precursor is selected from one or more combinations of In sources, Sn sources, Ce sources, Zn sources and Ga sources.

4. The molecular sieve catalyst of claim 1, wherein, The In source is selected from one or both of indium nitrate and indium chloride; and / or, The Sn source is selected from one or both of stannous chloride dihydrate and tin tetrachloride; and / or, The Ce source is selected from one or both of cerium nitrate and cerium chloride; and / or, The Zn source is selected from one or both of zinc nitrate hexahydrate and zinc chloride; and / or, The Ga source is selected from one or both of gallium chloride and gallium nitrate hydrate.

5. The preparation method according to claim 1, characterized in that, In the first solution, the molar ratio of the first metal precursor, the second metal precursor, the structure directing agent and the silicon source is (0.001-0.01):(0-0.009):0.1:

1.

6. The method of claim 1, wherein, In the step of heating and stirring in a sealed environment, the heating temperature is 90-100 DEG C, and the stirring time is 12-14 h.

7. The preparation method according to claim 1, characterized in that, The fluorine-containing compound is ammonium bifluoride; and / or, The molar ratio of the fluorine-containing compound to the silicon source is (1-1.6):1; and / or, In the step of heating and stirring in a sealed environment, the heating temperature is 90-100 DEG C, and the stirring time is 12-14 h.

8. The method of claim 1, wherein, In the step of static crystallization, the crystallization temperature is 90-100 DEG C, and the crystallization time is 72-96 h.

9. The method of claim 1, wherein, The high-temperature calcination is specifically carried out under a hydrogen atmosphere, and the calcination temperature is 550-600 DEG C.

10. A molecular sieve catalyst for direct dehydrogenation of n-butane, which is prepared by the preparation method in any one of claims 1 to 9.

11. A process for the direct dehydrogenation of n-butane to 1,3-butadiene, characterized in that, The application relates to a preparation method of a molecular sieve catalyst for direct dehydrogenation of n-butane. The application relates to a preparation method of a molecular sieve catalyst for direct dehydrogenation of n-butane. The application relates to a preparation method of a molecular sieve catalyst for direct dehydrogenation of n-butane. The application relates to a preparation method of a molecular sieve catalyst for direct dehydrogenation of n-butane.

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