Highly stable metal@molecular sieve catalyst for fixed-bed alkane dehydrogenation

Abstract

The present invention discloses a high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed, and its preparation method and application. The catalyst is prepared by adding a specific polyol to the molecular sieve synthesis to adjust the a-axis size of the molecular sieve grains, thereby obtaining a large-grain molecular sieve carrier, and stably encapsulating active metal clusters in the pores of the large-grain molecular sieve carrier to obtain the catalyst, wherein the a-axis length of the molecular sieve carrier grains is 0.07 to 4.00 μm, the size of the active metal clusters is 0.50 to 0.70 nm, and the metal is any one of Pt, Pd, Ir, and Rh. The catalyst obtained by the present invention can be applied to the high-temperature dehydrogenation reaction of ethane, propane, and butane. During the reaction process, the metal clusters do not sinter, and thus can remain completely inactivated during the reaction process of up to 6 months, with good prospects for promotion and application.

Description

Technical Field

[0001] The present invention belongs to the field of industrial catalyst preparation, and in particular relates to a high-stability metal@molecular sieve catalyst suitable for fixed-bed alkane dehydrogenation, and a preparation method and application thereof. Background Art

[0002] Light olefins, including ethylene, propylene, and butene, are among the most important basic raw materials in the global chemical industry and are widely used in the production of polymers, chemicals, and fuels. With the recent successful development of shale gas, the dehydrogenation of light alkanes to olefins has attracted considerable attention. This route offers advantages such as low investment, low operating costs, high olefin selectivity, and low energy consumption, making it considered a promising method for olefin production.

[0003] Pt / Al2O3 is the mainstream catalyst for the dehydrogenation of light alkanes. Pt is dispersed on the surface of Al2O3 in the form of clusters. However, during the high-temperature alkane dehydrogenation process, the Pt clusters sinter and migrate, slowly agglomerating to form larger particles, resulting in a sharp drop in the reaction conversion and selectivity. Therefore, the sintered Pt particles must be redispersed through frequent oxygen-chlorine cycles to restore the catalyst's activity. Therefore, alkane dehydrogenation using Pt / Al2O3 catalysts can only be achieved through a complex moving-bed process, which is not only costly and complex to operate, but also has poor operational stability. Therefore, the development of highly stable Pt catalysts suitable for fixed-bed operation is of great practical significance for upgrading light alkane dehydrogenation technology.

[0004] M. Cargnello, et al., Science , 2012, 337,713-717) prepared a sintering-resistant metal catalyst with a metal core layer and an oxide shell layer structure through a solution self-assembly route. Although this method can produce a high-temperature resistant metal catalyst, the preparation process is complicated and the cost is high, making it difficult to scale up the synthesis industrially. Chem. Commun. , 2017, 53, 6937-6940) et al. prepared a high-temperature-resistant Pt / SiO2 catalyst using a high-temperature reduction method. The Pt nanoparticles in the catalyst were subjected to strong metal-support interactions, which altered their electronic and geometric properties. The high-temperature treatment then formed a layer of SiO2 on the surface of the Pt particles, stabilizing them. Although the Pt particles in the Pt / SiO2 catalyst exhibited good sintering resistance, the particle size was approximately 3.2 nm, making it difficult to fully utilize the precious metal, leading to increased production costs.

[0005] In recent years, the stabilization of metal particles by spatial confinement of porous materials has attracted widespread attention. Corma and colleagues used the method of converting two-dimensional structures into three-dimensional MWW molecular sieves to prepare small-sized platinum clusters in pure silicon molecular sieves. Although the catalyst showed excellent catalytic performance in hydrogenation and dehydrogenation, its olefin selectivity and thermal stability were poor. Angew. Chem. Int. Ed., 2020, 59, 19450-19459, J Catal., 2020, 385,61-69 reported the preparation of Pt-Zn@S-1 catalysts through an in situ synthesis route. Although the stability of these catalysts has been greatly improved compared with the stability of industrial Pt / Al2O3 catalysts, the catalysts will still slowly deactivate during the long-term reaction process, and the stable alkane conversion rate cannot exceed 20 days. Therefore, these catalysts still cannot meet the requirements of the fixed-bed operation of the low-carbon alkane dehydrogenation process. Summary of the Invention

[0006] In order to solve the problem that precious metal nanoparticles in precious metal nanocatalysts are prone to migration and sintering under high-temperature process conditions, which will form larger precious metal nanoparticles and cause the deactivation of precious metal catalysts, the present invention provides a high-stability metal@molecular sieve catalyst suitable for high-temperature reactions and a preparation method thereof. By regulating the size of molecular sieve grains through the effect of polyols, a large-grain molecular sieve-encapsulated precious metal cluster catalyst is prepared. The catalyst exhibits excellent high-temperature and ultra-long-term reaction stability and can be used in fixed-bed processes.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A high-stability metal@molecular sieve catalyst suitable for fixed-bed alkane dehydrogenation, comprising a large-grain molecular sieve support and active metal clusters, wherein the active metal clusters are stably encapsulated in the pores of the large-grain molecular sieve support; the molecular sieve support has a grain a-axis length of 0.07 to 4.00 μm, the active metal clusters have a size of 0.50 to 0.70 nm, and the metal loading in the catalyst is 0.01 to 5.00 wt%.

[0009] Furthermore, the molecular sieve carrier is any one of S-1 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, and MCM-22.

[0010] Furthermore, the metal is any one of Pt, Pd, Ir, and Rh.

[0011] The preparation method of the high-stability metal@molecular sieve catalyst suitable for fixed bed alkane dehydrogenation comprises the following steps:

[0012] (1) Synthesis of catalyst precursors:

[0013] At room temperature, water, a silicon source, a template, an organic amine complexing agent, a metal salt, and a polyol are mixed and stirred thoroughly to obtain a uniform solution;

[0014] (2) Preparation of catalyst:

[0015] The uniform solution obtained in step (1) is added to a hydrothermal reactor for hydrothermal reaction, and then filtered, calcined, and reduced to obtain the high-stability metal@molecular sieve catalyst.

[0016] Furthermore, the molar ratio of the silicon source used in step (1) to the template, water, organic amine complexing agent, metal salt and polyol is 1:(0.05~1.00):(0.01~0.80):(0.00001~0.01):(0.00001~0.01):(1~10).

[0017] Furthermore, the silicon source is any one or more of sodium silicate, white carbon black, silica sol, solid silica gel, and ethyl orthosilicate.

[0018] Furthermore, the template is any one or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0019] Furthermore, the organic amine complexing agent is any one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine or pentaethylenehexamine.

[0020] Furthermore, the metal salt is any one of H2PtCl6·6H2O, PtCl2, PtCl4, H2PdCl4, Pd(NO3)2, PdCl2, Ir(OH)3, IrCl4, and RhCl3.

[0021] Furthermore, the polyol is any one or more of ethylene glycol, glycerol, 2-propylene glycol, and 1,4-butanediol.

[0022] Furthermore, the temperature of the hydrothermal reaction in step (2) is 80-180° C., and the time is 1-180 h.

[0023] Furthermore, the calcination temperature in step (2) is 400-600°C, and the calcination time is 2-18 hours.

[0024] Furthermore, the reduction in step (2) is carried out in a hydrogen atmosphere at 100-800° C. for 2-18 h.

[0025] The high stability metal@molecular sieve catalyst is suitable for the dehydrogenation reaction of light alkanes in a fixed bed. The conditions of the dehydrogenation reaction are: pure alkane feed, mass space velocity of 2.8-10.4 h -1 , reaction temperature is 450~650 ℃, reaction pressure is 0.1~0.2 MPa;

[0026] The alkane is ethane, propane or butane.

[0027] This invention utilizes a hydrothermal method to manipulate the length of the molecular sieve crystal axes by adding a polyol, resulting in a large-grain molecular sieve support with an a-axis length of 0.07 to 4.00 μm. Precious metal clusters are then encapsulated within the pores of the large-grain molecular sieve support, resulting in a highly stable metal@molecular sieve catalyst suitable for fixed-bed alkane dehydrogenation. Due to the long diffusion paths of the large-grain molecular sieve, precious metal clusters are difficult to diffuse out of the pores. Under prolonged high-temperature conditions, the precious metal nanoclusters in the catalyst exhibit minimal migration and sintering, resulting in the metal@molecular sieve developed in this invention exhibiting exceptionally high stability.

[0028] High-temperature experiments confirmed that the noble metal@molecular sieve catalyst prepared in this invention exhibited excellent long-term stability at high temperatures. Specifically, during a reaction at 900°C, the noble metal nanoclusters in the small-sized noble metal@molecular sieve catalyst exhibited severe sintering and aggregation, and the noble metal dispersion decreased from 85.1% to 27.2%. In contrast, the noble metal nanoclusters in the large-grained noble metal@molecular sieve catalyst were uniformly dispersed within the molecular sieve, with the dispersion only decreasing from 95.7% to 75.8%. Furthermore, compared to the small-grained molecular sieve, the catalyst prepared by encapsulating the metal nanoclusters with large-grained molecular sieve exhibited exceptional long-term stability, with no decrease in reaction conversion after six months. This catalyst is promising for the development of a fixed-bed light alkane dehydrogenation process.

[0029] The beneficial effects of the present invention are:

[0030] 1) The dispersion of metal clusters in the catalyst provided by the present invention is as high as 85%, the utilization rate is high, and it exhibits excellent catalytic activity in the propane dehydrogenation reaction.

[0031] 2) The catalyst of the present invention has ultra-high thermal stability and does not deactivate during reactions lasting up to 6 months, which reduces the catalyst regeneration process and greatly reduces operating costs.

[0032] 3) The dehydrogenation reaction of the present invention is carried out in the pores of the molecular sieve in the catalyst, and the carbon deposition process is suppressed. The carbon deposition amount of the catalyst during the reaction process is very low, which not only has high selectivity for olefins but also reduces the damage to the catalyst caused by the carbonization process.

[0033] 4) The catalyst of the present invention has high stability, low carbon deposition, and does not require frequent regeneration. Therefore, it is expected that a fixed-bed alkane dehydrogenation process with long-term stable operation can be developed based on this catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the SEM image of the Pt@ZSM-5 (0.07) catalyst prepared in the comparative example.

[0035] Figure 2 This is the SEM image of the Pt@ZSM-5 (0.50) catalyst prepared in Example 1.

[0036] Figure 3 This is the SEM image of the Pt@ZSM-5 (1.20) catalyst prepared in Example 2.

[0037] Figure 4 This is the SEM image of the Pt@ZSM-5 (4.00) catalyst prepared in Example 5.

[0038] Figure 5 This is the STEM image of the Pt@ZSM-5 (4.00) catalyst prepared in Example 5.

[0039] Figure 6 This is a diagram showing the evaluation of the catalytic activity of propane dehydrogenation of the Pt@ZSM-5 (4.00) catalyst prepared in Example 5 after 6 months of reaction. DETAILED DESCRIPTION

[0040] A high-stability metal@molecular sieve catalyst suitable for fixed-bed alkane dehydrogenation, the preparation method of which comprises the following steps:

[0041] (1) Synthesis of catalyst precursors:

[0042] At room temperature, a silicon source, a template, water, an organic amine complexing agent, a metal salt, and a polyol are mixed in a molar ratio of 1:(0.05-1.00):(0.01-0.80):(0.00001-0.01):(0.00001-0.01):(1-10), and stirred thoroughly to obtain a uniform solution;

[0043] (2) Preparation of catalyst:

[0044] The uniform solution obtained in step (1) is added to a hydrothermal reactor, and the reaction is carried out at 80-180°C for 1-180 hours, and then filtered, calcined at 400-600°C for 2-18 hours, and then treated at 100-800°C in a hydrogen atmosphere for 2-18 hours to obtain a high-stability metal@molecular sieve catalyst.

[0045] The silicon source is any one or more of sodium silicate, white carbon black, silica sol, solid silica gel, and tetraethyl orthosilicate. The template is any one or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. The organic amine complexing agent is any one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, or pentaethylenehexamine. The metal salt is any one of H2PtCl6·6H2O, PtCl2, PtCl4, H2PdCl4, Pd(NO3)2, PdCl2, Ir(OH)3, IrCl4, and RhCl3. The polyol is any one or more of ethylene glycol, glycerol, 2-propylene glycol, and 1,4-butanediol.

[0046] The a-axis length of the obtained molecular sieve support is 0.07-4.00 μm, the size of the active metal clusters is 0.50-0.70 nm, and the metal loading in the catalyst is 0.01-5.00 wt%.

[0047] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0048] Unless otherwise specified, the chemicals used in the following examples were purchased from commercial sources and were not processed. Tetraethyl orthosilicate (TEOS), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), chloroplatinic acid hexahydrate (H2PtCl6·6H2O), platinum dichloride (PtCl2), platinum tetrachloride (PtCl4), palladium nitrate (Pd(NO3)2), iridium tetrachloride (IrCl4), rhodium trichloride (RhCl3), ethylenediamine (NH2CH2CH2NH2), ethylene glycol, glycerol, 2-propylene glycol, and 1,4-butanediol were all purchased from Aladdin Reagent Co., Ltd. Deionized water used in the experiments was obtained from the laboratory's high-purity water system.

[0049] The catalysts in the comparative examples and examples are named Pt@ZSM-5(1.00), where Pt represents the active component and x represents the size of the ZSM-5 crystallite along the a-axis (μm). For example, a ZSM-5 ZSM-5 catalyst with a ZSM-5 crystallite a-axis size of 1.00 μm is named Pt@ZSM-5(1.00).

[0050] Comparative Example (without adding polyol)

[0051] (1) Weigh 16.1 g of TEOS and dissolve it in 7.5 g of deionized water. Stir in a water bath at 25 °C for 6 h to obtain a homogeneous solution after complete hydrolysis.

[0052] (2) Weigh 15.5 g of TPAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 2 h to obtain a uniform mixed solution;

[0053] (3) Weigh 40 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2 h to obtain a uniform solution of Pt-containing organic amine complex.

[0054] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 2 h to form a uniform mixed solution, which was then placed into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0055] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 170 °C and maintain hydrothermal crystallization for 48 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 500 °C for 6 h to obtain a catalyst powder precursor with small crystal particles;

[0056] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 5 h for reduction, finally obtaining the Pt@ZSM-5 (0.07) catalyst.

[0057] Figure 1 The SEM image of the prepared Pt@ZSM-5 (0.07) catalyst shows that the average size of the catalyst grains along the a-axis is 0.07 μm.

[0058] Example 1

[0059] (1) Weigh 16.1 g of TEOS and dissolve it in 7.5 g of deionized water. Stir in a water bath at 25 °C for 6 h to obtain a homogeneous solution after complete hydrolysis.

[0060] (2) Weigh 15.5 g of TPAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 2 h to obtain a uniform mixed solution;

[0061] (3) Weigh 40 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2 h to obtain a uniform solution of Pt-containing organic amine complex.

[0062] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 2 h to form a uniform mixed solution, 9.6 g of ethylene glycol was added, and the mixture was stirred for 2 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0063] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 170 °C and maintain hydrothermal crystallization for 48 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 500 °C for 6 h to obtain a catalyst powder precursor;

[0064] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 6 h for reduction, finally obtaining the Pt@ZSM-5(0.50) catalyst.

[0065] Figure 2 The SEM image of the prepared Pt@ZSM-5 (0.50) catalyst shows that the average size of the catalyst grains along the a-axis is 0.50 μm.

[0066] Example 2

[0067] (1) Weigh 20.1 g of TEOS and dissolve it in 9.7 g of deionized water. Stir in a 40 °C water bath for 9 h to obtain a homogeneous solution after complete hydrolysis.

[0068] (2) Weigh 18.6 g of TEAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 4 h to obtain a uniform mixed solution;

[0069] (3) Weigh 50 mg of H2PtCl6·6H2O and dissolve it in 2.90 g of deionized water. Stir in a 45 °C water bath for 3 h to form a uniform solution. Then slowly add 0.71 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0070] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, 11.5 g of ethylene glycol was added, and the mixture was stirred for 3.5 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0071] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 165 °C and maintain hydrothermal crystallization for 96 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 560 °C for 8 h to obtain a catalyst powder precursor;

[0072] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 6 h for reduction, finally obtaining the Pt@ZSM-5(1.20) catalyst.

[0073] Figure 3 The SEM image of the prepared Pt@ZSM-5 (1.20) catalyst shows that the average size of the catalyst grains along the a-axis is 1.20 μm.

[0074] Example 3

[0075] (1) Weigh 10.1 g of TEOS and dissolve it in 5.7 g of deionized water. Stir in a water bath at 25 °C for 5 h to obtain a homogeneous solution after complete hydrolysis.

[0076] (2) Weigh 9.6 g of TEAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 2.5 h to obtain a uniform mixed solution;

[0077] (3) Weigh 26 mg of PtCl4 and dissolve it in 1.90 g of deionized water. Stir in a water bath at 25 °C for 3 h to form a uniform solution. Then slowly add 0.36 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0078] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, 13.5 g of ethylene glycol was added, and the mixture was stirred for 2.5 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0079] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 180 °C and maintain hydrothermal crystallization for 48 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 550 °C for 7 h to obtain a catalyst powder precursor;

[0080] (7) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 7 h for reduction, finally obtaining the Pt@ZSM-5 (3.00) catalyst.

[0081] Example 4

[0082] (1) Weigh 13.1 g of TEOS and dissolve it in 7.7 g of deionized water. Stir in a water bath at 35 °C for 6 h to obtain a homogeneous solution after complete hydrolysis.

[0083] (2) Weigh 12.6 g of TPAOH solution and add it to the homogeneous solution of step (1), and continue stirring for 3 h to obtain a uniform mixed solution;

[0084] (3) Weigh 29 mg of H2PtCl6·6H2O and dissolve it in 2.3 g of deionized water. Stir the mixture in a 35 °C water bath for 3.5 h to form a uniform solution. Slowly add 0.42 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0085] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, 15.5 g of ethylene glycol was added, and the mixture was stirred for 4.0 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0086] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 175 °C and maintain hydrothermal crystallization for 120 h. After the crystallization is completed, cool, centrifuge, wash and dry at 570 °C for 3 h to obtain a catalyst powder precursor;

[0087] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 4 h for reduction, finally obtaining the Pt@ZSM-5(3.50) catalyst.

[0088] Example 5

[0089] (1) Weigh 13.8 g of TEOS and dissolve it in 7.9 g of deionized water. Stir in a 35 °C water bath for 5 h to obtain a homogeneous solution after complete hydrolysis.

[0090] (2) Weigh 12.9 g of TPAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 4 h to obtain a uniform mixed solution;

[0091] (3) Weigh 28 mg of PtCl2 and dissolve it in 2.4 g of deionized water. Stir in a 35 °C water bath for 4 h to form a uniform solution. Then slowly add 0.41 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0092] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, and then 17.5 g of ethylene glycol was added and stirred for 4.5 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0093] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 178 °C and maintain hydrothermal crystallization for 100 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 550 °C for 9 h to obtain a catalyst powder precursor;

[0094] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 4 h for reduction, finally obtaining the Pt@ZSM-5 (4.00) catalyst.

[0095] Figure 4 The SEM image of the prepared Pt@ZSM-5 (4.00) catalyst shows that the average size of the catalyst grains along the a-axis is 4.00 μm.

[0096] Figure 5 The STEM image of the prepared Pt@ZSM-5 (4.00) catalyst shows that the size of the Pt nanoclusters in the catalyst is approximately 0.65 nm.

[0097] Example 6

[0098] (1) Weigh 16.1 g of TEOS and dissolve it in 7.5 g of deionized water. Stir in a water bath at 25 °C for 6 h to obtain a homogeneous solution after complete hydrolysis.

[0099] (2) Weigh 15.5 g of TPAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 2 h to obtain a uniform mixed solution;

[0100] (3) Weigh 50 mg of Pd(NO3)2 and dissolve it in 2.0 g of deionized water. Stir it in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2 h to obtain a uniform solution of Pd-containing organic amine complex.

[0101] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 2 h to form a uniform mixed solution, 17.5 g of ethylene glycol was added, and the mixture was stirred for 2 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0102] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 170 °C and maintain hydrothermal crystallization for 48 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 500 °C for 6 h to obtain a catalyst powder precursor;

[0103] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 6 h for reduction, finally obtaining the Pd@ZSM-5 (4.00) catalyst.

[0104] Example 7

[0105] (1) Weigh 20.1 g of TEOS and dissolve it in 9.7 g of deionized water. Stir in a 40 °C water bath for 9 h to obtain a homogeneous solution after complete hydrolysis.

[0106] (2) Weigh 18.6 g of TEAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 4 h to obtain a uniform mixed solution;

[0107] (3) Weigh 26 mg of IrCl4 and dissolve it in 2.90 g of deionized water. Stir in a 45 °C water bath for 3 h to form a uniform solution. Then slowly add 0.71 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform Ir-containing organic amine complex solution.

[0108] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, 17.5 g of ethylene glycol was added, and the mixture was stirred for 3.5 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0109] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 165 °C and maintain hydrothermal crystallization for 96 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 560 °C for 8 h to obtain a catalyst powder precursor;

[0110] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 6 h for reduction, finally obtaining the Ir@ZSM-5 (4.00) catalyst.

[0111] Example 8

[0112] (1) Weigh 10.1 g of TEOS and dissolve it in 5.7 g of deionized water. Stir in a water bath at 25 °C for 5 h to obtain a homogeneous solution after complete hydrolysis.

[0113] (2) Weigh 9.6 g of TEAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 2.5 h to obtain a uniform mixed solution;

[0114] (3) Weigh 29 mg of RhCl3 and dissolve it in 1.90 g of deionized water. Stir in a water bath at 25 °C for 3 h to form a uniform solution. Slowly add 0.36 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform Rh-containing organic amine complex solution.

[0115] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, 17.5 g of ethylene glycol was added, and the mixture was stirred for 2.5 h. Finally, the mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0116] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 180 °C and maintain hydrothermal crystallization for 48 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 550 °C for 7 h to obtain a catalyst powder precursor;

[0117] (7) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 7 h for reduction, finally obtaining the Rh@ZSM-5 (4.00) catalyst.

[0118] Example 9

[0119] (1) Weigh 13.1 g of TEOS and dissolve it in 7.7 g of deionized water. Stir in a water bath at 35 °C for 6 h to obtain a homogeneous solution after complete hydrolysis.

[0120] (2) Weigh 12.6 g of TPAOH solution and add it to the homogeneous solution of step (1), and continue stirring for 3 h to obtain a uniform mixed solution;

[0121] (3) Weigh 29 mg of H2PtCl6·6H2O and dissolve it in 2.3 g of deionized water. Stir the mixture in a 35 °C water bath for 3.5 h to form a uniform solution. Slowly add 0.42 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0122] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, and then 17.5 g of 1,4-butanediol was added and stirred for 4.0 h. Finally, the obtained mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0123] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 175 °C and maintain hydrothermal crystallization for 120 h. After the crystallization is completed, cool, centrifuge, wash and dry at 570 °C for 3 h to obtain a catalyst powder precursor;

[0124] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 4 h for reduction, finally obtaining the Pt@ZSM-11 (4.00) catalyst.

[0125] Example 10

[0126] (1) Weigh 13.8 g of TEOS and dissolve it in 7.9 g of deionized water. Stir in a 35 °C water bath for 5 h to obtain a homogeneous solution after complete hydrolysis.

[0127] (2) Weigh 12.9 g of TPAOH solution and add it to the homogeneous solution in step (1), and continue stirring for 4 h to obtain a uniform mixed solution;

[0128] (3) Weigh 28 mg of PtCl2 and dissolve it in 2.4 g of deionized water. Stir in a 35 °C water bath for 4 h to form a uniform solution. Then slowly add 0.41 mL of NH2CH2CH2NH2 and continue stirring for 3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0129] (4) The solutions obtained in steps (2) and (3) were mixed and stirred for 3 h to form a uniform mixed solution, and then 17.5 g of 1,4-butanediol was added and stirred for 4.5 h. Finally, the obtained mixed solution was placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0130] (5) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 178 °C and maintain hydrothermal crystallization for 100 h. After the crystallization is completed, cool, centrifuge, wash and calcine at 550 °C for 9 h to obtain a catalyst powder precursor;

[0131] (6) The obtained catalyst powder precursor was placed in a tubular furnace, heated to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and maintained for 4 h for reduction, finally obtaining the Pt@ZSM-22 (4.00) catalyst.

[0132] The catalysts prepared in the comparative examples and examples were used for propane dehydrogenation reaction. The reaction conditions were: pure propane feed, mass space velocity of 6.0 h -1 , reaction temperature is 600 ℃, reaction pressure is 0.1 MPa, and the results of propane conversion and propylene selectivity are shown in Table 1.

[0133] Table 1 Comparison of propane conversion and propylene selectivity of different catalysts

[0134]

[0135] From the catalytic results of the comparative examples and Examples 1-5 in Table 1, it can be seen that the Pt@ZSM-5 (0.07) catalyst with a shorter a-axis is the most unstable and deactivates rapidly during the propane dehydrogenation reaction. However, the Pt@ZSM-5 molecular sieve catalyst with a longer a-axis (1.20-4.00 μm) shows little deactivation after a long period of catalytic reaction, indicating that its stability has been significantly enhanced. At the same time, the catalytic results of Examples 5-10 show that, under the conditions of the same a-axis length, changing the type of metal used and the type of carrier molecular sieve can produce highly stable M@ZSM-5 molecular sieve catalysts. This proves that increasing the a-axis length can obtain M@ molecular sieve catalysts with higher catalytic stability.

[0136] Figure 6 This figure shows the catalytic activity evaluation of the Pt@ZSM-5 (4.00) catalyst prepared in Example 5 for propane dehydrogenation after six months of reaction. As can be seen from the figure, the propane conversion rate of the catalyst barely decreases after a long period of propane dehydrogenation reaction, further demonstrating the excellent stability of the catalyst with a long a-axis size.

[0137] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A high-stability metal@molecular sieve catalyst suitable for fixed-bed alkane dehydrogenation, comprising a large-grain molecular sieve support and active metal clusters, wherein the active metal clusters are stably encapsulated in the pores of the large-grain molecular sieve support, characterized in that: The preparation method comprises the following steps: (1) Synthesis of catalyst precursors: At room temperature, water, a silicon source, a template, an organic amine complexing agent, a metal salt, and a polyol are mixed and stirred thoroughly to obtain a uniform solution; (2) Preparation of catalyst: The uniform solution obtained in step (1) is subjected to a hydrothermal reaction, and then filtered, calcined, and reduced to obtain the high-stability metal@molecular sieve catalyst; The a-axis length of the molecular sieve carrier is 0.50-4.00 μm, the size of the active metal cluster is 0.50-0.70 nm, and the loading amount of the metal in the catalyst is 0.01-5.00 wt%.

2. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The molecular sieve carrier is any one of S-1 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, and MCM-22.

3. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The metal is any one of Pt, Pd, Ir, and Rh.

4. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The molar ratio of the silicon source used in step (1) to the template, water, organic amine complexing agent, metal salt and polyol is 1:(0.05~1.00):(0.01~0.80):(0.00001~0.01):(0.00001~0.01):(1~10).

5. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1 or 4, characterized in that: The silicon source is any one or more of sodium silicate, white carbon black, silica sol, solid silica gel, and tetraethyl orthosilicate; the template is any one or more of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; the organic amine complexing agent is any one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, or pentaethylenehexamine; the metal salt is any one of H2PtCl6·6H2O, PtCl2, PtCl4, H2PdCl4, Pd(NO3)2, PdCl2, Ir(OH)3, IrCl4, and RhCl3; and the polyol is any one or more of ethylene glycol, glycerol, 2-propylene glycol, and 1,4-butanediol.

6. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step (2) is 80-180°C, and the time is 1-180 h.

7. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The calcination temperature in step (2) is 400-600°C and the calcination time is 2-18 h.

8. The high-stability metal@molecular sieve catalyst for alkane dehydrogenation suitable for a fixed bed according to claim 1, characterized in that: The reduction in step (2) is carried out in a hydrogen atmosphere at 100-800°C for 2-18 h.

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